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Sample records for upper crustal section

  1. The Upper- to Middle-Crustal Section of the Alisitos Oceanic Arc, (Baja, Mexico): an Analog of the Izu-Bonin-Marianas (IBM) Arc

    Science.gov (United States)

    Medynski, S.; Busby, C.; DeBari, S. M.; Morris, R.; Andrews, G. D.; Brown, S. R.; Schmitt, A. K.

    2016-12-01

    The Rosario segment of the Cretaceous Alisitos arc in Baja California is an outstanding field analog for the Izu-Bonin-Mariana (IBM) arc, because it is structurally intact, unmetamorphosed, and has superior three-dimensional exposures of an upper- to middle-crustal section through an extensional oceanic arc. Previous work1, done in the pre-digital era, used geologic mapping to define two phases of arc evolution, with normal faulting in both phases: (1) extensional oceanic arc, with silicic calderas, and (2) oceanic arc rifting, with widespread diking and dominantly mafic effusions. Our new geochemical data match the extensional zone immediately behind the Izu arc front, and is different from the arc front and rear arc, consistent with geologic relations. Our study is developing a 3D oceanic arc crustal model, with geologic maps draped on Google Earth images, and GPS-located outcrop information linked to new geochemical, geochronological and petrographic data, with the goal of detailing the relationships between plutonic, hypabyssal, and volcanic rocks. This model will be used by scientists as a reference model for past (IBM-1, 2, 3) and proposed IBM (IBM-4) drilling activities. New single-crystal zircon analysis by TIMS supports the interpretation, based on batch SIMS analysis of chemically-abraded zircon1, that the entire upper-middle crustal section accumulated in about 1.5 Myr. Like the IBM, volcanic zircons are very sparse, but zircon chemistry on the plutonic rocks shows trace element compositions that overlap to those measured in IBM volcanic zircons by A. Schmitt (unpublished data). Zircons have U-Pb ages up to 20 Myr older than the eruptive age, suggesting remelting of older parts of the arc, similar to that proposed for IBM (using different evidence). Like IBM, some very old zircons are also present, indicating the presence of old crustal fragments, or sediments derived from them, in the basement. However, our geochemical data show that the magmas are

  2. Enriched and depleted characters of the Amnay Ophiolite upper crustal section and the regionally heterogeneous nature of the South China Sea mantle

    Science.gov (United States)

    Perez, Americus d. C.; Faustino-Eslava, Decibel V.; Yumul, Graciano P.; Dimalanta, Carla B.; Tamayo, Rodolfo A.; Yang, Tsanyao Frank; Zhou, Mei-Fu

    2013-03-01

    The volcanic section of the Middle Oligocene Amnay Ophiolite in Mindoro, Philippines has previously been shown to be of normalmid-oceanic ridge basalt (NMORB) composition. Here we report for the first time an enriched mantle component that is additionally recorded in this crustal section. New whole rock major and trace element data are presented for nine mafic volcanic rocks from a section of the ophiolite that has not been previously examined. These moderately evolved tholeiitic basalts were found to have resulted from the bulk mixing of ˜10% ocean island basalt components with depleted mantle. Drawing together various geochemical characteristics reported for different rock suites taken as representatives of the South China Sea crust, including the enriched MORB (EMORB) and NMORB of the East Taiwan Ophiolite, the NMORB from previous studies of the Amnay Ophiolite and the younger ocean floor eruptives of the Scarborough Seamount-Reed Bank region, a veined mantle model is proposed for the South China Sea mantle. The NMORB magmatic products are suggested to have been derived from the more depleted portions of the mantle whereas the ocean island basalt (OIB) and EMORB-type materials from the mixing of depleted and veined/enriched mantle regions.

  3. Upper mantle and crustal structure of the East Greenland Caledonides

    DEFF Research Database (Denmark)

    Schiffer, Christian; Balling, N.; Jacobsen, B. H.

    The East Greenland and Scandinavian Caledonides once formed a major coherent mountain range, as a consequence of the collision of the continents of Laurentia and Baltica. The crustal and upper mantle structure was furthermore influenced by several geodynamic processes leading to the formation of ...

  4. Density heterogeneity of the upper mantle beneath Siberia from satellite gravity and a new regional crustal model

    DEFF Research Database (Denmark)

    Herceg, Matija; Thybo, Hans; Artemieva, Irina

    2013-01-01

    We present a new regional model for the density structure of the upper mantle below Siberia. The residual mantle gravity anomalies are based on gravity data derived from the GOCE gravity gradients and geopotential models, with crustal correction to the gravity field being calculated from a new...... on regional and global crustal models. We analyze how uncertainties and errors in the crustal model propagate from crustal densities to mantle residual gravity anomalies and the density model of the upper mantle. The new regional density model for the Siberian craton and the West Siberian Basin complements...... regional crustal model. This newly compiled database on the crustal seismic structure, complemented by additional constraints from petrological analysis of near-surface rocks and lower crustal xenoliths, allows for a high-resolution correction of the crustal effects as compared to previous studies based...

  5. Developing a Crustal and Upper Mantle Velocity Model for the Brazilian Northeast

    Science.gov (United States)

    Julia, J.; Nascimento, R.

    2013-05-01

    Development of 3D models for the earth's crust and upper mantle is important for accurately predicting travel times for regional phases and to improve seismic event location. The Brazilian Northeast is a tectonically active area within stable South America and displays one of the highest levels of seismicity in Brazil, with earthquake swarms containing events up to mb 5.2. Since 2011, seismic activity is routinely monitored through the Rede Sismográfica do Nordeste (RSisNE), a permanent network supported by the national oil company PETROBRAS and consisting of 15 broadband stations with an average spacing of ~200 km. Accurate event locations are required to correctly characterize and identify seismogenic areas in the region and assess seismic hazard. Yet, no 3D model of crustal thickness and crustal and upper mantle velocity variation exists. The first step in developing such models is to refine crustal thickness and depths to major seismic velocity boundaries in the crust and improve on seismic velocity estimates for the upper mantle and crustal layers. We present recent results in crustal and uppermost mantle structure in NE Brazil that will contribute to the development of a 3D model of velocity variation. Our approach has consisted of: (i) computing receiver functions to obtain point estimates of crustal thickness and Vp/Vs ratio and (ii) jointly inverting receiver functions and surface-wave dispersion velocities from an independent tomography study to obtain S-velocity profiles at each station. This approach has been used at all the broadband stations of the monitoring network plus 15 temporary, short-period stations that reduced the inter-station spacing to ~100 km. We expect our contributions will provide the basis to produce full 3D velocity models for the Brazilian Northeast and help determine accurate locations for seismic events in the region.

  6. Crustal and upper mantle velocity structure of the Salton Trough, southeast California

    Science.gov (United States)

    Parsons, T.; McCarthy, J.

    1996-01-01

    This paper presents data and modelling results from a crustal and upper mantle wide-angle seismic transect across the Salton Trough region in southeast California. The Salton Trough is a unique part of the Basin and Range province where mid-ocean ridge/transform spreading in the Gulf of California has evolved northward into the continent. In 1992, the U.S. Geological Survey (USGS) conducted the final leg of the Pacific to Arizona Crustal Experiment (PACE). Two perpendicular models of the crust and upper mantle were fit to wide-angle reflection and refraction travel times, seismic amplitudes, and Bouguer gravity anomalies. The first profile crossed the Salton Trough from the southwest to the northeast, and the second was a strike line that paralleled the Salton Sea along its western edge. We found thin crust (???21-22 km thick) beneath the axis of the Salton Trough (Imperial Valley) and locally thicker crust (???27 km) beneath the Chocolate Mountains to the northeast. We modelled a slight thinning of the crust further to the northeast beneath the Colorado River (???24 km) and subsequent thickening beneath the metamorphic core complex belt northeast of the Colorado River. There is a deep, apparently young basin (???5-6 km unmetamorphosed sediments) beneath the Imperial Valley and a shallower (???2-3 km) basin beneath the Colorado River. A regional 6.9-km/s layer (between ???15-km depth and the Moho) underlies the Salton Trough as well as the Chocolate Mountains where it pinches out at the Moho. This lower crustal layer is spatially associated with a low-velocity (7.6-7.7 km/s) upper mantle. We found that our crustal model is locally compatible with the previously suggested notion that the crust of the Salton Trough has formed almost entirely from magmatism in the lower crust and sedimentation in the upper crust. However, we observe an apparently magmatically emplaced lower crust to the northeast, outside of the Salton Trough, and propose that this layer in part

  7. a Baseline for Upper Crustal Velocity Variations Along the East Pacific Rise

    Science.gov (United States)

    Kappus, Mary Elizabeth

    Seismic measurements of the oceanic crust and theoretical models of its generation at mid-ocean ridges suggest several systematic variations in upper crustal velocity structure, but without constraints on the inherent variation in newly-formed crust these suggestions remain tentative. The Wide Aperture Profiles (WAPs) which form the database for this study have sufficient horizontal extent and resolution in the upper crust to establish a zero-age baseline. After assessing the adequacy of amplitude preservation in several tau - p transform methods we make a precise estimate of the velocity at the top of the crust from analysis of amplitudes in the tau - p domain. Along a 52-km segment we find less than 5% variation from 2.45 km/s. Velocity models of the uppermost crust are constructed using waveform inversion for both reflection and refraction arrivals. This method exploits the high quality of both primary and secondary phases and provides an objective process for iteratively improving trial models and for measuring misfit. The resulting models show remarkable homogeneity: on-axis variation is 5% or less within layers 2A and 2B, increasing to 10% at the sharp 2A/2B boundary. The extrusive volcanic layer is only 130 m thick along-axis and corresponds to the triangular -shaped neovolcanic zone. From this we infer that the sheeted dikes feeding the extrusive layer 2A come up to very shallow depths on axis. Along axis, a fourth-order deviation from axial linearity identified geochemically is observed as a small increase in thickness of the extrusive layer. Off -axis, the velocity increases only slightly to 2.49 km/s, while the thickness of the extrusives increases to 217 km and the variability in both parameters increases with distance from the ridge axis. In a separate section we present the first published analysis of seismic records of thunder. We calculate multi -taper spectra to determine the peak energy in the lightning bolt and apply time-dependent polarization

  8. Upper crustal structure of Madeira Island revealed from ambient noise tomography

    Science.gov (United States)

    Matos, Catarina; Silveira, Graça; Matias, Luís; Caldeira, Rita; Ribeiro, M. Luísa; Dias, Nuno A.; Krüger, Frank; Bento dos Santos, Telmo

    2015-06-01

    We present the first image of the Madeira upper crustal structure, using ambient seismic noise tomography. 16 months of ambient noise, recorded in a dense network of 26 seismometers deployed across Madeira, allowed reconstructing Rayleigh wave Green's functions between receivers. Dispersion analysis was performed in the short period band from 1.0 to 4.0 s. Group velocity measurements were regionalized to obtain 2D tomographic images, with a lateral resolution of 2.0 km in central Madeira. Afterwards, the dispersion curves, extracted from each cell of the 2D group velocity maps, were inverted as a function of depth to obtain a 3D shear wave velocity model of the upper crust, from the surface to a depth of 2.0 km. The obtained 3D velocity model reveals features throughout the island that correlates well with surface geology and island evolution.

  9. Control of early-formed vesicle cylinders on upper crustal prismatic jointing in compound pāhoehoe lavas of Elephanta Island, western Deccan Traps, India

    Science.gov (United States)

    Sheth, Hetu; Patel, Vanit; Samant, Hrishikesh

    2017-08-01

    Upper crustal prismatic joints and vesicle cylinders, common in pāhoehoe lava flows, form early and late, respectively, and are therefore independent features. However, small-scale compound pāhoehoe lava lobes on Elephanta Island (western Deccan Traps, India), which resemble S-type (spongy) pāhoehoe in some aspects, contain vesicle cylinders which apparently controlled the locations of upper crustal prismatic joints. The lobes are decimeters thick, did not experience inflation after emplacement, and solidified rapidly. They have meter-scale areas that are exceptionally rich in vesicle cylinders (up to 68 cylinders in 1 m2, with a mean spacing of 12.1 cm), separated by cylinder-free areas, and pervasive upper crustal prismatic jointing with T, curved T, and quadruple joint intersections. A majority (≥76.5%) of the cylinders are located exactly on joints or at joint intersections, and were not simply captured by downward growing joints, as the cylinders show no deflection in vertical section. We suggest that large numbers of cylinders originated in a layer of bubble-rich residual liquid at the top of a basal diktytaxitic crystal mush zone which was formed very early (probably within the first few minutes of the emplacement history). The locations where the rising cylinders breached the crust provided weak points or mechanical flaws towards which any existing joints (formed by thermal contraction) propagated. New joints may also have propagated outwards from the cylinders and linked up laterally. Some cylinders breached the crust between the joints, and thus formed a little later than most others. The Elephanta Island example reveals that, whereas thermal contraction is undoubtedly valid as a standard mechanism for forming upper crustal prismatic joints, abundant mechanical flaws (such as large concentrations of early-formed, crust-breaching vesicle cylinders) can also control the joint formation process.

  10. A New Comprehensive Model for Crustal and Upper Mantle Structure of the European Plate

    Science.gov (United States)

    Morelli, A.; Danecek, P.; Molinari, I.; Postpischl, L.; Schivardi, R.; Serretti, P.; Tondi, M. R.

    2009-12-01

    We present a new comprehensive model of crustal and upper mantle structure of the whole European Plate — from the North Atlantic ridge to Urals, and from North Africa to the North Pole — describing seismic speeds (P and S) and density. Our description of crustal structure merges information from previous studies: large-scale compilations, seismic prospection, receiver functions, inversion of surface wave dispersion measurements and Green functions from noise correlation. We use a simple description of crustal structure, with laterally-varying sediment and cristalline layers thickness and seismic parameters. Most original information refers to P-wave speed, from which we derive S speed and density from scaling relations. This a priori crustal model by itself improves the overall fit to observed Bouguer anomaly maps, as derived from GRACE satellite data, over CRUST2.0. The new crustal model is then used as a constraint in the inversion for mantle shear wave speed, based on fitting Love and Rayleigh surface wave dispersion. In the inversion for transversely isotropic mantle structure, we use group speed measurements made on European event-to-station paths, and use a global a priori model (S20RTS) to ensure fair rendition of earth structure at depth and in border areas with little coverage from our data. The new mantle model sensibly improves over global S models in the imaging of shallow asthenospheric (slow) anomalies beneath the Alpine mobile belt, and fast lithospheric signatures under the two main Mediterranean subduction systems (Aegean and Tyrrhenian). We map compressional wave speed inverting ISC travel times (reprocessed by Engdahl et al.) with a non linear inversion scheme making use of finite-difference travel time calculation. The inversion is based on an a priori model obtained by scaling the 3D mantle S-wave speed to P. The new model substantially confirms images of descending lithospheric slabs and back-arc shallow asthenospheric regions, shown in

  11. Upper crustal structure beneath East Java from ambient noise tomography: A preliminary result

    International Nuclear Information System (INIS)

    Martha, Agustya Adi; Widiyantoro, Sri; Cummins, Phil; Saygin, Erdinc; Masturyono

    2015-01-01

    East Java has a fairly complex geological structure. Physiographically East Java can be divided into three zones, i.e. the Southern Mountains zone in the southern part, the Kendeng zone in the middle part, and the Rembang zone in the northern part. Most of the seismic hazards in this region are due to processes in the upper crust. In this study, the Ambient Noise Tomography (ANT) method is used to image the upper crustal structure beneath East Java. We have used seismic waveform data recorded by 8Meteorological, Climatological and Geophysical Agency (BMKG) stationary seismographic stations and 16 portable seismographs installed for 2 to 8 weeks. The data were processed to obtain waveforms fromnoise cross-correlation between pairs of seismographic stations. Our preliminary results indicate that the Kendeng zone, an area of low gravity anomaly, is associated with a low velocity zone. On the other hand, the southern mountain range, which has a high gravity anomaly, is related to a high velocity anomaly as shown by our tomographic images

  12. Upper crustal structure beneath East Java from ambient noise tomography: A preliminary result

    Energy Technology Data Exchange (ETDEWEB)

    Martha, Agustya Adi [Meteorological, Climatological and Geophysical Agency, Jakarta (Indonesia); Graduate Research on Earthquakes and Active Tectonics, Institut Teknologi Bandung, Bandung (Indonesia); Widiyantoro, Sri [Global Geophysics Group, Institut Teknologi Bandung, Bandung (Indonesia); Center for Disaster Mitigation, Institut Teknologi Bandung, Bandung (Indonesia); Cummins, Phil; Saygin, Erdinc [Research School of Earth Sciences, Australian National University, Canberra (Australia); Masturyono [Meteorological, Climatological and Geophysical Agency, Jakarta (Indonesia)

    2015-04-24

    East Java has a fairly complex geological structure. Physiographically East Java can be divided into three zones, i.e. the Southern Mountains zone in the southern part, the Kendeng zone in the middle part, and the Rembang zone in the northern part. Most of the seismic hazards in this region are due to processes in the upper crust. In this study, the Ambient Noise Tomography (ANT) method is used to image the upper crustal structure beneath East Java. We have used seismic waveform data recorded by 8Meteorological, Climatological and Geophysical Agency (BMKG) stationary seismographic stations and 16 portable seismographs installed for 2 to 8 weeks. The data were processed to obtain waveforms fromnoise cross-correlation between pairs of seismographic stations. Our preliminary results indicate that the Kendeng zone, an area of low gravity anomaly, is associated with a low velocity zone. On the other hand, the southern mountain range, which has a high gravity anomaly, is related to a high velocity anomaly as shown by our tomographic images.

  13. Imaging of upper crustal structure beneath East Java-Bali, Indonesia with ambient noise tomography

    Science.gov (United States)

    Martha, Agustya Adi; Cummins, Phil; Saygin, Erdinc; Sri Widiyantoro; Masturyono

    2017-12-01

    The complex geological structures in East Java and Bali provide important opportunities for natural resource exploitation, but also harbor perils associated with natural disasters. Such a condition makes the East Java region an important area for exploration of the subsurface seismic wave velocity structure, especially in its upper crust. We employed the ambient noise tomography method to image the upper crustal structure under this study area. We used seismic data recorded at 24 seismographs of BMKG spread over East Java and Bali. In addition, we installed 28 portable seismographs in East Java from April 2013 to January 2014 for 2-8 weeks, and we installed an additional 28 seismographs simultaneously throughout East Java from August 2015 to April 2016. We constructed inter-station Rayleigh wave Green's functions through cross-correlations of the vertical component of seismic noise recordings at 1500 pairs of stations. We used the Neighborhood Algorithm to construct depth profiles of shear wave velocity (Vs). The main result obtained from this study is the thickness of sediment cover. East Java's southern mountain zone is dominated by higher Vs, the Kendeng basin in the center is dominated by very low Vs, and the Rembang zone (to the North of Kendeng zone) is associated with medium Vs. The existence of structures with oil and gas potential in the Kendeng and Rembang zones can be identified by low Vs.

  14. Geophysical Investigations of Crustal and Upper Mantle Structure of Oceanic Intraplate Volcanoes (OIVs)

    Science.gov (United States)

    Robinson, A. H.; Peirce, C.; Funnell, M.; Watts, A. B.; Grevemeyer, I.

    2016-12-01

    Oceanic intraplate volcanoes (OIVs) represent a record of the modification of the oceanic crust by volcanism related to a range of processes including hot-spots, small scale mantle convection, and localised lithospheric extension. Geophysical studies of OIVs show a diversity in crustal and upper mantle structures, proposed to exist on a spectrum between two end-members where the main control is the age of the lithosphere at the time of volcanism. This hypothesis states that where the lithosphere is older, colder, and thicker it is more resistant to vertical magmatism than younger, hotter, thinner lithosphere. It is suggested that the Moho acts as a density filter, permitting relatively buoyant magma to vertically intrude the crust, but preventing denser magma from ascending to shallow levels. A key control may therefore be the melting depth, known to affect magma composition, and itself related to lithosphere age. Combined geophysical approaches allow us to develop robust models for OIV crustal structures with quantifiable resolution and uncertainty. As a case study, we present results from a multi-approach geophysical experiment at the Louisville Ridge Seamount Chain, believed to have formed on young (travel-time modelling of picked arrivals, is tested against reflection and gravity data. We compare our observations with studies of other OIVs to test whether lithospheric age controls OIV structure. Comparisons are limited by the temporal and spatial distribution of lithosphere and volcano ages, but suggest the hypothesis does not hold for all OIV features. While age may be the main control on OIV structure, as it determines lithosphere thermal and mechanical properties, other factors such as thermal rejuvenation, mechanical weakening, and volcano load size and distribution, may also come into play.

  15. Density of alkaline magmas at crustal and upper mantle conditions by X-ray absorption

    Science.gov (United States)

    Seifert, R.; Malfait, W.; Petitgirard, S.; Sanchez-Valle, C.

    2011-12-01

    Silicate melts are essential components of igneous processes and are directly involved in differentiation processes and heat transfer within the Earth. Studies of the physical properties of magmas (e.g., density, viscosity, conductivity, etc) are however challenging and experimental data at geologically relevant pressure and temperature conditions remain scarce. For example, there is virtually no data on the density at high pressure of alkaline magmas (e.g., phonolites) typically found in continental rift zone settings. We present in situ density measurements of alkaline magmas at crustal and upper mantle conditions using synchrotron X-ray absorption. Measurements were conducted on ID27 beamline at ESRF using a panoramic Paris-Edinburgh Press (PE Press). The starting material is a synthetic haplo-phonolite glass similar in composition to the Plateau flood phonolites from the Kenya rift [1]. The glass was synthesized at 1673 K and 2.0 GPa in a piston-cylinder apparatus at ETH Zurich and characterized using EPMA, FTIR and density measurements. The sample contains less than 200 ppm water and is free of CO2. Single-crystal diamond cylinders (Øin = 0.5 mm, height = 1 mm) were used as sample containers and placed in an assembly formed by hBN spacers, a graphite heater and a boron epoxy gasket [2]. The density was determined as a function of pressure (1.0 to 3.1 GPa) and temperature (1630-1860 K) from the X-ray absorption contrast at 20 keV between the sample and the diamond capsule. The molten state of the sample during the data collection was confirmed by X-ray diffraction measurements. Pressure and temperature were determined simultaneously from the equation of state of hBN and platinum using the the double isochor method [3].The results are combined with available density data at room conditions to derive the first experimental equation of state (EOS) of phonolitic liquids at crustal and upper mantle conditions. We will compare our results with recent reports of the

  16. A new heat flux model for the Antarctic Peninsula incorporating spatially variable upper crustal radiogenic heat production

    Science.gov (United States)

    Burton-Johnson, A.; Halpin, J.; Whittaker, J. M.; Graham, F. S.; Watson, S. J.

    2017-12-01

    We present recently published findings (Burton-Johnson et al., 2017) on the variability of Antarctic sub-glacial heat flux and the impact from upper crustal geology. Our new method reveals that the upper crust contributes up to 70% of the Antarctic Peninsula's subglacial heat flux, and that heat flux values are more variable at smaller spatial resolutions than geophysical methods can resolve. Results indicate a higher heat flux on the east and south of the Peninsula (mean 81 mWm-2) where silicic rocks predominate, than on the west and north (mean 67 mWm-2) where volcanic arc and quartzose sediments are dominant. Whilst the data supports the contribution of HPE-enriched granitic rocks to high heat flux values, sedimentary rocks can be of comparative importance dependent on their provenance and petrography. Models of subglacial heat flux must utilize a heterogeneous upper crust with variable radioactive heat production if they are to accurately predict basal conditions of the ice sheet. Our new methodology and dataset facilitate improved numerical model simulations of ice sheet dynamics. The most significant challenge faced remains accurate determination of crustal structure, particularly the depths of the HPE-enriched sedimentary basins and the sub-glacial geology away from exposed outcrops. Continuing research (particularly detailed geophysical interpretation) will better constrain these unknowns and the effect of upper crustal geology on the Antarctic ice sheet. Burton-Johnson, A., Halpin, J.A., Whittaker, J.M., Graham, F.S., and Watson, S.J., 2017, A new heat flux model for the Antarctic Peninsula incorporating spatially variable upper crustal radiogenic heat production: Geophysical Research Letters, v. 44, doi: 10.1002/2017GL073596.

  17. Developing Tools to Test the Thermo-Mechanical Models, Examples at Crustal and Upper Mantle Scale

    Science.gov (United States)

    Le Pourhiet, L.; Yamato, P.; Burov, E.; Gurnis, M.

    2005-12-01

    Testing geodynamical model is never an easy task. Depending on the spatio-temporal scale of the model, different testable predictions are needed and no magic reciepe exist. This contribution first presents different methods that have been used to test themo-mechanical modeling results at upper crustal, lithospheric and upper mantle scale using three geodynamical examples : the Gulf of Corinth (Greece), the Western Alps, and the Sierra Nevada. At short spatio-temporal scale (e.g. Gulf of Corinth). The resolution of the numerical models is usually sufficient to catch the timing and kinematics of the faults precisely enough to be tested by tectono-stratigraphic arguments. In active deforming area, microseismicity can be compared to the effective rheology and P and T axes of the focal mechanism can be compared with local orientation of the major component of the stress tensor. At lithospheric scale the resolution of the models doesn't permit anymore to constrain the models by direct observations (i.e. structural data from field or seismic reflection). Instead, synthetic P-T-t path may be computed and compared to natural ones in term of rate of exhumation for ancient orogens. Topography may also help but on continent it mainly depends on erosion laws that are complicated to constrain. Deeper in the mantle, the only available constrain are long wave length topographic data and tomographic "data". The major problem to overcome now at lithospheric and upper mantle scale, is that the so called "data" results actually from inverse models of the real data and that those inverse model are based on synthetic models. Post processing P and S wave velocities is not sufficient to be able to make testable prediction at upper mantle scale. Instead of that, direct wave propagations model must be computed. This allows checking if the differences between two models constitute a testable prediction or not. On longer term, we may be able to use those synthetic models to reduce the residue

  18. How Deep is Shallow? Improving Absolute and Relative Locations of Upper Crustal Seismicity in Switzerland

    Science.gov (United States)

    Diehl, T.; Kissling, E. H.; Singer, J.; Lee, T.; Clinton, J. F.; Waldhauser, F.; Wiemer, S.

    2017-12-01

    Information on the structure of upper-crustal fault systems and their connection with seismicity is key to the understanding of neotectonic processes. Precisely determined focal depths in combination with structural models can provide important insight into deformation styles of the upper crust (e.g. thin- vs. versus thick-skinned tectonics). Detailed images of seismogenic fault zones in the upper crust, on the other hand, will contribute to the assessment of the hazard related to natural and induced earthquakes, especially in regions targeted for radioactive waste repositories or geothermal energy production. The complex velocity structure of the uppermost crust and unfavorable network geometries, however, often hamper precise locations (i.e. focal depth) of shallow seismicity and therefore limit tectonic interpretations. In this study we present a new high-precision catalog of absolute locations of seismicity in Switzerland. High-quality travel-time data from local and regional earthquakes in the period 2000-2017 are used to solve the coupled hypocenter-velocity structure problem in 1D. For this purpose, the well-known VELEST inversion software was revised and extended to improve the quality assessment of travel-time data and to facilitate the identification of erroneous picks in the bulletin data. Results from the 1D inversion are used as initial parameters for a 3D local earthquake tomography. Well-studied earthquakes and high-quality quarry blasts are used to assess the quality of 1D and 3D relocations. In combination with information available from various controlled-source experiments, borehole data, and geological profiles, focal depths and associated host formations are assessed through comparison with the resolved 3D velocity structure. The new absolute locations and velocity models are used as initial values for relative double-difference relocation of earthquakes in Switzerland. Differential times are calculated from bulletin picks and waveform cross

  19. 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.

  20. Magnitude and Surface Rupture Length of Prehistoric Upper Crustal Earthquakes in the Puget Lowland, Washington State

    Science.gov (United States)

    Sherrod, B. L.; Styron, R. H.

    2016-12-01

    Paleoseismic studies documented prehistoric earthquakes after the last glaciation ended 15 ka on 13 upper-crustal fault zones in the Cascadia fore arc. These fault zones are a consequence of north-directed fore arc block migration manifesting as a series of bedrock uplifts and intervening structural basins in the southern Salish Sea lowland between Vancouver, B.C. to the north and Olympia, WA to the south, and bounded on the east and west by the Cascade Mountains and Olympic Mountains, respectively. Our dataset uses published information and includes 27 earthquakes tabulated from observations of postglacial deformation at 63 sites. Stratigraphic offsets along faults consist of two types of measurements: 1) vertical separation of strata along faults observed in fault scarp excavations, and 2) estimates from coastal uplift and subsidence. We used probabilistic methods to estimate past rupture magnitudes and surface rupture length (SRL), applying empirical observations from modern earthquakes and point measurements from paleoseismic sites (Biasi and Weldon, 2006). Estimates of paleoearthquake magnitude ranged between M 6.5 and M 7.5. SRL estimates varied between 20 and 90 km. Paleoearthquakes on the Seattle fault zone and Saddle Mountain West fault about 1100 years ago were outliers in our analysis. Large offsets observed for these two earthquakes implies a M 7.8 and 200 km SRL, given the average observed ratio of slip/SRL in modern earthquakes. The actual mapped traces of these faults are less than 200km, implying these earthquakes had an unusually high static stress drop or, in the case of the Seattle fault, splay faults may have accentuated uplift in the hanging wall. Refined calculations incorporating fault area may change these magnitude and SRL estimates. Biasi, G.P., and Weldon, R.J., 2006, Estimating Surface Rupture Length and Magnitude of Paleoearthquakes from Point Measurements of Rupture Displacement: B. Seismol. Soc. Am., 96, 1612-1623.

  1. Density heterogeneity of the North American upper mantle from satellite gravity and a regional crustal model

    DEFF Research Database (Denmark)

    Herceg, Matija; Artemieva, Irina; Thybo, Hans

    2014-01-01

    -density conversion and (ii) uncertainties in knowledge of the crustal structure (thickness and average Vp velocities of individual crustal layers, including the sedimentary cover). In this study, we address both sources of possible uncertainties by applying different conversions from velocity to density...... and by introducing variations into the crustal structure which corresponds to the uncertainty of its resolution by highquality and low-quality seismic models. We examine the propagation of these uncertainties into determinations of lithospheric mantle density. Given a relatively small range of expected density...

  2. Receiver function and gravity constraints on crustal structure and vertical movements of the Upper Mississippi Embayment and Ozark Uplift

    Science.gov (United States)

    Liu, Lin; Gao, Stephen S.; Liu, Kelly H.; Mickus, Kevin

    2017-06-01

    The Upper Mississippi Embayment (UME), where the seismically active New Madrid Seismic Zone resides, experienced two phases of subsidence commencing in the Late Precambrian and Cretaceous, respectively. To provide new constraints on models proposed for the mechanisms responsible for the subsidence, we computed and stacked P-to-S receiver functions recorded by 49 USArray and other seismic stations located in the UME and the adjacent Ozark Uplift and modeled Bouguer gravity anomaly data. The inferred thickness, density, and Vp/Vs of the upper and lower crustal layers suggest that the UME is characterized by a mafic and high-density upper crustal layer of ˜30 km thickness, which is underlain by a higher-density lower crustal layer of up to ˜15 km. Those measurements, in the background of previously published geological observations on the subsidence and uplift history of the UME, are in agreement with the model that the Cretaceous subsidence, which was suggested to be preceded by an approximately 2 km uplift, was the consequence of the passage of a previously proposed thermal plume. The thermoelastic effects of the plume would have induced wide-spread intrusion of mafic mantle material into the weak UME crust fractured by Precambrian rifting and increased its density, resulting in renewed subsidence after the thermal source was removed. In contrast, the Ozark Uplift has crustal density, thickness, and Vp/Vs measurements that are comparable to those observed on cratonic areas, suggesting an overall normal crust without significant modification by the proposed plume, probably owing to the relatively strong and thick lithosphere.

  3. Crustal and upper mantle investigations of the Caribbean-South American plate boundary

    Science.gov (United States)

    Bezada, Maximiliano J.

    The evolution of the Caribbean --- South America plate boundary has been a matter of vigorous debate for decades and many questions remain unresolved. In this work, and in the framework of the BOLIVAR project, we shed light on some aspects of the present state and the tectonic history of the margin by using different types of geophysical data sets and techniques. An analysis of controlled-source traveltime data collected along a boundary-normal profile at ˜65°W was used to build a 2D P-wave velocity model. The model shows that the Caribbean Large Igenous Province is present offshore eastern Venezuela and confirms the uniformity of the velocity structure along the Leeward Antilles volcanic belt. In contrast with neighboring profiles, at this longitude we see no change in velocity structure or crustal thickness across the San Sebastian - El Pilar fault system. A 2D gravity modeling methodology that uses seismically derived initial density models was developed as part of this research. The application of this new method to four of the BOLIVAR boundary-normal profiles suggests that the uppermost mantle is denser under the South American continental crust and the island arc terranes than under the Caribbean oceanic crust. Crustal rocks of the island arc and extended island arc terranes of the Leeward Antilles have a relatively low density, given their P-wave velocity. This may be caused by low iron content, relative to average magmatic arc rocks. Finally, an analysis of teleseismic traveltimes with frequency-dependent kernels produced a 3D P-wave velocity perturbation model. The model shows the structure of the mantle lithosphere under the study area and clearly images the subduction of the Atlantic slab and associated partial removal of the lower lithosphere under northern South America. We also image the subduction of a section of the Caribbean plate under South America with an east-southeast direction. Both the Atlantic and Caribbean subducting slabs penetrate the

  4. Crustal and upper mantle structure of Siberia from teleseismic receiver functions

    DEFF Research Database (Denmark)

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

    2015-01-01

    ). With this method, we determine seismic P- and S-velocities that are comparable to the results of teleseismic body wave and surface wave tomography techniques. The RF model shows variations in the crustal thickness between 35 and 55 km. Intracrustal structures are identified, in particular using the high......This study presents seismic images of the crustal and lithospheric structure in Siberia based on the available broadband seismic data using teleseismic receiver functions (RFs). We invert P- and S-RFs jointly. The inversion technique is carried out by approach described by Vinnik et al. (2004....... The current results of RF analysis of the crustal and mantle structure will help to build a model for tectonic and geodynamic evolution of different provinces of Siberia. We compare our results to the recent detailed models of crustal structure in the area and with seismic models for similar geodynamic...

  5. Crustal and Upper Mantle Velocity Structure beneath Northwestern South America revealed by the CARMArray

    Science.gov (United States)

    Miao, W.; Cornthwaite, J.; Levander, A.; Niu, F.; Schmitz, M.; Dionicio, V.; Nader-Nieto, M. F.

    2017-12-01

    report the initial results of the inversion and discuss the lateral variations of crustal and upper mantle structure and their potential links with surface geology and regional tectonics.

  6. The upper crust laid on its side: tectonic implications of steeply tilted crustal slabs for extension in the basin and range

    Science.gov (United States)

    Howard, Keith A.

    2005-01-01

    Tilted slabs expose as much as the top 8–15 km of the upper crust in many parts of the Basin and Range province. Exposures of now-recumbent crustal sections in these slabs allow analysis of pre-tilt depth variations in dike swarms, plutons, and thermal history. Before tilting the slabs were panels between moderately dipping, active Tertiary normal faults. The slabs and their bounding normal faults were tilted to piggyback positions on deeper footwalls that warped up isostatically beneath them during tectonic unloading. Stratal dips within the slabs are commonly tilted to vertical or even slightly overturned, especially in the southern Basin and Range where the thin stratified cover overlies similarly tilted basement granite and gneiss. Some homoclinal recumbent slabs of basement rock display faults that splay upward into forced folds in overlying cover sequences, which thereby exhibit shallower dips. The 15-km maximum exposed paleodepth for the slabs represents the base of the brittle upper crust, as it coincides with the depth of the modern base of the seismogenic zone and the maximum focal depths of large normal-fault earthquakes in the Basin and Range. Many upended slabs accompany metamorphic core complexes, but not all core complexes have corresponding thick recumbent hanging-wall slabs. The Ruby Mountains core complex, for example, preserves only scraps of upper-plate rocks as domed-up extensional klippen, and most of the thick crustal section that originally overlay the uplifted metamorphic core now must reside below little-tilted hanging-wall blocks in the Elko-Carlin area to the west. The Whipple and Catalina Mountains core complexes in contrast are footwall to large recumbent hanging-wall slabs of basement rock exposing 8-15 km paleodepths that originally roofed the metamorphic cores; the exposed paleodepths require that a footwall rolled up beneath the slabs.

  7. A Crustal Cross Section over the Central North Iberian Margin: New Insights into the Bay of Biscay Inverted Hyperextended Rift

    Science.gov (United States)

    Cadenas Martínez, P.; Fernandez Viejo, G.; Pulgar, J. A.; Minshull, T. A.

    2015-12-01

    The Bay of Biscay is a V-shape failed arm of the Atlantic rift which was opened during the Mesozoic and partially closed during the Alpine orogeny in the Cenozoic, when the convergence of the Iberian and European Plates drove to the formation of the Pyrenean-Cantabrian realm in the North Iberian peninsula. A complete crustal cross section through the central part of the North Iberian Margin, representing the southern margin of the Bay of Biscay, is presented here from the interpretation of a high quality deep seismic reflection profile together with boreholes and well logs, acquired for oil and gas exploration purposes. The studied segment of this margin includes a basement high so called Le Danois Bank, and the Asturian basin, one of the sedimentary basins developed during the Mesozoic extensional processes, which was subsequently inverted during the Alpine orogeny. Most of the compression seems to have taken place through uplift of the continental platform and slope and the formation of an accretionary wedge at the bottom of the slope, so it is still possible to elucidate both extensional and compressional features. The basin appears as an asymmetric bowl bounded by synsedimentary normal faults with a maximum thickness of about 6 s TWT, which has been estimated to be equivalent to about 7 km. Depth migration of the seismic profile has revealed the presence of a deeper trough, with a maximum thickness of 13. 5 km at its main depocenter, which closely resembles the sedimentary thickness proposed for other contemporaneous proximal basins. These results support the high degree of extension and the exhumation processes proposed for this margin, deduced from refraction velocities and from the upper crustal and mantle rocks dredged at the slopes of Le Danois High. They will bring new insights to, and further constraints on, geodynamical models for this margin, where the amount of shortening linked with Cenozoic compression and the role of the rift structure during the

  8. Crustal and Upper Mantle Structure from Joint Inversion of Body Wave and Gravity Data

    Science.gov (United States)

    2012-09-01

    We use both free-air and Bouguer gravity anomalies derived from the global gravity model of the GRACE satellite mission. The gravity data provide...relocation analysis. We use both free-air and Bouguer gravity anomalies derived from the global gravity model of the GRACE satellite mission. The gravity...topographic relief this effect needs to be removed; thus, we converted free-air anomalies into Bouguer anomalies assuming a standard density for crustal rocks

  9. Oblique reactivation of lithosphere-scale lineaments controls rift physiography - the upper-crustal expression of the Sorgenfrei-Tornquist Zone, offshore southern Norway

    Science.gov (United States)

    Phillips, Thomas B.; Jackson, Christopher A.-L.; Bell, Rebecca E.; Duffy, Oliver B.

    2018-04-01

    Pre-existing structures within sub-crustal lithosphere may localise stresses during subsequent tectonic events, resulting in complex fault systems at upper-crustal levels. As these sub-crustal structures are difficult to resolve at great depths, the evolution of kinematically and perhaps geometrically linked upper-crustal fault populations can offer insights into their deformation history, including when and how they reactivate and accommodate stresses during later tectonic events. In this study, we use borehole-constrained 2-D and 3-D seismic reflection data to investigate the structural development of the Farsund Basin, offshore southern Norway. We use throw-length (T-x) analysis and fault displacement backstripping techniques to determine the geometric and kinematic evolution of N-S- and E-W-striking upper-crustal fault populations during the multiphase evolution of the Farsund Basin. N-S-striking faults were active during the Triassic, prior to a period of sinistral strike-slip activity along E-W-striking faults during the Early Jurassic, which represented a hitherto undocumented phase of activity in this area. These E-W-striking upper-crustal faults are later obliquely reactivated under a dextral stress regime during the Early Cretaceous, with new faults also propagating away from pre-existing ones, representing a switch to a predominantly dextral sense of motion. The E-W faults within the Farsund Basin are interpreted to extend through the crust to the Moho and link with the Sorgenfrei-Tornquist Zone, a lithosphere-scale lineament, identified within the sub-crustal lithosphere, that extends > 1000 km across central Europe. Based on this geometric linkage, we infer that the E-W-striking faults represent the upper-crustal component of the Sorgenfrei-Tornquist Zone and that the Sorgenfrei-Tornquist Zone represents a long-lived lithosphere-scale lineament that is periodically reactivated throughout its protracted geological history. The upper-crustal component of

  10. Barents Sea Crustal and Upper Mantle Structure from Deep Seismic and Potential Field Data

    Science.gov (United States)

    Aarseth, I.; Mjelde, R.; Breivik, A. J.; Minakov, A.; Huismans, R. S.; Faleide, J. I.

    2016-12-01

    The Barents Sea basement comprises at least two different domains; the Caledonian in the west and the Timanian in the east. Contrasting interpretations have been published recently, as the transition between these two domains is not well constrained. Interpretations of new high-quality magnetic data covering most of the SW Barents Sea challenged previous studies of the Late Paleozoic basin configurations in the western and central Barents Sea. Two major directions of Caledonian structures have been proposed by different authors: N-S and SW-NE. Two regional ocean bottom seismic (OBS) profiles, crossing these two major directions, were acquired in 2014.The primary goal in this project is to locate the main Caledonian suture in the western Barents Sea, as well as the possible Barentsia-Baltica suture postulated further eastwards. High velocity anomalies associated with Caledonian eclogites are particularly interesting as they may be related to Caledonian suture zones. The collapse of the Caledonian mountain range predominantly along these suture zones is expected to be closely linked to the deposition of Devonian erosional products, and subsequent rifting is likely to be influenced by inheritance of Caledonian trends. P-wave travel-time modelling is done by use of a combined ray-tracing and inversion scheme, and gravity modelling has been used to support the seismic model. The results indicate high P-wave velocities (mostly over 4 km/s) close to the seafloor as well as high velocity (around 6 km/s) zones at shallow depths which are interpreted as volcanic sills. The crustal transect reveals areas of complex geology and velocity inversions. Strong reflections from within the crystalline crust indicate a heterogeneous basement terrain. Gravity modelling agrees with this, as several blocks with variable densities had to be introduced in order to reproduce the observed gravity anomalies. Refractions from the top of the crystalline basement together with reflections from

  11. Electrical structure and its implication across the lower- and upper-crustal settings of South India

    Science.gov (United States)

    Raval, U.

    1988-01-01

    Measurements of a large scale MMA experiment covering both the granulite and greenstone terrains of Archeans in the southern part of India is re-visited and re-analyzed. The induced field variations contain the signatures of crustal and subcrustal electrical conductivities, although substantially distorted by the sea-land interfaces and cenozoic sediments. However, through a selection of some reconnaissance profiles and temporal variations, an attempt is made to deduce whether: (1) significant differences exist between the electrical structures of the high and low grade complexes (i.e., if the electrical conductivity of the lower crust is due to minerological composition or is intrinsic to the positioning at depths greater than 15 km); (2) the probable seaward extension of the continental crust and its transition to oceanic type may also contribute (through intracrustal DC-like telluric sheets) to the induction field in addition to or rather than the sharply localized zones; (3) the observed parameters are indicative of a formal anisotropy and/or undulations in the deep crust; and (4) the postulate of relatively hotter Indian shield is reflected particularly with regard to differential metamorphism. In the last case, the crust-mantle coupling in this region - unlike other similar areas - seems to be markedly affected by the evolution of Ne-plate velocity field.

  12. Upper crustal stress and seismotectonics of the Garhwal Himalaya using small-to-moderate earthquakes: Implications to the local structures and free fluids

    Science.gov (United States)

    Prasath, R. Arun; Paul, Ajay; Singh, Sandeep

    2017-03-01

    The work presents new focal-mechanism data of small-to-moderate (3.0 ⩾ ML ⩽ 5.0) upper crustal earthquakes for the Garhwal Himalaya from a local seismic network installed in July 2007. Majority of the epicenters of these earthquakes are located close to the Main Central Thrust (MCT) zone. We retrieved Moment Tensor (MT) solutions of 26 earthquakes by waveform inversion. The MT results and 11 small-to-moderate earthquakes from the published records are used for stress inversions. The MT solutions reveal dominatingly thrust mechanisms with few strike slip earthquakes near Chamoli. The seismic cross sections illustrate that, these earthquakes are located around the Mid-Crustal-Ramp (MCR) in the detachment. The optimally oriented faults from stress inversions suggest that, the seismogenic fault in this region is similar to a fault plane having dip angle between 12 and 25 degrees, which is compatible with the dip angle of the MCR (∼16°) in this region. P-axes and the maximum horizontal compressive stress are NE-SW oriented; the direction of the relative motion of Indian plate with respect to the Eurasian plate. The Friction Coefficient estimated from stress inversions show that the Chamoli region having low friction in comparison to the overall values. The free fluids trapped beneath the detachment are penetrating into the local faults, hence, decreasing the frictional strength and altering the prevailing stress conditions of the surroundings. The present study reveals that the MCR structure is seismogenically active and producing the small-moderate earthquakes in the region, while the MCT is probably dormant at present.

  13. A baseline for upper crustal velocity variations along the East Pacific Rise at 13 deg N

    Science.gov (United States)

    Kappus, Mary E.; Harding, Alistair J.; Orcutt, John A.

    1995-04-01

    A wide aperture profile of the East Pacific Rise at 13 deg N provides data necessary to make a high-resolution seismic velocity profile of the uppermost crust along a 52-km segment of ridge crest. Automated and objective processing steps, including r-p analysis and waveform inversion, allow the construction of models in a consistent way so that comparisons are meaningful. A continuous profile is synthesized from 70 independent one-dimensional models spaced at 750-km intervals along the ridge. The resulting seismic velocity structure of the top 500 m of crust is remarkable in its lack of variability. The main features are a thin low-velocity layer 2A at the top with a steep gradient to layer 2B. The seafloor velocity is nearly constant at 2.45 km/s +/- 3% along the entire ridge. The velocity at the top of layer 2B is 5.0 km/s +/- 10%. The depth to the 4 km/s isovelocity contour within layer 2A is 130 +/- 20 m from 13 deg to 13 deg 20 min N, north of which it increases to 180 m. The increase in thickness is coincident with a deviation from axial linearity (DEVAL) noted by both a slight change in axis depth and orientation and in geochemistry. The waveform inversion, providing more details plus velocity gradient information, shows a layer 2A with about 80 m of constant-velocity material underlain by 150 m of high velocity gradient material, putting the base of layer 2A at approximately 230 m depth south of 13 deg 20 min N and about 50 m thicker north of the DEVAL. The overall lack of variability, combined with other recent measurements of layer 2A thickness along and near the axis, indicates that the thickness of volcanic extrusives is controlled not by levels of volcanic productivity, but the dynamics of emplacement. The homogeneity along axis also provides a baseline of inherent variability in crustal structure of about 10% against which other observed variations in similar regimes can be compared.

  14. Cumulate xenoliths from St. Vincent, Lesser Antilles Island Arc: a window into upper crustal differentiation of mantle-derived basalts

    Science.gov (United States)

    Tollan, P. M. E.; Bindeman, I.; Blundy, J. D.

    2012-02-01

    In order to shed light on upper crustal differentiation of mantle-derived basaltic magmas in a subduction zone setting, we have determined the mineral chemistry and oxygen and hydrogen isotope composition of individual cumulus minerals in plutonic blocks from St. Vincent, Lesser Antilles. Plutonic rock types display great variation in mineralogy, from olivine-gabbros to troctolites and hornblendites, with a corresponding variety of cumulate textures. Mineral compositions differ from those in erupted basaltic lavas from St. Vincent and in published high-pressure (4-10 kb) experimental run products of a St. Vincent high-Mg basalt in having higher An plagioclase coexisting with lower Fo olivine. The oxygen isotope compositions (δ18O) of cumulus olivine (4.89-5.18‰), plagioclase (5.84-6.28‰), clinopyroxene (5.17-5.47‰) and hornblende (5.48-5.61‰) and hydrogen isotope composition of hornblende (δD = -35.5 to -49.9‰) are all consistent with closed system magmatic differentiation of a mantle-derived basaltic melt. We employed a number of modelling exercises to constrain the origin of the chemical and isotopic compositions reported. δ18OOlivine is up to 0.2‰ higher than modelled values for closed system fractional crystallisation of a primary melt. We attribute this to isotopic disequilibria between cumulus minerals crystallising at different temperatures, with equilibration retarded by slow oxygen diffusion in olivine during prolonged crustal storage. We used melt inclusion and plagioclase compositions to determine parental magmatic water contents (water saturated, 4.6 ± 0.5 wt% H2O) and crystallisation pressures (173 ± 50 MPa). Applying these values to previously reported basaltic and basaltic andesite lava compositions, we can reproduce the cumulus plagioclase and olivine compositions and their associated trend. We conclude that differentiation of primitive hydrous basalts on St. Vincent involves crystallisation of olivine and Cr-rich spinel at depth

  15. Higher Incision at Upper Part of Lower Segment Caesarean Section

    Directory of Open Access Journals (Sweden)

    Yong Shao

    2014-06-01

    Conclusions: An incision at the upper part of the lower segment reduces blood loss, enhances uterine retraction, predisposes to fewer complications, is easier to repair, precludes bladder adhesion to the suture line and reduces operation time. Keywords: caesarean section; higher incision technique; traditional uterine incision technique.

  16. Sensitivity analysis of crustal correction and its error propagation to upper mantle residual gravity and density anomalies

    DEFF Research Database (Denmark)

    Herceg, Matija; Artemieva, Irina; Thybo, Hans

    2013-01-01

    ) uncertainties in the velocity-density conversion and (ii) uncertainties in knowledge of the crustal structure (thickness and average Vp velocities of individual crustal layers, including the sedimentary cover). In this study, we address both sources of possible uncertainties by applying different conversions...... from velocity to density and by introducing variations into the crustal structure which corresponds to the uncertainty of its resolution by high-quality and low-quality seismic models. We examine the propagation of these uncertainties into determinations of lithospheric mantle density. The residual...

  17. The temporal and spatial distribution of upper crustal faulting and magmatism in the south Lake Turkana rift, East Africa

    Science.gov (United States)

    Muirhead, J.; Scholz, C. A.

    2017-12-01

    During continental breakup extension is accommodated in the upper crust largely through dike intrusion and normal faulting. The Eastern branch of the East African Rift arguably represents the premier example of active continental breakup in the presence magma. Constraining how faulting is distributed in both time and space in these regions is challenging, yet can elucidate how extensional strain localizes within basins as rifting progresses to sea-floor spreading. Studies of active rifts, such as the Turkana Rift, reveal important links between faulting and active magmatic processes. We utilized over 1100 km of high-resolution Compressed High Intensity Radar Pulse (CHIRP) 2D seismic reflection data, integrated with a suite of radiocarbon-dated sediment cores (3 in total), to constrain a 17,000 year history of fault activity in south Lake Turkana. Here, a set of N-S-striking intra-rift faults exhibit time-averaged slip-rates as high as 1.6 mm/yr, with the highest slip-rates occurring along faults within 3 km of the rift axis. Results show that strain has localized into a zone of intra-rift faults along the rift axis, forming an approximately 20 km-wide graben in central parts of the basin. Subsurface structural mapping and fault throw profile analyses reveal increasing basin subsidence and fault-related strain as this faulted graben approaches a volcanic island in the center of the basin (South Island). The long-axis of this island trends north-south, and it contains a number of elongate cones that support recent emplacement of N-S-striking dike intrusions, which parallel recently active intra-rift faults. Overall, these observations suggest strain localization into intra-rift faults in the rift center is likely a product of both volcanic loading and the mechanical and thermal effects of diking along the rift axis. These results support the establishment of magmatic segmentation in southern Lake Turkana, and highlight the importance of magmatism for focusing upper

  18. Role of upper-most crustal composition in the evolution of the Precambrian ocean-atmosphere system

    Science.gov (United States)

    Large, R. R.; Mukherjee, I.; Zhukova, I.; Corkrey, R.; Stepanov, A.; Danyushevsky, L. V.

    2018-04-01

    Recent research has emphasized the potential relationships between supercontinent cycles, mountain building, nutrient flux, ocean-atmosphere chemistry and the origin of life. The composition of the Upper-Most Continental Crust (UMCC) also figures prominently in these relationships, and yet little detailed data on each component of this complex relationship has been available for assessment. Here we provide a new set of data on the trace element concentrations, including the Rare Earth Elements (REE), in the matrix of 52 marine black shale formations spread globally through the Archean and Proterozoic. The data support previous studies on the temporal geochemistry of shales, but with some important differences. Results indicate a change in provenance of the black shales (upper-most crustal composition), from more mafic in the Archean prior to 2700 Ma, to more felsic from 2700 to 2200 Ma, followed by a return to mafic compositions from 2200 to 1850 Ma. Around 1850 to 1800 Ma there is a rapid change to uniform felsic compositions, which remained for a billion years to 800 Ma. The shale matrix geochemistry supports the assertion that the average upper-most continental source rocks for the shales changed from a mix of felsic, mafic and ultramafic prior to 2700 Ma to more felsic after 1850 Ma, with an extended transition period between. The return to more mafic UMCC from 2200 to 1850 Ma is supported by the frequency of Large Igneous Provinces (LIPs) and banded iron formations, which suggest a peak in major mantle-connected plume events and associated Fe-rich hydrothermal activity over this period. Support for the change to felsic UMCC around 1850 Ma is provided by previous geological data which shows that felsic magmas, including, A-type granites and K-Th-U-rich granites intruded vast areas of the continental crust, peaking around 1850 Ma and declining to 1000 Ma. The implications of this change in UMCC are far reaching and may go some way to explain the distinct

  19. Crustal Deformation across the Jericho Valley Section of the Dead Sea Fault as Resolved by Detailed Field and Geodetic Observations

    Science.gov (United States)

    Hamiel, Yariv; Piatibratova, Oksana; Mizrahi, Yaakov; Nahmias, Yoav; Sagy, Amir

    2018-04-01

    Detailed field and geodetic observations of crustal deformation across the Jericho Fault section of the Dead Sea Fault are presented. New field observations reveal several slip episodes that rupture the surface, consist with strike slip and extensional deformation along a fault zone width of about 200 m. Using dense Global Positioning System measurements, we obtain the velocities of new stations across the fault. We find that this section is locked for strike-slip motion with a locking depth of 16.6 ± 7.8 km and a slip rate of 4.8 ± 0.7 mm/year. The Global Positioning System measurements also indicate asymmetrical extension at shallow depths of the Jericho Fault section, between 0.3 and 3 km. Finally, our results suggest the vast majority of the sinistral slip along the Dead Sea Fault in southern Jorden Valley is accommodated by the Jericho Fault section.

  20. Three-dimensional Upper Crustal Velocity and Attenuation Structures of the Central Tibetan Plateau from Local Earthquake Tomography

    Science.gov (United States)

    Zhou, B.; Liang, X.; Lin, G.; Tian, X.; Zhu, G.; Mechie, J.; Teng, J.

    2017-12-01

    A series of V-shaped conjugate strike-slip faults are the most spectacular geologic features in the central Tibetan plateau. A previous study suggested that this conjugate strike-slip fault system accommodates the east-west extension and coeval north-south contraction. Another previous study suggested that the continuous convergence between the Indian and Eurasian continents and the eastward asthenospheric flow generated lithospheric paired general-shear (PGS) deformation, which then caused the development of conjugate strike-slip faults in central Tibet. Local seismic tomography can image three dimensional upper-crustal velocity and attenuation structures in central Tibet, which will provide us with more information about the spatial distribution of physical properties and compositional variations around the conjugate strike-slip fault zone. Ultimately, this information could improve our understanding of the development mechanism of the conjugate strike-slip fault system. In this study, we collected 6,809 Pg and 2,929 Sg arrival times from 414 earthquakes recorded by the temporary SANDWICH and permanent CNSN networks from November 2013 to November 2015. We also included 300 P and 17 S arrival times from 12 shots recorded by the INDEPTH III project during the summer of 1998 in the velocity tomography. We inverted for preliminary Vp and Vp/Vs models using the SIMUL2000 tomography algorithm, and then relocated the earthquakes with these preliminary velocity models. After that, we inverted for the final velocity models with these improved source locations and origin times. After the velocity inversion, we performed local attenuation tomography using t* measurements from the same dataset with an already existing approach. There are correlated features in the velocity and attenuation structures. From the surface to 10 km depth, the study area is dominated by high Vp and Qp anomalies. However, from 10 km to 20 km depth, there is a low Vp and Qp zone distributed along the

  1. Joint inversion of ambient noise surface wave and gravity data to image the upper crustal structure of the Tanlu fault zone to the southeast of Hefei, China

    Science.gov (United States)

    Wang, K.; Gu, N.; Zhang, H.; Zhou, G.

    2017-12-01

    The Tanlu fault is a major fault located in the eastern China, which stretches 2400 km long from Tancheng in the north to Lujiang in the south. It is generally believed that the Tanlu fault zone was formed in Proterozoic era and underwent a series of complicated processes since then. To understand the upper crustal structure around the southern segment of the Tanlu fault zone, in 2017 we deployed 53 short period seismic stations around the fault zone to the southeast of Hefei, capital city of Anhui province. The temporary array continuously recorded the data for about one month from 17 March to 26 April 2017. The seismic array spans an area of about 30km x 30Km with an average station spacing of about 5-6km. The vertical component data were used for extracting Rayleigh wave phase and group velocity dispersion data for the period of 0.2 to 5 seconds. To improve imaging the upper crustal structure of the fault zone, we jointly inverted the surface wave dispersion data and the gravity data because they have complementary strengths. To combine surface wave dispersion data and gravity observations into a single inversion framework, we used an empirical relationship between seismic velocity and density of Maceira and Ammon (2009). By finding the optimal relative weighting between two data types, we are able to find a shear wave velocity (Vs) model that fits both data types. The joint inversion can resolve the upper crustal fault zone structure down to about 7 km in depth. The Vs model shows that in this region the Tanlu fault is associated with high velocity anomalies, corresponding well to the Feidong complex seen on the surface. This indicates that the Tanlu fault zone may provide a channel for the intrusion of hot materials.

  2. Lithospheric strength in the active boundary between the Pacific Plate and Baja California microplate constrained from lower crustal and upper mantle xenoliths

    Science.gov (United States)

    Chatzaras, Vasileios; van der Werf, Thomas; Kriegsman, Leo M.; Kronenberg, Andreas; Tikoff, Basil; Drury, Martyn R.

    2017-04-01

    The lower crust is the most poorly understood of the lithospheric layers in terms of its rheology, particularly at active plate boundaries. We studied naturally deformed lower crustal xenoliths within an active plate boundary, in order to link their microstructures and rheological parameters to the well-defined active tectonic context. The Baja California shear zone (BCSZ), located at the western boundary of the Baja California microplate, comprises the active boundary accommodating the relative motion between the Pacific plate and Baja California microplate. The basalts of the Holocene San Quintin volcanic field carry lower crustal and upper mantle xenoliths, which sample the Baja California microplate lithosphere in the vicinity of the BCSZ. The lower crustal xenoliths range from undeformed gabbros to granoblastic two-pyroxene granulites. Two-pyroxene geothermometry shows that the granulites equilibrated at temperatures of 690-920 oC. Phase equilibria (P-T pseudosections using Perple_X) indicate that symplectites with intergrown pyroxenes, plagioclase, olivine and spinel formed at 3.6-5.4 kbar, following decompression from pressures exceeding 6 kbar. FTIR spectroscopy shows that the water content of plagioclase varies among the analyzed xenoliths; plagioclase is relatively dry in two xenoliths while one xenolith contains hydrated plagioclase grains. Microstructural observations and analysis of the crystallographic texture provide evidence for deformation of plagioclase by a combination of dislocation creep and grain boundary sliding. To constrain the strength of the lower crust and upper mantle near the BCSZ we estimated the differential stress using plagioclase and olivine grain size paleopiezomtery, respectively. Differential stress estimates for plagioclase range from 10 to 32 MPa and for olivine are 30 MPa. Thus the active microplate boundary records elevated crustal temperatures, heterogeneous levels of hydration, and low strength in both the lower crust and

  3. Using aerogravity and seismic data to model the bathymetry and upper crustal structure beneath the Pine Island Glacier ice shelf, West Antarctica

    Science.gov (United States)

    Muto, A.; Peters, L. E.; Anandakrishnan, S.; Alley, R. B.; Riverman, K. L.

    2013-12-01

    Recent estimates indicate that ice shelves along the Amundsen Sea coast in West Antarctica are losing substantial mass through sub-ice-shelf melting and contributing to the accelerating mass loss of the grounded ice buttressed by them. For Pine Island Glacier (PIG), relatively warm Circumpolar Deep Water has been identified as the key driver of the sub-ice-shelf melting although poor constraints on PIG sub-ice shelf have restricted thorough understanding of these ice-ocean interactions. Aerogravity data from NASA's Operation IceBridge (OIB) have been useful in identifying large-scale (on the order of ten kilometers) features but the results have relatively large uncertainties due to the inherent non-uniqueness of the gravity inversion. Seismic methods offer the most direct means of providing water thickness and upper crustal geological constraints, but availability of such data sets over the PIG ice shelf has been limited due to logistical constraints. Here we present a comparative analysis of the bathymetry and upper crustal structure beneath the ice shelf of PIG through joint inversion of OIB aerogravity data and in situ active-source seismic measurements collected in the 2012-13 austral summer. Preliminary results indicate improved resolution of the ocean cavity, particularly in the interior and sides of the PIG ice shelf, and sedimentary drape across the region. Seismically derived variations in ice and ocean water densities are also applied to the gravity inversion to produce a more robust model of PIG sub-ice shelf structure, as opposed to commonly used single ice and water densities across the entire study region. Misfits between the seismically-constrained gravity inversion and that estimated previously from aerogravity alone provide insights on the sensitivity of gravity measurements to model perturbations and highlight the limitations of employing gravity data to model ice shelf environments when no other sub-ice constraints are available.

  4. UPPER FRASNIAN (UPPER DEVONIAN POLYGNATHUS AND ICRIODUS CONODONTS FROM THE BAHRAM FORMATION, HUR SECTION, KERMAN PROVINCE, SOUTHEASTERN IRAN

    Directory of Open Access Journals (Sweden)

    TAYEBEH AHMADI

    2012-07-01

    Full Text Available Conodont fauna from the Upper Devonian (Frasnian Bahram Formation at the Hur section, north of Kerman, southeast Iran, is dominated by species of Icriodus and Polygnathus. This fauna allowed discrimination of two biointervals from the Lower rhenana Zone to an Upper rhenana-linguiformis interval. The age of the lower part of the studied section is tentatively considered to be older than the Lower rhenana Zone. 

  5. Incremental growth of an upper crustal, A-type pluton, Argentina: Evidence of a re-used magma pathway

    Science.gov (United States)

    Alasino, Pablo H.; Larrovere, Mariano A.; Rocher, Sebastián; Dahlquist, Juan A.; Basei, Miguel A. S.; Memeti, Valbone; Paterson, Scott; Galindo, Carmen; Macchioli Grande, Marcos; da Costa Campos Neto, Mario

    2017-07-01

    Carboniferous igneous activity in the Sierra de Velasco (NW Argentina) led to the emplacement of several magmas bodies at shallow levels (relationships) intrusive units are: (1) the Asha unit (340 ± 7 Ma): a tabular to funnel-shaped intrusion emplaced during a regional strain field dominated by WSW-ENE shortening with contacts discordant to regional host-rock structures; (2) the San Blas unit (344 ± 2 Ma): an approximate cylindrical-shaped intrusion formed by multiple batches of magmas, with a roughly concentric fabric pattern and displacement of the host rock by ductile flow of about 35% of shortening; and (3) the Hualco unit (346 ± 6 Ma): a small body with a possible mushroom geometry and contacts concordant to regional host-rock structures. The magma pulses making up these units define two groups of A-type granitoids. The first group includes the peraluminous granitic rocks of the Asha unit generated mostly by crustal sources (εNdt = - 5.8 and εHft in zircon = - 2.9 to - 4.5). The second group comprises the metaluminous to peraluminous granitic rocks of the youngest units (San Blas and Hualco), which were formed by a heterogeneous mixture between mantle and crustal sources (εNdt = + 0.6 to - 4.8 and εHft in zircon = + 3 to - 6). Our results provide a comprehensive view of the evolution of an intrusive complex formed from multiple non-consanguineous magma intrusions that utilized the same magmatic plumbing system during downward transfer of host materials. As the plutonic system matures, the ascent of magmas is governed by the visco-elastic flow of host rock that for younger batches include older hot magma mush. The latter results in ductile downward flow of older, during rise of younger magma. Such complexes may reflect the plutonic portion of volcanic centers where chemically distinct magmas are erupted.

  6. Magnetic Mineralogy of a Complete Oceanic Crustal Section (IODP hole 1256D)

    Science.gov (United States)

    Krasa, D.; Herrero-Bervera, E.; Acton, G.; Rodriguez Durand, S.

    2008-12-01

    Oceanic crust is the carrier of the marine magnetic anomalies and is therefore a valuable archive of geomagnetic information. Hole 1256D, which was drilled during ODP leg 206 and IODP expeditions 309 and 312, was the first to retrieve a core comprising of an entire sequence of oceanic crust down to the gabbro. This provides a unique opportunity to study the carriers of the marine magnetic anomalies. We used reflected light microscopy, scanning electron microscopy and energy dispersive x-ray analysis in addition to rock magnetic measurements to study the grain size, morphology, composition, and alteration state of the magnetic minerals. This comprehensive data set allows us not only to understand the magnetic stability of the minerals but also the mode and timing of remanence acquisition. The extrusive layer contains dendritic, low-temperature (LT) oxidized titanomagnetites (TMs) typical for mid- ocean ridge basalts (MORBs). The initial composition of these is close to previously reported values for MORB TMs with an ulvöspinel content of about 60%. The degree of LT oxidation remains fairly constant across the whole extrusive part of the section with an oxidation parameter z=0.6. Therefore, the increase in Curie temperature from 200C at the top to about 500C at the bottom of the extrusives cannot be accounted for by LT oxidation alone. Instead, we favor a model involving submicron inversion of LT oxidized TMs to an intergrowth of TMs and nonmagnetic phases, where the Ti-content of the TM phase is continuously decreasing with depth due to higher inversion temperatures. In the underlying sheeted dykes and gabbros, TMs precipitated as the primary opaque phase, as well. Due to the slower cooling rate, these particles are in most cases oxy-exsolved and form lamellar intergrowths of Ti- poor TMs and ilmenite. After emplacement, these minerals were altered to a much higher degree than the extrusive lavas. Secondary minerals frequently replace the original TMs, and the

  7. Geochemical Relationships between Volcanic and Plutonic Upper to Mid Crustal Exposures of the Rosario Segment, Alisitos Arc (Baja California, Mexico): An Outstanding Field Analog to the Izu-Bonin-Mariana Arc

    Science.gov (United States)

    Morris, R.; DeBari, S. M.; Busby, C. J.; Medynski, S.

    2015-12-01

    Exposed paleo-arcs, such as the Rosario segment of the Cretaceous Alisitos Arc in Baja California, Mexico, provide an opportunity to explore the evolution of arc crust through time. Remarkable 3-D exposures of the Rosario segment record crustal generation processes in the volcanic rocks and underlying plutonic rocks. In this study, we explore the physical and geochemical connection between the plutonic and volcanic sections of the extensional Alisitos Arc, and elucidate differentiation processes responsible for generating them. These results provide an outstanding analog for extensional active arc systems, such as the Izu-Bonin-Mariana (IBM) Arc. Upper crustal volcanic rocks have a coherent stratigraphy that is 3-5 km thick and ranges in composition from basalt to dacite. The most felsic compositions (70.9% SiO2) are from a welded ignimbrite unit. The most mafic compositions (51.5% SiO2, 3.2% MgO) are found in basaltic sill-like units. Phenocrysts in the volcanic units include plagioclase +/- amphibole and clinopyroxene. The transition to deeper plutonic rocks is clearly an intrusive boundary, where plutonic units intrude the volcanic units. Plutonic rocks are dominantly a quartz diorite main phase with a more mafic, gabbroic margin. A transitional zone is observed along the contact between the plutonic and volcanic rocks, where volcanics have coarsely recrystallized textures. Mineral assemblages in the plutonic units include plagioclase +/- quartz, biotite, amphibole, clinopyroxene and orthopyroxene. Most, but not all, samples are low K. REE patterns are relatively flat with limited enrichment. Normalization diagrams show LILE enrichment and HFSE depletion, where trends are similar to average IBM values. We interpret plutonic and volcanic units to have similar geochemical relationships, where liquid lines of descent show the evolution of least to most evolved magma types. We provide a model for the formation and magmatic evolution of the Alisitos Arc.

  8. An upper bound on the total inelastic cross section as a function of the total cross section

    International Nuclear Information System (INIS)

    Wu, Tai Tsun; Martin, Andre; Roy, Shasanka Mohan; Singh, Virendra

    2011-01-01

    Recently, Andre Martin has proved a rigorous upper bound on the inelastic cross sectionσ inel at high energy, which is one-fourth of the known Froissart-Martin-Lukaszuk upper bound on σ tot . Here, we obtain an upper bound on σ inel in terms of σ tot and show that the Martin bound on σ inel is improved significantly with this added information.

  9. Rayleigh waves from correlation of seismic noise in Great Island of Tierra del Fuego, Argentina: Constraints on upper crustal structure

    Directory of Open Access Journals (Sweden)

    Carolina Buffoni

    2018-01-01

    Full Text Available In this study, the ambient seismic noise cross-correlation technique is applied to estimate the upper structure of the crust beneath Great Island of Tierra del Fuego (TdF, Argentina, by the analysis of short-period Rayleigh wave group velocities. The island, situated in the southernmost South America, is a key area of investigation among the interaction between the South American and Scotia plates and is considered as a very seismically active one. Through cross-correlating the vertical components of ambient seismic noise registered at four broadband stations in TdF, we were able to extract Rayleigh waves which were used to estimate group velocities in the period band of 2.5–16 s using a time-frequency analysis. Although ambient noise sources are distributed inhomogeneously, robust empirical Green's functions could be recovered from the cross-correlation of 12 months of ambient noise. The observed group velocities were inverted considering a non-linear iterative damped least-squares inversion procedure and several 1-D shear wave velocity models of the upper crust were obtained. According to the inversion results, the S-wave velocity ranges between 1.75 and 3.7 km/s in the first 10 km of crust, depending on the pair of stations considered. These results are in agreement to the major known surface and sub-surface geological and tectonic features known in the area. This study represents the first ambient seismic noise analysis in TdF in order to constraint the upper crust beneath this region. It can also be considered as a successful feasibility study for future analyses with a denser station deployment for a more detailed imaging of structure.

  10. Insights upon upper crustal arhitecture of a subduction zone and its surroundings - Vrancea Zone and Focsani Basin - substantiated by geophysical studies

    Science.gov (United States)

    Bocin, A.; Stephenson, R.; Mocanu, V.

    2007-12-01

    The DACIA PLAN (Danube and Carpathian Integrated Action on Processes in the Lithosphere and Neotectonics) deep seismic reflection survey was performed in August-September 2001, with the proposed objective of obtaining new information on the deep structure of the external Carpathians nappes and the architecture of Tertiary/Quaternary basin developed within and adjacent to the Vrancea zone, including the rapidly subsiding Focsani Basin. The DACIA-PLAN profile is about 140 km long, having a roughly NW-SE direction, from near the southeast Transylvanian Basin, across the mountainous southeastern Carpathians and their foreland to near the Danube River. A high resolution 2.5D velocity model of the upper crust along the seismic profile has been determined from a tomographic inversion and a 2D ray tracing forward modelling of the DACIA PLAN first arrival data. Peculiar shallow high velocities indicate that pre-Tertiary basement in the Vrancea Zone (characterised by velocities greater than 5.6 km/s) is involved in Carpathian thrusting while rapid alternance, vertically or horizontally, of velocity together with narrowingly contemporary crustal events suggests uplifting. Further to the east, at the foreland basin-thrust belt transition zone (well defined within velocity values), the velocity model suggests a nose of the Miocene Subcarpathians nappe being underlain by Focsani Basin units. A Miocene and younger Focsani Basin sedimentary succession of ~10 km thickness is ascertained by a gradual increase of velocities and strongly defined velocity boundaries.

  11. Transient Upper Crustal Tear Illuminated by the Chi Chi Earthquake: Results from Strain Inversions in the Luliao Region, Taiwan

    Science.gov (United States)

    Lamont, E. A.; Lewis, J.; Byrne, T. B.; Crespi, J. M.; Rau, R.

    2010-12-01

    Modeling of earthquake focal mechanisms and coseismic GPS data from an area at the southern tip of the 1999 Chi Chi rupture suggests the existence of an evolving upper plate tear. The earthquakes occur in what we refer to as the Luliao seismic zone and define a steeply northeast-dipping tabular volume that extends from the surface to approximately 11 km. We find that the focal mechanisms from the six-month period following the 1999 Chi-Chi Earthquake yield best-fitting strain tensors that suggest the dominance of strike-slip faulting. Our strain inversions, using a micropolar continuum model, reveal orogen-perpendicular (NW-SE) minimum stretching (i.e., shortening) and orogen-parallel (NE-SW) maximum stretching. Additionally, our inversions indicate plane strain with positive, non-zero relative vorticity values, suggestive of counter-clockwise (map view) block rotations. Published coseismic GPS data provide additional evidence that this tabular volume of crust is the locus of strike-slip faulting accompanied by block rotation. Preliminary 2D strain inversions for GPS stations that span the inverted focal mechanisms reveal negative (counterclockwise) rotation values and principal strain axes that are generally consistent with our focal mechanism inversions. We interpret our findings to reflect an accommodation zone that is activated by differential westward expansion of the foreland fold and thrust belt. In particular, this zone separates an area of greater westward propagation near Taichung from an area of lesser propagation to the south near Chiayi. Differential expansion of the orogen appears to be influenced by an eastward pointing, lower-plate promontory south of the Sanyi-Puli seismic zone. Unlike the Luliao events, the Sanyi-Puli seismic zone extends from the near surface to approximately 30 km and we have interpreted it as a reactivated continental margin fracture zone inherited from South China Sea rifting. The lower-plate promontory is coincident with the

  12. Lower crustal section of the Oman Ophiolite drilled in Hole GT1A, ICDP Oman Drilling Project

    Science.gov (United States)

    Umino, S.; Kelemen, P. B.; Matter, J. M.; Coggon, J. A.; Takazawa, E.; Michibayashi, K.; Teagle, D. A. H.

    2017-12-01

    Hole GT1A (22° 53.535'N, 58° 30.904'E) was drilled by the Oman Drilling Project (OmDP) into GT1A of the Samail ophiolite, Oman. OmDP is an international collaboration supported by the International Continental Scientific Drilling Program, the Deep Carbon Observatory, NSF, IODP, JAMSTEC, and the European, Japanese, German and Swiss Science Foundations, with in-kind support in Oman from the Ministry of Regional Municipalities and Water Resources, Public Authority of Mining, Sultan Qaboos University, and the German University of Technology. Hole GT1A was diamond cored in 22 Jan to 08 Feb 2017 to a total depth of 403.05 m. The outer surfaces of the cores were imaged and described on site before being curated, boxed and shipped to the IODP drill ship Chikyu, where they underwent comprehensive visual and instrumental analysis. Hole GT1A drilled the lower crustal section in the southern Oman Ophiolite and recovered 401.52 m of total cores (99.6% recovery). The main lithology is dominated by olivine gabbro (65.9%), followed in abundance by olivine-bearing gabbro (21.5%) and olivine melagabbro (3.9%). Minor rock types are orthopyroxene-bearing olivine gabbro (2.4%), oxide-bearing olivine gabbro (1.5%), gabbro (1.1%), anorthositic gabbro (1%), troctolitic gabbro (0.8%); orthopyroxene-bearing gabbro (0.5%), gabbronorite (0.3%); and dunite (0.3%). These rocks are divided into Lithologic Unit I to VII at 26.62 m, 88.16 m, 104.72 m, 154.04 m, 215.22 m, 306.94 m in Chikyu Curated Depth in descending order; Unit I and II consist of medium-grained olivine gabbro with lower olivine abundance in Unit II. Unit III is medium-grained olivine melagabbros, marked by an increase in olivine. Unit IV is relatively homogenous medium-grained olivine gabbros with granular textures. Unit V is identified by the appearance of fine-grained gabbros, but the major rocktypes are medium grained olivine gabbros. Unit VI is medium-grained olivine gabbro, marked by appearance of orthopyroxene. Unit VII

  13. Temporal Evolution of the Upper Continental Crust: Implications for the Mode of Crustal Growth and the Evolution of the Hydrosphere

    Science.gov (United States)

    Rudnick, R. L.; Gaschnig, R. M.; Li, S.; Tang, M.; Qiu, L.; Valley, J. W.; Zurkowski, C.; McDonough, W. F.

    2014-12-01

    The upper continental crust (UCC), the interface between the atmosphere and solid Earth, is the site of weathering that produces sedimentary rocks, influences ocean chemistry through runoff of soluble elements, and affects climate through CO2 draw-down. The UCC also contains more than 50% of the crust's highly incompatible element budget (including K, Th, and U). Therefore, understanding its composition and evolution provides insight into how continents have formed, evolved, and interacted with the hydrosphere. New major and trace element compositions of >100 glacial diamictites and >100 Archean shales, plus δ7Li and δ18O for a subset of these samples, combined with data from the literature, show that the average composition of the UCC has changed through time, reflecting both the rise of atmospheric oxygen and its attendant effects on weathering, as well as the mode of crust formation and differentiation. Some changes that occur as a step function near the Archean/Proterozoic boundary (increased Th/U, decreased Mo/Pr, V/Lu) reflect the rise of oxygen at the great oxidation event (GOE) and its influence on chemical weathering signatures in the UCC. Other changes are more gradual with time (e.g., higher Th/Sc and δ18O, lower Ni/Co, La/Nb, Eu/Eu* and transition metal abundances) and reflect an UCC that has transitioned from a more mafic to a more felsic bulk composition, and which experienced increased interaction with the hydrosphere with time. The gradual nature of these compositional changes likely reflects the waning heat production of the Earth, rather than an abrupt change in tectonics or style of crust formation. These more gradual changes in crust composition, which contrast with the abrupt changes associated with the GOE, suggest that a fundamental change in the nature of crust differentiation is unlikely to be responsible for the rise of atmospheric oxygen (cf. Keller and Schoene, 2012). Indeed, it appears that the opposite may be true: that the rise of

  14. Upper and Middle Crustal Velocity Structure of the Colombian Andes From Ambient Noise Tomography: Investigating Subduction-Related Magmatism in the Overriding Plate

    Science.gov (United States)

    Poveda, Esteban; Julià, Jordi; Schimmel, Martin; Perez-Garcia, Nelson

    2018-02-01

    New maps of S velocity variation for the upper and middle crust making up the northwestern most corner of South America have been developed from cross correlation of ambient seismic noise at 52 broadband stations in the region. Over 1,300 empirical Green's functions, reconstructing the Rayleigh wave portion of the seismic wavefield, were obtained after time and frequency-domain normalization of the ambient noise recordings and stacking of 48 months of normalized data. Interstation phase and group velocity curves were then measured in the 6-38 s period range and tomographically inverted to produce maps of phase and group velocity variation in a 0.5° × 0.5° grid. Velocity-depth profiles were developed for each node after simultaneously inverting phase and group velocity curves and combined to produce 3-D maps of S velocity variation for the region. The S velocity models reveal a 7 km thick sedimentary cover in the Caribbean region, the Magdalena Valley, and the Cordillera Oriental, as well as crustal thicknesses in the Pacific and Caribbean region under 35 km, consistent with previous studies. They also display zones of slow velocity at 25-35 km depth under regions of both active and inactive volcanism, suggesting the presence of melts that carry the signature of segmented subduction into the overriding plate. A low-velocity zone in the same depth range is imaged under the Lower Magdalena Basin in the Caribbean region, which may represent either sublithospheric melts ponding at midcrustal levels after breaching through a fractured Caribbean flat slab or fluid migration through major faults within the Caribbean crust.

  15. Experimental Investigation of Biotite-Rich Schist Reacting with B-Bearing Fluids at Upper Crustal Conditions and Correlated Tourmaline Formation

    Directory of Open Access Journals (Sweden)

    Andrea Orlando

    2017-08-01

    Full Text Available Fluid–rock interaction experiments between a biotite-rich schist (from Mt. Calamita Formation, Elba Island, Italy and B-bearing aqueous fluids were carried out at 500–600 °C and 100–130 MPa. The experiments have been carried out in order to reproduce the reaction, which would have produced tourmalinisation of the biotite schist, supposedly by circulation of magmatic fluids issued from leucogranitic dykes. The reacting fluids were either NaCl-free or NaCl-bearing (20 wt % aqueous solutions, with variable concentration of H3BO3 (0.01–3.2 M. The experimental results show that tourmaline (belonging to the alkali group crystallise under high-temperature and upper crustal conditions (500–600 °C, 100–130 MPa when H3BO3 concentration in the system is greater than 1.6 M. The composition of tourmaline is either dravitic (Mg-rich or schorlitic (Fe-rich, depending if an NaCl-bearing or NaCl-free aqueous solution is used. In the first case, a significant amount of Fe released from biotite dissolution remains in the Cl-rich solution resulting from the experiment. By contrast, when pure water is used, Na/K exchange in feldspars makes Na available for tourmaline crystallisation. The high concentration of Fe in the residual fluid has an important metallogenic implication because it indicates that the interaction between the saline B-rich fluid of magmatic derivation and biotite-rich schists, besides producing tourmalinisation, is capable of mobilising significant amounts of Fe. This process could have produced, in part or totally, the Fe deposits located close to the quartz–tourmaline veins and metasomatic bodies of the Mt. Calamita Formation. Moreover, the super-hot reservoir that likely occurs in the deepest part of the Larderello–Travale geothermal field would also be the site of an extensive reaction between the B-rich fluid and biotite-bearing rocks producing tourmaline. Thus, tourmaline occurrence can be a useful guide during deep

  16. A tomographic image of upper crustal structure using P and S wave seismic refraction data in the southern granulite terrain (SGT), India

    Science.gov (United States)

    Rajendra Prasad, B.; Behera, Laxmidhar; Rao, P. Koteswara

    2006-07-01

    We present a 2-D tomographic P and S wave velocity (Vp and Vs) image with Vp/Vs ratios along N-S trending 220 km long deep seismic profile acquired in 2005, which traverses across major shear and tectonically disturbed zones in southern granulite terrain (SGT), India. The 2-D velocity model constrained down to maximum 8 km depth shows velocity anomalies (>0.2 km/s) beneath major shear zones with good spatial resolution (>0.05 km/s). The presence of high Vp (6.3-6.5 km/s), Vs (3.5-3.8 km/s), Vp/Vs (>1.75) and Poisson's ratio (0.25-0.29) indicate significant compositional changes of rocks at shallow depths (0.5 to 8 km) reveal rapid crustal exhumation of mid to lower crustal rocks. This crustal exhumation could be responsible due to Pan-African tectonothermal activity during Neoproterozoic period.

  17. Crustal Magnetic Field Anomalies and Global Tectonics

    Science.gov (United States)

    Storetvedt, Karsten

    2014-05-01

    A wide variety of evidence suggests that the ruling isochron (geomagnetic polarity versus age) hypothesis of marine magnetic lineations has no merit - undermining therefore one of the central tenets of plate tectonics. Instead, variable induction by the ambient geomagnetic field is likely to be the principal agent for mega-scale crustal magnetic features - in both oceanic and continental settings. This revitalizes the fault-controlled susceptibility-contrast model of marine magnetic lineations, originally proposed in the late 1960s. Thus, the marine magnetic 'striping' may be ascribed to tectonic shearing and related, but variable, disintegration of the original iron-oxide mineralogy, having developed primarily along one of the two pan-global sets of orthogonal fractures and faults. In this way, fault zones (having the more advanced mineral alteration) would be characterized by relatively low susceptibility, while more moderately affected crustal sections (located between principal fault zones) would be likely to have less altered oxide mineralogy and therefore higher magnetic susceptibility. On this basis, induction by the present geomagnetic field is likely to produce oscillating magnetic field anomalies with axis along the principal shear grain. The modus operandi of the alternative magneto-tectonic interpretation is inertia-driven wrenching of the global Alpine age palaeo-lithosphere - triggered by changes in Earth's rotation. Increasing sub-crustal loss to the upper mantle during the Upper Mesozoic had left the ensuing Alpine Earth in a tectonically unstable state. Thus, sub-crustal eclogitization and associated gravity-driven delamination to the upper mantle led to a certain degree of planetary acceleration which in turn gave rise to latitude-dependent, westward inertial wrenching of the global palaeo-lithosphere. During this process, 1) the thin and mechanically fragile oceanic crust were deformed into a new type of broad fold belts, and 2) the continents

  18. New experimental upper limit of the electron–proton spin-flip cross-section

    International Nuclear Information System (INIS)

    Oellers, D.; Weidemann, C.; Lenisa, P.; Meyer, H.O.; Rathmann, F.; Trusov, S.; Augustyniak, W.; Bagdasarian, Z.; Barion, L.; Barsov, S.

    2014-01-01

    In a previous publication, measurements of the depolarization of a stored proton beam by interaction with a co-propagating unpolarized electron beam at low relative energy have been presented and an upper limit of about 3 ×10 7 b for the electron–proton spin-flip cross-section was determined. A refined analysis presented in this paper reduces the previous upper limit by a factor of three by the introduction of a new procedure that also makes use of non-identified particles

  19. A geophysical cross-section of the Hockai Fault Zone (Eastern Belgium): imaging an intraplate weak crustal zone.

    Science.gov (United States)

    Lecocq, T.; Camelbeeck, T.

    2016-12-01

    with a higher degree of fracturation on a 4 km wide fault zone. Finally, we discuss the surface expression of the broad fault zone and the crustal structure around and beneath the HFZ using earthquake locations and deep geophysics under the massif.

  20. GPS measurements of crustal deformation across the southern Arava Valley section of the Dead Sea Fault and implications to regional seismic hazard assessment

    Science.gov (United States)

    Hamiel, Yariv; Masson, Frederic; Piatibratova, Oksana; Mizrahi, Yaakov

    2018-01-01

    Detailed analysis of crustal deformation along the southern Arava Valley section of the Dead Sea Fault is presented. Using dense GPS measurements we obtain the velocities of new near- and far-field campaign stations across the fault. We find that this section is locked with a locking depth of 19.9 ± 7.7 km and a slip rate of 5.0 ± 0.8 mm/yr. The geodetically determined locking depth is found to be highly consistent with the thickness of the seismogenic zone in this region. Analysis of instrumental seismic record suggests that only 1% of the total seismic moment accumulated since the last large event occurred about 800 years ago, was released by small to moderate earthquakes. Historical and paleo-seismic catalogs of this region together with instrumental seismic data and calculations of Coulomb stress changes induced by the 1995 Mw 7.2 Nuweiba earthquake suggest that the southern Arava Valley section of the Dead Sea Fault is in the late stage of the current interseismic period.

  1. Crustal permeability

    Science.gov (United States)

    Gleeson, Tom; Ingebritsen, Steven E.

    2016-01-01

    Permeability is the primary control on fluid flow in the Earth’s crust and is key to a surprisingly wide range of geological processes, because it controls the advection of heat and solutes and the generation of anomalous pore pressures.  The practical importance of permeability – and the potential for large, dynamic changes in permeability – is highlighted by ongoing issues associated with hydraulic fracturing for hydrocarbon production (“fracking”), enhanced geothermal systems, and geologic carbon sequestration.  Although there are thousands of research papers on crustal permeability, this is the first book-length treatment.  This book bridges the historical dichotomy between the hydrogeologic perspective of permeability as a static material property and the perspective of other Earth scientists who have long recognized permeability as a dynamic parameter that changes in response to tectonism, fluid production, and geochemical reactions. 

  2. Sr- and Nd- isotope variations along the Pleistocene San Pedro - Linzor volcanic chain, N. Chile: Tracking the influence of the upper crustal Altiplano-Puna Magma Body

    Science.gov (United States)

    Godoy, Benigno; Wörner, Gerhard; Le Roux, Petrus; de Silva, Shanaka; Parada, Miguel Ángel; Kojima, Shoji; González-Maurel, Osvaldo; Morata, Diego; Polanco, Edmundo; Martínez, Paula

    2017-07-01

    Subduction-related magmas that erupted in the Central Andes during the past 10 Ma are strongly affected by crustal assimilation as revealed by an increase in 87Sr/86Sr isotope ratios with time that in turn are correlated with increased crustal thickening during the Andean orogeny. However, contamination is not uniform and can be strongly influenced locally by crustal composition, structure and thermal condition. This appears to be the case along the NW-SE San Pedro - Linzor volcanic chain (SPLVC) in northern Chile, which straddles the boundary of a major zone of partial melt, the Altiplano_Puna Magma Body (APMB). Herein we report 40Ar/39Ar ages, compositional and isotope data on lavas from the SPLVC that track the influence of this zone of partial melting on erupted lavas with geochronological and geochemical data. Ages reported here indicate that SPLVC has evolved in the last 2 M.y., similar to other volcanoes of the Western Cordillera (e.g. Lascar, Uturuncu, Putana). 87Sr/86Sr ratios increase systematically along the chain from a minimum value of 0.7057 in San Pedro dacites to a maximum of 0.7093-0.7095 for the Toconce and Cerro de Leon dacites in the SE. These changes are interpreted to reflect the increasing interaction of SPLVC parental magmas with partial melt within the APMB eastwards across the chain. The 87Sr/86Sr ratio and an antithetic trend in 143Nd/144Nd is therefore a proxy for the contribution of melt from the APMB beneath this volcanic chain. Similar 87Sr/86Sr increases and 143Nd/144Nd decreases are observed in other transects crossing the boundary of the APMB. Such trends can be recognized from NW to SE between Aucanquilcha, Ollagüe, and Uturuncu volcanoes, and from Lascar volcano to the N-S-trending Putana-Sairecabur-Licancabur volcanic chain to the north. We interpret these isotopic trends as reflecting different degrees of interaction of mafic parental melts with the APMB. High 87Sr/86Sr, and low 143Nd/144Nd reveal zones where the APMB is

  3. Upper limits for the photoproduction cross section for the Φ--(1860) pentaquark state off the deuteron

    Science.gov (United States)

    Egiyan, H.; Langheinrich, J.; Gothe, R. W.; Graham, L.; Holtrop, M.; Lu, H.; Mattione, P.; Mutchler, G.; Park, K.; Smith, E. S.; Stepanyan, S.; Zhao, Z. W.; Adhikari, K. P.; Aghasyan, M.; Anghinolfi, M.; Baghdasaryan, H.; Ball, J.; Baltzell, N. A.; Battaglieri, M.; Bedlinskiy, I.; Bennett, R. P.; Biselli, A. S.; Bookwalter, C.; Branford, D.; Briscoe, W. J.; Brooks, W. K.; Burkert, V. D.; Carman, D. S.; Celentano, A.; Chandavar, S.; Contalbrigo, M.; D'Angelo, A.; Daniel, A.; Dashyan, N.; de Vita, R.; de Sanctis, E.; Deur, A.; Dey, B.; Dickson, R.; Djalali, C.; Doughty, D.; Dupre, R.; El Alaoui, A.; El Fassi, L.; Eugenio, P.; Fedotov, G.; Fegan, S.; Fradi, A.; Gabrielyan, M. Y.; Gevorgyan, N.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Goetz, J. T.; Gohn, W.; Golovatch, E.; Griffioen, K. A.; Guidal, M.; Guler, N.; Guo, L.; Gyurjyan, V.; Hafidi, K.; Hakobyan, H.; Hanretty, C.; Heddle, D.; Hicks, K.; Ilieva, Y.; Ireland, D. G.; Ishkhanov, B. S.; Jo, H. S.; Joo, K.; Khetarpal, P.; Kim, A.; Kim, W.; Klein, A.; Klein, F. J.; Kubarovsky, V.; Kuleshov, S. V.; Livingston, K.; MacGregor, I. J. D.; Mao, Y.; Mayer, M.; McKinnon, B.; Mokeev, V.; Munevar, E.; Nadel-Turonski, P.; Ni, A.; Niculescu, G.; Ostrovidov, A. I.; Paolone, M.; Pappalardo, L.; Paremuzyan, R.; Park, S.; Pasyuk, E.; Anefalos Pereira, S.; Phelps, E.; Pogorelko, O.; Pozdniakov, S.; Price, J. W.; Procureur, S.; Protopopescu, D.; Raue, B. A.; Ricco, G.; Rimal, D.; Ripani, M.; Ritchie, B. G.; Rosner, G.; Rossi, P.; Sabatié, F.; Saini, M. S.; Salgado, C.; Schott, D.; Schumacher, R. A.; Seder, E.; Seraydaryan, H.; Sharabian, Y. G.; Smith, G. D.; Sober, D. I.; Stepanyan, S. S.; Strauch, S.; Taiuti, M.; Tang, W.; Taylor, C. E.; Tedeschi, D. J.; Ungaro, M.; Voutier, E.; Watts, D. P.; Weinstein, L. B.; Weygand, D. P.; Wood, M. H.; Zachariou, N.; Zana, L.; Zhao, B.

    2012-01-01

    We searched for the Φ--(1860) pentaquark in the photoproduction process off the deuteron in the Ξ-π--decay channel using CLAS. The invariant-mass spectrum of the Ξ-π- system does not indicate any statistically significant enhancement near the reported mass M=1.860 GeV. The statistical analysis of the sideband-subtracted mass spectrum yields a 90%-confidence-level upper limit of 0.7 nb for the photoproduction cross section of Φ--(1860) with a consecutive decay into Ξ-π- in the photon-energy range 4.5GeV

  4. An upper bound solution for the spread extrusion of elliptical sections

    International Nuclear Information System (INIS)

    Abrinia, K.; Makaremi, M.

    2007-01-01

    The three dimensional problem of extrusion of elliptical sections with side material flow or spread has been formulated using the upper bound theory. The shape of the die for such a process is such that it could allow the material to flow sideways as well as in the forward direction. When flat faced dies are used a deforming region is developed with dead metal zones. Therefore this deforming region has been represented in the formulation based on the definitions of streamlines and stream surfaces. A generalized kinematically admissible velocity field was then derived for this formulation and strain rate components obtained for the upper bound solution. The general formulation for the deforming region and the velocity and strain rate fields allow for the optimization of the upper bound solution so that the nearest geometry of the deforming region and dead metal zone to the actual one was obtained.Using this geometry a die with similar surfaces to those of the dead metal zone is designed having converging and diverging surfaces to lead the material flow. The analysis was also carried out for this die and results were obtained showing a reduction in the extrusion pressure compared to the flat faced die. Effects of reduction of area, shape complexity, spread ratio and friction on the extrusion process were also investigated

  5. Lower-crustal xenoliths from Jurassic kimberlite diatremes, upper Michigan (USA): Evidence for Proterozoic orogenesis and plume magmatism in the lower crust of the southern Superior Province

    Science.gov (United States)

    Zartman, Robert E.; Kempton, Pamela D.; Paces, James B.; Downes, Hilary; Williams, Ian S.; Dobosi, Gábor; Futa, Kiyoto

    2013-01-01

    Jurassic kimberlites in the southern Superior Province in northern Michigan contain a variety of possible lower-crustal xenoliths, including mafic garnet granulites, rare garnet-free granulites, amphibolites and eclogites. Whole-rock major-element data for the granulites suggest affinities with tholeiitic basalts. P–T estimates for granulites indicate peak temperatures of 690–730°C and pressures of 9–12 kbar, consistent with seismic estimates of crustal thickness in the region. The granulites can be divided into two groups based on trace-element characteristics. Group 1 granulites have trace-element signatures similar to average Archean lower crust; they are light rare earth element (LREE)-enriched, with high La/Nb ratios and positive Pb anomalies. Most plot to the left of the geochron on a 206Pb/€204Pb vs 207Pb/€204Pb diagram, and there was probably widespread incorporation of Proterozoic to Archean components into the magmatic protoliths of these rocks. Although the age of the Group 1 granulites is not well constrained, their protoliths appear to be have been emplaced during the Mesoproterozoic and to be older than those for Group 2 granulites. Group 2 granulites are also LREE-enriched, but have strong positive Nb and Ta anomalies and low La/Nb ratios, suggesting intraplate magmatic affinities. They have trace-element characteristics similar to those of some Mid-Continent Rift (Keweenawan) basalts. They yield a Sm–Nd whole-rock errorchron age of 1046 ± 140 Ma, similar to that of Mid-Continent Rift plume magmatism. These granulites have unusually radiogenic Pb isotope compositions that plot above the 207Pb/€204Pb vs 206Pb/€204Pb growth curve and to the right of the 4·55 Ga geochron, and closely resemble the Pb isotope array defined by Mid-Continent Rift basalts. These Pb isotope data indicate that ancient continental lower crust is not uniformly depleted in U (and Th) relative to Pb. One granulite xenolith, S69-5, contains quartz, and has a

  6. Microstructural and seismic properties of the upper mantle underneath a rifted continental terrane (Baja California): An example of sub-crustal mechanical asthenosphere?

    NARCIS (Netherlands)

    Palasse, L.N.; Vissers, R.L.M.; Paulssen, H.; Basu, A.R.; Drury, M.R.

    2012-01-01

    The Gulf of California rift is a young and active plate boundary that links the San Andreas strike-slip fault system in California to the oceanic spreading system of the East Pacific Rise. The xenolith bearing lavas of the San Quintin volcanic area provide lower crust and upper mantle samples from

  7. Large mammals from the Upper Neopleistocene reference sections in the Tunka rift valley, southwestern Baikal Region

    Science.gov (United States)

    Shchetnikov, A. A.; Klementiev, A. M.; Filinov, I. A.; Semeney, E. Yu.

    2015-03-01

    This work presents the data on new finds of fossil macrotheriofauna in the reference sections of the Upper Neopleistocene sediments in the Tunka rift valley (southwestern Baikal Region). The osteological material of a number of Late Neopleistocene mammals including extinct species rare for the Baikal region such as Crocuta spelaea, Panthera spelaea, and Spirocerus kiakhtensis (?) was directly dated with a radiocarbon (AMS) method. The obtained 14C data (18000-35000 years) allow one to rejuvenate significantly the upper limit of the common age interval of habitat of these animals in southern part of Eastern Siberia. Cave hyena and spiral-horned antelope lived in the Tunka rift valley in the Baikal region in Late Kargino time (37-24 ka), and cave lion survived the maximum in the Sartan cryochron in the region (21-20 ka). The study of collected paleontological collections provides a basis for selection of independent Kargino (MIS 3) faunal assemblages to use them for regional biostratigraphic analysis of Pleistocene deposits. Radiocarbon age dating of samples allows one to attribute confidently all paleofaunal remains available to the second half of the Late Pleistocene.

  8. Upper gastrointestinal symptoms in autoimmune gastritis: A cross-sectional study.

    Science.gov (United States)

    Carabotti, Marilia; Lahner, Edith; Esposito, Gianluca; Sacchi, Maria Carlotta; Severi, Carola; Annibale, Bruno

    2017-01-01

    Autoimmune gastritis is often suspected for its hematologic findings, and rarely the diagnosis is made for the presence of gastrointestinal symptoms. Aims of this cross-sectional study were to assess in a large cohort of patients affected by autoimmune gastritis the occurrence and the pattern of gastrointestinal symptoms and to evaluate whether symptomatic patients are characterized by specific clinical features.Gastrointestinal symptoms of 379 consecutive autoimmune gastritis patients were systematically assessed and classified following Rome III Criteria. Association between symptoms and anemia pattern, positivity to gastric autoantibodies, Helicobacter pylori infection, and concomitant autoimmune disease were evaluated.In total, 70.2% of patients were female, median age 55 years (range 17-83). Pernicious anemia (53.6%), iron deficiency anemia (34.8%), gastric autoantibodies (68.8%), and autoimmune disorders (41.7%) were present. However, 56.7% of patients complained of gastrointestinal symptoms, 69.8% of them had exclusively upper symptoms, 15.8% only lower and 14.4% concomitant upper and lower symptoms. Dyspepsia, subtype postprandial distress syndrome was the most represented, being present in 60.2% of symptomatic patients. Univariate and multivariate analyses showed that age gastritis is associated in almost 60% of cases with gastrointestinal symptoms, in particular dyspepsia. Dyspepsia is strictly related to younger age, no smoking, and absence of anemia.

  9. First upper limits on the radar cross section of cosmic-ray induced extensive air showers

    Science.gov (United States)

    Abbasi, R. U.; Abe, M.; Abou Bakr Othman, M.; Abu-Zayyad, T.; Allen, M.; Anderson, R.; Azuma, R.; Barcikowski, E.; Belz, J. W.; Bergman, D. R.; Besson, D.; Blake, S. A.; Byrne, M.; Cady, R.; Chae, M. J.; Cheon, B. G.; Chiba, J.; Chikawa, M.; Cho, W. R.; Farhang-Boroujeny, B.; Fujii, T.; Fukushima, M.; Gillman, W. H.; Goto, T.; Hanlon, W.; Hanson, J. C.; Hayashi, Y.; Hayashida, N.; Hibino, K.; Honda, K.; Ikeda, D.; Inoue, N.; Ishii, T.; Ishimori, R.; Ito, H.; Ivanov, D.; Jayanthmurthy, C.; Jui, C. C. H.; Kadota, K.; Kakimoto, F.; Kalashev, O.; Kasahara, K.; Kawai, H.; Kawakami, S.; Kawana, S.; Kawata, K.; Kido, E.; Kim, H. B.; Kim, J. H.; Kim, J. H.; Kitamura, S.; Kitamura, Y.; Kunwar, S.; Kuzmin, V.; Kwon, Y. J.; Lan, J.; Lim, S. I.; Lundquist, J. P.; Machida, K.; Martens, K.; Matsuda, T.; Matsuyama, T.; Matthews, J. N.; Minamino, M.; Mukai, K.; Myers, I.; Nagasawa, K.; Nagataki, S.; Nakamura, T.; Nonaka, T.; Nozato, A.; Ogio, S.; Ogura, J.; Ohnishi, M.; Ohoka, H.; Oki, K.; Okuda, T.; Ono, M.; Oshima, A.; Ozawa, S.; Park, I. H.; Prohira, S.; Pshirkov, M. S.; Rezazadeh-Reyhani, A.; Rodriguez, D. C.; Rubtsov, G.; Ryu, D.; Sagawa, H.; Sakurai, N.; Sampson, A. L.; Scott, L. M.; Schurig, D.; Shah, P. D.; Shibata, F.; Shibata, T.; Shimodaira, H.; Shin, B. K.; Smith, J. D.; Sokolsky, P.; Springer, R. W.; Stokes, B. T.; Stratton, S. R.; Stroman, T. A.; Suzawa, T.; Takai, H.; Takamura, M.; Takeda, M.; Takeishi, R.; Taketa, A.; Takita, M.; Tameda, Y.; Tanaka, H.; Tanaka, K.; Tanaka, M.; Thomas, S. B.; Thomson, G. B.; Tinyakov, P.; Tkachev, I.; Tokuno, H.; Tomida, T.; Troitsky, S.; Tsunesada, Y.; Tsutsumi, K.; Uchihori, Y.; Udo, S.; Urban, F.; Vasiloff, G.; Venkatesh, S.; Wong, T.; Yamane, R.; Yamaoka, H.; Yamazaki, K.; Yang, J.; Yashiro, K.; Yoneda, Y.; Yoshida, S.; Yoshii, H.; Zollinger, R.; Zundel, Z.

    2017-01-01

    TARA (Telescope Array Radar) is a cosmic ray radar detection experiment colocated with Telescope Array, the conventional surface scintillation detector (SD) and fluorescence telescope detector (FD) near Delta, Utah, U.S.A. The TARA detector combines a 40 kW, 54.1 MHz VHF transmitter and high-gain transmitting antenna which broadcasts the radar carrier over the SD array and within the FD field of view, towards a 250 MS/s DAQ receiver. TARA has been collecting data since 2013 with the primary goal of observing the radar signatures of extensive air showers (EAS). Simulations indicate that echoes are expected to be short in duration (∼ 10 μs) and exhibit rapidly changing frequency, with rates on the order 1 MHz/μs. The EAS radar cross-section (RCS) is currently unknown although it is the subject of over 70 years of speculation. A novel signal search technique is described in which the expected radar echo of a particular air shower is used as a matched filter template and compared to waveforms obtained by triggering the radar DAQ using the Telescope Array fluorescence detector. No evidence for the scattering of radio frequency radiation by EAS is obtained to date. We report the first quantitative RCS upper limits using EAS that triggered the Telescope Array Fluorescence Detector. The transmitter is under the direct control of experimenters, and in a radio-quiet area isolated from other radio frequency (RF) sources. The power and radiation pattern are known at all times. Forward power up to 40 kW and gain exceeding 20 dB maximize energy density in the radar field. Continuous wave (CW) transmission gives 100% duty cycle, as opposed to pulsed radar. TARA utilizes a high sample rate DAQ (250 MS/s). TARA is colocated with a large state-of-the-art conventional CR observatory, allowing the radar data stream to be sampled at the arrival times of known cosmic ray events. Each of these attributes of the TARA detector has been discussed in detail in the literature [8]. A map

  10. Recent crustal movements

    Science.gov (United States)

    Maelzer, H.

    Calculation of temporal height changes for the determination of recent vertical crustal movements in northern, western, and southern Germany is described. Precise geodetic measurements and their analysis for the determination of recent crustal movements in north-eastern Iceland, western Venezuela, and central Peru are described. Determination of recent vertical crustal movements by leveling and gravity data; geodetic modeling of deformations and recent crustal movements; geodetic modeling of plate motions; and instrumental developments in geodetic measuring are discussed.

  11. Crustal and upper mantle shear velocities of Iberia, the Alboran Sea, and North Africa from ambient noise and ballistic finite-frequency Rayleigh wave tomography

    Science.gov (United States)

    Palomeras, I.; Villasenor, A.; Thurner, S.; Levander, A.; Gallart, J.; mimoun, H.

    2013-12-01

    The complex Mesozoic-Cenozoic Alpine deformation in the western Mediterranean extends from the Pyrenees in northern Spain to the Atlas Mountains in southern Morocco. The Iberian plate was accreted to the European plate in late Cretaceous, resulting in the formation of the Pyrenees. Cenozoic African-European convergence resulted in subduction of the Tethys oceanic plate beneath Europe. Rapid Oligocene slab rollback from eastern Iberia spread eastward and southward, with the trench breaking into three segments by the time it reached the African coast. One trench segment moved southwestward and westward creating the Alboran Sea, floored by highly extended continental crust, and building the encircling Betics Rif mountains comprising the Gibraltar arc, and the Atlas mountains, which formed as the inversion of a Jurassic rift. A number of recent experiments have instrumented this region with broad-band arrays (the US PICASSO array, Spanish IberArray and Siberia arrays, the University of Munster array), which, including the Spanish, Portuguese, and Moroccan permanent networks, provide a combined array of 350 stations having an average interstation spacing of ~60 km. Taking advantage of this dense deployment, we have calculated the Rayleigh waves phase velocities from ambient noise for short periods (4 s to 40 s) and teleseismic events for longer periods (20 s to 167 s). Approximately 50,000 stations pairs were used to measure the phase velocity from ambient noise and more than 160 teleseismic events to measure phase velocity for longer periods. The inversion of the phase velocity dispersion curves provides a 3D shear velocity for the crust and uppermost mantle. Our results show differences between the various tectonic regions that extend to upper mantle depths (~200 km). In Iberia we obtain, on average, higher upper mantle shear velocities in the western Variscan region than in the younger eastern part. We map high upper mantle velocities (>4.6 km/s) beneath the

  12. Biostratigraphy of the Upper Cretaceous deposits in north of Birjand, (Shushud section

    Directory of Open Access Journals (Sweden)

    farah jalili

    2014-11-01

    Full Text Available Introduction: One of the first works about Cretaceous deposits in eastern part of the Lut Block is done by Stocklin et al. (1972. They reported Orbitolina limestones in Shah Kuh area and Maasterichtian siliciclastic and limestone beds which have overlaid the older deposits with a gap. In geological maps of the east of Iran, Upper Cretaceous deposits have been reported (Berthiaux et al., 1990; Eftekharnejad, 1991; Berberian and Soheili, 1992; Alvai Naini, 1983; Guillou et al., 1981 that they have been mostly referred to shallow and relatively deep facies. Moreover, Gorgich (2002, Gorgich et al. (2009 and Motie (2010 reported Maastrichtian deposits in the east of Iran. The study area is located at Geological Quadrangle Map of Qayen (Berthiaux et al., 1990 and Geological Sheet Map of Roum (Shahidi et al., 2000. The measured section is geographically situated at 33o 05′ north latitude and 59o 02′ east longitude. Aims and Method: This paper aims to study lithostratigraphy, identification of foraminifera assemblage, age determination, and biostratigraphy and biozonation of the measured section. The authors hope this research lead to a better understanding of the regional geology and distribution of Cretaceous foraminifera that might describe the degree of lithostratigraphic and biostratigraphic precision. In this research 160 samples have been collected which 130 samples were cut and thin sections were prepared. The other samples were disaggregated in dilute H2O2 (10% vol. and washed. The washed residues were dried and picked the isolated forams. Thin sections studied under Olympus microscope and the foraminifera were identified and photographed. The isolated forms were photographed with Scanning Electronic Microscope (SEM device model XL30 Philips in Technical Faculty of Tehran University. Discussion and results (Lithostratigraphy and biostratigraphy: From point of view of lithostratigraphy, the lower contact of the succession is faulted and the

  13. Psychosocial reactions to upper extremity limb salvage: A cross-sectional study.

    Science.gov (United States)

    Sposato, Lindsay; Yancosek, Kathleen; Lospinoso, Josh; Cancio, Jill

    2017-08-09

    Descriptive cross-sectional survey study. Limb salvage spares an extremity at risk for amputation after a major traumatic injury. Psychosocial recovery for individuals with lower extremity limb salvage has been discussed in the literature. However, to date, psychosocial reactions for individuals with upper extremity (UE) limb salvage have not been examined. To determine which factors may influence psychosocial adaptation to UE limb salvage. Participants (n = 30; 28 males) were adults (mean, 30.13; range, 18-61) who sustained an UE limb salvage from a traumatic event. Adaptation was measured using a modified version of the Reactions to Impairment and Disability Inventory. A linear mixed-effects regression found that worse psychosocial adaptation was associated with having less than a college degree, being less than 6 months post-injury, being older than 23 years, and having more pain. Dominant hand injuries were found to influence poor adaptation on the denial Reactions to Impairment and Disability Inventory subscale only. The results of this study indicate that there is potential for nonadaptive reactions and psychological distress with certain variables in UE limb salvage. Therapists may use these results to anticipate which clients may be at risk for poor psychosocial outcomes. This study indicates the need for early consideration to factors that affect psychological prognosis for the UE limb salvage population. However, future research is indicated to better understand the unique psychosocial challenges and needs of these individuals. 4. Copyright © 2017 Hanley & Belfus. Published by Elsevier Inc. All rights reserved.

  14. Upper crustal structure of the northern part of the Bohemian ­Massif in ­rel­ation­ t­o geological, potential field data and new deep seismic data (Eger/Ohře Rift, Central Europe)

    Czech Academy of Sciences Publication Activity Database

    Skácelová, Z.; Mlčoch, B.; Novotný, Miroslav; Mrlina, Jan

    2011-01-01

    Roč. 39, č. 1 (2011), s. 1-18 ISSN 0303-4534 R&D Projects: GA AV ČR IAA300460602; GA MŽP SB/630/3/02 Institutional research plan: CEZ:AV0Z30120515 Keywords : upper crustal structure * Bohemian Massif * Eger/Ohře Rift * Saxothuringian Zone * Teplá-Barrandian Unit * Moldanubian Zone Subject RIV: DC - Siesmology, Volcanology, Earth Structure

  15. Thickening the outer margins of the Tibetan Plateau: The role of crustal shortening

    Science.gov (United States)

    Lease, R. O.; Burbank, D. W.

    2012-12-01

    One of the most direct consequences of the collision of two buoyant continents is large-scale crustal thickening that results in the upward and outward growth of high terrain. As the stronger Indian continent has collided with weaker Asia over at least the past 50 Myr, widespread crustal thickening has occurred over an area that is approximately 2.5 million km^2 at present. The resultant Tibetan crust is the thickest observed on Earth today with an average thickness of 65 km and a maximum that may reach 90 km in places. The mechanisms by which Tibetan crust has thickened, however, as well as the timing and distribution of these mechanisms across the plateau, remain debatable. Two of the most popular mechanisms for thickening the crust beneath the margins of the Tibetan Plateau are: 1) pure shear with faulting and folding in the upper crust and horizontal shortening below; and 2) flow and inflation of lower or middle crust without significant shortening of the upper crust. To help discriminate between the relative contributions of these two mechanisms, well-constrained estimates of upper crustal shortening are needed. Here we document the Cenozoic shortening budget across the northeastern Tibetan Plateau margin near 36°N 102.5°E with several 100- to 145-km-long balanced cross sections. Thermochronological and magnetostratigraphic data indicate that modest NNE-SSW shortening began in middle Eocene time, shortly after initial India-Asia collision. Accelerated east-west shortening, however, did not commence until ~35 Myr later. A five-fold acceleration in shortening rates in middle Miocene-to-Recent time accounts for more than half of the total Cenozoic crustal shortening and thickening in this region. Overall, the balanced cross sections indicate 11 ± 2 % east-west shortening since middle Miocene time, and ~9 ± 2 % NNE-SSW shortening between middle Eocene and middle Miocene times. Given the present-day crustal thickness of 56 ± 4 km in northeastern Tibet, crustal

  16. Upper Limits of the Fission Cross-Sections of Lead and Bismuth for Li-D Neutrons

    Energy Technology Data Exchange (ETDEWEB)

    Broda, E.

    1945-07-01

    This report was written by E. Broda and P.K. Wright at the Cavendish Laboratory (Cambridge) in April 1945 and is about the upper limits of the fission cross sections of lead and bismuth for Li-D neutrons. This report includes the experiment description and the discussion of the results. (nowak)

  17. Insights into the emplacement of upper-crustal plutons and their relationship to large silicic calderas, from field relationships, geochronology, and zircon trace element geochemistry in the Stillwater - Clan Alpine caldera complex, western Nevada, USA

    Science.gov (United States)

    Colgan, Joseph P.; John, David A.; Henry, Christopher D.; Watts, Kathryn E.

    2018-01-01

    Geologic mapping, new U-Pb zircon ages, and new and published 40Ar/39Ar sanidine ages document the timing and extent of Oligocene magmatism in the southern Stillwater Range and Clan Alpine Mountains of western Nevada, where Miocene extension has exposed at least six nested silicic calderas and underlying granitic plutons to crustal depths locally ≥ 9 km. Both caldera-forming rhyolitic tuffs and underlying plutons were emplaced in two episodes, one from about 30.4-28.2 Ma that included the Deep Canyon, Job Canyon, and Campbell Creek calderas and underlying plutons, and one from about 25.3-24.8 Ma that included the Louderback Mountains, Poco Canyon, and Elevenmile Canyon calderas and underlying plutons. In these two 1-2 m.y. periods, almost the entire Mesozoic upper crust was replaced by Oligocene intrusive and extrusive rocks to depths ≥ 9 km over an estimated total area of 1500 km2 (pre-extension). Zircon trace element geochemistry indicates that some plutonic rock can be solidified residual magma from the tuff eruptions. Most plutons are not solidified residual magma, although they directly underlie calderas and were emplaced along the same structures shortly after to as much as one million years after caldera formation. Magma chambers and plutons grew by floor subsidence accommodated by downward transfer of country rocks. If other Great Basin calderas are similar, the dense concentration of shallowly exposed calderas in central Nevada is underlain by a complexly zoned mid-Cenozoic batholith assembled in discrete pulses that coincided with formation of large silicic calderas up to 2500-5000 km3.

  18. Insights into the emplacement of upper-crustal plutons and their relationship to large silicic calderas, from field relationships, geochronology, and zircon trace element geochemistry in the Stillwater – Clan Alpine caldera complex, western Nevada, USA

    Science.gov (United States)

    Colgan, Joseph P.; John, David A.; Henry, Christopher D.; Watts, Kathryn E.

    2018-01-01

    Geologic mapping, new U-Pb zircon ages, and new and published 40Ar/39Ar sanidine ages document the timing and extent of Oligocene magmatism in the southern Stillwater Range and Clan Alpine Mountains of western Nevada, where Miocene extension has exposed at least six nested silicic calderas and underlying granitic plutons to crustal depths locally ≥ 9 km. Both caldera-forming rhyolitic tuffs and underlying plutons were emplaced in two episodes, one from about 30.4–28.2 Ma that included the Deep Canyon, Job Canyon, and Campbell Creek calderas and underlying plutons, and one from about 25.3–24.8 Ma that included the Louderback Mountains, Poco Canyon, and Elevenmile Canyon calderas and underlying plutons. In these two 1–2 m.y. periods, almost the entire Mesozoic upper crust was replaced by Oligocene intrusive and extrusive rocks to depths ≥ 9 km over an estimated total area of ~ 1500 km2 (pre-extension). Zircon trace element geochemistry indicates that some plutonic rock can be solidified residual magma from the tuff eruptions. Most plutons are not solidified residual magma, although they directly underlie calderas and were emplaced along the same structures shortly after to as much as one million years after caldera formation. Magma chambers and plutons grew by floor subsidence accommodated by downward transfer of country rocks. If other Great Basin calderas are similar, the dense concentration of shallowly exposed calderas in central Nevada is underlain by a complexly zoned mid-Cenozoic batholith assembled in discrete pulses that coincided with formation of large silicic calderas up to 2500–5000 km3.

  19. Modes of continental extension in a crustal wedge

    KAUST Repository

    Wu, Guangliang

    2015-07-01

    © 2015 Elsevier B.V. We ran numerical experiments of the extension of a crustal wedge as an approximation to extension in an orogenic belt or a continental margin. We study the effects of the strength of the lower crust and of a weak mid-crustal shear zone on the resulting extension styles. A weak mid-crustal shear zone effectively decouples upper crustal extension from lower crustal flow. Without the mid-crustal shear zone, the degree of coupling between the upper and the lower crust increases and extension of the whole crust tends to focus on the thickest part of the wedge. We identify three distinct modes of extension determined by the strength of the lower crust, which are characterized by 1) localized, asymmetric crustal exhumation in a single massif when the lower crust is weak, 2) the formation of rolling-hinge normal faults and the exhumation of lower crust in multiple core complexes with an intermediate strength lower crust, and 3) distributed domino faulting over the weak mid-crustal shear zone when the lower crust is strong. A frictionally stronger mid-crustal shear zone does not change the overall model behaviors but extension occurred over multiple rolling-hinges. The 3 modes of extension share characteristics similar to geological models proposed to explain the formation of metamorphic core complexes: 1) the crustal flow model for the weak lower crust, 2) the rolling-hinge and crustal flow models when the lower crust is intermediate and 3) the flexural uplift model when the lower crust is strong. Finally we show that the intensity of decoupling between the far field extension and lower crustal flow driven by the regional pressure gradient in the wedge control the overall style of extension in the models.

  20. Modes of continental extension in a crustal wedge

    KAUST Repository

    Wu, Guangliang; Lavier, Luc L.; Choi, Eunseo

    2015-01-01

    © 2015 Elsevier B.V. We ran numerical experiments of the extension of a crustal wedge as an approximation to extension in an orogenic belt or a continental margin. We study the effects of the strength of the lower crust and of a weak mid-crustal shear zone on the resulting extension styles. A weak mid-crustal shear zone effectively decouples upper crustal extension from lower crustal flow. Without the mid-crustal shear zone, the degree of coupling between the upper and the lower crust increases and extension of the whole crust tends to focus on the thickest part of the wedge. We identify three distinct modes of extension determined by the strength of the lower crust, which are characterized by 1) localized, asymmetric crustal exhumation in a single massif when the lower crust is weak, 2) the formation of rolling-hinge normal faults and the exhumation of lower crust in multiple core complexes with an intermediate strength lower crust, and 3) distributed domino faulting over the weak mid-crustal shear zone when the lower crust is strong. A frictionally stronger mid-crustal shear zone does not change the overall model behaviors but extension occurred over multiple rolling-hinges. The 3 modes of extension share characteristics similar to geological models proposed to explain the formation of metamorphic core complexes: 1) the crustal flow model for the weak lower crust, 2) the rolling-hinge and crustal flow models when the lower crust is intermediate and 3) the flexural uplift model when the lower crust is strong. Finally we show that the intensity of decoupling between the far field extension and lower crustal flow driven by the regional pressure gradient in the wedge control the overall style of extension in the models.

  1. Primary Lateral Sclerosis and Early Upper Motor Neuron Disease: Characteristics of a Cross-Sectional Population.

    Science.gov (United States)

    Fournier, Christina N; Murphy, Alyssa; Loci, Lorena; Mitsumoto, Hiroshi; Lomen-Hoerth, Catherine; Kisanuki, Yasushi; Simmons, Zachary; Maragakis, Nicholas J; McVey, April L; Al-Lahham, Tawfiq; Heiman-Patterson, Terry D; Andrews, Jinsy; McDonnell, Erin; Cudkowicz, Merit; Atassi, Nazem

    2016-03-01

    The goals of this study were to characterize clinical and electrophysiologic findings of subjects with upper motor neuron disease and to explore feasibility of clinical trials in this population. Twenty northeast amyotrophic lateral sclerosis consortium (northeast amyotrophic lateral sclerosis) sites performed chart reviews to identify active clinical pure upper motor neuron disease patients. Patients with hereditary spastic paraplegia or meeting revised El Escorial electrodiagnostic criteria for amyotrophic lateral sclerosis were excluded. Patients were classified into 2 groups according to the presence or absence of minor electromyography (EMG) abnormalities. Two hundred thirty-three subjects with upper motor neuron disease were identified; 217 had available EMG data. Normal EMGs were seen in 140 subjects, and 77 had minor denervation. Mean disease duration was 84 (±80) months for the entire cohort with no difference seen between the 2 groups. No difference was seen in clinical symptoms, disability, or outcome measures between the 2 groups after correcting for multiple comparisons. Minor EMG abnormalities were not associated with phenotypic differences in a clinical upper motor neuron disease population. These findings suggest that subtle EMG abnormalities can not necessarily be used as a prognostic tool in patients with clinical upper motor neuron disease. This study also demonstrates the availability of a large number of patients with upper motor neuron diseases within the northeast amyotrophic lateral sclerosis network and suggests feasibility for conducting clinical trials in this population.

  2. CLINICAL REABILITATION OF UPPER LIMB IN CHRONIC STROKE IN PORTUGAL A CROSS SECTIONAL SURVEY

    Directory of Open Access Journals (Sweden)

    Andre Vieira

    2016-02-01

    Full Text Available Background: More than 77% of stroke survivors have upper limb dysfunction. The scientific evidence for interventions in upper limb rehabilitation in stroke has shown variable results. To improve health care treatments in this domain it is needed to know what modalities are actually being used by physiotherapists. Methods: A national web-based survey focused in characterizing the profile of Portuguese physiotherapists working in post-stroke upper limb rehabilitation was conducted in 237 health institutions (n= 462 physiotherapists. The recruitment was conducted from August to December 2014. Analytic and descriptive analysis were used. Results: A total of 179 physiotherapists from 64 different locations from Portugal answered the survey, with a rate of response of 38.7%. The average age of respondents was 29.25±6.4 years old and predominantly finished the graduation or bachelor degree between 2001 and 2010. More than half hadn´t carried out any specialization in neurologic rehabilitation area. The top 5 modalities most used in the rehabilitation of upper limb in acute stroke are Goal Oriented Tasks (93.4% n=141, Motor Learning (89.4% n=135, Passive Mobilization (88.7% n=134, Task Repetition (87.4% n=132 and Bobath/Neurodevelopmental Therapy (86.9% n=131. Conclusions: The main modalities used for physiotherapists in upper limb rehabilitation in acute stroke have sparse levels of evidence. It is important to alert teachers, formers, physiotherapists and students for interventions with supported scientific results.

  3. Upper limb vein anatomy before hemodialysis fistula creation: cross-sectional anatomy using MR venography

    International Nuclear Information System (INIS)

    Laissy, Jean-Pierre; Fernandez, Pedro; Karila-Cohen, Pascale; Chillon, Sylvie; Schouman-Claeys, Elisabeth; Delmas, Vincent; Dupuy, Emmanuel; Mignon, Francoise

    2003-01-01

    Preoperative imaging is indicated to discriminate patent, adequate superficial veins of the upper limbs undetectable by clinical inspection that could be anastomosed for the creation of a durable and functional hemodialysis fistula. The aim of this pictorial review is to provide a venous anatomic map of the upper limbs using MR venography (MRV) which could help surgeons before creation of hemodialysis access fistulas (AVF). At the level of the forearm, the antebrachial cephalic vein is the most commonly identified as patent. At the level of the elbow and distal arm, the cephalic vein is patent in 80% of normal subjects, and less often patent (23-26%) than basilic vein (33-38%) in patients. Overall, reading transaxial MR views can help for assessing upper limb vein anatomy before creation of a hemodialysis access fistula. (orig.)

  4. Upper limb vein anatomy before hemodialysis fistula creation: cross-sectional anatomy using MR venography

    Energy Technology Data Exchange (ETDEWEB)

    Laissy, Jean-Pierre; Fernandez, Pedro; Karila-Cohen, Pascale; Chillon, Sylvie; Schouman-Claeys, Elisabeth [Department of Radiology, Hopital Bichat, 46 rue Henri Huchard, 75877 Paris Cedex 18 (France); Delmas, Vincent [Department of Urology, Hopital Bichat, 46 rue Henri Huchard, 75877 Paris Cedex 18 (France); Dupuy, Emmanuel; Mignon, Francoise [Department of Nephrology, Hopital Bichat, 46 rue Henri Huchard, 75877 Paris Cedex 18 (France)

    2003-02-01

    Preoperative imaging is indicated to discriminate patent, adequate superficial veins of the upper limbs undetectable by clinical inspection that could be anastomosed for the creation of a durable and functional hemodialysis fistula. The aim of this pictorial review is to provide a venous anatomic map of the upper limbs using MR venography (MRV) which could help surgeons before creation of hemodialysis access fistulas (AVF). At the level of the forearm, the antebrachial cephalic vein is the most commonly identified as patent. At the level of the elbow and distal arm, the cephalic vein is patent in 80% of normal subjects, and less often patent (23-26%) than basilic vein (33-38%) in patients. Overall, reading transaxial MR views can help for assessing upper limb vein anatomy before creation of a hemodialysis access fistula. (orig.)

  5. Upper Secondary French Students, Chemical Transformations and the "Register of Models": A Cross-Sectional Study

    Science.gov (United States)

    Cokelez, Aytekin; Dumon, Alain; Taber, Keith S.

    2008-01-01

    The purpose of this study is to identify how upper secondary school French students (Grade 10-12) interpret chemical transformation with regards to the changes within molecules and atoms, and in terms of intramolecular and/or intermolecular bond breaking. In order to identify and describe the students' assimilated knowledge, four questions were…

  6. Along-Axis Structure and Crustal Construction Processes of Spreading Segments in Iceland: Implications for Magmatic Rifts

    Science.gov (United States)

    Siler, D. L.; Karson, J. A.

    2017-10-01

    Magmatic rift systems are composed of discrete spreading segments defined by morphologic, structural, and volcanic features that vary systematically along strike. In Iceland, structural features mapped in the glaciated and exhumed Miocene age upper crust correlate with analogous features in the seismically and volcanically active neovolcanic zone. Integrating information from both the active rift zones and ancient crust provides a three-dimensional perspective of crustal structure and the volcanic and tectonic processes that construct crust along spreading segments. Crustal exposures in the Skagi region of northern Iceland reveal significant along-strike variations in geologic structure. The upper crust at exhumed magmatic centers (segment centers) is characterized by a variety of intrusive rocks, high-temperature hydrothermal alteration, and geologic evidence for kilometer-scale subsidence. In contrast, the upper crust along segment limbs, which extend along strike from magmatic centers, is characterized by thick sections of gently dipping lava flows, cut by varying proportions of subvertical dikes. This structure implies relatively minor upper crustal subsidence and lateral dike intrusion. The differing modes of subsidence beneath segment centers and segment limbs require along-axis mass redistribution in the underlying upper, middle, and lower crust during crustal construction. This along-axis material transport is accomplished through lateral dike intrusion in the upper crust and by along-axis flow of magmatic to high-temperature solid-state gabbroic material in the middle and lower crust. These processes, inferred from outcrop evidence in Skagi, are consistent with processes inferred to be important during active rifting in Iceland and at analogous magmatic oceanic and continental rifts.

  7. Spatial distribution of planktonic bacterial and archaeal communities in the upper section of the tidal reach in Yangtze River

    Science.gov (United States)

    Fan, Limin; Song, Chao; Meng, Shunlong; Qiu, Liping; Zheng, Yao; Wu, Wei; Qu, Jianhong; Li, Dandan; Zhang, Cong; Hu, Gengdong; Chen, Jiazhang

    2016-01-01

    Bacterioplankton and archaeaplankton communities play key roles in the biogeochemical processes of water, and they may be affected by many factors. In this study, we used high-throughput 16S rRNA gene sequencing to profile planktonic bacterial and archaeal community compositions in the upper section of the tidal reach in Yangtze River. We found that the predominant bacterial phyla in this river section were Proteobacteria, Firmicutes, and Actinobacteria, whereas the predominant archaeal classes were Halobacteria, Methanomicrobia, and unclassified Euryarchaeota. Additionally, the bacterial and archaeal community compositions, richnesses, functional profiles, and ordinations were affected by the spatial heterogeneity related to the concentration changes of sulphate or nitrate. Notably, the bacterial community was more sensitive than the archaeal community to changes in the spatial characteristics of this river section. These findings provide important insights into the distributions of bacterial and archaeal communities in natural water habitats. PMID:27966673

  8. Constraints on the crustal structure beneath the Sinai subplate, SE Mediterranean, from analysis of local and regional travel times

    Directory of Open Access Journals (Sweden)

    Mohamed K. Salah

    2013-03-01

    Full Text Available The Sinai Peninsula has been recognized as a subplate of the African Plate located at the triple junction of the Gulf of Suez rift, the Dead Sea Transform fault, and the Red Sea rift. The upper and lower crustal structures of this tectonically active, rapidly developing region are yet poorly understood because of many limitations. For this reason, a set of P- and S-wave travel times recorded at 14 seismic stations belonging to the Egyptian National Seismographic Network (ENSN from 111 local and regional events are analyzed to investigate the crustal structures and the locations of the seismogenic zones beneath central and southern Sinai. Because the velocity model used for routine earthquake location by ENSN is one-dimensional, the travel-time residuals will show lateral heterogeneity of the velocity structures and unmodeled vertical structures. Seismic activity is strong along the eastern and southern borders of the study area but low to moderate along the northern boundary and the Gulf of Suez to the west. The crustal Vp/Vs ratio is 1.74 from shallow (depth ≤ 10 km earthquakes and 1.76 from deeper (depth > 10 km crustal events. The majority of the regional and local travel-time residuals are positive relative to the Preliminary Reference Earth Model (PREM, implying that the seismic stations are located above widely distributed, tectonically-induced low-velocity zones. These low-velocity zones are mostly related to the local crustal faults affecting the sedimentary section and the basement complex as well as the rifting processes prevailing in the northern Red Sea region and the ascending of hot mantle materials along crustal fractures. The delineation of these low-velocity zones and the locations of big crustal earthquakes enable the identification of areas prone to intense seismotectonic activities, which should be excluded from major future development projects and large constructions in central and southern Sinai.

  9. Radial nerve measurements in nonsymptomatic upper extremities of Filipinos: A cross-sectional study.

    Science.gov (United States)

    Gonzalez-Suarez, Consuelo B; Dones, Valentin C; Grimmer, Karen; Thoirs, Kerry; Milanese, Steven; Atlas, Alvin

    2015-10-01

    Despite reports on the association of radial nerve (RN) size and lateral epicondylalgia (LE), Filipino normative values on RN size in healthy elbows are not established. An association with upper extremity anthropometric measurements is likewise not reported. Musculoskeletal ultrasound measurements of the RN at the level of the lateral epicondyle (RN-LE), posterior interosseous nerve at the level of the radial head and supinator (PIN-RH and PIN-sup), and superficial RN (SRN) in the elbows of healthy Filipinos were made in Manila from January-September 2011. A total of 198 elbows of 99 healthy participants aged 43 years (range, 33-48 years) [median(IQR)] were investigated. Men have larger PIN-RH, PIN-sup, and SRN compared with women. Arm length was associated with PIN-RH, PIN-sup, and SRN (P values can now be used for comparison in elbows with LE. © 2015 Wiley Periodicals, Inc.

  10. High Intensity Physical Exercise and Pain in the Neck and Upper Limb among Slaughterhouse Workers: Cross-Sectional Study

    Directory of Open Access Journals (Sweden)

    Emil Sundstrup

    2014-01-01

    Full Text Available Slaughterhouse work involves a high degree of repetitive and forceful upper limb movements and thus implies an elevated risk of work-related musculoskeletal disorders. High intensity strength training effectively rehabilitates musculoskeletal disorders among sedentary employees, but less is known about the effect among workers with repetitive and forceful work demands. Before performing randomized controlled trials it may be beneficial to assess the cross-sectional connection between exercise and musculoskeletal pain. We investigated the association between high intensity physical exercise and pain among 595 slaughterhouse workers in Denmark, Europe. Using logistic regression analyses, odds ratios for pain and work disability as a function of physical exercise, gender, age, BMI, smoking, and job position were estimated. The prevalence of pain in the neck, shoulder, elbow, and hand/wrist was 48%, 60%, 40%, and 52%, respectively. The odds for experiencing neck pain were significantly lower among slaughterhouse workers performing physical exercise (OR = 0.70, CI: 0.49–0.997, whereas the odds for pain in the shoulders, elbow, or hand/wrist were not associated with exercise. The present study can be used as general reference of pain in the neck and upper extremity among slaughterhouse workers. Future studies should investigate the effect of high intensity physical exercise on neck and upper limb pain in slaughterhouse workers.

  11. Microfacies characteristics, sedimentary environments and sequence stratigraphy of Upper Cretaceous deposits in northwest of Nehbandan (Basiran section

    Directory of Open Access Journals (Sweden)

    Mohammad nabi Gorgij

    2015-10-01

    Full Text Available Introduction   The Basiran stratigraphic section is located about 160 km northwest of Nehbandan.The section was measured in detail at 59 06 30 N and 31 52 50 E. Nehbandan area with respect to fourfold geological subdivision of Iran is part of Central Iran that is located in the eastern flank of Lut Block which first time are studied by Stocklin et al.in 1972. Gorgij (2001 stratigraphically and paleontologically investigate Upper Cretaceous deposits in Mighan and Basiran sections. Upper Cretaceous deposits in in this area consists of 275m conglomerate,alternation of conglomerate-sandstone, sandy limestone -marl and limy marl, marl with intercalation of limestone-sandy limestone thin beds and medium-bedded to massive limestone. Microfacies analysis led to the recognition of 9 microfacies that are related to 5 belts; Coast, tidal flat, lagoon, shoal, shallow open marine and deep open marine environments. Main part of the section are deposited in the open marine environment that consist of marl,marly limestone and limestone. The doals of this study are : (1 describing and determining main carbonate and siliciclastic microfacies of late Cretaceous deposits (2 interpreting and providing depositional model for reconstruction of its paleoenvironmental setting based on microfacies characteristics (3 dividing the section based on lithostratigraphic principles and (4 recognizing a sequence stratigraphic model of this successions based on the vertical variation of facies,stratal key beds and stratal packing pattern.       Material and Method   The Basiran section as a complete stratigraphic section was measured and described. Up to 68 samples (indicated by KB1 to KB68 were collected and 170 thin sections are prepared. Based on field observations, sedimentological characteristics, parasequence stacking patterns, sequence boundary types and other key stratigraphical surfaces are identified and were obtained. Scheme of Dunham (1962 and Embry and Klovan

  12. Microfacies characteristics, sedimentary environments and sequence stratigraphy of Upper Cretaceous deposits in northwest of Nehbandan (Basiran section

    Directory of Open Access Journals (Sweden)

    Azadeh Bordbar

    2015-09-01

    Full Text Available   Introduction   The Basiran stratigraphic section is located about 160 km northwest of Nehbandan.The section was measured in detail at 59 06 30 N and 31 52 50 E. Nehbandan area with respect to fourfold geological subdivision of Iran is part of Central Iran that is located in the eastern flank of Lut Block which first time are studied by Stocklin et al.in 1972. Gorgij (2001 stratigraphically and paleontologically investigate Upper Cretaceous deposits in Mighan and Basiran sections. Upper Cretaceous deposits in in this area consists of 275m conglomerate,alternation of conglomerate-sandstone, sandy limestone -marl and limy marl, marl with intercalation of limestone-sandy limestone thin beds and medium-bedded to massive limestone. Microfacies analysis led to the recognition of 9 microfacies that are related to 5 belts Coast, tidal flat, lagoon, shoal, shallow open marine and deep open marine environments. Main part of the section are deposited in the open marine environment that consist of marl,marly limestone and limestone. The doals of this study are : (1 describing and determining main carbonate and siliciclastic microfacies of late Cretaceous deposits (2 interpreting and providing depositional model for reconstruction of its paleoenvironmental setting based on microfacies characteristics (3 dividing the section based on lithostratigraphic principles and (4 recognizing a sequence stratigraphic model of this successions based on the vertical variation of facies,stratal key beds and stratal packing pattern.       Material and Method   The Basiran section as a complete stratigraphic section was measured and described. Up to 68 samples (indicated by KB1 to KB68 were collected and 170 thin sections are prepared. Based on field observations, sedimentological characteristics, parasequence stacking patterns, sequence boundary types and other key stratigraphical surfaces are identified and were obtained. Scheme of Dunham (1962 and Embry

  13. Crustal structure of Central Sicily

    Science.gov (United States)

    Giustiniani, Michela; Tinivella, Umberta; Nicolich, Rinaldo

    2018-01-01

    We processed crustal seismic profile SIRIPRO, acquired across Central Sicily. To improve the seismic image we utilized the wave equation datuming technique, a process of upward or downward continuation of the wave-field between two arbitrarily shaped surfaces. Wave equation datuming was applied to move shots and receivers to a given datum plane, removing time shifts related to topography and to near-surface velocity variations. The datuming procedure largely contributed to attenuate ground roll, enhance higher frequencies, increase resolution and improve the signal/noise ratio. Processed data allow recognizing geometries of crust structures differentiating seismic facies and offering a direct image of ongoing tectonic setting within variable lithologies characterizing the crust of Central Sicily. Migrated sections underline distinctive features of Hyblean Plateau foreland and above all a crustal thinning towards the Caltanissetta trough, to the contact with a likely deep Permo-Triassic rifted basin or rather a zone of a continent to oceanic transition. Inhomogeneity and fragmentation of Sicily crust, with a distinct separation of Central Sicily basin from western and eastern blocks, appear to have guided the tectonic transport inside the Caltanissetta crustal scale syncline and the accumulation of allochthonous terrains with south and north-verging thrusts. Major tectonic stack operated on the construction of a wide anticline of the Maghrebian chain in northern Sicily. Sequential south-verging imbrications of deep elements forming the anticline core denote a crust wedge indenting foreland structures. Deformation processes involved multiple detachment planes down to decoupling levels located near crust/mantle transition, supporting a presence of high-density lenses beneath the chain, interrelated to a southwards push of Tyrrhenian mantle and asthenosphere.

  14. The Middle and Upper Eocene sections of the Omsk trough, West Siberian Platform: Palynological, stratigraphic, hydrologic, and climatic aspects

    Science.gov (United States)

    Zaporozhets, N. I.; Akhmetiev, M. A.

    2013-01-01

    The thorough analysis and correlation of Middle-Upper Eocene sections in the Omsk trough (southern West Siberian Platform) recovered by Borehole 9 in its axial part near the Chistoozernoe Settlement (Novosibirsk region) and Borehole 8 on the southern limb near the Russkaya Polyana Settlement (southern Omsk region) revealed hiatuses at the base and top of the Russkaya Polyana Beds, a lithostratigraphic unit defined in the Lyulinvor Formation based on its substantially fine-grained composition and poor siliceous microplankton fossil remains. The overlying Tavda Formation (Middle-Upper Eocene) is traditionally accepted to consist of two subformations. The last formation was deposited in the West Siberian inner sea isolated from the Arctic basin. Particular attention is paid to eustatic sea level fluctuation especially during the period marked by accumulation of Azolla Beds under considerable desalination of surface waters in the basin. The curve of variations in the open sea factor based on the quantitative ratio between organic-walled phytoplankton fossils and higher plant palynomorphs is correlated with the modified version of the wellknown Vail curve. It is established that the West Siberian sea level experienced a brief rise in the terminal late Eocene prior to its complete desiccation at the Eocene-Oligocene transition because of global regression in response to glaciation in Antarctica.

  15. Global variations in gravity-derived oceanic crustal thickness: Implications on oceanic crustal accretion and hotspot-lithosphere interactions

    Science.gov (United States)

    Lin, J.; Zhu, J.

    2012-12-01

    the relatively wide partial melting zones in the upper mantle beneath the fast and intermediately fast ridges might act as "buffer" zones, thus diluting the melt anomalies from the underlying hotspots or regions of mantle heterogeneities. (3) As the crustal age increases and the lithospheric plate thickens, regions of thickened crust start to develop on ocean basins that were originally created at fast and intermediately fast ridges. The integrated crustal volume for fast and intermediately fast ocean crust appears to reach peak values for certain geological periods, such as 40-50 Ma and 70-80 Ma. The newly constructed global models of gravity-derived crustal thickness, combining with geochemical and other constraints, can be used to investigate the processes of oceanic crustal accretion and hotspot-lithosphere interactions.

  16. ASSESSMENT OF THE LOCALIZATION OF HYPOCENTERS OF CRUSTAL EARTHQUAKES RELATIVE TO THE DEPTH AND RELIEF OF THE BORDER DENSITY STRATIFICATION IN THE CRUST OF THE NORTHEASTERN SECTION OF THE REFERENCE GEOLOGICAL-GEOPHYSICAL PROFILE 3-DV

    Directory of Open Access Journals (Sweden)

    N. K. Gayday

    2017-01-01

    Full Text Available The total length of the seismic profiles in the northeastern regions ofRussiaand, accordingly, the area of the territories covered by the seismic data interpretations, remains insignificant in comparison with the total area of these regions. At the same time, the geological objects in the northeastern regions attract much attention in view of their prospects, including potential mineral resources. The challenge is to construct the regional models of the crust structure without deep seismic survey data, and to analyze the regional seismicity that depends on the features of the deep crust structure. We develop a density model of the crust structure using the new interpretational gravimetry method. The density modeling results show that the density changes in the crust can be used to estimate the position of a surface separating the lower (quasi-homogeneous and upper (heterogeneous parts of the crust, i.e. to assess the density boundary of stratification. This boundary is formed due to a complex of physical and chemical processes that facilitate the transition of the material in the lower part of the crust into the quasi-uniform (homogeneous state. The study area is the junction zone of the Ayan-Yuryakh anticlinorium and Inyali-Debin synclinorium (62‒63°N, 148‒152° E. The initial interpretation of the deep seismic survey data on the reference geological-geophysical profile 3-DV was available, so the ambiguity of the density modeling was reduced. In turn, the density modeling results can provide additional information for geological-geophysical interpretation of the DSS results on the sites wherein the seismic profiles go along the fault zones. The relationship between seismic events and the relief of the density boundary of stratification in the crust was studied quantitatively on the basis of the data from the regional catalog of seismic events and the results of the earlier analysis of seismicity in the study area. The analysis shows that

  17. Influence of mid-crustal rheology on the deformation behavior of continental crust in the continental subduction zone

    Science.gov (United States)

    Li, Fucheng; Sun, Zhen; Zhang, Jiangyang

    2018-06-01

    Although the presence of low-viscosity middle crustal layer in the continental crust has been detected by both geophysical and geochemical studies, its influence on the deformation behavior of continental crust during subduction remains poorly investigated. To illustrate the crustal deformation associated with layered crust during continental subduction, we conducted a suite of 2-D thermo-mechanical numerical studies with visco-brittle/plastic rheology based on finite-differences and marker-in-cell techniques. In the experiments, we established a three-layer crustal model with a quartz-rich middle crustal layer embedded between the upper and lower continental crust. Results show that the middle crustal layer determines the amount of the accreted upper crust, maximum subduction depth, and exhumation path of the subducted upper crust. By varying the initial effective viscosity and thickness of the middle crustal layer, the further effects can be summarized as: (1) a rheologically weaker and/or thicker middle crustal layer results in a larger percentage of the upper crust detaching from the underlying slab and accreting at the trench zone, thereby leading to more serious crustal deformation. The rest of the upper crust only subducts into the depths of high pressure (HP) conditions, causing the absence of ultra-high pressure (UHP) metamorphic rocks; (2) a rheologically stronger and/or thinner middle crustal layer favors the stable subduction of the continental crust, dragging the upper crust to a maximum depth of ∼100 km and forming UHP rocks; (3) the middle crustal layer flows in a ductile way and acts as an exhumation channel for the HP-UHP rocks in both situations. In addition, the higher convergence velocity decreases the amount of subducted upper crust. A detailed comparison of our modeling results with the Himalayan collisional belt are conducted. Our work suggests that the presence of low-viscosity middle crustal layer may be another possible mechanism for

  18. A Simple Endoscopic Technique for Measuring the Cross-Sectional Area of the Upper Airway in a Rabbit Model.

    Science.gov (United States)

    Wistermayer, Paul R; McIlwain, Wesley R; Ieronimakis, Nicholas; Rogers, Derek J

    2018-04-01

    Validate an accurate and reproducible method of measuring the cross-sectional area (CSA) of the upper airway. This is a prospective animal study done at a tertiary care medical treatment facility. Control images were obtained using endotracheal tubes of varying sizes. In vivo images were obtained from various timepoints of a concurrent study on subglottic stenosis. Using a 0° rod telescope, an instrument was placed at the level of interest, and a photo was obtained. Three independent and blinded raters then measured the CSA of the narrowest portion of the airway using open source image analysis software. Each blinded rater measured the CSA of 79 photos. The t testing to assess for accuracy showed no difference between measured and known CSAs of the control images ( P = .86), with an average error of 1.5% (SD = 5.5%). All intraclass correlation (ICC) values for intrarater agreement showed excellent agreement (ICC > .75). Interrater reliability among all raters in control (ICC = .975; 95% CI, .817-.995) and in vivo (ICC = .846;, 95% CI, .780-.896) images showed excellent agreement. We validate a simple, accurate, and reproducible method of measuring the CSA of the airway that can be used in a clinical or research setting.

  19. Magnetotelluric Investigations of the Yellowstone Caldera: Understanding the Emplacement of Crustal Magma Bodies

    Science.gov (United States)

    Gurrola, R. M.; Neal, B. A.; Bennington, N. L.; Cronin, R.; Fry, B.; Hart, L.; Imamura, N.; Kelbert, A.; Bowles-martinez, E.; Miller, D. J.; Scholz, K. J.; Schultz, A.

    2017-12-01

    Wideband magnetotellurics (MT) presents an ideal method for imaging conductive shallow magma bodies associated with contemporary Yellowstone-Snake River Plain (YSRP) magmatism. Particularly, how do these magma bodies accumulate in the mid to upper crust underlying the Yellowstone Caldera, and furthermore, what role do hydrothermal fluids play in their ascent? During the summer 2017 field season, two field teams from Oregon State University and the University of Wisconsin-Madison installed forty-four wideband MT stations within and around the caldera, and using data slated for joint 3-D inversion with existing seismic data, two 2-D vertical conductivity sections of the crust and upper mantle were constructed. These models, in turn, provide preliminary insight into the emplacement of crustal magma bodies and hydrothermal processes in the YSRP region.

  20. GIS-BASED EXPERIENCE OF INVESTIGATING THE STATUS OF SPAWNING AREAS WITHIN THE UPPER SECTION OF THE TSIMLYANSK RESERVOIR

    Directory of Open Access Journals (Sweden)

    N. S. Kalioujnaia

    2017-01-01

    Full Text Available This paper presents a GIS-based research approach to investigating the status and dynamics of spawning areas of the Tsimlyansk Reservoir (within Volgograd Region, one of the largest inland fishery water bodies in the South of Russia.The spawning areas were considered in terms of the concept of ecotone origin, of the highly dynamic aquatic-terrestrial transitional environment in which temporary flooding is the main factor determining the diversity of spawning habitats, recruitment conditions, as well as ecosystem productivity.The processing and interpretation of Landsat images for the spring and low-water seasons for years between 2005 and 2016, in combination with other data (large-scale topographic maps, fishery research, and scientific papers allowed revealing the location of main spawning areas within the reservoir’s Upper section and to calculate their areas.For three case study sites located on the left bank of the reservoir, the main natural and anthropogenic factors determining the spawning conditions were identified. Retrospective analysis and synthesis of data on young fish composition and abundance between 1980 and today confirmed the importance of these sites for fish recruitment as well as the opportunities for their improvement by means of restoration measures.The output maps present the spatial distribution of the spawning areas and the environmental factors directly or indirectly affecting fish recruitment conditions. The most impacted areas have been determined, including the areas affected by abrasion, siltation and eutrophication processes, as well as pollution of the aquatic zone and water protection zone of the reservoir.The results of the research are useful both for understanding the general environmental conditions of the Tsimlyansk Reservoir and for supporting management decisions towards its improvement. 

  1. Concurrent acute illness and comorbid conditions poorly predict antibiotic use in upper respiratory tract infections: a cross-sectional analysis

    Directory of Open Access Journals (Sweden)

    Perencevich Eli N

    2007-05-01

    Full Text Available Abstract Background Inappropriate antibiotic use promotes resistance. Antibiotics are generally not indicated for upper respiratory infections (URIs. Our objectives were to describe patterns of URI treatment and to identify patient and provider factors associated with antibiotic use for URIs. Methods This study was a cross-sectional analysis of medical and pharmacy claims data from the Pennsylvania Medicaid fee-for-service program database. We identified Pennsylvania Medicaid recipients with a URI office visit over a one-year period. Our outcome variable was antibiotic use within seven days after the URI visit. Study variables included URI type and presence of concurrent acute illnesses and chronic conditions. We considered the associations of each study variable with antibiotic use in a logistic regression model, stratifying by age group and adjusting for confounders. Results Among 69,936 recipients with URI, 35,786 (51.2% received an antibiotic. In all age groups, acute sinusitis, chronic sinusitis, otitis, URI type and season were associated with antibiotic use. Except for the oldest group, physician specialty and streptococcal pharyngitis were associated with antibiotic use. History of chronic conditions was not associated with antibiotic use in any age group. In all age groups, concurrent acute illnesses and history of chronic conditions had only had fair to poor ability to distinguish patients who received an antibiotic from patients who did not. Conclusion Antibiotic prevalence for URIs was high, indicating that potentially inappropriate antibiotic utilization is occurring. Our data suggest that demographic and clinical factors are associated with antibiotic use, but additional reasons remain unexplained. Insight regarding reasons for antibiotic prescribing is needed to develop interventions to address the growing problem of antibiotic resistance.

  2. Evidence for Late Permian-Upper Triassic ocean acidification from calcium isotopes in carbonate of the Kamura section in Japan

    Science.gov (United States)

    Ye, F.; Zhao, L., Sr.; Chen, Z. Q.; Wang, X.

    2017-12-01

    Calcium and carbon cycles are tightly related in the ocean, for example, through continental weathering and deposition of carbonate, thus, very important for exploring evolutions of marine environment during the earth history. The end-Permian mass extinction is the biggest biological disaster in the Phanerozoic and there are several studies talking about variations of calcium isotopes across the Permian-Triassic boundary (PTB). However, these studies are all from the Tethys regions (Payne et al., 2010; Hinojosa et al., 2012), while the Panthalassic Ocean is still unknown to people. Moreover, evolutions of the calcium isotopes during the Early to Late Triassic is also poorly studied (Blattler et al., 2012). Here, we studied an Uppermost Permian to Upper Triassic shallow water successions (Kamura section, Southwest Japan) in the Central Panthalassic Ocean. The Kamura section is far away from the continent without any clastic pollution, therefore, could preserved reliable δ44/40Cacarb signals. Conodont zonation and carbonate carbon isotope also provide precious time framework which is necessary for the explaining of the δ44/40Cacarb profile. In Kamura, δ44/40Cacarb and δ13Ccarb both exhibit negative excursions across the PTB, the δ44/40Cacarb value in the end-Permian is 1.0398‰ then abrupt decrease to the minimum value of 0.1524‰. CO2-driven global ocean acidification best explains the coincidence of the δ44/40Cacarb excursion with negative excursions in the δ13Ccarb of carbonates until the Early Smithian(N1a, N1b, N1c, P1, N2, P2). In the Middle and the Late Triassic, the δ44/40 Cacarb average approximately 1.1‰. During the Middle and Late Triassic, strong relationships between δ44/40Cacarb and δ13Ccarb are collapsed, indicating a normal pH values of the seawater in those time. The Siberian Trap volcanism probably played a significant role on the δ44/40Cacarb until the late Early Triassic. After that, δ44/40Cacarb was mostly controlled by carbonate

  3. Crustal response to lithosphere evolution

    DEFF Research Database (Denmark)

    Artemieva, Irina; Thybo, Hans; Cherepanova, Yulia

    2012-01-01

    We present a new model for the structure of the crust in an area which stretches from the North Atlantic region in the west to the Verkhoyansk Ridge in the east and encompasses Greenland, Iceland, most of Europe, West Siberian basin, and the Siberian cratons. The model is based on critically asse......, thicknesses of different crustal layers, and Pn seismic velocities....... assessed results from various seismic studies, including reflection and refraction profiles and receiver function studies. The region includes a nearly continuous age record for crustal evolution over ca. 3.6-3.8 billion years. We present an analysis of the crustal structure heterogeneity in relation...

  4. Precise tremor source locations and amplitude variations along the lower-crustal central San Andreas Fault

    Science.gov (United States)

    Shelly, David R.; Hardebeck, Jeanne L.

    2010-01-01

    We precisely locate 88 tremor families along the central San Andreas Fault using a 3D velocity model and numerous P and S wave arrival times estimated from seismogram stacks of up to 400 events per tremor family. Maximum tremor amplitudes vary along the fault by at least a factor of 7, with by far the strongest sources along a 25 km section of the fault southeast of Parkfield. We also identify many weaker tremor families, which have largely escaped prior detection. Together, these sources extend 150 km along the fault, beneath creeping, transitional, and locked sections of the upper crustal fault. Depths are mostly between 18 and 28 km, in the lower crust. Epicenters are concentrated within 3 km of the surface trace, implying a nearly vertical fault. A prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6.0 Parkfield earthquake.

  5. 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...

  6. Magnetotelluric evidence for a deep-crustal mineralizing system beneath the Olympic Dam iron oxide copper-gold deposit, southern Australia

    Science.gov (United States)

    Heinson, Graham S.; Direen, Nicholas G.; Gill, Rob M.

    2006-07-01

    The iron oxide copper-gold Olympic Dam deposit, situated along the margin of the Proterozoic Gawler craton, South Australia, is the world's largest uranium deposit and sixth-largest copper deposit; it also contains significant reserves of gold, silver, and rare earth elements. Gaining a better understanding of the mechanisms for genesis of the economic liberalization is fundamental for defining exploration models in similar crustal settings. To delineate crustal structures that may constrain mineral system fluid pathways, coincident deep crustal seismic and magnetotelluric (MT) transects were obtained along a 220 km section that crosses Olympic Dam and the major crustal boundaries. In this paper we present results from 58 long-period (10 104 s) MT sites, with site spacing of 5 10 km. A two-dimensional inversion of MT data from 33 sites to a depth of 100 km shows four notable features: (1) sedimentary cover sequences with low resistivity (1000 Ω·m) Archean crustal core from a more conductive crust and mantle to the north (typically Olympic Dam, the upper-middle crust to ˜20 km is quite resistive (˜1000 Ω·m), but the lower crust is much more conductive (Olympic Dam, we image a low-resistivity region (Olympic Dam may be due to the upward movement of CO2-bearing volatiles near the time of deposit formation that precipitated conductive graphite liberalization along grain boundaries, simultaneously annihilating acoustic impedance boundaries. The source of the volatiles may be from the mantle degassing or retrograde metamorphism of the lower crust associated with Proterozoic crustal deformation.

  7. TAXONOMY AND BIOSTRATIGRAPHIC RECORD OF THE UPPER TRIASSIC CONODONTS OF THE PIZZO MONDELLO SECTION (WESTERN SICILY, ITALY, GSSP CANDIDATE FOR THE BASE OF THE NORIAN

    Directory of Open Access Journals (Sweden)

    MICHELE MAZZA

    2012-03-01

    Full Text Available New taxonomic and biostratigraphic investigations on the late Carnian to Rhaetian (Upper Triassic platform conodonts from the Pizzo Mondello section (Western Sicily, Italy, Sicano basin are here presented. Pizzo Mondello is one of the two GSSP candidates for the Carnian/Norian boundary; the section is a 430 m thick continuous succession of upper Carnian to upper Norian marine limestones (Scillato Formation, characterized by uniform facies and high sedimentation rates, and ca. 20 m of Rhaetian white calcilutites (Portella Gebbia limestone. Pizzo Mondello offers one of the most complete conodont records for this time interval in the Tethys. The conodont faunas are characterized by a large variety of species, belonging to the genera Carnepigondolella, Epigondolella, Metapolygnathus, Misikella, Mockina, Neocavitella, Norigondolella, Paragondolella, and Parvigondolella. The richness of the populations allowed a detailed revision and description of all the Upper Triassic species and morphotypes recovered. The revision of the problematic species Carnepigondolella nodosa and "Metapolygnathus communisti B" was thus possible, leading to the establishment of two new species: Carnepigondolella tuvalica n.sp. and Carnepigondolella gulloae n.sp. The latter species would be a good proxy for the Carnian/Norian boundary in the case that the FAD of Halobia austriaca (sample FNP135a will be selected as the primary biomarker for the base of the Norian. 

  8. Crustal volumes of the continents and of oceanic and continental submarine plateaus

    Science.gov (United States)

    Schubert, G.; Sandwell, D.

    1989-01-01

    Using global topographic data and the assumption of Airy isostasy, it is estimated that the crustal volume of the continents is 7182 X 10 to the 6th cu km. The crustal volumes of the oceanic and continental submarine plateaus are calculated at 369 X 10 to the 6th cu km and 242 X 10 to the 6th cu km, respectively. The total continental crustal volume is found to be 7581 X 10 to the 6th cu km, 3.2 percent of which is comprised of continental submarine plateaus on the seafloor. An upper bound on the contintental crust addition rate by the accretion of oceanic plateaus is set at 3.7 cu km/yr. Subduction of continental submarine plateaus with the oceanic lithosphere on a 100 Myr time scale yields an upper bound to the continental crustal subtraction rate of 2.4 cu km/yr.

  9. Microfacies, Depositional environment and Sequence Stratigraphy of Upper Carboniferous- Lower Permian rocks from Ozbak-Kuh region (Zaladou Section, East Central Iran

    Directory of Open Access Journals (Sweden)

    Ali Ahmadi

    2016-01-01

    Full Text Available Zaladou section is located in Ozbak-Kuh mountains in the nourthen part of Tabas block and consist of shale, limy sandstone, limestone and dolomite. Continous relationship of Upper Carboniferous and Lower Permian deposits, is quite evident in Zaladou section. The lower boundry of this section is located on the Absheni formation of Sardar Group with disconformity surface, and upper boundry’s is covered by disconformity surface and bauxite horizon of Bagh-e-Vang formation. According to the lithological Characters and microscopic studies, tidal flat, lagoon, bar, tidal inlet and open marine sub-environment are identified for Zaladou section. Results of this study show that Zaladou section was deposited in silisiclastic-carbonate mix homoclinal ramp in late Carboniferous and in carbonate homoclinal ramp in early Permian. Field study, microfacies and analysis through the sequence led to recognition of main sequence surface, such as: sequence boundry, maximum flooding surface, marine flooding surface, system tracts and two depositional sequences.

  10. New Data on Conodonts of the Upper Devonian of the Polar Urals (Ostantsovy Section, Malaya Usa River

    Directory of Open Access Journals (Sweden)

    M.A. Soboleva

    2016-09-01

    Full Text Available The main features of the Upper Devonian sediments on the right side of the Ostantsovy Creek (the left tributary of the Malaya Usa River in the eastern part of the Bielsko-Eletskaya structural formational belt on the western slope of the Polar Urals have been considered. The late Frasnian age of these sediments has been determined on the basis of conodonts (the linguiformis zone of the standard conodont scale. The transition from clastic and organic limestones with massive stromatoporoid forms to limestones with fused (reservoir stromatoporoid forms and Palmatolepis biofacies is indicative of the transgressive shift of the linguiformis phase. This transgressive level is an indirect expression of the Upper Kellwasser global event.

  11. The nature of crustal reflectivity at the southwest Iberian margin

    Science.gov (United States)

    Buffett, G. G.; Torne, M.; Carbonell, R.; Melchiorre, M.; Vergés, J.; Fernàndez, M.

    2017-11-01

    Reprocessing of multi-channel seismic reflection data acquired over the northern margin of the Gulf of Cádiz (SW Iberian margin) places new constraints on the upper crustal structure of the Guadalquivir-Portimão Bank. The data presented have been processed with optimized stacking and interval velocity models, a better approach to multiple attenuation, preserved amplitude information to derive the nature of seismic reflectivity, and accurate time-to-depth conversion after migration. The reprocessed data reveal a bright upper crustal reflector just underneath the Paleozoic basement that spatially coincides with the local positive free-air gravity high called the Gulf of Cádiz Gravity High. To investigate the nature of this reflector and to decipher whether it could be associated with pieces of mantle material emplaced at upper crustal levels, we calculated its reflection coefficient and compared it to a buried high-density ultramafic body (serpentinized peridotite) at the Gorringe Bank. Its reflection coefficient ratio with respect to the sea floor differs by only 4.6% with that calculated for the high-density ultramafic body of the Gorringe Bank, while it differs by 35.8% compared to a drilled Miocene limestone unconformity. This means that the Gulf of Cádiz reflector has a velocity and/or density contrast similar to the peridotite at the Gorringe Bank. However, considering the depth at which it is found (between 2.0 and 4.0 km) and the available geological information, it seems unlikely that the estimated shortening from the Oligocene to present is sufficient to emplace pieces of mantle material at these shallow levels. Therefore, and despite the similarity in its reflection coefficient with the peridotites of the Gorringe Bank, our preferred interpretation is that the upper crustal Gulf of Cádiz reflector represents the seismic response of high-density intracrustal magmatic intrusions that may partially contribute to the Gulf of Cádiz Gravity High.

  12. Crustal Growth: In Defense of the Dogma

    Science.gov (United States)

    Albarede, F.; Blichert-Toft, J.; Guitreau, M.

    2012-12-01

    extraction of its low-melting point components, not in the steady-state processing of the rather barren upper mantle. This is why we surmise that steady-state does not provide an adequate account of crustal dynamics. [1] Coltice, N. et al. Science 288 (2000) 845 [2] Gurnies, M. & Davies, G. J. Geol. 14 (1986) 396 [3] Guitreau, M. et al., Earth Planet. Sci. Lettes 337-338 (2012) 211 [4] Albarede, F. AGU Monogr. 160 (2005) 25.

  13. Tracing crustal contamination along the Java segment of the Sunda Arc, Indonesia

    Science.gov (United States)

    Jolis, E. M.; Troll, V.; Deegan, F.; Blythe, L.; Harris, C.; Freda, C.; Hilton, D.; Chadwick, J.; Van Helden, M.

    2012-04-01

    Arc magmas typically display chemical and petrographic characteristics indicative of crustal input. Crustal contamination can take place either in the mantle source region or as magma traverses the upper crust (e.g. [1]). While source contamination is generally considered the dominant process (e.g. [2]), late-stage crustal contamination has been recognised at volcanic arcs too (e.g. [3]). In light of this, we aim to test the extent of upper crustal versus source contamination along the Java segment of the Sunda arc, which, due its variable upper crustal structure, is an exemplary natural laboratory. We present a detailed geochemical study of 7 volcanoes along a traverse from Anak-Krakatau in the Sunda strait through Java and Bali, to characterise the impact of the overlying crust on arc magma composition. Using rock and mineral elemental geochemistry, radiogenic (Sr, Nd and Pb) and, stable (O) isotopes, we show a correlation between upper crustal composition and the degree of upper crustal contamination. We find an increase in 87Sr/86Sr and δ18O values, and a decrease in 143Nd/144Nd values from Krakatau towards Merapi, indicating substantial crustal input from the thick continental basement present. Volcanoes to the east of Merapi and the Progo-Muria fault transition zone, where the upper crust is thinner, in turn, show considerably less crustal input in their isotopic signatures, indicating a stronger influence of the mantle source. Our new data represent a systematic and high-resolution arc-wide sampling effort that allows us to distinguish the effects of the upper crust on the compositional spectrum of individual volcanic systems along the Sunda arc. [1] Davidson, J.P, Hora, J.M, Garrison, J.M & Dungan, M.A 2005. Crustal Forensics in Arc Magmas. J. Geotherm. Res. 140, 157-170; [2] Debaille, V., Doucelance, R., Weis, D., & Schiano, P. 2005. Geochim. Cosmochim. Acta, 70,723-741; [3] Gasparon, M., Hilton, D.R., & Varne, R. 1994. Earth Planet. Sci. Lett., 126, 15-22.

  14. Crustal evolution inferred from apollo magnetic measurements

    International Nuclear Information System (INIS)

    Dyal, P.; Daily, W.D.; Vanyan, L.L.

    1978-09-01

    Magnetic field and solar wind plasma density measurements were analyzed to determine the scale size characteristics of remanent fields at the Apollo 12, 15, and 16 landing sites. Theoretical model calculations of the field-plasma interaction, involving diffusion of the remanent field into the solar plasma, were compared to the data. The information provided by all these experiments shows that remanent fields over most of the lunar surface are characterized by spatial variations as small as a few kilometers. Large regions (50 to 100 km) of the lunar crust were probably uniformly magnetized during early crustal evolution. Bombardment and subsequent gardening of the upper layers of these magnetized regions left randomly oriented, smaller scale (5 to 10 km) magnetic sources close to the surface. The larger scale size fields of magnitude approximately 0.1 gammas are measured by the orbiting subsatellite experiments and the small scale sized remanent fields of magnitude approximately 100 gammas are measured by the surface experiments

  15. Source and fractionation controls on subduction-related plutons and dike swarms in southern Patagonia (Torres del Paine area) and the low Nb/Ta of upper crustal igneous rocks

    Science.gov (United States)

    Müntener, Othmar; Ewing, Tanya; Baumgartner, Lukas P.; Manzini, Mélina; Roux, Thibaud; Pellaud, Pierre; Allemann, Luc

    2018-05-01

    The subduction system in southern Patagonia provides direct evidence for the variability of the position of an active continental arc with respect to the subducting plate through time, but the consequences on the arc magmatic record are less well studied. Here we present a geochemical and geochronological study on small plutons and dykes from the upper crust of the southern Patagonian Andes at 51°S, which formed as a result of the subduction of the Nazca and Antarctic plates beneath the South American continent. In situ U-Pb geochronology on zircons and bulk rock geochemical data of plutonic and dyke rocks are used to constrain the magmatic evolution of the retro-arc over the last 30 Ma. We demonstrate that these combined U-Pb and geochemical data for magmatic rocks track the temporal and spatial migration of the active arc, and associated retro-arc magmatism. Our dataset indicates that the rear-arc area is characterized by small volumes of alkaline basaltic magmas at 29-30 Ma that are characterized by low La/Nb and Th/Nb ratios with negligible arc signatures. Subsequent progressive eastward migration of the active arc culminated with the emplacement of calc-alkaline plutons and dikes 17-16 Ma with elevated La/Nb and Th/Nb ratios and typical subduction signatures constraining the easternmost position of the southern Patagonian batholith at that time. Geochemical data on the post-16 Ma igneous rocks including the Torres del Paine laccolith indicate an evolution to transitional K-rich calc-alkaline magmatism at 12.5 ± 0.2 Ma. We show that trace element ratios such as Nb/Ta and Dy/Yb systematically decrease with increasing SiO2, for both the 17-16 Ma calc-alkaline and the 12-13 Ma K-rich transitional magmatism. In contrast, Th/Nb and La/Nb monitor the changes in the source composition of these magmas. We suggest that the transition from the common calc-alkaline to K-rich transitional magmatism involves a change in the source component, while the trace element ratios

  16. Crustal deformation mechanism in southeastern Tibetan Plateau: Insights from numerical modeling

    Science.gov (United States)

    Li, Y.; Liu, S.; Chen, L.

    2017-12-01

    The Indo-Asian collision developed the complicated crustal deformation around the southeastern Tibetan plateau. Numerous models have proposed to explain the crustal deformation, but the mechanism remains controversial, especially the increasing multi-geophysics data, which demonstrate the existence of lower velocity, lower resistivity and high conductivity, implying that lower crustal flow is responsible for the crustal deformation, arguing for the lower crust flow model. To address the relations between the crust flow and the surface deformation, we employ a three-dimensional viscoelastic finite model to investigate the possible influence on the surface deformation, and discuss the stress field distribution under the model. Our preliminary results suggest that lower crustal flow plays an important role in crustal deformation in southeastern Tibetan plateau. The best fitting is achieved when the flow velocity of the lower crust is approximately 10-11 mm/a faster than that of the upper crust. Crustal rheological properties affect regional crustal deformation, when the viscosity of the middle and lower crust in the South China block reaches 1022 and 1023 Pa.s, respectively; the predicted match observations well, especially for the magnitude within the South China block. The maximum principal stress field exhibits clear zoning, gradually shifting from an approximately east-west orientation in the northern Bayan Har block to southeast in the South China block, southwest in the western Yunnan block, and a radially divergent distribution in the Middle Yunnan and Southern Yunnan blocks.

  17. Crustal Viscosity Structure Estimated from Multi-Phase Mixing Theory

    Science.gov (United States)

    Shinevar, W. J.; Behn, M. D.; Hirth, G.

    2014-12-01

    Estimates of lower crustal viscosity are typically constrained by analyses of isostatic rebound, post seismic creep, and laboratory-derived flow laws for crustal rocks and minerals. Here we follow a new approach for calculating the viscosity structure of the lower continental crust. We use Perple_X to calculate mineral assemblages for different crustal compositions. Effective viscosity is then calculated using the rheologic mixing model of Huet et al. (2014) incorporating flow laws for each mineral phase. Calculations are performed along geotherms appropriate for the Basin and Range, Tibetan Plateau, Colorado Plateau, and the San Andreas Fault. To assess the role of crustal composition on viscosity, we examined two compositional gradients extending from an upper crust with ~67 wt% SiO2 to a lower crust that is either: (i) basaltic with ~53 wt% SiO2 (Rudnick and Gao, 2003), or (ii) andesitic with ~64% SiO2 (Hacker et al., 2011). In all cases, the middle continental crust has a viscosity that is 2-3 orders of magnitude greater than that inferred for wet quartz, a common proxy for mid-crustal viscosities. An andesitic lower crust results in viscosities of 1020-1021 Pa-s and 1021-1022 Pa-s for hotter and colder crustal geotherms, respectively. A mafic lower crust predicts viscosities that are an order of magnitude higher for the same geotherm. In all cases, the viscosity calculated from the mixing model decreases less with depth compared to single-phase estimates. Lastly, for anhydrous conditions in which alpha quartz is stable, we find that there is a strong correlation between Vp/Vs and bulk viscosity; in contrast, little to no correlation exists for hydrous conditions.

  18. Oceanic crustal velocities from laboratory and logging measurements of Integrated Ocean Drilling Program Hole 1256D

    Science.gov (United States)

    Gilbert, Lisa A.; Salisbury, Matthew H.

    2011-09-01

    Drilling and logging of Integrated Ocean Drilling Program (IODP) Hole 1256D have provided a unique opportunity for systematically studying a fundamental problem in marine geophysics: What influences the seismic structure of oceanic crust, porosity or composition? Compressional wave velocities (Vp) logged in open hole or from regional refraction measurements integrate both the host rock and cracks in the crust. To determine the influence of cracks on Vp at several scales, we first need an accurate ground truth in the form of laboratory Vp on crack-free, or nearly crack-free samples. We measured Vp on 46 water-saturated samples at in situ pressures to determine the baseline velocities of the host rock. These new results match or exceed Vp logs throughout most of the hole, especially in the lower dikes and gabbros, where porosities are low. In contrast, samples measured at sea under ambient laboratory conditions, had consistently lower Vp than the Vp logs, even after correction to in situ pressures. Crack-free Vp calculated from simple models of logging and laboratory porosity data for different lithologies and facies suggest that crustal velocities in the lavas and upper dikes are controlled by porosity. In particular, the models demonstrate significant large-scale porosity in the lavas, especially in the sections identified as fractured flows and breccias. However, crustal velocities in the lower dikes and gabbros are increasingly controlled by petrology as the layer 2-3 boundary is approached.

  19. Crustal Ages of the Ocean Floor - Poster

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Crustal Ages of the Ocean Floor Poster was created at NGDC using the Crustal Ages of the Ocean Floor database draped digitally over a relief of the ocean floor...

  20. Lower crustal earthquakes in the North China Basin and implications for crustal rheology

    Science.gov (United States)

    Yuen, D. A.; Dong, Y.; Ni, S.; LI, Z.

    2017-12-01

    The North China Basin is a Mesozoic-Cenozoic continental rift basin on the eastern North China Craton. It is the central region of craton destruction, also a very seismically active area suffering severely from devastating earthquakes, such as the 1966 Xingtai M7.2 earthquake, the 1967 Hejian M6.3 earthquake, and the 1976 Tangshan M7.8 earthquake. We found remarkable discrepancies of depth distribution among the three earthquakes, for instance, the Xingtai and Tangshan earthquakes are both upper-crustal earthquakes occurring between 9 and 15 km on depth, but the depth of the Hejian earthquake was reported of about 30 72 km, ranging from lowermost crust to upper mantle. In order to investigate the focal depth of earthquakes near Hejian area, we developed a method to resolve focal depth for local earthquakes occurring beneath sedimentary regions by P and S converted waves. With this method, we obtained well-resolved depths of 44 local events with magnitudes between M1.0 and M3.0 during 2008 to 2016 at the Hejian seismic zone, with a mean depth uncertainty of about 2 km. The depth distribution shows abundant earthquakes at depth of 20 km, with some events in the lower crust, but absence of seismicity deeper than 25 km. In particular, we aimed at deducing some constraints on the local crustal rheology from depth-frequency distribution. Therefore, we performed a comparison between the depth-frequency distribution and the crustal strength envelop, and found a good fit between the depth profile in the Hejian seismic zone and the yield strength envelop in the Baikal Rift Systems. As a conclusion, we infer that the seismogenic thickness is 25 km and the main deformation mechanism is brittle fracture in the North China Basin . And we made two hypotheses: (1) the rheological layering of dominant rheology in the North China Basin is similar to that of the Baikal Rift Systems, which can be explained with a quartz rheology at 0 10 km depth and a diabase rheology at 10 35 km

  1. Deep Crustal Melting and the Survival of Continental Crust

    Science.gov (United States)

    Whitney, D.; Teyssier, C. P.; Rey, P. F.; Korchinski, M.

    2017-12-01

    Plate convergence involving continental lithosphere leads to crustal melting, which ultimately stabilizes the crust because it drives rapid upward flow of hot deep crust, followed by rapid cooling at shallow levels. Collision drives partial melting during crustal thickening (at 40-75 km) and/or continental subduction (at 75-100 km). These depths are not typically exceeded by crustal rocks that are exhumed in each setting because partial melting significantly decreases viscosity, facilitating upward flow of deep crust. Results from numerical models and nature indicate that deep crust moves laterally and then vertically, crystallizing at depths as shallow as 2 km. Deep crust flows en masse, without significant segregation of melt into magmatic bodies, over 10s of kms of vertical transport. This is a major mechanism by which deep crust is exhumed and is therefore a significant process of heat and mass transfer in continental evolution. The result of vertical flow of deep, partially molten crust is a migmatite dome. When lithosphere is under extension or transtension, the deep crust is solicited by faulting of the brittle upper crust, and the flow of deep crust in migmatite domes traverses nearly the entire thickness of orogenic crust in Recognition of the importance of migmatite (gneiss) domes as archives of orogenic deep crust is applicable to determining the chemical and physical properties of continental crust, as well as mechanisms and timescales of crustal differentiation.

  2. EFFECTS OF NITROGEN PHOTOABSORPTION CROSS SECTION RESOLUTION ON MINOR SPECIES VERTICAL PROFILES IN TITAN’S UPPER ATMOSPHERE

    International Nuclear Information System (INIS)

    Luspay-Kuti, A.; Mandt, K. E.; Greathouse, T. K.; Plessis, S.

    2015-01-01

    The significant variations in both measured and modeled densities of minor species in Titan’s atmosphere call for the evaluation of possible influencing factors in photochemical modeling. The effect of nitrogen photoabsorption cross section selection on the modeled vertical profiles of minor species is analyzed here, with particular focus on C 2 H 6 and HCN. Our results show a clear impact of cross sections used on all neutral and ion species studied. Affected species include neutrals and ions that are not primary photochemical products, including species that do not even contain nitrogen. The results indicate that photochemical models that employ low-resolution cross sections may significantly miscalculate the vertical profiles of minor species. Such differences are expected to have important implications for Titan’s overall atmospheric structure and chemistry

  3. EFFECTS OF NITROGEN PHOTOABSORPTION CROSS SECTION RESOLUTION ON MINOR SPECIES VERTICAL PROFILES IN TITAN’S UPPER ATMOSPHERE

    Energy Technology Data Exchange (ETDEWEB)

    Luspay-Kuti, A.; Mandt, K. E.; Greathouse, T. K. [Space Science and Engineering Division, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238 (United States); Plessis, S., E-mail: aluspaykuti@swri.edu [ICES, The University of Texas at Austin, 201 East 24th Street, Austin, TX 78712 (United States)

    2015-03-01

    The significant variations in both measured and modeled densities of minor species in Titan’s atmosphere call for the evaluation of possible influencing factors in photochemical modeling. The effect of nitrogen photoabsorption cross section selection on the modeled vertical profiles of minor species is analyzed here, with particular focus on C{sub 2}H{sub 6} and HCN. Our results show a clear impact of cross sections used on all neutral and ion species studied. Affected species include neutrals and ions that are not primary photochemical products, including species that do not even contain nitrogen. The results indicate that photochemical models that employ low-resolution cross sections may significantly miscalculate the vertical profiles of minor species. Such differences are expected to have important implications for Titan’s overall atmospheric structure and chemistry.

  4. The crustal thickness of Australia

    Science.gov (United States)

    Clitheroe, G.; Gudmundsson, O.; Kennett, B.L.N.

    2000-01-01

    We investigate the crustal structure of the Australian continent using the temporary broadband stations of the Skippy and Kimba projects and permanent broadband stations. We isolate near-receiver information, in the form of crustal P-to-S conversions, using the receiver function technique. Stacked receiver functions are inverted for S velocity structure using a Genetic Algorithm approach to Receiver Function Inversion (GARFI). From the resulting velocity models we are able to determine the Moho depth and to classify the width of the crust-mantle transition for 65 broadband stations. Using these results and 51 independent estimates of crustal thickness from refraction and reflection profiles, we present a new, improved, map of Moho depth for the Australian continent. The thinnest crust (25 km) occurs in the Archean Yilgarn Craton in Western Australia; the thickest crust (61 km) occurs in Proterozoic central Australia. The average crustal thickness is 38.8 km (standard deviation 6.2 km). Interpolation error estimates are made using kriging and fall into the range 2.5-7.0 km. We find generally good agreement between the depth to the seismologically defined Moho and xenolith-derived estimates of crustal thickness beneath northeastern Australia. However, beneath the Lachlan Fold Belt the estimates are not in agreement, and it is possible that the two techniques are mapping differing parts of a broad Moho transition zone. The Archean cratons of Western Australia appear to have remained largely stable since cratonization, reflected in only slight variation of Moho depth. The largely Proterozoic center of Australia shows relatively thicker crust overall as well as major Moho offsets. We see evidence of the margin of the contact between the Precambrian craton and the Tasman Orogen, referred to as the Tasman Line. Copyright 2000 by the American Geophysical Union.

  5. Glacial rebound and crustal stress in Finland

    International Nuclear Information System (INIS)

    Lambeck, K.; Purcell, A.

    2003-11-01

    The last ice age of Fennoscandinavia continues to have geological repercussions across Finland despite the last ice having retreated almost 10,000 years ago: land uplift, shoreline retreat, and the stress state of the crust continues to evolve. This report focusses on the glacial rebound signals for Finland and the Gulf of Bothnia and explores the consequences of the ongoing deformation. The rebound signals include the geological evidence as well as instrumental observations: the tide gauge and lake-level measurements of the past century, the changes in geodetic levels recorded in the repeat levelling surveys of the region and the direct measurement of crustal deformation (radial and horizontal) using high-precision space-geodesy measurements. These signals provide constraints on the Earth's rheology, its elasticity and viscosity, and the glacial history of the region. Once observationally constrained, the rebound models are used to predict both the ongoing evolution of shorelines and the changing state of stress within the crust. This report covers: (i) A review of glacial rebound modelling for Scandinavia (Sections 2 and 3). (ii) Review of observational evidence relating to sea-level change and crustal rebound (Section 4). (iii) New earth and ice-sheet model results from the inversion of the geological evidence for sea-level change, including models of shoreline evolution (Sections 5 and 6). (iv) Earth-model results from the inversion of the geodetic evidence for sea-level change (Section 7). (v) Development of crustal stress models for past and present stress states (Section 8). (vi) Conclusions and recommendations (Section 9). Specific conclusions reached pertain to: (i) Thickness of ice cover over Scandinavia since the Last Glacial Maximum, particularly for the Lateglacial period. (ii) Sea-level change and shoreline evolution for the Baltic area since the time the region became ice-free for the last time. (iii) The predicted rates of present-day crustal

  6. Compositional stratigraphy of crustal material from near-infrared spectra

    International Nuclear Information System (INIS)

    Pieters, C.M.

    1987-01-01

    An Earth-based telescopic program to acquire near-infrared spectra of freshly exposed lunar material now contains data for 17 large impact craters with central peaks. Noritic, gabbroic, anorthositic and troctolitic rock types can be distinguished for areas within these large craters from characteristic absorptions in individual spectra of their walls and central peaks. Norites dominate the upper lunar crust while the deeper crustal zones also contain significant amounts of gabbros and anorthosites. Data for material associated with large craters indicate that not only is the lunar crust highly heterogeneous across the nearside, but that the compositional stratigraphy of the lunar crust is nonuniform. Crustal complexity should be expected for other planetary bodies, which should be studied using high spatial and spectral resolution data in and around large impact craters

  7. Compositional stratigraphy of crustal material from near-infrared spectra

    Science.gov (United States)

    Pieters, Carle M.

    1987-01-01

    An Earth-based telescopic program to acquire near-infrared spectra of freshly exposed lunar material now contains data for 17 large impact craters with central peaks. Noritic, gabbroic, anorthositic and troctolitic rock types can be distinguished for areas within these large craters from characteristic absorptions in individual spectra of their walls and central peaks. Norites dominate the upper lunar crust while the deeper crustal zones also contain significant amounts of gabbros and anorthosites. Data for material associated with large craters indicate that not only is the lunar crust highly heterogeneous across the nearside, but that the compositional stratigraphy of the lunar crust is nonuniform. Crustal complexity should be expected for other planetary bodies, which should be studied using high spatial and spectral resolution data in and around large impact craters.

  8. Crustal Gravitational Potential Energy Change and Subduction Earthquakes

    Science.gov (United States)

    Zhu, P. P.

    2017-05-01

    CRW Model) as follows: for Type B and Type C subduction earthquakes, if the seawater average depth on the vertical up side of the rupture area is less than a tenth of the hypocenter depth, then take the approximation that the seawater above the continental plate is replaced by the upper crustal material of the continental plate. The formula of quantitative calculating the crustal GPE change is also provided for this model. Finally, for 16 September 2015 Mw 8.3 Illapel Chile earthquake, we apply CRW Model and obtain the following results: the crustal GPE change is equal to 1.8 × 1019 J, and the hanging wall vertical moving-up height is 1.9 m with respect to the footwall. We believe this paper might be the first report on the quantitative solution of the crustal GPE change for this subduction earthquake; our results and related method will be helpful in research into the earthquakes in Peru-Chile subduction zone and the Andean orogeny. In short, this study expounds a new method for quantitative determining the crustal GPE change caused by subduction earthquakes, which is different from other existing methods.

  9. Crustal Seismic Anisotropy: Implications for Understanding Crustal Dynamics

    Science.gov (United States)

    Meltzer, A.; Christensen, N.; Okaya, D.

    2003-12-01

    The Nanga Parbat - Haramosh massif, in the core of the western syntaxis of the Himalaya, represents a unique exposure of mid-lower continental crust from beneath a collisional orogen. The exhumed core of the massif forms a large scale antiformal structure with axial orientation of N10E and associated lineation directed north-south with near-vertical dips. Laboratory measurements of seismic velocity on a suite of quartzofeldspathic gneisses from the massif show a relatively strong degree of anisotropy, up to 12.5% for compressional waves and up to 21% for shear waves. The degree of velocity anisotropy is primarily a function of mica content and rock fabric strength. The strong anisotropy measured in these rocks should be observable in recorded seismic field data and provides a means of mapping rock fabric at depth provided the rock fabric is coherent over appropriate length scales. An IRIS/PASSCAL deployment of 50 short period instruments recorded local and regional earthquakes to characterize seismicity and determine crustal structure beneath the massif as part of a multidisciplinary NSF Continental Dynamics study investigating the active tectonic processes responsible for exhumation and crustal reworking at Nanga Parbat. Microseismicity at Nanga Parbat is distributed along strike beneath the massif but exhibits a sharp drop-off laterally into adjacent terranes and with depth. This data set is ideal for studying crustal seismic anisotropy because the raypaths are restricted to the crust, sharp onsets in P and S allow for clear identification of arrivals, and source-receiver geometries sample a range of azimuths with respect to structure. Preliminary analysis indicates that the majority of local events exhibit some degree of splitting and that splitting patterns, while complicated, are coherent. While splitting delay normally increases with distance traveled through anisotropic material, the range of delay times can be due to heterogeneity in composition, lateral

  10. Caregivers' practices, knowledge and beliefs of antibiotics in paediatric upper respiratorytract infections in Trinidad and Tobago: a cross-sectional study

    Directory of Open Access Journals (Sweden)

    Pereira Lexley

    2004-12-01

    Full Text Available Abstract Background Antibiotic overuse and misuse for upper respiratory tract infections in children is widespread and fuelled by public attitudes and expectations. This study assessed knowledge, beliefs, and practices regarding antibiotic use for these paediatric infections among children's caregivers' in Trinidad and Tobago in the English speaking Caribbean. Methods In a cross-sectional observational study, by random survey children's adult caregivers gave a telephone interview from November 1998 to January 1999. On a pilot-tested evaluation instrument, respondents provided information about their knowledge and beliefs of antibiotics, and their use of these agents to treat recent episodes ( Results Of the 417 caregivers, 70% were female and between 18–40 years, 77% were educated to high school and beyond and 43% lived in urban areas. Two hundred and forty nine (60% respondents scored high (≥ 12 on antibiotic knowledge and 149 (34% had used antibiotics in the preceding year. More caregivers with a high knowledge score had private health insurance (33%, (p Conclusions In Trinidad and Tobago, caregivers scoring low on antibiotic knowledge have erroneous beliefs and use antibiotics inappropriately. Children in their care receive antibiotics for upper respiratory tract infections without visiting a health clinic or a physician. Educational interventions in the community on the consequences of inappropriate antibiotic use in children are recommended. Our findings emphasise the need to address information, training, legislation and education at all levels of the drug delivery system towards discouraging self-medication with antibiotics in children.

  11. Sensitivity analysis of crustal correction for calculation of lithospheric mantle density from gravity data

    DEFF Research Database (Denmark)

    Herceg, Matija; Artemieva, Irina; Thybo, Hans

    2016-01-01

    for the crust and (ii) uncertainties in the seismic crustal structure (thickness and average VP velocities of individual crustal layers, including the sedimentary cover). We examine the propagation of these uncertainties into determinations of lithospheric mantle density and analyse both sources of possible......We investigate how uncertainties in seismic and density structure of the crust propagate to uncertainties in mantle density structure. The analysis is based on interpretation of residual upper-mantle gravity anomalies which are calculated by subtracting (stripping) the gravitational effect...... mantle, knowledge on uncertainties associated with incomplete information on crustal structure is of utmost importance for progress in gravity modelling. Uncertainties in the residual upper-mantle gravity anomalies result chiefly from uncertainties in (i) seismic VP velocity-density conversion...

  12. Correlation of Crustal Structures and Seismicity Patterns in Northern Appalachians

    Science.gov (United States)

    Yang, X.; Gao, H.

    2017-12-01

    The earthquake distributions in northern Appalachians are bounded by major geologically-defined terrane boundaries. There is a distinct seismic gap within Taconic Belt between the Western Quebec Seismic Zone (WQSZ) to the west and the seismically active Ganderia terrane to the east. It is not clear, however, what crustal structures control the characteristics of earthquake clustering in this region. Here we present a newly constructed crustal shear velocity model for the northern Appalachians using Rayleigh wave data extracted from ambient noises. Our tomographic model reveals strongly heterogeneous seismic structures in the crust. We observe multiple NW-dipping patches of high-velocity anomalies in the upper crust beneath the southeastern WQSZ. The upper crust shear velocities in the Ganderia and Avalonia region are generally lower than those beneath the WQSZ. The middle crust has relatively lower velocities in the study area. The earthquakes in the study area are constrained within the upper crust. Most of the earthquake hypocenters within the WQSZ are concentrated along the NW-dipping boundaries separating the high-velocity anomalies. In contrast, most of the earthquake hypocenters in the Ganderia and Avalonia region are diffusely distributed without clear vertical lineaments. The orientations of maximum compressive stresses change from W-E in the Ganderia and Avalonia region to SW-NE in the WQSZ. The contrasts in seismicity, velocity, and stress field across the Taconic Belt indicate that the Taconic Belt terrane may act as a seismically inactive buffer zone in northern Appalachians.

  13. Crustal heterogeneity and seismotectonics of the region around Beijing, China

    Science.gov (United States)

    Huang, Jinli; Zhao, Dapeng

    2004-07-01

    A detailed three-dimensional (3-D) P-wave velocity model of the crust and uppermost mantle under the Chinese capital (Beijing) region is determined with a spatial resolution of 25 km in the horizontal direction and 4-17 km in depth. We used 48,750 precise P-wave arrival times from 2973 events of local crustal earthquakes, controlled seismic explosions and quarry blasts. These events were recorded by a new digital seismic network consisting of 101 seismic stations equipped with high-sensitivity seismometers. The data are analyzed by using a 3-D seismic tomography method. Our tomographic model provides new insights into the geological structure and tectonics of the region, such as the lithological variations and large fault zones across the major geological terranes like the North China Basin, the Taihangshan and the Yanshan mountainous areas. The velocity images of the upper crust reflect well the surface geological and topographic features. In the North China Basin, the depression and uplift areas are imaged as slow and fast velocities, respectively. The Taihangshan and Yanshan mountainous regions are generally imaged as broad high-velocity zones, while the Quaternary intermountain basins show up as small low-velocity anomalies. Velocity changes are visible across some of the large fault zones. Large crustal earthquakes, such as the 1976 Tangshan earthquake ( M=7.8) and the 1679 Sanhe earthquake ( M=8.0), generally occurred in high-velocity areas in the upper to middle crust. In the lower crust to the uppermost mantle under the source zones of the large earthquakes, however, low-velocity and high-conductivity anomalies exist, which are considered to be associated with fluids. The fluids in the lower crust may cause the weakening of the seismogenic layer in the upper and middle crust and thus contribute to the initiation of the large crustal earthquakes.

  14. Boron isotope fractionation in magma via crustal carbonate dissolution.

    Science.gov (United States)

    Deegan, Frances M; Troll, Valentin R; Whitehouse, Martin J; Jolis, Ester M; Freda, Carmela

    2016-08-04

    Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ(11)B values down to -41.5‰, reflecting preferential partitioning of (10)B into the assimilating melt. Loss of (11)B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports (11)B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ(11)B melt values in arc magmas could flag shallow-level additions to the subduction cycle.

  15. Boron isotope fractionation in magma via crustal carbonate dissolution

    Science.gov (United States)

    Deegan, Frances M.; Troll, Valentin R.; Whitehouse, Martin J.; Jolis, Ester M.; Freda, Carmela

    2016-08-01

    Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ11B values down to -41.5‰, reflecting preferential partitioning of 10B into the assimilating melt. Loss of 11B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports 11B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ11B melt values in arc magmas could flag shallow-level additions to the subduction cycle.

  16. The upper Tortonian-lower Messinian at Monte dei Corvi (Northern Apennines, Italy) : Completing a Mediterranean reference section for the Tortonian Stage

    NARCIS (Netherlands)

    Hüsing, S. K.; Kuiper, K. F.; Link, W.; Hilgen, Frederik J.; Krijgsman, W.

    2009-01-01

    A high-resolution integrated stratigraphy including biostratigraphy, magnetostratigraphy, tephrostratigraphy and cyclostratigraphy is presented for the upper Tortonian and lower Messinian (Upper Miocene) at Monte dei Corvi. Numerical age control comes from a combination of magnetobiostratigrapic

  17. Nd isotopes in French Phanerzoic shales: external vs. internal aspects of crustal evolution

    International Nuclear Information System (INIS)

    Michard, A.; Gurriet, P.; Soudant, M.; Alberede, F.; Ecole Nationale Superieure de Geologie Appliquee et de Prospection Miniere, 54 - Nancy

    1985-01-01

    Nd isotopic composition has been determined on shales of Paleozoic (Brittany and Languedoc) and Mesozoic (Lorraine) age. epsilonsub(Nd)(T) values range from -6 to -12 while Nd crustal residence ages are typically in excess over their stratigraphic ages by some 1.4 Ga. Exceptions to this rule are the sediments coeval with Hercynian, Caledonian and Cadomian orogenic events, the epsilonsub(Nd)(T) values of which suggest addition of mantle material to the sediment in the form of volcanoclastic detritus. In Brittany, this is confirmed by the local zircon chronology which provides upper intercepts of Concordia up to 800 m.y. in excess of Nd crustal residence ages. Comparison of crustal residence ages with stratigraphic ages through geologic time suggests a three stage history: a) for rocks older than 2 Ga, stratigraphic and crustal residence ages coincide, b) from 2 to 1 Ga, crustal residence ages level off at ca. 2 Ga and then c) decrease down to 1.4 Ga in recent sediments. Two extreme models can account for the observed variations: an internally driven model, in which variable quantities of mantle material are added to the crust, and an externally driven model, in which the rate of crustal recycling is low in the Archean but increases rapidly at the onset of the atmospheric oxygen buildup. (author)

  18. Heavy mineral delineation of the Cretaceous, Paleocene, and Eocene stratigraphic sections at the Savannah River Site, Upper Coastal Plain of South Carolina

    International Nuclear Information System (INIS)

    Cathcart, E.M.; Sargent, K.A.

    1994-01-01

    The Upper Atlantic Coastal Plain of South Carolina consists of a fluvial-deltaic and shallow marine complex of unconsolidated sediments overlying the crystalline basement rocks of the North American continent. Because of the lateral and vertical variability of these sediments, stratigraphic boundaries have been difficult to distinguish. Portions of the Cretaceous, Paleocene, and eocene stratigraphic sections from cores recovered during the construction of two monitoring wells at the Savannah River Site were studied to determine if heavy mineral suites could be utilized to distinguish boundaries. The stratigraphic sections include: the Late Cretaceous Middendorf, Black Creek, and Steel Creek Formations, the Paleocene Snapp Formation, the late Paleocene-Early Eocene Fourmile Branch Formation, and the Early Eocene Congaree formation. In previous studies composite samples were taken over 2.5 ft. intervals along the cores and processed using a heavy liquid for heavy mineral recovery. During this study, heavy mineral distributions were determined by binocular microscope and the mineral identifications confirmed by x-ray diffraction analysis of hand-picked samples. The heavy mineral concentration data and grain size data were then compared to the stratigraphic boundary positions determined by other workers using more classical methods. These comparisons were used to establish the utility of this method for delineating the stratigraphic boundaries in the area of study

  19. The association of dementia with upper arm and waist circumference in seven low- and middle-income countries: the 10/66 cross-sectional surveys.

    Science.gov (United States)

    Taylor, Clare L; Albanese, Emiliano; Stewart, Robert

    2012-08-01

    Weight loss in dementia contributes to morbidity and mortality but the distribution of anthropometric change and its consistency between populations are less clear. Our aim was to investigate and compare the associations of dementia with waist and upper arm circumference in elders from seven low- and middle-income nations. Cross-sectional surveys were conducted of 15,022 residents aged 65 years and older in Cuba, Mexico, Venezuela, Peru, Dominican Republic, China, and India. Dementia was assessed using a cross-culturally validated algorithm, and anthropometric measurements were taken. Associations with dementia and dementia severity (clinical dementia rating scale) were investigated in linear regression models, with fixed-effects meta-analyses used to investigate between-country heterogeneity. Dementia and increased dementia severity were both associated with smaller arm and waist circumferences with little evidence of confounding by sociodemographic and health status. Associations between dementia/clinical dementia rating and arm circumference were homogeneous between countries (Higgins I(2) 0% and 7%, respectively), whereas those with waist circumference were more heterogeneous (Higgins I(2) 67% and 62%, respectively). Although cross-sectional, our findings are consistent with prospective observations of weight loss in dementia and suggest loss of both muscle and fat-the former being consistent across different settings and the latter being more context dependent.

  20. Clinical and endoscopic profile of the patients with upper gastrointestinal bleeding in central rural India: A hospital-based cross-sectional study

    Directory of Open Access Journals (Sweden)

    Jyoti Jain

    2018-01-01

    Full Text Available Introduction: Acute Upper Gastrointestinal bleeding (UGIB is one of the common causes with which the patients present to emergency. The upper gastrointestinal (UGI endoscopy remains a crucial tool in identification of UGIB. The aim of the present study was to determine the endoscopic profile of UGIB in adult population of rural central India admitted with history of UGIB (hemetemesis and/or malena. Methods: This prospective, cross sectional study was conducted in rural hospital in central India and we enrolled all consecutive patients aged 18 years and above who were admitted in the hospital ward with the history of UGIB. After obtaining the demographic data, all patients underwent clinical examination, laboratory investigations and video-endoscopy. We used Student's t test to compare means, Chi-square test to compare proportions and Mann-Whitney test to compare medians. P value <0.05 will be considered significant. Results: The mean age of our study population (N = 118 was 46.2 years. Among 118 patients who underwent endoscopy, 47.4% had esophageal varices, 27.1% had portal hypertensive gastropathy, 14.4% had gastric erosions, 5.9% each had duodenal ulcers and esophagitis, 5% had gastric ulcer disease, 4.2% each had Mallory-Weiss tear and had gastric malignancy, 1.7% had esophageal malignancy and 16.1% had normal endoscopic findings. Conclusion: Esophageal varices were the most common cause of UGIB in the adult population of rural central India presenting with UGIB, when diagnosed by video-endoscopy.

  1. Health-related quality of life in adults with congenital unilateral upper limb deficiency in Norway. A cross-sectional study.

    Science.gov (United States)

    Johansen, Heidi; Østlie, Kristin; Andersen, Liv Øinæs; Rand-Hendriksen, Svend

    2016-11-01

    To examine subjective health-related quality of life (HRQoL) in adults with congenital unilateral upper limb deficiency (UULD) in Norway and to explore the associations between demographic and clinical factors and HRQoL. Cross-sectional study comparing HRQoL, measured by SF-36, among adults with UULD and an age- and gender-matched control group from the Norwegian general population (NGP). Seventy-seven respondents, median age 42 years (range: 20-82); 71% were women. Most had left-sided (61%), below elbow (53%), transverse (73%) deficiency. Compared to the NGP, the UULD group reported reduced HRQoL on all SF-36 subscales except for the role emotional (RE) scale (p=0.321), mental health (MH) (p=0.055) and mental component summary (MCS) (p=0.064). The greatest difference was on the bodily pain (BP) scale (point difference of 20.0). Multiple linear regression models showed significant association between several physical- and mental SF-36 subscales and occupational status, occurrence of comorbidity and chronic pain. Persons with UULD reported reduced HRQoL on most SF-36 subscales, mostly in the physical health domain. Employment status, occurrence of comorbidity and chronic pain seem to have a negative impact on the HRQoL. Measures that can reduce pain and loss of function should be given particular attention in UULD rehabilitation. Implications for Rehabilitation Persons with congenital unilateral upper limb deficiency (UULD) who experience pain and discomfort should seek professional help for evaluating their everyday coping strategies. Professionals who meet persons with UULD should examine anomalies, comorbidity, pain and employment status before choosing advices and actions. Individually adapted grip-improving devices, environments, physical exercise and pain management programs should be implemented early to reduce pain, loss of function and decreased HRQoL. A multidisciplinary approach is often necessary when counseling persons with UULD.

  2. Studies towards the data acquisition of the PANDA experiment and measurement of a new upper limit of the production cross section of p anti p→hc

    International Nuclear Information System (INIS)

    Wagner, Milan Nicolas

    2016-01-01

    The PANDA experiment will be one of the main future FAIR experiments located at Darmstadt, Germany. It has a challenging concept of a new type of Data Acquisition (DAQ) including the full online reconstruction and filtering as well as a high precision synchronization mechanism. The new concept is needed due to a high data rate of 200 GB/s, which has to be reduced by three orders of magnitude before storing. In this thesis the prototype trigger-less DAQ, a field programmable gate array (FPGA) based system is presented. As a scalable system, it includes first parts of the final DAQ. Thus it is the first system allowing studies of the full DAQ-chain, including the synchronization mechanism. Furthermore, the functionalities during an in-beam environment test of the prototype of the PANDA electromagnetic calorimeter were investigated. This test showed that the PTDAQ can be used as a DAQ in prototype tests. In addition to hardware and firmware development, simulations of benchmark channels are crucial to extract filtering possibilities. Therefore the knowledge of the production cross section is necessary. In the framework of this thesis a new upper limit of the production cross section σ(p anti p→h c ) was extracted. h c is one of the most unknown charmonium states, and it is not possible to produce pure h c in one of the other ''charm factories'' directly. For this purpose, the branching ratio of the decay B(h c →p anti p)<5.6.10 -5 rate at 90% C.L. was determined. For this, data from the BES III experiment located at the BEPCII accelerator in Beijing, China was used. h c was produced in the decay of the ψ(2S) charmonium resonance, which itself was produced in e + e - collisions. A data set of (447.9±2.8).10 6 ψ(2S)-events was used for this analysis. The new upper limit of the cross section σ(p anti p→h c )<32 nb rate at 90% C.L. was calculated by using the method of detailed balance. Furthermore, the lower limit of the integrated

  3. New Paleomagnetic Data From Upper Gabbros Supports Limited Rotation of Central Semail Massif in Oman Ophiolite

    Science.gov (United States)

    Horst, A. J.; Sarah, T.; Hartley, E.; Martin, J.

    2017-12-01

    Paleomagnetic data from northern massifs of the Oman ophiolite demonstrate substantial clockwise rotations prior to or during obduction, yet data from southern massifs are recently suggested to be remagnetized during obduction and show subsequent smaller counterclockwise rotations. To better understand paleomagnetic data from the southern massifs, we conducted a detailed paleomagnetic and rock magnetic study of 21 sites in upper gabbros and 5 sites in lower crustal gabbros within the central Semail massif. Samples treated with progressive thermal demagnetization yield interpretable magnetizations with dominant unblocking between 500-580°C that implies characteristic remanent magnetization (ChRM) components carried by low-titanium magnetite and nearly pure magnetite. Rock magnetic and scanning electron microscopy data provide additional support of the carriers of magnetization. ChRMs from sites with samples containing partially-serpentinized olivine are similar to sites with samples lacking olivine, where the carriers appear to be fine magnetite intergrowths in pyroxene. The overall in situ and tilt-corrected mean directions from upper gabbros are distinct from the lower gabbros, from previous data within the massif, and also directions from similar crustal units in adjacent Rustaq and Wadi Tayin massifs. After tilt correction for 10-15° SE dip of the crust-mantle boundary, the mean direction from upper gabbros is nearly coincident with in situ lower gabbros. The tilt-corrected direction from upper gabbros is also consistent with an expected direction from the Late Cretaceous apparent polar wander path for Arabia at the age of crustal accretion ( 95Ma). These results suggest the upper crustal section in Semail has likely only experienced minor tilting since formation and acquisition of magnetization. Due to slow cooling of middle to lower gabbros in fast-spread crust, the lower gabbro sites likely cooled later or after obduction, and thus yield a distinct

  4. Crustal Stretching Style and Lower Crust Flow of the South China Sea Northern Margin

    Science.gov (United States)

    Bai, Y.; Dong, D.; Runlin, D.

    2017-12-01

    There is a controversy about crustal stretching style of the South China Sea (SCS) northern margin mainly due to considerable uncertainty of stretching factor estimation, for example, as much as 40% of upper crust extension (Walsh et al., 1991) would be lost by seismic profiles due to poor resolution. To discover and understand crustal stretching style and lower crustal flow on the whole, we map the Moho and Conrad geometries based on gravity inversion constrained by deep seismic profiles, then according to the assumption of upper and lower crust initial thickness, upper and lower crust stretching factors are estimated. According to the comparison between upper and lower crust stretching factors, the SCS northern margin could be segmented into three parts, (1) sediment basins where upper crust is stretched more than lower crust, (2) COT regions where lower crust is stretched more than upper crust, (3) other regions where the two layers have similar stretching factors. Stretching factor map shows that lower crust flow happened in both of COT and sediment basin regions where upper crust decouples with lower crust due to high temperature. Pressure contrast by sediment loading in basins and erosion in sediment-source regions will lead to lower crust flow away from sediment sink to source. Decoupled and fractured upper crust is stretched further by sediment loading and the following compensation would result in relatively thick lower crust than upper crust. In COT regions with thin sediment coverage, low-viscosity lower crust is easier to thin in extensional environment, also the lower crust tends to flow away induced by magma upwelling. Therefore, continental crust on the margin is not stretching in a constant way but varies with the tectonic setting changes. This work is supported by National Natural Science Foundation of China (Grant No. 41506055, 41476042) and Fundamental Research Funds for the Central Universities China (No.17CX02003A).

  5. New constraints on the crustal structure beneath northern Tyrrhenian Sea

    Science.gov (United States)

    Levin, V. L.; Park, J. J.

    2009-12-01

    We present new seismological data on the seismic structure beneath the Tyrrhenian Sea between Corsica and the coast of Italy. Teleseismic receiver functions from two Tyrrhenian islands (Elba and Gorgona) identify clear P-to-S mode-converted waves from two distinct interfaces, at ~20 and ~45 km depth. Both interfaces are characterized by an increase of seismic wavespeed with depth. Using a summation of direct and multiply-reflected body waves within the P wave coda we estimate the mean ratio of compressional and shear wave speeds above the 45 km interface to be 1.75-1.80. Using reflectivity computations in 1D layered models we develop a model of seismic wavespeed distribution that yields synthetic seismograms very similar to those observed. We apply a Ps-multiple summation procedure to the synthetic waveforms to further verify the match between observed and predicted wavefields. The lower layer of our model, between 20 and 45 km, has Vp ~ 7.5 km/sec, a value that can be ascribed to either very fast crustal rocks or very slow upper mantle rocks. The Vp/Vs ratio is ~1.8 in this intermediate layer. On the basis of a well-constrained downward increase in seismic wave speed beneath this second layer, we interpret it as the magmatically reworked lower crust, a lithology that has been proposed to explain high-Vp layers in the crustal roots of island-arc terranes and volcanically altered continental margins, as well as lower-crustal high-Vp features sometimes seen beneath continental rifts. The presence of a thick layer of high-Vp, but crustal, lithology beneath the Tyrrhenian Sea differs considerably from previous estimates that interpreted the interface at ~20 km as the Moho. Our new interpretation obviates a need for a crustal thickness change of over 20 km at the crest of the Apennines orogen. We propose an alteration in the properties of the lower crust instead. We argue that ongoing convergent subduction of the Adriatic lithospehre is not required beneath northern

  6. Seismic crustal structure of the North China Craton and surrounding area: Synthesis and analysis

    Science.gov (United States)

    Xia, B.; Thybo, H.; Artemieva, I. M.

    2017-07-01

    We present a new digital model (NCcrust) of the seismic crustal structure of the Neoarchean North China Craton (NCC) and its surrounding Paleozoic-Mesozoic orogenic belts (30°-45°N, 100°-130°E). All available seismic profiles, complemented by receiver function interpretations of crustal thickness, are used to constrain a new comprehensive crustal model NCcrust. The model, presented on a 0.25° × 0.25°grid, includes the Moho depth and the internal structure (thickness and velocity) of the crust specified for four layers (the sedimentary cover, upper, middle, and lower crust) and the Pn velocity in the uppermost mantle. The crust is thin (30-32 km) in the east, while the Moho depth in the western part of the NCC is 38-44 km. The Moho depth of the Sulu-Dabie-Qinling-Qilian orogenic belt ranges from 31 km to 51 km, with a general westward increase in crustal thickness. The sedimentary cover is 2-5 km thick in most of the region, and typical thicknesses of the upper crust, middle crust, and lower crust are 16-24 km, 6-24 km, and 0-6 km, respectively. We document a general trend of westward increase in the thickness of all crustal layers of the crystalline basement and as a consequence, the depth of the Moho. There is no systematic regional pattern in the average crustal Vp velocity and the Pn velocity. We examine correlation between the Moho depth and topography for seven tectonic provinces in the North China Craton and speculate on mechanisms of isostatic compensation.

  7. NASA plan for international crustal dynamics studies

    Science.gov (United States)

    1979-01-01

    The international activities being planned as part of the NASA geodynamics program are described. Methods of studying the Earth's crustal movements and deformation characteristics are discussed. The significance of the eventual formalations of earthquake predictions methods is also discussed.

  8. Influence of crustal layering and thickness on co-seismic effects of Wenchuan earthquake

    Directory of Open Access Journals (Sweden)

    Tan Hongbo

    2011-02-01

    Full Text Available Using the PSGRN/PSCMP software and the fault model offered by USGS and on the basis of finite rectangular dislocation theory and the local layered wave velocity structures of the crust-upper-mantle, the influences of crustal layering and thickness on co-seismic gravity changes and deformation of Wenchuan earthquake have been simulated. The results indicate that; the influences have a relationship with the attitude of faults and the relative position between calculated points and fault. The difference distribution form of simulated results between the two models is similar to that of co-seismic effect. For the per centum distribution, it’s restricted by the zero line of the co-seismic effects obviously. Its positive is far away from the zero line. For the crustal thickness, the effect is about 10% – 20%. The negative and the effect over 30% focus around the zero line. The average influences of crustal layering and thickness for the E-W displacement, N-S displacement, vertical displacement and gravity changes are 18.4%,18.0%, 15.8% and 16.2% respectively, When the crustal thickness is 40 km, they are 4.6%, 5.3%, 3.8% and 3.8%. Then the crustal thickness is 70 km, the average influences are 3.5%, 4.6%, 3.0% and 2.5% respectively.

  9. Seismotectonics of Taiwan Shoal region in northeastern SCS: Insights from crustal structure

    Science.gov (United States)

    Kuiyuan, Wan; Jinlong, Sun; Shaohong, Xia; Xiaoling, Xie; Xiang, Zhang; Huilong, Xu; Jinghe, Cao

    2017-04-01

    A seismicity cluster and a great 16 September 1994 earthquake occur in the Taiwan Shoal region, outer rise of the Manila subduction zone. To understand what mechanisms control and generate the earthquake cluster, it is important to investigate the deep crustal structure of the Taiwan Shoal region. We present a 2-D seismic tomographic image of the crustal structure along the OBS2012 profile based on ocean bottom seismographic (OBS) data. The structure exhibits that a high velocity anomaly in the upper crust beneath the Taiwan Shoal is flanked by lower velocity anomalies. Based on the crustal structure, we study the 765 earthquakes, which occurred in the period 1991-2015. These epicenters, combined with the regional faults, and crustal structure, allow us to better understand the nature of the active tectonics in this region. The high velocity area is interpreted as representing stronger, defining major asperities where stress is concentrated corresponding to the location of the earthquake cluster. The earthquake cluster is influenced by the fault interactions. However, the 16 September 1994 earthquake is independents of the seismic activities but associated with the reactivation of the preexisting fault. In Taiwan region, the slab-pull was resisted by the exposed pre-collision accretionary prism and the resistive force caused the in-plane compressive stress accumulation. This condition may favor the triggering of future damaging earthquakes in this region. Key words: earthquake cluster; crustal structure; fault interactions; outer rise; Taiwan Shoal

  10. Crustal balance and crustal flux from shortening estimates in the Central Andes

    Science.gov (United States)

    Hindle, David; Kley, Jonas; Oncken, Onno; Sobolev, Stephan

    2005-01-01

    The Central Andes of South America form the second largest high elevation plateau on earth. Extreme elevations have formed on a noncollisional margin with abundant associated arc magmatism. It has long been thought that the crustal thickness necessary to support Andean topography was not accounted for by known crustal shortening alone. We show that this may in part be due to a two-dimensional treatment of the problem. A three-dimensional analysis of crustal shortening and crustal thickness shows that displacement of material towards the axis of the bend in the Central Andes has added a significant volume of crust not accounted for in previous comparisons. We find that present-day crustal thickness between 12°S and 25°S is accounted for (∼-10% to ∼+3%)with the same shortening estimates, and the same assumed initial crustal thickness as had previously led to the conclusion of a ∼25-35% deficit in shortening relative to volume of crustal material. We suggest that the present-day measured crustal thickness distribution may not match that predicted due to shortening, and substantial redistribution of crust may have occurred by both erosion and deposition at the surface and lower crustal flow in regions of the thermally weakened middle and lower crust.

  11. Variation in the crustal structure across central Iceland

    Science.gov (United States)

    Du, Zhijun; Foulger, G. R.

    2001-04-01

    We determine the crustal structures beneath 12 broad-band seismic stations deployed in a swath across central Iceland along and around the ICEMELT explosion seismic profile by combining teleseismic receiver functions, surface wave dispersion curves and the waveforms of a large, local event in Iceland. By using teleseisms that approach from different backazimuths, we study lateral structural variability out of the line of the ICEMELT profile. Beneath Tertiary areas, the thickness of the upper crust, as defined by the 6.5kms-1 velocity horizon, is ~8km and the depth to the base of the lower crust, as defined by the 7.2kms-1 velocity horizon, is ~29-32km. Beneath the currently active rift zone the upper crust thins to ~6.0km and the depth to the base of the lower crust increases to ~35-40km. A substantial low-velocity zone underlies the Middle Volcanic Zone in the lower crust, which may indicate anomalously high geothermal gradients there. This suggests that the large-scale thermal centre of the hotspot may be more westerly than northwest Vatnajokull, where it is generally assumed to lie. Simplified description of the results notwithstanding, there is substantial variability in the overall style of crustal structure throughout Iceland, and a clear, tripartite division into upper and lower crusts and a sharp Moho is poorly supported by many of our results. The nature, distinctiveness and continuity of the Moho is variable and in many areas the crust-mantle transition is a zone with enhanced velocity gradients several kilometres thick.

  12. Crustal anisotropy from Moho converted Ps wave splitting and geodynamic implications in Northeastern margin of Tibetan Plateau

    Science.gov (United States)

    Xie, Z.; Wu, Q.; Zhang, R.

    2017-12-01

    Collision between Indian and Eurasian result in intense deformation and crustal shortening in the Tibetan Plateau. NE margin of Tibetan Plateau experienced complex deformation between Qilian orogen and its adjacent blocks, Alxa Block in the north and Ordos Block in the east. We focus on if there any evidences exist in the NE margin of Tibetan Plateau, which can support crustal channel flow model. China Earthquake Administration had deployed temporary seismic array which is called ChinaArray Phase Ⅱ, dense seismic stations covered NE margin of Tibetan Plateau. Seismic data recorded by 81 seismic stations is applied in this research. We calculated receiver functions with time-domain deconvolution. We selected RFs which have clear Ps phase both in radial and transverse components to measure Ps splitting owing to crustal anisotropy, and 130 pairs of anisotropy parameters of 51 seismic stations were obtained. We would like to discuss about dynamic mechanism of this area using crustal anisotropy associated with the result of SKS-splitting and surface constrains like GPS velocity. The result can be summarized as follows. The large scale of delay time imply that the crustal anisotropy mainly derives from middle to lower crust rather than upper crust. In the southeastern part of the research area, crustal anisotropy is well agree with the result computed form SKS-splitting and GPS velocity directions trending NWW-SEE or E-W direction. This result imply a vertically coherent deformation in the area as the directions of crustal anisotropy trend to be perpendicular to the direction of normal stress. In the middle and north part of the research area, the fast polarization direction of crustal anisotropy is NEE-SWW or E-W direction, parallels with direction of GPS velocity, but differ to the direction of the result of SKS-splitting. This result may imply that decoupled deformation in this area associated with middle to lower crustal flow.

  13. Crustal structure of the Eastern Alps and their foreland

    DEFF Research Database (Denmark)

    Grad, M.; Brückl, E.; Majdanski, M.

    2009-01-01

    The subject of this paper concerns the seismic modelling of the crustal structure in the transition zone from the Bohemian Massif, across the Molasse basin and the Eastern Alps to the Southern Alps, mainly on the territory of Austria. The CEL10/Alp04 profile crosses the triple point of the European......) are distinct up to 60-90 km offset and are characterized by large variations in apparent velocity and amplitude. The contact between the Molasse basin and the Eastern Alps represents a barrier for seismic waves. Mid-crustal reflections (Pc) are usually recorded at short distance intervals (20-50 km......, was undertaken using a ray-tracing technique. The P-wave velocity in the crystalline upper crust of the Bohemian Massif and Molasse basin is about 6.15 km s-1, which is slightly higher than in the Alpine area (about 6.0 km s-1). Below the northern accretionary wedge of the Eastern Alps low-velocity sediments...

  14. Testing Predictions of Continental Insulation using Oceanic Crustal Thicknesses

    Science.gov (United States)

    Hoggard, Mark; Shorttle, Oliver; White, Nicky

    2016-04-01

    The thermal blanketing effect of continental crust has been predicted to lead to elevated temperatures within the upper mantle beneath supercontinents. Initial break-up is associated with increased magmatism and the generation of flood basalts. Continued rifting and sea-floor spreading lead to a steady reduction of this thermal anomaly. Recently, evidence in support of this behaviour has come from the major element geochemistry of mid-ocean ridge basalts, which suggest excess rifting temperatures of ˜ 150 °C that decay over ˜ 100 Ma. We have collated a global inventory of ˜ 1000 seismic reflection profiles and ˜ 500 wide-angle refraction experiments from the oceanic realm. Data are predominantly located along passive margins, but there are also multiple surveys in the centres of the major oceanic basins. Oceanic crustal thickness has been mapped, taking care to avoid areas of secondary magmatic thickening near seamounts or later thinning such as across transform faults. These crustal thicknesses are a proxy for mantle potential temperature at the time of melt formation beneath a mid-ocean ridge system, allowing us to quantify the amplitude and duration of thermal anomalies generated beneath supercontinents. The Jurassic break-up of the Central Atlantic and the Cretaceous rifting that formed the South Atlantic Ocean are both associated with excess temperatures of ˜ 50 °C that have e-folding times of ˜ 50 Ma. In addition to this background trend, excess temperatures reach > 150 °C around the region of the Rio Grande Rise, associated with the present-day Tristan hotspot. The e-folding time of this more local event is ˜ 10 Ma, which mirrors results obtained for the North Atlantic Ocean south of Iceland. In contrast, crustal thicknesses from the Pacific Ocean reveal approximately constant potential temperature through time. This observation is in agreement with predictions, as the western Pacific was formed by rifting of an oceanic plate. In summary

  15. A deep crustal fluid channel into the San Andreas Fault system near Parkfield, California

    Science.gov (United States)

    Becken, M.; Ritter, O.; Park, S.K.; Bedrosian, P.A.; Weckmann, U.; Weber, M.

    2008-01-01

    Magnetotelluric (MT) data from 66 sites along a 45-km-long profile across the San Andreas Fault (SAF) were inverted to obtain the 2-D electrical resistivity structure of the crust near the San Andreas Fault Observatory at Depth (SAFOD). The most intriguing feature of the resistivity model is a steeply dipping upper crustal high-conductivity zone flanking the seismically defined SAF to the NE, that widens into the lower crust and appears to be connected to a broad conductivity anomaly in the upper mantle. Hypothesis tests of the inversion model suggest that upper and lower crustal and upper-mantle anomalies may be interconnected. We speculate that the high conductivities are caused by fluids and may represent a deep-rooted channel for crustal and/or mantle fluid ascent. Based on the chemical analysis of well waters, it was previously suggested that fluids can enter the brittle regime of the SAF system from the lower crust and mantle. At high pressures, these fluids can contribute to fault-weakening at seismogenic depths. These geochemical studies predicted the existence of a deep fluid source and a permeable pathway through the crust. Our resistivity model images a conductive pathway, which penetrates the entire crust, in agreement with the geochemical interpretation. However, the resistivity model also shows that the upper crustal branch of the high-conductivity zone is located NE of the seismically defined SAF, suggesting that the SAF does not itself act as a major fluid pathway. This interpretation is supported by both, the location of the upper crustal high-conductivity zone and recent studies within the SAFOD main hole, which indicate that pore pressures within the core of the SAF zone are not anomalously high, that mantle-derived fluids are minor constituents to the fault-zone fluid composition and that both the volume of mantle fluids and the fluid pressure increase to the NE of the SAF. We further infer from the MT model that the resistive Salinian block

  16. Reworked crustal of early Paleozoic WuYi Orogen revealed by receiver function data

    Science.gov (United States)

    Wei, Y.; Duan, Y.; Tian, X.; Zhao, Y.

    2017-12-01

    Intraplate orogenic belt, which occurs at the rigid and undeformable plate interiors, is a distinct new type of orogen rather than an interplate or plate marginal orogenic belt, whose deformation occurs exclusively at plate margins. Therefore, intraplate orogenic belts are the most obvious exception to the plate-tectonic paradigm, they are uncommon in Earth's history. The early Paleozoic Wuyi orogen in South China is one of the few examples of intraplate orogen, and is a key to understanding the process of intraplate orogenesis and global early Paleozoic geodynamics. In this study, we select teleseismic records from 45 mobile linear seismic stations deployed in Wuyi Mountain and 58 permanent stations setting in Jiangxi and Fujian provinces, from January 2011 to December 2012, and calculate the crustal thickness and average crustal Vp/Vs ratio using the H-κ stacking method. The main results include the following: 1) the crustal average Poission's ratio shows an increase tendency from land to sea, the interior of Wuyi orogen belt with an low ration less than 0.23, and the coastline with high ration which is up to 0.28, which indicate a very heterogeneous crustal structure and composition in Wuyi orogen and coast belt. 2) the crustal thickness ranges 28-34 km and shows a tendency of thinning from inland to coast in the region of SE China margin, which maight mean the eastern Eurasia lithospheric is extension and thinning induced by the subducted paleo-Pacific slab. To conclusion, we assume that Wuyi orogen experienced upper crustal thickening, lower crust and lithosphere delamination during the early Paleozoic orogeny, and lithosphere extension in Mesozoic. This research is founded by the Natural Science Foundation of China (41174052 and 41604048).

  17. Crustal thickness and Vp/Vs beneath the southeastern United States: Constraints from receiver function stacking

    Science.gov (United States)

    Yang, Q.; Gao, S. S.; Liu, K. H.

    2017-12-01

    To provide new constraints on crustal structure and evolution models beneath a collage of tectonic provinces in the southeastern United States, a total of 10,753 teleseismic receiver functions recorded by 125 USArray and other seismic stations are used to compute crustal thickness and Vp/Vs values. The resulting crustal thicknesses range from 25 km at the coast to 51 km beneath the peak of the southern Appalachians with an average of 36.2 km ± 5.5 km. The resulting crustal thicknesses correlate well with surface elevation and Bouguer gravity anomalies. Beneath the Atlantic Coastal Plain, the crustal thicknesses show a clear eastward thinning with a magnitude of 10 km, from about 40 km beneath the western margin to 30 km beneath the coast. The Vp/Vs values for the entire study area range from 1.71 to 1.90 with a mean value of 1.80 ± 0.04. The mean Vp/Vs value is 1.82±0.035 in the southern Appalachian Mountain. The slightly larger than normal crustal Vp/Vs for this area might be the result of significant erosion of the felsic upper crust over the past 300 million years. Alternatively, it could also suggest the existence of pervasive magmatic intrusion into the Appalachian crust. The Vp/Vs measurements in the Atlantic Coastal Plain increase toward the east, ranging from 1.75 to 1.82, probably indicating a gradual increase of mafic magmatic intrusion into thinner crust during the development of the passive continental margin.

  18. The Crustal Structure of the North-South Earthquake Belt in China Revealed from Deep Seismic Soundings and Gravity Data

    Science.gov (United States)

    Zhao, Yang; Guo, Lianghui; Shi, Lei; Li, Yonghua

    2018-01-01

    The North-South earthquake belt (NSEB) is one of the major earthquake regions in China. The studies of crustal structure play a great role in understanding tectonic evolution and in evaluating earthquake hazards in this region. However, some fundamental crustal parameters, especially crustal interface structure, are not clear in this region. In this paper, we reconstructed the crustal interface structure around the NSEB based on both the deep seismic sounding (DSS) data and the gravity data. We firstly reconstructed the crustal structure of crystalline basement (interface G), interface between upper and lower crusts (interface C) and Moho in the study area by compiling the results of 38 DSS profiles published previously. Then, we forwardly calculated the gravity anomalies caused by the interfaces G and C, and then subtracted them from the complete Bouguer gravity anomalies, yielding the regional gravity anomalies mainly due to the Moho interface. We then utilized a lateral-variable density interface inversion technique with constraints of the DSS data to invert the regional anomalies for the Moho depth model in the study area. The reliability of our Moho depth model was evaluated by comparing with other Moho depth models derived from other gravity inversion technique and receiver function analysis. Based on our Moho depth model, we mapped the crustal apparent density distribution in the study area for better understanding the geodynamics around the NSEB.

  19. Combined crustal-geological cross-section of Ellesmere Island

    DEFF Research Database (Denmark)

    Stephenson, Randell Alexander; Schiffer, Christian; Oakey, Gordon

    are reported in detail in another presentation at this symposium (Schiffer et al.). Moho depth, a number of intracrustal horizons and sedimentary thicknesses can be inferred. Meanwhile, geological mapping on Ellesmere Island in the framework of BGR’s (Germany) CASE (“Circum-Arctic Structural Events”) programme...

  20. 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.

  1. Sub-crustal seismic activity beneath Klyuchevskoy Volcano

    Science.gov (United States)

    Carr, M. J.; Droznina, S.; Levin, V. L.; Senyukov, S.

    2013-12-01

    Seismic activity is extremely vigorous beneath the Klyuchevskoy Volcanic Group (KVG). The unique aspect is the distribution in depth. In addition to upper-crustal seismicity, earthquakes take place at depths in excess of 20 km. Similar observations are known in other volcanic regions, however the KVG is unique in both the number of earthquakes and that they occur continuously. Most other instances of deep seismicity beneath volcanoes appear to be episodic or transient. Digital recording of seismic signals started at the KVG in early 2000s.The dense local network reliably locates earthquakes as small as ML~1. We selected records of 20 earthquakes located at depths over 20 km. Selection was based on the quality of the routine locations and the visual clarity of the records. Arrivals of P and S waves were re-picked, and hypocentral parameters re-established. Newl locations fell within the ranges outlined by historical seismicity, confirming the existence of two distinct seismically active regions. A shallower zone is at ~20 km depth, and all hypocenters are to the northeast of KVG, in a region between KVG and Shiveluch volcano. A deeper zone is at ~30 km, and all hypocenters cluster directly beneath the edifice of the Kyuchevskoy volcano. Examination of individual records shows that earthquakes in both zones are tectonic, with well-defined P and S waves - another distinction of the deep seismicity beneath KVG. While the upper seismic zone is unquestionably within the crust, the provenance of the deeper earthquakes is enigmatic. The crustal structure beneath KVG is highly complex, with no agreed-upon definition of the crust-mantle boundary. Rather, a range of values, from under 30 to over 40 km, exists in the literature. Similarly, a range of velocity structures has been reported. Teleseismic receiver functions (RFs) provide a way to position the earthquakes with respect to the crust-mantle boundary. We compare the differential travel times of S and P waves from deep

  2. Crustal characteristic variation in the central Yamato Basin, Japan Sea back-arc basin, deduced from seismic survey results

    Science.gov (United States)

    Sato, Takeshi; No, Tetsuo; Miura, Seiichi; Kodaira, Shuichi

    2018-02-01

    The crustal structure of the Yamato Bank, the central Yamato Basin, and the continental shelf in the southern Japan Sea back-arc basin is obtained based on a seismic survey using ocean bottom seismographs and seismic shot to elucidate the back-arc basin formation processes. The central Yamato Basin can be divided into three domains based on the crustal structure: the deep basin, the seamount, and the transition domains. In the deep basin domain, the crust without the sedimentary layer is about 12-13 km thick. Very few units have P-wave velocity of 5.4-6.0 km/s, which corresponds to the continental upper crust. In the seamount and transition domains, the crust without the sedimentary layer is about 12-16 km thick. The P-wave velocities of the upper and lower crusts differs among the deep basin, the seamount, and the transition domains. These results indicate that the central Yamato Basin displays crustal variability in different domains. The crust of the deep basin domain is oceanic in nature and suggests advanced back-arc basin development. The seamount domain might have been affected by volcanic activity after basin opening. In the transition domain, the crust comprises mixed characters of continental and oceanic crust. This crustal variation might represent the influence of different processes in the central Yamato Basin, suggesting that crustal development was influenced not only by back-arc opening processes but also by later volcanic activity. In the Yamato Bank and continental shelf, the upper crust has thickness of about 17-18 km and P-wave velocities of 3.3-4.1 to 6.6 km/s. The Yamato Bank and the continental shelf suggest a continental crustal character.

  3. Crustal structure in Tengchong Volcano-Geothermal Area, western Yunnan, China

    Science.gov (United States)

    Wang, Chun-Yong; Huangfu, Gang

    2004-02-01

    Based upon the deep seismic sounding profiles carried out in the Tengchong Volcano-Geothermal Area (TVGA), western Yunnan Province of China, a 2-D crustal P velocity structure is obtained by use of finite-difference inversion and forward travel-time fitting method. The crustal model shows that a low-velocity anomaly zone exists in the upper crust, which is related to geothermal activity. Two faults, the Longling-Ruili Fault and Tengchong Fault, on the profile extend from surface to the lower crust and the Tengchong Fault likely penetrates the Moho. Moreover, based on teleseismic receiver functions on a temporary seismic network, S-wave velocity structures beneath the geothermal field show low S-wave velocity in the upper crust. From results of geophysical survey, the crust of TVGA is characterized by low P-wave and S-wave velocities, low resistivity, high heat-flow value and low Q. The upper mantle P-wave velocity is also low. This suggests presence of magma in the crust derived from the upper mantle. The low-velocity anomaly in upper crust may be related to the magma differentiation. The Tengchong volcanic area is located on the northeast edge of the Indian-Eurasian plate collision zone, away from the eastern boundary of the Indian plate by about 450 km. Based on the results of this paper and related studies, the Tengchong volcanoes can be classified as plate boundary volcanoes.

  4. Self-reported musculoskeletal disorders of the distal upper extremities and the neck in German veterinarians: a cross-sectional study.

    Directory of Open Access Journals (Sweden)

    Agnessa Kozak

    Full Text Available BACKGROUND: Veterinary work is a physically demanding profession and entails the risk of injuries and diseases of the musculoskeletal system, particularly in the upper body. The prevalence of musculoskeletal disorders (MSD, the consequences and work-related accidents in German veterinarians were investigated. Work-related and individual factors associated with MSD of upper extremities and the neck were analyzed. METHODS: In 2011, a self-reporting Standardized Nordic Questionnaire was mailed to registered veterinarians in seven federal medical associations in Germany. A total of 3174 (38.4% veterinarians responded. Logistic regression analysis was used to determine the association between risk factors and MSD-related impairment of daily activities. RESULTS: MSD in the neck (66.6% and shoulder (60.5% were more prevalent than in the hand (34.5% or elbow (24.5%. Normal activities were affected in 28.7% (neck, 29.5% (shoulder, 19.4% (hand and 14% (elbow of the respondents. MSD in the upper body occurred significantly more often in large animal practitioners. Accidents that resulted in MSD were most frequently reported in the hand/wrist (14.3% or in the shoulder (10.8%. The majority of all accidents in the distal upper extremities were caused by animals than by other factors (19% vs. 9.2%. For each area of the body, a specific set of individual and work-related factors contributed significantly to severe MSD: Older age, gender, previous injuries, BMI, practice type, veterinary procedures such as dentistry, rectal procedures and obstetric procedures as well as high demands and personal burnout. CONCLUSION: From the perspective of occupational health and safety, it seems to be necessary to improve accident prevention and to optimize the ergonomics of specific tasks. Our data suggest the need for target group-specific preventive measures that also focus on the psychological factors at work.

  5. Effects of alcohol consumption, cigarette smoking, and betel quid chewing on upper digestive diseases: a large cross-sectional study and meta-analysis.

    Science.gov (United States)

    Chuang, Yun-Shiuan; Wu, Meng-Chieh; Yu, Fang-Jung; Wang, Yao-Kuang; Lu, Chien-Yu; Wu, Deng-Chyang; Kuo, Chie-Tong; Wu, Ming-Tsang; Wu, I-Chen

    2017-09-29

    Cigarette smoking is a well-known risk factor of upper digestive diseases. Findings on alcohol's effect on these diseases are inconsistent and with the exception of its association with esophageal cancer, little is known about betel quid chewing. This study investigated the association between use of these three substances and upper digestive diseases. We collected data from 9,275 patients receiving upper endoscopies between April 2008 and December 2013. Polynomial regressions were used to analyze the association between risk factors and diseases of the esophagus, stomach and duodenum. Meta-analysis for use of these substances and esophageal diseases was also performed. Participants who simultaneously consumed cigarettes, alcohol and betel quid had a 17.28-fold risk of esophageal cancer (95% CI = 7.59-39.33), 2.99-fold risk of Barrette's esophagus (95% CI = 2.40-4.39), 1.60-fold risk of grade A-B erosive esophagitis (95% CI = 1.29-2.00), 2.00-fold risk of gastric ulcer (95% CI = 1.52-2.63), 2.12-fold risk of duodenitis (95% CI = 1.55-2.89) and 1.29-fold risk of duodenal ulcer (95% CI = 1.01-1.65). Concurrent consumption of more substances was associated with significantly higher risk of developing these diseases. Meta-analysis also revealed use of the three substances came with a high risk of esophageal diseases. In conclusions, cigarette smoking, alcohol drinking and betel quid chewing were associated with upper digestive tract diseases.

  6. Modelling of crustal rock mechanics for radioactive waste storage in Fennoscandia - problem definition

    International Nuclear Information System (INIS)

    Stephansson, O.

    1987-05-01

    Existing knowledge of crustal stresses for Fennoscandia is presented. Generic, two-dimensional models are proposed for vertical and planar sections of a traverse having a direction NW-SE in Northern Fennoscandia. The proposed traverse will include the major neotectonic structures at Lansjaerv and Paervie, respectively, and also the study site for storage of spent nuclear fuel at Kamlunge. The influence of glaciation, deglaciation, glacial rebound on crustal rock mechanics and stability is studied for the modelling work. Global models, with a length of roughly 100 km, will increase our over all understanding of the change in stresses and deformations. These can provide boundary conditions for regional and near-field models. Properties of strength and stiffness of intact granitic rock masses, faults and joints are considered in the modelling of the crustal rock mechanics for any of the three models described. (orig./HP)

  7. Crustal tomographic imaging and geodynamic implications toward south of Southern Granulite Terrain (SGT), India

    Science.gov (United States)

    Behera, Laxmidhar

    2011-09-01

    The crustal structure toward southern part of SGT is poorly defined leaving an opportunity to understand the tectonic and geodynamic evolution of this high-grade granulite terrain surrounded by major shear and tectonically disturbed zones like Achankovil Shear Zone (AKSZ) and Palghat Cauvery Shear Zone (PCSZ). To develop a geologically plausible crustal tectonic model depicting major structural elements, a comprehensive tomographic image was derived using deep-seismic-sounding data corroborated by Bouguer gravity modeling, coincident-reflection-seismic, heat-flow and available geological/geochronological informations along the N-S trending Vattalkundu-Kanyakumari geotransect. The final tectonic model represents large compositional changes of subsurface rocks accompanied by velocity heterogeneities with crustal thinning (44-36 km) and Moho upwarping from north to south. This study also reveals and successfully imaged anomalous zone of exhumation near AKSZ having transpression of exhumed rocks at mid-to-lower crustal level (20-30 km) with significant underplating and mantle upwelling forming a complex metamorphic province. The presence of shear zones with high-grade charnockite massifs in the upper-crust exposed in several places reveal large scale exhumation of granulites during the Pan-African rifting (~ 550 Ma) and provide important insights of plume-continental lithosphere interaction with reconstruction of the Gondwanaland.

  8. Fine-scale crustal structure of the Azores Islands from teleseismic receiver functions

    Science.gov (United States)

    Spieker, K.; Rondenay, S.; Ramalho, R. S.; Thomas, C.; Helffrich, G. R.

    2016-12-01

    The Azores plateau is located near the Mid-Atlantic Ridge (MAR) and consists of nine islands, most of which lie east of the MAR. Various methods including seismic reflection, gravity, and passive seismic imaging have been used to investigate the crustal thickness beneath the islands. They have yielded thickness estimates that range between roughly 10 km and 30 km, but until now models of the fine-scale crustal structure have been lacking. A comparison of the crustal structure beneath the islands that lie west and east of the MAR might give further constraints on the evolution of the islands. For example, geochemical studies carried out across the region predict the existence of volcanic interfaces that should be detected seismically within the shallow crust of some of the islands. In this study, we use data from ten seismic stations located on the Azores Islands to investigate the crustal structure with teleseismic P-wave receiver functions. We query our resulting receiver functions for signals associated with the volcanic edifice, the crust-mantle boundary, and potential underplated layers beneath the various islands. The islands west of the MAR have a crustal structure comprising two discontinuities - an upper one at 1-2 km depth marking the base of the volcanic edifice, and a lower one at 10 km depth that we interpret as crust-mantle boundary. The islands east of the MAR can be subdivided into two groups. The central islands that are closer to the MAR exhibit a crustal structure similar to that of the western islands, with a volcanic edifice reaching a depth of 2 km and an average crust-mantle boundary at around 12 km depth. The easternmost islands, located on the oldest lithosphere, exhibit a more complex crustal structure with evidence for a mid-crustal interface and an underplated layer, yielding an effective crust-mantle boundary at >15 km depth. The difference in structure between proximal and distal islands might be related to the age of the plate at the

  9. Surface-water-quality assessment of the Upper Illinois River basin in Illinois, Indiana, and Wisconsin; cross-sectional and depth variation of water-quality constituents and properties in the Upper Illinois River basin, 1987-88

    Science.gov (United States)

    Marron, Donna C.; Blanchard, Stephen F.

    1995-01-01

    Data on water velocity, temperature, specific con- ductance, pH, dissolved oxygen concentration, chlorophyll concentration, suspended sediment con- centration, fecal-coliform counts, and the percen- tage of suspended sediment finer than 62 micrometers ranged up to 21 percent; and cross-section coefficients of variation of the concentrations of suspended sediment, fecal coliform, and chlorophyll ranged from 7 to 115 percent. Midchannel measure- ments of temperature, specific conductance, and pH were within 5 percent of mean cross-sectional values of these properties at the eight sampling sites, most of which appear well mixed because of the effect of dams and reservoirs. Measurements of the concentration of dissolved oxygen at various cross- section locations and at variable sampling depths are required to obtain a representative value of this constituent at these sites. The large varia- bility of concentrations of chlorophyll and suspended sediment, and fecal-coliform counts at the eight sampling sites indicates that composite rather than midchannel or mean values of these constituents are likely to be most representative of the channel cross section.

  10. Nd isotopes and crustal growth rate

    International Nuclear Information System (INIS)

    Albarede, F.

    1988-01-01

    Sm/Nd isotopic constraints on crustal growth is discussed. In order to constrain Sm/Nd fractionation between continental crust and depleted mantle, an extensive data base of isotopic measurements (assumed to be adequately representative of continental crust) was compiled. The results imply that the evolution of depleted mantles was roughly linear, with no major discontinuities over the course of geologic time. This is different from other determinations of depleting mantle evolution, which show nonlinear behavior. The Sm/Nd evolution lines for continental crust and depleted mantle intersect between 3.8 to 4.0 Ga, which may indicate that the onset of continental growth was later than 4.5 Ga. A mathematical model is described, the results of which imply that time integrated crustal additions from the mantle are about 1.8 to 2.5 cu km/a, whereas crustal subtractions by sediment recycling are about 0.6 to 1.5 cu km/a. This results in a net time integrated crustal growth rate of about 1 cu km/a, which is similar to present day rates determined, for example, by Reymer and Schubert

  11. Crustal structure of the Khartoum Basin, Sudan

    CSIR Research Space (South Africa)

    El Tahir, N

    2013-05-01

    Full Text Available Basin ranges between 33 and 37 km, with an average of 35 km, and that the crustal Vp/Vs ratio ranges from 1.74 to 1.81, with an average of 1.78. From the joint inversion of receiver functions and Rayleigh wave group velocities,we obtained similar results...

  12. Shear wave splitting and crustal anisotropy in the Eastern Ladakh-Karakoram zone, northwest Himalaya

    Science.gov (United States)

    Paul, Arpita; Hazarika, Devajit; Wadhawan, Monika

    2017-06-01

    Seismic anisotropy of the crust beneath the eastern Ladakh-Karakoram zone has been studied by shear wave splitting analysis of S-waves of local earthquakes and P-to-S or Ps converted phases originated at the crust-mantle boundary. The splitting parameters (Φ and δt), derived from S-wave of local earthquakes with shallow focal depths, reveal complex nature of anisotropy with NW-SE and NE oriented Fast Polarization directions (FPD) in the upper ∼22 km of the crust. The observed anisotropy in the upper crust may be attributed to combined effects of existing tectonic features as well as regional tectonic stress. The maximum delay time of fast and slow waves in the upper crust is ∼0.3 s. The Ps splitting analysis shows more consistent FPDs compared to S-wave splitting. The FPDs are parallel or sub parallel to the Karakoram fault (KF) and other NW-SE trending tectonic features existing in the region. The strength of anisotropy estimated for the whole crust is higher (maximum delay time δt: 0.75 s) in comparison to the upper crust. This indicates that the dominant source of anisotropy in the trans-Himalayan crust is confined within the middle and lower crustal depths. The predominant NW-SE trending FPDs consistently observed in the upper crust as well as in the middle and lower crust near the KF zone support the fact that the KF is a crustal-scale fault which extends at least up to the lower crust. Dextral shearing of the KF creates shear fabric and preferential alignment of mineral grains along the strike of the fault, resulting in the observed FPDs. A Similar observation in the Indus Suture Zone (ISZ) also suggests crustal scale deformation owing to the India-Asia collision.

  13. Yellowstone-Snake River Plain seismic profilling experiment: Crustal structure of the eastern Snake River Plain

    International Nuclear Information System (INIS)

    Braile, L.W.; Smith, R.B.; Ansorge, J.; Baker, M.R.; Sparlin, M.A.; Prodehl, C.; Schilly, M.M.; Healy, J.H.; Mueller, S.; Olsen, K.H.

    1982-01-01

    Seismic refraction profiles recorded along the eastern Snake River Plain (ESRP) in southeastern Idaho during the 1978 Yellowstone-Snake River Plain cooperative seismic profiling experiment are interpreted to infer the crustal velocity and attenuation (Q-1) structure of the ESRP. Travel-time and synthetic seismogram modeling of a 250 km reversed refraction profile as well as a 100 km detailed profile indicate that the crust of the ESRP is highly anomalous. Approximately 3 to 6 km of volcanic rocks (with some interbedded sediments) overlie an upper-crustal layer (compressional velocity approx. =6.1 km/s) which thins southwestward along the ESRP from a thickness of 10 km near Island Park Caldera to 2 to 3 km beneath the central and southwestern portions of the ESRP. An intermediate-velocity (approx. =6.5 km/s) layer extends from approx. =10 to approx. =20 km depth. a thick (approx. =22 km) lower crust of compressional velocity 6.8 km/s, a total crustall thickness of approx. =42 km, and a P/sub n/ velocity of approx. =7.9 km/s is observed in the ESRP, similar to the western Snake River Plain and the Rocky Mountains Provinces. High attenuation is evident on the amplitude corrected seismic data due to low-Q values in the volcanic rocks (Q/sub p/ = 20 to 200) and throughout the crust (Q/sub p/ = 160 to 300). Based on these characteristics of the crustal structure and volcanic-age progression data, it is suggested that the ESRP has resulted from an intensitive period of intrusion of mantle-derived basaltic magma into the upper crust generating explosive silicic volcanism and associated regional uplift and caldera collapse. This activity began about 15 m.y. ago in southwestern Idaho and has migrated northeast to its present position at Yellowstone. Subsequent cooling of the intruded upper crust results in the 6.5 km/s velocity intermediate layer. Crustal subsidence and periodic basaltic volcanism as represented by the ESRP complete the sequence of crustal evolution

  14. Crustal evolution derived from the Izu-Bonin-Mariana arc velocity images

    Science.gov (United States)

    Takahashi, N.; Kodaira, S.; Tatsumi, Y.; Miura, S.; Sato, T.; Yamashita, M.; No, T.; Takahashi, T.; Noguchi, N.; Takizawa, K.; Kaiho, Y.; Kaneda, Y.

    2010-12-01

    The Izu-Bonin-Mariana arc is known as one of typical oceanic island arcs, which has developed by subduction between oceanic crusts producing continental materials. Japan Agency for Marine-Earth Science and Technology has carried out seismic surveys using a multi-channel reflection survey system (MCS) and ocean bottom seismographs (OBSs) in the Izu-Bonin-Mariana (IBM) arc since 2002, and reported these crustal images. As the results, we identified the structural characteristics of whole Izu-Bonin-Mariana arc. Rough structural characteristics are, 1) middle crust with Vp of 6 km/s, 2) upper part of the lower crust with Vp of 6.5-6.8 km/s, 3) lower part of the lower crust with Vp of 6.8-7.5 km/s, and 4) lower mantle velocity beneath the arc crusts. In addition, structural variation along the volcanic front, for example, thickness variation of andesitic layers was imaged and the distributions is consistent with those of rhyolite volcanoes, that is, it suggested that the cause the structural variation is various degree of crustal growth (Kodaira et al., 2007). Moreover, crustal thinning with high velocity lower crust across arc was also imaged, and it is interpreted that such crust has been influenced backarc opening (Takahashi et al., 2009). According to Tatsumi et al. (2008), andesitic middle crust is produced by differentiation of basaltic lower crust and a part of the restites are transformed to the upper mantle. This means that region showing much crustal differentiation has large volume of transformation of dense crustal materials to the mantle. We calculated volume profiles of the lower crust along all seismic lines based on the petrologic model, and compared them with observed real volumes obtained by seismic images. If the real volume of the lower crust is large, it means that the underplating of dense materials to the crustal bottom is dominant rather than transformation of dense materials to the upper mantle. According to obtained profiles to judge if the

  15. Estimating the Crustal Power Spectrum From Vector Magsat Data: Crustal Power Spectrum

    Science.gov (United States)

    Lowe, David A. J.; Parker, Robert L.; Purucker, Michael E.; Constable, Catherine G.

    2000-01-01

    The Earth's magnetic field can be subdivided into core and crustal components and we seek to characterize the crustal part through its spatial power spectrum (R(sub l)). We process vector Magsat data to isolate the crustal field and then invert power spectral densities of flight-local components along-track for R(sub l) following O'Brien et al. [1999]. Our model (LPPC) is accurate up to approximately degree 45 (lambda=900 km) - this is the resolution limit of our data and suggests that global crustal anomaly maps constructed from vector Magsat data should not contain features with wavelengths less than 900 km. We find continental power spectra to be greater than oceanic ones and attribute this to the relative thicknesses of continental and oceanic crust.

  16. Constraints on the formation of the Martian crustal dichotomy from remnant crustal magnetism

    Science.gov (United States)

    Citron, Robert I.; Zhong, Shijie

    2012-12-01

    The Martian crustal dichotomy characterizing the topographic difference between the northern and southern hemispheres is one of the most important features on Mars. However, the formation mechanism for the dichotomy remains controversial with two competing proposals: exogenic (e.g., a giant impact) and endogenic (e.g., degree-1 mantle convection) mechanisms. Another important observation is the Martian crustal remnant magnetism, which shows a much stronger field in the southern hemisphere than in the northern hemisphere and also magnetic lineations. In this study, we examine how exogenic and endogenic mechanisms for the crustal dichotomy are constrained by the crustal remnant magnetism. Assuming that the dichotomy is caused by a giant impact in the northern hemisphere, we estimate that the average thickness of ejecta in the southern hemisphere is 20-25 km. While such a giant impact may cause crustal demagnetization in the northern hemisphere, we suggest that the impact could also demagnetize the southern hemisphere via ejecta thermal blanketing, impact demagnetization, and heat transfer from the hot layer of ejecta, thus posing a challenge for the giant impact model. We explore how the pattern of magnetic lineations relates to endogenic theories of dichotomy formation, specifically crustal production via degree-1 mantle convection. We observe that the pattern of lineations roughly corresponds to concentric circles about a single pole, and determine the pole for the concentric circles at 76.5° E and 84.5° S, which nearly overlaps with the centroid of the thickened crust in the southern hemisphere. We suggest that the crustal magnetization pattern, magnetic lineations, and crustal dichotomy (i.e., thickened crust in the highlands) can be explained by a simple endogenic process; one-plume convection causes melting and crustal production above the plume in the southern hemisphere, and strong crustal magnetization and magnetic lineations are formed in the southern

  17. Crustal parameters in the Iberian Peninsula

    Science.gov (United States)

    Banda, E.

    1988-06-01

    The structure of the crust in the Iberian Peninsula has been investigated for the last 15 years by Spanish and Portuguese groups in close collaboration with other European institutions. The first experiments were carried out in Portugal (Mueller et al., 1973) with the aim of investigating the crustal structure of the Hercynian belt in the southwest corner of the Iberian peninsula. Other experiments have been subsequently realized to study different aspects of the crust in various regions of Portugal. In Spain the main effort has been focused in Alpine areas, with the first experiments in the Alboran Sea and the Betic Cordilleras (Working Group for Deep Seismic Sounding in Spain, 1974-1975, 1977; Working Group for Deep Seismic Sounding in the Alboran Sea, 1974-1975, 1978). Follow-up experiments until 1981 completed the work in the Betic Cordillera. Extensive experiments were carried out in the Pyrenees in 1978. Further surveys covered the Balearic Islands in 1976, the Valencia Trough in 1976 and 1983, and the Celtiberian Chain (or Iberic system) in 1981. The Hercynian belt has only been studied in detail in the northwest corner of Spain in 1982, with smaller studies in the central Iberian Massif in 1976 and 1986. Mostaanpour (1984) has compiled some crustal parameters (crustal thickness, average crustal velocity and Pn velocity) for western Europe. Meanwhile, more complete data are available for the Iberian Peninsula. The results presented here were derived from a large number of seismic refraction experiments which have been carried out mostly along or close to coastal areas of the Iberian Peninsula. Offshore explosions of various sizes were used as the energy source in most cases, in addition to some quarry blasts. Unfortunately this leaves most of the inner part of the Iberian Peninsula unsurveyed. Our purpose is to summarize some of the crustal parameters obtained so far and to detail the appropriate literature for the interested reader.

  18. Diagnostic accuracy of age and alarm symptoms for upper GI malignancy in patients with dyspepsia in a GI clinic: a 7-year cross-sectional study.

    Directory of Open Access Journals (Sweden)

    Hooman Khademi

    Full Text Available OBJECTIVES: We investigated whether using demographic characteristics and alarm symptoms can accurately predict cancer in patients with dyspepsia in Iran, where upper GI cancers and H. pylori infection are common. METHODS: All consecutive patients referred to a tertiary gastroenterology clinic in Tehran, Iran, from 2002 to 2009 were invited to participate in this study. Each patient completed a standard questionnaire and underwent upper gastrointestinal endoscopy. Alarm symptoms included in the questionnaire were weight loss, dysphagia, GI bleeding, and persistent vomiting. We used logistic regression models to estimate the diagnostic value of each variable in combination with other ones, and to develop a risk-prediction model. RESULTS: A total of 2,847 patients with dyspepsia participated in this study, of whom 87 (3.1% had upper GI malignancy. Patients reporting at least one of the alarm symptoms constituted 66.7% of cancer patients compared to 38.9% in patients without cancer (p<0.001. Esophageal or gastric cancers in patients with dyspepsia was associated with older age, being male, and symptoms of weight loss and vomiting. Each single predictor had low sensitivity and specificity. Using a combination of age, alarm symptoms, and smoking, we built a risk-prediction model that distinguished between high-risk and low-risk individuals with an area under the ROC curve of 0.85 and acceptable calibration. CONCLUSIONS: None of the predictors demonstrated high diagnostic accuracy. While our risk-prediction model had reasonable accuracy, some cancer cases would have remained undiagnosed. Therefore, where available, low cost endoscopy may be preferable for dyspeptic older patient or those with history of weight loss.

  19. Long-term exercising video-endoscopic examination of the upper airway following laryngoplasty surgery: a prospective cross-sectional study of 41 horses.

    Science.gov (United States)

    Barnett, T P; O'Leary, J M; Parkin, T D H; Dixon, P M; Barakzai, S Z

    2013-09-01

    To investigate upper respiratory tract function in horses, previously undergoing laryngoplasty (LP), using exercising video-endoscopy. To evaluate arytenoid abduction and stability, diagnose any concurrent upper airway problems, and correlate these with the owners' perception of success. Horses undergoing LP during a 6-year period at one hospital were initially included. Those available for re-examination were exercised for a duration and intensity considered maximal for their discipline using an over-ground endoscope. Resting and exercising laryngeal and pharyngeal videos were analysed blindly. Multivariable analysis was used to test associations between resting and exercising endoscopic variables, and also between endoscopic variables and owner questionnaire findings. Forty-one horses were included and 78% had a form of upper airway collapse at exercise, with 41% having complex forms, despite 93% of owners reporting the surgery to have been beneficial. Horses with poor abduction (grades 4 or 5/5) were 6 times more likely to make respiratory noise compared with those with good (grades 2 or 3/5) abduction (P = 0.020; 95% confidence interval [CI] 1.3-27.0), and those not having a ventriculectomy were 4.9 times more likely to produce respiratory noise post operatively (P = 0.048; 95% CI 1.0-23.9). Palatal dysfunction was observed in 24% of horses at rest, and 56% at exercise, with the diagnosis at rest and exercise significantly associated (P = 0.001). Increasing severity of pharyngeal lymphoid hyperplasia (prevalence 61%) was significantly associated with increasing arytenoid abduction (P = 0.01). Thirty-four per cent of horses had aryepiglottic fold collapse and 22% of horses had vocal fold collapse. Many horses that had previously had LP were diagnosed with upper airway abnormalities, despite the procedure being considered as beneficial by most owners. When investigating cases of ongoing respiratory noise or poor performance following LP, exercising endoscopy must

  20. Decrease in oceanic crustal thickness since the breakup of Pangaea

    Science.gov (United States)

    van Avendonk, Harm J. A.; Davis, Joshua K.; Harding, Jennifer L.; Lawver, Lawrence A.

    2017-01-01

    Earth's mantle has cooled by 6-11 °C every 100 million years since the Archaean, 2.5 billion years ago. In more recent times, the surface heat loss that led to this temperature drop may have been enhanced by plate-tectonic processes, such as continental breakup, the continuous creation of oceanic lithosphere at mid-ocean ridges and subduction at deep-sea trenches. Here we use a compilation of marine seismic refraction data from ocean basins globally to analyse changes in the thickness of oceanic crust over time. We find that oceanic crust formed in the mid-Jurassic, about 170 million years ago, is 1.7 km thicker on average than crust produced along the present-day mid-ocean ridge system. If a higher mantle temperature is the cause of thicker Jurassic ocean crust, the upper mantle may have cooled by 15-20 °C per 100 million years over this time period. The difference between this and the long-term mantle cooling rate indeed suggests that modern plate tectonics coincide with greater mantle heat loss. We also find that the increase of ocean crustal thickness with plate age is stronger in the Indian and Atlantic oceans compared with the Pacific Ocean. This observation supports the idea that upper mantle temperature in the Jurassic was higher in the wake of the fragmented supercontinent Pangaea due to the effect of continental insulation.

  1. Upper Gastrointestinal Symptoms Predictive of Candida Esophagitis and Erosive Esophagitis in HIV and Non-HIV Patients: An Endoscopy-Based Cross-Sectional Study of 6011 Patients.

    Science.gov (United States)

    Takahashi, Yuta; Nagata, Naoyoshi; Shimbo, Takuro; Nishijima, Takeshi; Watanabe, Koji; Aoki, Tomonori; Sekine, Katsunori; Okubo, Hidetaka; Watanabe, Kazuhiro; Sakurai, Toshiyuki; Yokoi, Chizu; Mimori, Akio; Oka, Shinichi; Uemura, Naomi; Akiyama, Junichi

    2015-11-01

    Upper gastrointestinal (GI) symptoms are common in both HIV and non-HIV-infected patients, but the difference of GI symptom severity between 2 groups remains unknown. Candida esophagitis and erosive esophagitis, 2 major types of esophagitis, are seen in both HIV and non-HIV-infected patients, but differences in GI symptoms that are predictive of esophagitis between 2 groups remain unknown. We aimed to determine whether GI symptoms differ between HIV-infected and non-HIV-infected patients, and identify specific symptoms of candida esophagitis and erosive esophagitis between 2 groups.We prospectively enrolled 6011 patients (HIV, 430; non-HIV, 5581) who underwent endoscopy and completed questionnaires. Nine upper GI symptoms (epigastric pain, heartburn, acid regurgitation, hunger cramps, nausea, early satiety, belching, dysphagia, and odynophagia) were evaluated using a 7-point Likert scale. Associations between esophagitis and symptoms were analyzed by the multivariate logistic regression model adjusted for age, sex, and proton pump inhibitors.Endoscopy revealed GI-organic diseases in 33.4% (2010/6.011) of patients. The prevalence of candida esophagitis and erosive esophagitis was 11.2% and 12.1% in HIV-infected patients, respectively, whereas it was 2.9% and 10.7 % in non-HIV-infected patients, respectively. After excluding GI-organic diseases, HIV-infected patients had significantly (P symptom scores for heartburn, hunger cramps, nausea, early satiety, belching, dysphagia, and odynophagia than non-HIV-infected patients. In HIV-infected patients, any symptom was not significantly associated with CD4 cell count. In multivariate analysis, none of the 9 GI symptoms were associated with candida esophagitis in HIV-infected patients, whereas dysphagia and odynophagia were independently (P HIV-infected patients. However, heartburn and acid regurgitation were independently (P symptom scores were reliable in both HIV (α, 0.86) and non-HIV-infected patients (α, 0.85).This

  2. The Late Variscan control on the location and asymmetry of the Upper Rhine Graben

    Science.gov (United States)

    Grimmer, J. C.; Ritter, J. R. R.; Eisbacher, G. H.; Fielitz, W.

    2017-04-01

    The NNE-trending Upper Rhine Graben (URG) of the European Cenozoic Rift System developed from c. 47 Ma onwards in response to changing lithospheric stresses in the northwestern foreland of the Alps. The composite graben structure consists of three segments, each c. 100 km long and 30-40 km wide, but flares to c. 60 km near its southern and to c. 80 km near its northern termination. Normal faulting induced a total extension of 5-8 km of the 1-2 km thick Mesozoic sedimentary Franconian platform and underlying Variscan basement rocks. However, distribution of an up to 3.5 km thick sedimentary graben fill and cumulative displacements near Eastern and Western Main Border fault systems suggest that subsidence of the graben floor and shoulder uplift created strong cross-sectional asymmetries. Cumulative W-down displacements >3 km along strongly segmented transfer faults in the east contrast with E-down displacements emergence of the platform above sea level in late Mesozoic times, the deep-reaching W-dipping "extensional defects" of the East Rhine Detachment exerted a primary lithospheric scale control on both location and cross-sectional asymmetry of the Cenozoic graben structure. NE- and NW-striking, strongly altered and more shallow rooted Permocarboniferous or Mesozoic faults exerted secondary upper crustal controls on transfer faults and the accommodation zones near the terminations and segment boundaries of the URG. Deep crustal to upper lithospheric asymmetries continue to influence the neotectonic setting of the URG, such as westward rising earthquake hypocentres. Seismic activity along the URG appears to be part of a >600 km long zone that delimits the trailing edge of a SW-moving lithospheric block. In the URG area, NE-SW-oriented seismic anisotropy at sublithospheric depths of c. 60-80 km suggest active mantle flow in this direction as a possible driving force for the reactivation of pre-graben lithospheric shear zones.

  3. Interaction between mantle and crustal detachments: a non-linear system controlling lithospheric extension

    Science.gov (United States)

    Rosenbaum, G.; Regenauer-Lieb, K.; Weinberg, R. F.

    2009-12-01

    We use numerical modelling to investigate the development of crustal and mantle detachment faults during lithospheric extension. Our models simulate a wide range of rift systems with varying values of crustal thickness and heat flow, showing how strain localization in the mantle interacts with localization in the upper crust and controls the evolution of extensional systems. Model results reveal a richness of structures and deformation styles, which grow in response to a self-organized mechanism that minimizes the internal stored energy of the system by localizing deformation at different levels of the lithosphere. Crustal detachment faults are well developed during extension of overthickened (60 km) continental crust, even when the initial heat flow is relatively low (50 mW/m2). In contrast, localized mantle deformation is most pronounced when the extended lithosphere has a normal crustal thickness (30-40 km) and an intermediate (60-70 mW/m2) heat flow. Results show a non-linear response to subtle changes in crustal thickness or heat flow, characterized by abrupt and sometime unexpected switches in extension modes (e.g. from diffuse rifting to effective lithospheric-scale rupturing) or from mantle- to crust-dominated strain localization. We interpret this non-linearity to result from the interference of doming wavelengths. Disharmony of crust and mantle doming wavelengths results in efficient communication between shear zones at different lithospheric levels, leading to rupturing of the whole lithosphere. In contrast, harmonious crust and mantle doming inhibits interaction of shear zones across the lithosphere and results in a prolonged rifting history prior to continental breakup.

  4. Interaction between mantle and crustal detachments: A nonlinear system controlling lithospheric extension

    Science.gov (United States)

    Rosenbaum, Gideon; Regenauer-Lieb, Klaus; Weinberg, Roberto F.

    2010-11-01

    We use numerical modeling to investigate the development of crustal and mantle detachments during lithospheric extension. Our models simulate a wide range of extensional systems with varying values of crustal thickness and heat flow, showing how strain localization in the mantle interacts with localization in the upper crust and controls the evolution of extensional systems. Model results reveal a richness of structures and deformation styles as a response to a self-organized mechanism that minimizes the internal stored energy of the system by localizing deformation. Crustal detachments, here referred as low-angle normal decoupling horizons, are well developed during extension of overthickened (60 km) continental crust, even when the initial heat flow is relatively low (50 mW m-2). In contrast, localized mantle deformation is most pronounced when the extended lithosphere has a normal crustal thickness (30-40 km) and an intermediate heat flow (60-70 mW m-2). Results show a nonlinear response to subtle changes in crustal thickness or heat flow, characterized by abrupt and sometimes unexpected switches in extension modes (e.g., from diffuse extensional deformation to effective lithospheric-scale rupturing) or from mantle- to crust-dominated strain localization. We interpret this nonlinearity to result from the interference of doming wavelengths in the presence of multiple necking instabilities. Disharmonic crust and mantle doming wavelengths results in efficient communication between shear zones at different lithospheric levels, leading to rupturing of the whole lithosphere. In contrast, harmonic crust and mantle doming inhibits interaction of shear zones across the lithosphere and results in a prolonged history of extension prior to continental breakup.

  5. Crustal evolution of South American Platform based on Sm-Nd isotope geochemistry; Evolucao crustal da plataforma sul americana com base na geoquimica isotopica Sm-Nd

    Energy Technology Data Exchange (ETDEWEB)

    Sato, Kei

    1998-07-01

    Sm-Nd isotopic systematics is relevant to the topics of origin and evolution the of continental crust, where model ages refer to the time when crustal material was differentiated from the upper mantle. Alternative interpretations are due to a lack of adequate information on crustal processes and the variable composition of the mantle sources. The Sm-Nd methods are presented, and applied on rock materials from the South American Platform. The main conclusions indicate juvenile accretion with higher growth rates (peaks), around 3.7-3.5 Ga ({approx} 0.5% in volume), 3.1 - 2.9 Ga ({approx}16%), 2.7 - 2.6 ({approx} 9%), 2.2 - 1.9 (35%) and 1.3-1.0 (7%). The continental growth curve indicates that about 35 % of the crust was formed by 2.5 Ga, 88% by 1.8 Ga and 99% by 1.0 Ga, and the remaining {approx} 1 % was added in the Phanerozoic. Rapid crustal growth occurred between 2.2 and 1.9 Ga. The main period of continental crust formation occurred during the Paleoproterozoic, corresponding to 54 % in volume. Sm-Nd model ages, when compared with the crystallisation ages of granitoid rocks, furnish a rough estimate of juvenile vs. reworked material. Within the South American Platform about 45% of juvenile continental crust is still preserved within tectonic provinces of different ages. The remainder represents continental crust reworked in younger tectono-thermal events. In particular crustal reworking was predominating over juvenile accretion during Meso-Neoproterozoic. The Transbrasiliano Lineament is a megasuture, active in the Neoproterozoic, which separates a large northwestern mass, including the Amazonian and Sao Luis Cratons, from a southeastern mass, formed by a collage of cratonic fragments, of which the Sao Francisco and Rio de La Plata are the largest. The crustal evolutions of these two large continental masses are considered individually, and can be resumed following form: I - Old Archean rocks (>3.4 Ga) are found only within the south-eastern part (Gaviao Block

  6. Crustal structure beneath Beijing and its surrounding regions derived from gravity data

    Science.gov (United States)

    Jiang, Wenliang; Zhang, Jingfa; Lu, Xiaocui; Lu, Jing

    2011-06-01

    In this paper we use gravity data to study fine crustal structure and seismogenic environment beneath Beijing and its surrounding regions. Multi-scale wavelet analysis method is applied to separating gravity fields. Logarithmic power spectrum method is also used to calculate depth of gravity field source. The results show that the crustal structure is very complicated beneath Beijing and its surrounding areas. The crustal density exhibits laterally inhomogeneous. There are three large scale tectonic zones in North China, i.e., WNW-striking Zhangjiakou-Bohai tectonic zone (ZBTZ), NE-striking Taihang piedmont tectonic zone (TPTZ) and Cangxian tectonic zone (CTZ). ZBTZ and TPTZ intersect with each other beneath Beijing area and both of them cut through the lithosphere. The upper and middle crusts consist of many small-scale faults, uplifts and depressions. In the lower crust, these small-scale tectonic units disappear gradually, and they are replaced by large-scale tectonic units. In surrounding regions of Beijing, ZBTZ intersects with several other NE-striking tectonic units, such as Cangxian uplift, Jizhong depression and Shanxi Graben System (SGS). In west of Taihangshan uplift, gravity anomalies in upper and middle crusts are correlated with geological and topographic features on the surface. Compared with the crust, the structure is comparatively simple in uppermost mantle. Earthquakes mainly occurred in upper and middle crusts, especially in transitional regions between high gravity anomaly and low gravity anomaly. Occurrence of large earthquakes may be related to the upwelling of upper mantle and asthenosphere heat flow materials, such as Sanhe earthquake ( M S8.0) and Tangshan earthquake ( M S7.8).

  7. Orphan Basin crustal structure from a dense wide-angle seismic profile - Tomographic inversion

    Science.gov (United States)

    Watremez, Louise; Lau, K. W. Helen; Nedimović, Mladen R.; Louden, Keith E.; Karner, Garry D.

    2014-05-01

    Orphan Basin is located on the eastern margin of Canada, offshore of Newfoundland and East of Flemish Cap. It is an aborted continental rift formed by multiple episodes of rifting. The crustal structure across the basin has been determined by an earlier refraction study using 15 instruments on a 550 km long line. It shows that the continental crust was extended over an unusually wide region but did not break apart. The crustal structure of the basin thus documents stages in the formation of a magma-poor rifted margin up to crustal breakup. The OBWAVE (Orphan Basin Wide-Angle Velocity Experiment) survey was carried out to image crustal structures across the basin and better understand the processes of formation of this margin. The spacing of the 89 recording stations varies from 3 to 5 km along this 500-km-long line, which was acquired along a pre-existing reflection line. The highest resolution section corresponds to the part of the profile where the crust was expected to be the thinnest. We present the results from a joint tomography inversion of first and Moho reflected arrival times. The high data density allows us to define crustal structures with greater detail than for typical studies and to improve the understanding of the processes leading to the extreme stretching of continental crust. The final model was computed following a detailed parametric study to determine the optimal parameters controlling the ray-tracing and the inversion processes. The final model shows very good resolution. In particular, Monte Carlo standard deviations of crustal velocities and Moho depths are generally Orphan Basin is the result of rifting of a non-homogeneous Avalon terrane where the lower crust is primarily ductile.

  8. Low upper-shelf toughness, high transition temperature test insert in HSST [Heavy Section Steel Technology] PTSE-2 [Pressurized Thermal Shock Experiment-2] vessel and wide plate test specimens: Final report

    International Nuclear Information System (INIS)

    Domian, H.A.

    1987-02-01

    A piece of A387, Grade 22 Class 2 (2-1/4 Cr - 1 Mo) steel plate specially heat treated to produce low upper-shelf (LUS) toughness and high transition temperature was installed in the side wall of Heavy Section Steel Technology (HHST) vessel V-8. This vessel is to be tested by the Oak Ridge National Laboratory (ORNL) in the Pressurized Thermal Shock Experiment-2 (PTSE-2) project of the HSST program. Comparable pieces of the plate were made into six wide plate specimens and other samples. These samples underwent tensile tests, Charpy tests, and J-integral tests. The results of these tests are given in this report

  9. MAGNETAR FIELD EVOLUTION AND CRUSTAL PLASTICITY

    International Nuclear Information System (INIS)

    Lander, S. K.

    2016-01-01

    The activity of magnetars is believed to be powered by colossal magnetic energy reservoirs. We sketch an evolutionary picture in which internal field evolution in magnetars generates a twisted corona, from which energy may be released suddenly in a single giant flare, or more gradually through smaller outbursts and persistent emission. Given the ages of magnetars and the energy of their giant flares, we suggest that their evolution is driven by a novel mechanism: magnetic flux transport/decay due to persistent plastic flow in the crust, which would invalidate the common assumption that the crustal lattice is static and evolves only under Hall drift and Ohmic decay. We estimate the field strength required to induce plastic flow as a function of crustal depth, and the viscosity of the plastic phase. The star’s superconducting core may also play a role in magnetar field evolution, depending on the star’s spindown history and how rotational vortices and magnetic fluxtubes interact.

  10. Crustal anisotropy across northern Japan from receiver functions.

    Science.gov (United States)

    Bianchi, I; Bokelmann, G; Shiomi, K

    2015-07-01

    Northern Japan is a tectonically active area, with the presence of several volcanoes, and with frequent earthquakes among which the destructive M w  = 8.9-9.0 Tohoku-oki occurred on 11 March 2011. Tectonic activity leaves an imprint on the crustal structures, on both the upper and the lower layers. To investigate the crust in northern Japan, we construct a receiver function data set using teleseismic events recorded at 58 seismic stations belonging to the Japanese National (Hi-net) network. We isolate the signals, in the receiver function wavelet, that witness the presence of anisotropic structures at depth, with the aim of mapping the variation of anisotropy across the northern part of the island. This study focuses on the relation among anisotropy detected in the crust, stresses induced by plate convergence across the subduction zone, and the intrinsic characteristics of the rocks. Our results show how a simple velocity model with two anisotropic layers reproduces the observed data at the stations. We observe a negligible or small amount of signal related to anisotropy in the eastern part of the study area (i.e., the outer arc) for both upper and lower crust. Distinct anisotropic features are observed at the stations on the western part of the study area (i.e., the inner arc) for both upper and lower crust. The symmetry axes are mostly E-W oriented. Deviation from the E-W orientation is observed close to the volcanic areas, where the higher geothermal gradient might influence the deformation processes.

  11. Spatial relationships between crustal structures and mantle seismicity in the Vrancea Seismogenic Zone of Romania: Implications for geodynamic evolution

    Science.gov (United States)

    Enciu, Dana-Mihaela

    Integration of active and passive-source seismic data is employed to study the relationships between crustal structures and seismicity in the SE Carpathian foreland of Romania, and the connection with the Vrancea Seismogenic Zone. Relocated crustal epicenters and focal mechanisms are correlated with industry seismic profiles Comanesti, Ramnicu Sarat, Braila and Buzau, the reprocessed DACIA PLAN profile and the DRACULA (Deep Reflection Acquisition Constraining Unusual Lithospheric Activity) II and III profiles in order to understand the link between neo-tectonic foreland deformation and Vrancea mantle seismicity. Projection of crustal foreland hypocenters onto deep seismic profiles identified active crustal faults suggesting a mechanical coupling between sedimentary, crustal and upper mantle structures on the Trotus, Sinaia and newly observed Ialomita Faults. Seismic reflection imaging revealed the absence of west dipping reflectors in the crust and an east dipping to horizontal Moho in the proximity of the Vrancea area. These findings argue against both 'subduction-in-place' and 'slab break-off' as viable mechanisms for generating Vrancea mantle seismicity.

  12. Crustal Structure beneath Alaska from Receiver Functions

    Science.gov (United States)

    Zhang, Y.; Li, A.

    2017-12-01

    The crustal structure in Alaska has not been well resolved due to the remote nature of much of the state. The USArray Transportable Array (TA), which is operating in Alaska and northwestern Canada, significantly increases the coverage of broadband seismic stations in the region and allows for a more comprehensive study of the crust. We have analyzed P-receiver functions from earthquake data recorded by 76 stations of the TA and AK networks. Both common conversion point (CCP) and H-K methods are used to estimate the mean crustal thickness. The results from the CCP stacking method show that the Denali fault marks a sharp transition from thick crust in the south to thin crust in the north. The thickest crust up to 52 km is located in the St. Elias Range, which has been formed by oblique collision between the Yakutat microplate and North America. A thick crust of 48 km is also observed beneath the eastern Alaska Range. These observations suggest that high topography in Alaska is largely compensated by the thick crust root. The Moho depth ranges from 28 km to 35 km beneath the northern lowlands and increases to 40-45 km under the Books Range. The preliminary crustal thickness from the H-K method generally agrees with that from the CCP stacking with thicker crust beneath high mountain ranges and thinner crust beneath lowlands and basins. However, the offshore part is not well constrained due to the limited coverage of stations. The mean Vp/Vs ratio is around 1.7 in the Yukon-Tanana terrane and central-northern Alaska. The ratio is about 1.9 in central and southern Alaska with higher values at the Alaska Range, Wrangell Mountains, and St. Elias Range. Further data analyses are needed for obtaining more details of the crustal structure in Alaska to decipher the origin and development of different tectonic terranes.

  13. Modeling of periodic great earthquakes on the San Andreas fault: Effects of nonlinear crustal rheology

    Science.gov (United States)

    Reches, Ze'ev; Schubert, Gerald; Anderson, Charles

    1994-01-01

    We analyze the cycle of great earthquakes along the San Andreas fault with a finite element numerical model of deformation in a crust with a nonlinear viscoelastic rheology. The viscous component of deformation has an effective viscosity that depends exponentially on the inverse absolute temperature and nonlinearity on the shear stress; the elastic deformation is linear. Crustal thickness and temperature are constrained by seismic and heat flow data for California. The models are for anti plane strain in a 25-km-thick crustal layer having a very long, vertical strike-slip fault; the crustal block extends 250 km to either side of the fault. During the earthquake cycle that lasts 160 years, a constant plate velocity v(sub p)/2 = 17.5 mm yr is applied to the base of the crust and to the vertical end of the crustal block 250 km away from the fault. The upper half of the fault is locked during the interseismic period, while its lower half slips at the constant plate velocity. The locked part of the fault is moved abruptly 2.8 m every 160 years to simulate great earthquakes. The results are sensitive to crustal rheology. Models with quartzite-like rheology display profound transient stages in the velocity, displacement, and stress fields. The predicted transient zone extends about 3-4 times the crustal thickness on each side of the fault, significantly wider than the zone of deformation in elastic models. Models with diabase-like rheology behave similarly to elastic models and exhibit no transient stages. The model predictions are compared with geodetic observations of fault-parallel velocities in northern and central California and local rates of shear strain along the San Andreas fault. The observations are best fit by models which are 10-100 times less viscous than a quartzite-like rheology. Since the lower crust in California is composed of intermediate to mafic rocks, the present result suggests that the in situ viscosity of the crustal rock is orders of magnitude

  14. Ionization Efficiency in the Dayside Martian Upper Atmosphere

    Science.gov (United States)

    Cui, J.; Wu, X.-S.; Xu, S.-S.; Wang, X.-D.; Wellbrock, A.; Nordheim, T. A.; Cao, Y.-T.; Wang, W.-R.; Sun, W.-Q.; Wu, S.-Q.; Wei, Y.

    2018-04-01

    Combining the Mars Atmosphere and Volatile Evolution measurements of neutral atmospheric density, solar EUV/X-ray flux, and differential photoelectron intensity made during 240 nominal orbits, we calculate the ionization efficiency, defined as the ratio of the secondary (photoelectron impact) ionization rate to the primary (photon impact) ionization rate, in the dayside Martian upper atmosphere under a range of solar illumination conditions. Both the CO2 and O ionization efficiencies tend to be constant from 160 km up to 250 km, with respective median values of 0.19 ± 0.03 and 0.27 ± 0.04. These values are useful for fast calculation of the ionization rate in the dayside Martian upper atmosphere, without the need to construct photoelectron transport models. No substantial diurnal and solar cycle variations can be identified, except for a marginal trend of reduced ionization efficiency approaching the terminator. These observations are favorably interpreted by a simple scenario with ionization efficiencies, as a first approximation, determined by a comparison between relevant cross sections. Our analysis further reveals a connection between regions with strong crustal magnetic fields and regions with high ionization efficiencies, which are likely indicative of more efficient vertical transport of photoelectrons near magnetic anomalies.

  15. Conodonta, Trilobita, and Anthozoa near the Late Frasnian Upper Kellwasser Event of the Geipel Quarry section in Schleiz, Thuringian Mountains (Germany

    Directory of Open Access Journals (Sweden)

    D. Weyer

    2003-01-01

    Full Text Available New recoveries of Trilobita, Anthozoa and Conodonta from the linguiformis Zone close to the Frasnian/Famennian boundary and Immediately preceding the Upper Kellwasser Event level at Schleiz (Thuringia are investigated. The trilobites species are Harpes neogracilis Richter & Richter, 1924, Palpebralia cf. brecciae (Richter, 1913 and Acuticryphops acuticeps (Kayser, 1889, the latter is represented by several morphs with different numbers of eye-lenses; the trend to eye-reduction is discussed. The Rugosa fauna that was nearly unknown from the psychrospheric facies worldwide, comprise six taxa of the Cyathaxoniina. The rich conodont faunas permit tracing the exact boundary between the top of the Late Palmatolepis rhenana Zone and the Palmatolepis linguiformis Zone. Im Niveau der Frasnium/Famennium-Grenze werden neue Fossilfunde der letzten Trilobita, Anthozoa und Conodonta aus der linguiformis-Zone (vor dem Oberen Kellwasser-Event mitgeteilt. Harpes neogracilis Richter & Richter, 1924, Palpebralia cf. brecciae (Richter, 1913 und Acuticryphops acuticeps (Kayser, 1889 wurden beobachtet; bei letzterem wird an Hand verschiedener Morphen mit unterschiedlicher Linsenzahl der Trend zur Augenreduktion diskutiert. Von der Rugosa-Fauna, die weltweit aus solcher psychrosphaerischer Fazies fast unbekannt blieb, sind sechs Taxa der Cyathaxoniina skizziert. Die reichen Condonta-Faunen erlauben eine präzise Grenzziehung zwischen dem Top der Late Palmatolepis rhenana-Zone und der Palmatolepis linguiformis-Zone. doi:10.1002/mmng.20030060104

  16. Regional Crustal Deformation and Lithosphere Thickness Observed with Geodetic Techniques

    Science.gov (United States)

    Vermeer, M.; Poutanen, M.; Kollo, K.; Koivula, H.; Ahola, J.

    2009-04-01

    The solid Earth, including the lithosphere, interacts in many ways with other components of the Earth system, oceans, atmosphere and climate. Geodesy is a key provider of data needed for global and environmental research. Geodesy provides methods and accurate measurements of contemporary deformation, sea level and gravity change. The importance of the decades-long stability and availability of reference frames must be stressed for such studies. In the future, the need to accurately monitor 3-D crustal motions will grow, both together with increasingly precise GNSS (Global Navigation Satellite System) positioning, demands for better follow-up of global change, and local needs for crustal motions, especially in coastal areas. These demands cannot yet be satisfied. The project described here is a part of a larger entity: Upper Mantle Dynamics and Quaternary Climate in Cratonic Areas, DynaQlim, an International Lithosphere Project (ILP) -sponsored initiative. The aims of DynaQlim are to understand the relations between upper mantle dynamics, mantle composition, physical properties, temperature and rheology, to study the postglacial uplift and ice thickness models, sea level change and isostatic response, Quaternary climate variations and Weichselian (Laurentian and other) glaciations during the late Quaternary. We aim at studying various aspects of lithospheric motion within the Finnish and Fennoscandian area, but within a global perspective, by the newest geodetic techniques in a multidisciplinary setting. The studies involve observations of three-dimensional motions and gravity change in a multidisciplinary context on a range of spatial scales: the whole of Fennoscandia, Finland, a regional test area of Satakunta, and the local test site Olkiluoto. Objectives of the research include improving our insight into the 3-D motion of a thick lithosphere, and into the gravity effect of the uplift, using novel approaches; improving the kinematic 3-D models in the

  17. Crustal thickness and velocity structure across the Moroccan Atlas from long offset wide-angle reflection seismic data: The SIMA experiment

    Science.gov (United States)

    Ayarza, P.; Carbonell, R.; Teixell, A.; Palomeras, I.; Martí, D.; Kchikach, A.; Harnafi, M.; Levander, A.; Gallart, J.; Arboleya, M. L.; Alcalde, J.; Fernández, M.; Charroud, M.; Amrhar, M.

    2014-05-01

    The crustal structure and topography of the Moho boundary beneath the Atlas Mountains of Morocco has been constrained by a controlled source, wide-angle seismic reflection transect: the SIMA experiment. This paper presents the first results of this project, consisting of an almost 700 km long, high-resolution seismic profile acquired from the Sahara craton across the High and the Middle Atlas and the Rif Mountains. The interpretation of this seismic data set is based on forward modeling by raytracing, and has resulted in a detailed crustal structure and velocity model for the Atlas Mountains. Results indicate that the High Atlas features a moderate crustal thickness, with the Moho located at a minimum depth of 35 km to the S and at around 31 km to the N, in the Middle Atlas. Upper crustal shortening is resolved at depth through a crustal root where the Saharan crust underthrusts the northern Moroccan crust. This feature defines a lower crust imbrication that, locally, places the Moho boundary at ˜40-41 km depth in the northern part of the High Atlas. The P-wave velocity model is characterized by relatively low velocities, mostly in the lower crust and upper mantle, when compared to other active orogens and continental regions. These low deep crustal velocities together with other geophysical observables such as conductivity estimates derived from MT measurements, moderate Bouguer gravity anomaly, high heat flow, and surface exposures of recent alkaline volcanism lead to a model where partial melts are currently emplaced at deep crustal levels and in the upper mantle. The resulting model supports the existence of a mantle upwelling as mechanism that would contribute significantly to sustain the High Atlas topography. However, the detailed Moho geometry deduced in this work should lead to a revision of the exact geometry and position of this mantle feature and will require new modeling efforts.

  18. Critical Evaluation of Chemical Reaction Rates and Collision Cross Sections of Importance in the Earth's Upper Atmosphere and the Atmospheres of Other Planets, Moons, and Comets

    Science.gov (United States)

    Huestis, David L.

    2006-01-01

    We propose to establish a long-term program of critical evaluation by domain experts of the rates and cross sections for atomic and molecular processes that are needed for understanding and modeling the atmospheres in the solar system. We envision data products resembling those of the JPL/NASA Panel for Data Evaluation and the similar efforts of the international combustion modeling community funded by US DoE and its European counterpart.

  19. Antibiotic use for upper respiratory tract infections in children: A cross-sectional survey of knowledge, attitudes, and practices (KAP) of parents in Greece

    Science.gov (United States)

    2011-01-01

    Background Upper respiratory tract infections (URTIs) are common in children. The cause of URTIs is usually viral, but parents' attitudes often contribute to inappropriate prescription of antibiotics, promoting antibiotic resistance. The objective of this study was to document and analyse parental beliefs on antibiotic use for children with URTIs in Greece, a country with high levels of antibiotic use and antibiotic resistance. Methods A knowledge-attitude-practice questionnaire was developed and distributed to Greek parents caring for children who were 5-6 years old, between January and July of the same school year. The sample of the study contained parents from all geographic areas of Greece. Results The majority of Greek parents (80%) believed that UTRIs are mostly self-limited, although 74% of them expected to receive antibiotics when such a diagnosis was given. Earache was the most common reason for which parents expected antibiotics (45%). Greek parents rarely gave antibiotics to their children without medical advice (10%) and most (88%) believed that unnecessary antibiotic use drives antibiotic resistance and they were happy to receive symptomatic therapy if instructed by their physician. Almost 70% of parents confused antibiotics with other medicines used for symptomatic therapy for a child with URTI. Conclusion Greek parents have a trusted relationship with their paediatrician and rarely give antibiotics without medical advice, indicating that parents contribute less than expected to antibiotic misuse. Parents also appreciate the benign course of most URTIs and the fact that unnecessary antibiotic use is harmful. More time needs to be invested in educating mostly physicians on the potential benefit from reducing antibiotic prescribing for children with URTI. PMID:21729266

  20. Ophiolitic basement to the Great Valley forearc basin, California, from seismic and gravity data: Implications for crustal growth at the North American continental margin

    Science.gov (United States)

    Godfrey, N.J.; Beaudoin, B.C.; Klemperer, S.L.; Levander, A.; Luetgert, J.; Meltzer, A.; Mooney, W.; Tréhu, A.

    1997-01-01

    The nature of the Great Valley basement, whether oceanic or continental, has long been a source of controversy. A velocity model (derived from a 200-km-long east-west reflection-refraction profile collected south of the Mendocino triple junction, northern California, in 1993), further constrained by density and magnetic models, reveals an ophiolite underlying the Great Valley (Great Valley ophiolite), which in turn is underlain by a westward extension of lower-density continental crust (Sierran affinity material). We used an integrated modeling philosophy, first modeling the seismic-refraction data to obtain a final velocity model, and then modeling the long-wavelength features of the gravity data to obtain a final density model that is constrained in the upper crust by our velocity model. The crustal section of Great Valley ophiolite is 7-8 km thick, and the Great Valley ophiolite relict oceanic Moho is at 11-16 km depth. The Great Valley ophiolite does not extend west beneath the Coast Ranges, but only as far as the western margin of the Great Valley, where the 5-7-km-thick Great Valley ophiolite mantle section dips west into the present-day mantle. There are 16-18 km of lower-density Sierran affinity material beneath the Great Valley ophiolite mantle section, such that a second, deeper, "present-day" continental Moho is at about 34 km depth. At mid-crustal depths, the boundary between the eastern extent of the Great Valley ophiolite and the western extent of Sierran affinity material is a near-vertical velocity and density discontinuity about 80 km east of the western margin of the Great Valley. Our model has important implications for crustal growth at the North American continental margin. We suggest that a thick ophiolite sequence was obducted onto continental material, probably during the Jurassic Nevadan orogeny, so that the Great Valley basement is oceanic crust above oceanic mantle vertically stacked above continental crust and continental mantle.

  1. Crustal Poisson’s ratio anomalies in the eastern part of North China and their origins

    Directory of Open Access Journals (Sweden)

    Wencai Yang

    2011-07-01

    Full Text Available Seismic tomography can provide both fine P-wave and S-wave velocity structures of the crust and upper mantle. In addition, with proper computation, Poisson’s ratio images from the seismic velocities can be determined. However, it is unknown whether Poisson’s ratio images have any advantages when compared with the P-wave and S-wave velocity images. For the purposes of this study, high-resolution seismic tomography under the eastern part of North China region was used to determine detailed 3-D crustal P- and S-wave seismic velocities structure, as well as Poisson’s ratio images. Results of Poisson’s ratio imaging show high Poisson’s ratio (high-PR anomalies located in the Hengshan-North Taihang-Zhangjiakou (H-NT-Z region, demonstrating that Poisson’s ratio imaging can provide new geophysical constraints for regional tectonic evolution. The H-NT-Z region shows a prominent and continuous high-PR anomaly in the upper crust. Based on Poisson’s ratio images at different depths, we find that this high-PR anomaly is extending down to the middle crust with thickness up to about 26 km. According to rock physical property measurements and other geological data, this crustal Poisson’s ratio anomaly can be explained by Mesozoic partial melting of the upper mantle and basaltic magma underplating related to the lithospheric thinning of the North China craton.

  2. Reworked Middle Jurassic sandstones as a marker for Upper Cretaceous basin inversion in Central Europe—a case study for the U-Pb detrital zircon record of the Upper Cretaceous Schmilka section and their implication for the sedimentary cover of the Lausitz Block (Saxony, Germany)

    Science.gov (United States)

    Hofmann, Mandy; Voigt, Thomas; Bittner, Lucas; Gärtner, Andreas; Zieger, Johannes; Linnemann, Ulf

    2018-04-01

    The Saxonian-Bohemian Cretaceous Basin (Elbsandsteingebirge, E Germany and Czech Republic, Elbtal Group) comprises Upper Cretaceous sedimentary rocks from Upper Cenomanian to Santonian age. These sandstones were deposited in a narrow strait of the sea linking the northern Boreal shelf to the southern Tethyan areas. They were situated between the West Sudetic Island in the north and the Mid-European Island in the south. As known by former studies (e.g. Tröger, Geologie 6/7:717-730, 1964; Tröger, Geologie von Sachsen, Schweizerbart, 311-358, 2008; Voigt and Tröger, Proceedings of the 4th International Cretaceous Symposium, 275-290, 1996; Voigt, Dissertation, TU Bergakademie Freiberg, 1-130, 1995; Voigt, Zeitschrift der geologischen Wissenschaften 37(1-2): 15-39, 2009; Wilmsen et al., Freiberger Forschungshefte C540: 27-45, 2011) the main sedimentary input came from the north (Lausitz Block, southern West-Sudetic Island). A section of Turonian to Coniacian sandstones was sampled in the Elbsandsteingebirge near Schmilka (Elbtal Group, Saxony, Germany). The samples were analysed for their U-Pb age record of detrital zircon using LA-ICP-MS techniques. The results show main age clusters typical for the Bohemian Massif (local material) and are interpreted to reflect the erosion of uniform quartz-dominated sediments and basement rocks. Surprisingly, these rocks lack an expected Upper Proterozoic to Lower Palaeozoic age peak, which would be typical for the basement of the adjacent Lausitz Block (c. 540-c. 560 Ma). Therefore, the Lausitz Block basement must have been covered by younger sediments that acted as source rocks during deposition of the Elbtal Group. The sandstones of the Elbe valley (Elbtal Group, Schmilka section) represent the re-deposited sedimentary cover of the Lausitz Block in inverse order. This cover comprised Permian, Triassic, Jurassic and Lower Cretaceous deposits, which are eroded already today and cannot be investigated. Within the samples of the

  3. The Mars Crustal Magnetic Field Control of Plasma Boundary Locations and Atmospheric Loss: MHD Prediction and Comparison with MAVEN

    Science.gov (United States)

    Fang, Xiaohua; Ma, Yingjuan; Masunaga, Kei; Dong, Chuanfei; Brain, David; Halekas, Jasper; Lillis, Robert; Jakosky, Bruce M.; Connerney, Jack; Grebowsky, Joseph; hide

    2017-01-01

    We present results from a global Mars time-dependent MHD simulation under constant solar wind and solar radiation impact considering inherent magnetic field variations due to continuous planetary rotation. We calculate the 3-D shapes and locations of the bow shock (BS) and the induced magnetospheric boundary (IMB) and then examine their dynamic changes with time. We develop a physics-based, empirical algorithm to effectively summarize the multidimensional crustal field distribution. It is found that by organizing the model results using this new approach, the Mars crustal field shows a clear, significant influence on both the IMB and the BS. Specifically, quantitative relationships have been established between the field distribution and the mean boundary distances and the cross-section areas in the terminator plane for both of the boundaries. The model-predicted relationships are further verified by the observations from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Our analysis shows that the boundaries are collectively affected by the global crustal field distribution, which, however, cannot be simply parameterized by a local parameter like the widely used subsolar longitude. Our calculations show that the variability of the intrinsic crustal field distribution in Mars-centered Solar Orbital itself may account for approx.60% of the variation in total atmospheric loss, when external drivers are static. It is found that the crustal field has not only a shielding effect for atmospheric loss but also an escape-fostering effect by positively affecting the transterminator ion flow cross-section area.

  4. New Interpretation of Crustal Extension Evidences on Mars

    Science.gov (United States)

    Grin, E. A.

    The record of early evolution of life on Earth has been obscured by extensive surface activity. On the opposite, large fractions of the martian surface date back to an early clement epoch favorable to the needs of biological systems [1]. The upper martian surface reflects a wide variety of modifying processes which destroy the geological context. However, due to endogenic causes acting after the end of the primordial bombardment, abundant extensional structures display vertical sequences of stratigraphic units from late Noachian to early Hesperian periods [2]. Deep structural incisions in the upper crust provide unaltered strata, open flanks, and slope deposits that favor the use of an autonomous lander-rover-penetrator The strategy for an exobiology search of such an optimum site should be guided by the recent attention devoted to extensional structures and their global significance [4]. Geological evidence supporting the martian crustal extension is suggested by abundant fractures associated with the dichotomy boundary northland-south upland, i.e., Aeolis Region, and peak igneous activity (Elysium bulge). As pointed out by [5], the system of fractures correlates with the endogenic origin of the dichotomy, as related to a major difference in the thicknessof the crust. Perpendicular to this boundary, fractures of deep graben testify to a general tectonic crust relaxation. The opening of the graben, joined with compressive wrinkles, is the signature of a dynamical pervasive stress regime that implies a large scale roll-over of the upper crust over the ductile interface of a more dense mantle. This general motion is not a transport of material, as there is no thickening on the boundary of the dichotomy. The horizontal movement is due to the gravitational mechanism and differential thermal convection cells in the upper crust over the slope of the anti-flexure rigid interface consequential to Elysium bulge. The fracturation occurs as the neutral zone of the crust rises

  5. Mechanism of crustal extension in the Laxmi Basin, Arabian Sea

    Directory of Open Access Journals (Sweden)

    Anju Pandey

    2015-11-01

    Full Text Available Continental rifting and magmatism has been extensively studied worldwide as it is believed that continental rifting, break up of continents and associated magmatism lead to genesis of new oceanic crust. However, various regions of the world show that these processes may lead to genesis of other types of crust than the oceanic crust. Laxmi Basin in the western continental margin of the India is one such region with an enigmatic crust. Due to its extreme strategic significance for the palaeogeographic reconstruction of continents during Cretaceous continental breakup of India, this basin has attracted various workers for more than two decades. However, still the issue of nature of crust in the basin remains controversial. In this contribution, in order to identify nature of crust, mechanism of continental extension in the Laxmi Basin has been studied for the first time through newly acquired seismic data from the basin. Here, we propose a plausible mechanism of crustal extension in the Laxmi Basin which eventually constrains the nature of crust of the Laxmi Basin. We have demonstrated that the crust in the Laxmi Basin can be categorised in two zones of stretched and transitional crust. In the stretched zone several fault bounded horst and graben structures are identified which preserve syn- and post-rift sediments along with different periods of hiatus in sedimentations as unconformities. These faults are identified as listric faults in the upper crust which sole out in the detachment faults. Detachment faults decouples the upper brittle and lower ductile crust. The transitional crust is identified as heavily intruded by sills and basaltic volcanic which were emplaced due to melting of subcontinental mantle (SCM after hyper-stretching of crust and serpentinisation of the SCM. Panikkar Ridge is proposed to be one such basaltic volcanic body derived from melting of lower part of the SCM.

  6. A Comparison of Fourth-Year Health Sciences Students' Knowledge of Gross Lower and Upper Limb Anatomy: A Cross-Sectional Study.

    Science.gov (United States)

    Díaz-Mancha, Juan-Antonio; Castillo-López, José Manuel; Munuera-Martinez, Pedro V; Fernández-Seguín, Lourdes María; Polo-Padillo, Juan; Heredia-Rizo, Alberto Marcos

    2016-01-01

    The aim of the study was to assess and compare the knowledge of fourth-year medicine, physiotherapy (PT), nursing, and podiatry students in carpal and tarsal bone anatomy. A cross-sectional study was carried out. Based on a nonprobability convenience sampling, 177 fourth-year students (117 women and 60 men, mean age of 23.16 ± 3.82 years) from the podiatry (n = 39), nursing (n = 26), PT (n = 73), and medicine (n = 39) schools at a large Spanish university were included. Measurements were taken of their gross anatomy knowledge by means of the carpal and the tarsal bone tests. Students were asked to identify all carpal and tarsal bones in an illustration of the bony skeleton of both regions and were given a maximum of 5 minutes per test. Of a total of 15 bones to be labeled, the PT (11.07 ± 3.30) and podiatry (9.36 ± 2.93) students had the highest rate of correct answers compared with the medicine (6.13 ± 3.27) and nursing (4.04 ± 3.72) undergraduates. When assessing academic degrees and test scores, significant differences were observed between PT and podiatry participants vs those from the medicine and nursing schools (P students from the PT and podiatry programs correctly identified a higher number of carpal and tarsal bones than students from the nursing and medicine schools. Copyright © 2016. Published by Elsevier Inc.

  7. Crustal evolution of South American Platform based on Sm-Nd isotope geochemistry

    International Nuclear Information System (INIS)

    Sato, Kei

    1998-01-01

    Sm-Nd isotopic systematics is relevant to the topics of origin and evolution the of continental crust, where model ages refer to the time when crustal material was differentiated from the upper mantle. Alternative interpretations are due to a lack of adequate information on crustal processes and the variable composition of the mantle sources. The Sm-Nd methods are presented, and applied on rock materials from the South American Platform. The main conclusions indicate juvenile accretion with higher growth rates (peaks), around 3.7-3.5 Ga (∼ 0.5% in volume), 3.1 - 2.9 Ga (∼16%), 2.7 - 2.6 (∼ 9%), 2.2 - 1.9 (35%) and 1.3-1.0 (7%). The continental growth curve indicates that about 35 % of the crust was formed by 2.5 Ga, 88% by 1.8 Ga and 99% by 1.0 Ga, and the remaining ∼ 1 % was added in the Phanerozoic. Rapid crustal growth occurred between 2.2 and 1.9 Ga. The main period of continental crust formation occurred during the Paleoproterozoic, corresponding to 54 % in volume. Sm-Nd model ages, when compared with the crystallisation ages of granitoid rocks, furnish a rough estimate of juvenile vs. reworked material. Within the South American Platform about 45% of juvenile continental crust is still preserved within tectonic provinces of different ages. The remainder represents continental crust reworked in younger tectono-thermal events. In particular crustal reworking was predominating over juvenile accretion during Meso-Neoproterozoic. The Transbrasiliano Lineament is a megasuture, active in the Neoproterozoic, which separates a large northwestern mass, including the Amazonian and Sao Luis Cratons, from a southeastern mass, formed by a collage of cratonic fragments, of which the Sao Francisco and Rio de La Plata are the largest. The crustal evolutions of these two large continental masses are considered individually, and can be resumed following form: I - Old Archean rocks (>3.4 Ga) are found only within the south-eastern part (Gaviao Block, Contendas

  8. Electrical imaging of deep crustal features of Kutch, India

    Science.gov (United States)

    Sastry, R. S.; Nagarajan, Nandini; Sarma, S. V. S.

    2008-03-01

    A regional Magnetotelluric (MT) study, was carried out with 55 MT soundings, distributed along five traverses, across the Kutch Mainland Unit (KMU), on the west coast of India, a region characterized by a series of successive uplifts and intervening depressions in the form of half graben, bounded by master faults. We obtain the deeper electrical structure of the crust beneath Kutch, from 2-D modelling of MT data along the 5 traverses, in order to evaluate the geo-electrical signatures, if any, of the known primary tectonic structures in this region. The results show that the deeper electrical structure in the Kutch region presents a mosaic of high resistive crustal blocks separated by deep-rooted conductive features. Two such crustal conductive features spatially correlate with the known tectonic features, viz., the Kutch Mainland Fault (KMF), and the Katrol Hill Fault (KHF). An impressive feature of the geo-electrical sections is an additional, well-defined conductive feature, running between Jakhau and Mundra, located at the southern end of each of the five MT traverses and interpreted to be the electrical signature of yet another hidden fault at the southern margin of the KMU. This new feature is named as Jakhau-Mundra Fault (JMF). It is inferred that the presence of JMF together with the Kathiawar Fault (NKF), further south, located at the northern boundary of the Saurashtra Horst, would enhance the possibility of occurrence of a thick sedimentary column in the Gulf of Kutch. The region between the newly delineated fault (JMF) and the Kathiawar fault (NKF) could thus be significant for Hydrocarbon Exploration.

  9. Crustal structure in the Kiruna area, northern Sweden, based on seismic reflection profiling

    Science.gov (United States)

    Juhojuntti, Niklas; Bergman, Stefan; Olsson, Sverker

    2013-04-01

    Northernmost Sweden is currently one of the most active mining areas in Europe. In order to better understand the regional three-dimensional crustal structure and to support deep ore exploration, we have acquired a 74 km long seismic reflection profile in the Kiruna area. The upper crust in this area is largely composed of various supracrustal units, which are dominated by metabasalts, acidic metavolcanics and clastic metasedimentary rocks, resting on an Archaean metagranitoid complex. All of these units have been intruded by plutonic rocks, and to variable degrees folded, sheared and metamorphosed, during the Svecokarelian orogeny. The profile crosses several steep ductile shear zones, some of which extend for hundreds of kilometres along strike. Many of the lithological contacts and deformation zones are expected to be seismically reflective. The profile is located only a few kilometres from the world's largest underground iron-ore mine in Kiruna, and closer to the profile there are several known ore bodies, some of which are active exploration targets. For the seismic recording we used approximately 350 geophones in split-spread configuration, at a separation of 25 m. The main seismic source was the Vibsist system (an impact source), which normally was employed at every geophone station. We also fired explosive charges (8-16 kg) at a few locations distributed along the profile to image deeper structures, although at very low resolution. Wireless seismometers were placed along and to the side of the profile, mainly in order to achieve better velocity control and to study out-of-the-plane reflections. Some mining blasts in Kiruna were also recorded. The upper crust in the area is quite reflective, most clearly demonstrated by the dynamite shot records. Some of the reflections appear to originate from steeply dipping structures. The dynamite shot records show a set of reflections at 3-4 s twt, corresponding to a depth of roughly 10 km, the explanation for which is

  10. Crustal permeability: Introduction to the special issue

    Science.gov (United States)

    Ingebritsen, Steven E.; Gleeson, Tom

    2015-01-01

    The topic of crustal permeability is of broad interest in light of the controlling effect of permeability on diverse geologic processes and also timely in light of the practical challenges associated with emerging technologies such as hydraulic fracturing for oil and gas production (‘fracking’), enhanced geothermal systems, and geologic carbon sequestration. This special issue of Geofluids is also motivated by the historical dichotomy between the hydrogeologic concept of permeability as a static material property that exerts control on fluid flow and the perspective of economic geologists, geophysicists, and crustal petrologists who have long recognized permeability as a dynamic parameter that changes in response to tectonism, fluid production, and geochemical reactions. Issues associated with fracking, enhanced geothermal systems, and geologic carbon sequestration have already begun to promote a constructive dialog between the static and dynamic views of permeability, and here we have made a conscious effort to include both viewpoints. This special issue also focuses on the quantification of permeability, encompassing both direct measurement of permeability in the uppermost crust and inferential permeability estimates, mainly for the deeper crust.

  11. A numerical model for dynamic crustal-scale fluid flow

    Science.gov (United States)

    Sachau, Till; Bons, Paul; Gomez-Rivas, Enrique; Koehn, Daniel

    2015-04-01

    Fluid flow in the crust is often envisaged and modeled as continuous, yet minimal flow, which occurs over large geological times. This is a suitable approximation for flow as long as it is solely controlled by the matrix permeability of rocks, which in turn is controlled by viscous compaction of the pore space. However, strong evidence (hydrothermal veins and ore deposits) exists that a significant part of fluid flow in the crust occurs strongly localized in both space and time, controlled by the opening and sealing of hydrofractures. We developed, tested and applied a novel computer code, which considers this dynamic behavior and couples it with steady, Darcian flow controlled by the matrix permeability. In this dual-porosity model, fractures open depending on the fluid pressure relative to the solid pressure. Fractures form when matrix permeability is insufficient to accommodate fluid flow resulting from compaction, decompression (Staude et al. 2009) or metamorphic dehydration reactions (Weisheit et al. 2013). Open fractures can close when the contained fluid either seeps into the matrix or escapes by fracture propagation: mobile hydrofractures (Bons, 2001). In the model, closing and sealing of fractures is controlled by a time-dependent viscous law, which is based on the effective stress and on either Newtonian or non-Newtonian viscosity. Our simulations indicate that the bulk of crustal fluid flow in the middle to lower upper crust is intermittent, highly self-organized, and occurs as mobile hydrofractures. This is due to the low matrix porosity and permeability, combined with a low matrix viscosity and, hence, fast sealing of fractures. Stable fracture networks, generated by fluid overpressure, are restricted to the uppermost crust. Semi-stable fracture networks can develop in an intermediate zone, if a critical overpressure is reached. Flow rates in mobile hydrofractures exceed those in the matrix porosity and fracture networks by orders of magnitude

  12. Seismically constrained two-dimentional crustal thermal structure of ...

    Indian Academy of Sciences (India)

    Cambay basin; P-wave velocity; heat flow; heat generation; 2-D modelling; crustal thermal structure; Mohodepth; Curie isotherm. ... This work deals with the two-dimensional thermal modelling to delineate the crustal thermal structure along a 230 km long Deep Seismic Sounding (DSS) profile in the north Cambay basin.

  13. Crustal structure along the west flank of the Cascades, western Washington

    Science.gov (United States)

    Miller, K.C.; Keller, Gordon R.; Gridley, J.M.; Luetgert, J.H.; Mooney, W.D.; Thybo, H.

    1997-01-01

    Knowledge of the crustal structure of the Washington Cascades and adjacent Puget Lowland is important to both earthquake hazards studies and geologic studies of the evolution of this tectonically active region. We present a model for crustal velocity structure derived from analysis of seismic refraction/wide-angle reflection data collected in 1991 in western Washington. The 280-km-long north-south transect skirts the west flank of the Cascades as it crosses three tectonic provinces including the Northwest Cascades Thrust System (NWCS), the Puget Lowland, and the volcanic arc of the southern Cascades. Within the NWCS, upper crustal velocities range from 4.2 to 5.7 km s-1 and are consistent with the presence of a diverse suite of Mesozoic and Paleozoic metasediments and metavolcanics. In the upper 2-3 km of the Puget Lowland velocities drop to 1.7-3.5 km s-1 and reflect the occurrence of Oligocene to recent sediments within the basin. In the southern Washington Cascades, upper crustal velocities range from 4.0 to 5.5 km s-1 and are consistent with a large volume of Tertiary sediments and volcanics. A sharp change in velocity gradient at 5-10 km marks the division between the upper and middle crust. From approximately 10 to 35 km depth the velocity field is characterized by a velocity increase from ???6.0 to 7.2 km s-1. These high velocities do not support the presence of marine sedimentary rocks at depths of 10-20 km beneath the Cascades as previously proposed on the basis of magnetotelluric data. Crustal thickness ranges from 42 to 47 km along the profile. The lowermost crust consists of a 2 to 8-km-thick transitional layer with velocities of 7.3-7.4 km s-1. The upper mantle velocity appears to be an unusually low 7.6-7.8 km s-1. When compared to velocity models from other regions, this model most closely resembles those found in active continental arcs. Distinct seismicity patterns can be associated with individual tectonic provinces along the seismic transect. In

  14. Petrographic, geochemical and isotopic evidence of crustal assimilation processes in the Ponte Nova alkaline mafic-ultramafic massif, SE Brazil

    Science.gov (United States)

    Azzone, Rogério Guitarrari; Montecinos Munoz, Patricio; Enrich, Gaston Eduardo Rojas; Alves, Adriana; Ruberti, Excelso; Gomes, Celsode Barros

    2016-09-01

    be responsible for the increse in the K2O/Na2O, Ba/Sr and Rb/Sr ratios. This enrichment was associated with the relevant role of biotite breakdown in the assimilated host rock partial melts. The petrological model for the Ponte Nova massif is explained as repeated influxes of antecryst-laden basanite magmas that deposited most of their suspended crystals on the floor of the upper-crust magma chamber. Each intrusion is representative of relatively primitive olivine- and clinopyroxene-phyric basanites that had assimilated different degrees of partial melts of heterogeneous host rocks. This study reveals the relevant role of crustal assimilation processes in the magmatic evolution of nepheline-normative rocks, especially in upper-crust chamber environments.

  15. Crustal velocity structure of central Gansu Province from regional seismic waveform inversion using firework algorithm

    Science.gov (United States)

    Chen, Yanyang; Wang, Yanbin; Zhang, Yuansheng

    2017-04-01

    The firework algorithm (FWA) is a novel swarm intelligence-based method recently proposed for the optimization of multi-parameter, nonlinear functions. Numerical waveform inversion experiments using a synthetic model show that the FWA performs well in both solution quality and efficiency. We apply the FWA in this study to crustal velocity structure inversion using regional seismic waveform data of central Gansu on the northeastern margin of the Qinghai-Tibet plateau. Seismograms recorded from the moment magnitude ( M W) 5.4 Minxian earthquake enable obtaining an average crustal velocity model for this region. We initially carried out a series of FWA robustness tests in regional waveform inversion at the same earthquake and station positions across the study region, inverting two velocity structure models, with and without a low-velocity crustal layer; the accuracy of our average inversion results and their standard deviations reveal the advantages of the FWA for the inversion of regional seismic waveforms. We applied the FWA across our study area using three component waveform data recorded by nine broadband permanent seismic stations with epicentral distances ranging between 146 and 437 km. These inversion results show that the average thickness of the crust in this region is 46.75 km, while thicknesses of the sedimentary layer, and the upper, middle, and lower crust are 3.15, 15.69, 13.08, and 14.83 km, respectively. Results also show that the P-wave velocities of these layers and the upper mantle are 4.47, 6.07, 6.12, 6.87, and 8.18 km/s, respectively.

  16. The Transition from Volcanic to Rift Dominated Crustal Breakup - From the Vøring Plateau to the Lofoten Margin, Norway

    Science.gov (United States)

    Breivik, A. J.; Faleide, J. I.; Mjelde, R.; Flueh, E.; Murai, Y.

    2017-12-01

    The Vøring Plateau was part of the Northeast Atlantic igneous province (NAIP) during early Cenozoic crustal breakup. Crustal breakup at the Vøring Plateau occurred marginal to the deep Cretaceous basins on the shelf, with less extension of the crust. Intrusive magmatism and oceanic crust up to three times normal thickness caused a period of sub-aerial magmatism around breakup time. The transition to the Lofoten Margin is rapid to a deep-water plain. Still, there is some excess magmatism north of this transition, where early oceanic crustal thickness is reduced to half of that of the Vøring Plateau 150 km away. Our estimates of the earliest seafloor spreading rates using new ship-track magnetic profiles on different margin segments offer a clue to what caused this rapid transition. While crustal breakup occurred within the magnetic polarity C24r in other parts of the NAIP, there is a delayed breakup for the Lofoten/Vesterålen margin. Modeling of the earliest seafloor spreading with geomagnetic reversals, indicate a breakup within C24n.3n (anomaly 24b), approximately 1 m.y. later. Both old wide-angle seismic models (from Ocean Bottom Seismometers) off southern Lofoten and a newly published profile farther north show a strongly extended outer margin. Applying early seafloor half-spreading rates ( 30 mm/y) from other NAIP margin segments for 1 m.y. can account for 30 km extra extension, giving a factor of three crustal thinning, and gives a high strain rate of 3.2 ·10-14. Crustal breakup at the magma-poor Iberian Margin occurred at a low strain rate of 4.4·10-15, allowing the ascending mantle to cool, favoring tectonic extension over magmatism. Similar strain rates are found within the main Ethiopian Rift, but there is much magmatism and crustal separation is dominated by dike injection. Mantle tomography models show an exceptionally low seismic velocity below the area interpreted as an unusually hot upper mantle, which will favor magmatism. The transition from

  17. Thermal and petrologic constraints on lower crustal melt accumulation under the Salton Sea Geothermal Field

    Science.gov (United States)

    Karakas, Ozge; Dufek, Josef; Mangan, Margaret T.; Wright, Heather M.; Bachmann, Olivier

    2017-06-01

    In the Salton Sea region of southern California (USA), concurrent magmatism, extension, subsidence, and sedimentation over the past 0.5 to 1.0 Ma have led to the creation of the Salton Sea Geothermal Field (SSGF)-the second largest and hottest geothermal system in the continental United States-and the small-volume rhyolite eruptions that created the Salton Buttes. In this study, we determine the flux of mantle-derived basaltic magma that would be required to produce the elevated average heat flow and sustain the magmatic roots of rhyolite volcanism observed at the surface of the Salton Sea region. We use a 2D thermal model to show that a lower-crustal, partially molten mush containing Salton Trough, and are consistent with seismic observations. Our results indicate limited melting and assimilation of pre-existing rocks in the lower crust. Instead, we find that basalt fractionation in the lower crust produces derivative melts of andesitic to dacitic composition. Such melts are then expected to ascend and accumulate in the upper crust, where they further evolve to give rise to small-volume rhyolite eruptions (Salton Buttes) and fuel local spikes in surface heat flux as currently seen in the SSGF. Such upper crustal magma evolution, with limited assimilation of hydrothermally altered material, is required to explain the slight decrease in δ18 O values of zircons (and melts) that have been measured in these rhyolites.

  18. GPS-derived crustal deformation in Azerbaijan

    Science.gov (United States)

    Safarov, Rafig; Mammadov, Samir; Kadirov, Fakhraddin

    2017-04-01

    Crustal deformations of the Earth's crust in Azerbaijan were studied based on GPS measurements. The GPS velocity vectors for Azerbaijan, Iran, Georgia, and Armenia were used in order to estimate the deformation rates. It is found that compression is observable along the Greater Caucasus, in Gobustan, the Kura depression, Nakhchyvan Autonomous Republic, and adjacent areas of Iran. The axes of compression/contraction of the crust in the Greater Caucasus region are oriented in the S-NE direction. The maximum strain rate is observed in the zone of mud volcanism at the SHIK site (Shykhlar), which is marked by a sharp change in the direction of the compression axes (SW-NE). It is revealed that the deformation field also includes the zones where strain rates are very low. These zones include the Caspian-Guba and northern Gobustan areas, characterized by extensive development of mud volcanism. The extension zones are confined to the Lesser Caucasus and are revealed in the Gyadabei (GEDA) and Shusha (SHOU) areas. The analysis of GPS data for the territory of Azerbaijan and neighboring countries reveals the heterogeneous patterns of strain field in the region. This fact suggests that the block model is most adequate for describing the structure of the studied region. The increase in the number of GPS stations would promote increasing the degree of detail in the reconstructions of the deformation field and identifying the microplate boundaries.It is concluded that the predominant factor responsible for the eruption of mud volcanoes is the intensity of gasgeneration processes in the earth's interior, while deformation processes play the role of a trigger. The zone of the epicenters of strong earthquakes is correlated to the gradient zone in the crustal strain rates.

  19. Fractal behavior in continental crustal heat production

    Directory of Open Access Journals (Sweden)

    N. Vedanti

    2011-02-01

    Full Text Available The distribution of crustal heat production, which is the most important component in the elucidation of continental thermal structure, still remains a theoretical assumption. In general the heat production values must decrease with depth, but the form of decrease of heat production in the crust is not well understood. The commonly used heat production models are: "block model", in which heat production is constant from the surface to a given depth and the "exponential model", in which heat production diminishes as an exponential function of depth. The exponential model is more widely used wherein sources of the errors are heterogeneity of rock and long wavelength changes due to changes in lithology and tectonic elements, and as such exponential distribution does not work satisfactorily for the entire crust. In the present study, we analyze for the first time, deep crustal heat production data of six global areas namely Dharwar craton (India, Kaapvaal craton (South Africa, Baltic shield (Kola, Russia, Hidaka metamorphic belt (Japan, Nissho pluton (Japan and Continental Deep Drilling site (KTB, Germany. The power spectrum of all the studied data sets exhibits power law behaviour. This would mean slower decay of heat production with depth, which conforms to the known geologic composition of the crust. Minimum value of the scaling exponent has been found for the KTB borehole, which is apparently related to higher heat production of gneisses, however for other study areas, scaling exponent is almost similar. We also found that the lower values of scaling exponents are related to higher heat production in the crust as is the case in KTB. Present finding has a direct relevance in computation of temperature-depth profiles in continental regions.

  20. Fractal behavior in continental crustal heat production

    Science.gov (United States)

    Vedanti, N.; Srivastava, R. P.; Pandey, O. P.; Dimri, V. P.

    2011-02-01

    The distribution of crustal heat production, which is the most important component in the elucidation of continental thermal structure, still remains a theoretical assumption. In general the heat production values must decrease with depth, but the form of decrease of heat production in the crust is not well understood. The commonly used heat production models are: "block model", in which heat production is constant from the surface to a given depth and the "exponential model", in which heat production diminishes as an exponential function of depth. The exponential model is more widely used wherein sources of the errors are heterogeneity of rock and long wavelength changes due to changes in lithology and tectonic elements, and as such exponential distribution does not work satisfactorily for the entire crust. In the present study, we analyze for the first time, deep crustal heat production data of six global areas namely Dharwar craton (India), Kaapvaal craton (South Africa), Baltic shield (Kola, Russia), Hidaka metamorphic belt (Japan), Nissho pluton (Japan) and Continental Deep Drilling site (KTB, Germany). The power spectrum of all the studied data sets exhibits power law behaviour. This would mean slower decay of heat production with depth, which conforms to the known geologic composition of the crust. Minimum value of the scaling exponent has been found for the KTB borehole, which is apparently related to higher heat production of gneisses, however for other study areas, scaling exponent is almost similar. We also found that the lower values of scaling exponents are related to higher heat production in the crust as is the case in KTB. Present finding has a direct relevance in computation of temperature-depth profiles in continental regions.

  1. The Glacial BuzzSaw, Isostasy, and Global Crustal Models

    Science.gov (United States)

    Levander, A.; Oncken, O.; Niu, F.

    2015-12-01

    The glacial buzzsaw hypothesis predicts that maximum elevations in orogens at high latitudes are depressed relative to temperate latitudes, as maximum elevation and hypsography of glaciated orogens are functions of the glacial equilibrium line altitude (ELA) and the modern and last glacial maximum (LGM) snowlines. As a consequence crustal thickness, density, or both must change with increasing latitude to maintain isostatic balance. For Airy compensation crustal thickness should decrease toward polar latitudes, whereas for Pratt compensation crustal densities should increase. For similar convergence rates, higher latitude orogens should have higher grade, and presumably higher density rocks in the crustal column due to more efficient glacial erosion. We have examined a number of global and regional crustal models to see if these predictions appear in the models. Crustal thickness is straightforward to examine, crustal density less so. The different crustal models generally agree with one another, but do show some major differences. We used a standard tectonic classification scheme of the crust for data selection. The globally averaged orogens show crustal thicknesses that decrease toward high latitudes, almost reflecting topography, in both the individual crustal models and the models averaged together. The most convincing is the western hemisphere cordillera, where elevations and crustal thicknesses decrease toward the poles, and also toward lower latitudes (the equatorial minimum is at ~12oN). The elevation differences and Airy prediction of crustal thickness changes are in reasonable agreement in the North American Cordillera, but in South America the observed crustal thickness change is larger than the Airy prediction. The Alpine-Himalayan chain shows similar trends, however the strike of the chain makes interpretation ambiguous. We also examined cratons with ice sheets during the last glacial period to see if continental glaciation also thins the crust toward

  2. An attempt to evaluate horizontal crustal movement by geodetic and geological approach in the Horonobe area, Northern Hokkaido, Japan

    International Nuclear Information System (INIS)

    Tokiwa, Tetsuya; Niizato, Tadafumi; Nohara, Tsuyoshi; Asamori, Koichi; Matsuura, Yuki; Kosaka, Hideki

    2011-01-01

    In this study, we present the preliminary results for the estimation of a horizontal crustal movement by using geodetic and geological approach in the Horonobe area, northern Hokkaido, Japan. The estimations have been carried out by using a GPS data and a geological cross section obtained by applying balanced-section method. As results of this study, both of the shortening rates estimated by GPS data and balanced-section method indicate several millimeters per year. Namely, there is no contradiction between geodetic and geological data, and it is considered that Horonobe area is still situated similar tendency and magnitude of a crustal movement. It is seemingly considered that geodetic data is unhelpful for estimating the long-term crustal movement, because period of geodetic observations is a very short. However, the result of this study indicates that geodetic data provide valuable information for estimating the long-term crustal movement in the area, and it is considered that geodetic approach play an important role in improvement of the credibility of evaluation for prediction of long-term stability. (author)

  3. 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.

  4. Crustal Accretion at Subduction Initiation Along Izu-Bonin-Mariana Arc and the Link to SSZ Ophiolites

    Science.gov (United States)

    Ishizuka, O.; Tani, K.; Reagan, M. K.; Kanayama, K.; Umino, S.; Harigane, Y.; Sakamoto, I.

    2014-12-01

    The Izu-Bonin-Mariana (IBM) forearc preserves the earliest arc magmatic history from subduction initiation to the establishment of the arc. Recent investigations have established a bottom to top igneous stratigraphy of: 1) mantle peridotite, 2) gabbroic rocks, 3) a sheeted dyke complex, 4) basaltic pillow lavas (forearc basalts: FAB), 5) boninites and magnesian andesites, 6) tholeiites and calcalkaline arc lavas. This stratigraphy has many similarities to supra-subduction zone (SSZ) ophiolites. One of the most important common characteristics between the SSZ ophiolites and the forearc crust is the occurrence of MORB-like basaltic lavas underlying or accompanying boninites and early arc volcanic suites. A key observation from the IBM forearc is that FAB differs from nearby back-arc lavas in chemical characteristics, including a depletion in moderately incompatible elements. This indicates that FAB is not a pre-existing oceanic basement of the arc, but the first magmatic product after subduction initiation. Sheeted dikes of FAB composition imply that this magmatism was associated with seafloor spreading, possibly triggered by onset of slab sinking. Recognition of lavas with transitional geochemical characteristics between the FAB and the boninites strongly implies genetic linkage between these two magma types. The close similarity of the igneous stratigraphy of SSZ ophiolites to the IBM forearc section strongly implies a common magmatic evolutionary path, i.e., decompressional melting of a depleted MORB-type mantle is followed by melting of an even more depleted mantle with the addition of slab-derived fluid/melt to produce boninite magma. Similarity of magmatic process between IBM forearc and Tethyan ophiolites appears to be reflected on common characteristics of upper mantle section. Peridotite from both sections show more depleted characteristics compared to upper mantle rocks from mid-ocean ridges. Age determinations reveal that first magmatism at the IBM arc

  5. Satellite measurements of the earth's crustal magnetic field

    Science.gov (United States)

    Schnetzler, C. C.

    1989-01-01

    The literature associated with the Magsat mission has evaluated the capabilities and limitations of satellite measurements of the earth's crustal magnetic field, and demonstrated that there exists a 300-3000 km magnetic field, related to major features in the earth's crust, which is primarily caused by induction. Due to its scale and sensitivity, satellite data have been useful in the development of models for such large crustal features as subduction zones, submarine platforms, continental accretion boundaries, and rifts. Attention is presently given to the lack of agreement between laboratory and satellite estimates of lower crustal magnetization.

  6. Crustal and uppermost mantle structure and deformation in east-central China

    Science.gov (United States)

    Li, H.; Yang, X.; Ouyang, L.; Li, J.

    2017-12-01

    We conduct a non-linear joint inversion of receiver functions and Rayleigh wave dispersions to obtain the crustal and upper mantle velocity structure in east-central China. In the meanwhile, the lithosphere and upper mantle deformation beneath east-central China is also evaluated with teleseismic shear wave splitting measurements. The resulting velocity model reveals that to the east of the North-South Gravity Lineament, the crust and the lithosphere are significantly thinned. Furthermore, three extensive crustal/lithospheric thinning sub-regions are clearly identified within the study area. This indicates that the modification of the crust and lithosphere in central-eastern China is non-uniform due to the heterogeneity of the lithospheric strength. Extensive crustal and lithospheric thinning could occur in some weak zones such as the basin-range junction belts and large faults. The structure beneath the Dabie orogenic belt is complex due to the collision between the North and South China Blocks during the Late Paleozoic-Triassic. The Dabie orogenic belt is generally delineated by a thick crust with a mid-crust low-velocity zone and a two-directional convergence in the lithospheric scale. Obvious velocity contrast exhibits in the crust and upper mantle at both sides of the Tanlu fault, which suggests the deep penetration of this lithospheric-scale fault. Most of our splitting measurements show nearly E-W trending fast polarization direction which is slightly deviating from the direction of plate motion. The similar present-day lithosphere structure and upper mantle deformation may imply that the eastern NCC and the eastern SCB were dominated by a common dynamic process after late Mesozoic, i.e., the westward subduction of Pacific plate and the retreat of the subduction plate. The westward subduction of the Philippine plate and the long-range effects of the collision between the Indian plate and Eurasia plate during Cenozoic may have also contributed to the present

  7. Crustal structure beneath two seismic stations in the Sunda-Banda arc transition zone derived from receiver function analysis

    Energy Technology Data Exchange (ETDEWEB)

    Syuhada, E-mail: hadda9@gmail.com [Graduate Research on Earthquake and Active Tectonics (GREAT), Bandung Institute of Technology, Jalan Ganesha 10, Bandung 40132 (Indonesia); Research Centre for Physics - Indonesian Institute of Sciences (LIPI), Kompleks Puspiptek Serpong, Tangsel 15314, Banten Indonesia (Indonesia); Hananto, Nugroho D.; Handayani, Lina [Research Centre for Geotechnology - Indonesian Institute of Sciences (LIPI), Jl. Sangkuriang (Kompleks LIPI) Bandung 40135 (Indonesia); Puspito, Nanang T; Yudistira, Tedi [Faculty of Mining and Petroleum Engineering ITB, Jalan Ganesha 10, Bandung 40132 (Indonesia); Anggono, Titi [Research Centre for Physics - Indonesian Institute of Sciences (LIPI), Kompleks Puspiptek Serpong, Tangsel 15314, Banten Indonesia (Indonesia)

    2015-04-24

    We analyzed receiver functions to estimate the crustal thickness and velocity structure beneath two stations of Geofon (GE) network in the Sunda-Banda arc transition zone. The stations are located in two different tectonic regimes: Sumbawa Island (station PLAI) and Timor Island (station SOEI) representing the oceanic and continental characters, respectively. We analyzed teleseismic events of 80 earthquakes to calculate the receiver functions using the time-domain iterative deconvolution technique. We employed 2D grid search (H-κ) algorithm based on the Moho interaction phases to estimate crustal thickness and Vp/Vs ratio. We also derived the S-wave velocity variation with depth beneath both stations by inverting the receiver functions. We obtained that beneath station PLAI the crustal thickness is about 27.8 km with Vp/Vs ratio 2.01. As station SOEI is covered by very thick low-velocity sediment causing unstable solution for the inversion, we modified the initial velocity model by adding the sediment thickness estimated using high frequency content of receiver functions in H-κ stacking process. We obtained the crustal thickness is about 37 km with VP/Vs ratio 2.2 beneath station SOEI. We suggest that the high Vp/Vs in station PLAI may indicate the presence of fluid ascending from the subducted plate to the volcanic arc, whereas the high Vp/Vs in station SOEI could be due to the presence of sediment and rich mafic composition in the upper crust and possibly related to the serpentinization process in the lower crust. We also suggest that the difference in velocity models and crustal thicknesses between stations PLAI and SOEI are consistent with their contrasting tectonic environments.

  8. Crustal structure across the NE Tibetan Plateau and Ordos Block from the joint inversion of receiver functions and Rayleigh-wave dispersions

    Science.gov (United States)

    Li, Yonghua; Wang, Xingchen; Zhang, Ruiqing; Wu, Qingju; Ding, Zhifeng

    2017-05-01

    We investigated the crustal structure at 34 stations using the H-κ stacking method and jointly inverting receiver functions with Rayleigh-wave phase and group velocities. These seismic stations are distributed along a profile extending across the Songpan-Ganzi Terrane, Qinling-Qilian terranes and southwestern Ordos Basin. Our results reveal the variation in crustal thickness across this profile. We found thick crust beneath the Songpan-Ganzi Terrane (47-59 km) that decreases to 45-47 km in the west Qinling and Qilian terranes, and reaches its local minimum beneath the southwestern Ordos Block (43-51 km) at an average crustal thickness of 46.7 ± 2.5 km. A low-velocity zone in the upper crust was found beneath most of the stations in NE Tibet, which may be indicative of partial melt or a weak detachment layer. Our observations of low to moderate Vp/Vs (1.67-1.79) represent a felsic to intermediate crustal composition. The shear velocity models estimated from joint inversions also reveal substantial lateral variations in velocity beneath the profile, which is mainly reflected in the lower crustal velocities. For the Ordos Block, the average shear wave velocities below 20 km are 3.8 km/s, indicating an intermediate-to-felsic lower crust. The thick NE Tibet crust is characterized by slow shear wave velocities (3.3-3.6 km/s) below 20 km and lacks high-velocity material (Vs ≥ 4.0 km/s) in the lower crust, which may be attributed to mafic lower crustal delamination or/and the thickening of the upper and middle crust.

  9. Early Neoarchaean A-type granitic magmatism by crustal reworking ...

    Indian Academy of Sciences (India)

    29

    marginal part of the Singhbhum craton whose origin and role in crustal evolution are poorly ...... Lu-Hf and Sm-Nd isotope systematics of Archean komatiites; Earth Planet. ..... Association Commission on New Minerals and Mineral Names; Can.

  10. Early Neoarchaean A-type granitic magmatism by crustal reworking ...

    Indian Academy of Sciences (India)

    29

    understand their petrogenesis and tectonic setting. .... crystallize from magmas with temperatures significantly higher than those of other intracrustal ...... blanketing by greenstone belt volcanic rocks, crustal thickening and hot subduction or a. 1.

  11. Crustal structure and tectonic model of the Arctic region

    DEFF Research Database (Denmark)

    Petrov, Oleg; Morozov, Andrey; Shokalsky, Sergey

    2016-01-01

    We present a new model of the crustal and tectonic structure of the Arctic region north of 60° N latitude, constrained as a part of the international Atlas of Geological Maps of the Circumpolar Arctic under the aegis of the Commission for the Geological Map of the World. The region is largely...... formed by (i) Archean-Paleoproterozoic shields and platforms, (ii) orogenic belts of the Neoproterozoic to the Late Mesozoic ages overlain by platform and basin sediments, (iii) Cenozoic rift structures formed in part as a consequence of seafloor spreading in the North East Atlantic Ocean...... and thickness of the sedimentary cover and presents tectonic regionalization based on 18 major crustal types (oceanic, transitional, and continental) recognized in the Arctic. A 7600. km-long crustal geotransect across the region illustrates the details of its crustal and tectonic structure. We discuss...

  12. Continental crustal formation and recycling: Evidence from oceanic basalts

    Science.gov (United States)

    Saunders, A. D.; Tarney, J.; Norry, M. J.

    1988-01-01

    Despite the wealth of geochemical data for subduction-related magma types, and the clear importance of such magmas in the creation of continental crust, there is still no concensus about the relative magnitudes of crustal creation versus crustal destruction (i.e., recycling of crust into the mantle). The role of subducted sediment in the formation of the arc magmas is now well documented; but what proportion of sediment is taken into the deeper mantle? Integrated isotopic and trace element studies of magmas erupted far from presently active subduction zones, in particular basaltic rocks erupted in the ocean basins, are providing important information about the role of crustal recycling. By identifying potential chemical tracers, it is impossible to monitor the effects of crustal recycling, and produce models predicting the mass of material recycled into the mantle throughout long periods of geological time.

  13. Crustal Structure of Active Deformation Zones in Africa: Implications for Global Crustal Processes

    Science.gov (United States)

    Ebinger, C. J.; Keir, D.; Bastow, I. D.; Whaler, K.; Hammond, J. O. S.; Ayele, A.; Miller, M. S.; Tiberi, C.; Hautot, S.

    2017-12-01

    The Cenozoic East African rift (EAR), Cameroon Volcanic Line (CVL), and Atlas Mountains formed on the slow-moving African continent, which last experienced orogeny during the Pan-African. We synthesize primarily geophysical data to evaluate the role of magmatism in shaping Africa's crust. In young magmatic rift zones, melt and volatiles migrate from the asthenosphere to gas-rich magma reservoirs at the Moho, altering crustal composition and reducing strength. Within the southernmost Eastern rift, the crust comprises 20% new magmatic material ponded in the lower crust and intruded as sills and dikes at shallower depths. In the Main Ethiopian Rift, intrusions comprise 30% of the crust below axial zones of dike-dominated extension. In the incipient rupture zones of the Afar rift, magma intrusions fed from crustal magma chambers beneath segment centers create new columns of mafic crust, as along slow-spreading ridges. Our comparisons suggest that transitional crust, including seaward dipping sequences, is created as progressively smaller screens of continental crust are heated and weakened by magma intrusion into 15-20 km thick crust. In the 30 Ma Recent CVL, which lacks a hot spot age progression, extensional forces are small, inhibiting the creation and rise of magma into the crust. In the Atlas orogen, localized magmatism follows the strike of the Atlas Mountains from the Canary Islands hot spot toward the Alboran Sea. CVL and Atlas magmatism has had minimal impact on crustal structure. Our syntheses show that magma and volatiles are migrating from the asthenosphere through the plates, modifying rheology, and contributing significantly to global carbon and water fluxes.

  14. Ionospheric precursors for crustal earthquakes in Italy

    Directory of Open Access Journals (Sweden)

    L. Perrone

    2010-04-01

    Full Text Available Crustal earthquakes with magnitude 6.0>M≥5.5 observed in Italy for the period 1979–2009 including the last one at L'Aquila on 6 April 2009 were considered to check if the earlier obtained relationships for ionospheric precursors for strong Japanese earthquakes are valid for the Italian moderate earthquakes. The ionospheric precursors are based on the observed variations of the sporadic E-layer parameters (h'Es, fbEs and foF2 at the ionospheric station Rome. Empirical dependencies for the seismo-ionospheric disturbances relating the earthquake magnitude and the epicenter distance are obtained and they have been shown to be similar to those obtained earlier for Japanese earthquakes. The dependences indicate the process of spreading the disturbance from the epicenter towards periphery during the earthquake preparation process. Large lead times for the precursor occurrence (up to 34 days for M=5.8–5.9 tells about a prolong preparation period. A possibility of using the obtained relationships for the earthquakes prediction is discussed.

  15. The crustal dynamics intelligent user interface anthology

    Science.gov (United States)

    Short, Nicholas M., Jr.; Campbell, William J.; Roelofs, Larry H.; Wattawa, Scott L.

    1987-01-01

    The National Space Science Data Center (NSSDC) has initiated an Intelligent Data Management (IDM) research effort which has, as one of its components, the development of an Intelligent User Interface (IUI). The intent of the IUI is to develop a friendly and intelligent user interface service based on expert systems and natural language processing technologies. The purpose of such a service is to support the large number of potential scientific and engineering users that have need of space and land-related research and technical data, but have little or no experience in query languages or understanding of the information content or architecture of the databases of interest. This document presents the design concepts, development approach and evaluation of the performance of a prototype IUI system for the Crustal Dynamics Project Database, which was developed using a microcomputer-based expert system tool (M. 1), the natural language query processor THEMIS, and the graphics software system GSS. The IUI design is based on a multiple view representation of a database from both the user and database perspective, with intelligent processes to translate between the views.

  16. Cooperative research in space geodesy and crustal dynamics

    Science.gov (United States)

    1994-01-01

    This research grant, which covered the period of July 1991 to August 1994, was concerned with a variety of topics within the geodesy and crustal dynamics fields. The specific topics of this grant included satellite tracking and gravity field determinations and crustal dynamics (this concentrated of space geodetic site stability for VLBI sites). Summaries of the specific research projects are included along with a list of publications and presentations supported by this research grant.

  17. 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.

  18. Lithospheric Structure, Crustal Kinematics, and Earthquakes in North China: An Integrated Study

    Science.gov (United States)

    Liu, M.; Yang, Y.; Sandvol, E.; Chen, Y.; Wang, L.; Zhou, S.; Shen, Z.; Wang, Q.

    2007-12-01

    The North China block (NCB) is geologically part of the Archaean Sino-Korean craton. But unusual for a craton, it was thermally rejuvenated since late Mesozoic, and experienced widespread extension and volcanism through much of the Cenozoic. Today, the NCB is characterized by strong internal deformation and seismicity, including the 1976 Tangshan earthquake that killed ~250,000 people. We have started a multidisciplinary study to image the lithospheric and upper mantle structure using seismological methods, to delineate crustal kinematics and deformation via studies of neotectonics and space geodesy, and to investigate the driving forces, the stress states and evolution, and seismicity using geodynamic modeling. Both seismic imaging and GPS results indicate that the Ordos plateau, which is the western part of the NCB and a relic of the Sino-Korean craton, has been encroached around its southern margins by mantle flow and thus is experiencing active cratonic destruction. Some of the mantle flow may be driven by the Indo-Asian collision, although the cause of the broad mantle upwelling responsible for the Mesozoic thinning of the NCB lithosphere remains uncertain. At present, crustal deformation in the NCB is largely driven by gravitational spreading of the expanding Tibetan Plateau. Internal deformation within the NCB is further facilitated by the particular tectonic boundary conditions around the NCB, and the large lateral contrasts of lithospheric strength and rheology. Based on the crustal kinematics and lithospheric structure, we have developed a preliminary geodynamic model for stress states and strain energy in the crust of the NCB. The predicted long-term strain energy distribution is comparable with the spatial pattern of seismic energy release in the past 2000 years. We are exploring the cause of the spatiotemporal occurrence of large earthquakes in the NCB, especially the apparent migration of seismicity from the Weihe-Shanxi grabens around the Ordos to

  19. Basinal Structure Of Yola Arm Of The Upper Benue Trough Nigeria ...

    African Journals Online (AJOL)

    Aeromagnetic data interpretation of the Yola arm of the Upper Benue Trough has previously been carried out. However, no detail modeling of the Crustal Structures has been undertaken. Two composite reduced Aeromagnetic maps on a scale of 1:250,000 were digitized and processed using computer techniques.

  20. Effective stress, friction and deep crustal faulting

    Science.gov (United States)

    Beeler, N.M.; Hirth, Greg; Thomas, Amanda M.; Burgmann, Roland

    2016-01-01

    Studies of crustal faulting and rock friction invariably assume the effective normal stress that determines fault shear resistance during frictional sliding is the applied normal stress minus the pore pressure. Here we propose an expression for the effective stress coefficient αf at temperatures and stresses near the brittle-ductile transition (BDT) that depends on the percentage of solid-solid contact area across the fault. αf varies with depth and is only near 1 when the yield strength of asperity contacts greatly exceeds the applied normal stress. For a vertical strike-slip quartz fault zone at hydrostatic pore pressure and assuming 1 mm and 1 km shear zone widths for friction and ductile shear, respectively, the BDT is at ~13 km. αf near 1 is restricted to depths where the shear zone is narrow. Below the BDT αf = 0 is due to a dramatically decreased strain rate. Under these circumstances friction cannot be reactivated below the BDT by increasing the pore pressure alone and requires localization. If pore pressure increases and the fault localizes back to 1 mm, then brittle behavior can occur to a depth of around 35 km. The interdependencies among effective stress, contact-scale strain rate, and pore pressure allow estimates of the conditions necessary for deep low-frequency seismicity seen on the San Andreas near Parkfield and in some subduction zones. Among the implications are that shear in the region separating shallow earthquakes and deep low-frequency seismicity is distributed and that the deeper zone involves both elevated pore fluid pressure and localization.

  1. Intensity attenuation for active crustal regions

    Science.gov (United States)

    Allen, Trevor I.; Wald, David J.; Worden, C. Bruce

    2012-07-01

    We develop globally applicable macroseismic intensity prediction equations (IPEs) for earthquakes of moment magnitude M W 5.0-7.9 and intensities of degree II and greater for distances less than 300 km for active crustal regions. The IPEs are developed for two distance metrics: closest distance to rupture ( R rup) and hypocentral distance ( R hyp). The key objective for developing the model based on hypocentral distance—in addition to more rigorous and standard measure R rup—is to provide an IPE which can be used in near real-time earthquake response systems for earthquakes anywhere in the world, where information regarding the rupture dimensions of a fault may not be known in the immediate aftermath of the event. We observe that our models, particularly the model for the R rup distance metric, generally have low median residuals with magnitude and distance. In particular, we address whether the direct use of IPEs leads to a reduction in overall uncertainties when compared with methods which use a combination of ground-motion prediction equations and ground motion to intensity conversion equations. Finally, using topographic gradient as a proxy and median model predictions, we derive intensity-based site amplification factors. These factors lead to a small reduction of residuals at shallow gradients at strong shaking levels. However, the overall effect on total median residuals is relatively small. This is in part due to the observation that the median site condition for intensity observations used to develop these IPEs is approximately near the National Earthquake Hazard Reduction Program CD site-class boundary.

  2. Crustal contamination processes traced by helium isotopes: Examples from the Sunda arc, Indonesia

    Science.gov (United States)

    Gasparon, M.; Hilton, D. R.; Varne, R.

    1994-08-01

    Helium isotope data have been obtained on well-characterised olivine and clinopyroxene phenocrysts and xenocrysts from thirteen volcanic centres located between central Sumatra and Sumbawa in the Sunda arc of Indonesia. Olivine crystals in mantle xenoliths (Iherzolite) from Bukit Telor basalts are primitive (Mg# = 90), and their He-3/He-4 value (R/R(sub A) = 8.8) indicates that the Sumatran mantle wedge is MORB-like in helium isotope composition. All other samples have lower He-3/He-4 ratios ranging from 8.5R(sub A) to 4.5R(sub A), with most (thirteen out of eighteen) following a trend of more radiogenic He-3/He-4 values with decreasing Mg#. The only exceptions to this trend are phenocrysts from Batur, Agung and Kerinci, which have MORB-like He-3/He-4 values but relatively low Mg# (Mg# = 70-71), and two highly inclusion-rich clinopyroxenes which have He-3/He-4 values lower than other samples of similar Mg#. The results indicate that crustal contamination unrelated to subduction in the Sunda arc is clearly recorded in the He-3/He-4 characteristics of mafic phenocrysts of subaerial volcanics, and that addition of radiogenic helium is related to low-pressure differentiation processes affecting the melts prior to eruption. These conclusions may have widespread applicability and indicate that helium isotope variations can act as an extremely sensitive tracer of upper crustal contamination.

  3. Low crustal velocities and mantle lithospheric variations in southern Tibet from regional Pnl waveforms

    Science.gov (United States)

    Rodgers, Arthur J.; Schwartz, Susan Y.

    We report low average crustal P-wave velocities (5.9-6.1 km/s, Poisson's ratio 0.23-0.27, thickness 68-76 km) in southern Tibet from modelling regional Pnl waveforms recorded by the 1991-1992 Tibetan Plateau Experiment. We also find that the mantle lithosphere beneath the Indus-Tsangpo Suture and the Lhasa Terrane is shield-like (Pn velocity 8.20-8.25 km/s, lid thickness 80-140 km, positive velocity gradient 0.0015-0.0025 s-1). Analysis of relative Pn travel time residuals requires a decrease in the mantle velocities beneath the northern Lhasa Terrane, the Banggong-Nujiang Suture and the southern Qiangtang Terrane. Tectonic and petrologic considerations suggest that low bulk crustal velocities could result from a thick (50-60 km) felsic upper crust with vertically limited and laterally pervasive partial melt. These results are consistent with underthrusting of Indian Shield lithosphere beneath the Tibetan Plateau to at least the central Lhasa Terrane.

  4. Upper crustal structure of the Hawaiian Swell from seafloor compliance measurements

    Science.gov (United States)

    Doran, A. K.; Laske, G.

    2017-12-01

    We present new constraints on elastic properties of the marine sediments and crust surrounding the Hawaiian Islands derived from seafloor compliance measurements. We analyze long-period seismic and pressure data collected during the Plume-Lithosphere Undersea Mantle Experiment [Laske et al, 2009], a deployment consisting of nearly 70 broadband ocean-bottom seismometers with an array aperture of over 1000 kilometers. Our results are supported by previous reflection & refraction studies and by direct sampling of the crust from regional drilling logs. We demonstrate the importance of simultaneously modeling density, compressional velocity, and shear velocity, the former two of which are often ignored during compliance investigations. We find variable sediment thickness and composition across the Hawaiian Swell, with the thickest sediments located within the Hawaiian Moat. Improved resolution of near-surface structure of the Hawaiian Swell is crucially important to improve tomographic images of the underlying lithosphere and asthenosphere and to address outstanding questions regarding the size, source, and location of the hypothesized mantle plume.

  5. The density, compressibility and seismic velocity of hydrous melts at crustal and upper mantle conditions

    Science.gov (United States)

    Ueki, K.; Iwamori, H.

    2015-12-01

    Various processes of subduction zone magmatism, such as upward migration of partial melts and fractional crystallization depend on the density of the hydrous silicate melt. The density and the compressibility of the hydrous melt are key factors for the thermodynamic calculation of phase relation of the hydrous melt, and the geophysical inversion to predict physicochemical conditions of the melting region based on the seismic velocity. This study presents a new model for the calculations of the density of the hydrous silicate melts as a function of T, P, H2O content and melt composition. The Birch-Murnaghan equation is used for the equation of state. We compile the experimentally determined densities of various hydrous melts, and optimize the partial molar volume, compressibility, thermal expansibility and its pressure derivative, and K' of the H2O component in the silicate melt. P-T ranges of the calibration database are 0.48-4.29 GPa and 1033-2073 K. As such, this model covers the P-T ranges of the entire melting region of the subduction zone. Parameter set provided by Lange and Carmichael [1990] is used for the partial molar volume and KT value of the anhydrous silicate melt. K' of anhydrous melt is newly parameterized as a function of SiO2 content. The new model accurately reproduces the experimentally determined density variations of various hydrous melts from basalt to rhyolite. Our result shows that the hydrous melt is more compressive and less dense than the anhydrous melt; with the 5 wt% of H2O in melt, density and KT decrease by ~10% and ~30% from those of the anhydrous melt, respectively. For the application of the model, we calculated the P-wave velocity of the hydrous melt. With the 5 wt% of H2O, P-wave velocity of the silicate melt decreases by >10%. Based on the melt P-wave velocity, we demonstrate the effect of the melt H2O content on the seismic velocity of the partially molten zone of the subduction zone.

  6. Regionalization of Crustal and Upper Mantle Q Structure in Eastern Eurasia Using Multiple Regional Waves

    National Research Council Canada - National Science Library

    Gaherty, James; Lerner-Lam, Arthur

    2007-01-01

    .... The Q Omicron model contains values that vary between 100 and 900. Q Omicron are the lowest in the Tibetan plateau, increase to moderate levels towards the east and north, and reach maxima in the Siberian and eastern Europe Cratons...

  7. Eurasian Surface Wave Phenomenology and Inversion for Crustal and Upper Mantle Structures

    National Research Council Canada - National Science Library

    Levshin, Anatoli

    1997-01-01

    Earthquake seismograms recorded by several global and regional networks between 1988 and late-1995 were used to measure the group velocity dispersion of fundamental Rayleigh and Love waves crossing Eurasia...

  8. Eurasian Surface Wave Phenomenology and Inversion for Crustal and Upper Mantle Structures

    National Research Council Canada - National Science Library

    Levshin, Anatoli

    1997-01-01

    Earthquake seismograms recorded by several global and regional networks between 1988 and late 1995 were used to measure the group velocity dispersion of fundamental Rayleigh and Love waves crossing Eurasia...

  9. Regionalization of Crustal and Upper Mantle Q Structure in Eastern Eurasia Using Multiple Regional Waves

    National Research Council Canada - National Science Library

    Gaherty, James; Lerner-Lam, Arthur

    2007-01-01

    We have mapped lateral variations in seismic Q in eastern Eurasia, including continental China, central Asia, Mongolia and Siberia, using high-frequency regional phases Lg and Pn, as well as long-period Rayleigh waves...

  10. Structure of the crust and upper mantle beneath the Balearic Islands (Western Mediterranean)

    Science.gov (United States)

    Banda, E.; Ansorge, J.; Boloix, M.; Córdoba, D.

    1980-09-01

    Data are presented from deep seismic sounding along the strike of the Balearic Islands carried out in 1976. The interpretation of the data gives the following results: A sedimentary cover of 4 km around Ibiza to 7 km under Mallorca overlies the crystalline basement. This basement with a P-wave velocity of 6.0 km/s at the top reaches a depth of at least 15 km under Ibiza and 17 km under Mallorca with an increase to 6.1 km/s at these depths. The crust-mantle boundary lies at a depth of 20 km and 25 km, respectively. A well documented upper-mantle velocity of 7.7 km/s is found along the entire profile. The Moho rises to a depth of 20 km about 30 km north of Mallorca and probably continues rising towards the center of the North Balearic Sea. The newly deduced crustal structure together with previously determined velocity-depth sections in the North Balearic Sea as well as heat flow and aeromagnetic data can be interpreted as an extended rift structure caused by large-scale tensional processes in the upper mantle. The available data suggest that the entire zone from the eastern Alboran Sea to the area north of the Balearic Islands represents the southeastern flank of this rift system. In this model the provinces of Spain along the east coast would represent the northwestern rift flank.

  11. Crustal processes of the Mid-Ocean Ridge

    Science.gov (United States)

    Ballard, Richard D.; Craig, H.; Edmond, J.; Einaudi, M.; Holcomb, R.; Holland, H.D.; Hopson, C.A.; Luyendyk, B.P.; Macdonald, K.; Morton, J.; Orcutt, J.; Sleep, N.

    1981-01-01

    Independent geological and geophysical investigations of the Mid-Ocean Ridge system have begun to focus on the nature of the magma chamber system underlying its central axis. Thermal models predict the existence of a steady-state chamber beneath a thin crustal lid ranging in thickness from 2 to 13 kilometers. The only aspect of the system that these models fail to account for is the extremely slow spreading rates. Seismological studies reveal the existence of a low-velocity zone beneath segments of the East Pacific Rise, which is thought to correspond to a chamber system having a half-width of approximately 5 to 10 kilometers. These estimates compare favorably with those derived separately through petrological investigations of deep-sea drilling results, various sampling programs, and field and laboratory studies of ophiolites. The chamber is thought to be wing-shaped and to remain continuously open; it is thought to be fed from the center while simultaneously solidifying at the sides as spreading carries the two halves apart. Progressive fractionation occurs by crystal settling coupled with repeated replenishment and magma mixing in an open steady-state system. Near-bottom studies reveal that the zone of extrusion above the chamber is narrow, but its eruptive history is cyclic in nature, in conflict with the predictions of a steady-state model. On-bottom gravity data at 21 ??N on the East Pacific Rise reveal a negative gravity anomaly that may be related to the uppermost part of the chamber. The anomaly is only 2 kilometers wide and 1 kilometer below the sea floor. This feature may be associated with a short-term upper magma reservoir. The cyclic volcanic activity is directly related to the active phase of hydrothermal circulation responsible for the observed negative thermal anomaly. The volume of water associated with this circulation is equal to the entire ocean volume passing through the accretion zone approximately every 8 million years. This is about 0

  12. Crustal processes of the mid-ocean ridge.

    Science.gov (United States)

    1981-07-03

    Independent geological and geophysical investigations of the Mid-Ocean Ridge system have begun to focus on the nature of the magma chamber system underlying its central axis. Thermal models predict the existence of a steady-state chamber beneath a thin crustal lid ranging in thickness from 2 to 13 kilometers. The only aspect of the system that these models fail to account for is the extremely slow spreading rates. Seismological studies reveal the existence of a low-velocity zone beneath segments of the East Pacific Rise, which is thought to correspond to a chamber system having a half-width of approximately 5 to 10 kilometers. These estimates compare favorably with those derived separately through petrological investigations of deep-sea drilling results, various sampling programs, and field and laboratory studies of ophiolites. The chamber is thought to be wing-shaped and to remain continuously open; it is thought to be fed from the center while simultaneously solidifying at the sides as spreading carries the two halves apart. Progressive fractionation occurs by crystal settling coupled with repeated replenishment and magma mixing in an open steady-state system. Near-bottom studies reveal that the zone of extrusion above the chamber is narrow, but its eruptive history is cyclic in nature, in conflict with the predictions of a steady-state model. On-bottom gravity data at 21 degrees N on the East Pacific Rise reveal a negative gravity anomaly that may be related to the uppermost part of the chamber. The anomaly is only 2 kilometers wide and 1 kilometer below the sea floor. This feature may be associated with a short-term upper magma reservoir. The cyclic volcanic activity is directly related to the active phase of hydrothermal circulation responsible for the observed negative thermal anomaly. The volume of water associated with this circulation is equal to the entire ocean volume passing through the accretion zone approximately every 8 million years. This is about 0

  13. New Crustal Thickness for Djibouti, Afar, Using Seismic Techniques

    Science.gov (United States)

    Dugda, Mulugeta; Bililign, Solomon

    2008-10-01

    Crustal thickness and Poisson's ratio for the seismic station ATD in Djibouti, Afar, has been investigated using two seismic techniques (H-κ stacking of receiver functions and a joint inversion of receiver functions and surface wave group velocities). Both techniques give consistent results of crustal thickness 23±1.5 km and Poisson's ratio 0.31±0.02. We also determined a mean P-wave velocity (Vp) of ˜6.2 km/s but ˜6.9-7.0 km/s below a 2 - 5 km thick low velocity layer at the surface. Previous studies of crustal structure for Djibouti reported that the crust is 6 to 11 km thick while our study shows that the crust beneath Djibouti is between 20 and 25 km. This study argues that the crustal thickness values reported for Djibouti for the last 3 decades were not consistent with the reports for the other neighboring region in central and eastern Afar. Our results for ATD in Djibouti, however, are consistent with the reports of crustal thickness in many other parts of central and eastern Afar. We attribute this difference to how the Moho (the crust-mantle discontinuity) is defined (an increase of Vp to 7.4 km/s in this study vs. 6.9 km/s in previous studies).

  14. Detailed measured sections, cross sections, and paleogeographic reconstructions of the upper cretaceous and lower tertiary nonmarine interval, Wind River Basin, Wyoming: Chapter 10 in Petroleum systems and geologic assessment of oil and gas resources in the Wind River Basin Province, Wyoming

    Science.gov (United States)

    Johnson, Ronald C.

    2007-01-01

    Detailed measured sections and regional stratigraphic cross sections are used to reconstruct facies maps and interpret paleogeographic settings for the interval from the base of Upper Cretaceous Mesaverde Formation to top of lower member of the Paleocene Fort Union Formation in the Wind River Basin, Wyoming. The Mesaverde Formation spans the time during which the Upper Cretaceous seaway retreated eastward out of central Wyoming in Campanian time and the initial stages of the Lewis transgression in earliest Maastrichtian time. This retreat stalled for a considerable period of time during deposition of the lower part of the Mesaverde, creating a thick buildup of marginal marine sandstones and coaly coastal plain deposits across the western part of the basin. The Lewis sea transgressed into the northeast part of Wind River Basin, beginning in early Maastrichtian time during deposition of the Teapot Sandstone Member of the Mesaverde Formation. The Meeteetse Formation, which overlies the Teapot, was deposited in a poorly-drained coastal plain setting southwest of the Lewis seaway. The Lewis seaway, at maximum transgression, covered much of the northeast half of the Wind River Basin area but was clearly deflected around the present site of the Wind River Range, southwest of the basin, providing the first direct evidence of Laramide uplift on that range. Uplift of the Wind River Range continued during deposition of the overlying Maastrichtian Lance Formation. The Granite Mountains south of the basin also became a positive feature during this time. A rapidly subsiding trough during the Maastrichtian time formed near the presentday trough of the Wind River Basin in which more than 6,000 feet of Lance was deposited. The development of this trough appears to have begun before the adjacent Owl Creek Mountains to the north started to rise; however, a muddy facies in the upper part of Lance in the deep subsurface, just to the south, might be interpreted to indicate that the

  15. Lower Crustal Seismicity, Volatiles, and Evolving Strain Fields During the Initial Stages of Cratonic Rifting

    Science.gov (United States)

    Lambert, C.; Muirhead, J.; Ebinger, C. J.; Tiberi, C.; Roecker, S. W.; Ferdinand-Wambura, R.; Kianji, G.; Mulibo, G. D.

    2014-12-01

    The volcanically active East African rift system in southern Kenya and northern Tanzania transects thick cratonic lithosphere, and comprises several basins characterized by deep crustal seismicity. The US-French-Tanzania-Kenya CRAFTI project aims to understand the role of magma and volatile movement during the initiation and evolution of rifting in cratonic lithosphere. Our 38-station broadband network spans all or parts of fault-bounded rift segments, enabling comparison of lithospheric structure, fault kinematics, and seismogenic layer thickness with age and proximity to the deeply rooted Archaen craton. Seismicity levels are high in all basins, but we find profound differences in seismogenic layer thickness along the length of the rift. Seismicity in the Manyara basin occurs almost exclusively within the lower crust, and in spatial clusters that have been active since 1990. In contrast, seismicity in the ~ 5 My older Magadi basin is localized in the upper crust, and the long border fault bounding the west side of the basin is seismically inactive. Between these two basins lies the Natron rift segment, which shows seismicity between ~ 20 and ~2 km depth, and high concentrations at Oldoinyo Lengai and Gelai volcanoes. Older volcanoes on the uplifted western flank (e.g., Ngorongoro) experience swarms of activity, suggesting that active magmatism and degassing are widespread. Focal mechanisms of the frequent earthquakes recorded across the array are spatially variable, and indicate a stress field strongly influenced by (1) Holocene volcanoes, (2) mechanical interactions between adjacent rift basins, and (3) a far-field ESE-WNW extensional stress regime. We explore the spatial correlation between zones of intense degassing along fault systems and seismicity, and examine the influence of high gas pressures on lower and upper crustal seismicity in this youthful cratonic rift zone.

  16. A First Layered Crustal Velocity Model for the Western Solomon Islands: Inversion of Measured Group Velocity of Surface Waves using Ambient Noise Cross-Correlation

    Science.gov (United States)

    Ku, C. S.; Kuo, Y. T.; Chao, W. A.; You, S. H.; Huang, B. S.; Chen, Y. G.; Taylor, F. W.; Yih-Min, W.

    2017-12-01

    Two earthquakes, MW 8.1 in 2007 and MW 7.1 in 2010, hit the Western Province of Solomon Islands and caused extensive damage, but motivated us to set up the first seismic network in this area. During the first phase, eight broadband seismic stations (BBS) were installed around the rupture zone of 2007 earthquake. With one-year seismic records, we cross-correlated the vertical component of ambient noise recorded in our BBS and calculated Rayleigh-wave group velocity dispersion curves on inter-station paths. The genetic algorithm to invert one-dimensional crustal velocity model is applied by fitting the averaged dispersion curves. The one-dimensional crustal velocity model is constituted by two layers and one half-space, representing the upper crust, lower crust, and uppermost mantle respectively. The resulted thickness values of the upper and lower crust are 6.4 and 14.2 km, respectively. Shear-wave velocities (VS) of the upper crust, lower crust, and uppermost mantle are 2.53, 3.57 and 4.23 km/s with the VP/VS ratios of 1.737, 1.742 and 1.759, respectively. This first layered crustal velocity model can be used as a preliminary reference to further study seismic sources such as earthquake activity and tectonic tremor.

  17. Anomalous Structure of Oceanic Lithosphere in the North Atlantic and Arctic Oceans: A Preliminary Analysis Based on Bathymetry, Gravity and Crustal Structure

    Science.gov (United States)

    Barantsrva, O.

    2014-12-01

    We present a preliminary analysis of the crustal and upper mantle structure for off-shore regions in the North Atlantic and Arctic oceans. These regions have anomalous oceanic lithosphere: the upper mantle of the North Atlantic ocean is affected by the Iceland plume, while the Arctic ocean has some of the slowest spreading rates. Our specific goal is to constrain the density structure of the upper mantle in order to understand the links between the deep lithosphere dynamics, ocean spreading, ocean floor bathymetry, heat flow and structure of the oceanic lithosphere in the regions where classical models of evolution of the oceanic lithosphere may not be valid. The major focus is on the oceanic lithosphere, but the Arctic shelves with a sufficient data coverage are also included into the analysis. Out major interest is the density structure of the upper mantle, and the analysis is based on the interpretation of GOCE satellite gravity data. To separate gravity anomalies caused by subcrustal anomalous masses, the gravitational effect of water, crust and the deep mantle is removed from the observed gravity field. For bathymetry we use the global NOAA database ETOPO1. The crustal correction to gravity is based on two crustal models: (1) global model CRUST1.0 (Laske, 2013) and, for a comparison, (2) a regional seismic model EUNAseis (Artemieva and Thybo, 2013). The crustal density structure required for the crustal correction is constrained from Vp data. Previous studies have shown that a large range of density values corresponds to any Vp value. To overcome this problem and to reduce uncertainty associated with the velocity-density conversion, we account for regional tectonic variations in the Northern Atlantics as constrained by numerous published seismic profiles and potential-field models across the Norwegian off-shore crust (e.g. Breivik et al., 2005, 2007), and apply different Vp-density conversions for different parts of the region. We present preliminary results

  18. Full 40 km crustal reflection seismic datasets in several Indonesian basins

    Science.gov (United States)

    Dinkelman, M. G.; Granath, J. W.; Christ, J. M.; Emmet, P. A.; Bird, D. E.

    2010-12-01

    Long offset, deep penetration regional 2D seismic data sets have been acquired since 2002 by GX Technology in a number of regions worldwide (www.iongeo.com/Data_Libraries/Spans/). Typical surveys consist of 10+ lines located to image specific critical aspects of basin structure. Early surveys were processed to 20 km, but more recent ones have extended to 40-45 km from 16 sec records. Pre-stack time migration is followed by pre-stack depth migration using gravity and in some cases magnetic modeling to constrain the velocity structure. We illustrate several cases in the SE Asian and Australasian area. In NatunaSPAN™ two generations of inversion can be distinguished, one involving Paleogene faults with Neogene inversion and one involving strike slip-related uplift in the West Natuna Basin. Crustal structure in the very deep Neogene East Natuna Basin has also been imaged. The JavaSPAN™ program traced Paleogene sediments onto oceanic crust of the Flores Sea, thus equating back arc spreading there to the widespread Eocene extension. It also imaged basement in the Makassar Strait beneath as much as 6 km of Cenozoic sedimentary rocks that accumulated Eocene rift basins (the North and South Makassar basins) on the edge of Sundaland, the core of SE Asia. The basement is seismically layered: a noisy upper crust overlies a prominent 10 km thick transparent zone, the base of which marks another change to slightly noisier reflectivity. Eocene normal faults responsible for the opening of extensional basins root in the top of the transparent layer which may be Moho or a brittle-ductile transition within the extended continental crust. Of particular significance is the first image of thick Precambrian basins comprising the bulk of continental crust under the Arafura Sea in the ArafuraSPAN™ program. Four lines some 1200 km long located between Australia and New Guinea on the Arafura platform image a thin Phanerozoic section overlying a striking Precambrian basement composed of

  19. High-resolution and Deep Crustal Imaging Across The North Sicily Continental Margin (southern Tyrrhenian Sea)

    Science.gov (United States)

    Agate, M.; Bertotti, G.; Catalano, R.; Pepe, F.; Sulli, A.

    Three multichannel seismic reflection profiles across the North Sicily continental mar- gin have been reprocessed and interpreted. Data consist of an unpublished high pene- tration seismic profile (deep crust Italian CROP Project) and a high-resolution seismic line. These lines run in the NNE-SSW direction, from the Sicilian continental shelf to the Tyrrhenian abyssal plain (Marsili area), and are tied by a third, high penetration seismic line MS104 crossing the Sisifo High. The North Sicily continental margin represents the inner sector of the Sicilian-Maghrebian chain that is collapsed as con- sequence of extensional tectonics. The chain is formed by a tectonic wedge (12-15 km thick. It includes basinal Meso-Cenozoic carbonate units overthrusting carbonate platform rock units (Catalano et al., 2000). Presently, main culmination (e.g. Monte Solunto) and a number of tectonic depressions (e.g. Cefalù basin), filled by >1000 m thick Plio-Pleistocene sedimentary wedge, are observed along the investigated tran- sect. Seismic attributes and reflector pattern depicts a complex crustal structure. Be- tween the coast and the M. Solunto high, a transparent to diffractive band (assigned to the upper crust) is recognised above low frequency reflective layers (occurring be- tween 9 and 11 s/TWT) that dips towards the North. Their bottom can be correlated to the seismological (African?) Moho discontinuity which is (26 km deep in the Sicilian shelf (Scarascia et al., 1994). Beneath the Monte Solunto ridge, strongly deformed re- flectors occurring between 8 to 9.5 s/TWT (European lower crust?) overly the African (?) lower crust. The resulting geometry suggests underplating of the African crust respect to the European crust (?). The already deformed crustal edifice is dissected by a number of N-dipping normal faults that open extensional basins and are associ- ated with crustal thinning. The Plio-Pleistocene fill of the Cefalù basin can be subdi- vided into three subunits by

  20. The geophysical character of southern Alaska - Implications for crustal evolution

    Science.gov (United States)

    Saltus, R.W.; Hudson, T.L.; Wilson, Frederic H.

    2007-01-01

    The southern Alaska continental margin has undergone a long and complicated history of plate convergence, subduction, accretion, and margin-parallel displacements. The crustal character of this continental margin is discernible through combined analysis of aeromagnetic and gravity data with key constraints from previous seismic interpretation. Regional magnetic data are particularly useful in defining broad geophysical domains. One of these domains, the south Alaska magnetic high, is the focus of this study. It is an intense and continuous magnetic high up to 200 km wide and ∼1500 km long extending from the Canadian border in the Wrangell Mountains west and southwest through Cook Inlet to the Bering Sea shelf. Crustal thickness beneath the south Alaska magnetic high is commonly 40–50 km. Gravity analysis indicates that the south Alaska magnetic high crust is dense. The south Alaska magnetic high spatially coincides with the Peninsular and Wrangellia terranes. The thick, dense, and magnetic character of this domain requires significant amounts of mafic rocks at intermediate to deep crustal levels. In Wrangellia these mafic rocks are likely to have been emplaced during Middle and (or) Late Triassic Nikolai Greenstone volcanism. In the Peninsular terrane, the most extensive period of mafic magmatism now known was associated with the Early Jurassic Talkeetna Formation volcanic arc. Thus the thick, dense, and magnetic character of the south Alaska magnetic high crust apparently developed as the response to mafic magmatism in both extensional (Wrangellia) and subduction-related arc (Peninsular terrane) settings. The south Alaska magnetic high is therefore a composite crustal feature. At least in Wrangellia, the crust was probably of average thickness (30 km) or greater prior to Triassic mafic magmatism. Up to 20 km (40%) of its present thickness may be due to the addition of Triassic mafic magmas. Throughout the south Alaska magnetic high, significant crustal growth

  1. A frozen record of density-driven crustal overturn in lava lakes: The example of Kilauea Iki 1959

    Science.gov (United States)

    Stovall, W.K.; Houghton, Bruce F.; Harris, A.J.L.; Swanson, D.A.

    2009-01-01

    Lava lakes are found at basaltic volcanoes on Earth and other planetary bodies. Density-driven crustal foundering leading to surface renewal occurs repeatedly throughout the life of a lava lake. This process has been observed and described in a qualitative sense, but due to dangerous conditions, no data has been acquired to evaluate the densities of the units involved. Kilauea Iki pit crater in Hawai'i houses a lava lake erupted during a 2 month period in 1959. Part of the surface of the Kilauea Iki lake now preserves the frozen record of a final, incomplete, crustal-overturn cycle. We mapped this region and sampled portions of the foundering crust, as well as overriding and underlying lava, to constrain the density of the units involved in the overturn process. Overturn is driven by the advance of a flow front of fresh, low-density lava over an older, higher density surface crust. The advance of the front causes the older crust to break up, founder, and dive downwards into the lake to expose new, hot, low-density lava. We find density differences of 200 to 740 kg/m3 between the foundering crust and over-riding and under-lying lava respectively. In this case, crustal overturn is driven by large density differences between the foundering and resurfacing units. These differences lead, inevitably, to frequent crustal renewal: simple density differences between the surface crust and underlying lake lava make the upper layers of the lake highly unstable. ?? Springer-Verlag 2008.

  2. Crustally derived granites in Dali, SW China: new constraints on silicic magmatism of the Central Emeishan Large Igneous Province

    Science.gov (United States)

    Zhu, Bei; Peate, David W.; Guo, Zhaojie; Liu, Runchao; Du, Wei

    2017-10-01

    We have identified a new crustally derived granite pluton that is related to the Emeishan Large Igneous Province (ELIP). This pluton (the Wase pluton, near Dali) shows two distinct SHRIMP zircon U-Pb age groups ( 768 and 253 Ma). As it has an intrusive relationship with Devonian limestone, the younger age is interpreted as its formation, which is related to the ELIP event, whereas the 768 Ma Neoproterozoic-aged zircons were inherited from Precambrian crustal component of the Yangtze Block, implying the pluton has a crustally derived origin. This is consistent with its peraluminous nature, negative Nb-Ta anomaly, enrichment in light rare earth elements, high 87Sr/86Sr(i) ratio (0.7159-0.7183) and extremely negative ɛ(Nd)(i) values (-12.15 to -13.70), indicative of melts derived from upper crust materials. The Wase pluton-intruded Devonian strata lie stratigraphically below the Shangcang ELIP sequence, which is the thickest volcanic sequence ( 5400 m) in the whole ELIP. The uppermost level of the Shangcang sequence contains laterally restricted rhyolite. Although the rhyolite has the same age as the Wase pluton, its geochemical features demonstrate a different magma origin. The rhyolite displays moderate 87Sr/86Sr(i) (0.7053), slightly negative ɛ(Nd)(i) (-0.18) and depletions in Ba, Cs, Eu and Sr, implying derivation from differentiation of a mantle-derived mafic magma source. The coexistence of crustally and mantle-derived felsic systems, along with the robust development of dike swarms, vent proximal volcanics and thickest flood basalts piles in Dali, shows that the Dali area was probably where the most active Emeishan magmatism had once existed.

  3. Crustal fraction of moment of inertia in pulsars

    International Nuclear Information System (INIS)

    Atta, Debasis; Mukhopadhyay, Somnath; Basu, D.N.

    2015-01-01

    In the present work, stability of the β-equilibrated dense nuclear matter is analyzed with respect to the thermodynamic stability conditions. Based on the density dependent M3Y (DDM3Y) effective nucleon-nucleon (NN) interaction, the location of the inner edge of neutron star crusts and core-crust transition density and pressure are calculated and crustal fraction of moment of inertia is determined. These results for pressure and density at core-crust transition together with the observed minimum crustal fraction of the total moment of inertia provide a new limit for the radius of the Vela pulsar

  4. 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...

  5. The Upper Atmosphere; Threshold of Space.

    Science.gov (United States)

    Bird, John

    This booklet contains illustrations of the upper atmosphere, describes some recent discoveries, and suggests future research questions. It contains many color photographs. Sections include: (1) "Where Does Space Begin?"; (2) "Importance of the Upper Atmosphere" (including neutral atmosphere, ionized regions, and balloon and investigations); (3)…

  6. Extreme Mesozoic crustal thinning in the Eastern Iberia margin: The example of the Columbrets Basin (Valencia Trough)

    Science.gov (United States)

    Mohn, G.; Etheve, N.; Frizon de Lamotte, D.; Roca, E.; Tugend, J.; Gómez-Romeu, J.

    2017-12-01

    Eastern Iberia preserves a complex succession of Mesozoic rifts partly or completely inverted during the Late Cretaceous and Cenozoic in relation with Africa-Eurasia convergence. Notably, the Valencia Trough, classically viewed as part of the Cenozoic West Mediterranean basins, preserves in its southwestern part a thick Mesozoic succession (locally »10km thick) over a highly thinned continental basement (locally only »3,5km thick). This sub-basin referred to as the Columbrets Basin, represents a Late Jurassic-Early Cretaceous hyper-extended rift basin weakly overprinted by subsequent events. Its initial configuration is well preserved allowing us to unravel its 3D architecture and tectono-stratigraphic evolution in the frame of the Mesozoic evolution of eastern Iberia. The Columbrets Basin benefits from an extensive dataset combining high resolution reflection seismic profiles, drill holes, refraction seismic data and Expanding Spread Profiles. Its Mesozoic architecture is controlled by interactions between extensional deformation and halokinesis involving the Upper Triassic salt. The thick uppermost Triassic to Cretaceous succession describes a general synclinal shape, progressively stretched and dismembered towards the basin borders. The SE-border of the basin is characterized by a large extensional detachment fault acting at crustal scale and interacting locally with the Upper Triassic décollement. This extensional structure accommodates the exhumation of the continental basement and part of the crustal thinning. Eventually our results highlight the complex interaction between extreme crustal thinning and occurrence of a pre-rift salt level for the deformation style and tectono-stratigraphic evolution of hyper-extended rift basins.

  7. Crustal surface wave velocity structure of the east Albany-Fraser Orogen, Western Australia, from ambient noise recordings

    Science.gov (United States)

    Sippl, C.; Kennett, B. L. N.; Tkalčić, H.; Gessner, K.; Spaggiari, C. V.

    2017-09-01

    Group and phase velocity maps in the period range 2-20 s for the Proterozoic east Albany-Fraser Orogen, Western Australia, are extracted from ambient seismic noise recorded with the 70-station ALFREX array. This 2 yr temporary installation provided detailed coverage across the orogen and the edge of the Neoarchean Yilgarn Craton, a region where no passive seismic studies of this scale have occurred to date. The surface wave velocities are rather high overall (>3 km s-1 nearly everywhere), as expected for exposed Proterozoic basement rocks. No clear signature of the transition between Yilgarn Craton and Albany-Fraser Orogen is observed, but several strong anomalies corresponding to more local geological features were obtained. A prominent, NE-elongated high-velocity anomaly in the northern part of the array is coincident with a Bouguer gravity high caused by the upper crustal metamorphic rocks of the Fraser Zone. This feature disappears towards longer periods, which hints at an exclusively upper crustal origin for this anomaly. Further east, the limestones of the Cenozoic Eucla Basin are clearly imaged as a pronounced low-velocity zone at short periods, but the prevalence of low velocities to periods of ≥5 s implies that the uppermost basement in this area is likewise slow. At longer periods, slightly above-average surface wave velocities are imaged below the Eucla Basin.

  8. Mars - Crustal structure inferred from Bouguer gravity anomalies.

    Science.gov (United States)

    Phillips, R. J.; Saunders, R. S.; Conel, J. E.

    1973-01-01

    Bouguer gravity has been computed for the equatorial region of Mars by differencing free air gravity and the gravity predicted from topographic variations. The free air gravity was generated from an eighth-order set of spherical harmonic coefficients. The gravity from topographic variations was generated by integrating a two-dimensional Green's function over each contour level. The Bouguer gravity indicates crustal inhomogeneities on Mars that are postulated to be variations in crustal thickness. The Tharsis ridge is a region of thick continental type crust. The gravity data, structural patterns, topography, and surface geology of this region lead to the interpretation of the Tharsis topographic high as a broad crustal upwarp possibly associated with local formation of lower-density crustal material and subsequent rise of a thicker crust. The Amazonis region is one of several basins of relatively thin crust, analogous to terrestrial ocean basins. The Libya and Hellas basins, which are probable impact features, are also underlain by thin crust and are possible regions of mantle upwelling.

  9. Seismically constrained two-dimensional crustal thermal structure of ...

    Indian Academy of Sciences (India)

    The temperature field within the crust is closely related to tectonic history as well as many other geological processes inside the earth. Therefore, knowledge of the crustal thermal structure of a region is of great importance for its tectonophysical studies. This work deals with the two-dimensional thermal modelling to ...

  10. An Approach to the Crustal Thickness Inversion Problem

    Science.gov (United States)

    De Marchi, F.; Di Achille, G.

    2017-12-01

    We describe a method to estimate the crustal thickness of a planet and we apply it to Venus. As in the method of (Parker, 1972), modified by (Wieczorek & Phillips, 1998), the gravity field anomalies of a planet are assumed to be due to the combined effect of topography and relief on the crust-mantle interface. No assumptions on isostasy are necessary. In our case, rather than using the expansion of the powers of the relief in Taylor series, we model the gravitational field of topography/relief by means of a large number of prism-shaped masses covering the whole surface of the planet. Under the hypothesis that crustal and mantle densities are the same everywhere, we solve for the relief depths on the crust-mantle interface by imposing that observed and modeled gravity field at a certain reference spherical surface (external to the planet) must be equal. This method can be extended to the case of non-uniform densities. Finally, we calculate a map of the crustal thickness of Venus and compare our results with those predicted by previous work and with the global distribution of main geological features (e.g. rift zones, tesserae, coronae). We discuss the agremeent between our results and the main geodynamical and crustal models put forth to explain the origin of such features and the applicability of this method in the context of the mission VOX (Venus Origins Explore), proposed for NASA's NF4 call.

  11. Thinning Mechanism of the South China Sea Crust: New Insight from the Deep Crustal Images

    Science.gov (United States)

    Chang, S. P.; Pubellier, M. F.; Delescluse, M.; Qiu, Y.; Liang, Y.; Chamot-Rooke, N. R. A.; Nie, X.; Wang, J.

    2017-12-01

    The passive margin in the South China Sea (SCS) has experienced a long-lived extension period from Paleocene to late Miocene, as well as an extreme stretching which implies an unusual fault system to accommodate the whole amount of extension. Previous interpretations of the fault system need to be revised to explain the amount of strain. We study a long multichannel seismic profile crossing the whole rifted margin in the southwest of SCS, using 6 km- and 8 km-long streamers. After de-multiple processing by SRME, Radon and F-K filtering, an enhanced image of the crustal geometry, especially on the deep crust, allows us to illustrate two levels of detachment at depth. The deeper detachment is around 7-8 sec TWT in the profile. The faults rooting at this detachment are characterized by large offset and are responsible for thicker synrift sediment. A few of these faults appear to reach the Moho. The geometry of the acoustic basement between these boundary faults suggests gentle tilting with a long wavelength ( 200km), and implies some internal deformation. The shallower detachment is located around 4-5 sec TWT. The faults rooting at this detachment represent smaller offset, a shorter wavelength of the basement and thinner packages of synrift sediment. Two detachments separate the crust into upper, middle and lower crust. If the lower crust shows ductile behavior, the upper and middle crust is mostly brittle and form large wavelength boudinage structure, and the internal deformation of the boudins might imply low friction detachments at shallower levels. The faults rooting to deep detachment have activated during the whole rifting period until the breakup. Within the upper and middle crust, the faults resulted in important tilting of the basement at shallow depth, and connect to the deep detachment at some places. The crustal geometry illustrates how the two detachments are important for the thinning process, and also constitute a pathway for the following magmatic

  12. Topography of the Betics: crustal thickening, dynamic topography and relief inheritance

    Science.gov (United States)

    Janowski, Marianne; Loget, Nicolas; Bellahsen, Nicolas; Husson, Laurent; Le Pourhiet, Laetitia; Meyer, Bertrand

    2017-04-01

    The main mechanism that explains high orogenic topographies is the isostatic adjustment due to crustal thickening. However in the Betic Cordillera (South Spain), the present-day elevation and crustal thickness are not correlated. That is at odds with the general premise of isostasy and requires reappraising the question of the driving mechanisms leading to the current topography. The Betics are located at the western edge of the alpine Mediterranean belt. Its Cenozoic orogenic building was disrupted by a major crustal thinning event induced by a slab rollback in the internal zones (Alboran domain) during Neogene. Topography was largely levelled and flooded by the sea during Neogene extension, and then has been folded since the Late Tortonian inversion. The present-day topography shows flat summits still preserved from fluvial regression in the internal zones (central and eastern Betics). These low-relief surfaces may be inherited from the Neogene planation toward sea-level as rocks cooling histories inferred from low-temperature thermochronology seem to point it out. Post-Tortonian shortening estimated thanks to a crustal-scale N-S cross-section in the eastern Betics (at the Sierra Nevada longitude) does not exceed few kilometers which is much lower than the shortening required by isostatic equilibrium, and is thus insufficient to explain the post-Tortonian topography building. We tested the hypothesis that mantle dynamics could in fact be an important mechanism that explains the topography of the Betics. We first computed the residual topography (i.e. the non-isostatic component of the elevation) using the most recent published Moho mapping of the area. In the western Betics, our results show important negative residual topography (down to -3 km) possibly associated with the west-Alboran slab suction. In the eastern Betics however, positive residual topography is important (up to +3 km) and can be explained by the dynamic mantle support of the topography, possibly

  13. Rheological and physical characteristics of crustal-scaled materials for centrifuge analogue modelling

    Science.gov (United States)

    Waffle, Lindsay; Godin, Laurent; Harris, Lyal B.; Kontopoulou, M.

    2016-05-01

    We characterize a set of analogue materials used for centrifuge analogue modelling simulating deformation at different levels in the crust simultaneously. Specifically, we improve the rheological characterization in the linear viscoelastic region of materials for the lower and middle crust, and cohesive synthetic sands without petroleum-binding agents for the upper crust. Viscoelastic materials used in centrifuge analogue modelling demonstrate complex dynamic behaviour, so viscosity alone is insufficient to determine if a material will be an effective analogue. Two series of experiments were conducted using an oscillating bi-conical plate rheometer to measure the storage and loss moduli and complex viscosities of several modelling clays and silicone putties. Tested materials exhibited viscoelastic and shear-thinning behaviour. The silicone putties and some modelling clays demonstrated viscous-dominant behaviour and reached Newtonian plateaus at strain rates clays demonstrated elastic-dominant power-law relationships. Based on these results, the elastic-dominant modelling clay is recommended as an analogue for basement cratons. Inherently cohesive synthetic sands produce fine-detailed fault and fracture patterns, and developed thrust, strike-slip, and extensional faults in simple centrifuge test models. These synthetic sands are recommended as analogues for the brittle upper crust. These new results increase the accuracy of scaling analogue models to prototype. Additionally, with the characterization of three new materials, we propose a complete lithospheric profile of analogue materials for centrifuge modelling, allowing future studies to replicate a broader range of crustal deformation behaviours.

  14. Complex, multilayered azimuthal anisotropy beneath Tibet: evidence for co-existing channel flow and pure-shear crustal thickening

    Science.gov (United States)

    Agius, Matthew R.; Lebedev, Sergei

    2017-09-01

    Of the two debated, end-member models for the late-Cenozoic thickening of Tibetan crust, one invokes 'channel flow' (rapid viscous flow of the mid-lower crust, driven by topography-induced pressure gradients and transporting crustal rocks eastward) and the other 'pure shear' (faulting and folding in the upper crust, with viscous shortening in the mid-lower crust). Deep-crustal deformation implied by each model is different and would produce different anisotropic rock fabric. Observations of seismic anisotropy can thus offer a discriminant. We use broad-band phase-velocity curves-each a robust average of tens to hundreds of measurements-to determine azimuthal anisotropy in the entire lithosphere-asthenosphere depth range and constrain its amplitude. Inversions of the differential dispersion from path pairs, region-average inversions and phase-velocity tomography yield mutually consistent results, defining two highly anisotropic layers with different fast-propagation directions within each: the middle crust and the asthenosphere. In the asthenosphere beneath central and eastern Tibet, anisotropy is 2-4 per cent and has an NNE-SSW fast-propagation azimuth, indicating flow probably driven by the NNE-ward, shallow-angle subduction of India. The distribution and complexity of published shear wave splitting measurements can be accounted for by the different anisotropy in the mid-lower crust and asthenosphere. The estimated splitting times that would be accumulated in the crust alone are 0.25-0.8 s; in the upper mantle-0.5-1.2 s, depending on location. In the middle crust (20-45 km depth) beneath southern and central Tibet, azimuthal anisotropy is 3-5 and 4-6 per cent, respectively, and its E-W fast-propagation directions are parallel to the current extension at the surface. The rate of the extension is relatively low, however, whereas the large radial anisotropy observed in the middle crust requires strong alignment of mica crystals, implying large finite strain and

  15. The effects of lower crustal strength and preexisting midcrustal shear zones on the formation of continental core complexes and low-angle normal faults

    KAUST Repository

    Wu, Guangliang; Lavier, Luc L.

    2016-01-01

    To investigate the formation of core complexes and low-angle normal faults, we devise thermomechanical simulations on a simplified wedge-like orogenic hinterland that has initial topography, Moho relief, and a preexisting midcrustal shear zone that can accommodate shear at very low angles (<20°). We mainly vary the strength of the lower crust and the frictional strength of the preexisting midcrustal shear zone. We find that the strength of the lower crust and the existence and strength of a preexisting shear zone significantly affect the formation and evolution of core complexes. With increasing lower crustal strength, we recognize varying extensional features with decreasing exhumation rate: these are characterized by bivergent metamorphic massifs, classic Cordilleran metamorphic core complexes, multiple consecutive core complexes (or boudinage structures), and a flexural core complex underlined by a large subsurface low-angle detachment fault with a small convex curvature. Topographic loading and mantle buoyancy forces, together with divergent boundaries, drive a regional lower crustal flow that leads to the exhumation of the lower crust where intensive upper crustal faulting induces strong unloading. The detachment fault is a decoupling zone that accommodates large displacement and accumulates sustained shear strain at very low angle between upper and lower crust. Though the regional stress is largely Andersonian, we find non-Andersonian stress in regions adjacent to the preexisting shear zone and those with high topographic gradient. Our new models provide a view that is generally consistent with geological and geophysical observations on how core complexes form and evolve.

  16. The effects of lower crustal strength and preexisting midcrustal shear zones on the formation of continental core complexes and low-angle normal faults

    KAUST Repository

    Wu, Guangliang

    2016-08-22

    To investigate the formation of core complexes and low-angle normal faults, we devise thermomechanical simulations on a simplified wedge-like orogenic hinterland that has initial topography, Moho relief, and a preexisting midcrustal shear zone that can accommodate shear at very low angles (<20°). We mainly vary the strength of the lower crust and the frictional strength of the preexisting midcrustal shear zone. We find that the strength of the lower crust and the existence and strength of a preexisting shear zone significantly affect the formation and evolution of core complexes. With increasing lower crustal strength, we recognize varying extensional features with decreasing exhumation rate: these are characterized by bivergent metamorphic massifs, classic Cordilleran metamorphic core complexes, multiple consecutive core complexes (or boudinage structures), and a flexural core complex underlined by a large subsurface low-angle detachment fault with a small convex curvature. Topographic loading and mantle buoyancy forces, together with divergent boundaries, drive a regional lower crustal flow that leads to the exhumation of the lower crust where intensive upper crustal faulting induces strong unloading. The detachment fault is a decoupling zone that accommodates large displacement and accumulates sustained shear strain at very low angle between upper and lower crust. Though the regional stress is largely Andersonian, we find non-Andersonian stress in regions adjacent to the preexisting shear zone and those with high topographic gradient. Our new models provide a view that is generally consistent with geological and geophysical observations on how core complexes form and evolve.

  17. Mechanisms of unsteady shallow creep on major crustal faults

    Science.gov (United States)

    Jiang, J.; Fialko, Y. A.

    2017-12-01

    A number of active crustal faults are associated with geodetically detectable shallow creep, while other faults appear to be locked all the way to the surface over the interseismic period. Faults that exhibit shallow creep also often host episodic accelerated creep events. Examples include the Ismetpasa segment of the North Anatolian Fault (NAF) in Turkey and the Southern San Andreas and Superstition Hills (SHF) faults in Southern California. Recent geodetic observations indicate that shallow creep events can involve large fault sections (tens of km long) and persist throughout different stages of a seismic cycle. A traditional interpretation of shallow creep in terms of a velocity-strengthening (VS) layer atop the seismogenic velocity-weakening (VW) zone fails to explain episodic creep events. Wei et al. (2013) proposed that such events can be due to a thin VW layer within the VS shallow crust, implying rather special structural and lithologic conditions. We explore the rheologic controls on aseismic episodic slip and its implications for seismic faulting in the framework of laboratory rate-and-state friction. Observations of co-, post- and inter-seismic slip from the NAF and SHF are used to infer depth-dependent frictional properties in a 2D fault model. In particular, creep events with displacements on the order of millimeters and periods of months are reproduced in a model having monotonic depth variations in rate-and-state parameters. Such a model includes a velocity-neutral (VN) layer sandwiched between the surface layer with VS frictional properties, constrained by observed postseismic afterslip, and a deeper VW layer that largely controls the recurrence of major earthquakes. With the presence of the VN layer, the amount of surface-breaching coseismic slip critically depends on how dynamic weakening varies with depth in the seismogenic layer. Observations of limited surface slip during prior events on the NAF and SHF suggest that coseismic fault weakening is

  18. Deep structure of crust and the upper mantle of the Mendeleev Rise on the Arktic­-2012 DSS profile

    DEFF Research Database (Denmark)

    Kashubin, Sergey; Petrov, Oleg; Artemieva, Irina

    2016-01-01

    During high­latitude combined geological and geophysical expedition “Arctic­-2012”, deep seismic sounding (DSS) with ocean bottom seismometers were carried out in the Arctic Ocean along the line 740 km long, crossing the Mendeleev Rise at about 77° N. Crustal and upper mantle Vp­velocity and Vp...

  19. Upper Gastrointestinal (GI) Series

    Science.gov (United States)

    ... standard barium upper GI series, which uses only barium a double-contrast upper GI series, which uses both air and ... evenly coat your upper GI tract with the barium. If you are having a double-contrast study, you will swallow gas-forming crystals that ...

  20. High resolution 2D numerical models from rift to break-up: Crustal hyper-extension, Margin asymmetry, Sequential faulting

    Science.gov (United States)

    Brune, Sascha; Heine, Christian; Pérez-Gussinyé, Marta; Sobolev, Stephan

    2013-04-01

    Numerical modelling is a powerful tool to integrate a multitude of geological and geophysical data while addressing fundamental questions of passive margin formation such as the occurrence of crustal hyper-extension, (a-)symmetries between conjugate margin pairs, and the sometimes significant structural differences between adjacent margin segments. This study utilises knowledge gathered from two key examples of non-magmatic, asymmetric, conjugate margin pairs, i.e. Iberia-New Foundland and Southern Africa-Brazil, where many published seismic lines provide solid knowledge on individual margin geometry. While both margins involve crustal hyper-extension, it is much more pronounced in the South Atlantic. We investigate the evolution of these two margin pairs by carefully constraining our models with detailed plate kinematic history, laboratory-based rheology, and melt fraction evaluation of mantle upwelling. Our experiments are consistent with observed fault patterns, crustal thickness, and basin stratigraphy. We conduct 2D thermomechanical rift models using the finite element code SLIM3D that operates with nonlinear stress- and temperature-dependent elasto-visco-plastic rheology, with parameters provided by laboratory experiments on major crustal and upper mantle rocks. In our models we also calculate the melt fraction within the upwelling asthenosphere, which allows us to control whether the model indeed corresponds to the non-magmatic margin type or not. Our modelling highlights two processes as fundamental for the formation of hyper-extension and margin asymmetry at non-magmatic margins: (1) Strain hardening in the rift center due to cooling of upwelling mantle material (2) The formation of a weak crustal domain adjacent to the rift center caused by localized viscous strain softening and heat transfer from the mantle. Simultaneous activity of both processes promotes lateral rift migration in a continuous way that generates a wide layer of hyper-extended crust on

  1. Crustal structure of the Murray Ridge, northwest Indian Ocean, from wide-angle seismic data

    Science.gov (United States)

    Minshull, T. A.; Edwards, R. A.; Flueh, E. R.

    2015-07-01

    The Murray Ridge/Dalrymple Trough system forms the boundary between the Indian and Arabian plates in the northern Arabian Sea. Geodetic constraints from the surrounding continents suggest that this plate boundary is undergoing oblique extension at a rate of a few millimetres per year. We present wide-angle seismic data that constrains the composition of the Ridge and of adjacent lithosphere beneath the Indus Fan. We infer that Murray Ridge, like the adjacent Dalrymple Trough, is underlain by continental crust, while a thin crustal section beneath the Indus Fan represents thinned continental crust or exhumed serpentinized mantle that forms part of a magma-poor rifted margin. Changes in crustal structure across the Murray Ridge and Dalrymple Trough can explain short-wavelength gravity anomalies, but a long-wavelength anomaly must be attributed to deeper density contrasts that may result from a large age contrast across the plate boundary. The origin of this fragment of continental crust remains enigmatic, but the presence of basement fabrics to the south that are roughly parallel to Murray Ridge suggests that it separated from the India/Seychelles/Madagascar block by extension during early breakup of Gondwana.

  2. Lower crustal strength controls on melting and type of oceanization at magma-poor margins

    Science.gov (United States)

    Ros, E.; Perez-Gussinye, M.; Araujo, M. N.; Thoaldo Romeiro, M.; Andres-Martinez, M.; Morgan, J. P.

    2017-12-01

    Geodynamical models have been widely used to explain the variability in the architectonical style of conjugate rifted margins as a combination of lithospheric deformation modes, which are strongly influenced by lower crustal strength. We use 2D numerical models to show that the lower crustal strength also plays a key role on the onset and amount of melting and serpentinization during continental rifting. The relative timing between melting and serpentinization onsets controls whether the continent-ocean transition (COT) of margins will be predominantly magmatic or will mainly consist of exhumed and serpentinized mantle. Based on our results for magma-poor continental rifting, we propose a genetic link between margin architecture and COT styles that can be used as an additional tool to help interpret and understand the processes leading to margin formation. Our results show that strong lower crusts and very slow extension velocities (architecture of the magma-poor section of the South Atlantic, we suggest that the COT of the northern sector, Camamu-Gabon basins, is more likely to consist of exhumed mantle with intruded magmatism, while to the South, the Camamu-Kwanza and North Santos-South Kwanza conjugates, may be better characterized by a predominantly magmatic COT.

  3. Inconsistent diagnosis of acute malnutrition by weight-for-height and mid-upper arm circumference: contributors in 16 cross-sectional surveys from South Sudan, the Philippines, Chad, and Bangladesh.

    Science.gov (United States)

    Roberfroid, Dominique; Huybregts, Lieven; Lachat, Carl; Vrijens, France; Kolsteren, Patrick; Guesdon, Benjamin

    2015-08-25

    The two anthropometric indicators of acute malnutrition in children under 5 years, i.e. a Mid-Upper Arm Circumference malnutrition given its strong association with age, sex and stunting, and its low sensitivity to detect slim children. Having 'longer legs' moderately increases the diagnosis of acute malnutrition by WHZ-2. Prospective studies are urgently needed to elucidate the clinical and physiological outcomes of the various anthropometric indicators of malnutrition.

  4. Application of FE software Elmer to the modeling of crustal-scale processes

    Science.gov (United States)

    Maierová, Petra; Guy, Alexandra; Lexa, Ondrej; Cadek, Ondrej

    2010-05-01

    We extended Elmer (the open source finite element software for multiphysical problems, http://www.csc.fi/english/pages/elmer) by user-written procedures for the two-dimensional modeling of crustal-scale processes. The standard version of Elmer is an appropriate tool for modeling of thermomechanical convection with non-linear viscous rheology. In geophysics, it might be suitable for some type of mantle convection modeling. Unlike the mantle, the crust is very heterogeneous. It consists of materials with distinct rheological properties that are subject to highly varied conditions: low pressure and temperature near the surface of the Earth and relatively high pressure and temperature at a depth of several tens of kilometers. Moreover, the deformation in the upper crust is mostly brittle and the strain is concentrated into narrow shear zones and thrusts. In order to simulate the brittle behavior of the crust, we implemented pressure-dependent visco-plastic rheology. The material heterogeneity and chemical convection is implemented in terms of active markers. Another special feature of the crust, the moving free surface, is already included in Elmer by means of a moving computational grid. Erosion can easily be added in this scheme. We tested the properties of our formulation of plastic flow on several numerical experiments simulating the deformation of material under compressional and extensional stresses. In the first step, we examined angles of shear zones that form in a plastically deforming material for different material parameters and grid resolutions. A more complex setting of "sandbox-type" experiments containing heterogeneous material, strain-softening and boundary friction was considered as a next testing case. To illustrate the abilities of the extended Elmer software in crustal deformation studies, we present two models of geological processes: diapirism of the lower crust and a channel flow forced by indentation. Both these processes are assumed to take

  5. Anomalous crustal movements with low seismic efficiency - Campi Flegrei, Italy and some examples in Japan

    Directory of Open Access Journals (Sweden)

    A. Nazzaro

    2002-06-01

    Full Text Available Campi Flegrei is a unique volcanic region located near Naples, Italy. Anomalous crustal movements at Pozzuoli in Campi Flegrei have been documented since the Roman period. The movements were gradual and have continued to the present, occasionally accompanying swarms of local earthquakes and volcanic eruptions. Generally the movements proceed with low seismicity. After the 1538 eruption of Monte Nuovo, Pozzuoli had subsided monotonously, but it changed to uplift abruptly in 1969. The uplift accelerated in 1983 and 1984 reaching more than 2 m, and thereafter began to subside. Many discussions of this event have been published. In Japan, we have examples of deformations similar to those at Campi Flegrei, mainly in volcanic areas, and rarely in non-volcanic areas. The former includes Iwojima, Miyakejima and Aira caldera while the latter is represented by Cape Omaezaki. Iwojima is a volcano island, and its secular uplifts since the 18th century are recognized as an unusual event. Miyakejima volcano and Aira caldera exhibited anomalous movements with low seismicity after their eruptions. Cape Omaezaki is not situated in volcanic zone but near a subduction zone, and gradually and continuously subsides as a precursor to a large earthquake. In such cases as Campi Flegrei and the Japanese localities, we would question whether the deformations are accompanied by normal seismicity or low seismicity. To examine quantitatively the relationship between seismicity and related deformation, seismic efficiency is generally useful. The crustal deformations in all the regions cited above are characterized by exceptionally low seismic efficiencies. In the present paper, the deformations at Pozzuoli and Iwojima are mainly described and a comparative discussion among these and other localities in Japan is supplemented. It is concluded that such anomalous phenomena in volcanic areas are attributable to peculiar rheological aspects of the material composing the local

  6. Crustal-scale tilting of the central Salton block, southern California

    Science.gov (United States)

    Dorsey, Rebecca; Langenheim, Victoria

    2015-01-01

    The southern San Andreas fault system (California, USA) provides an excellent natural laboratory for studying the controls on vertical crustal motions related to strike-slip deformation. Here we present geologic, geomorphic, and gravity data that provide evidence for active northeastward tilting of the Santa Rosa Mountains and southern Coachella Valley about a horizontal axis oriented parallel to the San Jacinto and San Andreas faults. The Santa Rosa fault, a strand of the San Jacinto fault zone, is a large southwest-dipping normal fault on the west flank of the Santa Rosa Mountains that displays well-developed triangular facets, narrow footwall canyons, and steep hanging-wall alluvial fans. Geologic and geomorphic data reveal ongoing footwall uplift in the southern Santa Rosa Mountains, and gravity data suggest total vertical separation of ∼5.0–6.5 km from the range crest to the base of the Clark Valley basin. The northeast side of the Santa Rosa Mountains has a gentler topographic gradient, large alluvial fans, no major active faults, and tilted inactive late Pleistocene fan surfaces that are deeply incised by modern upper fan channels. Sediments beneath the Coachella Valley thicken gradually northeast to a depth of ∼4–5 km at an abrupt boundary at the San Andreas fault. These features all record crustal-scale tilting to the northeast that likely started when the San Jacinto fault zone initiated ca. 1.2 Ma. Tilting appears to be driven by oblique shortening and loading across a northeast-dipping southern San Andreas fault, consistent with the results of a recent boundary-element modeling study.

  7. 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

  8. Crustal structure and evolution of the Pyrenean-Cantabrian belt: A review and new interpretations from recent concepts and data

    Science.gov (United States)

    Teixell, A.; Labaume, P.; Ayarza, P.; Espurt, N.; de Saint Blanquat, M.; Lagabrielle, Y.

    2018-01-01

    This paper provides a synthesis of current data and interpretations on the crustal structure of the Pyrenean-Cantabrian orogenic belt, and presents new tectonic models for representative transects. The Pyrenean orogeny lasted from Santonian ( 84 Ma) to early Miocene times ( 20 Ma), and consisted of a spatial and temporal succession of oceanic crust/exhumed mantle subduction, rift inversion and continental collision processes at the Iberia-Eurasia plate boundary. A good coverage by active-source (vertical-incidence and wide-angle reflection) and passive-source (receiver functions) seismic studies, coupled with surface data have led to a reasonable knowledge of the present-day crustal architecture of the Pyrenean-Cantabrian belt, although questions remain. Seismic imaging reveals a persistent structure, from the central Pyrenees to the central Cantabrian Mountains, consisting of a wedge of Eurasian lithosphere indented into the thicker Iberian plate, whose lower crust is detached and plunges northwards into the mantle. For the Pyrenees, a new scheme of relationships between the southern upper crustal thrust sheets and the Axial Zone is here proposed. For the Cantabrian belt, the depth reached by the N-dipping Iberian crust and the structure of the margin are also revised. The common occurrence of lherzolite bodies in the northern Pyrenees and the seismic velocity and potential field record of the Bay of Biscay indicate that the precursor of the Pyrenees was a hyperextended and strongly segmented rift system, where narrow domains of exhumed mantle separated the thinned Iberian and Eurasian continental margins since the Albian-Cenomanian. The exhumed mantle in the Pyrenean rift was largely covered by a Mesozoic sedimentary lid that had locally glided along detachments in Triassic evaporites. Continental margin collision in the Pyrenees was preceded by subduction of the exhumed mantle, accompanied by the pop-up thrust expulsion of the off-scraped sedimentary lid above

  9. From the Atlas to the Rif a Crustal seismic image across Morocco: The SIMA & RIFSEIS control source wide-angle seismic reflection data

    Science.gov (United States)

    Carbonell, Ramon; Ayarza, Puy; Gallart, Josep; Diaz, Jordi; Harnafi, Mimoun; Levander, Alan; Teixell, Antonio

    2014-05-01

    The velocity structure of the crust and the geometry of the Moho across Morocco has been the main target of two recently acquired wide-angle seismic reflection transects. One is the SIMA experiment which provided seismic constraints beneath the Atlas Mountains and the second has been the RIFSEIS experiment which sampled the RIF orogen. Jointly these controlled source wide-angle seismic reflection data results in an almost 700 km, seismic profile going from the the Sahara craton across the High and Middle Atlas and Rif Mountain till the Gibraltar-Arc (Alboran). Current work on the interpretation of the seismic data-set is based on forward modeling, ray-tracing, as well as low fold wide-angle stacking. The data has resulted in a detailed crustal structure and velocity model for the Atlas Mountains and a 700 km transect revealing the irregular topography of the Moho beneath these two mountain orogens. Results indicate that the High Atlas features a moderate crustal thickness and that shortening is resolved at depth through a crustal root where the Saharan crust under-thrusts below the Moroccan crust, defining a lower crust imbrication which locally places the Moho boundary at, approximately, 40 km depth. The P-wave velocity model is characterized, in averaged, by relatively low velocities. These low deep crustal velocities together with other geophysical observables such as: conductivity estimates derived from Mt measurements; moderate Bouguer gravity anomaly; surface exposures of recent alkaline volcanics; lead the interpretation to propose that partial melts are currently emplaced in the deep crustal levels and in the upper mantle. The Moho discontinuity defines a crust which is in average relatively thin beneath the Atlas which is almost a 4000 m high orogenic belt. The resulting model supports existence of mantle upwelling as a possible mechanism that contributes, significantly, to maintain the High Atlas topography.

  10. Upper-Mantel Earthquakes in the Australia-Pacific Plate Boundary Zone and the Roots of the Alpine Fault

    Science.gov (United States)

    Boese, C. M.; Warren-Smith, E.; Townend, J.; Stern, T. A.; Lamb, S. H.

    2016-12-01

    Seismicity in the upper mantle in continental collision zones is relatively rare, but observed around the world. Temporary seismometer deployments have repeatedly detected mantle earthquakes at depths of 40-100 km within the Australia-Pacific plate boundary zone beneath the South Island of New Zealand. Here, the transpressive Alpine Fault constitutes the primary plate boundary structure linking subduction zones of opposite polarity farther north and south. The Southern Alps Microearthquake Borehole Array (SAMBA) has been operating continuously since November 2008 along a 50 km-long section of the central Alpine Fault, where the rate of uplift of the Southern Alps is highest. To date it has detected more than 40 small to moderate-sized mantle events (1≤ML≤3.9). The Central Otago Seismic Array (COSA) has been in operation since late 2012 and detected 15 upper mantle events along the sub-vertical southern Alpine Fault. Various mechanisms have been proposed to explain the occurrence of upper mantle seismicity in the South Island, including intra-continental subduction (Reyners 1987, Geology); high shear-strain gradients due to depressed geotherms and viscous deformation of mantle lithosphere (Kohler and Eberhart-Phillips 2003, BSSA); high strain rates resulting from plate bending (Boese et al. 2013, EPSL), and underthrusting of the Australian plate (Lamb et al. 2015, G3). Focal mechanism analysis reveals a variety of mechanisms for the upper mantle events but predominantly strike-slip and reverse faulting. In this study, we apply spectral analysis to better constrain source parameters for these mantle events. These results are interpreted in conjunction with new information about crustal structure and low-frequency earthquakes near the Moho and in light of existing velocity, attenuation and resistivity models.

  11. Reconstitutable control assembly having removable control rods with detachable split upper end plugs

    International Nuclear Information System (INIS)

    Gjertsen, R.K.; Knott, R.P.; Sparrow, J.A.

    1991-01-01

    This patent describes, for use in facilitating replacement of a neutron absorber control rod on a control assembly spider structure, an end plug. It comprises a pair of separate upper and lower plug portions; the upper section of the upper plug portion being configured for rigid attachment; the middle section of the upper plug portion having angularly displaced flat surfaces formed on the exterior

  12. Rapid Crustal Uplift at Birch Bay, Washington

    Science.gov (United States)

    Sherrod, B. L.; Kelsey, H. M.; Blakely, R. J.

    2010-12-01

    Geomorphology and coastal marsh stratigraphy suggest late Holocene uplift of the shoreline at Birch Bay, located northwest of Bellingham, Washington, during an earthquake on a shallow fault. LiDAR images show a raised, late Holocene shoreline along Birch Bay, with ~1 m of elevation difference between the modern shoreline and the inferred paleoshoreline. Commercial seismic reflection images reveal an anticline in Tertiary and possibly Quaternary deposits underlying Birch Bay. NW-trending magnetic anomalies are likely associated with the Birch Bay anticline and other nearby structures. Taken together, the geophysical data and lidar images suggest uplift of young deposits along a NW-trending blind reverse fault. Stratigraphy from Terrell Creek marsh, located just south of Birch Bay, shows freshwater peat buried by lower intertidal muds, indicating local submergence ~1300 yr BP. Stratigraphy of a 70-cm sediment core from Birch Bay marsh, sitting astride the anticline imaged with seismic reflection data, shows mud buried by detrital peat. One radiocarbon age from the core places the abrupt change from mud to peat prior to 1520-1700 yr BP. We divide fossil diatom assemblages straddling the mud-peat contact at Birch Bay into three zones. The oldest zone consists primarily of intertidal and marine diatoms, dominated by Paralia sulcata, Scoleoneis tumida, Grammataphora oceanica, and Gyrosigma balticum. An intermediate zone, beginning at the sharp contact between mud and overlying peat, consists of a mixture of brackish marsh and freshwater species, dominated by Diploneis interrupta, with lesser amounts of Aulacoseira sp., Pinnularia viridis, Eunotia pectinalis, and Paralia sulcata. A third and youngest zone lies in the upper half of the peat and is dominated by poorly preserved freshwater diatoms, mostly Aulacoseira cf. crassapuntata, Pinnularia viridis, P. maior, Eunotia pectinalis, and E. praerupta. Paleoecological inferences, based on distributions of modern diatoms

  13. A new model of crustal structure of Siberia

    DEFF Research Database (Denmark)

    Cherepanova, Yulia; Artemieva, Irina; Thybo, Hans

    2010-01-01

    to the Verkoyansk Ridge/Lena river in the east, and from the Arctic shelf in the north to the Tien Shan and Altay-Sayans mountains in the south. The new crustal model is based on our new ("from scratch") compilation of all available reliable seismic data and includes the results of seismic reflection, refraction...... orientation. Low surface heat flow (on average around 20-22 microW/m3) and the absence of the high-velocity (Vp>7.2 km/s) lowercrustal layer in the block with the thick crust suggest that eclogitization in the crustal root was subdued, thus allowing preservation of the ultra thick, seismically distinguishable...

  14. Investigating Microbial Biofilm Formations on Crustal Rock Substrates

    Science.gov (United States)

    Weiser, M.; D'Angelo, T.; Carr, S. A.; Orcutt, B.

    2017-12-01

    Ocean crust hosts microbial life that, in some cases, alter the component rocks as a means of obtaining energy. Variations in crust lithology, included trace metal and mineral content, as well as the chemistry of the fluids circulating through them, provide substrates for some microbes to metabolize, leading to formation of biofilm community structures. Microbes have different parameters for the situations in which they will form biofilms, but they must have some source of energy in excess at the site of biofilm formation for them to become stationary and form the carbohydrate-rich structures connecting the cells to one another and the substrate. Generally, the requirements for microbes to form biofilms on crustal minerals are unclear. We designed two experiments to test (1) mineral preference and biofilm formation rates by natural seawater microbial communities, and (2) biofilm development as a function of phosphate availability for an organism isolated from subseafloor ocean crust. In Experiment 1, we observed that phyric basalt groundmass is preferentially colonized over aphyric basalt or metal sulfides in a shallow water and oxic seawater environment. In experiment 2, tests of the anaerobic heterotroph Thalassospira bacteria isolated from oceanic crustal fluids showed that they preferentially form biofilms, lose motility, and increase exponentially in number over time in higher-PO4 treatments (50 micromolar), including with phosphate-doped basalts, than in treatments with low phosphate concentrations (0.5 micromolar) often found in crustal fluids. These observations suggest phosphate as a main driver of biofilm formation in subsurface crust. Overall, these data suggest that the drivers of microbial biofilm formation on crustal substrates are selective to the substrate conditions, which has important implications for estimating the global biomass of life harbored in oceanic crust.

  15. Parallel Fast Multipole Boundary Element Method for crustal dynamics

    International Nuclear Information System (INIS)

    Quevedo, Leonardo; Morra, Gabriele; Mueller, R Dietmar

    2010-01-01

    Crustal faults and sharp material transitions in the crust are usually represented as triangulated surfaces in structural geological models. The complex range of volumes separating such surfaces is typically three-dimensionally meshed in order to solve equations that describe crustal deformation with the finite-difference (FD) or finite-element (FEM) methods. We show here how the Boundary Element Method, combined with the Multipole approach, can revolutionise the calculation of stress and strain, solving the problem of computational scalability from reservoir to basin scales. The Fast Multipole Boundary Element Method (Fast BEM) tackles the difficulty of handling the intricate volume meshes and high resolution of crustal data that has put classical Finite 3D approaches in a performance crisis. The two main performance enhancements of this method: the reduction of required mesh elements from cubic to quadratic with linear size and linear-logarithmic runtime; achieve a reduction of memory and runtime requirements allowing the treatment of a new scale of geodynamic models. This approach was recently tested and applied in a series of papers by [1, 2, 3] for regional and global geodynamics, using KD trees for fast identification of near and far-field interacting elements, and MPI parallelised code on distributed memory architectures, and is now in active development for crustal dynamics. As the method is based on a free-surface, it allows easy data transfer to geological visualisation tools where only changes in boundaries and material properties are required as input parameters. In addition, easy volume mesh sampling of physical quantities enables direct integration with existing FD/FEM code.

  16. Magnetization of lower oceanic crust and upper mantle

    Science.gov (United States)

    Kikawa, E.

    2004-05-01

    The location of the magnetized rocks of the oceanic crust that are responsible for sea-floor spreading magnetic anomalies has been a long-standing problem in geophysics. The recognition of these anomalies was a key stone in the development of the theory of plate tectonics. Our present concept of oceanic crustal magnetization is much more complex than the original, uniformly magnetized model of Vine-Matthews-Morley Hypothesis. Magnetic inversion studies indicated that the upper oceanic extrusive layer (Layer 2A of 0.5km thick) was the only magnetic layer and that it was not necessary to postulate any contribution from deeper parts of oceanic crust. Direct measurements of the magnetic properties of the rocks recovered from the sea floor, however, have shown that the magnetization of Layer 2A, together with the observations that this layer could record geomagnetic field reversals within a vertical section, is insufficient to give the required size of observed magnetic anomalies and that some contribution from lower intrusive rocks is necessary. Magnetization of oceanic intrusive rocks were observed to be reasonably high enough to contribute to sea-floor spreading magnetic anomalies, but were considered somewhat equivocal until late 1980Os, in part because studies had been conducted on unoriented dredged and ophiolite samples and on intermittent DSDP/ODP cores. Since ODP Leg 118 that cored and recovered continuous 500m of oceanic intrusive layer at Site 735B, Southwest Indian Ridge with an extremely high recovery of 87 percent, there have been several ODP Legs (legs 147, 153, 176, 179 and 209) that were devoted to drilling gabbroic rocks and peridotites. In terms of the magnetization intensities, all of the results obtained from these ODP Legs were supportive of the model that a significant contribution must come from gabbros and peridotites and the source of the lineated magnetic anomalies must reside in most of the oceanic crust as well as crust-mantle boundary

  17. Crustal thickness of Antarctica estimated using data from gravimetric satellites

    Science.gov (United States)

    Llubes, Muriel; Seoane, Lucia; Bruinsma, Sean; Rémy, Frédérique

    2018-04-01

    Computing a better crustal thickness model is still a necessary improvement in Antarctica. In this remote continent where almost all the bedrock is covered by the ice sheet, seismic investigations do not reach a sufficient spatial resolution for geological and geophysical purposes. Here, we present a global map of Antarctic crustal thickness computed from space gravity observations. The DIR5 gravity field model, built from GOCE and GRACE gravimetric data, is inverted with the Parker-Oldenburg iterative algorithm. The BEDMAP products are used to estimate the gravity effect of the ice and the rocky surface. Our result is compared to crustal thickness calculated from seismological studies and the CRUST1.0 and AN1 models. Although the CRUST1.0 model shows a very good agreement with ours, its spatial resolution is larger than the one we obtain with gravimetric data. Finally, we compute a model in which the crust-mantle density contrast is adjusted to fit the Moho depth from the CRUST1.0 model. In East Antarctica, the resulting density contrast clearly shows higher values than in West Antarctica.

  18. Crustal thickness of Antarctica estimated using data from gravimetric satellites

    Directory of Open Access Journals (Sweden)

    M. Llubes

    2018-04-01

    Full Text Available Computing a better crustal thickness model is still a necessary improvement in Antarctica. In this remote continent where almost all the bedrock is covered by the ice sheet, seismic investigations do not reach a sufficient spatial resolution for geological and geophysical purposes. Here, we present a global map of Antarctic crustal thickness computed from space gravity observations. The DIR5 gravity field model, built from GOCE and GRACE gravimetric data, is inverted with the Parker–Oldenburg iterative algorithm. The BEDMAP products are used to estimate the gravity effect of the ice and the rocky surface. Our result is compared to crustal thickness calculated from seismological studies and the CRUST1.0 and AN1 models. Although the CRUST1.0 model shows a very good agreement with ours, its spatial resolution is larger than the one we obtain with gravimetric data. Finally, we compute a model in which the crust–mantle density contrast is adjusted to fit the Moho depth from the CRUST1.0 model. In East Antarctica, the resulting density contrast clearly shows higher values than in West Antarctica.

  19. Precambrian crustal history of the Nimrod Group, central Transantarctic Mountains

    International Nuclear Information System (INIS)

    Goodge, J.W.; Fanning, C.M.

    2002-01-01

    High-grade metamorphic and igneous rocks of the Nimrod Group represent crystalline basement to the central Transantarctic Mountains. Despite metamorphism and penetrative deformation during the Ross Orogeny, they preserve a deep record of Precambrian geologic history in this sector of the East Antarctic shield. A review of available U-Pb geochronometric data reveals multiple geologic events spanning 2.5 b.y. of Archean to Early Paleozoic time, including: (1) juvenile Archean crust production by magmatism between 3150 and 3000 Ma; (2) crustal stabilisation and metamorphism between 2955 and 2900 Ma; (3) ultra-metamorphism or anatexis at c. 2500 Ma; (4) deep-crustal metamorphism and magmatism between 1720 and 1730 Ma, redefining the Nimrod Orogeny; (5) post-1700 Ma sedimentation; and (6) basement reactivation involving high-grade metamorphism, magmatism, and penetrative deformation during the Ross Orogeny between 540 and 515 Ma. A strong regional metamorphic and deformational Ross overprint, dated by U-Pb and Ar thermochronology, had pronounced thermomechanical effects on the basement assemblage, yet rocks of the Nimrod Group retain robust evidence of their Precambrian ancestry. The zircon U-Pb record therefore demonstrates that primary crustal lithosphere of the East Antarctic shield extends to the central Transantarctic Mountains, and that it has undergone multiple episodes of reactivation culminating in the Ross Orogeny. (author). 48 refs., 2 figs., 1 tab

  20. Study on 3-D velocity structure of crust and upper mantle in Sichuan-yunnan region, China

    Science.gov (United States)

    Wang, C.; Mooney, W.D.; Wang, X.; Wu, J.; Lou, H.; Wang, F.

    2002-01-01

    Based on the first arrival P and S data of 4 625 regional earthquakes recorded at 174 stations dispersed in the Yunnan and Sichuan Provinces, the 3-D velocity structure of crust and upper mantle in the region is determined, incorporating with previous deep geophysical data. In the upper crust, a positive anomaly velocity zone exists in the Sichuan basin, whereas a negative anomaly velocity zone exists in the western Sichuan plateau. The boundary between the positive and negative anomaly zones is the Longmenshan fault zone. The images of lower crust and upper mantle in the Longmenshan fault, Xianshuihe fault, Honghe fault and others appear the characteristic of tectonic boundary, indicating that the faults litely penetrate the Moho discontinuity. The negative velocity anomalies at the depth of 50 km in the Tengchong volcanic area and the Panxi tectonic zone appear to be associated with the temperature and composition variations in the upper mantle. The overall features of the crustal and the upper mantle structures in the Sichuan-Yunnan region are the lower average velocity in both crust and uppermost mantle, the large crustal thickness variations, and the existence of high conductivity layer in the crust or/and upper mantle, and higher geothermal value. All these features are closely related to the collision between the Indian and the Asian plates. The crustal velocity in the Sichuan-Yunnan rhombic block generally shows normal.value or positive anomaly, while the negative anomaly exists in the area along the large strike-slip faults as the block boundary. It is conducive to the crustal block side-pressing out along the faults. In the major seismic zones, the seismicity is relative to the negative anomaly velocity. Most strong earthquakes occurred in the upper-mid crust with positive anomaly or normal velocity, where the negative anomaly zone generally exists below.

  1. The PROTEUS Experiment: Active Source Seismic Imaging of the Crustal Magma Plumbing Structure of the Santorini Arc Volcano

    Science.gov (United States)

    Hooft, E. E. E.; Morgan, J. V.; Nomikou, P.; Toomey, D. R.; Papazachos, C. V.; Warner, M.; Heath, B.; Christopoulou, M. E.; Lampridou, D.; Kementzetzidou, D.

    2016-12-01

    The goal of the PROTEUS seismic experiment (Plumbing Reservoirs Of The Earth Under Santorini) is to examine the entire crustal magma plumbing system beneath a continental arc volcano and determine the magma geometry and connections throughout the crust. These physical parameters control magma migration, storage, and eruption and inform the question of how physical and chemical processing of magma at arc volcanoes forms the andesitic rock compositions that dominate the lower continental crust. These physical parameters are also important to understand volcanic-tectonic interactions and geohazards. Santorini is ideal for these goals because the continental crust has been thinned by extension and so the deep magmatic system is more accessible, also it is geologically well studied. Since the volcano is a semi-submerged, it was possible to collect a unique 3D marine-land active source seismic dataset. During the PROTEUS experiment in November-December of 2015, we recorded 14,300 marine sound sources from the US R/V Langseth on 89 OBSIP short period ocean bottom seismometers and 60 German and 5 Greek land seismometers. The experiment was designed for high-density spatial sampling of the seismic wavefield to allow us to apply two state-of-the-art 3D inversion methods: travel time tomography and full waveform inversion. A preliminary travel time tomography model of the upper crustal seismic velocity structure of the volcano and surrounding region is presented in an accompanying poster. We also made marine geophysical maps of the seafloor using multi-beam bathymetry and of the gravity and magnetic fields. The new seafloor map reveals the detailed structure of the major fault system between Santorini and Amorgos, of associated landslides, and of newly discovered volcanic features. The PROTEUS project will provide new insights into the structure of the whole crustal magmatic system of a continental arc volcano and its evolution within the surrounding tectonic setting.

  2. Seismotectonics of the Taiwan Shoal region in the northeastern South China Sea: Insights from the crustal structure

    Science.gov (United States)

    Wan, Kuiyuan; Sun, Jinlong; Xu, Huilong; Xie, Xiaoling; Xia, Shaohong; Zhang, Xiang; Cao, Jinghe; Zhao, Fang; Fan, Chaoyan

    2018-02-01

    A cluster of earthquakes occurred in the Taiwan Shoal region on the outer rise of the Manila Trench. Although most were of small to medium magnitudes, one strong earthquake occurred on September 16, 1994. Several previous studies have provided important information to progress our understanding of this single earthquake. However, little is currently known about the earthquake cluster, and it is necessary to investigate the deep crustal structure of the Taiwan Shoal region to understand the mechanisms involved in controlling and generating it. This study presents a two-dimensional seismic tomographic image of the crustal structure along the OBS2012 profile based on ocean-bottom seismograph (OBS) data, which exhibits a high-velocity anomaly flanked by low-velocity anomalies in the upper crust beneath the Taiwan Shoal. In this study, 765 earthquakes (Richter magnitude ML > 1.5) occurring between 1991 and 2015 were studied and analyses of earthquake epicenters, regional faults, and the crustal structure provides an improved understanding of the nature of active tectonics in this region. Results of analyses indicate firstly that the high-velocity area represents major asperities that correspond to the location of the earthquake cluster and where stress is concentrated. It is also depicted that the earthquake cluster was influenced by fault interactions. However, the September 1994 earthquake occurred independently of these seismic activities and was associated with reactivation of a preexisting fault. It is also determined that slab pull is resisted by the exposed precollision accretionary prism, and the resistive force is causing accumulation of inplane compressive-stress. This may trigger a future damaging earthquake in the Taiwan Shoal region.

  3. "Storms of crustal stress" and AE earthquake precursors

    Directory of Open Access Journals (Sweden)

    G. P. Gregori

    2010-02-01

    Full Text Available Acoustic emission (AE displays violent paroxysms preceding strong earthquakes, observed within some large area (several hundred kilometres wide around the epicentre. We call them "storms of crustal stress" or, briefly "crustal storms". A few case histories are discussed, all dealing with the Italian peninsula, and with the different behaviour shown by the AE records in the Cephalonia island (Greece, which is characterized by a different tectonic setting.

    AE is an effective tool for diagnosing the state of some wide slab of the Earth's crust, and for monitoring its evolution, by means of AE of different frequencies. The same effect ought to be detected being time-delayed, when referring to progressively lower frequencies. This results to be an effective check for validating the physical interpretation.

    Unlike a seismic event, which involves a much limited focal volume and therefore affects a restricted area on the Earth's surface, a "crustal storm" typically involves some large slab of lithosphere and crust. In general, it cannot be easily reckoned to any specific seismic event. An earthquake responds to strictly local rheological features of the crust, which are eventually activated, and become crucial, on the occasion of a "crustal storm". A "crustal storm" lasts typically few years, eventually involving several destructive earthquakes that hit at different times, at different sites, within that given lithospheric slab.

    Concerning the case histories that are here discussed, the lithospheric slab is identified with the Italian peninsula. During 1996–1997 a "crustal storm" was on, maybe elapsing until 2002 (we lack information for the period 1998–2001. Then, a quiet period occurred from 2002 until 26 May 2008, when a new "crustal storm" started, and by the end of 2009 it is still on. During the 1996–1997 "storm" two strong earthquakes occurred (Potenza and

  4. Elastic wave velocities, chemistry and modal mineralogy of crustal rocks sampled by the Outokumpu scientific drill hole: Evidence from lab measurements and modeling

    Science.gov (United States)

    Kern, H.; Mengel, K.; Strauss, K. W.; Ivankina, T. I.; Nikitin, A. N.; Kukkonen, I. T.

    2009-07-01

    The Outokumpu scientific deep drill hole intersects a 2500 m deep Precambrian crustal section comprising a 1300 m thick biotite-gneiss series (mica schists) at top, followed by a 200 m thick meta-ophiolite sequence, underlain again by biotite gneisses (mica schists) (500 m thick) with intercalations of amphibolite and meta-pegmatoids (pegmatitic granite). From 2000 m downward the dominating rock types are meta-pegmatoids (pegmatitic granite). Average isotropic intrinsic P- and S-wave velocities and densities of rocks were calculated on the basis of the volume fraction of the constituent minerals and their single crystal properties for 29 core samples covering the depth range 198-2491 m. The modal composition of the rocks is obtained from bulk rock (XRF) and mineral chemistry (microprobe), using least squares fitting. Laboratory seismic measurements on 13 selected samples representing the main lithologies revealed strong anisotropy of P- and S-wave velocities and shear wave splitting. Seismic anisotropy is strongly related to foliation and is, in particular, an important property of the biotite gneisses, which dominate the upper and lower gneiss series. At in situ conditions, velocity anisotropy is largely caused by oriented microcracks, which are not completely closed at the pressures corresponding to the relatively shallow depth drilled by the borehole, in addition to crystallographic preferred orientation (CPO) of the phyllosilicates. The contribution of CPO to bulk anisotropy is confirmed by 3D velocity calculations based on neutron diffraction texture measurements. For vertical incidence of the wave train, the in situ velocities derived from the lab measurements are significantly lower than the measured and calculated intrinsic velocities. The experimental results give evidence that the strong reflective nature of the ophiolite-derived rock assemblages is largely affected by oriented microcracks and preferred crystallographic orientation of major minerals, in

  5. Along Arc Structural Variation in the Izu-Bonin Arc and its Implications for Crustal Evolution Processes

    Science.gov (United States)

    Kodaira, S.; Sato, T.; Takahashi, N.; Ito, A.; Kaneda, Y.

    2005-12-01

    crust (6. 4 km/s), and a negative correlation between the thickness of the 6.0 - 6.7 km/s block and the average crustal seismic velocity is recognized. In conclusion, the continental-type of the crust efficiently grow at the Quaternary volcanoes along Izu arc, but even at those areas the bulk composition of the entire crustal section shows more mafic than a continental crust due to the uniformly existing high velocity lower crust. A delamination process may be necessary to form a continental crust form the Izu island arc crust

  6. Crustal contributions to arc magmatism in the Andes of Central Chile

    Science.gov (United States)

    Hildreth, W.; Moorbath, S.

    1988-01-01

    an abundance of Paleozoic and Triassic rocks, whereas the proportion of younger arc-intrusive basement increases southward. Primitive basalts are unknown anywhere along the arc. Base-level isotopic and chemical values for each volcano are established by blending of subcrustal and deep-crustal magmas in zones of melting, assimilation, storage and homogenization (MASH) at the mantle-crust transition. Scavenging of mid-to upper-crustal silicic-alkalic melts and intracrustal AFC (prominent at the largest center) can subsequently modify ascending magmas, but the base-level geochemical signature at each center reflects the depth of its MASH zone and the age, composition, and proportional contribution of the lowermost crust. ?? 1988 Springer-Verlag.

  7. Crustal tomography of the 2016 Kumamoto earthquake area in West Japan using P and PmP data

    Science.gov (United States)

    Wang, Haibo; Zhao, Dapeng; Huang, Zhouchuan; Xu, Mingjie; Wang, Liangshu; Nishizono, Yukihisa; Inakura, Hirohito

    2018-05-01

    A high-resolution model of three-dimensional (3-D) P-wave velocity (Vp) tomography of the crust in the source area of the 2016 Kumamoto earthquake (M 7.3) in West Japan is determined using a large number of arrival times of first P-waves and reflected P-waves from the Moho discontinuity (PmP). The PmP data are collected from original seismograms of the Kumamoto aftershocks and other local crustal events in Kyushu. Detailed resolution tests show that the addition of the PmP data can significantly improve the resolution of the crustal tomography, especially that of the lower crust. Our results show that significant low-velocity (low-V) anomalies exist in the entire crust beneath the active arc volcanoes, which may reflect the pathway of arc magmas. The 2016 Kumamoto earthquake occurred at the edge of a small low-V zone in the upper crust. A significant low-V anomaly is revealed in the lower crust beneath the source zone, which may reflect the arc magma and fluids ascending from the mantle wedge. These results suggest that the rupture nucleation of the 2016 Kumamoto earthquake was affected by fluids and arc magma.

  8. 3-D crustal P-wave velocity tomography of the Italian region using local and regional seismicity data

    Directory of Open Access Journals (Sweden)

    F. M. Mele

    1995-06-01

    Full Text Available A tomographic experiment was performed in the Italian region using local and regional arrivaI times of p and S seismological phases selected from the Italian National Bulletin in the time interval 1984-1991. We deter- mined a 3-D crustal P-wave velocity model using a simultaneous inversion method that iteratively re1ocates the hypocenters and computes the unknown model parameters. A fast two-point ray tracing algorithm was adopted to compute the ray paths and travel times of P", S", P g' Sg phases with good accuracy. Synthetic tests were performed using the "true" hypocenter and station distribution to rough1y evaluate the extension of the areas most densely spanned by the ray paths; the agreement between synthetic and computed models is more satisfactory at Moho depths than in the upper crust. The qua1ity of the model resulting from inversion of real data is examined by the ca1culation of the Spread Function (Toomey and Foulger, 1989. The 3-D crustal P-wave velocity mode1 of the Italian region shows remarkab1e trends at Moho depths: the areas east of the Apennines call for positive adjustments of the initial velocity va1ue, while the west region shows negative ad- justments. The correspondence among the main features of the velocity field, the map of Moho isobaths and the map of the gravity anoma1ies is also outlined.

  9. Vertical crustal movements in Southern California, 1974 to 1978

    Science.gov (United States)

    Burford, R.O.; Gilmore, Thomas D.

    1984-01-01

    An extensive resurvey of most of the first-order leveling network in southern California, known as the Southern California Releveling Program (SCRP), was carried out during the first 5 months of 1978. The primary scientific purpose of these measurements was to rapidly update the vertical control record throughout a recently uplifted region of southern California in order to more thoroughly document the vertical component of tectonic movement and to provide a reliable base for comparison with future levelings. Analyses of historic first-order leveling results have clearly demonstrated that a broad crustal upwarping, largely contained within a region consisting of the Transverse Ranges province and an area along the intervening section of the San Andreas fault system, had developed between about 1959 and 1974. Unfortunately, there is strong evidence that parts of the 1978 SCRP data are contaminated by the effects of intrasurvey tectonic deformation, limited surficial failures, and, less certainly, magnetically induced systematic error associated with the use of automatic levels. However, any distortions in leveling results caused by these or other factors are not so serious as to render the SCRP data useless. In fact, the bulk of these data can be accepted at face value, and most of the remaining data can be incorporated with some caution to augment the more reliable parts of the network. The evaluation of the 1978 leveling is based on a combination of circuit-misclosures, local timing of the field observations, analysis of profiles of apparent height changes derived from comparisons with previous levelings, and an analysis of the position and orientation of the various routes in relation to the regional structural grain and the gradients of differential vertical motion established by previous investigations. Comparisons of the 1978 SCRP results with the latest of the previous surveys along each route retained in the analysis show that all but about one-third of the

  10. Provenance and tectonic setting of the supra-crustal succession of the Qinling Complex: Implications for the tectonic affinity of the North Qinling Belt, Central China

    Science.gov (United States)

    Shi, Yu; Huang, Qianwen; Liu, Xijun; Krapež, Bryan; Yu, Jinhai; Bai, Zhian

    2018-06-01

    The Qinling Complex lies in the Qinling orogenic belt of Central China and holds the key to understanding the evolution of this feature. The Qinling Complex comprises a basement complex composed of amphibolite and ecologite, overlain by a supra-crustal succession that has been metamorphosed to the upper greenschist facies at approximately 516-509 Ma. The protoliths of the meta-sedimentary rocks are graywackes, which are divided into lower, middle and upper units. Detrital zircons from nine samples of the supra-crustal succession have ages ranging from 1182 to 1158 Ma for the lower unit, 957 to 955 Ma for the middle unit and 917 to 840 Ma for the upper unit. The lower unit is intruded by a ca. 960 Ma pluton. The bulk compositions of these meta-sedimentary rocks and their detrital zircon ages clearly indicate derivation from Meso- and Neo-proterozoic granites. Thus, we suggest that the sedimentary succession was derived from an arc-related tectonic setting and that none of the detritus was sourced from the southern margin of the North China Block or from the northern and western margins of the South China Block. We conclude that the North Qinling Belt was an independent micro-continental block during the Meso- to Neo-proterozoic.

  11. Nonvariceal upper gastrointestinal bleeding

    International Nuclear Information System (INIS)

    Burke, Stephen J.; Weldon, Derik; Sun, Shiliang; Golzarian, Jafar

    2007-01-01

    Nonvariceal upper gastrointestinal bleeding (NUGB) remains a major medical problem even after advances in medical therapy with gastric acid suppression and cyclooxygenase (COX-2) inhibitors. Although the incidence of upper gastrointestinal bleeding presenting to the emergency room has slightly decreased, similar decreases in overall mortality and rebleeding rate have not been experienced over the last few decades. Many causes of upper gastrointestinal bleeding have been identified and will be reviewed. Endoscopic, radiographic and angiographic modalities continue to form the basis of the diagnosis of upper gastrointestinal bleeding with new research in the field of CT angiography to diagnose gastrointestinal bleeding. Endoscopic and angiographic treatment modalities will be highlighted, emphasizing a multi-modality treatment plan for upper gastrointestinal bleeding. (orig.)

  12. Nonvariceal upper gastrointestinal bleeding

    Energy Technology Data Exchange (ETDEWEB)

    Burke, Stephen J.; Weldon, Derik; Sun, Shiliang [University of Iowa, Department of Radiology, Iowa, IA (United States); Golzarian, Jafar [University of Iowa, Department of Radiology, Iowa, IA (United States); University of Iowa, Department of Radiology, Carver College of Medicine, Iowa, IA (United States)

    2007-07-15

    Nonvariceal upper gastrointestinal bleeding (NUGB) remains a major medical problem even after advances in medical therapy with gastric acid suppression and cyclooxygenase (COX-2) inhibitors. Although the incidence of upper gastrointestinal bleeding presenting to the emergency room has slightly decreased, similar decreases in overall mortality and rebleeding rate have not been experienced over the last few decades. Many causes of upper gastrointestinal bleeding have been identified and will be reviewed. Endoscopic, radiographic and angiographic modalities continue to form the basis of the diagnosis of upper gastrointestinal bleeding with new research in the field of CT angiography to diagnose gastrointestinal bleeding. Endoscopic and angiographic treatment modalities will be highlighted, emphasizing a multi-modality treatment plan for upper gastrointestinal bleeding. (orig.)

  13. Three-dimensional crust and upper mantle structure at the Nevada test site

    International Nuclear Information System (INIS)

    Taylor, S.R.

    1983-01-01

    The three-dimensional crust and upper mantle structure at the Nevada Test Site (NTS) is derived by combining teleseismic P wave travel time residuals with Pn source time terms. The NTS time terms and relative teleseismic residuals are calculated by treating the explosions as a network of 'receivers' which record 'shots' located at the surrounding stations. Utilization of the Pn time terms allows for better crustal resolution than is possible from teleseismic information alone. Average relative teleseismic P wave residuals show a consistent progression of positive (late arrivals) to negative residuals from east to west across the NTS. However, Pn time terms beneath Rainier Mesa are at least 0.3 and 0.5 s less than those beneath Pahute Mesa and Yucca Flat, respectively, indicating the presence of high-velocity crustal material or crustal thinning beneath Rainier Mesa. The time terms at Pahute Mesa are surprisingly uniform, and the largest time terms and residuals are observed in the northwest and southern parts of Yucca Flat. The Pn time terms show a slight correlation with the working-point velocity at the shot point for Pahute Mesa and Yucca Flat, indicating that part of the observed lateral variations are caused by shallow effects of the upper crust. Three-dimensional inversion of the travel time residuals suggests that Yucca Flat is characterized by low-velocity anomalies confined to the upper crust, Rainer Mesa by very high velocities in the upper and middle crust, and Pahute Mesa by a high-velocity anomaly extending through the crust and into the upper mantle. Relatively low velocities are observed in the lower crust beneath the Timber Mountain caldera south of Pahute Mesa with no expression in the upper mantle. These observed differences in velocity beneath the Tertiary Silent Canyon and Timber Mountain calderas may be related to their magma volume and mode of enrichment from a mantle-derived magma source

  14. The T-Reflection and the deep crustal structure of the Vøring Margin offshore Mid-Norway

    Science.gov (United States)

    Abdelmalak, M. M.; Faleide, J. I.; Planke, S.; Gernigon, L.; Zastrozhnov, D.; Shephard, G. E.; Myklebust, R.

    2017-12-01

    Volcanic passive margins are characterized by massive occurrence of mafic extrusive and intrusive rocks, before and during plate breakup, playing major role in determining the evolution pattern and the deep structure of magma-rich margins. Deep seismic reflection data frequently provide imaging of strong continuous reflections in the middle/lower crust. In this context, we have completed a detailed 2D seismic interpretation of the deep crustal structure of the Vøring volcanic margin, offshore mid-Norway, where high-quality seismic data allow the identification of high-amplitude reflections, locally referred to as the T-Reflection (TR). Using the dense seismic grid we have mapped the top of the TR in order to compare it with filtered Bouguer gravity anomalies and seismic refraction data. The TR is identified between 7 and 10 s. Sometimes it consists of one single smooth reflection. However, it is frequently associated with a set of rough multiple reflections displaying discontinuous segments with varying geometries, amplitude and contact relationships. The TR seems to be connected to deep sill networks and locally located at the continuation of basement high structures or terminates over fractures and faults. The spatial correlation between the filtered positive Bouguer gravity anomalies and the TR indicates that the latter represents a high impedance boundary contrast associated with a high-density/velocity body. Within an uncertainty of ± 2.5 km, the depth of the mapped TR is found to correspond to the depth of the top of the Lower Crustal Body (LCB), characterized by high P-wave velocities (>7 km/s), in 50% of the outer Vøring Margin areas, whereas different depths between the TR and the top LCB are estimated for the remaining areas. We present a tectonic scenario, where a large part of the deep structure could be composed of preserved upper continental basement and middle to lower crustal lenses of inherited and intruded high-grade metamorphic rocks. Deep

  15. Geometry and subsidence history of the Dead Sea basin: A case for fluid-induced mid-crustal shear zone?

    Science.gov (United States)

    ten Brink, Uri S.; Flores, C.H.

    2012-01-01

    Pull-apart basins are narrow zones of crustal extension bounded by strike-slip faults that can serve as analogs to the early stages of crustal rifting. We use seismic tomography, 2-D ray tracing, gravity modeling, and subsidence analysis to study crustal extension of the Dead Sea basin (DSB), a large and long-lived pull-apart basin along the Dead Sea transform (DST). The basin gradually shallows southward for 50 km from the only significant transverse normal fault. Stratigraphic relationships there indicate basin elongation with time. The basin is deepest (8-8.5 km) and widest (???15 km) under the Lisan about 40 km north of the transverse fault. Farther north, basin depth is ambiguous, but is 3 km deep immediately north of the lake. The underlying pre-basin sedimentary layer thickens gradually from 2 to 3 km under the southern edge of the DSB to 3-4 km under the northern end of the lake and 5-6 km farther north. Crystalline basement is ???11 km deep under the deepest part of the basin. The upper crust under the basin has lower P wave velocity than in the surrounding regions, which is interpreted to reflect elevated pore fluids there. Within data resolution, the lower crust below ???18 km and the Moho are not affected by basin development. The subsidence rate was several hundreds of m/m.y. since the development of the DST ???17 Ma, similar to other basins along the DST, but subsidence rate has accelerated by an order of magnitude during the Pleistocene, which allowed the accumulation of 4 km of sediment. We propose that the rapid subsidence and perhaps elongation of the DSB are due to the development of inter-connected mid-crustal ductile shear zones caused by alteration of feldspar to muscovite in the presence of pore fluids. This alteration resulted in a significant strength decrease and viscous creep. We propose a similar cause to the enigmatic rapid subsidence of the North Sea at the onset the North Atlantic mantle plume. Thus, we propose that aqueous fluid flux

  16. Effect of Crustal Density Structures on GOCE Gravity Gradient Observables

    Directory of Open Access Journals (Sweden)

    Robert Tenzer Pavel Novák

    2013-01-01

    Full Text Available We investigate the gravity gradient components corrected for major known anomalous density structures within the Earth¡¦s crust. Heterogeneous mantle density structures are disregarded. The gravimetric forward modeling technique is utilized to compute the gravity gradients based on methods for a spherical harmonic analysis and synthesis of a gravity field. The Earth¡¦s gravity gradient components are generated using the global geopotential model GOCO-03s. The topographic and stripping gravity corrections due to the density contrasts of the ocean and ice are computed from the global topographic/bathymetric model DTM2006.0 (which also includes the ice-thickness dataset. The discrete data of sediments and crust layers taken from the CRUST2.0 global crustal model are then used to apply the additional stripping corrections for sediments and remaining anomalous crustal density structures. All computations are realized globally on a one arc-deg geographical grid at a mean satellite elevation of 255 km. The global map of the consolidated crust-stripped gravity gradients reveals distinctive features which are attributed to global tectonics, lithospheric plate configuration, lithosphere structure and mantle dynamics (e.g., glacial isostatic adjustment, mantle convection. The Moho signature, which is the most pronounced signal in these refined gravity gradients, is superimposed over a weaker gravity signal of the lithospheric mantle. An interpretational quality of the computed (refined gravity gradient components is mainly limited by a low accuracy and resolution of the CRUST2.0 sediment and crustal layer data and unmodeled mantle structures.

  17. What drives the Tibetan crust to the South East Asia? Role of upper mantle density discontinuities as inferred from the continental geoid anomalies

    Science.gov (United States)

    Rajesh, S.

    2012-04-01

    The Himalaya-Tibet orogen formed as a result of the northward convergence of India into the Asia over the past 55 Ma had caused the north south crustal shortening and Cenozoic upliftment of the Tibetan plateau, which significantly affected the tectonic and climatic framework of the Asia. Geodetic measurements have also shown eastward crustal extrusion of Tibet, especially along major east-southeast strike slip faults at a slip rate of 15-20 mm a-1 and around 40 mm a-1. Such continental scale deformations have been modeled as block rotation by fault boundary stresses developed due to the India-Eurasia collision. However, the Thin Sheet model explained the crustal deformation mechanism by considering varying gravitational potential energy arise out of varying crustal thickness of the viscous lithosphere. The Channel Flow model, which also suggests extrusion is a boundary fault guided flow along the shallow crustal brittle-ductile regime. Although many models have proposed, but no consensus in these models to explain the dynamics of measured surface geodetic deformation of the Tibetan plateau. But what remains conspicuous is the origin of driving forces that cause the observed Tibetan crustal flow towards the South East Asia. Is the crustal flow originated only because of the differential stresses that developed in the shallow crustal brittle-ductile regime? Or should the stress transfer to the shallow crustal layers as a result of gravitational potential energy gradient driven upper mantle flow also to be accounted. In this work, I examine the role of latter in the light of depth distribution of continental geoid anomalies beneath the Himalaya-Tibet across major upper mantle density discontinuities. These discontinuity surfaces in the upper mantle are susceptible to hold the plastic deformation that may occur as a result of the density gradient driven flow. The distribution of geoid anomalies across these density discontinuities at 220, 410 and 660 km depth in the

  18. Improved H-κ Method by Harmonic Analysis on Ps and Crustal Multiples in Receiver Functions with respect to Dipping Moho and Crustal Anisotropy

    Science.gov (United States)

    Li, J.; Song, X.; Wang, P.; Zhu, L.

    2017-12-01

    The H-κ method (Zhu and Kanamori, 2000) has been widely used to estimate the crustal thickness and Vp/Vs ratio with receiver functions. However, in regions where the crustal structure is complicated, the method may produce uncertain or even unrealistic results, arising particularly from dipping Moho and/or crustal anisotropy. Here, we propose an improved H-κ method, which corrects for these effects first before stacking. The effect of dipping Moho and crustal anisotropy on Ps receiver function has been well studied, but not as much on crustal multiples (PpPs and PpSs+PsPs). Synthetic tests show that the effect of crustal anisotropy on the multiples are similar to Ps, while the effect of dipping Moho on the multiples is 5 times that on Ps (same cosine trend but 5 times in time shift). A Harmonic Analysis (HA) method for dipping/anisotropy was developed by Wang et al. (2017) for crustal Ps receiver functions to extract parameters of dipping Moho and crustal azimuthal anisotropy. In real data, the crustal multiples are much more complicated than the Ps. Therefore, we use the HA method (Wang et al., 2017), but apply separately to Ps and the multiples. It shows that although complicated, the trend of multiples can still be reasonably well represented by the HA. We then perform separate azimuthal corrections for Ps and the multiples and stack to obtain a combined receiver function. Lastly, the traditional H-κ procedure is applied to the stacked receiver function. We apply the improved H-κ method on 40 CNDSN (Chinese National Digital Seismic Network) stations distributed in a variety of geological setting across the Chinese continent. The results show apparent improvement compared to the traditional H-κ method, with clearer traces of multiples and stronger stacking energy in the grid search, as well as more reliable H-κ values.

  19. Preliminary study of lateral variation in crustal structure of Northeast China from teleseismic receiver functions

    Science.gov (United States)

    Chen, Youlin; Liu, Ruifeng; Huang, Zhibin; Sun, Li

    2011-02-01

    We conducted comprehensive receiver function analyses for a large amount of high-quality broadband teleseismic waveforms data recorded at 19 China National Digital Seismic Network (CNDSN) stations deployed in Northeast China. An advanced H- κ domain search method was adopted to accurately estimate the crustal thickness and ν P/ ν S ratio. The crust has an average thickness of about 34.4 km. The thinnest crust occurs in the central region of Northeast China, while the thickest crust is beneath the Yanshan belt. The ν P/ ν S ratio is relatively uniform with an average of about 1.733. The highest ν P/ ν S ratio is found beneath the Changbaishan, likely associated with its volcanic activities. We found significant lateral heterogeneity beneath three stations CN2, MDJ, and MIH located along the Suolon suture from the back-zimuthal dependence of Moho depth. The velocity modeling from receiver functions indicated complicated Earth structure beneath these stations with large crust-mantle transition zone, noticeable velocity jump in upper mantle, and low velocity zone in middle crust. Dipping velocity interface in the crust with strike approximately parallel to the Suolon suture and down-dip to the south or southeast might explain the observed lateral heterogeneity.

  20. Sm-Nd study of Precambrian crustal development in the Prieska-Copperton region, Cape Province

    International Nuclear Information System (INIS)

    Cornell, D.H.; Hawkesworth, C.J.; Van Calsteren, P.; Scott, W.D.

    1986-01-01

    Samples representing the major lithological units between Copperton and Prieskapoort in the Cape Province have been analysed for Sm and Nd concentrations and Nd isotopic compositions. The ∼ 3000 Ma Marydale Group is shown to extend without major chronostratigraphic breaks from slightly metamorphosed basalt and arkose west of the Doornberg Fault at Prieskapoort to highly metamorphosed gneisses east of the Brakbos Fault at Copperton. Evidence is found of plutonic alkaline igneous activity, and possibly volcanism, which occurred during the ∼ 1 900 Ma Kheis tectogenesis. Early Proterozoic material apparently dominates the lower crustal region of the eastern Namaqua Province sampled by kimberlites. Sm-Nd data for the Copperton Formation of the Namaqua Province places an upper limit of ∼ 1 514 Ma and lower limit of ∼ 1 350 Ma on its origin. Omission of basaltic samples from the isochron regression yields the younger age, which is more easily reconciled with Pb isotope data. Volcanism is envisaged from a mantle source with a history of light rare-earth depletion relative to the chondritic earth model. By analogy with modern tectonic environments, the Copperton Formation probably formed in an active continental margin or island arc environment

  1. Petrogenesis of early cretaceous silicic volcanism in SE Uruguay. The role of mantle and crustal sources

    International Nuclear Information System (INIS)

    Lustrino, Michele; Morbidelli, Lucio; Marrazzo, Marianna; Melluso, Leone; Brotzu, Pietro; Tassinari, Colombo C.G.; Gomes, Celso B.; Ruberti, Excelso

    2010-01-01

    Early Cretaceous (∼129 Ma) silicic rocks crop out in SE Uruguay between the Laguna Merin and Santa Lucia basins in the Lascano, Sierra Sao Miguel, Salamanca and Minas areas. They are mostly rhyolites with minor quartz-trachytes and are nearly contemporaneous with the Parana-Etendeka igneous province and with the first stages of South Atlantic Ocean opening. A strong geochemical variability (particularly evident from Rb/Nb, Nb/Y trace element ratios) and a wide range of Sr-Nd isotopic ratios ( 143 Nd/ 144 Nd (129) =0.51178-0.51209; 87 Sr/ 86 Sr (129) =0.70840-0.72417) characterize these rocks. Geochemistry allows to distinguish two compositional groups, corresponding to the north-eastern (Lascano and Sierra Sao Miguel, emplaced on the Neo-Proterozoic southern sector of the Dom Feliciano mobile belt) and south-eastern localities (Salamanca, Minas, emplaced on the much older (Archean) Nico Perez terrane or on the boundary between the Dom Feliciano and Nico Perez terranes). These compositional differences between the two groups are explained by variable mantle source and crust contributions. The origin of the silicic magmas is best explained by complex processes involving assimilation and fractional crystallization and mixing of a basaltic magma with upper crustal lithologies, for Lascano and Sierra Sao Miguel rhyolites. In the Salamanca and Minas rocks genesis, a stronger contribution from lower crust is indicated. (author)

  2. Lower crustal intrusions beneath the southern Baikal Rift Zone

    DEFF Research Database (Denmark)

    Nielsen, Christoffer; Thybo, Hans

    2009-01-01

    centre. The BEST (Baikal Explosion Seismic Transect) project acquired a 360-km long, deep seismic, refraction/wide-angle reflection profile in 2002 across southern Lake Baikal. The data from this project is used for identification of large-scale crustal structures and modelling of the seismic velocities....../s and 7.9 km/s. We interpret this feature as resulting from mafic to ultra-mafic intrusions in the form of sills. Petrological interpretation of the velocity values suggests that the intrusions are sorted by fractional crystallization into plagioclase-rich low-velocity layers and pyroxene- and olivine...

  3. 3D Crustal Velocity Structure Model of the Middle-eastern North China Craton

    Science.gov (United States)

    Duan, Y.; Wang, F.; Lin, J.; Wei, Y.

    2017-12-01

    Lithosphere thinning and destruction in the middle-eastern North China Craton (NCC), a region susceptible to strong earthquakes, is one of the research hotspots in solid earth science. Up to 42 wide-angle reflection/refraction deep seismic sounding (DSS) profiles have been completed in the middle-eastern NCC, we collect all the 2D profiling results and perform gridding of the velocity and interface depth data, and build a 3D crustal velocity structure model for the middle-eastern NCC, named HBCrust1.0, using the Kriging interpolation method. In this model, four layers are divided by three interfaces: G is the interface between the sedimentary cover and crystalline crust, with velocities of 5.0-5.5 km/s above and 5.8-6.0 km/s below. C is the interface of the upper and lower crust, with velocity jump from 6.2-6.4 km/s to 6.5-6.6 km/s. M is the interface between the crust and upper mantle, with velocity 6.7-7.0 km/s at the crust bottom and 7.9-8.0 km/s on mantle top. Our results show that the first arrival time calculated from HBCust1.0 fit well with the observation. It also demonstrates that the upper crust is the main seismogenic layer, and the brittle-ductile transition occurs at depths near interface C. The depth of interface Moho varies beneath the source area of the Tangshan earth-quake, and a low-velocity structure is found to extend from the source area to the lower crust. Based on these observations, it can be inferred that stress accumulation responsible for the Tangshan earthquake may have been closely related to the migration and deformation of the mantle materials. Comparisons of the average velocities of the whole crust, the upper and the lower crust show that the average velocity of the lower crust under the central part of the North China Basin (NCB) in the east of the craton is obviously higher than the regional average, this high-velocity probably results from longterm underplating of the mantle magma. This research is founded by the Natural Science

  4. Upper bounds of deformation in the Upper Rhine Graben from GPS data - First results from GURN (GNSS Upper Rhine Graben Network)

    Science.gov (United States)

    Masson, Frederic; Knoepfler, Andreas; Mayer, Michael; Ulrich, Patrice; Heck, Bernhard

    2010-05-01

    In September 2008, the Institut de Physique du Globe de Strasbourg (Ecole et Observatoire des Sciences de la Terre, EOST) and the Geodetic Institute (GIK) of Karlsruhe University (TH) established a transnational cooperation called GURN (GNSS Upper Rhine Graben Network). Within the GURN initiative these institutions are cooperating in order to establish a highly precise and highly sensitive network of permanently operating GNSS sites for the detection of crustal movements in the Upper Rhine Graben region. At the beginning, the network consisted of the permanently operating GNSS sites of SAPOS®-Baden-Württemberg, different data providers in France (e.g. EOST, Teria, RGP) and some further sites (e.g. IGS). In July 2009, the network was extended to the South when swisstopo (Switzerland) and to the North when SAPOS®-Rheinland-Pfalz joined GURN. Therefore, actually the GNSS network consists of approx. 80 permanently operating reference sites. The presentation will discuss the actual status of GURN, main research goals, and will present first results concerning the data quality as well as time series of a first reprocessing of all available data since 2002 using GAMIT/GLOBK (EOST working group) and the Bernese GPS Software (GIK working group). Based on these time series, the velocity as well as strain fields will be calculated in the future. The GURN initiative is also aiming for the estimation of the upper bounds of deformation in the Upper Rhine Graben region.

  5. Growth of sulfate reducers in deep-subseafloor sediments stimulated by crustal fluids

    Directory of Open Access Journals (Sweden)

    Katja eFichtel

    2012-02-01

    Full Text Available On a global scale, crustal fluids fuel a substantial part of the deep subseafloor biosphere by providing electron acceptors for microbial respiration. In this study, we examined bacterial cultures from a sediment column of the Juan de Fuca Ridge, Northeast Pacific (IODP Site U1301 which is divided into three distinctive compartments: an upper sulfate-containing zone, formed by bottom-seawater diffusion, a sulfate-depleted zone and a second (~140 m thick sulfate-containing zone influenced by fluid diffusion from the basaltic aquifer. Sulfate reducers were isolated from near-surface and near-basement sediments. All initial enrichments harboured specific communities of heterotrophic microorganisms. Among those, the number of isolated spore-forming Firmicutes decreased from 60% to 21% with sediment depth. Strains affiliated to Desulfosporosinus lacus, Desulfotomaculum sp. and Desulfovibrio aespoeensis were recovered from the upper sediment layers (1.3-9.1 meters below seafloor, mbsf. Several strains of Desulfovibrio indonesiensis and one relative of Desulfotignum balticum were isolated from near-basement sediments (240-262 mbsf. The physiological investigation of strains affiliated to D. aespoeensis, D. indonesiensis and D. balticum indicated that they were all able to use sulfate, thiosulfate and sulfite as electron acceptors. In the presence of sulfate, they grew strain-specifically on a few short-chain n-alcohols and fatty acids, only. The strains fermented either ethanol, pyruvate or betaine. Interestingly, all strains utilized hydrogen and the isolate affiliated to D. indonesiensis even exhibited an autotrophic life-mode. Thus, in the deep subseafloor where organic substrates are limited or hardly degradable, hydrogen might become an essential electron donor. The isolation of non-sporeforming sulfate reducers from fluid-influenced layers indicates that they have survived the long-term burial as active populations even after the separation from

  6. Nanocalorimetric characterization of microbial activity in deep subsurface oceanic crustal fluids

    Directory of Open Access Journals (Sweden)

    Alberto eRobador

    2016-04-01

    Full Text Available Although fluids within the upper oceanic basaltic crust harbor a substantial fraction of the total prokaryotic cells on Earth, the energy needs of this microbial population are unknown. In this study, a nanocalorimeter (sensitivity down to 4.3 x 10-3 mJ h-1 ml-1 was used to measure the enthalpy of microbially catalyzed reactions as a function of temperature in samples from two distinct crustal fluid aquifers. Microorganisms in unamended, warm (63 °C and geochemically altered anoxic fluids taken from 292 meters sub-basement (msb near the Juan de Fuca Ridge produced 267.3 mJ of heat over the course of 97 hours during a step-wise isothermal scan from 35.5 to 85.0 °C. Most of this heat signal likely stems from the germination of thermophilic endospores (6.66 x 104 cells ml-1FLUID and their subsequent metabolic activity at temperatures greater than 50 °C. The average cellular energy consumption (1.79 x 10-7 kJ h-1 cell-1 reveals the high metabolic potential of a dormant community transported by fluids circulating through the ocean crust. By contrast, samples taken from 293 msb from cooler (3.8 °C, relatively unaltered oxic fluids, produced 12.8 mJ of heat over the course of 14 hours as temperature ramped from 34.8 to 43.0 °C. Corresponding cell-specific energy turnover rates (0.18 pW cell-1 were converted to oxygen uptake rates of 24.5 nmol O2 ml-1FLUID d-1, validating previous model predictions of microbial activity in this environment. Given that the investigated fluids are characteristic of expansive areas of the upper oceanic crust, the measured metabolic heat rates can be used to constrain boundaries of habitability and microbial activity in the oceanic crust.

  7. Regional magnetic anomalies, crustal strength, and the location of the northern Cordilleran fold-and-thrust belt

    Science.gov (United States)

    Saltus, R.W.; Hudson, T.L.

    2007-01-01

    The northern Cordilleran fold-and-thrust belt in Canada and Alaska is at the boundary between the broad continental margin mobile belt and the stable North American craton. The fold-and-thrust belt is marked by several significant changes in geometry: cratonward extensions in the central Yukon Territory and northeastern Alaska are separated by marginward re-entrants. These geometric features of the Cordilleran mobile belt are controlled by relations between lithospheric strength and compressional tectonic forces developed along the continental margin. Regional magnetic anomalies indicate deep thermal and compositional characteristics that contribute to variations in crustal strength. Our detailed analysis of one such anomaly, the North Slope deep magnetic high, helps to explain the geometry of the fold-and-thrust front in northern Alaska. This large magnetic anomaly is inferred to reflect voluminous mafic magmatism in an old (Devonian?) extensional domain. The presence of massive amounts of malic material in the lower crust implies geochemical depletion of the underlying upper mantle, which serves to strengthen the lithosphere against thermal erosion by upper mantle convection. We infer that deep-source magnetic highs are an important indicator of strong lower crust and upper mantle. This stronger lithosphere forms buttresses that play an important role in the structural development of the northern Cordilleran fold-and-thrust belt. ?? 2007 The Geological Society of America.

  8. Crustal Deformation In the Northwestern Margin of the South China Sea: Results From Wide-angle Seismic Modeling

    Science.gov (United States)

    Huang, H.; Klingelhoefer, F.

    2017-12-01

    The South China Sea (SCS) has undergone episodic spreading during the Cenozoic Era. The long-term extension has shaped the continental margins of the SCS, leading to a progressive breakup of the lithosphere. Separated blocks and rift troughs, as controlled by tectonic stretching, contains key information about the deforming mechanism of the crust. In this work, we present a P-wave velocity model of a wide-angle seismic profile OBS2013-1 which passes through the NW margin of the SCS. Modeling of 25 ocean bottom seismometers (OBS) data revealed a detailed crustal structure and shallow complexities along the profile (Figure 1). The crust thins symmetrically across the Xisha Trough, from more than 20 km on flanks to 10 km in the central valley where the sediments thickens over 5 km; A volcano is situated on top of the centre basement high where the Moho drops slightly. At the distal margin around the Zhongsha Trough, the upper crust was detached and accordingly made the middle crust exhumed in a narrow area ( 20 km wide). Meanwhile, materials from the lower crust rises asymmetrically, increasing the crustal velocity by 0.3 km/s and may also giving rise to volcanisms along the hanging side. A 40 km wide hyper-stretched crust (with thickness of 5 km) was identified next to the Zhongsha Trough and covered by overflowing magma and post-rift sediments on the top. These observations argue for a depth-related and asymmetrically extension of the crust, including (1) detachment fault controls the deformation of the upper crust, leading to exhumation of the middle crust and asymmetrically rising of the lower crust, (2) The region adjacent to the exhumation region and with highly thinned crust can be considered as extinct OCT due to magma-starved supplying.

  9. 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.

  10. Variable crustal thickness beneath Thwaites Glacier revealed from airborne gravimetry, possible implications for geothermal heat flux in West Antarctica

    Science.gov (United States)

    Damiani, Theresa M.; Jordan, Tom A.; Ferraccioli, Fausto; Young, Duncan A.; Blankenship, Donald D.

    2014-12-01

    and subaerial volcanoes indicate the absence of supporting crustal roots, suggesting either (1) thermal support from a warm lithosphere or alternatively, and arguably less likely; (2) flexural support of the topography by a cool and rigid lithosphere, or (3) Pratt-like compensation. Although forward modeling of gravity data is non-unique in respect to these alternative possibilities, we prefer the hypothesis that Marie Byrd Land volcanoes are thermally-supported by warmer upper mantle. The presence of such inferred warm upper mantle also suggests regionally elevated geothermal heat flux in this sector of the West Antarctic Rift System and consequently the potential for enhanced meltwater production beneath parts of Thwaites Glacier itself. Our new crustal thickness estimates and geothermal heat flux inferences in the Thwaites Glacier region are significant both for studies of the structure of the broader West Antarctic Rift System and for assessments of geological influences on West Antarctic Ice Sheet dynamics and glacial isostatic adjustment models.

  11. Using crustal thickness and subsidence history on the Iberia-Newfoundland margins to constrain lithosphere deformation modes during continental breakup

    Science.gov (United States)

    Jeanniot, Ludovic; Kusznir, Nick; Manatschal, Gianreto; Mohn, Geoffroy

    2014-05-01

    Observations at magma-poor rifted margins such as Iberia-Newfoundland show a complex lithosphere deformation history during continental breakup and seafloor spreading initiation leading to complex OCT architecture with hyper-extended continental crust and lithosphere, exhumed mantle and scattered embryonic oceanic crust and continental slivers. Initiation of seafloor spreading requires both the rupture of the continental crust and lithospheric mantle, and the onset of decompressional melting. Their relative timing controls when mantle exhumation may occur; the presence or absence of exhumed mantle provides useful information on the timing of these events and constraints on lithosphere deformation modes. A single lithosphere deformation mode leading to continental breakup and sea-floor spreading cannot explain observations. We have determined the sequence of lithosphere deformation events for two profiles across the present-day conjugate Iberia-Newfoundland margins, using forward modelling of continental breakup and seafloor spreading initiation calibrated against observations of crustal basement thickness and subsidence. Flow fields, representing a sequence of lithosphere deformation modes, are generated by a 2D finite element viscous flow model (FeMargin), and used to advect lithosphere and asthenosphere temperature and material. FeMargin is kinematically driven by divergent deformation in the upper 15-20 km of the lithosphere inducing passive upwelling beneath that layer; extensional faulting and magmatic intrusions deform the topmost upper lithosphere, consistent with observations of deformation processes occurring at slow spreading ocean ridges (Cannat, 1996). Buoyancy enhanced upwelling, as predicted by Braun et al. (2000) is also kinematically included in the lithosphere deformation model. Melt generation by decompressional melting is predicted using the parameterization and methodology of Katz et al. (2003). The distribution of lithosphere deformation, the

  12. 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.

  13. Seismotectonics and Crustal Thickness of Northwest Mindoro, Philippines

    Science.gov (United States)

    Chen, P. F.; Olavere, E. A.; Lee, K. M.; Bautista, B.; Solidum, R., Jr.; Huang, B. S.

    2015-12-01

    Mindoro Island locates where the Palawan Continental Block (PCB) indented into the Philippine Mobile Belt (PMB) during the Early Miocene and where the Manila Trench terminates, having ceased convergence due to collision. On the transition from subduction to collision, Northwest Mindoro exhibits vigorous seismic activity and has been debated about its affiliation being PCB or PMB. Here, we use data from both the EHB and Global Centroid Moment Tensor catalogues to study the regional seismotectonics. We also deployed five broadband stations to probe the crustal thickness beneath NW Mindoro using receiver function analysis. Results show that, following the southeasterly reduction of convergence rates at the southern termination of the Manila Trench, the slab dipping angles steepen, were initiated at depth (~200 km) and propagate upwards. The horizontal distances of the trench and slab, as measured from the Wadati-Benioff zone at 200 km depth, also reduce in a southeasterly direction. Observations of intermediate-depth earthquakes that exhibit predominantly down-dip extensional stress patterns attest that the steepening of slab dipping angles is due to the negative buoyancy of the slab. Preliminary results of receiver function analysis suggest that the crustal thickness beneath NW Mindoro is about 40 km and is probably PCB affiliated.

  14. 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.

  15. Lower crustal xenoliths, Chinese Peak lava flow, central Sierra Nevada.

    Science.gov (United States)

    Dodge, F.C.W.; Calk, L.C.; Kistler, R.W.

    1986-01-01

    This assemblage of pyroxenite, peridotite and mafic granulite xenoliths in the toe of a 10 m.y. trachybasalt flow remnant overlying late Cretaceous granitic rocks, indicates the presence of a mafic-ultramafic complex beneath this part of central California; orthopyroxenites, websterites and clinopyroxenites are dominant. A few of the xenoliths contain ovoid opaque patches that are apparently pseudomorphs after garnet and have pyralspite garnet compositions; using a garnet-orthopyroxene geobarometer, they indicate a lower crustal depth of approx 40 km. Abundant mafic granulites can be subdivided into those with Al2O3 = or 15% and showing considerable scatter on oxide variation diagrams. The high-alumina granulite xenoliths have relatively low 87Rb/86Sr but high 87Sr/86Sr, whereas the low-alumina and ultramafic xenoliths have a wide range of 87Rb/86Sr, but lower 87Sr/86Sr; the isotopic data indicate roughly the same age as that of overlying granitic plutons (approx 100 m.y.). However, the granitic rocks have initial 87Sr/86Sr ratios intermediate between those of the high-alumina and ultramafic xenoliths, suggesting that they result from the mixing of basaltic magma (represented by the ultramafic rocks) and crustal materials, with subsequent crystal fractionation.-R.A.H.

  16. ADMAP-2: The second generation Antarctic crustal magnetic anomaly map.

    Science.gov (United States)

    Ferraccioli, F.; Golynsky, A.; Golynsky, D.; Young, D. A.; Eagles, G.; Damaske, D.; Finn, C.; Aitken, A.; von Frese, R. R. B.; Ghidella, M. E.; Kim, H. R.; Hong, J.

    2017-12-01

    ADMAP-2 is the second generation crustal magnetic anomaly compilation for the Antarctic region south of 60°S. It was produced from more than 3.5 million line-km of near-surface terrestrial, airborne and marine magnetic observations collected since the International Geophysical Year 1957/58 through 2013. The data were edited, IGRF corrected, profile levelled and gridded at a 1.5-km interval on a polar stereographic projection using the minimum curvature technique. Given the ubiquitous polar cover of snow, ice and sea water, the magnetic anomaly compilation offers important constraints on the global tectonic processes and crustal properties of the Antarctic. It also links widely separated areas of outcrop to help unify disparate geologic studies, and provides insights on the lithospheric transition between Antarctica and adjacent oceans, as well as the geodynamic evolution of the Antarctic lithosphere in the assembly and break-up of the Gondwana, Rodinia, and Columbia supercontinents and key piercing points for reconstructing linkages between the protocontinents. The magnetic data together with ice-probing radar and gravity information greatly facilitate understanding the evolution of fundamental large-scale geological processes such as continental rifting, intraplate mountain building, subduction and terrane accretion processes, and intraplate basin formation.

  17. Crustal and mantle structure of the greater Jan Mayen-East Greenland region (NE Atlantic) from combined 3D structural, S-wave velocity, and gravity modeling

    Science.gov (United States)

    Tan, P.; Sippel, J.; Scheck-Wenderoth, M.; Meeßen, C.; Breivik, A. J.

    2016-12-01

    The study area is located between the Jan Mayen Ridge and the east coast of Greenland. It has a complex geological setting with the ultraslow Kolbeinsey and Mohn's spreading ridges, the anomalously shallow Eggvin Bank, the Jan Mayen Microcontinent (JMMC), and the tectonically active West Jan Mayen Fracture Zone (WJMFZ). In this study, we present the results of forward 3D structural, S-wave velocity, and gravity modeling which provide new insights into the deep crust and mantle structure and the wide-ranging influence of the Iceland Plume. The crustal parts of the presented 3D structural model are mainly constrained by local seismic refraction and reflection data. Accordingly, greatest crustal thicknesses (24 km) are observed on the northern boundary of the JMMC, while the average crustal thickness is 8.5 km and 4 km in the Kolbeinsey and Mohn's Ridge, respectively. The densities of the crustal parts are from previous studies. Additionally, the mantle density is derived from S-wave velocity data (between 50 and 250 km depth), while densities of the lithospheric mantle between the Moho and 50 km are calculated assuming isostatic equilibrium at 250 km depth. This is used as a starting density model which is further developed to obtain a reasonable fit between the calculated and measured (free-air) gravity fields. The observed S-wave tomographic data and the gravity modeling prove that the Iceland plume anomaly in the asthenosphere affects the lithospheric thickness and temperature, from the strongly influenced Middle Kolbeinsey Ridge, to the less affected North Kolbeinsey Ridge (Eggvin Bank), and to the little impacted Mohn's Ridge. Thus, the age-temperature relations of the different mid-ocean ridges of the study area are perturbed to different degrees controlled by the distance from the Iceland Plume. Furthermore, we find that the upper 50 km of lithospheric mantle are thermally affected by the plume only in the southwestern parts of the study area.

  18. Upper respiratory tract (image)

    Science.gov (United States)

    The major passages and structures of the upper respiratory tract include the nose or nostrils, nasal cavity, mouth, throat (pharynx), and voice box (larynx). The respiratory system is lined with a mucous membrane that ...

  19. ACA Federal Upper Limits

    Data.gov (United States)

    U.S. Department of Health & Human Services — Affordable Care Act Federal Upper Limits (FUL) based on the weighted average of the most recently reported monthly average manufacturer price (AMP) for...

  20. Upper gastrointestinal bleeding.

    Science.gov (United States)

    Feinman, Marcie; Haut, Elliott R

    2014-02-01

    Upper gastrointestinal (GI) bleeding remains a commonly encountered diagnosis for acute care surgeons. Initial stabilization and resuscitation of patients is imperative. Stable patients can have initiation of medical therapy and localization of the bleeding, whereas persistently unstable patients require emergent endoscopic or operative intervention. Minimally invasive techniques have surpassed surgery as the treatment of choice for most upper GI bleeding. Copyright © 2014 Elsevier Inc. All rights reserved.

  1. Crustal structure at the western end of the North Anatolian Fault Zone from deep seismic sounding

    Directory of Open Access Journals (Sweden)

    B. Baier

    2001-06-01

    Full Text Available The first deep seismic sounding experiment in Northwestern Anatolia was carried out in October 1991 as part of the "German - Turkish Project on Earthquake Prediction Research" in the Mudurnu area of the North Anatolian Fault Zone. The experiment was a joint enterprise by the Institute of Meteorology and Geophysics of Frankfurt University, the Earthquake Research Institute (ERI in Ankara, and the Turkish Oil Company (TPAO. Two orthogonal profiles, each 120 km in length with a crossing point near Akyazi, were covered in succession by 30 short period tape recording seismograph stations with 2 km station spacing. 12 shots, with charge sizes between 100 and 250 kg, were fired and 342 seismograms out of 360 were used for evaluation. By coincidence an M b = 4.5 earthquake located below Imroz Island was also recorded and provided additional information on Moho and the sub-Moho velocity. A ray tracing method orginally developed by Weber (1986 was used for travel time inversion. From a compilation of all data two generalized crustal models were derived, one with velocity gradients within the layers and one with constant layer velocities. The latter consists of a sediment cover of about 2 km with V p » 3.6 km/s, an upper crystalline crust down to 13 km with V p » 5.9 km/s, a middle crust down to 25 km depth with V p » 6.5 km/s, a lower crust down to 39 km Moho depth with V p » 7.0 km/s and V p » 8.05 km/s below the Moho. The structure of the individual profiles differs slightly. The thickest sediment cover is reached in the Izmit-Sapanca-trough and in the Akyazi basin. Of particular interest is a step of about 4 km in the lower crust near Lake Sapanca and probably an even larger one in the Moho (derived from the Imroz earthquake data. After the catastrophic earthquake of Izmit on 17 August 1999 this significant heterogeneity in crustal structure appears in a new light with regard to the possible cause of the Izmit earthquake. Heterogeneities in

  2. Subsidence history, crustal structure and evolution of the Nogal Rift, Northern Somalia

    Science.gov (United States)

    Ali, M. Y.; Watts, A. B.

    2013-12-01

    Seismic reflection profile, gravity anomaly, and biostratigraphic data from deep exploration wells have been used to determine the tectonic subsidence, structure and evolution of the Nogal basin, Northern Somalia, one of a number of ENE-WSW trending early Mesozoic rifts that formed prior to opening of the Gulf of Aden. Backstripping of biostratigraphic data at the Nogal-1 and Kali-1 wells provides new constraints on the age of rifting, and the amount of crustal and mantle extension. The tectonic subsidence and uplift history at the wells can be generally explained as a consequence of two, possibly three, major rifting events. The first event initiated in the Late Jurassic (~156 Ma) and lasted for ~10 Myr. We interpret the rift as a late stage event associated with the break-up of Gondwana and the separation of Africa and Madagascar. The second event initiated in the Late Cretaceous (~80 Ma) and lasted for ~20 Myr. This event probably correlates with a rapid increase in spreading rate on the ridges separating the African and Indian and African and Antarctica plates and a contemporaneous slowing down of Africa's plate motion. The backstripped tectonic subsidence data can be explained by a multi-rift extensional model with a stretching factor, β, in the range 1.17-1.38. The third and most recent event occurred in the Oligocene (~32 Ma) and lasted for ~10 Myr. This rift only developed at the centre of the basin close to Nogal-1 well, and is related to the opening of the Gulf of Aden. The amount of crustal thinning inferred at the Kali-1 well is consistent with the results of Process-Oriented Gravity and Flexure (POGM) modelling, assuming an elastic thickness of ~30 km. The thinning at the Nogal-1 well, however, is greater by ~ 7 km than predicted suggesting that the basin may be locally underplated by magmatic material. Irrespective, POGM suggests the transition between thick crust beneath Northern Somalia to thin crust beneath the Indian Ocean forms a ~500 km wide

  3. Deep crustal structure of the northeastern margin of the Arabian plate from seismic and gravity data

    Science.gov (United States)

    Pilia, Simone; Ali, Mohammed; Watts, Anthony; Keats, Brook; Searle, Mike

    2017-04-01

    The United Arab Emirates-Oman mountains constitute a 700 km long, 50 km wide compressional orogenic belt that developed during the Cainozoic on an underlying extensional Tethyan rifted margin. It contains the world's largest and best-exposed thrust sheet of oceanic crust and upper mantle (Semail Ophiolite), which was obducted onto the Arabian rifted continental margin during the Late Cretaceous. Although the shallow structure of the UAE-Oman mountain belt is reasonably well known through the exploitation of a diverse range of techniques, information on deeper structure remains little. Moreover, the mechanisms by which dense oceanic crustal and mantle rocks are emplaced onto less dense and more buoyant continental crust are still controversial and remain poorly understood. The focus here is on an active-source seismic and gravity E-W transect extending from the UAE-mountain belt to the offshore. Seismic refraction data were acquired using the survey ship M/V Hawk Explorer, which was equipped with a large-volume airgun array (7060 cubic inches, 116 liters). About 400 air gun shots at 50-second time interval were recorded on land by eight broadband seismometers. In addition, reflection data were acquired at 20 seconds interval and recorded by a 5-km-long multichannel streamer. Results presented here include an approximately 85 km long (stretching about 35 km onshore and 50 km offshore) P-wave velocity crustal profile derived by a combination of forward modelling and inversion of both diving and reflected wave traveltimes using RAYINVR software. We employ a new robust algorithm based on a Monte Carlo approach (VMONTECARLO) to address the velocity model uncertainties. We find ophiolite seismic velocities of about 5.5 km/s and a thick sedimentary package in the offshore. Furthermore, the velocity model reveals a highly stretched crust with the Moho discontinuity lying at about 20 km. A prestack depth-migrated profile (about 50 km long) coincident with the offshore part

  4. Deep crustal structure of the UAE-Oman mountain belt from seismic and gravity data

    Science.gov (United States)

    Pilia, S.; Tanveer, M.; Ali, M.; Watts, A. B.; Searle, M. P.; Keats, B. S.

    2016-12-01

    The UAE-Oman mountains constitute a 700 km long, 50 km wide compressional orogenic belt that developed during the Cenozoic on an underlying extensional Tethyan rifted margin. It contains the world's largest and best-exposed thrust sheet of oceanic crust and upper mantle (Semail Ophiolite), which was obducted onto the Arabian rifted continental margin during the Late Cretaceous. Although the shallow structure of the UAE-Oman mountain belt is reasonably well known through the exploitation of a diverse range of techniques, information on deeper structure remains little. Moreover, the mechanisms by which dense oceanic crustal and mantle rocks are emplaced onto less dense and more buoyant continental crust are still controversial and remain poorly understood. The focus here is on an active-source seismic and gravity E-W transect extending from the UAE-mountain belt to the offshore. Seismic refraction data were acquired using the survey ship M/V Hawk Explorer, which was equipped with a large-volume airgun array (116 liters). About 400 air gun shots at 50-second time interval were recorded on land by eight broadband seismometers. In addition, reflection data were acquired at 20 seconds interval and recorded by a 5-km-long multichannel streamer. Results presented here include an approximately 85 km long (stretching about 35 km onshore and 50 km offshore) P-wave velocity crustal profile derived by a combination of forward modelling and inversion of both diving and reflected wave traveltimes using RAYINVR software. We employ a new robust algorithm based on a Monte Carlo approach (VMONTECARLO) to address the velocity model uncertainties. We find ophiolite seismic velocities of about 5.5 km/s, underlain by a thin layer of slower material (about 4.5 km/s). Furthermore, the velocity model reveals a Moho depth that rises from ca 30 km in the west to ca 20 km in the east. A poststack depth-migrated profile (about 50 km long) coincident with the offshore part of the refraction

  5. Crustal structure of the southeast Greenland margin from joint refraction and reflection seismic tomography

    Science.gov (United States)

    Korenaga, J.; Holbrook, W. S.; Kent, G. M.; Kelemen, P. B.; Detrick, R. S.; Larsen, H.-C.; Hopper, J. R.; Dahl-Jensen, T.

    2000-09-01

    We present results from a combined multichannel seismic reflection (MCS) and wideangle onshore/offshore seismic experiment conducted in 1996 across the southeast Greenland continental margin. A new seismic tomographic method is developed to jointly invert refraction and reflection travel times for a two-dimensional velocity structure. We employ a hybrid ray-tracing scheme based on the graph method and the local ray-bending refinement to efficiently obtain an accurate forward solution, and we employ smoothing and optional damping constraints to regularize an iterative inversion. We invert 2318 Pg and 2078 PmP travel times to construct a compressional velocity model for the 350-km-long transect, and a long-wavelength structure with strong lateral heterogeneity is recovered, including (1) ˜30-km-thick, undeformed continental crust with a velocity of 6.0 to 7.0 km/s near the landward end, (2) 30- to 15-km-thick igneous crust within a 150-km-wide continent-ocean transition zone, and (3) 15- to 9-km-thick oceanic crust toward the seaward end. The thickness of the igneous upper crust characterized by a high-velocity gradient also varies from 6 km within the transition zone to ˜3 km seaward. The bottom half of the lower crust generally has a velocity higher than 7.0 km/s, reaching a maximum of 7.2 to 7.5 km/s at the Moho. A nonlinear Monte Carlo uncertainty analysis is performed to estimate the a posteriori model variance, showing that most velocity and depth nodes are well determined with one standard deviation of 0.05-0.10 km/s and 0.25-1.5 km, respectively. Despite significant variation in crustal thickness, the mean velocity of the igneous crust, which serves as a proxy for the bulk crustal composition, is surprisingly constant (˜7.0 km/s) along the transect. On the basis of a mantle melting model incorporating the effect of active mantle upwelling, this velocity-thickness relationship is used to constrain the mantle melting process during the breakup of Greenland

  6. Three-Dimensional Numerical Modeling of Crustal Growth at Active Continental Margins

    Science.gov (United States)

    Zhu, G.; Gerya, T.; Tackley, P. J.

    2011-12-01

    Active margins are important sites of new continental crust formation by magmatic processes related to the subduction of oceanic plates. We investigate these phenomena using a three-dimensional coupled petrological-geochemical-thermomechanical numerical model, which combines a finite-difference flow solver with a non-diffusive marker-in-cell technique for advection (I3ELVIS code, Gerya and Yuen, PEPI,2007). The model includes mantle flow associated with the subducting plate, water release from the slab, fluid propagation that triggers partial melting at the slab surface, melt extraction and the resulting volcanic crustal growth at the surface. The model also accounts for variations in physical properties (mainly density and viscosity) of both fluids and rocks as a function of local conditions in temperature, pressure, deformation, nature of the rocks, and chemical exchanges. Our results show different patterns of crustal growth and surface topography, which are comparable to nature, during subduction at active continental margins. Often, two trench-parallel lines of magmatic activity, which reflect two maxima of melt production atop the slab, are formed on the surface. The melt extraction rate controls the patterns of new crust at different ages. Moving free water reflects the path of fluids, and the velocity of free water shows the trend of two parallel lines of magmatic activity. The formation of new crust in particular time intervals is distributed in finger-like shapes, corresponding to finger-like and ridge-like cold plumes developed atop the subducting slabs (Zhu et al., G-cubed,2009; PEPI,2011). Most of the new crust is basaltic, formed from peridotitic mantle. Granitic crust extracted from melted sediment and upper crust forms in a line closer to the trench, and its distribution reflects the finger-like cold plumes. Dacitic crust extracted from the melted lower crust forms in a line farther away from the trench, and its distribution is anticorrelated with

  7. Lateral variation in crustal and mantle structure in Bay of Bengal based on surface wave data

    Science.gov (United States)

    Kumar, Amit; Mukhopadhyay, Sagarika; Kumar, Naresh; Baidya, P. R.

    2018-01-01

    Surface waves generated by earthquakes that occurred near Sumatra, Andaman-Nicobar Island chain and Sunda arc are used to estimate crustal and upper mantle S wave velocity structure of Bay of Bengal. Records of these seismic events at various stations located along the eastern coast of India and a few stations in the north eastern part of India are selected for such analysis. These stations lie within regional distance of the selected earthquakes. The selected events are shallow focused with magnitude greater than 5.5. Data of 65, 37, 36, 53 and 36 events recorded at Shillong, Bokaro, Visakhapatnam, Chennai and Trivandrum stations respectively are used for this purpose. The ray paths from the earthquake source to the recording stations cover different parts of the Bay of Bengal. Multiple Filtering Technique (MFT) is applied to compute the group velocities of surface waves from the available data. The dispersion curves thus obtained for this data set are within the period range of 15-120 s. Joint inversion of Rayleigh and Love wave group velocity is carried out to obtain the subsurface information in terms of variation of S wave velocity with depth. The estimated S wave velocity at a given depth and layer thickness can be considered to be an average value for the entire path covered by the corresponding ray paths. However, we observe variation in the value of S wave velocity and layer thickness from data recorded at different stations, indicating lateral variation in these two parameters. Thick deposition of sediments is observed along the paths followed by surface waves to Shillong and Bokaro stations. Sediment thickness keeps on decreasing as the surface wave paths move further south. Based on velocity variation the sedimentary layer is further divided in to three parts; on top lay unconsolidated sediment, underlain by consolidated sediment. Below this lies a layer which we consider as meta-sediments. The thickness and velocity of these layers decrease from north

  8. Associated factors of atrophic gastritis diagnosed by double-contrast upper gastrointestinal barium X-ray radiography: a cross-sectional study analyzing 6,901 healthy subjects in Japan.

    Directory of Open Access Journals (Sweden)

    Nobutake Yamamichi

    Full Text Available Double-contrast upper gastrointestinal barium X-ray radiography (UGI-XR is one of the most widely conducted gastric cancer screening methods. It has been executed to find gastric cancer, but has not been usually executed to detect premalignant atrophic mucosa of stomach. To understand the meaning of UGI-XR-based atrophic gastritis, we analyzed its association with several causative factors including Helicobacter pylori (HP infection.We evaluated 6,901 healthy adults in Japan. UGI-XR-based atrophic gastritis was diagnosed based on the irregular shape of areae gastricae and its expansion in the stomach.Of the 6,433 subjects with no history of HP eradication and free from gastric acid suppressants, 1,936 were diagnosed as UGI-XR-based atrophic gastritis (mild: 234, moderate: 822, severe: 880. These were univariately associated with serum HP IgG and serum pepsinogen I/II ratio with statistical significance. The multiple logistic analysis calculating standardized coefficients (β and odds ratio (OR demonstrated that serum HP IgG (β = 1.499, OR = 4.48, current smoking (β = 0.526, OR = 1.69, age (β = 0.401, OR = 1.49, low serum pepsinogen I/II ratio (β = 0.339, OR = 1.40, and male gender (β = 0.306, OR = 1.36 showed significant positive association with UGI-XR-based atrophic gastritis whereas drinking and body mass index did not. Among the age/sex/smoking/drinking-matched 227 pairs derived from chronically HP-infected and successfully HP-eradicated subjects, UGI-XR-based atrophic gastritis was detected in 99.1% of the former but in only 59.5% of the latter subjects (p<0.0001. Contrastively, UGI-XR-based atrophic gastritis was detected in 13 of 14 HP-positive proton pump inhibitor users (92.9% and 33 of 34 HP-positive histamine H2-receptor antagonist users (97.1%, which are not significantly different from gastric acid suppressant-free subjects.The presence of UGI-XR-based atrophic gastritis is positively

  9. Associated Factors of Atrophic Gastritis Diagnosed by Double-Contrast Upper Gastrointestinal Barium X-Ray Radiography: A Cross-Sectional Study Analyzing 6,901 Healthy Subjects in Japan

    Science.gov (United States)

    Yamamichi, Nobutake; Hirano, Chigaya; Shimamoto, Takeshi; Minatsuki, Chihiro; Takahashi, Yu; Nakayama, Chiemi; Matsuda, Rie; Fujishiro, Mitsuhiro; Konno-Shimizu, Maki; Kato, Jun; Kodashima, Shinya; Ono, Satoshi; Niimi, Keiko; Mochizuki, Satoshi; Tsuji, Yosuke; Sakaguchi, Yoshiki; Asada-Hirayama, Itsuko; Takeuchi, Chihiro; Yakabi, Seiichi; Kakimoto, Hikaru; Wada, Ryoichi; Mitsushima, Toru; Ichinose, Masao; Koike, Kazuhiko

    2014-01-01

    Background Double-contrast upper gastrointestinal barium X-ray radiography (UGI-XR) is one of the most widely conducted gastric cancer screening methods. It has been executed to find gastric cancer, but has not been usually executed to detect premalignant atrophic mucosa of stomach. To understand the meaning of UGI-XR-based atrophic gastritis, we analyzed its association with several causative factors including Helicobacter pylori (HP) infection. Methods We evaluated 6,901 healthy adults in Japan. UGI-XR-based atrophic gastritis was diagnosed based on the irregular shape of areae gastricae and its expansion in the stomach. Results Of the 6,433 subjects with no history of HP eradication and free from gastric acid suppressants, 1,936 were diagnosed as UGI-XR-based atrophic gastritis (mild: 234, moderate: 822, severe: 880). These were univariately associated with serum HP IgG and serum pepsinogen I/II ratio with statistical significance. The multiple logistic analysis calculating standardized coefficients (β) and odds ratio (OR) demonstrated that serum HP IgG (β = 1.499, OR = 4.48), current smoking (β = 0.526, OR = 1.69), age (β = 0.401, OR = 1.49), low serum pepsinogen I/II ratio (β = 0.339, OR = 1.40), and male gender (β = 0.306, OR = 1.36) showed significant positive association with UGI-XR-based atrophic gastritis whereas drinking and body mass index did not. Among the age/sex/smoking/drinking-matched 227 pairs derived from chronically HP-infected and successfully HP-eradicated subjects, UGI-XR-based atrophic gastritis was detected in 99.1% of the former but in only 59.5% of the latter subjects (pgastritis was detected in 13 of 14 HP-positive proton pump inhibitor users (92.9%) and 33 of 34 HP-positive histamine H2-receptor antagonist users (97.1%), which are not significantly different from gastric acid suppressant-free subjects. Conclusions The presence of UGI-XR-based atrophic gastritis is positively associated with

  10. Associated factors of atrophic gastritis diagnosed by double-contrast upper gastrointestinal barium X-ray radiography: a cross-sectional study analyzing 6,901 healthy subjects in Japan.

    Science.gov (United States)

    Yamamichi, Nobutake; Hirano, Chigaya; Shimamoto, Takeshi; Minatsuki, Chihiro; Takahashi, Yu; Nakayama, Chiemi; Matsuda, Rie; Fujishiro, Mitsuhiro; Konno-Shimizu, Maki; Kato, Jun; Kodashima, Shinya; Ono, Satoshi; Niimi, Keiko; Mochizuki, Satoshi; Tsuji, Yosuke; Sakaguchi, Yoshiki; Asada-Hirayama, Itsuko; Takeuchi, Chihiro; Yakabi, Seiichi; Kakimoto, Hikaru; Wada, Ryoichi; Mitsushima, Toru; Ichinose, Masao; Koike, Kazuhiko

    2014-01-01

    Double-contrast upper gastrointestinal barium X-ray radiography (UGI-XR) is one of the most widely conducted gastric cancer screening methods. It has been executed to find gastric cancer, but has not been usually executed to detect premalignant atrophic mucosa of stomach. To understand the meaning of UGI-XR-based atrophic gastritis, we analyzed its association with several causative factors including Helicobacter pylori (HP) infection. We evaluated 6,901 healthy adults in Japan. UGI-XR-based atrophic gastritis was diagnosed based on the irregular shape of areae gastricae and its expansion in the stomach. Of the 6,433 subjects with no history of HP eradication and free from gastric acid suppressants, 1,936 were diagnosed as UGI-XR-based atrophic gastritis (mild: 234, moderate: 822, severe: 880). These were univariately associated with serum HP IgG and serum pepsinogen I/II ratio with statistical significance. The multiple logistic analysis calculating standardized coefficients (β) and odds ratio (OR) demonstrated that serum HP IgG (β = 1.499, OR = 4.48), current smoking (β = 0.526, OR = 1.69), age (β = 0.401, OR = 1.49), low serum pepsinogen I/II ratio (β = 0.339, OR = 1.40), and male gender (β = 0.306, OR = 1.36) showed significant positive association with UGI-XR-based atrophic gastritis whereas drinking and body mass index did not. Among the age/sex/smoking/drinking-matched 227 pairs derived from chronically HP-infected and successfully HP-eradicated subjects, UGI-XR-based atrophic gastritis was detected in 99.1% of the former but in only 59.5% of the latter subjects (p<0.0001). Contrastively, UGI-XR-based atrophic gastritis was detected in 13 of 14 HP-positive proton pump inhibitor users (92.9%) and 33 of 34 HP-positive histamine H2-receptor antagonist users (97.1%), which are not significantly different from gastric acid suppressant-free subjects. The presence of UGI-XR-based atrophic gastritis is positively

  11. Upper GI Bleeding in Children

    Science.gov (United States)

    Upper GI Bleeding in Children What is upper GI Bleeding? Irritation and ulcers of the lining of the esophagus, stomach or duodenum can result in upper GI bleeding. When this occurs the child may vomit blood ...

  12. 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

  13. Nucleogenic production of Ne isotopes in Earth's crust and upper mantle induced by alpha particles from the decay of U and Th

    Science.gov (United States)

    Leya, Ingo; Wieler, Rainer

    1999-07-01

    The production of nucleogenic Ne in terrestrial crust and upper mantle by alpha particles from the decay of U and Th was calculated. The calculations are based on stopping powers for the chemical compounds and thin-target cross sections. This approach is more rigorous than earlier studies using thick-target yields for pure elements, since our results are independent of limiting assumptions about stopping-power ratios. Alpha induced reactions account for >99% of the Ne production in the crust and for most of the 20,21Ne in the upper mantle. On the other hand, our 22Ne value for the upper mantle is a lower limit because the reaction 25Mg(n,α)22Ne is significant in mantle material. Production rates calculated here for hypothetical crustal and upper mantle material with average major element composition and homogeneously distributed F, U, and Th are up to 100 times higher than data presented by Kyser and Rison [1982] but agree within error limits with the results by Yatsevich and Honda [1997]. Production of nucleogenic Ne in "mean" crust and mantle is also given as a function of the weight fractions of O and F. The alpha dose is calculated by radiogenic 4He as well as by the more retentive fissiogenic 136Xe. U and Th is concentrated in certain accessory minerals. Since the ranges of alpha particles from the three decay chains are comparable to mineral dimensions, most nucleogenic Ne is produced in U- and Th-rich minerals. Therefore nucleogenic Ne production in such accessories was also calculated. The calculated correlation between nucleogenic 21Ne and radiogenic 4He agrees well with experimental data for Earth's crust and accessories. Also, the calculated 22Ne/4He ratios as function of the F concentration and the dependence of 21Ne/22Ne from O/F for zircon and apatite agree with measurements.

  14. Crustal heat production and estimate of terrestrial heat flow in central East Antarctica, with implications for thermal input to the East Antarctic ice sheet

    Science.gov (United States)

    Goodge, John W.

    2018-02-01

    Terrestrial heat flow is a critical first-order factor governing the thermal condition and, therefore, mechanical stability of Antarctic ice sheets, yet heat flow across Antarctica is poorly known. Previous estimates of terrestrial heat flow in East Antarctica come from inversion of seismic and magnetic geophysical data, by modeling temperature profiles in ice boreholes, and by calculation from heat production values reported for exposed bedrock. Although accurate estimates of surface heat flow are important as an input parameter for ice-sheet growth and stability models, there are no direct measurements of terrestrial heat flow in East Antarctica coupled to either subglacial sediment or bedrock. As has been done with bedrock exposed along coastal margins and in rare inland outcrops, valuable estimates of heat flow in central East Antarctica can be extrapolated from heat production determined by the geochemical composition of glacial rock clasts eroded from the continental interior. In this study, U, Th, and K concentrations in a suite of Proterozoic (1.2-2.0 Ga) granitoids sourced within the Byrd and Nimrod glacial drainages of central East Antarctica indicate average upper crustal heat production (Ho) of about 2.6 ± 1.9 µW m-3. Assuming typical mantle and lower crustal heat flux for stable continental shields, and a length scale for the distribution of heat production in the upper crust, the heat production values determined for individual samples yield estimates of surface heat flow (qo) ranging from 33 to 84 mW m-2 and an average of 48.0 ± 13.6 mW m-2. Estimates of heat production obtained for this suite of glacially sourced granitoids therefore indicate that the interior of the East Antarctic ice sheet is underlain in part by Proterozoic continental lithosphere with an average surface heat flow, providing constraints on both geodynamic history and ice-sheet stability. The ages and geothermal characteristics of the granites indicate that crust in central

  15. Investigation of a marine magnetic polarity reversal boundary in cross section at the northern boundary of the Kane Megamullion, Mid-Atlantic Ridge, 23°40'N

    Science.gov (United States)

    Xu, Min; Tivey, M. A.

    2016-05-01

    Near-bottom magnetic field measurements made by the submersible Nautile during the 1992 Kanaut Expedition define the cross-sectional geometry of magnetic polarity reversal boundaries and the vertical variation of crustal magnetization in lower oceanic crust exposed along the Kane Transform Fault (TF) at the northern boundary of the Kane Megamullion (KMM). The KMM exposes lower crust and upper mantle rocks on a low-angle normal fault that was active between 3.3 Ma and 2.1 Ma. The geometry of the polarity boundaries is estimated from an inversion of the submarine magnetic data for crustal magnetization. In general, the polarity boundaries dip away from the ridge axis along the Kane TF scarp, with a west dipping angle of ~45° in the shallow (Williams (2007) that the lower crust cools through the Curie temperature of magnetite to become magnetic, with the polarity boundaries representing both frozen isotherms and isochrons. We also test the effects of the rotation of this isotherm structure and/or footwall rotation and find that the magnetic polarity boundary geometry is not sensitive to these directional changes.

  16. The deep thermal field of the Upper Rhine Graben

    Science.gov (United States)

    Freymark, Jessica; Sippel, Judith; Scheck-Wenderoth, Magdalena; Bär, Kristian; Stiller, Manfred; Fritsche, Johann-Gerhard; Kracht, Matthias

    2017-01-01

    The Upper Rhine Graben has a significant socioeconomic relevance as it provides a great potential for geothermal energy production. The key for the utilisation of this energy resource is to understand the controlling factors of the thermal field in this area. We have therefore built a data-based lithospheric-scale 3D structural model of the Upper Rhine Graben and its adjacent areas. In addition, 3D gravity modelling was performed to constrain the internal structure of the crystalline crust consistent with seismic information. Based on this lithosphere scale 3D structural model the present-day conductive thermal field was calculated and compared to measured temperatures. Our results show that the regional thermal field is mainly controlled by the configuration of the upper crust, which has different thermal properties characteristic for the Variscan and Alpine domains. Temperature maxima are predicted for the Upper Rhine Graben where thick insulating Cenozoic sediments cause a thermal blanketing effect and where the underlying crustal units are characterised by high radiogenic heat production. The comparison of calculated and measured temperatures overall shows a reasonable fit, while locally occuring model deviations indicate where a larger influence of groundwater flow may be expected.

  17. Combined Gravimetric-Seismic Crustal Model for Antarctica

    Science.gov (United States)

    Baranov, Alexey; Tenzer, Robert; Bagherbandi, Mohammad

    2018-01-01

    The latest seismic data and improved information about the subglacial bedrock relief are used in this study to estimate the sediment and crustal thickness under the Antarctic continent. Since large parts of Antarctica are not yet covered by seismic surveys, the gravity and crustal structure models are used to interpolate the Moho information where seismic data are missing. The gravity information is also extended offshore to detect the Moho under continental margins and neighboring oceanic crust. The processing strategy involves the solution to the Vening Meinesz-Moritz's inverse problem of isostasy constrained on seismic data. A comparison of our new results with existing studies indicates a substantial improvement in the sediment and crustal models. The seismic data analysis shows significant sediment accumulations in Antarctica, with broad sedimentary basins. According to our result, the maximum sediment thickness in Antarctica is about 15 km under Filchner-Ronne Ice Shelf. The Moho relief closely resembles major geological and tectonic features. A rather thick continental crust of East Antarctic Craton is separated from a complex geological/tectonic structure of West Antarctica by the Transantarctic Mountains. The average Moho depth of 34.1 km under the Antarctic continent slightly differs from previous estimates. A maximum Moho deepening of 58.2 km under the Gamburtsev Subglacial Mountains in East Antarctica confirmed the presence of deep and compact orogenic roots. Another large Moho depth in East Antarctica is detected under Dronning Maud Land with two orogenic roots under Wohlthat Massif (48-50 km) and the Kottas Mountains (48-50 km) that are separated by a relatively thin crust along Jutulstraumen Rift. The Moho depth under central parts of the Transantarctic Mountains reaches 46 km. The maximum Moho deepening (34-38 km) in West Antarctica is under the Antarctic Peninsula. The Moho depth minima in East Antarctica are found under the Lambert Trench (24

  18. Evidence for crustal low shear-wave speed in western Saudi Arabia from multi-scale fundamental-mode Rayleigh-wave group-velocity tomography

    KAUST Repository

    Tang, Zheng

    2018-05-15

    We investigate the crustal and upper-mantle shear-velocity structure of Saudi Arabia by fundamental-mode Rayleigh-wave group-velocity tomography and shear-wave velocity inversion. The seismic dataset is compiled using ∼140 stations of the Saudi National Seismic Network (SNSN) operated by the Saudi Geological Survey (SGS). We measure Rayleigh-wave group-velocities at periods of 8–40 s from regional earthquakes. After obtaining 1-D shear-wave velocity models by inverting group-velocities at each grid node, we construct a 3-D shear-velocity model for Saudi Arabia and adjacent regions by interpolating the 1-D models. Our 3-D model indicates significant lateral variations in crustal and lithospheric thickness, as well as in the shear-wave velocity over the study region. In particular, we identify zones of reduced shear-wave speed at crustal levels beneath the Cenozoic volcanic fields in the Arabian Shield. The inferred reductions of 2–5% in shear-wave speed may be interpreted as possibly indicating the presence of partial melts. However, their precise origin we can only speculate about. Our study also reveals an upper-mantle low velocity zone (LVZ) below the Arabian Shield, supporting the model of lateral mantle flow from the Afar plume. Further geophysical experiments are needed to confirm (or refute) the hypothesis that partial melts may exist below the Cenozoic volcanism in western Saudi Arabia, and to build a comprehensive geodynamic–geological model for the evolution and present state of the lithosphere of the Arabian Plate and the Red Sea.

  19. Evidence for crustal low shear-wave speed in western Saudi Arabia from multi-scale fundamental-mode Rayleigh-wave group-velocity tomography

    KAUST Repository

    Tang, Zheng; Mai, Paul Martin; Chang, Sung-Joon; Zahran, Hani

    2018-01-01

    We investigate the crustal and upper-mantle shear-velocity structure of Saudi Arabia by fundamental-mode Rayleigh-wave group-velocity tomography and shear-wave velocity inversion. The seismic dataset is compiled using ∼140 stations of the Saudi National Seismic Network (SNSN) operated by the Saudi Geological Survey (SGS). We measure Rayleigh-wave group-velocities at periods of 8–40 s from regional earthquakes. After obtaining 1-D shear-wave velocity models by inverting group-velocities at each grid node, we construct a 3-D shear-velocity model for Saudi Arabia and adjacent regions by interpolating the 1-D models. Our 3-D model indicates significant lateral variations in crustal and lithospheric thickness, as well as in the shear-wave velocity over the study region. In particular, we identify zones of reduced shear-wave speed at crustal levels beneath the Cenozoic volcanic fields in the Arabian Shield. The inferred reductions of 2–5% in shear-wave speed may be interpreted as possibly indicating the presence of partial melts. However, their precise origin we can only speculate about. Our study also reveals an upper-mantle low velocity zone (LVZ) below the Arabian Shield, supporting the model of lateral mantle flow from the Afar plume. Further geophysical experiments are needed to confirm (or refute) the hypothesis that partial melts may exist below the Cenozoic volcanism in western Saudi Arabia, and to build a comprehensive geodynamic–geological model for the evolution and present state of the lithosphere of the Arabian Plate and the Red Sea.

  20. Magma Supply of Southwest Indian Ocean: Implication from Crustal Thickness Anomalies

    Science.gov (United States)

    Chiheng, L.; Jianghai, L.; Huatian, Z.; Qingkai, F.

    2017-12-01

    The Southwest Indian Ridge (SWIR) is one of the world's slowest spreading ridges with a full spreading rate of 14mm a-1, belonging to ultraslow spreading ridge, which are a novel class of spreading centers symbolized by non-uniform magma supply and crustal accretion. Therefore, the crustal thickness of Southwest Indian Ocean is a way to explore the magmatic and tectonic process of SWIR and the hotspots around it. Our paper uses Residual Mantle Bouguer Anomaly processed with the latest global public data to invert the relative crustal thickness and correct it according to seismic achievements. Gravity-derived crustal thickness model reveals a huge range of crustal thickness in Southwest Indian Ocean from 0.04km to 24km, 7.5km of average crustal thickness, and 3.5km of standard deviation. In addition, statistics data of crustal thickness reveal the frequency has a bimodal mixed skewed distribution, which indicates the crustal accretion by ridge and ridge-plume interaction. Base on the crustal thickness model, we divide three types of crustal thickness in Southwest Indian Ocean. About 20.31% of oceanic crust is 9.8km thick as thick crust. Furthermore, Prominent thin crust anomalies are associated with the trend of most transform faults, but thick crust anomalies presents to northeast of Andrew Bain transform fault. Cold and depleted mantle are also the key factors to form the thin crust. The thick crust anomalies are constrained by hotspots, which provide abundant heat to the mantle beneath mid-ocean ridge or ocean basin. Finally, we roughly delineate the range of ridge-plume interaction and transform fault effect.

  1. An assessment of the Th-Hf-Ta diagram as a discriminant for tectomagnetic classifications and in the detection of crustal contamination of magmas

    International Nuclear Information System (INIS)

    Thompson, R.N.; Morrison, M.A.; Mattey, D.P.; Dickin, A.P.; Moorbath, S.

    1980-01-01

    The Th-Hf-Ta diagram, recently proposed as a means of discriminating basalts erupted in various tectonic environments and of detecting crustal contamination in such magmas, is shown to be unsatisfactory for both of its stated purposes. Data are presented for Th, Hf, Ta, Sr and Sr- and Pb-isotopes in basic lavas and a dolerite sill from the ensialic British Tertiary Volcanic Province (BTVP). Taken in conjunction with published results, the isotopic ratios show that some of the BTVP basic magmas are essentially uncontaminated by continental crust, except for the selective introduction of small variable amounts of unradiogenic Pb. Those BTVP magmas which show appreciable isotopic contamination have interacted with either upper or lower crust, or both. Th/(Hf + Ta) is insensitive to contamination with the Th-poor lower crust of cratons but rises during gross contamination with Th-rich upper crust. BTVP basic magmas containing negligible to moderate crustal isotopic components plot in the field of the Th-Hf-Ta diagram occupied by normal mid-ocean ridge basalts. Other volcanic provinces of known tectonic setting which plot wholly or partially outside their appropriate fields on the Th-Hf-Ta diagram are: the Hawaii-Emperor Seamount Chain, the Snake River Plain (Idaho, U.S.A.), the Azores and the Gregory Rift (Kenya). (orig.)

  2. Physics of Earthquake Disaster: From Crustal Rupture to Building Collapse

    Science.gov (United States)

    Uenishi, Koji

    2018-05-01

    Earthquakes of relatively greater magnitude may cause serious, sometimes unexpected failures of natural and human-made structures, either on the surface, underground, or even at sea. In this review, by treating several examples of extraordinary earthquake-related failures that range from the collapse of every second building in a commune to the initiation of spontaneous crustal rupture at depth, we consider the physical background behind the apparently abnormal earthquake disaster. Simple but rigorous dynamic analyses reveal that such seemingly unusual failures actually occurred for obvious reasons, which may remain unrecognized in part because in conventional seismic analyses only kinematic aspects of the effects of lower-frequency seismic waves below 1 Hz are normally considered. Instead of kinematics, some dynamic approach that takes into account the influence of higher-frequency components of waves over 1 Hz will be needed to anticipate and explain such extraordinary phenomena and mitigate the impact of earthquake disaster in the future.

  3. PIXEL: Japanese InSAR community for crustal deformation research

    Science.gov (United States)

    Furuya, M.; Shimada, M.; Ozawa, T.; Fukushima, Y.; Aoki, Y.; Miyagi, Y.; Kitagawa, S.

    2007-12-01

    In anticipation of the launch of ALOS (Advanced Land Observation Satellite) by JAXA (Japan Aerospace eXploration Agency), and in order to expand and bolster the InSAR community for crustal deformation research in Japan, a couple of scientists established a consortium, PIXEL, in November 2005 in a completely bottom-up fashion. PIXEL stands for Palsar Interferometry Consortium to Study our Evolving Land. Formally, it is a research contract between JAXA and Earthquake Research Institute (ERI), University of Tokyo. As ERI is a shared institute of the Japanese universities and research institutes, every scientist at all Japanese universities and institutes can participate in this consortium. The activity of PIXEL includes information exchange by mailing list, tutorial workshop for InSAR software, research workshop, and PALSAR data sharing. After the launch of ALOS, we have already witnessed several earthquakes and volcanic activities using PALSAR interferometry. We will briefly show and digest some of those observation results.

  4. Investigation of lunar crustal structure and isostasy. Final technical report

    International Nuclear Information System (INIS)

    Thurber, C.H.

    1987-07-01

    The lunar mascon basins have strongly free air gravity anomalies, generally exceeding 100 milligals at an elevation of 100 km. The source of the anomalies is a combination of mantle uplift beneath the impact basins and subsequent infilling by high-density mare basalts. The relative contribution of these two components is still somewhat uncertain, although it is generally accepted that the amount of mantle uplift greatly exceeds the thickness of the basalts. Extensive studies have been carried out of the crustal structure of mare basins, based on gravity data, and their tectonic evolution, based on compressive and extensional tectonic features. The present study endeavored to develop a unified, self-consistent model of the lunar crust and lithosphere incorporating both gravity and tectonic constraints

  5. Alps, Carpathians and Dinarides-Hellenides: about plates, micro-plates and delaminated crustal blocks

    Science.gov (United States)

    Schmid, Stefan

    2014-05-01

    thickened crust ripped of the African plate, invaded the northern part of this oceanic embayment, virtually floating on asthenospheric mantle. The presently still surviving semi-detached Vrancea slab in Romania manifests of the combined effect of roll back and delamination of mantle lithosphere. On the other hand Tisza-Dacia, another crustal block formerly ripped off the European plate and forming a single entity since mid-Cretaceous times, also at least partly floating on asthenospheric mantle, invaded the Carpathian embayment from the south. Thereby the Tisza-Dacia crustal block underwent clockwise rotation by as much as 90° due to the corner effect of the Moesian platform firmly attached to Europe since mid-Cretaceous times (Ustaszewski et al. 2008). In the Dinaric-Aegean realm collision occurred much earlier than in the Alps and the Carpathians, i.e. at around the Cretaceous-Cenozoic boundary, provided that one accepts that there is yet no convincing evidence for the existence of a second "Pindos oceanic domain" closing later, i.e. in Eocene times. However, in spite of early collision, the old subduction zone that consumed the northern branch of Neotethys (Meliata-Vardar) since at least mid-Cretaceous times persisted in the eastern Hellenides (but not in the Dinarides) until now, penetrating the transition zone all the way to a depth of some 1500km (Bijwaard et al. 1998). Continued subduction of mantle lithosphere in the Aegean since 60 Ma was concomitant with complete delamination of lithospheric mantle and lower crust from non-subducted or re-exhumed high pressure crustal flakes of largely continental derivation that were piled up to form the subsequently extended Hellenic orogen (Jolivet & Brun 2010). At around 25 Ma when the southern branch of Neotethys (the present-day Eastern Mediterranean ocean) entered this subduction zone, massive extension and core complex formation in the upper plate combined with an acceleration of south-directed hinge retreat of the lower

  6. Right upper quadrant pain

    International Nuclear Information System (INIS)

    Ralls, P.W.; Colletti, P.M.; Boswell, W.D. Jr.; Halls, J.M.

    1984-01-01

    Historically, assessment of acute right upper quadrant abdominal pain has been a considerable clinical challenge. While clinical findings and laboratory data frequently narrow the differential diagnosis, symptom overlap generally precludes definitive diagnosis among the various diseases causing acute right upper quadrant pain. Fortunately, the advent of newer diagnostic imaging modalities has greatly improved the rapidity and reliability of diagnosis in these patients. An additional challenge to the physician, with increased awareness of the importance of cost effectiveness in medicine, is to select appropriate diagnostic schema that rapidly establish accurate diagnoses in the most economical fashion possible. The dual goals of this discussion are to assess not only the accuracy of techniques used to evaluate patients with acute right upper quadrant pain, but also to seek out cost-effective, coordinated imaging techniques to achieve this goal

  7. Crustal structure of Australia from ambient seismic noise tomography

    Science.gov (United States)

    Saygin, Erdinc; Kennett, B. L. N.

    2012-01-01

    Surface wave tomography for Australian crustal structure has been carried out using group velocity measurements in the period range 1-32 s extracted from stacked correlations of ambient noise between station pairs. Both Rayleigh wave and Love wave group velocity maps are constructed for each period using the vertical and transverse component of the Green's function estimates from the ambient noise. The full suite of portable broadband deployments and permanent stations on the continent have been used with over 250 stations in all and up to 7500 paths. The permanent stations provide a useful link between the various shorter-term portable deployments. At each period the group velocity maps are constructed with a fully nonlinear tomographic inversion exploiting a subspace technique and the Fast Marching Method for wavefront tracking. For Rayleigh waves the continental coverage is good enough to allow the construction of a 3D shear wavespeed model in a two stage approach. Local group dispersion information is collated for a distribution of points across the continent and inverted for a 1D SV wavespeed profile using a Neighbourhood Algorithm method. The resulting set of 1D models are then interpolated to produce the final 3D wavespeed model. The group velocity maps show the strong influence of thick sediments at shorter periods, and distinct fast zones associated with cratonic regions. Below the sediments the 3D shear wavespeed model displays significant heterogeneity with only moderate correlation with surface tectonic features. For example, there is no evident expression of the Tasman Line marking the eastern edge of Precambrian outcrop. The large number of available inter-station paths extracted from the ambient noise analysis provide detailed shear wavespeed information for crustal structure across the Australian continent for the first time, including regions where there was no prior sampling because of difficult logistics.

  8. Shallow and deep crustal velocity models of Northeast Tibet

    Science.gov (United States)

    Karplus, M.; Klemperer, S. L.; Mechie, J.; Shi, D.; Zhao, W.; Brown, L. D.; Wu, Z.

    2009-12-01

    The INDEPTH IV seismic profile in Northeast Tibet is the highest resolution wide-angle refraction experiment imaging the Qaidam Basin, North Kunlun Thrusts (NKT), Kunlun Mountains, North and South Kunlun Faults (NKT, SKT), and Songpan-Ganzi terrane (SG). First arrival refraction modeling using ray tracing and least squares inversion has yielded a crustal p-wave velocity model, best resolved for the top 20 km. Ray tracing of deeper reflections shows considerable differences between the Qaidam Basin and the SG, in agreement with previous studies of those areas. The Moho ranges from about 52 km beneath the Qaidam Basin to 63 km with a slight northward dip beneath the SG. The 11-km change must occur between the SKF and the southern edge of the Qaidam Basin, just north of the NKT, allowing the possibility of a Moho step across the NKT. The Qaidam Basin velocity-versus-depth profile is more similar to the global average than the SG profile, which bears resemblance to previously determined “Tibet-type” velocity profiles with mid to lower crustal velocities of 6.5 to 7.0 km/s appearing at greater depths. The highest resolution portion of the profile (100-m instrument spacing) features two distinct, apparently south-dipping low-velocity zones reaching about 2-3 km depth that we infer to be the locations of the NKF and SKF. A strong reflector at 35 km, located entirely south of the SKF and truncated just south of it, may be cut by a steeply south-dipping SKF. Elevated velocities at depth beneath the surface location of the NKF may indicate the south-dipping NKF meets the SKF between depths of 5 and 10 km. Undulating regions of high and low velocity extending about 1-2 km in depth near the southern border of the Qaidam Basin likely represent north-verging thrust sheets of the NKT.

  9. Chemical cycles and health risks of some crustal nuclides

    International Nuclear Information System (INIS)

    McKone, T.E.

    1981-01-01

    This dissertation describes and utilizes an approach for assessing long term health risks due to dispersion of naturally occurring radionuclide series and chemical toxins by normal and altered landscape chemical cycles. In particular, the health risks resulting from geochemical mobilizations of arsenic, lead, uranium and radium are considered. Based on a review of toxic waste hazard-measures and risk assessment studies, a general expression is developed for quantifying health risks imposed by the introduction of toxic materials to components of the total environment. This general measure deals with long term interactions within and between the internal human environment and the external biogeochemical environment. Health hazards are expressed as dose factors which convert environmental concentrations into a corresponding dose field (organ doses in rad for radionuclides; daily intake for toxic elements). The dose field is translated into population health risk expressed as lifetime cancer risk for carcinogens and average blood levels for other toxins. The landscape cell (or prism) is presented as a tool for visualizing and mapping toxic material cycles near the crustal surface. The overall process is incorporated in the GEOTOX code which is a geochemical systems model for describing the dynamics of crustal toxins within a landscape and the resulting health risks. GEOTOX is used to investigate the response of regional landscapes to increased soil and rock inventories of 238 U, 226 Ra, arsenic and lead. It is found that each decay series of element imposes a hazard by its behavior in the total environment that can not be quantified by a similar measure of toxicity

  10. Uranium favorability of tertiary sedimentary rocks of the western Okanogan highlands and of the upper Columbia River valley, Washington. [Measurement and sampling of surface sections, collection of samples from isolated outcrops, and chemical and mineralogical analyses of samples; no known uranium deposits

    Energy Technology Data Exchange (ETDEWEB)

    Marjaniemi, D.K.; Robins, J.W.

    1975-08-01

    Tertiary sedimentary rocks in the northern portions of the western Okanogan highlands and in the upper Columbia River valley were investigated during a regional study to determine the favorability for potential uranium resources of the Tertiary sedimentary rocks of northeastern Washington. This project involved measurement and sampling of surface sections, collection of samples from isolated outcrops, and chemical and mineralogical analyses of samples. No portion of the project area of this report is rated of high or of medium favorability for potential uranium resources. Low favorability ratings are given to Oroville, Tonasket, and Pine Creek areas of the Okanogan River valley; to the Republic graben; and to the William Lakes, Colville, and Sheep Creek areas of the upper Columbia River valley. All these areas contain some fluvial, poorly sorted feldspathic or arkosic sandstones and conglomerates. These rocks are characterized by very low permeability and a consistently high siliceous matrix suggesting very low initial permeability. There are no known uranium deposits in any of these areas, and low level uranium anomalies are rare.

  11. Modeling and Inversion of three-dimensional crustal structures beneath the Pyrenees and their foreland basins based upon geological, gravimetric and seismological data

    Science.gov (United States)

    Spangenberg, Hannah; Chevrot, Sébastien; Courrioux, Gabriel; Guillen, Antonio

    2017-04-01

    Our goal is to obtain a three-dimensional (3D) model of mass density and seismic velocities beneath the Pyrenees and their foreland basins (Aquitaine and Ebro basins), which accounts for all the geological and geophysical information available for that region. This model covers the whole mountain range going from the Atlantic Ocean to the Mediterranean Sea, and from the Iberian range to the Massif Central. The model is described by different units: the lower, middle, and upper crusts, the accretionary prism, and the consolidated and unconsolidated sediment layers. Furthermore, a sub-continental, serpentinized European mantle is introduced to describe the exhumed mantle bodies which are responsible for the positive Bouguer gravity anomalies in the western Pyrenees. We build a first 3D model using all the geological information: drill-hole surveys, seismic sections, and the geological map. We use the potential field method implemented in Geomodeler to interpolate these geological data. However, these data are too sparse to build a model that explains seismic travel times or gravimetric data, especially the Labourd and the St. Gaudens Bouguer gravity anomalies. In addition, inconsistencies between the different data sets exist. We thus add by trial and error additional data points, comparing modeled and observed Bouguer gravimetric anomalies. The result of this procedure is a 3D geological model that respects the geological data and explains the measured Bouguer gravimetric anomalies. In a second step, we use this model to determine the average density and seismic velocities inside each geological unit assuming uniform layers. To constrain the seismic velocities we use travel time picks extracted from the bulletin of the Pyrenean seismicity released by the Observatoire Midi Pyrenées. In a third step, we use this 3D a priori model in a Monte Carlo inversion to invert jointly gravimetric data and seismic travel times from the bulletin. This probabilistic approach

  12. 7 CFR 1030.2 - Upper Midwest marketing area.

    Science.gov (United States)

    2010-01-01

    ... 7 Agriculture 9 2010-01-01 2009-01-01 true Upper Midwest marketing area. 1030.2 Section 1030.2 Agriculture Regulations of the Department of Agriculture (Continued) AGRICULTURAL MARKETING SERVICE (Marketing Agreements and Orders; Milk), DEPARTMENT OF AGRICULTURE MILK IN THE UPPER MIDWEST MARKETING AREA Order...

  13. Upper limb function in adults with Duchenne muscular dystrophy

    NARCIS (Netherlands)

    B. Bartels (Bart); R.F. Pangalila (Robert); M.P. Bergen (Michael); N.A.M. Cobben (Nicolle); H.J. Stam (Henk); M.E. Roebroeck (Marij)

    2011-01-01

    textabstractTo determine upper limb function and associated factors in adults with Duchenne muscular dystrophy. Design: Cross-sectional study. Subjects: A sample of 70 men with Duchenne muscular dystrophy (age range 20-43 years). Methods: General motor function and, in particular, upper limb distal

  14. Upper airway evaluation

    International Nuclear Information System (INIS)

    Hoffman, E.A.; Gefter, W.B.; Schnall, M.; Nordberg, J.; Listerud, J.; Lenkinski, R.E.

    1988-01-01

    The authors are evaluating upper-airway sleep disorders with magnetic resonance (MR) imaging and x-ray cine computed tomography (CT). Fixed structural anatomy is visualized with multisection spin-echo MR imaging, the dynamic component with cine CT. Unique aspects of the study are described in this paper

  15. Subsidence history, crustal structure, and evolution of the Somaliland-Yemen conjugate margin

    Science.gov (United States)

    Ali, M. Y.; Watts, A. B.

    2013-04-01

    We have used biostratigraphic data from deep exploration wells to determine the tectonic subsidence history of the Somaliland (northwestern Somalia)-Yemen conjugate margin, a poorly known margin in the central part of the Gulf of Aden. Bathymetry and magnetic anomaly data suggest the Gulf of Aden is a young feature that formed following the rifting apart and breakup of the African and Arabian plates ~32 Ma. Our tectonic subsidence data suggest, however, that the present-day Gulf of Aden developed on an earlier Mesozoic rift system. The oldest episode of rifting initiated at ~156 Ma and lasted for ~10 Ma and had a NW-SE trend. We interpret the rift as a late stage event associated with the breakup of Gondwana and the separation of Africa and Madagascar. At ~80 Ma, there is evidence of an intermediate rift event which correlates with a rapid increase in spreading rate on the ridges separating the African and Indian and African and Antarctica plates and a contemporaneous slowing down of Africa's plate motion. The combined effect of all three rifting events has been to thin the crust and upper mantle by up to a factor of 2. The amount of thinning deduced from the wells is in accord with the crustal structure inferred from available seismic refraction data and process-oriented gravity and flexure modeling. The margin is asymmetric with a steeper gradient in the Moho on the Yemen side than the Somaliland side. The main discrepancy is on the Yemen side where the gravity-derived Moho is 10 km deeper than the well-derived Moho. We attribute the discrepancy to the addition of material at the base of the crust since rifting, possibly magma sourced from the Afar plume.

  16. Pb and O isotope systematics in granulite facies xenoliths, French Massif Central: Implications for crustal processes

    International Nuclear Information System (INIS)

    Downes, H.; Kempton, P.D.; Harmon, R.S.; Briot, D.; Leyreloup, A.F.

    1991-01-01

    Pb and O isotope data are represented for a suite of granulite facies xenoliths found within Tertiary alkaline volcanic rocks of the Massif Central, France. The suite consists of ultramafic and mafic cumulates, metagabbros which are considered to represent basic liquids, felsic meta-igneous lithologies (charnockites) and metasediments. Ranges of δ 18 O values are +6.9 to +9.8per mille for mafic xenoliths, +9.3 to +10.2per mille for felsic meta-igneous samples and +6.1 to +11.8per mille for the metasediments. By comparison, δ 18 O values for mantle peridotites from the same region range from +5.1 to +6.9per mille, whilst local Hercynian granitoids vary from +8.6 to +12.0per mille. The 206 Pb/ 204 Pb ratios of the granulite xenoliths are between 17.77 and 19.19, 207 Pb/ 204 Pb ratios vary from 15.51 to 15.69, and 208 Pb/ 204 Pb ratios range from 38.07 to 40.07. In general, metasedimentary granulites have the more radiogenic Pb isotope compositions, whereas mafic meta-igneous samples are less radiogenic. These isotopic characteristics can be explained as the result of the interaction of mafic magmas with the metasedimentary crust into which they intruded. The release of heat also provoked melting of the more fusible parts of the lower crust and led to the formation of late-orogenic Hercynian granitoids. However, an additional component which provides less radiogenic Pb is also needed in the source of the granitoids; this may be the felsic meta-igneous xenoliths or middle/upper crustal gneisses. (orig.)

  17. Crustal structure across Tancheng-Lujiang fault belt in East China

    Science.gov (United States)

    Zhang, Zhongjie; Xu, Tao; Tian, Xiaobo; Teng, Jiwen; Bai, Zhiming

    2013-04-01

    Tancheng-Lujiang (T-L) fault extends more than 3,000km in the eastern China continent. T-L fault is closely related to strong earthquake occurrences such as Ms 7.8 Tangshan earthquake in 1976, basin development with rich oil/gas reserves and mineral resource concentration. The mechanism to form this fault is still in dispute. The proposed models include: post-collisional offset model (Okay and Sengor, 1992); indenter model (Yin and Nie, 1994); thrust model (Li, 1994); North China Craton penetration into South China model (Yokoyama et al., 2001) and Scissor collision model (Zhang et al., 2002, 2006). T-L fault is characterized with its segmentation, while the south segment is favored to understand the deep continental subduction and ultra-high pressure rocks extrusion from the collision between the convergence between Yangtze and North China Craton. In order to provide constraints on the evaluation of the proposed tectonic models, we carried out a 400-km-long wide-angle seismic profiling across the southern segment of the T-L fault. Here we present seismic P-wave data and the interpretation results. Seismic events of reflection and refraction from Moho discontinuity and other intracrustal reflections are remarkably observed with high signal/noise ratio. Crustal P-wave velocity model was reconstructed with forward modelling inversion, and T-L fault penetrates the whole crust, with gentle penetration angle in the upper crust, but very steep angle in the lower crust, which are probably seismic indicators of two phases of lateral escaping to accommodate the collision and extrusion of continental crust of the Yangtze block.

  18. Crustal structural survey for the state of Minas Gerais, Brazil, utilizing geophysical and geological information

    International Nuclear Information System (INIS)

    Haralyi, N.L.E.; Hasui, Y.; Mioto, J.A.; Hamza, V.M.

    1985-01-01

    Gravity, Magnetic (airborne, Magnet and Magsat), heat flow and seismicity available data for the state of Minas Gerais and adjacent regions is here analyzed, discussed and integrated with geologic information. The Late Archean crustal structure is defined as blocks of granite-greenstone separated by belts of high-grade terrains. The belts in eastern and southern Minas Gerais represent the lower parts of the Vitoria, Sao Paulo and Parana Blocks, which were up thrusted over the Brasilia Block through low-angle ductile simple shear Zones. That regional structure is cut and somewhat displaced by NW, ENE, NE and Ns fault sets. These faults are mostly related to the Transamazonian Event, and their geological expression appears to be as high-angle ductile simple shear zones. The development of the Middle/upper proterozoic folded sequences, the incidence of the Brasiliano/Uruacuano thermo tectonic events and the geometry of the Sao Francisco Craton were highly influenced by the preexistent weakness zones. The high-grade terrains, the borders of the Brasilia Block and the Transamazonian lineaments have been preferentially affected. The tectono-magmatic manifestations of the Wealdenian Reactivation, related to the opening of the Atlantic Ocean, occurred mostly among the uplifted zones (Alto Paranaiba Uplift) that developed partially until the rift stage (Mantiqueira Uplift). These processes clearly reveal the influence of the old structures of the state of Minas Gerais. The Mantiqueira Uplift presents a more accentuated seismic activity and thermal flow regime than the neighboring regions, so corresponding to the present less stable area of Minas Gerais. (DJM) [pt

  19. Crustal structure of the rifted volcanic margins and uplifted plateau of Western Yemen from receiver function analysis

    Science.gov (United States)

    Ahmed, Abdulhakim; Tiberi, Christel; Leroy, Sylvie; Stuart, Graham W.; Keir, Derek; Sholan, Jamal; Khanbari, Khaled; Al-Ganad, Ismael; Basuyau, Clémence

    2013-06-01

    We analyse P-wave receiver functions across the western Gulf of Aden and southern Red Sea continental margins in Western Yemen to constrain crustal thickness, internal crustal structure and the bulk seismic velocity characteristics in order to address the role of magmatism, faulting and mechanical crustal thinning during continental breakup. We analyse teleseismic data from 21 stations forming the temporary Young Conjugate Margins Laboratory (YOCMAL) network together with GFZ and Yemeni permanent stations. Analysis of computed receiver functions shows that (1) the thickness of unextended crust on the Yemen plateau is ˜35 km; (2) this thins to ˜22 km in coastal areas and reaches less than 14 km on the Red Sea coast, where presence of a high-velocity lower crust is evident. The average Vp/Vs ratio for the western Yemen Plateau is 1.79, increasing to ˜1.92 near the Red Sea coast and decreasing to 1.68 for those stations located on or near the granitic rocks. Thinning of the crust, and by inference extension, occurs over a ˜130-km-wide transition zone from the Red Sea and Gulf of Aden coasts to the edges of the Yemen plateau. Thinning of continental crust is particularly localized in a <30-km-wide zone near the coastline, spatially co-incident with addition of magmatic underplate to the lower crust, above which on the surface we observe the presence of seaward dipping reflectors (SDRs) and thickened Oligo-Miocene syn-rift basaltic flows. Our results strongly suggest the presence of high-velocity mafic intrusions in the lower crust, which are likely either synrift magmatic intrusion into continental lower crust or alternatively depleted upper mantle underplated to the base of the crust during the eruption of the SDRs. Our results also point towards a regional breakup history in which the onset of rifting was synchronous along the western Gulf of Aden and southern Red Sea volcanic margins followed by a second phase of extension along the Red Sea margin.

  20. 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

    Full Text Available The lower plate is the dominant agent in modern convergent margins characterized by active subduction, as negatively buoyant oceanic lithosphere sinks into the asthenosphere under its own weight. This is a strong plate-driving force because the slab-pull force is transmitted through the stiff sub-oceanic lithospheric mantle. As geological and geochemical data seem inconsistent with the existence of modern-style ridges and arcs in the Archaean, a periodically-destabilized stagnant-lid crust system is proposed instead. Stagnant-lid intervals may correspond to periods of layered mantle convection where efficient cooling was restricted to the upper mantle, perturbing Earth's heat generation/loss balance, eventually triggering mantle overturns. Archaean basalts were derived from fertile mantle in overturn upwelling zones (OUZOs, which were larger and longer-lived than post-Archaean plumes. Early cratons/continents probably formed above OUZOs as large volumes of basalt and komatiite were delivered for protracted periods, allowing basal crustal cannibalism, garnetiferous crustal restite delamination, and coupled development of continental crust and sub-continental lithospheric mantle. Periodic mixing and rehomogenization during overturns retarded development of isotopically depleted MORB (mid-ocean ridge basalt mantle. Only after the start of true subduction did sequestration of subducted slabs at the core-mantle boundary lead to the development of the depleted MORB mantle source. During Archaean mantle overturns, pre-existing continents located above OUZOs would be strongly reworked; whereas OUZO-distal continents would drift in response to mantle currents. The leading edge of drifting Archaean continents would be convergent margins characterized by terrane accretion, imbrication, subcretion and anatexis of unsubductable oceanic lithosphere. As Earth cooled and the background oceanic lithosphere became denser and stiffer, there would be an increasing

  1. Crustal Structure of the Andean Foreland in Northern Argentina: Results From Data-Integrative Three-Dimensional Density Modeling

    Science.gov (United States)

    Meeßen, C.; Sippel, J.; Scheck-Wenderoth, M.; Heine, C.; Strecker, M. R.

    2018-02-01

    Previous thermomechanical modeling studies indicated that variations in the temperature and strength of the crystalline crust might be responsible for the juxtaposition of domains with thin-skinned and thick-skinned crustal deformation along strike the foreland of the central Andes. However, there is no evidence supporting this hypothesis from data-integrative models. We aim to derive the density structure of the lithosphere by means of integrated 3-D density modeling, in order to provide a new basis for discussions of compositional variations within the crust and for future thermal and rheological modeling studies. Therefore, we utilize available geological and geophysical data to obtain a structural and density model of the uppermost 200 km of the Earth. The derived model is consistent with the observed Bouguer gravity field. Our results indicate that the crystalline crust in northern Argentina can be represented by a lighter upper crust (2,800 kg/m3) and a denser lower crust (3,100 kg/m3). We find new evidence for high bulk crustal densities >3,000 kg/m3 in the northern Pampia terrane. These could originate from subducted Puncoviscana wackes or pelites that ponded to the base of the crystalline crust in the late Proterozoic or indicate increasing bulk content of mafic material. The precise composition of the northern foreland crust, whether mafic or felsic, has significant implications for further thermomechanical models and the rheological behavior of the lithosphere. A detailed sensitivity analysis of the input parameters indicates that the model results are robust with respect to the given uncertainties of the input data.

  2. Magmatism and crustal extension: Constraining activation of the ductile shearing along the Gediz detachment, Menderes Massif (western Turkey)

    Science.gov (United States)

    Rossetti, Federico; Asti, Riccardo; Faccenna, Claudio; Gerdes, Axel; Lucci, Federico; Theye, Thomas

    2017-06-01

    The Menderes Massif of western Turkey is a key area to study feedback relationships between magma generation/emplacement and activation of extensional detachment tectonics. Here, we present new textural analysis and in situ U-(Th)-Pb titanite dating from selected samples collected in the transition from the undeformed to the mylonitized zones of the Salihli granodiorite at the footwall of the Neogene, ductile-to-brittle, top-to-the-NNE Gediz-Alaşheir (GDF) detachment fault. Ductile shearing was accompanied by the fluid-mediated sub-solidus transformation of the granodiorite to orthogneiss, which occurred at shallower crustal levels and temperatures compatible with the upper greenschist-to-amphibolite facies metamorphic conditions (530-580 °C and P system ages during fluid-assisted syn-tectonic re-crystallisation in the transition from magma crystallization and emplacement (at 16-17 Ma) to the syn-tectonic, solid-state shearing (at 14-15 Ma). A minimum time lapse of ca. 1-2 Ma is then inferred between the crustal emplacement of the Salihli granodiorite and nucleation of the ductile extensional shearing along the Gediz detachment. The reconstruction of the cooling history of the Salihli granodiorite documents a punctuated evolution dominated by two episodes of rapid cooling, between 14 Ma and 12 Ma ( 100 °C/Ma) and between 3 and 2 Ma ( 105 °C/Ma). We relate the first episode to nucleation and development of post-emplacement of ductile shearing along the GDF and the second to brittle high-angle faulting, respectively. Our dataset suggests that in the Menderes Massif the activation of ductile extension was a consequence, rather than the cause, of magma emplacement in the extending crust.

  3. High resolution crustal structure for the region between the Chilenia and Cuyania terrane above the Pampean flat slab of Argentina from local receiver function and petrological analyses

    Science.gov (United States)

    Ammirati, J. B.; Alvarado, P. M.; Pérez, S. B.; Beck, S. L.; Porter, R. C.; Zandt, G.

    2015-12-01

    Jean-Baptiste Ammirati 1,Sofía Perez 1, Patricia Alvarado 1, Susan L. Beck 2, Ryan Porter 3 and George Zandt 2(1) CIGEOBIO-CONICET, Universidad Nacional de San Juan, Argentina (2) The University of Arizona, USA (3) Northern Arizona University, USA At ~31ºS, The subduction of the Nazca plate under the South American plate presents along-strike variations of its dip angle referred to the Chilean-Pampean flat slab. Geological observations suggest that the regional crustal structure is inherited from the accretion of different terranes at Ordovician times and later reactivated during Andean compression since Miocene. Geophysical observations confirmed that the structure is extending in depth with décollement levels that accommodate crustal shortening in the region. In order to get a better insight on the shallow tectonics we computed high frequency local receiver functions from slab seismicity (~100 km depth). Local earthquakes present a higher frequency content that permits a better vertical resolution. Using a common conversion point (CCP) stacking method we obtained cross sections showing high-resolution crustal structure in the western part of the Pampean flat slab region, at the transition between the Precordillera and the Frontal Cordillera. Our results show a well-defined structure and their lateral extent for both units down to 80 km depth. In good agreement with previous studies, our higher resolution images better identify very shallow discontinuities putting more constraints on the relationships with the regional structural geology. Recent petrological analyses combined with RF high-resolution structure also allow us to better understand the regional crustal composition. Interestingly, we are able to observe a shifting structure beneath the Uspallata-Calingasta Valley, highlighting the differences in terms of crustal structure between the Precordillera and the Frontal Cordillera. Previously determined focal mechanisms in the region match well this

  4. Upper Limb Absence : Predictors of Work Participation and Work Productivity

    NARCIS (Netherlands)

    Postema, Sietke G; Bongers, Raoul M; Brouwers, Michael A; Burger, Helena; Norling-Hermansson, Liselotte M; Reneman, Michiel F; Dijkstra, Pieter U; van der Sluis, Corry K

    OBJECTIVES: To analyze work participation, work productivity, contributing factors, and physical work demands of individuals with upper limb absence (ULA). DESIGN: Cross-sectional study: postal survey (response rate, 45%). SETTING: Twelve rehabilitation centers and orthopedic workshops.

  5. A crustal-upper mantle model for southeastern Sicily (Italy) from the integration of petrologic and geophysical data

    Science.gov (United States)

    Manuella, Fabio Carmelo; Brancato, Alfonso; Carbone, Serafina; Gresta, Stefano

    2013-05-01

    An interdisciplinary approach is proposed to investigate the structure and composition of the Permo-Triassic basement of the Hyblean Plateau and Sicily Channel. Comparisons of published data on peridotites and spinels from different geodynamic settings, and new data on Hyblean spinels, reveal the affinity of the Hyblean basement with an ultra-slow spreading oceanic lithosphere, rather than with the Africa continental plate. Similar results derive from volcanic rocks of the studied area, whose Nb/Yb vs. Th/Yb ratio hints at their affinity with the MORB-OIB array, even excluding any possible contamination with continental crust lithologies, unlike North Africa lavas. The comparison of He isotopic ratios from Hyblean Plateau and Sicily Channel highlights their similarity with values measured in fluids emitted from the Rainbow and Logatchev hydrothermal fields in Mid-Atlantic Ridge. Based on petrologic and geochemical evidence for the oceanic nature of the Permo-Triassic basement in southeastern Sicily, and the occurrence of serpentinized harzburgite xenoliths in Hyblean diatremes, the P-wave velocity model proposed for the investigated area is used to estimate lithospheric pressure, density, degree of serpentinization and magnetic susceptibility also considering both abyssal and ophiolitic serpentinites. The resulting values suggest the presence of peridotites affected by different degrees of serpentinization (35-100 vol.%) ranging to a depth of 8-19 km. As a whole, combined seismic, gravimetric and magnetic data indicate the presence of a marked anomaly at a depth of about 19 km. As a consequence, we consider the Moho discontinuity as a serpentinization front, by fixing the relative top at a depth of 19 km. Our results suggest that the oceanic lithospheric model for southeastern Sicily could be broadened to the Sicily Channel, which is possibly correlated to the adjacent Ionian oceanic basin, inferred as belonging to the Oman-Iraq-Levantine-Sicily seaway.

  6. Upper mantle flow in the western Mediterranean

    Energy Technology Data Exchange (ETDEWEB)

    Panza, G F [Dipartimento di Scienze della Terra, Universita degli Studi di Trieste, Trieste (Italy) and Abdus Salam International Centre for Theoretical Physics, Trieste (Italy); Raykova, R [Geophysical Institute of BAS, Sofia (Bulgaria) and Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna (Italy); Carminati, E; Doglioni, C [Dipartimento di Scienze della Terra, Universita degli Studi di Trieste, Trieste (Italy)

    2006-07-15

    Two cross-sections of the western Mediterranean Neogene-to-present backarc basin are presented, in which geological and geophysical data of the Transmed project are tied to a new shear-wave tomography. Major results are i) the presence of a well stratified upper mantle beneath the older African continent, with a marked low-velocity layer between 130-200 km of depth; ii) the dilution of this layer within the younger western Mediterranean backarc basin to the north, and iii) the easterly raising of a shallower low-velocity layer from about 140 km to about 30 km in the Tyrrhenian active part of the backarc basin. These findings suggest upper mantle circulation in the western Mediterranean backarc basin, mostly easterly-directed and affecting the boundary between upper asthenosphere (LVZ) and lower asthenosphere, which undulates between about 180 km and 280 km. (author)

  7. Upper mantle flow in the western Mediterranean

    International Nuclear Information System (INIS)

    Panza, G.F.; Raykova, R.; Carminati, E.; Doglioni, C.

    2006-07-01

    Two cross-sections of the western Mediterranean Neogene-to-present backarc basin are presented, in which geological and geophysical data of the Transmed project are tied to a new shear-wave tomography. Major results are i) the presence of a well stratified upper mantle beneath the older African continent, with a marked low-velocity layer between 130-200 km of depth; ii) the dilution of this layer within the younger western Mediterranean backarc basin to the north, and iii) the easterly raising of a shallower low-velocity layer from about 140 km to about 30 km in the Tyrrhenian active part of the backarc basin. These findings suggest upper mantle circulation in the western Mediterranean backarc basin, mostly easterly-directed and affecting the boundary between upper asthenosphere (LVZ) and lower asthenosphere, which undulates between about 180 km and 280 km. (author)

  8. Cesarean Sections

    Science.gov (United States)

    ... birth after a C-section, called a VBAC ) Emergency C-Sections Some C-sections are unexpected emergency ... side to nurse or using the clutch (or football) hold can take the pressure off your abdomen. ...

  9. Fluvial archives, a valuable record of vertical crustal deformation

    Science.gov (United States)

    Demoulin, A.; Mather, A.; Whittaker, A.

    2017-06-01

    The study of drainage network response to uplift is important not only for understanding river system dynamics and associated channel properties and fluvial landforms, but also for identifying the nature of crustal deformation and its history. In recent decades, geomorphic analysis of rivers has proved powerful in elucidating the tectonic evolution of actively uplifting and eroding orogens. Here, we review the main recent developments that have improved and expanded qualitative and quantitative information about vertical tectonic motions (the effects of horizontal deformation are not addressed). Channel long profiles have received considerable attention in the literature, and we briefly introduce basic aspects of the behaviour of bedrock rivers from field and numerical modelling perspectives, before describing the various metrics that have been proposed to identify the information on crustal deformation contained within their steady-state characteristics. Then, we review the literature dealing with the transient response of rivers to tectonic perturbation, through the production of knickpoints propagating through the drainage network. Inverse modelling of river profiles for uplift in time and space is also shown to be very effective in reconstructing regional tectonic histories. Finally, we present a synthetic morphometric approach for deducing the tectonic record of fluvial landscapes. As well as the erosional imprint of tectonic forcing, sedimentary deposits, such as fluvial terrace staircases, are also considered as a classical component of tectonic geomorphology. We show that these studies have recently benefited from rapid advances in dating techniques, allowing more reliable reconstruction of incision histories and estimation of incision rates. The combination of progress in the understanding of transient river profiles and larger, more rigorous data sets of terrace ages has led to improved understanding of river erosion and the implications for terrace

  10. Crustal and deep seismicity in Italy (30 years after

    Directory of Open Access Journals (Sweden)

    G. Selvaggi

    1997-06-01

    Full Text Available The first modern studies of seismicity in Italy date back to the late 60's and early 70's. Although with a sparse seismic network available and only a few telemetered short-period stations, significant studies were carried out that outlined the main features of Italian seismicity (see, e.g., Boschi et al., 1969. Among these studies, one of the most important achievements was the reconnaissance of a Wadati-Benioff zone in Southern Tyrrhenian, described for the first time in detail in the papers of Caputo et al.(1970, 1973. Today, after three decades of more and more detailed seismological monitoring of the Italian region and tens of thousands earthquakes located since then, the knowledge of the earthquake generation processes in our country is much improved, although some of the conclusions reached in these early papers still hold. These improvements were made possible by the efforts of many institutions and seismologists who have been working hard to bring seismological research in Italy to standards of absolute quality, under the pivoting role of the Istituto Nazionale di Geofisica (ING. From the relocation of about 30000 crustal earthquakes and detailed studies on intermediate and deep shocks carried out in the last few years, we show that seismic release in peninsular Italy is only weakly related to the Africa-Eurasia convergence, but rather is best explained by the existence of two separate subduction/collision arcs (Northern Apennines and Southern Apennines-Calabria-Sicily. The width of the deforming belt running along peninsular Italy is 30 to 60 km, it is broader in the north than in the south, and the two arcs are separated by a region of more distributed deformation and stress rotations in the Central Apennines. Along the belt, the reconnaissance of regions of continuous and weak release of seismic energy, adjacent to fault areas which are currently «locked» (and therefore are the best candidates for future earthquakes is another

  11. Magnetotelluric images of deep crustal structure of the Rehai geothermal field near Tengchong, southern China

    Science.gov (United States)

    Bai, Denghai; Meju, Maxwell A.; Liao, Zhijie

    2001-12-01

    Broadband (0.004-4096s) magnetotelluric (MT) soundings have been applied to the determination of the deep structure across the Rehai geothermal field in a Quaternary volcanic area near the Indo-Eurasian collisional margin. Tensorial analysis of the data show evidence of weak to strong 3-D effects but for approximate 2-D imaging, we obtained dual-mode MT responses for an assumed strike direction coincident with the trend of the regional-scale faults and with the principal impedance azimuth at long periods. The data were subsequently inverted using different approaches. The rapid relaxation inversion models are comparable to the sections constructed from depth-converted invariant impedance phase data. The results from full-domain 2-D conjugate-gradient inversion with different initial models are concordant and evoke a picture of a dome-like structure consisting of a conductive (50-1000 Ωm) cap which is about 5-6km thick in the central part of the known geothermal field and thickens outwards to about 15-20km. The anomalous structure rests on a mid-crustal zone of 20-30 Ωm resistivity extending down to about 25km depth where there appears to be a moderately resistive (>30 Ωm) substratum. The MT images are shown to be in accord with published geological, isotopic and geochemical results that suggested the presence of a magma body underneath the area of study.

  12. Upper urinary tract tumors

    DEFF Research Database (Denmark)

    Gandrup, Karen L; Nordling, Jørgen; Balslev, Ingegerd

    2014-01-01

    BACKGROUND: Computed tomography urography (CTU) is used widely in the work-up of patients with symptoms of urinary tract lesions. Preoperative knowledge of whether a tumor is invasive or non-invasive is important for the choice of surgery. So far there are no studies about the distinction...... of invasive and non-invasive tumors in ureter and renal pelvis based on the enhancement measured with Hounsfield Units. PURPOSE: To examine the value of CTU using split-bolus technique to distinguish non-invasive from invasive urothelial carcinomas in the upper urinary tract. MATERIAL AND METHODS: Patients...... obtained at CTU could distinguish between invasive and non-invasive lesions. No patients had a CTU within the last year before the examination that resulted in surgery. CONCLUSION: A split-bolus CTU cannot distinguish between invasive and non-invasive urothelial tumors in the upper urinary tract...

  13. Different Phases of Earthquake Cycle Reflected in GPS Measured Crustal Deformations along the Andes

    Science.gov (United States)

    Khazaradze, G.; Klotz, J.

    2001-12-01

    largest ever recorded earthquake on the earth. To properly interpret given observations, we developed the fully \\textsc{3D} Andean Elastic Dislocation Model (AEDM), which is used to explain the dominant inter-seismic signal. The subtraction of the AEDM predicted deformation rates from the observations leads towards the "filtered" residual velocity field, that can be used to highlight, for example, the post-seismic deformation effects. Also, in the central section of the SAGA network, the residual velocity field indicates the existence of more long-term (i.e. geologic) deformations. In summary, the changing spatial-temporal pattern of GPS measured crustal deformation rates along the central and southern Andes is governed by the relative importance of different phases of earthquake deformation cycle.

  14. Crustal structure of an exhumed IntraCONtinental Sag (ICONS): the Mekele Basin in Northern Ethiopia.

    Science.gov (United States)

    Alemu, T. B.; Abdelsalam, M. G.

    2017-12-01

    The Mekele Sedimentary Basin (MSB) in Ethiopia is a Paleozoic-Mesozoic IntraCONtinental Sag (ICONS) exposed due to Cenozoic domal and rift flank uplift associated with the Afar mantle plume and Afar Depression (AD). ICONS are formed over stable lithosphere, and in contrast to rift and foreland basins, show circular-elliptical shape in map view, saucer shaped in cross section, and concentric gravity minima. Surface geological features of the MSB have been shown to exhibit geologic characteristics similar to those of other ICONS. We used the World Gravity Map (WGM 2012) data to investigate subsurface-crustal structure of the MSB. We also used 2D power spectrum analysis and inversion of the gravity field to estimate the Moho depth. Our results show the Bouguer anomalies of the WGM 2012 ranges between 130 mGal and - 110 mGal with the highest values within the AD. Despite the effect of the AD on the gravity anomalies, the MSB is characterized by the presence of gravity low anomaly that reaches in places -110 mGal, especially in its western part. The Moho depth estimates, from both spectral analysis and inversion of the gravity data, is between 36 and 40 km depth over most of the western and southern margins of the MSB. However, as the AD is approached, in the eastern margins of the MSB, crustal thickness estimates are highly affected by the anomalously thin and magmatic segment of the AD, and the Moho depth range between 30 and 25 km. Our results are consistent with that of seismic studies in areas far from the MSB, but within the Northwestern Ethiopian Plateau where the MSB is located. Those studies have reported an abrupt decrease in Moho depth from 40 km beneath the Northwestern plateau, to 20 km in the adjacent AD. Though the MSB is small (100 kmX100 km) compared to other ICONS, and affected by the neighboring AD, it is characterized by elliptical gravity minima and a relatively thicker crust that gradually thickens away from the rift. In addition, seismic imaging

  15. Crustal seismicity and active fault system in the SE of Romania

    International Nuclear Information System (INIS)

    Raileanu, V; Bala, A.; Radulian, M.; Popescu, E.; Mateciuc, D.; Popa, M.; Dinu, C.; Diaconescu, V.

    2007-01-01

    Romania is known as a country with a high seismicity located in the Vrancea region where 2-3 strong intermediate depth earthquakes/century generate great damages and casualties. A moderate crustal seismicity is also observed in other zones of the country, with events having a moderate magnitude but sometimes with important economic and social effects on the locale scale. The crustal seismogenic zones are located in front of the Eastern Carpathian Bend, South Carpathians, Dobrogea, Banat, Crisana and Maramures regions. The SE part of Romania comprises some of the most active crustal seismic sources that generated earthquakes up to Mw=6.5 concentrated in more zones, namely: Vrancea crustal domain, E Vrancea zone that is overlapped on the Focsani basin, Barlad and Predobrogean depressions along with the North Dobrogea Orogen, Intramoesian and Shabla (Bulgaria) zones and Fagaras-Campulung-Sinaia zone. (authors)

  16. 2-D Crustal thermal structure along Thuadara–Sindad DSS profile ...

    Indian Academy of Sciences (India)

    Thuadara–Sindad Deep Seismic Sounding (DSS) profile which runs almost in the N–S direction ... These studies include four Deep Seis- ... Geology and tectonic frame work ..... alous high-velocity layer at shallow crustal depths in the.

  17. 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...

  18. The Chaotic Terrains of Mercury: A History of Large-Scale Crustal Devolatilization

    Science.gov (United States)

    Rodriguez, J. A. P.; Domingue, D. L.; Berman, D. C.; Kargel, J. S.; Baker, V. R.; Teodoro, L. F.; Banks, M.; Leonard, G.

    2018-05-01

    Approximately 400 million years after the Caloris basin impact, extensive collapse formed Mercury's chaotic terrains. Collapse likely resulted from regionally elevated heat flow devolatilizing crustal materials along NE and NW extensional faults.

  19. Further Mapping of Mercury's Crustal Magnetic Field Using MESSENGER Magnetometer Data

    Science.gov (United States)

    Hood, L. L.; Oliveira, J. S.; Spudis, P. D.; Galluzzi, V.

    2018-05-01

    Further mapping of Mercury's crustal magnetic field shows that anomalies are associated with some impact craters but not others. Differences in impactor composition (e.g., iron content) may be indicated by this new observation.

  20. A preliminary investigation of vertical crustal movements in the United Kingdom in the context of subsurface nuclear waste isolation for the Department of the Environment

    International Nuclear Information System (INIS)

    1981-03-01

    The report falls under the headings: vertical crustal movements - a manifestation of intraplate geological processes (reports of vertical crustal movements observed by geodetic levelling in intraplate environments; vertical crustal movements and the geological record; possible causes of vertical crustal movements); an investigation of recent crustal movements in a test area of the United Kingdom by comparison of geodetic levelling records; vertical crustal movements and the isolation of nuclear waste in intraplate geological systems (conventional methods of site appraisal - a perspective of geological hazard assessment; the role of vertical crustal movements as a tool for rationalisation of hazard assessment, site selection and the assessment of future geological change); research options. (U.K.)

  1. The Jeffers Brook diorite-granodiorite pluton: style of emplacement and role of volatiles at various crustal levels in Avalonian appinites, Canadian Appalachians

    Science.gov (United States)

    Pe-Piper, Georgia; Piper, David J. W.

    2018-04-01

    Small appinite plutons ca. 610 Ma outcrop in the peri-Gondwanan Avalon terrane of northern Nova Scotia, with different structural levels exposed. Field mapping shows that the Jeffers Brook pluton is a laccolith emplaced along an upper crustal thrust zone, likely in a dilational jog in a regional dextral strike-slip system. The oldest rocks are probably mafic sills, which heated the area facilitating emplacement of intermediate magmas. Cross-cutting relationships show that both mafic and intermediate magmas were supplied throughout the history of pluton emplacement. The modal composition, mineral chemistry, and bulk chemistry of gabbro, diorite, tonalite, granodiorite, and granite have been studied in the main plutonic phases, dykes, and sills, and mafic microgranular enclaves. As with the type appinites in the Scottish Caledonides, the pluton shows evidence of high water content: the dominance of hornblende, locally within pegmatitic texture; vesicles and irregular felsic patches in enclaves; and late aplite dykes. Analyzed mafic microgranular enclaves are geochemically similar to larger diorite bodies in the pluton. Tonalite-granodiorite is distinct from the diorite in trace-element geochemistry and radiogenic isotopes. Elsewhere to the east, similar rocks of the same age form vertically sheeted complexes in major shear zones; hornblende chemistry shows that they were emplaced at a deeper upper crustal level. This implies that little of the observed geochemical variability in the Jeffers Brook pluton was developed within the pluton. The general requirements to form appinites are proposed to be small magma volumes of subduction-related magmas that reach the upper crust because of continual heating by mafic magmas moving through strike-slip fault pathways and trapping of aqueous fluids rather than venting through volcanic activity.

  2. Seismic cycle feedbacks in a mid-crustal shear zone

    Science.gov (United States)

    Melosh, Benjamin L.; Rowe, Christie D.; Gerbi, Christopher; Smit, Louis; Macey, Paul

    2018-07-01

    Mid-crustal fault rheology is controlled by alternating brittle and plastic deformation mechanisms, which cause feedback cycles that influence earthquake behavior. Detailed mapping and microstructural observations in the Pofadder Shear Zone (Namibia and South Africa) reveal a lithologically heterogeneous shear zone core with quartz-rich mylonites and ultramylonites, plastically overprinted pseudotachylyte and active shear folds. We present evidence for a positive feedback cycle in which coseismic grain size reduction facilitates active shear folding by enhancing competency contrasts and promoting crystal plastic flow. Shear folding strengthens a portion of a shear zone by limb rotation, focusing deformation and promoting plastic flow or brittle slip in resulting areas of localized high stress. Using quartz paleopiezometry, we estimate strain and slip rates consistent with other studies of exhumed shear zones and modern plate boundary faults, helping establish the Pofadder Shear Zone as an ancient analogue to modern, continental-scale, strike-slip faults. This feedback cycle influences seismicity patterns at the scale of study (10s of meters) and possibly larger scales as well, and contributes to bulk strengthening of the brittle-plastic transition on modern plate boundary faults.

  3. 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.

  4. in upper gastrointestinal endoscopy

    Directory of Open Access Journals (Sweden)

    Sinan Uzman

    2016-07-01

    Full Text Available Introduction : There is increasing interest in sedation for upper gastrointestinal endoscopy (UGE. Prospective randomized studies comparing sedation properties and complications of propofol and midazolam/meperidine in upper gastrointestinal endoscopy (UGE are few. Aim: To compare propofol and midazolam/meperidine sedation for UGE in terms of cardiopulmonary side effects, patient and endoscopist satisfaction and procedure-related times. Material and methods: This was a prospective, randomized, double-blind study of propofol versus midazolam and meperidine in 100 patients scheduled for diagnostic upper gastrointestinal endoscopy. The patients were divided into propofol and midazolam/meperidine groups. Randomization was generated by a computer. Cardiopulmonary side effects (hypotension, bradycardia, hypoxemia, procedure-related times (endoscopy time, awake time, time to hospital discharge, and patient and endoscopist satisfaction were compared between groups. Results: There was no significant difference between the groups with respect to the cost, endoscopy time, or demographic and clinical characteristics of the patients. Awake time and time to hospital discharge were significantly shorter in the propofol group (6.58 ±4.72 vs. 9.32 ±4.26 min, p = 0.030 and 27.60 ±7.88 vs. 32.00 ±10.54 min, p = 0.019. Hypotension incidence was significantly higher in the propofol group (12% vs. 0%, p = 0.027. The patient and endoscopist satisfaction was better with propofol. Conclusions : Propofol may be preferred to midazolam/meperidine sedation, with a shorter awake and hospital discharge time and better patient and endoscopist satisfaction. However, hypotension risk should be considered with propofol, and careful evaluation is needed, particularly in cardiopulmonary disorders.

  5. Upper extremity golf injuries.

    Science.gov (United States)

    Cohn, Michael A; Lee, Steven K; Strauss, Eric J

    2013-01-01

    Golf is a global sport enjoyed by an estimated 60 million people around the world. Despite the common misconception that the risk of injury during the play of golf is minimal, golfers are subject to a myriad of potential pathologies. While the majority of injuries in golf are attributable to overuse, acute traumatic injuries can also occur. As the body's direct link to the golf club, the upper extremities are especially prone to injury. A thorough appreciation of the risk factors and patterns of injury will afford accurate diagnosis, treatment, and prevention of further injury.

  6. Crustal architecture of the eastern margin of Japan Sea: back-arc basin opening and contraction

    Science.gov (United States)

    No, T.; Sato, T.; Takahashi, N.; Kodaira, S.; Kaneda, Y.; Ishiyama, T.; Sato, H.

    2012-12-01

    Basin and Japan Basin; however, the development of an asymmetric anticline and its associated reverse fault was observed off Akita prefecture, which could indicate a very recent growth structure. This development is associated with an active structure on the southern extension of the fault that caused the 1983 Nihonkai-Chubu Earthquake. On the other hand, the results from the seismic refraction/wide-angle reflection imaging using OBSs indicated that the area from the basin to the continental shelf, including the source area of the 1964 Niigata Earthquake, and the island arc crust had a large lateral variation in the upper and middle crust. In contrast, beneath the source area of the 1983 Nihonkai-Chubu Earthquake, the crustal structure is interpreted as a transitional crust between oceanic and island arc crusts, with larger variation in the P-wave velocity than those of the surrounding areas. Furthermore, the crust of the Yamato Basin area is thicker than a typical oceanic crust, whereas the crust of the Japan Basin area is similar to a typical oceanic crust.

  7. Subduction zone and crustal dynamics of western Washington; a tectonic model for earthquake hazards evaluation

    Science.gov (United States)

    Stanley, Dal; Villaseñor, Antonio; Benz, Harley

    1999-01-01

    buttress occurs under the North Cascades region of Washington and under southern Vancouver Island. We find that regional faults zones such as the Devils Mt. and Darrington zones follow the margin of this buttress and the Olympic-Wallowa lineament forms its southern boundary east of the Puget Lowland. Thick, high-velocity, lower-crustal rocks are interpreted to be a mafic/ultramafic wedge occuring just above the subduction thrust. This mafic wedge appears to be jointly deformed with the arch, suggesting strong coupling between the subducting plate and upper plate crust in the Puget Sound region at depths >30 km. Such tectonic coupling is possible if brittle-ductile transition temperatures for mafic/ultramafic rocks on both sides of the thrust are assumed. The deformation models show that dominant north-south compression in the coast ranges of Washington and Oregon is controlled by a highly mafic crust and low heat flow, allowing efficient transmission of margin-parallel shear from Pacific plate interaction with North America. Complex stress patterns which curve around the Puget Sound region require a concentration of northwest-directed shear in the North Cascades of Washington. The preferred model shows that greatest horizontal shortening occurs across the Devils Mt. fault zone and the east end of the Seattle fault.

  8. 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

  9. 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)

  10. Shallow Crustal Thermal Structures of Central Taiwan Foothills Region

    Directory of Open Access Journals (Sweden)

    Shao-Kai Wu

    2013-01-01

    Full Text Available Crustal thermal structures are closely related to metamorphism, rock rheology, exhumation processes, hydrocarbon maturation levels, frictional faulting and other processes. Drilling is the most direct way to access the temperature fields in the shallow crust. However, a regional drilling program for geological investigation is usually very expensive. Recently, a large-scale in-situ investigation program in the Western Foothills of Central Taiwan was carried out, providing a rare opportunity to conduct heat flow measurements in this region where there are debates as to whether previous measured heat flows are representative of the thermal state in this region. We successfully collected 28 geothermal gradients from these wells and converted them into heat flows. The new heat flow dataset is consistent with previous heat flows, which shows that the thermal structures of Central Taiwan are different from that of other subduction accretionary prisms. We then combine all the available heat flow information to analyze the frictional parameters of the Chelungpu fault zone that ruptured during the 1999, Chi-Chi, Taiwan, earthquake. The heat flow dataset gave consistent results compared with the frictional parameters derived from another independent study that used cores recovered from the Chelungpu fault zone at depth. This study also shows that it is suitable for using heat-flow data obtained from shallow subsurface to constrain thrusting faulting parameters, similar to what had been done for the strike-slip San Andreas Fault in California. Additional fieldworks are planned to study heat flows in other mountainous regions of Taiwan for more advanced geodynamic modeling efforts.

  11. Solitary Waves of Ice Loss Detected in Greenland Crustal Motion

    Science.gov (United States)

    Adhikari, S.; Ivins, E. R.; Larour, E. Y.

    2017-12-01

    The annual cycle and secular trend of Greenland mass loading are well recorded in measurements of solid Earth deformation. While bedrock vertical displacements are in phase with loading as inferred from space observations, horizontal motions have received almost no attention. The horizontal bedrock displacements can potentially track the spatiotemporal detail of mass changes with great fidelity. Our analysis of Greenland crustal motion data reveals that a significant excitation of horizontal amplitudes occurs during the intense Greenland melting. A suite of space geodetic observations and climate reanalysis data cannot explain these large horizontal displacements. We discover that solitary seasonal waves of substantial mass transport traveled through Rink Glacier in 2010 and 2012. We deduce that intense summer melting enhanced either basal lubrication or shear softening, or both, causing the glacier to thin dynamically. The newly routed upstream sublglacial water was likely to be both retarded and inefficient, thus providing a causal mechanism for the prolonged ice transport to continue well into the winter months. As the climate continues to produce increasingly warmer spring and summer, amplified seasonal waves of mass transport may become ever more present in years of future observations. Increased frequency of amplified seasonal mass transport may ultimately strengthen the Greenland's dynamic ice mass loss, a component of the balance that will have important ramifications for sea level rise. This animation shows a solitary wave passing through Rink Glacier, Greenland, in 2012, recorded by the motion of a GPS station (circle with arrow). Darker blue colors within the flow indicate mass loss, red colors show mass gain. The star marks the center of the wave. Credit: NASA/JPL-Caltech

  12. Folded fabric tunes rock deformation and failure mode in the upper crust.

    Science.gov (United States)

    Agliardi, F; Dobbs, M R; Zanchetta, S; Vinciguerra, S

    2017-11-10

    The micro-mechanisms of brittle failure affect the bulk mechanical behaviour and permeability of crustal rocks. In low-porosity crystalline rocks, these mechanisms are related to mineralogy and fabric anisotropy, while confining pressure, temperature and strain rates regulate the transition from brittle to ductile behaviour. However, the effects of folded anisotropic fabrics, widespread in orogenic settings, on the mechanical behaviour of crustal rocks are largely unknown. Here we explore the deformation and failure behaviour of a representative folded gneiss, by combining the results of triaxial deformation experiments carried out while monitoring microseismicity with microstructural and damage proxies analyses. We show that folded crystalline rocks in upper crustal conditions exhibit dramatic strength heterogeneity and contrasting failure modes at identical confining pressure and room temperature, depending on the geometrical relationships between stress and two different anisotropies associated to the folded rock fabric. These anisotropies modulate the competition among quartz- and mica-dominated microscopic damage processes, resulting in transitional brittle to semi-brittle modes under P and T much lower than expected. This has significant implications on scales relevant to seismicity, energy resources, engineering applications and geohazards.

  13. Oriental upper blepharoplasty.

    Science.gov (United States)

    Weng, Chau-Jin

    2009-02-01

    Aesthetic surgery of the upper eyelids is a very common procedure performed in cosmetic practices around the world. The word blepharoplasty, however, has a different meaning in Asia than it does elsewhere. Orientals have different periorbital anatomic characteristics, their motivations for seeking eyelid treatment are different, and operative techniques have been adapted consequently. There are also many eyelid shapes among Orientals, mostly with regard to the presence and location of the supratarsal fold and/or presence of an epicanthal fold. The surgeon must therefore master a range of surgical procedures to treat these variations adequately. It is critical to know the indications for each blepharoplasty technique as well as their complications to select the right surgery and avoid unfavorable results. Epicanthoplasty performed on the right patient can greatly improve aesthetic results while retaining ethnic characteristics. This article will discuss Oriental eyelid characteristics, preoperative patient assessment, commonly used corrective techniques for the "double-eyelid" creation, and complications and how to avoid them.

  14. 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

  15. Spatial Relationship Between Crustal Structure and Mantle Seismicity in the Vrancea Seismogenic Zone of Romania

    Science.gov (United States)

    Knapp, C. C.; Enciu, D. M.; Knapp, J. H.

    2007-12-01

    Active crustal deformation and subsidence in the Southeast Carpathian foreland has previously been attributed to active foundering of thickened continental lithosphere beneath the Carpathian bend region (Knapp et al, 2005). The present study involves integration of active and passive-source seismic data in order to place constraints on the duration, timing, and scale of crustal deformation in the Carpathian foreland, and in particular to assess the genetic relationship with the Vrancea intermediate-depth seismogenic zone (VSZ). Relocated crustal earthquakes and focal mechanisms were correlated with four deep industry seismic profiles, the reprocessed DACIA PLAN deep seismic profile, and the DRACULA (Deep Reflection Acquisition Constraining Unusual Lithospheric Activity) II and III profiles. Projection of foreland crustal hypocenters onto the deep seismic lines correlates well with previously identified crustal faults such as the Trotus and Sinaia, as well as the newly identified Ialomita Fault. Specifically, results of this study (1) image the full crustal and uppermost mantle structure of the Focsani Basin in the close proximity of the VSZ, (2) show evidence for a sub-horizontal, slightly east-dipping Moho in the vicinity of the VSZ and thinning of the crust towards the Carpathian orogen, (3) illustrate the conspicuous absence of west-dipping fabrics or structures in the crust and across the Moho, (4) present evidence that the Trotus Fault is a crustal-scale active fault with a dextral sense of motion, (5) suggest that the Paleozoic age Peceneaga-Camena and Capidava-Ovidiu Faults have not been active in post-Paleozoic time, and (6) show evidence for a new active crustal scale sinistral fault, named the Ialomita fault. Both the seismogenic Vrancea body and deformation in the Focsani Basin appear to be concentrically bound by the Trotus Fault in the north and east and the Sinaia-Ialomita Fault in the south, suggesting a coupled deformation between the VSZ and the

  16. Constraints on fault and crustal strength of the Main Ethiopian Rift from formal inversion of earthquake focal mechanism data

    Science.gov (United States)

    Muluneh, Ameha A.; Kidane, Tesfaye; Corti, Giacomo; Keir, Derek

    2018-04-01

    We evaluate the frictional strength of seismogenic faults in the Main Ethiopian Rift (MER) by inverting the available, well-constrained earthquake focal mechanisms. The regional stress field is given by - 119.6°/77.2°, 6.2°/7.6°, and 97.5°/10.2° for trend/plunge of σ1, σ2 and σ3, respectively agrees well with previous fault kinematic and focal mechanism inversions. We determine the coefficient of friction, μ, for 44 seismogenic faults by assuming the pore pressure to be at hydrostatic conditions. Slip on 36 seismogenic faults occurs with μ ≥ 0.4. Slip on the remaining eight faults is possible with low μ. In general, the coefficient of friction in the MER is compatible with a value of μ of 0.59 ± 0.16 (2σ standard deviation). The shear stresses range from 16 to 129 MPa, is similar to crustal shear stress observed in extensional tectonic regimes and global compilations of shear stresses from major fault zones. The maximum shear stress is observed in the ductile crust, below the seismologically determined brittle-ductile transition (BDT) zone. Below the BDT, the crust is assumed to be weak due to thermal modification and/or high pore fluid pressure. Our results indicate linearly increasing μ and shear stress with depth. We argue that in the MER upper crust is strong and deforms according to Coulomb frictional-failure criterion.

  17. Crustal structure of norther Oaxaca terrane; The Oaxaca and caltepec faults, and the Tehuacan Valley. A gravity study.

    Science.gov (United States)

    Campos-Enriquez, J. O.; Alatorre-Zamora, M. A.; Ramón, V. M.; Belmonte, S.

    2014-12-01

    Northern Oaxaca terrane, southern Mexico, is bound by the Caltepec and Oaxaca faults to the west and east, respectively. These faults juxtapose the Oaxaca terrane against the Mixteca and Juarez terranes, respectively. The Oaxaca Fault also forms the eastern boundary of the Cenozoic Tehuacan depression. Several gravity profiles across these faults and the Oaxaca terrane (including the Tehuacan Valley) enables us to establish the upper crustal structure of this region. Accordingly, the Oaxaca terrane is downward displaced to the east in two steps. First the Santa Lucia Fault puts into contact the granulitic basamental rocks with Phanerozoic volcanic and sedimentary rocks. Finally, the Gavilan Fault puts into contact the Oaxaca terrane basement (Oaxaca Complex) into contact with the volcano-sedimentary infill of the valley. This gravity study reveals that the Oaxaca Fault system gives rise to a series of east tilted basamental blocks (Oaxaca Complex?). A structural high at the western Tehuacan depression accomadates the east dipping faults (Santa Lucia and Gavilan faults) and the west dipping faults of the Oaxaca Fault System. To the west of this high structural we have the depper depocenters. The Oaxaca Complex, the Caltepec and Santa Lucia faults continue northwestwards beneath Phanerozoic rocks. The faults are regional tectonic structures. They seem to continue northwards below the Trans-Mexican Volcanic Belt. A major E-W to NE-SW discontinuity on the Oaxaca terrane is inferred to exist between profiles 1 and 2. The Tehuacan Valley posses a large groundwater potential.

  18. Development of simulator for studying formation process of crustal structure. 1; Chikaku kozo keisei simulator no kaihatsu. 1

    Energy Technology Data Exchange (ETDEWEB)

    Matsushima, J. [The University of Tokyo, Tokyo (Japan). Faculty of Engineering; Murakami, Y.; Okubo, Y.; Matsubayashi, O.; Tanaka, A.; Nakajima, Y.; Morijiri, R. [Geological Survey of Japan, Tsukuba (Japan); Rokugawa, S. [The University of Tokyo, Tokyo (Japan)

    1997-05-27

    The purpose of this study is to combine seismic activity and volcanic activity by reproducing the formation process of the crustal structure from a physical viewpoint or developing as its extension a numerical simulator which can predict the future. The phenomenon to which attention is especially paid at present is a relation between the dynamic process and the thermal process in the domain including the crust or the upper mantle. Namely, to elucidate the formation process of the crust structure, diastrophism also including seismic activity, igneous activity, etc., it is important to evaluate effects of the behavior of heat supplied from the deep on the dynamic process. In the finite element method, it is not easy to make the effect of gravity reflect to the calculation for boundary conditions. Accordingly, it is general to pay attention to stress difference, considering that stress by gravity is in proportion to static rock pressure stress. Further, to realize interaction between the thermal process and the dynamic process, effects of thermal stress are expressed combining the heat conducting analysis and the plastic flow analysis. 3 refs., 7 figs.

  19. An Amphibious Seismic Study of the Crustal Structure of the Adriatic Microplate

    Science.gov (United States)

    Dannowski, A.; Kopp, H.; Schurr, B.; Improta, L.; Papenberg, C. A.; Krabbenhoeft, A.; Argnani, A.; Ustaszewski, K. M.; Handy, M.; Glavatovic, B.

    2016-12-01

    The present-day structure of the southern Adriatic area is controlled by two oppositely-vergent fold-and-thrust belt systems (Apennines and Dinarides). The Adriatic continental domain is one of the most enigmatic segments of the Alpine-Mediterranean collision zone. It separated from the African plate during the Mesozoic extensional phase that led to the opening of the Ionian Sea. Basin widening and deepening peaked during Late Triassic-Liassic extension, resulting in the formation of the southern Adriatic basin, bounded on either side by the Dinaric and Apulian shallow water carbonate platforms. Because of its present foreland position with respect to the Dinaric part of orogenic belt, the southern Adriatic basin represents the only remnant of the Neotethyan margin and offers the unique opportunity to image a segment of Mesozoic passive margin in the Mediterranean. To study the deep crustal structure, the upper mantle and the shape of the plate margin, the German research vessel Meteor acquired 2D seismic refraction and wide-angle reflection data during an onshore-offshore experiment (cruise M86-3). We present two profiles: Profile P03 crossed Adria from the Gargano Promontory into Albania. A second profile (P01) was shot parallel to the coastlines, extending from the southern Adriatic basin to a possible mid-Adriatic strike-slip fault that purportedly segments the Adriatic microplate. Two different approaches of travel time tomography are applied to the data set: A non-linear approach is used for the shorter profile P01. A linear approach is applied to profile P03 (360 km length) and allows for the integration of the 36 ocean bottom stations and 19 land stations. First results show a good resolution of the sedimentary part of the Adriatic region. The depth of the basement as well as the depth of the Moho discontinuity vary laterally and deepen towards the North-East, consistent with the notion of flexural loading of the externally propagating orogenic wedge of the

  20. Physical and chemical consequences of crustal melting in fossil mature intra-oceanic arcs

    Science.gov (United States)

    Berger, J.; Burg, J.-P.

    2012-04-01

    Seismic velocity models of active intra-oceanic arcs show roots with densities and P-wave velocities intermediate to classical lower oceanic crust (density; ~3.0, Vp: ~7.0 km/s) and uppermost harzburgitic mantle (density: 3.2-3.3, Vp: 7.9-8.0 km/s). Most studies on active and fossil exhumed island arcs interpret the petrological nature of this root as ultramafic cumulates crystallized from primitive melts and/or as pyroxenites formed via basalt-peridotite reactions. Igneous cumulates and pyroxenites have densities close to or above that of uppermost mantle rocks; they can consequently undergo gravity-driven delamination, a process thought to drive the bulk composition of the arc toward an andesitic, continental crust-like composition. Dehydration and melting reactions are reported from exposed arc roots (Jijal complex in Kohistan; Amalaoulaou arc in Mali; Fiordland arc in New-Zealand). Intense influx of mantle-derived basaltic magmas at high pressure in a thickening island arc can enable lower crustal rocks to locally cross the dehydration-melting solidus of hydrous subalkaline basalts. Thermodynamic modeling using Perple_X, geochemical analysis and compilation of experimental and field data have been combined to constrain processes, conditions and consequences of intra-arc melting. The position of the solidus in a P-T grid is strongly dependent of the bulk water content: at 1 GPa, it is as low as 750 °C for water saturated hornblende-gabbros (>1 wt% H2O) and 830°C for gabbros with 0.1 wt% H2O. Incipient melting (F conditions to trigger gravity-driven delamination of the root and could lead to introduction of fertile arc garnet pyroxenites within the upper mantle. However, in Kohistan and at Amalaoulaou, the dense garnet-clinopyroxene residues are dispersed in the arc roots; they are intermingled with hornblendite and pyroxenite bodies. The small density contrast between garnet granulites and the harzburgitic mantle, and the low volumes of garnet

  1. Qinghai-Tibet Plateau crustal thickness derived from EGM2008 and CRSUT2.0

    Directory of Open Access Journals (Sweden)

    Zhou Hao

    2014-11-01

    Full Text Available Qinghai-Tibet Plateau is the most complex region for crustal thickness inversion, while high-resolution earth gravity model (EGM makes it possible to obtain high precision gravity anomaly, which is a key parameter to depict the Earth’s inner structure in geodesy domain. On the basis of this principle, we calculated the Bouguer gravity anomalies in Qinghai-Tibet Plateau with EGM2008 and SRTM6. 0 by efficient high-degree spherical harmonic synthesis algorithm. In order to obtain the gravity anomaly caused by Moho density mutant, the noises caused by the topography was removed by wavelet details. Then, the crustal thickness was corrected on the basis of CRUST 2. 0 with the deep-large-scale single density interface formula. The inversion result indicates that the crustal thickness in Qinghai-Tibet Plateau is between 50 km and 75 km, which is in correspondence with the recent science research result. Compared with the 2 degree CRUST 2. 0 model, the spatial resolution of crustal thickness in our research can reach 40 arc minutes. In addition, there is a positive relationship between the inversed crustal thickness and topography, which can prove the effectiveness of Airy-Heiskanen isostatic model in gravity reduction.

  2. Obtaining Crustal Properties From the P Coda Without Deconvolution: an Example From the Dakotas

    Science.gov (United States)

    Frederiksen, A. W.; Delaney, C.

    2013-12-01

    Receiver functions are a popular technique for mapping variations in crustal thickness and bulk properties, as the travel times of Ps conversions and multiples from the Moho constrain both Moho depth (h) and the Vp/Vs ratio (k) of the crust. The established approach is to generate a suite of receiver functions, which are then stacked along arrival-time curves for a set of (h,k) values (the h-k stacking approach of Zhu and Kanamori, 2000). However, this approach is sensitive to noise issues with the receiver functions, deconvolution artifacts, and the effects of strong crustal layering (such as in sedimentary basins). In principle, however, the deconvolution is unnecessary; for any given crustal model, we can derive a transfer function allowing us to predict the radial component of the P coda from the vertical, and so determine a misfit value for a particular crustal model. We apply this idea to an Earthscope Transportable Array data set from North and South Dakota and western Minnesota, for which we already have measurements obtained using conventional h-k stacking, and so examine the possibility of crustal thinning and modification by a possible failed branch of the Mid-Continent Rift.

  3. Crustal moment of inertia of glitching pulsars with the KDE0v1 Skyrme interaction

    Energy Technology Data Exchange (ETDEWEB)

    Madhuri, K.; Routray, T.R.; Pattnaik, S.P. [Sambalpur University, School of Physics, Jyotivihar (India); Basu, D.N. [Variable Energy Cyclotron Center, Kolkata (India)

    2017-07-15

    The mass, radius and crustal fraction of moment of inertia in neutron stars are calculated using β-equilibrated nuclear matter obtained from the Skyrme effective interaction. The transition density, pressure and proton fraction at the inner edge separating the liquid core from the solid crust of the neutron stars are determined from the thermodynamic stability conditions using the KDE0v1 set. The neutron star masses obtained by solving the Tolman-Oppenheimer-Volkoff equations using neutron star matter obtained from this set are able to describe highly massive compact stars ∝ 2M {sub CircleDot}. The crustal fraction of the moment of inertia can be extracted from studying pulsar glitches. This fraction is highly dependent on the core-crust transition pressure and corresponding density. These results for pressure and density at core-crust transition together with the observed minimum crustal fraction of the total moment of inertia provide a limit for the radius of the Vela pulsar, R ≥ 3.69 + 3.44M/M {sub CircleDot}. Present calculations suggest that the crustal fraction of the total moment of inertia can be ∝ 6.3% due to crustal entrainment caused by the Bragg reflection of unbound neutrons by lattice ions. (orig.)

  4. Crustal CO2 liberation during the 2006 eruption and earthquake events at Merapi volcano, Indonesia

    Science.gov (United States)

    Troll, Valentin R.; Hilton, David R.; Jolis, Ester M.; Chadwick, Jane P.; Blythe, Lara S.; Deegan, Frances M.; Schwarzkopf, Lothar M.; Zimmer, Martin

    2012-06-01

    High-temperature volcanic gas is widely considered to originate from ascending, mantle-derived magma. In volcanic arc systems, crustal inputs to magmatic gases mainly occur via subducted sediments in the mantle source region. Our data from Merapi volcano, Indonesia imply, however, that during the April-October 2006 eruption significant quantities of CO2 were added from shallow crustal sources. We show that prior to the 2006 events, summit fumarole gas δ13C(CO2) is virtually constant (δ13C1994-2005 = -4.1 ± 0.3‰), but during the 2006 eruption and after the shallow Yogyakarta earthquake of late May, 2006 (M6.4; hypocentres at 10-15 km depth), carbon isotope ratios increased to -2.4 ± 0.2‰. This rise in δ13C is consistent with considerable addition of crustal CO2 and coincided with an increase in eruptive intensity by a factor of ˜3 to 5. We postulate that this shallow crustal volatile input supplemented the mantle-derived volatile flux at Merapi, intensifying and sustaining the 2006 eruption. Late-stage volatile additions from crustal contamination may thus provide a trigger for explosive eruptions independently of conventional magmatic processes.

  5. Isostatic and Decompensative Gravity Anomalies of the Arabian Plate and Surrounding Regions: a Key for the Crustal Structure

    Science.gov (United States)

    Kaban, M. K.; El Khrepy, S.; Al-Arifi, N. S.

    2016-12-01

    The isostatic anomalies are often considered as one of the most useful correction of the gravity field for investigation of the upper crust structure in many practical applications. By applying this correction, a substantial part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomaly, can be removed. With this approach, it is not even necessary to know the deep density structure of the crust and upper mantle in details; it is sufficient to prescribe some type of compensation (regional vs. local) and a compensation depth. However, even when all the parameters are chosen correctly, this reduction of the gravity field does not show the full gravity effect of unknown anomalies in the crust. The last ones should be also compensated to some extent; therefore their impact is substantially reduced by the isostatic compensation. Long ago (Cordell et al., 1991), it was suggested a so-called decompensative correction of the isostatic anomalies, which provides a possibility to separate these effects. However, the decompensative correction is very sensitive to the parameters of the compensation scheme. In the present study we analyse the ways to choose these parameters and extend this approach by assuming a possibility for the regional compensation via elastic deformations of the lithosphere. Based on this technique, we estimate the isostatic and decompensative anomalies for the Arabian plate and surrounding regions. The parameters of the isostatic model are chosen based on previous studies. It was demonstrated that the decompensative correction is very significant at the mid-range wavelengths and may exceed 100 mGal, therefore ignoring this effect would lead to wrong conclusions about the upper crust structure. The total amplitude of the decompensative anomalies reaches ±250 mGal, evidencing for both, large density anomalies of the upper crust (including sediments) and strong isostatic disturbances of the lithosphere. These results improve

  6. Fine crustal and uppermost mantle S-wave velocity structure beneath the Tengchong volcanic area inferred from receiver function and surface-wave dispersion: constraints on magma chamber distribution

    Science.gov (United States)

    Li, Mengkui; Zhang, Shuangxi; Wu, Tengfei; Hua, Yujin; Zhang, Bo

    2018-03-01

    The Tengchong volcanic area is located in the southeastern margin of the collision zone between the Indian and Eurasian Plates. It is one of the youngest intraplate volcano groups in mainland China. Imaging the S-wave velocity structure of the crustal and uppermost mantle beneath the Tengchong volcanic area is an important means of improving our understanding of its volcanic activity and seismicity. In this study, we analyze teleseismic data from nine broadband seismic stations in the Tengchong Earthquake Monitoring Network. We then image the crustal and uppermost mantle S-wave velocity structure by joint analysis of receiver functions and surface-wave dispersion. The results reveal widely distributed low-velocity zones. We find four possible magma chambers in the upper-to-middle crust and one in the uppermost mantle. The chamber in the uppermost mantle locates in the depth range from 55 to 70 km. The four magma chambers in the crust occur at different depths, ranging from the depth of 7 to 25 km in general. They may be the heat sources for the high geothermal activity at the surface. Based on the fine crustal and uppermost mantle S-wave velocity structure, we propose a model for the distribution of the magma chambers.

  7. Crustal Structure of Khövsgöl, Mongolia

    Science.gov (United States)

    Scott, A. M.; Meltzer, A.; Stachnik, J.; Russo, R.; Munkhuu, U.; Tsagaan, B.

    2017-12-01

    Mongolia is part of the Central Asian Orogenic Belt, an accretionary event that spanned 800 million years from the mid-Proterozoic to mid-Phanerozoic. As a result of the past collisional and rifting events, the modern Khövsgöl rift system of northern Mongolia contains a heterogeneous lithospheric structure. The current rift system has three parallel N-S trending basins that roughly align with terrane boundaries. Structures inherited during the accretionary events may be a factor influencing regional deformation. The forces that drive local deformation are not well understood, but varying processes have been proposed: far-field effects of India-Eurasian plate convergence, westward subduction of the Pacific plate, magmatic underplating at the base of the crust, mantle plume activity, and asthenospheric mantle convection. Determining the nature of crustal features within this poorly understood region may illuminate processes that control rifting within intracontinental settings. A network of 26 broadband seismic stations encompassing 200 square kilometers of the Khövsgöl rift system were deployed from August 2014 to June 2016. More than 2100 events were detected, and most earthquakes were concentrated near rift structures. Events between Busiin-Gol and Darkhad, the westernmost and central basins of the Khövsgöl rift system, are distributed within the crust. An active fault is outlined along the eastern border of the Darkhad basin. Khövsgöl earthquakes bound both sides of the rift. Along the northern border of Lake Khövsgöl, seismic events define a shallow active fault orthogonal to the basin. The largest event recorded within the network was a magnitude ml=5.2 located near the northeastern border of Lake Khövsgöl on 12-05-2014. The focal mechanism of this earthquake is predominantly strike-slip, but also includes an extensional component. This work focuses on earthquake relocation and calculating moment tensors and focal mechanisms of larger regional

  8. 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

  9. Modeling and Crustal Structure in the Future Reservoir of Jequitaí, Brazil

    Science.gov (United States)

    Teixeira, C. D.; Von Huelsen, M. G.; Chemale, F., Jr.; Nascimento, A. V. D. S., Sr.; do Sacramento, V., Sr.; Garcia, V. B. P., Sr.

    2017-12-01

    Integrated geophysical and geological data analysis in the state of Minas Gerais, Brazil, allowed the modeling of the subsurface framework in a region where a reservoir - the Jequitaí reservoir - will be constructed. Studies of this nature during the previous stages of the construction of large hydroelectric projects are highly important, because the regional geology understanding associated with geophysical data interpretation can help to prevent damage in the physical structure of the dam, which will aid in its preservation. The use of gravity and magnetic data in a 2D crustal model provided information on a possible framework of the area and revealed features not mapped until now, which may be useful for further studies and can contribute to the understanding of this portion of the crust. The results show the presence of high gravity anomalies in the southern part of the study area, besides extensive lineaments that cross the whole area, interpreted as possible faults and dykes. Depth estimation techniques, such as Euler deconvolution and radially averaged power spectrum, allowed the identification of continuous structures up to 400 m depth, and showed differences in the basement depth in the northern and southern portions of the study area. Inversion of the gravity data along a profile crossing a gravity anomaly yielded to information about the depth, thickness and shape of a possible intrusive body. The geological-geophysical model was consistent with the interpretations based on surface geology and in the gravity and magnetic signal, because the section could be modeled respecting the geophysical data and the pre-existing structural proposals.

  10. Crustal Deformation along San Andreas Fault System revealed by GPS and Sentinel-1 InSAR

    Science.gov (United States)

    Xu, X.; Sandwell, D. T.

    2017-12-01

    We present a crustal deformation velocity map along the San Andreas Fault System by combining measurements from Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) velocity models (CGM V1). We assembled 5 tracks of descending Sentinel-1 InSAR data spanning 2014.11-2017.02, and produced 545 interferograms, each of which covers roughly 250km x 420km area ( 60 bursts). These interferograms are unwrapped using SNAPHU [Chen & Zebker, 2002], with the 2Npi unwrapping ambiguity corrected with a sparse recovery method. We used coherence-based small baseline subset (SBAS) method [Tong & Schmidt, 2016] together with atmospheric correction by common-point stacking [Tymofyeyeva and Fialko, 2015] to construct deformation time series [Xu et. al., 2017]. Then we project the horizontal GPS model and vertical GPS data into satellite line-of-sight directions separately. We first remove the horizontal GPS model from InSAR measurements and perform elevation-dependent atmospheric phase correction. Then we compute the discrepancy between the remaining InSAR measurements and vertical GPS data. We interpolate this discrepancy and remove it from the residual InSAR measurements. Finally, we restore the horizontal GPS model. Preliminary results show that fault creep over the San Jacinto fault, the Elsinore fault, and the San Andreas creeping section is clearly resolved. During the period of drought, the Central Valley of California was subsiding at a high rate (up to 40 cm/yr), while the city of San Jose is uplifting due to recharge, with a quaternary fault acting as a ground water barrier. These findings will be reported during the meeting.

  11. Crustal structure revealed by a deep seismic sounding profile of Baijing-Gaoming-Jinwan in the Pearl River Delta

    Science.gov (United States)

    Zhang, Xiang; Ye, Xiuwei; Lv, Jinshui; Sun, Jinlong; Wang, Xiaona

    2018-02-01

    The Pearl River Estuary area, located in the middle part of the southern China coastal seismic belt, has long been considered a potential source of strong earthquakes above magnitude 7.0. To scientifically assess the potential strong earthquake risk in this area, a three-dimensional artificial seismic sounding experiment, consisting of a receiving array and seabed seismograph, was performed to reveal the deep crustal structure in this region. We used artificial ship-borne air-gun excitation shots as sources, and fixed and mobile stations as receivers to record seismic data from May to August 2015. This paper presents results along a line from the western side of the Pearl River Estuary to the western side of the Baijing-Gaoming-Jinwan profile. A two-dimensional velocity structure was constructed using seismic travel-time tomography. The inversion results show that the Moho depth is 27 km in the coastal area and 30 km in the northwest of the Pearl River Estuary area, indicating that the crust thins from land to sea. Two structural discontinuities and multiple low-velocity anomalies appear in the crustal section. Inside both discontinuity zones, a low-velocity layer, with a minimum velocity of 6.05 km s-1, exists at a depth of about 15 km, and another, with a minimum velocity of 6.37 km s-1, exists at a depth of about 21.5 km between the middle and lower crust. These low velocities suggest that the discontinuities may consist of partly molten material. Earthquakes with magnitudes higher than 5.0 occurred in the low-velocity layer along the profile. The deep Kaiping-Enping fault, rooted in the crust, may be one of the most important channels for deep material upwelling and is related to tectonic movement since the Cretaceous in the Pearl River Delta tectonic rift basin.

  12. Estimates of stress drop and crustal tectonic stress from the 27 February 2010 Maule, Chile, earthquake: Implications for fault strength

    Science.gov (United States)

    Luttrell, K.M.; Tong, X.; Sandwell, D.T.; Brooks, B.A.; Bevis, M.G.

    2011-01-01

    The great 27 February 2010 Mw 8.8 earthquake off the coast of southern Chile ruptured a ???600 km length of subduction zone. In this paper, we make two independent estimates of shear stress in the crust in the region of the Chile earthquake. First, we use a coseismic slip model constrained by geodetic observations from interferometric synthetic aperture radar (InSAR) and GPS to derive a spatially variable estimate of the change in static shear stress along the ruptured fault. Second, we use a static force balance model to constrain the crustal shear stress required to simultaneously support observed fore-arc topography and the stress orientation indicated by the earthquake focal mechanism. This includes the derivation of a semianalytic solution for the stress field exerted by surface and Moho topography loading the crust. We find that the deviatoric stress exerted by topography is minimized in the limit when the crust is considered an incompressible elastic solid, with a Poisson ratio of 0.5, and is independent of Young's modulus. This places a strict lower bound on the critical stress state maintained by the crust supporting plastically deformed accretionary wedge topography. We estimate the coseismic shear stress change from the Maule event ranged from-6 MPa (stress increase) to 17 MPa (stress drop), with a maximum depth-averaged crustal shear-stress drop of 4 MPa. We separately estimate that the plate-driving forces acting in the region, regardless of their exact mechanism, must contribute at least 27 MPa trench-perpendicular compression and 15 MPa trench-parallel compression. This corresponds to a depth-averaged shear stress of at least 7 MPa. The comparable magnitude of these two independent shear stress estimates is consistent with the interpretation that the section of the megathrust fault ruptured in the Maule earthquake is weak, with the seismic cycle relieving much of the total sustained shear stress in the crust. Copyright 2011 by the American

  13. Crustal structure beneath the southern Korean Peninsula from local earthquakes

    Science.gov (United States)

    Kim, Kwang-Hee; Park, Jung-Ho; Park, Yongcheol; Hao, Tian-Yao; Kim, Han-Joon

    2017-05-01

    The 3-D subsurface structure beneath the southern Korean Peninsula is poorly known, even though such information could be key in verifying or rejecting several competing models of the tectonic evolution of East Asia. We constructed a 3-D velocity model of the upper crust beneath the southern Korean Peninsula using 19 935 P-wave arrivals from 747 earthquakes recorded by high-density local seismic networks. Results show significant lateral and vertical variations: velocity increases from northwest to southeast at shallow depths, and significant velocity variations are observed across the South Korea Tectonic Line between the Okcheon Fold Belt and the Youngnam Massif. Collision between the North and South China blocks during the Early Cretaceous might have caused extensive deformation and the observed negative velocity anomalies in the region. The results of the tomographic inversion, combined with the findings of previous studies of Bouguer and isostatic gravity anomalies, indicate the presence of high-density material in the upper and middle crust beneath the Gyeongsang Basin in the southeastern Korean Peninsula. Although our results partially support the indentation tectonic model, it is still premature to discard other tectonic evolution models because our study only covers the southern half of the peninsula.

  14. Inferring regional vertical crustal velocities from averaged relative sea level trends: A proof of concept

    Directory of Open Access Journals (Sweden)

    Bâki Iz H.

    2017-02-01

    Full Text Available This study demonstrates that relative sea level trends calculated from long-term tide gauge records can be used to estimate relative vertical crustal velocities in a region with high accuracy. A comparison of the weighted averages of the relative sea level trends estimated at six tide gauge stations in two clusters along the Eastern coast of United States, in Florida and in Maryland, reveals a statistically significant regional vertical crustal motion of Maryland with respect to Florida with a subsidence rate of −1.15±0.15 mm/yr identified predominantly due to the ongoing glacial isostatic adjustment process. The estimate is a consilience value to validate vertical crustal velocities calculated from GPS time series as well as towards constraining predictive GIA models in these regions.

  15. Upper functional gastrointestinal disorders in young adults.

    Science.gov (United States)

    Adibi, Peyman; Behzad, Ebrahim; Shafieeyan, Mohammad; Toghiani, Ali

    2012-01-01

    Functional Gastrointestinal disorders (FGID) are common disorders in gastroenterology which are common in young adults. The aim of this study is evaluating the prevalence of upper FGID in iranian young adults. This was a cross-sectional study which was on 995 persons who were going to marry. A ROME III based questionnaire was used to determine the frequency of upper GI Syndromes among the sample population. Our results determined 74 subjects had functional dyspepsia (36 subjects diagnosed as postprandial distress syndrome patient and Epigastric pain syndrome was seen in 38 subjects). Functional heartburn was diagnosed in 52 participants. Globus was seen in 35 subjects and 41 had unspecified excessive belching. Many epidemiologic studies were done all around the world but there are different reports about prevalence and incidence of FGIDs. Our results were agreed with reported prevalence of FGIDs in Iran in adults. And our findings were agreed with some other Asian studies.

  16. Upper airway resistance syndrome.

    Science.gov (United States)

    Montserrat, J M; Badia, J R

    1999-03-01

    This article reviews the clinical picture, diagnosis and management of the upper airway resistance syndrome (UARS). Presently, there is not enough data on key points like the frequency of UARS and the morbidity associated with this condition. Furthermore, the existence of LIARS as an independent sleep disorder and its relation with snoring and obstructive events is in debate. The diagnosis of UARS is still a controversial issue. The technical limitations of the classic approach to monitor airflow with thermistors and inductance plethysmography, as well as the lack of a precise definition of hypopnea, may have led to a misinterpretation of UARS as an independent diagnosis from the sleep apnea/hypopnea syndrome. The diagnosis of this syndrome can be missed using a conventional polysomnographic setting unless appropriate techniques are applied. The use of an esophageal balloon to monitor inspiratory effort is currently the gold standard. However, other sensitive methods such as the use of a pneumotachograph and, more recently, nasal cannula/pressure transducer systems or on-line monitoring of respiratory impedance with the forced oscillation technique may provide other interesting possibilities. Recognition and characterization of this subgroup of patients within sleep breathing disorders is important because they are symptomatic and may benefit from treatment. Management options to treat UARS comprise all those currently available for sleep apnea/hypopnea syndrome (SAHS). However, the subset of patients classically identified as LIARS that exhibit skeletal craneo-facial abnormalities might possibly obtain further benefit from maxillofacial surgery.

  17. Upper Illinois River basin

    Science.gov (United States)

    Friedel, Michael J.

    1998-01-01

    During the past 25 years, industry and government made large financial investments that resulted in better water quality across the Nation; however, many water-quality concerns remain. Following a 1986 pilot project, the U.S. Geological Survey began implementation of the National Water-Quality Assessment (NAWQA) Program in 1991. This program differs from other national water-quality assessment studies in that the NAWQA integrates monitoring of surface- and ground-water quality with the study of aquatic ecosystems. The goals of the NAWQA Program are to (1) describe current water-quality conditions for a large part of the Nation's freshwater streams and aquifers (water-bearing sediments and rocks), (2) describe how water quality is changing over time, and (3) improve our understanding of the primary natural and human factors affecting water quality.The Upper Illinois River Basin National Water- Quality Assessment (NAWQA) study will increase the scientific understanding of surface- and ground-water quality and the factors that affect water quality in the basin. The study also will provide information needed by water-resource managers to implement effective water-quality management actions and evaluate long-term changes in water quality.

  18. Crustal structure of north Peru from analysis of teleseismic receiver functions

    Science.gov (United States)

    Condori, Cristobal; França, George S.; Tavera, Hernando J.; Albuquerque, Diogo F.; Bishop, Brandon T.; Beck, Susan L.

    2017-07-01

    In this study, we present results from teleseismic receiver functions, in order to investigate the crustal thickness and Vp/Vs ratio beneath northern Peru. A total number of 981 receiver functions were analyzed, from data recorded by 28 broadband seismic stations from the Peruvian permanent seismic network, the regional temporary SisNort network and one CTBTO station. The Moho depth and average crustal Vp/Vs ratio were determined at each station using the H-k stacking technique to identify the arrival times of primary P to S conversion and crustal reverberations (PpPms, PpSs + PsPms). The results show that the Moho depth correlates well with the surface topography and varies significantly from west to east, showing a shallow depth of around 25 km near the coast, a maximum depth of 55-60 km beneath the Andean Cordillera, and a depth of 35-40 km further to the east in the Amazonian Basin. The bulk crustal Vp/Vs ratio ranges between 1.60 and 1.88 with the mean of 1.75. Higher values between 1.75 and 1.88 are found beneath the Eastern and Western Cordilleras, consistent with a mafic composition in the lower crust. In contrast values vary from 1.60 to 1.75 in the extreme flanks of the Eastern and Western Cordillera indicating a felsic composition. We find a positive relationship between crustal thickness, Vp/Vs ratio, the Bouguer anomaly, and topography. These results are consistent with previous studies in other parts of Peru (central and southern regions) and provide the first crustal thickness estimates for the high cordillera in northern Peru.

  19. Monitoring Vertical Crustal Deformation and Gravity Variations during Water Level Changes at the Three Gorges Reservoir

    Directory of Open Access Journals (Sweden)

    WANG Wei

    2017-06-01

    Full Text Available Monitoring vertical crustal deformation and gravity changes during water level changes at the Three Gorges reservoir is important for the safe operation of the Three Gorges Dam and for the monitoring and prevention of a regional geological disaster. In this study, we determined vertical crustal deformation and gravity changes during water level variations of the Three Gorges reservoir from direct calculations and actual measurements and a comprehensive solution. We used water areas extracted image data from the ZY-3 satellite and water level data to calculate gravity changes and vertical crustal deformation caused by every 5 m change in the water level due to storage and drainage of the Three Gorges reservoir from 145 m to 175 m. The vertical crustal deformation was up to 30 mm. The location of gravity change above 20 μ Gal(1 Gal=10-2 m/s2 was less than 2 km from the centerline of the Yangtze River. The CORS ES13 in Badong, near the reservoir, measured the vertical crustal deformation during water level changes. Because of the small number of CORS and gravity stations in the Three Gorges reservoir area, monitoring deformation and gravity related to changes in the Three Gorges reservoir water level cannot be closely followed. Using 26 CORS and some of the gravity stations in the Three Gorges area and based on loading deformation and the spherical harmonic analysis method, an integrated solution of vertical deformation and gravity variations during water level changes of the reservoir was determined, which is consistent with the actual CORS monitoring results. By comparison, we found that an integrated solution based on a CORS network can effectively enhance the capability of monitoring vertical crustal deformation and gravity changes during water level variations of the reservoir.

  20. Modeling the blockage of Lg waves from 3-D variations in crustal structure

    Science.gov (United States)

    Sanborn, Christopher J.; Cormier, Vernon F.

    2018-05-01

    Comprised of S waves trapped in Earth's crust, the high frequency (2-10 Hz) Lg wave is important to discriminating earthquakes from explosions by comparing its amplitude and waveform to those of Pg and Pn waves. Lateral variations in crustal structure, including variations in crustal thickness, intrinsic attenuation, and scattering, affect the efficiency of Lg propagation and its consistency as a source discriminant at regional (200-1500 km) distances. To investigate the effects of laterally varying Earth structure on the efficiency of propagation of Lg and Pg, we apply a radiative transport algorithm to model complete, high-frequency (2-4 Hz), regional coda envelopes. The algorithm propagates packets of energy with ray theory through large-scale 3-D structure, and includes stochastic effects of multiple-scattering by small-scale heterogeneities within the large-scale structure. Source-radiation patterns are described by moment tensors. Seismograms of explosion and earthquake sources are synthesized in canonical models to predict effects on waveforms of paths crossing regions of crustal thinning (pull-apart basins and ocean/continent transitions) and thickening (collisional mountain belts), For paths crossing crustal thinning regions, Lg is amplified at receivers within the thinned region but strongly disrupted and attenuated at receivers beyond the thinned region. For paths crossing regions of crustal thickening, Lg amplitude is attenuated at receivers within the thickened region, but experiences little or no reduction in amplitude at receivers beyond the thickened region. The length of the Lg propagation within a thickened region and the complexity of over- and under-thrust crustal layers, can produce localized zones of Lg amplification or attenuation. Regions of intense scattering within laterally homogeneous models of the crust increase Lg attenuation but do not disrupt its coda shape.

  1. A hybrid origin of the Martian crustal dichotomy: Degree-1 convection antipodal to a giant impact

    Science.gov (United States)

    Citron, Robert I.; Manga, Michael; Tan, Eh

    2018-06-01

    The Martian crustal dichotomy is the stark ∼5 km difference in surface elevation and ∼26 km difference in crustal thickness between the northern lowlands and southern highlands that originated within 100s of Myr of Mars' formation. The origin of the dichotomy has broad implications for the geodynamic history of Mars, but purely exogenic or endogenic theories so far cannot explain all of the large scale geophysical observations associated with dichotomy formation. A giant impact can produce the shape and slope of the dichotomy boundary, but struggles to explain Mars' remanent crustal magnetic signatures and the ultimate formation of Tharsis. Degree-1 mantle convection can relate the crustal dichotomy to the formation of Tharsis, but does not explain the elliptical dichotomy shape and must be initiated by a large pre-existing viscosity jump in the mantle. We propose a hybrid model of dichotomy formation in which a giant impact induces degree-1 convection with an upwelling antipodal to the impact site. In this scenario, a giant impact in the northern hemisphere excavates crust, creating an initial difference in crustal thickness and possibly composition between the two hemispheres. Over 10s to 100s of Myr, the dominant upwelling(s) would migrate to be under the thicker, insulating crust in the southern hemisphere, generating melt that further thickens the southern crust. We examine this process using 3-D mantle convection simulations, and find that a hemispherical difference in crustal thickness and composition caused by a giant impact can induce degree-1 convection with the upwelling(s) antipodal to the impact site in <100 Myr.

  2. Calcareous nannofossils from the Boreal upper Campanian-Maastrichtian Chalk of Denmark

    DEFF Research Database (Denmark)

    Thibault, Nicolas Rudolph

    2010-01-01

    Boreal calcareous nannofossil assemblages have been documented from three sections in Denmark. from the Upper Campanian to Upper Maastrichtian (nannofossil zones UC16a(BP) to UC20d(BP)): the Stevns-1 borehole, next to the Cretaceous/Palaeogene boundary section of Stevns Klint, eastern Sjaelland...

  3. Prediction of long-term crustal movement for geological disposal of radioactive waste

    International Nuclear Information System (INIS)

    Sasaki, Takeshi; Morikawa, Seiji; Tabei, Kazuto; Koide, Hitoshi; Tashiro, Toshiharu

    2000-01-01

    Long-term stability of the geological environment is essential for the safe geological disposal of radioactive waste, for which it is necessary to predict the crustal movement during an assessment period. As a case study, a numerical analysis method for the prediction of crustal movement in Japan is proposed. A three-dimensional elastic analysis by FEM for the geological block structure of the Kinki region and the Awaji-Rokko area is presented. Stability analysis for a disposal cavern is also investigated. (author)

  4. Fault offsets and lateral crustal movement on Europa - Evidence for a mobile ice shell

    International Nuclear Information System (INIS)

    Schenk, P.M.; Mckinnon, W.B.

    1989-01-01

    An examination is conducted of Europa's cross-cutting structural relationships between various lineament types, in order to constrain the type of structure involved in each such case and, where possible, to also constrain the degree of extension across the lineaments. Evidence is adduced for significant lateral crustal movement, allowing alternative models and mechanisms for lineament formation to be discussed, as well as plausible lithospheric and crustal models. The question as to whether any of the water-ice layer has been, or currently is, liquid, is also treated in light of the evidence obtained. 53 refs

  5. Terrestrial spreading centers under Venus conditions - Evaluation of a crustal spreading model for Western Aphrodite Terra

    Science.gov (United State