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Sample records for plate tectonics seismic

  1. Seismic gaps and plate tectonics: seismic potential for major boundaries

    Energy Technology Data Exchange (ETDEWEB)

    McCann, W R; Nishenko, S P; Sykes, L R; Krause, J

    1979-01-01

    The theory of plate tectonics provides a basic framework for evaluating the potential for future great earthquakes to occur along major plate boundaries. Along most of the transform and convergent plate boundaries considered in this paper, the majority of seismic slip occurs during large earthquakes, i.e., those of magnitude 7 or greater. The concepts that rupture zones, as delineated by aftershocks, tend to abut rather than overlap, and large events occur in regions with histories of both long-and short-term seismic quiescence are used in this paper to delineate major seismic gaps. The term seismic gap is taken to refer to any region along an active plate boundary that has not experienced a large thrust or strike-slip earthquake for more than 30 years. A region of high seismic potential is a seismic gap that, for historic or tectonic reasons, is considered likely to produce a large shock during the next few decades. The seismic gap technique provides estimates of the location, size of future events and origin time to within a few tens of years at best. The accompanying map summarizes six categories of seismic potential for major plate boundaries in and around the margins of the Pacific Ocean and the Caribbean, South Sandwich and Sunda (Indonesia) regions for the next few decades. These six categories are meant to be interpreted as forecasts of the location and size of future large shocks and should not be considered to be predictions in which a precise estimate of the time of occurrence is specified. The categories of potential assigned here provide a rationale for assigning priorities for instrumentation, for future studies aimed at predicting large earthquakes and for making estimates of tsunami potential.

  2. Spreading continents kick-started plate tectonics.

    Science.gov (United States)

    Rey, Patrice F; Coltice, Nicolas; Flament, Nicolas

    2014-09-18

    Stresses acting on cold, thick and negatively buoyant oceanic lithosphere are thought to be crucial to the initiation of subduction and the operation of plate tectonics, which characterizes the present-day geodynamics of the Earth. Because the Earth's interior was hotter in the Archaean eon, the oceanic crust may have been thicker, thereby making the oceanic lithosphere more buoyant than at present, and whether subduction and plate tectonics occurred during this time is ambiguous, both in the geological record and in geodynamic models. Here we show that because the oceanic crust was thick and buoyant, early continents may have produced intra-lithospheric gravitational stresses large enough to drive their gravitational spreading, to initiate subduction at their margins and to trigger episodes of subduction. Our model predicts the co-occurrence of deep to progressively shallower mafic volcanics and arc magmatism within continents in a self-consistent geodynamic framework, explaining the enigmatic multimodal volcanism and tectonic record of Archaean cratons. Moreover, our model predicts a petrological stratification and tectonic structure of the sub-continental lithospheric mantle, two predictions that are consistent with xenolith and seismic studies, respectively, and consistent with the existence of a mid-lithospheric seismic discontinuity. The slow gravitational collapse of early continents could have kick-started transient episodes of plate tectonics until, as the Earth's interior cooled and oceanic lithosphere became heavier, plate tectonics became self-sustaining.

  3. The tectonic plates are moving!

    CERN Document Server

    Livermore, Roy

    2018-01-01

    Written in a witty and informal style, this book explains modern plate tectonics in a non-technical manner, showing not only how it accounts for phenomena such as great earthquakes, tsunamis, and volcanic eruptions, but also how it controls conditions at the Earth’s surface, including global geography and climate, making it suitable for life. The book presents the advances that have been made since the establishment of plate tectonics in the 1960s, highlighting, on the fiftieth anniversary of the theory, the contributions of a small number of scientists who have never been widely recognized for their discoveries. Beginning with the publication of a short article in Nature by Vine and Matthews, the book traces the development of plate tectonics through two generations of the theory. First-generation plate tectonics covers the exciting scientific revolution of the 1960s, its heroes, and its villains. The second generation includes the rapid expansions in sonar, satellite, and seismic technologies during the 1...

  4. Earth's Decelerating Tectonic Plates

    Energy Technology Data Exchange (ETDEWEB)

    Forte, A M; Moucha, R; Rowley, D B; Quere, S; Mitrovica, J X; Simmons, N A; Grand, S P

    2008-08-22

    Space geodetic and oceanic magnetic anomaly constraints on tectonic plate motions are employed to determine a new global map of present-day rates of change of plate velocities. This map shows that Earth's largest plate, the Pacific, is presently decelerating along with several other plates in the Pacific and Indo-Atlantic hemispheres. These plate decelerations contribute to an overall, globally averaged slowdown in tectonic plate speeds. The map of plate decelerations provides new and unique constraints on the dynamics of time-dependent convection in Earth's mantle. We employ a recently developed convection model constrained by seismic, geodynamic and mineral physics data to show that time-dependent changes in mantle buoyancy forces can explain the deceleration of the major plates in the Pacific and Indo-Atlantic hemispheres.

  5. Numerical modeling of intraplate seismicity with a deformable loading plate

    Science.gov (United States)

    So, B. D.; Capitanio, F. A.

    2017-12-01

    We use finite element modeling to investigate on the stress loading-unloading cycles and earthquakes occurrence in the plate interiors, resulting from the interactions of tectonic plates along their boundary. We model a visco-elasto-plastic plate embedding a single or multiple faults, while the tectonic stress is applied along the plate boundary by an external loading visco-elastic plate, reproducing the tectonic setting of two interacting lithospheres. Because the two plates deform viscously, the timescale of stress accumulation and release on the faults is self-consistently determined, from the boundary to the interiors, and seismic recurrence is an emerging feature. This approach overcomes the constraints on recurrence period imposed by stress (stress-drop) and velocity boundary conditions, while here it is unconstrained. We illustrate emerging macroscopic characteristics of this system, showing that the seismic recurrence period τ becomes shorter as Γ and Θ decreases, where Γ = ηI/ηL the viscosity ratio of the viscosities of the internal fault-embedded to external loading plates, respectively, and Θ = σY/σL the stress ratio of the elastic limit of the fault to far-field loading stress. When the system embeds multiple, randomly distributed faults, stress transfer results in recurrence period deviations, however the time-averaged recurrence period of each fault show the same dependence on Γ and Θ, illustrating a characteristic collective behavior. The control of these parameters prevails even when initial pre-stress was randomly assigned in terms of the spatial arrangement and orientation on the internal plate, mimicking local fluctuations. Our study shows the relevance of macroscopic rheological properties of tectonic plates on the earthquake occurrence in plate interiors, as opposed to local factors, proposing a viable model for the seismic behavior of continent interiors in the context of large-scale, long-term deformation of interacting tectonic

  6. Transpressional Tectonics across the N. American-Caribbean Plate Boundary: Preliminary Results of a Multichannel Seismic Survey of Lake Azuei, Haiti.

    Science.gov (United States)

    Hearn, C. K.; Cormier, M. H.; Sloan, H.; Wattrus, N. J.; Boisson, D.; Brown, B.; Guerrier, K.; King, J. W.; Knotts, P.; Momplaisir, R.; Sorlien, C. C.; Stempel, R.; Symithe, S. J.; Ulysse, S. M. J.

    2017-12-01

    On January 12, 2010, a Mw 7.0 earthquake struck Haiti, killing over 200,000 people and devastating the Capital city of Port-au-Prince and the surrounding regions. It ruptured a previously unknown blind-thrust fault that abuts the Enriquillo Plantain Garden Fault (EPGF), one of two transform faults that define the North American-Caribbean plate boundary. That earthquake highlighted how transpression across this complex boundary is accommodated by slip partitioning into strike-slip and compressional structures. Because the seismic hazard is higher for a rupture on a reverse or oblique-slip fault than on a vertical strike-slip fault, the need to characterize the geometry of that fault system is clear. Lake Azuei overlies this plate boundary 60 km east of the 2010 epicenter. The lake's 23 km long axis trends NW-SE, parallel to the Haitian fold-and-thrust belt and oblique to the EPGF. This tectonic context makes it an ideal target for investigating the partitioning of plate motion between strike-slip and compressional structures. In January 2017, we acquired 222 km of multichannel seismic (MCS) profiles in the lake, largely concurrent with subbottom seismic (CHIRP) profiles. The MCS data were acquired using a high-frequency BubbleGun source and a 75 m-long, 24-channel streamer, achieving a 24 seismic fold with a penetration of 200 m below lakebed. With the goal of resolving tectonic structures in 3-D, survey lines were laid out in a grid with profiles spaced 1.2 km apart. Additional profiles were acquired at the SE end of the lake where most of the tectonic activity is presumably occurring. The co-located CHIRP and MCS profiles document the continuity of tectonic deformation between the surficial sediments and the deeper strata. Preliminary processing suggests that a SW-dipping blind thrust fault, expressed updip as a large monocline fold, may control the western edge of the lake. Gentle, young folds that protrude from the flat lakebed are also imaged with the CHIRP

  7. Seismic tomographic constraints on plate-tectonic reconstructions of Nazca subduction under South America since late Cretaceous (˜80 Ma)

    Science.gov (United States)

    Chen, Y. W.; Wu, J.; Suppe, J.

    2017-12-01

    Global seismic tomography has provided new and increasingly higher resolution constraints on subducted lithospheric remnants in terms of their position, depth, and volumes. In this study we aim to link tomographic slab anomalies in the mantle under South America to Andean geology using methods to unfold (i.e. structurally restore) slabs back to earth surface and input them to globally consistent plate reconstructions (Wu et al., 2016). The Andean margin of South America has long been interpreted as a classic example of a continuous subduction system since early Jurassic or later. However, significant gaps in Andean plate tectonic reconstructions exist due to missing or incomplete geology from extensive Nazca-South America plate convergence (i.e. >5000 km since 80 Ma). We mapped and unfolded the Nazca slab from global seismic tomography to produce a quantitative plate reconstruction of the Andes back to the late Cretaceous 80 Ma. Our plate model predicts the latest phase of Nazca subduction began in the late Cretaceous subduction after a 100 to 80 Ma plate reorganization, which is supported by Andean geology that indicates a margin-wide compressional event at the mid-late Cretaceous (Tunik et al., 2010). Our Andean plate tectonic reconstructions predict the Andean margin experienced periods of strike-slip/transtensional and even divergent plate tectonics between 80 to 55 Ma. This prediction is roughly consistent with the arc magmatism from northern Chile between 20 to 36°S that resumed at 80 Ma after a magmatic gap. Our model indicates the Andean margin only became fully convergent after 55 Ma. We provide additional constraints on pre-subduction Nazca plate paleogeography by extracting P-wave velocity perturbations within our mapped slab surfaces following Wu et al. (2016). We identified localized slow anomalies within our mapped Nazca slab that apparently show the size and position of the subducted Nazca ridge, Carnegie ridge and the hypothesized Inca plateau

  8. A new plate tectonic concept for the eastern-most Mediterranean

    Science.gov (United States)

    Huebscher, C.; McGrandle, A.; Scaife, G.; Spoors, R.; Stieglitz, T.

    2012-04-01

    Owing to the seismogenic faults bordering the Levant-Sinai realm and the discovery of giant gas reservoirs in the marine Levant Basin the scientific interest in this tectonically complex setting increased in recent years. Here we provide a new model for the Levant Basin architecture and adjacent plate boundaries emphasizing the importance of industrial seismic data for frontier research in earth science. PSDM seismics, residual gravity and depth to basement maps give a clear line of evidence that the Levant Basin, formerly considered as a single tectonic entity, is divided into two different domains. Highly stretched continental crust in the southern domain is separated from deeper and presumably Tethyan oceanic crust in the north. A transform continuing from southwest Cyprus to the Carmel Fault in northern Israel is considered as the boundary. If this interpretation holds, the Carmel-Cyprus Transform represents a yet unknown continent-ocean boundary in the eastern Mediterranean, thus adding new constrains for the Mediterranean plate tectonic puzzle. The Eratosthenes Seamount, considered as the spearhead of incipient continental collision in the eastern Mediterranean, is interpreted as a carbonate platform that developed above a volcanic basement. NW-SE trending strike-slip faults are abundant in the entire Levant region. Since this trend also shapes the topography of the Levant hinterland including Quaternary deposits their recent tectonic activity is quite likely. Thus, our study supports previous studies which attributed the evolution of submarine canyons and Holocene triggering of mass failures not only to salt tectonics or depositional processes, but also to active plate-tectonics.

  9. Using Tectonic Tremor to Constrain Seismic-wave Attenuation in Cascadia

    Science.gov (United States)

    Littel, G.; Thomas, A.; Baltay, A.

    2017-12-01

    In addition to fast, seismic slip, many subduction zones also host slow, largely aseismic slip, accompanied by a weak seismic signal known as tectonic tremor. Tremor is a small amplitude, low-frequency seismic signal that originates at the plate interface, down-dip of where large earthquakes typically occur. The Cascadia subduction zone has not seen a large megathrust earthquake since 1700, yet its recurrence interval of 350-500 years motivates heightened interest in understanding the seismic hazard of the region. Of great importance is to understand the degree to which waves are attenuated as they leave the plate interface and travel towards populated regions of interest. Ground motion prediction equations (GMPEs) relate ground motion to a number of parameters, including earthquake magnitude, depth, style of faulting, and anelastic attenuation, and are typically determined empirically from earthquake ground motion recordings. In Cascadia, however, earthquakes of the moderate size typically used to constrain GMPEs occur relatively infrequently compared to tectonic tremor events, which, in contrast, occur periodically approximately every 10-19 months. Studies have shown that the abundant tectonic tremor in Cascadia, despite its small amplitudes, can be used to constrain seismic wave attenuation in GMPEs. Here we quantify seismic wave attenuation and determine its spatial variations in Cascadia by performing an inversion using tremor ground motion amplitudes, taken as peak ground acceleration (PGA) and peak ground velocity (PGV) from 1 min window waveforms of each individual tremor event. We estimate the anelastic attenuation parameter for varying regional sections along the Cascadia margin. Changes in seismic-wave attenuation along the Cascadia Subduction Zone could result in significantly different ground motions in the event of a very large earthquake, hence quantifying attenuation may help to better estimate the severity of shaking in densely populated

  10. Plate tectonics, mantle convection and D'' seismic structures

    Science.gov (United States)

    Wen, Lianxing

    This thesis adopts multidisciplinary (geodynamical and seismological) approaches toward understanding dynamics of the Earth's mantle. My geodynamical approach is directed at understanding the relationship between large-scale surface observables (geoid, topography, plate motions) and mantle rheology and convection of the present-day Earth. In chapter 2, I remove shallow mantle structure of various tectonic features to generate "residual tomography." In chapter 3, I show that the pattern, spectrum and amplitude of the "residual topography" are consistent with shallow origin of the "Earth surface dynamic topography;" the long wavelength geoid and topography (l = 2-3) are successfully explained by density models inferred from the "residual tomography," assuming layered mantle convection stratified at the "920 km seismic discontinuity." In chapter 4, I develop a new method to calculate mantle flow with lateral variation of viscosity. The viscosity contrast between continental and oceanic regions is identified to have dominating effects on both the observed poloidal/toroidal ratio and pattern of toroidal motions at long wavelengths. My seismological approach is focused on exploring fine structures near the core-mantle boundary (CMB) and developing new seismic techniques. I discuss the method development and strategies to explore fine structures in the following chapters. In chapter 5, I develop a hybrid method, a combination of analytical and numerical methods, with numerical methods applied in heterogeneous regions only. In chapter 6, I constrain the general structures of the ultra low velocity zones (ULVZ) near the CMB under the south-east Pacific and Iceland. The SKS-SPdKS data are explained by ULVZ with P-velocity reduction of 10%, horizontal length-scales of about 250 km and height of about 40 km. S-velocity reduction of 30% is consistent with the data. In chapter 7, I constrain the detailed structures of the ULVZ near the CMB from observed broadband PKP precursors

  11. Earthquake recurrence and magnitude and seismic deformation of the northwestern Okhotsk plate, northeast Russia

    Science.gov (United States)

    Hindle, D.; Mackey, K.

    2011-02-01

    Recorded seismicity from the northwestern Okhotsk plate, northeast Asia, is currently insufficient to account for the predicted slip rates along its boundaries due to plate tectonics. However, the magnitude-frequency relationship for earthquakes from the region suggests that larger earthquakes are possible in the future and that events of ˜Mw 7.5 which should occur every ˜100-350 years would account for almost all the slip of the plate along its boundaries due to Eurasia-North America convergence. We use models for seismic slip distribution along the bounding faults of Okhotsk to conclude that relatively little aseismic strain release is occurring and that larger future earthquakes are likely in the region. Our models broadly support the idea of a single Okhotsk plate, with the large majority of tectonic strain released along its boundaries.

  12. Seismicity and tectonics of Bangladesh

    International Nuclear Information System (INIS)

    Hossain, K.M.

    1989-05-01

    Northern and eastern Bangladesh and surrounding areas belong to a seismically active zone and are associated with the subduction of the Indian plate. The seismicity and tectonics have been studied in detail and the observations have been correlated to understand the earthquake phenomenon in the region. The morphotectonic behaviour of northern Bangladesh shows that it is deeply related to the movement of the Dauki fault system and relative upliftment of the Shillong plateau. Contemporary seismicity in the Dauki fault system is relatively quiet comparing to that in the Naga-Disang-Haflong thrust belt giving rise to the probability of sudden release of energy being accumulated in the vicinity of the Dauki fault system. This observation corresponds with the predicted average return period of a large earthquake (1897 type) and the possibility of M > 8 earthquake in the vicinity of the Dauki fault within this century should not be ruled out. The seismicity in the folded belt in the east follows the general trend of Arakan-Yoma anticlinorium and represents shallow and low-angled thrust movements in conformity with the field observation. Seismotectonic behaviour in the deep basin part of Bangladesh demonstrates that an intraplate movement in the basement rock has been taking place along the deep-seated faults causing relative upliftment and subsidence in the basin. Bangladesh has been divided into three seismic zones on the basis of morphotectonic and seismic behaviour. Zone-I has been identified as the zone of high seismic risk. (author). 43 refs, 5 figs, 3 tabs

  13. Playing jigsaw with Large Igneous Provinces—A plate tectonic reconstruction of Ontong Java Nui, West Pacific

    Science.gov (United States)

    Hochmuth, Katharina; Gohl, Karsten; Uenzelmann-Neben, Gabriele

    2015-11-01

    The three largest Large Igneous Provinces (LIP) of the western Pacific—Ontong Java, Manihiki, and Hikurangi Plateaus—were emplaced during the Cretaceous Normal Superchron and show strong similarities in their geochemistry and petrology. The plate tectonic relationship between those LIPs, herein referred to as Ontong Java Nui, is uncertain, but a joined emplacement was proposed by Taylor (2006). Since this hypothesis is still highly debated and struggles to explain features such as the strong differences in crustal thickness between the different plateaus, we revisited the joined emplacement of Ontong Java Nui in light of new data from the Manihiki Plateau. By evaluating seismic refraction/wide-angle reflection data along with seismic reflection records of the margins of the proposed "Super"-LIP, a detailed scenario for the emplacement and the initial phase of breakup has been developed. The LIP is a result of an interaction of the arriving plume head with the Phoenix-Pacific spreading ridge in the Early Cretaceous. The breakup of the LIP shows a complicated interplay between multiple microplates and tectonic forces such as rifting, shearing, and rotation. Our plate kinematic model of the western Pacific incorporates new evidence from the breakup margins of the LIPs, the tectonic fabric of the seafloor, as well as previously published tectonic concepts such as the rotation of the LIPs. The updated rotation poles of the western Pacific allow a detailed plate tectonic reconstruction of the region during the Cretaceous Normal Superchron and highlight the important role of LIPs in the plate tectonic framework.

  14. Plate tectonics

    Digital Repository Service at National Institute of Oceanography (India)

    Chaubey, A.K.

    's continental drift theory was later disproved, it was one of the first times that the idea of crustal movement had been introduced to the scientific community; and it has laid the groundwork for the development of modern plate tectonics. In the early... of the structure of the atom was to physical sciences and the theory of evolution was to the life sciences. Tectonics is the study of the forces within the Earth that give rise to continents, ocean basins, mountain ranges, earthquake belts and other large-scale...

  15. Soft Plate and Impact Tectonics

    Science.gov (United States)

    Tikoff, Basil

    In the field of tectonics, most of our ideas are published in journals. This is not true of other fields, such as history, in which ideas are primarily published in books. Within my own field of structural geology, I can recall only one book, Strain Fades by E. Hansen (Springer-Verlag, 1971), which presents a new idea in book form. However, even this book is more useful for its philosophical approach and particular methodology of determining directions of folding, than for its overarching idea.Enter Soft Plate and Impact Tectonics, a new book with an interesting hypothesis that has been informally discussed in the geoscience community: A fundamental tenet of plate tectonics is incorrect—namely, that the plates are rigid. This assertion is evident when looking at any mountain range, and is perhaps most clearly stated in Molnar [1988].

  16. From Plate Tectonic to Continental Dynamics

    Science.gov (United States)

    Molnar, P. H.

    2017-12-01

    By the early 1970s, the basics of plate tectonics were known. Although much understanding remained to be gained, as a topic of research, plate tectonics no longer defined the forefront of earth science. Not only had it become a foundation on which to build, but also the methods used to reveal it became tools to take in new directions. For me as a seismologist studying earthquakes and active processes, the deformation of continents offered an obvious topic to pursue. Obviously examining the deformation of continents and ignoring the widespread geologic evidence of both ongoing and finite deformation of crust would be stupid. I was blessed with the opportunity to learn from and collaborate with two of the best, Paul Tapponnier and Clark Burchfiel. Continental deformation differed from plate tectonics both because deformation was widespread but more importantly because crust shortens (extends) horizontally and thickens (thins), processes that can be ignored where plate tectonics - the relative motion of rigid plates - occurs. Where a plate boundary passes into a continent, not only must the forces that move plates do work against friction or other dissipative processes, but where high terrain is created, they must also do work against gravity, to create gravitational potential energy in high terrain. Peter Bird and Kenneth Piper and Philip England and Dan McKenzie showed that a two-dimensional thin viscous sheet with vertically averaged properties enabled both sources of resistance to be included without introducing excessive complexity and to be scaled by one dimensionless number, what the latter pair called the Argand number. Increasingly over the past thirty years, emphasis has shifted toward the role played by the mantle lithosphere, because of both its likely strength and its negative buoyancy, which makes it gravitationally unstable. Despite progress since realizing that rigid plates (the essence of plate tectonics) provides a poor description of continental

  17. Pennsylvania seismic monitoring network and related tectonic studies

    International Nuclear Information System (INIS)

    Alexander, S.S.

    1991-06-01

    This report summarizes the results of the operation of the Pennsylvania Seismic Monitoring Network during the interval May 1, 1983--March 31, 1985 to monitor seismic activity in Pennsylvania and surrounding areas, to characterize the earthquake activity in terms of controlling tectonic structures and related tectonic stress conditions in the crust, and to obtain improved crustal velocity models for hypocentral determinations. Most of the earthquake activity was concentrated in the Lancaster, PA area. The magnitude 4.2 mainshock that occurred there on April 23, 1984 was the largest ever recorded instrumentally and its intensity of VI places it among the largest in the historic record for that area. Other activity during the monitoring interval of this report was confined to eastern Pennsylvania. The very large number of quarry explosions that occur regularly in Pennsylvania account for most of the seismic events recorded and they provide important crustal velocity data that are needed to obtain accurate hypocenter estimates. In general the earthquakes that occurred are located in areas of past historic seismicity. Block-tectonic structures resulting from pre-Ordovician tectonic displacements appear to influence the distribution of contemporary seismicity in Pennsylvania and surrounding areas. 17 refs., 5 figs

  18. Looking for Plate Tectonics in all the wrong fluids

    Science.gov (United States)

    Davaille, Anne

    2017-04-01

    Ever since the theory of Plate Tectonics in the 1960's, the dream of the geomodeler has been to generate plate tectonics self-consistently from thermal convection in the laboratory. By selfconsistenly, I mean that the configuration of the plate boundaries is in no way specified a priori, so that the plates develop and are wholly consumed without intervention from the modeler. The reciepe is simple : put a well-chosen fluid in a fishtank heated from below and cooled from above, wait and see. But the « well-chosen » is the difficult part... and the interesting one. Plate tectonics is occuring on Earth because of the characteristics of the lithosphere rheology. The latter are complex to estimate as they depend on temperature, pressure, phase, water content, chemistry, strain rate, memory and scale. As a result, the ingredients necessary for plate tectonics are still debated, and it would be useful to find an analog fluid who could reproduce plate tectonics in the laboratory. I have therefore spent the last 25 years to try out fluids, and I shall present a number of failures to generate plate tectonics using polymers, colloids, ketchup, milk, chocolate, sugar, oils. To understand why they failed is important to narrow down the « well-chosen » fluid.

  19. LOWLID FORMATION AND PLATE TECTONICS ON EXOPLANETS

    Science.gov (United States)

    Stamenkovic, V.; Noack, L.; Breuer, D.

    2009-12-01

    The last years of astronomical observation have opened the doors to a universe filled with extrasolar planets. Detection techniques still only offer the possibility to detect mainly Super-Earths above five Earth masses. But detection techniques do steadily improve and are offering the possibility to detect even smaller planets. The observations show that planets seem to exist in many possible sizes just as the planets and moons of our own solar system do. It is only a natural question to ask if planetary mass has an influence on some key habitability factors such as on plate tectonics, allowing us to test which exoplanets might be more likely habitable than others, and allowing us to understand if plate tectonics on Earth is a stable or a critical, instable process that could easily be perturbed. Here we present results derived from 1D parameterized thermal evolution and 2D/3D computer models, showing how planetary mass influences the propensity of plate tectonics for planets with masses ranging from 0.1 to 10 Earth masses. Lately [2, 3] studied the effect of planetary mass on the ability to break plates and hence initiate plate tectonics - but both derived results contradictory to the other. We think that one of the reasons why both studies [2, 3] are not acceptable in their current form is partly due to an oversimplification. Both treated viscosity only temperature-dependent but neglected the effect pressure has on enlarging the viscosity in the deep mantle. More massive planets have therefore a stronger pressure-viscosity-coupling making convection at high pressures sluggish or even impossible. For planets larger than two Earth masses we observe that a conductive lid (termed low-lid) forms above the core-mantle boundary and thus reduces the effective convective part of the mantle when including a pressure-dependent term into the viscosity laws as shown in [1]. Moreover [2, 3] use time independent steady state models neglecting the fact that plate tectonics is a

  20. Plate tectonics in the late Paleozoic

    Directory of Open Access Journals (Sweden)

    Mathew Domeier

    2014-05-01

    Full Text Available As the chronicle of plate motions through time, paleogeography is fundamental to our understanding of plate tectonics and its role in shaping the geology of the present-day. To properly appreciate the history of tectonics—and its influence on the deep Earth and climate—it is imperative to seek an accurate and global model of paleogeography. However, owing to the incessant loss of oceanic lithosphere through subduction, the paleogeographic reconstruction of ‘full-plates’ (including oceanic lithosphere becomes increasingly challenging with age. Prior to 150 Ma ∼60% of the lithosphere is missing and reconstructions are developed without explicit regard for oceanic lithosphere or plate tectonic principles; in effect, reflecting the earlier mobilistic paradigm of continental drift. Although these ‘continental’ reconstructions have been immensely useful, the next-generation of mantle models requires global plate kinematic descriptions with full-plate reconstructions. Moreover, in disregarding (or only loosely applying plate tectonic rules, continental reconstructions fail to take advantage of a wealth of additional information in the form of practical constraints. Following a series of new developments, both in geodynamic theory and analytical tools, it is now feasible to construct full-plate models that lend themselves to testing by the wider Earth-science community. Such a model is presented here for the late Paleozoic (410–250 Ma together with a review of the underlying data. Although we expect this model to be particularly useful for numerical mantle modeling, we hope that it will also serve as a general framework for understanding late Paleozoic tectonics, one on which future improvements can be built and further tested.

  1. Is plate tectonics needed to evolve technological species on exoplanets?

    Directory of Open Access Journals (Sweden)

    Robert J. Stern

    2016-07-01

    Full Text Available As we continue searching for exoplanets, we wonder if life and technological species capable of communicating with us exists on any of them. As geoscientists, we can also wonder how important is the presence or absence of plate tectonics for the evolution of technological species. This essay considers this question, focusing on tectonically active rocky (silicate planets, like Earth, Venus, and Mars. The development of technological species on Earth provides key insights for understanding evolution on exoplanets, including the likely role that plate tectonics may play. An Earth-sized silicate planet is likely to experience several tectonic styles over its lifetime, as it cools and its lithosphere thickens, strengthens, and becomes denser. These include magma ocean, various styles of stagnant lid, and perhaps plate tectonics. Abundant liquid water favors both life and plate tectonics. Ocean is required for early evolution of diverse single-celled organisms, then colonies of cells which specialized further to form guts, appendages, and sensory organisms up to the complexity of fish (central nervous system, appendages, eyes. Large expanses of dry land also begin in the ocean, today produced above subduction zones in juvenile arcs and by their coalescence to form continents, although it is not clear that plate tectonics was required to create continental crust on Earth. Dry land of continents is required for further evolution of technological species, where modification of appendages for grasping and manipulating, and improvement of eyes and central nervous system could be perfected. These bioassets allowed intelligent creatures to examine the night sky and wonder, the beginning of abstract thinking, including religion and science. Technology arises from the exigencies of daily living such as tool-making, agriculture, clothing, and weapons, but the pace of innovation accelerates once it is allied with science. Finally, the importance of plate

  2. Reducing risk where tectonic plates collide

    Science.gov (United States)

    Gomberg, Joan S.; Ludwig, Kristin A.

    2017-06-19

    Most of the world’s earthquakes, tsunamis, landslides, and volcanic eruptions are caused by the continuous motions of the many tectonic plates that make up the Earth’s outer shell. The most powerful of these natural hazards occur in subduction zones, where two plates collide and one is thrust beneath another. The U.S. Geological Survey’s (USGS) “Reducing Risk Where Tectonic Plates Collide—A USGS Plan to Advance Subduction Zone Science” is a blueprint for building the crucial scientific foundation needed to inform the policies and practices that can make our Nation more resilient to subduction zone-related hazards.

  3. Understanding seismic heterogeneities in the lower mantle beneath the Americas from seismic tomography and plate tectonic history

    NARCIS (Netherlands)

    Ren, Y.; Stutzmann, E.; Hilst, R.D. van der; Besse, J.

    2007-01-01

    We combine results from seismic tomography and plate motion history to investigate slabs of subducted lithosphere in the lower mantle beneath the Americas. Using broadband waveform cross correlation, we measured 37,000 differential P and S traveltimes, 2000 PcP-P and ScS-S times along a wide

  4. Plate tectonics and planetary habitability: current status and future challenges.

    Science.gov (United States)

    Korenaga, Jun

    2012-07-01

    Plate tectonics is one of the major factors affecting the potential habitability of a terrestrial planet. The physics of plate tectonics is, however, still far from being complete, leading to considerable uncertainty when discussing planetary habitability. Here, I summarize recent developments on the evolution of plate tectonics on Earth, which suggest a radically new view on Earth dynamics: convection in the mantle has been speeding up despite its secular cooling, and the operation of plate tectonics has been facilitated throughout Earth's history by the gradual subduction of water into an initially dry mantle. The role of plate tectonics in planetary habitability through its influence on atmospheric evolution is still difficult to quantify, and, to this end, it will be vital to better understand a coupled core-mantle-atmosphere system in the context of solar system evolution. © 2012 New York Academy of Sciences.

  5. Structural and Tectonic Map Along the Pacific-North America Plate Boundary in Northern Gulf of California, Sonora Desert and Valle de Mexicali, Mexico, from Seismic Reflection Evidence

    Science.gov (United States)

    Gonzalez-Escobar, M.; Suarez-Vidal, F.; Mendoza-Borunda, R.; Martin Barajas, A.; Pacheco-Romero, M.; Arregui-Estrada, S.; Gallardo-Mata, C.; Sanchez-Garcia, C.; Chanes-Martinez, J.

    2012-12-01

    Between 1978 and 1983, Petróleos Mexicanos (PEMEX) carried on an intense exploration program in the northern Gulf of California, the Sonora Desert and the southern part of the Mexicali Valley. This program was supported by a seismic reflection field operation. The collected seismic data was 2D, with travel time of 6 s recording, in 48 channels, and the source energy was: dynamite, vibroseis and air guns. Since 2007 to present time, the existing seismic data has been re-processing and ire-interpreting as part of a collaboration project between the PEMEX's Subdirección de Exploración (PEMEX) and CICESE. The study area is located along a large portion of the Pacific-North America plate boundary in the northern Gulf of California and the Southern part of the Salton Trough tectonic province (Mexicali Valley). We present the result of the processes reflection seismic lines. Many of the previous reported known faults were identify along with the first time described located within the study region. We identified regions with different degree of tectonic activity. In structural map it can see the location of many of these known active faults and their associated seismic activity, as well as other structures with no associated seismicity. Where some faults are mist placed they were deleted or relocated based on new information. We included historical seismicity for the region. We present six reflection lines that cross the aftershocks zone of the El Mayor-Cucapah earthquake of April 4, 2010 (Mw7.2). The epicenter of this earthquake and most of the aftershocks are located in a region where pervious to this earthquake no major earthquakes are been reported. A major result of this study is to demonstrate that there are many buried faults that increase the seismic hazard.

  6. Indonesian Landforms and Plate Tectonics

    Directory of Open Access Journals (Sweden)

    Herman Th. Verstappen

    2014-06-01

    Full Text Available DOI: 10.17014/ijog.v5i3.103The horizontal configuration and vertical dimension of the landforms occurring in the tectonically unstable parts of Indonesia were resulted in the first place from plate tectonics. Most of them date from the Quaternary and endogenous forces are ongoing. Three major plates – the northward moving Indo-Australian Plate, the south-eastward moving SE-Asian Plate and the westward moving Pacific Plate - meet at a plate triple-junction situated in the south of New Guinea’s Bird’s Head. The narrow North-Moluccan plate is interposed between the Asia and Pacific. It tapers out northward in the Philippine Mobile Belt and is gradually disappearing. The greatest relief amplitudes occur near the plate boundaries: deep ocean trenches are associated with subduction zones and mountain ranges with collision belts. The landforms of the more stable areas of the plates date back to a more remote past and, where emerged, have a more subdued relief that is in the first place related to the resistance of the rocks to humid tropical weathering Rising mountain ranges and emerging island arcs are subjected to rapid humid-tropical river erosions and mass movements. The erosion products accumulate in adjacent sedimentary basins where their increasing weight causes subsidence by gravity and isostatic compensations. Living and raised coral reefs, volcanoes, and fault scarps are important geomorphic indicators of active plate tectonics. Compartmental faults may strongly affect island arcs stretching perpendicular to the plate movement. This is the case on Java. Transcurrent faults and related pull-apart basins are a leading factor where plates meet at an angle, such as on Sumatra. The most complicated situation exists near the triple-junction and in the Moluccas. Modern research methods, such as GPS measurements of plate movements and absolute dating of volcanic outbursts and raised coral reefs are important tools. The mega-landforms resulting

  7. Miocene uplift of the NE Greenland margin linked to plate tectonics: Seismic evidence from the Greenland Fracture Zone, NE Atlantic

    DEFF Research Database (Denmark)

    Døssing Andreasen, Arne; Japsen, Peter; Watts, Anthony B.

    2016-01-01

    Tectonic models predict that, following breakup, rift margins undergo only decaying thermal subsidence during their post-rift evolution. However, post-breakup stratigraphy beneath the NE Atlantic shelves shows evidence of regional-scale unconformities, commonly cited as outer margin responses to ...... by plate tectonic forces, induced perhaps by a change in the Iceland plume (a hot pulse) and/or by changes in intra-plate stresses related to global tectonics.......Tectonic models predict that, following breakup, rift margins undergo only decaying thermal subsidence during their post-rift evolution. However, post-breakup stratigraphy beneath the NE Atlantic shelves shows evidence of regional-scale unconformities, commonly cited as outer margin responses...... backstripping. We explain the thermo-mechanical coupling and the deposition of contourites by the formation of a continuous plate boundary along the Mohns and Knipovich ridges, leading to an accelerated widening of the Fram Strait. We demonstrate that the IMU event is linked to onset of uplift and massive shelf...

  8. Plate tectonics, habitability and life

    Science.gov (United States)

    Spohn, Tilman; Breuer, Doris

    2016-04-01

    The role of plate tectonics in defining habitability of terrestrial planets is being increasingly discussed (e.g., Elkins-Tanton, 2015). Plate tectonics is a significantly evolved concept with a large variety of aspects. In the present context, cycling of material between near surface and mantle reservoirs is most important. But increased heat transport through mixing of cold lithosphere with the deep interior and formation of continental crust may also matter. An alternative mechanism of material cycling between these reservoirs is hot-spot volcanism combined with crust delamination. Hot-spot volcanism will transport volatiles to the atmosphere while delamination will mix crust, possibly altered by sedimentation and chemical reactions, with the mantle. The mechanism works as long as the stagnant lithosphere plate has not grown thicker than the crust and as long as volcanic material is added onto the crust. Thermal evolution studies suggest that the mechanism could work for the first 1-2 Ga of planetary evolution. The efficiency of the mechanism is limited by the ratio of extrusive to intrusive volcanism, which is thought to be less than 0.25. Plate tectonics would certainly have an advantage by working even for more evolved planets. A simple, most-used concept of habitability requires the thermodynamic stability of liquid water on the surface of a planet. Cycling of CO2between the atmosphere, oceans and interior through subduction and surface volcanism is an important element of the carbonate-silicate cycle, a thermostat feedback cycle that will keep the atmosphere from entering into a runaway greenhouse. Calculations for a model Earth lacking plate tectonics but degassing CO2, N, and H2O to form a surface ocean and a secondary atmosphere (Tosi et al, 2016) suggest that liquid water can be maintained on the surface for 4.5Ga. The model planet would then qualify as habitable. It is conceivable that the CO2 buffering capability of its ocean together with silicate

  9. History and Evolution of Precambrian plate tectonics

    Science.gov (United States)

    Fischer, Ria; Gerya, Taras

    2014-05-01

    Plate tectonics is a global self-organising process driven by negative buoyancy at thermal boundary layers. Phanerozoic plate tectonics with its typical subduction and orogeny is relatively well understood and can be traced back in the geological records of the continents. Interpretations of geological, petrological and geochemical observations from Proterozoic and Archean orogenic belts however (e.g., Brown, 2006), suggest a different tectonic regime in the Precambrian. Due to higher radioactive heat production the Precambrian lithosphere shows lower internal strength and is strongly weakened by percolating melts. The fundamental difference between Precambrian and Phanerozoic tectonics is therefore the upper-mantle temperature, which determines the strength of the upper mantle (Brun, 2002) and the further tectonic history. 3D petrological-thermomechanical numerical modelling experiments of oceanic subduction at an active plate at different upper-mantle temperatures show these different subduction regimes. For upper-mantle temperatures 250 K above the present day value no subduction occurs any more. The whole lithosphere is delaminating and due to strong volcanism and formation of a thicker crust subduction is inhibited. This stage of 200-250 K higher upper mantle temperature which corresponds roughly to the early Archean (Abbott, 1994) is marked by strong volcanism due to sublithospheric decompression melting which leads to an equal thickness for both oceanic and continental plates. As a consequence subduction is inhibited, but a compressional setup instead will lead to orogeny between a continental or felsic terrain and an oceanic or mafic terrain as well as internal crustal convection. Small-scale convection with plume shaped cold downwellings also in the upper mantle is of increased importance compared to the large-scale subduction cycle observed for present temperature conditions. It is also observed that lithospheric downwellings may initiate subduction by

  10. Oil prospection using the tectonic plate model

    Science.gov (United States)

    Pointu, Agnès

    2015-04-01

    Tectonic plate models are an intellectual setting to understand why oil deposits are so uncommon and unequally distributed and how models can be used in actual oil and gas prospection. In this case, we use the example of the Ghawar deposit (Saudi Arabia), one of the largest producing well in the world. In the first step, physical properties of rocks composing the oil accumulation are studied by laboratory experiments. Students estimate the porosity of limestone and clay by comparing their mass before and after water impregnation. Results are compared to microscopic observations. Thus, students come to the conclusion that oil accumulations are characterized by superposition of rocks with very different properties: a rich organic source rock (clays of the Hanifa formation), a porous reservoir rock to store the petroleum in (limestones of the Arab formation) and above an impermeable rock with very low porosity (evaporites of the Tithonien). In previous lessons, students have seen that organic matter is usually mineralized by bacteria and that this preservation requires particular conditions. The aim is to explain why biomass production has been so important during the deposit of the clays of the Hanifa formation. Tectonic plate models make it possible to estimate the location of the Arabian Peninsula during Jurassic times (age of Hanifa formation). In order to understand why the paleo-location of the Arabian Peninsula is important to preserve organic matter, students have different documents showing: - That primary production of biomass by phytoplankton is favored by climatic conditions, - That the position of continents determinate the ocean currents and the positions of upwelling zones and zones where organic matter will be able to be preserved, - That north of the peninsula there was a passive margin during Jurassic times. An actual seismic line is studied in order to highlight that this extensive area allowed thick sedimentary deposits to accumulate and that fast

  11. The ultra low frequency electromagnetic radiation observed in the topside ionosphere above boundaries of tectonic plates

    Directory of Open Access Journals (Sweden)

    Michael A. Athanasiou

    2015-01-01

    Full Text Available In this paper we present results of a comparison between ultra low frequency (ULF electromagnetic (EM radiation, recorded by an electric field instrument onboard the satellite detection of electromagnetic emissions transmitted from earthquake regions in the topside ionosphere, and the seismicity of regions with high and low seismic activity. In particular, we evaluated the energy variations of the ULF Ezelectric field component during a period of four years (2006-2009, in order to examine the possible relation of ULF EM radiation with seismogenic regions located in Central America, Indonesia, the Eastern Mediterranean Basin and Greece. As a tool for evaluating the ULF Ez energy variations we used singular spectrum analysis techniques. The results of our analysis clearly show a significant increase of the ULF EM energy emitted from regions of highest seismic activity at the boundaries tectonic plates. Furthermore, we found that higher electromagnetic radiation was detected in a region above the northern- western Greek Arc (R1 than above the adjacent region including Athens and its urban area. We interpret these results of the present study as suggesting that: i the seismogenic regions at the boundary of tectonic plates radiate ULF EM emissions observed by satellites in the topside ionosphere; and ii that this EM radiation is not only related with the occurrence time of great (M≥5 earthquakes, but it is often present in intermediate times and it appears as a quasi-permanent phenomenon.

  12. The Role of Tectonic and Seismicity in Siting of Nuclear Power Plant

    International Nuclear Information System (INIS)

    Abdel Aziz, M.A.H.

    2008-01-01

    The site selection for the a nuclear power plant (NPP) is controlled by many criteria. One of the most important criterion is the tectonic and seismicity of the site and its surroundings. Since, it is preferable the site in concern is characterized by low tectonic and low seismicity to avoid the damage effects associated with the occurrence of destructive earthquakes. The investigation of the tectonic and seismicity maps of egypt has been carried out to candidate potential areas or sites for nuclear power plant installation from seismicity point of view. Also, the design basis ground motion in terms of peak ground acceleration and response spectra of some of the potential sites are defined through the conduct of probabilistic seismic hazard analysis The study revealed that although there is no criterion to exclude areas of high tectonic and high seismicity as potential sites for nuclear power plant installation but, it is preferable avoiding such areas. This is attributed to the critical seismic curve that characterizes such areas and is required high seismic design levels to resist the destructive vibratory ground motion associated with the expected earthquake. Consequently, the required high seismic design levels will have a negative impact on the economic cost of the facility compared with that built in low and moderate seismic areas. Hence, areas like the gulf of suez, the northern part of the Red Sea and the southern part of Sinai Peninsula should be avoided as potential sites for NPP from the tectonic and seismicity point of view. On the other hand, areas like Nile delta and its valley, the Northern and Southern parts of Western desert and the central and southern parts of the Eastern Desert should be candidate as potential sites on condition, the other criteria meet the IAEA's regulations. Also, the seismic hazard curve of the Northwest littoral zone reflects low design basis ground motion values compared with the Nile delta region

  13. The alternative concept of global tectonics

    Science.gov (United States)

    Anokhin, Vladimir; Kholmyansky, Mikhael

    2016-04-01

    The existing plate tectonic paradigm becomes more questionable in relation to the new facts of the Earth. The most complete to date criticism of plate tectonics provisions contained in the article (Pratt, 2000). Authors can recall a few facts that contradict the idea of long-range movement of plates: - The absence of convection cells in the mantle, detected by seismic tomography; - The presence of long-lived deep regmatic network in the crust, not distorted by the movement of plates; - The inability of linking the global geometry of the of mutual long-distance movement of plates. All this gives reason to believe that correct, or at least a satisfactory concept of global tectonics are not exist now. After overcoming the usual inertia of thinking the plate paradigm in the foreseeable future will replace by different concept, more relevant as the observable facts of the Earth and the well-known physical laws. The authors suggest that currently accumulated sufficient volume of facts and theoretical ideas for the synthesis of a new general hypothesis of the structure and dynamics of the Earth. Analysis of the existing tectonic theory suggests that most of their provisions are mutually compatible. Obviously, plume tectonics perfectly compatible with any of classical models. It contradicts the only plate tectonics (movement of hot spots in principle not linked either with each other or with the general picture of the plate movements, the presence of mantle convection and mantle streams are mutually exclusive, and so on). The probable transfer of the heated material down up within the Earth may occur in various forms, the simplest of which (and, consequently, the most probable) are presented plumes. The existence in the mantle numerous large volumes of decompressed substances (detected seismic tomography), can be correlated with the bodies of plumes at different stages of uplift. Plumes who raise to the bottom of the lithosphere, to spread out to the sides and form a set

  14. A transparent and data-driven global tectonic regionalization model for seismic hazard assessment

    Science.gov (United States)

    Chen, Yen-Shin; Weatherill, Graeme; Pagani, Marco; Cotton, Fabrice

    2018-05-01

    A key concept that is common to many assumptions inherent within seismic hazard assessment is that of tectonic similarity. This recognizes that certain regions of the globe may display similar geophysical characteristics, such as in the attenuation of seismic waves, the magnitude scaling properties of seismogenic sources or the seismic coupling of the lithosphere. Previous attempts at tectonic regionalization, particularly within a seismic hazard assessment context, have often been based on expert judgements; in most of these cases, the process for delineating tectonic regions is neither reproducible nor consistent from location to location. In this work, the regionalization process is implemented in a scheme that is reproducible, comprehensible from a geophysical rationale, and revisable when new relevant data are published. A spatial classification-scheme is developed based on fuzzy logic, enabling the quantification of concepts that are approximate rather than precise. Using the proposed methodology, we obtain a transparent and data-driven global tectonic regionalization model for seismic hazard applications as well as the subjective probabilities (e.g. degree of being active/degree of being cratonic) that indicate the degree to which a site belongs in a tectonic category.

  15. On the relative significance of lithospheric weakening mechanisms for sustained plate tectonics

    Science.gov (United States)

    Araceli Sanchez-Maes, Sophia

    2018-01-01

    Plate tectonics requires the bending of strong plates at subduction zones, which is difficult to achieve without a secondary weakening mechanism. Two classes of weakening mechanisms have been proposed for the generation of ongoing plate tectonics, distinguished by whether or not they require water. Here we show that the energy budget of global subduction zones offers a simple yet decisive test on their relative significance. Theoretical studies of mantle convection suggest bending dissipation to occupy only 10-20 % of total dissipation in the mantle, and our results indicate that the hydrous mechanism in the shallow part of plates is essential to satisfy the requirement. Thus, surface oceans are required for the long-term operation of plate tectonics on terrestrial worlds. Establishing this necessary and observable condition for sustained plate tectonics carries important implications for planetary habitability at large.

  16. Crustal thickness controlled by plate tectonics

    DEFF Research Database (Denmark)

    Artemieva, Irina M.; Meissner, Rolf

    2012-01-01

    /gabbro–eclogite phase transition in crustal evolution and the links between lithosphere recycling, mafic magmatism, and crustal underplating. We advocate that plate tectonics processes, togetherwith basalt/gabbro–eclogite transition, limit crustal thickness worldwide by providing effective mechanisms of crustal...

  17. Analysis of the seismicity of Southeastern Sicily: a proposed tectonic interpretation

    Directory of Open Access Journals (Sweden)

    M. S. Barbano

    2000-06-01

    Full Text Available Southeastern Sicily is one of the Italian regions with high seismic risk and is characterised by the occurrence in the past of large destructive events (MS = 6.4-7.3 over a territory which is densely urbanised today. The main earthquakes were analysed and some minor damaging shocks reviewed to investigate the main seismogenic features of the region. The comparison between the pattern of seismicity and evidence of Quaternary tectonics allowed us to propose a first tentative, tectonic interpretation of the earthquakes. On the whole, the seismicity of SE Sicily seems distributed along regional fault systems which have had a role in the recent geodynamic evolution of the area. The Malta escarpment, the only structure whose late Quaternary-recent activity is currently known, appears the most probable source for earthquakes with about 7 magnitude. Although no evidence of tectonics subsequent to the middle Pleistocene is available for them, the Scicli line and the NE-SW fault system delimiting the northern sector of the Hyblean plateau seem seismically active with events with maximum magnitude of 5.2 and 6.4, respectively.

  18. Global Dynamic Numerical Simulations of Plate Tectonic Reorganizations

    Science.gov (United States)

    Morra, G.; Quevedo, L.; Butterworth, N.; Matthews, K. J.; Müller, D.

    2010-12-01

    We use a new numerical approach for global geodynamics to investigate the origin of present global plate motion and to identify the causes of the last two global tectonic reorganizations occurred about 50 and 100 million years ago (Ma) [1]. While the 50 Ma event is the most well-known global plate-mantle event, expressed by the bend in the Hawaiian-Emperor volcanic chain, a prominent plate reorganization at about 100 Ma, although presently little studied, is clearly indicated by a major bend in the fracture zones in the Indian Ocean and by a change in Pacific plate motion [2]. Our workflow involves turning plate reconstructions into surface meshes that are subsequently employed as initial conditions for global Boundary Element numerical models. The tectonic setting that anticipates the reorganizations is processed with the software GPlates, combining the 3D mesh of the paleo-plate morphology and the reconstruction of paleo-subducted slabs, elaborated from tectonic history [3]. All our models involve the entire planetary system, are fully dynamic, have free surface, are characterized by a spectacular computational speed due to the simultaneous use of the multi-pole algorithm and the Boundary Element formulation and are limited only by the use of sharp material property variations [4]. We employ this new tool to unravel the causes of plate tectonic reorganizations, producing and comparing global plate motion with the reconstructed ones. References: [1] Torsvik, T., Müller, R.D., Van der Voo, R., Steinberger, B., and Gaina, C., 2008, Global Plate Motion Frames: Toward a unified model: Reviews in Geophysics, VOL. 46, RG3004, 44 PP., 2008 [2] Wessel, P. and Kroenke, L.W. Pacific absolute plate motion since 145 Ma: An assessment of the fixed hot spot hypothesis. Journal of Geophysical Research, Vol 113, B06101, 2008 [3] L. Quevedo, G. Morra, R. D. Mueller. Parallel Fast Multipole Boundary Element Method for Crustal Dynamics, Proceeding 9th World Congress and 4th Asian

  19. Seismic evidence for deep fluid circulation in the overriding plate of subduction zones

    Science.gov (United States)

    Tauzin, B.; Reynard, B.; Bodin, T.; Perrillat, J. P.; Debayle, E.

    2015-12-01

    In subduction zones, non-volcanic tremors are associated with fluid circulations (Obara, 2002). Their sources are often located on the interplate boundary (Rogers and Dragert, 2003; Shelly et al, 2006; La Rocca, 2009), consistent with fluids released by the dehydration of subducted plates (Hacker et al., 2003). Reports of tremors in the overriding continental crust of several subduction zones in the world (Kao et al., 2005; Payero et al., 2008; Ide, 2012) suggest fluid circulation at shallower depths but potential fluid paths are poorly documented. Here we obtained seismic observations from receiver functions that evidence the close association between the shallow tremor zone, electrical conductivity, and tectonic features of the Cascadia overriding plate. A seismic discontinuity near 15 km depth in the crust of the overriding North American plate is attributed to the Conrad discontinuity. This interface is segmented, and its interruption is spatially correlated with conductive regions and shallow swarms of seismicity and non-volcanic tremors. These observations suggest that shallow fluid circulation, tremors and seismicity are controlled by fault zones limiting blocks of accreted terranes in the overriding plate (Brudzinski and Allen, 2007). These zones constitute fluid "escape" routes that may contribute unloading fluid pressure on the megathrust. Obara, K. (2002). Science, 296, 1679-1681. Rogers, G., & Dragert, H. (2003). Science, 300, 1942-1943. Shelly, D. R., et al. (2006). Nature, 442, 188-191. La Rocca, M., et al. (2009). Science, 323, 620-623. Kao, H., et al. (2005). Nature, 436, 841-844. Payero, J. S., et al. (2008). Geophysical Research Letters, 35. Ide, S. (2012). Journal of Geophysical Research: Solid Earth, 117. Brudzinski, M. R., & Allen, R. M. (2007). Geology, 35, 907-910.

  20. Active tectonics and earthquake potential of the Myanmar region

    OpenAIRE

    Wang, Yu; Sieh, Kerry; Tun, Soe Thura; Lai, Kuang-Yin; Myint, Than

    2014-01-01

    This paper describes geomorphologic evidence for the principal neotectonic features of Myanmar and its immediate surroundings. We combine this evidence with published structural, geodetic, and seismic data to present an overview of the active tectonic architecture of the region and its seismic potential. Three tectonic systems accommodate oblique collision of the Indian plate with Southeast Asia and extrusion of Asian territory around the eastern syntaxis of the Himalayan mountain range. Subd...

  1. Seismic studies of crustal structure and tectonic evolution across the central California margin and the Colorado Plateau margin

    Science.gov (United States)

    Howie, John Mark

    This thesis presents results from two integrated deep-crustal seismic-reflection and wide-angle-reflection/refraction studies that improve our understanding of crustal structure and tectonic evolution in two tectonically active areas of the western United States. A multi-faceted approach to the study of crustal structure includes the use of compressional and shear wave seismic data. Supplementing the controlled source seismic observations with seismicity, gravity, heat flow, laboratory measurements and available geologic information allows a much improved understanding of crustal structure and tectonic evolution than would be available from the seismic data alone. Chapter 1 introduces the data integration strategy applied to the studies completed. In Chapter 2, an integrated crustal-velocity model across the south-central California margin west of the San Adreas fault is presented. The crustal structure defines tectonostratigraphic terranes 15 to 20 km thick underlain by a 6-km-thick high-velocity layer (6.8-7.0 km/s) interpreted as tectonically underplated oceanic crust. Structures defined in the oceanic crust indicate significant compressional and strike-slip deformation within the oceanic crust that probably formed during the final stages of subduction from 24-16 Ma. In Chapter 3, the crustal model from Chapter 2 is used as a constraint for models of the tectonic evolution of the Pacific-North American transform plate boundary. By combining the crustal structure with thermal models for asthenospheric upwelling associated with a slab-free window, I find that the mantle lithosphere east of the coast beneath south-central California probably delaminated from the oceanic crust, stranding the oceanic crust beneath the margin. In Chapter 4, results from a high-resolution reflection experiment in central Arizona across the southwestern edge of the Colorado Plateau address the relationship between strength of the crust and localization of extensional tectonism. A low

  2. Subduction and Plate Edge Tectonics in the Southern Caribbean

    Science.gov (United States)

    Levander, A.; Schmitz, M.; Niu, F.; Bezada, M. J.; Miller, M. S.; Masy, J.; Ave Lallemant, H. G.; Pindell, J. L.; Bolivar Working Group

    2013-05-01

    The southern Caribbean plate boundary consists of a subduction zone at at either end of a complex strike-slip fault system: In the east at the Lesser Antilles subduction zone, the Atlantic part of the South American plate subducts beneath the Caribbean. In the north and west in the Colombia basin, the Caribbean subducts under South America. In a manner of speaking, the two plates subduct beneath each other. Finite-frequency teleseismic P-wave tomography confirms this, imaging the Atlantic and the Caribbean plates subducting steeply in opposite directions to transition zone depths under northern South America (Bezada et al, 2010). The two subduction zones are connected by the El Pilar-San Sebastian strike-slip fault system, a San Andreas scale system that has been cut off at the Bocono fault, the southeastern boundary fault of the Maracaibo block. A variety of seismic probes identify subduction features at either end of the system (Niu et al, 2007; Clark et al., 2008; Miller et al. 2009; Growdon et al., 2009; Huang et al., 2010; Masy et al, 2011). The El Pilar system forms at the southeastern corner of the Antilles subduction zone with the Atlantic plate tearing from South America. The deforming plate edges control mountain building and basin formation at the eastern end of the strike-slip system. Tearing the Atlantic plate from the rest of South America appears to cause further lithospheric instability continentward. In northwestern South America the Caribbean plate very likely also tears, as its southernmost element subducts at shallow angles under northernmost Colombia but then rapidly descends to the transition zone under Lake Maracaibo (Bezada et al., 2010). We believe that the flat slab controls the tectonics of the Neogene Merida Andes, Perija, and Santa Marta ranges. The nonsubducting part of the Caribbean plate also underthrusts northern Venezuela to about the width of the coastal mountains (Miller et al., 2009). We infer that the edge of the underthrust

  3. Archean greenstone-tonalite duality: Thermochemical mantle convection models or plate tectonics in the early Earth global dynamics?

    Science.gov (United States)

    Kerrich, Robert; Polat, Ali

    2006-03-01

    were intruded by voluminous norites from the Neoarchean through Proterozoic; norites are accounted for by melting of subduction metasomatized Archean continental lithospheric mantle (CLM). Deep CLM defines Archean cratons; it extends to ˜ 350 km, includes the diamond facies, and xenoliths signify a composition of the buoyant, refractory, residue of plume melting, a natural consequence of imbricated plateau-arc crust. Voluminous tonalites of Archean greenstone-granitoid terranes show a secular trend of increasing Mg#, Cr, Ni consistent with slab melts hybridizing with thicker mantle wedge as subduction angle steepens. Strike-slip faults of 1000 km scale; diachronous accretion of distinct tectonostratigraphic terranes; and broad Cordilleran-type orogens featuring multiple sutures, and oceanward migration of arcs, in the Archean Superior and Yilgarn cratons, are in common with the Altaid and Phanerozoic Cordilleran orogens. There is increasing geological evidence of the supercontinent cycle operating back to ˜ 2.7 Ga: Kenorland or Ur ˜ 2.7-2.4 Ga; Columbia ˜ 1.6-1.4 Ga; Rodinia ˜ 1100-750 Ma; and Pangea ˜ 230 Ma. High-resolution seismic reflection profiling of Archean terranes reveals a prevalence of low angle structures, and evidence for paleo-subduction zones. Collectively, the geological-geochemical-seismic records endorse the operation of plate tectonics since the early Archean.

  4. Mechanics and Partitioning of Deformation of the Northwestern Okhostk Plate, Northeast Russia

    Science.gov (United States)

    Hindle, D.; Mackey, K.; Fujita, K.

    2007-12-01

    The tectonic evolution and present day deformation of northeastern Russia remains one of the major challenges in plate tectonics. Arguments over the existence of at least a separate Okhotsk plate between North America and Eurasia appear to be resolved on the basis of the latest GPS studies combined with elastic modeling. The question of the mechanical behaviour of the Okhotsk plate, caught between the slowly, obliquely converging North American and Eurasian plates now becomes important. We present an analysis of geological lineaments, micro-seismicity, total seismic moment release and seismic deformation rate and GPS campaign data and global plate tectonic model data (REVEL) to estimate the likelihood of future seismicity and the relative amount of elastic and viscous deformation of the lithosphere of the northwestern Okhotsk plate. We find that it is likely that the Okhotsk plate is cracked into slivers, but that rates of relative motion of these slivers are close to indistinguishable from the behaviour of a single, rigid plate. The analysis also suggests the upper bound for large earthquakes in the region to be Mw 7-7.5 which we expect to occur only on the plate boundary fault itself. This fits geological evidence for a long term offset rate 5-10 times higher on the major plate boundary fault than other lineaments cutting the Okhotsk plate itself.

  5. Barrel organ of plate tectonics - a new tool for outreach and education

    Science.gov (United States)

    Broz, Petr; Machek, Matěj; Šorm, Zdar

    2016-04-01

    Plate tectonics is the major geological concept to explain dynamics and structure of Earth's outer shell, the lithosphere. In the plate tectonic theory processes in the Earth lithosphere and its dynamics is driven by the relative motion and interaction of lithospheric plates. Geologically most active regions on Earth often correlate with the lithospheric plate boundaries. Thus for explaining the earth surface evolution, mountain building, volcanism and earthquake origin it is important to understand processes at the plate boundaries. However these processes associated with plate tectonics usually require significant period of time to take effects, therefore, their entire cycles cannot be directly observed in the nature by humans. This makes a challenge for scientists studying these processes, but also for teachers and popularizers trying to explain them to students and to the general public. Therefore, to overcome this problem, we developed a mechanical model of plate tectonics enabling demonstration of most important processes associated with plate tectonics in real time. The mechanical model is a wooden box, more specifically a special type of barrel organ, with hand painted backdrops in the front side. These backdrops are divided into several components representing geodynamic processes associated with plate tectonics, specifically convective currents occurring in the mantle, sea-floor spreading, a subduction of the oceanic crust under the continental crust, partial melting and volcanism associated with subduction, a formation of magmatic stripes, an ascent of mantle plume throughout the mantle, a volcanic activity associated with hot spots, and a formation and degradation of volcanic islands on moving lithospheric plate. All components are set in motion by a handle controlled by a human operator, and the scene is illuminated with colored lights controlled automatically by an electric device embedded in the box. Operation of the model may be seen on www

  6. The Role of Long-Term Tectonic Deformation on the Distribution of Present-Day Seismic Activity in the Caribbean and Central America

    Science.gov (United States)

    Schobelock, J.; Stamps, D. S.; Pagani, M.; Garcia, J.; Styron, R. H.

    2017-12-01

    The Caribbean and Central America region (CCAR) undergoes the entire spectrum of earthquake types due to its complex tectonic setting comprised of transform zones, young oceanic spreading ridges, and subductions along its eastern and western boundaries. CCAR is, therefore, an ideal setting in which to study the impacts of long-term tectonic deformation on the distribution of present-day seismic activity. In this work, we develop a continuous tectonic strain rate model based on inter-seismic geodetic data and compare it with known active faults and earthquake focal mechanism data. We first create a 0.25o x 0.25o finite element mesh that is comprised of block geometries defined in previously studies. Second, we isolate and remove transient signals from the latest open access community velocity solution from UNAVCO, which includes 339 velocities from COCONet and TLALOCNet GNSS data for the Caribbean and Central America, respectively. In a third step we define zones of deformation and rigidity by creating a buffer around the boundary of each block that varies depending on the size of the block and the expected deformation zone based on locations of GNSS data that are consistent with rigid block motion. We then assign each node within the buffer a 0 for the deforming areas and a plate index outside the buffer for the rigid. Finally, we calculate a tectonic strain rate model for CCAR using the Haines and Holt finite element approach to fit bi-cubic Bessel splines to the the GNSS/GPS data assuming block rotation for zones of rigidity. Our model of the CCAR is consistent with compression along subduction zones, extension across the mid-Pacific Rise, and a combination of compression and extension across the North America - Caribbean plate boundary. The majority of CCAR strain rate magnitudes range from -60 to 60 nanostrains/yr. Modeling results are then used to calculate expected faulting behaviors that we compare with mapped geologic faults and seismic activity.

  7. Petroleum and natural gas geology and plate tectonics

    Energy Technology Data Exchange (ETDEWEB)

    Koebel, B.

    1984-01-01

    Several processes of oil and gas geology are studied in connection with plate-tectonical processes. Thus it becomes clear, that there is a distinct difference between the Paleozoic development of the European plate and the Mesozoic development. One can state, that the Paleozoic development is essentially influenced by the positions of the mobile belts and the cratonized parts of the plates. The development during Meso-Caenozoic is mainly characterized by crustal processes in the result of the disintegration of Pangaea.

  8. Learning Plate Tectonics Using a Pre-Analogy Step

    Science.gov (United States)

    Glesener, G. B.; Sandoval, W. A.

    2011-12-01

    Previous research has shown that children tend to demonstrate lower performance on analogical reasoning tasks at a causal relations level compared to most adults (Gentner & Toupin, 1986). This tendency is an obstacle that geoscience educators must overcome because of the high frequency of analogies used in geoscience pedagogy. In particular, analog models are used to convey complex systems of non-everyday/non-observable events found in nature, such as plate tectonics. Key factors in successful analogical reasoning that have been suggested by researchers include knowledge of the causal relations in the base analog (Brown & Kane, 1988; Gentner, 1988; Gentner & Toupin, 1986), and development of learning strategies and metaconceptual competence(Brown & Kane, 1988). External factors, such as guiding cues and hints have been useful cognitive supports that help students reason through analogical problems (Gick & Holyoak, 1980). Cognitive supports have been seen by researchers to decrease processing demands on retrieval and working memory (Richland, Zur, & Holyoak, 2007). We observed third and fourth graders learning about plate tectonics beginning with a pre-analogy step-a cognitive support activity a student can do before working with an analogy to understand the target. This activity was designed to aid students in developing their understanding of object attributes and relations within an analog model so that more focus can be placed on mapping the corresponding higher-order relations between the base and target. Students learned targeted concepts of plate tectonics, as measured by pre to post gains on items adapted from the Geosciences Concept Inventory. Analyses of classroom interaction showed that students used the object attributes and higher-order relations highlighted in the pre-analogy activity as resources to reason about plate boundaries and plate movement during earthquakes.

  9. Ore-lead isotopes and Grenville plate tectonics

    International Nuclear Information System (INIS)

    Farquhar, R.M.; Fletcher, I.R.

    1980-01-01

    Recent advances in the 'whole earth' modelling of evolutionary processes of Pb isotopes shed light upon the origin of the metals found in various types of ore deposits. On the bases of these models and several recently published data sets, we believe that the ore deposits formed in various plate tectonic environments may carry 'isotopic fingerprints' which, when used with other characteristics such as mineral assemblages, may identify the depositional environments of many ore bodies. In the present study Pb-isotopic measurements have been made of a number of Precambrain mineralization types and localities throughout the Central Metasedimentary Belt of the Grenville Province. The data for individual deposits are at best ambiguous, but fall into two groups sufficiently distinctive to allow some degree of 'fingerprint' identification. Comparisons with data from other areas suggest that the major periods of sedimentation within the Central Metasedimentary Belt accompanied plate rifting and/or island arc tectonic activity, with most of the mineralized lead being derived from mantle sources. Detailed comparisons between the Grenville and other regions are uncertain, mainly because there are few detailed high-accuracy data sets from younger, tectonically unambiguous mineral occurrences. We suggest that once these data sets are availble, isotopic fingerprinting may become diagnostic for deposits ranging well back into the Precambrain

  10. Active tectonics and earthquake potential of the Myanmar region

    Science.gov (United States)

    Wang, Yu; Sieh, Kerry; Tun, Soe Thura; Lai, Kuang-Yin; Myint, Than

    2014-04-01

    This paper describes geomorphologic evidence for the principal neotectonic features of Myanmar and its immediate surroundings. We combine this evidence with published structural, geodetic, and seismic data to present an overview of the active tectonic architecture of the region and its seismic potential. Three tectonic systems accommodate oblique collision of the Indian plate with Southeast Asia and extrusion of Asian territory around the eastern syntaxis of the Himalayan mountain range. Subduction and collision associated with the Sunda megathrust beneath and within the Indoburman range and Naga Hills accommodate most of the shortening across the transpressional plate boundary. The Sagaing fault system is the predominant locus of dextral motion associated with the northward translation of India. Left-lateral faults of the northern Shan Plateau, northern Laos, Thailand, and southern China facilitate extrusion of rocks around the eastern syntaxis of the Himalaya. All of these systems have produced major earthquakes within recorded history and continue to present major seismic hazards in the region.

  11. Plate Tectonics as a Far-From-Equilibrium Self-Organized Dissipative System

    Science.gov (United States)

    Anderson, D. L.

    2001-12-01

    A fluid above the critical Rayleigh number is far from equilibrium and spontaneously organizes itself into patterns involving the collective motion of large numbers of molecules which are resisted by the viscosity of the fluid. No external template is involved in forming the pattern. In 1928 Pearson showed that Bénard's experiments were driven by variations in surface tension at the top of the fluid and the surface motions drove convection in the fluid. In this case, the surface organized itself AND the underlying fluid. Both internal buoyancy driven flow and flow driven by surface forces can be far-from-equilibrium self-organized open systems that receive energy and matter from the environment. In the Earth, the cold thermal boundary layer at the surface drives plate tectonics and introduces temperature, shear and pressure gradients into the mantle that drive mantle convection. The mantle provides energy and material but may not provide the template. Plate tectonics is therefore a candidate for a far-from-equilibrium dissipative self-organizing system. Alternatively, one could view mantle convection as the self-organized system and the plates as simply the surface manifestation. Lithospheric architecture also imposes lateral temperature gradients onto the mantle which can drive and organize flow. Far-from-equilibrium self-organization requires; an open system, interacting parts, nonlinearities or feedbacks, an outside steady source of energy or matter, multiple possible states and a source of dissipation. In uniform fluids viscosity is the source of dissipation. Sources of dissipation in the plate system include bending, breaking, folding, shearing, tearing, collision and basal drag. These can change rapidly, in contrast to plate driving forces, and introduce the sort of fluctuations that can reorganize far-from-equilibrium systems. Global plate reorganizations can alternatively be thought of as convective overturns of the mantle, or thermal weakening of plates

  12. Seismic potential of weak, near-surface faults revealed at plate tectonic slip rates.

    Science.gov (United States)

    Ikari, Matt J; Kopf, Achim J

    2017-11-01

    The near-surface areas of major faults commonly contain weak, phyllosilicate minerals, which, based on laboratory friction measurements, are assumed to creep stably. However, it is now known that shallow faults can experience tens of meters of earthquake slip and also host slow and transient slip events. Laboratory experiments are generally performed at least two orders of magnitude faster than plate tectonic speeds, which are the natural driving conditions for major faults; the absence of experimental data for natural driving rates represents a critical knowledge gap. We use laboratory friction experiments on natural fault zone samples at driving rates of centimeters per year to demonstrate that there is abundant evidence of unstable slip behavior that was not previously predicted. Specifically, weak clay-rich fault samples generate slow slip events (SSEs) and have frictional properties favorable for earthquake rupture. Our work explains growing field observations of shallow SSE and surface-breaking earthquake slip, and predicts that such phenomena should be more widely expected.

  13. Tectonic styles of future earthquakes in Italy as input data for seismic hazard

    Science.gov (United States)

    Pondrelli, S.; Meletti, C.; Rovida, A.; Visini, F.; D'Amico, V.; Pace, B.

    2017-12-01

    In a recent elaboration of a new seismogenic zonation and hazard model for Italy, we tried to understand how many indications we have on the tectonic style of future earthquake/rupture. Using all available or recomputed seismic moment tensors for relevant seismic events (Mw starting from 4.5) of the last 100 yrs, first arrival focal mechanisms for less recent earthquakes and also geological data on past activated faults, we collected a database gathering a thousands of data all over the Italian peninsula and regions around it. After several summations of seismic moment tensors, over regular grids of different dimensions and different thicknesses of the seismogenic layer, we applied the same procedure to each of the 50 area sources that were designed in the seismogenic zonation. The results for several seismic zones are very stable, e.g. along the southern Apennines we expect future earthquakes to be mostly extensional, although in the outer part of the chain strike-slip events are possible. In the Northern part of the Apennines we also expect different, opposite tectonic styles for different hypocentral depths. In several zones, characterized by a low seismic moment release, defined for the study region using 1000 yrs of catalog, the next possible tectonic style of future earthquakes is less clear. It is worth to note that for some zones the possible greatest earthquake could be not represented in the available observations. We also add to our analysis the computation of the seismic release rate, computed using a distributed completeness, identified for single great events of the historical seismic catalog for Italy. All these information layers, overlapped and compared, may be used to characterize each new seismogenic zone.

  14. Evidence of Apulian crustal structures related to low energy seismicity (Murge, Southern Italy)

    Energy Technology Data Exchange (ETDEWEB)

    Del Gaudio, V.; Ripa, R. R.; Iurilli, V.; Moretti, M.; Pieri, P. [Bari Univ., Bari (Italy). Dipt. di Geologia e Geofisica; Festa, V. [Bari Univ., Bari (Italy). Dipt. Geomineralogico; Pierri, P. [Bari Univ., Bari (Italy). Osservatorio Sismologico; Calcagnile, G. [Bari Univ., Bari (Italy). Dipt. di Geologia e Geofisica; Bari Univ., Bari (Italy). Osservatorio Sismologico; Tropeano, M [Potenza Universita' della Basilicata, Potenza (Italy). Dipt. di Scienze Geologiche

    2001-12-01

    The discovery of recent co-seismic sedimentary structures and the detection of low energy seismic activity in the Murgian plateau (Apulia, Southern Italy) motivated a more detailed examination of the tectonics in this part of the Apulian plate commonly believed to be aseismic. In particular, it was examined the north-western zone where a seismic sequence with maximum magnitude 3.2 and tensional focal mechanism occurred in 1991. The analysis of the existing gravimetric data, integrated by three new profiles carried out across the epicentral area, disclosed an anomaly possibly due to an old tensional tectonic structure located within the upper crust. Even though the depth and the age hypothesised for the anomaly source would exclude a direct causal connection with the observed seismicity, this structure could be a shallower expression of a tectonic structure extending down to the crystalline basement: it could represent a zone of relative weakness where the regional stress, due to the interactions between Apennines and Apulian plate, encounters conditions facilitating the release of seismic energy.

  15. Driving Forces of Plate Tectonics and Evolution of the Oceanic Lithosphere and Asthenosphere

    Science.gov (United States)

    Forsyth, D. W.

    2017-12-01

    As plate tectonics became established as an excellent kinematic description of the relative motions of different blocks of the Earth's lithosphere, many investigators also began exploring the forces involved in driving the plate motions. Because the plates move at nearly constant velocities over long periods of time and inertial terms are unimportant, driving forces must always be balanced by resisting forces in a way that regulates the velocities. Forsyth and Uyeda (1975) incorporated the balancing of torques on the individual plates to help constrain the relative importance of the driving and resisting forces, as parameterized in a way based on prior model investigations of individual parts of the convecting system. We found that the primary driving force was sinking of subducting lithosphere at trenches, balanced largely by viscous resisting forces in the sub-asthenospheric mantle; that viscous drag beneath the oceanic plates was negligible; and that mid-ocean ridges provided a relatively small push. One of the early questions was whether there was buoyant upwelling on a large scale beneath mid-ocean ridges as part of a whole mantle convection system with subduction of the plates representing the downwelling limb. If so, then it would be likely that the plates were just riding on top of large convection cells. Seismic tomography has demonstrated that, on average, there are no deep roots beneath mid-ocean ridges, so that active, buoyant upwelling from the deep mantle does not exist beneath spreading centers. However, more recent tomographic studies have found asymmetry of the shear velocity structure beneath ridges in some areas, pointing to a smaller scale of active convection in the shallow mantle perhaps induced by melt retention buoyancy or the local effects of ridge/hotspot interaction.

  16. Tectonic Divisions Based on Gravity Data and Earthquake Distribution Characteristics in the North South Seismic Belt, China

    Science.gov (United States)

    Tian, T.; Zhang, J.; Jiang, W.

    2017-12-01

    The North South Seismic Belt is located in the middle of China, and this seismic belt can be divided into 12 tectonic zones, including the South West Yunnan (I), the Sichuan Yunnan (II), the Qiang Tang (III), the Bayan Har (IV), the East Kunlun Qaidam (V), the Qi Lian Mountain (VI), the Tarim(VII), the East Alashan (VIII), the East Sichuan (IX), the Ordos(X), the Middle Yangtze River (XI) and the Edge of Qinghai Tibet Block (XII) zone. Based on the Bouguer Gravity data calculated from the EGM2008 model, the Euler deconvolution was used to obtain the edge of tectonic zone to amend the traditional tectonic divisions. In every tectonic zone and the whole research area, the logarithm of the total energy of seismic was calculated. The Time Series Analysis (TSA) for all tectonic zones and the whole area were progressed in R, and 12 equal divisions were made (A1-3, B1-3, C1-3, D1-3) by latitude and longitude as a control group. A simple linear trend fitting of time was used, and the QQ figure was used to show the residual distribution features. Among the zones according to Gravity anomalies, I, II and XII show similar statistical characteristic, with no earthquake free year (on which year there was no earthquake in the zone), and it shows that the more seismic activity area is more similar in statistical characteristic as the large area, no matter how large the zone is or how many earthquakes are in the zone. Zone IV, V, IX, III, VII and VIII show one or several seismic free year during 1970s (IV, V and IX) and 1980s (III, VII and VIII), which may implicate the earthquake activity were low decades ago or the earthquake catalogue were not complete in these zones, or both. Zone VI, X and XI show many earthquake free years even in this decade, which means in these zones the earthquake activity were very low even if the catalogue were not complete. In the control group, the earthquake free year zone appeared random and independent of the seismic density, and in all equal

  17. Tectonic History and Deep Structure of the Demerara Plateau from Combined Wide-Angle and Reflection Seismic Data and Plate Kinematic Reconstructions

    Science.gov (United States)

    Klingelhoefer, F.; Museur, T.; Roest, W. R.; Graindorge, D.; Chauvet, F.; Loncke, L.; Basile, C.; Poetisi, E.; Deverchere, J.; Lebrun, J. F.; Perrot, J.; Heuret, A.

    2017-12-01

    Many transform margins have associated intermediate depth marginal plateaus, which are commonly located between two oceanic basins. The Demerara plateau is located offshore Surinam and French Guiana. Plate kinematic reconstructions show that the plateau is located between the central and equatorial Atlantic in a position conjugate to the Guinean Plateau. In the fall of 2016, the MARGATS cruise acquired geophysical data along the 400 km wide Demerara plateau. The main objective of the cruise was to image the deep structure of the Demerara plateau and to study its tectonic history. A set of 4 combined wide-angle and reflection seismic profiles was acquired along the plateau, using 80 ocean-bottom seismometers, a 3 km long seismic streamer and a 8000 cu inch tuned airgun array. Forward modelling of the wide-angle seismic data on a profile, located in the eastern part of the plateau and oriented in a NE-SW direction, images the crustal structure of the plateau, the transition zone and the neighbouring crust of oceanic origin, up to a depth of 40 km. The plateau itself is characterised by a crust of 30 km thickness, subdivided into three distinct layers. However, the velocities and velocity gradients do not fit typical continental crust, with a lower crustal layer showing untypically high velocities and an upper layer having a steep velocity gradient. From this model we propose that the lowermost layer is probably formed from volcanic underplated material and that the upper crustal layer likely consists of the corresponding extrusive volcanic material, forming thick seaward-dipping reflector sequences on the plateau. A basement high is imaged at the foot of the slope and forms the ocean-continent transition zone. Further oceanward, a 5-6 km thick crust is imaged with velocities and velocity gradients corresponding to a thin oceanic crust. A compilation of magnetic data from the MARGATS and 3 previous cruises shows a high amplitude magnetic anomaly along the northern

  18. Andean tectonics: Implications for Satellite Geodesy

    Science.gov (United States)

    Allenby, R. J.

    1984-01-01

    Current knowledge and theories of large scale Andean tectonics as they relate to site planning for the NASA Crustal Dynamics Program's proposed high precision geodetic measurements of relative motions between the Nazca and South American plates are summarized. The Nazca Plate and its eastern margin, the Peru-Chile Trench, is considered a prototype plate marked by rapid motion, strong seismicity and well defined boundaries. Tectonic activity across the Andes results from the Nazca Plate subducting under the South American plate in a series of discrete platelets with different widths and dip angles. This in turn, is reflected in the tectonic complexity of the Andes which are a multitutde of orogenic belts superimposed on each other since the Precambrian. Sites for Crustal Dynamics Program measurements are being located to investigate both interplate and extraplate motions. Observing operations have already been initiated at Arequipa, Peru and Easter Island, Santiago and Cerro Tololo, Chile. Sites under consideration include Iquique, Chile; Oruro and Santa Cruz, Bolivia; Cuzco, Lima, Huancayo and Bayovar, Peru; and Quito and the Galapagos Islands, Ecuador. Based on scientific considerations, Santa Cruz, Huancayo (or Lima), Quito and the Galapagos Islands should be replaced by Isla San Felix, Chile; Brazilia or Petrolina, Brazil; and Guayaquil, Ecuador. If resources permit, additional important sites would be Buenaventura and Villavicencio or Puerto La Concordia, Colombia; and Mendoza and Cordoba, Argentina.

  19. The analysis of the Tectonics - SSS - Seismicity System in the 3D-model of the Rasvumchorr Mine - Central Open Pit Natural and Technical System (Khibiny)

    Science.gov (United States)

    Zhirov, Dmitry; Klimov, Sergey; Zhirova, Anzhela; Panteleev, Alexey; Rybin, Vadim

    2017-04-01

    Main hazardous factors during the operation of deposits represent tectonics (structural dislocation), strain and stress state (SSS), and seismicity. The cause and effect relationships in the Fault Tectonics - SSS - Seismicity system were analyzed using a 3D geological and structural Rasvumchorr Mine - Central Open Pit model. This natural and technical system (NTS) has resulted from the development of the world-class apatite-nepheline deposits the Apatite Circus and Rasvumchorr Plateau. The 3D model integrates various spatial data on the earth's surface topography before and after mining, geometry of mines and dumps, SSS measurements and rock pressure, seismicity, fault tectonics and etc. The analysis of the 3D model has clearly demonstrated the localization of three main seismic emanation zones in the areas of maximum anthropogenic variation of the initial rock state, and namely: ore pass zone under the Southern edge of the Central open pit, collapse and joining zone of the Rasvumchorr Mine and NW edge of the open pit, and zone under the Apatite Circus plate - collapse console. And, on the contrary, in the area of a large dump under the underground mine, a perennial seismic minimum zone was identified. The relation of the seismicity and fault tectonics was revealed only in three local sectors near come certain echelon fissures of the Main Fault(MF). No confinement of increased seismicity areas to the MF and other numerous echelon fissures is observed. The same picture occurs towards manifestations of rock pressure. Only an insignificant part of echelon fissures (including low rank of hierarchy) controls hazardous manifestations of rock pressure (dumps, strong deformations of the mine contour, etc.). It is shown that the anthropogenic factor (explosive, geometry and arrangement of mined spaces and collapse console), as well as the time factor significantly change orientation and structure (contrast and heterogeneity) of the stress fields. Time series of natural

  20. The Biggest Plates on Earth. Submarine Ring of Fire--Grades 5-6. Plate Tectonics.

    Science.gov (United States)

    National Oceanic and Atmospheric Administration (DOC), Rockville, MD.

    This activity is designed to teach how tectonic plates move, what some consequences of this motion are, and how magnetic anomalies document the motion at spreading centers do. The activity provides learning objectives, a list of needed materials, key vocabulary words, background information, day-to-day procedures, internet connections, career…

  1. Comparing the New Madrid Seismic Zone with the Osning Thrust: implications for GIA-induced intraplate tectonics in northern Germany

    Science.gov (United States)

    Brandes, Christian; Steffen, Holger; Wu, Patrick; Tanner, David; Winsemann, Jutta

    2013-04-01

    Continental intraplate tectonics is a widespread phenomenon that causes significant earthquakes. These earthquakes even occur in areas that are characterized by low strain rates and there are often long intervals between the individual seismic events (Gangopadhyay & Talwani, 2003) that result in a hazard potential. To better understand the controlling factors of intraplate plate earthquakes in northern Germany, we compare the Osning Thrust with the intensively-studied New Madrid Seismic Zone in the Midwest USA. Both areas share major similarities such as a failed rift-basin setting, the presence of intrusive magmatic bodies in the subsurface, tectonic reactivation during the Late Cretaceous, paleo- and historic seismicity and comparable fault parameters. In addition, both areas have a very similar Late Pleistocene deglaciation history. New Madrid was c. 340 km south of the Laurentide ice sheet and ice retreat started around 21 ka and was completed by 8.5 ka (Grollimund & Zoback, 2001). The Osning Thrust was c. 310 km south of the Scandinavian ice sheet and deglaciation began at 24 ka. Both areas show historic seismicity in a similar time frame (New Madrid Seismic Zone: 1811-1812, Johnston & Schweig, 1996); Osning Thrust: 1612 and 1767, Grünthal & Bosse, 1997). We use numerical simulations to identify the timing of potentially GIA-induced fault activity, which are based on the fault stability margin concept of Wu & Hasegawa (1996). From our modelling results it is evident that the fault stability margin changed to negative between 16 and 13 ka for the Osning Thrust, which matches the OSL data of fault-related growth strata (Brandes et al., 2012). For the New Madrid Seismic Zone, the fault stability margin becomes zero between 2.5 ka BP (before 1812) to about 2 ka after the 1812 event, depending on the parameters of the model. This indicates that for both seismic zones, seismicity due to deglaciation was and still is very likely. From this study it can be derived

  2. Plate tectonic model for the oligo-miocene evolution of the western Mediterranean

    Science.gov (United States)

    Cohen, Curtis R.

    1980-10-01

    This paper outlines a plate tectonic model for the Oligo-Miocene evolution of the western Mediterranean which incorporates recent data from several tectonic domains (Corsica, Sardinia, the Kabylies, Balearic promontory, Iberia, Algero-Provençal Basin and Tunisian Atlas). Following late Mesozoic anticlockwise rotation of the Iberian peninsula (including the Balearic promontory and Sardinia), late Eocene collision occurred between the Kabylies and Balearic promontory forming a NE-trending suture with NW-tectonic polarity. As a result of continued convergence between the African and European plates, a polarity flip occurred and a southward-facing trench formed south of the Kabylie—Balearic promontory suture. During late Oligocene time an E-W-trending arc and marginal basin developed behind the southward-facing trench in the area of the present-day Gulf of Lion. Opening of this basin moved the Corsica—Sardinia—Calabria—Petit Kabylie—Menorca plate southward, relative to the African plate. Early Miocene back-arc spreading in the area between the Balearic promontory and Grand Kabylie emplaced the latter in northern Algeria and formed the South Balearic Basin. Coeval with early Miocene back-arc basin development, the N-S-extension in the Gulf of Lion marginal basin changed to a more NW-SE direction causing short-lived extension in the area of the present-day Valencia trough and a 30° anticlockwise rotation of the Corsica-Sardinia-Calabria—Petit Kabylie plate away from the European plate. Early—middle Miocene deformation along the western Italian and northeastern African continental margins resulted from this rotation. During the early late Miocene (Tortonian), spreading within a sphenochasm to the southwest of Sardinia resulted in the emplacement of Petit Kabylie in northeastern Algeria.

  3. The magma ocean as an impediment to lunar plate tectonics

    Science.gov (United States)

    Warren, Paul H.

    1993-01-01

    The primary impediment to plate tectonics on the moon was probably the great thickness of its crust and particularly its high crust/lithosphere thickness ratio. This in turn can be attributed to the preponderance of low-density feldspar over all other Al-compatible phases in the lunar interior. During the magma ocean epoch, the moon's crust/lithosphere thickness ratio was at the maximum theoretical value, approximately 1, and it remained high for a long time afterwards. A few large regions of thin crust were produced by basin-scale cratering approximately contemporaneous with the demise of the magma ocean. However, these regions probably also tend to have uncommonly thin lithosphere, since they were directly heated and indirectly enriched in K, Th, and U by the same cratering process. Thus, plate tectonics on the moon in the form of systematic lithosphere subduction was impeded by the magma ocean.

  4. Full Waveform Adjoint Seismic Tomography of the Antarctic Plate

    Science.gov (United States)

    Lloyd, A. J.; Wiens, D.; Zhu, H.; Tromp, J.; Nyblade, A.; Anandakrishnan, S.; Aster, R. C.; Huerta, A. D.; Winberry, J. P.; Wilson, T. J.; Dalziel, I. W. D.; Hansen, S. E.; Shore, P.

    2017-12-01

    Recent studies investigating the response and influence of the solid Earth on the evolution of the cryosphere demonstrate the need to account for 3D rheological structure to better predict ice sheet dynamics, stability, and future sea level impact, as well as to improve glacial isostatic adjustment models and more accurately measure ice mass loss. Critical rheological properties like mantle viscosity and lithospheric thickness may be estimated from shear wave velocity models that, for Antarctica, would ideally possess regional-scale resolution extending down to at least the base of the transition zone (i.e. 670 km depth). However, current global- and continental-scale seismic velocity models are unable to obtain both the resolution and spatial coverage necessary, do not take advantage of the full set of available Antarctic data, and, in most instance, employ traditional seismic imaging techniques that utilize limited seismogram information. We utilize 3-component earthquake waveforms from almost 300 Antarctic broadband seismic stations and 26 southern mid-latitude stations from 270 earthquakes (5.5 ≤ Mw ≤ 7.0) between 2001-2003 and 2007-2016 to conduct a full-waveform adjoint inversion for Antarctica and surrounding regions of the Antarctic plate. Necessary forward and adjoint wavefield simulations are performed utilizing SPECFEM3D_GLOBE with the aid of the Texas Advanced Computing Center. We utilize phase observations from seismogram segments containing P, S, Rayleigh, and Love waves, including reflections and overtones, which are autonomously identified using FLEXWIN. The FLEXWIN analysis is carried out over a short (15-50 s) and long (initially 50-150 s) period band that target body waves, or body and surface waves, respectively. As our model is iteratively refined, the short-period corner of the long period band is gradually reduced to 25 s as the model converges over 20 linearized inversion iterations. We will briefly present this new high

  5. A Plate Tectonic Model for the Neoproterozoic with Evolving Plate Boundaries

    Science.gov (United States)

    Merdith, Andrew; Collins, Alan; Williams, Simon; Pisarevsky, Sergei; Müller, Dietmar

    2017-04-01

    The Neoproterozoic was dominated by the formation of the supercontinent Rodinia, its break-up and the subsequent amalgamation of Gondwana, during which, the planet experienced large climatic variations and the emergence of complex life. Here we present a topological plate model of the Neoproterozoic based on a synthesis of available geological and palaeomagnetic data. Subduction zones, which are well preserved in the geological record, are used as a proxy for convergent margins; evidence for mid-ocean ridges and transform motion is less clearly preserved, though passive margins are used as a proxy for spreading centres, and evidence for strike-slip motions are used to model transform boundaries. We find that the model presented here only predicts 70% of the total length of subduction active today, though it models similar lengths of both transform and divergent boundaries, suggesting that we have produced a conservative model and are probably underestimating the amount of subduction. Where evidence for convergent, divergent or transform motion is not preserved, we interpret the locations of plate boundaries based on the relative motions of cratonic crust as suggested through either palaeomagnetic data or the geological record. Using GPlates, we tie these boundaries together to generate a plate model that depicts the motion of tectonic plates through the Neoproterozoic. We omit India and South China from Rodinia completely, due to long-lived subduction preserved on margins of India and conflicting palaeomagnetic data for the Cryogenian, but tie them together due to similar Tonian aged accretionary patterns along their respective (present-day) north-western and northern margins, such that these two cratons act as a "lonely wanderer" for much of the Neoproterozoic, and form their own tectonic plate. We also introduce a Tonian-Cryogenian aged rotation of the Congo-São Francisco Craton relative to Rodinia to better fit palaeomagnetic data and account for thick passive

  6. An evaluation of criteria for defining tectonic, seismic, or seismotectonic provinces

    International Nuclear Information System (INIS)

    1980-05-01

    A compilation and generic critique of the diagnostic siting criteria now in use throughout the world to delineate or approximate bounded tectonic, seismic, or seismotectonic provinces or zones, are presented. The criteria are referenced and tabulated to facilitate determination of their regulatory, scientific and practical application to siting of important engineered structures in Canada

  7. Piedmont seismic reflection study: A program integrated with tectonics to probe the cause of eastern seismicity

    Energy Technology Data Exchange (ETDEWEB)

    Glover, L. III; Coruh, C.; Costain, J.K.; Bollinger, G.A. (Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Geological Sciences)

    1992-03-01

    A new tectonic model of the Appalachian orogen indicates that one, not two or more, terrane boundaries is present in the Piedmont and Blue Ridge of the central and southern Appalachians. This terrane boundary is the Taconic suture, it has been transported in the allochthonous Blue Ridge/Piedmont crystalline thrust nappe, and it is repeated at the surface by faulting and folding associated with later Paleozoic orogenies. The suture passes through the lower crust and lithosphere somewhere east of Richmond. It is spatially associated with seismicity in the central Virginia seismic zone, but is not conformable with earthquake focal planes and appears to have little causal relation to their localization.

  8. Tectonics earthquake distribution pattern analysis based focal mechanisms (Case study Sulawesi Island, 1993–2012)

    International Nuclear Information System (INIS)

    Ismullah M, Muh. Fawzy; Lantu,; Aswad, Sabrianto; Massinai, Muh. Altin

    2015-01-01

    Indonesia is the meeting zone between three world main plates: Eurasian Plate, Pacific Plate, and Indo – Australia Plate. Therefore, Indonesia has a high seismicity degree. Sulawesi is one of whose high seismicity level. The earthquake centre lies in fault zone so the earthquake data gives tectonic visualization in a certain place. This research purpose is to identify Sulawesi tectonic model by using earthquake data from 1993 to 2012. Data used in this research is the earthquake data which consist of: the origin time, the epicenter coordinate, the depth, the magnitude and the fault parameter (strike, dip and slip). The result of research shows that there are a lot of active structures as a reason of the earthquake in Sulawesi. The active structures are Walannae Fault, Lawanopo Fault, Matano Fault, Palu – Koro Fault, Batui Fault and Moluccas Sea Double Subduction. The focal mechanism also shows that Walannae Fault, Batui Fault and Moluccas Sea Double Subduction are kind of reverse fault. While Lawanopo Fault, Matano Fault and Palu – Koro Fault are kind of strike slip fault

  9. Tectonics earthquake distribution pattern analysis based focal mechanisms (Case study Sulawesi Island, 1993–2012)

    Energy Technology Data Exchange (ETDEWEB)

    Ismullah M, Muh. Fawzy, E-mail: mallaniung@gmail.com [Master Program Geophysical Engineering, Faculty of Mining and Petroleum Engineering (FTTM), Bandung Institute of Technology (ITB), Jl. Ganesha no. 10, Bandung, 40116, Jawa Barat (Indonesia); Lantu,; Aswad, Sabrianto; Massinai, Muh. Altin [Geophysics Program Study, Faculty of Mathematics and Natural Sciences, Hasanuddin University (UNHAS), Jl. PerintisKemerdekaan Km. 10, Makassar, 90245, Sulawesi Selatan (Indonesia)

    2015-04-24

    Indonesia is the meeting zone between three world main plates: Eurasian Plate, Pacific Plate, and Indo – Australia Plate. Therefore, Indonesia has a high seismicity degree. Sulawesi is one of whose high seismicity level. The earthquake centre lies in fault zone so the earthquake data gives tectonic visualization in a certain place. This research purpose is to identify Sulawesi tectonic model by using earthquake data from 1993 to 2012. Data used in this research is the earthquake data which consist of: the origin time, the epicenter coordinate, the depth, the magnitude and the fault parameter (strike, dip and slip). The result of research shows that there are a lot of active structures as a reason of the earthquake in Sulawesi. The active structures are Walannae Fault, Lawanopo Fault, Matano Fault, Palu – Koro Fault, Batui Fault and Moluccas Sea Double Subduction. The focal mechanism also shows that Walannae Fault, Batui Fault and Moluccas Sea Double Subduction are kind of reverse fault. While Lawanopo Fault, Matano Fault and Palu – Koro Fault are kind of strike slip fault.

  10. Crustal deformation and volcanism at active plate boundaries

    Science.gov (United States)

    Geirsson, Halldor

    Most of Earth's volcanoes are located near active tectonic plate boundaries, where the tectonic plates move relative to each other resulting in deformation. Likewise, subsurface magma movement and pressure changes in magmatic systems can cause measurable deformation of the Earth's surface. The study of the shape of Earth and therefore studies of surface deformation is called geodesy. Modern geodetic techniques allow precise measurements (˜1 mm accuracy) of deformation of tectonic and magmatic systems. Because of the spatial correlation between tectonic boundaries and volcanism, the tectonic and volcanic deformation signals can become intertwined. Thus it is often important to study both tectonic and volcanic deformation processes simultaneously, when one is trying to study one of the systems individually. In this thesis, I present research on crustal deformation and magmatic processes at active plate boundaries. The study areas cover divergent and transform plate boundaries in south Iceland and convergent and transform plate boundaries in Central America, specifically Nicaragua and El Salvador. The study is composed of four main chapters: two of the chapters focus on the magma plumbing system of Hekla volcano, Iceland and the plate boundary in south Iceland; one chapter focuses on shallow controls of explosive volcanism at Telica volcano, Nicaragua; and the fourth chapter focuses on co- and post-seismic deformation from a Mw = 7.3 earthquake which occurred offshore El Salvador in 2012. Hekla volcano is located at the intersection of a transform zone and a rift zone in Iceland and thus is affected by a combination of shear and extensional strains, in addition to co-seismic and co-rifting deformation. The inter-eruptive deformation signal from Hekla is subtle, as observed by a decade (2000-2010) of GPS data in south Iceland. A simultaneous inversion of this data for parameters describing the geometry and source characteristics of the magma chamber at Hekla, and

  11. Crustal structure and tectonics of the Ninetyeast Ridge from seismic and gravity studies

    Digital Repository Service at National Institute of Oceanography (India)

    Krishna, K.S.; Neprochnov, Y.P.; Rao, D.G.; Grinko, B.N.

    Seismic reflection and refraction, gravity, and bathymetric data across and along the central part of the Ninetyeast Ridge were analyzed to determine the crustal structure of the ridge and to understand its tectonics. The ridge in the study area...

  12. Discrimination and Assessment of Induced Seismicity in Active Tectonic Zones: A Case Study from Southern California

    Science.gov (United States)

    Bachmann, C. E.; Lindsey, N.; Foxall, W.; Robertson, M.

    2014-12-01

    Earthquakes induced by human activity have become a matter of heightened public concern during recent years. Of particular concern is seismicity associated with wastewater injection, which has included events having magnitudes greater than 5. The causes of the induced events are primarily changes in pore-pressure, fluid volume and perhaps temperature due to injection. Recent research in the US has focused on mid-continental regions having low rates of naturally-occurring seismicity, where induced events can be identified by relatively straightforward spatial and temporal correlation of seismicity with high-volume injection activities. Recent examples include events correlated with injection of wastewater in Oklahoma, Arkansas, Texas and Ohio, and long-term brine injection in the Paradox Valley in Colorado. Even in some of the cases where there appears at first sight to be a clear spatial correlation between seismicity and injection, it has been difficult to establish causality definitively. Here, we discuss methods to identify induced seismicity in active tectonic regions. We concentrate our study on Southern California, where large numbers of wastewater injection wells are located in oil-producing basins that experience moderate to high rates of naturally-occurring seismicity. Using the catalog of high-precision CISN relocations produced by Hauksson et al. (BSSA, 2012), we aim to discriminate induced from natural events based on spatio-temporal patterns of seismicity occurrence characteristics and their relationships to injection activities, known active faults and other faults favorably oriented for slip under the tectonic stress field. Since the vast majority of induced earthquakes are very small, it is crucial to include all events above the detection threshold of the CISN in each area studied. In addition to exploring the correlation of seismicity to injection activities in time and space, we analyze variations in frequency-magnitude distributions, which can

  13. Identifying tectonic parameters that influence tsunamigenesis

    Science.gov (United States)

    van Zelst, Iris; Brizzi, Silvia; van Dinther, Ylona; Heuret, Arnauld; Funiciello, Francesca

    2017-04-01

    The role of tectonics in tsunami generation is at present poorly understood. However, the fact that some regions produce more tsunamis than others indicates that tectonics could influence tsunamigenesis. Here, we complement a global earthquake database that contains geometrical, mechanical, and seismicity parameters of subduction zones with tsunami data. We statistically analyse the database to identify the tectonic parameters that affect tsunamigenesis. The Pearson's product-moment correlation coefficients reveal high positive correlations of 0.65 between, amongst others, the maximum water height of tsunamis and the seismic coupling in a subduction zone. However, these correlations are mainly caused by outliers. The Spearman's rank correlation coefficient results in more robust correlations of 0.60 between the number of tsunamis in a subduction zone and subduction velocity (positive correlation) and the sediment thickness at the trench (negative correlation). Interestingly, there is a positive correlation between the latter and tsunami magnitude. In an effort towards multivariate statistics, a binary decision tree analysis is conducted with one variable. However, this shows that the amount of data is too scarce. To complement this limited amount of data and to assess physical causality of the tectonic parameters with regard to tsunamigenesis, we conduct a numerical study of the most promising parameters using a geodynamic seismic cycle model. We show that an increase in sediment thickness on the subducting plate results in a shift in seismic activity from outerrise normal faults to splay faults. We also show that the splay fault is the preferred rupture path for a strongly velocity strengthening friction regime in the shallow part of the subduction zone, which increases the tsunamigenic potential. A larger updip limit of the seismogenic zone results in larger vertical surface displacement.

  14. Is Active Tectonics on Madagascar Consistent with Somalian Plate Kinematics?

    Science.gov (United States)

    Stamps, D. S.; Kreemer, C.; Rajaonarison, T. A.

    2017-12-01

    The East African Rift System (EARS) actively breaks apart the Nubian and Somalian tectonic plates. Madagascar finds itself at the easternmost boundary of the EARS, between the Rovuma block, Lwandle plate, and the Somalian plate. Earthquake focal mechanisms and N-S oriented fault structures on the continental island suggest that Madagascar is experiencing east-west oriented extension. However, some previous plate kinematic studies indicate minor compressional strains across Madagascar. This inconsistency may be due to uncertainties in Somalian plate rotation. Past estimates of the rotation of the Somalian plate suffered from a poor coverage of GPS stations, but some important new stations are now available for a re-evaluation. In this work, we revise the kinematics of the Somalian plate. We first calculate a new GPS velocity solution and perform block kinematic modeling to evaluate the Somalian plate rotation. We then estimate new Somalia-Rovuma and Somalia-Lwandle relative motions across Madagascar and evaluate whether they are consistent with GPS measurements made on the island itself, as well as with other kinematic indicators.

  15. Crustal structure and active tectonics in the Eastern Alps

    DEFF Research Database (Denmark)

    Brückl, E.; Behm, M.; Decker, K.

    2010-01-01

    fragment (PA), was interpreted and a triple junction was inferred. The goal of this study has been to relate these deep crustal structures to active tectonics. We used elastic plate modeling to reconsider the Moho fragmentation. We interpret subduction of EU below AD and PA from north to south......During the last decade, a series of controlled source seismic experiments brought new insight into the crustal and lithospheric structure of the Eastern Alps and their adjacent tectonic provinces. A fragmentation of the lithosphere into three blocks, Europe (EU), Adria (AD), and the new Pannonian...

  16. Coupling intensity and isostatic competition between subducting slab and overriding plate control trench motions and tectonics of the overriding plate

    Science.gov (United States)

    Wu, G.; Moresi, L. N.

    2017-12-01

    Trench motions not only reflect tectonic regimes on the overriding plate but also shed light on the competition between subducting slab and overriding plate, however, major controls over trench advance or retreat and their consequences are still illusive. We use 2D thermo-mechanical experiments to study the problem. We find that the coupling intensity particularly in the uppermost 200 km and the isostatic competition between subducting slab and overriding plate largely determine trench motion and tectonics of in the overriding plate. Coupling intensity is the result of many contributing factors, including frictional coefficient of brittle part of the subducting interface and the viscosity of the ductile part, thermal regime and rheology of the overriding plate, and water contents and magmatic activity in the subducting slab and overriding plate. In this study, we are not concerned with the dynamic evolution of individual controlling parameter but simply use effective media. For instance, we impose simple model parameters such as frictional coefficient and vary the temperature and strain-rate dependent viscosity of the weak layer between the subducting slab and overriding plate. In the coupled end-member case, strong coupling leads to strong corner flow, depth-dependent compression/extension, and mantle return flow on the overriding plate side. It results in fast trench retreat, broad overriding plate extension, and even slab breakoff. In the decoupled end-member case, weak coupling causes much weaker response on the overriding plate side compared with the coupled end-member case, and the subducting slab can be largely viewed as a conveyer belt. We find that the isostatic competition between the subducting slab and overriding plate also has a major control over trench motion, and may better be viewed in 3D models. This is consistent with the findings in previous 3D studies that trench motion is most pronounced close to the slab edge. Here we propose that the

  17. The San Andreas fault experiment. [gross tectonic plates relative velocity

    Science.gov (United States)

    Smith, D. E.; Vonbun, F. O.

    1973-01-01

    A plan was developed during 1971 to determine gross tectonic plate motions along the San Andreas Fault System in California. Knowledge of the gross motion along the total fault system is an essential component in the construction of realistic deformation models of fault regions. Such mathematical models will be used in the future for studies which will eventually lead to prediction of major earthquakes. The main purpose of the experiment described is the determination of the relative velocity of the North American and the Pacific Plates. This motion being so extremely small, cannot be measured directly but can be deduced from distance measurements between points on opposite sites of the plate boundary taken over a number of years.

  18. SECULAR CHANGES IN RELATIONSHIPS BETWEEN PLATE-TECTONIC AND MANTLE-PLUME ENGENDERED PROCESSES DURING PRECAMBRIAN TIME

    Directory of Open Access Journals (Sweden)

    M. V. Mints

    2016-01-01

    Full Text Available Paradoxically, the lists of “proxies” of both plate- and plume-related settings are devoid of even a mention of the high-grade metamorphic rocks (granulite, amphibolite and high-temperature eclogite facies. However, the granulite-gneiss belts and areas which contain these rocks, have a regional distribution in both the Precambrian and the Phanerozoic records. The origin and evolution of the granulite-gneiss belts correspond to the activity of plumes expressed in vigorous heating of the continental crust; intraplate magmatism; formation of rift depressions filled with sediments, juvenile lavas, and pyroclastic flow deposits; and metamorphism of lower and middle crustal complexes under conditions of granulite and high-temperature amphibolite facies that spreads over the fill of rift depressions also. Granulite-gneiss complexes of the East European Craton form one of the main components of the large oval intracontinental tectonic terranes of regional or continental rank. Inclusion of the granulite-gneiss complexes from Eastern Europe, North and South America, Africa, India, China and Australia in discussion of the problem indicated in the title to this paper, suggests consideration of a significant change in existing views on the relations between the plate- and plume-tectonic processes in geological history, as well as in supercontinent assembly and decay. The East European and North American cratons are fragments of the long-lived supercontinent Lauroscandia. After its appearance at ~2.8 Ga, the crust of this supercontinent evolved under the influence of the sequence of powerful mantle plumes (superplumes up to ~0.85 Ga. During this time Lauroscandia was subjected to rifting, partial breakup and the following reconstruction of the continent. The processes of plate-tectonic type (rifting with the transition to spreading and closing of the short-lived ocean with subduction within Lauroscandia were controlled by the superplumes. Revision of the

  19. Seafloor morphology of the Eurasia-Nubia (Africa) plate boundary between the Tore-Madeira Rise and the Straits of Gibraltar: a case of coexistent Mesozoic through Present day features of tectonic, oceanographic and sedimentary origin

    Science.gov (United States)

    Terrinha, Pedro; Duarte, João.; Valadares, Vasco; Batista, Luis; Zitellini, Nevio; Grácia, Eulalia; Lourenço, Nuno; Rosas, Filipe; Roque, Cristina

    2010-05-01

    The joint use of more than 10.000 km multichannel seismic reflection profiles and 180.000km2 of multibeam swath bathymetry and backscatter allowed for a new vision of the seafloor tectonic and geomorphic processes of the area that encompasses the present day plate boundary between Africa and Eurasia, between the Gibraltar Straits and the Tore-Madeira Rise, in the southern sector of the North Atlantic Ocean. The interpretation of this data allowed for the detailed description of the seafloor morphology (i.e. a morphologic map) and the classification of the morphologic features in what respects the genetic process and age. It can be seen that in the same region coexist morphologic features that result from tectonic processes associated with the Triassic-Cretaceous break-up of Pangea, the Paleogene-Miocene compressive phase, the Miocene through Present subduction under the Gibraltar Arc (Gutscher et al., 2002), the Pliocene-Quaternary wrench tectonics and possible coeval plate boundary (Zitellini et al., 2009), the Present day mud volcanism and propagation of the compressive deformation along the West Continental Margin of Portugal (Terrinha et al., 2009). Interpretation of the seismic profiles together with the bathymetry allows the understanding of endogenous and exogenous processes that creates reliefs associated with active structures (related to the Miocene through Present compressive stress field). Other reliefs generated in Mesozoic times by analogous processes can be as well preserved as these active ones. In what concerns exogenous processes, the analysis of the two datasets (reflection seismics and bathymetry) allowed for the description of morphologic features associated with oceanic currents that interact with the seafloor forming these important features. As is the case of the well known active contourites but also less known features, like giant scours at 4 km water depth that have recently been described, suggesting the interaction of deep currents and

  20. The tectonic evolution of the southeastern Terceira Rift/São Miguel region (Azores)

    Science.gov (United States)

    Weiß, B. J.; Hübscher, C.; Lüdmann, T.

    2015-07-01

    The eastern Azores Archipelago with São Miguel being the dominant subaerial structure is located at the intersection of an oceanic rift (Terceira Rift) with a major transform fault (Gloria Fault) representing the westernmost part of the Nubian-Eurasian plate boundary. The evolution of islands, bathymetric highs and basin margins involves strong volcanism, but the controlling geodynamic and tectonic processes are currently under debate. In order to study this evolution, multibeam bathymetry and marine seismic reflection data were collected to image faults and stratigraphy. The basins of the southeastern Terceira Rift are rift valleys whose southwestern and northeastern margins are defined by few major normal faults and several minor normal faults, respectively. Since São Miguel in between the rift valleys shows an unusual W-E orientation, it is supposed to be located on a leaky transform. South of the island and separated by a N120° trending graben system, the Monacco Bank represents a N160° oriented flat topped volcanic ridge dominated by tilted fault blocks. Up to six seismic units are interpreted for each basin. Although volcanic ridges hamper a direct linking of depositional strata between the rift and adjacent basins, the individual seismic stratigraphic units have distinct characteristics. Using these units to provide a consistent relative chrono-stratigraphic scheme for the entire study area, we suggest that the evolution of the southeastern Terceira Rift occurred in two stages. Considering age constrains from previous studies, we conclude that N140° structures developed orthogonal to the SW-NE direction of plate-tectonic extension before ~ 10 Ma. The N160° trending volcanic ridges and faults developed later as the plate tectonic spreading direction changed to WSW-ENE. Hence, the evolution of the southeastern Terceira Rift domain is predominantly controlled by plate kinematics and lithospheric stress forming a kind of a re-organized rift system.

  1. A combined rigid/deformable plate tectonic model for the evolution of the Indian Ocean

    Science.gov (United States)

    Watson, J. G.; Glover, C. T.; Adriasola Munoz, A. C.; Harris, J. P.; Goodrich, M.

    2012-04-01

    Plate tectonic reconstructions are essential for placing geological information in its correct spatial context, understanding depositional environments, defining basin dimensions and evolution, and serve as a basis for palaeogeographic mapping and for palaeo-climate modelling. Traditional 'rigid' plate reconstructions often result in misfits (overlaps and underfits) in the geometries of juxtaposed plate margins when restored to their pre-rift positions. This has been attributed to internal deformation pre- and/or syn- continental break-up. Poorly defined continent-ocean boundaries add to these problems. To date, few studies have integrated continental extension within a global model. Recent plate tectonic reconstructions based on the relative motions of Africa, Madagascar, India and Antarctica during the break-up of eastern Gondwana have not taken into account the effects of deformation; particularly between India and Madagascar, and India and the Seychelles. A deformable plate model is in development that builds on the current rigid plate model to describe the complex multiphase break-up history between Africa, Madagascar, Seychelles and India, the associated magmatic activity and subsequent India/Eurasia collision. The break-up of eastern Gondwana occurred in the mid Jurassic by rifting between Africa and the India-Madagascar-Australian-Antarctica plates, followed by the Late Jurassic drift of India away from Australia and the Cretaceous break-up of Australia and Antarctica. The northwards drift of the Seychelles-India block in the Tertiary was accommodated by the opening of the Laxmi Basin. This was followed by the eruption of the extensive Deccan flood basalts and the separation of India and the Seychelles. Crustal domains on volcanic margins can be very difficult to define due to the accretion of magmatic material. On these margins, there is much speculation on the position of the continent-ocean boundary and the timing of rifting and sea-floor spreading. The

  2. Commentary: The Feasibility of Subduction and Implications for Plate Tectonics on Jupiter's Moon Europa

    Science.gov (United States)

    Kattenhorn, Simon A.

    2018-03-01

    A new modeling-based study by Johnson et al. (2017, https://doi.org/10.1002/2017JE005370) lends support to the hypothesis that portions of Europa's surface may have been removed by the process of subduction, as suggested by Kattenhorn and Prockter (2014, https://doi.org/10.1038/NGEO2245). Using a simple 1-D model that tracks the thermal and density structure of a descending ice plate, Johnson et al. show that ice plates with 10% porosity and overall salt contents of 5%, which differ in salt content by 2.5% from the surrounding reference ice shell, are nonbuoyant and thus likely to sink through the underlying, convecting portion of the ice shell. The feasibility of subduction in an ice shell is critical to the existence of icy plate tectonics, which is hypothesized to exist at least locally on Europa, potentially making it the only other Solar System body other than Earth with a surface modified by plate tectonics.

  3. Plateau subduction, intraslab seismicity, and the Denali (Alaska) volcanic gap

    Science.gov (United States)

    Chuang, Lindsay Yuling; Bostock, Michael; Wech, Aaron; Plourde, Alexandre

    2018-01-01

    Tectonic tremors in Alaska (USA) are associated with subduction of the Yakutat plateau, but their origins are unclear due to lack of depth constraints. We have processed tremor recordings to extract low-frequency earthquakes (LFEs), and generated a set of six LFE waveform templates via iterative network matched filtering and stacking. The timing of impulsive P (compressional) wave and S (shear) wave arrivals on template waveforms places LFEs at 40–58 km depth, near the upper envelope of intraslab seismicity and immediately updip of increased levels of intraslab seismicity. S waves at near-epicentral distances display polarities consistent with shear slip on the plate boundary. We compare characteristics of LFEs, seismicity, and tectonic structures in central Alaska with those in warm subduction zones, and propose a new model for the region’s unusual intraslab seismicity and the enigmatic Denali volcanic gap (i.e., an area of no volcanism where expected). We argue that fluids in the Yakutat plate are confined to its upper crust, and that shallow subduction leads to hydromechanical conditions at the slab interface in central Alaska akin to those in warm subduction zones where similar LFEs and tremor occur. These conditions lead to fluid expulsion at shallow depths, explaining strike-parallel alignment of tremor occurrence with the Denali volcanic gap. Moreover, the lack of double seismic zone and restriction of deep intraslab seismicity to a persistent low-velocity zone are simple consequences of anhydrous conditions prevailing in the lower crust and upper mantle of the Yakutat plate.

  4. Time-domain study of tectonic strain-release effects on seismic waves from underground nuclear explosions

    International Nuclear Information System (INIS)

    Nakanishi, K.K.; Sherman, N.W.

    1982-09-01

    Tectonic strain release affects both the amplitude and phase of seismic waves from underground nuclear explosions. Surface wave magnitudes are strongly affected by the component of tectonic strain release in the explosion. Amplitudes and radiation patterns of surface waves from explosions with even small tectonic components change magnitudes significantly and show a strong dependence on receiver locations. A thrust-slip source superimposed on an isotropic explosion can explain observed reversals in waveform at different azimuths and phase delays between normal and reversed Rayleigh waves. The mechanism of this reversal is due to the phase relationship between reasonable explosion and tectonic release sources. Spallation or an unusual source time function are not required. The observations of Shagan River events imply thrust-slip motion along faults in a northwest-southeast direction, which is consistent with regional tectonics

  5. Paleoarchean bedrock lithologies across the Makhonjwa Mountains of South Africa and Swaziland linked to geochemical, magnetic and tectonic data reveal early plate tectonic genes flanking subduction margins

    Directory of Open Access Journals (Sweden)

    Maarten de Wit

    2018-05-01

    Full Text Available The Makhonjwa Mountains, traditionally referred to as the Barberton Greenstone Belt, retain an iconic Paleoarchean archive against which numerical models of early earth geodynamics can be tested. We present new geologic and structural maps, geochemical plots, geo- and thermo-chronology, and geophysical data from seven silicic, mafic to ultramafic complexes separated by major shear systems across the southern Makhonjwa Mountains. All reveal signs of modern oceanic back-arc crust and subduction-related processes. We compare the rates of processes determined from this data and balance these against plate tectonic and plume related models. Robust rates of both horizontal and vertical tectonic processes derived from the Makhonjwa Mountain complexes are similar, well within an order of magnitude, to those encountered across modern oceanic and orogenic terrains flanking Western Pacific-like subduction zones. We conclude that plate tectonics and linked plate-boundary processes were well established by 3.2–3.6 Ga. Our work provides new constraints for modellers with rates of a ‘basket’ of processes against which to test Paleoarchean geodynamic models over a time period close to the length of the Phanerozoic. Keywords: Paleoarchean, Barberton Greenstone Belt, Onverwacht Suite, Geologic bedrock and structural maps, Geochemistry and geophysics, Plate tectonics

  6. Plate tectonics hiati as the cause of global glaciations: 2. The late Proterozoic 'Snowball Earth'

    Science.gov (United States)

    Osmaston, M. F.

    2003-04-01

    A fundamental reappraisal of the mechanisms that drive plate tectonics has yielded the remarkable conclusion that, for at least the past 130 Ma, the principal agent has not been ridge-push or slab-pull but a CW-directed torque (probably of electromagnetic origin at the CMB) reaching the deep (>600 km, e.g.[1]) tectospheric keel of the Antarctica craton. Major changes in spreading direction marked both ends of the 122--85 Ma Cretaceous Superchron and started by forming the Ontong Java Plateau. Action of MORs as gearlike linkages has driven Africa and India CCW since Gondwana breakup and continues to drive the Pacific plate CCW. In the Arctic there is now no cratonic keel to pick up any corresponding polar torque, so northern hemisphere plate tectonics is far less active. The thesis of this contribution is that in the Neoproterozoic the lack of cratons at high latitudes would have deprived plate tectonics of this motivation, causing MORs to die (see below) and a major fall in sea-level, leading to global glaciation as outlined in Part 1 for the Huronian events. Like that seen during that first hiatus, dyke-swarm volcanism could have arisen from thermal shrinkage of the global lithosphere, providing CO2 and ash-covering that interrrupted glacial episodes. In oceanic settings this volcanism would have lowered pH and supplied Fe2+ for shallow bio-oxygenic action to deposit as BIF. My multifacet studies of the subduction process convince me that the rapid development of "flat-slab" interface profiles involves the physical removal of hanging-wall material in front of the downbend by basal subduction tectonic erosion (STE). Historically this, and its inferred ubiquity in the Archaean as the precursor to PSM (Part 1), suggests that the required subducting-plate buoyancy is thermal. Accordingly, a redesign [2] of the MOR process has incorporated the heat-containing LVZ as an integral part of the plate and luckily provides a lot more ridge-push to ensure the subduction of

  7. Strike-slip tectonics during rift linkage

    Science.gov (United States)

    Pagli, C.; Yun, S. H.; Ebinger, C.; Keir, D.; Wang, H.

    2017-12-01

    The kinematics of triple junction linkage and the initiation of transforms in magmatic rifts remain debated. Strain patterns from the Afar triple junction provide tests of current models of how rifts grow to link in area of incipient oceanic spreading. Here we present a combined analysis of seismicity, InSAR and GPS derived strain rate maps to reveal that the plate boundary deformation in Afar is accommodated primarily by extensional tectonics in the Red Sea and Gulf of Aden rifts, and does not require large rotations about vertical axes (bookshelf faulting). Additionally, models of stress changes and seismicity induced by recent dykes in one sector of the Afar triple junction provide poor fit to the observed strike-slip earthquakes. Instead we explain these patterns as rift-perpendicular shearing at the tips of spreading rifts where extensional strains terminate against less stretched lithosphere. Our results demonstrate that rift-perpendicular strike-slip faulting between rift segments achieves plate boundary linkage during incipient seafloor spreading.

  8. Using a Web GIS Plate Tectonics Simulation to Promote Geospatial Thinking

    Science.gov (United States)

    Bodzin, Alec M.; Anastasio, David; Sharif, Rajhida; Rutzmoser, Scott

    2016-01-01

    Learning with Web-based geographic information system (Web GIS) can promote geospatial thinking and analysis of georeferenced data. Web GIS can enable learners to analyze rich data sets to understand spatial relationships that are managed in georeferenced data visualizations. We developed a Web GIS plate tectonics simulation as a capstone learning…

  9. Transoceanic Dispersal and Plate Tectonics Shaped Global Cockroach Distributions: Evidence from Mitochondrial Phylogenomics.

    Science.gov (United States)

    Bourguignon, Thomas; Tang, Qian; Ho, Simon Y W; Juna, Frantisek; Wang, Zongqing; Arab, Daej A; Cameron, Stephen L; Walker, James; Rentz, David; Evans, Theodore A; Lo, Nathan

    2017-04-01

    Following the acceptance of plate tectonics theory in the latter half of the 20th century, vicariance became the dominant explanation for the distributions of many plant and animal groups. In recent years, however, molecular-clock analyses have challenged a number of well-accepted hypotheses of vicariance. As a widespread group of insects with a fossil record dating back 300 My, cockroaches provide an ideal model for testing hypotheses of vicariance through plate tectonics versus transoceanic dispersal. However, their evolutionary history remains poorly understood, in part due to unresolved relationships among the nine recognized families. Here, we present a phylogenetic estimate of all extant cockroach families, as well as a timescale for their evolution, based on the complete mitochondrial genomes of 119 cockroach species. Divergence dating analyses indicated that the last common ancestor of all extant cockroaches appeared ∼235 Ma, ∼95 My prior to the appearance of fossils that can be assigned to extant families, and before the breakup of Pangaea began. We reconstructed the geographic ranges of ancestral cockroaches and found tentative support for vicariance through plate tectonics within and between several major lineages. We also found evidence of transoceanic dispersal in lineages found across the Australian, Indo-Malayan, African, and Madagascan regions. Our analyses provide evidence that both vicariance and dispersal have played important roles in shaping the distribution and diversity of these insects.

  10. Intra-Arc extension in Central America: Links between plate motions, tectonics, volcanism, and geochemistry

    Science.gov (United States)

    Phipps Morgan, Jason; Ranero, Cesar; Vannucchi, Paola

    2010-05-01

    This study revisits the kinematics and tectonics of Central America subduction, synthesizing observations of marine bathymetry, high-resolution land topography, current plate motions, and the recent seismotectonic and magmatic history in this region. The inferred tectonic history implies that the Guatemala-El Salvador and Nicaraguan segments of this volcanic arc have been a region of significant arc tectonic extension; extension arising from the interplay between subduction roll-back of the Cocos Plate and the ~10-15 mm/yr slower westward drift of the Caribbean plate relative to the North American Plate. The ages of belts of magmatic rocks paralleling both sides of the current Nicaraguan arc are consistent with long-term arc-normal extension in Nicaragua at the rate of ~5-10 mm/yr, in agreement with rates predicted by plate kinematics. Significant arc-normal extension can ‘hide' a very large intrusive arc-magma flux; we suggest that Nicaragua is, in fact, the most magmatically robust section of the Central American arc, and that the volume of intrusive volcanism here has been previously greatly underestimated. Yet, this flux is hidden by the persistent extension and sediment infill of the rifting basin in which the current arc sits. Observed geochemical differences between the Nicaraguan arc and its neighbors which suggest that Nicaragua has a higher rate of arc-magmatism are consistent with this interpretation. Smaller-amplitude, but similar systematic geochemical correlations between arc-chemistry and arc-extension in Guatemala show the same pattern as the even larger variations between the Nicaragua arc and its neighbors. We are also exploring the potential implications of intra-arc extension for deformation processes along the subducting plate boundary and within the forearc ‘microplate'.

  11. The Sunda-Banda Arc Transition: New Insights From Marine Wide-Angle Seismic Data

    Science.gov (United States)

    Planert, L.; Shulgin, A.; Kopp, H.; Mueller, C.; Flueh, E.; Lueschen, E.; Engels, M.; Dayuf Jusuf, M.

    2007-12-01

    End of 2006, RV SONNE cruise SO190 SINDBAD (Seismic and Geoacoustic Investigations along the Sunda- Banda Arc Transition) went south of the Indonesian archipelago to acquire various geophysical datasets between 112 °E and 122 °E. The main goal of the project is to investigate the modifications of the lower plate (variability in the plate roughness, transition from oceanic to continental lower plate) and their effects on the tectonics of the upper plate (development of an outer high and forearc basin, accretionary and erosive processes). The tectonic style changes in neighboring margin segments from an oceanic plate-island arc subduction along the eastern Sunda margin to a continental plate-island arc collision along the Banda margin. Moreover, the character of the incoming oceanic plate varies from the rough topography in the area where the Roo Rise is subducting off eastern Java, to the smooth oceanic seafloor of the Argo- Abyssal Plain subducting off Bali, Lombok, and Sumbawa. In order to cover the entire variations of the lower plate, seven seismic refraction profiles were conducted along four major north-south oriented corridors of the margin, at 113 °E, 116 °E, 119 °E, and 121 °E, as well as three profiles running perpendicular to the major corridors. A total of 239 ocean bottom hydrophone and seismometer deployments were successfully recovered. Shooting was conducted along 1020 nm of seismic profiles using a G-gun cluster of 64 l. Here, we present velocity models obtained by applying a tomographic approach which jointly inverts for refracted and reflected phases. Additional geometry and velocity information for the uppermost layers, obtained by prestack depth migration of multichannel seismic reflection data (see poster of Mueller et al. in this session), is incorporated into our models and held fixed during the iterations. geomar.de/index.php?id=sindbad

  12. The new Central American seismic hazard zonation: Mutual consensus based on up to day seismotectonic framework

    Science.gov (United States)

    Alvarado, Guillermo E.; Benito, Belén; Staller, Alejandra; Climent, Álvaro; Camacho, Eduardo; Rojas, Wilfredo; Marroquín, Griselda; Molina, Enrique; Talavera, J. Emilio; Martínez-Cuevas, Sandra; Lindholm, Conrad

    2017-11-01

    Central America is one of the most active seismic zones in the World, due to the interaction of five tectonic plates (North America, Caribbean, Coco, Nazca and South America), and its internal deformation, which generates almost one destructive earthquakes (5.4 ≤ Mw ≤ 8.1) every year. A new seismological zonation for Central America is proposed based on seismotectonic framework, a geological context (tectonic and geological maps), geophysical and geodetic evidence (gravimetric maps, magnetometric, GPS observations), and previous works. As a main source of data a depurated earthquake catalog was collected covering the period from 1522 to 2015. This catalog was homogenized to a moment magnitude scale (Mw). After a careful analysis of all the integrated geological and seismological information, the seismogenic zones were established into seismic areas defined by similar patterns of faulting, seismicity, and rupture mechanism. The tectonic environment has required considering seismic zones in two particular seismological regimes: a) crustal faulting (including local faults, major fracture zones of plate boundary limits, and thrust fault of deformed belts) and b) subduction, taking into account the change in the subduction angle along the trench, and the type and location of the rupture. The seismicity in the subduction zone is divided into interplate and intraplate inslab seismicity. The regional seismic zonation proposed for the whole of Central America, include local seismic zonations, avoiding discontinuities at the national boundaries, because of a consensus between the 7 countries, based on the cooperative work of specialists on Central American seismotectonics and related topics.

  13. Integrating EarthScope Data to Constrain the Long-Term Effects of Tectonism on Continental Lithosphere

    Science.gov (United States)

    Porter, R. C.; van der Lee, S.

    2017-12-01

    One of the most significant products of the EarthScope experiment has been the development of new seismic tomography models that take advantage of the consistent station design, regular 70-km station spacing, and wide aperture of the EarthScope Transportable Array (TA) network. These models have led to the discovery and interpretation of additional compositional, thermal, and density anomalies throughout the continental US, especially within tectonically stable regions. The goal of this work is use data from the EarthScope experiment to better elucidate the temporal relationship between tectonic activity and seismic velocities. To accomplish this, we compile several upper-mantle seismic velocity models from the Incorporated Research Institute for Seismology (IRIS) Earth Model Collaboration (EMC) and compare these to a tectonic age model we compiled using geochemical ages from the Interdisciplinary Earth Data Alliance: EarthChem Database. Results from this work confirms quantitatively that the time elapsed since the most recent tectonic event is a dominant influence on seismic velocities within the upper mantle across North America. To further understand this relationship, we apply mineral-physics models for peridotite to estimate upper-mantle temperatures for the continental US from tomographically imaged shear velocities. This work shows that the relationship between the estimated temperatures and the time elapsed since the most recent tectonic event is broadly consistent with plate cooling models, yet shows intriguing scatter. Ultimately, this work constrains the long-term thermal evolution of continental mantle lithosphere.

  14. The Earth's Mantle Is Solid: Teachers' Misconceptions About the Earth and Plate Tectonics.

    Science.gov (United States)

    King, Chris

    2000-01-01

    Discusses the misconceptions revealed by the teachers' answers and outlines more accurate answers and explanations based on established evidence and uses these to provide a more complete understanding of plate tectonic process and the structure of Earth. (Author/YDS)

  15. Does permanent extensional deformation in lower forearc slopes indicate shallow plate-boundary rupture?

    Science.gov (United States)

    Geersen, J.; Ranero, C. R.; Kopp, H.; Behrmann, J. H.; Lange, D.; Klaucke, I.; Barrientos, S.; Diaz-Naveas, J.; Barckhausen, U.; Reichert, C.

    2018-05-01

    Seismic rupture of the shallow plate-boundary can result in large tsunamis with tragic socio-economic consequences, as exemplified by the 2011 Tohoku-Oki earthquake. To better understand the processes involved in shallow earthquake rupture in seismic gaps (where megathrust earthquakes are expected), and investigate the tsunami hazard, it is important to assess whether the region experienced shallow earthquake rupture in the past. However, there are currently no established methods to elucidate whether a margin segment has repeatedly experienced shallow earthquake rupture, with the exception of mechanical studies on subducted fault-rocks. Here we combine new swath bathymetric data, unpublished seismic reflection images, and inter-seismic seismicity to evaluate if the pattern of permanent deformation in the marine forearc of the Northern Chile seismic gap allows inferences on past earthquake behavior. While the tectonic configuration of the middle and upper slope remains similar over hundreds of kilometers along the North Chilean margin, we document permanent extensional deformation of the lower slope localized to the region 20.8°S-22°S. Critical taper analyses, the comparison of permanent deformation to inter-seismic seismicity and plate-coupling models, as well as recent observations from other subduction-zones, including the area that ruptured during the 2011 Tohoku-Oki earthquake, suggest that the normal faults at the lower slope may have resulted from shallow, possibly near-trench breaking earthquake ruptures in the past. In the adjacent margin segments, the 1995 Antofagasta, 2007 Tocopilla, and 2014 Iquique earthquakes were limited to the middle and upper-slope and the terrestrial forearc, and so are upper-plate normal faults. Our findings suggest a seismo-tectonic segmentation of the North Chilean margin that seems to be stable over multiple earthquake cycles. If our interpretations are correct, they indicate a high tsunami hazard posed by the yet un

  16. 3-D velocity structures, seismicity patterns, and their tectonic implications across the Andean Foreland of San Juan Argentina

    Science.gov (United States)

    Asmerom, Biniam Beyene

    Three-dimensional velocity structures and seismicity patterns have been studied across the Andean Foreland of San Juan Argentina using data acquired by PANDA deployment. Distinct velocity variations are revealed between Precordillera in the west and Pie de Palo in the east. The low velocity anomaly beneath Precordillera is associated with the presence of thick sedimentary rocks and thick sediment cover of Matagusanos valley. Similarly, the high velocity anomaly east of Eastern Precordillera is correlated with the presence of basement rocks. These anomalies are observed from the station corrections of Joint Hypocentral Determination (JHD) analysis. A northeast trending west dipping high velocity anomaly is imaged beneath the southern half of Pie de Palo. This anomaly represents a Grenvillian suture zone formed when Pie de Palo collided with the Precordillera. Relocated seismicity using 3-D Vp and Vs models obtained in this study revealed crustal scale buried faults beneath the Eastern Precordillera and Sierra Pie de Palo. The fault defined by the seismicity extend down to a depth of ˜ 40 km and ~35 km beneath Precordillera and Pie de Palo, respectively, defining the lower bound of the brittle to ductile transition of the crust. These results confirm that present day active crustal thickening involves the entire crust in the tectonic process and results in thick-skinned deformation beneath both the Eastern Precordillera and Pie de Palo. Based on the seismicity pattern, geomorphology, and velocity structures, Sierra Pie de Palo, a basement uplift block, can be divided into two separate semi-blocks separated by a northeast trending fracture zone. The northern block is characterized by a well-defined west dipping fault and low Vp/Vs ratio particularly at a depth of 12 to 16 km, while the southern block shows a poorly-defined east dipping fault with high Vp/Vs ratio at a depth of 20 to 26 km. Spatial distribution of the well-relocated crustal earthquakes along these

  17. Subduction Drive of Plate Tectonics

    Science.gov (United States)

    Hamilton, W. B.

    2003-12-01

    Don Anderson emphasizes that plate tectonics is self-organizing and is driven by subduction, which rights the density inversion generated as oceanic lithosphere forms by cooling of asthenosphere from the top. The following synthesis owes much to many discussions with him. Hinge rollback is the key to kinematics, and, like the rest of actual plate behavior, is incompatible with bottom-up convection drive. Subduction hinges (which are under, not in front of, thin leading parts of arcs and overriding plates) roll back into subducting plates. The Pacific shrinks because bounding hinges roll back into it. Colliding arcs, increasing arc curvatures, back-arc spreading, and advance of small arcs into large plates also require rollback. Forearcs of overriding plates commonly bear basins which preclude shortening of thin plate fronts throughout periods recorded by basin strata (100 Ma for Cretaceous and Paleogene California). This requires subequal rates of advance and rollback, and control of both by subduction. Convergence rate is equal to rates of rollback and advance in many systems but is greater in others. Plate-related circulation probably is closed above 650 km. Despite the popularity of concepts of plumes from, and subduction into, lower mantle, there is no convincing evidence for, and much evidence against, penetration of the 650 in either direction. That barrier not only has a crossing-inhibiting negative Clapeyron slope but also is a compositional boundary between fractionated (not "primitive"), sluggish lower mantle and fertile, mobile upper mantle. Slabs sink more steeply than they dip. Slabs older than about 60 Ma when their subduction began sink to, and lie down on and depress, the 650-km discontinuity, and are overpassed, whereas younger slabs become neutrally buoyant in mid-upper mantle, into which they are mixed as they too are overpassed. Broadside-sinking old slabs push all upper mantle, from base of oceanic lithosphere down to the 650, back under

  18. GIS Based Study on Seismicity of Makran over 100 Years

    Directory of Open Access Journals (Sweden)

    Mubarik Ali

    2015-12-01

    Full Text Available The earthquakes in Makran have a history of 600 years (1483-2015. The new ventures of development, urbanization, mining, and exploration for hydrocarbons in Makran region demand recent studies on seismicity. The major tectonic earthquakes are although infrequent in Makran, but are responsible for generating tsunami in coastal areas of Pakistan and Iran and have a long tail of aftershocks of shallow to deep focal depths. The oceanic part of Arabian plate which is underthrusting Eurasian plate (northwards, contributes a major share in producing seismicity of low magnitude (ML 6 on Richter scale has a relation with the rotation of moon (lunar dates in Makran.

  19. Active Deformation in the Overriding Plate Associated with Temporal Changes of the Philippine Sea Plate Motion

    Science.gov (United States)

    Ishiyama, T.; Sato, H.; Van Horne, A.

    2015-12-01

    We present detailed geologic evidence linking changes over time in Philippine Sea plate (PHS) motion and intracontinental deformation in central and southwest (SW) Japan during the Pliocene and after. In the early Pliocene, subduction of the PHS plate under SW Japan restarted in a northerly direction after period of deceleration or cessation. Later, motion changed to a more westerly direction. Corresponding geological changes found in the overriding plate include unconformities in the forearc basins, changes in slip sense on faults, depocenter migration, re-organization of drainage systems and volcanism. Quaternary intraplate deformation is prominent north of the Median Tectonic Line (MTL) inactive segment, above a shallow flat slab. In contrast, less Quaternary tectonic activity is found north of the MTL active segment which lies over a steadily-slipping portion of the subducting slab that behaves as a less-deformed rigid block. Depocenters and active thrusting have migrated north/northwestward over the past 5 My above the shallow flat slab segment of the PHS. We reconstructed the Plio-Pleistocene migration history using Neogene stratigraphy and shallow seismic reflection profiles. We see shallow PHS slab contact with the lower continental crust in our deep seismic reflection profiles, which may explain its enhanced downward drag of the overriding plate and synchronous strong compression in the crust. We find evidence of more westerly PHS plate subduction since the middle Pleistocene in (1) unconformities in the Kumano forearc basin deposits in SW Japan, (2) drastic stream captures in Shikoku, and (3) concordant changes in fault slip sense from thrust to dextral slip along the MTL. Oblique subduction could have induced stronger horizontal stress in the overriding plate above the shallow flat slab which could account for the increasing geologic slip rate observed on active structures. During four repetitions of megathrust earthquake sequences since the 17th century

  20. A Possible Differentially Shortened Strike-slip Plate Boundary: the Okhotsk Plate Example.

    Science.gov (United States)

    Hindle, D.; Egorov, V.; Mackey, K. G.; Fujita, K.

    2004-12-01

    The Okhotsk plate has been postulated based on a combination of GPS geodetic inversions (REVEL1), seimsicity, geologic and lineament data. Lying between the North American and Eurasian plates, its northwestern corner would appear to be undergoing compression in a scissors motion between the two bounding plates. Extrusion tectonics along multiple, large strike-slip faults within the Okhotsk plate itself have been suggested to allow the escape of material away from the apex of Eurasia-North America. The plate boundary between Okhotsk and North America has been suggested to be diffuse, based on widely scattered minor seismicity. However, the large, left lateral, Ulakhan fault has also been suggested as a candidate plate boundary. We present field geological and geomorphological evidence of the partitioning of deformation between the Ulakhan fault, and several parallel and oblique, linked faults. The Ulakhan fault strand appears to have a maximum displacement of 24 km based on river valley offsets and closing large pull apart basins. Some of the displacement from the Ulakhan fault appears relayed into the plate margin along oblique trending, thrust/oblique slip faults. Estimated shortening over these faults is equivalent to the amount of shortening relayed into the plate margin from the plate boundary. There may be several thrust/oblique slip faults along the Ulakhan fault, which leads to the interesting situation of a segmented, strike-slip plate boundary being actively shortened in a margin parallel direction. This may be the result of postulated extrusion of the Okhotsk plate due to North America/Eurasia convergence. Such a situation would have important consequences for the interpretation of GPS data in a plate tectonic context.

  1. Seismicity and crustal structure at the Mendocino triple junction, Northern California

    Energy Technology Data Exchange (ETDEWEB)

    Dicke, M.

    1998-12-01

    A high level of seismicity at the Mendocino triple junction in Northern California reflects the complex active tectonics associated with the junction of the Pacific, North America, and Gorda plates. To investigate seismicity patterns and crustal structure, 6193 earthquakes recorded by the Northern California Seismic Network (NCSN) are relocated using a one-dimensional crustal velocity model. A near vertical truncation of the intense seismic activity offshore Cape Mendocino follows the strike of the Mattole Canyon fault and is interpreted to define the Pacific plate boundary. Seismicity along this boundary displays a double seismogenic layer that is attributed to interplate activity with the North America plate and Gorda plate. The interpretation of the shallow seismogenic zone as the North America - Pacific plate boundary implies that the Mendocino triple junction is situated offshore at present. Seismicity patterns and focal mechanisms for events located within the subducting Gorda pl ate are consistent with internal deformation on NE-SW and NW-SE trending rupture planes in response to north-south compression. Seismic sections indicate that the top of the Gorda plate locates at a depth of about 18 Km beneath Cape Mendocino and dips gently east-and southward. Earthquakes that are located in the Wadati-Benioff zone east of 236{sup o}E show a change to an extensional stress regime indicative of a slab pull force. This slab pull force and scattered seismicity within the contractional forearc region of the Cascadia subduction zone suggest that the subducting Gorda plate and the overriding North America plate are strongly coupled. The 1992 Cape Mendocino thrust earthquake is believed to have ruptured a blind thrust fault in the forearc region, suggesting that strain is accumulating that must ultimately be released in a potential M 8+ subduction earthquake.

  2. Tectonics and Non-isostatic Topography of the Mariana Trench and Adjacent Plates

    Science.gov (United States)

    Hongyu, L.; Lin, J.; Zhou, Z.; Zhang, F.

    2017-12-01

    Multi-types of geophysical data including multibeam bathymetry, sediment thickness, gravity anomaly, and crustal magnetic age were analyzed to investigate tectonic processes of the Mariana Trench and the surrounding plates. We calculated non-Airy-isostatic topography by removing from the observed bathymetry the effects of sediment loading, thermal subsidence, and Airy local isostatically-compensated topography. The Mariana Trench was found to be associated with a clearly defined zone of negative non-isostatic topography, which was caused by flexural bending of the subducting Pacific plate and with the maximum depth anomaly and flexural bending near the Challenger Deep. In contrast, the Caroline Ridge and Caroline Islands Chain have much more subdued non-isostatic topography, indicating their higher topography is largely compensated by thicker crust. Along the Mariana Trough, the northern and central segments appear to be associated with relatively low magma supply as indicated by the relatively low topography and thin crust. In contrast, the southern Mariana Trough is associated with relatively high magma supply as indicated by the relatively high and smoother topography, an axial high spreading center, and relatively thick crust. The southern end of the Mariana Trough was also found to be associated with positive non-isostatic topographic anomaly, which might be caused by the complex tectonic deformation of the overriding Mariana and Philippine Sea plates and their interaction with the subducting Pacific plate. Analysis further revealed that the southern Mariana Arc, located between the Mariana Trench and Mariana Trough, is associated with positive non-isostatic topographic anomalies, which may be explained by the late stage magmatic loading on the older and thus stronger lithospheric plate of the Mariana volcanic arc.

  3. CRUSTAL THICKNESS VARIATIONS AND SEISMICITY OF NORTHWESTERN SOUTH AMERICA

    Directory of Open Access Journals (Sweden)

    Woo Kim Jeong

    2007-06-01

    Full Text Available Any uncompensated mass of the northern Andes Mountains is presumably under pressure to adjust within the Earth to its ideal state of isostatic equilibrium. Isostasy is the ideal state that any
    uncompensated mass seeks to achieve in time. These pressures interact with the relative motions between adjacent plates that give rise to earthquakes along the plate boundaries. By combining the
    gravity MOHO estimates and crustal discontinuities with historical and instrumental seismological catalogs the correlation between isostatically disturbed terrains and seismicity has been established.
    The thinner and thicker crustal regions were mapped from the zero horizontal curvature of the crustal thickness estimates. These boundaries or edges of crustal thickness variations were compared to
    crustal discontinuities inferred from gravity and magnetic anomalies and the patterns of seismicity that have been catalogued for the last 363 years. The seismicity is very intense along the Nazca-North
    Andes, Caribbean-North American and North Andes-South American collision zones and associated with regional tectonic compressional stresses that have locally increased and/or diminished by
    compressional and tensional stress, respectively, due to crustal thickness variations. High seismicity is also associated with the Nazca-Cocos diverging plate boundary whereas low seismicity is associated with the Panama-Nazca Transform Fault and the South American Plate.

  4. Ionospheric quasi-static electric field anomalies during seismic activity in August–September 1981

    Directory of Open Access Journals (Sweden)

    M. Gousheva

    2009-01-01

    Full Text Available The paper proposes new results, analyses and information for the plate tectonic situation in the processing of INTERCOSMOS-BULGARIA-1300 satellite data about anomalies of the quasi-static electric field in the upper ionosphere over activated earthquake source regions at different latitudes. The earthquake catalogue is made on the basis of information from the United State Geological Survey (USGS website. The disturbances in ionospheric quasi-static electric fields are recorded by IESP-1 instrument aboard the INTERCOSMOS-BULGARIA-1300 satellite and they are compared with significant seismic events from the period 14 August–20 September 1981 in magnetically very quiet, quiet and medium quiet days. The main tectonic characteristics of the seismically activated territories are also taken in account. The main goal of the above research work is to enlarge the research of possible connections between anomalous vertical electric field penetrations into the ionosphere and the earthquake manifestations, also to propose tectonic arguments for the observed phenomena. The studies are represented in four main blocks: (i previous studies of similar problems, (ii selection of satellite, seismic and plate tectonic data, (iii data processing with new specialized software and observations of the quasi-static electric field and (iiii summary, comparison of new with previous results in our studies and conclusion. We establish the high informativity of the vertical component Ez of the quasi-static electric field in the upper ionosphere according observations by INTERCOSMOS-BULGARIA-1300 that are placed above considerably activated earthquake sources. This component shows an increase of about 2–10 mV/m above sources, situated on mobile structures of the plates. The paper discusses the observed effects. It is represented also a statistical study of ionospheric effects 5–15 days before and 5–15 days after the earthquakes with magnitude M 4.8–7.9.

  5. Strong crustal seismic anisotropy in the Kalahari Craton based on Receiver Functions

    DEFF Research Database (Denmark)

    Thybo, Hans; Soliman, Mohammad Youssof Ahmad; Artemieva, Irina

    2015-01-01

    Earlier seismic studies of the Kalahari Craton in southern Africa infer deformation of upper mantle by flow with fast direction of seismic anisotropy being parallel to present plate motion, and/or report anisotropy frozen into the lithospheric mantle. We present evidence for very strong seismic...... is uniform within tectonic units and parallel to orogenic strike in the Limpopo and Cape fold belts. It is further parallel to the strike of major dyke swarms which indicates that a large part of the observed anisotropy is controlled by lithosphere fabrics and macroscopic effects. The directions of the fast...... that the crust and lithospheric mantle may have been coupled since cratonisation. If so, the apparent match between mantle anisotropy and the present plate motion is coincidental....

  6. Plate tectonic reconstruction of the Carpathian-Pannonian region

    Science.gov (United States)

    Csontos, L.; Vörös, A.

    2003-04-01

    Plate tectonics of the Carpathian area is controlled by microcontinents between the European and African margins and the relative movements of these margins. Beside the generally accepted Apulian (Austroalpine, West Carpathian, Dinaric) microcontinents two others: the Bihor-Getic (Tisza) and Drina-Ivanjica are introduced. The first was attached to the European margin, the second to the Apulian microcontinent. During Permian a major ocean was obliquely subducted south of the Apulian microcontinents. Drina-Ivanjica rifted off the Apulian microcontinent in the Late Permian-Middle Triassic, as a consequence of back-arc rifting. Short-lived oceans subducted by the end of Jurassic, causing Drina-Ivanjica to collide with the internal Dinaric-West Carpathian and Bihor-Getic margins. An external Penninic-Váhic ocean tract began opening in the Early Jurassic, separating the East Alpine-West Carpathian microcontinent (and its fauna) from the European shelf. Further south, the Severin-Ceahlau-Magura also began opening in the Early Jurassic, but final separation of the Bihor-Getic (and its fauna) from the European shelf did not take place until the Middle-Late Jurassic. Two oroclinal bends: the Alcapa on the Dinaric margin and the Tisza-Dacia on the South Carpathian-Getic margin are essential elements of these reconstructions. Their bending (Aptian and Albian-Maastrichtian, respectively) are suggested by paleomagnetic and tectonic transport data. The two oroclinal bends are finally opposed and pushed into the Carpathian embayment by the Paleogene. In Miocene a back-arc basin develops on older tectonic elements. Differential rotations affect the wealded microcontinents.

  7. Homogenised constitutive model dedicated to reinforced concrete plates subjected to seismic solicitations

    International Nuclear Information System (INIS)

    Combescure, Christelle

    2013-01-01

    Safety reassessments are periodically performed on the EDF nuclear power plants and the recent seismic reassessments leaded to the necessity of taking into account the non-linear behaviour of materials when modeling and simulating industrial structures of these power plants under seismic solicitations. A large proportion of these infrastructures is composed of reinforced concrete buildings, including reinforced concrete slabs and walls, and literature seems to be poor on plate modeling dedicated to seismic applications for this material. As for the few existing models dedicated to these specific applications, they present either a lack of dissipation energy in the material behaviour, or no micromechanical approach that justifies the parameters needed to properly describe the model. In order to provide a constitutive model which better represents the reinforced concrete plate behaviour under seismic loadings and whose parameters are easier to identify for the civil engineer, a constitutive model dedicated to reinforced concrete plates under seismic solicitations is proposed: the DHRC (Dissipative Homogenised Reinforced Concrete) model. Justified by a periodic homogenisation approach, this model includes two dissipative phenomena: damage of concrete matrix and internal sliding at the interface between steel rebar and surrounding concrete. An original coupling term between damage and sliding, resulting from the homogenisation process, induces a better representation of energy dissipation during the material degradation. The model parameters are identified from the geometric characteristics of the plate and a restricted number of material characteristics, allowing a very simple use of the model. Numerical validations of the DHRC model are presented, showing good agreement with experimental behaviour. A one dimensional simplification of the DHRC model is proposed, allowing the representation of reinforced concrete bars and simplified models of rods and wire mesh

  8. Pattern of seismic deformation in the Western Mediterranean

    Directory of Open Access Journals (Sweden)

    S. Pondrelli

    1999-06-01

    Full Text Available The seismic deformation of the Western Mediterranean was studied with the aim of defining the strain pattern that characterizes the Africa-Eurasia plate boundary in this area. Within different sections along the boundary the cumulative moment tensor was computed over 90 years of seismological data. The results were compared with NUVELlA plate motion model and geodetic data. A stable agreement was found along Northern Africa to Sicily, where only Africa and Eurasia plates are involved. In this zone it is evident that changes in the strike of the boundary correspond to variations in the prevailing geometry of deformation, tectonic features and in the percentage of seismic with respect to total expected deformation. The geometry of deformation of periadriatic sections (Central to Southern Apennines, Eastern Alps and the Eastern Adriatic area agrees well with VLBI measurements and with regional geological features. Seismicity seems to account for low rates, from 3% to 31%, of total expected deformation. Only in the Sicily Strait, characterized by extensional to strike slip deformation, does the ratio reach a higher value (79%. If the amount of deformation deduced from seismicity seems low, because 90 years are probably not representative of the recurrence seismic cycle of the Western Mediterranean, the strain pattern we obtain from cumulative moment tensors is more representative of the kinematics of this area than global plate motion models and better identifies lower scale geodynamic features.

  9. Preliminary review and summary of the potential for tectonic, seismic, and volcanic activity at the Nevada Test Site defense waste disposal site

    International Nuclear Information System (INIS)

    Metcalf, L.A.

    1983-03-01

    A change from compressional to extensional tectonics, which occurred about 17 m.y. ago, marks the emergence of the present tectonic regime in the southern Great Basin. Crustal extension is continuing at the present time, oriented in a NW-SE direction in the NTS region. Concurrently with the onset of crustal extension a system of NW- and NE-trending shear zones developed, along which mutual offset has occurred. Present seismic and tectonic activity in the NTS region is concentrated along the intersections of the shear zones and in areas of deep basin formation. Natural historic seismicity of the NTS region has been low to moderate. Seismic hazard assessments suggest a maximum magnitude 6-7 earthquake, associated with a maximum peak acceleration of 0.7 to 0.9 g, is probable for the NTS. A return period of 12,700 to 15,000 y for the maximum peak acceleration indicates a relatively low seismic hazard. Silicic volcanism in the NTS region was active from 16 to 6 m.y. ago, followed by a transition to basaltic volcanism. The tectonic settings most favorable for Quaternary basaltic activity are areas of young basin-range extension, caldera ring fracture zones, and intersections of conjugate shear zones. Probability calculations for the Yucca Mountain waste repository result in a volcanic disruption hazard of 10 - 8 to 10 - 9 /y. This value is extremely low and is probably representative of the hazard at Frenchman Flat. However, due to its tectonic setting, Frenchman Flat may be an area conducive to future basaltic volcanism; further investigation is needed to properly assess volcanic hazard

  10. Emergence of silicic continents as the lower crust peels off on a hot plate-tectonic Earth

    Science.gov (United States)

    Chowdhury, Priyadarshi; Gerya, Taras; Chakraborty, Sumit

    2017-09-01

    The rock record and geochemical evidence indicate that continental recycling has been occurring since the early history of the Earth. The stabilization of felsic continents in place of Earth's early mafic crust about 3.0 to 2.0 billion years ago, perhaps due to the initiation of plate tectonics, implies widespread destruction of mafic crust during this time interval. However, the physical mechanisms of such intense recycling on a hotter, (late) Archaean and presumably plate-tectonic Earth remain largely unknown. Here we use thermomechanical modelling to show that extensive recycling via lower crustal peeling-off (delamination but not eclogitic dripping) during continent-continent convergence was near ubiquitous during the late Archaean to early Proterozoic. We propose that such destruction of the early mafic crust, together with felsic magmatism, may have caused both the emergence of silicic continents and their subsequent isostatic rise, possibly above the sea level. Such changes in the continental character have been proposed to influence the Great Oxidation Event and, therefore, peeling-off plate tectonics could be the geodynamic trigger for this event. A transition to the slab break-off controlled syn-orogenic recycling occurred as the Earth aged and cooled, leading to reduced recycling and enhanced preservation of the continental crust of present-day composition.

  11. Seismicity of the Earth 1900–2010 Middle East and vicinity

    Science.gov (United States)

    Jenkins, Jennifer; Turner, Bethan; Turner, Rebecca; Hayes, Gavin P.; Davies, Sian; Dart, Richard L.; Tarr, Arthur C.; Villaseñor, Antonio; Benz, Harley M.

    2013-01-01

    No fewer than four major tectonic plates (Arabia, Eurasia, India, and Africa) and one smaller tectonic block (Anatolia) are responsible for seismicity and tectonics in the Middle East and surrounding region. Geologic development of the region is a consequence of a number of first-order plate tectonic processes that include subduction, large-scale transform faulting, compressional mountain building, and crustal extension. In the east, tectonics are dominated by the collision of the India plate with Eurasia, driving the uplift of the Himalaya, Karakorum, Pamir and Hindu Kush mountain ranges. Beneath the Pamir‒Hindu Kush Mountains of northern Afghanistan, earthquakes occur to depths as great as 200 km as a result of remnant lithospheric subduction. Along the western margin of the India plate, relative motions between India and Eurasia are accommodated by strike-slip, reverse, and oblique-slip faulting, resulting in the complex Sulaiman Range fold and thrust belt, and the major translational Chaman Fault in Afghanistan. Off the south coasts of Pakistan and Iran, the Makran trench is the surface expression of active subduction of the Arabia plate beneath Eurasia. Northwest of this subduction zone, collision between the two plates forms the approximately 1,500-km-long fold and thrust belts of the Zagros Mountains, which cross the whole of western Iran and extend into northeastern Iraq. Tectonics in the eastern Mediterranean region are dominated by complex interactions between the Africa, Arabia, and Eurasia plates, and the Anatolia block. Dominant structures in this region include: the Red Sea Rift, the spreading center between the Africa and Arabia plates; the Dead Sea Transform, a major strike-slip fault, also accommodating Africa-Arabia relative motions; the North Anatolia Fault, a right-lateral strike-slip structure in northern Turkey accommodating much of the translational motion of the Anatolia block westwards with respect to Eurasia and Africa; and the Cyprian

  12. Seismic hazard assessment in intra-plate areas and backfitting

    International Nuclear Information System (INIS)

    Asmis, G.J.K.; Eng, P.

    2001-01-01

    Typically, fuel cycle facilities have been constructed over a 40 year time period incorporating various ages of seismic design provisions ranging from no specific seismic requirements to the life safety provisions normally incorporated in national building codes through to the latest seismic nuclear codes that provide not only for structural robustness but also include operational requirements for continued operation of essential safety functions. The task is to ensure uniform seismic risk in all facilities. Since the majority of the fuel cycle infrastructure has been built the emphasis is on re-evaluation and backfitting. The wide range of facilities included in the fuel cycle and the vastly varying hazard to safety, health and the environment suggest a performance based approach. This paper presents such an approach, placed in an intra-plate setting of a Stable Continental Region (SCR) typical to that found in Eastern Canada. (author)

  13. New Insights on the Structure of the Cascadia Subduction Zone from Amphibious Seismic Data

    Science.gov (United States)

    Janiszewski, Helen Anne

    A new onshore-offshore seismic dataset from the Cascadia subduction zone was used to characterize mantle lithosphere structure from the ridge to the volcanic arc, and plate interface structure offshore within the seismogenic zone. The Cascadia Initiative (CI) covered the Juan de Fuca plate offshore the northwest coast of the United States with an ocean bottom seismometer (OBS) array for four years; this was complemented by a simultaneous onshore seismic array. Teleseismic data recorded by this array allows the unprecedented imaging of an entire tectonic plate from its creation at the ridge through subduction initiation and back beyond the volcanic arc along the entire strike of the Cascadia subduction zone. Higher frequency active source seismic data also provides constraints on the crustal structure along the plate interface offshore. Two seismic datasets were used to image the plate interface structure along a line extending 100 km offshore central Washington. These are wide-angle reflections from ship-to-shore seismic data from the Ridge-To-Trench seismic cruise and receiver functions calculated from a densely spaced CI OBS focus array in a similar region. Active source seismic observations are consistent with reflections from the plate interface offshore indicating the presence of a P-wave velocity discontinuity. Until recently, there has been limited success in using the receiver function technique on OBS data. I avoid these traditional challenges by using OBS constructed with shielding deployed in shallow water on the continental shelf. These data have quieter horizontals and avoid water- and sediment-multiple contamination at the examined frequencies. The receiver functions are consistently modeled with a velocity structure that has a low velocity zone (LVZ) with elevated P to S-wave velocity ratios at the plate interface. A similar LVZ structure has been observed onshore and interpreted as a combination of elevated pore-fluid pressures or metasediments

  14. A probabilistic approach towards understanding how planet composition affects plate tectonics - through time and space.

    Science.gov (United States)

    Stamenkovic, V.

    2017-12-01

    We focus on the connections between plate tectonics and planet composition — by studying how plate yielding is affected by surface and mantle water, and by variable amounts of Fe, SiC, or radiogenic heat sources within the planet interior. We especially explore whether we can make any robust conclusions if we account for variable initial conditions, current uncertainties in model parameters and the pressure dependence of the viscosity, as well as uncertainties on how a variable composition affects mantle rheology, melting temperatures, and thermal conductivities. We use a 1D thermal evolution model to explore with more than 200,000 simulations the robustness of our results and use our previous results from 3D calculations to help determine the most likely scenario within the uncertainties we still face today. The results that are robust in spite of all uncertainties are that iron-rich mantle rock seems to reduce the efficiency of plate yielding occurring on silicate planets like the Earth if those planets formed along or above mantle solidus and that carbon planets do not seem to be ideal candidates for plate tectonics because of slower creep rates and generally higher thermal conductivities for SiC. All other conclusions depend on not yet sufficiently constrained parameters. For the most likely case based on our current understanding, we find that, within our range of varied planet conditions (1-10 Earth masses), planets with the greatest efficiency of plate yielding are silicate rocky planets of 1 Earth mass with large metallic cores (average density 5500-7000 kg m-3) with minimal mantle concentrations of iron (as little as 0% is preferred) and radiogenic isotopes at formation (up to 10 times less than Earth's initial abundance; less heat sources do not mean no heat sources). Based on current planet formation scenarios and observations of stellar abundances across the Galaxy as well as models of the evolution of the interstellar medium, such planets are

  15. Evidence for a continental unstable triple junction as an alternate model for Vrancea seismicity

    International Nuclear Information System (INIS)

    Besutiu, L.

    2002-01-01

    The Vrancea active seismic zone located in the bending area of Romanian Carpathians stands for a long time as a challenge to geoscientists all over the world. Deep seismicity in continental collision circumstances is rather rare and always constraints on dynamics of subduction. The pattern of the intermediate-depth seismicity in the Vrancea region suggests a confined prismatic nearly vertical seismic body. The small size and geometry of the seismic zone have made it difficult to interpret the kinematics of subduction and continental collision in the area. During the years, several models, almost all subduction-related, have more or less successfully tried to explain this phenomenon. The paper represents an attempt to explain the Vrancea intermediate depth seismicity starting from a new concept, as introduced by the plate tectonics theory: the triple junction. A continental unstable triple junction is proposed as an alternate model to explain the unusual seismicity in the Vrancea seismic area. Three tectonic plates / microplates seem to join in the region: East European Plate (EEP), Moesian microplate (MoP), and the Intra-Alpine microplate (IaP). Their edges are geophysically documented and their motion is evidenced. The differentiation in their relative velocities generated an unstable transform-transform-compression triple junction that determined the vertical collapse of the lithospheric segment to which the intermediate seismicity within Vrancea zone is associated. Three major plates' wedges bound the seismic body: Tornquist-Teissyere zone, Peceneaga-Camena fault, and Trans-Getica fault. Temperature accommodation phenomena associated to the sinking lithospheric body into the hotter upper mantle environment (such as convective cells, phase-transform processes, and devolatilization) could be responsible for the earthquakes occurrence. The problem of the missing subduction related volcanism within Vrancea triple junction (VTJ) area is definitely solved in the case

  16. Multi-type Tectonic Responses to Plate Motion Changes of Mega-Offset Transform Faults at the Pacific-Antarctic Ridge

    Science.gov (United States)

    Zhang, F.; Lin, J.; Yang, H.; Zhou, Z.

    2017-12-01

    Magmatic and tectonic responses of a mid-ocean ridge system to plate motion changes can provide important constraints on the mechanisms of ridge-transform interaction and lithospheric properties. Here we present new analysis of multi-type responses of the mega-offset transform faults at the Pacific-Antarctic Ridge (PAR) system to plate motion changes in the last 12 Ma. Detailed analysis of the Heezen, Tharp, and Udintsev transform faults showed that the extensional stresses induced by plate motion changes could have been released through a combination of magmatic and tectonic processes: (1) For a number of ridge segments with abundant magma supply, plate motion changes might have caused the lateral transport of magma along the ridge axis and into the abutting transform valley, forming curved "hook" ridges at the ridge-transform intersection. (2) Plate motion changes might also have caused vertical deformation on steeply-dipping transtensional faults that were developed along the Heezen, Tharp, and Udintsev transform faults. (3) Distinct zones of intensive tectonic deformation, resembling belts of "rift zones", were found to be sub-parallel to the investigated transform faults. These rift-like deformation zones were hypothesized to have developed when the stresses required to drive the vertical deformation on the steeply-dipping transtensional faults along the transform faults becomes excessive, and thus deformation on off-transform "rift zones" became favored. (4) However, to explain the observed large offsets on the steeply-dipping transtensional faults, the transform faults must be relatively weak with low apparent friction coefficient comparing to the adjacent lithospheric plates.

  17. The modest seismicity of the northern Red Sea rift

    Science.gov (United States)

    Mitchell, Neil C.; Stewart, Ian C. F.

    2018-05-01

    Inferring tectonic movements from earthquakes (`seismotectonics') relies on earthquakes faithfully recording tectonic motions. In the northern half of the Red Sea, however, events of magnitude 5.0 and above are almost entirely absent from global catalogues, even though GPS and other plate motion data suggest that the basin is actively rifting at ˜10 mm yr-1. Seismic moments computed here from event magnitudes contributed to the International Seismology Centre (ISC) suggest that the moment release rate is more than an order of magnitude smaller than for the southern Red Sea and for the Southwest Indian Ridge (SWIR), which is spreading at a comparable rate to the central Red Sea and is more remote from recording stations. A smaller moment release rate in the northern Red Sea might be anticipated from its smaller spreading rate, but seismic coupling coefficients, which account for spreading rate variations, are also one order of magnitude smaller than for the other two areas. We explore potential explanations for this apparently reduced seismicity. The northern Red Sea is almost continuously covered with thick evaporites and overlying Plio-Pleistocene sediments. These deposits may have reduced the thickness of the seismogenic layer, for example, by elevating lithosphere temperatures by a thermal blanketing effect or by leading to excess pore fluid pressures that reduce effective stress. The presence of subdued seismicity here implies that tectonic movements can in places be poorly recorded by earthquake data and requires that alternative data be sought when investigating the active tectonics of sedimented rifts in particular.

  18. The Okhotsk Plate and the Eurasia-North America plate boundary zone.

    Science.gov (United States)

    Hindle, David; Mackey, Kevin

    2014-05-01

    The Eurasia-North America plate boundary zone transitions from spreading at rates of ~ 25mm/yr in the North Atlantic, to compression at rates of ~ 5mm/yr in the region of the Okhotsk plate. Because the pole of rotation between Eurasia and North America lies more or less on their mutual boundary, there is a linear change in rate along the boundary, and regions near the euler pole are subject to extremely low deformation rates. The Okhotsk - Eurasia - North America triple junction lies slightly south of the rotation pole, placing the Okhotsk plate entirely in a weakly contractional setting. Regions near the triple junction absorb 1mm/yr contraction. Further south, towards the shoreline of the Okhotsk sea, up to 5 mm/yr contraction may be absorbed within the plate. How shortening is accommodated across the boundary remains an open question. One possibility is wholesale extrusion of the entire Okhotsk plate (or possibly its northwestern corner) along two plate boundary strike slip faults (Eurasia-Okhostk and North America Okhotsk). The problem with this model is that the seismic record does not presently clearly support it, with the largest events distributed both within the plate interior and on its boundaries. This may suggest that instead, the Okhotsk plate, and particularly its north-western end, consists of a series of smaller blocks which shuffle against each other, partially accommodating extrusion, but also permitting some internal deformation and change of shape of the Okhotsk plate itself. We present analyses of the very sparse seismic record from the region, as well as geometric-kinematic, tectonic models of the possible deformation of northwest Okhotsk to try to better understand the different probabilities of how this slowly deforming plate boundary zone is behaving.

  19. France's seismic zoning

    International Nuclear Information System (INIS)

    Mohammadioun, B.

    1997-01-01

    In order to assess the seismic hazard in France in relation to nuclear plant siting, the CEA, EDF and the BRGM (Mine and Geology Bureau) have carried out a collaboration which resulted in a seismic-tectonic map of France and a data base on seismic history (SIRENE). These studies were completed with a seismic-tectonic zoning, taking into account a very long period of time, that enabled a probabilistic evaluation of the seismic hazard in France, and that may be related to adjacent country hazard maps

  20. Influence of increasing convergence obliquity and shallow slab geometry onto tectonic deformation and seismogenic behavior along the Northern Lesser Antilles zone

    Science.gov (United States)

    Laurencin, M.; Graindorge, D.; Klingelhoefer, F.; Marcaillou, B.; Evain, M.

    2018-06-01

    In subduction zones, the 3D geometry of the plate interface is one of the key parameters that controls margin tectonic deformation, interplate coupling and seismogenic behavior. The North American plate subducts beneath the convex Northern Lesser Antilles margin. This convergent plate boundary, with a northward increasing convergence obliquity, turns into a sinistral strike-slip limit at the northwestern end of the system. This geodynamic context suggests a complex slab geometry, which has never been imaged before. Moreover, the seismic activity and particularly the number of events with thrust focal mechanism compatible with subduction earthquakes, increases northward from the Barbuda-Anguilla segment to the Anguilla-Virgin Islands segment. One of the major questions in this area is thus to analyze the influence of the increasing convergence obliquity and the slab geometry onto tectonic deformation and seismogenic behavior of the subduction zone. Based on wide-angle and multichannel reflection seismic data acquired during the Antithesis cruises (2013-2016), we decipher the deep structure of this subduction zone. Velocity models derived from wide-angle data acquired across the Anegada Passage are consistent with the presence of a crust of oceanic affinity thickened by hotspot magmatism and probably affected by the Upper Cretaceous-Eocene arc magmatism forming the 'Great Arc of the Caribbean'. The slab is shallower beneath the Anguilla-Virgin Islands margin segment than beneath the Anguilla-Barbuda segment which is likely to be directly related to the convex geometry of the upper plate. This shallower slab is located under the forearc where earthquakes and partitioning deformations increase locally. Thus, the shallowing slab might result in local greater interplate coupling and basal friction favoring seismic activity and tectonic partitioning beneath the Virgin Islands platform.

  1. Geomorphology and Neogene tectonic evolution of the Palomares continental margin (Western Mediterranean)

    Science.gov (United States)

    Gómez de la Peña, Laura; Gràcia, Eulàlia; Muñoz, Araceli; Acosta, Juan; Gómez-Ballesteros, María; R. Ranero, César; Uchupi, Elazar

    2016-10-01

    The Palomares continental margin is located in the southeastern part of Spain. The margin main structure was formed during Miocene times, and it is currently part of the wide deformation zone characterizing the region between the Iberian and African plates, where no well-defined plate boundary occurs. The convergence between these two plates is here accommodated by several structures, including the left lateral strike-slip Palomares Fault. The region is characterized by sparse, low to moderate magnitude (Mw shallow instrumental earthquakes, although large historical events have also occurred. To understand the recent tectonic history of the margin we analyze new high-resolution multibeam bathymetry data and re-processed three multichannel seismic reflection profiles crossing the main structures. The analysis of seafloor morphology and associated subsurface structure provides new insights of the active tectonic features of the area. In contrast to other segments of the southeastern Iberian margin, the Palomares margin contains numerous large and comparatively closely spaced canyons with heads that reach near the coast. The margin relief is also characterized by the presence of three prominent igneous submarine ridges that include the Aguilas, Abubacer and Maimonides highs. Erosive processes evidenced by a number of scars, slope failures, gullies and canyon incisions shape the present-day relief of the Palomares margin. Seismic images reveal the deep structure distinguishing between Miocene structures related to the formation of the margin and currently active features, some of which may reactivate inherited structures. The structure of the margin started with an extensional phase accompanied by volcanic accretion during the Serravallian, followed by a compressional pulse that started during the Latemost Tortonian. Nowadays, tectonic activity offshore is subdued and limited to few, minor faults, in comparison with the activity recorded onshore. The deep Algero

  2. Plate-Tectonic Circulation is Driven by Cooling From the Top and is Closed Within the Upper Mantle

    Science.gov (United States)

    Hamilton, W. B.

    2001-12-01

    Subduction drives plate tectonics and is due to cooling from the top: circulation is self-organized, and likely is closed above the discontinuity near 660 km. The contrary consensus that plate tectonics is driven by bottom heating and involves the entire mantle combines misunderstood kinematics with flawed concepts of through-the-mantle plumes and subduction. Plume conjecture came from the Emperor-Hawaii progression, the 45 Ma inflection in which was assumed to mark a 60-degree change in direction of that part of the Pacific plate over a fixed plume. Smooth spreading patterns around the east and south margin of the Pacific plate, and paleomagnetic data, disprove such a change. Speculations that plumes move, jump, etc. do not revive falsified conjecture. Geochemical distinctions between enriched island and depleted ridge basalts (which overlap) are expected products of normal upper-mantle processes, not plumes. MORB traverses solidus-T asthenosphere, whereas OIB zone-refines through subsolidus lithosphere and crust, crystallizing refractories to retain T of diminishing melt while assimilating and retaining fusibles. Tomographic inference of deep-mantle subduction is presented misleadingly and may reflect methodological and sampling artifacts (downward smearing, and concentration of recorded body waves in bundles within broad anomalies otherwise poorly sampled). Planetological and other data require hot Earth accretion, and thorough early fractionation, from material much more refractory than primitive meteorites, and are incompatible with the little-fractionated lower mantle postulated to permit whole-mantle circulation. The profound seismic discontinuity near 660 km is a thermodynamic and physical barrier to easy mass transfer in either direction. Refractory lower mantle convects slowly, perhaps in layers, and loses primarily original heat, whereas upper mantle churns rapidly, and the 660 decoupling boundary must have evolved into a compositional barrier also

  3. Crustal structure and tectonic deformation of the southern Ecuadorian margin

    Science.gov (United States)

    Calahorrano, Alcinoe; Collot, Jean-Yves; Sage, Françoise; Ranero, César R.

    2010-05-01

    Multichannel seismic lines acquired during the SISTEUR cruise (2000) provide new constraints on the structure and deformation of the subduction zone at the southern Ecuadorian margin, from the deformation front to the continental shelf of the Gulf of Guayaquil. The pre-stack depth migrated images allows to characterise the main structures of the downgoing and overriding plates and to map the margin stratigraphy in order to propose a chronology of the deformation, by means of integrating commercial well data and industry seismic lines located in the gulf area. The 100-km-long seismic lines show the oceanic Nazca plate underthrusting the South American plate, as well as the subduction channel and inter-plate contact from the deformation front to about 90 km landward and ~20 km depth. Based on seismic structure we identify four upper-plate units, consisting of basement and overlaying sedimentary sequences A, B and C. The sedimentary cover varies along the margin, being few hundreds of meters thick in the lower and middle slope, and ~2-3 km thick in the upper slope. Exceptionally, a ~10-km -thick basin, here named Banco Peru basin, is located on the upper slope at the southernmost part of the gulf. This basin seems to be the first evidence of the Gulf of Guayaquil opening resulting from the NE escaping of the North Andean Block. Below the continental shelf, thick sedimentary basins of ~6 to 8 km occupy most of the gulf area. Tectonic deformation across most of the upper-plate is dominated by extensional regime, locally disturbed by diapirism. Compression evidences are restricted to the deformation front and surrounding areas. Well data calibrating the seismic profiles indicate that an important portion of the total thickness of the sedimentary coverage of the overriding plate are Miocene or older. The data indicate the extensional deformation resulting from the NE motion of the North Andean Block and the opening of the Gulf of Guayaquil, evolves progressively in age

  4. Tectonics in the Northwestern West Philippine Basin

    Institute of Scientific and Technical Information of China (English)

    Ni Xianglong; Wu Shiguo; Shinjo Ryuichi

    2008-01-01

    The West Philippine basin (WPB) is a currently inactive marginal basin belonging to Philippine Sea plate, which has a complex formation history and various crust structures. Based on gravity, magnetic and seismic data, the tectonics in West Philippine basin is characterized by amagnma spreading stage and strike slip fractures. NNE trending Okinawa-Luzon fracture zone is a large fracture zone with apparent geomorphology and shows a right-handed movement. The results of joint gravity-magnetic-seismic inversion suggest that the Okinawa-Luzon fracture zone has intensive deformation and is a transform fault. Western existence of the NW trending fractures under Ryukyu Islands Arc is the main cause of the differences between south and north Okinawa Trough. The Urdaneta plateau is not a remained arc, but remnant of mantle plume although its lava chemistry is similar to oceanic island basalt (OIB).

  5. Tectonic implications of seismic activity recorded by the northern Ontario seismograph network

    International Nuclear Information System (INIS)

    Wetmiller, R.J.; Cajka, M.G.

    1989-01-01

    The northern Ontario seismograph network, which has operated under the Canadian Nuclear Fuel Waste Management Program since 1982, has provided valuable data to supplement those recorded by the Canadian national networks on earthquake activity, rockburst activity, the distribution of regional seismic velocities, and the contemporary stress field in northern Ontario. The combined networks recorded the largest earthquake known in northwestern Ontario, M 3.9 near Sioux Lookout on February 11, 1984, and many smaller earthquakes in northeastern Ontario. Focal mechanism solutions of these and older events showed high horizontal stress and thrust faulting to be dominant features of the contemporary tectonics of northern Ontario. The zone of more intense earthquake activity in western Quebec appeared to extend northwestward into the Kapuskasing area of northeastern Ontario, where an area of persistent microearthquake activity had been identified by a seismograph station near Kapuskasing. Controlled explosions of the 1984 Kapuskasing Uplift seismic profile experiment recorded on the northern Ontario seismograph network showed the presence of anomalously high LG velocities in northeastern Ontario (3.65 km/s) that when properly taken into account reduced the mislocation errors of well-recorded seismic events by 50% on average

  6. Seismicity and Seismic Hazard along the Western part of the Eurasia-Nubia plate boundary

    Science.gov (United States)

    Bezzeghoud, Mourad; Fontiela, João; Ferrão, Celia; Borges, José Fernando; Caldeira, Bento; Dib, Assia; Ousadou, Farida

    2016-04-01

    The seismic phenomenon is the most damaging natural hazard known in the Mediterranean area. The western part of the Eurasia-Nubia plate boundary extends from the Azores to the Mediterranean region. The oceanic part of the plate boundary is well delimited from the Azores Islands, along the Azores-Gibraltar fault to approximately 12°W (west of the Strait of Gibraltar). From 12°W to 3.5°E, including the Iberia-Nubia region and extending to the western part of Algeria, the boundary is more diffuse and forms a wider area of deformation. The boundary between the Iberia and Nubia plates is the most complex part of the margin. This region corresponds to the transition from an oceanic boundary to a continental boundary, where Iberia and Nubia collide. Although most earthquakes along this plate boundary are shallow and generally have magnitudes less than 5.5, there have been several high-magnitude events. Many devastating earthquakes, some of them tsunami-triggering, inflicted heavy loss and considerable economic damage to the region. From 1920 to present, three earthquakes with magnitudes of about 8.0 (Mw 8.2, 25 November 1941; Ms 8.0, 25 February 1969; and Mw 7.9, 26 May 1975) occurred in the oceanic region, and four earthquakes with magnitudes of about 7.0 (Mw 7.1, 8 May 1939, Santa Maria Island and Mw 7.1, January 1980, Terceira and Graciosa Islands, both in the Azores; Ms 7.1, 20 May 1931, Azores-Gibraltar fracture zone; and Mw 7.3, 10 October 1980, El Asnam, Algeria) occurred along the western part of the Eurasia-Nubia plate boundary. In general, large earthquakes (M ≥7) occur within the oceanic region, with the exception of the El Asnam (Algeria) earthquakes. Some of these events caused extensive damage. The 1755 Lisbon earthquake (˜Mw 9) on the Portugal Atlantic margin, about 200 km W-SW of Cape St. Vincent, was followed by a tsunami and fires that caused the near-total destruction of Lisbon and adjacent areas. Estimates of the death toll in Lisbon alone (~70

  7. The influence of climatically-driven surface loading variations on continental strain and seismicity

    Science.gov (United States)

    Craig, Tim; Calais, Eric; Fleitout, Luce; Bollinger, Laurent; Scotti, Oona

    2016-04-01

    In slowly deforming regions of plate interiors, secondary sources of stress and strain can result in transient deformation rates comparable to, or greater than, the background tectonic rates. Highly variable in space and time, these transients have the potential to influence the spatio-temporal distribution of seismicity, interfering with any background tectonic effects to either promote or inhibit the failure of pre-existing faults, and potentially leading to a clustered, or 'pulse-like', seismic history. Here, we investigate the ways in which the large-scale deformation field resulting from climatically-controlled changes in surface ice mass over the Pleistocene and Holocene may have influenced not only the seismicity of glaciated regions, but also the wider seismicity around the ice periphery. We first use a set of geodynamic models to demonstrate that a major pulse of seismic activity occurring in Fennoscandia, coincident with the time of end-glaciation, occurred in a setting where the contemporaneous horizontal strain-rate resulting from the changing ice mass, was extensional - opposite to the reverse sense of coseismic displacement accommodated on these faults. Therefore, faulting did not release extensional elastic strain that was building up at the time of failure, but compressional elastic strain that had accumulated in the lithosphere on timescales longer than the glacial cycle, illustrating the potential for a non-tectonic trigger to tap in to the background tectonic stress-state. We then move on to investigate the more distal influence that changing ice (and ocean) volumes may have had on the evolving strain field across intraplate Europe, how this is reflected in the seismicity across intraplate Europe, and what impact this might have on the paleoseismic record.

  8. Seismic structure of the western U.S. mantle and its relation to regional tectonic and magmatic activity

    Science.gov (United States)

    Schmandt, Brandon

    Vigorous convective activity in the western U.S. mantle has long been inferred from the region's widespread intra-plate crustal deformation, volcanism, and high elevations, but the specific form of convective activity and the degree and nature of lithospheric involvement have been strongly debated. I design a seismic travel-time tomography method and implement it with seismic data from the EarthScope Transportable Array and complementary arrays to constrain three-dimensional seismic structure beneath the western U.S. Tomographic images of variations in compressional velocity, shear velocity, and the ratio of shear to compressional velocity in the western U.S. mantle to a depth of 1000 km are produced. Using these results I investigate mantle physical properties, Cenozoic subduction history, and the influence of small-scale lithospheric convection on regional tectonic and magmatic activity, with particular focus on southern California and the Pacific Northwest. This dissertation includes previously published co-authored material. Chapter II presents a travel-time tomography method I designed and first implemented with data from southern California and the surrounding southwestern U.S. The resulting images provide a new level of constraint on upper mantle seismic anomalies beneath the Transverse Ranges, southern Great Valley, Salton Trough, and southwestern Nevada volcanic field. Chapter III presents tomographic images of the western U.S. mantle, identifies upper mantle volumes where partial melt is probable, and discusses implications of the apparently widespread occurrence of gravitational instabilities of continental lithsophere and the complex geometry and buoyancy of subducted ocean lithosphere imaged beneath the western U.S. In Chapter IV, tomography images are used in conjunction with geologic constraints on major transitions in crustal deformation and magmatism to construct a model for Pacific Northwest evolution since the Cretaceous. Accretion in the Pacific

  9. A harbinger of plate tectonics: a commentary on Bullard, Everett and Smith (1965) ?The fit of the continents around the Atlantic?

    OpenAIRE

    Dewey, John F.

    2015-01-01

    In the 1960s, geology was transformed by the paradigm of plate tectonics. The 1965 paper of Bullard, Everett and Smith was a linking transition between the theories of continental drift and plate tectonics. They showed, conclusively, that the continents around the Atlantic were once contiguous and that the Atlantic Ocean had grown at rates of a few centimetres per year since the Early Jurassic, about 160?Ma. They achieved fits of the continental margins at the 500 fathom line (approx. 900?m),...

  10. Recent advances in seismic non-destructive testing of concrete plate like structures

    International Nuclear Information System (INIS)

    Ryden, N.; Kristensen, A.; Jovall, O.

    2009-01-01

    This paper describes recent advances in seismic/acoustic non-destructive testing of concrete containment walls. The presented technique is focused on the characterization of the mean stiffness (seismic velocities) and thickness of the containment wall. The Impact Echo (IE) method is a well-established technique to measure the thickness of concrete plates or to locate defects in concrete plate like structures. The method relies on a good estimate of the mean velocity through the thickness of the plate and a precisely measured thickness resonant frequency. Recently the underlying theory of the IE method has been redefined and improved based on Lamb waves in a free plate. Based on this theory we have developed a new data processing technique where both propagating and standing Lamb waves are analysed in a combined manner using multichannel data. With this approach the mean velocity through the plate thickness is evaluated by using the fundamental mode Lamb wave dispersion curves. The accuracy and detection ability of the measured resonant frequency is improved by utilizing both amplitude and phase information from the multichannel record. The method has been tested on several nuclear power plants in Sweden and Finland and proved to be more robust compared to conventional IE and surface wave measurements

  11. Glacier ice mass fluctuations and fault instability in tectonically active Southern Alaska

    Science.gov (United States)

    Sauber, Jeanne M.; Molnia, Bruce F.

    2004-07-01

    Across the plate boundary zone in south central Alaska, tectonic strain rates are high in a region that includes large glaciers undergoing wastage (glacier retreat and thinning) and surges. For the coastal region between the Bering and Malaspina Glaciers, the average ice mass thickness changes between 1995 and 2000 range from 1 to 5 m/year. These ice changes caused solid Earth displacements in our study region with predicted values of -10 to 50 mm in the vertical and predicted horizontal displacements of 0-10 mm at variable orientations. Relative to stable North America, observed horizontal rates of tectonic deformation range from 10 to 40 mm/year to the north-northwest and the predicted tectonic uplift rates range from approximately 0 mm/year near the Gulf of Alaska coast to 12 mm/year further inland. The ice mass changes between 1995 and 2000 resulted in discernible changes in the Global Positioning System (GPS) measured station positions of one site (ISLE) located adjacent to the Bagley Ice Valley and at one site, DON, located south of the Bering Glacier terminus. In addition to modifying the surface displacements rates, we evaluated the influence ice changes during the Bering glacier surge cycle had on the background seismic rate. We found an increase in the number of earthquakes ( ML≥2.5) and seismic rate associated with ice thinning and a decrease in the number of earthquakes and seismic rate associated with ice thickening. These results support the hypothesis that ice mass changes can modulate the background seismic rate. During the last century, wastage of the coastal glaciers in the Icy Bay and Malaspina region indicates thinning of hundreds of meters and in areas of major retreat, maximum losses of ice thickness approaching 1 km. Between the 1899 Yakataga and Yakutat earthquakes ( Mw=8.1, 8.1) and prior to the 1979 St. Elias earthquake ( Ms=7.2), the plate interface below Icy Bay was locked and tectonic strain accumulated. We used estimated ice mass

  12. Interaction between central volcanoes and regional tectonics along divergent plate boundaries: Askja, Iceland

    Science.gov (United States)

    Trippanera, Daniele; Ruch, Joël; Acocella, Valerio; Thordarson, Thor; Urbani, Stefano

    2018-01-01

    Activity within magmatic divergent plate boundaries (MDPB) focuses along both regional fissure swarms and central volcanoes. An ideal place to investigate their mutual relationship is the Askja central volcano in Iceland. Askja consists of three nested calderas (namely Kollur, Askja and Öskjuvatn) located within a hyaloclastite massif along the NNE-SSW trending Icelandic MDPB. We performed an extensive field-based structural analysis supported by a remote sensing study of tectonic and volcanic features of Askja's calderas and of the eastern flank of the hyaloclastite massif. In the massif, volcano-tectonic structures trend N 10° E to N 40° E, but they vary around the Askja caldera being both parallel to the caldera rim and cross-cutting on the Western side. Structural trends around the Öskjuvatn caldera are typically rim parallel. Volcanic vents and dikes are preferentially distributed along the caldera ring faults; however, they follow the NNE-SSW regional structures when located outside the calderas. Our results highlight that the Askja volcano displays a balanced amount of regional (fissure-swarm related) and local (shallow-magma-chamber related) tectonic structures along with a mutual interaction among these. This is different from Krafla volcano (to the north of Askja) dominated by regional structures and Grímsvötn (to the South) dominated by local structures. Therefore, Askja represents an intermediate tectono-magmatic setting for volcanoes located in a slow divergent plate boundary. This is also likely in accordance with a northward increase in the spreading rate along the Icelandic MDPB.

  13. Interaction between central volcanoes and regional tectonics along divergent plate boundaries: Askja, Iceland

    KAUST Repository

    Trippanera, Daniele

    2017-12-04

    Activity within magmatic divergent plate boundaries (MDPB) focuses along both regional fissure swarms and central volcanoes. An ideal place to investigate their mutual relationship is the Askja central volcano in Iceland. Askja consists of three nested calderas (namely Kollur, Askja and Öskjuvatn) located within a hyaloclastite massif along the NNE-SSW trending Icelandic MDPB. We performed an extensive field-based structural analysis supported by a remote sensing study of tectonic and volcanic features of Askja’s calderas and of the eastern flank of the hyaloclastite massif. In the massif, volcano-tectonic structures trend N 10° E to N 40° E, but they vary around the Askja caldera being both parallel to the caldera rim and cross-cutting on the Western side. Structural trends around the Öskjuvatn caldera are typically rim parallel. Volcanic vents and dikes are preferentially distributed along the caldera ring faults; however, they follow the NNE-SSW regional structures when located outside the calderas. Our results highlight that the Askja volcano displays a balanced amount of regional (fissure-swarm related) and local (shallow-magma-chamber related) tectonic structures along with a mutual interaction among these. This is different from Krafla volcano (to the north of Askja) dominated by regional structures and Grímsvötn (to the South) dominated by local structures. Therefore, Askja represents an intermediate tectono-magmatic setting for volcanoes located in a slow divergent plate boundary. This is also likely in accordance with a northward increase in the spreading rate along the Icelandic MDPB.

  14. Impacts of sediment supply and local tectonics on clinoform distribution: the seismic stratigraphy of the mid Pleistocene-Holocene Indus Shelf

    Science.gov (United States)

    Limmer, David R.; Henstock, Timothy J.; Giosan, Liviu; Ponton, Camilo; Tabrez, Ali R.; Macdonald, David I. M.; Clift, Peter D.

    2012-09-01

    We present results from the first high-resolution seismic reflection survey of the inner Western Indus Shelf, and Indus Delta, Arabian Sea. The results show major regional differences in sedimentation across the shelf from east to west, as well as north to south, both since the Last Glacial Maximum (~20 ka) and over longer time scales. We identify 10 major regional reflectors, interpreted as representing sea level lowstands. Strong compressive folding is observed underlying a reflector we have called Horizon 6 in the north-western shelf, probably compression associated with the transpressional deformation of the Murray Ridge plate boundary. Downslope profiles show a series of well developed clinoforms, principally at the shelf edge, indicating significant preservation of large packages of sediment during lowstands. These clinoforms have developed close to zones of deformation, suggesting that subsidence is a factor in controlling sedimentation and consequently erosion of the Indus Shelf. These clinoforms fan out from dome features (tectonic anticlines) mostly located close to the modern shoreline.

  15. The Oldman River triangle zone: a complicated tectonic wedge delineated by new structural mapping and seismic interpretation

    Energy Technology Data Exchange (ETDEWEB)

    Stockmal, G. S. [Geological Survey of Canada, Calgary, AB (Canada). Inst. of Sedimentary and Petroleum Geology; Lawton, D. C.; Spratt, D. [Calgary Univ., AB (Canada). Dept. of Geology and Geophysics; MacKay, P. A.

    1996-06-01

    The triangle zone exposed along and adjacent to the Alberta Foothills was characterized on the basis of new structural mapping and seismic surveys. Results indicate that the zone is comprised of a complicated structure involving significant deformation in the hanging wall of the upper detachment, including orogenic thrusts and large orogen-vergent folds, as well as secondary orogen-directed tectonic wedging. This structure is considered to be an example of a `nested` triangle zone, where an `outer` tectonic wedge with modest shortening encases an `inner` counterpart with substantially more shortening. Both of these wedges show evidence of synchronous deformation. 23 refs., 9 figs.

  16. Seismicity of the North of the Russian Plate: Relocation of Recent Earthquakese

    Science.gov (United States)

    Morozov, A. N.; Vaganova, N. V.; Asming, V. E.; Mikhailova, Ya. A.

    2018-03-01

    The hypocenters of the earthquakes recorded in the north of the Russian Plate from 1982 to 2013 are relocated. The relocation of the hypocenters is based on the common velocity section, common methodology, and the entire set of the initial data and bulletins available from the Russian and foreign seismic stations. The efficiency of the algorithm for calculating the hypocentral parameters and the velocity section is demonstrated by the example of two nonmilitary nuclear explosions in July 18, 1985 and September 6, 1988 in the northern part of the European Russia. For the first time, two earthquakes of July 19, 1982 and October 7, 2012, which have not been previously reported in the catalogs for the north of the Russian plate, are included in the seismic catalog.

  17. Feeling and Understanding Plate Tectonics - How can We attract Museum Visitors Attention?

    Science.gov (United States)

    Simon, Gilla; Apel, Michael

    2017-04-01

    Earthquakes, volcano eruptions and other natural hazards are commonly paid attention to, if news about disastrous events reach us. The mission of an Earth Science or Natural History Museum, however, goes beyond explaining the causes of natural disasters, but should also present science history and cutting edge research. Since dealing with a subject, especially with one, which seems to be in the abstract, is more effective, we realised two new projects where our visitors can feel and understand plate tectonics in a more exciting way. In 2015 we installed an earthquake simulator in our permanent exhibition to allow our visitors the physical experience of an earthquake. Because of static restrictions the simulator is housed in a container outside the building where it can be visited as a booked program upon prior reservation or by joining public tours on Sundays and special occasions. The simulation of six real earthquakes in two spatial directions is accompanied by a movie presenting facts about the earthquake itself (e.g. location, magnitude, damage and victims), but also general information about plate tectonics. This standard program takes about 20 minutes. During an educational program, however, not only the simulator is visited, but also the permanent exhibition, where the guide can focus on different aspects and then might choose specific earthquakes and information blocs in the simulator. In addition workshops with experiments are offered for school classes and other groups. This allows us to offer an individual program fitting to the visitor group. In 2016 we converted an old movie room to a state of the art media room. In cooperation with Media Informatics students we developed a quiz for three different levels and various themes like earthquakes, volcanoes, history and plate tectonics in general. Starting the quiz, a virtual earthquake destroys a building which will be reconstructed if the participants answer multiple choice questions correctly. Though, the

  18. The tectonics of the area around the Konrad Mine (Salzgitter) based on reflection seismic studies

    International Nuclear Information System (INIS)

    Jaritz, W.

    1986-01-01

    Reflection seismic investigations were carried out to determine the safety of the final disposal of radioactive waste in the Konrad mine. The layer thickness since the Zechstein and the position of the most important geological horizons are described. On the basis of the seismic sections, the Thiede and Vechelde-Broistedt salt structures and the fault systems of the Konrad Graben and Immendorf fault are briefly analysed. The development of the structures in this area is explained by a combination of halokinesis and epirogenic-tectonic processes. The iron-ore deposit is syngenetic with the surrounding salt stocks. This has to be taken into consideration for a reconstruction of the paleogeography and assessment of the deposit. (orig.) [de

  19. Juan de Fuca slab geometry and its relation to Wadati-Benioff zone seismicity

    Science.gov (United States)

    McCrory, Patricia A.; Blair, J. Luke; Waldhause, Felix; Oppenheimer, David H.

    2012-01-01

    A new model of the subducted Juan de Fuca plate beneath western North America allows first-order correlations between the occurrence of Wadati-Benioff zone earthquakes and slab geometry, temperature, and hydration state. The geo-referenced 3D model, constructed from weighted control points, integrates depth information from earthquake locations and regional seismic velocity studies. We use the model to separate earthquakes that occur in the Cascadia forearc from those that occur within the underlying Juan de Fuca plate and thereby reveal previously obscured details regarding the spatial distribution of earthquakes. Seismicity within the slab is most prevalent where the slab is warped beneath northwestern California and western Washington suggesting that slab flexure, in addition to expected metamorphic dehydration processes, promotes earthquake occurrence within the subducted oceanic plate. Earthquake patterns beneath western Vancouver Island are consistent with slab dehydration processes. Conversely, the lack of slab earthquakes beneath western Oregon is consistent with an anhydrous slab. Double-differenced relocated seismicity resolves a double seismic zone within the slab beneath northwestern California that strongly constrains the location of the plate interface and delineates a cluster of seismicity 10 km above the surface that includes the 1992 M7.1 Mendocino earthquake. We infer that this earthquake ruptured a surface within the Cascadia accretionary margin above the Juan de Fuca plate. We further speculate that this earthquake is associated with a detached fragment of former Farallon plate. Other subsurface tectonic elements within the forearc may have the potential to generate similar damaging earthquakes.

  20. Seismicity and Seismotectonic Properties of The Sultandağı Fault Zone (Afyonkarahisar-Konya): Western Anatolia,Turkey

    Science.gov (United States)

    Kalafat, D.; Gunes, Y.; Kekovali, K.; Kara, M.; Gorgun, E.

    2017-12-01

    n this study we investigated seismicity and source characteristics of the Sultandağı Fault Zone (SFZ). As known Western Anatolia is one of the most important seismically active region in Turkey. The relative movement of the African-Arabian plates, it causes the Anatolian Plate to movement to the west-Southwest direction 2.5 cm per year and this result provides N-S direction with extensional regime in the recent tectonic. In this study, especially with the assessment of seismic activity occurring in Afyon and around between 200-2002 years, we have been evaluated to date with seismic activity as well as fault mechanism solution. We analyzed recent seismicity and distribution of earthquakes in this region. In the last century, 3 important earthquakes occurred in the Sultandağı Fault zone (Afyon-Akşehir Graben), this result shown it was seismic active and broken fault segments caused stress balance in the region and it caused to occur with short intervals of earthquakes in 2000 and 2002, triggering each other. The scope of this tudy, we installed new BB stations in the region and we have been done of the fault plane solutions for important earthquakes. The focal mechanisms clearly exhibit the activation of a NE-SW trending normal faulting system along the SFZ region. The results of stress analysis showed that the effective current tectonic evolution of normal faulting in this region. This study is supported by Bogazici University Research Projects Commission under SRP/BAP project No. 12280. Key Words: Sultandağı fault zone, normal faulting, seismicity, fault mechanism

  1. Estimating tectonic history through basin simulation-enhanced seismic inversion: Geoinformatics for sedimentary basins

    Science.gov (United States)

    Tandon, K.; Tuncay, K.; Hubbard, K.; Comer, J.; Ortoleva, P.

    2004-01-01

    A data assimilation approach is demonstrated whereby seismic inversion is both automated and enhanced using a comprehensive numerical sedimentary basin simulator to study the physics and chemistry of sedimentary basin processes in response to geothermal gradient in much greater detail than previously attempted. The approach not only reduces costs by integrating the basin analysis and seismic inversion activities to understand the sedimentary basin evolution with respect to geodynamic parameters-but the technique also has the potential for serving as a geoinfomatics platform for understanding various physical and chemical processes operating at different scales within a sedimentary basin. Tectonic history has a first-order effect on the physical and chemical processes that govern the evolution of sedimentary basins. We demonstrate how such tectonic parameters may be estimated by minimizing the difference between observed seismic reflection data and synthetic ones constructed from the output of a reaction, transport, mechanical (RTM) basin model. We demonstrate the method by reconstructing the geothermal gradient. As thermal history strongly affects the rate of RTM processes operating in a sedimentary basin, variations in geothermal gradient history alter the present-day fluid pressure, effective stress, porosity, fracture statistics and hydrocarbon distribution. All these properties, in turn, affect the mechanical wave velocity and sediment density profiles for a sedimentary basin. The present-day state of the sedimentary basin is imaged by reflection seismology data to a high degree of resolution, but it does not give any indication of the processes that contributed to the evolution of the basin or causes for heterogeneities within the basin that are being imaged. Using texture and fluid properties predicted by our Basin RTM simulator, we generate synthetic seismograms. Linear correlation using power spectra as an error measure and an efficient quadratic

  2. Brittle deformation during Alpine basal accretion and the origin of seismicity nests above the subduction interface

    Science.gov (United States)

    Menant, Armel; Angiboust, Samuel; Monié, Patrick; Oncken, Onno; Guigner, Jean-Michel

    2018-04-01

    Geophysical observations on active subduction zones have evidenced high seismicity clusters at 20-40 km depth in the fore-arc region whose origin remains controversial. We report here field observations of pervasive pseudotachylyte networks (interpreted as evidence for paleo-seismicity) in the now-exhumed Valpelline continental unit (Dent Blanche complex, NW. Alps, Italy), a tectonic sliver accreted to the upper plate at c. 30 km depth during the Paleocene Alpine subduction. Pre-alpine granulite-facies paragneiss from the core of the Valpelline unit are crosscut by widespread, mm to cm-thick pseudotachylyte veins. Co-seismic heating and subsequent cooling led to the formation of Ti-rich garnet rims, ilmenite needles, Ca-rich plagioclase, biotite microliths and hercynite micro-crystals. 39Ar-40Ar dating yields a 51-54 Ma age range for these veins, thus suggesting that frictional melting events occurred near peak burial conditions while the Valpelline unit was already inserted inside the duplex structure. In contrast, the base of the Valpelline unit underwent synchronous ductile and brittle, seismic deformation under water-bearing conditions followed by a re-equilibration at c. 40 Ma (39Ar-40Ar on retrograded pseudotachylyte veins) during exhumation-related deformation. Calculated rheological profiles suggest that pseudotachylyte veins from the dry core of the granulite unit record upper plate micro-seismicity (Mw 2-3) formed under very high differential stresses (>500 MPa) while the sheared base of the unit underwent repeated brittle-ductile deformation at much lower differential stresses (<40 MPa) in a fluid-saturated environment. These results demonstrate that some of the seismicity clusters nested along and above the plate interface may reflect the presence of stiff tectonic slivers rheologically analogous to the Valpelline unit acting as repeatedly breaking asperities in the basal accretion region of active subduction zones.

  3. Plate tectonic influences on Earth's baseline climate: a 2 billion-year record

    Science.gov (United States)

    McKenzie, R.; Evans, D. A.; Eglington, B. M.; Planavsky, N.

    2017-12-01

    Plate tectonic processes present strong influences on the long-term carbon cycle, and thus global climate. Here we utilize multiple aspects of the geologic record to assess the role plate tectonics has played in driving major icehouse­-greenhouse transitions for the past 2 billion years. Refined paleogeographic reconstructions allow us to quantitatively assess the area of continents in various latitudinal belts throughout this interval. From these data we are able to test the hypothesis that concentrating continental masses in low-latitudes will drive cooler climates due to increased silicate weathering. We further superimpose records of events that are believed to increase the `weatherability' of the crust, such as large igneous province emplacement, island-arc accretion, and continental collisional belts. Climatic records are then compared with global detrital zircon U-Pb age data as a proxy for continental magmatism. Our results show a consistent relationship between zircon-generating magmatism and icehouse-greenhouse transitions for > 2 billion years, whereas paleogeographic records show no clear consistent relationship between continental configurations and prominent climate transitions. Volcanic outgassing appears to exert a first-order control on major baseline climatic shifts; however, paleogeography likely plays an important role in the magnitude of this change. Notably, climatic extremes, such as the Cryogenian icehouse, occur during a combination of reduce volcanism and end-member concentrations of low-latitudinal continents.

  4. Regional P-wave Tomography in the Caribbean Region for Plate Reconstruction

    Science.gov (United States)

    Li, X.; Bedle, H.; Suppe, J.

    2017-12-01

    The complex plate-tectonic interactions around the Caribbean Sea have been studied and interpreted by many researchers, but questions still remain regarding the formation and subduction history of the region. Here we report current progress towards creating a new regional tomographic model, with better lateral and spatial coverage and higher resolution than has been presented previously. This new model will provide improved constraints on the plate-tectonic evolution around the Caribbean Plate. Our three-dimensional velocity model is created using taut spline parameterization. The inversion is computed by the code of VanDecar (1991), which is based on the ray theory method. The seismic data used in this inversion are absolute P wave arrival times from over 700 global earthquakes that were recorded by over 400 near Caribbean stations. There are over 25000 arrival times that were picked and quality checked within frequency band of 0.01 - 0.6 Hz by using a MATLAB GUI-based software named Crazyseismic. The picked seismic delay time data are analyzed and compared with other studies ahead of doing the inversion model, in order to examine the quality of our dataset. From our initial observations of the delay time data, the more equalized the ray azimuth coverage, the smaller the deviation of the observed travel times from the theoretical travel time. Networks around the NE and SE side of the Caribbean Sea generally have better ray coverage, and smaller delay times. Specifically, seismic rays reaching SE Caribbean networks, such as XT network, generally pass through slabs under South American, Central American, Lesser Antilles, Southwest Caribbean, and the North Caribbean transform boundary, which leads to slightly positive average delay times. In contrast, the Puerto Rico network records seismic rays passing through regions that may lack slabs in the upper mantle and show slightly negative or near zero average delay times. These results agree with previous tomographic

  5. Magmatism and underplating, a broadband seismic perspective on the Proterozoic tectonics of the Great Falls and Snowbird Tectonic Zones

    Science.gov (United States)

    Chen, Y.; Gu, Y. J.; Dokht, R.; Wang, R.

    2017-12-01

    The crustal and lithospheric structures beneath the Western Canada Sedimentary Basin (WCSB) and northern Montana contain vital records of the Precambrian tectonic development of Laurentia. In this study, we analyze the broadband seismic data recorded by the USArray and the most complete set of regional seismic networks to date near the WCSB. We adopt an integrated approach to investigate crustal structure and history, based primarily on P-to-S receiver functions but incorporate results from noise correlation functions, finite-frequency tomography and potential field measurements. In comparison with existing regional and global models, our stacked receiver functions show considerable improvements in the resolution of both Moho depth and Vp/Vs ratio. We identify major variations in Moho depth from the WCSB to the adjacent Cordillera. The Moho deepens steeply from 40 km in the Alberta basin to 50 km beneath the foothills, following Airy isostasy, but thermal buoyancy may be responsible for a flat, shallow ( 35 km) Moho to the west of the Rocky Mountain Trench. The Moho depth also increases sharply near the Snowbird Tectonic Zone (STZ), which is consistent with earlier findings from active-source data. Multiple lower crustal phases, a high velocity shallow mantle and elevated Vp/Vs ratios along the westernmost STZ jointly suggest major Proterozoic subduction and magmatism along this collisional boundary. In northern Montana, the Moho deepens along the Great Falls Tectonic Zone (GFTZ), a proposed Proterozoic suture between the Medicine Hat Block and Wyoming craton. This transition occurs near the Little Belt Mountain, which is located south of the Great Falls Shear Zone, an extensive northeast striking fault system characterized by strong potential field gradients. Similar to the STZ, our receiver functions offer new evidence for Proterozoic underplating in the vicinity of the GFTZ. In view of similar rock ages near the collisional boundaries in all parts of northern

  6. WAVE TECTONICS OF THE EARTH

    Directory of Open Access Journals (Sweden)

    Tatiana Yu. Tveretinova

    2010-01-01

    Full Text Available In the Earth's lithosphere, wavy alternation of positive and negative heterochronous structures is revealed; such structures are variable in ranks and separated by vergence zones of fractures and folds. In the vertical profile of the lithosphere, alternating are layers characterized by relatively plastic or fragile rheological properties and distinguished by different states of stress. During the Earth’s evolution, epochs of compression and extension are cyclically repeated, including planetary-scale phenomena which are manifested by fluctuating changes of the planet’s volume. Migration of geological and geophysical (geodynamic processes takes place at the Earth's surface and in its interior. The concept of the wave structure and evolution of the Earth's lithosphere provides explanations to the abovementioned regularities. Wavy nature of tectonic structures of the lithosphere, the cyclic recurrence of migration and geological processes in space and time can be described in terms of the multiple-order wave geodynamics of the Earth's lithosphere that refers to periodical variations of the state of stress. Effects of structure-forming tectonic forces are determined by «interference» of tangential and radial stresses of the Earth. The tangential stresses, which occur primarily due to the rotational regime of the planet, cause transformations of the Earth’s shape, redistributions of its substance in depths, the westward drift of the rock mass in its upper levels, and changes of structural deformation plans. The radial stresses, which are largely impacted by gravity, determine the gravitational differentiation of the substance, vertical flattening and sub-horizontal flow of the rock masses, and associated fold-rupture deformation. Under the uniform momentum geodynamic concept proposed by [Vikulin, Tveritinova, 2004, 2005, 2007, 2008], it is possible to provide consistent descriptions of seismic and volcanic, tectonic and geological processes

  7. An Investigation of Seismicity for Western Anatolia

    International Nuclear Information System (INIS)

    Sayil, N.

    2007-01-01

    In order to determine the seismicity of western Anatolia limited with the coordinates of 36degree-40degreeN, 26degree-32degreeE, Gutenberg-Richter magnitude-frequency relation, seismic risk and recurrence period have been computed. The data belonging to both the historical period before 1900 (I0 3 6.0 corresponding to MS 3 5.0) and the instrumental period until 2005 (MS 3 4.0) have been used in the analysis. The study area has been divided into 13 sub-regions due to certain seismotectonic characteristics, plate tectonic models and geology of the region. Computations from a and b parameters and seismic risk and recurrence period for each sub-regions have showed that subregions 1 and 8 (Balikesir and Izmir-Sakiz Island), where have the lowest b values, have the highest risks and the shortest recurrence periods

  8. Rotational inertia of continents: A proposed link between polar wandering and plate tectonics

    Science.gov (United States)

    Kane, M.F.

    1972-01-01

    A mechanism is proposed whereby displacement between continents and the earth's pole of rotation (polar wandering) gives rise to latitudinal transport of continental plates (continental drift) because of their relatively greater rotational inertia. When extended to short-term polar wobble, the hypothesis predicts an energy change nearly equivalent to the seismic energy rate.

  9. Scaling of Convection and Plate Tectonics in Super-Earths

    Science.gov (United States)

    Valencia, D. C.; O'Connell, R. J.; Sasselov, D. D.

    2006-12-01

    The discovery of three Super-Earths around different stars, possible only in the last year, prompts us to study the characteristics of our planet within a general context. The Earth, being the most massive terrestrial object in the solar system is the only planet that exhibits plate tectonics. We think this might not be a coincidence and explore the role that mass plays in determining the mode of convection. We use the scaling of convective vigor with Rayleigh number commonly used in parameterized convection. We study how the parameters controlling convection: Rayleigh number (Ra), boundary layer thickness (δ), internal temperature (T_i) and convective velocities (u) scale with mass. This is possible from the scaling of heat flux, mantle density, size and gravity with mass which we reported in Valencia, et. al 2006. The extrapolation to massive rocky planets is done from our knowledge of the Earth. Even though uncertainties arise from extrapolation and assumptions are needed we consider this simple scaling to be a first adequate step. As the mass of a planet increases, Ra increases, yielding a decrease in δ and an increase in u, while T_i increases very slightly. This is true for an isoviscous case and is more accentuated in a temperature dependent viscosity scenario. In a planet with vigorous convection (high u), a thin lithosphere (low δ) is easier to subduct and hence, initiate plate tectonics. The lithosphere also has to be dense enough (cold and thick) to have the bouyancy necessary for subduction. We calculate that a convective cycle for an isoviscous planet is τ ~ M^{-0.3} considering whole mantle convection. Meaning that if these planets have continents, the timescale for continental rearrangement is shorter (about half the Earth's for a 5 earth-mass planet). Additionally, we explore the negative feedback cycle between convection and temperature dependent viscosity and estimate a timescale for this effect.

  10. Global Ocean Sedimentation Patterns: Plate Tectonic History Versus Climate Change

    Science.gov (United States)

    Goswami, A.; Reynolds, E.; Olson, P.; Hinnov, L. A.; Gnanadesikan, A.

    2014-12-01

    Global sediment data (Whittaker et al., 2013) and carbonate content data (Archer, 1996) allows examination of ocean sedimentation evolution with respect to age of the underlying ocean crust (Müller et al., 2008). From these data, we construct time series of ocean sediment thickness and carbonate deposition rate for the Atlantic, Pacific, and Indian ocean basins for the past 120 Ma. These time series are unique to each basin and reflect an integrated response to plate tectonics and climate change. The goal is to parameterize ocean sedimentation tied to crustal age for paleoclimate studies. For each basin, total sediment thickness and carbonate deposition rate from 0.1 x 0.1 degree cells are binned according to basement crustal age; area-corrected moments (mean, variance, etc.) are calculated for each bin. Segmented linear fits identify trends in present-day carbonate deposition rates and changes in ocean sedimentation from 0 to 120 Ma. In the North and South Atlantic and Indian oceans, mean sediment thickness versus crustal age is well represented by three linear segments, with the slope of each segment increasing with increasing crustal age. However, the transition age between linear segments varies among the three basins. In contrast, mean sediment thickness in the North and South Pacific oceans are numerically smaller and well represented by two linear segments with slopes that decrease with increasing crustal age. These opposing trends are more consistent with the plate tectonic history of each basin being the controlling factor in sedimentation rates, rather than climate change. Unlike total sediment thickness, carbonate deposition rates decrease smoothly with crustal age in all basins, with the primary controls being ocean chemistry and water column depth.References: Archer, D., 1996, Global Biogeochem. Cycles 10, 159-174.Müller, R.D., et al., 2008, Science, 319, 1357-1362.Whittaker, J., et al., 2013, Geochem., Geophys., Geosyst. DOI: 10.1002/ggge.20181

  11. Interaction between two subducting plates under Tokyo and its possible effects on seismic hazards

    Science.gov (United States)

    Wu, Francis; Okaya, David; Sato, Hiroshi; Hirata, Naoshi

    2007-09-01

    Underneath metropolitan Tokyo the Philippine Sea plate (PHS) subducts to the north on top of the westward subducting Pacific plate (PAC). New, relatively high-resolution tomography images the PHS as a well-defined subduction zone under western Kanto Plain. As PAC shoals under eastern Kanto, the PHS lithosphere is being thrusted into an increasingly tighter space of the PAC-Eurasian mantle wedge. As a result, zones of enhanced seismicity appear under eastern Kanto at the top of PHS, internal to PHS and also at its contact with PAC. These zones are located at depths greater than the causative fault of the disastrous 1923 Great Tokyo ``megathrust'' earthquake, in the vicinity of several well-located historical, damaging (M6 and M7) earthquakes. Thus a rather unique interaction between subducting plates under Tokyo may account for additional seismic hazards in metropolitan Tokyo.

  12. Gravity distribution characteristics and their relationship with the distribution of earthquakes and tectonic units in the North–South seismic belt, China

    Directory of Open Access Journals (Sweden)

    Guiju Wu

    2015-05-01

    Full Text Available The North–South Seismic Belt (NSSB is a Chinese tectonic boundary with a very complex structure, showing a sharp change in several geophysical field characteristics. To study these characteristics and their relationship with the distribution of earthquakes and faults in the study area, we first analyze the spatial gravity anomaly to achieve the Bouguer gravity anomaly (EGM2008 BGA and the regional gravity survey Bouguer gravity anomaly. Next, we ascertain the Moho depth and crustal thickness of the study area using interface inversion with the control points derived from the seismic and magnetotelluric sounding profiles achieved in recent years. In this paper, we summarize the relief, trend, Moho gradient, and crustal nature, in addition to their relationship with the distribution of earthquakes and faults in the study area. The findings show that earthquakes with magnitudes greater than Ms7.0 are mainly distributed in the Moho Bouguer anomaly variation belt and faults. The results of the study are important for future research on tectonic characteristics, geological and geophysical surveys, and seismicity patterns.

  13. Geomorphology and seismic risk

    Science.gov (United States)

    Panizza, Mario

    1991-07-01

    The author analyses the contributions provided by geomorphology in studies suited to the assessment of seismic risk: this is defined as function of the seismic hazard, of the seismic susceptibility, and of the vulnerability. The geomorphological studies applicable to seismic risk assessment can be divided into two sectors: (a) morpho-neotectonic investigations conducted to identify active tectonic structures; (b) geomorphological and morphometric analyses aimed at identifying the particular situations that amplify or reduce seismic susceptibility. The morpho-neotectonic studies lead to the identification, selection and classification of the lineaments that can be linked with active tectonic structures. The most important geomorphological situations that can condition seismic susceptibility are: slope angle, debris, morphology, degradational slopes, paleo-landslides and underground cavities.

  14. 3-D Simulation of Tectonic Evolution in Mariana with a Coupled Model of Plate Subduction and Back-Arc Spreading

    Science.gov (United States)

    Hashima, A.; Matsu'Ura, M.

    2006-12-01

    We obtained the expressions for internal deformation fields due to a moment tensor in an elastic-viscoelastic layered holf-space. This unified formulation of internal deformation fields for shear faulting and crack opening enabled us to deal with the problem of tectonic deformation at a composite type of plate boundary zones. The tectonic deformation can be ascribed to mechanical interaction at plate boundaries, which make a closed circuit with the mode of relative plate motion changing from divergence to convergence through transcurrent motion. One of the rational ways to represent mechanical interaction at plate boundaries is specifying the increase rates of normal or tangential displacement discontinuity across plate interfaces. On the basis of such a basic idea we developed a 3-D simulation model for the nonlinear, coupled system of plate subduction and back-arc spreading in Mariana. Through numerical simulations we revealed the evolution process of back-arc spreading. At the first stage, steady plate subduction (shear faulting at a plate interface) gradually forms tensile stress fields in the back-arc region of the overriding plate. When the accumulated tensile stress reaches a critical level, back-arc spreading (crack opening) starts at a structurally weak portion of the overriding plate. The horizontal motion of the frontal part of the overriding plate due to back-arc spreading pushes out the plate boundary toward the oceanic plate. In steady-state plate subduction the shear stress acting on a plate interface must balance with the maximum frictional resistance (shear strength) of the plate interface. Therefore, the increase of shear stress at the plate interface leads to the increase of slip rate at the plate interface. The local increase of slip rate at the plate interface produces the additional tensile stress in the back-arc region. The increased tensile stress must be canceled out by the additional crack opening. Such a feedback mechanism between plate

  15. Quantitative tectonic reconstructions of Zealandia based on crustal thickness estimates

    Science.gov (United States)

    Grobys, Jan W. G.; Gohl, Karsten; Eagles, Graeme

    2008-01-01

    Zealandia is a key piece in the plate reconstruction of Gondwana. The positions of its submarine plateaus are major constraints on the best fit and breakup involving New Zealand, Australia, Antarctica, and associated microplates. As the submarine plateaus surrounding New Zealand consist of extended and highly extended continental crust, classic plate tectonic reconstructions assuming rigid plates and narrow plate boundaries fail to reconstruct these areas correctly. However, if the early breakup history shall be reconstructed, it is crucial to consider crustal stretching in a plate-tectonic reconstruction. We present a reconstruction of the basins around New Zealand (Great South Basin, Bounty Trough, and New Caledonia Basin) based on crustal balancing, an approach that takes into account the rifting and thinning processes affecting continental crust. In a first step, we computed a crustal thickness map of Zealandia using seismic, seismological, and gravity data. The crustal thickness map shows the submarine plateaus to have a uniform crustal thickness of 20-24 km and the basins to have a thickness of 12-16 km. We assumed that a reconstruction of Zealandia should close the basins and lead to a most uniform crustal thickness. We used the standard deviation of the reconstructed crustal thickness as a measure of uniformity. The reconstruction of the Campbell Plateau area shows that the amount of extension in the Bounty Trough and the Great South Basin is far smaller than previously thought. Our results indicate that the extension of the Bounty Trough and Great South Basin occurred simultaneously.

  16. Why is North China seismically active while South China largely aseismic?

    Science.gov (United States)

    Yang, Y.; Liu, M.

    2002-12-01

    The North China block (also known as the Sino-Korean craton) is a region of strong intraplate seismicity and active crustal deformation. Many large earthquakes, including the most devastating earthquake in modern history at Tangshan in 1976 (M=7.5), occurred in this heavily populated region. The South China block (i.e., the Yangtz craton), in contrast, is largely aseismic, although its basement rocks are younger and much of the region is closer to the present plate boundaries than the North China block. We have investigated the contrasting active tectonics between the North and South China blocks using a three-dimensional finite element model. The model approximates the geometry of the two blocks and the surrounding tectonic units. The first-order variations of lithospheric rheology, both laterally and vertically, of these blocks are considered. The kinematic boundary conditions based on the GPS data are applied to the model, and the distribution of gravitational buoyancy force within the Asian continent is calculated using digital topography. Our results suggest that the particular boundary conditions surrounding the North and South China blocks may provide the basic explanation for the contrasting seismicity between these two regions. Aligned with the axis of compression from the indenting Indian plate and supported by the stable eastern Siberia, the North China block is predicted to experience strong deviatoric stresses. A weaker crust, as indicated by the widespread Late Cenozoic volcanism and rifts and high heat flow today, further explain the abundance of seismicity in the North China block. The South China block, on the other hand, sits in the "pressure shadow" of the Indo-Asian collision with little tectonic stresses transmitted from the collision zone. The east-southeastward extrusion of the Asian continent following the Indo-Asian collision allowed the South China block to move as a coherent block as shown by the GPS data, resulting in little internal

  17. Seismotectonic features of the African plate: the possible dislocation of a continent

    Science.gov (United States)

    Meghraoui, Mustapha

    2014-05-01

    , the Libyan rifting and Maghreb thrusting. Although bearing a relatively slow deformation with regards to the East Africa Rift System, the Nubia plate previously considered as a homogeneous tectonic block appears to be dislocating progressively also forming a system of microplates. A synthesis of earthquake studies and regional deformation exposed in a seismotectonic map hitherto serves as a basis for the seismic hazard evaluations and the reduction of seismic risks. * IGCP/SIDA: International Geoscience Program/Swedish International Cooperation Authority http://www.unesco.org/science/IGCP IGCP-601 Working Group: Paulina Amponsah (Ghana Atomic Energy Commission), Atalay Ayele (Addis Ababa University, Ethiopia), Bekoa Ateba (Inst. of Geol. and Min. Res., Buea, Cameroon), Abdelhakim Ayadi (CRAAG, Algeria), Abdunnur Bensuleman (University of Tripoli, Libya), Damien Delvaux (Royal Museum for Central Africa, Tervuren, Belgium), Mohamed El Gabry (National Research Institute of Geophysics, Cairo, Egypt), Rui-Manuel Fernandes (Universidade da Beira Interior, Portugal), Mustapha Meghraoui (IPG Strasbourg, France), Vunganai Midzi & Magda Roos (Council for Geoscience, Pretoria, South Africa), and Youssef Timoulali (CNRST, Rabat, Morocco).

  18. Experimental Research on Seismic Performance of a New-Type of R/C Beam-Column Joints with End Plates

    Directory of Open Access Journals (Sweden)

    Shufeng Li

    2017-01-01

    Full Text Available This paper presents a new-type of fabricated beam-column connections with end plates. The joint details are as follows: the concrete beams are connected to column by end plates and six high strength long bolts passing through the core area. In addition, in order to increase the stiffness and shear strength, stirrups are replaced by the steel plate hoop in the core zone. To examine the fail behavior of the fabricated beam-column connection specimens, a quasi-static test is conducted for nine full-scale models to obtain the hysteresis curves, skeleton curves, ductility, energy dissipation capacity, and other seismic indicators. The experimental results show that all specimens failed in bending in a malleable way with a beam plastic hinge and the hysteresis curves are excellently plump for the end plate connections. From the seismic indexes, the fabricated connection specimens exhibit better seismic performance, which can provide reference for the application of prefabricated frame structure in the earthquake area.

  19. Peculiarity of the Relationship between the Seismicity and Tectonic Structure of the Pyrenees

    Science.gov (United States)

    Lukk, A. A.; Shevchenko, V. I.

    2018-05-01

    The geotectonic position of the Pyrenees mountain massif in the Alpine-Indonesian mobile belt is considered. The geological data testify to the formation of the structure of the Pyrenees in the setting of a subhorizontal compression perpendicular to the ridge. The commonly accepted interpretation considers this compression in the context of plate tectonic notions related to the collision between the Iberian and Eurasian lithospheric plates resulting from the convergence of the Eurasian and African plates. However, this interpretation is challenged by the the geodetic and seismological measurements. The GPS measurements suggest a certain cross-strike spreading rather than shortening of the Earth's crust; the focal mechanisms of the earthquakes indicate the predominance of a subhorizontal extension perpendicular to the strike of the Pyrenees mountain range. The processes of the gravitational collapse of the mountain chain during the isostatic upwelling of the orogenic crust are considered as the most probable cause of this spreading by a number of the authors.

  20. The Investigation of Active Tectonism Offshore Cide-Sinop, Southern Black Sea by Seismic Reflection and Bathymetric Data

    Science.gov (United States)

    Alp, Y. I.; Ocakoglu, N.; Kılıc, F.; Ozel, A. O.

    2017-12-01

    The active tectonism offshore Cide-Sinop at the Southern Black Sea shelf area was first time investigated by multi-beam bathymetric and multi-channel seismic reflection data under the Research Project of The Scientific and Technological Research Council of Turkey (TUBİTAK-ÇAYDAG-114Y057). The multi-channel seismic reflection data of about 700 km length were acquired in 1991 by Turkish Petroleum Company (TP). Multibeam bathymetric data were collected between 2002-2008 by the Turkish Navy, Department of Navigation, Hydrography and Oceanography (TN-DNHO). Conventional data processing steps were applied as follows: in-line geometry definition, shot-receiver static correction, editing, shot muting, gain correction, CDP sorting, velocity analysis, NMO correction, muting, stacking, predictive deconvolution, band-pass filtering, finite-difference time migration, and automatic gain correction. Offshore area is represented by a quite smooth and large shelf plain with an approx. 25 km wide and the water depth of about -100 m. The shelf gently deepens and it is limited by the shelf break with average of -120 m contour. The seafloor morphology is charasterised by an erosional surface. Structurally, E-W trending strike-slip faults with generally compression components and reverse/thrust faults have been regionally mapped for the first time. Most of these faults deform all seismic units and reach the seafloor delimiting the morphological highs and submarine plains. Thus, these faults are intepreted as active faults. These results support the idea that the area is under the active compressional tectonic regime

  1. Geodetic, Geologic and Seismic Interdisciplinary Research of Tectonically Caused Movements in the Wider Area of the City of Zagreb

    Science.gov (United States)

    Dapo, A.; Pribicevic, B.; Herak, M.; Prelogovic, E.

    2012-04-01

    Since the last great earthquake in 1880 which shook the Zagreb area with IX° MCS, tectonic movements and models of numerous Zagreb faults have been the focal point of Croatian geologists, seismologists and in the last 15 years also geodetic scientists, who all have been working in the scope of their scientific branches on bringing the light to the tectonic mechanisms in the wider Zagreb area. Since it is tectonically very active area and being the Capitol city of the Croatia with very high population density it is of utmost importance to understand those mechanisms and to according to them find the best possible measures for protecting people and valuables. Best results are certainly going to be achieved through the interdisciplinary approach. That is why this paper presents first interdisciplinary results from geodetic, geologic and seismic researches and their contribution to the collective knowledge about tectonic movements in the wider area of the City of Zagreb.

  2. Imaging the structure of the Northern Lesser Antilles (Guadeloupe - Virgin Island) to assess the tectonic and thermo-mechanical behavior of an arcuate subduction zone that undergoes increasing convergence obliquity

    Science.gov (United States)

    Laurencin, M.; Marcaillou, B.; Klingelhoefer, F.; Jean-Frederic, L.; Graindorge, D.; Bouquerel, H.; Conin, M.; Crozon, J.; De Min, L.; De Voogd, B.; Evain, M.; Heuret, A.; Laigle, M.; Lallemand, S.; Lucazeau, F.; Pichot, T.; Prunier, C.; Rolandone, F.; Rousset, D.; Vitard, C.

    2015-12-01

    Paradoxically, the Northern Lesser Antilles is the less-investigated and the most tectonically and seismically complex segment of the Lesser Antilles subduction zone: - The convergence obliquity between the North American and Caribbean plates increases northward from Guadeloupe to Virgin Islands raising questions about the fore-arc tectonic partitioning. - The margin has undergone the subduction of the rough sediment-starved Atlantic Ocean floor spiked with ridges as well as banks docking, but the resulting tectonic deformation remains hypothetical in the absence of a complete bathymetry and of any seismic line. - Recent geodetic data and low historical seismic activity suggest a low interplate coupling between Saint-Martin and Anegada, but the sparse onshore seismometers located far from source zone cast doubt on this seismic gap. To shed new light on these questions, the ANTITHESIS project, 5 Marine Geophysical legs totaling 72 days, aims at recording a complete bathymetric map, deep and shallow seismic reflexion lines, wide-angle seismic data, heat-flow measurements and the seismic activity with a web of sea-bottom seismometers. Our preliminary results suggest that: - A frontal sliver of accretionary prism is stretched and expulsed northward by 50km along the left-lateral Bunce fault that limits the prism from the margin basement as far southward as 18.5°N. So far, this structure is the only interpreted sign of tectonic partitioning in the fore-arc. - The Anegada Passage extends eastward to the accretionary prism through strike-slip faults and pull-apart basins that possibly form a lef-lateral poorly-active system inherited from a past tectonic phase, consistently with geodetic and seismologic data. - The anomalously cold interplate contact, consistent with a low interseismic coupling, is possibly due to fluid circulation within the shallow crustal aquifer or a depressed thermal structure of the oceanic crust related to the slow-spreading at the medio

  3. Anatomy of the western Java plate interface from depth-migrated seismic images

    Science.gov (United States)

    Kopp, H.; Hindle, D.; Klaeschen, D.; Oncken, O.; Reichert, C.; Scholl, D.

    2009-01-01

    Newly pre-stack depth-migrated seismic images resolve the structural details of the western Java forearc and plate interface. The structural segmentation of the forearc into discrete mechanical domains correlates with distinct deformation styles. Approximately 2/3 of the trench sediment fill is detached and incorporated into frontal prism imbricates, while the floor sequence is underthrust beneath the d??collement. Western Java, however, differs markedly from margins such as Nankai or Barbados, where a uniform, continuous d??collement reflector has been imaged. In our study area, the plate interface reveals a spatially irregular, nonlinear pattern characterized by the morphological relief of subducted seamounts and thicker than average patches of underthrust sediment. The underthrust sediment is associated with a low velocity zone as determined from wide-angle data. Active underplating is not resolved, but likely contributes to the uplift of the large bivergent wedge that constitutes the forearc high. Our profile is located 100 km west of the 2006 Java tsunami earthquake. The heterogeneous d??collement zone regulates the friction behavior of the shallow subduction environment where the earthquake occurred. The alternating pattern of enhanced frictional contact zones associated with oceanic basement relief and weak material patches of underthrust sediment influences seismic coupling and possibly contributed to the heterogeneous slip distribution. Our seismic images resolve a steeply dipping splay fault, which originates at the d??collement and terminates at the sea floor and which potentially contributes to tsunami generation during co-seismic activity. ?? 2009 Elsevier B.V.

  4. Anatomy of the western Java plate interface from depth-migrated seismic images

    Science.gov (United States)

    Kopp, H.; Hindle, D.; Klaeschen, D.; Oncken, O.; Reichert, C.; Scholl, D.

    2009-11-01

    Newly pre-stack depth-migrated seismic images resolve the structural details of the western Java forearc and plate interface. The structural segmentation of the forearc into discrete mechanical domains correlates with distinct deformation styles. Approximately 2/3 of the trench sediment fill is detached and incorporated into frontal prism imbricates, while the floor sequence is underthrust beneath the décollement. Western Java, however, differs markedly from margins such as Nankai or Barbados, where a uniform, continuous décollement reflector has been imaged. In our study area, the plate interface reveals a spatially irregular, nonlinear pattern characterized by the morphological relief of subducted seamounts and thicker than average patches of underthrust sediment. The underthrust sediment is associated with a low velocity zone as determined from wide-angle data. Active underplating is not resolved, but likely contributes to the uplift of the large bivergent wedge that constitutes the forearc high. Our profile is located 100 km west of the 2006 Java tsunami earthquake. The heterogeneous décollement zone regulates the friction behavior of the shallow subduction environment where the earthquake occurred. The alternating pattern of enhanced frictional contact zones associated with oceanic basement relief and weak material patches of underthrust sediment influences seismic coupling and possibly contributed to the heterogeneous slip distribution. Our seismic images resolve a steeply dipping splay fault, which originates at the décollement and terminates at the sea floor and which potentially contributes to tsunami generation during co-seismic activity.

  5. African Plate Seismicity and Gravity Field Anomalies

    Science.gov (United States)

    Ryzhii, B. P.; Nachapkin, N. I.; Milanovsky, Svet

    The analysis of connection plate of earthquakes of the African continent with Bouguer gravity anomalies is carried out. As input dataSs were used the catalog of earthquakes and numeral map of Bouguer gravity field. The catalog contains geographical coor- dinates of epicenters and magnitudes of 8027 earthquakes recorded on continent and adjacent oceanic areas for the period from 1904 to 1988 years. The values of a gravity field preset in knots of a grid with a step 1 grade. For the analysis of plate seismicity from the catalog the parameters of 6408 earthquakes were chosen, which one have taken place in the field of restricted shore line. The earthquakes fixed in a band of a concatenation of continent with the Arabian plate were excluded from the analysis. On the basis of a numeral gravity map for everyone epicenter the value of Bouguer anomaly was calculated. The allocation of epicenters of earthquakes with magnitude M is obtained depending on value of a gravity Bouguer field. The outcomes of a sta- tistical analysis testify that practically all earthquakes are associated with the areas with negative values of Bouguer gravity field. Thus in areas with values of a field -160 mgal to -100 mgal there was 80 % of all earthquakes. It is necessary to note, that the mean value of the field for the African continent is -70 mgal. Obtained result gives us the possibility to make a conclusion about connection of plate earthquakes of Africa predominantly with structural complexes of earth crust with lower density. These out- comes are in the consent with a hypothesis of one of the authors (Ryzhii B.P.) about connection of plate earthquakes hypocenters on the territory of Russia with negative values of a gravity field and heightened silica content in the Earth crust. This work was supported with RFFI grant N 00-05-65067

  6. Global tectonics and space geodesy

    Science.gov (United States)

    Gordon, Richard G.; Stein, Seth

    1992-01-01

    Much of the success of plate tectonics can be attributed to the near rigidity of tectonic plates and the availability of data that describe the rates and directions of motion across narrow plate boundaries of about 1 to 60 kilometers. Nonetheless, many plate boundaries in both continental and oceanic lithosphere are not narrow but are hundreds to thousands of kilometers wide. Wide plate boundary zones cover approximately 15 percent of earth's surface area. Space geodesy, which includes very long baseline radio interferometry, satellite laser ranging, and the global positioning system, provides the accurate long-distance measurements needed to estimate the present motion across and within wide plate boundary zones. Space geodetic data show that plate velocities averaged over years are remarkably similar to velocities avaraged over millions of years.

  7. 3-D thermo-mechanical laboratory modeling of plate-tectonics: modeling scheme, technique and first experiments

    Directory of Open Access Journals (Sweden)

    D. Boutelier

    2011-05-01

    Full Text Available We present an experimental apparatus for 3-D thermo-mechanical analogue modeling of plate tectonic processes such as oceanic and continental subductions, arc-continent or continental collisions. The model lithosphere, made of temperature-sensitive elasto-plastic analogue materials with strain softening, is submitted to a constant temperature gradient causing a strength reduction with depth in each layer. The surface temperature is imposed using infrared emitters, which allows maintaining an unobstructed view of the model surface and the use of a high resolution optical strain monitoring technique (Particle Imaging Velocimetry. Subduction experiments illustrate how the stress conditions on the interplate zone can be estimated using a force sensor attached to the back of the upper plate and adjusted via the density and strength of the subducting lithosphere or the lubrication of the plate boundary. The first experimental results reveal the potential of the experimental set-up to investigate the three-dimensional solid-mechanics interactions of lithospheric plates in multiple natural situations.

  8. A tale of two arcs? Plate tectonics of the Izu-Bonin-Mariana (IBM) arc using subducted slab constraints

    Science.gov (United States)

    Wu, J. E.; Suppe, J.; Renqi, L.; Kanda, R. V. S.

    2014-12-01

    Published plate reconstructions typically show the Izu-Bonin Marianas arc (IBM) forming as a result of long-lived ~50 Ma Pacific subduction beneath the Philippine Sea. These reconstructions rely on the critical assumption that the Philippine Sea was continuously coupled to the Pacific during the lifetime of the IBM arc. Because of this assumption, significant (up to 1500 km) Pacific trench retreat is required to accommodate the 2000 km of Philippine Sea/IBM northward motion since the Eocene that is constrained by paleomagnetic data. In this study, we have mapped subducted slabs of mantle lithosphere from MITP08 global seismic tomography (Li et al., 2008) and restored them to a model Earth surface to constrain plate tectonic reconstructions. Here we present two subducted slab constraints that call into question current IBM arc reconstructions: 1) The northern and central Marianas slabs form a sub-vertical 'slab wall' down to maximum 1500 km depths in the lower mantle. This slab geometry is best explained by a near-stationary Marianas trench that has remained +/- 250 km E-W of its present-day position since ~45 Ma, and does not support any significant Pacific slab retreat. 2) A vanished ocean is revealed by an extensive swath of sub-horizontal slabs at 700 to 1000 km depths in the lower mantle below present-day Philippine Sea to Papua New Guinea. We call this vanished ocean the 'East Asian Sea'. When placed in an Eocene plate reconstruction, the East Asian Sea fits west of the reconstructed Marianas Pacific trench position and north of the Philippine Sea plate. This implies that the Philippine Sea and Pacific were not adjacent at IBM initiation, but were in fact separated by a lost ocean. Here we propose a new IBM arc reconstruction constrained by subducted slabs mapped under East Asia. At ~50 Ma, the present-day IBM arc initiated at equatorial latitudes from East Asian Sea subduction below the Philippine Sea. A separate arc was formed from Pacific subduction below

  9. Rescaled Range analysis of Induced Seismicity: rapid classification of clusters in seismic crisis

    Science.gov (United States)

    Bejar-Pizarro, M.; Perez Lopez, R.; Benito-Parejo, M.; Guardiola-Albert, C.; Herraiz, M.

    2017-12-01

    Different underground fluid operations, mainly gas storing, fracking and water pumping, can trigger Induced Seismicity (IS). This seismicity is normally featured by small-sized earthquakes (M<2.5), although particular cases reach magnitude as great as 5. It has been up for debate whether earthquakes greater than 5 can be triggered by IS or this level of magnitude only corresponds to tectonic earthquakes caused by stress change. Whatever the case, the characterization of IS for seismic clusters and seismic series recorded close but not into the gas storage, is still under discussion. Time-series of earthquakes obey non-linear patterns where the Hurst exponent describes the persistency or anti-persistency of the sequence. Natural seismic sequences have an H-exponent close to 0.7, which combined with the b-value time evolution during the time clusters, give us valuable information about the stationarity of the phenomena. Tectonic earthquakes consist in a main shock with a decay of time-occurrence of seismic shocks obeying the Omori's empirical law. On the contrary, IS does not exhibit a main shock and the time occurrence depends on the injection operations instead of on the tectonic energy released. In this context, the H-exponent can give information about the origin of the sequence. In 2013, a seismic crisis was declared from the Castor underground gas storing located off-shore in the Mediterranean Sea, close to the Northeastern Spanish cost. The greatest induced earthquake was 3.7. However, a 4.2 earthquake, probably of tectonic origin, occurred few days after the operations stopped. In this work, we have compared the H-exponent and the b-value time evolution according to the timeline of gas injection. Moreover, we have divided the seismic sequence into two groups: (1) Induced Seismicity and (2) Triggered Seismicity. The rescaled range analysis allows the differentiation between natural and induced seismicity and gives information about the persistency and long

  10. Seismotectonics of Vrancea (Romania) zone: the case of crustal seismicity in the foredeep area

    International Nuclear Information System (INIS)

    Tugui, A.; Craiu, M.; Rogozea, M.; Popa, M.; Radulian, M.; http://www.infp.ro

    2009-01-01

    Vrancea seismic zone is located in Romania at the South-Easter Carpathians bend, where at least three major tectonic units are in contact: East European Plate, Intra-Alpine Plate and Moesian Plate. The seismicity of the Vrancea zone consists of both crustal and intermediate-depth earthquakes. The crustal events are moderate (M w ≤ 5.5) and generally occur in clusters in space (the subzones Ramnicu Sarat and Vrancioaia, situated in the Vrancea epicentral area and adjacent to it) and in time (main shocks accompanied by aftershocks and sometimes by foreshocks or swarms). Seismic activity in Ramnicu Sarat zone consists of shallow earthquakes with moderate magnitudes M s ≤ 5.2, which frequently occur in clusters. The hypocenters are generally situated at focal depths between 15 and 30 km within the foredeep region lying in front of the major bending of the Carpathian Arc. The sequence of 29 November - 03 December, 2007 consists of 37 events with 1.8 ≤ M D ≤ 3.9. The earthquakes hypocenters are grouped in a parallel direction with the Carpathian Bend, and the fault plane solution (of the main shock) is reverse. The seismic sequence from Ramnicu Sarat, 2007 was compared with the previous sequences knowing the regional seismotectonics. (authors)

  11. Crustal-scale alpine tectonic evolution of the western Pyrenees - eastern Cantabrian Mountains (N Spain) from integration of structural data, low-T thermochronology and seismic constraint

    Science.gov (United States)

    DeFelipe, I.; Pedreira, D.; Pulgar, J. A.; Van der Beek, P.; Bernet, M.; Pik, R.

    2017-12-01

    The Pyrenean-Cantabrian Mountain belt extends in an E-W direction along the northern border of Spain and resulted from the convergence between the Iberian and European plates from the Late Cretaceous to the Miocene, in the context of the Alpine orogeny. The main aim of this work is to characterize the tectonic evolution at a crustal-scale of the transition zone from the Pyrenees to the Cantabrian Mountains, in the eastern Basque-Cantabrian Basin (BCB). We integrate structural work, thermochronology (apatite fission track and zircon (U-Th)/He) and geophysical information (shallow seismic reflection profiles, deep seismic refraction/wide-angle reflection profiles and seismicity distribution) to propose an evolutionary model since the Jurassic to the present. During the Albian, hyperextension related to the opening of the Bay of Biscay yielded to mantle unroofing to the base of the BCB. This process was favored by a detachment fault that connected the mantle in its footwall with the base of a deep basin in its hanging wall. During this process, the basin experienced HT metamorphism and fluid circulation caused the serpentinization of the upper part of the mantle. There is no evidence of seafloor mantle exhumation before the onset of the Alpine orogeny. The thermochronological study points to a N-vergent phase of contractional deformation in the late Eocene represented by the thin-skinned Leiza fault system followed in the early Oligocene by the S-vergent, thick-skinned, Ollín thrust. Exhumation rates for the late Eocene-early Oligocene are of 0.2-0.7 km/Myr. After that period, deformation continues southwards until the Miocene. The crustal-scale structure resultant of the Alpine orogeny consists of an Iberian plate that subducts below the European plate. The crust is segmented into four blocks separated by three S-vergent crustal faults inherited from the Cretaceous extensional period. The P-wave velocities in this transect show anomalous values (7.4 km/s) in the

  12. A planet in transition: The onset of plate tectonics on Earth between 3 and 2 Ga?

    Directory of Open Access Journals (Sweden)

    Kent C. Condie

    2018-01-01

    Full Text Available Many geological and geochemical changes are recorded on Earth between 3 and 2 Ga. Among the more important of these are the following: (1 increasing proportion of basalts with “arc-like” mantle sources; (2 an increasing abundance of basalts derived from enriched (EM and depleted (DM mantle sources; (3 onset of a Great Thermal Divergence in the mantle; (4 a decrease in degree of melting of the mantle; (5 beginning of large lateral plate motions; (6 appearance of eclogite inclusions in diamonds; (7 appearance and rapid increase in frequency of collisional orogens; (8 rapid increase in the production rate of continental crust as recorded by zircon age peaks; (9 appearance of ophiolites in the geologic record, and (10 appearance of global LIP (large igneous province events some of which correlate with global zircon age peaks. All of these changes may be tied directly or indirectly to cooling of Earth's mantle and corresponding changes in convective style and the strength of the lithosphere, and they may record the gradual onset and propagation of plate tectonics around the planet. To further understand the changes that occurred between 3 and 2 Ga, it is necessary to compare rocks, rock associations, tectonics and geochemistry during and between zircon age peaks. Geochemistry of peak and inter-peak basalts and TTGs needs to be evaluated in terms of geodynamic models that predict the existence of an episodic thermal regime between stagnant-lid and plate tectonic regimes in early planetary evolution.

  13. Seismic swarm associated with the 2008 eruption of Kasatochi Volcano, Alaska: earthquake locations and source parameters

    Science.gov (United States)

    Ruppert, Natalia G.; Prejean, Stephanie G.; Hansen, Roger A.

    2011-01-01

    An energetic seismic swarm accompanied an eruption of Kasatochi Volcano in the central Aleutian volcanic arc in August of 2008. In retrospect, the first earthquakes in the swarm were detected about 1 month prior to the eruption onset. Activity in the swarm quickly intensified less than 48 h prior to the first large explosion and subsequently subsided with decline of eruptive activity. The largest earthquake measured as moment magnitude 5.8, and a dozen additional earthquakes were larger than magnitude 4. The swarm exhibited both tectonic and volcanic characteristics. Its shear failure earthquake features were b value = 0.9, most earthquakes with impulsive P and S arrivals and higher-frequency content, and earthquake faulting parameters consistent with regional tectonic stresses. Its volcanic or fluid-influenced seismicity features were volcanic tremor, large CLVD components in moment tensor solutions, and increasing magnitudes with time. Earthquake location tests suggest that the earthquakes occurred in a distributed volume elongated in the NS direction either directly under the volcano or within 5-10 km south of it. Following the MW 5.8 event, earthquakes occurred in a new crustal volume slightly east and north of the previous earthquakes. The central Aleutian Arc is a tectonically active region with seismicity occurring in the crusts of the Pacific and North American plates in addition to interplate events. We postulate that the Kasatochi seismic swarm was a manifestation of the complex interaction of tectonic and magmatic processes in the Earth's crust. Although magmatic intrusion triggered the earthquakes in the swarm, the earthquakes failed in context of the regional stress field.

  14. Seismic Interpretation of the Nam Con Son Basin and its Implication for the Tectonic Evolution

    Directory of Open Access Journals (Sweden)

    Nguyen Quang Tuan

    2016-06-01

    Full Text Available DOI:10.17014/ijog.3.2.127-137The Nam Con Son Basin covering an area of circa 110,000 km2 is characterized by complex tectonic settings of the basin which has not fully been understood. Multiple faults allowed favourable migration passageways for hydrocarbons to go in and out of traps. Despite a large amount of newly acquired seismic and well data there is no significant update on the tectonic evolution and history of the basin development. In this study, the vast amount of seismic and well data were integrated and reinterpreted to define the key structural events in the Nam Con Son Basin. The results show that the basin has undergone two extentional phases. The first N - S extensional phase terminated at around 30 M.a. forming E - W trending grabens which are complicated by multiple half grabens filled by Lower Oligocene sediments. These grabens were reactivated during the second NW - SE extension (Middle Miocene, that resulted from the progressive propagation of NE-SW listric fault from the middle part of the grabens to the margins, and the large scale building up of roll-over structure. Further to the SW, the faults of the second extentional phase turn to NNE-SSW and ultimately N - S in the SW edge of the basin. Most of the fault systems were inactive by Upper Miocene except for the N - S fault system which is still active until recent time.

  15. Investigating on the Differences between Triggered and Background Seismicity in Italy and Southern California.

    Science.gov (United States)

    Stallone, A.; Marzocchi, W.

    2017-12-01

    Earthquake occurrence may be approximated by a multidimensional Poisson clustering process, where each point of the Poisson process is replaced by a cluster of points, the latter corresponding to the well-known aftershock sequence (triggered events). Earthquake clusters and their parents are assumed to occur according to a Poisson process at a constant temporal rate proportional to the tectonic strain rate, while events within a cluster are modeled as generations of dependent events reproduced by a branching process. Although the occurrence of such space-time clusters is a general feature in different tectonic settings, seismic sequences seem to have marked differences from region to region: one example, among many others, is that seismic sequences of moderate magnitude in Italian Apennines seem to last longer than similar seismic sequences in California. In this work we investigate on the existence of possible differences in the earthquake clustering process in these two areas. At first, we separate the triggered and background components of seismicity in the Italian and Southern California seismic catalog. Then we study the space-time domain of the triggered earthquakes with the aim to identify possible variations in the triggering properties across the two regions. In the second part of the work we focus our attention on the characteristics of the background seismicity in both seismic catalogs. The assumption of time stationarity of the background seismicity (which includes both cluster parents and isolated events) is still under debate. Some authors suggest that the independent component of seismicity could undergo transient perturbations at various time scales due to different physical mechanisms, such as, for example, viscoelastic relaxation, presence of fluids, non-stationary plate motion, etc, whose impact may depend on the tectonic setting. Here we test if the background seismicity in the two regions can be satisfactorily described by the time

  16. 3D upper crustal seismic structure across Santorini volcanic field: Constraints on magmatic and tectonic interactions

    Science.gov (United States)

    Heath, B.; Hooft, E. E. E.; Toomey, D. R.; Papazachos, C. V.; Walls, K.; Paulatto, M.; Morgan, J. V.; Nomikou, P.; Warner, M.

    2017-12-01

    To investigate magmatic-tectonic interactions at an arc volcano, we collected a dense, active-source, seismic dataset across the Santorini Volcano, Greece, with 90 ocean bottom seismometers, 65 land seismometers, and 14,300 marine sound sources. We use over 140,000 travel-time picks to obtain a P-wave tomography model of the upper crustal structure of the Santorini volcano and surrounding tectonically extended region. Regionally, the shallow (Bouguer gravity anomalies and preliminary shallow attenuation results (using waveform amplitudes and t* values). We find regional Pliocene and younger faults bounding basement grabens and horsts to be predominately oriented in a NE-SW direction with Santorini itself located in a graben bounded by faults striking in this direction. In contrast, volcanic vents and dikes expressed at the surface seem to strike about 20° clockwise relative to these regional faults. In the northern caldera of Santorini, a 4-km wide region of anomalously low velocities and high attenuation directly overlies an inferred source of 2011-2012 inflation (4-4.5 km depth), however it is located at shallower depths ( 1-2km). The imaged low-velocity anomaly may correspond to hydrothermal activity (due to increased porosity and alteration) and/or brecciation from a prior episode of caldera collapse. It is bounded by anomalously fast velocities (at 1-2 km depth) that parallel the regional fault orientation and are correspondingly rotated 20° to surface dikes. At 4-5 km depth beneath the northern caldera basin, low-velocity anomalies and attenuated seismic arrivals provide preliminary evidence for a magma body; the low-velocity anomaly is elongated in the same direction as regional volcanic vents. The difference in strike of volcanic and tectonic features indicates oblique extension and potential time-variation in the minimum stress direction.

  17. Seismic sequence stratigraphy of Miocene deposits related to eustatic, tectonic and climatic events, Cap Bon Peninsula, northeastern Tunisia

    Science.gov (United States)

    Gharsalli, Ramzi; Zouaghi, Taher; Soussi, Mohamed; Chebbi, Riadh; Khomsi, Sami; Bédir, Mourad

    2013-09-01

    The Cap Bon Peninsula, belonging to northeastern Tunisia, is located in the Maghrebian Alpine foreland and in the North of the Pelagian block. By its paleoposition, during the Cenozoic, in the edge of the southern Tethyan margin, this peninsula constitutes a geological entity that fossilized the eustatic, tectonic and climatic interactions. Surface and subsurface study carried out in the Cap Bon onshore area and surrounding offshore of Hammamet interests the Miocene deposits from the Langhian-to-Messinian interval time. Related to the basin and the platform positions, sequence and seismic stratigraphy studies have been conducted to identify seven third-order seismic sequences in subsurface (SM1-SM7), six depositional sequences on the Zinnia-1 petroleum well (SDM1-SDM6), and five depositional sequences on the El Oudiane section of the Jebel Abderrahmane (SDM1-SDM5). Each sequence shows a succession of high-frequency systems tract and parasequences. These sequences are separated by remarkable sequence boundaries and maximum flooding surfaces (SB and MFS) that have been correlated to the eustatic cycles and supercycles of the Global Sea Level Chart of Haq et al. (1987). The sequences have been also correlated with Sequence Chronostratigraphic Chart of Hardenbol et al. (1998), related to European basins, allows us to arise some major differences in number and in size. The major discontinuities, which limit the sequences resulted from the interplay between tectonic and climatic phenomena. It thus appears very judicious to bring back these chronological surfaces to eustatic and/or local tectonic activity and global eustatic and climatic controls.

  18. Subduction zone locking, strain partitioning, intraplate deformation and their implications to Seismic Hazards in South America

    Science.gov (United States)

    Galgana, G. A.; Mahdyiar, M.; Shen-Tu, B.; Pontbriand, C. W.; Klein, E.; Wang, F.; Shabestari, K.; Yang, W.

    2014-12-01

    We analyze active crustal deformation in South America (SA) using published GPS observations and historic seismicity along the Nazca Trench and the active Ecuador-Colombia-Venezuela Plate boundary Zone. GPS-constrained kinematisc models that incorporate block and continuum techniques are used to assess patterns of regional tectonic deformation and its implications to seismic potential. We determine interplate coupling distributions, fault slip-rates, and intraplate crustal strain rates in combination with historic earthquakes within 40 seismic zones crust to provide moment rate constraints. Along the Nazca subduction zone, we resolve a series of highly coupled patches, interpreted as high-friction producing "asperities" beneath the coasts of Ecuador, Peru and Chile. These include areas responsible for the 2010 Mw 8.8 Maule Earthquake and the 2014 Mw 8.2 Iquique Earthquake. Predicted tectonic block motions and fault slip rates reveal that the northern part of South America deforms rapidly, with crustal fault slip rates as much as ~20 mm/a. Fault slip and locking patterns reveal that the Oca Ancón-Pilar-Boconó fault system plays a key role in absorbing most of the complex eastward and southward convergence patterns in northeastern Colombia and Venezuela, while the near-parallel system of faults in eastern Colombia and Ecuador absorb part of the transpressional motion due to the ~55 mm/a Nazca-SA plate convergence. These kinematic models, in combination with historic seismicity rates, provide moment deficit rates that reveal regions with high seismic potential, such as coastal Ecuador, Bucaramanga, Arica and Antofagasta. We eventually use the combined information from moment rates and fault coupling patterns to further constrain stochastic seismic hazard models of the region by implementing realistic trench rupture scenarios (see Mahdyiar et al., this volume).

  19. Marine and land active-source seismic investigation of geothermal potential, tectonic structure, and earthquake hazards in Pyramid Lake, Nevada

    Energy Technology Data Exchange (ETDEWEB)

    Eisses, A.; Kell, A.; Kent, G. [UNR; Driscoll, N. [UCSD; Karlin, R.; Baskin, R. [USGS; Louie, J. [UNR; Pullammanappallil, S. [Optim

    2016-08-01

    Amy Eisses, Annie M. Kell, Graham Kent, Neal W. Driscoll, Robert E. Karlin, Robert L. Baskin, John N. Louie, Kenneth D. Smith, Sathish Pullammanappallil, 2011, Marine and land active-source seismic investigation of geothermal potential, tectonic structure, and earthquake hazards in Pyramid Lake, Nevada: presented at American Geophysical Union Fall Meeting, San Francisco, Dec. 5-9, abstract NS14A-08.

  20. Lithosphere Structure of the Rivera Plate - Jalisco Block Contact Zone: Septentrional Region of the Islas Marías (Mexico)

    Science.gov (United States)

    Madrigal-Ávalos, L. A.; Nunez, D.; Escalona-Alcazar, F. D. J.; Nuñez-Cornu, F. J.; Barba, D. C., Sr.; Danobeitia, J.

    2017-12-01

    The western margin of Mexico is a tectonic complex region where large earthquakes occurred with very destructive consequences, including the generation of big tsunamis. This fact is mainly the result of the Rivera plate subduction beneath the North American plate and the Jalisco Block implying a high potential seismic risk. In the north, between the Tamayo Fracture Zone and the Mesoamerican Trench, the Islas Marías region is a complex tectonic limit within the interaction of the Rivera plate oceanic crust and the Jalisco Block continental crust. In order to know the shallow and deep structure of the Rivera plate - Jalisco Block contact zone and to be able to determine these potential seismic sources, the TSUJAL geophysical experiment was carried out from 2012 to 2016. As part of this project, we present the results of the processed and analyzed MCS and WAS data along the TS09 and RTSIM01 seismic transects, respectively, across the septentrional region of Islas Marías. These marine seismic lines are coincident with 110 km length for MCS and 240 km for WAS, and perpendicular to the coastline with SW-NE orientation. The seismic sources used in this work aboard RRS James Cook consisted of 12 guns with a total capacity for WAS data of 5800 in3 every 120 s and 3540 in3 every 50 m for MCS data. The MCS data were acquired with a 5.85 km length streamer with a 468 active channels, while the WAS data were recorded by a network of 4 OBS and 27 land seismic stations. After data processing and joint interpretation, it was possible to determine that shallow structure is mainly constituted by normal faults associated to graben structures forming sedimentary basins with non-deformed sediments in the basement. While the deep structure is characterized by depths from 9 to 12 km in the oceanic crust and 18 to 21 km in the continental crust. The deepest layers of the upper mantle were determined up to 35 km depth. In this study, it was possible to calculate a dip angle between 6

  1. Reconstructing mantle heterogeneity with data assimilation based on the back-and-forth nudging method: Implications for mantle-dynamic fitting of past plate motions

    Science.gov (United States)

    Glišović, Petar; Forte, Alessandro

    2016-04-01

    The paleo-distribution of density variations throughout the mantle is unknown. To address this question, we reconstruct 3-D mantle structure over the Cenozoic era using a data assimilation method that implements a new back-and-forth nudging algorithm. For this purpose, we employ convection models for a compressible and self-gravitating mantle that employ 3-D mantle structure derived from joint seismic-geodynamic tomography as a starting condition. These convection models are then integrated backwards in time and are required to match geologic estimates of past plate motions derived from marine magnetic data. Our implementation of the nudging algorithm limits the difference between a reconstruction (backward-in-time solution) and a prediction (forward-in-time solution) on over a sequence of 5-million-year time windows that span the Cenozoic. We find that forward integration of reconstructed mantle heterogeneity that is constrained to match past plate motions delivers relatively poor fits to the seismic-tomographic inference of present-day mantle heterogeneity in the upper mantle. We suggest that uncertainties in the past plate motions, related for example to plate reorganization episodes, could partly contribute to the poor match between predicted and observed present-day heterogeneity. We propose that convection models that allow tectonic plates to evolve freely in accord with the buoyancy forces and rheological structure in the mantle could provide additional constraints on geologic estimates of paleo-configurations of the major tectonic plates.

  2. PRESENTDAY STRESS STATE OF THE SHANXI TECTONIC BELT

    Directory of Open Access Journals (Sweden)

    Wang Kaiying

    2012-01-01

    Full Text Available The Shanxi tectonic belt is a historically earthquakeabundant area. For the majority of strong earthquakes in this area, the distribution of earthquake foci was controlled by the N–S oriented local structures on the tectonic belt. Studies of the present stress state of the Shanxi tectonic belt can contribute to the understanding of the relationship between strong earthquakes’ occurrence and their structural distribution and also facilitate assessments of regional seismic danger and determination of the regions wherein strong earthquakes may occur in future. Using the Cataclastic Analysis Method (CAM, we performed stress inversion based on the focal mechanism data of earthquakes which took place in the Shanxi tectonic belt from 1967 to 2010. Our results show that orientations of the maximum principal compressive stress axis of the Shanxi tectonic belt might have been variable before and after the 2001 Kunlun MS=8.1 strong earthquake, with two different superior trends of the NW–SE and NE–SW orientation in different periods. When the maximum principal compressive stress axis is oriented in the NE–SW direction, the pattern of the space distribution of the seismic events in the Shanxi tectonic belt shows a trend of their concentration in the N–S oriented tectonic segments. At the same time, the stress state is registered as horizontal shearing and horizontal extension in the N–S and NE–SW oriented local segments in turn. When the maximum principal compressive stress axis is NW–SE oriented, the stress state of the N–S and NE–SW oriented tectonic segments is primarily registered as horizontal shearing. Estimations of plunges of stress axes show that seismicity in the Shanxi belt  corresponds primarily to the activity of lowangle faults, and highangle stress sites are located in the NE–SW oriented extensional tectonic segments of the Shanxi belt. This indicates that the stress change of the Shanxi belt is

  3. Modeling the Geometry of Plate Boundary and Seismic Structure in the Southern Ryukyu Trench Subduction Zone, Japan, Using Amphibious Seismic Observations

    Science.gov (United States)

    Yamamoto, Y.; Takahashi, T.; Ishihara, Y.; Kaiho, Y.; Arai, R.; Obana, K.; Nakanishi, A.; Miura, S.; Kodaira, S.; Kaneda, Y.

    2018-02-01

    Here we present the new model, the geometry of the subducted Philippine Sea Plate interface beneath the southern Ryukyu Trench subduction zone, estimated from seismic tomography and focal mechanism estimation by using passive and active data from a temporary amphibious seismic network and permanent land stations. Using relocated low-angle thrust-type earthquakes, repeating earthquakes, and structural information, we constrained the geometry of plate boundary from the trench axis to a 60 km depth with uncertainties of less than 5 km. The estimated plate geometry model exhibited large variation, including a pronounced convex structure that may be evidence of a subducted seamount in the eastern portion of study area, whereas the western part appeared smooth. We also found that the active earthquake region near the plate boundary, defined by the distance from our plate geometry model, was clearly separated from the area dominated by short-term slow-slip events (SSEs). The oceanic crust just beneath the SSE-dominant region, the western part of the study area, showed high Vp/Vs ratios (>1.8), whereas the eastern side showed moderate or low Vp/Vs (<1.75). We interpreted this as an indication that high fluid pressures near the surface of the slab are contributing to the SSE activities. Within the toe of the mantle wedge, P and S wave velocities (<7.5 and <4.2 km/s, respectively) lower than those observed through normal mantle peridotite might suggest that some portions of the mantle may be at least 40% serpentinized.

  4. ACTIVITY AND Vp/Vs RATIO OF VOLCANO-TECTONIC SEISMIC SWARM ZONES AT NEVADO DEL RUIZ VOLCANO, COLOMBIA

    Directory of Open Access Journals (Sweden)

    Londoño B. John Makario

    2010-06-01

    Full Text Available An analysis of the seismic activity for volcano-tectonic earthquake (VT swarms zones at Nevado del Ruiz Volcano (NRV was carried out for the interval 1985- 2002, which is the most seismic active period at NRV until now (2010. The swarm-like seismicity of NRV was frequently concentrated in very well defined clusters around the volcano. The seismic swarm zone located at the active crater was the most active during the entire time. The seismic swarm zone located to the west of the volcano suggested some relationship with the volcanic crises. It was active before and after the two eruptions occurred in November 1985 and September 1989. It is believed that this seismic activity may be used as a monitoring tool of volcanic activity. For each seismic swarm zone the Vp/Vs ratio was also calculated by grouping of earthquakes and stations. It was found that each seismic swarm zone had a distinct Vp/Vs ratio with respect to the others, except for the crater and west swarm zones, which had the same value. The average Vp/Vs ratios for the seismic swarm zones located at the active crater and to the west of the volcano are about 6-7% lower than that for the north swarm zone, and about 3% lower than that for the south swarm zone. We suggest that the reduction of the Vp/Vs ratio is due to degassing phenomena inside the central and western earthquake swarm zones, or due to the presence of microcracks inside the volcano. This supposition is in agreement with other studies of geophysics, geochemistry and drilling surveys carried out at NRV.

  5. Deformation patterns and seismic hazard along the eastern Sunda margin

    Science.gov (United States)

    Kopp, Heidrun; Djajadihardja, Yusuf; Flueh, Ernst R.; Hindle, David; Klaeschen, Dirk; Mueller, Christian; Planert, Lars; Reichert, Christian; Shulgin, Alexey; Wittwer, Andreas

    2010-05-01

    The eastern Sunda margin offshore Java, Bali, Lombok and Sumba is the site of oceanic subduction of the Indo-Australian plate underneath the Indonesian archipelago. Data from a suite of geophysical experiments conducted between 1997-2006 using RV SONNE as platform include seismic and seismological studies, potential field measurements and high-resolution seafloor bathymetry mapping. Tomographic inversions provide an image of the ongoing deformation of the forearc and the deep subsurface. We investigate the role of various key mechanisms that shape the first-order features characterizing the present margin architecture. Our contribution evaluates the differences in architecture and evolution along the Java forearc from a marine perspective to better understand the variation in tectonic styles and segmentation of the convergent margin, including its seismic risk potential.

  6. Seismic Performance and Design of Steel Plate Shear Walls with Low Yield Point Steel Infill Plates

    OpenAIRE

    Zirakian, Tadeh

    2013-01-01

    Steel plate shear walls (SPSWs) have been frequently used as the primary or part of the primary lateral force-resisting system in design of low-, medium-, and high-rise buildings. Their application has been based on two different design philosophies as well as detailing strategies. Stiffened and/or stocky-web SPSWs with improved buckling stability and high seismic performance have been mostly used in Japan, which is one of the pioneering countries in design and application of these systems. U...

  7. Tectonic evolution of the Qumran Basin from high-resolution 3.5-kHz seismic profiles and its implication for the evolution of the northern Dead Sea Basin

    Science.gov (United States)

    Lubberts, Ronald K.; Ben-Avraham, Zvi

    2002-02-01

    The Dead Sea Basin is a morphotectonic depression along the Dead Sea Transform. Its structure can be described as a deep rhomb-graben (pull-apart) flanked by two block-faulted marginal zones. We have studied the recent tectonic structure of the northwestern margin of the Dead Sea Basin in the area where the northern strike-slip master fault enters the basin and approaches the western marginal zone (Western Boundary Fault). For this purpose, we have analyzed 3.5-kHz seismic reflection profiles obtained from the northwestern corner of the Dead Sea. The seismic profiles give insight into the recent tectonic deformation of the northwestern margin of the Dead Sea Basin. A series of 11 seismic profiles are presented and described. Although several deformation features can be explained in terms of gravity tectonics, it is suggested that the occurrence of strike-slip in this part of the Dead Sea Basin is most likely. Seismic sections reveal a narrow zone of intensely deformed strata. This zone gradually merges into a zone marked by a newly discovered tectonic depression, the Qumran Basin. It is speculated that both structural zones originate from strike-slip along right-bending faults that splay-off from the Jordan Fault, the strike-slip master fault that delimits the active Dead Sea rhomb-graben on the west. Fault interaction between the strike-slip master fault and the normal faults bounding the transform valley seems the most plausible explanation for the origin of the right-bending splays. We suggest that the observed southward widening of the Dead Sea Basin possibly results from the successive formation of secondary right-bending splays to the north, as the active depocenter of the Dead Sea Basin migrates northward with time.

  8. Innovative Approaches for Seismic Studies of Mars (Invited)

    Science.gov (United States)

    Banerdt, B.

    2010-12-01

    In addition to its intrinsic interest, Mars is particularly well-suited for studying the full range of processes and phenomena related to early terrestrial planet evolution, from initial differentiation to the start of plate tectonics. It is large and complex enough to have undergone most of the processes that affected early Earth but, unlike the Earth, has apparently not undergone extensive plate tectonics or other major reworking that erased the imprint of early events (as evidenced by the presence of cratered surfaces older than 4 Ga). The martian mantle should have Earth-like polymorphic phase transitions and may even support a perovskite layer near the core (depending on the actual core radius), a characteristic that would have major implications for core cooling and mantle convection. Thus even the most basic measurements of planetary structure, such as crustal thickness, core radius and state (solid/liquid), and gross mantle velocity structure would provide invaluable constraints on models of early planetary evolution. Despite this strong scientific motivation (and several failed attempts), Mars remains terra incognita from a seismic standpoint. This is due to an unfortunate convergence of circumstances, prominent among which are our uncertainty in the level of seismic activity and the relatively high cost of landing multiple long-lived spacecraft on Mars to comprise a seismic network for body-wave travel-time analysis; typically four to ten stations are considered necessary for this type of experiment. In this presentation I will address both of these issues. In order to overcome the concern about a possible lack of marsquakes with which to work, it is useful to identify alternative methods for using seismic techniques to probe the interior. Seismology without quakes can be accomplished in a number of ways. “Unconventional” sources of seismic energy include meteorites (which strike the surface of Mars at a relatively high rate), artificial projectiles

  9. Extending Whole-earth Tectonics To The Terrestrial Planets

    Science.gov (United States)

    Baker, V. R.; Maruyama, S.; Dohm, J. M.

    Based on the need to explain a great many geological and geophysical anomalies on Mars, and stimulated by the new results from the Mars Global Surveyor Mission, we propose a conceptual model of whole-EARTH (Episodic Annular Revolving Thermal Hydrologic) tectonics for the long-term evolution of terrestrial planets. The theory emphasizes (1) the importance of water in planetary evolution, and (2) the physi- cal transitions in modes of mantle convection in relation to planetary heat produc- tion. Depending on their first-order geophysical parameters and following accretion and differentiation from volatile-rich planetessimals, terrestrial planets should evolve through various stages of mantle convection, including magma ocean, plate tectonic, and stagnant lid processes. If a water ocean is able to condense from the planet's early steam atmosphere, an early regime of plate tectonics will follow the initial magma ocean. This definitely happened on earth, probably on Mars, and possibly on Venus. The Mars history led to transfer of large amounts of water to the mantle during the pe- riod of heavy bombardment. Termination of plate tectonics on Mars during the heavy bombardment period led to initiation of superplumes at Tharsis and Elysium, where long-persistent volcanism and water outbursts dominated much of later Martian his- tory. For Venus, warming of the early sun made the surface ocean unstable, eliminating its early plate-tectonic regime. Although Venus now experiences stagnant-lid convec- tion with episodic mantle overturns, the water subducted to its lower mantle during the ancient plate-tectonic regime manifests itself in the initation of volatile-rich plumes that dominate its current tectonic regime.

  10. Tectonics of the Philippine Sea plate before and after 52 Ma subduction initiation to form the Izu-Bonin-Mariana arc

    Science.gov (United States)

    Ishizuka, O.; Tani, K.; Harigane, Y.; Umino, S.; Stern, R. J.; Reagan, M. K.; Hickey-Vargas, R.; Yogodzinski, G. M.; Kusano, Y.; Arculus, R. J.

    2016-12-01

    Robust tectonic reconstruction of the evolving Philippine Sea Plate for the period immediately before and after subduction initiation 52 Ma to form the Izu-Bonin-Mariana (IBM) arc is prerequisite to understand cause of subduction initiation (SI) and test competing hypotheses for SI such as spontaneous or induced nucleation. Understanding of nature and origin of overriding and subducting plates is especially important because plate density is a key parameter controlling SI based on numerical modeling (e.g., Leng and Gurnis 2015). There is increasing evidence that multiple geological events related to changing stress fields took place in and around Philippine Sea plate about the time of SI 52 Ma (Ishizuka et al., 2011). For our understanding of the early IBM arc system to increase, it is important to understand the pattern and tempo of these geological events, particularly the duration and extent of seafloor spreading in the proto arc associated with SI, and its temporal relationship with spreading in the West Philippine Basin (WPB). IODP Exp. 351 provided evidence of SI-related seafloor spreading west of the Kyushu-Palau Ridge (Arculus et al., 2015). Planned age determination of the basement crust at Site U1438 will constrain the timing and geometry of SI-related spreading and its relationship to variation in mode of spreading in the WPB including rotation of spreading axis. Some tectonic reconstructions suggest that part of the IBM arc could have formed on "young" WPB crust. Dredging of the northern Mariana forearc crust and mantle in 2014 aimed to test this hypothesis. Preliminary data indicates that early arc crustal section of the N. Mariana forearc is geochemically and temporally similar to that exposed in the Bonin and southern Mariana forearcs. New tectonic reconstructions for the nascent IBM system will be presented based on these observations.

  11. Seismicity of the Earth 1900–2010 Himalaya and vicinity

    Science.gov (United States)

    Turner, Bethan; Jenkins, Jennifer; Turner, Rebecca; Parker, Amy; Sinclair, Alison; Davies, Sian; Hayes, Gavin P.; Villaseñor, Antonio; Dart, Rirchard L.; Tarr, Arthur C.; Furlong, Kevin P.; Benz, Harley M.

    2013-01-01

    Seismicity in the Himalaya region predominantly results from the collision of the India and Eurasia continental plates, which are converging at a relative rate of 40–50 mm/yr. Northward underthrusting of India beneath Eurasia generates numerous earthquakes and consequently makes this area one of the most seismically hazardous regions on Earth. The surface expression of the plate boundary is marked by the foothills of the north-south trending Sulaiman Range in the west, the Indo-Burmese Arc in the east, and the east-west trending Himalaya Front in the north of India. Along the western margin of the India plate, relative motions between India and Eurasia are accommodated by strike-slip, reverse, and oblique-slip faulting resulting in the complex Sulaiman Range fold and thrust belt, and the major translational Chaman Fault in Afghanistan. Beneath the Pamir‒Hindu Kush Mountains of northern Afghanistan, earthquakes occur to depths as great as 200 km as a result of remnant lithospheric subduction. Further north again, the Tian Shan is a seismically active intra-continental mountain belt defined by a series of east-west trending thrust faults thought to be related to the broad footprint of the India-Eurasia collision. Tectonics in northern India are dominated by motion along the Main Frontal Thrust and associated thrust faults of the India-Eurasia plate boundary, which have resulted in a series of large and devastating earthquakes in (and prior to) the 20th century. The Tibetan Plateau to the north of the main plate boundary is a broad region of uplift associated with the India-Eurasia collision, and is cut by a series of generally east-west trending strike-slip faults. These include the Kunlun, Haiyuan, and the Altyn Tagh faults, all of which are left-lateral structures, and the Kara-Koram right-lateral fault. Throughout the plateau, thrust faults accommodate the north-south compressional component of crustal shortening associated with the ongoing collision of India

  12. The northern Lesser Antilles oblique subduction zone: new insight about the upper plate deformation, 3D slab geometry and interplate coupling.

    Science.gov (United States)

    Marcaillou, B.; Laurencin, M.; Graindorge, D.; Klingelhoefer, F.

    2017-12-01

    In subduction zones, the 3D geometry of the plate interface is thought to be a key parameter for the control of margin tectonic deformation, interplate coupling and seismogenic behavior. In the northern Caribbean subduction, precisely between the Virgin Islands and northern Lesser Antilles, these subjects remain controversial or unresolved. During the ANTITHESIS cruises (2013-2016), we recorded wide-angle seismic, multichannel reflection seismic and bathymetric data along this zone in order to constrain the nature and the geometry of the subducting and upper plate. This experiment results in the following conclusions: 1) The Anegada Passage is a 450-km long structure accross the forearc related to the extension due to the collision with the Bahamas platform. 2) More recently, the tectonic partitioning due to the plate convergence obliquity re-activated the Anegada Passage in the left-lateral strike-slip system. The partitioning also generated the left-lateral strike-slip Bunce Fault, separating the accretionary prism from the forearc. 3) Offshore of the Virgin Islands margin, the subducting plate shows normal faults parallel to the ancient spreading center that correspond to the primary fabric of the oceanic crust. In contrast, offshore of Barbuda Island, the oceanic crust fabric is unresolved (fracture zone?, exhumed mantle? ). 4) In the direction of the plate convergence vector, the slab deepening angle decreases northward. It results in a shallower slab beneath the Virgin Islands Platform compared to the St Martin-Barbuda forearc. In the past, the collision of the Bahamas platform likely changed the geodynamic settings of the northeastern corner of the Caribbean subduction zone and we present a revised geodynamic history of the region. Currently, various features are likely to control the 3D geometry of the slab: the margin convexity, the convergence obliquity, the heterogeneity of the primary fabric of the oceanic crust and the Bahamas docking. We suggest that

  13. Strain, Stress and Seismicity pattern in Switzerland

    Science.gov (United States)

    Houlié, Nicolas; Woessner, Jochen; Villiger, Arturo; Deichmann, Nicholas; Rothacher, Markus; Giardini, Domenico; Geiger, Alain

    2013-04-01

    Switzerland lies across one of the most complex plate boundary in the world. With a 100 Ma of deformation history, and a wide diversity of deformation mechanism, it is an ideal place to study the link(s) between small strain rates measured at the surface and stress dissipated at depth. The link is of genuine interest for seismic hazard assessment as it provides an independent estimate for moment release within the seismogenic volume. We use geodetic (GPS velocities, shortening axes, strain maps) and seismic (anisotropy, P-axes, focal mechanisms) datasets in order to assess whether the stress accumulated at depth due to the continental collision reflects the deformation rates measured at the surface and correlates with the seismic activity as well as the stress directions deduced from earthquake focal mechanisms throughout the area - or not. While the deformation amplitudes of the area are small (less than 10-7 yr-1) in some areas of Switzerland, we can relate long- and short-term features of the tectonic processes occurring over the last 10+ Ma. Preliminary results suggest that while deformation rates measured by GPS are large in the Ticino compared to the Valais region - its seismic activity rate is lower. This implies other processes might play important roles in the generation of seismicity.

  14. Seismic Structure of the Oceanic Plate Entering the Central Part of the Japan Trench Obtained from Ocean-Bottom Seismic Data

    Science.gov (United States)

    Ohira, A.; Kodaira, S.; Fujie, G.; No, T.; Nakamura, Y.; Miura, S.

    2017-12-01

    In trench-outer rise regions, the normal faults develop due to the bending of the incoming plate, which cause numerous normal-faulting earthquakes and systematic structural variations toward trenches. In addition to the effects on the bend-related normal fault, structural variations which are interpreted to be attributed to pseudofaults, a fracture zone, and petit-spot volcanic activities are observed in the oceanic plate entering the central part of the Japan Trench, off Miyagi. In May-June 2017, to understand detail structural variations and systematic structural changes of the oceanic plate toward the trench, we conducted an active-source seismic survey off Miyagi using R/V Kaimei, a new research vessel of JAMSTEC. Along a 100 km-long seismic profile which is approximately perpendicular to the trench axis, we deployed 40 ocean-bottom seismometers at intervals of 2 km and fired a large airgun array (total volume 10,600 cubic inches) with 100 m shooting intervals. Multi-channel seismic reflection data were also collected along the profile. On OBS records we observed refractions from the sedimentary layer and the oceanic crust (Pg), wide-angle reflections from the crust-mantle boundary (PmP), and refractions from the uppermost mantle (Pn). Pg is typically observed clearly at near offsets (approximately 20 km) but it highly attenuates at far offsets (> 20 km). A triplication of Pg-PmP-Pn with strong amplitudes is observed at ranges from 30 km to 60 km offsets. Pn is typically weak and its apparent velocity is approximately 8 km/sec. High attenuation of Pg and weak Pn may indicate the complex crustal structure related to petit-spot volcanic activities and/or a fracture zone, which are recognized in bathymetry data around the profile.

  15. Cenozoic exhumation and tectonic evolution of the Qimen Tagh Range, northern Tibetan Plateau: Insights from the heavy mineral compositions, detrital zircon U-Pb ages and seismic interpretations

    Science.gov (United States)

    Zhu, W.; Wu, C.; Wang, J.; Zhou, T.; Zhang, C.; Li, J.

    2017-12-01

    The Qaidam Basin is the largest intermountain basin within the Tibetan Plateau. The Cenozoic sedimentary flling characteristics of the basin was significantly influenced by the surrounding tectonic belt, such as the Altyn Tagh Range to the north-west and Qimen Tagh Range to the south. The tectonic evolution of the Qimen Tagh Range and the structural relationship between the Qaidam Basin and Qimen Tagh Range remain controversial. To address these issues, we analyzed thousands of heavy mineral data, 720 detrital zircon ages and seismic data of the Qaidam Basin. Based on the regional geological framework and our kinematic analyses, the Cenozoic tectonic evolution of the Qimen Tagh Range can be divided into two stages. From the Early Eocene to the Middle Miocene, the Devonian (400-360 Ma) and Permian to Triassic (300-200 Ma) zircons which were sourced from the Qimen Tagh Range and the heavy mineral assemblage of zircon-leucoxene-garnet-sphene on the north flank of the Qimen Tagh Range indicated that the Qimen Tagh Range has been exhumed before the Eocene and acted as the primary provenance of the Qaidam Basin. The Kunbei fault system (i.e. the Kunbei, Arlar and Hongliuquan faults) in the southwest of the Qaidam Basin, which can be seen as a natural study window of the Qimen Tagh Range, was characterized by left-lateral strike-slip faults and weak south-dipping thrust faults based on the seismic sections. This strike-slip motion was generated by the uplift of the Tibetan Plateau caused by the onset of the Indian-Eurasian collision. Since the Middle Miocene, the primary mineral assemblages along the northern flank of the Qimen Tagh Range changed from the zircon-leucoxene-garnet-sphene assemblage to the epidote-hornblende-garnet-leucoxene assemblage. Simultaneously, the Kunbei fault system underwent intense south-dipping thrusting, and a nearly 2.2-km uplift can be observed in the hanging wall of the Arlar fault. We attributed these variations to the rapid uplift event of

  16. Geodynamic Constraints on the Sources of Seismic Anisotropy Beneath Madagascar

    Science.gov (United States)

    Rajaonarison, T. A.; Stamps, D. S.; Fishwick, S.

    2017-12-01

    The rheological structure of the lithosphere-asthenosphere system controls the degree in which the mantle drives surface motions. Seismic anisotropy is a proxy to infer information about previous tectonic events imprinted in lithospheric structures and/or asthenospheric flow pattern in regions absent of active volcanism, however, distinguishing between the shallow and deeper sources, respectively, remains ambiguous. Madagascar is an ideal natural laboratory to study the sources of anisotropy and the rheological implications for lithosphere-asthenosphere system because 1) active volcanism is minimal or absent, 2) there are well-exposed tectonic fabrics for comparison, and 3) numerous geological and geophysical observations provides evidence of present-day tectonic activities. Recent studies suggest new seismic anisotropy observations in southern Madagascar are sourced from both fossilized lithospheric structure and asthenospheric flow driven by rigid lithospheric plate motion. In this work we compare geodynamic simulations of the lithosphere-asthenosphere system with seismic anisotropy data set that includes all of Madagascar. We use the numerical code Advanced Solver for Problems in Earth's ConvecTion (ASPECT) to calculate instantaneous deformation in the lithosphere and edge-driven convective flow in the asthenosphere accounting for variations in buoyancy forces and temperature dependent viscosity. The initial temperature conditions are based on interpretations from high resolution regional surface wave tomography. We assume visco-plastic rheology for a uniform crust, dislocation creep for a laterally varying mantle lithospheric structure, and diffusion creep for the asthenosphere. To test for the source of anisotropy we compare our velocity solution azimuths with azimuths of anisotropy at 25 km depth intervals. Calculated asthenospheric flow aligns with measured seismic anisotropy with a 15° WRMS at 175 km depth and possibly down to 250 km suggesting the

  17. Gravity modeling of the Muertos Trough and tectonic implications (north-eastern Caribbean)

    Science.gov (United States)

    Granja, Bruna J.L.; Muñoz-Martín, A.; ten Brink, Uri S.; Carbó-Gorosabel, Andrés; Llanes, Estrada P.; Martín-Dávila, J.; Cordoba-Barba, D.; Catalan, Morollon M.

    2010-01-01

    The Muertos Trough in the northeast Caribbean has been interpreted as a subduction zone from seismicity, leading to infer a possible reversal subduction polarity. However, the distribution of the seismicity is very diffuse and makes definition of the plate geometry difficult. In addition, the compressive deformational features observed in the upper crust and sandbox kinematic modeling do not necessarily suggest a subduction process. We tested the hypothesized subduction of the Caribbean plate's interior beneath the eastern Greater Antilles island arc using gravity modeling. Gravity models simulating a subduction process yield a regional mass deficit beneath the island arc independently of the geometry and depth of the subducted slab used in the models. This mass deficit results from sinking of the less dense Caribbean slab beneath the lithospheric mantle replacing denser mantle materials and suggests that there is not a subducted Caribbean plateau beneath the island arc. The geologically more realistic gravity model which would explain the N-S shortening observed in the upper crust requires an overthrusted Caribbean slab extending at least 60 km northward from the deformation front, a progressive increase in the thrusting angle from 8?? to 30?? reaching a maximum depth of 22 km beneath the insular slope. This new tectonic model for the Muertos Margin, defined as a retroarc thrusting, will help to assess the seismic and tsunami hazard in the region. The use of gravity modeling has provided targets for future wide-angle seismic surveys in the Muertos Margin. ?? 2010 Springer Science+Business Media B.V.

  18. Recent Vs. Historical Seismicity Analysis For Banat Seismic Region (Western Part Of Romania)

    OpenAIRE

    Oros Eugen; Diaconescu Mihai

    2015-01-01

    The present day seismic activity from a region reflects the active tectonics and can confirm the seismic potential of the seismogenic sources as they are modelled using the historical seismicity. This paper makes a comparative analysis of the last decade seismicity recorded in the Banat Seismic Region (western part of Romania) and the historical seismicity of the region (Mw≥4.0). Four significant earthquake sequences have been recently localized in the region, three of them nearby the city of...

  19. Methodology of seismotectonic zoning in an intraplate low seismicity domain. Examples of France surrounding areas

    International Nuclear Information System (INIS)

    Philip, H.; Grellet, B.; Combes, P.; Haessler, H.

    1991-01-01

    Until now, the dominant factor in seismic hazard assessments has been historical seismicity. This approach is justified if the data derived from historical seismicity in a region are representative of its seismic activity and if we consider that in areas where damaging earthquakes have happened, they may happen again. This can be seen when seismotectonic relationships are well established in areas such as well localised plate boundaries (subduction zones, transform faults) and/or with a high rate of deformation. In these cases, the areas where future earthquakes might occur are usually well determined and the recurrences short enough on the time scale of historical observations. However, in areas where recent tectonic deformations are diffused and moderate, the historical period of seismicity data (a few centuries) is not long enough to observe a sample of historical seismicity representative of the present-day tectonic activity of the area. The studies on the most recent damaging earthquakes (El Asnam 1980, Spitak 1988, Cherchell Tipasa 1989) show that it would have been extremely difficult to predict the magnitude and the localisation of these events considering historical seismicity alone. It is the same in Provence (south of France) where the risk of occurrence of a damaging earthquake would have been underestimated before the June 1909 event. In all these cases, seismotectonic studies 'a posteriori' show that the geometry and kinematic of the faults responsible for these earthquakes can be identified and that all of them have presented seismic activity in the last thousand years. So it is necessary to emphasis a global approach of the problem through specific studies such as neotectonics, teledetection, geodesy, present-day stress field, strain field, paleoseismology etc. These studies will enlarge the period of observation compared with the data derived only from historical and present-day seismicity. In France seismicity is moderate and recent tectonic

  20. Slab tears and intermediate-depth seismicity

    Science.gov (United States)

    Meighan, Hallie E.; ten Brink, Uri S.; Pulliam, Jay

    2013-01-01

    Active tectonic regions where plate boundaries transition from subduction to strike slip can take several forms, such as triple junctions, acute, and obtuse corners. Well-documented slab tears that are associated with high rates of intermediate-depth seismicity are considered here: Gibraltar arc, the southern and northern ends of the Lesser Antilles arc, and the northern end of Tonga trench. Seismicity at each of these locations occurs, at times, in the form of swarms or clusters, and various authors have proposed that each marks an active locus of tear propagation. The swarms and clusters start at the top of the slab below the asthenospheric wedge and extend 30–60 km vertically downward within the slab. We propose that these swarms and clusters are generated by fluid-related embrittlement of mantle rocks. Focal mechanisms of these swarms generally fit the shear motion that is thought to be associated with the tearing process.

  1. Seismic anisotropy in localized shear zones versus distributed tectonic fabrics: examples from geologic and seismic observations in western North America and the European Alps

    Science.gov (United States)

    Mahan, Kevin H.; Schulte-Pelkum, Vera; Condit, Cailey; Leydier, Thomas; Goncalves, Philippe; Raju, Anissha; Brownlee, Sarah; Orlandini, Omero F.

    2017-04-01

    Modern methods for detecting seismic anisotropy offer an array of promising tools for imaging deep crustal deformation but also present challenges, especially with respect to potential biases in both the detection methods themselves as well as in competing processes for localized versus distributed deformation. We address some of these issues from the geophysical perspective by employing azimuthally dependent amplitude and polarity variations in teleseismic receiver functions combined with a compilation of published rock elasticity tensors from middle and deep crustal rocks, and from the geological perspective through studies of shear zone deformation processes. Examples are highlighted at regional and outcrop scales from western North America and the European Alps. First, in regional patterns, strikes of seismically detected fabric from receiver functions in California show a strong alignment with current strike-slip motion between the Pacific and North American plates, with high signal strength near faults and from depths below the brittle-ductile transition suggesting these faults have deep ductile roots. In contrast, despite NE-striking shear zones being the most prominent features portrayed on Proterozoic tectonic maps of the southwestern USA, receiver function anisotropy from the central Rocky Mountain region appears to more prominently reflect broadly distributed Proterozoic fabric domains that preceded late-stage localized shear zones. Possible causes for the discrepancy fall into two categories: those that involve a) bias in seismic sampling and/or b) deformation processes that lead to either weaker anisotropy in the shear zones compared to adjacent domains or to a symmetry that is different from that conventionally assumed. Most of these explanations imply that the seismically sampled domains contain important structural information that is distinct from the shear zones. The second set of examples stem from studies of outcrop-scale shear zones in upper

  2. Subducting plate geology in three great earthquake ruptures of the western Alaska margin, Kodiak to Unimak

    Science.gov (United States)

    von Huene, Roland E.; Miller, John J.; Weinrebe, Wilhelm

    2012-01-01

    Three destructive earthquakes along the Alaska subduction zone sourced transoceanic tsunamis during the past 70 years. Since it is reasoned that past rupture areas might again source tsunamis in the future, we studied potential asperities and barriers in the subduction zone by examining Quaternary Gulf of Alaska plate history, geophysical data, and morphology. We relate the aftershock areas to subducting lower plate relief and dissimilar materials in the seismogenic zone in the 1964 Kodiak and adjacent 1938 Semidi Islands earthquake segments. In the 1946 Unimak earthquake segment, the exposed lower plate seafloor lacks major relief that might organize great earthquake rupture. However, the upper plate contains a deep transverse-trending basin and basement ridges associated with the Eocene continental Alaska convergent margin transition to the Aleutian island arc. These upper plate features are sufficiently large to have affected rupture propagation. In addition, massive slope failure in the Unimak area may explain the local 42-m-high 1946 tsunami runup. Although Quaternary geologic and tectonic processes included accretion to form a frontal prism, the study of seismic images, samples, and continental slope physiography shows a previous history of tectonic erosion. Implied asperities and barriers in the seismogenic zone could organize future great earthquake rupture.

  3. Relationship between the frequency magnitude distribution and the visibility graph in the synthetic seismicity generated by a simple stick-slip system with asperities.

    Directory of Open Access Journals (Sweden)

    Luciano Telesca

    Full Text Available By using the method of the visibility graph (VG the synthetic seismicity generated by a simple stick-slip system with asperities is analysed. The stick-slip system mimics the interaction between tectonic plates, whose asperities are given by sandpapers of different granularity degrees. The VG properties of the seismic sequences have been put in relationship with the typical seismological parameter, the b-value of the Gutenberg-Richter law. Between the b-value of the synthetic seismicity and the slope of the least square line fitting the k-M plot (relationship between the magnitude M of each synthetic event and its connectivity degree k a close linear relationship is found, also verified by real seismicity.

  4. Hypocenter relocation along the Sunda arc in Indonesia, using a 3D seismic velocity model

    Science.gov (United States)

    Nugraha, Andri Dian; Shiddiqi, Hasbi A.; Widiyantoro, Sri; Thurber, Clifford H.; Pesicek, Jeremy D.; Zhang, Haijiang; Wiyono, Samsul H.; Ramadhan, Mohamad; Wandano,; Irsyam, Mahsyur

    2018-01-01

    The tectonics of the Sunda arc region is characterized by the junction of the Eurasian and Indo‐Australian tectonic plates, causing complex dynamics to take place. High‐seismicity rates in the Indonesian region occur due to the interaction between these tectonic plates. The availability of a denser network of seismometers after the earthquakes of Mw">Mw 9.1 in 2004 and  Mw">Mw 8.6 in 2005 supports various seismic studies, one of which regards the precise relocation of the hypocenters. In this study, hypocenter relocation was performed using a teleseismic double‐difference (DD) relocation method (teletomoDD) combining arrival times of P and S waves from stations at local, regional, and teleseismic distances. The catalog data were taken from the Agency of Meteorology, Climatology, and Geophysics (BMKG) of Indonesia, and the International Seismological Centre (ISC) for the time period of April 2009 to May 2015. The 3D seismic‐wave velocity model with a grid size 1°×1°">1°×1° was used in the travel‐time calculations. Relocation results show a reduction in travel‐time residuals compared with the initial locations. The relocation results better illuminate subducted slabs and active faults in the region such as the Mentawai back thrust and the outer rise in the subduction zone south of Java. Focal mechanisms from the Global Centroid Moment Tensor catalog are analyzed in conjunction with the relocation results, and our synthesis of the results provides further insight into seismogenesis in the region.

  5. Deformation of "stable" continental interiors by mantle convection: Implications for intraplate stress in the New Madrid Seismic Zone

    Science.gov (United States)

    Forte, A. M.; Moucha, R.; Simmons, N. A.; Grand, S. P.; Mitrovica, J. X.

    2011-12-01

    The enigmatic origin of large-magnitude earthquakes far from active plate boundaries, especially those occurring in so-called "stable" continental interiors, is a source of continuing controversy that has eluded a satisfactory explanation using past geophysical models of intraplate deformation and faulting. One outstanding case of such major intraplate earthquakes is the 1811-1812 series of events in the New Madrid Seismic Zone (NMSZ). We contend that the origin of some of these enigmatic intraplate events is due to regional variations in the pattern of tectonic stress generated by mantle convective flow acting on the overlying lithosphere and crust. Mantle convection affects the entire surface of the planet, irrespective of the current configuration of surface plate boundaries. In addition, it must be appreciated that plate tectonics is not a 2-D process, because the convective flow that drives the observed horizontal motions of the tectonic plates also drives vertical displacements of the crust across distances as great as 2 to 3 km. This dynamic topography is directly correlated with convection-driven stress field variations in the crust and lithosphere and these stresses can be locally focussed if the mantle rheology below the lithosphere is characterised by sufficiently low viscosities. We have developed global models of convection-driven mantle flow [Forte et al. 2009,2010] that are based on recent high-resolution 3-D tomography models derived from joint inversions of seismic, geodynamic and mineral physics data [Simmons et al. 2007,2008,2010]. These tomography-based mantle convection models also include a full suite of surface geodynamic (postglacial rebound and convection) constraints on the depth-dependent average viscosity of the mantle [Mitrovica & Forte 2004]. Our latest tomography-based and geodynamically-constrained convection calculations reveal that mantle flow under the central US are driven by density anomalies within the lower mantle associated

  6. Application of random seismic inversion method based on tectonic model in thin sand body research

    Science.gov (United States)

    Dianju, W.; Jianghai, L.; Qingkai, F.

    2017-12-01

    The oil and gas exploitation at Songliao Basin, Northeast China have already progressed to the period with high water production. The previous detailed reservoir description that based on seismic image, sediment core, borehole logging has great limitations in small scale structural interpretation and thin sand body characterization. Thus, precise guidance for petroleum exploration is badly in need of a more advanced method. To do so, we derived the method of random seismic inversion constrained by tectonic model.It can effectively improve the depicting ability of thin sand bodies, combining numerical simulation techniques, which can credibly reducing the blindness of reservoir analysis from the whole to the local and from the macroscopic to the microscopic. At the same time, this can reduce the limitations of the study under the constraints of different geological conditions of the reservoir, accomplish probably the exact estimation for the effective reservoir. Based on the research, this paper has optimized the regional effective reservoir evaluation and the productive location adjustment of applicability, combined with the practical exploration and development in Aonan oil field.

  7. Interseismic Coupling and Seismic Potential along the Indo-Burmese Arc and the Sagaing fault

    Science.gov (United States)

    Earnest, A.

    2017-12-01

    The Indo-burmese arc is formed by the oblique subduction of the Indian plate under the Eurasia. This region is a transition zone between the main Himalayan collision belt and the Andaman subduction zone. This obliquity causes strain partitioning which causes separation of a sliver plate, the Burma Plate. Considering the geomorphic, tectonic and geophysical signatures, IBR comprises all the structural features of an active subduction zone, whereas the present day tectonics of this region is perplexing. Ni et al. [1989] and Rao and Kalpana [2005] suggested that the subduction might have stopped in recent times or continues relatively in an aseismic fashion. This is implied by the NNE compressional stress orientations, instead of its downdip direction. The focal mechanism stress inversions show distinct stress fields above and below the 90 km depth. It is widely believed that the partitioning of Indian-Eurasia plate motion along the Indo-buremse arc and the Sagaing fault region the reason for earthquake occurrence in this region. The relative motion of 36mm/yr, between India and Eurasia, is partitioned across the Sagaing fault through a dextral movement of ˜20mm/yr and remaining velocity is accommodated at the Churachandapur-Mao fault (CMF) through dextral motion. The CMF and its surroundings are considered as seismically a low hazard region, an observation made from the absence of significant earthquakes and lack of field evidences. This made Kundu and Gahalaut [2013] to propose that the motion across the CMF happens in an aseismic manner. Recently, based on GPS studies Steckler et al. [2016] suggested that the region is still actively subducting and the presence of a locked megathrust plate boundary depicts the region as highly vulnerable for large magnitude seismic activities. Our study, based on various geodetic solutions and earthquake slip vectors, focus on interseisimic block models for the Indo-burmese arc and Sagaing fault region so as to model the crustal

  8. An Investigation of Seismicity for the West Sumatra Region Indonesia

    Science.gov (United States)

    Syafriani, S.

    2018-04-01

    The purpose of this research was to investigate the seismicity of the West Sumatra region in the coordinates area of 94° E – 104° E and 2° N - 4° S. Guttenberg-Richer magnitude-frequency relation and seismic risk have been computed. Historical data of earthquakes used from year of 1970 to 2017 with magnitude higher than 4. The study area was divided into 8 sub-regions based on seismotectonic characteristics, plate tectonic and geological models. The determination of seismotectonic characteristics was based on the level of seismic activity in a region (a value) and rock stress condition (b value). High a value was associated with high seismic activity, whereas high b values were associated with low stress rock conditions, and vice versa. Based on the calculation results, a and b values were obtained in the interval of 5.5-11.3 and 0.7-2. The highest b value was obtained in the sub region 5 (Nias islands), while the lowest b value was obtained in sub region 7 (the Mentawai islands). The sub region 7, Mentawai Islands was indicated as the seismic risk potential areas.

  9. A harbinger of plate tectonics: a commentary on Bullard, Everett and Smith (1965) 'The fit of the continents around the Atlantic'.

    Science.gov (United States)

    Dewey, John F

    2015-04-13

    In the 1960s, geology was transformed by the paradigm of plate tectonics. The 1965 paper of Bullard, Everett and Smith was a linking transition between the theories of continental drift and plate tectonics. They showed, conclusively, that the continents around the Atlantic were once contiguous and that the Atlantic Ocean had grown at rates of a few centimetres per year since the Early Jurassic, about 160 Ma. They achieved fits of the continental margins at the 500 fathom line (approx. 900 m), not the shorelines, by minimizing misfits between conjugate margins and finding axes, poles and angles of rotation, using Euler's theorem, that defined the unique single finite difference rotation that carried congruent continents from contiguity to their present positions, recognizing that the real motion may have been more complex around a number of finite motion poles. Critically, they were concerned only with kinematic reality and were not restricted by considerations of the mechanism by which continents split and oceans grow. Many of the defining features of plate tectonics were explicit or implicit in their reconstructions, such as the torsional rigidity of continents, Euler's theorem, closure of the Tethyan ocean(s), major continental margin shear zones, the rapid rotation of small continental blocks (Iberia) around nearby poles, the consequent opening of small wedge-shaped oceans (Bay of Biscay), and misfit overlaps (deltas and volcanic piles) and underlaps (stretched continental edges). This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.

  10. Quantitative morphometric analysis for the tectonic characterisation of northern Tunisia.

    Science.gov (United States)

    Camafort, Miquel; Pérez-Peña, José Vicente; Booth-Rea, Guillermo; Ranero, César R.; Gràcia, Eulàlia; Azañón, José Miguel; Melki, Fetheddine; Ouadday, Mohamed

    2016-04-01

    Northern Tunisia is characterized by low deformation rates and low to moderate seismicity. Although instrumental seismicity reaches maximum magnitudes of Mw 5.5, some historical earthquakes have occurred with catastrophic consequences in this region. Aiming to improve our knowledge of active tectonics in Tunisia, we carried out both a quantitative morphometric analysis and field study in the north-western region. We applied different morphometric tools, like river profiles, knickpoint analysis, hypsometric curves and integrals and drainage pattern anomalies in order to differentiate between zones with high or low recent tectonic activity. This analysis helps identifying uplift and subsidence zones, which we relate to fault activity. Several active faults in a sparse distribution were identified. A selected sector was studied with a field campaign to test the results obtained with the quantitative analysis. During the fieldwork we identified geological evidence of recent activity and a considerable seismogenic potential along El Alia-Teboursouk (ETF) and Dkhila (DF) faults. The ETF fault could be responsible of one of the most devastating historical earthquakes in northern Tunisia that destroyed Utique in 412 A.D. Geological evidence include fluvial terraces folded by faults, striated and cracked pebbles, clastic dikes, sand volcanoes, coseismic cracks, etc. Although not reflected in the instrumental seismicity, our results support an important seismic hazard, evidenced by the several active tectonic structures identified and the two seismogenic faults described. After obtaining the current active tectonic framework of Tunisia we discuss our results within the western Mediterranean trying to contribute to the understanding of the western Mediterranean tectonic context. With our results, we suggest that the main reason explaining the sparse and scarce seismicity of the area in contrast with the adjacent parts of the Nubia-Eurasia boundary is due to its extended

  11. Spatial distribution of the earthquakes in the Vrancea zone and tectonic correlations

    International Nuclear Information System (INIS)

    Bala, Andrei; Diaconescu, Mihai; Biter, Mircea

    2001-01-01

    The tectonic plate evolution of the whole Carpathian Arc and Pannonian back-arc Basin indicates that at least three tectonic units have been in contact and at the same time in relative motion: the East European Plate, the Moesian plate and the Intra-Alpine plate. There were plotted graphically all the earthquake hypocentres from the period 1982-2000 situated in an area which includes Vrancea zone. Because of the great number of events plotted, they were found to describe well the limits of the tectonic plate (plate fragment?) which is supposed to be subducted in this region down to 200 km depth. The hypothesis of a plate fragment delaminated from an older subduction can not be overruled. These limits were put in direct relations with the known geology and tectonics of the area. Available fault plane solutions for the crustal earthquakes are analyzed in correlation with the main faults of the area. A graphic plot of the sunspot number is correlated with the occurrence of the earthquakes with magnitudes greater than 5. (authors)

  12. The Mid-Hungarian line: a zone of repeated tectonic inversions

    Science.gov (United States)

    Csontos, László; Nagymarosy, András

    1998-11-01

    The Mid-Hungarian line is a major tectonic feature of the Intra-Carpathian area separating two terranes of different origin and tectonic structure. Although this tectonic line was known from borehole records, it has not been described in seismic sections. The study presents interpreted seismic lines crossing the supposed trace of the Mid-Hungarian line. These seismic sections show north-dipping normal faults and thrust faults as well as cross-cutting young strike-slip faults. A complex tectonic history is deduced, including intra-Oligocene-Early Miocene thrusting, Middle Miocene extension, local Late Miocene inversion and Late Miocene-Pliocene normal faulting and left-lateral wrenching. In the light of our seismic study we think that the best candidate for the Mid-Hungarian line is a north-dipping detachment fault beneath large masses of Neogene volcanics. The auxiliary structures to the north seen on seismic sections suggest that it moved as a south-vergent thrust fault during the Palaeogene-Early Miocene which later was reactivated as a set of normal faults. The northern Alcapa unit overrode the southern Tisza-Dacia unit along this fault zone. The same relative positions are observed in the northern termination of the line. Other structures along the supposed trace of the line are north-dipping normal- or strike-slip faults which frequently were reactivated as smaller thrust faults during the late Neogene. Palaeogene-Early Miocene thrusting along the line might be the result of the opposite Tertiary rotations of the two major units, as suggested by palaeomagnetic measurements and earlier models.

  13. Anatomy of the western Java plate interface from depth-migrated seismic images

    OpenAIRE

    Kopp, Heidrun; Hindle, David; Klaeschen, Dirk; Oncken, O.; Scholl, D.

    2009-01-01

    Newly pre-stack depth-migrated seismic images resolve the structural details of the western Java forearc and plate interface. The structural segmentation of the forearc into discrete mechanical domains correlates with distinct deformation styles. Approximately 2/3 of the trench sediment fill is detached and incorporated into frontal prism imbricates, while the floor sequence is underthrust beneath the décollement. Western Java, however, differs markedly from margins such as Nankai or Barbados...

  14. Seismic activity parameters of the Finnish potential repository sites

    International Nuclear Information System (INIS)

    Saari, J.

    2000-10-01

    Posiva Oy has started a project for estimating the possible earthquake induced rock movements on the deposition holes containing canisters of spent nuclear fuel. These estimates will be made for the four investigation sites, Romuvaara, Kivetty, Olkiluoto and Haestholmen. This study deals with the current and future seismicity associated with the above mentioned sites. Seismic belts that participate the seismic behaviour of the studied sites have been identified and the magnitude-frequency distributions of these belts have been estimated. The seismic activity parameters of the sites have been deduced from the characteristics of the seismic belts in order to forecast the seismicity during the next 100,000 years. The report discusses the possible earthquakes induced by future glaciation. The seismic interpretation seems to indicate that the previous postglacial faults in Finnish Lapland have been generated in compressional environment. The orientation of the rather uniform compression has been NW-SE, which coincide with the current stress field. It seems that, although the impact of postglacial crustal rebound must have been significant, the impact of plate tectonics has been dominant. A major assumption of this study has been that future seismicity will generally resemble the current seismicity. However, when the postglacial seismicity is concerned, the magnitude-frequency distribution is likely different and the expected maximum magnitude will be higher. Maximum magnitudes of future postglacial earthquakes have been approximated by strain release examinations. Seismicity has been examined within the framework of the lineament maps, in order to associate the future significant earthquakes with active fault zones in the vicinity of the potential repository sites. (orig.)

  15. Raft tectonics in northern Campos Basin; Tectonica de jangada (raft tectonics) na area norte da Bacia de Campos

    Energy Technology Data Exchange (ETDEWEB)

    Castro, Marilia R. de [Universidade Estadual do Norte Fluminense (UENF), Campos dos Goytacases, RJ (Brazil)]|[PETROBRAS, Macae, RJ (Brazil). Unidade de Negocio da Bacia de Campos; Fugita, Adhemar M. [Universidade do Estado, Rio de Janeiro, RJ (Brazil). Programa de Recursos Humanos da ANP

    2004-07-01

    In the northern area of Campos Basin salt gliding/spreading processes promoted the break-up and transport of Cretaceous and Tertiary rocks overlying the evaporites. This process is known as raft tectonics, and it represents the most extreme form of thin-skinned extension above the salt decollement surface. Three distinct geotectonic domains were recognized that formed in response to the raft tectonics. The first one, confined to the shallower shelf portion of the basin, is characterized by minor extension (pre-raft domain), probably because of small salt thickness and low gradient. In the second domain (or disorganized rafts domain), located in distal platformal and slope areas, seismic sections show the occurrence of blocks or rafts with angular shapes, sometimes imbricated and frequently discontinuous. In the third domain, or domain of organized rafts, located in bacinal region, seismic sections show a more continuous raft pattern, often folded because of salt compression in the distal portions of the basin. The main purposes of this work is to characterize these three tectonic domains distinguished by raft tectonics, as well as their importance in hydrocarbon accumulations in calcarenites. (author)

  16. Earthquake source studies and seismic imaging in Alaska

    Science.gov (United States)

    Tape, C.; Silwal, V.

    2015-12-01

    Alaska is one of the world's most seismically and tectonically active regions. Its enhanced seismicity, including slab seismicity down to 180 km, provides opportunities (1) to characterize pervasive crustal faulting and slab deformation through the estimation of moment tensors and (2) to image subsurface structures to help understand the tectonic evolution of Alaska. Most previous studies of earthquakes and seismic imaging in Alaska have emphasized earthquake locations and body-wave travel-time tomography. In the past decade, catalogs of seismic moment tensors have been established, while seismic surface waves, active-source data, and potential field data have been used to improve models of seismic structure. We have developed moment tensor catalogs in the regions of two of the largest sedimentary basins in Alaska: Cook Inlet forearc basin, west of Anchorage, and Nenana basin, west of Fairbanks. Our moment tensor solutions near Nenana basin suggest a transtensional tectonic setting, with the basin developing in a stepover of a left-lateral strike-slip fault system. We explore the effects of seismic wave propagation from point-source and finite-source earthquake models by performing three-dimensional wavefield simulations using seismic velocity models that include major sedimentary basins. We will use our catalog of moment tensors within an adjoint-based, iterative inversion to improve the three-dimensional tomographic model of Alaska.

  17. Mesozoic to Cenozoic tectonic transition process in Zhanhua Sag, Bohai Bay Basin, East China

    Science.gov (United States)

    Cheng, Yanjun; Wu, Zhiping; Lu, Shunan; Li, Xu; Lin, Chengyan; Huang, Zheng; Su, Wen; Jiang, Chao; Wang, Shouye

    2018-04-01

    The Zhanhua sag is part of the Bohai Bay intracontinental basin system that has developed since the Mesozoic in East China. The timing of this basin system coincides with the final assembly of East Asia and the development of Western Pacific-type plate margin. Here we use 3-D seismic and core log data to investigate the evolution of this basin and discuss its broad tectonic settings. Our new structural study of Zhanhua sag suggests that there are four major tectonic transitions occurred in the Bohai Bay Basin during Mesozoic and Cenozoic: (1) The first tectonic transition was from stable Craton to thrusting during the Triassic, mainly caused by the South China Block's subduction northward beneath the North China Block, which induced the formation of the NW-striking thrust faults. (2) The second tectonic transition was mainly characterized by a change from compression to extension, which can be further divided into two-stages. At the first stage, two episodes of NW-SE shortening occurred in East Asia during Early-Middle Jurassic and Late Jurassic-earliest Cretaceous, respectively. At the second stage, the extension and left-lateral shearing took place during Early Cretaceous while compression occurred during Late Cretaceous. The NW-striking thrust faults changed to normal faults and the NNE-striking left-lateral strike-slip faults started to influence the eastern part of the basin. (3) The third transition occurred when the NW-SE extension and NNE-striking right-lateral shearing started to form during Paleogene, and the peak deformation happen around 40 Ma due to the change of the subduction direction of Pacific Plate relative to Eurasia Plate. The NE-striking normal faults are the main structure, and the pre-existing NNE-striking strike-slip faults changed from left-lateral to right-lateral. (4) The fourth transition saw the regional subsidence during Neogene, which was probably caused by the India-Asia "Hard collision" between 25 and 20 Ma.

  18. Lunar seismicity, structure, and tectonics

    Science.gov (United States)

    Lammlein, D. R.; Latham, G. V.; Dorman, J.; Nakamura, Y.; Ewing, M.

    1974-01-01

    Natural seismic events have been detected by the long-period seismometers at Apollo stations 16, 14, 15, and 12 at annual rates of 3300, 1700, 800, and 700, respectively, with peak activity at 13- to 14-day intervals. The data are used to describe magnitudes, source characteristics, and periodic features of lunar seismicity. In a present model, the rigid lithosphere overlies an asthenosphere of reduced rigidity in which present-day partial melting is probable. Tidal deformation presumably leads to critical stress concentrations at the base of the lithosphere, where moonquakes are found to occur. The striking tidal periodicities in the pattern of moonquake occurrence and energy release suggest that tidal energy is the dominant source of energy released as moonquakes. Thus, tidal energy is dissipated by moonquakes in the lithosphere and probably by inelastic processes in the asthenosphere.

  19. A harbinger of plate tectonics: a commentary on Bullard, Everett and Smith (1965) ‘The fit of the continents around the Atlantic’

    Science.gov (United States)

    Dewey, John F.

    2015-01-01

    In the 1960s, geology was transformed by the paradigm of plate tectonics. The 1965 paper of Bullard, Everett and Smith was a linking transition between the theories of continental drift and plate tectonics. They showed, conclusively, that the continents around the Atlantic were once contiguous and that the Atlantic Ocean had grown at rates of a few centimetres per year since the Early Jurassic, about 160 Ma. They achieved fits of the continental margins at the 500 fathom line (approx. 900 m), not the shorelines, by minimizing misfits between conjugate margins and finding axes, poles and angles of rotation, using Euler's theorem, that defined the unique single finite difference rotation that carried congruent continents from contiguity to their present positions, recognizing that the real motion may have been more complex around a number of finite motion poles. Critically, they were concerned only with kinematic reality and were not restricted by considerations of the mechanism by which continents split and oceans grow. Many of the defining features of plate tectonics were explicit or implicit in their reconstructions, such as the torsional rigidity of continents, Euler's theorem, closure of the Tethyan ocean(s), major continental margin shear zones, the rapid rotation of small continental blocks (Iberia) around nearby poles, the consequent opening of small wedge-shaped oceans (Bay of Biscay), and misfit overlaps (deltas and volcanic piles) and underlaps (stretched continental edges). This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society. PMID:25750142

  20. Water, oceanic fracture zones and the lubrication of subducting plate boundaries—insights from seismicity

    Science.gov (United States)

    Schlaphorst, David; Kendall, J.-Michael; Collier, Jenny S.; Verdon, James P.; Blundy, Jon; Baptie, Brian; Latchman, Joan L.; Massin, Frederic; Bouin, Marie-Paule

    2016-03-01

    We investigate the relationship between subduction processes and related seismicity for the Lesser Antilles Arc using the Gutenberg-Richter law. This power law describes the earthquake-magnitude distribution, with the gradient of the cumulative magnitude distribution being commonly known as the b-value. The Lesser Antilles Arc was chosen because of its along-strike variability in sediment subduction and the transition from subduction to strike-slip movement towards its northern and southern ends. The data are derived from the seismicity catalogues from the Seismic Research Centre of The University of the West Indies and the Observatoires Volcanologiques et Sismologiques of the Institut de Physique du Globe de Paris and consist of subcrustal events primarily from the slab interface. The b-value is found using a Kolmogorov-Smirnov test for a maximum-likelihood straight line-fitting routine. We investigate spatial variations in b-values using a grid-search with circular cells as well as an along-arc projection. Tests with different algorithms and the two independent earthquake cataloges provide confidence in the robustness of our results. We observe a strong spatial variability of the b-value that cannot be explained by the uncertainties. Rather than obtaining a simple north-south b-value distribution suggestive of the dominant control on earthquake triggering being water released from the sedimentary cover on the incoming American Plates, or a b-value distribution that correlates with on the obliquity of subduction, we obtain a series of discrete, high b-value `bull's-eyes' along strike. These bull's-eyes, which indicate stress release through a higher fraction of small earthquakes, coincide with the locations of known incoming oceanic fracture zones on the American Plates. We interpret the results in terms of water being delivered to the Lesser Antilles subduction zone in the vicinity of fracture zones providing lubrication and thus changing the character of the

  1. The Subduction of an Exhumed and Serpentinized Magma-Poor Basement Beneath the Northern Lesser Antilles Reveals the Early Tectonic Fabric at Slow-Spreading Mid-Oceanic Ridges

    Science.gov (United States)

    Marcaillou, B.; Klingelhoefer, F.; Laurencin, M.; Biari, Y.; Graindorge, D.; Jean-Frederic, L.; Laigle, M.; Lallemand, S.

    2017-12-01

    Multichannel and wide-angle seismic data as well as heat-flow measurements (ANTITHESIS cruise, 2016) reveal a 200x200km patch of magma-poor oceanic basement in the trench and beneath the outer fore-arc offshore of Antigua to Saint Martin in the Northern Lesser Antilles. These data highlight an oceanic basement with the following features: 1/ Absence of any reflection at typical Moho depth and layer2/layer3 limit depths. 2/ High Velocity Vp at the top (>5.5 km/s), low velocity gradient with depth (serpentinized at the slow-spreading mid-Atlantic Ridge 80 Myr ago, is currently subducting beneath the Northern Lesser Antilles. During the exhumation, early extension triggers penetrative shear zones sub-parallel to the ridge and to the transform fault. Eventually, this early extension generates sliding along the so-called detachment fault, while the other proto-detachment abort. Approaching the trench, the plate bending reactivates these weak zones in normal faults and fluid pathways promoting deep serpentinisation and localizing tectonic deformation at the plate interface. These subducting fluid-rich mechanically weak mantle rocks rise questions about their relation to the faster slab deepening, the lower seismic activity and the pervasive tectonic partitioning in this margin segment.

  2. Multi scenario seismic hazard assessment for Egypt

    Science.gov (United States)

    Mostafa, Shaimaa Ismail; Abd el-aal, Abd el-aziz Khairy; El-Eraki, Mohamed Ahmed

    2018-05-01

    Egypt is located in the northeastern corner of Africa within a sensitive seismotectonic location. Earthquakes are concentrated along the active tectonic boundaries of African, Eurasian, and Arabian plates. The study area is characterized by northward increasing sediment thickness leading to more damage to structures in the north due to multiple reflections of seismic waves. Unfortunately, man-made constructions in Egypt were not designed to resist earthquake ground motions. So, it is important to evaluate the seismic hazard to reduce social and economic losses and preserve lives. The probabilistic seismic hazard assessment is used to evaluate the hazard using alternative seismotectonic models within a logic tree framework. Alternate seismotectonic models, magnitude-frequency relations, and various indigenous attenuation relationships were amended within a logic tree formulation to compute and develop the regional exposure on a set of hazard maps. Hazard contour maps are constructed for peak ground acceleration as well as 0.1-, 0.2-, 0.5-, 1-, and 2-s spectral periods for 100 and 475 years return periods for ground motion on rock. The results illustrate that Egypt is characterized by very low to high seismic activity grading from the west to the eastern part of the country. The uniform hazard spectra are estimated at some important cities distributed allover Egypt. The deaggregation of seismic hazard is estimated at some cities to identify the scenario events that contribute to a selected seismic hazard level. The results of this study can be used in seismic microzonation, risk mitigation, and earthquake engineering purposes.

  3. Tectonic characteristics and structural styles of a continental rifted basin: Revelation from deep seismic reflection profiles

    Directory of Open Access Journals (Sweden)

    Yuan Li

    2016-09-01

    Full Text Available The Fushan Depression is a half-graben rifted sub-basin located in the southeast of the Beibuwan Basin, South China Sea. The Paleogene Liushagang sequence is the main hydrocarbon-bearing stratigraphic unit in the sub-basin. Using three-dimensional (3-D seismic data and logging data over the sub-basin, we analyzed structural styles and sedimentary characteristics of the Liushagang sequence. Five types of structural styles were defined: ancient horst, traditional slope, flexure slope-break, faulted slope-break and multiple-stage faults slope, and interpretations for positions, background and development formations of each structural style were discussed. Structural framework across the sub-basin reveals that the most remarkable tectonic setting is represented by the central transfer zone (CTZ which divides the sub-basin into two independent depressions, and two kinds of sequence architectures are summarized: (i the western multi-stage faults slope; (ii the eastern flexure slope break belt. Combined with regional stress field of the Fushan Depression, we got plane combinations of the faults, and finally built up plan distribution maps of structural system for main sequence. Also, we discussed the controlling factors mainly focused on subsidence history and background tectonic activities such as volcanic activity and earthquakes. The analysis of structural styles and tectonic evolution provides strong theoretical support for future prospecting in the Fushan sub-basin and other similar rifted basins of the Beibuwan Basin in South China Sea.

  4. The Role of a Weak Layer at the Base of an Oceanic Plate on Subduction Dynamics

    Science.gov (United States)

    Carluccio, R.; Moresi, L. N.; Kaus, B. J. P.

    2017-12-01

    Plate tectonics relies on the concept of an effectively rigid lithospheric lid moving over a weaker asthenosphere. In this model, the lithosphere asthenosphere boundary (LAB) is a first-order discontinuity that accommodates differential motion between tectonic plates and the underlying mantle. Recent seismic studies have revealed the existence of a low velocity and high electrical conductivity layer at the base of subducting tectonic plates. This thin layer has been interpreted as being weak and slightly buoyant and it has the potential to influence the dynamics of subducting plates. However, geodynamically, the role of a weak layer at the base of the lithosphere remains poorly studied, especially at subduction zones. Here, we use numerical models to investigate the first-order effects of a weak buoyant layer at the LAB on subduction dynamics. We employ both 2-D and 3-D models in which the slab and the mantle are either linear viscous or have a more realistic temperature-dependent, visco-elastic-plastic rheology and we vary the properties of the layer at the base of the oceanic lithosphere. Our results show that the presence of a weak layer affects the dynamics of plates, primarily by increasing the subduction speed and also influences the morphology of subducting slab. For moderate viscosity contrasts (1000), it can also change the morphology of the subduction itself and for thinner and more buoyant layers, the overall effect is reduced. The overall impact of this effects may depend on the effective contrast between the properties of the slab and the weak layer + mantle systems, and so, by the layer characteristics modelled such as its viscosity, density, thickness and rheology. In this study, we show and summarise this impact consistently with the recent seismological constraints and observations, for example, a pile-up of weak material in the bending zone of the subducting plate.

  5. Tectonic Storytelling with Open Source and Digital Object Identifiers - a case study about Plate Tectonics and the Geopark Bergstraße-Odenwald

    Science.gov (United States)

    Löwe, Peter; Barmuta, Jan; Klump, Jens; Neumann, Janna; Plank, Margret

    2014-05-01

    The communication of advances in research to the common public for both education and decision making is an important aspect of scientific work. An even more crucial task is to gain recognition within the scientific community, which is judged by impact factor and citation counts. Recently, the latter concepts have been extended from textual publications to include data and software publications. This paper presents a case study for science communication and data citation. For this, tectonic models, Free and Open Source Software (FOSS), best practices for data citation and a multimedia online-portal for scientific content are combined. This approach creates mutual benefits for the stakeholders: Target audiences receive information on the latest research results, while the use of Digital Object Identifiers (DOI) increases the recognition and citation of underlying scientific data. This creates favourable conditions for every researcher as DOI names ensure citeability and long term availability of scientific research. In the developed application, the FOSS tool for tectonic modelling GPlates is used to visualise and manipulate plate-tectonic reconstructions and associated data through geological time. These capabilities are augmented by the Science on a Halfsphere project (SoaH) with a robust and intuitive visualisation hardware environment. The tectonic models used for science communication are provided by the AGH University of Science and Technology. They focus on the Silurian to Early Carboniferous evolution of Central Europe (Bohemian Massif) and were interpreted for the area of the Geopark Bergstraße Odenwald based on the GPlates/SoaH hardware- and software stack. As scientific story-telling is volatile by nature, recordings are a natural means of preservation for further use, reference and analysis. For this, the upcoming portal for audiovisual media of the German National Library of Science and Technology TIB is expected to become a critical service

  6. Tectonic and climatic considerations for deep geological disposal of radioactive waste: A UK perspective

    International Nuclear Information System (INIS)

    McEvoy, F.M.; Schofield, D.I.; Shaw, R.P.; Norris, S.

    2016-01-01

    Identifying and evaluating the factors that might impact on the long-term integrity of a deep Geological Disposal Facility (GDF) and its surrounding geological and surface environment is central to developing a safety case for underground disposal of radioactive waste. The geological environment should be relatively stable and its behaviour adequately predictable so that scientifically sound evaluations of the long-term radiological safety of a GDF can be made. In considering this, it is necessary to take into account natural processes that could affect a GDF or modify its geological environment up to 1 million years into the future. Key processes considered in this paper include those which result from plate tectonics, such as seismicity and volcanism, as well as climate-related processes, such as erosion, uplift and the effects of glaciation. Understanding the inherent variability of process rates, critical thresholds and likely potential influence of unpredictable perturbations represent significant challenges to predicting the natural environment. From a plate-tectonic perspective, a one million year time frame represents a very short segment of geological time and is largely below the current resolution of observation of past processes. Similarly, predicting climate system evolution on such time-scales, particularly beyond 200 ka AP is highly uncertain, relying on estimating the extremes within which climate and related processes may vary with reasonable confidence. The paper highlights some of the challenges facing a deep geological disposal program in the UK to review understanding of the natural changes that may affect siting and design of a GDF. - Highlights: • Natural processes are key to developing a safety case for geological disposal. • Key factors include plate tectonic and climate-mediated processes. • Process variability is a challenge to predicting the natural environment. • We highlight the challenges for geological disposal programs using

  7. Tectonic and climatic considerations for deep geological disposal of radioactive waste: A UK perspective

    Energy Technology Data Exchange (ETDEWEB)

    McEvoy, F.M., E-mail: fmcevoy@bgs.ac.uk [British Geological Survey, Keyworth, Nottingham NG12 5GG (United Kingdom); Schofield, D.I. [British Geological Survey, Tongwynlais, CF15 7NE (United Kingdom); Shaw, R.P. [British Geological Survey, Keyworth, Nottingham NG12 5GG (United Kingdom); Norris, S. [Radioactive Waste Management Limited, B587, Curie Avenue, Harwell, Didcot OX11 0RH (United Kingdom)

    2016-11-15

    Identifying and evaluating the factors that might impact on the long-term integrity of a deep Geological Disposal Facility (GDF) and its surrounding geological and surface environment is central to developing a safety case for underground disposal of radioactive waste. The geological environment should be relatively stable and its behaviour adequately predictable so that scientifically sound evaluations of the long-term radiological safety of a GDF can be made. In considering this, it is necessary to take into account natural processes that could affect a GDF or modify its geological environment up to 1 million years into the future. Key processes considered in this paper include those which result from plate tectonics, such as seismicity and volcanism, as well as climate-related processes, such as erosion, uplift and the effects of glaciation. Understanding the inherent variability of process rates, critical thresholds and likely potential influence of unpredictable perturbations represent significant challenges to predicting the natural environment. From a plate-tectonic perspective, a one million year time frame represents a very short segment of geological time and is largely below the current resolution of observation of past processes. Similarly, predicting climate system evolution on such time-scales, particularly beyond 200 ka AP is highly uncertain, relying on estimating the extremes within which climate and related processes may vary with reasonable confidence. The paper highlights some of the challenges facing a deep geological disposal program in the UK to review understanding of the natural changes that may affect siting and design of a GDF. - Highlights: • Natural processes are key to developing a safety case for geological disposal. • Key factors include plate tectonic and climate-mediated processes. • Process variability is a challenge to predicting the natural environment. • We highlight the challenges for geological disposal programs using

  8. Theoretical models for crustal displacement assessment and monitoring in Vrancea-Focsani seismic zone by integrated remote sensing and local geophysical data for seismic prognosis

    International Nuclear Information System (INIS)

    Zoran, Maria; Ciobanu, Mircea; Mitrea, Marius Gabriel; Talianu, Camelia; Cotarlan, Costel; Mateciuc, Doru; Radulescu, Florin; Biter Mircea

    2002-01-01

    The majority of strong Romanian earthquakes has the origin in Vrancea region. Subduction of the Black Sea Sub-Plate under the Pannonian Plate produces faulting processes. Crustal displacement identification and monitoring is very important for a seismically active area like Vrancea-Focsani. Earthquake displacements are very well revealed by satellite remote sensing data. At the same time, geomorphologic analysis of topographic maps is carried out and particularly longitudinal and transverse profiles are constructed, as well as structural-geomorphologic maps. Faults are interpreted by specific features in nature of relief, straightness of line of river beds and their tributaries, exits of springs, etc. Remote sensing analysis and field studies of active faults can provide a geologic history that overcomes many of the shortcomings of instrumental and historic records. Our theoretical models developed in the frame of this project are presented as follows: a) Spectral Mixture Analysis model of geomorphological and topographic characteristics for Vrancea region proposed for satellite images analysis which assumes that the different classes present in a pixel (image unit) contribute independently to its reflectance. Therefore, the reflectance of a pixel at a particular frequency is the sum of the reflectances of the components at that frequency. The same test region in Vrancea area is imaged at several different frequencies (spectral bands), leading to multispectral observations for each pixel. It is useful to merge different satellite data into a hybrid image with high spatial and spectral resolution to create detailed images map of the abundance of various materials within the scene based on material spectral fingerprint. Image fusion produces a high-resolution multispectral image that is then unmixed into high-resolution material maps. b) Model of seismic cross section analysis which is applied in seismic active zones morphology. Since a seismic section can be

  9. Update of the tectonic model for the Pannonian basin: a contribution to the seismic hazard reassessment of the Paks NPP (Hungary)

    Science.gov (United States)

    Horváth, Ferenc; Tóth, Tamás; Wórum, Géza; Koroknai, Balázs; Kádi, Zoltán; Kovács, Gábor; Balázs, Attila; Visnovitz, Ferenc

    2015-04-01

    The planned construction of two new units at the site of the Paks NPP requires a comprehensive site investigation including complete reassessment of the seismic hazard according to the Hungarian as well as international standards. Following the regulations of the Specific Safety Guide no. 9 (IAEA 2010), the approved Hungarian Geological Investigation Program (HGIP) includes integrated geological-geophysical studies at different scales. The regional study aims at to elaborate a new synthesis of all published data for the whole Pannonian basin. This task is nearly completed and the main outcomes have already been published (Horváth et al. 2015). The near regional study is in progress and addresses the construction of a new tectonic model for the circular area with 50 km radius around the NPP using a wealth of unpublished oil company seismic and borehole data. The site vicinity study has also been started with a core activity of 300 km² 3D seismic data acquisition, processing and interpretation assisted by a series of additional geophysical surveys, new drillings and geological mapping. This lecture will present a few important results of the near regional study, which sheds new light on the intricate tectonic evolution of the Mid-Hungarian Fault Zone (MHFZ), which is a strongly deformed belt between the Alcapa and Tisza-Dacia megatectonic units. The nuclear power plant is located at the margin of the Tisza unit near to the southern edge of the MHFZ. Reassessment of seismic hazard at the site of the NPP requires better understanding of the Miocene to Recent tectonic evolution of this region in the central part of the Pannonian basin. Early to Middle Miocene was a period of rifting with formation of 1 to 3 km deep half-grabens filled with terrestrial to marine deposits and large amount of rift-related volcanic material. Graben fill became strongly deformed as a consequence of juxtaposition of the two megatectonic units leading to strong compression and development of

  10. Scaling and spatial complementarity of tectonic earthquake swarms

    KAUST Repository

    Passarelli, Luigi

    2017-11-10

    Tectonic earthquake swarms (TES) often coincide with aseismic slip and sometimes precede damaging earthquakes. In spite of recent progress in understanding the significance and properties of TES at plate boundaries, their mechanics and scaling are still largely uncertain. Here we evaluate several TES that occurred during the past 20 years on a transform plate boundary in North Iceland. We show that the swarms complement each other spatially with later swarms discouraged from fault segments activated by earlier swarms, which suggests efficient strain release and aseismic slip. The fault area illuminated by earthquakes during swarms may be more representative of the total moment release than the cumulative moment of the swarm earthquakes. We use these findings and other published results from a variety of tectonic settings to discuss general scaling properties for TES. The results indicate that the importance of TES in releasing tectonic strain at plate boundaries may have been underestimated.

  11. Regional tectonics and seismicity of eastern Nebraska. Annual report, June 1, 1976--June 1, 1977

    International Nuclear Information System (INIS)

    Burchett, R.R.

    1978-03-01

    Several nuclear and fossil fuel plant site studies in Nebraska have been prepared by industry recently to evaluate seismic risk factors. These studies were prepared for the Nuclear Regulatory Commission (NRC) using available data to fill a lack of continuity across state lines. Therefore, it was proposed to the NRC that a detailed multi-state study of the Nemaha Ridge Area would be helpful in the site evaluation for present and future power plants. It was proposed to: (1) compile and coordinate the available seismo-tectonic data, (2) perform specific studies of potentially key locations for tectonic data, and (3) participate in an area wide microearthquake recording network. It was proposed to conduct a one year study during the period June 1, 1976 to June 1, 1977. After this initial study, continuation studies would be proposed over a several year period. Proposed products, during the initial year, would utilize existing data for the preparation of the following maps at a scale of 1 to 500,000; (1) Earthquake epicenter and intensity, (2) Precambrian configuration, (3) Precambrian rock type, (4) Bouguer gravity, (5) Aeromagnetic, (6) Bedrock geology, (7) Structural contour base Kansas City, (Pennsylvania), and (8) Surface lineations. All of these maps and possibly other maps in other areas could be recompiled and coordinated with adjoining areas on completion of the total study. During the initial year specific sites for detailed investigation would be identified. Portions of these studies may be carried out in cooperation with adjoining states. These site studies will include detailed geophysical surveys, laboratory analysis, dating of recent tectonic activity, core drilling programs, and field mapping projects

  12. Stagnant lid tectonics: Perspectives from silicate planets, dwarf planets, large moons, and large asteroids

    Directory of Open Access Journals (Sweden)

    Robert J. Stern

    2018-01-01

    Full Text Available To better understand Earth's present tectonic style–plate tectonics–and how it may have evolved from single plate (stagnant lid tectonics, it is instructive to consider how common it is among similar bodies in the Solar System. Plate tectonics is a style of convection for an active planetoid where lid fragment (plate motions reflect sinking of dense lithosphere in subduction zones, causing upwelling of asthenosphere at divergent plate boundaries and accompanied by focused upwellings, or mantle plumes; any other tectonic style is usefully called “stagnant lid” or “fragmented lid”. In 2015 humanity completed a 50+ year effort to survey the 30 largest planets, asteroids, satellites, and inner Kuiper Belt objects, which we informally call “planetoids” and use especially images of these bodies to infer their tectonic activity. The four largest planetoids are enveloped in gas and ice (Jupiter, Saturn, Uranus, and Neptune and are not considered. The other 26 planetoids range in mass over 5 orders of magnitude and in diameter over 2 orders of magnitude, from massive Earth down to tiny Proteus; these bodies also range widely in density, from 1000 to 5500 kg/m3. A gap separates 8 silicate planetoids with ρ = 3000 kg/m3 or greater from 20 icy planetoids (including the gaseous and icy giant planets with ρ = 2200 kg/m3 or less. We define the “Tectonic Activity Index” (TAI, scoring each body from 0 to 3 based on evidence for recent volcanism, deformation, and resurfacing (inferred from impact crater density. Nine planetoids with TAI = 2 or greater are interpreted to be tectonically and convectively active whereas 17 with TAI <2 are inferred to be tectonically dead. We further infer that active planetoids have lithospheres or icy shells overlying asthenosphere or water/weak ice. TAI of silicate (rocky planetoids positively correlates with their inferred Rayleigh number. We conclude that some type of stagnant lid tectonics is

  13. Micro-seismicity and seismotectonic study in Western Himalaya-Ladakh-Karakoram using local broadband seismic data

    Science.gov (United States)

    Kanna, Nagaraju; Gupta, Sandeep; Prakasam, K. S.

    2018-02-01

    We document the seismic activity and fault plane solutions (FPSs) in the Western Himalaya, Ladakh and Karakoram using data from 16 broadband seismographs operated during June 2002 to December 2003. We locate 206 earthquakes with a local magnitude in the range of 1.5 to 4.9 and calculate FPSs of 19 selected earthquakes based on moment tensor solutions. The earthquakes are distributed throughout the study region and indicate active tectonics in this region. The observed seismicity pattern is quite different than a well-defined pattern of seismicity, along the Main Central Thrust zone, in the eastern side of the study region (i.e., Kumaon-Garhwal Himalaya). In the Himalaya region, the earthquakes are distributed in the crust and upper mantle, whereas in the Ladakh-Karakoram area the earthquakes are mostly confined up to crustal depths. The fault plane solutions show a mixture of thrust, normal and strike-slip type mechanisms, which are well corroborated with the known faults/tectonics of the region. The normal fault earthquakes are observed along the Southern Tibet Detachment, Zanskar Shear Zone, Tso-Morari dome, and Kaurik-Chango fault; and suggest E-W extension tectonics in the Higher and Tethys Himalaya. The earthquakes of thrust mechanism with the left-lateral strike-slip component are seen along the Kistwar fault. The right-lateral strike-slip faulting with thrust component along the bending of the Main Boundary Thrust and Main Central Thrust shows the transpressional tectonics in this part of the Himalaya. The observed earthquakes with right-lateral strike-slip faulting indicate seismically active nature of the Karakoram fault.

  14. Structure and Deformation in the Transpressive Zone of Southern California Inferred from Seismicity, Velocity, and Qp Models

    Science.gov (United States)

    Hauksson, E.; Shearer, P.

    2004-12-01

    We synthesize relocated regional seismicity and 3D velocity and Qp models to infer structure and deformation in the transpressive zone of southern California. These models provide a comprehensive synthesis of the tectonic fabric of the upper to middle crust, and the brittle ductile transition zone that in some cases extends into the lower crust. The regional seismicity patterns in southern California are brought into focus when the hypocenters are relocated using the double difference method. In detail, often the spatial correlation between background seismicity and late Quaternary faults is improved as the hypocenters become more clustered, and the spatial patterns are more sharply defined. Along some of the strike-slip faults the seismicity clusters decrease in width and form alignments implying that in many cases the clusters are associated with a single fault. In contrast, the Los Angeles Basin seismicity remains mostly scattered, reflecting a 3D distribution of the tectonic compression. We present the results of relocating 327,000 southern California earthquakes that occurred between 1984 and 2002. In particular, the depth distribution is improved and less affected by layer boundaries in velocity models or other similar artifacts, and thus improves the definition of the brittle ductile transition zone. The 3D VP and VP/VS models confirm existing tectonic interpretations and provide new insights into the configuration of the geological structures in southern California. The models extend from the US-Mexico border in the south to the Coast Ranges and Sierra Nevada in the north, and have 15 km horizontal grid spacing and an average vertical grid spacing of 4 km, down to 22 km depth. The heterogeneity of the crustal structure as imaged in both the VP and VP/VS models is larger within the Pacific than the North America plate, reflecting regional asymmetric variations in the crustal composition and past tectonic processes. Similarly, the relocated seismicity is

  15. Seismic characterization of a `compound tectonic wedge` beneath the Rocky Mountain foreland basin, Alberta

    Energy Technology Data Exchange (ETDEWEB)

    Lawton, D. C.; Sukaramongkol, C.; Spratt, D. A. [Calgary Univ., AB (Canada). Dept. of Geology and Geophysics

    1996-06-01

    The detailed internal geometry of a `compound tectonic wedge` beneath an eastward-dipping homocline in the Sundre area of southern Alberta was described. Data for the description was obtained by interpreting reflection seismic data. The wedge has been driven into the foreland succession beneath the gently dipping upper detachment which occurs within coal horizons of the Upper Brazeau Group. Shape of the upper detachment near its toe indicates that rocks in its hanging wall were decoupled from strain associated with forward emplacement of the wedge. Folding of the upper detachment occurs in the hinterland region of the wedge, with a new upper detachment developing above the fold. Emplacement of the wedge is suspected to be the result of excess pore fluid pressure, although proof of this happening awaits quantification of the mechanical model. 25 refs., 8 figs.

  16. Plate tectonic regulation of global marine animal diversity

    Science.gov (United States)

    Zaffos, Andrew; Finnegan, Seth; Peters, Shanan E.

    2017-05-01

    Valentine and Moores [Valentine JW, Moores EM (1970) Nature 228:657-659] hypothesized that plate tectonics regulates global biodiversity by changing the geographic arrangement of continental crust, but the data required to fully test the hypothesis were not available. Here, we use a global database of marine animal fossil occurrences and a paleogeographic reconstruction model to test the hypothesis that temporal patterns of continental fragmentation have impacted global Phanerozoic biodiversity. We find a positive correlation between global marine invertebrate genus richness and an independently derived quantitative index describing the fragmentation of continental crust during supercontinental coalescence-breakup cycles. The observed positive correlation between global biodiversity and continental fragmentation is not readily attributable to commonly cited vagaries of the fossil record, including changing quantities of marine rock or time-variable sampling effort. Because many different environmental and biotic factors may covary with changes in the geographic arrangement of continental crust, it is difficult to identify a specific causal mechanism. However, cross-correlation indicates that the state of continental fragmentation at a given time is positively correlated with the state of global biodiversity for tens of millions of years afterward. There is also evidence to suggest that continental fragmentation promotes increasing marine richness, but that coalescence alone has only a small negative or stabilizing effect. Together, these results suggest that continental fragmentation, particularly during the Mesozoic breakup of the supercontinent Pangaea, has exerted a first-order control on the long-term trajectory of Phanerozoic marine animal diversity.

  17. Approaches that use seismic hazard results to address topics of nuclear power plant seismic safety, with application to the Charleston earthquake issue

    International Nuclear Information System (INIS)

    Sewell, R.T.; McGuire, R.K.; Toro, G.R.; Stepp, J.C.; Cornell, C.A.

    1990-01-01

    Plant seismic safety indicators include seismic hazard at the SSE (safe shut-down earthquake) acceleration, seismic margin, reliability against core damage, and reliability against offsite consequences. This work examines the key role of hazard analysis in evaluating these indicators and in making rational decisions regarding plant safety. The paper outlines approaches that use seismic hazard results as a basis for plant seismic safety evaluation and applies one of these approaches to the Charleston earthquake issue. This approach compares seismic hazard results that account for the Charleston tectonic interpretation, using the EPRI-Seismicity Owners Group (SOG) methodology, with hazard results that are consistent with historical tectonic interpretations accepted in regulation. Based on hazard results for a set of 21 eastern U.S. nuclear power plant sites, the comparison shows that no systematic 'plant-to-plant' increase in hazard accompanies the Charleston hypothesis; differences in mean hazards for the two interpretations are generally insignificant relative to current uncertainties in seismic hazard. (orig.)

  18. Tectonic lineaments in the Baltic from Gaevle to Simrishamn

    International Nuclear Information System (INIS)

    Floden, T.

    1977-12-01

    The present report deals with the tectonic pattern within the offshore area of middle and SE Sweden. The study is restricted to the large scale pattern that can be detected by seismic reflection profiling. Neotectonic events are discussed in connection with the special study of echosounding and seismic records from the Baltic Sea. This report is mainly based on investigations performed during the period 1966-1976 by means of continuous seismic reflection profiling. The investigations were mainly concentrated to areas with a sedimentary rock cover and thus, there is a large discrepance in the amount of available information between different parts of the Baltic. In the coastal zone, only those tectonic lineaments that are of importance for the understanding of the offshore conditions are included in the present maps. References to other known lineaments are made in the text

  19. Dinosaur tectonics

    DEFF Research Database (Denmark)

    Graversen, Ole; Milàn, Jesper; B. Loope, David

    2007-01-01

    A dinosaur trackway in the Middle Jurassic eolian Entrada Sandstone of southern Utah, USA, exposes three undertracks that we have modeled as isolated tectonic regimes showing the development of fold-thrust ramp systems induced by the dinosaur's feet. The faulted and folded sequence is comparable...... to crustal scale tectonics associated with plate tectonics and foreland fold-thrust belts. A structural analysis of the dinosaur tracks shows the timing and direction of the forces exercised on the substrate by the animal's foot during the stride. Based on the structural analysis, we establish a scenario...... the back. As the body accelerated, the foot was forced backward. The rotated disc was forced backward along a detachment fault that was bounded by lateral ramps. The interramp segment matches the width of the dinosaur's foot which created an imbricate fan thrust system that extended to the far end...

  20. Teaching Tectonics to Undergraduates with Web GIS

    Science.gov (United States)

    Anastasio, D. J.; Bodzin, A.; Sahagian, D. L.; Rutzmoser, S.

    2013-12-01

    Geospatial reasoning skills provide a means for manipulating, interpreting, and explaining structured information and are involved in higher-order cognitive processes that include problem solving and decision-making. Appropriately designed tools, technologies, and curriculum can support spatial learning. We present Web-based visualization and analysis tools developed with Javascript APIs to enhance tectonic curricula while promoting geospatial thinking and scientific inquiry. The Web GIS interface integrates graphics, multimedia, and animations that allow users to explore and discover geospatial patterns that are not easily recognized. Features include a swipe tool that enables users to see underneath layers, query tools useful in exploration of earthquake and volcano data sets, a subduction and elevation profile tool which facilitates visualization between map and cross-sectional views, drafting tools, a location function, and interactive image dragging functionality on the Web GIS. The Web GIS platform is independent and can be implemented on tablets or computers. The GIS tool set enables learners to view, manipulate, and analyze rich data sets from local to global scales, including such data as geology, population, heat flow, land cover, seismic hazards, fault zones, continental boundaries, and elevation using two- and three- dimensional visualization and analytical software. Coverages which allow users to explore plate boundaries and global heat flow processes aided learning in a Lehigh University Earth and environmental science Structural Geology and Tectonics class and are freely available on the Web.

  1. Tectonic predictions with mantle convection models

    Science.gov (United States)

    Coltice, Nicolas; Shephard, Grace E.

    2018-04-01

    Over the past 15 yr, numerical models of convection in Earth's mantle have made a leap forward: they can now produce self-consistent plate-like behaviour at the surface together with deep mantle circulation. These digital tools provide a new window into the intimate connections between plate tectonics and mantle dynamics, and can therefore be used for tectonic predictions, in principle. This contribution explores this assumption. First, initial conditions at 30, 20, 10 and 0 Ma are generated by driving a convective flow with imposed plate velocities at the surface. We then compute instantaneous mantle flows in response to the guessed temperature fields without imposing any boundary conditions. Plate boundaries self-consistently emerge at correct locations with respect to reconstructions, except for small plates close to subduction zones. As already observed for other types of instantaneous flow calculations, the structure of the top boundary layer and upper-mantle slab is the dominant character that leads to accurate predictions of surface velocities. Perturbations of the rheological parameters have little impact on the resulting surface velocities. We then compute fully dynamic model evolution from 30 and 10 to 0 Ma, without imposing plate boundaries or plate velocities. Contrary to instantaneous calculations, errors in kinematic predictions are substantial, although the plate layout and kinematics in several areas remain consistent with the expectations for the Earth. For these calculations, varying the rheological parameters makes a difference for plate boundary evolution. Also, identified errors in initial conditions contribute to first-order kinematic errors. This experiment shows that the tectonic predictions of dynamic models over 10 My are highly sensitive to uncertainties of rheological parameters and initial temperature field in comparison to instantaneous flow calculations. Indeed, the initial conditions and the rheological parameters can be good enough

  2. Dependence of Subduction Zone seismicity on Strain-Rate-Dependent Critical Homologous Temperature

    Science.gov (United States)

    Davis, P. M.

    2016-12-01

    Earthquakes mainly occur in crust or mantle that is below a critical temperature for the tectonic strain-rate, such that stress builds up to the breaking point before it can relax due to creep. Then long-range stress correlation gives rise to power law seismicity with large events. The limiting temperature depends on pressure, which is taken into account by finding a critical homologous temperature THc=T/TM above which earthquakes are rarely observed. We find that THc for ocean plates is ˜0.55. For California earthquakes, it is also close to 0.55. The uppermost mantle layer of oceanic plates of thickness ˜50 km is composed of harzburgite and depleted peridotite from which basalt has been removed to form ocean crust. Thus it has a higher melting temperature than the peridotite of the surrounding mantle, or the lower halves of plates. Thicknesses of seismicity in deep subduction zones, determined from 2D polynomial fits to a relocated catalog, are ˜50 km, which suggests that the earthquake channel is confined to this layer. We construct models to find homologous temperatures in slabs, and find that seismicity thicknesses are also, on average, confined to TH ≤ 0.55 ± 0.05. The associated rheology is compared with that obtained from flexure models of ocean lithosphere. The brittle-ductile transition occurs where viscosity drops from high values in the cold cores of slabs to values of 1022 to $1023 Pa s, i.e., where creep strain-rates become comparable to tectonic rates. The cutoff for deep earthquakes is not sharp. However they appear unlikely to occur if homologous temperature is high TH>0.55. Exceptions to the rule are anomalously deep earthquakes such as those beneath the Iceland and the Hawaiian hotspots, and the Newport Inglewood Fault. These are smaller events with short-range stress correlation, and can be explained if strain-rates are 2 to 3 orders of magnitude higher than those associated with earthquakes located where TH ≤0.55. We conclude that the

  3. Tectonic tremor

    Science.gov (United States)

    Shelly, David R.

    2016-01-01

    Tectonic, non-volcanic tremor is a weak vibration of ground, which cannot be felt by humans but can be detected by sensitive seismometers. It is defined empirically as a low-amplitude, extended duration seismic signal associated with the deep portion (∼20–40 km depth) of some major faults. It is typically observed most clearly in the frequency range of 2–8 Hz and is depleted in energy at higher frequencies relative to regular earthquakes.

  4. The seismic cycle at subduction thrusts: 1. Insights from laboratory models

    KAUST Repository

    Corbi, F.; Funiciello, F.; Moroni, M.; van Dinther, Y.; Mai, Paul Martin; Dalguer, L. A.; Faccenna, C.

    2013-01-01

    Subduction megathrust earthquakes occur at the interface between the subducting and overriding plates. These hazardous phenomena are only partially understood because of the absence of direct observations, the restriction of the instrumental seismic record to the past century, and the limited resolution/completeness of historical to geological archives. To overcome these restrictions, modeling has become a key-tool to study megathrust earthquakes. We present a novel model to investigate the seismic cycle at subduction thrusts using complementary analog (paper 1) and numerical (paper 2) approaches. Here we introduce a simple scaled gelatin-on-sandpaper setup including realistic tectonic loading, spontaneous rupture nucleation, and viscoelastic response of the lithosphere. Particle image velocimetry allows to derive model deformation and earthquake source parameters. Analog earthquakes are characterized by “quasi-periodic” recurrence. Consistent with elastic theory, the interseismic stage shows rearward motion, subsidence in the outer wedge and uplift of the “coastal area” as a response of locked plate interface at shallow depth. The coseismic stage exhibits order of magnitude higher velocities and reversal of the interseismic deformation pattern in the seaward direction, subsidence of the coastal area, and uplift in the outer wedge. Like natural earthquakes, analog earthquakes generally nucleate in the deeper portion of the rupture area and preferentially propagate upward in a crack-like fashion. Scaled rupture width-slip proportionality and seismic moment-duration scaling verifies dynamic similarities with earthquakes. Experimental repeatability is statistically verified. Comparing analog results with natural observations, we conclude that this technique is suitable for investigating the parameter space influencing the subduction interplate seismic cycle.

  5. The seismic cycle at subduction thrusts: 1. Insights from laboratory models

    KAUST Repository

    Corbi, F.

    2013-04-01

    Subduction megathrust earthquakes occur at the interface between the subducting and overriding plates. These hazardous phenomena are only partially understood because of the absence of direct observations, the restriction of the instrumental seismic record to the past century, and the limited resolution/completeness of historical to geological archives. To overcome these restrictions, modeling has become a key-tool to study megathrust earthquakes. We present a novel model to investigate the seismic cycle at subduction thrusts using complementary analog (paper 1) and numerical (paper 2) approaches. Here we introduce a simple scaled gelatin-on-sandpaper setup including realistic tectonic loading, spontaneous rupture nucleation, and viscoelastic response of the lithosphere. Particle image velocimetry allows to derive model deformation and earthquake source parameters. Analog earthquakes are characterized by “quasi-periodic” recurrence. Consistent with elastic theory, the interseismic stage shows rearward motion, subsidence in the outer wedge and uplift of the “coastal area” as a response of locked plate interface at shallow depth. The coseismic stage exhibits order of magnitude higher velocities and reversal of the interseismic deformation pattern in the seaward direction, subsidence of the coastal area, and uplift in the outer wedge. Like natural earthquakes, analog earthquakes generally nucleate in the deeper portion of the rupture area and preferentially propagate upward in a crack-like fashion. Scaled rupture width-slip proportionality and seismic moment-duration scaling verifies dynamic similarities with earthquakes. Experimental repeatability is statistically verified. Comparing analog results with natural observations, we conclude that this technique is suitable for investigating the parameter space influencing the subduction interplate seismic cycle.

  6. Evidence of a plate-wide tectonic pressure pulse provided by extensometric monitoring in the Balkan Mountains (Bulgaria)

    Czech Academy of Sciences Publication Activity Database

    Briestenský, Miloš; Rowberry, Matthew David; Stemberk, Josef; Stefanov, P.; Vozár, J.; Šebela, S.; Petro, L.; Bella, P.; Gaal, L.; Ormukov, Ch.

    2015-01-01

    Roč. 66, č. 5 (2015), s. 427-438 ISSN 1335-0552 R&D Projects: GA MŠk LM2010008; GA MŠk OC 625.10; GA ČR GA205/05/2770; GA ČR GA205/06/1828; GA ČR GA205/09/2024 Institutional support: RVO:67985891 Keywords : Eurasian Plate * Balkan Peninsula * active tectonics research * aseismic transient deformations * slow-slip phenomena Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 1.523, year: 2015 http://www.geologicacarpathica.com/browse-journal/volumes/66-5/article-780

  7. Seismic risk assessment for road in Indonesia

    Science.gov (United States)

    Toyfur, Mona Foralisa; Pribadi, Krishna S.

    2016-05-01

    Road networks in Indonesia consist of 446,000 km of national, provincial and local roads as well as toll highways. Indonesia is one of countries that exposed to various natural hazards, such as earthquakes, floods, landslides, etc. Within the Indonesian archipelago, several global tectonic plates interact, such as the Indo-Australian, Pacific, Eurasian, resulting in a complex geological setting, characterized by the existence of seismically active faults and subduction zones and a chain of more than one hundred active volcanoes. Roads in Indonesia are vital infrastructure needed for people and goods movement, thus supporting community life and economic activities, including promoting regional economic development. Road damages and losses due to earthquakes have not been studied widely, whereas road disruption caused enormous economic damage. The aim of this research is to develop a method to analyse risk caused by seismic hazard to roads. The seismic risk level of road segment is defined using an earthquake risk index, adopting the method of Earthquake Disaster Risk Index model developed by Davidson (1997). Using this method, road segments' risk level can be defined and compared, and road risk map can be developed as a tool for prioritizing risk mitigation programs for road networks in Indonesia.

  8. MIGRATION OF SEISMIC AND VOLCANIC ACTIVITY AS DISPLAY OF WAVE GEODYNAMIC PROCESS

    Directory of Open Access Journals (Sweden)

    Alexander V. Vikulin

    2012-01-01

    Full Text Available Publications about the earthquake foci migration have been reviewed. An important result of such studies is establishment of wave nature of seismic activity migration that is manifested by two types of rotational waves; such waves are responsible for interaction between earthquakes foci and propagate with different velocities. Waves determining long-range interaction of earthquake foci are classified as Type 1; their limiting velocities range from 1 to 10 cm/s. Waves determining short-range interaction of foreshocks and aftershocks of individual earthquakes are classified as Type 2; their velocities range from 1 to 10 km/s. According to the classification described in [Bykov, 2005], these two types of migration waves correspond to slow and fast tectonic waves. The most complete data on earthquakes (for a period over 4.1 million of years and volcanic eruptions (for 12 thousand years of the planet are consolidated in a unified systematic format and analyzed by methods developed by the authors. For the Pacific margin, Alpine-Himalayan belt and the Mid-Atlantic Ridge, which are the three most active zones of the Earth, new patterns of spatial and temporal distribution of seismic and volcanic activity are revealed; they correspond to Type 1 of rotational waves. The wave nature of the migration of seismic and volcanic activity is confirmed. A new approach to solving problems of geodynamics is proposed with application of the data on migration of seismic and volcanic activity, which are consolidated in this study, in combination with data on velocities of movement of tectonic plate boundaries. This approach is based on the concept of integration of seismic, volcanic and tectonic processes that develop in the block geomedium and interact with each other through rotating waves with a symmetric stress tensor. The data obtained in this study give grounds to suggest that a geodynamic value, that is mechanically analogous to an impulse

  9. New interpretations based on seismic and modelled well data and their implications for the tectonic evolution of the west Greenland continental margin

    DEFF Research Database (Denmark)

    Mcgregor, E.D.; Nielsen, S.B.; Stephenson, R.A.

    Davis Strait is situated between Baffin Island and Greenland and forms part of a sedimentary basin system, linking Labrador Sea and Baffin Bay, developed during Cretaceous and Palaeocene rifting that culminated in a brief period of sea-floor spreading in the late Palaeocene and Eocene. Seismic...... reflection profiles and exploration wells along the Greenland margin of Davis Strait have been analysed in order to elucidate uplift events affecting sedimentary basin development during the Cenozoic with a focus on postulated Neogene (tectonic) uplift affecting the west Greenland continental margin...... tectonic event. An interpretation in which the inferred onshore cooling is related to erosion of pre-existing topography is more consistent with our new results from the offshore region. These results will have important implications for other continental margins developed throughout the Atlantic...

  10. New seismic sources parameterization in El Salvador. Implications to seismic hazard.

    OpenAIRE

    Alonso-Henar, Jorge; Staller, A.; Martínez Díaz, José J.; Benito, Belén; Álvarez Gómez, José Antonio; Canora Catalán, Carolina

    2014-01-01

    El Salvador is located at the pacific active margin of Central America, here, the subduction of the Cocos Plate under the Caribbean Plate at a rate of 80 mm/yr is the main seismic source. Although the seismic sources located in the Central American Volcanic Arc have been responsible for some of the most damaging earthquakes in El Salvador. The El Salvador Fault Zone is the main geological structure in El Salvador and accommodates 14 mm/yr of horizontal displacement between the Caribbean Plate...

  11. Relocation of earthquakes at southwestern Indian Ocean Ridge and its tectonic significance

    Science.gov (United States)

    Luo, W.; Zhao, M.; Haridhi, H.; Lee, C. S.; Qiu, X.; Zhang, J.

    2015-12-01

    The southwest Indian Ridge (SWIR) is a typical ultra-slow spreading ridge (Dick et al., 2003) and further plate boundary where the earthquakes often occurred. Due to the lack of the seismic stations in SWIR, positioning of earthquakes and micro-earthquakes is not accurate. The Ocean Bottom Seismometers (OBS) seismic experiment was carried out for the first time in the SWIR 49 ° 39 'E from Jan. to March, 2010 (Zhao et al., 2013). These deployed OBS also recorded the earthquakes' waveforms during the experiment. Two earthquakes occurred respectively in Feb. 7 and Feb. 9, 2010 with the same magnitude of 4.4 mb. These two earthquakes were relocated using the software HYPOSAT based on the spectrum analysis and band-pass (3-5 Hz) filtering and picking up the travel-times of Pn and Sn. Results of hypocentral determinations show that there location error is decreased significantly by joined OBS's recording data. This study do not only provide the experiences for the next step deploying long-term wide-band OBSs, but also deepen understanding of the structure of SWIR and clarify the nature of plate tectonic motivation. This research was granted by the Natural Science Foundation of China (41176053, 91028002, 91428204). Keywords: southwest Indian Ridge (SWIR), relocation of earthquakes, Ocean Bottom Seismometers (OBS), HYPOSAT References:[1] Dick, H. J. B., Lin J., Schouten H. 2003. An ultraslow-spreading class of ocean ridge. Nature, 426(6965): 405-412. [2] Zhao M. H., et al. 2013. Three-dimensional seismic structure of the Dragon Flag oceanic core complex at the ultraslow spreading Southwest Indian Ridge (49°39' E). Geochemistry Geophysics Geosystems, 14(10): 4544-4563.

  12. Seismic hazard assessment of the Three Gorges Project

    Directory of Open Access Journals (Sweden)

    Yao Yunsheng

    2013-05-01

    Full Text Available Seismic monitoring data for the past 50 years in the Three Gorges Reservoir area show that the reservoir head area is a typical weak seismic region with low seismicity before impoundment and that the epicenters were concentrated in the east and west sides of the Zigui Basin, most of which were natural tectonic earthquakes. After impoundment, the seismic activity shifted to the segment between Badong and Zigui along the Yangtze River, mainly within 5 km of the reservoir bank. The seismogenesis was categorized into four types; Karst collapse earthquakes, earthquakes caused by Karst gas explosion, mining tunnel collapse earthquakes, and rock (terrane slip earthquakes, all of which are related to the lithology, structure, and tectonics of near-surface geological bodies of the area. Compared with the seismicity before impoundment, the seismic frequency increase was remarkable, with most of the magnitudes below Ms2. 0. Therefore, the intensity of the earthquakes remained at a low level. On November 22, 2008, a magnitude 4. 1 earthquake, the largest earthquake recorded since impoundment, occurred in Quyuan Town, Zigui County. The intensity and PGA of reservoir-induced earthquakes are higher than those of tectonic earthquakes with equal magnitude, but the peak intensity of reservoir-induced earthquakes is not likely to go beyond that of the estimated range from earlier studies.

  13. Stationary levitation and vibration transmission characteristic in a superconducting seismic isolation device with a permanent magnet system and a copper plate

    Energy Technology Data Exchange (ETDEWEB)

    Sasaki, S., E-mail: s.sasaki@ecei.tohoku.ac.j [Electrical Engineering Department, Graduate School, Tohoku University, 6-6-05 Aoba Aramaki, Aoba-ku, Sendai, Miyagi 980-8579 (Japan); Shimada, K.; Yagai, T.; Tsuda, M.; Hamajima, T. [Electrical Engineering Department, Graduate School, Tohoku University, 6-6-05 Aoba Aramaki, Aoba-ku, Sendai, Miyagi 980-8579 (Japan); Kawai, N.; Yasui, K. [Okumura Corporation, 5-6-1 Shiba, Minato-ku, Tokyo 180-8381 (Japan)

    2010-11-01

    We have devised a magnetic levitation type superconducting seismic isolation device taking advantage of the specific characteristic of HTS bulk that the HTS bulk returns to its original position by restoring force against a horizontal displacement. The superconducting seismic isolation device is composed of HTS bulks and permanent magnets (PM rails). The PMs are fixed on an iron plate to realize the same polarities in the longitudinal direction and the different polarities in the transverse direction. The superconducting seismic isolation device can theoretically remove any horizontal vibrations completely. Therefore, the vibration transmissibility in the longitudinal direction of the PM rail becomes zero in theory. The zero vibration transmissibility and the stationary levitation, however, cannot be achieved in the real device because a uniform magnetic field distribution in the longitudinal direction of PM rail cannot be realized due to the individual difference of the PMs. Therefore, to achieve stationary levitation in the real device we adopted a PM-PM system that the different polarities are faced each other. The stationary levitation could be achieved by the magnetic interaction between the PMs in the PM-PM system, while the vibration transmitted to the seismic isolation object due to the magnetic interaction. We adopted a copper plate between the PMs to reduce the vibration transmissibility. The PM-PM system with the copper plate is very useful for realizing the stationary levitation and reducing the vibration transmissibility.

  14. Stationary levitation and vibration transmission characteristic in a superconducting seismic isolation device with a permanent magnet system and a copper plate

    International Nuclear Information System (INIS)

    Sasaki, S.; Shimada, K.; Yagai, T.; Tsuda, M.; Hamajima, T.; Kawai, N.; Yasui, K.

    2010-01-01

    We have devised a magnetic levitation type superconducting seismic isolation device taking advantage of the specific characteristic of HTS bulk that the HTS bulk returns to its original position by restoring force against a horizontal displacement. The superconducting seismic isolation device is composed of HTS bulks and permanent magnets (PM rails). The PMs are fixed on an iron plate to realize the same polarities in the longitudinal direction and the different polarities in the transverse direction. The superconducting seismic isolation device can theoretically remove any horizontal vibrations completely. Therefore, the vibration transmissibility in the longitudinal direction of the PM rail becomes zero in theory. The zero vibration transmissibility and the stationary levitation, however, cannot be achieved in the real device because a uniform magnetic field distribution in the longitudinal direction of PM rail cannot be realized due to the individual difference of the PMs. Therefore, to achieve stationary levitation in the real device we adopted a PM-PM system that the different polarities are faced each other. The stationary levitation could be achieved by the magnetic interaction between the PMs in the PM-PM system, while the vibration transmitted to the seismic isolation object due to the magnetic interaction. We adopted a copper plate between the PMs to reduce the vibration transmissibility. The PM-PM system with the copper plate is very useful for realizing the stationary levitation and reducing the vibration transmissibility.

  15. Plate flexure and volcanism: Late Cenozoic tectonics of the Tabar-Lihir-Tanga-Feni alkalic province, New Ireland Basin, Papua New Guinea

    Science.gov (United States)

    Lindley, I. D.

    2016-05-01

    Late Cenozoic Tabar-Lihir-Tanga-Feni (TLTF) alkaline volcanism, New Ireland Basin, PNG, is associated with extensional cracks along the crests of flexed ridges developed on the New Ireland Microplate (New name). The tectonic alignment of the TLTF volcanic arc is essentially perpendicular to the flexed ridges, suggesting that fractures parallel to the direction of maximum horizontal compression facilitated the rapid ascent of alkaline magmas from the mantle region, perhaps 60-70 km depth. The mainly Pliocene to Pleistocene volcanoes were localized at the intersection of ridge-parallel Kabang structures and arc-parallel Niffin structures, suggesting that the Kabang-Niffin structural intersections underlying each of the TLTF island groups provided a well developed, clustered network of open conduits which tapped the mantle source region. Periodic post-Miocene locking and unlocking along the strike-slip Kilinailau Fault (New name) are thought to have functioned as a valve, turning on (Pliocene) and then turning off (Pleistocene) volcanic activity, respectively. Partial locking of the Kilinailau Fault during the Pliocene resulted in the accumulation of intraplate stresses within the New Ireland Microplate, and caused plate flexure and ridge development, plate-cracking along ridge crests and the development of arc-parallel regional fractures parallel to the direction of maximum compression. Unlocking of the Kilinailau Fault in the Pleistocene resulted in the release of intraplate stresses in the New Ireland Microplate and a cessation of volcanic activity across most of the TLTF arc. The style and scale of plate flexure and cracking, accompanied by within-plate alkaline volcanism from equally spaced ridge-top eruptive centers confined to a narrow, linear volcanic arc are unknown from any other tectonic province.

  16. Tectonic context of the penetrative fracture system origin in the Early Paleozoic shale complex (Baltic Basin, Poland/Sweden).

    Science.gov (United States)

    Jarosiński, Marek; Gluszynski, Andrzej; Bobek, Kinga; Dyrka, Ireneusz

    2017-04-01

    Characterization of natural fracture and fault pattern play significant role for reservoir stimulation design and evaluation of its results. Having structural observations limited to immediate borehole surrounding it is a common need to build up a fracture model of reservoir in a range of stimulation reservoir volume or even beyond. To do this we need both a 3D seismic model and a consistent concept of the regional tectonic evolution. We present the result of integrated tectonic study in several deep boreholes target the Lower Paleozoic shale complex of Baltic Basin (BB), combined with analysis of 3D seismic survey and outcrop screening in Scania (Swedish part of the BB). During deposition of shale complex in the Ordovician and Silurian the research area was located 200-300 km away from the continental margin of Baltica involved in the Caledonian collision with the Eastern Avalonia. This distance allowed the shale complex to avoid significant tectonic deformation. Regional seismic cross section reveals the general pattern of the BB infill characteristic for the foreland basin underwent post-collisional isostatic rebound. Due to stress changes in collisional context the shale complex was cross-cut by steep, mostly inverse faults trending NW-SE and NE-SW. The fault zones oriented NW-SE are associated with an array of en echelon faults characteristic for strike-slip displacement. In our interpretation, these faults of Silurian (Wenlock) age create pattern of the regional pop-up structure, which is simultaneously involved in the plate flexure extension. Seismic attributes (e.g. curvature or ant tracking) highlight lineaments which mostly mimic the faults orientation. However, attributes show also some artefacts that come from regular array of seismic sources and receivers, which mimic the orthogonal joint system. Structural observations on borehole core lead us to conclusion that regular, orthogonal fracture system developed after maximum burial of the complex

  17. Microseismicity, tectonics and seismic potential in the Western Himalayan segment, NW Himalaya, India

    Science.gov (United States)

    Parija, Mahesh Prasad; Kumar, Sushil; Tiwari, V. M.; Rao, N. Purnachandra; Kumar, Narendra; Biswal, Shubhasmita; Singh, Ishwar

    2018-06-01

    The tectonics and seismic potential of the western Himalayan segment (30-33°N; 76-80°E) of the NW Himalayan (India) region have been determined in this study. 423 earthquakes were located in the NW Himalaya between 2004 and 2013 using more than 4495 P and 4453 S differential travel times to determine the moment tensors for 8 (Mw ≥ 4.0) of these earthquakes using their broadband regional waveforms. The geometry of the Main Himalayan Thrust (MHT) plane which varies along the strike of the Himalaya in flat and ramp segments with a dip ranging between ∼2.5 to ∼4° to ∼19° below the Himalayan Frontal Thrust (HFT) in the south to the South Tibetan Detachment (STD) in the north has also been deduced in this study. Two crustal ramps were reported in this study with a depth variance below the Main Central Thrust (MCT) and to the South Tibetan Detachment (STD) between 12 to 22 km and 28 to 40 km depth respectively. The estimated earthquake potential prevailing in the western Himalayan seismic gap lying between the epicentral zone of the 1905 Kangra earthquake and the 1975 Kinnaur earthquake reveals that the total amount of energy released since the last great event is only a fraction (3-5%) of the accommodated energy i.e.1.1E+28 dyne-cm/yr. This suggests that if an earthquake hits this NW Himalayan segment in the future, its magnitude might be around Mw ≥ 8.0.

  18. Cenozoic intraplate tectonics in Central Patagonia: Record of main Andean phases in a weak upper plate

    Science.gov (United States)

    Gianni, G. M.; Echaurren, A.; Folguera, A.; Likerman, J.; Encinas, A.; García, H. P. A.; Dal Molin, C.; Valencia, V. A.

    2017-11-01

    Contraction in intraplate areas is still poorly understood relative to similar deformation at plate margins. In order to contribute to its comprehension, we study the Patagonian broken foreland (PBF) in South America whose evolution remains controversial. Time constraints of tectonic events and structural characterization of this belt are limited. Also, major causes of strain location in this orogen far from the plate margin are enigmatic. To unravel tectonic events, we studied the Cenozoic sedimentary record of the central sector of the Patagonian broken foreland (San Bernardo fold and thrust belt, 44°30‧S-46°S) and the Andes (Meseta de Chalia, 46°S) following an approach involving growth-strata detection, U-Pb geochronology and structural modeling. Additionally, we elaborate a high resolution analysis of the effective elastic thickness (Te) to examine the relation between intraplate contraction location and variations in lithospheric strength. The occurrence of Eocene growth-strata ( 44-40 Ma) suggests that contraction in the Andes and the Patagonian broken foreland was linked to the Incaic phase. Detection of synextensional deposits suggests that the broken foreland collapsed partially during Oligocene to early Miocene. During middle Miocene times, the Quechua contractional phase produced folding of Neogene volcanic rocks and olistostrome deposition at 17 Ma. Finally, the presented Te map shows that intraplate contraction related to Andean phases localized preferentially along weak lithospheric zones (Te < 15 km). Hence, the observed strain distribution in the PBF appears to be controlled by lateral variations in the lithospheric strength. Variations in this parameter could be related to thermo-mechanical weakening produced by intraplate rifting in Paleozoic-Mesozoic times.

  19. Seismic Tomography of the Northwest Himalayas, Western Syntaxis and Pamir-Hindu Kush Region: Implications for Underlying Geodynamics

    Science.gov (United States)

    Raoof, J.; Mukhopadhyay, S.

    2017-12-01

    Travel time tomography of the study region using regional as well as local earthquake data illuminate a very heterogeneous structure of this geologically and tectonically complex region. The tomographic image is well resolved up to 150 km depth in the Western Himalayas and up to 300 km depth in the Pamir and Hindu Kush region. The top low velocity anomaly imaged up to 80 km depth correlates well with the thicker crust with deeper low density roots under the high mountains in the northwest Himalayas as well as in the Pamir and Hindu Kush region. Average crustal thickness increases from south to north in the Himalayas as well as along the tectonic trend of the Himalayas. This might be an effect of first collision between Indian and Eurasian plates in the NW and then subsequent anticlockwise rotation of Indian plate, leading to crumpling of the crust. This could also be due to variable thickness of more rigid portion of the incoming crust of Indian plate. The Indian lithospheric slab is imaged as a gently underthrusting high velocity anomaly under the northwest Himalayas and subducted Indian lithospheric slab which follows the trend of intermediate depth seismicity under the Pamir and Hindu Kush region. On the other hand beneath the Pamir-Tien Shan the dipping high velocity anomaly which follows the trend of intermediate depth seismicity, represents the remnant of the southward subducted Asian slab. In the southwest of Hindu Kush the Indian lithospheric slab rolls over and overturns at a depth of 250 km and dips southward. The Delhi-Haridwar Ridge (DHR) and Salt Ranges orthogonal to the strike of the Himalayas are well imaged as high velocity structures. The DHR is butting against the northwest Himalayas that led to ramming and locally buckling of the crust below the Higher Himalayas just NE of DHR. Seismicity pattern follows this trend of the crust. It shows for the first time the effect of ramming of the Himalayas by DHR and most importantly how the Indian plate

  20. Anatomy of the Java plate interface from depth-migrated seismic images: Implications for sediment transfer

    Science.gov (United States)

    Kopp, H.; Hindle, D.; Klaeschen, D.; Oncken, O.; Reichert, C.; Scholl, D.

    2008-12-01

    We present seismic data from the western Java margin off Indonesia. The newly pre-stack depth migrated seismic images resolve the structural details of the western Java forearc and the fate of sediment subducted at the trench. Approximately 2/3 of the trench sediment fill is detached and incorporated into frontal prism imbricates, while the floor sequence is transported down a subduction channel. Basal mass transfer occurs by episodic accretion of sediment beneath the submerged forearc as the active detachment stepwise descends to a deeper level below the outer wedge. Fluctuations in subduction channel dimensions are enhanced by deep-reaching thrust faults that are traced from a velocity singularity marking the top of the oceanic basement towards the seafloor. These thrust faults breach the subduction channel and inhibit recycling of material to mantle depth, while serving as an incremental ramp along which the active detachment is transferred to a lower position. The high ratio of accreted/subducted sediment is associated with the evolution of a large bivergent wedge (>100 km) despite the comparatively low sediment input to the trench (<2 km). We used quantitative DEM modeling to gain some insight into the evolution of the distinct tectonic units. In the modelling, initiation of sediment accretion occurs against the arc rock framework, which is imaged in the MCS data. Overthrusting of the wedge onto the forearc basin is also expressed in a prominent retro-thrust imaged in the seismic data. The seismic data document an end-member type of subduction zone where near-complete accretion of the trench sediment fill by frontal and basal accretion is supported by the lack of evidence for subducted sediment in the geochemical signature of Mt. Guntur and Mt. Gallunggung, two volcanoes positioned in the prolongation of our seismic line on Java.

  1. Surveys on environmental tectonics. Special volume.

    NARCIS (Netherlands)

    Cloetingh, S.A.P.L.; Cornu, T.

    2005-01-01

    Until now, research on neotectonics and related seismicity has mostly focused on active plate boundaries characterized by generally high earthquake activity. Current seismic hazard estimates for intraplate areas are commonly based on probabilistic analyses of historical and instrumental earthquake

  2. Seismic structure and tectonics of the Alasehir--Gediz Graben, Western Turkey

    Science.gov (United States)

    Turk, Sezer

    The Aegean Extensional Province (AEP) in Western Anatolia includes three major graben systems that have formed as a result of N-S tectonic extension in the latest Cenozoic. The 6 to 30-km-wide Alasehir--Gediz Graben (AGG) in the north contains ˜3-km-thick Miocene and Plio-Quaternary, alluvial--fluvial and lacustrine sedimentary rocks. I have used seismic profiles, well-log data and the regional stratigraphy to identify the key stratigraphic units, their bounding surfaces and vertical thicknesses, and to document the subsurface structural architecture of the AGG. A north-dipping detachment fault exposed in the southern shoulder of the AGG basin occurs at 2--2.5 km at depth beneath the graben fill, and is dissected by ˜E--W--striking, synthetic to antithetic, high-angle normal faults. The graben system is crosscut by NNE-oriented cross faults, showing several km of recurrence interval and 10s of meters of vertical displacement. These faults divide the graben into several sub-basins and display positive and negative flower structures. The structural architecture in the sub-basins shows important variations in stratigraphic thicknesses, fault geometry-displacement and deformation patterns, indicating that cross faulting played a critical role in the evolution of the AAG.

  3. Structure of the Lithosphere-Asthenosphere Boundary Onshore and Offshore the California Continental Margin from Three-Dimensional Seismic Anisotropy

    Science.gov (United States)

    Gomez, C. D.; Escobar, L., Sr.; Rathnayaka, S.; Weeraratne, D. S.; Kohler, M. D.

    2016-12-01

    The California continental margin, a major transform plate boundary in continental North America, is the locus of complex tectonic stress fields that are important in interpreting both remnant and ongoing deformational strain. Ancient subduction of the East Pacific Rise spreading center, the rotation and translation of tectonic blocks and inception of the San Andreas fault all contribute to the dynamic stress fields located both onshore and offshore southern California. Data obtained by the ALBACORE (Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment) and the CISN (California Integrated Seismic Network) seismic array are analyzed for azimuthal anisotropy of Rayleigh waves from 80 teleseismic events at periods 16 - 78 s. Here we invert Rayleigh wave data for shear wave velocity structure and three-dimensional seismic anisotropy in the thee regions designated within the continental margin including the continent, seafloor and California Borderlands. Preliminary results show that seismic anisotropy is resolved in multiple layers and can be used to determine the lithosphere-asthenosphere boundary (LAB) in offshore and continental regions. The oldest seafloor in our study at age 25-35 Ma indicates that the anisotropic transition across the LAB occurs at 73 km +/- 25 km with the lithospheric fast direction oriented WNW-ESE, consistent with current Pacific plate motion direction. The continent region west of the San Andreas indicates similar WNW-ESE anisotropy and LAB depth. Regions east of the San Andreas fault indicate NW-SE anisotropy transitioning to a N-S alignment at 80 km depth north of the Garlock fault. The youngest seafloor (15 - 25 Ma) and outer Borderlands indicate a more complex three layer fabric where shallow lithospheric NE-SW fast directions are perpendicular with ancient Farallon subduction arc, a mid-layer with E-W fast directions are perpendicular to remnant fossil fabric, and the deepest layer

  4. Seismic and Tectonic Regionalization of the State of Michoacan.

    Science.gov (United States)

    Vazquez Rosas, R.; Aguirre, J.; Garduño-Monroy, V. H.; Ramirez-Guzman, L.

    2017-12-01

    In Mexico it is a country with seismically active regions, mainly the zones that are next to the pacific where the zone of subduction is located, in this work we focus on the state of Michoacán, since this has not been completely studied in the last 30 years after the earthquake in Michoacán in 1985. The first most important step is to know the region which are the most seismic zones within the state and one way is to carry out the regionalization of Michoacán identifying the sources of earthquakes as well as where occur more frequently.If we could know each of the factors that influence seismicity and describe every point of the terrain, every rupture, every rock, etc., then we could describe in an analytical way the seismic process and predict the occurrence of earthquakes such as eclipses. Unfortunately the number of parameters is so enormous that we cannot arrive at an exact description; however, we can take advantage of statistical properties to evaluate probabilities, even in the case of small systems such as a particular seismic zone.In this paper, epicenter data were collected from 1970 to 2014, and with them a statistical study was carried out and the epicenter data plotted using data reported by the National Seismological Service and the IRIS catalog as well as some data from the Institute of engineering UNAM. Where earthquakes of equal and greater than M = 4 were used. Graphing these in function with the depth and with that it was graficaron and was made an overlapping the faults of the state and with that it was divided in 4 seismic zones in function of the faults and the localized seismicity.Zone A. is located within the Michoacán Block set of faults, as well as part of the subduction zone on the coast of the state. Seismicity in this area is high. Zone B-1. This is located between the limits of Jalisco and Michoacán in the set of faults called Tepalcatepec depression and limits with the Jorullo-Tacámbaro fracture. At this site seismicity is

  5. Waveform through the subducted plate under the Tokyo region in Japan observed by a ultra-dense seismic network (MeSO-net) and seismic activity around mega-thrust earthquakes area

    Science.gov (United States)

    Sakai, S.; Kasahara, K.; Nanjo, K.; Nakagawa, S.; Tsuruoka, H.; Morita, Y.; Kato, A.; Iidaka, T.; Hirata, N.; Tanada, T.; Obara, K.; Sekine, S.; Kurashimo, E.

    2009-12-01

    In central Japan, the Philippine Sea plate (PSP) subducts beneath the Tokyo Metropolitan area, the Kanto region, where it causes mega-thrust earthquakes, such as the 1703 Genroku earthquake (M8.0) and the 1923 Kanto earthquake (M7.9) which had 105,000 fatalities. A M7 or greater earthquake in this region at present has high potential to produce devastating loss of life and property with even greater global economic repercussions. The Central Disaster Management Council of Japan estimates the next great earthquake will cause 11,000 fatalities and 112 trillion yen (1 trillion US$) economic loss. This great earthquake is evaluated to occur with a probability of 70 % in 30 years by the Earthquake Research Committee of Japan. We had started the Special Project for Earthquake Disaster Mitigation in Tokyo Metropolitan area (2007-2012). Under this project, the construction of the Metropolitan Seismic Observation network (MeSO-net) that consists of about 400 observation sites was started [Kasahara et al., 2008; Nakagawa et al., 2008]. Now, we had 178 observation sites. The correlation of the wave is high because the observation point is deployed at about 2 km intervals, and the identification of the later phase is recognized easily thought artificial noise is very large. We also discuss the relation between a deformation of PSP and intra-plate M7+ earthquakes: the PSP is subducting beneath the Honshu arc and also colliding with the Pacific plate. The subduction and collision both contribute active seismicity in the Kanto region. We are going to present a high resolution tomographic image to show low velocity zone which suggests a possible internal failure of the plate; a source region of the M7+ intra-plate earthquake. Our study will contribute a new assessment of the seismic hazard at the Metropolitan area in Japan. Acknowledgement: This study was supported by the Earthquake Research Institute cooperative research program.

  6. Survey explores active tectonics in northeastern Caribbean

    Science.gov (United States)

    Carbó, A.; Córdoba, D.; Muñoz-Martín, A.; Granja, J.L.; Martín-Dávila, J.; Pazos, A.; Catalán, M.; Gómez, M.; ten Brink, Uri S.; von Hillebrandt, Christa; Payero, J.

    2005-01-01

    There is renewed interest in studying the active and complex northeastern Caribbean plate boundary to better understand subduction zone processes and for earthquake and tsunami hazard assessments [e.g., ten Brink and Lin, 2004; ten Brink et al., 2004; Grindlay et al., 2005]. To study the active tectonics of this plate boundary, the GEOPRICO-DO (Geological, Puerto Rico-Dominican) marine geophysical cruise, carried out between 28 March and 17 April 2005 (Figure 1), studied the active tectonics of this plate boundary.Initial findings from the cruise have revealed a large underwater landslide, and active faults on the seafloor (Figures 2a and 2c). These findings indicate that the islands within this region face a high risk from tsunami hazards, and that local governments should be alerted in order to develop and coordinate possible mitigation strategies.

  7. Strain transformation between tectonic extrusion and crustal thickening in the growth of the Tibetan Plateau

    Science.gov (United States)

    Liu, M.; Li, Y.; Sun, Y.; Shen, X.

    2017-12-01

    The Indo-Eurasian continental collision since 50 Ma has thickened the crust to raise the Himalayan-Tibetan Plateau and driven lateral extrusion of Asian lithospheric blocks to affect Cenozoic tectonics in central and east Asia. The relative roles of crustal thickening and tectonic extrusion, and the strain partitioning between them over time and space, remain controversial. We have analyzed the strain rates using GPS velocities, and correlated the results with vertical motion derived from precise leveling. We found that tectonic extrusion largely transforms to crustal thickening near the margins of the Tibetan Plateau. Near the NW margin of the Tibetan Plateau, the shear stain transforms to compressive strain, consistent with neotectonic studies that indicate crustal shortening and uplift. Around the SE margin, shear stain largely terminates in the southern Yunnan province of China. The present-day crustal motion in SE Tibetan Plateau can be well explained by gravitational spreading without invoking plate-edge push as envisioned in the tectonic extrusion model. Using data collected from local seismic arrays, we derived receiver functions to image the lithospheric structures across the Tibetan Plateau and the Alashan block to its north and the Ordos block to its east. Our results indicate that the mantle lithosphere of these bounding Asian blocks has not been reworked by Tibetan tectonics; instead they have acted as restrictive walls to the growing Tibetan Plateau. Our finite element modeling shows that crustal deformation along the margins of the Tibetan Plateau are consistent with the notion that the east- and southeastward extrusion of the Tibetan lithosphere is largely confined to the Tibetan Plateau because of the restrictive bounding blocks of the Asian lithosphere. Thus the tectonic impact of the Indo-Eurasian collision on the Cenozoic Asian tectonics may not be as extensive as previously thought.

  8. GEODYNAMIC ACTIVITY OF MODERN STRUCTURES AND TECTONIC STRESS FIELDS IN NORTHEAST ASIA

    Directory of Open Access Journals (Sweden)

    L. P. Imaeva

    2017-01-01

    Full Text Available Based on the analysis of changes in the stress-strain state of the crust at the boundary of the Eurasian and North American tectonic plates, we develop a dynamic model of the main seismogenerating structures inNortheast Asia. We have established a regularity in changes of geodynamic regimes within the interplate boundary between the Kolyma-Chukotka crustal plate and the Eurasian, North American and Pacific tectonic plates: spreading in the Gakkel Ridge area; rifting in the Laptev Sea shelf; a mixture of tectonic stress types in the Kharaulakh segment; transpression in the Chersky seismotectonic zone, in the segment from the Komandor to the Aleutian Islands, and in the Koryak segment; and crustal stretching in the Chukotka segment.

  9. MIGRATIONS OF RELEASED SEISMIC ENERGY IN VARIOUS GEODYNAMIC CONDITIONS

    Directory of Open Access Journals (Sweden)

    A. V. Novopashina

    2018-01-01

    Full Text Available The properties of slow seismic activity migration have been revealed by the space-time analysis of the total earthquake energy (LgEsum. Our study of seismic activity covers the fragments of  the Central Asian, Pacific and Alpine seismic belts: the Baikal rift system (BRS, Russia, the San Andreas fault zone (California, USA, the Christchurch fault (New Zealand, the North and East Anatolian faults (Turkey, the Philippine subduction zone, and the central fragment of the Mid-Atlantic oceanic ridge. The chains of LgEsum clusters mark the propagation of the maximum stresses front in the weaker crust areas, the zones of fault dynamic influence, and the regions of conjugated tectonic structures. The migration process is characterized by a periodicity, changes in direction, and similar modular values of the migration rates within a single fault segment (or a fault zone, which is probably related to the mechanical and rheological crust and upper mantle properties. The data analysis shows that a strong earthquake source may occur at a location wherein the front of seismic activity propagates with periodical changes in direction, and such a source can develop within a period that is multiple of the migration fluctuations, probably associated with the influence of external periodic factors. The main periods of migration fluctuations (2–4 years, and 9–13 years, in different ratios are present in the seismic regimes of different seismic belts. The migration rate, as well as the propagation velocity of the maximum stresses front, directly depends on the velocity of movements between the plates in the region.

  10. Gravity anomaly and crustal structure characteristics in North-South Seismic Belt of China

    Science.gov (United States)

    Shen, Chongyang; Xuan, Songtbai; Yang, Guangliang; Wu, Guiju

    2017-04-01

    The North-South Seismic Belt (NSSB) is the binary system boundary what is formed by the western Indian plate subduction pushing and the eastern west Pacific asthenosphere rising, and it is one of the three major seismic belts (Tianshan, Taiwan and NSSB) and mainly located between E102°and E107°. And it is mainly composed of topographic gradient zones, faults, cenozoic basins and strong earthquake zones, which form two distinct parts of tectonic and physical features in the west and east. The research results of geophysical and deep tectonic setting in the NSSB show that it is not only a gravity anomaly gradient zone, it is but also a belt of crustal thickness increasing sharply westward of abrupt change. Seismic tomography results show that the anomaly zone is deeper than hundreds of kilometers in the NSSB, and the composition and structure of the crust are more complex. We deployed multiple Gravity and GNSS synchronous detection profiles in the NSSB, and these profiles crossed the mainly faults structure and got thousands of points data. In the research, source analysis, density structure inversion, residual gravity related imaging and normalized full gradient methods were used, and analyzed gravity field, density and their structure features in different positions, finally obtained the crustal density structure section characteristics and depth structure differences. The research results showed that the gravity Bouguer anomaly is similar to the existing large scale result. The Bouguer anomaly is rising significantly from west to east, its trend variation coincides well with the trend change of Moho depth, which is agreeing with the material flows to the peripheral situation of the Tibetan plateau. The obvious difference changes of the residual anomaly is relative to the boundary of structure or main tectonics, it's also connected with the stop degree of the eurasian plate when the material migrates around. The density structure of the gravity profiles mainly

  11. Salton Trough Post-seismic Afterslip, Viscoelastic Response, and Contribution to Regional Hazard

    Science.gov (United States)

    Parker, J. W.; Donnellan, A.; Lyzenga, G. A.

    2012-12-01

    The El Mayor-Cucapah M7.2 April 4 2010 earthquake in Baja California may have affected accumulated hazard to Southern California cities due to loading of regional faults including the Elsinore, San Jacinto and southern San Andreas, faults which already have over a century of tectonic loading. We examine changes observed via multiple seismic and geodetic techniques, including micro seismicity and proposed seismicity-based indicators of hazard, high-quality fault models, the Plate Boundary Observatory GNSS array (with 174 stations showing post-seismic transients with greater than 1 mm amplitude), and interferometric radar maps from UAVSAR (aircraft) flights, showing a network of aseismic fault slip events at distances up to 60 km from the end of the surface rupture. Finite element modeling is used to compute the expected coseismic motions at GPS stations with general agreement, including coseismic uplift at sites ~200 km north of the rupture. Postseismic response is also compared, with GNSS and also with the CIG software "RELAX." An initial examination of hazard is made comparing micro seismicity-based metrics, fault models, and changes to coulomb stress on nearby faults using the finite element model. Comparison of seismicity with interferograms and historic earthquakes show aseismic slip occurs on fault segments that have had earthquakes in the last 70 years, while other segments show no slip at the surface but do show high triggered seismicity. UAVSAR-based estimates of fault slip can be incorporated into the finite element model to correct Coloumb stress change.

  12. Post-Jurassic tectonic evolution of Southeast Asia

    Science.gov (United States)

    Zahirovic, Sabin; Seton, Maria; Dietmar Müller, R.; Flament, Nicolas

    2014-05-01

    terminate PSCS south-dipping subduction and culminates in the Sarawak Orogeny on Borneo and ophiolite obduction on Palawan. We account for the regional plate reorganizations related to the initiation of Pacific subduction along the Izu-Bonin-Mariana Arc, the extrusion tectonics resulting from the India-Eurasia collision, and the shift from basin extension to inversion on Sundaland as an indicator of collision between the Australian continent and the active Asian margin. We generate continuously closing and evolving plate boundaries, seafloor age-grids and global plate velocity fields using the open-source and cross-platform GPlates plate reconstruction software. We link our plate motions to numerical mantle flow models in order to predict mantle structure at present-day that can be qualitatively compared to P- and S- wave seismic tomography models. This method allows us to analyse the evolution of the mantle related to Tethyan and Pacific subduction and to test alternative plate reconstructions. This iterative approach can be used to improve plate reconstructions in the absence of preserved seafloor and conjugate passive margins of continental blocks, which may have been destroyed or highly deformed by multiple episodes of accretion along the Asian margins.

  13. The bright spot in the West Carpathian upper mantle: a trace of the Tertiary plate collision-and a caveat for a seismologist

    Science.gov (United States)

    Środa, Piotr

    2010-07-01

    The 2-D full waveform modelling of the mantle arrivals from the CELEBRATION 2000 profiles crossing the Carpathian orogen suggests two possible tectonic models for the collision of ALCAPA (Alpine-Carpathian-Pannonian) and the European Plate in the West Carpathians in southern Poland and Slovakia. Due to an oblique (NE-SW) convergence of plates, the character of the collision may change along the zone of contact of the plates: in the western part of the area an earlier collision might have caused substantial crustal shortening and formation of a crocodile-type structure, with the delaminated lower crust of ~100km length acting as a north-dipping reflecting discontinuity in the uppermost mantle. In the eastern part, a less advanced collision only involved the verticalization of the subducted slab remnant after a slab break-off. The lower crustal remnant of ~10km size in the uppermost mantle acts as a pseudo-diffractor generating observable mantle arrivals. Due to the similarity of synthetic data generated by both models, the question of the non-uniqueness of seismic data interpretation, that may lead to disparate tectonic inferences, is also discussed.

  14. Geodynamics of kimberlites on a cooling Earth: Clues to plate tectonic evolution and deep volatile cycles

    Science.gov (United States)

    Tappe, Sebastian; Smart, Katie; Torsvik, Trond; Massuyeau, Malcolm; de Wit, Mike

    2018-02-01

    Kimberlite magmatism has occurred in cratonic regions on every continent. The global age distribution suggests that this form of mantle melting has been more prominent after 1.2 Ga, and notably between 250-50 Ma, than during early Earth history before 2 Ga (i.e., the Paleoproterozoic and Archean). Although preservation bias has been discussed as a possible reason for the skewed kimberlite age distribution, new treatment of an updated global database suggests that the apparent secular evolution of kimberlite and related CO2-rich ultramafic magmatism is genuine and probably coupled to lowering temperatures of Earth's upper mantle through time. Incipient melting near the CO2- and H2O-bearing peridotite solidus at >200 km depth (1100-1400 °C) is the petrologically most feasible process that can produce high-MgO carbonated silicate melts with enriched trace element concentrations akin to kimberlites. These conditions occur within the convecting asthenospheric mantle directly beneath thick continental lithosphere. In this transient upper mantle source region, variable CHO volatile mixtures control melting of peridotite in the absence of heat anomalies so that low-degree carbonated silicate melts may be permanently present at ambient mantle temperatures below 1400 °C. However, extraction of low-volume melts to Earth's surface requires tectonic triggers. Abrupt changes in the speed and direction of plate motions, such as typified by the dynamics of supercontinent cycles, can be effective in the creation of lithospheric pathways aiding kimberlite magma ascent. Provided that CO2- and H2O-fluxed deep cratonic keels, which formed parts of larger drifting tectonic plates, existed by 3 Ga or even before, kimberlite volcanism could have been frequent during the Archean. However, we argue that frequent kimberlite magmatism had to await establishment of an incipient melting regime beneath the maturing continents, which only became significant after secular mantle cooling to below

  15. Seismic Evidence for the North China Plate Underthrusting Beneath Northeastern Tibet and its Implications for Plateau Growth

    Science.gov (United States)

    Ye, Z.; Gao, R.; Li, Q.; Zhang, H.

    2016-12-01

    The effects of India-Asia collision and the subsequent interaction between the two continents on northeastern Tibet (NE Tibet), i.e., the tectonic transition zone between the Tibetan plateau and the North China craton (NCC) for example, remain uncertain due to inadequate geophysical data coverage in NE Tibet. Here in this research, based on new dataset collected from a dense linear array of 38 broadband seismograph stations, we applied seismic receiver functions (Sp and Ps converted waves) to imaging the lithospheric structure and shear wave splitting (XKS waves) to inspecting the anisotropy in the lithosphere and upper mantle beneath NE Tibet. The seismic array traverses NE Tibet to the westernmost NCC (Alxa block) in an SSW-NNE direction. The lithosphere-asthenosphere boundary (LAB) is clearly defined and appears as a south-dipping interface that runs continuously from the Alxa interior to the Qilian orogen on the S-wave receiver function images. Shear wave splitting measurements show significant lateral variations of seismic anisotropy across NE Tibet. Under joint constraints from both the lithospheric structure imaging and the regional anisotropic regime, combined with previous studies and through a thorough analysis/comparison/integration, we finally constructed a comprehensive lithospheric model of NE Tibet. The model tells that the NCC lithospheric mantle has been persistently underthrust beneath the Qilian orogen in response to on-going convergence/compression between the interior Tibetan plateau and the NCC. This process forms the syntectonic crustal thrust. The regional anisotropic regime can be well accommodated in our interpretation. The lithospheric model summarized here can be well accommodated in a scenario of northeastward migration of stepwise/multiple Aisan mantle lithosphere underthrusting beneath the Tibetan plateau. The multiple Aisan lithospheric blocks underthrust the plateau stepwise in small scale. Our results provide a new section from

  16. Seismic source zone characterization for the seismic hazard assessment project PEGASOS by the Expert Group 2 (EG1b)

    International Nuclear Information System (INIS)

    Burkhard, M.; Gruenthal, G.

    2009-01-01

    A comprehensive study of the seismic hazard related to the four NNP sites in NW Switzerland was performed within the project PEGASOS. To account for the epistemic uncertainties involved in the process of the characterization of seismic source zones in the frame of probabilistic seismic hazard assessments, four different expert teams have developed and defended their models in the frame of an intensive elicitation process. Here, the results of one out of four expert groups are presented. The model of this team is based first of all on considerations regarding the large scale tectonics in the context of the Alpine collision, and neotectonic constraints for defining seismic source zones. This leads to a large scale subdivision based on the structural 'architectural' considerations with little input from the present seismicity. Each of the eight large zones was characterized by the style of present-day faulting, fault orientation, and hypo central depth distribution. A further subdivision of the larger zones is performed based on information provided by the seismicity patterns. 58 small source zones have been defined in this way, each of them characterized by the available tectonic constrains, as well as the pros and cons of different existing geologic views connected to them. Of special concern in this respect were the discussion regarding thin skinned vs. thick skinned tectonics, the tectonic origin of the 1356 Basel earthquake, the role of the Permo-Carboniferous graben structures, and finally the seismogenic orientation of faults with respect to the recent crustal stress field. The uncertainties connected to the delimitations of the small source zones have been handled in form of their regrouping, formalized by the logic tree technique. The maximum magnitudes were estimated as discretized probability distribution functions. After de-clustering the used ECOS earthquake catalogue and an analysis of data completeness as a function of time the parameters of the

  17. Passive seismic monitoring of natural and induced earthquakes: case studies, future directions and socio-economic relevance

    Science.gov (United States)

    Bohnhoff, Marco; Dresen, Georg; Ellsworth, William L.; Ito, Hisao; Cloetingh, Sierd; Negendank, Jörg

    2010-01-01

    An important discovery in crustal mechanics has been that the Earth’s crust is commonly stressed close to failure, even in tectonically quiet areas. As a result, small natural or man-made perturbations to the local stress field may trigger earthquakes. To understand these processes, Passive Seismic Monitoring (PSM) with seismometer arrays is a widely used technique that has been successfully applied to study seismicity at different magnitude levels ranging from acoustic emissions generated in the laboratory under controlled conditions, to seismicity induced by hydraulic stimulations in geological reservoirs, and up to great earthquakes occurring along plate boundaries. In all these environments the appropriate deployment of seismic sensors, i.e., directly on the rock sample, at the earth’s surface or in boreholes close to the seismic sources allows for the detection and location of brittle failure processes at sufficiently low magnitude-detection threshold and with adequate spatial resolution for further analysis. One principal aim is to develop an improved understanding of the physical processes occurring at the seismic source and their relationship to the host geologic environment. In this paper we review selected case studies and future directions of PSM efforts across a wide range of scales and environments. These include induced failure within small rock samples, hydrocarbon reservoirs, and natural seismicity at convergent and transform plate boundaries. Each example represents a milestone with regard to bridging the gap between laboratory-scale experiments under controlled boundary conditions and large-scale field studies. The common motivation for all studies is to refine the understanding of how earthquakes nucleate, how they proceed and how they interact in space and time. This is of special relevance at the larger end of the magnitude scale, i.e., for large devastating earthquakes due to their severe socio-economic impact.

  18. Using Seismic Interferometry to Investigate Seismic Swarms

    Science.gov (United States)

    Matzel, E.; Morency, C.; Templeton, D. C.

    2017-12-01

    Seismicity provides a direct means of measuring the physical characteristics of active tectonic features such as fault zones. Hundreds of small earthquakes often occur along a fault during a seismic swarm. This seismicity helps define the tectonically active region. When processed using novel geophysical techniques, we can isolate the energy sensitive to the fault, itself. Here we focus on two methods of seismic interferometry, ambient noise correlation (ANC) and the virtual seismometer method (VSM). ANC is based on the observation that the Earth's background noise includes coherent energy, which can be recovered by observing over long time periods and allowing the incoherent energy to cancel out. The cross correlation of ambient noise between a pair of stations results in a waveform that is identical to the seismogram that would result if an impulsive source located at one of the stations was recorded at the other, the Green function (GF). The calculation of the GF is often stable after a few weeks of continuous data correlation, any perturbations to the GF after that point are directly related to changes in the subsurface and can be used for 4D monitoring.VSM is a style of seismic interferometry that provides fast, precise, high frequency estimates of the Green's function (GF) between earthquakes. VSM illuminates the subsurface precisely where the pressures are changing and has the potential to image the evolution of seismicity over time, including changes in the style of faulting. With hundreds of earthquakes, we can calculate thousands of waveforms. At the same time, VSM collapses the computational domain, often by 2-3 orders of magnitude. This allows us to do high frequency 3D modeling in the fault region. Using data from a swarm of earthquakes near the Salton Sea, we demonstrate the power of these techniques, illustrating our ability to scale from the far field, where sources are well separated, to the near field where their locations fall within each other

  19. Towards absolute plate motions constrained by lower-mantle slab remnants

    NARCIS (Netherlands)

    Meer, D.G. van der; Spakman, W.; Hinsbergen, D.J.J. van; Amaru, M.L.; Torsvik, T.H.

    2010-01-01

    Since the first reconstruction of the supercontinent Pangaea, key advances in plate tectonic reconstructions have been made1. Although the movement of tectonic plates since the start of the mid-Cretaceous period (~100 million years (Myr) ago) is relatively well understood1, 2, the longitudinal

  20. The seismicity of Ethiopia; active plate tectonics

    Science.gov (United States)

    Mohr, P.

    1981-01-01

    "But I tell you, when you look at the way the pieces of the northeastern portion of the African continent seem to fit together, separated by a narrow gulf, you could almost make a believer [in continental drift] of anybody" Astronaut Harrison Schmidt, on the view from Apollo 17.

  1. GPS Imaging suggests links between climate, magmatism, seismicity, and tectonics in the Sierra Nevada-Long Valley Caldera-Walker Lane system, western United States

    Science.gov (United States)

    Hammond, W. C.; Blewitt, G.; Kreemer, C.; Smith, K.

    2017-12-01

    The Walker Lane is a region of complex active crustal transtension in the western Great Basin of the western United States, accommodating about 20% of the 50 mm/yr relative motion between the Pacific and North American plates. The Long Valley caldera lies in the central Walker Lane in eastern California, adjacent to the eastern boundary of the Sierra Nevada/Great Valley microplate, and experiences intermittent inflation, uplift, and volcanic unrest from the magma chamber that resides at middle crustal depths. Normal and transform faults accommodating regional tectonic transtension pass by and through the caldera, complicating the interpretation of the GPS-measured strain rate field, estimates of fault slip rates, and seismic hazard. Several dozen continuously recording GPS stations measure strain and uplift in the area with mm precision. They observe that the most recent episode of uplift at Long Valley began in mid-2011, continuing until late 2016, raising the surface by 100 mm in 6 years. The timing of the initiation of uplift coincides with the beginning of severe drought in California. Furthermore, the timing of a recent pause in uplift coincides with the very wet 2016-2017 winter, which saw approximately double normal snow pack. In prior studies, we showed that the timing of changes in geodetically measured uplift rate of the Sierra Nevada coincides with the timing of drought conditions in California, suggesting a link between hydrological loading and Sierra Nevada elevation. Here we take the analysis three steps further to show that changes in Sierra Nevada uplift rate coincide in time with 1) enhanced inflation at the Long Valley caldera, 2) shifts in the patterns and rates of horizontal tensor strain rate, and 3) seismicity patterns in the central Walker Lane. We use GPS solutions from the Nevada Geodetic Laboratory and the new GPS Imaging technique to produce robust animations of the time variable strain and uplift fields. The goals of this work are to

  2. Influence of LOD variations on seismic energy release

    Science.gov (United States)

    Riguzzi, F.; Krumm, F.; Wang, K.; Kiszely, M.; Varga, P.

    2009-04-01

    Tidal friction causes significant time variations of geodynamical parameters, among them geometrical flattening. The axial despinning of the Earth due to tidal friction through the change of flattening generates incremental meridional and azimuthal stresses. The stress pattern in an incompressible elastic upper mantle and crust is symmetric to the equator and has its inflection points at the critical latitude close to ±45°. Consequently the distribution of seismic energy released by strong, shallow focus earthquakes should have also sharp maxima at this latitude. To investigate the influence of length of day (LOD) variations on earthquake activity an earthquake catalogue of strongest seismic events (M>7.0) was completed for the period 1900-2007. It is shown with the use of this catalogue that for the studied time-interval the catalogue is complete and consists of the seismic events responsible for more than 90% of released seismic energy. Study of the catalogue for earthquakes M>7.0 shows that the seismic energy discharged by the strongest seismic events has significant maxima at ±45°, what renders probably that the seismic activity of our planet is influenced by an external component, i.e. by the tidal friction, which acts through the variation of the hydrostatic figure of the Earth caused by it. Distribution along the latitude of earthquake numbers and energies was investigated also for the case of global linear tectonic structures, such as mid ocean ridges and subduction zones. It can be shown that the number of the shallow focus shocks has a repartition along the latitude similar to the distribution of the linear tectonic structures. This means that the position of foci of seismic events is mainly controlled by the tectonic activity.

  3. Extrusive and Intrusive Magmatism Greatly Influence the Tectonic Mode of Earth-Like Planets

    Science.gov (United States)

    Lourenco, D.; Tackley, P. J.; Rozel, A.; Ballmer, M.

    2017-09-01

    Plate tectonics on Earth-like planets is typically modelling using a strongly temperature-dependent visco-plastic rheology. Previous analyses have generally focussed on purely thermal convection. However, we have shown that the influence of compositional heterogeneity in the form of continental or oceanic crust can greatly influence plate tectonics by making it easier (i.e. it occurs at a lower yield stress or friction coefficient). Here we present detailed results on this topic, in particular focussing on the influence of intrusive vs. extrusive magmatism on the tectonic mode.

  4. Probabilistic seismic hazard assessment for the two layer fault system of Antalya (SW Turkey) area

    Science.gov (United States)

    Dipova, Nihat; Cangir, Bülent

    2017-09-01

    Southwest Turkey, along Mediterranean coast, is prone to large earthquakes resulting from subduction of the African plate under the Eurasian plate and shallow crustal faults. Maximum observed magnitude of subduction earthquakes is Mw = 6.5 whereas that of crustal earthquakes is Mw = 6.6. Crustal earthquakes are sourced from faults which are related with Isparta Angle and Cyprus Arc tectonic structures. The primary goal of this study is to assess seismic hazard for Antalya area (SW Turkey) using a probabilistic approach. A new earthquake catalog for Antalya area, with unified moment magnitude scale, was prepared in the scope of the study. Seismicity of the area has been evaluated by the Gutenberg-Richter recurrence relationship. For hazard computation, CRISIS2007 software was used following the standard Cornell-McGuire methodology. Attenuation model developed by Youngs et al. Seismol Res Lett 68(1):58-73, (1997) was used for deep subduction earthquakes and Chiou and Youngs Earthq Spectra 24(1):173-215, (2008) model was used for shallow crustal earthquakes. A seismic hazard map was developed for peak ground acceleration and for rock ground with a hazard level of a 10% probability of exceedance in 50 years. Results of the study show that peak ground acceleration values on bedrock change between 0.215 and 0.23 g in the center of Antalya.

  5. Plate boundary deformation at the latitude of the Salton Trough - northern Gulf of California (Invited)

    Science.gov (United States)

    Stock, J. M.

    2013-12-01

    Along the Pacific-North America plate boundary zone, the segment including the southern San Andreas fault to Salton Trough and northern Gulf of California basins has been transtensional throughout its evolution, based on Pacific-North America displacement vectors calculated from the global plate circuit (900 × 20 km at N54°W since 20 Ma; 460 × 20 km at N48°W since 11 Ma). Nevertheless, active seismicity and focal mechanisms show a broad zone of plate boundary deformation within which the inferred stress regime varies locally (Yang & Hauksson 2013 GJI), and fault patterns in some regions suggest ongoing tectonic rotation. Similar behavior is inferred to have occurred in this zone over most of its history. Crustal structure in this region is constrained by surface geology, geophysical experiments (e.g., the 2011 Salton Seismic Imaging Project (SSIP), USGS Imperial Valley 1979, PACE), and interdisciplinary marine and onland studies in Mexico (e.g., NARS-Baja, Cortes, and surveys by PEMEX). Magnetic data (e.g., EMAG-2) aids in the recognition of large-scale crustal provinces and fault boundaries in regions lacking detailed geophysical surveys. Consideration of existing constraints on crustal thickness and architecture, and fault and basin evolution suggests that to reconcile geological deformation with plate motion history, the following additional factors need to be taken into account. 1) Plate boundary displacement via interacting systems of rotating blocks, coeval with slip on steep strike slip faults, and possibly related to slip on low angle extensional faults (e.g, Axen & Fletcher 1998 IGR) may be typical prior to the onset of seafloor spreading. This fault style may have accommodated up to 150 km of plate motion in the Mexican Continental Borderland and north of the Vizcaino Peninsula, likely between 12 and 15 Ma, as well as explaining younger rotations adjacent to the Gulf of California and current deformation southwest of the Salton Sea. 2) Geophysical

  6. Tectonic history in the Fort Worth Basin, north Texas, derived from well-log integration with multiple 3D seismic reflection surveys: implications for paleo and present-day seismicity in the basin

    Science.gov (United States)

    Magnani, M. B.; Hornbach, M. J.

    2016-12-01

    Oil and gas exploration and production in the Fort Worth Basin (FWB) in north Texas have accelerated in the last 10 years due to the success of unconventional gas production. Here, hydraulic fracturing wastewater is disposed via re-injection into deep wells that penetrate Ordovician carbonate formations. The rise in wastewater injection has coincided with a marked rise in earthquake rates, suggesting a causal relationship between industry practices and seismicity. Most studies addressing this relationship in intraplate regions like the FWB focus on current seismicity, which provides an a-posteriori assessment of the processes involved. 3D seismic reflection data contribute complementary information on the existence, distribution, orientation and long-term deformation history of faults that can potentially become reactivated by the injection process. Here we present new insights into the tectonic evolution of faults in the FWB using multiple 3D seismic reflection surveys in the basin, west of the Dallas Fort-Worth Metroplex, where high-volume wastewater injection wells have increased most significantly in number in the past few years. The datasets image with remarkable clarity the 3,300 m-thick sedimentary rocks of the basin, from the crystalline basement to the Cretaceous cover, with particular detail of the Paleozoic section. The data, interpreted using coincident and nearby wells to correlate seismic reflections with stratigraphic markers, allow us to identify faults, extract their orientation, length and displacements at several geologic time intervals, and therefore, reconstruct the long-term deformation history. Throughout the basin, the data show that all seismically detectable faults were active during the Mississippian and Pennsylvanian, but that displacement amounts drop below data resolution ( 7 m) in the post-Pennsylvanian deposits. These results indicate that faults have been inactive for at least the past 300 Ma, until the recent 2008 surge in

  7. Finding the last 200Ma of subducted lithosphere in tomography and incorporating it into plate reconstructions

    Science.gov (United States)

    Suppe, J.; Wu, J.; Chen, Y. W.

    2016-12-01

    Precise plate-tectonic reconstruction of the Earth has been constrained largely by the seafloor magnetic-anomaly record of the present oceans formed during the dispersal of the last supercontinent since 200Ma. The corresponding world that was lost to subduction has been only sketchily known. We have developed methodologies to map in 3D these subducted slabs of lithosphere in seismic tomography and unfold them to the Earth surface, constraining their initial size, shapes and locations. Slab edges are commonly formed at times of plate reorganization (for example bottom edges typically record initiation of subduction) such that unfolded slabs fit together at times of reorganization, as we illustrate for the Nazca slab at 80Ma and the western Pacific slabs between Kamchatka and New Zealand at 50Ma. Mapping to date suggests that a relatively complete and decipherable record of lithosphere subducted over the last 200Ma may exist in the mantle today, providing a storehouse for new discoveries. We briefly illustrate our procedure for obtaining slab-constrained plate-tectonic models from tomography with our recent study of the Philippine Sea plate, whose motions and tectonic history have been the least known of the major plates because it has been isolated from the global plate and hotspot circuit by trenches. We mapped and unfolded 28 subducted slabs in the mantle under East Asia and Australia/Oceania to depths of 1200km, with a subducted area of 25% of present-day global oceanic lithosphere, and incorporated them as constraints into a new globally-consistent plate reconstruction of the Philippine Sea and surrounding East Asia, leading to a number of new insights, including: [1] discovery of a major (8000 km x 2500 km) set of vanished oceans that we call the East Asia Sea that existed between the Pacific and Indian Oceans, now represented by flat slabs in the lower mantle under present-day Philippine Sea, eastern Sundaland and northern Australia and [2] the Philippine Sea

  8. Application of plate tectonics to the location of new mineral targets in the Appalachians. Progress report no. 3

    International Nuclear Information System (INIS)

    Kutina, J.

    1979-01-01

    This report is concerned with the application of plate tectonics to the location of new mineral targets in the U.S. It reviews analyses presented in previous reports which suggest that the basement of the Central and Eastern U.S. consists of large crustal blocks separated by major zones of tectonic weakness. The curvature of the Appalachian Fold Belt appears to be related to the east-west boundaries caused by subsiding and uplifting at these zones. A plot of epigenetic uranium occurrences reveals that they tend to cluster along the greater curvatures of the Appalachian orogeny. These findings have led to a systematic study of the regularities in the distribution of ore deposits in the Appalachians presented in this report. They include a description of geologic and geographic base maps, preparation of maps showing distribution of individual minerals, and regularities in the distribution of uranium in the Appalachians. Comments on the segmentation of the Appalachian orogeny by transverse lineaments are presented. The report contains seventeen maps of the eastern half of the U.S. showing specific mineral deposits in relation to geologic formations

  9. Presentation of new tectonic map (and accompanying sections) of Trinidad and Tobago

    Energy Technology Data Exchange (ETDEWEB)

    Persad, K.M.

    1984-04-01

    The Geologic Map of Trinidad, compiled by H.G. Kugler and published in 1961, is currently out of print. While it is the most widely available geologic map, it is confined to onshore Trinidad. This map remains an important reference source, but there have been significant increases in our knowledge of Trindad and Tobago geology since its publication. In particular, there has been: (1) considerable geophysical work, on land and offshore, including 20,000 km (12,400 mi) of seismic lines; (2) approximately 1000 exploration and development wells drilled, including wells in the previously unexplored north and east coast of Trinidad; and (3) significant advances in our understanding of the tectonic evolution of the area, which has resulted largely from the development of the plate tectonic theory. The following items, which take into account many of these new data and concepts, have been compiled. (1) A geologic tectonic map of the entire territory of Trinidad and Tobago, at a scale of 1:200,000. Apart from the surface geology of the land areas, this map shows the major faults and their displacements and locations, total depths and status of exploration wells, and the positions of major petroleum fields. (2) Five accompanying geologic sections at the same scale. (3) A new stratigraphic correlation chart. These new compilations attempt to fill the gap in the published literature on the petroleum geology of Trinidad and Tobago.

  10. Recent Vs. Historical Seismicity Analysis For Banat Seismic Region (Western Part Of Romania

    Directory of Open Access Journals (Sweden)

    Oros Eugen

    2015-03-01

    Full Text Available The present day seismic activity from a region reflects the active tectonics and can confirm the seismic potential of the seismogenic sources as they are modelled using the historical seismicity. This paper makes a comparative analysis of the last decade seismicity recorded in the Banat Seismic Region (western part of Romania and the historical seismicity of the region (Mw≥4.0. Four significant earthquake sequences have been recently localized in the region, three of them nearby the city of Timisoara (January 2012 and March 2013 and the fourth within Hateg Basin, South Carpathians (October 2013. These sequences occurred within the epicentral areas of some strong historical earthquakes (Mw≥5.0. The main events had some macroseismic effects on people up to some few kilometers from the epicenters. Our results update the Romanian earthquakes catalogue and bring new information along the local seismic hazard sources models and seismotectonics.

  11. Stress state reconstruction and tectonic evolution of the northern slope of the Baikit anteclise, Siberian Craton, based on 3D seismic data

    Science.gov (United States)

    Moskalenko, A. N.; Khudoley, A. K.; Khusnitdinov, R. R.

    2017-05-01

    In this work, we consider application of an original method for determining the indicators of the tectonic stress fields in the northern Baikit anteclise based on 3D seismic data for further reconstruction of the stress state parameters when analyzing structural maps of seismic horizons and corresponded faults. The stress state parameters are determined by the orientations of the main stress axes and shape of the stress ellipsoid. To calculate the stress state parameters from data on the spatial orientations of faults and slip vectors, we used the algorithms from quasiprimary stress computation methods and cataclastic analysis, implemented in the software products FaultKinWin and StressGeol, respectively. The results of this work show that kinematic characteristics of faults regularly change toward the top of succession and that the stress state parameters are characterized by different values of the Lode-Nadai coefficient. Faults are presented as strike-slip faults with normal or reverse component of displacement. Three stages of formation of the faults are revealed: (1) partial inversion of ancient normal faults, (2) the most intense stage with the predominance of thrust and strike-slip faults at north-northeast orientation of an axis of the main compression, and (3) strike-slip faults at the west-northwest orientation of an axis of the main compression. The second and third stages are pre-Vendian in age and correlate to tectonic events that took place during the evolution of the active southwestern margin of the Siberian Craton.

  12. a Revision to the Tectonics of the Flores Back-Arc Thrust Zone, Indonesia?

    Science.gov (United States)

    Tikku, A. A.

    2011-12-01

    The Flores and Bali Basins are continental basins in the Flores back-arc thrust zone associated with Eocene subduction of the Indo-Australian plate beneath the Sunda plate followed by Miocene to present-day inversion/thrusting. The basins are east of Java and north of the islands of Bali, Lombok, Sumbawa and Flores in the East Java Sea area of Indonesia. The tectonic interpretation of these basins is based on seismic, bathymetry and gravity data and is also supported by present-day GPS measurements that demonstrate subduction is no longer active across the Flores thrust zone. Current thinking about the area is that the Flores Basin (on the east end of the thrust zone) had the most extension in the back-arc thrust and may be a proto-oceanic basin, though the option of a purely continental extensional basin can not be ruled out. The Bali Basin (on the west end of the thrust zone) is thought to be shallower and have experienced less continental thinning and extension than the Flores Basin. Depth to basement estimates from recently collected marine magnetic data indicate the depth of the Bali Basin may be comparable to the depth of the Flores Basin. Analysis of the marine magnetic data and potential implications of relative plate motions will be presented.

  13. Gondwana Tales: an inquiry approach to plate tectonics

    Science.gov (United States)

    Domènech Casal, Jordi

    2014-05-01

    Plate tectonics and its effects on the constitution of seas and continents are key models in science education. Fossil evidences are usually taught in demostrative key when Wegener's discoverings about Pangea are introduced. In order to introduce inquiry-based science education (IBSE) approaches to this topic, we propose "Gondwana Tales", an activity where students are asked to use fossil data to reconstruct the geologic history of an imaginary planet. Grouped in independent teams, each team is furnished with stratigraphic columns from several sites containing faunistic successions of real organisms existing in the past in Earth. Students are told to reconstruct a model of the evolution of the continents, by making calculations of relative ages of the fossils, and relating each fossil to a geologic era. The different teams have incomplete and complementary information. After a first step where they have to propose a partial model based on incomplete data, each team receives a "visitor scientist" from another team, this implying an informal scientific communication event. This process is performed several times, engaging a discussion in each team and getting a final consensus model created by the whole class. Correct answer is not given to the students, even at the end of the activity, to keep the activity under the parameters of real scientific experience, where there is not a "correct answer" to compare. Instead of this, and following the IBSE standards, a reflection on the process is proposed to students. The lack of complete information and the need to collaborate are part of classroom dynamics focused to the understanding of the process of creation of the scientific knowledge. This activity is part of the C3 Project on Creation of Scientific Knowledge that is being applied in the school.

  14. Time-reversibility in seismic sequences: Application to the seismicity of Mexican subduction zone

    Science.gov (United States)

    Telesca, L.; Flores-Márquez, E. L.; Ramírez-Rojas, A.

    2018-02-01

    In this paper we investigate the time-reversibility of series associated with the seismicity of five seismic areas of the subduction zone beneath the Southwest Pacific Mexican coast, applying the horizontal visibility graph method to the series of earthquake magnitudes, interevent times, interdistances and magnitude increments. We applied the Kullback-Leibler divergence D that is a metric for quantifying the degree of time-irreversibility in time series. Our findings suggest that among the five seismic areas, Jalisco-Colima is characterized by time-reversibility in all the four seismic series. Our results are consistent with the peculiar seismo-tectonic characteristics of Jalisco-Colima, which is the closest to the Middle American Trench and belongs to the Mexican volcanic arc.

  15. High-resolution numerical modeling of tectonic underplating in circum-Pacific subduction zones: toward a better understanding of deformation in the episodic tremor and slip region?

    Science.gov (United States)

    Menant, A.; Angiboust, S.; Gerya, T.; Lacassin, R.; Simoes, M.; Grandin, R.

    2017-12-01

    Study of now-exhumed ancient subduction systems have evidenced km-scale tectonic units of marine sediments and oceanic crust that have been tectonically underplated (i.e. basally accreted) from the downgoing plate to the overriding plate at more than 30-km depth. Such huge mass transfers must have a major impact, both in term of long-term topographic variations and seismic/aseismic deformation in subduction zones. However, the quantification of such responses to the underplating process remains poorly constrained. Using high-resolution visco-elasto-plastic thermo-mechanical models, we present with unprecedented details the dynamics of formation and destruction of underplated complexes in subductions zones. Initial conditions in our experiments are defined in order to fit different subduction systems of the circum-Pacific region where underplating process is strongly suspected (e.g. the Cascadia, SW-Japan, New Zealand, and Chilean subduction zones). It appears that whatever the subduction system considered, underplating of sediments and oceanic crust always occur episodically forming a coherent nappe stacking at depths comprised between 10 and 50 km. At higher depth, a tectonic mélange with a serpentinized mantle wedge matrix developed along the plates interface. The size of these underplated complexes changes according to the subduction system considered. For instance, a 15-km thick nappe stacking is obtained for the N-Chilean subduction zone after a series of underplating events. Such an episodic event lasts 4-5 Myrs and can be responsible of a 2-km high uplift in the forearc region. Subsequent basal erosion of these underplated complexes results in their only partial preservation at crustal and mantle depth, suggesting that, after exhumation, only a tiny section of the overall underplated material can be observed nowadays in ancient subduction systems. Finally, tectonic underplating in our numerical models is systematically associated with (1) an increasing

  16. Full Seismic Waveform Tomography of the Japan region using Adjoint Methods

    Science.gov (United States)

    Steptoe, Hamish; Fichtner, Andreas; Rickers, Florian; Trampert, Jeannot

    2013-04-01

    We present a full-waveform tomographic model of the Japan region based on spectral-element wave propagation, adjoint techniques and seismic data from dense station networks. This model is intended to further our understanding of both the complex regional tectonics and the finite rupture processes of large earthquakes. The shallow Earth structure of the Japan region has been the subject of considerable tomographic investigation. The islands of Japan exist in an area of significant plate complexity: subduction related to the Pacific and Philippine Sea plates is responsible for the majority of seismicity and volcanism of Japan, whilst smaller micro-plates in the region, including the Okhotsk, and Okinawa and Amur, part of the larger North America and Eurasia plates respectively, contribute significant local intricacy. In response to the need to monitor and understand the motion of these plates and their associated faults, numerous seismograph networks have been established, including the 768 station high-sensitivity Hi-net network, 84 station broadband F-net and the strong-motion seismograph networks K-net and KiK-net in Japan. We also include the 55 station BATS network of Taiwan. We use this exceptional coverage to construct a high-resolution model of the Japan region from the full-waveform inversion of over 15,000 individual component seismograms from 53 events that occurred between 1997 and 2012. We model these data using spectral-element simulations of seismic wave propagation at a regional scale over an area from 120°-150°E and 20°-50°N to a depth of around 500 km. We quantify differences between observed and synthetic waveforms using time-frequency misfits allowing us to separate both phase and amplitude measurements whilst exploiting the complete waveform at periods of 15-60 seconds. Fréchet kernels for these misfits are calculated via the adjoint method and subsequently used in an iterative non-linear conjugate-gradient optimization. Finally, we employ

  17. Seismic link at plate boundary

    Indian Academy of Sciences (India)

    process constrain the seismic hazard assessment. Some frequent issues .... to obtain information on the causality between .... 2004), and low frequency deep triggering. (Miyazawa .... can trigger shallow thrust fault earthquakes; Science 306.

  18. Seismic evidence for central Taiwan magnetic low and deep-crustal deformation caused by plate collision

    Science.gov (United States)

    Cheng, Win-Bin

    2018-01-01

    Crustal seismic velocity structure was determined for the northern Taiwan using seismic travel-time data to investigate the northeastern extension of the northern South China Sea's high-magnetic belt. In order to increase the model resolution, a joint analysis of gravity anomaly and seismic travel-time data have been conducted. A total of 3385 events had been used in the inversion that was collected by the Central Weather Bureau Seismological Network from 1990 to 2015. The main features of the obtained three-dimensional velocity model are: (1) a relatively high Vp zone with velocity greater than 6.5 km/s is observed in the middle to lower crust, (2) the high Vp zone generally parallels to the north-south structural trending of the Chuchih fault and Hsuehshan Range, (3) at 25 km depth-slice, the high Vp zone shows structural trends change from northeastward to northward in central Taiwan, where the values of high-magnetic anomalies are rapidly decreasing to low values. A combination of seismic, GPS, and structural interpretations suggests that the entire crust has been deformed and demagnetized in consequence of the collision between the Philippine Sea plate and the Asian continental margin. We suggest that the feature of sharp bending of the high Vp zone would migrate southwestward and cause further crustal deformation of the Peikang High in the future.

  19. Seismic and Geodetic Monitoring of the Nicoya, Costa Rica, Seismic Gap

    Science.gov (United States)

    Protti, M.; Gonzalez, V.; Schwartz, S.; Dixon, T.; Kato, T.; Kaneda, Y.; Simila, G.; Sampson, D.

    2007-05-01

    The Nicoya segment of the Middle America Trench has been recognized as a mature seismic gap with potential to generate a large earthquake in the near future (it ruptured with large earthquakes in 1853, 1900 and 1950). Low level of background seismicity and fast crustal deformation of the forearc are indicatives of strong coupling along the plate interface. Given its high seismic potential, the available data and especially the fact that the Nicoya peninsula extends over large part of the rupture area, this gap was selected as one of the two sites for a MARGINS-SEIZE experiment. With the goal of documenting the evolution of loading and stress release along this seismic gap, an international effort involving several institutions from Costa Rica, the United States and Japan is being carried out for over a decade in the region. This effort involves the installation of temporary and permanent seismic and geodetic networks. The seismic network includes short period, broad band and strong motion instruments. The seismic monitoring has provided valuable information on the geometry and characteristics of the plate interface. The geodetic network includes temporary and permanent GPS stations as well as surface and borehole tiltmeters. The geodetic networks have helped quantify the extend and degree of coupling. A continuously recording, three- station GPS network on the Nicoya Peninsula, Costa Rica, recorded what we believe is the first slow slip event observed along the plate interface of the Costa Rica subduction zone. We will present results from these monitoring networks. Collaborative international efforts are focused on expanding these seismic and geodetic networks to provide improved resolution of future creep events, to enhanced understanding of the mechanical behavior of the Nicoya subduction segment of the Middle American Trench and possibly capture the next large earthquake and its potential precursor deformation.

  20. Mantle structure and tectonic history of SE Asia

    Science.gov (United States)

    Hall, Robert; Spakman, Wim

    2015-09-01

    Seismic travel-time tomography of the mantle under SE Asia reveals patterns of subduction-related seismic P-wave velocity anomalies that are of great value in helping to understand the region's tectonic development. We discuss tomography and tectonic interpretations of an area centred on Indonesia and including Malaysia, parts of the Philippines, New Guinea and northern Australia. We begin with an explanation of seismic tomography and causes of velocity anomalies in the mantle, and discuss assessment of model quality for tomographic models created from P-wave travel times. We then introduce the global P-wave velocity anomaly model UU-P07 and the tectonic model used in this paper and give an overview of previous interpretations of mantle structure. The slab-related velocity anomalies we identify in the upper and lower mantle based on the UU-P07 model are interpreted in terms of the tectonic model and illustrated with figures and movies. Finally, we discuss where tomographic and tectonic models for SE Asia converge or diverge, and identify the most important conclusions concerning the history of the region. The tomographic images of the mantle record subduction beneath the SE Asian region to depths of approximately 1600 km. In the upper mantle anomalies mainly record subduction during the last 10 to 25 Ma, depending on the region considered. We interpret a vertical slab tear crossing the entire upper mantle north of west Sumatra where there is a strong lateral kink in slab morphology, slab holes between c.200-400 km below East Java and Sumbawa, and offer a new three-slab explanation for subduction in the North Sulawesi region. There is a different structure in the lower mantle compared to the upper mantle and the deep structure changes from west to east. What was imaged in earlier models as a broad and deep anomaly below SE Asia has a clear internal structure and we argue that many features can be identified as older subduction zones. We identify remnants of slabs

  1. Basement Structure and Styles of Active Tectonic Deformation in Central Interior Alaska

    Science.gov (United States)

    Dixit, N.; Hanks, C.

    2017-12-01

    Central Interior Alaska is one of the most seismically active regions in North America, exhibiting a high concentration of intraplate earthquakes approximately 700 km away from the southern Alaska subduction zone. Based on increasing seismological evidence, intraplate seismicity in the region does not appear to be uniformly distributed, but concentrated in several discrete seismic zones, including the Nenana basin and the adjacent Tanana basin. Recent seismological and neotectonics data further suggests that these seismic zones operate within a field of predominantly pure shear driven primarily by north-south crustal shortening. Although the location and magnitude of the seismic activity in both basins are well defined by a network of seismic stations in the region, the tectonic controls on intraplate earthquakes and the heterogeneous nature of Alaska's continental interior remain poorly understood. We investigated the current crustal architecture and styles of tectonic deformation of the Nenana and Tanana basins using existing geological, geophysical and geochronological datasets. The results of our study demonstrate that the basements of the basins show strong crustal heterogeneity. The Tanana basin is a relatively shallow (up to 2 km) asymmetrical foreland basin with its southern, deeper side controlled by the northern foothills of the central Alaska Range. Northeast-trending strike-slip faults within the Tanana basin are interpreted as a zone of clockwise crustal block rotation. The Nenana basin has a fundamentally different geometry; it is a deep (up to 8 km), narrow transtensional pull-apart basin that is deforming along the left-lateral Minto Fault. This study identifies two distinct modes of tectonic deformation in central Interior Alaska at present, and provides a basis for modeling the interplay between intraplate stress fields and major structural features that potentially influence the generation of intraplate earthquakes in the region.

  2. Seismically active column and volcanic plumbing system beneath the island arc of the Izu-Bonin subduction zone

    Science.gov (United States)

    Špičák, Aleš; Vaněk, Jiří; Hanuš, Václav

    2009-12-01

    A detailed spatio-temporal analysis of teleseismic earthquake occurrence (mb > 4.0) along the convergent margin of the Izu-Bonin-Mariana arc system reveals an anomalously high concentration of events between 27° and 30.5°N, beneath a chain of seamounts between Tori-shima and Nishino-shima volcanoes. This seismicity is dominated by the 1985/1986 earthquake swarm represented in the Engdahl-van der Hilst-Buland database by 146 earthquakes in the body wave magnitude range 4.3-5.8 and focal depth range 1-100 km. The epicentral cluster of the swarm is elongated parallel to the volcanic chain. Available focal mechanisms are consistent with an extensional tectonic regime and reveal nodal planes with azimuths close to that of the epicentral cluster. Earthquakes of the 1985/1986 swarm occurred in seven time phases. Seismic activity migrated in space from one phase to the other. Earthquake foci belonging to individual phases of the swarm aligned in vertically disposed seismically active columns. The epicentral zones of the columns are located in the immediate vicinity of seamounts Suiyo and Mokuyo, recently reported by the Japanese Meteorological Agency as volcanically active. The three observations-episodic character of earthquake occurrence, column-like vertically arranged seismicity pattern, and existence of volcanic seamounts at the seafloor above the earthquake foci-led us to interpret the 1985/1986 swarm as a consequence of subduction-related magmatic and/or fluid activity. A modification of the shallow earthquake swarm magmatic model of D. Hill fits earthquake foci distribution, tectonic stress orientation and fault plane solutions. The 1985/1986 deep-rooted earthquake swarm in the Izu-Bonin region represents an uncommon phenomenon of plate tectonics. The portion of the lithospheric wedge that was affected by the swarm should be composed of fractured rigid, brittle material so that the source of magma and/or fluids which might induce the swarm should be situated at a

  3. Sedimentary structure and tectonic setting of the abyssal basins adjoining the southeast part of the Ontong Java Plateau, western Pacific Ocean

    Science.gov (United States)

    Shimizu, S.; Masato, N.; Miura, S.; Suetsugu, D.

    2017-12-01

    Ontong Java Plateau(OJP) in the western Pacific Ocean is one of the largest oceanic plateau in the world. Radioactive ages of drilling samples indicate that the most part of the OJP was emplaced about 122 Ma (Mahoney et al., 1993). Taylor (2006) proposed that the OJP formed as a single large volcanic province together with the Manihiki and Hikurangi plateaus. OJP is surrounding by East Mariana, Pigafetta, Nauru, Ellice, Stewart, and Lyra basins. The East Mariana and Pigafetta basins were formed at the Pacific-Izanagi ridge and the Nauru basin was formed at Pacific-Phoenix ridges (Nakanishi et al., 1992). The tectonic history of the Ellice, Stewart, and Lyra basins is still unknown because of lack of magnetic anomaly lineations. Tectonic setting during the OJP formation is thus a matter of controversy. To expose the tectonic setting of the Ellice, Stewart, and Lyra basins, we conducted the Multi-Channel Seismic (MCS) survey in the basins during the research cruise by R/V Mirai of JAMSTEC in 2014. We present our preliminary results of the MCS survey in the Stewart basin(SB) and Ellice Basin(EB). After the regular data processing, we compared the seismic facies of MCS profile with DSDP Site 288 and ODP Site 1184 to assign ages to seismic reflectors. Our processing exposed several remarkable structures in the basins. The graben structures deformed only the igneous basement in the northwestern and northeastern and southwestern margins of the SB. This suggests the graben structures were formed before sedimentary layer deposited. Taylor (2006) proposed that the basin was formed by the NW-SE rifting during the separation of OJP and Manihiki Plateau around 120 Ma. Neal (1997) proposed that the NE-SW rifting formed the basin around 80 Ma. Our study supports the rifting model proposed by Neal et al. (1997) because the displacement of graben in northeastern and southwestern margins of the SB is larger than that in northwestern of the SB. We found several igneous diapirs in the

  4. Seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing.

    Science.gov (United States)

    Audet, Pascal; Bostock, Michael G; Christensen, Nikolas I; Peacock, Simon M

    2009-01-01

    Water and hydrous minerals play a key part in geodynamic processes at subduction zones by weakening the plate boundary, aiding slip and permitting subduction-and indeed plate tectonics-to occur. The seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization. However, seismological observations bearing on the presence of water within the subducting plate itself are less well documented. Here we use converted teleseismic waves to obtain observations of anomalously high Poisson's ratios within the subducted oceanic crust from the Cascadia continental margin to its intersection with forearc mantle. On the basis of pressure, temperature and compositional considerations, the elevated Poisson's ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values. Combined with observations of a strong negative velocity contrast at the top of the oceanic crust, our results imply that the megathrust is a low-permeability boundary. The transition from a low- to high-permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization. These results may have important implications for our understanding of seismogenesis, subduction zone structure and the mechanism of episodic tremor and slip.

  5. Tools for educational access to seismic data

    Science.gov (United States)

    Taber, J. J.; Welti, R.; Bravo, T. K.; Hubenthal, M.; Frechette, K.

    2017-12-01

    Student engagement can be increased both by providing easy access to real data, and by addressing newsworthy events such as recent large earthquakes. IRIS EPO has a suite of access and visualization tools that can be used for such engagement, including a set of three tools that allow students to explore global seismicity, use seismic data to determine Earth structure, and view and analyze near-real-time ground motion data in the classroom. These tools are linked to online lessons that are designed for use in middle school through introductory undergraduate classes. The IRIS Earthquake Browser allows discovery of key aspects of plate tectonics, earthquake locations (in pseudo 3D) and seismicity rates and patterns. IEB quickly displays up to 20,000 seismic events over up to 30 years, making it one of the most responsive, practical ways to visualize historical seismicity in a browser. Maps are bookmarkable and preserve state, meaning IEB map links can be shared or worked into a lesson plan. The Global Seismogram Plotter automatically creates visually clear seismic record sections from selected large earthquakes that are tablet-friendly and can also to be printed for use in a classroom without computers. The plots are designed to be appropriate for use with no parameters to set, but users can also modify the plots, such as including a recording station near a chosen location. A guided exercise is provided where students use the record section to discover the diameter of Earth's outer core. Students can pick and compare phase arrival times onscreen which is key to performing the exercise. A companion station map shows station locations and further information and is linked to the record section. jAmaSeis displays seismic data in real-time from either a local instrument and/or from remote seismic stations that stream data using standard seismic data protocols, and can be used in the classroom or as a public display. Users can filter data, fit a seismogram to travel time

  6. Vertical deformation through a complete seismic cycle at Isla Santa María, Chile

    Science.gov (United States)

    Wesson, Robert L.; Melnick, Daniel; Cisternas, Marco; Moreno, Marcos; Ely, Lisa

    2014-01-01

    Individual great earthquakes are posited to release the elastic strain energy that has accumulated over centuries by the gradual movement of tectonic plates1, 2. However, knowledge of plate deformation during a complete seismic cycle—two successive great earthquakes and the intervening interseismic period—remains incomplete3. A complete seismic cycle began in south-central Chile in 1835 with an earthquake of about magnitude 8.5 (refs 4, 5) and ended in 2010 with a magnitude 8.8 earthquake6. During the first earthquake, an uplift of Isla Santa María by 2.4 to 3 m was documented4, 5. In the second earthquake, the island was uplifted7 by 1.8 m. Here we use nautical surveys made in 1804, after the earthquake in 1835 and in 1886, together with modern echo sounder surveys and GPS measurements made immediately before and after the 2010 earthquake, to quantify vertical deformation through the complete seismic cycle. We find that in the period between the two earthquakes, Isla Santa María subsided by about 1.4 m. We simulate the patterns of vertical deformation with a finite-element model and find that they agree broadly with predictions from elastic rebound theory2. However, comparison with geomorphic and geologic records of millennial coastline emergence8, 9 reveal that 10–20% of the vertical uplift could be permanent.

  7. Problems of the active tectonics of the Eastern Black Sea

    Science.gov (United States)

    Javakhishvili, Z.; Godoladze, T.; Dreger, D. S.; Mikava, D.; Tvaliashvili, A.

    2016-12-01

    The Black Sea Basin is the part of the Arabian Eurasian Collision zone and important unit for understanding the tectonic process of the region. This complex basin comprises two deep basins, separated by the mid-Black Sea Ridge. The basement of the Black Sea includes areas with oceanic and continental crust. It was formed as a "back-arc" basin over the subduction zone during the closing of the Tethys Ocean. In the past decades the Black Sea has been the subject of intense geological and geophysical studies. Several papers were published about the geological history, tectonics, basement relief and crustal and upper mantle structure of the basin. New tectonic schemes were suggested (e. g. Nikishin et al 2014, Shillington et al. 2008, Starostenko et al. 2004 etc.). Nevertheless, seismicity of the Black Sea is poorly studied due to the lack of seismic network in the coastal area. It is considered, that the eastern basin currently lies in a compressional setting associated with the uplift of the Caucasus and structural development of the Caucasus was closely related to the evolution of the Eastern Black Sea Basin. Analyses of recent sequence of earthquakes in 2012 can provide useful information to understand complex tectonic structure of the Eastern Black Sea region. Right after the earthquake of 2012/12/23, National Seismic monitoring center of Georgia deployed additional 4 stations in the coastal area of the country, close to the epicenter area, to monitor aftershock sequence. Seismic activity in the epicentral area is continuing until now. We have relocated approximately 1200 aftershocks to delineate fault scarf using data from Georgian, Turkish and Russian datacenters. Waveforms of the major events and the aftershocks were inverted for the fault plane solutions of the events. For the inversion were used green's functions, computed using new 1D velocity model of the region. Strike-slip mechanism of the major events of the earthquake sequence indicates extensional

  8. Teaching And Learning Tectonics With Web-GIS

    Science.gov (United States)

    Anastasio, D. J.; Sahagian, D. L.; Bodzin, A.; Teletzke, A. L.; Rutzmoser, S.; Cirucci, L.; Bressler, D.; Burrows, J. E.

    2012-12-01

    Tectonics is a new curriculum enhancement consisting of six Web GIS investigations designed to augment a traditional middle school Earth science curriculum. The investigations are aligned to Disciplinary Core Ideas: Earth and Space Science from the National Research Council's (2012) Framework for K-12 Science Education and to tectonics benchmark ideas articulated in the AAAS Project 2061 (2007) Atlas of Science Literacy. The curriculum emphasizes geospatial thinking and scientific inquiry and consists of the following modules: Geohazards, which plate boundary is closest to me? How do we recognize plate boundaries? How does thermal energy move around the Earth? What happens when plates diverge? What happens when plate move sideways past each other? What happens when plates collide? The Web GIS interface uses JavaScript for simplicity, intuition, and convenience for implementation on a variety of platforms making it easier for diverse middle school learners and their teachers to conduct authentic Earth science investigations, including multidisciplinary visualization, analysis, and synthesis of data. Instructional adaptations allow students who are English language learners, have disabilities, or are reluctant readers to perform advanced desktop GIS functions including spatial analysis, map visualization and query. The Web GIS interface integrates graphics, multimedia, and animation in addition to newly developed features, which allow users to explore and discover geospatial patterns that would not be easily visible using typical classroom instructional materials. The Tectonics curriculum uses a spatial learning design model that incorporates a related set of frameworks and design principles. The framework builds on the work of other successful technology-integrated curriculum projects and includes, alignment of materials and assessments with learning goals, casting key ideas in real-world problems, engaging students in scientific practices that foster the use of key

  9. Reassessment of seismic hazards at the Los Alamos National Laboratory

    International Nuclear Information System (INIS)

    Wong, I.G.; Hemphill-Haley, M.A.; Kelson, K.I.; Gardner, J.N.; House, L.S.

    1991-01-01

    A comprehensive seismic hazards evaluation program has been initiated at the Los Alamos National Laboratory (LANL) to update the current seismic design criteria. In part, this program has been motivated by recent studies which suggest that faults of the nearby Pajarito fault system may be capable of generating a large magnitude earthquake (M > 7). The specific objectives of this program are to: (1) characterize the tectonic setting of the LANL area; (2) characterize the nature, amount, and timing of late Quaternary fault displacements; (3) reevaluate the recorded seismicity in the LANL region to allow for the evaluation of seismogenic faults and the tectonic state of stress; (4) characterize the subsurface geologic conditions beneath the LANL required for the estimation of strong ground motions and site response; (5) estimate potential strong ground shaking both deterministically and probabilistically; and (6) develop the appropriate seismic design criteria. The approach and initial results of this seismic hazards program are described in this paper

  10. Revisit of Criteria and Evidence for the Tectonic Erosion vs Accretion in East Asian Margin

    Science.gov (United States)

    Kimura, G.; Hamahashi, M.

    2015-12-01

    Accretionary and erosive margins provide tectonic end-members in subduction zone and how these tectonic processes might be recorded and recognizable in ancient subduction complexes remains a challenging issue. Tectonic erosion includes sediment subduction and basal erosion along the plate boundary megathrust and drags down the crust of the upper plate into the mantle. Geologic evidence for the erosion is commonly based on lost geological tectono-stratigraphic data, i.e. gaps in the record and indirect phenomena such as subsidence of the forearc slopes. A topographically rough surface such as seamount has been suggested to work like an erosive saw carving the upper plate. Another mechanism of basal erosion has been suggested to be hydrofracturing of upper plate materials due to dehydration-induced fluid pressures, resulting in entrainment of upper plate materials into the basal décollement. Considering the interaction between the ~30 km thick crust of the upper plate and subducting oceanic plate, a subduction dip angle of ~15°, and convergent rate of ~10 cm/year, at least ~1 Ma of continuous basal erosion is necessary to induce clear subsidence of the forearc because the width of plate interface between the upper crustal and subducting plates is about 115 km (30/cos15°). In several examples of subduction zones, for example the Japan Trench and the Middle America Trench off Costa Rica, the subsidence of a few thousand metres of the forearc, combined with a lack of accretionary prism over a period of several million years, suggest that the erosive condition needs to be maintained for several to tens of million years.Such age gaps in the accretionary complex, however, do not automatically imply that tectonic erosion has taken place, as other interpretations such as no accretion, cessation of subduction, and/or later tectonic modification, are also possible. Recent drilling in the forearc of the Nankai Trough suggests that the accretion was ceased between ~12 Ma to

  11. Imaging the Iceland Hotspot Track Beneath Greenland with Seismic Noise Correlations

    Science.gov (United States)

    Mordret, A.

    2017-12-01

    During the past 65 million years, the Greenland craton drifted over the Iceland hotspot; however, uncertainties in geodynamic modeling and a lack of geophysical evidence prevent an accurate reconstruction of the hotspot track. I image the Greenland lithosphere down to 300 km depth with seismic noise tomography. The hotspot track is observed as a linear high-velocity anomaly in the middle crust associated with magmatic intrusions. In the upper mantle, the remnant thermal signature of the hotspot manifests as low velocity and low viscosity bodies. This new detailed picture of the Greenland lithosphere will drive more accurate geodynamic reconstructions of tectonic plate motions and prediction of Greenland heat flow, which in turn will enable more precise estimations of the Greenland ice-sheet mass balance.

  12. Phanerozoic tectonic evolution of the Circum-North Pacific

    Science.gov (United States)

    Nokleberg, Warren J.; Parfenov, Leonid M.; Monger, James W.H.; Norton, Ian O.; Khanchuk, Alexander I.; Stone, David B.; Scotese, Christopher R.; Scholl, David W.; Fujita, Kazuya

    2000-01-01

    the ancestral margins of present-day Northeast Asia and northwestern North America. The rifting resulted in the fragmentation of each continent and the formation of cratonal and passive continental-margin terranes that eventually migrated and accreted to other sites along the evolving margins of the original or adjacent continents. (2) From about the Late Triassic through the mid-Cretaceous, a succession of island arcs and tectonically paired subduction zones formed near the continental margins. (3) From about mainly the mid-Cretaceous through the present, a succession of igneous arcs and tectonically paired subduction zones formed along the continental margins. (4) From about the Jurassic to the present, oblique convergence and rotations caused orogenparallel sinistral and then dextral displacements within the upper-plate margins of cratons that have become Northeast Asia and North America. The oblique convergences and rotations resulted in the fragmentation, displacement, and duplication of formerly more nearly continuous arcs, subduction zones, and passive continental margins. These fragments were subsequently accreted along the expanding continental margins. (5) From the Early Jurassic through Tertiary, movement of the upper continental plates toward subduction zones resulted in strong plate coupling and accretion of the former island arcs and subduction zones to the continental margins. Accretions were accompanied and followed by crustal thickening, anatexis, metamorphism, and uplift. The accretions resulted in substantial growth of the North Asian and North American Continents. (6) During the middle and late Cenozoic, oblique to orthogonal convergence of the Pacifi c plate with present-day Alaska and Northeast Asia resulted in formation of the modern-day ring of volcanoes around the Circum-North Pacific. Oblique convergence between the Pacific plate and Alaska also resulted in major dextral-slip faulting in interior and southern Alaska and along the western p

  13. The April 2017 M6.7 Botswana Earthquake: Implications for African Intraplate Seismicity.

    Science.gov (United States)

    Gardonio, B.; Calais, E.; Jolivet, R.

    2017-12-01

    The last decades have seen a rapidly increasing number of studies of interplate seismicity, revealing for instance the fundamental relationship between seismic and aseismic slip along plate boundary faults. To the contrary, intraplate earthquakes, occurring far from plate boundaries are still misunderstood and by far less studied. Key questions are the mechanisms through which elastic strain builds up and is released in the seismogenic crust in such contexts, in the absence of (yet) measurable intraplate strain rates. The April 2017 M6.7 Botswana earthquake was a surprise in many ways. This is the largest recorded event that struck this ordinarily seismically quiet region, West to the East-African Rift system where most of the usual southern seismicity occurs. It may also be the largest intraplate event recorded since the 1988 Tennant Creek earthquake in central Australia. No active structure can be mapped at the surface. Active extension related to the east African rifting may occur several hundreds of kilometers to the north-east with low rates of a few mm per year. Closer to the event, the Okavango delta, located at 20° of latitude and 23° of longitude is considered by some as an incipient rift with very low deformation rates, similar to a large part of the southern African continent. Interestingly, seismic activity in the area of the recent Botswana earthquake is more important than the world average intraplate activity, potentially due to rifting to the east and/or large stresses induced by lateral gradients in gravitational potential energy (this part of the world has an altitude of 1000 to 2000 m.). The aim of this study is to better constrain the tectonic setting and the dynamics of the Botswana earthquake area. To do so, we analyze a Sentinel 1 interferogram of the event to constrain the strike, dip, depth, magnitude and location of the earthquake. We also analyze continuous teleseismic signals during two months centered on the mainshock using a template

  14. Seismic attenuation structure beneath Nazca Plate subduction zone in southern Peru

    Science.gov (United States)

    Jang, H.; Kim, Y.; Clayton, R. W.

    2017-12-01

    We estimate seismic attenuation in terms of quality factors, QP and QS using P and S phases, respectively, beneath Nazca Plate subduction zone between 10°S and 18.5°S latitude in southern Peru. We first relocate 298 earthquakes with magnitude ranges of 4.0-6.5 and depth ranges of 20-280 km. We measure t*, which is an integrated attenuation through the seismic raypath between the regional earthquakes and stations. The measured t* are inverted to construct three-dimensional attenuation structures of southern Peru. Checkerboard test results for both QP and QS structures ensure good resolution in the slab-dip transition zone between flat and normal slab subduction down to a depth of 200 km. Both QP and QS results show higher attenuation continued down to a depth of 50 km beneath volcanic arc and also beneath the Quimsachata volcano, the northernmost young volcano, located far east of the main volcanic front. We also observe high attenuation in mantle wedge especially beneath the normal subduction region in both QP and QS (100-130 in QP and 100-125 in QS) and slightly higher QP and QS beneath the flat-subduction and slab-dip transition regions. We plan to relate measured attenuation in the mantle wedge to material properties such as viscosity to understand the subduction zone dynamics.

  15. Current deformation in the Tibetan Plateau: a stress gauge in the large-scale India-Asia collision tectonics

    Science.gov (United States)

    Capitanio, F. A.

    2017-12-01

    The quantification of the exact tectonic forces budget on Earth has remained thus far elusive. Geodetic velocities provide relevant constraints on the current dynamics of the coupling between collision and continental tectonics, however in the Tibetan plateau these support contrasting, non-unique models. Here, we compare numerical models of coupled India-Asia plate convergence, collision and continent interiors tectonics to the geodetically-constrained motions in the Tibetan Plateau to provide a quantitative assessment of the driving forces of plate tectonics in the area. The models develop a range of long-term evolutions remarkably similar to the Asian tectonics in the Cenozoic, reproducing the current large-scale motions pattern under a range of conditions. Balancing the convergent margin forces, following subduction, and the far-field forcing along the trail of the subducting continent, the geodetic rates in the Tibetan Plateau can be matched. The comparisons support the discussion on the likely processes at work, allowing inferences on the drivers of plateau formation and its role on the plate margin-interiors tectonics. More in general, the outcomes highlight the unique role of the Tibetan Plateau as a pressure gauge for the tectonic forces on Earth.

  16. Dynamic response to strike-slip tectonic control on the deposition and evolution of the Baranof Fan, Gulf of Alaska

    Science.gov (United States)

    Walton, Maureen A. L.; Gulick, Sean P. S.; Reece, Robert S.; Barth, Ginger A.; Christeson, Gail L.; VanAvendonk, Harm J.

    2014-01-01

    The Baranof Fan is one of three large deep-sea fans in the Gulf of Alaska, and is a key component in understanding large-scale erosion and sedimentation patterns for southeast Alaska and western Canada. We integrate new and existing seismic reflection profiles to provide new constraints on the Baranof Fan area, geometry, volume, and channel development. We estimate the fan’s area and total sediment volume to be ∼323,000 km2 and ∼301,000 km3, respectively, making it among the largest deep-sea fans in the world. We show that the Baranof Fan consists of channel-levee deposits from at least three distinct aggradational channel systems: the currently active Horizon and Mukluk channels, and the waning system we call the Baranof channel. The oldest sedimentary deposits are in the northern fan, and the youngest deposits at the fan’s southern extent; in addition, the channels seem to avulse southward consistently through time. We suggest that Baranof Fan sediment is sourced from the Coast Mountains in southeastern Alaska, transported offshore most recently via fjord to glacial sea valley conduits. Because of the translation of the Pacific plate northwest past sediment sources on the North American plate along the Queen Charlotte strike-slip fault, we suggest that new channel formation, channel beheadings, and southward-migrating channel avulsions have been influenced by regional tectonics. Using a simplified tectonic reconstruction assuming a constant Pacific plate motion of 4.4 cm/yr, we estimate that Baranof Fan deposition initiated ca. 7 Ma.

  17. The 2016 seismic series in the south Alboran Sea: Seismotectonics, Coulomb Failure Stress changes and implications for the active tectonics in the area.

    Science.gov (United States)

    Alvarez-Gómez, José A.; Martín, Rosa; Pérez-López, Raul; Stich, Daniel; Cantavella, Juan V.; Martínez-Díaz, José J.; Morales, José; Soto, Juan I.; Carreño, Emilio

    2017-04-01

    System towards the south, but also in near pure reverse faults in the fault zone bounding the the Alboran Ridge. Both types of faults and rupture-mechanisms coexist, linked mechanically by stress transfer, being coeval the uplift of the Alboran Ridge and its northwestward displacement due to the left-lateral motion of the Al-Idrisi Fault. It is also discussed how the contrasting faulting processes and seismic ruptures are developed in two differentially oriented fault zones in the context the current NW-SE plate convergence between the African and Eurasian plates in the Westernmost Mediterranean.

  18. Seismicity, state of stress and induced seismicity in the molasse basin and Jura (N-Switzerland)

    Energy Technology Data Exchange (ETDEWEB)

    Deichmann, N. [Schweizerischer Erdbebendienst, ETH Zuerich, Zuerich (Switzerland); Burlini, L. [Institut of Geology, ETH Zuerich, Zuerich (Switzerland)

    2010-07-01

    This illustrated report for the Swiss Federal Office of Energy (SFOE) is one of a series of appendices dealing with the potential for geological sequestration of CO{sub 2} in Switzerland. This report takes a look at the seismicity, state of stress and induced seismicity in the molasse basin and Jura Mountains in northern Switzerland. Data collected since 1983 by the Swiss Earthquake Service and the National Cooperative for the Disposal of Radioactive Wastes NAGRA on the tectonics and seismic properties of North-western Switzerland is noted. The results are illustrated with a number of maps and graphical representations and are discussed in detail. Cases of induced seismicity as resulting from both natural and man-made causes are examined.

  19. Thrust-wrench interference tectonics in the Gulf of Cadiz (Africa-Iberia plate boundary in the North-East Atlantic): Insights from analog models

    OpenAIRE

    Duarte , João ,; Rosas , Filipe ,; Terrinha , Pedro; Gutscher , Marc-André ,; Malavielle , Jacques; Silva , Sonia; Matias , Luis

    2011-01-01

    International audience; In the Gulf of Cadiz key segment of the Africa-Iberia plate boundary (North-East Atlantic ocean), three main different modes of tectonic interference between a recently identified wrench system (SWIM) and the Gulf of Cadiz Accretionary Wedge (GCAW) were tested through analog sand-box modeling: a) An active accretionary wedge on top of a pre-existent inactive basement fault; b) An active strike-slip fault cutting a previously formed, inactive, accretionary wedge; and c)...

  20. Tectonic and climatic considerations for deep geological disposal of radioactive waste: A UK perspective.

    Science.gov (United States)

    McEvoy, F M; Schofield, D I; Shaw, R P; Norris, S

    2016-11-15

    Identifying and evaluating the factors that might impact on the long-term integrity of a deep Geological Disposal Facility (GDF) and its surrounding geological and surface environment is central to developing a safety case for underground disposal of radioactive waste. The geological environment should be relatively stable and its behaviour adequately predictable so that scientifically sound evaluations of the long-term radiological safety of a GDF can be made. In considering this, it is necessary to take into account natural processes that could affect a GDF or modify its geological environment up to 1millionyears into the future. Key processes considered in this paper include those which result from plate tectonics, such as seismicity and volcanism, as well as climate-related processes, such as erosion, uplift and the effects of glaciation. Understanding the inherent variability of process rates, critical thresholds and likely potential influence of unpredictable perturbations represent significant challenges to predicting the natural environment. From a plate-tectonic perspective, a one million year time frame represents a very short segment of geological time and is largely below the current resolution of observation of past processes. Similarly, predicting climate system evolution on such time-scales, particularly beyond 200ka AP is highly uncertain, relying on estimating the extremes within which climate and related processes may vary with reasonable confidence. The paper highlights some of the challenges facing a deep geological disposal program in the UK to review understanding of the natural changes that may affect siting and design of a GDF. Crown Copyright © 2016. Published by Elsevier B.V. All rights reserved.

  1. Stress Transfer Processes during Great Plate Boundary Thrusting Events: A Study from the Andaman and Nicobar Segments

    Science.gov (United States)

    Andrade, V.; Rajendran, K.

    2010-12-01

    The response of subduction zones to large earthquakes varies along their strike, both during the interseismic and post-seismic periods. The December 26, 2004 earthquake nucleated at 3° N latitude and its rupture propagated northward, along the Andaman-Sumatra subduction zone, terminating at 15°N. Rupture speed was estimated at about 2.0 km per second in the northern part under the Andaman region and 2.5 - 2.7 km per second under southern Nicobar and North Sumatra. We have examined the pre and post-2004 seismicity to understand the stress transfer processes within the subducting plate, in the Andaman (10° - 15° N ) and Nicobar (5° - 10° N) segments. The seismicity pattern in these segments shows distinctive characteristics associated with the outer rise, accretionary prism and the spreading ridge, all of which are relatively better developed in the Andaman segment. The Ninety East ridge and the Sumatra Fault System are significant tectonic features in the Nicobar segment. The pre-2004 seismicity in both these segments conform to the steady-state conditions wherein large earthquakes are fewer and compressive stresses dominate along the plate interface. Among the pre-2004 great earthquakes are the 1881 Nicobar and 1941 Andaman events. The former is considered to be a shallow thrust event that generated a small tsunami. Studies in other subduction zones suggest that large outer-rise tensional events follow great plate boundary breaking earthquakes due to the the up-dip transfer of stresses within the subducting plate. The seismicity of the Andaman segment (1977-2004) concurs with the steady-state stress conditions where earthquakes occur dominantly by thrust faulting. The post-2004 seismicity shows up-dip migration along the plate interface, with dominance of shallow normal faulting, including a few outer rise events and some deeper (> 100 km) strike-slip faulting events within the subducting plate. The September 13, 2002, Mw 6.5 thrust faulting earthquake at

  2. Seismic Constraints on the Lithosphere-Asthenosphere Boundary Beneath the Izu-Bonin Area: Implications for the Oceanic Lithospheric Thinning

    Science.gov (United States)

    Cui, Qinghui; Wei, Rongqiang; Zhou, Yuanze; Gao, Yajian; Li, Wenlan

    2018-01-01

    The lithosphere-asthenosphere boundary (LAB) is the seismic discontinuity with negative velocity contrasts in the upper mantle. Seismic detections on the LAB are of great significance in understanding the plate tectonics, mantle convection and lithospheric evolution. In this paper, we study the LAB in the Izu-Bonin subduction zone using four deep earthquakes recorded by the permanent and temporary seismic networks of the USArray. The LAB is clearly revealed with sP precursors (sdP) through the linear slant stacking. As illustrated by reflected points of the identified sdP phases, the depth of LAB beneath the Izu-Bonin Arc (IBA) is about 65 km with a range of 60-68 km. The identified sdP phases with opposite polarities relative to sP phases have the average relative amplitude of 0.21, which means a 3.7% velocity drop and implies partial melting in the asthenosphere. On the basis of the crustal age data, the lithosphere beneath the IBA is located at the 1100 °C isotherm calculated with the GDH1 model. Compared to tectonically stable areas, such as the West Philippine Basin (WPB) and Parece Vela Basin (PVB) in the Philippine Sea, the lithosphere beneath the Izu-Bonin area shows the obvious lithospheric thinning. According to the geodynamic and petrological studies, the oceanic lithospheric thinning phenomenon can be attributed to the strong erosion of the small-scale convection in the mantle wedge enriched in volatiles and melts.

  3. LWD lithostratigraphy, physical properties and correlations across tectonic domains at the NanTroSEIZE drilling transect, Nankai Trough subduction zone, Japan

    Science.gov (United States)

    Tudge, J.; Webb, S. I.; Tobin, H. J.

    2013-12-01

    Since 2007 the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) has drilled a total of 15 sites across the Nankai Trough subduction zone, including two sites on the incoming sediments of the Philippine Sea plate (PSP). Logging-while-drilling (LWD) data was acquired at 11 of these sites encompassing the forearc Kumano Basin, upper accretionary prism, toe region and input sites. Each of these tectonic domains is investigated for changes in physical properties and LWD characteristics, and this work fully integrates a large data set acquired over multiple years and IODP expeditions, most recently Expedition 338. Using the available logging-while-drilling data, primarily consisting of gamma ray, resistivity and sonic velocity, a log-based lithostratigraphy is developed at each site and integrated with the core, across the entire NanTroSEIZE transect. In addition to simple LWD characterization, the use of Iterative Non-hierarchical Cluster Analysis (INCA) on the sites with the full suite of LWD data clearly differentiates the unaltered forearc and slope basin sediments from the deformed sediments of the accretionary prism, suggesting the LWD is susceptible to the subtle changes in the physical properties between the tectonic domains. This differentiation is used to guide the development of tectonic-domain specific physical properties relationships. One of the most important physical property relationships between is the p-wave velocity and porosity. To fully characterize the character and properties of each tectonic domain we develop new velocity-porosity relationships for each domain found across the NanTroSEIZE transect. This allows the porosity of each domain to be characterized on the seismic scale and the resulting implications for porosity and pore pressure estimates across the plate interface fault zone.

  4. Cenozoic tectonic jumping and implications for hydrocarbon accumulation in basins in the East Asia Continental Margin

    Science.gov (United States)

    Suo, Yanhui; Li, Sanzhong; Yu, Shan; Somerville, Ian D.; Liu, Xin; Zhao, Shujuan; Dai, Liming

    2014-07-01

    Tectonic migration is a common geological process of basin formation and evolution. However, little is known about tectonic migration in the western Pacific margins. This paper focuses on the representative Cenozoic basins of East China and its surrounding seas in the western Pacific domain to discuss the phenomenon of tectonic jumping in Cenozoic basins, based on structural data from the Bohai Bay Basin, the South Yellow Sea Basin, the East China Sea Shelf Basin, and the South China Sea Continental Shelf Basin. The western Pacific active continental margin is the eastern margin of a global convergent system involving the Eurasian Plate, the Pacific Plate, and the Indian Plate. Under the combined effects of the India-Eurasia collision and retrogressive or roll-back subduction of the Pacific Plate, the western Pacific active continental margin had a wide basin-arc-trench system which migrated or ‘jumped’ eastward and further oceanward. This migration and jumping is characterized by progressive eastward younging of faulting, sedimentation, and subsidence within the basins. Owing to the tectonic migration, the geological conditions associated with hydrocarbon and gashydrate accumulation in the Cenozoic basins of East China and its adjacent seas also become progressively younger from west to east, showing eastward younging in the generation time of reservoirs, seals, traps, accumulations and preservation of hydrocarbon and gashydrate. Such a spatio-temporal distribution of Cenozoic hydrocarbon and gashydrate is significant for the oil, gas and gashydrate exploration in the East Asian Continental Margin. Finally, this study discusses the mechanism of Cenozoic intrabasinal and interbasinal tectonic migration in terms of interplate, intraplate and underplating processes. The migration or jumping regimes of three separate or interrelated events: (1) tectonism-magmatism, (2) basin formation, and (3) hydrocarbon-gashydrate accumulation are the combined effects of the

  5. Seismogenic structures of the central Apennines and its implication for seismic hazard

    Science.gov (United States)

    Zheng, Y.; Riaz, M. S.; Shan, B.

    2017-12-01

    The central Apennines belt is formed during the Miocene-to-Pliocene epoch under the environment where the Adriatic Plate collides with and plunges beneath the Eurasian Plate, eventually formed a fold and thrust belt. This active fold and thrust belt has experienced relatively frequent moderate-magnitude earthquakesover, as well as strong destructive earthquakes such as the 1997 Umbira-Marche sequence, the 2009 Mw 6.3 L'Aquila earthquake sequence, and three strong earthquakes occurred in 2016. Such high seismicity makes it one of the most active tectonic zones in the world. Moreover, most of these earthquakes are normal fault events with shallow depths, and most earthquakes occurred in the central Apennines are of lower seismic energy to moment ratio. What seismogenic structure causes such kind of seismic features? and how about the potential seismic hazard in the study region? In order to make in-depth understanding about the seismogenic structures in this reion, we collected seismic data from the INGV, Italy, to model the crustal structure, and to relocate the earthquakes. To improve the spatial resolution of the tomographic images, we collected travel times from 27627 earthquakes with M>1.7 recorded at 387 seismic stations. Double Difference Tomography (hereafter as DDT) is applied to build velocity structures and earthquake locations. Checkerboard test confirms that the spatial resolution between the depths range from 5 20km is better than 10km. The travel time residual is significantly decreased from 1208 ms to 70 ms after the inversion. Horizontal Vp images show that mostly earthquakes occurred in high anomalies zones, especially between 5 10km, whereas at the deeper depths, some of the earthquakes occurred in the low Vp anomalies. For Vs images, shallow earthquakes mainly occurred in low anomalies zone, at depths range of 10 15km, earthquakes are mainly concentrated in normal velocity or relatively lower anomalies zones. Moreover, mostly earthquakes occurred

  6. Stagnant lids and mantle overturns: Implications for Archaean tectonics, magmagenesis, crustal growth, mantle evolution, and the start of plate tectonics

    Directory of Open Access Journals (Sweden)

    Jean H. Bédard

    2018-01-01

    probability that oceanic crustal segments could founder in an organized way, producing a gradual evolution of pre-subduction convergent margins into modern-style active subduction systems around 2.5 Ga. Plate tectonics today is constituted of: (1 a continental drift system that started in the Early Archaean, driven by deep mantle currents pressing against the Archaean-age sub-continental lithospheric mantle keels that underlie Archaean cratons; (2 a subduction-driven system that started near the end of the Archaean.

  7. Radon emanations: a tectonic indicator in the Dharamsala area of Himalayan Frontal Zone, Himachal Pradesh

    International Nuclear Information System (INIS)

    Dhar, Sunil

    2013-01-01

    While throughout the length of Himalayas good exposures of the tertiary and the pre-Tertiary occurs occur, but in the Dharamsala and its adjoining areas of Himalayan Frontal Zone, tertiary and the pre-Tertiary rocks are present within a short aerial distance. This diverse lithology within a short span of distance along with the structural heterogeneity has made this region of Himalayas tectonically significant. This unique tectano-stratigraphic configuration of this area is primarily attributed to the major faults and folds which are either along the Himalayan trend or transverse to it. Interestingly the area is seismically active and falls in the High Seismic Zone-V of seismic atlas of India. It has been observed that regional thrusts systems and lineaments, control seismo-tectonic activity in the region. Contemporary geomorphological re-adjustments in the form of erosion intensity (meandering/drainage pattern or river incision) as a result of active nature of lineaments have been observed. In addition, due to the rampant seismic activity in the region especially in year 2013, the area has witnessed a sequence of landslides. The study further reveals these the signatures of morphological adjustment coincide with zones which have deciphered higher proportions of radon activity. Because radon transport through rocks is largely dependent on the geology of the area, which includes lithology, compaction, porosity structural/tectonic features like thrusts, faults, joints and fractures. Occurrences of landslide the thrust zones, coupled with high emanations of radon (both in soil and water) alludes attention towards dominant role of neo-tectonic activity in the area. (author)

  8. Isostatic Model and Isostatic Gravity Anomalies of the Arabian Plate and Surroundings

    Science.gov (United States)

    Kaban, Mikhail K.; El Khrepy, Sami; Al-Arifi, Nassir

    2016-04-01

    The isostatic modeling represents one of the most useful "geological" reduction methods of the gravity field. With the isostatic correction, it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. Although there exist several isostatic compensation schemes, it is usually supposed that a choice of the model is not an important factor to first order, since the total weight of compensating masses remains the same. We compare two alternative models for the Arabian plate and surrounding area. The Airy model gives very significant regional isostatic anomalies, which cannot be explained by the upper crust structure or disturbances of the isostatic equilibrium. Also, the predicted "isostatic" Moho is very different from existing seismic observations. The second isostatic model includes the Moho, which is based on seismic determinations. Additional compensation is provided by density variations within the lithosphere (chiefly in the upper mantle). According to this model, the upper mantle under the Arabian Shield is less dense than under the Platform. In the Arabian platform, the maximum density coincides with the Rub' al Khali, one of the richest oil basin in the world. This finding agrees with previous studies, showing that such basins are often underlain by dense mantle, possibly related to an eclogite layer that has caused their subsidence. The mantle density variations might be also a result of variations of the lithosphere thickness. With the combined isostatic model, it is possible to minimize regional anomalies over the Arabian plate. The residual local anomalies correspond well to tectonic structure of the plate. Still very significant anomalies, showing isostatic disturbances of the lithosphere, are associated with the Zagros fold belt, the collision zone of the Arabian and Eurasian plates.

  9. Conceptual design by analysis of KALIMER seismic isolation

    International Nuclear Information System (INIS)

    You, Bong; Koo, Kyung Hoi; Lee, Jae Han

    1996-06-01

    The objectives of this report are to preliminarily evaluate the seismic isolation performance of KALIMER (Korea Advance LIquid MEtal Reactor) by seismic analyses, investigate the design feasibility, and find the critical points of KALIMER reactor structures. The work scopes performed in this study are 1) the establishment of seismic design basis, 2) the development of seismic analysis model of KALIMER, 3) the modal analysis, 4) seismic time history analysis, 5) the evaluations of seismic isolation performance and seismic design margins, and 6) the evaluation of seismic capability of KALIMER. The horizontal fundamental frequency of KALIMER reactor structure is 8 Hz, which is far remote from the seismic isolation frequency, 0.7 Hz. The vertical first and second natural frequencies are about 2 Hz and 8 Hz respectively. These vertical natural frequencies are in a dominant ground motion frequency bands, therefore these modes will result in large vertical response amplifications. From the results of seismic time history analyses, the horizontal isolation performance is great but the large vertical amplifications are occurred in reactor structures. The RV Liner has the smallest seismic design margin as 0.18. From the results of seismic design margins evaluation, the critical design change are needed in the support barrel, separation plate, and baffle plate points. The seismic capability of KALIMER is about 0.35g. This value can be increased by the design changes of the separation plate and etc.. 11 tabs., 29 figs., 7 refs. (Author) .new

  10. Seismic hazard assessment of Iran

    Directory of Open Access Journals (Sweden)

    M. Ghafory-Ashtiany

    1999-06-01

    Full Text Available The development of the new seismic hazard map of Iran is based on probabilistic seismic hazard computation using the historical earthquakes data, geology, tectonics, fault activity and seismic source models in Iran. These maps have been prepared to indicate the earthquake hazard of Iran in the form of iso-acceleration contour lines, and seismic hazard zoning, by using current probabilistic procedures. They display the probabilistic estimates of Peak Ground Acceleration (PGA for the return periods of 75 and 475 years. The maps have been divided into intervals of 0.25 degrees in both latitudinal and longitudinal directions to calculate the peak ground acceleration values at each grid point and draw the seismic hazard curves. The results presented in this study will provide the basis for the preparation of seismic risk maps, the estimation of earthquake insurance premiums, and the preliminary site evaluation of critical facilities.

  11. Cenozoic structures and the tectonic evolution of the eastern North Sea

    DEFF Research Database (Denmark)

    Clausen, O.R.; Nielsen, S.B.; Egholm, D.L.

    2011-01-01

    Abundant seismic sections and well data from the Cenozoic succession in the eastern North Sea area generally reveal normal faulting, salt tectonics and localized tectonic inversion. However, inferences on the Cenozoic dynamic evolution of the region require thorough analysis of interactions between...... or cover tectonism took place. Our objectives are thus 1) to analyze the interaction between basement and cover structures, and if possible 2) to relate the structures to the regional tectonic evolution. The Zechstein evaporites pinch out onto the Ringkøbing-Fyn High, which in the eastern North Sea...... influencede.g. Miocene deposition and controlled the generation of second order faults. The latter detached along the top Chalk Group due to the topography generated during faulting, i.e. they are second order detachment surfaces. We conclude that the regional tectonic significance of the Cenozoic structures...

  12. Seismic Evidence of Ancient Westward Residual Slab Subduction Beneath Southern Taiwan

    Directory of Open Access Journals (Sweden)

    Cheng-Horng Lin

    2015-01-01

    Full Text Available The northeastern convergence of the Philippine Sea plate toward the Eurasian plate causes the major western Philippine Sea plate boundary to subduct toward the northwest or west directions. However, this phenomenon is not clearly observed along the plate boundary between Luzon and Taiwan. Careful examination of deep seismicity in the southern Taiwan area from the earthquake catalog reported by the Central Weather Bureau shows two seismic zones dipping toward the opposing directions. The first dips toward the east from the surface down to 150 km in depth, while the second dips westward at depths between 150 and 200 km. These two seismic zones are confirmed further by seismogram observation and modeling results generated by two deep faults in the southern Taiwan area. The eastward seismic zone clearly results from the Eurasia plate subduction along the Manila trench, while a small section of the westward seismic zone might likely be a residual slab from the ancient subducted Philippine Sea plate. Based on the subduction speed obtained from GPS observations and the subducted Eurasian plate geometry, we can further estimate the eastward Eurasian plate subduction started at least 3.35 million years ago. This result is roughly consistent with the volcanic ages (3 - 4 Ma observed in the arc between Luzon and Taiwan.

  13. Balanced Cross Section for Restoration of Tectonic Evolution in the Southwest Okinawa Trough

    Institute of Scientific and Technical Information of China (English)

    Wu Shiguo; Ni Xianglong; Guo Junhua

    2007-01-01

    On the basis of the multi-channel seismic data and the other data, using 2DMove software,the tectonic evolution in three seismic profiles was restored since Pliocene. The tectonic restoration results show that: (1) the initial active center lay in the west slope and then was transferred to east and south via trough center during the evolution process; (2) several main normal faults controlled the evolution of the southern Okinawa Trough; (3) since Late Pliocene, the southern Okinawa Trough has experienced two spreading stages. The early is depression in Early-Middle Pleistocene and the late is back-arc spreading in Late Pleistocene and Holocene, which is in primary oceanic crust spreading stage.

  14. Tectonostratigraphy of the Passive Continental Margin Offshore Indus Pakistan

    Science.gov (United States)

    Aslam, K.; Khan, M.; Liu, Y.; Farid, A.

    2017-12-01

    The tectonic evolution and structural complexities are poorly understood in the passive continental margin of the Offshore Indus of Pakistan. In the present study, an attempt has been made to interpret the structural trends and seismic stratigraphic framework in relation to the tectonics of the region. Seismic reflection data revealed tectonically controlled, distinct episodes of normal faulting representing rifting at different ages and transpression in the Late Eocene time. This transpression has resulted in the reactivation of the Pre-Cambrian basement structures. The movement of these basement structures has considerably affected the younger sedimentary succession resulting in push up structures resembling anticlines. The structural growth of the push-up structures was computed. The most remarkable tectonic setting in the region is represented by the normal faulting and by the basement uplift which divides the rifting and transpression stages. Ten mappable seismic sequences have been identified on the seismic records. A Jurassic aged paleo-shelf has also been identified on all regional seismic profiles which is indicative of Indian-African Plates separation during the Jurassic time. Furthermore, the backstripping technique was applied which has been proved to be a powerful technique to quantify subsidence/uplift history of rift-type passive continental margins. The back strip curves suggest that transition from an extensional rifted margin to transpression occurred during Eocene time (50-30 Ma). The backstripping curves show uplift had happened in the area. We infer that the uplift has occurred due to the movement of basement structures by the transpression movements of Arabian and Indian Plates. The present study suggests that the structural styles and stratigraphy of the Offshore Indus Pakistan were significantly affected by the tectonic activities during the separation of Gondwanaland in the Mesozoic and northward movement of the Indian Plate, post

  15. Seismic ACROSS Transmitter Installed at Morimachi above the Subducting Philippine Sea Plate for the Test Monitoring of the Seismogenic Zone of Tokai Earthquake not yet to Occur

    Science.gov (United States)

    Kunitomo, T.; Kumazawa, M.; Masuda, T.; Morita, N.; Torii, T.; Ishikawa, Y.; Yoshikawa, S.; Katsumata, A.; Yoshida, Y.

    2008-12-01

    Here we report the first seismic monitoring system in active and constant operation for the wave propagation characteristics in tectonic region just above the subducting plate driving the coming catastrophic earthquakes. Developmental works of such a system (ACROSS; acronym for Accurately Controlled, Routinely Operated, Signal System) have been started in 1994 at Nagoya University and since 1996 also at TGC (Tono Geoscience Center) of JAEA promoted by Hyogoken Nanbu Earthquakes (1995 Jan.17, Mj=7.3). The ACROSS is a technology system including theory of signal and data processing based on the brand new concept of measurement methodology of Green function between a signal source and observation site. The works done for first generation system are reported at IWAM04 and in JAEA report (Kumazawa et al.,2007). The Meteorological Research Institute of JMA has started a project of test monitoring of Tokai area in 2004 in corporation with Shizuoka University to realize the practical use of the seismic ACROSS for earthquake prediction researches. The first target was set to Tokai Earthquake not yet to take place. The seismic ACROSS transmitter was designed so as to be appropriate for the sensitive monitoring of the deep active fault zone on the basis of the previous technology elements accumulated so far. The ground coupler (antenna) is a large steel-reinforced concrete block (over 20m3) installed in the basement rocks in order to preserve the stability. Eccentric moment of the rotary transmitter is 82 kgm at maximum, 10 times larger than that of the first generation. Carrier frequency of FM signal for practical use can be from 3.5 to 15 Hz, and the signal phase is accurately controlled by a motor with vector inverter synchronized with GPS clock with a precision of 10-4 radian or better. By referring to the existing structure model in this area (Iidaka et al., 2003), the site of the transmitting station was chosen at Morimachi so as to be appropriate for detecting the

  16. Three-phase tectonic evolution of the Andaman backarc basin

    Digital Repository Service at National Institute of Oceanography (India)

    KameshRaju, K.A.

    , very smooth t o- po graphic plane on either side characterizes segment C. Si n- gle - channel seismic reflection data over this segment depict a thick pile of sediments, with expressions of e x- tensional tectonics. Seismic eviden ce indicates... that there is more than 2 km thick sediment overburden over this spreading segment 2,8 . The axial trough along the entire length of segment C is well maintained in spite of high sediment influx in the region. Flanks of the spreading segment A, define a fan...

  17. DISCUSSION: When and How did Plate Tectonics Begin, What Came Before, and Why is this Controversy important for Understanding the Earth and Exoplanets?

    Science.gov (United States)

    Stern, R. J.; Gerya, T.; Sobolev, S. V.; Tackley, P.

    2015-12-01

    Because all 5 presentations in the Union session "When and How did Plate Tectonics Begin, What Came Before, and Why is this Controversy important for Understanding the Earth and Exoplanets?" will have 5 minute discussion periods, the scheduled 15 minute end-of-session discussion period is intended to allow other perspectives to be presented by the scientific community. We invite brief (2 powerpoint slides) comments from the community about any aspect of the topic at hand. We encourage anyone who has something pertinent or interesting to say to submit 2 powerpoint slides directly to any one of the four co-convenors listed on this abstract. The first slide should be a simple title with the name and affiliation of the commenter. The second slide should be the content of the comment. The convenors will compile all of these that are submitted up to the noon on the day before the session occurs, when we will upload the compiled files in the order that they were received (if we have received digital scans of signed waivers by that time, see below). During the discussion, we will call on those who have submitted 2 slides to the podium to make their points in 2 minutes or less (total time from being called to leaving the podium). Because this AGU Union session including the discussion period will be live-streamed and recorded, all Discussion Session commenters will be required to sign an AGU waiver acknowledging this and giving permission to be recorded. These will be sent via e-mail to those who submit 2 slide powerpoints. Commenters that do not sign and return the waiver will be scheduled after all commenters who have returned signed waivers and AGU will terminate live streaming and recording accordingly. If no one submits anything then we will have open discussion from the floor. We will also advertise the Monte Verita conference in Locarno Switzerland 17-22 July 2016. This conference will explore in greater detail the 5 key aspects of Plate Tectonic evolution briefly

  18. Role of tectonic inheritance in the instauration of Tunisian Atlassic fold-and-thrust belt: Case of Bouhedma - Boudouaou structures

    Science.gov (United States)

    Ghanmi, Mohamed Abdelhamid; Ghanmi, Mohamed; Aridhi, Sabri; Ben Salem, Mohamed Sadok; Zargouni, Fouad

    2016-07-01

    Tectonic inversion in the Bouhedma-Boudouaou Mountains was investigated through recent field work and seismic lines interpretation calibrated with petroleum well data. Located to the Central-Southern Atlas of Tunisia, this area signed shortened intra-continental fold-and-thrust belts. Two dissymmetric anticlines characterize Bouhedma - Boudouaou major fold. These structures show a strong virgation respectively from E-W to NNE-SSW as a response to the interference between both tectonic inversion and tectonic inheritance. This complex geometry is driven by Mesozoic rifting, which marked an extensional inherited regime. A set of late Triassic-Early Jurassic E-W and NW-SE normal faults dipping respectively to the North and to the East seems to widely affect the overall geodynamic evolution of this domain. They result in major thickness changes across the hanging wall and the footwall blocks in response with the rifting activity. Tectonic inversion is inferred from convergence between African and European plates since late Cretaceous. During Serravalian - Tortonian event, NW-SE trending paroxysm led to: 1) folding of pre-inversion and syn-inversion strata, 2) reactivation of pre-existing normal faults to reverse ones and 3) orogeny of the main structures with NE-SW and E-W trending. The compressional feature still remains active during Quaternary event (Post-Villafranchian) with N-S trending compression. Contraction during inversion generates folding and internal deformation as well as Fault-Propagation-Fold and folding related strike.

  19. Seismic behavior and design of a primary shield structure consisting of steel-plate composite (SC) walls

    Energy Technology Data Exchange (ETDEWEB)

    Booth, Peter N., E-mail: boothpn@purdue.edu [Lyles School of Civil Engineering, Purdue University, W. Lafayette, IN (United States); Varma, Amit H., E-mail: ahvarma@purdue.edu [Lyles School of Civil Engineering, Purdue University, W. Lafayette, IN (United States); Sener, Kadir C., E-mail: ksener@purdue.edu [Lyles School of Civil Engineering, Purdue University, W. Lafayette, IN (United States); Mori, Kentaro, E-mail: kentaro_mori@mhi.co.jp [Mitsubishi Heavy Industries, Ltd, Kobe (Japan)

    2015-12-15

    This paper presents an analytical evaluation of the seismic behavior and design of a unique primary shield (PSW) structure consisting of steel-plate composite (SC) walls designed for a typical pressurized water reactor (PWR) nuclear power plant. Researchers in Japan have previously conducted a reduced (1/6th) scale test of a PSW structure to evaluate its seismic (lateral) load-deformation behavior. This paper presents the development and benchmarking of a detailed 3D nonlinear inelastic finite element (NIFE) model to predict the lateral load-deformation response and behavior of the 1/6th scale test structure. The PSW structure consists of thick SC wall segments with complex and irregular geometry that surround the central reactor vessel cavity. The wall segments have three layers of steel plates (one each on the interior and exterior surfaces and one embedded in the middle) that are anchored to the concrete infill with stud anchors. The results from the 3D NIFE analyses include: (i) the lateral load-deformation behavior of the PSW structure, (ii) the progression of yielding in the steel plates, concrete cracking, formation of compression struts, and (iii) the final failure mode. These results are compared and benchmarked using experimental measurements and observations reported by Shodo et al. (2003). The analytical results provide significant insight into the lateral behavior and strength of the PSW structure, and are used for developing a design approach. This design approach starts with ACI 349 code equations for reinforced concrete shear walls and modifies them for application to the PSW structure. A simplified 3D linear elastic finite element (LEFE) model of the PSW structure is also proposed as a conventional structural analysis tool for estimating the design force demands for various load combinations.

  20. Seismic behavior and design of a primary shield structure consisting of steel-plate composite (SC) walls

    International Nuclear Information System (INIS)

    Booth, Peter N.; Varma, Amit H.; Sener, Kadir C.; Mori, Kentaro

    2015-01-01

    This paper presents an analytical evaluation of the seismic behavior and design of a unique primary shield (PSW) structure consisting of steel-plate composite (SC) walls designed for a typical pressurized water reactor (PWR) nuclear power plant. Researchers in Japan have previously conducted a reduced (1/6th) scale test of a PSW structure to evaluate its seismic (lateral) load-deformation behavior. This paper presents the development and benchmarking of a detailed 3D nonlinear inelastic finite element (NIFE) model to predict the lateral load-deformation response and behavior of the 1/6th scale test structure. The PSW structure consists of thick SC wall segments with complex and irregular geometry that surround the central reactor vessel cavity. The wall segments have three layers of steel plates (one each on the interior and exterior surfaces and one embedded in the middle) that are anchored to the concrete infill with stud anchors. The results from the 3D NIFE analyses include: (i) the lateral load-deformation behavior of the PSW structure, (ii) the progression of yielding in the steel plates, concrete cracking, formation of compression struts, and (iii) the final failure mode. These results are compared and benchmarked using experimental measurements and observations reported by Shodo et al. (2003). The analytical results provide significant insight into the lateral behavior and strength of the PSW structure, and are used for developing a design approach. This design approach starts with ACI 349 code equations for reinforced concrete shear walls and modifies them for application to the PSW structure. A simplified 3D linear elastic finite element (LEFE) model of the PSW structure is also proposed as a conventional structural analysis tool for estimating the design force demands for various load combinations.

  1. Seismic variability of subduction thrust faults: Insights from laboratory models

    Science.gov (United States)

    Corbi, F.; Funiciello, F.; Faccenna, C.; Ranalli, G.; Heuret, A.

    2011-06-01

    Laboratory models are realized to investigate the role of interface roughness, driving rate, and pressure on friction dynamics. The setup consists of a gelatin block driven at constant velocity over sand paper. The interface roughness is quantified in terms of amplitude and wavelength of protrusions, jointly expressed by a reference roughness parameter obtained by their product. Frictional behavior shows a systematic dependence on system parameters. Both stick slip and stable sliding occur, depending on driving rate and interface roughness. Stress drop and frequency of slip episodes vary directly and inversely, respectively, with the reference roughness parameter, reflecting the fundamental role for the amplitude of protrusions. An increase in pressure tends to favor stick slip. Static friction is a steeply decreasing function of the reference roughness parameter. The velocity strengthening/weakening parameter in the state- and rate-dependent dynamic friction law becomes negative for specific values of the reference roughness parameter which are intermediate with respect to the explored range. Despite the simplifications of the adopted setup, which does not address the problem of off-fault fracturing, a comparison of the experimental results with the depth distribution of seismic energy release along subduction thrust faults leads to the hypothesis that their behavior is primarily controlled by the depth- and time-dependent distribution of protrusions. A rough subduction fault at shallow depths, unable to produce significant seismicity because of low lithostatic pressure, evolves into a moderately rough, velocity-weakening fault at intermediate depths. The magnitude of events in this range is calibrated by the interplay between surface roughness and subduction rate. At larger depths, the roughness further decreases and stable sliding becomes gradually more predominant. Thus, although interplate seismicity is ultimately controlled by tectonic parameters (velocity of

  2. Repeating Deep Very Low Frequency Earthquakes: An Evidence of Transition Zone between Brittle and Ductile Zone along Plate Boundary

    Science.gov (United States)

    Ishihara, Y.; Yamamoto, Y.; Arai, R.

    2017-12-01

    Recently slow or low frequency seismic and geodetic events are focused under recognition of important role in tectonic process. The most western region of Ryukyu trench, Yaeyama Islands, is very active area of these type events. It has semiannual-like slow slip (Heki et.al., 2008; Nishimura et.al.,2014) and very frequent shallow very low frequency earthquakes near trench zone (Ando et.al.,2012; Nakamura et.al.,2014). Arai et.al.(2016) identified clear reverse phase discontinuity along plate boundary by air-gun survey, suggesting existence of low velocity layer including fluid. The subducting fluid layer is considered to control slip characteristics. On the other hand, deep low frequency earthquake and tremor observed at south-western Honshu and Shikoku of Japan are not identified well due to lack of high-quality seismic network. A broadband seismic station(ISG/PS) of Pacific21 network is operating in last 20 years that locates on occurrence potential area of low frequency earthquake. We tried to review continuous broadband record, searching low frequency earthquakes. In pilot survey, we found three very low frequency seismic events which are dominant in less than 0.1Hz component and are not listed in earthquake catalogue. Source locates about 50km depth and at transition area between slow slip event and active area of general earthquake along plate boundary. To detect small and/or hidden very low frequency earthquake, we applied matched filter analysis to continuous three components waveform data using pre-reviewed seismogram as template signal. 12 events with high correlation are picked up in last 10 years. Most events have very similar waveform, which means characteristics of repeating deep very low frequency earthquake. The event history of very low frequency earthquake is not related with one of slow slip event in this region. In Yaeyama region, low frequency earthquake, general earthquake and slow slip event occur dividing in space and have apparent

  3. Glacio-Seismotectonics: Ice Sheets, Crustal Deformation and Seismicity

    Science.gov (United States)

    Sauber, Jeanne; Stewart, Iain S.; Rose, James

    2000-01-01

    The last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity. This growth has been driven largely by the emergence of postglacial rebound models (PGM) constrained by new field observations that incorporate increasingly realistic rheological, mechanical, and glacial parameters. In this paper, we highlight some of these recent field-based investigations and new PGMs, and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation. The emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern Canada and Fennoscandia. However, many of these models neglect important parameters, such as topography, lateral variations in lithospheric strength and tectonic strain built up during glaciation. In glaciated mountainous terrains, glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism. Such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields.

  4. Impact of The N - S Fracture Zone Along The Indo-Australia Plate Analyzed from Local Seismic Data In The Western Offshore of Sumatra, Indonesia

    Science.gov (United States)

    Haridhi, H. A.; Klingelhoefer, F.; Huang, B. S.; Lee, C. S.

    2015-12-01

    Large subduction earthquake have repeatedly occurred along the Sumatra and Andaman subduction zones where the Indo-Australia plate is subducting beneath the Eurasian plate. We have analyzed earthquake data from local seismic network along the Sumatra region that provided by the Meteorology Climatology Geophysical Agencies of Indonesia (MCGAI), giving a reliable P-wave velocity model by using joint inversion of picked P-wave travel time using VELEST and a re-scanned single channel seismic reflection of Sumatra cruise I and II. As much as 1,503 events are being analyzed, that is from two years and three months of data recording (2009/04 - 2011/07). The VELEST and DD technique are used to relocate all events by forcing the obtained velocity model. It is found that the surface deformation and earthquake cluster are strongly influenced by the impact of an N - S subparalel fracture zone along the Indo-Australia plate. This also explains the seismic gaps along the Sumatra and Andaman subduction zones. So far, the intriguing seismogenic behaviour and forearc structure are not well explained by the existing models. Therefore, the planned IODP Expedition 362 is trying to ground truth the scientific questions. The aftershock earthquake data are huge, but they will provide a gateway to help the understanding of this shallow megathrust slip and reduce its devastated harzards.

  5. Tectonically asymmetric Earth: From net rotation to polarized westward drift of the lithosphere

    Directory of Open Access Journals (Sweden)

    Carlo Doglioni

    2015-05-01

    Full Text Available The possibility of a net rotation of the lithosphere with respect to the mantle is generally overlooked since it depends on the adopted mantle reference frames, which are arbitrary. We review the geological and geophysical signatures of plate boundaries, and show that they are markedly asymmetric worldwide. Then we compare available reference frames of plate motions relative to the mantle and discuss which is at best able to fit global tectonic data. Different assumptions about the depths of hotspot sources (below or within the asthenosphere, which decouples the lithosphere from the deep mantle predict different rates of net rotation of the lithosphere relative to the mantle. The widely used no-net-rotation (NNR reference frame, and low (1°/Ma net rotation (shallow hotspots source, all plates, albeit at different velocity, move westerly along a curved trajectory, with a tectonic equator tilted about 30° relative to the geographic equator. This is consistent with the observed global tectonic asymmetries.

  6. Heterogeneous subduction structure within the Pacific plate beneath the Izu-Bonin arc

    Science.gov (United States)

    Gong, Wei; Xing, Junhui; Jiang, Xiaodian

    2018-05-01

    The Izu-Bonin subduction zone is a subduction system formed in early Eocene. The structure of the subduction zone becomes complicated with the evolution of the surrounding plate motion, and many aspects are still unkown or ambiguous. The geodynamic implications are further investigated in related to published seismic observations and geochemical characters of the Izu-Bonin subduction zone. As indicated by seismic tomography and epicentral distributions, the dip angle of the plate beneath the segment to the south of 29°-30°N (the southern Izu-Bonin) is much steeper than the northern one (the northern Izu-Bonin). Deep focus events in the southern segment extend to the depth of ∼600 km, whereas in the northern section deep events just terminate at 420-450 km. Particularly, tomographic images show an obvious boundary between the northern and southern Izu-Bonin at depths of 150-600 km neglected in the previous studies. The northern and southern segments are even separated by a wide range of low-velocity anomaly in P and S wave tomography at 380 km and 450 km depths. In this depth range, three events near 30°N are characterized by strike-slip mechanisms with slab parallel σ1 and horizontally north-south trending σ3, which differ with the typical down-dip compression mechanisms for neighboring events. These events could be attributed to an abrupt change of the morphology and movement of the slab in the transition segment between the northern and southern Izu-Bonin. Indicated by the focal mechanisms, the northern and southern Izu-Bonin exhibits an inhomogeneous stress field, which is closely related to age differences of the downgoing slab. Because of the reheating process, the thermal age of the Pacific plate entering the Izu-Bonin trench in the past 10 Ma, is only 60-90 ± 20 Ma, along with the younger plate subducting in the northern segment. The seismic anisotropy implies that mantle wedge flow orientation is between the motion direction of the Pacific plate and

  7. Extensional tectonics on continents and the transport of heat and matter

    Science.gov (United States)

    Neugebauer, H. J.

    1985-01-01

    Intracontinental zones of extensional tectonic style are commonly of finite width and length. Associated sedimentary troughs are fault-controlled. The evolution of those structures is accompanied by volcanic activity of variable intensity. The characteristic surface structures are usually underlaid by a lower crust of the transitional type while deeper subcustal areas show delayed travel times of seismic waves especially at young tectonic provinces. A correspondence between deep-seated processes and zones of continental extension appears obvious. A sequential order of mechanisms and their importance are discussed in the light of modern data compilations and quantitative kinematic and dynamic approaches. The Cenozoic exensional tectonics related with the Rhine River are discussed.

  8. Northeastern Brazilian margin: Regional tectonic evolution based on integrated analysis of seismic reflection and potential field data and modelling

    Science.gov (United States)

    Blaich, Olav A.; Tsikalas, Filippos; Faleide, Jan Inge

    2008-10-01

    Integration of regional seismic reflection and potential field data along the northeastern Brazilian margin, complemented by crustal-scale gravity modelling, is used to reveal and illustrate onshore-offshore crustal structure correlation, the character of the continent-ocean boundary, and the relationship of crustal structure to regional variation of potential field anomalies. The study reveals distinct along-margin structural and magmatic changes that are spatially related to a number of conjugate Brazil-West Africa transfer systems, governing the margin segmentation and evolution. Several conceptual tectonic models are invoked to explain the structural evolution of the different margin segments in a conjugate margin context. Furthermore, the constructed transects, the observed and modelled Moho relief, and the potential field anomalies indicate that the Recôncavo, Tucano and Jatobá rift system may reflect a polyphase deformation rifting-mode associated with a complex time-dependent thermal structure of the lithosphere. The constructed transects and available seismic reflection profiles, indicate that the northern part of the study area lacks major breakup-related magmatic activity, suggesting a rifted non-volcanic margin affinity. In contrast, the southern part of the study area is characterized by abrupt crustal thinning and evidence for breakup magmatic activity, suggesting that this region evolved, partially, with a rifted volcanic margin affinity and character.

  9. Tectonic reactivation in the Indian Ocean: Evidences from seamount morphology and manganese nodule characteristics

    Digital Repository Service at National Institute of Oceanography (India)

    Mukhopadhyay, R.; Khadge, N.H.

    The Central Indian Ocean Basin (CIOB) was subjected to tectonic reactivation in geological past which is unusual for a basin occurring on an apparently single tectonic plate. ENE-WSW trending latitude parallel zone of reactivation across the central...

  10. The Formation of Laurentia: Evidence from Shear Wave Splitting and Seismic Tomography

    Science.gov (United States)

    Liddell, M. V.; Bastow, I. D.; Rawlinson, N.; Darbyshire, F. A.; Gilligan, A.

    2017-12-01

    The northern Hudson Bay region of Canada comprises several Archean cratonic nuclei, assembled by Paleoproterozoic orogenies including the 1.8 Ga Trans-Hudson Orogen (THO) and Rinkian-Nagssugtoqidian Orogen (NO). Questions remain about how similar in scale and nature these orogens were compared to modern orogens like the Himalayas. Also in question is whether the thick Laurentian cratonic root below Hudson Bay is stratified, with a seismically-fast Archean core underlain by a lower, younger, thermal layer. We investigate these problems via shear-wave splitting and teleseismic tomography using up to 25 years of data from 65 broadband seismic stations across northern Hudson Bay. The results of the complementary studies comprise the most comprehensive study to date of mantle seismic velocity and anisotropy in northern Laurentia. Splitting parameter patterns are used to interpret multiple layers, lithospheric boundaries, dipping anisotropy, and deformation zone limits for the THO and NO. Source-side waveguide effects from Japan and the Aleutian trench are observed despite the tomographic data being exclusively relative arrival time. Mitigating steps to ensure data quality are explained and enforced. In the Hudson Strait, anisotropic fast directions (φ) generally parallel the THO, which appears in tomographic images as a strong low velocity feature relative to the neighbouring Archean cratons. Several islands in northern Hudson Bay show short length-scale changes in φ coincident with strong velocity contrasts. These are interpreted as distinct lithospheric blocks with unique deformational histories, and point to a complex, rather than simple 2-plate, collisional history for the THO. Strong evidence is presented for multiple anisotropic layers beneath Archean zones, consistent with the episodic development model of cratonic keels (e.g., Yuan & Romanowicz 2010). We show via both tomographic inversion models and SKS splitting patterns that southern Baffin Island was

  11. Detecting Micro-seismicity and Long-duration Tremor-like Events from the Oklahoma Wavefield Experiment

    Science.gov (United States)

    Li, C.; Li, Z.; Peng, Z.; Zhang, C.; Nakata, N.

    2017-12-01

    Oklahoma has experienced abrupt increase of induced seismicity in the last decade. An important way to fully understand seismic activities in Oklahoma is to obtain more complete earthquake catalogs and detect different types of seismic events. The IRIS Community Wavefield Demonstration Experiment was deployed near Enid, Oklahoma in Summer of 2016. The dataset from this ultra-dense array provides an excellent opportunity for detecting microseismicity in that region with wavefield approaches. Here we examine continuous waveforms recorded by 3 seismic lines using local coherence for ultra-dense arrays (Li et al., 2017), which is a measure of cross-correlation of waveform at each station with its nearby stations. So far we have detected more than 5,000 events from 06/22/2016 to 07/20/2016, and majority of them are not listed on the regional catalog of Oklahoma or global catalogs, indicating that they are local events. We also identify 15-20 long-period long-duration events, some of them lasting for more than 500 s. Such events have been found at major plate-boundary faults (also known as deep tectonic tremor), as well as during hydraulic fracturing, slow-moving landslides and glaciers. Our next step is to locate these possible tremor-like events with their relative arrival times across the array and compare their occurrence times with solid-earth tides and injection histories to better understand their driving mechanisms.

  12. Seismic characteristics of central Brazil crust and upper mantle: A deep seismic refraction study

    Science.gov (United States)

    Soares, J.E.; Berrocal, J.; Fuck, R.A.; Mooney, W.D.; Ventura, D.B.R.

    2006-01-01

    A two-dimensional model of the Brazilian central crust and upper mantle was obtained from the traveltime interpretation of deep seismic refraction data from the Porangatu and Cavalcante lines, each approximately 300 km long. When the lines were deployed, they overlapped by 50 km, forming an E-W transect approximately 530 km long across the Tocantins Province and western Sa??o Francisco Craton. The Tocantins Province formed during the Neoproterozoic when the Sa??o Francisco, the Paranapanema, and the Amazon cratons collided, following the subduction of the former Goia??s ocean basin. Average crustal VP and VP/VS ratios, Moho topography, and lateral discontinuities within crustal layers suggest that the crust beneath central Brazil can be associated with major geological domains recognized at the surface. The Moho is an irregular interface, between 36 and 44 km deep, that shows evidences of first-order tectonic structures. The 8.05 and 8.23 km s-1 P wave velocities identify the upper mantle beneath the Porangatu and Cavalcante lines, respectively. The observed seismic features allow for the identification of (1) the crust has largely felsic composition in the studied region, (2) the absence of the mafic-ultramafic root beneath the Goia??s magmatic arc, and (3) block tectonics in the foreland fold-and-thrust belt of the northern Brasi??lia Belt during the Neoproterozoic. Seismic data also suggested that the Bouguer gravimetric discontinuities are mainly compensated by differences in mass distribution within the lithospheric mantle. Finally, the Goia??s-Tocantins seismic belt can be interpreted as a natural seismic alignment related to the Neoproterozoic mantle domain. Copyright 2006 by the American Geophysical Union.

  13. Some preliminary results of a worldwide seismicity estimation: a case study of seismic hazard evaluation in South America

    Directory of Open Access Journals (Sweden)

    C. V. Christova

    2000-06-01

    Full Text Available Global data have been widely used for seismicity and seismic hazard assessment by seismologists. In the present study we evaluate worldwide seismicity in terms of maps of maximum observed magnitude (Mmax, seismic moment (M 0 and seismic moment rate (M 0S. The data set used consists of a complete and homogeneous global catalogue of shallow (h £ 60 km earthquakes of magnitude MS ³ 5.5 for the time period 1894-1992. In order to construct maps of seismicity and seismic hazard the parameters a and b derived from the magnitude-frequency relationship were estimated by both: a the least squares, and b the maximum likelihood, methods. The values of a and b were determined considering circles centered at each grid point 1° (of a mesh 1° ´1° and of varying radius, which starts from 30 km and moves with a step of 10 km. Only a and b values which fulfill some predefined conditions were considered in the further procedure for evaluating the seismic hazard maps. The obtained worldwide M max distribution in general delineates the contours of the plate boundaries. The highest values of M max observed are along the circum-Pacific belt and in the Himalayan area. The subduction plate boundaries are characterized by the largest amount of M 0 , while areas of continental collision are next. The highest values of seismic moment rate (per 1 year and per equal area of 10 000 km 2 are found in the Southern Himalayas. The western coasts of U.S.A., Northwestern Canada and Alaska, the Indian Ocean and the eastern rift of Africa are characterized by high values of M 0 , while most of the Pacific subduction zones have lower values of seismic moment rate. Finally we analyzed the seismic hazard in South America comparing the predicted by the NUVEL1 model convergence slip rate between Nazca and South America plates with the average slip rate due to earthquakes. This consideration allows for distinguishing between zones of high and low coupling along the studied convergence

  14. Tectonic Inversion Along the Algerian and Ligurian Margins: On the Insight Provided By Latest Seismic Processing Techniques Applied to Recent and Vintage 2D Offshore Multichannel Seismic Data

    Science.gov (United States)

    Schenini, L.; Beslier, M. O.; Sage, F.; Badji, R.; Galibert, P. Y.; Lepretre, A.; Dessa, J. X.; Aidi, C.; Watremez, L.

    2014-12-01

    Recent studies on the Algerian and the North-Ligurian margins in the Western Mediterranean have evidenced inversion-related superficial structures, such as folds and asymmetric sedimentary perched basins whose geometry hints at deep compressive structures dipping towards the continent. Deep seismic imaging of these margins is difficult due to steep slope and superficial multiples, and, in the Mediterranean context, to the highly diffractive Messinian evaporitic series in the basin. During the Algerian-French SPIRAL survey (2009, R/V Atalante), 2D marine multi-channel seismic (MCS) reflection data were collected along the Algerian Margin using a 4.5 km, 360 channel digital streamer and a 3040 cu. in. air-gun array. An advanced processing workflow has been laid out using Geocluster CGG software, which includes noise attenuation, 2D SRME multiple attenuation, surface consistent deconvolution, Kirchhoff pre-stack time migration. This processing produces satisfactory seismic images of the whole sedimentary cover, and of southward dipping reflectors in the acoustic basement along the central part of the margin offshore Great Kabylia, that are interpreted as inversion-related blind thrusts as part of flat-ramp systems. We applied this successful processing workflow to old 2D marine MCS data acquired on the North-Ligurian Margin (Malis survey, 1995, R/V Le Nadir), using a 2.5 km, 96 channel streamer and a 1140 cu. in. air-gun array. Particular attention was paid to multiple attenuation in adapting our workflow. The resulting reprocessed seismic images, interpreted with a coincident velocity model obtained by wide-angle data tomography, provide (1) enhanced imaging of the sedimentary cover down to the top of the acoustic basement, including the base of the Messinian evaporites and the sub-salt Miocene series, which appear to be tectonized as far as in the mid-basin, and (2) new evidence of deep crustal structures in the margin which the initial processing had failed to

  15. ON TECTONIC PROBLEMS OF THE OKINAWA TROUGH

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The Okinawa Trough is a very active tectonic zone at the margin of the Northwest Pacific and is typical of back-arc rifting at the young stage of tectonic evolution. Many scientists from Japan, China, Germany, France, the U.S.A. and Russia have done a lot of geologic and geophysical investigations there. It is well known that the Okinawa Trough is an active back-arc rift with extremely high heat flow, very strong hydrothermal circulation, strong volcanic and magmatic activity, frequent earthquakes, rapid subsidence and rifting, well-developed fault and central graben. But up to now, there are still some important tectonic problems about the Okinawa Trough that require clarification on some aspects such as the type of its crust, its forming time, its tectonic evolution, the distribution of its central grabens, the relationship between its high heat flow and tectonic activity. Based on the data obtained from seismic survey, geomagnetic and gravity measurements, submarine sampling and heat flow measurements in the last 15 years, the author discusses the following tectonic problems about the Okinawa Trough: (1) If the Okinawa Trough develops oceanic crust or not. (2) Is the South Okinawa Trough tectonically more active than the North Okinawa Trough with shallower water and few investigation data on it. (3) The formation time of the Okinawa Trough and its tectonic evolution. The Okinawa Trough has a very thin continental crust. Up to now, there is no evidence of oceanic crust in the Okinawa Trough. The North, Middle and South Okinawa Trough are all very strongly active areas. From 6 Ma B.P., the Okinawa Trough began to form. Since 2 Ma, the Okinawa Trough has been very active.

  16. GEOMAGNETIC CONJUGACY OF MODERN TECTONIC STRUCTURES

    Directory of Open Access Journals (Sweden)

    G. Ya. Khachikyan

    2013-01-01

    Full Text Available An earthquake is an element of the global electric circuit (GEC –  this new idea suggested in the space age is tested in our study. In the frame of the GEC concept, one may expect that tectonic structures of the northern and southern hemispheres may be magnetically conjugated. It is found that the midocean ridges of the southern hemisphere, located along the boundary of the Antarctic lithosphere plate, are magnetically conjugated with the areas of the junction of continental orogens and platforms in the northern hemisphere. The closest geomagnetic conjugacy exists between the southern boundary of Nazca lithospheric plate and the northern boundaries of Cocos and Caribbean lithospheric plates.

  17. Evaluation of seismic hazard of the Gökova bay in terms of seismotectonics

    Energy Technology Data Exchange (ETDEWEB)

    Erkoç, Ebru Aktepe, E-mail: ebru.aktepe@deu.edu.tr [The Graduate School of Natural and Applied Sciences, Dokuz Eylül University, İzmir-Turkey (Turkey); Uluğ, Atilla, E-mail: atilla.ulug@deu.edu.tr [Institute of Marine Science and Technology, Dokuz Eylül University, İzmir-Turkey (Turkey)

    2016-04-18

    While discovering the seismicity of our country, knowing the array of earthquake occurrence which reflects the characteristic tectonic features of each region makes vital contributions to the earthquakes that have occurred and to the pursuit of the processes which might occur in the future. When considering the region’s seismic activity, the presence of active faults that create earthquake within the bay is obvious. Many active fault parts in the Gulf of Gökova region continues their seismic activity with the opening effect that is generally prevailing in Western Anatolia. The region has generally been continuing its seismic activity under the control of normal faults. Considering the marine studies that are made and marine continuity of the faults which are on land in addition to the seismological and tectonic studies, the determination of seismic hazard in the Gulf of Gökova and its surroundings is also important in terms of introducing the earthquake scenarios with minimized errors.

  18. Evaluation of seismic hazard of the Gökova bay in terms of seismotectonics

    International Nuclear Information System (INIS)

    Erkoç, Ebru Aktepe; Uluğ, Atilla

    2016-01-01

    While discovering the seismicity of our country, knowing the array of earthquake occurrence which reflects the characteristic tectonic features of each region makes vital contributions to the earthquakes that have occurred and to the pursuit of the processes which might occur in the future. When considering the region’s seismic activity, the presence of active faults that create earthquake within the bay is obvious. Many active fault parts in the Gulf of Gökova region continues their seismic activity with the opening effect that is generally prevailing in Western Anatolia. The region has generally been continuing its seismic activity under the control of normal faults. Considering the marine studies that are made and marine continuity of the faults which are on land in addition to the seismological and tectonic studies, the determination of seismic hazard in the Gulf of Gökova and its surroundings is also important in terms of introducing the earthquake scenarios with minimized errors.

  19. Seismicity and Tectonics of the West Kaibab Fault Zone, AZ

    Science.gov (United States)

    Wilgus, J. T.; Brumbaugh, D. S.

    2014-12-01

    The West Kaibab Fault Zone (WKFZ) is the westernmost bounding structure of the Kaibab Plateau of northern Arizona. The WKFZ is a branching complex of high angle, normal faults downthrown to the west. There are three main faults within the WKFZ, the Big Springs fault with a maximum of 165 m offset, the Muav fault with 350 m of displacement, and the North Road fault having a maximum throw of approximately 90 m. Mapping of geologically recent surface deposits at or crossing the fault contacts indicates that the faults are likely Quaternary with the most recent offsets occurring one of the most seismically active areas in Arizona and lies within the Northern Arizona Seismic Belt (NASB), which stretches across northern Arizona trending NW-SE. The data set for this study includes 156 well documented events with the largest being a M5.75 in 1959 and including a swarm of seven earthquakes in 2012. The seismic data set (1934-2014) reveals that seismic activity clusters in two regions within the study area, the Fredonia cluster located in the NW corner of the study area and the Kaibab cluster located in the south central portion of the study area. The fault plane solutions to date indicate NE-SW to EW extension is occurring in the study area. Source relationships between earthquakes and faults within the WKFZ have not previously been studied in detail. The goal of this study is to use the seismic data set, the available data on faults, and the regional physiography to search for source relationships for the seismicity. Analysis includes source parameters of the earthquake data (location, depth, and fault plane solutions), and comparison of this output to the known faults and areal physiographic framework to indicate any active faults of the WKFZ, or suggested active unmapped faults. This research contributes to a better understanding of the present nature of the WKFZ and the NASB as well.

  20. Uniquely Acquired Vintage Seismic Reflection Data Reveal the Stratigraphic and Tectonic History of the Montana Disturbed Belt, USA

    Science.gov (United States)

    Speece, M. A.; Link, C. A.; Stickney, M.

    2011-12-01

    techniques including linear noise suppression of the air wave and ground roll, refraction statics, and prestack migration. Reprocessing of these data using state-of-the-art seismic reflection processing techniques will provide a detailed picture of the stratigraphy and tectonic framework for this region. Moreover, extended correlations of the Vibroseis records to Moho depths might reveal new insights on crustal thickness and provide a framework for understanding crustal thickening during the Laramide Orogeny as well as later Cenozoic extension.

  1. Geoprospective study of a nuclear waste repository. Prospective tectonics: convergent and divergent episodes, evolution of stress during the next 100,000 years

    International Nuclear Information System (INIS)

    Gros, Y.

    1985-01-01

    Within the frame of a contract with the CEC, dealing with storage and disposal of radioactive wastes in geological formations, the B.R.G.M. has been involved in a research on prospective tectonics. Within the Western European continental plate, since Mesozoic times, one sees the alternation or succession of convergent and divergent tectonic episodes. These tectonic episodes, although representing geologically discontinuous phenomena, still have time periods of between 4 to 40 millions years. These tectonic phenomena are the cause of the formation or reactivation, at all scales in the continental plate, of brittle, fault-like structures. Tectonic analysis and the in situ measures of stress and the earthquake focal phenomena show that, from the lower Quaternary to the present, the Western European continental plate has been subjected to NNW to SSE convergent stress. A study of the arrangement of European and African plates in the Western Mediterranean shows that the entire region, is undergoing a period of continental collision. The change in the process implies a westerly continental drift of the Spanish plate, a movement which would take several million years. On the Western European scale, the most likely hypothesis during the next 100,000 years is the persistance of the present stress trending approximately N-5. On the other hand, on a local scale, reorganisations of this stress are possible, owing to the presence of tectonic or lithological heterogeneities

  2. Volcano-tectonic earthquakes: A new tool for estimating intrusive volumes and forecasting eruptions

    Science.gov (United States)

    White, Randall A.; McCausland, Wendy

    2016-01-01

    We present data on 136 high-frequency earthquakes and swarms, termed volcano-tectonic (VT) seismicity, which preceded 111 eruptions at 83 volcanoes, plus data on VT swarms that preceded intrusions at 21 other volcanoes. We find that VT seismicity is usually the earliest reported seismic precursor for eruptions at volcanoes that have been dormant for decades or more, and precedes eruptions of all magma types from basaltic to rhyolitic and all explosivities from VEI 0 to ultraplinian VEI 6 at such previously long-dormant volcanoes. Because large eruptions occur most commonly during resumption of activity at long-dormant volcanoes, VT seismicity is an important precursor for the Earth's most dangerous eruptions. VT seismicity precedes all explosive eruptions of VEI ≥ 5 and most if not all VEI 4 eruptions in our data set. Surprisingly we find that the VT seismicity originates at distal locations on tectonic fault structures at distances of one or two to tens of kilometers laterally from the site of the eventual eruption, and rarely if ever starts beneath the eruption site itself. The distal VT swarms generally occur at depths almost equal to the horizontal distance of the swarm from the summit out to about 15 km distance, beyond which hypocenter depths level out. We summarize several important characteristics of this distal VT seismicity including: swarm-like nature, onset days to years prior to the beginning of magmatic eruptions, peaking of activity at the time of the initial eruption whether phreatic or magmatic, and large non-double couple component to focal mechanisms. Most importantly we show that the intruded magma volume can be simply estimated from the cumulative seismic moment of the VT seismicity from:

  3. Plate boundary deformation of the Pacific plate. Two case studies. (1) Crustal structure of the northwestern Vizcaino block and Gorda escarpment, offshore northern California, and implications for postsubduction deformation of a paleoaccretionary margin. (2) A focused look at the Alpine fault, New Zealand: Seismicity, focal mechanisms and stress observations

    Science.gov (United States)

    Leitner, Beate

    Two examples of Pacific rim plate boundary deformation are presented. In the first part of the thesis crustal models are derived for the northwestern part of the Vizcaino block in California using marine seismic and gravity data collected by the Mendocino Triple Junction Seismic Experiment. A northwest-southeast trending kink in the Moho is imaged and interpreted to have formed under compression by reactivation of preexisting thrust faults in the paleoaccretionary prism at the seaward margin of the Vizcaino block. The study suggests that the deformation resulted from mainly north-south compression between the Pacific-Juan de Fuca plates across the Mendocino transform fault and predates late Pliocene Pacific-North America plate convergence. In the second part, 195 earthquakes recorded during the duration of the Southern Alps Passive Seismic Experiment (SAPSE) are analysed. Precise earthquake locations and focal mechanisms provide unprecedented detail of the seismotectonics in the central South Island. The short term (6 month) SAPSE seismicity is compared with long term (8 years) seismicity recorded by the New Zealand National Seismic network and the Lake Pukaki network. The seismicity rate of the Alpine fault is low, but comparable to locked sections of the San Andreas fault, with large earthquakes expected. Changes of the depth of the seismogenic zone, generally uniform at about 10--12 km, occur only localised over distances smaller than 30 km, suggesting that thermal perturbations must be of similar scale. This implies that the thermal effects of the uplift of the Southern Alps do not change the seismogenic depth significantly and are not in accordance with most of the present thermal models. Both the Hope and Porters Pass fault zones are seismically active and deformation is accommodated near the fault zones and in the adjacent crust. North of Mt Cook, a triangular shaped region along the Alpine fault is characterised by absence of earthquakes. We interpret this

  4. From Extension to Shortening: Tectonic Inversion Distributed in Time and Space in the Alboran Sea, Western Mediterranean

    Science.gov (United States)

    Martínez-García, Pedro; Comas, Menchu; Lonergan, Lidia; Watts, Anthony B.

    2017-12-01

    2D seismic reflection data tied to biostratigraphical and log information from wells in the central and southeastern Alboran Sea have allowed us to constrain the spatial and temporal distribution of rifting and inversion. Normal faults, tilted basement blocks, and growth wedges reveal a thinned continental crust that formed in response to NW-SE extension. To the east, a secondary SW-NE trend of extension affects the transitional crust adjacent to the oceanic Algerian Basin. The maximum thickness of syn-rift sediments is 3.5 km, and the oldest recorded deposits are Serravallian. The WNW-ESE Yusuf fault formed a buttress separating and accommodating variable extension between two different tectonic domains: the thinned continental crust of Alboran and the oceanic spreading of the Algerian Basin. Late Tortonian to present-day NW-SE Africa/Eurasia plate convergence drove shortening and reactivation of some of the earlier extensional structures as reverse and strike-slip faults, forming complex, compartmentalised subbasins. Tectonic inversion coexisted with the formation of new faults and folds. Inversion was partial along the Habibas Basin and Al-Idrisi fault, but complete along the Alboran Ridge, where some SW-NE trending faults were perpendicular to the recent NW-SE plate convergence and were reactivated as thrusts. The WNW-ESE Yusuf fault is oblique to the convergence vector, and therefore, reactivation is mainly expressed as transpressional deformation. Volcanic rocks intruded along the Alboran Ridge and Yusuf faults during the latest stages of extension formed rheological anisotropies that localised the later inversion.

  5. Pickering seismic safety margin

    International Nuclear Information System (INIS)

    Ghobarah, A.; Heidebrecht, A.C.; Tso, W.K.

    1992-06-01

    A study was conducted to recommend a methodology for the seismic safety margin review of existing Canadian CANDU nuclear generating stations such as Pickering A. The purpose of the seismic safety margin review is to determine whether the nuclear plant has sufficient seismic safety margin over its design basis to assure plant safety. In this review process, it is possible to identify the weak links which might limit the seismic performance of critical structures, systems and components. The proposed methodology is a modification the EPRI (Electric Power Research Institute) approach. The methodology includes: the characterization of the site margin earthquake, the definition of the performance criteria for the elements of a success path, and the determination of the seismic withstand capacity. It is proposed that the margin earthquake be established on the basis of using historical records and the regional seismo-tectonic and site specific evaluations. The ability of the components and systems to withstand the margin earthquake is determined by database comparisons, inspection, analysis or testing. An implementation plan for the application of the methodology to the Pickering A NGS is prepared

  6. Exploration of the South-Eastern Alps lithosphere with 3D refraction seismics project Alp 2002 – data acquisition in Slovenia

    Directory of Open Access Journals (Sweden)

    Andrej Gosar

    2003-06-01

    Full Text Available Using combined seismic refraction/wide-angle reflection method project Alp 2002 explored the contact zone between South-Eastern Alps, Dinarides and Pannonian basin. In a network of 12 profiles of 4100 km total length, which are spread over seven countries,1055 portable seismographs were deployed and 31 strong (300 kg explosions fired. In Slovenia 127 seismographs were deployed along five profiles totalling 575 km and two explosions fired near Vojnik and Gradin. The collected data will allow construction of athree-dimensional model of the lithosphere and will contribute to the understanding of the tectonics and geodynamics at the junction of European, Adriatic and Tisza plates.

  7. Seismic swarms and fluid flow offshore Central America

    Science.gov (United States)

    Dzierma, Yvonne; Thorwart, Martin; Hensen, Christian; Rabbel, Wolfgang; Wolf, Florian

    2010-05-01

    Offshore Nicaragua and Northern Costa Rica, the Cocos Plate subducts beneath the Caribbean Plate, carrying with it a large amount of fluids and volatiles. While some of these are set free at great depth beneath the volcanic arc, causing the extremely high water content observed in Nicaraguan mafic magmas (Carr et al., 2003; Kutterolf et al., 2007), some early dehydration reactions already release fluids from the subducting plate underneath the continental slope. Unlike in accretionary margins, where these fluids migrate up along the decollement towards the deformation front, fluid release at erosional margins seems to occur through fractures in the overriding plate (Ranero et al., 2008). Fluid seeps in this region have be observed at seafloor mounds, appearing as side-scan sonar backscatter anomalies or revealed by the presence of chemosynthetic communities (Sahling et al., 2008). In the framework of the General Research Area SFB 574 "Volatiles and Fluids in Subduction Zones", a network of 20 ocean-bottom-stations was deployed offshore Sta Elena Peninsula, Northern Costa Rica, from December 2005 to June 2006. Several distinct swarms of small earthquakes were observed at the seismic stations, which occurred clustered over a time period of several days and have very similar seismic waveforms. Since a correlation of fluid-release sites with the occurrence of sporadic seismic swarms would indicate that fluid migration and fracturing is the mechanism responsible for triggering the earthquake swarms, the events are re-analysed by double-difference localisation to enhance the resolution of the earthquake locations. The results are then considered to estimate the migration velocity and direction and compare the localisations with the known mound sites. Carr, M., Feigenson, M. D., Patino, L. C., and Walker, J. A., 2003: Volcanism and geochemistry in Central America: Progress and problems, in Eiler, J. (ed.), Inside the subduction factory, pp. 153-179, American Geophysical

  8. DELP Symposium: Tectonics of eastern Asia and western Pacific Continental Margin

    Science.gov (United States)

    Eastern Asia and the western Pacific make up a broad region of active plate tectonic interaction. The area is a natural laboratory for studying the processes involved in the origin and evolution of volcanic island arcs, marginal basins, accretionary prisims, oceanic trenches, accreted terranes, ophiolite emplacement, and intracontinental deformation. Many of our working concepts of plate tectonics and intraplate deformation were developed in this region, even though details of the geology and geophysics there must be considered of a reconnaissance nature.During the past few years researchers have accumulated a vast amount of new and detailed information and have developed a better understanding of the processes that have shaped the tectonic elements in this region. To bring together scientists from many disciplines and to present the wide range of new data and ideas that offer a broader perspective on the interrelations of geological, geochemical, geophysical and geodetic studies, the symposium Tectonics of Eastern Asia and Western Pacific Continental Margin was held December 13-16, 1988, at the Tokyo Institute of Technology in Japan, under the auspicies of DELP (Dynamics and Evolution of the Lithosphere Project).

  9. Late Cretaceous sub-volcanic structure in the continental shelf off Portugal and its implications on tectonics and seismicity

    Science.gov (United States)

    Neres, Marta; Terrinha, Pedro; Custódio, Susana; Noiva, João; Brito, Pedro; Santos, Joana; Carrilho, Fernando

    2017-04-01

    West Iberia during the Late Cretaceous and at Present, specifically: What was the tectonic control for the emplacement of these magmatic bodies emplaced on the rifted margin? Is the rheological contrast between magmatic bodies and host-rocks controlling the seismicity localization? Publication supported by FCT- project UID/GEO/50019/2013 - Instituto Dom Luiz.

  10. A new view for the geodynamics of Ecuador: Implication in seismogenic source definition and seismic hazard assessment

    Science.gov (United States)

    Yepes, Hugo; Audin, Laurence; Alvarado, Alexandra; Beauval, Céline; Aguilar, Jorge; Font, Yvonne; Cotton, Fabrice

    2016-05-01

    A new view of Ecuador's complex geodynamics has been developed in the course of modeling seismic source zones for probabilistic seismic hazard analysis. This study focuses on two aspects of the plates' interaction at a continental scale: (a) age-related differences in rheology between Farallon and Nazca plates—marked by the Grijalva rifted margin and its inland projection—as they subduct underneath central Ecuador, and (b) the rapidly changing convergence obliquity resulting from the convex shape of the South American northwestern continental margin. Both conditions satisfactorily explain several characteristics of the observed seismicity and of the interseismic coupling. Intermediate-depth seismicity reveals a severe flexure in the Farallon slab as it dips and contorts at depth, originating the El Puyo seismic cluster. The two slabs position and geometry below continental Ecuador also correlate with surface expressions observable in the local and regional geology and tectonics. The interseismic coupling is weak and shallow south of the Grijalva rifted margin and increases northward, with a heterogeneous pattern locally associated to the Carnegie ridge subduction. High convergence obliquity is responsible for the North Andean Block northeastward movement along localized fault systems. The Cosanga and Pallatanga fault segments of the North Andean Block-South American boundary concentrate most of the seismic moment release in continental Ecuador. Other inner block faults located along the western border of the inter-Andean Depression also show a high rate of moderate-size earthquake production. Finally, a total of 19 seismic source zones were modeled in accordance with the proposed geodynamic and neotectonic scheme.

  11. Crustal Structure of the Tengchong Intra-plate Volcanic Area

    Science.gov (United States)

    Qian, Rongyi; Tong, Vincent C. H.

    2015-09-01

    We here provide an overview of our current understanding of the crustal structure of Tengchong in southwest China, a key intra-plate volcanic area along the Himalayan geothermal belt. Given that there is hitherto a lack of information about the near-surface structure of intra-plate volcanic areas, we present the first seismic reflection and velocity constraints on the shallow crust between intra-plate volcanoes. Our near-surface seismic images reveal the existence of dome-shaped seismic reflectors (DSRs) in the shallow crust between intra-plate volcanic clusters in Tengchong. The two DSRs are both ~2 km wide, and the shallowest parts of the DSRs are found at the depth of 200-300 m. The velocity model shows that the shallow low-velocity layer (<4 km/s) is anomalously thick (~1 km) in the region where the DSRs are observed. The presence of DSRs indicates significant levels of intra-plate magmatism beneath the along-axis gap separating two volcano clusters. Along-axis gaps between volcano clusters are therefore not necessarily an indicator of lower levels of magmatism. The seismic images obtained in this technically challenging area for controlled-source seismology allow us to conclude that shallow crustal structures are crucial for understanding the along-axis variations of magmatism and hydrothermal activities in intra-plate volcanic areas.

  12. ON TECTONIC PROBLEMS OF THE OKINAWA TROUGH

    Institute of Scientific and Technical Information of China (English)

    李乃胜

    2001-01-01

    The Okinawa Trough is a very active tectonic zone at the margin of the Northwest Pacific and is typical of back-arc rifting at the young stage of tectonic evolution. Many scientists from Japan,China, Germany, France, the U. S.A. and Russia have done a lot of geologic and geophysical investigations there. It is well known that the Okinawa Trough is an active back-arc rift with extremely high heat flow, very strong hydrothermal circulation, strong volcanic and magmatic activity, frequent earthquakes,rapid subsidence and rifting, well-developed fault and central graben. But up to now, there are still some important tectonic problems about the Okinawa Trough that require clarification on some aspects such as the type of its crust, its forming time, its tectonic evolution, the distribution of its central grabens, the relationship between its high heat flow and tectonic activity. Based on the data obtained from seismic sur-vey, geomagnetic and gravity measurements, submarine sampling and heat flow measurements in the last 15 years, the author discusses the following tectonic problems about the Okinawa Trough: (1) If the Okinawa Trough develops oceanic crust or not. (2) Is the South Okinawa Trough tectonically more active than the North Okinawa Trough with shallower water and few investigation data on it. (3) The formation time of the Okinawa Trough and its tectonic evolution. The Okinawa Trough has a very thin continental crust. Up to now, there is no evidence of oceanic crust in the Okinawa Trough. The North, Middle and South Okinawa Trough are all very strongly active areas. From 6 Ma B.P. , the Okinawa Trough began to form. Since 2 Ma, the Okinawa Trough has been very active.

  13. Present mantle flow in North China Craton constrained by seismic anisotropy and numerical modelling

    Science.gov (United States)

    Qu, W.; Guo, Z.; Zhang, H.; Chen, Y. J.

    2017-12-01

    North China Carton (NCC) has undergone complicated geodynamic processes during the Cenozoic, including the westward subduction of the Pacific plate to its east and the collision of the India-Eurasia plates to its southwest. Shear wave splitting measurements in NCC reveal distinct seismic anisotropy patterns at different tectonic blocks, that is, the predominantly NW-SE trending alignment of fast directions in the western NCC and eastern NCC, weak anisotropy within the Ordos block, and N-S fast polarization beneath the Trans-North China Orogen (TNCO). To better understand the origin of seismic anisotropy from SKS splitting in NCC, we obtain a high-resolution dynamic model that absorbs multi-geophysical observations and state-of-the-art numerical methods. We calculate the mantle flow using a most updated version of software ASPECT (Kronbichler et al., 2012) with high-resolution temperature and density structures from a recent 3-D thermal-chemical model by Guo et al. (2016). The thermal-chemical model is obtained by multi-observable probabilistic inversion using high-quality surface wave measurements, potential fields, topography, and surface heat flow (Guo et al., 2016). The viscosity is then estimated by combining the dislocation creep, diffusion creep, and plasticity, which is depended on temperature, pressure, and chemical composition. Then we calculate the seismic anisotropy from the shear deformation of mantle flow by DREX, and predict the fast direction and delay time of SKS splitting. We find that when complex boundary conditions are applied, including the far field effects of the deep subduction of Pacific plate and eastward escaping of Tibetan Plateau, our model can successfully predict the observed shear wave splitting patterns. Our model indicates that seismic anisotropy revealed by SKS is primarily resulting from the LPO of olivine due to the shear deformation from asthenospheric flow. We suggest that two branches of mantle flow may contribute to the

  14. Geophysical constraints on geodynamical processes at convergent margins

    DEFF Research Database (Denmark)

    Artemieva, Irina; Thybo, Hans; Shulgin, Alexey

    2016-01-01

    Convergent margins, being the boundaries between colliding lithospheric plates, form the most disastrous areas in the world due to intensive, strong seismicity and volcanism. We review global geophysical data in order to illustrate the effects of the plate tectonic processes at convergent margins......, at least, one of the plates is oceanic. However, the oldest oceanic plate in the Pacific ocean has the smallest convergence rate. (2) The presence of an oceanic plate is, in general, required for generation of high-magnitude (M>8.0) earthquakes and for generating intermediate and deep seismicity along...... to shallow mantle levels....

  15. Seismic reflection and structuring characterization of deep aquifer system in the Dakhla syncline (Cap Bon, North-Eastern Tunisia)

    Science.gov (United States)

    Bellali, Abir; Jarraya Horriche, Faten; Gabtni, Hakim; Bédir, Mourad

    2018-04-01

    The Dakhla syncline is located in the North-Eastern Tunisia. It is bounded by Abd El Rahmene anticline to the North-West, El Haouaria Graben to the North-East, Grombalia Graben to the South-West and the Mediterranean Sea to the East. The main aquifer reservoirs of Dakhla syncline are constituted by stacks of fluvial to deltaic Neogene sequences and carbonates. The interpretation of eight seismic reflection profiles, calibrated by wire line logging data of three oil wells, hydraulic wells and geologic field sections highlighted the impact of tectonics on the structuring geometry of aquifers and their distribution in elevated structures and subsurface depressions. Lithostratigraphic correlations and seismic profiles analysis through the syncline show that the principal aquifers are thickest within the central and northern part of the study area and thinnest to the southern part of the syncline. Seismic sections shows that the fracture/fault pattern in this syncline is mainly concentrated along corridors with a major direction of NW-SE and secondary directions of N-S, E-W and NE-SW with different release. This is proved by the complexity structure of Eastern Tunisia, resulted from the interaction between the African and Eurasiatic plates. Isochron maps of aquifers systems exhibited the structuring of this syncline in sub-surface characterized by important lateral and vertical geometric and thickness variations. Seismic sections L1, L2, L3, L4, L5 and petroleum wells showed an heterogeneous multilayer aquifers of Miocene formed by the arrangement of ten sandstone bodies, separated by impermeable clay packages. Oligo-Miocene deposits correspond to the most great potential aquifers, with respectively an average transmissivity estimated: Somaa aquifer 6.5 10-4 m2/s, Sandstone level aquifer 2.6 10-3 m2/s, Beglia aquifer 1.1 10-3 m2/s, Ain Ghrab aquifer 1.3 10-4 m2/s and Oligocene aquifer 2 10-3 m2/s. The interpretation of spatial variations of seismic units and the

  16. Tectonic Mechanism for the Mid-Cretaceous - Early Paleogene Intraplate Magmatism from the Gulf of Mexico to Northwestern Canada

    Science.gov (United States)

    Liu, Y.; Murphy, M. A.; Snow, J. E.; van Wijk, J.; Cannon, J. M.; Parsons, C.

    2017-12-01

    Tectonic mechanisms have remained controversial for a number of intraplate igneous suites of mid-Cretaceous - early Paleogene age across North America. They span the northern Gulf of Mexico (GoM), through Arkansas and Kansas in the US, to Saskatchewan and Northwestern Territories in Canada, resembling a belt that is located 1000+ km inboard from, and aligned sub-parallel to, the western margin of North America. The northern GoM magmatism is characterized by lamproites, carbonatites, nephelinites, with other alkaline rocks, whereas the rest igneous provinces are dominated by kimberlites. Their geochemical signatures, in general, point to a sub-lithospheric mantle origin. Hypotheses that explain the tectonic origin of these magmatic rocks include: (1) hotspots and mantle plumes, (2) edge-driven convection, (3) lithospheric reactivation, and (4) low-angle subduction. Evaluation based on our integration of published geological and geophysical data shows that contradictions exist in each model between observations and predictions. To explain this plate-scale phenomenon, we propose that the Farallon slab may have stagnated within or around the mantle transition zone during the Early Cretaceous, with its leading edge reaching ca. 1600 km inland beneath the North American plate. Dehydration and decarbonation of the slab produces sporadic, dense, low-degree partial melts at the mantle transition zone depths. As the slab descends into the lower mantle, Rayleigh-Taylor instabilities are induced at slab edges, causing passive upwelling that brings alkali-rich carbonate silicate melts to the base of the overriding plate. Subsequently, the North American lithosphere with varying thicknesses, discontinuities, and compositions interacts with the rising partial melts, generating a spectrum of igneous rocks. Fragments of the once-stagnated slab may still be detectable in the lower mantle beneath eastern US in seismic tomography models. This study highlights a profound plate

  17. One Dimensional Backstripping Results from IODP Expedition 318, Site U1356: Tectonic Implications for the Wilkes Land Margin of Antarctica

    Science.gov (United States)

    Hayden, T. G.; Kominz, M. A.; González, J. J.; Escutia, C.; Brinkhuis, H.; Scientific Party of IODP Expedition 318

    2011-12-01

    The Wilkes Land margin of Antarctica is the conjugate margin of the Great Australian Bight, which underwent extension, thinning and rifting from ~160 Ma until breakup at ~83 Ma. Both Wilkes Land and the Great Australian Bight are considered passive margins, and were thought to be tectonically inactive since breakup at 83 Ma. We have backstripped the U1356 Core recovered from the continental rise off Wilkes Land, Antarctica by IODP Expedition 318. Backstripping input included lithological and sedimentary analysis, paleo-environmental indicators, combined paleomagnetic and biostratigraphic chronologies, and physical properties measurements. Tectonic subsidence shows a major event between 50 and 33.6 Ma, a time represented by a hiatus in the U1356 core. The magnitude of subsidence requires it to be tectonic in origin, and the timing matches with a reorganization of plate motions that represents the transition from slow spreading to fast spreading between Antarctica and Australia, which occurred at approximately 43 Ma. Coupled with a regional seismic framework, and using other Expedition 318 site analyses, the Wilkes Land margin is shown to be far more complex then the simple passive margin currently assumed. We explore several possible mechanisms for the subsidence and erosion observed; including thermal uplift due to continental insulation of the asthenosphere and it's interaction with a recently rifted margin, asthenospheric convection, transtensional or transpressional basin development and loading, and edge-driven asthenospheric convection.

  18. Active crustal deformation of the El Salvador Fault Zone (ESFZ) using GPS data: Implications in seismic hazard assessment

    Science.gov (United States)

    Staller, Alejandra; Benito, Belen; Jesús Martínez-Díaz, José; Hernández, Douglas; Hernández-Rey, Román; Alonso-Henar, Jorge

    2014-05-01

    El Salvador, Central America, is part of the Chortis block in the northwestern boundary of the Caribbean plate. This block is interacting with a diffuse triple junction point with the Cocos and North American plates. Among the structures that cut the Miocene to Pleistocene volcanic deposits stands out the El Salvador Fault Zone (ESFZ): It is oriented in N90º-100ºE direction, and it is composed of several structural segments that deform Quaternary deposits with right-lateral and oblique slip motions. The ESFZ is seismically active and capable of producing earthquakes such as the February 13, 2001 with Mw 6.6 (Martínez-Díaz et al., 2004), that seriously affected the population, leaving many casualties. This structure plays an important role in the tectonics of the Chortis block, since its motion is directly related to the drift of the Caribbean plate to the east and not with the partitioning of the deformation of the Cocos subduction (here not coupled) (Álvarez-Gómez et al., 2008). Together with the volcanic arc of El Salvador, this zone constitutes a weakness area that allows the motion of forearc block toward the NW. The geometry and the degree of activity of the ESFZ are not studied enough. However their knowledge is essential to understand the seismic hazard associated to this important seismogenic structure. For this reason, since 2007 a GPS dense network was established along the ESFZ (ZFESNet) in order to obtain GPS velocity measurements which are later used to explain the nature of strain accumulation on major faults along the ESFZ. The current work aims at understanding active crustal deformation of the ESFZ through kinematic model. The results provide significant information to be included in a new estimation of seismic hazard taking into account the major structures in ESFZ.

  19. Seismic Structure of Mantle Transition Zone beneath Northwest Pacific Subduction Zone and its Dynamic Implication

    Science.gov (United States)

    Li, J.; Guo, G.; WANG, X.; Chen, Q.

    2017-12-01

    The northwest Pacific subduction region is an ideal location to study the interaction between the subducting slab and upper mantle discontinuities. Various and complex geometry of the Pacific subducting slab can be well traced downward from the Kuril, Japan and Izu-Bonin trench using seismicity and tomography images (Fukao and Obayashi, 2013). Due to the sparse distribution of seismic stations in the sea, investigation of the deep mantle structure beneath the broad sea regions is very limited. In this study, we applied the well- developed multiple-ScS reverberations method (Wang et al., 2017) to analyze waveforms recorded by the Chinese Regional Seismic Network, the densely distributed temporary seismic array stations installed in east Asia. A map of the topography of the upper mantle discontinuities beneath the broad oceanic regions in northwest Pacific subduction zone is imaged. We also applied the receiver function analysis to waveforms recorded by stations in northeast China and obtain the detailed topography map beneath east Asia continental regions. We then combine the two kinds of topography of upper mantle discontinuities beneath oceanic and continental regions respectively, which are obtained from totally different methods. A careful image matching and spatial correlation is made in the overlapping study regions to calibrate results with different resolution. This is the first time to show systematically a complete view of the topography of the 410-km and 660-km discontinuities beneath the east Asia "Big mantle wedge" (Zhao and Ohtani, 2009) covering the broad oceanic and continental regions in the Northwestern Pacific Subduction zone. Topography pattern of the 660 and 410 is obtained and discussed. Especially we discovered a broad depression of the 410-km discontinuity covering more than 1000 km in lateral, which seems abnormal in the cold subducting tectonic environment. Based on plate tectonic reconstruction studies and HTHP mineral experiments, we

  20. Analysis and seismic tests of composite shear walls with CFST columns and steel plate deep beams

    Science.gov (United States)

    Dong, Hongying; Cao, Wanlin; Wu, Haipeng; Zhang, Jianwei; Xu, Fangfang

    2013-12-01

    A composite shear wall concept based on concrete filled steel tube (CFST) columns and steel plate (SP) deep beams is proposed and examined in this study. The new wall is composed of three different energy dissipation elements: CFST columns; SP deep beams; and reinforced concrete (RC) strips. The RC strips are intended to allow the core structural elements — the CFST columns and SP deep beams — to work as a single structure to consume energy. Six specimens of different configurations were tested under cyclic loading. The resulting data are analyzed herein. In addition, numerical simulations of the stress and damage processes for each specimen were carried out, and simulations were completed for a range of location and span-height ratio variations for the SP beams. The simulations show good agreement with the test results. The core structure exhibits a ductile yielding mechanism characteristic of strong column-weak beam structures, hysteretic curves are plump and the composite shear wall exhibits several seismic defense lines. The deformation of the shear wall specimens with encased CFST column and SP deep beam design appears to be closer to that of entire shear walls. Establishing optimal design parameters for the configuration of SP deep beams is pivotal to the best seismic behavior of the wall. The new composite shear wall is therefore suitable for use in the seismic design of building structures.

  1. Active tectonic deformation of the western Indian plate boundary: A case study from the Chaman Fault System

    Science.gov (United States)

    Crupa, Wanda E.; Khan, Shuhab D.; Huang, Jingqiu; Khan, Abdul S.; Kasi, Aimal

    2017-10-01

    Collision of the Eurasian and Indian plates has resulted in two spatially offset subduction zones, the Makran subduction zone to the south and the Himalayan convergent margin to the north. These zones are linked by a system of left-lateral strike-slip faults known as the Chaman Fault System, ∼1200 km, which spans along western Pakistan. Although this is one of the greatest strike-slip faults, yet temporal and spatial variation in displacement has not been adequately defined along this fault system. This study conducted geomorphic and geodetic investigations along the Chaman Fault in a search for evidence of spatial variations in motion. Four study areas were selected over the span of the Chaman Fault: (1) Tarnak-Rud area over the Tarnak-Rud valley, (2) Spinatizha area over the Spinatizha Mountain Range, (3) Nushki area over the Nushki basin, and (4) Kharan area over the northern tip of the Central Makran Mountains. Remote sensing data allowed for in depth mapping of different components and faults within the Kohjak group. Wind and water gap pairs along with offset rivers were identified using high-resolution imagery and digital-elevation models to show displacement for the four study areas. The mountain-front-sinuosity ratio, valley height-to-width-ratio, and the stream-length-gradient index were calculated and used to determine the relative tectonic activity of each area. These geomorphic indices suggest that the Kharan area is the most active and the Tarnak-Rud area is the least active. GPS data were processed into a stable Indian plate reference frame and analyzed. Fault parallel velocity versus fault normal distance yielded a ∼8-10 mm/yr displacement rate along the Chaman Fault just north of the Spinatizha area. InSAR data were also integrated to assess displacement rates along the fault system. Geodetic data support that ultra-slow earthquakes similar to those that strike along other major strike-slip faults, such as the San Andreas Fault System, are

  2. Global Models of Ridge-Push Force, Geoid, and Lithospheric Strength of Oceanic plates

    Science.gov (United States)

    Mahatsente, Rezene

    2017-12-01

    An understanding of the transmission of ridge-push related stresses in the interior of oceanic plates is important because ridge-push force is one of the principal forces driving plate motion. Here, I assess the transmission of ridge-push related stresses in oceanic plates by comparing the magnitude of the ridge-push force to the integrated strength of oceanic plates. The strength is determined based on plate cooling and rheological models. The strength analysis includes low-temperature plasticity (LTP) in the upper mantle and assumes a range of possible tectonic conditions and rheology in the plates. The ridge-push force has been derived from the thermal state of oceanic lithosphere, seafloor depth and crustal age data. The results of modeling show that the transmission of ridge-push related stresses in oceanic plates mainly depends on rheology and predominant tectonic conditions. If a lithosphere has dry rheology, the estimated strength is higher than the ridge-push force at all ages for compressional tectonics and at old ages (>75 Ma) for extension. Therefore, under such conditions, oceanic plates may not respond to ridge-push force by intraplate deformation. Instead, the plates may transmit the ridge-push related stress in their interior. For a wet rheology, however, the strength of young lithosphere (stress may dissipate in the interior of oceanic plates and diffuses by intraplate deformation. The state of stress within a plate depends on the balance of far-field and intraplate forces.

  3. Measurements of Active Tectonic Deformation on the Guerrero Coast, Mexico

    Science.gov (United States)

    Ramirez, T.; Cundy, A.; Carranza-Edwards, A.; Morales, E.; Kostoglodov, V.; Urrutia-Fucugauchi, J.

    2004-12-01

    The study of tectonic deformation rates using displaced shoreline features is relatively well-established, and has provided much useful information on seismic hazard. Such studies have frequently been complemented by analysis of the coastal sedimentary record, where past marine to terrestrial environmental changes (and vice versa) may be recorded by clear changes in stratigraphy. Studies of this type are particularly valuable for tectonically-active areas where the preservation of former shoreline features is poor, or where long-term subsidence has resulted in their erosion, drowning or burial. The specific objective of this study is to derive rates of tectonic deformation from geomorphic and stratigraphic studies of the Guerrero coastal area, and to examine the feasibility of this stratigraphic approach in the coastal lagoons of the Mexican Pacific coast, in the Guerrero gap. The Guerrero gap coastal area, where a major earthquake is expected to occur, parallels the Cocos plate subduction zone. Here convergence rates vary from 5.2 cm/yr to 5.8 cm/yr. The Guerrero gap has experienced several historical earthquakes, notably the 1911 (7.8 Ms). However, no large magnitude events since the 1911 earthquake and only a few Ms~6 events have occurred near the Guerrero gap edges. It is expected that a major interplate earthquake of estimated magnitude Mw=8.1 to 8.4 has a high probability to occur. Landforms within the Guerrero gap indicate that the coast is subsiding. A series of key indicators such as elongated islands reminiscent of ancient barriers, submerged barriers island, extensive marshy environments, increased depths in the lagoons, and submerged anthropogenic features (shell mounds), among others, suggest active tectonic subsidence of the coast. In contrast, the adjacent northwest area off the Guerrero gap exhibits landforms characteristic of tectonic uplift (marine terraces and uplifted beach ridges), indicating a different seismo-tectonic regime northwest of the

  4. Comparison of seismic sources for shallow seismic: sledgehammer and pyrotechnics

    Directory of Open Access Journals (Sweden)

    Brom Aleksander

    2015-10-01

    Full Text Available The pyrotechnic materials are one of the types of the explosives materials which produce thermal, luminous or sound effects, gas, smoke and their combination as a result of a self-sustaining chemical reaction. Therefore, pyrotechnics can be used as a seismic source that is designed to release accumulated energy in a form of seismic wave recorded by tremor sensors (geophones after its passage through the rock mass. The aim of this paper was to determine the utility of pyrotechnics for shallow seismic engineering. The work presented comparing the conventional method of seismic wave excitation for seismic refraction method like plate and hammer and activating of firecrackers on the surface. The energy released by various sources and frequency spectra was compared for the two types of sources. The obtained results did not determine which sources gave the better results but showed very interesting aspects of using pyrotechnics in seismic measurements for example the use of pyrotechnic materials in MASW.

  5. Volcanism/tectonics working group summary

    International Nuclear Information System (INIS)

    Kovach, L.A.; Young, S.R.

    1995-01-01

    This article is a summary of the proceedings of a group discussion which took place at the Workshop on the Role of Natural Analogs in Geologic Disposal of High-Level Nuclear Waste in San Antonio, Texas on July 22-25, 1991. The working group concentrated on the subject of the impacts of earthquakes, fault rupture, and volcanic eruption on the underground repository disposal of high-level radioactive wastes. The tectonics and seismic history of the Yucca Mountain site in Nevada is discussed and geologic analogs to that site are described

  6. Net Rotation of the Lithosphere in Mantle Convection Models with Self-consistent Plate Generation

    Science.gov (United States)

    Gerault, M.; Coltice, N.

    2017-12-01

    Lateral variations in the viscosity structure of the lithosphere and the mantle give rise to a discordant motion between the two. In a deep mantle reference frame, this motion is called the net rotation of the lithosphere. Plate motion reconstructions, mantle flow computations, and inferences from seismic anisotropy all indicate some amount of net rotation using different mantle reference frames. While the direction of rotation is somewhat consistent across studies, the predicted amplitudes range from 0.1 deg/Myr to 0.3 deg/Myr at the present-day. How net rotation rates could have differed in the past is also a subject of debate and strong geodynamic arguments are missing from the discussion. This study provides the first net rotation calculations in 3-D spherical mantle convection models with self-consistent plate generation. We run the computations for billions of years of numerical integration. We look into how sensitive the net rotation is to major tectonic events, such as subduction initiation, continental breakup and plate reorganisations, and whether some governing principles from the models could guide plate motion reconstructions. The mantle convection problem is solved with the finite volume code StagYY using a visco-pseudo-plastic rheology. Mantle flow velocities are solely driven by buoyancy forces internal to the system, with free slip upper and lower boundary conditions. We investigate how the yield stress, the mantle viscosity structure and the properties of continents affect the net rotation over time. Models with large lateral viscosity variations from continents predict net rotations that are at least threefold faster than those without continents. Models where continents cover a third of the surface produce net rotation rates that vary from nearly zero to over 0.3 deg/Myr with rapide increase during continental breakup. The pole of rotation appears to migrate along no particular path. For all models, regardless of the yield stress and the

  7. 3D seismic investigation of the structural and stratigraphic characteristics of the Pagasa Wedge, Southwest Palawan Basin, Philippines, and their tectonic implications

    Science.gov (United States)

    Ilao, Kimberly A.; Morley, Christopher K.; Aurelio, Mario A.

    2018-04-01

    The Pagasa Wedge is a poorly imaged deepwater orogenic wedge that has been variously interpreted as representing an accretionary prism, a former accretionary prism modified by thrusting onto a thinned continental margin, and a gravity-driven fold-thrust belt. This study, using 2D and 3D seismic data, together with well information indicates that at least the external part of the wedge is dominantly composed of mass transport complexes, capped by syn-kinematic sediments that have thrusts and normal faults superimposed upon them. Drilling shows that despite stratigraphic repetition of Eocene Middle Miocene units, there is stratigraphic omission of Oligocene and Early Miocene units. This absence suggests that mass transport processes have introduced the Eocene section into the wedge rather than tectonic thrusting. The accretionary prism stage (Oligocene) of the Central Palawan Ophiolite history appears to be marked by predominantly north-vergent deformation. The Deep Regional Unconformity (∼17 Ma) likely indicates the approximate time when obduction ceased in Palawan. The Pagasa Wedge is a late-stage product of the convergence history that was active in its final phase sometime above the top of the Nido Limestone (∼16 Ma) and the base of the Tabon Limestone in the Aboabo-A1X well (∼9 Ma). The top of the wedge is traditionally associated with the Middle Miocene Unconformity (MMU), However the presence of multiple unconformities, diachronous formation tops, local tectonic unconformities and regional diachronous events (e.g. migrating forebulges) all suggest simply giving a single age (or assigning a single unconformity, such as the MMU as defining the top of the Pagasa Wedge is inappropriate. The overall NE-SW trend of the wedge, and the dominant NW transport of structures within the wedge diverge from the more northerly transport direction determined from outcrops in Palawan, and also from the Nido Limestone in the SW part of the Pagasa Wedge. Possibly this NW

  8. Study of time dynamics of seismicity for the Mexican subduction zone by means of the visibility graph method.

    Science.gov (United States)

    Ramírez-Rojas, Alejandro; Telesca, Luciano; Lovallo, Michele; Flores, Leticia

    2015-04-01

    By using the method of the visibility graph (VG), five magnitude time series extracted from the seismic catalog of the Mexican subduction zone were investigated. The five seismic sequences represent the seismicity which occurred between 2005 and 2012 in five seismic areas: Guerrero, Chiapas, Oaxaca, Jalisco and Michoacan. Among the five seismic sequences, the Jalisco sequence shows VG properties significantly different from those shown by the other four. Such a difference could be inherent in the different tectonic settings of Jalisco with respect to those characterizing the other four areas. The VG properties of the seismic sequences have been put in relationship with the more typical seismological characteristics (b-value and a-value of the Gutenberg-Richter law). The present study was supported by the Bilateral Project Italy-Mexico "Experimental Stick-slip models of tectonic faults: innovative statistical approaches applied to synthetic seismic sequences", jointly funded by MAECI (Italy) and AMEXCID (Mexico) in the framework of the Bilateral Agreement for Scientific and Technological Cooperation PE 2014-2016

  9. Time-variable stress transfer across a megathrust from seismic to Wilson cycle scale

    Science.gov (United States)

    Rosenau, Matthias; Angiboust, Samuel; Moreno, Marcos; Schurr, Bernd; Oncken, Onno

    2013-04-01

    During the lifetime of a convergent plate margin stress transfer across the plate interface (a megathrust) can be expected to vary at multiple timescales. At short time scales (years to decades), a subduction megathrust interface appears coupled (accumulating shear stress) at shallow depth (seismogenic zone proportional to effective normal load but also to relative shear stress. For areas of near complete stress drop locking might systematically decrease over the interseismic period from >80-95 % shortly after an earthquake to backslip at significant fractions of plate convergence rate (non-volcanic tremor and slow slip below the seismogenic zone represent short term episodes of metamorphic fluid infiltration into the shallow megathrust. A megathrust fault valve mechanism clocked by the greatest earthquakes then accounts for cyclic fluid pressure build up and drainage at sub-seismic cycle scale. As pore pressure dynamics are controlled primarily by permeability which in turn is controlled by structure and material properties, then more long term coupling transients associated with structural evolution of the plate margin can be implied. Fluid controlled transients might interfere with transients and secular trends resulting from changes in material strength and plate tectonic forces over the Wilson cycle resulting in a multispectral stress-transfer pattern associated with convergent margin evolution. Because of the viscous damping effect of the underlying asthenosphere, however, only longterm transients (periods >1-10 ka) are transmitted into the engaged plates. We therefore speculate that the multispectral nature of stress transfer across a megathrust filtered through the asthenosphere explains transient fault activity in some intraplate settings.

  10. The Rapid Drift of the Indian Tectonic Plate

    Science.gov (United States)

    Kumar, P.; Yuan, X.; Kumar, R.; Kind, R.; Li, X.; Chadha, R.

    2007-12-01

    The breakup of the supercontinent Gondwanaland into Africa, Antarctica, Australia and India about 140 million years ago and consequently the opening of the Indian Ocean was caused by heating of the lithosphere from below by a large plume whose relicts are the Marion, Kerguelen and Reunion plumes. Plate reconstructions based on paleomagnetic data suggest that the Indian plate attained a very high speed (18-20 cm/yr during late Cretaceous) subsequent to its breakup from the Gondwanaland and slowed down to ~5 cm/yr since the continental collision with Asia during the last ~50 Ma. The Australian and African plates moved comparatively lesser distances and at much lesser speed of 2-4 cm/yr. Antarctica remained almost stationary. This super mobility makes India unique compared to the other fragments of Gondwanaland. We propose that when the parts of Gondwanaland were separated by the plume, the penetration of their lithospheric roots into the asthenosphere played an important role in determining their speed. We estimated the thickness of the lithospheric plates of the different parts of Gondwanaland around the Indian Ocean using the S-receiver function technique. We found that the part of Gondwanaland with clearly the thinnest lithosphere has travelled with the highest speed - India. The lithospheric root in South Africa, Australia and Antarctica is between 180 and 300 km deep. The Indian lithosphere is in contrast only about 100 km thick. Our interpretation is that the plume that partitioned Gondwanaland has also melted the lower half of the Indian lithosphere thus permitting faster motion due to the ridge push or slab pull.

  11. A workflow for sub-/seismic structure and deformation quantification of 3-D reflection seismic data sets across different scales

    Energy Technology Data Exchange (ETDEWEB)

    Krawczyk, C.M.; Lohr, T.; Oncken, O. [GFZ Potsdam (Germany); Tanner, D.C. [Goettingen Univ. (Germany). GZG; Endres, H. [RWTH Aachen (Germany)]|[TEEC, Isernhagen (Germany); Trappe, H.; Kukla, P. [TEEC, Isernhagen (Germany)

    2007-09-13

    The evolution of a sedimentary basin is mostly affected by deformation. Large-scale, subsurface deformation is typically identified by seismic data, sub-seismic small-scale fractures by well data. Between these two methods, we lack a deeper understanding of how deformation scales. We analysed a 3-D reflection seismic data set in the North German Basin, in order to determine the magnitude and distribution of deformation and its accumulation in space and time. A five-step approach is introduced for quantitative deformation and fracture prediction. An increased resolution of subtle tectonic lineaments is achieved by coherency processing, allowing to unravel the kinematics in the North German Basin from structural interpretation. Extensional events during basin initiation and later inversion are evident. 3-D retrodeformation shows major-strain magnitudes between 0-20% up to 1.3 km away from a fault trace, and variable deviations of associated extensional fractures. Good correlation of FMI data, strain distribution from retro-deformation and from geostatistic tools (see also Trappe et al., this volume) allows the validation of the results and makes the prediction of small-scale faults/fractures possible. The temporal component will be gained in the future by analogue models. The suggested workflow is applicable to reflection seismic surveys and yields in great detail both the tectonic history of a region as well as predictions for hydrocarbon plays or deep groundwater or geothermal reservoirs. (orig.)

  12. Petrology, geochemistry and tectonic settings of the mafic dikes and ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    margins of the basin, whereas, others are aligned .... areas of mantle upwelling, igneous intrusions, deep ... to and during the sedimentary accumulation, and ...... The development of continental margins in plate tectonic theory; J. Aust. Petrol.

  13. Isostatic models and isostatic gravity anomalies of the Arabian plate and surroundings

    Science.gov (United States)

    Kaban, Mikhail K.; El Khrepy, Sami; Al-Arifi, Nassir

    2015-04-01

    Isostaic anomalies represent one of the most useful "geological" reduction of the gravity field. With the isostatic correction it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. This correction is based on the fact that a major part of the near-surface load is compensated by variations of the lithosphere boundaries (chiefly the Moho and LAB) and by density variations within the crust and upper mantle. It is usually supposed that it is less important to a first order, what is the actual compensation model when reducing the effect of compensating masses, since their total weight is exactly opposite to the near-surface load. We compare several compensating models for the Arabian plate and surrounding area. The Airy model gives very significant regional isostatic anomalies, which can not be explained by the upper crust structure or disturbances of the isostatic equilibrium. Also the predicted "isostatic" Moho is very different from the existing observations. The second group of the isostatic models includes the Moho, which is based on existing seismic determinations. Additional compensation is provided by density variations within the lithosphere (chiefly in the upper mantle). In this way we minimize regional anomalies over the Arabian plate. The residual local anomalies well correspond to tectonic structure of the plate. Still very significant anomalies are associated with the Zagros fold belt, the collision zone of the Arabian and Eurasian plates.

  14. Reassessment of the historical seismic activity with major impact on S. Miguel Island (Azores

    Directory of Open Access Journals (Sweden)

    D. Silveira

    2003-01-01

    Full Text Available On account of its tectonic setting, both seismic and volcanic events are frequent in the Azores archipelago. During the historical period earthquakes and seismic swarms of tectonic and/or volcanic origin have struck S. Miguel Island causing a significant number of casualties and severe damages. The information present in historical records made possible a new macroseismic analysis of these major events using the European Macroseismic Scale-1998 (EMS-98. Among the strongest earthquakes of tectonic origin that affected S. Miguel Island, six events were selected for this study. The isoseismal maps drawn for these events enabled the identification of areas characterized by anomalous values of seismic intensity, either positive or negative, to constrain epicentre locations and to identify some new seismogenic areas. Regarding seismic activity associated with volcanic phenomena six cases were also selected. For each of the studied cases cumulative intensity values were assessed for each locality. The distribution of local intensity values shows that the effects are not homogeneous within a certain distance from the eruptive centre, the area of major impacts relates with the eruptive style and damages equivalent to high intensities may occur in Furnas and Sete Cidades calderas. Combining all the historical macroseismic data, a maximum intensity map was produced for S. Miguel Island.

  15. Birth of an oceanic spreading center at a magma-poor rift system.

    Science.gov (United States)

    Gillard, Morgane; Sauter, Daniel; Tugend, Julie; Tomasi, Simon; Epin, Marie-Eva; Manatschal, Gianreto

    2017-11-08

    Oceanic crust is continuously created at mid-oceanic ridges and seafloor spreading represents one of the main processes of plate tectonics. However, if oceanic crust architecture, composition and formation at present-day oceanic ridges are largely described, the processes governing the birth of a spreading center remain enigmatic. Understanding the transition between inherited continental and new oceanic domains is a prerequisite to constrain one of the last major unsolved problems of plate tectonics, namely the formation of a stable divergent plate boundary. In this paper, we present newly released high-resolution seismic reflection profiles that image the complete transition from unambiguous continental to oceanic crusts in the Gulf of Guinea. Based on these high-resolution seismic sections we show that onset of oceanic seafloor spreading is associated with the formation of a hybrid crust in which thinned continental crust and/or exhumed mantle is sandwiched between magmatic intrusive and extrusive bodies. This crust results from a polyphase evolution showing a gradual transition from tectonic-driven to magmatic-driven processes. The results presented in this paper provide a characterization of the domain in which lithospheric breakup occurs and enable to define the processes controlling formation of a new plate boundary.

  16. Tectonics, Deep-Seated Structure and Recent Geodynamics of the Caucasus

    Science.gov (United States)

    Amanatashvili, I.; Adamia, Sh.; Lursmanashvili, N.; Sadradze, N.; Meskhia, V.; Koulakov, I.; Zabelina, I.; Jakovlev, A.

    2012-04-01

    The tectonics and deep-seated structure of the Caucasus are determined by its position between the still converging Eurasian and Africa-Arabian plates, within a wide zone of continental collision. The region in the Late Proterozoic - Early Cenozoic belonged to the Tethys Ocean and its Eurasian and Africa-Arabian margins. During Oligocene-Middle Miocene and Late Miocene-Quaternary time as a result of collision back-arc basins were inverted to form fold-thrust mountain belts and the Transcaucasian intermontane lowlands. The Caucasus is divided into platform and fold-thrust units, and forelands superimposed mainly on the rigid platform zones. The youngest structural units composed of Neogene-Quaternary continental volcanic formations of the Armenian and Javakheti highlands and extinct volcanoes of the Great Caucasus. As a result of detailed geophysical study of the gravity, magnetic, seismic, and thermal fields, the main features of the deep crustal structure of the Caucasus have been determined. Knowledge on the deep lithospheric structure of the Caucasus region is based on surface geology and deep and super deep drilling data combined with gravity, seismic, heat flow, and magnetic investigations. Close correlation between the geology and its deep-seated structures appears in the peculiarities of spatial distribution of gravitational, thermal and magnetic fields, particularly generally expressed in orientation of regional anomalies that is in good agreement with general tectonic structures. In this study we present two tomographic models derived for the region based on two different tomographic approaches. In the first case, we use the travel time data on regional seismicity recorded by networks located in Caucasus. The tomographic inversion is based on the LOTOS code which enables simultaneous determination of P and S velocity distributions and source locations. The obtained model covers the crustal and uppermost mantle depths. The second model, which is constructed

  17. Study of seismicity around Toba area based on relocation hypocenter result from BMKG catalogue

    Energy Technology Data Exchange (ETDEWEB)

    Ramdhan, Mohamad [Indonesia' s Agency for Meteorology, Climatology and Geophysics (BMKG) Jl. Angkasa 1 No. 2 Kemayoran, Jakarta Pusat, 10720 (Indonesia); Nugraha, Andri Dian [Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institute of Technology Bandung, Indonesia, Jl. Ganesa 10, Bandung, 40132 (Indonesia)

    2013-09-09

    Toba area has complex tectonic setting attracting many earth scientists to study and understand tectonic and geological process or setting. The area is affected by oblique subduction zone, Renun Sumatran fault sub segment and some volcanoes that are near it. The earthquake catalogue provided by BMKG from April, 2009 to December, 2011 must be relocated firstly to get the precise hypocenter. We used catalogue data of P and S phase or P phase only and double-difference method to relocate the earthquakes. The results show hypocenter position enhancement that can be interpreted tectonically. The earthquakes after relocation relating to the Sumatran fault, subduction zone, volcanoes and seismic activities beneath Toba caldera can be mapped clearly. The relocated hypocenters in this study are very important to provide information for seismic hazard assessment and disaster mitigation study.

  18. Seismicity and source spectra analysis in Salton Sea Geothermal Field

    Science.gov (United States)

    Cheng, Y.; Chen, X.

    2016-12-01

    The surge of "man-made" earthquakes in recent years has led to considerable concerns about the associated hazards. Improved monitoring of small earthquakes would significantly help understand such phenomena and the underlying physical mechanisms. In the Salton Sea Geothermal field in southern California, open access of a local borehole network provides a unique opportunity to better understand the seismicity characteristics, the related earthquake hazards, and the relationship with the geothermal system, tectonic faulting and other physical conditions. We obtain high-resolution earthquake locations in the Salton Sea Geothermal Field, analyze characteristics of spatiotemporal isolated earthquake clusters, magnitude-frequency distributions and spatial variation of stress drops. The analysis reveals spatial coherent distributions of different types of clustering, b-value distributions, and stress drop distribution. The mixture type clusters (short-duration rapid bursts with high aftershock productivity) are predominately located within active geothermal field that correlate with high b-value, low stress drop microearthquake clouds, while regular aftershock sequences and swarms are distributed throughout the study area. The differences between earthquakes inside and outside of geothermal operation field suggest a possible way to distinguish directly induced seismicity due to energy operation versus typical seismic slip driven sequences. The spatial coherent b-value distribution enables in-situ estimation of probabilities for M≥3 earthquakes, and shows that the high large-magnitude-event (LME) probability zones with high stress drop are likely associated with tectonic faulting. The high stress drop in shallow (1-3 km) depth indicates the existence of active faults, while low stress drops near injection wells likely corresponds to the seismic response to fluid injection. I interpret the spatial variation of seismicity and source characteristics as the result of fluid

  19. An automated multi-scale network-based scheme for detection and location of seismic sources

    Science.gov (United States)

    Poiata, N.; Aden-Antoniow, F.; Satriano, C.; Bernard, P.; Vilotte, J. P.; Obara, K.

    2017-12-01

    We present a recently developed method - BackTrackBB (Poiata et al. 2016) - allowing to image energy radiation from different seismic sources (e.g., earthquakes, LFEs, tremors) in different tectonic environments using continuous seismic records. The method exploits multi-scale frequency-selective coherence in the wave field, recorded by regional seismic networks or local arrays. The detection and location scheme is based on space-time reconstruction of the seismic sources through an imaging function built from the sum of station-pair time-delay likelihood functions, projected onto theoretical 3D time-delay grids. This imaging function is interpreted as the location likelihood of the seismic source. A signal pre-processing step constructs a multi-band statistical representation of the non stationary signal, i.e. time series, by means of higher-order statistics or energy envelope characteristic functions. Such signal-processing is designed to detect in time signal transients - of different scales and a priori unknown predominant frequency - potentially associated with a variety of sources (e.g., earthquakes, LFE, tremors), and to improve the performance and the robustness of the detection-and-location location step. The initial detection-location, based on a single phase analysis with the P- or S-phase only, can then be improved recursively in a station selection scheme. This scheme - exploiting the 3-component records - makes use of P- and S-phase characteristic functions, extracted after a polarization analysis of the event waveforms, and combines the single phase imaging functions with the S-P differential imaging functions. The performance of the method is demonstrated here in different tectonic environments: (1) analysis of the one year long precursory phase of 2014 Iquique earthquake in Chile; (2) detection and location of tectonic tremor sources and low-frequency earthquakes during the multiple episodes of tectonic tremor activity in southwestern Japan.

  20. Plate convergence, crustal delamination, extrusion tectonics and minimization of shortening work as main controlling factors of the recent Mediterranean deformation pattern

    Directory of Open Access Journals (Sweden)

    D. Babbucci

    1997-06-01

    Full Text Available It is argued that the time-space distribution of major post middle Miocene deformation events in the Central-Eastern Mediterranean region, deduced from the relevant literature, can be coherently explained as a consequence of the convergence between the Africa/Arabia and Eurasia blocks. This plate convergence has mainly been accommodated by the consumption of the thinnest parts of the Northern African (Ionian and Levantine basins and peri-Adriatic margins. During each evolutionary phase the space distribution of trench zones is controlled by the basic physical requirement of minimizing the work of horizontal forces, induced by plate convergence, against the resisting forces, i.e., the cohesion of the upper brittle crustal layer and the buoyancy forces at the consuming boundaries. The significant changes of tectonic styles which determined the transition from one phase to the next, like those which occurred around the Messinian and the late Pliocene-early Pleistocene, were determined by the suture of consuming boundaries. When such an event occurs, the system must activate alternative consuming processes to accommodate the convergence of the major confining blocks. The observed deformations in the study area suggest that this tectonic reorganization mostly developed by the lateral extrusion of crustal wedges away from the sutured borders. This mechanism allowed the translation of maximum horizontal stresses from the locked collisional fronts to the zones where consumable lithosphere was still present, in order to activate the next consuming processes. The extensional episodes which led to the formation of basins and troughs in the Tyrrhenian and Aegean zones are interpreted as secondary effects of the outward escape of crustal wedges, like those which occurred in response to longitudinal compressional regimes in the Apennines and Aegean regions.

  1. Statistical Seismology and Induced Seismicity

    Science.gov (United States)

    Tiampo, K. F.; González, P. J.; Kazemian, J.

    2014-12-01

    While seismicity triggered or induced by natural resources production such as mining or water impoundment in large dams has long been recognized, the recent increase in the unconventional production of oil and gas has been linked to rapid rise in seismicity in many places, including central North America (Ellsworth et al., 2012; Ellsworth, 2013). Worldwide, induced events of M~5 have occurred and, although rare, have resulted in both damage and public concern (Horton, 2012; Keranen et al., 2013). In addition, over the past twenty years, the increase in both number and coverage of seismic stations has resulted in an unprecedented ability to precisely record the magnitude and location of large numbers of small magnitude events. The increase in the number and type of seismic sequences available for detailed study has revealed differences in their statistics that previously difficult to quantify. For example, seismic swarms that produce significant numbers of foreshocks as well as aftershocks have been observed in different tectonic settings, including California, Iceland, and the East Pacific Rise (McGuire et al., 2005; Shearer, 2012; Kazemian et al., 2014). Similarly, smaller events have been observed prior to larger induced events in several occurrences from energy production. The field of statistical seismology has long focused on the question of triggering and the mechanisms responsible (Stein et al., 1992; Hill et al., 1993; Steacy et al., 2005; Parsons, 2005; Main et al., 2006). For example, in most cases the associated stress perturbations are much smaller than the earthquake stress drop, suggesting an inherent sensitivity to relatively small stress changes (Nalbant et al., 2005). Induced seismicity provides the opportunity to investigate triggering and, in particular, the differences between long- and short-range triggering. Here we investigate the statistics of induced seismicity sequences from around the world, including central North America and Spain, and

  2. RESERVOIR CHARACTERIZATION USING SEISMIC AND WELL ...

    African Journals Online (AJOL)

    Osondu

    2012-06-19

    Jun 19, 2012 ... analysis of the entire pay zone is impractical. A typical seismic section of Niger Delta will reveal number of synsedimentary structures resulting from the deltaic tectonic. The structures include growth faults; which are normal faults characterization by a concave fault plane resulting from the decrease of dip at ...

  3. Angola Seismicity MAP

    Science.gov (United States)

    Neto, F. A. P.; Franca, G.

    2014-12-01

    The purpose of this job was to study and document the Angola natural seismicity, establishment of the first database seismic data to facilitate consultation and search for information on seismic activity in the country. The study was conducted based on query reports produced by National Institute of Meteorology and Geophysics (INAMET) 1968 to 2014 with emphasis to the work presented by Moreira (1968), that defined six seismogenic zones from macro seismic data, with highlighting is Zone of Sá da Bandeira (Lubango)-Chibemba-Oncócua-Iona. This is the most important of Angola seismic zone, covering the epicentral Quihita and Iona regions, geologically characterized by transcontinental structure tectono-magmatic activation of the Mesozoic with the installation of a wide variety of intrusive rocks of ultrabasic-alkaline composition, basic and alkaline, kimberlites and carbonatites, strongly marked by intense tectonism, presenting with several faults and fractures (locally called corredor de Lucapa). The earthquake of May 9, 1948 reached intensity VI on the Mercalli-Sieberg scale (MCS) in the locality of Quihita, and seismic active of Iona January 15, 1964, the main shock hit the grade VI-VII. Although not having significant seismicity rate can not be neglected, the other five zone are: Cassongue-Ganda-Massano de Amorim; Lola-Quilengues-Caluquembe; Gago Coutinho-zone; Cuima-Cachingues-Cambândua; The Upper Zambezi zone. We also analyzed technical reports on the seismicity of the middle Kwanza produced by Hidroproekt (GAMEK) region as well as international seismic bulletins of the International Seismological Centre (ISC), United States Geological Survey (USGS), and these data served for instrumental location of the epicenters. All compiled information made possible the creation of the First datbase of seismic data for Angola, preparing the map of seismicity with the reconfirmation of the main seismic zones defined by Moreira (1968) and the identification of a new seismic

  4. The 1946 Unimak Tsunami Earthquake Area: revised tectonic structure in reprocessed seismic images and a suspect near field tsunami source

    Science.gov (United States)

    Miller, John J.; von Huene, Roland E.; Ryan, Holly F.

    2014-01-01

    In 1946 at Unimak Pass, Alaska, a tsunami destroyed the lighthouse at Scotch Cap, Unimak Island, took 159 lives on the Hawaiian Islands, damaged island coastal facilities across the south Pacific, and destroyed a hut in Antarctica. The tsunami magnitude of 9.3 is comparable to the magnitude 9.1 tsunami that devastated the Tohoku coast of Japan in 2011. Both causative earthquake epicenters occurred in shallow reaches of the subduction zone. Contractile tectonism along the Alaska margin presumably generated the far-field tsunami by producing a seafloor elevation change. However, the Scotch Cap lighthouse was destroyed by a near-field tsunami that was probably generated by a coeval large undersea landslide, yet bathymetric surveys showed no fresh large landslide scar. We investigated this problem by reprocessing five seismic lines, presented here as high-resolution graphic images, both uninterpreted and interpreted, and available for the reader to download. In addition, the processed seismic data for each line are available for download as seismic industry-standard SEG-Y files. One line, processed through prestack depth migration, crosses a 10 × 15 kilometer and 800-meter-high hill presumed previously to be basement, but that instead is composed of stratified rock superimposed on the slope sediment. This image and multibeam bathymetry illustrate a slide block that could have sourced the 1946 near-field tsunami because it is positioned within a distance determined by the time between earthquake shaking and the tsunami arrival at Scotch Cap and is consistent with the local extent of high runup of 42 meters along the adjacent Alaskan coast. The Unimak/Scotch Cap margin is structurally similar to the 2011 Tohoku tsunamigenic margin where a large landslide at the trench, coeval with the Tohoku earthquake, has been documented. Further study can improve our understanding of tsunami sources along Alaska’s erosional margins.

  5. Accurate relocation of seismicity along the North Aegean Trough and its relation to active tectonics

    Science.gov (United States)

    Konstantinou, K. I.

    2017-10-01

    The tectonics of northern Aegean are affected by the westward push of Anatolia and the gravitational spreading of the Aegean lithosphere that promote transtensional deformation in the area. This regime is also responsible for the creation of a series of pull-apart basins, collectively known as the North Aegean Trough. This work accurately relocates a total of 2300 earthquakes that were recorded along the North Aegean Trough during 2011-2016 by stations of the Hellenic Unified Seismic Network (HUSN) and strong-motion sensors. Absolute locations for these events were obtained using a nonlinear probabilistic algorithm and utilizing a minimum 1D velocity model with station corrections. The hypocentral depth distribution of these events shows a peak at 8 km diminishing gradually down to 20 km. A systematic overestimation of hypocentral depths is observed in the routine locations provided by the National Observatory of Athens where the majority of events appear to be deeper than 15 km. In order to obtain more accurate relative locations these events were relocated using the double-difference method. A total of 1693 events were finally relocated with horizontal and vertical uncertainties that do not exceed 0.11 km and 0.22 km respectively. Well-defined clusters of seismicity can be observed along the Saros and Sporades basins as well as the Kassandra and Sithonia peninsulas. These clusters either occur along the well-known NE-SW strike-slip faults bounding the basins, or along normal faults whose strike is perpendicular to the regional minimum stress axis. Locking depth along the North Aegean Trough is found to be remarkably stable between 13 and 17 km. This is likely a consequence of simultaneous reduction along the SW direction of heat flow (from 89 to 51 mW/m2) and strain rate (from 600 to 50 nstrain/yr) whose opposite effects are canceled out, precluding any sharp changes in locking depth.

  6. Three-Dimensional Seismic Structure of the Mid-Atlantic Ridge: An Investigation of Tectonic, Magmatic, and Hydrothermal Processes in the Rainbow Area

    Science.gov (United States)

    Dunn, Robert A.; Arai, Ryuta; Eason, Deborah E.; Canales, J. Pablo; Sohn, Robert A.

    2017-12-01

    To test models of tectonic, magmatic, and hydrothermal processes along slow-spreading mid-ocean ridges, we analyzed seismic refraction data from the Mid-Atlantic Ridge INtegrated Experiments at Rainbow (MARINER) seismic and geophysical mapping experiment. Centered at the Rainbow area of the Mid-Atlantic Ridge (36°14'N), this study examines a section of ridge with volcanically active segments and a relatively amagmatic ridge offset that hosts the ultramafic Rainbow massif and its high-temperature hydrothermal vent field. Tomographic images of the crust and upper mantle show segment-scale variations in crustal structure, thickness, and the crust-mantle transition, which forms a vertical gradient rather than a sharp boundary. There is little definitive evidence for large regions of sustained high temperatures and melt in the lower crust or upper mantle along the ridge axes, suggesting that melts rising from the mantle intrude as small intermittent magma bodies at crustal and subcrustal levels. The images reveal large rotated crustal blocks, which extend to mantle depths in some places, corresponding to off-axis normal fault locations. Low velocities cap the Rainbow massif, suggesting an extensive near-surface alteration zone due to low-temperature fluid-rock reactions. Within the interior of the massif, seismic images suggest a mixture of peridotite and gabbroic intrusions, with little serpentinization. Here diffuse microearthquake activity indicates a brittle deformation regime supporting a broad network of cracks. Beneath the Rainbow hydrothermal vent field, fluid circulation is largely driven by the heat of small cooling melt bodies intruded into the base of the massif and channeled by the crack network and shallow faults.

  7. Swath sonar mapping of Earth's submarine plate boundaries

    Science.gov (United States)

    Carbotte, S. M.; Ferrini, V. L.; Celnick, M.; Nitsche, F. O.; Ryan, W. B. F.

    2014-12-01

    The recent loss of Malaysia Airlines flight MH370 in an area of the Indian Ocean where less than 5% of the seafloor is mapped with depth sounding data (Smith and Marks, EOS 2014) highlights the striking lack of detailed knowledge of the topography of the seabed for much of the worlds' oceans. Advances in swath sonar mapping technology over the past 30 years have led to dramatic improvements in our capability to map the seabed. However, the oceans are vast and only an estimated 10% of the seafloor has been mapped with these systems. Furthermore, the available coverage is highly heterogeneous and focused within areas of national strategic priority and community scientific interest. The major plate boundaries that encircle the globe, most of which are located in the submarine environment, have been a significant focus of marine geoscience research since the advent of swath sonar mapping. While the location of these plate boundaries are well defined from satellite-derived bathymetry, significant regions remain unmapped at the high-resolutions provided by swath sonars and that are needed to study active volcanic and tectonic plate boundary processes. Within the plate interiors, some fossil plate boundary zones, major hotspot volcanoes, and other volcanic provinces have been the focus of dedicated research programs. Away from these major tectonic structures, swath mapping coverage is limited to sparse ocean transit lines which often reveal previously unknown deep-sea channels and other little studied sedimentary structures not resolvable in existing low-resolution global compilations, highlighting the value of these data even in the tectonically quiet plate interiors. Here, we give an overview of multibeam swath sonar mapping of the major plate boundaries of the globe as extracted from public archives. Significant quantities of swath sonar data acquired from deep-sea regions are in restricted-access international archives. Open access to more of these data sets would

  8. Petrogenesis of the NE Gondwanan uppermost Ediacaran-Lower Cretaceous siliciclastic sequence of Jordan: Provenance, tectonic, and climatic implications

    Science.gov (United States)

    Amireh, Belal S.

    2018-04-01

    Detrital framework modes of the NE Gondwanan uppermost Ediacaran-Lower Cretaceous siliciclastic sequence of Jordan are determined employing the routine polarized light microscope. The lower part of this sequence constitutes a segment of the vast lower Paleozoic siliciclastic sheet flanking the northern Gondwana margin that was deposited over a regional unconformity truncating the outskirts of the East African orogen in the aftermath of the Neoproterozoic amalgamation of Gondwana. The research aims to evaluate the factors governing the detrital light mineral composition of this sandstone. The provenance terranes of the Arabian craton controlled by plate tectonics appear to be the primary factor in most of the formations, which could be either directly inferred employing Dickinson's compositional triangles or implied utilizing the petrographic data achieved and the available tectonic and geological data. The Arabian-Nubian Shield constitutes invariably the craton interior or the transitional provenance terrane within the NE Gondwana continental block that consistently supplied sandy detritus through northward-flowing braided rivers to all the lower Paleozoic formations. On the other hand, the Lower Cretaceous Series received siliciclastic debris, through braided-meandering rivers having same northward dispersal direction, additionally from the lower Paleozoic and lower-middle Mesozoic platform strata in the Arabian Craton. The formations making about 50% of the siliciclastic sequence represent a success for Dickinson's plate tectonics-provenance approach in attributing the detrital framework components primarily to the plate tectonic setting of the provenance terranes. However, even under this success, the varying effects of the other secondary sedimentological and paleoclimatological factors are important and could be crucial. The inapplicability of this approach to infer the appropriate provenance terranes of the remaining formations could be ascribed either to the

  9. Structural analysis and Miocene-to-Present tectonic evolution of a lithospheric-scale, transcurrent lineament: The Sciacca Fault (Sicilian Channel, Central Mediterranean Sea)

    Science.gov (United States)

    Fedorik, Jakub; Toscani, Giovanni; Lodolo, Emanuele; Civile, Dario; Bonini, Lorenzo; Seno, Silvio

    2018-01-01

    Seismo-stratigraphic and structural analysis of a large number of multichannel seismic reflection profiles acquired in the northern part of the Sicilian Channel allowed a 3-D reconstruction of a regional NS-trending transfer zone which displays a transcurrent tectonic regime, and that is of broad relevance for its seismotectonic and geodynamic implications. It is constituted of two major transcurrent faults delimiting a 30-km-wide, mostly undeformed basin. The western fault (Capo Granitola) does not show clear evidence of present-day tectonic activity, and toward the south it is connected with the volcanic area of the Graham Bank. The eastern fault (Sciacca) is structurally more complex, showing active deformation at the sea-floor, particularly evident along the Nerita Bank. The Sciacca Fault is constituted of a master and splay faults compatible with a right-lateral kinematics. Sciacca Fault is superimposed on an inherited weakness zone (a Mesozoic carbonate ramp), which borders to the east a 2.5-km-thick Plio-Quaternary basin, and that was reactivated during the Pliocene. A set of scaled claybox analogue models was carried out in order to better understand the tectonic processes that led to the structural setting displayed by seismic data. Tectonic structures and uplift/subsidence patterns generated by the models are compatible with the 3-D model obtained from seismic reflection profiles. The best fit between the tectonic setting deriving from the interpretation of seismic profiles and the analogue models was obtained considering a right-lateral movement for the Sciacca Fault. Nevertheless, the stress field in the study area derived from GPS measurements does not support the present-day modelled right-lateral kinematics along the Sciacca Fault. Moreover, seismic events along this fault show focal mechanisms with a left-lateral component. We ascribe the slip change along the Sciacca Fault, from a right-lateral transcurrent regime to the present-day left

  10. Spatial variations of current tectonic stress field and its relationship to the structure and rheology of lithosphere around the Bohai Sea, North China

    Science.gov (United States)

    Li, Xianrui; Wang, Jie; Zeng, Zuoxun; Dai, Qingqin

    2017-05-01

    The tectonic stress field in the middle-upper crust is closely related to the structure and rheology of the lithosphere. To determine the stress field in the deep crust, we inversed the focal mechanism solutions (FMSs) of 62 earthquakes that occurred between 2009 and 2015 in the Bohai Sea and its surrounding areas using broadband seismic waveforms collected from 140 stations. We then derived the tectonic stress field using the software SATSI (Spatial And Temporal Stress Inversion) based on the damped linear inversion method. The inversion results show that both the maximum (σ1) and minimum (σ3) principle stress axes throughout the entire region are nearly horizontal except in the Tangshan and Haicheng areas, suggesting that the study area is predominantly under a strike-slip faulting stress regime. The σ1 and σ3 axes are found to be oriented in the NEE-SWW or nearly E-W and NNW-SSE or nearly S-N directions, respectively. These results indicate that the stress field in the North China Craton is controlled by the combined effects of the Pacific Plate westward subduction and the India-Eurasia Plate collision. However, localized normal faulting stress regimes (where the vertical stress σv ≈ σ1) are observed in the Tangshan and Haicheng areas, where low viscosity bodies (LVBs) were identified using geophysical data. Based on the analysis of focal mechanism solutions, active faults and lithosphere rheology characteristics in the Tangshan and Haicheng areas, we speculate that the anomalous stress regime is caused by the local extension resulting from the movement of strike-slip faults under the action of the regional stress field. The existence of LVB may indicate weakness in the crust that favors the accumulation of tectonic stress and triggers large earthquakes.

  11. Late Mesozoic basin and range tectonics and related magmatism in Southeast China

    Directory of Open Access Journals (Sweden)

    Dezi Wang

    2012-03-01

    Full Text Available During the Late Mesozoic Middle Jurassic–Late Cretaceous, basin and range tectonics and associated magmatism representative of an extensional tectonic setting was widespread in southeastern China as a result of Pacific Plate subduction. Basin tectonics consists of post-orogenic (Type I and intra-continental extensional basins (Type II. Type I basins developed in the piedmont and intraland during the Late Triassic to Early Jurassic, in which coarse-grained terrestrial clastic sediments were deposited. Type II basins formed during intra-continental crustal thinning and were characterized by the development of grabens and half-grabens. Graben basins were mainly generated during the Middle Jurassic and were associated with bimodal volcanism. Sediments in half-grabens are intercalated with rhyolitic tuffs and lavas and are Early Cretaceous in age with a dominance of Late Cretaceous–Paleogene red beds. Ranges are composed of granitoids and bimodal volcanic rocks, A-type granites and dome-type metamorphic core complexes. The authors analyzed lithological, geochemical and geochronological features of the Late Mesozoic igneous rock assemblages and proposed some geodynamical constraints on forming the basin and range tectonics of South China. A comparison of the similarities and differences of basin and range tectonics between the eastern and western shores of the Pacific is made, and the geodynamical evolution model of the Southeast China Block during Late Mesozoic is discussed. Studied results suggest that the basin and range terrane within South China developed on a pre-Mesozoic folded belt was derived from a polyphase tectonic evolution mainly constrained by subduction of the western Pacific Plate since the Late Mesozoic, leading to formation of various magmatism in a back-arc extensional setting. Its geodynamic mechanism can compare with that of basin and range tectonics in the eastern shore of the Pacific. Differences of basin and range

  12. Seismic hazard assessment of the Hanford region, Eastern Washington State

    International Nuclear Information System (INIS)

    Youngs, R.R.; Coppersmith, K.J.; Power, M.S.; Swan, F.H. III

    1985-01-01

    A probabilistic seismic hazard assessment was made for a site within the Hanford region of eastern Washington state, which is characterized as an intraplate region having a relatively low rate of seismic activity. Probabilistic procedures, such as logic trees, were utilized to account for the uncertainties in identifying and characterizing the potential seismic sources in the region. Logic trees provide a convenient, flexible means of assessing the values and relative likelihoods of input parameters to the hazard model that may be dependent upon each other. Uncertainties accounted for in this way include the tectonic model, segmentation, capability, fault geometry, maximum earthquake magnitude, and earthquake recurrence rate. The computed hazard results are expressed as a distribution from which confidence levels are assessed. Analysis of the results show the contributions to the total hazard from various seismic sources and due to various earthquake magnitudes. In addition, the contributions of uncertainties in the various source parameters to the uncertainty in the computed hazard are assessed. For this study, the major contribution to uncertainty in the computed hazard are due to uncertainties in the applicable tectonic model and the earthquake recurrence rate. This analysis serves to illustrate some of the probabilistic tools that are available for conducting seismic hazard assessments and for analyzing the results of these studies. 5 references, 7 figures

  13. The Cenozoic geological evolution of the Central and Northern North Sea based on seismic sequence stratigraphy

    Energy Technology Data Exchange (ETDEWEB)

    Jordt, Henrik

    1996-03-01

    This thesis represents scientific results from seismic sequence stratigraphic investigations. These investigations and results are integrated into an ongoing mineralogical study of the Cenozoic deposits. the main results from this mineralogical study are presented and discussed. The seismic investigations have provided boundary conditions for a forward modelling study of the Cenozoic depositional history. Results from the forward modelling are presented as they emphasise the influence of tectonics on sequence development. The tectonic motions described were important for the formation of the large oil and gas fields in the North Sea.

  14. Deformation of the Northwestern Okhotsk Plate: How is it happening?

    OpenAIRE

    Hindle, D.; Fujita, K.; Mackey, K.

    2009-01-01

    The Eurasia (EU) – North America (NA) plate boundary zone across Northeast Asia still presents many open questions within the plate tectonic paradigm. Constraining the geometry and number of plates or microplates present in the plate boundary zone is especially difficult because of the location of the EU-NA euler pole close to or even upon the EU-NA boundary. One of the major challenges remains the geometry of the Okhotsk plate (OK). whose northwestern portion terminates on ...

  15. Habitability from Tidally Induced Tectonics

    Science.gov (United States)

    Valencia, Diana; Tan, Vivian Yun Yan; Zajac, Zachary

    2018-04-01

    The stability of Earth’s climate on geological timescales is enabled by the carbon–silicate cycle that acts as a negative feedback mechanism stabilizing surface temperatures via the intake and outgassing of atmospheric carbon. On Earth, this thermostat is enabled by plate tectonics that sequesters outgassed CO2 back into the mantle via weathering and subduction at convergent margins. Here we propose a separate tectonic mechanism—vertical recycling—that can serve as the vehicle for CO2 outgassing and sequestration over long timescales. The mechanism requires continuous tidal heating, which makes it particularly relevant to planets in the habitable zone of M stars. Dynamical models of this vertical recycling scenario and stability analysis show that temperate climates stable over timescales of billions of years are realized for a variety of initial conditions, even as the M star dims over time. The magnitude of equilibrium surface temperatures depends on the interplay of sea weathering and outgassing, which in turn depends on planetary carbon content, so that planets with lower carbon budgets are favored for temperate conditions. The habitability of planets such as found in the Trappist-1 system may be rooted in tidally driven tectonics.

  16. Structure and tectonics of the Main Himalayan Thrust and associated faults from recent earthquake and seismic imaging studies using the NAMASTE array

    Science.gov (United States)

    Karplus, M. S.; Pant, M.; Velasco, A. A.; Nabelek, J.; Kuna, V. M.; Sapkota, S. N.; Ghosh, A.; Mendoza, M.; Adhikari, L. B.; Klemperer, S. L.

    2017-12-01

    The India-Eurasia collision zone presents a significant earthquake hazard, as demonstrated by the recent, devastating April 25, 2015 M=7.8 Gorkha earthquake and the following May 12, 2015 M=7.3 earthquake. Important questions remain, including distinguishing possible geometries of the Main Himalayan Thrust (MHT), the role of other regional faults, the crustal composition and role of fluids in faulting, and the details of the rupture process, including structural causes and locations of rupture segmentation both along-strike and down-dip. These recent earthquakes and their aftershocks provide a unique opportunity to learn more about this collision zone. In June 2015, funded by NSF, we deployed the Nepal Array Measuring Aftershock Seismicity Trailing Earthquake (NAMASTE) array of 46 seismic stations distributed across eastern and central Nepal, spanning the region with most of the aftershocks. This array remained in place for 11 months from June 2015 to May 2016. We combine new results from this aftershock network in Nepal with previous geophysical and geological studies across the Himalaya to derive a new understanding of the tectonics of the Himalaya and southern Tibet in Nepal and surrounding countries. We focus on structure and composition of the Main Himalayan Thrust and compare this continent-continent subduction megathrust with megathrusts in other subduction zones.

  17. Radon in soil variations for Vrancea seismic area

    International Nuclear Information System (INIS)

    Zoran, M.

    2002-01-01

    Earthquakes occur as a result of a build up of pressure between colliding sections of the Earth's crust. These sections, known as continental plates, meet at 'fault lines'. According to classical earthquake theory, small earthquakes should continue to grow into large earthquakes until they spread all along the fault line. Vrancea region is fitted to such a model. The mechanical processes of earthquake preparation are always accompanied by deformations, afterwards complex short- or long term precursory phenomena can appear. Macro-fracturing processes are preceded by micro-fracturing phenomena with a resulting radon and other gas precursors (He, CH 4 , NO) anomalies in soil-gas and groundwater. Studies of geochemical and hydrological anomalies preceding significant earthquakes have been reported from China, Japan, Uzbekistan, Mexico, Italy, India and Germany. However, studies of these pre-seismic phenomena have been controversial for several reasons. Temporal variations of radon in soil or water, can give evidence that the emanation of this gas can be correlated with tectonic disturbances. I used nuclear track detectors LR-115 and CN-85 for radon concentration monitoring in soil at 50 cm depth exposed for a period of 30 days in Vrancioaia test area. Time series radon data in soil-gas during of two years long observation period have established that more than 50% of radon concentration increases were correlated with microseismic events of 2-4 magnitude on Richter scale. A clear positive correlation for radon concentration prior one month of seismic event was associated with a registered event of magnitude 5. In order to differentiate the changes due to tectonic disturbances and that of meteorological parameters, were measured barometric pressure, precipitation and temperature. Negative correlation between radon concentration in soil and meteorological parameters was found. To predict a future earthquake, all precursory phenomena must be investigated. The

  18. Active crustal deformation of the El Salvador Fault Zone by integrating geodetic, seismological and geological data: application in seismic hazard assessment

    Science.gov (United States)

    Staller, A.; Benito, B.; Martínez-Díaz, J.; Hernández, D.; Hernández-Rey, R.

    2013-05-01

    El Salvador, Central America, is part of the Chortis block in the northwestern boundary of the Caribbean plate. This block is interacting with a diffuse triple junction point with the Cocos and North American plates. Among the structures that cut the Miocene to Pleistocene volcanic deposits stands out the El Salvador Fault Zone (ESFZ): It is oriented in N90-100E direction, and it is composed of several structural segments that deform Quaternary deposits with right-lateral and oblique slip motions. The ESFZ is seismically active and capable of producing earthquakes such as the February 13, 2001 with Mw 6.6 (Martínez-Díaz et al., 2004), that seriously affected the population, leaving many casualties. This structure plays an important role in the tectonics of the Chortis block, since its motion is directly related to the drift of the Caribbean plate to the east and not with the partitioning of the deformation of the Cocos subduction (here not coupled) (Álvarez-Gómez et al., 2008). Together with the volcanic arc of El Salvador, this zone constitutes a weakness area that allows the motion of forearc block toward the NW. The geometry and the degree of activity of the ESFZ are not studied enough. However their knowledge is essential to understand the seismic hazard associated to this important seismogenic structure. For this reason, since 2007 a GPS dense network was established along the ESFZ (ZFESNet) in order to obtain GPS velocity measurements which are later used to explain the nature of strain accumulation on major faults along the ESFZ. The current work aims at understanding active crustal deformation of the ESFZ through kinematic model. The results provide significant information to be included in a new estimation of seismic hazard taking into account the major structures in ESFZ.

  19. Petrogenesis and tectonic association of rift-related basic Panjal dykes from the northern Indian plate, North-Western Pakistan: evidence of high-Ti basalts analogous to dykes from Tibet

    Science.gov (United States)

    Sajid, Muhammad; Andersen, Jens; Arif, Mohammad

    2017-10-01

    Rift related magmatism during Permian time in the northern margin of Indian plate is represented by basic dykes in several Himalayan terranes including north western Pakistan. The field relations, mineralogy and whole rock geochemistry of these basic dykes reveal significant textural, mineralogical and chemical variation between two major types (a) dolerite and (b) amphibolite. Intra-plate tectonic settings for both rock types have been interpreted on the basis of low Zr/Nb ratios (primitive mantle using Dy/Yb, La/Yb, Sm/Yb and La/Sm ratios show that amphibolite formed by smaller degrees (< 5%) of partial melting than the dolerites (< 10%). The trace elements ratios suggest the origination of dolerites from the subcontinental lithospheric mantle with some crustal contamination. This is consistent with a petrogenetic relationship with Panjal trap magmatism, reported from Kashmir and other parts of north western India. The amphibolites, in contrast, show affinity towards Ocean Island basalts (OIB) with a relatively deep asthenospheric mantle source and minimal crustal contribution and are geochemically similar to the High-Ti mafic dykes of southern Qiangtang, Tibet. These similarities combined with Permian tectonic restoration of Gondwana indicate the coeval origin for both dykes from distinct mantle source during continental rifting related to formation of the Neotethys Ocean.

  20. State of the art of earthquake engineering in nuclear power plant design

    International Nuclear Information System (INIS)

    Schildknecht, P.O.

    1976-12-01

    A brief outline of definitions based on the USNRC, Seismic and Geologic Siting Criteria for Nuclear Power Plants, and on the plate tectonics and earthquake terminology is given. An introduction into plate tectonics and the associated earthquake phenomena is then presented. Ground motion characteristics are described in connection with the selection of design earthquakes. Mathematical methods of dynamic structural analyses are discussed for linear and nonlinear systems. Response analysis techniques for nuclear power plants are explained considering soil-structure interaction effects. (Auth.)

  1. A global earthquake discrimination scheme to optimize ground-motion prediction equation selection

    Science.gov (United States)

    Garcia, Daniel; Wald, David J.; Hearne, Michael

    2012-01-01

    We present a new automatic earthquake discrimination procedure to determine in near-real time the tectonic regime and seismotectonic domain of an earthquake, its most likely source type, and the corresponding ground-motion prediction equation (GMPE) class to be used in the U.S. Geological Survey (USGS) Global ShakeMap system. This method makes use of the Flinn–Engdahl regionalization scheme, seismotectonic information (plate boundaries, global geology, seismicity catalogs, and regional and local studies), and the source parameters available from the USGS National Earthquake Information Center in the minutes following an earthquake to give the best estimation of the setting and mechanism of the event. Depending on the tectonic setting, additional criteria based on hypocentral depth, style of faulting, and regional seismicity may be applied. For subduction zones, these criteria include the use of focal mechanism information and detailed interface models to discriminate among outer-rise, upper-plate, interface, and intraslab seismicity. The scheme is validated against a large database of recent historical earthquakes. Though developed to assess GMPE selection in Global ShakeMap operations, we anticipate a variety of uses for this strategy, from real-time processing systems to any analysis involving tectonic classification of sources from seismic catalogs.

  2. TERRAIN TECTONICS OF THE CENTRAL ASIAN FOLDED BELT

    Directory of Open Access Journals (Sweden)

    M. M. Buslov

    2014-01-01

    Full Text Available The terrain analysis concept envisages primarily a possibility of approximation of fragments / terrains of various geodynamic settings which belong to different plates. The terrain analysis can supplement the theory of plate tectonics in solving problems of geodynamics and tectonics of regions of the crust with complex structures. The Central Asian belt is among such complicated regions. Terrain structures occurred as a result of combined movements in the system of 'frontal' and/or oblique subduction – collision. In studies of geological objects, it is required first of all to prove their (vertical and horizontal autochthony in relations to each other and then proceed to paleogeodynamic, paleotectonic and paleogeographic reconstructions. Obviously, such a complex approach needs data to be obtained by a variety of research methods, including those applied to study geologic structures, stratigraphy, paleontology, paleogeography, lithothlogy, geochemistry, geochronology, paleomagnetism etc. Only by correlating such data collected from inter-disciplinary studies of the regions, it is possible to establish reliable characteristics of the geological settings and avoid mistakes and misinterpretations that may be associated with the 'stratigraphic' approach to solutions of both regional and global problems of geodynamics and tectonics of folded areas. The terrain analysis of the Central Asian folded belt suggests that its tectonic structure combines marginal continental rock complexes that were formed by the evolution of two major oceanic plates. One of them is the plate of the Paleo-Asian Ocean. As the analogue of the current Indo-Atlantic segment of Earth, it is characterised by the presence of continental blocks in the composition of the oceanic crust and the formation of oceanic basins resulting from the breakup of Rodinia and Gondvana. In the course of its evolution, super-continents disintegrated, and the blocks were reunited into the Kazakhstan

  3. An Alternative view of Earth's Tectonics : The Moon's explosive origin out of SE Asia.

    Science.gov (United States)

    Coleman, P. F.

    2017-12-01

    A lunar birth scar is typically considered untenable, under the standard paradigm (GTS-4.6-0 Ga, Giant Impact/Plate Tectonics), since it would have been erased by a combination of Wilson recycling, and erosion. This paradigm, while supported by robust, absolute dating, is still provisional, and, like all scientifc paradigms, is nonetheless open to refutation. It cannot, a priori, rule out such a scar. If empirical evidence were to be discovered, in favor of a lunar birthmark, it would have profound implications for the standard view. Coleman (2015) proposed an alternative paradigm based on an internal explosion of Proto-Earth (PE) that ejected the Moon into orbit and left coeval global signatures, such as; ocean-continent antipodality, the global geoid, origin of water, continents, trenches, fault lines, LIPs, hotspots, seamount chains, from the high TP shock/seismic waves. The abrupt deceleration also led to inertial effects of PE's crustal layers, possibly explaining subduction/obduction and fold and thrust fold belts. One major, first order, line of evidence is the actual fission signature ( 4000+ km long) where the Moon was explosively thrust tangentially (to the core) through ductile mantle (see Fig B) to escape into orbit. The proposed path, (locus Moon's center) is from (0°, 78.5°E) (Fig A), near present day India, to (+14.4°, 119°E) out of SE Asia (See Fig C). Possible evidence in favor of this path (but not limited to) include: the Indian Geoid Anomaly Low ( Moon's exhumation?), the Himalayas and Tibetan Plateau (generated by the Moon's NE collisional movement and temporary hole and mantle rebound), SE Asia with many minor plates and back arc basins ( the Moon's exit zone), the East African Rifts (EARs) form a NE-directed pull apart region (explained as a set explosive crustal fragments or "plates") moving towards this relic unconsolidated Asian sink hole (See Fig D). The existence of a fossilised lunar birth points to a recent Earth-Moon, since

  4. Tectonics of East Siberian Sea Basin and its influence on petroleum systems

    Science.gov (United States)

    Karpov, Yury; Antonina, Stoupakova; Anna, Suslova; Mariia, Agasheva

    2016-04-01

    The East Siberian Sea basin (ESSB) is the largest part of the Siberian Arctic shelf, extending for over 1000 km from New Siberian Islands archipelago to Wrangel Island. Nowadays East Siberian Sea margin is considered as a region with probable high petroleum potential. This part of Russian Arctic shelf is the least studied. The major problems in geological investigation of East Siberian Sea shelf are absence of deep wells in area and low seismic exploration maturity. Only general conclusions on its geology and hydrocarbon systems can be drawn based on limited seismic, gravity and magnetic data, supported by projection of onshore geological data to offshore. So, that's why now only complex geological and seismic stratigraphy interpretations are provided. Today we have several concepts and can summarize the tectonic history of the basin. The basin is filled with siliclastic sediments. In the deepest depocentres sediments thickness exceed 8 km in average. Seismic data was interpreted using methods of seismic stratigraphy. Stratigraphic interpretation was possible to achieve because seismic reflections follow chronostratigraphic correlations. Finally, main seismic horizons were indicated. Each indicated horizon follows regional stratigraphic unconformity. In case of absence of deep wells in ESSB, we can only prove possible source rocks by projection of data about New Siberian Islands archipelago source rocks on offshore. The petroleum potential of these rocks was investigated by several authors [1, 2, 3]. Perspective structures, investigated in ESSB were founded out by comparing seismogeological cross-sections with explored analogs in other Russian and foreign onshore and offshore basins. The majority of structures could be connected with stratigraphic and fault traps. New data on possible petroleum plays was analyzed, large massif of data on geology and tectonic history of the region was collected, so now we can use method of basin modelling to evaluate hydrocarbon

  5. Erosion influences the seismicity of active thrust faults.

    Science.gov (United States)

    Steer, Philippe; Simoes, Martine; Cattin, Rodolphe; Shyu, J Bruce H

    2014-11-21

    Assessing seismic hazards remains one of the most challenging scientific issues in Earth sciences. Deep tectonic processes are classically considered as the only persistent mechanism driving the stress loading of active faults over a seismic cycle. Here we show via a mechanical model that erosion also significantly influences the stress loading of thrust faults at the timescale of a seismic cycle. Indeed, erosion rates of about ~0.1-20 mm yr(-1), as documented in Taiwan and in other active compressional orogens, can raise the Coulomb stress by ~0.1-10 bar on the nearby thrust faults over the inter-seismic phase. Mass transfers induced by surface processes in general, during continuous or short-lived and intense events, represent a prominent mechanism for inter-seismic stress loading of faults near the surface. Such stresses are probably sufficient to trigger shallow seismicity or promote the rupture of deep continental earthquakes up to the surface.

  6. Detailed crustal structure of the North China and its implication for seismicity

    Science.gov (United States)

    Jiang, Wenliang; Wang, Xin; Tian, Tian; Zhang, Jingfa; Wang, Donglei

    2014-02-01

    Since the Mesozoic-Cenozoic era the North China Craton has experienced an important tectonic transition and it has given rise to complicated crustal structure and strong earthquake activity. Based on the large-scale surface gravity data, we studied the detailed crustal structure and seismogenic mechanism of the North China. The results indicate that the North China presents typical characteristics of adjoining depression and uplift, alternating basins and hills, inhomogeneous density and also great differences in crustal structure and Moho topography. The upper and middle crustal structures are dominated by the NNE-striking tectonic units, with many faults cut down to the middle crust. The lower crust is characterized by the folding-structure, with high and low-density placed alternately from west to east, presenting lateral heterogeneous feature. Adjusted by the gravity isostasy, Moho topography of the North China fluctuates greatly. Compared with the North China Basin, crustal thickness in the Western Taihang, northern Yanshan and Luzhong areas are much thicker while those densities are lower than the North China Basin. The dominating tectonic direction of the Moho topography strikes NE to NNE and undulates alternately from west to east. The epicenters are mostly concentrated in the upper and middle crust, especially the transitional areas between the high and low-gravity anomalies. The Tancheng earthquake in 1668, Sanhe earthquake in 1673, Tangshan earthquake in 1976, and all other seismic tectonic zones of the North China are all distributed in area where magma moves strongly beneath the crust, which is considered to be related to the movement of the high density, unstable and heat flows along the deep passage from the uppermost and asthenosphere due to the subduction of the Pacific slab towards the Eurasian plate.

  7. ISOSTATICALLY DISTURBED TERRAIN OF NORTHWESTERN ANDES MOUNTAINS FROM SPECTRALLY CORRELATED FREE-AIR AND GRAVITY TERRAIN DATA

    Directory of Open Access Journals (Sweden)

    Hernández P Orlando

    2006-12-01

    Full Text Available Recently revised models on global tectonics describe the convergence of the North Andes, Nazca, Caribbean and South American Plates and their seismicity, volcanism, active faulting and extreme
    topography. The current plate boundaries of the area are mainly interpreted from volcanic and seismic datasets with variable confidence levels. New insights on the isostatic state and plate boundaries of
    the northwestern Andes Mountains can be obtained from the spectral analysis of recently available gravity and topography data.
    Isostatically disturbed terrain produces free-air anomalies that are highly correlated with the gravity effects of the terrain. The terrain gravity effects (TGE and free air gravity anomalies (FAGA of the
    Andes mountains spectral correlation data confirms that these mountains are isostatically disturbed. Strong negative terrain-correlated FAGA along western South America and the Greater and Lesser Antilles are consistent with anomalously deepened mantle displaced by subducting oceanic plates.

    Inversion of the compensated terrain gravity effects (CTGE reveals plate subduction systems with alternating shallower and steeper subduction angles. The gravity modeling highlights crustal
    deformation from plate collision and subduction and other constraints on the tectonism of the plate boundary zones for the region.

  8. End Late Paleozoic tectonic stress field in the southern edge of Junggar Basin

    Directory of Open Access Journals (Sweden)

    Wei Ju

    2012-09-01

    Full Text Available This paper presents the end Late Paleozoic tectonic stress field in the southern edge of Junggar Basin by interpreting stress-response structures (dykes, folds, faults with slickenside and conjugate joints. The direction of the maximum principal stress axes is interpreted to be NW–SE (about 325°, and the accommodated motion among plates is assigned as the driving force of this tectonic stress field. The average value of the stress index R′ is about 2.09, which indicates a variation from strike-slip to compressive tectonic stress regime in the study area during the end Late Paleozoic period. The reconstruction of the tectonic field in the southern edge of Junggar Basin provides insights into the tectonic deformation processes around the southern Junggar Basin and contributes to the further understanding of basin evolution and tectonic settings during the culmination of the Paleozoic.

  9. The great triangular seismic region in eastern Asia: Thoughts on its dynamic context

    Directory of Open Access Journals (Sweden)

    Xianglin Gao

    2011-01-01

    Full Text Available A huge triangle-shaped tectonic region in eastern Asia plays host to numerous major earthquakes. The three boundaries of this region, which contains plateaus, mountains, and intermountain basins, are roughly the Himalayan arc, the Tianshan-Baikal, and longitude line ∼105°E. Within this triangular region, tectonism is intense and major deformation occurs both between crustal blocks and within most of them. Outside of this region, rigid blocks move as a whole with relatively few major earthquakes and relatively weak Cenozoic deformation. On a large tectonic scale, the presence of this broad region of intraplate deformation results from dynamic interactions between the Indian, Philippine Sea-West Pacific, and Eurasian plates, as well as the influence of deep-level mantle flow. The Indian subcontinent, which continues to move northwards at ∼40 mm/a since its collision with Eurasia, has plunged beneath Tibet, resulting in various movements and deformations along the Himalayan arc that diffuse over a long distance into the hinterland of Asia. The northward crustal escape of Asia from the Himalayan collisional zone turns eastwards and southeastwards along 95°–100°E longitude and defines the eastern Himalayan syntaxis. At the western Himalayan syntaxis, the Pamirs continue to move into central Asia, leading to crustal deformation and earthquakes that are largely accommodated by old EW or NW trending faults in the bordering areas between China, Mongolia, and Russia, and are restricted by the stable landmass northwest of the Tianshan-Altai-Baikal region. The subduction of the Philippine and Pacific plates under the Eurasian continent has generated a very long and narrow seismic zone along trenches and island arcs in the marginal seas while imposing only slight horizontal compression on the Asian continent that does not impede the eastward motion of eastern Asia. In the third dimension, there may be southeastward deep mantle flow beneath most of

  10. Neogene Tectonics of Part of the Junction of Cyprus and Hellenic Arcs in the Eastern Mediterranean Sea

    Science.gov (United States)

    Küçük, H. M.; Dondurur, D.; ćifçi, G.; Gürçay, S.; Hall, J.; Yaltırak, C.; Aksu, A. E.

    2012-04-01

    The junction between the Hellenic and Cyprus Arcs is one of the tectonically most active regions of the eastern Mediterranean. This junction developed in association with convergence between the African and Eurasian Plates, and the re-organization of the smaller Aegean-Anatolian and Arabian Microplates. Recent studies have shown that the predominant Miocene deformation process in the eastern Mediterranean is compressional tectonism. However, many studies have also shown that the strain is partitioned in the Pliocene-Quaternary and the area displays regions dominated by compression, strike slip and extensional tectonism. The junction between the Hellenic and Cyprus Arcs exhibits complex morphological features including submarine mountains, rises, ridges and trenches. Approximately 600 km of high resolution 72-channel seismic profiles were collected from the junction of Cyprus and Hellenic Arcs using a 450 m long 6.25 m hydrophone spacing streamer and a seven gun array with a 200 cubic inch total volume. This project was part of the joint scientific venture between Dokuz Eylül University (Turkey) and Memorial University of Newfoundland (Canada), and was funded by TÜBITAK and NSERC. The study area includes the southwestern Antalya Basin and the Anaxagoras Mountain of the larger Anaximander Mountains. The multichannel data were processed both at Dokuz Eylül and Memorial University of Newfoundland, using the Landmark Graphics ProMAX software, with automatic gain control, short-gap deconvolution, velocity analysis, normal move-out correction, stack, filter (typically 50-200 Hz bandpass), f-k time migration, and adjacent trace sum. Despite the fact that the source volume was modest, reflections are imaged to 2-3 s two-way time below seabed, even in 2 km water depth. The processed seismic reflection profiles show that there are three distinct sedimentary units, separated by two prominent markers: the M-reflector separates the Pliocene-Quaternary from the underlying

  11. Seismic hazard of American Samoa and neighboring South Pacific Islands--methods, data, parameters, and results

    Science.gov (United States)

    Petersen, Mark D.; Harmsen, Stephen C.; Rukstales, Kenneth S.; Mueller, Charles S.; McNamara, Daniel E.; Luco, Nicolas; Walling, Melanie

    2012-01-01

    American Samoa and the neighboring islands of the South Pacific lie near active tectonic-plate boundaries that host many large earthquakes which can result in strong earthquake shaking and tsunamis. To mitigate earthquake risks from future ground shaking, the Federal Emergency Management Agency requested that the U.S. Geological Survey prepare seismic hazard maps that can be applied in building-design criteria. This Open-File Report describes the data, methods, and parameters used to calculate the seismic shaking hazard as well as the output hazard maps, curves, and deaggregation (disaggregation) information needed for building design. Spectral acceleration hazard for 1 Hertz having a 2-percent probability of exceedance on a firm rock site condition (Vs30=760 meters per second) is 0.12 acceleration of gravity (1 second, 1 Hertz) and 0.32 acceleration of gravity (0.2 seconds, 5 Hertz) on American Samoa, 0.72 acceleration of gravity (1 Hertz) and 2.54 acceleration of gravity (5 Hertz) on Tonga, 0.15 acceleration of gravity (1 Hertz) and 0.55 acceleration of gravity (5 Hertz) on Fiji, and 0.89 acceleration of gravity (1 Hertz) and 2.77 acceleration of gravity (5 Hertz) on the Vanuatu Islands.

  12. Continental tectonics and continental kinetics

    International Nuclear Information System (INIS)

    Allegre, C.J.; Jaupart, C.; Paris-7 Univ., 75

    1985-01-01

    We present a model of continental growth which combines the results of geochemical studies and tectonic ideas about the evolution of continents through geological time. The process of continental growth is mainly controlled by surface phenomena. Continental material is extracted from the mantle along subduction zones at the periphery of oceans, and is destroyed in collision zones where it is remobilized and made available for subduction. We derive an equation for S, the portion of the Earth's surface occupied by continents, which reads as follows: dS/dt=a . √(1-S)-b . S. Coefficients a and b depend on the geometry of plates, on their number and on their velocities. We assume that they decrease exponentially with time with the same time-scale α. This model satisfies both geochemical and tectonic constraints, and allows the integration of several current observations in a single framework. (orig.)

  13. Seismic waves and earthquakes in a global monolithic model

    Science.gov (United States)

    Roubíček, Tomáš

    2018-03-01

    The philosophy that a single "monolithic" model can "asymptotically" replace and couple in a simple elegant way several specialized models relevant on various Earth layers is presented and, in special situations, also rigorously justified. In particular, global seismicity and tectonics is coupled to capture, e.g., (here by a simplified model) ruptures of lithospheric faults generating seismic waves which then propagate through the solid-like mantle and inner core both as shear (S) or pressure (P) waves, while S-waves are suppressed in the fluidic outer core and also in the oceans. The "monolithic-type" models have the capacity to describe all the mentioned features globally in a unified way together with corresponding interfacial conditions implicitly involved, only when scaling its parameters appropriately in different Earth's layers. Coupling of seismic waves with seismic sources due to tectonic events is thus an automatic side effect. The global ansatz is here based, rather for an illustration, only on a relatively simple Jeffreys' viscoelastic damageable material at small strains whose various scaling (limits) can lead to Boger's viscoelastic fluid or even to purely elastic (inviscid) fluid. Self-induced gravity field, Coriolis, centrifugal, and tidal forces are counted in our global model, as well. The rigorous mathematical analysis as far as the existence of solutions, convergence of the mentioned scalings, and energy conservation is briefly presented.

  14. Kinematics and Seismotectonics of the Montello Thrust Fault (Southeastern Alps, Italy) Revealed by Local GPS and Seismic Networks

    Science.gov (United States)

    Serpelloni, E.; Anderlini, L.; Cavaliere, A.; Danesi, S.; Pondrelli, S.; Salimbeni, S.; Danecek, P.; Massa, M.; Lovati, S.

    2014-12-01

    The southern Alps fold-and-thrust belt (FTB) in northern Italy is a tectonically active area accommodating large part of the ~N-S Adria-Eurasia plate convergence, that in the southeastern Alps ranges from 1.5 to 2.5 mm/yr, as constrained by a geodetically defined rotation pole. Because of the high seismic hazard of northeastern Italy, the area is well monitored at a regional scale by seismic and GPS networks. However, more localized seismotectonic and kinematic features, at the scale of the fault segments, are not yet resolved, limiting our knowledge about the seismic potential of the different fault segments belonging to the southeastern Alps FTB. Here we present the results obtained from the analysis of data collected during local seismic and geodetic experiments conducted installing denser geophysical networks across the Montello-Bassano-Belluno system, a segment of the FTB that is presently characterized by a lower sismicity rate with respect to the surrounding domains. The Montello anticline, which is the southernmost tectonic features of the southeastern Alps FTB (located ~15 km south of the mountain front), is a nice example of growing anticline associated with a blind thrust fault. However, how the Adria-Alps convergence is partitioned across the FTB and the seismic potential of the Montello thrust (the area has been struck by a Mw~6.5 in 1695 but the causative fault is still largely debated) remained still unresolved. The new, denser, GPS data show that this area is undergoing among the highest geodetic deformation rates of the entire south Alpine chain, with a steep velocity gradient across the Montello anticline. The earthquakes recorded during the experiment, precisely relocated with double difference methods, and the new earthquake focal mechanisms well correlate with available information about sub-surface geological structures and highlight the seismotectonic activity of the Montello thrust fault. We model the GPS velocities using elastic

  15. High-resolution seismic imaging of the Sohagpur Gondwana basin ...

    Indian Academy of Sciences (India)

    The quality of the high-resolution seismic data depends mainly on the data ..... metric rift geometry. Based on the .... Biswas S K 2003 Regional tectonic framework of the .... Sheth H C, Ray J S, Ray R, Vanderkluysen L, Mahoney J. J, Kumar A ...

  16. Shear-wave polarization analysis of the seismic swarm following the July 9th 1998 Faial (Azores) earthquake

    Science.gov (United States)

    Dias, N. A.; Matias, L.; Tellez, J.; Senos, L.; Gaspar, J. L.

    2003-04-01

    The Azores Islands, located at a tectonic triple Junction, geodynamically are a highly active place. The seismicity in this region occurs mainly in the form of two types of seismic swarms with tectonic and/or volcanic origins, lasting from hours to years. In some cases the swarm follows a main stronger shock, while in others the more energetic event occurs sometime after the beginning of the swarm. In order to understand the complex phenomena of this region, a multidisciplinary approach is needed, involving geophysical, geological and geochemical studies such as the one being carried under the MASHA project (POCTI/CTA/39158/2001), On July 9th 1998 an Mw=6.2 earthquake stroked the island of Faial, in the central group of the Azores archipelago, followed by a seismic swarm still active today. We will present some preliminary results of the shear-wave polarization analysis of a selected dataset of events of this swarm. These correspond to the 112 best- constrained events, record during the first 2 weeks by the seismic network deployed on the 3 islands surrounding the area of the main shock. The objective was to analyse the behaviour of the S wave polarization and the eventual relationship with the presence of seismic anisotropy under the seismic stations, and to correlate this with the regional structure and origin of the Azores plateau. Two main tectonic features are observable on the islands, one primarily orientated SE-NW and the other crossing it roughly with the WNW-ESE direction. The polarization direction observed in the majority of the seismic stations is not stable, varying from SE-NW to WSW-ENE, and showing also the presence in same cases of shear-wave splitting, indicating the presence of anisotropy. Part of the polarization seems to be coherent with the direction of the local tectonic features, but its instability suggest a more complex seismic anisotropy than that proposed by the model EDA of Crampin. Furthermore, the dataset revealed some limitations to

  17. The natural seismic hazard and induced seismicity of the european HDR (hot dry rock) geothermal energy project at Soultz-sous-Forets (Bas-Rhin, France); Alea sismique naturel et sismicite induite du projet geothermique europeen RCS (roche chaude seche) de Soultz-sous-Forets (Bas-Rhin, France)

    Energy Technology Data Exchange (ETDEWEB)

    Helm, J A

    1996-06-07

    Development of the Soultz-sous-Forets HDR (Hot Dry Rock) geothermal energy project will involve important fluid injections which will induce micro-seismic events. This thesis discusses the natural seismicity of the region and induced seismicity associated with fluid injections. A catalogue of all historical and instrument seismicity of the Soultz-sous-Forets (SSF) region has been compiled. This seismicity does not correspond to movements along the major tectonic features of the region. The area around SSF has been identified as being one where high heat flow corresponds to low seismicity. The largest well documented seismic event in the region which took place in 1952 had an epicentral intensity of VI. All important data pertaining to the series of seismic events which took place in the region from August to October 1952 have been collected and are presented. This work details the installation and operation of a permanent 3 station network of accelerometers and seismometers around the HDR site. Also the installation and operation of a mobile network of vertical seismometers during fluid injections. 167 micro-seismic events were recorded on the surface network, with magnitudes from -0.5 to 1.9. The preferential alignment of the micro-seismic cloud is N160 deg. Individual focal mechanisms of the larger seismic events correspond to an extensional tectonic regime. Stress inversion of P wave polarities indicates that the maximum stress is vertical and the intermediate and minimum stress axes horizontal. The largest of the horizontal stresses is orientated N124 deg and the smallest N34 deg. Induced seismic movement is taking place on pre-existing fractures controlled by the in situ stress seismic movement is taking place on pre-existing tectonic fractures controlled by the in situ stress field, and the largest of the induced events had a magnitude 1.9. This level of seismicity does not pose any environmental hazard to the region around Soultz-sous-Forets. (author) 151

  18. Faunal breaks and species composition of Indo-Pacific corals: the role of plate tectonics, environment and habitat distribution

    Science.gov (United States)

    Keith, S. A.; Baird, A. H.; Hughes, T. P.; Madin, J. S.; Connolly, S. R.

    2013-01-01

    Species richness gradients are ubiquitous in nature, but the mechanisms that generate and maintain these patterns at macroecological scales remain unresolved. We use a new approach that focuses on overlapping geographical ranges of species to reveal that Indo-Pacific corals are assembled within 11 distinct faunal provinces. Province limits are characterized by co-occurrence of multiple species range boundaries. Unexpectedly, these faunal breaks are poorly predicted by contemporary environmental conditions and the present-day distribution of habitat. Instead, faunal breaks show striking concordance with geological features (tectonic plates and mantle plume tracks). The depth range over which a species occurs, its larval development rate and genus age are important determinants of the likelihood that species will straddle faunal breaks. Our findings indicate that historical processes, habitat heterogeneity and species colonization ability account for more of the present-day biogeographical patterns of corals than explanations based on the contemporary distribution of reefs or environmental conditions. PMID:23698011

  19. Continental Extensional Tectonics in the Basins and Ranges and Aegean Regions: A Review

    Science.gov (United States)

    Cemen, I.

    2017-12-01

    The Basins and Ranges of North America and the Aegean Region of Eastern Europe and Asia Minor have been long considered as the two best developed examples of continental extension. The two regions contain well-developed normal faults which were considered almost vertical in the 1950s and 1960s. By the mid 1980s, however, overwhelming field evidence emerged to conclude that the dip angle normal faults in the two regions may range from almost vertical to almost horizontal. This led to the discovery that high-grade metamorphic rocks could be brought to surface by the exhumation of mid-crustal rocks along major low-angle normal faults (detachment faults) which were previously either mapped as thrust faults or unconformity. Within the last three decades, our understanding of continental extensional tectonics in the Basins and Ranges and the Aegean Region have improved substantially based on fieldwork, geochemical analysis, analog and computer modeling, detailed radiometric age determinations and thermokinematic modelling. It is now widely accepted that a) Basin and Range extension is controlled by the movement along the San Andreas fault zone as the North American plate moved southeastward with respect to the northwestward movement of the Pacific plate; b) Aegean extension is controlled by subduction roll-back associated with the Hellenic subduction zone; and c) the two regions contain best examples of detachment faulting, extensional folding, and extensional basins. However, there are still many important questions of continental extensional tectonics in the two regions that remain poorly understood. These include determining a) precise amount and percentage of cumulative extension; b) role of strike-slip faulting in the extensional processes; c) exhumation history along detachment surfaces using multimethod geochronology; d) geometry and nature of extensional features in the middle and lower crust; e) the nature of upper mantle and asthenospheric flow; f) evolutions

  20. Co-seismic slip, post-seismic slip, and largest aftershock associated with the 1994 Sanriku-haruka-oki, Japan, earthquake

    Science.gov (United States)

    Yagi, Yuji; Kikuchi, Masayuki; Nishimura, Takuya

    2003-11-01

    We analyzed continuous GPS data to investigate the spatio-temporal distribution of co-seismic slip, post-seismic slip, and largest aftershock associated with the 1994 Sanriku-haruka-oki, Japan, earthquake (Mw = 7.7). To get better resolution for co-seismic and post-seismic slip distribution, we imposed a weak constraint as a priori information of the co-seismic slip determined by seismic wave analyses. We found that the post-seismic slip during 100 days following the main-shock amount to as much moment release as the main-shock, and that the sites of co-seismic slip and post-seismic slip are partitioning on a plate boundary region in complimentary fashion. The major post-seismic slip was triggered by the mainshock in western side of the co-seismic slip, and the extent of the post-seismic slip is almost unchanged with time. It rapidly developed a shear stress concentration ahead of the slip area, and triggered the largest aftershock.

  1. Seismic anisotropy; a window on how the Earth works: multiple mechanisms and sites, from shallow mantle to inner core

    Science.gov (United States)

    Osmaston, Miles

    2013-04-01

    them, with lower seismic property, thus giving the anisotropy. A.m. conservation in the poleward outer-core flow just below the CMB, needed to provide that cooler polar downwelling flow to the IC, would accelerate it clockwise. This seems likely to be the ultimate agent of Antarctica's CW rotation. Finally we come right back to the surface, to the nominally continental crust. Important thermal epeirogenic sensitivity resides in its deep constitution [13]. But much of the crust of continental shelves and beneath deep sedimentary basins appears to lack this sensitivity. So I have reasoned [13] that this 'intermediate crust' (IC) is the product, not of stretching, but of a sedimentation-dominated pre-oceanic stage of continental splitting that has modified crustal genesis by the MOR process but retained the accreting-deep-narrow-crack aspect and resulting seismic anisotropy. If, as geometrical reconstructions lead me to believe, this is the origin of the widespread block-and-basin structures in continents, then it offers also a fascinating explanation of the seismic anisotropy, and its direction, increasingly reported beneath the epeirogenically identifiable IC areas of crust. In that case, as noted at the beginning, crystallization from melt would indeed emerge as the principal agent of seismic anisotropy in the Earth. [1] Raitt RW et al. (1969) Anisotropy of the Pacific upper mantle. JGR 74, 3095-3109. [2] Karato S (1986) Does partial melting reduce the creep strength of the upper mantle? Nature 319, 309. [3] Hirth G & Kohlstedt DL (1996) Water in the oceanic upper mantle: implication for rheology, melt extraction, and the evolution of the lithosphere. EPSL 144, 93-108. [4] Osmaston MF (2010) On the actual variety of plate dynamical mechanisms and how mantle evolution affected them through time, from core formation to the Indian collision. Geophys. Res. Abstr. 12, EGU2010-6101. [5] Osmaston MF (2006) Global tectonic actions emanating from Arctic opening in the

  2. Precursory changes in seismic velocity for the spectrum of earthquake failure modes

    Science.gov (United States)

    Scuderi, M.M.; Marone, C.; Tinti, E.; Di Stefano, G.; Collettini, C.

    2016-01-01

    Temporal changes in seismic velocity during the earthquake cycle have the potential to illuminate physical processes associated with fault weakening and connections between the range of fault slip behaviors including slow earthquakes, tremor and low frequency earthquakes1. Laboratory and theoretical studies predict changes in seismic velocity prior to earthquake failure2, however tectonic faults fail in a spectrum of modes and little is known about precursors for those modes3. Here we show that precursory changes of wave speed occur in laboratory faults for the complete spectrum of failure modes observed for tectonic faults. We systematically altered the stiffness of the loading system to reproduce the transition from slow to fast stick-slip and monitored ultrasonic wave speed during frictional sliding. We find systematic variations of elastic properties during the seismic cycle for both slow and fast earthquakes indicating similar physical mechanisms during rupture nucleation. Our data show that accelerated fault creep causes reduction of seismic velocity and elastic moduli during the preparatory phase preceding failure, which suggests that real time monitoring of active faults may be a means to detect earthquake precursors. PMID:27597879

  3. Identification of seismically susceptible areas in western Himalaya ...

    Indian Academy of Sciences (India)

    Earthquakes cause tremendous loss of life and to the built environment. The amount of ... and reasonable decisions about categories of pat- terns. The main .... tion data. A classification criterion was formulated and tested. Seismicity data was compiled from var- ious earthquake catalogues, tectonic data was stud- ied and ...

  4. Current deformation rates and extrusion of the northwestern Okhotsk plate, northeast Russia

    Science.gov (United States)

    Hindle, D.; Fujita, K.; Mackey, K.

    2006-01-01

    Northeast Asia is a region of broad deformation resulting from the convergence of the Eurasian (EU) and North American (NA) plates. Part of this convergence has been suggested to be relieved by the extrusion and deformation of the Okhotsk plate (OK). Three models for the deformation of the seismically active northwestern corner of the Okhotsk plate, based on different modes of deformation partitioning, are calculated and compared to observations from GPS, seismicity, and geology. The results suggest that this region is being extruded southeastward and deforming internally by a mixture of pure contraction, ``smooth'' extrusion, and ``rigid'' extrusion. Calculated extrusion rates are ~3-5.5 mm/yr, comparable to estimates from geologic data, and internal deformation rates are ~3.0 × 10-9 yr -1. Internal deformation may be only partially accommodated by seismicity, but the short time span of seismic data leaves this subject to large uncertainty.

  5. Crustal structure and regional tectonics of SE Sweden and the Baltic Sea

    International Nuclear Information System (INIS)

    Milnes, A.G.; Gee, D.G.; Lund, C.E.

    1998-11-01

    In this desk study, the available geophysical and geological data on the crustal structure and regional tectonics of the wider surroundings of the Aespoe site (SE Sweden and adjacent parts of the Baltic Sea) are compiled and assessed. The aim is to contribute to the knowledge base for long-term rock mechanical modeling, using the Aespoe site as a proxy for a high-level radioactive waste repository site in Swedish bedrock. The geophysical data reviewed includes two new refraction/wide-angle reflection seismic experiments carried out within the EUROBRIDGE project, in addition to the numerous earlier refraction seismic profiles. The BABEL normal-incidence deep seismic profile is also considered. New geological data, presented at EUROBRIDGE workshops, and in recent SGU publications, are reviewed for the same area. In combination with the seismic data, these provide a base for interpreting the present composition and structure, and the Palaeoproterozoic-Mesoproterozoic evolution, of the crustal segment within which the Aespoe site lies - the Smaaland mega-block. This is characterized by having undergone little regionally significant deformation or magmatism since Neoproterozoic times (the last 1000 million years). It is shown that, at this scale of observation (of the order of 100 km), the long-term rheology of the lithosphere can be argued from a relatively tight observational network, when combined with the results of earlier SKB studies (seismo-tectonics, uplift patterns, state of stress, heat flow) and published research. Although many uncertainties exist, the present state of knowledge would suffice for first exploratory calculations and sensitivity studies of long-term, large-scale rock mechanics

  6. Seismic and tsunami hazard in Puerto Rico and the Virgin Islands

    Science.gov (United States)

    Dillon, William P.; Frankel, Arthur D.; Mueller, Charles S.; Rodriguez, Rafael W.; ten Brink, Uri S.

    1999-01-01

    Executive SummaryPuerto Rico and the Virgin Islands are located at an active plate boundary between the North American plate and the northeast corner of the Caribbean plate. The region was subject in historical times to large magnitude earthquakes and devastating tsunamis. A major downward tilt of the sea floor north of Puerto Rico and the Virgin Islands, large submarine rockslides, and an unusually large negative gravity anomaly are also indicative of a tectonically active region. Scientists have so far failed to explain the deformation of this region in a coherent and predictable picture, such as in California, and this has hampered their ability to assess seismic and tsunami hazards in the region. The NE corner of the Caribbean is unique among the seismically-active regions of the United States in that it is mostly covered by water. This fact presents an additional challenge for seismic and tsunami hazard assessment and mitigation.The workshop, convened in San Juan on March 23-24, 1999, was "historic" in that it brought together for the first time a broad spectrum of scientists, engineers, and public and private sector officials who deal with such diverse questions as tectonic models, probabilistic assessment of seismic hazard, prediction of tsunami runup, strong ground motion, building codes, stability of man-made structures, and the public’s preparedness for natural disasters. It was an opportunity for all the participants to find out how their own activity fit into the broad picture of science and how it aids society in hazard assessment and mitigation. In addition, the workshop was offered as a continuing education course at the Colegio de Ingenieros y Agrimensores de Puerto Rico, which assured a rapid dissemination of the results to the local community. A news conference which took place during the workshop alerted the public to the efforts of the USGS, other Federal agencies, the Commonwealth of Puerto Rico, universities and the private sector.During the

  7. Elasto-plastic deformation and plate weakening due to normal faulting in the subducting plate along the Mariana Trench

    Science.gov (United States)

    Zhou, Zhiyuan; Lin, Jian

    2018-06-01

    We investigated variations in the elasto-plastic deformation of the subducting plate along the Mariana Trench through an analysis of flexural bending and normal fault characteristics together with geodynamic modeling. Most normal faults were initiated at the outer-rise region and grew toward the trench axis with strikes mostly subparallel to the local trench axis. The average trench relief and maximum fault throws were measured to be significantly greater in the southern region (5 km and 320 m, respectively) than the northern and central regions (2 km and 200 m). The subducting plate was modeled as an elasto-plastic slab subjected to tectonic loading at the trench axis. The calculated strain rates and velocities revealed an array of normal fault-like shear zones in the upper plate, resulting in significant faulting-induced reduction in the deviatoric stresses. We then inverted for solutions that best fit the observed flexural bending and normal faulting characteristics, revealing normal fault penetration to depths of 21, 20, and 32 km beneath the seafloor for the northern, central, and southern regions, respectively, which is consistent with the observed depths of the relocated normal faulting earthquakes in the central Mariana Trench. The calculated deeper normal faults of the southern region might lead to about twice as much water being carried into the mantle per unit trench length than the northern and central regions. We further calculated that normal faulting has reduced the effective elastic plate thickness Te by up to 52% locally in the southern region and 33% in both the northern and central regions. The best-fitting solutions revealed a greater apparent angle of the pulling force in the southern region (51-64°) than in the northern (22-35°) and central (20-34°) regions, which correlates with a general southward increase in the seismically-determined dip angle of the subducting slab along the Mariana Trench.

  8. Multi-phase structural and tectonic evolution of the Andaman Sea Region

    Science.gov (United States)

    Masterton, Sheona; Hill, Catherine; Sagi, David Adam; Webb, Peter; Sevastjanova, Inga

    2017-04-01

    We present a new regional tectonic interpretation for Myanmar and the Andaman Sea, built within the framework of global plate motions. In our model the Present Day Andaman Sea region has been subjected to multiple phases of extension, culminating in its mid-Miocene to Present Day opening as a rhomboidal pull-apart basin. The Andaman Sea region is historically thought to have developed as a consequence of back-arc opening associated with plate convergence at the Andaman-Nicobar subduction system. We have undertaken detailed structural interpretation of potential field, Landsat and SRTM data, supported by 2-D crustal models of the Andaman Sea. From this analysis we identified several major north-south striking faults and a series of northeast-southwest striking structures across the region. We have also mapped the extent of the Andaman-Nicobar Accretionary Prism, a fore arc trough and volcanic arc, which we associate with a phase of traditional trench-parallel back-arc extension from the Paleocene to the middle Miocene. A regional tectonic event occurred during the middle Miocene that caused the cessation of back-arc extension in the Present Day Andaman Sea and an eastward shift in the locus of arc-related volcanism. At that time, N-S striking faults onshore and offshore Myanmar were reactivated with widespread right-lateral motion. This motion, accompanied by extension along new NE-SW striking faults, facilitated the opening of the Central Andaman Basin as a pull-apart basin (rhombochasm) in which a strike-slip tectonic regime has a greater impact on the mode of opening than the subduction process. The integration of our plate model solution within a global framework allows identification of major plate reorganisation events and their impact on a regional scale. We therefore attribute the onset of pull-apart opening in the Andaman Sea to ongoing clockwise rotation of the western Sundaland margin throughout the late Paleogene and early Miocene, possibly driven by the

  9. Erosion Associated with Seismically-Induced Landslides in the Middle Longmen Shan Region, Eastern Tibetan Plateau, China

    Directory of Open Access Journals (Sweden)

    Zhikun Ren

    2017-08-01

    Full Text Available The 2008 Wenchuan earthquake and associated co-seismic landslide was the most recent expression of the rapid deformation and erosion occurring in the eastern Tibetan Plateau. The erosion associated with co-seismic landslides balances the long-term tectonic uplift in the topographic evolution of the region; however, the quantitative relationship between earthquakes, uplift, and erosion is still unknown. In order to quantitatively distinguish the seismically-induced erosion in the total erosion, here, we quantify the Wenchuan earthquake-induced erosion using the digital elevation model (DEM differential method and previously-reported landslide volumes. Our results show that the seismically-induced erosion is comparable with the pre-earthquake short-term erosion. The seismically-induced erosion rate contributes ~50% of the total erosion rate, which suggests that the local topographic evolution of the middle Longmen Shan region may be closely related to tectonic events, such as the 2008 Wenchuan earthquake. We propose that seismically-induced erosion is a very important component of the total erosion, particularly in active orogenic regions. Our results demonstrate that the remote sensing technique of differential DEM provides a powerful tool for evaluating the volume of co-seismic landslides produced in intermountain regions by strong earthquakes.

  10. Strong Motion Network of Medellín and Aburrá Valley: technical advances, seismicity records and micro-earthquake monitoring

    Science.gov (United States)

    Posada, G.; Trujillo, J. C., Sr.; Hoyos, C.; Monsalve, G.

    2017-12-01

    The tectonics setting of Colombia is determined by the interaction of Nazca, Caribbean and South American plates, together with the Panama-Choco block collision, which makes a seismically active region. Regional seismic monitoring is carried out by the National Seismological Network of Colombia and the Accelerometer National Network of Colombia. Both networks calculate locations, magnitudes, depths and accelerations, and other seismic parameters. The Medellín - Aburra Valley is located in the Northern segment of the Central Cordillera of Colombia, and according to the Colombian technical seismic norm (NSR-10), is a region of intermediate hazard, because of the proximity to seismic sources of the Valley. Seismic monitoring in the Aburra Valley began in 1996 with an accelerometer network which consisted of 38 instruments. Currently, the network consists of 26 stations and is run by the Early Warning System of Medellin and Aburra Valley (SIATA). The technical advances have allowed the real-time communication since a year ago, currently with 10 stations; post-earthquake data is processed through operationally near-real-time, obtaining quick results in terms of location, acceleration, spectrum response and Fourier analysis; this information is displayed at the SIATA web site. The strong motion database is composed by 280 earthquakes; this information is the basis for the estimation of seismic hazards and risk for the region. A basic statistical analysis of the main information was carried out, including the total recorded events per station, natural frequency, maximum accelerations, depths and magnitudes, which allowed us to identify the main seismic sources, and some seismic site parameters. With the idea of a more complete seismic monitoring and in order to identify seismic sources beneath the Valley, we are in the process of installing 10 low-cost shake seismometers for micro-earthquake monitoring. There is no historical record of earthquakes with a magnitude

  11. Global crustal movement and tectonic plate boundary deformation constrained by the ITRF2008

    Directory of Open Access Journals (Sweden)

    Zhu Ze

    2012-08-01

    Full Text Available On the basis of the newly released International Terrestrial Reference Frame(ITRF2008 by the International Earth Rotation Service (IERS, a new global plate model ITRF2008 plate for the major plates is established. This ITRF2008-derived model is analyzed in comparison with NNR-NUVEL1A model, which is mainly based on geological and geophysical data. The Eurasia and Pacific plates display obvious differences in terms of the velocity fields derived from the two plate motion models. Plate acceleration is also introduced to characterize the differences of the two velocity fields which obtained from ITRF2008 -plate and NNR-NUVEL1A models for major individual plates. The results show that the Africa, South America and Eurasia plates are undergoing acceleration, while the North America and Australia plates are in the state of deceleration motion.

  12. Do cratons preserve evidence of stagnant lid tectonics?

    Directory of Open Access Journals (Sweden)

    Derek Wyman

    2018-01-01

    Full Text Available Evidence for episodic crustal growth extending back to the Hadean has recently prompted a number of numerically based geodynamic models that incorporate cyclic changes from stagnant lid to mobile lid tectonics. A large part of the geologic record is missing for the times at which several of these cycles are inferred to have taken place. The cratons, however, are likely to retain important clues relating to similar cycles developed in the Mesoarchean and Neoarchean. Widespread acceptance of a form of plate tectonics by ∼3.2 Ga is not at odds with the sporadic occurrence of stagnant lid tectonics after this time. The concept of scale as applied to cratons, mantle plumes and Neoarchean volcanic arcs are likely to provide important constraints on future models of Earth's geodynamic evolution. The Superior Province will provide some of the most concrete evidence in this regard given that its constituent blocks may have been locked into a stagnant lid relatively soon after their formation and then assembled in the next global plate tectonic interval. Perceived complexities associated with inferred mantle plume – volcanic arc associations in the Superior Province and other cratons may be related to an over estimation of plume size. A possible stagnant lid episode between ∼2.9 Ga and ∼2.8 Ga is identified by previously unexplained lapses in volcanism on cratons, including the Kaapvaal, Yilgarn and Superior Province cratons. If real, then mantle dynamics associated with this episode likely eliminated any contemporaneous mantle plume incubation sites, which has important implications for widespread plumes developed at ∼2.7 Ga and favours a shallow mantle source in the transition zone. The Superior Province provides a uniquely preserved local proxy for this global event and could serve as the basis for detailed numerical models in the future.

  13. Tectonic map of the Circum-Pacific region, Pacific basin sheet

    Science.gov (United States)

    Scheibner, E.; Moore, G.W.; Drummond, K.J.; Dalziel, Corvalan Q.J.; Moritani, T.; Teraoka, Y.; Sato, T.; Craddock, C.

    2013-01-01

    Circum-Pacific Map Project: The Circum-Pacific Map Project was a cooperative international effort designed to show the relationship of known energy and mineral resources to the major geologic features of the Pacific basin and surrounding continental areas. Available geologic, mineral, and energy-resource data are being complemented by new, project-developed data sets such as magnetic lineations, seafloor mineral deposits, and seafloor sediment. Earth scientists representing some 180 organizations from more than 40 Pacific-region countries are involved in this work. Six overlapping equal-area regional maps at a scale of 1:10,000,000 form the cartographic base for the project: the four Circum-Pacific Quadrants (Northwest, Southwest, Southeast, and Northeast), and the Antarctic and Arctic Sheets. There is also a Pacific Basin Sheet at a scale of 1:17,000,000. The Base Map Series and the Geographic Series (published from 1977 to 1990), the Plate-Tectonic Series (published in 1981 and 1982), the Geodynamic Series (published in 1984 and 1985), and the Geologic Series (published from 1984 to 1989) all include six map sheets. Other thematic map series in preparation include Mineral-Resources, Energy-Resources and Tectonic Maps. Altogether, more than 50 map sheets are planned. The maps were prepared cooperatively by the Circum-Pacific Council for Energy and Mineral Resources and the U.S. Geological Survey and are available from the Branch of Distribution, U. S. Geological Survey, Box 25286, Federal Center, Denver, Colorado 80225, U.S.A. The Circum-Pacific Map Project is organized under six panels of geoscientists representing national earth-science organizations, universities, and natural-resource companies. The six panels correspond to the basic map areas. Current panel chairmen are Tomoyuki Moritani (Northwest Quadrant), R. Wally Johnson (Southwest Quadrant), Ian W.D. Dalziel (Antarctic Region), vacant. (Southeast Quadrant), Kenneth J. Drummond (Northeast Quadrant), and

  14. The crustal structure and tectonic development of the continental margin of the Amundsen Sea Embayment, West Antarctica: implications from geophysical data

    Science.gov (United States)

    Kalberg, Thomas; Gohl, Karsten

    2014-07-01

    The Amundsen Sea Embayment of West Antarctica represents a key component in the tectonic history of Antarctic-New Zealand continental breakup. The region played a major role in the plate-kinematic development of the southern Pacific from the inferred collision of the Hikurangi Plateau with the Gondwana subduction margin at approximately 110-100 Ma to the evolution of the West Antarctic Rift System. However, little is known about the crustal architecture and the tectonic processes creating the embayment. During two `RV Polarstern' expeditions in 2006 and 2010 a large geophysical data set was collected consisting of seismic-refraction and reflection data, ship-borne gravity and helicopter-borne magnetic measurements. Two P-wave velocity-depth models based on forward traveltime modelling of nine ocean bottom hydrophone recordings provide an insight into the lithospheric structure beneath the Amundsen Sea Embayment. Seismic-reflection data image the sedimentary architecture and the top-of-basement. The seismic data provide constraints for 2-D gravity modelling, which supports and complements P-wave modelling. Our final model shows 10-14-km-thick stretched continental crust at the continental rise that thickens to as much as 28 km beneath the inner shelf. The homogenous crustal architecture of the continental rise, including horst and graben structures are interpreted as indicating that wide-mode rifting affected the entire region. We observe a high-velocity layer of variable thickness beneath the margin and related it, contrary to other `normal volcanic type margins', to a proposed magma flow along the base of the crust from beneath eastern Marie Byrd Land-West Antarctica to the Marie Byrd Seamount province. Furthermore, we discuss the possibility of upper mantle serpentinization by seawater penetration at the Marie Byrd Seamount province. Hints of seaward-dipping reflectors indicate some degree of volcanism in the area after break-up. A set of gravity anomaly data

  15. A comparison of seismicity in world's subduction zones: Implication by the difference of b-values

    Science.gov (United States)

    Nishikawa, T.; Ide, S.

    2013-12-01

    from plate tectonic velocities (Scholz and Campos, 2012). Lithosphere age also has a weak negative correlation with the degree of seismic coupling. Based on differences in b-values for the types of faulting, Schorlemmer et al. (2005) suggested that b-value depends inversely on differential stress. This idea, taken together with correlations in the present study, suggests a model where the buoyancy of subducting slabs which depends on the lithosphere age determines stress state and the b-value in each sunbduction zone. The stress state also controls the seismic coupling. This model is basically consistent with the idea of Ruff and Kanamori (1980). Subduction zones with younger and lighter lithosphere are in a compressive stress state and associate with high coupling and small b-values (Chile), while those with older and heavier lithosphere are in a tensional stress state and correlate with low coupling and large b-values (Mariana). Subduction zones such as Nicaragua and El Salvador where b-values are much higher than the expectation from the above correlations may be explained by considering the fact that local tectonics affects the seismic coupling (LaFemina et al., 2009; Scholz and Campos, 2012).

  16. Introduction to Plate Boundaries and Natural Hazards

    NARCIS (Netherlands)

    Duarte, João C.; Schellart, Wouter P.

    2016-01-01

    A great variety of natural hazards occur on Earth, including earthquakes, volcanic eruptions, tsunamis, landslides, floods, fires, tornadoes, hurricanes, and avalanches. The most destructive of these hazards, earthquakes, tsunamis, and volcanic eruptions, are mostly associated with tectonic plate

  17. Seismic refraction data constrain along-axis structure of the Mid-Cayman spreading center

    Science.gov (United States)

    Van Avendonk, H. J.; Hayman, N. W.; Harding, J.; Grevemeyer, I.; Peirce, C.; Dannowski, A.; Papenberg, C. A.

    2015-12-01

    The Mid-Cayman Spreading Center (MCSC) is an ultraslow (15 mm/yr) spreading ridge between the Caribbean and North American plates. From north to south the MCSC is just ~140 km long, as it is bounded to the north by the Oriente transform fault, and to the south by the Swan Islands and Walton fault systems. The neovolcanic zone is characterized by an axial valley with depths to 6000 m, and a few off-axis bathymetric highs that can be as shallow as 2000 m. The role of tectonic and magmatic processes in the creation of this bathymetric relief is not yet understood. In the 2015 CaySEIS experiment, a collaboration between German, US and UK scientists, we gathered ocean-bottom seismic refraction data along five lines across and parallel to the MCSC to determine its crustal structure. We here present the tomographic analysis of marine seismic refractions recorded along the spreading axis. The presence of thin crust here shows that the bathymetric relief of the MCSC is at least in part isostatically compensated. Much of the older ultraslow spread crust on the flanks of the MCSC may not have accreted along the deep axial valley, but it may instead have formed by exhumation of gabbros along extensional faults in the adjacent seafloor.

  18. Preliminary sequence stratigraphy and tectonic evolution of the Tokar Delta, (Southern Sudanese Red Sea)

    OpenAIRE

    Yagoub, Abbas Musa

    2007-01-01

    The study area comprises about 2500sq.Kms. From the seismic data acquired by the Oil Companies (Chevron 1975-76 Total 1980 and IPC 1992), thirty two seismic lines were selected Fig (2). Also synthetic seismograms of Suakin-1, Bashayer-1 A and Bashayer-2A wells are used. The stratigraphy and sedimentation of the Sudanese Red Sea can be placed into four major tectonic phases, Pre-rifting stratigraphy, Syn-Rift Pre-Salt Stratigarphy, Salt Phase and Syn-Rift Post Salt Stratigraphy. Basic conce...

  19. Bedload transport rates in a gravel bedded-river derived from high-resolution monitoring using seismic impact plates

    Science.gov (United States)

    Downs, Peter; Soar, Philip

    2015-04-01

    Accurate characterisation of bedload transport rates is critical for a better understanding of geomorphological process dynamics, aquatic habitats, sediment budgets and strategies for catchment-scale initiatives in sediment management under conditions of climate change. However, rate estimation is challenging in practice: direct measurements are costly and logistically difficult to achieve with acceptable accuracy over geomorphologically-relevant time periods, and the uncertainty in transport rates predicted from empirical formulae and numerical simulation is rarely below 50 per cent. Partly reflecting these issues, passive technologies for continuous bedload monitoring are becoming increasingly popular. Sensors such as seismic impact plates offer the opportunity to characterise bedload activity at exceptionally high resolution - monitoring from the River Avon, (Devon, UK) indicated that despite significant intra-event and between-plate differences in apparent bedload transport aggregated over 5-minute periods, the magnitude-frequency product of discharge and impact frequency result in a highly plausible effective discharge, supporting the potential value of impact plates as indicators of relative sediment transport loads over annual timescales. Whereas the focus in bedload rate estimation to date has been on developing satisfactory sediment rating curves from detection signals, we instead develop a method for directly estimating bedload transport rates from impact plate data as a function of intensity of transport (count, n, per second), bed material mass (kg) and cross-stream transport variability. Bulk sediment samples are converted to a mass in transit for each instantaneous discharge according to the intensity of transport and a Monte Carlo simulation of the load in transit determined at random from the bed material particle size distribution. The lower detection threshold is determined using experimental calibration and the upper size limit is determined from

  20. Convergent plate margin dynamics : New perspectives from structural geology, geophysics and geodynamic modelling

    NARCIS (Netherlands)

    Schellart, W. P.; Rawlinson, N.

    2010-01-01

    Convergent plate margins occur when two adjoining tectonic plates come together to form either a subduction zone, where at least one of the converging plates is oceanic and plunges beneath the other into the mantle, or a collision zone, where two continents or a continent and a magmatic arc collide.

  1. Global regionalized seismicity in view of Non-Extensive Statistical Physics

    Science.gov (United States)

    Chochlaki, Kalliopi; Vallianatos, Filippos; Michas, Georgios

    2018-03-01

    In the present work we study the distribution of Earth's shallow seismicity on different seismic zones, as occurred from 1981 to 2011 and extracted from the Centroid Moment Tensor (CMT) catalog. Our analysis is based on the subdivision of the Earth's surface into seismic zones that are homogeneous with regards to seismic activity and orientation of the predominant stress field. For this, we use the Flinn-Engdahl regionalization (FE) (Flinn and Engdahl, 1965), which consists of fifty seismic zones as modified by Lombardi and Marzocchi (2007). The latter authors grouped the 50 FE zones into larger tectonically homogeneous ones, utilizing the cumulative moment tensor method, resulting into thirty-nine seismic zones. In each one of these seismic zones we study the distribution of seismicity in terms of the frequency-magnitude distribution and the inter-event time distribution between successive earthquakes, a task that is essential for hazard assessments and to better understand the global and regional geodynamics. In our analysis we use non-extensive statistical physics (NESP), which seems to be one of the most adequate and promising methodological tools for analyzing complex systems, such as the Earth's seismicity, introducing the q-exponential formulation as the expression of probability distribution function that maximizes the Sq entropy as defined by Tsallis, (1988). The qE parameter is significantly greater than one for all the seismic regions analyzed with value range from 1.294 to 1.504, indicating that magnitude correlations are particularly strong. Furthermore, the qT parameter shows some temporal correlations but variations with cut-off magnitude show greater temporal correlations when the smaller magnitude earthquakes are included. The qT for earthquakes with magnitude greater than 5 takes values from 1.043 to 1.353 and as we increase the cut-off magnitude to 5.5 and 6 the qT value ranges from 1.001 to 1.242 and from 1.001 to 1.181 respectively, presenting

  2. The Crustal Structure and Seismicity of Eastern Venezuela

    Science.gov (United States)

    Schmitz, M.; Martins, A.; Sobiesiak, M.; Alvarado, L.; Vasquez, R.

    2001-12-01

    Eastern Venezuela is characterized by a moderate to high seismicity, evidenced recently by the 1997 Cariaco earthquake located on the El Pilar Fault, a right lateral strike slip fault which marks the plate boundary between the Caribbean and South-American plates in this region. Recently, the seismic activity seems to migrate towards the zone of subduction of the Lesser Antilles in the northeast, where a mb 6.0 earthquake occurred in October 2000 at 120 km of depth. Periodical changes in the seismic activity are related to the interaction of the stress fields of the strike-slip and the subduction regimes. The seismic activity decreases rapidly towards to the south with some disperse events on the northern edge of the Guayana Shield, related to the Guri fault system. The crustal models used in the region are derived from the information generated by the national seismological network since 1982 and by microseismicity studies in northeastern Venezuela, coinciding in a crustal thickness of about 35 km in depth. Results of seismic refraction measurements for the region were obtained during field campains in 1998 (ECOGUAY) for the Guayana Shield and the Cariaco sedimentary basin and in 2001 (ECCO) for the Oriental Basin. The total crustal thickness decreases from about 45 km on the northern edge of the Guayana Shield to some 36 km close to El Tigre in the center of the Oriental Basin. The average crustal velocity decreases in the same sense from 6.5 to 5.8 km/s. In the Cariaco sedimentary basin a young sedimentary cover of 1 km thickness with a seismic velocity of 2 km/s was derived. Towards the northern limit of the South-American plate, no deep seismic refraction data are available up to now. The improvement of the crustal models used in that region would constitute a step forward in the analysis of the seismic hazard. Seismic refraction studies funded by CONICIT S1-97002996 and S1-2000000685 projects and PDVSA (additional drilling and blasting), recording equipment

  3. Seismological observations at the Northern Andean region of Colombia: Evidence for a shallowly subducting Caribbean Slab and an extensional regime in the upper plate

    Science.gov (United States)

    Monsalve, G.; Cardona, A.; Yarce, J.; Alvira, D.; Poveda, E.

    2013-05-01

    A number of seismological observations, among which we can mention teleseismic travel time residuals, P to S receiver functions and Pn velocity quantification, suggest a clear distinction between the seismic structure of the crust and uppermost mantle between the plains on the Caribbean coast of Colombia and the mountains at the Northern Andean region. Absolute and relative travel time residuals indicate the presence of a seismically fast material in the upper mantle beneath northern Colombia; preliminary results of Pn studies show a region of relatively slow Pn velocities (between 7.8 and 7.9 km/s) underneath the Caribbean coast, contrasting with values greater than 8 km/s beneath the Central and Western cordilleras of Colombia, and the Pacific coast; receiver functions suggest a significantly thinner crust beneath the Caribbean coast, with a crustal thickness between 25 and 30 km, than beneath the Northern Andean zone at the cordilleras of Colombia, where it exceeds 40 km and reaches about 57 km at the location of Bogota. Besides the obviuos discrepancies that appear in response to different topography, we think that the seismological observations are a consequence of the presence of two very distinct slab segments beneath Colombia and contrasting behaviors of the upper plate, which correspond to Caribbean and Nazca subductions. Our seismic observations can be explained by a shallowly subducting Caribbean Plate, in the absence of an asthenospheric wedge, that steepens at about the location of the Bucaramanga nest, and a thinned continental crust that reflects an extensional component linked to oblique convergence of the Caribbean, which contrasts with the crustal thickening in the Andean Cordillera linked to crustal shortening and Nazca plate subuction. These new data are consistent with the idea of of a relatively warm Nazca slab of Neogene age which seems to have a relatively frontal convergence, and a colder, more buoyant Caribbean slab which represents an

  4. Worldwide seismicity in view of non-extensive statistical physics

    Science.gov (United States)

    Chochlaki, Kaliopi; Vallianatos, Filippos; Michas, George

    2014-05-01

    In the present work we study the distribution of worldwide shallow seismic events occurred from 1981 to 2011 extracted from the CMT catalog, with magnitude equal or greater than Mw 5.0. Our analysis based on the subdivision of the Earth surface into seismic zones that are homogeneous with regards to seismic activity and orientation of the predominant stress field. To this direction we use the Flinn-Engdahl regionalization (Flinn and Engdahl, 1965), which consists of 50 seismic zones as modified by Lombardi and Marzocchi (2007), where grouped the 50 FE zones into larger tectonically homogeneous ones, utilizing the cumulative moment tensor method. As a result Lombardi and Marzocchi (2007), limit the initial 50 regions to 39 ones, in which we apply the non- extensive statistical physics approach. The non-extensive statistical physics seems to be the most adequate and promising methodological tool for analyzing complex systems, such as the Earth's interior. In this frame, we introduce the q-exponential formulation as the expression of probability distribution function that maximizes the Sq entropy as defined by Tsallis, (1988). In the present work we analyze the interevent time distribution between successive earthquakes by a q-exponential function in each of the seismic zones defined by Lombardi and Marzocchi (2007).confirming the importance of long-range interactions and the existence of a power-law approximation in the distribution of the interevent times. Our findings supports the ideas of universality within the Tsallis approach to describe Earth's seismicity and present strong evidence on temporal clustering of seismic activity in each of the tectonic zones analyzed. Our analysis as applied in worldwide seismicity with magnitude equal or greater than Mw 5.5 and 6.) is presented and the dependence of our result on the cut-off magnitude is discussed. This research has been funded by the European Union (European Social Fund) and Greek national resources under the

  5. Pn-waves Travel-time Anomaly beneath Taiwan from Dense Seismic Array Observations and its Possible Tectonic Implications

    Science.gov (United States)

    Lin, Y. Y.; Huang, B. S.; Ma, K. F.; Hsieh, M. C.

    2015-12-01

    We investigated travel times of Pn waves, which are of great important for understanding the Moho structure in Taiwan region. Although several high quality tomographic studies had been carried out, observations of Pn waves are still the most comprehensive way to elucidate the Moho structure. Mapping the Moho structure of Taiwan had been a challenging due to the small spatial dimension of Taiwan island with two subduction systems. To decipher the tectonic structure and understanding of earthquake hazard, the island of Taiwan have been implemented by several high density seismic stations, including 71 short-period stations of Central Weather Bureau Seismic Network (CWBSN) and 42 broardband stations of Broadband Array in Taiwan for Seismology (BATS). High quality seismic records of these stations would be used to identify precise Pn-wave arrival times. After station-elevation correction, we measure the difference between the observed and theoretical Pn arrivals from the IASPI 91 model for each station. For correcting uncertainties of earthquake location and origin time, we estimate relative Pn anomaly, ΔtPn , between each station and a reference station. The pattern of ΔtPn reflects the depth anomaly of Moho beneath Taiwan. In general, Pn waves are commonly observed from shallow earthquake at epicentral distance larger than 120 km. We search the global catalog since 2005 and the criteria are M > 5.5, focal depth 150 km. The 12 medium earthquakes from north Luzon are considered for analysis. We choose a station, TWKB, in the most southern point of Taiwan as the reference station due to that all events are from the south. The results indicate obvious different patterns of ΔtPn from different back-azimuths. The ΔtPn pattern of the events in the first group from the south south-east indicates that the Pn arrivals delay suddenly when the Pn waves pass through the Central Range, suggesting the Moho becomes deep rapidly. However, we cannot recognize the same pattern when

  6. Tectonic evolution of the North Patagonian Andes (41°-44° S) through recognition of syntectonic strata

    Science.gov (United States)

    Echaurren, A.; Folguera, A.; Gianni, G.; Orts, D.; Tassara, A.; Encinas, A.; Giménez, M.; Valencia, V.

    2016-05-01

    The North Patagonian fold-thrust belt (41°-44° S) is characterized by a low topography, reduced crustal thickness and a broad lateral development determined by a broken foreland system in the retroarc zone. This particular structural system has not been fully addressed in terms of the age and mechanisms that built this orogenic segment. Here, new field and seismic evidence of syntectonic strata constrain the timing of the main deformational stages, evaluating the prevailing crustal regime for the different mountain domains through time. Growth strata and progressive unconformities, controlled by extensional or compressive structures, were recognized in volcanic and sedimentary rocks from the cordilleran to the extra-Andean domain. These data were used to construct a balanced cross section, whose deep structure was investigated through a thermomechanical model that characterizes the upper plate rheology. Our results indicate two main compressive stages, interrupted by an extensional relaxation period. The first contractional stage in the mid-Cretaceous inverted Jurassic-Lower Cretaceous half graben systems, reactivating the western Cañadón Asfalto rift border ~ 500 km away from the trench, at a time of arc foreland expansion. For this stage, available thermochronological data reveal forearc cooling episodes, and global tectonic reconstructions indicate mid-ocean ridge collisions against the western edge of an upper plate with rapid trenchward displacement. Widespread synextensional volcanism is recognized throughout the Paleogene during plate reorganization; retroarc Paleocene--Eocene flare up activity is interpreted as product of a slab rollback, and fore-to-retroarc Oligocene slab/asthenospheric derived products as an expression of enhanced extension. The second stage of mountain growth occurred in Miocene time associated with Nazca Plate subduction, reaching nearly the same amplitude than the first compressive stage. Extensional weakening of the upper plate

  7. Data base and seismicity studies for Fagaras, Romania crustal earthquakes

    International Nuclear Information System (INIS)

    Moldovan, I.-A.; Enescu, B. D.; Pantea, A.; Constantin, A.; Bazacliu, O.; Malita, Z.; Moldoveanu, T.

    2002-01-01

    Besides the major impact of the Vrancea seismic region, one of the most important intermediate earthquake sources of Europe, the Romanian crustal earthquake sources, from Fagaras, Banat, Crisana, Bucovina or Dobrogea regions, have to be taken into consideration for seismicity studies or seismic hazard assessment. To determine the characteristics of the seismicity for Fagaras seismogenic region, a revised and updated catalogue of the Romanian earthquakes, recently compiled by Oncescu et al. (1999) is used. The catalogue contains 471 tectonic earthquakes and 338 induced earthquakes and is homogenous starting with 1471 for I>VIII and for I>VII starting with 1801. The catalogue is complete for magnitudes larger than 3 starting with 1982. In the studied zone only normal earthquakes occur, related to intracrustal fractures situated from 5 to 30 km depth. Most of them are of low energy, but once in a century a large destructive event occurs with epicentral intensity larger than VIII. The maximum expected magnitude is M GR = 6.5 and the epicenter distribution outlines significant clustering in the zones and on the lines mentioned in the tectonic studies. Taking into account the date of the last major earthquake (1916) and the return periods of severe damaging shocks of over 85 years it is to be expected very soon a large shock in the area. That's why a seismicity and hazard study for this zone is necessary. In the paper there are studied the b parameter variation (the mean value is 0.69), the activity value, the return periods, and seismicity maps and different histograms are plotted. At the same time there are excluded from the catalogue the explosions due to Campulung quarry. Because the catalogue contains the aftershocks for the 1916 earthquake for the seismicity studies we have excluded these shocks. (authors)

  8. Seismicity of the Earth 1900-2012 Java and vicinity

    Science.gov (United States)

    Jones, Eric S.; Hayes, Gavin P.; Bernardino, Melissa; Dannemann, Fransiska K.; Furlong, Kevin P.; Benz, Harley M.; Villaseñor, Antonio

    2014-01-01

    The Sunda convergent margin extends for 5,600 km from the Bay of Bengal and the Andaman Sea, both located northwest of the map area, towards the island of Sumba in the southeast, and then continues eastward as the Banda arc system. This tectonically active margin is a result of the India and Australia plates converging with and subducting beneath the Sunda plate at a rate of approximately 50 to 70 mm/yr. The main physiographic feature associated with this convergent margin is the Sunda-Java Trench, which stretches for 3,000 km parallel to the Java and Sumatra land masses and terminates at 120° E. The convergence of the Indo-Australia and Sunda plates produces two active volcanic arcs: Sunda, which extends from 105 to 122° E and Banda, which extends from 122 to 128° E. The Sunda arc results solely from relatively simple oceanic plate subduction, while the Banda arc represents the transition from oceanic subduction to continental collision, where a complex, broad deforming zone is found. Based on modern activity, the Banda arc can be divided into three distinct zones: an inactive section, the Wetar Zone, bound by two active segments, the Flores Zone in the west and the Damar Zone in the east. The lack of volcanism in the Wetar Zone is attributed to the collision of Australia with the Sunda plate. The absence of gap in volcanic activity is underlain by a gap in intermediate depth seismicity, which is in contrast to nearly continuous, deep seismicity below all three sections of the arc. The Flores Zone is characterized by down-dip compression in the subducted slab at intermediate depths and late Quaternary uplift of the forearc. These unusual features, along with GPS data interpretations indicate that the Flores Zone marks the transition between subduction of oceanic crust in the west and the collision of continental crust in the east. The Java section of the Sunda arc is considered relatively aseismic historically when compared to the highly seismically active

  9. Plate tectonics and the origin of the Juan Fernández Ridge: analysis of bathymetry and magnetic patterns

    Directory of Open Access Journals (Sweden)

    Cristián Rodrigo

    2014-10-01

    Full Text Available Juan Fernández Ridge (JFR is a cα. 800 km long alignment of seamounts and islands which is thought to be fed by a deep mantle plume. JFR includes the Friday and Domingo seamounts in the western active edge close to the active hotspot, and the O'Higgins Seamount and Guyot at the eastern limit just in front of the Chile-Perú trench. Recent bathymetric (Global Topography and magnetic (EMAG-2 datasets were interpreted both qualitatively and quantitatively by means of 3D inverse modeling and 2D direct modeling for geometry and susceptibility, together with an interpretation of the synthetic anomalies related to the classical hypothesis of deep seafloor spreading. Topographic and magnetic patterns are used to understand the tectonic evolution and origin of the JFR, especially in the western segment. Results show a continuous corridor with a base at ~3900 m depth formed by four groups of seamounts/islands with a number of summits. The deep ocean floor is ~22 to ~37 Myr old and is younger to the south of the Challenger Fracture Zone that runs in a SW-NE direction. The magnetic pattern of the western JFR segment, which is different than the eastern one, has no correlation with bathymetry and does not present a common polarity nor fit with magnetic models for isolated bodies. This superposition of magnetic patterns indicates a role of the faults/fractures of the Nazca Plate. Geological evidence supports the hypothesis of a fixed mantle plume for the origin of JFR but our data suggest that tectonic processes play a role, thus fueling the global controversy about these competing processes.

  10. Seismic activity and thermal regime of low temperature fumaroles at Mt. Vesuvius in 2004-2011: distinguishing among seismic, volcanic and hydrological signals

    Directory of Open Access Journals (Sweden)

    Paola Cusano

    2013-11-01

    Full Text Available Seismological, soil temperature and hydrological data from Mt. Vesuvius are collected to characterize the present-day activity of the volcanic/hydrothermal system and to detect possible unrest-related phenomena. We present patterns of seismicity and soil temperature in the crater area during the period February 2004-December 2011. The temporal distribution of number and depth of Volcano-Tectonic earthquakes and the energy release are considered. Hourly data of soil temperature have been acquired since January 2004 in different locations along the rim and within the crater. The observed changes of temperature are studied to establish a temporal-based correlation with the volcanic activity and/or with external forcing, as variations of the regional and local stress field acting on the volcano or meteorological phenomena. The comparison between seismic activity and temperature data highlights significant variations possibly related to changes in fluid circulation in the hydrothermal system of the volcano. The common continuous observations start just before a very shallow earthquake occurred in August 2005, which was preceded by a thermal anomaly. This coincidence has been interpreted as related to fluid-driven rock fracturing, as observed in other volcanoes. For the successive temporal patterns, the seismicity rate and energy release are characterized by slight variations accompanied by changes in temperature. This evidence of reactivity of the fumarole thermal field to seismic strain can be used to discriminate between tectonic and volcanic signals at Mt. Vesuvius.

  11. Anisotropic analysis for seismic sensitivity of groundwater monitoring wells

    Science.gov (United States)

    Pan, Y.; Hsu, K.

    2011-12-01

    Taiwan is located at the boundaries of Eurasian Plate and the Philippine Sea Plate. The movement of plate causes crustal uplift and lateral deformation to lead frequent earthquakes in the vicinity of Taiwan. The change of groundwater level trigged by earthquake has been observed and studied in Taiwan for many years. The change of groundwater may appear in oscillation and step changes. The former is caused by seismic waves. The latter is caused by the volumetric strain and reflects the strain status. Since the setting of groundwater monitoring well is easier and cheaper than the setting of strain gauge, the groundwater measurement may be used as a indication of stress. This research proposes the concept of seismic sensitivity of groundwater monitoring well and apply to DonHer station in Taiwan. Geostatistical method is used to analysis the anisotropy of seismic sensitivity. GIS is used to map the sensitive area of the existing groundwater monitoring well.

  12. Dynamics of subduction and continental collision: Influence of the nature of the plate contact. Geologica Ultraiectina (284)

    NARCIS (Netherlands)

    De Franco, R.

    2008-01-01

    At convergent plate boundaries, the properties of the actual plate contact are important for the overall dynamics. Convergent plate boundaries both mechanically decouple and link tectonic plates and accommodate large amounts of strain. We investigate two fundamental physical states of the subduction

  13. Cenozoic sedimentation in the Mumbai Offshore Basin: Implications for tectonic evolution of the western continental margin of India

    Science.gov (United States)

    Nair, Nisha; Pandey, Dhananjai K.

    2018-02-01

    Interpretation of multichannel seismic reflection data along the Mumbai Offshore Basin (MOB) revealed the tectonic processes that led to the development of sedimentary basins during Cenozoic evolution. Structural interpretation along three selected MCS profiles from MOB revealed seven major sedimentary sequences (∼3.0 s TWT, thick) and the associated complex fault patterns. These stratigraphic sequences are interpreted to host detritus of syn- to post rift events during rift-drift process. The acoustic basement appeared to be faulted with interspaced intrusive bodies. The sections also depicted the presence of slumping of sediments, subsidence, marginal basins, rollover anticlines, mud diapirs etc accompanied by normal to thrust faults related to recent tectonics. Presence of upthrusts in the slope region marks the locations of local compression during collision. Forward gravity modeling constrained with results from seismic and drill results, revealed that the crustal structure beneath the MOB has undergone an extensional type tectonics intruded with intrusive bodies. Results from the seismo-gravity modeling in association with litholog data from drilled wells from the western continental margin of India (WCMI) are presented here.

  14. The assessment of the transformation of global tectonic plate models and the global terrestrial reference frames using the Velocity Decomposition Analysis

    Science.gov (United States)

    Ampatzidis, Dimitrios; König, Rolf; Glaser, Susanne; Heinkelmann, Robert; Schuh, Harald; Flechtner, Frank; Nilsson, Tobias

    2016-04-01

    The aim of our study is to assess the classical Helmert similarity transformation using the Velocity Decomposition Analysis (VEDA). The VEDA is a new methodology, developed by GFZ for the assessment of the reference frames' temporal variation and it is based on the separation of the velocities into two specified parts: The first is related to the reference system choice (the so called datum effect) and the latter one which refers to the real deformation of the terrestrial points. The advantage of the VEDA is its ability to detect the relative biases and reference system effects between two different frames or two different realizations of the same frame, respectively. We apply the VEDA for the assessment between several modern tectonic plate models and the recent global terrestrial reference frames.

  15. The use of vertical and horizontal surface displacements at EPOS GNSS stations in Greenland to study ice sheet mass balance

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas

    2014-01-01

    The European Plate Observing System (EPOS) includes e.g. seismic and geodetic permanent national monitoring networks on a European scale. The main purpose is to create data platforms for monitoring and study geophysics processes like earthquakes, volcanoes, surface dynamics and tectonics. Here we...... present data from arctic GNSS stations included in the EPOS network. The arctic EPOS GNSS network consists of 16 continuous GPS stations spread across Greenland. This network is able to map the velocity fields associated with, plate motion, postglacial rebound and improve our understanding of tectonic...

  16. Earthquakes in Action: Incorporating Multimedia, Internet Resources, Large-scale Seismic Data, and 3-D Visualizations into Innovative Activities and Research Projects for Today's High School Students

    Science.gov (United States)

    Smith-Konter, B.; Jacobs, A.; Lawrence, K.; Kilb, D.

    2006-12-01

    The most effective means of communicating science to today's "high-tech" students is through the use of visually attractive and animated lessons, hands-on activities, and interactive Internet-based exercises. To address these needs, we have developed Earthquakes in Action, a summer high school enrichment course offered through the California State Summer School for Mathematics and Science (COSMOS) Program at the University of California, San Diego. The summer course consists of classroom lectures, lab experiments, and a final research project designed to foster geophysical innovations, technological inquiries, and effective scientific communication (http://topex.ucsd.edu/cosmos/earthquakes). Course content includes lessons on plate tectonics, seismic wave behavior, seismometer construction, fault characteristics, California seismicity, global seismic hazards, earthquake stress triggering, tsunami generation, and geodetic measurements of the Earth's crust. Students are introduced to these topics through lectures-made-fun using a range of multimedia, including computer animations, videos, and interactive 3-D visualizations. These lessons are further enforced through both hands-on lab experiments and computer-based exercises. Lab experiments included building hand-held seismometers, simulating the frictional behavior of faults using bricks and sandpaper, simulating tsunami generation in a mini-wave pool, and using the Internet to collect global earthquake data on a daily basis and map earthquake locations using a large classroom map. Students also use Internet resources like Google Earth and UNAVCO/EarthScope's Jules Verne Voyager Jr. interactive mapping tool to study Earth Science on a global scale. All computer-based exercises and experiments developed for Earthquakes in Action have been distributed to teachers participating in the 2006 Earthquake Education Workshop, hosted by the Visualization Center at Scripps Institution of Oceanography (http

  17. New aero-gravity results from the Arctic: Linking the latest Cretaceous-early Cenozoic plate kinematics of the North Atlantic and Arctic Ocean

    DEFF Research Database (Denmark)

    Døssing, Arne; Hopper, J.R.; Olesen, Arne Vestergaard

    2013-01-01

    The tectonic history of the Arctic Ocean remains poorly resolved and highly controversial. Details regarding break up of the Lomonosov Ridge from the Barents-Kara shelf margins and the establishment of seafloor spreading in the Cenozoic Eurasia Basin are unresolved. Significantly, the plate...... tectonic evolution of the Mesozoic Amerasia Basin is essentially unknown. The Arctic Ocean north of Greenland is at a critical juncture that formed at the locus of a Mesozoic three-plate setting between the Lomonosov Ridge, Greenland, and North America. In addition, the area is close to the European plate...... plateau against an important fault zone north of Greenland. Our results provide new constraints for Cretaceous-Cenozoic plate reconstructions of the Arctic. Key Points Presentation of the largest aero-gravity survey acquired over the Arctic Ocean Plate tectonic link between Atlantic and Arctic spreading...

  18. Satellite Gravity Transforms Unmask Tectonic Pattern of Arabian-African Region

    Science.gov (United States)

    Eppelbaum, Lev; Katz, Youri

    2017-04-01

    central parts of the Arabian and Somalian plates. Both these plates are countered by low-thickness lithospheric zones corresponding to the active rift zones. As it is indicated in the map, the thick lithospheric zones are associated with collisional zones at boundaries between the cratons and mobile belts. We suggest that the lowered values in the northern boundaries of the Arabian Plate correspond to subduction zones. The zones of lowered values in the middle of western part of the region correspond to the Neoproterozoic belt where ophiolitic and back-arc complexes with a thinned crust (e.g., Stern et al., 2004) are developed. Compiled satellite derived gravity field and a set of SGT were utilized for development of a novel tectono-geophysical zonation map of the Arabian-African region. Structurally- geodynamically this region is one of the key Earth's megastructures where are closely disposed remain elements of the Tethys Ocean crust (Ben-Avraham et al., 2002; Robertson, 2004), most ancient Early Permian reversly magnetized Kiama zone (Eppelbaum and Katz, 2012b; Eppelbaum et al., 2014), and the youngest modern oceanic crust of the Afar triangle developed among the continental lumps (Yirgu et al., 2006; Bastow et al., 2011). The tectonic zonation was carried out with application of three main principles of tectonic analysis: (1) classic basis of space-temporary reflection of structural complexes, (2) modern structural-geodynamic approach derived from the plate tectonic reconstructions where essential role plays analysis of rift, tectonic transform and collision forms of Earth's development, (3) revealing of intricate correlation between the mapped tectono-structural elements and lithospheric-mantle complexes delineated by using both conventional geophysical methods (seismic, seismological, thermal data, etc.) and comprehensive analysis of satellite derived gravity data. Compiled tectonic map of the region (00 - 35.60 north, and 300 - 570 east) indicates that Precambrian

  19. Gradual unlocking of plate boundary controlled initiation of the 2014 Iquique earthquake.

    Science.gov (United States)

    Schurr, Bernd; Asch, Günter; Hainzl, Sebastian; Bedford, Jonathan; Hoechner, Andreas; Palo, Mauro; Wang, Rongjiang; Moreno, Marcos; Bartsch, Mitja; Zhang, Yong; Oncken, Onno; Tilmann, Frederik; Dahm, Torsten; Victor, Pia; Barrientos, Sergio; Vilotte, Jean-Pierre

    2014-08-21

    On 1 April 2014, Northern Chile was struck by a magnitude 8.1 earthquake following a protracted series of foreshocks. The Integrated Plate Boundary Observatory Chile monitored the entire sequence of events, providing unprecedented resolution of the build-up to the main event and its rupture evolution. Here we show that the Iquique earthquake broke a central fraction of the so-called northern Chile seismic gap, the last major segment of the South American plate boundary that had not ruptured in the past century. Since July 2013 three seismic clusters, each lasting a few weeks, hit this part of the plate boundary with earthquakes of increasing peak magnitudes. Starting with the second cluster, geodetic observations show surface displacements that can be associated with slip on the plate interface. These seismic clusters and their slip transients occupied a part of the plate interface that was transitional between a fully locked and a creeping portion. Leading up to this earthquake, the b value of the foreshocks gradually decreased during the years before the earthquake, reversing its trend a few days before the Iquique earthquake. The mainshock finally nucleated at the northern end of the foreshock area, which skirted a locked patch, and ruptured mainly downdip towards higher locking. Peak slip was attained immediately downdip of the foreshock region and at the margin of the locked patch. We conclude that gradual weakening of the central part of the seismic gap accentuated by the foreshock activity in a zone of intermediate seismic coupling was instrumental in causing final failure, distinguishing the Iquique earthquake from most great earthquakes. Finally, only one-third of the gap was broken and the remaining locked segments now pose a significant, increased seismic hazard with the potential to host an earthquake with a magnitude of >8.5.

  20. Seismic sequences in the Sombrero Seismic Zone

    Science.gov (United States)

    Pulliam, J.; Huerfano, V. A.; ten Brink, U.; von Hillebrandt, C.

    2007-05-01

    The northeastern Caribbean, in the vicinity of Puerto Rico and the Virgin Islands, has a long and well-documented history of devastating earthquakes and tsunamis, including major events in 1670, 1787, 1867, 1916, 1918, and 1943. Recently, seismicity has been concentrated to the north and west of the British Virgin Islands, in the region referred to as the Sombrero Seismic Zone by the Puerto Rico Seismic Network (PRSN). In the combined seismicity catalog maintained by the PRSN, several hundred small to moderate magnitude events can be found in this region prior to 2006. However, beginning in 2006 and continuing to the present, the rate of seismicity in the Sombrero suddenly increased, and a new locus of activity developed to the east of the previous location. Accurate estimates of seismic hazard, and the tsunamigenic potential of seismic events, depend on an accurate and comprehensive understanding of how strain is being accommodated in this corner region. Are faults locked and accumulating strain for release in a major event? Or is strain being released via slip over a diffuse system of faults? A careful analysis of seismicity patterns in the Sombrero region has the potential to both identify faults and modes of failure, provided the aggregation scheme is tuned to properly identify related events. To this end, we experimented with a scheme to identify seismic sequences based on physical and temporal proximity, under the assumptions that (a) events occur on related fault systems as stress is refocused by immediately previous events and (b) such 'stress waves' die out with time, so that two events that occur on the same system within a relatively short time window can be said to have a similar 'trigger' in ways that two nearby events that occurred years apart cannot. Patterns that emerge from the identification, temporal sequence, and refined locations of such sequences of events carry information about stress accommodation that is obscured by large clouds of

  1. Reduction of uncertainties in probabilistic seismic hazard analysis

    Energy Technology Data Exchange (ETDEWEB)

    Seo, Jeong Moon; Choun, Young Sun; Choi, In Kil [Korea Atomic Energy Research Institute, Taejon (Korea)

    1999-02-01

    An integrated research for the reduction of conservatism and uncertainties in PSHA in Korea was performed. The research consisted of five technical task areas as follows; Task 1: Earthquake Catalog Development for PSHA. Task 2: Evaluation of Seismicity and Tectonics of the Korea Region. Task 3: Development of a Ground Motion Relationships. Task 4: Improvement of PSHA Modelling Methodology. Task 5: Development of Seismic Source Interpretations for the region of Korea for Inputs to PSHA. A series of tests on an ancient wooden house and an analysis on medium size earthquake in Korea were performed intensively. Signification improvement, especially in the estimation of historical earthquake, ground motion attenuation, and seismic source interpretations, were made through this study. 314 refs., 180 figs., 54 tabs. (Author)

  2. Segmentation of the eastern North Greenland oblique-shear margin – regional plate tectonic implications

    DEFF Research Database (Denmark)

    Andreasen, Arne Døssing; Stemmerik, Lars; Dahl-Jensen, T.

    2010-01-01

    a highly complex, Paleozoic–early Cenozoic pre-opening setting. However, due to extreme ice conditions, very little is known about the offshore areas seawards of – and between – the peninsulas. Consequently, prevailing structural-tectonic models of the margin tend to be significantly oversimplified...... anticipated. In particular, we interpret strong margin segmentation along N/NE-striking fault structures. The structures are likely to have formed by Late Mesozoic–early Cenozoic strike-slip tectonics and have continued to be active during the late Cenozoic. A more than 8 km deep sedimentary basin...

  3. Seismic investigation of the Kunlun Fault: Analysis of the INDEPTH IV 2-D active-source seismic dataset

    Science.gov (United States)

    Seelig, William George

    The Tibetan Plateau has experienced significant crustal thickening and deformation since the continental subduction and collision of the Asian and Indian plates in the Eocene. Deformation of the northern Tibetan Plateau is largely accommodated by strike-slip faulting. The Kunlun Fault is a 1000-km long strike-slip fault near the northern boundary of the Plateau that has experienced five magnitude 7.0 or greater earthquakes in the past 100 years and represents a major rheological boundary. Active-source, 2-D seismic reflection/refraction data, collected as part of project INDEPTH IV (International Deep Profiling of Tibet and the Himalaya, phase IV) in 2007, was used to examine the structure and the dip of the Kunlun fault. The INDEPTH IV data was acquired to better understand the tectonic evolution of the northeastern Tibetan Plateau, such as the far-field deformation associated with the continent-continent collision and the potential subduction of the Asian continent beneath northern Tibet. Seismic reflection common depth point (CDP) stacks were examined to look for reflectivity patterns that may be associated with faulting. A possible reflection from the buried North Kunlun Thrust (NKT) is identified at 18-21 km underneath the East Kunlun Mountains, with an estimated apparent dip of 15°S and thrusting to the north. Minimally-processed shot gathers were also inspected for reflections off near-vertical structures such as faults and information on first-order velocity structure. Shot offset and nearest receiver number to reflection was catalogued to increase confidence of picks. Reflections off the North Kunlun (NKF) and South Kunlun Faults (SKF) were identified and analyzed for apparent dip and subsurface geometry. Fault reflection analysis found that the North Kunlun Fault had an apparent dip of approximately 68ºS to an estimated depth of 5 km, while the South Kunlun Fault dipped at approximately 78ºN to an estimated 3.5 km depth. Constraints on apparent dip and

  4. Evaluation of seismic characteristics and structural integrity for the cabinet of HANARO seismic monitoring analysis system

    Energy Technology Data Exchange (ETDEWEB)

    Ryu, Jeong Soo; Yoon, Doo Byung

    2003-06-01

    The HANARO SMAS(Seismic Monitoring Analysis System) is classified as Non-Nuclear Safety(NNS), seismic category I, and quality class T. It is required that this system can perform required functions, which are to preserve its structural integrity during and after an OBE or SSE. In this work, the structural integrity and seismic characteristics of the cabinet of the newly developed SMAS have been estimated. The most parts of the cabinet are identically designed with those of Yonggwhang and Gori Nuclear Power Plants(NPPs), unit 1 that successfully completed the required seismic qualification tests. The structure of the cabinet of the SMAS is manufactured by the manufacturer of the cabinet of Yonggwhang and Gori NPPs. To evaluate the seismic characteristics of the SMAS, the RRS(Required Response Spectra) of the newly developed cabinet are compared with those of Yonggwhang and Gori NPPs, unit 1. In addition, natural frequencies of the cabinet of HANARO, Yonggwhang, and Gori NPPs were measured for the comparison of the seismic characteristics of the installed cabinets. In case of HANARO, the bottom of the cabinet is welded to the base plate. The base plate is fixed to the concrete foundation by using anchor bolts. For the evaluation of the structural integrity of the welding parts and the anchor bolts, the maximum stresses and forces of the welding parts and the anchor bolts due to seismic loading are estimated. The analysis results show that maximum stresses and forces are less than the allowable limits. This new SMAS is operating at HANARO instrument room to acquire and analyze the signal of earthquake.

  5. Seismological and structural constraints on the 2011-2013, Mmax 4.6 seismic sequence at the south-eastern edge of the Calabrian arc (North-eastern Sicily, Italy)

    Science.gov (United States)

    Cammarata, Laura; Catalano, Stefano; Gambino, Salvatore; Palano, Mimmo; Pavano, Francesco; Romagnoli, Gino; Scaltrito, Antonio; Tortorici, Giuseppe

    2018-01-01

    Between June 2011 and September 2013, the Nebrodi Mountains region was affected by a seismic swarm consisting of > 2700 events with local magnitude 1.3 ≤ ML ≤ 4.6 and located in the 5-9 km depth interval. The seismic swarm defines a seismogenetic volume elongated along the E-W direction and encompasses the NW-SE-oriented tectonic boundary between the Calabrian arc (north-eastward) and the Sicilide units (south-westward). By exploring the recent tectonic deformation and the seismic behavior of the region, this study aims at providing additional constraints on the seismogenetic faults at the southern termination of the Calabrian arc. Waveform similarities analysis allowed observing that 45% of the whole dataset can be grouped into six different families of seismic events. Earthquake multiplet families are mainly located in the eastern part of the seismogenetic volume. We suggest that such a feature is responsive to the lateral lithological variations as highlighted by geology (at the surface) and P-wave seismic tomography (at depth of 10 km). Stress tensor inversions performed on FPSs indicate that the investigated region is currently subject to a nearly biaxial stress state in an extensional regime, such that crustal stretching occurs along both NW-SE and NE-SW directions. Accordingly, mesoscale fault geometries and kinematics analyses evidence that a younger normal faulting stress regime led to a tectonic negative inversion by replacing the pre-existing strike-slip one. Based on our results and findings reported in recent literature, we refer such a crustal stretching to mantle upwelling process (as evidenced by diffuse mantle-derived gas emissions) coupled with a tectonic uplift involving north-eastern Sicily since Middle Pleistocene. Moreover, seismic swarms striking the region would be related to the migration of mantle and sub-crustal fluids toward the surface along the complex network of tectonic structures cutting the crust and acting as pathways.

  6. Weak Tectono-Magmatic Relationships along an Obliquely Convergent Plate Boundary: Sumatra, Indonesia

    Directory of Open Access Journals (Sweden)

    Valerio Acocella

    2018-02-01

    Full Text Available The tectono-magmatic relationships along obliquely convergent plate boundaries, where strain partitioning promotes strike-slip structures along the volcanic arc, are poorly known. Here it is unclear if and, in case, how the strike-slip structures control volcanic processes, distribution and size. To better define the possible tectono-magmatic relationships along strike-slip arcs, we merge available information on the case study of Sumatra (Indonesia with field structural data. The Sumatra arc (entire volcanic belt consists of 48 active volcanoes. Of these, 46% lie within 10 km from the dextral Great Sumatra Fault (GSF, which carries most horizontal displacement on the overriding plate, whereas 27% lie at >20 km from the GSF. Among the volcanoes at <10 km from GSF, 48% show a possible structural relation to the GSF, whereas only 28% show a clear structural relation, lying in pull-aparts or releasing bends; these localized areas of transtension (local extensional zone do not develop magmatic segments. There is no relation between the GSF along-strike slip rate variations and the volcanic productivity. The preferred N30°-N40°E volcano alignment and elongation are subparallel to the convergence vector or to the GSF. The structural field data, collected in the central and southern GSF, show, in addition to the dextral motions along NW-SE to N-S striking faults, also normal motions (extending WNW-ESE or NE-SW, suggesting local reactivations of the GSF. Overall, the collected data suggest a limited tectonic control on arc volcanism. The tectonic control is mostly expressed by the mean depth of the slab surface below the volcanoes (130 ± 20 km and, subordinately, local extension along the GSF. The latter, when WNW-ESE oriented (more common, may be associated with the overall tectonic convergence, as suggested by the structural data; conversely, when NE-SW oriented (less common, the extension may result from co- and post-seismic arc normal extension

  7. Seismic-fragility tests of new and accelerated-aged Class 1E battery cells

    International Nuclear Information System (INIS)

    Bonzon, L.L.; Janis, W.J.; Black, D.A.; Paulsen, G.A.

    1987-01-01

    The seismic-fragility response of naturally-aged nuclear station safety-related batteries is of interest for two reasons: (1) to determine actual failure modes and thresholds and (2) to determine the validity of using the electrical capacity of individual cells as an indicator of the potential survivability of a battery given a seismic event. Prior reports in this series discussed the seismic-fragility tests and results for three specific naturally-aged cell types: 12-year old NCX-2250, 10-year old LCU-13, and 10-year old FHC-19. This report focuses on the complementary approach, namely, the seismic-fragility response of accelerated-aged batteries. Of particular interest is the degree to which such approaches accurately reproduce the actual failure modes and thresholds. In these tests the significant aging effects observed, in terms of seismic survivability, were: embrittlement of cell cases, positive bus material and positive plate grids; and excessive sulphation of positive plate active material causing hardening and expansion of positive plates. The IEEE Standard 535 accelerated aging method successfully reproduced seismically significant aging effects in new cells but accelerated grid embrittlement an estimated five years beyond the conditional age of other components

  8. Holocene compression in the Acequión valley (Andes Precordillera, San Juan province, Argentina): Geomorphic, tectonic, and paleoseismic evidence

    Science.gov (United States)

    Audemard, M.; Franck, A.; Perucca, L.; Laura, P.; Pantano, Ana; Avila, Carlos R.; Onorato, M. Romina; Vargas, Horacio N.; Alvarado, Patricia; Viete, Hewart

    2016-04-01

    The Matagusanos-Maradona-Acequión Valley sits within the Andes Precordillera fold-thrust belt of western Argentina. It is an elongated topographic depression bounded by the roughly N-S trending Precordillera Central and Oriental in the San Juan Province. Moreover, it is not a piggy-back basin as we could have expected between two ranges belonging to a fold-thrust belt, but a very active tectonic corridor coinciding with a thick-skinned triangular zone, squeezed between two different tectonic domains. The two domains converge, where the Precordillera Oriental has been incorporated to the Sierras Pampeanas province, becoming the western leading edge of the west-verging broken foreland Sierras Pampeanas domain. This latter province has been in turn incorporated into the active deformation framework of the Andes back-arc at these latitudes as a result of enhanced coupling between the converging plates due to the subduction of the Juan Fernández ridge that flattens the Nazca slab under the South American continent. This study focuses on the neotectonics of the southern tip of this N-S elongated depression, known as Acequión (from the homonym river that crosses the area), between the Del Agua and Los Pozos rivers. This depression dies out against the transversely oriented Precordillera Sur, which exhibits a similar tectonic style as Precordillera Occidental and Central (east-verging fold-thrust belt). This contribution brings supporting evidence of the ongoing deformation during the Late Pleistocene and Holocene of the triangular zone bounded between the two leading and converging edges of Precordillera Central and Oriental thrust fronts, recorded in a multi-episodic lake sequence of the Acequión and Nikes rivers. The herein gathered evidence comprise Late Pleistocene-Holocene landforms of active thrusting, fault kinematics (micro-tectonic) data and outcrop-scale (meso-tectonic) faulting and folding of recent lake and alluvial sequences. In addition, seismically

  9. Feasibility study on development of plate-type heat exchanger for BWR plants

    International Nuclear Information System (INIS)

    Ohyama, Nobuhiro; Suda, Kenichi; Ogata, Hiroshi; Matsuda, Shinichi; Nagasaka, Kazuhiro; Fujii, Toshi; Nozawa, Toshiya; Ishihama, Kiyoshi; Higuchi, Tomokazu

    2004-01-01

    In order to apply plate-type heat exchanger to RCW, TCW and FPC system in BWR plants, heat test and seismic test of RCW system heat exchanger sample were carried out. The results of these tests showed new design plate-type heat exchanger satisfied the fixed pressure resistance and seismic resistance and keep the function. The evaluation method of seismic design was constructed and confirmed by the results of tests. As anti-adhesion measure of marine organism, an ozone-water circulation method, chemical-feed method and combination of circulation of hot water and air bubbling are useful in place of the chlorine feeding method. Application of the plate-type heat exchanger to BWR plant is confirmed by these investigations. The basic principles, structure, characteristics, application limit and reliability are stated. (S.Y.)

  10. Recognized Multiple Rifts of the Neoproterozoic in the Initiation of the Tarim Craton (NW China) and Their Tectonic Implications

    Science.gov (United States)

    He, B.; Jiao, C.; Huang, T.; Zhou, X.; Cai, Z.; Cao, Z.; Jiang, Z.; Cui, J.; Yu, Z.; Chen, W.

    2017-12-01

    The Tarim Basin is the largest, oil-bearing and superimposed basin in the northwest of China. The development and tectonic property of the initial Tarim basin have been acutely disputed and remain enigmatic. Urgently need to reveal the origin and formation dynamics of the Tarim Carton and evaluate the potential of the deep energy resources. However, covered by vast desert and huge-thickness sedimentary strata, suffered by multiple tectonic movements, seismic data with low signal- to- noise ratio in the deep are the critical difficulties. We analyse 4 field outcrops, 18 wells, 27 reprocessed seismic reflection profiles with high SNR across the basin and many ancillary ones and aeromagnetic data. We find about 20 normal fault-controlled rift depressions of the Cryogenian and Ediacaran scattered in the Tarim basin, which developed on the Precambrian metamorphic and crystalline basements and covered by the epeiric sea and basin facies sediments of the Lower Cambrian. The structural styles of the rifts are mainly half grabens, symmetrical troughs and horst-grabens. The regional differences exist obviously in spatial and temporal. The WNW-ESE-trending faults occur in the central part and northern of the basin and the NE, and the NEE-trending faults occur in the southern parts, which response with the anomaly of aeromagnetic. Some main faults of the Ediacaran inherited from the Cryogenian and some occurred newly, the more rifting depressions occurred during the Ediacaran. The extensional NNW-SSE-oriented and NNE-SSW-oriented paleostress field occurred simultaneously during rifting, and accompanied with the clockwise shearing. According to the activities of syn-sedimentary faults, magmatic events and sediments, the tectonic properties of the rifts are different depending on their locations in the Tarim craton. The rifting phases mainly occurred from 780 Ma to 615 Ma. The formation of rifts were associated with the opening of the South Tianshan Ocean and the South Altun

  11. Microzonation of Seismic Hazard Potential in Taipei, Taiwan

    Science.gov (United States)

    Liu, K. S.; Lin, Y. P.

    2017-12-01

    The island of Taiwan lies at the boundary between the Philippine Sea plate and the Eurasia plate. Accordingly, the majority of seismic energy release near Taiwan originates from the two subduction zones. It is therefore not surprising that Taiwan has repeatedly been struck by large earthquakes such as 1986 Hualien earthquake, 1999 Chi Chi and 2002 Hualien earthquake. Microzonation of seismic hazard potential becomes necessary in Taipei City for the Central Geological Survey announced the Sanchiao active fault as Category II. In this study, a catalog of more than 2000 shallow earthquakes occurred from 1900 to 2015 with Mw magnitudes ranging from 5.0 to 8.2, and 11 disastrous earthquakes occurred from 1683-1899, as well as Sanchiao active fault in the vicinity are used to estimate the seismic hazard potential in Taipei City for seismic microzonation. Furthermore, the probabilities of seismic intensity exceeding CWB intensity 5, 6, 7 and MMI VI, VII, VIII in 10, 30, and 50-year periods in the above areas are also analyzed for the seismic microzonation. Finally, by comparing with the seismic zoning map of Taiwan in current building code that was revised after 921 earthquakes, Results of this study will show which areas with higher earthquake hazard potential in Taipei City. They provide a valuable database for the seismic design of critical facilities. It will help mitigate Taipei City earthquake disaster loss in the future, as well as provide critical information for emergency response plans.

  12. Geometry and structure of the pull-apart basins developed along the western South American-Scotia plate boundary (SW Atlantic Ocean)

    Science.gov (United States)

    Esteban, F. D.; Tassone, A.; Isola, J. I.; Lodolo, E.; Menichetti, M.

    2018-04-01

    The South American-Scotia plate boundary is a left-lateral fault system which runs roughly E-W for more than 3000 km across the SW Atlantic Ocean and the Tierra del Fuego Island, reaching to the west the southern Chile Trench. Analyses of a large dataset of single- and multi-channel seismic reflection profiles acquired offshore has allowed to map the trace of the plate boundary from Tierra del Fuego to the Malvinas Trough, a tectonic depression located in the eastern part of the fault system, and to reconstruct the shape and geometry of the basins formed along the principal displacement zone of the fault system. Three main Neogene pull-apart basins that range from 70 to 100 km in length, and from 12 to 22 km in width, have been identified along this segment of the plate boundary. These basins have elongated shapes with their major axes parallel to the ENE-WSW direction of the fault zone. The sedimentary architecture and the infill geometry of the basins suggest that they represent mostly strike-slip dominated transtension basins which propagated from E to W. The basins imaged by seismic data show in some cases geometrical and structural features linked to the possible reactivation of previous wedge-top basins and inherited structures pertaining to the external front of the Magallanes fold-and-thrust compression belt, along which the South American-Scotia fault system has been superimposed. It is suggested that the sequence of the elongated basins occur symmetrically to a thorough going strike-slip fault, in a left-stepping geometrical arrangement, in a manner similar to those basins seen in other transcurrent environments.

  13. Crustal structure and regional tectonics of SE Sweden and the Baltic Sea

    Energy Technology Data Exchange (ETDEWEB)

    Milnes, A.G. [Bergen Univ. (Norway). Dept. of Geology; Gee, D.G.; Lund, C.E. [Uppsala Univ. (Sweden). Dept. of Earth Sciences

    1998-11-01

    In this desk study, the available geophysical and geological data on the crustal structure and regional tectonics of the wider surroundings of the Aespoe site (SE Sweden and adjacent parts of the Baltic Sea) are compiled and assessed. The aim is to contribute to the knowledge base for long-term rock mechanical modeling, using the Aespoe site as a proxy for a high-level radioactive waste repository site in Swedish bedrock. The geophysical data reviewed includes two new refraction/wide-angle reflection seismic experiments carried out within the EUROBRIDGE project, in addition to the numerous earlier refraction seismic profiles. The BABEL normal-incidence deep seismic profile is also considered. New geological data, presented at EUROBRIDGE workshops, and in recent SGU publications, are reviewed for the same area. In combination with the seismic data, these provide a base for interpreting the present composition and structure, and the Palaeoproterozoic-Mesoproterozoic evolution, of the crustal segment within which the Aespoe site lies - the Smaaland mega-block. This is characterized by having undergone little regionally significant deformation or magmatism since Neoproterozoic times (the last 1000 million years). It is shown that, at this scale of observation (of the order of 100 km), the long-term rheology of the lithosphere can be argued from a relatively tight observational network, when combined with the results of earlier SKB studies (seismo-tectonics, uplift patterns, state of stress, heat flow) and published research. Although many uncertainties exist, the present state of knowledge would suffice for first exploratory calculations and sensitivity studies of long-term, large-scale rock mechanics 101 refs, 22 figs

  14. Three-dimensional dynamic laboratory models of subduction with an overriding plate and variable interplate rheology

    NARCIS (Netherlands)

    Duarte, João C.; Schellart, Wouter P.; Cruden, Alexander R.

    2013-01-01

    Subduction zones are complex 3-D features in which one tectonic plate sinks underneath another into the deep mantle. During subduction the overriding plate (OP) remains in physical contact with the subducting plate and stresses generated at the subduction zone interface and by mantle flowforce the

  15. Marginal inherited structures impact on the oblique convergent N American Plate/ Central Caribbean plate-boundary in the Northern Caribbean. The tectonic evolution since Miocene times based on Haiti data acquired onshore and offshore since 2012- a step toward an ADP Drilling Proposal (Haiti-DRILL).

    Science.gov (United States)

    Ellouz, N.; Hamon, Y.; Deschamps, R.; Battani, A.; Wessels, R.; Boisson, D.; Prepetit, C.; Momplaisir, R.

    2017-12-01

    Since Early Paleogene times, the North Caribbean plate is colliding obliquely with the south continental part of the old N. American Margins, which is represented by various segments from West to East, inherited from Jurassic times. Location, amount of displacement, rotation and the structural deformation of these margin segments, resulting from the dislocation of the continental N American margin, are not clearly yet established. At present, the plate limits are marked either by two left lateral faults west and inside Haiti (OSF in the North and EPGF in the South), oblique collision front (further west in Cuba), oblique subducted segments (to the East, Porto-Rico). From our recent works operated both offshore (Haiti-SIS and Haiti-BGF surveys 2012-2015) and onshore (field campaigns 2013-2017) in Haitian zone, the position of the present-day and paleo major limits have been redefined. These paleolimits have been reconstructed up to early Miocene times, based on: restoration of regional structural cross-sections, sedimentology and on paleoenvironement studies. In a preliminary way, we analyzed the complexity of the tectonic heritage with possible nature, heterogeneity of the crustal fragments and associated margins close to Haiti (age, structure, environment, location of the dislocated blocks through times) which profoundly impact the partitioning of the deformation along this complex transformed margin. The change in the structure wavelength, decollement level variations are primary constraints in the restoration of the main units and do impose a deep connection along specific segments either related to strike-slip or to splay faults. The asymmetry on the repartition of the fault activity tend to prove that the past motion related to "EPGF transfer zone" is mainly partitioned in Haiti to the North of the present-day EPGF position. At present, these results are still coherent with the distribution of the aftershoks registered after 2010, and with the present

  16. Imaging paleoslabs in the D″ layer beneath Central America and the Caribbean using seismic waveform inversion.

    Science.gov (United States)

    Borgeaud, Anselme F E; Kawai, Kenji; Konishi, Kensuke; Geller, Robert J

    2017-11-01

    D″ (Dee double prime), the lowermost layer of the Earth's mantle, is the thermal boundary layer (TBL) of mantle convection immediately above the Earth's liquid outer core. As the origin of upwelling of hot material and the destination of paleoslabs (downwelling cold slab remnants), D″ plays a major role in the Earth's evolution. D″ beneath Central America and the Caribbean is of particular geodynamical interest, because the paleo- and present Pacific plates have been subducting beneath the western margin of Pangaea since ~250 million years ago, which implies that paleoslabs could have reached the lowermost mantle. We conduct waveform inversion using a data set of ~7700 transverse component records to infer the detailed three-dimensional S-velocity structure in the lowermost 400 km of the mantle in the study region so that we can investigate how cold paleoslabs interact with the hot TBL above the core-mantle boundary (CMB). We can obtain high-resolution images because the lowermost mantle here is densely sampled by seismic waves due to the full deployment of the USArray broadband seismic stations during 2004-2015. We find two distinct strong high-velocity anomalies, which we interpret as paleoslabs, just above the CMB beneath Central America and Venezuela, respectively, surrounded by low-velocity regions. Strong low-velocity anomalies concentrated in the lowermost 100 km of the mantle suggest the existence of chemically distinct denser material connected to low-velocity anomalies in the lower mantle inferred by previous studies, suggesting that plate tectonics on the Earth's surface might control the modality of convection in the lower mantle.

  17. Evaluation of the deformation parameters of the northern part of Eg

    Directory of Open Access Journals (Sweden)

    Abdel-Monem S. Mohamed

    2016-06-01

    Full Text Available The northern part of Egypt is a rapidly growing development accompanied by the increased levels of standard living particularly in its urban areas. From tectonic and seismic point of views, the northern part of Egypt is one of the interested regions. It shows an active geologic structure attributed to the tectonic movements of the African and Eurasian plates from one side and the Arabian plate from the other side. From historical point of view and recent instrumental records, the northern part of Egypt is one of the seismo-active regions in Egypt. The investigations of the seismic events and their interpretations had led to evaluate the seismic hazard for disaster mitigation, for the safety of the densely populated regions and the vital projects. In addition to the monitoring of the seismic events, the most powerful technique of Global Navigation Satellite System (GNSS will be used in determining crustal deformation where a geodetic network covers the northern part of Egypt. Joining the GPS Permanent stations of the northern part of Egypt with the Southern part of Europe will give a clear picture about the recent crustal deformation and the African plate velocity. The results from the data sets are compared and combined in order to determine the main characteristics of the deformation and hazard estimation for specified regions. Final compiled output from the seismological and geodetic analysis will throw lights upon the geodynamical regime of these seismo-active regions. This work will throw lights upon the geodynamical regime and to delineate the crustal stress and strain fields in the study region. This also enables to evaluate the active tectonics and surface deformation with their directions from repeated geodetic observations. The results show that the area under study suffers from continuous seismic activity related to the crustal movements taken place along trends of major faults

  18. Evaluation of the deformation parameters of the northern part of Eg

    Science.gov (United States)

    Mohamed, Abdel-Monem S.; Radwan, Ali M.; Sharf, Mohamed; Hamimi, Zakaria; Hegazy, Esraa E.; Abou Aly, Nadia; Gomaa, Mahmoud

    2016-06-01

    The northern part of Egypt is a rapidly growing development accompanied by the increased levels of standard living particularly in its urban areas. From tectonic and seismic point of views, the northern part of Egypt is one of the interested regions. It shows an active geologic structure attributed to the tectonic movements of the African and Eurasian plates from one side and the Arabian plate from the other side. From historical point of view and recent instrumental records, the northern part of Egypt is one of the seismo-active regions in Egypt. The investigations of the seismic events and their interpretations had led to evaluate the seismic hazard for disaster mitigation, for the safety of the densely populated regions and the vital projects. In addition to the monitoring of the seismic events, the most powerful technique of Global Navigation Satellite System (GNSS) will be used in determining crustal deformation where a geodetic network covers the northern part of Egypt. Joining the GPS Permanent stations of the northern part of Egypt with the Southern part of Europe will give a clear picture about the recent crustal deformation and the African plate velocity. The results from the data sets are compared and combined in order to determine the main characteristics of the deformation and hazard estimation for specified regions. Final compiled output from the seismological and geodetic analysis will throw lights upon the geodynamical regime of these seismo-active regions. This work will throw lights upon the geodynamical regime and to delineate the crustal stress and strain fields in the study region. This also enables to evaluate the active tectonics and surface deformation with their directions from repeated geodetic observations. The results show that the area under study suffers from continuous seismic activity related to the crustal movements taken place along trends of major faults

  19. Ball-and-socket tectonic rotation during the 2013 Mw7.7 Balochistan earthquake

    Science.gov (United States)

    Barnhart, William D.; Hayes, Gavin P.; Briggs, Richard W.; Gold, Ryan D.; Bilham, R.

    2014-01-01

    The September 2013 Mw7.7 Balochistan earthquake ruptured a ∼200-km-long segment of the curved Hoshab fault in southern Pakistan with 10±0.2 m of peak sinistral and ∼1.7±0.8 m of dip slip. This rupture is unusual because the fault dips 60±15° towards the focus of a small circle centered in northwest Pakistan, and, despite a 30° increase in obliquity along strike, the ratios of strike and dip slip remain relatively uniform. Surface displacements and geodetic and teleseismic source inversions quantify a bilateral rupture that propagated rapidly at shallow depths from a transtensional jog near the northern end of the rupture. Static friction prior to rupture was unusually weak (μstructural unit in southeast Makran that rotates – akin to a 2-D ball-and-socket joint – counter-clockwise in response to India's penetration into the Eurasian plate. This rotation accounts for complexity in the Chaman fault system and, in principle, reduces seismic potential near Karachi; nonetheless, these findings highlight deficiencies in strong ground motion equations and tectonic models that invoke Anderson–Byerlee faulting predictions.

  20. Estimating Fault Friction From Seismic Signals in the Laboratory

    Science.gov (United States)

    Rouet-Leduc, Bertrand; Hulbert, Claudia; Bolton, David C.; Ren, Christopher X.; Riviere, Jacques; Marone, Chris; Guyer, Robert A.; Johnson, Paul A.

    2018-02-01

    Nearly all aspects of earthquake rupture are controlled by the friction along the fault that progressively increases with tectonic forcing but in general cannot be directly measured. We show that fault friction can be determined at any time, from the continuous seismic signal. In a classic laboratory experiment of repeating earthquakes, we find that the seismic signal follows a specific pattern with respect to fault friction, allowing us to determine the fault's position within its failure cycle. Using machine learning, we show that instantaneous statistical characteristics of the seismic signal are a fingerprint of the fault zone shear stress and frictional state. Further analysis of this fingerprint leads to a simple equation of state quantitatively relating the seismic signal power and the friction on the fault. These results show that fault zone frictional characteristics and the state of stress in the surroundings of the fault can be inferred from seismic waves, at least in the laboratory.