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Sample records for active thrust fault

  1. Erosion influences the seismicity of active thrust faults.

    PubMed

    Steer, Philippe; Simoes, Martine; Cattin, Rodolphe; Shyu, J Bruce H

    2014-11-21

    Assessing seismic hazards remains one of the most challenging scientific issues in Earth sciences. Deep tectonic processes are classically considered as the only persistent mechanism driving the stress loading of active faults over a seismic cycle. Here we show via a mechanical model that erosion also significantly influences the stress loading of thrust faults at the timescale of a seismic cycle. Indeed, erosion rates of about ~0.1-20 mm yr(-1), as documented in Taiwan and in other active compressional orogens, can raise the Coulomb stress by ~0.1-10 bar on the nearby thrust faults over the inter-seismic phase. Mass transfers induced by surface processes in general, during continuous or short-lived and intense events, represent a prominent mechanism for inter-seismic stress loading of faults near the surface. Such stresses are probably sufficient to trigger shallow seismicity or promote the rupture of deep continental earthquakes up to the surface.

  2. Duration of activity on lobate-scarp thrust faults on Mercury

    NASA Astrophysics Data System (ADS)

    Banks, Maria E.; Xiao, Zhiyong; Watters, Thomas R.; Strom, Robert G.; Braden, Sarah E.; Chapman, Clark R.; Solomon, Sean C.; Klimczak, Christian; Byrne, Paul K.

    2015-11-01

    Lobate scarps, landforms interpreted as the surface manifestation of thrust faults, are widely distributed across Mercury and preserve a record of its history of crustal deformation. Their formation is primarily attributed to the accommodation of horizontal shortening of Mercury's lithosphere in response to cooling and contraction of the planet's interior. Analyses of images acquired by the Mariner 10 and MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft during flybys of Mercury showed that thrust faults were active at least as far back in time as near the end of emplacement of the largest expanses of smooth plains. However, the full temporal extent of thrust fault activity on Mercury, particularly the duration of this activity following smooth plains emplacement, remained poorly constrained. Orbital images from the MESSENGER spacecraft reveal previously unrecognized stratigraphic relations between lobate scarps and impact craters of differing ages and degradation states. Analysis of these stratigraphic relations indicates that contraction has been a widespread and long-lived process on the surface of Mercury. Thrust fault activity had initiated by a time near the end of the late heavy bombardment of the inner solar system and continued through much or all of Mercury's subsequent history. Such deformation likely resulted from the continuing secular cooling of Mercury's interior.

  3. Connecting the Yakima fold and thrust belt to active faults in the Puget Lowland, Washington

    USGS Publications Warehouse

    Blakely, R.J.; Sherrod, B.L.; Weaver, C.S.; Wells, R.E.; Rohay, A.C.; Barnett, E.A.; Knepprath, N.E.

    2011-01-01

    High-resolution aeromagnetic surveys of the Cascade Range and Yakima fold and thrust belt (YFTB), Washington, provide insights on tectonic connections between forearc and back-arc regions of the Cascadia convergent margin. Magnetic surveys were measured at a nominal altitude of 250 m above terrain and along flight lines spaced 400 m apart. Upper crustal rocks in this region have diverse magnetic properties, ranging from highly magnetic rocks of the Miocene Columbia River Basalt Group to weakly magnetic sedimentary rocks of various ages. These distinctive magnetic properties permit mapping of important faults and folds from exposures to covered areas. Magnetic lineaments correspond with mapped Quaternary faults and with scarps identified in lidar (light detection and ranging) topographic data and aerial photography. A two-dimensional model of the northwest striking Umtanum Ridge fault zone, based on magnetic and gravity data and constrained by geologic mapping and three deep wells, suggests that thrust faults extend through the Tertiary section and into underlying pre-Tertiary basement. Excavation of two trenches across a prominent scarp at the base of Umtanum Ridge uncovered evidence for bending moment faulting possibly caused by a blind thrust. Using aeromagnetic, gravity, and paleoseismic evidence, we postulate possible tectonic connections between the YFTB in eastern Washington and active faults of the Puget Lowland. We suggest that faults and folds of Umtanum Ridge extend northwestward through the Cascade Range and merge with the Southern Whidbey Island and Seattle faults near Snoqualmie Pass 35 km east of Seattle. Recent earthquakes (MW ≤ 5.3) suggest that this confluence of faults may be seismically active today.

  4. Exhumed analogues of seismically active carbonate-bearing thrusts: fault architecture and deformation mechanisms

    NASA Astrophysics Data System (ADS)

    Tesei, T.; Collettini, C.; Viti, C.; Barchi, M. R.

    2012-12-01

    In May 2012 a M = 5.9 earthquake followed by a long aftershock sequence struck the Northern Italy. The sequence occurred at 4-10 km depth within the active front of Northern Apennines Prism and the major events nucleate within, or propagate through, a thick sequence of carbonates. In an inner sector of the Northern Apennines, ancient carbonate-bearing thrusts exposed at the surface, represent exhumed analogues of structures generating seismicity in the active front. Here we document fault architecture and deformation mechanisms of three regional carbonate bearing thrusts with displacement of several kilometers and exhumation in the range of 1-4 km. Fault zone structure and deformation mechanisms are controlled by the lithology of the faulted rocks. In layered limestones and marly-limestones the fault zone is up to 200 m thick and is characterized by intense pressure solution. In massive limestones the deformation generally occurs along thin and sharp slip planes that are in contact with fault portions affected by either cataclasis or pressure solution. SEM and TEM observations show that pressure solution surfaces, made of smectite lamellae, with time tend to form an interconnected network affected by frictional sliding. Sharp slipping planes along massive limestones show localization along Y shear planes that separate an extremely comminuted cataclasites from an almost undeformed protolith. The comparison of the three shear zones depicts a fault zone structure extremely heterogeneous as the result of protolith lithology, geometrical complexities and the presence of inherited structures. We observe the competition between brittle (cataclasis, distributed frictional sliding along phyllosilicates and extremely localized slip within carbonates) and pressure solution processes, that suggest a multi-mode of slip behaviour. Extreme localization along carbonate-bearing Y shear planes is our favorite fault zone feature representing past seismic ruptures along the studied

  5. Recent tectonic activity on Mercury revealed by small thrust fault scarps

    NASA Astrophysics Data System (ADS)

    Watters, Thomas R.; Daud, Katie; Banks, Maria E.; Selvans, Michelle M.; Chapman, Clark R.; Ernst, Carolyn M.

    2016-10-01

    Large tectonic landforms on the surface of Mercury, consistent with significant contraction of the planet, were revealed by the flybys of Mariner 10 in the mid-1970s. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission confirmed that the planet's past 4 billion years of tectonic history have been dominated by contraction expressed by lobate fault scarps that are hundreds of kilometres long. Here we report the discovery of small thrust fault scarps in images from the low-altitude campaign at the end of the MESSENGER mission that are orders of magnitude smaller than the large-scale lobate scarps. These small scarps have tens of metres of relief, are only kilometres in length and are comparable in scale to small young scarps on the Moon. Their small-scale, pristine appearance, crosscutting of impact craters and association with small graben all indicate an age of less than 50 Myr. We propose that these scarps are the smallest members of a continuum in scale of thrust fault scarps on Mercury. The young age of the small scarps, along with evidence for recent activity on large-scale scarps, suggests that Mercury is tectonically active today and implies a prolonged slow cooling of the planet's interior.

  6. Redefining Medlicott-Wadia's main boundary fault from Jhelum to Yamuna: An active fault strand of the main boundary thrust in northwest Himalaya

    NASA Astrophysics Data System (ADS)

    Thakur, V. C.; Jayangondaperumal, R.; Malik, M. A.

    2010-06-01

    The MBT demarcates a tectonic boundary between the Tertiary Sub Himalaya and the pre-Tertiary Lesser Himalaya. South of the MBT, another tectonically important fault extends from Muzaffarabad and Riasi in Jammu-Kashmir to Bilaspur and Nahan in Himachal. Medlicott and Wadia had designated this fault the Main Boundary Fault (MBF) in Simla Hills and Jammu region respectively. In between these two areas, later workers gave local-area names to the MBF as the Riasi Thrust in Jammu, Palampur Thrust in Kangra, Bilaspur Thrust in Simla Hills and Nahan Thrust in Sirmur. We have reviewed and established the tectonostratigraphic framework and physical continuity of the lower Tertiary belt and the MBF. The lower Tertiary belt, lying south of the MBT, has characteristic tectonostratigraphic setting with discontinuous bodies of stromatolite-bearing Proterozoic limestone overlain with depositional contact by the Paleocene-lower part Middle Eocene marine Subathu/Patala formation which in turn overlain by the Upper Oligocene-Lower Miocene non-marine Dharamsala/Murree Formation. To avoid confusion with the MBT, we designate collectively the MBF and related faults as the Medlicott-Wadia Thrust (MWT). The MWT extends east of Hazara-Kashmir syntaxis to river Yamuna, covering a distance of ˜ 700 km. Further east of Yamuna, the lower Tertiary belt pinches out and the MWT merges with the sensuo-stricto MBT. The Proterozoic limestone represents the basement over which the lower Tertiary sediments were deposited. The limestone basement with its cover was detached by the MWT, exhuming to the surface and thrusting over largely the Siwalik group. The reactivated Balakot-Bagh Fault, causative fault for the 2005 Kashmir earthquake, extends southeast with right-step to the Riasi Thrust. The Riasi Thrust shows evidence of reactivation and active tectonic activity in Jammu region. It extends further east to the Palampur Thrust in Kangra reentrant, which lies within the 1905 Kangra earthquake

  7. InSAR Evidence for the Spokane Fault, an Active Shallow Thrust Fault Beneath the City of Spokane Washington, USA

    NASA Astrophysics Data System (ADS)

    Wicks, C.; Weaver, C. S.; Bodin, P.; Sherrod, B. L.

    2012-12-01

    In 2001 a nearly five month long sequence of shallow, mostly small magnitude earthquakes occurred beneath Spokane, a city with a population of about 200,000, in the state of Washington. The Spokane area, an area of low background seismicity, is on the northeastern edge of the Columbia Basin, a physiographic province largely covered with Miocene flood basalts of the Columbia River Basalt Group. The earthquake sequence appears to have begun with an isolated magnitude 2 earthquake on May 24, 2001, but began in earnest with a magnitude 3.9 earthquake on June 25, 2001 and ended on November 23, 2001, with a total of 105 earthquakes recorded up to a magnitude 4. During most of the sequence, the earthquakes were not well located because seismic instrumentation was sparse. Despite poor-quality locations, the earthquake hypocenters were likely very shallow, because residents in small areas of Spokane reported feeling many of the earthquakes in the sequence and hearing explosion-like noises associated with some of the earthquakes. Using interferometric synthetic aperture radar (InSAR) data from the European Space Agency ERS2 and ENVISAT satellites and the Canadian Space Agency RADARSAT-1 satellite we are able to show that slip on a shallow previously unknown thrust fault, that we name the Spokane Fault, is the source of the earthquake sequence. The fault strikes northeast, dips ~30 degrees to the northwest, and the maximum slip was ~45 mm. The part of the Spokane Fault that slipped during the 2001 earthquake sequence underlies the north part of the city, and slip on the fault was concentrated between ~0.3 and 2 km depth. Projecting the buried fault plane to the surface gives a possible surface trace for the Spokane Fault; it strikes northeast from the city center into north Spokane. An accurate assessment of the hazard potential of the Spokane Fault requires additional studies to delineate the fault and map the subsurface geology.

  8. Active faulting within a megacity: the geometry and slip rate of the Pardisan thrust in central Tehran, Iran

    NASA Astrophysics Data System (ADS)

    Talebian, M.; Copley, A. C.; Fattahi, M.; Ghoraishi, M.; Jackson, J. A.; Nazari, H.; Sloan, R. A.; Walker, R. T.

    2016-09-01

    Tehran, the capital city of Iran with a population of over 12 million, is one of the largest urban centres within the seismically active Alpine-Himalayan orogenic belt. Although several historic earthquakes have affected Tehran, their relation to individual faults is ambiguous for most. This ambiguity is partly due to a lack of knowledge about the locations, geometries, and seismic potential of structures that have been obscured by dramatic urban growth over the past three decades, and which have covered most of the young geomorphic markers and natural exposures. Here we use aerial photographs from 1956, combined with an ˜1 m DEM derived from stereo Pleiades satellite imagery, to investigate the geomorphology of a growing anticline above a thrust fault - the Pardisan thrust - within central Tehran. The topography across the ridge is consistent with a steep ramp extending from close to the surface to a depth of ˜2 km, where it presumably connects with a shallow-dipping detachment. No primary fault is visible at the surface, and it is possible that the faulting dissipates in the near surface as distributed shearing. We use optically-stimulated luminescence to date remnants of uplifted and warped alluvial deposits that are offset vertically across the Pardisan fault, providing minimum uplift and slip-rates of at least 1 mm/yr. Our study shows that the faults within the Tehran urban region have relatively rapid rates of slip, are important in the regional tectonics, and have a great impact on earthquake hazard assessment of the city and surrounding region.

  9. Active emergent thrust associated with a detachment fold: A case study of the eastern boundary fault of Takada plain, central Japan

    NASA Astrophysics Data System (ADS)

    Kato, N.; Ishiyama, T.; Sato, H.; Saito, H.; Kurashimo, E.; Abe, S.

    2012-04-01

    To estimate seismic hazards, understanding the relationship between active fault and seismic source fault is crucial. Along the Japan Sea coast of Northern Honshu, Japan, thick sediments, deposited in the Miocene rift-grabens, formed fold-and-thrust belt, due to the shortening deformation since the Pliocene time. Most of the thrusts are active and show clear geomorphological evidences. Some of the thrusts are secondary faults, produced by the folding of competent layers. To elucidate the relationship between an emergent thrust and deep-sited seismogenic source fault, we performed shallow high-resolution seismic reflection profiling across the eastern boundary fault of the Takada plain, central Japan. Based on the moropho-tectonic data, the vertical slip rate of the Eastern boundary fault of the Takada plain is 0.9 mm/y and has potential to produce M7.2 earthquake (AIST, 2006). For shallow structure, we obtained CMP-seismic reflection data from a 7-km-long seismic line, using 541 channels of off-line recorders. Seismic source was an Envirovibe (IVI). Receiver and shot intervals are 12.5 m and seismic signals were recorded by fixed channels. Shallow seismic data were acquired as a piggy-bag project of 70 km-long onshore-offshore deep seismic profiling. High-resolution seismic section portrays the emergent thrust, dipping to the east at about 30 degrees. The hanging wall consist Pliocene interbedded mudstone and sandstone and deeper extension of the thrust can be traced down to the Miocene mudstone of the Teradoamri Formation as a low-angle fault. In the Niigata basin, the lower part of the Teradomari Formation is known as over pressured mudstone and shallow detachments are commonly developed in this unit. Based on the deep seismic section, including velocity profile obtained by refraction tomography, deep sited fault does not connect to the shallow active fault directly.

  10. New insights into fault activation and stress transfer between en echelon thrusts: The 2012 Emilia, Northern Italy, earthquake sequence

    NASA Astrophysics Data System (ADS)

    Cheloni, D.; Giuliani, R.; D'Agostino, N.; Mattone, M.; Bonano, M.; Fornaro, G.; Lanari, R.; Reale, D.; Atzori, S.

    2016-06-01

    Here we present the results of the inversion of a new geodetic data set covering the 2012 Emilia seismic sequence and the following 1 year of postseismic deformation. Modeling of the geodetic data together with the use of a catalog of 3-D relocated aftershocks allows us to constrain the rupture geometries and the coseismic and postseismic slip distributions for the two main events (Mw 6.1 and 6.0) of the sequence and to explore how these thrust events have interacted with each other. Dislocation modeling reveals that the first event ruptured a slip patch located in the center of the Middle Ferrara thrust with up to 1 m of reverse slip. The modeling of the second event, located about 15 km to the southwest, indicates a main patch with up to 60 cm of slip initiated in the deeper and flatter portion of the Mirandola thrust and progressively propagated postseismically toward the top section of the rupture plane, where most of the aftershocks and afterslip occurred. Our results also indicate that between the two main events, a third thrust segment was activated releasing a pulse of aseismic slip equivalent to a Mw 5.8 event. Coulomb stress changes suggest that the aseismic event was likely triggered by the preceding main shock and that the aseismic slip event probably brought the second fault closer to failure. Our findings show significant correlations between static stress changes and seismicity and suggest that stress interaction between earthquakes plays a significant role among continental en echelon thrusts.

  11. Initiation process of a thrust fault revealed by analog experiments

    NASA Astrophysics Data System (ADS)

    Yamada, Yasuhiro; Dotare, Tatsuya; Adam, Juergen; Hori, Takane; Sakaguchi, Hide

    2016-04-01

    We conducted 2D (cross-sectional) analog experiments with dry sand using a high resolution digital image correlation (DIC) technique to reveal initiation process of a thrust fault in detail, and identified a number of "weak shear bands" and minor uplift prior to the thrust initiation. The observations suggest that the process can be divided into three stages. Stage 1: characterized by a series of abrupt and short-lived weak shear bands at the location where the thrust will be generated later. Before initiation of the fault, the area to be the hanging wall starts to uplift. Stage 2: defined by the generation of the new thrust and its active displacement. The location of the new thrust seems to be constrained by its associated back-thrust, produced at the foot of the surface slope (by the previous thrust). The activity of the previous thrust turns to zero once the new thrust is generated, but the timing of these two events is not the same. Stage 3: characterized by a constant displacement along the (new) thrust. Similar minor shear bands can be seen in the toe area of the Nankai accretionary prism, SW Japan and we can correlate the along-strike variations in seismic profiles to the model results that show the characteristic features in each thrust development stage.

  12. Evolution of the Puente Hills Thrust Fault

    NASA Astrophysics Data System (ADS)

    Bergen, K. J.; Shaw, J. H.; Dolan, J. F.

    2013-12-01

    This study aims to assess the evolution of the blind Puente Hills thrust fault system (PHT) by determining its age of initiation, lateral propagation history, and changes in slip rate over time. The PHT presents one of the largest seismic hazards in the United States, given its location beneath downtown Los Angeles. The PHT is comprised of three fault segments: the Los Angeles (LA), Santa Fe Springs (SFS), and Coyote Hills (CH). The LA and SFS segments are characterized by growth stratigraphy where folds formed by uplift on the fault segments have been continually buried by sediment from the Los Angeles and San Gabriel rivers. The CH segment has developed topography and is characterized by onlapping growth stratigraphy. This depositional setting gives us the unique opportunity to measure uplift on the LA and SFS fault segments, and minimum uplift on the CH fault segment, as the difference in sediment thicknesses across the buried folds. We utilize depth converted oil industry seismic reflection data to image the fold geometries. Identifying time-correlative stratigraphic markers for slip rate determination in the basin has been a problem for researchers in the past, however, as the faunal assemblages observed in wells are time-transgressive by nature. To overcome this, we utilize the sequence stratigraphic model and well picks of Ponti et al. (2007) as a basis for mapping time-correlative sequence boundaries throughout our industry seismic reflection data from the present to the Pleistocene. From the Pleistocene to Miocene we identify additional sequence boundaries in our seismic reflection data from imaged sequence geometries and by correlating industry well formation tops. The sequence and formation top picks are then used to build 3-dimensional surfaces in the modeling program Gocad. From these surfaces we measure the change in thicknesses across the folds to obtain uplift rates between each sequence boundary. Our results show three distinct phases of

  13. Coseismic Faulting and Folding in an Active Thrust Sheet over Multiple Rupture Cycles Resolved by Integrating Surface and Subsurface Records of Earthquake Deformation

    NASA Astrophysics Data System (ADS)

    Stockmeyer, J. M.; Shaw, J. H.; Brown, N.; Rhodes, E. J.; Wang, M.; Lavin, L. C.; Guan, S.

    2015-12-01

    Many recent thrust fault earthquakes have involved coseismic surface faulting and folding, revealing the complex nature of surface deformation in active thrust sheets. In this study, we characterize deformation along the active Southern Junggar Thrust (SJT) in the Junggar basin, NW China - which sourced the 1906 M8 Manas earthquake - to gain insight into how fault slip at depth is partitioned between faulting and folding strains at Earth's surface by integrating deformed terrace records, subsurface geophysical data, and luminescence geochronology. Using a 1-m digital elevation model and field surveys, we have mapped the precise geometries of fluvial terraces across the entire Tugulu anticline, which lies in the hanging wall of the SJT. These profiles reveal progressive uplift of several terraces along prominent fault scarps where the SJT is surface-emergent. Similarly aged terraces are folded in the backlimb of the Tugulu fold, providing a sequential record of surface folding. These folded terraces are progressively rotated such that the oldest terraces are dipping much steeper than younger terraces within the same fold limb. Using 2- and 3-D seismic reflection data, we integrate subsurface deformation constraints with records of surface strain. Structural interpretations of these seismic data define the geometry of the SJT and reveal that folding is localized across synclinal bends along the SJT. We evaluate a range of distinct fault-related fold models (e.g. fault-bend folding, shear fault-bend folding) to assess which structural style best describes the geometries of the subsurface and surface fold patterns. By doing so, we have the opportunity to directly relate surface fault slip measures from terrace folding and uplift to total fault slip at depth. This integration of surface and subsurface deformation - combined with constraints on terrace ages from post-IR IRSL geochronology - allows us to characterize how fault slip and seismic moment are partitioned

  14. Initiation of a thrust fault revealed by analog experiments

    NASA Astrophysics Data System (ADS)

    Dotare, Tatsuya; Yamada, Yasuhiro; Adam, Juergen; Hori, Takane; Sakaguchi, Hide

    2016-08-01

    To reveal in detail the process of initiation of a thrust fault, we conducted analog experiments with dry quartz sand using a high-resolution digital image correlation technique to identify minor shear-strain patterns for every 27 μm of shortening (with an absolute displacement accuracy of 0.5 μm). The experimental results identified a number of "weak shear bands" and minor uplift prior to the initiation of a thrust in cross-section view. The observations suggest that the process is closely linked to the activity of an adjacent existing thrust, and can be divided into three stages. Stage 1 is characterized by a series of abrupt and short-lived weak shear bands at the location where the thrust will subsequently be generated. The area that will eventually be the hanging wall starts to uplift before the fault forms. The shear strain along the existing thrust decreases linearly during this stage. Stage 2 is defined by the generation of the new thrust and active displacements along it, identified by the shear strain along the thrust. The location of the new thrust may be constrained by its back-thrust, generally produced at the foot of the surface slope. The activity of the existing thrust falls to zero once the new thrust is generated, although these two events are not synchronous. Stage 3 of the thrust is characterized by a constant displacement that corresponds to the shortening applied to the model. Similar minor shear bands have been reported in the toe area of the Nankai accretionary prism, SW Japan. By comparing several transects across this subduction margin, we can classify the lateral variations in the structural geometry into the same stages of deformation identified in our experiments. Our findings may also be applied to the evaluation of fracture distributions in thrust belts during unconventional hydrocarbon exploration and production.

  15. Stress, strain, and fault behavior at a thrust ramp: Insights from the Naukluft thrust, Namibia

    NASA Astrophysics Data System (ADS)

    Fagereng, Åke; Smith, Zach; Rowe, Christie D.; Makhubu, Bandile; Sylvester, Fernando Y. G.

    2014-01-01

    We report observations from a kilometer-scale thrust ramp on the Naukluft thrust, Namibia. The Naukluft thrust is a low angle thrust that was active at subgreenschist facies conditions and accommodated several tens of kilometers of displacement at the base of the Naukluft Nappe Complex in the Pan-African Damara Orogeny. The fault zone is generally planar and a few meters thick, comprising predominantly a dolomite-rich cataclasite. At the ramp, the fault-rock assemblage increases in thickness, and the hanging-wall, which elsewhere is relatively intact, contains a high density network of inclined quartz veins, subvertical dolomite and calcite veins, breccia zones, as well as injectites of cataclastic fault rock emanating from the fault surface. The geometry of the hanging-wall structures indicates local subhorizontal extension. Local tensile stress can be explained by bending in the hanging-wall as it deformed to slide above the ramp structure. High fluid pressures created dynamically during fast slip by decarbonation of carbonate fault rock, and by dewatering of the footwall under an impermeable fault during interseismic periods, led to additional reduction in local effective compressive stresses. In this location, the ramp is more optimally oriented for slip in the inferred regional stress field, and therefore likely to fail before the contiguous thrust flats that are subparallel to the maximum principal stress. As such, the ramp represents the likely location for nucleation of fault slip, which could both trigger dynamic failure of the adjacent thrust faults, and produce hanging-wall extensional structures.

  16. Local Thrust Faulting Along the Southern Hayward Fault in Fremont, California

    NASA Astrophysics Data System (ADS)

    Johnson, P. L.; Sayre, T. M.

    2015-12-01

    The southern Hayward fault is an active, northwest-striking, right lateral strike slip fault within the densely populated eastern San Francisco Bay area. Recent subsurface investigation along the southern Hayward fault has revealed unexpectedly complex deformation between subparallel fault traces. In the city of Fremont, the southern Hayward fault crosses Mission Boulevard (MB) as three parallel to subparallel traces, the eastern, central, and western traces. Recent exploratory trenches excavated near MB by another consultant and logged by the authors revealed that the western and central traces of the Hayward fault are nearly parallel with limited secondary deformation between them. However, along strike farther to the northwest, abundant secondary deformation in the form of multiple northeast-dipping thrust faults was encountered in the exploratory trenches. The thrust faults locally place Plio-Pleistocene Irvington Gravels Formation over slope wash deposits and Bk horizon soils, implying late Quaternary activity. Field reconnaissance and review of historical aerial photographs that pre-date urbanization revealed no geomorphic evidence of landslides in the vicinity of the identified thrust faults, and subsurface investigation did not identify evidence of a landslide graben on the upper slope. Slope inclinations in this area are mostly low to moderate (6° to 12°) with few steeper inclinations (up to 20°). Thus, these compressional structures appear to be unrelated to landsliding. Our working hypothesis for the origin of the thrust faults northwest of MB involves compression related to a small left step along the central trace. This left step corresponds closely to the location of the observed thrust faults. The resulting compression is manifest as a series of thrust faults that do not appear to continue north or south of the step over region.

  17. Mercury's global fabric of thrust faults

    NASA Astrophysics Data System (ADS)

    Klimczak, C.; Byrne, P. K.; Solomon, S. C.

    2014-12-01

    Mercury's global tectonic history is thought to have been shaped by two major processes: tidal despinning and global contraction. Each process is expected to have produced a distinctive global stress field and resultant fault pattern. Data from three years of orbital operations by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft reveal thousands of thrust faults that are attributed to global contraction, but no global signature of tidal despinning has been conclusively documented. Global contraction operated throughout an extended portion of Mercury's geologic history, whereas tidal despinning likely operated for a shorter duration. Therefore, any tidal despinning pattern, if not entirely obliterated by the late heavy bombardment, either would have formed together with global contraction, or would have been modified by global contraction after despinning was complete. Here, we reassess global fracture patterns predicted to result from tidal despinning alone, and from a combination of tidal despinning and global contraction. We specifically make use of rock strength and deformability parameters appropriate for Mercury's fractured lithosphere. Our results indicate that a tidal despinning pattern would consist only of a global set of opening-mode fractures (joints) in the upper part of the lithosphere, whereas the combination of tidal despinning and global contraction would have produced a global population of thrust faults, with no preferred orientations in the polar regions but with an increasing preference for north-south orientations toward the equator. If an equatorial bulge from an early state of rapid spin were supported by Mercury's lithosphere, two end-member scenarios for the timing and duration of these two processes can be considered. In one, tidal despinning predated global contraction; in the other, tidal despinning and global contraction temporally overlapped. We test the predictions for both scenarios against the

  18. InSAR Evidence for an active shallow thrust fault beneath the city of Spokane Washington, USA

    USGS Publications Warehouse

    Wicks, Charles W.; Weaver, Craig S.; Bodin, Paul; Sherrod, Brian

    2013-01-01

    In 2001, a nearly five month long sequence of shallow, mostly small magnitude earthquakes occurred beneath the city of Spokane, a city with a population of about 200,000, in the state of Washington. During most of the sequence, the earthquakes were not well located because seismic instrumentation was sparse. Despite poor-quality locations, the earthquake hypocenters were likely very shallow, because residents near the city center both heard and felt many of the earthquakes. The combination of poor earthquake locations and a lack of known surface faults with recent movement make assessing the seismic hazards related to the earthquake swarm difficult. However, the potential for destruction from a shallow moderate-sized earthquake is high, for example Christchurch New Zealand in 2011, so assessing the hazard potential of a seismic structure involved in the Spokane earthquake sequence is important. Using interferometric synthetic aperture radar (InSAR) data from the European Space Agency ERS2 and ENVISAT satellites and the Canadian Space Agency RADARSAT-1, satellite we are able to show that slip on a shallow previously unknown thrust fault, which we name the Spokane Fault, is the source of the earthquake sequence. The part of the Spokane Fault that slipped during the 2001 earthquake sequence underlies the north part of the city, and slip on the fault was concentrated between ~0.3 and 2 km depth. Projecting the buried fault plane to the surface gives a possible surface trace for the Spokane Fault that strikes northeast from the city center into north Spokane.

  19. Was Himalayan normal faulting triggered by initiation of the Ramgarh-Munsiari Thrust?

    USGS Publications Warehouse

    Robinson, Delores M.; Pearson, Ofori N.

    2013-01-01

    The Ramgarh–Munsiari thrust is a major orogen-scale fault that extends for more than 1,500 km along strike in the Himalayan fold-thrust belt. The fault can be traced along the Himalayan arc from Himachal Pradesh, India, in the west to eastern Bhutan. The fault is located within the Lesser Himalayan tectonostratigraphic zone, and it translated Paleoproterozoic Lesser Himalayan rocks more than 100 km toward the foreland. The Ramgarh–Munsiari thrust is always located in the proximal footwall of the Main Central thrust. Northern exposures (toward the hinterland) of the thrust sheet occur in the footwall of the Main Central thrust at the base of the high Himalaya, and southern exposures (toward the foreland) occur between the Main Boundary thrust and Greater Himalayan klippen. Although the metamorphic grade of rocks within the Ramgarh–Munsiari thrust sheet is not significantly different from that of Greater Himalayan rock in the hanging wall of the overlying Main Central thrust sheet, the tectonostratigraphic origin of the two different thrust sheets is markedly different. The Ramgarh–Munsiari thrust became active in early Miocene time and acted as the roof thrust for a duplex system within Lesser Himalayan rocks. The process of slip transfer from the Main Central thrust to the Ramgarh–Munsiari thrust in early Miocene time and subsequent development of the Lesser Himalayan duplex may have played a role in triggering normal faulting along the South Tibetan Detachment system.

  20. Active upper plate thrust faulting in regions of low plate interface coupling, repeated slow slip events, and coastal uplift: Example from the Hikurangi Margin, New Zealand

    NASA Astrophysics Data System (ADS)

    Mountjoy, Joshu J.; Barnes, Philip M.

    2011-01-01

    Contractional fore-arc faulting and deformation is a characteristic feature of many subduction systems. Definition of the three-dimensional geometry and displacement rates of active, upper plate, out-of-sequence thrust faults along ˜250 km of the upper Hikurangi Margin enables us to examine the relationship between fore-arc deformation and the subduction interface in light of interseismic coupling estimates and distribution of slow slip events, both modeled from GPS measurements. These mid-fore-arc structures include the seaward vergent, outer shelf Lachlan and Ariel faults, with vertical separation rates up to 5 mm/yr, and several other major inner shelf faults with rates that are up to 3.8 mm/yr and comparable with Holocene coastal uplift rates. Seismic reflection imaging and geometric projection of these faults at depth indicate that they splay from the region of the plate interface where geodetic inversions for interseismic coupling and slow slip events suggest that the plate boundary undergoes aseismic slip. This observation may indicate either (1) that frictional properties and interseismic coupling on the plate interface are independent and unrelated to the active splay fault deformation in the inner-middle fore arc or (2) that the active splay faulting reflects long-term mechanical coupling related to higher shear stress, or the relative yield strength of the plate interface to the overriding plate, and that the current pattern of interseismic coupling may not be persistent over geological time scales of 20 ka. We compare structure and processes on the northern Hikurangi and Costa Rican margins and find similarities and significant differences astride these subduction systems.

  1. Boundary Element Modeling of Fault Cored Anticlines and Associated Blind Thrust Faults in Central California

    NASA Astrophysics Data System (ADS)

    Williams, M. K.; Johnson, K. M.

    2015-12-01

    Recent literature investigating active folding indicates that crustal-scale anticlines grow primarily through slip on underlying faults. Such studies use the geometry and uplift rates of active fault-related folds to infer fault slip rate based upon an assumed kinematic relationship between fault slip and particle motion in the surrounding crust. Our method uses a boundary element model of flexural slip folding called BEAFS (Boundary Element Analysis of Flexural Slip), allowing us to focus on the mechanics of deformation.In many cases, the shallow geometry (<5km) of natural folds are well constrained by subsurface data. However, the geometry of the causative blind thrust faults are often not well imaged. By comparing our numerical simulations with published subsurface and surface data on naturally occurring active folds, we can determine fault geometry and the extent to which various mechanisms are controlling fold evolution. For this work, we present our model results for the underlying faults at Kettleman Hills South Dome, Kettleman Hills North Dome, and Coalinga Anticline in the San Joaquin Valley of Central California. The rupturing of blind thrust faults associated with actively growing anticlines such as these pose a significant global seismic hazard. Our study area is of particular interest as it is the site of two such recent earthquakes—a Mw=6.5 earthquake in 1983 at Coalinga and a Mw=6.1 in 1985 at Kettleman Hills North Dome. Thus, we can compare the published earthquake data from these events to the parameters predicted by our model results from BEAFS.

  2. Evaluation of thrusting and folding of the Deadman Creek Thrust Fault, Sangre de Cristo range, Saguache County, Colorado

    NASA Astrophysics Data System (ADS)

    Weigel, Jacob F., II

    The Deadman Creek Thrust Fault was mapped in a structural window on the west side of the Sangre de Cristo Range. The study area, located in southern Colorado, is a two square mile area halfway between the town of Crestone and the Great Sand Dunes National Park. The Deadman Creek Thrust Fault is the center of this study because it delineates the fold structure in the structural window. The fault is a northeast-directed low-angle thrust folded by subsequent additional compression. This study was directed at understanding the motion of the Deadman Creek Thrust Fault as affected by subsequent folding, and the driving mechanism behind the folding of the Pole Creek Anticline as part of a broader study of Laramide thrust faulting in the range. This study aids in the interpretation of the geologic structure of the San Luis Valley, which is being studied by staff of the United States Geological Survey (USGS), to understand Rio Grande Rift basin evolution by focusing on rift and pre-rift tectonic activity. It also provides a geologic interpretation for the Saguache County Forest Service, Great Sand Dunes National Park, and its visitors. The Sangre de Cristo Mountain Range has undergone tectonic events in the Proterozoic, Pennsylvanian (Ancestral Rocky Mountains), Cretaceous-Tertiary (Laramide Orogeny) and mid-Tertiary (Rio Grande Rift). During the Laramide Orogeny the Deadman Creek Thrust Fault emplaced Proterozoic gneiss over Paleozoic sedimentary rocks and Proterozoic granodiorite in the area. Continued deformation resulted in folding of the fault to form the Pole Creek Anticline. The direction of motion of both the fault and fold is northeastward. A self-consistent net of cross-sections and stereonet plots generated from existing and new field data show that the anticline is an overturned isoclinal fold in Pole Creek Canyon, which shows an increasing inter-limb angle and a more vertical axial surface northwestward toward Deadman Creek Canyon. Southwest-directed apparent

  3. Faulting, fracturing, and sealing in foreland thrust belts: Examples from the subalpine chains

    SciTech Connect

    Bowler, S.; Butler, R.W.H.

    1988-08-01

    The hydrocarbon potential of foreland thrust belts arises from source and reservoir rocks juxtaposed by the movement of thrust sheets, promoting maturation by loading and generating structural traps. Deformation in thrust belts can be localized on fault zones or distributed throughout thrust sheets; different deformation mechanisms operate to increase and decrease permeability. Migration and reservoir properties may be enhanced or reduced by faulting and fault-related deformation. These processes are examined in detail using examples from the northwest subalpine chains of France, a fold-and-thrust belt of well-differentiated Mesozoic shales and carbonates. Seeps of bitumen in foreland basin sediments indicate some migration of hydrocarbons along faults linking probable source and reservoir areas. Detailed examination of fault rocks and thrust sheets shows that fracture formation is an important strain mechanism which has the potential to form regions of enhanced permeability in structures such as hanging wall anticlines. However, the fractures observed are in general recemented, forming with crack-seal crystal growth. The faults themselves are complex zones up to tens of meters thick of subparallel anastomosing gouge, fractures, stylolites, and crystalline calcite, indicating synchronous cataclasis and pressure solution. The range of scales of fracturing suggests stick-slip (microseismic) fault activity. Permeability of the fault zones is enhanced during seismic fault slip and is otherwise steadily decreased by pressure solution and calcite deposition. The available migration pathways, and hence the location of potential reservoirs, is controlled by the timing, mechanisms, and extent of fault activity in this common and productive tectonic regime.

  4. Shallow seismic imaging of folds above the Puente Hills blind-thrust fault, Los Angeles, California

    USGS Publications Warehouse

    Pratt, T.L.; Shaw, J.H.; Dolan, J.F.; Christofferson, S.A.; Williams, R.A.; Odum, J.K.; Plesch, A.

    2002-01-01

    High-resolution seismic reflection profiles image discrete folds in the shallow subsurface (<600 m) above two segments of the Puente Hills blind-thrust fault system, Los Angeles basin, California. The profiles demonstrate late Quaternary activity at the fault tip, precisely locate the axial surfaces of folds within the upper 100 m, and constrain the geometry and kinematics of recent folding. The Santa Fe Springs segment of the Puente Hills fault zone shows an upward-narrowing kink band with an active anticlinal axial surface, consistent with fault-bend folding above an active thrust ramp. The Coyote Hills segment shows an active synclinal axial surface that coincides with the base of a 9-m-high scarp, consistent with tip-line folding or the presence of a backthrust. The seismic profiles pinpoint targets for future geologic work to constrain slip rates and ages of past events on this important fault system.

  5. Mechanical Initiation and Propagation Mechanism of a Thrust Fault: A Case Study of the Yima Section of the Xiashi-Yima Thrust (North Side of the Eastern Qinling Orogen, China)

    NASA Astrophysics Data System (ADS)

    Cai, Wu; Dou, Linming; Li, Zhenlei; He, Jiang; He, Hu; Ding, Yanlu

    2015-09-01

    Thrust faults exist extensively in nature, and their activities often cause earthquakes and disasters involving underground engineering, such as the May 12, 2008 Wenchuan Earthquake; the April 20, 2013 Ya'an Earthquake; and the Nov. 3, 2011 Yima Qianqiu Coal-Mining Accident in China. In this paper, the initiation and propagation of a thrust are discussed from a mechanical viewpoint using fault mechanics and fault-slip analysis, taking as an example the Yima section of the Xiashi-Yima thrust (north side of the eastern Qinling Orogen, China). The research primarily focuses on the stress field and the formation trajectory of the thrust and the genesis of the large-scale inversion thrust sheet. The results show that the thrust results from failures in the compressive deformation state and that its stress state is entirely compressive shear. The rupture trajectory of the thrust develops upward, and the fault fracture zone forms similarly to a listric fault, up-narrow and down-wide. The model results and the genesis of the large-scale inversion thrust sheet are consistent with in situ exploration observations. This investigation can be extended to other thrust faults with similar characteristics, particularly for the design of mining operations in tectonic-active areas. Moreover, this research can be used to further study the mechanism of thrust faults and provide support for the feasibility of using fault-slip analysis to assess fault stability.

  6. Geometry of Thrust Faults Beneath Amenthes Rupes, Mars

    NASA Technical Reports Server (NTRS)

    Vidal, A.; Mueller, K. M.; Golombek, M. P.

    2005-01-01

    Amenthes Rupes is a 380 km-long lobate fault scarp located in the eastern hemisphere of Mars near the dichotomy boundary. The scarp is marked by about 1 km of vertical separation across a northeast dipping thrust fault (top to the SW) and offsets heavily-cratered terrain of Late Noachian age, the visible portion of which was in place by 3.92 Ga and the buried portion in place between 4.08 and 4.27 Ga. The timing of scarp formation is difficult to closely constrain. Previous geologic mapping shows that near the northern end of Amenthes Rupes, Hesperian age basalts terminate at the scarp, suggesting that fault slip predated the emplacement of these flows at 3.69 to 3.9 Ga. Maxwell and McGill also suggest the faulting ceased before the final emplacement of the Late Hesperian lavas on Isidis Planitia. The trend of the faults at Amenthes, like many thrust faults at the dichotomy boundary, parallels the boundary itself. Schultz and Watters used a dislocation modeling program to match surface topography and vertical offset of the scarp at Amenthes Rupes, varying the dip and depth of faulting, assuming a slip of 1.5 km on the fault. They modeled faulting below Amenthes Rupes as having a dip of between 25 and 30 degrees and a depth of 25 to 35 km, based on the best match to topography. Assuming a 25 degree dip and surface measurements of vertical offset of between 0.3 and 1.2 km, Watters later estimated the maximum displacement on the Amenthes Rupes fault to be 2.90 km. However, these studies did not determine the geometry of the thrust using quantitative constraints that included shortening estimates. Amenthes Rupes deforms large preexisting impact craters. We use these craters to constrain shortening across the scarp and combine this with vertical separation to infer fault geometry. Fault dip was also estimated using measurements of scarp morphology. Measurements were based on 460 m (1/128 per pixel) digital elevation data from the Mars Orbiter Laser Altimeter (MOLA), an

  7. Blueschist-facies metamorphism related to regional thrust faulting

    USGS Publications Warehouse

    Blake, M.C.; Irwin, W.P.; Coleman, R.G.

    1969-01-01

    Rocks of the blueschist (glaucophane schist) facies occur throughout the world in narrow tectonic belts associated with ultramafic rocks. In the Coast Range province of California, blueschist rocks are devloped in the eugeosynclinal Franciscan Formation of Late Mesozoic age. The blueschist rocks form a narrow belt for more than 800 km along the eastern margin of this province and commonly are separated from rocks of an overlying thrust plate by serpentinite. Increasing metamorphism upward toward the thrust fault is indicated mineralogically by a transition from pumpellyite to lawsonite and texturally by a transition from metagraywacke to schist. The blueschist metamorphism probably occurred during thrusting in a zone of anomalously high water pressure in the lower plate along the sole of the thrust fault. This tectonic mode of origin for blueschist differs from the generally accepted hypothesis involving extreme depth of burial. Other belts of blueschist-facies rocks, including the Sanbagawa belt of Japan, the marginal synclinal belt of New Zealand, and the blueschist-ultramafic belts of Venezuela, Kamchatka, Ural mountains, and New Caledonia have similar geologic relations and might be explained in the same manner. ?? 1969.

  8. The susitna glacier thrust fault: Characteristics of surface ruptures on the fault that initiated the 2002 denali fault earthquake

    USGS Publications Warehouse

    Crone, A.J.; Personius, S.F.; Craw, P.A.; Haeussler, P.J.; Staft, L.A.

    2004-01-01

    The 3 November 2002 Mw 7.9 Denali fault earthquake sequence initiated on the newly discovered Susitna Glacier thrust fault and caused 48 km of surface rupture. Rupture of the Susitna Glacier fault generated scarps on ice of the Susitna and West Fork glaciers and on tundra and surficial deposits along the southern front of the central Alaska Range. Based on detailed mapping, 27 topographic profiles, and field observations, we document the characteristics and slip distribution of the 2002 ruptures and describe evidence of pre-2002 ruptures on the fault. The 2002 surface faulting produced structures that range from simple folds on a single trace to complex thrust-fault ruptures and pressure ridges on multiple, sinuous strands. The deformation zone is locally more than 1 km wide. We measured a maximum vertical displacement of 5.4 m on the south-directed main thrust. North-directed backthrusts have more than 4 m of surface offset. We measured a well-constrained near-surface fault dip of about 19?? at one site, which is considerably less than seismologically determined values of 35??-48??. Surface-rupture data yield an estimated magnitude of Mw 7.3 for the fault, which is similar to the seismological value of Mw 7.2. Comparison of field and seismological data suggest that the Susitna Glacier fault is part of a large positive flower structure associated with northwest-directed transpressive deformation on the Denali fault. Prehistoric scarps are evidence of previous rupture of the Sustina Glacier fault, but additional work is needed to determine if past failures of the Susitna Glacier fault have consistently induced rupture of the Denali fault.

  9. The role of thrust faulting in the formation of the eastern Alaska Range: Thermochronological constraints from the Susitna Glacier Thrust Fault region of the intracontinental strike-slip Denali Fault system

    NASA Astrophysics Data System (ADS)

    Riccio, Steven J.; Fitzgerald, Paul G.; Benowitz, Jeff A.; Roeske, Sarah M.

    2014-11-01

    Horizontal-slip along restraining bends of strike-slip faults is often partitioned into a vertical component via splay faults. The active Susitna Glacier Thrust Fault (SGTF), as shown by its initiation of the 2002 M7.9 Denali Fault earthquake, lies south of, and intersects the dextral strike-slip Denali Fault. Geochronology and thermochronology data from samples across the SGTF constrain the region's tectonic history and the role of thrusting in the formation of the eastern Alaska Range south of the Denali fault. U-Pb zircon ages indicate intrusion of plutons in the footwall (~57 Ma) and hanging wall (~98 Ma). These U-Pb zircon ages correlate to those from the Ruby Batholith/Kluane Terrane ~400 km east along the Denali Fault, supporting geologic correlations and hence constraints on long-term slip rates. 40Ar/39Ar mica and K-feldspar data from footwall and hanging wall samples (~54 to ~46 Ma) reflect cooling following magmatism and/or regional Eocene metamorphism related to ridge subduction. Combined with apatite fission track data (ages 43-28 Ma) and thermal models, both sides of the SGTF acted as a coherent block during the Eocene and early Oligocene. Contrasting apatite (U-Th)/He ages across the Susitna Glacier (~25 Ma footwall, ~15 Ma hanging wall) suggest initiation of faulting during the middle Miocene. Episodic cooling and exhumation is related to thrusting on known or hypothesized faults that progressively activate due to varying partition of strain along the Denali Fault associated with changing kinematics and plate interaction (Yakutat microplate collision, flat-slab subduction and relative plate motion change) at the southern Alaskan plate margin.

  10. The Pietra Grande thrust (Brenta Dolomites, Italy): looking for co-seismic indicators along a main fault in carbonate sequences

    NASA Astrophysics Data System (ADS)

    Viganò, Alfio; Tumiati, Simone; Martin, Silvana; Rigo, Manuel

    2013-04-01

    /or breccias of the fault zone. Host and fault rocks are locally folded, with fold axes having a rough E-W direction compatible with simultaneous thrust activation, suggesting deformation under brittle-ductile conditions. A late brittle deformation is testified by near-vertical fractures and strike-slip faults (WNW-directed) intersecting the whole thrust system. Field structure, microtextures, chemical and mineralogical compositions of host rocks, cataclasites and breccias are analysed. In particular, red veins are carefully compared with the very similar Grigne carbonate pseudotachylytes (Viganò et al. 2011, Terra Nova, vol. 23, pp.187-194), in order to evaluate if they could represent a certain geological record of seismic faulting of the Pietra Grande thrust.

  11. Determining the causes of fault slip rate variability for Northern Apennine thrusts on intermediate timescales

    NASA Astrophysics Data System (ADS)

    Gunderson, K. L.; Anastasio, D. J.; Pazzaglia, F. J.

    2012-12-01

    Documenting fault slip rate variability on intermediate (10^4-10^5 yr) timescales is crucial for understanding the process-linkages of short-term (10^1-10^3 yr) and long-term (10^6 yr) patterns of deformation; however, the lack of long records of fault slip with 10^4-10^5 yr resolution presents a major barrier to understanding the underlying process responsible for slip rate variability at those timescales. Taking advantage of spectacular, continuous exposure of growth strata, we document 10^4-10^5 yr resolution records of unsteady fault slip for the past 3.0 myr for three unconnected, shallow blind thrust anticlines growing along the Northern Apennine mountain front, Italy. Fault slip rates for these thrusts were determined from progressive restorations of marine and continental growth strata deposited on the anticlinal limbs. These restorations were supported by subsurface corre-lations of the measured growth sections in order to constrain the fold geometries and kin-ematics. Magnetostratigraphy, cyclostratigraphy, cosmogenic radionuclide (CRN) burial dating, and optically stimulated luminescence (OSL) burial dating provided the high-resolution age models for the growth sections. Slip histories determined from our pro-gressive restorations indicate that all three of the thrust faults exhibited high-frequency slip rate variability. This variability is typically manifest by longer periods of decelerated fault slip punctuated by shorter periods of accelerated fault slip, typically lasting between 80-200 kyr. During times when slip rates were slow, growth strata geometries show ac-celerated slip was accommodated by more foreland structures, suggesting slip partitioning at 10^4-10^5 yr timescales. This high frequency variability is superimposed on a low frequency slip rate variability manifest by an overall deceleration in slip on the shallow thrusts since 3.0 myr. Major decelerations in slip rates were coincident with the activation of thick-skinned thrusting in the

  12. Characteristics of thrust fault imbrication near the frontal edge of the Blue Ridge thrust sheet, Buffalo Mountain, Tennessee

    SciTech Connect

    Duddy, M.M.; Woodward, N.B.

    1985-01-01

    The Buffalo Mountain thrust sheet, located along the western margin of the Blue Ridge in northeastern Tennessee, provides an excellent opportunity to examine transitional structural styles and deformation mechanisms between the Valley and Ridge and Blue Ridge. Previous interpretation suggests that, because of pre-fault tilting, thrust faults within the Buffalo Mountain complex cut down stratigraphic section. Geometric data from the present study indicate, however, that the thrust faults cut up section with stratigraphic separations of up to 16,500'. Footwall and hanging wall bedding orientations reveal a stair-step thrust geometry; the Unicoi Fm. (basal Chilhowee Gp. quartzite) is a hanging wall flat, and the Knox Gp. (Cambro-Ordovician carbonate) is a footwall ramp. Ductile and brittle deformation mechanisms are represented by mesofabric elements. Important deformation mechanisms and elements include: flexural slip and flexural flow folding styles, pressure solution cleavage, extensional and contractional fractures, quartz filled tensional fractures and cataclastic fault zones. Although previous workers have determined that thrusting within the Blue Ridge occurs in an out-of-sequence pattern, the Buffalo Mountain thrust complex provides an example of in-sequence thrusting. Thus, based on this example, deformation styles and mechanisms within the Blue Ridge appear to be similar to Valley and Ridge deformation styles and mechanisms.

  13. Coseismic fault-related fold model, growth structure, and the historic multisegment blind thrust earthquake on the basement-involved Yoro thrust, central Japan

    NASA Astrophysics Data System (ADS)

    Ishiyama, Tatsuya; Mueller, Karl; Sato, Hiroshi; Togo, Masami

    2007-03-01

    We use high-resolution seismic reflection profiles, boring transects, and mapping of fold scarps that deform late Quaternary and Holocene sediments to define the kinematic evolution, subsurface geometry, coseismic behavior, and fault slip rates for an active, basement-involved blind thrust system in central Japan. Coseismic fold scarps on the Yoro basement-involved fold are defined by narrow fold limbs and angular hinges on seismic profiles, suggesting that at least 3.9 km of fault slip is consumed by wedge thrust folding in the upper 10 km of the crust. The close coincidence and kinematic link between folded horizons and the underlying thrust geometry indicate that the Yoro basement-involved fold has accommodated slip at an average rate of 3.2 ± 0.1 mm/yr on a shallowly west dipping thrust fault since early Pleistocene time. Past large-magnitude earthquakes, including an historic M˜7.7 event in A.D. 1586 that occurred on the Yoro blind thrust, are shown to have produced discrete folding by curved hinge kink band migration above the eastward propagating tip of the wedge thrust. Coseismic fold scarps formed during the A.D. 1586 earthquake can be traced along the en echelon active folds that extend for at least 60 km, in spite of different styles of folding along the apparently hard-linked Nobi-Ise blind thrust system. We thus emphasize the importance of this multisegment earthquake rupture across these structures and the potential risk for similar future events in en echelon active fold and thrust belts.

  14. Signature of coseismic decarbonation in dolomitic fault rocks of the Naukluft Thrust, Namibia

    NASA Astrophysics Data System (ADS)

    Rowe, Christie D.; Fagereng, Åke; Miller, Jodie A.; Mapani, Ben

    2012-06-01

    Unequivocal geological signatures of seismic slip are rare, exceptionally so in carbonate-hosted faults where carbonate minerals dissociate at temperatures lower than those required for producing a friction melt. This thermal dissociation leads to significant fault weakening by increased fluid pressure and/or nanoparticle lubrication, preventing further heating of the fault surface. Pseudotachylyte is therefore unlikely to form in carbonate-hosted faults, and other evidence for seismic slip must be identified. We studied the lower Cambrian Naukluft Thrust which crops out in central Namibia. It contains a cataclastic dolomite fault rock, referred to as “gritty dolomite”, which we interpret as a signature of coseismic carbonate dissociation and subsequent fluid-rock interactions. The fault was active at ambient temperatures below 200°C. “Gritty dolomite” contains: rounded, low aspect ratio dolomite clasts with a uniform Fe-rich dolomite coating, euhedral to subhedral magnetite, quartz, and K-feldspar in a fine-grained, massive to laminated carbonate matrix of particulate dolomite and crystalline calcite cement. The fault rock texture, combined with evidence of injectites of gritty dolomite into the wallrock, indicates the cataclasite deformed as a fluidized granular flow. At seismic slip velocities, frictional heating caused dissociation of dolomite to CO2 and Ca-, Fe- and Mg-oxides. This release of CO2 decreased the pH of the pore fluid in the fault, causing dissolution and rounding of dolomite clasts within an inertial grain flow, and precipitation of carbonate coatings and euhedral silicates and oxides during subsequent cooling and CO2 escape. Examples of similar rocks having some, if not all of these characteristics have been described from other carbonate-hosted faults. The geological setting of the Naukluft Thrust is unique in spatial extent and quality of exposure, allowing us to eliminate alternative hypotheses for sources of CO2 to drive

  15. Termination of major strike-slip faults against thrust faults in a syntaxis, as interpreted from landsat images

    SciTech Connect

    Iranpanah, A.

    1988-01-01

    The north to northeast-striking Minab fault (Zendan fault) in western Makran, Iran, is interpreted as an intracontinental transform structure that separates, along its length, the Zagros foldbelt from the Makran active trench-arc system. The 200-km long fault has a right-lateral strike-slip component and is terminated at its northern end by the north-northwest and northwest-striking Zagros main thrust. The Minab transform zone delimits the western margin of the Makran convergence zone where an oceanic part of the Afro-Arabian lithosphere is being subducted beneath the Lut and Afghan microplates. A northern extension of the Minab transform zone terminates at an internal convergence boundary within the Bandar Abbas-Minab syntaxis. The Minab transform fault consists of a zone of generally north-northwest-trending thombic conjugate strike-slip faults. The pattern of faulting for the Minab strike-slip fault zone, when traced over the entire area on the Landsat image, shows that areas with rhombic sets of conjugate strike-slip faults are separated by a few areas showing only extensional zones. This is compatible with the traditionally idealized reverse-S pattern for the strike-slip faults reported from the United States Basin and Range province. The mechanical explanation for the rhombic pattern of the fault system is consistent with the same pattern and motion as currently exists in the Makran accretionary belt. The origin of the Bandar Abbas-Minab syntaxis is believed to be related to convergence between the Afro-Arabian plate and the Lut and Afghan microplates. The convergence zone is a well-developed trench-arc gap. The western edge of this trench-arc system has been dragged to the north along the Minab dextral fault zone. This zone, which started developing in the Late Cretaceous-Paleocene, is directly responsible for the development of the Bandar Abbas-Minab syntaxis.

  16. Seismic variability of subduction thrust faults: Insights from laboratory models

    NASA Astrophysics Data System (ADS)

    Corbi, F.; Funiciello, F.; Faccenna, C.; Ranalli, G.; Heuret, A.

    2011-06-01

    Laboratory models are realized to investigate the role of interface roughness, driving rate, and pressure on friction dynamics. The setup consists of a gelatin block driven at constant velocity over sand paper. The interface roughness is quantified in terms of amplitude and wavelength of protrusions, jointly expressed by a reference roughness parameter obtained by their product. Frictional behavior shows a systematic dependence on system parameters. Both stick slip and stable sliding occur, depending on driving rate and interface roughness. Stress drop and frequency of slip episodes vary directly and inversely, respectively, with the reference roughness parameter, reflecting the fundamental role for the amplitude of protrusions. An increase in pressure tends to favor stick slip. Static friction is a steeply decreasing function of the reference roughness parameter. The velocity strengthening/weakening parameter in the state- and rate-dependent dynamic friction law becomes negative for specific values of the reference roughness parameter which are intermediate with respect to the explored range. Despite the simplifications of the adopted setup, which does not address the problem of off-fault fracturing, a comparison of the experimental results with the depth distribution of seismic energy release along subduction thrust faults leads to the hypothesis that their behavior is primarily controlled by the depth- and time-dependent distribution of protrusions. A rough subduction fault at shallow depths, unable to produce significant seismicity because of low lithostatic pressure, evolves into a moderately rough, velocity-weakening fault at intermediate depths. The magnitude of events in this range is calibrated by the interplay between surface roughness and subduction rate. At larger depths, the roughness further decreases and stable sliding becomes gradually more predominant. Thus, although interplate seismicity is ultimately controlled by tectonic parameters (velocity of

  17. Seismic constraints and coulomb stress changes of a blind thrust fault system, 2: Northridge, California

    USGS Publications Warehouse

    Stein, Ross S.; Lin, Jian

    2006-01-01

    We review seismicity, surface faulting, and Coulomb stress changes associated with the 1994 Northridge, California, earthquake. All of the observed surface faulting is shallow, extending meters to tens of meters below the surface. Relocated aftershocks reveal no seismicity shallower than 2 km depth. Although many of the aftershocks lie along the thrust fault and its up-dip extension, there are also a significant number of aftershocks in the core of the gentle anticline above the thrust, and elsewhere on the up-thrown block. These aftershocks may be associated with secondary ramp thrusts or flexural slip faults at a depth of 2-4 km. The geological structures typically associated with a blind thrust fault, such as anticlinal uplift and an associated syncline, are obscured and complicated by surface thrust faults associated with the San Fernando fault that overly the Northridge structures. Thus the relationship of the geological structure and topography to the underlying thrust fault is much more complex for Northridge than it is for the 1983 Coalinga, California, earthquake. We show from a Coulomb stress analysis that secondary surface faulting, diffuse aftershocks, and triggered sequences of moderate-sized mainshocks, are expected features of moderate-sized blind thrust earthquakes.

  18. Central Asia Active Fault Database

    NASA Astrophysics Data System (ADS)

    Mohadjer, Solmaz; Ehlers, Todd A.; Kakar, Najibullah

    2014-05-01

    The ongoing collision of the Indian subcontinent with Asia controls active tectonics and seismicity in Central Asia. This motion is accommodated by faults that have historically caused devastating earthquakes and continue to pose serious threats to the population at risk. Despite international and regional efforts to assess seismic hazards in Central Asia, little attention has been given to development of a comprehensive database for active faults in the region. To address this issue and to better understand the distribution and level of seismic hazard in Central Asia, we are developing a publically available database for active faults of Central Asia (including but not limited to Afghanistan, Tajikistan, Kyrgyzstan, northern Pakistan and western China) using ArcGIS. The database is designed to allow users to store, map and query important fault parameters such as fault location, displacement history, rate of movement, and other data relevant to seismic hazard studies including fault trench locations, geochronology constraints, and seismic studies. Data sources integrated into the database include previously published maps and scientific investigations as well as strain rate measurements and historic and recent seismicity. In addition, high resolution Quickbird, Spot, and Aster imagery are used for selected features to locate and measure offset of landforms associated with Quaternary faulting. These features are individually digitized and linked to attribute tables that provide a description for each feature. Preliminary observations include inconsistent and sometimes inaccurate information for faults documented in different studies. For example, the Darvaz-Karakul fault which roughly defines the western margin of the Pamir, has been mapped with differences in location of up to 12 kilometers. The sense of motion for this fault ranges from unknown to thrust and strike-slip in three different studies despite documented left-lateral displacements of Holocene and late

  19. Structural analysis using thrust-fault hanging-wall sequence diagrams: Ogden duplex, Wasatch Range, Utah

    SciTech Connect

    Schirmer, T.W.

    1988-05-01

    Detailed mapping and cross-section traverses provide the control for structural analysis and geometric modeling of the Ogden duplex, a complex thrust system exposed in the Wasatch Mountains, east of Ogden, Utah. The structures consist of east-dipping folded thrust faults, basement-cored horses, lateral ramps and folds, and tear faults. The sequence of thrusting determined by means of lateral overlap of horses, thrust-splay relationships, and a top-to-bottom piggyback development is Willard thrust, Ogden thrust, Weber thrust, and Taylor thrust. Major decollement zones occur in the Cambrian shales and limestones. The Tintic Quartzite is the marker for determining gross geometries of horses. This exposed duplex serves as a good model to illustrate the method of constructing a hanging-wall sequence diagram - a series of longitudinal cross sections that move forward in time and space, and show how a thrust system formed as it moved updip over various footwall ramps. A hanging wall sequence diagram also shows the complex lateral variations in a thrust system and helps to locate lateral ramps, lateral folds, tear faults, and other features not shown on dip-oriented cross sections. 8 figures.

  20. Geomorphology, kinematic history, and earthquake behavior of the active Kuwana wedge thrust anticline, central Japan

    NASA Astrophysics Data System (ADS)

    Ishiyama, Tatsuya; Mueller, Karl; Togo, Masami; Okada, Atsumasa; Takemura, Keiji

    2004-12-01

    We combine surface mapping of fault and fold scarps that deform late Quaternary alluvial strata with interpretation of a high-resolution seismic reflection profile to develop a kinematic model and determine fault slip rates for an active blind wedge thrust system that underlies Kuwana anticline in central Japan. Surface fold scarps on Kuwana anticline are closely correlated with narrow fold limbs and angular hinges on the seismic profile that suggest at least ˜1.3 km of fault slip completely consumed by folding in the upper 4 km of the crust. The close coincidence and kinematic link between folded terraces and the underlying thrust geometry indicate that Kuwana anticline has accommodated slip at an average rate of 2.2 ± 0.5 mm/yr on a 27°, west dipping thrust fault since early-middle Pleistocene time. In contrast to classical fault bend folds the fault slip budget in the stacked wedge thrusts also indicates that (1) the fault tip propagated upward at a low rate relative to the accrual of fault slip and (2) fault slip is partly absorbed by numerous bedding plane flexural-slip faults above the tips of wedge thrusts. An historic earthquake that occurred on the Kuwana blind thrust system possibly in A.D. 1586 is shown to have produced coseismic surface deformation above the doubly vergent wedge tip. Structural analyses of Kuwana anticline coupled with tectonic geomorphology at 103-105 years timescales illustrate the significance of active folds as indicators of slip on underlying blind thrust faults and thus their otherwise inaccessible seismic hazards.

  1. Deciphering thrust fault nucleation and propagation and the importance of footwall synclines

    NASA Astrophysics Data System (ADS)

    Ferrill, David A.; Morris, Alan P.; Wigginton, Sarah S.; Smart, Kevin J.; McGinnis, Ronald N.; Lehrmann, Daniel

    2016-04-01

    In this paper, we analyze small scale examples of thrust faults and related folding in outcrops of the Cretaceous Boquillas Formation within Big Bend National Park in west Texas to develop detailed understanding of the fault nucleation and propagation that may aid in the interpretation of larger thrust system structure. Thrust faults in the outcrop have maximum displacements ranging from 0.5 cm to 9 cm within competent limestone beds, and these displacements diminish both upward into anticlines and downward into synclines within the interbedded and weaker mudrock layers. We interpret the faults as having nucleated within the competent units and partially propagated into the less competent units without developing floor or roof thrusts. Faults that continued to propagate resulted in hanging wall anticlines above upwardly propagating fault tips, and footwall synclines beneath downwardly propagating fault tips. The observed structural style may provide insights in the nucleation of faults at the formation scale and the structural development at the mountain-range scale. Décollement or detachment layers may be a consequence rather than cause of thrust ramps through competent units and could be over interpreted from seismic data.

  2. Fault-related fold styles and progressions in fold-thrust belts: Insights from sandbox modeling

    NASA Astrophysics Data System (ADS)

    Yan, Dan-Ping; Xu, Yan-Bo; Dong, Zhou-Bin; Qiu, Liang; Zhang, Sen; Wells, Michael

    2016-03-01

    Fault-related folds of variable structural styles and assemblages commonly coexist in orogenic belts with competent-incompetent interlayered sequences. Despite their commonality, the kinematic evolution of these structural styles and assemblages are often loosely constrained because multiple solutions exist in their structural progression during tectonic restoration. We use a sandbox modeling instrument with a particle image velocimetry monitor to test four designed sandbox models with multilayer competent-incompetent materials. Test results reveal that decollement folds initiate along selected incompetent layers with decreasing velocity difference and constant vorticity difference between the hanging wall and footwall of the initial fault tips. The decollement folds are progressively converted to fault-propagation folds and fault-bend folds through development of fault ramps breaking across competent layers and are followed by propagation into fault flats within an upper incompetent layer. Thick-skinned thrust is produced by initiating a decollement fault within the metamorphic basement. Progressive thrusting and uplifting of the thick-skinned thrust trigger initiation of the uppermost incompetent decollement with formation of a decollement fold and subsequent converting to fault-propagation and fault-bend folds, which combine together to form imbricate thrust. Breakouts at the base of the early formed fault ramps along the lowest incompetent layers, which may correspond to basement-cover contacts, domes the upmost decollement and imbricate thrusts to form passive roof duplexes and constitute the thin-skinned thrust belt. Structural styles and assemblages in each of tectonic stages are similar to that in the representative orogenic belts in the South China, Southern Appalachians, and Alpine orogenic belts.

  3. San Cayetano fault: near surface expression of a midcrustal thrust in the California Transverse Ranges

    SciTech Connect

    Cemen, I.; Yeats, R.S.

    1985-01-01

    The north-dipping San Cayetano reverse fault (SCF) extends 40 km from Horn Canyon in Ojai Valley eastward to Piru Creek in the Ventura basin. The eastern lobe (ESCF) is separated from the western lobe by a lateral ramp just east of Sespe Creek. North of Fillmore, the ESCF dips 45/sup 0/ to 50/sup 0/ and shows a stratigraphic separation of at least 7300 m. Between Fillmore and Piru, the fault follows the northern edge of the Santa Clara River Valley with generally low dips, loses separation progressively eastward, and dies out in the northern flank of Santa Clara syncline east of Piru. Microearthquakes with north-over-south reverse fault focal mechanisms determined by Yerkes and Lee (1979) suggest that the 50/sup 0/ dip is maintained to depths of 7 to 8 km. Because these earthquakes are near the base of crustal seismicity in the western Transverse Ranges, the authors suggest that the SCF may become horizontal at the brittle-ductile transition zone in the middle crust. The trends of the fold axes in the hanging-wall and footwall blocks of the ESCF are generally parallel to the strike of the fault. Thrust faults of the upper plate trend parallel to bedding and show sense of slip perpendicular to bedding, suggesting that they are flexural-slip faults responding to flexural-slip folding between stiff and less stiff members of the Miocene Modelo Formation. These structural features are attributable to horizontal shortening of the Transverse Ranges in late Cenozoic time. Warping in alluvium observed along the ESCF at the mouth of Hopper Canyon and Piru Creek suggests that the fault may be potentially active.

  4. Influence of ancient thrust faults on the hydrogeology of the Blue Ridge Province.

    PubMed

    Seaton, William J; Burbey, Thomas J

    2005-01-01

    The Blue Ridge Province contains ubiquitous northeast-southwest-trending thrust faults or smaller thrust "slivers" that greatly impact the nature and character of ground water flow in this region. Detailed investigations at a field site in Floyd County, Virginia, indicate that high-permeability zones occur in the brittle crystalline rocks above these thrust faults. Surface and borehole geophysics, aquifer tests, and chlorofluorocarbon and geochemical data reveal that the shallow saprolite aquifer is separated from the deeper fault-zone aquifer by a low-fracture permeability bedrock confining unit, the hydraulic conductivity of which has been estimated to be six orders of magnitude less than the conductivity of the fault zones at the test site. Within the Blue Ridge Province, these fault zones can occur at depths of 300 m or more, can contain a significant amount of storage, and yield significant quantities of water to wells. Furthermore, it is expected that these faults may compartmentalize the deep aquifer system. Recharge to and discharge from the deep aquifer occurs by slow leakage through the confining unit or through localized breach zones that occur where quartz accumulated in high concentrations during metamorphism and later became extensively fractured during episodes of deformation. The results of this investigation stress the importance of thrust faults in this region and suggest that hydrogeologic models for the Blue Ridge Province include these ancient structural features. Faults in crystalline-rock environments may not only influence the hydrology, they may dominate the flow characteristics of a region. PMID:15882322

  5. Thrust fault segmentation and downward fault propagation in accretionary wedges: New Insights from 3D seismic reflection data

    NASA Astrophysics Data System (ADS)

    Orme, Haydn; Bell, Rebecca; Jackson, Christopher

    2016-04-01

    The shallow parts of subduction megathrust faults are typically thought to be aseismic and incapable of propagating seismic rupture. The 2011 Tohoku-Oki earthquake, however, ruptured all the way to the trench, proving that in some locations rupture can propagate through the accretionary wedge. An improved understanding of the structural character and physical properties of accretionary wedges is therefore crucial to begin to assess why such anomalously shallow seismic rupture occurs. Despite its importance, we know surprisingly little regarding the 3D geometry and kinematics of thrust network development in accretionary prisms, largely due to a lack of 3D seismic reflection data providing high-resolution, 3D images of entire networks. Thus our current understanding is largely underpinned by observations from analogue and numerical modelling, with limited observational data from natural examples. In this contribution we use PSDM, 3D seismic reflection data from the Nankai margin (3D Muroto dataset, available from the UTIG Academic Seismic Portal, Marine Geoscience Data System) to examine how imbricate thrust fault networks evolve during accretionary wedge growth. We unravel the evolution of faults within the protothrust and imbricate thrust zones by interpreting multiple horizons across faults and measuring fault displacement and fold amplitude along-strike; by doing this, we are able to investigate the three dimensional accrual of strain. We document a number of local displacement minima along-strike of faults, suggesting that, the protothrust and imbricate thrusts developed from the linkage of smaller, previously isolated fault segments. Although we often assume imbricate faults are likely to have propagated upwards from the décollement we show strong evidence for fault nucleation at shallow depths and downward propagation to intersect the décollement. The complex fault interactions documented here have implications for hydraulic compartmentalisation and pore

  6. Anastomosing grabens, low-angle faults, and Tertiary thrust( ) faults, western Markagunt Plateau, southwestern Utah

    SciTech Connect

    Maldonado, F.; Sable, E.G. )

    1993-04-01

    A structurally complex terrane composed of grabens and horsts, low-angle faults, Tertiary thrust( ) faults, gravity-slide blocks, and debris deposits has been mapped along the western Markagunt Plateau, east of Parowan and Summit, southwestern Utah. This terrane, structurally situated within the transition between the Basin and Range and Colorado Plateau provinces, contains Tertiary volcanic and sedimentary and Cretaceous sedimentary rocks. The structures are mostly Miocene to Oligocene but some are Pleistocene. The oldest structure is the Red Hills low-angle shear zone, interpreted as a shallow structure that decoupled an upper plate composed of a Miocene-Oligocene volcanic ash-flow tuff and volcaniclastic succession from a lower plate of Tertiary sedimentary rocks. The period of deformation on the shear zone is bracketed from field relationships between 22.5 and 20 Ma. The graben-horst system trends northeast and formed after about 20 Ma (and probably much later) based on displacement of dated dikes and a laccolith. The central part of the system contains many grabens that merge toward its southerly end to become a single graben. Within these grabens, (1) older structures are preserved, (2) debris eroded from horst walls forms lobe-shaped deposits, (3) Pleistocene basaltic cinder cones have localized along graben-bounding faults, and (4) rock units are locally folded suggesting some component of lateral translation along graben-bounding faults. Megabreccia deposits and landslide debris are common. Megabreccia deposits are interpreted as gravity-slide blocks of Miocene-Oligocene( ) age resulting from formation of the Red Hills shear zone, although some may be related to volcanism, and still others to later deformation. The debris deposits are landslides of Pleistocene-Pliocene( ) age possibly caused by continued uplift of the Markagunt Plateau.

  7. Neogene compressional deformation and possible thrust faulting in southwest Dominican Republic

    NASA Technical Reports Server (NTRS)

    Golombek, M. P.; Goreau, P.; Dixon, T. H.

    1985-01-01

    Analysis of regional and high resolution remote sensing data coupled with detailed field investigations indicates Neogene compressional deformation in the southwest Dominican Republic. Airborne synthetic aperture radar data and high resolution near infrared photography show folds in Tertiary sediments and possible thrust fault scarps implying NE to SW compression in the region. Large road cuts through the scarps allow study of otherwise poorly accessible, heavily vegetated karst terrain. Deformation increases toward scrap fronts where small bedding-plane thrust faults become more numerous. Analysis of mesoscopic faults with slickensides indicates compression oriented between N to S and E to W. The lowermost scarp has highly sheared fault breccia and undeformed frontal talus breccias implying it is the basal thrust into which the higher thrust faults sole. Thus, the scarps probably formed in a regional NE to SW compressional stress regime and are the toes of thrust sheets. Previous workers have suggested that these scarps are ancient shorelines. However, the gross morphology of the scarps differs substantially from well known erosional terraces on the north coast.

  8. Thrust-faulting earthquake induced many normal-faulting aftershocks, in northeastern Chiba Prefecture, Japan

    NASA Astrophysics Data System (ADS)

    Sakai, S.; Kato, A.; Hirata, N.; Nakagawa, S.; Kasahara, K.; Sato, H.; Kurashimo, E.; Nanjo, K.; Panayotopoulos, Y.; Obara, K.; Aketagawa, T.; Kimura, H.

    2010-12-01

    A thrust faulting type earthquake of a local body wave magnitude (MJMA) of 4.9 occurred near the upper interface of the subducting Philippine Sea Plate (PHS) in northeastern Chiba Prefecture on July 22, 2010. We have been developing a dense seismic net work call the MeSO-net in the Tokyo Metropolitan area. So far, 249 stations are available for the study of a large felt earthquakes and small event as low as M=1.5. We also deployed a temporary seismic array 24 of which were used for the analysis of the aftershocks. We locate the July 22 earthquake(MJMA=4.9) and its 19 aftershocks (M>1.5) by the double difference location algorithm. We also determine focal mechanisms for the main- and after-shocks. The locations of the main shock and three aftershocks are closely distributed near the upper interface of PHS, which is consistent with the idea that the event occurred on the plate interface. However, most aftershocks whose focal mechanism is normal-fault type with a T-axis directing NE-SW are located off the upper interface indicating that intra-slab events are also generated by the event. Acknowledgement: The present study is supported by Special Project for Earthquake Disaster Mitigation in Tokyo Metropolitan Area from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

  9. Stress triggering in thrust and subduction earthquakes and stress interaction between the southern San Andreas and nearby thrust and strike-slip faults

    USGS Publications Warehouse

    Lin, J.; Stein, R.S.

    2004-01-01

    We argue that key features of thrust earthquake triggering, inhibition, and clustering can be explained by Coulomb stress changes, which we illustrate by a suite of representative models and by detailed examples. Whereas slip on surface-cutting thrust faults drops the stress in most of the adjacent crust, slip on blind thrust faults increases the stress on some nearby zones, particularly above the source fault. Blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks. Short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults. We calculate that during a progressive thrust sequence in central California the 1983 Mw = 6.7 Coalinga earthquake brought the subsequent 1983 Mw = 6.0 Nunez and 1985 Mw = 6.0 Kettleman Hills ruptures 10 bars and 1 bar closer to Coulomb failure. The idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events, in agreement with findings of prior investigations. Subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust-faulting events on the periphery of the seismic rupture and its downdip extension. These features are evident in aftershocks of the 1957 Mw = 9.1 Aleutian and other large subduction earthquakes. We further examine stress changes on the rupture surface imparted by the 1960 Mw = 9.5 and 1995 Mw = 8.1 Chile earthquakes, for which detailed slip models are available. Calculated Coulomb stress increases of 2-20 bars correspond closely to sites of aftershocks and postseismic slip, whereas aftershocks are absent where the stress drops by more than 10 bars. We also argue that slip on major strike-slip systems modulates the stress acting on nearby thrust and strike-slip faults. We calculate that the 1857 Mw = 7.9 Fort Tejon earthquake on the San Andreas fault and subsequent interseismic slip brought

  10. Thrust fault growth within accretionary wedges: New Insights from 3D seismic reflection data

    NASA Astrophysics Data System (ADS)

    Orme, H.; Bell, R. E.; Jackson, C. A. L.

    2015-12-01

    The shallow parts of subduction megathrust faults are typically thought to be aseismic and incapable of propagating seismic rupture. The 2011 Tohoku-Oki earthquake, however, ruptured all the way to the trench, proving that in some locations rupture can propagate through the accretionary wedge. An improved understanding of the structural character and physical properties of accretionary wedges is therefore crucial to begin to assess why such anomalously shallow seismic rupture occurs. Despite its importance, we know surprisingly little regarding the 3D geometry and kinematics of thrust network development in accretionary prisms, largely due to a lack of 3D seismic reflection data providing high-resolution, 3D images of entire networks. Thus our current understanding is largely underpinned by observations from analogue and numerical modelling, with limited observational data from natural examples. In this contribution we use PSDM, 3D seismic reflection data from the Nankai margin (3D Muroto dataset, available from the UTIG Academic Seismic Portal, Marine Geoscience Data System) to examine how imbricate thrust fault networks evolve during accretionary wedge growth. Previous studies have reported en-echelon thrust fault geometries from the NW part of the dataset, and have related this complex structure to seamount subduction. We unravel the evolution of faults within the protothrust and imbricate thrust zones by interpreting multiple horizons across faults and measuring fault displacement and fold amplitude along-strike; by doing this, we are able to investigate the three dimensional accrual of strain. We document a number of local displacement minima along-strike of faults, suggesting that, the protothrust and imbricate thrusts developed from the linkage of smaller, previously isolated fault segments. We also demonstrate that the majority of faults grew upward from the décollement, although there is some evidence for downward fault propagation. Our observations

  11. Control of preexisting faults on geometry and kinematics in the northernmost part of the Jura fold-and-thrust belt

    NASA Astrophysics Data System (ADS)

    Ustaszewski, Kamil; Schmid, Stefan M.

    2006-10-01

    This study investigates the formation of the northernmost anticlines of the late Miocene to early Pliocene thin-skinned Jura fold-and-thrust belt and provides evidence that a transition to thick-skinned tectonics did occur in this particular area during the late Pliocene. The northernmost anticlines of the Jura fold-and-thrust belt are characterized by pronounced along-strike asymmetries that were predetermined by a fault pattern inherited from Paleogene Upper Rhine Graben rifting. This fault pattern had disrupted the Triassic basal décollement of the Jura Mountains and controlled the nucleation of thrusts and folds, as well as transfer zones during the generally (N)NW directed transport of the detached sedimentary cover. Sinistral, transpressive oblique ramps nucleated along Paleogene, NNE trending basement normal faults and led to a northward protrusion of the Jura front, encroaching onto the southernmost Upper Rhine Graben. Shortening across the frontal anticlines is greatest along the oblique ramps and decreases along strike toward the east, necessitating a gentle clockwise rotation of the detached sediments. Despite the fact that the stress field in the sedimentary cover remained unchanged, thin-skinned folding and thrusting came to a halt in the early Pliocene, giving way to thick-skinned tectonics, very probably governing neotectonic activity in the area. This transition might represent a geodynamic reorganization of the northwestern Alpine foreland.

  12. Deformation mechanisms adjacent to a thrust fault, Sangre de Cristo Mountains, Colorado

    SciTech Connect

    Kelly, J.C.; McConnell, D.A.; Friberg, V.M. . Dept. of Geology)

    1994-04-01

    The purpose of this study is to examine the character of grain-scale deformation adjacent to a Laramide thrust fault in the Sangre de Cristo Mountains. This site represents a window through the hanging wall of a thrust sheet which juxtaposes Precambrian rocks over Pennsylvanian rocks. It provides a rare opportunity to examine deformation mechanisms in the footwall of a basement-involved thrust. Brittle deformation is evident at both outcrop and grain-scale. Filled fractures and slickensides composed of quartz and epidote are present throughout the area, and increase in abundance adjacent to the fault zone, as does the frequency of mesoscopic faulting. Variations in deformation mechanisms can be seen between the Precambrian rocks of the thrust sheet and the Pennsylvanian metasedimentary rocks, and between the metamorphosed arkoses and metapelites within the Pennsylvanian section. Cataclastic textures are present in deformed Precambrian rocks, and the degree of cataclasis is greatest immediately adjacent to the fault zone. Deformation in the Pennsylvanian rocks is largely dependent upon the abundance of fine-grained matrix within each sample. The degree of brittle deformation is negatively correlated to the percentage of matrix. Coarser-grained sections show microscopic faults which offset quartz and feldspar grains. Offsets decrease on the faults as they pass from coarse grains into the matrix.

  13. Thrust-wrench fault interference in a brittle medium: new insights from analogue modelling experiments

    NASA Astrophysics Data System (ADS)

    Rosas, Filipe; Duarte, Joao; Schellart, Wouter; Tomas, Ricardo; Grigorova, Vili; Terrinha, Pedro

    2015-04-01

    We present analogue modelling experimental results concerning thrust-wrench fault interference in a brittle medium, to try to evaluate the influence exerted by different prescribed interference angles in the formation of morpho-structural interference fault patterns. All the experiments were conceived to simulate simultaneous reactivation of confining strike-slip and thrust faults defining a (corner) zone of interference, contrasting with previously reported discrete (time and space) superposition of alternating thrust and strike-slip events. Different interference angles of 60°, 90° and 120° were experimentally investigated by comparing the specific structural configurations obtained in each case. Results show that a deltoid-shaped morpho-structural pattern is consistently formed in the fault interference (corner) zone, exhibiting a specific geometry that is fundamentally determined by the different prescribed fault interference angle. Such angle determines the orientation of the displacement vector shear component along the main frontal thrust direction, determining different fault confinement conditions in each case, and imposing a complying geometry and kinematics of the interference deltoid structure. Model comparison with natural examples worldwide shows good geometric and kinematic similarity, pointing to the existence of matching underlying dynamic process. Acknowledgments This work was sponsored by the Fundação para a Ciência e a Tecnologia (FCT) through project MODELINK EXPL/GEO-GEO/0714/2013.

  14. The Dauki Thrust Fault and the Shillong Anticline: An incipient plate boundary in NE India?

    NASA Astrophysics Data System (ADS)

    Ferguson, E. K.; Seeber, L.; Steckler, M. S.; Akhter, S. H.; Mondal, D.; Lenhart, A.

    2012-12-01

    The Shillong Massif is a regional contractional structure developing across the Assam sliver of the Indian plate near the Eastern Syntaxis between the Himalaya and Burma arcs. Faulting associated with the Shillong Massif is a major source of earthquake hazard. The massif is a composite basement-cored asymmetric anticline and is 100km wide, >350km long and 1.8km high. The high relief southern limb preserves a Cretaceous-Paleocene passive margin sequence despite extreme rainfall while the gentler northern limb is devoid of sedimentary cover. This asymmetry suggests southward growth of the structure. The Dauki fault along the south limb builds this relief. From the south-verging structure, we infer a regional deeply-rooted north-dipping blind thrust fault. It strikes E-W and obliquely intersects the NE-SW margin of India, thus displaying three segments: Western, within continental India; Central, along the former passive margin; and Eastern, overridden by the west-verging Burma accretion system. We present findings from recent geologic fieldwork on the western and central segments. The broadly warped erosional surface of the massif defines a single anticline in the central segment, east of the intersection with the hinge zone of the continental margin buried by the Ganges-Brahmaputra Delta. The south limb of the anticline forms a steep topographic front, but is even steeper structurally as defined by the Cretaceous-Eocene cover. Below it, Sylhet Trap Basalts intrude and cover Precambrian basement. Dikes, presumably parallel to the rifted margin, are also parallel to the front, suggesting thrust reactivation of rift-related faults. Less competent Neogene clastics are preserved only near the base of the mountain front. Drag folds in these rocks suggest north-vergence and a roof thrust above a blind thrust wedge floored by the Dauki thrust fault. West of the hinge zone, the contractional structure penetrates the Indian continent and bifurcates. After branching into the

  15. Fault-related fluid flow, Beech Mountain thrust sheet, Blue Ridge Province, Tennessee-North Carolina

    SciTech Connect

    Waggoner, W.K.; Mora, C.I. . Dept. of Geological Sciences)

    1992-01-01

    The latest proterozoic Beech Granite is contained within the Beech Mountain thrust sheet (BMTS), part of a middle-late Paleozoic thrust complex located between Mountain City and Grandfather Mountain windows in the western Blue Ridge of TN-NC. At the base of the BMTS, Beech Granite is juxtaposed against lower Paleozoic carbonate and elastics of the Rome Fm. along the Stone Mountain thrust on the southeaster margin of the Mountain City window. At the top of the BMTS, Beech Granite occurs adjacent to Precambrian mafic rocks of the Pumpkin Patch thrust sheet (PPTS). The Beech Granite is foliated throughout the BMTS with mylonitization and localized cataclasis occurring within thrust zones along the upper and lower margins of the BMTS. Although the degree of mylonitization and cataclasis increases towards the thrusts, blocks of relatively undeformed granite also occur within these fault zones. Mylonites and thrusts are recognized as conduits for fluid movement, but the origin of the fluids and magnitude and effects of fluid migration are not well constrained. This study was undertaken to characterize fluid-rock interaction within the Beech Granite and BMTS. Extensive mobility of some elements/compounds within the thrust zones, and the isotopic and mineralogical differences between the thrust zones and interior of the BMTS indicate that fluid flow was focused within the thrust zones. The wide range of elevated temperatures (400--710 C) indicated by qz-fsp fractionations suggest isotopic disequilibrium. Using a more likely temperature range of 300--400 C for Alleghanian deformation, calculated fluid compositions indicate interactions with a mixture of meteoric-hydrothermal and metamorphic water with delta O-18 = 2.6--7.5[per thousand] for the upper thrust zone and 1.3 to 6.2[per thousand] for the lower thrust zone. These ranges are similar to isotopic data reported for other Blue Ridge thrusts and may represent later periods of meteoric water influx.

  16. Strike-slip movements and thrusting along a transpressive fault zone: The North Giudicarie line (Insubric line, northern Italy)

    NASA Astrophysics Data System (ADS)

    Prosser, Giacomo

    1998-12-01

    This paper analyzes the kinematic evolution and the deformation partitioning within an important transpressive fault zone located in the central part of the Alpine chain. The North Giudicarie line is a NNE trending fault which offsets the dextral Insubric line with an apparent left-lateral displacement of about 70 km. The main fault plane of the North Giudicarie line dips about 35°-45° to the NW. The footwall is characterized by N-S striking strike-slip faults, which reactivate extensional faults of Early Jurassic to Late Cretaceous age. The early deformation history of the North Giudicarie line is revealed by basement-and limestone-mylonites. Shear sense of mylonites indicates on average top-to-the-east thrusting. These movements took place during the late Oligocene-early Miocene, when the Insubric line was active as a right-lateral strike-slip fault. Therefore, in this time span the North Giudicarie line can be interpreted as a dextral transpressive bend of the Insubric line. Mylonites have later been overprinted by brittle faults related to top-to-the-SE thrusting of middle-late Miocene age. During this event the shape of the Insubric line was strongly modified by left-lateral transpression along the Giudicarie fault zone. Deformation was partitioned between prevailing compression along the Giudicarie line and left-lateral strike-slip movements along the N-S striking faults. These faults transferred the strike-slip component of the Giudicarie line into a wider area of the central southern Alps.

  17. Active thrusting within the Himalayan orogenic wedge in the Kashmir Himalayas

    NASA Astrophysics Data System (ADS)

    Gavillot, Y.

    2011-12-01

    Numerous lines of evidence indicate that significant distributed deformation occurs within the Himalayan fold-thrust belt. Active thrust faults lie as much as 100 km north of the active thrust front. Whereas geochemical and topographical data provide circumstantial evidence for internal deformation in Nepal, new mapping demonstrates that an active emergent thrust fault system extends stepwise from the Balakot-Bagh fault (source of the Mw 7.6 2005 Kashmir earthquake in Pakistan) more than 200 km to the southeast on the Riasi fault (RT). The RT with a fault length of ~70 km, is a ~50° northeast-dipping reverse fault system, which sits ~40 km north of the deformation front in the Kashmiri Himalaya of northwest India. Our mapping demonstrates that the Riasi thrust consists of two strands. The northern strand, Main Riasi thrust (MRT) strand, places Precambrian Sirban Limestone on folded unconsolidated (Pleistocene?) conglomerates. Undeformed younger alluvial deposits (Holocene?) overlyie the MRT, which implies no Holocene (?) surface rupture on this strand. To the south, the surface expression of the Riasi frontal thrust (RFT) includes a fault scarp and offset ~10 ka terrace deposits dated with 36CL depth profiles. OSL and 10Be depth profile dating indicate an age range between ~80 ka to ~30 ka for the Bidda terrace in the upper plate of the MRT, yielding estimates of long-term uplift rate of 5.0 ± 2.2 mm/yr, slip rate of 6.4 ± 2.9 mm/yr, and shortening rate of 4.1 ± 1.9mm/yr. Given a ~34 mm/yr India-Asia convergence rate in the NW Himalaya, our results indicate that internal deformation within the orogenic belt accounts for at least ~10% of the total India-Eurasia plate convergence, with remaining shortening absorbed mainly at the deformation front.

  18. Rock magnetic expression of fluid infiltration in the Yingxiu-Beichuan fault (Longmen Shan thrust belt, China)

    NASA Astrophysics Data System (ADS)

    Yang, Tao; Yang, Xiaosong; Duan, Qingbao; Chen, Jianye; Dekkers, Mark J.

    2016-03-01

    Fluid infiltration within fault zones is an important process in earthquake rupture. Magnetic properties of fault rocks convey essential clues pertaining to physicochemical processes in fault zones. In 2011, two shallow holes (134 and 54 m depth, respectively) were drilled into the Yingxiu-Beichuan fault (Longmen Shan thrust belt, China), which accommodated most of the displacement of the 2008 Mw 7.9 Wenchuan earthquake. Fifty-eight drill core samples, including granitic host rock and various fault rocks, were analyzed rock-magnetically, mineralogically, and geochemically. The magnetic behavior of fault rocks appears to be dominated by paramagnetic clay minerals. Magnetite in trace amounts is identified as the predominant ferrimagnetic fraction in all samples, decreasing from the host rock, via fault breccia to (proto-)cataclasite. Significant mass-losses (10.7-45.6%) are determined for the latter two with the "isocon" method. Volatile contents and alteration products (i.e., chlorite) are enriched toward the fault core relative to the host rocks. These observations suggest that magnetite depletion occurred in these fault rocks—exhumed from the shallow crust—plumbed by fluid-assisted processes. Chlorite, interpreted to result from hydrothermal activity, occurs throughout almost the entire fault core and shows high coefficients of determination (R2 > 0.6) with both low and high-field magnetic susceptibility. Close relationships, with R2 > 0.70, are also observed between both low and high-field magnetic susceptibility and the immobile elements (e.g., TiO2, P2O5, MnO), H2O+, and the calculated mass-losses of fault rocks. Hence, magnetic properties of fault rocks can serve as proxy indicators of fluid infiltration within shallow fault zones.

  19. Initial faulting age of the Longmen Shan thrust fault belt: Paleo-earthquake information from Scientific Drilling (WFSD)

    NASA Astrophysics Data System (ADS)

    Wang, H.; Li, H.; Sun, Z.; Si, J.; Huang, Y.

    2013-12-01

    The Longmen Shan thrust fault belt has got much more attention after the 2008 Wenchuan earthquake, but there is still no accordant cognition about its formation age. The frequently fault activities of the Longmen Shan thrust fault belt have triggered several strong ancient seismic activities in the geological history, and induced unconsolidated soft-sediment deformed. Soft-sediment deformation structures formed during or shortly after deposition are important indicators of past seismic activity. These structures are a direct response to processes of fluid escape during liquefaction and fluidization related to past seismic activity in the area, suggest they could play an important role in analyzing the distribution and intensity of ancient tectonic activity. Many layers of conglomerate with peculiar shapes of breccias occur in the Xujiahe Formation sediments in the WFSD-1 drilling core. The peculiar conglomerate layers spaced at irregular intervals, which can be classified into 4 groups, from top to bottom, the depths are: 759.03-812.48 m, 932.8-978 m, 991.88-1025.25 m and 1097.4-1156.51 m. The breccias in the peculiar conglomerate are mostly black calcareous fine-grained siltstone, with the sizes varying from a few millimeters to dozens of centimeters, mostly are 1-5 cm. The cementing material is fine-grained quartz sandstone (particle diameter: 0.05-0.2 mm). The content of the calcareous siltstone breccia in sandstone is about 5-60%. The breccias vary in their morphology and pattern, such as embay structure, small irregular flame structure, liquefied droplet and homogeneous layer. Those are typical liquefied deformation features caused by earthquake without remote transport. The original rock is alternating layers of black calcium siltstone and yellow-grey fine-grained sandstone, formed below epicontinental sea wave base. Strong earthquake triggered the fine-grained sandstone liquefied, then traversed and flowed into the soft sedimentary siltstone layer made it

  20. Middle Proterozoic belt basin syndepositional faults and their influence on Phanerozoic thrusting and extension

    SciTech Connect

    Winston, D.

    1983-08-01

    During the middle Proterozoic, continental crust of the Belt region was cut by nearly east-west and northwest-striking faults that produced a mosaic of large basement blocks. Blocks that subsided formed the Belt basin and were surrounded mostly by uplifted blocks. The Dillon block bounded the basin on the south along the Perry line, and, together with blocks to the south and west, furnished most of the sediment that filled the basin. Great alluvial aprons sloped basinward from the uplifted blocks down to extensive flats that bordered the Belt intracratonic sea. Sediments were deposited in the deeper parts of the sea by underflows and interflows. The graben blocks, including the Helena embayment and the diagonal block to the northwest, received the thickest sediments. Cretaceous to Paleocene compression thrust the Belt rocks and Phanerozoic cover rocks eastward and northeastward, forming first a western, and then an eastern thrust belt. Thrusts on the blocks formed long sheets that deflected and tore along the block boundaries, where depth to basement and tectonic transport distances changed. Where thrust crossed northwest-trending basement faults, they ramped locally. Eocene extension produced fault patterns that change from block to block. Differential extension formed right-lateral strike-slip faults across block boundaries. Proterozoic faults that cut the continental crust, not only formed the framework of the Belt basin, but affected patterns of later compression and extension.

  1. Evidence of recent thrust faulting on the Moon revealed by the Lunar Reconnaissance Orbiter Camera.

    PubMed

    Watters, Thomas R; Robinson, Mark S; Beyer, Ross A; Banks, Maria E; Bell, James F; Pritchard, Matthew E; Hiesinger, Harald; van der Bogert, Carolyn H; Thomas, Peter C; Turtle, Elizabeth P; Williams, Nathan R

    2010-08-20

    Lunar Reconnaissance Orbiter Camera images reveal previously undetected lobate thrust-fault scarps and associated meter-scale secondary tectonic landforms that include narrow extensional troughs or graben, splay faults, and multiple low-relief terraces. Lobate scarps are among the youngest landforms on the Moon, based on their generally crisp appearance, lack of superposed large-diameter impact craters, and the existence of crosscut small-diameter impact craters. Identification of previously known scarps was limited to high-resolution Apollo Panoramic Camera images confined to the equatorial zone. Fourteen lobate scarps were identified, seven of which are at latitudes greater than +/-60 degrees, indicating that the thrust faults are globally distributed. This detection, coupled with the very young apparent age of the faults, suggests global late-stage contraction of the Moon. PMID:20724632

  2. The ground deformation field induced by a listric thrust fault with an overburden soil layer

    NASA Astrophysics Data System (ADS)

    Zeng, Shaogang; Cai, Yong'en

    2013-12-01

    The surface deformation field induced by a listric thrust fault with a thick, overburden soil layer is studied in this paper by the finite element method (FEM). The results show: (a) The maximum slip induced by the buried fault is not located at upper tip of the fault, but below it. (b) The vertical displacement changes remarkably near the fault, forming a fault scarp. With the increase of the soil layer thickness, the height of the scarp is decreased for the same earthquake magnitude. (c) The strong strain zone on the surface is localized near the projection of the fault tip on the ground surface. The horizontal strains in the zone are in tension above the hanging wall and in compression above the foot wall, and the vertical strains in the zone are vice versa, which is favorable for tensileshear, compression-shear fissures above hanging wall and foot wall, respectively.

  3. Earth tides can trigger shallow thrust fault earthquakes.

    PubMed

    Cochran, Elizabeth S; Vidale, John E; Tanaka, Sachiko

    2004-11-12

    We show a correlation between the occurrence of shallow thrust earthquakes and the occurrence of the strongest tides. The rate of earthquakes varies from the background rate by a factor of 3 with the tidal stress. The highest correlation is found when we assume a coefficient of friction of mu = 0.4 for the crust, although we see good correlation for mu between 0.2 and 0.6. Our results quantify the effect of applied stress on earthquake triggering, a key factor in understanding earthquake nucleation and cascades whereby one earthquake triggers others.

  4. Displacement-Length Relationship of Thrust Faults Associated with Lobate Scarps on the Moon

    NASA Astrophysics Data System (ADS)

    Banks, M. E.; Watters, T. R.

    2016-11-01

    A linear fit to plotted displacement-length data yields a γ value of 1.8 × 10-2 (θ = 30°) for the lunar lobate scarps. This result is higher than estimates of γ for scarps on Mars and Mercury but lower than that for thrust faults on earth.

  5. Microtectonic analysis of an incipient thrust fault in Opalinus Clay.

    NASA Astrophysics Data System (ADS)

    Laurich, B.; Urai, J. L.; Desbois, G.; Vollmer, C.; Nussbaum, C.

    2014-12-01

    The microfabric of a fault rock controls the fault's mechanical and hydrological properties. Knowing the fabric is thus essential for estimating seismic behavior and potential fluid flow. We studied well-preserved core and outcrop samples from the Main Fault, an up to 3 m wide zone of approximately 10 m offset in the Mont Terri Underground Research Laboratory (CH), a site to evaluate long-term safety of radioactive waste disposal. We found four main structural elements: (1) slickensided shear surfaces, (2) veins, (3) fine-grained gouge, and (4) scaly clay fabric. We investigated each element by ultra-thin section microscopy, by broad-ion-beam scanning electron microscopy (BIB-SEM) and focused-ion-beam transmission electron microscopy (FIB-TEM), by X-ray diffraction crystallography (XRD) and by naked-eye analysis. We found extremely thin shear zones (<4μm) along which several samples broke, revealing slickensides. BIB-SEM and FIB-TEM showed that these thin shear zones comprise strongly aligned nano-sized clay particles. The porosity of the shear zones is dramatically reduced compared to the protolith. The strong alignment of clay particles, which wrap larger grains as quartz, calcite fossils and feldspar, yields a shiny, smooth surface morphology of the slickensides. Occasionally, calcite and celestite veins are associated to releasing sections such as risers of the slickenside. Gouge comprises much finer particles, a higher fabric intensity and a strong reduction in porosity and calcite content compared to the protolith. These findings suggest that gouge evolved by a cataclastic deformation mechanism aided by pressure solution of calcite. Scaly clay occurs in varying intensity and comprises thin shear zones, which sometimes act as flexural-slip faults of microfolds and C'-type shear bands. We propose that next to cataclastic processes, pressure solution and precipitation are important micro-scale mechanisms in faulting in Opalinus Clay and thus need to be

  6. Syn-orogenic extensional pulses within the contractional history of thrust wedges. The Val di Lima low-angle normal fault case study, Northern Apennines, Italy.

    NASA Astrophysics Data System (ADS)

    Clemenzi, Luca; Molli, Giancarlo; Storti, Fabrizio; Muchez, Philippe; Swennen, Rudy; Torelli, Luigi

    2014-05-01

    In this contribution we describe the Val di Lima low-angle fault system, a kilometric-scale extensional structure exposed in the central sector of the Northern Apennines thrust wedge, Italy. The low-angle extensional fault system delaminates the right-side-up limb of a km-scale recumbent isoclinal anticline that affects the carbonate-dominated Late Triassic to early Early Miocene non-metamorphic Tuscan succession. The low-angle fault system, in turn, is affected by superimposed folding and late-tectonic high-angle extensional faulting. The three-dimensional configuration of the low-angle fault system has been investigated through detailed structural mapping and restoration of the superimposed deformations, while the fault damage zone architecture has been characterized in outcrops with appropriate exposure. Pressure-depth conditions and palaeofluid evolution of the fault system have been studied through microstructural, mineralogical, petrographic, fluid inclusion and stable isotope analysis of fault rocks and fault-related calcite and quartz veins. Our results show that the low-angle fault system was active during exhumation of the Tuscan succession, at estimated conditions of about 180°C and 5.2 km depth. The fault system had a twofold influence on fluid circulation within the orogenic wedge: i) it allowed the migration of low-salinity fluids, due to the increased permeability along the fault zone; ii) it favored footwall fluid overpressures where the fault core acted as an efficient hydraulic barrier. Abundant fluid circulation in fault damage zones also characterized the late-stage evolution of the low-angle fault system, allowing the recrystallization of calcite veins and limestone host rocks at shallower conditions (~ 4 km). Within this P-T framework, the fault zone architecture shows important differences, related to the different lithologies involved in the fault system and to the role played by the fluids during deformation. In particular, footwall fluid

  7. Decimeter Scale Ultra-Fine Fault Rocks (Possible Pseudotachylites) in an Ancient Subduction Thrust Zone

    NASA Astrophysics Data System (ADS)

    Rowe, C. D.; Moore, J. C.; Meneghini, F.; McKiernan, A. W.

    2004-12-01

    Large bodies of ultrafine fault rock (possible pseudotachylite or frictional melt) occur within cataclastic thrust zones in the Ghost Rocks Formation, Kodiak Accretionary Complex, Alaska. The Paleocene Ghost Rocks Formation includes map-scale mélange belts formed by flattening and shearing of seafloor sediments and volcanic rocks at about 250 degrees C and 325 MPa (~13 km depth) during subduction between 65-60Ma. Ten to 15-meter thick cataclastite zones crosscut the mélange fabric at a low angle, representing a stage of increasingly localized shear during subduction thrusting. Ultrafine fault rocks occur as thick (10-25cm) continuous planar beds along the boundaries of cataclastites, or in discontinuous accumulation bodies within cataclastite zones. The boundaries of the ultrafine fault rocks are intrusive, sharp but irregular and deform the cataclastite host fabric. Single pulse intrusions of the ultrafine fault rock range up to 0.5m in intrusive dimension and form complex morphologies resembling both upward and downward directed flame structures and dike-sill complexes, as well as sheath folds and disharmonic flow banding and folding. These field characteristics indicate fluidization and perhaps frictional melting of the ultrafine fault rocks. Ultrafine fault rock bodies can be traced laterally for meters to tens of meters at individual outcrops and occur for about 2 km along strike. Preliminary SEM analysis reveals that the primary matrix material is physically and chemically homogenous down to few-micron scale, consistent with the field identification of pseudotachylite. Thin sections show rounded remnant quartz aggregates, typical of pseudotachylytes. Although some thin sections show suggest melting others may represent ultracataclastite. Some ultrafine fault rock material is rebrecciated and cataclastized to a fine scale, indicating reactivation of previous fault rock generation surfaces. These ultrafine fault rock zones represent the most highly deformed

  8. Three-thrust fault system at the plate suture of arc-continent collision in the southernmost Longitudinal Valley, eastern Taiwan

    NASA Astrophysics Data System (ADS)

    Lee, J.; Chen, H.; Hsu, Y.; Yu, S.

    2013-12-01

    Active faults developed into a rather complex three-thrust fault system at the southern end of the narrow Longitudinal Valley in eastern Taiwan, a present-day on-land plate suture between the Philippine Sea plate and Eurasia. Based on more than ten years long geodetic data (including GPS and levelling), field geological investigation, seismological data, and regional tomography, this paper aims at elucidating the architecture of this three-thrust system and the associated surface deformation, as well as providing insights on fault kinematics, slip behaviors and implications of regional tectonics. Combining the results of interseismic (secular) horizontal and vertical velocities, we are able to map the surface traces of the three active faults in the Taitung area. The west-verging Longitudinal Valley Fault (LVF), along which the Coastal Range of the northern Luzon arc is thrusting over the Central Range of the Chinese continental margin, braches into two active strands bounding both sides of an uplifted, folded Quaternary fluvial deposits (Peinanshan massif) within the valley: the Lichi fault to the east and the Luyeh fault to the west. Both faults are creeping, to some extent, in the shallow surface level. However, while the Luyeh fault shows nearly pure thrust type, the Lichi fault reveals transpression regime in the north and transtension in the south end of the LVF in the Taitung plain. The results suggest that the deformation in the southern end of the Longitudinal Valley corresponds to a transition zone from present arc-collision to pre-collision zone in the offshore SE Taiwan. Concerning the Central Range, the third major fault in the area, the secular velocities indicate that the fault is mostly locked during the interseismic period and the accumulated strain would be able to produce a moderate earthquake, such as the example of the 2006 M6.1 Peinan earthquake, expressed by an oblique thrust (verging toward east) with significant left-lateral strike slip

  9. Geodetically constrained slip on the Main Himalayan Thrust fault from the 2015 Gorkha earthquake

    NASA Astrophysics Data System (ADS)

    Elliott, J. R.; Jolivet, R.; González, P. J.; Avouac, J. P.; Hollingsworth, J.; Searle, M. P.; Stevens, V.

    2015-12-01

    Large thrust faults accommodate crustal shortening caused by the collision of tectonic plates, contributing to the growth of topography over geological timescales. The Himalayan belt, which results from the collision of India into Asia, has been the locus of some of the largest earthquakes to strike the continents, including the recent 2015 magnitude 7.8 Gorkha earthquake. Competing hypotheses have been proposed to explain how topography is sustained and how the current convergence across the Himalaya is accommodated - whether this is predominately along a single thrust or is more distributed, involving out-of-sequence additional faulting. Here we use geodetically-derived surface displacements to show that whilst the Gorkha earthquake was blind, it ruptured the Main Himalayan Thrust (MHT), highlighting its ramp-and-flat geometry. Reconciling independent geological, geomorphological, geophysical and geodetic observations, we quantify the geometry of the MHT in the Kathmandu area. Present-day convergence across the Himalaya is mostly accommodated along the MHT, and no out-of-sequence thrusting is required to explain the higher uplift and incision rates at the front of the high range. Whilst the vast majority of slip is buried at depth, triggered near surface slip was imaged in the Sentinel-1 coseismic interferograms along a 26 km long discontinuity, 10 km north of the Main Frontal Thrust. This surface break follows the trace of the Main Dun Thrust (MDT), a relatively minor splay. This displacement is seen to grow in the central portion of the splay in the proceeding week. Slip from the largest (Mw 7.3) aftershock that occurred 17 days later fills in most of the eastern gap in the slip contours of the mainshock at the lower edge of the fault rupture. In addition to the region west of the Gorkha rupture, a large portion of the MHT remains unbroken south of Kathmandu presenting a continuing seismic hazard. At the shallow end of the rupture, slip tapers off sharply and

  10. Seismic images and fault relations of the Santa Monica thrust fault, West Los Angeles, California

    USGS Publications Warehouse

    Catchings, R.D.; Gandhok, G.; Goldman, M.R.; Okaya, D.

    2001-01-01

    In May 1997, the US Geological Survey (USGS) and the University of Southern California (USC) acquired high-resolution seismic reflection and refraction images on the grounds of the Wadsworth Veterans Administration Hospital (WVAH) in the city of Los Angeles (Fig. 1a,b). The objective of the seismic survey was to better understand the near-surface geometry and faulting characteristics of the Santa Monica fault zone. In this report, we present seismic images, an interpretation of those images, and a comparison of our results with results from studies by Dolan and Pratt (1997), Pratt et al. (1998) and Gibbs et al. (2000). The Santa Monica fault is one of the several northeast-southwest-trending, north-dipping, reverse faults that extend through the Los Angeles metropolitan area (Fig. 1a). Through much of area, the Santa Monica fault trends subparallel to the Hollywood fault, but the two faults apparently join into a single fault zone to the southwest and to the northeast (Dolan et al., 1995). The Santa Monica and Hollywood faults may be part of a larger fault system that extends from the Pacific Ocean to the Transverse Ranges. Crook et al. (1983) refer to this fault system as the Malibu Coast-Santa Monica-Raymond-Cucamonga fault system. They suggest that these faults have not formed a contiguous zone since the Pleistocene and conclude that each of the faults should be treated as a separate fault with respect to seismic hazards. However, Dolan et al. (1995) suggest that the Hollywood and Santa Monica faults are capable of generating Mw 6.8 and Mw 7.0 earthquakes, respectively. Thus, regardless of whether the overall fault system is connected and capable of rupturing in one event, individually, each of the faults present a sizable earthquake hazard to the Los Angeles metropolitan area. If, however, these faults are connected, and they were to rupture along a continuous fault rupture, the resulting hazard would be even greater. Although the Santa Monica fault represents

  11. Style and magnitude of Mesozoic thrust faulting in the hinterland of the Sevier thrust belt Pequop Mountains-Wood Hills-East Humboldt Range region, northeast Nevada

    SciTech Connect

    Camilleri, P.A. . Dept. of Geology and Geophysics)

    1993-04-01

    The Pequop Mountains (PM), Wood Hills (WH) and East Humboldt Range (EHR), NE Nevada, provide evidence that the hinterland of the Sevier thrust belt experienced large-magnitude Mesozoic shortening ([>=]55 km) and crustal thickening ([>=] 30 km). These ranges expose a structurally continuous crustal cross section of unmetamorphosed to high pressure upper amphibolite facies Triassic to Precambrian miogeoclinal strata. This sequence lies structurally beneath unmetamorphosed extensional klippen that omit metamorphic grade and crustal section, but also repeat stratigraphic units. Because they repeat stratigraphic units, the underlying miogeoclinal section, or footwall, must have once lain beneath a thrust fault (herein named the Windermere thrust). The footwall of the Windermere thrust was exhumed by two generations of top-to-the-W-NW low-angle normal faults that are distinguished by whether they are depositionally overlapped by Eocene volcanic rocks or if they cut the volcanic rocks in their hanging walls. The latter phase is associated with development of the mid-Tertiary extensional mylonitic shear zone in the EHR. An integration of geobarometric, metamorphic, and map data suggest (1) a NW dip of the footwall of the Windermere thrust with metamorphic facies belts trending perpendicular to dip direction and metamorphic grade increasing down dip, and (2) a top-to-the-SE sense-of-slip for the Windermere thrust. Assuming that the Windermere thrust comprised a flat on the youngest rocks exposed in the footwall (Triassic), the Mesozoic depth to the Windermere thrust in the northern PM is [>=] 7 km, in WH is [approximately]10--16 km, and in the EHR[>=]30 km. The Windermere thrust accommodated a minimum of 50 km of shortening associated with the Independence thrust is [>=] 5 km. These data indicate that the amount of hinterland shortening in NE Nevada greatly exceeds that to the south in the Eureka belt.

  12. Locations of Major Thrust Faults on Mercury Point to a Formation Mechanism Associated with Crustal Thickening

    NASA Astrophysics Data System (ADS)

    Selvans, M. M.; Watters, T. R.; James, P. B.; Phillips, R. J.; Solomon, S. C.

    2014-12-01

    Large thrust faults on Mercury are the expression of horizontal contraction that resulted from cooling of the planet; their uneven distribution may indicate that other stress fields contributed to their formation and development. We explore the relationship in the northern hemisphere between locations of lobate scarps and high-relief ridges >50 km in length and inferred crustal thickness to understand whether mechanisms that result in crustal thickening and thinning may have also influenced the locations of large thrust faults. These landforms are concentrated in areas with >53 km crustal thickness (at the 99% confidence level, on the basis of a two-sided single proportion test), an extreme end of the normal distribution (with a mean of 40 km) of modeled crustal thickness values. One possible mechanism for thickening crust and concentrating prominent thrust faults is mantle flow; a broad pattern of mantle upwelling and downwelling is compatible with Mercury's gravity anomaly and topography fields at long (>1000 km) horizontal wavelengths. On Earth (e.g., central Australia), midplate mantle downwelling has been invoked as a mechanism to thicken overlying continental crust and increase compressional stresses in the rigid upper portion of the lithosphere. Downwelling in some areas requires upwelling in others; horizontal divergence could decrease levels of compressive stresses over upwelling regions and might account for the deficiency of large thrust faults in areas of thinnest crust (<27 km, significant at the 95% confidence level). We tested the possibility that this deficiency instead corresponds to burial by thick volcanic flows within areas of smooth plains by excluding the northern plains and Caloris interior plains (the two largest expanses of smooth plains), but there was no significant change from the result for the full hemisphere. If mantle flow contributed to the current patterns of crustal thickness and large thrust fault locations, an implication is

  13. Millennium recurrence interval of morphogenic earthquakes on the Qingchuan fault, northeastern segment of the Longmen Shan Thrust Belt, China

    NASA Astrophysics Data System (ADS)

    Lin, A.

    2015-12-01

    In this study, I present new paleoseismic and topographic evidence for the Holocene faulting activity, including the recurrence interval of morphogenic earthquakes and the slip rate along the Qingchuan fault, the northern segment of the Longmen Shan Thrust Belt, central China, and discuss its tectonic implications for the zone at the eastern margin of the Tibetan Plateau. Field investigations, trench excavations, and radiocarbon dating results reveal that: (i) the Qingchuan fault is currently active as a seismogenic fault, along which six morphogenic earthquakes occurred in the past 6000 years; (ii) the most recent event prior to the 2008 Wenchuan earthquake took place in the period between AD 600 and 1400, which probably corresponds to the late Tang-Song (AD 800-1000) (M~8) earthquake that occurred in the central and southwestern segments of the LSTB; (iii) the penultimate paleoseismic event occurred in the period around 2000 yr BP, suggesting a millennium recurrence interval of morphogenic earthquakes in the late Holocene. The present results are comparable with those inferred in the central and southwestern segments of the LSTB within which the Wenchuan-magnitude earthquakes occurred in a millennium recurrence interval, that are in contrast with previous estimates of 2000-10,000 years for the recurrence interval of morphogenic earthquakes within the LSTB, and thereby necessitating substantial modifications to exiting seismic-hazard models for the densely populated region at the Sichuan region. References: 1) Lin, A., Rao, G., and Yan, B., 2012. Field evidence of rupture of the Qingchuan Fault during the 2008 Mw7.9 Wenchuan earthquake, northeastern segment of the Longmen Shan Thrust Belt, China. Tectonophysics, 522-523, 243-252, doi:10.1016/j.tecto.2011.12.012 2) Lin, A., Rao, G., and Yan, B., 2014. Structural analysis of the right-lateral strike-slip Qingchuan fault, northeastern segment of the Longmen Shan thrust belt, central China. Journal of Structural

  14. Implications of the Northridge earthquake for strong ground motions from thrust faults

    USGS Publications Warehouse

    Somerville, P.; Saikia, C.; Wald, D.; Graves, R.

    1996-01-01

    The peak accelerations recorded on alluvial sites during the Northridge earthquake were about 50% larger than the median value predicted by current empirical attenuation relations at distances less than about 30 km. This raises the question of whether the ground motions from the Northridge earthquake are anomalous for thrust events or are representative of ground motions expected in future thrust earthquakes. Since the empirical data base contains few strong-motion records close to large-thrust earthquakes, it is difficult to assess whether the Northridge ground motions are anomalous based on recorded data alone. For this reason, we have used a broadband strong-motion simulation procedure to help assess whether the ground motions were anomalous. The simulation procedure has been validated against a large body of strong-motion data from California earthquakes, and so we expect it to produce accurate estimates of ground motions for any given rupture scenario, including blind-thrust events for which no good precedent existed in the strong-motion data base until the occurrence of the Northridge earthquake. The ground motions from the Northridge earthquake and our simulations of these ground motions have a similar pattern of departure from empirical attenuation relations for thrust earthquakes: the peak accelerations are at about the 84th percentile level for distances within 20 to 30 km and follow the median level for larger distances. This same pattern of departure from empirical attenuation relations was obtained in our simulations of the peak accelerations of an Elysian Park blind-thrust event prior to the occurrence of the Northridge earthquake. Since we are able to model this pattern with broadband simulations, and had done so before the Northridge earthquake occurred, this suggests that the Northridge strong-motion records are not anomalous and are representative of ground motions close to thrust faults. Accordingly, it seems appropriate to include these

  15. Mesozoic pre-thrusting high-angle faults and stratigraphic variations, Plomosa Mountains, W. Arizona

    SciTech Connect

    Richard, S.M.; Spencer, J.E. )

    1993-04-01

    Three contrasting stratigraphic assemblages characterize fault-bounded terranes in the Southern Plomosa Mtns. (1) The Six Price sequence (SPS) consists of Proterozoic coarse-grained granitoid overlain by Paleozoic and Mesozoic strata. (2) The Apache Wash sequence consists of a basal mega-breccia and conglomerate unit overlain by sandstone in a fining-upward sequence. Paleozoic blocks in the mega-breccia include a Cambrian Muav-like lithology not present in the SPS Paleozoic section. The thickness and clast size in conglomerate associated with the mega-breccia increases the S suggesting a source in that direction. (3) The Crystal Hill sequence consists of strata correlated with the lower McCoy Mountains Formation deposited across a previously tilted unconformity between Jurassic volcanic rocks and the Proterozoic Scadden Mountain quartz monzonite. The lower McCoy Mountain Formation consists of basal quartz-arenite that grades up into fine-grained volcanic-lithic sandstones, and then into lithic-feldspathic sandstone and locally conglomerate, forming a coarsening-upward sequence. Because the Apache Wash sequence is cut by the Poorman thrust, the breccias at its base are not related to the Poorman thrust. Derivation of these creccias entirely from the SPS Paleozoic section is precluded by the presence of the Muav-lithology blocks; their source is not exposed. Thrusting in the area, correlated with deformation in the Maria Fold and Thrust Belt, was preceded by faulting to produce the megabreccias, tilting, and formation of NW-trending high-angle fault one of which forms the major lithotectonic boundary in the range.

  16. Pliocene transpressional modification of depositional basins by convergent thrusting adjacent to the "Big Bend" of the San Andreas fault: An example from Lockwood Valley, southern California

    USGS Publications Warehouse

    Kellogg, K.S.; Minor, S.A.

    2005-01-01

    The "Big Bend" of the San Andreas fault in the western Transverse Ranges of southern California is a left stepping flexure in the dextral fault system and has long been recognized as a zone of relatively high transpression compared to adjacent regions. The Lockwood Valley region, just south of the Big Bend, underwent a profound change in early Pliocene time (???5 Ma) from basin deposition to contraction, accompanied by widespread folding and thrusting. This change followed the recently determined initiation of opening of the northern Gulf of California and movement along the southern San Andreas fault at about 6.1 Ma, with the concomitant formation of the Big Bend. Lockwood Valley occupies a 6-km-wide, fault-bounded structural basin in which converging blocks of Paleoproterozoic and Cretaceous crystalline basement and upper Oligocene and lower Miocene sedimentary rocks (Plush Ranch Formation) were thrust over Miocene and Pliocene basin-fill sedimentary rocks (in ascending order, Caliente Formation, Lockwood Clay, and Quatal Formation). All the pre-Quatal sedimentary rocks and most of the Pliocene Quatal Formation were deposited during a mid-Tertiary period of regional transtension in a crustal block that underwent little clockwise vertical-axis rotation as compared to crustal blocks to the south. Ensuing Pliocene and Quaternary transpression in the Big Bend region began during deposition of the poorly dated Quatal Formation and was marked by four converging thrust systems, which decreased the areal extent of the sedimentary basin and formed the present Lockwood Valley structural basin. None of the thrusts appears presently active. Estimated shortening across the center of the basin was about 30 percent. The fortnerly defined eastern Big Pine fault, now interpreted to be two separate, oppositely directed, contractional reverse or thrust faults, marks the northwestern structural boundary of Lockwood Valley. The complex geometry of the Lockwood Valley basin is similar

  17. Repeated pseudotachylytes generation events along regional scale faults: the Orobic and Porcile thrusts (Southern Alps, N Italy)

    NASA Astrophysics Data System (ADS)

    Zanchetta, Stefano; D'Adda, Paolo; Barberini, Valentina; Villa, Igor Maria; Zanchi, Andrea

    2010-05-01

    many cases re-melting phenomena of pre-existing pseudotachylytes were observed at the micro-scale. Old pseudotachylyte fragments with evident resorption features are present within new veins, and "intrusive" contact were locally observed between different vein generations. Different melt pulses along the same vein are differentiated on the base of clast/matrix ratios and chemical composition of both matrix and crystallites. Brittle deformation producing brecciation of old pseudotachylytes seems to be contemporaneous with new melt injection and flow, resulting in the coexistence, within the same vein, of old fractured pseudotachylyte layers and new, undeformed, ones. Structural data relative to fault veins point out that both old and young pseudotachylytes formed along reverse fault planes with similar geometric features. This suggest that no significant changes occurred in the main stress axes orientations and resulting deformation structures correlated to the Late Cretaceous and the Eocene compressive deformation events along the Orobic and Porcile fault zones. Field data, 40Ar/39Ar ages, microstructural and mineralogical data on pseudotachylytes along the Orobic and Porcile thrusts reveal that repeated coseismic friction-induced melting occurred along same faults with a time interval in excess of 15 Ma. This implies that the seismic history of regional scale faults could be very complex and polyphasic, with successive long time range re-activations that can be individuated exploring the geological record associated to fault zones.

  18. Lidar reveals paleoseismic sites and recent strike-slip and thrust faulting along the central Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    De Pascale, G. P.; Langridge, R. M.; Davies, T. R.

    2013-12-01

    In the South Island of New Zealand, the dextral-reverse Alpine fault forms the major plate boundary structure between the Pacific and Australian plates and is thought to fail in large to great earthquakes approximately every 100 to 400 years, with the most recent major surface rupture event occurring in 1717 AD. We used a recently collected lidar dataset to evaluate the central section of the fault to both measure recent slip along the fault, recent co-seismic uplift, and to find new paleoseismic sites. The new high-resolution topography in the dense temperate rainforest allowed insight into the fault that was previously unavailable. Lidar mapping, combined with field mapping facilitated the discovery of a multi-event thrust fault scarp of the Alpine Fault that was later trenched at Gaunt Creek. C-14 dating of units in the trench and mapping there, show that the last earthquake was probably the 1717 event. Along the length of the lidar survey, small (< 25 m) dextral offsets were also mapped along the fault, which were rated for quality, and then visited in the field. The lidar itself was a guide to locate these offsets, and the offset measurements in the field have lower uncertainties than the lidar resolution; dextral slip in the 1717 earthquake here was c. 7 m × 1 m. Additional sites with evidence for cumulative slip were also mapped in the field which showing repetitive slip of ~ 7 to 8 m per event for the past three surface ruptures on the fault. Sag ponds discovered during field mapping are important new targets for investigation and will likely yield slip-rate information here for the correlation of slip with events. Additional field mapping near the Whataroa River and Mint Creek demonstrates that between debris flow fans that cross the Alpine Fault at the rangefront of the Southern Alps, preservation of strike-slip scarps is rare due to post-earthquake deposition and erosion. However, one likely scarp was found in a post-earthquake aggradation surface

  19. Millennium recurrence interval of morphogenic earthquakes on the Qingchuan fault, northeastern segment of the Longmen Shan Thrust Belt, China

    NASA Astrophysics Data System (ADS)

    Lin, Aiming; Yan, Bing; Rao, Gang

    2016-04-01

    The 2008 M w 7.9 Wenchuan produced a ˜285-300-km-long coseismic surface rupture zone, including a 60-km-long segment along the Qingchuan fault, the northeastern segment of the Longmen Shan Thrust Belt (LSTB), Sichuan Basin, central China. Field investigations, trench excavations, and radiocarbon dating results reveal that (i) the Qingchuan fault is currently active as a seismogenic fault, along which four morphogenic earthquakes including the 2008 Wenchuan earthquake occurred in the past ca. 3500 years, suggesting an average millennium recurrence interval of morphogenic earthquakes in the late Holocene; (ii) the most recent event prior to the 2008 Wenchuan earthquake took place in the period between AD 1400 and AD 1100; (iii) the penultimate paleoseismic event occurred in the period around 2000 years BP in the Han Dynasty (206 BC-AD 220); (iv) the third paleoseismic event occurred in the period between 900 and 1800 BC; and (v) at least three seismic faulting events occurred in the early Holocene. The present results are comparable with those inferred in the central and southwestern segments of the LSTB within which the Wenchuan magnitude earthquakes occurred in a millennium recurrence interval, that are in contrast with previous estimates of 2000-10,000 years for the recurrence interval of morphogenic earthquakes within the LSTB and thereby necessitating substantial modifications to existing seismic hazard models for the densely populated region at the Sichuan region.

  20. Out-of-sequence thrusting in experimental Coulomb wedges: Implications for the structural development of mega-splay faults and forearc basins

    NASA Astrophysics Data System (ADS)

    Haq, Saad S. B.

    2012-10-01

    We have investigated how an arc-ward increase in bulk mechanical strength in an experimental accretionary prism influences the development, timing, and duration of slip on out-of-sequence thrusts. We have monitored the structural development and kinematics, in side-view, during the development of a frontally accreting Coulomb wedge growing out in front of a critically tapered and mechanically stronger inner wedge. The inner-wedge initially behaved as classic backstop to deformation with the most actively slipping thrust occurring near the deformation front on the forward most thrust structures. With continued growth, however, significant out-of-sequence slip on reactivated fore-thrusts occurred in conjunction with slip on newly formed back-thrusts in the inner-wedge. This out-of-sequence deformation resulted in punctuated, rapid uplift of the model forearc basin and a noticeable break in topographic slope in the outer pro-wedge. Cyclical out-of-sequence fore- and back-thrusting, driven by ongoing frontal thrust imbrication, continued with periodic recovery of taper and was followed by additional out-of-sequence faulting and associated basin uplift.

  1. Out-Of-Sequence Thrusting In Coulomb Wedges: Implications For The Structural Development Of Mega-Splay Faults And Forearc Basins

    NASA Astrophysics Data System (ADS)

    Haq, S. S.

    2012-12-01

    By quantifying deformation in frictional analog models we have investigated how an arc-ward increase in bulk mechanical strength in an accretionary prism influences the development, timing, and duration of slip on out-of-sequence thrusts. We have monitored the structural development and kinematics, in side-view, during the development of a frontally accreting Coulomb wedge growing out in front of a critically tapered and mechanically stronger inner wedge. The inner-wedge initially behaved as classic backstop to deformation with the most actively slipping thrust occurring near the deformation front on the forward most thrust structures. With continued growth, however, significant out-of-sequence slip on reactivated fore-thrusts occurred in conjunction with slip on newly formed back-thrusts in the inner-wedge. This out-of-sequence deformation resulted in punctuated, rapid uplift of the model forearc basin and a noticeable break in topographic slope in the outer pro-wedge. Cyclical out-of-sequence fore- and back-thrusting, driven by ongoing frontal thrust imbrication, continued with periodic recovery of taper and was followed by additional out-of-sequence faulting and associated basin uplift.

  2. Origin of mountains on Io by thrust faulting and large-scale mass movements

    PubMed

    Schenk; Bulmer

    1998-03-01

    Voyager stereoimages of Euboea Montes, Io, indicate that this mountain formed when a large crustal block was uplifted 10.5 kilometers and tilted by approximately 6 degrees. Uplift triggered a massive slope failure on the northwest flank, forming one of the largest debris aprons in the solar system. This slope failure probably involved relatively unconsolidated layers totaling approximately 2 kilometers in thickness, overlying a rigid crust (or lithosphere) at least 11 kilometers thick. Mountain formation on Io may involve localized deep-rooted thrust faulting and block rotation, due to compression at depth induced during vertical recycling of Io's crust. PMID:9488645

  3. Origin of mountains on Io by thrust faulting and large-scale mass movements

    PubMed

    Schenk; Bulmer

    1998-03-01

    Voyager stereoimages of Euboea Montes, Io, indicate that this mountain formed when a large crustal block was uplifted 10.5 kilometers and tilted by approximately 6 degrees. Uplift triggered a massive slope failure on the northwest flank, forming one of the largest debris aprons in the solar system. This slope failure probably involved relatively unconsolidated layers totaling approximately 2 kilometers in thickness, overlying a rigid crust (or lithosphere) at least 11 kilometers thick. Mountain formation on Io may involve localized deep-rooted thrust faulting and block rotation, due to compression at depth induced during vertical recycling of Io's crust.

  4. Permian magmatism, Permian detachment faulting, and Alpine thrusting in the Orobic Anticline, southern Alps, Italy

    NASA Astrophysics Data System (ADS)

    Pohl, Florian; Froitzheim, Niko; Geisler-Wierwille, Thorsten; Schlöder, Oliver

    2014-05-01

    Lombardo. It is therefore an Alpine structure. (4) Several south-directed Alpine thrusts duplicate the lithostratigraphy, including the detachment, and are related to the Orobic thrust further north. They also offset the Biandino Fault. U-Pb zircon ages measured with LA-ICP-MS (work in progress) will further clarify the temporal relations between the intrusions, volcanics, and the shear zones. Froitzheim, N., Derks, J.F., Walter, J.M. & Sciunnach, D. 2008. Evolution of an Early Permian extensional detachment fault from synintrusive, mylonitic flow to brittle faulting (Grassi Detachment Fault, Orobic Anticline, southern Alps, Italy) Geological Society, London, Special Publications, 298; 69-82. doi:10.1144/SP298.4 Thöni, M., Mottana, A., Delitala, M. C., De Capitani, L. & Liborio, G. 1992. The Val Biandino composite pluton: A late Hercynian intrusion into the South-Alpine metamorphic basement of the Alps (Italy). Neues Jahrbuch für Mineralogie-Monatshefte, 12, 545-554. Sciunnach, D. 2001. Early Permian palaeofaults at the western boundary of the Collio Basin (Valsassina, Lombardy). Natura Bresciana. Annuario del Museo Civico di Scienze Naturali, Brescia, Monografia, 25, 37-43.

  5. Dynamic rupture modeling of the transition from thrust to strike-slip motion in the 2002 Denali fault earthquake, Alaska

    USGS Publications Warehouse

    Aagaard, B.T.; Anderson, G.; Hudnut, K.W.

    2004-01-01

    We use three-dimensional dynamic (spontaneous) rupture models to investigate the nearly simultaneous ruptures of the Susitna Glacier thrust fault and the Denali strike-slip fault. With the 1957 Mw 8.3 Gobi-Altay, Mongolia, earthquake as the only other well-documented case of significant, nearly simultaneous rupture of both thrust and strike-slip faults, this feature of the 2002 Denali fault earthquake provides a unique opportunity to investigate the mechanisms responsible for development of these large, complex events. We find that the geometry of the faults and the orientation of the regional stress field caused slip on the Susitna Glacier fault to load the Denali fault. Several different stress orientations with oblique right-lateral motion on the Susitna Glacier fault replicate the triggering of rupture on the Denali fault about 10 sec after the rupture nucleates on the Susitna Glacier fault. However, generating slip directions compatible with measured surface offsets and kinematic source inversions requires perturbing the stress orientation from that determined with focal mechanisms of regional events. Adjusting the vertical component of the principal stress tensor for the regional stress field so that it is more consistent with a mixture of strike-slip and reverse faulting significantly improves the fit of the slip-rake angles to the data. Rotating the maximum horizontal compressive stress direction westward appears to improve the fit even further.

  6. The 2013, Mw 7.7 Balochistan earthquake, energetic strike-slip reactivation of a thrust fault

    NASA Astrophysics Data System (ADS)

    Avouac, Jean-Philippe; Ayoub, Francois; Wei, Shengji; Ampuero, Jean-Paul; Meng, Lingsen; Leprince, Sebastien; Jolivet, Romain; Duputel, Zacharie; Helmberger, Don

    2014-04-01

    We analyse the Mw 7.7 Balochistan earthquake of 09/24/2013 based on ground surface deformation measured from sub-pixel correlation of Landsat-8 images, combined with back-projection and finite source modeling of teleseismic waveforms. The earthquake nucleated south of the Chaman strike-slip fault and propagated southwestward along the Hoshab fault at the front of the Kech Band. The rupture was mostly unilateral, propagated at 3 km/s on average and produced a 200 km surface fault trace with purely strike-slip displacement peaking to 10 m and averaging around 6 m. The finite source model shows that slip was maximum near the surface. Although the Hoshab fault is dipping by 45° to the North, in accordance with its origin as a thrust fault within the Makran accretionary prism, slip was nearly purely strike-slip during that earthquake. Large seismic slip on such a non-optimally oriented fault was enhanced possibly due to the influence of the free surface on dynamic stresses or to particular properties of the fault zone allowing for strong dynamic weakening. Strike-slip faulting on thrust fault within the eastern Makran is interpreted as due to eastward extrusion of the accretionary prism as it bulges out over the Indian plate. Portions of the Makran megathrust, some thrust faults in the Kirthar range and strike-slip faults within the Chaman fault system have been brought closer to failure by this earthquake. Aftershocks cluster within the Chaman fault system north of the epicenter, opposite to the direction of rupture propagation. By contrast, few aftershocks were detected in the area of maximum moment release. In this example, aftershocks cannot be used to infer earthquake characteristics.

  7. A Unification of Earthquake Cycle and Structural Evolution Models for Thrust Faults

    NASA Astrophysics Data System (ADS)

    Meade, B. J.

    2014-12-01

    Geodetic observations of interseismic deformation near dip-slip faults may be used to estimate slip rates on both isolated structures and across geometrically complex thrust systems. Interpreting these kinematic measurements requires integrating the effects of interseismic elastic strain accumulation from quasi-static earthquake cycle models. While a kinematically consistent theory for planar thick-skinned models has been widely applied the theory for thin-skinned models has remained less satisfactory due to an inadequate treatment of vertical velocities. Here we develop a kinematically consistent model of horizontal and vertical interseismic deformation in thin-skinned thrust systems including non-planar faults. The key aspect of this model is the integration of kinematic structural evolution models with elastic deformation models. Predictions include localized interseismic hanging wall uplift as well as smoothly varying horizontal and vertical velocities. Additionally, this model implies slightly modified patterns of elastic coseismic deformation in the hanging wall including coseismic folding. The interseismic deformation model described here provides a step toward more unified interpretation of both decadal-scale geodetic observations and long-term tectonic uplift.

  8. Thrust Faults, Folds, Both, or Neither? Accommodating Lithospheric Shortening on Icy Worlds.

    NASA Astrophysics Data System (ADS)

    Bland, M. T.; McKinnon, W. B.

    2015-12-01

    Enceladus' surface exhibits numerous tectonic features interpreted to form by lithospheric shortening, including long-wavelength folds, smaller-scale folds and ridges, branching ridges with 1 km of relief (dorsa), and curvilinear ridge belts [1]. The morphology of many of these features suggests that thrust faulting plays a dominant role in their formation [2,3]. In contrast, Europa, where lithospheric shortening must have occurred [4], exhibits just a few putative contractional features: subtle long-wavelength folds [5], and regions of missing surface area that may have been subsumed into the interior [6]. Here we utilize numerical models of lithospheric shortening on icy satellites to elucidate the processes and conditions that lead to faulting and folding. These simulations indicate that cold surface temperatures (~70 K), a thin lithosphere (rapid viscosity decrease with depth due to a high heat flux and/or low thermal conductivity), and low surface gravity promote localization of strain into fault-like deformation bands. Warmer surface temperatures (~100-120 K), thicker lithospheres, and weaker rheological transitions promote folding or uniform thickening. With its generally colder surface and potentially high heat flow of >100 mW m-2 [7,8,9,10], our models predict that faulting should occur more readily on Enceladus than Europa, which is consistent with observations. In particular, localizing contractional strain into fault-like zones on Europa is challenging due to its warmer surface temperature, and may require very high heat flows. The difficulty in forming large-scale thrust faults presents a challenge to the hypothesis that regions of the Europa's surface have been subsumed into the interior. We continue to evaluate the role of ice shell thickness on lithospheric shortening. [1] Crow-Willard and Pappalardo, 2015. JGR 120, doi:10.1002/2015JE004818. [2] Pappalardo et al. 2014. LPSC #2143. [3] Beddingfield et al. 2013. LPSC #1254. [4] Bland and McKinnon 2012

  9. Seismic reflection geometry of the Newark basin margin in Eastern Pennsylvania. Evidence for extensional reactivation of Paleozoic thrust faults

    SciTech Connect

    Ratcliffe, N.M.; Burton, W.C.; D'Angelo, R.M.; Costain, J.K.

    1986-07-01

    Low-angle 25/sup 0/ to 35/sup 0/ dips have been determined for the border fault of the Newark basin near Riegelsville, Pennsylvania, based on a VIBROSEIS profile and two continuously-cored drill holes across faults at the basin margin. A group of moderately strong planar reflections in a zone 0.5 km thick in gneiss and carbonate rocks of the footwall block coincide with the updip projection of imbricate fault slices and mylonites associated with the Musconetcong thrust system of Drake and others (1967). Contrasts in acoustic impedance among mylonitic dolostone and mylonitic gneiss and their protoliths, determined from measurements on core samples, are sufficiently large to account for reflections seen in the footwall block. Analysis of drill core and surface outcrops supports the conclusion that low-angle extensional faulting in the Early Mesozoic was localized by reactivation of Paleozoic imbricate thrust faults in the basement rocks. Extension in the NW-SE quadrant was approximately perpendicular to the strike of the ancient thrust faults in Eastern Pennsylvania and a passive origin of the Newark basin here is suggested. The data presented here represent some of the most explicit three-dimensional information obtained thus far, in the Eastern United States, in support of the concept of fault reactivation in controlling formation of Early Mesozoic extensional basins.

  10. Influence of mobile shale on thrust faults: Insights from discrete element simulations

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    thrusts are listric, similar to those in the Niger Delta, steepening updip and curving near the intersection with the mobile shale layer. The décollements in our simulations, however, are much more diffuse then interpreted in nature. Discrete thrust faults within the pre-delta layer sole into broader zones of distributed strain within the mobile shale layer. In the frontal fold and thrust belt, both backthrusts and forethrusts were observed, also seen in the western lobe of the Niger Delta. In our simulations, this dual vergence is caused by the rotation of the principal stress in the pre-delta layer from sub-vertical under the sediment wedge, to nearly horizontal in front of the wedge. This rotation is thought to be due to a basinward 'push' created by updip extension along normal faults, which slide within the mobile layer and along the base of the model. This rotation of stresses is not found in the underlying weak mobile layer. The amount of contraction in the fold and thrust belt was about half the amount of extension accommodated beneath the sediment wedge, indicating that a large amount of contraction was distributed throughout the models, including in front of the toe thrusts, rather than being concentrated solely in the fold and thrust belt.

  11. Fold-to-fault progression of a major thrust zone revealed in horses of the North Mountain fault zone, Virginia and West Virginia, USA

    USGS Publications Warehouse

    Orndorff, Randall C.

    2012-01-01

    The method of emplacement and sequential deformation of major thrust zones may be deciphered by detailed geologic mapping of these important structures. Thrust fault zones may have added complexity when horse blocks are contained within them. However, these horses can be an important indicator of the fault development holding information on fault-propagation folding or fold-to-fault progression. The North Mountain fault zone of the Central Appalachians, USA, was studied in order to better understand the relationships of horse blocks to hanging wall and footwall structures. The North Mountain fault zone in northwestern Virginia and eastern panhandle of West Virginia is the Late Mississippian to Permian Alleghanian structure that developed after regional-scale folding. Evidence for this deformation sequence is a consistent progression of right-side up to overturned strata in horses within the fault zone. Rocks on the southeast side (hinterland) of the zone are almost exclusively right-side up, whereas rocks on the northwest side (foreland) of the zone are almost exclusively overturned. This suggests that the fault zone developed along the overturned southeast limb of a syncline to the northwest and the adjacent upright limb of a faulted anticline to the southeast.

  12. Implications of perennial saline springs for abnormally high fluid pressures and active thrusting in western California

    SciTech Connect

    Unruh, J.R.; Davisson, M.L.; Criss, R.E.; Moores, E.M. )

    1992-05-01

    Perennial saline springs in the Rumsey Hills area, southwestern Sacramento Valley, California, locally discharge at high elevations and near ridgetops. The springs are cold, are commonly associated with natural gas seeps, and typically emerge along west-vergent thrust faults. Stable isotope analyses indicate that the spring waters are similar to oil-field formation fluids and they have had a significant residence time in the subsurface at moderate temperatures. The nonmeteoric character of the springs demonstrates that they are not being fed by perched water tables. The authors propose that these subsurface formation waters are being forced to the surface by anomalously high porefluid pressures. The Rumsey Hills area is one of Quaternary uplift, thrusting, and crustal shortening, and prospect wells drilled there have encountered anomalously high fluid pressures at shallow depths. They attribute these high fluid pressures to active tectonic compression and shortening of Cretaceous marine sedimentary rocks. The widespread occurrence of anomalously high pore-fluid pressures and perennial saline springs in the Coast Ranges and western Great Valley suggests that much of western California may be characterized as a seismically active, overpressured thrust belt. The emergence of formation waters along thrust faults further suggests that patterns of subsurface fluid flow in western California may be similar to those in overpressured accretionary prisms, and that excess fluid pressures may also play a role in the distribution of seismicity.

  13. Fault interaction along the Central Andean thrust front: The Las Peñas thrust, Cerro Salinas thrust and the Montecito Anticline

    NASA Astrophysics Data System (ADS)

    Schoenbohm, L. M.; Costa, C. H.; Brooks, B. A.; Bohon, W.; Gardini, C.; Cisneros, H.

    2013-12-01

    The region in west-central Argentina between the thin-skinned Precordillera and the thick-skinned Sierras Pampeanas structural domain is among the most active zones of thrust tectonics in the world. We quantify the rates of deformation on the east-vergent Las Peñas thrust (LPT), and the west-vergent Cerro Salinas thrust (CST). The Montecito anticline (MA) is located at their intersection. We mapped three key locations, collected stratigraphic logs from the MA, dated three ashes using U-Pb in zircon and dated 10 terraces using cosmogenic Be-10 depth profiles. Five terrace levels are present where the Rio Las Peñas crosses the LPT, up to 45 m above the modern river. Cosmogenic dating of the uppermost terrace (T1) yields and age of 123.8 +26.5/-12.3 ka. A reconstruction of this surface using a blind thrust rupture scenario indicates 73 +/- 7 m horizontal shortening and 34 +/- 3 m vertical displacement. Shortening across the structure is therefore 0.59 +0.10/-0.13 mm/yr with a vertical uplift rate of 0.27 +0.05/-0.06 mm/a. Previous work indicates higher rates to the south on the order of 2 mm/yr (Schmidt et al., 2011). Lower terraces give ages of 38.0 +11/-6.2 ka (T2) and 1.5 +5.0/-0.6 ka (T4). Three terrace levels are preserved near the center of the CST. The middle surface (T2) is folded across the axis of the structure and yields an age of 112.5 +33/-14.4 ka. Given 22.9 m surface uplift, this indicates a vertical uplift rate of 0.20 +0.05/-0.06 mm/yr, similar to the rate on the LPT. The upper terrace (T1) yields a younger age (97.1 +29.8/-12.4 ka); the T1 and T2 ages overlap within uncertainty, indicating rapid river incision at the time of their formation. An intercalated ash within the Neogene strata gives an age of 16.2 +/- 0.2. Previous work indicates long-term shortening rates of 0.8 mm/yr (Verges et al., 2007) and that the CST initiated after 8.5 Ma. The lowermost unit exposed in the MA is the Los Pozos Fm., with no indication of syn-depositional deformation

  14. Active faulting in apparently stable peninsular India: Rift inversion and a Holocene-age great earthquake on the Tapti Fault

    NASA Astrophysics Data System (ADS)

    Copley, Alex; Mitra, Supriyo; Sloan, R. Alastair; Gaonkar, Sharad; Reynolds, Kirsty

    2014-08-01

    We present observations of active faulting within peninsular India, far from the surrounding plate boundaries. Offset alluvial fan surfaces indicate one or more magnitude 7.6-8.4 thrust-faulting earthquakes on the Tapti Fault (Maharashtra, western India) during the Holocene. The high ratio of fault displacement to length on the alluvial fan offsets implies high stress-drop faulting, as has been observed elsewhere in the peninsula. The along-strike extent of the fan offsets is similar to the thickness of the seismogenic layer, suggesting a roughly equidimensional fault rupture. The subsiding footwall of the fault is likely to have been responsible for altering the continental-scale drainage pattern in central India and creating the large west flowing catchment of the Tapti river. A preexisting sedimentary basin in the uplifting hanging wall implies that the Tapti Fault was active as a normal fault during the Mesozoic and has been reactivated as a thrust, highlighting the role of preexisting structures in determining the rheology and deformation of the lithosphere. The slip sense of faults and earthquakes in India suggests that deformation south of the Ganges foreland basin is driven by the compressive force transmitted between India and the Tibetan Plateau. The along-strike continuation of faulting to the east of the Holocene ruptures we have studied represents a significant seismic hazard in central India.

  15. Fault plane reflectivity along subduction thrusts: What does it really tell us?

    NASA Astrophysics Data System (ADS)

    Saffer, D. M.; Tobin, H. J.

    2014-12-01

    At subduction zones, variations in fault zone seismic reflectivity provide key information about in situ physical properties. Commonly, negative polarity reflectors, which result from large impedance contrasts across the fault interface, are taken to indicate anomalously high porosity and pore fluid pressures. However, this idea has not been explored rigorously in the context of realistic sediment loading paths and consolidation behavior. We use a forward model to quantify the effects of stress state and drainage conditions on fault zone reflection coefficient (R), focused on case studies from the Nankai and Costa Rican margins. We define constitutive relationships between: (1) stress state (mean and differential stress) and porosity (Φ); and (2) P-wave velocity (Vp) and Φ using data from triaxial laboratory consolidation experiments conducted on core samples. One key aspect of our approach is the consideration of differing stress states in the overriding wedge, which is likely to have experienced conditions at or near thrust failure, vs. the subducting sediment section, which likely undergoes uniaxial consolidation, at least in the near trench region. For Costa Rica, the full range of pore pressure from hydrostatic to lithostatic yields negative values of R. Both the observation of decreased reflection amplitude beyond ~45 km from the trench and reported P-wave interval velocities in the subducting section are most consistent with modest overpressures (λ<~0.7). Decreased reflection amplitude landward of this point does not require the onset of drainage. Similarly, for Nankai, a wide range of pore fluid pressure conditions lead to negative values of R, because increased mean effective stress in the wedge leads to decreased Φ and higher Vp relative to the footwall. Positive polarity arises only if the underthrusting sediment transitions from a state of uniaxial compression to thrust failure, in combination with the onset of drainage - as might accompany d

  16. Tectonic history and thrust-fold deformation style of seismically active structures near Coalinga

    SciTech Connect

    Namson, J.S. ); Davis, T.L.; Lagoe, M.B.

    1990-01-01

    The stratigraphy of the Coalinga region can be divided into tectostratigraphic facies whose boundaries delineate two major tectonic events - one in the mid-Cenozoic (38-17 Ma) and one in the late Cenozoic (less than 3 Ma). The succession of these tectostratigraphic facies, and an integration of geology, subsurface well data, a seismic-reflection profile, and earthquake seismicity on a retrodeformable cross section, yield a model for the tectonic evolution of the Coalinga region. This model suggests that the structural style of both deformational events is characteristic of fold and thrust belts. The model also indicates that the causative fault of the May 2 earthquake is a ramped thrust. The results of this study, in combination with regional geologic relations, suggest that the Coalinga region is part of an active fold and thrust belt which borders the west and south sides of the San Joaquin Valley. The potential for future earthquakes due to movement of other blind thrust faults within this belt should be evaluated.

  17. Seismic constraints and coulomb stress changes of a blind thrust fault system, 1: Coalinga and Kettleman hills, California

    USGS Publications Warehouse

    Lin, Jian; Stein, Ross S.

    2006-01-01

    This report reviews the seismicity and surface ruptures associated with the 1982-1985 earthquake sequence in the Coalinga region in California, and the role of Coulomb stress in triggering the mainshock sequence and aftershocks. The 1982-1985 New Idria, Coalinga, and Kettleman Hills earthquakes struck on a series of west-dipping, en echelon blind thrust faults. Each earthquake was accompanied by uplift of a Quaternary anticline atop the fault, and each was accompanied by a vigorous aftershock sequence. Aftershocks were widely dispersed, and are seen above and below the thrust fault, as well as along the up-dip and down-dip projection of the main thrust fault. For the Coalinga and Kettleman Hills earthquakes, high-angle reverse faults in the core of the anticlines are evident in seismic reflection profiles, and many of these faults are associated with small aftershocks. The shallowest aftershocks extended to within 3-4 km of the ground surface. There is no compelling evidence for aftershocks associated with flexural slip faulting. No secondary surface rupture was found on any of the anticlines. In contrast, the 1983 Nu?ez rupture struck on a high-angle reverse fault 10 km west of the Coalinga epicenter, and over a 40-80-day period, up to 1 m of oblique surface slip occurred. The slip on this Holocene fault likely extended from the ground surface to a depth of 8-10 km. We argue that both the Nu?ez and Kettleman earthquakes were triggered by stresses imparted by the Coalinga mainshock, which was the largest of the four events in the sequence.

  18. Active oblique ramp faulting in the Southern Tunisian Atlas

    NASA Astrophysics Data System (ADS)

    Saïd, Aymen; Chardon, Dominique; Baby, Patrice; Ouali, Jamel

    2011-03-01

    The Gafsa fault is the longest and most active structure of the fold-and-thrust belt achieving southeastward propagation of the Atlas belt of Eastern North Africa onto the Saharan platform. The Gafsa fault is a 75-km long dextral-oblique basement fault ramp that poses a sizable challenge in earthquake hazard assessment because the post-Paleozoic sedimentary cover is decoupled from its basement above the basement fault. In this study, we combine seismic lines interpretation, tectonic geomorphology and paleoseismological investigations to assess the level of seismic hazard of this fault and evaluate its role in the geodynamic framework of the Central Mediterranean. We show that despite a moderate instrumental and historical seismicity, the fault has produced M ≥ 6 earthquakes with a return period of ca. 500-5000 years during the Late Quaternary. The latest large event having produced a surface rupture on the fault occurred around 8000 yr BP, suggesting an M ≥ 6 earthquake is overdue on the fault. The fault has a minimum reverse component of slip rate of 0.21-0.34 mm/yr over the past 50 Ka. The occurrence of M ≥ 7 paleoearthquakes on the fault may be suspected but not established. Such very strong earthquakes would require transient coseismic linkage of the buried basement fault with the overlying listric fault ramping off the décollement layer. The level of seismic hazard may be underestimated on the Gafsa fault. Indeed, given the geometry of the basement-cover fault system, a number of earthquakes generated in the basement would have led to coseismic surface folding instead of to surface rupture. The Gafsa fault is a major structure accommodating eastward extrusion / spreading of the Atlas belt onto the Saharan and Pelagian plateforms above the retreating Ionian lithospheric slab.

  19. Neogene exhumation in the eastern Alaska Range and its relationship to splay fault activity in the Denali fault system

    NASA Astrophysics Data System (ADS)

    Waldien, T.; Roeske, S.; Benowitz, J.; Allen, W. K.; Ridgway, K.

    2015-12-01

    Dextral oblique convergence in the Denali fault system results from subduction zone strain in the Alaska syntaxis that is partitioned into the upper plate. This convergence is accommodated by dextral-reverse oblique slip on segments of the main strand of the Denali fault in the center of the Alaska Range and by splay faults north and south of the Denali fault at the margins of the Alaska Range. Low-temp. thermochronometry applied to basement rocks bounded by faults within the Denali fault system aids stratigraphic data to determine the timing and locations of exhumation in the Alaska Range, which augment regional seismicity studies aimed at resolving modern fault activity in the Denali fault system. The McCallum Creek and Broxson Gulch faults are north-dipping faults that splay southward from the Denali fault near the Delta River and mark the southern margin of the eastern Alaska Range. Apatite fission track thermochronometry on rocks north of the McCallum Creek fault shows rapid cooling in the hanging wall coeval with basin development in the footwall initiating at the Miocene-Pliocene boundary. Apatite fission track and apatite (U-Th)/He ages from plutonic rocks in the hanging wall of the Broxson Gulch fault, west of the McCallum Creek fault, show final cooling in the Miocene, slightly younger than hanging wall cooling associated with the Susitna Glacier thrust further to the west. Neogene low-temp. cooling ages in the hanging walls of the Susitna Glacier thrust, Broxson Gulch, and McCallum Creek faults suggest that these structures have been accommodating convergence in the Denali fault system throughout the Neogene. More recent cooling in the hanging wall of the McCallum Creek compared to the Susitna Glacier thrust suggests that this fault-related exhumation has migrated eastward throughout the Neogene. Convergence on these splay faults south of the Denali fault results in internal contraction of the crust south of the Denali fault, implying that the Southern

  20. Structural styles of the High Atlas mountains, Morocco: Potential hydrocarbon traps in the footwall of thrusts developed from the reactivation of syn-rift normal faults

    SciTech Connect

    Beauchamp, W.; Allmendinger, R.W.; Barazangi, M. )

    1996-01-01

    Large asymmetrical folds and box folds created by fault bend and fault propagation folding characterize the style of deformation in the High Atlas mountains. Several compressional phases of faulting and folding from the Lower Jurassic through Cenozoic indicate a long and varied tectonic origin for the High Atlas intracontinental mountain belt. Footwall shortcut faults are formed with the inversion of syn-rift listric: normal faults, and progress into low angle thrust faults with fault bend fold geometries. This style of deformation is illustrated on reprocessed seismic reflection data and confirmed by field mapping. Geological field mapping, air photographs, and Thematic Mapper imagery provide important constraints for the interpretation of seismic reflection profiles along the margins of the High Atlas mountains. Balanced cross sections across the High Atlas suggest large horizontal displacements along low angle thrust faults. These thrusts place massive Lower Jurassic carbonates above post-rift Upper Cretaceous and Tertiary rocks. Refolding of thrusts and large scale regional folds indicate oblique slip deformation during and after the inversion of syn-rift normal faults. Low angle thrusts propagate along detachments in shales and marts of the Lower Jurassic. Lower Jurassic shales provide an excellent seal for potential sandstone reservoirs in the Middle Jurassic and Triassic sandstones in the footwall of thrusts.

  1. Structural styles of the High Atlas mountains, Morocco: Potential hydrocarbon traps in the footwall of thrusts developed from the reactivation of syn-rift normal faults

    SciTech Connect

    Beauchamp, W.; Allmendinger, R.W.; Barazangi, M.

    1996-12-31

    Large asymmetrical folds and box folds created by fault bend and fault propagation folding characterize the style of deformation in the High Atlas mountains. Several compressional phases of faulting and folding from the Lower Jurassic through Cenozoic indicate a long and varied tectonic origin for the High Atlas intracontinental mountain belt. Footwall shortcut faults are formed with the inversion of syn-rift listric: normal faults, and progress into low angle thrust faults with fault bend fold geometries. This style of deformation is illustrated on reprocessed seismic reflection data and confirmed by field mapping. Geological field mapping, air photographs, and Thematic Mapper imagery provide important constraints for the interpretation of seismic reflection profiles along the margins of the High Atlas mountains. Balanced cross sections across the High Atlas suggest large horizontal displacements along low angle thrust faults. These thrusts place massive Lower Jurassic carbonates above post-rift Upper Cretaceous and Tertiary rocks. Refolding of thrusts and large scale regional folds indicate oblique slip deformation during and after the inversion of syn-rift normal faults. Low angle thrusts propagate along detachments in shales and marts of the Lower Jurassic. Lower Jurassic shales provide an excellent seal for potential sandstone reservoirs in the Middle Jurassic and Triassic sandstones in the footwall of thrusts.

  2. The San Gabriel mountains bright reflective zone: Possible evidence of young mid-crustal thrust faulting in southern California

    USGS Publications Warehouse

    Ryberg, T.; Fuis, G.S.

    1998-01-01

    During the Los Angeles Region Seismic Experiment (LARSE), a reflection/retraction survey was conducted along a line extending northeastward from Seal Beach, California, to the Mojave Desert, crossing the Los Angeles basin and San Gabriel Mountains. Shots and receivers were spaced most densely through the San Gabriel Mountains for the purpose of obtaining a combined reflection and refraction image of the crust in that area. A stack of common-midpoint (CMP) data reveals a bright reflective zone, 1-s thick, that dominates the stack and extends throughout most of the mid-crust of the San Gabriel Mountains. The top of this zone ranges in depth from 6 s (???18-km depth) in the southern San Gabriel Mountains to 7.5 s (???23-km depth) in the northern San Gabriel Mountains. The zone bends downward beneath the surface traces of the San Gabriel and San Andreas faults. It is brightest between these two faults, where it is given the name San Gabriel Mountains 'bright spot' (SGMBS). and becomes more poorly defined south of the San Gabriel fault and north of the San Andreas fault. The polarity of the seismic signal at the top of this zone is clearly negative, and our analysis suggests it represents a negative velocity step. The magnitude of the velocity step is approximately 1.7 km/s. In at least one location, an event with positive polarity can be observed 0.2 s beneath the top of this zone, indicating a thickness of the order of 500 m for the low-velocity zone at this location. Several factors combine to make the preferred interpretation of this bright reflective zone a young fault zone, possibly a 'master' decollement. (1) It represents a significant velocity reduction. If the rocks in this zone contain fluids, such a reduction could be caused by a differential change in fluid pressure between the caprock and the rocks in the SGMBS; near-lithostatic fluid pressure is required in the SGMBS. Such differential changes are believed to occur in the neighborhood of active fault

  3. Characterization of Appalachian faults

    SciTech Connect

    Hatcher, R.D. Jr.; Odom, A.L.; Engelder, T.; Dunn, D.E.; Wise, D.U.; Geiser, P.A.; Schamel, S.; Kish, S.A.

    1988-02-01

    This study presents a classification/characterization of Appalachian faults. Characterization factors include timing of movement relative to folding, metamorphism, and plutonism; tectonic position in the orogen; relations to existing anisotropies in the rock masses; involvement of particular rock units and their ages, as well as the standard Andersonian distinctions. Categories include faults with demonstrable Cenozoic activity, wildflysch-associated thrusts, foreland bedding-plane thrusts, premetamorphic to synmetamorphic thrusts in medium- to high-grade terranes, postmetamorphic thrusts in medium- to high-grade terranes, thrusts rooted in Precambrian basement, reverse faults, strike-slip faults, normal (block) faults, compound faults, structural lineaments, faults associated with local centers of disturbance, and geomorphic (nontectonic) faults.

  4. A Role of Low-angle Thrust Fault for the Occurrence of rain-induced Rockslides in an Accretionary Complex

    NASA Astrophysics Data System (ADS)

    Arai, N.; Chigira, M.

    2015-12-01

    Recently, extreme weather related to global warming occurs frequently all over the world; there have been many record-setting rainfall events. Accordingly, potential of rain-induced rockslides increases. Examples of recent rain-induced rock avalanches with tens or more than a hundred of fatalities are a rockslide in Shiaolin village, Taiwan by 2009 Typhoon Morakot, and rockslides induced by 2011 typhoon Talas in Japan. However, the method to predict potential sites of rockslides is not established. Geological causes of rockslides are site specific and they must be clarified for each case. 2011 Typhoon Talas induced more than 50 rockslides in the outer belt of the Southwest Japan, where is underlain by Cretaceous - lower Miocene accretionary complexes. We performed thorough geological mapping in the Akatani area, where two huge rockslides occurred with volumes of 2 million and 8 million m3 respectively. As a result, we found that these two rockslides had their sliding surfaces along a low-angle-thrust with a dip of 29°~40° extending more than 5 km, which fault we name Kawarabi-thrust. This thrust has a fracture zone of 6.0 m in the maximum width, composed of clayey fault breccia with a few layers of black gouges. These fault materials are very weak and impermeable, so the fracture zone is expected to prevent the groundwater filtration and build up the pore pressure. This thrust had been exposed along the riversides at the foot of the two rockslides, which suggests that the slopes on the thrust had been destabilized by the undercutting of long-term river incision. The destabilization induced gravitational slope deformation with small scarps before the catastrophic failure. Our finding suggests that locating a large-scale low-angle-thrust is essentially important to predict potential sites of catastrophic rockslides as well as interpreting the internal structure of gravitationally deformed slopes.

  5. Active tectonics west of New Zealand's Alpine Fault: South Westland Fault Zone activity shows Australian Plate instability

    NASA Astrophysics Data System (ADS)

    De Pascale, Gregory P.; Chandler-Yates, Nicholas; Dela Pena, Federico; Wilson, Pam; May, Elijah; Twiss, Amber; Cheng, Che

    2016-04-01

    The 300 km long South Westland Fault Zone (SWFZ) is within the footwall of the Central Alpine Fault (<20 km away) and has 3500 m of dip-slip displacement, but it has been unknown if the fault is active. Here the first evidence for SWFZ thrust faulting in the "stable" Australian Plate is shown with cumulative dip-slip displacements up to 5.9 m (with 3 m throw) on Pleistocene and Holocene sediments and gentle hanging wall anticlinal folding. Cone penetration test (CPT) stratigraphy shows repeated sequences within the fault scarp (consistent with thrusting). Optically stimulated luminescence (OSL) dating constrains the most recent rupture post-12.1 ± 1.7 ka with evidence for three to four events during earthquakes of at least Mw 6.8. This study shows significant deformation is accommodated on poorly characterized Australian Plate structures northwest of the Alpine Fault and demonstrates that major active and seismogenic structures remain uncharacterized in densely forested regions on Earth.

  6. Extraction faulting and out-of-sequence thrusting in collisional orogeny - An example from the Swiss-Italian Western Alps

    NASA Astrophysics Data System (ADS)

    Kirst, F.; Froitzheim, N.; Nagel, T.; Leiss, B.; Pleuger, J.

    2012-04-01

    In the Pennine Alps of Switzerland and Italy a stack of nappes derived from oceanic and continental units of the Piemont-Ligurian paleogeographic domain is exposed. From bottom to top these are the oceanic Zermatt-Saas and Combin zones and the continental Sesia/Dent Blanche nappe. Different Alpine peak pressures have been estimated for these units with the highest pressures of ca. 3.2 GPa in the Zermatt-Saas zone (Groppo et al., 2009), lower pressures of ca. 1.3 GPa in the Combin zone (Bousquet et al, 2008) and intermediate pressures of up to 2.0 GPa in the Sesia/Dent Blanche nappe (Lardeaux & Spalla, 1991). Therefore, a pressure gap of 1.9 GPa exists along the Combin Fault, the contact between the Zermatt-Saas and Combin zones, and a gap of 0.7 GPa along the Dent Blanche Basal Thrust which separates the Sesia/Dent Blanche nappe from the underlying Combin zone. Due to the difference in peak pressures, the Combin Fault has often been interpreted as a large top-SE normal fault accommodating exhumation of the underlying (ultra)high-pressure rocks (e.g. Reddy et al., 1999). However, there is structural evidence that the Combin Fault is in fact an extraction fault (Froitzheim et al., 2006) and that exhumation of Zermatt-Saas (ultra)high-pressure rocks was due to SE-directed extraction of the Sesia/Dent Blanche block originally located between the Zermatt-Saas and Combin zones. Therefore, the Dent Blanche Basal Thrust would represent a top-NW out-of-sequence thrust along which high-pressure rocks of the Sesia/Dent Blanche nappe were thrust over greenschist-facies rocks of the Combin zone. On the basis of the above-mentioned peak pressure estimates and our own structural observations we propose the following tectonic scenario: Initial nappe stacking resulted in a configuration with the Zermatt-Saas zone in the footwall of the Sesia/Dent Blanche nappe and the Combin zone as the structurally highest unit which was thrust over the Sesia/Dent Blanche nappe in the SE and the

  7. Evolution of fracture and fault-controlled fluid pathways in carbonates of the Albanides fold-thrust belt

    USGS Publications Warehouse

    Graham, Wall B.R.; Girbacea, R.; Mesonjesi, A.; Aydin, A.

    2006-01-01

    The process of fracture and fault formation in carbonates of the Albanides fold-thrust belt has been systematically documented using hierarchical development of structural elements from hand sample, outcrop, and geologic-map scales. The function of fractures and faults in fluid migration was elucidated using calcite cement and bitumen in these structures as a paleoflow indicator. Two prefolding pressure-solution and vein assemblages were identified: an overburden assemblage and a remote tectonic stress assemblage. Sheared layer-parallel pressure-solution surfaces of the overburden assemblage define mechanical layers. Shearing of mechanical layers associated with folding resulted in the formation of a series of folding assemblage fractures at different orientations, depending on the slip direction of individual mechanical layers. Prefolding- and folding-related fracture assemblages together formed fragmentation zones in mechanical layers and are the sites of incipient fault localization. Further deformation along these sites was accommodated by rotation and translation of fragmented rock, which formed breccia and facilitated fault offset across multiple mechanical layers. Strike-slip faults formed by this process are organized in two sets in an apparent conjugate pattern. Calcite cement and bitumen that accumulated along fractures and faults are evidence of localized fluid flow along fault zones. By systematic identification of fractures and faults, their evolution, and their fluid and bitumen contents, along with subsurface core and well-log data, we identify northeast-southwest-trending strike-slip faults and the associated structures as dominant fluid pathways in the Albanides fold-thrust belt. Copyright ?? 2006. The American Association of Petroleum Geologists. All rights reserved.

  8. Packaged Fault Model for Geometric Segmentation of Active Faults Into Earthquake Source Faults

    NASA Astrophysics Data System (ADS)

    Nakata, T.; Kumamoto, T.

    2004-12-01

    In Japan, the empirical formula proposed by Matsuda (1975) mainly based on the length of the historical surface fault ruptures and magnitude, is generally applied to estimate the size of future earthquakes from the extent of existing active faults for seismic hazard assessment. Therefore validity of the active fault length and defining individual segment boundaries where propagating ruptures terminate are essential and crucial to the reliability for the accurate assessments. It is, however, not likely for us to clearly identify the behavioral earthquake segments from observation of surface faulting during the historical period, because most of the active faults have longer recurrence intervals than 1000 years in Japan. Besides uncertainties of the datasets obtained mainly from fault trenching studies are quite large for fault grouping/segmentation. This is why new methods or criteria should be applied for active fault grouping/segmentation, and one of the candidates may be geometric criterion of active faults. Matsuda (1990) used _gfive kilometer_h as a critical distance for grouping and separation of neighboring active faults. On the other hand, Nakata and Goto (1998) proposed the geometric criteria such as (1) branching features of active fault traces and (2) characteristic pattern of vertical-slip distribution along the fault traces as tools to predict rupture length of future earthquakes. The branching during the fault rupture propagation is regarded as an effective energy dissipation process and could result in final rupture termination. With respect to the characteristic pattern of vertical-slip distribution, especially with strike-slip components, the up-thrown sides along the faults are, in general, located on the fault blocks in the direction of relative strike-slip. Applying these new geometric criteria to the high-resolution active fault distribution maps, the fault grouping/segmentation could be more practically conducted. We tested this model

  9. The 2015 Gorkha earthquake: A large event illuminating the Main Himalayan Thrust fault

    NASA Astrophysics Data System (ADS)

    Duputel, Zacharie; Vergne, Jérôme; Rivera, Luis; Wittlinger, Gérard; Farra, Véronique; Hetényi, György

    2016-03-01

    The 2015 Gorkha earthquake sequence provides an outstanding opportunity to better characterize the geometry of the Main Himalayan Thrust (MHT). To overcome limitations due to unaccounted lateral heterogeneities, we perform Centroid Moment Tensor inversions in a 3-D Earth model for the main shock and largest aftershocks. In parallel, we recompute S-to-P and P-to-S receiver functions from the Hi-CLIMB data set. Inverted centroid locations fall within a low-velocity zone at 10-15 km depth and corresponding to the subhorizontal portion of the MHT that ruptured during the Gorkha earthquake. North of the main shock hypocenter, receiver functions indicate a north dipping feature that likely corresponds to the midcrustal ramp connecting the flat portion to the deep part of the MHT. Our analysis of the main shock indicates that long-period energy emanated updip of high-frequency radiation sources previously inferred. This frequency-dependent rupture process might be explained by different factors such as fault geometry and the presence of fluids.

  10. Teleseismic body waves from dynamically rupturing shallow thrust faults: Are they opaque for surface-reflected phases?

    USGS Publications Warehouse

    Smith, D.E.; Aagaard, B.T.; Heaton, T.H.

    2005-01-01

    We investigate whether a shallow-dipping thrust fault is prone to waveslip interactions via surface-reflected waves affecting the dynamic slip. If so, can these interactions create faults that are opaque to radiated energy? Furthermore, in this case of a shallow-dipping thrust fault, can incorrectly assuming a transparent fault while using dislocation theory lead to underestimates of seismic moment? Slip time histories are generated in three-dimensional dynamic rupture simulations while allowing for varying degrees of wave-slip interaction controlled by fault-friction models. Based on the slip time histories, P and SH seismograms are calculated for stations at teleseismic distances. The overburdening pressure caused by gravity eliminates mode I opening except at the tip of the fault near the surface; hence, mode I opening has no effect on the teleseismic signal. Normalizing by a Haskell-like traditional kinematic rupture, we find teleseismic peak-to-peak displacement amplitudes are approximately 1.0 for both P and SH waves, except for the unrealistic case of zero sliding friction. Zero sliding friction has peak-to-peak amplitudes of 1.6 for P and 2.0 for SH waves; the fault slip oscillates about its equilibrium value, resulting in a large nonzero (0.08 Hz) spectral peak not seen in other ruptures. These results indicate wave-slip interactions associated with surface-reflected phases in real earthquakes should have little to no effect on teleseismic motions. Thus, Haskell-like kinematic dislocation theory (transparent fault conditions) can be safety used to simulate teleseismic waveforms in the Earth.

  11. Nanograins, roughness and organic matters on a glossy fault surface with striation - An example from an exhumed subduction megasplay fault, the Nobeoka Thrust, Japan

    NASA Astrophysics Data System (ADS)

    Kitamura, Y.; Kimura, G.; Kameda, J.; Yamaguchi, A.; Kouketsu, Y.; Hamahashi, M.; Fukuchi, R.; Hamada, Y.; Fujimoto, K.; Hashimoto, Y.; Saito, S.; Kawasaki, R.; Koge, H.; Shimizu, M.; Fujii, T.

    2013-12-01

    Friction on the fault plane controls the behavior of faulting during seismic slip. Recent studies suggest that the frictional process on faults shows scale dependency [e.g. Li and Kim, 2008]. It is critically important to observe structures on the fault planes in various scales, especially in smaller scale in the sub-micron range. The roughness on fault planes has long been thought to hold fractal property [e.g. Candela et al., 2009], however, a recent work observed that a mirror fault plane, when examined up to nanometer-scale, does not obey self-affine roughness [Siman-Tov et al., 2013]. Their observation revealed that the fault surface is coated by grains of several ten nanometers in diameter. In this abstract, we show a detailed observation of a glossy fault plane with striations sampled from drilled core of the Nobeoka Thrust taken by a scientific drilling project, the Nobeoka Thrust Drilling Project (NOBELL). The NOBELL recovered cores with a total depth of 255 m penetrating the Nobeoka Thrust at 41 m below ground surface. The visual observation of the cores and the wireline log of the borehole clearly differentiate the hanging wall and the footwall [Hamahashi et al., in revision]. In this study, we analyzed a fault plane just below the Nobeoka Thrust main fault core on which gloss and striation develop using an integrated apparatus of Confocal Laser Scanning Microscope (CLSM) and Atomic Force Microscope (AFM) (SHIMADZU SFT-3500/4500). We also analyzed the sample surface applying Raman spectroscopy. The sample surface was imaged by the CLSM and AFM in various scale and its topography was obtained. The bright and dark colored area image on the sample surface was mapped using CLSM. The high surface topography corresponds to the dark colored area and the low land to the bright area. The X-Z measurement by CLSM revealed an interface of around 1 micrometer below the surface. The interference fringe was observed at the rim of dark area. These facts suggest that the

  12. Quaternary evolution of mechanical fault-linkage between the North Tehran Thrust (NTT) and Mosha Fasham Fault (MFF), Alborz Mountains, Iran

    NASA Astrophysics Data System (ADS)

    Landgraf, A.; Ballato, P.; Strecker, M. R.; Friedrich, A.; Tabatabaei, S. H.

    2006-12-01

    The kinematic relationship between the neighboring MFF and the NTT is an open question in the fault interaction during the late Cenozoic evolution of the Alborz Mountains. Despite numerous Quaternary faults and their importance for hazard mitigation, the interaction and linkage between these structures are not understood. The ENE-striking NTT is a frontal thrust that delimits the Alborz Mountains to the south, but no instrumentally recorded earthquakes are known here. The E-striking MFF, with a double-bend toward a NW- strike in its central part, is located within the Alborz Mountains. Sinistral motion along its eastern part is corroborated by microseismicity and fault kinematic data, documenting ongoing transtension. Four possible kinematic scenarios may be inferred for both fault systems: (1) each is a separate entity without interaction, (2) progressive eastward propagation of the NTT and linkage with the MFF, resulting in a "master" fault, (3) a "triple junction" with three interacting blocks or (4) a transpressional duplex involving the NW- prolongation of the NTT as frontal, and the ENE-striking NTT segments as lateral ramps between the E-striking east-central and westernmost MFF. The eastern MFF is characterized by sinistral offsets and stream deflections. However, these phenomena are absent in the central-western fault branch. Structural observations along the eastern, slightly north-convex NTT imply dip-slip faulting, where Eocene volcanic units were thrust onto Plio-Pleistocene conglomerates. In addition, fluvial knickpoints, narrow bedrock channels, fluvial terrace remnants, and wineglass-shaped canyons in the hanging wall suggest Quaternary uplift along this fault. However, there must have been a Pleistocene kinematic change along the NTT, involving sinistral reactivation as shown by 80m stream-offsets and horizontal striations on dip-slip faults. NE-trending ravines are sigmoidally shaped, suggesting conjugate shearing by shortening oblique to the

  13. Thrust-induced collapse of mountains-an example from the "Big Bend" region of the San Andreas Fault, western transverse ranges, California

    USGS Publications Warehouse

    Kellogg, Karl S.

    2005-01-01

    Mount Pinos and Frazier Mountain are two prominent mountains just south of the San Andreas fault in the western Transverse Ranges of southern California, a region that has undergone rapid Quaternary contraction and uplift. Both mountains are underlain, at least in part, by thrusts that place granitic and gneissic rocks over sedimentary rocks as young as Pliocene. Broad profiles and nearly flat summits of each mountain have previously been interpreted as relicts of a raised erosion surface. However, several features bring this interpretation into question. First, lag or stream gravels do not mantle the summit surfaces. Second, extensive landslide deposits, mostly pre?Holocene and deeply incised, mantle the flanks of both mountains. Third, a pervasive fracture and crushed?rock network pervades the crystalline rocks underlying both mountains. The orientation of the fractures, prominent in roadcuts on Mount Pinos, is essentially random. 'Hill?and?saddle' morphology characterizes ridges radiating from the summits, especially on Mount Pinos; outcrops are sparse on the hills and are nonexistent in the saddles, suggesting fractures are concentrated in the saddles. Latest movement on the thrusts underlying the two mountain massifs is probably early Quaternary, during which the mountains were uplifted to considerably higher (although unknown) elevations than at present. A model proposes that during thrusting, ground accelerations in the hanging wall, particularly near thrust tips, were high enough to pervasively fracture the hanging?wall rocks, thereby weakening them and producing essentially an assemblage of loose blocks. Movement over flexures in the fault surface accentuated fracturing. The lowered shear stresses necessary for failure, coupled with deep dissection and ongoing seismic activity, reduced gravitational potential by spreading the mountain massifs, triggering flanking landslides and producing broad, flat?topped mountains. This study developed from mapping in

  14. Thrust faults of southern Diamond Mountains, central Nevada: Implications for hydrocarbons in Diamond Valley and at Yucca Mountain

    SciTech Connect

    French, D.E.

    1993-04-01

    Overmature Mississippian hydrocarbon source rocks in the southern Diamond Mountains have been interpreted to be a klippe overlying less mature source rocks and represented as an analogy to similar conditions near Yucca Mountain (Chamberlain, 1991). Geologic evidence indicates an alternative interpretation. Paleogeologic mapping indicates the presence of a thrust fault, referred to here as the Moritz Nager Thrust Fault, with Devonian rocks emplaced over Permian to Mississippian strata folded into an upright to overturned syncline, and that the overmature rocks of the Diamond Mountains are in the footwall of this thrust. The upper plate has been eroded from most of the Diamond Mountains but remnants are present at the head of Moritz Nager Canyon and at Sentinel Mountain. Devonian rocks of the upper plate comprised the earliest landslide megabreccia. Later, megabreccias of Pennsylvanian and Permian rocks of the overturned syncline of the lower plate were deposited. By this interpretation the maturity of lower-plate source rocks in the southern Diamond Mountains, which have been increased by tectonic burial, is not indicative of conditions in Diamond Valley, adjacent to the west, where upper-plate source rocks might be present in generating conditions. The interpretation that overmature source rocks of the Diamond Mountains are in a lower plate rather than in a klippe means that this area is an inappropriate model for the Eleana Range near Yucca Mountain.

  15. Advanced Active-Magnetic-Bearing Thrust-Measurement System

    NASA Technical Reports Server (NTRS)

    Imlach, Joseph; Kasarda, Mary; Blumber, Eric

    2008-01-01

    An advanced thrust-measurement system utilizes active magnetic bearings to both (1) levitate a floating frame in all six degrees of freedom and (2) measure the levitation forces between the floating frame and a grounded frame. This system was developed for original use in measuring the thrust exerted by a rocket engine mounted on the floating frame, but can just as well be used in other force-measurement applications. This system offers several advantages over prior thrust-measurement systems based on mechanical support by flexures and/or load cells: The system includes multiple active magnetic bearings for each degree of freedom, so that by selective use of one, some, or all of these bearings, it is possible to test a given article over a wide force range in the same fixture, eliminating the need to transfer the article to different test fixtures to obtain the benefit of full-scale accuracy of different force-measurement devices for different force ranges. Like other active magnetic bearings, the active magnetic bearings of this system include closed-loop control subsystems, through which the stiffness and damping characteristics of the magnetic bearings can be modified electronically. The design of the system minimizes or eliminates cross-axis force-measurement errors. The active magnetic bearings are configured to provide support against movement along all three orthogonal Cartesian axes, and such that the support along a given axis does not produce force along any other axis. Moreover, by eliminating the need for such mechanical connections as flexures used in prior thrust-measurement systems, magnetic levitation of the floating frame eliminates what would otherwise be major sources of cross-axis forces and the associated measurement errors. Overall, relative to prior mechanical-support thrust-measurement systems, this system offers greater versatility for adaptation to a variety of test conditions and requirements. The basic idea of most prior active

  16. Project DAFNE - Drilling Active Faults in Northern Europe

    NASA Astrophysics Data System (ADS)

    Kukkonen, I. T.; Ask, M. S. V.; Olesen, O.

    2012-04-01

    We are currently developing a new ICDP project 'Drillling Active Faults in Northern Europe' (DAFNE) which aims at investigating, via scientific drilling, the tectonic and structural characteristics of postglacial (PG) faults in northern Fennoscandia, including their hydrogeology and associated deep biosphere [1, 2]. During the last stages of the Weichselian glaciation (ca. 9,000 - 15,000 years B.P.), reduced ice load and glacially affected stress field resulted in active faulting in Fennoscandia with fault scarps up to 160 km long and 30 m high. These postglacial (PG) faults are usually SE dipping, SW-NE oriented thrusts, and represent reactivated, pre-existing crustal discontinuities. Postglacial faulting indicates that the glacio-isostatic compensation is not only a gradual viscoelastic phenomenon, but includes also unexpected violent earthquakes, suggestively larger than other known earthquakes in stable continental regions. The research is anticipated to advance science in neotectonics, hydrogeology and deep biosphere studies, and provide important information for nuclear waste and CO2 disposal, petroleum exploration on the Norwegian continental shelf and studies of mineral resources in PG fault areas. We expect that multidisciplinary research applying shallow and deep drilling of postglacial faults would provide significant scientific results through generating new data and models, namely: (1) Understanding PG fault genesis and controls of their locations; (2) Deep structure and depth extent of PG faults; (3) Textural, mineralogical and physical alteration of rocks in the PG faults; (4) State of stress and estimates of paleostress of PG faults; (5) Hydrogeology, hydrochemistry and hydraulic properties of PG faults; (6) Dating of tectonic reactivation(s) and temporal evolution of tectonic systems hosting PG faults; (7) Existence/non-existence of deep biosphere in PG faults; (8) Data useful for planning radioactive waste disposal in crystalline bedrock; (9) Data

  17. Principal fault zone width and permeability of the active Neodani fault, Nobi fault system, Southwest Japan

    NASA Astrophysics Data System (ADS)

    Tsutsumi, A.; Nishino, S.; Mizoguchi, K.; Hirose, T.; Uehara, S.; Sato, K.; Tanikawa, W.; Shimamoto, T.

    2004-02-01

    The internal structure and permeability of the Neodani fault, which was last activated at the time of the 1891 Nobi earthquake (M8.0), were examined through field survey and experiments. A new exposure of the fault at a road construction site reveals a highly localized feature of the past fault deformation within a narrow fault core zone. The fault of the area consists of three zone units towards the fault core: (a) protolith rocks; (b) 15 to 30 m of fault breccia, and (c) 200 mm green to black fault gouge. Within the fault breccia zone, cataclastic foliation oblique to the fault has developed in a fine-grained 2-m-wide zone adjacent to the fault. Foliation is defined by subparallel alignment of intact lozenge shaped clasts, or by elongated aggregates of fine-grained chert fragments. The mean angle of 20°, between the foliation and the fault plane suggests that the foliated breccia accommodated a shear strain of γ<5 assuming simple shear for the rotation of the cataclastic foliation. Previous trench surveys have revealed that the fault has undergone at least 70 m of fault displacement within the last 20,000 years in this locality. The observed fault geometry suggests that past fault displacements have been localized into the 200-mm-wide gouge zone. Gas permeability analysis of the gouges gives low values of the order of 10 -20 m 2. Water permeability as low as 10 -20 m 2 is therefore expected for the fault gouge zone, which is two orders of magnitude lower than the critical permeability suggested for a fault to cause thermal pressurization during a fault slip.

  18. Updating the Displacement-Length Relationship of Thrust Faults Associated with Lobate Scarps on the Moon: Preliminary Results

    NASA Astrophysics Data System (ADS)

    Banks, M. E.; Watters, T. R.; Robinson, M. S.; Williams, N. R.

    2012-12-01

    Lobate scarps on the Moon are relatively small-scale tectonic landforms observed in mare basalts and more commonly, highland material. These thrust fault scarps are the most common tectonic landform on the lunar farside. Prior to Lunar Reconnaissance Orbiter Camera (LROC) observations, lobate scarps were only detected in equatorial regions because of limited Apollo Panoramic Camera and high resolution Lunar Orbiter coverage with optimum lighting geometry for identifying low-relief features. Thus, our previous understanding of lobate scarp morphometry was based on measurements of a limited number of low-latitude scarps. LROC images combined with Lunar Orbiter Laser Altimeter (LOLA) ranging enable detection and detailed morphometric analysis of lobate scarps at all latitudes; previously undetected scarps have been identified in more than 150 different locations, and are globally distributed. Measurements of the maximum relief, h, of lobate scarps provide a means to estimate the displacement-length (D-L) relation of the thrust faults. Measurements of h are used to estimate displacement, D, by assuming it is a function of the relief of the lobate scarp and the dip of the surface-breaking fault-plane (θ) such that D = h/sin θ (assuming h is a function of the total slip on the thrust fault). Maximum displacement on a fault scales with the planimetric length, L, of the fault. Populations of terrestrial faults formed in uniform rock types indicate a linear relationship such that D = γL, where γ is a constant determined by tectonic setting and rock type. If the D-L relationship of a fault population is known, the strain can be calculated using only fault lengths. In this ongoing study, LROC stereo-derived digital terrain models (DTMs) and where possible LOLA altimetry, are used to accurately determine the maximum relief of lobate scarps. So far we have measured the maximum relief for 11 scarp segments resulting in ranges of ~8 to 164 m for maximum relief, ~0.8 to 14 km

  19. Not so simple "simply-folded Zagros": The role of pre-collisional extensional faulting, salt tectonics and multi-stage thrusting in the Sarvestan transfer zone (Fars, Iran)

    NASA Astrophysics Data System (ADS)

    Carminati, Eugenio; Aldega, Luca; Bigi, Sabina; Minelli, Giorgio; Shaban, Ali

    2016-03-01

    The Sarvestan plain is bounded by highly elevated anticlines associated with thrusts or transpressional faults and hosts the NNW-SSE Sarvestan transfer zone. Surface and subsurface geological data, and 22 seismic lines allowed us to reconstruct the 3D geometry of the area. Mixed layer illite-smectite and 1D burial and thermal modelling were used to constrain the complex geological evolution of the Sarvestan plain where inherited structures strongly controlled the geometry of syn- to post-collisional contractional structures. Paleozoic-Mesozoic rifting related extension generated E-W and NNW-SSE normal fault systems. Such faults were associated with changes in the thickness of the sedimentary cover. Lateral facies changes were later induced by the Cretaceous obduction of ophiolites, cropping out some tens of km north of the study area. During the Miocene the footwall and the hanging wall of the Sarvestan Fault had different thermal evolution. This is tentatively explained by flow of Cambrian salt from the plain area towards the hanging wall of the Sarvestan Fault, associated with salt diapirism during Lower-Middle Miocene time. Salt tectonics is invoked also to explain, at least in part, the development of the overturned anticline in the hanging wall of the Sarvestan Fault. An early phase of contractional deformation occurred in the Middle Miocene (since 15 My, i.e., after the deposition of the Agha Jari Fm) generating the E-W oriented folds buried below the plain, likely inverting inherited normal faults. The erosion of these structures was followed by the deposition of the Bakhtiari Fm conglomerates in Middle-Late Miocene times. A later phase of contractional tectonics generated the thrust faults and the anticlines bounding the Sarvestan plain some 6-5 My ago. The Sarvestan dextral transpressional fault, that likely acted as a strongly oblique ramp of the Maharlu thrust, mainly structured in this period, although its activity may have continued until present.

  20. Geomorphic features of active faults around the Kathmandu Valley, Nepal, and no evidence of surface rupture associated with the 2015 Gorkha earthquake along the faults

    NASA Astrophysics Data System (ADS)

    Kumahara, Yasuhiro; Chamlagain, Deepak; Upreti, Bishal Nath

    2016-04-01

    The M7.8 April 25, 2015, Gorkha earthquake in Nepal was produced by a slip on the low-angle Main Himalayan Thrust, a décollement below the Himalaya that emerges at the surface in the south as the Himalayan Frontal Thrust (HFT). The analysis of the SAR interferograms led to the interpretations that the event was a blind thrust and did not produce surface ruptures associated with the seismogenic fault. We conducted a quick field survey along four active faults near the epicentral area around the Kathmandu Valley (the Jhiku Khola fault, Chitlang fault, Kulekhani fault, Malagiri fault and Kolphu Khola fault) from July 18-22, 2015. Those faults are located in the Lesser Himalaya on the hanging side of the HFT. Based on our field survey carried out in the area where most typical tectonic landforms are developed, we confirmed with local inhabitants the lack of any new surface ruptures along these faults. Our observations along the Jhiku Khola fault showed that the fault had some definite activities during the Holocene times. Though in the past it was recognized as a low-activity thrust fault, our present survey has revealed that it has been active with a predominantly right-lateral strike-slip with thrust component. A stream dissecting a talus surface shows approximately 7-m right-lateral offset, and a charcoal sample collected from the upper part of the talus deposit yielded an age of 870 ± 30 y.B.P, implying that the talus surface formed close to 870 y.B.P. Accordingly, a single or multiple events of the fault must have occurred during the last 900 years, and the slip rate we estimate roughly is around 8 mm/year. The fault may play a role to recent right-lateral strike-slip tectonic zone across the Himalayan range. Since none of the above faults showed any relationship corresponding to the April 25 Gorkha earthquake, it is possibility that a potential risk of occurrence of large earthquakes does exist close to the Kathmandu Valley due to movements of these active

  1. Salted matters: modifying gelatine rheology for subduction thrust fault seismicity models

    NASA Astrophysics Data System (ADS)

    Brizzi, Silvia; Funiciello, Francesca; Corbi, Fabio; Di Giuseppe, Erika; Mojoli, Giorgio

    2016-04-01

    Most of the world's greatest earthquakes (Mw > 8.5, usually known as mega-earthquakes) occur at shallow depths along the subduction thrust fault (STF), i.e., the frictional interface between the subducting and overriding plates. The contribution of each subduction zone to the globally released seismic moment is not homogeneous, as well as the maximum Mw recorded in the instrumental and historical catalogues. To contribute to the unravelling of the seismic cycle along the STF, we used analogue models. Viscoelastic laboratory experiments realised with type A gelatine 2.5 wt% at 10 °C (Corbi et al., 2013) successfully simulate the seismic cycle along the STF, providing dynamic similarities with earthquakes in nature. However, analogue earthquakes are still not perfectly comparable to the natural prototype. In this work, we try to improve STF seismicity models by modifying the rheological behaviour of gelatine with the addition of NaCl. After testing salted gelatine rheology as a function of increasing concentration of NaCl, we selected 20 wt% NaCl gelatine, as this NaCl concentration provides a quasi-viscoelastic lithospheric analogue. Subduction interplate seismicity models were performed using both pure and salted gelatine to highlight the strengths and advantages this new material can provide for simulating the seismic cycle along the STF. We analysed analogue earthquakes Mw, recurrence time and rupture duration, which at first-order characterise the seismogenic behaviour of the STF. Results show that the experimental source parameters cover a wider range of values than obtained with pure gelatine, which is more compatible to the high variability globally observed. In particular, salted gelatine allows to simulate also smaller seismic events, giving the opportunity to apply the G-R law to the experimental seismicity of STF. Recurrence time and rupture duration are also characterised by an increased range of values when salted gelatine is used as analogue material

  2. Kinematics and surface fracture pattern of the Anaran basement fault zone in NW of the Zagros fold-thrust belt

    NASA Astrophysics Data System (ADS)

    Joudaki, M.; Farzipour-Saein, A.; Nilfouroushan, F.

    2016-04-01

    The preexisting north-south trending basement faults and their reactivation played an important role during the evolution of the Zagros fold-thrust belt. The Anaran Basement Fault (ABF) in the Lurestan region, NW of the Zagros, has been considered as a N-S trending basement lineament, although its surface structural expression is still debated. In this study, we use satellite images and field observations to identify and analyze the fractures in the sedimentary cover above the ABF. Fracture analysis demonstrates that approaching the ABF, the fracture pattern changes. The fractures association with reactivation of the deep-seated preexisting ABF can be categorized in four sets based on their directions. The mean direction for maximum compressional stress is different between the fault- and fold-related fractures within and around the ABF shear zone. We estimated an orientation of N30° ± 5° for the fault-related fractures and N45° ± 5° for the fold-related fracture sets outside of the ABF shear zone. This difference suggests that the fold-related and fault-related fracture sets have been formed in different two stages of deformation throughout the area. The axial traces of some folds, especially the Anaran anticline, demonstrate a right-lateral offset along the ABF, such that, in central part of the Anaran anticline, the fold axis of this anticline is changed from its original NW-SE trend to approximately north-south trend of the ABF.

  3. Medium-frequency impulsive-thrust-activated liquid hydrogen reorientation with Geyser

    NASA Technical Reports Server (NTRS)

    Hung, R. J.; Shyu, K. L.

    1992-01-01

    Efficient technique are studied for accomplishing propellant resettling through the minimization of propellant usage through impulsive thrust. A comparison between the use of constant-thrust and impulsive-thrust accelerations for the activation of propellant resettlement shows that impulsive thrust is superior to constant thrust for liquid reorientation in a reduced-gravity environment. This study shows that when impulsive thrust with 0.1-1.0-, and 10-Hz frequencies for liquid-fill levels in the range between 30-80 percent is considered, the selection of 1.0-Hz-frequency impulsive thrust over the other frequency ranges of impulsive thrust is the optimum. Characteristics of the slosh waves excited during the course of 1.0-Hz-frequency impulsive-thrust liquid reorientation were also analyzed.

  4. The property of fault zone and fault activity of Shionohira Fault, Fukushima, Japan

    NASA Astrophysics Data System (ADS)

    Seshimo, K.; Aoki, K.; Tanaka, Y.; Niwa, M.; Kametaka, M.; Sakai, T.; Tanaka, Y.

    2015-12-01

    The April 11, 2011 Fukushima-ken Hamadori Earthquake (hereafter the 4.11 earthquake) formed co-seismic surface ruptures trending in the NNW-SSE direction in Iwaki City, Fukushima Prefecture, which were newly named as the Shionohira Fault by Ishiyama et al. (2011). This earthquake was characterized by a westward dipping normal slip faulting, with a maximum displacement of about 2 m (e.g., Kurosawa et al., 2012). To the south of the area, the same trending lineaments were recognized to exist even though no surface ruptures occurred by the earthquake. In an attempt to elucidate the differences of active and non-active segments of the fault, this report discusses the results of observation of fault outcrops along the Shionohira Fault as well as the Coulomb stress calculations. Only a few outcrops have basement rocks of both the hanging-wall and foot-wall of the fault plane. Three of these outcrops (Kyodo-gawa, Shionohira and Betto) were selected for investigation. In addition, a fault outcrop (Nameishi-minami) located about 300 m south of the southern tip of the surface ruptures was investigated. The authors carried out observations of outcrops, polished slabs and thin sections, and performed X-ray diffraction (XRD) to fault materials. As a result, the fault zones originating from schists were investigated at Kyodo-gawa and Betto. A thick fault gouge was cut by a fault plane of the 4.11 earthquake in each outcrop. The fault materials originating from schists were fault bounded with (possibly Neogene) weakly deformed sandstone at Shionohira. A thin fault gouge was found along the fault plane of 4.11 earthquake. A small-scale fault zone with thin fault gouge was observed in Nameishi-minami. According to XRD analysis, smectite was detected in the gouges from Kyodo-gawa, Shionohira and Betto, while not in the gouge from Nameishi-minami.

  5. The Beaufort Sea fold-and-thrust belt, northwestern Canada: Implications for thrust-belt evolution

    SciTech Connect

    Root, K.G. )

    1991-06-01

    The northeasternmost segment of the Cordilleran thrust belt of western North American underlies the Beaufort Sea continental margin. Folds and associated northesat-directed thrusts in this region formed synchronously with Tertiary sedimentation. As a result, the times of fold development can be determined from reflection seismic data by analyzing lateral thickness changes in stratigraphic sequences of known ages, and onlap and truncation relationships at unconformities. Thrust faulting occurred throughout the late Paleocene-Pliocene. The abundant temporal data indicate the deformational seuqence was significantly differet from the simple, steplike, foreland-propagating model formulated in other less well-dated thrust belts. Many thrusts were active simultaneously, especially during the late Eocnee, when the region of active thrusting had an across-strike width of greater than 200 km. This observation calls into question the popular concept that only one thrust moves at a time as a thrust belt develops. The thrust belt propagated along, as well as across, strike. During the late Paleocene-middle Eocene, the area of active thrusting was bounded on the southeast by poorly imaged zones of right-lateral strike-slip faults that apparently are the northern offshore continuation of the Rapid fault array. The change in the age of thrusting along strike results in no obvious geometrical anomalies and could not be deduced without timing information. This has an important implication: temporal data cannot necessarily be projected along strike in a thrust belt.

  6. Seismic sources and stress transfer interaction among axial normal faults and external thrust fronts in the Northern Apennines (Italy): A working hypothesis based on the 1916-1920 time-space cluster of earthquakes

    NASA Astrophysics Data System (ADS)

    Bonini, Marco; Corti, Giacomo; Donne, Dario Delle; Sani, Federico; Piccardi, Luigi; Vannucci, Gianfranco; Genco, Riccardo; Martelli, Luca; Ripepe, Maurizio

    2016-06-01

    In this study we analyse the main potential seismic sources in some axial and frontal sectors of the Northern Apennines, in Italy. This region was hit by a peculiar series of earthquakes that started in 1916 on the external thrust fronts near Rimini. Later, in 1917-1921, seismicity (up to Mw ≈ 6.5) shifted into the axial zone and clearly migrated north-westward, along the belt of active normal faults. The collection of fault-slip data focused on the active normal faults potentially involved in this earthquake series. The acquired data allowed us to better characterize the geometry and kinematics of the faults. In a few instances, the installation of local seismic networks during recent seismic sequences allowed the identification of the causative faults that are hinted to be also responsible for past earthquakes, particularly in the Romagna region and north-eastern Mugello. The Coulomb stress changes produced by the historical earthquakes generally brought closer to failure all the faults that supposedly caused the main seismic events of 1916-1921. However, the stress change magnitude is generally small and thus the static stress interaction among the main seismic sources is not supported by a significant seismic correlation. Significant stress change loading may be instead inferred for the triggering of a number of seismic events on neighbouring normal faults by the Garfagnana 1920 earthquake. In addition, the computation of the seismic stress changes suggests that seismic events with magnitude ≥ 6 may transmit stresses from the axial normal faults to specific external thrusts and vice versa. It is possible that a correlation may be made between loading applied by the major 1917-1920 extensional ruptures and the increased seismicity on the distal external thrusts.

  7. Predicting pore pressure in active fold-thrust systems: An empirical model for the deepwater Sabah foldbelt

    NASA Astrophysics Data System (ADS)

    Couzens-Schultz, Brent A.; Azbel, Konstantin

    2014-12-01

    Measurements related to mudrock (shale and siltstone) porosity such as acoustic velocity, density or electrical resistivity, have traditionally been used to predict pore pressures in extensional stress settings. The underlying assumption is that burial and vertical effective stress (VES), which is the overburden minus the pore pressure, controls the compaction of these rocks through porosity loss. The dataset presented here compares VES and acoustic velocity of similar composition mudrocks in both an extensional and a compressional stress setting. In the extensional stress environment, the mudrocks follow a typical compaction trend with a porosity loss and increase in acoustic velocity that can be related to VES. In an active fold-thrust belt, the compressive stresses further reduce the porosity and increase the acoustic velocity of the mudrocks. First a layer-parallel shortening compacts sediments beyond what is observed for the VES. This additional compaction is further enhanced near thrust faults and in anticlinal forelimbs, presumably due to additional shear stress in these areas. The mudrocks located in folds that are buried by additional sedimentation do not compact again until the tectonic compaction is overridden by enough new burial. After that, the mudrocks follow the observed extensional setting compaction trend. In the fold-thrust belt, the observed reduction in porosity by stresses other than burial leads to an under-prediction of pore pressure using traditional methods. To account for this, we present a correction that can be applied to the acoustic velocity (or porosity) using two parameters: (a) proximity to thrust faults and anticlinal forelimbs and (b) the amount of burial after fold formation. With these corrections, the extensional velocity-VES compaction trend can be used to accurately predict pore pressure within the active fold-thrust belt. The correction is calibrated with well data and is empirical. None-the-less, it is a first step toward

  8. Multidisciplinary approach to constrain kinematics of fault zones at shallow depths: a case study from the Cameros-Demanda thrust (North Spain)

    NASA Astrophysics Data System (ADS)

    Casas-Sainz, A. M.; Román-Berdiel, T.; Oliva-Urcia, B.; García-Lasanta, C.; Villalaín, J. J.; Aldega, L.; Corrado, S.; Caricchi, C.; Invernizzi, C.; Osácar, M. C.

    2016-06-01

    Thrusting at shallow depths often precludes analysis by means of structural indicators effective in other geological contexts (e.g., mylonites, sheath folds, shear bands). In this paper, a combination of techniques (including structural analysis, magnetic methods, as anisotropy of magnetic susceptibility and paleomagnetism, and paleothermometry) is used to define thrusting conditions, deformation, and transport directions in the Cameros-Demanda thrust (North Spain). Three outcrops were analyzed along this intraplate, large-scale major structure having 150 km of outcropping length, 30 km of maximum horizontal displacement, and 5 km of vertical throw. Results obtained by means of the different techniques are compared with data derived from cross sections and stratigraphic analysis. Mixed-layer illite-smectite and vitrinite reflectance indicating deep diagenetic conditions and mature stage of hydrocarbon generation suggests shallow depths during deformation, thus confirming that the protolith for most of the fault rocks is the footwall of the main thrust. Kinematic indicators (foliation, S/C structures, and slickenside striations) indicate altogether a dominant NNW movement of the hanging wall in the western zone and NE in the eastern zone of the thrust, thus implying strain partitioning between different branches of the main thrust. The study of AMS in fault rocks (nearly 400 samples of fault gouge, breccia, and microbreccia) indicates that the strike of magnetic foliation is oblique to the transport direction and that the magnetic lineation parallelizes the projection of the transport direction onto the k max/k int plane in sites with strong shear deformation. Paleomagnetism applied to fault rocks indicates the existence of remagnetizations linked to thrusting, in spite of the shallow depth for deformation, and a strong deformation or scattering of the magnetic remanence vectors in the fault zone. The application of the described techniques and consistency of

  9. Earthquake-by-earthquake fold growth above the Puente Hills blind thrust fault, Los Angeles, California: Implications for fold kinematics and seismic hazard

    USGS Publications Warehouse

    Leon, L.A.; Christofferson, S.A.; Dolan, J.F.; Shaw, J.H.; Pratt, T.L.

    2007-01-01

    Boreholes and high-resolution seismic reflection data collected across the forelimb growth triangle above the central segment of the Puente Hills thrust fault (PHT) beneath Los Angeles, California, provide a detailed record of incremental fold growth during large earthquakes on this major blind thrust fault. These data document fold growth within a discrete kink band that narrows upward from ???460 m at the base of the Quaternary section (200-250 m depth) to 82% at 250 m depth) folding and uplift occur within discrete kink bands, thereby enabling us to develop a paleoseismic history of the underlying blind thrust fault. The borehole data reveal that the youngest part of the growth triangle in the uppermost 20 m comprises three stratigraphically discrete growth intervals marked by southward thickening sedimentary strata that are separated by intervals in which sediments do not change thickness across the site. We interpret the intervals of growth as occurring after the formation of now-buried paleofold scarps during three large PHT earthquakes in the past 8 kyr. The intervening intervals of no growth record periods of structural quiescence and deposition at the regional, near-horizontal stream gradient at the study site. Minimum uplift in each of the scarp-forming events, which occurred at 0.2-2.2 ka (event Y), 3.0-6.3 ka (event X), and 6.6-8.1 ka (event W), ranged from ???1.1 to ???1.6 m, indicating minimum thrust displacements of ???2.5 to 4.5 m. Such large displacements are consistent with the occurrence of large-magnitude earthquakes (Mw > 7). Cumulative, minimum uplift in the past three events was 3.3 to 4.7 m, suggesting cumulative thrust displacement of ???7 to 10.5 m. These values yield a minimum Holocene slip rate for the PHT of ???0.9 to 1.6 mm/yr. The borehole and seismic reflection data demonstrate that dip within the kink band is acquired incrementally, such that older strata that have been deformed by more earthquakes dip more steeply than younger

  10. Field study and three-dimensional reconstruction of thrusts and strike-slip faults in the Central Andes: implications for deep-seated geothermal circulation and ore deposits exploration

    NASA Astrophysics Data System (ADS)

    Norini, Gianluca; Groppelli, Gianluca; Giordano, Guido; Baez, Walter; Becchio, Raul; Viramonte, Jose; Arnosio, Marcelo

    2014-05-01

    The Puna plateau (NW Argentina), located in the back-arc of the Central Andes, is a plateau characterized by both orogen-parallel and orogen-oblique deformation styles, extensive magmatic and geothermal activity, and the broad occurrence of igneous and hydrothermal ore-forming minerals. In this area, like in other convergent margins, the behaviour of the magma-tectonics interplay can affect the circulation of hydrothermal fluids, so that the full comprehension of the tectonic control on the magmas and fluids paths in the continental crust is crucial to plan the geothermal and ore exploration. In this study, we present a structural analysis of the back-arc portion of the orogen-oblique Calama-Olacapato-El Toro fault system and the surrounding orogen-parallel thrust faults in the central-eastern Puna Plateau, comprising the Cerro Tuzgle-Tocomar geothermal volcanic area, with high geothermal potential, and silicic calderas and domes associated with epithermal ore deposits. We also focused on the tectonic and volcanotectonic structures of the Chimpa and Tuzgle stratovolcanoes, two of the most important polygenetic volcanic centres of the plateau. Morphostructural analysis and field mapping reveal the geometry, kinematics and dynamics of the tectonic structures of the studied area. These data and the available stratigraphic and geophysical data have been integrated with the software MOVE and PETREL in a three-dimensional reconstruction of the main fault planes, showing their attitude and intersections at depth. As a result of our study, we show that despite different geometry and kinematics of the Calama-Olacapato-El Toro fault system and the thrust faults, they formed and evolved under the same progressive evolving dynamic state, forming a single tectonic system and accommodating crustal shortening of a thickened crust. In this frame, the crust underwent simultaneous deformation along both the low-angle thrust faults and the vertical transcurrent strike-slip faults

  11. Kinematic significance of L tectonites in the footwall of a major terrane-bounding thrust fault, Klamath Mountains, California, USA

    NASA Astrophysics Data System (ADS)

    Sullivan, W. A.

    2009-11-01

    Detailed geologic mapping, cross-section reconstructions, strain analyses, and kinematic analyses, enable the reconstruction of a ˜one-kilometer-wide domain of L tectonites in the east-west-striking, subhorizontal to gently south-dipping Pigeon Point high-strain zone (PPHSZ) associated with a major thrust fault separating oceanic- and arc-affinity terranes in the Klamath Mountains, California. L tectonites are associated with: (1) a convex-upward warp of the upper high-strain-zone boundary, (2) a transition from mafic metavolcaniclastic rocks to micaceous quartzites, (3) folds subparallel with mineral lineations, (4) emplacement of synkinematic ultramafic/mafic intrusive bodies, and (5) a local temperature increase from greenschist- to amphibolite-facies conditions. Pure-shear-dominated deformation accommodated zone-normal shortening and transport-parallel elongation coupled with subordinate top-to-the-west-directed, thrust-style simple shear. L tectonite formation was controlled by the shape of the high-strain-zone boundary driving lateral flow into the apex of the lens-shaped zone in response to a favorable kinematic geometry and bulk strain in the constrictional field. Localized magmatic heating best explains the shape of the high-strain-zone boundary, but L tectonites are not partitioned into a single rheological domain. During terrane amalgamation strain-path partitioning occurred with localized top-to-the-west-directed simple shear partitioned into a structurally overlying thrust zone and pure-shear-dominated subvertical shortening and transport-parallel elongation partitioned into the PPHSZ.

  12. Faulting process of the August 8, 1993, Guam earthquake: A thrust event in an otherwise weakly coupled subduction zone

    NASA Astrophysics Data System (ADS)

    Campos, J.; Madariaga, R.; Scholz, C.

    1996-08-01

    We study a large Mw = 7.7 earthquake that occurred on June 8, 1993, slightly offshore and under the island of Guam in the southern Mariana island arc. From a complete study of P and SH body waves, a relocation of the aftershocks, and the subevents of the main shock, we propose a relatively simple model of the rupture process of this event. We propose that this earthquake ruptured a shallow-dipping thrust fault that corresponds to the subduction interface under Guam. Like many other earthquakes, this event started with a small foreshock and was followed by two large energy release events located to the northeast of the epicenter along the subduction zone. The rupture process had a relatively short duration of about 32 s, with a weak starting phase that lasted about 8 s. Seismic moments estimated from body waves, surface waves, and Global Positioning System (GPS) are very similar of the order of 4.5 × 1020 N m. The displacement field produced by our best model was compared to the GPS measurements of coseismic slip obtained by Beavan et al. [1994]. We find an excellent agreement both in displacement direction and magnitude between the predicted and observed GPS displacements. This appears to be then the largest earthquake to have occurred on a shallow-dipping thrust fault in the Mariana subduction zone during this century. Its occurrence requires a reassessment of the concept of seismic coupling in this subduction zone.

  13. Oroclinal bending, distributed thrust and strike-slip faulting, and the accommodation of Arabia-Eurasia convergence in NE Iran since the Oligocene

    NASA Astrophysics Data System (ADS)

    Hollingsworth, James; Fattahi, Morteza; Walker, Richard; Talebian, Morteza; Bahroudi, Abbas; Bolourchi, Mohammad Javad; Jackson, James; Copley, Alex

    2010-06-01

    Regional shortening is accommodated across NE Iran in response to the collision of Arabia with Eurasia. We examine how N-S shortening is achieved on major thrust systems bounding the eastern branch of the Alborz (east of 57°E), Sabzevar and Kuh-e-Sorkh mountain ranges, which lie south of the Kopeh Dagh mountains in NE Iran. Although these ranges have experienced relatively few large earthquakes over the last 50 yr, they have been subject to a number of devastating historical events at Neyshabur, Esfarayen and Sabzevar. A significant change in the tectonics of the eastern Alborz occurs directly south of the Central Kopeh Dagh, near 57°E. To the east, shortening occurs on major thrust faults which bound the southern margin of the range, resulting in significant crustal thickening, and forming peaks up to 3000 m high. Active shortening dies out eastward into Afghanistan, which is thought to belong to stable Eurasia. The rate of shortening across thrust faults bounding the south side of the eastern Alborz north of Neyshabur is determined using optically stimulated luminescence dating of displaced river deposits, and is likely to be 0.4-1.7 mm yr-1. Shortening across the Sabzevar range 150 km west of Neyshabur has previously been determined at 0.4-0.6 mm yr-1, although reassessment of the rate here suggests it may be as high as 1 mm yr-1. Migration of thrust faulting into foreland basins is common across NE Iran, especially in the Esfarayen region near 57°E, where the northward deflection of the East Alborz range reaches a maximum of 200 +/- 20 km (from its presumed linear E-W strike at the beginning of the Oligocene). West of 57°E, the tectonics of the Alborz are affected by the westward motion of the South Caspian region, which results in the partitioning of shortening onto separate thrust and left-lateral strike-slip faults north and south of the range. At the longitude of 59°E, published GPS velocities indicate that 50 per cent of the overall shortening across

  14. Late Quaternary Blind Thrust Faults along the Southern Margin of the Cul-de-Sac Plain, Haiti: A Newly Recognized Seismic Source?

    NASA Astrophysics Data System (ADS)

    Briggs, R. W.; Prentice, C. S.; Crone, A. J.; Gold, R. D.; Hudnut, K. W.; Narcisse, R.

    2012-12-01

    Joint inversion of geologic, geodetic, and seismologic data showed that most of the moment release associated with the 2010 M 7.0 Haiti earthquake occurred on a blind thrust fault, the Léogâne fault, adjacent to the transpressional plate-bounding Enriquillo-Plantain Garden fault (EPGF). Preliminary geomorphic and stratigraphic analysis of folded alluvial-fan deposits north of the EPGF and beneath and directly east of Port-au-Prince suggests that they have a similar style and orientation to the structure or structures associated with the 2010 earthquake. A series of east-southeast-trending, unnamed, low hills extend across the southern Cul-de-Sac Plain adjacent to a right bend in the EPGF. The hills are the surface expression of doubly-plunging folds that trend approximately 285°, or 15-25° more northwesterly than the neighboring EPGF. We used optical imagery and LiDAR topographic data to identify two main fold belts: a western belt that spans at least 12 km of southern Port-au-Prince and Petionville and an eastern belt that extends more than 20 km from Fond Parisien to Croix-des-Bouquets. Our field reconnaissance along the eastern belt shows that these hills are cored by steeply folded to overturned alluvial-fan deposits of probable Quaternary age. Active folding has sequentially deflected north-flowing drainages, and wind gaps indicate that the folding was sufficiently active to defeat drainages and deform river channels. When folding defeated the drainages, lacustrine sediment locally ponded against the south flank of the folds. In an unnamed drainage about 2 km west of Ganthier, charcoal from a 10-m-thick section of interbedded fluvial and ponded lacustrine sediments yielded a calibrated radiocarbon age of 4978 ± 158 cal. yr B.P. We speculate that the base of each fine-grained lacustrine section may be an event horizon corresponding with an earthquake that rejuvenated the fold; however, more detailed mapping of these sediments is needed to test this

  15. Active faults and seismogenic models for the Urumqi city, Xinjiang Autonomous Region, China

    NASA Astrophysics Data System (ADS)

    Li, Yingzhen; Yu, Yang; Shen, Jun; Shao, Bo; Qi, Gao; Deng, Mei

    2016-06-01

    We have studied the characteristics of the active faults and seismicity in the vicinity of Urumqi city, the capital of Xinjiang Autonomous Region, China, and have proposed a seismogenic model for the assessment of earthquake hazard in this area. Our work is based on an integrated analysis of data from investigations of active faults at the surface, deep seismic reflection soundings, seismic profiles from petroleum exploration, observations of temporal seismic stations, and the precise location of small earthquakes. We have made a comparative study of typical seismogenic structures in the frontal area of the North Tianshan Mountains, where Urumqi city is situated, and have revealed the primary features of the thrust-fold-nappe structure there. We suggest that Urumqi city is comprised two zones of seismotectonics which are interpreted as thrust-nappe structures. The first is the thrust nappe of the North Tianshan Mountains in the west, consisting of the lower (root) thrust fault, middle detachment, and upper fold-uplift at the front. Faults active in the Pleistocene are present in the lower and upper parts of this structure, and the detachment in the middle spreads toward the north. In the future, M7 earthquakes may occur at the root thrust fault, while the seismic risk of frontal fold-uplift at the front will not exceed M6.5. The second structure is the western flank of the arc-like Bogda nappe in the east, which is also comprised a root thrust fault, middle detachment, and upper fold-uplift at the front, of which the nappe stretches toward the north; several active faults are also developed in it. The fault active in the Holocene is called the South Fukang fault. It is not in the urban area of Urumqi city. The other three faults are located in the urban area and were active in the late Pleistocene. In these cases, this section of the nappe structure near the city has an earthquake risk of M6.5-7. An earthquake M S6.6, 60 km east to Urumqi city occurred along the

  16. Cyclic ductile and brittle deformation related to coseismic thrust fault propagation: Structural record at the base of a basement nappe (Preveli, Crete)

    NASA Astrophysics Data System (ADS)

    Nüchter, Jens-Alexander; Wassmann, Sara; Stöckhert, Bernhard

    2013-09-01

    structural record at the base of a basement nappe (Preveli nappe, Crete, Greece) thrust upon sedimentary rocks is investigated, aimed on understanding mechanisms which result in decoupling of the thrust sheet from its original substratum. We identify several superimposed deformation stages, each with characteristic structural style and indications of episodic deformation at initially high differential stress. The final stage involves formation of a matrix supported breccia transected by pseudotachylytes, comprising the lowermost 30 m of the nappe. Brecciation and pseudotachylyte formation occurred in a single event, and structures were not modified afterward. Complete induration of breccia and composition of phengite crystallized during devitrification of pseudotachylytes place the sequence of events into the middle crust. We propose a model relating episodic deformation and cyclic stress history to propagation of a thrust fault in a limited number of seismic events. Terminal brecciation and frictional fusion record passage of the fault front beneath the site of observation and decoupling of the thrust sheet. Absence of discernible further deformation is consistent with negligible basal friction during transport as a nappe. Brecciation and pseudotachylyte formation mark the switch from a history of repeated coseismic loading and postseismic stress relaxation in the plastosphere, driven by seismic events on the approaching thrust fault, to passive transport with deformation localized in a weak thrust plane. For a sequence of superimposed ductile to brittle structures, our model provides an alternative to progressive cooling and exhumation concomitant with deformation over millions of years.

  17. Stress transfer among en echelon and opposing thrusts and tear faults: Triggering caused by the 2003 Mw = 6.9 Zemmouri, Algeria, earthquake

    USGS Publications Warehouse

    Lin, J.; Stein, R.S.; Meghraoui, M.; Toda, S.; Ayadi, A.; Dorbath, C.; Belabbes, S.

    2011-01-01

    The essential features of stress interaction among earthquakes on en echelon thrusts and tear faults were investigated, first through idealized examples and then by study of thrust faulting in Algeria. We calculated coseismic stress changes caused by the 2003 Mw = 6.9 Zemmouri earthquake, finding that a large majority of the Zemmouri afterslip sites were brought several bars closer to Coulomb failure by the coseismic stresses, while the majority of aftershock nodal planes were brought closer to failure by an average of ~2 bars. Further, we calculated that the shallow portions of the adjacent Thenia tear fault, which sustained ~0.25 m slip, were brought >2 bars closer to failure. We calculated that the Coulomb stress increased by 1.5 bars on the deeper portions of the adjacent Boumerdes thrust, which lies just 10–20 km from the city of Algiers; both the Boumerdes and Thenia faults were illuminated by aftershocks. Over the next 6 years, the entire south dipping thrust system extending 80 km to the southwest experienced an increased rate of seismicity. The stress also increased by 0.4 bar on the east Sahel thrust fault west of the Zemmouri rupture. Algiers suffered large damaging earthquakes in A.D. 1365 and 1716 and is today home to 3 million people. If these shocks occurred on the east Sahel fault and if it has a ~2 mm/yr tectonic loading rate, then enough loading has accumulated to produce a Mw = 6.6–6.9 shock today. Thus, these potentially lethal faults need better understanding of their slip rate and earthquake history.

  18. Late Quaternary activity along the Ferrara thrust inferred from stratigraphic architecture and geophysical surveys

    NASA Astrophysics Data System (ADS)

    Stefani, Marco; Bignardi, Samuel; Caputo, Riccardo; Minarelli, Luca; Abu-Zeid, Nasser; Santarato, Giovanni

    2010-05-01

    Since Late Miocene, the Emilia-Romagna portion of the Po Plain-Adriatic foredeep basin was progressively affected by compressional deformation, due to the northward propagation of the Apennines fold-and-thrust belt. The major tectonic structures within the basin have been recognised and are relatively well known, thanks to the widespread, even if outdated, seismic survey, performed after WW II, for hydrocarbon exploration. More recently, a large amount of surface and shallow-subsurface information has been provided by the CARG geological mapping project. The region therefore provides a valuable opportunity to discuss the genetic relationship between tectonic deformation, eustatic-paleoclimatic fluctuations, and depositional architecture. The activity of blind thrusts and fault-propagation folds induced repeated angular unconformities and impressive lateral variations in the Pliocene-Quaternary stratigraphy, causing thickness changes, from a few metres, close to the Apennines piedmont line, to more than 9 km, in fast subsiding depocenters (e.g. Lido di Savio). In the Ferrara region, the post-Miocene succession ranges from about 4 km, west of Sant'Agostino, to less than 200 m, on the Casaglia anticline, where Late Quaternary fluvial strata rest on Miocene marine marls, with an angular unconformity relationship. In this sector of the Po Plain, the tip-line of the northernmost thrust has been reconstructed north of the Po River (Occhiobello) and is associated with the growth of a large fold (Ferrara-Casaglia anticline), cross-cut by a complex splay of minor backthrusts and reverse faults. The thrust-anticline structure hosts an energy producing geothermal field, whose hydrogeological behaviour is largely influenced by the fracture pattern. The Apennines frontal thrust probably provided the seismic source for the earthquakes that severely damaged Ferrara, during the 1570 a.D. fall season, as documented by the structural damage still visible in many historic buildings (e

  19. Imaging the migration of seismicity along the Zongwulongshan thrust fault zone in Qinghai, China from 2003 to 2009 using spaceborne radar interferometry

    NASA Astrophysics Data System (ADS)

    Feng, W.; Li, Z.; Hoey, T.; Xu, Z.

    2013-12-01

    Three MW ~6.3 earthquakes followed by a series of large aftershocks occurred on the north margin of Qaidam Basin in Qinghai, China during the period from 2003 to 2009. All the observed events were located within a 150-km-long and 50-km-wide zone along the Zongwulongshan thrust fault. In this study, over 400 unwrapped interferograms covering the entire earthquake areas from 5 ENVISAT ASAR tracks were generated by using the JPL/Caltech ROI_PAC software. We attempted to retrieve surface displacements in different phases (coseismic and postseismic) , rather than to obtain a simple mean velocity. A novel iterative time series (TS) analysis method was used to separate surface displacements from various sources of errors (e.g. orbital ramps, DEM errors and atmospheric delays (APS)) by fully utilizing the datapoints from overlapping regions. Combining a network strategy, a wavelet-based algorithm was employed to estimate topography-related APS. Five independent coseismic interferograms resulting from 6 different events were generated, of which one displacement map resulted from the 28th Aug 2009 MW 6.3 earthquake and its latest largest aftershock 3 days after the mainshock together. Significant postseismic displacements following all the three mainshocks were observed even during the period from Nov 2008 to Aug 2009. In the first three months after the Nov 2008 mainshock, a maximum accumulative displacement of ~ 3 cm was detected. From then until the 2009 mainshock, no clear surface displacement was found. Using geodetic modeling, the fault parameters of three mainshocks were determined, which are consistent with seismic solutions. The principal thrust slips characterized the Qilianshan-nanshan compressional belt caused by the collision of India to Eurasian plates. However, the oblique slip mechanisms of another three large aftershocks were not consistent with their mainshocks, suggesting that the main shocks had possibly changed the stress state in the vicinity of the

  20. Active folding and thrusting in North Africa: A framework for a seismotectonic model of the Atlas Mountains

    NASA Astrophysics Data System (ADS)

    Meghraoui, Mustapha; Maouche, Said; Timoulali, Youssef; Bouhadad, Youcef; Bouaziz, Samir

    2013-04-01

    Large earthquakes in the Atlas Mountains of North Africa are often generated on thrust or reverse faults. For inland faults, surface ruptures and long-term active tectonics appear as a thrust escarpment and fold-related faulting visible in the field and using remote sensing images, or measured using space-borne geodesy (GPS or INSAR). For coastal faults, major uplifts of late Quaternary marine terraces and folding with steplike morphology are exposed indicating the incremental development of coastal active deformation. We have investigated the similarities and differences between different active fault-related folding along the Africa - Eurasia convergent plate boundary. These active structures are seismogenic and the striking case studies are the 1960 Agadir (Mw 5.9), the 1954 Orleansville (Mw 6.7), the 1980 El Asnam (Mw 7.3), the 1992 Gafsa (Mw 5.3), the 1999 Ain Temouchent (Mw 6.0), and the 2003 Zemmouri (Mw 6.8) earthquakes. From paleoseismic investigations the El Asnam active fold shows 0.6 to 1.0 mm/yr uplift rate. West of Algiers on the Sahel anticline, the levelling of uplifted successive coastal benches and notches document the incremental folding uplift with ~ 0.84 - 1.2 mm/yr uplift rate in the last 120-140 ka. The relatively fast folding growth during late Pleistocene and Holocene in the Atlas Mountains attests for the significance of earthquake activity and the importance of convergent movements between Africa and Eurasia in the Western Mediterranean. This work is prepared in the framework of the UNESCO (SIDA) - IGCP Project 601 "Seismotectonics and Seismic Hazards in Africa".

  1. Active fault, fault growth and segment linkage along the Janauri anticline (frontal foreland fold), NW Himalaya, India

    NASA Astrophysics Data System (ADS)

    Malik, Javed N.; Shah, Afroz A.; Sahoo, Ajit K.; Puhan, B.; Banerjee, Chiranjib; Shinde, Dattatraya P.; Juyal, Navin; Singhvi, Ashok K.; Rath, Shishir K.

    2010-03-01

    The 100 km long frontal foreland fold — the Janauri anticline in NW Himalayan foothills represents a single segment formed due to inter-linking of the southern (JS1) and the northern (JS2) Janauri segments. This anticline is a product of the fault related fold growth that facilitated lateral propagation by acquiring more length and linkage of smaller segments giving rise to a single large segment. The linked portion marked by flat-uplifted surface in the central portion represents the paleo-water gap of the Sutlej River. This area is comparatively more active in terms of tectonic activity, well justified by the occurrence of fault scarps along the forelimb and backlimb of the anticline. Occurrence of active fault scarps on either side of the anticline suggests that the slip accommodated in the frontal part is partitioned between the main frontal thrust i.e. the Himalayan Frontal Thrust (HFT) and associated back-thrust. The uplift in the piedmont zone along southern portion of Janauri anticline marked by dissected younger hill range suggests fore-landward propagation of tectonic activity along newly developed Frontal Piedmont Thrust (FPT), an imbricated emergent thrust branching out from the HFT system. We suggests that this happened because the southern segment JS1 does not linked-up with the northwestern end of Chandigarh anticline segment (CS). In the northwestern end of the Janauri anticline, due to no structural asperity the tectonic activity on HFT was taken-up by two (HF1 — in the frontal part and HF2 — towards the hinterland side) newly developed parallel active faults ( Hajipur Fault) branched from the main JS2 segment. The lateral propagation and movements along HF1 and HF2 resulted in uplift of the floodplain as well as responsible for the northward shift of the Beas River. GPR and trench investigations suggest that earthquakes during the recent past were accompanied with surface rupture. OSL (optical stimulated luminescence) dates from the trench

  2. Measuring active deformation of the Yakima fold and thrust belt using GPS and InSAR

    NASA Astrophysics Data System (ADS)

    Schmalzle, G. M.; Baker, M. S.; McCaffrey, R.; King, R. W.; Osmanoglu, B.

    2011-12-01

    The Yakima fold-thrust belt (YFTB; also known as Yakima Fold Belt), forming the distinct geomorphology of northernmost Oregon and south-central Washington, is one of the few actively deforming fold and thrust belts in the conterminous United States. Although controversial, currently available data suggest that the YFTB is "thick-skinned", i.e., its faults penetrate the seismogenic layer, allowing for large (~M7) earthquakes. The YFTB is bisected by the Olympic-Wallowa Lineament (OWL) that runs from eastern Washington into the highly populated Puget Sound. Together, the YFTB and OWL make up the boundary between the clockwise rotating Oregon block and eastern Washington, which is largely moving with the North American plate. Paleomagnetic data suggest that Oregon has been rotating at its present (GPS-derived) rate for more than 15 million years with the predicted consequence of a long history of shortening across the YFTB. GPS data obtained over the past ~20 years indicate a NE-directed shortening strain rate of about 9 x 10^-9 /yr, but how this strain is partitioned across the YFTB is unclear due to the sparse locations of GPS sites. We use Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data to examine the degree to which strain rates are localized or distributed within this continental thrust belt, shedding light on the controversy regarding the behavior of the continental lithosphere under contraction. These data are compared to local seismicity, gravity surveys, recent high-resolution aeromagnetic work and paleoseismic studies.

  3. Kinematic model for out-of-sequence thrusting: Motion of two ramp-flat faults and the production of upper plate duplex systems

    NASA Astrophysics Data System (ADS)

    Pavlis, Terry L.

    2013-06-01

    Kinematic models developed here suggest a bewildering array of structural styles can be generated during out-of-sequence thrusting. Many of these structures would be difficult to distinguish from a normally stacked thrust sequence and the process can produce younger-on-older faults that could easily be misinterpreted as normal faults. This paper considers a small subset of this problem within a large model space by considering structures that develop along a pair of ramp-flat faults that are moving simultaneously, or sequentially. Motion on the lower ramp warps the structurally higher fault due to fault-bend folding and when the fault ruptures through the warp it transfers a horse to the upper hanging wall. Continuity of the process generates what is referred to here as an "upper plate duplex" to distinguish the structure from a conventional duplex. Kinematic parameters are developed for two models within this general problem: 1) a system with a fixed ramp in the lower thrust, overridden by an upper thrust; and 2) a double-duplex system where a conventional duplex develops along the lower fault at the same time as an upper plate duplex is formed along the upper fault. The theory is tested with forward models using 2D Move software and these tests indicate different families of structural styles form in association with relative scaling of ramp systems, slip-ratio between faults, and aspect ratios of horse blocks formed in the upper-plate duplex. A first-order result of the analysis is that an upper plate duplex can be virtually indistinguishable from a conventional duplex unless the trailing branch lines of the horses are exposed or imaged; a condition seldom met in natural exposures. Restoration of an upper-plate duplex produces counterintuitive fault geometry in the restored state, and thus, restorations of upper plate duplexes that erroneously assume a conventional duplex model would produce restored states that are seriously in error. In addition, in most of

  4. Drainage response to active tectonics and evolution of tectonic geomorphology across the Himalayan Frontal Thrust, Kumaun Himalaya

    NASA Astrophysics Data System (ADS)

    Luirei, Khayingshing; Bhakuni, Surendra S.; Kothyari, Girish Ch.

    2015-06-01

    We present the results of integrated studies of geomorphic indices of drainage networks and landforms developed across the mountain front along the Himalayan Frontal Thrust (HFT) between the Dabka and Baur rivers, Kumaun Himalaya. The HFT is a morphogenic structure in nature, creating a 100-m-high E-W trending escarpment that extends ~ 21 km. Geomorphological evidence indicates ~ 10.5 km westward migration of the Dabka River and ~ 5.2 km eastward migration of the Baur River. These migrations are a result of uplift of the hanging wall along the HFT. The HFT is offset by a transverse fault, which suggests that the latter postdates the reactivation of the HFT between 500 and 100 ka. Presence of different levels of strath terraces along the mountain front suggests the active nature of the HFT. To assess the relative tectonic activity, morphometric indices such as stream-gradient (SL) index, mountain front sinuosity (Smf) index, and ratio of valley floor width to valley height (Vf) have been analyzed. Results of the former two are consistent with the tectonic landforms developed in thrust zones. Paleochannels of the Dabka and Baur rivers are characterized by high Vf values while other valleys show low Vf values. Quaternary alluvial sediments have been deformed along the Pawalgarth Thrust, a splay of the HFT. Deformation has resulted in the formation of the Pawalgarh Anticline, a thrust-related asymmetric fold.

  5. Lateral propagation of active normal faults throughout pre-existing fault zones: an example from the Southern Apennines, Italy

    NASA Astrophysics Data System (ADS)

    Agosta, Fabrizio; Prosser, Giacomo; Ivo Giano, Salvatore

    2013-04-01

    The main active structures in the Southern Apennines are represented by a set of NW-trending normal faults, which are mainly located in the axial sector of the chain. Evidences arising from neotectonics and seismology show activity of a composite seismic source, the Irpinia - Agri Valley, located across the Campania-Basilicata border. This seismic source is made up of two right-stepping, individual seismic sources forming a relay ramp. Each individual seismic source consists of a series of nearly parallel normal fault segments. The relay ramp area, located around the Vietri di Potenza town, is bounded by two seismic segments, the San Gregorio Magno Fault, to the NW, and the Pergola-Melandro Fault, to the SE. The possible interaction between the two right-stepping fault segments has not been proven yet, since the fault system of the area has never been analyzed in detail. This work is aimed at assessing the geometry of such fault system, inferring the relative age of the different fault sets by studying the crosscutting relationships, characterizing the micromechanics of fault rocks associated to the various fault sets, and understanding the modalities of lateral propagation of the two bounding fault segments. Crosscutting relationships are recognized by combining classical geological mapping with morphotectonic methods. This latter approach, which include the analysis of aerial photographs and field inspection of quaternary slope deposits, is used to identify the most recent structures among those cropping out in the field area. In the relay ramp area, normal faults crosscut different tectonic units of the Apennine chain piled up, essentially, during the Middle to Late Miocene. The topmost unit (only few tens of meter-thick) consists of a mélange containing blocks of different lithologies in a clayish matrix. The intermediate thrust sheet consists of 1-1.5 km-thick platform carbonates of late Triassic-Jurassic age, with dolomites at the base and limestones at the

  6. Imaging the complexity of an active normal fault system: The 1997 Colfiorito (central Italy) case study

    USGS Publications Warehouse

    Chiaraluce, L.; Ellsworth, W.L.; Chiarabba, C.; Cocco, M.

    2003-01-01

    Six moderate magnitude earthquakes (5 < Mw < 6) ruptured normal fault segments of the southern sector of the North Apennine belt (central Italy) in the 1997 Colfiorito earthquake sequence. We study the progressive activation of adjacent and nearby parallel faults of this complex normal fault system using ???1650 earthquake locations obtained by applying a double-difference location method, using travel time picks and waveform cross-correlation measurements. The lateral extent of the fault segments range from 5 to 10 km and make up a broad, ???45 km long, NW trending fault system. The geometry of each segment is quite simple and consists of planar faults gently dipping toward SW with an average dip of 40??-45??. The fault planes are not listric but maintain a constant dip through the entire seismogenic volume, down to 8 km depth. We observe the activation of faults on the hanging wall and the absence of seismicity in the footwall of the structure. The observed fault segmentation appears to be due to the lateral heterogeneity of the upper crust: preexisting thrusts inherited from Neogene's compressional tectonic intersect the active normal faults and control their maximum length. The stress tensor obtained by inverting the six main shock focal mechanisms of the sequence is in agreement with the tectonic stress active in the inner chain of the Apennine, revealing a clear NE trending extension direction. Aftershock focal mechanisms show a consistent extensional kinematics, 70% of which are mechanically consistent with the main shock stress field.

  7. Active fold-thrust belts in the foreland of eastern Tibet, the Longquan and Xiongpu anticlines in Sichuan, China

    NASA Astrophysics Data System (ADS)

    Lee, Jian-Cheng; Chan, Yu-Chang; Lu, Chia-Yu; Chen, Chih-Tung; Chu, Hao-Tsu; Liu, Yuiping; Li, Jianzhong

    2016-04-01

    The 2008 M7.9 Wenchuan earthquake ruptured from the Longmenshan fault system, which is the frontal thrust system in eastern Tibet. Further east toward the foreland area in the Sichuan basin, it sits two anticlinal structures, the Longquan and Xiongpu anticlines, which trends sub-parallel to the Longmenshan range with a distance of about 70-100 km to the mountain front. It is widely considered that these two anticlinal features are attributed to propagation of the eastward extrusion of the eastern Tibetan plateau, similar to the stress system the Wenchuan earthquake. In this study, we carried out field investigations on these two active anticlinal structures in order to characterize the bulk deformation of the anticlines. We also conducted fracture analysis and fault-slip data analysis, in an attempt to characterize the fracture developments of the rock and the paleostress states related to the faulting events associated growth of the anticlines. We thus constructed a series of geological cross sections along these two anticlines. Our results show that the Longquan anticline is characterized by pop up structure with a dominant west-vergent thrust (i.e., backthrust) on the western limb. On the other hand to the eastern limb, an east-vergent thrust only well developed in the middle part of the anticline and die out toward the north and the south. For the Xiongpu anticline, it is characterized by a pre-dominant west-vergent backthrust system without developing an east-vergent thrust. A strike-slip fault and a series of N-S-trending pop-up thrusts cut across the Xiongpu anticline indicate a rather complex stress system with two dominant compression directions, NW-SE and E-W, subsequently or alternatively affected the area. Finally, the fracture analysis revealed that 2-3 pre-dominant bedding-perpendicular fracture sets are commonly developed in the massive sandstone layers. Most of them seemingly are of the characteristics of the mode I open joint, without clear

  8. Thrust faulting and 3D ground deformation of the 3 July 2015 Mw 6.4 Pishan, China earthquake from Sentinel-1A radar interferometry

    NASA Astrophysics Data System (ADS)

    Sun, Jianbao; Shen, Zheng-Kang; Li, Tao; Chen, Jie

    2016-06-01

    Boosted by the launch of Sentinel-1A radar satellite from the European Space Agency (ESA), we now have the opportunity of fast, full and multiple coverage of the land based deformation field of earthquakes. Here we use the data to investigate a strong earthquake struck Pishan, western China on July 3, 2015. The earthquake fault is blind and no ground break features are found on-site, thus Synthetic Aperture Radar (SAR) data give full play to its technical advantage for the recovery of coseismic deformation field. By using the Sentinel-1A radar data in the Interferometric Wide Swath mode, we obtain 3 tracks of InSAR data over the struck region, and resolve the 3D ground deformation generated by the earthquake. Then the Line-of-Sight (LOS) InSAR data are inverted for the slip-distribution of the seismogenic fault. The final model shows that the earthquake is completely blind with pure-thrust motion. The maximum slip is ~ 0.48 m at a depth of ~ 7 km, consistent with the depth estimate from seismic reflection data. In particular, the inverted model is also compatible with a south-dipping fault ramp among a group of fault interfaces detected by the seismic reflection profile over the region. The seismic moment obtained equals to a Mw 6.4 earthquake. The Pishan earthquake ruptured the frontal part of the thrust ramps under the Slik anticline, and unloaded the coulomb stress of them. However, it may have loaded stress to the back-thrust above the thrust ramps by ~ 1-4 bar, and promoted it for future failure. Moreover, the stress loading on the west side of the earthquake fault is much larger than that on the east side, indicating a higher risk for failure to the west of the Zepu fault.

  9. Neotectonics and structure of the Himalayan deformation front in the Kashmir Himalaya, India: Implication in defining what controls a blind thrust front in an active fold-thrust belt

    NASA Astrophysics Data System (ADS)

    Gavillot, Y. G.; Meigs, A.; Yule, J. D.; Rittenour, T. M.; Malik, M. O. A.

    2014-12-01

    Active tectonics of a deformation front constrains the kinematic evolution and structural interaction between the fold-thrust belt and most-recently accreted foreland basin. In Kashmir, the Himalayan Frontal thrust (HFT) is blind, characterized by a broad fold, the Suruin-Mastargh anticline (SMA), and displays no emergent faults cutting either limb. A lack of knowledge of the rate of shortening and structural framework of the SMA hampers quantifying the earthquake potential for the deformation front. Our study utilized the geomorphic expression of dated deformed terraces on the Ujh River in Kashmir. Six terraces are recognized, and three yield OSL ages of 53 ka, 33 ka, and 0.4 ka. Vector fold restoration of long terrace profiles indicates a deformation pattern characterized by regional uplift across the anticlinal axis and back-limb, and by fold limb rotation on the forelimb. Differential uplift across the fold trace suggests localized deformation. Dip data and stratigraphic thicknesses suggest that a duplex structure is emplaced at depth along the basal décollement, folding the overlying roof thrust and Siwalik-Muree strata into a detachment-like fold. Localized faulting at the fold axis explains the asymmetrical fold geometry. Folding of the oldest dated terrace, suggest that rock uplift rates across the SMA range between 2.0-1.8 mm/yr. Assuming a 25° dipping ramp for the blind structure on the basis of dip data constraints, the shortening rate across the SMA ranges between 4.4-3.8 mm/yr since ~53 ka. Of that rate, ~1 mm/yr is likely absorbed by minor faulting in the near field of the fold axis. Given that Himalaya-India convergence is ~18.8-11 mm/yr, internal faults north of the deformation front, such as the Riasi thrust absorbs more of the Himalayan shortening than does the HFT in Kashmir. We attribute a non-emergent thrust at the deformation front to reflect deformation controlled by pre-existing basin architecture in Kashmir, in which the thick succession

  10. Carbonates in thrust faults: High temperature investigations into deformation processes in calcite-dolomite systems

    NASA Astrophysics Data System (ADS)

    Kushnir, A.; Kennedy, L.; Misra, S.; Benson, P.

    2012-04-01

    The role of dolomite on the strength and evolution of calcite-dolomite fold and thrust belts and nappes (as observed in the Canadian Rockies, the Swiss Alps, the Italian Apennines, and the Naukluft Nappe Complex) is largely unknown. Field investigations indicate that strain in natural systems is localized in calcite, resulting in a ductile response, while dolomite deforms in a dominantly brittle manner. To date, experimental studies on polymineralic carbonate systems are limited to homogeneous, fine-grained, calcite-dolomite composites of relatively low dolomite content. The effect of dolomite on limestone rheology, the onset of crystal-plastic deformation in dolomite in composites, and the potential for strain localization in composites have not yet been fully quantified. Constant displacement rate (3x10-4 s-1and 10-4 s-1), high confining pressure (300 MPa) and high temperature (750° C and 800° C) torsion experiments were conducted to address the role of dolomite on the strength of calcite-dolomite composites. Experiments were performed on samples produced by hot isostatic pressing (HIP) amalgams of a natural, pure dolomite and a reagent, pure calcite. We performed experiments on the following mixtures (given as dolomite%): 25%, 35%, 50%, and 75%. These synthetic HIP products eliminated concerns of mineralogical impurities and textural anomalies due to porosity, structural fabrics (e.g., foliation) and fossil content. The samples were deformed up to a maximum finite shear strain of 5.0 and the experimental set up was unvented to inhibit sample decarbonation. Mechanical data shows a considerable increase in sample yield strength with increasing dolomite content. Experimental products with low starting dolomite content (dol%: 25% and 35%) display macroscopic strain localization along compositionally defined foliation. Experimental products with high dolomite content (dol%: 50% and 75%) demonstrate no macroscopic foliation. Post-deformation microstructure analysis

  11. Age and source of water in springs associated with the Jacksonville Thrust Fault Complex, Calhoun County, Alabama

    USGS Publications Warehouse

    Robinson, James L.

    2004-01-01

    Water from wells and springs accounts for more than 90 percent of the public water supply in Calhoun County, Alabama. Springs associated with the Jacksonville Thrust Fault Complex are used for public water supply for the cities of Anniston and Jacksonville. The largest ground-water supply is Coldwater Spring, the primary source of water for Anniston, Alabama. The average discharge of Coldwater Spring is about 32 million gallons per day, and the variability of discharge is about 75 percent. Water-quality samples were collected from 6 springs and 15 wells in Calhoun County from November 2001 to January 2003. The pH of the ground water typically was greater than 6.0, and specific conductance was less than 300 microsiemens per centimeter. The water chemistry was dominated by calcium, carbonate, and bicarbonate ions. The hydrogen and oxygen isotopic composition of the water samples indicates the occurrence of a low-temperature, water-rock weathering reaction known as silicate hydrolysis. The residence time of the ground water, or ground-water age, was estimated by using analysis of chlorofluorocarbon, sulfur hexafluoride, and regression modeling. Estimated ground-water ages ranged from less than 10 to approximately 40 years, with a median age of about 18 years. The Spearman rho test was used to identify statistically significant covariance among selected physical properties and constituents in the ground water. The alkalinity, specific conductance, and dissolved solids increased as age increased; these correlations reflect common changes in ground-water quality that occur with increasing residence time and support the accuracy of the age estimates. The concentration of sodium and chloride increased as age increased; the correlation of these constituents is interpreted to indicate natural sources for chloride and sodium. The concentration of silica increased as the concentration of potassium increased; this correlation, in addition to the isotopic data, is evidence that

  12. An elastic wedge model for the development of coeval normal and thrust faulting in the Mauna Loa-Kilauea rift system in Hawaii

    NASA Astrophysics Data System (ADS)

    Yin, An; Kelty, T. K.

    2000-11-01

    A long-standing enigma of the Mauna Loa-Kilauea rift system in Hawaii is the coeval development of normal and thrust faults that are vertically partitioned. To address this question, we developed a simple elastic wedge model that explores plausible boundary conditions in terms of tractions for generating such a fault pattern. Analytical solutions that best simulate the observed faulting style and geodetically determined strain at the surface require that (1) the pore fluid pressure ratio within the wedge (λ) and along the basal decollement (λb,) must be exceedingly high (i.e., λ = λb= 0.90-0.95) and (2) a tensile stress of the order of 10-30 MPa must have existed in the very top part of the rift zone at the back side of the wedge-shaped rift flank. The high pore fluid pressure within the rift flank may be induced by pumping of fluids during emplacement of magma, whereas the high pore fluid pressure along the basal decollement may be caused by compaction of water-saturated sediments between the volcanic pile above and the oceanic floor below. Although the predicted tensile stress in the rift zone could be related to the presence of a relatively steep topographic slope, our results show that this is not a prerequisite. Therefore we attribute occurrence of tensile stress to either upward bending of the Hawaiian volcanic pile due to emplacement of magma, or inflation of a shallow magma chamber several kilometers beneath the surface. In any case, the results of our model indicate that magma emplacement in the shallow part of the rift zone may be a passive process, while the deep rift zone experiences forceful emplacement (i.e., active rifting via magma push).

  13. Sediment dewatering and pore fluid migration along thrust faults in a foreland basin inferred from isotopic and elemental geochemical analyses (Eocene southern Pyrenees, Spain)

    NASA Astrophysics Data System (ADS)

    Travé, Anna; Labaume, Pierre; Calvet, Francesc; Soler, Albert

    1997-12-01

    The lower Eocene Ainsa basin was formed during the first stages of the south-Pyrenean foreland basin evolution due to southwestward migration of imbricated thrust-folds. Isotopic and elemental geochemistry of syn-kinematic veins (calcite and celestite) and their marly host-rock, sampled in three thrust-fault zones and one footwall syncline, allows us to characterize the origin of pore fluids and the early stages of their evolution and circulation during the early deformation of the basin-fill. The isotopic composition of sulfur and the {87Sr }/{86Sr } ratios of calcites and celestites from the veins in the footwall syncline show that the original fluid had the isotopic composition of Eocene seawater. The different {87Sr }/{86Sr } ratio in veins from the thrust-fault zones compared with the same ratio in the marly host-rock of the footwall syncline indicates that the thrust-fault zones acted as conduits for advective fluids. The relatively high {87Sr }/{86Sr } ratio in the veins related to the thrust-fault zones indicates that the fluid originated from the interaction of seawater with an external fluid coming from deeper sources or from the meteoric weathering of the emerged part of the belt. δ 18O and δ 13C values of calcites show that the isotopic composition of the calcite-cements in veins was controlled by the isotopic composition of the marly host sediment. Depletion of both δ 18O and δ 13C with respect to Eocene seawater composition, together with elemental geochemistry of calcite cements in the veins, points to burial transformations of a seawater-derived fluid to a formation water composition. The distribution of δ 18O and δ 13C values of the marly host-rock and calcite cements in veins of the four outcrops probably resulted from differences in the meteoric water influences. The hydrogeological regime at the toe of the submarine thrust system was dominated by tectonically-induced dewatering of the foreland basin sediments. The thrust-fault zones were

  14. Active Faults of the Northwest Himalaya: Pattern, Rate, and Timing of Surface Rupturing Earthquakes

    NASA Astrophysics Data System (ADS)

    Yule, J.; Madden, C.; Gavillot, Y.; Hebeler, A.; Meigs, A.; Hussein, A.; Malik, M.; Bhat, M.; Kausar, A.; Ramzan, S.; Sayab, M.; Yeats, R. S.

    2012-12-01

    The 2005 Kashmir earthquake (Mw 7.6) is the only Himalayan earthquake to rupture the surface since the 15th to 16th century A.D. when >Mw 8.5 earthquakes ruptured the Himalayan Frontal thrust (HFT) in the central Himalaya. Megathrust-type earthquakes like these seem to relieve a majority of the accumulated interseismic strain and concentrate permanent strain across a narrow width at the deformation front (faults within the orogen appear to accommodate little strain). The 2005 within-plate rupture in Kashmir may be a clue that a different seismotectonic model applies to the northwest Himalaya where active deformation occurs on faults distributed more than 120 km across the orogen. An asymmetric anticline marks the deformation front in Kashmir where the HFT is inferred to be blind, though ~20 m-high escarpments suggest that unrecognized thrust fault(s) may reach the surface locally. Folded river terraces and dip data also suggest that this frontal fold contains a SW-dipping back thrust. In Pakistan the Salt Range thrust system (SRT) defines the thrust front. New mapping and preliminary OSL dates from deformed Holocene sediments exposed along the westernmost SRT reveal that the fault slips at 1-7 mm/yr and last ruptured within the last several thousand years. Within the orogenic wedge to the north of the deformation front, active shortening occurs along a system of surface-rupturing reverse faults, extending from the Balakot-Bagh fault (source of the 2005 Kashmir earthquake) to the Reasi fault (RF) in Indian Kashmir to the southeast. One strand of the RF displaces a 350 m-high, 80 ± 6 ka (preliminary OSL age) fluvial terrace, yielding a minimum shortening rate of 3-5 mm/yr. Trenches excavated across the RF nearby reveal a distinct angular unconformity that likely formed during a surface rupture ~4500 yrs BP. Farther north, three northeast-dipping reverse faults cut Quaternary terraces on the southwest side of the Kashmir Valley. Trenches expose evidence for at least

  15. Identification of recently active faults and folds in Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Marliyani, G. I.; Arrowsmith, R.; Helmi, H.

    2013-12-01

    We analyze the spatial pattern of active deformation in Java, Indonesia with the aim of characterizing the deformation of the upper plate of the subduction zone in this region. The lack of detailed neotectonic studies in Java is mostly because of its relatively low rate of deformation in spite of significant historical seismic activity. In addition, the abundance of young volcanic materials as well as the region's high precipitation rate and vegetation cover obscure structural relationships and prevent reliable estimates of offset along active faults as well as exhumed intra-arc faults. Detailed maps of active faults derived from satellite and field-based neotectonic mapping, paleoseismic data, as well as new data on the fault kinematics and estimates of orientation of principal stresses from volcano morphology characterize recently active faults and folds. The structures in West Java are dominated by strike-slip faulting, while Central and northern part of East Java are dominated by folds and thrusting with minor normal faulting. The structures vary in length from hundreds meters to tens of kilometers and mainly trend N75°E, N8°E with some minor N45°W. Our preliminary mapping indicates that there are no large scale continuous structures in Java, and that instead deformation is distributed over wide areas along small structures. We established several paleoseismic sites along some of the identified structures. We excavated two shallow trenches along the Pasuruan fault, a normal fault striking NW-SE that forms a straight 13 km scarp cutting Pleistocene deltaic deposits of the north shore of East Java. The trenches exposed faulted and folded fluvial, alluvial and colluvial strata that record at least four ground-rupturing earthquakes since the Pleistocene. The Pasuruan site proves its potential to provide a paleoseismic record rarely found in Java. Abundant Quaternary volcanoes are emplaced throughout Java; most of the volcanoes show elongation in N100°E and N20

  16. Numerical simulation of earthquake rupture sequences on the Manila thrust fault: Effects of seamount subduction

    NASA Astrophysics Data System (ADS)

    Yu, H.; Liu, Y.; Ning, J.; He, C.; Zhang, L.

    2015-12-01

    The Manila subduction zone is located at the convergent boundary between the Philippine Sea Plate and the Sunda/Eurasian Plate from offshore Taiwan to northern Luzon of Philippines, where only infrequent M7 earthquakes were observed in modern seismological instrumentation history. The lack of great events (M8+) indicates the subduction fault is either aseismically slipping or is accumulating strain energy toward rapid release in a great earthquake. Here we conduct numerical simulations of earthquake rupture sequences in the framework of rate-state-friction along the 15-19.5ºN segment of the 3D plate boundary with subducted seamounts. Rate-state frictional properties are constrained by laboratory friction experiments conducted on IODP Expedition 349, South China Sea (SCS), drilling samples from the basaltic basement rock under 100ºC - 600ºC, effective normal stress of 50 MPa and pore pressure of 100 MPa. During the modeled 2000-year period, the maximum magnitude of earthquakes is Mw7. Each sequence repeats every ~200 years and is consisted of three sub-events, event 1 (Mw7) that can overcome the barrier, where dip angle changes most rapidly along the strike, to rupture the entire fault. Events 2 (Mw 6.4) and 3 (Mw 5.7) are of smaller magnitudes and result in north-south segmented rupture pattern. We further quantify the potential of earthquake nucleation by the S-ratio (lower S ratio means the initial stress is closer to peak strength, hence more likely to nucleate an earthquake). The subducted seamount shows higher S-ratios than its surroundings mostly, implying an unlikely nucleate area. Our results are qualitatively similar to 2D subduction earthquake modeling by Herrendörfer et al. (2015, 2-3 events per supercycle and median long-term S is 0.5-1). Finally, we plan to use our coseismic rupture model results as inputs for a tsunami propagation model in SCS. Compared to the kinematic seafloor deformation input, our physics-based earthquake source model and its

  17. Faults and associated landslides on the Torrey Pines mesa, an expression of the active Rose Canyon fault zone, La Jolla, California

    SciTech Connect

    Rindell, A.K. )

    1993-04-01

    The Rose Canyon fault zone (RCFZ), San Diego's active NW striking right-lateral wrench, bends to the left at La Jolla, creating a poorly understood zone of transpression. North of La Jolla, continuing investigations along seacliffs and road-cuts have exposed a number of en echelon, NE striking antithetic faults previously interpreted as either E-W striking faults, landslides, and/or Eocene soft-sediment deformations. However, thrust faulting and left-lateral movement, in addition to antithetic strikes, indicates that at least one of these, the Marine Fisheries fault, is associated with the RCFZ. A graben formed by a left-step along this fault has led to land subsidence and engineering problems for the National Marine Fisheries building. In addition, progressive seacliff retreat here and at other locations is partly controlled by fault associated fractures. A cliff-face exposure of the Salk fault reveals diverging fault splays flattening to the near horizontal with movement occurring along bedding planes within the sedimentary section, creating the appearance of landsliding. Classic flower structures have also been found up to 5 km inland, along NE strikes to the shoreline exposures of the Salk and Scripps faults. Faults traces are generally obscured by urbanization and numerous ancient and/or presently active coherent landslides. Although these faults are classified as only potentially active, timing and risk of seismic movement are not well constrained. In addition, record rainfalls in San Diego County have dramatically increased landsliding potential. A well exposed dike, dated at 11 Ma (older than the Pliocene age of the RCFZ), is exposed from the seacliffs offshore towards the RCFZ. It has a significant magnetic anomaly ranging up to 450 gammas and appears to be offset by the Marine Fisheries and Scripps faults. Measuring offsets of this and other reported and suspected offshore dikes may better define total offset from both the RCFZ and antithetic faulting.

  18. Active, capable, and potentially active faults - a paleoseismic perspective

    USGS Publications Warehouse

    Machette, M.N.

    2000-01-01

    Maps of faults (geologically defined source zones) may portray seismic hazards in a wide range of completeness depending on which types of faults are shown. Three fault terms - active, capable, and potential - are used in a variety of ways for different reasons or applications. Nevertheless, to be useful for seismic-hazards analysis, fault maps should encompass a time interval that includes several earthquake cycles. For example, if the common recurrence in an area is 20,000-50,000 years, then maps should include faults that are 50,000-100,000 years old (two to five typical earthquake cycles), thus allowing for temporal variability in slip rate and recurrence intervals. Conversely, in more active areas such as plate boundaries, maps showing faults that are <10,000 years old should include those with at least 2 to as many as 20 paleoearthquakes. For the International Lithosphere Programs' Task Group II-2 Project on Major Active Faults of the World our maps and database will show five age categories and four slip rate categories that allow one to select differing time spans and activity rates for seismic-hazard analysis depending on tectonic regime. The maps are accompanied by a database that describes evidence for Quaternary faulting, geomorphic expression, and paleoseismic parameters (slip rate, recurrence interval and time of most recent surface faulting). These maps and databases provide an inventory of faults that would be defined as active, capable, and potentially active for seismic-hazard assessments.

  19. Selected Performance Measurements of the F-15 ACTIVE Axisymmetric Thrust-Vectoring Nozzle

    NASA Technical Reports Server (NTRS)

    Orme, John S.; Sims, Robert L.

    1999-01-01

    Flight tests recently completed at the NASA Dryden Flight Research Center evaluated performance of a hydromechanically vectored axisymmetric nozzle onboard the F-15 ACTIVE. A flight-test technique whereby strain gages installed onto engine mounts provided for the direct measurement of thrust and vector forces has proven to be extremely valuable. Flow turning and thrust efficiency, as well as nozzle static pressure distributions were measured and analyzed. This report presents results from testing at an altitude of 30,000 ft and a speed of Mach 0.9. Flow turning and thrust efficiency were found to be significantly different than predicted, and moreover, varied substantially with power setting and pitch vector angle. Results of an in-flight comparison of the direct thrust measurement technique and an engine simulation fell within the expected uncertainty bands. Overall nozzle performance at this flight condition demonstrated the F100-PW-229 thrust-vectoring nozzles to be highly capable and efficient.

  20. Selected Performance Measurements of the F-15 Active Axisymmetric Thrust-vectoring Nozzle

    NASA Technical Reports Server (NTRS)

    Orme, John S.; Sims, Robert L.

    1998-01-01

    Flight tests recently completed at the NASA Dryden Flight Research Center evaluated performance of a hydromechanically vectored axisymmetric nozzle onboard the F-15 ACTIVE. A flight-test technique whereby strain gages installed onto engine mounts provided for the direct measurement of thrust and vector forces has proven to be extremely valuable. Flow turning and thrust efficiency, as well as nozzle static pressure distributions were measured and analyzed. This report presents results from testing at an altitude of 30,000 ft and a speed of Mach 0.9. Flow turning and thrust efficiency were found to be significantly different than predicted, and moreover, varied substantially with power setting and pitch vector angle. Results of an in-flight comparison of the direct thrust measurement technique and an engine simulation fell within the expected uncertainty bands. Overall nozzle performance at this flight condition demonstrated the F100-PW-229 thrust-vectoring nozzles to be highly capable and efficient.

  1. UAV's for active tectonics : case example from the Longitudinal Valley and the Chishan Faults (Southern Taiwan)

    NASA Astrophysics Data System (ADS)

    Deffontaines, Benoit; Chang, Kuo-Jen; Chan, Yu-Chang; Chen, Rou-Fei; Hsieh, Yu-Chung

    2015-04-01

    Taiwan is a case example to study active tectonics due to the active NW-SE collision of the Philippine and Eurasian Sea Plates as the whole convergence reaches 10cm/y. In order to decipher the structural active tectonics geometry, we used herein UAV's to get high resolution Digital Terrain Model (DTM) in local active tectonics key areas. Classical photo-interpretation where then developped in order to structurally interprete these data, confirmed by field studies. Two location had first been choosen in order to highlight the contribution of such high resolution DTM in SW Taiwan on the Longitudinal Valley Fault (SE Taiwan) on its southern branch from Pinting to Luyeh terraces (Pinanshan) where UAV's lead to better interprete the location of the outcropping active deformations. Combined with available GPS data and PALSAR interferometry (Deffontaines et Champenois et al., submitted) it is then possible to reconstruct the way of the present deformation in this local area. In the Pinting terraces, If the western branch of the fault correspond to an outcroping thrust fault, the eastern branch act as a a growing active anticline that may be characterized and quantified independantly. The interpretation of the UAV's high resolution DTM data on the Chishan Fault (SW Taiwan) reveals also the geometry of the outcropping active faults complex structural behaviour. If the Chishan Fault act as a thrusting in its northern tip (close to Chishan city), it acts as a right lateral strike-slip fault north of Chaoshan (Kaohsiung city) as described by Deffontaines et al. 2014. Therefore UAV's are a so useful tool to get very high resolution topographic data in Taiwan that are of great help to get the geometry of the active neotectonic structures in Taiwan.

  2. Slip rates on the Chelungpu and Chushiang thrust faults inferred from a deformed strath terrace along the Dungpuna river, west central Taiwan

    NASA Astrophysics Data System (ADS)

    Simoes, Martine; Avouac, Jean Philippe; Chen, Yue-Gau

    2007-03-01

    The Chelungpu fault produced the September 1999 Mw = 7.6 Chi-Chi earthquake, central Taiwan. The shortening rate accommodated by this structure, integrated over several seismic cycles, and its contribution to crustal shortening across the Taiwanese range have remained unresolved. To address the issues, we focus our study on the Chelungpu and Chushiang thrust faults within the southernmost portion of the Chi-Chi rupture area. Structural measurements and available seismic profiles are used to infer the subsurface geometry of structures. The Chushiang and Chelungpu faults appear as two splay faults branching onto a common ramp that further north connects only to the Chelungpu surface trace. We survey a deformed strath terrace along the Dungpuna river, buried under a 11,540 ± 309 years old fill deposit. Given this age, the dip angles of the faults, and the vertical throw determined from the offset of the strath terrace across the surface fault traces, we estimate slip rates of 12.9 ± 4.8 and 2.9 ± 1.6 mm/yr on the Chelungpu and Chushiang faults, respectively. These yield a total shortening rate of 15.8 ± 5.1 mm/yr to be absorbed on their common decollement at depth. This total value is an upper bound for the slip rate on the Chelungpu fault further north, where the Chushiang fault disappears and transfers shortening to adjacent faults. Combining these results with the recently constrained shortening rate on the Changhua blind thrust reveals that all these frontal faults presently absorb most of the long-term horizontal shortening across the Taiwanese range. They thus stand as the major sources of seismic hazards in this heavily populated area. The return period of earthquakes similar to the Chi-Chi event over a ˜80 km long stretch of the Western Foothills is estimated to be ˜64 years. This value is an underestimate because it assumes that all the faults locked during the interseismic period slip only during such large events. Comparison with historical seismicity

  3. InSAR measurements around active faults: creeping Philippine Fault and un-creeping Alpine Fault

    NASA Astrophysics Data System (ADS)

    Fukushima, Y.

    2013-12-01

    Recently, interferometric synthetic aperture radar (InSAR) time-series analyses have been frequently applied to measure the time-series of small and quasi-steady displacements in wide areas. Large efforts in the methodological developments have been made to pursue higher temporal and spatial resolutions by using frequently acquired SAR images and detecting more pixels that exhibit phase stability. While such a high resolution is indispensable for tracking displacements of man-made and other small-scale structures, it is not necessarily needed and can be unnecessarily computer-intensive for measuring the crustal deformation associated with active faults and volcanic activities. I apply a simple and efficient method to measure the deformation around the Alpine Fault in the South Island of New Zealand, and the Philippine Fault in the Leyte Island. I use a small-baseline subset (SBAS) analysis approach (Berardino, et al., 2002). Generally, the more we average the pixel values, the more coherent the signals are. Considering that, for the deformation around active faults, the spatial resolution can be as coarse as a few hundred meters, we can severely 'multi-look' the interferograms. The two applied cases in this study benefited from this approach; I could obtain the mean velocity maps on practically the entire area without discarding decorrelated areas. The signals could have been only partially obtained by standard persistent scatterer or single-look small-baseline approaches that are much more computer-intensive. In order to further increase the signal detection capability, it is sometimes effective to introduce a processing algorithm adapted to the signal of interest. In an InSAR time-series processing, one usually needs to set the reference point because interferograms are all relative measurements. It is difficult, however, to fix the reference point when one aims to measure long-wavelength deformation signals that span the whole analysis area. This problem can be

  4. Deformation Monitoring of AN Active Fault

    NASA Astrophysics Data System (ADS)

    Ostapchuk, A.

    2015-12-01

    The discovery of low frequency earthquakes, slow slip events and other deformation phenomena, new for geophysics, change our understanding of how the energy accumulated in the Earth's crust do release. The new geophysical data make one revise the underlying mechanism of geomechanical processes taking place in fault zones. Conditions for generating different slip modes are still unclear. The most vital question is whether a certain slip mode is intrinsic for a fault or may be controlled by external factors. This work presents the results of two and a half year deformation monitoring of a discontinuity in the zone of the Main Sayanskiy Fault. Main Sayanskiy Fault is right-lateral strike-slip fault. Observations were performed in the tunnel of Talaya seismic station (TLY), Irkutsk region, Russia. Measurements were carried out 70 m away from the entrance of the tunnel, the thickness of overlying rock was about 30 m. Inductive sensors of displacement were mounted at the both sides of a discontinuity, which recorded three components of relative fault side displacement with the accuracy of 0.2 mcm. Temperature variation inside the tunnel didn't exceed 0.5oC during the all period of observations. Important information about deformation properties of an active fault was obtained. A pronounced seasonality of deformation characteristics of discontinuity is observed in the investigated segment of rock. A great number of slow slip events with durations from several hours to several weeks were registered. Besides that alterations of fault deformation characteristics before the megathrust earthquake M9.0 Tohoku Oki 11 March 2011 and reaction to the event itself were detected. The work was supported by the Russian Science Foundation (grant no. 14-17-00719).

  5. Using optical dating to assess the recent activity of active faults in Hsinchu Area, northwestern Taiwan

    NASA Astrophysics Data System (ADS)

    Watanuki, T.; Chen, Y.

    2003-12-01

    The aim of this study is to evaluate the recent activity of active fault systems mapped in Hsinchu area, northwestern Taiwan. Since it is the largest site of industrial park and highly populated, it is essential to assess potential of earthquake hazards. As a result of previous work, two active fault systems (Hsinchu and Hsincheng) were identified as active. However, they have not been included in dangerous active faults on published map because Holocene offset has not been confirmed yet. Relationship between five river terraces and faults were discussed by mapping on geomorphic features; both of these thrust faults contain active anticlines in their hanging walls based on folded terraces that are composed of young alluvial deposits. Neither long-term nor short-term slip rate has been reported due to lack of age control on development timing of the terraces mentioned above. We collected samples from these terraces and open-pit trench on the highest terrace, where intercalated sandy layers are found within cobbles. As literatures optically stimulated luminescence (OSL) dating method can directly measure the burial ages of sedimentary deposits that underwent a short period of sunlight bleaching. Therefore, OSL dating is applied via single aliquot regeneration method on sand size quartz extract from our study terraces. OSL ages about 46ka and 68-75ka are obtained from 4 fluvial deposits at trenching site. We tentatively suggest that the terrace was abandoned by the main channel after 68ka and then upper strata were subsequently deposited by local small creeks. The vertical displacements cross these Hsinchu and Hsincheng active faults are ca. 90m and 70m, respectively since 68ka. Consequently, the derived long-term rates of vertical slip are 1.3 and 1.0 m/ka respectively for both of them. The details of the other age results and discussion on recent structural behavior will be presented.

  6. Active faults in the Kashmir Valley

    NASA Astrophysics Data System (ADS)

    Shah, A.

    2012-04-01

    The risk of earthquake is ever increasing in mountains along with rapid growth of population and urbanization. Over half a million people died in the last decade due to earthquakes. The devastations of Sumatra and Thai coasts in 2004, of Kashmir and New Orleans in 2005, of SW Java in 2006, of Sumatra again in 2007, W Sichuan and Myanmar in 2008, of Haiti in 2010, Japan, New Zealand and Turkey in 2011, brought enormous damage. The primary step in this regard could be to establish an earthquake risk model. The Kashmir valley is a NW-SE trending oval-shaped inter-mountain basin. A number of low magnitude earthquakes have recently been reported from the border and few inside the Kashmir valley. A number of active reverse faults were identified in this valley using remote sensing images and active geomorphic features. NE dipping reverse faults uplifted the young alluvial fan at the SW side. An active tectonic environment has been created by these reverse faults; sediment filled streams at NE, and uplifted quaternary deposits at SW. These resulted in an overall tilting of the entire Kashmir valley towards NE. Dating of displaced deposits is required to estimate the total convergence along these faults. Broadly, these faults are because of the convergence of Indian plate beneath the Eurasian plate.

  7. 3D Fault modeling of the active Chittagong-Myanmar fold belt, Bangladesh

    NASA Astrophysics Data System (ADS)

    Peterson, D. E.; Hubbard, J.; Akhter, S. H.; Shamim, N.

    2013-12-01

    The Chittagong-Myanmar fold belt (CMFB), located in eastern Bangladesh, eastern India and western Myanmar, accommodates east-west shortening at the India-Burma plate boundary. Oblique subduction of the Indian Plate beneath the Burma Plate since the Eocene has led to the development of a large accretionary prism complex, creating a series of north-south trending folds. A continuous sediment record from ~55 Ma to the present has been deposited in the Bengal Basin by the Ganges-Brahmaputra-Meghna rivers, providing an opportunity to learn about the history of tectonic deformation and activity in this fold-and-thrust belt. Surface mapping indicates that the fold-and-thrust belt is characterized by extensive N-S-trending anticlines and synclines in a belt ~150-200 km wide. Seismic reflection profiles from the Chittagong and Chittagong Hill Tracts, Bangladesh, indicate that the anticlines mapped at the surface narrow with depth and extend to ~3.0 seconds TWTT (two-way travel time), or ~6.0 km. The folds of Chittagong and Chittagong Hill Tracts are characterized by doubly plunging box-shaped en-echelon anticlines separated by wide synclines. The seismic data suggest that some of these anticlines are cored by thrust fault ramps that extend to a large-scale décollement that dips gently to the east. Other anticlines may be the result of detachment folding from the same décollement. The décollement likely deepens to the east and intersects with the northerly-trending, oblique-slip Kaladan fault. The CMFB region is bounded to the north by the north-dipping Dauki fault and the Shillong Plateau. The tectonic transition from a wide band of E-W shortening in the south to a narrow zone of N-S shortening along the Dauki fault is poorly understood. We integrate surface and subsurface datasets, including topography, geological maps, seismicity, and industry seismic reflection profiles, into a 3D modeling environment and construct initial 3D surfaces of the major faults in this

  8. Active faulting and tectonics of the Ningxia-Hui Autonomous Region, China

    NASA Astrophysics Data System (ADS)

    Qidong, Deng; Sung, Fengmin; Zhu, Shilong; Li, Mengluan; Wang, Tielin; Zhang, Weiqi; Burchfiel, B. C.; Molnar, Peter; Zhang, Peizhen

    1984-06-01

    Strike-slip, thrust, and normal faulting all seem to play an active role in the tectonics of Ningxia. In the southernmost part of the region a major left-lateral strike-slip fault enters the region from the neighboring Gansu province to the west and trends about S65°E. This fault is very clear on Landsat imagery and on aerial photos, and the portion in eastern Gansu and Ningxia broke in the Haiyuan earthquake of December 16, 1920. Displacements of 5-10 m caused by that earthquake are clear in numerous localities and accord with a revised value of the seismic moment of 1.2×1021N m. The eastern end of the Haiyuan fault terminates in a narrow south trending fold and thrust zone. Several other similar, north to northwest trending fold and thrust belts are present in the area about 50-200 km northeast of the Haiyuan fault and divide it into small, apparently relatively undeformed blocks 10-40 km in dimensions. The geometry of the structures in the fold and thrust zones and the apparently shallow depths at the time of deformation suggest that current deformation is similar to that that occurred in the fold and thrust belt of the Idaho-Wyoming Rocky Mountains. North of this area, both the Helan Shan (a horst) and the Yinchuan graben are bounded by clear, active northerly trending normal faults, in some cases with right-lateral strike-slip components. The overall deformation, hence, seems to include dominant components of east-west left-lateral strike-slip movement, northeast-southwest crustal shortening, and northwest-southeast extension. We interpret the extension as a response to a northeast directed force applied to the Ordos block and both this northeast directed force and the left-lateral slip on the Haiyuan fault to the eastward displacement of material on the northeast edge of the Tibetan plateau with respect to Eurasia north of it.

  9. Continuity of slip rates over various time scales on the Puente Hills Blind-thrust Fault, Los Angeles, California

    NASA Astrophysics Data System (ADS)

    Bergen, Kristian J.; Shaw, John H.; Leon, Lorraine A.; Dolan, James F.; Pratt, Thomas L.; Ponti, Daniel J.; Barrera, Wendy; Rhodes, Edward J.; Murari, Madhav K.; Owen, Lewis A.

    2014-05-01

    Our study seeks to assess the history of slip on the Los Angeles segment of the Puente Hills blind-thrust fault system (PHT) from its inception through the Holocene by integrating a suite of geological and geophysical datasets. The PHT presents one of the largest seismic hazards in the United States, given its location beneath downtown Los Angeles. It is also well suited to slip rate studies, as fold scarps formed by slip on the PHT at depth have been continually buried by flood deposits from the Los Angeles and San Gabriel Rivers, preserving a record of uplift in the form of growth stratigraphy. We determined uplift from the growth stratigraphy by measuring the difference in sediment thickness across the folded layers. At our study site above the western segment of the PHT, the fold structure was imaged by industry seismic reflection data and a pair of high-resolution (100 to 700 m depth) seismic reflection profiles acquired by the authors for this study using weight drop and small vibrator sources. The industry and high-resolution profiles were stacked, migrated and depth converted using a velocity model based on the stacking velocities and the Southern California Earthquake Center Community Velocity Model. The shallowest layers of growth stratigraphy were geometrically constrained by lithological correlations across a series of cone penetration tests and continuously cored boreholes. Age control was provided by radiocarbon dating, optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL) dating, and sequence-stratigraphic boundaries. Radiocarbon dating was used to constrain individual earthquake event ages in the borehole transect. Using a novel coring procedure, light-protected samples for quartz OSL and feldspar IRSL dating were acquired from a 171-m-deep borehole that we drilled within the growth fold. These samples provided age constraints on growth strata that were tied to prominent seismic reflections and were combined with

  10. A slow-slipping active fold and thrust system at the SE corner of the Atacama basin, northern Chile

    NASA Astrophysics Data System (ADS)

    Lin, Y.; Shyu, J. H.; González, G.

    2009-12-01

    The western South American offshore is one of the major active convergent plate boundaries in the world, where the Nazca plate is subducting northeastward beneath the South American plate at a rate of about 84 mm/yr. Despite of this rapid plate convergence, the forearc region of western Andes does not seem to undergo large deformation at present. In order to understand the characteristics and mechanisms of active forearc deformation related to the plate convergence, we investigated tectono-geomorphic features in the area of Tilocalar, near the SE margin of the Atacama Basin in northern Chile, where active structures have been previously identified. To map topographic features produced by active structures, we used a combination of several remote-sensing data sets, including digital elevation models (DEM) made from Shuttle Radar Topographic Mission (SRTM), as well as higher resolution ASTER and QuickBird satellite images. Detailed geomorphic surveys using real time kinematic (RTK) GPS are carried out in the field to obtain high-resolution topographic profiles across these features. We also performed 40Ar/39Ar dating of deformed volcanic rocks in order to determine the long-term slip rates of the active structures. The hyper-aridity of the Atacama Basin results in extremely low erosion and sedimentation rates in the area. As a result, the present relief of land surface is mostly produced by neotectonic activity, and can be used as deformation marker. In the Tilocalar area, several N-S trending ridges are present. These ridges, generally several tens of meters high, are likely formed by asymmetric anticlines or monoclines with steep forelimbs facing east, and these folds are likely fault-propagation folds produced by underlying thrust faults. We suggest that these faults merge at depth to become a major active thrust system. From 40Ar/39Ar plateau ages, we found that the surface ignimbrites mostly deposited in latest Pliocene (2.3~4.3 Ma). If the structures have been

  11. Upper Pleistocene - Holocene activity of the Carrascoy Fault (Murcia, SE Spain): preliminary results from paleoseismological research.

    NASA Astrophysics Data System (ADS)

    Martin-Banda, Raquel; Garcia-Mayordomo, Julian; Insua-Arevalo, Juan M.; Salazar, Angel; Rodriguez-Escudero, Emilio; Alvarez-Gomez, Jose A.; Martinez-Diaz, Jose J.; Herrero, Maria J.; Medialdea, Alicia

    2014-05-01

    The Carrascoy Fault is located in the Internal Zones of the Betic Cordillera (Southern Spain). In particular, the Carrascoy Fault is one of the major faults forming the Eastern Betic Shear Zone, the main structure accommodating the convergence between Nubian and Eurasian plates in the westernmost Mediterranean. So far, the Carrascoy Fault has been defined as a left-lateral strike-slip fault. It extends for at least 31 km in a NE-SW trend from the village of Zeneta (Murcia) at its northeastern tip, to the Cañaricos village, controlling the northern edge of the Carrascoy Range and its linkage to the Guadalentin Depression towards the southwest. This is an area of moderate seismic activity, but densely populated, the capital of the region, Murcia, being settled very close to the fault. Hence, the knowledge of the structure and kinematics of the Carrascoy Fault is essential for assessing reliably the seismic hazard of the region. We present a detailed-scale geological and geomorphological map along the fault zone created from a LIDAR DEM combined with fieldwork, and geological and geophysical information. Furthermore, a number of trenches have been dug across the fault at different locations providing insights in the fault most recent activity as well as paleoseismic data. Preliminary results suggest that the Cararscoy Fault has recently changed its kinematic showing a near pure reverse motion. According to this, the fault can be divided into two distinct segments, the eastern one: Zeneta - Fuensanta, and the western one: Fuensanta - Cañaricos, each one having its own characteristic style and geodynamics. Some new active strands of the fault locate at the foot of the very first relief towards the North of the older strand, forming the current southern border of the Guadalentin Depression. These new faults show an increasingly reverse component westwards, so that the Fuensanta - Cañaricos segment is constituted by thrusts, which are blind at its western end

  12. North-vergent thrust fault between Baltica and Laurentian affinity rocks in the frontal part of Romanzof orogen, NE Brooks Range, Alaska

    NASA Astrophysics Data System (ADS)

    Moore, T. E.; O'Sullivan, P. B.

    2012-12-01

    One of the most striking features of Arctic physiography is the long, linear Canadian Arctic margin of the Arctic Basin, which extends from the Lincoln Sea north of Greenland to the eastern Beaufort Sea and projects into northeastern Alaska. Among other ideas, this margin has been proposed to have developed by sinistral transform faulting in the Middle Devonian as a result of tectonic escape of terranes from the Caledonites (the so-called "Northwest Passage"). The faults on which the transform motion might have occurred, however, have not been recognized along the northern margin of North America. One candidate for such a fault is exposed at the southern boundary of the Sadlerochit Mountains province in the Tertiary frontal part of the NE Brooks Range. In the Plunge Creek area of the Arctic National Wildlife Refuge, a contact between rocks of Laurentian affinity and Baltica affinity is exposed on the back limb of a basement-involved map-scale thrust block formed by Brookian thrusting. The regional unconformity at the base of the Mississippian to Triassic Ellesmerian Sequence provides a near flat-lying datum that overlaps the contact between the pre-Mississippian tectonic units and demonstrates that it was not reactivated by Brookian thrusting. The Sadlerochit Mountains succession to the north of the contact consists of a Neoproterozoic and lower Paleozoic carbonate sequence that rests on metaclastic rocks that yield Grenville-Sveconorwegian (0.95-1.2 Ga) and other Mesoproterozoic detrital zircon U-Pb age populations similar to those reported from the northern parts of Baltica and eastern Greenland. In contrast, the Romanzof Mountains succession to the south consists of Neoproterozoic deep-marine clastic rocks (Neruokpuk Quartzite) and overlying lower Paleozoic chert and argillite. Detrital zircon U-Pb age populations from the Neruokpuk are very similar to those from Laurentian-derived clastic rocks in the Canadian margin of North America. Field relations show that

  13. Soro West: A non-seismically defined, fault cut-off prospect in the Papuan Fold and Thrust Belt, Papua New Guinea

    SciTech Connect

    Robinson, W.F.; Swift, C.M. Jr.

    1996-12-31

    Soro West is a fault cut-off prospect located in the frontal portion of the Papuan Fold and Thrust Belt. Prospective Toro and Imburu sandstones are interpreted to be in the hanging wall of the Soro Thrust. Truncation against the thrust, both updip and through lateral ramps, provides the trapping mechanism. The Soro West Prospect was defined using geological, geochemical, remote sensing, and geophysical data. The definition and location of the trap is a primary risk and work was focused on this aspect. Surface geological data (lithology, strikes, and dips) topography and synthetic aperture radar imagery were incorporated into the evaluation. Statistical curvature analysis techniques helped define the shape of the structure and the locations of the lateral ramps. Strontium isotope analyses of Darai Limestone surface samples refined erosional levels using a locally-derived reference curve. Severe karst precludes the acquisition of coherent surface seismic data, so the primary geophysical tool used was magnetotellurics (MT). A detailed, pre-survey feasibility study defined expected responses from alternative structural models. The MT data demonstrated that the limestone at surface is underlain by thick conductive clastics and not another Darai Limestone sheet. The data also constrained the range of fault cut-off positions significantly. Multiple, three-dimensionally consistent, restorable alternative structural models were created using results from all analyses. These led to a positive assessment of the prospect and an exploratory test is to be drilled in 1996.

  14. [Comment on “Investigations unveil Holocene thrusting for onshore Portugal”] Paleoseismological studies near Lisbon: Holocene thrusting or landslide activity?

    NASA Astrophysics Data System (ADS)

    Cabral, João M. L.; Marques, Fernando M. S. F.

    A paper on paleoseismological investigations in the Lower Tagus River Valley (LTV) region, northeast of Lisbon, Portugal, was recently published in Eos Transactions by Fonseca et al. (2000a). The LTV is an area of significant seismicity attested by the occurrence of magnitude 6.5-7 historical earthquakes, and has been the subject of several geological studies. Nevertheless, major uncertainties on the regional tectonic structure have subsisted until now, mainly due to a Cenozoic sedimentary cover that hides most of the active faults rooted in the basement.

  15. Lake Clark fault, assessment of tectonic activity based on reconnaissance mapping of glacial deposits, northwestern Cook Inlet Alaska

    NASA Astrophysics Data System (ADS)

    Reger, R. D.; Koehler, R. D.

    2009-12-01

    The Lake Clark fault extends ~247 km from the vicinity of Lake Clark in the Alaska-Aleutian Range batholith northeastward to the Castle Mountain fault along the northern margin of Cook Inlet. Documented Tertiary deformation along the fault includes dextral offsets (5-26 km) and north-side-up reverse displacements (500-1,000 m). The fault is along strike with the Holocene-active Castle Mountain fault and adjacent to the active northern Cook Inlet fold belt. As part of the STATEMAP program, the State of Alaska has begun a 2-year geologic mapping project in the vicinity of the Lake Clark fault, including assessment of Quaternary fault activity and its role in accommodating deformation in the Aleutian forearc. Here we present preliminary Quaternary mapping and tectonic geomorphic observations aimed at assessing the fault activity. Between the Beluga and Chakachatna rivers, large lateral moraines of the late Wisconsinan Naptowne glaciation cross the fault and are not displaced. In the vicinity of Lone Ridge, the fault is expressed as a ~25-m southeast-facing scarp in bedrock associated with springs and vertically offset Stage 4 or 6 moraines. In the Chuitna River drainage basin beyond the Naptowne ice limit, the fault extends across a fairly flat plateau with drumlins and ice-stagnation deposits related to Stage 4 or 6 glaciation. There the fault is expressed by subtle vegetation and tonal lineaments on air photos; however, scarps and lateral offsets were not observed. Stream profiles perpendicular to the fault along the Chuitna River and Chuitna Creek have convex profiles that could be related to tectonic folding. Our observations indicate that this part of the Lake Clark fault may be Quaternary active, but has been relatively quiescent in the late Pleistocene. Thus, blind thrust faults associated with the northern Cook Inlet fold belt may accommodate the majority of the tectonic deformation in this part of the Aleutian forearc. This information is applicable to

  16. Precarious rock and overturned transformer evidence for ground shaking in the Ms 7.7 Kern County earthquake: An analog for disastrous shaking from a major thrust fault in the Los Angeles basin

    USGS Publications Warehouse

    Brune, J.N.; Anooshehpoor, A.; Shi, B.; Zheng, Yen

    2004-01-01

    Precariously balanced rocks and overturned transformers in the vicinity of the White Wolf fault provide constraints on ground motion during the 1952 Ms 7.7 Kern County earthquake, a possible analog for an anticipated large earthquake in the Los Angeles basin (Shaw et al., 2002; Dolan et al., 2003). On the northeast part of the fault preliminary estimates of ground motion on the footwall give peak accelerations considerably lower than predicted by standard regression curves. On the other hand, on the hanging-wall, there is evidence of intense ground shattering and lack of precarious rocks, consistent with the intense hanging-wall accelerations suggested by foam-rubber modeling, numerical modeling, and observations from previous thrust fault earthquakes. There is clear evidence of the effects of rupture directivity in ground motions on the hanging-wall side of the fault (from both precarious rocks and numerical simulations). On the southwest part of the fault, which is covered by sediments, the thrust fault did not reach the surface ("blind" thrust). Overturned and damaged transformers indicate significant transfer of energy from the hanging wall to the footwall, an effect that may not be as effective when the rupture reaches the surface (is not "blind"). Transformers near the up-dip projection of the fault tip have been damaged or overturned on both the hanging-wall and footwall sides of the fault. The transfer of energy is confirmed in a numerical lattice model and could play an important role in a similar situation in Los Angeles. We suggest that the results of this study can provide important information for estimating the effects of a large thrust fault rupture in the Los Angeles basin, specially given the fact that there is so little instrumental data from large thrust fault earthquakes.

  17. Large-scale thrusting along the northern margin of the Tibetan Plateau and the southwest Tarim basin: 230 km long active Hotian thrust sheet

    NASA Astrophysics Data System (ADS)

    Suppe, J.; Wang, X.; He, D.; Liang, H.

    2015-12-01

    We present the geometry, kinematics and mechanics of large-scale active thrusting in the western Kunlunshan and southwest Tarim basin, which accounts for ~130-165km total shortening of Tarim crust at the northern margin of Tibet. The great frontal structure is the ~230km long bedding-parallel Hotian thrust sheet, which is perhaps the longest active intact thrust sheet in the world, composed of flat-lying strata of the Tarim basin sliding northward on a regional gypsum detachment at the base of the Cenozoic sequence. The toe of the Hotian thrust ramps to the surface two thirds of the way across the Tarim basin, forming the Selibuya-Mazartag hills in the Taklamakan sand desert. At the southern edge of the Tarim basin in the Kunlunshan foothills, a set of high-amplitude anticlines are growing by complex break-forward ramping and wedging in the Hotian thrust sheet as it steps up to the Cenozoic gypsum detachment from a regional Cambrian evaporate detachment that extends under Tibet. More interior structures such as the Tiklik thrust bring older strata and Proterozoic basement to the surface, together with their Cenozoic Tarim cover in the Buya basin. The Cambrian detachment also extends northward under the Tarim basin with minor hanging-wall deformation that locally warps the overlying Hotian thrust sheet, producing a complete syntectonic record in seismically imaged growth strata of its northward motion over these warps. Seismic profiles in the southwest Tarim foothill belt also reveal widespread growth strata that record much of the structural history beginning in the early Pliocene Atushi Formation. Ages of seismic reflectors are calibrated to a surface magnetostratigraphic sequence (Zheng et al., 2000). The beginning of thrusting and folding in the southwest Tarim basin north of the Tiklik thrust is dated at 3.6Ma with shortening >25km and a progressive northward propagation toward the Selibuya-Mazartag hills. The overall shortening rate is ~10 mm/yr. The gypsum

  18. Changing mechanical response during continental collision: Active examples from the foreland thrust belts of Pakistan

    NASA Astrophysics Data System (ADS)

    Davis, Dan M.; Lillie, Robert J.

    1994-01-01

    We have used data from teleseismic, seismic reflection and field geologic studies, along with both geomechanical and gravity modeling to contrast the tectonics of four active orogenic wedges in Pakistan: the Kashmir Himalaya, the Salt Range-Potwar Plateau foldbelt, the Sulaiman Range and the Makran accretionary wedge. In Makran, oceanic crust is still being subducted, and a thick pile of sediments is being accreted and underplated. Undercompaction and excess pore pressures can explain the narrow cross-sectional taper and frontal aseismicity of this wedge. Beneath the Sulaiman wedge, continental crust is just starting to be underthrust. Indirect evidence suggests that fine-grained carbonate rocks found in abundance deep in the stratigraphic section may be deforming ductilely at the base of the Sulaiman wedge and provide a zone of ductile detachment. The collision has proceeded to a much more mature stage in the Salt Range-Potwar Plateau foldbelt and the Kashmir Himalaya. Isostatic response to underthrusting of continental crust has kept the sedimentary pile quite thin in both of these wedges, so in that respect the two foldbelts are similar. However, thick Eocambrian salt beneath the Salt Range and Potwar Plateau permits that foldbelt to be much wider in map view, with a thinner cross-sectional taper and a mixture of thrust vergence directions. A major normal fault in basement causes the Salt Range to rise in front of the mildly deformed molasse basin of the southern Potwar Plateau. Much of the diversity among these mountain belts can be understood in terms of differences in the maturity of the collision process in each area, the resulting thickness of the sedimentary pile encountered at the deformation front, and the presence or absence of large contrasts in strength between the various layers of the stratigraphic section and basement relief.

  19. Fault Segmentation and its Implication to the Evaluation of Future Earthquakes from Active Faults in Japan

    NASA Astrophysics Data System (ADS)

    Awata, Y.; Yoshioka, T.

    2005-12-01

    Segmentation of active faults is essential for the evaluation both of past and future faulting using geologic data from paleoseismological sites. A behavioral segment is defined as the smallest segment of fault having a characteristic history of faulting. More over, we have to estimate the earthquake segments that can be consist of multiple faulting along a system of behavioral segments. Active fault strands in Japan are segmented into behavioral segments based on fault discontinuity of 2-3 km and larger (Active Fault Res. Group, GSJ, 2000), large bend of fault strand and paleoseismicity. 431 behavioral segments, >= 10 km in length and >= 0.1 m/ky in long-term slip-rate, are identified from a database of active faults in Japan, that is constructed at AFRC, GSJ/AIST. The length of the segments is averaged 21 km and approximately 70 km in maximum. Only 8 segments are exceed 45 km in length. These lengths are very similar to those of historical surface ruptures not only in Japan since 1891 Nobi earthquake, but also in other regions having different tectonic setting. According to the scaling law between fault length and amount of displacement of behavioral segment, a maximum length of ca. 70 km can estimate a slip of ca. 14 m. This amount of slip is as large as world largest slip occurred during the 1931 Fuyun earthquake of M 8, 1999 Chichi earthquake of M 7.4 and the 2001 Central Kunlun earthquake of M 7.9 in East Asia. Recent geological and seismological studies on large earthquakes have revealed that multiple-rupturing is very common during large earthquakes. Therefore, evaluation of simultaneous faulting along a system of active faults is indispensable for the estimation of earthquake size. A Matsuda's (1990) idea of "seismogenic faults", that is divided or grouped based on the geometric discontinuity of 5 km, may useful for the best estimation of earthquake segment. The Japanese behavioral segments are grouped into "seismogenic faults", each consists of about 2

  20. Interseismic strain accumulation across an active thrust system: an InSAR case study in the Himalaya

    NASA Astrophysics Data System (ADS)

    Grandin, R.; Doin, M.; Ducret, G.; Bollinger, L.; Pinel-Puysségur, B.; Lasserre, C.; Jolivet, R.

    2011-12-01

    The major active thrust system underlying the Himalayan range produces recurrent large earthquakes, posing a significant threat to the densely populated Indo-Gangetic basin. Measuring the interseismic deformation associated with this fault system could provide important constraints on the geometry of the locked faults that are bound to rupture in future great earthquakes. This has so far been considered out of reach of InSAR techniques, due to decorrelation, prominent topographic features, and unfavourable climatic conditions. However, preliminary tests carried out with the archived ASAR data provided by ESA's ENVISAT satellite since 2002 have shown that recent advances in InSAR processing may now allow geodesists to tackle most of these perturbations. In this context, applying these advanced techniques to the case of the Himalayas is both a challenging and necessary task. We will present the methodology and the first results of an InSAR study of interseismic strain accumulation across the Himalayas. Small-baseline processing of ENVISAT data using a combination of ROI_PAC software, NSBAS processing chain and MulSAR technique yields a sufficient number of coherent interferograms to compute a preliminary average velocity map of interseismic uplift. Time-space variations of stratified tropospheric delay observed in these interferogrames are mitigated using a prediction deduced from outputs of the ECMWF global meteorological reanalysis ERA-Interim. Finally, a correction of DEM errors from the wrapped InSAR data set further improves the coherence of interferograms with a large perpendicular baseline. Comparison of the InSAR LOS velocity maps with microseismic activity detected near the transition zone at the base of the seismogenic portion of the Main Himalayan Thrust is expected to provide constraints on the process of elastic strain accumulation during the interseismic period. This will help in understanding the interaction between the construction of topography

  1. F-15B ACTIVE with thrust vectoring nozzles on test stand

    NASA Technical Reports Server (NTRS)

    1995-01-01

    This November 13, 1995, photograph of the F-15 Advanced Controls Technology for Integrated Vehicles (ACTIVE) at NASA's Dryden Flight Research Center, Edwards, California, shows the thrust stand being used for ground testing of a new thrust-vectoring concept involving two new Pratt & Whitney nozzles that can turn up to 20 degrees in any direction. These nozzles give the aircraft thrust control in the pitch (up and down) and yaw (left and right) directions. This will reduce drag and increase fuel economy or range as compared with conventional aerodynamic controls, which increase the retarding forces (drag) acting upon the aircraft. These tests could lead to significant performance increases for military and commercial aircraft. The research program is the product of a collaborative effort by NASA, the Air Force's Wright Laboratory, Pratt & Whitney, and McDonnell Douglas Aerospace.

  2. Faults Activities And Crustal Deformation near Hualien City, eastern Taiwan Analysed By Persistent Scatterer InSAR

    NASA Astrophysics Data System (ADS)

    Lu, C.; Lin, M.; Yen, J.; Chang, C.

    2008-12-01

    Hualien is located in eastern part of Taiwan, and is the collision boundary in the northern of Huatung Longitudinal Valley between the Philippine Sea tectonic plate and Eurasian tectonic plate(Biq, 1981; Barrier and Angelier, 1986). There are several active faults, such as Milun fault, Beipu fault and Minyi fault, pass through the Hualien city, and create many crustal deformation. According to previous researches (Hsu, 1956; Lin, 1962; Yu, 1997) we know Milun fault is a thrust and left lateral fault, and the fault plane incline to east. Minyi fault also is a left lateral and a slight reverse fault, but it's fault plane incline to west. (Chang, 1994; Yu, 1997) We applied the Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR, Hooper, 2007) to observe temporally-variable processes of Hualien city between 2004 to 2008. At the same time, precise leveling and GPS data were taken for the auxiliary data to verify the deformation rate and pattern in this area. In the Hualien city area, our observation showed that the active faults separate this area into several distinct blocks. Most of the blocks moved slowly, but the hanging wall of the Milun fault decreases 5- 8mm in line of sight (LOS) direction between 15 May 2004 to 24 Feb 2007, then increases 3-6mm in LOS between 1 Dec 2007 to 5 Jan 2008. The deformation reversed its direction in 2007. The western surface of Hualien City displays continuous deformation about 1.5-2mm/yr , which spread along the Beipu fault. Our preliminary investigation indicated that between late 2004 and middle 2005 there had been an abrupt increase in seismicity, which coincided with PSInSAR observation of a large displacement. The distribution of shallow source earthquakes correlate with the area with large deformation. Our following works include continuing observation of the Hualien City, and decipher the relationship between earthquakes and surface deformation, and model the fault action in Hualien City with time series.

  3. Direct Dating of Brittle Faults and Episodic Orogeny, illustrated by Illite Age Analysis of Major Thrusts in the Canadian Rocky Mountains (Invited)

    NASA Astrophysics Data System (ADS)

    van der Pluijm, B.; Pana, D.

    2013-12-01

    Illitization is a common process in shallow fault rocks, which allows direct dating of faulting through a combination of illite polytype quantification from XRD analysis and Ar-Ar encapsulation dating of multiple grain size fractions of clay gouge. The application of Illite Age Analysis (IAA) to fault rocks has the benefit that very small sample volumes can be analyzed, that potassium and argon are measured simultaneously, and that it has high precision. Grain size fraction separation into 3-4 subsamples, typically in the range of <2.0 μm to <0.02 μm, and illite characterization and quantification using modeling of XRD spectra that determines the relative abundance of detrital (2M1) and authigenic (1M/1Md) polytypes, are key to obtaining geologically meaningful results. Both a total gas age, incorporating the recoiled argon fraction after irradiation, and a retention age, omitting the recoiled fraction, are determined for each grain size population. The respective application of these ages is a function of effective illite crystallite thickness, which is determined from XRD patterns and the Scherrer equation. Total gas ages are representative of crystallite sizes on the order of thicknesses obtained from the Ar recoil percentage (<10-15nm), while retention ages are representative of thicker crystallites. Plotting [apparent age] v. [authigenic/detrital illite ratio] for each size fraction and using York data regression produces a lower intercept and error that dates gouge formation (authigenic illite), and an upper intercept and error that reflects phyllosilicate ages in the host rock (detrital illite). Regional application of IAA to 18 fault gouge sites along major thrusts in addition to selected host rocks in the Canadian Rocky Mountains shows that this fold-thrust belt formed through a series of four, eastward-propagating orogenic pulses. In the Main ranges, thrust range from 158-149 Ma, coinciding with Late Jurassic deposition of Kootenay

  4. Assessing fault activity in intracontinental settings: paleoseismology and geomorphology in SE Kazakhstan

    NASA Astrophysics Data System (ADS)

    Grützner, Christoph; Carson, Emily; Mackenzie, David; Elliott, Austin; Campbell, Grace; Walker, Richard; Abdrakhmatov, Kanatbek

    2016-04-01

    Earthquake recurrence intervals of active faults often exceed the time span covered by instrumental, historical, and archaeological earthquake records in continental interiors. The identification of active faults then often relies on finding the geomorphological expression of surface faulting preserved in the landscape. In rather arid areas, single earthquake scarps can be preserved for thousands of years, but erosional and depositional processes will eventually obliterate features such as fault scarps and offset geological markers. Active faults with very long intervals between surface ruptures might therefore remain undetected, which constitutes a major problem for tectonic studies and seismic hazard assessment. Here we present data from the 50 km-long 'Charyn Canyon' thrust fault in the northern Tien Shan (SE Kazakhstan). Remote sensing, Structure-from-Motion (SfM), differential GPS, field mapping, and paleoseismic trenching were used to reveal the earthquake history of this fault. Radiocarbon dating, infra-red stimulated luminescence (IRSL), and scarp diffusion modelling were used for bracketing the occurrence of paleo-earthquakes. In the paleoseismological trenches we identified two surface rupturing events within the last ~37 ka BP. The most recent earthquake took place between 3.5 - 7.3 ka BP, the penultimate event occurred between ~17-37 ka BP. We estimate magnitudes of ~MW6.5-7.3. Only the younger event has a morphological expression as a 25 km-long fault scarp of ~2 m height. This implicates that a major landscape reset occurred between these two earthquakes, most likely related to the significant climatic change that marked the end of the last glacial maximum. Similar observations from other paleoseismic investigation sites in this area support this interpretation. Our study shows that faults in the northern Tien Shan tend to break in strong earthquakes with very long recurrence intervals. As a consequence, morphological evidence for the most recent

  5. Active Tectonics of the Lower Tagus Valley Fault(Portugal) and Implications for Seismic Hazard Assessment

    NASA Astrophysics Data System (ADS)

    Vilanova, S. P.; Meghraoui, M.; Bosi, V.; Fonseca, J. F.

    2001-12-01

    The Lower Tagus Valley (LTV) has been the locus of M6 to M7 onshore historical earthquakes in the vicinity of Lisbon, the best studied being those of 1531 and 1909 (Moreira, 1984). The distribution of damage in these events shows an elongated shape along the river valley, leading several authors to infer the existence of an active fault following the valley (Choffat and Bensaude, 1912; Fonseca, 1989; Cabral, 1995). However, no direct evidence of such structure - other than the occurrence of large earthquakes - was put forward until now. To address this problem we developed a series of geomorphic, geophysical and paleoseismological investigations along the LTV which indicated displacement of drainage system, uplifted alluvial terrace, and the presence of a scarp for a minimum length of 20 km. Upon trenching, we identified NNE-SSW trending thrust planes affecting Pliocene and Holocene formations, and measured a minimum displacement of 3m over the last 4000 years. The age of thrusting was constrained by radiocarbon dating and corroborated by archaeological findings. The most recent faulting event can likely be correlated with the M7 1531 earthquake. The thrust geometry shows a significant left-lateral component, as it is pointed out by the imbricate pattern of fault planes and kinematic indicators (striations), which suggest a N-S direction of maximum compression. A gravitational origin for the deformation exposed in the trenches is discussed and discarded. On a larger scale, fault segments inland may be a continuation of the offshore source of the 1755 Lisbon Earthquake (Vilanova et al., this conference). We present new calculations of seismic hazard for Western Iberia, and discuss the impact of the new seismotectonic data for the Lower Tagus Valley.

  6. Quaternary Geology and Surface Faulting Hazard: Active and Capable Faults in Central Apennines, Italy

    NASA Astrophysics Data System (ADS)

    Falcucci, E.; Gori, S.

    2015-12-01

    The 2009 L'Aquila earthquake (Mw 6.1), in central Italy, raised the issue of surface faulting hazard in Italy, since large urban areas were affected by surface displacement along the causative structure, the Paganica fault. Since then, guidelines for microzonation were drew up that take into consideration the problem of surface faulting in Italy, and laying the bases for future regulations about related hazard, similarly to other countries (e.g. USA). More specific guidelines on the management of areas affected by active and capable faults (i.e. able to produce surface faulting) are going to be released by National Department of Civil Protection; these would define zonation of areas affected by active and capable faults, with prescriptions for land use planning. As such, the guidelines arise the problem of the time interval and general operational criteria to asses fault capability for the Italian territory. As for the chronology, the review of the international literature and regulatory allowed Galadini et al. (2012) to propose different time intervals depending on the ongoing tectonic regime - compressive or extensional - which encompass the Quaternary. As for the operational criteria, the detailed analysis of the large amount of works dealing with active faulting in Italy shows that investigations exclusively based on surface morphological features (e.g. fault planes exposition) or on indirect investigations (geophysical data), are not sufficient or even unreliable to define the presence of an active and capable fault; instead, more accurate geological information on the Quaternary space-time evolution of the areas affected by such tectonic structures is needed. A test area for which active and capable faults can be first mapped based on such a classical but still effective methodological approach can be the central Apennines. Reference Galadini F., Falcucci E., Galli P., Giaccio B., Gori S., Messina P., Moro M., Saroli M., Scardia G., Sposato A. (2012). Time

  7. Active faulting and neotectonics in the Baelo Claudia area, Campo de Gibraltar (southern Spain)

    NASA Astrophysics Data System (ADS)

    Grützner, Christoph; Reicherter, Klaus; Hübscher, Christian; Silva, Pablo G.

    2012-07-01

    The Strait of Gibraltar area is part of the western Eurasian-African convergence zone characterized by a complex pattern of deformation, including thrusting and folding and active normal faulting. Generally, the area is of low-seismicity; only some minor earthquakes have been recorded in the last hundred years. Archaeoseismological data evidences earthquake destruction occurring twice during Roman times. A better neotectonic framework and knowledge on the paleostress evolution of the Strait of Gibraltar area is necessary to find the local sources for those events and to establish an understanding of the recent deformation. Paleoseismic evidence for one moderate earthquake event around 6000-5000 BP along the normal Carrizales Fault is described in this paper. Off-shore high-resolution seismic investigations, structural and paleostress data, high-resolution GPR and geoelectrical resistivity measurements, outcrop investigations and trenching studies are discussed. The data reveal that active faulting takes place along N-S trending normal faults. Hence, N-S directed normal faults in the area are claimed as local candidates for moderate earthquake activity. Return periods of moderate earthquakes in the order of at least 2000-2500 years in the study area may have to be taken into account. Structural data, such a paleostress data and joints are presented and a deformation history for the Strait of Gibraltar area in southern Spain is developed in this study.

  8. On the seismic activity of the Malibu Coast Fault Zone, and other ethical problems in engineering geoscience

    SciTech Connect

    Cronin, V.S. . Geosciences Dept.)

    1992-01-01

    The Malibu Coast Fault Zone (MCFZ) merges eastward with the active Santa Monica, Hollywood, Raymond Hill, Sierra Madre, and Cucamonga Faults of the central Transverse Ranges. West of Point Dume, the MCFZ extends offshore to join the active Santa Cruz Island Fault. Active microearthquake seismicity along the MCFZ trend indicates that it is seismogenic. Focal mechanism solutions for several of these earthquakes indicate thrusting along faults with the same orientation as the MCFZ. The geomorphology of the MCFZ is consistent with the interpretation that the MCFZ is active. Scarps in unconsolidated sands along the continental shelf just south of Malibu indicate recent offset. In the Santa Monica Mountains, late Tertiary and Quaternary marine sedimentary strata are exposed on the hanging-wall side of the MCFZ, indicating active uplift of the Santa Monica Mountains. Given the other indicators of fault activity, the trench studies that must still be undertaken across the MCFZ are more likely to establish the chronology of recent displacement along the MCFZ than to indicate that the fault is not active. It has been suggested that the MCFZ has not yet been formally recognized as an active, seismogenic fault zone because of the expected loss of property value should the MCFZ be designated an active fault. Geoscientists fear being held liable for loss of property value, even though their assessment of fault activity may be scientifically valid. What are the ethical responsibilities of geoscientists involved in seismic risk assessment along the MCFZ Are political or financial considerations valid criteria to use in assessing the activity of a fault These are not abstract questions of geoethics, because the lives and properties of countless people are potentially at risk.

  9. Active Fault Characterization in the Urban Area of Vienna

    NASA Astrophysics Data System (ADS)

    Decker, Kurt; Grupe, Sabine; Hintersberger, Esther

    2016-04-01

    The identification of active faults that lie beneath a city is of key importance for seismic hazard assessment. Fault mapping and characterization in built-up areas with strong anthropogenic overprint is, however, a challenging task. Our study of Quaternary faults in the city of Vienna starts from the re-assessment of a borehole database of the municipality containing several tens of thousands of shallow boreholes. Data provide tight constraints on the geometry of Quaternary deposits and highlight several locations with fault-delimited Middle to Late Pleistocene terrace sediments of the Danube River. Additional information is obtained from geological descriptions of historical outcrops which partly date back to about 1900. The latter were found to be particularly valuable by providing unprejudiced descriptions of Quaternary faults, sometimes with stunning detail. The along-strike continuations of some of the identified faults are further imaged by industrial 2D/3D seismic acquired outside the city limits. The interpretation and the assessment of faults identified within the city benefit from a very well constrained tectonic model of the active Vienna Basin fault system which derived from data obtained outside the city limits. This data suggests that the urban faults are part of a system of normal faults compensating fault-normal extension at a releasing bend of the sinistral Vienna Basin Transfer Fault. Slip rates estimated for the faults in the city are in the range of several hundredths of millimetres per year and match the slip rates of normal faults that were trenched outside the city. The lengths/areas of individual faults estimated from maps and seismic reach up to almost 700 km² suggesting that all of the identified faults are capable of producing earthquakes with magnitudes M>6, some with magnitudes up to M~6.7.

  10. Geometry and kinematics of the fold-thrust belt and structural evolution of the major Himalayan fault zones in the Darjeeling -- Sikkim Himalaya, India

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Kathakali

    The Darjeeling-Sikkim Himalaya lies in the eastern part of the Himalayan fold-thrust belt (FTB) in a zone of high arc-perpendicular convergence between the Indian and Eurasian plates. In this region two distinct faults form the Main Central thrust (MCT), the structurally higher MCT1 and the lower MCT2; both these faults have translated the Greater Himalayan hanging wall rocks farther towards the foreland than in the western Himalaya. The width of the sub-MCT Lesser Himalayan rocks progressively decreases from the western Himalaya to this part of the eastern Himalaya, and as a result, the width of the FTB is narrower in this region compared to the western Himalaya. Our structural analysis shows that in the Darjeeling-Sikkim Himalaya the sub-MCT Lesser Himalayan duplex is composed of two duplex systems and has a more complex geometry than in the rest of the Himalayan fold-thrust belt. The structurally higher Dating duplex is a hinterland-dipping duplex; the structurally lower Rangit duplex varies in geometry from a hinterland-dipping duplex in the north to an antiformal stack in the middle and a foreland-dipping duplex in the south. The MCT2 is the roof thrust of the Daling duplex and the Ramgarh thrust is the roof thrust of the Rangit duplex. In this region, the Ramgarh thrust has a complex structural history with continued reactivation during footwall imbrication. The foreland-dipping component of the Rangit duplex, along with the large displacement associated with the reactivation of the Ramgarh thrust accounts for the large translation of the MCT sheets in the Darjeeling-Sikkim Himalaya. The growth of the Lesser Himalayan duplex modified the final geometry of the overlying MCT sheets, resulting in a plunge culmination that manifests itself as a broad N-S trending "anticline" in the Darjeeling-Sikkim Himalaya. This is not a "river anticline" as its trace lies west of the Teesta river. A transport parallel balanced cross section across this region has accommodated

  11. Fault zone structure and inferences on past activities of the active Shanchiao Fault in the Taipei metropolis, northern Taiwan

    NASA Astrophysics Data System (ADS)

    Chen, C.; Lee, J.; Chan, Y.; Lu, C.

    2010-12-01

    The Taipei Metropolis, home to around 10 million people, is subject to seismic hazard originated from not only distant faults or sources scattered throughout the Taiwan region, but also active fault lain directly underneath. Northern Taiwan including the Taipei region is currently affected by post-orogenic (Penglai arc-continent collision) processes related to backarc extension of the Ryukyu subduction system. The Shanchiao Fault, an active normal fault outcropping along the western boundary of the Taipei Basin and dipping to the east, is investigated here for its subsurface structure and activities. Boreholes records in the central portion of the fault were analyzed to document the stacking of post- Last Glacial Maximum growth sediments, and a tulip flower structure is illuminated with averaged vertical slip rate of about 3 mm/yr. Similar fault zone architecture and post-LGM tectonic subsidence rate is also found in the northern portion of the fault. A correlation between geomorphology and structural geology in the Shanchiao Fault zone demonstrates an array of subtle geomorphic scarps corresponds to the branch fault while the surface trace of the main fault seems to be completely erased by erosion and sedimentation. Such constraints and knowledge are crucial in earthquake hazard evaluation and mitigation in the Taipei Metropolis, and in understanding the kinematics of transtensional tectonics in northern Taiwan. Schematic 3D diagram of the fault zone in the central portion of the Shanchiao Fault, displaying regional subsurface geology and its relation to topographic features.

  12. Contradicting Estimates of Location, Geometry, and Rupture History of Highly Active Faults in Central Japan

    NASA Astrophysics Data System (ADS)

    Okumura, K.

    2011-12-01

    Accurate location and geometry of seismic sources are critical to estimate strong ground motion. Complete and precise rupture history is also critical to estimate the probability of the future events. In order to better forecast future earthquakes and to reduce seismic hazards, we should consider over all options and choose the most likely parameter. Multiple options for logic trees are acceptable only after thorough examination of contradicting estimates and should not be a result from easy compromise or epoche. In the process of preparation and revisions of Japanese probabilistic and deterministic earthquake hazard maps by Headquarters for Earthquake Research Promotion since 1996, many decisions were made to select plausible parameters, but many contradicting estimates have been left without thorough examinations. There are several highly-active faults in central Japan such as Itoigawa-Shizuoka Tectonic Line active fault system (ISTL), West Nagano Basin fault system (WNBF), Inadani fault system (INFS), and Atera fault system (ATFS). The highest slip rate and the shortest recurrence interval are respectively ~1 cm/yr and 500 to 800 years, and estimated maximum magnitude is 7.5 to 8.5. Those faults are very hazardous because almost entire population and industries are located above the fault within tectonic depressions. As to the fault location, most uncertainties arises from interpretation of geomorphic features. Geomorphological interpretation without geological and structural insight often leads to wrong mapping. Though non-existent longer fault may be a safer estimate, incorrectness harm reliability of the forecast. Also this does not greatly affect strong motion estimates, but misleading to surface displacement issues. Fault geometry, on the other hand, is very important to estimate intensity distribution. For the middle portion of the ISTL, fast-moving left-lateral strike-slip up to 1 cm/yr is obvious. Recent seismicity possibly induced by 2011 Tohoku

  13. Illuminating Northern California’s Active Faults

    USGS Publications Warehouse

    Prentice, Carol S.; Crosby, Christopher J.; Whitehill, Caroline S.; Arrowsmith, J. Ramon; Furlong, Kevin P.; Philips, David A.

    2009-01-01

    Newly acquired light detection and ranging (lidar) topographic data provide a powerful community resource for the study of landforms associated with the plate boundary faults of northern California (Figure 1). In the spring of 2007, GeoEarthScope, a component of the EarthScope Facility construction project funded by the U.S. National Science Foundation, acquired approximately 2000 square kilometers of airborne lidar topographic data along major active fault zones of northern California. These data are now freely available in point cloud (x, y, z coordinate data for every laser return), digital elevation model (DEM), and KMZ (zipped Keyhole Markup Language, for use in Google EarthTM and other similar software) formats through the GEON OpenTopography Portal (http://www.OpenTopography.org/data). Importantly, vegetation can be digitally removed from lidar data, producing high-resolution images (0.5- or 1.0-meter DEMs) of the ground surface beneath forested regions that reveal landforms typically obscured by vegetation canopy (Figure 2)

  14. A review of recently active faults in Taiwan

    USGS Publications Warehouse

    Bonilla, Manuel G.

    1975-01-01

    Six faults associated with five large earthquakes produced surface displacements ranging from 1 to 3 m in the period 1906 through 1951. Four of the ruptures occurred in the western coastal plain and foothills, and two occurred in the Longitudinal Valley of eastern Taiwan. Maps are included showing the locations and dimensions of the displacements. The published geological literature probably would not lead one to infer the existence of a fault along most of the 1906 rupture, except for descriptions of the rupture itself. Over most of its length the 1935 rupture on the Chihhu fault is parallel to but more than 0.5 km from nearby faults shown on geologic maps published in 1969 and 1971; only about 1.5 km of its 15 km length coincides with a mapped fault. The coastal plain part of the Tuntzuchio fault which ruptured in 1935 is apparently not revealed by landforms, and only suggested by other data. Part of the 1946 Hsinhua faulting coincides with a fault identified in the subsurface by seismic work but surface indications of the fault are obscure. The 1951 Meilun faulting occurred along a conspicuous pre-1951 scarp and the 1951 Yuli faulting occurred near or in line with pre-1951 scarps. More than 40 faults which, according to the published literature, have had Pleistocene or later movement are shown on a small-scale map. Most of these faults are in the densely-populated western part of Taiwan. The map and text calls attention to faults that may be active and therefore may be significant in planning important structures. Equivocal evidence suggestive of fault creep was found on the Yuli fault and the Hsinhua fault. Fault creep was not found at several places examined along the 1906 fault trace. Tectonic uplift has occurred in Taiwan in the last 10,000 years and application of eustatic sea level curves to published radiocarbon dates shows that the minimum rate of uplift is considerably different in different parts of the island. Incomplete data indicate that the rate is

  15. Probabilistic seismic hazard study based on active fault and finite element geodynamic models

    NASA Astrophysics Data System (ADS)

    Kastelic, Vanja; Carafa, Michele M. C.; Visini, Francesco

    2016-04-01

    We present a probabilistic seismic hazard analysis (PSHA) that is exclusively based on active faults and geodynamic finite element input models whereas seismic catalogues were used only in a posterior comparison. We applied the developed model in the External Dinarides, a slow deforming thrust-and-fold belt at the contact between Adria and Eurasia.. is the Our method consists of establishing s two earthquake rupture forecast models: (i) a geological active fault input (GEO) model and, (ii) a finite element (FEM) model. The GEO model is based on active fault database that provides information on fault location and its geometric and kinematic parameters together with estimations on its slip rate. By default in this model all deformation is set to be released along the active faults. The FEM model is based on a numerical geodynamic model developed for the region of study. In this model the deformation is, besides along the active faults, released also in the volumetric continuum elements. From both models we calculated their corresponding activity rates, its earthquake rates and their final expected peak ground accelerations. We investigated both the source model and the earthquake model uncertainties by varying the main active fault and earthquake rate calculation parameters through constructing corresponding branches of the seismic hazard logic tree. Hazard maps and UHS curves have been produced for horizontal ground motion on bedrock conditions VS 30 ≥ 800 m/s), thereby not considering local site amplification effects. The hazard was computed over a 0.2° spaced grid considering 648 branches of the logic tree and the mean value of 10% probability of exceedance in 50 years hazard level, while the 5th and 95th percentiles were also computed to investigate the model limits. We conducted a sensitivity analysis to control which of the input parameters influence the final hazard results in which measure. The results of such comparison evidence the deformation model and

  16. Geometry and kinematics of the fold-thrust belt and structural evolution of the major Himalayan fault zones in the Darjeeling -- Sikkim Himalaya, India

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Kathakali

    The Darjeeling-Sikkim Himalaya lies in the eastern part of the Himalayan fold-thrust belt (FTB) in a zone of high arc-perpendicular convergence between the Indian and Eurasian plates. In this region two distinct faults form the Main Central thrust (MCT), the structurally higher MCT1 and the lower MCT2; both these faults have translated the Greater Himalayan hanging wall rocks farther towards the foreland than in the western Himalaya. The width of the sub-MCT Lesser Himalayan rocks progressively decreases from the western Himalaya to this part of the eastern Himalaya, and as a result, the width of the FTB is narrower in this region compared to the western Himalaya. Our structural analysis shows that in the Darjeeling-Sikkim Himalaya the sub-MCT Lesser Himalayan duplex is composed of two duplex systems and has a more complex geometry than in the rest of the Himalayan fold-thrust belt. The structurally higher Dating duplex is a hinterland-dipping duplex; the structurally lower Rangit duplex varies in geometry from a hinterland-dipping duplex in the north to an antiformal stack in the middle and a foreland-dipping duplex in the south. The MCT2 is the roof thrust of the Daling duplex and the Ramgarh thrust is the roof thrust of the Rangit duplex. In this region, the Ramgarh thrust has a complex structural history with continued reactivation during footwall imbrication. The foreland-dipping component of the Rangit duplex, along with the large displacement associated with the reactivation of the Ramgarh thrust accounts for the large translation of the MCT sheets in the Darjeeling-Sikkim Himalaya. The growth of the Lesser Himalayan duplex modified the final geometry of the overlying MCT sheets, resulting in a plunge culmination that manifests itself as a broad N-S trending "anticline" in the Darjeeling-Sikkim Himalaya. This is not a "river anticline" as its trace lies west of the Teesta river. A transport parallel balanced cross section across this region has accommodated

  17. Active faults of the Baikal depression

    USGS Publications Warehouse

    Levi, K.G.; Miroshnichenko, A.I.; San'kov, V. A.; Babushkin, S.M.; Larkin, G.V.; Badardinov, A.A.; Wong, H.K.; Colman, S.; Delvaux, D.

    1997-01-01

    The Baikal depression occupies a central position in the system of the basins of the Baikal Rift Zone and corresponds to the nucleus from which the continental lithosphere began to open. For different reasons, the internal structure of the Lake Baikal basin remained unknown for a long time. In this article, we present for the first time a synthesis of the data concerning the structure of the sedimentary section beneath Lake Baikal, which were obtained by complex seismic and structural investigations, conducted mainly from 1989 to 1992. We make a brief description of the most interesting seismic profiles which provide a rough idea of a sedimentary unit structure, present a detailed structural interpretation and show the relationship between active faults in the lake, heat flow anomalies and recent hydrothermalism.

  18. Distribution of active faulting along orogenic wedges: Minimum-work models and natural analogue

    NASA Astrophysics Data System (ADS)

    Yagupsky, Daniel L.; Brooks, Benjamin A.; Whipple, Kelin X.; Duncan, Christopher C.; Bevis, Michael

    2014-09-01

    Numerical 2-D models based on the principle of minimum work were used to examine the space-time distribution of active faulting during the evolution of orogenic wedges. A series of models focused on thin-skinned thrusting illustrates the effects of arid conditions (no erosion), unsteady state conditions (accretionary influx greater than erosional efflux) and steady state conditions (accretionary influx balances erosional efflux), on the distribution of fault activity. For arid settings, a general forward accretion sequence prevails, although a significant amount of internal deformation is registered: the resulting fault pattern is a rather uniform spread along the profile. Under fixed erosional efficiency settings, the frontal advance of the wedge-front is inhibited, reaching a steady state after a given forward propagation. Then, the applied shortening is consumed by surface ruptures over a narrow frontal zone. Under a temporal increase in erosional efficiency (i.e., transient non-steady state mass balance conditions), a narrowing of the synthetic wedge results; a rather diffuse fault activity distribution is observed during the deformation front retreat. Once steady balanced conditions are reached, a single long-lived deformation front prevails. Fault activity distribution produced during the deformation front retreat of the latter scenario, compares well with the structural evolution and hinterlandward deformation migration identified in southern Bolivian Subandes (SSA) from late Miocene to present. This analogy supports the notion that the SSA is not in steady state, but is rather responding to an erosional efficiency increase since late Miocene. The results shed light on the impact of different mass balance conditions on the vastly different kinematics found in mountain ranges, suggesting that those affected by growing erosion under a transient unbalanced mass flux condition tend to distribute deformation along both frontal and internal faults, while others

  19. F-15B ACTIVE with thrust vectoring nozzles on test stand view from rear

    NASA Technical Reports Server (NTRS)

    1995-01-01

    This November 13, 1995, photograph of the F-15 Advanced Controls Technology for Integrated Vehicles (ACTIVE) at NASA's Dryden Flight Research Center, Edwards, California, shows the aircraft's two new Pratt & Whitney nozzles that can turn up to 20 degrees in any direction. These nozzles give the aircraft thrust control in the pitch (up and down) and yaw (left and right) directions. This will reduce drag and increase fuel economy or range as compared with conventional aerodynamic controls, which increase the retarding forces (drag) acting upon the aircraft. Ground testing of a new thrust-vectoring concept employing the nozzles took place during the first two weeks of November 1995 and went well, and flight tests began in March 1996. These tests could result in significant performance increases for military and commercial aircraft. The research program is the product of a collaborative effort by NASA, the Air Force's Wright Laboratory, Pratt & Whitney, and McDonnell Douglas Aerospace.

  20. Seismological evidence of an active footwall shortcut thrust in the Northern Itoigawa-Shizuoka Tectonic Line derived by the aftershock sequence of the 2014 M 6.7 Northern Nagano earthquake

    NASA Astrophysics Data System (ADS)

    Panayotopoulos, Yannis; Hirata, Naoshi; Hashima, Akinori; Iwasaki, Takaya; Sakai, Shin'ichi; Sato, Hiroshi

    2016-06-01

    A destructive M 6.7 earthquake struck Northern Nagano prefecture on November 22, 2014. The main shock occurred on the Kamishiro fault segment of the northern Itoigawa-Shizuoka Tectonic Line (ISTL). We used data recorded at 41 stations of the local seismographic network in order to locate 2118 earthquakes that occurred between November 18 and November 30, 2014. To estimate hypocenters, we assigned low Vp models to stations within the Northern Fossa Magna (NFM) basin thus accounting for large lateral crustal heterogeneities across the Kamishiro fault. In order to further improve accuracy, the final hypocenter locations were recalculated inside a 3D velocity model using the double-difference method. We used the aftershock activity distribution and focal mechanism solutions of major events in order to estimate the source fault area of the main shock. Our analysis suggests that the shallow part of the source fault corresponds to the surface trace of the Kamishiro fault and dips 30°-45° SE, while the deeper part of the source fault corresponds to the downdip portion of the Otari-Nakayama fault, a high angle fault dipping 50°-65° SE that formed during the opening of the NFM basin in the Miocene. Along its surface trace the Otari-Nakayama fault has been inactive during the late Quaternary. We verified the validity of our model by calculating surface deformation using a simple homogeneous elastic half-space model and comparing it to observed surface deformation from satellite interferometry, assuming large coseismic slip in the areas of low seismicity and small coseismic slip in the areas of high seismicity. Shallowing of the source fault from 50°-65° to 30°-45° in the upper 4 km, in the areas where both surface fault traces are visible, is a result of footwall shortcut thrusting by the Kamishiro fault off the Otari-Nakayama fault.

  1. Structural characteristics of an active fold-and-thrust system in the southeastern Atacama Basin, northern Chile

    NASA Astrophysics Data System (ADS)

    Lin, Yen-Sheng; Chuang, Yi-Rung; Shyu, J. Bruce H.; González, Gabriel; Shen, Chuan-Chou; Lo, Ching-Hua; Liou, Ya-Hsuan

    2016-08-01

    The western South American margin is one of the most active plate boundaries in the world. Using various remote sensing data sets, we mapped the neotectonic characteristics of an area at the southeastern corner of the Atacama Basin, northern Chile, in the Andean forearc. There, one major N-S trending ridge is clearly visible both in the satellite images and in the field. This ridge reaches 250 m above the basin floor in its middle part and is asymmetrical, with a steep eastern slope and a much gentler western slope. The geometry of the ridge indicates that it formed as an asymmetrical anticline. This anticline is likely formed as a shear fault-bend fold, with a major décollement at a depth of about 2.5 km in the Naranja Formation. We suggest that this décollement is a major structure of the Atacama Basin area. From the ages of the ignimbrites and lake deposits that were deformed by this anticline, we obtained a long-term shortening rate of the major underlying structure at about 0.2 mm/yr. This thin-skinned fold-and-thrust system appears to be active since at least about 3 Ma, and could be as long as since middle Miocene. Therefore, crustal structures may play important roles in the Neogene development of the western Andean margin.

  2. Duplex development and abandonment during evolution of the Lewis thrust system, southern Glacier National Park, Montana

    NASA Astrophysics Data System (ADS)

    Yin, An; Kelty, Thomas K.; Davis, Gregory A.

    1989-09-01

    Geologic mapping in southern Glacier National Park, Montana, reveals the presence of two duplexes sharing the same floor thrust fault, the Lewis thrust. The westernmost duplex (Brave Dog Mountain) includes the low-angle Brave Dog roof fault and Elk Mountain imbricate system, and the easternmost (Rising Wolf Mountain) duplex includes the low-angle Rockwell roof fault and Mt. Henry imbricate system. The geometry of these duplexes suggests that they differ from previously described geometric-kinematic models for duplex development. Their low-angle roof faults were preexisting structures that were locally utilized as roof faults during the formation of the imbricate systems. Crosscutting of the Brave Dog fault by the Mt. Henry imbricate system indicates that the two duplexes formed at different times. The younger Rockwell-Mt. Henry duplex developed 20 km east of the older Brave Dog-Elk Mountain duplex; the roof fault of the former is at a higher structural level. Field relations confirm that the low-angle Rockwell fault existed across the southern Glacier Park area prior to localized formation of the Mt. Henry imbricate thrusts beneath it. These thrusts kinematically link the Rockwell and Lewis faults and may be analogous to P shears that form between two synchronously active faults bounding a simple shear system. The abandonment of one duplex and its replacement by another with a new and higher roof fault may have been caused by (1) warping of the older and lower Brave Dog roof fault during the formation of the imbricate system (Elk Mountain) beneath it, (2) an upward shifting of the highest level of a simple shear system in the Lewis plate to a new decollement level in subhorizontal belt strata (= the Rockwell fault) that lay above inclined strata within the first duplex, and (3) a reinitiation of P-shear development (= Mt. Henry imbricate faults) between the Lewis thrust and the subparallel, synkinematic Rockwell fault.

  3. Left-lateral active deformation along the Mosha-North Tehran fault system (Iran): Morphotectonics and paleoseismological investigations

    NASA Astrophysics Data System (ADS)

    Solaymani Azad, Shahryar; Ritz, Jean-François; Abbassi, Mohammad Reza

    2011-01-01

    The Mosha and North Tehran faults correspond to the nearest seismic sources for the northern part of the Tehran megacity. The present-day structural relationships and the kinematics of these two faults, especially at their junction in Lavasanat region, is still a matter of debate. In this paper, we present the results of a morphotectonic analysis (aerial photos and field investigations) within the central part of the Mosha and eastern part of the North Tehran faults between the Mosha valley and Tehran City. Our investigations show that, generally, the traces of activity do not follow the older traces corresponding to previous long-term dip-slip thrusting movements. The recent faulting mainly occurs on new traces trending E-W to ENE-WSW affecting Quaternary features (streams, ridges, risers, and young glacial markers) and cutting straight through the topography. Often defining en-echelon patterns (right- and left-stepping), these new traces correspond to steep faults with either north- or south-dipping directions, along which clear evidences for left-lateral strike-slip motion are found. At their junction zone, the two sinistral faults display a left-stepping en-echelon pattern defining a positive flower structure system clearly visible near Ira village. Further west, the left-lateral strike-slip motion is transferred along the ENE-WSW trending Niavaran fault and other faults. The cumulative offsets associated with this left-lateral deformation is small compared with the topography associated with the previous Late Tertiary thrusting motion, showing that it corresponds to a recent change of kinematics.

  4. Role of detachments and thrust kinematics in Structural evolution of Kohat and Potwar fold thrust belt in Pakistan

    NASA Astrophysics Data System (ADS)

    Ghani, Humaad; Zeilinger, Gerold; Sobel, Edward; Heidarzadeh, Ghasem

    2016-04-01

    The Kohat and Potwar fold thrust belts in Pakistan represent the outermost external zone of the Himalayan fold and thrust system. The Main Boundary thrust marks their northern extent, showing that they are genetically linked; however, both exhibit a distinct contrast between the structural style at the surface and subsurface. This contrast becomes more conspicuous at the leading edge of the thrust belt where the Potwar allochothon extends further south, linked to Kohat in the north via an active strike-slip fault. Previous workers explained the structural evolution of the two belts separately, disregarding the influence of similar fold and thrusts developed in both belts. This research focuses on the preparation of a 3D structural model at the boundary of the two thrust belts to understand similarities and differences in their structural style and evolution. The model is constrained by integrating field, seismic and well data for better subsurface interpretation. Cross sections show that Potwar evolved on thrust faults originating from a basal detachment in Precambrian (pC) salt and terminating in Miocene Molasse forming duplexes of pre Himalayan strata. To the south, the Potwar allochothon is glided over a salt detachment with rare internal deformation toward its leading edge, forming fault bend fold thrust structure known as Salt range. The structural evolution towards the west in Kohat results from deformation on multiple detachment horizons at the pC salt, Eocene evaporites and Miocene Molasse. Disharmonic folding over Eocene evaporites is evident from their presence in the cores of outcropping folds. In the subsurface, closely spaced thrusts cut up section from basal detachment terminates in Eocene evaporites forming duplex in northern part of area. In south change of lithological facies from evaporites to limestone shift detachment level upward in to molasse strata which resemble structural style in northern Potwar. Thrusts at the surface evolved from the

  5. Tectonic Significance of Intraoceanic Thrusts in the Nankai Trough

    NASA Astrophysics Data System (ADS)

    Tsuji, T.; Kodaira, S.; Park, J.; Ashi, J.; Fukao, Y.; Moore, G. F.; Matsuoka, T.

    2009-12-01

    The Nankai Trough is a convergent margin where the Philippine Sea plate is subducting beneath southwest Japan. Because this subduction zone has repeatedly generated great earthquakes with Mw>8, seismic reflection studies have been intensively carried out in the whole Nankai Trough region. However, the role of oceanic crust in plate convergent margins was not well understood. Recently, Tsuji et al. [2009] identified intraoceanic thrusts developed as imbricate structures within the subducting Philippine Sea plate off the Kii Peninsula in central Japan manifesting as strong-amplitude reflections observed in an industry-standard 3D seismic reflection data set. In this study, we use other 2D and 3D seismic reflection data acquired in the whole Nankai Trough region and extract geometries of (1) intraoceanic thrusts, (2) surface of oceanic crust and (3) Moho in order to discuss characteristics of intraoceanic thrusts distributed in the whole Nankai Trough region. We mainly use seismic reflection data acquired by JAMSTEC. Seismic profiles demonstrate that intraoceanic faults are densely distributed eastern side of the Cape Shionomisaki (southern edge of the Kii Peninsula). Large displacements of a few major intraoceanic thrusts elevate the crust surface, and the offset due to cumulative displacements reaches >1 km at the sediment-igneous crust interface. A part of Kashinozaki-Knoll is also uplifted by the thrust displacement. These imbricate intraoceanic thrusts cut through the oceanic crust as a discontinuous thrust plane. The intraoceanic thrusts strike nearly parallel to the trend of the trough axis. However the fault traces are bending at the western termination; the fault planes extend upward from side edges of the underlying intraoceanic thrusts and work as lateral faults. The deformation within oceanic crust may have continued until recently with subduction, because the shallow sediment as well as the seafloor is deformed due to the thrust displacement [Kodaira et

  6. Detecting Significant Stress Drop Variations in Large Micro-Earthquake Datasets: A Comparison Between a Convergent Step-Over in the San Andreas Fault and the Ventura Thrust Fault System, Southern California

    NASA Astrophysics Data System (ADS)

    Goebel, T. H. W.; Hauksson, E.; Plesch, A.; Shaw, J. H.

    2016-06-01

    A key parameter in engineering seismology and earthquake physics is seismic stress drop, which describes the relative amount of high-frequency energy radiation at the source. To identify regions with potentially significant stress drop variations, we perform a comparative analysis of source parameters in the greater San Gorgonio Pass (SGP) and Ventura basin (VB) in southern California. The identification of physical stress drop variations is complicated by large data scatter as a result of attenuation, limited recording bandwidth and imprecise modeling assumptions. In light of the inherently high uncertainties in single stress drop measurements, we follow the strategy of stacking large numbers of source spectra thereby enhancing the resolution of our method. We analyze more than 6000 high-quality waveforms between 2000 and 2014, and compute seismic moments, corner frequencies and stress drops. Significant variations in stress drop estimates exist within the SGP area. Moreover, the SGP also exhibits systematically higher stress drops than VB and shows more scatter. We demonstrate that the higher scatter in SGP is not a generic artifact of our method but an expression of differences in underlying source processes. Our results suggest that higher differential stresses, which can be deduced from larger focal depth and more thrust faulting, may only be of secondary importance for stress drop variations. Instead, the general degree of stress field heterogeneity and strain localization may influence stress drops more strongly, so that more localized faulting and homogeneous stress fields favor lower stress drops. In addition, higher loading rates, for example, across the VB potentially result in stress drop reduction whereas slow loading rates on local fault segments within the SGP region result in anomalously high stress drop estimates. Our results show that crustal and fault properties systematically influence earthquake stress drops of small and large events and should

  7. Medieval pulse of great earthquakes in the central Himalaya: Viewing past activities on the frontal thrust

    NASA Astrophysics Data System (ADS)

    Rajendran, C. P.; John, Biju; Rajendran, Kusala

    2015-03-01

    The Himalaya has experienced three great earthquakes during the last century—1934 Nepal-Bihar, 1950 Upper Assam, and arguably the 1905 Kangra. Focus here is on the central Himalayan segment between the 1905 and the 1934 ruptures, where previous studies have identified a great earthquake between thirteenth and sixteenth centuries. Historical data suggest damaging earthquakes in A.D. 1255, 1344, 1505, 1803, and 1833, although their sources and magnitudes remain debated. We present new evidence for a great earthquake from a trench across the base of a 13 m high scarp near Ramnagar at the Himalayan Frontal Thrust. The section exposed four south verging fault strands and a backthrust offsetting a broad spectrum of lithounits, including colluvial deposits. Age data suggest that the last great earthquake in the central Himalaya most likely occurred between A.D. 1259 and 1433. While evidence for this rupture is unmistakable, the stratigraphic clues imply an earlier event, which can most tentatively be placed between A.D. 1050 and 1250. The postulated existence of this earlier event, however, requires further validation. If the two-earthquake scenario is realistic, then the successive ruptures may have occurred in close intervals and were sourced on adjacent segments that overlapped at the trench site. Rupture(s) identified in the trench closely correlate with two damaging earthquakes of 1255 and 1344 reported from Nepal. The present study suggests that the frontal thrust in central Himalaya may have remained seismically inactive during the last ~700 years. Considering this long elapsed time, a great earthquake may be due in the region.

  8. Faulting processes in active faults - Evidences from TCDP and SAFOD drill core samples

    SciTech Connect

    Janssen, C.; Wirth, R.; Wenk, H. -R.; Morales, L.; Naumann, R.; Kienast, M.; Song, S. -R.; Dresen, G.

    2014-08-20

    The microstructures, mineralogy and chemistry of representative samples collected from the cores of the San Andreas Fault drill hole (SAFOD) and the Taiwan Chelungpu-Fault Drilling project (TCDP) have been studied using optical microscopy, TEM, SEM, XRD and XRF analyses. SAFOD samples provide a transect across undeformed host rock, the fault damage zone and currently active deforming zones of the San Andreas Fault. TCDP samples are retrieved from the principal slip zone (PSZ) and from the surrounding damage zone of the Chelungpu Fault. Substantial differences exist in the clay mineralogy of SAFOD and TCDP fault gouge samples. Amorphous material has been observed in SAFOD as well as TCDP samples. In line with previous publications, we propose that melt, observed in TCDP black gouge samples, was produced by seismic slip (melt origin) whereas amorphous material in SAFOD samples was formed by comminution of grains (crush origin) rather than by melting. Dauphiné twins in quartz grains of SAFOD and TCDP samples may indicate high seismic stress. The differences in the crystallographic preferred orientation of calcite between SAFOD and TCDP samples are significant. Microstructures resulting from dissolution–precipitation processes were observed in both faults but are more frequently found in SAFOD samples than in TCDP fault rocks. As already described for many other fault zones clay-gouge fabrics are quite weak in SAFOD and TCDP samples. Clay-clast aggregates (CCAs), proposed to indicate frictional heating and thermal pressurization, occur in material taken from the PSZ of the Chelungpu Fault, as well as within and outside of the SAFOD deforming zones, indicating that these microstructures were formed over a wide range of slip rates.

  9. Latest Pleistocene to Holocene thrust faulting paleoearthquakes at Monte Netto (Brescia, Italy): lessons learned from the Middle Ages seismic events in the Po Plain

    NASA Astrophysics Data System (ADS)

    Michetti, Alessandro Maria; Berlusconi, Andrea; Livio, Franz; Sileo, Giancanio; Zerboni, Andrea; Serva, Leonello; Vittori, Eutizio; Rodnight, Helena; Spötl, Christoph

    2010-05-01

    The seismicity of the Po Plain in Northern Italy is characterized by two strong Middle Ages earthquakes, the 1117, I° X MCS Verona, and the December 25, 1222, I° IX-X Brescia, events. Historical reports from these events describe relevant coseismic environmental effects, such as drainage changes, ground rupture and landslides. Due to the difficult interpretation of intensity data from such old seismic events, considerable uncertainty exists about their source parameters, and therefore about their causative tectonic structures. In a recent review, Stucchi et al. (2008) concluded that 'the historical data do not significantly help to constrain the assessment of the seismogenic potential of the area, which remains one of the most unknown, although potentially dangerous, seismic areas of the Italian region'. This issue needs therefore to be addressed by using the archaeological and geological evidence of past earthquakes, that is, archeoseismology and paleoseismology. Earthquake damage to archaeological sites in the study area has been the subject of several recent papers. Here we focus on new paleoseismological evidence, and in particular on the first observation of Holocene paleoseismic surface faulting in the Po Plain identified at the Monte Netto site, located ca. 10 km S of Brescia, in the area where the highest damage from the Christmas 1222 earthquake have been recorded. Monte Netto is a small hill, ca. 30 m higher than the surrounding piedmont plain, which represent the top of a growing fault-related fold belonging to the Quaternary frontal sector of the Southern Alps; the causative deep structure is a N-verging back thrust, well imaged in the industrial seismic reflection profiles kindly made available by ENI E&P. New trenching investigations have been conducted at the Cava Danesi of Monte Netto in October 2009, focused on the 1:10 scale analysis of the upper part of the 7 m high mid-Pleistocene to Holocene stratigraphic section exposed along the quarry

  10. Detecting Taiwan's Shanchiao Active Fault Using AMT and Gravity Methods

    NASA Astrophysics Data System (ADS)

    Liu, H.-C.; Yang, C.-H.

    2009-04-01

    Taiwan's Shanchiao normal fault runs in a northeast-southwest direction and is located on the western edge of the Taipei Basin in northern Taiwan. The overburden of the fault is late Quaternary sediment with a thickness of approximately a few tenth of a meter to several hundred meters. No detailed studies of the western side of the Shanchiao fault are available. As Taiwan is located on the Neotectonic Belt in the western Pacific, detecting active faults near the Taipei metropolitan area will provide necessary information for further disaster prevention. It is the responsibility of geologists and geophysicists in Taiwan to perform this task. Examination of the resistivity and density contrasts of subsurface layers permits a mapping of the Shanchiao fault and the deformed Tertiary strata of the Taipei Basin. The audio-frequency magnetotelluric (AMT) method and gravity method were chosen for this study. Significant resistivity and gravity anomalies were observed in the suspected fault zone. The interpretation reveals a good correlation between the features of the Shanchiao fault and resistivity and density distribution at depth. In this observation, AMT and gravity methods provides a viable means for mapping the Shanchiao fault position and studying its features associated with the subsidence of the western side of the Taipei Basin. This study indicates the AMT and gravity methods' considerable potential for accurately mapping an active fault.

  11. Interplay of thrust, back-thrust, strike-slip and salt tectonics in a fold and thrust belt system: an example from Zakynthos Island, Greece

    NASA Astrophysics Data System (ADS)

    Zelilidis, A.; Papatheodorou, G.; Maravelis, A. G.; Christodoulou, D.; Tserolas, P.; Fakiris, E.; Dimas, X.; Georgiou, N.; Ferentinos, G.

    2016-10-01

    The southwestern flank of the Hellenic fold and thrust belt, situated along the southern edge of the Dinarides-Albanides-Hellenides continental convergent zone, was examined for reconstructing the tectonic deformation. This investigation presents an integrated study of onshore sedimentological and structural analyses, as well as offshore seismic lines, across the Pliocene-Pleistocene sedimentary succession in Zakynthos Island. Back-thrust faults, using the Triassic evaporites as decollement surface, during the Pliocene, and coeval diapiric intrusions formed three sub-basins on the hangingwall of the Kalamaki back-thrust fault. This interaction is responsible for the growth of the Skopos Mountain and the soft sediment deformation that formed synclines and slumps, respectively. Back-thrust and strike-slip faults were active during the early Pleistocene, and diapiric intrusions modified the bathymetry on the sea floor, giving rise to slumps and recumbent folds. At least five events of synsedimentary diapiric intrusions have been recognized and are marked by five slump horizons. During the Holocene, the diapiric intrusions between the Kalamaki back-thrust and the Vrachionas anticline could be either related to normal faults or gravitationally driven.

  12. Faults paragenesis and paleostress state in the zone of actively propagating continental strike-slip on the example of North Khangai fault (Northern Mongolia)

    NASA Astrophysics Data System (ADS)

    Sankov, Vladimir; Parfeevets, Anna

    2014-05-01

    Sublatitudinal North Khangai fault extends from Ubsunuur basin to the eastern part of the Selenga corridor trough 800 km. It is the northern boundary of the massive Mongolian block and limits of the Baikal rift system structures propagation in the south (Logatchev, 2003). Late Cenozoic and present-day fault activity are expressed in the left-lateral displacements of a different order of river valleys and high seismicity. We have carried out studies of the kinematics of active faults and palaeostresses reconstruction in the zone of the dynamic influence of North Khangai fault, the width of which varies along the strike and can exceeds 100 km. The result shows that the fault zone has a longitudinal and a transverse zoning. Longitudinal zonation presented gradual change from west to east regions of compression and transpression regimes (Khan-Khukhey ridge) to strike-slip regime (Bolnay ridge) and strike-slip and transtensive regimes (west of Selenga corridor). Strike-slip zones are represented by linearly concentrated rupture deformations. In contrast, near the termination of the fault the cluster fault deformation formed. Here, from north to south, there are radical changes in the palaeostress state. In the north-western sector (east of Selenga corridor) strike-slip faults, strike-slip faults with normal components and normal faults are dominated. For this sector the stress tensors of extensive, transtension and strike-slip regimes are typical. South-western sector is separated from the north-eastern one by massive Buren Nuruu ridge within which the active faults are not identified. In the south-western sector between the Orkhon and Tola rivers the cluster of NW thrusts and N-S strike-slip faults with reverse component are discovered. The faults are perfectly expressed by NW and N-S scarps in the relief. The most structures dip to the east and north-east. Holocene fault activity is demonstrated by the hanging river valleys and horizontal displacements with amplitudes

  13. Insurance Applications of Active Fault Maps Showing Epistemic Uncertainty

    NASA Astrophysics Data System (ADS)

    Woo, G.

    2005-12-01

    Insurance loss modeling for earthquakes utilizes available maps of active faulting produced by geoscientists. All such maps are subject to uncertainty, arising from lack of knowledge of fault geometry and rupture history. Field work to undertake geological fault investigations drains human and monetary resources, and this inevitably limits the resolution of fault parameters. Some areas are more accessible than others; some may be of greater social or economic importance than others; some areas may be investigated more rapidly or diligently than others; or funding restrictions may have curtailed the extent of the fault mapping program. In contrast with the aleatory uncertainty associated with the inherent variability in the dynamics of earthquake fault rupture, uncertainty associated with lack of knowledge of fault geometry and rupture history is epistemic. The extent of this epistemic uncertainty may vary substantially from one regional or national fault map to another. However aware the local cartographer may be, this uncertainty is generally not conveyed in detail to the international map user. For example, an area may be left blank for a variety of reasons, ranging from lack of sufficient investigation of a fault to lack of convincing evidence of activity. Epistemic uncertainty in fault parameters is of concern in any probabilistic assessment of seismic hazard, not least in insurance earthquake risk applications. A logic-tree framework is appropriate for incorporating epistemic uncertainty. Some insurance contracts cover specific high-value properties or transport infrastructure, and therefore are extremely sensitive to the geometry of active faulting. Alternative Risk Transfer (ART) to the capital markets may also be considered. In order for such insurance or ART contracts to be properly priced, uncertainty should be taken into account. Accordingly, an estimate is needed for the likelihood of surface rupture capable of causing severe damage. Especially where a

  14. Cross-strike Discontinuities in the Moine Thrust Belt of NW Scotland; their identity, tectonic significance, and visualisation.

    NASA Astrophysics Data System (ADS)

    Kelly, Michael; Kearsey, Tim; Leslie, Graham; Ritchie, Calum; Krabbendam, Maarten; Williams, Graham

    2013-04-01

    Abrupt lateral changes in thrust geometry occur in many mountain-building fold-and-thrust belts. Whilst many works have dealt with palinspastic reconstructions and transport-direction-parallel balanced cross-sections, far fewer show a full three-dimensional architecture, or examine how these lateral variations in thrust architecture can be linked via so-called 'transverse zones' that serve to demarcate different segments of the thrust belt. When identified, these transverse zones are commonly thought to be related to kinematic responses to irregularities generated across pre-existing, sometimes re-activated, sub-décollement basement faults, contrasts in pre-thrusting cover strata deformation across basement faults, development of duplex structures/antiformal stacks, and/or along-strike variations in mechanical stratigraphy. In many cases however the causative structure is concealed, either by distal parts of the thrust belt or by the foreland basin, and so must be deduced from the overall structural architecture. The amplitude and complexity of the disturbance associated with the transverse zone is typically much greater than amplitude of any irregularity identified in the basement below the thrust belt. In NW Scotland, the classic WNW-vergent Caledonian Moine Thrust Belt (MTB) incorporates a variety of crustal-scale segments. In the Assynt Culmination of the thrust belt, the Traligill Transverse Zone trends sub-parallel to the thrust transport direction, and is associated with an en echelon fault system cutting thrusts, with discontinuity of the thrust and thrust sheet architecture, and with oblique fold and thrust structures. This transverse zone is developed above a basement cross-fault which records repeated brittle reactivation of a Proterozoic shear zone. Thrusting thus deformed a sedimentary sequence that was already disrupted by faults aligned sub-parallel to the thrust transport direction. In the Kinlochewe district where the Loch Maree Fault Zone (LMF

  15. Initiation of subduction by post-collision foreland thrusting and back-thrusting

    NASA Astrophysics Data System (ADS)

    Mitchell, A. H. G.

    1984-07-01

    While postulated causes of initial subduction and trench formation include underthrusting, controls on its location and age have not been determined. Consideration of the age of subduction zones bordering five collisional orogens suggests that subduction may have been initiated by foreland thrusts and back-thrusts. Foreland thrusts develop within a continental foreland on the subducting plate mostly within 50 my of collision with an arc system; where the foreland is narrow the thrusts may intersect the continent-ocean crust boundary. Back-thrusts develop in the fore-arc or back-arc area on the overriding plate within 10 to 20 my of collision, and can result in tectonic burial of the magmatic arc; where the arc system is oceanic the back-thrusts may intersect the arc-ocean crust boundary. Possible examples of subduction initiated by foreland thrusts are the start of subduction in the late Jurassic beneath the northern Sunda Arc, and at the end-Miocene in the Negros Trench. Examples of back-thrusts which have initiated or may initiate subduction are the late Cenozoic eastward translation of Taiwan over the Philippine Sea plate, the incipient southward subduction of the Banda Sea beneath Timor, and the W-dipping back-thrust comprising the Highland Boundary Fault zone and postulated early Ordovician thrusts to the SE in Scotland. The suggested relationship of subduction to collision helps to explain the persistence of Wilson cycles in the still-active late Mesozoic to Cenozoic orogenic belts and implies that orogeny will cease only with collision between major continents.

  16. Active faulting in the Inner California Borderlands: new constraints from high-resolution multichannel seismic and multibeam bathymetric data.

    NASA Astrophysics Data System (ADS)

    Bormann, J. M.; Holmes, J. J.; Sahakian, V. J.; Klotsko, S.; Kent, G.; Driscoll, N. W.; Harding, A. J.; Wesnousky, S. G.

    2014-12-01

    Geodetic data indicate that faults offshore of Southern California accommodate 6-8 mm/yr of dextral Pacific-North American relative plate motion. In the Inner California Borderlands (ICB), modern strike-slip deformation is overprinted on topography formed during plate boundary reorganization 30-15 Ma. Despite its proximity to urban Southern California, the hazard posed by active faults in the ICB remains poorly understood. We acquired a 4000-line-km regional grid of high-resolution, 2D multichannel seismic (MCS) reflection data and multibeam bathymetry to examine the fault architecture and tectonic evolution of the ICB. We interpret the MCS data using a sequence stratigraphic approach to establish a chronostratigraphy and identify discrete episodes of deformation. We present our results in a regional fault model that distinguishes active deformation from older structures. Significant differences exist between our model of ICB deformation and existing models. Mounting evidence suggests a westward temporal migration of slip between faults in the ICB. In the eastern ICB, slip on the Newport-Inglewood/Rose Canyon fault and the neighboring Coronado Bank fault (CBF) diminishes to the north and appears to decrease over time. Undeformed Late Pliocene sediments overlie the northern extent of the CBF and the breakaway zone of the purported Oceanside Blind Thrust. Therefore, CBF slip rate estimates based on linkage with the Palos Verdes fault to the north are unwarranted. Deformation along the San Mateo, San Onofre, and Carlsbad trends is best explained as localized deformation resulting from geometrical complexities in a dextral strike-slip fault system. In the western ICB, the San Diego Trough fault (SDTF) offsets young sediments between the US/Mexico border and the eastern margin of Avalon Knoll, where the fault is spatially coincident with the San Pedro Basin fault (SPBF). Farther west, the San Clemente fault (SCF) has a strong linear bathymetric expression. The length

  17. Intermediate decollement activation in response to the basal friction variation and its effect on folding style in the Zagros fold-thrust belt, an analogue modeling approach

    NASA Astrophysics Data System (ADS)

    Farzipour-Saein, Ali; Koyi, Hemin

    2016-09-01

    Although the role of various basal and intermediate decollement levels on structural style is well documented individually in many folded terrains, the interaction between basal and intermediate decollements is poorly constrained. This study uses results of two scaled sand-box models shortened from one end to study the variation in structural development in response to varying basal friction and its consequent interaction with intermediate decollement horizons. Two models with similar incompetent intermediate decollement, but with different basal friction (with and without a thick basal decollement), were prepared analogous for the eastern and the western parts of the Razak basement fault in the Fars Region of the eastern part of the Zagros fold thrust belt (ZFTB). Combined results of scaled models with geological observations are used to argue that the basal decollement friction characteristics govern propagation of deformation front. In addition, model results, analogues to north-south direction, show that deformation complexity and disharmonic folding exist in the section where the intermediate decollement has been activated in response to the shortening without the basal decollement (throughout the western part of the Razak basement fault where less thickness of the Hormuz series as the basal decollement has been documented compared to its eastern part). In other words, the complexity in deformation is less portrayed along sections where basal friction beneath the model decreases (e.g. the eastern part of the Razak basement fault). We argue here that, in addition to other parameters (not presented in this study) interaction of intermediate decollement levels with basal decollement friction characteristics could explain decoupling between structures within the sedimentary column of the Fars Region of the eastern part of the Zagros fold thrust belt.

  18. Active faulting and deformation of the Coalinga anticline as interpreted from three-dimensional velocity structure and seismicity

    USGS Publications Warehouse

    Eberhart-Phillips, D.

    1989-01-01

    This work gives a clear picture of the geometry of aftershock seismicity in a large thrust earthquake. Interpretation of hypocenters and fault plane solutions, from the 1983 Coalinga, Coast Range California, earthquake sequence, in combination with the three-dimensional velocity structure shows that the active faulting beneath the fold primarily consists of a set of southwest dipping thrusts uplifting blocks of higher-velocity material. With the three-dimensional velocity model each individual hypocenter moved slightly (0-2km) in accord with the details of the surrounding velocity structure, so that secondary features in the seismicity pattern are more detailed than with a local one-dimensional model and station corrections. The overall character of the fault plane solutions was not altered by the three-dimensional model, but the more accurate ray paths did result in distinct changes. In particular, the mainshock has a fault plane dipping 30?? southwest instead of the 23?? obtained with the one-dimensional model. -from Author

  19. Research of Earthquake Potential from Active Fault Observation in Taiwan

    NASA Astrophysics Data System (ADS)

    Chien-Liang, C.; Hu, J. C.; Liu, C. C.; En, C. K.; Cheng, T. C. T.

    2015-12-01

    We utilize GAMIT/GLOBK software to estimate the precise coordinates for continuous GPS (CGPS) data of Central Geological Survey (CGS, MOEA) in Taiwan. To promote the software estimation efficiency, 250 stations are divided by 8 subnets which have been considered by station numbers, network geometry and fault distributions. Each of subnets include around 50 CGPS and 10 international GNSS service (IGS) stations. After long period of data collection and estimation, a time series variation can be build up to study the effect of earthquakes and estimate the velocity of stations. After comparing the coordinates from campaign-mode GPS sites and precise leveling benchmarks with the time series from continuous GPS stations, the velocity field is consistent with previous measurement which show the reliability of observation. We evaluate the slip rate and slip deficit rate of active faults in Taiwan by 3D block model DEFNODE. First, to get the surface fault traces and the subsurface fault geometry parameters, and then establish the block boundary model of study area. By employing the DEFNODE technique, we invert the GPS velocities for the best-fit block rotate rates, long term slip rates and slip deficit rates. Finally, the probability analysis of active faults is to establish the flow chart of 33 active faults in Taiwan. In the past two years, 16 active faults in central and northern Taiwan have been assessed to get the recurrence interval and the probabilities for the characteristic earthquake occurred in 30, 50 and 100 years.

  20. Geodynamics of the Dead Sea Fault: Do active faulting and past earthquakes determine the seismic gaps?

    NASA Astrophysics Data System (ADS)

    Meghraoui, Mustapha

    2014-05-01

    The ~1000-km-long North-South trending Dead Sea transform fault (DSF) presents structural discontinuities and includes segments that experienced large earthquakes (Mw>7) in historical times. The Wadi Araba and Jordan Valley, the Lebanese restraining bend, the Missyaf and Ghab fault segments in Syria and the Ziyaret Fault segment in Turkey display geometrical complexities made of step overs, restraining and releasing bends that may constitute major obstacles to earthquake rupture propagation. Using active tectonics, GPS measurements and paleoseismology we investigate the kinematics and long-term/short term slip rates along the DSF. Tectonic geomorphology with paleoseismic trenching and archeoseismic investigations indicate repeated faulting events and left-lateral slip rate ranging from 4 mm/yr in the southern fault section to 6 mm/yr in the northern fault section. Except for the northernmost DSF section, these estimates of fault slip rate are consistent with GPS measurements that show 4 to 5 mm/yr deformation rate across the plate boundary. However, recent GPS results showing ~2.5 mm/yr velocity rate of the northern DSF appears to be quite different than the ~6 mm/yr paleoseismic slip rate. The kinematic modeling that combines GPS and seismotectonic results implies a complex geodynamic pattern where the DSF transforms the Cyprus arc subduction zone into transpressive tectonics on the East Anatolian fault. The timing of past earthquake ruptures shows the occurrence of seismic sequences and a southward migration of large earthquakes, with the existence of major seismic gaps along strike. In this paper, we discuss the role of the DSF in the regional geodynamics and its implication on the identification of seismic gaps.

  1. Challenges and perspectives in the geological study of active faults.

    NASA Astrophysics Data System (ADS)

    Rizza, M.

    2011-12-01

    Identification of active faults is important for understanding regional seismicity and seismic hazard. A large part of the world's population lives in areas where destructive earthquakes or tsunamis were recorded in the past. Most of the difficulties in estimating seismic hazard and anticipating earthquakes are due to a lack of knowledge about the location of active faults and their seismic history. Even where active faults are known the characteristics of past earthquakes and the seismic cycle are uncertain and subject to discussion. Investigations carried out on active faults during the past decade, however, have provided new high-quality data and powerful tools to better understand crustal deformation and the recurrence of earthquakes. In morphotectonic studies, the ever-improving resolution of satellites images allows geologists to identify with more certainty the traces of active faults and even earthquake surface ruptures of the past. The advantage of satellite imagery for identifying neotectonic features is it gives access to large areas, sometimes difficult to reach in the field and provides synoptic views. Using the potential of high-resolution imagery and digital elevation models, geologists can produce detailed 3D reconstructions of fault morphology and geometry, including the kinematics of repeated slip. The development of new dating techniques, coupled with paleoseismology and quantitative geomorphology, now allows bracketing the occurrence of paleoearthquakes back to several thousand years, as well as analyzing long time sequences of events. Despite such wealth of new data, however, the work remaining to do is huge. Earthquake forecast (location, timing, magnitude) remains an unsolved problem for the earthquake community at large (seismologists, geodesists, paleoseismologists and modelers). The most important challenges in the next decade will be to increase the efficiency of neotectonic studies to create more complete active fault databases and

  2. Tectonic implications of a late Mesozoic fold and thrust belt in northwestern Nevada

    NASA Astrophysics Data System (ADS)

    Oldow, John S.

    1983-09-01

    The Luning-Fencemaker fold and thrust belt of northwestern Nevada formed east of the Mesozoic Sierran arc in a back-arc setting where noncontinental crust localized marine deposition and subsequent deformation. The fold-thrust belt was active in Middle or Late Jurassic and Early Cretaceous time and evolved during major northwest-southeast contraction. Comparable shortening was not developed in the Sierran arc, and for much of the Mesozoic the arc and the back-arc regions were at least partially decoupled and separated by the regionally extensive Pine Nut fault system, which underwent substantial left-lateral displacement. Development of the fold-thrust belt and associated strike-slip fault is attributed to oblique subduction. The shortening axis of the fold-thrust belt and inferred displacement of the strike-slip fault are incompatible with right-oblique subduction and call for an interval of left-oblique convergence during part of Jurassic-Cretaceous time.

  3. Evolution of fault activity reflecting the crustal deformation: Insights from crustal stress and fault orientations in the northeast-southwest Japan

    NASA Astrophysics Data System (ADS)

    Miyakawa, A.; Otsubo, M.

    2015-12-01

    We evaluated fault activity in northeast- southwest Japan based on the regional stress and the fault orientation field for both active faults and inactive faults (here, an inactive fault is a fault which activity has not been identified in Quaternary). The regional stress field was calculated using the stress inversion method [Hardebeck and Michael, 2006] applied to earthquake focal mechanisms in the northeast-southwest Japan. The locations and orientations (i.e., strike and dip, assuming a planar fault geometry) of active faults in the study area were obtained from the Active Fault Database of Japan and inactive faults from a database compiled by Kosaka et al. [2011]. We employed slip tendency analysis [Morris et al., 1996] to evaluate the likelihood of fault slip. The values of the slip tendency is generally higher along active faults than along inactive faults. The difference between the slip tendencies of active and inactive faults reflects the difference in their activities. Furthermore the high slip tendency observed for some inactive faults suggests their high activity. These high slip tendencies imply that they have potential to be active. We propose the temporal evolution from inactive to active faulting during long-term crustal deformation to explain the potential for fault activity along inactive faults. When a region undergoes the transition from inactive to active faulting, potential active faults are observed as inactive faults with a high Part of this findig have been submitted to Tectonics (AGU Journal) (2015-07-27). We will presentate some new findings.slip tendency. The average slip tendency of inactive faults gradually increases from northeast to southwest Japan, because a relatively large number of inactive faults in southwest Japan have a high slip tendency. The representative deformation zones in Japan shows a relationship with the observed spatial variations in the evolution from inactive to active faulting. This study was supported by MEXT

  4. F-15B ACTIVE with thrust vectoring nozzles on test stand at sunrise

    NASA Technical Reports Server (NTRS)

    1995-01-01

    This November 13, 1995, photograph of the F-15 Advanced Controls Technology for Integrated Vehicles (ACTIVE) at NASA's Dryden Flight Research Center, Edwards, California, shows the aircraft on a test stand at sunrise. Not shown in this photograph are the aircraft's two new Pratt & Whitney nozzles that can turn up to 20 degrees in any direction. These nozzles give the aircraft thrust control in the pitch (up and down) and yaw (left and right) directions. This will reduce drag and increase fuel economy or range as compared with conventional aerodynamic controls, which increase the retarding forces (drag) acting upon the aircraft. These tests could result in significant performance increases for military and commercial aircraft. The research program is the product of a collaborative effort by NASA, the Air Force's Wright Laboratory, Pratt & Whitney, and McDonnell Douglas Aerospace. The aircraft was originally built as an F-15B (Serial #71-0290).

  5. Active Fault Deformation Along the South Boundary of the Western Transverse Ranges Province, Point Dume to the Northern Channel Islands, Southern California

    NASA Astrophysics Data System (ADS)

    Fisher, M. A.; Langenheim, V. E.; Sorlien, C. C.; Nicholson, C.; Sliter, R. W.

    2005-12-01

    The regional fault system forming the south boundary of the Western Transverse Ranges Province (WTRP) extends for about 200 km, from near the city of Los Angeles westward along the south flank of the Santa Monica Mountains and through the northern Channel Islands. Multichannel seismic-reflection data show that fault strands within the province-bounding system are active, and some have dip-slip displacements measured in kilometers. The left-oblique Dume fault is active and shows large displacement as far west as Sycamore knoll, but farther west, the fault tip and a superjacent fold are deeply buried. Thus during future earthquakes, the structural transition near the knoll could represent a boundary between earthquake-rupture segments. The east-west province-bounding fault system strikes at a high angle across and terminates the northwest-trending faults, basins and ridges of the California Continental Borderland. Borderland structures considered here form the western limit of intense middle Miocene oblique extension that accompanied rotation of the WTRP. The transition between extended and intact crust lies along the northwest-trending Santa Cruz-Catalina and Santa Rosa-Cortes Ridges. After the Miocene rotation, structures within these ridges became involved in regional transpression, such that northwestward along the Santa Cruz-Catalina Ridge, thrust faulting becomes increasingly more intense, and adjacent to the province boundary, thrust-faulted rocks completely override Miocene extensional structures. In contrast, rocks making up the Santa Rosa-Cortez Ridge are little deformed. The difference in deformation of the two ridges could result from a combination of: 1) eastward crustal thinning and consequent weakening that developed during the Miocene extension; 2) a difference in horizontal strain across the right-slip San Clemente fault near its termination at the WTRP boundary; 3) strain partitioning along this boundary; and 4) a contrast in bulk rheological

  6. Deep reaching versus vertically restricted Quaternary normal faults: Implications on seismic potential assessment in tectonically active regions: Lessons from the middle Aterno valley fault system, central Italy

    NASA Astrophysics Data System (ADS)

    Falcucci, E.; Gori, S.; Moro, M.; Fubelli, G.; Saroli, M.; Chiarabba, C.; Galadini, F.

    2015-05-01

    We investigate the Middle Aterno Valley fault system (MAVF), a poorly investigated seismic gap in the central Apennines, adjacent to the 2009 L'Aquila earthquake epicentral area. Geological and paleoseismological analyses revealed that the MAVF evolved through hanging wall splay nucleation, its main segment moving at 0.23-0.34 mm/year since the Middle Pleistocene; the penultimate activation event occurred between 5388-5310 B.C. and 1934-1744 B.C., the last event after 2036-1768 B.C. and just before 1st-2nd century AD. These data define hard linkage (sensu Walsh and Watterson, 1991; Peacock et al., 2000; Walsh et al., 2003, and references therein) with the contiguous Subequana Valley fault segment, able to rupture in large magnitude earthquakes (up to 6.8), that did not rupture since about two millennia. By the joint analysis of geological observations and seismological data acquired during to the 2009 seismic sequence, we derive a picture of the complex structural framework of the area comprised between the MAVF, the Paganica fault (the 2009 earthquake causative fault) and the Gran Sasso Range. This sector is affected by a dense array of few-km long, closely and regularly spaced Quaternary normal fault strands, that are considered as branches of the MAVF northern segment. Our analysis reveals that these structures are downdip confined by a decollement represented by to the presently inactive thrust sheet above the Gran Sasso front limiting their seismogenic potential. Our study highlights the advantage of combining Quaternary geological field analysis with high resolution seismological data to fully unravel the structural setting of regions where subsequent tectonic phases took place and where structural interference plays a key role in influencing the seismotectonic context; this has also inevitably implications for accurately assessing seismic hazard of such structurally complex regions.

  7. Active fault database of Japan: Its construction and search system

    NASA Astrophysics Data System (ADS)

    Yoshioka, T.; Miyamoto, F.

    2011-12-01

    The Active fault database of Japan was constructed by the Active Fault and Earthquake Research Center, GSJ/AIST and opened to the public on the Internet from 2005 to make a probabilistic evaluation of the future faulting event and earthquake occurrence on major active faults in Japan. The database consists of three sub-database, 1) sub-database on individual site, which includes long-term slip data and paleoseismicity data with error range and reliability, 2) sub-database on details of paleoseismicity, which includes the excavated geological units and faulting event horizons with age-control, 3) sub-database on characteristics of behavioral segments, which includes the fault-length, long-term slip-rate, recurrence intervals, most-recent-event, slip per event and best-estimate of cascade earthquake. Major seismogenic faults, those are approximately the best-estimate segments of cascade earthquake, each has a length of 20 km or longer and slip-rate of 0.1m/ky or larger and is composed from about two behavioral segments in average, are included in the database. This database contains information of active faults in Japan, sorted by the concept of "behavioral segments" (McCalpin, 1996). Each fault is subdivided into 550 behavioral segments based on surface trace geometry and rupture history revealed by paleoseismic studies. Behavioral segments can be searched on the Google Maps. You can select one behavioral segment directly or search segments in a rectangle area on the map. The result of search is shown on a fixed map or the Google Maps with information of geologic and paleoseismic parameters including slip rate, slip per event, recurrence interval, and calculated rupture probability in the future. Behavioral segments can be searched also by name or combination of fault parameters. All those data are compiled from journal articles, theses, and other documents. We are currently developing a revised edition, which is based on an improved database system. More than ten

  8. Evaluation of feasibility of mapping seismically active faults in Alaska

    NASA Technical Reports Server (NTRS)

    Gedney, L. D.; Vanwormer, J. D. (Principal Investigator)

    1973-01-01

    The author has identified the following significant results. The sharp bend in the Alaska Range near 65 deg N, 150 deg W in now thought to enclose a corner of the northwesterly migrating north Pacific lithospheric plate. Subduction of the plate beneath the continent is believed, on the basis of hypocentral distribution, to occur along Cook Inlet and the eastern flanks of the Aleutian and Alaska Ranges as far northward as Mt. McKinley. The nature of tectonic deformation here, particularly in the area of the bend in the Alaska Range, is understandably complex. The Denali fault is thought to be a transform character in the vicinity of Mt. McKinley (i.e., it is thought to be the surface along which the oceanic plate separates from the continental plate). On the ERTS-1 imagery, however, it appears that there are a number of sub-parallel faults which branch off of the Denali fault in a southwesterly direction. Slippage along these would tend to squeeze material around the inside of the band rather than the plate being directly underthrust. All of these sub-parallel faults are seismically active. The right-lateral fault-plane solution obtained for this event is consistent with the concept of slippage around the bend on a set of sub-parallel faults in the manner postulated. The best images to show these features are 1066-20444 and 1266-20572.

  9. Active faulting on the Wallula fault within the Olympic-Wallowa Lineament (OWL), eastern Washington State

    NASA Astrophysics Data System (ADS)

    Sherrod, B. L.; Lasher, J. P.; Barnett, E. A.

    2013-12-01

    Several studies over the last 40 years focused on a segment of the Wallula fault exposed in a quarry at Finley, Washington. The Wallula fault is important because it is part of the Olympic-Wallowa lineament (OWL), a ~500-km-long topographic and structural lineament extending from Vancouver Island, British Columbia to Walla Walla, Washington that accommodates Basin and Range extension. The origin and nature of the OWL is of interest because it contains potentially active faults that are within 50 km of high-level nuclear waste facilities at the Hanford Site. Mapping in the 1970's and 1980's suggested the Wallula fault did not offset Holocene and late Pleistocene deposits and is therefore inactive. New exposures of the Finley quarry wall studied here suggest otherwise. We map three main packages of rocks and sediments in a ~10 m high quarry exposure. The oldest rocks are very fine grained basalts of the Columbia River Basalt Group (~13.5 Ma). The next youngest deposits include a thin layer of vesicular basalt, white volcaniclastic deposits, colluvium containing clasts of vesicular basalt, and indurated paleosols. A distinct angular unconformity separates these vesicular basalt-bearing units from overlying late Pleistocene flood deposits, two colluvium layers containing angular clasts of basalt, and Holocene tephra-bearing loess. A tephra within the loess likely correlates to nearby outcrops of Mazama ash. We recognize three styles of faults: 1) a near vertical master reverse or oblique fault juxtaposing very fine grained basalt against late Tertiary-Holocene deposits, and marked by a thick (~40 cm) vertical seam of carbonate cemented breccia; 2) subvertical faults that flatten upwards and displace late Tertiary(?) to Quaternary(?) soils, colluvium, and volcaniclastic deposits; and 3) flexural slip faults along bedding planes in folded deposits in the footwall. We infer at least two Holocene earthquakes from the quarry exposure. The first Holocene earthquake deformed

  10. Neogene contraction between the San Andreas fault and the Santa Clara Valley, San Francisco Bay region, California

    USGS Publications Warehouse

    McLaughlin, R.J.; Langenheim, V.E.; Schmidt, K.M.; Jachens, R.C.; Stanley, R.G.; Jayko, A.S.; McDougall, K.A.; Tinsley, J.C.; Valin, Z.C.

    1999-01-01

    In the southern San Francisco Bay region of California, oblique dextral reverse faults that verge northeastward from the San Andreas fault experienced triggered slip during the 1989 M7.1 Loma Prieta earthquake. The role of these range-front thrusts in the evolution of the San Andreas fault system and the future seismic hazard that they may pose to the urban Santa Clara Valley are poorly understood. Based on recent geologic mapping and geophysical investigations, we propose that the range-front thrust system evolved in conjunction with development of the San Andreas fault system. In the early Miocene, the region was dominated by a system of northwestwardly propagating, basin-bounding, transtensional faults. Beginning as early as middle Miocene time, however, the transtensional faulting was superseded by transpressional NE-stepping thrust and reverse faults of the range-front thrust system. Age constraints on the thrust faults indicate that the locus of contraction has focused on the Monte Vista, Shannon, and Berrocal faults since about 4.8 Ma. Fault slip and fold reconstructions suggest that crustal shortening between the San Andreas fault and the Santa Clara Valley within this time frame is ~21%, amounting to as much as 3.2 km at a rate of 0.6 mm/yr. Rates probably have not remained constant; average rates appear to have been much lower in the past few 100 ka. The distribution of coseismic surface contraction during the Loma Prieta earthquake, active seismicity, late Pleistocene to Holocene fluvial terrace warping, and geodetic data further suggest that the active range-front thrust system includes blind thrusts. Critical unresolved issues include information on the near-surface locations of buried thrusts, the timing of recent thrust earthquake events, and their recurrence in relation to earthquakes on the San Andreas fault.

  11. Transition from collision to subduction in Western Greece: the Katouna-Stamna active fault system and regional kinematics

    NASA Astrophysics Data System (ADS)

    Pérouse, E.; Sébrier, M.; Braucher, R.; Chamot-Rooke, N.; Bourlès, D.; Briole, P.; Sorel, D.; Dimitrov, D.; Arsenikos, S.

    2016-06-01

    Transition from subduction to collision occurs in Western Greece and is accommodated along the downgoing plate by the Kefalonia right-lateral fault that transfers the Hellenic subduction front to the Apulian collision front. Here we present an active tectonic study of Aitolo-Akarnania (Western Greece) that highlights how such a transition is accommodated in the overriding plate. Based on new multi-scale geomorphic and tectonic observations, we performed an accurate active fault trace mapping in the region, and provide evidence for active normal and left-lateral faulting along the Katouna-Stamna Fault (KSF), a 65-km-long NNW-striking fault system connecting the Amvrakikos Gulf to the Patras Gulf. We further show that the Cenozoic Hellenide thrusts located west of the KSF are no longer active, either in field observation or in GPS data, leading us to propose that the KSF forms the northeastern boundary of a rigid Ionian Islands-Akarnania Block (IAB). Cosmic ray exposure measurements of 10Be and 36Cl were performed on a Quaternary alluvial fan offset along the KSF (~50 m left-lateral offset). A maximum abandonment age of ~12-14 ka for the alluvial fan surface can be determined, giving an estimated KSF minimum geological left-lateral slip rate of ~4 mm year-1, in agreement with high GPS slip rates (~10 mm year-1). Despite this high slip rate, the KSF is characterized by subdued morphological evidence of tectonic activity, a gypsum-breccia bedrock and a low level of seismicity, suggesting a dominantly creeping behavior for this fault. Finally, we discuss how the IAB appears to have been progressively individualized during the Pleistocene (younger than ~1.5 Ma).

  12. Sandbox modeling of evolving thrust wedges with different preexisting topographic relief: Implications for the Longmen Shan thrust belt, eastern Tibet

    NASA Astrophysics Data System (ADS)

    Sun, Chuang; Jia, Dong; Yin, Hongwei; Chen, Zhuxin; Li, Zhigang; Shen, Li; Wei, Dongtao; Li, Yiquan; Yan, Bin; Wang, Maomao; Fang, Shaozhi; Cui, Jian

    2016-06-01

    To understand the effects of substantial topographic relief on deformation localization in the seismically active mountains, like the Longmen Shan thrust belt in the eastern Tibet, sandbox experiments were performed based on the framework of the critical taper theory. First, a reference experiment revealed that the critical taper angle was 12° for our experimental materials. Subsequently, different proto wedges (subcritical (6° in taper angle), critical (12°), and supercritical (20°)) were introduced to cover the range of natural topographic relief, and we used two setups: setup A considered only across-strike topographic relief, whereas setup B investigated along-strike segmentation of topography, consist of two adjacent proto wedges. In all experiments, thrust wedges grew by in-sequence accretion of thrust sheets. Setup A revealed an alternating mode of slip partitioning on the accreted thrusts, with large-displacement thrust and small-displacement thrust developing in turn. And contrasting wedge evolutions occurred according to whether the proto wedge was subcritical or critical-supercritical. In setup B, the differential deformation along the strike produced transverse structures such as tear fault and lateral ramp during frontal accretion. The observed tear fault and its associated thrust system resemble the seismogenic fault system of the 2008 Mw7.9 Wenchuan earthquake. Our experimental results could also explain first-order deformation features observed in the Longmen Shan. Consequently, we conclude that topographic features, including topographic relief across the range and along-strike segmentation of topography, contribute significantly to the kinematics and deformation localization in such active mountains.

  13. Active faulting and devastating earthquakes in continental China

    NASA Astrophysics Data System (ADS)

    Zhang, P.

    2003-04-01

    The primary pattern of active tectonics in continental China is characterized by relative movements and interactions of tectonic blocks bounded by major active faults. Earthquakes are results of abrupt releases of accumulated strain energy that excesses the threshold of strength of brittle part of the earth’s crust. Boundaries of tectonic blocks are the locations of most discontinuous deformation and highest gradient of stress accumulation, thus are the most likely places for strain energy accumulation and releases, and in turn, devastating earthquakes. Almost all earthquakes of magnitude larger than 8 and 80~90% of earthquakes of magnitude over 7 occur along boundaries of active tectonic blocks. This fact indicates that differential movements and interactions of active tectonic blocks are the primary mechanism for the occurrences of devastating earthquakes. Northeastern margin of Tibetan Plateau consists of two active fault zones, the Haiyuan and the Xiangshan fault zones. Each of the zones can be further divided into several segments. Historical earthquakes during the past 800 years ruptured all of them except one segment, the so-called Tianzhu seismic gap. We have conducted paleoseismological studies on each of the segments of the fault zones. Preliminary results reveal temporal clustering features of long-term paleoearthquake activity along these two fault zones. The 1920 Haiyuan earthquake of magnitude 8.5, for example, ruptured three segments of the fault zone. We dug 19 trenches along different segments of the surface ruptures. There were 3 events along the eastern segment during the past 14000 years, 7 events along the middle segment during the past 9000 years, and 6 events along the western segment during the past 10000 years. These events clearly depict two temporal clusters. The first cluster occurs from 4600 to 6400 years, and the second occurs from 1000 to 2800 years, approximately. Each cluster lasts about 2000 years. Time period between these two

  14. Recent faulting and active shortening of the Middle Atlas Mountains, Morocco, within the diffuse African-Eurasian plate boundary

    NASA Astrophysics Data System (ADS)

    Rigby, M.; Gomez, F.; Zakir, A.; Hahou, Y.; Jabour, N.

    2007-12-01

    The NE-SW trending Middle Atlas Mountains are an active intracontinental mountain belt within the diffuse African - Eurasian plate boundary. The mountain belt is obliquely oriented to the NNW-SSE direction of Late Cenozoic plate convergence. Both shear and compressional features are exhibited with apparent slip partitioning: Folding and thrusting is concentrated in the Folded Middle Atlas, whereas strike-slip dominates in the Tabular Middle Atlas. In the central part of the Folded Middle Atlas, fault scarps of Quaternary alluvium, including a 4.5 meter (probably composite) scarp and a 1 meter (possibly single event) scarp, attest to recent faulting along the mountain front. Detailed topographic mapping of the scarps provides a basis for geomorphic analysis and degradation modeling. Furthermore, the reconstruction of longitudinal stream terrace profiles helps constrain a long term deformation history. Radiocarbon and pending cosmogenic dates provide age constraints on the faulted surfaces and the multiple stream terraces in the area. To place these active tectonic observations in a larger context, the fault and fold geometry has been assessed by completing a 10 km structural transect across the frontal thrust, providing basis for the construction of a balanced cross-section. By combining the structural geometry with the uplift rate, a minimum estimate of the rate of horizontal shortening in the Middle Atlas can be evaluated. Preliminary results suggest the Middle Atlas may accommodate 5 - 10 percent of the total 4.5 mm/yr convergence between the African and Eurasian plates. These results demonstrate that the Middle Atlas Mountains are a integral part of the diffuse plate boundary, as well as suggesting a modest level of earthquake hazard in the region.

  15. Effect of Spinal Manipulation Thrust Duration on Trunk Mechanical Activation Thresholds of Nociceptive-Specific Lateral Thalamic Neurons

    PubMed Central

    Reed, William R.; Sozio, Randall; Pickar, Joel G.; Onifer, Stephen M.

    2015-01-01

    Objective The objective of this preliminary study was to determine if high-velocity, low-amplitude spinal manipulation (HVLA-SM) thrust duration alters mechanical trunk activation thresholds of nociceptive-specific (NS) lateral thalamic neurons. Methods Extracellular recordings were obtained from 18 NS neurons located in 2 lateral thalamic nuclei (ventrolateral [n = 12] and posterior [n = 6]) in normal anesthetized Wistar rats. Response thresholds to electronic von Frey anesthesiometer (rigid tip) mechanical trunk stimuli applied in 3 lumbar directions (dorsal-ventral, 45° caudal, and 45° cranial) were determined before and immediately after the delivery of 3 HVLA-SM thrust durations (time control 0, 100, and 400 milliseconds). Mean changes in mechanical trunk activation thresholds were compared using a mixed model analysis of variance. Results High-velocity, low-amplitude spinal manipulation duration did not significantly alter NS lateral thalamic neurons’ mechanical trunk responses to any of the 3 directions tested with the anesthesiometer. Conclusions This study is the first to examine the effect of HVLA-SM thrust duration on NS lateral thalamic mechanical response thresholds. High-velocity, low-amplitude spinal manipulation thrust duration did not affect mechanical trunk thresholds. PMID:25220757

  16. An developing ICDP drilling project on intraplate seismicity: Drilling Active Faults in Northern Europe (DAFNE)

    NASA Astrophysics Data System (ADS)

    Ask, M. V.; Kukkonen, I. T.; Olesen, O.; Steffen, H.; Schmitt, D.

    2011-12-01

    The combined effects of reduced ice load and glacially affected rock stresses are believed to have generated dramatic postglacial fault (PGF) structures in northern Europe, reflecting a special type of intraplate seismicity. A total of 14 PGFs have been identified up to date, with fault scarps up to 160 km in length and 30 m in height. They are usually SE dipping, SW-NE oriented thrusts that represent reactivated, pre-existing crustal discontinuities. Local and national seismic networks reveal that, at least some of the faults are still very active, with several hundreds of microseismic events each year. It is evident that if they were formed in single events, they would imply massive intraplate earthquakes (up to M 7-8). Hence, PGFs may generate larger intraplate earthquakes than generally assumed. Similar structures in North America have not been reported yet. Currently, an International Continental Drilling Program (ICDP) project on Drilling Active Faults in Northern Europe (DAFNE) is under development. The aim of the project is to investigate tectonic and structural characteristics of PGFs in northern Fennoscandia, including their hydrogeology and associated deep biosphere. The research is anticipated to advance science in neotectonics, hydrogeology and deep biosphere studies, and provide important information for nuclear waste and CO2 disposal, petroleum exploration on the Norwegian continental shelf and studies of mineral resources in PG fault areas. We expect that multidisciplinary research applying shallow and deep drilling of PGFs would provide significant scientific results through generating new data and models, namely: 1. Understanding PGF genesis and controls of their locations; 2. Deep structure and depth extent of PGFs; 3. Textural, mineralogical and physical alteration of rocks in the PGFs; 4. State of stress and estimates of paleostress of PGFs; 5. Hydrogeology, hydrochemistry and hydraulic properties of PGFs; 6. Dating of tectonic reactivation

  17. Antiformal closure in ductile and brittle-ductile in fold-and-thrust belt tranverse zones, Moine Thrust Belt, NW Scotland

    NASA Astrophysics Data System (ADS)

    Leslie, G.; Krabbendam, M.

    2009-04-01

    Abrupt lateral changes in thrust geometry occur in many mountain-building fold-and-thrust belts. Such changes in architecture are referred to as so-called transverse zones, and are commonly thought to be related to kinematic responses to irregularities generated across pre-existing, sometimes re-activated, basement faults. In many cases however the causative structure is concealed, either by distal parts of the thrust belt or the foreland basin. Sharp lateral changes in the structural geometry of ductile thrust stacks are less widely studied and reported. In NW Scotland, the classic Caledonian WNW-vergent Moine Thrust Belt exposes excellent examples of the structural architecture in such transverse zones, both in kilometre-scale thick monolithic (meta-)sandstone packages subject to ductile deformation, and in much thinner heterolithic packages subject to brittle-ductile deformation. In both cases the amplitude of the antiformal disturbance associated with the transverse zone is much greater than amplitude of any irregularity identified in the basement below. In Neoproterozoic Moine rocks in the hanging wall of the Moine Thrust, a large-scale lateral culmination wall forms a component part of the Oykel Transverse Zone (OTZ), a kilometre-scale thick constrictional ductile shear zone striking sub-parallel to the WNW-directed thrust transport direction. The OTZ forms the SW limit of the Cassley Culmination. ESE-plunging mullions are an integral part of the fabric of the transverse zone and were generated by constriction sub-parallel to the WNW-directed thrust transport direction. Main folds and fabrics in the transverse zone hanging-wall are folded by main folds and fabrics in the footwall, demonstrating the overall foreland-propagating record of ductile deformation as the Cassley Culmination grew. Constriction and mullion development are attributed to differential, transtensional movement across the transverse zone during the later stages of culmination development

  18. Evaluation of feasibility of mapping seismically active faults in Alaska

    NASA Technical Reports Server (NTRS)

    Gedney, L. D. (Principal Investigator); Vanwormer, J. D.

    1973-01-01

    The author has identified the following significant results. ERTS-1 imagery is proving to be exceptionally useful in delineating structural features in Alaska which have never been recognized on the ground. Previously unmapped features such as seismically active faults and major structural lineaments are especially evident. Among the more significant results of this investigation is the discovery of an active strand of the Denali fault. The new fault has a history of scattered activity and was the scene of a magnitude 4.8 earthquake on October 1, 1972. Of greater significance is the disclosure of a large scale conjugate fracture system north of the Alaska Range. This fracture system appears to result from compressive stress radiating outward from around Mt. McKinley. One member of the system was the scene of a magnitude 6.5 earthquake in 1968. The potential value of ERTS-1 imagery to land use planning is reflected in the fact that this earthquake occurred within 10 km of the site which was proposed for the Rampart Dam, and the fault on which it occurred passes very near the proposed site for the bridge and oil pipeline crossing of the Yukon River.

  19. Duplex development and abandonment during evolution of the Lewis thrust system, southern Glacier National Park, Montana

    SciTech Connect

    Yin, An; Kelty, T.K.; Davis, G.A. )

    1989-09-01

    The westernmost duplex (Brave Dog Mountain) includes the low-angle Brave Dog roof fault and Elk Mountain imbricate system, and the easternmost (Rising Wolf Mountain) duplex includes the low-angle Rockwell roof fault and Mt. Henry imbricate system. The geometry of these duplexes suggests that they differ from previously described geometric-kinematic models for duplex development. Their low-angle roof faults were preexisting structures that were locally utilized as roof faults during the formation of the imbricate systems. Crosscutting of the Brave Dog fault by the Mt. Henry imbricate system indicates that the two duplexes formed at different times. The younger Rockwell-Mt. Henry duplex developed 20 km east of the older Brave Dog-Elk Mountain duplex; the roof fault of the former is at a higher structural level. Field relations confirm that the low-angle Rockwell fault existed across the southern Glacier Park area prior to localized formation of the Mt. Henry imbricate thrusts beneath it. These thrusts kinematically link the Rockwell and Lewis faults and may be analogous to P shears that form between two synchronously active faults bounding a simple shear system. The abandonment of one duplex and its replacement by another with a new and higher roof fault may have been caused by (1) warping of the older and lower Brave Dog roof fault during the formation of the imbricate system (Elk Mountain) beneath it, (2) an upward shifting of the highest level of a simple shear system in the Lewis plate to a new decollement level in subhorizontal belt strata (= the Rockwell fault) that lay above inclined strata within the first duplex, and (3) a reinitiation of P-shear development (= Mt. Henry imbricate faults) between the Lewis thrust and the subparallel, synkinematic Rockwell fault.

  20. Exhumation history of an active fault to constrain a fault-based seismic hazard scenario: the Pizzalto fault (central Apennines, Italy) example.

    NASA Astrophysics Data System (ADS)

    Tesson, Jim; Pace, Bruno; Benedetti, Lucilla; Visini, Francesco; Delli Rocioli, Mattia; Didier, Bourles; Karim, keddadouche; Gorges, Aumaitre

    2016-04-01

    A prerequisite to constrain fault-based and time-dependent earthquake rupture forecast models is to acquire data on the past large earthquake frequency on an individual seismogenic source and to compare all the recorded occurrences in the active fault-system. We investigated the Holocene seismic history of the Pizzalto normal fault, a 13 km long fault segment belonging to the Pizzalto-Rotella-Aremogna fault system in the Apennines (Italy). We collected 44 samples on the Holocene exhumed Pizzalto fault plane and analyzed their 36Cl and rare earth elements content. Conjointly used, the 36Cl and REE concentrations show that at least 6 events have exhumed 4.4 m of the fault scarp between 3 and 1 ka BP, the slip per event ranging from 0.3 to 1.2 m. No major events have been detected over the last 1 ka. The Rotella-Aremogna-Pizzalto fault system has a clustered earthquake behaviour with a mean recurrence time of 1.2 ka and a low to moderate probability (ranging from 4% to 26%) of earthquake occurrence over the next 50 years. We observed similarities between seismic histories of several faults belonging to two adjacent fault systems. This could again attest that non-random processes occurring in the release of the strain accumulated on faults, commonly referred to as fault interactions and leading to apparent synchronization. If these processes were determined as being the main parameter controlling the occurrence of earthquakes, it would be crucial to take them into account in seismic hazard models.

  1. Potential earthquake faults offshore Southern California, from the eastern Santa Barbara Channel south to Dana Point

    USGS Publications Warehouse

    Fisher, M.A.; Sorlien, C.C.; Sliter, R.W.

    2009-01-01

    Urban areas in Southern California are at risk from major earthquakes, not only quakes generated by long-recognized onshore faults but also ones that occur along poorly understood offshore faults. We summarize recent research findings concerning these lesser known faults. Research by the U.S. Geological Survey during the past five years indicates that these faults from the eastern Santa Barbara Channel south to Dana Point pose a potential earthquake threat. Historical seismicity in this area indicates that, in general, offshore faults can unleash earthquakes having at least moderate (M 5-6) magnitude. Estimating the earthquake hazard in Southern California is complicated by strain partitioning and by inheritance of structures from early tectonic episodes. The three main episodes are Mesozoic through early Miocene subduction, early Miocene crustal extension coeval with rotation of the Western Transverse Ranges, and Pliocene and younger transpression related to plate-boundary motion along the San Andreas Fault. Additional complication in the analysis of earthquake hazards derives from the partitioning of tectonic strain into strike-slip and thrust components along separate but kinematically related faults. The eastern Santa Barbara Basin is deformed by large active reverse and thrust faults, and this area appears to be underlain regionally by the north-dipping Channel Islands thrust fault. These faults could produce moderate to strong earthquakes and destructive tsunamis. On the Malibu coast, earthquakes along offshore faults could have left-lateral-oblique focal mechanisms, and the Santa Monica Mountains thrust fault, which underlies the oblique faults, could give rise to large (M ??7) earthquakes. Offshore faults near Santa Monica Bay and the San Pedro shelf are likely to produce both strike-slip and thrust earthquakes along northwest-striking faults. In all areas, transverse structures, such as lateral ramps and tear faults, which crosscut the main faults, could

  2. Thrust Augmentation Through Active Flow Control: Lessons from a Bluegill Sunfish

    NASA Astrophysics Data System (ADS)

    Akhtar, Imran; Mittal, Rajat; Lauder, George

    2002-11-01

    Numerical simulations are being used to analyze the effect that vortices shed from the dorsal fin have on the thrust of the tail fin for a Bluegill Sunfish. The simulations are being carried out using a Cartesian grid method which allows us to simulate flows with complex moving boundararies on stationary Cartesian grids. The simulations attempt to model the kinematics of the fin motion and the flow conditions as measured by Drucker & Lauder (J. Exp. Bio. Vol. 202, pp 2393-2412, 1999) for a live specimen using PIV. Our simulations indicate that vortex shedding from the upstream dorsal fin is indeed capable of increasing the thrust of the tail fin significantly. However, this thrust augmentation is found to be quite sensitive to the phase relationship between the two flapping fins. Furthermore, the maximum thrust augmentation is found for phase angles that match those observed for the Bluegill Sunfish! The numerical simulation allow us to examine the underlying physical mechanism for this thrust augmentation and results pertaining to this will be presented.

  3. On the possible fault activation induced by UGS in depleted reservoirs

    NASA Astrophysics Data System (ADS)

    Feronato, Massimiliano; Gambolati, Giuseppe; Janna, Carlo; Teatini, Pietro; Tosattto, Omar

    2014-05-01

    Underground gas storage (UGS) represents an increasingly used approach to cope with the growing energy demand and occurs in many countries worldwide. Gas is injected in previously depleted deep reservoirs during summer when consumption is limited and removed in cold season mainly for heating. As a major consequence the pore pressure p within a UGS reservoir fluctuates yearly between a maximum close to the value pi prior to the field development and a minimum usually larger than the lowest pressure experienced by the reservoir at the end of its production life. The high frequency pressure fluctuations generally confine the pressure change volume to the reservoir volume without significantly involving the aquifers hydraulically connected to the hydrocarbon field (lateral and/or bottom waterdrive). The risk of UGS-induced seismicity is therefore restricted to those cases where existing faults cross or bound the reservoir. The possible risk of anthropogenic seismicity due to UGS operations is preliminary investigated by an advanced Finite Element (FE) - Interface Element (IE) 3-D elasto-plastic geomechanical model in a representative 1500 m deep reservoir bounded by a regional sealing fault and compartimentalized by an internal non-sealing thrust. Gas storage/production is ongoing with p ranging between pi in October/November and 60%pi in April/May. The yearly pressure fluctuation is assumed to be on the order of 50 bar. The overall geomechanical response of the porous medium has been calibrated by reproducing the vertical and horizontal cyclic displacements measured above the reservoir by advanced persistent scatterer interferometry. The FE-IE model shows that the stress variations remain basically confined within the gas field and negligibly propagate within the caprock and the waterdrive. Based on the Mohr-Coulomb failure criterion, IEs allow for the prediction of the fault activated area A, located at the reservoir depth as expected, and slip displacement d. A

  4. Inferences on active faults at the Southern Alps-Liguria basin junction from accurate analysis of low energy seismicity

    NASA Astrophysics Data System (ADS)

    Turino, Chiara; Scafidi, Davide; Eva, Elena; Solarino, Stefano

    2009-10-01

    Seismotectonic studies concern themselves with understanding the distribution of earthquakes in space, time, size and style. Therefore, the better these parameters are known, the most correct the association of any seismic event with the faulting structure that caused it will result. The use of accurate location methods is especially required when dealing with very complex areas, where several faulting systems or relatively small seismogenic structures exist. In fact, even though routinely determined epicentres are capable of revealing the rough picture of the seismicity, they are not suitable for studies of the fine structure of the causative fault, as their location uncertainties are often larger than the source dimension itself. In this work the probabilistic approach of the "Non Linear Localization" has been used to compute precise locations for earthquakes occurred in the last twenty years nearby the Saorge-Taggia line, a complex fault system situated in Western Liguria, close to the border between Italy and France. Together with the Breil-Sospel-Monaco and the Peille-Laghet faults, this line is responsible for the seismic activity of the area. The seismotectonic study is completed through a local tomographic study and the analysis of the focal mechanisms computed for an enlarged area. The results show that the seismicity associated with this fault system is confined within the first 10 km depth. Many clusters of seismic events are identified along the Saorge-Taggia line. The existence of a not previously mapped branch perpendicular to the Saorge-Taggia line is also recognized. Although its position may suggest it to be the continuation of the Breil-Sospel-Monaco fault system towards NE, our finding would rather suggest no association with the fault. The overall results confirm the complexity of the area; in particular the hypothesis that the Saorge-Taggia system may represent the eastward limit of a subalpine crustal block comprised within the Nice Arc, the

  5. Multiscale seismic imaging of active fault zones for hazard assessment: A case study of the Santa Monica fault zone, Los Angeles, California

    USGS Publications Warehouse

    Pratt, T.L.; Dolan, J.F.; Odum, J.K.; Stephenson, W.J.; Williams, R.A.; Templeton, M.E.

    1998-01-01

    High-resolution seismic reflection profiles at two different scales were acquired across the transpressional Santa Monica Fault of north Los Angeles as part of an integrated hazard assessment of the fault. The seismic data confirm the location of the fault and related shallow faulting seen in a trench to deeper structures known from regional studies. The trench shows a series of near-vertical strike-slip faults beneath a topographic scarp inferred to be caused by thrusting on the Santa Monica fault. Analysis of the disruption of soil horizons in the trench indicates multiple earthquakes have occurred on these strike-slip faults within the past 50 000 years, with the latest being 1000 to 3000 years ago. A 3.8-km-long, high-resolution seismic reflection profile shows reflector truncations that constrain the shallow portion of the Santa Monica Fault (upper 300 m) to dip northward between 30?? and 55??, most likely 30?? to 35??, in contrast to the 60?? to 70?? dip interpreted for the deeper portion of the fault. Prominent, nearly continuous reflectors on the profile are interpreted to be the erosional unconformity between the 1.2 Ma and older Pico Formation and the base of alluvial fan deposits. The unconformity lies at depths of 30-60 m north of the fault and 110-130 m south of the fault, with about 100 m of vertical displacement (180 m of dip-slip motion on a 30??-35?? dipping fault) across the fault since deposition of the upper Pico Formation. The continuity of the unconformity on the seismic profile constrains the fault to lie in a relatively narrow (50 m) zone, and to project to the surface beneath Ohio Avenue immediately south of the trench. A very high-resolution seismic profile adjacent to the trench images reflectors in the 15 to 60 m depth range that are arched slightly by folding just north of the fault. A disrupted zone on the profile beneath the south end of the trench is interpreted as being caused by the deeper portions of the trenched strike

  6. Palaeoseismology of the L'Aquila faults (central Italy, 2009, Mw 6.3 earthquake): implications for active fault linkage

    NASA Astrophysics Data System (ADS)

    Galli, Paolo A. C.; Giaccio, Biagio; Messina, Paolo; Peronace, Edoardo; Zuppi, Giovanni Maria

    2011-12-01

    Urgent urban-planning problems related to the 2009 April, Mw 6.3, L'Aquila earthquake prompted immediate excavation of palaeoseismological trenches across the active faults bordering the Aterno river valley; namely, the Mt. Marine, Mt. Pettino and Paganica faults. Cross-cutting correlations amongst existing and new trenches that were strengthened by radiocarbon ages and archaeological constraints show unambiguously that these three investigated structures have been active since the Last Glacial Maximum period, as seen by the metric offset that affected the whole slope/alluvial sedimentary succession up to the historical deposits. Moreover, in agreement with both 18th century accounts and previous palaeoseismological data, we can affirm now that these faults were responsible for the catastrophic 1703 February 2, earthquake (Mw 6.7). The data indicate that the Paganica-San Demetrio fault system has ruptured in the past both together with the conterminous Mt. Pettino-Mt. Marine fault system, along more than 30 km and causing an Mw 6.7 earthquake, and on its own, along ca. 19 km, as in the recent 2009 event and in the similar 1461 AD event. This behaviour of the L'Aquila faults has important implications in terms of seismic hazard assessment, while it also casts new light on the ongoing fault linkage processes amongst these L'Aquila faults.

  7. The southern Whidbey Island fault: An active structure in the Puget Lowland, Washington

    USGS Publications Warehouse

    Johnson, S.Y.; Potter, C.J.; Armentrout, J.M.; Miller, J.J.; Finn, C.; Weaver, C.S.

    1996-01-01

    Information from seismic-reflection profiles, outcrops, boreholes, and potential field surveys is used to interpret the structure and history of the southern Whidbey Island fault in the Puget Lowland of western Washington. This northwest-trending fault comprises a broad (as wide as 6-11 km), steep, northeast-dipping zone that includes several splays with inferred strike-slip, reverse, and thrust displacement. Transpressional deformation along the southern Whidbey Island fault is indicated by alongstrike variations in structural style and geometry, positive flower structure, local unconformities, out-of-plane displacements, and juxtaposition of correlative sedimentary units with different histories. The southern Whidbey Island fault represents a segment of a boundary between two major crustal blocks. The Cascade block to the northeast is floored by diverse assemblages of pre-Tertiary rocks; the Coast Range block to the southwest is floored by lower Eocene marine basaltic rocks of the Crescent Formation. The fault probably originated during the early Eocene as a dextral strike-slip fault along the eastern side of a continental-margin rift. Bending of the fault and transpressional deformation began during the late middle Eocene and continues to the present. Oblique convergence and clockwise rotation along the continental margin are the inferred driving forces for ongoing deformation. Evidence for Quaternary movement on the southern Whidbey Island fault includes (1) offset and disrupted upper Quaternary strata imaged on seismic-reflection profiles; (2) borehole data that suggests as much as 420 m of structural relief on the Tertiary-Quaternary boundary in the fault zone; (3) several meters of displacement along exposed faults in upper Quaternary sediments; (4) late Quaternary folds with limb dips of as much as ???9??; (5) large-scale liquefaction features in upper Quaternary sediments within the fault zone; and (6) minor historical seismicity. The southern Whidbey

  8. Seismic data, geometry, evolution, and shortening in the active Sulaiman fold-and-thrust belt of Pakistan, southwest of the Himalayas

    SciTech Connect

    Jadoon, I.A.K. ); Lawrence, R.D.; Lillie, R.J. )

    1994-05-01

    Despite its long history of exploration, the Sulaiman fold and thrust belt is a poorly known structure and detailed structural and geochemical investigations are vital for the successful exploration, evaluation and exploitation of any hydrocarbons. Recent nappe and duplex structural models provide a framework for exploration. Surface and subsurface data from the Sulaiman fold-and-thrust belt are integrated to analyze the deep structure, tectonic, shortening, and kinematics of the Sulaiman fold-and-thrust belt at the western margin of the Indian subcontinent. Seismic reflection data show that nearly all the 10-km-thick sequence of dominantly platform (>7 km) and molasse strata is detached at the deformation front. The strata thicken tectonically to about 20 km in the hinterland without significant thrust faults in the foreland. A balanced structural cross-section suggests that structural uplift in the Sulaiman fold-and-thrust belt is a result of a thin-skinned, passive-roof duplex style of deformation. Sequential restoration of the balanced section reveals a series of structural and geometrical features including: (1) development of low-amplitude, broad concentric folds at the tip of the decollement; (2) increase in amplitude of a detachment fold to a critical level for development of ramp and duplex structures; and (3) out-of-sequence thrusting to create required critical taper for an outward translation of the foreland fold-and-thrust belt. A balanced structural cross-section 349 km long from the Sulaiman fold-and-thrust belt restores to an original length of 727 km, suggesting a maximum of 378 km of shortening since 21 Ma in the cover strata of the Indian subcontinent. Calculation of displacement rates over the Sulaiman fold-and-thrust belt (18 mm/yr) added to the resolved rate of the Chaman fault vector for the component parallel to the plate convergence direction (15 mm/yr) are close to the current India-Asia plate convergence rate (37 mm/yr). 68 refs., 13 figs.

  9. Abdominal thrusts

    MedlinePlus

    ... call 911 . If the person loses consciousness, start CPR . If you are not comfortable performing abdominal thrusts, ... American Red Cross. First Aid/CPR/AED Participant's Manual. 2nd ... Red Cross; 2014. Berg RA, Hemphill R, Abella BS, et al. Part 5: ...

  10. Active fault segments as potential earthquake sources: Inferences from integrated geophysical mapping of the Magadi fault system, southern Kenya Rift

    NASA Astrophysics Data System (ADS)

    Kuria, Z. N.; Woldai, T.; van der Meer, F. D.; Barongo, J. O.

    2010-06-01

    Southern Kenya Rift has been known as a region of high geodynamic activity expressed by recent volcanism, geothermal activity and high rate of seismicity. The active faults that host these activities have not been investigated to determine their subsurface geometry, faulting intensity and constituents (fluids, sediments) for proper characterization of tectonic rift extension. Two different models of extension direction (E-W to ESE-WNW and NW-SE) have been proposed. However, they were based on limited field data and lacked subsurface investigations. In this research, we delineated active fault zones from ASTER image draped on ASTER DEM, together with relocated earthquakes. Subsequently, we combined field geologic mapping, electrical resistivity, ground magnetic traverses and aeromagnetic data to investigate the subsurface character of the active faults. Our results from structural studies identified four fault sets of different age and deformational styles, namely: normal N-S; dextral NW-SE; strike slip ENE-WSW; and sinistral NE-SW. The previous studies did not recognize the existence of the sinistral oblique slip NE-SW trending faults which were created under an E-W extension to counterbalance the NW-SE faults. The E-W extension has also been confirmed from focal mechanism solutions of the swarm earthquakes, which are located where all the four fault sets intersect. Our findings therefore, bridge the existing gap in opinion on neo-tectonic extension of the rift suggested by the earlier authors. Our results from resistivity survey show that the southern faults are in filled with fluid (0.05 and 0.2 Ωm), whereas fault zones to the north contain high resistivity (55-75 Ωm) material. The ground magnetic survey results have revealed faulting activity within active fault zones that do not contain fluids. In addition, the 2D inversion of the four aero-magnetic profiles (209 km long) revealed: major vertical to sub vertical faults (dipping 75-85° east or west); an

  11. Active faulting in the frontal Rif Cordillera (Fes region, Morocco): Constraints from GPS data

    NASA Astrophysics Data System (ADS)

    Chalouan, Ahmed; Gil, Antonio J.; Galindo-Zaldívar, Jesús; Ahmamou, M.'Fedal; Ruano, Patricia; de Lacy, Maria Clara; Ruiz-Armenteros, Antonio Miguel; Benmakhlouf, Mohamed; Riguzzi, Federica

    2014-07-01

    The southern Rif cordillera front, between Fes and Meknes, is formed by the Prerif Ridges, which constitute a thrust and fold belt, in contact with the Saïss foreland basin. Geological evidence and regional GPS network data support recent and active tectonics of this Alpine cordillera, with a top-to-the-S-SW motion with respect to stable Africa. A local non-permanent GPS network was installed in 2007 around Fes to constrain the present-day activity of the mountain front. Six GPS sites are located in the Prerif mountain front (jbel Thratt and jbel Zalarh), the Saïss basin and the foreland constituted by the tabular Middle Atlas. Measurements of the GPS network in 2007, 2009 and 2012, over a five year span, seem to indicate that this region is tectonically active and is subjected to significant horizontal motions: (i) a regional displacement toward the SW with respect to stable Africa, showing an average rate of 2 mm/yr; (ii) a southwestward convergent motion between the jbel Thratt with respect to the Saïss basin and the eastern Zalarh ridge, with an average rate of about 4 mm/yr; and (iii) moderate NNE-SSW divergent dextral motion between the Saïss basin and the northern front of the tabular Middle Atlas with an average rate of about 1-2 mm/yr. The regional southwestward motion is related to the activity of the NE-SW sinistral North Middle Atlas-Kert fault zone, which follows the Moroccan Hot Line. Convergence between the Prerif ridges, located at the southern edge of the Rif, and the Saïss basin is accommodated by ENE-WSW striking northward dipping reverse sinistral faults and south vergent folds. In addition, increasing deformation toward the western ridges is in agreement with the stepped mountain front and the development of the arched structures of the Prerif ridges. Normal faults located south of the Saïss basin are responsible for local extension. Whereas the most active deformation occurs in the southern front of the jbel Thratt near Fes, the Sa

  12. Active tectonics of the Seattle fault and central Puget sound, Washington - Implications for earthquake hazards

    USGS Publications Warehouse

    Johnson, S.Y.; Dadisman, S.V.; Childs, J. R.; Stanley, W.D.

    1999-01-01

    We use an extensive network of marine high-resolution and conventional industry seismic-reflection data to constrain the location, shallow structure, and displacement rates of the Seattle fault zone and crosscutting high-angle faults in the Puget Lowland of western Washington. Analysis of seismic profiles extending 50 km across the Puget Lowland from Lake Washington to Hood Canal indicates that the west-trending Seattle fault comprises a broad (4-6 km) zone of three or more south-dipping reverse faults. Quaternary sediment has been folded and faulted along all faults in the zone but is clearly most pronounced along fault A, the northernmost fault, which forms the boundary between the Seattle uplift and Seattle basin. Analysis of growth strata deposited across fault A indicate minimum Quaternary slip rates of about 0.6 mm/yr. Slip rates across the entire zone are estimated to be 0.7-1.1 mm/yr. The Seattle fault is cut into two main segments by an active, north-trending, high-angle, strike-slip fault zone with cumulative dextral displacement of about 2.4 km. Faults in this zone truncate and warp reflections in Tertiary and Quaternary strata and locally coincide with bathymetric lineaments. Cumulative slip rates on these faults may exceed 0.2 mm/yr. Assuming no other crosscutting faults, this north-trending fault zone divides the Seattle fault into 30-40-km-long western and eastern segments. Although this geometry could limit the area ruptured in some Seattle fault earthquakes, a large event ca. A.D. 900 appears to have involved both segments. Regional seismic-hazard assessments must (1) incorporate new information on fault length, geometry, and displacement rates on the Seattle fault, and (2) consider the hazard presented by the previously unrecognized, north-trending fault zone.

  13. Determining the Through-Going Active Fault Geometry of the Western North Anatolian Fault Through Stress Modeling

    NASA Astrophysics Data System (ADS)

    Karimi, B.; McQuarrie, N.

    2015-12-01

    The North Anatolian Fault (NAF) is a seismically active 1200 km long dextral strike-slip fault part of an east-west trending dextral shear zone (NAF system) between the Anatolian and Eurasian plates. This shear zone widens to the west, complicating potential earthquake rupture paths and highlighting the importance of understanding the geometry of active fault systems. West of the town of Bolu - the NAF bifurcates into the northern and southern strands, which converge and are linked through the Mudurnu Valley, then diverge to border the Marmara Sea. The westward continuation of these two fault traces is marked by further complexities in potential active fault geometry, particularly in the Marmara Sea (northern strand), and the Biga Peninsula (southern strand). We evaluate potential active fault geometries for both strands by comparing stress models of various fault geometries in these regions to a record of focal mechanisms and inferred paleostress from a lineament analysis. For the Marmara region, two of the three possible geometries matched the maximum horizontal stress (σH) orientations determined from a record of focal mechanisms; however, only one represented the northern and southern sidewalls associated with the principal zone of deformation of the developing Marmara basin. This suggests that it is the most likely representation of the active through-going fault geometry in the region. In the Biga Peninsula region, the active geometry of the southern strand has the southern component approaching and intersecting the northern component through a linking feature in a narrow topographic valley. This geometry was selected over two others as it overlaps the σH orientation determined from focal mechanism data and a lineament analysis. Additionally, this geometry does not develop a prominent mis-oriented NE-SW stress feature observed in the model results of the other two geometries, otherwise absent in the focal mechanism data or inferred from a lineament analysis.

  14. Effect of increased shear stress along a plate boundary fault on the formation of an out-of-sequence thrust and a break in surface slope within an accretionary wedge, based on numerical simulations

    NASA Astrophysics Data System (ADS)

    Miyakawa, Ayumu; Yamada, Yasuhiro; Matsuoka, Toshifumi

    2010-03-01

    We investigated the effect on accretionary wedge structure of increased shear stress, which describes the frictional sliding resistance along a decollement arising from an increase in material friction or reduction in pore pressure. To clarify the nature of the effect, we performed numerical simulations using two models: a Stable Friction model and an Increased Friction model. The Stable Friction model produced a low-angle, smooth, surface slope and an in-sequence thrust, whereas the Increased Friction model produced a break in surface slope (scarp) and an out-of-sequence thrust (OST) that cuts through the thrust sheet. The OST formed via the connection of segments of two adjacent thrusts, and its formation resulted in a change in the thickening mode of the wedge from thrust-sheet rotation and back-thrust activity to underplating. This contrast in thickening mode between the landward high-friction zone and seaward low-friction zone resulted in the formation of a clear break in slope, as the landward zone is steeper than the seaward zone, consistent with critical taper theory. The subduction of a basement slice or seamount can produce similar structures arising from an increase in resistance to basal shear sliding. However the distinctive structures arising in an accretionary wedge as a result of increased shear sliding resistance include a flat basal plane and absence of slope-failure sediments beneath the OST. These structural features are observed in accretionary wedges of the Nankai Trough off Muroto (Japan), the Sunda Strait, and the Barbados Ridge.

  15. Active flexural-slip faulting: A study from the Pamir-Tian Shan convergent zone, NW China

    NASA Astrophysics Data System (ADS)

    Li, Tao; Chen, Jie; Thompson, Jessica A.; Burbank, Douglas W.; Yang, Xiaodong

    2015-06-01

    The flexural-slip fault (FSF), a type of secondary fault generated by bed-parallel slip, occurs commonly and plays an important role in accommodating fold growth. Although the kinematics and mechanics of FSFs are well studied, relatively few field observations or geometric models explore its geomorphic expression. In the Pamir-Tian Shan convergent zone, NW China, suites of well-preserved FSF scarps displace fluvial terraces in the Mingyaole and Wulagen folds. Integrating interpretations of Google Earth images, detailed geologic and geomorphic mapping, and differential GPS measurements of terrace surfaces, we summarize geomorphic features that typify these faults and create kinematic models of active flexural-slip faulting. Our study indicates the following: (i) FSF scarps commonly occur near synclinal hinges, irrespective of whether (a) the dip direction of beds on either side of the hinge is unidirectional or in opposite directions, (b) the hinge is migrating or fixed, or (c) the hinge shape is narrow and angular or wide and curved. (ii) Active FSFs are likely to produce higher scarps on steeper beds, whereas lower or no topographic scarps typify gentler beds. (iii) Tilt angles of the terrace surface displaced above FSFs progressively decrease farther away from the hinge, with abrupt changes in slope coinciding with FSF scarps; the changes in tilt angle and scarp height have a predictable geometric relationship. (iv) Active FSFs can accommodate a significant fraction of total slip and play a significant role in folding deformation. (v) Active FSFs may be used to assess seismic hazards associated with active folds and associated blind thrusts.

  16. Tectonic activity and structural features of active intracontinental normal faults in the Weihe Graben, central China

    NASA Astrophysics Data System (ADS)

    Rao, Gang; Lin, Aiming; Yan, Bing; Jia, Dong; Wu, Xiaojun

    2014-12-01

    This study examines the tectonic activity and structural features of active normal faults in the Weihe Graben, central China. The Weihe Graben is an area with a high level of historic seismicity, and it is one of the intracontinental systems that developed since Tertiary in the extensional environment around the Ordos Block. Analysis of high-resolution remote-sensing imagery data, field observations, and radiocarbon dating results reveal the following: i) active normal faults are mainly developed within a zone < 500 m wide along the southern border of the eastern part of the Weihe Graben; ii) the active faults that have been identified are characterized by stepwise fault scarps dipping into the graben at angles of 40°-71°; iii) there are numerous discontinuous individual fault traces, ranging in length from a few tens of meters to 450 m (generally < 200 m); iv) fault zone structures, topographic features, and fault striations on the main fault planes indicate almost pure normal-slip; and v) late Pleistocene-Holocene terrace risers, loess, and alluvial deposits have been vertically offset by up to ~ 80 m, with a non-uniform dip-slip rate (throw-rates) ranging from ~ 2.1 to 5.7 mm/yr, mostly 2-3 mm/yr. Our results reveal that active normal faults have been developing in the Weihe Graben under an ongoing extensional environment, probably associated with the pre-existing graben and spreading of the continental crust, and this is in contrast with the Ordos Block and neighboring orogenic regions. These results provide new insights into the nature of extensional tectonic deformation in intracontinental graben systems.

  17. Safety enhancement of oil trunk pipeline crossing active faults on Sakhalin Island

    NASA Astrophysics Data System (ADS)

    Tishkina, E.; Antropova, N.; Korotchenko, T.

    2015-11-01

    The article explores the issues concerning safety enhancement of pipeline active fault crossing on Sakhalin Island. Based on the complexity and analysis results, all the faults crossed by pipeline system are classified into five categories - from very simple faults to extremely complex ones. The pipeline fault crossing design is developed in accordance with the fault category. To enhance pipeline safety at fault crossing, a set of methods should be applied: use of pipes of different safety classes and special trench design in accordance with soil permeability characteristics.

  18. Active Fault Tolerant Control for Ultrasonic Piezoelectric Motor

    NASA Astrophysics Data System (ADS)

    Boukhnifer, Moussa

    2012-07-01

    Ultrasonic piezoelectric motor technology is an important system component in integrated mechatronics devices working on extreme operating conditions. Due to these constraints, robustness and performance of the control interfaces should be taken into account in the motor design. In this paper, we apply a new architecture for a fault tolerant control using Youla parameterization for an ultrasonic piezoelectric motor. The distinguished feature of proposed controller architecture is that it shows structurally how the controller design for performance and robustness may be done separately which has the potential to overcome the conflict between performance and robustness in the traditional feedback framework. A fault tolerant control architecture includes two parts: one part for performance and the other part for robustness. The controller design works in such a way that the feedback control system will be solely controlled by the proportional plus double-integral PI2 performance controller for a nominal model without disturbances and H∞ robustification controller will only be activated in the presence of the uncertainties or an external disturbances. The simulation results demonstrate the effectiveness of the proposed fault tolerant control architecture.

  19. Searching for Seismically Active Faults in the Gulf of Cadiz

    NASA Astrophysics Data System (ADS)

    Custodio, S.; Antunes, V.; Arroucau, P.

    2015-12-01

    The repeated occurrence of large magnitude earthquakes in southwest Iberia in historical and instrumental times suggests the presence of active fault segments in the region. However, due to an apparently diffuse seismicity pattern defining a broad region of distributed deformation west of Gibraltar Strait, the question of the location, dimension and geometry of such structures is still open to debate. We recently developed a new algorithm for earthquake location in 3D complex media with laterally varying interface depths, which allowed us to relocate 2363 events having occurred from 2007 to 2013, using P- and S-wave catalog arrival times obtained from the Portuguese Meteorological Institute (IPMA, Instituto Portugues do Mar e da Atmosfera), for a study area lying between 8.5˚W and 5˚W in longitude and 36˚ and 37.5˚ in latitude. The most remarkable change in the seismicity pattern after relocation is an apparent concentration of events, in the North of the Gulf of Cadiz, along a low angle northward-dipping plane rooted at the base of the crust, which could indicate the presence of a major fault. If confirmed, this would be the first structure clearly illuminated by seismicity in a region that has unleashed large magnitude earthquakes. Here, we present results from the joint analysis of focal mechanism solutions and waveform similarity between neighboring events from waveform cross-correlation in order to assess whether those earthquakes occur on the same fault plane.

  20. Kozu-Matsuda fault system in northern Izu collision zone, western part of Kanagawa Prefecture, central Japan

    NASA Astrophysics Data System (ADS)

    Odawara, K.; Aketagawa, T.; Yoshida, A.

    2010-12-01

    Western area of Kanagawa Prefecture is techtonically highlighted by its geological setting that the Izu-Bonin volcanic arc collides with the Japan Island arc there. The Kozu-Matsuda fault system which consists of the Kozu-Matsuda fault, the Matsuda-kita fault, the Hinata fault and the Hirayama fault is a surface manifestation of the plate boundary. Research of the Kozu-Matsuda fault has advanced dramatically after the 1995 Kobe Earthquake. Having conducted a trench survey, Kanagawa Prefectural Government (2004) reported that the Kozu-Matsuda fault was activated at least four times in the past 4000 years and the latest activity occurred 650-950 years ago (AD. 1350-1050). However, details of the activity of the Hinata and Hirayama faults, the northern extension of the Kozu-Matsuda fault, are not well understood. The Special Project for Earthquake Disaster Mitigation in Urban areas (DaiDaiToku) made a 2040 m deep drilling in 2004 in Yamakita Town (Hayashi et al., 2006). DaiDaiToku also carried out the seismic reflection profiling along a route from Odawara to Yamanashi in 2005 (Sato et al., 2005). The study done by DaiDaiToku elucidated presence of two north-dipping thrusts. The northern thrust corresponds to the Hinata fault, and the southern one which is also considered to be a continuation of the Kozu-Matsuda fault probably represents a frontal thrust (Miyauchi et al., 2006). We have conducted paleoseismic investigations using data from boreholes across these thrusts.

  1. Block-like motion of Tibetan Plateau: Evidences from active faults , GPS velocities and recent earthquake slips

    NASA Astrophysics Data System (ADS)

    Xu, X.; Cheng, J.

    2012-12-01

    Collision of India with Eurasia during the past ~ 55 million years has created the high Tibetan Plateau with a flat interior at an average altitude of ~ 5000 m (Matte et al., 1996; Tapponnier et al., 1986, 2001). Two alternative end-member models of how the Tibetan Plateau formed have been proposed: (1) continuous thickening and widespread viscous channel flow of the crust and mantle of the entire plateau (e. g. Bai et al., 2011; Beaumont et al., 2001; Bendick and Flesch, 2007; Clark and Royden, 2000; Houseman and England, 1996; Royden et al., 1997; Shen F. et al., 2001; Zhang et al., 2004; Bai et al., 2010), and (2) time-dependent, localized shear between coherent lithospheric blocks (e. g. Avouac and Tapponnier, 1993; Peltzer and Saucier, 1996; Replumaz and Tapponnier, 2003; Ryerson et al., 2006; Tapponnier et al., 2001; Thatcher, 2007). A new 3-D mechanical model, in which the underthrust India and Tibet are strongly coupled, seems to explain spatial variation in faulting style, and to be inconsistent with channel-flow model for the southern Tibet (Copley et al., 2011). This 3-D model has placed important new constraints on mechanical behavior of the Tibetan lithosphere in its most extreme environment and forced a critical evaluation of the Tibetan channel flow models (Freymueller, 2011), but does not match details of the GPS velocity field, and underestimates the EW extension rate across the southern Tibet. More important is that the model approximates Tibet as a continuous medium, and cannot include localized slip on the mega-strike-slip fault systems, and thus cannot further discuss relationship among the eastward block-like motion, mega-strike-slip faults, normal faults and thrust faults in and around the Tibetan Plateau. It has been recognized for many years that GPS data are likely to be ultimately decisive in distinguishing between block-like and continuous models, at least for describing present-day deformation. Nonetheless, both block-like models and

  2. Active tectonic deformation along rejuvenated faults in tropical Borneo: Inferences obtained from tectono-geomorphic evaluation

    NASA Astrophysics Data System (ADS)

    Mathew, Manoj Joseph; Menier, David; Siddiqui, Numair; Kumar, Shashi Gaurav; Authemayou, Christine

    2016-08-01

    active folding of the Rajang Group fold-thrust belt to present and these events reactivated old major faults and minor related dislocations. From geomorphic analysis associated with sedimentary record, we posit that the terrain could have undergone high uplift rates since 5 Ma or multi-phased uplift with periodic intermittent pulses of high and low uplift rates.

  3. Activation of Fault Structures South of the La Habra Earthquake Rupture As Evidenced By UAVSAR Imaging

    NASA Astrophysics Data System (ADS)

    Donnellan, A.; Parker, J. W.; Grant Ludwig, L.; Hauksson, E.

    2014-12-01

    The 28 March, 2014 M 5.2 La Habra earthquake occurred on a northeast striking, northwest dipping left-lateral oblique thrust fault at the northeastern margin of the LA Basin, where regional right-lateral shear is accommodated by major northwest trending faults of the Peninsular Ranges, and north-south shortening is accommodated by north-dipping thrust faults and east-west trending folds of the Transverse Ranges. The La Habra mainshock location and focal mechanism is northwest of but sub-parallel to the Puente Hills thrust fault. Relocated seismicity highlights a northeast-trending rupture plane consistent with the magnitude and focal mechanism of the event. NASA's UAVSAR L-Band radar instrument was flown for north and south looking lines before the earthquake on 22 January 2014. The north looking line was reflown three days after the earthquake on 31 March, 2014, and the south looking line was reflown a week later on 4 April 2014. The UAVSAR Repeat Pass Interferogram (RPI) products show deformation consistent with the location of the mainshock beneath the town of La Habra. The results also show considerable aseismic northward horizontal deformation with minor uplift in the West Coyote Hills, south of the relocated seismicity. Inversion of the combined interferograms is consistent with south dipping low-angle (7°) shallow slip that corresponds to bedding plane attitudes and a mapped unconformity. The entire West Coyote Hills show 37 mm of modeled northward slip with an additional 34 mm of modeled slip concentrated near the Coyote Hills Park northeast of the intersection of Rosecrans Avenue and North Gilbert Street. A narrow band of shortening was also observed with UAVSAR, and confirmed with on-the-ground field observations, at the Trojan Way Kink Band, nearly one fault dimension southwest of the main rupture.

  4. THRUST BEARING

    DOEpatents

    Heller, P.R.

    1958-09-16

    A thrust bearing suitable for use with a rotor or blower that is to rotate about a vertical axis is descrihed. A centrifagal jack is provided so thnt the device may opernte on one hearing at starting and lower speeds, and transfer the load to another bearing at higher speeds. A low viscosity fluid is used to lubricate the higher speed operation bearing, in connection with broad hearing -surfaces, the ability to withstand great loads, and a relatively high friction loss, as contraated to the lower speed operatio;n bearing which will withstand only light thrust loads but is sufficiently frictionfree to avoid bearing seizure during slow speed or startup operation. An axially aligned shaft pin provides the bearing surface for low rotational speeds, but at higher speed, weights operating against spring tension withdraw nthe shaft pin into the bearing proper and the rotor shaft comes in contact with the large bearing surfaces.

  5. Estimate of the post-Last Glacial Maximum tectonic subsidence and attempt to elucidate the subsurface geometry of the active Shanchiao Fault in the Taipei metropolis, Taiwan

    NASA Astrophysics Data System (ADS)

    Chen, C.; Lee, J.; Chan, Y.; Lu, C.; Teng, L. S.

    2011-12-01

    The Taipei Metropolis, home to some 10 million people, is subject to seismic hazard originated from not only ground shaking in thick alluvial deposits due to distant faults or sources scattered throughout the Taiwan region, but also active faulting directly underneath. Northern Taiwan including the Taipei region is currently affected by post-orogenic (Plio-Pleistocene arc-continent collision) processes related to backarc extension of the Ryukyu subduction system. The Shanchiao Fault, an active normal fault outcropping along the western boundary of the Taipei Basin and dipping to the east, is investigated here for the areal extent and magnitude of its recent activity. Based on the growth faulting analysis in the Wuku profile in the central portion of the fault, one key horizon - the top of the Jingmei Conglomerate which was an alluvial fan formed rapidly when a major drainage reorganization occurred during the Last Glacial Maximum - serves to be the marker of tectonic subsidence since its inception around 23 ka. A determination and compilation of the depths of the Jingmei Conglomerate top horizon from nearly 500 borehole records within the Taipei Basin demonstrates that the hanging-wall deforms in a roll-over fashion and the offset is largest in the Wuku-Luzhou area in the central portion of the fault and decreases toward the southern tip of the fault. A geologic profile across the fault zone in the Luzhou area reveals the similar main-branch fault half-negative flower structural pattern observed in the Wuku profile, a phenomenon we interpreted to be originated from the geometry of the basin basement and the strong rheological contrast between unconsolidated basin sediments and basement rocks. We also attempt to resolve the poorly-known subsurface geometry of the Shanchiao Fault by simple elastic dislocation models. The surface deformation recorded by the above compilation is representative of the latest Quaternary period as it spans probably more than 10 earthquake

  6. Kinematics of syn- and post-exhumational shear zones at Lago di Cignana (Western Alps, Italy): constraints on the exhumation of Zermatt-Saas (ultra)high-pressure rocks and deformation along the Combin Fault and Dent Blanche Basal Thrust

    NASA Astrophysics Data System (ADS)

    Kirst, Frederik; Leiss, Bernd

    2016-03-01

    Kinematic analyses of shear zones at Lago di Cignana in the Italian Western Alps were used to constrain the structural evolution of units from the Piemont-Ligurian oceanic realm (Zermatt-Saas and Combin zones) and the Adriatic continental margin (Dent Blanche nappe) during Palaeogene syn- and post-exhumational deformation. Exhumation of Zermatt-Saas (U)HP rocks to approximately lower crustal levels at ca. 39 Ma occurred during normal-sense top-(S)E shearing under epidote-amphibolite-facies conditions. Juxtaposition with the overlying Combin zone along the Combin Fault at mid-crustal levels occurred during greenschist-facies normal-sense top-SE shearing at ca. 38 Ma. The scarcity of top-SE kinematic indicators in the hanging wall of the Combin Fault probably resulted from strain localization along the uppermost Zermatt-Saas zone and obliteration by subsequent deformation. A phase of dominant pure shear deformation around 35 Ma affected units in the direct footwall and hanging wall of the Combin Fault. It is interpreted to reflect NW-SE crustal elongation during updoming of the nappe stack as a result of underthrusting of European continental margin units and the onset of continental collision. This phase was partly accompanied and followed by ductile bulk top-NW shearing, especially at higher structural levels, which transitioned into semi-ductile to brittle normal-sense top-NW deformation due to Vanzone phase folding from ca. 32 Ma onwards. Our structural observations suggest that syn-exhumational deformation is partly preserved within units and shear zones exposed at Lago di Cignana but also that the Combin Fault and Dent Blanche Basal Thrust experienced significant post-exhumational deformation reworking and overprinting earlier structures.

  7. New Constraints on the Geometry and Kinematics of Active Faults in the Hinterland of the Northwest Himalaya

    NASA Astrophysics Data System (ADS)

    Morell, K. D.; Sandiford, M.; Rajendran, C. C. P.; Fink, D.; Kohn, B. P.

    2014-12-01

    The geometry and kinematics of the active, and potentially seismogenic, fault structures within the hinterland of the Himalaya have proven challenging to constrain in the past, primarily because active faults in this region tend to be buried beneath the subsurface and active seismicity often does not align with surficially mapped fault traces. Here we present a series of complementary datasets, including results from low temperature thermochronology, basin-wide erosion rates from 10Be concentrations, and topographic and longitudinal profile analyses, that place constraints on the spatial distribution of fault-related rock uplift and erosion across a ~400-km long region of the lower and high Himalaya of northwest India. Results from our analyses reveal that hillslope morphology and channel steepness are relatively invariant parallel to strike but vary significantly across strike, with the most prominent and abrupt variations occurring at the physiographic transition between the lower and high Himalaya (PT2), near the axial trace of the ramp-flat transition in the Main Himalayan Thrust (MHT). The cross-strike changes in geomorphology observed across the PT2 correlate with an order of magnitude northward increase in basin-wide erosion rates (~0.06-0.8 mm/a) and a corresponding decrease in apatite (~5-2 Ma) and zircon (U-Th)/He (~10-2 Ma) cooling ages. Combined with published geophysical and seismicity data, we interpret these results to reflect spatial variations in rock uplift and exhumation induced by a segment of the MHT ramp-flat system that is at least ~400 km long and ~125 km wide. The relatively young (U-Th)/He ages (<10 Ma) greater than 20 km south of the MHT ramp-flat transition preliminarily suggest that the kinematics of this system are best explained by a model which incorporates an accreting duplex on the MHT ramp but additional forthcoming analyses, including thermal modeling, will confirm if this hypothesis is robust.

  8. Active surface faulting or landsliding in the Lower Tagus Valley (Portugal)? A solved controversy concerning the Vila Chã de Ourique site

    NASA Astrophysics Data System (ADS)

    Cabral, João Manuel; Marques, Fernando; Figueiredo, Paula; Matias, Luís

    2011-04-01

    The Lower Tagus Valley has experienced significant (M 6-7) historical seismicity, evidencing the presence of seismogenic faults. These are still deficiently known due to the low strain rates and the recent alluvial sedimentation of the Tagus River that buries most of the structures, though Paleoseismic evidence was allegedly found by a research team in the Tagus valley, at a site 60 km N of Lisbon, near Vila Chã de Ourique (VCO). According to this team, trenching at the VCO site exposed an active thrust fault, evidencing the surface rupture of a large earthquake that occurred in 1531. Our studies performed at this site, comprising field observations with a reappraisal of the trench outcrops previously excavated, borehole drilling, soil mechanics laboratory testing, and seismic reflection acquisition, pointed to the alternative interpretation that the outcropping structures are gravitational and not of tectonic origin. The interpretation of new outcrops crosscutting the structures exposed at the trenches, as well as newly acquired high-resolution seismic reflection data, definitely exclude the active thrust fault explanation and support a gravitational slip model for all the observed structures. Gravitational slip in the river bank slope was promoted by low shear strength clays and high pore water pressure coupled with slope toe river erosion. Gravitational slides must have occurred prior to development of the present sedimentation level of the Tagus alluvial plain, which was attained in the last few thousand years as indicated by borehole data and estimations of sedimentation rates.

  9. Structural development and petroleum potential of the Dagestan foreland thrust belt, Terek-Caspian Basin, Russia

    SciTech Connect

    Sobornov, K. )

    1994-07-01

    The Dagestan foreland thrust belt represents a transition zone between the Terek-Caspian basin and Caucasus. Boreholes and seismic data obtained during the last decade in the course of petroleum exploration reveal considerable differences between the surface and subsurface structures of the area. The new data suggest that the allochthonous assemblage of the belt is formed mainly by stacked north-verging thrust sheets made up mostly of Mesozoic carbonates and sandstones bounded at the top and bottom by conjugate detachment surfaces. The thrust sheets are interpreted to be inserted into the clastic section of the Terek-Caspian foredeep along the base of Oligocene-early Miocene mudstones. The interpreted geometry of the thrust-belt front implies a shortening of about 20-50 km. The blind subsurface thrusts have been active since late Miocene and Holocene. The interpreted structural relationships between Mesozoic-Cenozoic stratigraphic units imply that principal thrusts were formed due to reactivation and inversion of low-angle normal faults, which were active in the Jurassic - early Miocene. Mechanical weakness and low density of the overpressured Oligocene - lower Miocene Maykop Formation aided subsurface thrusting. The new interpretation of the regional structure offers a petroleum exploration play consisting of structural traps within the buried antiformal stacks. Oil- and gas-bearing Upper Cretaceous and Upper Jurassic carbonate rocks involved in thrust sheets are considered primary prospecting targets.

  10. Aftershocks illuninate the 2011 Mineral, Virginia, earthquake causative fault zone and nearby active faults

    USGS Publications Warehouse

    Horton, Jr., J. Wright; Shah, Anjana K.; McNamara, Daniel E.; Snyder, Stephen L.; Carter, Aina M

    2015-01-01

    Deployment of temporary seismic stations after the 2011 Mineral, Virginia (USA), earthquake produced a well-recorded aftershock sequence. The majority of aftershocks are in a tabular cluster that delineates the previously unknown Quail fault zone. Quail fault zone aftershocks range from ~3 to 8 km in depth and are in a 1-km-thick zone striking ~036° and dipping ~50°SE, consistent with a 028°, 50°SE main-shock nodal plane having mostly reverse slip. This cluster extends ~10 km along strike. The Quail fault zone projects to the surface in gneiss of the Ordovician Chopawamsic Formation just southeast of the Ordovician–Silurian Ellisville Granodiorite pluton tail. The following three clusters of shallow (<3 km) aftershocks illuminate other faults. (1) An elongate cluster of early aftershocks, ~10 km east of the Quail fault zone, extends 8 km from Fredericks Hall, strikes ~035°–039°, and appears to be roughly vertical. The Fredericks Hall fault may be a strand or splay of the older Lakeside fault zone, which to the south spans a width of several kilometers. (2) A cluster of later aftershocks ~3 km northeast of Cuckoo delineates a fault near the eastern contact of the Ordovician Quantico Formation. (3) An elongate cluster of late aftershocks ~1 km northwest of the Quail fault zone aftershock cluster delineates the northwest fault (described herein), which is temporally distinct, dips more steeply, and has a more northeastward strike. Some aftershock-illuminated faults coincide with preexisting units or structures evident from radiometric anomalies, suggesting tectonic inheritance or reactivation.

  11. Constant reverse thrust activated reorientation of liquid hydrogen with Geyser initiation

    NASA Technical Reports Server (NTRS)

    Hung, R. J.; Shyu, K. L.

    1992-01-01

    A key objective of the cryogenic fluid management of the spacecraft propulsion system is to develop the technology necessary for acquisition or positioning of liquid outflow or vapor venting. Numerical simulation of positive liquid acquisition is attempted by introducing reverse gravity acceleration, resulting from the propulsive thrust of auxiliary engines, which exceeds critical value for the initiation of geyser. Based on the computer simulation of flowfields during the course of fluid reorientation, six dimensionless parameters resulted in this study. It shows that these parameters hold near-constant values through the entire ranges of liquid filled levels, from 30-80 percent, during the course of fluid reorientation.

  12. NASA Fixed Wing Project Propulsion Research and Technology Development Activities to Reduce Thrust Specific Energy Consumption

    NASA Technical Reports Server (NTRS)

    Hathaway, Michael D.; DelRasario, Ruben; Madavan, Nateri K.

    2013-01-01

    This paper presents an overview of the propulsion research and technology portfolio of NASA Fundamental Aeronautics Program Fixed Wing Project. The research is aimed at significantly reducing the thrust specific fuel/energy consumption of notional advanced fixed wing aircraft (by 60 % relative to a baseline Boeing 737-800 aircraft with CFM56-7B engines) in the 2030-2035 time frame. The research investments described herein are aimed at improving propulsive efficiency through higher bypass ratio fans, improving thermal efficiency through compact high overall pressure ratio gas generators, and exploring the potential benefits of boundary layer ingestion propulsion and hybrid gas-electric propulsion concepts.

  13. NASA Fixed Wing Project Propulsion Research and Technology Development Activities to Reduce Thrust Specific Energy Consumption

    NASA Technical Reports Server (NTRS)

    Hathaway, Michael D.; Rosario, Ruben Del; Madavan, Nateri K.

    2013-01-01

    This paper presents an overview of the propulsion research and technology portfolio of NASA Fundamental Aeronautics Program Fixed Wing Project. The research is aimed at significantly reducing the thrust specific fuel/energy consumption of notional advanced fixed wing aircraft (by 60 percent relative to a baseline Boeing 737-800 aircraft with CFM56-7B engines) in the 2030 to 2035 time frame. The research investments described herein are aimed at improving propulsive efficiency through higher bypass ratio fans, improving thermal efficiency through compact high overall pressure ratio gas generators, and exploring the potential benefits of boundary layer ingestion propulsion and hybrid gas-electric propulsion concepts.

  14. How does a brittle-ductile fault nucleate and grow in dolostone? A lesson learnt from a structural, geochemical and K-Ar chronological study of a reactivated Paleozoic thrust fault

    NASA Astrophysics Data System (ADS)

    Viola, G.; Torgersen, E.; Zwingmann, H.; Harris, C.

    2014-12-01

    Carbonate-hosted faults in the upper crust are mechanically strong, yet, under certain environmental conditions, carbonates may decompose into mechanically weak minerals, with major consequences for faults´ rheological behavior. We combine structural analysis, geochemistry, stable isotopes and K-Ar dating of synkinematic illite/muscovite to investigate the processes that control localization and weakening of initially strong, seismogenic brittle faults. We aim at better understanding how the constantly evolving architecture and composition of brittle-ductile faults affect their seismogenic properties. The Kvenklubben fault in northern Norway is part of a Caledonian compressional imbricate stack. It juxtaposes greenschist facies metabasalts in the hanging wall against meta-dolostones and has a 2.5 m thick fault core consisting of talc-bearing calc-phyllonites and chlorite phyllonites. Petrographic and geochemical results indicate that the phyllonites formed mainly through fluid-rock interaction and progressive decomposition of the adjacent wall rocks. K-Ar dating and chlorite geothermometry documents that the fault damage zone developed from the base upwards with fault initiation at 530 Ma around 200°C and the main development during reactivation around 440 Ma at c. 285°C. Early strain increments were accommodated in the dolostone by pressure-solution, formation of optimally oriented tensional fractures and cataclasis along geometrical irregularities of the growing fault plane. Fluids caused sequential decarbonation of the dolostones and carbonation of the metabasalts, resulting in the formation of phyllosilicate-decorated planar fabrics. The newly formed phyllosilicate levels weakened the fault under overall viscous creep conditions. The strongly anisotropic fluid-flow within the phyllonites, together with vein sealing following localized and transient high pore pressure-driven embrittlement, caused strain hardening. Together, the interaction between strain

  15. Stable isotopic evidence for fluid flow and fluid/rock interaction during thrust faulting in Pumpkin Valley shale and Rome Formation, east Tennessee

    SciTech Connect

    Butler, B.K.; Haase, C.S. )

    1989-08-01

    The Pumpkin Valley Shale and the underlying Rome Formation form the lower portions of the Copper Creek and White Oak Mountain thrust sheets in east Tennessee. The Pumpkin Valley Shale consists of shale and mudstone with subordinate amounts of interbedded siltstone. The Rome Formation is composed predominantly of sandstone with interbedded shale and siltstone toward the base of the formation. The percentage of illite increases from 20% to over 80% of the bulk clay mineralogy toward the base of the section. Porosity is occluded by quartz, phyllosilicate, and calcite cements. Both formations contain calcite-filled and, less commonly, quartz-filled Alleghenian fractures and joints.

  16. The northwest trending north Boquerón Bay-Punta Montalva Fault Zone; A through going active fault system in southwestern Puerto Rico

    USGS Publications Warehouse

    Roig‐Silva, Coral Marie; Asencio, Eugenio; Joyce, James

    2013-01-01

    The North Boquerón Bay–Punta Montalva fault zone has been mapped crossing the Lajas Valley in southwest Puerto Rico. Identification of the fault was based upon detailed analysis of geophysical data, satellite images, and field mapping. The fault zone consists of a series of Cretaceous bedrock faults that reactivated and deformed Miocene limestone and Quaternary alluvial fan sediments. The fault zone is seismically active (local magnitude greater than 5.0) with numerous locally felt earthquakes. Focal mechanism solutions suggest strain partitioning with predominantly east–west left-lateral displacements with small normal faults striking mostly toward the northeast. Northeast-trending fractures and normal faults can be found in intermittent streams that cut through the Quaternary alluvial fan deposits along the southern margin of the Lajas Valley, an east–west-trending 30-km-long fault-controlled depression. Areas of preferred erosion within the alluvial fan trend toward the west-northwest parallel to the onland projection of the North Boquerón Bay fault. The North Boquerón Bay fault aligns with the Punta Montalva fault southeast of the Lajas Valley. Both faults show strong southward tilting of Miocene strata. On the western end, the Northern Boquerón Bay fault is covered with flat-lying Holocene sediments, whereas at the southern end the Punta Montalva fault shows left-lateral displacement of stream drainage on the order of a few hundred meters.

  17. The paradox of vertical σ2 in foreland fold and thrust belts

    NASA Astrophysics Data System (ADS)

    Tavani, Stefano

    2014-05-01

    Occurrence of aesthetically appealing thrust systems and associated large scale anticlines, in both active and fossil foreland fold and thrust belts, is commonly interpreted as an evidence for Andersonian compressional framework. Indeed, these structures would testify for a roughly vertical σ3. Such a correlation between thrusts occurrence and stress field orientation, however, frequently fails to explain denser observations at a smaller scale. The syn-orogenic deformation meso-structures hosted in exposed km-scale thrust-related folds, in fact, frequently and paradoxically witness for a syn-thrusting strike-slip stress configuration, with a near-vertical σ2 and a sub-horizontal σ3. This apparent widespread inconsistency between syn-orogenic meso-structures and stress field orientation is here named "the σ2 paradox". A possible explanation for such a paradox is provided by inherited extensional deformation structures commonly developed prior to thrusting, in the flexural foreland basins located ahead of fold and thrust belts. Thrust nucleation and propagation is facilitated and driven by the positive inversion of the extensional inheritances, and their subsequent linkage. This process eventually leads to the development of large reverse fault zones and can occur both in compressive and strike-slip stress configurations.

  18. Tsunamigenic potential of Mediterranean fault systems and active subduction zones

    NASA Astrophysics Data System (ADS)

    Petricca, Patrizio; Babeyko, Andrey

    2016-04-01

    Since the North East Atlantic and Mediterranean Tsunami Warning System (NEAMTWS) is under development by the European scientific community, it becomes necessary to define guidelines for the characterization of the numerous parameters must be taken into account in a fair assessment of the risk. Definition of possible tectonic sources and evaluation of their potential is one of the principal issues. In this study we systematically evaluate tsunamigenic potential of up-to-now known real fault systems and active subduction interfaces in the NEAMTWS region. The task is accomplished by means of numerical modeling of tsunami generation and propagation. We have simulated all possible uniform-slip ruptures populating fault and subduction interfaces with magnitudes ranging from 6.5 up to expected Mmax. A total of 15810 individual ruptures were processed. For each rupture, a tsunami propagation scenario was computed in linear shallow-water approximation on 1-arc minute bathymetric grid (Gebco_08) implying normal reflection boundary conditions. Maximum wave heights at coastal positions (totally - 23236 points of interest) were recorded for four hours of simulation and then classified according to currently adopted warning level thresholds. The resulting dataset allowed us to classify the sources in terms of their tsunamigenic potential as well as to estimate their minimum tsunamigenic magnitude. Our analysis shows that almost every source in the Mediterranean Sea is capable to produce local tsunami at the advisory level (i.e., wave height > 20 cm) starting from magnitude values of Mw=6.6. In respect to the watch level (wave height > 50 cm), the picture is less homogeneous: crustal sources in south-west Mediterranean as well as East-Hellenic arc need larger magnitudes (around Mw=7.0) to trigger watch levels even at the nearby coasts. In the context of the regional warning (i.e., source-to-coast distance > 100 km) faults also behave more heterogeneously in respect to the minimum

  19. Structural and Lithologic Characteristics of the Wenchuan Earthquake Fault Zone and its Relationship with Seismic Activity

    NASA Astrophysics Data System (ADS)

    Wang, H.; Li, H.; Pei, J.; Li, T.; Huang, Y.; Zhao, Z.

    2010-12-01

    the older earthquake, but rather along the edge of the gouge. According to the gouge statistics of the whole fault zone, seismic events have the obvious tendency towards the foot wall, and the thickness of gouge is proportional to the activity of the fault, indicating that the width of fault zone is directly related to the number and evolution history of earthquakes . Repeated earthquakes maybe the main cause for the formation of the Longmenshan Moutains

  20. Structural Evidence for Fault Reactivation: the Active Priene-Sazli Fault Zone, Söke-Milet Basin, Western Anatolia

    NASA Astrophysics Data System (ADS)

    Sümer, Ö.; Inci, U.; Sözbilir, H.; Uzel, B.

    2009-04-01

    Western Anatolia is located at tha eastern part of the Aegean region that forms one of the most seismically active and rapidly extending regions in the world. One of the most prominent structural component of the Western Anatolia is E-W trending grabens. One of them is the Büyük Menderes Graben (BMG) showing a major change in strike ranging from E-W to NE-SW in its western end. This NE-SW oriented part of the graben is known as the Söke-Milet basin (SMB). The depression is 35 km long and 16 km wide. NW border of the basin is characterized by a morphotectonic structure namely Priene-Sazlı fault zone (PSFZ). The 16 July 1955 Söke-Balat earthquake (M=6.8) was atributed to this fault (Eyidogan and Jackson, 1985; Sengör, 1987; Altunel, 1998). However, field based kinematic studies on the PSFZ are lacking except for Gürer et. al. (2001). In this paper, we studied several reactivated fault segments of the PSFZ that are repeatedly formed under changing stress fields in order to evaluate the kinematic and stress history of the region by using structural relationships between striations and fault-plane related structures. The PSFZ consists of 5 fault segments which are en échelon arranged on the basis of mapping geological structures. The northern segments that strikes NE in the north and bends into an approximately E-W direction around Doganbey to the SW. Each segment is identified as steep opographic scarps ranging in height from a few meters to several hundred meters. Fault segments become to linkage and show breaching of the relay ramps between them. We interpret that such fault patterns have been formed in a region where extension has reactivated on pre-existing structures in an oblique sense. Evidence for this is the presence of three sets of striations each with different orientations on the same slip surface of the studied fault segments. Here, two differently oriented strike-slip slickenlines are postdated by dip-slip striations. Based on our structural

  1. A Comparison of Gluteus Maximus, Biceps Femoris, and Vastus Lateralis Electromyographic Activity in the Back Squat and Barbell Hip Thrust Exercises.

    PubMed

    Contreras, Bret; Vigotsky, Andrew D; Schoenfeld, Brad J; Beardsley, Chris; Cronin, John

    2015-12-01

    The back squat and barbell hip thrust are both popular exercises used to target the lower body musculature; however, these exercises have yet to be compared. Therefore, the purpose of this study was to compare the surface electromyographic (EMG) activity of the upper and lower gluteus maximus, biceps femoris, and vastus lateralis between the back squat and barbell hip thrust. Thirteen trained women (n = 13; age = 28.9 years; height = 164 cm; mass = 58.2 kg) performed estimated 10-repetition maximums (RM) in the back squat and barbell hip thrust. The barbell hip thrust elicited significantly greater mean (69.5% vs 29.4%) and peak (172% vs 84.9%) upper gluteus maximus, mean (86.8% vs 45.4%) and peak (216% vs 130%) lower gluteus maximus, and mean (40.8% vs 14.9%) and peak (86.9% vs 37.5%) biceps femoris EMG activity than the back squat. There were no significant differences in mean (99.5% vs 110%) or peak (216% vs 244%) vastus lateralis EMG activity. The barbell hip thrust activates the gluteus maximus and biceps femoris to a greater degree than the back squat when using estimated 10RM loads. Longitudinal training studies are needed to determine if this enhanced activation correlates with increased strength, hypertrophy, and performance.

  2. Relative tectonic activity assessment along the East Anatolian strike-slip fault, Eastern Turkey

    NASA Astrophysics Data System (ADS)

    Khalifa, Abdelrahman

    2016-04-01

    The East Anatolian transform fault is a morphologically distinct and seismically active left-lateral strike-slip fault that extends for ~ 500 km from Karlıova to the Maraş defining the boundary between the Anatolian Block and Syrian Foreland. Deformed landforms along the East Anatolian fault provide important insights into the nature of landscape development within an intra-continental strike-slip fault system. Geomorphic analysis of the East Anatolian fault using geomorphic indices including mountain front sinuosity, stream length-gradient index, drainage density, hypsometric integral, and the valley-width to valley height ratio helped differentiate the faulting into segments of differing degrees of the tectonic and geomorphic activity. Watershed maps for the East Anatolian fault showing the relative relief, incision, and maturity of basins along the fault zone help define segments of the higher seismic risk and help evaluate the regional seismic hazard. The results of the geomorphic indices show a high degree of activity, reveal each segment along the fault is active and represent a higher seismic hazard along the entire fault.

  3. Late Quaternary tectonic activity and paleoseismicity of the Eastern Messinia Fault Zone, SW Peloponessus (Messinia, Greece).

    NASA Astrophysics Data System (ADS)

    Valkaniotis, Sotirios; Betzelou, Konstantina; Zygouri, Vassiliki; Koukouvelas, Ioannis; Ganas, Athanassios

    2015-04-01

    The southwestern part of Peloponnesus, Messinia and Laconia, is an area of significant tectonic activity situated near the Hellenic trench. Most of the deformation in this area is accommodated by the Eastern Messinia Fault Zone, bordering the western part of Taygetos Mt range and the west coast of Mani peninsula. The Eastern Messinia Fault Zone (EMFZ) is a complex system of primarily normal faults dipping westwards with a strike of NNW-SSE to N-S direction attaining a total length of more than 100 km from the northern Messinia plain in the north to the southern part of Mani peninsula in the south. The continuity of the EMFZ is disrupted by overlapping faults and relay ramp structures. The central part of the EMFZ, from the town of Oichalia to the city of Kalamata, was investigated by detailed field mapping of fault structures and post-alpine sediment formations together with re-evaluation of historical and modern seismicity. Several fault segments with lengths of 6 to 10 km were mapped, defined and evaluated according to their state of activity and age. Analysis of fault striation measurements along fault planes of the fault zone shows a present regime of WSW-ENE extension, in accordance with focal mechanisms from modern seismicity. Known faults like the Katsareika and Verga faults near the city of Kalamata are interpreted as older-generation faults that are re-activated (e.g. the 1986 Ms 6.0 Kalamata earthquake on Verga Fault) as part of a system of distributed deformation. New fault segments, some of them previously unmapped like the Asprohoma fault to the west of Kalamata, and offshore faults like Kitries and Kourtissa, are being assigned to the EMFZ. Moreover, a paleoseismological trench was excavated in the northern part of Pidima fault segment, one of the most prominent active segments of the central part of the EMFZ, in order to examine the paleoearthquake record of the fault system. A significant number of historical and instrumental earthquakes in the area

  4. Early Cenozoic thrust in Qiangtang block, Northern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Wu, Z.; Ye, P.; Hu, D.; Lu, L.; Zhang, Y.

    2011-12-01

    Huge thrust systems, North Qiangtang Thrust (NQT) and South Qiangtang Thrust (SQT), were discovered in Qiangtang block, northern Tibetan Plateau. North Qiangtang thrust (NQT), including Dogai Coren thrust (DCT) and Longwei Co Thrust (LCT) formed in northern Qiangtang block. Triassic shale, sandstone and slate were thrusted southward over Late Cretaceous-Early Cenozoic conglomerate and sandstone (simplified as red-beds) along thrust faults of DCT, and Jurassic limestone and sandstone were thrusted over Late Cretaceous-Paleogene red-beds and Paleozoic metamorphic rocks along thrust faults of LCT in north of Central Qiangtang Uplift (CQU). South Qiangtang Thrust (SQT), including Xiaocaka-Shuanghu thrust (XST), Doma-Qixiang Co thrust (DQT) and Saibu Co-Zagya thrust (SZT), formed in southern Qiangtang block, accompanied by Nima-Silin thrust (NST) in northern Lhasa block. Permian marbleized limestone and dolomite, Triassic sandstone and shale, Jurassic limestone and ophiolite were thrusted southward over Paleogene red-beds along thrust faults of XST, DQT and SZT. Early Cenozoic thrust along NQT and SQT formed variety of tectonic slices, outliers and nappes of Permian-Jurassic rocks overlying Late Cretaceous-Paleogene red-beds in northern, central and southern Qiangtang block. Minimal estimation on southward offsets of DCT and LCT is 25km and 50km respectively, corresponding to 43% shortening in northern Qiangtang block, and minimal estimation on southward thrust offsets of XST, DQT and SZT yields ~90km southward thrust displacement of SQT, corresponding to ~47% shortening in southern Qiangtang block. Major thrust faults of NQT and SQT formed in upper crust according to seismic reflection profile, and such thrust and shortening were geodynamically related to northward subduction of India continental plate. Intensive thrust of NQT and SQT stopped before Early Miocene, followed by regional peneplanation, widespread lacustrine deposits in Early Miocene and crust extension as

  5. Fluid overpressure along an Oligocene out-of-sequence thrust in the Shimanto Belt, SW Japan

    NASA Astrophysics Data System (ADS)

    Passelègue, François X.; Fabbri, Olivier; Dubois, Michel; Ventalon, Sandra

    2014-06-01

    Out-of-sequence thrusts (OSTs) exposed in ancient accretionary prisms are considered as fossil analogs of present-day megasplay faults in subduction margins and can provide direct information about the conditions of deformation during thrust activity. In modern as well as in ancient accretionary prisms, first-order megasplay faults or OSTs truncate or merge with faults of lesser importance called second-order OSTs. Structural analysis of the Makinokuchi fault, a branch of an Oligocene to lower Miocene second-order OST in the Tertiary Shimanto Belt of central Kyushu, SW Japan, brings information about the conditions of deformation at the time of thrusting. The studied exposure shows that the fault footwall and, to a much lesser extent, the fault hanging-wall, consist of quartz-cemented syntectonic dilatant hydraulic breccias testifying to pore fluid pressures larger than the least principal stress component. The footwall sandstones are crossed by several centimeters thick quartz veins that merge with the footwall breccias. The continuity between the veins and the breccias suggest that the veins acted as conduits which likely collected fluids from the footwall side sandstones upward and toward the fault. Fluid inclusions indicate that the quartz cementing the breccias and that filling the feeder veins crystallized from similar fluids and under similar pressure and temperature conditions (245-285 °C and 5-8 km depth). These similarities suggest that the fluids responsible for syn-tectonic hydraulic brecciation were collected from the footwall through the conduits. The fluid inclusion trapping temperatures are close to the temperatures expected to be reached along the seismogenic zone. Our analysis shows that fluid overpressures can play a key role in the growth and activity of second-order OSTs in accretionary prisms and suggests that fluids collected along second-order OSTs or splay faults may flow upward along first-order OSTs or megasplay faults.

  6. Delineation of Urban Active Faults Using Multi-scale Gravity Analysis in Shenzhen, South China

    NASA Astrophysics Data System (ADS)

    Xu, C.; Liu, X.

    2015-12-01

    In fact, many cities in the world are established on the active faults. As the rapid urban development, thousands of large facilities, such as ultrahigh buildings, supersized bridges, railway, and so on, are built near or on the faults, which may change the balance of faults and induce urban earthquake. Therefore, it is significant to delineate effectively the faults for urban planning construction and social sustainable development. Due to dense buildings in urban area, the ordinary approaches to identify active faults, like geological survey, artificial seismic exploration and electromagnetic exploration, are not convenient to be carried out. Gravity, reflecting the mass distribution of the Earth's interior, provides a more efficient and convenient method to delineate urban faults. The present study is an attempt to propose a novel gravity method, multi-scale gravity analysis, for identifying urban active faults and determining their stability. Firstly, the gravity anomalies are decomposed by wavelet multi-scale analysis. Secondly, based on the decomposed gravity anomalies, the crust is layered and the multilayer horizontal tectonic stress is inverted. Lastly, the decomposed anomalies and the inverted horizontal tectonic stress are used to infer the distribution and stability of main active faults. For validating our method, a case study on active faults in Shenzhen City is processed. The results show that the distribution of decomposed gravity anomalies and multilayer horizontal tectonic stress are controlled significantly by the strike of the main faults and can be used to infer depths of the faults. The main faults in Shenzhen may range from 4km to 20km in the depth. Each layer of the crust is nearly equipressure since the horizontal tectonic stress has small amplitude. It indicates that the main faults in Shenzhen are relatively stable and have no serious impact on planning and construction of the city.

  7. Active faults crossing trunk pipeline routes: some important steps to avoid the disaster

    NASA Astrophysics Data System (ADS)

    Besstrashnov, Vladimir; Strom, Alexander

    2010-05-01

    Trunk pipelines that pass through tectonically active areas connecting oil and gas reservoirs with terminals and refineries cross active faults that can produce large earthquakes. Besides strong motion affecting vast areas, these earthquakes are often associated with surface faulting that provides additional hazard to pipelines. To avoid significant economic losses and environmental pollution, pipelines should be designed to sustain both effects (shaking and direct rupturing) without pipe damage and spill. Special studies aimed to provide necessary input data for the designers should be performed in the course of engineering survey. However, our experience on conducting and review of such studies for several oil and gas trunk pipelines in Russia show urgent need of more strict definition of basic conceptions and approaches used for identification and localization of these potentially hazardous tectonic features. Identification of active faults (fault zones) considered as causative faults - sources of strong motion caused by seismic waves that affect dozens kilometers of pipeline route can be done by use of both direct and indirect evidence of Late Pleistocene - Holocene activity of faults and fault zones. Since strong motion parameters can be considered as constant within the near-field zone, which width in case of large earthquake is up to dozens kilometers, accuracy of active fault location is not so critical and ±1-2 km precision provided by use of indirect evidence is acceptable. In contrast, if one have to identify and characterize zones of potential surface rupturing that require special design of the endangered pipeline section, only direct evidence of such activity can provide reliable input data for crossing design with relevant accuracy of fault location, amount and direction of displacement. Only traces of surface faults displacing Late Pleistocene - Holocene sediments and/or geomorphic features are considered as direct evidence of fault activity. Just

  8. Thrusting of the Hindu Kush over the Southeastern Tadjik Basin, Afghanistan: Evidence from two large earthquakes

    NASA Astrophysics Data System (ADS)

    Abers, Geoffrey; Bryan, Carol; Roecker, Steven; McCaffrey, Robert

    1988-02-01

    We infer from the mechanisms and depths of two large earthquakes that the Hindu Kush is actively thrusting northwest over the Tadjik basin and that the basin is closing rather than being displaced to the west. Teleseismic body waves were used to determine focal mechanisms and depths for the two largest shallow earthquakes on the southern edge of the basin. The two earthquakes, on June 24, 1972 (mb=6.0), and December 16, 1982 (mb=6.2), have seismic moments of 2 × 1018 N-m and 6 × 1018 N-m, respectively. Focal mechanisms of both events indicate almost pure thrust faulting with nodal planes striking northeast-southwest. The inferred fault planes dip southeast, at 20° for the first event and 50° for the second. The P axes for both events are oblique to the direction of relative motion between India and Asia, suggesting that the Pamir is overthrusting the basin to the west. Depths for both earthquakes are between 20 and 25 km and place them well below the Tadjik basin sediments. The depths and steep fault planes suggest that these earthquakes represent a downdip extension within the basement of shallow folding and thrusting seen in the sediments northwest of the events. Thus convergence in Afghanistan between India and Eurasia is taken up along southeast dipping thrust faults north of the Hindu Kush as well as by northward subduction under the southern part of the range.

  9. Retrodeformable cross sections and Oak Ridge fault, Ventura basin, California

    SciTech Connect

    Yeats, R.S.; Huftile, G.F.

    1988-03-01

    A retrodeformable (balanced) cross section is constructed such that stratified rocks are restored to their undeformed state without loss or gain of bed length or bed thickness. Ductile strata may be area-balanced if original thickness is known. Near Ventura, folds in Pliocene-Pleistocene turbidites and Miocene-early Pliocene shales (Rincon, Monterey, Sisquoc) overlie an unfolded competent Paleogene sequence. The basal decollement of the foldbelt is in the ductile Rincon Formation (lower Miocene). The overlying Sulphur Mountain, Ventura Avenue, San Miguelito, and Rincon anticlines are fault-propagation folds developing from south-dipping, largely late Quaternary frontal ramp thrusts (Sisar-Big Canyon-Lion fault set, Barnard fault set, padre Juan fault, and C-3 fault, respectively) that rise from the decollement. Cross-section balancing shows that the overlying fold-thrust belt has shortened 2.5-6 km more than subjacent Paleogene competent strata. This excess bed length is taken up in the Paleogene sequence on the Oak Ridge fault as a ramp from the brittle-plastic transition zone through the upper crust. This implies that the basal decollement is the frontal active thrust of the Oak Ridge fault. The decollement dies out southeast of a line between Timber Canyon oil field and the west end of Oak Ridge, possibly because of decreased ductility in the Miocene decollement sequence due to appearance of sandstone interbeds. Farther southeast, late Quaternary displacement concentrated on the Oak Ridge fault itself at rates greater than 10 mm/year.

  10. Evolution and dynamics of active faults in southeastern Egyptian Western Desert

    NASA Astrophysics Data System (ADS)

    Abdeen, Mamdouh

    2016-07-01

    Remote sensing data processing and analysis together with interpretation of earthquake data that are followed by extensive field studies on some of the prevailing NS and EW striking faults indicate that these faults have an intimate relationship and were formed synchronously as a conjugate Riedel shears. Parallel to the NS and the EW faults open fractures filled with blown sand dominate the area of study. The Quaternary terraces adjacent to these faults are offset by the faults. Kinematic indicators on the NS striking faults indicate major sinistral (left-lateral) strike slip and minor dip-slip (normal) movement. On the other hand, kinematic indicators on the EW striking faults indicate major dextral (right-lateral) strike slip and minor dip-slip (normal) movement. Paleo-stress analysis of the fault striae measured on the NS and EW faults indicate that these faults were formed under NNE-SSW oriented extension. Instrumental earthquake data analysis shows a comparable extension direction to that derived from field measurements of slickenlineation. These observations indicate that the NS- and EW-striking faults are contemporaneous and are related to the Red Sea rifting that is currently active.

  11. High-resolution imagery of active faulting offshore Al Hoceima, Northern Morocco

    NASA Astrophysics Data System (ADS)

    d'Acremont, E.; Gutscher, M.-A.; Rabaute, A.; Mercier de Lépinay, B.; Lafosse, M.; Poort, J.; Ammar, A.; Tahayt, A.; Le Roy, P.; Smit, J.; Do Couto, D.; Cancouët, R.; Prunier, C.; Ercilla, G.; Gorini, C.

    2014-09-01

    Two recent destructive earthquakes in 1994 and 2004 near Al Hoceima highlight that the northern Moroccan margin is one of the most seismically active regions of the Western Mediterranean area. Despite onshore geodetic, seismological and tectonic field studies, the onshore-offshore location and extent of the main active faults remain poorly constrained. Offshore Al Hoceima, high-resolution seismic reflection and swath-bathymetry have been recently acquired during the Marlboro-2 cruise. These data at shallow water depth, close to the coast, allow us to describe the location, continuity and geometry of three active faults bounding the offshore Nekor basin. The well-expressed normal-left-lateral onshore Trougout fault can be followed offshore during several kilometers with a N171°E ± 3° trend. Westward, the Bousekkour-Aghbal normal-left-lateral onshore fault is expressed offshore with a N020°E ± 4° trending fault. The N030°E ± 2° Bokkoya fault corresponds to the western boundary of the Plio-Quaternary offshore Nekor basin in the Al Hoceima bay and seems to define an en échelon tectonic pattern with the Bousekkour-Aghbal fault. We propose that these three faults are part of the complex transtensional system between the Nekor fault and the Al-Idrissi fault zone. Our characterization of the offshore expression of active faulting in the Al Hoceima region is consistent with the geometry and nature of the active fault planes deduced from onshore geomorphological and morphotectonic analyses, as well as seismological, geodetic and geodynamic data.

  12. Analecta of structures formed during the 28 June 1992 Landers-Big Bear, California earthquake sequence (including maps of shear zones, belts of shear zones, tectonic ridge, duplex en echelon fault, fault elements, and thrusts in restraining steps)

    SciTech Connect

    Johnson, A.M.; Johnson, N.A.; Johnson, K.M.; Wei, W.; Fleming, R.W.; Cruikshank, K.M.; Martosudarmo, S.Y.

    1997-12-31

    The June 28, 1992, M{sub s} 7.5 earthquake at Landers, California, which occurred about 10 km north of the community of Yucca Valley, California, produced spectacular ground rupturing more than 80 km in length (Hough and others, 1993). The ground rupturing, which was dominated by right-lateral shearing, extended along at least four distinct faults arranged broadly en echelon. The faults were connected through wide transfer zones by stepovers, consisting of right-lateral fault zones and tension cracks. The Landers earthquakes occurred in the desert of southeastern California, where details of ruptures were well preserved, and patterns of rupturing were generally unaffected by urbanization. The structures were varied and well-displayed and, because the differential displacements were so large, spectacular. The scarcity of vegetation, the aridity of the area, the compactness of the alluvium and bedrock, and the relative isotropy and brittleness of surficial materials collaborated to provide a marvelous visual record of the character of the deformation zones. The authors present a series of analecta -- that is, verbal clips or snippets -- dealing with a variety of structures, including belts of shear zones, segmentation of ruptures, rotating fault block, en echelon fault zones, releasing duplex structures, spines, and ramps. All of these structures are documented with detailed maps in text figures or in plates (in pocket). The purpose is to describe the structures and to present an understanding of the mechanics of their formation. Hence, most descriptions focus on structures where the authors have information on differential displacements as well as spatial data on the position and orientation of fractures.

  13. Recently active traces of the Bartlett Springs Fault, California: a digital database

    USGS Publications Warehouse

    Lienkaemper, James J.

    2010-01-01

    The purpose of this map is to show the location of and evidence for recent movement on active fault traces within the Bartlett Springs Fault Zone, California. The location and recency of the mapped traces is primarily based on geomorphic expression of the fault as interpreted from large-scale aerial photography. In a few places, evidence of fault creep and offset Holocene strata in trenches and natural exposures have confirmed the activity of some of these traces. This publication is formatted both as a digital database for use within a geographic information system (GIS) and for broader public access as map images that may be browsed on-line or download a summary map. The report text describes the types of scientific observations used to make the map, gives references pertaining to the fault and the evidence of faulting, and provides guidance for use of and limitations of the map.

  14. Seismicity, fault plane solutions, depth of faulting, and active tectonics of the Andes of Peru, Ecuador, and southern Colombia

    NASA Technical Reports Server (NTRS)

    Suarez, G.; Molnar, P.; Burchfiel, B. C.

    1983-01-01

    The long-period P waveforms observed for 17 earthquakes in the Peruvian Andes during 1963-1976 are compared with synthetic waveforms to obtain fault-plane solutions and focal depths. The morphological units of the Peruvian Andes are characterized: coastal plains, Cordillera Occidental, altiplano and central high plateau, Cordillera Oriental, and sub-Andes. The data base and analysis methodology are discussed, and the results are presented in tables, diagrams, graphs, maps, and photographs illustrating typical formations. Most of the earthquakes are shown to occur in the transition zone from the sub-Andes to the Cordillera Oriental under formations of about 1 km elevation at focal depths of 10-38 km. It is suggested that the sub-Andean earthquakes reflect hinterland deformation of a detached fold and thrust belt, perhaps like that which occurred in parts of the Canadian Rockies. From the total crustal shortening evident in Andean morphology and the shortening rate of the recent earthquakes it is estimated that the topography and crustal root of the Andes have been formed during the last 90-135 Myr.

  15. Active tectonics of the Ganzi-Yushu fault in the southeastern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Shi, Feng; He, Honglin; Densmore, Alexander L.; Li, An; Yang, Xiaoping; Xu, Xiwei

    2016-04-01

    The ongoing convergence between India and Eurasia apparently is accommodated not merely by crustal shortening in Tibet, instead also by motions along strike slip faults which are usually boundaries between tectonic blocks, especially in the Tibetan Plateau. Quantification of this strike slip faulting is fundamental for understanding the collision between India and Eurasia. Here, we use a variety of geomorphic observations to place constraints on the late Quaternary kinematics and slip rates of the Ganzi-Yushu fault, one of the significant strike-slip faults in eastern Tibet. The Ganzi-Yushu fault is an active, dominantly left-lateral strike-slip structure that can be traced continuously for up to 500 km along the northern boundary of the clockwise-rotating southeastern block of the Tibetan Plateau. We analyse geomorphic evidence for deformation, and calculate the late Quaternary slip rates at four sites along the eastern portion of the fault trace. The latest Quaternary apparent throw rates are variable along strike but are typically ~ 1 mm/a. Rates of strike-slip displacement are likely to be an order of magnitude higher, 8-11 mm/a. Trenching at two locations suggests that the active fault behaviour is dominated by strike-slip faulting and reveals several earthquake events with refined information of timing. The 2010 Mw 6.9 Yushu earthquake, which occurred on the northwestern segment of the Ganzi-Yushu fault zone, provides additional evidence for fault activity. These observations agree with GPS-derived estimates, and show that late Quaternary slip rates on the Ganzi-Yushu fault are comparable to those on other major active strike-slip faults in the eastern Tibetan Plateau.

  16. The Plio-Pleistocene evolution of the Southern Middle Atlas Fault Zone (SMAFZ) front of Morocco

    NASA Astrophysics Data System (ADS)

    Laville, E.; Delcaillau, B.; Charroud, M.; Dugué, O.; Ait Brahim, L.; Cattaneo, G.; Deluca, P.; Bouazza, A.

    2007-06-01

    The South Middle Atlas front constitutes a northeast-trending shear zone, located north of the Neogene Missour basin and east of the Taza Guercif basin. This paper analyses the Southern Middle Atlas Fault Zone (SMAFZ) deformation since the Pliocene. The set of structures observed suggests that reverse and thrust faulting along the central part of the SMAFZ are combined with left-lateral slip along N S striking faults of its south-western termination and right-lateral faulting along E NE striking faults of the east northeast termination. Thrusts and oblique thrust-related anticlines of the two lateral ramps partly accommodate north-west directed motion of the African plate. The Thrusts probably resulted from rejuvenation of Jurassic normal faults; they were active during the Upper Miocene Pliocene and the Pleistocene. The geometries of positive inversion structures and buttressing effects are clearly dependent on the geometry and sedimentology of the original basin-controlling fault system and on the presence of a décollement level. Field mapping is integrated with Landsat imagery and a digital elevation model to investigate the morphotectonic evolution of the south-eastern range front of the Middle Atlas. Geomorphological features provide significant information on the processes that govern lateral propagation of active anticlines. Both suggest that the deformation front may have been active since Pliocene.

  17. Digital Database of Recently Active Traces of the Hayward Fault, California

    USGS Publications Warehouse

    Lienkaemper, James J.

    2006-01-01

    The purpose of this map is to show the location of and evidence for recent movement on active fault traces within the Hayward Fault Zone, California. The mapped traces represent the integration of the following three different types of data: (1) geomorphic expression, (2) creep (aseismic fault slip),and (3) trench exposures. This publication is a major revision of an earlier map (Lienkaemper, 1992), which both brings up to date the evidence for faulting and makes it available formatted both as a digital database for use within a geographic information system (GIS) and for broader public access interactively using widely available viewing software. The pamphlet describes in detail the types of scientific observations used to make the map, gives references pertaining to the fault and the evidence of faulting, and provides guidance for use of and limitations of the map. [Last revised Nov. 2008, a minor update for 2007 LiDAR and recent trench investigations; see version history below.

  18. Palaeoseismological evidence for Holocene activity on the Manisa Fault Zone,Western Anatolia

    NASA Astrophysics Data System (ADS)

    Özkaymak, Ç.; Sözbilir, H.; Uzel, B.; Akyüz, H. S.

    2009-04-01

    Manisa Fault Zone (MFZ) is an active structural discontinuity that is geomorphologically expressed as a trace of north-facing Quaternary fault scarps bounding the southern margin of the Manisa basin which is subsidiary to the Gediz Graben. We note that the present-day fault trace is over 50 km long from Manisa city in the northwest to the Turgutlu town in the southeast. The MFZ consists of two major sections: (i) eastern section that strikes NW-SE direction in the south and bends into an approximately E-W direction around Manisa to the northwest, (ii) an approximately 10-km-long western section that strikes approximately WNW-ESE direction from Manisa city in the east to the Akgedik town in the west. In this study, we present the geologic, geomorphologic, and palaeoseismologic observations indicating Holocene activity on the western section of the fault zone. We identify that the MFZ, at its western end, consists of three fault segments which are en échelon arranged in left step; the fault segments show evidence for linkage and breaching at the relay ramps. One of them is named as the Manastir Fault. In front of this fault, two Holocene colluvial fans older of which is uncorformity bounded are cut and displaced by the syntethic faults. Palaeoseismologic data show that the syntethic fault segments correspond to the surface ruptures of the historical earthquakes. As a result of detailed stratigraphic, sedimentologic and structural observations on the trench walls, some evidences for at least two earthquakes are recorded which are supported by radio-carbon dating. Besides this, an archaic aqueduct that were used to transport water from Emlakdere town, located on the hanging wall of the Manastir Fault, to the basin is cut and displaced by the syntethic fault egments. It is known that this archaic architecture were in use after 11. century by the Ottomans. On the basis of the mentioned data, fault segments which are belong to the western part of the Manisa Fault Zone

  19. Significance of active growth faulting on marsh accretion processes in the lower Pearl River, Louisiana

    NASA Astrophysics Data System (ADS)

    Yeager, Kevin M.; Brunner, Charlotte A.; Kulp, Mark A.; Fischer, Dane; Feagin, Rusty A.; Schindler, Kimberly J.; Prouhet, Jeremiah; Bera, Gopal

    2012-06-01

    Neotectonic processes influence marsh accretion in the lower Pearl River valley. Active growth faults are suggested by groupings of ponded river channel sections, transverse and linear river channel sections, and down- and across-valley contrasts in channel sinuosity. Seismic profiles identified several likely, fault-induced structural anomalies, two of which parallel the axes of surface distributary networks. Lithostratigraphy and biostratigraphy of six cores from across a suspected fault in the West Middle River, combined with 14C-based age control, yielded evidence of vertical offsets, indicating that this river section is on the plane of a growth fault. These data were used to estimate fault slip rates over two time intervals, 1.2 mm/y over the last 1300 yr, and 0.2 mm yr- 1 over the last 3700 yr, and delineated a sinusoidal pattern of deformation moving distally from the fault, which we interpret as resulting from fault-propagation folding. Higher rates of sediment accumulation (of the order of cm yr- 1 from 210Pbxs and 137Cs activity data) on the down-thrown side are consistent with sedimentary response to increased accommodation space, and mass-based sediment accumulation rates (g cm- 2 yr- 1) exhibit a pattern inverse of that shown by fault-driven sinusoidal deformation. We contend that near-surface growth faults are critically important to driving accretion rates and marsh response to sea-level rise.

  20. Active faulting south of the Himalayan Front: Establishing a new plate boundary

    NASA Astrophysics Data System (ADS)

    Yeats, Robert S.; Thakur, V. C.

    2008-06-01

    New tectonic uplifts south of the Salt Range Thrust and Himalayan Front Thrust (HFT) represent an outward step of the plate boundary from the principal tectonic displacement zone into the Indo-Gangetic Plain. In Pakistan, the Lilla Anticline deforms fine-grained overbank deposits of the Jhelum River floodplain 15 km south of the Salt Range. The anticline is overpressured in Eocambrian non-marine strata. In northwest India south of Dehra Dun, the Piedmont Fault (PF) lies 15 km south of the HFT. Coalescing fans derived from the Himalaya form a piedmont (Old Piedmont Zone) 15-20 km wide east of the Yamuna River. This zone is uplifted as much as 15-20 m near the PF, and bedding is tilted 5-7° northeast. Holocene thermoluminescence-optically-stimulated luminescence dates for sediments in the Old Piedmont Zone suggest that the uplift rate might be as high as several mm/a. The Old Piedmont Zone is traced northwest 200 km and southeast another 200 km to the Nepal border. These structures, analogous to protothrusts in subduction zones, indicate that the Himalayan plate boundary is not a single structure but a series of structures across strike, including reactivated parts of the Main Boundary Thrust north of the range front, the HFT sensu stricto, and stepout structures on the Indo-Gangetic Plain. Displacement rates on all these structures must be added to determine the local India-Himalaya convergence rate.

  1. Paleoseismology of latest Pleistocene and Holocene fault activity in central Oregon

    SciTech Connect

    Pezzopane, S.K.; Weldon, R.J. II . Dept. of Geological Sciences)

    1993-04-01

    Latest Pleistocene and Holocene fault activity in Oregon concentrates along four zones that splay northward from seismically active faults along the Central Nevada and Eastern California seismic zones. The Central Oregon fault zone is one of these zones, which splays northward from dextral faults of the Walker Lane, stretching across the flanks of several ranges in south-central Oregon along a N20[degree]W trend, and ultimately merges with the Cascade volcanic arc near Newberry volcano. Aerial-photo interpretations and field investigations reveal fault scarps with, on average about 4 m, but in places as much as [approximately]10 m of vertical expression across latest Pleistocene pluvial lake deposits and geomorphic surfaces. Trenches across three different faults in the Central Oregon zone reveal evidence for multiple episodes of faulting in the form of fault-related colluvial deposits and deformed horizons which have been cut by younger fault movements. Trench exposures reveal faults with relatively steep dips and anastomosing traces, which are interpreted locally as evidence for a small oblique-slip component. Vertical offsets measured in the trenches are [approximately]2 m or more for each event. Radiocarbon analyses and preliminary tephra correlations indicate that the exposed deposits are [approximately]30,000 yr in age and younger, and record the decline of latest Pleistocene pluvial lakes. Commonly, reworked or deformed lacustrine deposits and interlayered and faulted colluvial deposits mark the second and third events back, which probably occurred in the Latest Pleistocene, at a time during low to moderate lake levels. If offsets of the past 18,000 yr are representative of the long-term average, then faults along this zone have slip rates of from 0.2 mm/yr to 0.6 mm/yr and recurrence intervals that range from [approximately]4,000 yr to 11,000 yr.

  2. Architectural evolution of the Nojima fault and identification of the activated slip layer by Kobe earthquake

    NASA Astrophysics Data System (ADS)

    Tanaka, Hidemi; Omura, Kentaro; Matsuda, Tatsuo; Ikeda, Ryuji; Kobayashi, Kenta; Murakami, Masaki; Shimada, Koji

    2007-07-01

    Evolutionary history of Nojima Fault zone is clarified by comprehensive examinations of petrological, geophysical, and geochemical characterizations on a fault zone in deep-drilled core penetrating the Nojima Fault. On the basis of the results, we reconstruct a whole depth profile of the architecture of the Nojima Fault and identify the primal slip layer activated by 1995 Kobe earthquake. The deepest part (8- to 12-km depth) of the fault zone is composed of thin slip layers of pseudotachylite (5 to 10 mm thick each, 10 cm in total). Middle depth (4- to 8-km depth) of the fault zone is composed of fault core (6 to 10 m thick), surrounded by thick (100 m thick) damage zone, characterized by zeolite precipitation. The shallow part of the fault zone (1- to 4-km depth) is composed of distributed narrow shear zones, which are characterized by combination of thin (0.5 cm thick each, 10 cm in total) ultracataclasite layers at the core of shear zones, surrounded by thicker (1 to 3 m thick) damage zones associated with carbonate precipitation. An extremely thin ultracataclasite layer (7 mm thick), activated by the 1995 Kobe earthquake, is clearly identified from numerous past slip layers, overprinting one of the shear zones, as evidenced by conspicuous geological and geophysical anomalies. The Nojima Fault zone was 10 to 100 times thicker at middle depth than that of shallower and deeper depths. The thickening would be explained as a combination of physical and chemical effects as follows. (1) Thickening of "fault core" at middle depth would be attributed to normal stress dependence on thickness of the shear zone and (2) an extreme thickening of "damage zone" in middle depth of the crust would result from the weakening of the fault zone due to super hydrostatic fluid pressure at middle depths. The high fluid pressure would result from faster sealing with low-temperature carbonate at the shallower fault zone.

  3. Determination of paleoseismic activity over a large time-scale: Fault scarp dating with 36Cl

    NASA Astrophysics Data System (ADS)

    Mozafari Amiri, Nasim; Tikhomirov, Dmitry; Sümer, Ökmen; Özkaymak, Çaǧlar; Uzel, Bora; Ivy-Ochs, Susan; Vockenhuber, Christof; Sözbilir, Hasan; Akçar, Naki

    2016-04-01

    Bedrock fault scarps are the most direct evidence of past earthquakes to reconstruct seismic activity in a large time-scale using cosmogenic 36Cl dating if built in carbonates. For this method, a surface along the fault scarp with a minimum amount of erosion is required to be chosen as an ideal target point. The section of the fault selected for sampling should cover at least two meters of the fault surface from the lower part of the scarp, where intersects with colluvium wedge. Ideally, sampling should be performed on a continuous strip along the direction of the fault slip direction. First, samples of 10 cm high and 15 cm wide are marked on the fault surface. Then, they are collected using cutters, hammer and chisel in a thickness of 3 cm. The main geometrical factors of scarp dip, scarp height, top surface dip and colluvium dip are also measured. Topographic shielding in the sampling spot is important to be estimated as well. Moreover, density of the fault scarp and colluvium are calculated. The physical and chemical preparations are carried in laboratory for AMS and chemical analysis of the samples. A Matlab® code is used for modelling of seismically active periods based on increasing production rate of 36Cl following each rupture, when a buried section of a fault is exposed. Therefore, by measuring the amount of cosmogenic 36Cl versus height, the timing of major ruptures and their offsets are determined. In our study, Manastır, Mugırtepe and Rahmiye faults in Gediz graben, Priene-Sazlı, Kalafat and Yavansu faults in Büyük Menderes graben and Ören fault in Gökava half-graben have been examined in the seismically active region of Western Turkey. Our results reconstruct at least five periods of high seismic activity during the Holocene time, three of which reveal seismic ruptures beyond the historical pre-existing data.

  4. The western limits of the Seattle and Tacoma faults and their interaction with faults of the Olympic Massif, Washington (Invited)

    NASA Astrophysics Data System (ADS)

    Lamb, A.; Blakely, R. J.; Liberty, L. M.; Pratt, T. L.; Sherrod, B. L.

    2013-12-01

    Recently acquired high-resolution seismic-reflection and magnetic data show that the Seattle fault of Washington State extends 24-km west of its previously mapped extent and thus comprises a >100-km-long active fault zone. These same data reveal largely concealed faults and folds that kinematically link the Seattle fault with active faults in the Olympic Massif. Linkage between the Seattle fault and the north-northeast-striking Saddle Mountain fault in the Olympic Massif may explain the synchroneity of M7 earthquakes occurring on both these faults approximately 1,100 years ago. The western limits of the 20-km-long east-striking Tacoma fault, a backthrust in the hanging wall of the Seattle fault zone, forms the southern margin of the Seattle uplift in contact with the Tacoma basin to the south. A ~20-km-long potential-field lineament extends from the western limits of the Tacoma fault northward to the Seattle fault and may reflect a structure linking these active faults. A geologic model based on magnetic, gravity, and seismic data shows that this potential-field lineament is likely caused by a low-angle, west-verging thrust fault, that we refer to as the Dewatto fault. We suggest that the Dewatto fault was initiated during exhumation of the Olympic Massif but, because of changes in principal strain direction, today largely accommodates north-directed, strike-slip motion along the west margin of the Seattle uplift. Thus, the Dewatto and Saddle Mountain faults and the western parts of the Seattle and Tacoma faults kinematically interact to accommodate north-directed horizontal displacement of the Seattle uplift relative to the Olympic Massif.

  5. Surface ruptures of large Himalayan earthquakes in Western Nepal: Evidence along a reactivated strand of the Main Boundary Thrust

    NASA Astrophysics Data System (ADS)

    Hossler, T.; Bollinger, L.; Sapkota, S. N.; Lavé, J.; Gupta, R. M.; Kandel, T. P.

    2016-01-01

    The chronology of the seismic ruptures along the active faults of Western Nepal remains almost unconstrained despite their high seismogenic potential. We present here a slip history of one of these structures, a 120 km-long reactivated segment of the Main Boundary Thrust named the Surkhet-Gorahi fault. This slip history is based on geomorphologic and neotectonic mapping of active faults deduced from the analysis of a high resolution total station digital elevation model and 15 detrital charcoals radiocarbon ages constraining the age of deposition or abandonment of 4 alluvial terraces of the Bheri river in Botechaur. Our results show that the last two earthquakes occurred on this fault after 1860 and 640 BP, respectively, and accommodated slip greater than 8 m each, a value corresponding to the incremental vertical offset of the terraces. Such events released a significant part of the slip deficit accumulated on the Main Himalayan thrust fault. However, given the geometry of this fault system as well as the date of occurrence of the last events, the ruptures could be associated with major earthquakes also rupturing the Main Frontal Thrust, such as the great 1505 earthquake.

  6. Late Quaternary Deformation Along the Wairarapa Fault, North Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Schermer, E. R.; Little, T. A.

    2006-12-01

    The Wairarapa fault, one of the largest active faults in the hanging wall of the Hikurangi subduction margin, New Zealand, averaged 16m dextral slip during the M >8.1 1855 earthquake. Previous workers inferred that uplift of 2.7m at the coast, observed by a surveyor in 1855, occurred on the southern continuation of the Wairarapa fault, the Wharekauhau (WH) thrust. New mapping, stratigraphic, and paloseismologic results from the WH thrust suggest the pattern of surface rupture in 1855 and earlier earthquakes was significantly different than previously inferred, requiring a more complex model for seismic hazard and tectonic evolution of the region. Detailed mapping indicates that the coastal segment of the WH thrust did not rupture the surface in 1855. The thrust, a major range-bounding fault, emplaces Mesozoic graywacke over ~80-100 ka last- interglacial marine, and lacustrine rocks, and in part coeval to younger alluvial gravels. Fault activity is indicated by facies and thickness changes. This older sequence is tilted and overlapped unconformably by a silt layer and much less deformed alluvial fan gravels that range in age from >22ka to <9 ka. These younger gravels were deposited in a valley incised across the fault scarp, in-filled this topography, and show no evidence of syn-depositional deformation. New 14C ages record a period of fault inactivity from 14 - 9 ka (calib yrs BP). The abandoned, overlapping fan surface is slightly deformed across the fault (15 m of folding- related throw). We infer that the thrust has propagated eastward in the subsurface, uplifting the abandoned WH fault, an inference that is supported by the pattern of Holocene incision. The only recent faulting consists of subvertical en echelon segments that have undergone minor dip-slip and dextral slip. A trench excavated across the fault scarp in late Holocene gravels suggests that the only fault along the trace of the WH thrust that broke within 3 m of the surface in 1855 was a minor

  7. Middle Proterozoic thrusting in central New Mexico

    SciTech Connect

    Grambling, J.A.; Thompson, A.G. . Dept. of Earth and Planetary Sciences); Dallmeyer, R.D. . Dept. of Geology)

    1992-01-01

    Ductile thrust faults truncate contact-metamorphic aureoles surrounding two 1.4 Ga plutons in central New Mexico. The Priest quartz monzonite (1440 Ma) and Sandia granite (1420 Ma) are 50 km apart in the continuous Sandia/Manzano mountain chain. Thermobarometry and phase relations demonstrate that country-rock temperatures rose from 700 C toward the pluton, at pressure near 4 kb. The northern edge of this aureole is cut by the southeast-dipping ductile Monte Largo thrust fault. Prograde, greenschist-facies metamorphism of footwall rocks accompanied local retrogression of hangingwall rocks during thrusting. This second metamorphism took place at P-T conditions of 2-3 kb and 450-475 C. Another contact aureole surrounds the Sandia granite. Mafic rocks near the granite reflect amphibolite-facies conditions, whereas pelites display low-pressure contact assemblages. Quantitative temperatures increase from 500--750 C toward the granite, at pressures of 2.5--3.5 kb. The shallowly southeast-dipping Vincent Moore fault truncates the Sandia granite and the southern portion of its contact aureole. This ductile shear zone emplaced greenschist-facies rocks northwestward above the Sandia contact aureole. Footwall rocks were retrograded to the greenschist facies within 100 m of this fault; the retrograde phases are aligned parallel to the trace of the thrust. Metamorphic temperatures in hangingwall rocks (during thrusting ) were 400-475 C at pressures above 2.75 kb. Additional northwest-vergent ductile thrusts are found elsewhere in the mountain chain. This may represent the age of thrusting and of the related greenschist and the related greenschist-facies metamorphic overprint.

  8. A 665 year record of Coulomb stress changes on active faults in the central Apennines, Italy.

    NASA Astrophysics Data System (ADS)

    Wedmore, L. N. J.; Faure Walker, J.; Roberts, G.; McCaffrey, K. J. W.; Sammonds, P. R.

    2014-12-01

    Active extension in the central Apennines is accommodated on numerous 20-30km long normal faults. Over multiple earthquake cycles fault slip is controlled by viscous flow in narrow shear zones, which are below the brittle seismogenic crust and are driven by upwelling mantle beneath the central Apennines. However, on short timescales, there is evidence for clustering along strike on the north eastern set of faults in the region, with the south western faults comparatively quiet during the period of reliable historical earthquake records (since 1349 AD). In contrast, 15±3ka strain rates show no evidence of skewness towards the north eastern faults. This suggests that on short timescales, elastic loading and fault interaction may be controlling the location of earthquakes and the seismic hazard, as opposed to the view that fault activity has permanently migrated from the south west flank of the central Apennines to the north east flank. We used Coulomb stress modelling to test whether the sequence of historical earthquakes can be explained by stress triggering and elastic loading. Palaeoseismic and historical records were used to reconstruct the co-seismic static Coulomb stress changes for 27 earthquakes in central Italy from 1349-2009. 15±3ka throws measured across faults in the area were used as an analogue for the slip distributions, with the slip direction constrained by field measurements of frictional wear striae on exposed bedrock fault scarps. Interseismic loading was modelled using a shear zone rheology below the seismogenic zone of each fault; slip rates measured at the surface were used to control the rate of loading. The sensitivity of the model was explored by iterating varying slip distributions, fault kinematics and earthquake locations. We show that for sequences of clustered earthquakes that occurred on timescales of days to weeks, co-seismic static Coulomb stress transfer can explain the pattern of faulting with stress changes of 0.001-0.1 MPa

  9. Aseismic deformation of a fold-and-thrust belt imaged by SAR interferometry near Shahdad, southeast Iran

    NASA Technical Reports Server (NTRS)

    Fielding, Eric J.; Wright, Tim J.; Muller, Jordan; Parsons, Barry E.; Walker, Richard

    2004-01-01

    At depth, many fold-and-thrust belts are composed of a gently dipping, basal thrust fault and steeply dipping, shallower splay faults that terminate beneath folds at the surface. Movement on these buried faults is difficult to observe, but synthetic aperture radar (SAR) interferometry has imaged slip on at least 600 square kilometers of the Shahdad basal-thrust and splay-fault network in southeast Iran.

  10. Contemporary fault mechanics in southern Alaska

    NASA Astrophysics Data System (ADS)

    Kalbas, James L.; Freed, Andrew M.; Ridgway, Kenneth D.

    Thin-shell finite-element models, constrained by a limited set of geologic slip rates, provide a tool for evaluating the organization of contemporary faulting in southeastern Alaska. The primary structural features considered in our analysis are the Denali, Duke River, Totschunda, Fairweather, Queen Charlotte, and Transition faults. The combination of fault configurations and rheological properties that best explains observed geologic slip rates predicts that the Fairweather and Totschunda faults are joined by an inferred southeast-trending strike-slip fault that crosses the St. Elias Mountains. From a regional perspective, this structure, which our models suggest slips at a rate of ˜8 mm/a, transfers shear from the Queen Charlotte fault in southeastern Alaska and British Columbia northward to the Denali fault in central Alaska. This result supports previous hypotheses that the Fairweather-Totschunda connecting fault constitutes a newly established northward extension of the Queen Charlotte-Fairweather transform system and helps accommodate right-lateral motion (˜49 mm/a) of the Pacific plate and Yakutat microplate relative to stable North America. Model results also imply that the Transition fault separating the Yakutat microplate from the Pacific plate is favorably oriented to accommodate significant thrusting (23 mm/a). Rapid dip-slip displacement on the Transition fault does not, however, draw shear off of the Queen Charlotte-Fairweather transform fault system. Our new modeling results suggest that the Totschunda fault, the proposed Fairweather-Totschunda connecting fault, and the Fairweather fault may represent the youngest stage of southwestward migration of the active strike-slip deformation front in the long-term evolution of this convergent margin.

  11. Tectonothermal history of an exhumed thrust-sheet-top basin: An example from the south Pyrenean thrust belt

    NASA Astrophysics Data System (ADS)

    Labaume, Pierre; Meresse, Florian; Jolivet, Marc; Teixell, Antonio; Lahfid, Abdeltif

    2016-05-01

    This paper presents a new balanced structural cross section of the Jaca thrust-sheet-top basin of the southern Pyrenees combined with paleothermometry and apatite fission track (AFT) thermochronology data. The cross section, based on field data and interpretation of industrial seismic reflection profiles, allows refinement of previous interpretations of the south directed thrust system, involving the identification of new thrust faults, and of the kinematic relationships between basement and cover thrusts from the middle Eocene to the early Miocene. AFT analysis shows a southward decrease in the level of fission track resetting, from totally reset Paleozoic rocks and lower Eocene turbidites (indicative of heating to Tmax > ~120°C), to partially reset middle Eocene turbidites and no/very weak resetting in the upper Eocene-lower Oligocene molasse (Tmax < ~60°C). AFT results indicate a late Oligocene-early Miocene cooling event throughout the Axial Zone and Jaca Basin. Paleomaximum temperatures determined by vitrinite reflectance measurements and Raman spectroscopy of carbonaceous material reach up to ~240°C at the base of the turbidite succession. Inverse modeling of AFT and vitrinite reflectance data with the QTQt software for key samples show compatibility between vitrinite-derived Tmax and the AFT reset level for most of the samples. However, they also suggest that the highest temperatures determined in the lowermost turbidites correspond to a thermal anomaly rather than burial heating, possibly due to fluid circulation during thrust activity. From these results, we propose a new sequential restoration of the south Pyrenean thrust system propagation and related basin evolution.

  12. Active fault tolerant control of a flexible beam

    NASA Astrophysics Data System (ADS)

    Bai, Yuanqiang; Grigoriadis, Karolos M.; Song, Gangbing

    2007-04-01

    This paper presents the development and application of an H∞ fault detection and isolation (FDI) filter and fault tolerant controller (FTC) for smart structures. A linear matrix inequality (LMI) formulation is obtained to design the full order robust H∞ filter to estimate the faulty input signals. A fault tolerant H∞ controller is designed for the combined system of plant and filter which minimizes the control objective selected in the presence of disturbances and faults. A cantilevered flexible beam bonded with piezoceramic smart materials, in particular the PZT (Lead Zirconate Titanate), in the form of a patch is used in the validation of the FDI filter and FTC controller design. These PZT patches are surface-bonded on the beam and perform as actuators and sensors. A real-time data acquisition and control system is used to record the experimental data and to implement the designed FDI filter and FTC. To assist the control system design, system identification is conducted for the first mode of the smart structural system. The state space model from system identification is used for the H∞ FDI filter design. The controller was designed based on minimization of the control effort and displacement of the beam. The residuals obtained from the filter through experiments clearly identify the fault signals. The experimental results of the proposed FTC controller show its e effectiveness for the vibration suppression of the beam for the faulty system when the piezoceramic actuator has a partial failure.

  13. Active fault systems and tectono-topographic configuration of the central Trans-Mexican Volcanic Belt

    NASA Astrophysics Data System (ADS)

    Szynkaruk, Ewa; Graduño-Monroy, Víctor Hugo; Bocco, Gerardo

    2004-07-01

    The central Trans-Mexican Volcanic Belt (TMVB) reflects the interplay between three regional fault systems: the NNW-SSE to NW-SE striking Taxco-Querétaro fault system, the NE-SW striking system, and the E-W striking Morelia-Acambay fault system. The latter is the youngest and consists of fault scarps up to 500 m high, whose formation caused structural and morphological reorganization of the region. In this paper, we investigate possible activity of the three systems within the central TMVB, and assess the role that they play in controlling the tectono-topographic configuration of the area. Our study is based on DEM-derived morphometric maps, longitudinal river profiles, geomorphologic mapping, and structural field data concerning recent faulting. We find that all three regional fault systems are active within the central TMVB, possibly with different displacement rates and/or type of motion; and that NNW-SSE and NE-SW striking faults control the major tectono-topographic elements that build up the region, which are being re-shaped by E-W striking faults. We also find that tectonic information can be deciphered from the topography of the youthful volcanic arc in question, regardless its complexity.

  14. Active low-angle (?) normal faulting along the North Lunggar rift, western Tibet

    NASA Astrophysics Data System (ADS)

    Logan, M. A.; Taylor, M. H.; Styron, R. H.; Gosse, J. C.; Ding, L.; Yang, G.

    2012-12-01

    Here we present surface exposure ages of faulted fluvial terraces using cosmogenic nuclides from the North Lunggar rift. The Lunggar rift is one of seven major north-striking rift basins accommodating east-west directed extension on the Tibetan Plateau. The Lunggar rift in west-central Tibet is divided into two distinct north and south segments based on fault geometry. The North Lunggar range is bounded on its east side by a <40 degree dipping, ~N-striking normal fault. This normal fault is considered inactive as the main detachment is unconformably overlain by unfaulted moraines and alluvial fans. Farther into the hanging wall basin, approximately 6 km eastward, several fault scarps parallel the Lunggar detachment. Locally, active faulting is distributed in the hanging wall with as many as seven normal fault scarps accommodating active east-west directed extension. Recent activity of these smaller faults is apparent from cross-cut fluvial terraces that have been uplifted by as much as 75 m. The geomorphology and fault geometry of the North Lunggar rift are consistent with high-angle normal faults that sole into a single master detachment fault at depth. A high-resolution digital elevation model constructed from real-time kinematic-GPS data has made details of the geomorphology clear and allowed for precise measurements of geomorphic offsets across the fault scarps. We estimate the surface abandonment ages using the depth profiling approach with cosmogenic nuclides. Three cosmogenic depth profiles are being analyzed in this study with each depth profile consisting of five samples at varying depths in order to account for inheritance. Site 1 is the southernmost and is on the highest uplifted fluvial terrace and is being prepared for 10Be analysis. Site 2 comprises two depth profiles on the highest and intermediate uplifted terraces, respectively. Samples at site 2 have low quartz yields and are being prepared for 36Cl analysis. Combining the fault offsets and

  15. Evidence for active creep on the Alto Tiberina low angle normal fault inferred using GPS geodesy

    NASA Astrophysics Data System (ADS)

    Rick, Bennett; Jackson, Lily; Mencin, David; Casale, Gabriele

    2014-05-01

    range ~43.2ºN and 43.5ºN. We also test the regional extent of the fault by extending the fault model to the north and south of the well-imaged portion of the fault, assuming a 20º dip. We estimated fault coupling along-strike and down-dip to assess spatial variations in creep on the model fault. Our modeling suggests that the portion of the model fault in the latitude band ~43.1ºN to ~43.7ºN, encompassing the geophysically imaged ATF fault, creeps at nearly the full fault slip rate of ~2 mm/yr below a depths of 3-5 km. Our model corroborates previous inferences, suggesting active creep at shallow depth on the well-imaged portion of the ATF. However, outside of this range of latitudes, where the existence of a regional low angle normal fault is speculative, the model fault appears to be coupled to greater depths (7-8 km or deeper). Interestingly, the apparent locked zones to the north and south of the creeping zone correlate with the locations of instrumentally recorded large magnitude hanging wall earthquakes. In contrast, there have been no instrumentally recorded large magnitude earthquakes in the hanging wall overlying the creeping portion of the fault.

  16. Results From NICLAKES Survey of Active Faulting Beneath Lake Nicaragua, Central American Volcanic Arc

    NASA Astrophysics Data System (ADS)

    Funk, J.; Mann, P.; McIntosh, K.; Wulf, S.; Dull, R.; Perez, P.; Strauch, W.

    2006-12-01

    In May of 2006 we used a chartered ferry boat to collect 520 km of seismic data, 886 km of 3.5 kHz subbottom profiler data, and 35 cores from Lake Nicaragua. The lake covers an area of 7700 km2 within the active Central American volcanic arc, forms the largest lake in Central America, ranks as the twentieth largest freshwater lake in the world, and has never been previously surveyed or cored in a systematic manner. Two large stratovolcanoes occupy the central part of the lake: Concepcion is presently active, Maderas was last active less than 2000 years ago. Four zones of active faulting and doming of the lake floor were mapped with seismic and 3.5 kHz subbottom profiling. Two of the zones consist of 3-5-km-wide, 20-30-km-long asymmetric rift structures that trend towards the inactive cone of Maderas Volcano in a radial manner. The northeastern rift forms a 20-27-m deep depression on the lake bottom that is controlled by a north-dipping normal fault. The southwestern rift forms a 25-35-m deep depression controlled by a northeast-dipping normal fault. Both depressions contain mound-like features inferred to be hydrothermal deposits. Two zones of active faulting are associated with the active Concepcion stratovolcano. A 600-m-wide and 6-km-long fault bounded horst block extends westward beneath the lake from a promontory on the west side of the volcano. Like the two radial rift features of Maderas, the horst points roughly towards the active caldera of Concepcion. A second north-south zone of active faulting, which also forms a high, extends off the north coast of Concepcion and corresponds to a localized zone of folding and faulting mapped by previous workers and inferred by them to have formed by gravitational spreading of the flank of the volcano. The close spatial relation of these faults to the two volcanic cones in the lake suggests that the mechanism for faulting is a result of either crustal movements related to magma intrusion or gravitational sliding and is

  17. Mapping Active Faults and Tectonic Geomorphology offshore central California

    NASA Astrophysics Data System (ADS)

    Johnson, S. Y.; Watt, J. T.; Hart, P. E.; Sliter, R. W.; Wong, F. L.

    2009-12-01

    In June 2008, and July 2009, the USGS conducted two high-resolution, marine, seismic-reflection surveys across the continental shelf and upper slope between Piedras Blancas and Point Sal, central California, in order to better characterize regional earthquake sources. More than 1,300 km of single-channel seismic data were acquired aboard the USGS R/V Parke Snavely using a 500-joule mini-sparker source fired at a 0.5-second shot interval and recorded with a 15-meter streamer. Most tracklines were run perpendicular to the coast at 800-meter spacing, extending from the nearshore (~ 10-15 m water depth) to as far as 20 km offshore. Sub-bottom imaging varies with substrate, ranging from outstanding (100 to 150 m of penetration) in inferred Quaternary shallow marine, shelf and upper slope deposits to poor (0 to 10 m) in the Mesozoic basement rocks. Marine magnetic data were collected simultaneously on this survey, and both data sets are being integrated with new aeromagnetic data, publicly available industry seismic-reflection data, onshore geology, seismicity, and high-resolution bathymetry. Goals of the study are to map geology, structure, and sediment distribution; to document fault location, length, segmentation, shallow geometry and structure; and to identify possible sampling targets for constraining fault slip rates, earthquake recurrence, and tsunami hazard potential. The structure and tectonic geomorphology of the >100-km-long, right-lateral, Hosgri fault zone and its connections to the Los Osos, Pecho, Oceano and other northwest-trending inboard faults are the focus of this ongoing work. The Hosgri fault forms the eastern margin of the offshore Santa Maria basin and coincides in places with the outer edge of the narrow (5- to 15-km-wide), structurally complex continental shelf. The Hosgri is imaged as a relatively continuous, vertical fault zone that extends upward to the seafloor; varies significantly and rapidly along strike; and incorporates numerous

  18. Taconian foreland-style thrust system in the Great Smoky Mountains, Tennessee

    SciTech Connect

    Connelly, J.B. ); Woodward, N.B. )

    1992-02-01

    Four major thrust faults dominate the Great Smoky Mountains foothills region: the Greenbrier, Dunn Creek, Miller Cove, and Great Smoky. The Greenbrier and Dunn Creek thrust sheets were emplaced prior to Taconian regional cleavage development and peak metamorphism. Cleavage and most deformation features formed during the emplacement of a thrust sheet now floored by the Miller Cove thrust fault. Alleghanian emplacement of the Great Smoky-Miller Cove thrust sheet dissected these earlier structures. If the effects of the younger structures are removed, the basal faults of the Dunn Creek and Greenbrier sheets reveal ramp-flat geometries typical of foreland fold-thrust belts including bedding-parallel faults, ramps, and angular ramp-related folds. The Great Smoky Mountains region is therefore unique in the southern Appalachians because a foreland-style fold-thrust belt of Taconian age is well preserved.

  19. Style of the surface deformation by the 1999 Chichi earthquake at the central segment of Chelungpu fault, Taiwan, with special reference to the presence of the main and subsidiary faults and their progressive deformation in the Tsauton area

    NASA Astrophysics Data System (ADS)

    Ota, Y.; Watanabe, M.; Suzuki, Y.; Yanagida, M.; Miyawaki, A.; Sawa, H.

    2007-11-01

    We describe the style of surface deformation in the 1999 Chichi earthquake in the central segment of the Chelungpu Fault. The study covers the Kung-fu village, north of Han River, to the south of Tsauton area. A characteristic style of the surface deformation is a convex scarp in profile and sinuous plan view, due to the low angle thrust fault. Two subparallel faults, including the west facing Tsauton West fault, and the east facing Tsauton East fault, limit the western and eastern margin of the Tsauton terraced area. The Tsauton West fault is the continuation of the main Chelungpu fault and the Tsauton East fault is located about 2 km apart. Both faults record larger amounts of vertical displacement on the older terraces. The 1999 surface rupture occurred exactly on a pre-existing fault scarp of the Tsauton West and East faults. Thus, repeated activities of these two faults during the Holocene, possibly since the late Quaternary, are confirmed. The amount of vertical offset of the Tsauton East fault is smaller, and about 40-50% of that of the Tsauton West fault for the pre-existing fault. This indicates that the Tsauton East fault is a subsidiary fault and moved together with the main fault, but accommodated less amount.

  20. Distribution of fault activity in the early stages of continental breakup: an analysis of faults and volcanic products of the Natron Basin, East African Rift, Tanzania

    NASA Astrophysics Data System (ADS)

    Muirhead, J. D.; Kattenhorn, S. A.

    2012-12-01

    Recent magmatic-tectonic crises in Ethiopia (e.g. 2005 Dabbahu rifting episode, Afar) have informed our understanding of the spatial and temporal distribution of strain in magmatic rifts transitioning to sea-floor spreading. However, the evolving contributions of magmatic and tectonic processes during the initial stages of rifting, is a subject of ongoing debate. The <5 Ma northern Tanzania and southern Kenya sectors of the East Africa Rift provide ideal locations to address this problem. We present preliminary findings from an investigation of fault structures utilizing aerial photography and satellite imagery of the ~35 km wide Natron rift-basin in northern Tanzania. Broad-scale structural mapping will be supplemented by field observations and 40Ar-39Ar dating of lava flows cut by faults to address three major aspects of magma-assisted rifting: (1) the relative timing of activity between the border fault and smaller faults distributed across the width of the rift; (2) time-averaged slip rates along rift-zone faults; and (3) the spatial distribution of faults and volcanic products, and their relative contributions to strain accommodation. Preliminary field observations suggest that the ~500 m high border fault system along the western edge of the Natron basin is either inactive or has experienced a reduced slip rate and higher recurrence interval between surface-breaking events, as evidence by a lack of recent surface-rupture along the main fault escarpments. An exception is an isolated, ~2 km-long segment of the Natron border fault, which is located in close proximity (< 5km) to the active Oldoinyo Lengai volcano. Here, ~10 m of seemingly recent throw is observed in volcaniclastic deposits. The proximity of the fault segment to Oldoinyo Lengai volcano and the localized distribution of fault-slip are consistent with magma-assisted faulting. Faults observed within the Natron basin and on the flanks of Gelai volcano, located on the eastern side of the rift, have

  1. Segmentation and thrusting along the offshore Newport-Inglewood-Rose Canyon zone of deformation

    SciTech Connect

    Mills, G.I.; Fischer, P.J. )

    1991-02-01

    The offshore Newport-Inglewood-Rose Canyon (NI-RC) zone of deformation is a 106-km-long, linear zone of folds and faults that extend from Newport Beach to La Jolla. Using seismicity and high-resolution and digitally processed seismic reflection data, three distinct fault segments are defined. These segments control the position and trend of shelf break: (1) the Laguna Beach segment (Corona Del Mar to San Mateo Point), a right-stepping zone with activity decreasing southward to San Mateo Point, where the latest activity was middle Holocene. (2) The San Onofre segment (San Mateo Point to Oceanside), where a major, 2-km-wide, left-stepping break occurs near the center of this segment opposite San Onofre; it is associated with an apparent basement discontinuity, a major blind thrust ramp and bowing of the continental slope. Shoreward of the NI-RC zone a 20-km-long synclinal fold trends subparallel to the zone. (3) The La Jolla segment (Oceanside to La Jolla), north of Encinitas, overlapping, left-stepping fault splays are associated with folding and thrusting. Preliminary earthquake focal mechanism studies suggest that right-lateral faulting, with a minor reverse component, is dominant along the NI-RC Zone. Earthquake foci do not seem to be related to the thrust faults. Compressional deformation along the zone is thought to be a direct result of relative North American/Pacific plate motion direction changes at 4 Ma. Deformation was concentrated near the left-stepping break in the San Onofre segment, perhaps producing a detached block or flake. Mapped structures suggest the NI-RC is dislocated by the blind' thrust ramp.

  2. The variety of subaerial active salt deformations in the Kuqa fold-thrust belt (China) constrained by InSAR

    NASA Astrophysics Data System (ADS)

    Colón, Cindy; Webb, A. Alexander G.; Lasserre, Cécile; Doin, Marie-Pierre; Renard, François; Lohman, Rowena; Li, Jianghai; Baudoin, Patrick F.

    2016-09-01

    Surface salt bodies in the western Kuqa fold-thrust belt of northwestern China allow study of subaerial salt kinematics and its possible correlations with weather variations. Ephemeral subaerial salt exposure during the evolution of a salt structure can greatly impact the subsequent development and deformation of its tectonic setting. Here, we present a quantitative time-lapse survey of surface salt deformation measured from interferometric synthetic aperture radar (InSAR) using Envisat radar imagery acquired between 2003 and 2010. Time series analysis and inspection of individual interferograms confirm that the majority of the salt bodies in western Kuqa are active, with significant InSAR observable displacements at 3 of 4 structures studied in the region. Subaerial salt motion toward and away from the satellite at rates up to 5 mm/yr with respect to local references. Rainfall measurements from the Tropical Rainfall Measuring Mission (TRMM) and temperature from a local weather station are used to test the relationship between seasonality and surface salt motion. We observe decoupling between surface salt motion and seasonality and interpret these observations to indicate that regional and local structural regimes exert primary control on surface salt displacement rates.

  3. Slip-rate Estimation of Active Fault by Luminescence Dating on Deformed River Terraces at Tsaotun, Central Taiwan

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Chen, W.; Lee, C.

    2003-12-01

    This study carried out luminescence ages of the deformed terraces located at Tsaotun in central Taiwan. These terraces are considered as a result of crustal deformation caused by recent activity of the Chelungpu fault, 1999 surface rupture. Since this active fault runs through urban area, it is urgently needed to figure out its neotectonic behavior, including slip-rate and recurrence interval. Based on new ages, we also discuss the terrace correlation and its related structures. The study terraces are all strath terraces with only a few meters of veneered fluvial deposits on top. Due to the strong stream-power, nearly all the outcrops are dominated by fluvial cobbles, which is worst condition to preserve the syndepositional carbonaceous materials. Alternatively, optical stimulated luminescence (OSL) dating uses sandy quartz as the material and even has longer dating upper limit (up to several hundreds of years). Fortunately, sandy layer are found intercalated within the fluvial cobbles in studying terraces. We adopted the Single-Aliquot Regenerative (SAR) dose protocol on large aliquots of 90-150μ m quartz, which were cleaned using HCL, H2O2 and HF in the usual way. In case of incomplete bleaching during quick deposition, the OSL/TL ratio was adopted to approach the true De. Dosimetry is derived by ICP-MS and XRF analyses. For ascertainment of the initial bleaching of fluvial sediment, the modern samples collected in river bed of Wuhsi were also measured. Based on the results of modern samples, we believe that the residuals are inevitable in younger sediments, especially along the upper stream. On the contrary, the samples older than 10 kyr are little influenced due to the larger age error than the younger ones. The OSL age of the terrace samples in the hanging wall is dated ca. 13 kyr, which has been corrected for poorly-bleaching problem. Comparing to the ages collected down hole in the footwalls, we found out vertical displacements of ca. 67 and 37 m, has been

  4. Earthquake mechanism studies by active-fault drilling: Chi-Chi Taiwan to Wenchuan earthquakes

    NASA Astrophysics Data System (ADS)

    Togo, T.; Shimamoto, T.; Ma, S.; Noda, H.; Hirose, T.; Tanikawa, W.

    2010-12-01

    Why drill into active faults? How can such big projects be justified to society? We believe that a very important task for such projects is to understand earthquake mechanisms, i.e., to reproduce big earthquakes just occurred based on measured fault-zone properties. Post-earthquake fault-zone drilling provides rare opportunities for seeing and analyzing fault zones with minimum changes as “RAPID” group summarized its merits. Shallow and deep drilling into Chelungpu fault, that caused the 1999 Chi-Chi Taiwan earthquake, has demonstrated that reproducing an earthquake based on measured properties is becoming possible (Tanikawa and Shimamoto, 2009, JGR; Noda and Lapusta, 2009, JpGU). Another important outcome from Chelungpu drilling is finding of numerous changes in a fault zone during seismic fault motion (e.g., decomposition due to frictional heating), as highlighted by “black gouge” (many papers). Those changes can be reproduced now by high-velocity friction experiments. No so long ago, a renown geologist expressed his feeling that faults will not preserve a record of seismic slip, except for pseudotachylite (Cowan, 1999, JSG). In other words, seismic slip is of such a short duration that important changes, other than shearing deformation, will not occur in fault zones. Nojima and Chelungpu drilling has shown that this is not the case. On the other hand, seismic fault motion has been reproduced in laboratory for the last twenty years, demonstrating dramatic weakening of many natural fault gouges. We report here a set of data using fault gouge from Hongkou outcrop of Longmenshan fault system, very close to the first drilling site, under a constant slip rate and variable slip histories. Slip and velocity weakening behavior depends on slip history and can be described by an empirical equation. Importance of such experiments can be justified only by confirmation that the same processes indeed occur in natural fault zones. Integrated field and laboratory studies

  5. Control of structural inheritance on thrust initiation and material transfer in accretionary wedges

    NASA Astrophysics Data System (ADS)

    Leever, Karen; Geersen, Jacob; Ritter, Malte; Lieser, Kathrin; Behrmann, Jan

    2016-04-01

    Faults in the incoming sediment layer are commonly observed in subduction zone settings and well developed in the incoming plate off Sumatra. To investigate how they affect the structural development of the accretionary wedge, we conducted a series of 2D analogue tectonic experiments in which a 2 cm thick quartz sand layer on top of a thin detachment layer of glass beads was pulled against a rigid backstop by a basal conveyor belt in a 20cm wide box with glass walls. A gap at the base of the back wall avoids entrainment of the glass beads. At regular spacing of either 2.3, 5.5 or 7.8 cm (fractions of the thrust sheet length in the reference model), conjugate pairs of weakness zones dipping 60deg were created by cutting the sand layer with a thin (1 mm) metal blade. Both the undisturbed sand and the pre-cuts have an angle of internal friction of ~29o, but their cohesion is different by 50 Pa (110 Pa for the undisturbed material, 60 Pa along the pre-cuts). Friction of the glass beads is ~24deg. The experiments are monitored with high resolution digital cameras; displacement fields derived from digital image correlation are used to constrain fault activity. In all experiments, a critically tapered wedge developed with a surface slope of 7.5deg. In the reference model (no weakness zones in the input section), the position of new thrust faults is controlled by the frontal slope break. The average length of the thrust sheets is 11 cm and the individual thrusts accommodate on average 8 cm displacement each. The presence of weakness zones causes thrust initiation at a position different from the reference case, and affects their dip. For a fault spacing of 7.8 cm (or 75% of the reference thrust sheet length), every single incoming weakness zone causes the formation of a new thrust, thus resulting in thrust sheets shorter than the equilibrium case. In addition, less displacement is accommodated on each thrust. As a consequence, the frontal taper is smaller than expected

  6. Subsurface geometry and evolution of the Seattle fault zone and the Seattle Basin, Washington

    USGS Publications Warehouse

    ten Brink, U.S.; Molzer, P.C.; Fisher, M.A.; Blakely, R.J.; Bucknam, R.C.; Parsons, T.; Crosson, R.S.; Creager, K.C.

    2002-01-01

    The Seattle fault, a large, seismically active, east-west-striking fault zone under Seattle, is the best-studied fault within the tectonically active Puget Lowland in western Washington, yet its subsurface geometry and evolution are not well constrained. We combine several analysis and modeling approaches to study the fault geometry and evolution, including depth-converted, deep-seismic-reflection images, P-wave-velocity field, gravity data, elastic modeling of shoreline uplift from a late Holocene earthquake, and kinematic fault restoration. We propose that the Seattle thrust or reverse fault is accompanied by a shallow, antithetic reverse fault that emerges south of the main fault. The wedge enclosed by the two faults is subject to an enhanced uplift, as indicated by the boxcar shape of the shoreline uplift from the last major earthquake on the fault zone. The Seattle Basin is interpreted as a flexural basin at the footwall of the Seattle fault zone. Basin stratigraphy and the regional tectonic history lead us to suggest that the Seattle fault zone initiated as a reverse fault during the middle Miocene, concurrently with changes in the regional stress field, to absorb some of the north-south shortening of the Cascadia forearc. Kingston Arch, 30 km north of the Seattle fault zone, is interpreted as a more recent disruption arising within the basin, probably due to the development of a blind reverse fault.

  7. Fluid involvement in the active Helike normal Fault, Gulf of Corinth, Greece

    NASA Astrophysics Data System (ADS)

    Koukouvelas, Ioannis K.; Papoulis, Dimitris

    2009-03-01

    Rock fabric and mineralogical composition from the fault core and the unaffected protolith have been used to define the role of the segmented Helike Fault to fluid flow. Sixty samples were investigated by XRD, SEM observation and SEM-EDS microanalyses. Detrital smectite, calcite, and quartz represent the mineral assemblage at the crest of the footwall block in Foniskaria sampling site. In this site smectite is enriched at the rims of the fault core. All other sampling sites located at the base of the fault scarp are characterized by detrital and newly formed minerals. Detrital minerals include plagioclase, quartz, calcite and illite in Nikolaiika sampling site, and smectite, illite, kaolinite, quartz, calcite in Selinous sampling site. In the latter sampling site erionite and cerussite are newly formed minerals with erionite considered as the hydrothermal alteration product of fluids at 80-100 °C. At the eastern fault segment illite, quartz and calcite (T13 site) corresponds to detrital minerals. Mineralogy in the fault core reflects its high permeability to down-flowing meteoric water and weak hydrothermal alteration. The rock fabric suggests mineral alignment parallel to the fault plane. Mineralogy indicates that the Aigion, Helike and Pyrgaki Faults in the Gulf of Corinth host hydrothermal activity at shallow levels.

  8. Paleoseismic investigations along a key active fault within the Gulf of Corinth, Greece

    NASA Astrophysics Data System (ADS)

    Koukouvelas, I. K.; Kokkalas, S.; Xypolias, P.

    2008-07-01

    The study of paleoseismological and archaeological excavations provide clues for the evolution of Helike Fault, located along the westernmost end of the Gulf of Corinth, that displays high activity and exerts control on the landscape. In this study we present evidence from paleoseismic trenches which revealed well defined fault strands and clear colluvial stratigraphy. We focus on the two main segments of the Helike Fault and their implications on strong earthquake activity. The Helike Fault is a major tectonic structure that influenced the evolution of ancient settlements on the Helike Delta, from the Early Bronze Age through the Byzantine period, till present times. The eastern fault segment appears to control the southern Gulf morphology, while the western segment is controlling the large Aigion basin. Interbedded organic-rich soils and gravels dominate in all trenches. Fault strands that control successive scarp-derived colluvial deposits were identified within the trenches and indicate the continuous seismic activity along the fault trace. Co-seismic offsets, open cracks filled with debris and liquefaction related deformation was also recognized. At least seven seismic events were identified inside the excavated trenches, during the last 10 ka. The estimated vertical throw along the fault segments, observed within the trenches, is on the order of 1 meter per event. Based on dating of colluvial wedges we estimated the Holocene slip rate on the Helike Fault, which shows an increase from ~0.3 mm/yr to 2 mm/yr in the last 2 ka. We consider the derived slip rates to be minimum values due to the implication of erosional effects and sediment accumulation from the upthrown block. The Helike fault appears to play a crucial role both in subsidence of the Helike delta plain and in shifting Kerynites river course that runs between the two Helike fault segments. The Helike Fault activity and the clustering of surface rupturing events on the Helike fault seems to fit well

  9. Active normal faulting along the Mt. Morrone south-western slopes (central Apennines, Italy)

    NASA Astrophysics Data System (ADS)

    Gori, Stefano; Giaccio, Biagio; Galadini, Fabrizio; Falcucci, Emanuela; Messina, Paolo; Sposato, Andrea; Dramis, Francesco

    2011-01-01

    In the present work we analyse one of the active normal faults affecting the central Apennines, i.e. the Mt. Morrone normal fault system. This tectonic structure, which comprises two parallel, NW-SE trending fault segments, is considered as potentially responsible for earthquakes of magnitude ≥ 6.5 and its last activation probably occurred during the second century AD. Structural observations performed along the fault planes have allowed to define the mainly normal kinematics of the tectonic structure, fitting an approximately N 20° trending extensional deformation. Geological and geomorphological investigations performed along the whole Mt. Morrone south-western slopes permitted us to identify the displacement of alluvial fans, attributed to Middle and Late Pleistocene by means of tephro-stratigraphic analyses and geomorphological correlations with dated lacustrine sequences, along the western fault branch. This allowed to evaluate in 0.4 ± 0.07 mm/year the slip rate of this segment. On the other hand, the lack of synchronous landforms and/or deposits that can be correlated across the eastern fault segment prevented the definition of the slip rate related to this fault branch. Nevertheless, basing on a critical review of the available literature dealing with normal fault systems evolution, we hypothesised a total slip rate of the fault system in the range of 0.4 ± 0.07 to 0.8 ± 0.09 mm/year. Moreover, basing on the length at surface of the Mt. Morrone fault system (i.e. 22-23 km) we estimated the maximum expected magnitude of an earthquake that might originate along this tectonic structure in the order of 6.6-6.7.

  10. Geomorphic Indicators and Tectonic Implications of the Active Chaochou Fault, Southern Taiwan

    NASA Astrophysics Data System (ADS)

    Hung, J.; Liao, H.

    2003-12-01

    The Chaochou Fault, lying on the easternmost edge of the Pingtung plain, is the major geologic boundary between the Slate Belt to the east and the Western Foothills to the west. According to previous studies, the Chaochou fault is a high-angle reverse fault dipping 75-80 degrees to the east. Along strike, several transverse rivers cut across the fault and form alluvial fans in the foothills, which provide unique morphotectonic features to study the activity of the Chaochou Fault. Digitized data from topographic maps of 1/5,000 to 1/25,000 scales and digital elevation data of 40m resolution were input into GIS software and analyzed to quantitatively evaluate geomorphic indicators such as hypsometric integral, stream length-gradient index and drainage basin asymmetry etc. Anomalies of these indices are further checked in the field on bedrocks, man-made structures and fold and faults, to clarify spatial variations of indicators. These, coupled with GPS data, field survey in the slate belt and uplifted terraces and subsurface seismic profiles, can further constrain spatial and temporal kinematics of the Chaochou fault and the relationship between topographic evolution and subsurface structures. Our preliminary results show that river landforms are highly related to the Chaochou Fault. Drainages were tilted to the west in response to uplifting in the east of the Chaochou Fault. Geomorphic indices indicate that the uplift rate is higher in the north and decreases progressively toward the south. The peak tectonic activity occurs in the area between the Chaochou and the Chishan Fault.

  11. Kinematic modeling of folding above listric propagating thrusts

    NASA Astrophysics Data System (ADS)

    Cardozo, Nestor; Brandenburg, J. P.

    2014-03-01

    We describe a kinematic approach to simulate folds above listric propagating thrusts. The model is based on a pre-defined circular thrust geometry with a maximum central angle beyond which the thrust is planar, inclined shear above the circular thrust, and trishear in front of the thrust. Provided the trajectory of thrust propagation is established, the model can be run forward and backwards. We use this last feature to implement a global simulated annealing, inverse modeling strategy. This inverse modeling strategy is applied to synthetic folds as well as two real examples in offshore Venezuela and the Niger Delta toe-thrust system. These three examples illustrate the benefits of the algorithm, particularly in predicting the possible range of models that can fit the structures. Thrust geometry, depth to detachment level, and backlimb geometry have high impact in model parameters such as backlimb shear angle and fault slip; while forelimb geometry is critical to constrain parameters such as fault propagation to fault slip ratio and trishear angle. Steep to overturned beds in forelimb areas are often not imaged by seismic, so in the absence of additional well data, considering all possible thrust-fold geometries is critical for the modeling and whatever prediction (e.g. hydrocarbon trap integrity) is made from it.

  12. Research program on Indonesian active faults to support the national earthquake hazard assesments

    NASA Astrophysics Data System (ADS)

    Natawidjaja, D. H.

    2012-12-01

    In mid 2010 an Indonesian team of earthquake scientists published the new Indonesian probabilistic seismic hazard analysis (PSHA) map. The new PSHA map replaced the previous version that is published in 2002. One of the major challenges in developing the new map is that data for many active fault zones in Indonesia is sparse and mapped only at regional scale, thus the input fault parameters for the PSHA introduce unavoidably large uncertainties. Despite the fact that most Indonesian islands are torn by active faults, only Sumatra has been mapped and studied in sufficient details. In other areas, such as Java and Bali, the most populated regions as well as in the east Indonesian region, where tectonic plate configurations are far more complex and relative plate motions are generally higher, many major active faults and plate boundaries are not well mapped and studied. In early 2011, we have initiated a research program to study major active faults in Indonesia together with starting a new graduate study program, GREAT (Graduate Research for Earthquake and Active Tectonics), hosted by ITB (Institute of Technology bandung) and LIPI (Indonesian Institute of Sciences) in partnership with the Australia-Indonesia Facility for Disaster Reduction (AIFDR). The program include acquisition of high-resolution topography and images required for detailed fault mapping, measuring geological slip rates and locating good sites for paleoseismological studies. It is also coupled by seismological study and GPS surveys to measure geodetic slip rates. To study submarine active faults, we collect and incorporate bathymetry and marine geophysical data. The research will be carried out, in part, through masters and Ph.D student theses. in the first four year of program we select several sites for active fault studies, particulary the ones that pose greater risks to society.

  13. Continuity, segmentation and faulting type of active fault zones of the 2016 Kumamoto earthquake inferred from analyses of a gravity gradient tensor

    NASA Astrophysics Data System (ADS)

    Matsumoto, Nayuta; Yoshihiro, Hiramatsu; Sawada, Akihiro

    2016-10-01

    We analyze Bouguer anomalies in/around the focal region of the 2016 Kumamoto earthquake to examine features, such as continuity, segmentation and faulting type, of the active fault zones related to the earthquake. Several derivatives and structural parameters calculated from a gravity gradient tensor are applied to highlight the features. First horizontal and vertical derivatives, as well as a normalized total horizontal derivative, characterize well the continuous subsurface fault structure along the Futagawa fault zone. On the other hand, the Hinagu fault zone is not clearly detected by these derivatives, especially in the case of the Takano-Shirahata segment, suggesting a difference of cumulative vertical displacement between the two fault zones. The normalized total horizontal derivative and the dimensionality index indicate a discontinuity of the subsurface structure of the Hinagu fault zone, that is, a segment boundary between the Takano-Shirahata and the Hinagu segments. The aftershock distribution does not extend beyond this segment boundary. In other words, this segment boundary controls the southern end of the rupture area of the foreshock. We also recognize normal fault structures dipping to the northwest in some areas of the fault zones from estimations of dip angles.[Figure not available: see fulltext.

  14. Model-based fault detection and isolation for intermittently active faults with application to motion-based thruster fault detection and isolation for spacecraft

    NASA Technical Reports Server (NTRS)

    Wilson, Edward (Inventor)

    2008-01-01

    The present invention is a method for detecting and isolating fault modes in a system having a model describing its behavior and regularly sampled measurements. The models are used to calculate past and present deviations from measurements that would result with no faults present, as well as with one or more potential fault modes present. Algorithms that calculate and store these deviations, along with memory of when said faults, if present, would have an effect on the said actual measurements, are used to detect when a fault is present. Related algorithms are used to exonerate false fault modes and finally to isolate the true fault mode. This invention is presented with application to detection and isolation of thruster faults for a thruster-controlled spacecraft. As a supporting aspect of the invention, a novel, effective, and efficient filtering method for estimating the derivative of a noisy signal is presented.

  15. The Eastern Lower Tagus Valley Fault Zone in central Portugal: Active faulting in a low-deformation region within a major river environment

    NASA Astrophysics Data System (ADS)

    Canora, Carolina; Vilanova, Susana P.; Besana-Ostman, Glenda M.; Carvalho, João; Heleno, Sandra; Fonseca, Joao

    2015-10-01

    Active faulting in the Lower Tagus Valley, Central Portugal, poses a significant seismic hazard that is not well understood. Although the area has been affected by damaging earthquakes during historical times, only recently has definitive evidence of Quaternary surface faulting been found along the western side of the Tagus River. The location, geometry and kinematics of active faults along the eastern side of the Tagus valley have not been previously studied. We present the first results of mapping and paleoseismic analysis of the eastern strand of the Lower Tagus Valley Fault Zone (LTVFZ). Geomorphological, paleoseismological, and seismic reflection studies indicate that the Eastern LTVFZ is a left-lateral strike-slip fault. The detailed mapping of geomorphic features and studies in two paleoseismic trenches show that surface fault rupture has occurred at least six times during the past 10 ka. The river offsets indicate a minimum slip rate on the order of 0.14-0.24 mm/yr for the fault zone. Fault trace mapping, geomorphic analysis, and paleoseismic studies suggest a maximum magnitude for the Eastern LTVFZ of Mw ~ 7.3 with a recurrence interval for surface ruptures ~ 1.7 ka. At least two events occurred after 1175 ± 95 cal yr BP. Single-event displacements are unlikely to be resolved in the paleoseismic trenches, thus our observations most probably represent the minimum number of events identified in the trenches.

  16. Tectonic evolution of the frontal Longmen San thrust belt

    NASA Astrophysics Data System (ADS)

    Chang, C.-P.; Xu, X.-W.; Yuan, R.-M.; Li, K.; Sun, X.-Z.; Chen, W.-S.

    2012-04-01

    The Longmen Shan thrust belt in the eastern margin of the Tibetan Plateau underwent deformation associated with the eastward growth of the Tibetan Plateau. Many geological features indicate that this range is not a typical active convergent mountain belt. Some of the features that indicated that this range is atypical are the fact that it is a young, high mountain, has a thickened crust with a very low GPS shortening rate, and has no corresponding foreland subsidence. Many geologists believe that the crustal thickening that occurred in this area is caused by ductile deformation rather than by thrust faulting or crustal shortening. This hypothesis successfully explains why the upper crust is largely uplifted although the horizontal shortening at the surface is still very small. However, some recent studies based on quantitative structural analysis and a balanced cross-section indicates that a large increase in shortening occurs near the range front, and the structural relief produced by folds and faults is also closely related to the topography of this front. These imply that upper-crustal deformation is the primary mechanism for generating uplift and topography in the foothills of Longmen Shan Range. This idea obviates the need for lower-crustal flow and inflation to produce and maintain the Longmen Shan Range. Scientists have created many different conceptions for the mode of tectonic deformation across the eastern margin of the Tibetan Plateau. However, almost all scientists agree that the eastern Tibetan Plateau has an exceptionally low mechanical strength, inherited from Mesozoic tectonics of the region. On the 12th of May 2008, Mw 7.9 Wenchuan earthquake occurred in this area provides a direct manifestation of the active crustal shortening and documents the importance of active crustal shortening in developing and supporting the Longmen Shan Range. The co-seismic surface rupture pattern of Wenchuan earthquake, involving multiple structures, is one of the most

  17. Dielectric Barrier Discharge (DBD) Plasma Actuators Thrust-Measurement Methodology Incorporating New Anti-Thrust Hypothesis

    NASA Technical Reports Server (NTRS)

    Ashpis, David E.; Laun, Matthew C.

    2014-01-01

    We discuss thrust measurements of Dielectric Barrier Discharge (DBD) plasma actuators devices used for aerodynamic active flow control. After a review of our experience with conventional thrust measurement and significant non-repeatability of the results, we devised a suspended actuator test setup, and now present a methodology of thrust measurements with decreased uncertainty. The methodology consists of frequency scans at constant voltages. The procedure consists of increasing the frequency in a step-wise fashion from several Hz to the maximum frequency of several kHz, followed by frequency decrease back down to the start frequency of several Hz. This sequence is performed first at the highest voltage of interest, then repeated at lower voltages. The data in the descending frequency direction is more consistent and selected for reporting. Sample results show strong dependence of thrust on humidity which also affects the consistency and fluctuations of the measurements. We also observed negative values of thrust or "anti-thrust", at low frequencies between 4 Hz and up to 64 Hz. The anti-thrust is proportional to the mean-squared voltage and is frequency independent. Departures from the parabolic anti-thrust curve are correlated with appearance of visible plasma discharges. We propose the anti-thrust hypothesis. It states that the measured thrust is a sum of plasma thrust and anti-thrust, and assumes that the anti-thrust exists at all frequencies and voltages. The anti-thrust depends on actuator geometry and materials and on the test installation. It enables the separation of the plasma thrust from the measured total thrust. This approach enables more meaningful comparisons between actuators at different installations and laboratories. The dependence on test installation was validated by surrounding the actuator with a large diameter, grounded, metal sleeve.

  18. Active Fault Near-Source Zones Within and Bordering the State of California for the 1997 Uniform Building Code

    USGS Publications Warehouse

    Petersen, M.D.; Toppozada, Tousson R.; Cao, T.; Cramer, C.H.; Reichle, M.S.; Bryant, W.A.

    2000-01-01

    The fault sources in the Project 97 probabilistic seismic hazard maps for the state of California were used to construct maps for defining near-source seismic coefficients, Na and Nv, incorporated in the 1997 Uniform Building Code (ICBO 1997). The near-source factors are based on the distance from a known active fault that is classified as either Type A or Type B. To determine the near-source factor, four pieces of geologic information are required: (1) recognizing a fault and determining whether or not the fault has been active during the Holocene, (2) identifying the location of the fault at or beneath the ground surface, (3) estimating the slip rate of the fault, and (4) estimating the maximum earthquake magnitude for each fault segment. This paper describes the information used to produce the fault classifications and distances.

  19. Analysis of Landsat TM data for active tectonics: the case of the Big Chino Fault, Arizona

    NASA Astrophysics Data System (ADS)

    Salvi, Stefano

    1994-12-01

    The Big Chino Valley is a 50 km-long tectonic depression of the Basin and Range province of the South- western United States. It is bordered on the NE side by an important normal fault, the Big Chino Fault. The activity of the latter has been hypothesised on the basis of the presence of a 20 m-high fault scarp and on local geomorphological studies. Moreover, a magnitude 4.9 earthquake occurred in southern Arizona in 1976 has been attributed to this fault. The climate in the Big Chino Valley is semi-arid with average rainfall of about 400 mm per year; a very sparse vegetation cover is present, yielding a good possibility for the geo-lithologic application of remote sensing data. The analysis of the TM spectral bands shows, in the short wave infrared, a clear variation in the reflected radiance across the fault scarp. Also the available radar (SLAR) images show a marked difference in response between the two sides of the fault. An explanation of this phenomena has been found in the interaction between the geomorphic evolution, the pedological composition, and the periodic occurrence of coseismic deformation along the fault. Other effects of the latter process have been investigated on colour D- stretched images whose interpretation allowed to detect two paleoseismic events of the Big Chino Fault. This work demonstrates that important information on the seismological parameters of active faults in arid and semiarid climates can be extracted from the analysis of satellite spectral data in the visible and near -infrared.

  20. Complex Faulting within the New Madrid Seismic Zone

    NASA Astrophysics Data System (ADS)

    Deshon, H. R.; Powell, C. A.; Magnani, M.; Bisrat, S. T.

    2010-12-01

    Relative relocations derived using double-difference tomography techniques reveal a complex sequence of faulting within the New Madrid Seismic Zone (NMSZ) and upper Mississippi Embayment. The majority of NMSZ seismicity recorded over the last 30 years occurs along four limbs: 1) a NE-SW trending dextral strike-slip fault, termed the Axial fault, coincident with the central valley of the Cambrian Reelfoot Rift system; 2) the SE-NW trending Reelfoot thrust fault; 3) a E-W trending left lateral strike-slip fault extending off of the northern terminus of the Reelfoot fault, here termed New Madrid west; and 4) a NE-SW dextral strike-slip fault also extending off of the northern terminus of the Reelfoot fault, here termed New Madrid north. Each of these segments is thought to have ruptured during the 1811-1812 large earthquake sequence. A fifth segment, the Bootheel lineament, is marked by 1811-1812 related liquefaction features but appears largely aseismic, though we suggest there are at least five events in the catalog associated with this feature. Geological and geophysical evidence across the embayment suggests that the region is crossed by additional faults at shallow depths (<1-2 km), while seismicity is generally confined to the 3-20 km depth range. Here we present relative relocations derived using catalog and waveform cross-correlation differential times of the 1989-1992 local PANDA network and the 1995-2010 Cooperative New Madrid Seismic Network. We show that the four known seismic lineations exhibit internal complexity. For example, New Madrid north is composed of two parallel faults rather then a single fault, and seismicity associated with the Axial lineation exhibits temporal changes along strike and becomes spatially more diffuse south of the Axial fault/Bootheel lineament intersection. Seismicity along the southern Reelfoot fault does not define a dipping plane consistent with thrust faulting, unlike the northern Reelfoot fault, and is associated with

  1. Imbricate stacking on a highly oblique ramp, but no antiformal culmination - the Dundonnell sector of the Caledonian Moine Thrust Belt, Northwest Highlands of Scotland.

    NASA Astrophysics Data System (ADS)

    Leslie, Graham; Krabbendam, Maarten; Goodenough, Kathryn

    2010-05-01

    Abrupt lateral changes in the structural geometry of ductile thrust stacks occur in many contractional fold-and-thrust belts. Such transverse zones are not widely studied and reported but are commonly thought to be related to kinematic responses to irregularities generated across pre-existing, sometimes re-activated, basement faults. Antiformal culminations, often much greater in amplitude than any irregularity identified in the basement below, are frequently associated with such transverse zones; risk evaluation of any hydrocarbon play in such a setting presents a complex challenge. In many cases, the causative structure is concealed, either by distal parts of the thrust belt or the foreland basin. Breaching focussed above the weakness in basement further complicates assessment of the structural integrity of the setting. In NW Scotland, the classic Caledonian WNW-vergent Moine Thrust Belt exposes excellent examples of the structural architecture in such transverse zones. One such example, the Dundonnell Culmination has been interpreted as the type example of an antiformal-stack duplex in a fold-and-thrust belt (Boyer & Elliot 1982). This interpretation derives from the primary Geological Survey of the region (Peach et al. 1907) which identified a WSW-ENE elongate antiformal structure formed in Neoproterozoic (Torridonian) and Cambro-Ordovician sedimentary strata immediately beneath the Moine Thrust. The Moine Thrust was shown to be deformed by this structure, the antiformal axis was shown to be aligned oblique to the trace of the Moine Thrust Belt, and to the (top-to-WNW) thrust transport direction. New geological mapping does not support an antiformal-stack duplex at Dundonnell. There is no folded repetition of the stratigraphy or lithology across the culmination; instead moderate to steep SSE-dips are observed right across the structure. On the south side of the structure, clastic rocks immediately beneath the Moine Thrust are intensely mylonitic; in contrast on

  2. Glacier Ice Mass Fluctuations and Fault Instability in Tectonically Active Southern Alaska

    NASA Technical Reports Server (NTRS)

    SauberRosenberg, Jeanne M.; Molnia, Bruce F.

    2003-01-01

    Across southern Alaska the northwest directed subduction of the Pacific plate is accompanied by accretion of the Yakutat terrane to continental Alaska. This has led to high tectonic strain rates and dramatic topographic relief of more than 5000 meters within 15 km of the Gulf of Alaska coast. The glaciers of this area are extensive and include large glaciers undergoing wastage (glacier retreat and thinning) and surges. The large glacier ice mass changes perturb the tectonic rate of deformation at a variety of temporal and spatial scales. We estimated surface displacements and stresses associated with ice mass fluctuations and tectonic loading by examining GPS geodetic observations and numerical model predictions. Although the glacial fluctuations perturb the tectonic stress field, especially at shallow depths, the largest contribution to ongoing crustal deformation is horizontal tectonic strain due to plate convergence. Tectonic forces are thus the primary force responsible for major earthquakes. However, for geodetic sites located < 10-20 km from major ice mass fluctuations, the changes of the solid Earth due to ice loading and unloading are an important aspect of interpreting geodetic results. The ice changes associated with Bering Glacier s most recent surge cycle are large enough to cause discernible surface displacements. Additionally, ice mass fluctuations associated with the surge cycle can modify the short-term seismicity rates in a local region. For the thrust faulting environment of the study region a large decrease in ice load may cause an increase in seismic rate in a region close to failure whereas ice loading may inhibit thrust faulting.

  3. Active Crustal Faults in the Forearc Region, Guerrero Sector of the Mexican Subduction Zone

    NASA Astrophysics Data System (ADS)

    Gaidzik, Krzysztof; Ramírez-Herrera, Maria Teresa; Kostoglodov, Vladimir

    2016-10-01

    This work explores the characteristics and the seismogenic potential of crustal faults on the overriding plate in an area of high seismic hazard associated with the occurrence of subduction earthquakes and shallow earthquakes of the overriding plate. We present the results of geomorphic, structural, and fault kinematic analyses conducted on the convergent margin between the Cocos plate and the forearc region of the overriding North American plate, within the Guerrero sector of the Mexican subduction zone. We aim to determine the active tectonic processes in the forearc region of the subduction zone, using the river network pattern, topography, and structural data. We suggest that in the studied forearc region, both strike-slip and normal crustal faults sub-parallel to the subduction zone show evidence of activity. The left-lateral offsets of the main stream courses of the largest river basins, GPS measurements, and obliquity of plate convergence along the Cocos subduction zone in the Guerrero sector suggest the activity of sub-latitudinal left-lateral strike-slip faults. Notably, the regional left-lateral strike-slip fault that offsets the Papagayo River near the town of La Venta named "La Venta Fault" shows evidence of recent activity, corroborated also by GPS measurements (4-5 mm/year of sinistral motion). Assuming that during a probable earthquake the whole mapped length of this fault would rupture, it would produce an event of maximum moment magnitude Mw = 7.7. Even though only a few focal mechanism solutions indicate a stress regime relevant for reactivation of these strike-slip structures, we hypothesize that these faults are active and suggest two probable explanations: (1) these faults are characterized by long recurrence period, i.e., beyond the instrumental record, or (2) they experience slow slip events and/or associated fault creep. The analysis of focal mechanism solutions of small magnitude earthquakes in the upper plate, for the period between 1995

  4. Geometry, kinematics and slip rate along the Mosha active fault, Central Alborz, Iran

    NASA Astrophysics Data System (ADS)

    Ritz, J.-F.; Pics Geological Team

    2003-04-01

    The Mosha fault is one of the major active fault in Central Alborz as shown by its strong historical seismicity and its clear morphological signature. Situated at the vicinity of Tehran city, this ~150 km long ~N100°E trending fault represents an important potential seismic source that threatens the Iranian metropolis. In the framework of an Iranian-French joint research program (PICS) devoted to seismic hazard assessment in the Tehran region, we undertook a morphotectonic (determination of the cumulative displacements and the ages of offset morphologic markers) and paleoseismic (determination of the ages and magnitudes of ancient events) study along the Mosha fault. Our objectives are the estimation of the long-term slip rate (Upper Pleistocene-Holocene) and the mean recurrence interval of earthquakes along the different segments of the fault. Our investigations within the Tar Lake valley, along the eastern part of the fault potentially the site of the 1665 (VII, 6.5) historical earthquake - allows us to calculate a preliminary 2 ± 0.1 mm/yr minimum left lateral slip rate. If we assume a characteristic coseismic average displacement comprised between 0.35 m (Mw 6.5) and 1.2 m (Mw 7.1) calculated from Wells &Coppersmith’s functions (1994) and taking the moment magnitudes attributed to the 1665 and 1830 earthquakes (e.g. Berberian &Yeats, 2001) the mean maximum recurrence intervals along this segment of the Mosha fault are comprised between 160 and 620 yrs.

  5. Eocene activity on the Western Sierra Fault System and its role incising Kings Canyon, California

    NASA Astrophysics Data System (ADS)

    Sousa, Francis J.; Farley, Kenneth A.; Saleeby, Jason; Clark, Marin

    2016-04-01

    Combining new and published apatite (U-Th)/He and apatite 4He/3He data from along the Kings River canyon, California we rediscover a west-down normal fault on the western slope of the southern Sierra Nevada, one of a series of scarps initially described by Hake (1928) which we call the Western Sierra Fault System. Integrating field observations with apatite (U-Th)/He data, we infer a single fault trace 30 km long, and constrain the vertical offset across this fault to be roughly a kilometer. Thermal modeling of apatite 4He/3He data documents a pulse of footwall cooling near the fault and upstream in the footwall at circa 45-40 Ma, which we infer to be the timing of a kilometer-scale incision pulse resulting from the fault activity. In the context of published data from the subsurface of the Sacramento and San Joaquin Valleys, our data from the Western Sierra Fault System suggests an Eocene tectonic regime dominated by low-to-moderate magnitude extension, surface uplift, and internal structural deformation of the southern Sierra Nevada and proximal Great Valley forearc.

  6. Gorringe Ridge gravity and magnetic anomalies are compatible with thrusting at a crustal scale

    NASA Astrophysics Data System (ADS)

    Galindo-Zaldívar, J.; Maldonado, A.; Schreider, A. A.

    2003-06-01

    The main features of the deep structure of the Gorringe Ridge are analysed on the basis of gravity and magnetic measurements, as well as seismic profiles, drill holes, rock dredges, submersible observations and seismicity data. The gravity and magnetic models of the Gettysburg and Ormonde seamounts, which form the Gorringe Ridge, suggest that the Moho is approximately flat and the upper part of the ridge corresponds to a northwestwards vergent fold. This structure is the result of a northwestward vergent thrust that deformed the oceanic crust, with a minimum slip of approximately 20 km. The activity of the thrust probably started 20 Myr, and produced the recent stages of seamount uplift. The seamount is mainly composed of gabbros of the oceanic crust, serpentinized rocks and alkaline basalts. The large antiform, located in the hangingwall of the thrust, is probably deformed by minor faults. This oceanic ridge is a consequence of the oblique convergence between the African Plate and the overlapping Eurasian Plate.

  7. Southern San Andreas Fault evaluation field activity: approaches to measuring small geomorphic offsets--challenges and recommendations for active fault studies

    USGS Publications Warehouse

    Scharer, Katherine M.; Salisbury, J. Barrett; Arrowsmith, J. Ramon; Rockwell, Thomas K.

    2014-01-01

    In southern California, where fast slip rates and sparse vegetation contribute to crisp expression of faults and microtopography, field and high‐resolution topographic data (<1  m/pixel) increasingly are used to investigate the mark left by large earthquakes on the landscape (e.g., Zielke et al., 2010; Zielke et al., 2012; Salisbury, Rockwell, et al., 2012, Madden et al., 2013). These studies measure offset streams or other geomorphic features along a stretch of a fault, analyze the offset values for concentrations or trends along strike, and infer that the common magnitudes reflect successive surface‐rupturing earthquakes along that fault section. Wallace (1968) introduced the use of such offsets, and the challenges in interpreting their “unique complex history” with offsets on the Carrizo section of the San Andreas fault; these were more fully mapped by Sieh (1978) and followed by similar field studies along other faults (e.g., Lindvall et al., 1989; McGill and Sieh, 1991). Results from such compilations spurred the development of classic fault behavior models, notably the characteristic earthquake and slip‐patch models, and thus constitute an important component of the long‐standing contrast between magnitude–frequency models (Schwartz and Coppersmith, 1984; Sieh, 1996; Hecker et al., 2013). The proliferation of offset datasets has led earthquake geologists to examine the methods and approaches for measuring these offsets, uncertainties associated with measurement of such features, and quality ranking schemes (Arrowsmith and Rockwell, 2012; Salisbury, Arrowsmith, et al., 2012; Gold et al., 2013; Madden et al., 2013). In light of this, the Southern San Andreas Fault Evaluation (SoSAFE) project at the Southern California Earthquake Center (SCEC) organized a combined field activity and workshop (the “Fieldshop”) to measure offsets, compare techniques, and explore differences in interpretation. A thorough analysis of the measurements from the

  8. Active faults, stress field and plate motion along the Indo-Eurasian plate boundary

    NASA Astrophysics Data System (ADS)

    Nakata, Takashi; Otsuki, Kenshiro; Khan, S. H.

    1990-09-01

    The active faults of the Himalayas and neighboring areas are direct indicators of Recent and sub-Recent crustal movements due to continental collision between the Indian and Eurasian plates. The direction of the maximum horizontal shortening or horizontal compressive stress axes deduced from the strike and type of active faulting reveals a characteristic regional stress field along the colliding boundary. The trajectories of the stress axes along the transcurrent faults and the Eastern Himalayan Front, are approximately N-S, parallel to the relative motion of the two plates. However, along the southern margin of the Eurasian plate, they are NE-SW in the Western Himalayan Front and NW-SE to E-W in the Kirthar-Sulaiman Front, which is not consistent with the direction of relative plate motion. A simple model is proposed in order to explain the regional stress pattern. In this model, the tectonic sliver between the transcurrent faults and the plate margin, is dragged northward by the oblique convergence of the Indian plate. Thus, the direction of relative motion between the tectonic sliver and the Indian plate changes regionally, causing local compressive stress fields. Judging from the long-term slip rates along the active faults, the relative motion between the Indian and Eurasian plates absorbed in the colliding zone is about one fourth of its total amount; the rest may be consumed along the extensive strike-slip faults in Tibet and China.

  9. Modeling of fault activation and seismicity by injection directly into a fault zone associated with hydraulic fracturing of shale-gas reservoirs

    DOE PAGES

    Rutqvist, Jonny; Rinaldi, Antonio P.; Cappa, Frédéric; Moridis, George J.

    2015-03-01

    We conducted three-dimensional coupled fluid-flow and geomechanical modeling of fault activation and seismicity associated with hydraulic fracturing stimulation of a shale-gas reservoir. We simulated a case in which a horizontal injection well intersects a steeply dip- ping fault, with hydraulic fracturing channeled within the fault, during a 3-hour hydraulic fracturing stage. Consistent with field observations, the simulation results show that shale-gas hydraulic fracturing along faults does not likely induce seismic events that could be felt on the ground surface, but rather results in numerous small microseismic events, as well as aseismic deformations along with the fracture propagation. The calculated seismicmore » moment magnitudes ranged from about -2.0 to 0.5, except for one case assuming a very brittle fault with low residual shear strength, for which the magnitude was 2.3, an event that would likely go unnoticed or might be barely felt by humans at its epicenter. The calculated moment magnitudes showed a dependency on injection depth and fault dip. We attribute such dependency to variation in shear stress on the fault plane and associated variation in stress drop upon reactivation. Our simulations showed that at the end of the 3-hour injection, the rupture zone associated with tensile and shear failure extended to a maximum radius of about 200 m from the injection well. The results of this modeling study for steeply dipping faults at 1000 to 2500 m depth is in agreement with earlier studies and field observations showing that it is very unlikely that activation of a fault by shale-gas hydraulic fracturing at great depth (thousands of meters) could cause felt seismicity or create a new flow path (through fault rupture) that could reach shallow groundwater resources.« less

  10. Modeling of fault activation and seismicity by injection directly into a fault zone associated with hydraulic fracturing of shale-gas reservoirs

    SciTech Connect

    Rutqvist, Jonny; Rinaldi, Antonio P.; Cappa, Frédéric; Moridis, George J.

    2015-03-01

    We conducted three-dimensional coupled fluid-flow and geomechanical modeling of fault activation and seismicity associated with hydraulic fracturing stimulation of a shale-gas reservoir. We simulated a case in which a horizontal injection well intersects a steeply dip- ping fault, with hydraulic fracturing channeled within the fault, during a 3-hour hydraulic fracturing stage. Consistent with field observations, the simulation results show that shale-gas hydraulic fracturing along faults does not likely induce seismic events that could be felt on the ground surface, but rather results in numerous small microseismic events, as well as aseismic deformations along with the fracture propagation. The calculated seismic moment magnitudes ranged from about -2.0 to 0.5, except for one case assuming a very brittle fault with low residual shear strength, for which the magnitude was 2.3, an event that would likely go unnoticed or might be barely felt by humans at its epicenter. The calculated moment magnitudes showed a dependency on injection depth and fault dip. We attribute such dependency to variation in shear stress on the fault plane and associated variation in stress drop upon reactivation. Our simulations showed that at the end of the 3-hour injection, the rupture zone associated with tensile and shear failure extended to a maximum radius of about 200 m from the injection well. The results of this modeling study for steeply dipping faults at 1000 to 2500 m depth is in agreement with earlier studies and field observations showing that it is very unlikely that activation of a fault by shale-gas hydraulic fracturing at great depth (thousands of meters) could cause felt seismicity or create a new flow path (through fault rupture) that could reach shallow groundwater resources.

  11. Polyphase evolution of the Chaîne des Matheux frontal thrust (Haiti)

    NASA Astrophysics Data System (ADS)

    Wessels, Richard; Ellouz-Zimmermann, Nadine; Rosenberg, Claudio; Bellahsen, Nicolas; Hamon, Youri; Deschamps, Remy; Battani, Anne; Leroy, Sylvie; Momplaisir, Roberte

    2016-04-01

    The NW - SE trending Haitian fold-and-thrust belt (HFTB) is located in the western part of the Caribbean island of Hispaniola. It covers the suture between the Cretaceous Caribbean island arc in the north and the Late Cretaceous thickened oceanic crust in the south. The HFTB is bounded to the north and south by the left-lateral Septentrional (SFZ) and Enriquillo-Plantain Garden (EPGFZ) fault zones, respectively. Compressional deformation on the HFTB commenced as early as Eocene times. It was followed by transpressional deformation from the early Miocene onwards, with in sequence progressive stacking of thrust sheets towards the SW. Seismicity at the junction between the HFTB and the EPGFZ is recorded by the 12 January 2010 Mw 7.0 earthquake. Surface mapping did not reveal a rupture, as the main activity occurred on the steep NNW dipping oblique transpressional Léogâne fault, while aftershocks documented motion on a shallow SW dipping thrust segment. The structural style of deformation of the HFTB, either the stacking of thrust sheets on basement heterogeneities or basement-involved thrusting, has not been studied in detail. Also lacking are conceptual models addressing the amount of convergence between the northern and southern domains, and describing how convergence was accommodated. To address these problems we conducted a detailed fieldwork on the southernmost thrust sheet, known as the Chaîne des Matheux front. Using stratigraphy, geological mapping, cross sections, kinematic fault slip data, analysis of mineralizations and fluid inclusions, and geochemical analysis of fluid seeps, we decipher the evolution of this anticlinal structure. Stratigraphic data reveal stable Eocene platform sedimentation over the whole region, which preceded deepening of the basin throughout Oligocene and early Miocene times. A diachronous evolution is evident from the middle Miocene onwards. The NE flank displays a shallowing upwards trend and clastic sedimentation, while the

  12. Delineation of Active Basement Faults in the Eastern Tennessee and Charlevoix Intraplate Seismic Zones

    NASA Astrophysics Data System (ADS)

    Powell, C. A.; Langston, C. A.; Cooley, M.

    2013-12-01

    Recognition of distinct, seismogenic basement faults within the eastern Tennessee seismic zone (ETSZ) and the Charlevoix seismic zone (CSZ) is now possible using local earthquake tomography and datasets containing a sufficiently large number of earthquakes. Unlike the New Madrid seismic zone where seismicity clearly defines active fault segments, earthquake activity in the ETSZ and CSZ appears diffuse. New arrival time inversions for hypocenter relocations and 3-D velocity variations using datasets in excess of 1000 earthquakes suggest the presence of distinct basement faults in both seismic zones. In the ETSZ, relocated hypocenters align in near-vertical segments trending NE-SW, parallel to the long dimension of the seismic zone. Earthquakes in the most seismogenic portion of the ETSZ delineate another set of near-vertical faults trending roughly E-ESE. These apparent trends and steep dips are compatible with ETSZ focal mechanism solutions. The solutions are remarkably consistent and indicate strike-slip motion along the entire length of the seismic zone. Relocated hypocenter clusters in the CSZ define planes that trend and dip in directions that are compatible with known Iapitan rift faults. Seismicity defining the planes becomes disrupted where the rift faults encounter a major zone of deformation produced by a Devonian meteor impact. We will perform a joint statistical analysis of hypocenter alignments and focal mechanism nodal plane orientations in the ETSZ and the CSZ to determine the spatial orientations of dominant seismogenic basement faults. Quantifying the locations and dimensions of active basement faults will be important for seismic hazard assessment and for models addressing the driving mechanisms for these intraplate zones.

  13. Paper 58714 - Exploring activated faults hydromechanical processes from semi-controled field injection experiments

    NASA Astrophysics Data System (ADS)

    Guglielmi, Y.; Cappa, F.; Nussbaum, C.

    2015-12-01

    The appreciation of the sensitivity of fractures and fault zones to fluid-induced-deformations in the subsurface is a key question in predicting the reservoir/caprock system integrity around fluid manipulations with applications to reservoir leakage and induced seismicity. It is also a question of interest in understanding earthquakes source, and recently the hydraulic behavior of clay faults under a potential reactivation around nuclear underground depository sites. Fault and fractures dynamics studies face two key problems (1) the up-scaling of laboratory determined properties and constitutive laws to the reservoir scale which is not straightforward when considering faults and fractures heterogeneities, (2) the difficulties to control both the induced seismicity and the stimulated zone geometry when a fault is reactivated. Using instruments dedicated to measuring coupled pore pressures and deformations downhole, we conducted field academic experiments to characterize fractures and fault zones hydromechanical properties as a function of their multi-scale architecture, and to monitor their dynamic behavior during the earthquake nucleation process. We show experiments on reservoir or cover rocks analogues in underground research laboratories where experimental conditions can be optimized. Key result of these experiments is to highlight how important the aseismic fault activation is compared to the induced seismicity. We show that about 80% of the fault kinematic moment is aseismic and discuss the complex associated fault friction coefficient variations. We identify that the slip stability and the slip velocity are mainly controlled by the rate of the permeability/porosity increase, and discuss the conditions for slip nucleation leading to seismic instability.

  14. GPR measurements to assess the Emeelt active fault's characteristics in a highly smooth topographic context, Mongolia

    NASA Astrophysics Data System (ADS)

    Dujardin, Jean-Rémi; Bano, Maksim; Schlupp, Antoine; Ferry, Matthieu; Munkhuu, Ulziibat; Tsend-Ayush, Nyambayar; Enkhee, Bayarsaikhan

    2014-07-01

    To estimate the seismic hazard, the geometry (dip, length and orientation) and the dynamics (type of displacements and amplitude) of the faults in the area of interest need to be understood. In this paper, in addition to geomorphologic observations, we present the results of two ground penetrating radar (GPR) campaigns conducted in 2010 and 2011 along the Emeelt fault in the vicinity of Ulaanbaatar, capital of Mongolia, located in an intracontinental region with low deformation rate that induces long recurrence time between large earthquakes. As the geomorphology induced by the fault activity has been highly smoothed by erosion processes since the last event, the fault location and geometry is difficult to determine precisely. However, by using GPR first, a non-destructive and fast investigation, the fault and the sedimentary deposits near the surface can be characterized and the results can be used for the choice of trench location. GPR was performed with a 50 MHz antenna over 2-D lines and with a 500 MHz antenna for pseudo-3-D surveys. The 500 MHz GPR profiles show a good consistency with the trench observations, dug next to the pseudo-3-D surveys. The 3-D 500 MHz GPR imaging of a palaeochannel crossed by the fault allowed us to estimate its lateral displacement to be about 2 m. This is consistent with a right lateral strike-slip displacement induced by an earthquake around magnitude 7 or several around magnitude 6. The 2-D 50 MHz profiles, recorded perpendicular to the fault, show a strong reflection dipping to the NE, which corresponds to the fault plane. Those profiles provided complementary information on the fault such as its location at shallow depth, its dip angle (from 23° to 35°) and define its lateral extension.

  15. Holocene activity of the Rose Canyon fault zone in San Diego, California

    NASA Astrophysics Data System (ADS)

    Lindvall, Scott C.; Rockwell, Thomas K.

    1995-12-01

    The Rose Canyon fault zone in San Diego, California, has many well-expressed geomorphic characteristics of an active strike-slip fault, including scarps, offset and deflected drainages and channel walls, pressure ridges, a closed depression, and vegetation lineaments. Geomorphic expression of the fault zone from Mount Soledad south to Mission Bay indicates that the Mount Soledad strand is the most active. A network of trenches excavated across the Mount Soledad strand in Rose Creek demonstrate a minimum of 8.7 m of dextral slip in a distinctive early to middle Holocene gravel-filled channel that crosses the fault zone. The gravel-filled channel was preserved within and east of the fault but was removed west of the fault zone by erosion or possibly grading during development. Consequently, the actual displacement of the channel could be greater than 8.7 m. Radiocarbon dates on detrital charcoal recovered from the sediments beneath the channel yield a maximum calibrated age of about 8.1±0.2 kyr. The minimum amount of slip along with the maximum age yield a minimum slip rate of 1.07±0.03 mm/yr on this strand of the Rose Canyon fault zone for much of Holocene time. Other strands of the Rose Canyon fault zone, which are east and west of our site, may also have Holocene activity. Based on an analysis of the geomorphology of fault traces within the Rose Canyon fault zone, along with the results of our trenching study, we estimate the maximum likely slip rate at about 2 mm/yr and a best estimate of about 1.5 mm/yr. Stratigraphie evidence of at least three events is present during the past 8.1 kyr. The most recent surface rupture displaces the modern A horizon (topsoil), suggesting that this event probably occurred within the past 500 years. Stratigraphie and structural relationships also indicate the occurrence of a scarp-forming event at about 8.1 kyr, prior to deposition of the gravel-filled channel that was used as a piercing line. A third event is indicated by the

  16. Active faulting in northern Chile: ramp stacking and lateral decoupling along a subduction plate boundary?

    NASA Astrophysics Data System (ADS)

    Armijo, Rolando; Thiele, Ricardo

    1990-04-01

    Two large features parallel to the coastline of northern Chile have long been suspected to be the sites of young or active deformation: (1) The 700-km long Coastal Scarp, with average height (above sea level) of about 1000 m; (2) The Atacama Fault zone, that stretches linearly for about 1100 km at an average distance of 30-50 km from the coastline. New field observations combined with extensive analysis of aerial photographs demonstrate that both the Coastal Scarp and the Atacama Fault are zones of Quaternary and current fault activity. Little-degraded surface breaks observed in the field indicate that these fault zones have recently generated large earthquakes ( M = 7-8). Normal fault offsets observed in marine terraces in the Coastal Scarp (at Mejillones Peninsula) require tectonic extension roughly orthogonal to the compressional plate boundary. Strike-slip offsets of drainage observed along the Salar del Carmen and Cerro Moreno faults (Atacama Fault system) imply left-lateral displacements nearly parallel to the plate boundary. The left-lateral movement observed along the Atacama Fault zone may be a local consequence of E-W extension along the Coastal Scarp. But if also found everywhere along strike, left-lateral decoupling along the Atacama Fault zone would be in contradiction with the right lateral component of Nazca-South America motion predicted by models of present plate kinematics. Clockwise rotation with left-lateral slicing of the Andean orogen south of the Arica bend is one way to resolve this contradiction. The Coastal Scarp and the Atacama Fault zone are the most prominent features with clear traces of activity within the leading edge of continental South America. The great length and parallelism of these features with the subduction zone suggest that they may interact with the subduction interface at depth. We interpret the Coastal Scarp to be a west-dipping normal fault or flexure and propose that it is located over an east-dipping ramp stack at

  17. Recently Active Traces of the Berryessa Fault, California: A Digital Database

    USGS Publications Warehouse

    Lienkaemper, James J.

    2012-01-01

    The purpose of this map is to show the location of and evidence for recent movement on active fault traces within the Berryessa section and parts of adjacent sections of the Green Valley Fault Zone, California. The location and recency of the mapped traces is primarily based on geomorphic expression of the fault as interpreted from large-scale 2010 aerial photography and from 2007 and 2011 0.5 and 1.0 meter bare-earth LiDAR imagery (that is, high-resolution topographic data). In a few places, evidence of fault creep and offset Holocene strata in trenches and natural exposures have confirmed the activity of some of these traces. This publication is formatted both as a digital database for use within a geographic information system (GIS) and for broader public access as map images that may be browsed on-line or download a summary map. The report text describes the types of scientific observations used to make the map, gives references pertaining to the fault and the evidence of faulting, and provides guidance for use of and limitations of the map.

  18. A 3-D Model of Stacked Thrusts in the Sevier Thrust Belt, Eastern Idaho

    NASA Astrophysics Data System (ADS)

    Clayton, R. W.; Clayton, S. R.

    2014-12-01

    Using published and new geologic map data and two exploratory wells for control, we constructed a three-dimensional geological model of the Pine Creek area in the Big Hole Mountains of eastern Idaho, where stacked Sevier thrust sheets are exposed at the surface. In this area, Cretaceous crustal shortening displaced and folded strata from Cambrian to Cretaceous in age. Using geologic map data as a primary input to a 3-D model presents a number of challenges, especially representing fault geometries at depth and maintaining strata thicknesses. The highly variable attitudes measured at the surface are also difficult to represent in a subsurface model because they require extensive extrapolation to depth. To overcome these challenges we EarthVision software, which has tools for model construction with minimal data inputs and uses a minimum tension algorithm to create geologically realistic surfaces. We also constructed two primary cross-sections to constrain strata and fault geometries according to structural principles, and used these to guide construction of fault and horizon surfaces. We then designated horizons with the best control as reference horizons to constrain strata geometries, and built the remaining horizons using isochores to add or subtract from those surfaces. The model shows classic flat-ramp thrust geometries as seen farther southeast in the Wyoming section of the thrust belt. The model also shows uniform southwestward tilting of faults and strata in the north end above younger thrusts, but strong effects from a duplex on a younger thrust fault encountered in the southern well, which rotated the strata and older faults above it.

  19. Unravelling the competing influence of regional uplift and active normal faulting in SW Calabria, Italy

    NASA Astrophysics Data System (ADS)

    Whittaker, Alex; Roda Boluda, Duna; Boulton, Sarah; Erhardt, Sebastian

    2015-04-01

    The Neogene geological and geomorphological evolution of Southern Italy is complex and is fundamentally controlled by the subduction of the Ionian slab along the Apennine belt from the Calabrian Arc, and back-arc extension driven by trench rollback. In the area of Calabria and the Straits of Messina the presence of (i) uplifted, deformed and dissected basin sediments and marine terraces, ranging in age from the early to mid-Pleistocene and (ii) seismicity associated with NE-SW normal faults that have well-developed footwall topography and triangular facets have led workers to suggest that both significant regional uplift and extensional faulting in SW Calabria have played a role in generating relief in the area since the mid Pleistocene. However, there is considerable uncertainty in the rates of total surface uplift relative to sea level in both time and space, and the relative partitioning of this uplift between a mantle-driven regional signal, potentially related to a slab tear, and the active extensional structures. Additionally, despite the widespread recognition of normal faults in Calabria to which historical earthquakes are often linked, there is much less agreement on (i) which ones are active and for what length of time; (ii) how the faults interact; and (iii) what their throw and throw rates are. In particular, the ability to resolve both regional uplift and normal faulting in SW Calabria is essential in order to fully understand the tectonic history of the region, while an understanding of location and slip rate of active faults, in an area where the population numbers more than two million people, is essential to assess regional seismic hazards. Here we address these important questions using a combination of tectonic geomorphology and structural geology. We critically examine existing constraints on the rates and distribution of active normal faulting and regional uplift in the area, and we derive new constraints on the along-strike variation in throw

  20. Three-dimensional geometry, strain rates and basement deformation mechanisms of thrust-bend folding

    NASA Astrophysics Data System (ADS)

    Wibberley, Christopher A. J.

    1997-03-01

    Models for thrust-bend folding of an isotropic medium are used to predict initial basement thrust sheet geometries and sub-surface thrust fault shapes from final basement thrust sheet structure. Predicted strains and strain rates from these models are compared with data on deformation fabrics in an example of a basement thrustbend fold in order to characterise the deformation response to thrust-bend folding. The Glencoul thrust sheet in the Moine Thrust Zone of north-west Scotland is restored to an initial thrust sheet geometry. Spatial and orientation distribution data of syn-emplacement fractures and cataclastic fault zones from within the Glencoul thrust sheet are then compared with the strain and strain rate histories predicted by thrust-bend folding models. A different set of cataclastic fault seams is demonstrated to have been generated at each frontal thrust bend. Cataclastic failure is restricted to portions of the thrust sheet that have moved over frontal bends with smaller radii of curvature. From model thrust-bend geometries and an assumed slip rate of 1 x 10 -10 ms -1, estimated minimum (critical) strain rates required for fracture failure of the Lewisian basement are 10 -11 to 10 -14 s -1 for shear strain rates and 10 -12 to 10 -15 s -1 for extensional strain rates.

  1. Fault fragment control in the 1997 Umbria-Marche, central Italy, Earthquake Sequence

    NASA Astrophysics Data System (ADS)

    Meghraoui, Mustapha; Bosi, Vittorio; Camelbeeck, Thierry

    The Umbria-Marche region in central Italy experienced a sequence of shallow earthquakes in late 1997, including three mainshocks on September 26th (Ms 5.5 and 5.9) and October 14th (Ms 5.5). This seismic sequence illustrates the relationships between small-scale active faults and moderate-magnitude earthquakes. We suggest that a small-scale active fault corresponds to a “fault fragment” and that it refers to the fault area required for producing a coseismic deformation at the ground surface. The seismic activity and related three mainshocks occurred along three fault fragments which total ∼25 km in length and show a listric geometry at depth. Fault fragments are laterally controlled by pre-existing transverse fold-and-thrust structures and may constitute a major component of the seismic strain release in active continental regions.

  2. Intra-event and Inter-event Ground Motion Variability from 3-D Broadband (0-8 Hz) Ensemble Simulations of Mw 6.7 Thrust Events Including Rough Fault Descriptions, Small-Scale Heterogeneities and Q(f)

    NASA Astrophysics Data System (ADS)

    Withers, K.; Olsen, K. B.; Shi, Z.; Day, S. M.

    2015-12-01

    We model blind thrust scenario earthquakes matching the fault geometry of 1994 Mw 6.7 Northridge earthquake up to 8 Hz by first performing dynamic rupture propagation using a support operator method (SORD). We extend the ground motion by converting the slip-rate data to a kinematic source for the finite difference wave propagation code AWP-ODC, which incorporates an improved frequency-dependent attenuation approach. This technique has high accuracy for Q values down to 15. The desired Q function is fit to the 'effective' Q over the coarse grained-cell for low Q, and a simple interpolation formula is used to interpolate the weights for arbitrary Q. Here, we use a power-law model Q above a reference frequency in the form Q 0 f^n with exponents ranging from 0.0-0.9. We find envelope and phase misfits only slightly larger than that of the elastic case when compared with that of the frequency-wavenumber solution for both a homogenous and a layered model with a large-velocity contrast. We also include small-scale medium complexity in both a 1D layered model and a 3D medium extracted from SCEC CVM-S4 including a surface geotechnical layer (GTL). We model additional realizations of the scenario by varying the hypocenter location, and find that similar moment magnitudes are generated. We observe that while the ground motion pattern changes, the median ground motion is not affected significantly, when binned as a function of distance, and is within 1 interevent standard deviation from the median GMPEs. We find that intra-event variability for the layered model simulations is similar to observed values of single-station standard deviation. We show that small-scale heterogeneity can significantly affect the intra-event variability at frequencies greater than ~1 Hz, becoming increasingly important at larger distances from the source. We perform a parameter space study by varying statistical parameters and find that the variability is fairly independent of the correlation length

  3. Slip Rates of Main Active Fault Zones Through Turkey Inferred From GPS Observations

    NASA Astrophysics Data System (ADS)

    Ozener, H.; Aktug, B.; Dogru, A.; Tasci, L.; Acar, M.; Emre, O.; Yilmaz, O.; Turgut, B.; Halicioglu, K.; Sabuncu, A.; Bal, O.; Eraslan, A.

    2015-12-01

    Active Fault Map of Turkey was revised and published by General Directorate of Mineral Research and Exploration in 2012. This map reveals that there are about 500 faults can generate earthquakes.In order to understand the earthquake potential of these faults, it is needed to determine the slip rates. Although many regional and local studies were performed in the past, the slip rates of the active faults in Turkey have not been determined. In this study, the block modelling, which is the most common method to produce slip rates, will be done. GPS velocities required for block modeling is being compiled from the published studies and the raw data provided then velocity field is combined. To form a homogeneous velocity field, different stochastic models will be used and the optimal velocity field will be achieved. In literature, GPS site velocities, which are computed for different purposes and published, are combined globally and this combined velocity field are used in the analysis of strain accumulation. It is also aimed to develop optimal stochastic models to combine the velocity data. Real time, survey mode and published GPS observations is being combined in this study. We also perform new GPS observations. Furthermore, micro blocks and main fault zones from Active Fault Map Turkey will be determined and homogeneous velocity field will be used to infer slip rates of these active faults. Here, we present the result of first year of the study. This study is being supported by THE SCIENTIFIC AND TECHNOLOGICAL RESEARCH COUNCIL OF TURKEY (TUBITAK)-CAYDAG with grant no. 113Y430.

  4. Active faulting and natural hazards in Armenia, eastern Turkey and northwestern Iran

    NASA Astrophysics Data System (ADS)

    Karakhanian, Arkady S.; Trifonov, Vladimir G.; Philip, Herve; Avagyan, Ara; Hessami, Khaled; Jamali, Farshad; Salih Bayraktutan, M.; Bagdassarian, H.; Arakelian, S.; Davtian, V.; Adilkhanyan, A.

    2004-03-01

    Active fault zones of Armenia, SE Turkey and NW Iran present a diverse set of interrelated natural hazards. Three regional case studies in this cross-border zone are examined to show how earthquakes interact with other hazards to increase the risk of natural disaster. In northern Armenia, a combination of several natural and man-made phenomena (earthquakes, landslides and unstable dams with toxic wastes) along the Pambak-Sevan-Sunik fault (PSSF) zone lowers from 0.4 to 0.2-0.3 g the maximum permissible level (MPL) of seismic hazard that may induce disastrous destruction and loss of life in the adjacent Vanadzor depression. In the Ararat depression, a large active fault-bounded pull-apart basin at the junction of borders of Armenia, Turkey, Iran and Azerbaijan, an earthquake in 1840 was accompanied by an eruption of Ararat Volcano, lahars, landslides, floods, soil subsidence and liquefaction. The case study demonstrates that natural hazards that are secondary with respect to earthquakes may considerably increase the damage and the casualties and increase the risk associated with the seismic impact. The North Tabriz-Gailatu fault system poses a high seismic hazard to the border areas of NW Iran, eastern Turkey, Nakhichevan (Azerbaijan) and southern Armenia. Right-lateral strike-slip motions along the North Tabriz fault have given rise to strong earthquakes, which threaten the city of Tabriz with its population of 1.2 million. The examples illustrate how the concentration of natural hazards in active fault zones increases the risk associated with strong earthquakes in Armenia, eastern Turkey and NW Iran. This generally occurs across the junctions of international borders. Hence, the transboundary character of active faults requires transboundary cooperation in the study and mitigation of the natural risk.

  5. Reply to comments by Ahmad et al. on: Shah, A. A., 2013. Earthquake geology of Kashmir Basin and its implications for future large earthquakes International Journal of Earth Sciences DOI:10.1007/s00531-013-0874-8 and on Shah, A. A., 2015. Kashmir Basin Fault and its tectonic significance in NW Himalaya, Jammu and Kashmir, India, International Journal of Earth Sciences DOI:10.1007/s00531-015-1183-1

    NASA Astrophysics Data System (ADS)

    Shah, A. A.

    2016-03-01

    Shah (Int J Earth Sci 102:1957-1966, 2013) mapped major unknown faults and fault segments in Kashmir basin using geomorphological techniques. The major trace of out-of-sequence thrust fault was named as Kashmir basin fault (KBF) because it runs through the middle of Kashmir basin, and the active movement on it has backtilted and uplifted most of the basin. Ahmad et al. (Int J Earth Sci, 2015) have disputed the existence of KBF and maintained that faults identified by Shah (Int J Earth Sci 102:1957-1966, 2013) were already mapped as inferred faults by earlier workers. The early works, however, show a major normal fault, or a minor out-of-sequence reverse fault, and none have shown a major thrust fault.

  6. Upper crustal mechanical stratigraphy and the evolution of thrust wedges: insights from sandbox analogue experiments

    NASA Astrophysics Data System (ADS)

    Milazzo, Flavio; Storti, Fabrizio; Nestola, Yago; Cavozzi, Cristian; Magistroni, Corrado; Meda, Marco; Salvi, Francesca

    2016-04-01

    Crustal mechanical stratigraphy i.e. alternating mechanically weaker and stronger layers within the crust, plays a key role in determining how contractional deformations are accommodated at convergent plate boundaries. In the upper crust, evaporites typically provide preferential décollement layers for fault localization and foreland ward propagation, thus significantly influencing evolution of thrust-fold belts in terms of mechanical balance, geometries, and chronological sequences of faulting. Evaporites occur at the base of many passive margin successions that underwent positive inversion within orogenic systems. They typically produce salient geometries in deformation fronts, as in the Jura in the Northern Alps, the Salakh Arch in the Oman Mountains, or the Ainsa oblique thrust-fold belt in the Spanish Pyrenees. Evaporites frequently occur also in foredeep deposits, as in the Apennines, the Pyrenees, the Zagros etc. causing development of additional structural complexity. Low-friction décollement layers also occur within sedimentary successions involved in thrust-fold belts and they contribute to the development of staircase fault trajectories. The role of décollement layers in thrust wedge evolution has been investigated in many experimental works, particularly by sandbox analogue experiments that have demonstrated the impact of basal weak layers on many first order features of thrust wedges, including the dominant fold vergence, the timing of fault activity, and the critical taper. Some experiments also investigated on the effects of weak layers within accreting sedimentary successions, showing how this triggers kinematic decoupling of the stratigraphy above and below the décollements, thus enhancing disharmonic deformation. However, at present a systematic experimental study of the deformation modes of an upper crustal mechanical stratigraphy consisting of both low-friction and viscous décollement layers is still missing in the specific literature. In

  7. Multilayer stress from gravity and its tectonic implications in urban active fault zone: A case study in Shenzhen, South China

    NASA Astrophysics Data System (ADS)

    Xu, Chuang; Wang, Hai-hong; Luo, Zhi-cai; Ning, Jin-sheng; Liu, Hua-liang

    2015-03-01

    It is significant to identify urban active faults for human life and social sustainable development. The ordinary methods to detect active faults, such as geological survey, artificial seismic exploration, and electromagnetic exploration, are not convenient to be carried out in urban area with dense buildings. It is also difficult to supply information about vertical extension of the deeper faults by these methods. Gravity, reflecting the mass distribution of the Earth's interior, provides an alternative way to detect faults, which is more efficient and convenient for urban active fault detection than the aforementioned techniques. Based on the multi-scale decomposition of gravity anomalies, a novel method to invert multilayer horizontal tectonic stresses is proposed. The inverted multilayer stress fields are further used to infer the distribution and stability of the main faults. In order to validate our method, the multilayer stress fields in the Shenzhen fault zone are calculated as a case study. The calculated stress fields show that their distribution is controlled significantly by the strike of the main faults and can be used to derive depths of the faults. The main faults in Shenzhen may range from 4 km to 20 km in the depth. Each layer of the crust is nearly equipressure since the horizontal tectonic stress has small amplitude. It indicates that the main faults in Shenzhen are relatively stable and have no serious impact on planning and construction of the city.

  8. Interactions between active faulting, volcanism, and sedimentary processes at an island arc: Insights from Les Saintes channel, Lesser Antilles arc

    NASA Astrophysics Data System (ADS)

    Leclerc, F.; Feuillet, N.; Deplus, C.

    2016-07-01

    New high-resolution marine geophysical data allow to characterize a large normal fault system in the Lesser Antilles arc, and to investigate the interactions between active faulting, volcanism, sedimentary, and mass-wasting processes. Les Saintes fault system is composed of several normal faults that form a 30 km wide half-graben accommodating NE-SW extension. It is bounded by the Roseau fault, responsible for the destructive Mw 6.3 21 November 2004 earthquake. The Roseau fault has been identified from the island of Basse-Terre to Dominica. It is thus 40 km long, and it could generate Mw 7 earthquakes in the future. Several submarine volcanoes are also recognized. We show that the fault system initiated after the main volcanic construction and subsequently controls the emission of volcanic products. The system propagates southward through damage zones. At the tip of the damage zones, several volcanic cones were recently emplaced probably due to fissures opening in an area of stress increase. A two-way interaction is observed between active faulting and sedimentary processes. The faults control the development of the main turbiditic system made of kilometer-wide canyons, as well as the location of sediment ponding. In turn, erosion and sedimentation prevent scarp growth at the seafloor. Faulting also enhances mass-wasting processes. Since its initiation, the fault system has consequently modified the morphologic evolution of the arc through perturbation of the sedimentary processes and localization of the more recent volcanic activity.

  9. Trishear for curved faults

    NASA Astrophysics Data System (ADS)

    Brandenburg, J. P.

    2013-08-01

    Fault-propagation folds form an important trapping element in both onshore and offshore fold-thrust belts, and as such benefit from reliable interpretation. Building an accurate geologic interpretation of such structures requires palinspastic restorations, which are made more challenging by the interplay between folding and faulting. Trishear (Erslev, 1991; Allmendinger, 1998) is a useful tool to unravel this relationship kinematically, but is limited by a restriction to planar fault geometries, or at least planar fault segments. Here, new methods are presented for trishear along continuously curved reverse faults defining a flat-ramp transition. In these methods, rotation of the hanging wall above a curved fault is coupled to translation along a horizontal detachment. Including hanging wall rotation allows for investigation of structures with progressive backlimb rotation. Application of the new algorithms are shown for two fault-propagation fold structures: the Turner Valley Anticline in Southwestern Alberta, and the Alpha Structure in the Niger Delta.

  10. Seismic Risk Assessment of Active Faults in Japan in Terms of Population Exposure to Seismic Intensity

    NASA Astrophysics Data System (ADS)

    Nojima, Nobuoto; Fujiwara, Hiroyuki; Morikawa, Nobuyuki; Ishikawa, Yutaka; Okumura, Toshihiko; Miyakoshi, Junichi

    This study evaluates and compares seismic risks associated with inland crustal earthquakes in Japan on the basis of published data available on the Japan Seismic Hazard Information Station (J-SHIS). First, taking account of prediction uncertainty of the attenuation law of seismic intensity, the evaluation method for population exposure (PEX) to seismic intensity is presented. The method is applied to 333 seismic events potentially caused by main active faults (154 cases) and other active faults (179 cases). The relationship between population exposure and the probability of occurrence of seismic events ("P-PEX relation") and the resultant seismic risk curves are obtained. Generalized risk index which incorporates the effects of focusing on urgency (probability) or significance (PEX) is defined, producing various risk rankings of active faults.

  11. Soil Moisture Active Passive Mission: Fault Management Design Analyses

    NASA Technical Reports Server (NTRS)

    Meakin, Peter; Weitl, Raquel

    2013-01-01

    As a general trend, the complexities of modern spacecraft are increasing to include more ambitious mission goals with tighter timing requirements and on-board autonomy. As a byproduct, the protective features that monitor the performance of these systems have also increased in scope and complexity. Given cost and schedule pressures, there is an increasing emphasis on understanding the behavior of the system at design time. Formal test-driven verification and validation (V&V) is rarely able to test the significant combinatorics of states, and often finds problems late in the development cycle forcing design changes that can be costly. This paper describes the approach the SMAP Fault Protection team has taken to address some of the above-mentioned issues.

  12. Reconciling Himalayan midcrustal discontinuities: The Main Central thrust system

    NASA Astrophysics Data System (ADS)

    Larson, Kyle P.; Ambrose, Tyler K.; Webb, A. Alexander G.; Cottle, John M.; Shrestha, Sudip

    2015-11-01

    The occurrence of thrust-sense tectonometamorphic discontinuities within the exhumed Himalayan metamorphic core can be explained as part of the Main Central thrust system. This imbricate thrust structure, which significantly thickened the orogenic midcrustal core, comprises a series of thrust-sense faults that all merge into a single detachment. The existence of these various structures, and their potential for complex overprinting along the main detachment, may help explain the contention surrounding the definition, mapping, and interpretation of the Main Central thrust. The unique evolution of specific segments of the Main Central thrust system along the orogen is interpreted to be a reflection of the inherent basement structure and ramp position, and structural level of exposure of the mid-crust. This helps explain the variation in the timing and structural position of tectonometamorphic discontinuities along the length of the mountain belt.

  13. Fault slip during a glacial cycle

    NASA Astrophysics Data System (ADS)

    Steffen, Rebekka; Wu, Patrick; Steffen, Holger; Eaton, Dave

    2013-04-01

    Areas affected by glacial isostatic adjustment (GIA) generally show uplift after deglaciation. These regions are also characterized by a moderate past and present-day seismicity, at seismic moment release rates that exceed those expected under stable tectonic conditions. Several faults have been found in North America and Europe, which have been activated during or after the last deglaciation. Large-magnitude earthquakes have generated fault offsets of up to 120 m. Due to the recent melting of Greenland and Antarctic ice sheets, an understanding of the occurrence of these earthquakes is important. With a new finite-element model, we are able to estimate, for the first time, fault slip during a glacial cycle for continental ice sheets. A two-dimensional earth model based on former GIA studies is developed, which is loaded with a hyperbolic ice sheet. The fault is able to move in a stress field consisting of rebound stress, tectonic background stress, and lithostatic stress. The sensitivity of this fault is tested regarding lithospheric and crustal thickness, viscosity structure of upper and lower mantle, ice-sheet thickness and width, and fault parameters including coefficient of friction, depth, angle and location. Fault throws of up to 30 m are obtained using a fault of 45° dipping below the ice sheet centre. The thickness of the crust is one of the major parameters affecting the total fault throw, e.g. higher values for a thinner crust. Most faults start to move close to the end of deglaciation, and movement stops after one thrusting/reverse earthquake. However, certain conditions may also lead to several fault movements after the end of glaciations.

  14. Assessment of Morphotectonic Influences on Hydrological Environment in Vicinity of an Active Fault

    NASA Astrophysics Data System (ADS)

    Singh, A.; Mukherjee, S.

    2011-12-01

    Studying effects of faulted zones in shaping the hydrological environment of any landscape in a long run is difficult, though these can play a crucial role in regulating the flow and accumulation of water. While aquifer recharge is directly influenced by the structural changes associated with tectonic activity, surface flow may also be influenced depending upon the topography. While planning for water resource management, groundwater remediation or hydrological restoration it is imperative to understand and suitably include these influences to derive maximum benefit. This study aimed at characterization of surface as well as subsurface hydrological conditions in a hard-rock terrain, morphed under the influence of neotectonic activity, associated with tensional type of faulting. The area selected lies approximately between 28.20 - 28.60 N and 77.00 - 77.40 E, in vicinity of an active fault, with quartzitic rocks showing signs of multiple folding. Associated tear faults in adjoining areas have also been observed. To initially identify sites suitable for geophysical surveys, a spatial analysis involving seismic data and 3D visualization was done to identify the lineaments. The information thus obtained was correlated with geological information derived from hyperspectral satellite imagery. Geochemical analysis was also performed to verify the same. Influence of faulting activity on regulating water flow on surface as well as groundwater was studied. For surface water bodies hydrological analysis on elevation data (DEM) was performed whereas for subsurface recharge, margins of geological units were targeted. This was confirmed by actual field geophysical (resistivity) surveys at suitable strategic locations. The relative influences of structural lineaments on regulating subsurface water storage were also determined. The resulting database in GIS platform can also be used for flow modeling and aquifer potential / vulnerability studies. Also, the role of faulting

  15. Geodetic Network Design and Optimization on the Active Tuzla Fault (Izmir, Turkey) for Disaster Management

    PubMed Central

    Halicioglu, Kerem; Ozener, Haluk

    2008-01-01

    Both seismological and geodynamic research emphasize that the Aegean Region, which comprises the Hellenic Arc, the Greek mainland and Western Turkey is the most seismically active region in Western Eurasia. The convergence of the Eurasian and African lithospheric plates forces a westward motion on the Anatolian plate relative to the Eurasian one. Western Anatolia is a valuable laboratory for Earth Science research because of its complex geological structure. Izmir is a large city in Turkey with a population of about 2.5 million that is at great risk from big earthquakes. Unfortunately, previous geodynamics studies performed in this region are insufficient or cover large areas instead of specific faults. The Tuzla Fault, which is aligned trending NE–SW between the town of Menderes and Cape Doganbey, is an important fault in terms of seismic activity and its proximity to the city of Izmir. This study aims to perform a large scale investigation focusing on the Tuzla Fault and its vicinity for better understanding of the region's tectonics. In order to investigate the crustal deformation along the Tuzla Fault and Izmir Bay, a geodetic network has been designed and optimizations were performed. This paper suggests a schedule for a crustal deformation monitoring study which includes research on the tectonics of the region, network design and optimization strategies, theory and practice of processing. The study is also open for extension in terms of monitoring different types of fault characteristics. A one-dimensional fault model with two parameters – standard strike-slip model of dislocation theory in an elastic half-space – is formulated in order to determine which sites are suitable for the campaign based geodetic GPS measurements. Geodetic results can be used as a background data for disaster management systems.

  16. Numerical simulation of coastal flooding after potential reactivation of an active normal fault in northern Taiwan

    NASA Astrophysics Data System (ADS)

    Chan, Yu-Chang; Kuo, Chih-Yu; Chang, Kuo-Jen; Chen, Rou-Fei; Hsieh, Yu-Chung

    2016-04-01

    Rapid coastal flooding from seawards may be resulted from storm surge, tsunamis, and sudden land subsidence due to fault activities. Many observations and numerical modeling of flooding have been made for cases resulted from storm surge and tsunami events; however, coastal flooding caused by a potential normal faulting event nearby coastal areas is rarely reported. In addition to the earthquake hazards from fault rupturing and ground shaking, the accompanied hazards of earthquake-induced flooding is also important to be investigated. The Jinshan area in northern Taiwan was reported to have been flooded by a tsunami event in the year of 1867 possibly resulted from the reactivation of the Shanchiao normal fault offshore. Historical records have shown that the Shanchiao Fault that extends from Shulin along the western edge of the Taipei Basin to the town of Jinshan may have also ruptured in the year of 1694. The rupturing event has created a depression on the western side of the Taipei Basin that was later filled by sea water called the Taipei Lake. The geological conditions in northern Taiwan provide an opportunity for numerically simulating the dynamic processes of sea water flooding nearby the coastal area immediately after an earthquake-induced normal faulting event. In this study, we focused on the potential active normal faulting that may occur and result in an expected catastrophic flooding in lowland area of Jinshan in northern Taiwan. We applied the continuum shallow water equation to evaluate the unknown inundation processes including location, extent, velocity and water depths after the flooding initiated and the final state of the flooding event. The modeling results were well compared with borehole observations of the extent of previous flooding events possibly due to tsunami events. In addition, the modeling results may provide a future basis for safety evaluation of the two nuclear power plants nearby the region.

  17. Low Thrust Propulsion

    NASA Technical Reports Server (NTRS)

    1990-01-01

    This video presents an overview of low thrust rocket engine propulsion concepts for space missions. Chemical and electrical rocket engines are shown. Animation illustrates various propulsion applications.

  18. Measuring axial pump thrust

    DOEpatents

    Suchoza, B.P.; Becse, I.

    1988-11-08

    An apparatus for measuring the hydraulic axial thrust of a pump under operation conditions is disclosed. The axial thrust is determined by forcing the rotating impeller off of an associated thrust bearing by use of an elongate rod extending coaxially with the pump shaft. The elongate rod contacts an impeller retainer bolt where a bearing is provided. Suitable measuring devices measure when the rod moves to force the impeller off of the associated thrust bearing and the axial force exerted on the rod at that time. The elongate rod is preferably provided in a housing with a heat dissipation mechanism whereby the hot fluid does not affect the measuring devices. 1 fig.

  19. Measuring axial pump thrust

    DOEpatents

    Suchoza, Bernard P.; Becse, Imre

    1988-01-01

    An apparatus for measuring the hydraulic axial thrust of a pump under operation conditions is disclosed. The axial thrust is determined by forcing the rotating impeller off of an associated thrust bearing by use of an elongate rod extending coaxially with the pump shaft. The elongate rod contacts an impeller retainer bolt where a bearing is provided. Suitable measuring devices measure when the rod moves to force the impeller off of the associated thrust bearing and the axial force exerted on the rod at that time. The elongate rod is preferably provided in a housing with a heat dissipation mechanism whereby the hot fluid does not affect the measuring devices.

  20. Comparative study of two active faults in different stages of the earthquake cycle in central Japan -The Atera fault (with 1586 Tensho earthquake) and the Nojima fault (with 1995 Kobe earthquake)-

    NASA Astrophysics Data System (ADS)

    Matsuda, T.; Omura, K.; Ikeda, R.

    2003-12-01

    National Research Institute for Earth Science and Disaster Prevention (NIED) has been conducting _gFault zone drilling_h. Fault zone drilling is especially important in understanding the structure, composition, and physical properties of an active fault. In the Chubu district of central Japan, large active faults such as the Atotsugawa (with 1858 Hietsu earthquake) and the Atera (with 1586 Tensho earthquake) faults exist. After the occurrence of the 1995 Kobe earthquake, it has been widely recognized that direct measurements in fault zones by drilling. This time, we describe about the Atera fault and the Nojima fault. Because, these two faults are similar in geological situation (mostly composed of granitic rocks), so it is easy to do comparative study of drilling investigation. The features of the Atera fault, which have been dislocated by the 1586 Tensho earthquake, are as follows. Total length is about 70 km. That general trend is NW45 degree with a left-lateral strike slip. Slip rate is estimated as 3-5 m / 1000 years. Seismicity is very low at present and lithologies around the fault are basically granitic rocks and rhyolite. Six boreholes have been drilled from the depth of 400 m to 630 m. Four of these boreholes (Hatajiri, Fukuoka, Ueno and Kawaue) are located on a line crossing in a direction perpendicular to the Atera fault. In the Kawaue well, mostly fractured and alternating granitic rock continued from the surface to the bottom at 630 m. X-ray fluorescence analysis (XRF) is conducted to estimate the amount of major chemical elements using the glass bead method for core samples. The amounts of H20+ are about from 0.5 to 2.5 weight percent. This fractured zone is also characterized by the logging data such as low resistivity, low P-wave velocity, low density and high neutron porosity. The 1995 Kobe (Hyogo-ken Nanbu) earthquake occurred along the NE-SW-trending Rokko-Awaji fault system, and the Nojima fault appeared on the surface on Awaji Island when this

  1. Neogene deformation of thrust-top Rzeszów Basin (Outer Carpathians, Poland)

    NASA Astrophysics Data System (ADS)

    Uroda, Joanna

    2015-04-01

    The Rzeszów Basin is a 220 km2 basin located in the frontal part of Polish Outer Carpathians fold-and-thrust belt. Its sedimentary succession consist of ca. 600 m- thick Miocene evaporates, litoral and marine sediments. This basin developed between Babica-Kąkolówka anticline and frontal thrust of Carpathian Orogen. Rzeszów thrust-top basin is a part of Carpathian foreland basin system- wedge-top depozone. The sediments of wedge -top depozone were syntectonic deformed, what is valuable tool to understand kinematic history of the orogen. Analysis of field and 3D seismic reflection data showed the internal structure of the basin. Seismic data reveal the presence of fault-bend-folds in the basement of Rzeszów basin. The architecture of the basin - the presence of fault-releated folds - suggest that the sediments were deformed in last compressing phase of Carpathian Orogen deformation. Evolution of Rzeszów Basin is compared with Bonini et.al. (1999) model of thrust-top basin whose development is controlled by the kinematics of two competing thrust anticlines. Analysis of seismic and well data in Rzeszów basin suggest that growth sediments are thicker in south part of the basin. During the thrusting the passive rotation of the internal thrust had taken place, what influence the basin fill architecture and depocentre migration opposite to thrust propagation. Acknowledgments This study was supported by grant No 2012/07/N/ST10/03221 of the Polish National Centre of Science "Tectonic activity of the Skole Nappe based on analysis of changes in the vertical profile and depocentre migration of Neogene sediments in Rzeszów-Strzyżów area (Outer Carpathians)". Seismic data by courtesy of the Polish Gas and Oil Company. References Bonini M., Moratti G., Sani F., 1999, Evolution and depocentre migration in thrust-top basins: inferences from the Messinian Velona Basin (Northern Apennines, Italy), Tectonophysics 304, 95-108.

  2. Co-seismic ruptures of the 12 May 2008, Ms 8.0 Wenchuan earthquake, Sichuan: East-west crustal shortening on oblique, parallel thrusts along the eastern edge of Tibet

    USGS Publications Warehouse

    Liu-Zeng, J.; Zhang, Z.; Wen, L.; Tapponnier, P.; Sun, Jielun; Xing, X.; Hu, G.; Xu, Q.; Zeng, L.; Ding, L.; Ji, C.; Hudnut, K.W.; van der Woerd, J.

    2009-01-01

    The Ms 8.0, Wenchuan earthquake, which devastated the mountainous western rim of the Sichuan basin in central China, produced a surface rupture over 200??km-long with oblique thrust/dextral slip and maximum scarp heights of ~ 10??m. It thus ranks as one of the world's largest continental mega-thrust events in the last 150??yrs. Field investigation shows clear surface breaks along two of the main branches of the NE-trending Longmen Shan thrust fault system. The principal rupture, on the NW-dipping Beichuan fault, displays nearly equal amounts of thrust and right-lateral slip. Basin-ward of this rupture, another continuous surface break is observed for over 70??km on the parallel, more shallowly NW-dipping Pengguan fault. Slip on this latter fault was pure thrusting, with a maximum scarp height of ~ 3.5??m. This is one of the very few reported instances of crustal-scale co-seismic slip partitioning on parallel thrusts. This out-of-sequence event, with distributed surface breaks on crustal mega-thrusts, highlights regional, ~ EW-directed, present day crustal shortening oblique to the Longmen Shan margin of Tibet. The long rupture and large offsets with strong horizontal shortening that characterize the Wenchuan earthquake herald a re-evaluation of tectonic models anticipating little or no active shortening of the upper crust along this edge of the plateau, and require a re-assessment of seismic hazard along potentially under-rated active faults across the densely populated western Sichuan basin and mountains. ?? 2009 Elsevier B.V.

  3. Multibeam study of the Flores Backarc Thrust Belt, Indonesia

    NASA Astrophysics Data System (ADS)

    Silver, Eli A.; Breen, Nancy A.; Prasetyo, Hardi; Hussong, Donald M.

    1986-03-01

    Using the SeaMARC II seafloor mapping tool in conjunction with closely spaced seismic reflection profiles, we have mapped a segment of the Flores back arc thrust zone. Structural irregularities along the deformation front of the thrust zone result from changing stratigraphy and basement structure of the lower plate. NE trending faults cutting the outer slope of the Flores basin are easily mapped because they truncate dense drainage patterns obliquely. Mud diapirs, probably indicating elevated fluid pressures, have formed throughout the accretionary wedge but appear to be concentrated (as do back arc thrust earthquakes) at the ends of thrust faults. The overall orientation of the deformation front of the accretionary wedge is 100°, suggesting a NNE sense of thrust motion and supporting an origin of the thrust zone by collision of the arc with Australia rather than by magmatic forcing or gravitational sliding or spreading. Orientations of faults and folds close to the arc are not consistent with the trends of the frontal thrusts, however, and the difference may be due to either different initial orientations or to later rotations of structural features as the accretionary wedge grew.

  4. Recent Fault Activity in the 1886 Charleston, South Carolina Earthquake Epicentral Area and its Relation to Buried Structures

    NASA Astrophysics Data System (ADS)

    Pratt, T. L.; Shah, A. K.; Horton, J. W., Jr.; Chapman, M. C.; Beale, J.

    2014-12-01

    The 1886 Charleston, SC earthquake (M6.8-7.3) is the largest recorded earthquake to strike the U.S. east of the Appalachian Mountains. It occurred along the U.S. passive margin within an area of extensive Mesozoic rifting and beneath the ~800-m thick, subhorizontal Atlantic Coastal Plain (ACP) strata. The fault(s) that caused the 1886 earthquake remain the subject of debate. We examine reprocessed seismic reflection data in the epicentral area to discern faults cutting the Cretaceous and Cenozoic ACP strata, and relate them to deeper structures revealed by the seismic profiles and filtered aeromagnetic data. Faults are identified on the seismic profiles by sharp vertical displacements of strata, abrupt but small changes in dip, and folding of the ACP strata. Some of these faults dip steeply and locally displace deeper reflectors within the underlying South Georgia rift basin with minor displacement; in places they bound uplifted blocks of ACP strata. These observations and the lack of surface scarps during the 1886 earthquake suggest a component of strike-slip for the Cretaceous and Cenozoic displacements, whereas some modern focal mechanisms show thrust motion. A prominent magnetic anomaly high shows a NE-trending west edge in the epicentral area, and short-wavelength magnetic anomalies show disruptions aligned along NE trends. These latter disruptions appear to be related to the seismically imaged faults that offset ACP strata. One of the faults, previously interpreted by Chapman and Beale (2010), shows folding and perhaps faulting of ACP strata with ~50 m vertical displacement and is aligned along the NW edge of the magnetic high. The vertical uplift is nearly equal through the ACP section with little or no upward decrease across the fault, indicating the motion is primarily Cenozoic. The fault lies near Summerville about 35 km NW of Charleston, where 1886 ground deformation was focused. Another NE-trending fault, crossing beneath the Ashley River ~15 km NW of

  5. Analysis of microseismic activity detected by the WIZARD array, Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Feenstra, J. P.; Roecker, S. W.; Thurber, C. H.; Lord, N.; O'Brien, G.; Pesicek, J. D.; Townend, J.; Bannister, S. C.

    2012-12-01

    A primary goal for the UW-Madison-RPI WIZARD array is the characterization of background seismicity around the Deep Fault Drilling Project (DFDP) site on the Alpine Fault, South Island, New Zealand. The WIZARD array consists of 20 stations, half broadband, deployed for a planned 2-year period around the Whataroa Valley DFDP-2 drill site. Two neighboring arrays, SAMBA (Victoria University of Wellington) to the southwest and ALFA'12 (GNS Science) to the northeast, along with several GeoNet permanent stations, provide broad coverage of the region. The earthquakes that are detected will (1) help to define the geometry of the Alpine Fault and other active faults at depth, (2) provide data for seismic imaging, focal mechanisms, and shear-wave splitting analysis, and (3) enable the assessment of possible changes in seismic activity induced by future fault zone drilling. We are currently analyzing data from the first 2 months of the deployment. Dozens of nearby earthquakes (S-P time of up to a few seconds) have been detected, far more than are in the New Zealand GeoNET catalog. This is expected because the magnitude completion level of the GeoNet seismometer network is around 2.5 in the Whataroa region, due to a relatively sparse station coverage. In this presentation, we report on earthquake location results for 8 months of WIZARD data, along with focal mechanisms for selected larger events.

  6. Crossing Active Faults on the Sakhalin II Onshore Pipeline Route: Analysis Methodology and Basic Design

    SciTech Connect

    Vitali, Luigino; Mattiozzi, Pierpaolo

    2008-07-08

    Twin oil (20 and 24 inch) and gas (20 and 48 inch) pipeline systems stretching 800 km are being constructed to connect offshore hydrocarbon deposits from the Sakhalin II concession in the North to an LNG plant and oil export terminal in the South of Sakhalin island. The onshore pipeline route follows a regional fault zone and crosses individual active faults at 19 locations. Sakhalin Energy, Design and Construction companies took significant care to ensure the integrity of the pipelines, should large seismic induced ground movements occur during the Operational life of the facilities. Complex investigations including the identification of the active faults, their precise location, their particular displacement values and assessment of the fault kinematics were carried out to provide input data for unique design solutions. Lateral and reverse offset displacements of 5.5 and 4.5 m respectively were determined as the single-event values for the design level earthquake (DLE)--the 1000-year return period event. Within the constraints of a pipeline route largely fixed, the underground pipeline fault crossing design was developed to define the optimum routing which would minimize stresses and strain using linepipe materials which had been ordered prior to the completion of detailed design, and to specify requirements for pipe trenching shape, materials, drainage system, etc. This Paper describes the steps followed to formulate the concept of the special trenches and the analytical characteristics of the Model.

  7. Crossing Active Faults on the Sakhalin II Onshore Pipeline Route: Pipeline Design and Risk Analysis

    SciTech Connect

    Mattiozzi, Pierpaolo; Strom, Alexander

    2008-07-08

    Twin oil (20 and 24 inch) and gas (20 and 48 inch) pipeline systems stretching 800 km are being constructed to connect offshore hydrocarbon deposits from the Sakhalin II concession in the North to an LNG plant and oil export terminal in the South of Sakhalin island. The onshore pipeline route follows a regional fault zone and crosses individual active faults at 19 locations. Sakhalin Energy, Design and Construction companies took significant care to ensure the integrity of the pipelines, should large seismic induced ground movements occur during the Operational life of the facilities. Complex investigations including the identification of the active faults, their precise location, their particular displacement values and assessment of the fault kinematics were carried out to provide input data for unique design solutions. Lateral and reverse offset displacements of 5.5 and 4.5 m respectively were determined as the single-event values for the design level earthquake (DLE) - the 1000-year return period event. Within the constraints of a pipeline route largely fixed, the underground pipeline fault crossing design was developed to define the optimum routing which would minimize stresses and strain using linepipe materials which had been ordered prior to the completion of detailed design, and to specify requirements for pipe trenching shape, materials, drainage system, etc. Detailed Design was performed with due regard to actual topography and to avoid the possibility of the trenches freezing in winter, the implementation of specific drainage solutions and thermal protection measures.

  8. Crossing Active Faults on the Sakhalin II Onshore Pipeline Route: Analysis Methodology and Basic Design

    NASA Astrophysics Data System (ADS)

    Vitali, Luigino; Mattiozzi, Pierpaolo

    2008-07-01

    Twin oil (20 & 24 inch) and gas (20 & 48 inch) pipeline systems stretching 800 km are being constructed to connect offshore hydrocarbon deposits from the Sakhalin II concession in the North to an LNG plant and oil export terminal in the South of Sakhalin island. The onshore pipeline route follows a regional fault zone and crosses individual active faults at 19 locations. Sakhalin Energy, Design and Construction companies took significant care to ensure the integrity of the pipelines, should large seismic induced ground movements occur during the Operational life of the facilities. Complex investigations including the identification of the active faults, their precise location, their particular displacement values and assessment of the fault kinematics were carried out to provide input data for unique design solutions. Lateral and reverse offset displacements of 5.5 and 4.5 m respectively were determined as the single-event values for the design level earthquake (DLE)—the 1000-year return period event. Within the constraints of a pipeline route largely fixed, the underground pipeline fault crossing design was developed to define the optimum routing which would minimize stresses and strain using linepipe materials which had been ordered prior to the completion of detailed design, and to specify requirements for pipe trenching shape, materials, drainage system, etc. This Paper describes the steps followed to formulate the concept of the special trenches and the analytical characteristics of the Model.

  9. Crossing Active Faults on the Sakhalin II Onshore Pipeline Route: Pipeline Design and Risk Analysis

    NASA Astrophysics Data System (ADS)

    Mattiozzi, Pierpaolo; Strom, Alexander

    2008-07-01

    Twin oil (20 & 24 inch) and gas (20 & 48 inch) pipeline systems stretching 800 km are being constructed to connect offshore hydrocarbon deposits from the Sakhalin II concession in the North to an LNG plant and oil export terminal in the South of Sakhalin island. The onshore pipeline route follows a regional fault zone and crosses individual active faults at 19 locations. Sakhalin Energy, Design and Construction companies took significant care to ensure the integrity of the pipelines, should large seismic induced ground movements occur during the Operational life of the facilities. Complex investigations including the identification of the active faults, their precise location, their particular displacement values and assessment of the fault kinematics were carried out to provide input data for unique design solutions. Lateral and reverse offset displacements of 5.5 and 4.5 m respectively were determined as the single-event values for the design level earthquake (DLE)—the 1000-year return period event. Within the constraints of a pipeline route largely fixed, the underground pipeline fault crossing design was developed to define the optimum routing which would minimize stresses and strain using linepipe materials which had been ordered prior to the completion of detailed design, and to specify requirements for pipe trenching shape, materials, drainage system, etc. Detailed Design was performed with due regard to actual topography and to avoid the possibility of the trenches freezing in winter, the implementation of specific drainage solutions and thermal protection measures.

  10. Deformation and fluid flow of a major out-of-sequence thrust located at seismogenic depth in an accretionary complex: Nobeoka Thrust in the Shimanto Belt, Kyushu, Japan

    NASA Astrophysics Data System (ADS)

    Kondo, Hideki; Kimura, Gaku; Masago, Hideki; Ohmori-Ikehara, Kotoe; Kitamura, Yujin; Ikesawa, Eisei; Sakaguchi, Arito; Yamaguchi, Asuka; Okamoto, Shin'ya

    2005-12-01

    Nobeoka Thrust in Kyushu, southwest Japan, was investigated to understand the relationship between the seismogenic out-of-sequence thrust (OST) and fluid flow in accretionary prisms. The Nobeoka Thrust is a fossilized OST, being active at seismogenic depth. The hanging wall exhibits a penetrative plastic deformation, while a brittle, cataclastic mélange-like occurrence characterizes the footwall, although both of them have same shale and sandstone-dominant protolith. Vitrinite reflectance analyses indicate that the maximum temperatures of the hanging wall and footwall are approximately 320 and 250°C, respectively. This thermal gap across the thrust corresponds to 8.6-14.4 km of displacement assuming a 28-47°C/km geothermal gradient. The brittle damage zone of the thrust is asymmetric: only 2 m for hanging wall side and 100 m for footwall. Three types of mineral veins, quartz, and carbonate are well developed, especially in the damaged footwall: the tension crack-filling vein, the fault-filling vein, and postmélange one. The first is harmonious with fabric, perpendicular to the P surface. Fluid inclusion geothermobarometry indicates the P-T of fluid in the intensively damaged zone of the footwall is ˜300°C, 230-250 MPa, higher than that from vitrinite reflectance, which suggests that hydrothermal fluid flow is associated with deformation. The same type vein in the lowest portion of the footwall-damaged zone includes a much lower P-T fluid. This difference suggests that continuous underplating caused the damaged zone to propagate downward with cooling and shallowing, which differs from faults characterized by shear localization and might be unique to aquiferous OST in accretionary complexes.

  11. Paleoseismic and geomorphologic evidence of recent tectonic activity of the Pozohondo Fault (Betic Cordillera, SE Spain)

    USGS Publications Warehouse

    Rodríguez-Pascua, M.A.; Pérez-López, R.; Garduño-Monroy, V.H.; Giner-Robles, J.L.; Silva, P.G.; Perucha-Atienza, M.A.; Hernández-Madrigal, V.M.; Bischoff, J.

    2012-01-01

    Instrumental and historical seismicity in the Albacete province (External Prebetic Zone) has been scarcely recorded. However, major strike-slip faults showing NW-SE trending provide geomorphologic and paleoseismic evidence of recent tectonic activity (Late Pleistocene to Present). Moreover, these faults are consistently well oriented under the present stress tensor and therefore, they can trigger earthquakes of magnitude greater than M6, according to the lengths of surface ruptures and active segments recognized in fieldwork. Present landscape nearby the village of Hellin (SE of Albacete) is determined by the recent activity of the Pozohondo Fault (FPH), a NW-SE right-lateral fault with 90 km in length. In this study, we have calculated the Late Quaternary tectonic sliprate of the FPH from geomorphological, sedimentological, archaeoseimological, and paleoseismological approaches. All of these data suggest that the FPH runs with a minimum slip-rate of 0.1 mm/yr during the last 100 kyrs (Upper Pleistocene-Holocene). In addition, we have recognized the last two major paleoearthquakes associated to this fault. Magnitudes of these paleoearthquakes were gretarer than M6 and their recurrence intervals ranged from 6600 to 8600 yrs for the seismic cycle of FPH. The last earthquake was dated between the 1st and 6th centuries, though two earthquakes could be interpreted in this wide time interval, one at the FPH and other from a far field source. Results obtained here, suggest an increasing of the tectonic activity of the Pozohondo Fault during the last 10,000 yrs.

  12. The Trans-Atlantic Geotraverse hydrothermal field: A hydrothermal system on an active detachment fault

    NASA Astrophysics Data System (ADS)

    Humphris, Susan E.; Tivey, Margaret K.; Tivey, Maurice A.

    2015-11-01

    Over the last ten years, geophysical studies have revealed that the Trans-Atlantic Geotraverse (TAG) hydrothermal field (26°08‧N on the Mid-Atlantic Ridge) is located on the hanging wall of an active detachment fault. This is particularly important in light of the recognition that detachment faulting accounts for crustal accretion/extension along a significant portion of the Mid-Atlantic Ridge, and that the majority of confirmed vent sites on this slow-spreading ridge are hosted on detachment faults. The TAG hydrothermal field is one of the largest sites of high-temperature hydrothermal activity and mineralization found to date on the seafloor, and is comprised of active and relict deposits in different stages of evolution. The episodic nature of hydrothermal activity over the last 140 ka provides strong evidence that the complex shape and geological structure of the active detachment fault system exerts first order, but poorly understood, influences on the hydrothermal circulation patterns, fluid chemistry, and mineral deposition. While hydrothermal circulation extracts heat from a deep source region, the location of the source region at TAG is unknown. Hydrothermal upflow is likely focused along the relatively permeable detachment fault interface at depth, and then the high temperature fluids leave the low-angle portion of the detachment fault and rise vertically through the highly fissured hanging wall to the seafloor. The presence of abundant anhydrite in the cone on the summit of the TAG active mound and in veins in the crust beneath provides evidence for a fluid circulation system that entrains significant amounts of seawater into the shallow parts of the mound and stockwork. Given the importance of detachment faulting for crustal extension at slow spreading ridges, the fundamental question that still needs to be addressed is: How do detachment fault systems, and the structure at depth associated with these systems (e.g., presence of plutons and/or high

  13. Coseismic and Early Post-Seismic Slip Distributions of the 2012 Emilia (Northern Italy) Seismic Sequence: New Insights in the Faults Activation and Resulting Stress Changes on Adjacent Faults

    NASA Astrophysics Data System (ADS)

    Cheloni, D.; Giuliani, R.; D'Agostino, N.; Mattone, M.; Bonano, M.; Fornaro, G.; Lanari, R.; Reale, D.

    2015-12-01

    The 2012 Emilia sequence (main shocks Mw 6.1 May 20 and Mw 5.9 May 29) ruptured two thrust segments of a ~E-W trending fault system of the buried Ferrara Arc, along a portion of the compressional system of the Apennines that had remained silent during past centuries. Here we use the rupture geometry constrained by the aftershocks and new geodetic data (levelling, InSAR and GPS measurements) to estimate an improved coseismic slip distribution of the two main events. In addition, we use post-seismic displacements, described and analyzed here for the first time, to infer a brand new post-seismic slip distribution of the May 29 event in terms of afterslip on the same coseismic plane. In particular, in this study we use a catalog of precisely relocated aftershocks to explore the different proposed geometries of the proposed thrust segments that have been published so far and estimate the coseismic and post-seismic slip distributions of the ruptured planes responsible for the two main seismic events from a joint inversion of the geodetic data.Joint inversion results revealed that the two earthquakes ruptured two distinct planar thrust faults, characterized by single main coseismic patches located around the centre of the rupture planes, in agreement with the seismological and geological information pointing out the Ferrara and the Mirandola thrust faults, as the causative structures of the May 20 and May 29 main shocks respectively.The preferred post-seismic slip distribution related to the 29 May event, yielded to a main patch of afterslip (equivalent to a Mw 5.6 event) located westward and up-dip of the main coseismic patch, suggesting that afterslip was triggered at the edges of the coseismic asperity. We then use these co- and post-seismic slip distribution models to calculate the stress changes on adjacent fault.

  14. Distribution of deformation on an active normal fault network, NW Corinth Rift

    NASA Astrophysics Data System (ADS)

    Ford, Mary; Meyer, Nicolas; Boiselet, Aurélien; Lambotte, Sophie; Scotti, Oona; Lyon-Caen, Hélène; Briole, Pierre