Sample records for madrid seismic zone

  1. New Madrid Seismic Zone


    Pittsburgh, Boston, Buffalo, Detroit, and Chicago . Even though the system consists of multiple parallel underground pipeline, a major earthquake would...24 Ibid., 74. 25 Norma Hayes Bagnall, On Shaky Ground, the New Madrid Earthquakes of 1811-1812 (Columbia, MO: University of Missouri Press, 1996...blank, 36 BIBLIOGRAPHY Bagnall, Norma Hayes. On Shaky Ground, the New Madrid Earthquakes of 1811-1812. Columbia, Missouri: University of

  2. Tectonic stress within the New Madrid seismic zone

    Grana, Jeffrey P.; Richardson, Randall M.


    Refraction data indicate a significant high-density rift pillow beneath the New Madrid seismic zone. We present results of linear and nonlinear viscoelastic finite element modeling to determine whether support of the rift pillow may contribute significantly to the total present-day stress field, and we consider the implications for intraplate seismicity. These models were run for a loading time of 100 m.y. to account for relaxation and transfer of stress since the last reactivation of the rift in the mid-Mesozoic. Results indicate that the nonlinear viscoelastic model with rheological stratification based on composition and temperature agrees well with the observed deformation within the seismic zone and with estimates of regional stress magnitudes. The model predicts a maximum compression of 30-40 MPa above the rift pillow in the center of the rift axis. If the magnitude of local compression predicted by the nonlinear model produces the inferred clockwise rotation of the order of 10°-30° in the direction of SHmax (maximum horizontal compression) near the rift axis, the magnitude of regional compression is a factor of 1 to 2 times the magnitude of local compression and consistent with an origin due to ridge push forces. The addition of the local stress associated with the rift pillow, however, results in an approximately 30% reduction in the resolved maximum horizontal shear stress. Thus, while the stress associated with the rift pillow can rotate the stress field into an orientation favorable for failure, reduction in the resolved shear stress requires a separate mechanism for strength reduction. Results of the modeling indicate that stresses from the load of the rift pillow may still be present in the upper crust even after 100 m.y. and may still play a role in present-day deformation and seismicity of the New Madrid seismic zone. Local stress fields of significant tectonic magnitudes may also occur around other ancient rift pillows and help explain the

  3. Seismic-wave attenuation associated with crustal faults in the new madrid seismic zone.

    Hamilton, R M; Mooney, W D


    The attenuation of upper crustal seismic waves that are refracted with a velocity of about 6 kilometers per second varies greatly among profiles in the area of the New Madrid seismic zone in the central Mississippi Valley. The waves that have the strongest attenuation pass through the seismic trend along the axis of the Reelfoot rift in the area of the Blytheville arch. Defocusing of the waves in a low-velocity zone and/or seismic scattering and absorption could cause the attenuation; these effects are most likely associated with the highly deformed rocks along the arch. Consequently, strong seismic-wave attenuation may be a useful criterion for identifying seismogenic fault zones.

  4. CPT site characterization for seismic hazards in the New Madrid seismic zone

    Liao, T.; Mayne, P.W.; Tuttle, M.P.; Schweig, E.S.; Van Arsdale, R.B.


    A series of cone penetration tests (CPTs) were conducted in the vicinity of the New Madrid seismic zone in central USA for quantifying seismic hazards, obtaining geotechnical soil properties, and conducting studies at liquefaction sites related to the 1811-1812 and prehistoric New Madrid earthquakes. The seismic piezocone provides four independent measurements for delineating the stratigraphy, liquefaction potential, and site amplification parameters. At the same location, two independent assessments of soil liquefaction susceptibility can be made using both the normalized tip resistance (qc1N) and shear wave velocity (Vs1). In lieu of traditional deterministic approaches, the CPT data can be processed using probability curves to assess the level and likelihood of future liquefaction occurrence. ?? 2002 Elsevier Science Ltd. All rights reserved.

  5. Reconciling short recurrence intervals with minor deformation in the new madrid seismic zone.

    Schweig, E S; Ellis, M A


    At least three great earthquakes occurred in the New Madrid seismic zone in 1811 and 1812. Estimates of present-day strain rates suggest that such events may have a repeat time of 1000 years or less. Paleoseismological data also indicate that earthquakes large enough to cause soil liquefaction have occurred several times in the past 5000 years. However, pervasive crustal deformation expected from such a high frequency of large earthquakes is not observed. This suggests that the seismic zone is a young feature, possibly as young as several tens of thousands of years old and no more than a few million years old.

  6. Estimating Strain Accumulation in the New Madrid and Wabash Valley Seismic Zones

    Craig, T. J.; Calais, E.


    The mechanical behaviour -- and hence earthquake potential -- of faults in continental interiors is a question of critical importance for the resultant seismic hazard, but no consensus has yet been reached on this controversial topic. The debate has focused on the central and eastern United States, in particular the New Madrid Seismic Zone, struck by three magnitude 7 or greater earthquakes in 1811--1812, and to a lesser extent the Wabash Valley Seismic Zone just to the north. A key aspect of this issue is the rate at which strain is currently accruing on those faults in the plate interior, a quantity that remains debated. Understanding if the present-day strain rates indicate sufficient motion to account for the historical and paleoseismological earthquakes by steady-state fault behaviour, or if strain accumulation is time-dependent in this area, is critical for investigating the causative process driving this seismicity in the plate interior, and how regional strain reflects the interplay between stresses arising from different geological processes. Here we address this issue with an analysis of up to 14 years of continuous GPS data from a network of 200 sites in the central United States centred on the New Madrid and Wabash Valley seismic zones. We find that high-quality sites in these regions show motions that are consistently within the 95% confidence limit of zero deformation relative to a rigid background. These results place an upper bound on regional strain accrual of 0.2 mm/yr and 0.5 mm/yr in the New Madrid and Wabash Valley Seismic Zones, respectively. These results, together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors, indicate that either tectonic loading rates or fault properties vary with time in the NMSZ and possibly plate-wide.

  7. Use of archaeology to date liquefaction features and seismic events in the new madrid seismic zone, Central United States

    Tuttle, M.P.; Lafferty, R. H.; Guccione, M.J.; Schweig, E. S.; Lopinot, N.; Cande, R.F.; Dyer-Williams, K.; Haynes, M.


    Prehistoric earthquake-induced liquefaction features occur in association with Native American occupation horizons in the New Madrid seismic zone. Age control of these liquefaction features, including sand-blow deposits, sand-blow craters, and sand dikes, can be accomplished by extensive sampling and flotation processing of datable materials as well as archaeobotanical analysis of associated archaeological horizons and pits. This approach increases both the amount of carbon for radiocarbon dating and the precision dating of artifact assemblages. Using this approach, we dated liquefaction features at four sites northwest of Blytheville, Arkansas, and found that at least one significant earthquake occurred in the New Madrid seismic zone between A.D. 1180 and 1400, probably about A.D. 1300 ?? 100 yr. In addition, we found three buried sand blows that formed between 3340 B.C. and A.D. 780. In this region where very large to great earthquakes appear to be closely timed, archaeology is helping to develop a paleoearthquake chronology for the New Madrid seismic zone. ?? 1996 John Wiley & Sons, Inc.

  8. An analysis of seismic hazard in the Upper Rhine Graben enlightened by the example of the New Madrid seismic zone.

    Doubre, Cécile; Masson, Frédéric; Mazzotti, Stéphane; Meghraoui, Mustapha


    Seismic hazard in the "stable" continental regions and low-level deformation zones is one of the most difficult issues to address in Earth sciences. In these zones, instrumental and historical seismicity are not well known (sparse seismic networks, seismic cycle too long to be covered by the human history, episodic seismic activity) and many active structures remain poorly characterized or unknown. This is the case of the Upper Rhine Graben, the central segment of the European Cenozoic rift system (ECRIS) of Oligocene age, which extends from the North Sea through Germany and France to the Mediterranean coast over a distance of some 1100 km. Even if this region has already experienced some destructive earthquakes, its present-day seismicity is moderate and the deformation observed by geodesy is very small (below the current measurement accuracy). The strain rate does not exceed 10-10 and paleoseismic studies indicate an average return period of 2.5 to 3 103 ka for large earthquakes. The largest earthquake known for this zone is the 1356 Basel earthquake, with a magnitude generally estimated about 6.5 (Meghraoui et al., 2001) but recently re-evaluated between 6.7 and 7.1 (Fäh et al et al., 2009). A comparison of the Upper Rhine Graben with equivalent regions around the world could help improve our evaluation of seismic hazard of this region. This is the case of the New Madrid seismic zone, one of the best studied intraplate system in central USA, which experienced an M 7.0 - 7.5 earthquake in 1811-1812 and shares several characteristics with the Upper Rhine Graben, i.e. the general framework of inherited geological structures (reactivation of a failed rift / graben), seismicity patterns (spatial variability of small and large earthquakes), the null or low rate of deformation, and the location in a "stable" continental interior. Looking at the Upper Rhine Graben as an analogue of the New Madrid seismic zone, we can re-evaluate its seismic hazard and consider the

  9. Shear Wave Splitting from Local Earthquakes in the New Madrid Seismic Zone

    Martin, P.; Arroucau, P.; Vlahovic, G.


    In this study we investigate crustal anisotropy in the New Madrid seismic zone (NMSZ), by analyzing shear wave splitting from local earthquake data. The NMSZ is centrally located in the United States, spanning portions of western Tennessee, northeastern Arkansas, and southeastern Missouri. The NMSZ is also the location in which three of the largest known earthquakes took place in North America, occurring in 1811-1812. Although many seismic studies have been performed in this region, there is no consensus about which driving mechanism could satisfy both the current observations, as well as the historically observed seismicity. Therefore, it is important to continue investigating the NMSZ, to gain a better understanding of its seismicity, and the possible mechanisms that drive it. The automated technique developed by Savage et al. (2010) is used to perform the shear wave splitting measurements at 120 seismic stations within the NMSZ. The Center for Earthquake Research and Information (CERI) at the University of Memphis provided data for 1151 earthquakes spanning the years 2003-2011. The initial event selection was reduced to 245 earthquakes ranging in magnitude from 2.0 to 4.6, which fell within the shear wave window of one or more of the stations. The results of this study provide information about orientation of microcracks in the upper portion of the crust; future work will include analysis for temporal and spatial variations in order to assess the state of stress in the region.

  10. Crustal deformation in the New Madrid seismic zone and the role of postseismic processes

    Boyd, Oliver; Robert Smalley, Jr; Zeng, Yuehua


    Global Navigation Satellite System data across the New Madrid seismic zone (NMSZ) in the central United States over the period from 2000 through 2014 are analyzed and modeled with several deformation mechanisms including the following: (1) creep on subsurface dislocations, (2) postseismic frictional afterslip and viscoelastic relaxation from the 1811–1812 and 1450 earthquakes in the NMSZ, and (3) regional strain. In agreement with previous studies, a dislocation creeping at about 4 mm/yr between 12 and 20 km depth along the downdip extension of the Reelfoot fault reproduces the observations well. We find that a dynamic model of postseismic frictional afterslip from the 1450 and February 1812 Reelfoot fault events can explain this creep. Kinematic and dynamic models involving the Cottonwood Grove fault provide minimal predictive power. This is likely due to the smaller size of the December 1811 event on the Cottonwood Grove fault and a distribution of stations better suited to constrain localized strain across the Reelfoot fault. Regional compressive strain across the NMSZ is found to be less than 3 × 10−9/yr. If much of the present-day surface deformation results from afterslip, it is likely that many of the earthquakes we see today in the NMSZ are aftershocks from the 1811–1812 New Madrid earthquakes. Despite this conclusion, our results are consistent with observations and models of intraplate earthquake clustering. Given this and the recent paleoseismic history of the region, we suggest that seismic hazard is likely to remain significant.

  11. Dense lower crust elevates long-term earthquake rates in the New Madrid seismic zone

    Levandowski, Will; Boyd, Oliver S.; Ramirez-Guzmán, Leonardo


    Knowledge of the local state of stress is critical in appraising intraplate seismic hazard. Inverting earthquake moment tensors, we demonstrate that principal stress directions in the New Madrid seismic zone (NMSZ) differ significantly from those in the surrounding region. Faults in the NMSZ that are incompatible with slip in the regional stress field are favorably oriented relative to local stress. We jointly analyze seismic velocity, gravity, and topography to develop a 3-D crustal and upper mantle density model, revealing uniquely dense lower crust beneath the NMSZ. Finite element simulations then estimate the stress tensor due to gravitational body forces, which sums with regional stress. The anomalous lower crust both elevates gravity-derived stress at seismogenic depths in the NMSZ and rotates it to interfere more constructively with far-field stress, producing a regionally maximal deviatoric stress coincident with the highest concentration of modern seismicity. Moreover, predicted principal stress directions mirror variations (observed independently in moment tensors) at the NMSZ and across the region.

  12. Late Pleistocene and Holocene paleoseismology of an intraplate seismic zone in a large alluvial valley, the New Madrid seismic zone, Central USA

    Guccione, Margaret J.


    The New Madrid seismic zone (NMSZ) is an intraplate right-lateral strike-slip and thrust fault system contained mostly within the Mississippi Alluvial Valley. The most recent earthquake sequence in the zone occurred in 1811 1812 and had estimated moment magnitudes of 7 8 (e.g., [Johnston, A.C., 1996. Seismic moment assessment of stable continental earthquakes, Part 3: 1811 1812 New Madrid, 1886 Charleston, and 1755 Lisbon. Geophysical Journal International 126, 314 344; Johnston, A.C., Schweig III, E.S, 1996. The enigma of the New Madrid earthquakes of 1811 1812. Annual Reviews of Earth and Planetary Sciences 24, 339 384; Hough, S.E., Armbruster, J.G., Seeber, L., Hough, J.F., 2000. On the modified Mercalli intensities and magnitudes of the New Madrid earthquakes. Journal of Geophysical Research 105 (B10), 23,839 23,864; Tuttle, M.P., 2001. The use of liquefaction features in paleoseismology: Lessons learned in the New Madrid seismic zone, central United States. Journal of Seismology 5, 361 380]). Four earlier prehistoric earthquakes or earthquake sequences have been dated A.D. 1450 ± 150, 900 ± 100, 300 ± 200, and 2350 B.C. ± 200 years using paleoliquefaction features, particularly those associated with native American artifacts, and in some cases surface deformation ([Craven, J. A. 1995. Paleoseismology study in the New Madrid seismic zone using geological and archeological features to constrain ages of liquefaction deposits. M.S thesis, University of Memphis, Memphis, TN, U.S.A.; Tuttle, M.P., Lafferty III, R.H., Guccione, M.J., Schweig III, E.S., Lopinot, N., Cande, R., Dyer-Williams, K., Haynes, M., 1996. Use of archaeology to date liquefaction features and seismic events in the New Madrid seismic zone, central United States. Geoarchaeology 11, 451 480; Guccione, M.J., Mueller, K., Champion, J., Shepherd, S., Odhiambo, B., 2002b. Stream response to repeated co-seismic folding, Tiptonville dome, western Tennessee. Geomorphology 43(2002), 313 349; Tuttle, M

  13. Crust and Upper Mantle Velocity Structure of the New Madrid Seismic Zone

    Nyamwandha, C. A.; Powell, C. A.; Langston, C. A.


    Detailed P wave velocity (Vp) and S wave velocity models (Vs) and Vp/Vs ratios for the crust and upper mantle associated with the New Madrid Seismic Zone (NMSZ) are presented. The specific study region spans latitude 34 to 39.5 degrees north and longitude 87 to 93 degrees west and extends to a depth of at least 500 km. The density of data from three networks - The Cooperative New Madrid Seismic Network (CNMSN) operated by CERI, the Earthscope transportable array (TA), and the FlexArray (FA) Northern Embayment Lithospheric Embayment (NELE) project stations - provides us with the opportunity to derive detailed velocity models for this region. We use arrival times from local and regional earthquakes and travel time residuals from teleseismic earthquakes recorded by the three networks from September 2011 to date. The teleseismic body wave arrival times are measured using an Automated and Interactive Measurement of Body Wave Arrival Times (AIMBAT) package (Lou et al., 2012). We perform a joint local and teleseismic inversion (Zhao et al.,1994) to determine the velocity structure. For the local events, the hypocenters are relocated iteratively in the inversion process using an efficient 3-D ray tracing technique. We image a significant low velocity anomaly in the upper mantle with a concentration at about 200 - 300 km depth and it is a consistent feature in both the Vp and Vs tomography results. Checkerboard tests show that the spatial resolution is high in the upper mantle especially for the Vp model. The spatial resolution in the crust is fairly high for most of the study area except at the edges and the southeastern part, which can be attributed to diminished local earthquake activity. We perform synthetic tests to isolate smearing effects and further confirm the features in the tomographic images. Vp/Vs ratios are determined for the portions of the model with highest resolution. Preliminary results indicate that significant Vp/Vs ratio variations are present only at

  14. Types of damage that could result from a great earthquake in the New Madrid, Missouri, seismic zone

    Hopper, M.G.; Algermissen, S.T.


    In the winter of 1811–1812 a series of three great earthquakes occurred in the New Madrid seismic zone. In addition to the three principal shocks, at least 15 other earthquakes, Io ≥ VIII, occurred within a year of the first large earthquake on December 16, 1811. The three main shocks were felt over the entire eastern United States. They were strong enough to cause minor damage as far away as Indiana and Ohio on the north, the Carolinas on the east, and southern Mississippi on the south. They were strong enough to cause severe or structural damage in parts of Missouri, Illinois, Indiana, Kentucky, Tennessee, Mississippi, and Arkansas. The section of this poster titled "Seismic history of the New Madrid region" describes what happened in the epicentral region. Fortunately, few people lived in the severely shaken area in 1811; that is not the case today. What would happen if a series of earthquakes as large and numerous as the "New Madrid" earthquakes were to occur in the New Madrid seismic zone today?

  15. Stressing of the New Madrid Seismic Zone by a lower crust detachment fault

    Stuart, William D.; Hildenbrand, Thomas G.; Simpson, Robert W.


    A new mechanical model for the cause of the New Madrid seismic zone in the central United States is analyzed. The model contains a subhorizontal detachment fault which is assumed to be near the domed top surface of locally thickened anomalous lower crust ("rift pillow"). Regional horizontal compression induces slip on the fault, and the slip creates a stress concentration in the upper crust above the rift pillow dome. In the coseismic stage of the model earthquake cycle, where the three largest magnitude 7-8 earthquakes in 1811-1812 are represented by a single model mainshock on a vertical northeast trending fault, the model mainshock has a moment equivalent to a magnitude 8 event. During the interseismic stage, corresponding to the present time, slip on the detachment fault exerts a right-lateral shear stress on the locked vertical fault whose failure produces the model mainshock. The sense of shear is generally consistent with the overall sense of slip of 1811-1812 and later earthquakes. Predicted rates of horizontal strain at the ground surface are about 10-7 year-1 and are comparable to some observed rates. The model implies that rift pillow geometry is a significant influence on the maximum possible earthquake magnitude.

  16. New evidence for a large earthquake in the New Madrid seismic zone between A.D. 1400 and 1670

    Tuttle, M. P.; Collier, J.; Wolf, L. W.; Lafferty, R. H., III


    In an integrated geological, archaeological, and geophysical study in the New Madrid seismic zone of the southeastern United States, we documented a prehistoric sand blow and related feeder dikes at an archaeological site near Steele, Missouri. Archaeological analysis combined with radiocarbon dating suggest that the earthquake-induced features formed between A.D. 1400 and 1670. This paleoseismic study provides the best evidence to date for a large earthquake occurring in the zone within ˜400 yr prior to the 1811 1812 New Madrid earthquake sequence. To determine an optimal location for excavating at the study site, we mapped surficial artifact density and conducted geophysical surveys. In doing so, we were able to reveal critical relationships for constraining the age of the prehistoric earthquake with minimal impact to the archaeological site.

  17. Local Wave Propagation in the Kachchh Basin, India: Synergy With the New Madrid Seismic Zone

    Langston, C. A.; Kang, D.; Bodin, P.; Horton, S.


    Aftershocks of the Mw7.6 Bhuj earthquake are used to infer velocity structure and the nature of wave propagation within the Kachchh Basin, India. The data were collected from a joint MAEC/ISTAR deployment of seismographs within 3 weeks of the main event and from existing broadband stations in the region under the India Meteorological Department. Waveforms are available from events that span the entire thickness of the crust and display a variety of wave propagation effects due to low-velocity near-surface site structure and larger structure of the Mesozoic Kachchh basin. These effects include near-site, high frequency reverberations in P and S waves, Sp and Ps mode conversions, PL waves within the Mesozoic basin, basin S multiples, and surface waves. Surface wave group velocity dispersion yields estimates of basin shear wave velocity, and when coupled to analysis of large observed Sp conversions, give a migrated image of stratigraphy within the Banni plains that agrees favorably with published stratigraphy. Identification of basin structure effects allows constraints to be placed on aftershock source depths that are needed in evaluating standard earthquake locations. Structure models are used to construct Green's functions for determining source parameters through waveform modeling. Although stations of the aftershock network were situated on a variety of sites that varied from consolidated Mesozoic bedrock to unconsolidated recent sediments, all stations show major wave propagation effects due to basin fill that must be included in source parameter estimation. These effects seen in India have many similarities to wave propagation effects observed within the Mississippi embayment from microearthquakes in the New Madrid Seismic Zone (NMSZ) of the central U.S. Joint waveform studies are motivating new ways of understanding wave propagation and source processes within both areas.

  18. Mapping of Crustal Anisotropy in the New Madrid Seismic Zone with Shear Wave Splitting

    Martin, P.; Arroucau, P.; Vlahovic, G.


    Crustal anisotropy in the New Madrid seismic zone (NMSZ) is investigated by analyzing shear wave splitting measurements from local earthquake data. For the initial data set, the Center for Earthquake Research and Information (CERI) provided over 3000 events, along with 900 seismograms recorded by the Portable Array for Numerical Data Acquisition (PANDA) network. Data reduction led to a final data set of 168 and 43 useable events from the CERI and PANDA data, respectively. From this, 186 pairs of measurements were produced from the CERI data set as well as 49 from the PANDA data set, by means of the automated shear wave splitting measurement program MFAST. Results from this study identified two dominant fast polarization directions, striking NE-SW and WNW-ESE. These are interpreted to be due to stress aligned microcracks in the upper crust. The NE-SW polarization direction is consistent with the maximum horizontal stress orientation of the region and has previously been observed in the NMSZ, while the WNW-ESE polarization direction has not. Path normalized time delays from this study range from 1-33 ms/km for the CERI network data, and 2-31 ms/km for the PANDA data, giving a range of estimated differential shear wave anisotropy between 1% and 8%, with the majority of large path normalized time delays (>20 ms/km) located along the Reelfoot fault segment. The estimated differential shear wave anisotropy values from this study are higher than those previously determined in the region, and are attributed to high crack densities and high pore fluid pressures, which agree with previous results from local earthquake tomography and microseismic swarm analysis in the NMSZ.

  19. Recognizing and dating prehistoric liquefaction features: Lessons learned in the New Madrid seismic zone, central United States

    Tuttle, M.P.; Schweig, E.S.


    The New Madrid seismic zone (NMSZ), which experienced severe liquefaction during the great New Madrid, Missouri, earthquakes of 1811 and 1812 as well as during several prehistoric earthquakes, is a superb laboratory for the study of world-class, arthquake-induced liquefaction features and their use in paleoseismology. In seismically active regions like the NMSZ, frequent large earthquakes can produce a complex record of liquefaction events that is difficult to interpret. Lessons learned studying liquefaction features in the NMSZ may help to unravel the paleoseismic record in other seismically active regions. Soil characteristics of liquefaction features, as well as their structural and sratigraphic relations to Native American occupation horizons and other cultural features, an help to distinguish prehistoric liquefaction features from historic features. In addition, analyses of artifact assemblages and botanical content of cultural horizons can help to narrow the age ranges of liquefaction features. Future research should focus on methods for defining source areas and estimating magnitudes of prehistoric earthquakes from liquefaction features. Also, new methods for dating liquefaction features are needed.

  20. Statistical analysis of factors affecting landslide distribution in the new Madrid seismic zone, Tennessee and Kentucky

    Jibson, R.W.; Keefer, D.K.


    and earth flows in the area are spatially related to the 1811-12 earthquake hypocenters and were thus probably triggered by those earthquakes. These results are consistent with findings of other recent investigations of landslides in the area that presented field, historical, and analytical evidence to demonstrate that old landslides in the area formed during the 1811-12 New Madrid earthquakes. Results of the multiple linear regression can also be used to approximate the relative susceptibility of the bluffs in the study area to seismically induced landsliding. ?? 1989.

  1. Seismic anisotropy beneath the Mississippi Embayment and the New Madrid Seismic Zone: A study of shear wave splitting

    Nyamwandha, Cecilia A.; Powell, Christine A.


    Shear wave splitting associated with the Mississippi Embayment (ME) is determined using teleseismic SKS phases recorded by the Northern Embayment Lithosphere Experiment (NELE), the USArray Transportable Array (TA), and the New Madrid seismic network for the period 2005-2016. Our data set consists of 5900 individual splitting measurements from 257 earthquakes recorded at 151 stations within and outside the ME. Stations outside of the ME exhibit significant shear wave splitting, with average delay times between 0.4 s and 1.8 s. To the northeast and east of the ME, nearly all observed fast orientations are approximately oriented northeast-southwest, in agreement with absolute plate motion (APM) predicted by HS3-Nuvel-1A. The homogeneity of the fast orientations in this region suggests that the splitting is due to active flow in the asthenosphere. A counterclockwise rotation in the splitting orientation is observed moving northeast to northwest across the study area. Inside the ME, some stations show large and systematic deviations of the measured fast orientations from the APM. The delay times within the entire ME range from 0.9 s to 2.1 s. Splitting complexity is attributed to relic lithospheric fabrics formed during past tectonic events including passage of a hot spot in mid-Cretaceous time. The anisotropy may also be linked to the presence of a southwest dipping region of low P and S wave velocities below the ME or to deeper flow in the asthenosphere.

  2. Earthquake-induced liquefaction features in the coastal setting of South Carolina and in the fluvial setting of the New Madrid seismic zone

    Obermeier, S.F.; Jacobson, R.B.; Smoot, J.P.; Weems, R.E.; Gohn, G.S.; Monroe, J.E.; Powars, D.S.


    Many types of liquefaction-related features (sand blows, fissures, lateral spreads, dikes, and sills) have been induced by earthquakes in coastal South Carolina and in the New Madrid seismic zone in the Central United States. In addition, abundant features of unknown and nonseismic origin are present. Geologic criteria for interpreting an earthquake origin in these areas are illustrated in practical applications; these criteria can be used to determine the origin of liquefaction features in many other geographic and geologic settings. In both coastal South Carolina and the New Madrid seismic zone, the earthquake-induced liquefaction features generally originated in clean sand deposits that contain no or few intercalated silt or clay-rich strata. The local geologic setting is a major influence on both development and surface expression of sand blows. Major factors controlling sand-blow formation include the thickness and physical properties of the deposits above the source sands, and these relationships are illustrated by comparing sand blows found in coastal South Carolina (in marine deposits) with sand blows found in the New Madrid seismic zone (in fluvial deposits). In coastal South Carolina, the surface stratum is typically a thin (about 1 m) soil that is weakly cemented with humate, and the sand blows are expressed as craters surrounded by a thin sheet of sand; in the New Madrid seismic zone the surface stratum generally is a clay-rich deposit ranging in thickness from 2 to 10 m, in which case sand blows characteristically are expressed as sand mounded above the original ground surface. Recognition of the various features described in this paper, and identification of the most probable origin for each, provides a set of important tools for understanding paleoseismicity in areas such as the Central and Eastern United States where faults are not exposed for study and strong seismic activity is infrequent.

  3. The Effects of Mississippi Embayment Sediments on Local Earthquake Tomography Models for the New Madrid Seismic Zone

    Powell, C.; Withers, M.


    The effects of velocity and thickness variations in thick, unconsolidated Mississippi Embayment sediments on local earthquake tomography for the New Madrid seismic zone are investigated using normal station corrections, synthetic modeling, and application of a sediment correction based upon independent knowledge of sediment thickness and velocity structure. Synthetic modeling indicates that smearing from strong velocity perturbations in the unconsolidated sediments can influence the uppermost basement portion of the P wave velocity solution and can extend into deeper portions of the S wave velocity solution. However, there is little evidence for smearing due to velocity perturbations in the unconsolidated sediments in inversion results obtained using real arrival time data. The clustered distribution of hypocenters makes station corrections sensitive to velocity variations located deeper than the unconsolidated sediments and application of station corrections removes useful information about the basement from the inversion solution. The sediment correction also appears to remove useful information from the inversion solution but is an improvement for the P wave solution over removal of station corrections. There is no evidence that the sediment correction is removing smearing effects produced by velocity perturbations in the unconsolidated sediments. The unconsolidated sediments do not appear to be exerting a first order effect on local earthquake tomography solutions.

  4. Attenuation of Lg waves in the New Madrid seismic zone of the central United States using the coda normalization method

    Nazemi, Nima; Pezeshk, Shahram; Sedaghati, Farhad


    Unique properties of coda waves are employed to evaluate the frequency dependent quality factor of Lg waves using the coda normalization method in the New Madrid seismic zone of the central United States. Instrument and site responses are eliminated and source functions are isolated to construct the inversion problem. For this purpose, we used 121 seismograms from 37 events with moment magnitudes, M, ranging from 2.5 to 5.2 and hypocentral distances from 120 to 440 km recorded by 11 broadband stations. A singular value decomposition (SVD) algorithm is used to extract Q values from the data, while the geometric spreading exponent is assumed to be a constant. Inversion results are then fitted with a power law equation from 3 to 12 Hz to derive the frequency dependent quality factor function. The final results of the analysis are QVLg (f) = (410 ± 38) f0.49 ± 0.05 for the vertical component and QHLg (f) = (390 ± 26) f0.56 ± 0.04 for the horizontal component, where the term after ± sign represents one standard error. For stations within the Mississippi embayment with an average sediment depth of 1 km around the Memphis metropolitan area, estimation of quality factor using the coda normalization method is not well-constrained at low frequencies (f < 3 Hz). There may be several reasons contributing to this issue, such as low frequency surface wave contamination, site effects, or even a change in coda wave scattering regime which can exacerbate the scatter of the data.

  5. Topography and tectonics of the central New Madrid seismic zone: Results of numerical experiements using a three-dimensional boundary element program

    Gomberg, Joan; Ellis, Michael


    We present results of a series of numerical experiments designed to test hypothetical mechanisms that derive deformation in the New Madrid seismic zone. Experiments are constrained by subtle topography and the distribution of seismicity in the region. We use a new boundary element algorithm that permits calcuation of the three-dimensional deformation field. Surface displacement fields are calculated for the New Madrid zone under both far-field (plate tectonics scale) and locally derived driving strains. Results demonstrate that surface displacement fields cannot distinguish between either a far-field simple or pure shear strain field or one that involves a deep shear zone beneath the upper crustal faults. Thus, neither geomorphic nor geodetic studies alone are expected to reveal the ultimate driving mechanism behind the present-day deformation. We have also tested hypotheses about strain accommodation within the New Madrid contractional step-over by including linking faults, two southwest dipping and one vertical, recently inferred from microearthquake data. Only those models with step-over faults are able to predict the observed topography. Surface displacement fields for long-term, relaxed deformation predict the distribution of uplift and subsidence in the contractional step-over remarkably well. Generation of these displacement fields appear to require slip on both the two northeast trending vertical faults and the two dipping faults in the step-over region, with very minor displacements occurring during the interseismic period when the northeast trending vertical faults are locked. These models suggest that the gently dippling central step-over fault is a reverse fault and that the steeper fault, extending to the southeast of the step-over, acts as a normal fault over the long term.

  6. Topography and tectonics of the central New Madrid seismic zone: Results of numerical experiements using a three-dimensional boundary element program

    Gomberg, Joan; Ellis, Michael


    We present results of a series of numerical experiments designed to test hypothetical mechanisms that derive deformation in the New Madrid seismic zone. Experiments are constrained by subtle topography and the distribution of seismicity in the region. We use a new boundary element algorithm that permits calcuation of the three-dimensional deformation field. Surface displacement fields are calculated for the New Madrid zone under both far-field (plate tectonics scale) and locally derived driving strains. Results demonstrate that surface displacement fields cannot distinguish between either a far-field simple or pure shear strain field or one that involves a deep shear zone beneath the upper crustal faults. Thus, neither geomorphic nor geodetic studies alone are expected to reveal the ultimate driving mechanism behind the present-day deformation. We have also tested hypotheses about strain accommodation within the New Madrid contractional step-over by including linking faults, two southwest dipping and one vertical, recently inferred from microearthquake data. Only those models with step-over faults are able to predict the observed topography. Surface displacement fields for long-term, relaxed deformation predict the distribution of uplift and subsidence in the contractional step-over remarkably well. Generation of these displacement fields appear to require slip on both the two northeast trending vertical faults and the two dipping faults in the step-over region, with very minor displacements occurring during the interseismic period when the northeast trending vertical faults are locked. These models suggest that the gently dippling central step-over fault is a reverse fault and that the steeper fault, extending to the southeast of the step-over, acts as a normal fault over the long term.

  7. Experiment in New Madrid Zone to employ active source

    Langston, Charles A.; Mooney, Walter; Bodin, Paul; Powell, Christine; Withers, Mitch

    An active source seismic experiment is scheduled for the end of October in the central United States' New Madrid Seismic Zone (NMSZ). Researchers from the center for Earthquake Research and Information (CERI) of the University of Memphis and the U.S. Geological Survey are planning 2600-lb and 5000-lb explosions at the southern and northern ends of the NMSZ, respectively. Broadband seismic instruments, other temporary broadband seismic stations, and an array of accelerographs near each source will record the large surface waves generated by the explosions in the unconsolidated sediments of the Mississippi embayment.

  8. Stratigraphic evidence for millennial-scale temporal clustering of earthquakes on a continental-interior fault: Holocene Mississippi River floodplain deposits, New Madrid seismic zone, USA

    Holbrook, John; Autin, Whitney J.; Rittenour, Tammy M.; Marshak, Stephen; Goble, Ronald J.


    The earthquake cycles that characterize continental-interior areas that are far from active plate boundaries have proven highly cryptic and difficult to resolve. We used a novel paleoseismic proxy to address this issue. Namely, we reconstructed Holocene Mississippi River channels from maps of floodplain strata in order to identify channel perturbations reflective of major displacement events on the high-hazard and mid-plate Reelfoot thrust fault, New Madrid seismic zone, U.S.A. Only three discrete slip events are currently documented for the Reelfoot fault (˜ AD 900, ˜ AD 1450, and AD 1812). This study extends this record and, thus, illustrates the utility of stratigraphic proxies as paleoseismic tools. We concurrently offer here some of the first quantified response times for tectonically induced channel pattern changes in large alluvial rivers. We identified at least two cycles of pervasive meandering that were interrupted by channel-straightening responses occurring upstream of the Reelfoot fault scarp. These straightening responses initiated at 2244 BC +/- 269 to 1620 BC +/- 220 and ˜ AD 900, respectively, and each records initiation of a period of Reelfoot fault slip after millennia of relative tectonic quiescence. The second (or New Madrid) straightening response was triggered by the previously known ˜ AD 900 fault slip event, and this initial low sinuosity has been protracted until the modern day by the latter ˜ AD 1450 and AD 1812 events. The first (or Bondurant) straightening response began a period of several hundred to ˜ 1400 years of low river sinuosity which evidences a similar period of multiple recurrent displacement events on the Reelfoot fault. These Bondurant events predate the existing paleoseismic record for the Reelfoot fault. These data offer initial evidence that slip events on the Reelfoot fault were temporally clustered on millennial scales and, thus, offers the first direct evidence for millennial-scale clustering of earthquakes on a

  9. A joint local, regional and teleseismic tomography study and shear wave splitting beneath the Mississippi Embayment and New Madrid seismic zone

    Nyamwandha, Cecilia Anyango

    Part 1: We have determined detailed crust and upper mantle 3-D P wave and S wave velocity models to a depth of 400 km for the Mississippi Embayment (ME) and the New Madrid seismic zone (NMSZ). This study incorporates data from three networks; the New Madrid Seismic Network (CNMSN) operated by the Center for Earthquake Research and Information (CERI), the Earthscope Transportable Array (TA), and the FlexArray (FA) Northern Embayment Lithospheric Experiment (NELE) project stations to aid in constructing the most detailed velocity images for the NMSZ to date. For the crust we observe a separation of velocity highs from velocity lows along the axis of the Mississippi Valley Graben (MVG). For the upper mantle, we image a significant low velocity anomaly of ˜ -3% to -5 % at depths of 100 - 250 km. A high velocity anomaly of ˜ +3% to +4% is observed at depths of 80 - 160 km and it occurs along the sides and top of the low velocity anomaly. The Vp and Vs solutions in the upper mantle show a remarkable similarity both in shape and anomaly magnitude. We propose that the observed low velocity features in the upper mantle are as a result of various tectonic activities in the area, which could result in: 1) Rejuvenated/primitive mantle, 2) Elevated temperatures, and 3) Increased fluid content. A combination of elevated temperatures and increased fluid content reduce P wave velocity (Vp) whereas the three effects combined significantly reduce S wave velocity (Vs). The high velocity anomalies observed are associated with mafic rocks emplaced in the lithosphere beneath the ME during initial rifting in the early Paleozoic and/or remnants of the depleted, lower portion of the lithosphere. Part 2: Using teleseismic SKS phases recorded with the Northern Embayment Lithosphere Experiment (NELE), and the USArray Transportable Array (TA), we apply the SplitLab processing environment to measure shear wave splitting within and outside the Mississippi Embayment (ME) for the period 2011

  10. Madrid



    The capital of Spain since 1562, Madrid is located on the geographic center of the Iberian Peninsula. Because of its central location and high altitude, the climate of Madrid is characterized by warm dry summers and cool winters. Madrid is a city of great monuments. Among its highlights are the medieval center dating back to the Habsburg Empire and the Prado Museum. "El Madrid de los Austrias" is how Spaniards call the part of

  11. New national seismic zoning map of China



    A new set of seismic zoning maps were published in August 1,200l. It includes two maps, one is the seismic zon-ing map of peak acceleration, and the other is the zoning map of the characteristic period of the response spectrum.The exceeding probability of the map is 10% within 50 years. The scale of the map is 1:4 000 000. These mapsserve as the national standard. The background of this project, technical approach and key scientific measures, thebasic feature and the application of the maps are introduced in this paper.

  12. Seismically induced liquefaction structures in La Magdalena archaeological site, the 4th century AD Roman Complutum (Madrid, Spain)

    Rodríguez-Pascua, M. A.; Silva, P. G.; Perucha, M. A.; Giner-Robles, J. L.; Heras, C.; Bastida, A. B.; Carrasco, P.; Roquero, E.; Lario, J.; Bardaji, T.; Pérez-López, R.; Elez, J.


    The ancient Roman city of Complutum (Alcalá de Henares, Madrid), founded in the 1st century AD, was one of the most important cities of Hispania. The old Roman city was destroyed, abruptly abandoned, relocated close by and rebuilt during the late 4th century AD. Destruction of the city and its relocation has not yet been explained by archaeologists. In this paper, with our multidisciplinary approach, we identify and characterize earthquake archaeological effects (EAEs) affecting the archaeological site, the La Magdalena, an agricultural holding 4 km from the core of Complutum. The most important EAEs in the site are liquefactions (sand dikes and explosive sand-gravel craters) affecting Roman structures, such as water tanks (cisterns), houses and graves. Ground liquefaction generated significant ground cracks, explosive craters and folds in foundations of buildings. Several other Roman sites throughout the valley were also abandoned abruptly during the 4th century AD, in some cases with EAEs of similar origin. This suggests the occurrence of a 5.0-6.6 Mw seismic event in the zone, in accordance with the minimum empirical limit of seismically-induced liquefaction and the maximum surface rupture length of the Henares fault.

  13. Seismic fault zone trapped noise

    Hillers, G; Campillo, M; Ben‐Zion, Y; Roux, P


    Systematic velocity contrasts across and within fault zones can lead to head and trapped waves that provide direct information on structural units that are important for many aspects of earthquake and fault mechanics...

  14. Seismic probing of continental subduction zones

    Zhao, Liang; Xu, Xiaobing; Malusà, Marco G.


    High-resolution images of Earth's interior provide pivotal information for the understanding of a range of geodynamic processes, including continental subduction and exhumation of ultrahigh-pressure (UHP) metamorphic rocks. Here we present a synthesis of available global seismic observations on continental subduction zones, and selected examples of seismic probing from the European Alps, the Himalaya-Tibet and the Qinling-Dabie orogenic belts. Our synthesis and examples show that slabs recognized beneath exhumed continental UHP terranes generally have shallow dip angles (100 km. Slabs underlined by a clear high velocity anomaly from Earth's surface to the mantle are generally Cenozoic in age. Some of these slabs are continuous, whereas other continental subduction zones are located above discontinuous high velocity anomalies possibly suggesting slab breakoff. The density of seismic stations and the quality of recordings are of primary importance to get high-resolution images of the upper mantle to be used as a starting point to provide reliable geodynamic interpretations. In some cases, areas previously indicated as possible site of slab breakoff, such as the European Alps, have been later proven to be located above a continuous slab by using higher quality travel time data from denser seismic arrays. Discriminating between oceanic and continental slabs can be challenging, but valuable information can be provided by combining teleseismic tomography and receiver function analysis. The upper mantle beneath most continental UHP terranes generally shows complex seismic anisotropy patterns that are potentially preserved even in pre-Cenozoic subduction zones. These patterns can be used to provide information on continental slabs that are no longer highlighted by a clear high-velocity anomaly.

  15. Discussion about the relationship between seismic belt and seismic statistical zone

    潘华; 金严; 胡聿贤


    This paper makes a summary of status of delimitation of seismic zones and belts of China firstly in aspects of studying history, purpose, usage, delimiting principles, various presenting forms and main specialties. Then the viewpoints are emphasized, making geographical divisions by seismicity is just the most important purpose of delimiting seismic belts and the concept of seismic belt is also quite different from that of seismic statistical zone used in CPSHA method. The concept of seismic statistical zone and its history of evolvement are introduced too. Large differences between these two concepts exist separately in their statistical property, actual meaning, gradation, required scale, and property of refusing to overlap each other, aim and usage of delimitation. But in current engineering practice, these two concepts are confused. On the one hand, it causes no fit theory for delimiting seismic statistical zone in PSHA to be set up; on the other hand, researches about delimitation of seismic belts with purposes of seismicity zoning and studying on structural environment, mechanism of earthquake generating also pause to go ahead. Major conclusions are given in the end of this paper, that seismic statistical zone bases on the result of seismic belt delimiting, it only arises in and can be used in the especial PSHA method of China with considering spatially and temporally inhomogeneous seismic activities, and its concept should be clearly differentiated from the concept of seismic belt.

  16. High Resolution Seismic Imaging of the Brawley Seismic Fault Zone

    Goldman, M.; Catchings, R. D.; Rymer, M. J.; Lohman, R. B.; McGuire, J. J.; Sickler, R. R.; Criley, C.; Rosa, C.


    In March 2010, we acquired a series of high-resolution P-wave seismic reflection and refraction data sets across faults in the Brawley seismic zone (BSZ) within the Salton Sea Geothermal Field (SSGF). Our objectives were to determine the dip, possible structural complexities, and seismic velocities within the BSZ. One dataset was 3.4 km long trending east-west, and consisted of 334 shots recorded by a 2.4 km spread of 40 hz geophones placed every 10 meters. The spread was initially laid out from the first station at the eastern end of the profile to roughly 2/3 into the profile. After about half the shots, the spread was shifted from roughly 1/3 into the profile to the last station at the western end of the profile. P-waves were generated by Betsy-Seisgun 'shots' spaced every 10 meters. Initial analysis of first breaks indicate near-surface velocities of ~500-600 meters/sec, and deeper velocities of around 2000 meters/sec. Preliminary investigation of shot gathers indicate a prominent fault that extends to the ground surface. This fault is on a projection of the Kalin fault from about 40 m to the south, and broke the surface down to the west with an approximately north-south strike during a local swarm of earthquakes in 2005 and also slipped at the surface in association with the 2010 El Mayor-Cucapah earthquake in Baja California. The dataset is part of the combined Obsidian Creep data set, and provides the most detailed, publicly available subsurface images of fault structures in the BSZ and SSGF.

  17. 40 CFR 258.14 - Seismic impact zones.


    ... 40 Protection of Environment 24 2010-07-01 2010-07-01 false Seismic impact zones. 258.14 Section 258.14 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) SOLID WASTES CRITERIA FOR MUNICIPAL SOLID WASTE LANDFILLS Location Restrictions § 258.14 Seismic impact zones. (a) New MSWLF units...

  18. Study on Seismic Zoning of Sino-Mongolia Arc Areas

    Xu, G.


    According to the agreement of Cooperation on seismic zoning between Institute of Geophysics, China Earthquake Administration and Research Center of Astronomy and Geophysics, Mongolian Academy of Science, the data of geotectonics, active faults, seismicity and geophysical field were collected and analyzed, then field investigation proceeded for Bolnay Faults, Ar Hutul Faults and Gobi Altay Faults, and a uniform earthquake catalogue of Mongolia and North China were established for the seismic hazard study in Sino-Mongolia arc areas. Furthermore the active faults and epicenters were mapped and 2 seismic belts and their 54 potential seismic sources are determined. Based on the data and results above mentioned the seismicity parameters for the two seismic belts and their potential sources were studied. Finally, the seismic zoning with different probability in Sino-Mongolia arc areas was carried out using China probabilistic hazard analysis method. By analyzing the data and results, we draw the following main conclusions. Firstly, the origin of tectonic stress field in the study areas is the collision and pressure of the India Plate to Eurasian Plate, passing from the Qinghai-Tibet Plateau. This is the reason why the seismicity is higher in the west than in the east, and all of earthquakes with magnitude 8 or greater occurred in the west. Secondly, the determination of the 2 arc seismic belts, Altay seismic belt and Bolnay-Baikal seismic belt, are reasonable in terms of their geotectonic location, geodynamic origin and seismicity characteristics. Finally, there are some differences between our results and the Mongolia Intensity Zoning map published in 1985 in terms of shape of seismic zoning map, especially in the areas near Ulaanbaatar. We argue that our relsults are reasonable if we take into account the data use of recent study of active faults and their parameters, so it can be used as a reference for seismic design.

  19. Seismic Zone of Craiova and its Surroundings

    Nita, Laura-Simona


    The mapping of the Romanian area, based of the seismic range, put Craiova and the metropolitan zone, in seismic class C of level 8. This increased level is due to crustal fissure, oriented N-S on the Craiova meridian, which resonates with seismic waves from Vrancea epicenter. Craiova and the metropolitan zone is placed on the separated lithologic substrates, so, the effects of seism are not uniform between urban and peri-urban areas. The highest piedmont area and the terraces (V, IV, III), with a predominant substrate of conglomerate and sandstone, decrease effect of the earthquake. The first and the second terraces and the meadow, with a predominant content of marls and clays, are very elastic and increase the effect of earthquake. The most exposed are the villages placed on the right side of the Jiu River, where these landforms are very common and in case of earthquake, can be reactivated. In Romania there are just shallow depth and intermediate depth earthquakes. The frequency of earthquakes with a greater than 7.2 magnitude on the Richter scale is three times in a century. The most magnitude for a Romanian earthquake took place on 10 of November 1940 and it has a magnitude of 7.6 on the Richter scale. The 1977 Vrancea Earthquake occurred on March 4, 21:20 local time. It had a magnitude of 7.2 with an epicenter in Vrancea. The fracture occurred at a depth of 94 kilometers but it was a multishock earthquake with several outbreaks in the south-west part of Vrancea County. In 55 seconds the earthquake killed about 1,500 people in Romania (1,400 in Bucharest), wounded more than 11,300 and about 33,000 buildings and structures collapsed. The shock wave was felt in almost all countries in the Balkan Peninsula, as well as Ukraine and Moldova, but with a lower intensity. When the moving is vertically, in a time of 7-8 seconds, the next move is horizontally. The horizontally waves, shear waves, carry 75% of total energy. The poorly constructed buildings will fall even

  20. Delineation of seismic source zones based on seismicity parameters and probabilistic evaluation of seismic hazard using logic tree approach

    K S Vipin; T G Sitharam


    The delineation of seismic source zones plays an important role in the evaluation of seismic hazard. In most of the studies the seismic source delineation is done based on geological features. In the present study, an attempt has been made to delineate seismic source zones in the study area (south India) based on the seismicity parameters. Seismicity parameters and the maximum probable earthquake for these source zones were evaluated and were used in the hazard evaluation. The probabilistic evaluation of seismic hazard for south India was carried out using a logic tree approach. Two different types of seismic sources, linear and areal, were considered in the present study to model the seismic sources in the region more precisely. In order to properly account for the attenuation characteristics of the region, three different attenuation relations were used with different weightage factors. Seismic hazard evaluation was done for the probability of exceedance (PE) of 10% and 2% in 50 years. The spatial variation of rock level peak horizontal acceleration (PHA) and spectral acceleration (Sa) values corresponding to return periods of 475 and 2500 years for the entire study area are presented in this work. The peak ground acceleration (PGA) values at ground surface level were estimated based on different NEHRP site classes by considering local site effects.

  1. Integrated seismic interpretation of the Carlsberg Fault zone, Copenhagen, Denmark

    Nielsen, Lars; Thybo, Hans; Jørgensen, Mette Iwanouw


    We locate the concealed Carlsberg Fault zone along a 12-km-long trace in the Copenhagen city centre by seismic refraction, reflection and fan profiling. The Carlsberg Fault is located in a NNW-SSE striking fault system in the border zone between the Danish Basin and the Baltic Shield. Recent eart...

  2. Quaternary grabens in southernmost Illinois: Deformation near an active intraplate seismic zone

    Nelson, W.J.; Denny, F.B.; Follmer, L.R.; Masters, J.M.


    Narrow grabens displace Quaternary sediments near the northern edge of the Mississippi Embayment in extreme southern Illinois, east-central United States. Grabens are part of the Fluorspar Area Fault Complex (FAFC), which has been recurrently active throughout Phanerozoic time. The FAFC strikes directly toward the New Madrid Seismic Zone (NMSZ), scene of some of the largest intra-plate earthquakes in history. The NMSZ and FAFC share origin in a failed Cambrian rift (Reelfoot Rift). Every major fault zone of the FAFC in Illinois exhibits Quaternary displacement. The structures appear to be strike-slip pull-apart grabens, but the magnitude and direction of horizontal slip and their relationship to the current stress field are unknown. Upper Tertiary strata are vertically displaced more than 100 m, Illinoian and older Pleistocene strata 10 to 30 m, and Wisconsinan deposits 1 m or less. No Holocene deformation has been observed. Average vertical slip rates are estimated at 0.01 to 0.03 mm/year, and recurrence intervals for earthquakes of magnitude 6 to 7 are on the order of 10,000s of years for any given fault. Previous authors remarked that the small amount of surface deformation in the New Madrid area implies that the NMSZ is a young feature. Our findings show that tectonic activity has shifted around throughout the Quaternary in the central Mississippi Valley. In addition to the NMSZ and southern Illinois, the Wabash Valley (Illinois-Indiana), Benton Hills (Missouri), Crowley's Ridge (Arkansas-Missouri), and possibly other sites have experienced Quaternary tectonism. The NMSZ may be only the latest manifestation of seismicity in an intensely fractured intra-plate region.

  3. Assessing the Seismic Potential Hazard of the Makran Subduction Zone

    Frohling, E.; Szeliga, W. M.; Melbourne, T. I.; Abolghasem, A.; Lodi, S. H.


    Long quiescent subduction zones like the Makran, Sunda, and Cascadia, which have long recurrence intervals for large (> Mw 8) earthquakes, often have poorly known seismic histories and are particularly vulnerable and often ill-prepared. The Makran subduction zone has not been studied extensively, but the 1945 Mw 8.1 earthquake and subsequent tsunami, as well as more recent mid magnitude, intermediate depth (50-100 km) seismicity, demonstrates the active seismic nature of the region. Recent increases in regional GPS and seismic monitoring now permit the modeling of strain accumulations and seismic potential of the Makran subduction zone. Subduction zone seismicity indicates that the eastern half of the Makran is presently more active than the western half. It has been hypothesized that the relative quiescence of the western half is due to aseismic behavior. However, based on GPS evidence, the entire subduction zone generally appears to be coupled and has been accumulating stress that could be released in another > 8.0 Mw earthquake. To assess the degree of coupling, we utilize existing GPS data to create a fault coupling model for the Makran using a preliminary 2-D fault geometry derived from ISC hypocenters. Our 2-D modeling is done using the backslip approach and defines the parameters in our coupling model; we forego the generation of a 3-D model due to the low spatial density of available GPS data. We compare the use of both NUVEL-1A plate motions and modern Arabian plate motions derived from GPS station velocities in Oman to drive subduction for our fault coupling model. To avoid non-physical inversion results, we impose second order smoothing to eliminate steep strain gradients. The fit of the modeled inter-seismic deformation vectors are assessed against the observed strain from the GPS data. Initial observations indicate that the entire subduction zone is currently locked and accumulating strain, with no identifiable gaps in the interseismic locking

  4. Study on Uncertainties of Seismicity Parameters b and v4 in Seismic Statistical Zones


    For several seismic statistical zones in North China, the key factors causing uncertainties in the important seismicity parameters b and v4 and the features of their uncertainties are discussed in this paper. The magnitude of uncertainty is also analyzed. It can be seen that the key influencing factors are statistical period, methods of processing statistical samples, lower limit magnitude and the annual average occurrence ratio of large earthquakes. The variation ranges of b and v4 in the Tancheng-Lujiang zone are as high as 0.2 and 1.4 respectively, which are similar to those in the Fenwei zone. They are much smaller however in the Hebei zone because of its sufficient statistical samples.

  5. Imaging fault zones using 3D seismic image processing techniques

    Iacopini, David; Butler, Rob; Purves, Steve


    and collecting these into "disturbance geobodies". These seismic image processing methods represents a first efficient step toward a construction of a robust technique to investigate sub-seismic strain, mapping noisy deformed zones and displacement within subsurface geology (Dutzer et al.,2011; Iacopini et al.,2012). In all these cases, accurate fault interpretation is critical in applied geology to building a robust and reliable reservoir model, and is essential for further study of fault seal behavior, and reservoir compartmentalization. They are also fundamental for understanding how deformation localizes within sedimentary basins, including the processes associated with active seismogenetic faults and mega-thrust systems in subduction zones. Dutzer, JF, Basford., H., Purves., S. 2009, Investigating fault sealing potential through fault relative seismic volume analysis. Petroleum Geology Conference series 2010, 7:509-515; doi:10.1144/0070509 Marfurt, K.J., Chopra, S., 2007, Seismic attributes for prospect identification and reservoir characterization. SEG Geophysical development Iacopini, D., Butler, RWH. & Purves, S. (2012). 'Seismic imaging of thrust faults and structural damage: a visualization workflow for deepwater thrust belts'. First Break, vol 5, no. 30, pp. 39-46.


    S. I. Sherman


    Full Text Available Deformation waves as a trigger mechanism of seismic activity and migration of earthquake foci have been under discussion by researchers in seismology and geodynamics for over 50 years. Four sections of this article present available principal data on impacts of wave processes on seismicity and new data. The first section reviews analytical and experimental studies aimed at identification of relationships between wave processes in the lithosphere and seismic activity manifested as space-and-time migration of individual earthquake foci or clusters of earthquakes. It is concluded that with a systematic approach, instead of using a variety of terms to denote waves that trigger seismic process in the lithosphere, it is reasonable to apply the concise definition of ‘deformation waves’, which is most often used in fact.The second section contains a description of deformation waves considered as the trigger mechanism of seismic activity. It is concluded that a variety of methods are applied to identify deformation waves, and such methods are based on various research methods and concepts that naturally differ in sensitivity concerning detection of waves and/or impact of the waves on seismic process. Epicenters of strong earthquakes are grouped into specific linear or arc-shaped systems, which common criterion is the same time interval of the occurrence of events under analysis. On site the systems compose zones with similar time sequences, which correspond to the physical notion of moving waves (Fig. 9. Periods of manifestation of such waves are estimated as millions of years, and a direct consideration of the presence of waves and wave parameters is highly challenging. In the current state-of-the-art, geodynamics and seismology cannot provide any other solution yet.The third section presents a solution considering record of deformation waves in the lithosphere. With account of the fact that all the earthquakes with М≥3.0 are associated with

  7. Influence of uncertainty in delimitation of seismic statistical zone on results of PSHA

    潘华; 黄玮琼


    The seismic hazard of research area is evaluated by probabilistic analysis method for three different seismic statistical zone scenarios. The influence of uncertainty in seismic statistical zone delimiting on the evaluation result is discussed too. It can be seen that for those local sites along zone's border or withinareas with vast change of upper bound magnitude among different scenarios the influence on seismic hazard result should not be neglected.

  8. Risk-Informed Selection of Steel Connections for Seismic Zones

    De León-Escobedo D.


    Full Text Available The findings about the fragile behavior of steel welded connections after the Northridge 1994 earthquake, specially for frames designed to withstand lateral force, has brought an amount of new attention to the design and safety issues of the welded connections for structures located on seismic zones. In México, practitioners and designers are wondering about the seismic effectiveness of the several kinds of connections as used in steel structures. A decision must be made to balance the safety required with the costs incurred after exceeding the serviceability limit state. Structural reliability techniques provide the proper framework to include the inherent uncertainties into the design process. Registered motions after the 1985 Mexico City earthquake are properly scaled according to the seismic hazard curve for soft soil in Mexico City. Earthquake occurrence is modeled as a Poisson process and the expected life-cycle cost is taken as the decision criteria. Parametric analyses allow the identification of dominant variables and ranges where one option is more recommendable than the other one. The proposed formulation may support designers and builders for the decision making process about the selection of the convenient connection type for the seismic zones with soft soil in Mexico City.

  9. Seismicity and Tectonics of the West Kaibab Fault Zone, AZ

    Wilgus, J. T.; Brumbaugh, D. S.


    The West Kaibab Fault Zone (WKFZ) is the westernmost bounding structure of the Kaibab Plateau of northern Arizona. The WKFZ is a branching complex of high angle, normal faults downthrown to the west. There are three main faults within the WKFZ, the Big Springs fault with a maximum of 165 m offset, the Muav fault with 350 m of displacement, and the North Road fault having a maximum throw of approximately 90 m. Mapping of geologically recent surface deposits at or crossing the fault contacts indicates that the faults are likely Quaternary with the most recent offsets occurring one of the most seismically active areas in Arizona and lies within the Northern Arizona Seismic Belt (NASB), which stretches across northern Arizona trending NW-SE. The data set for this study includes 156 well documented events with the largest being a M5.75 in 1959 and including a swarm of seven earthquakes in 2012. The seismic data set (1934-2014) reveals that seismic activity clusters in two regions within the study area, the Fredonia cluster located in the NW corner of the study area and the Kaibab cluster located in the south central portion of the study area. The fault plane solutions to date indicate NE-SW to EW extension is occurring in the study area. Source relationships between earthquakes and faults within the WKFZ have not previously been studied in detail. The goal of this study is to use the seismic data set, the available data on faults, and the regional physiography to search for source relationships for the seismicity. Analysis includes source parameters of the earthquake data (location, depth, and fault plane solutions), and comparison of this output to the known faults and areal physiographic framework to indicate any active faults of the WKFZ, or suggested active unmapped faults. This research contributes to a better understanding of the present nature of the WKFZ and the NASB as well.

  10. Evidence Against the New Madrid Long-Lived Aftershock Hypothesis

    Page, M. T.; Hough, S. E.


    It has been suggested that continuing seismicity in the New Madrid, central U.S. region is primarily composed of the continuing long-lived aftershock sequence of the 1811-1812 sequence, and thus cannot be taken as an indication of present-day strain accrual in the region. We examine historical and instrumental seismicity in the New Madrid region to determine if such a model is feasible given 1) the observed protracted nature of past New Madrid sequences, with multiple mainshocks with apparently similar magnitudes; 2) historical rates of M≥6 earthquakes after the initial activity in 1811-1812; and 3) the modern seismicity rate in the region. We use ETAS modeling to search for sub-critical sets of direct Omori parameters that are consistent with all of these datasets, given a realistic consideration of their uncertainties. High aftershock productivity is required both to match the observation of multiple mainshocks and to explain the modern level of activity as aftershocks; synthetic sequences consistent with these observations substantially overpredict the number of events of M≥6 that were observed in the past 200 years. Our results imply that ongoing background seismicity in the New Madrid region is driven by ongoing strain accrual processes and that, despite low deformation rates, seismic activity in the zone is not decaying with time.

  11. Seismic imaging constraints on megathrust fault zone properties

    Abers, G. A.; Janiszewski, H. A.; Keranen, K. M.; Saffer, D. M.; Shillington, D. J.


    Several lines of evidence suggest that subduction zone thrusts lie within overpressured channels. Seismic reflection data often shows a relatively thin, high-reflectivity surface with occasional bright spots, indicative of rapidly varying impedance contrasts over length scales of tens of meters. Scattered coda of teleseismic P waves, such as in receiver functions, often show a thin low-velocity layer corresponding to the top of the subducting plate. The latter have been best documented in Cascadia, where a 2-4 km thick very low velocity channel is seen above a moderately slow subducting crust, and in Alaska where similar structure has been seen. High-reflectivity bright spots occur in the same region, although perhaps over more limited areas. The low velocity zones are characterized by elevated Vp/Vs ratios (>2.0), and extend both throughout the locked, seismogenic fault zone and downdip into the region where episodic tremor and slip occur. Commonly, this combination of low velocities and high Vp/Vs is taken to indicate high pore pressures, and hence a fault zone that can withstand only very low shear stresses. However, models of the low wavespeeds suggest static porosities of 2-5% throughout a 2-4 km thick layer, extending to depths of 40 km, a situation that seems difficult to sustain. At both the Alaska and Cascadia margins, low Vp, high Poisson's ratios, and high anisotropies should result in part from the subduction of sediments well into and beyond the seismogenic zone. The presence of a significant thickness of subducted and underplated sediment is consistent with observations of preserved subduction "channels" in exhumed examples from tens of km depth. Although some elevation of pore pressure may be still needed to explain observations, if the subduction of 2-4 km of sediment is a significant factor in generating the seismic signatures, then the geophysical observations could reflect a much stronger thrust zone than one sustained by high pore pressure alone.

  12. Receiver Function Analysis of the Eastern Tennessee Seismic Zone

    Graw, J. H.; Powell, C. A.; Langston, C. A.


    We present receiver/transfer functions determined for a seismic network associated with an active, intraplate seismic zone. Basement studies within eastern Tennessee are sparse despite the fact that these rocks host the eastern Tennessee seismic zone (ETSZ) and are associated with an extensive aeromagnetic lineament called the New York-Alabama (NY-AL) lineament. The NY-AL lineament is prominent in eastern Tennessee, with a SW-NE trend, and is characterized by a lateral change in magnetic and gravity anomalies in a NW to SE direction; high magnetic and low gravity anomalies lie west of the lineament, while low magnetic and high gravity anomalies are located east of the lineament. The NY-AL lineament is thought to be an ancient strike-slip fault that is reactivating in the present day stress field. A better understanding of the basement structure within the ETSZ will aid in the assessment of its seismic hazard potential. A network maintained by the Center for Earthquake Research and Information (CERI) at the University of Memphis is located within the study area and consists of 23 short-period and three broadband seismometers. An additional station (TZTN) is maintained by IRIS and is included in our dataset. Receiver functions are computed using teleseismic earthquakes within a 30°-90° epicentral distance, at hypocentral depths greater than 30 km, and with magnitudes greater than Mw 6.0. A vertical component stack is used to obtain the best source function. A spectral waterlevel deconvolution is then used to calculate the receiver functions. Results indicate a thickening of the crust west of the NY-AL lineament and show vertical variation within the crust and upper mantle with abrupt polarity changes and strong positive and negative amplitude values. Crustal structure west of the NY-AL lineament appears to be much more complex than that east of the NY-AL lineament.

  13. Background seismicity rate at subduction zones linked to slab-bending-related hydration

    Nishikawa, Tomoaki; Ide, Satoshi


    Tectonic properties strongly control variations in seismicity among subduction zones. In particular, fluid distribution in subduction zones influences earthquake occurrence, and it varies among subduction zones due to variations in fluid sources such as hydrated oceanic plates. However, the relationship between variations in fluid distribution and variations in seismicity among subduction zones is unclear. Here we divide Earth's subduction zones into 111 regions and estimate background seismicity rates using the epidemic type aftershock sequence model. We demonstrate that background seismicity rate correlates to the amount of bending of the incoming oceanic plate, which in turn is related to the hydration of oceanic plates via slab-bending-related faults. Regions with large bending may have high-seismicity rates because a strongly hydrated oceanic plate causes high pore fluid pressure and reduces the strength of the plate interface. We suggest that variations in fluid distribution can also cause variations in seismicity in subduction zones.

  14. Seismic exploration noise reduction in the Marginal Ice Zone.

    Tollefsen, Dag; Sagen, Hanne


    A sonobuoy field was deployed in the Marginal Ice Zone of the Fram Strait in June 2011 to study the spatial variability of ambient noise. High noise levels observed at 10-200 Hz are attributed to distant (1400 km range) seismic exploration. The noise levels decreased with range into the ice cover; the reduction is fitted by a spreading loss model with a frequency-dependent attenuation factor less than for under-ice interior Arctic propagation. Numerical modeling predicts transmission loss of the same order as the observed noise level reduction and indicates a significant loss contribution from under-ice interaction.

  15. Seismic Performance Evaluation of Reinforced Concrete Moment Resisting Frames with Various Ductility in Low Seismic Zone

    N. Choopool


    Full Text Available Problem statement: Bangkok, the capital of Thailand, is at moderate risk for distant earthquake due to the ability of soft soil to amplify ground motion about 3-4 times although it locates in low seismic zone. In addition, before the enforcement of seismic loading for buildings in the Ministerial Law in 2007, many existing reinforced concrete buildings in Bangkok may have been designed without consideration for seismic loading and did not incorporate the special detailing provisions that required for ductile concrete frames. Now, guidelines for seismic loading of buildings of Thailand (DPT 1302-52 have been recently improved by adopting ASCE7-05. Approach: This study is focused on the effects of the new guidelines on cost estimates and the seismic performance of a nine-story reinforced concrete apartment building with various ductility by the nonlinear static and nonlinear dynamic analyses compared with a Gravity Load Designed (GLD building. Five selected ground motion records are investigated in the analyses. In order to examine the influence of design ductility classes, the seismic forces on moment resisting frame buildings are defined according to the newly proposed seismic specifications of Thailand with ductility from 8, 5 and 3, corresponding to Special Ductile (SDF, Intermediate Ductile (IDF and Ordinary Ductile (ODF frames, respectively. The various frames are assumed to have collapsed if the local drift exceed of 3, 2.5, 2 and 1% for SDF, IDF, ODF and GLD, respectively. Results: SDF is more ductile than that of ODF, however, the strength of SDF is less than ODF. For inelastic designs, SDF decreases stiffness and increases deflection of structures. As for the effect on cost estimates, ODF is the most expensive among ODF, IDF and SDF. Costs of SDF and IDF in Bangkok are quite similar. The study found that the average PGAs for the failure state for SDF, IDF, ODF and GLD are 0.76, 0.60, 0.50 and 0.29g, respectively. Moreover, for the

  16. From the Surface Topography to the Upper Mantle Beneath Central-Iberian-Zone. the Alcudia Seismic Experiments.

    Carbonell, R.; Ehsan, S. A.; Ayarza, P.; Martinez-Poyatos, D. J.; Simancas, J. F.; Azor, A.; Pérez-Estaún, A.


    Normal incidence and wide-angle seismic reflection data acquired in the Central and southern parts of the Iberia Peninsula resolve the internal architecture and constrain the distribution of the physical properties along an almost 350 km long transect that samples the major tectonic domains of the Iberian Massif, including the Central Iberian Zone (CIZ) and the associated sutures. The internal architecture down to almost 70 km depth (~15 s TWTT) is resolved by the normal incidence data set. It images a number of elements that characterize the tectonics of the study area, which is one of the best exposed fragment of the Variscan orogenic Belt. A well marked brittle-to-ductile (B2D) transition separates the crust in two, the upper and mid-lower parts, approximately, 13 km and 18 km thick, respectively. The upper crust appears to be decoupled from the mid-lower crust and responded differently to shortening. The Mohorovicic discontinuity is located at ~10.5 s (TWTT) , it is relatively thick, and highly reflective beneath the CIZ. The wide-angle seismic transect extended the lithospheric section towards the north across the Madrid Basin. This profile provides very strong constraints on the distribution of physical properties (P- and S- wave velocities, Poisson's ratio) of the upper lithosphere as well as a high resolution image of the base of the crust beneath the area. This data is one of the first datasets to present solid evidence of a relatively significant crustal thickening beneath the Madrid Basin. The crustal thickness varies from ~31 km beneath the CIZ to ~35.5 km beneath the Madrid Basin. This data set also reveals two major discontinuity levels, the B2D and the Moho, both represent levels of lithological/rheological variations. The characteristics of the the PmP and SmS seismic phases suggest further details on the internal structure of the Moho. Furthermore, low fold wide-angle P and S wave stacks reveal a marked crust-mantle transition which is most

  17. Location of high seismic activity zones and seismic hazard assessment in Zabrze Bielszowice coal mine using passive tomography



    In the paper results of passive tomography calculations have been presented to assess rockburst hazard and locate high seismic activity zones in the vicinity of longwall 306 in Zabrze Bielszowice coal mine. The area of study was 1000 m in X direction by 900 m in Y direction. The zones of high values of P-wave propagation velocity have been found to correlate with the distribution of large seismic tremors.

  18. Teleseismic Tomography in the Eastern Tennessee Seismic Zone

    Agbaje, T.; Arroucau, P.; Vlahovic, G.; Powell, C. A.


    The Eastern Tennessee Seismic Zone (ETSZ) is the second most active seismic region in the eastern United States and is located in the southern Appalachian fold-and-thrust belt. The earthquakes mostly occur between 5 and 25 km depth, below the decollement surface, and tend to align along the New York Alabama magnetic lineament, a linear feature attributed to a strike-slip fault affecting the Precambrian basement but having no signature in surface geology. Recent results from local tomography also show some relationship between the body-wave velocity field and earthquake distribution down to about 20 km depth. In this work, we investigate the deep 3D P-wave velocity structure of the lithosphere in the ETSZ by means of teleseismic tomography We use seismograms recorded in the last 10 years at a local array of 30 short-period stations operated by the Center for Earthquake Research and Information (CERI) in Memphis, TN. Events with magnitude greater than 5.5 and epicentral distance greater than 2500 km were selected. Relative P-wave arrival time residuals were obtained from an adaptive stacking procedure and were subsequently used in a tomographic inversion to map the 3D P-wave velocity variations beneath the array.

  19. Analysis of natural neutron flux in a seismically active zone

    V. F. Ostapenko


    Full Text Available In a seismically active zone in the near Almaty area (Kazakhstan since 1996 observations of variations of a natural neutron flux have been conducted. Sometimes the neutron flux rises sharply within the one-hour interval in comparison with the background. It occurs on the eve of activation of seismic processes. Increase of the neutron flux level had taken place from 1 h to 10 days prior to earthquakes. It is also indicated a tendency of growth of the anomaly level in accordance with the growth of energetic class of the subsequent earthquake. A character of connection between the neutron flux and earthquakes is still not clear. It is proposed that the neutron flux anomalies caused by variations of cosmic radiation intensity under action of fluxes of solar material, which is burst into interplanetary space (solar wind during solar flares. Energy of the solar wind transferred to Earth puts into action a trigger mechanism of the process of initiation of earthquakes at those places where conditions have already been prepared for them. The neutron flux anomalies can be used as substantial additional information for classical geophysical methods of short-term earthquake prediction.

  20. The Salton Seismic Imaging Project (SSIP): Active Rift Processes in the Brawley Seismic Zone

    Han, L.; Hole, J. A.; Stock, J. M.; Fuis, G. S.; Rymer, M. J.; Driscoll, N. W.; Kent, G.; Harding, A. J.; Gonzalez-Fernandez, A.; Lazaro-Mancilla, O.


    The Salton Seismic Imaging Project (SSIP), funded by NSF and USGS, acquired seismic data in and across the Salton Trough in southern California and northern Mexico in March 2011. The project addresses both rifting processes at the northern end of the Gulf of California extensional province and earthquake hazards at the southern end of the San Andreas Fault system. Seven lines of onshore refraction and low-fold reflection data were acquired in the Coachella, Imperial, and Mexicali Valleys, two lines and a grid of airgun and OBS data were acquired in the Salton Sea, and onshore-offshore data were recorded. Almost 2800 land seismometers and 50 OBS's were used in almost 5000 deployments at almost 4300 sites, in spacing as dense as 100 m. These instruments received seismic signals from 126 explosive shots up to 1400 kg and over 2300 airgun shots. In the central Salton Trough, North American lithosphere appears to have been rifted completely apart. Based primarily on a 1979 seismic refraction project, the 20-22 km thick crust is apparently composed entirely of new crust added by magmatism from below and sedimentation from above. Active rifting of this new crust is manifested by shallow (geothermal energy production. This presentation is focused on an onshore-offshore line of densely sampled refraction and low-fold reflection data that crosses the Brawley Seismic Zone and Salton Buttes in the direction of plate motion. At the time of abstract submission, data analysis was very preliminary, consisting of first-arrival tomography of the onshore half of the line for upper crustal seismic velocity. Crystalline basement (>5 km/s), comprised of late-Pliocene to Quaternary sediment metamorphosed by the high heat flow, occurs at ~2 km depth beneath the Salton Buttes and geothermal field and ~4 km depth south of the BSZ. Preliminary result suggests that the velocity of basement is lower in the BSZ than to the south, which may result from fracturing. Basement velocity appears to be

  1. Seismic source zoning and maximum credible earthquake prognosis of the Greater Kashmir Territory, NW Himalaya

    Sana, Hamid; Nath, Sankar Kumar


    We present the seismic source zoning of the tectonically active Greater Kashmir territory of the Northwestern Himalaya and seismicity analysis (Gutenberg-Richter parameters) and maximum credible earthquake ( m max) estimation of each zone. The earthquake catalogue used in the analysis is an extensive one compiled from various sources which spans from 1907 to 2012. Five seismogenic zones were delineated, viz. Hazara-Kashmir Syntaxis, Karakorum Seismic Zone, Kohistan Seismic Zone, Nanga Parbat Syntaxis, and SE-Kashmir Seismic Zone. Then, the seismicity analysis and maximum credible earthquake estimation were carried out for each zone. The low b value (Nanga Parbat Syntaxis Seismic Zone and SE-Kashmir Seismic Zone. The m max was estimated following three different methodologies, the fault parameter approach, convergence rates using geodetic measurements, and the probabilistic approach using the earthquake catalogue and is estimated to be M w 7.7, M w 8.5, and M w 8.1, respectively. The maximum credible earthquake ( m max) estimated for each zone shows that Hazara Kashmir Syntaxis Seismic Zone has the highest m max of M w 8.1 (±0.36), which is espoused by the historical 1555 Kashmir earthquake of M w 7.6 as well as the recent 8 October 2005 Kashmir earthquake of M w 7.6. The variation in the estimated m max by the above discussed methodologies is obvious, as the definition and interpretation of the m max change with the method. Interestingly, historical archives (˜900 years) do not speak of a great earthquake in this region, which is attributed to the complex and unique tectonic and geologic setup of the Kashmir Himalaya. The convergence is this part of the Himalaya is distributed not only along the main boundary faults but also along the various active out-of-sequence faults as compared to the Central Himalaya, where it is mainly adjusted along the main boundary fault.

  2. Seismic hazard impact of the Lower Tagus Valley Fault Zone (SW Iberia)

    Vilanova, Susana P.; Fonseca, Joao F. B. D.

    The seismic hazard of SW Iberia is composed of two contributions: offshore, large to very large events on the plate boundary between Africa and Eurasia such as the Lisbon earthquake of 1755 or the Gorringe Bank earthquake of 1969; and onshore, moderate to strong intraplate earthquakes on inherited crustal fractures. One of these zones of crustal weakness is the Lower Tagus Valley (LTV) fault zone, which displays the highest level of seismic hazard in Western Iberia. In this paper we review the active tectonics and seismicity of the LTV, integrating previous geophysical data with recent results of paleoseismological investigations, and discuss its impact on the seismic hazard of SW Iberia. We conclude that the seismic zonation for hazard assessment currently in force in the building code is biased towards the scenario of distant offshore rupture, and does not take adequately into account the LTV seismic source.



    @@ General Seismic Zoning Map of the USSR(GSZ-78),included in the Building Code,in spite of relative improvement in comparison with previous ones(1937,1957,1968),is characterized by significant reduction of seismic hazard.In some regions strong earthquakes exceeding the predicted intensity occurred almost every year.Such cases in Kazakhstan are the earthquakes of Bakanasskoye(1979,M=14,I=6~7)and Zaysanskoye (1990,M=7.0,K=16,I=8).Besides,there are territories that are platforms in tectonic aspect,but which have been undergone activization at neotectonic evolution stage (Mangishlak,Ariskum desert near the Aral sea).Their potential seismic hazards are not estimated in General Seismic Zoning Map(GSZ-78).Mentioned circumstances induce the necessity to compile new seismic zoning map.

  4. Seismic image of the Ivanhoe Lake Fault Zone in the Kapuskasing Uplift of the Canadian Shield

    Wu, Jianjun; Mereu, Robert F.; Percival, John A.


    The Kapuskasing uplift, located in the central Canadian shield, represents an oblique exposure of the Archean middle to lower crust. The Ivanhoe Lake fault zone, believed to be the basal thrust carrying the high-grade rocks of the Kapuskasing zone over the low-grade Abitibi greenstone belt, holds the key to understanding the nature and evolution of the Kapuskasing uplift. Despite numerous geological and geophysical studies, including LITHOPROBE deep seismic reflection profiles, and because of very limited bedrock exposure in the area, the shallow structure of the Ivanhoe Lake fault zone remains obscure. Here we present results obtained by reprocessing data from a LITHOPROBE seismic reflection profile across the fault zone. For the first time, the Ivanhoe Lake fault zone is clearly imaged on the seismic section as a series of west-dipping reflectors with an average dip of 20°, which can be traced to the surface. The results support the conclusion that fault zones form good reflectors.

  5. Seismic source zoning and maximum credible earthquake prognosis of the Greater Kashmir Territory, NW Himalaya

    Sana, Hamid; Nath, Sankar Kumar


    We present the seismic source zoning of the tectonically active Greater Kashmir territory of the Northwestern Himalaya and seismicity analysis (Gutenberg-Richter parameters) and maximum credible earthquake (m max) estimation of each zone. The earthquake catalogue used in the analysis is an extensive one compiled from various sources which spans from 1907 to 2012. Five seismogenic zones were delineated, viz. Hazara-Kashmir Syntaxis, Karakorum Seismic Zone, Kohistan Seismic Zone, Nanga Parbat Syntaxis, and SE-Kashmir Seismic Zone. Then, the seismicity analysis and maximum credible earthquake estimation were carried out for each zone. The low b value (methodologies, the fault parameter approach, convergence rates using geodetic measurements, and the probabilistic approach using the earthquake catalogue and is estimated to be M w 7.7, M w 8.5, and M w 8.1, respectively. The maximum credible earthquake (m max) estimated for each zone shows that Hazara Kashmir Syntaxis Seismic Zone has the highest m max of M w 8.1 (±0.36), which is espoused by the historical 1555 Kashmir earthquake of M w 7.6 as well as the recent 8 October 2005 Kashmir earthquake of M w 7.6. The variation in the estimated m max by the above discussed methodologies is obvious, as the definition and interpretation of the m max change with the method. Interestingly, historical archives (˜900 years) do not speak of a great earthquake in this region, which is attributed to the complex and unique tectonic and geologic setup of the Kashmir Himalaya. The convergence is this part of the Himalaya is distributed not only along the main boundary faults but also along the various active out-of-sequence faults as compared to the Central Himalaya, where it is mainly adjusted along the main boundary fault.

  6. Prediction of subsurface fracture in mining zone of Papua using passive seismic tomography based on Fresnel zone

    Setiadi, Herlan; Nurhandoko, Bagus Endar B.; Wely, Woen [WISFIR Lab., Physics of Complex System, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Bandung 40132 (Indonesia); Riyanto, Erwin [PT Freeport Indonesia, Tembagapura, Indonesia (Indonesia)


    Fracture prediction in a block cave of underground mine is very important to monitor the structure of the fracture that can be harmful to the mining activities. Many methods can be used to obtain such information, such as TDR (Time Domain Relectometry) and open hole. Both of them have limitations in range measurement. Passive seismic tomography is one of the subsurface imaging method. It has advantage in terms of measurements, cost, and rich of rock physical information. This passive seismic tomography studies using Fresnel zone to model the wavepath by using frequency parameter. Fresnel zone was developed by Nurhandoko in 2000. The result of this study is tomography of P and S wave velocity which can predict position of fracture. The study also attempted to use sum of the wavefronts to obtain position and time of seismic event occurence. Fresnel zone tomography and the summation wavefront can predict location of geological structure of mine area as well.

  7. An Algorithm for Evaluating Fresnel-Zone Textural Roughness for Seismic Facies Interpretation

    Di, H.; Gao, D.


    In reflection seismic interpretation, a 1-D convolutional model is commonly used to interpret amplitude variations based on the geometric ray theory assuming seismic wave to reflect at a reflection point; however, the propagation of seismic waves actually occurs in a finite zone around the geometric ray path and gets reflected from a zone known as Fresnel zone. The collected signal at the surface turns out to be the superposition of reflections from within the Fresnel zone, which is a function of texture. Generally, for a rough texture such as sandstone, the dominant reflection is from the zone margin, while for a smooth texture such as marine shale, the dominant reflection is from the zone center. Based on this concept, Fresnel-zone texture directly affects amplitude variations with offset (AVO), azimuth (AVAZ), and frequency (AVF). Here we develop a computer algorithm for evaluating Fresnel-zone textural roughness. The algorithm starts with dividing the Fresnel zone into a set of micro-zones. It then builds an initial texture model to be convolved with an extracted wavelet. By comparing the synthetic signal from a Fresnel zone to the real seismic signal within an analysis window at a target location, the model is adjusted and updated until both synthetic and real signals match best. The roughness is evaluated as the correlation coefficient between the generated texture model within the Fresnel zone and the ideal model for a rough texture medium. Our new algorithm is applied to a deep-water 3D seismic volume over offshore Angola, west Africa. The results show that a rough texture is associated with channel sands, whereas a smooth texture with marine shale.

  8. The proportionality between relative plate velocity and seismicity in subduction zones

    Ide, S.


    Seismic activity differs among subduction zones due to various factors such as relative plate velocity, temperature, stress, and subducting materials. Relative plate velocity has a direct control on tectonic deformation and an overall correlation with seismicity has been suggested, as a global average or for large regions. Here I show a positive correlation between relative plate velocity and seismicity by estimating the background seismicity rate for 117 sections of subduction zones worldwide using the epidemic type aftershock sequence (ETAS) model. The background rate is stably estimated even for the period following M9-class earthquakes in Chile and Japan. A prominent proportional relationship is evident in the southwestern Pacific Ocean. Given that M9-class earthquakes occur independently of one another, the lack of M9 earthquakes in the southwestern Pacific Ocean over the last century is difficult to explain by chance. On the other hand, some subduction zones have extremely low background seismicity, and have experienced very large earthquakes. Slow earthquakes have been discovered in many of these quiet zones. Thus, this proportionality relation may be useful in assessing the seismic risk in subduction zones worldwide between two apparently confusing end members: 'active and moderate' and 'quiet and extreme'.

  9. Final Report: Seismic Hazard Assessment at the PGDP

    Wang, Zhinmeng [KY Geological Survey, Univ of KY


    Selecting a level of seismic hazard at the Paducah Gaseous Diffusion Plant for policy considerations and engineering design is not an easy task because it not only depends on seismic hazard, but also on seismic risk and other related environmental, social, and economic issues. Seismic hazard is the main focus. There is no question that there are seismic hazards at the Paducah Gaseous Diffusion Plant because of its proximity to several known seismic zones, particularly the New Madrid Seismic Zone. The issues in estimating seismic hazard are (1) the methods being used and (2) difficulty in characterizing the uncertainties of seismic sources, earthquake occurrence frequencies, and ground-motion attenuation relationships. This report summarizes how input data were derived, which methodologies were used, and what the hazard estimates at the Paducah Gaseous Diffusion Plant are.

  10. High Resolution Seismic Imaging of Fault Zones: Methods and Examples From The San Andreas Fault

    Catchings, R. D.; Rymer, M. J.; Goldman, M.; Prentice, C. S.; Sickler, R. R.; Criley, C.


    Seismic imaging of fault zones at shallow depths is challenging. Conventional seismic reflection methods do not work well in fault zones that consist of non-planar strata or that have large variations in velocity structure, two properties that occur in most fault zones. Understanding the structure and geometry of fault zones is important to elucidate the earthquake hazard associated with fault zones and the barrier effect that faults impose on subsurface fluid flow. In collaboration with the San Francisco Public Utilities Commission (SFPUC) at San Andreas Lake on the San Francisco peninsula, we acquired combined seismic P-wave and S-wave reflection, refraction, and guided-wave data to image the principal strand of the San Andreas Fault (SAF) that ruptured the surface during the 1906 San Francisco earthquake and additional fault strands east of the rupture. The locations and geometries of these fault strands are important because the SFPUC is seismically retrofitting the Hetch Hetchy water delivery system, which provides much of the water for the San Francisco Bay area, and the delivery system is close to the SAF at San Andreas Lake. Seismic reflection images did not image the SAF zone well due to the brecciated bedrock, a lack of layered stratigraphy, and widely varying velocities. Tomographic P-wave velocity images clearly delineate the fault zone as a low-velocity zone at about 10 m depth in more competent rock, but due to soil saturation above the rock, the P-waves do not clearly image the fault strands at shallower depths. S-wave velocity images, however, clearly show a diagnostic low-velocity zone at the mapped 1906 surface break. To image the fault zone at greater depths, we utilized guided waves, which exhibit high amplitude seismic energy within fault zones. The guided waves appear to image the fault zone at varying depths depending on the frequency of the seismic waves. At higher frequencies (~30 to 40 Hz), the guided waves show strong amplification at the

  11. Transition Zone of the Cascadia Subduction Fault: Insights from Seismic Imaging of Slow Earthquakes

    Ghosh, A.


    Transition zone lies between the updip locked and downdip freely slipping zone, and presumably marks the downdip extent of rupture during large megathrust earthquakes. Tectonic behavior of the transition zone and its possible implications on the occurrence of destructive megathurst earthquakes, however, remain poorly understood mainly due to lack of seismic events in this zone. Slow earthquakes, marked by seismically observed tremor and geodetically observed slow slip, occur in the transition zone offering a unique window to this zone, and allow us to study the dynamics of this enigmatic part of the fault. I developed a novel multi beam-backprojection (MBBP) algorithm to image slow earthquakes with high resolution using small-aperture seismic arrays. Application of MBBP technique on slow earthquakes in Cascadia indicates that the majority of the tremor is located near the plate interface [Ghosh et al., JGR, 2012]. Spatiotemporal distribution of tremor is fairly complex, and strikingly different over different time scales. Transition zone appears to be characterized by several patches with dimension of tens of kilometers. The patches behave like asperities, and possibly represent more seismic part of the fault embedded within a relatively aseismic background. Tremor asperities are spatially stable and marked by prolific tremor activity. These tremor asperities seem to control evolution of slow earthquakes and likely represent rheological and/or frictional heterogeneity on the fault plane. In addition, structural features on the fault plane of the transition zone seem to play an important role in shaping the characteristics of the seismic energy radiated from here. Dynamically evolving state-of-stress during slow earthquakes and its interaction with the fault structures possibly govern near-continuous rapid streaking of tremor [Ghosh et al., G-cubed, 2010] and diverse nature of tremor propagations observed over different time scales. Overall, slow quakes are giving

  12. Subduction of oceanic plate irregularities and seismicity distribution along the Mexican Subduction Zone

    Manea, Marina; Constantin Manea, Vlad; Gerya, Taras; Wong, Raul-Valenzuela; Radulian, Mircea


    It is known that oceanic plates morphology is not a simple one, but rather complicated by a series of irregularities as seamounts, fracture zones and mid-ocean ridges. These features present on the oceanic floor form part of the fabric of oceanic crust, and once formed they move together with the oceanic plates until eventually enter a subduction zone. Offshore Mexico the oceanic Cocos plate seafloor is littered with relatively small but numerous seamounts and seamount chains, and also large fracture zones. In this study we investigate the relationship between these oceanic irregularities located in the vicinity of the trench in Mexico and the distribution of subduction seismicity, including the rupture history of large subduction zone earthquakes. Since the interseismic locking degree is influenced by the rheological properties of crustal and mantle rocks, any variations along strike will result in significant changes in seismic behavior due to a change in frictional stability. Our preliminary study shows a direct relationship between the presence of seamounts chains on the incoming oceanic plate and the subduction seismicity distribution. We also found a clear relationship between the subduction of the Tehuantepec fracture zone (TFZ) and the low seismic activity in the region where this fracture zone intersects the trench. This region is also long term conspicuously quiet and considered a seismic gap where no significant large earthquake has occurred in more than 100 years. Using high-resolution three-dimensional coupled petrological-thermomechanical numerical simulations specifically tailored for the subduction of the Cocos plate in the region of TFZ we show that the weakened serpentinized fracture zone is partially scraped out in the forearc region because of its low strength and positive buoyancy. The presence of serpentinite in the fore arc apparently lowers the degree of interseismic locking, producing a seismic gap in southern Mexico.

  13. Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones

    Van Keken, P.E. [Michigan Univ., Ann Arbor, MI (United States). Dept. of Earth and Environmental Sciences; Kita, S.; Nakajima, J. [Tohoku Univ., Sendai (Japan). Research Center for Prediction of Earthquakes and Volcanic Eruptions


    The cause of intermediate-depth (>40 km) seismicity in subduction zones is not well understood. The viability of proposed mechanisms, which include dehydration embrittlement, shear instabilities and the presence of fluids in general, depends significantly on local conditions, including pressure, temperature and composition. The wellinstrumented and well-studied subduction zone below Northern Japan (Tohoku and Hokkaido) provides an excellent testing ground to study the conditions under which intermediate-depth seismicity occurs. This study combines new finite element models that predict the dynamics and thermal structure of the Japan subduction system with a high-precision hypocenter data base. The upper plane of seismicity is principally contained in the crustal portion of the subducting slab and appears to thin and deepen within the crust at depths >80 km. The disappearance of seismicity overlaps in most of the region with the predicted phase change of blueschist to hydrous eclogite, which forms a major dehydration front in the crust. The correlation between the thermally predicted blueschist-out boundary and the disappearance of seismicity breaks down in the transition from the northern Japan to Kurile arc below western Hokkaido. Adjusted models that take into account the seismically imaged modified upper mantle structure in this region fail to adequately recover the correlation that is seen below Tohoku and eastern Hokkaido. We conclude that the thermal structure below Western Hokkaido is significantly affected by timedependent, 3-D dynamics of the slab. This study generally supports the role of fluids in the generation of intermediate-depth seismicity. (orig.)

  14. Seismic structure of the mantle ; from subduction zone to craton

    Kennett, B.L.N.; Hilst, R.D. van der


    Seismological techniques have provided much of the currently available information on the internal structure of the Earth, and in particular on the mantle. Early studies revealed the need for an increase in seismic velocity with depth in the Earth, and by 1915 Gutenberg was able to make a good estim

  15. Seismic imaging of deformation zones associated with normal fault-related folding

    Lapadat, Alexandru; Imber, Jonathan; Iacopini, David; Hobbs, Richard


    Folds associated with normal faulting, which are mainly the result of fault propagation and linkage of normal fault segments, can exhibit complex deformation patterns, with multiple synthetic splay faults, reverse faults and small antithetic Riedel structures accommodating flexure of the beds. Their identification is critical in evaluating connectivity of potential hydrocarbon reservoirs and sealing capacity of faults. Previous research showed that seismic attributes can be successfully used to image complex structures and deformation distribution in submarine thrust folds. We use seismic trace and coherency attributes, a combination of instantaneous phase, tensor discontinuity and semblance attributes to identify deformation structures at the limit of seismic resolution, which accommodate seismic scale folding associated with normal faulting from Inner Moray Firth Basin, offshore Scotland. We identify synthetic splay faults and reverse faults adjacent to the master normal faults, which are localized in areas with highest fold amplitudes. This zone of small scale faulting is the widest in areas with highest fault throw / fold amplitude, or where a bend is present in the main fault surface. We also explore the possibility that changes in elastic properties of the rocks due to deformation can contribute to amplitude reductions in the fault damage zones. We analyse a pre-stack time-migrated 3D seismic data-set, where seismic reflections corresponding to a regionally-continuous and homogeneous carbonate layer display a positive correlation between strain distribution and amplitude variations adjacent to the faults. Seismic amplitude values are homogeneously distributed within the undeformed area of the footwall, with a minimum deviation from a mean amplitude value calculated for each seismic line. Meanwhile, the amplitude dimming zone is more pronounced (negative deviation increases) and widens within the relay zone, where sub-seismic scale faults, which accommodate

  16. Storage of fluids and melts at subduction zones detectable by seismic tomography

    Luehr, B. G.; Koulakov, I.; Rabbel, W.; Brotopuspito, K. S.; Surono, S.


    During the last decades investigations at active continental margins discovered the link between the subduction of fluid saturated oceanic plates and the process of ascent of these fluids and partial melts forming a magmatic system that leads to volcanism at the earth surface. For this purpose the geophysical structure of the mantle and crustal range above the down going slap has been imaged. Information is required about the slap, the ascent paths, as well as the reservoires of fluids and partial melts in the mantle and the crust up to the volcanoes at the surface. Statistically the distance between the volcanoes of volcanic arcs down to their Wadati Benioff zone results of approximately 100 kilometers in mean value. Surprisingly, this depth range shows pronounced seismicity at most of all subduction zones. Additionally, mineralogical laboratory investigations have shown that dehydration of the diving plate has a maximum at temperature and pressure conditions we find at around 100 km depth. The ascent of the fluids and the appearance of partial melts as well as the distribution of these materials in the crust can be resolved by seismic tomographic methods using records of local natural seismicity. With these methods these areas are corresponding to lowered seismic velocities, high Vp/Vs ratios, as well as increased attenuation of seismic shear waves. The anomalies and their time dependence are controlled by the fluids. The seismic velocity anomalies detected so far are within a range of a few per cent to more than 30% reduction. But, to explore plate boundaries large and complex amphibious experiments are required, in which active and passive seismic investigations should be combined to achieve best results. The seismic station distribution should cover an area from before the trench up to far behind the volcanic chain, to provide under favorable conditions information down to 150 km depth. Findings of different subduction zones will be compared and discussed.

  17. Scientific overview and historical context of the 1811-1812 New Madrid earthquake sequence

    S. E. Hough


    Full Text Available The central and eastern United States has experienced only 5 historic earthquakes with Mw 7.0, four during the New Madrid sequence of 1811-1812: three principal mainshocks and the so-called «dawn aftershock» following the first mainshock. Much of the historic earthquake research done in the United States has focused on the New Madrid Seismic Zone (NMSZ, because the largest New Madrid earthquakes may represent the archetype for the most damaging earthquakes to be expected in intraplate regions. Published magnitude values ranging from 7.0 to 8.75 have generally been based on macroseismic effects, which provide the most direct constraint on source size for the events. Critical to the interpretation of these accounts is an understanding of their historic context. Early settlments clustered along waterways, where substantial amplification of seismic waves is expected. Analyzing the New Madrid intensity values with a consideration of these effects yields preferred values of Mw 7.2-7.3, 7.0, and 7.4-7.5 for the December, January, and February mainshocks, respectively, and of 7.0 for the «dawn aftershock». These values are consistent with other lines of evidence, including scaling relationships. Finally, I show that accounts from the New Madrid sequence reveal evidence for remotely triggered earthquakes well outside the NMSZ. Remotely triggered earthquakes represent a potentially important new wrinkle in historic earthquake research, as their ground motions can sometimes be confused with mainshock ground motions.

  18. The Salton Seismic Imaging Project: Seismic velocity structure of the Brawley Seismic Zone, Salton Buttes and Geothermal Field, Salton Trough, California

    Delph, J.; Hole, J. A.; Fuis, G. S.; Stock, J. M.; Rymer, M. J.


    The Salton Trough is an active rift in southern California in a step-over between the plate-bounding Imperial and San Andreas Faults. In March 2011, the Salton Seismic Imaging Project (SSIP) investigated the rift's crustal structure by acquiring several seismic refraction and reflection lines. One of the densely sampled refraction lines crosses the northern-most Imperial Valley, perpendicular to the strike-slip faults and parallel to a line of small Quaternary rhyolitic volcanoes. The line crosses the obliquely extensional Brawley Seismic Zone and goes through one of the most geothermally productive areas in the United States. Well logs indicate the valley is filled by several kilometers of late Pliocene-recent lacustrine, fluvial, and shallow marine sediment. The 42-km long seismic line was comprised of eleven 110-460 kg explosive shots and receivers at a 100 m spacing. First arrival travel times were used to build a tomographic seismic velocity image of the upper crust. Velocity in the valley increases smoothly from 5 km/s, indicating diagenesis and gradational metamorphism of rift sediments at very shallow depth due to an elevated geotherm. The velocity gradient is much smaller in the relatively low velocity (Chocolate Mountains. The tomographic model shows that the shallow metasedimentary basement as well as the geothermal and volcanic activity seem to be bounded by the sharp western and eastern margins of the Brawley Seismic Zone. At this location, strongly fractured crust allows both hydrothermal and magmatic fluids to rise to the surface in the most rapidly extending portion of the rift basin.

  19. Pre-eruption deformation and seismic anomalies in 2012 in Tolbachik volcanic zone, Kamchatka

    Kugaenko, Yulia; Saltykov, Vadim; Titkov, Nikolay


    Tolbachik volcanic zone (active volcano Plosky Tolbachik, dormant volcano Ostry Tolbachik and Tolbachik zone of cinder cones) is situated in the south part of Klyuchevskaya group of volcanoes in Kamchatka. All historical fissure eruptions of Tolbachik volcanic zone (1740, 1941, 1975-76 and 2012-13) were connected with one or another activity of Plosky Tolbachik volcano. In 1941 the fissure vent was occurred during the completion of 1939-41 terminal eruption of Plosky Tolbachik. In 1975 the Large Tolbachik Fissure Eruption (LTFE) was forestalled by Plosky Tolbachik terminal activity of the Hawaiian type and then was accompanied by the catastrophic collapse in the crater of Plosky Tolbachik. What events took place in the vicinity of Plosky Tolbachik in 2012 before the 2012-13 fissure eruption? In contrast of the 1975-76 LTFE the eruption 2012-13 was not preceded by intensive seismic preparation. Nowadays Klyuchevskaya group of volcanoes is under monitoring by 12 seismic stations, so we can investigate seismicity in details on the lower energy level then forty years ago. We analyzed seismicity of Plosky Tolbachik using regional catalogue 1999-2012. Anomalies of low-energy (M≥1.5) seismicity parameters (increase of seismicity rate and seismic energy) were discovered. This is evidence of seismic activization covered the whole Plosky Tolbachik volcano. The significance of this anomaly was estimated by distribution function of emitted seismic energy. Statistically significant transition of seismicity from background level to high and extremely high levels was revealed. It corresponds to multiple growth of earthquake number and seismic energy in 2012, July-November (five months before the eruption). The seismicity transition from background level to high level was happen in August 2012. During last three weeks before fissure eruption seismicity of analyzed seismoactive volume was on extremely high level. Earthquakes from fissure site directly appeared only on November 27

  20. Some Probabilistic and Statistical Properties of the Seismic Regime of Zemmouri (Algeria Seismoactive Zone

    Baddari Kamel


    Full Text Available Statistical tests have been used to adjust the Zemmouri seismic data using a distribution function. The Pareto law has been used and the probabilities of various expected earthquakes were computed. A mathematical expression giving the quantiles was established. The extreme values limiting law confirmed the accuracy of the adjustment method. Using the moment magnitude scale, a probabilistic model was made to predict the occurrences of strong earthquakes. The seismic structure has been characterized by the slope of the recurrence plot γ, fractal dimension D, concentration parameter Ksr, Hurst exponents Hr and Ht. The values of D, γ, Ksr, Hr, and Ht diminished many months before the principal seismic shock (M = 6.9 of the studied seismoactive zone has occurred. Three stages of the deformation of the geophysical medium are manifested in the variation of the coefficient G% of the clustering of minor seismic events.

  1. Some Probabilistic and Statistical Properties of the Seismic Regime of Zemmouri (Algeria) Seismoactive Zone

    Baddari, Kamel; Bellalem, Fouzi; Baddari, Ibtihel; Makdeche, Said


    Statistical tests have been used to adjust the Zemmouri seismic data using a distribution function. The Pareto law has been used and the probabilities of various expected earthquakes were computed. A mathematical expression giving the quantiles was established. The extreme values limiting law confirmed the accuracy of the adjustment method. Using the moment magnitude scale, a probabilistic model was made to predict the occurrences of strong earthquakes. The seismic structure has been characterized by the slope of the recurrence plot γ, fractal dimension D, concentration parameter K sr, Hurst exponents H r and H t. The values of D, γ, K sr, H r, and H t diminished many months before the principal seismic shock ( M = 6.9) of the studied seismoactive zone has occurred. Three stages of the deformation of the geophysical medium are manifested in the variation of the coefficient G% of the clustering of minor seismic events.

  2. Tsunami potential assessment based on rupture zones, focal mechanisms and repeat times of strong earthquakes in the major Atlantic-Mediterranean seismic fracture zone

    Agalos, Apostolos; Papadopoulos, Gerassimos A.; Kijko, Andrzej; Papageorgiou, Antonia; Smit, Ansie; Triantafyllou, Ioanna


    In the major Atlantic-Mediterranean seismic fracture zone, extended from Azores islands in the west to the easternmost Mediterranean Sea in the east, including the Marmara and Black Seas, a number of 22 tsunamigenic zones have been determined from historical and instrumental tsunami documentation. Although some tsunamis were produced by volcanic activity or landslides, the majority of them was generated by strong earthquakes. Since the generation of seismic tsunamis depends on several factors, like the earthquake size, focal depth and focal mechanism, the study of such parameters is of particular importance for the assessment of the potential for the generation of future tsunamis. However, one may not rule out the possibility for tsunami generation in areas outside of the 22 zones determined so far. For the Atlantic-Mediterranean seismic fracture zone we have compiled a catalogue of strong, potentially tsunamigenic (focal depth less than 100 km) historical earthquakes from various data bases and other sources. The lateral areas of rupture zones of these earthquakes were determined. Rupture zone is the area where the strain after the earthquake has dropped substantially with respect the strain before the earthquake. Aftershock areas were assumed to determine areas of rupture zones for instrumental earthquakes. For historical earthquakes macroseismic criteria were used such as spots of higher-degree seismic intensity and of important ground failures. For the period of instrumental seismicity, focal mechanism solutions from CMT, EMMA and other data bases were selected for strong earthquakes. From the geographical distribution of seismic rupture zones and the corresponding focal mechanisms in the entire Atlantic-Mediterranean seismic fracture zone we determined potentially tsunamigenic zones regardless they are known to have produced seismic tsunamis in the past or not. An attempt has been made to calculate in each one of such zones the repeat times of strong

  3. Comparing seismic parameters for different source zone models in the Iberian Peninsula

    Amaro-Mellado, J. L.; Morales-Esteban, A.; Asencio-Cortés, G.; Martínez-Álvarez, F.


    Seismical parameters of five seismogenic zonings for the Iberian Peninsula have been determined in this work. For that purpose, this research has two key goals. The first is to generate a seismic catalog. The second to calculate the seismical parameters of all the zones of the seismogenic zonings selected. The first key goal has been the creation of a catalog of earthquakes for the Iberian Peninsula and adjacent areas. First, the National Geographic Institute of Spain's catalog has been completed and reviewed with the information from other catalog reviews and specific studies. Second, all magnitude calculations have been homogenized. Third, all dependent data have been eliminated through declustering. Finally, the year of completeness for each magnitude has been considered. The Quaternary active faults database of Iberia has also been used as input data. All of this information has been integrated into a geographic information system. The second key aim is the calculation of the seismical parameters. The first parameter obtained has been the b-value. A method which considers different years of completeness in accordance with the magnitude has been used. Also, the annual rate of earthquakes per square kilometer has been calculated. Moreover, the maximum magnitude known that Quaternary active faults might generate and maximum magnitude recorded in the catalog have been determined. Finally, based solely on the statistical parameters obtained, a critical discussion of the seismogenic zonings of the Iberian Peninsula has been conducted. The results show that some zonings possess insufficient data for a proper calculation of the seismic parameters, from a statistical point of view.

  4. Suture Zones, Seismic Wave Propagation and Tectonics of Central Asia.


    prominent strike-slip faults in the Eurasian hinter- lands of the frontal fold and thrust belt (e.g., the Chaman and Herat faults) have shown only...with dextral shear (associated with crustal shortening) in the Quetta-Sibi syntaxial region and sinistral shear along the Chaman fault. Similar zones

  5. Seismic Evidence for a Low-Velocity Zone in the Upper Crust Beneath Mount Vesuvius

    Zollo, A.; Gasparini, P.; Virieux, J.; Le Meur, H.; de Natale, G.; Biella, G.; Boschi, E.; Capuano, P.; de Franco, R.; dell'Aversna, P.; de Matteis, R.; Guerra, I.; Iannaccone, G.; Mirabile, L.; Vilardo, G.


    A two-dimensional active seismic experiment was performed on Mount Vesuvius: Explosive charges were set off at three sites, and the seismic signal along a dense line of 82 seismometers was recorded. A high-velocity basement, formed by Mesozoic carbonates, was identified 2 to 3 kilometers beneath the volcano. A slower (P-wave velocity V_P backsimeq 3.4 to 3.8 kilometers per second) and shallower high-velocity zone underlies the central part of the volcano. Large-amplitude late arrivals with a dominant horizontal wave motion and low-frequency content were identified as a P to S phase converted at a depth of about 10 kilometers at the top of a low-velocity zone (V_P < 3 kilometers per second), which might represent a melting zone.


    Dolenc, D.; Romanowicz, B. A.


    Ocean-bottom broadband seismic stations (OBSs) are installed at the interface of the solid earth and the ocean. As such, they are sensitive to the processes that originate in the solid earth (e.g., earthquakes), ocean (e.g., tsunamis), and even atmosphere (e.g., cyclones). Observations of ground motions at the OBSs can therefore be used to study and monitor processes that contribute to hazards in the coastal zones. These processes include earthquakes, underwater landslides, underwater volcanoes, and tsunamis. Numerous offshore faults are located too far from the shore for their background seismicity to be studied by land seismic stations alone, yet they are capable of generating large earthquakes that can threaten coastal communities. OBSs can record offshore seismicity that would be missed by relying only on the land stations. OBS data can also significantly improve locations and source mechanism determination for stronger offshore events that are observed on the land stations as they can significantly improve azimuthal coverage. As such, OBSs are essential for identifying seismic hazard from offshore faults. In addition, nearshore OBSs can improve studies of earthquakes on the land faults, in particular when the faults are located close to the ocean, resulting in limited azimuthal coverage provided by land stations alone. OBSs can also provide information about the offshore subsurface velocity structure, which can significantly affect the amount of shaking in the coastal regions. Velocity structure can be determined by compliance analysis that takes advantage of the seafloor deformation due to infragravity waves (long-period ocean surface waves). Reliable offshore velocity models are needed for modeling seismic wave propagation and for subsequent modeling of the amount of shaking expected in the coastal regions due to strong local and regional offshore earthquakes. We will present examples from the permanent ocean-bottom broadband seismic station MOBB located at


    Londoño B. John Makario


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

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

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


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

  9. Seismic behavior and zoning of the sabkha soils in Jubail industrial city, Saudi Arabia

    Ahmed, H. R.; Al Shayea, N. A.


    This study aimed at the micro-level seismic behavior and zoning of the saline sabkha strata in Jubail industrial area in Eastern Saudi Arabia. It encompasses the evaluation of the site-specific seismic response parameters and the liquefaction potential for various possible subsurface conditions under the probable seismic event(s). The approach to achieve the objectives of this study included the following: analysis of geologic, hydrologic, and geotechnical data of the area; performance of field and laboratory dynamic testing; and dynamic modeling and analysis of the subsurface profiles. The results of the simulation have been used to develop liquefaction potential maps and site-specific spectra of the study area, consisting of ten seismic zones under a range of probable peak horizontal ground acceleration (PHA). Results do not show significant probability of liquefaction of the loose soil layers in the study area at the maximum possible design PHA of 0.035 g; however, liquefaction is anticipated at higher PHA values. Site-specific spectral response resulted in values of S s and S 1 spectral accelerations to be different as compared to those suggested by local standards. The resulting seismic micro-zonation maps and the corresponding parameters are very useful for the stability analysis of the existing and planned structures in the Jubail area.

  10. Characterizing fractures and shear zones in crystalline rock using anisotropic seismic inversion and GPR imaging

    Doetsch, Joseph; Krietsch, Hannes; Lajaunie, Myriam; Jordi, Claudio; Gischig, Valentin; Schmelzbach, Cedric; Maurer, Hansrudi


    Understanding the natural or artificially created hydraulic conductivity of a rock mass is critical for the successful exploitation of enhanced geothermal systems (EGS). The hydraulic response of fractured crystalline rock is largely governed by the spatial organization of permeable fractures. Defining the 3D geometry of these fractures and their connectivity is extremely challenging, because fractures can only be observed directly at their intersections with tunnels or boreholes. In the framework of an in-situ stimulation experiment at the Grimsel Test Site, a detailed rock mass characterization was carried out, combining geological and geophysical methods. While geological observations from tunnel mapping, core- and geophysical borehole-logging are reliable, the obtained data could just be interpolated between tunnels and boreholes. The geophysical surveys, including ground-penetration radar (GPR) imaging and tunnel-tunnel seismic tomography were able to image shear and fracture zones throughout the experimental volume. Clear GPR reflections up to a distance of 30 m from the tunnels allow to define the geometry of tunnel-mapped shear zones in the center of the experimental volume. Anisotropic traveltime inversion of tunnel-tunnel seismic data reveals fracture zones as low velocity zones and ductile shear zones as areas of increased seismic anisotropy. It is thus possible to characterize both type and geometry of shear and fracture zones, which is important for the planned rock stimulation. Combining the GPR and seismic results with the geological information, the geological model could be significantly improved, demonstrating the potential to characterize even subtle geological features in 3D.

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

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


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

  12. Deep Structure and Earthquake Generating Properties in the Yamasaki Fault Zone Estimated from Dense Seismic Observation

    Nishigami, K.; Shibutani, T.; Katao, H.; Yamaguchi, S.; Mamada, Y.


    We have been estimating crustal heterogeneous structure and earthquake generating properties in and around the Yamasaki fault zone, which is a left-lateral strike-slip active fault with a total length of about 80 km in southwest Japan. We deployed dense seismic observation network, composed of 32 stations with average spacing of 5-10 km around the Yamasaki fault zone. We estimate detailed fault structure such as fault dip and shape, segmentation, and possible location of asperities and rupture initiation point, as well as generating properties of earthquakes in the fault zone, through analyses of accurate hypocenter distribution, focal mechanism, 3-D velocity tomography, coda wave inversion, and other waveform analyses. We also deployed a linear seismic array across the fault, composed of 20 stations with about 20 m spacing, in order to delineate the fault-zone structure in more detail using the seismic waves trapped inside the low velocity zone. We also estimate detailed resistivity structure at shallow depth of the fault zone by AMT (audio-frequency magnetotelluric) and MT surveys. In the scattering analysis of coda waves, we used 2,391 wave traces from 121 earthquakes that occurred in 2002, 2003, 2008 and 2009, recorded at 60 stations, including dense temporary and routine stations. We estimated 3-D distribution of relative scattering coefficients along the Yamasaki fault zone. Microseismicity is high and scattering coefficient is relatively larger in the upper crust along the entire fault zone. The distribution of strong scatterers suggests that the Ohara and Hijima faults, which are the segments in the northwestern part of the Yamasaki fault zone, have almost vertical fault plane from surface to a depth of about 15 km. We used seismic network data operated by Universities, NIED, AIST, and JMA. This study has been carried out as a part of the project "Study on evaluation of earthquake source faults based on surveys of inland active faults" by Japan Nuclear

  13. Seismic properties of lawsonite eclogites from the southern Motagua fault zone, Guatemala

    Kim, Daeyeong; Wallis, Simon; Endo, Shunsuke; Ree, Jin-Han


    We present new data on the crystal preferred orientation (CPO) and seismic properties of omphacite and lawsonite in extremely fresh eclogite from the southern Motagua fault zone, Guatemala, to discuss the seismic anisotropy of subducting oceanic crust. The CPO of omphacite is characterized by (010)[001], and it shows P-wave seismic anisotropies (AVP) of 1.4%-3.2% and S-wave seismic anisotropies (AVS) of 1.4%-2.7%. Lawsonite exhibits (001) planes parallel to the foliation and [010] axes parallel to the lineation, and seismic anisotropies of 1.7%-6.6% AVP and 3.4%-14.7% AVS. The seismic anisotropy of a rock mass consisting solely of omphacite and lawsonite is 1.2%-4.1% AVP and 1.8%-6.8% AVS. For events that propagate more or less parallel to the maximum extension direction, X, the fast S-wave velocity (VS) polarization is parallel to the Z in the Y-Z section (rotated from the X-Z section), causing trench-normal seismic anisotropy for orthogonal subduction. Based on the high modal abundance and strong fabric of lawsonite, the AVS of eclogites is estimated as ~ 11.7% in the case that lawsonite makes up ~ 75% of the rock mass. On this basis, we suggest that lawsonite in both blueschist and eclogite may play important roles in the formation of complex pattern of seismic anisotropy observed in NE Japan: weak trench-parallel anisotropy in the forearc basin domains and trench-normal anisotropy in the backarc region.

  14. Seismicity and structure of Nazca Plate subduction zone in southern Peru

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


    We image the Nazca plate subduction zone system by detecting and (re)locating intra-slab earthquakes in southern Peru. Dense seismic arrays (PeruSE, 2013) were deployed along four lines to target geophysical characterization of the subduction system in the transition zone between flat and normal dipping segments of the Nazca plate (2-15°S). The arc volcanism is absent near the flat slab segment, and currently, the correlation between the location of the active volcanic front and corresponding slab depth is neither clear nor consistent between previously published models from seismicity. We detect 620 local earthquakes from August 2008 to February 2013 by manually picking 6559 and 4145 arrival times for P- and S-phases, respectively. We observe that the S-phase data is helpful to reduce the trade-off between origin time and depth of deeper earthquakes (>100 km). Earthquake locations are relocated to constrain the Nazca slab-mantle interface in the slab-dip transition zone using 7322 measurements of differential times of nearby earthquake pairs by waveform cross-correlation. We also employ the double-difference tomography (Zhang and Thurber, 2003) to further improve earthquake source locations and the spatial resolution of the velocity structure simultaneously. The relocated hypocenters clearly delineate the dipping Wadati-Benioff zone in the slab-dip transition zone between the shallow- (25°) to-flat dipping slab segment in the north and the normal (40°) dipping segment in the south. The intermediate-depth seismicity in the flat slab region stops at a depth of ~100 km and a horizontal distance of ~400 km from the trench. We find a significant slab-dip difference (up to 10°) between our relocated seismicity and previously published slab models along the profile region sampling the normal-dip slab at depth (>100 km).

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

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


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

  16. Northern Wabash Valley Seismic Zone and the La Salle anticline seismicity determined by a short period phased array

    Brazitis, Daniel

    The Wabash Valley Seismic Zone (WVSZ) has produced three moderate sized earthquakes greater than or equal to mb 5.0 in the past 50 years. The majority of Wabash Valley faults originate near the junction of the Rough Creek and Cottage Grove faults and extend northeastward along the Wabash River. These faults extend through the Paleozoic and into the Precambrian and are believe to be associated with the Reelfoot Rift. Two of these moderate sized earthquakes have occurred north of the terminus of the Wabash Valley faults that the WVSZ is commonly associated with. This suggests that other sources of seismicity exist. The La Salle anticline, a Precambrian basement feature, is oriented NW to SE just north of the termination of these faults. The La Salle anticline creates up to a 750 meter uplift in the above Paleozoic strata. This uplift creates faults within the Paleozoic strata and within the La Salle anticline. This study uses seismometers arranged in a phased array near the southern terminus of the La Salle anticline to analyze the seismicity of the region. Analyzing the seismicity of the region over a 6-month period found 834 events. The vast majority were determined to be mine blasts or otherwise human induced. Two small earthquakes ( M 1.0) located near the La Salle anticline. These earthquakes likely occur on faults associated with the anticline. The lack of earthquakes suggested the b-value of the La Salle region could be as low as 0.56. This is lower than the typical value of 1, but consistent with other intraplate regions and previous studies of the WVSZ finding values nearer 0.7.

  17. Comparison Between Structural Analysis of Residential Building (Flat Scheme Subjected to Gravity With Respect to Seismic Forces (In zone II and zone III For Different Storey Heights

    Pranita R. Kayarkar


    Full Text Available The recent development in methods to analyze the RC frame structure brings us to this study. This paper is approach to introduce the comparison between structural analysis of Residential building (Flat Scheme subjected to gravity with respect to seismic forces ( in zone II and zone III for different storey heights. For structural engineers, seismic load should be considered as important aspect that needs to be included in the building design. However majority of buildings constructed in India are designed for gravity loading only and poorly detailed to accommodate lateral loads. The purpose of this paper is to investigate the comparison between structural analysis of residential building subjected to gravity with respect to seismic forces in zone II and zone III for different storey heights. The analysis for residential building (G+3 is carried out by using software SAP by seismic coefficient method. Columns, beams and footing has been drawn. Microsoft office Excel 2007 programs were used for drafting , and analysis of columns, beams and footing. This analysis gives better understanding the seismic performance of buildings. The results show that the building which is designed only for gravity load is found inadequate to resist seismic load in zone II and zone III.

  18. Microstructures, deformation mechanisms and seismic properties of a Palaeoproterozoic shear zone: The Mertz shear zone, East-Antarctica

    Lamarque, Gaëlle; Bascou, Jérôme; Maurice, Claire; Cottin, Jean-Yves; Riel, Nicolas; Ménot, René-Pierre


    The Mertz shear zone (MSZ) is a lithospheric scale structure that recorded mid-crustal deformation during the 1.7 Ga orogeny. We performed a microstructural and crystallographic preferred orientation (CPO) study of samples from both mylonites and tectonic boudins that constitute relics of the Terre Adélie Craton (TAC). The deformation is highly accommodated in the MSZ by anastomosed shear bands, which become more scattered elsewhere in the TAC. Most of the MSZ amphibolite-facies mylonites display similar CPO, thermal conditions, intensity of deformation and dominant shear strain. Preserved granulite-facies boudins show both coaxial and non-coaxial strains related to the previous 2.45 Ga event. This former deformation is more penetrative and less localized and shows a deformation gradient, later affected by a major phase of recrystallization during retrogression at 2.42 Ga. Both MSZ samples and granulite-facies tectonic boudins present microstructures that reflect a variety of deformation mechanisms associated with the rock creep that induce contrasted CPO of minerals (quartz, feldspar, biotite, amphibole and orthopyroxene). In particular, we highlight the development of an "uncommon" CPO in orthopyroxene from weakly deformed samples characterized by (010)-planes oriented parallel to the foliation plane, [001]-axes parallel to the stretching lineation and clustering of [100]-axes near the Y structural direction. Lastly, we computed the seismic properties of the amphibolite and granulite facies rocks in the MSZ area in order to evaluate the contribution of the deformed intermediate and lower continental crust to the seismic anisotropy recorded above the MSZ. Our results reveal that (i) the low content of amphibole and biotite in the rock formations of the TAC, and (ii) the interactions between the CPO of the different mineralogical phases, generate a seismically isotropic crust. Thus, the seismic anisotropy recorded by the seismic stations of the TAC, including the

  19. Zones of the origin of seismic centers in the Pamir-Tien Shan sector of High Asia

    Gatinsky, Yu. G.; Prokhorova, T. V.; Rundquist, D. V.


    The zones of the origin of seismic centers within highly seismic areas of the Pamirs and Tien Shan are established. The majority of catastrophic earthquakes coincide with them in this part of High Asia. Their establishment is based on the distribution of the most intensive epicenters and the maximal volumes of the seismic energy together with its calculation and forecasting of the possible manifestations of high seismicity. The investigation of the deep structure of these zones allows us to determine the connection of the seismicity with geophysical field anomalies and some factors of the deep and near surface lithosphere and crust structure, which influence the present-day geodynamics. The results of our research enable us to appreciate the level of the seismic danger in different parts of the region investigated.


    M. G. Mel’nikov


    Full Text Available The study is focused on earthquake migrations along active faults in seismic zones of Mongolia. The earthquake migrations are interpreted as a result of the influence of deformational waves. Vector velocities and other parameters of the deformational waves are studied. Based on data from largescale maps, local faults are compared, and differences and similarities of parameters of waves related to faults of different ranks are described.

  1. Pyrometamorphism of Fault Zone Rocks Induced by Frictional Heating in High-velocity Friction Tests: Reliable Records of Seismic Slip?

    Ree, J.; Ando, J.; Kim, J.; Han, R.; Shimamoto, T.


    Recognition of seismic slip zone is important for a better understanding of earthquake generation processes in fault zones and paleoseismology. However, there has been no reliable record of ancient seismic slip except pseudotachylyte. Recently, it has been suggested that decomposition (dehydration or decarbonation) products due to frictional heating can be used as a seismic slip record. The decomposition products, however, can be easily rehydrated or recarbonated with pervasive fluid migration in the fault zone after seismic slip, raising some question about their stability as a seismic slip record. Here, we review microstructural and mineralogical changes of the simulated fault zones induced by frictional heating (pyrometamorphism) from high-velocity friction tests (HVFT) on siltstone, sandstone and carbonates at seismic slip rates, and discuss on their stability after seismic slip. HVFT on siltstone generates pseuodotachylyte in the principal slip zone (0.30-0.75 mm thick) with 'damage' layer (0.1-0.2 mm thick) along its margins. Chlorite in the damage layer suffers an incipient dehydration with many voids (0.2-1.0 μm in diameter) in transmission electron microscopy (TEM), appearing as dark tiny spots both in plane-polarized light and back-scattered electron (BSE) photomicrographs. HVFT on brown sandstone induces a color change of wall rocks adjacent to the principal slip zone (brown to red) due to the dehydration of iron hydroxides with frictional heating. These dehydration products in siltstone and sandstone due to frictional heating may be unstable since they would be easily rehydrated with fluid infiltration after a seismic slip. HVFT on carbonates including Carrara marble and siderite-bearing gouges produces decarbonation products of nano-scale lime (CaO) and magnetite (Fe3O4), respectively. Lime is a very unstable phase whereas magnetite is a stable and thus may be used as an indicator of seismic slip. The simulated fault zones of Carrara marble contain

  2. Seismic evidence for flow in the hydrated mantle wedge of the Ryukyu subduction zone

    Nagaya, Takayoshi; Walker, Andrew M.; Wookey, James; Wallis, Simon R.; Ishii, Kazuhiko; Kendall, J.-Michael


    It is widely accepted that water-rich serpentinite domains are commonly present in the mantle above shallow subducting slabs and play key roles in controlling the geochemical cycling and physical properties of subduction zones. Thermal and petrological models show the dominant serpentine mineral is antigorite. However, there is no good consensus on the amount, distribution and alignment of this mineral. Seismic velocities are commonly used to identify antigorite-rich domains, but antigorite is highly-anisotropic and depending on the seismic ray path, its properties can be very difficult to distinguish from non-hydrated olivine-rich mantle. Here, we utilize this anisotropy and show how an analysis of seismic anisotropy that incorporates measured ray path geometries in the Ryukyu arc can constrain the distribution, orientation and amount of antigorite. We find more than 54% of the wedge must consist of antigorite and the alignment must change from vertically aligned to parallel to the slab. This orientation change suggests convective flow in the hydrated forearc mantle. Shear wave splitting analysis in other subduction zones indicates large-scale serpentinization and forearc mantle convection are likely to be more widespread than generally recognized. The view that the forearc mantle of cold subduction zones is dry needs to be reassessed.

  3. Finite-frequency sensitivity kernels of seismic waves to fault zone structures

    Allam, A. A.; Tape, C.; Ben-Zion, Y.


    We analyse the volumetric sensitivity of fault zone seismic head and trapped waves by constructing finite-frequency sensitivity (Fréchet) kernels for these phases using a suite of idealized and tomographically derived velocity models of fault zones. We first validate numerical calculations by waveform comparisons with analytical results for two simple fault zone models: a vertical bimaterial interface separating two solids of differing elastic properties, and a `vertical sandwich' with a vertical low velocity zone surrounded on both sides by higher velocity media. Establishing numerical accuracy up to 12 Hz, we compute sensitivity kernels for various phases that arise in these and more realistic models. In contrast to direct P body waves, which have little or no sensitivity to the internal fault zone structure, the sensitivity kernels for head waves have sharp peaks with high values near the fault in the faster medium. Surface wave kernels show the broadest spatial distribution of sensitivity, while trapped wave kernels are extremely narrow with sensitivity focused entirely inside the low-velocity fault zone layer. Trapped waves are shown to exhibit sensitivity patterns similar to Love waves, with decreasing width as a function of frequency and multiple Fresnel zones of alternating polarity. In models that include smoothing of the boundaries of the low velocity zone, there is little effect on the trapped wave kernels, which are focused in the central core of the low velocity zone. When the source is located outside a shallow fault zone layer, trapped waves propagate through the surrounding medium with body wave sensitivity before becoming confined. The results provide building blocks for full waveform tomography of fault zone regions combining high-frequency head, trapped, body, and surface waves. Such an imaging approach can constrain fault zone structure across a larger range of scales than has previously been possible.

  4. Ambient Noise Cross-Correlation in the Eastern Tennessee Seismic Zone (United States)

    Kuponiyi, A. P.; Arroucau, P.; Vlahovic, G.; Yongan, T.; Vlahovic, B.


    The Eastern Tennessee Seismic Zone (ETSZ) is an intraplate seismic region characterized by frequent but low magnitude earthquakes and is the second most active seismic area in the United States east of the Rocky Mountains. Since the middle of the seventies, the Center for Earthquake Research and Information (CERI) has installed and maintained several seismic networks in central and eastern United States. In this work, we use the continuous waveforms recorded at 24 short-period stations located in the vicinity of the eastern Tennessee seismic zone (ETSZ) and compute the cross-correlation function of the vertical component of the ambient noise wavefield for simultaneously recording station pairs. The resulting cross-correlograms are analysed by means of frequency-time analysis to extract Rayleigh wave group velocities that we subsequently use to compute Rayleigh wave tomographic maps of the region for periods ranging between 2 and 10 s, i.e. for periods sensitive to the structure of the upper crust. One key question in the ETSZ is the actual relationship between earthquake distribution and geological structure at depth. Seismicity is mostly confined in the Precambrian basement, below the Paleozoic cover of the southern Appalachian fold-and-thrust belt and shows little to no correlation with surface geological features. On the other hand, the earthquakes of the ETSZ clearly follow the trend of a feature observed on magnetic data: the New York-Alabama magnetic lineament (NYAL), a 1600-km long, northeast trending feature that is thought to be the expression of a major strike-slip fault affecting the Precambrian basement from the Mississippi embayment to the Green Mountains (northeast US). The actual extent at depth of this feature is not well established and is of primary interest to understand the seismicity of the ETSZ. By providing new information about the upper crustal structure of this region, this work is a contribution to the understanding of the seismic

  5. Modelling of Seismic Ground Motion in Santiago de Cuba City from Earthquakes in Oriente Fault Seismic Zone

    Alvarez, L.; Panza, G. F.; Vaccari, F.; González, B. E.

    We present the results of complete P-SV and SH waves modelling, up to a maximum frequency of 1Hz, along two profiles in Santiago de Cuba city. The seismic sources are located in the depth range from 10 to 40km on the Oriente fault zone at distances of several tens of kilometres from the city. The calculation has been made by a hybrid method: Modal summation in the regional anelastic model (one-dimensional) where the source is buried, and finite differences in the local sedimentary anelastic models (two-dimensional). The analysis of the influence of the depth and of the distance of the source on the site effects shows that standard traditional methods, based on the deconvolution analysis of the rock outcrop motion, can lead to erroneous results.

  6. Shallow seismicity patterns in the northwestern section of the Mexico Subduction Zone

    Abbott, Elizabeth R.; Brudzinski, Michael R.


    This study characterizes subduction related seismicity with local deployments along the northwestern section of the Mexico Subduction Zone where 4 portions of the plate interface have ruptured in 1973, 1985, 1995, and 2003. It has been proposed that the subducted boundary between the Cocos and Rivera plates occurs beneath this region, as indicated by inland volcanic activity, a gap in tectonic tremor, and the Manzanillo Trough and Colima Graben, which are depressions thought to be associated with the splitting of the two plates after subduction. Data from 50 broadband stations that comprised the MARS seismic array, deployed from January 2006 to June 2007, were processed with the software program Antelope and its generalized source location algorithm, genloc, to detect and locate earthquakes within the network. Slab surface depth contours from the resulting catalog indicate a change in subduction trajectory between the Rivera and Cocos plates. The earthquake locations are spatially anti-correlated with tectonic tremor, supporting the idea that they represent different types of fault slip. Hypocentral patterns also reveal areas of more intense seismic activity (clusters) that appear to be associated with the 2003 and 1973 megathrust rupture regions. Seismicity concentrated inland of the 2003 rupture is consistent with slip on a shallowly dipping trajectory for the Rivera plate interface as opposed to crustal faulting in the overriding North American plate. A prominent cluster of seismicity within the suspected 1973 rupture zone appears to be a commonly active portion of the megathrust as it has been active during three previous deployments. We support these interpretations by determining focal mechanisms and detailed relocations of the largest events within the 1973 and inland 2003 clusters, which indicate primarily thrust mechanisms near the plate interface.

  7. Evidence of Possible Induced Seismicity in the Wabash Valley Seismic Zone from Improved Microearthquake Locations

    Eagar, K. C.; Pavlis, G. L.; Hamburger, M. W.


    We reanalyzed data from a temporary seismic network in southern Indiana and Illinois deployed in November 1995 through July 1996. We produced the first comprehensive catalog of the complete 211 days of that experiment. The results are dominated by a cluster of 534 microearthquakes that occurred near the town of New Harmony, Indiana. Waveform similarity among all of the events suggests a more closely spaced grouping than that found by independent earthquake locations. We relocated the earthquakes using time-domain cross-correlation of the vertical traces and complex cross-correlation of the horizontal traces to improve arrival times for P- and S-waves, respectively. Additional constraints on the absolute locations were applied using arrival time difference analysis of earthquakes recorded by two stations. Average source depths from standard location methods and waveform modeling with synthetic seismograms indicate, in contrast to larger events in the region, the earthquakes occurred at depths oil production, in particular water-injection for the purpose of secondary recovery. The primary evidence for this includes: (1) tight spatial clustering of earthquakes; (2) unusually shallow earthquake depths; (3) good spatial correlation of the relocated hypocenters to the existing wells and oil fields; and (4) an unusually steep slope in the log-linear relationship of earthquake magnitude and frequency. It is therefore necessary to discard the events in the cluster before consideration of magnitude-frequency relations for earthquake hazards estimates.

  8. Seismicity and shallow slab geometry in the central Vanuatu subduction zone

    Baillard, Christian; Crawford, Wayne C.; Ballu, Valérie; Régnier, Marc; Pelletier, Bernard; Garaebiti, Esline


    The Vanuatu arc in the southwest Pacific Ocean is one of the world's most seismically active regions, with almost 39 magnitude 7+ earthquakes in the past 43 years. Convergence rates are around 90-120 mm/yr along most of the arc, but drop to 25-43 mm/yr in the central section, probably due to the subduction of the d'Entrecasteaux ridge. We characterize the slab geometry and tectonic state in this central section by analyzing data from a 10 month deployment of 30 seismometers over this section. We located more than 30,000 events (all less than magnitude 5.5), constructed an improved 1-D velocity model, calculated focal mechanisms and cluster geometries, and determined the 3-D geometry of the interplate seismogenic zone. The seismogenic zone has a shallow bulge in front of the d'Entrecasteaux ridge, which could be explained by the ridge's buoyancy contributing to the uplift of the fore-arc islands. The seismogenic zone extends to ~45 km depth, significantly below the 26-27 km depth of the fore-arc Moho, indicating that the upper mantle wedge is not significantly serpentinized, which is consistent with the relatively high thermal parameter of the subducting plate. The maximum width of the seismogenic zone is 80 km, indicating an upper earthquake magnitude limit of Mw 7.85 ± 0.4, assuming standard rupture zone aspect ratios. The data also reveal a double seismic zone, 20 to 30 km below the seismogenic zone, which is presumably caused by flexure of the downgoing plate.

  9. Correlation of seismic wave velocities with fracture densities: Implications for the critical zone in mountain watersheds

    Peters, M. P.; Holbrook, W. S.; Flinchum, B. A.; Pasquet, S.


    Despite increasing scientific interest in the critical zone, the accurate determination of fracture density in the subsurface remains difficult as access and costs can prohibit ground-truthing through drilling. A more precise characterization of the fracturing process provides critical insight in to subsurface structures. This is particularly important in determining the point at which protolithic rock becomes fractured bedrock and then degrades to soil through the process of weathering. We studied outcrops in the Laramie Range of southeastern Wyoming were studied and fracture densities were correlated with seismic pressure (P) wave velocities. We used the Differential Effective Medium (DEM) rock physics model to validate our findings and provide a more robust characterization of the role of P-wave velocities acquired on outcrops play in critical zone science. This approach marks a significant departure from previous research, which has not applied P-wave fracture relationships in outcrops onto the critical zone for subsurface characterization. We compared our results with borehole data to establish a relationship between surface outcrops and subsurface rock structures. We found a clear, inverse relationship between a decrease in P-wave velocity and an increase in fracture density consistent with borehole data in the studied area. Our findings suggest that outcrops can be used to determine fracture density in the critical zone. We show that the use of seismic refraction surveys on outcrops provides a non-invasive, highly transferrable method through which we can predict fracturing densities in the subsurface.

  10. Imaging the Seismic Cycle in the Central Andean Subduction Zone from Geodetic Observations

    Ortega-Culaciati, F.; Becerra-Carreño, V. C.; Socquet, A.; Jara, J.; Carrizo, D.; Norabuena, E. O.; Simons, M.; Vigny, C.; Bataille, K. D.; Moreno, M.; Baez, J. C.; Comte, D.; Contreras-Reyes, E.; Delorme, A.; Genrich, J. F.; Klein, E.; Ortega, I.; Valderas, M. C.


    We aim to quantify spatial and temporal evolution of fault slip behavior during all stages of the seismic cycle in subduction megathrusts, with the eventual goal of improving our understanding of the mechanical behavior of the subduction system and its implications for earthquake and tsunami hazards. In this work, we analyze the portion of the Nazca-SouthAmerican plates subduction zone affected by the 1868 southern Peru and 1877 northern Chile mega-earthquakes. The 1868 and 1878 events defined a seismic gap that did not experience a large earthquake for over 124 years. Only recently, the 1995 Mw 8.1 Antofagasta, 2001 Mw 8.4 Arequipa, 2007 Mw 7.7 Tocopilla, and 2014 Mw 8.2 Pisagua earthquakes released only a small fraction of the potential slip budget, thereby raising concerns about continued seismic and tsunami hazard. We use over a decade of observations from continuous and campaign GPS networks to analyze inter-seismic strain accumulation, as well as co-seimic deformation associated to the more recent earthquakes in the in the Central Andean region. We obtain inferences of slip (and back-slip) behavior using a consistent and robust inversion framework that accounts for the spatial variability of the constraint provided by the observations on slip across the subduction megathrust. We present an updated inter-seismic coupling model and estimates of pre-, co- and post- seismic slip behavior associated with the most recent 2014 Mw 8.2 Pisagua earthquake. We analyze our results, along with published information on the recent and historical large earthquakes, to characterize the regions of the megathrust that tend to behave aseismically, and those that are capable to accumulate a slip budget (ultimately leading to the generation of large earthquakes), to what extent such regions may overlap, and discuss the potential for large earthquakes in the region.

  11. Seismic imaging of shallow reflectors in the eastern Kapuskasing structural zone, with correction of crossdip attitudes

    Kim, Jisoo; Moon, Wooil M.; Percival, John A.; West, F. G.


    Cascaded processes of crossdip correction and residual statics are tested and applied in the reprocessing of regional data from LITHOPROBE Kapuskasing Transect line 2. The objective was to improve seismic imaging of shallow, gently dipping reflectors in the eastern Kapuskasing structural zone, a thrusted slice of Archean middle to lower crust. This focusing strategy proved to be very effective in improving the image of the reflected energy and in identifying a set of conformally dipping reflectors whose true crossdip is estimated to be approximately 17 deg NW. The estimated crossdip for a reflective, compositionally layered zone and for the basal thrust, the Ivanhoe Lake Fault zone, support the previously estimated average dip of 15-20 deg.

  12. Continent-sized anomalous zones with low seismic velocity at the base of Earth's mantle

    Garnero, Edward J.; McNamara, Allen K.; Shim, Sang-Heon


    Seismic images of Earth's interior reveal two massive anomalous zones at the base of the mantle, above the core, where seismic waves travel slowly. The mantle materials that surround these anomalous regions are thought to be composed of cooler rocks associated with downward advection of former oceanic tectonic plates. However, the origin and composition of the anomalous provinces is uncertain. These zones have long been depicted as warmer-than-average mantle materials related to convective upwelling. Yet, they may also be chemically distinct from the surrounding mantle, and potentially partly composed of subducted or primordial material, and have therefore been termed thermochemical piles. From seismic, geochemical and mineral physics data, the emerging view is that these thermochemical piles appear denser than the surrounding mantle materials, are dynamically stable and long-lived, and are shaped by larger-scale mantle flow. Whether remnants of a primordial layer or later accumulations of more-dense materials, the composition of the piles is modified over time by stirring and by chemical reactions with material from the surrounding mantle, underlying core and potentially from volatile elements transported into the deep Earth by subducted plates. Upwelling mantle plumes may originate from the thermochemical piles, so the unusual chemical composition of the piles could be the source of distinct trace-element signatures observed in hotspot lavas.

  13. The Obsidian Creep Project: Seismic Imaging in the Brawley Seismic Zone and Salton Sea Geothermal Field, Imperial County, California

    Catchings, R. D.; Rymer, M. J.; Goldman, M.; Lohman, R. B.; McGuire, J. J.


    In March 2010, we acquired medium- and high-resolution P- and S-wave seismic reflection and refraction data across faults in the Brawley seismic zone (BSZ) and across part of the Salton Sea Geothermal Field (SSGF), Imperial Valley, California. Our objectives were to determine the dip, possible structural complexities, and seismic velocities associated with the BSZ and SSGF. We acquired multiple seismic data sets along a north-south profile and a high-resolution P-wave profile along an east-west profile. The north-south profile included: 1) a 6.4-km-long P-wave (main) profile that was recorded on 320 Texan seismographs spaced at 20-m intervals, 2) a 1.2-km-long cabled, high-resolution profile along the northern end of the main profile, and 3) an approximately 1.2-km-long S-wave profile along the cabled profile. P-wave sources along the main profile were generated by 0.15- to 0.45-kg buried explosions spaced every 40 m, and P-wave sources along the cabled profile were generated by Betsy-Seisgun ‘shots’ spaced every 10 m. S-waves sources were generated by hammer impacts on the ends of an aluminum block. The east-west profile consisted of a 3.4-km-long high-resolution P-wave seismic profile with shots (Betsy-Seisgun) and geophones spaced every 10 m. Preliminary interpretation of shot gathers from blasts in the north-south profile suggests that the BSZ and SSGF are structurally complex, with abundant faults extending to or near the ground surface. Also, we observe relatively high-velocity material, apparent velocities of about 4.0 km/s in one direction and about 2.8 km/s in another relative to about 1.6 km/s for shallower material, that shallows beneath the SSGF. This may be due to high temperatures and resultant metamorphism of buried materials in the SSGF. From preliminary interpretation of shot gathers along the east-west profile we interpret a prominent fault that extends to the ground surface. This fault is on projection of the Kalin fault, from about 40 m to

  14. Global seismic data reveal little water in the mantle transition zone

    Houser, C.


    Knowledge of the Earth's present water content is necessary to constrain the amount of water and other volatiles the Earth acquired during its formation and the amount that is cycled back into the interior from the surface. This study compares 410 and 660 km discontinuity depth with shear wave tomography within the mantle transition zone to identify regions with seismic signals consistent with water. The depth of the 410 and 660 km discontinuities is determined from a large updated dataset of SS-S410S and SS-S660S differential travel times, known as SS precursors. The discontinuity depths measured from binning and stacking the SS precursor data are then compared to the shear velocity model HMSL-S06 in the transition zone. Mapping all the possible combinations, very few locations match the predictions from mineral physics for the effects of water on discontinuity depth and shear velocity. The predictions, although not yet measured at actual transition zone temperatures and pressures, are a shallow 410 km discontinuity, a deep 660 km discontinuity, and a slow shear velocity. Only 8% of the bins with high-quality data are consistent with these predictions, and the calculated average water content within these bins is around 0.6 wt.%. A few isolated locations have patterns of velocity/topography that are consistent with water, while there are large regional-scale patterns consistent with cold/hot temperature anomalies. Combining this global analysis of long period seismic data and the current mineral physics predictions for water in transition zone minerals, I find that the mantle transition zone is generally dry, containing less than one Earth ocean of water. Although subduction zones could be locally hydrated, the combined discontinuity and velocity data show no evidence that wadsleyite or ringwoodite have been globally hydrated by subduction or initial Earth conditions.

  15. Lateral wave-field stacking of seismic Fresnel zones for the generalized-offset case

    Tian, Nan; Fan, Ting-En; Wang, Zong-Jun; Cai, Wen-Tao


    To unify different seismic geometries, the concept of generalized offset is defined and the expressions for Fresnel zones of different order on a plane are presented. Based on wave theory, the equation of the lateral wave-field stacking for generalized-offset Fresnel zones is derived. For zero and nonzero offsets, the lateral stacking amplitude of diffraction bins of different sizes is analyzed by referring to the shape of the Fresnel zones of different order. The results suggest the following. First, the contribution of diffraction bins to wave-field stacking is related to the offset, surface relief, interface dip, the depth of the shot point to the reflection interface, the observational geometry, and the size of the interference stacking region. Second, the first-order Fresnel zone is the main constructive interference, and its contribution to the reflection amplitude is slightly smaller than half the contribution of all Fresnel zones. Finally, when the size of the diffraction bin is smaller than the first-order Fresnel zone, the larger the size of the diffraction bin, the larger is the amplitude of the receiver, even in the nonzero offset-case.

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

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


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

  17. Seismic response of earth dams considering dynamic properties of unsaturated zone

    Ariyan M.


    Full Text Available It is conventionally assumed in the analysis and design of earth dams that the soil located above the phreatic line, i.e. the uppermost seepage flow line, is completely dry. However, there is often an unsaturated flow of water through an unsaturated zone above this borderline and variation in moisture content in this zone results in variation of matric suction throughout this region. Variation of matric suction, in turn, results in variation of effective stresses in this zone. In this research, the seismic response of earth dams in terms of the displacement and acceleration at the crown of the dam as well as the stress distribution in the dam body is investigated. Taking into account the effect of unsaturated zone, a comparison is made to investigate the effect of conventional simplification in ignoring the dynamic characteristics of the unsaturated zone above the phreatic line and the more complicated analysis which includes the unsaturated zone. A function for the soil-water retention curve (SWRC was assigned to the soil in the unsaturated zone to determine the variation of matric suction in this zone and analyses were made using finite difference software (FLAC. Results are then compared to the conventional method for homogeneous dams. In these analyzes the soil shear modulus was assumed to vary with the mean effective stress both for saturated and unsaturated zones. Among various results, it was notable that the history of crest x-displacement, and acceleration show higher values in models accounting for the unsaturated region. It was attributed to the considerably lower values of damping ratio in the crest region in the unsaturated models.

  18. Historical seismicity near Chagos - A complex deformation zone in the equatorial Indian Ocean

    Wiens, D. A.


    The historical seismicity of the Chagos region of the Indian Ocean is analyzed, using earthquake relocation methods and a moment variance technique to determine the focal mechanisms of quakes occurring before 1964. Moment variance analysis showed a thrust faulting mechanism associated with the earthquake of 1944 near the Chagos-Laccadive Ridge; a strike-slip mechanism was associated with a smaller 1957 event occurring west of the Chagos Bank. The location of the 1944 event, one of the largest intraplate earthquakes known (1.4 x 10 to the 27th dyne/cm), would imply that the Chagos seismicity is due to a zone of tectonic deformation stretching across the equatorial Indian Ocean. The possibility of a slow diffuse boundary extending west of the Central Indian Ridge is also discussed. This boundary is confirmed by recent plate motion studies which suggest that it separates the Australian plate from a single Indo-Arabian plate.

  19. Preliminary results of characteristic seismic anisotropy beneath Sunda-Banda subduction-collision zone

    Wiyono, Samsul H.; Nugraha, Andri Dian


    Determining of seismic anisotropy allowed us for understanding the deformation processes that occured in the past and present. In this study, we performed shear wave splitting to characterize seismic anisotropy beneath Sunda-Banda subduction-collision zone. For about 1,610 XKS waveforms from INATEWS-BMKG networks have been analyzed. From its measurements showed that fast polarization direction is consistent with trench-perpendicular orientation but several stations presented different orientation. We also compared between fast polarization direction with absolute plate motion in the no net rotation and hotspot frame. Its result showed that both absolute plate motion frame had strong correlation with fast polarization direction. Strong correlation between the fast polarization direction and the absolute plate motion can be interpreted as the possibility of dominant anisotropy is in the asthenosphere..

  20. Preliminary results of characteristic seismic anisotropy beneath Sunda-Banda subduction-collision zone

    Wiyono, Samsul H., E-mail: [Study Program of Earth Sciences, Faculty of Earth Sciences and Technology, Institute of Technology Bandung, Bandung 40132 (Indonesia); Indonesia’s Agency for Meteorology Climatology and Geophysics, Jakarta 10610 (Indonesia); Nugraha, Andri Dian, E-mail: [Indonesia’s Agency for Meteorology Climatology and Geophysics, Jakarta 10610 (Indonesia); Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institute of Technology Bandung, Bandung 40132, Indonesia, Phone: +62-22 2534137 (Indonesia)


    Determining of seismic anisotropy allowed us for understanding the deformation processes that occured in the past and present. In this study, we performed shear wave splitting to characterize seismic anisotropy beneath Sunda-Banda subduction-collision zone. For about 1,610 XKS waveforms from INATEWS-BMKG networks have been analyzed. From its measurements showed that fast polarization direction is consistent with trench-perpendicular orientation but several stations presented different orientation. We also compared between fast polarization direction with absolute plate motion in the no net rotation and hotspot frame. Its result showed that both absolute plate motion frame had strong correlation with fast polarization direction. Strong correlation between the fast polarization direction and the absolute plate motion can be interpreted as the possibility of dominant anisotropy is in the asthenosphere.

  1. The upper crust of the Eastern Tennessee Seismic Zone: Insights from potential fields inversion

    Brandmayr, Enrico; Vlahovic, Gordana


    The study investigates the crustal structure of the eastern Tennessee seismic zone (ETSZ) by means of potential field inversion through the located Euler deconvolution method. Inversion of magnetic field data shows that the top of the magnetic basement ranges between 6 and 12 km depth in the Valley and Ridge physiographic province while it is shallower (< 2 km depth) and locally outcropping in the Blue Ridge and Cumberland Plateau provinces. The estimated depth to the top of the magnetic basement is in general agreement with existing sedimentary cover maps of the broad study area. The inversion of gravity data is much more ambiguous, pointing to a generally deeper source, than magnetic data inversion. The findings support the interpretation of ETSZ seismicity as originating in basement structures not related to Appalachian orogeny and likely dating to Grenville age.

  2. Characterization and application of microearthquake clusters to problems of scaling, fault zone dynamics, and seismic monitoring at Parkfield, California

    Nadeau, Robert Michael [Univ. of California, Berkeley, CA (United States)


    This document contains information about the characterization and application of microearthquake clusters and fault zone dynamics. Topics discussed include: Seismological studies; fault-zone dynamics; periodic recurrence; scaling of microearthquakes to large earthquakes; implications of fault mechanics and seismic hazards; and wave propagation and temporal changes.

  3. The Seismogenic Zone in Southern Chile: Insights from high resolution receiver function analysis and seismic Tomography

    Rietbrock, A.; Haberland, C.; Lange, D.; Bataille, K.


    Subduction zones, the expression of convergent plate boundaries, generate the world's largest and most destructive earthquakes. The Southern Chilean subduction zone is an ideal natural laboratory to study the processes involved in generating these devastat- ing earthquakes and is one of the main aims of the international and interdisciplinary research initiative TIPTEQ (from The Incoming Plate to megaThrust EarthQuake pro- cesses). High resolution images, using different techniques as well as different physi- cal parameters, form the base for identifying the processes involved. Here we present new data from teleseismic receiver function analysis and 3D seismic tomography to study in detail the down-dip end of the seismogenic zone in the nucleation area of the 1960 magnitude Mw=9.5 Valdivia, Chile, earthquake. Within the project TIPTEQ two dense amphibious passive seismic networks have been installed between Nov. 2004 and Oct. 2005, both covering the entire forearc from the trench to the active volcanic front. The Northern array was located between 37° and 39° South including the epicentre of the 1960 Chile earthquake. It consisted out of 120 continuously recording, three component stations on land and 10 continuously recording Ocean Bottom Seismometers/Hydrophones (OBS/H) at sea. The Southern array was located between 41.5° and 43.5° South roughly in the middle of the rupture zone of the Valdivia earthquake. It consisted out of 20 continuously recording three component stations on land and 20 continuously recording Ocean Bottom Seismometers/Hydrophones (OBS/H) at sea. Several hundreds of micro earthquakes could be located using manual picked P- and S-wave arrivals. Joint 2D/3D inversions for earthquake location, P-wave velocity and vp/vs-ratio were carried out and give a detailed image of the structure as well as a snapshot of the seismicity distribution in both study regions. The subducting Nazca plate can be clearly identified in both regions dipping at a

  4. Seismic imaging of a megathrust splay fault in the North Chilean subduction zone (Central Andes)

    Storch, Ina; Buske, Stefan; Schmelzbach, Cedric; Wigger, Peter


    Prominent trench-parallel fault systems in the arc and fore-arc of the Chilean subduction zone can be traced for several thousand kilometers in north-south direction. These fault systems possibly crosscut the entire crust above the subduction megathrust and are expected to have a close relationship to transient processes of the subduction earthquake cycles. With the motivation to image and characterize the structural inventory and the processes that occur in the vicinity of these large-scale fault zones, we re-processed the ANCORP'96 controlled-source seismic data set to provide images of the faults at depth and to allow linking geological information at the surface to subsurface structures. The correlation of the imaging results with observed hypocenter locations around these fault systems reveals the origin and the nature of the seismicity bound to these fault systems. Active and passive seismic data together yield a picture of a megathrust splay fault beneath the Longitudinal Valley at mid-crustal level, which can be observed from the top of the subduction plate interface and which seems to be connected to the Precordilleran Fault System (PFS) known at the surface. This result supports a previously proposed tectonic model where a megathrust splay fault defines the Western Altiplano as a crustal-scale fault-bend-fold. Furthermore, we clearly imaged two branches of the Uyuni-Kenayani Fault (UKF) in a depth range between 0 and 20 km. In summary, imaging of these faults is important for a profound understanding of the tectonic evaluation and characterization of the subduction zone environment, for which the results of this study provide a reliable basis.

  5. Joint hypocenter-velocity inversion for the eastern Tennessee seismic zone

    Vlahovic, Gordana; Powell, Christine A.; Chapman, Martin C.; Sibol, Matthew S.


    A joint hypocenter-velocity inversion for the eastern Tennessee seismic zone (ETSZ) has resolved velocity features in basement rock below detached Appalachian thrust sheets. P and S wave arrival times from 492 earthquakes have been inverted for one-(1-D) and three-dimensional (3-D) velocity models to midcrustal depths. The 3-D P and S wave velocity solutions are computed independly and are very similar. In relation to the 1-D model, velocity anomalies range from -8% to +16% in the first layer (upper 5 km) and between ±7% in deeper layers. Prominent velocity anomalies parallel the seismic zone and are consistent from layer to layer. The most persistent anomaly is a low-velocity region that borders the seismic zone to the northwest and is flanked on either side by regions of anomalously high velocity. The New York-Alabama (NY-AL) magnetic lineament coincides with or lies close to the southeast boundary of the prominent velocity low in both the P and S wave velocity images. The spatial coincidence between velocity, gravity, and magnetic gradients suggests that major discontinuities are present in the basement. Relocation in the 3-D velocity model reduced the number of very deep earthquakes (below 20 km) and further accentuated differences in seismogenic properties on either side of the NY-AL lineament. After relocation, most earthquakes occur in a vertically bounded region roughly 30 km wide extending from 4 to 22 km in depth. Most earthquakes occur in regions characterized by either average velocity or small velocity anomalies.

  6. Methods of seismic zone localization in the highly stressed geological environment in mining natural-engineering system

    Kozyrev, A.; Fedotova, Iu.; Zhuravleva, O.


    During developing mineral deposits in the geological environment the anomalous energy-saturated zones (parts of highly stressed rocks) are being formed. As a result in the rock mass rockbursts and mining-induced earthquakes occur. The largest mining-induced earthquakes (M 4.0 - 4.2) were registered at the mines of the Khibiny and Lovozersky massifs of the Kola Peninsula. The energy-saturated zones migrate subject to displacement of front of working faces. Location and dimensions of the zones are estimated according to data of analytical investigations and experimental determinations in the rock mass. In some cases (for example, when developing blocks-pillars and transition zones between open and underground mining operations or adjacent mines) all the mining area is a united energy-saturated zone, where the main problems occur concerning mining workings stability management, and under rockbursts hazardous conditions there occur problems concerning mining-induced seismicity manifestations. Parameters of geological environment seismic emission are objective indicators of geological environment energy-saturation. The assessment of their changing is a basis of methods of seismic zones localization and detection of their migration during mining operations development. To assess a current state and determine conditions of transition of geological environment parts into the critical state there carried out investigations concerning space-time regularities of rock mass seismicity parameters changing in the mines' geomechanical space. The following parameters are considered as characteristics of rock mass seismicity: fractal criterion, dip angle criterion for seismic events recurrence graph, concentration criterion, and criterion of fissures' average length. A complex assessment of single parameters range is applied to get the better results. The analysis also takes into account influence of deterministic factors: fracture disturbances and stope face boundaries. Analysis

  7. Upper-mantle seismic discontinuities and the thermal structure of subduction zones

    Vidale, J.E.; Benz, H.M.


    The precise depths at which seismic velocities change abruptly in the upper mantle are revealed by the analysis of data from hundreds of seismometers across the western United States. The boundary near 410 km depth is locally elevated, that near 660 km depressed. The depths of these boundaries, which mark phase transitions, provide an in situ thermometer in subduction zones: the observed temperature contrasts require at least moderate thickening of the subducting slab near 660 km depth. In addition, a reflector near 210 km depth may mark the bottom of the aesthenosphere.

  8. Slow slip events and seismic tremor at circum-Pacific subduction zones

    Schwartz, Susan Y.; Rokosky, Juliana M.


    It has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements. However, only recently has a fuller spectrum of strain release processes, including normal, slow, and silent earthquakes (or slow slip events) and continuous and episodic slip, been observed and generated by numerical simulations of the earthquake cycle. Despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive. The concurrence of seismic tremor with slow slip episodes in Cascadia and southwestern Japan provides insight into the process of slow slip. A perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface. Alternatively, evidence is accumulating to support the notion that tremor results from shear failure during slow slip. Global observations of the location, spatial extent, magnitude, duration, slip rate, and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation. Most slow slip events occur just downdip of the seismogenic zone, consistent with rate- and state-dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation. At a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation. Slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault, bringing it closer to or farther from earthquake failure, respectively. This paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide, with a focus on circum-Pacific subduction zones. Trends in global observations of slow slip events suggest that (1) slow slip is a

  9. Galicia Bank ocean-continent transition zone: New seismic reflection constraints

    Dean, S. L.; Sawyer, D. S.; Morgan, J. K.


    The West Iberia continental margin is a type locale for magma-poor rifting, and studies there have been instrumental in changing the classical view of the ocean-continent transition (OCT) from a discrete boundary juxtaposing continental and oceanic crust, into a more complicated zone of varying width that can include exhumed mantle. This study examines two new seismic lines in the Galicia Bank area extending west of the Peridotite Ridge, showing high resolution images of five new ridges. These ridges could be hyperextended continental crust, exhumed continental mantle, or rough ultra-slow spreading oceanic crust. There are no tilted fault blocks with pre-syn rift stratigraphy that would indicate continental crust. There are also no faults indicating mid-ocean spreading with seismic layer stratigraphy indicating normal oceanic crust. The ridges have no coherent internal seismic structure, and some resemble the topographic profile of the Peridotite Ridge. Therefore, it is likely the western ridges are also mainly composed of serpentinized mantle. These western ridges are also similar to small oceanic core complexes observed along the active part of the Mid-Atlantic Ridge, which also contain exhumed serpentinized mantle. This implies that there is a gradual transition within our study area from continental extension to seafloor spreading. Exhumation of continental mantle results in the formation of peridotite ridges, then transitions to episodic volcanism, which produces local thin basaltic crust, and exhumation of oceanic core complexes. Asymmetric processes during initial rifting and spreading result in contrasting structures on the two resulting margins.

  10. Seismic event, sequence and tectonic significance in Canglangpu Stage in Paleo-Tanlu Fault Zone

    QIAO; Xiufu(乔秀夫); GAO; Linzhi(高林志); PENG; Yang(彭阳); LI; Haibing(李海兵)


    The Canglangpu Stage of Lower Cambrian Series is widely distributed along both sides of the Tanlu (Tancheng-Lujiang) Fault Zone in the Jiao-Liao-Xu-Huai regions. In the Liaodong Peninsula, the Canglangpu Stage consists of three formations, i.e. Gejiatun, Dalinzi and Jianchang formations in ascending order (lying on the eastern side of the Tanlu Fault Zone). The Dalinzi Formation, developing in a littoral Sabkha environment, is full of catastrophic event records of violent seism, such as liquefied muddy-sandy veins, hydroplastic folds, hydroplastic micro-faults (three forming an organic whole), liquefied crinkled deformations, liquefied breccia and sandy dikes. Based on such records, the seismic liquified sequence of argillaceous rocks in Sabkha is built up. In northern Jiangsu and Anhui provinces, however, there hardly observe seismic records in the Canglangpu Stage, which consists of Jinshanzhai and lower Gouhou and upper Gouhou formations (lying on the western side of the Tanlu Fault Zone). Even if the Gouhou Formation, developing in a lagoon-dry environment, is in the same climate zone as the Dalinzi Formation, and 4 depositional sequences have been identified in the Canglangpu Stage in Northern Jiangsu and Anhui provinces, however, in the same stage in the Liaodong Peninsula, there exist only 3 ones. Therefore, it is not supported by the above mentioned evidence (such as catastrophic events, sequences stratigraphy and lithologic correlation of formations) that the Canglangpu Stage in the Liaodong Peninsula came from northern Jiangsu and Anhui provinces through a long-distance, about hundreds kilometers, left-hand displacement of the Tanlu Fault in the Mesozoic era.

  11. Active faults in the deformation zone off Noto Peninsula, Japan, revealed by high- resolution seismic profiles

    Inoue, T.; Okamura, Y.; Murakami, F.; Kimura, H.; Ikehara, K.


    Recently, a lot of earthquakes occur in Japan. The deformation zone which many faults and folds have concentrated exists on the Japan Sea side of Japan. The 2007 Noto Hanto Earthquake (MJMA 6.9) and 2007 Chuetsu-oki Earthquake (MJMA 6.8) were caused by activity of parts of faults in this deformation zone. The Noto Hanto Earthquake occurred on 25 March, 2007 under the northwestern coast of Noto Peninsula, Ishikawa Prefecture, Japan. This earthquake is located in Quaternary deformation zone that is continued from northern margin of Noto Peninsula to southeast direction (Okamura, 2007a). National Institute of Advanced Industrial Science and Technology (AIST) carried out high-resolution seismic survey using Boomer and 12 channels short streamer cable in the northern part off Noto Peninsula, in order to clarify distribution and activities of active faults in the deformation zone. A twelve channels short streamer cable with 2.5 meter channel spacing developed by AIST and private corporation is designed to get high resolution seismic profiles in shallow sea area. The multi-channel system is possible to equip on a small fishing boat, because the data acquisition system is based on PC and the length of the cable is short and easy to handle. Moreover, because the channel spacing is short, this cable is very effective for a high- resolution seismic profiling survey in the shallow sea, and seismic data obtained by multi-channel cable can be improved by velocity analysis and CDP stack. In the northern part off Noto Peninsula, seismic profiles depicting geologic structure up to 100 meters deep under sea floor were obtained. The most remarkable reflection surface recognized in the seismic profiles is erosion surface at the Last Glacial Maximum (LGM). In the western part, sediments about 30 meters (40 msec) thick cover the erosional surface that is distributed under the shelf shallower than 100m in depth and the sediments thin toward offshore and east. Flexures like deformation in

  12. A Global Review of Slow Slip Events and Seismic Tremor at Circum-Pacific Subduction Zones

    Schwartz, S. Y.; Rokosky, J. M.


    It has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements. However, only recently has a fuller spectrum of strain release processes, including normal, slow and silent earthquakes (or slow slip events), and continuous and episodic creep, been observed and generated by numerical simulations of the earthquake cycle. Despite a profusion of observations and modeling studies, the physical mechanism of slow slip events (SSEs) remains elusive. The concurrence of seismic tremor, similar to signals observed at volcanoes, with slow slip episodes in Cascadia and southwestern Japan suggests that SSEs may be related to fluid migration on or near the plate interface. We compare the location, spatial extent, magnitude, duration, slip rate, recurrence behavior and associated tremor and seismicity of aseismic slip transients worldwide to better understand their generation and earthquake hazard implications. We find that slow slip events occur at either the down-dip edge of the seismogenic zone, or at complementary locations to strongly locked patches or co-seismic asperities within the seismogenic zone. Nucleation of SSEs at frictional transitions is supported by rate- and state-dependent frictional modeling. We find a global scaling relationship between SSE duration and equivalent moment magnitude that implies a constant rate of slow slip propagation, consistent with the small range in observed SSE migration rates. Afterslip following moderate to large earthquakes suggests a relationship between slow slip and higher velocity rupture (earthquakes). We assess if such a cause-and-effect relationship exists between interseismic SSEs and earthquake activity. We find that although isolated episodes of interseismic slow slip can be related to nearby earthquake activity, a consistent triggering pattern has yet to emerge and further study is clearly warranted.

  13. Abundant off-fault seismicity and orthogonal structures in the San Jacinto fault zone

    Ross, Zachary E.; Hauksson, Egill; Ben-Zion, Yehuda


    The trifurcation area of the San Jacinto fault zone has produced more than 10% of all earthquakes in southern California since 2000, including the June 2016 Mw (moment magnitude) 5.2 Borrego Springs earthquake. In this area, the fault splits into three subparallel strands and is associated with broad VP/VS anomalies. We synthesize spatiotemporal properties of historical background seismicity and aftershocks of the June 2016 event. A template matching technique is used to detect and locate more than 23,000 aftershocks, which illuminate highly complex active fault structures in conjunction with a high-resolution regional catalog. The hypocenters form dipping seismicity lineations both along strike and nearly orthogonal to the main fault, and are composed of interlaced strike-slip and normal faults. The primary faults change dip with depth and become listric by transitioning to a dip of ~70° near a depth of 10 km. The Mw 5.2 Borrego Springs earthquake and past events with M > 4.0 occurred on the main faults, whereas most of the low-magnitude events are located in a damage zone (several kilometers wide) at seismogenic depths. The lack of significant low-magnitude seismicity on the main fault traces suggests that they do not creep. The very high rate of aftershocks likely reflects the large geometrical fault complexity and perhaps a relatively high stress due to a significant length of time elapsed since the last major event. The results provide important insights into the physics of faulting near the brittle-ductile transition. PMID:28345036

  14. Structure and Local Seismicity From the Incoming Nazca Plate in the Southern Chile Subduction Zone

    Scherwath, M.; Grevemeyer, I.; Flueh, E.; Contreras-Reyes, E.; Tilmann, F.; Kaul, N.; Weinrebe, W.


    Lithospheric deformation near the Chile Triple Junction is under investigation in the TIPTEQ (from The Incoming Plate to mega-Thrust EarthQuake processes) project. During R/V Sonne cruise SO181 (December 2004 to February 2005) various geophysical and geological data sets along several large transects across differently aged subducting oceanic lithosphere were acquired. TIPTEQ aims at studying the influence of the incoming plate on the seismogenic zone in the area of the 1960 great Chile earthquake (Mw=9.5), in particular the effects of the thermal regime (i.e., age).We compare structure and local seismicity on two of these transects, one where the incoming oceanic Nazca Plate was formed 6.5 Ma ago, the other 14.5 Ma in age at the trench, thus both of different thermal states. New magnetic data show that the older lithosphere was generated at a spreading rate of 40 mm/a compared to 25 mm/a for the younger one, yet the current convergence of both sections with the South American Plate is about the same (~80 mm/a). Bathymetric and vertical incidence seismic data show smooth and thicker sediments at the older transect whereas the rugged basement of the younger line is less covered, though the sedimentary thickness at the trench is ~2 km in both locations. The crust of the older transect is slightly thicker, shows a clear outer rise, and subducts at a slightly steeper angle than the younger line. On the latter, where the outer rise bulge has not yet been developed, the outer rise seismicity rate is higher and more concentrated in the crust. The local seismicity in the older region is less frequent and occurs predominantly in the upper mantle (see also Tilmann et al., this conference).

  15. A journey to the seismic low velocity zone beneath the ocean (Beno Gutenberg Medal Lecture)

    Kawakatsu, Hitoshi


    The seismic low velocity zone (LVZ), first proposed by Beno Gutenberg, is an enigmatic layer of the Earth that has been drawing attention of earth scientists, most-likely because of its close association with the asthenosphere that enables plate motions in the plate tectonics context. "A journey to the LVZ", therefore, is equivalent to a journey to elucidate the lithosphere-asthenosphere system (LAS) beneath the ocean (at least that is what I mean by this title). Plate tectonics started as a theory of ocean basins nearly 50 years ago, but the mechanical details of how it works are still highly debated. It has been hampered partly by our inability to characterize the physical properties of the LAS beneath the ocean. I will discuss existing observational constraints, including our own results, on the physical properties of the LAS for normal oceanic regions, where plate tectonics is expected to present its simplest form. While a growing number of seismic data on land have provided remarkable advances in large scale pictures, seafloor observations have been shedding new light on the essential details. Particularly, recent advances in ocean bottom broadband seismometry, together with advances in the seismic analysis methodology, have now enabled us to resolve the regional 1-D structure of the entire LAS, from the surface to a depth of 200km, including seismic anisotropy (azimuthal), with deployments of 15 broadband ocean bottom seismometers for 1 2 years. We have thus succeeded to model the entire oceanic LAS without a priori assumption for the shallow-most structure, the assumption often made for the global surface wave tomography. I hope to convince the audience that we are now at an exciting stage that a large-scale array experiment in the ocean (e.g., Pacific Array: is becoming approachable to elucidate the enigma of the LVZ, thus the lithosphere-asthenosphere system, beneath the ocean.

  16. Characterizing potentially induced earthquake rate changes in the Brawley Seismic Zone, southern California

    Llenos, Andrea L.; Michael, Andrew J.


    The Brawley seismic zone (BSZ), in the Salton trough of southern California, has a history of earthquake swarms and geothermal energy exploitation. Some earthquake rate changes may have been induced by fluid extraction and injection activity at local geothermal fields, particularly at the North Brawley Geothermal Field (NBGF) and at the Salton Sea Geothermal Field (SSGF). We explore this issue by examining earthquake rate changes and interevent distance distributions in these fields. In Oklahoma and Arkansas, where considerable wastewater injection occurs, increases in background seismicity rate and aftershock productivity and decreases in interevent distance were indicative of fluid‐injection‐induced seismicity. Here, we test if similar changes occur that may be associated with fluid injection and extraction in geothermal areas. We use stochastic epidemic‐type aftershock sequence models to detect changes in the underlying seismogenic processes, shown by statistically significant changes in the model parameters. The most robust model changes in the SSGF roughly occur when large changes in net fluid production occur, but a similar correlation is not seen in the NBGF. Also, although both background seismicity rate and aftershock productivity increased for fluid‐injection‐induced earthquake rate changes in Oklahoma and Arkansas, the background rate increases significantly in the BSZ only, roughly corresponding with net fluid production rate increases. Moreover, in both fields the interevent spacing does not change significantly during active energy projects. This suggests that, although geothermal field activities in a tectonically active region may not significantly change the physics of earthquake interactions, earthquake rates may still be driven by fluid injection or extraction rates, particularly in the SSGF.

  17. Fractal properties and simulation of micro-seismicity for seismic hazard analysis: a comparison of North Anatolian and San Andreas Fault Zones

    Naside Ozer


    Full Text Available We analyzed statistical properties of earthquakes in western Anatolia as well as the North Anatolian Fault Zone (NAFZ in terms of spatio-temporal variations of fractal dimensions, p- and b-values. During statistically homogeneous periods characterized by closer fractal dimension values, we propose that occurrence of relatively larger shocks (M >= 5.0 is unlikely. Decreases in seismic activity in such intervals result in spatial b-value distributions that are primarily stable. Fractal dimensions decrease with time in proportion to increasing seismicity. Conversely, no spatiotemporal patterns were observed for p-value changes. In order to evaluate failure probabilities and simulate earthquake occurrence in the western NAFZ, we applied a modified version of the renormalization group method. Assuming an increase in small earthquakes is indicative of larger shocks, we apply the mentioned model to micro-seismic (M<= 3.0 activity, and test our results using San Andreas Fault Zone (SAFZ data. We propose that fractal dimension is a direct indicator of material heterogeneity and strength. Results from a model suggest simulated and observed earthquake occurrences are coherent, and may be used for seismic hazard estimation on creeping strike-slip fault zones.

  18. Tomographic Imaging of a New Seismic Zone in Northern Taiwan: Implications for Crustal Magnetism and Tectonic Inheritance

    Cheng, Win-Bin; Chang, Gen-Sin; Hsu, Shu-Kun


    To the west of 121°E, we found that the northern South China Sea magnetic anomaly in central Taiwan is coincident with high seismic velocity zone derived from a joint analysis of gravity anomaly and seismic travel time data. To the east of 121°E, we found a new seismic zone which remains enigmatic because of its apparent relationship with both the emplacement of high magnetic anomaly and termination of Okinawa Trough. In order to understand the new seismic zone and breakup of the high magnetic anomaly, a joint analysis of gravity anomaly and seismic travel time data have been used to construct three-dimensional velocity structure for the study area. Earthquake data were collected by the Central Weather Bureau Seismological Network from 2000 to 2012. A modified velocity model obtained by previously local earthquake tomography, was used to construct an initial three-dimensional gravity model, using a linear velocity-density relationship. To derive a crustal velocity-density model that accounts for both types of observations, this study performed a sequential inversion of traveltime and gravity data. The main features of our three-dimensional velocity model are: (1) an uplifted zone with velocity greater than 6.5 km/s is observed in the lower crust, (2) the width and the shape of the uplifted zone is found strongly correlated with the high magnetic belt, (3) the trend of the high-velocity zone turns from NE to N in central Taiwan, where the feature of high magnetic was truncated. This study suggested that integration of seismic data with new perspectives on crustal magnetism will provide a better understanding of terrane accretion, rifting processes, and passive margin formation in the Taiwan region.

  19. Dietary attitudes and behaviours of women in China after the 2008 Wenchuan earthquake in three seismically different zones.

    Hu, Ping; Han, Ling-Li; Hou, Feng-Gang; Xu, Xiang-Long; Sharma, Manoj; Zhao, Yong


    The sudden occurrence of the 2008 Wenchuan Earthquake not only devastated people's health, but also may have impacted on the psychological and dietary attitudes and behaviours of the survivors. Although the influence of natural disaster on people's health has been extensively investigated, there is a lack of information about the effects on people's dietary attitudes and behaviours. Our aim was to evaluate the influence of the Wenchuan earthquake on the dietary attitudes and behaviours of adult women from different zones of China in July 2008. 736 women, aged 18-55 years old, were randomly selected and interviewed after the earthquake. Women were selected from three zones: the earthquake zone (n=206), the shaking zone (n=326), and the non-seismic zone (n=204). Although nutrition knowledge mean scores of women in the three zones were relatively low, the women in the earthquake zone became more vigilant about the nutritional value and acceptability of food than women in the other two zones. Nevertheless, women in the earthquake zone also developed some arguably untoward, if understandable, behaviour after the disaster. They increased their consumption and tendency to stock instant food and snack items. That said, these findings were modulated by other factors such as age, residence, Body Mass Index (BMI), and nutrition knowledge itself, as were post-earthquake eating behaviours, as judged by the ordinal logistic regression analyses performed. The major Wenchuan earthquake was associated with differentials in dietary attitudes and behaviours among women by seismic zone.

  20. High resolution seismic velocity structure around the Yamasaki fault zone of southwest Japan as revealed from travel-time tomography

    Nugraha, Andri Dian; Ohmi, Shiro; Mori, Jim; Shibutani, Takuo


    The Yamasaki fault zone in southwestern Japan currently has a high potential for producing a large damaging earthquake. We carried out a seismic tomographic study to determine detailed crustal structures for the region. The velocity model clearly images a low-velocity and high V p / V s (high Poisson's ratio) anomaly in the lower crust beneath the Yamasaki fault zone at a depth of ~15-20 km. This anomaly may be associated with the existence of partially-melted minerals. The existence of this anomaly below the fault zone may contribute to changing the long-term stress concentration in the seismogenic zone.

  1. Seismic attenuation structure associated with episodic tremor and slip zone beneath Shikoku and the Kii peninsula, southwestern Japan, in the Nankai subduction zone

    Kita, Saeko; Matsubara, Makoto


    The three-dimensional seismic attenuation structure (frequency-independent Q) beneath southwestern Japan was analyzed using t* estimated by applying the S coda wave spectral ratio method to the waveform data from a dense permanent seismic network. The seismic attenuation (Qp-1) structure is clearly imaged for the region beneath Shikoku, the Kii peninsula, and eastern Kyushu at depths down to approximately 50 km. At depths of 5 to 35 km, the seismic attenuation structure changes at the Median tectonic line and other geological boundaries beneath Shikoku and the southwestern Kii peninsula. High-Qp zones within the lower crust of the overlying plate are found just above the slip regions at the centers of the long-term slow-slip events (SSEs) beneath the Bungo and Kii channels and central Shikoku. Beneath central Shikoku, within the overlying plate, a high-Qp zone bounded by low-Qp zones is located from the land surface to the plate interface of the subducting plate. The high-Qp zone and low-Qp zones correspond to high-Vp and low-Vp zones of previous study, respectively. The boundaries of the high- and low-Qp zones are consistent with the segment boundaries of tremors (segment boundaries of short-term SSEs). These results indicated that the locations of the long- and short-term SSEs could be limited by the inhomogeneous distribution of the materials and/or condition of the overlying plate, which is formed due to geological and geographical process. The heterogeneity of materials and/or condition within the fore-arc crust possibly makes an effect on inhomogeneous rheological strength distribution on the interface.

  2. Subduction Zone Science - Examples of Seismic Images of the Central Andes and Subducting Nazca Slab

    Beck, S. L.; Zandt, G.; Scire, A. C.; Ward, K. M.; Portner, D. E.; Bishop, B.; Ryan, J. C.; Wagner, L. S.; Long, M. D.


    Subduction has shaped large regions of the Earth and constitute over 55,000 km of convergent plate margin today. The subducting slabs descend from the surface into the lower mantle and impacts earthquake occurrence, surface uplift, arc volcanism and mantle convection as well as many other processes. The subduction of the Nazca plate beneath the South America plate is one example and constitutes the largest present day ocean-continent convergent margin system and has built the Andes, one of the largest actively growing mountain ranges on Earth. This active margin is characterized by along-strike variations in arc magmatism, upper crustal shortening, crustal thickness, and slab geometry that make it an ideal region to study the relationship between the subducting slab, the mantle wedge, and the overriding plate. After 20 years of portable seismic deployments in the Central Andes seismologists have combined data sets and used multiple techniques to generate seismic images spanning ~3000 km of the South American subduction zone to ~800 km depth with unprecedented resolution. For example, using teleseismic P- waves we have imaged the Nazca slab penetrating through the mantle transition zone (MTZ) and into the uppermost lower mantle. Our tomographic images show that there is significant along-strike variation in the morphology of the Nazca slab in the upper mantle, MTZ, and the lower mantle, including possible tears, folding, and internal deformation. Receiver function studies and surface wave tomography have revealed major changes in lithospheric properties in the Andes. Improved seismic images allow us to more completely evaluate tectonic processes in the formation and uplift of the Andes including: (1) overthickened continental crust driven by crustal shortening, (2) changes in slab dip and coupling with the overlying plate (3) localized lithospheric foundering, and (4) large-scale mantle and crustal melting leading to magmatic addition and/or crustal flow. Although

  3. Earthquakes in the Orozco transform zone: seismicity, source mechanisms, and tectonics

    Trehu, Anne M.; Solomon, Sean C.


    As part of the Rivera Ocean Seismic Experiment, a network of ocean bottom seismometers and hydrophones was deployed in order to determine the seismic characteristics of the Orozco transform fault in the central eastern Pacific. We present hypocentral locations and source mechanisms for 70 earthquakes recorded by this network. All epicenters are within the transform region of the Orozco Fracture Zone and clearly delineate the active plate boundary. About half of the epicenters define a narrow line of activity parallel to the spreading direction and situated along a deep topographic trough that forms the northern boundary of the transform zone (region 1). Most focal depths for these events are very shallow, within 4 km of the seafloor; several well-determined focal depths, however, are as great as 7 km. No shallowing of seismic activity is observed as the rise-transform intersection is approached; to the contrary, the deepest events are within 10 km of the intersection. First motion polarities for most of the earthquakes in region 1 are compatible with right-lateral strike slip faulting along a nearly vertical plane, striking parallel to the spreading direction. Another zone of activity is observed in the central part of the transform (region 2). The apparent horizontal and vertical distribution of activity in this region is more scattered than in the first, and the first motion radiation patterns of these events do not appear to be compatible with any known fault mechanism. Pronounced lateral variations in crustal velocity structure are indicated for the transform region from refraction data and measurements of wave propagation directions. The effect of this lateral heterogeneity on hypocenters and fault plane solutions is evaluated by tracing rays through a three-dimensional velocity grid. While findings for events in region 1 are not significantly affected, in region 2, epicentral mislocations of up to 10 km and azimuthal deflections of up to 45° may result from

  4. Comparing the Gibraltar and Calabrian subduction zones (central western Mediterranean) based on seismic tomography

    Argnani, Andrea; Battista Cimini, Giovanni; Frugoni, Francesco; Monna, Stephen; Montuori, Caterina


    The Central Western Mediterranean (CWM) was shaped by a complex tectonic and geodynamic evolution. Deep seismicity and tomographic studies point to the existence, under the Alboran and Tyrrhenian Seas, of lithospheric slabs extending down to the bottom of the mantle transition zone, at 660 km depth. Two narrow arcs correspond to the two slabs, the Gibraltar and Calabrian Arcs (e.g., Monna et al., 2013; Montuori et al., 2007). Similarities in the tectonic and mantle structure of the two areas have been explained by a common subduction and roll-back mechanism for the opening of the CWM, in which the two arcs are symmetrical end products. In spite of this unifying model, a wide amount of literature from different disciplines shows that many aspects of the two areas are still controversial. We present a new 3-D tomographic model at mantle scale for the Calabrian Arc and compare it with a recently published 3-D tomographic model for the Gibraltar Arc by Monna et al (2013). The two models are based on non-linear inversion of teleseismic phase arrivals, and have scale and parametrization that allow for a direct comparison. Unlike previous studies the tomographic models here presented include Ocean Bottom Seismometer broadband data, which improved the resolution of the mantle structures in the marine areas surrounding the arcs. We focus on key features of the two models that constrain reconstructions of the geodynamic evolution of the CWM (e.g., Monna et al., 2015). At Tortonian time the opening of the Tyrrhenian basin was in its initial stage, and the Calabrian arc formed subsequently; on the contrary, the Gibraltar arc was almost completely defined. We hypothesize that the complexity of the continental margin approaching the subduction zone played a key role during the final stages of the arc formation. References Monna, S., G. B. Cimini, C. Montuori, L. Matias, W. H. Geissler, and P. Favali (2013), New insights from seismic tomography on the complex geodynamic evolution

  5. Quaternary layer anomalies around the Carlsberg Fault zone mapped with high-resolution shear-wave seismics south of Copenhagen

    Kammann, Janina; Hübscher, Christian; Nielsen, Lars

    . In the Upper Cretaceous growth faulting documents continued rifting. This finding contrasts the Late Cretaceous to Paleogene inversion tectonics in neighboring structures, as the Tornquist Zone. The high-resolution shear-wave seismic method was used to image structures in Quaternary layers in the Carlsberg....... In the shear-wave profile, we imaged the 30 m of the upward continuation of the Carlsberg Fault zone. In our area of investigation, the fault zone appears to comprise normal block faults and one reverse block fault showing the complexity of the fault zone. The observed faults appear to affect both the Danian......The Carlsberg Fault zone is located in the N-S striking Höllviken Graben and traverses the city of Copenhagen. The fault zone is a NNW-SSE striking structure in direct vicinity to the transition zone of the Danish Basin and the Baltic Shield. Recent small earthquakes indicate activity in the area...

  6. Mapping of crustal scale tectonic boundaries in the Ossa-Morena Zone using reprocessed IBERSEIS reflection seismic data

    Kashubin, A. S.; Juhlin, C.


    The IBERSEIS deep seismic reflection profile imaged crustal scale structures in the SW Iberian Variscan belt, crossing the South Portuguese Zone, the Ossa-Morena Zone and the Central Iberian Zone in Spain. Two subsets of the profile, corresponding to the South Portuguese Zone-Ossa-Morena Zone and the Ossa-Morena Zone-Central Iberian Zone tectonic contacts, have been reprocessed with the aim of investigating the influence of cross-dip and to better image steeply dipping features. Alternative strategies for binning midpoints into common depth point (CDP) bins using different azimuths were examined for synthetic data. We show that the choice of the CDP-processing line and the bin azimuth orientation has a significant impact on the normal moveout and dip-moveout velocities and is crucial to optimizing the quality of the stacked seismic image along the crooked profile. Multi-azimuth binning, normal moveout/dip-moveout, and migration velocity analysis on synthetic and real data show the presence of clear sub-vertical upper crustal structures near the South Portuguese Zone-Ossa-Morena Zone suture, the Aroche fault. This sub-vertical reflectivity that was not imaged earlier, projects into a location in the lower crust with low reflectivity.

  7. An Examination of Seismicity Linking the Solomon Islands and Vanuatu Subduction Zones

    Neely, J. S.; Furlong, K. P.


    The Solomon Islands-Vanuatu composite subduction zone represents a tectonically complex region along the Pacific-Australia plate boundary in the southwest Pacific Ocean. Here the Australia plate subducts under the Pacific plate in two segments: the South Solomon Trench and the Vanuatu Trench. The two subducting sections are offset by a 200 km long, transform fault - the San Cristobal Trough (SCT) - which acts as a Subduction-Transform Edge Propagator (STEP) fault. The subducting segments have experienced much more frequent and larger seismic events than the STEP fault. The northern Vanuatu trench hosted a M8.0 earthquake in 2013. In 2014, at the juncture of the western terminus of the SCT and the southern South Solomon Trench, two earthquakes (M7.4 and M7.6) occurred with disparate mechanisms (dominantly thrust and strike-slip respectively), which we interpret to indicate the tearing of the Australia plate as its northern section subducts and southern section translates along the SCT. During the 2013-2014 timeframe, little seismic activity occurred along the STEP fault. However, in May 2015, three M6.8-6.9 strike-slip events occurred in rapid succession as the STEP fault ruptured east to west. These recent events share similarities with a 1993 strike-slip STEP sequence on the SCT. Analysis of the 1993 and 2015 STEP earthquake sequences provides constraints on the plate boundary geometry of this major transform fault. Preliminary research suggests that plate motion along the STEP fault is partitioned between larger east-west oriented strike-slip events and smaller north-south thrust earthquakes. Additionally, the differences in seismic activity between the subducting slabs and the STEP fault can provide insights into how stress is transferred along the plate boundary and the mechanisms by which that stress is released.

  8. Subduction of the Tehuantepec oceanic fracture zone and the relationship with a seismic gap in southern Mexico

    Constantin Manea, Vlad; Manea, Marina; Taras, Gerya; Valenzuela, Raul W.


    It is accepted that key constraints on the size and recurrence time of large subduction earthquakes originate from the degree of locking between the subducting and overriding plates. Since the interseismic locking degree is influenced by the rheological properties of crustal and mantle rocks, any variations along strike will result in significant changes in seismic behavior due to a change in frictional stability. Additionally, recent seismic studies show that the subduction of hydrothermally altered oceanic fracture zones induces strong pore-fluid pressure variations that control the degree of interseismic locking. The Mexico Subduction Zone (MSZ) is characterized by major along-strike changes in subduction geometry, as well as important structural variations of the incoming oceanic plate. One of the main tectonic features of the Cocos plate is the Tehuantepec fracture zone (FZ) that is currently subducting beneath southern Mexico. The analysis of seismicity revealed that the area around where Tehuantepec fracture zone is currently subducting is conspicuously quiet and considered a seismic gap. Here, no significant quake (Ms ≥ 7.0) has occurred in more than 100 years, and the origin of Tehuantepec Seismic Gap (TSG) has not been elucidated yet. Based on the dimensions of the Tehuantepec gap (125 km length and 80 km width), an earthquake of Mw = 8.0 may be possible. This study aims to shed some light on the relationship between the TSG with the subduction of Tehuantepec oceanic fracture zone. Previous studies show that the uppermost oceanic lithosphere beneath the Tehuantepec FZ is partially serpentinized due to seawater infiltrations along faults. Using high-resolution three-dimensional coupled petrological-thermomechanical numerical simulations specifically tailored for the subduction of the Tehuantepec FZ at MSZ we show that the weakened serpentinized fracture zone is partially scraped out in the forearc region because of its low strength and positive buoyancy

  9. Seismic anisotropy and mantle dynamics beneath the Malawi Rift Zone, East Africa

    Reed, Cory A.; Liu, Kelly H.; Yu, Youqiang; Gao, Stephen S.


    SKS, SKKS, and PKS splitting parameters measured at 34 seismic stations that we deployed in the vicinity of the Cenozoic Malawi Rift Zone (MRZ) of the East African Rift System demonstrate systematic spatial variations with an average splitting time of 1.0 ± 0.3 s. The overall NE-SW fast orientations are consistent with absolute plate motion (APM) models of the African Plate constructed under the assumption of no-net rotation of the global lithosphere and are inconsistent with predicted APM directions from models employing a fixed hot spot reference frame. They also depart considerably from the trend of most of the major tectonic features. These observations, together with the results of anisotropy depth estimation using the spatial coherency of the splitting parameters, suggest a mostly asthenospheric origin of the observed azimuthal anisotropy. The single-layered anisotropy observed at 30 and two-layered anisotropy observed at 4 of the 34 stations can be explained by APM-related simple shear within the rheologically transitional layer between the lithosphere and asthenosphere, as well as by the horizontal deflection of asthenospheric flow along the southern and western edges of a continental block with relatively thick lithosphere revealed by previous seismic tomography and receiver function investigations. This first regional-scale shear wave splitting investigation of the MRZ suggests the absence of rifting-related active mantle upwelling or small-scale mantle convection and supports a passive-rifting process for the MRZ.

  10. Deformation and seismicity associated with continental rift zones propagating toward continental margins

    Lyakhovsky, V.; Segev, A.; Schattner, U.; Weinberger, R.


    We study the propagation of a continental rift and its interaction with a continental margin utilizing a 3-D lithospheric model with a seismogenic crust governed by a damage rheology. A long-standing problem in rift-mechanics, known as thetectonic force paradox, is that the magnitude of the tectonic forces required for rifting are not large enough in the absence of basaltic magmatism. Our modeling results demonstrate that under moderate rift-driving tectonic forces the rift propagation is feasible even in the absence of magmatism. This is due to gradual weakening and "long-term memory" of fractured rocks that lead to a significantly lower yielding stress than that of the surrounding intact rocks. We show that the style, rate and the associated seismicity pattern of the rift zone formation in the continental lithosphere depend not only on the applied tectonic forces, but also on the rate of healing. Accounting for the memory effect provides a feasible solution for thetectonic force paradox. Our modeling results also demonstrate how the lithosphere structure affects the geometry of the propagating rift system toward a continental margin. Thinning of the crystalline crust leads to a decrease in the propagation rate and possibly to rift termination across the margin. In such a case, a new fault system is created perpendicular to the direction of the rift propagation. These results reveal that the local lithosphere structure is one of the key factors controlling the geometry of the evolving rift system and seismicity pattern.

  11. Enriquillo–Plantain Garden fault zone in Jamaica: paleoseismology and seismic hazard

    Koehler, R.D.; Mann, P.; Prentice, Carol S.; Brown, L.; Benford, B.; Grandison-Wiggins, M.


    The countries of Jamaica, Haiti, and the Dominican Republic all straddle the Enriquillo–Plantain Garden fault zone ( EPGFZ), a major left-lateral, strike-slip fault system bounding the Caribbean and North American plates. Past large earthquakes that destroyed the capital cities of Kingston, Jamaica (1692, 1907), and Port-au-Prince, Haiti (1751, 1770), as well as the 2010 Haiti earthquake that killed more than 50,000 people, have heightened awareness of seismic hazards in the northern Caribbean. We present here new geomorphic and paleoseismic information bearing on the location and relative activity of the EPGFZ, which marks the plate boundary in Jamaica. Documentation of a river bank exposure and several trenches indicate that this fault is active and has the potential to cause major destructive earthquakes in Jamaica. The results suggest that the fault has not ruptured the surface in at least 500 yr and possibly as long as 28 ka. The long period of quiescence and subdued geomorphic expression of the EPGFZ indicates that it may only accommodate part of the ∼7–9 mm=yr plate deformation rate measured geodetically and that slip may be partitioned on other undocumented faults. Large uncertainties related to the neotectonic framework of Jamaica remain and more detailed fault characterization studies are necessary to accurately assess seismic hazards.

  12. Characterizing a large shear-zone with seismic and magnetotelluric methods: The case of the Dead Sea Transform

    Maercklin, N.; Bedrosian, P.A.; Haberland, C.; Ritter, O.; Ryberg, T.; Weber, M.; Weckmann, U.


    Seismic tomography, imaging of seismic scatterers, and magnetotelluric soundings reveal a sharp lithologic contrast along a ???10 km long segment of the Arava Fault (AF), a prominent fault of the southern Dead Sea Transform (DST) in the Middle East. Low seismic velocities and resistivities occur on its western side and higher values east of it, and the boundary between the two units coincides partly with a seismic scattering image. At 1-4 km depth the boundary is offset to the east of the AF surface trace, suggesting that at least two fault strands exist, and that slip occurred on multiple strands throughout the margin's history. A westward fault jump, possibly associated with straightening of a fault bend, explains both our observations and the narrow fault zone observed by others. Copyright 2005 by the American Geophysical Union.

  13. Wide-Angle Seismic Experiment Across the Oeste Fault Zone, Central Andes, Northern Chile.

    Lorenzo, J. M.; Yáñez, G. A.; Vera, E. E.; Sepúlveda, J.


    From December 6-21, 2007, we conducted a 3-component, radio-telemetric, seismic survey along a ~ 15-km wide E-W transect in the Central Andes, at a latitude of ~ 22.41° S, centered north of the city of Calama (68.9° W), Chile. The study area is sandwiched between the Central Depression in the west and the Andean Western Cordillera of Chile. Recording stations, nominally spaced at intervals of either 125 or 250 m collected up to 3.5 s of refracted seismic arrivals at maximum source-receiver offsets exceeding 15 km. Ten shothole sources, spaced 2-6 km apart focused energy on the shallow (0-3 km), crustal, Paleogene-age structures. Preliminary, tomographic inversions of refracted first arrivals show the top of a shallow ( 600 km), strike-slip fault zone known as the Oeste fault. Turning ray densities suggest the base of the overlying velocity gradient unit (VP, 2-4 km/s) dips inwardly from both east and west directions toward the Oeste fault to depths of almost 1 km. Plate reorganization commencing at least by the latter half of the Oligocene led from oblique to more orthogonal convergence between the South American and the Nazca (Farallon) Plates. We interpret previously mapped, older, minor faults as being generated within the right-lateral, orogen-parallel, Oeste strike-slip fault zone, and postdated by Neogene, N-S striking thrust faults. In this context we also interpret that the spatial distribution of velocity units requires an period of extensional activity that may (1) postdate the transpressional strike slip fault activity of the Neogene, (2) be related to a later releasing bend through the translation and interaction of rigid blocks hidden at depth or even (3) be the consequence of inelastic failure from the result of flexural loading.

  14. A double seismic zone in the Nazca flat slab beneath central Chile (29°-34°S)

    Marot, Marianne; Monfret, Tony; Pardo, Mario; Ranalli, Giorgio


    The Nazca plate subducts beneath central Chile and western Argentina (29°-34°S) with a dip angle ~27° from the trench until ~100 km depth. North of 32oS the slab becomes sub-horizontal at this depth and continues sub-horizontally for approximately 250 km eastward before resuming sinking with dip angle ~25°. The location and extent of this "Pampean" flat subduction is very well correlated, seismically and tectonically on the continent, with the continuing subduction of the Juan Fernandez Ridge (JFR). We use the recorded seismicity from three local temporary networks, OVA99 (1999-2000), CHARSME (2002-2003) and CHASE (2005-2006) to characterize the earthquake distribution within the slab in this area. Around 7000 earthquakes were located with magnitude ranging between 1.6 and 5.7, and around 1500 focal mechanisms were calculated. A double seismic zone (or DBZ) is present in the dipping part of the slab landward from the trench. The lower seismic zone of this Pampean DBZ begins at ~50 km depth and extends to 100-120 km depth, where it merges with the upper seismic zone. The separation between the two zones is ~30 km at the shallowest depth. The lower seismic zone shows higher seismic activity relative to the upper zone. Both zones show a similar magnitude distribution, with predominantly tensional focal mechanisms. The Pampean DBZ is best observed within the subducting JFR, which is marked by a dense and thick seismic activity. This seismicity drops substantially outside the JFR ridge limits, making the Pampean DBZ more difficult to detect. Focal mechanisms for earthquakes delineating the DBZ (50-100 km depth) show a strong tendency of the focal planes to strike NS, parallel to the trench axis, suggesting that intermediate-depth earthquakes in the subducting Nazca plate occur on pre-existing reactivated outer rise faults. The separation distance between the two seismic zones cannot be explained by plate age models which predict a much smaller separation distance

  15. The Crustal Structure of the Central Iberian Zone form the ALCUDIA Deep Seismic Reflection transect.

    Martí, D.


    The ALCUDIA transect is a 250 km long, vertical incidence Vibroseis seismic reflection profile acquired in 2007. It extends IBERSEIS transect to the N and NE imaging from within the Ossa Morena Zone (OMZ) to the Central Iberian Zone (CIZ) from 20 km south of Fuenteovejuna in the S to Toledo in the N. The southern part of the transect samples the suture zone between the OMZ and the CIZ. It continues in a N-NE direction crossing the Pedroches batholith and a series of relatively long wavelength synclinal structures limited by sub-vertical and relatively narrow folds (e.g. the Almaden syncline, the Alcudia anticline). Lower Paleozoic quartzites and slates cover most of these synclynal structures. Farther to the N, the profile crosses several major faults system (e.g Santa Elena and Toledo) . The acquisition parameters, 35 m station spacing, 70 m VP spacing resulted in a 60-90 fold high resolution seismic reflection image. A 20 s long Vibroseis sweep with frequencies between 8-120 Hz was recorded by a 400 station recording cable a long a 14 km long split spread configuration. The new processing sequence significantly increased the signal-to-noise ratio. It includes: crooked line geometry, geometrical divergence corrections, elevation statics, surface-wave attenuation, surface consistent zero-phase spiking deconvolution, time-variant band pass filtering., refraction and residual static corrections velocity analysis, NMO, surface consistent amplitude balancing, CMP stacking F-X deconvolution. The seismic image reveals the geometry of the suture between the OMZ and the CIZ. This is a reworked transpression suture (the Badajoz-Cordoba Sherar zone) includes the Central Unit (CU) as a north dipping wedge structure limited by two bands of reflectors that reach the middle crust (5 s twtt). This CU includes amphibolites with some oceanic affinity, orthogneisses, paragneisses, schists and minor amounts of peridotites. To the north the upper crust shows a moderate reflectivity

  16. The May 29 2008 earthquake aftershock sequence within the South Iceland Seismic Zone: Fault locations and source parameters of aftershocks

    Brandsdottir, B.; Parsons, M.; White, R. S.; Gudmundsson, O.; Drew, J.


    The mid-Atlantic plate boundary breaks up into a series of segments across Iceland. The South Iceland Seismic Zone (SISZ) is a complex transform zone where left-lateral E-W shear between the Reykjanes Peninsula Rift Zone and the Eastern Volcanic Zone is accommodated by bookshelf faulting along N-S lateral strike-slip faults. The SISZ is also a transient feature, migrating sideways in response to the southward propagation of the Eastern Volcanic Zone. Sequences of large earthquakes (M > 6) lasting from days to years and affecting most of the seismic zone have occurred repeatedly in historical time (last 1100 years), separated by intervals of relative quiescence lasting decades to more than a century. On May 29 2008, a Mw 6.1 earthquake struck the western part of the South Iceland Seismic Zone, followed within seconds by a slightly smaller event on a second fault ~5 km further west. Aftershocks, detected by a temporal array of 11 seismometers and three permanent Icelandic Meteorological Office stations were located using an automated Coalescence Microseismic Mapping technique. The epicenters delineate two major and several smaller N-S faults as well as an E-W zone of activity stretching further west into the Reykjanes Peninsula Rift Zone. Fault plane solutions show both right lateral and oblique strike slip mechanisms along the two major N-S faults. The aftershocks deepen from 3-5 km in the north to 8-9 km in the south, suggesting that the main faults dip southwards. The faulting is interpreted to be driven by the local stress due to transform motion between two parallel segments of the divergent plate boundary crossing Iceland.

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

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


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

  18. Seismic Noise Characterization in the Northern Mississippi Embayment

    Wiley, S.; Deshon, H. R.; Boyd, O. S.


    We present a study of seismic noise sources present within the northern Mississippi embayment near the New Madrid Seismic Zone (NMSZ). The northern embayment contains up to 1 km of unconsolidated coastal plain sediments overlying bedrock, making it an inherently noisy environment for seismic stations. The area is known to display high levels of cultural noise caused by agricultural activity, passing cars, trains, etc. We characterize continuous broadband seismic noise data recorded for the months of March through June 2009 at six stations operated by the Cooperative New Madrid Seismic Network. We looked at a single horizontal component of data during nighttime hours, defined as 6:15PM to 5:45AM Central Standard Time, which we determined to be the lowest amplitude period of noise for the region. Hourly median amplitudes were compared to daily average wind speeds downloaded from the National Oceanic and Atmospheric Administration. We find a correlation between time periods of increased noise and days with high wind speeds, suggesting that wind is likely a prevalent source of seismic noise in the area. The effects of wind on seismic recordings may result from wind induced tree root movement which causes ground motion to be recorded at the vaults located ~3m below ground. Automated studies utilizing the local network or the EarthScope Transportable Array, scheduled to arrive in the area in 2010-11, should expect to encounter wind induced noise fluctuations and must account for this in their analysis.

  19. The Carboneras Fault Zone (SE Spain): Constraints on Fault Zone Properties and Geometry from Controlled-Source-Generated Guided Seismic Waves

    Rietbrock, A.; Haberland, C. A.; Faulkner, D. R.; Nippress, S.; Rutter, E. H.; Kelly, C. M.; Teixido, T.


    We combine geophysical data, field-geological mapping and lab measurements to study the Carboneras fault zone (CFZ) in SE Spain. The CFZ is part of the Trans-Alborán Shear Zone which constitutes part of the diffuse plate boundary between Africa and Iberia. The CFZ is inferred to behave as a stretching transform fault with˜40 km left-lateral offset. It was active principally between 12 - 6 Ma BP, and has been exhumed from ca. 1 - 2 km depth. The relatively recent movement history and the semi-arid terrain lead to excellent exposure.The phyllosilicate-rich fault gougeis excellently preserved. In 2010 we conducted a controlled source seismic experiment at the CFZ in which explosive sources in boreholes (two groups of 3 explosions) were placed in two strands of the fault zone. The signals were observed with dense linear seismic arrays crossing the CFZ at 3.5km and 8.3km distance, respectively. The recordings show clear high-energy P-phases at receivers and from sources located at or near the fault zone. We interpret these phases as P-waves trapped in the low-velocity layer (waveguide) formed by the damage zone of the fault(s). With waveform modeling (using an analytical solution assuming a straight waveguide embedded in two quarter spaces and a line source at depth) we derive basic models well-explaining the observations. Lab-measurements of the different rocks constrain the possible models. Additionally, we employed extensive three-dimensional finite-difference (3D-FD) modeling with more realistic (curved and anastomosing) waveguide geometries. It seems that the studied segments of the CFZ form effective waveguides for seismic waves with connectivity over several kilometers. The derived seismic models together with lab measurements of the seismic velocities indicate that the average fault zone core widths are in the order of 15 to 25m which is in good agreement with surface geological mapping.

  20. Using thermodynamic data to reproduce main seismic features of transition zone

    Fomin, Ilya; Saukko, Anna; Edwards, Paul; Schiffer, Christian


    Most of the seismic tomography studies nowadays are based on comprehensive models with optimization of lots of parameters. These models are able to resolve very subtle features of the Earth's mantle, but the influence of each specific parameter is not seen directly. In our research we try to minimize the number of processed parameters to produce simple synthetic cases. The main goals of our model are to see how water content influences the depth of the transition zone, and if melting at the transition zone is plausible. We also attempt to see how water content and the presence of melts influence the signal strength of the transition zone in receiver functions. Our MATLAB-code calculates phase assemblage according to specific temperature and pressure within 2D numerical domain (e.g. 300x700 km). Phase properties are calculated with database of Stixrude and Lithgow-Bertelloni [2011], with corrections for water impact on elastic constants according to Liu et al., [2012]. We use the mantle phase composition 55% garnet and 45% olivine-polymorph, soliduses by Ohtani et al. [2004] and melt properties by Sakamaki et al. [2006]. These data are used to calculate seismic velocities and, furthermore, receiver functions with standard routines (e.g.[Schiffer et al., 2012]). Model predicts Vs within 5 to 5.5 km/s and Vp around 9.5-10 km/s within transition zone (Vp/Vs = 1.84-1.87), which is close to standard values. The presence of water enlarges the wadsleyite region, but also dampens the peak of receiver functions down to background level. Increase in water content causes melting at much shallower depths. Using a normal thermal gradient, we can get up to 10% of melt at depths around 390 km with 80% of water saturation, shown by a negative anomaly on receiver functions. This result is similar to data obtained for Afar Plateau [Thompson et al., 2015]. With cratonic thermal gradient, the olivine-wadsleyite transition and corresponding melt layer appear at depths around 350 km

  1. Segmentation of the Nazca and South American plates along the Ecuador subduction zone from wide angle seismic profiles

    Gailler, Audrey; Charvis, Philippe; Flueh, Ernst R.


    We describe the deep structure of the south Colombian-northern Ecuador convergent margin using travel time inversion of wide-angle seismic data recently collected offshore. The margin appears segmented into three contrasting zones. In the North Zone, affected by four great subduction earthquakes during the 20th century, normal oceanic crust subducts beneath the oceanic Cretaceous substratum of the margin underlined by seismic velocities as high as 6.0-6.5 km/s. In the Central Zone the subducting oceanic crust is over-thickened beneath the Carnegie Ridge. A steeper slope and a well-developed, high velocity, Cretaceous oceanic basement characterizes the margin wedge. This area coincides with a gap in significant subduction earthquake activity. In the South Zone, the subducting oceanic crust is normal. The fore-arc is characterized by large sedimentary basins suggesting significant subsidence. Velocities in the margin wedge are significantly lower and denote a different nature or a higher degree of fracturing. Even if the distance between the three profiles exceeds 150 km, the structural segmentation obtained along the Ecuadorian margin correlates well with the distribution of seismic activity and the neotectonic zonation.

  2. A Bayesian approach for Inter-seismic Inter-plate Coupling Probabilities for the Central Andes Subduction Zone

    Ortega Culaciati, F. H.; Simons, M.


    We aim to characterize the apparent extent of plate coupling on subduction zone megathrusts with the eventual goal of understanding spatial variations of fault zone rheology. In this study we approach the problem from a Bayesian perspective, where we ask not for a single optimum model, but rather for a posteriori estimates of the range of allowable models, exploiting the full potential of Bayesian methods to completely characterize the model parameter space. Adopting a simple kinematic back-slip model and a 3D geometry of the inter-plate contact zone, we use the Bayesian approach to provide the inter-seismic inter-plate coupling probabilities that are consistent with physically plausible a-priori information and available geodetic measurements. We highlight the importance of using the vertical component of the velocity field to properly constrain the downdip limit of the coupled zone, and also we show how the chosen parameterization of the model plays an important role along with the a-priori, and a-posteriori information on the model parameters. We apply this methodology in the Chilean-Peruvian subduction zone (12S - 24S) with the desire to understand the state of inter-seismic coupling on that margin. We obtain patch like features for the probability of 100% apparent inter-seismic coupling with higher values located between 15km and 60km depth. The larger of these features are located in the regions associated with the rupture process of the 2001 (Mw 8.4) Arequipa and the 2007 (Mw 8.0) Pisco Earthquakes, both occurred after the time period where the measurements take place; and the region identified as the Arica bend seismic gap, which has not experienced a large earthquake since 1877.

  3. Faulting at Thebes Gap, Mo. -Ill. : Implications for New Madrid tectonism

    Harrison, R.W.; Schultz, A.P. (Geological Survey, Reston, VA (United States))


    Recent geologic mapping in the Thebes Gap area has identified numerous NNE- and NE-striking faults having a long-lived and complex structural history. The faults are located in an area of moderate recent seismicity at the northern margin of the Mississippi embayment, approximately 45 km north of the New Madrid seismic zone. Earliest deformation occurred along dextral strike-slip faults constrained as post-Devonian and pre-Cretaceous. Uplift and erosion of all Carboniferous strata suggest that this faulting is related to development of the Pascola arch (Ouachita orogeny). This early deformation is characterized by strongly faulted and folded Ordovician through Devonian rocks overlain in places with angular unconformity by undeformed Cretaceous strata. Elsewhere, younger deformation involves Paleozoic, Cretaceous, Paleocene, and Eocene formations. These units have experienced both minor high-angle normal faulting and major, dextral strike-slip faulting. Quaternary-Tertiary Mounds Gravel is also involved in the latest episode of strike-slip deformation. Enechelon north-south folds, antithetic R[prime] shears, and drag folds indicate right-lateral motion. Characteristic positive and negative flower structures are commonly revealed in cross section. Right-stepping fault strands have produced pull-apart basins where Ordovician, Silurian, Devonian, Cretaceous, and Tertiary units are downdropped several hundreds of meters and occur in chaotic orientations. Similar fault orientations and kinematics, as well as recent seismicity and close proximity, clearly suggest a structural relationship between deformation at Thebes Gap and tectonism associated with the New Madrid area.

  4. Reflection seismic imaging of a hydraulically conductive fracture zone in a high noise area, Forsmark, Sweden

    Juhlin, C.; Stephens, M. B.; Cosma, C.


    High resolution reflection seismic methods have proven to be useful tools for locating fracture zones in crystalline rock. Siting of potential high-level nuclear waste repositories is a particularly important application of these methods. By using small explosive sources (15-75 grams), high resolution images of the sub-surface have been obtained in the depth range 100 m to 2 km in Sweden, Canada and elsewhere. Although ambient noise conditions in areas such as the Fennoscandian and Canadian shields are generally low, industrial noise can be high in some areas, particularly at potential sites suitable for repositories, since these are often close to existing infrastructure. In addition, the presence of this infrastructure limits the choice of sources available to the geophysicist. Forsmark, located about 140 km north of Stockholm, is one such potential site where reflection seismics have been carried out. Existing infrastructure includes nuclear reactors for power generation and a low- level waste repository. In the vicinity of the reactors, it was not possible to use an explosive source due to permitting restrictions. Instead, a VIBSIST system consisting of a tractor mounted hydraulic hammer was used in the vicinity of the reactors. By repeatedly hitting the pavement, without breaking it, at predefined sweeps and then stacking the signals, shot records comparable to explosive data could be generated. These shot records were then processed using standard methods to produce stacked sections along 3 profiles within the reactor area. Clear reflections are seen in the uppermost 600 m along 3 of these profiles. Correlation of crossing profiles shows that the strongest reflection (B8) is generated by a gently east-southeast dipping interface. Prior to construction of the reactors, several boreholes were drilled to investigate the bedrock in the area. One of these boreholes was located close to where two of the profiles cross. Projection of the B8 reflection into the

  5. Monitoring in situ deformation induced by a fluid injection in a fault zone in shale using seismic velocity changes

    Rivet, D.; De Barros, L.; Guglielmi, Y.; Castilla, R.


    We monitor seismic velocity changes during an experiment at decametric scale aimed at artificially reactivate a fault zone by a high-pressure hydraulic injection in a shale formation of the underground site of Tournemire, South of France. A dense and a multidisciplinary instrumentation, with measures of pressure, fluid flow, strain, seismicity, seismic properties and resistivity allow for the monitoring of this experiment. We couple hydromechanical and seismic observations of the fault and its adjacent areas to better understand the deformation process preceding ruptures, and the role played by fluids. 9 accelerometers recorded repeated hammers shots on the tunnel walls. For each hammer shot we measured small travel time delays on direct P and S waves. We then located the seismic velocity perturbations using a tomography method. At low injection pressure, i.e. Pchange in S waves velocity. When the pressure overcomes 15 Bars, velocity perturbations dramatically increase with both P and S waves affected. A decrease of velocity is observed close to the injection point and is surrounded by regions of increasing velocity. Our observations are consistent with hydromechanical measures. Below 15 Bars, we interpret the P-wave velocity increase to be related to the compression of the fault zone around the injection chamber. Above 15 Bars, we measure a shear and dilatant fault movement, and a rapid increase in the injected fluid flow. At this step, our measures are coherent with a poroelastic opening of the fault with velocities decrease at the injection source and velocities increase related to stress transfer in the far field. Velocity changes prove to be efficient to monitor stress/strain variation in an activated fault, even if these observations might produce complex signals due to the highly contrasted hydromechanical responses in a heterogeneous media such as a fault zone.

  6. The seismicity and tectonic stress field characteristics of the Longmenshan fault zone before the Wenchuan Ms8.0 earthquake

    Zhiwei Zhang; Wanzheng Cheng; Xiang Ruan; Peng Wu


    The seismicity of Longmenshan fault zone and its vicinities before the 12 May 2008 Wenchuan A/s8.0 earthquake is studied. Based on the digital seismic waveform data observed from regional seismic networks and mobile stations, the focal mechanism solutions are determined. Our analysis results show that the seismicities of Longmenshan fault zone before the 12 May 2008 Wenchuan earthquake were in stable state. No obvious phenomena of seismic activity intensifying appeared. According to focal mechanism solutions of some small earthquakes before the 12 May 2008 Wenchuan earthquake, the direction of principal compressive stress P-axis is WNW-ESE. The two hypocenter fault planes are NE-striking and NW-striking. The plane of NE direction is among N50°-70°E, the dip angles of fault planes are 60°-70° and it is very steep. The faultings of most earthquakes are dominantly characterized by dip-slip reverse and small part of faultings present strike-slip. The azimuths of principal compressive stress, the strikes of source fault planes and the dislocation types calculated from some small earthquakes before the 12 May 2008 Wenchuan earthquake are in accordance with that of the main shock. The average stress field of micro-rupture along the Longmenshan fault zone before the great earthquake is also consistent with that calculated from main shock. Zipingpu dam is located in the east side 20 km from the initial rupture area of the 12 May 2008 Wenchuan earthquake. The activity increment of small earthquakes in the Zipingpu dam is in the period of water discharging. The source parameter results of the small earthquakes which occurred near the initial rupture area of the 12 May 2008 Wenchuan earthquake indicate that the focal depths are 5 to 14 km and the source parameters are identical with that of earthquake.

  7. A seismic attenuation zone below Popocatépetl volcano inferred from coda waves of local earthquakes

    D. A. Novelo-Casanova; A. Martínez-Bringas


    Using a single scattering model, weighted averages of the quality factor Qc were estimated at 6 Hz for coda wave windows 25s after S-wave arrival at depths ranging from 2 to 10 km and magnitudes between 2 and 3. Considering Qc -1 as intrinsic attenuation, we find a zone of seismic wave attenuation between 6 and 8 km depth attributed to the presence of magma and partial melting of rock.

  8. Long-Term Seismic Quiescences and Great Earthquakes in and Around the Japan Subduction Zone Between 1975 and 2012

    Katsumata, Kei


    An earthquake catalog created by the International Seismological Center (ISC) was analyzed, including 3898 earthquakes located in and around Japan between January 1964 and June 2012 shallower than 60 km with the body wave magnitude of 5.0 or larger. Clustered events such as earthquake swarms and aftershocks were removed from the ISC catalog by using a stochastic declustering method based on Epidemic-Type Aftershock Sequence (ETAS) model. A detailed analysis of the earthquake catalog using a simple scanning technique (ZMAP) shows that the long-term seismic quiescences lasting more than 9 years were recognized ten times along the subduction zone in and around Japan. The three seismic quiescences among them were followed by three great earthquakes: the 1994 Hokkaido-toho-oki earthquake (M w 8.3), the 2003 Tokachi-oki earthquake (M w 8.3), and the 2011 Tohoku earthquake (M w 9.0). The remaining seven seismic quiescences were followed by no earthquake with the seismic moment M 0 ≥ 3.0 × 1021 Nm (M w 8.25), which are candidates of the false alarm. The 2006 Kurile Islands earthquake (M w 8.3) was not preceded by the significant seismic quiescence, which is a case of the surprise occurrence. As a result, when limited to earthquakes with the seismic moment of M 0 ≥ 3.0 × 1021 Nm, four earthquakes occurred between 1976 and 2012 in and around Japan, and three of them were preceded by the long-term seismic quiescence lasting more than 9 years.

  9. Long-Term Seismic Quiescences and Great Earthquakes in and Around the Japan Subduction Zone Between 1975 and 2012

    Katsumata, Kei


    An earthquake catalog created by the International Seismological Center (ISC) was analyzed, including 3898 earthquakes located in and around Japan between January 1964 and June 2012 shallower than 60 km with the body wave magnitude of 5.0 or larger. Clustered events such as earthquake swarms and aftershocks were removed from the ISC catalog by using a stochastic declustering method based on Epidemic-Type Aftershock Sequence (ETAS) model. A detailed analysis of the earthquake catalog using a simple scanning technique (ZMAP) shows that the long-term seismic quiescences lasting more than 9 years were recognized ten times along the subduction zone in and around Japan. The three seismic quiescences among them were followed by three great earthquakes: the 1994 Hokkaido-toho-oki earthquake ( M w 8.3), the 2003 Tokachi-oki earthquake ( M w 8.3), and the 2011 Tohoku earthquake ( M w 9.0). The remaining seven seismic quiescences were followed by no earthquake with the seismic moment M 0 ≥ 3.0 × 1021 Nm ( M w 8.25), which are candidates of the false alarm. The 2006 Kurile Islands earthquake ( M w 8.3) was not preceded by the significant seismic quiescence, which is a case of the surprise occurrence. As a result, when limited to earthquakes with the seismic moment of M 0 ≥ 3.0 × 1021 Nm, four earthquakes occurred between 1976 and 2012 in and around Japan, and three of them were preceded by the long-term seismic quiescence lasting more than 9 years.

  10. 3D shear-wave velocity structure of the eastern Tennessee seismic zone from ambient noise correlation data

    Arroucau, Pierre; Kuponiyi, Ayodeji; Vlahovic, Gordana; Powell, Chris


    The Eastern Tennessee Seismic Zone (ETSZ) is an intraplate seismic region characterized by frequent but low magnitude earthquakes and is the second most active seismic area in the United States east of the Rocky Mountains. One key question in the ETSZ is the actual relationship between earthquake distribution and geological structure at depth. Seismicity is mostly confined in the Precambrian basement, below the Paleozoic cover of the southern Appalachian foreland fold-and-thrust belt and shows little to no correlation with surface geological features. Since the middle of the seventies, the Center for Earthquake Research and Information (CERI) has installed and maintained several seismic networks in central and eastern United States. In this work, we use Rayleigh wave group and phase velocity dispersion information obtained from cross-correlation of seismic ambient noise at 24 short-period stations located in the vicinity of the ETSZ. The 3D velocity structure is estimated in four steps. First, dispersion curves are obtained for simultaneously recording station pairs for periods ranging from 2 to 20 s. Then, 2D group and phase velocity maps are determined for each period. Those maps are further used to reconstruct dispersion curves at fixed, regularly spaced locations. For each of these locations, a 1D shear-wave velocity profile is finally inverted for, that takes velocity information from previous studies into account. By providing new information about the upper crustal structure of this region, this work is a contribution to the understanding of the seismic activity of the ETSZ, and -to a broader extent- of the structure and evolution of the North American lithosphere.

  11. Geochemistry of soil gas in the seismic fault zone produced by the Wenchuan Ms 8.0 earthquake, southwestern China

    Cui Yueju


    Full Text Available Abstract The spatio-temporal variations of soil gas in the seismic fault zone produced by the 12 May 2008 Wenchuan Ms 8.0 earthquake were investigated based on the field measurements of soil gas concentrations after the main shock. Concentrations of He, H2, CO2, CH4, O2, N2, Rn, and Hg in soil gas were measured in the field at eight short profiles across the seismic rupture zone in June and December 2008 and July 2009. Soil-gas concentrations of more than 800 sampling sites were obtained. The data showed that the magnitudes of the He and H2 anomalies of three surveys declined significantly with decreasing strength of the aftershocks with time. The maximum concentrations of He and H2 (40 and 279.4 ppm, respectively were found in three replicates at the south part of the rupture zone close to the epicenter. The spatio-temporal variations of CO2, Rn, and Hg concentrations differed obviously between the north and south parts of the fault zone. The maximum He and H2 concentrations in Jun 2008 occurred near the parts of the rupture zone where vertical displacements were larger. The anomalies of He, H2, CO2, Rn, and Hg concentrations could be related to the variation in the regional stress field and the aftershock activity.

  12. Change in Seismic Attenuation of the Nojima Fault Zone Measured Using Spectral Ratios from Borehole Seismometers

    Kano, Y.; Tadokoro, K.; Nishigami, K.; Mori, J.


    We measured the seismic attenuation of the rock mass surrounding the Nojima fault, Japan, by estimating the P-wave quality factor, Qp, using spectral ratios derived from a multi-depth (800 m and 1800 m) seismometer array. We detected an increase of Qp in 2003-2006 compared to 1999-2000. Following the 1995 Kobe earthquake, the project "Fault Zone Probe" drilled three boreholes to depths of 500 m, 800 m, 1800 m, in Toshima, along the southern part of the Nojima fault. The 1800-m borehole was reported to reach the fault surface. One seismometer (TOS1) was installed at the bottom of the 800-m borehole in 1996 and another (TOS2) at the bottom of 1800-m borehole in 1997. The sampling rate of the seismometers is 100 Hz. The slope of the spectral ratios for the two stations plotted on a linear-log plot is -π t^{*}, where t^{*} is the travel time divided by the Qp for the path difference between the stations. For the estimation of Qp, we used events recorded by both TOS1 and TOS2 for periods of 1999-2000 and 2003-2006. To improve the signal-to-noise ratio of the spectral ratios, we first calculated spectra ratios between TOS1 and TOS2 for each event and averaged the values over the earthquakes for each period. We used the events that occurred within 10 km from TOS2, and the numbers of events are 74 for 1999-2000 and 105 for 2003-2006. Magnitudes of the events range from M0.5 to M3.1. The average value of Qp for 1999-2000 increased significantly compared to 2003-2006. The attenuation of rock mass surrounding the fault in 2003-2006 is smaller than that in 1999-2000, which suggests that the fault zone became stiffer after the earthquake. At the Nojima fault, permeability measured by repeated pumping tests decreased with time from the Kobe earthquake, infering the closure of cracks and a fault healing process occurred The increase of Qp is another piece of evidence for the healing process of the Nojima fault zone.

  13. Fault zone damage, nonlinear site response, and dynamic triggering associated with seismic waves

    Wu, Chunquan

    My dissertation focuses primarily on the following three aspects associated with passing seismic waves in the field of earthquake seismology: temporal changes of fault zone properties, nonlinear site response, and dynamic triggering. I systematically analyze temporal changes of fault zone (FZ) site response along the Karadere-Duzce branch of the North Anatolian fault that ruptured during the 1999 Izmit and Duzce earthquake sequences. These results provide a bridge between the large-amplitude near-instantaneous changes and the lower-amplitude longer-duration variations observed in previous studies. The temporal changes measured from this high-resolution spectral ratio analysis also provide a refinement for the beginning of the longer more gradual process typically observed by analyzing repeating earthquakes. I use the same sliding-window spectral ratio technique to analyze temporal changes in site response associated with the strong ground motion of the Mw6.6 2004 Mid-Niigata earthquake sequence recorded by the borehole stations in Japanese Digital Strong-Motion Seismograph Network (KiK-Net). The results suggest that at a given site the input ground motion plays an important role in controlling both the coseismic change and postseismic recovery in site response. In a follow-up study, I apply the same sliding-window spectral ratio technique to surface and borehole strong motion records at 6 KiK-Net sites, and stack results associated with different earthquakes that produce similar PGAs. In some cases I observe a weak coseismic drop in the peak frequency when the PGA is as small as ˜20--30 Gal, and near instantaneous recovery after the passage of the direct S waves. The percentage of drop in the peak frequency starts to increase with increasing PGA values. A coseismic drop in the peak spectral ratio is also observed at 2 sites. When the PGA is larger than ˜60 Gal to more than 100 Gal, considerably stronger coseismic drops of the peak frequencies are observed

  14. Crustal deformation styles along the reprocessed deep seismic reflection transect of the Central Iberian Zone (Iberian Peninsula)

    Ehsan, Siddique Akhtar; Carbonell, Ramon; Ayarza, Puy; Martí, David; Pérez-Estaún, Andrés; Martínez-Poyatos, David Jesús; Simancas, Jose Fernando; Azor, Antonio; Mansilla, Luis


    The multichannel normal incidence (230 km long) deep seismic reflection profile ALCUDIA was acquired in summer 2007. This transect samples an intracontinental Variscan orogenic crust going across, from north to south, the major crustal domain (the Central Iberian Zone) and its suture zone with the Ossa-Morena Zone (the Central Unit) both build up most of the southwestern part of the Iberian Peninsula basement. This high resolution (60-90 fold) profile images about 70 km depth (20 s TWTT) of the continental lithosphere. A new data processing flow provides better structural constraints on the shallow and deep structures resulting in an image that reveals indentation features which strongly suggest horizontal tectonics. The ALCUDIA seismic image shows an upper crust c. 13 km thick decoupled from the comparatively reflective lower crust. The shallow reflectivity of the upper crust can be correlated with surface geological features mapped in the field whereas the deep reflectivity represents inferred imbricate thrust systems and listric extensional faults. The reflectivity of the mid-lower crust is continuous, high amplitude, and horizontal to arcuate though evidences of deformation are present as ductile boudinage structures, thrusting and an upper mantle wedge, suggesting a transpressional flower structure. The image reveals a laminated c. 1.5 km thick, subhorizontal to flat Moho indicating an average crustal thickness of 31-33 km. The Moho shows laterally variable signature, being highly reflective beneath the Central Iberian Zone, but discontinuous and diffuse below the Ossa-Morena Zone. The gravity response suggests relatively high density bodies in the mid-lower crust of the southern half of the transect. The seismic results suggest two major horizontal limits, a horizontal discontinuity at c. 13-15 km (corresponding to the brittle-ductile transition) and the Moho boundary both suggested to act as decoupling surfaces.

  15. Terrace Zone Structure in the Chicxulub Impact Crater Based on 2-D Seismic Reflection Profiles: Preliminary Results From EW#0501

    McDonald, M. A.; Gulick, S. P.; Gorney, D. L.; Christeson, G. L.; Barton, P. J.; Morgan, J. V.; Warner, M. R.; Urrutia-Fucugauchi, J.; Melosh, H. J.; Vermeesch, P. M.; Surendra, A. T.; Goldin, T.; Mendoza, K.


    Terrace zones, central peaks, and flat floors characterize complex craters like the Chicxulub impact crater located near the northeast coast of the Yucatan Peninsula. The subsurface crater structure was studied using seismic reflection surveying in Jan/Feb 2005 by the R/V Maurice Ewing. We present 2-D seismic profiles including constant radius, regional, and grid profiles encompassing the 195 km width of the crater. These diversely oriented lines clearly show the terrace zones and aid in the search for crater ejecta as we investigate the formation of the crater including the incidence angle and direction of the extraterrestrial object that struck the Yucatan Peninsula 65 million years ago (K-T boundary). Terrace zones form in complex craters after the modification stage as a result of the gravitational collapse of overextended sediment back into the crater cavity. The terrace zone is clearly imaged on seismic profiles confirming the complex structure of the Chixculub crater. Recent work on reprocessed 1996 profiles found different sizes and spacing of the terraces and concluded that the variations in radial structure are a result of an oblique impact. A SW-NE profile from this study was the only line to show a concentration of deformation near the crater rim hinting that the northeast was the downrange direction of impact. We confirm this narrowing in terrace spacing using a profile with a similar orientation in the 2005 images. Through integration of the new dense grid of profiles and radial lines from the 1996 and 2005 surveys we map the 3-D variability of the terrace zones to further constrain impact direction and examine the formative processes of the Chixculub and other large impact craters.

  16. Structure of the Koyna-Warna Seismic Zone, Maharashtra, India: A possible model for large induced earthquakes elsewhere

    Catchings, Rufus D.; Dixit, M.M.; Goldman, Mark R.; Kumar, S.


    The Koyna-Warna area of India is one of the best worldwide examples of reservoir-induced seismicity, with the distinction of having generated the largest known induced earthquake (M6.3 on 10 December 1967) and persistent moderate-magnitude (>M5) events for nearly 50 years. Yet, the fault structure and tectonic setting that has accommodated the induced seismicity is poorly known, in part because the seismic events occur beneath a thick sequence of basalt layers. On the basis of the alignment of earthquake epicenters over an ~50 year period, lateral variations in focal mechanisms, upper-crustal tomographic velocity images, geophysical data (aeromagnetic, gravity, and magnetotelluric), geomorphic data, and correlation with similar structures elsewhere, we suggest that the Koyna-Warna area lies within a right step between northwest trending, right-lateral faults. The sub-basalt basement may form a local structural depression (pull-apart basin) caused by extension within the step-over zone between the right-lateral faults. Our postulated model accounts for the observed pattern of normal faulting in a region that is dominated by north-south directed compression. The right-lateral faults extend well beyond the immediate Koyna-Warna area, possibly suggesting a more extensive zone of seismic hazards for the central India area. Induced seismic events have been observed many places worldwide, but relatively large-magnitude induced events are less common because critically stressed, preexisting structures are a necessary component. We suggest that releasing bends and fault step-overs like those we postulate for the Koyna-Warna area may serve as an ideal tectonic environment for generating moderate- to large- magnitude induced (reservoir, injection, etc.) earthquakes.

  17. Post-Seismic Fault Healing on the Rupture Zone of the 1999 M7.1 Hector Mine, California Earthquake

    Li, Y.; Vidale, J. E.; Day, S. M.; Oglesby, D. D.; Cochran, E.; Gross, K.; Burdette, T.; Alvarez, M.


    We probed the rupture zone of the October 1999 M7.1 Hector Mine earthquake using repeated near-surface explosions in October, 2000 and November, 2001. Three dense linear seismic arrays were deployed across the north and south Lavic Lake faults (LLF) that broke to the surface in the mainshock, and across the Bullion fault (BF) that experienced minor slip in that event. Two explosions each year were detonated in the rupture zone on the middle and south LLF, respectively. We found that P and S velocities of fault-zone rocks increased by ~0.7 to 1.4% and ~0.5 to 1.0% between 2000 and 2001, respectively. In contrast, the velocities for P and S waves in surrounding rocks increased much less. This trend indicates the Hector Mine rupture zone has been healing by strengthening after the mainshock, which we attribute to the closure of cracks that opened during the 1999 earthquake. The 'crack dilatancy' mechanisms are most likely to operate for fault healing at shallow depth although the healing may be controlled by a combination of mechanical and chemical processes on the fault during the earthquake cycle. The observed fault-zone strength recovery is consistent with an apparent crack density decrease of 1.5% within the rupture zone. The ratio of travel time decrease for P to S waves was 0.72, consistent with partially fluid-filled cracks near the fault zone were. We also find variability in healing rates between the fault segments. The velocity increase with time varies from one fault segment to another at the Hector Mine rupture zone. We see greater changes on the LLF than on the BF, and the greatest change is on the middle LLF at shallow depth. We speculate that greater damage was inflicted, and thus greater healing is observed, in regions with larger slip in the mainshock. This post-seismic restrengthening of the Hector Mine rupture zone is similar to that observed on the Johnson Valley fault which ruptured in the 1992 M7.4 Landers earthquake (Li and Vidale, GRL, 2001

  18. Interseismic coupling and seismic potential along the Central Andes subduction zone

    Chlieh, Mohamed; Perfettini, Hugo; Tavera, Hernando; Avouac, Jean-Philippe; Remy, Dominique; Nocquet, Jean-Mathieu; Rolandone, FréDéRique; Bondoux, Francis; Gabalda, Germinal; Bonvalot, Sylvain


    We use about two decades of geodetic measurements to characterize interseismic strain build up along the Central Andes subduction zone from Lima, Peru, to Antofagasta, Chile. These measurements are modeled assuming a 3-plate model (Nazca, Andean sliver and South America Craton) and spatially varying interseismic coupling (ISC) on the Nazca megathrust interface. We also determine slip models of the 1996 Mw = 7.7 Nazca, the 2001 Mw = 8.4 Arequipa, the 2007 Mw = 8.0 Pisco and the Mw = 7.7 Tocopilla earthquakes. We find that the data require a highly heterogeneous ISC pattern and that, overall, areas with large seismic slip coincide with areas which remain locked in the interseismic period (with high ISC). Offshore Lima where the ISC is high, a Mw˜8.6-8.8 earthquake occurred in 1746. This area ruptured again in a sequence of four Mw˜8.0 earthquakes in 1940, 1966, 1974 and 2007 but these events released only a small fraction of the elastic strain which has built up since 1746 so that enough elastic strain might be available there to generate a Mw > 8.5 earthquake. The region where the Nazca ridge subducts appears to be mostly creeping aseismically in the interseismic period (low ISC) and seems to act as a permanent barrier as no large earthquake ruptured through it in the last 500 years. In southern Peru, ISC is relatively high and the deficit of moment accumulated since the Mw˜8.8 earthquake of 1868 is equivalent to a magnitude Mw˜8.4 earthquake. Two asperities separated by a subtle aseismic creeping patch are revealed there. This aseismic patch may arrest some rupture as happened during the 2001 Arequipa earthquake, but the larger earthquakes of 1604 and 1868 were able to rupture through it. In northern Chile, ISC is very high and the rupture of the 2007 Tocopilla earthquake has released only 4% of the elastic strain that has accumulated since 1877. The deficit of moment which has accumulated there is equivalent to a magnitude Mw˜8.7 earthquake. This study thus

  19. Apparent stress, fault maturity and seismic hazard for normal-fault earthquakes at subduction zones

    Choy, G.L.; Kirby, S.H.


    The behavior of apparent stress for normal-fault earthquakes at subduction zones is derived by examining the apparent stress (?? a = ??Es/Mo, where E s is radiated energy and Mo is seismic moment) of all globally distributed shallow (depth, ?? 1 MPa) are also generally intraslab, but occur where the lithosphere has just begun subduction beneath the overriding plate. They usually occur in cold slabs near trenches where the direction of plate motion across the trench is oblique to the trench axis, or where there are local contortions or geometrical complexities of the plate boundary. Lower ??a (tectonic regime suggests that the level of ?? a is related to fault maturity. Lower stress drops are needed to rupture mature faults such as those found at plate interfaces that have been smoothed by large cumulative displacements (from hundreds to thousands of kilometres). In contrast, immature faults, such as those on which intraslab-normal-fault earthquakes generally occur, are found in cold and intact lithosphere in which total fault displacement has been much less (from hundreds of metres to a few kilometres). Also, faults on which high ??a oceanic strike-slip earthquakes occur are predominantly intraplate or at evolving ends of transforms. At subduction zones, earthquakes occurring on immature faults are likely to be more hazardous as they tend to generate higher amounts of radiated energy per unit of moment than earthquakes occurring on mature faults. We have identified earthquake pairs in which an interplate-thrust and an intraslab-normal earthquake occurred remarkably close in space and time. The intraslab-normal member of each pair radiated anomalously high amounts of energy compared to its thrust-fault counterpart. These intraslab earthquakes probably ruptured intact slab mantle and are dramatic examples in which Mc (an energy magnitude) is shown to be a far better estimate of the potential for earthquake damage than Mw. This discovery may help explain why loss of

  20. Reflection seismic survey across a fault zone in the Leinetal Graben, Germany, using P- and SH-waves

    Musmann, P.; Polom, U.; Buness, H.; Thomas, R.


    Fault systems are considered as a valuable hydro-geothermal reservoir for heat and energy extraction, as permeability may be enhanced compared to the surrounding host rock. Seismic measurements are a well established tool to reveal their structure at depth. Apart from structural parameters like dip, extent and throw, they allow us to derive lithologic parameters, e.g. seismic velocities and impedance. Usually, only compressional waves have been used so far. In the context of the "gebo" Collaborative Research Program, seismic methods are revised to image and characterize geological fault zones in order to minimize the geological and technical risk for geothermal projects. In doing so, we evaluate and develop seismic acquisition, processing and interpretation techniques both for compressional and shear wave surveys to estimate the geothermal potential of fault zones. Here, we present results from high-resolution P- and SH-wave reflection seismic surveys along one and the same profile. They were carried out across the eastern border of the Leinetal Graben, Lower Saxony, Germany. At this survey site, primarily Triassic units crop out that are disrupted by major fault system probably extending down into Permian Zechstein. The seismic P-wave measurements (2.5 m CDP spacing, 20 - 180 Hz sweep sent out by a small vibrator) imaged the structure of the subsurface and its fault inventory with high resolution. Imaging ranges from approximately 50 m (base Keuper) to approximately 1.8 km (within Zechstein) depth. The profiles reveal that the area has undergone multiphase tectonics. This becomes manifest in a complex seismic reflection pattern. In addition the P-wave velocity model shows several features that can be related to folding and faulting. Preliminary results of the SH-wave measurements (0.5 m CDP spacing, 10 - 100 Hz sweep) show that the complex structural geological settings in the subsurface, as imaged by the P-wave survey, can also be imaged by a reflection shear


    A. A. Stepashko


    Full Text Available  The evolution and specific features of seismogynamics of the Baikal zones are reviewed in the context of interactions between deep deformation waves and the regional structure of the lithospheric mantle. The study is based on a model of the mantle structure with reference to chemical compositions of mantle peridotites from ophiolotic series located in the south-western framing of the Siberian craton (Fig. 1. The chemical zonation of the lithospheric mantle at the regional scale is determined from results of analyses of the heterogeneity of compositions of peridotites (Fig. 2, Table 1 and variations of contents of whole rock major components, such as iron, magnesium and silica (Fig. 3. According to spatial variations of the compositions of peridotites, the mantle has the concentric zonal structure, and the content of SiO2 is regularly decreasing, while concentrations of FeO∑ and MgO are increasing towards the centre of such structure (Fig. 4. This structure belongs to the mantle of the Siberian craton, which deep edge extends beyond the surface contour of the craton and underlies the north-western segment of the Central Asian orogenic belt.Results of the studies of peridotites of the Baikal region are consistent with modern concepts [Snyder, 2002; O’Reilly, Griffin, 2006; Chen et al., 2009] that suggest that large mantle lenses underlie the Archaean cratons (Fig. 5. The lenses are distinguished by high-density ultrabasic rocks and compose high-velocity roots of cratons which have remained isolated from technic processes. Edges of the mantle lenses may extend a few hundred kilometers beyond the limits of the cratons and underlie orogenic belts that frame the cratons, and this takes place in the south-western segment of the Siberian craton.The revealed structure of the lithospheric mantle is consistent with independent results of seismic and magmatectonical studies of the region. The Angara geoblock is located above the central part of the

  2. Subduction processes off chile (SPOC) - results from The amphibious wide-angle seismic experiment across The chilean subduction zone

    Lueth, S.; Spoc Resaerch Group


    One component of the onshore-offshore, active-passive seismic experiment SPOC (Krawczyk et al., Stiller et al., this vol.) was a 2-D wide-angle seismic experiment covering the Chilean subduction zone from the Nazca Plate to the Magmatic Arc in the main cordillera. Three W-E-profiles of 52 stations each and up to 240 km long were deployed between 36° and 39° S. These profiles recorded chemical shots at their ends and, in order to extend the onshore profiles, the airgun pulses from RV SONNE cruising simultaneously on offshore profiles. On the southernmost of the three profiles OBHs/OBSs were deployed offshore, thus providing continuous wide-angle seismic data from the Nazca Plate to the South-American continent. Data examples, correlations, and velocity models along the three transects will be presented. The Moho of the subducted oceanic crust can be constrained by PmP-reflections down to 45 km depth under the coastal cordillera. The P-wave velocity field of the crust of the upper plate is characterized by gradually increasing P-wave velocities from East to West. Low seismic velocities (Vp ~6.5 km/s below 10 km depth) are observed at the eastern margin of the investigated area.

  3. Deformation Sources in Kīlauea's Southwest Rift Zone Inferred from the Modeling of Geodetic and Seismic Data

    Wauthier, C.; Roman, D. C.; Poland, M. P.; Miklius, A.; Fukushima, Y.; Hooper, A. J.; Cayol, V.


    For much of the first 20 years of Kīlauea's 1983-present ERZ (East Rift Zone) eruption, deformation was characterized by subsidence at the summit and along both rift zones. We speculate that subsidence of the rift zones was caused by deep rift opening and basal fault slip. A 3D Mixed-Boundary Element model including deep rift-zone opening (running from ~3 to 9 km depth beneath Kīlauea's East and Southwest Rift Zones) as well as slip on the décollement fault that underlies the volcano's south flank (at ~9 km depth) can indeed explain most of the deformation imaged by InSAR data from RADARSAT-1 and JERS-1 spanning two distinct background periods: 1993-1997 and 2000-2003, respectively. At the end of 2003, however, Kīlauea's summit began a 4-year-long period of inflation that culminated in an ERZ dike intrusion and small eruption during 17-19 June 2007—the "Father's Day" (FD) event. On the basis of deformation, seismicity, effusion rate, and lava chemistry and temperature, the FD event was interpreted as the result of forcible intrusion of magma driven by high pressure within the summit magma storage area, as opposed to a passive response to deep rift zone opening. This period of summit inflation is particularly interesting in 2006. According to daily GPS data, two distinct periods can be defined, spanning January to March 2006 and March to end of 2006. A major seismic swarm occurred during the first period while the south caldera area was inflating. The beginning of the second period corresponds to a switch from subsidence to inflation of the SWRZ (Southwest Rift Zone). The SWRZ had been subsiding since the last eruptive episode there in 1974, with the exception of a few dike injections in 1981-82. To investigate the magmatic processes which occurred during 2006 and their implications in terms of the magma plumbing system and local stress field, we integrate contemporary geodetic data from InSAR and GPS with seismic and geologic observations of the SWRZ.

  4. Double seismic zone of the Nazca plate in northern Chile: High-resolution velocity structure, petrological implications, and thermomechanical modeling

    Dorbath, Catherine; Gerbault, Muriel; Carlier, Gabriel; Guiraud, Michel


    This paper presents an interdisciplinary study of the northern Chile double seismic zone. First, a high-resolution velocity structure of the subducting Nazca plate has been obtained by the tomoDD double-difference tomography method. The double seismic zone (DSZ) is observed between 80 and 140 km depth, and the two seismic planes is 20 km apart. Then, the chemical and petrologic characteristics of the oceanic lithosphere associated with this DSZ are deduced by using current thermal-petrological-seismological models and are compared to pressure-temperature conditions provided by a numerical thermomechanical model. Our results agree with the common hypothesis that seismicity in both upper and lower planes is related to fluid releases associated with metamorphic dehydration reactions. In the seismic upper plane located within the upper crust, these reactions would affect material of basaltic (MORB) composition and document different metamorphic reactions occurring within high-P (>2.4 GPa) and low-T (130 km), lawsonite-amphibole eclogite conditions. The lower plane lying in the oceanic mantle can be associated with serpentinite dehydration reactions. The Vp and Vs characteristics of the region in between both planes are consistent with a partially (˜25-30 vol % antigorite, ˜0-10% vol % brucite, and ˜4-10 vol % chlorite) hydrated harzburgitic material. Discrepancies persist that we attribute to complexities inherent to heterogeneous structural compositions. While various geophysical indicators evidence particularly cold conditions in both the descending Nazca plate and the continental fore arc, thermomechanical models indicate that both seismic planes delimit the inner slab compressional zone around the 400°C (±50°C) isotherm. Lower plane earthquakes are predicted to occur in the slab's flexural neutral plane, where fluids released from surrounding metamorphic reactions could accumulate and trigger seismicity. Fluids migrating upward from the tensile zone below

  5. Periodic variation of stress field in the Koyna-Warna reservoir triggered seismic zone inferred from focal mechanism studies

    Rao, N. Purnachandra; Shashidhar, D.


    The Koyna-Warna region in western India is globally recognized as the premier site of reservoir triggered seismicity (RTS) associated with the Koyna and Warna reservoirs. The region is characterized by continuous seismic activity observed since several decades, including the world's largest triggered earthquake of M6.3 which occurred in Koyna in 1967. While the role of reservoirs in triggering earthquakes has been widely discussed, the actual tectonic mechanism controlling earthquake genesis in this region is hardly understood. The Koyna-Warna region is exclusively governed by earthquakes of strike-slip and normal fault mechanism distinct from the thrust faulting seen in other active zones in the Indian region. In the present study, a comprehensive catalog of 50 focal mechanism solutions of earthquakes that occurred during the last 45 years in the Koyna-Warna region is developed, both from previous literature and from moment tensor inversion studies by the authors using broadband data from a local seismic network operating since 2005. The seismicity and fault plane data have enabled precise delineation of trends of the major causative faults, which are further accentuated using the double-difference technique. Stress inversion of the focal mechanism data has provided the best fitting principal compressive and tensile stress field of the region, which in conjunction with the deciphered fault zones provides a feasible model of seismogenesis in this region. Based on the observed temporal variation of faulting mechanism a model of alternating cycles of predominantly strike-slip and normal faulting is proposed, which is attributed to a periodic peaking and relaxation respectively of the horizontal compressive stress field in this region due to the Indian plate collision with Eurasia.

  6. Investigating the possible effects of salt in the fault zones on rates of seismicity - insights from analogue and numerical modeling

    Urai, Janos; Kettermann, Michael; Abe, Steffen


    The presence of salt in dilatant normal faults may have a strong influence on fault mechanics and related seismicity. However, we lack a detailed understanding of these processes. This study is based on the geological setting of the Groningen area. During tectonic faulting in the Groningen area, rock salt may have flown downwards into dilatant faults, which thus may contain lenses of rock salt at present. Because of its viscous properties, the presence of salt lenses in a fault may introduce a strain-rate dependency to the faulting and affect the distribution of magnitudes of seismic events. We present a "proof of concept" showing that the above processes can be investigated using a combination of analogue and numerical modeling. Full scaling and discussion of the importance of these processes to induced seismicity in Groningen require further, more detailed study. The analogue experiments are based on a simplified stratigraphy of the Groningen area, where it is generally thought that most of the Rotliegend faulting has taken place in the Jurassic, after deposition of the Zechstein. This is interpreted to mean that at the time of faulting the sulphates were brittle anhydrite. If these layers were sufficiently brittle to fault in a dilatant fashion, rock salt could flow downwards into the dilatant fractures. To test this hypothesis, we use sandbox experiments where we combine cohesive powder as analog for brittle anhydrites and carbonates with viscous salt analogs to explore the developing fault geometry and the resulting distribution of salt in the faults. In the numerical models we investigate the stick-slip behavior of fault zones containing ductile material using the Discrete Element Method (DEM). Results show that the DEM approach is in principle suitable for the modeling of the seismicity of faults containing salt: the stick-slip motion of the fault becomes dependent on shear loading rate with a modification of the frequency magnitude distribution of the

  7. Shallow seismogenic zone detected from an offshore-onshore temporary seismic network in the Esmeraldas area (northern Ecuador)

    Pontoise, B.; Monfret, T.


    For a given site, many factors control the seismic risk. Earthquake magnitude, hypocentral distance, rupture mechanism, site effects and site vulnerability are among the most important. This article deals with one of these factors: the depth of the seismogenic zone, in the northern Ecuadorian subduction system, beneath a highly vulnerable site, the city of Esmeraldas and its industrial complex, the Ecuadorian oil refinery and shipping terminal. To address this problem, we analyzed data from a three weeks passive seismological experiment, conducted in the spring of 1998, using 13 Ocean Bottom Seismometers and 10 portable land-stations. A preliminary interpretation of wide-angle data obtained in the fall of 2000, in the Manta area, 100 km South of the study area, unambiguously indicates the presence of a velocity inversion in the Ecuadorian margin velocity structure. This velocity inversion is characterized by a shadow-zone of ˜1 s on the record-sections, and is interpreted as the result of a velocity contrast between the upper plate structure and the sedimentary and basaltic layer II of the subducted oceanic Nazca plate. One-dimensional velocity models are deduced from these wide-angle data and are used for earthquake location in the Esmeraldas area. This highly improved the hypocentral parameter determinations. The updip limit of the seismogenic zone is found at a depth of ˜12 km, 35 km eastward of the trench, and the depth of the seismogenic zone below the Esmeraldas city is found at ˜20 km. This shallow depth of the seismogenic zone dramatically increases the seismic hazard of the area.

  8. Crustal structure at the western end of the North Anatolian Fault Zone from deep seismic sounding

    B. Baier


    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

  9. Seismic Tomography of the Arabian-Eurasian Collision Zone and Surrounding Areas


    current tectonics of the region are controlled by the collision and continuing convergence of the Arabian and Eurasian plates . The Arabian the Arabian Plate and surrounding regions, Geophys. J. Int. 157: 775–795. Alinaghi, A., I. Koulakov, and H. Thybo (2007). Seismic tomographic...Tectonophysics 50: 307–336. Brune, J. N. (1970). Tectonic stress and the spectra of seismic shear waves from earthquakes, J. Geophys. Res. 75, 4997-5009. Cong

  10. Optimizing the design of vertical seismic profiling (VSP) for imaging fracture zones over hardrock basement geothermal environments

    Reiser, Fabienne; Schmelzbach, Cedric; Maurer, Hansruedi; Greenhalgh, Stewart; Hellwig, Olaf


    A primary focus of geothermal seismic imaging is to map dipping faults and fracture zones that control rock permeability and fluid flow. Vertical seismic profiling (VSP) is therefore a most valuable means to image the immediate surroundings of an existing borehole to guide, for example, the placing of new boreholes to optimize production from known faults and fractures. We simulated 2D and 3D acoustic synthetic seismic data and processed it through to pre-stack depth migration to optimize VSP survey layouts for mapping moderately to steeply dipping fracture zones within possible basement geothermal reservoirs. Our VSP survey optimization procedure for sequentially selecting source locations to define the area where source points are best located for optimal imaging makes use of a cross-correlation statistic, by which a subset of migrated shot gathers is compared with a target or reference image from a comprehensive set of source gathers. In geothermal exploration at established sites, it is reasonable to assume that sufficient à priori information is available to construct such a target image. We generally obtained good results with a relatively small number of optimally chosen source positions distributed over an ideal source location area for different fracture zone scenarios (different dips, azimuths, and distances from the surveying borehole). Adding further sources outside the optimal source area did not necessarily improve the results, but rather resulted in image distortions. It was found that fracture zones located at borehole-receiver depths and laterally offset from the borehole by 300 m can be imaged reliably for a range of the different dips, but more source positions and large offsets between sources and the borehole are required for imaging steeply dipping interfaces. When such features cross-cut the borehole, they are particularly difficult to image. For fracture zones with different azimuths, 3D effects are observed. Far offset source positions

  11. Shallow seismic structure of Kunlun fault zone in northern Tibetan Plateau, China: Implications for the 2001 M s8.1 Kunlun earthquake

    Wang, Chun-Yong; Mooney, W.D.; Ding, Z.; Yang, J.; Yao, Z.; Lou, H.


    The shallow seismic velocity structure of the Kunlun fault zone (KLFZ) was jointly deduced from seismic refraction profiling and the records of trapped waves that were excited by five explosions. The data were collected after the 2001 Kunlun M s8.1 earthquake in the northern Tibetan Plateau. Seismic phases for the in-line record sections (26 records up to a distance of 15 km) along the fault zone were analysed, and 1-D P- and S-wave velocity models of shallow crust within the fault zone were determined by using the seismic refraction method. Sixteen seismic stations were deployed along the off-line profile perpendicular to the fault zone. Fault-zone trapped waves appear clearly on the record sections, which were simulated with a 3-D finite difference algorithm. Quantitative analysis of the correlation coefficients of the synthetic and observed trapped waveforms indicates that the Kunlun fault-zone width is 300 m, and S-wave quality factor Q within the fault zone is 15. Significantly, S-wave velocities within the fault zone are reduced by 30-45 per cent from surrounding rocks to a depth of at least 1-2 km, while P-wave velocities are reduced by 7-20 per cent. A fault-zone with such P- and S-low velocities is an indication of high fluid pressure because Vs is affected more than Vp. The low-velocity and low-Q zone in the KLFZ model is the effect of multiple ruptures along the fault trace of the 2001 M s8.1 Kunlun earthquake. ?? 2009 The Authors Journal compilation ?? 2009 RAS.

  12. Deep seismic reflection profile across the juncture zone between the Tarim Basin and the West Kunlun Mountains


    Fine structures of the crust and upper mantle of the basin-and-range juncture on the northwestern margin of the Qinghai-Tibetan Plateau are first delineated by the deep seismic reflection profile across the juncture zone between the Tarim Basin and the West Kunlun Mountains. Evidence is found for the northward subduction of the northwest marginal lithosphere of the Qinghai-Tibetan Plateau and its collision with Tarim lithosphere beneath the West Kunlun Mountains. The lithosphere image of the face-to-face subduction and collision determines the coupling relationship between the Tarim Basin and the West Kunlun Mountains at the lithosphere scale and reflects the process of continent- continent collision.

  13. Las noticias de Madrid (News from Madrid

    Wahrle Suzanne


    Full Text Available Abstract Over 5,000 participants attended the 10th International Conference on Alzheimer's Disease (ICAD and Related Disorders in Madrid, Spain from July 15–20, 2006. Highlights of the conference included reports on brain imaging, the discovery of mutations in the progranulin gene that cause frontotemporal dementia, the finding that neuregulin-1 is a substrate for BACE1 and new interest in the connection between Alzheimer's disease and metabolic syndromes.


    Gevorg G. Kocharyan


    Full Text Available Association of earthquake hypocenters with fault zones appears more pronounced in cases with more accurately determined positions of the earthquakes. For complex, branched structures of major fault zones, it is assumed that some of the earthquakes occur at feathering fractures of smaller scale.It is thus possible to develop a «seismological» criterion for definition of a zone of dynamic influence of faults, i.e. the zone containing the majority of earthquakes associated with the fault zone under consideration.In this publication, seismogenic structures of several fault zones located in the San-Andreas fault system are reviewed. Based on the data from a very dense network of digital seismic stations installed in this region and with application of modern data processing methods, differential coordinates of microearthquakes can be determined with errors of about first dozens of meters.It is thus possible to precisely detect boundaries of the areas wherein active deformation processes occur and to reveal spatial patterns of seismic event localization.In our analyses, data from the most comprehensive seismic catalog were used. The catalogue includes information on events which occurred and were registered in North California in the period between January 1984 and May 2003. In this publication, the seismic data processing results and regularities revealed during the analyses are compared with the data obtained from studies of fault structures, modeling and numerical simulation results. Results of quantitative research of regularities of localization of seismic sources inside fault zones are presented.It is demonstrated by 3D models that seismic events are localized in the vicinity of an almost plain surface with a nearly constant angle of dip, the majority of events being concentrated at that conventional surface.Detection of typical scopes of seismicity localization may prove critical for solution of problems of technogenic impact on fault zones

  15. Effect of Seismic Zone and Story Height on Response Reduction Factor for SMRF Designed According to IS 1893(Part-1):2002

    Rao, P. Pravin Venkat; Gupta, L. M.


    Indian seismic code design procedure, which permit the estimation of inelastic deformation capacity of lateral force resisting systems, has been questioned since no coherence exists for determining the values of response reduction factor tabulated in code. Indian code at present does not give any deterministic values of ductility reduction factor and overstrength factor to be used in the design, because of the inadequacy of research results currently available. Hence, this study focuses on the variation of overstrength and ductility factors in steel moment resisting frame with different seismic zones and number of story. A total of 12 steel moment resisting frames were analyzed and designed. Response reduction factor has been determined by performing the non-linear static pushover analysis. The result shows that overstrength and ductility factors varies with number of story and seismic zones. It is also observed that for different seismic zones and story, ductility reduction factor is found to be different from overall structural ductility. It is observed that three buildings of different heights had an average overstrength of 63% higher in Zone-II as compared to Zone-V. These observations are extremely significant for building seismic provision codes, that at present not taking into consideration the variation of response reduction factor.

  16. A double seismic zone in the subducting Juan Fernandez Ridge of the Nazca Plate (32°S), central Chile

    Marot, M.; Monfret, T.; Pardo, M.; Ranalli, G.; Nolet, G.


    The region of central Chile offers a unique opportunity to study the links between the subducting Juan Fernandez Ridge, the flat slab, the double seismic zone (DSZ), and the absence of modern volcanism. Here we report the presence and characteristics of the first observed DSZ within the intermediate-depth Nazca slab using two temporary seismic catalogs (Ovalle 1999 and Chile Argentina Seismological Measurement Experiment). The lower plane of seismicity (LP) is located 20-25 km below the upper plane, begins at 50 km depth, and merges with the lower plane at 120 km depth, where the slab becomes horizontal. Focal mechanism analysis and stress tensor calculations indicate that the slab's state of stress is dominantly controlled by plate convergence and overriding crust thickness: Above 60-70 km depth, the slab is in horizontal compression, and below, it is in horizontal extension, parallel to plate convergence, which can be accounted for by vertical loading of the overriding lithosphere. Focal mechanisms below 60-70 km depth are strongly correlated with offshore outer rise bend faults, suggesting the reactivation of preexisting faults below this depth. The large interplane distances for all Nazca DSZs can be related to the slab's unusually cold thermal structure with respect to its age. Since LPs globally seem to mimic mantle mineral dehydration paths, we suggest that fluid migration and dehydration embrittlement provide the mechanism necessary to weaken the rock and that the stress field determines the direction of rupture.

  17. High-resolution seismic velocities and shallow structure of the San Andreas fault zone at Middle Mountain, Parkfield, California

    Catchings, R.D.; Rymer, M.J.; Goldman, M.R.; Hole, J.A.; Huggins, R.; Lippus, C.


    A 5-km-long, high-resolution seismic imaging survey across the San Andreas fault (SAF) zone and the proposed San Andreas Fault Observatory at Depth (SAFOD) drill site near Parkfield, California, shows that velocities vary both laterally and vertically. Velocities range from 4.0 km/sec) probably correspond to granitic rock of the Salinian block, which is exposed a few kilometers southwest of the SAF. The depth to the top of probable granitic rock varies laterally along the seismic profile but is about 600 m below the surface at the proposed SAFOD site. We observe a prominent, lateral low-velocity zone (LVZ) beneath and southwest of the surface trace of the SAF. The LVZ is about 1.5 km wide at 300-m depth but tapers to about 600 m wide at 750-m depth. At the maximum depth of the velocity model (750 m), the LVZ is centered approximately 400 m southwest of the surface trace of the SAF. Similar velocities and velocity gradients are observed at comparable depths on both sides of the LVZ, suggesting that the LVZ is anomalous relative to rocks on either side of it. Velocities within the LVZ are lower than those of San Andreas fault gouge, and the LVZ is also anomalous with respect to gravity, magnetic, and resistivity measurements. Because of its proximity to the surface trace of the SAF, it is tempting to suggest that the LVZ represents a zone of fractured crystalline rocks at depth. However, the LVZ instead probably represents a tectonic sliver of sedimentary rock that now rests adjacent to or encompasses the SAF. Such a sliver of sedimentary rock implies fault strands on both sides and possibly within the sliver, suggesting a zone of fault strands at least 1.5 km wide at a depth of 300 m, tapering to about 600 m wide at 750-m depth. Fluids within the sedimentary sliver are probably responsible for observed low-resistivity values.

  18. Coulomb Stress evolution and seismic hazard along the Xianshuihe-Xiaojiang Fault Zone of Western Sichuan, China

    Shan, B.; Xiong, X.; Zheng, Y.


    The Xianshuihe-Xiaojiang fault system (XXFS) in southwestern China is a curved left-lateral strike-slip structure extending at least 1400 km in the eastern margin of the Tibetan Plateau. Fieldworks confirm that the XXFS, whose slip motion releases strain that is related to the convergence between the Indian and Eurasian plates, is one of the largest and most seismically active faults in China. The entire fault has experienced at least 35 earthquakes of M>6 since 1700, and almost all segments of the system have been the locus of major earthquakes within the historic record. Since the XXFS region is heavily populated (over 50 million people), understanding the distribution of large earthquakes in space and time in this region is crucial for improving forecasting and reducing catastrophic life and monetary losses. We investigated a sequence of twenty-five earthquakes (M≥6.5) that occurred along the XXFS since 1713, and the interaction between the historical earthquakes and the Mw7.9 Wenchuan earthquake occurred on the Longmenshan Fault last year. The layered model used in the study and relevant parameters were constrained by seismic studies. Fault rupture locations and geometries, as well as slip distributions of earthquakes were taken from field observations and seismic studies. Numerical results showed a good correlation between stress transfer, accumulation and earthquakes. Fourteen of the twenty-four earthquakes occurred after the 1713 Xundian were encouraged by the preceding earthquakes with positive stress loading. Three events occurred in the stress shadow induced by preceding events. And others occurred in the probable area with Coulomb stress increment. The triggering process on the fault zone may exist. According to our results, there are three visible earthquake gaps along the fault zone, which are consistent with the results of historical earthquake study. The seismic activity and tectonic motion on XXFS reduced the shear stress on the epicenter of M8

  19. Geothermal and seismic evidence for a southeastern continuation of the three pagodas fault zone into the Gulf of Thailand

    Prinya Putthapiban


    Full Text Available Aerial photographic maps and landsat image interpretations suggest the major fault segments of the Three PagodaFault (TPF Zone and Sri Swat Fault (SSF Zone are oriented parallel or sub-parallel in the same NW-SE directions. The KwaeNoi River is running along the TPF in the south whereas the Kwae Yai River is running along the SSF in the north. Thesoutheastern continuation of both faults is obscured by thick Cenozoic sediments. Hence, surface lineaments cannot betraced with confidence. However, based on some interpretations of the airborne magnetic survey data, the trace of such faultsare designated to run through the western part of Bangkok and the northern end of the Gulf of Thailand. Paleo-earthquakesand the presence of hot springs along the fault zones indicate that they are tectonically active. The changes of both physicaland chemical properties of the water from Hin Dart Hot Spring and those of the surface water from a shallow well at Ban KhaoLao during the Great Sumatra–Andaman Earthquake on 26th of December 2004 clearly indicated that the southeastern continuation of the TPF is at least as far south as Pak Tho District, Ratburi. Our new evidence of the alignment of the high heatflow in the upper part of the Gulf of Thailand verified that the TPF also extend into the Gulf via Samut Songkhram Province.Studies of the seismic data from two survey lines along the Western part of the upper Gulf of Thailand acquired by BritoilPlc. in 1986, namely Line A which is approximately 60 km long, starting from Bang Khen passing through Bang Khae andending in Samut Songkhram and Line B is approximately 30 km long starting from Samut Sakon ending in Samut Song Khramsuggest that all the faults or fractures along these seismic profiles are covered by sediments of approximately 230 m thickwhich explain that the fault underneath these seismic lines is quite old and may not be active. The absent of sign or trace ofthe TPF Path to the west suggested that there

  20. High Holocene coastal uplift gives insight into the seismic behavior at the Arica Bend (Peru-Chile subduction zone)

    Madella, Andrea; Delunel, Romain; Szidat, Sönke; Schlunegger, Fritz


    KEYWORDS: northern Chile, coastal uplift, plate coupling, seismic cycle The Peru-Chile subduction zone offshore of the Arica Bend (18.3° S) is characterized by a seaward-concave geometry, which represents a very uncommon tectonic setting. Several published estimates of plate coupling suggest that the locking degree in the curved segment may be significantly lower than to the north and south of it, however, the lack of historical slip events hinders a full understanding of the seismic behavior in this particular portion of plate interface. We have mapped a terrace located at 35 m a.s.l. ca. 3 km onshore from the mouth of the Lluta river, which debouches immediately to the north of Arica. The sedimentology of the terrace has been described and three wood fragments embedded therein have been collected for radiocarbon dating. In addition, we compared the long stream profile of the Lluta river with its modeled steady-state profile, aiming to detect any possible tectonic perturbation along the trunk stream. Results show that the dated terrace consists of a thin storm deposit embedded within fluvial delta conglomerates, which have been most likely deposited near sea-level at ~10 ka. We thus infer that the coast of the Arica Bend, although characterized by long-term quiescence, has undergone remarkable uplift (~5 mm/y) throughout the Holocene. The vertical displacement has been inferred at roughly 175 km from the trench, which corresponds to the landward termination of the locked zone. Considering this structural position and the long-term absence of coseismic events in this trench segment, we propose that the inferred uplift signal might be related to interseismic flexural buckling, which does not result in permanent crustal deformation. Contrariwise, in the adjacent coastal regions north and south of the Arica Bend, repeated seismic cycles have resulted in long-term permanent crustal deformation, as observable in the uplifted Coastal Cordillera.

  1. Active crustal deformation of the El Salvador Fault Zone (ESFZ) using GPS data: Implications in seismic hazard assessment

    Staller, Alejandra; Benito, Belen; Jesús Martínez-Díaz, José; Hernández, Douglas; Hernández-Rey, Román; Alonso-Henar, Jorge


    El Salvador, Central America, is part of the Chortis block in the northwestern boundary of the Caribbean plate. This block is interacting with a diffuse triple junction point with the Cocos and North American plates. Among the structures that cut the Miocene to Pleistocene volcanic deposits stands out the El Salvador Fault Zone (ESFZ): It is oriented in N90º-100ºE direction, and it is composed of several structural segments that deform Quaternary deposits with right-lateral and oblique slip motions. The ESFZ is seismically active and capable of producing earthquakes such as the February 13, 2001 with Mw 6.6 (Martínez-Díaz et al., 2004), that seriously affected the population, leaving many casualties. This structure plays an important role in the tectonics of the Chortis block, since its motion is directly related to the drift of the Caribbean plate to the east and not with the partitioning of the deformation of the Cocos subduction (here not coupled) (Álvarez-Gómez et al., 2008). Together with the volcanic arc of El Salvador, this zone constitutes a weakness area that allows the motion of forearc block toward the NW. The geometry and the degree of activity of the ESFZ are not studied enough. However their knowledge is essential to understand the seismic hazard associated to this important seismogenic structure. For this reason, since 2007 a GPS dense network was established along the ESFZ (ZFESNet) in order to obtain GPS velocity measurements which are later used to explain the nature of strain accumulation on major faults along the ESFZ. The current work aims at understanding active crustal deformation of the ESFZ through kinematic model. The results provide significant information to be included in a new estimation of seismic hazard taking into account the major structures in ESFZ.

  2. Induced seismicity of a normal blind undetected reservoir-bounding fault influenced by dissymmetric fractured damage zones

    Rohmer, J.


    Fluid injection in deep sedimentary porous formations might induce shear reactivation of reservoir bounding faults. Here, we focus on `blind' 1000-m-long normal faults (with shear displacement ≤10 m), which can hardly be detected using conventional seismic surveys, but might potentially induce seismicity felt on surface. The influence of the dissymmetry in the internal structure of the fractured damage zone DZ is numerically investigated by using 2-D plane-strain finite-element simulations of a 1500-m-deep fluid injection into a porous reservoir. The problem is solved within the framework of fully saturated isothermal elasto-plastic porous media by both accounting for fault slip weakening and shear-induced degradation of fault core permeability. The numerical results show that the presence of a thick fractured hanging wall's DZ (with Young's modulus decreasing with the distance to the fault core due to the presence of fractures) strongly controls the magnitude M of the seismic event induced by the rupture. In the case modelled, M changed by more than 1.0 unit when the DZ thickness is varied from 5 to 50 m (M ranges from ˜0.1 to ˜1.5, i.e. from a `low' to a `low-to-moderate' seismicity activity). However, further extending DZ up to 90 m has little effect and the relationship reaches a quasi-horizontal plateau. This tendency is confirmed considering other initial conditions and injection scenarios. Finally, the presence of a thicker footwall DZ appears to lower the influence of hanging wall's DZ, but with lesser impact than the degree of fracturing.

  3. Response spectrum of seismic design code for zones lack of near-fault strong earthquake records

    LI Xin-le; DOU Hui-juan; ZHU Xi; SUN Jian-gang


    It was shown from the study on the recently near-fault earthquake ground motions that the near-fault effects were seldom considered in the existing Chinese seismic code. Referring to the UBC97 design concept for near-fault factors, based on the collected world-widely free-site records of near-fault earthquakes ground motions classified by earthquake magnitude and site condition, the attenuation relationship expressions of the acceleration spectrum demand at the key points within the long period and moderate period were established in term of the earthquake magnitude and the site condition. Furthermore, the near-fault factors' expressions about the earthquake magnitude and the fault distance were deduced for the area lack of near-fault strong earthquake records. Based on the current Chinese Building Seismic Design Code, the near-fault effect factors and the modified design spectral curves, which were valuable for the seismic design, were proposed to analyze the seismic response of structures.

  4. Seismic monitoring at the geothermal zone of Acoculco, Pue., Mexico; Monitoreo sismico en la zona geotermica de Acoculco, Pue., Mexico

    Lermo, Javier; Antayhua, Yanet; Bernal, Isabel [Universidad Nacional Autonoma de Mexico (UNAM), Instituto de Ingenieria Mexico, D.F. (Mexico); Venegas, Saul; Arredondo, Jesus [Comision Federal de Electricidad, Gerencia de Proyectos Geotermoelectricos, Morelia, Michoacan (Mexico)]. E-mail:


    Results are presented of a research project to study seismic activity in the Acoculco geothermal zone, Puebla, Mexico. Geological and geophysical information was collected for the zone and a seismic network composed of seven digital seismographs was installed over four months (August-November 2004). Of the 30 regional earthquakes located by the National Seismological Service, 14 were at the subduction zone, 7 in the intra-plate zone, 6 of cortical type were in the Mexican Volcanic Belt, and 3 had deep origins in the Veracruz and Chiapas regions. Although there were no local earthquakes, probably due to the short monitoring span or lack of currently active zones, velocity models were defined near the springs of Los Azufres and Alcaparrosa, with lineal arrangements of wide-band seismic stations (SPAC) and strata identified in the exploratory well EAC-1, drilled by the Comision Federal de Electricidad. By using the registers of regional earthquakes, the site-effects were estimated on the six temporary seismic stations, whose empirical transfer functions were used to validate a velocities model proposed for the endhoreic basin. The proposed velocity models, both for the endhoreic basin and outside it, enhance the previous interpretations. They confirm the geo-electrical model proposed for the zone is adequate and they provide dynamic conditions for the model, such as propagation velocities of the P and S waves and densities and attenuation. [Spanish] Se presentan los resultados de un proyecto de investigacion para estudiar la actividad sismica de la zona geotermica de Acoculco, Puebla, Mexico. Con este fin se recopilo informacion geologica y geofisica de la zona y se instalo durante cuatro meses (de agosto a noviembre de 2004) una red sismica conformada por siete sismografos digitales. Se registraron 30 sismos regionales que fueron localizados por el Servicio Sismologico Nacional en la zona de subduccion (14), en la zona de intraplaca (7), de tipo cortical del Eje

  5. USGS National Seismic Hazard Maps

    Frankel, A.D.; Mueller, C.S.; Barnhard, T.P.; Leyendecker, E.V.; Wesson, R.L.; Harmsen, S.C.; Klein, F.W.; Perkins, D.M.; Dickman, N.C.; Hanson, S.L.; Hopper, M.G.


    The U.S. Geological Survey (USGS) recently completed new probabilistic seismic hazard maps for the United States, including Alaska and Hawaii. These hazard maps form the basis of the probabilistic component of the design maps used in the 1997 edition of the NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures, prepared by the Building Seismic Safety Council arid published by FEMA. The hazard maps depict peak horizontal ground acceleration and spectral response at 0.2, 0.3, and 1.0 sec periods, with 10%, 5%, and 2% probabilities of exceedance in 50 years, corresponding to return times of about 500, 1000, and 2500 years, respectively. In this paper we outline the methodology used to construct the hazard maps. There are three basic components to the maps. First, we use spatially smoothed historic seismicity as one portion of the hazard calculation. In this model, we apply the general observation that moderate and large earthquakes tend to occur near areas of previous small or moderate events, with some notable exceptions. Second, we consider large background source zones based on broad geologic criteria to quantify hazard in areas with little or no historic seismicity, but with the potential for generating large events. Third, we include the hazard from specific fault sources. We use about 450 faults in the western United States (WUS) and derive recurrence times from either geologic slip rates or the dating of pre-historic earthquakes from trenching of faults or other paleoseismic methods. Recurrence estimates for large earthquakes in New Madrid and Charleston, South Carolina, were taken from recent paleoliquefaction studies. We used logic trees to incorporate different seismicity models, fault recurrence models, Cascadia great earthquake scenarios, and ground-motion attenuation relations. We present disaggregation plots showing the contribution to hazard at four cities from potential earthquakes with various magnitudes and

  6. Detailed seismic velocity of the incoming subducting sediments in the 2004 great Sumatra earthquake rupture zone from full waveform inversion of long offset seismic data

    Qin, Yanfang; Singh, Satish C.


    The nature of incoming sediments defines the locking mechanism on the megathrust, and the development and evolution of the accretionary wedge. Here we present results from seismic full waveform inversion of 12 km long offset seismic reflection data within the trench in the 2004 Sumatra earthquake rupture zone area that provide detailed quantitative information on the incoming oceanic sediments and the trench-fill sediments. The thickness of sediments in this area is 3-4 km, and P wave velocity is as much as 4.5 km/s just above the oceanic crust, suggesting the presence of silica-rich highly compacted and lithified sediments leading to a strong coupling up to the subduction front. We also find an 70-80 m thick low-velocity layer, capped by a high-velocity layer, at 0.8 km above the subducting plate. This low-velocity layer, previously identified as high-amplitude negative polarity reflection, could have porosity of up to 30% containing overpressured fluids, which could act as a protodécollement seaward from the accretionary prism and décollement beneath the forearc. This weak protodécollement combined with the high-velocity indurated sediments above the basement possibly facilitated the rupture propagating up to the front during the 2004 earthquake and enhancing the tsunami. We also find another low-velocity layer within the sediments that may act as a secondary décollement observed offshore central Sumatra, forming bivergent pop-up structures and acting as a conveyer belt in preserving these pop-up structures in the forearc region.

  7. Estimation of recurrence interval of large earthquakes on the central Longmen Shan fault zone based on seismic moment accumulation/release model.

    Ren, Junjie; Zhang, Shimin


    Recurrence interval of large earthquake on an active fault zone is an important parameter in assessing seismic hazard. The 2008 Wenchuan earthquake (Mw 7.9) occurred on the central Longmen Shan fault zone and ruptured the Yingxiu-Beichuan fault (YBF) and the Guanxian-Jiangyou fault (GJF). However, there is a considerable discrepancy among recurrence intervals of large earthquake in preseismic and postseismic estimates based on slip rate and paleoseismologic results. Post-seismic trenches showed that the central Longmen Shan fault zone probably undertakes an event similar to the 2008 quake, suggesting a characteristic earthquake model. In this paper, we use the published seismogenic model of the 2008 earthquake based on Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data and construct a characteristic seismic moment accumulation/release model to estimate recurrence interval of large earthquakes on the central Longmen Shan fault zone. Our results show that the seismogenic zone accommodates a moment rate of (2.7 ± 0.3) × 10¹⁷ N m/yr, and a recurrence interval of 3900 ± 400 yrs is necessary for accumulation of strain energy equivalent to the 2008 earthquake. This study provides a preferred interval estimation of large earthquakes for seismic hazard analysis in the Longmen Shan region.

  8. Quantitative Inversion of Seismic Fault Zone Waveforms in the Rupture Zone of the 1992 Landers Earthquake for Structural Properties at Depth

    Peng, Z.; Ben-Zion, Y.; Michael, A. J.


    Waveform modeling of seismic fault zone (FZ) trapped waves has the potential for providing a high-resolution imaging of seismic velocities, seismic attenuation, FZ width, and structural continuity at depth. From a digital waveform data set generated by 238 aftershocks of the 1992 Landers earthquake [William Lee, per. com., '99], we identified 60 events with good candidate trapped waves. Each event was recorded by 33 three-component, short-period (2 Hz), L-22 seismometers, 22 of which on a line crossing the surface rupture zone of the mainshock. Locations of 102 events out of the 238 aftershocks are given in the catalog of Richards-Dinger and Shearer [JGR, '00]. These include 16 events generating candidate trapped waves. A plane-wave fitting technique is applied to estimate the back-azimuth angle of the unlocated events that produce candidate trapped waves. The source-receiver distance for these events is estimated from the S - P travel time. Of the 60 candidate trapped waves, about 75% are generated by events with locations close to the FZ, while the reminder are likely produced by events at considerable distance from the fault. The latter observation is compatible with 3D numerical calculations of Igel et al. [Pageoph, '01]. The FZ waveforms with candidate trapped waves are modeled with a genetic inversion algorithm (GIA) that maximizes the correlation between observed and synthetic waveforms [Michael and Ben-Zion, ms. in preparation, '01]. The synthetic seismograms are generated with a two-dimensional analytical solution for a scalar wavefield in a layered vertical FZ between two quarter-spaces [Ben-Zion and Aki, BSSA,'90; Ben-Zion, JGR, '98]. Our previous results showed that the GIA is able to provide very good fits for Landers FZ waveforms with a model consisting of a single uniform FZ layer in a half space. However, it is possible to get equally good fits for a wide range of parameters. This is due to significant trade-offs among FZ width, propagation distance

  9. Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array

    Share, Pieter-Ewald; Ben-Zion, Yehuda; Ross, Zachary E.; Qiu, Hongrui; Vernon, Frank L.


    Local and teleseismic earthquake waveforms recorded by a 180-m-long linear array (BB) with seven seismometers crossing the Clark fault of the San Jacinto fault zone northwest of Anza are used to image a deep bimaterial interface and core damage structure of the fault. Delay times of P waves across the array indicate an increase in slowness from the southwest most (BB01) to the northeast most (BB07) station. Automatic algorithms combined with visual inspection and additional analyses are used to identify local events generating fault zone head and trapped waves. The observed fault zone head waves imply that the Clark fault in the area is a sharp bimaterial interface, with lower seismic velocity on the southwest side. The moveout between the head and direct P arrivals for events within ˜40 km epicentral distance indicates an average velocity contrast across the fault over that section and the top 20 km of 3.2 per cent. A constant moveout for events beyond ˜40 km to the southeast is due to off-fault locations of these events or because the imaged deep bimaterial interface is discontinuous or ends at that distance. The lack of head waves from events beyond ˜20 km to the northwest is associated with structural complexity near the Hemet stepover. Events located in a broad region generate fault zone trapped waves at stations BB04-BB07. Waveform inversions indicate that the most likely parameters of the trapping structure are width of ˜200 m, S velocity reduction of 30-40 per cent with respect to the bounding blocks, Q value of 10-20 and depth of ˜3.5 km. The trapping structure and zone with largest slowness are on the northeast side of the fault. The observed sense of velocity contrast and asymmetric damage across the fault suggest preferred rupture direction of earthquakes to the northwest. This inference is consistent with results of other geological and seismological studies.

  10. Integrated geophysical investigations for seismic zoning in a coastal area of Northern Sicily



    Full Text Available The area, about 225 km2 large, ranging from the Eleuterio river to the S.
    Leonardo river on the northern coast of Sicily, has suffered many earthquakes in
    the past centuries and has for many years recognized as a seismic area. This paper
    presents a set of integrated geophysical studies carried out in that area, including:
    i a statistical study of the past earthquakes in order to define the earthquake risk
    (PGV or PGA risk, ii a set of laboratory density measurements carried out on
    samples of rocks (82 samples, Hi a shallow refraction investigation (290 profiles
    in order to study the mechanical properties of such rocks, iv a deep geoelectrical
    investigation (200 VES in order to reconstruct the main geological features with
    particular regard to the geometrical distribution of the elastic and plastic
    formations which have been piled up during the complex overthrusting of the
    Sicilian chain, and v a detailed study of the possible amplifications of the
    groundmotions due to the geometry and the mechanical characteristics of the
    shallow and intermediate rocks. The results, combined wih the knowledge of the
    regional tectonic features and the locations of the involved seismogenetic volumes,
    allow the formation of a picture of the seismic responses and the connected seismic

  11. Sanitation system for Madrid

    Sánchez, Félix Cristóbal


    The Full Sanitation Plan for Madrid is the final action of a series undertaken for several years with the purpose to reach the completion of the sanitation system of the town. With the whole of these actions it could be said that the basic substructure has acquired enough level to deserve de real needs of the town.

  12. Mad about Real Madrid


    CHINESE football fans have never expended so much on one football game. Real Madrid's six football superstars, two million euro the richer after this trip to China, will doubtless look back on it as the pinnacle of their earning power. Fans were ecstatic at seeing

  13. Puerta del Sol, Madrid

    Reeh, Henrik


    Professor Eric Corijn (Vrije Universiteit Brussel) og hans virke som dynamisk urbanist blev sat i scene, da 4Cities-masterprogrammet ( underviste i Madrid midt under bosættelsen på pladsen Puerta del Sol i maj 2011. Artiklen tematiserer forbindelsen mellem det sociale og rumlige liv på...

  14. Strike-slip faulting at Thebes Gap, Missouri and Illinois: Implications for New Madrid tectonism

    Harrison, Richard W.; Schultz, Art


    Numerous NNE and NE striking strike-slip faults and associated normal faults, folds, and transtensional grabens occur in the Thebes Gap area of Missouri and Illinois. These structures developed along the northwestern margin of the buried Reelfoot rift of Precambrian-Cambrian age at the northern edge of the Mississippi embayment. They have had a long-lived and complex structural history. This is an area of recent moderate seismicity, approximately 45 km north of the New Madrid seismic zone. Stratigraphic evidence suggests that these faults were active during the Middle Ordovician. They were subsequently reactivated between the Early Devonian and Late Cretaceous, probably in response to both the Acadian and Ouachita orogenies. Deformation during this period was characterized by strongly faulted and folded Ordovician through Devonian rocks. In places, these deformed rocks are overlain with angular unconformity by undeformed Cretaceous strata. Fault motion is interpreted as dominantly strike slip. A still younger period of reactivation involved Late Cretaceous and Cenozoic formations as young as the Miocene or Pliocene Mounds Gravel. These formations have experienced both minor high-angle normal faulting and subsequent major, right-lateral strike-slip faulting. En echelon north-south folds, ENE striking normal faults, regional fracture patterns, and drag folds indicate the right-lateral motion for this major episode of faulting which predates deposition of Quaternary loess. Several nondefinitive lines of evidence suggest Quaternary faulting. Similar fault orientations and kinematics, as well as recent seismicity and proximity, clearly suggest a structural relationship between deformation at Thebes Gap and tectonism associated with the New Madrid area.

  15. Refraction and reflection seismic investigations for geological energy-storage site characterization: Dalby (Tornquist Zone), southwest Sweden

    Malehmir, Alireza; Bergman, Bo; Andersson, Benjamin; Sturk, Robert; Johansson, Mattis


    Three high-resolution, 5 m shot and receiver spacing using 141-172 receivers, refraction and reflection seismic profiles for the planning of a major underground energy-storage site near the town of Dalby-Lund within the Scania Tornquist suture zone in southwest of Sweden were acquired during August 2015. The site is situated ca. 1 km north of the RFZ (Romeleåsen fault and flexure zone) with a complex geologic and tectonic history. Near vertical dikes are observed from several quarries in the area crosscutting granitic-gneissic-amphibiotic rocks and form clear magnetic lineaments. These dikes likely have also acted as surfaces on which further faulting have occurred. Although a major high-speed and traffic road runs in the middle of the study area, the seismic data show excellent quality particularly for the data along two profiles (profiles 2 and 3) perpendicular to the road, and slightly noisy, due to high wind, for the data along a profile (profile 4) parallel to the road. A bobcat-mounted drop hammer (500 kg) was used to generate the seismic signal. To provide continuity from one side of the road to another, 51 wireless recorders connected to 10 Hz geophones and operating in an autonomous mode were used. GPS times of the source impacts were used to extract the data from the wireless recorders and then merged with the data from the cabled recorders (also 10 Hz geophones). Three shot records per source position were generated and vertically stacked to improve the signal-to-noise ratio. First arrivals are clear in most shot gathers allowing them to be used for traditional refraction seismic data analysis and also for more advanced traveltime tomography. The velocity models obtained through traveltime tomography clearly depict bedrock surface and its undulations and in many places show good correlation with the boreholes recently drilled in the area. At places where bedrock is intersected at greater depths than usual, for example 25 m at one place, depression

  16. Seismic evidence for a possible deep crustal hot zone beneath Southwest Washington

    Flinders, Ashton; Shen, Yang


    Crustal pathways connecting deep sources of melt and the active volcanoes they supply are poorly understood. Beneath Mounts St. Helens, Adams, and Rainier these pathways connect subduction-induced ascending melts to shallow magma reservoirs. Petrogenetic modeling predicts that when these melts are emplaced as a succession of sills into the lower crust they generate deep crustal hot zones. While these zones are increasingly recognized as a primary site for silicic differentiation at a range of volcanic settings globally, imaging them remains challenging. Near Mount Rainier, ascending melt has previously been imaged ~28 km northwest of the volcano, while to the south, the volcano lies on the margin of a broad conductive region in the deep crust. Using 3D full-waveform tomography, we reveal an expansive low-velocity zone, which we interpret as a possible hot zone, linking ascending melts and shallow reservoirs. This hot zone may supply evolved magmas to Mounts St. Helens and Adams, and possibly Rainier, and could contain approximately twice the melt volume as the total eruptive products of all three volcanoes combined. Hot zones like this may be the primary reservoirs for arc volcanism, influencing compositional variations and spatial-segmentation along the entire 1100 km-long Cascades Arc.

  17. Seismic evidence for a possible deep crustal hot zone beneath Southwest Washington.

    Flinders, Ashton F; Shen, Yang


    Crustal pathways connecting deep sources of melt and the active volcanoes they supply are poorly understood. Beneath Mounts St. Helens, Adams, and Rainier these pathways connect subduction-induced ascending melts to shallow magma reservoirs. Petrogenetic modeling predicts that when these melts are emplaced as a succession of sills into the lower crust they generate deep crustal hot zones. While these zones are increasingly recognized as a primary site for silicic differentiation at a range of volcanic settings globally, imaging them remains challenging. Near Mount Rainier, ascending melt has previously been imaged ~28 km northwest of the volcano, while to the south, the volcano lies on the margin of a broad conductive region in the deep crust. Using 3D full-waveform tomography, we reveal an expansive low-velocity zone, which we interpret as a possible hot zone, linking ascending melts and shallow reservoirs. This hot zone may supply evolved magmas to Mounts St. Helens and Adams, and possibly Rainier, and could contain approximately twice the melt volume as the total eruptive products of all three volcanoes combined. Hot zones like this may be the primary reservoirs for arc volcanism, influencing compositional variations and spatial-segmentation along the entire 1100 km-long Cascades Arc.

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

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


    Tectonic models predict that, following breakup, rift margins undergo only decaying thermal subsidence during their post-rift evolution. However, post-breakup stratigraphy beneath the NE Atlantic shelves shows evidence of regional-scale unconformities, commonly cited as outer margin responses to ...... by plate tectonic forces, induced perhaps by a change in the Iceland plume (a hot pulse) and/or by changes in intra-plate stresses related to global tectonics.......Tectonic models predict that, following breakup, rift margins undergo only decaying thermal subsidence during their post-rift evolution. However, post-breakup stratigraphy beneath the NE Atlantic shelves shows evidence of regional-scale unconformities, commonly cited as outer margin responses...... to inner margin episodic uplift, including the formation of coastal mountains. The origin of these events remains enigmatic. We present a seismic reflection study from the Greenland Fracture Zone – East Greenland Ridge (GFZ-EGR) and the NE Greenland shelf. We document a regional intra-Miocene seismic...

  19. Shallow seismic reflection profiling over a Mylonitic Shear Zone, Ruby Mountains-East Humboldt Range Metamorphic Core Complex, NE Nevada

    Hawman, Robert B.; Ahmed, Hishameldin O.

    Seismic reflection profiling carried out with a sledgehammer source has imaged Tertiary extensional structures over a depth range of 45-500 m within lower plate rocks of the Ruby Mountains-East Humboldt Range metamorphic core complex. The 400-m CMP profile straddles an exposed contact between tectonic slices of dolomitic marble and metaquartzite emplaced by low-angle ductile-brittle normal faulting. Subhorizontal reflections from layering within the tectonic slices give way at 160 ms (160-220 m depth) to reflections that dip 15-45° to the east, in contrast with dips indicated in a poorly imaged segment of a coincident regional seismic line but in agreement with dips of foliation mapped for nearby up-plunge exposures of a late Proterozoic - early Cambrian sequence of metaquartzites, marbles, schists, and granitic rocks that forms the bulk of the underlying shear zone. Differences with the regional profile are attributed to the higher frequencies (30-100 Hz) generated by the smaller hammer source and the enhanced lateral resolution provided by the straighter profile and much smaller shot-receiver offsets (46-157 m) contributing to the stack for each CMP. The results suggest that the near-surface, east-dipping component of the anastomozing shear zone extends at least 2 km farther east than previously interpreted. Rough estimates of interval velocities (1500-4500 m/s) inferred from stacking velocities are consistent with velocities of mylonitic rocks measured perpendicular to foliation at low confining pressures when the effects of macroscopic fractures and joints are taken into account. Peaks in amplitude spectra of stacked traces suggest long-wavelength components of layering resolved at scales from 5-8 m (depth: 50 m) to 15-25 m (depth: 500 m).

  20. Mantle transition zone beneath a normal seafloor in the northwestern Pacific: Electrical conductivity, seismic thickness, and water content

    Matsuno, Tetsuo; Suetsugu, Daisuke; Baba, Kiyoshi; Tada, Noriko; Shimizu, Hisayoshi; Shiobara, Hajime; Isse, Takehi; Sugioka, Hiroko; Ito, Aki; Obayashi, Masayuki; Utada, Hisashi


    We conducted a joint electromagnetic (EM) and seismic experiment to reveal the mantle structure beneath a normal seafloor at 130-145 Ma in the northwestern Pacific, where the seafloor is relatively flat and the underlying mantle is expected to be normal (free from tectonic perturbations). In the experiment, we deployed state-of-the-art instruments in two arrays from 2010-2015. Here, we report the result of analyses of the EM and seismic data for investigating the mantle transition zone (MTZ) structure. The EM data analysis revealed that an electrical conductivity structure below both arrays was approximated by an average 1-D model of the north Pacific, and showed a possible downward increase in conductivity at the top of the MTZ. From the P-wave receiver function analysis, perturbations in the MTZ thickness from a global average were estimated to be +20 km and +2 km below the northern and southern arrays, respectively, from which temperature profiles in the MTZ below these two arrays were then estimated. We jointly interpreted the profiles of electrical conductivity and thus estimated temperature, with reference to the experimental values of the effects of water on the electrical conductivities of MTZ minerals (wadsleyite and ringwoodite) from mineral physics. The upper bound of the water content below the northern array was determined to be 0.4 wt.% or 0.04 wt.%, depending on different results of mineral physics, and that below the southern array was determined to be slightly smaller. The lower bound of the water content was not constrained by our data. Our results indicate that the MTZ beneath the normal seafloor in the northwestern Pacific is drier than subduction zones, and may be a water-poor region in a plum-pudding mantle model.

  1. Seismic-sequence stratigraphy and geologic structure of the Floridan aquifer system near "Boulder Zone" deep wells in Miami-Dade County, Florida

    Cunningham, Kevin J.


    The U.S. Geological Survey, in cooperation with the Miami-Dade Water and Sewer Department, acquired, processed, and interpreted seismic-reflection data near the North and South District “Boulder Zone” Well Fields to determine if geologic factors may contribute to the upward migration of injected effluent into that upper part of the Floridan aquifer system designated by the U.S. Environmental Protection Agency as an underground source of drinking water. The depth of the Boulder Zone at the North and South District “Boulder Zone” Well Fields ranges from about 2,750 to 3,300 feet below land surface (ft bls), whereas overlying permeable zones used as alternative drinking water supply range in depth from about 825 to 1,580 ft bls at the North and South District “Boulder Zone” Well Fields. Seismic-sequence stratigraphy and geologic structures imaged on seismic-reflection profiles created for the study describe the part of the Floridan aquifer system overlying and within the Boulder Zone. Features of the Floridan aquifer system underlying the Boulder Zone were not studied because seismic-reflection profiles acquired near the North and South District “Boulder Zone” Well Fields lacked adequate resolution at such depths.

  2. Subduction Zone Geometry and Pre-seismic Tectonic Constraints From the Andaman Micro- plate Region.

    Earnest, A.; Freymueller, J. T.; Rajendran, K.; C. P, R.


    The 2004 Sumatra-Andaman mega-thrust rupture broke along the narrow fore-arc sliver boundary of the Indo- Burmese collision. Earlier events of 1679 (M~7.5), 1941 (M 7.7), 1881 (M~7.9) and 2002 (Mw 7.3) generated spatially restricted ruptures along this margin. Spatio-temporal analysis of the pre-seismic earthquakes showed dense seismicity in the back-arc region but negligible activity towards the trench. The hypocentral distribution highlights the shallow subduction at the northern segment, which becomes steeper and deeper to the south. The pre-earthquake stress distribution, inferred from the P and T-axes of earthquake faulting mechanisms, represents the compressional fore-arc and extensional back-arc stress regimes. Shallow NNE-SSW under- thrusting and NNW-SSE opening up of the marginal sea basin stresses were observed and this trend changes to NE-SW to N-S at intermediate depths. We collected three epochs of campaign mode GPS data along the arc from May 2002 to September 2004. These observations show nearly pure convergence along the Andaman trench prior to the earthquake. During this period the GPS sites moved westward relative to India at ~5.5 mm/yr, consistent with the earlier results. Along arc GPS velocity vectors suggest that the Andaman trench is part of a purely slip partitioned boundary, with the strike- slip component of the India-Sunda relative plate motion being taken up on the transform fault in the Andaman Sea or on the West Andaman Fault, and the convergent component on the Andaman trench. Although near normal convergence was observed, it sampled only a fraction of a possible full Andaman microplate convergence velocity, because elastic deformation from the locked shallow megathrust caused displacements toward the overriding plate, that is, away from India. Based on the Indian plate velocity and Andaman spreading rates, this component amounts to ~85% of the pre-seismic convergence. These geodetic velocities represent the present day geologic

  3. Double-Difference Tomography in the West Bohemia Seismic Zone: A Study of the 2011 Earthquake Swarm

    Löberich, Eric; Alexandrakis, Catherine; Calo, Marco; Vavryčuk, Václav; Buske, Stefan


    Fluid migration, gas springs and particularly earthquake swarms are indications of ongoing geodynamic processes in the Bohemian Massif. This tectonically active region can be subdivided into several microplates, such as the Moldanubian and Saxothuringian and the block of the Teplá-Barrandian, which formed a complex sutured crust during the Variscian collision. Beyond this subdivision, the geological situation of the Bohemian Massif is further defined by the Eger Rift, the Cheb basin and the Smrčiny pluton. Moreover a thinned crust and lithosphere is typical for the region, whereby the seismic activity is controlled by the Mariánske Láznĕ Fault and the Počatky-Plesná Shear Zone. Former investigations have shown a relationship between the activated fault and the occurrence of swarm earthquakes. In this study, the analysis of the 2011 earthquake swarm was in the focus of the consideration, following previous findings from the 2008 earthquake swarm. Here, the aim is to improve the understanding between the mantle fluids and the generation of earthquake swarms in the West Bohemia Seismic Zone. Thereby double-difference tomography (tomoDD) was applied to the 2011 earthquake swarm data, leading to an enhanced location accuracy of the hypocenters and a sharper image of the fault system, which can be further controlled by hypoDD relocations. The rupture time series and clustering are also investigated. Additionally, a 3D velocity model for the P- and S-wave are derived and evaluated by considering the results of synthetic tests. The P- to S- wave velocity ratio, which is sensitive to the presence of fluids, is calculated directly from the P- and S-wave model and interpreted in relation to the potential presence of mantle fluids. In summary, this study combines the past knowledge about the fault systems and swarms, with the newly calculated velocity model, source migration pattern and cluster analysis. Moreover the earthquake characteristics are investigated in

  4. Geodetic and seismic signatures of episodic tremor and slip in the northern Cascadia subduction zone

    Dragert, H.; Wang, K.; Rogers, G.


    Slip events with an average duration of about 10 days and effective total slip displacements of severalc entimetres have been detected on the deeper (25 to 45 km) part of the northern Cascadia subduction zone interface by observing transient surface deformation on a network of continuously recording Global Positioning System (GPS) sites. The slip events occur down-dip from the currently locked, seismogenic portion of the subduction zone, and, for the geographic region around Victoria, British Columbia, repeat at 13 to 16 month intervals. These episodes of slip are accompanied by distinct, low-frequency tremors, similar to those reported in the forearc region of southern Japan. Although the processes which generate this phenomenon of episodic tremor and slip (ETS) are not well understood, it is possible that the ETS zone may constrain the landward extent of megathrust rupture, and conceivable that an ETS event could precede the next great thrust earthquake.

  5. High-resolution shear-wave seismics across the Carlsberg Fault zone south of Copenhagen - Implications for linking Mesozoic and late Pleistocene structures

    Kammann, Janina; Hübscher, Christian; Boldreel, Lars Ole; Nielsen, Lars


    The Carlsberg Fault zone (CFZ) is a NNW-SSE striking structure close to the transition zone between the Danish Basin and the Baltic Shield. We examine the fault evolution by combining very-high-resolution onshore shear-wave seismic data, one conventional onshore seismic profile and marine reflection seismic profiles. The faulting geometry indicates a strong influence of Triassic subsidence and rifting in the Central European Basin System. Growth strata within the CFZ surrounding Höllviken Graben reveal syntectonic sedimentation in the Lower Triassic, indicating the opening to be a result of Triassic rifting. In the Upper Cretaceous growth faulting documents continued rifting. These findings contrast the Late Cretaceous to Paleogene inversion tectonics in neighboring structures, such as the Tornquist Zone. The high-resolution shear-wave seismic method was used to image faulting in Quaternary and Danian layers in the CFZ. The portable compact vibrator source ElViS III S8 was used to acquire a 1150 m long seismic section on the island Amager, south of Copenhagen. The shallow subsurface in the investigation area is dominated by Quaternary glacial till deposits in the upper 5-11 m and Danian limestone below. In the shear-wave profile, we imaged the uppermost 30 m of the western part of CFZ. The complex fault zone comprises normal block faults and one reverse block fault. The observed faults cut through the Danian as well as the Quaternary overburden. Hence, there are strong indicators for ongoing faulting, like mapped faulting in Quaternary sediments and ongoing subsidence of the eastern block of the CFZ as interpreted by other authors. The lack of earthquakes localized in the fault zone implies that either the frequency of occurring earthquakes is too small to be recorded in the observation time-span, or that the movement of the shallow sub-surface layers may be due to other sources than purely tectonic processes.

  6. Edificio de oficinas, en Madrid

    Barbero Rebolledo, M.


    Full Text Available This office building was designed according to a module of 1.60 X 1.60 m, to allow for maximum flexibility in its distribution and optimum adaptation to possible future changes in the internal organisation. The structure is metallic; the external walls are in brick or glass, depending on the zone, and both the internal and external treatment have been wisely chosen in order to follow the two basic principles of functionality and comfort. This building, besides containing the main offices of the Spanish Society of Touring Cars in Madrid, also provides room for a lecture hall, an automobile exhibition hall and a department of electronic computing.Este edificio para oficinas fue proyectado según un módulo de 1,60 x 1,60 m, de tal manera que admitiese la máxima flexibilidad en su distribución y se adaptase a todos los cambios de organización que pudieran presentarse en el futuro. La estructura es metálica; los cerramientos, de ladrillo visto y cristal, según conviene a cada zona; y en su composición y tratamientos exterior e interior se han aunado sabiamente los dos principios básicos de representatividad y confort exigidos. Además de alojar las oficinas centrales de la Sociedad Española de Automóviles de Turismo en Madrid, como elementos singulares dispone de: salón de actos, exposición de automóviles y servicio de ordenador electrónico.

  7. Seismic heating signatures in the Japan Trench subduction plate-boundary fault zone: evidence from a preliminary rock magnetic `geothermometer'

    Yang, Tao; Dekkers, Mark J.; Zhang, Bo


    Frictional heating during earthquake rupture reveals important information on earthquake mechanisms and energy dissipation. The amount of annealing varies widely and is, as yet, poorly constrained. Here we use magnetic susceptibility versus temperature measurements during cycling to increasingly elevated temperatures to constrain the maximum temperature a slip zone has experienced. The case study comprises sheared clay cored from the Japan Trench subduction plate-boundary fault zone (décollement), which accommodated the large slip of the 2011 Mw 9.0 Tohoku-oki earthquake. The décollement was cored during the Integrated Ocean Drilling Program (IODP) Expedition 343, the Japan Trench Fast Drilling Project (JFAST). Heating signatures with estimated maximum temperatures ranging from ˜300 to over 500 °C are determined close to the multiple slip surfaces within the décollement. Since it is impossible to tie a specific slip surface to a certain earthquake, thermal evidence for the cumulative effect of several earthquakes is unveiled. This as yet preliminary rock magnetic `geothermometer' would be a useful tool to detect seismic heating along faults that experienced medium temperature rise, a range which is difficult to assess with other approaches.

  8. Observations at a San Jacinto Fault Zone site (Sage Brush Flat) Using a Nodal Seismic High Frequency Array

    Vernon, F.; Reyes, J. C.; White, M. C. A.; Davis, G. A.; Meyer, J. C.; Sahakian, V. J.; Mancinelli, N. J.; Ben-Zion, Y.; Zigone, D.; Harris, C.; Liu, X.; Qiu, H.; Share, P. E.; Ozakin, Y.; Hollis, D.; Barklage, M.


    Between 7 May 2014 and 13 June 2014 we deployed a tight 1108 element array of 10 Hz vertical geophones in a two-dimensional array with 700 meter aperture centered on the Clark Fault of the San Jacinto Fault Zone. The array was designed to make detailed observations of the shallow damage zone, local failure processes and noise properties of the Clark Fault near the Anza seismic gap. The core of the array consisted of a grid organized with 20 rows perpendicular to and centered on the fault trace, each row with 50 sensors at a nominal 10 meter interstation spacing. The spacing between rows was nominally 30 meters. The remaining 108 sensors were deployed as extensions to multiple rows providing a maximum 700 meter aperture. Each sensor was surveyed using a Real Time Kinematic (RTK) GPS system to an accuracy of approximately 30 cm. The RTK survey was enabled via ad-hoc networking using HPWREN. We will present observations of earthquakes with magnitudes -1 100 kilometers, along with prosperities of local structures and noise characteristics.

  9. Evolution of seismic signals and slip patterns along subduction zones: insights from a friction lab scale experiment

    Voisin, Christophe; Larose, Eric; Renard, François


    Continuous GPS and broadband seismic monitoring have revealed a variety of disparate slip patterns especially in shallow dipping subduction zones, among which regular earthquakes, slow slip events and silent quakes1,2. Slow slip events are sometimes accompanied by Non Volcanic Tremors (NVT), which origin remains unclear3, either related to fluid migration or to friction. The present understanding of the whole menagerie of slip patterns is based upon numerical simulations imposing ad hoc values of the rate and state parameters a and b4-6 derived from the temperature dependence of a and b of a wet granite gouge7. Here we investigate the influence of the cumulative slip on the frictional and acoustic patterns of a lab scale subduction zone. Shallow loud earthquakes (stick-slip events), medium depth slow, deeper silent quakes (smooth sliding oscillations) and deepest steady-state creep (continuous sliding) are reproduced by the ageing of contact interface with cumulative displacement8. The Acoustic Emission evolv...

  10. Seismic response of earth dams considering dynamic properties of unsaturated zone

    Ariyan, M.; Habibagahi, G.; Nikooee, E.


    It is conventionally assumed in the analysis and design of earth dams that the soil located above the phreatic line, i.e. the uppermost seepage flow line, is completely dry. However, there is often an unsaturated flow of water through an unsaturated zone above this borderline and variation in

  11. Seismic response of earth dams considering dynamic properties of unsaturated zone

    Ariyan, M.; Habibagahi, G.; Nikooee, E.


    It is conventionally assumed in the analysis and design of earth dams that the soil located above the phreatic line, i.e. the uppermost seepage flow line, is completely dry. However, there is often an unsaturated flow of water through an unsaturated zone above this borderline and variation in moistu

  12. Casa en Torrelodones, Madrid

    Cubillo de Arteaga, L.


    Full Text Available El monte bajo de la parte norte de Madrid, hacia la sierra, es de una serena y agreste belleza, con alteraciones pronunciadas y conjuntos rocosos de valor ornamental extraordinario. En uno de sus rincones: Torrelodones, y encaramado en la cima de un montículo, con vistas al hermoso paisaje y a las escarpadas montañas, se ha construido una vivienda de dimensiones medias, ocupando unos 200 m2 de planta edificada.

  13. Seismicity in the platform regions of Ukraine in the zones of anomalous electrical conductivity

    Kushnir, A. N.; Kulik, S. N.; Burakhovich, T. K.


    It is established for the first time that there are several regions in Ukraine, in which the earthquakes occurring within platform territory are correlated to the anomalous conductive structures in the Earth's crust and upper mantle. These regions are identified as (1) Donbass and the eastern part of the Dnieper-Donetsk Depression (DDD); (2) eastern margin of the Ingulets-Krivoi Rog suture zone in the area of the Krivoi Rog-Kremenchug fault zone; (3) the western part of the Cis-Azov megablock; (4) the western boundary of the Ukrainian Shield and its slope; (5) North Dobruja and Pre-Dobrujan Depression. The reconstructed tree-dimensional (3D) geoelectrical models of the Earth's crust and upper mantle feature anomalously low values of electric resistivity. The earthquake sources in the platform areas of Ukraine are localized above the top and in the upper parts of the crustal anomalies of electrical conductivity.

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

    Døssing, Arne; Japsen, Peter; Watts, Anthony; Nielsen, Tove; Jokat, Wilfried; Thybo, Hans


    Tectonic models predict that, following breakup, rift margins undergo only decaying thermal subsidence during their post-rift evolution. However, post-breakup stratigraphy beneath the NE Atlantic shelves shows evidence of regional-scale unconformities, commonly cited as outer margin responses to inner margin episodic uplift, including the formation of coastal mountains. The origin of these events remains enigmatic. We present a seismic reflection study from the Greenland Fracture Zone - East Greenland Ridge (GFZ-EGR) and the NE Greenland shelf. We document a regional intra-Miocene seismic unconformity (IMU), which marks the termination of syn-rift deposition in the deep-sea basins and onset of: (i) thermo-mechanical coupling across the GFZ, (ii) basin compression, and (iii) contourite deposition, north of the EGR. The onset of coupling across the GFZ is constrained by results of 2-D flexural backstripping. We explain the thermo-mechanical coupling and the deposition of contourites by the formation of a continuous plate boundary along the Mohns and Knipovich ridges, leading to an accelerated widening of the Fram Strait. We demonstrate that the IMU event is linked to onset of uplift and massive shelf-progradation on the NE Greenland margin. Given an estimated middle-to-late Miocene (~15-10 Ma) age of the IMU, we speculate that the event is synchronous with uplift of the East and West Greenland margins. The correlation between margin uplift and plate-motion changes further indicates that the uplift was triggered by plate tectonic forces, induced perhaps by a change in the Iceland plume (a hot pulse) and/or by changes in intra-plate stresses related to global tectonics.

  15. Constraining the shear zone along the Dead Sea transform fault in the crust and upper mantle using seismic anisotropy

    Kaviani, Ayoub; Rümpker, Georg; Asch, Günter; Desire Group


    We study seismic anisotropy along the Dead Sea Transform fault (DST) by shear-wave splitting analysis of SKS and SKKS waveforms recorded at a dense network of broad-band and short-period stations of the DESIRE experiment. The DST accommodates the relative motion between Africa and Arabia through a sinistral strike-slip motion. The Dead Sea is a pull-apart basin formed along the DST as a result of stepwise fault-normal displacement. The DESIRE array of stations cover this portion of the DST. We measured the splitting parameters (delay times between the fast and slow components of the shear wave and fast polarization direction) in different period bands. We observed consistent fast polarization directions varying from N14W to N19E at different stations and delay times ranging between 1.0 and 2.5 s. Our preliminary examination reveals that the splitting parameters do not exhibit significant frequency dependence. However, we observe variations in the splitting parameters (mostly delay times) along an E-W profile crossing the DST, with smaller delay times in the middle of the profile, within the surface exposure of the DST shear zone, and with two lobes of relatively large delay times on both sides of the central region. The fast polarization directions along this profile change from a dominant NNW trend in the western side of the DST to a general N-S orientation in the central part and a dominant NNE trend to the east. Waveform modeling is required to infer the lateral and depth variations of the strength and orientation of anisotropy in the crust and upper mantle from these observations. We will also complement our results with the data from the DESERT experiment to provide an overall pattern of seismic anisotropy and structural fabric beneath the DST and surrounding regions from the north of the Dead Sea down to the Red sea.

  16. Mantle transition zone beneath a normal seafloor in the northwestern Pacific: Electrical conductivity, seismic discontinuity, and water content

    Matsuno, Tetsuo; Suetsugu, Daisuke; Utada, Hisashi; Baba, Kiyoshi; Tada, Noriko; Shimizu, Hisayoshi; Shiobara, Hajime; Isse, Takehi; Sugioka, Hiroko; Ito, Aki


    We conducted a joint electromagnetic and seismic field experiment to probe water content reserved in the mantle transition zone (MTZ) beneath a normal seafloor around the Shatsky Rise in the northwestern Pacific. Specifically for the investigation of the MTZ structure, we developed new ocean bottom instruments for providing higher S/N ratio data and having higher mobility in field experiment than ever. We installed our state-of-the-art instruments in two arrays to the north and south of the Shatsky Rise for 5 years from 2010 to 2015. We first analyzed data obtained in our and previous studies to elucidate an electrical conductivity structure through the magnetotelluric and geomagnetic depth sounding methods and seismic discontinuity depths or thickness of the MTZ through the P-wave receiver function method. An electrical conductivity structure beneath two observational arrays is represented well by an average 1-D model beneath the northern Pacific. A MTZ thickness beneath the north array is thicker than a global average of MTZ thickness by 22 km, and that beneath the south array is similar to the average. For estimating water content in the MTZ, we implemented a series of forward modeling of the electromagnetic responses based on the average 1-D electrical conductivity model, temperature profiles of the MTZ involving temperature anomalies estimated from the MTZ thickness perturbations, and electrical conductivities of dry and hydrous MTZ materials (wadsleyite and ringwoodite). A result of the forward modeling indicates that the maximum water content in the MTZ beneath the north array is 0.5 wt.%.

  17. Crustal structure of the Trans-European suture zone region along POLONAISE'97 seismic profile P4

    Grad, Marek; Jensen, Susanne L.; Keller, G. Randy; Guterch, Aleksander; Thybo, Hans; Janik, Tomasz; Tiira, Timo; Yliniemi, Jukka; Luosto, Urmas; Motuza, Gediminas; Nasedkin, Viktor; Czuba, Wojciech; GaczyńSki, Edward; ŚRoda, Piotr; Miller, Kate C.; Wilde-Piórko, Monika; Komminaho, Kari; Jacyna, Juozas; Korabliova, Larisa


    The large-scale POLONAISE'97 seismic experiment investigated the velocity structure of the crust and upper mantle in the Trans-European suture zone (TESZ) region between the Precambrian east European craton (EEC) and Paleozoic platform that comprises terranes added during the Caledonian and Variscan orogenies (530-370 and 370-225 Ma, respectively). This experiment included 64 shots recorded by 613 seismic stations during two deployments. Very good quality data were recorded along five profiles, and the longest and most important one (P4) is the focus of this paper. Clear first arrivals and later phases of waves reflected/refracted in the crust and Moho were interpreted using two-dimensional (2-D) tomographic inversion and ray-tracing techniques. The crustal thickness along the profile varies from 30-35 km in the Paleozoic platform area to ˜40 km below and due northeast of the TESZ, to ˜43 km in the Polish part of the EEC, and to ˜50 km in Lithuania. The Paleozoic platform and EEC are divided by the Polish basin, so the upper crustal structure varies considerably. In the area of the Polish basin, the P wave velocity is very low (VP < 6.1 km/s) down to depths of 15-20 km, indicating that a very thick sedimentary sequence is present. We suggest two possible tectonic interpretations of the velocity models: (1) Baltica indented Avalonia, obducting its upper crust and underthrusting its lower crust in a tectonic flake structure and (2) a rifted margin of Baltica underlies the Polish basin. This model is similar to other interpretations of seismic profiles recorded in the Baltic Sea. The second model implies that the Paleozoic platform solely consists of Avalonian lithosphere and the EEC of Baltica lithosphere. It offers a simple explanation of the difference in crustal thickness of the two platforms. It also implies that the Caledonian and Variscan orogenies in this area were relatively "soft" collisions that left this continental margin largely intact.

  18. Quantifying Regional Body Wave Attenuation in a Seismic Prone Zone of Northeast India

    Bora, Nilutpal; Biswas, Rajib


    We evaluated the body wave attenuation parameter in Kopili region of northeast India. Using the modified algorithm of coda normalization method, we delineated frequency-dependent attenuation for both P and S waves. Taking more than 300 seismograms as input, we comprehensively studied microearthquake spectra in the frequency range of 1.5-12 Hz. The estimated values of {Q}_{P}^{-1} and {Q}_{S}^{-1} show strong frequency dependence. Based on this, we formulated empirical relationships corresponding to {Q}_{P}^{-1} and {Q}_{S}^{-1} for the study region. The relationships emerge to be {Q}_{P}^{-1} = ( {23.8 ± 6} ) × 10^{-3} {f}^{{( {-1.2 ± 0.008} )}} and {Q}_{S}^{-1} = ( {10.2 ± 2} ) × 10^{-3} {f}^{{( {-1.3 ± 0.02} )}} , respectively. The ratio {Q}_{P}^{-1} /{Q}_{S}^{-1} is found to be larger than unity for the entire frequency band which implies profound seismic activity and macroscale heterogeneity prevailing in the region. The study may act as the building block towards determination of source parameter and hazard-related studies in the region.

  19. Validation of tectonic models for an intraplate seismic zone, Charleston, South Carolina, with GPS geodetic data

    Talwani, P.; Kellogg, J.N.; Trenkamp, R. [South Carolina Univ., Columbia, SC (United States). Dept. of Geological Sciences


    Although the average strain rate in intraplate settings is 2--3 orders of magnitude lower than at plate boundaries, there are pockets of high strain rates within intraplate regions. The results of a Global Positioning System survey near the location of current seismicity (and the inferred location of the destructive 1886 Charleston, South Carolina earthquake) suggest that there is anomalous strain build-up occurring there. By reoccupying 1930 triangulation and 1980 GPS sites with six Trimble SST dual frequency receivers, a strain rate of 0.4 {times} 10{sup {minus}7} yr{sup {minus}1} was observed. At the 95% confidence level, this value is not significant; however, at a lower level of confidence ({approximately} 85%) it is about two orders of magnitude greater than the background of 10{sup {minus}9} to 10{sup {minus}10} yr{sup {minus}1}. The direction of contraction inferred from the GPS survey 66{degree} {+-} 11{degree} is in excellent agreement with the direction of the maximum horizontal stress (N 60{degree} E) in the area, suggesting that the observed strain rate is also real. 66 refs.

  20. Full waveform modelling using the VERCE platform - application to aftershock seismicity in the Chile subduction zone

    Garth, Thomas; Rietbrock, Andreas; Hicks, Steve; Fuenzalida Velasco, Amaya; Casarotti, Emanuele; Spinuso, Alessandro


    The VERCE platform is an online portal that allows full waveform simulations to be run for any region where a suitable velocity model exists. We use this facility to simulate the waveforms from aftershock earthquakes from the 2014 Pisagua earthquake, and 2010 Maule earthquake that occurred at the subduction zone mega thrust in Northern and Central Chile respectively. Simulations are performed using focal mechanisms from both global earthquake catalogues, and regional earthquake catalogues. The VERCE platform supports specFEM Cartesian, and simulations are run using meshes produced by CUBIT. The full waveform modelling techniques supported on the VERCE platform are used to test the validity of a number of subduction zone velocity models from the Chilean subduction zone. For the Maule earthquake we use a 2D and 3D travel time tomography model of the rupture area (Hicks et al. 2011; 2014). For the Pisagua earthquake we test a 2D/3D composite velocity model based on tomographic studies of the region (e.g. Husen et al. 2000, Contreyes-Reyes et al. 2012) and slab1.0 (Hayes et al. 2012). Focal mechanisms from the cGMT catalogue and local focal mechanisms calculated using ISOLA (e.g. Agurto et al. 2012) are used in the simulations. The waveforms produced are directly compared to waveforms recorded on the temporary deployment for the Maule earthquake aftershocks, and waveforms recorded on the IPOC network for the Pisagua earthquake aftershocks. This work demonstrates how the VERCE platform allows waveforms from the full 3D simulations to be easily produced, allowing us to quantify the validity of both the velocity model and the source mechanisms. These simulations therefore provide an independent test of the velocity models produced synthetically and by travel time tomography studies. Initial results show that the waveform is reasonably well reproduced in the 0.05 - 0.25 frequency band using a refined 3D travel time tomography, and locally calculated focal mechanisms.

  1. Interseismic coupling and seismic potential along the Central Andes subduction zone

    Chlieh, Mohamed; Perfettini, Hugo; Tavera, Hernando; Avouac, Jean-Philippe; Remy, Dominique; Nocquet, Jean-Mathieu; Rolandone, Frédérique; Bondoux, Francis; Gabalda, Germinal; Bonvalot, Sylvain


    We use about two decades of geodetic measurements to characterize interseismic strain build up along the Central Andes subduction zone from Lima, Peru, to Antofagasta, Chile. These measurements are modeled assuming a 3-plate model (Nazca, Andean sliver and South America Craton) and spatially varying interseismic coupling (ISC) on the Nazca megathrust interface. We also determine slip models of the 1996 M(w) = 7.7 Nazca, the 2001 M(w) = 8.4 Arequipa, the 2007 M(w) = 8.0 Pisco and the M(w) = 7....

  2. Crustal Structure Across the Okavango Rift Zone, Botswana: Initial Results From the PRIDE-SEISORZ Active-Source Seismic Profile

    Canales, J. P.; Moffat, L.; Lizarralde, D.; Laletsang, K.; Harder, S. H.; Kaip, G.; Modisi, M.


    The PRIDE project aims to understand the processes of continental rift initiation and evolution by analyzing along-axis trends in the southern portion of the East Africa Rift System, from Botswana through Zambia and Malawi. The SEISORZ active-source seismic component of PRIDE focused on the Okavango Rift Zone (ORZ) in northwestern Botswana, with the main goal of imaging the crustal structure across the ORZ. This will allow us to estimate total crustal extension, determine the pattern and amount of thinning, assess the possible presence of melt within the rift zone, and assess the contrasts in crustal blocks across the rift, which closely follows the trend of a fold belt. In November 2014 we conducted a crustal-scale, 450-km-long seismic refraction/wide-angle reflection profile consisting of 19 sources (shots in 30-m-deep boreholes) spaced ~25 km apart from each other, and 900 receivers (IRIS/PASSCAL "Texan" dataloggers and 4.5Hz geophones) with ~500 m spacing. From NW to SE, the profile crosses several tectonic domains: the Congo craton, the Damara metamorphic belt and the Ghanzi-Chobe fold belt where the axis of the ORZ is located, and continues into the Kalahari craton. The record sections display clear crustal refraction (Pg) and wide-angle Moho reflection (PmP) phases for all 17 of the good-quality shots, and a mantle refraction arrival (Pn), with the Pg-PmP-Pn triplication appearing at 175 km offset. There are distinct changes in the traveltime and amplitude of these phases along the transect, and on either side of the axis, that seem to correlate with sharp transitions across tectonic terrains. Initial modeling suggests: (1) the presence of a sedimentary half-graben structure at the rift axis beneath the Okavango delta, bounded to the SE by the Kunyere-Thamalakane fault system; (2) faster crustal Vp in the domains to the NW of the ORZ; and (3) thicker crust (45-50 km) at both ends of the profile within the Congo and Kalahari craton domains than at the ORZ and

  3. On the duration of seismic motion incident onto the Valley of Mexico for subduction zone earthquakes

    Shapiro, Nikolai M.; Olsen, Kim B.; Singh, K.


    We have used finite difference simulations in 2-D models of the lithosphere to estimate the duration of long-period (>2 s) ground motion incident onto the Valley of Mexico for subduction zone earthquakes. Our simulations suggest that two heterogeneous structures extend the duration of the ground motion between the subduction zone and Mexico City by more than 1 min: (1) the Mexican Volcanic Belt and (2) two low-velocity layers in the coastal region; the accretionary prism and the water layer. The duration generated by a crustal model including these structures is similar to that for earthquake records observed in between the coast and Mexico City. In the Valley of Mexico, our models including only regional-scale heterogeneity reproduce approximately one half of the observed duration. The results suggest that both the regional- and the local-scale low-velocity structures must be taken into account in order to explain the observed extended signal duration in the Valley of Mexico.

  4. Seismic attribute detection of faults and fluid pathways within an active strike-slip shear zone: New insights from high-resolution 3D P-Cable™ seismic data along the Hosgri Fault, offshore California

    Kluesner, Jared; Brothers, Daniel


    Poststack data conditioning and neural-network seismic attribute workflows are used to detect and visualize faulting and fluid migration pathways within a 13.7 km2 13.7 km2 3D P-Cable™ seismic volume located along the Hosgri Fault Zone offshore central California. The high-resolution 3D volume used in this study was collected in 2012 as part of Pacific Gas and Electric’s Central California Seismic Imaging Project. Three-dimensional seismic reflection data were acquired using a triple-plate boomer source (1.75 kJ) and a short-offset, 14-streamer, P-Cable system. The high-resolution seismic data were processed into a prestack time-migrated 3D volume and publically released in 2014. Postprocessing, we employed dip-steering (dip and azimuth) and structural filtering to enhance laterally continuous events and remove random noise and acquisition artifacts. In addition, the structural filtering was used to enhance laterally continuous edges, such as faults. Following data conditioning, neural-network based meta-attribute workflows were used to detect and visualize faults and probable fluid-migration pathways within the 3D seismic volume. The workflow used in this study clearly illustrates the utility of advanced attribute analysis applied to high-resolution 3D P-Cable data. For example, results from the fault attribute workflow reveal a network of splayed and convergent fault strands within an approximately 1.3 km wide shear zone that is characterized by distinctive sections of transpressional and transtensional dominance. Neural-network chimney attribute calculations indicate that fluids are concentrated along discrete faults in the transtensional zones, but appear to be more broadly distributed amongst fault bounded anticlines and structurally controlled traps in the transpressional zones. These results provide high-resolution, 3D constraints on the relationships between strike-slip fault mechanics, substrate deformation, and fluid migration along an active

  5. Seismic micro-zoning in the alpine valleys and local application in urban planning regulations

    Stéphane Cartier


    Full Text Available Confrontées au risque sismique, les vallées sédimentaires alpines testent différentes solutions politiques pour transcrire en règles d’urbanisme les connaissances apportées par les micro-zonages. France, Italie, Slovénie et Suisse composent avec leur tradition politique et l’adoption de codes européens pour améliorer la sécurité selon la vulnérabilité et la géologie locales.Management of earthquake risks in the sedimentary valleys of the Alps depends on the ability to transcribe scientific knowledge obtained from micro-zoning into urban planning regulations. France, Italy, Slovenia and Switzerland are working with new European codes, and within their respective political contexts, to improve earthquake safety on the basis of enhanced input on local geological conditions and vulnerability levels.

  6. Ground motion parameters of Shillong plateau: One of the most seismically active zones of northeastern India

    Saurabh Baruah; Santanu Baruah; Naba Kumar Gogoi; Olga Erteleva; Felix Aptikaev; J.R.Kayal


    Strong ground motion parameters for Shillong plateau of northeastern India are examined. Empirical relations are obtained for main parameters of ground motions as a function of earthquake magnitude, fault type, source depth, velocity characterization of medium and distance. Correlation between ground motion parameters and characteristics of seismogenic zones are established. A new attenuation relation for peak ground acceleration is developed, which predicts higher expected PGA in the region. Parameters of strong motions, particularly the predominant periods and duration of vibrations, depend on the morphology of the studied area. The study measures low estimates of logarithmic width in Shillong plateau. The attenuation relation estimated for pulse width critically indicates increased pulse width dependence on the logarithmic distance which accounts for geometrical spreading and anelastic attenuation.

  7. Use of 3D Seismic Azimuthal Iso-Frequency Volumes for the Detection and Characterization of High Porosity/Permeability Zones in Carbonate Reservoirs

    Toelle, Brian E.

    Among the most important properties controlling the production from conventional oil and gas reservoirs is the distribution of porosity and permeability within the producing geologic formation. The geometry of the pore space within these reservoirs, and the permeability associated with this pore space geometry, impacts not only where production can occur and at what flow rates but can also have significant influence on many other rock properties. Zones of high matrix porosity can result in an isotropic response for certain reservoir properties whereas aligned porosity/permeability, such as open, natural fracture trends, have been shown to result in reservoirs being anisotropic in many properties. The ability to identify zones within a subsurface reservoir where porosity/permeability is significantly higher and to characterize them according to their geometries would be of great significance when planning where new boreholes, particularly horizontal boreholes, should be drilled. The detection and characterization of these high porosity/permeability zones using their isotropic and anisotropic responses may be possible through the analysis of azimuthal (also referred to as azimuth-limited) 3D seismic volumes. During this study the porosity/permeability systems of a carbonate, pinnacle reef within the northern Michigan Basin undergoing enhanced oil recovery were investigated using selected seismic attributes extracted from azimuthal 3D seismic volumes. Based on the response of these seismic attributes an interpretation of the geometry of the porosity/permeability system within the reef was made. This interpretation was supported by well data that had been obtained during the primary production phase of the field. Additionally, 4D seismic data, obtained as part of the CO2 based EOR project, supported reservoir simulation results that were based on the porosity/permeability interpretation.

  8. The movement age of hidden fault and analysis on width of its effect zone from shallow seismic sounding and drilling data

    杨晓平; 李德庆; 赵成斌; 刘保金; 孙振国; 赵景尧


    Field experimental seismic sounding permitted us to obtain optimal shallow seismic reflection sounding parame-ters. In process of data processing, we obtained a high-qualitative shallow seismic reflection sounding profile byusing the techniques such as filtering, edition surgical blanking, prediction deconvolution, fitting static correlationof first arrival time, and velocity analysis. Comprehensive analysis on the information of reflection wave groupsalong the seismic sounding profile and the stratigraphic and neogeochronological data obtained from many drillsnear the sounding line reveals that the upper termination of the detected fault zone is located at depth of 75~80 m,in the Middle Pleistocene deposits dated to be about 220 ka BP. The continuity, discontinuity, increasing and de-creasing amount of reflection wave groups and change of their configurations, in combination with geologicalcolumns of drills, permitted us to know that the width of upper termination of the fault zone is 100 m. It can beinferred from the variation of number of reflection wave groups along the profile that the scarp of hidden fault is200 m wide and the fault is a synsedimentary active fault in the Early Pleistocene and the early stage of MiddlePleistocene. No tectonic movement, which offset the covering deposits, had occurred since the late stage of Middle Pleistocene.

  9. Upper plate deformation and seismic barrier in front of Nazca subduction zone : the Chololo Fault System and active tectonics along the Coastal Cordillera, southern Peru

    Audin, Laurence; Lacan, P.; Tavera, H.; Bondoux, Francis


    The South America plate boundary is one of the most active subduction zone. The recent Mw=8.4 Arequipa 2001 earthquake ruptured the subduction plane toward the south over 400 km and stopped abruptly on the Ilo Peninsula. In this exact region, the subduction seismic crisis induced the reactivation of continental fault systems in the coastal area. We studied the main reactivated fault system that trends perpendicular to the trench by detailed mapping of fault related-geomorphic features. Also, ...

  10. Post-seismic velocity changes along the 2008 M7.9 Wenchuan earthquake rupture zone revealed by S coda of repeating events

    Li, Le; Niu, Fenglin; Chen, Qi-Fu; Su, Jinrong; He, Jiabin


    We investigated post-seismic velocity changes within the fault zone of the 2008 M7.9 Wenchuan earthquake using coda wave data of repeating small earthquakes. We employed template matching and grid search methods to identify well-defined repeating earthquakes in order to minimize artefacts induced by variations in source location. We identified a total of 12 isolated patches in the fault zone that ruptured more than twice in a 1 yr period after the M7.9 earthquake. We applied the coda wave interferometry technique to the waveform data of the 34 identified repeating earthquakes to estimate velocity changes between the first and subsequent events in each cluster. We found that major post-seismic velocity changes occurred in the southwestern part of the rupture area, where the main rupture was initiated and characterized by thrust motion, while the Beichuan area in the northeastern part of the rupture zone appears to experience very little post-seismic velocity changes.

  11. The nexus of soil radon and hydrogen dynamics and seismicity of the northern flank of the Kuril-Kamchatka subduction zone

    O. P. Malysheva


    Full Text Available The comparison of kinematics and dynamic parameters of radon and molecular hydrogen concentration in subsoil air on the stations network at the Petropavlovsk-Kamchatsky geodynamic proving ground with seismicity of the northern flank of the Kuril-Kamchatka subduction zone was fulfilled in the period from July till August 2004. On the basis of correlation analysis of the regional seismicity and variations of radon flux density calculated using the data of gas-discharge counters of STS-6 type and SSNTDs it was shown that the radon mass transfer abnormal variations are conditioned by both regional seismicity in total and the subduction zone of proving ground. The azimuths of «geodeformation waves» coming to the registration points are calculated during clearly expressed anomaly beginnings, which coincide with directions to earthquake epicenters taking place at the same time. The geochemical anomalies recorded are presumptively deformative by nature and can be conditioned by processes of «quasi-viscous» flow of the lithosphere during rearrangement of tectonic stress fields of the subduction zone. The short-term (predicted time ? <14 days precursor of the earthquakes swarm was revealed in hydrogen dynamics on August, 4-5 (four earthquakes had M?5.3 and epicentral distance about 130 km from the Paratunka base station.

  12. Increasing seismicity in the U. S. midcontinent: Implications for earthquake hazard

    Ellsworth, William L.; Llenos, Andrea L.; McGarr, Arthur F.; Michael, Andrew J.; Rubinstein, Justin L.; Mueller, Charles S.; Petersen, Mark D.; Calais, Eric


    Earthquake activity in parts of the central United States has increased dramatically in recent years. The space-time distribution of the increased seismicity, as well as numerous published case studies, indicates that the increase is of anthropogenic origin, principally driven by injection of wastewater coproduced with oil and gas from tight formations. Enhanced oil recovery and long-term production also contribute to seismicity at a few locations. Preliminary hazard models indicate that areas experiencing the highest rate of earthquakes in 2014 have a short-term (one-year) hazard comparable to or higher than the hazard in the source region of tectonic earthquakes in the New Madrid and Charleston seismic zones.

  13. Evidence for New Madrid earthquakes in A.D. 300 and 2350 B.C

    Tuttle, M.P.; Schweig, E. S.; Campbell, J.; Thomas, P.M.; Sims, J.D.; Lafferty, R. H.


    Six episodes of earthquake-induced liquefaction are associated with soil horizons containing artifacts of the Late Archaic (3000-500 B.C.) and Early to Middle Woodland (500 B.C.-A.D. 400) cultural periods at the Burkett archaeological site in the northern part of the New Madrid seismic zone, where little information about prehistoric earthquakes has been available. Radiocarbon dating of organic material and analysis of artifacts are used to estimate the ages of the liquefaction features and times of the causative earthquakes. The most recent episode of liquefaction occurred after A.D. 1670, produced small sand dikes, and is probably related to the 1895 Charleston, Missouri earthquake. The preceding episode struck the area in A.D. 300 ?? 200 years and generated a sand blow that contains Late Woodland artifacts and buries an Early to Middle Woodland cultural horizon. Four older episodes of liquefaction occurred in 2350 B.C. ?? 200 years and may have been produced by a sequence of closely timed earthquakes. The four earlier episodes produced graben structures, sand dikes, and associated sand blows on which a cultural mound was constructed. The Burkett liquefaction features that formed about 2350 B.C. and A.D. 300 are relatively large and similar in age to other liquefaction features in northeastern Arkansas and southeastern Missouri, respectively. If the prehistoric features at the Burkett site and those of similar age elsewhere in the region are the result of the same earthquakes, then this suggests that they were similar in size to the three largest (M 7-8) 1811-1812 New Madrid earthquakes. A New Madrid-type earthquake in A.D. 300 ?? 200 years would support an average recurrence time of 500 years. Although this study extends the earthquake chronology back to 2500 B.C., it is uncertain that the record of New Madrid events is complete for the period between 2350 B.C. and A.D. 300. As demonstrated by this study, information about other prehistoric earthquakes may be

  14. Active seismic monitoring of changes of the reflection response of a crystalline shear zone due to fluid injection in the crust at the Continental Deep Drilling Site, Germany

    Beilecke, T.; Kurt, B.; Stefan, B.


    In theory and in the laboratory variations of the hydraulic pressure can be detected with seismic methods: A lowering of the hydraulic pressure leads to the closure of micro-cracks within the rock (increase of the differential or effective pressure). Subsequently, the seismic velocities increase. An increase of the hydraulic pressure leads to reverse seismic effects. Consequently, seismic impedance contrasts and associated reflection amplitudes vary in the case of a propagating fluid pressure front in a rock matrix with inhomogeneous permeability - as is the case at shear zones. The largest amplitude changes can be expected with vertical ray inclination on the impedance contrast. Generally, the expected effects are small however (Kaselow, 2004). The practical utilization of active seismics for the detection of pressure changes at large scale in hard rock is currently being studied at the Continental Deep Drilling Site (KTB). The injection of water (200 l/min) in a depth of about 4000 m into the so-called SE2 shear zone in the KTB pilot hole was monitored with active seismics between May 2004 and April 2005. The core of the experiment layout is a fixed 5-arm geophone array consisting of 24 3-component geophones, buried at about 70 cm depth. The source signal is a vertical vibrator sweep of 30 s length with the spectrum 30-120 Hz. The signal is sent into the ground 32 times during each cycle, detected with the array and recorded separately for each geophone channel, without prior correlation with the source signal. This allows maximum post-processing with seismic processing and analysis tools and especially permits the use of array properties to increase the signal-to-noise ratio. Critical parameters of the experiment are the repeatability of the source signal as well as the stability of the receiver properties. Another pivot is the hydraulic pressure and its distribution built up within the rock matrix. Estimations based on model calculations show that a change of

  15. Ground motion-simulations of 1811-1812 New Madrid earthquakes, central United States

    Ramirez-Guzman, L.; Graves, Robert; Olsen, Kim B.; Boyd, Oliver; Cramer, Chris H.; Hartzell, Stephen; Ni, Sidao; Somerville, Paul G.; Williams, Robert; Zhong, Jinquan


    We performed a suite of numerical simulations based on the 1811–1812 New Madrid seismic zone (NMSZ) earthquakes, which demonstrate the importance of 3D geologic structure and rupture directivity on the ground‐motion response throughout a broad region of the central United States (CUS) for these events. Our simulation set consists of 20 hypothetical earthquakes located along two faults associated with the current seismicity trends in the NMSZ. The hypothetical scenarios range in magnitude from M 7.0 to 7.7 and consider various epicenters, slip distributions, and rupture characterization approaches. The low‐frequency component of our simulations was computed deterministically up to a frequency of 1 Hz using a regional 3D seismic velocity model and was combined with higher‐frequency motions calculated for a 1D medium to generate broadband synthetics (0–40 Hz in some cases). For strike‐slip earthquakes located on the southwest–northeast‐striking NMSZ axial arm of seismicity, our simulations show 2–10 s period energy channeling along the trend of the Reelfoot rift and focusing strong shaking northeast toward Paducah, Kentucky, and Evansville, Indiana, and southwest toward Little Rock, Arkansas. These waveguide effects are further accentuated by rupture directivity such that an event with a western epicenter creates strong amplification toward the northeast, whereas an eastern epicenter creates strong amplification toward the southwest. These effects are not as prevalent for simulations on the reverse‐mechanism Reelfoot fault, and large peak ground velocities (>40  cm/s) are typically confined to the near‐source region along the up‐dip projection of the fault. Nonetheless, these basin response and rupture directivity effects have a significant impact on the pattern and level of the estimated intensities, which leads to additional uncertainty not previously considered in magnitude estimates of the 1811–1812 sequence based only on historical

  16. Cockade-textured cataclasite and silica gel from damage zone in carbonated ultramafics: markers of cycles of seismic activity?

    Scarsi, Marco; Crispini, Laura; Garofalo, Paolo; Capponi, Giovanni


    Shallow crustal processes occurring during seismic slips and generating fracture networks are of great interest due to their complex interplay with a spectrum of other geological processes . Our study focuses on faults with peculiar core textures, similar to those of "cockade breccia" (Genna et al., 1996) and "clast cortex grains" (Rempe et al., 2014), and on their relation with syntectonic hydrothermal alteration linked with Au bearing-quartz and chalcedony veins. Our work aims to study the enviromental conditions for the formation of such peculiar texture, their relation with the hydrothermal vein system and their potential as shallow seismic indicators. We present field, microstructural and petrochemical data of a peculiar damage zone of fault rocks located in carbonated peridotites and serpentinites of the Ligurian Alps (Voltri Massif, Italy). These are mainly reverse faults, which are coeval with syntectonic Au-bearing quartz veins and chalcedony veins (Giorza et al., 2010), in which lherzolites occupy the hangingwall of the faults and serpentinites the footwall. The fault rocks show evidence for carbonation, as olivine and serpentine are clearly transformed into an assemblage made of magnesite, dolomite and minor ankerite. The damage zones of the faults are serpentinite-rich and about 10 m in thickness, while the cataclasite cores are carbonate-rich and ca. 1 m thick. The top of the fault core shows the occurrence of a chalcedony shear veins with chatter marks and slikenlines on the surface. The "cockade breccia" is made of spherical aggregates of Fe-Mg carbonates and are 1 mm to 3 cm in size. These aggregates show cores of microcrystalline Fe-Mg carbonates, and concentric outer layers of relatively coarser Fe-Mg carbonates with radial or laminated texture. In some cases, these aggregates show evidence for rotation along secondary slip zones. We interpret all these features as the products of chemical interaction between the olivine and serpentine initially

  17. Monitoring of crustal seismic velocity variations in the L'Aquila fault zone inferred from noise cross-correlation

    Soldati, Gaia; Zaccarelli, Lucia; Faenza, Licia; Michelini, Alberto


    The relative seismic velocity variations possibly associated to large earthquakes can be readily monitored via cross-correlation of seismic noise. In a recently published study, more than 2 yr of continuous seismic records have been analysed from three stations surrounding the epicentre of the 2009 April 6, Mw 6.1 L'Aquila earthquake, observing a clear decrease of seismic velocities likely corresponding to the co-seismic shaking. Here, we extend the analysis in space, including seismic stations within a radius of 60 km from the main shock epicentre, and in time, collecting 5 yr of data for the six stations within 40 km of it. Our aim is to investigate how far the crustal damage is visible through this technique, and to detect a potential post-seismic recovery of velocity variations. We find that the co-seismic drop in velocity variations extends up to 40 km from the epicentre, with spatial distribution (maximum around the fault and in the north-east direction from it) in agreement with the horizontal co-seismic displacement detected by global positioning system (GPS). In the first few months after L'Aquila earthquake, the crust's perturbation in terms of velocity variations displays a very unstable behaviour, followed by a slow linear recovery towards pre-earthquake conditions; by almost 4 yr after the event, the co-seismic drop of seismic velocity is not yet fully recovered. The strong oscillations of the velocity changes in the first months after the earthquake prevent to detect the fast exponential recovery seen by GPS data. A test of differently parametrized fitting curves demonstrate that the post-seismic recovery is best explained by a sum of a logarithmic and a linear term, suggesting that processes like viscoelastic relaxation, frictional afterlip and poroelastic rebound may be acting concurrently.

  18. Offshore double-planed shallow seismic zone in the NE Japan forearc region revealed by sP depth phases recorded by regional networks

    Gamage, S.S.N.; Umino, N.; Hasegawa, A.; Kirby, S.H.


    We detected the sP depth phase at small epicentral distances of about 150 km or more in the seismograms of shallow earthquakes in the NE Japan forearc region. The focal depths of 1078 M > 3 earthquakes that occurred from 2000 to 2006 were precisely determined using the time delay of the sP phase from the initial P-wave arrival. The distribution of relocated hypocentres clearly shows the configuration of a double-planed shallow seismic zone beneath the Pacific Ocean. The upper plane has a low dip angle near the Japan Trench, increasing gradually to ???30?? at approximately 100 km landward of the Japan Trench. The lower plane is approximately parallel to the upper plane, and appears to be the near-trench counterpart of the lower plane of the double-planed deep seismic zone beneath the land area. The distance between the upper and lower planes is 28-32 km, which is approximately the same as or slightly smaller than that of the double-planed deep seismic zone beneath the land area. Focal mechanism solutions of the relocated earthquakes are determined from P-wave initial motion data. Although P-wave initial motion data for these offshore events are not ideally distributed on the focal sphere, we found that the upper-plane events that occur near the Japan Trench are characterized by normal faulting, whereas lower-plane events are characterized by thrust faulting. This focal mechanism distribution is the opposite to that of the double-planed deep seismic zone beneath the land area. The characteristics of these focal mechanisms for the shallow and deep doubled-planed seismic zones can be explained by a bending-unbending model of the subducting Pacific plate. Some of relocated earthquakes took place in the source area of the 1933 Mw8.4 Sanriku earthquake at depths of 10-23 km. The available focal mechanisms for these events are characterized by normal faulting. Given that the 1933 event was a large normal-fault event that occurred along a fault plane dipping landward, the

  19. Slab stagnation and buckling in the mantle transition zone: Rheology, phase transition, trench migration, and seismic structure

    Bina, Craig; Cizkova, Hana


    Subducting slabs may exhibit buckling instabilities and consequent folding behavior in the mantle transition zone for various combinations of dynamical parameters, accompanied by temporal variations in dip angle, plate velocity, and trench retreat. Parameters governing such behavior include both viscous forces (slab and mantle rheology) and buoyancy forces (slab thermal structure and mineral phase relations). 2D numerical experiments show that many parameter sets lead to slab deflection at the base of the transition zone, typically accompanied by quasi-periodic oscillations (consistent with previous scaling analyses) in largely anticorrelated plate and rollback velocities, resulting in undulating stagnant slabs as buckle folds accumulate subhorizontally atop the lower mantle. Slab interactions with mantle phase transitions are important components of this process (Bina and Kawakatsu, 2010; Čížková and Bina, 2013). For terrestrial parameter sets, trench retreat is found to be nearly ubiquitous, and trench advance is quite rare - due to both rheological structure and ridge-push effects (Čížková and Bina, 2013). Recent analyses of global plate motions indicate that significant trench advance is also rare on Earth, being largely restricted to the Izu-Bonin arc (Matthews et al., 2013). Consequently, we explore the conditions necessary for terrestrial trench advance through dynamical models involving the unusual geometry associated with the Philippine Sea region. Detailed images of buckled stagnant slabs are difficult to resolve due to smoothing effects inherent in seismic tomography, but velocity structures computed for compositionally layered slabs, using laboratory data on relevant mineral assemblages, can be spatially low-pass filtered for comparison with tomographic images of corresponding resolution. When applied to P-wave velocity anomalies from stagnant slab material beneath northeast China, model slabs which undulate due to compound buckling fit

  20. Upper plate deformation and seismic barrier in front of Nazca subduction zone: The Chololo Fault System and active tectonics along the Coastal Cordillera, southern Peru

    Audin, Laurence; Lacan, Pierre; Tavera, Hernando; Bondoux, Francis


    The South America plate boundary is one of the most active subduction zone. The recent Mw = 8.4 Arequipa 2001 earthquake ruptured the subduction plane toward the south over 400 km and stopped abruptly on the Ilo Peninsula. In this exact region, the subduction seismic crisis induced the reactivation of continental fault systems in the coastal area. We studied the main reactivated fault system that trends perpendicular to the trench by detailed mapping of fault related-geomorphic features. Also, at a longer time scale, a recurrent Quaternary transtensive tectonic activity of the CFS is expressed by offset river gullies and alluvial fans. The presence of such extensional fault systems trending orthogonal to the trench along the Coastal Cordillera in southern Peru is interpreted to reflect a strong coupling between the two plates. In this particular case, stress transfer to the upper plate, at least along the coastal fringe, appears to have induced crustal seismic events that were initiated mainly during and after the 2001 earthquake. The seafloor roughness of the subducting plate is usually thought to be a cause of segmentation along subduction zones. However, after comparing and discussing the role of inherited structures within the upper plate to the subduction zone segmentation in southern Peru, we suggest that the continental structure itself may exert some feedback control on the segmentation of the subduction zone and thus participate to define the rupture pattern of major subduction earthquakes along the southern Peru continental margin.

  1. Nature of the proto-décollement in the 2010 Mentawai tsunami earthquake rupture zone from full waveform inversion of seismic reflection data

    Huot, Gabriel; Singh, Satish


    Since the beginning of the 21st century, three great interplate earthquakes (Mw > 8.0) occurred in the Sumatran subduction zone. Although the 2004 Mw 9.2 Sumatra-Adaman earthquake generated a destructive tsunami, the 2005 Mw 8.6 Sumatra and 2007 Mw 8.4 Nias-Simeulue earthquakes did not. However, the 2010 Mw 7.9 Mentawai earthquake generated an unexpectedly powerful tsunami, and was interpreted as a tsunami earthquake. Although the mechanism of larger tsunami generation is not fully understood, rupture of the subduction front, supposed to be aseismic, is inferred to be the cause. In order to assess the tsunami risk in the locked zone of the Mentawai region, north of the 2007 rupture zone, seismic data were recorded in 2009 by CGG, using a 15-km-long streamer. Seismic line CGGV20, designed to cross the 2007 rupture zone, also crossed the southern part of the 2010 rupture zone. We combined downward continuation, traveltime tomography and full waveform inversion on this 15-km-long streamer and low frequency seismic data. The downward continuation makes it possible to extrapolate the streamer seismic reflection data as it was recorded 200 m above the seafloor at more than 5 km depth. The resolution of the velocity model obtained by traveltime tomography was increased, particularly in the shallow subsurface compared to the conventional method. A reliable velocity model was obtained to use as starting model for the full waveform inversion. The velocity inversion results and the porosity computation highlight a low velocity (˜ 1500 m/s), high porosity (˜ 70%) layer, corresponding to a high amplitude reverse polarity reflector in pelagic sediments, interpreted as a proto-décollement. The up-dip limit of the seismogenic zone might be located at the toe of the accretionary wedge, where the porosity drops to 23% into the décollement. The décollement might allow frontal rupture, which could propagate along active landward and seaward-vergent thrust faults, generating a

  2. High-Resolution Seismicity Image of the Shallow Part of the Subduction Zone Beneath Mejillones in Northern Chile

    Kummerow, Jörn; Bloch, Wasja; Salazar, Pablo; Wigger, Peter; Asch, Günter; Shapiro, Serge A.


    We analyze slab-related seismicity which has been recorded by a recently (June 2013) installed local seismic monitoring system on the Mejillones peninsula in the forearc region of Northern Chile. The monitoring system consists of 20 seismic stations and is complemented by components of the permanent IPOC (Integrated Plate Boundary Obervatory Chile) seismic network, providing a singular on-shore possibility to study in detail the relatively shallow seismicity of the subducting Nazca slab. To date, about thousand local seismic events have been identified. Precise earthquake relocation involving a local 2.5D velocity model and improved arrival time picks from an iterative cross-correlation based technique allows to trace sharply the slab interface between 25km and 40km depth. Furthermore, we observe distinct and continuous seismic activity on a near-vertical structure which transects the subducting oceanic crust from 40km to 50km depth. Location, orientation and size of this plane correspond to the rupture fault of the MW6.8 Michilla intraslab earthquake which occurred weeks after the MW7.7 Tocopilla earthquake of November 2007. We discuss here particularly the results from cluster analysis and the spatio-temporal signatures of the recorded seismicity.

  3. Structural and thermal control of seismic activity and megathrust rupture dynamics in subduction zones: Lessons from the Mw 9.0, 2011 Tohoku earthquake

    Satriano, Claudio; Dionicio, Viviana; Miyake, Hiroe; Uchida, Naoki; Vilotte, Jean-Pierre; Bernard, Pascal


    The 2011 Tohoku megathrust earthquake ruptured a vast region of the northeast Japan Trench subduction zone in a way that had not been enough anticipated by earthquake and tsunami risk scenarios. We analyzed the Tohoku rupture combining high-frequency back-projection analysis with low frequency kinematic inversion of the co-seismic slip. Results support the to-day well-accepted broadband characteristics of this earthquake. Most of the seismic moment is released during the first 100 s, with large co-seismic slip (up to 55 m) offshore Miyagi in a compact region on the landward side of the trench. Coherent high-frequency radiation areas and relatively low co-seismic slip are a distinctive signature of the slab-mantle interface. The broadband characteristics of the Tohoku rupture are interpreted, integrating the seismic activity and structure information on the NE Japan forearc region, as a signature of along-dip segmentation and segment interactions, that result from thermal structure, plate geometry, material composition and fracture heterogeneities along the plate boundary interface. Deep mantle corner flow and low dehydration rates along the cold subduction slab interface lead to an extended seismogenic slab-mantle interface, with strong bi-material contrast controlling larger propagation distance in the downdip preferred rupture direction. Off Miyagi, plate bending below the mantle wedge, ∼142.3°E at ∼25 km depth, is associated with the eastern limit of the deep M7-8-class thrust-earthquakes, and of the strongest coherent high-frequency generation areas. The region of the slab-crust interface between the mantle wedge limit, ∼142.7°E at ∼20 km depth, and a trenchward plate bending, ∼143.2°E at ∼15 km, acted as an effective barrier resisting for many centuries to stress-loading gradient induced by deep stable sliding and large earthquakes along the slab-mantle interface. The 2011 Tohoku earthquake, whose hypocenter is located on the east side of the

  4. Evaluation of Seismicity Using Density Analysis of 2000-2015 Earthquakes in The West Coastal Zone of Anatolia (Turkey) And Its Correlation with Geothermal Areas

    Bakak, Özde


    The purpose of the study is to evaluate the seismic activity using the density analysis methods (point density and Kernel density analysis) for 2000-2015 earthquake catalogue belonging to the study area surrounded by Qanakkale to the north, Fethiye to the south and Denizli (Buharkent) to the east, and also to apply its correlation with geothermal regions. The earthquake data, in total 6.675 earthquakes with M>3 magnitudes were obtained from DDA Catalogue of Prime Ministry Disaster & Emergency Management Authority (AFAD) official website. In this survey, data analysis and maps were prepared using ArcGIS (version_10.1) program. The analysis maps present (1) the intensity clustered earthquakes dominant in Sigacik and Gokova Gulfs, (2) regions which have high seismic risk were determined according to Buffer analysis for 2 km distance, (3) geothermal areas (21.4-153°C) in the west coastal zone of Anatolia were mapped, (4) regions the most affected by seismic activity for the last 15 years were detected from 2015 population data, and as latest (5) Seferihisar, Urla, Gulbahge, Demircili, Bodrum, and Datga provinces are identified as areas having high seismic activity for the last 15 years. Consequently, all analysis results were compared with the geothermal areas, and the review made that earthquake catalogue has not the relationship with hot regions and also these shocks triggered by active faults in this region using ArcGIS program. the author recommends that these regions should be investigated the earthquake sensitivity analysis in the near future.

  5. Angola Seismicity MAP

    Neto, F. A. P.; Franca, G.


    The purpose of this job was to study and document the Angola natural seismicity, establishment of the first database seismic data to facilitate consultation and search for information on seismic activity in the country. The study was conducted based on query reports produced by National Institute of Meteorology and Geophysics (INAMET) 1968 to 2014 with emphasis to the work presented by Moreira (1968), that defined six seismogenic zones from macro seismic data, with highlighting is Zone of Sá da Bandeira (Lubango)-Chibemba-Oncócua-Iona. This is the most important of Angola seismic zone, covering the epicentral Quihita and Iona regions, geologically characterized by transcontinental structure tectono-magmatic activation of the Mesozoic with the installation of a wide variety of intrusive rocks of ultrabasic-alkaline composition, basic and alkaline, kimberlites and carbonatites, strongly marked by intense tectonism, presenting with several faults and fractures (locally called corredor de Lucapa). The earthquake of May 9, 1948 reached intensity VI on the Mercalli-Sieberg scale (MCS) in the locality of Quihita, and seismic active of Iona January 15, 1964, the main shock hit the grade VI-VII. Although not having significant seismicity rate can not be neglected, the other five zone are: Cassongue-Ganda-Massano de Amorim; Lola-Quilengues-Caluquembe; Gago Coutinho-zone; Cuima-Cachingues-Cambândua; The Upper Zambezi zone. We also analyzed technical reports on the seismicity of the middle Kwanza produced by Hidroproekt (GAMEK) region as well as international seismic bulletins of the International Seismological Centre (ISC), United States Geological Survey (USGS), and these data served for instrumental location of the epicenters. All compiled information made possible the creation of the First datbase of seismic data for Angola, preparing the map of seismicity with the reconfirmation of the main seismic zones defined by Moreira (1968) and the identification of a new seismic

  6. Depth-Dependent Low-Velocity Structure of the San Andreas Fault near the SAFOD Drilling Site at Parkfield from Fault-Zone Seismic Waves

    Alvarez, M.; Li, Y.; Vidale, J.; Cochran, E.


    Coordinated by the SAFOD PIs, we used 96 PASSCAL short-period three-component seismometers in linear arrays deployed across and along the San Andreas fault (SAF) near the town of Parkfield and the SAFOD drilling site in 2002 and 2003, respectively. The data recorded for near-surface explosions detonated in the experiments (Li and Vidale), PASO project (Thurber and Roecker) and refraction profiling (Hole), and local earthquakes show fault-zone trapped waves clearly for the source and receivers located close to the fault. The time duration of the dominant trapped energy after S-arrivals increases with the event-to-array distance and focal depth progressively. Using a finite-difference code, we first synthesize fault-zone trapped waves generated by explosions to determine the shallowest 1 or 2 km fault zone structure with the velocity constraints from seismic profiling of the shallow SAF at Parkfield [Catchings et al., 2002]. We then strip shallow effects to resolve deeper structure of the fault zone, and synthesize trapped waves from earthquakes at depths between 2.5 and 11 km to complete a model of the SAF with depth-variable structure in 3-D. We also use the P-first arrivals and polarity as additional information in modeling of velocities and location of the material interface with the structural constraints from seismic tomography at Parkfield [Thurber et al., 2004] to the bed-rock velocities. In grid-search modeling, we tested various values for fault zone depth, width, velocity, Q, and source location. The best-fit model parameters from this study show evidence of a damaged core zone on the main SAF, which likely extends to seismogenic depths. The zone is marked by a low-velocity waveguide ~150 m wide, in which Q is 10-50 and shear velocities are reduced by 30-45% from wall-rock velocities. We also find some seismic energy trapped partitioned in the branching faults that connect to the San Andreas main fault at a shallow depth near Parkfield.

  7. Updated Episodic Tremor and Slip on the Cocos-Caribbean Subduction zone as measured by a GPS and Seismic Network on the Nicoya Peninsula, Costa Rica

    Psencik, K. C.; Dixon, T. H.; Schwartz, S.; Walter, J.; Protti, M.; Gonzalez, V.


    The close proximity of the Nicoya Peninsula to the Cocos-Caribbean Subduction zone plate boundary makes it a prime location to use GPS to study episodic tremor and slip. Nicoya Peninsula currently has an operating network of 13 continuous GPS (CGPS) and 12 seismic stations designed to identify and characterize the pattern of episodic tremor and slip (ETS) events along the seismogenic zone under Costa Rica's Pacific Margin. The CGPS stations have varying degrees of equipment and communication. Of the 13 sites, five are equipped with SIM cards and modems for direct download capabilities, two of which are connected to a router for direct internet access. These sites, LMNL, located in Limonal, and LEPA, located in Lepanta are being monitored on the PBO network by UNAVCO with all of the quality and systems checks that this implies. All sites with NetRS receivers are currently partitioned to record both 5Hz and 30 second position data. The advantage to recording at a 5 Hz interval is that the receivers may be used to record long period dynamic events during large earthquakes along the Cocos-Caribbean plate boundary. The occurrence of slow slip events has been previously postulated in this region based on correlated fluid flow and seismic tremor events recorded near the margin wedge in 2000 and from sparse GPS observations in 2003. Paucity of data prevented details of these events from being resolved. In May 2007 a slow slip event was recorded on our densified GPS network and accompanied by seismic tremor. We will present the refined GPS time series and correlated seismic tremor for both likely slow slip events in September 2003 and May 2007. We will also present the inferred pattern of slip on the plate interface. Future plans include installation of additional sites, including the interior of the peninsula and reference sites on the stable Caribbean plate.

  8. Climatic changes, streamflow, and long-term forecasting of intraplate seismicity

    Costain, J. K.; Bollinger, G. A.


    bisected by the Mississippi River, Illinois, and James River, Virginia, in the period range of 11-13 years that might be associated with sunspot activity. In addition, there is positive correlation between periods of above average values of the standard deviation of streamflow time series and periods of seismicity in the central Virginia seismic zone. Many aspects of the weather appear to be modulated by a 20-year cycle. We observe a similar periodicity (18-20 years) in seismicity in the central Virginia seismic zone. A good agreement is observed when a streamflow time series is superimposed on the record of the earthquake strain factor if a value of 50 km 2/year is assumed for crustal hydraulic diffusivity. In the central Virginia seismic zone, it is found that the number of earthquakes versus depth, ψ, is directly proportional to pressure fluctuations at the depth ψ. In addition, the fractal dimension determined from downward-continued streamflow is approximately the same as the fractal dimension of intraplate seismicity. Furthermore, using the Gutenberg-Richter relation and assuming that the earthquake data sets in the New Madrid and central Virginia seismic zones are complete for all magnitudes m ⩾ 2, the ratio of the number of earthquakes occurring per year in the New Madrid zone to the central Virginia zone is about 40. The ratio of the standard deviations of downward-continued Mississippi River streamflow (at Thebes, Illinois) to the James River streamflow is also about 40. One interpretation of this common ratio is that the number of intraplate earthquakes generated in a seismogenic crust is directly proportional to the standard deviation of vertical variations in the elevation of the water table. If the hydroseismicity hypothesis is correct, then long-term variations in streamflow can be used to forecast long-term statistical variations in intraplate seismic activity.

  9. Temporal variations of the fractal properties of seismicity in the western part of the north Anatolian fault zone: possible artifacts due to improvements in station coverage

    A. O. Öncel


    Full Text Available Seismically-active fault zones are complex natural systems exhibiting scale-invariant or fractal correlation between earthquakes in space and time, and a power-law scaling of fault length or earthquake source dimension consistent with the exponent b of the Gutenberg-Richter frequency-magnitude relation. The fractal dimension of seismicity is a measure of the degree of both the heterogeneity of the process (whether fixed or self-generated and the clustering of seismic activity. Temporal variations of the b-value and the two-point fractal (correlation dimension Dc have been related to the preparation process for natural earthquakes and rock fracture in the laboratory These statistical scaling properties of seismicity may therefore have the potential at least to be sensitive short- term predictors of major earthquakes. The North Anatolian Fault Zone (NAFZ is a seismicallyactive dextral strike slip fault zone which forms the northern boundary of the westward moving Anatolian plate. It is splayed into three branches at about 31oE and continues westward toward the northern Aegean sea. In this study, we investigate the temporal variation of Dc and the Gutenberg-Richter b-value for seismicity in the western part of the NAFZ (including the northern Aegean sea for earthquakes of Ms > 4.5 occurring in the period between 1900 and 1992. b ranges from 0.6-1.6 and Dc from 0.6 to 1.4. The b-value is found to be weakly negatively correlated with Dc (r=-0.56. However the (log of event rate N is positively correlated with b, with a similar degree of statistical significance (r=0.42, and negatively correlated with Dc (r=-0.48. Since N increases dramatically with improved station coverage since 1970, the observed negative correlation between b and Dc is therefore more likely to be due to this effect than any underlying physical process in this case. We present this as an example of how man-made artefacts of recording can have similar statistical effects to

  10. High-Resolution Seismic Reflection and Marine Magnetic Data Along the Hosgri Fault Zone--Cayucos to Pismo Beach, California

    U.S. Geological Survey, Department of the Interior — This report consists of high-resolution chirp and single-channel mini-sparker seismic-reflection profile data from the offshore San Luis Obispo County, California....

  11. Formation of diapiric structure in the deformation zone, central Indian Ocean: A model from gravity and seismic reflection data

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

    Analyses of bathymetry, gravity and seismic reflection data of the diffusive plate boundary in the central Indian Ocean reveal a new kind of deformed structure besides the well-reported structures of long-wavelength anticlinal basement rises...

  12. High-Resolution Seismic Reflection and Marine Magnetic Data Along the Hosgri Fault Zone--Cayucos to Pismo Beach, California

    U.S. Geological Survey, Department of the Interior — This report consists of high-resolution chirp and single-channel mini-sparker seismic-reflection profile data from the offshore San Luis Obispo County, California....

  13. Coulomb Stress Change and Seismic Hazard of Rift Zones in Southern Tibet after the 2015 Mw7.8 Nepal Earthquake and Its Mw7.3 Aftershock

    Dai, Z.; Zha, X.; Lu, Z.


    In southern Tibet (30~34N, 80~95E), many north-trending rifts, such as Yadong-Gulu and Lunggar rifts, are characterized by internally drained graben or half-graben basins bounded by active normal faults. Some developed rifts have become a portion of important transportation lines in Tibet, China. Since 1976, eighty-seven >Mw5.0 earthquakes have happened in the rift regions, and fifty-five events have normal faulting focal mechanisms according to the GCMT catalog. These rifts and normal faults are associated with both the EW-trending extension of the southern Tibet and the convergence between Indian and Tibet. The 2015 Mw7.8 Nepal great earthquake and its Mw7.3 aftershock occurred at the main Himalayan Thrust zone and caused tremendous damages in Kathmandu region. Those earthquakes will lead to significant viscoelastic deformation and stress changes in the southern Tibet in the future. To evaluate the seismic hazard in the active rift regions in southern Tibet, we modeled the slip distribution of the 2015 Nepal great earthquakes using the InSAR displacement field from the ALOS-2 satellite SAR data, and calculated the Coulomb failure stress (CFS) on these active normal faults in the rift zones. Because the estimated CFS depends on the geometrical parameters of receiver faults, it is necessary to get the accurate fault parameters in the rift zones. Some historical earthquakes have been studied using the field data, teleseismic data and InSAR observations, but results are in not agreement with each other. In this study, we revaluated the geometrical parameters of seismogenic faults occurred in the rift zones using some high-quality coseismic InSAR observations and teleseismic body-wave data. Finally, we will evaluate the seismic hazard in the rift zones according to the value of the estimated CFS and aftershock distribution.

  14. Vp model at the junction of Taiwan Orogeny and the western-most Ryukyu Subduction Zone from the integration of Ocean Bottom Seismometer Networks and onland seismic data

    Chin, S. J.; Lin, J. Y.; Kuochen, H.; Wang, S. Y.; Liang, C. W.


    In Taiwan, since all the seismic stations located in the onland area, previous studies about velocity model of this region should only have high resolution for the onland part and could not provide sufficient constrains for the marine domain. However, most earthquakes with magnitude larger than 7 occur in the eastern offshore Taiwan area, suggesting the presence of high-activity tectonic processes. A better understanding of geological structures in the area must provide important information about the tectonic environments. In this study, we constructed a Vp model by combining earthquake travel times determined from inland stations and 5 temporal Ocean Bottom Seismometer (OBS) arrays, which had been deployed in different time periods from 2008 to 2012, and relocated earthquakes in a decade (2006-2015) provided by Central Weather Bureau (CWB), Taiwan. As a result of a better coverage of seismic ray-paths in eastern flank of the island, this model provides sufficient resolution for the junction area of the Taiwan orogeny and the western-most Ryukyu subduction system. The most notable feature in the model is a low velocity zone underlying along the northwestward subducted Philippine Sea Plate (PSP) extending along 122oE, which could be the product of the subducted forearc basement. The relocated earthquakes sit on the top of the low velocity zone, suggesting its active deformation. It is worth noted that, along the subducted PSP, the relocated earthquake hypocenters present a double Benioff zone east of 122oE, and merged together, getting a relatively larger dipping angle toward the west. This change of seismic pattern was not reported previously and may provide important index for the tectonic evolution. However, further studies will be needed to get more understanding.

  15. Upper crust structure of eastern A'nyemaqên suture zone: Results of Barkam-Luqu-Gulang deep seismic sounding profile

    ZHANG Xian-kang; SUN Guo-wei; YANG Zhuo-xin; XU Zhao-fan; PAN Ji-shun; LIU Zhi; WANG Fu-yun; JIA Shi-xu; ZHAO Jin-ren; ZHANG Cheng-ke


    Barkam-Luqu-Gulang deep seismic sounding profile runs from north of Sichuan Province to south of Gansu Province. It is located at the northeastern edge of Tibetan Plateau and crosses eastern A'nyemaqên suture zone. The upper crust structures around eastern A'nyemaqên suture zone and its adjacent area are reconstructed based on the arrival times of refracted Pg and Sg waves by using finite difference method, ray tracing inversion, time-term method and travel-time curve analysis. The results show that the depth variation of basement along profile is very strong as indicated by Pg and Sg waves. The basement rose in Zoigê basin and depressed in eastern A'nyemaqên suture zone, and it gradually rose again northward and then depressed. The results also indicate that eastern A'nyemaqên suture zone behaves as inhomogeneous low velocity structures in the upper crust and is inclined toward the south. Hoh Sai Hu-Maqên fault, Wudu-Diebu fault and Zhouqu-Liangdang fault are characterized by low velocity distributions with various scales. The distinct variation in basement depth occurred near Hoh Sai Hu-Maqên fault and Zhouqu-Liangdang fault, which are main tectonic boundaries of A'nyemaqên suture zone.Wudu-Diebu fault, located at the depth variation zone of the basement, possibly has the same deep tectonic background with Zhouqu-Liangdang fault. The strongly depressed basement characterized by low velocity distribution and lateral inhomogeneity in A'nyemaqên suture zone implies crushed zone features under pinching action.

  16. Conjunto industrial «BINESA», Madrid

    Barbero Rebolledo, Manuel


    Full Text Available This project is near Madrid and is intented for the manufacture of pharmaceutical products. It includes a manufacturing section, a storage zone, one devoted to offices, dressing rooms and cafeteria. There is also an elevated water tank, a control house, a bicycle parking place and a transformer hut. The whole set of buildings is of untreated concrete and straw coloured bricks: they add up to a highly varied and beautifully plastic set of space forms.Situado en las proximidades de Madrid, está destinado a la fabricación de productos farmacéuticos y se compone de los siguientes edificios independientes: un núcleo de fabricación y almacenamiento y otro de oficinas, vestuario y cafetería. Forman parte también del conjunto: un depósito elevado, la caseta de control, un bicicletero y una caseta de transformación. Todo ello en hormigón visto y ladrillo pajizo, componiendo volúmenes de gran variedad y belleza plástica.

  17. Electrification of high-speed line Madrid-Lerida; Elektrifizierung der Hochgeschwindigkeitsstrecke Madrid-Lerida

    Ortiz, J.M.G.; Wipfler, H.P. [UTE EUROASCE, Madrid (Spain); Tessun, H. [Balfour Beatty Rail GmbH, Power Systems, Muenchen (Germany); Martens, G. [Balfour Beatty Rail GmbH, Power Systems, Offenbach (Germany)


    The 450 km long section Madrid-Lerida of the new high-speed line Madrid-Barcelone has been equipped with a new overhead contact line type designed for 350 km/h. (orig.) [German] Der 450 km lange Abschnitt Madrid-Lerida der neuen Hochgeschwindigkeitsstrecke Madrid-Barcelona wurde mit einer fuer 350 km/h ausgelegten neuen Oberleitungsbauart ausgeruestet. (orig.)

  18. Strong ground motion inferred from liquefaction caused by the 1811-1812 New Madrid, Missouri, earthquakes

    Holzer, Thomas L.; Noce, Thomas E.; Bennett, Michael J.


    Peak ground accelerations (PGAs) in the epicentral region of the 1811–1812 New Madrid, Missouri, earthquakes are inferred from liquefaction to have been no greater than ∼0.35g. PGA is inferred in an 11,380  km2 area in the Lower Mississippi Valley in Arkansas and Missouri where liquefaction was extensive in 1811–1812. PGA was inferred by applying liquefaction probability curves, which were originally developed for liquefaction hazard mapping, to detailed maps of liquefaction by Obermeier (1989). The low PGA is inferred because both a shallow (1.5 m deep) water table and a large moment magnitude (M 7.7) earthquake were assumed in the analysis. If a deep (5.0 m) water table and a small magnitude (M 6.8) earthquake are assumed, the maximum inferred PGA is 1.10g. Both inferred PGA values are based on an assumed and poorly constrained correction for sand aging. If an aging correction is not assumed, then the inferred PGA is no greater than 0.22g. A low PGA value may be explained by nonlinear site response. Soils in the study area have an averageVS30 of 220±15  m/s. A low inferred PGA is consistent with PGA values estimated from ground‐motion prediction equations that have been proposed for the New Madrid seismic zone when these estimates are corrected for nonlinear soil site effects. This application of liquefaction probability curves demonstrates their potential usefulness in paleoseismology.

  19. Enhancement of Seismic Data Processing and Interpretation of Fracture Zones on the Upper Part of Granitic Basement in Cuu Long Basin, Vietnam

    Tan, Mai Thanh; Ha, Mai Thanh; Marfurt, Kurt J.; Hieu, Nguyen Trung; Hanh, Nguyen Thi My


    The fractured granite basement is the primary oil and gas reservoir in the Cuu Long Basin, Vietnam. Due to the complexity of this non-layered unconventional target, combined with complicated fault and fracture systems, the seismic data quality near and within the basement section is very low. For this reason, it is important to apply improved seismic data processing workflows, filtering and migration techniques, as wells as attribute processing methods to enhance the imaging quality. Our studies show that applying different types of filters, including the f-k, Radon transform and Tau-P, improves signal to noise ratio, removing multiples, revealing basement's top and its related fractured and fault zones. In addition, the application of multi-arrival-solution migration algorithms, such as Kirchhoff Migration and Controlled Beam Migration, provides improved imaging for identifying basement top and faults and fractures within the basement. Furthermore, the application of seismic attributes such as curvature, apparent dip, or energy gradient, is important in locating faults and fractures, whereas mapping of intensity and orientation of such structures assists the delineation of "sweet spots" and assists the planning of exploration.

  20. Seismic structure of the Costa Rican subduction system from active-source onshore-offshore seismic data and imaging plate boundary processes at the Cascadia subduction zone offshore Washington

    Everson, Erik D.

    The goal of this thesis is to use seismic methods, either wide-angle refraction or multi-channel seismic (MCS) reflection, to characterize the physical processes occurring at the subduction zones occurring offshore Costa Rica and Cascadia. The first two chapters use wide-angle refraction data to characterize lithospheric structure and velocities, based on the modeling of wide-angle refractions and reflections from the crust, Moho and upper mantle. They also use MCS data to characterize the uppermost structure that wide-angle refraction data alone cannot provide. The first chapter uses both wide-angle refraction and MCS data to address the hypothesis that bending-related normal faulting, clearly imaged in the MCS data, provides a pathway for seawater to percolate down into the uppermost mantle and serpentinize it. This process causes a reduction in the seismic p-wave velocity in the upper mantle, which can be detected by wide-angle refraction analysis. We found the upper 1-2 km of the mantle has reduced velocities of 7.5 - 7.6 km/s in the area of pervasive normal faulting within the CNS-2 segment, and regular upper mantle velocities of 8.0 - 8.2 km/s in the CNS-1 segment, which lacks pervasive normal faulting. Our results suggest a link between bending-related large-offset normal faults seen in bathymetric and MCS reflection data in subduction trenches and serpentinization of the upper mantle. The second chapter uses both wide-angle refraction and MCS data like the first chapter but addresses the hypothesis that juvenile continental crust is created at some volcanic arcs. We addressed this hypothesis by creating a lithospheric velocity and structural model for the Central American subduction system through Costa Rica. This model allows us to estimate the seismic velocity, structure, infer bulk composition (from seismic velocities), and estimate a magmatic flux rate for the volcanic arc. We found a total crustal thickness of ~44 km and mid-to-lower-crustal velocities

  1. Seismic hazard in low slip rate crustal faults, estimating the characteristic event and the most hazardous zone: study case San Ramón Fault, in southern Andes

    Estay, Nicolás P.; Yáñez, Gonzalo; Carretier, Sebastien; Lira, Elias; Maringue, José


    Crustal faults located close to cities may induce catastrophic damages. When recurrence times are in the range of 1000-10 000 or higher, actions to mitigate the effects of the associated earthquake are hampered by the lack of a full seismic record, and in many cases, also of geological evidences. In order to characterize the fault behavior and its effects, we propose three different already-developed time-integration methodologies to define the most likely scenarios of rupture, and then to quantify the hazard with an empirical equation of peak ground acceleration (PGA). We consider the following methodologies: (1) stream gradient and (2) sinuosity indexes to estimate fault-related topographic effects, and (3) gravity profiles across the fault to identify the fault scarp in the basement. We chose the San Ramón Fault on which to apply these methodologies. It is a ˜ 30 km N-S trending fault with a low slip rate (0.1-0.5 mm yr-1) and an approximated recurrence of 9000 years. It is located in the foothills of the Andes near the large city of Santiago, the capital of Chile (> 6 000 000 inhabitants). Along the fault trace we define four segments, with a mean length of ˜ 10 km, which probably become active independently. We tested the present-day seismic activity by deploying a local seismological network for 1 year, finding five events that are spatially related to the fault. In addition, fault geometry along the most evident scarp was imaged in terms of its electrical resistivity response by a high resolution TEM (transient electromagnetic) profile. Seismic event distribution and TEM imaging allowed the constraint of the fault dip angle (˜ 65°) and its capacity to break into the surface. Using the empirical equation of Chiou and Youngs (2014) for crustal faults and considering the characteristic seismic event (thrust high-angle fault, ˜ 10 km, Mw = 6.2-6.7), we estimate the acceleration distribution in Santiago and the hazardous zones. City domains that are under

  2. Episodic Tremor and Slip on the Cocos-Caribbean Subduction zone as measured by a GPS and Seismic Network on the Nicoya Peninsula, Costa Rica

    Psencik, K. C.; Dixon, T. H.; Schwartz, S.; Protti, M.; Gonzalez, V.; Walter, J.; Biggs, J.


    The close proximity of the Nicoya Peninsula land mass to the Cocos-Caribbean subduction zone plate boundary makes it a prime location to use GPS to study such plate boundary processes as locking zone dynamics and episodic tremor and slip. Nicoya Peninsula currently has an operating network of 12 continuous GPS (CGPS) and 10 seismic stations designed to identify and characterize the pattern of episodic tremor and slip (ETS) events along the seismogenic zone under Costa Rica's Pacific Margin. The CGPS stations have varying degrees of equipment and communication. Of the 12 sites, four are equipped with SIM cards and modems for direct download capabilities, one of which is connected to a router for direct internet access. This site, LMNL, located in Limonal, is being monitored on the PBO network by UNAVCO with all of the quality and systems checks that this implies. All sites with NetRS receivers are currently partitioned to record both 5Hz and 30 second position data. The advantage to recording at a 5 Hz interval is that the receivers may be used to record long period dynamic events during large earthquakes along the Cocos-Caribbean plate boundary. The occurrence of slow slip events has been previously postulated in this region based on correlated fluid flow and seismic tremor events recorded near the margin wedge in 2000 and from sparse GPS observations in 2003. Paucity of data prevented details of these events from being resolved. In May 2007 a slow slip event was recorded on our densified GPS network and accompanied by seismic tremor. We will present the preliminary GPS time series and correlated seismic tremor for both likely slow slip events in September 2003 and May 2007. Once the displacement patterns have been characterized, we intend to model both the transient motion on the fault plane as well as the locking pattern before and after the events in an effort to determine if the occurrence of an ETS event has any impact on the nature and distribution of the

  3. Fault zones ruptured during the early 2014 Cephalonia Island (Ionian Sea, Western Greece) earthquakes (January 26 and February 3, Mw 6.0) based on the associated co-seismic surface ruptures

    Lekkas, Efthymios L.; Mavroulis, Spyridon D.


    The early 2014 Cephalonia Island (Ionian Sea, Western Greece) earthquake sequence comprised two main shocks with almost the same magnitude (moment magnitude (Mw) 6.0) occurring successively within a short time (January 26 and February 3) and space (Paliki peninsula in Western Cephalonia) interval. Εach earthquake was induced by the rupture of a different pre-existing onshore active fault zone and produced different co-seismic surface rupture zones. Co-seismic surface rupture structures were predominantly strike-slip-related structures including V-shaped conjugate surface ruptures, dextral and sinistral strike-slip surface ruptures, restraining and releasing bends, Riedel structures ( R, R', P, T), small-scale bookshelf faulting, and flower structures. An extensional component was present across surface rupture zones resulting in ground openings (sinkholes), small-scale grabens, and co-seismic dip-slip (normal) displacements. A compressional component was also present across surface rupture zones resulting in co-seismic dip-slip (reverse) displacements. From the comparison of our field geological observations with already published surface deformation measurements by DInSAR Interferometry, it is concluded that there is a strong correlation among the surface rupture zones, the ruptured active fault zones, and the detected displacement discontinuities in Paliki peninsula.

  4. Geomagnetic signal induced by the M5.7 earthquake occurred on September 24-th, 2016, in the seismic active Vrancea zone, Romania

    Stanica, Dumitru; Armand Stanica, Dragos


    In this paper, we used the geomagnetic time series collected in real time by the electromagnetic monitoring system, placed at the Geomagnetic Observatory Provita de Sus, to emphasize possible relationships between the pre-seismic anomalous behavior of the normalized function Bzn and M5.7 earthquake occurrence in Vrancea seismic active zone, on September 24, 2016. It has already been demonstrated (Stanica and Stanica, 2012, Stanica et al., 2015) that for a 2D geoelectric structure, in pre-seismic conditions, the normalized function Bzn has significant changes in magnitudes due to the electrical conductivity changes, possibly associated with the earthquake-induced rupture-processes and high-pressure fluid flow through the faulting systems developed inside the Vrancea seismogenic volume and along the Carpathian electrical conductivity anomaly. In this circumstances, the daily mean distributions of the Bzn = Bz/Bperp (where Bz is vertical component of the geomagnetic field; Bperp is geomagnetic component perpendicular to the geoelectric strike) and its standard deviation (SD) are performed in the ULF frequency range 0.001Hz to 0.0083Hz by using both the FFT band-pass filter analysis and statistical analysis based on a standardized random variable equation. After analyzing the pre-seismic anomalous intervals, a pre-seismic geomagnetic signal greater than 5 SD was identified on September 22, 2016, what means a lead time of 2 days before the M5.7 earthquake occurred on September 24, emphasized in real time on the web site ( The final conclusion is that the proposed geomagnetic methodology might be used to provide suitable information for the extreme seismic hazard assessment and risk mitigation. References: Dumitru Stanica and Dragos Armand Stanica, Earthquakes precursors, in "Earthquake Research and Analysis-Statistical Studies, Observations and Planning" Book 5, edited by: Dr. Sebastiano D'Amico, ISBN 978-953-51-0134-5, InTech open access publisher

  5. Active crustal deformation of the El Salvador Fault Zone by integrating geodetic, seismological and geological data: application in seismic hazard assessment

    Staller, A.; Benito, B.; Martínez-Díaz, J.; Hernández, D.; Hernández-Rey, R.


    El Salvador, Central America, is part of the Chortis block in the northwestern boundary of the Caribbean plate. This block is interacting with a diffuse triple junction point with the Cocos and North American plates. Among the structures that cut the Miocene to Pleistocene volcanic deposits stands out the El Salvador Fault Zone (ESFZ): It is oriented in N90-100E direction, and it is composed of several structural segments that deform Quaternary deposits with right-lateral and oblique slip motions. The ESFZ is seismically active and capable of producing earthquakes such as the February 13, 2001 with Mw 6.6 (Martínez-Díaz et al., 2004), that seriously affected the population, leaving many casualties. This structure plays an important role in the tectonics of the Chortis block, since its motion is directly related to the drift of the Caribbean plate to the east and not with the partitioning of the deformation of the Cocos subduction (here not coupled) (Álvarez-Gómez et al., 2008). Together with the volcanic arc of El Salvador, this zone constitutes a weakness area that allows the motion of forearc block toward the NW. The geometry and the degree of activity of the ESFZ are not studied enough. However their knowledge is essential to understand the seismic hazard associated to this important seismogenic structure. For this reason, since 2007 a GPS dense network was established along the ESFZ (ZFESNet) in order to obtain GPS velocity measurements which are later used to explain the nature of strain accumulation on major faults along the ESFZ. The current work aims at understanding active crustal deformation of the ESFZ through kinematic model. The results provide significant information to be included in a new estimation of seismic hazard taking into account the major structures in ESFZ.

  6. Mineralogical Controls of Fault Healing in Natural and Simulated Gouges with Implications for Fault Zone Processes and the Seismic Cycle

    Carpenter, B. M.; Ikari, M.; Marone, C.


    The frictional strength and stability of tectonic faults is determined by asperity contact processes, granular deformation, and fault zone fabric development. The evolution of grain-scale contact area during the seismic cycle likely exhibits significant control on overall fault stability by influencing frictional restrengthening, or healing, during the interseismic period, and the rate-dependence of sliding friction, which controls earthquake nucleation and the mode of fault slip. We report on laboratory experiments designed to explore the affect of mineralogy on fault healing. We conducted frictional shear experiments in a double-direct shear configuration at room temperature, 100% relative humidity, and a normal stress of 20 MPa. We used samples from a wide range of natural faults, including outcrop samples and core recovered during scientific drilling. Faults include: Alpine (New Zealand), Zuccale (Italy), Rocchetta (Italy), San Gregorio (California), Calaveras (California), Kodiak (Alaska), Nankai (Japan), Middle America Trench (Costa Rica), and San Andreas (California). To isolate the role of mineralogy, we also tested simulated fault gouges composed of talc, montmorillonite, biotite, illite, kaolinite, quartz, andesine, and granite. Frictional healing was measured at an accumulated shear strain of ~15 within the gouge layers. We conducted slide-hold-slide tests ranging from 3 to 3000 seconds. The main suite of experiments used a background shearing rate of 10 μm/s; these were augmented with sub-suites at 1 and 100 μm/s. We find that phyllosilicate-rich gouges (e.g. talc, montmorillonite, San Andreas Fault) show little to no healing over all hold times. We find the highest healing rates (β ≈ 0.01, Δμ per decade in time, s) in gouges from the Alpine and Rocchetta faults, with the rest of our samples falling into an intermediate range of healing rates. Nearly all gouges exhibit log-linear healing rates with the exceptions of San Andreas Fault gouge and

  7. Are rupture zone limits of great subduction earthquakes controlled by upper plate structures? Evidence from multichannel seismic reflection data acquired across the northern Ecuador-southwest Colombia margin

    Collot, Jean-Yves; Marcaillou, Boris; Sage, FrançOise; Michaud, FrançOis; Agudelo, William; Charvis, Philippe; Graindorge, David; Gutscher, Marc-André; Spence, George


    Subduction of the Nazca plate beneath the Ecuador-Colombia margin has produced four megathrust earthquakes during the last century. The 500-km-long rupture zone of the 1906 (Mw = 8.8) event was partially reactivated by three thrust events, in 1942 (Mw = 7.8), 1958 (Mw = 7.7), and 1979 (Mw = 8.2), whose rupture zones abut one another. Multichannel seismic reflection and bathymetric data acquired during the SISTEUR cruise show evidence that the margin wedge is segmented by transverse crustal faults that potentially correlate with the limits of the earthquake coseismic slip zones. The Paleogene-Neogene Jama Quininde and Esmeraldas crustal faults define a ˜200-km-long margin crustal block that coincides with the 1942 earthquake rupture zone. Subduction of the buoyant Carnegie Ridge is inferred to partially lock the plate interface along central Ecuador. However, coseismic slip during the 1942 and 1906 earthquakes may have terminated against the subducted northern flank of the ridge. We report on a newly identified Manglares crustal fault that cuts transversally through the margin wedge and correlates with the limit between the 1958 and 1979 rupture zones. During the earthquake cycle the fault is associated with high-stress concentration on the plate interface. An outer basement high, which bounds the margin seaward of the 1958 rupture zone, may act as a deformable buttress to seaward propagation of coseismic slip along a megathrust splay fault. Coseismic uplift of the basement high is interpreted as the cause for the 1958 tsunami. We propose a model of weak transverse faults which reduce coupling between adjacent margin segments, together with a splay fault and an asperity along the plate interface as controlling the seismogenic rupture of the 1958 earthquake.

  8. Application of advanced seismic reflection imaging techniques to mapping permeable zones at Dixie Valley, Nevada. Final technical report



    Multifold seismic reflection data from the Dixie Valley geothermal field in Nevada were reprocessed using a nonlinear optimization scheme called simulated annealing to model subsurface acoustic velocities, followed by a pre-stack Kirchhoff migration to produce accurate and detailed depth-migrated images of subsurface structure. In contrast to conventional processing techniques, these methods account for significant lateral variations in velocity and thus have the potential ability to image steeply-dipping faults and fractures that may affect permeability within geothermal fields. The optimization scheme develops two-dimensional velocity models to within 6% of velocities obtained from well and surface geologic data. Only the seismic data (i.e., first arrival times of P waves) are used to construct the velocity models and pre-stack migration images, and no other a priori assumptions are invoked. Velocities obtained by processing individual seismic tracks were integrated to develop a block diagram of velocities to 2.3 km depth within the Dixie Valley geothermal field. Details of the tectonic and stratigraphic structure allowed three dimensional extension of the interpretations of two dimensional data. Interpretations of the processed seismic data are compared with well data, surface mapping, and other geophysical data. The Dixie Valley fault along the southeastern Stillwater Range Piedmont is associated with a pronounced lateral velocity gradient that is interpreted to represent the juxtaposition of relatively low velocity basin-fill strata in the hanging wall against higher velocity crystalline rocks in the footwall. The down-dip geometry of the fault was evaluated by inverting arrival times from a negative move-out event, which we associate with the dipping fault plane, on individual shot gathers for seismic line SRC-3 for the location and depth of the associated reflection points on the fault.

  9. Bloque de viviendas, en Madrid

    Muñoz Monasterio, M.


    Full Text Available En el nuevo barrio madrileño surgido en las inmediaciones de la prolongación de la Castellana se eleva este bloque de viviendas, frente al fondo sur del Estadio del Real Madrid, obra proyectada por el mismo arquitecto y con cuyas torres armoniza el bloque alto que preside su composición de volumen.

  10. An integrated approach to earthquake-induced landslide hazard zoning based on probabilistic seismic scenario for Phlegrean Islands (Ischia, Procida and Vivara), Italy

    Caccavale, Mauro; Matano, Fabio; Sacchi, Marco


    's displacements (DN) under different probability of exceeding or return periods (probabilistic seismic scenarios). As a further step, in order to estimate the earthquake-induced landslide hazard, we defined three DN threshold values that have considered capable to trigger shallow seismic-induced landslides in the regional context, and mapped the sectors with DN values exceeding such thresholds. On this basis, we constructed frequency-magnitude curves to estimate the probability of slope failures at the source areas, as a function of DN, by correlating the annual probability of landslide occurrence with the number of terrain cells associated with DN values greater than the selected threshold. Finally, based on the estimated annual landslide frequency of the seismic triggering event for each terrain cell, we implemented a 1:5000 scale map of Earthquake-induced Landslide Hazard for Ischia, Procida and Vivara Islands. The map reports the zoning and ranking of study area into sub-zones, on a pixel basis, according to the degree of the potential hazard from landslides derived by the frequency of the triggering event.

  11. Identifying active interplate and intraplate fault zones in the western Caribbean plate from seismic reflection data and the significance of the Pedro Bank fault zone in the tectonic history of the Nicaraguan Rise

    Ott, B.; Mann, P.


    The offshore Nicaraguan Rise in the western Caribbean Sea is an approximately 500,000 km2 area of Precambrian to Late Cretaceous tectonic terranes that have been assembled during the Late Cretaceous formation of the Caribbean plate and include: 1) the Chortis block, a continental fragment; 2) the Great Arc of the Caribbean, a deformed Cretaceous arc, and 3) the Caribbean large igneous province formed in late Cretaceous time. Middle Eocene to Recent eastward motion of the Caribbean plate has been largely controlled by strike-slip faulting along the northern Caribbean plate boundary zone that bounds the northern margin of the Nicaraguan Rise. These faults reactivate older rift structures near the island of Jamaica and form the transtensional basins of the Honduran Borderlands near Honduras. Recent GPS studies suggest that small amount of intraplate motion within the current margin of error of GPS measurements (1-3 mm/yr) may occur within the center of the western Caribbean plate at the Pedro Bank fault zone and Hess Escarpment. This study uses a database of over 54,000 km of modern and vintage 2D seismic data, combined with earthquake data and results from previous GPS studies to define the active areas of inter- and intraplate fault zones in the western Caribbean. Intraplate deformation occurs along the 700-km-long Pedro Bank fault zone that traverses the center of the Nicaraguan Rise and reactivates the paleo suture zone between the Great Arc of the Caribbean and the Caribbean large igneous province. The Pedro Bank fault zone also drives active extension at the 200-km-long San Andres rift along the southwest margin of the Nicaraguan Rise. Influence of the Cocos Ridge indentor may be contributing to reactivation of faulting along the southwesternmost, active segment of the Hess Escarpment.

  12. Marine geophysical research helps to assess the seismic hazard at the Hispaniola Island

    Carbó-Gorosabel, A.; Granja Bruña, J.; Llanes Estrada, M.; Munoz Martin, A.; Gómez Ballesteros, M.; Druet, M.; Martín-Dávila, J.; Pazos, A.; Catalan, M.; ten Brink, U. S.; Hernaiz-Huerta, P.; Olaiz, A. J.; Torres, R.; Brothers, D. S.


    Detailed swath bathymetry mapping of complete geological provinces together with high-resolution seismic profiles provide critical perspective for the detection and study of active faults and their seismic and tsunami hazard. Since 2003 the Universidad Complutense de Madrid has been leading an international research group to study the north-eastern Caribbean, from the Lesser Antilles to Jamaica. This area comprises the 200 km-wide boundary zone between the North American and the Caribbean plates, where the relative plate motion is 18-20 ±3 mm/year towards 070-075. The highly-oblique convergence between the plates in Hispaniola is accommodated by strain partitioning on seismic fault systems sub-parallel to the plate boundary: strike-slip (the Enriquillo-Plantain Garden and the Septentrional fault zones) and the compressive deformed belts (the Muertos thrust belt and the North Hispaniola thrust belt). Results from several research cruises offshore Hispaniola have identified and characterized zones of active deformation that were not observed onshore, such as the Muertos out-of-sequence thrust or the Beata Ridge crest fault zone. The Muertos out-of-sequence thrust could be related to the M≈8 event occurred the 18th of October in 1751 that shook central and south-eastern Hispaniola. In other seismic fault zones, such as the Enriquillo-Plantain Garden and the Septentrional fault zones, knowledge of their offshore continuity is limited. Future research cruises will target the offshore continuity of these strike-slip seismic fault zones in the vicinity of Southern Peninsula of Haiti, in the Jamaica Passage and in the Gonave Bay. As part of the NORCARIBE project, a research cruise will be taking place in the spring of 2012 aboard the Spanish R/V Hespérides. Multichannel, high-resolution and wide-angle seismic profiles will be acquired together with swath bathymetry, magnetic and gravity data. The scientific and social interest in studying this region has greatly

  13. A circum-earth shear zone at low-latitudes and episodic large earthquakes in it and the circum-Pacific seismic zone

    MA; Zongjin; DU; Pinren; REN; Jinwei; GAO; Xianglin


    Because of the differential motions between the Northern and Southern Hemispheres of the Earth, there exists a motion discordant zone between them. On the surface this zone consists of 13 large faults dominant with strike-slip. We call it a global shear zone at low-latitudes (E system). By statistical analysis of temporal distribution of earthquakes Mw≥7.5 in the E system and the circum-Pacific (P system) during 1900-2003, we find that there exist quasi-episodic and alternative activities in and between these two systems. This phenomenon is likely associated with the half-sphere oscillation in dilation and contraction and the change of the Earth's rotation rate.

  14. Thermal regime from bottom simulating reflectors along the N Ecuador - S Colombia margin: relation between tectonic segmentation, thermal variation and the limit of the seismic rupture zones.

    Marcaillou, B.; Spence, G.; Collot, J.; Wang, K.; Ribodetti, A.


    In the North Ecuador South Columbian (NESC) convergent margin (0°N) three megathrust events, in 1942, 1958 and 1979, present rupture zones that abut one another. Multichannel seismic (MCS) reflection and bathymetric data acquired during the SISTEUR (2000) and AMADEUS (2005) cruises highlighted that the margin comprises four transverse segments (called, from south to north, the Esmeraldas, Manglares, Tumaco and Patia segments), each with clearly different tectonic and structural patterns. The central Manglares and Tumaco segments are separated by the newly discovered NW trending Manglares fault that matches the boundary between the 1958 and 1979 rupture zones. North of the fault, the fore-arc basin is shortened deformed and uplifted, while to the south the fore-arc basin, located landward of a prominent Outer Basement High (OBH), is widely subsiding and undeformed. Moreover, to the north of the Manglares fault, the underthrusting Nazca plate present an intense normal faulting is absent to the south. To investigate the relationships between seismogenesis and thermal structure along the plate boundary, we conducted thermal modelling constrained by sediment heat flow measurements and by heat flow derived from Bottom Simulating Reflectors (BSRs) on MCS lines collected during the SISTEUR and AMADEUS cruises. Just landward of the deformation front in the region of the Tumaco segment, a zone of anomalously low heat flow values is present and results in a thermal segmentation of the margin consistent with the tectonic segmentation. Finite-element thermal models carried out for each thermal segment show that: The along-strike heat flow variations are produced by changes in the age of the oceanic plate, the dip of the decollement and hydrothermal cooling due to the subduction of the strongly faulted part of the Nazca crust. The hypocenters for both the 1958 and 1979 earthquakes occurred at a depth on the interface where the temperature is ~160°C. For the seismogenic zone

  15. Refined Views of Strike-slip Fault Zones, Seismicity, and State of Stress Associated With the Pacific-North America Plate Boundary in Southern California

    Hauksson, E.; Nicholson, C.; Shaw, J. H.; Plesch, A.; Shearer, P. M.; Sandwell, D. T.; Yang, W.


    The mostly strike-slip plate boundary in southern California is expressed as a system of late Quaternary faults or principal slip zones (PSZs), with numerous adjacent smaller slip surfaces. It is complex, even after large cumulative displacements, and consists of major fault systems with multi-stranded, non-planar fault geometry, including some in close proximity to each other. There are also secondary cross faults and low-angle detachments that interact with the PSZs accommodating main plate boundary motion. The loading of plate-tectonic strain causes the largest earthquakes along PSZs, moderate-sized events in their immediate vicinity, and small earthquakes across the whole region. We apply relocated earthquake and refined focal mechanism (1981-2013) catalogs, as well as other geophysical datasets to provide refined views of the 3D fault geometry of these active fault systems. To determine properties of individual fault zones, we measure the Euclidian distance from every hypocenter to the nearest PSZ. In addition, we assign crustal geophysical parameters such as heat flow value and shear or dilatation strain rates to each epicenter. We investigate seismogenic thickness and fault zone width as well as earthquake source processes. We find that the seismicity rate is a function of location, with the rate dying off exponentially with distance from the PSZ. About 80% of small earthquakes are located within 5 km of a PSZ. For small earthquakes, stress drops increase in size with distance away from the PSZs. The magnitude distribution near the PSZs suggests that large earthquakes are more common close to PSZs, and they are more likely to occur at greater depth than small earthquakes. In contrast, small quakes can occur at any geographical location. An optimal combination of heat flow and strain rate is required to concentrate the strain along rheologically weak fault zones, which accommodate the crustal deformation processes, causing seismicity. The regional trend of

  16. Neotectonics and seismicity of a slowly deforming segment of the Adria-Europe convergence zone - the northern Dinarides fold-and-thrust belt

    Ustaszewski, Kamil; Herak, Marijan; Tomljenović, Bruno; Herak, Davorka; Matej, Srebrenka


    With GPS-derived shortening rates of c. 3-5 mm/a, the Adria-Europe convergence zone across the fold-and-thrust belt of the Dinarides (Balkan Peninsula) is a slowly deforming plate boundary by global standards. We have analysed the active tectonics and instrumental seismicity of the northernmost segment of this fold-and-thrust belt at its border to the Pannonian Basin. This area hosts a Maastrichtian collisional suture formed by closure of Mesozoic fragments of the Neotethys, overprinted by Miocene back-arc extension, which led to the exhumation of greenschist- to amphibolite-grade rocks in several core complexes. Geological, geomorphological and reflection seismic data provide evidence for a compressive or transpressive reactivation of extensional faults after about 5 Ma. The study area represents the seismically most active region of the Dinarides apart from the Adriatic Sea coast and the area around Zagreb. The strongest instrumentally recorded earthquake (27 October 1969) affected the city of Banja Luka (northern Bosnia and Herzegovina). Fault plane solutions for the main shock (ML 6.4) and its largest foreshock (ML 6.0) indicate reverse faulting along ESE-WNW-striking nodal planes and generally N-S trending pressure axes. The spatial distribution of epicentres and focal depths, analyses of the macroseismic field and fault-plane solutions for several smaller events suggest on-going shortening in the internal Dinarides. Our results therefore imply that current Adria-Europe convergence is widely distributed across c. 300 km, rendering the entire Dinarides fold-and-thrust belt a slowly deforming plate boundary.

  17. Ambient seismic noise tomography reveals a hidden caldera and its relation to the Tarutung pull-apart basin at the Sumatran Fault Zone, Indonesia

    Ryberg, Trond; Muksin, Umar; Bauer, Klaus


    We analyzed the noise recordings of a short-period seismic network to derive a shallow crustal S-wave velocity model at the Sumatra Fault in Northern Sumatra, Indonesia. By correlating the noise of 40 seismic stations' recording for 9 months, we could recover Rayleigh waves from vertical component recordings with sufficient signal-to-noise ratio. Group velocities of the Rayleigh waves could be determined in the period range from 0.71 to 4.4 s. These group velocities were used to invert for 2D group velocity maps at specific periods. Finally, the derived group velocity maps were inverted for a 3D S-wave velocity model. This model shows a region of a strong velocity decrease off the Great Sumatran Fault Zone, at the northeastern margin of the young Tarutung pull-apart basin. This observed low velocity block coincides with a caldera-like morphological feature which is interpreted as the surface expression of a hidden volcanic caldera. Considering the surface manifestations of geothermal activity around this anomaly, we conclude that the caldera is still acting as a heat source. On the other hand, the weak morphological expression at the surface indicates a certain age of the caldera which might be older than the Tarutung pull-apart basin. The findings provide important constraints on general concepts for the formation of pull-apart basins along the Sumatran fault and their relation to volcanism.

  18. Estimation of present-day inter-seismic deformation in Kopili fault zone of north-east India using GPS measurements

    Prakash Barman


    Full Text Available Current study reports the present-day inter-seismic deformation of Kopili fault zone of north-east India and slip rate estimate of Kopili fault using five epochs of global positioning system (GPS data collected from seven campaigns and five permanent sites. The rate of baseline length change of the GPS sites across the Kopili fault indicates ∼2.0 mm/yr E–W convergence across the fault. The fault parallel GPS site velocities clearly indicate dextral slip of the Kopili fault. The fault normal velocities show convergence across the Kopili fault, suggesting it to be a transpressional fault. The fault parallel velocities are inverted for fault slip and locking depth using an elastic dislocation model. The first-order, best-fit elastic dislocation model suggest average right lateral slip of 2.62 ± 0.79 mm/yr and a shallow locking depth (3 ± 2 km of the Kopili Fault. The slip of the Kopili fault is contributing to seismic moment accumulation (∼70.74 × 1015 Nm/yr, sufficient to drive possible future earthquakes (Mw ≥ 5.17.

  19. Seismic imaging of deep low-velocity zone beneath the Dead Sea basin and transform fault: Implications for strain localization and crustal rigidity

    ten Brink, U.S.; Al-Zoubi, A. S.; Flores, C.H.; Rotstein, Y.; Qabbani, I.; Harder, S.H.; Keller, Gordon R.


    New seismic observations from the Dead Sea basin (DSB), a large pull-apart basin along the Dead Sea transform (DST) plate boundary, show a low velocity zone extending to a depth of 18 km under the basin. The lower crust and Moho are not perturbed. These observations are incompatible with the current view of mid-crustal strength at low temperatures and with support of the basin's negative load by a rigid elastic plate. Strain softening in the middle crust is invoked to explain the isostatic compensation and the rapid subsidence of the basin during the Pleistocene. Whether the deformation is influenced by the presence of fluids and by a long history of seismic activity on the DST, and what the exact softening mechanism is, remain open questions. The uplift surrounding the DST also appears to be an upper crustal phenomenon but its relationship to a mid-crustal strength minimum is less clear. The shear deformation associated with the transform plate boundary motion appears, on the other hand, to cut throughout the entire crust. Copyright 2006 by the American Geophysical Union.

  20. Shallow seismic reflection profiles and geological structure in the Benton Hills, southeast Missouri

    Palmer, J.R.; Hoffman, D.; Stephenson, W.J.; Odum, J.K.; Williams, R.A.


    During late May and early June of 1993, we conducted two shallow, high-resolution seismic reflection surveys (Mini-Sosie method) across the southern escarpment of the Benton Hills segment of Crowleys Ridge. The reflection profiles imaged numerous post-late Cretaceous faults and folds. We believe these faults may represent a significant earthquake source zone. The stratigraphy of the Benton Hills consists of a thin, less than about 130 m, sequence of mostly unconsolidated Cretaceous, Tertiary and Quaternary sediments which unconformably overlie a much thicker section of Paleozoic carbonate rocks. The survey did not resolve reflectors within the upper 75-100 ms of two-way travel time (about 60-100 m), which would include all of the Tertiary and Quaternary and most of the Cretaceous. However, the Paleozoic-Cretaceous unconformity (Pz) produced an excellent reflection, and, locally a shallower reflector within the Cretaceous (K) was resolved. No coherent reflections below about 200 ms of two-way travel time were identified. Numerous faults and folds, which clearly offset the Paleozoic-Cretaceous unconformity reflector, were imaged on both seismic reflection profiles. Many structures imaged by the reflection data are coincident with the surface mapped locations of faults within the Cretaceous and Tertiary succession. Two locations show important structures that are clearly complex fault zones. The English Hill fault zone, striking N30??-35??E, is present along Line 1 and is important because earlier workers indicated it has Pleistocene Loess faulted against Eocene sands. The Commerce fault zone striking N50??E, overlies a major regional basement geophysical lineament, and is present on both seismic lines at the southern margin of the escarpment. The fault zones imaged by these surveys are 30 km from the area of intense microseismicity in the New Madrid seismic zone (NMSZ). If these are northeast and north-northeast oriented fault zones like those at Thebes Gap they are

  1. Seismic energy trapped in a low velocity zone: the effects of the Yogyakarta earthquake at LUSI, Indonesia

    Lupi, Matteo; Saenger, Erik H.; Fuchs, Florian; Miller, Stephen A.


    On May 27, 2006, a M6.3 strike slip earthquake shook Yogyakarta, Java. Forty-seven hours later, hot mud reached the surface near Surabaya, 250 km far from the epicenter, creating several mud vents aligned along a NW-SE direction. The mud eruption reached a peak of 180.000 km3 of erupted material per day and it is still ongoing. The mud flooded several villages and caused a loss of approximately 4 billions to Indonesia. Geochemical analysis, geological data, and numerical simulations suggest that the earthquake may have initiated the liquefaction of the mud that then injected and reactivated a fault plane. However, the trigger mechanism of the eruption is still debated because a second hypothesis suggests that Lusi may have been triggered by a blowout following drilling problems in the nearby Banjar Panji-1 well. The earthquake-triggering hypothesis is supported by the evidence immediately after the main shock ongoing drilling operations experienced a loss of the drilling mud downhole. In addition, the eruption of the mud began only 47 hours after the Yogyakarta earthquake and the mud reached the surface at different locations aligned along the Watukosek fault, a strike-slip fault system that bridges LUSI with the nearby volcanic complex. Moreover, the Yogyakarta earthquake also affected the volcanic activity of Mt. Semeru, located even further than Lusi from the epicenter of the earthquake. However, the drilling-triggering hypothesis points out that the earthquake was too far from LUSI for inducing relevant stress changes at depth and highlights how upwelling fluids that reached the surface first emerged only 200 m far from the drilling rig that was operative at the time. Hence, was LUSI triggered by the earthquake or by drilling operations? We conducted a seismic wave propagation study on a geological model based on vp, vs, and density values for the different lithologies and seismic profiles of the crust beneath LUSI. Our analysis shows compelling evidence for

  2. Possibility of prediction of strong seismic events in the Middle Odra Fault Zone based on variations of kinematic activity of the Świebodzice Depression

    Kaczorowski, Marek; Kasza, Damian; Zdunek, Ryszard; Wronowski, Roman; Szczerbowski, Zbigniew


    Książ Geodynamic Laboratory of Space Research Centre is located in the Świebodzice Depression unit. The laboratory was built inside underground corridors made in the castle hill about 50 m below surface. The main instruments which provide us most of information about tectonic activity of Świebodzice Depression are two long water-tubes tiltmeters 65 and 92 meters long (WT). The WT are situated on several rocky blocks which motions provided tectonic signals to WT. The instruments register numerous irregularly occurred epochs of water levels variations in hydrodynamic systems of magnitudes exceeding tidal signals dozens or so times. These observations are interpreted as result of tiltings of foundation and vertical motions of rock blocks. Signals of tiltings of foundation and vertical motions are superposed by the WT registration system. The resultant signals from four channels of WT were defined by us as tectonic activity functions of the massif. Variations of the tectonic activity functions as well as their first derivatives were compared with the seismic activity in Fore-Sudetic Monocline. We found correlation in time and amplitudes domains between extremes and inflection points of the first derivative of the tectonic activity function and the seismic events in the Middle Odra Fault Zone of the Fore-Sudetic Monocline. High correlation concerns only the strong earthquakes the energies of which were larger than 4 MJ. Almost all the high energy seismic events from 2005 to 2015 took place in surroundings of minima, maxima or inflection points of tectonic activity functions when first derivatives were close to zero. In the epochs of large absolute values of amplitudes of first derivatives i.e. during high tectonic activity of Świebodzice Depression, the strong energy earthquakes never happened. The observation shows that the origin of the low and high energy earthquakes is different. The high energy earthquakes are produced by natural tectonic activity, while the

  3. The Gibraltar Arc seismogenic zone (part 2): Constraints on a shallow east dipping fault plane source for the 1755 Lisbon earthquake provided by tsunami modeling and seismic intensity

    Gutscher, M.-A.; Baptista, M. A.; Miranda, J. M.


    The Great Lisbon earthquake has the largest documented felt area of any shallow earthquake and an estimated magnitude of 8.5-9.0. The associated tsunami ravaged the coast of SW Portugal and the Gulf of Cadiz, with run-up heights reported to have reached 5-15 m. While several source regions offshore SW Portugal have been proposed (e.g.— Gorringe Bank, Marquis de Pombal fault), no single source appears to be able to account for the great seismic moment as well as all the historical tsunami amplitude and travel time observations. A shallow east dipping fault plane beneath the Gulf of Cadiz associated with active subduction beneath Gibraltar, represents a candidate source for the Lisbon earthquake of 1755. Here we consider the fault parameters implied by this hypothesis, with respect to total slip, seismic moment, and recurrence interval to test the viability of this source. The geometry of the seismogenic zone is obtained from deep crustal studies and can be represented by an east dipping fault plane with mean dimensions of 180 km (N-S) × 210 km (E-W). For 10 m of co-seismic slip an Mw 8.64 event results and for 20 m of slip an Mw 8.8 earthquake is generated. Thus, for convergence rates of about 1 cm/yr, an event of this magnitude could occur every 1000-2000 years. Available kinematic and sedimentological data are in general agreement with such a recurrence interval. Tsunami wave form modeling indicates a subduction source in the Gulf of Cadiz can partly satisfy the historical observations with respect to wave amplitudes and arrival times, though discrepancies remain for some stations. A macroseismic analysis is performed using site effect functions calculated from isoseismals observed during instrumentally recorded strong earthquakes in the region (M7.9 1969 and M6.8 1964). The resulting synthetic isoseismals for the 1755 event suggest a subduction source, possibly in combination with an additional source at the NW corner of the Gulf of Cadiz can satisfactorily

  4. Vivienda unifamiliar en Madrid

    Lamela, Antonio


    Full Text Available In the building of this house, the architect has sought to make the best possible use of the texture and external quality of the materials employed. The indoor distribution is straightforwardly modern and the various functional zones of the house have been clearly differentiated. The garden has been made as continuous as possible with the porch and the inside of the building, especially with the living and dining rooms. The aspect of the house is very simple, formal, and reflects with much sincerity the true purpose of each part of the building.En la construcción de esta vivienda unifamiliar se ha procurado obtener el máximo aprovechamiento de los materiales empleados, en cuanto a su textura y calidad. La distribución interior es clara y simple, y en su organización se han seguido las directrices más actuales en este tipo de vivienda, estableciendo una zonificación adecuada y el debido aislamiento y conexión entre sus distintas partes. En todo lo posible, se ha procurado prolongar el jardín dentro del porche y la vivienda, sobre todo en el cuarto de estar y comedor. En cuanto a su composición arquitectónica, responde a un concepto de gran sencillez, formal, lleno de sinceridad y de autenticidad.

  5. Fichas descriptivas de bibliotecas localizadas en Madrid

    Maldonado Martínez, Ángeles


    [EN] Sheets on some libraries located in Madrid. These sheets are part of the section "Documentation Centres" in the journal "ALFOZ. Madrid, Territorio, Economia y Sociedad" and were published between 1985 and 1987. The libraries described are: - Biblioteca Municipal - Biblioteca de la Cámara de Comercio e Industria de Madrid - Biblioteca y Centro de Documentación del Instituto de Estudios de la Administración Central (IEAL) - Biblioteca del Instituto Nacional de Estadística - ...

  6. Fichas descriptivas de bibliotecas localizadas en Madrid


    [EN] Sheets on some libraries located in Madrid. These sheets are part of the section "Documentation Centres" in the journal "ALFOZ. Madrid, Territorio, Economia y Sociedad" and were published between 1985 and 1987. The libraries described are: - Biblioteca Municipal - Biblioteca de la Cámara de Comercio e Industria de Madrid - Biblioteca y Centro de Documentación del Instituto de Estudios de la Administración Central (IEAL) - Biblioteca del Instituto Nacional de Estadística - ...

  7. Formation of diapiric structure in the deformation zone, central Indian Ocean: A model from gravity and seismic reflection data

    K S Krishna; D Gopala Rao; Yu P Neprochnov


    Analyses of bathymetry, gravity and seismic reflection data of the diffusive plate boundary in the central Indian Ocean reveal a new kind of deformed structure besides the well-reported structures of long-wavelength anticlinal basement rises and high-angle reverse faults. The structure (basement trough) has a length of about 150 km and deepens by up to 1 km from its regional trend (northward dipping). The basement trough includes a rise at its center with a height of about 1.5 km. The rise is about 10 km wide with rounded upper surface and bounded by vertical faults. A broad free-air gravity low of about 20 mGal and a local high of 8 mGal in its center are associated with the identified basement trough and rise structure respectively. Seismic results reveal that the horizontal crustal compression prevailing in the diffusive plate boundary might have formed the basement trough possibly in early Pliocene time. Differential loading stresses have been generated from unequal crust/sediment thickness on lower crustal and upper mantle rocks. A thin semi-ductile serpentinite layer existing near the base of the crust that is interpreted to have been formed at mid-ocean ridge and become part of the lithosphere, may have responded to the downward loading stresses generated by the sediments and crustal rocks to inject the serpentinites into the overlying strata to form a classic diapiric structure.

  8. Instituto de Psicoterapia, Madrid

    Schoebel Ungria, Willi


    Full Text Available This building is situated within the «Peña Retama» estate, in the midst of an extensive garden, where it is planned to build in the immediate future a swimming pool and a pelota court. Basically, this Institute provides facilities for leading a form of life that is both peaceful and busy. With this object in view training courses in languages, painting, and amateur film making are organised. There is a book and recordings library. Furthermore, the close relationship between the doctor and the patient is not neglected, and a very discreet surveillance is maintained over the patients. The general distribution of the Institute involves three main zones: one for men, one for women and a relaxation zone. Each of them has individual apartments and small drawing and living rooms, which can be easily transformed into dining rooms. The wing of the building devoted to sleeping treatment is more isolated and independent and includes ample terraces suitable for summer and winter use. The interior decoration has been carefully planned, aiming to make it both intimate and pleasant. Colour schemes are so-called «tranquil», and avoid vivid, exciting and intense colour patterns. The outside of the building harmonises with the background of mountain scenery, and as a whole, the project is eminently functional and efficient in its detailed design.Se alza sobre la finca «Peña Retama», dentro de un extenso espacio ajardinado donde se prevé, en un futuro próximo, la construcción de una piscina y un frontón. Fundamentalmente, se trata de un Centro con posibilidades para hacer una vida, a la vez tranquila y ocupada; con esta finalidad se organizan clases de idiomas, pintura, sesiones de cine-club, y se dispone de una biblioteca-discoteca; pero sin descuidar la necesaria relación y contacto muy personal de enfermo y médico, y una vigilancia discretísima sobre aquél. En su distribución general se acusan tres zonas: hombres, mujeres y zona de reposo, que

  9. Use of an Educational Seismic Network for Monitoring Intraplate Seismicity in the Central United States

    Webb, S. M.; Bailey, L.; Lindsey, J.; Pavlis, G. L.; Hamburger, M. W.; Bauer, M.


    The Indiana PEPP seismic network is a 21-station broadband, digital seismic network operated as a collaboration between Indiana University and area high schools, colleges, and museums. Since 1999 the network has used internet data transmission to provide real-time network recording and archiving at the IRIS Data Management Center. The network provides expanded coverage of intraplate seismicity, quarry and mining explosion, and teleseismic earthquakes. We analyzed the signal-to-noise ratio for 11 local events tabulated in the ANSS catalog and used this to project the detection threshold for the network. We define a detection threshold for these events as the minimum projected equivalent event with 5 phases having a signal to noise ration of 3 or larger. We found that the detection threshold for events in southern Indiana, which is the approximate center of the network, varied from 1.7 to 2.3. For events outside this area the estimated detection floor ranges from 2.5 to 3.3. We also examined 264 regional earthquakes (300 to 1500 km) tabulated in the ANSS catalog during 2002. We found events larger than approximately 2.5 in the New Madrid region were consistently detectable. Regional events larger than 3.0 in the 700 to 1500 km distance range were consistently recorded. To further clarify detection capabilities we carefully scanned all data from a 114- day period, from day 51 through 164 of 2002. During this test period we observed 3520 mining explosions (29 events/day), all teleseismic events larger than about 5.0, and only 2 unambiguous earthquakes (the June 18, M_L = 5.0, Evansville (Caborn) mainshock and a single aftershock). This result illustrates an important practical issue in appraising seismicity levels in this area: less than 0.1% of the detected signals were local earthquakes. We extended this review period to include the remaining 251 days of 2002, but examining only the nighttime hours (0000-1200 UTC), when the levels of noise and blasting are minimal

  10. Quantitative analysis of seismic trapped waves in the rupture zone of the Landers, 1992, California earthquake: Evidence for a shallow trapping structure

    Peng, Z.; Ben-Zion, Y.; Michael, A. J.; Zhu, L.


    Waveform modeling of seismic fault zone (FZ) trapped waves has been claimed to provide a high resolution imaging of FZ structure at seismogenic depth. We analyze quantitatively a waveform data set generated by 238 Landers aftershocks recorded by a portable seismic array (Lee, 1999). The array consists of 33 three-component L-22 seismometers, 22 of which on a line crossing the surface rupture zone of the mainshock. A subset of 93 aftershocks were also recorded by the Southern California Seismic Network, while the other events were recorded only by the FZ array. We locate the latter subset of events with a "grid-search relocation method" using accurately picked P and S arrival times, a half-space velocity model, and back-azimuth adjustment to correct the effect of low velocity FZ material on phase arrivals. Next we determine the quality of FZ trapped wave generation from the ratio of trapped waves to S-wave energy for stations relatively close to and far from the FZ. Energy ratios exceeding 4, between 2 and 4, and less than 2, are assigned quality A, B, and C of trapped wave generation. We find that about 70% of nearby events with S-P time less than 2 sec, including many clearly off the fault, generate FZ trapped waves with quality A or B. This distribution is in marked contrast with previous claims that trapped waves at Landers are generated only by sources close to or inside the fault zone (Li et al., 1994, 2000). The existence of trapped waves due to sources outside the Landers rupture zone indicates that the generating structure is shallow, as demonstrated in recent 3D calculations of wave propagation in irregular FZ structures (Fohrmann et al., 2002). The time difference between the S arrivals and trapped wave group does not grow systematically with increasing source-receiver distance along the fault, in agreement with the above conclusion. The dispersion of trapped waves at Landers is rather weak, again suggesting a short propagation distance inside the low

  11. Geological and hydrogeological conditions of the Aigion seismic active fault zone (Deep Geodynamic Laboratory Corinth) based on borehole data and hydraulic tests

    Rettenmaier, D.; Giurgea, V.; Pizzino, L.; Unkel, I.; Hoetzl, H.; Foerster, A.; Quattrocchi, F.; Nikas, K.


    The Gulf of Corinth and the northern part of the Peloponnesus/Greece, an area of asymmetric graben structure, step faults and tilted blocks, is one of the most active seismic zones in the world. Six major faults are known to be most responsible for the historic and present seismic activities in the area of Aigion. Our study focuses preliminarily on the area around the Aigion fault, whose trace runs E-W through the harbour of Aigion. Investigations of the stratigraphic sequence, tectonic structure and hydrogeologic conditions of the southern Corinth graben shoulder and first drilling activities there, have started in summer 2001. From July until September 2002 the International Continental Deep Drilling Project (ICDP) and the EU Project DGLab-Gulf of Corinth drilled the AIG10 borehole in the harbour of Aigion to a total depth of 1001 m. Our investigations in this ICDP/EU framework are aimed at studying the thermal-hydraulic conditions on the southern graben shoulder. Here we report the first results on sampling and hydraulic testing. The deep AIG10 borehole has successfully cored in approx. 760 m depth the fault plane, which separates fractured radiolarite in the hanging wall from highly fractured and karstified platy, micritic limestone (Olonos-Pindos Unit) in the footwall. A complete lithologic section is now available through the monitoring of cuttings and cores, which built a major cornerstone for defining an integrated regional tectonic and geologic model. Several pumping tests and hydrochemical investigations made in the region of Aigion and especially in the AIG10 borehole deliver together with geophysical borehole logging the database for a thermo-hydraulic heat flow model. The pumping test AIG10C in the conglomerates of the graben sediments show a hydraulic conductivity of about 2 x 10E-5 m/s - 3 x 10E-4 m/s at a depth of approximately 211 m. The result was a residual drawdown, which indicates a closed hydraulic system between the semi-permeable Aigion

  12. Edificio Cogesol, en Madrid

    Alas, Genaro


    Full Text Available The functions to be met by this building were as follows. The housing of the necessary machinery for the manufacture of caffein free coffee, reception store, silo, stores, nightwatchman's house, offices, garage and workshop, dressing rooms. As the northern side, facing the Barajas highway, was the more important, the main building of the factory was placed on that side. Along the south, facing a secondary access road, the office block, the staff rooms and the watchman's house have been located. Between the two nuclei is the loading yard. The manufacturing tower has a metal structure, slender and smooth. The vertical and horizontal columns and beams have been hidden within the rear wall, the intermediate partition and the lift shaft. The main longitudinal stabilising member crosses this lift shaft, hence the former is discontinuous. The wind pressure acting on the tower is transmitted to the adjacent building, but as the two are separated by a dilation joint, flexible thrust connections are fitted between them. The long structural members were erected in sections, and the weldings were done with great care to avoid subsequent deformations, which would have shown on the smooth exterior. To an external observer the factory zone stands out clearly from the rest, for the tower is enclosed largely in transparent glass, so that all the machinery can be seen from outside. The stores, on the other hand, are enclosed with brick walls, and enhance the light and transparent quality of the tower. This contrast is further developed by the relative volumes and shapes of the various parts of the project, which produce an organic but spectacular sense of dynamic unity.El programa de necesidades se desarrolló según el siguiente esquema: edificio para la maquinaria destinada a la fabricación del café descafeinado, almacén de entrada, silo, almacenes varios, vivienda para el guarda, oficinas, garajes y taller y vestuario. Como de las dos fachadas principales

  13. Co-seismic secondary surface fractures on southeastward extension of the rupture zone of the 2005 Kashmir earthquake

    Jayangondaperumal, R.; Thakur, V. C.


    After the 2005 Kashmir earthquake, we mapped surface ground fractures in Tangdhar, Uri, Rajouri and Punch sectors and liquefaction features in Jammu area lying close to the eastern side of the Line of Control (LOC) in Kashmir, India. The NW trending ground fractures occurred largely in the hanging wall zone of the southeastern extension of the causative fault in Tangdhar and Uri sectors. The principal compressive stress deduced from the earthquake induced ground fractures is oriented at N10°, whereas the causative Balakot-Bagh fault strikes 330°. The fault-plane solution indicates primarily SW thrusting of the causative fault with a component of strike-slip motion. The ground fractures reflect pronounced strike-slip together with some tensile component. The Tangdhar area showing left-lateral strike-slip motion lies on the hanging wall, and the Uri region showing right-lateral strike-slip movement is located towards the southeastern extension of the causative fault zone. The shear fractures are related to static stress that was responsible for the failure of causative fault. The tensile fractures with offsets are attributed to combination of both static and dynamic stresses, and the fractures and openings without offsets owe their origin due to dynamic stress. In Punch-Rajouri and Jammu area, which lies on the footwall, the fractures and liquefactions were generated by dynamic stress. The occurrence of liquefaction features in the out board part of the Himalayan range front near Jammu is suggestive of stress transfer ˜ 230 km southeast of the epicenter. The Balakot-Bagh Fault (BBF), the Muzaffarabad anticline, the rupture zone of causative fault and the zone of aftershocks — all are aligned in a ˜ 25 km wide belt along the NW-SE trending regional Himalayan strike of Kashmir region and lying between the MBT and the Riasi Thrust (Murree Thrust), suggesting a seismogenic zone that may propagate towards the southeast to trigger an earthquake in the eastern part of

  14. Microstructures and petro-fabrics of lawsonite blueschist in the North Qilian suture zone, NW China: Implications for seismic anisotropy of subducting oceanic crust

    Cao, Yi; Jung, Haemyeong; Song, Shuguang


    We conducted a detailed study on the microstructures and petro-fabrics of massive and foliated lawsonite blueschist (LBS) in North Qilian suture zone, NW China. The lattice preferred orientation (LPO) of glaucophane and lawsonite in foliated lawsonite blueschist (LBS) is considered to be dominantly formed by the deformation mechanism of dislocation creep and rigid-body rotation, respectively. The LPO of glaucophane is mainly characterized by the [001] axis aligning parallel to lineation and the [100] axis and (110) pole plunging perpendicular to foliation. In contrast, the LPO of lawsonite features the maximum [010] axis concentrated close to lineation and the [001] axis strongly clustered normal to foliation. The preferred orientation of [010] axis of lawsonite parallel to lineation is supported by a two-dimensional numerical modeling using the finite-volume method (FVM). The mineral LPOs are much stronger in foliated LBS than in massive LBS. In addition, a kinematic vorticity analysis suggests that both pure shear dominant (Wm = 0.18-0.26) and simple shear dominant (Wm = 0.86-0.93) deformation regimes are present in foliated LBS. The [001] axis and (010) pole of glaucophane, and the [100] and [010] axes of lawsonite, tend to distribute in a foliation-parallel girdle in the pure shear dominant samples, but simple shear dominant samples display more lineation-parallel concentrations of a [001] axis of glaucophane and a [010] axis of lawsonite. Because the whole-rock seismic anisotropies in foliated LBS are significantly higher than those in massive LBS and a counteracting effect on seismic anisotropies occurs between glaucophane and lawsonite, the delay time of fast S-wave polarization anisotropy induced by an actual subducting oceanic crust with a high subducting angle (> 45-60°) is expected to range from 0.03 to 0.09 s (lower bound for massive LBS) and from 0.1 to 0.3 s (upper bound for foliated epidote blueschist).

  15. Residencia para personas mayores en Villa del Prado, Madrid

    García-Vaquero Alvaro, Javier


    Full Text Available Basic faci lities fo r socia l serv ices. Building designed as a home fo r the elderly, with 120 beds plus adult day care service for 40 seniors; erected under an agreement between the Madrid Housing Institute (IVIMA and the Regional Department ofFamily Affairs and Social Services in a small tOWlI in the region ofMadrid with a population of4.350. The design lends particular auention to zoning and spatial distribution based 0 11 a specific organisational chart as wel! as to daylight-related questions. The choice ofmaterials and colours is in keeping with the intended use ofthe building and the characteristics ofits users.Equipamiento Básico para Asistencia Social. Edificio destinado a Residencia pa ra Personas Mayores con una capacidad para 120 plazas residenciales con Centro de Estancias Diurnas para 40 plazas externas, realizado mediante Convenio entre el Instituto de la Vivienda de Madrid (IVIMA y la Consejeria de Familia y Servicios Sociales de la Comunidad de Madrid, en un pequeño municipio de esta Comunidad con una población de 4.350 habitantes. El proyecto dedica especial atención a la zonificación y a la distribució n espacial, en fu nci án de IIt I claro organigrama, y al manej o de la luz natural. La elección de materiales y colores se realiza en funci án del uso a que se destina el edificio ya las especiales características de sus usuarios.

  16. Estimation of earthquake source parameters in the Kachchh seismic zone, Gujarat, India, using three component S-wave spectra

    Nagamani, Durgada; Mandal, Prantik


    Earthquake source parameters and crustal Q0 values for the 138 selected local events of (Mw{:}2.5{-}4.4) the 2001 Bhuj earthquake sequence have been computed through inversion modelling of S-waves from three-component broadband seismometer data. SEISAN software has been used to locate the identified local earthquakes, which were recorded at least three or more stations of the Kachchh seismological network. Three component spectra of S-wave are being inverted by using the Levenberg-Marquardt non-linear inversion technique, wherein the inversion scheme is formulated based on ω 2 source model. SAC Software (seismic analysis code) is being utilized for calculating three-component displacement and velocity spectra of S-wave. The displacement spectra are used for estimating corner frequency (in Hz) and long period spectral level (in nm-s). These two parameters play a key role in estimating earthquake source parameters. The crustal {Q}0 values have been computed simultaneously for each component of three-component broadband seismograph. The estimated seismic moment (M0) and source radius ( r) using S-wave spectra range from 7.03E+12 to 5.36E+15 N-m and 178.56 to 565.21 m, respectively. The corner frequencies for S-wave vary from 3.025 to 7.425 Hz. We also estimated the radiated energy (ES) using velocity spectra, which is varying from 2.76E+06 to 4.07E+11 Joules. The estimated apparent stress drop and static stress drop values range from 0.01 to 2.56 and 0.53 to 36.79 MPa, respectively. Our study also reveals that estimated Q0 values vary from 119.0 to 7229.5, with an average Q0 value of 701. Another important parameter, by which the earthquake rupture process can be recognized, is Zuniga parameter. It suggests that most of the Kachchh events follow the frictional overshoot model. Our estimated static stress drop values are higher than the apparent stress drop values. And the stress drop values are quite larger for intraplate earthquakes than the interplate earthquakes.

  17. Estimation of earthquake source parameters in the Kachchh seismic zone, Gujarat, India, using three component S-wave spectra

    Durgada Nagamani; Prantik Mandal


    Earthquake source parameters and crustal $Q_{0}$ values for the 138 selected local events of ($\\hbox {M}_{\\mathrm{w}}{:}2.5{-}4.4$) the 2001 Bhuj earthquake sequence have been computed through inversion modelling of S-waves from three-component broadband seismometer data. SEISAN software has been used to locate the identified local earthquakes, which were recorded at least three or more stations of the Kachchh seismological network. Three component spectra of S-wave are being inverted by using the Levenberg–Marquardt non-linear inversion technique, wherein the inversion scheme is formulated based on $\\omega ^{2}$ source model. SAC Software (seismic analysis code) is being utilized for calculating three-component displacement and velocity spectra of S-wave. The displacement spectra are used for estimating corner frequency (in Hz) and long period spectral level (in nm-s). These two parameters play a key role in estimating earthquake source parameters. The crustal ${Q}_{0}$ values have been computed simultaneously for each component of three-component broadband seismograph. The estimated seismic moment (M0) and source radius (r) using S-wave spectra range from 7.03E+12 to 5.36E+15 N-m and 178.56 to 565.21 m, respectively. The corner frequencies for S-wave vary from 3.025 to 7.425 Hz. We also estimated the radiated energy ($E_{S}$) using velocity spectra, which is varying from 2.76E+06 to 4.07E+11 Joules. The estimated apparent stress drop and static stress drop values range from 0.01 to 2.56 and 0.53 to 36.79 MPa, respectively. Our study also reveals that estimated $Q_{0}$ values vary from 119.0 to 7229.5, with an average $Q_{0}$ value of 701. Another important parameter, by which the earthquake rupture process can be recognized, is Zuniga parameter. It suggests that most of the Kachchh events follow the frictional overshoot model. Our estimated static stress drop values are higher than the apparent stress drop values. And the stress drop values are quite larger

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

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


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

  19. Modeling the seismic cycle in subduction zones: The role and spatiotemporal occurrence of off-megathrust earthquakes

    van Dinther, Y.


    Shallow off-megathrust subduction events are important in terms of hazard assessment and coseismic energy budget. Their role and spatiotemporal occurrence, however, remain poorly understood. We simulate their spontaneous activation and propagation using a newly developed 2-D, physically consistent, continuum, viscoelastoplastic seismo-thermo-mechanical modeling approach. The characteristics of simulated normal events within the outer rise and splay and normal antithetic events within the wedge resemble seismic and seismological observations in terms of location, geometry, and timing. Their occurrence agrees reasonably well with both long-term analytical predictions based on dynamic Coulomb wedge theory and short-term quasi-static stress changes resulting from the typically triggering megathrust event. The impact of off-megathrust faulting on the megathrust cycle is distinct, as more both shallower and slower megathrust events arise due to occasional off-megathrust triggering and increased updip locking. This also enhances tsunami hazards, which are amplified due to the steeply dipping fault planes of especially outer rise events.

  20. Crustal structure beneath the Northern Mississippi Embayment from travel time inversion of vintage wide-angle seismic data

    Guo, L.; Magnani, M.


    The northern Mississippi Embayment (ME) in the central US is located along the southern margin of Laurentia, a region that has been shaped by a long history of tectonic and magmatic events, including episodes of continental rifting, collision and amalgamation. In the ME these events have fundamentally altered the structure and composition of the continental lithosphere, resulting in the formation and failure of the Paleozoic Reelfoot Rift, and in the emplacement of the enigmatic mafic rift pillow at lower crustal and upper mantle depths beneath the Reelfoot Rift. Because of the spatial correlation between the present, historical and prehistorical seismicity in the New Madrid seismic zone and the mafic rift pillow, it has been proposed that this magmatic feature plays a key role in localizing strain in the Central US. Emerging evidence, however, shows that Quaternary deformation in the ME is not restricted to the New Madrid seismic zone, but encompasses a region beyond the presently seismogenic area, perhaps suggesting that the mafic rift pillow extends beyond its previously detected location. To test this hypothesis and to better constrain the lateral extent, dimension, and velocity structure of the mafic rift pillow in lower crust and upper mantle beneath the ME, we perform a travel time tomographic inversion using recent modeling codes on two vintage wide-angle seismic datasets available in the region. The data were acquired by the USGS in 1980 and 1991, and are the only seismic wide-angle crustal data constraining the geometry of the rift pillow. The 1980 USGS seismic refraction investigation consisted of a total of 34 900-1800 kg shots gathered in 9 locations and recorded by 100 portable seismographs along a series of profiles targeting the structure of the Reelfoot Rift north of Memphis, Tennessee. The 1991 USGS survey acquired a N-S 400 km-long seismic profile from Memphis, Tennessee to St. Louis, Missouri, and included 3 680-2260 kg shots recorded by ~200

  1. Investigation of Icelandic rift zones reveals systematic changes in hydrothermal outflow in concert with seismic and magmatic events: Implications for investigation of Mid-Ocean Ridge hydrothermal systems

    Curewitz, D.; Karson, J. A.


    Co-registration of several generations of geological data was carried out for hydrothermal fields along active rift zones of the Iceland plate boundary zone. Significant short- and long-term changes in vent locations, flow rates and styles, and fluid characteristics over short periods take place in concert with recorded earthquakes, dike intrusions, and fissure eruptions. Higher resolution, more detailed analysis of the Icelandic hydrothermal sites will inform investigation of similar data from mid-ocean ridge hydrothermal systems along the RIDGE 2000 focus sites. Initial results from the Hengill and Krafla geothermal areas covering a time-span of nearly 40 years at ~10 year intervals reveal limited changes in the surface expression of fault populations, with the exception of local fault and fracture systems. The location and population density of individual vents and groups of vents underwent significant changes over the same time period, with either vents shifting location, or new vents opening and old vents closing. Registration of changes in vent fluid temperatures, vent field ground temperatures, fluid flow rates, and vent eruptive styles reveal changes in hydrothermal flow systematics in concert with the observed changes in vent location and vent population density. Significant local seismic and volcanological events (earthquakes, earthquake swarms, dike intrusions, eruptions, inflation/deflation) that are potential triggers for the observed changes take place in intervening years between production of successive maps. Changes in modeled stress intensities and local fracture/fault density and geometry associated with these tectono-magmatic events correspond well to inferred locations of increased or decreased shallow permeability thought to control hydrothermal outflow behavior. Recent seismic events are strongly linked to well-mapped changes in fracture/fault population and hydrothermal flow behavior in the Hveragerdi region, near Hengill, and provide higher

  2. Static stress transfer within the Cephalonia Transfer Fault Zone (CTFZ) during the 2014 seismic sequence in Cephalonia and the 2015 earthquake in Lefkada

    Sboras, Sotiris; Chatzipetros, Alexandros; Pavlides, Spyros; Karastathis, Vassilis; Papadopoulos, Gerassimos


    The 2014 seismic sequence in Cephalonia and the following 2015 earthquake in Lefkada Islands, Greece, showed that the Cephalonia Transfer Fault Zone (CTFZ), which runs along the western coasts of both islands, comprises a wide fault zone of parallel to sub-parallel fault segments. The January-February 2014 sequence of Cephalonia consisted of three moderate to strong events. According to published focal mechanisms, the first strongest shock (January 26, Mw 6.1) was produced by a W-dipping, oblique (right-lateral reverse) fault, the second (January 26, Mw 5.3) by a ENE-dipping, pure reverse fault and the third by a ESE-dipping, almost pure right-lateral strike slip fault. The November 17 2015 (Mw 6.4) Lefkada earthquake was produced by a WNW-dipping, roughly vertical, almost pure right-lateral strike-slip fault. None of the shocks above produced any direct coseismic ground rupture, while published relocated hypocentral locations for the Cephalonia sequence revealed various depths indicating a complex fault pattern. Based on published seismological, geological and satellite data (i.e. InSAR), the respective seismic sources were modelled in order to calculate the static stress changes i) during the Cephalonia and Lefkada sequences, and ii) after the sequences for the surrounding faults from the Greek Database of Seismogenic Sources (GreDaSS). Results showed that the February 3 2014 Cephalonia fault was variously affected by the rupture of the two January 26 faults. Stress change distribution on the fault plane showed that both stress drop and rise occurred. The November 17 2015 Lefkada fault was slightly loaded after the rupture of the whole Cephalonia fault system due to the great distance. The post-sequence stress changes variously affect the surrounding faults: the southern segment of the CTFZ is relieved from stresses, while the central ones show a mixed situation. The large northern segment, offshore from Lefkada Island, is mainly under stress drop. Stress drop is

  3. Seismic reflection-based evidence of a transfer zone between the Wagner and Consag basins: implications for defining the structural geometry of the northern Gulf of California

    González-Escobar, Mario; Suárez-Vidal, Francisco; Hernández-Pérez, José Antonio; Martín-Barajas, Arturo


    This study examines the structural characteristics of the northern Gulf of California by processing and interpreting ca. 415 km of two-dimensional multi-channel seismic reflection lines (data property of Petróleos Mexicanos PEMEX) collected in the vicinity of the border between the Wagner and Consag basins. The two basins appear to be a link between the Delfín Superior Basin to the south, and the Cerro Prieto Basin to the north in the Mexicali-Imperial Valley along the Pacific-North America plate boundary. The seismic data are consistent with existing knowledge of four main structures (master faults) in the region, i.e., the Percebo, Santa María, Consag Sur, and Wagner Sur faults. The Wagner and Consag basins are delimited to the east by the Wagner Sur Fault, and to the west by the Consag Sur Fault. The Percebo Fault borders the western margin of the modern Wagner Basin depocenter, and is oriented N10°W, dipping (on average) ˜40° to the northeast. The trace of the Santa María Fault located in the Wagner Basin strikes N19°W, dipping ˜40° to the west. The Consag Sur Fault is oriented N14°W, and dips ˜42° to the east over a distance of 21 km. To the east of the study area, the Wagner Sur Fault almost parallels the Consag Sur Fault over a distance of ˜86 km, and is oriented N10°W with an average dip of 59° to the east. Moreover, the data provide new evidence that the Wagner Fault is discontinuous between the two basins, and that its structure is more complex than previously reported. A structural high separates the northern Consag Basin from the southern Wagner Basin, comprising several secondary faults oriented NE oblique to the main faults of N-S direction. These could represent a zone of accommodation, or transfer zone, where extension could be transferred from the Wagner to the Consag Basin, or vice versa. This area shows no acoustic basement and/or intrusive body, which is consistent with existing gravimetric and magnetic data for the region.

  4. La nueva embajada alemana, en Madrid

    Schoebel Ungria, G.


    Full Text Available This embassy involves two buildings, which, because of their style, appropriate aspect, the fine taste of their design, and the highly efficient manner in which the volumes agree with the building site, constitutes a singular ornament to one of the best zones of Madrid. All the materials are traditional in Spanish constructional practice, and were carefully chosen: their full plastic and chromatic quality being well utilised.Los dos edificios que componen el conjunto constituyen, por su tratamiento, por su representatividad, por el gusto con que han sido construidos y por el respetuoso trato dado a los volúmenes del aprovechamiento autorizado, un ornato singular en una de las zonas más nobles y vistosas de la capital de España. Todos los materiales empleados son los tradicionales del país anfitrión y fueron elegidos con esmero, conservándolos en toda su pureza plástica de carácter y cromática.



    <正>20091465 Cai Xuelin(College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,China);Cao Jiamin Preliminary Study on the 3-D Crust Structure for the Longmen Lithosphere and the Genesis of the Huge Wenchuan Earthquake,Sichuan Province,China(Journal of Chengdu University of Technology,ISSN1671-9727,CN51-1634/N,35(4),2008,p.357-365,8 illus.,39 refs.)Key words:deep-seated structures,large earthquakes,Longmenshan Fracture ZoneBased on a structural analysis of many seismic sounding profiles,there are two fault systems in Longmen collisional orogenic belt,Sichuan Province,China.They are both different obviously and correlative closely.One is shallow fault system composed mainly of brittle shear zones in surface crust,and the other is deep fault system composed mainly of crust-mantle ductile shear zones cutting Moho discontinuity.Based on the result of researching geological structure and seismic sounding profiles,

  6. Seismic Catalogue and Seismic Network in Haiti

    Belizaire, D.; Benito, B.; Carreño, E.; Meneses, C.; Huerfano, V.; Polanco, E.; McCormack, D.


    The destructive earthquake occurred on January 10, 2010 in Haiti, highlighted the lack of preparedness of the country to address seismic phenomena. At the moment of the earthquake, there was no seismic network operating in the country, and only a partial control of the past seismicity was possible, due to the absence of a national catalogue. After the 2010 earthquake, some advances began towards the installation of a national network and the elaboration of a seismic catalogue providing the necessary input for seismic Hazard Studies. This paper presents the state of the works carried out covering both aspects. First, a seismic catalogue has been built, compiling data of historical and instrumental events occurred in the Hispaniola Island and surroundings, in the frame of the SISMO-HAITI project, supported by the Technical University of Madrid (UPM) and Developed in cooperation with the Observatoire National de l'Environnement et de la Vulnérabilité of Haiti (ONEV). Data from different agencies all over the world were gathered, being relevant the role of the Dominican Republic and Puerto Rico seismological services which provides local data of their national networks. Almost 30000 events recorded in the area from 1551 till 2011 were compiled in a first catalogue, among them 7700 events with Mw ranges between 4.0 and 8.3. Since different magnitude scale were given by the different agencies (Ms, mb, MD, ML), this first catalogue was affected by important heterogeneity in the size parameter. Then it was homogenized to moment magnitude Mw using the empirical equations developed by Bonzoni et al (2011) for the eastern Caribbean. At present, this is the most exhaustive catalogue of the country, although it is difficult to assess its degree of completeness. Regarding the seismic network, 3 stations were installed just after the 2010 earthquake by the Canadian Government. The data were sent by telemetry thought the Canadian System CARINA. In 2012, the Spanish IGN together

  7. Crustal structure and mantle transition zone thickness beneath a hydrothermal vent at the ultra-slow spreading Southwest Indian Ridge (49°39'E): a supplementary study based on passive seismic receiver functions

    Ruan, Aiguo; Hu, Hao; Li, Jiabiao; Niu, Xiongwei; Wei, Xiaodong; Zhang, Jie; Wang, Aoxing


    As a supplementary study, we used passive seismic data recorded by one ocean bottom seismometer (OBS) station (49°41.8'E) close to a hydrothermal vent (49°39'E) at the Southwest Indian Ridge to invert the crustal structure and mantle transition zone (MTZ) thickness by P-to-S receiver functions to investigate previous active seismic tomographic crustal models and determine the influence of the deep mantle thermal anomaly on seafloor hydrothermal venting at an ultra-slow spreading ridge. The new passive seismic S-wave model shows that the crust has a low velocity layer (2.6 km/s) from 4.0 to 6.0 km below the sea floor, which is interpreted as partial melting. We suggest that the Moho discontinuity at 9.0 km is the bottom of a layer (2-3 km thick); the Moho (at depth of 6-7 km), defined by active seismic P-wave models, is interpreted as a serpentinized front. The velocity spectrum stacking plot made from passive seismic data shows that the 410 discontinuity is depressed by 15 km, the 660 discontinuity is elevated by 18 km, and a positive thermal anomaly between 182 and 237 K is inferred.

  8. Changing theory, changing role of Coriolis effect - The East-West asymmetry of the Wadati-Benioff seismic zones

    Scalera, Giancarlo


    It is a long history the tale of the recognized asymmetries of the Earth. In 1600 William Gilbert (1544-1603) published De Magnete in which the North and South geomagnetic pole are described. In 1620 Francis Bacon (1561-1628) in the XXVIIth aphorism of the Novum Organum (second part) describes the southern tips of the continents, and many other asymmetries were later described. In 1975 Samuel Warren Carey (1911-2002) stated: Neither north and south, nor east and west are tectonically equivalent. A non exhaustive list of asymmetries of the Earth is: The magnetic polarity; The land-hemisphere and the water-hemisphere; Southern tips of the continents; Larger extension of expanding mid-oceanic ridges on the southern hemisphere; South-eastward trend of younger ages in the long Pacific seafloor volcanic chains; A larger width of the seafloor isochrones bands on the Nazca region; A pear-shaped Earth; etc. It is a few decades that the different slopes of the Wadati-Benioff zones oriented towards the east and west has been enclosed in the list. Under the Americas they have angles of about 30 degrees, while under the Pacific east coasts (Asia, Japan) the angles are steeper (Luyendyk, 1970; Isacks & Barazangi, 1977; and many others). The cause of this difference has been identified in the tidal drag that would cause a global shift of the lithosphere towards west - the so called westward drift (Bostrom, 1971; Stevenson & Turner, 1977; among others). This solution has been many times criticized on the basis of the irrelevance of the tidal forces with respect to viscous friction (Jordan, 1974; Ranalli, 2000; Caputo & Caputo, 2012). Moreover, a simplistic evaluation of the regime of the convective motion in the mantle and of the order of magnitude of the involved forces (viscous, buoyancy, inertial) hastily judges as negligible the role of the Coriolis effect in producing the observed slope differences of the Wadati-Benioff regions. Instead, it is possible to show that changing

  9. AstroMadrid: Astrophysics and technological developments in Comunidad de Madrid

    Mas-Hesse, J. M.


    AstroMadrid is a network constituted by different research groups in the Comunidad de Madrid area, with the objective of coordinating the activities related to the development of astronomical instrumentation in the various centres. AstroMadrid is a multidisciplinar team which benefits from the synergies provided by the different participating groups, optimizing our capabilities to develop instrumentation, and minimizing the problems related to the geographical dispersion within our region. AstroMadrid is also participated by several aerospace industries, which complement the capabilities and facilities available in the research centres. In addition to optimizing the development of instrumentation, AstroMadrid plays an essential role in the formation of new engineers and scientists, by actively contributing to some Master degree courses organized by different Universities in Madrid.

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

    Syuhada, E-mail: [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)


    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.

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

    Syuhada, Hananto, Nugroho D.; Puspito, Nanang T.; Anggono, Titi; Handayani, Lina; Yudistira, Tedi


    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.

  12. Distinct Variations in Seismic Velocity Structure of the Crust and Upper Mantle across the Ailao Shan-Red River Shear Zone in Northern Vietnam

    Hung, S.; Pan, Y.; Huang, B.; Huang, W.; Le, T.; Dinh, V.


    The tectonic evolution of the Aliao Shan-Red River shear zone (RRSZ) that runs from southeast Tibet through North Vietnam to the South China Sea and marks the boundary between the Indochina and South China blocks has been considered closely linked with the northward indention of the strong Indian plate into the Eurasian continent and the consequent uplift of the Tibetan Plateau. A variety of models have been proposed to explain the postcollisional deformation and magmatism of SE Asia and movement along the RRSZ. Since December 2005, Institute of Earth Science, Academia Sinica of Taiwan has deployed a regional broadband array with station spacing of ~50 km in Northern Vietnam for earthquake and seismic structure studies. We collect data from earthquakes with magnitude≥5.5 and epicentral distances of 30-90o between December, 2005 and June, 2008. Using this new dataset, we report 3-D variations of P- and S-wave speeds (δlnVP and δlnVS) and Poisson's ratios via δln(VP/VS) in the crust and upper mantle across the shear zone, obtained with tomographic inversion of P and S relative travel time residuals measured by inter-station cross-correlation of waveforms at both high- and low-frequencies. We employ physically realistic 3-D sensitivity kernels for frequency-dependent traveltime data and data-adaptive, multi-scale parameterization in the inversion. The resulting models reveal noticeable differences across the RRSZ, where the anomalies of distinctly low VS and VP/VS are widely-dispersed in the lower crust and uppermost mantle down to the depth of 100 km to the southwest of the RRSZ. This may indicate that ductile crustal mass has flowed out of Tibet into Indochina accompanying extrusion of relatively hot lithospheric mantle along the RRSZ related to Late Cenozoic volcanism in the region. Though less distinct in the S velocity model, an elongated fast anomaly about 60 km wide that strikes parallel to the RRSZ and subvertically extends to the depth of 60 km clearly

  13. Physical property and Textural transition across the Unconformity and Major Seismic Reflectors in the Upper plate of the Costa Rica Subduction zone offshore Osa Peninsula

    Hamahashi, M.; Screaton, E.; Tanikawa, W.; Hashimoto, Y.; Martin, K. M.; Saito, S.; Kimura, G.


    At the Costa Rica subduction zone offshore Osa Peninsula, the Cocos plate and Cocos Ridge subduct under the Caribbean plate along the Middle America Trench, creating active seismicity. In this region, the Caribbean plate is characterized by a well-consolidated, high velocity framework material beneath the slope sediments, but the nature of the upper plate material is yet unknown. During Integrated Ocean Drilling Program (IODP) Expedition 334 and 344, the unconformity between the slope sediments (Unit 1) and upper plate material (Units 2 and 3) consisting of lithic sedimentary units was penetrated at mid-slope Site 1380. In the current study, to characterize the compaction behavior of the upper plate material, we investigate the physical properties, texture and composition of the sediments at Site 1380 by conducting microstructural observations, resistivity measurements, particle size analyses, X-ray fluorescence and X-ray diffraction analyses. The microstructures of sediments observed through the microscope tend to develop dense and cohesive textures in low porosity sediments, and particle size changes across several unconformities. In particular, the small particle-sized lithic fragments compose larger bodies and form cohesive structures. The cross correlation between measured particle size and shipboard porosity show negative correlation especially at Unit 2, indicating that larger sized particles form smaller or fewer pores. From the results of XRF and XRD analyses, we found that Al, K, Ti tend to concentrate in the higher porosity sediments of Unit 1, whereas Si, Ca, P, Mg, Na, and Mn concentrate in the lower porosity sediments of Unit 2 and 3. The higher concentration in Mg, Na, Mn, Si may be due to minerals such as chlorite, serpentine, amphibole, and sodium manganese. The crossplots between porosity and element concentration show negative correlations in Mg, Na, and Mn with porosity, suggesting that the minerals rich in these elements may relate with the

  14. Wind energy resource assessment in Madrid region

    Migoya, Emilio; Crespo, Antonio; Jimenez, Angel; Garcia, Javier; Manuel, Fernando [Laboratorio de Mecanica de Fluidos, Departamento de Ingenieria Energetica y Fluidomecanica, Escuela Tecnica Superior Ingenieros Industriales (ETSII), Universidad Politecnica de Madrid (UPM), C/Jose Gutierrez Abascal, 2-28006, Madrid (Spain)


    The Comunidad Autonoma de Madrid (Autonomous Community of Madrid, in the following Madrid Region), is a region located at the geographical centre of the Iberian Peninsula. Its area is 8.028 km{sup 2}, and its population about five million people. The Department of Economy and Technological Innovation of the Madrid Region, together with some organizations dealing on energy saving and other research institutions have elaborated an Energy Plan for the 2004-12 period. As a part of this work, the Fluid Mechanics Laboratory of the Superior Technical School of Industrial Engineers of the Polytechnic University of Madrid has carried out the assessment of the wind energy resources [Crespo A, Migoya E, Gomez Elvira R. La energia eolica en Madrid. Potencialidad y prospectiva. Plan energetico de la Comunidad de Madrid, 2004-2012. Madrid: Comunidad Autonoma de Madrid; 2004]; using for this task the WAsP program (Wind Atlas Analysis and Application Program), and the own codes, UPMORO (code to study orography effects) and UPMPARK (code to study wake effects in wind parks). Different kinds of data have been collected about climate, topography, roughness of the land, environmentally protected areas, town and village distribution, population density, main facilities and electric power supply. The Spanish National Meteorological Institute has nine wind measurement stations in the region, but only four of them have good and reliable temporary wind data, with time measurement periods that are long enough to provide representative correlations among stations. The Observed Wind Climates of the valid meteorological stations have been made. The Wind Atlas and the resource grid have been calculated, especially in the high wind resource areas, selecting appropriate measurements stations and using criteria based on proximity, similarity and ruggedness index. Some areas cannot be used as a wind energy resource mainly because they have environmental regulation or, in some cases, are very close

  15. Airborne LiDAR analysis and geochronology of faulted glacial moraines in the Tahoe-Sierra frontal fault zone reveal substantial seismic hazards in the Lake Tahoe region, California-Nevada USA

    Howle, James F.; Bawden, Gerald W.; Schweickert, Richard A.; Finkel, Robert C.; Hunter, Lewis E.; Rose, Ronn S.; von Twistern, Brent


    We integrated high-resolution bare-earth airborne light detection and ranging (LiDAR) imagery with field observations and modern geochronology to characterize the Tahoe-Sierra frontal fault zone, which forms the neotectonic boundary between the Sierra Nevada and the Basin and Range Province west of Lake Tahoe. The LiDAR imagery clearly delineates active normal faults that have displaced late Pleistocene glacial moraines and Holocene alluvium along 30 km of linear, right-stepping range front of the Tahoe-Sierra frontal fault zone. Herein, we illustrate and describe the tectonic geomorphology of faulted lateral moraines. We have developed new, three-dimensional modeling techniques that utilize the high-resolution LiDAR data to determine tectonic displacements of moraine crests and alluvium. The statistically robust displacement models combined with new ages of the displaced Tioga (20.8 ± 1.4 ka) and Tahoe (69.2 ± 4.8 ka; 73.2 ± 8.7 ka) moraines are used to estimate the minimum vertical separation rate at 17 sites along the Tahoe-Sierra frontal fault zone. Near the northern end of the study area, the minimum vertical separation rate is 1.5 ± 0.4 mm/yr, which represents a two- to threefold increase in estimates of seismic moment for the Lake Tahoe basin. From this study, we conclude that potential earthquake moment magnitudes (Mw) range from 6.3 ± 0.25 to 6.9 ± 0.25. A close spatial association of landslides and active faults suggests that landslides have been seismically triggered. Our study underscores that the Tahoe-Sierra frontal fault zone poses substantial seismic and landslide hazards.

  16. Limits of the seismogenic zone in the epicentral region of the 26 December 2004 great Sumatra-Andaman earthquake: Results from seismic refraction and wide-angle reflection surveys and thermal modeling

    Klingelhoefer, Frauke; Ladage, S; Dessa, J -X; Graindorge, David; Franke, D; André, C; Permana, Haryadi; Yudistira, T; Chauhan, Ajay; 10.1029/2009JB006569


    The 26 December 2004 Sumatra earthquake (Mw = 9.1) initiated around 30 km depth and ruptured 1300 km of the Indo-Australian Sunda plate boundary. During the Sumatra OBS (ocean bottom seismometer) survey, a wide angle seismic profile was acquired across the epicentral region. A seismic velocity model was obtained from combined travel time tomography and forward modeling. Together with reflection seismic data from the SeaCause II cruise, the deep structure of the source region of the great earthquake is revealed. Four to five kilometers of sediments overlie the oceanic crust at the trench, and the subducting slab can be imaged down to a depth of 35 km. We find a crystalline backstop 120 km from the trench axis, below the fore arc basin. A high velocity zone at the lower landward limit of the raycovered domain, at 22 km depth, marks a shallow continental Moho, 170 km from the trench. The deep structure obtained from the seismic data was used to construct a thermal model of the fore arc in order to predict the li...

  17. 2017 one-year seismic hazard forecast for the central and eastern United States from induced and natural earthquakes

    Petersen, Mark D.; Mueller, Charles; Moschetti, Morgan P.; Hoover, Susan M.; Shumway, Allison; McNamara, Daniel E.; Williams, Robert A.; Llenos, Andrea L.; Ellsworth, William L.; Michael, Andrew J.; Rubinstein, Justin L.; McGarr, Arthur F.; Rukstales, Kenneth S.


    We produce the 2017 one-year seismic hazard forecast for the central and eastern United States from induced and natural earthquakes that updates the 2016 one-year forecast; this map is intended to provide information to the public and to facilitate the development of induced seismicity forecasting models, methods, and data. The 2017 hazard model applies the same methodology and input logic tree as the 2016 forecast, but with an updated earthquake catalog. We also evaluate the 2016 seismic hazard forecast to improve future assessments. The 2016 forecast indicated high seismic hazard (greater than 1% probability of potentially damaging ground shaking in one-year) in five focus areas: Oklahoma-Kansas, the Raton Basin (Colorado/New Mexico border), north Texas, north Arkansas, and the New Madrid Seismic Zone. During 2016, several damaging induced earthquakes occurred in Oklahoma within the highest hazard region of the 2016 forecast; all of the 21 magnitude (M) ≥ 4 and three M ≥ 5 earthquakes occurred within the highest hazard area in the 2016 forecast. Outside the Oklahoma-Kansas focus area two earthquakes with M ≥ 4 occurred near Trinidad, Colorado (in the Raton Basin focus area), but no earthquakes with M ≥ 2.7 were observed in the north Texas or north Arkansas focus areas. Several observations of damaging ground shaking levels were also recorded in the highest hazard region of Oklahoma. The 2017 forecasted seismic rates are lower in regions of induced activity due to lower rates of earthquakes in 2016 compared to 2015, which may be related to decreased wastewater injection, caused by regulatory actions or by a decrease in unconventional oil and gas production. Nevertheless, the 2017 forecasted hazard is still significantly elevated in Oklahoma compared to the hazard calculated from seismicity before 2009.

  18. [Hospitals and surgeons: Madrid 1940].

    de Quevedo, Francisco Vázquez


    The history of the hospitals and general surgeons that best represent the centres in Madrid are here in reviewed, comprising the period between 1940 and the closure of the Hospital Clinico (1957) as well as the Hospital General (General Hospital) (1967), both in Atocha. Other hospitals which are reviewed and highlighted are: the H. de la Princesa (the Princess Hospital), the H. del Nifio Jesus (Hospital of the Child Jesus), the H. Militar (Military Hospital) and the Cruz Roja (Red Cross). Data is provided on the permanent surgeons in the following centres: H. General: J. Goyanes, J. Die, J. de la Villa, T. Rodriguez, E. Diaz, G. Bueno e H. Huerta; H. Clinico: L. de la Peña, L. Cardenal, L. Olivares, R. Argüelles, J. Estella y M. F. Zumel; H. Militar: M. G. Ulla, M. Bastos, M. G. Durán, J. S. Galindo, y A. G. Durán; Hospital de la Cruz Roja: V. M. Noguera, L. Serrada, F. Luque y L. L. Durán; H. de la Princesa: P. Cifuentes, P. G. Duarte, L. Estella y R. Aiguabella; H. del Niño Jesús: J. Garrido Lestache; H. Clinico, last time, Atocha: F. M. Lagos, R. Vara y A. de la Fuente.

  19. Update of the USGS 2016 One-year Seismic Hazard Forecast for the Central and Eastern United States From Induced and Natural Earthquakes

    Petersen, M. D.; Mueller, C. S.; Moschetti, M. P.; Hoover, S. M.; Llenos, A. L.; Ellsworth, W. L.; Michael, A. J.; Rubinstein, J. L.; McGarr, A.; Rukstales, K. S.


    The U.S. Geological Survey released a 2016 one-year forecast for seismic hazard in the central and eastern U.S., which included the influence from both induced and natural earthquakes. This forecast was primarily based on 2015 declustered seismicity rates but also included longer-term rates, 10- and 20- km smoothing distances, earthquakes between Mw 4.7 and maximum magnitudes of 6.0 or 7.1, and 9 alternative ground motion models. Results indicate that areas in Oklahoma, Kansas, Colorado, New Mexico, Arkansas, Texas, and the New Madrid Seismic Zone have a significant chance for damaging ground shaking levels in 2016 (greater than 1% chance of exceeding 0.12 PGA and MMI VI). We evaluate this one-year forecast by considering the earthquakes and ground shaking levels that occurred during the first half of 2016 (earthquakes not included in the forecast). During this period the full catalog records hundreds of events with M ≥ 3.0, but the declustered catalog eliminates most of these dependent earthquakes and results in much lower numbers of earthquakes. The declustered catalog based on USGS COMCAT indicates a M 5.1 earthquake occurred in the zone of highest hazard on the map. Two additional earthquakes of M ≥ 4.0 occurred in Oklahoma, and about 82 earthquakes of M ≥ 3.0 occurred with 77 in Oklahoma and Kansas, 4 in Raton Basin Colorado/New Mexico, and 1 near Cogdell Texas. In addition, 72 earthquakes occurred outside the zones of induced seismicity with more than half in New Madrid and eastern Tennessee. The catalog rates in the first half of 2016 and the corresponding seismic hazard were generally lower than in 2015. For example, the zones for Irving, Venus, and Fashing, Texas; Sun City, Kansas; and north-central Arkansas did not experience any earthquakes with M≥ 2.7 during this period. The full catalog rates were lower by about 30% in Raton Basin and the Oklahoma-Kansas zones but the declustered catalog rates did not drop as much. This decrease in earthquake

  20. New Seismic Hazard study in Spain Aimed at the revision of the Spanish Building Code

    Rivas-Medina, A.; Benito, B.; Cabañas, L.; Martínez-Solares, J. M.; Ruíz, S.; Gaspar-Escribano, J. M.; Carreño, E.; Crespo, M.; García-Mayordomo, J.


    In this paper we present a global overview of the recent study carried out in Spain for the new hazard map, which final goal is the revision of the Building Code in our country (NCSE-02). The study was carried our for a working group joining experts from The Instituto Geografico Nacional (IGN) and the Technical University of Madrid (UPM) , being the different phases of the work supervised by an expert Committee integrated by national experts from public institutions involved in subject of seismic hazard. The PSHA method (Probabilistic Seismic Hazard Assessment) has been followed, quantifying the epistemic uncertainties through a logic tree and the aleatory ones linked to variability of parameters by means of probability density functions and Monte Carlo simulations. In a first phase, the inputs have been prepared, which essentially are: 1) a project catalogue update and homogenization at Mw 2) proposal of zoning models and source characterization 3) calibration of Ground Motion Prediction Equations (GMPE's) with actual data and development of a local model with data collected in Spain for Mw logic tree and their weights. Finally, the hazard estimation was done with the logic tree shown in figure 1, including nodes for quantifying uncertainties corresponding to: 1) method for estimation of hazard (zoning and zoneless); 2) zoning models, 3) GMPE combinations used and 4) regression method for estimation of source parameters. In addition, the aleatory uncertainties corresponding to the magnitude of the events, recurrence parameters and maximum magnitude for each zone have been also considered including probability density functions and Monte Carlo simulations The main conclusions of the study are presented here, together with the obtained results in terms of PGA and other spectral accelerations SA (T) for return periods of 475, 975 and 2475 years. The map of the coefficient of variation (COV) are also represented to give an idea of the zones where the dispersion among

  1. Enhancement of Seismic Data Processing and Interpretation of Fracture Zones on the Upper Part of Granitic Basement in Cuu Long Basin, Vietnam

    Tan Mai Thanh


    Full Text Available The fractured granite basement is the primary oil and gas reservoir in the Cuu Long Basin, Vietnam. Due to the complexity of this non-layered unconventional target, combined with complicated fault and fracture systems, the seismic data quality near and within the basement section is very low. For this reason, it is important to apply improved seismic data processing workflows, filtering and migration techniques, as wells as attribute processing methods to enhance the imaging quality.

  2. The seismogenic Gole Larghe Fault Zone (Italian Southern Alps): quantitative 3D characterization of the fault/fracture network, mapping of evidences of fluid-rock interaction, and modelling of the hydraulic structure through the seismic cycle

    Bistacchi, A.; Mittempergher, S.; Di Toro, G.; Smith, S. A. F.; Garofalo, P. S.


    The Gole Larghe Fault Zone (GLFZ) was exhumed from 8 km depth, where it was characterized by seismic activity (pseudotachylytes) and hydrous fluid flow (alteration halos and precipitation of hydrothermal minerals in veins and cataclasites). Thanks to glacier-polished outcrops exposing the 400 m-thick fault zone over a continuous area > 1.5 km2, the fault zone architecture has been quantitatively described with an unprecedented detail, providing a rich dataset to generate 3D Discrete Fracture Network (DFN) models and simulate the fault zone hydraulic properties. The fault and fracture network has been characterized combining > 2 km of scanlines and semi-automatic mapping of faults and fractures on several photogrammetric 3D Digital Outcrop Models (3D DOMs). This allowed obtaining robust probability density functions for parameters of fault and fracture sets: orientation, fracture intensity and density, spacing, persistency, length, thickness/aperture, termination. The spatial distribution of fractures (random, clustered, anticlustered…) has been characterized with geostatistics. Evidences of fluid/rock interaction (alteration halos, hydrothermal veins, etc.) have been mapped on the same outcrops, revealing sectors of the fault zone strongly impacted, vs. completely unaffected, by fluid/rock interaction, separated by convolute infiltration fronts. Field and microstructural evidence revealed that higher permeability was obtained in the syn- to early post-seismic period, when fractures were (re)opened by off-fault deformation. We have developed a parametric hydraulic model of the GLFZ and calibrated it, varying the fraction of faults/fractures that were open in the post-seismic, with the goal of obtaining realistic fluid flow and permeability values, and a flow pattern consistent with the observed alteration/mineralization pattern. The fraction of open fractures is very close to the percolation threshold of the DFN, and the permeability tensor is strongly anisotropic

  3. Un sistema de saneamiento para Madrid

    Sánchez, Félix Cristóbal


    The Full Sanitation Plan for Madrid is the final action of a series undertaken for several years with the purpose to reach the completion of the sanitation system of the town. With the whole of these actions it could be said that the basic substructure has acquired enough level to deserve de real needs of the town.El Plan de Saneamiento Integral de Madrid representaba la culminación de una serie de acciones emprendidas, durante varios años, para conseguir que la ciudad completase su sistema d...

  4. La huelga de 1917 en Madrid

    Oscar Hernández Chinarro


    Full Text Available We found a huge number of studies on the various aspects that came together in Spain 1917 (crisis of the Restoration, Juntas, Parliamentary Assembly, etc., but it is unlikely, that historians have not delved into the events during that year in Madrid, namely, General Strike. Social tension Spain who lived in the early twentieth century, erupted in the summer of 1917 when for the first time in history was summoned indefinite strike, whose objectives were no longer working type but political. This article analyzes the roots, development and consequences of the strike during the events between 13 and 18 August 1917 in Madrid.

  5. Inmigrantes extranjeros y vivienda marginal en Madrid


    Madrid, la comunidad receptora de inmigrantes extranjeros más importante de España, tiene ya planteado un serio problema de integración con la población procedente de países del Tercer Mundo y Portugal. «Los inmigrantes de los países débiles están ampliando la base de la pobreza en Madrid. En su mayoría, ios extranjeros del Tercer Mundo están formando parte de los estratos pobres y marginados de la ciudad» (GIMÉNEZ, C. 1992).

  6. Ciudad Mercado, infraestructura en red. Madrid.

    Carruthers, Luz María


    Los mercados de abastos de Madrid atraviesan uno profunda crisis que conlleva su decadencia arquitectónica. Si bien han sido una pieza el clave en la construcción social y urbana de Madrid. no son considerados una infraestructura, lo cual repercute en el tipo y calidad de intervenciones a los que se los somete. Recuperar su condición infraestructura, supone pensar en los mercados como red, enfocándose en las interacciones que plantean con el entorno a múltiples escalas. Éstas, pueden deber...

  7. Risk-Targeted versus Current Seismic Design Maps for the Conterminous United States

    Luco, Nicolas; Ellingwood, Bruce R.; Hamburger, Ronald O.; Hooper, John D.; Kimball, Jeffrey K.; Kircher, Charles A.


    The probabilistic portions of the seismic design maps in the NEHRP Provisions (FEMA, 2003/2000/1997), and in the International Building Code (ICC, 2006/2003/2000) and ASCE Standard 7-05 (ASCE, 2005a), provide ground motion values from the USGS that have a 2% probability of being exceeded in 50 years. Under the assumption that the capacity against collapse of structures designed for these "uniformhazard" ground motions is equal to, without uncertainty, the corresponding mapped value at the location of the structure, the probability of its collapse in 50 years is also uniform. This is not the case however, when it is recognized that there is, in fact, uncertainty in the structural capacity. In that case, siteto-site variability in the shape of ground motion hazard curves results in a lack of uniformity. This paper explains the basis for proposed adjustments to the uniform-hazard portions of the seismic design maps currently in the NEHRP Provisions that result in uniform estimated collapse probability. For seismic design of nuclear facilities, analogous but specialized adjustments have recently been defined in ASCE Standard 43-05 (ASCE, 2005b). In support of the 2009 update of the NEHRP Provisions currently being conducted by the Building Seismic Safety Council (BSSC), herein we provide examples of the adjusted ground motions for a selected target collapse probability (or target risk). Relative to the probabilistic MCE ground motions currently in the NEHRP Provisions, the risk-targeted ground motions for design are smaller (by as much as about 30%) in the New Madrid Seismic Zone, near Charleston, South Carolina, and in the coastal region of Oregon, with relatively little (<15%) change almost everywhere else in the conterminous U.S.

  8. The Impressive 1811-1812 New Madrid Earthquake Sequence and the Geologic Record of at Least Two Other Sequences in the Last 1000 Years

    Williams, R. A.


    The currently active New Madrid seismic zone (NMSZ) was the source of a series of major earthquakes and hundreds of aftershocks that began on December 16, 1811 and continued through 1812. At the time, the region was sparsely populated but today it is home to about 12 million people. Four earthquakes in this 1811-1812 sequence had magnitudes (M) from about 6.8-8.0 and were felt widely across the eastern U.S. as far as the Atlantic seaboard 1,700 km away. About a dozen aftershocks in the M5.0-6.3 range were also felt widely across the eastern U.S. The first earthquake occurred December 16, 1811, at 2:15 a.m. followed by the largest aftershock in the sequence (M6.8-7.0) at about 7:15 a.m.; the second main shock at 9 a.m. on January 23, 1812; and the third main shock on February 7, 1812, at 3:45 a.m. These four principle shocks were among the largest to strike North America since European settlement. Because of low seismic attenuation in the eastern U.S., the area of strong shaking of the December 16 main shock was about 10 times larger than that of the 1906 M7.8 San Francisco earthquake. The NMSZ produced large earthquakes in the M6.0-6.6 range in 1843 and 1895 and currently generates about 150 earthquakes annually in the M1.5-4 range. Though no instrumental data for the 1811-1812 earthquakes exist, first-hand accounts indicate that the mainshocks were followed by hundreds of aftershocks that lasted for months. They caused general alarm from Detroit (800 km) to New Orleans (700 km). In the epicentral region, Memphis, Tenn. was not yet established, but many homes were damaged in the 5500-inhabitant town of St. Louis, Mo. (250 km). The frontier trading towns of Little Prairie (now Caruthersville) and New Madrid, Mo., were severely damaged and temporarily evacuated. The 1811-1812 sequence left its mark on the landscape that endures today. During the earthquake, witnesses reported that the ground rose, fell, and cracked, and that trees snapped. Large landslides were

  9. 日本东北地区双震带高精度重定位研究%Precise earthquake relocation of double seismic zone beneath Tohoku region in Japan

    傅煜铭; 江国明; 魏衍雯; 周智文; 马潇


    日本所在的西太平洋地区是世界上中深源地震发生最为频繁的地区。早期研究已表明,日本东北地区下方的中深源地震呈双层分布。为进一步分析该双震带的空间分布特征,本文通过方法测试证明了采用球坐标系下的三维射线追踪法改进后的双差定位法进行地震重定位的精确性和有效性,对使用该方法进行重定位前、后各方向上的误差进行了分析,并确定了最佳的定位参数。在此基础上,对日本东北地区的中深源地震进行了高精度重定位,并对重定位得到的震源位置进行了空间拟合,其结果表明地震呈明显的双层分布,且与西太平洋俯冲板块几近平行。本文研究结果对揭示双震带中地震的发震机理以及俯冲板块内的精细结构均具有重要意义。%Japan is located in western Pacific,where the intermediate-deep earth-quakes occur frequently.Early researches indicate that the intermediate-deep earthquakes beneath Tohoku region in Japan constitute a double seismic zone. In order to analyze the spatial distribution characteristics of the double seismic zone in Tohoku region,we use a method test to show the precision and validity of the double-difference location algorithm,which has been improved by 3-D ray tracing method in spherical coordinate system.We analyse the errors before and after relocation along different directions,and determine the most suitable parameters for relocation.Then we obtain the precise relocated earthquakes in the double seismic zone beneath Tohoku region,and fit the relocated hypocen-ters in three-dimensional space.The relocation results of intermediate-deep earthquakes in Tohoku region indicate that the earthquakes in the seismic zone are distributed obviously in double layers,which are approximately parallel to the subducting western Pacific Plate.The results of this paper are significant to reveal the mechanisms of earthquakes in double

  10. Seismic hazard estimation of northern Iran using smoothed seismicity

    Khoshnevis, Naeem; Taborda, Ricardo; Azizzadeh-Roodpish, Shima; Cramer, Chris H.


    This article presents a seismic hazard assessment for northern Iran, where a smoothed seismicity approach has been used in combination with an updated seismic catalog and a ground motion prediction equation recently found to yield good fit with data. We evaluate the hazard over a geographical area including the seismic zones of Azerbaijan, the Alborz Mountain Range, and Kopeh-Dagh, as well as parts of other neighboring seismic zones that fall within our region of interest. In the chosen approach, seismic events are not assigned to specific faults but assumed to be potential seismogenic sources distributed within regular grid cells. After performing the corresponding magnitude conversions, we decluster both historical and instrumental seismicity catalogs to obtain earthquake rates based on the number of events within each cell, and smooth the results to account for the uncertainty in the spatial distribution of future earthquakes. Seismicity parameters are computed for each seismic zone separately, and for the entire region of interest as a single uniform seismotectonic region. In the analysis, we consider uncertainties in the ground motion prediction equation, the seismicity parameters, and combine the resulting models using a logic tree. The results are presented in terms of expected peak ground acceleration (PGA) maps and hazard curves at selected locations, considering exceedance probabilities of 2 and 10% in 50 years for rock site conditions. According to our results, the highest levels of hazard are observed west of the North Tabriz and east of the North Alborz faults, where expected PGA values are between about 0.5 and 1 g for 10 and 2% probability of exceedance in 50 years, respectively. We analyze our results in light of similar estimates available in the literature and offer our perspective on the differences observed. We find our results to be helpful in understanding seismic hazard for northern Iran, but recognize that additional efforts are necessary to

  11. Seismic hazard estimation of northern Iran using smoothed seismicity

    Khoshnevis, Naeem; Taborda, Ricardo; Azizzadeh-Roodpish, Shima; Cramer, Chris H.


    This article presents a seismic hazard assessment for northern Iran, where a smoothed seismicity approach has been used in combination with an updated seismic catalog and a ground motion prediction equation recently found to yield good fit with data. We evaluate the hazard over a geographical area including the seismic zones of Azerbaijan, the Alborz Mountain Range, and Kopeh-Dagh, as well as parts of other neighboring seismic zones that fall within our region of interest. In the chosen approach, seismic events are not assigned to specific faults but assumed to be potential seismogenic sources distributed within regular grid cells. After performing the corresponding magnitude conversions, we decluster both historical and instrumental seismicity catalogs to obtain earthquake rates based on the number of events within each cell, and smooth the results to account for the uncertainty in the spatial distribution of future earthquakes. Seismicity parameters are computed for each seismic zone separately, and for the entire region of interest as a single uniform seismotectonic region. In the analysis, we consider uncertainties in the ground motion prediction equation, the seismicity parameters, and combine the resulting models using a logic tree. The results are presented in terms of expected peak ground acceleration (PGA) maps and hazard curves at selected locations, considering exceedance probabilities of 2 and 10% in 50 years for rock site conditions. According to our results, the highest levels of hazard are observed west of the North Tabriz and east of the North Alborz faults, where expected PGA values are between about 0.5 and 1 g for 10 and 2% probability of exceedance in 50 years, respectively. We analyze our results in light of similar estimates available in the literature and offer our perspective on the differences observed. We find our results to be helpful in understanding seismic hazard for northern Iran, but recognize that additional efforts are necessary to

  12. Proposed New Madrid NWR Contaminant Survey

    US Fish and Wildlife Service, Department of the Interior — The area studied in this report is near New Madrid in southeast Missouri. This area consists of the St. John's Bayou, 8,500 acres and Eagle's Nest area, 3,500 acres....

  13. Palinocam Network: airborne pollen vigilance in Madrid

    Patricia Cervigón Morales


    Full Text Available Asthma Regional Programme started to give up in 1992 with four big areas. Palinocam network project was first set up in Madrid as a part of Asthma Regional Programme, comprised in a wider Environmental Subprogram: Palynological Network of Madrid Region (PALINOCAM NETWORK.Palynological network is a multidisciplinary organization which has been working since 1993. In that moment an Experts Committee was created with This Experts Committee is coordinated by the Public Health Institute, under the technical Direction of Faculty of Pharmacy and is integrated by all of the involved institutions. This juridical framework is completed with individual agreements signed between the Councils and the Public Health Department, and with a Collaboration Agreement signed with the Madrid ́s Complutense University Faculty of Pharmacy.This network main aim is to watch for aerobiological content in Madrid's air, for a best knowledge of patients expositions in each geographical area in en different moment. This information has a great interest for Public Health.Palinocam Network is a useful tool in Public Health for offering information of aerobiological levels by Internet and Telephonic Service yearly .In this way allergic patients, sanitarians and media can know the most frequent pollen types in each season and its airborne level.

  14. Colegio Alemán Madrid

    Scmoebel, Willi


    Full Text Available El edificio del Colegio Alemán en Madrid es un Centro docente cuidadosamente proyectado y construido con especial cariño, circunstancias estas que han permitido un logro perfecto y son la causa de que podamos catalogarlo como ejemplar en su género.

  15. Seismic hazard assessment of Iran

    M. Ghafory-Ashtiany


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

  16. [Spatial analysis of syphilis and gonorrhea infections in a Public Health Service in Madrid].

    Wijers, Irene G M; Sánchez Gómez, Amaya; Taveira Jiménez, Jose Antonio


    Sexually transmitted diseases are a significant public health problem. Within the Madrid Autonomous Region, the districts with the highest syphilis and gonorrhea incidences are part of the same Public Health Service (Servicio de Salud Pública del Área 7, SSPA 7). The objective of this study was to identify, by spatial analysis, clusters of syphilis and gonorrhea infections in this SSPA in Madrid. All confirmed syphilis and gonorrhea cases registered in SSPA 7 in Madrid were selected. Moran's I was calculated in order to identify the existence of spatial autocorrelation and a cluster analysis was performed. Clusters and cumulative incidences (CI) per health zone were mapped. The district with most cases was Centro (CI: 67.5 and 160.7 per 100.000 inhabitants for syphilis and gonorrhea, respectively) with the highest CI (120.0 and 322.6 per 100.000 inhabitants) in the Justicia health zone.91.6% of all syphilis cases and 89.6% of gonorrhea cases were among men who have sex with men (MSM). Moran's I was 0.54 and 0.55 (p=0.001) for syphilis and gonorrhea, respectively. For syphilis, a cluster was identified including the six health zones of the Centro district, with a relative risk (RR)of 6.66 (p=0.001). For gonorrhea, a cluster was found including the Centro district, three health zones of the Chamberí district and one of Latina (RR 5.05; p=0.001). Centro was the district with most cases of syphilis and gonorrhea and the most affected population were MSM. For both infections, clusters were found with an important overlap. By identifying the most vulnerable health zones and populations, these results can help to design public health measures for preventing sexually transmitted diseases.

  17. Seafloor spreading event in western Gulf of Aden during the November 2010-March 2011 period captured by regional seismic networks: evidence for diking events and interactions with a nascent transform zone

    Ahmed, Abdulhakim; Doubre, Cécile; Leroy, Sylvie; Kassim, Mohamed; Keir, Derek; Abayazid, Ahmadine; Julie, Perrot; Laurence, Audin; Vergne, Jérome; Alexandre, Nercessian; Jacques, Eric; Khanbari, Khaled; Sholan, Jamal; Rolandone, Frédérique; Al-Ganad, Ismael


    , the opening is estimated to be ˜1.76-8.8 m across the segment. A striking feature of this episode is that the seismicity remained confined within one individual segment, whereas the adjacent en-echelon segments were totally quiescent, suggesting that the magma supply system of one segment is disconnected from those of the neighbouring segments. Second, we identify activity induced by the first intrusion with epicentres aligned along an N035°E-trending, ˜30 km long at the northwestern end of the active opening segment. This group encompasses more than seven earthquakes with magnitude larger than 5.0, and with strike-slip focal mechanisms consistent with the faults identified in the bathymetry and the structural pattern of the area. We propose that a transform fault is currently in formation which indicates an early stage of the ridge segmentation, at the locus of the trend change of the spreading ridge, which also corresponds to the boundary between a clear oceanic lithosphere and the zone of transform between continental and oceanic crust.

  18. Casa de viviendas en Madrid

    Lamela Martínez, Antonio


    Full Text Available This building occupies a site of 1990 sq. ms, and includes 29 apartments distributed in a semi ground floor, five standard floor levels, an attic and a double attic. The services have been located in a second basement, and the ground floor and first basement are being devoted to commercial uses, such as shops. In order to provide more free space for the commercial zone, the beginning of the stairs and the entry to the lifts is situated on the semi ground floor level. The porter's quarters, refuse reception cubicle and porter's hall have also been placed at this level. The basic nuclei of the apartments are clearly separated into zones daytime living quarters, night quarters and services. It is noteworthy that passages have been largely eliminated, and circulation problems have been otherwise solved, avoiding to some extent the crossing of the main lines of human circulation. The area devoted to social life has been increased as far as possible, and its environment has been enlarged by means of balcony-terraces. The fine aesthetic quality of the building, in its external aspect, is largely due to the clever way in which the materials have been used, exploiting their textures and combining these harmoniously.Ha sido construida sobre un solar de 1.991,41 m2 y consta de 29 viviendas distribuidas en cinco plantas- tipo, ático, doble ático y entreplanta. Los servicios generales de la casa están situados en el segundo sótano; la planta baja y el primer sótano albergan los locales comerciales. Para conseguir una mayor superficie en dichos locales se ha adoptado la solución de situar el arranque de escalera y ascensores en la entreplanta, donde, asimismo, aparecen ubicados los servicios de vigilancia, cuarto de recepción de basuras y vivienda del portero.

  19. Evidences of Paleoearthquakes in Palaeolithic settlements within fluvial sequences of the Tagus Basin (Madrid, Central Spain).

    Silva, Pablo G.; Rodríguez Pascua, M. A.; Pérez López, R.; Giner Robles, J. L.; Roquero, E.; Tapias, F.; López Recio, M.; Rus, I.; Morin, J.


    Multiple evidences of soft-sediment to brittle deformation within the Pleistocene fluvial terraces of the Tagus, Jarama, Tajuña and Manzanares river valleys have been described since the middle 20th Century. Cryoturbation, hydroplastic deformations due to underlying karstic collapses or halokinesis on the substratum of neogene gypsums, and seismic shaking have been proposed to interpret these structures. These deformations are typically concentrated in the +18-20 m terrace levels, and closely linked to well-known Palaeolithic sites, in some cases overlaying and/or affecting true prehistoric settlements (i.e. Arganda, Arriaga and Tafesa sites) within the Jarama and Manzanares valleys. The affected settlements typically display acheulian lithic industry linked to the scavenging of large Pleistocene mammals (i.e. Elephas antiquus). Commonly, deformational structures are concentrated in relatively thin horizons (10-50 cm thick) bracketed by undeformed fluvial sands and gravels. The soft-sediment deformations usually consist on medium to fine sized sands injected and protruded in overlaying flood-plain clayey silts, showing a wide variety of convolutes, injections, sand-dikes, dish and pillar structures, mud volcanoes, faults and folds, some times it is possible to undertake their 3D geometrical analysis due to the exceptional conservation of the structures (Tafesa). Recent geo-archaeological prospecting on the for the Palaeolithic Site of Arriaga (South Madrid City) conducted during the year 2009, let to find out an exceptional horizon of deformation of about 1.20 m thick. It consisted on highly disturbed and pervasively liquefacted sands, which hardly can be attributed to no-seismic processes. The acheulian lithic industry of the Madrid Region have been classically attributed the Late Middle Pleistocene (Comunidad de Madrid, AUDEMA S.A. (Proyecto Arriaga-2009). This is a contribution of GQM-AEQUA.

  20. Casas y jardines nobles de Madrid


    Cuando en 1787 el viajero inglés William Beckford visita en Madrid a la duquesa de Berwick, elogia su palacio el «más espléndido de Madrid :.., del más puro estilo parisino moderno» (1). Al margen de lo desacertado de la filiación estilística de la arquitectura del palacio, más vinculado a nuestro juicio a prototipos italianos, Beckford, quería referirse especialmente al carácter exento del edificio y al «espacioso patio de entrada», sobre el que en el siglo xix surgiría la pradera y árboles ...

  1. Un sistema de saneamiento para Madrid

    Sánchez, Félix Cristóbal


    Full Text Available The Full Sanitation Plan for Madrid is the final action of a series undertaken for several years with the purpose to reach the completion of the sanitation system of the town. With the whole of these actions it could be said that the basic substructure has acquired enough level to deserve de real needs of the town.El Plan de Saneamiento Integral de Madrid representaba la culminación de una serie de acciones emprendidas, durante varios años, para conseguir que la ciudad completase su sistema de saneamiento. Con este conjunto de acciones comprendidas en el Plan puede decirse que esta infraestructura básica ha adquirido un nivel suficiente, capaz de prestar un servicio acorde con las auténticas necesidades de la Villa.

  2. Improved Lg attenuations maps in the central U.S.-Rocky Mountain transition zone: New insight from induced seismicity in Oklahoma, Kansas, and the Raton Basin

    AbdelHameid, D.; Levandowski, W. B.; Boyd, O. S.; McNamara, D. E.


    Regional-scale differences in seismic attenuation exist across the continental United States, and it is well established that attenuation of Lg-phase waves is greater west of the Rocky Mountains than east of the Rocky Mountains. Yet there is less clarity in defining the transition in attenuation, as few near-field strong motion observations have been available in the central United States. A recent abundance of induced earthquakes in Oklahoma, southern Kansas, and the Raton Basin have provided unprecedented coverage. Utilizing Lg-phase waves recorded at regional distances (200-1500 km) at 300 seismic stations from Oklahoma to central Nevada, we compute the path-averaged apparent Q, source terms, and local amplification factors at one-octave frequency bands centered at 0.75, 1.0, 3.0, 6.0, and 12.0 Hz. Amplification correlates better with km-scale topographic relief than local slope on the Great Plains and Gulf Coast, and is generally greater east of the Rocky Mountain Front than west. We do not observe any difference between magnitude-source term scaling for induced events and for natural seismicity, suggesting that either source term is not a proxy for stress drop or that the stress drops of induced events are not lower than for natural events. Subsequently subdividing the study area into distinct physiographic regions, we quantify the average path-averaged Q in the Basin and Range, Colorado Plateau, Rocky Mountains, Gulf Coast, and Great Plains. As in previous work, we find roughly 50-100% greater Q in the Plains and Plateau than in the Rockies and Basin and Range. Preliminary 2-D tomography delineates a sharp (100-200 km-wide) boundary between adjacent Q-provinces. Our refined Q(f) model supplements the attenuation component of the USGS National Crustal Model and provides improved ground motion characterization in the USGS National Seismic Hazard map, particularly in the central United States in which shaking from induced seismicity is of increasing concern.

  3. Vivienda unifamiliar, en Majadahonda (Madrid

    Lamela, Antonio


    Full Text Available This house is designed in accordance with the modern practice of separating the building into zones, and suitable separation and connection the various functional sectors. The solution is noteworthy because of the simplicity and clarity of design. An attempt has been made to integrate as far as as possible the garden, the porch and the internal part of the building. Also, the servant's bedroom has a triple function: it serves as ironing room, and also as dining room for the children and the servant. This house is modern, and highly authentic in its overall quality.La distribución interior de esta vivienda unifamiliar, que se diseñó siguiendo los conceptos actuales de zonificacion, y de un adecuado aislamiento y conexión entre las distintas zonas creadas, destaca por su claridad y sencillez. Señalamos asimismo que, en todo lo posible, se ha procurado introducir el jardín en el porche y la vivienda, y que el dormitorio de servicio tenga un triple uso: dormitorio, cuarto de plancha y comedor de servicio y niños. Su arquitectura es simple y actual, plena de autenticidad.

  4. Modeling of fault activation and seismicity by injection directly into a fault zone associated with hydraulic fracturing of shale-gas reservoirs

    LBNL, in consultation with the EPA, expanded upon a previous study by injecting directly into a 3D representation of a hypothetical fault zone located in the geologic units between the shale-gas reservoir and the drinking water aquifer.

  5. Imported submicroscopic malaria in Madrid

    Ramírez-Olivencia Germán


    been previously described in endemic zones, and presence of vector in Europe has also been reported. Implementation of molecular tests in all asymptomatic individuals coming from endemic area is not economically feasible. So re-emergence of malaria (Plasmodium vivax in Europe may be speculated.

  6. Seismic techniques in coal mining

    Bhattacharyya, A.K.; Belleza, G.V.


    The aim of this study is to investigate the peripheral fracture zones in coal pillars left for support in underground mines. The fracture zones are caused by the redistribution of stresses in strata resulting from the process of excavation and blasting if it is used. The extent and degree of these fracture zones, in turn, have a direct influence on the ability of pillars to provide stable support to the overlying strata. Seismic methods such as refraction, uphole, and collinear techniques outlined in previous reports are being used to investigate the extent and degree of the peripheral fracture zones. Some of the work that has been carried out and is described in this report, relates to the study of peripheral fracture zones in coal pillars using seismic techniques.

  7. Application of micro-seismic monitoring technology in mining engineering

    Sun Jian; Wang Lianguo; Hou Huaqiang


    Micro-seismic phenomena,occurring when rock masses are subjected to forces and failures,allow the determination of their unstable states and failure zones by analyzing micro-seismic signals.We first present the principles of micro-seismic monitoring and location,as well as an underground explosion-proof micro-seismic monitoring system.Given a practical engineering application,we describe the application of micro-seismic monitoring technology in determining the height of a "two-zone" overburden,i.e.,a caving zone and a fracture zone,the width of a coal-pillar section and the depth of failure of a floor.The workfaces monitored accomplished safe and highly efficient mining based on our micro-seismic monitoring results and provide direct proof of the reliability and validity of micro-seismic monitoring technology.

  8. 基于Matlab的断裂带温泉水地球化学特征及地震活动性研究%Research on Geochemical Characteristic of Hot Spring Water and Seismicity in Fault Zone Based on MATLAB

    伍剑波; 张慧; 苏鹤军; 李晨桦


    The Matlab high-performance language for technical computing integrates computation,visualization,and programming in an easy-to-use environment where problems and solutions are expressed in familiar mathematical notation.It allows you to solve many technical computing problems,especially those with matrix and vector formulations,in a fraction of the time it would take to write a program in a scalar noninteractive language.The Matlab had a important application in seismic studies,such as,the ZMAP software used for scanning b value and application of Matlab software on intensity rapid report of Tianjin strong mation network.Authors developed the analysis software of the subsurface fluid based on Matlab,which combined with the function of some other geochemical software.This paper mainly discussed the water quality analysis by means of the software,and studied on the spring water in the north margin of western QinLing fault zone and comparatively analyzed the chemical composition characteristics of hot spring water in Wushan,Jiezi and Qingshui.In this paper,the types,water qualities,supply sources,the state of water-rock reaction and circulation depth of the water were discussed.And the paper analyzed that the circulation depth of hot spring water impacted on the seismicity of fault zone.In this paper,we drew the linear correlation diagram of δD and δ18O of hot spring water samples in the north margin of western Qinling fault zone.By the composition analysis of Hydrogen and Oxygen isotopes,it was showed that the supply sources of the water in three springs are precipitation and the isotope exchange effects caused positive shift of the 18O.Based on Rectangle hydrochemical diagram,it was the results that the hot spring water in Wushan and Jiezi was belonged to Na-HCO3·SO4·Cl and carbonated water of hydrochemical type,but the water in the Qingshui hot spring was belonged to Na-SO4·C1 and sulfuric water of hydrochemical type.In overall,three hot springs was the type

  9. Formalized morphostructural zoning of the mountain zone of the Andes

    Gabrielov, A.M.; Gvishiani, A.D.; Zhidkov, M.P.


    A plan is presented for morphostructural zoning of the Andes compiled according to formalized signs for purposes of seismic forecasting. Characteristics are presented for the basic morphostructural subdivisions of the Andes.

  10. High-frequency seismic radiation during Maule earthquake (Chile, 27/02/2010, Mw 8.8) inferred by backprojection of P waves: evidence of activation of two distinct zones at the downdip part of the plate interface

    Palo, M.; Tilmann, F. J.; Krueger, F.; Ehlert, L.; Lange, D.; Rietbrock, A.; Jenkins, J.; Hicks, S. P.


    zones of the subduction interface at different depths, the deeper of which is characterised by a large number of repeating event clusters (Rietbrock, Jenkins et al., this session). Thus, our backprojection analysis in combination with the aftershock distribution demonstrates the existence of a peculiar doubled downdip transition from seismogenic behaviour to stable sliding. We suspect fluids released from the downgoing plate to be the cause of the transitions in frictional behaviour because of (1) the co-location of high Vp/Vs ratios with the deep interface seismicity, (2) systematic decrease of depth of onset of deeper seismicity with younging incoming plate age, (3) patchy occurrence along-strike of deeper seismicity.

  11. Estacionamientos subterráneos, en Madrid

    López Saiz, J. M.


    Full Text Available Work on five underground parking sites in Madrid was initiated in September 1967. These parking sites were rented by the Madrid Town Council to the firm Estacionamientos Subterráneos, S. A. The engineering, design, and traffic and construction planning of these parking sites was allocated to Viales y Estacionamientos, S. A., whilst the actual construction was carried out by the firm Huarte y Cía., S. A. The five parking sites were located at the Paseo Calvo Sotelo, Plaza del Marqués de Salamanca, Plaza Mayor, Plaza de las Cortes and at Calle de Fuencarral, all within the centre of Madrid. These projects are of special interest, since each design represents an advance with respect to the earlier ones in regard to their structural and functional arrangements, with a view to achieving easier construction and less interference with road and pedestrian traffic. In the present article a description is given of each the five parking sites, following the sequence of their construction, which corresponds to the order in which they were design and planned.En septiembre de 1967 comenzaron las obras de cinco estacionamientos subterráneos en Madrid, adjudicadas por el Ayuntamiento en régimen de concesión a Estacionamientos Subterráneos, S. A. Los trabajos de ingeniería de tráfico, proyecto y control fueron encomendados a Viales y Estacionamientos, Sociedad Anteima (VIESA, y la ejecución de las obras se contrató con Huarte y Cía., S. A. Las ubicaciones de los estacionamientos cuya realización se comenta en este artículo son: Paseo de Calvo Sotelo, Plaza del Marqués de Salamanca - Plaza Mayor - Plaza de las Cortes - Calle de Fuencarral. Nos parece muy interesante exponer estas realizaciones, en las que se ve una clara evolución en su esquema estructural y la relación de éste con el esquema funcional, para lograr una mayor facilidad en la ejecución de las obras, junto con una interferencia mínima en superficie con los tráficos rodado y de

  12. Summary report of MINSIS workshop in Madrid

    Alonso, Rodrigo; Blennow, Mattias; Coloma, Pilar; de Gouvea, Andre; Fernandez-Martinez, Enrique; Gavela, Belen; Gonzalez-Garcia, Concha; Hortner, Sergio; Laveder, Marco; Li, Tracey; Lopez-Pavon, Jacobo; Maltoni, Michele; Mena, Olga; Migliozzi, Pasquale; Ota, Toshihiko; Ruiz, Sergio Palomares; Para, Adam; Parke, Stephen J; Rius, Nuria; Schwetz-Mangold, Thomas; Soler, F J P; Sorel, Michel; Yasuda, Osamu; Winter, Walter


    Recent developments on tau detection technologies and the construction of high intensity neutrino beams open the possibility of a high precision search for non-standard {\\mu} - {\\tau} flavour transition with neutrinos at short distances. The MINSIS - Main Injector Non-Standard Interaction Search- is a proposal under discussion to realize such precision measurement. This document contains the proceedings of the workshop which took place on 10-11 December 2009 in Madrid to discuss both the physics reach as well as the experimental requirements for this proposal.

  13. Patrimonio Minero: Las caleras de Lozoya, Madrid


    Este trabajo está encuadrado en la tercera fase del proyecto "Arqueología Industrial: Patrimonio Minero-Metalúrgico madrileño", subvencionado por la Comunidad de Madrid. Se trata del inventario de antiguos hornos de fabricación de cal, existentes en localidades de la Sierra Norte (Lozoya). La fabricación de cal por medios artesanales tuvo una cierta importancia en el Alto Valle del Lozoya, sobre todo con vistas a su utilización para encalar las fachadas de las casas o como desinfectante. Se t...

  14. Seismic architecture and sedimentology of a major grounding zone system deposited by the Bjørnøyrenna Ice Stream during Late Weichselian deglaciation

    Rüther, Denise Christina; Mattingsdal, Rune; Andreassen, Karin; Forwick, Matthias; Husum, Katrine


    A 280 km wide sediment wedge in outer Bjørnøyrenna (Bear Island Trough), south-western Barents Sea, has been investigated using 2D and 3D seismic data, sediment gravity cores, as well as regional swath and large scale bathymetry data. The bathymetry data indicate a division into an up to 35 m high frontal wedge with large depressions, and an upstream part characterized by mega scale glacial lineations (MSGL). From seismic sections increasing erosion is demonstrated for the upstream part, coinciding with the location of MSGL. Whether the latter are depositional features postdating an extensive erosional event or formed by erosion remains inconclusive. Based on the distinct morphology and internal structures, we infer that the system was deposited during a rapid readvance whereby the ice front pushed and bulldozed predominantly soft, diluted proglacial sediments. Analyses in the eastern part of the sediment system reveal the existence of imbricated thrust sheets in the frontal part of the wedge. This is suggested to imply upstream erosion of sedimentary rock and incorporation of thrusted blocks into the moraine, forming a composite ridge locally. We argue that observed large scale depressions are dead-ice features in the marine environment. It is envisioned that intense englacial thrusting may have developed into a decollement as the cold glacier snout got overrun by ice masses from the interior, thereby enabling the inclusion of slabs of ice in the push moraine mass. Radiocarbon dates indicate that the sediment wedge was deposited around 17,090 cal yrs BP (14,530 14C yrs BP) and that the ice front probably remained stable until 16,580 cal yrs BP (13,835 14C yrs BP).

  15. Probabilistic Seismic Hazard Analysis for Yemen

    Rakesh Mohindra


    Full Text Available A stochastic-event probabilistic seismic hazard model, which can be used further for estimates of seismic loss and seismic risk analysis, has been developed for the territory of Yemen. An updated composite earthquake catalogue has been compiled using the databases from two basic sources and several research publications. The spatial distribution of earthquakes from the catalogue was used to define and characterize the regional earthquake source zones for Yemen. To capture all possible scenarios in the seismic hazard model, a stochastic event set has been created consisting of 15,986 events generated from 1,583 fault segments in the delineated seismic source zones. Distribution of horizontal peak ground acceleration (PGA was calculated for all stochastic events considering epistemic uncertainty in ground-motion modeling using three suitable ground motion-prediction relationships, which were applied with equal weight. The probabilistic seismic hazard maps were created showing PGA and MSK seismic intensity at 10% and 50% probability of exceedance in 50 years, considering local soil site conditions. The resulting PGA for 10% probability of exceedance in 50 years (return period 475 years ranges from 0.2 g to 0.3 g in western Yemen and generally is less than 0.05 g across central and eastern Yemen. The largest contributors to Yemen’s seismic hazard are the events from the West Arabian Shield seismic zone.

  16. Pasarela atirantada sobre el Manzanares en Madrid

    Gil, Miguel A.


    Full Text Available A new cable-stayed pedestrian bridge which has just been built in Madrid is presented in this pap ero The structure has an innovative design where tubular elements have been used to salve some specífic structural and f ormal problems . Four aspects are mainly addressed in this pap er: designo analysis, construction and structural behaviour. In each one ofthese parts the most characteristic and innovative aspects ofthe project are presentedEn este artículo se presenta una nueva pasarela atirantada que se acaba de construir en Madrid. Se trata de una estructura innovadora tanto por el esquema de atirantamiento como por la utilización de elementos tubulares para resol ver tanto problemas estructurales como formales. En el artículo se tratan los cuatro aspectos fundamentales del proyecto: diseño, cálculo. construcción y comportamiento estructural. En cada uno de estos apartados se tratan específicamente los aspectos más característicos e innovadores del proyecto.

  17. Methods for Estimating Mean Annual Rate of Earthquakes in Moderate and Low Seismicity Regions~

    Peng Yanju; Zhang Lifang; Lv Yuejun; Xie Zhuojuan


    Two kinds of methods for determining seismic parameters are presented, that is, the potential seismic source zoning method and grid-spatially smoothing method. The Gaussian smoothing method and the modified Gaussian smoothing method are described in detail, and a comprehensive analysis of the advantages and disadvantages of these methods is made. Then, we take centrai China as the study region, and use the Gaussian smoothing method and potential seismic source zoning method to build seismic models to calculate the mean annual seismic rate. Seismic hazard is calculated using the probabilistic seismic hazard analysis method to construct the ground motion acceleration zoning maps. The differences between the maps and these models are discussed and the causes are investigated. The results show that the spatial smoothing method is suitable for estimating the seismic hazard over the moderate and low seismicity regions or the hazard caused by background seismicity; while the potential seismic source zoning method is suitable for estimating the seismic hazard in well-defined seismotectonics. Combining the spatial smoothing method and the potential seismic source zoning method with an integrated account of the seismicity and known seismotectonics is a feasible approach to estimate the seismic hazard in moderate and low seismicity regions.

  18. Geomorphic and Structural Analysis of the Verona-Williams-Pleasanton fault zone and implications for seismic hazard, eastern San Francisco Bay Area, California

    Sawyer, T. L.; Unruh, J. R.; Hoirup, D. F.; Barry, G.; Pearce, J. T.


    Folds and thrust faults adjacent to and beneath the Livermore Valley have accommodated Quaternary crustal shortening between major dextral faults of the eastern San Andreas fault system. The Verona and Williams faults are NE-dipping thrust or reverse faults that have uplifted the Pliocene-Pleistocene Livermore gravels along the western and southern margins of the valley. The Williams fault extends ~13 km northwest from the Mt. Lewis seismic trend to the sinistral Las Positas fault, which forms the southern margin of the valley. A 3-km left step along the Las Positas fault separates the surface traces of the Verona and Williams faults. The Verona fault extends ~8 km northwest from the stepover to southwestern Livermore Valley. It is possible that the Las Positas fault extends to the base of the seismogenic crust and separates the Verona and Williams faults into two kinematically independent structures. Alternatively, the Verona and Williams faults may merge downdip into a common thrust fault plane, with the Las Positas fault confined to the hanging wall as a tear fault. The Verona and Williams faults exhibit geomorphic evidence for late Quaternary fault rupture propagating to or very near the ground surface. The Williams fault tightly folds and overturns the Livermore gravels, and appears to form scarps that impound late Quaternary alluvium and cross Holocene landslide deposits. Many Holocene(?) alluvial fans exhibit distinct convex longitudinal profiles across the fault trace suggesting active folding above the Verona fault. The geomorphic position of a stream-terrace remnant suggests that >7 m of tectonic uplift is possible across the Verona fault during the late Quaternary. Surficial geologic mapping and geomorphic analysis of the ancestral Arroyo Valle drainage system reveals numerous paleochannels that generally decrease in elevation (age) to the northwest, and provide useful isochronous markers delineating a subtle tectonic uplift in western Livermore Valley

  19. Comparison among different strengthening methods for a typical RC classroom frame in zones with seismic intensity Ⅶ%7度区典型框架教学楼抗震加强措施效果对比

    陆新征; 马玉虎; 陈浩宇; 周萌; 叶列平


    In the Wenchuan Earthquake, many school buildings collapsed, which caused serious casualties. So after the earthquake, Ministry of Housing and Urban-Rural Development, China Academic of Engineering, and China Earthquake Administrator proposed different strengthening methods to upgrade the seismic design of school buildings. However, the actual effects of these proposals have not been quantitatively evaluated. So in this work, fiber-beam element model with validated stirrups confined concrete constitutive law is used to build the nonlinear finite element model of a typical reinforced concrete (RC) classroom frame in zones with seismic intensity Ⅶ during the Wenchuan Earthquake. The effects of different strengthening methods on collapse-resistance are studied with collapse-fragility analysis that is based on the incremental dynamic analysis (IDA). Further design suggestions are then proposed.%由于汶川地震导致大量中小学校建筑倒塌,造成巨大伤亡,住建部、中国工程院和中国地震局分别提出了不同的校舍抗震设计加强要求,但这些加强措施的实际抗倒塌效果尚缺乏定量研究.本文采用纤维梁模型,并选择合适的钢筋约束混凝土本构,对汶川地震7度区典型钢筋混凝土框架结构教学楼进行了基于IDA的倒塌率分析,研究了不同抗震加强措施的防倒塌效果,进而给出了相应的设计建议.

  20. Seismic risk perception in Italy

    Crescimbene, Massimo; La Longa, Federica; Camassi, Romano; Pino, Nicola Alessandro; Peruzza, Laura


    Risk perception is a fundamental element in the definition and the adoption of preventive counter-measures. In order to develop effective information and risk communication strategies, the perception of risks and the influencing factors should be known. This paper presents results of a survey on seismic risk perception in Italy conducted from January 2013 to present . The research design combines a psychometric and a cultural theoretic approach. More than 7,000 on-line tests have been compiled. The data collected show that in Italy seismic risk perception is strongly underestimated; 86 on 100 Italian citizens, living in the most dangerous zone (namely Zone 1), do not have a correct perception of seismic hazard. From these observations we deem that extremely urgent measures are required in Italy to reach an effective way to communicate seismic risk. Finally, the research presents a comparison between groups on seismic risk perception: a group involved in campaigns of information and education on seismic risk and a control group.

  1. Estimation of seismic hazard in the Kaliningrad region

    Ulomov, V. I.; Akatova, K. N.; Medvedeva, N. S.


    The paper discusses problems of seismic zoning of the Kaliningrad region, where a series of perceptible earthquakes occurred in 2004; the strongest event had a magnitude of M s = 4.3 and produced shakings of an intensity of 6 in the coastal zone of the Sambiiskii Peninsula, classified as a 5-intensity zone. The enhanced seismic effect is shown to be caused by bad ground conditions, long-term action of seismic effects, resonance phenomena, and other factors. To gain additional constraints on the seismic hazard degree in the Kaliningrad region, the paper discusses an improved version of the model of earthquake sources underlying the compilation of normative maps of seismic zoning (OSR-97). Modified fragments of OSR-97 probability maps of the Kaliningrad region are constructed at different levels of probability that the seismic effect indicated in the maps will be exceeded over 50 yr. It is shown that additional seismological investigations should be conducted in this region.

  2. A Review of Seismicity in 2004

    Li Gang; Liu Jie; Yu Surong


    @@ 1. SURVEY OF GLOBE SEISMICITY IN 2004 A total of 19 strong earthquakes with Ms≥7.0 occurred in the world according to the Chinese Seismic Station Network in 2004 (Table 1 ). The strongest earthquake was the Sumatra earthquake with Ms 8.7 near the northwest coast of Sumatra on December 26 ( Fig. 1 ). Global seismicity maintains the same patterns from recent years, being distributed mainly on the western part of the circum-Pacific seismic zone. Remarkable macroseismic activities were seen in the India-Australian plate and in the Japan region. The macroseismic activities of Ms≥7.0 in 2004 were as follows:

  3. Seismic Creep

    National Oceanic and Atmospheric Administration, Department of Commerce — Seismic creep is the constant or periodic movement on a fault as contrasted with the sudden erupture associated with an earthquake. It is a usually slow deformation...

  4. Seismic evaluation methods for existing buildings

    Hsieh, B.J.


    Recent US Department of Energy natural phenomena hazards mitigation directives require the earthquake reassessment of existing hazardous facilities and general use structures. This applies also to structures located in accordance with the Uniform Building Code in Seismic Zone 0 where usually no consideration is given to seismic design, but where DOE specifies seismic hazard levels. An economical approach for performing such a seismic evaluation, which relies heavily on the use of preexistent structural analysis results is outlined below. Specifically, three different methods are used to estimate the seismic capacity of a building, which is a unit of a building complex located on a site considered low risk to earthquakes. For structures originally not seismically designed, which may not have or be able to prove sufficient capacity to meet new arbitrarily high seismic design requirement and which are located on low-seismicity sites, it may be very cost effective to perform detailed site-specific seismic hazard studies in order to establish the true seismic threat. This is particularly beneficial, to sites with many buildings and facilities to be seismically evaluated.

  5. Foreign minorities from developing countries in Madrid.

    Rodriguez, V; Aguilera, M J; Gonzalez-yanci, M P


    "Spain, which has always been a land of emigrants, is currently a centre of attraction for immigrants, as are other countries in Mediterranean Europe. The proportion is not as high as in other countries with a longer tradition of immigration. In this survey we selected the six nationalities which provide the highest numbers of immigrants from the developing world, and which have the greatest racial or cultural contrast to the native population. We analyse their structural features, whether or not immigrants from the same country...collect in the Madrid Metropolitan Area, the recent mobility of the immigrant population, and the evolution of immigration since the Administration carried out a regularization process, as well as Spaniards' opinion of foreign immigrants."

  6. Seismic seiches

    McGarr, Arthur; Gupta, Harsh K.


    Seismic seiche is a term first used by Kvale (1955) to discuss oscillations of lake levels in Norway and England caused by the Assam earthquake of August 15, 1950. This definition has since been generalized to apply to standing waves set up in closed, or partially closed, bodies of water including rivers, shipping channels, lakes, swimming pools and tanks due to the passage of seismic waves from an earthquake.

  7. Slip Distribution of Two Recent Large Earthquakes in the Guerrero Segment of the Mexican Subduction Zone, and Their Relation to Previous Earthquakes, Silent Slip Events and Seismic Gaps

    Hjorleifsdottir, V.; Ji, C.; Iglesias, A.; Cruz-Atienza, V. M.; Singh, S. K.


    In 2012 and 2014 mega-thrust earthquakes occurred approximately 300 km apart, in the state of Guerrero, Mexico. The westernmost half of the segment between them has not had a large earthquake in at least 100 years and most of the easternmost half last broke in 1957. However, down dip of both earthquakes, silent slip events have been reported, as well as in the gap between them (Kostoglodov et al 2003, Graham 2014). There are indications that the westernmost half has different frictional properties than the areas surrounds it. However, the two events at the edges of the zone also seem to behave in different manners, indicating a broad range of frictional properties in this area, with changes occurring over short distances. The 2012/03/20, M7.5 earthquake occurred near the Guerrero-Oaxaca border, between the towns of Ometepec (Gro.) and Pinotepa Nacional (Oax.). This earthquake is noteworthy for breaking the same asperities as two previously recorded earthquakes, the M7.2 1937 and M6.9 1982(a) earthquakes, in very large "repeating earthquakes". Furthermore, the density of repeating smaller events is larger in this zone than in other parts of the subduction zone (Dominguez et al, submitted) and this earthquake has had very many aftershocks for its size (UNAM Seis. group, 2013). The 2012 event may have broken two asperities (UNAM Seis. group, 2013). How the two asperities relate to the previous relatively smaller "large events", to the repeating earthquakes, the high number of aftershocks and to the slow slip event is not clear. The 2014/04/18 M 7.2 earthquake broke a patch on the edge of the Guerrero gap, that previously broke in the 1979 M7.4 earthquake as well as the 1943 M 7.4 earthquake. This earthquake, despite being smaller, had a much larger duration, few aftershocks and clearly ruptured two separate patches (UNAM Seis. group 2015). In this work we estimate the slip distributions for the 2012 and 2014 earthquakes, by combining the data used separately in

  8. Plastic Deformation and Seismic Properties in Fore-arc Mantles: A Petrofabric Analysis of the Yushigou Harzburgites, North Qilian Suture Zone, NW China

    Cao, Y.; Jung, H.; Song, S.; Park, M.; Jung, S.; Lee, J.


    The fore-arc mantle above a subducting slab is a unique site where complex partial melting, melt/fluid-rock interaction, and deformation of mantle rocks occur. To constrain these processes, we analyzed the deformation microstructures, crystal preferred orientations (CPO), and water content in natural harzburgites that occur as exhumed massifs in the North Qilian suture zone, NW China. These harzburgites are very fresh, and have mineral assemblages of olivine ( 81‒87 vol.%), orthopyroxene ( 11‒17 vol.%), clinopyroxene ( 1‒2 vol. %), and spinel ( 1 vol.%). Detailed analyses of mineral textures, CPO patterns, and rotation axis distributions suggested that the plastic deformation of olivine and pyroxene were accommodated by activating a series of slip systems of dislocation. The olivine (A-/D-type fabric) showed dominant (010)[100] and/or (001)[100] slip systems, as well as other minor [100]-glide, {0kl}[100], and [001]-glide slip systems. The orthopyroxene showed dominant (100)[001] and subordinate (010)[001] slip systems, with minor (100)[010], (100)[0vw] slip systems. The water content was extremely low in the orthopyroxene (38‒44 wt. ppm), equilibrated olivine (4‒7 wt. ppm), and bulk-rock samples (9‒14 wt. ppm). Integrated with the previously reported refractory mineral and whole-rock compositions (Song et al., 2009), as well as the estimated low pressure ( 1‒2 GPa), high temperature ( 1100‒1300 °C), low stress ( 1‒4 MPa), and water-poor conditions of deformation, it is concluded that these harzburgites represent a remnant of a fossil fore-arc lithospheric mantle which was probably both formed and deformed in a young and warm fore-arc mantle setting (i.e. infant subduction zone). Based on these results, a refined schematic model of olivine fabric distributions in subduction zones was proposed. In this model, the opposing polarizing directions of A-/D-type olivine fabrics (prevalent in the fore-arc lithospheric mantle) with other underlying

  9. Chequeo constructivo de fachadas de Madrid

    Monjo Garrió, Juan


    Full Text Available This article can be considered as the continuation and culmination of the one published on the number 396, july/august - 1989, under the same headline. Objectives and methodology are reminded of the work done at the Dept. of "Construcción y Tecnología Arquitectónicas" of the U.P.M., whose scope was the stablishement of a data bank on constructive pathology of facades at Madrid for its study and stadistic analysis. It is completed with a first analysis of the general data of the pathological situation of those facades as well as some characteristic data related to the problem of DETACHING, as a sample of the interest and posibilities of the data bank made.

    Este artículo puede considerarse como la continuación y complemento del publicado bajo el mismo título en el nº 396 de julio/agosto de 1989. En él se recuerdan los objetivos y metodología de trabajo llevado a cabo en el Departamento de "Construcción y Tecnología Arquitectónicas" de la U.P.M., que perseguía la constitución de un banco de datos sobre patología constructiva de fachadas en la ciudad de Madrid para su estudio y análisis estadístico, y se complementa con un primer análisis, tanto de los datos generales del estado patológico de dichas fachadas, como de algunos datos característicos relativos a la lesión DESPRENDIMIENTOS, como muestra del interés y las posibilidades del banco de datos que se ha confeccionado.

  10. Study of the superficial ozone concentrations in the atmosphere of Comunidad de Madrid using passive samplers

    D. Galán Madruga


    Full Text Available The ozone is a secondary atmospheric pollutant which is generated for photochemical reactions of volatil organic compounds (VOC’s and nitrogen oxides (NOx. In Spain the ozone is a big problem as a consequence of the solar radiation to reach high levels. Exposure over a period of time to elevated ozone concentrations can cause damage in the public health and alterations in the vegetation.The aim of this study is to carry out the development and validation of a measurement method to let asses the superficial ozone levels in the Comunidad de Madrid, by identifing the zones more significants, where to measure with UV photometric monitors (automatics methods this pollutant and where the health and the vegetation can be affected. To such effect, passive samplers are used, which have glass fiber filters coated with a solution of sodium nitrite, potassium carbonate, glycerol and water. The nitrite ion in the presence of ozone is oxidized to nitrato ion, which it is extrated with ultrapure water and analyzed for ion chromatography, by seen proportional to the concentration existing in the sampling point.The results of validation from field tests indicate a excellent correlation between the passive and the automatic method.The higher superficial ozone concentrations are placed in rural zones, distanced of emission focus of primary pollutants (nitrogen oxides and volatil organic compounds... principally in direction soutwest and northwest of the Comunidad of Madrid.

  11. Red Palinocam: vigilancia en Madrid del polen aerovagante Palinocam Network: airborne pollen vigilance in Madrid

    Patricia Cervigón Morales


    Full Text Available El Programa Regional de Control y Prevención del Asma surge en el año 1992. El programa abordaba una estrategia con cuatro grandes áreas, entre ellas la Vigilancia Ambiental, que en el año 1993 formalizó la Red Palinológica de la Comunidad de Madrid (Red Palinocam. La red se constituye mediante la creación de un comité de expertos, coordinado desde el Instituto de Salud Pública, bajo la dirección técnica de la Facultad de Farmacia de la Universidad Complutense y está integrado por representantes de cada una de las instituciones involucradas. El marco jurídico se completa con acuerdos firmados con los ayuntamientos y con un convenio de colaboración entre la Universidad Complutense de Madrid y la Consejería de Sanidad y Consumo.El objetivo prioritario, basado en la red de muestreo de polen para el territorio de la Comunidad de Madrid, es el conocimiento del contenido polínico de su atmósfera que incide sobre la población afectada de polinosis en cada zona de nuestra área geográfica y en cada momento del año, datos de gran interés desde Salud Pública.La Red Palinocam constituye una herramienta útil en Salud Pública, proporcionando información puntual, a través de Internet y del Servicio de Información Telefónica, durante todo el año de los muestreos aerobiológicos realizados. Así las personas que sufren problemas de alergia y los profesionales sanitarios que se encargan de sus cuidados y los distintos medios de comunicación, pueden conocer los tipos polínicos más frecuentes en cada momento y su concentración en el aire ambiente.Asthma Regional Programme started to give up in 1992 with four big areas. Palinocam network project was first set up in Madrid as a part of Asthma Regional Programme, comprised in a wider Environmental Subprogram: Palynological Network of Madrid Region (PALINOCAM NETWORK.Palynological network is a multidisciplinary organization which has been working since 1993. In that moment an Experts

  12. 缅甸高地震区某电站重力坝深层抗滑稳定分析%Deep Stability against Sliding Analysis of Gravity Dam in Active Seismic Zone of Burma

    余昕卉; 龚道勇; 曹艳辉; 胡清义


    以缅甸高地震区某电站为例,针对坝基岩体存在不整合面(带)、缓倾角及中倾角、陡倾角裂隙问题,采用被动抗力法分析计算了该地区重力坝方案深层抗滑稳定性,并分析了各种荷载工况下的安全裕度,提出了裕度不足的基础处理措施.%The rock mass of dam foundation exists unconformity facet band). Low-angle, middle-angle and steep-angle dip crack. Taking a hydropower station in active seismic zone of Burma for an example, the passive resistance method is adopted to calculate deep stability against sliding of gravity dam. And then the safety margin is analyzed under the conditions of various loads. Finally, the measure of insufficient margin is pui forward to deal with dam foundation.

  13. New sedimentary-core records and a recent co-seismic turbidite help to unravel the paleoseismicity of the Hikurangi Subduction Zone, New Zealand

    Barnes, Philip; Orpin, Alan; Howarth, Jamie; Patton, Jason; Lamarche, Geoffroy; Woelz, Susanne; Hopkins, Jenni; Gerring, Peter; Mitchell, John; Quinn, Will; McKeown, Monique; Ganguly, Aratrika; Banks, Simon; Davidson, Sam


    emplaced, still-fluidised, co-seismic turbidite about 10-20 cm thick over a very large region offshore of Marlborough and Wairarapa. This event appears to extend at least 300 km from Kaikoura and offers a rare opportunity to calibrate our paleoseismic data and to test hypotheses of turbidite triggering and emplacement. Up to five cores detected this highly fluidised layer overlying the pre-earthquake seabed, clearly visible as an oxidised layer. Our sampling spanned channel, channel-levee, and basin floor environments. On-board observations indicated that the turbidite was still settling on the seabed and the boundary with the overlying water column was diffuse. Further laboratory characterisation of the stratigraphy, physical properties, and benthic assemblages along with radionuclide analyses will test this hypothesis further.

  14. The Militant Prison. Ventas (Madrid) and Les Corts (Barcelona)



    This work attempts to assess the history of two of the most important prisons of the Franco’s dictactorship, Ventas and Les Corts, corresponding to the most populated Spanish cities, Madrid and Barcelona...

  15. Madrid Symposium Promotes China-Spain Local Government Cooperation


    <正>With the concerted efforts of the CPAFFC and the Spanish Federation of Municipalities and Provinces (SFMP), the China-Spain Local Government Cooperation Symposium was held in Madrid on March 24, 2010.

  16. China-Spain Economic and Trade Forum Held in Madrid


    @@ On June 29, Chi na-Spain Eco nomic and Trade Forum, sponsored jointly by CCPIT, Federation of Spanish Entrepreneur Orga nizations and Spanish Trade and Investment Agency, was held in Madrid, capital of Spain.

  17. Estación de Chamartín Madrid – España

    López Astorga, Roberto


    Full Text Available This group of constructions which constitutes the final phase in the Chamartín railway station, situated in the northern part of Madrid, consist of: — A 18,250 m2 local train station which comprises halls, cafeterias, shops, luggage room, offices of Zone 1 of the Renfe and various other service installations. - A building for goods and sleeping carriages with storage department, customs, etc., and 7,025 m2 of usable area. — A 71,380 m2 long distance station with similar, although more ample services to those of the local train station; moreover, it is provided with a covered parking site and various complementary installation. — A 24,670 m2 hotel with a capacity of 210 rooms, distributed over five storeys, to which 4 more storeys can be added, whereby the capacity would be increased to 378 rooms. — A thermic central of 5,810 m2 contains all the installations required for this group of buildings. The complex is completed by service corridors for luggage and goods, parking places, connecting pedestrian crossing, and a complete road system with roads both at ground level as well as overhead and underground; a theatre and a big pedestrian square that forms the focus and connecting element between all the buildings. The design of the complex was determined according to the following factors: — Integration with the city: By means of the open arrangement of the various constructions towards the city and by the big pedestrian square that constitutes an efficient link with the adjoinining zones. — Connection with the city: Direct access to two main highways and several means of public transport, such as: underground station parallel to the platforms; bus lines with a stop at the entrance of the terminal; taxi station, etc. — Separation of the traffic within the complex from the city traffic: By means of traffic ways at different levels. — Maximum use of already constructed parts: By utilizing already finished works

  18. Pockmarks, fluid flow, and sediments outboard of the deformation front at the Cascadia Subduction Zone from analysis of multi-channel seismic and multi-beam sonar data

    Gibson, J. C.; Carbotte, S. M.; Han, S.; Carton, H. D.; Canales, P.; Nedimovic, M. R.


    Evidence of active fluid flow and the nature of the sediment section near the Cascadia deformation front are explored using multi-channel (MCS) seismic and multi-beam sonar data collected in summer 2012 using the R/V Marcus G. Langseth during the Juan de Fuca Ridge to Trench Survey. The MCS data were collected along two full plate transects (the 'Oregon' and 'Washington' transects) and one trench parallel line using a 6600 cubic inch source, and an 8 km streamer with 636 channels (12.5 m spacing). The MCS data pre-stack processing sequence includes geometry definition, trace editing, F-K filter, and deconvolution. Velocity analysis is performed via semblance and constant velocity stacks in order to create a velocity model of the sediments and upper oceanic crust. The traces are then stacked, and post-stack time migrated. The sonar data were collected using the R/V Langseth's Kongsberg EM122 1°x1° multi-beam sonar with 288 beams and 432 total soundings across track. Using MB-system the sonar data are cleaned, and the bathymetry data are then gridded at 35 m, while the backscatter data are gridded at 15 m. From the high-resolution mapping data 48 pockmarks varying in diameter from 50 m - 1 km are identified within 60 km outboard of the deformation front. The surface expression of these large features in an area of heavy sedimentation is likely indicative of active fluid flow. In order to gain sub-seafloor perspective on these features the MCS data are draped below the bathymetry/backscatter grids using QPS Fledermaus. From this perspective, specific locations for detailed velocity and attribute analysis of the sediment section are chosen. Sediment velocity and attribute analysis also provide insight into apparent differences in the sediment section and décollement formation along the Oregon and Washington plate transects. While both lines intersect areas of dense pockmark concentration, the area around the Oregon transect has been shown to contain a continuous

  19. Causality between expansion of seismic cloud and maximum magnitude of induced seismicity in geothermal field

    Mukuhira, Yusuke; Asanuma, Hiroshi; Ito, Takatoshi; Häring, Markus


    Occurrence of induced seismicity with large magnitude is critical environmental issues associated with fluid injection for shale gas/oil extraction, waste water disposal, carbon capture and storage, and engineered geothermal systems (EGS). Studies for prediction of the hazardous seismicity and risk assessment of induced seismicity has been activated recently. Many of these studies are based on the seismological statistics and these models use the information of the occurrence time and event magnitude. We have originally developed physics based model named "possible seismic moment model" to evaluate seismic activity and assess seismic moment which can be ready to release. This model is totally based on microseismic information of occurrence time, hypocenter location and magnitude (seismic moment). This model assumes existence of representative parameter having physical meaning that release-able seismic moment per rock volume (seismic moment density) at given field. Seismic moment density is to be estimated from microseismic distribution and their seismic moment. In addition to this, stimulated rock volume is also inferred by progress of microseismic cloud at given time and this quantity can be interpreted as the rock volume which can release seismic energy due to weakening effect of normal stress by injected fluid. Product of these two parameters (equation (1)) provide possible seismic moment which can be released from current stimulated zone as a model output. Difference between output of this model and observed cumulative seismic moment corresponds the seismic moment which will be released in future, based on current stimulation conditions. This value can be translated into possible maximum magnitude of induced seismicity in future. As this way, possible seismic moment can be used to have feedback to hydraulic stimulation operation in real time as an index which can be interpreted easily and intuitively. Possible seismic moment is defined as equation (1), where D

  20. Seismic Studies

    R. Quittmeyer


    This technical work plan (TWP) describes the efforts to develop and confirm seismic ground motion inputs used for preclosure design and probabilistic safety 'analyses and to assess the postclosure performance of a repository at Yucca Mountain, Nevada. As part of the effort to develop seismic inputs, the TWP covers testing and analyses that provide the technical basis for inputs to the seismic ground-motion site-response model. The TWP also addresses preparation of a seismic methodology report for submission to the U.S. Nuclear Regulatory Commission (NRC). The activities discussed in this TWP are planned for fiscal years (FY) 2006 through 2008. Some of the work enhances the technical basis for previously developed seismic inputs and reduces uncertainties and conservatism used in previous analyses and modeling. These activities support the defense of a license application. Other activities provide new results that will support development of the preclosure, safety case; these results directly support and will be included in the license application. Table 1 indicates which activities support the license application and which support licensing defense. The activities are listed in Section 1.2; the methods and approaches used to implement them are discussed in more detail in Section 2.2. Technical and performance objectives of this work scope are: (1) For annual ground motion exceedance probabilities appropriate for preclosure design analyses, provide site-specific seismic design acceleration response spectra for a range of damping values; strain-compatible soil properties; peak motions, strains, and curvatures as a function of depth; and time histories (acceleration, velocity, and displacement). Provide seismic design inputs for the waste emplacement level and for surface sites. Results should be consistent with the probabilistic seismic hazard analysis (PSHA) for Yucca Mountain and reflect, as appropriate, available knowledge on the limits to extreme ground

  1. Imported malaria in pregnancy in Madrid

    Jiménez Beatriz C


    Full Text Available Abstract Background Malaria in pregnancy is associated with maternal and foetal morbidity and mortality in endemic areas, but information on imported cases to non-endemic areas is scarce. The aim of this study was to describe the clinical and epidemiological characteristics of malaria in pregnancy in two general hospitals in Madrid, Spain. Methods Retrospective descriptive study of laboratory-confirmed malaria in pregnant women at the Fuenlabrada University Hospital and the Príncipe de Asturias University Hospital, in Madrid, over a six- and 11-year period, respectively. Relevant epidemiological, clinical and laboratory data was obtained from medical records. Results There were 19 pregnant women among 346 malaria cases (5.4%. The average age was 27 years. The gestational age (trimester was: 53% 3rd, 31% 1st, 16% 2nd. All but one were multigravidae. Three were HIV positive. All were sub-Saharan immigrants: two were recently arrived immigrants and seventeen (89% had visited friends and relatives. None had taken prophylaxis nor seeked pre-travel advice. Presentation: 16 symptomatic patients (fever in fourteen, asthenia in two, three asymptomatic. Median delay in diagnosis: 7.5 days. Laboratory tests: anaemia (cut off Hb level 11 g/dl 78.9% (mild 31.6%, moderate 31.6%, severe 15.8% thrombocytopaenia 73.7%, hypoglycaemia 10.5%. All cases were due to Plasmodium falciparum, one case of hyperparasitaemia. Quinine + clindamycin prescribed in 84%. Outcomes: no severe maternal complications or deaths, two abortions, fifteen term pregnancies, no low-birth-weight newborns, two patients were lost to follow-up. Conclusions Though cases of malaria in pregnancy are uncommon, a most at risk group is clearly defined: young sub-Saharan mothers visiting friends and relatives without pre-travel counselling and recently-arrived immigrants. The most common adverse maternal and foetal effects were anaemia and stillbirth. Given that presentation can be asymptomatic

  2. Seismicity at Jalisco-Nayarit Border, Mexico

    Rutz, M.; Nunez-Cornu, F.; Camarena, M.; Trejo, E.; Reyes-Davila, G.; Suarez-Plasencia, C.


    Since 2002 a regional seismic network from Jalisco Civil Defense and University of Guadalalajara is monitoring seismicity at the northwest border of Jalisco block. With the installation of a seismic station on Ceboruco Volcano, by Nayarit Civil Defense, coverage of the network extends to east. Ceboruco Volcano is located on the Tepic-Zacoalco graben, the east border of Jalisco block, this allow us to begin to monitoring this area. The zone of Bahia de Banderas, between the north coast of Jalisco and south coast of Nayarit, probably on a tectonic triple point, is a region of high seismic potential. Activ tectonic structures and clusters in the zone of El Tuito and the Dam Cajon de Pe¤as have been identified. The seismicity in the north area of the bay is low, meanwhile in the south, where the bay is deeper, the seismicity level is higher with an East-West tendency. At the east, the Amatlan de Ca¤as-Ameca zone presents continue activity, here have been possible to locate events with local magnitude between 2 and 4. Tectonovolcanic events registred at Ceboruco station presents waveform with scattering. The seismic distribution of the coast of Jalisco shows parallel alignments to the trench throughout al the coast. Other perpendicular alignments to the coastline show active morphologic structures within the Jalisco block related to the subduction of the Rivera plate under the Jalisco block.

  3. [Authoritarian attitudes and violence in Madrid].

    Moreno Martín, F


    One of the objectives of the Multicentric Study on Cultural Norms and Attitudes Toward Violence (Estudio Multicéntrico sobre Actitudes y Normas Culturales frente a la Violencia, the ACTIVA project) is to analyze the relationship between those attitudes that foster violence and the violent behaviors themselves. This article examines the relationship between attitudes and two components of violence: its justification and its actual occurrence. Data were collected in Madrid between October and December 1996 from a representative sample of 1,219 people, who were interviewed at home with the common questionnaire used for the ACTIVA project, with some additional questions. Overall, the sample respondents scored low on the authoritarianism scale. Persons who most strongly justified the use of violence scored higher on authoritarianism, along with those who customarily displayed a higher level of aggression. Attitudes that were more strongly authoritarian were found in low-income neighborhoods, in people who were not part of the workforce, in people with less education, and in those persons who described themselves as having a right-wing ideology. If people who are more authoritarian justify and practice violence more than others, it becomes necessary to encourage criticism of those who abuse their power and tolerance toward differences, in order to prevent such behaviors without disregarding the influence of the social variables previously mentioned.

  4. El patrimonio industrial urbano de Madrid

    Carlos J. Pardo Abad


    Full Text Available El artículo analiza la trascendencia del patrimonio industrial de la ciudad de Madrid desde un punto de vista geográfico y, a la vez, histórico en el que se expone la evolución de la industrialización madrileña desde el siglo XIX hasta el momento actual, incluyéndose también las fundaciones de las manufacturas reales de tipo preindustrial del siglo XVIII. Como consecuencia de dicho desarrollo hay un patrimonio industrial que merece ser destacado por sus valores culturales y sus posibilidades de reutilización, aunque más escaso que en otras ciudades de más intensa industrialización. Se exponen los casos más significativos tanto del patrimonio preindustrial como del industrial desaparecido y de aquel otro que ha sido preservado y recuperado para nuevos usos como legado del pasado fabril de la ciudad.

  5. El patrimonio industrial urbano de Madrid

    Carlos J. Pardo Abad


    Full Text Available El artículo analiza la trascendencia del patrimonio industrial de la ciudad de Madrid desde un punto de vista geográfico y, a la vez, histórico en el que se expone la evolución de la industrialización madrileña desde el siglo XIX hasta el momento actual, incluyéndose también las fundaciones de las manufacturas reales de tipo preindustrial del siglo XVIII. Como consecuencia de dicho desarrollo hay un patrimonio industrial que merece ser destacado por sus valores culturales y sus posibilidades de reutilización, aunque más escaso que en otras ciudades de más intensa industrialización. Se exponen los casos más significativos tanto del patrimonio preindustrial como del industrial desaparecido y de aquel otro que ha sido preservado y recuperado para nuevos usos como legado del pasado fabril de la ciudad.

  6. Seismic basement in Poland

    Grad, Marek; Polkowski, Marcin


    The area of contact between Precambrian and Phanerozoic Europe in Poland has complicated structure of sedimentary cover and basement. The thinnest sedimentary cover in the Mazury-Belarus anteclize is only 0.3-1 km thick, increases to 7-8 km along the East European Craton margin, and 9-12 km in the Trans-European Suture Zone (TESZ). The Variscan domain is characterized by a 1- to 2-km-thick sedimentary cover, while the Carpathians are characterized by very thick sediments, up to c. 20 km. The map of the basement depth is created by combining data from geological boreholes with a set of regional seismic refraction profiles. These maps do not provide data about the basement depth in the central part of the TESZ and in the Carpathians. Therefore, the data set is supplemented by 32 models from deep seismic sounding profiles and a map of a high-resistivity (low-conductivity) layer from magnetotelluric soundings, identified as a basement. All of these data provide knowledge about the basement depth and of P-wave seismic velocities of the crystalline and consolidated type of basement for the whole area of Poland. Finally, the differentiation of the basement depth and velocity is discussed with respect to geophysical fields and the tectonic division of the area.


    Vadim A. Saltykov


    estimations give evidence that the year of 2008 was not anomalous in terms of seismicity. Based on 2D distribution of recurrence graph slope γ, it is possible to locate an area of lower values of γ in the southern part of the Kamchatka seismic zone (Fig. 4. Data on maps of normalized variation of γ for 2007–2008 and 2006–2008 (Fig. 5 confirm statistical importance of γ reduction through the last three years in the given area. Maps of 2D distribution of seismic activity A10 are constructed for 2008 and the perdiod from 1962 to 2008; values of seismic activity A10 that are normalized to the average annual seismic activity are also mapped (Fig. 6. In 2008, increased values of A10 were observed at the southern part of the Avachinsky gulf and at the northern part of the Kamchatka gulf, as well as in the northern water area of Bering Island. The anomalous behavior of parameters RTL, ΔS and clustering of earthquakes may have predictive character [Sobolev, 2000]. Negative values of RTL-parameter correspond to seismic quiescence; increasing areas of seismic ruptures ΔS correspond to foreshock activation; clustering of earthquakes can evidence that activation tends to accumulate at a future main rupture location. For 2008, three zones of seismic quiescence were defined by data (Fig. 7. For estimation points with maximum modular values of RTL (marked by the Roman numerals in Fig. 7, RTL time curves are constructed for each of the above mentioned zones (Fig. 8; they provide for defining durations of anomalies and degrees of manifestation. A map of variations of seismic rupture areas ΔS (Fig. 9 shows that seismic activity of 2008 was mainly manifested at the southern part of the Kamchatka seismic zone. In 2008, most of the earthquake clusters varying in energy also occurred in the southern part of Kamchatka (Fig. 10. The northern chain of clusters is located at the border of the developing seismic anomaly, as defined by RTL parameter. Similar to RTL technique, an objective of

  8. Localized seismic deformation in the upper mantle revealed by dense seismic arrays

    Inbal, Asaf; Ampuero, Jean Paul; Clayton, Robert W.


    Seismicity along continental transform faults is usually confined to the upper half of the crust, but the Newport-Inglewood fault (NIF), a major fault traversing the Los Angeles basin, is seismically active down to the upper mantle. We use seismic array analysis to illuminate the seismogenic root of the NIF beneath Long Beach, California, and identify seismicity in an actively deforming localized zone penetrating the lithospheric mantle. Deep earthquakes, which are spatially correlated with geochemical evidence of a fluid pathway from the mantle, as well as with a sharp vertical offset in the lithosphere-asthenosphere boundary, exhibit narrow size distribution and weak temporal clustering. We attribute these characteristics to a transition from strong to weak interaction regimes in a system of seismic asperities embedded in a ductile fault zone matrix.

  9. Seismic Symphonies

    Strinna, Elisa; Ferrari, Graziano


    The project started in 2008 as a sound installation, a collaboration between an artist, a barrel organ builder and a seismologist. The work differs from other attempts of sound transposition of seismic records. In this case seismic frequencies are not converted automatically into the "sound of the earthquake." However, it has been studied a musical translation system that, based on the organ tonal scale, generates a totally unexpected sequence of sounds which is intended to evoke the emotions aroused by the earthquake. The symphonies proposed in the project have somewhat peculiar origins: they in fact come to life from the translation of graphic tracks into a sound track. The graphic tracks in question are made up by copies of seismograms recorded during some earthquakes that have taken place around the world. Seismograms are translated into music by a sculpture-instrument, half a seismograph and half a barrel organ. The organ plays through holes practiced on paper. Adapting the documents to the instrument score, holes have been drilled on the waves' peaks. The organ covers about three tonal scales, starting from heavy and deep sounds it reaches up to high and jarring notes. The translation of the seismic records is based on a criterion that does match the highest sounds to larger amplitudes with lower ones to minors. Translating the seismogram in the organ score, the larger the amplitude of recorded waves, the more the seismogram covers the full tonal scale played by the barrel organ and the notes arouse an intense emotional response in the listener. Elisa Strinna's Seismic Symphonies installation becomes an unprecedented tool for emotional involvement, through which can be revived the memory of the greatest disasters of over a century of seismic history of the Earth. A bridge between art and science. Seismic Symphonies is also a symbolic inversion: the instrument of the organ is most commonly used in churches, and its sounds are derived from the heavens and

  10. El Abasto de Pan en el Madrid del Siglo XVII Bread provision in seventeenth century Madrid

    José Ignacio ANDRÉS UCENDO


    Full Text Available El mercado del pan era el más importante de los mercados de abastos, pero también el que contaba con el más complejo sistema de intervención. Los objetivos de la política de abastos eran asegurar un suministro continuo a precios estables y moderados.Los instrumentos incluían la regulación de los precios del grano y el pan, la provisión directa a través del pósito municipal y, en el caso de la corte, el pan de registro. En este trabajo examinamos la política de tasas, las disposiciones del gobierno y el comportamiento de los precios del pan en Madrid y del trigo en los mercados de origen.Bread market was the most important provision markets, so the complexity of intervention system. The aim of provision policy was to guarantee the continuous supply of bread at moderate and stable prices. The means included the regulation the price, the direct provision by the public granary and, in the case of the court, the named registered bread. This paper examines the tax policy, the government requirements and the movement of bread prices in Madrid and wheat prices in the markets of origin.

  11. Accretion and Subduction of Oceanic Lithosphere: 2D and 3D Seismic Studies of Off-Axis Magma Lenses at East Pacific Rise 9°37-40'N Area and Downgoing Juan de Fuca Plate at Cascadia Subduction Zone

    Han, Shuoshuo

    Two thirds of the Earth's lithosphere is covered by the ocean. The oceanic lithosphere is formed at mid-ocean ridges, evolves and interacts with the overlying ocean for millions of years, and is eventually consumed at subduction zones. In this thesis, I use 2D and 3D multichannel seismic (MCS) data to investigate the accretionary and hydrothermal process on the ridge flank of the fast-spreading East Pacific Rise (EPR) at 9°37-40'N and the structure of the downgoing Juan de Fuca plate at the Cascadia subduction zone offshore Oregon and Washington. Using 3D multichannel seismic (MCS) data, I image a series of off-axis magma lenses (OAML) in the middle or lower crust, 2-10 km from the ridge axis at EPR 9°37-40'N. The large OAMLs are associated with Moho travel time anomalies and local volcanic edifices above them, indicating off-axis magmatism contributes to crustal accretion though both intrusion and eruption (Chapter 1). To assess the effect of OAMLs on the upper crustal structure, I conduct 2-D travel time tomography on downward continued MCS data along two across-axis lines above a prominent OAML in our study area. I find higher upper crustal velocity in a region ~ 2 km wide above this OAML compared with the surrounding crust. I attribute these local anomalies to enhanced precipitation of alteration minerals in the pore space of upper crust associated with high-temperature off-axis hydrothermal circulation driven by the OAML (Chapter 2). At Cascadia, a young and hot end-member of the global subduction system, the state of hydration of the downgoing Juan de Fuca (JdF) plate is important to a number of subduction processes, yet is poorly known. As local zones of higher porosity and permeability, faults constitute primary conduits for seawater to enter the crust and potentially uppermost mantle. From pre-stack time migrated MCS images, I observe pervasive faulting in the sediment section up to 200 km from the deformation front. Yet faults with large throw and

  12. The development of the Moldova digital seismic network

    Ilies, I.; Ionescu, C.; Grigore, A. G.


    The Republic of Moldova is located in the seismically active region, about 70% of its area is predisposed to shaking intensity 7 - 8 points MSK. Focal zones of the primary seismic danger to the territory of the Republic of Moldova are: Vrancea zone - for the whole of its territory and Dobrogea zone - for the southern part. Monitoring of seismic instrumentation in the republic is provided by the Center of Experimental Seismology, Institute of Geology and Seismology, Academy of Sciences of Moldova. According to the seismic zoning map of the Republic of Moldova, seismic stations "Cahul, Leova" and "Giurgiulesti" located in 8 - degree zone, the central regional station "Chisinau" - in 7 - degree, a station "Soroca" - in 6 - degree zone MSK scale. The development of seismic network since 2004, going through a transition to a modern digital recording, improving working conditions for staff and the construction of new buildings for seismic stations, equipping the new network equipment and improve the methods of collecting and processing seismic data. The works to modernize the network of seismic stations in Moldova were initiated in 2003 with the acquisition of the first three axial digital accelerometer. The device was installed initially in Chisinau, and from it we received the first digital recordings of earthquakes from September 27 and October 27, 2004. In joint efforts with National Institute of Research and Development for Earth Physics from Bucharest, Romania, four seismic stations from Republic of Moldavia was upgraded by broadband and strong motion sensors connected at Q 330 digital recorders that issue continuous recording and real time data stream. Starting from spring of 2008, real time seismic data exchange between IGG Republic of Moldavia and NIEP Romania is running using internet connection.

  13. Seismic link at plate boundary

    Faical Ramdani; Omar Kettani; Benaissa Tadili


    Seismic triggering at plate boundaries has a very complex nature that includes seismic events at varying distances. The spatial orientation of triggering cannot be reduced to sequences from the main shocks. Seismic waves propagate at all times in all directions, particularly in highly active zones. No direct evidence can be obtained regarding which earthquakes trigger the shocks. The first approach is to determine the potential linked zones where triggering may occur. The second step is to determine the causality between the events and their triggered shocks. The spatial orientation of the links between events is established from pre-ordered networks and the adapted dependence of the spatio-temporal occurrence of earthquakes. Based on a coefficient of synchronous seismic activity to grid couples, we derive a network link by each threshold. The links of high thresholds are tested using the coherence of time series to determine the causality and related orientation. The resulting link orientations at the plate boundary conditions indicate that causal triggering seems to be localized along a major fault, as a stress transfer between two major faults, and parallel to the geothermal area extension.

  14. New Methodology for Rapid Seismic Risk Assessment

    Melikyan, A. E.; Balassanian, S. Y.


    Seismic risk is growing worldwide and is, increasingly, a problem of developing countries. Along with growing urbanization future earthquakes will have more disastrous social and economic consequences. Seismic risk assessment and reduction are important goals for each country located in seismically active zone. For Armenia these goals are of primary importance because the results of studies carried out by Armenian NSSP for assessment of the losses caused by various types of disasters in Armenia had shown that earthquakes are the most disastrous hazard for Armenia. The strategy for seismic risk reduction in 1999 was adopted by the Government of Armenia as a high priority state program. The world experience demonstrates that for efficient response the rapid assessment of seismic losses is necessary. There are several state-of-the-art approaches for seismic risk assessment (Radius, Hazus, etc.). All of them required large amount of various input data, which is impossible to collect in many developing countries, in particular in Armenia. Taking into account this very serious problem existing for developing countries, as well as rapid seismic risk assessment need immediately after strong earthquake the author undertake the attempt to contribute into a new approach for rapid seismic risk assessment under the supervision of Prof. S. Balassanian. The analysis of numerous factors influencing seismic risk in Armenia shows that the following elements contribute most significantly to the possible losses: seismic hazard; density of population; vulnerability of structures. Proposed approach for rapid seismic risk assessment based on these three factors has been tested for several seismic events. These tests have shown that such approach might represent from 80 to 90 percent of real losses.

  15. La construcción de la marca Madrid

    Elia Canosa Zamora


    Full Text Available Durante los últimos veinte años, los sucesivos gobiernos de Madrid, han centrado en el posicionamiento internacional de la ciudad sus expectativas de desarrollo económico, de transformación urbana y de bienestar ciudadano. La construcción de la Marca Madrid forma parte de esta estrategia que ha terminado por convertirse en el eje director de gestión y la ordenación urbana. La relevancia de este fenómeno se analizará en tres vertientes fundamentales: valorando el significado de la opción oficial de Madrid ciudad global, planteando el ascenso de la imagen como base vertebradora de las operaciones destinadas a favorecer esta internacionalización y profundizando en el valor de la arquitectura como icono urbano.

  16. The origin of Cenozoic basalts from central Inner Mongolia, East China: The consequence of recent mantle metasomatism genetically associated with seismically observed paleo-Pacific slab in the mantle transition zone

    Guo, Pengyuan; Niu, Yaoling; Sun, Pu; Ye, Lei; Liu, Jinju; Zhang, Yu; Feng, Yue-xing; Zhao, Jian-xin


    We present new major element, trace element and Sr-Nd-Hf isotope data on Cenozoic basalts from central Inner Mongolia (CIM) in eastern China to study the origin of the incompatible-element enriched component in these basalts by testing whether or not the paleo-Pacific plate lying in the mantle transition zone beneath eastern China is the immediate cause. The Cenozoic CIM basalts have a large variation in major element, trace element and isotope compositions. Fractional crystallization of olivine and clinopyroxene can readily explain much of the major element compositional variation, while trace element and isotope ratio variation largely reflect source heterogeneities and source histories. The variably low 87Sr/86Sr, high εNd, high εHf and elevated ratios of high field strength element over large ion lithophile element (HFSE/LILE, e.g., Nb/U, Nb/La) indicate that the CIM basalts are of asthenospheric origin, which is characterized by mixing between DMM and EM1. However, the CIM basalts are enriched in incompatible elements and enriched in the progressively more incompatible elements (e.g., variably high [La/Sm]N = 1.66-3.38), suggesting that the magma source(s) must have been enriched prior to the major episode of the magmatism. Participation of subducted ocean crust in the mantle source region of these basalts is recognized, but cannot be the major source material because the subducted ocean crust is expectedly too depleted in incompatible elements (e.g., [La/Sm]N ≪ 1) to produce magmas highly enriched in incompatible elements with [La/Sm]N ≫ 1. With the new data, we consider that low mass fraction (low-F) melt metasomatism in the seismic low velocity zone (LVZ) beneath eastern China as the most likely process to generate incompatible-element enriched source(s) for mantle melts parental to the Cenozoic CIM basalts. The low-F metasomatic agent most likely resulted from dehydration melting of the transition-zone paleo-Pacific slab, which has been taking place

  17. A preliminary research based on the Matlab minimum phase filtering in dealing with the seismic event in shadow zone%基于Matlab的最小相位滤波在处理影区地震中的初步研究

    隆爱军; 夏仕安; 陈海博; 王燚坤


    研究基于Matlab的最小相位滤波器在处理影区地震中的应用.使用共轭倒序法设计滤波器对合肥地震台记录的中国台湾影区地震进行滤波处理,有效抑制地动噪声干扰,突出地震信号特征,为地震分析提供较好的帮助.%This thesis carries out a study on the application of Matlab minimum phase filter and uses reverse conjugate array method to devise the filter. Through the record of the filtering processing in the shadow zone of Taiwan by Hefei Seismic Station, the filter lowered the noise interference of the ground movement and highlighted the features of the seismic signals. It provides good help for the analysis of earthquake and achieves good effects.


    马秀敏; 彭华; 姜景捷; 彭立国


    5.12汶川特大地震后,为了监测地震的发展趋势,探讨大范围的构造应力场作用,在龙门山断裂带上及时布设临时数字地震台网.数字台网由11个数字地震台组成,遍布龙门山断裂带的北东缘和南西端.为了分析WFSD数字地震台网监测能力及其动态范围,随机抽取一定数量台站观测数据,通过傅立叶变换和功率谱密度分析,获得台基地动噪声均值,进而分析观测系统的动态范围和台网监测能力.根据计算结果与记录的大量微震对比研究,表明在龙门山断裂带上,WFSD数字地震台网具有监测ML 1.5级微地震的能力,且与中国地震局台网中心发布的地震结果基本吻合.因此,WFSD数字地震台网可为龙门山断裂带变形机制研究提供基础的观测资料.%After the 5. 12 earthquake in Wenchuan, the temporary digital seismic network has been layout in time in Longmenshan fault zone in order to monitor earthquake trends and probe into the large-scale tectonic stress field activity. Digital seismic network is made of 11 digital seismic instruments, and which are arranged at north eastern margin and southwestern side of Longmenshan fault zone. A certain number of data from observation stations are randomly selected in order to analyze the monitoring capability and dynamic range of WFSD digital seismic network. The dynamic noises of station base are acquired through the Fourier Transform and power spectral density analysis. And then, the dynamic range of observing systems and monitoring capacity of network are analyzed. WFSD digital seismic network has a monitoring ML1.5 micro-seismic capacity in Longmenshan fault zone based on Comparing the computing results with the record of a large number of micro-seismic. And it basically accorded with the results of that by Seismological Bureau Networks Center of China. Therefore, WFSD digital seismic network can provide a basic observing datum for the deformation mechanism research

  19. Toward Forecasting Volcanic Eruptions using Seismic Noise

    Brenguier, Florent; Campillo, Michel; Ferrazzini, Valerie; Duputel, Zacharie; Coutant, Olivier; Nercessian, Alexandre


    During inter-eruption periods, magma pressurization yields subtle changes of the elastic properties of volcanic edifices. We use the reproducibility properties of the ambient seismic noise recorded on the Piton de la Fournaise volcano to measure relative seismic velocity variations of less than 0.1 % with a temporal resolution of one day. Our results show that five studied volcanic eruptions were preceded by clearly detectable seismic velocity decreases within the zone of magma injection. These precursors reflect the edifice dilatation induced by magma pressurization and can be useful indicators to improve the forecasting of volcanic eruptions.

  20. El Real Madrid, ?"equipo de Espana"? Futbol e identidades durante el franquismo

    Gonzalez Calleja, Eduardo


    ... de las identidades nacionales. Palabras clave: deporte, franquismo, fútbol, identidad nacional, Real Madrid C. de F. Real Madrid, "team of Spain"? Football and identities during the francoism Abstract: In the 50s and 60s of the last century, Real Madrid Club of Football became the sportive herald of "Spanish miracle", generating in Spain and abroad a wav...

  1. Assembly of Drift Tubes (DT) Chambers at CIEMAT (Madrid)

    Jesus Puerta-Pelayo


    The construction of muon drift tube chambers (DT) has been carried out in four different european institutes: Aachen (Germany), CIEMAT-Madrid (Spain), Legnaro and Turin (Italy), all of them following similar procedures and quality tests. Each chamber is composed by three or two independent units called superlayers, with four layers of staggered drift cells each. The assembly of a superlayer is a succesive glueing of aluminium plates and I-beams with electrodes previously attached, forming a rectangular and gas-tight volume. These pictures illustrate the various processes of material preparation, construction, equipment and assembly of full chambers at CIEMAT (Madrid).

  2. Seismic hazard maps for Haiti

    Frankel, Arthur; Harmsen, Stephen; Mueller, Charles; Calais, Eric; Haase, Jennifer


    We have produced probabilistic seismic hazard maps of Haiti for peak ground acceleration and response spectral accelerations that include the hazard from the major crustal faults, subduction zones, and background earthquakes. The hazard from the Enriquillo-Plantain Garden, Septentrional, and Matheux-Neiba fault zones was estimated using fault slip rates determined from GPS measurements. The hazard from the subduction zones along the northern and southeastern coasts of Hispaniola was calculated from slip rates derived from GPS data and the overall plate motion. Hazard maps were made for a firm-rock site condition and for a grid of shallow shear-wave velocities estimated from topographic slope. The maps show substantial hazard throughout Haiti, with the highest hazard in Haiti along the Enriquillo-Plantain Garden and Septentrional fault zones. The Matheux-Neiba Fault exhibits high hazard in the maps for 2% probability of exceedance in 50 years, although its slip rate is poorly constrained.

  3. Seismic hazard estimation based on the distributed seismicity in northern China

    YANG Yong; SHI Bao-ping; SUN Liang


    In this paper, we have proposed an alternative seismic hazard modeling by using distributed seismicites. The distributed seismicity model does not need delineation of seismic source zones, and simplify the methodology of probabilistic seismic hazard analysis. Based on the devastating earthquake catalogue, we established three seismi- city model, derived the distribution of a-value in northern China by using Gaussian smoothing function, and cal- culated peak ground acceleration distributions for this area with 2%, 5% and 10% probability of exceedance in a 50-year period by using three attenuation models, respectively. In general, the peak ground motion distribution patterns are consistent with current seismic hazard map of China, but in some specific seismic zones which in- clude Shanxi Province and Shijiazhuang areas, our results indicated a little bit higher peak ground motions and zonation characters which are in agreement with seismicity distribution patterns in these areas. The hazard curves have been developed for Beijing, Tianjin, Taiyuan, Tangshan, and Ji'nan, the metropolitan cities in the northern China. The results showed that Tangshan, Taiyuan, Beijing has a higher seismic hazard than that of other cities mentioned above.

  4. Centro Princesa, en Madrid (España

    Lamela, A.


    Full Text Available This is a luxury commercial centre, in the very centre of Madrid, and within a high class residential zone. It occupies a whole block, facing four streets, and it includes a luxury hotel, apartments, shopping facilities, offices, car park, and the official headquarters of one of the most important Spanish travelling agencies. The outstanding feature of the «Centro Princesa» is the luxury hotel, which has 250 rooms, suits, social rooms, conventions halls, dance hall, bar, hairdressers saloon, sauna bath, shopping centre, restaurants and secondary services. The luxury flats occupy seven storeys of the central block, 15 apartments per story. Each of these has a sitting room, bedroom, bathroom and kitchen. The carpark, which can hold 300 cars, occupies four underground floor levels. This project is attractive because of its balanced spatial pattern, its clean outline and the quality of the materials, whilst the excellence of its internal appointment also contributes to its overall architectural merit.Este conjunto, situado en una zona residencial de primera categoría, está destinado a: hotel de lujo, apartamentos, locales comerciales, oficinas, aparcamientos de automóviles y a sede de la oficina-despacho central de una de las más importantes agencias de viaje españolas. Ocupa una manzana entera. La unidad predominante del «Centro Princesa» es un hotel de lujo, con 250 habitaciones, «suits», salones sociales, de actos y convenciones, sala de fiestas, bar americano, peluquerías, saunas, galería comercial, restaurantes y dependencias de servicio. Siete plantas del bloque central albergan los apartamentos de lujo, 15 por planta; el apartamento tipo consta de salón, cocina, dormitorio y baño. En cuatro de las plantas de sótano funciona un aparcamiento con capacidad para 300 automóviles. Atrae este conjunto, tanto por el acertado juego de volúmenes, y la limpieza de líneas y materiales —que muestra su composición estética—, como

  5. Transfer knowledge and technology in Madrid; La transferencia de conocimiento y tecnologia en la comunidad de Madrid

    Vicente Oliva, M. de; Manera Bassa, J.; Martin del Peso, M.


    This paper aims to establish a typology of business behaviour patterns related to Knowledge and Technology Transfer (KTT), as well as an assessment of the situation of the transference process from the Madrid Region companies point of view. Working with data obtained from a survey designed and carried out by the authors to the companies registered in Madrid database and, as a consequence, knowing KTT, we have built groups of enterprises with different behaviours. To obtain the groups we have used cluster techniques over the factors resulting from a correspondence analysis. (Author) 24 refs.

  6. Bilingual Baby: Foreign Language Intervention in Madrid's Infant Education Centers

    Ferjan Ramirez, Naja; Kuhl, Patricia


    The first years of life represent a unique window of opportunity for foreign language learning. However, key questions are: How much and what kind of foreign language exposure is needed to ignite learning? We conducted a foreign language (English) intervention in four public Infant Education Centers in Madrid, Spain. Intervention children (N =…

  7. Decreased tuberculosis incidence and declining clustered case rates, Madrid.

    Iñigo, Jesús; Arce, Araceli; Palenque, Elia; García de Viedma, Darío; Chaves, Fernando


    To determine effect of recent tuberculosis transmission rates on incidence rates, we conducted 2 prospective population-based molecular epidemiologic studies in Madrid during 1997-1999 (4% immigrants) and 2002-2004 (14.9% immigrants). Case rates decreased in association with declining clustered case rates among Spanish-born persons. New strains were introduced through immigration.

  8. Torre de iluminación y comunicaciones de Madrid

    Pérez Arroyo, Salvador


    Full Text Available This article describes the communication and lighting tower of the Avenida de la Victoria in Madrid, a work belonging to the project of Madrid the Cultural Capital of Europe 1992. The aim of this construction is to light this road junction and, at the same time present a visual landmark of the city. The lantern-tower will light an area of about one hectare and will serve as a base for locating the traffic control cameras and other services.

    En este artículo se describe la farola de iluminación y comunicaciones de la Avenida de la Victoria, en Madrid, obra enmarcada dentro del Madrid Cultural de 1992. El objetivo de esta construcción es iluminar este nudo de confluencia vial y, al mismo tiempo, marcar un hito visual de la ciudad. La torre-farola ilumina una superficie no menor de una hectárea y es base para la ubicación de cámaras para el control del tráfico y otros servicios.

  9. Anisotropic seismic-waveform inversion: Application to a seismic velocity model from Eleven-Mile Canyon in Nevada

    Chen, Yu [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Gao, Kai [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Huang, Lianjie [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Sabin, Andrew [Geothermal Program Office, China Lake, CA (United States)


    Accurate imaging and characterization of fracture zones is crucial for geothermal energy exploration. Aligned fractures within fracture zones behave as anisotropic media for seismic-wave propagation. The anisotropic properties in fracture zones introduce extra difficulties for seismic imaging and waveform inversion. We have recently developed a new anisotropic elastic-waveform inversion method using a modified total-variation regularization scheme and a wave-energy-base preconditioning technique. Our new inversion method uses the parameterization of elasticity constants to describe anisotropic media, and hence it can properly handle arbitrary anisotropy. We apply our new inversion method to a seismic velocity model along a 2D-line seismic data acquired at Eleven-Mile Canyon located at the Southern Dixie Valley in Nevada for geothermal energy exploration. Our inversion results show that anisotropic elastic-waveform inversion has potential to reconstruct subsurface anisotropic elastic parameters for imaging and characterization of fracture zones.

  10. Deep Geothermal energy potential in Madrid basin; Potencial de la Geotermia profunda en la Cuenca de Madrid

    Hidalgo, R.; Sanchez, J.; Ungemach, P.


    The Madrid Basin geothermal potential was evidenced in 1980 thanks to an oil exploration well drilled by Shell-Campsa which showed temperatures of 88 degree centigrade and 150 degree centigrade at 1,700 mts and 3,400 mts depth respectively. The low enthalpy geothermal reservoir could be further assessed by four exploratory wells the first one, Pradillo (originals Shell-Campsa oil well), two drilled by ADARO and IGME (Geological survey of Spain) in San Sebastian de los Reyes and Tres Cantos respectively. The latest well, Geomadrid 1, was drilled in 1990 by the Madrid Regional government. The afore mentioned wells have identified a dependable geothermal resource, hosted in a tertiary, clastic, consolidated sandstone reservoir consisting of a thick multilayered sequence (200-800m), with temperatures ranging from 70 degree centigrade to 90 degree centigrade and depths of 1,500 to 2,150 m., overlying a Mesozoic sequence, suitable to be exploited for thermal uses in several district heating grids around Madrid in areas displaying adequate heat loads. A medium temperature reservoir was also identified at the contact between Mesozoic Cretaceous limestones and fractured basement granites at 3,400mts depth, with measured temperatures of 156 degree centigrade, that could be developed and exploited in view of a combined power and heat production (CPH) within the Madrid suburban areas. (Author) 7 refs.

  11. Spatial-Temporal variability of seismic hazard in Peninsular India

    Kishor Jaiswal; Ravi Sinha


    This paper examines the variability of seismic activity observed in the case of different geological zones of peninsular India (10°N–26°N; 68°E–90°E) based on earthquake catalog between the period 1842 and 2002 and estimates earthquake hazard for the region. With compilation of earthquake catalog in terms of moment magnitude and establishing broad completeness criteria, we derive the seismicity parameters for each geologic zone of peninsular India using maximum likelihood procedure. The estimated parameters provide the basis for understanding the historical seismicity associated with different geological zones of peninsular India and also provide important inputs for future seismic hazard estimation studies in the region. Based on present investigation, it is clear that earthquake recurrence activity in various geologic zones of peninsular India is distinct and varies considerably between its cratonic and rifting zones. The study identifies the likely hazards due to the possibility of moderate to large earthquakes in peninsular India and also presents the influence of spatial rate variation in the seismic activity of this region. This paper presents the influence of source zone characterization and recurrence rate variation pattern on the maximum earthquake magnitude estimation. The results presented in the paper provide a useful basis for probabilistic seismic hazard studies and microzonation studies in peninsular India.

  12. Seismic Imaging of Sandbox Models

    Buddensiek, M. L.; Krawczyk, C. M.; Kukowski, N.; Oncken, O.


    Analog sandbox simulations have been applied to study structural geological processes to provide qualitative and quantitative insights into the evolution of mountain belts and basins. These sandbox simulations provide either two-dimensional and dynamic or pseudo-three-dimensional and static information. To extend the dynamic simulations to three dimensions, we combine the analog sandbox simulation techniques with seismic physical modeling of these sandbox models. The long-term objective of this approach is to image seismic and seismological events of static and actively deforming 3D analog models. To achieve this objective, a small-scale seismic apparatus, composed of a water tank, a PC control unit including piezo-electric transducers, and a positioning system, was built for laboratory use. For the models, we use granular material such as sand and glass beads, so that the simulations can evolve dynamically. The granular models are required to be completely water saturated so that the sources and receivers are directly and well coupled to the propagating medium. Ultrasonic source frequencies (˜500 kHz) corresponding to wavelengths ˜5 times the grain diameter are necessary to be able to resolve small scale structures. In three experiments of different two-layer models, we show that (1) interfaces of layers of granular materials can be resolved depending on the interface preparation more than on the material itself. Secondly, we show that the dilation between the sand grains caused by a string that has been pulled through the grains, simulating a shear zone, causes a reflection that can be detected in the seismic data. In the third model, we perform a seismic reflection survey across a model that contains both the prepared interface and a shear zone, and apply 2D-seismic reflection processing to improve the resolution. Especially for more complex models, the clarity and penetration depth need to be improved to study the evolution of geological structures in dynamic

  13. Seismic source characterization for the Shillong Plateau in Northeast India

    Baro, Olympa; Kumar, Abhishek


    The present study aims at understanding the seismotectonic province of the Shillong Plateau (SP) by identifying the potential seismic source zones within a radius of 500 km from the centre of the SP. From existing literature and earthquake (EQ) data, the seismotectonic region is found to vary in terms of seismicity, tectonic features, geology, thickness of overburden, rupture characteristics and rate of movement. Thus, entire 500-km-radius seismotectonic region is divided into four seismic source zones: namely (1) the Shillong Plateau-Assam Valley Zone (SP-AVZ), (2) the Indo-Burma Ranges Zone (IBRZ), (3) the Bengal Basin Zone (BBZ) and (4) the Eastern Himalaya Zone (EHZ). EQ catalogues for each source zone is analysed for completeness of magnitude and time. Seismic parameter b estimated using a maximum likelihood method is found to be 0.91 ± 0.03, 0.94 ± 0.02, 0.80 ± 0.03 and 0.89 ± 0.03 for the SP-AVZ, IBRZ, BBZ and EHZ, respectively. In addition, the maximum likelihood method is used to estimate the mean annual activity rate, maximum possible magnitude ( m max), return period and probability of exceedance for the four zones. The b values estimated suggest that the BBZ is seismically more active; however, the rate of occurrence of EQs is highest in the IBRZ. Findings from this study are an indication of the relative contribution from each of the four seismic source zones towards a seismic hazard of the SP.

  14. Predicting the distribution of reservoirs by applying the method of seismic data structure characteristics: Example from the eighth zone in Tahe Oilfield%应用地震数据体结构特征法预测塔河油田八区油层分布规律

    林昌荣; 王尚旭; 张勇


    地震数据体结构特征,指对二维或三维地震数据体中每一地震道离散数据点按时间顺序排列所显示的波形特征.应用地震数据体结构特征法对储层进行油气预测,是近年来新兴的一项储层预测技术.塔河油田八区的主产层为碳酸盐岩裂缝-缝洞型储层,具有很强的非均质性,给储层的油气预测带来了一定的困难.针对塔河油田八区特殊的地质条件,采用了地震数据体结构特征法对该区奥陶系储层进行了油气预测,并对油区内、外的区域进行了有利区块的划分.在有利区块中设计的18口钻探井位,经钻井证实均获得了较高的油气产量,取得了很好的经济效益.%Seismic data structure characteristics means the waveform character arranged in the time sequence at discrete data points in each 2-D or 3-D seismic trace. Hydrocarbon prediction using seismic data structure characteristics is a new reservoir prediction technique.When the main pay interval is in carbonate fracture and fissure-cavern type reservoirs with very strong inhomogeneity, there are some difficulties with hydrocarbon prediction. Because of the special geological conditions of the eighth zone in the Tahe oil field, we apply seismic data structure characteristics to hydrocarbon prediction for the Ordovician reservoir in this zone. We divide the area oil zone into favorable and unfavorable blocks. Eighteen well locations were proposed in the favorable oil block, drilled, and recovered higher output of oil and gas.

  15. Southern Appalachian Regional Seismic Network

    Chiu, S.C.C.; Johnston, A.C.; Chiu, J.M. [Memphis State Univ., TN (United States). Center for Earthquake Research and Information


    The seismic activity in the southern Appalachian area was monitored by the Southern Appalachian Regional Seismic Network (SARSN) since late 1979 by the Center for Earthquake Research and Information (CERI) at Memphis State University. This network provides good spatial coverage for earthquake locations especially in east Tennessee. The level of activity concentrates more heavily in the Valley and Ridge province of eastern Tennessee, as opposed to the Blue Ridge or Inner Piedmont. The large majority of these events lie between New York - Alabama lineament and the Clingman/Ocoee lineament, magnetic anomalies produced by deep-seated basement structures. Therefore SARSN, even with its wide station spacing, has been able to define the essential first-order seismological characteristics of the Southern Appalachian seismic zone. The focal depths of the southeastern U.S. earthquakes concentrate between 8 and 16 km, occurring principally beneath the Appalachian overthrust. In cross-sectional views, the average seismicity is shallower to the east beneath the Blue Ridge and Piedmont provinces and deeper to the west beneath the Valley and Ridge and the North American craton. Results of recent focal mechanism studies by using the CERI digital earthquake catalog between October, 1986 and December, 1991, indicate that the basement of the Valley and Ridge province is under a horizontal, NE-SW compressive stress. Right-lateral strike-slip faulting on nearly north-south fault planes is preferred because it agrees with the trend of the regional magnetic anomaly pattern.

  16. Seismic hazard studies in Egypt

    Mohamed, Abuo El-Ela A.; El-Hadidy, M.; Deif, A.; Abou Elenean, K.


    The study of earthquake activity and seismic hazard assessment of Egypt is very important due to the great and rapid spreading of large investments in national projects, especially the nuclear power plant that will be held in the northern part of Egypt. Although Egypt is characterized by low seismicity, it has experienced occurring of damaging earthquake effect through its history. The seismotectonic sitting of Egypt suggests that large earthquakes are possible particularly along the Gulf of Aqaba-Dead Sea transform, the Subduction zone along the Hellenic and Cyprean Arcs, and the Northern Red Sea triple junction point. In addition some inland significant sources at Aswan, Dahshour, and Cairo-Suez District should be considered. The seismic hazard for Egypt is calculated utilizing a probabilistic approach (for a grid of 0.5° × 0.5°) within a logic-tree framework. Alternative seismogenic models and ground motion scaling relationships are selected to account for the epistemic uncertainty. Seismic hazard values on rock were calculated to create contour maps for four ground motion spectral periods and for different return periods. In addition, the uniform hazard spectra for rock sites for different 25 periods, and the probabilistic hazard curves for Cairo, and Alexandria cities are graphed. The peak ground acceleration (PGA) values were found close to the Gulf of Aqaba and it was about 220 gal for 475 year return period. While the lowest (PGA) values were detected in the western part of the western desert and it is less than 25 gal.

  17. Seismicity dynamics and earthquake predictability

    G. A. Sobolev


    Full Text Available Many factors complicate earthquake sequences, including the heterogeneity and self-similarity of the geological medium, the hierarchical structure of faults and stresses, and small-scale variations in the stresses from different sources. A seismic process is a type of nonlinear dissipative system demonstrating opposing trends towards order and chaos. Transitions from equilibrium to unstable equilibrium and local dynamic instability appear when there is an inflow of energy; reverse transitions appear when energy is dissipating. Several metastable areas of a different scale exist in the seismically active region before an earthquake. Some earthquakes are preceded by precursory phenomena of a different scale in space and time. These include long-term activation, seismic quiescence, foreshocks in the broad and narrow sense, hidden periodical vibrations, effects of the synchronization of seismic activity, and others. Such phenomena indicate that the dynamic system of lithosphere is moving to a new state – catastrophe. A number of examples of medium-term and short-term precursors is shown in this paper. However, no precursors identified to date are clear and unambiguous: the percentage of missed targets and false alarms is high. The weak fluctuations from outer and internal sources play a great role on the eve of an earthquake and the occurrence time of the future event depends on the collective behavior of triggers. The main task is to improve the methods of metastable zone detection and probabilistic forecasting.

  18. Quantitative Seismic Amplitude Analysis

    Dey, A. K.


    The Seismic Value Chain quantifies the cyclic interaction between seismic acquisition, imaging and reservoir characterization. Modern seismic innovation to address the global imbalance in hydrocarbon supply and demand requires such cyclic interaction of both feed-forward and feed-back processes. Currently, the seismic value chain paradigm is in a feed-forward mode. Modern seismic data now have the potential to yield the best images in terms of spatial resolution, amplitude accuracy, and incre...

  19. Probabilistic seismic hazard estimation of Manipur, India

    Pallav, Kumar; Raghukanth, S. T. G.; Darunkumar Singh, Konjengbam


    This paper deals with the estimation of spectral acceleration for Manipur based on probabilistic seismic hazard analysis (PSHA). The 500 km region surrounding Manipur is divided into seven tectonic zones and major faults located in these zones are used to estimate seismic hazard. The earthquake recurrence relations for the seven zones have been estimated from past seismicity data. Ground motion prediction equations proposed by Boore and Atkinson (2008 Earthq. Spectra 24 99-138) for shallow active regions and Atkinson and Boore (2003 Bull. Seismol. Soc. Am. 93 1703-29) for the Indo-Burma subduction zone are used for estimating ground motion. The uniform hazard response spectra for all the nine constituent districts of Manipur (Senapati, Tamenglong, Churachandpur, Chandel, Imphal east, Imphal west, Ukhrul, Thoubal and Bishnupur) at 100-, 500- and 2500-year return periods have been computed from PSHA. A contour map of peak ground acceleration over Manipur is also presented for 100-, 500-, and 2500-year return periods with variations of 0.075-0.225, 0.18-0.63 and 0.3-0.1.15 g, respectively, throughout the state. These results may be of use to planners and engineers for site selection, designing earthquake resistant structures and, further, may help the state administration in seismic hazard mitigation.

  20. Velocity structure and seismicity of southeastern Tennessee

    Kaufmann, Ronald Douglas; Long, Leland Timothy


    The seismic zone in southeastern Tennessee is at the confluence of major crustal features, which have been interpreted largely from potential data, and their relation to seismicity could help us understand why major earthquakes sometimes occur in the eastern United States. In this paper we solve for the previously unknown velocity structure of the upper crust by an inversion of travel time residuals from relocated earthquakes. The gravity anomalies are included by using a linear relation between average anomalous density and average anomalous velocity. The velocity model demonstrates that the seismicity is concentrated in areas of average to below average velocity and does not appear to be associated with one of the previously identified major crustal features. The high-velocity zones mark areas that are generally lacking in seismicity. The association of earthquake hypocenters with regions of low-velocity crustal rocks is consistent with other intraplate seismic zones, and this association supports the conjecture that intraplate earthquakes occur in crust that may have been weakened. The velocity anomalies at midcrustal depths do not support the New York-Alabama (NY-AL) lineament as a linear feature extending through southeastern Tennessee and parallel to contours in gravity anomalies as originally proposed. A continuation of the (NY-AL) lineament to the southwest requires either a 15 degree southwestward change in direction or a displacement to be consistent with the velocity anomalies. The seismically active areas in southeastern Tennessee do not appear to be constrained by the major crustal features, but instead, the seismicity is characterized by the distribution of hypocenters and their association with low-velocity regions at midcrustal depths.

  1. Structural concepts and details for seismic design


    This manual discusses building and building component behavior during earthquakes, and provides suggested details for seismic resistance which have shown by experience to provide adequate performance during earthquakes. Special design and construction practices are also described which, although they might be common in some high-seismic regions, may not be common in low and moderate seismic-hazard regions of the United States. Special attention is given to describing the level of detailing appropriate for each seismic region. The UBC seismic criteria for all seismic zones is carefully examined, and many examples of connection details are given. The general scope of discussion is limited to materials and construction types common to Department of Energy (DOE) sites. Although the manual is primarily written for professional engineers engaged in performing seismic-resistant design for DOE facilities, the first two chapters, plus the introductory sections of succeeding chapters, contain descriptions which are also directed toward project engineers who authorize, review, or supervise the design and construction of DOE facilities. 88 refs., 188 figs.

  2. Seismic imaging capabilities optimize reservoir management

    Kristiansen, P. [Geco-Prakla, Oslo (Norway); Currie, M.T. [BP Exploration, Aberdeen (United Kingdom)


    Despite the fact that seismic is the only known method for illuminating the subsurface at any distance from a well, little has been done to use seismic as a tool for monitoring changes in the reservoir over time. This will change as 4-D, or time-lapse, seismic becomes more common. A permanent 4-D system has been installed at the Foinaven field, West of Shetlands in the North Sea. Tracking fluid or gas movements through seismic reservoir monitoring is the primary objective of 4-D seismic technology. Areas that do not show significant changes in the seismic response over time may indicate pools of bypassed oil that could be drilled and drained. This in itself could contribute an increased recovery by several percent. Unexpected changes in reservoir contacts could be used to identify hydraulic barriers and high permeability zones not interpreted on the original seismic or identified through well testing. Another application of monitoring the fluid or gas front would be to anticipate and possibly avoid early breakthrough in time to mitigate loss of flow rate and ultimate recovery.

  3. Structure of the Kasbah fold zone (Agadir bay, Morocco. Implications on the chronology of the recent tectonics of the western High Atlas and on the seismic hazard of the Agadir area

    Samaka, F.


    Full Text Available Detailed re-interpretation of the north-eastern segment of a profile realized across the Agadir bay along a NE-SW trend and crosscutting the main structures, together with analysis of available isochron maps, allowed us to retrace the geological history of the offshore western High Atlas. Two tectonostratigraphic sequences were distinguished: Unit II, which displays a simple structure, laying unconformably on Unit I, with a more complex structure dominated by a reverse fault (F1 striking E-W with a dip to the north. Correlation to boreholes Souss-1 and AGM-1 allowed us to assign Unit I to the Triassic – Palaeogene and Unit II to the Miocene – Present. The NE fault block shows a ramp-flat fault plane (F2 with an overlying SW-vergent fold that can be interpreted as a fault-bend fold. Three main stages were distinguished: (1 during the Cretaceous, F1 could have been a syndepositional normal fault with the NE block moving downwards; (2 towards the beginning of the Tertiary, the displacement of plane F2 induced the development of a fault-bend fold and erosion of the forelimb and hinge of the fold; displacement along F2 was transferred to fault F1; (3 afterwards, during the Miocene, reverse motion of F1 deformed and tilted the plane F2 and accentuated the folded structure. This evolution is typical for a frontal basin above a fault-related fold. Evaluation of the thickness and bed depth differences shows that the largest growth rate was recorded in Late Miocene times. Seismic activity recorded in the Agadir bay appears to be clearly related to this fault zone, as inferred from focal mechanisms. Seismic moment evaluation suggests that earthquakes of magnitude Mw≥6 are likely to occur, but could not be much larger because of the fault segmentation geometry of the High Atlas Front.

    A partir de una detallada reinterpretación del segmento nororiental de un perfil que corta las principales estructuras de la bahía de Agadir a lo largo de una

  4. 2 obras de Fisac en Madrid: Edificio «Vega» para oficinas y vivienda unifamiliar en Somosaguas

    Fisac, M.


    Full Text Available 2 Buildings by M. Fisac «Vega» office building in Madrid This aesthetically thought out building is eminently urban, with natural gardens and no enclosing fences or artificial obstacles separating the site from the street. The «Vega» building comprises a central block, with the vertical communications, including stairs and three lifts, and and three wings that correspond to the triangular shape of the site. The basic constructional mediiun, which has been very wisely used, both for the paraments and flooring, is untreated reinforced concrete. Single family dwelling at Somosaguas, Madrid The various zones of the building have been planned mainly in relation to their orientation, so that the living zone faces to the South, and the bedrooms are on the East. Also, the separate parts of the building are situated at various levels, to have as much sunshine as possible, and achieve optimum adaptation to the site profile. The garden is also planned on multip