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Sample records for active thrust faults

  1. Erosion influences the seismicity of active thrust faults.

    PubMed

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

    2014-01-01

    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. PMID:25412707

  2. Erosion influence the seismicity of active thrust faults

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Assessing seismic hazards remains one of the most challenging scientific issue 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 with 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 to 20 mm/yr, as documented in Taiwan and in other active compressional orogens, can raise the Coulomb stress by ~0.1 to ~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 promote the rupture of deep continental earthquakes up to the surface or to trigger shallow seismicity. We illustrate this last point by identifying seismic events in Taiwan, by the mean of a coupled statistical and mechanical approach, that were induced by intense erosional events.

  3. Erosion influence the seismicity of active thrust faults

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    Assessing seismic hazards remains one of the most challenging scientific issue 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 with 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 to 20 mm/yr, as documented in Taiwan and in other active compressional orogens, can raise the Coulomb stress by ˜0.1 to ˜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 promote the rupture of deep continental earthquakes up to the surface or to trigger shallow seismicity. We illustrate this last point by identifying seismic events in Taiwan, by the mean of a coupled statistical and mechanical approach, that were induced by intense erosional events.

  4. 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.

  5. Earthquake hazards of active blind-thrust faults under the central Los Angeles basin, California

    NASA Astrophysics Data System (ADS)

    Shaw, John H.; Suppe, John

    1996-04-01

    We document several blind-thrust faults under the Los Angeles basin that, if active and seismogenic, are capable of generating large earthquakes (M = 6.3 to 7.3). Pliocene to Quaternary growth folds imaged in seismic reflection profiles record the existence, size, and slip rates of these blind faults. The growth structures have shapes characteristic of fault-bend folds above blind thrusts, as demonstrated by balanced kinematic models, geologic cross sections, and axial-surface maps. We interpret the Compton-Los Alamitos trend as a growth fold above the Compton ramp, which extends along strike from west Los Angeles to at least the Santa Ana River. The Compton thrust is part of a larger fault system, including a decollement and ramps beneath the Elysian Park and Palos Verdes trends. The Cienegas and Coyote Hills growth folds overlie additional blind thrusts in the Elysian Park trend that are not closely linked to the Compton ramp. Analysis of folded Pliocene to Quaternary strata yields slip rates of 1.4 ± 0.4 mm/yr on the Compton thrust and 1.7 ± 0.4 mm/yr on a ramp beneath the Elysian Park trend. Assuming that slip is released in large earthquakes, we estimate magnitudes of 6.3 to 6.8 for earthquakes on individual ramp segments based on geometric segment sizes derived from axial surface maps. Multiple-segment ruptures could yield larger earthquakes (M = 6.9 to 7.3). Relations among magnitude, coseismic displacement, and slip rate yield an average recurrence interval of 380 years for single-segment earthquakes and a range of 400 to 1300 years for multiple-segment events. If these newly documented blind thrust faults are active, they will contribute substantially to the seismic hazards in Los Angeles because of their locations directly beneath the metropolitan area.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

    Blakely, Richard J.; Sherrod, Brian L.; Weaver, Craig S.; Wells, Ray E.; Rohay, Alan C.; Barnett, Elizabeth A.; Knepprath, Nichole E.

    2011-07-01

    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.

  8. 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

  9. Active Faulting and Pore-Fluid Pressure in the Taiwan Thrust Belt

    NASA Astrophysics Data System (ADS)

    Yue, L.; Suppe, J.

    2004-12-01

    compaction trend shown by sonic log data using standard petroleum techniques that show the magnitude of uplift and erosion and the fossil and present pore-fluid pressures. The fossil top of the overpressured zone in several wells drilled through major thrusts and eroded anticlines is at a substantially higher (~1-2 km) stratigraphic level than the present top of fluid pressures, but never reaches the level of the Pliocene Chinshui Shale. It implies uplift and erosion of the active fold-and-thrust belt causes a major drop in fluid pressures in the formerly overpressured zone. Finally, a preliminary estimate of Hubbert-Rubey fluid pressure ratio needed to slide the Chelungpu thrust sheet (and also the Changhua thrust) using normal Byerlee's Law friction is about 0.8 (which is higher than any observed fluid pressures even within the deeper overpressured zone). Therefore the Hubbert and Rubey mechanism of static excess fluid pressure does not appear to be important for major thrusts such as the Chelungpu thrust that slipped in the Chi-Chi earthquake. The many other proposed non-Hubbert-Rubey mechanisms of reduction of fault strength should be considered, including dynamical mechanisms, fluid-pressure transients and non Byerlee coefficients of friction.

  10. The chi-Chi earthquake sequence: active, out-of-sequence thrust faulting in taiwan

    PubMed

    Kao; Chen

    2000-06-30

    We combined precise focal depths and fault plane solutions of more than 40 events from the 20 September 1999 Chi-Chi earthquake sequence with a synthesis of subsurface geology to show that the dominant structure for generating earthquakes in central Taiwan is a moderately dipping (20 degrees to 30 degrees ) thrust fault away from the deformation front. A second, subparallel seismic zone lies about 15 kilometers below the main thrust. These seismic zones differ from previous models, indicating that both the basal decollement and relic normal faults are aseismic. PMID:10875915

  11. 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

  12. An active footwall shortcut thrust revealed by seismic reflection profiling: a case study of the Futaba fault, northern Honshu, Japan

    NASA Astrophysics Data System (ADS)

    Sato, Hiroshi; Ishiyama, Tatsuya; Kato, Naoko; Higashinaka, Motonori; Kurashimo, Eiji; Iwasaki, Takaya; Abe, Susumu

    2013-04-01

    The Futaba fault is located along the Pacific cast of southern part of Northern Honshu and continues at least 100 km. Based on tectonic morphological research, its central part show the active tectonic features. Due to the effect of M9 Tohoku Oki earthquake 2011, the evaluation of Coulomb stress changes on the fault surface is concerned for the assess of seismic hazards. To investigate the deep geometry of seismogenic source fault and basic crustal structure, we performed deep seismic reflection profiling along the 58-km-long seismic line across the Futaba fault. The seismic data were obtained using four vibroseis trucks and 1164 channel recorders. The seismic section portrays the half graben filled by 1000-m-thick lower Miocene fluvial sediments, suggesting that the Futaba fault reactivated as a west dipping normal fault during the early Miocene associated with opening of the Sea of Japan. On the hanging wall of the Miocene normal fault, Mesozoic metamorphic rocks are cropping out forming a narrow range parallel to the fault. On the footwall of this range, footwall shortcut thrust is clearly identified by the deformation of Plio-Pleistocene sediments on the seismic section. The deeper extension of the Futaba fault can be traced down to 4.5 seconds (TWT) and sub-horizontal reflectors are developed around 6-7 seconds (TWT). The dip angle of the Futaba fault in the seismogenic zone is about 45 degrees. The footwall shortcut thrust was formed at the shallow high-angle part of the Futaba fault as a low-angle (30 degrees) reverse fault. The formation of half graben is limited along the northern part of this fault system. The footwall shortcut thrust was developed along a 40-km-long segment only accompanied with the Miocene half graben. The southern segment of the surface trace of the Futaba fault suggests a straight geometry may represent a change in dip angle.

  13. Active thrust faulting offshore Boumerdes, Algeria, and its relations to the 2003 Mw 6.9 earthquake

    NASA Astrophysics Data System (ADS)

    Déverchère, J.; Yelles, K.; Domzig, A.; Mercier de Lépinay, B.; Bouillin, J.-P.; Gaullier, V.; Bracène, R.; Calais, E.; Savoye, B.; Kherroubi, A.; Le Roy, P.; Pauc, H.; Dan, G.

    2005-02-01

    We investigate the active seismogenic fault system in the area of the 2003 Mw 6.9 Boumerdes earthquake, Algeria, from a high-resolution swath bathymetry and seismic survey. A series of 5 main fault-propagation folds ~20-35 km long leave prominent cumulative escarpments on the steep slope and in the deep basin. Fault activity creates Plio-Quaternary growth strata within uplifted areas such as a rollover basin on the slope and piggyback basins in the deep ocean. Most thrusts turn to fault-propagation folds at the sub-surface and depict ramp-flat trajectories. We find that the two main slip patches of the 2003 Mw 6.9 Boumerdes earthquake are spatially correlated to two segmented cumulative scarps recognized on the slope and at the foot of the margin. The overall geometry indicates the predominance of back thrusts implying underthrusting of the Neogene oceanic crust.

  14. Weakening inside incipient thrust fault

    NASA Astrophysics Data System (ADS)

    Lacroix, B.; Tesei, T.; Collettini, C.; Oliot, E.

    2013-12-01

    In fold-and-thrust belts, shortening is mainly accommodated by thrust faults that nucleate along décollement levels. Geological and geophysical evidence suggests that these faults might be weak because of a combination of processes such as pressure-solution, phyllosilicates reorientation and delamination, and fluid pressurization. In this study we aim to decipher the processes and the kinetics responsible for weakening of tectonic décollements. We studied the Millaris thrust (Southern Pyrenees): a fault representative of a décollement in its incipient stage. This fault accommodated a total shortening of about 30 meters and is constituted by a 10m thick, intensively foliated phyllonite developed inside a homogeneous marly unit. Detailed chemical and mineralogical analyses have been carried out to characterize the mineralogical change, the chemical transfers and volume change in the fault zone compared to non-deformed parent sediments. We also carried out microstructural analysis on natural and experimentally deformed rocks. Illite and chlorite are the main hydrous minerals. Inside fault zone, illite minerals are oriented along the schistosity whereas chlorite coats the shear surfaces. Mass balance calculations demonstrated a volume loss of up to 50% for calcite inside fault zone (and therefore a relative increase of phyllosilicates contents) because of calcite pressure solution mechanisms. We performed friction experiments in a biaxial deformation apparatus using intact rocks sheared in the in-situ geometry from the Millaris fault and its host sediments. We imposed a range of normal stresses (10 to 50 MPa), sliding velocity steps (3-100 μm/s) and slide-hold slide sequences (3 to 1000 s hold) under saturated conditions. Mechanical results demonstrate that both fault rocks and parent sediments are weaker than average geological materials (friction μ<<0.6) and have velocity-strengthening behavior because of the presence of phyllosilicate horizons. Fault rocks are

  15. Active Fault Mapping of Naga-Disang Thrust (Belt of Schuppen) for Assessing Future Earthquake Hazards in NE India

    NASA Astrophysics Data System (ADS)

    Kumar, A.

    2014-12-01

    We observe the geodynamic appraisal of Naga-Disang Thrust North East India. The Disang thrust extends NE-SW over a length of 480 km and it defines the eastern margin of Neogene basin. It branches out from Haflong-Naga thrust and in the NE at Bulbulia in the right bank of Noa Dihing River, it is terminated by Mishmi thrust, which extends into Myanmar as 'Sagaing fault,which dip generally towards SE. It extends between Dauki fault in the SW and Mishmi thrust in the NE. When the SW end of 'Belt of Schuppen' moved upwards and towards east along the Dauki fault, the NE end moved downwards and towards west along the Mishmi thrust, causing its 'S' shaped bending. The SRTM generated DEM is used to map the topographic expression of the schuppen belt, where these thrusts are significantly marked by topographic break. Satellite imagery map also shows presence lineaments supporting the post tectonic activities along Naga-Disang Thrusts. The southern part of 'Belt of Schuppen' extends along the sheared western limb of southerly plunging Kohima synform, a part of Indo Burma Ranges (IBR) and it is seismically active.The crustal velocity at SE of Schuppen is 39.90 mm/yr with a azimuth of 70.780 at Lumami, 38.84 mm/yr (Azimuth 54.09) at Senapati and 36.85 mm/yr (Azimuth 54.09) at Imphal. The crustal velocity at NW of Schuppen belt is 52.67 mm/yr (Azimuth 57.66) near Dhauki Fault in Meghalaya. It becomes 43.60 mm/yr (Azimuth76.50) - 44.25 (Azimuth 73.27) at Tiding and Kamlang Nagar around Mishmi thrust. The presence of Schuppen is marked by a change in high crustal velocity from Indian plate to low crustal velocity in Mishmi Suture as well as Indo Burma Ranges. The difference in crustal velocities results in building up of strain along the Schuppen which may trigger a large earthquake in the NE India in future. The belt of schuppean seems to be seismically active, however, the enough number of large earthquakes are not recorded. These observations are significant on Naga

  16. Fault Geometry and Kinematics of the Main Frontal Thrust in Central Nepal Constrained With Active Source Seismic Data

    NASA Astrophysics Data System (ADS)

    Almeida, R. V.; Foster, A. E.; Hubbard, J.; Liberty, L. M.; Sapkota, S. N.

    2015-12-01

    The foreland thrust belt of the Himalayan orogen has been active since at least 2 Ma, deforming the Siwaliks Group, a 5-6 km thick section of continental Miocene-Pliocene strata. This terrane is bounded by the Main Boundary Thrust to the north and by the Main Frontal Thrust (MFT) to the south. For a long time, the MFT was long considered a blind system; only recently have surface exposures been identified, tied to large historical earthquakes. In many maps, the MFT is drawn as a single, continuous fault. However, it is actually composed of many fault segments, with overlaps and steps, whose timing and structural linkage are poorly constrained. This complex fault system represents the frontal portion of the large, active megathrust that is accommodating the India-Eurasia collision. We present some of the first seismic reflection profiles ever acquired across these thrusts. These profiles were acquired with a 7 ton Vibroseis source and a 264 channel seismic recording system over three field seasons in 2014 and 2015. As part of our study, we acquired 12 serial 2D profiles totalling ~70 km across a right-step of the fault system, where both fault segments have been identified as having slipped in the1934 Mw8.4 Nepal-Bihar earthquake. Our data image to a depth of 2-2.5 km and constrain the geometries and kinematics of these overlapping faults, with associated folding. Our data show that the faults are listric, that they overlap for over 10 (?) km along strike and produce short wavelength (~1 km) fault-propagation folds and longer wavelength fault-bend folds. Fault slip in this area has led to the progressive uplift and abandonment of strath terraces. Our new data will allow us to constrain the dips and kinematics of the different fault segments in order to convert uplift rates into slip rates on the fault segments, to more accurately assess the rate of shortening on the MFT in central Nepal.

  17. Late Holocene activity and historical earthquakes of the Qiongxi thrust fault system in the southern Longmen Shan fold-and-thrust belt, eastern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Wang, Maomao; Jia, Dong; Lin, Aiming; Shen, Li; Rao, Gang; Li, Yiquan

    2013-01-01

    The 12 May 2008 Wenchuan earthquake (Mw 7.9) generated a 285-km-long surface rupture zone along the Longmen Shan fold-and-thrust belt (LSFTB) on the eastern margin of Tibetan Plateau. The Wenchuan earthquake did not rupture into the southwestern Longmen Shan, along which there is no evidence for large paleo- or historical earthquakes. Seismic reflection profiles and field investigations reveal that the 50-km-long Qiongxi thrust fault (QTF) of the southern LSFTB is currently active. The QTF consists of three west-dipping ramp segments overlain by fault-bend folds rooted in a regional detachment that transfers shortening from the mountain belt into the Sichuan basin. Trench investigations, coupled with interpretations of seismic reflection profiles and radiocarbon results, show that a recent surface-rupturing earthquake occurred on the QTF during the Late Ming to Qing Dynasty, between AD 1600 and 1800. In addition, seismic reflection profile and topographic analysis indicate the presence of a subtle topographic, produced by kink-band migration folding above a fault bend at about 5 km depth. These findings confirm that the QTF is a significant seismic hazard, and that it should be incorporated into current regional seismic hazard models for the densely populated Sichuan basin.

  18. Recognizing thrust faults on remote sensing images

    SciTech Connect

    Prost, G.L. )

    1990-09-01

    This article examines the geomorphic evidence for thrusting and compares it to the expression of other faults and unconformities on remote sensing images. No single feature identifies thrusting, but rather the coincidence of several factors builds a case for a thrust interpretation. An example from Pakistan illustrates the geomorphic criteria in an area with excellent exposures and classic thrust features. The structure interpretation is supported by construction of cross sections; together these are used to suggest areas of exploration interest.

  19. Geological and geophysical evidences of late Quaternary activity of the range-front fault along the mid-segment of the Longmen Shan thrust belt

    NASA Astrophysics Data System (ADS)

    Ren, J.; Xu, X.; Sun, X.; Tan, X.; Li, K.; Kang, W.; Liu, B.

    2011-12-01

    The Longmen Shan fault zone consists of three main Longmen Shan faults and the blind fault in the Chengdu Basin. Along the range front of the middle segment of the Longmen Shan, there is the lithological border in published geological maps. The existence and the latest active time of the range-front fault along the mid-segment of the Longmen Shan thrust belts are controversial for a long period. Petroleum seismic reflection and high-resolution shallow seismic reflection profile discovered the existence of the range-front fault and the fault offset the Quaternary strata. Based on detailed field observation, we found that there is an obvious linear feature along the mid-segment of the Longmen Shan front and the range-front fault displaced the late Quaternary fluvial terrace. Trench log indicates that a surface-rupture event occurred before ~1500a along the range-front fault. Differential GPS surveying and dating of fluvial terrace show that the range-front fault during late Quaternary underwent a vertical slip rate of bigger than 0.36mm/a, approximately equivalent to that along the main faults of the longmen Shan thrust belts, which demonstrates that the range-front fault also took an important role in accommodating the deformation of the Longmen Shan thrust zone. This study not only provides the fundamental data for seismic hazard assessment of the Chengdu Plain, but is helpful for the overall understanding of uplift mechanism of east Tibet.

  20. 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.

  1. 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.

  2. 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.

  3. Quaternary slip-rates of the Kazerun and the Main Recent Faults: active strike-slip partitioning in the Zagros fold-and-thrust belt

    NASA Astrophysics Data System (ADS)

    Authemayou, Christine; Bellier, Olivier; Chardon, Dominique; Benedetti, Lucilla; Malekzade, Zaman; Claude, Christelle; Angeletti, Bernard; Shabanian, Esmaeil; Abbassi, Mohammad Reza

    2009-07-01

    The aim of this work is to constrain the Late Quaternary activity of two major dextral strike-slip faults of the Zagros fold-and-thrust belt of Southern Iran, within the framework of right-oblique convergence between Arabia and Eurasia. The NW-trending Main Recent fault marks the rear of the belt along two thirds of its length. Its southeastern tip connects to the northern termination of the N-trending Kazerun Fault, which affects the entire width of the belt. Horizontal slip rates have been estimated on these two faults over the last 140 ka from lateral offsets of streams and fans and in situ cosmogenic 36Cl exposure dating of cobbles sampled on the surface of these geomorphic features. Compared to GPS data, the obtained minimum slip rate of 3.5-12.5 mm yr-1 on the Main Recent Fault implies strike-slip partitioning of the convergence along this fault. Minimum slip rate of the Kazerun Fault is 2.5-4 mm yr-1 for its northern strand, 1.5-3.5 mm yr-1 for its central segment and is negligible for its southern segment. These results are consistent with southward distribution of the slip from along the Main Recent Fault to the longitudinal thrusts and folds of the fold-and-thrust belt through the Kazerun Fault, with a decrease of slip from the southeastern tip of the Main Recent Fault towards the southern termination of the Kazerun Fault. The Kazerun and associated faults form the horsetail termination of the Main Recent fault and may be seen as the propagating southeastern front of the fault system that accommodates indentation of Eurasia by Arabia.

  4. Tectonic Geomorphology in the Laboratory: Evolution of landscape along an active thrust, normal and strike-slip fault

    NASA Astrophysics Data System (ADS)

    Graveleau, Fabien; Strak, Vincent; Dominguez, Stéphane; Malavieille, Jacques; Chatton, Marina; Manighetti, Isabelle; Petit, Carole

    2015-04-01

    Tectonically controlled landforms develop morphologic features that provide useful markers to investigate crustal deformation and relief growth dynamics. We present here results of morphotectonic experiments obtained with an innovative approach combining tectonic and surface processes (erosion, transport and sedimentation), coupled with accurate model monitoring techniques. This approach allows for a qualitative and quantitative analysis of landscape evolution in response to active deformation in the three end-member geological settings: compression, extension and strike-slip. Experimental results outline first that experimental morphologies evolve significantly at a short timescale. Numerous morphologic markers form continuously, but their lifetime is generally short because erosion and sedimentation processes tend to destroy or bury them. For the compressional setting, the formation of terraces above an active thrust appears mainly controlled by narrowing and incision of the main channel through the uplifting hanging-wall and by avulsion of deposits on fan-like bodies. Terrace formation is irregular even under steady tectonic rates and erosional conditions. Terrace deformation analysis allows retrieving the growth history of the structure and the fault slip rate evolution. For the extensional setting, the dynamics of hanging-wall sedimentary filling appears to control the position of the base level, which in turn controls footwall erosion. Two phases of relief evolution can be evidenced: the first is a phase of relief growth and the second is a phase of upstream propagation of topographic equilibrium that is reached first in the sedimentary basin. During the phase of relief growth, the formation of triangular facets occurs by degradation of the fault scarp and their geometry (height) becomes stationary during the phase of upstream propagation of the topographic equilibrium. For the strike-slip setting, the complex morphology of the wrench zone, composed of

  5. 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

  6. 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

  7. Segmentation and kinematics of the Kazerun fault system (southern Iran): Implications for active deformation partitioning within the Zagros fold-and-thrust belt

    NASA Astrophysics Data System (ADS)

    Authemayou, C. A.; Bellier, O. B.; Chardon, D. C.; Malekzade, Z. M.; Abbassi, M. A.

    2003-04-01

    Iran is located within the interaction zone between the Arabian and Eurasian plates that currently converge at 30 mm/yr. Since the Miocene, continental collision resulted in the formation of the NW-trending Zagros fold-and-thrust belt that accommodates c.a. 10 mm/yr of NNE-trending shortening. The southeastern part of the thrust belt is affected by the north-trending, right lateral Kazerun Fault System (KFS) stretching from the Main Reverse Fault (i.e., the back-stop of the fold-and-thrust belt) in the vicinity of Borujen, in the North, to the Persian Gulf coast near Kormuj, in the south. Reconnaissance tectonic and geomorphic observations, combined with SPOT satellite image analyses allows characterising the KFS active trace geometry and kinematics as well as its relations with the folds and the thrust faults. This further allows evaluating the transfer process from right-lateral slip along the KSF to the fold-and-thrust system. The KFS consists in three North-trending fault zones of equivalent lengths (100 km) that show evidence for a northward increasing activity. The southern terminations of the fault zones are bent towards SE strikes and are generally connected westward with WNW-trending thrusts and ramp anticlines. Those terminations display a horsetail splay fault geometry associated with an eastward decrease of both the strike-slip and dip-slip component of finite offsets. Fault slip-vectors analyses indicate a consistent right-lateral strike-slip tectonic regime all along the KFS associated with a regionally homogeneous NNE-trending 1 direction. The central and northern fault zones show evidence for systematic Quaternary right-lateral offsets of geomorphic features such as stream beds and alluvial fans, as well as shutter ridges and faceted spurs. The northern termination of the KFS shows the most obvious criteria for active slip and the highest geomorphic offsets. This fault zone connects the southeastern tip of the Main Recent Fault, the major active

  8. Thrust faulting and hydrocarbon generation: discussion

    SciTech Connect

    Warner, M.A.; Royse, F.

    1987-07-01

    Following the discovery of large volumes of hydrocarbons in the Cordilleran thrust belt of southwestern Wyoming and northern Utah, Angevine and Turcotte (1983), Edman and Surdam (1984), and Furlong and Edman (1984) discussed the role of thrust faulting in hydrocarbon generation. The authors concluded that overthrusting plays an important or even dominant role in the process of hydrocarbon generation in overthrust terrains. These conclusions may be in error because they are based on a mathematical analysis of thermal and geologic models that have little resemblance to actual thrust-belt geology. In this discussion, the authors discuss shortcomings of the thermal model used in the papers referred to above; emphasize the differences between their model and the geologic facts as they exist in thrust belts in general and in western Wyoming in particular; and caution readers about applying the conclusions based on such a model in the search for hydrocarbons. They contend that the temperature effects of thrust faulting were rather insignificant in the process of hydrocarbon generation in the Wyoming thrust belt.

  9. Exploring the shallow structure of the San Ramón thrust fault in Santiago, Chile (~33.5° S), using active seismic and electric methods

    NASA Astrophysics Data System (ADS)

    Díaz, D.; Maksymowicz, A.; Vargas, G.; Vera, E.; Contreras-Reyes, E.; Rebolledo, S.

    2014-08-01

    The crustal-scale west-vergent San Ramón thrust fault system, which lies at the foot of the main Andean Cordillera in central Chile, is a geologically active structure with manifestations of late Quaternary complex surface rupture on fault segments along the eastern border of the city of Santiago. From the comparison of geophysical and geological observations, we assessed the subsurface structural pattern that affects the sedimentary cover and rock-substratum topography across fault scarps, which is critical for evaluating structural models and associated seismic hazard along the related faults. We performed seismic profiles with an average length of 250 m, using an array of 24 geophones (Geode), with 25 shots per profile, to produce high-resolution seismic tomography to aid in interpreting impedance changes associated with the deformed sedimentary cover. The recorded travel-time refractions and reflections were jointly inverted by using a 2-D tomographic approach, which resulted in variations across the scarp axis in both the velocities and the reflections that are interpreted as the sedimentary cover-rock substratum topography. Seismic anisotropy observed from tomographic profiles is consistent with sediment deformation triggered by west-vergent thrust tectonics along the fault. Electrical soundings crossing two fault scarps were used to construct subsurface resistivity tomographic profiles, which reveal systematic differences between lower resistivity values in the hanging wall with respect to the footwall of the geological structure, and clearly show well-defined east-dipping resistivity boundaries. These boundaries can be interpreted in terms of structurally driven fluid content change between the hanging wall and the footwall of the San Ramón fault. The overall results are consistent with a west-vergent thrust structure dipping ~55° E in the subsurface beneath the piedmont sediments, with local complexities likely associated with variations in fault

  10. Exploring the shallow structure of the San Ramón thrust fault in Santiago, Chile (∼33.5° S), using active seismic and electric methods

    NASA Astrophysics Data System (ADS)

    Díaz, D.; Maksymowicz, A.; Vargas, G.; Vera, E.; Contreras-Reyes, E.; Rebolledo, S.

    2014-01-01

    The crustal-scale west-vergent San Ramón thrust fault system at the foot of the main Andean Cordillera in central Chile is a geologically active structure with Quaternary manifestations of complex surface rupture along fault segments in the eastern border of Santiago city. From the comparison of geophysical and geological observations, we assessed the subsurface structure pattern affecting sedimentary cover and rock-substratum topography across fault scarps, which is critic for evaluating structural modeling and associated seismic hazard along this kind of faults. We performed seismic profiles with an average length of 250 m, using an array of twenty-four geophones (GEODE), and 25 shots per profile, supporting high-resolution seismic tomography for interpreting impedance changes associated to deformed sedimentary cover. The recorded traveltime refractions and reflections were jointly inverted by using a 2-D tomographic approach, which resulted in variations across the scarp axis in both velocities and reflections interpreted as the sedimentary cover-rock substratum topography. Seismic anisotropy observed from tomographic profiles is consistent with sediment deformation triggered by west-vergent thrust tectonics along the fault. Electrical soundings crossing two fault scarps supported subsurface resistivity tomographic profiles, which revealed systematic differences between lower resistivity values in the hanging wall with respect to the footwall of the geological structure, clearly limited by well-defined east-dipping resistivity boundaries. The latter can be interpreted in terms of structurally driven fluid content-change between the hanging wall and the footwall of a permeability boundary associated with the San Ramón fault. The overall results are consistent with a west-vergent thrust structure dipping ∼55° E at subsurface levels in piedmont sediments, with local complexities being probably associated to fault surface rupture propagation, fault-splay and

  11. Experimental Investigation of Thrust Fault Rupture Mechanics

    NASA Astrophysics Data System (ADS)

    Gabuchian, Vahe

    Thrust fault earthquakes are investigated in the laboratory by generating dynamic shear ruptures along pre-existing frictional faults in rectangular plates. A considerable body of evidence suggests that dip-slip earthquakes exhibit enhanced ground motions in the acute hanging wall wedge as an outcome of broken symmetry between hanging and foot wall plates with respect to the earth surface. To understand the physical behavior of thrust fault earthquakes, particularly ground motions near the earth surface, ruptures are nucleated in analog laboratory experiments and guided up-dip towards the simulated earth surface. The transient slip event and emitted radiation mimic a natural thrust earthquake. High-speed photography and laser velocimeters capture the rupture evolution, outputting a full-field view of photo-elastic fringe contours proportional to maximum shearing stresses as well as continuous ground motion velocity records at discrete points on the specimen. Earth surface-normal measurements validate selective enhancement of hanging wall ground motions for both sub-Rayleigh and super-shear rupture speeds. The earth surface breaks upon rupture tip arrival to the fault trace, generating prominent Rayleigh surface waves. A rupture wave is sensed in the hanging wall but is, however, absent from the foot wall plate: a direct consequence of proximity from fault to seismometer. Signatures in earth surface-normal records attenuate with distance from the fault trace. Super-shear earthquakes feature greater amplitudes of ground shaking profiles, as expected from the increased tectonic pressures required to induce super-shear transition. Paired stations measure fault parallel and fault normal ground motions at various depths, which yield slip and opening rates through direct subtraction of like components. Peak fault slip and opening rates associated with the rupture tip increase with proximity to the fault trace, a result of selective ground motion amplification in the

  12. 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.

  13. Regional pore-fluid pressures in the active western Taiwan thrust belt: A test of the classic Hubbert-Rubey fault-weakening hypothesis

    NASA Astrophysics Data System (ADS)

    Yue, Li-Fan; Suppe, John

    2014-12-01

    We document regional pore-fluid pressures in the active Taiwan thrust belt using 55 deep boreholes to test the classic Hubbert-Rubey hypothesis that high static fluid pressures (depth normalized as λ = Pf/ρrgz) account for the extreme weakness of thrust faults, since effective friction μf∗ =μf(1 - λ) . Taiwan fluid pressures are dominated by disequilibrium compaction, showing fully compacted sediments with hydrostatic fluid pressures at shallow depths until the fluid-retention depth zFRD ≈ 3 km, below which sediments are increasingly undercompacted and overpressured. The Hubbert-Rubey fault weakening coefficient is a simple function of depth (1 - λ) ≈ 0.6zFRD/z. We map present-day and pre-erosion fluid pressures and weakening (1 - λ) regionally and show that active thrusts are too shallow relative to zFRD for the classic Hubbert-Rubey mechanism to be important, which requires z ≥ ˜4zFRD ≈ 12 km to have the required order-of-magnitude Hubbert-Rubey fault weakening of (1 - λ) ≤ ˜0.15. The best-characterized thrust is the Chelungpu fault that slipped in the 1999 (Mw = 7.6) Chi-Chi earthquake, which has a low effective friction μf∗ ≈ 0.08- 0.12 , yet lies near the base of the hydrostatic zone at depths of 1-5 km with a modest Hubbert-Rubey weakening of (1 - λ) ≈ 0.4-0.6. Overpressured Miocene and Oligocene detachments at 5-7 km depth have (1 - λ) ≈ 0.3. Therefore, other mechanisms of fault weakening are required, such as the dynamical mechanisms documented for the Chi-Chi earthquake.

  14. Early weakening processes inside thrust fault

    NASA Astrophysics Data System (ADS)

    Lacroix, B.; Tesei, T.; Oliot, E.; Lahfid, A.; Collettini, C.

    2015-07-01

    Observations from deep boreholes at several locations worldwide, laboratory measurements of frictional strength on quartzo-feldspathic materials, and earthquake focal mechanisms indicate that crustal faults are strong (apparent friction μ ≥ 0.6). However, friction experiments on phyllosilicate-rich rocks and some geophysical data have demonstrated that some major faults are considerably weaker. This weakness is commonly considered to be characteristic of mature faults in which rocks are altered by prolonged deformation and fluid-rock interaction (i.e., San Andreas, Zuccale, and Nankai Faults). In contrast, in this study we document fault weakening occurring along a marly shear zone in its infancy (<30 m displacement). Geochemical mass balance calculation and microstructural data show that a massive calcite departure (up to 50 vol %) from the fault rocks facilitated the concentration and reorganization of weak phyllosilicate minerals along the shear surfaces. Friction experiments carried out on intact foliated samples of host marls and fault rocks demonstrated that this structural reorganization lead to a significant fault weakening and that the incipient structure has strength and slip behavior comparable to that of the major weak faults previously documented. These results indicate that some faults, especially those nucleating in lithologies rich of both clays and high-solubility minerals (such as calcite), might experience rapid mineralogical and structural alteration and become weak even in the early stages of their activity.

  15. 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.

  16. Paleoseismic investigations at the Cal thrust fault, Mendoza, Argentina

    NASA Astrophysics Data System (ADS)

    Salomon, Eric; Schmidt, Silke; Hetzel, Ralf; Mingorance, Francisco

    2010-05-01

    Along the active mountain front of the Andean Precordillera between 30°S and 34°S in western Argentina several earthquakes occurred in recent times, including a 7.0 Ms event in 1861 which destroyed the city of Mendoza and killed two thirds of its population. The 1861 event and two other earthquakes (Ms = 5.7 in 1929 and Ms = 5.6 in 1967) were generated on the Cal thrust fault, which extends over a distance of 31 km north-south and runs straight through the center of Mendoza. In the city, which has now more than 1 million inhabitants, the fault forms a 3-m-high fault scarp. Although the Cal thrust fault poses a serious seismic hazard, the paleoseismologic history of this fault and its long-term slip rate remains largely unknown (Mingorance, 2006). We present the first results of an ongoing paleoseismologic study of the Cal thrust at a site located 5 km north of Mendoza. Here, the fault offsets Late Holocene alluvial fan sediments by 2.5 m vertically and exhibits a well developed fault scarp. A 15-m-long and 2-3-m-deep trench across the scarp reveals three east-vergent folds that we interpret to have formed during three earthquakes. Successive retrodeformation of the two youngest folds suggests that the most recent event (presumably the 1861 earthquake) caused ~1.1 m of vertical offset and ~1.8 m of horizontal shortening. For the penultimate event we obtain a vertical offset of ~0.7 m and a horizontal shortening of ~1.9 m. A vertical displacement of ~0.7 m observed on a steeply west-dipping fault may be associated with an older event. The cumulative vertical offset of 2.5 m for the three inferred events is in excellent agreement with the height of the scarp. Based on the retrodeformation of the trench deposits the fault plane dips ~25° to the west. In the deepest part of the trench evidence for even older seismic events is preserved beneath an angular unconformity that was formed during a period of erosion and pre-dates the present-day scarp. Dating of samples to

  17. 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.

  18. The 1998 March 14 Fandoqa earthquake (Mw 6.6) in Kerman province, southeast Iran: re-rupture of the 1981 Sirch earthquake fault, triggering of slip on adjacent thrusts and the active tectonics of the Gowk fault zone

    NASA Astrophysics Data System (ADS)

    Berberian, M.; Jackson, J. A.; Fielding, E.; Parsons, B. E.; Priestley, K.; Qorashi, M.; Talebian, M.; Walker, R.; Wright, T. J.; Baker, C.

    2001-08-01

    The 1998 March 14 Fandoqa earthquake (Ms6.6) was the penultimate in a series of five substantial earthquakes on the Gowk fault system of southeast Iran since 1981, all of which were associated with co-seismic surface ruptures. We use observations of surface faulting, analysis of P and SH body waves, SAR interferometry and geomorphology to investigate the ruptures in these earthquakes and how they are related both to each other and to the regional active tectonics. The 1998 Fandoqa earthquake produced 23km of surface faulting with up to 3m right-lateral strike-slip and 1m vertical offsets. SAR interferometry and seismic waveforms show that the main rupture plane dipped west at ~50° and had a normal component, although the surface ruptures were more complicated, being downthrown to both the east and the west on steep faults in near-surface sediments. In addition, SAR interferometry shows that a nearby thrust with a similar strike but dipping at ~6°W moved about 8cm in a time interval and in a position that makes it likely that its slip was triggered by the Fandoqa earthquake. The 1998 surface ruptures in the Gowk valley followed part of a much longer (~80km) set of co-seismic ruptures with smaller offsets that were observed after larger earthquakes in 1981 (Mw6.6 and 7.1). The main ruptures in these 1981 earthquakes probably occurred on different, deeper parts of the same fault system, producing only minor reactivation of the shallower faults at the surface. Although the 1981-1998 earthquake sequence apparently ruptured parts of the same fault system repeatedly, these earthquakes had very different rupture characteristics: an important lesson for the interpretation of both palaeoseismological trenching investigations and historical accounts of earthquakes. The regional kinematics, which involve oblique right-lateral and convergent motion, are evidently achieved by a complex configuration of faults with normal, reverse and strike-slip components. Some of the

  19. Thrust faulting and hydrocarbon generation: reply

    SciTech Connect

    Edman, J.D.; Furlong, K.P.

    1987-07-01

    This paper is a rebuttal of an earlier paper trying to refute the claims of these authors. They believe this reply illustrates that the simplifications used by Warner and Royse (1987) in their model are generally inappropriate to describe the thermal history of units in the Western Overthrust belt, as well as other overthrust regions. Although their shortcuts produce results that are generally consistent with measured maturity values for some specific modeling sites, the differences in maturation history and the mismatch for the general thrust case make their model a less effective predictive tool. At this stage in the understanding of overthrust thermal processes, you cannot predict a priori when the thermal effects of thrusting will be significant and when they will be minimal. Defining the exact relationship between thrusting and hydrocarbon accumulations in overthrust areas requires additional work and data collection. In particular, workers must consider case histories where the hanging wall contains thick sequences of resistant strata. By incorporating additional constraints, instead of returning to the simplified assumption of constant thermal gradients in tectonic regions, the understanding of the evolution and maturation history of thrust belts is improved.

  20. 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.

  1. Thrust faults and back thrust in Madison range of southwestern Montana foreland

    SciTech Connect

    Tysdal, R.G.

    1986-04-01

    In the Rocky Mountain foreland of southwestern Montana, a zone of Late Cretaceous thrust faults, named the Hilgard fault system, extends along the west side of the Madison Range from Hebgen Lake northward for about 50 mi (80 km). The thrust faults are steep at their leading edges but flatten westward beneath the associated plates, where they commonly dip 25/sup 0/-30/sup 0/. Structural lows and highs are apparent beneath the Beaver Creek plate, the major thrust sheet of the system, and correlate with salients and reentrants of the plate. The Beaver Creek plate consists primarily of Archean metamorphic rocks, but Phanerozoic strata are preserved along the northern part of the plate's leading edge. Only the forward part of the plate is preserved in the Madison Range because Cenozoic normal faults of the Madison Range fault system dropped much of the plate beneath the Madison Valley on the west. The Kirkwood plate lies east of and beneath the Beaver Creek plate, and contains structures of the eastern part of the Hilgard system. The central segment of the leading edge of the Kirkwood plate is not completely detached from underlying strata. The leading edge of the northern part of the plate, defined by the Cache Creek fault, is flanked on the west by an associated anticline. The southern end of the Cache Creek fault is an eastward-dipping back thrust, which abruptly steepens on the west adjacent to the anticline. Both the fault and the anticline are believed to have formed above a concealed detachment fault. The southern part of the Kirkwood plate displays structures interpreted to represent displacement transfer from the Beaver Creek plate. 9 figures.

  2. Fault rheology in an aseismic fold-thrust belt (Shahdad, eastern Iran)

    NASA Astrophysics Data System (ADS)

    Copley, A.; Jolivet, R.

    2015-12-01

    This presentation describes geodetic observations of aseismic deformation in a thrust belt near Shahdad in eastern Iran, which have been used to place constraints on the rheology of creeping faults in a thin-skinned thrust belt. Creep on shallow and high-angle thrust ramps at the range-front occurs at a steady rate, in response to the topographic gradient across the thrust belt. Parts of these thrust ramps, and the low-angle basal thrust they connect to at depth in a ramp-and-flat geometry, underwent accelerated creep following the nearby Mw 6.6 Fandoqa earthquake in 1998. Estimates of the rate of fault slip and the driving stresses in these two contrasting times reveal a non-linear relationship between the stresses and sliding velocity. The degree of non-linearity rules out bulk shear of a weak layer in the sedimentary section (e.g. evaporites) as the deformation mechanism, and suggests that the motions are accommodated by slip on faults governed by a friction law with a rate or state dependence, or possibly both. The high-angle thrust ramps are responsible for building aspects of the geological and geomorphological signs of active shortening visible at the surface, but the folding preserved in the geology must be accomplished by other methods, possibly during the rapid transient postseismic deformation following nearby earthquakes.

  3. Fault rheology in an aseismic fold-thrust belt (Shahdad, eastern Iran)

    NASA Astrophysics Data System (ADS)

    Copley, Alex; Jolivet, Romain

    2016-01-01

    Geodetic observations of aseismic deformation in a thrust belt near Shahdad in eastern Iran have been used to place constraints on the rheology of creeping faults in a thin-skinned thrust belt (<5 km thickness). Creep on shallow and high-angle thrust ramps at the range front occurs at a steady rate, in response to the topographic gradient across the thrust belt. Parts of these thrust ramps, and the low-angle basal thrust they connect to at depth in a ramp-and-flat geometry, underwent accelerated creep following the nearby Mw 6.6 Fandoqa earthquake in 1998. Estimates of the rate of fault slip and the driving stresses in these two contrasting times reveal a nonlinear relationship between the stresses and sliding velocity. The degree of nonlinearity rules out bulk shear of a weak layer in the sedimentary section (e.g., evaporites) as the deformation mechanism. Instead, we suggest that the motions are accommodated by slip on faults governed by a friction law with a highly nonlinear relationship between shear stress and slip rate (e.g., as predicted by "rate and state" models). The high-angle thrust ramps are responsible for building aspects of the geological and geomorphological signs of active shortening visible at the surface, but the folding preserved in the geology must be accomplished by other methods, possibly during the rapid transient postseismic deformation following nearby earthquakes.

  4. Regional structure and kinematic history of a large subduction back thrust: Taranaki Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Stagpoole, V.; Nicol, A.

    2008-01-01

    The Taranaki Fault is a back thrust antithetic to the Hikurangi margin subduction thrust. Subduction back thrusts, like the Taranaki Fault, accrue displacement transferred from the subducting plate, and growth analyses of these structures contribute to an improved understanding of subduction processes. The Taranaki Fault forms the eastern margin of the Taranaki Basin and is part of a system that extends for at least 600 km in continental crust of western New Zealand. The fault is preserved beneath young sedimentary cover and provides a rare opportunity to investigate the geometry and kinematic history of a large subduction back thrust. Two-dimensional seismic reflection lines (2-5 km spacing), tied to recently drilled wells and outcrop, together with magnetotelluric and gravity models are used to examine the fault. These data indicate that the fault is thick skinned with dips of 25-45° to depths of at least 12 km. The fault accommodated at least 12-15 km of dip-slip displacement since the middle Eocene (circa 40-43 Ma). The northern tip of the active section of the fault stepped southward at least three times between the middle Eocene and early Pliocene, producing a total tip retreat of 400-450 km. The history of displacements on the Taranaki Fault is consistent with initiation of Hikurangi margin subduction during the middle Eocene, up to 20 Ma earlier than some previous estimates. Fault tip retreat may have been generated by clockwise rotation of the subduction margin and associated progressive isolation of the fault from the driving downgoing Pacific Plate.

  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. Geomorphotectonic studies of the Wilshire blind thrust fault and the San Andreas fault, Los Angeles area, California

    SciTech Connect

    Thiessen, R.L.

    1996-08-01

    WSUs Nodes program finds geomorphologic features formed by active faults and folds using a DEM. Two active faults in the Los Angeles basin, California were studied. The Wilshire fault was recently designated a fault based on the presence of the Wilshire Arch cored by a blind thrust. A new Nodes detector was designed to look for the observed parabolic ridge over it. The detector was 2.5 km in diameter with ridges 1 to 6 m high. The axis of the Wilshire arch, freeways, other oil fields probably controlled by arches, and interfluve dissection drainage ridges in older alluvium were all detected. Complex strike slip and thrust faults exist near Cajon Pass. The major strike slip faults (San Andreas, San Jacinto) have a {open_quotes}rift{close_quotes} valley 1 km wide that was found with a 41 pixel (1200 m) diameter Nodes detector, as were east-west oriented thrusts. The SAF and SJF were also found with a slope break detector.

  8. Blueschist-facies metamorphism related to regional thrust faulting

    USGS Publications Warehouse

    Blake, M.C., Jr.; 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.

  9. Milankovitch time-scale record of unsteady fault slip, Salsomaggiore thrust, Northern Apennines, Italy

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    In many active orogens geodetic (10^1 yr) and geologic (10^6 yr) rates of shortening do not agree, indicating unsteadiness in wedge strain partitioning or in plate boundary stresses, neither of which are well understood. Our research explores fault unsteadiness in the temporal gap between geodesy and geology. We present the 10^4-10^5 yr resolution, Pliocene-recent, unsteady slip history of the Salsomaggiore thrust, a blind thrust coring an anticline at the modern-day mountain front in the Northern Apennines, Italy. We do this by using progressively deformed marine and continental growth strata exposed on the forelimb of the growing anticline where the subsurface growth strata and fault geometries are constrained by seismic and well data. We integrate lithostratigraphic, magnetostratigraphic, and rock-magnetic cyclostratigraphic methods to construct a high-resolution chronology for the growth section. The integration of these methods allow us to reconstruct the slip history of the Salsomaggiore thrust at multiple timescales and document unsteady behavior at each scale. We use fault-related fold modeling to invert forelimb growth strata geometries for fault slip. The long-term average slip rate on the Salsomaggiore thrust is ~0.3 mm/yr during the last ~7 Myr; however, the thrust was essentially inactive during the Messinian - early Pliocene time, while shortening was accommodated on a more foreland thrust. In contrast, the fault was active between 3.2-2.5 Ma, exhibiting an average slip rate of ~0.6-0.7 mm/yr, followed by an acceleration to ~0.8-1.0 mm/yr between 2.5-1.0 Ma. Finally, a deceleration to < 0.5 mm/yr in the last 1.0 Myr occurred. A detailed look at the time period between 3.0-1.8 Ma using the high-resolution, rock-magnetic cyclostratigraphic chronology reveals unsteady fault-related folding on orbital timescales (23 kyr precession and 41 kyr obliquity frequencies). Modeling of the angular unconformities observed in this part of the section reveal fault

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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

  15. Carbonate mineralogy and Illite crystallinity in the Nobeoka thrust fault zone SW Japan, ancient megaspray fault in a subduction zone

    NASA Astrophysics Data System (ADS)

    Fukuchi, R.; Fujimoto, K.; Hamahashi, M.; Yamaguchi, A.; Kimura, G.; Kameda, J.; Hamada, Y.; Hina, S.; Hashimoto, Y.; Eida, M.; Kitamura, Y.; Saito, S.; Mizuochi, Y.; Hase, K.; Akashi, T.

    2012-12-01

    The Nobeka thrust is a fossilized OOST in the Shimanto belts, Cretaceous and Paleogene accretionary complex in SW Japan. A bore hole penetrating the Nobeoka thrust was drilled at Nobeoka city, SW Japan as analogue of NanTroSEIZE project. Total drilling length was 255 m and continuous core samples were recovered. The borehole runs through the Nobeoka thrust at the depth of 41.3m. The hangingwall is mainly phyllite of Kitagawa group and the footwall is melange of Hyuga group (Kondo et al., 2005). The depth interval between 29m and 78.4m is suffered intense cataclasis due to Nobeoka thrust. Quartz and carbonate veins are enriched in this interval except 41.3-52 m depth interval. We identified from 41.31m to 41.8 m to be a main thrust zone. We also recognize fault breccia at 115m depth. We collected fragmented core samples from every three meters and analyzed constituent minerals by powder X-ray diffraction. Quartz, plagioclase, illite, chlorite, calcite are main constituent minerals from the top to the bottom. Ankerite sometimes occurs as a vein mineral. Here, we focus on the carbonate and illite with special reference to fault activity and paleotemperature. In the borehole, calcite occurs from the top to the bottom, whereas, ankerite is densely distributed above 126m depth. Ankerite often fills veins trending NNW-SSE to NE-SW. At the outcrop near the borehole cite, ankerite occurs as a fault vein mineral in the footwall of Nobeoka thurst (Yamaguchi et al., 2011). The orientation of the fault vein is concordant with the ankerite vein in the borehole. Illite crystallinity (IC) is considered to indicate paleotemperature. ICvalues (FWHM of illite 001 peak) in the hangingwall range from 0.143 to 0.205 Δo2 θ, those in the main thrust zone range from 0.485 to 0.580Δo2 θ, and those in the footwall ranges from 0.379 to 0.578Δo2 θ. The IC values show clear difference among the hangingwall, the main thrust zone and footwall. The paleotemperatures, calculated after the

  16. 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.

  17. Optimally oriented ``fault-valve'' thrusts: Evidence for aftershock-related fluid pressure pulses?

    NASA Astrophysics Data System (ADS)

    Micklethwaite, S.

    2008-04-01

    A thrust-vein network from the Triumph gold deposit, Western Australia, is explained in terms of an extremely high rate of fluid-pressure increase, prior to failure, relative to the rate of stress increase. The thrust fault is a small-displacement fault characterized by a thick, fault-parallel shear vein, plus multiple low-angle extension veins, with orientations that demonstrate the thrust was optimally oriented relative to the locally imposed crustal stresses. Large extension veins have irregular margins, are dominantly composed of coarse milky quartz with no obvious laminations or solid inclusion trails, and are regularly spaced along the thrust (1-2 m). The fault-vein geometries indicate the Triumph thrust is a rare candidate for "fault-valve" failure of an optimally oriented thrust, and it is possible the structure formed in a small number of failure events, during load weakening of the thrust. An analysis using the Coulomb criterion shows that load weakening of a thrust occurs when fluid pressure increases relative to tectonic stress by a factor dependent on the orientation of the thrust. Thrust and reverse faults in dry crust load strengthen prior to failure, but the poroelastic behavior of sealed, fluid-saturated crust is enough to induce load weakening in compressive environments; thus poroelastic load weakening is expected to be an important failure mechanism in hydrothermal environments. However, in the case of the Triumph thrust, dilatant shear failure necessitates a fluid pressure increase which is an order of magnitude larger still. The observations and results are consistent with a pulse of high fluid pressure migrating up through fault or fracture networks that have elevated permeability relative to the wall rock, under conditions of transiently low differential stress. Fluid pressure differences resulted between the fault and wall rock, leading to extension fracture and fault failure. Such conditions may occur when adjacent large earthquakes induce

  18. Structural and seismic data on a new branch of the North Anatolian Fault: A reworked Tertiary thrust fault in northwestern Turkey

    NASA Astrophysics Data System (ADS)

    Aylan, E.; Akbayram, K.; Imren, C.

    2012-04-01

    The North Anatolian Fault (NAF) is an over 1200 km long dextral strike-slip fault in the eastern Mediterranean. The North Anatolian Fault (NAF) and its related branches together make up the North Anatolian Shear Zone (NASZ). The NASZ has two well known active segments in Adapazarı - Sakarya - Bolu region, northwestern Turkey. We provide new structural, stratigraphical and seismic data showing that a previously unknown third segment also exists and created as a result of reworking of Cenozoic thrust faults by the recent deformation of the NAF, in northwest Turkey. Our study area is within Sakarya Basin which consists of ~6 km thick Jurassic - Lower Tertiary sediments, located between the main branch of the NAF in the north and a Mesozoic suture zone in the south. During Tertiary the units in the Sakarya Basin is folded and faulted as a result of north - south shortening. Interestingly one of these thrust faults, so called Pirler Fault, is a deep angle fault dipping 70° south. Later regional analysis on the Pirler Fault shows that this fault is approximately 200 km long, extended southwest to northeast, from the southern border of a Quaternary basin (Gölpazarı Basin of Sakarya city) to the main segment of the NAF (Gerede region of Bolu city). Distribution of the epicenters of recent earthquakes also shows that there is much activity going on the Pirler Fault, generating Mw = 2 - 4 earthquakes.

  19. 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

  20. Low grade metamorphism fluid circulation in a sedimentary environment thrust fault zone: properties and modeling

    NASA Astrophysics Data System (ADS)

    Trincal, Vincent; Lacroix, Brice; Buatier, Martine D.; Charpentier, Delphine; Labaume, Pierre; Lahfid, Abdeltif

    2014-05-01

    analyses were conducted in order to compare the green phyllonites from the fault core zone with the red pelites from the damage zone. Quartz, muscovite 2M1, chlorite (clinochlore), calcite and rutile are present in all samples. Hematite occurs in the damage zone but is absent in the core zone. Synkinematic chlorites are abundant in the core and damage zones and are mainly located in veins, sometimes in association with quartz. The temperature of formation of these newly-formed chlorites is 300-350° C according to Inoue (2009) geothermometer. Mössbauer spectroscopic analyses were performed on bulk rock samples. In the damage zone, Fe3+/Fetotal vary between 0.7 and 0.8, whereas in the core zone Fe3+/Fetotal is about 0.35. This decrease in Fe3+ from the damage zone to the core zone can be related to the dissolution of hematite. In contrast, Fe3+/Fetotal in phyllosilicates is clearly related to the chlorite content relative to mica, as Fe2+ increases with chlorite content. All these data allow us to propose a model of fluid circulation in relation with the Pic de Port Vieux thrust activity. The origin of the fluid, its interactions with host-rock and the consequences on fault zone mineralizations will be discussed. Inoue, A., Meunier, A., Patrier-Mas, P., Rigault, C., Beaufort, D., Vieillard, P., 2009. Application of chemical geothermometry to low-temperature trioctahedral chlorites. Clay Clay Min. 57, 371-382.

  1. 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.

  2. 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.

  3. 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.

  4. Displacement transfer from fault-bend to fault-propagation fold geometry: An example from the Himalayan thrust front

    NASA Astrophysics Data System (ADS)

    Qayyum, Mazhar; Spratt, Deborah A.; Dixon, John M.; Lawrence, Robert D.

    2015-08-01

    The leading edge of the ENE-trending Himalayan thrust front in Pakistan exhibits along-strike changes in deformational style, ranging from fault-bend to fault-propagation folds. Although the structural geometry is very gently deformed throughout the Salt Range, it becomes progressively more complex to the east as the leading edge of the emergent Salt Range Thrust becomes blind. Surface geology, seismic reflection, petroleum well, and chronostratigraphic data are synthesized to produce a 3-D kinematic model that reconciles the contrasting structural geometries along this part of the Himalayan thrust front. We propose a model whereby displacement was transferred, across a newly-identified lateral ramp, from a fault-bend fold in the west to fault-propagation folds in the east and comparable shortening was synchronously accommodated by two fundamentally different mechanisms: translation vs. telescoping. However, substantially different shortening distribution patterns within these structurally contrasting segments require a tear fault, which later is reactivated as a thrust fault. The present geometry of this S-shaped displacement transfer zone is a combined result of the NW-SE compression of the lateral culmination wall and associated tear fault, and their subsequent modification due to mobilization of underlying ductile salt.

  5. Shallow Structure and Location of the Piedmont Thrust Splay of the Hayward Fault, Oakland, California

    NASA Astrophysics Data System (ADS)

    Goldman, M.; Catchings, R.; Trench, D. G.; Buga, M.; Chan, J. H.; Criley, C.

    2015-12-01

    The Piedmont Fault (PF) is interpreted as a thrust or reverse fault that may be associated with the historically active Hayward Fault (HF). The PF may represent a seismic risk due to its location in a densely populated urban area. In February 2015, we acquired high-resolution P- and S-wave seismic data across the approximately mapped trace of the PF at Dimond Canyon Park in Oakland, California to constrain the near-surface location and dip of the fault. Our seismic profile extended 315 m along a southwest to northeast trend. P- and S-wave data were acquired separately using hammer sources. Each shot was co-located with and recorded by 106 40-Hz (P-wave) and 4.5 Hz (S-wave) geophones, spaced 3 m apart. Both the P- and S-wave data show large differences in velocities on the southwest side of the profile (Vp =600-2100 m/s; Vs = 260-520 m/s) compared to the northeast side (Vp =800-3200 m/s; Vs = 500-800 m/s), with a near-vertical dip of velocity contours between the two sides. We interpret the abrupt, near-vertical zone of velocity transition to coincide with the PF. Vp/Vs and Poisson's ratio models show pronounced lows associated with the apparent fault zone. Reflection images show diffractions and near-surface (~ 5 m) breaks in the continuity of reflectors at the location of our interpreted fault. We also evaluated the velocity structure along the profile using two different 2-D surface-wave techniques (MASW and MALW) that show velocities and structures similar to those determined by the tomographic method. Based on our interpreted location of the PF, drilling studies are planned to evaluate the recency of faulting along the PF.

  6. The Channel Islands Thrust Fault, Southern California: Structure at the Juncture Between the Western Transverse Ranges and the Continental Borderland

    NASA Astrophysics Data System (ADS)

    Fisher, M. A.; Langenheim, V. E.

    2004-12-01

    Potential-field data over the northern Channel Islands and Santa Barbara basin and seismic reflection data collected near these islands show the crustal structure near the tip of the Channel Island thrust fault. This fault dips north to underlie the Santa Barbara basin and is part of the regional fault system that separates the western Transverse Ranges from the California Continental Borderland. Our investigation focuses on Santa Cruz Island, where a local exposure of mainly Jurassic ophiolitic basement rocks includes the Willows Plutonic Complex. These mafic and ultramafic igneous rocks produce strong magnetic and gravity anomalies, showing that fragments of the Willows Plutonic Complex have been carried northwestward into or below the basin by sinistral translation of hanging-wall blocks in the thrust system. The potential-field anomalies indicate a cumulative left-lateral offset of about 20 km along what is probably the Santa Cruz Island fault. This fault is known from onshore trenching to be primarily a left-lateral strike-slip fault that was active during late Quaternary time. Seismic-reflection data show that where the Santa Cruz Island fault projects into the offshore a fault-bend fold deforms stratified rock in the Santa Barbara basin. Slip along this fault is partitioned into strike-slip and southwest-vergent reverse components. The Santa Cruz Island fault formed where structures of the California Borderland terminate to the northwest against the rocks that make up the northern Channel Islands. Structures developed at this termination may be similar to ones that formed where the Newport-Inglewood and the San Pedro Basin faults end to the northwest against the Santa Monica Mountains. These terminating faults pose a considerable earthquake hazard, and findings from the area of Santa Cruz Island may help elucidate this hazard.

  7. Controls on low-stress hydro-fracture dilatancy in thrust, wrench and normal fault terrains

    NASA Astrophysics Data System (ADS)

    Sibson, Richard H.

    1981-02-01

    Arrays of parallel extension fractures and veins are sometimes associated with exhumed faults and seem to be the product of repeated hydro-fracturing under a shared stress regime. Here theoretical considerations are used to suggest that this type of hydro-fracture dilatancy is essentially a low differential stress phenomenon. It may develop under hydrostatic fluid pressures around normal faults at shallow depths, but can only occur in association with thrusts when fluid pressures exceed the litho-static load. This contrasts with most existing models for dilatancy, where the effects only become pronounced at high stress levels and are best developed around thrust faults.

  8. 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.

  9. Synkinematic phyllosilicates in a thrust fault zone : good proxy for PT conditions, deformation mechanism and mass transfers (example of the Monte perdido Thrust in southern Pyrenees)

    NASA Astrophysics Data System (ADS)

    Buatier, Martine; Lacroix, Brice; Trincal, Vincent; Charpentier, Delphine; Labaume, Pierre; Trave, Anna

    2013-04-01

    1.67Fe2.31Mg1.71)6(OH)8). Temperatures of chlorite formation calculated by thermodynamic models range from 210°C to 265°C. Taking into account thermometric data from fluid inclusions in calcite and quartz veins, we established that the formation of the synkinematic chlorite occurred under about 6.5km burial. These data suggest that calcite and quartz pressure solution was not the only mechanism of deformation but that thrust fault activity induced mineralogical reactions implying partial dissolution and recrystallisation of phyllosilicates in the presence of fluid in a relatively closed system.

  10. 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.

  11. 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.

  12. 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

  13. Soil bentonite wall protects foundation from thrust faulting: analyses and experiment

    NASA Astrophysics Data System (ADS)

    Fadaee, Meysam; Anastasopoulos, I.; Gazetas, G.; Jafari, M. K.; Kamalian, M.

    2013-09-01

    When seismic thrust faults emerge on the ground surface, they are particularly damaging to buildings, bridges and lifelines that lie on the rupture path. To protect a structure founded on a rigid raft, a thick diaphragm-type soil bentonite wall (SBW) is installed in front of and near the foundation, at sufficient depth to intercept the propagating fault rupture. Extensive numerical analyses, verified against reduced-scale (1 g) split box physical model tests, reveal that such a wall, thanks to its high deformability and low shear resistance, "absorbs" the compressive thrust of the fault and forces the rupture to deviate upwards along its length. As a consequence, the foundation is left essentially intact. The effectiveness of SBW is demonstrated to depend on the exact location of the emerging fault and the magnitude of the fault offset. When the latter is large, the unprotected foundation experiences intolerable rigid-body rotation even if the foundation structural distress is not substantial.

  14. 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.

  15. 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.

  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. 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

  18. 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.

  19. Thrust faults and the near-surface strength of asteroid 433 Eros

    NASA Astrophysics Data System (ADS)

    Watters, Thomas R.; Thomas, Peter C.; Robinson, Mark S.

    2011-01-01

    NEAR Shoemaker images reveal widespread occurrence of tectonic landforms on asteroid 433 Eros. Hinks Dorsum is a ridge that extends for about 18 km around the asteroid and strongly resembles thrust fault structures on the terrestrial planets. Tectonic landforms can provide information on the mechanical properties of asteroids, a subject of much controversy. Modeling constrained by topographic data shows that Hinks Dorsum can be accounted for by a shallow rooted thrust fault no greater than 250 m in depth with ˜90 m of cumulative slip. Strength envelopes based on frictional and rock mass strength criteria suggest the near-surface shear strength of Eros is from ˜1 to 6 MPa. A spatial correlation is found between Shoemaker crater, a transition from low to high crater density, and Hinks Dorsum. This spatial relation along with the estimated strength of the asteroid suggests the thrust fault was formed by impact induced compression.

  20. Deep-seated thrust faults bound the Mare Crisium lunar mascon

    NASA Astrophysics Data System (ADS)

    Byrne, Paul K.; Klimczak, Christian; McGovern, Patrick J.; Mazarico, Erwan; James, Peter B.; Neumann, Gregory A.; Zuber, Maria T.; Solomon, Sean C.

    2015-10-01

    Mare Crisium is composed of a set of volcanic deposits situated in an impact basin on the Moon's near side. The topography of the mare is dominated by an annulus of elevated topography, the inner edge of which is delineated by basin-concentric wrinkle ridges. From a combination of remotely sensed image and topographic data and numerical modeling, we show that the thrust faults that underlie these ridges penetrate up to 20 km in depth, considerably below the base of the mare deposits themselves. Thrust faults of this scale have not heretofore been recognized on the Moon. Mare Crisium sits above a region of uplifted mantle, which contributes to a mass excess beneath the basin, and we demonstrate by comparison with free-air gravity anomaly and derived crustal thickness data for Crisium that the thrust faults structurally bound this elevated mantle material. By means of finite-element models of stresses induced by lithospheric loading within the basin, we argue that the deep-seated thrusts may have been localized by the boundary between the superisostatic mantle material and a sub-isostatic collar of thickened crust that resulted from basin formation and modification shortly after impact. Importantly, numerous other mare-filled mascon basins on the Moon share the same topographic and tectonic characteristics as Crisium, suggesting that they, too, are underlain by deep-seated thrust faults that formed in a similar manner.

  1. 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.

  2. 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

  3. The 2003 M=6.9 Zemmouri, Algeria, Earthquake Brought Thrust and Strike-Slip Faults Near Algiers Closer to Coulomb Failure

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    We investigate key features of thrust earthquake triggering, inhibition, and clustering associated with the stress transferred by the 2003 M=6.9 Zemmouri quake on an offshore hidden thrust fault in coastal Algeria. A crucial question is whether the seismic hazard increased on the Boumerdes and Thenia faults, which lie just west of the Zemmouri rupture and only 10-20 km from the city of Algiers. The capital city suffered large damaging quakes in A.D. 1365 and 1716, and is today home to 3 million people. Slip on blind thrust faults tend to increase the stress above the source fault and in much of the surrounding crust, whereas slip on surface-cutting thrust faults drops the stress in most of the adjacent crust. We examined the sensitivity of the imparted stress to different published source models of the 2003 Zemmouri event inferred from geodetic and seismic inversions, and focus here on the robust results. We calculate that the 2003 M=6.9 Zemmouri quake brought the Coulomb stress 1.0 bars closer to failure on the reverse Boumerdes and 0.5 bars closer on the right-lateral Thenia faults that bound the populated Mitidja basin, although the Thenia fault may not be tectonically active. The calculated pattern of the stress increase appears consistent with aftershock distribution determined from double difference earthquake tomography by Ayadi et al. (submitted); both of these faults were illuminated by aftershocks during the first three months of the sequence. The East Sahel and Larbaa faults, which lie further to the west, are calculated to have sustained a weak 0.1-bar stress increase and show no associated aftershocks. We also calculate a 1.0-bar stress increase on the NNW-SSE trending vertical right-lateral Kabyle fault located south of the Zemmouri fault, although there is no evidence of recent Quaternary tectonic movement, no geomorphology typical of active zones, and little seismicity along the Kabyle fault.

  4. Holocene paleoearthquake history on the Qingchuan fault in the northeastern segment of the Longmenshan Thrust Zone and its implications

    NASA Astrophysics Data System (ADS)

    Sun, Haoyue; He, Honglin; Ikeda, Yasutaka; Kano, Ken'ichi; Shi, Feng; Gao, Wei; Echigo, Tomoo; Okada, Shinsuke

    2015-10-01

    Although much work has been performed for faults with high slip-rates, little attention has been paid to low slip-rate faults, such as the Longmenshan Thrust Zone (LTZ), on which the Wenchuan earthquake occurred. The LTZ is a long and matured fault that evolved during the Mesozoic as a structural boundary, but its Quaternary activity had been considered insignificant. The Wenchuan earthquake on the central segment of the LTZ and the following Lushan earthquake on the southwestern segment illustrate the necessity of assessing the regional seismic potential around the northeastern extension of the LTZ. However, little is known about its activity and paleoearthquake history. To solve these problems, we conducted paleoseismological trench excavations at two sites on the Qingchuan fault to establish its paleoearthquake history. Only one (and the latest) event that occurred in the Holocene is identified. Based on the radiocarbon dating, the faulting event is constrained to occur between 4115 and 3820 B.C., and a long recurrence interval of greater than ~ 6000 years is thus estimated. Judging from the matured fault structure of the Qingchuan fault, the latest event was likely to have ruptured the full length of the fault. According to the empirical scaling laws between magnitude and rupture length, the magnitude of the event is estimated to be Mw 7.6-7.9. On the basis of the slip rate from GPS measurements and the elapsed time since the last event, it is estimated that a seismic moment equivalent to Mw ~ 7.5 has been accumulated on the Qingchuan fault. Considering the increased Coulomb failure stress and the shortened time of earthquake recurrence triggered by the Wenchuan earthquake, it is suggested a high seismic risk along the Qingchuan fault and its neighboring area. Furthermore, the slow strain buildup, unadapted geometry, and matured fault structure of the LTZ may be the reason why it produces rare but large intraplate earthquakes.

  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-thrusting polygonal normal faults exposed in the hinge of the Cingoli anticline, northern Apennines, Italy

    NASA Astrophysics Data System (ADS)

    Petracchini, Lorenzo; Antonellini, Marco; Billi, Andrea; Scrocca, Davide

    2015-11-01

    The Cingoli arcuate anticline is part of the Apennines fold-thrust belt in Italy. The anticline involves sedimentary carbonate strata generally affected by syn-thrusting contractional structures such as bed-normal pressure solution seams, folds, and reverse faults. An exception is constituted by an outcrop in the anticline hinge, where sub-horizontal carbonate and chert beds are affected by joints and intraformational short normal faults. These faults are poorly-systematic and conceivably polygonal in map view. They cut through the carbonate beds while usually stop against the chert layers that are bent and extended along the faults themselves. At the fault tips, the displacement is generally transferred, via a lateral step, to an adjacent similar fault segment. The fault surfaces are often characterized by slickolites, greenish clayey residue, and micro-breccias including chert and carbonate clasts. Fault displacement is partly or largely accommodated by pressure solution. The faults, in effect, are usually accompanied by bed-parallel pressure solution seams in the two contractional quadrants located at the present or past fault tips. The pressure solution features fade away departing from the faults. This evidence and others are analytically explained with fault tip stress distributions. The faults are interpreted as polygonal normal faults syn-tectonically (syn-thrusting) nucleated in response to multi-directional stretching processes occurred at the Cingoli triple-folded anticline extrados. The faults then grew through a four-stage process: (1. stop) the faults stopped at the competent chert beds; (2. shrink) faulting produced shrinkage (pressure solution) of carbonate beds at the fault compressive tips; (3. shrink and step) the faults stepped laterally at the competent chert beds; (4. shatter) the chert beds were shattered along the fault surfaces. The case presented constitutes the first reported one of syn-thrusting non-diagenetic polygonal normal faults.

  7. Lower Miocene coeval thrusting and strike-slip faulting in the Western Betics

    NASA Astrophysics Data System (ADS)

    Frasca, Gianluca; Gueydan, Frédéric; Brun, Jean-Pierre

    2015-04-01

    In the framework of the Africa-Europe convergence, the Mediterranean system presents a complex interaction between subduction rollback and upper subduction plate deformation since 30 Ma. The western end of the system shows an arcuate geometry across the Gibraltar arc, the Betico-Rifean belt, in which the relationship between slab dynamics and onshore tectonics is poorly constrained. The present study focuses on the Western Betics, which is characterized by two major thrusts: 1/ the Alboran Front limits the metamorphic domain (Alboran Domain) from the fold-and-thrust belts involving the Mesozoic cover of the Iberian margin (Subbetics Domain); 2/ the Alboran Internal Thrust allows the juxtaposition of a strongly attenuated lithosphere section, containing the large Ronda subcontinental mantle bodies, on top of crustal rocks. New structural data show that two major E-W strike-slip corridors controlled the deformation pattern of the Alboran Domain, in which E-W dextral strike-slip faults, N60° thrusts and N140° normal faults developed simultaneously during dextral strike-slip simple shear. The Alozaina piggy-back Basin, mainly formed by olistotromic deposits of Lower Miocene age, provides an age estimate for the continuous westward translation of the Alboran Domain, with reference to Iberia, that is accommodated mainly by an E-W lateral strike-slip ramp and a N60° frontal thrust ramp. In this context, a thrust sequence led to the piling up of thrust units in the Western Betics and to the crustal emplacement of the Ronda Peridotites bodies.

  8. 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

  9. 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

  10. 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

  11. Stress triggering in en echelon thrust ruptures and related tear faults: The 2003 M=6.9 Zemmouri, Algeria, earthquake and fault interactions

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    The contractional tectonics of northern Algeria is characterized by a series of en echelon thrust faults of moderate lengths (Meghraoui et al., 2000). This tectonic deformation pattern is similar in geometry to other continental thrust fault systems, such as the Coalinga-Kettleman Hills faults in central California, but differs significantly from that of subduction zones, where thrust segments are often more geometrically continuous along the strike of subduction zones. In this study we first illustrate the essential features of stress interaction between earthquakes occurring on en echelon thrust faults and adjacent tear faults. Our model results reveal that earthquakes on en echelon thrust segments could significantly promote strike-slip motion on the intervening tear faults. Furthermore, if the source earthquake has mixed thrust and strike-slip components, the resultant stress increases on the tear faults are even greater. Thus, tear faults may play an important role in stress transfer between adjacent thrust segments. We next examine the stress transferred by the 2003 M=6.9 Zemmouri quake to nearby thrust and strike-slip faults in northern Algeria. Mahsas et al. (2008) illustrated that the observed afterslip in 2003-2005 appears to be concentrated at the upper parts of the 2003 Zemmouri rupture surface. Our calculations support the hypothesis that a significant portion (more than 75%) of the observed afterslip area might have experienced Coulomb stress increases during the Zemmouri main shock. Calculations further reveal that the majority (more than 90%) of the 30 best-relocated aftershocks as determined by Ayadi et al. (2008) also sustained Coulomb stress increases on at least one of their nodal planes. Finally, we calculated that the Zemmouri main shock brought the Coulomb stress 1 bar closer to failure on the adjacent Boumerdes reverse fault and 0.5 bars closer on the right-lateral Thenia faults that bound the Mitidja basin. Both of these faults experienced

  12. Mare ridges and related studies: Part C: lunar thrust faults in the Taurus-Littrow region

    USGS Publications Warehouse

    Howard, K.A.; Muehlberger, W.R.

    1973-01-01

    "Wrinkle ridges" in the Taurus-Littrow region along the eastern margin of the Mare Serenitatis appear very fresh and are probably among the youngest on the Moon. They include both mare ridges and similar-looking one-sided scarps. Evidence will be presented here to suggest that these ridges and scarps may be anticlines and thrust faults that resulted from sliding on a décollement surface. Alternative interpretations are presented by Scott (part D) and Hodges (part B).

  13. 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.

  14. 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

  15. 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

  16. 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.

  17. Landward vergent thrust faults in marine accretionary prisms off Cascadia, Sumatra, and Southern Chile: Where do they occur and what may control them?

    NASA Astrophysics Data System (ADS)

    Geersen, J.; Wilson, D. J.; Cook, B.; McNeill, L. C.; Henstock, T.; Polonia, A.; Klaeschen, D.; Gaedicke, C.; Goldfinger, C.

    2013-12-01

    Over the last decades seismic investigations have identified a number of places where landward vergent thrust faults occur in active accretionary prisms. These unusual deformation structures, that differ from the common fold-and-thrust belt model in the dip direction of the thrust sheets, have been found at the Cascadia, Sumatra and Southern Chile margins. Parameters that have been suggested to control their formation include strength, position and dip of the décollement, pore-fluid pressure, heat-flow, formation and dip direction of a backstop, strength of the wedge, and subduction of topographic features. However, the ultimate causes for their development are not adequately understood. To test the impact of the above mentioned parameters and to further shed light on the question of what drives these fault structures we investigate reflection seismic and bathymetric data from Cascadia, Sumatra, and Southern Chile. We map the detailed spatial distribution of landward vergence and investigate along and across-strike variations in fault structure, spacing, and fault initiation and development along the three margins. We further compile a synthesis of input parameters (e.g. pre-subduction deformation of the oceanic plate, convergence rate and direction, subducting plate dip, sediment thickness and composition, position of the décollement, oceanic plate roughness) for all regions that host landward vergent faults. This provides the base to identify key parameters that control the development of such fault structures on a local and potentially global scale.

  18. Paleoseismic evidence from trench investigation along Hajipur fault, Himalayan Frontal Thrust, NW Himalaya: Implications of the faulting pattern on landscape evolution and seismic hazard

    NASA Astrophysics Data System (ADS)

    Malik, Javed N.; Sahoo, Ajit K.; Shah, Afroz A.; Shinde, Dattatraya P.; Juyal, Navin; Singhvi, Ashok K.

    2010-03-01

    The study area falls within the mesoseismal zone of 1905 Kangra earthquake (Mw 7.8). Two parallel NNW-SSE striking active fault scarps named as Hajipur Faults (HF1 and HF2) along the northwestern end of the Janauri anticline in the foothill zone, have displaced floodplain sediments of the Beas River. The HF1 and HF2 represent the imbricate faults of the Himalayan Frontal Thrust (HFT), and are the result of lateral propagation of deformation from two fold segments i.e., JF1 and JF2 respectively in northwest direction along the strike. Ground Penetrating Radar (GPR) profiles and trenching across the HF2 reveal two low-angle thrust fault strands (F1 and F2). Displacements of ˜7.5 m on F2 and ˜1.5 m on the associated branching faults (f a, f b and f c) were observed. Total four stratigraphic units: unit A (gravel) - with a lens of medium sand (unit A') is the oldest; overlain by units B - medium to coarse sand; unit C - with fine to medium sand; and unit D - fine to medium sand with scattered gravel were observed in trench. Radiocarbon ages of the charcoal samples from unit B and unit D, optical ages of sediments from units A', B and C, GPR data and trench log, suggest two major events along F1 and F2 strands. Event I along F1 occurred during 2600-800 yr BP and Event II along F2 around 400 yr BP and before 300 yr BP. Given the uncertainty in dates it is suggested that the latest event occurred during 1500-1600 AD. Considering the oldest unit (unit A) exposed in trench with vertical displacement of 7.5-8 m, age of 2600 ± 500 yr BP and net displacement of ˜9 m during single event along low-angle fault ( θ = 25°), implies slip rate = 7.6 ± 1.7 mm/yr, uplift rate = 3.2 ± 0.6 mm/yr, shortening rate = 6.9 ± 1.4 mm/yr and recurrence interval = 1160 ± 250 yr for large-magnitude event with Mw >7.0. With the recurrence of 1100 yr, the penultimate event probably occurred at around 1400-1500 yr BP. Given the recent GPS based slip rate of 14 ± 1 mm/yr in Kangra reentrant

  19. JPL micro-thrust propulsion activities

    NASA Technical Reports Server (NTRS)

    Mueller, J.; Marrese, C.; Ziemer, J.; Green, A.; Yang, E.; Mojarradi, M.; Johnson, T.; White, V.; Bame, D.

    2002-01-01

    Formation flying and microspacecraft constellation missions pose new propulsion requirements. Formationflying spacecraft, due to the tight positioning and pointing control requirements, may need thrust control within 1- 20 uN to an accuracy of 0.1 uN for LISA and ST-7, for example. Future missions may have extended thrust ranges into the sub - mN range. However, all do require high specific impulses (>500 sec) due to long required thruster firings.

  20. 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

  1. Viscoelastic-gravitational deformation by a rectangular thrust fault in a layered earth

    SciTech Connect

    Rundle, J.B.

    1982-09-10

    Previous papers in this series have been concerned with developing the numerical techniques required for the evaluation of vertical displacements which are the result of thrust faulting in a layered, elastic-gravitational earth model. This paper extends these methods to the calculation of fully time-dependent vertical surface deformation from a rectangular, dipping thrust fault in an elastic-gravitational layer over a viscoelastic-gravitational half space. The elastic-gravitational solutions are used together with the correspondence principle of linear viscoelasticity to give the solution in the Laplace transform domain. The technique used here to invert the displacements into the time domain is the Prony series technique, wherein the transformed solution is fit to the transformed representation of a truncated series of decaying exponentials. Purely viscoelastic results obtained are checked against results found previously using a different inverse transform method, and agreement is excellent. A series of results are obtained for a rectangular, 30/sup 0/ dipping thrust fault in an elastic-gravitational layer over viscoelastic-gravitational half space. Time-dependent displacements are calculated out to 50 half space relaxation times tau/sub a/, or 100 Maxwell times 2tau/sub m/ = tau/sub a/. Significant effects due to gravity are shown to exist in the solutions as early as several tau/sub a/. The difference between the purely viscoelastic solution and the viscoelastic-gravitational solutions grows as time progresses. Typically, the solutions with gravity reach an equilibrium value after 10--20 relaxation times, when the purely viscoelastic solutions are still changing significantly. Additionally, the length scaling which was apparent in the purely viscoelastic problem breaks down in the viscoelastic-gravitational problem.

  2. Coastal uplift and thrust faulting associated with the Mw = 6.8 Zemmouri (Algeria) earthquake of 21 May, 2003

    NASA Astrophysics Data System (ADS)

    Meghraoui, M.; Maouche, S.; Chemaa, B.; Cakir, Z.; Aoudia, A.; Harbi, A.; Alasset, P.-J.; Ayadi, A.; Bouhadad, Y.; Benhamouda, F.

    2004-10-01

    A shoreline uplift marked by a continuous white band visible at rocky headlands occurred during the 21 May 2003 earthquake (Mw 6.8) in northern Algeria. We measured the amount of coastal uplift on a white band (emerged algae) and harbors quays between Boumerdes and Dellys. Most of measured points were collected using tape and differential GPS on rocky headlands with σ +/- 0.15 m error bar (tidal prism). Leveling lines running parallel and orthogonal to the coast also provide the precise amount of uplift in the epicentral area. The uplift distribution shows an average 0.55 m along the shoreline with a maximum 0.75 m east of Boumerdes and a minimum close to 0 near Cap Djinet. The active deformation related to a thrust fault is modeled along the ~55 km coastline. The dislocation model predicts surface slip on a N 54°E trending reverse fault, dipping 50° SE in agreement with CMT solution and coastal uplift. The faulting characteristics imply a fault geometry with possible sea bottom ruptures between 5 to 10 km offshore.

  3. Coastal Uplift and Thrust Faulting Associated With the Mw=6.8 Zemmouri (Algeria) Earthquake of 21 May, 2003

    NASA Astrophysics Data System (ADS)

    Meghraoui, M.; Maouche, S.; Chemaa, B.; Cakir, Z.; Aoudia, K.; Harbi, A.; Alasset, P.; Ayadi, A.; Bouhadad, Y.; Benhamouda, F.

    2004-12-01

    A shoreline uplift marked by a continuous white band visible at rocky headlands occurred during the 21 May 2003 earthquake (Mw 6.8) in northern Algeria. We measured the amount of coastal uplift on a white band (emerged algae) and harbors quays between Boumerdes and Dellys. Most of measured points were collected using tape and differential GPS on rocky headlands with ƒa ,b 0.15 m error bar (tidal prism). Leveling lines running parallel and orthogonal to the coast also provide the precise amount of uplift in the epicentral area. The uplift distribution shows an average 0.55 m along the shoreline with a maximum 0.75 m east of Boumerdes and a minimum close to 0 near Cap Djinet. The active deformation related to a thrust fault is modeled along the ƒî 55 km coastline. The dislocation model predicts surface slip on a N 54øXE trending reverse fault, dipping 50øX SE in agreement with CMT solution and coastal uplift. The faulting characteristics imply a fault geometry with possible sea bottom ruptures between 5 to 10 km offshore.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Connecting Crustal Faults and Tectonics from Puget Sound across the Cascade Range to the Yakima Fold and Thrust Belt, Washington: Evidence from New High-Resolution Aeromagnetic Data

    NASA Astrophysics Data System (ADS)

    Blakely, R. J.; Sherrod, B. L.; Weaver, C. S.; Wells, R. E.

    2009-05-01

    through the entire Tertiary CRBG section and into underlying pre-Tertiary rocks, suggesting that thick-skinned tectonism is dominant here. Magnetic anomalies over Umtanum Ridge extend northwestward well beyond exposures of CRBG, thus allowing us to map this zone of deformation over large distances. Using the new aeromagnetic survey and older gravity and magnetic data, we speculate on possible tectonic connections between the Yakima fold belt in eastern Washington and active faults of the Puget Lowland. We suggest that the southern Whidbey Island fault truncates the Seattle fault about 35 km east of Seattle, then continues through the Cascade Range where it transfers strain southeastward to the Umtanum Ridge fault zone. The Tacoma fault may connect in the subsurface with the White River-Naches River fault zone in the Cascade Range and then may merge with the Umtanum Ridge fault zone farther east. In this view, active Puget Lowland faults converge near Snoqualmie Pass in the Cascade Range before connecting with the Yakima fold and thrust belt farther to the southeast. The distribution of earthquakes (MW ≤ 5.3) occurring during the past 35 years suggests that this confluence of faults 35 km east of Seattle may be seismically active.

  9. Is There any Relationship Between Active Tabriz Fault Zone and Bozkush Fault Zones, NW Iran?

    NASA Astrophysics Data System (ADS)

    ISIK, V.; Saber, R.; Caglayan, A.

    2012-12-01

    Tectonic plate motions and consequent earthquakes can be actively observed along the northwestern Iran. The Tabriz fault zone (TFZ), also called the North Tabriz fault, active right-lateral strike-slip fault zone with slip rates estimated as ~8 mm/yr, has been vigorously deforming much of northwestern Iran for over the past several million years. Historical earthquakes on the TFZ consist of large magnitude, complimentary rupture length and changed the landscape of regions surrounding the fault zone. The TFZ in the city of Bostanabad is more segmented with several strands and joined by a series of WNW-ESE trending faults, called the Bozkush fault zones. The Bozkush fault zones (BFZ's) (south and north), bounding arch-shaped Bozkush mountains, generates not only hundreds of small earthquakes each year but also has provided significant earthquakes that have been historically documented. The rock units deformed within the BFZ's include Eocene-Oligocene volcanic rocks with intercalation limestone, Oligo-Miocene clastic rocks with intercalation gypsiferous marl and Plio-Quaternary volcano-sedimentary rocks, travertine and alluvium. The North and South Bozkush fault zones are characterized by development of structures typically associated with transpression. These include right-lateral strike-slip faults, thrust faults and foldings. Our field studies indicate that these zones include step to sub-vertical fault surfaces trending NW and NE with slickenlines. Slickensides preserve brittle kinematic indicators (e.g., Riedel shear patterns, slickenside marks) suggesting both dextral displacements and top-to-the-NE/NW and-SE/SW sense of shearing. Besides, mesoscopic and microscopic ductile kinematic indicators (e.g., asymmetric porphyroclasts, C/S fabrics) within Miocene gypsum marl show dextral displacements. Fault rocks along most of these faults consist of incohesive fault breccia and gauge. Adjacent to the fault contact evidence of bedding in Oligo-Miocene and Plio

  10. 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.

  11. Fault mirrors in seismically active fault zones: A fossil of small earthquakes at shallow depths

    NASA Astrophysics Data System (ADS)

    Kuo, Li-Wei; Song, Sheng-Rong; Suppe, John; Yeh, En-Chao

    2016-03-01

    Fault mirrors (FMs) are naturally polished and glossy fault slip surfaces that can record seismic deformation at shallow depths. They are important for investigating the processes controlling dynamic fault slip. We characterize FMs in borehole samples from the hanging wall damage zone of the active Hsiaotungshi reverse fault, Taiwan. Here we report the first documented occurrence of the combination of silica gel and melt patches coating FMs, with the silica gel resembling those observed on experimentally formed FMs that were cataclastically generated. In addition, the melt patches, which are unambiguous indicators of coseismic slip, suggest that the natural FMs were produced at seismic rates, presumably resulting from flash heating at asperities on the slip surfaces. Since flash heating is efficient at small slip, we propose that these natural FMs represent fossils of small earthquakes, formed in either coseismic faulting and folding or aftershock deformation in the active Taiwan fold-and-thrust belt.

  12. Stress interaction of strike-slip and thrust faults associated with the 2010 M=7.0 Haiti earthquake

    NASA Astrophysics Data System (ADS)

    Lin, J.; Stein, R. S.; Sevilgen, V.; Toda, S.

    2010-12-01

    Recent investigations from combined seismological and space geodetic constraints suggest that the mainshock source faults of the 12 January 2010 Haiti earthquake might be complex and consist of both strike-slip and thrust faults. We calculate Coulomb stress changes on adjacent strike-slip and thrust faults caused by the 2010 M=7.0 rupture by considering a range of mainshock and receiver fault models. We find that for all of the mainshock source models examined, including Hayes et al. (submitted to Nature Geoscience), the Coulomb stress is calculated to have increased on sections of the Enriquillo Fault to both the east and west of the January ruptures. We assume the Enriquillo is dominantly strike-slip. While the magnitude of the calculated stress increase depends on the complexity of the proposed mainshock models, the Enriquillo Fault segment immediately south of Port-au-Prince is calculated to be within a zone of stress increases regardless if the Enriquillo Fault is assumed south dipping or vertical. We further calculate that 60-70% of the nodal planes of the aftershocks determined by Nettles & Hjorleifsdottir (GJI, 2010) were brought closer to failure by the mainshock. Relocating these aftershock locations north by 10 km would bring additional 10% of the aftershock nodal planes into Coulomb stress increases. Overall the 2010 Haiti earthquake illustrates the complex stress interaction between strike-slip and thrust motion on various segments of a larger compressional fault system.

  13. 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

  14. Contrasting strike-slip motions on thrust and normal faults: Implications for space-geodetic monitoring of surface deformation

    NASA Astrophysics Data System (ADS)

    Hampel, Andrea; Li, Tao; Maniatis, Georgios

    2013-04-01

    Recent GPS records of surface deformation caused by earthquakes on intra-continental dip-slip faults revealed in unprecedented detail a significant strike-slip component near the fault tips, which is markedly different for thrust and normal faults. In the hanging wall of the thrust fault ruptured during the 2003 Chengkung (Taiwan) earthquake, a divergent displacement pattern was recorded (Hsu et al., 2009). In contrast, a convergent slip pattern was observed in the hanging wall of the normal fault that produced the 2009 L'Aquila (Italy) earthquake (Cheloni et al., 2010; Serpelloni et al., 2012). Remarkably, such convergent slip patterns are also evident in field records of cumulative fault slip (e.g., Jackson et al., 1982; Roberts & Koukouvelas 1996), which underlines the coseismic origin of the cumulative slip pattern. Here we use three-dimensional numerical modeling to demonstrate that the observed fault-parallel motions are a characteristic feature of the coseismic slip pattern on normal and thrust faults (Hampel et al., in press). Modeled slip vectors converge toward the center of normal faults whereas they diverge for thrust faults, which causes contrasting fault-parallel displacements at the model surface. Our model also predicts divergent movements in normal fault footwalls, which were recorded for the first time during the L'Aquila earthquake. During the postseismic phase, viscous flow in the lower crust induces fault-parallel surface displacements, which have the same direction as the coseismic displacements but are distributed over a larger area that extends far beyond the fault tips. Hence, detecting this signal requires GPS stations in the prolongation of the fault's strike. Postseismic velocities vary over several orders of magnitude depending on the lower-crustal viscosity and may reach tens of millimeters per year for low viscosities. Our study establishes the link between coseismic and cumulative slip patterns on normal and thrust faults and

  15. Imaging of the seismogenic source fault in the fold-and-thrust belt, Niigata basin, central Japan

    NASA Astrophysics Data System (ADS)

    Kato, N.; Sato, H.; Abe, S.; Kawai, N.; Saito, H.; Iwasaki, T.; Shiraishi, K.; Ishiyama, T.; Inaba, M.

    2010-12-01

    Associated with the opening of the Japan Sea, volcanic rift-basins have been developed along the Japan Sea coast of northern Honshu. The Niigata basin, central Japan, is one of such basins and filled by thick (< 7 km) Neogene sediments. By subsequent convergence since the Pliocene, an arc-parallel fold-and-thrust-belt has been developed along the Miocene rift-basins. In this belt devastative earthquakes, such as 1964 Niigata (M7.5), 2004 Chuetsu (M6.8) and 2007 Chuetsu-oki (M6.8) earthquakes, occurred by reverse faulting. Due to thick Neogene sediments, relationship between active faults/folds at near the surface and deep-sited seismogenic source faults is poorly understood. To reveal the crustal structure, in particular geometry of source faults, onshore-offshore integrated deep seismic profiling was undertaken along the three seismic lines in 2008, 2009 and 2010. The 2009 Aizu-Sado Seismic line is a 135-km-long, onshore-offshore seismic line across Niigata basin and Sado island, which is located in the eastern part of Japan Sea. The 2008 Sanjo-Yahiko Seismic line is located 20 km south of the seismic line and trending parallel to it. The 2010 Higashiyama-Mishima seismic line cut through the northern part of the epicentral area of the 2007 Chuetsu-oki earthquake. The seismic sources were air-gun (3020 cu. inch), four vibroseis trucks and explosives (< 200 kg). Along the Sado strait, seismic data was acquired using two-ships to make large offset shot gathers. Seismic signals were recorded by ocean bottom cables, cable-connected-recording system and offline recorders, forming a maximum 2400 channels receiver array. The basin fill consists of early to middle Miocene volcaniclastic rocks and overlying Neogene sedimentary rocks showing upward coarsening facies deposited under bathyal to fluvial environment. Main features of basin development, such as early Miocene normal faulting, associated with the formation of Japan Sea, and shortening deformation since the Pliocene

  16. 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.

  17. 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.

  18. 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.

  19. Development of normal faults during emplacement of a thrust sheet: an example from the Lewis allochthon, Glacier National Park, Montana (U.S.A.)

    NASA Astrophysics Data System (ADS)

    Yin, An; Kelty, Thomas K.

    Geologic mapping in southern Glacier National Park, Montana, reveals the presence of widespread, E-dipping normal faults within the basal portion of the Lewis allochthon. The displacement along the normal faults increases downward from less than 1 m at the highest exposure, 200-300 m above the Lewis Thrust, to a maximum of 200 m near or at the Lewis Thrust. The normal faults are located below discrete, bedding-parallel shear zones associated with mesoscopic structures characterized by NE- or SW-trending striations on bedding surfaces and asymmetric E-verging folds. These shear zones lie directly below the E-directed Brave Dog Fault, a major bedding-subparallel fault within the Lewis allochthon. The shear zones are interpreted to have formed during the development of the Brave Dog Fault. Striations on the Brave Dog Fault, normal faults and shear surfaces in the shear zones are consistent with the transport direction of the Lewis Thrust. The kinematic compatibility of the normal faults with the Lewis Thrust, the concentration of the normal faults along the basal part of the Lewis plate, and the increase in displacement along them toward the Lewis Thrust, all suggest that their development was synkinematic with eastward emplacement of the Lewis allochthon. The normal faults may have formed as Riedel shears (R) that accommodated a bulk, simple-shear strain within the thrust plate between the simultaneously moving subhorizontal Brave Dog and Lewis faults.

  20. 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.

  1. 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

  2. Improved thrust calculations of active magnetic bearings considering fringing flux

    NASA Astrophysics Data System (ADS)

    Jang, Seok-Myeong; Kim, Kwan-Ho; Ko, Kyoung-Jin; Choi, Ji-Hwan; Sung, So-Young; Lee, Yong-Bok

    2012-04-01

    A methodology for deriving fringing permeance in axisymmetric devices such as active thrust magnetic bearings (ATMBs) is presented. The methodology is used to develop an improved equivalent magnetic circuit (EMC) for ATMBs, which considers the fringing effect. This EMC was used to characterize the force between the housing and mover and the dependence of thrust and inductance on the air gap and input current, respectively. These characteristics were validated by comparison with those obtained by the finite element method and in experiments.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. Detachments and normal faulting in the Marche fold-and-thrust belt (central Apennines, Italy): inferences on fluid migration paths

    NASA Astrophysics Data System (ADS)

    Ghisetti, Francesca; Vezzani, Livio

    2000-04-01

    In the outermost domains of the central Apennines fold-and-thrust belt, the structural architecture of the late Miocene-early Pliocene contractional edifice was controlled by competence contrasts in the Calcareous-Marly sequences of Mesozoic-Tertiary age, and by a different state of lithification of the rock units at the onset of deformation. Field data on relative chronology of outcrop-scale structures (cleavage, veins, faults, folds) are presented for the three largest thrust-ramp anticlines of the Marche fold-and-thrust belt: Monte Gorzano, Acquasanta and Montagna dei Fiori-Montagnone. The data show that the timing and geometry of deformation structures differ for: (1) the lower Calcareous interval of late Triassic-early Cretaceous age (LCI) bounded on top by the intermediate detachment (ID) of the Fucoidi Marls; (2) the upper Calcareous-Marly interval (UCMI) of late Cretaceous-Oligocene age; (3) the uppermost detachment zone (UDZ) of lower-middle Miocene age; (4) the topmost Messinian Flysch sequence (FS). In the UDZ early episodes of deformation are manifested by compaction of a poorly lithified sequence followed by pervasive development of layer-parallel pressure-solution cleavage. Reverse faults ramp obliquely across the stratigraphic sequence, and are coated by multiple overgrowths of calcite fibers. These structures are deformed by large, eastward-verging asymmetric folds with N-S axial trends, and are cut by late generations of reverse faults. Normal faults started to develop in the fold backlimbs during the final stages of shortening, in middle-late Pliocene times. These early normal faults were reactivated during episodes of late Pliocene-Pleistocene extensional downfaulting, and are now superposed on the compressional edifice. The UDZ is interpreted to have temporarily sealed the upward escape of fluids during the initial episodes of shortening. Pervasive interlayer flow in the poorly lithified sequence was responsible for development of broken beds

  11. Deep structure of a major subduction back thrust: Magneto-telluric investigations of the Taranaki Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Stagpoole, V. M.; Bennie, S. L.; Bibby, H. M.; Dravitzki, S.; Ingham, M. R.

    2009-01-01

    A magneto-telluric (MT) pilot study is used to investigate the Taranaki Fault, a major thrust along the eastern margin of the Taranaki Basin, New Zealand. Analysis of the survey data (MT phase tensor analysis and 2D models), along a 25 km east-west oriented line perpendicular the fault, indicates the Taranaki Fault is the tectonic boundary between major Permian and Mesozoic basement terranes with differing resistivities. Models show the resistivity boundary at the fault dips eastward at about 45° to a depth of at least 12 km. These results suggest that the fault is a major long lived tectonic feature that formed in Mesozoic time during the terrane accretionary phase and has subsequently reactivated during the Cretaceous and Tertiary. At depths less than 5 km, MT models that use constraints from seismic and borehole data show low resistivity sediments extend about 4 km eastward, beneath the tip of the fault. The sedimentary succession beneath the thrust wedge is a petroleum exploration target and with a higher density of MT measurements, a better image of this region may be achieved.

  12. 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

  13. 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.

  14. How can K-Ar geochronology of clay-size mica/illite help constrain reactivation histories of brittle faults? An example from a Paleozoic thrust fault in Northern Norway

    NASA Astrophysics Data System (ADS)

    Torgersen, Espen; Viola, Giulio; Zwingmann, Horst

    2013-04-01

    invariably a strong correlation with grain-size, wherein the finer the grain size, the younger the age. We interpret the ages of the finest fractions as representing the actual time of faulting. The finest grain-size fraction in the sample from the upper, extensionally-reactivated part of the fault records a Cretaceous age (c. 130 Ma), while the coarser micas have significantly older ages (c. 420 Ma). We interpret the ages of intermediate size fractions and the c. 300 Ma age spread to be the result of physical mixing between the two end-member generations of mica/illite: the younger neoformed, reflecting the Cretaceous fault reactivation, and the older inherited Caledonian component. Although lower greenschist facies conditions were reached within the fault during its Caledonian main activity and probably also the Mesozoic reactivation, mica/illite ages from the lower sample were not reset, and vary between c. 790 to 530 Ma. The age of the finest fraction suggests that the fault's first brittle top-to-the-SE thrust faulting occurred before the peak ductile Caledonian deformation, which is consistent with the documented microstructural evidence. This age is interpreted as reflecting faulting during an early Cambrian "Finnmarkian" compressional phase in Northern Norway. Our new results show that fault reactivation in the brittle regime can be better understood and constrained by the combined approach documented by this study. By establishing the isotopic age of multiple faulting episodes accommodated within the same fault zone, the method provides the backbone toward the development of robust, well-constrained tectonic models.

  15. Experimental Constraints On The Mechanical Strength Of Limestone On Shale Fault Zones: Implications For Natural Thrust Faults

    NASA Astrophysics Data System (ADS)

    Haywood, J.; Kennedy, L.

    2009-12-01

    Carbonates and shales are common in fold and thrust belts worldwide: carbonates typically comprise the hanging wall of fault zones and the shale forms the footwall. Generally, a cataclasite is developed in both the carbonate and shale materials. Despite the wide occurrence of carbonate and shale cataclasites, little is known about the rheological behavior of these composites. We report on the results of velocity-stepping frictional sliding experiments conducted on calcite and shale composites. We examine the effect of gouge composition on the strength, fabric development and microstructural evolution of calcite and shale gouge zones. Room temperature, triaxial frictional sliding experiments were conducted on 2.54 mm diameter by 5 mm length cores containing a 1 mm thick, water saturated gouge layer along a 35° angle sawcut. Berea Sandstone, having a porosity of 17% comprises the upper forcing block while impermeable Badshot Dolomite comprises the lower forcing block. Experiments were conducted at 70 MPa confining pressure and displacement rates varied between 1 to 100 μm s-1. Gouge material was created from quartz-bearing phyllosilicate-rich shale (31% quartz, 39% muscovite, 18% clinochlore, 11% feldspar) combined in various volumetric proportions with reagent grade calcite powder with an average grain size of ~5 μm. Experiments were performed on each endmember composition as well as 75%, 50% and 25% mixtures of shale and calcite. Results show that all gouge compositions display velocity strengthening at the conditions tested. 100% calcite gouge is the strongest and displays initial rapid strain hardening followed by the evolution to ‘steady state’ on a load-displacement curve. Microstructural analysis shows moderately well developed R1 shears in the gouge that can extend into the sandstone and be filled with gouge material. The weakest material is the calcite/shale composites. At the highest shear strain, the 50% composites are the weakest material

  16. 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.

  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)

    Wang, Xin; Suppe, John; Liang, Hang; He, Dengfa

    2014-05-01

    We present the geometry, kinematics and mechanics of large-scale thrusting in the West Kunlun Shan and the southwest Tarim Basin, which is associated with the northward motion of Tibet. The great frontal structure is the ~230km long intact bedding parallel Hotian thrust sheet composed of strata of the Tarim Basin lying above a regional gypsum horizon at the base of the Cenozoic sequence. The toe of the Hotian thrust sheet steps steeply to the surface two thirds of the way across the basin forming the Selibuya-Mazartag hills in the sand desert. The Hotan thrust constitutes one of the longest active intact thrust sheets in the world, showing little internal deformation, however at its back it steps down to a Cambrian detachment at the base of the Paleozoic below a belt of complex high-amplitude anticlines near the front of the West Kunlun Shan, which display break-forward imbricate and wedge structure. More interior, steep reverse faults such as the Tieklik thrust bring older strata to the surface, including Paleozoic basement. The Cambrian detachment also extends northward under the Tarim basin with minor hanging-wall deformation that warps the Hotian Thrust sheet locally, causing the development of growth strata in the Hotian thrust sheet that providesa quantitative record of its motion over these warps. Seismic profiles in the southwest Tarim basin 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(from Zheng et al., 2000)and traced throughout the seismic grid. The bottom of the growth strata is dated at 3.6 Ma indicating a Pliocene and younger age of thrusting and folding in the southwest Tarim Basin. Structural restoration suggests minimum shortening greater than 35km. The Tieklik thrust consumed at least 10 km in early Pliocene. The fold-and-thrust belts of the southwest Tarim basin shortened >25km in

  18. Testing thick-skinned vs thin-skinned faulting in the Yakima fold and thrust belt, Washington: kinematic modeling based on new geologic mapping

    NASA Astrophysics Data System (ADS)

    Miller, B. A.; Crider, J. G.

    2012-12-01

    The greater Cascadia region contains abundant evidence for geologically recent deformation due to movement on upper crustal faults, which pose a seismic hazard independent of great earthquakes on the subduction zone interface. Located in the backarc of Cascadia, the structures of the Yakima fold and thrust belt in central Washington record Miocene to present deformation of the Columbia River Basalt Group (CRBG); however, the geometry of the faults responsible is not well constrained by prior work. Depth of faulting in particular plays a first-order role in determining the maximum credible earthquake for seismic hazard planning. Previous studies assuming thin-skinned tectonics for the Yakima fold and thrust belt imply significantly lower estimates for the maximum credible earthquake. Evidence from geophysical anomalies requires km scale relief on the pre-Tertiary basement underneath the CRBG and Tertiary continental sedimentary rocks. If pre-Tertiary basement relief is due to slip on basement involved reverse faults kinematically coherent with the shallower folds and faults, then the estimates for the maximum credible earthquakes may have to be revisited. These end-member hypotheses of thin-skinned versus basement-involved deformation can be tested with kinematic models of different fault geometries. Kinematic modeling software (Midland Valley's Move) provides a robust method for the construction of balanced (retro-deformable) cross sections constrained by surficial and subsurface geologic data. We present new geologic mapping in the area of the intersection between Umtanum Ridge and the Yakima River Canyon north of Selah, Washington. Umtanum Ridge lies along the Olympic-Wallowa lineament (OWL), which may be the physiographic manifestation of active structures that extend through the Cascade Range and into western Washington. Geologic mapping was facilitated by high resolution DEMs from airborne laser swath mapping (lidar), along with chemo

  19. 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

  20. 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

  1. 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

  2. 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.

  3. Structural Analysis of Active North Bozgush Fault Zone (NW Iran)

    NASA Astrophysics Data System (ADS)

    Saber, R.; Isik, V.; Caglayan, A.

    2013-12-01

    NW Iran is one of the seismically active regions between Zagros Thrust Belt at the south and Caucasus at the north. Not only large magnitude historical earthquakes (Ms>7), but also 1987 Bozgush, 1997 Ardebil (Mw 6.1) and 2012 Ahar-Varzagan (Mw 6.4) earthquakes reveal that the region is seismically active. The North Bozgush Fault Zone (NBFZ) in this region has tens of kilometers in length and hundreds of meters in width. The zone has produced some large and destructive earthquakes (1593 M:6.1 and 1883 M:6.2). The NBFZ affects the Cenozoic units and along this zone Eocene units thrusted over Miocene and/or Plio-Quaternary sedimentary units. Together with morphologic features (stream offsets and alluvial fan movements) affecting the young unites reveal that the zone is active. The zone is mainly characterized by strike-slip faults with reverse component and reverse faults. Reverse faults striking N55°-85°E and dip of 40°-50° to the SW while strike-slip faults show right lateral slip with N60°-85°W and N60°-80°E directions. Our structural data analysis in NBFZ indicates that the axis direction of σ2 principal stress is vertical and the stress ratio (R) is 0.12. These results suggest that the tectonic regime along the North Bozgush Fault Zone is transpressive. Obtained other principal stresses (σ1, σ3) results are compatible with stress directions and GPS velocity suggested for NW Iran.

  4. Dynamic rupture activation of backthrust fault branching

    NASA Astrophysics Data System (ADS)

    Xu, Shiqing; Fukuyama, Eiichi; Ben-Zion, Yehuda; Ampuero, Jean-Paul

    2015-03-01

    We perform dynamic rupture simulations to investigate the possible reactivation of backthrust branches triggered by ruptures along a main thrust fault. Simulations with slip-weakening fault friction and uniform initial stress show that fast propagation speed or long propagation distance of the main rupture promotes reactivation of backthrust over a range of branch angles. The latter condition may occur separately from the former if rupture speed is limited by an increasing slip-weakening distance towards the junction direction. The results suggest a trade-off between the amplitude and duration of the dynamic stress near the main rupture front for backthrust reactivation. Termination of the main rupture by a barrier can provide enhanced loading amplitude and duration along a backthrust rooted near the barrier, facilitating its reactivation especially with a high frictional resistance. The free surface and depth-dependent initial stress can have several additional effects. The sign of the triggered motion along the backthrust can be reversed from thrust to normal if a deeply nucleated main rupture breaks the free surface, while it is preserved as thrust if the main rupture is terminated by a barrier at depth. The numerical results are discussed in relation to several recent megathrust earthquakes in Sumatra, Chile, and Japan, and related topics such as branch feedbacks to the main fault. The dynamic view on backthrust fault branching provided by the study fills a gap not covered by quasi-static models or observations. A specific examined case of antithetic fault branching may be useful for indicating a barrier-like behavior along the main fault.

  5. The Mechanics, Geometry and Distribution of Strike Slip Faults in a Fold and Thrust Belt, County Clare, Ireland

    NASA Astrophysics Data System (ADS)

    Nenna, F. A.; Aydin, A.

    2010-12-01

    Fundamental structures such as opening mode joints and veins, and closing mode pressure solution seams (PSSs) can form dense orthogonal arrays in collisional deformation belts and play important roles in the initiation and development of larger scale faults. We describe the deformation processes and the evolution of fault architecture using systematic documentation of field observations from arrays of strike-slip faults in the Carboniferous Ross Sandstone. This unit is exposed on the Loop Head Peninsula, County Clare, Ireland and was subject to compressive stresses associated with the Variscan orogeny at the end of the Carboniferous producing broad regional east-west trending folds and also tight low-amplitude folds cored by thrust faults. Near these faults, orthogonal sets of PSSs and joints/veins form contemporaneous arrays with pressure solution seams that are sub-parallel to the thrust fault traces and fold axes. A stress or material rotation during the Variscan Orogeny (or perhaps a major second stage of deformation either in late phase of the orogeny or post-orogeny) has lead to left-lateral shear of the PSSs evidenced by pressure solution splays and pull-aparts between their sheared segments, and right-lateral shear on the joints/veins evidenced by splay fractures. The splays of the sheared joints are in the same orientation of the joints in the pull-aparts of the sheared PSSs with which they merge. This indicates that the shearing of the joints/veins and the PSSs was likely to have occurred simultaneously under the same remote loading conditions. With increased shear, extensive splay fractures and pull-apart networks form weak damage zones through which strike-slip faults systems develop with slip of up to 2km. As a higher proportion of the shear is resolved on the joint system than that of the PSS system, the more prominent strike-slip faults are sub-parallel to or slightly inclined to the pre-existing joint/vein set and have a right-lateral sense of slip

  6. 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.

  7. 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

  8. 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

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. Illuminating Northern California's Active Faults

    NASA Astrophysics Data System (ADS)

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

    2009-02-01

    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 Earth™ 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).

  1. Active tectonics and rheology of slow-moving thrusts in the Tibetan foreland of peninsular India

    NASA Astrophysics Data System (ADS)

    Copley, Alex; Mitra, Supriyo; Sloan, Alastair; Gaonkar, Sharad; Avouac, Jean-Philippe; Hollingsworth, James

    2016-04-01

    Peninsular India is cut by active thrust faults that break in earthquakes in response to the compressive force exerted between India and the Tibetan Plateau. The rate of deformation is low, with 2 +/- 1 mm/yr of shortening being accommodated over the entire N-S extent of the Indian sub-continent. However, the large seismogenic thickness in the region (40-50 km), and the long faults, mean that the rare earthquakes that do occur can have magnitudes up to at least 8. This contribution describes studies of two large Indian earthquakes, and their rheological and hazard implications, using a range of techniques. First, the Mw 7.6 Bhuj (Gujarat) earthquake of 2001 is examined using a combination of seismology, InSAR, and levelling data. A slip model for the earthquake will be presented, which allows the material properties of the fault plane to be examined. Second, a Holocene-age earthquake rupture from central India will be discussed. Geomorphic analysis of the scarps produced by the event suggest a magnitude of 7.6 - 8.4. Both of these earthquakes had unusually large stress-drops, amongst the largest recorded for shallow earthquakes. The information provided by these two events will be combined with calculations for the total compressive force being transmitted through the Indian peninsular in order to suggest that the faults are characterised by a low coefficient of friction (approximately 0.1), and that the stress-drops in the earthquakes are close to complete. In turn, these results imply that the majority of the force being transmitted through the Indian plate is supported by the brittle crust. Finally, the along-strike continuation of the faults will be described, with implications for hazard assessment and material properties throughout India.

  2. 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.

  3. 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

  4. 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.

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

    NASA Astrophysics Data System (ADS)

    Lin, Jian; Stein, Ross S.; Meghraoui, Mustapha; Toda, Shinji; Ayadi, Abdelhakim; Dorbath, Catherine; Belabbes, Samir

    2011-03-01

    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.

  6. 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".

  7. Modelling the role of basement block rotation and strike-slip faulting on structural pattern in the cover units of fold-and-thrust belts

    NASA Astrophysics Data System (ADS)

    Koyi, Hemin; Nilfouroushan, Faramarz; Hessami, Khaled

    2015-04-01

    A series of scaled analogue models are run to study the degree of coupling between basement block kinematics and cover deformation. In these models, rigid basal blocks were rotated about vertical axis in a "bookshelf" fashion, which caused strike-slip faulting along the blocks and, to some degrees, in the overlying cover units of loose sand. Three different combinations of cover basement deformations are modeled; cover shortening prior to basement fault movement; basement fault movement prior to shortening of cover units; and simultaneous cover shortening with basement fault movement. Model results show that the effect of basement strike-slip faults depends on the timing of their reactivation during the orogenic process. Pre- and syn-orogen basement strike-slip faults have a significant impact on the structural pattern of the cover units, whereas post-orogenic basement strike-slip faults have less influence on the thickened hinterland of the overlying fold-and-thrust belt. The interaction of basement faulting and cover shortening results in formation of rhomb features. In models with pre- and syn-orogen basement strike-slip faults, rhomb-shaped cover blocks develop as a result of shortening of the overlying cover during basement strike-slip faulting. These rhombic blocks, which have resemblance to flower structures, differ in kinematics, genesis and structural extent. They are bounded by strike-slip faults on two opposite sides and thrusts on the other two sides. In the models, rhomb-shaped cover blocks develop as a result of shortening of the overlying cover during basement strke-slip faulting. Such rhomb features are recognized in the Alborz and Zagros fold-and-thrust belts where cover units are shortened simultaneously with strike-slip faulting in the basement. Model results are also compared with geodetic results obtained from combination of all available GPS velocities in the Zagros and Alborz FTBs. Geodetic results indicate domains of clockwise and

  8. Three-dimensional Geometry of Buried Fold Scarps Associated With Ancient Earthquakes on the Puente Hills Blind Thrust Fault

    NASA Astrophysics Data System (ADS)

    Leon, L. A.; Dolan, J. F.; Hoeft, J. S.; Shaw, J. H.; Hartleb, R. D.

    2003-12-01

    The Puente Hills thrust fault (PHT) is a large blind thrust fault that extends east-west beneath the heart of the metropolitan Los Angeles region (Shaw and Shearer, 1999; Shaw et al., 2003). Christofferson (2002; in prep.) and Dolan et al. (2003) identified four buried fold scarps associated with large (Mw greater than or equal to 7), ancient earthquakes on the PHT beneath the City of Bellflower, in northern Orange County. One of the major outstanding questions regarding this research concerns the subsurface, three-dimensional geometry of these buried scarps. Specifically, we want to determine the extent to which the subsurface geometry of these scarps is controlled by tectonic versus fluvial processes. In order to begin addressing these questions, we drilled a north-south transect of hollow-stem, continuously cored boreholes across the buried fold scarps. This new borehole transect, which comprises six, 20-m-deep boreholes, was drilled parallel to, and ˜ 100 m west of, the original Carfax Avenue transect of Christofferson (2002) and Dolan et al. (2003). The overall pattern of progressive southward thickening of sedimentary units observed in the Carfax borehole transect extends westward to the new transect. Moreover, several key sedimentary contacts that are traceable laterally between the two transects occur at approximately the same depths at all locations along both transects. This three-dimensional data set thus defines several buried fold scarps that extend east-west beneath the study site. These observations confirm that the buried scarps are primarily tectonic, rather than fluvial features.

  9. 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.

  10. 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.

  11. 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

  12. Near-Surface Seasonal Creeping and Subsurface Repeated Seismicity on the Plate-Suture Thrust Fault in Chihshang, Eastern Taiwan

    NASA Astrophysics Data System (ADS)

    Lee, J.; Chu, H.; Angelier, J.; Hu, J.; Rau, R.

    2002-12-01

    The Chihshang fault is one of the most active segments of the Longitudinal Valley Fault, the plate suture between the converging Philippine and Eurasian plates. A destructive earthquake of M 6.2 with substantial surface scarps resulted from rupturing of the Chihshang fault in 1951. From that on, no big earthquake greater than M 6 occurred in this area. Instead, the Chihshang fault reveals a creeping behavior at least during the past 18 observation years. The creepmeter data of daily basis at Chihshang since 1998 revealed different behaviors of surface fault motion at two sites but similar annual shortening rates, 16.2 mm at Tapo site and 15.0 mm at Chinyuan site. Four of five creepmeters showed a seasonal variation, in which the fault only moved, as steadily rapid creeping, during the rainy season, generally from April to October, and remained quite during the rest of year. The only exception is due to the creepmeter located on the mélange-composed slope, where local gravitational landslide played a significant role combined with the tectonic faulting. Comparing to the precipitation data, we inferred that the relatively moderate rainfall is seemingly enough for triggering or facilitating slippages on the surface fault, one or two months before the heavy rains dropped in the wet season. During this observation period from 1998 to 2001, the subsurface seismicity exhibited clusters of micro-earthquakes occurred on the Chihshang fault at the depth of 15-25 km. The repeated earthquakes continuously occurred regardless the wet or the dry seasons, indicating the stress on the Chihshang fault in the shallow crust level of less than 10 km released only by creeping during the wet season. Combination of the near-surface creeping and the subsurface repeated earthquakes provided insights on the mechanical behaviors of the Chihshang fault, which are likely related to the geological materials of the converging island-arc: week mélange in the near-surface fault zone and strong

  13. 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

  14. 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.

  15. Is the Lishan fault of Taiwan active?

    NASA Astrophysics Data System (ADS)

    Kuo-Chen, Hao; Wu, Francis; Chang, Wu-Lung; Chang, Chih-Yu; Cheng, Ching-Yu; Hirata, Naoshi

    2015-10-01

    The Lishan fault has been characterized alternately as a major discontinuity in stratigraphy, structures and metamorphism, a ductile shear zone, a tectonic suture or non-existent. In addition to being a geological boundary, it also marks transitions in subsurface structures. Thus, the seismicity to the west of the fault permeates through the upper and mid-crust while beneath the Central Range it is noticeably less and largely concentrated in the upper 12 km. A prominent west-dipping conductive zone extends upward to meet the Lishan fault. Also, the eastward increase of crust thickness from ~ 30 km in the Taiwan Strait quickens under the Lishan fault to form a root of over 50 km under the Central Range. In the past, the small magnitude seismicity along the Lishan fault has been noticed but is too diffuse for definitive association with the fault. Recent processing of aftershock records of the 1999 Mw 7.6 Chi-Chi earthquake using Central Weather Bureau data and, especially, data from three post-Chi-Chi deployments of seismic stations across central Taiwan yielded hypocenters that appear to link directly to the Lishan structure. The presence of a near 4-km-long vertical seismic zone directly under the surface trace of the Lishan fault indicates that it is an active structure from the surface down to about 35 km, and the variety of focal mechanisms indicates that the fault motion can be complex and depth-dependent.

  16. 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

  17. 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

  18. 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

  19. 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

  20. Active faulting in the Walker Lane

    NASA Astrophysics Data System (ADS)

    Wesnousky, Steven G.

    2005-06-01

    Deformation across the San Andreas and Walker Lane fault systems accounts for most relative Pacific-North American transform plate motion. The Walker Lane is composed of discontinuous sets of right-slip faults that are located to the east and strike approximately parallel to the San Andreas fault system. Mapping of active faults in the central Walker Lane shows that right-lateral shear is locally accommodated by rotation of crustal blocks bounded by steep-dipping east striking left-slip faults. The left slip and clockwise rotation of crustal blocks bounded by the east striking faults has produced major basins in the area, including Rattlesnake and Garfield flats; Teels, Columbus and Rhodes salt marshes; and Queen Valley. The Benton Springs and Petrified Springs faults are the major northwest striking structures currently accommodating transform motion in the central Walker Lane. Right-lateral offsets of late Pleistocene surfaces along the two faults point to slip rates of at least 1 mm/yr. The northern limit of northwest trending strike-slip faults in the central Walker Lane is abrupt and reflects transfer of strike-slip to dip-slip deformation in the western Basin and Range and transformation of right slip into rotation of crustal blocks to the north. The transfer of strike slip in the central Walker Lane to dip slip in the western Basin and Range correlates to a northward broadening of the modern strain field suggested by geodesy and appears to be a long-lived feature of the deformation field. The complexity of faulting and apparent rotation of crustal blocks within the Walker Lane is consistent with the concept of a partially detached and elastic-brittle crust that is being transported on a continuously deforming layer below. The regional pattern of faulting within the Walker Lane is more complex than observed along the San Andreas fault system to the west. The difference is attributed to the relatively less cumulative slip that has occurred across the Walker

  1. The Impact of Frictional Anisotropy of Serpentine on Thrust Fault Slip at Subduction Zones

    NASA Astrophysics Data System (ADS)

    Campione, M.; Capitani, G. C.

    2013-12-01

    Models describing the slip dynamics of a fault assume generally an isotropic interface giving rise to shear forces which are parallel to the slip direction. However, structured surfaces may be associated with an anisotropic frictional behavior, which is characterized by a dependence of the magnitude of friction force on slip direction and the presence of friction force components transverse to the slip direction. The arrangement of atoms in the crystal structure of the minerals composing the rock slab, the foliation and lineations originating from the rock deformation, and the presence of gouges formed as a consequence of rock erosion, contribute to the structuring of the surface on different length scales. Among these aspects, only the former is related to intrinsic properties of the fault, and its influence on the frictional properties is therefore independent on the rock history. In order to study the relation between frictional properties and crystal structure, we performed a nanotribological characterization of the surface of prominent mineral species with a scanning force microscope, where a micrometric tip mounted on an elastic cantilever is scanned by piezoelectric actuation along all directions of the sample surface on a nanoscopic area, while vertical deflection and lateral torsion of the cantilever are monitored in real-time, allowing for the quantitative determination of the friction force vectors. Antigorite, the high-temperature, high pressure polymorph of serpentine, is a mineral with a prominent role in defining the mechanical behavior of faulted regions. Indeed, there is general consensus that it forms in the forearc mantle wedge by hydration of olivine and pyroxenes through aqueous fluids released in the downgoing slab, upon increasing pressure and temperature. We asses frictional anisotropies as high as 100% of individual crystal domains of antigorite [1]. This anisotropy is related to the peculiar wavy arrangement of the TO-layer and the

  2. 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.

  3. Fault activation due to glacially induced stresses

    NASA Astrophysics Data System (ADS)

    Steffen, R.; Lund, B.; Wu, P. P.

    2013-12-01

    Melting glaciers worldwide have an effect on sea level, but also on the stability of pre-existing faults. The load due to continental ice sheets or glaciers depresses the surface below, leading to changes in the lithospheric stresses. The accumulation of ice mass increases the vertical stress, and the horizontal stresses increase due to the accompanying flexure of the lithosphere. During deglaciation, ice-mass loss causes a simultaneous decrease in vertical stress; however, horizontal stresses decrease only slowly due to the slow readjusting of the Earth. After the end of deglaciation, only the induced horizontal stresses remain as the process of glacial isostatic adjustment (GIA) proceeds visco-elastically. The modelling of this process and the estimation of fault slip is enabled by a new GIA-fault model. However, this finite-element model is only available in two dimensions, and the extension to three dimensions is a necessary step further to allow the comparison of obtained fault slips to observations of glacially induced faults in Europe and North America. The model has several input parameters, which affect the activation time of faults and their resulting slip (e.g. ice history, rheology of the Earth, frictional properties, pore-fluid pressure). We will present the results of the new 3D model and show the sensitivity of faults with respect to modelling parameters. Furthermore, a comparison to observations will be presented.

  4. Fault activation due to glacially induced stresses

    NASA Astrophysics Data System (ADS)

    Steffen, Rebekka; Lund, Björn

    2014-05-01

    Melting glaciers worldwide have an effect on sea level, but also on the stability of pre-existing faults. The load due to continental ice sheets or glaciers depresses the surface below, leading to changes in the lithospheric stresses. The accumulation of ice mass increases the vertical stress, and the horizontal stresses increase due to the accompanying flexure of the lithosphere. During deglaciation, ice-mass loss causes a simultaneous decrease in vertical stress; however, horizontal stresses decrease only slowly due to the slow readjusting of the Earth. After the end of deglaciation, only the induced horizontal stresses remain as the process of glacial isostatic adjustment (GIA) proceeds visco-elastically. The modelling of this process and the estimation of fault slip is enabled by a new GIA-fault model. However, this finite-element model is only available in two dimensions, and the extension to three dimensions is a necessary step further to allow the comparison of obtained fault slips to observations of glacially induced faults in Europe and North America. The model has several input parameters, which affect the activation time of faults and their resulting slip (e.g. ice history, rheology of the Earth, frictional properties, pore-fluid pressure). We will present the results of the new 3D model and show the sensitivity of faults with respect to modelling parameters. Furthermore, a comparison to observations will be presented.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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).

  11. Intracontinental active normal faulting and paleoseismicity in the eastern Weihe Graben, central China

    NASA Astrophysics Data System (ADS)

    Rao, G.; Lin, A.; Yan, B.; Jia, D.; Wu, X.

    2012-12-01

    During the past decades, tectonic deformation and seismogenic behavior of active strike-slip and thrust faults have been well investigated, due to the high-frequent occurrence of large-magnitude strike-slip and thrust-type earthquakes. In contrast, normal-faulting earthquakes of M≥7 scarcely occurred, and the rupture process and deformation features of seismogenic normal-faults are still not clear. The intracontinental graben systems around the stable Ordos Block, central China, experienced extension over the past ~50 Ma, which are ideal places to study the extensional tectonic deformation. As well, these regions with high historical seismicity including 3 large earthquakes of M≥8, provide a good chance to learn the rupture mechanism of large intracontinental normal-faulting earthquakes. Based on the 3D analysis of high-resolution remote-sensing images (0.5-m WorldView and 1-m IKONOS images) and field investigations, active normal faults are mainly distributed along the margin zones of the uplifted mountainous blocks (e.g., Weinan Loess Tableland and Huashan Mountains), characterized by the distributed fault scarps. Striations and scratch steps observed on the main fault planes, reveal a normal slip-sense of active faults in study area. In combination with the 14C age dating, the vertical offset amount of ~30 m during the past 14,050-16,270 years was observed, yielding an average vertical displacement-rate of ~1.8-2.1 mm/a, which is consistent with previous estimation in the Weihe Graben. According to the field observations of fault outcrops and the exposed trench walls, the offset strata, scarp-derived colluvial deposits and in-filled fissures generally can be observed, indicating the occurrence of paleoearthquakes. Together with the 14C ages, the late Pleistocene-Holocene activity of normal faults was demonstrated. Especially, it is concluded that at least 3 strong earthquakes associated with surface-faulting in the past 2600 years, including the most recent

  12. Active Thrusting Offshore Mount Lebanon: Source of the Tsunamigenic A.D. 551 Beirut-Tripoli Earthquake

    NASA Astrophysics Data System (ADS)

    Tapponnier, P.; Elias, A.; Singh, S.; King, G.; Briais, A.; Daeron, M.; Carton, H.; Sursock, A.; Jacques, E.; Jomaa, R.; Klinger, Y.

    2007-12-01

    On July 9, AD 551, a large earthquake, followed by a tsunami destroyed most of the coastal cities of Phoenicia (modern-day Lebanon). This was arguably one of the most devastating historical submarine earthquakes in the eastern Mediterranean. Geophysical data from the Shalimar survey unveils the source of this Mw=7.5 event: rupture of the offshore, hitherto unknown, 100?150 km-long, active, east-dipping Mount Lebanon Thrust (MLT). Deep-towed sonar swaths along the base of prominent bathymetric escarpments reveal fresh, west facing seismic scarps that cut the sediment-smoothed seafloor. The MLT trace comes closest (~ 8 km) to the coast between Beirut and Enfeh, where as 13 radiocarbon-calibrated ages indicate, a shoreline-fringing Vermetid bench suddenly emerged by ~ 80 cm in the 6th century AD. At Tabarja, the regular vertical separation (~ 1 m) of higher fossil benches, suggests uplift by 3 more comparable-size earthquakes since the Holocene sea-level reached a maximum ca. 7-6 ka, implying a 1500?1750 yr recurrence time. Unabated thrusting on the MLT likely orchestrated the growth of Mt. Lebanon since the late Miocene. The newly discovered MLT has been the missing piece in the Dead Sea Transform and eastern Mediterranean tectonic scheme. Identifying the source of the AD 551 event thus ends a complete reassessment of the sources of the major historical earthquakes on the various faults of the Lebanese Restraining Bend of the Levant Fault System (or Dead Sea Transform).

  13. Active Thrusting Offshore Mount Lebanon: Source of the Tsunamigenic A.D. 551 Beirut-Tripoli Earthquake

    NASA Astrophysics Data System (ADS)

    Tapponnier, P.; Elias, A.; Singh, S.; King, G.; Briais, A.; Daeron, M.; Carton, H.; Sursock, A.; Jacques, E.; Jomaa, R.; Klinger, Y.

    2004-12-01

    On July 9, AD 551, a large earthquake, followed by a tsunami destroyed most of the coastal cities of Phoenicia (modern-day Lebanon). This was arguably one of the most devastating historical submarine earthquakes in the eastern Mediterranean. Geophysical data from the Shalimar survey unveils the source of this Mw=7.5 event: rupture of the offshore, hitherto unknown, 100?150 km-long, active, east-dipping Mount Lebanon Thrust (MLT). Deep-towed sonar swaths along the base of prominent bathymetric escarpments reveal fresh, west facing seismic scarps that cut the sediment-smoothed seafloor. The MLT trace comes closest (~ 8 km) to the coast between Beirut and Enfeh, where as 13 radiocarbon-calibrated ages indicate, a shoreline-fringing Vermetid bench suddenly emerged by ~ 80 cm in the 6th century AD. At Tabarja, the regular vertical separation (~ 1 m) of higher fossil benches, suggests uplift by 3 more comparable-size earthquakes since the Holocene sea-level reached a maximum ca. 7-6 ka, implying a 1500?1750 yr recurrence time. Unabated thrusting on the MLT likely orchestrated the growth of Mt. Lebanon since the late Miocene. The newly discovered MLT has been the missing piece in the Dead Sea Transform and eastern Mediterranean tectonic scheme. Identifying the source of the AD 551 event thus ends a complete reassessment of the sources of the major historical earthquakes on the various faults of the Lebanese Restraining Bend of the Levant Fault System (or Dead Sea Transform).

  14. Active and inactive faults in southern California viewed from Skylab

    NASA Technical Reports Server (NTRS)

    Merifield, P. M.; Lamar, D. L.

    1975-01-01

    The application is discussed of Skylab imagery along with larger scale photography and field investigations in preparing fault maps of California for use in land use planning. The images were used to assist in distinguishing active from inactive faults (by recognizing indications of recent displacement), determining the length of potentially active faults, identifying previously unmapped faults, and gaining additional information on regional tectonic history.

  15. Late Pleistocene to Holocene slip rates for the Gurvan Bulag thrust fault (Gobi-Altay, Mongolia) estimated with 10Be dates

    NASA Astrophysics Data System (ADS)

    Ritz, J.-F.; BourlèS, D.; Brown, E. T.; Carretier, S.; ChéRy, J.; Enhtuvshin, B.; Galsan, P.; Finkel, R. C.; Hanks, T. C.; Kendrick, K. J.; Philip, H.; Raisbeck, G.; Schlupp, A.; Schwartz, D. P.; Yiou, F.

    2003-03-01

    We surveyed morphotectonic markers along the central part of the Gurvan Bulag thrust, a fault that ruptured with the Bogd fault during the Gobi-Altay earthquake (1957, M 8.3), to document climatic and tectonic processes along the fault for the late Pleistocene-Holocene period. The markers were dated using 10Be produced in situ. Two major periods of alluviation ended at 131 ± 20 and 16 ± 4.8 ka. These appear to be contemporaneous with global climatic changes at the terminations of marine isotope stages (MIS) 6 and 2. The vertical slip rates, determined from offset measurements and surfaces ages, are 0.14 ± 0.03 mm/yr over the late Pleistocene-Holocene and between 0.44 ± 0.11 and 1.05 ± 0.25 mm/yr since the end of the late Pleistocene. The higher of these slip rates for the last ˜16 kyr is consistent with paleoseismic investigations along the fault [, 2002], and suggests that, at the end of late Pleistocene, the fault evolved from quiescence to having recurrence intervals of 4.0 ± 1.2 kyr for surface ruptures with ˜4 m vertical offset (similar to that of 1957). The inferred recurrence interval is comparable to that of the Bogd fault (3.7 ± 1.3 kyr) suggesting that the two faults may have ruptured together also earlier during the last ˜16 kyr.

  16. Partition between collision and subduction accretionary prisms along an inherited transcurrent fault zone: New insights on the Taiwan fold and thrust belt

    NASA Astrophysics Data System (ADS)

    Brusset, StéPhane; Souquet, Pierre; DéRamond, Joachim; Sibuet, Jean-Claude; Hsu, Shu-Kun; Deffontaines, Benoã®T.; Chu, Hao-Tsu

    1999-06-01

    A new geotectonic framework of the Taiwan orogen is presented in accordance with the hypothesis of an oblique arc-arc collision. The colliding Luzon arc is physically connected to the eastern Coastal Range in which a subduction complex remnant is preserved and backthrust with intra-arc sediments in a small retroforeland basin. A southern and extinct extension of the Ryukyu arc is characterized in western Taiwan. It displays a duplex structure (Tananao and Backbone horses and Lishan triangle zone) between a buried floor thrust located in the arc crust and a roof thrust developed in the arc cover (Hsüehshan Range and South Backbone Range). Westward the basal thrust climbs in the sedimentary series of the western proforeland (Foothills and Hengchun Peninsula) and dies out hi a buried tip line. The northern part of the orogen, including all the Tananao arc core, is shown as an intra-oceanic-continental arc-arc collision belt characterized by an unroofed duplex culmination above a leading floor thrust and both proforeland and retroforeland basins. The southern part, which displays a roof thrust sequence above a buried duplex, is shown as an accretionary prism built in a transition zone between continent and oceanic subduction (transition from the Asian continental crust, including the former Ryukyu arc, to the oceanic Old Philippine Sea crust). The partition is believed to be induced by a deep intracontinental transcurrent fault zone able to influence the difference in shortening, duplex pattern, and leading thrust depth. The evolution was controlled by the Ryukyu subduction (backarc extension, arc magmatism extinction, and cooling and intra-arc collapse) until the early middle Miocene (around 15 Ma) and then it was controlled by the Luzon arc progression (continental subduction, collision, indentation, and hinterland uplift and frontal thrust propagation).

  17. Active fault traces along Bhuj Fault and Katrol Hill Fault, and trenching survey at Wandhay, Kachchh, Gujarat, India

    NASA Astrophysics Data System (ADS)

    Morino, Michio; Malik, Javed N.; Mishra, Prashant; Bhuiyan, Chandrashekhar; Kaneko, Fumio

    2008-06-01

    Several new active fault traces were identified along Katrol Hill Fault (KHF). A new fault (named as Bhuj Fault, BF) that extends into the Bhuj Plain was also identified. These fault traces were identified based on satellite photo interpretation and field survey. Trenches were excavated to identify the paleoseismic events, pattern of faulting and the nature of deformation. New active fault traces were recognized about 1km north of the topographic boundary between the Katrol Hill and the plain area. The fault exposure along the left bank of Khari River with 10m wide shear zone in the Mesozoic rocks and showing displacement of the overlying Quaternary deposits is indicative of continued tectonic activity along the ancient fault. The E-W trending active fault traces along the KHF in the western part changes to NE-SW or ENE-WSW near Wandhay village. Trenching survey across a low scarp near Wandhay village reveals three major fault strands F1, F2, and F3. These fault strands displaced the older terrace deposits comprising Sand, Silt and Gravel units along with overlying younger deposits from units 1 to 5 made of gravel, sand and silt. Stratigraphic relationship indicates at least three large magnitude earthquakes along KHF during Late Holocene or recent historic past.

  18. 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

  19. Zipper Faults

    NASA Astrophysics Data System (ADS)

    Platt, J. P.; Passchier, C. W.

    2015-12-01

    Intersecting simultaneously active pairs of faults with different orientations and opposing slip sense ("conjugate faults") present geometrical and kinematic problems. Such faults rarely offset each other, even when they have displacements of many km. A simple solution to the problem is that the two faults merge, either zippering up or unzippering, depending on the relationship between the angle of intersection and the slip senses. A widely recognized example of this is the so-called blind front developed in some thrust belts, where a backthrust branches off a decollement surface at depth. The decollement progressively unzippers, so that its hanging wall becomes the hanging wall of the backthrust, and its footwall becomes the footwall of the active decollement. The opposite situation commonly arises in core complexes, where conjugate low-angle normal faults merge to form a single detachment; in this case the two faults zipper up. Analogous situations may arise for conjugate pairs of strike-slip faults. We present kinematic and geometrical analyses of the Garlock and San Andreas faults in California, the Najd fault system in Saudi Arabia, the North and East Anatolian faults, the Karakoram and Altyn Tagh faults in Tibet, and the Tonale and Guidicarie faults in the southern Alps, all of which appear to have undergone zippering over distances of several tens to hundreds of km. The zippering process may produce complex and significant patterns of strain and rotation in the surrounding rocks, particularly if the angle between the zippered faults is large. A zippering fault may be inactive during active movement on the intersecting faults, or it may have a slip rate that differs from either fault. Intersecting conjugate ductile shear zones behave in the same way on outcrop and micro-scales.

  20. 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

  1. 2010 M=7.0 Haiti Earthquake Calculated to Increase Failure Stress on Adjacent Segments of the Enriquillo Fault and Adjacent Thrust Systems

    NASA Astrophysics Data System (ADS)

    Lin, Jian; Stein, Ross S.; Sevilgen, Volkan; Toda, Shinji

    2010-05-01

    We calculate that the Haiti earthquake increased the failure stress on the adjacent segments of the Enriquillo Fault and other thrust faults. Of particular concern is the segment on the Enriquillo Fault immediately to the east of the 12 January rupture. This fault section, which comes within 5 km of Port-au-Prince, is calculated to have been brought about 2-5 bars closer to failure. The inference of stress increase on this eastern section is relatively robust regardless of the specific source models used from available seismic and geodetic inversions. The next most loaded section on the Enriquillo Fault lies to the west of the 12 January rupture, where stress is calculated to have been brought about 1 bar closer to failure. The calculated stress increases on this western section, however, are more sensitive to the source models used in the calculation. Thus far we have tested several teleseismic and InSAR-based models, all of which assume slip occurred on a single north-dipping planar surface. If significant coseismic slip took place on a reverse fault at the western end of the 12 January rupture, these models will need further revision. Previous GPS measurements have shown tectonic loading of 7 ± 2 mm/yr on the Enriquillo Fault, yielding about 1.7 m of accumulated loading since large quakes last struck this region in 1751 and 1770. One or both of these appear to be coupled events separated by days to months, but it is unclear if these struck on the Enriquillo Fault. Thus, there is at least a possibility of future large quakes on these segments of the Enriquillo Fault. We also calculate stress increase of about 0.1-0.5 bars on some surrounding thrust faults, as well as a small increase of 0.05 bars on the Septentrional Fault between Port-de-Paix and Cap-Haitien, which lie 155 km north of the 12 January rupture. Preliminary models are available at http://pubs.usgs.gov/of/2010/1019/.

  2. 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

  3. 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

  4. Active tectonics evidences and seismicity registry of Servitá Fault, Colombia

    NASA Astrophysics Data System (ADS)

    Chicangana, G.; Vargas-Jimenez, C. A.; Pedraza, P.; Kammer, A.; Ochoa Gutierrez, L. H.

    2013-05-01

    The Servita fault is a thrust whose scarp is located 5km west of Villavicencio in the center of Colombia. Here with neotectonic evidences and the seismicity record obtained by the Colombian National Seismological Network for the 1993-2012 period confirms the potential occurrence of earthquakes in this region related to this fault because is the biggest thrust of the region.

  5. Lateral migration of fault activity in Weihe basin

    NASA Astrophysics Data System (ADS)

    Feng, Xi-Jie; Dai, Wang-Qiang

    2004-03-01

    Lateral migration of fault activity in Weihe basin is a popular phenomenon and its characteristics are also typical. Taking the activity migrations of Wangshun Mountain piedmont fault toward Lishan piedmont fault and Weinan platform front fault, Dabaopi-Niujiaojian fault toward Shenyusi-Xiaojiazhai fault, among a serial of NE-trending faults from Baoji city to Jingyang County as examples, their migration time and process are analyzed and discussed in the present paper. It is useful for further understanding the structure development and physiognomy evolution history of Weihe basin.

  6. 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.

  7. The December 7, 2012 Japan Trench intraplate doublet (Mw 7.2, 7.1) and interactions between near-trench intraplate thrust and normal faulting

    NASA Astrophysics Data System (ADS)

    Lay, Thorne; Duputel, Zacharie; Ye, Lingling; Kanamori, Hiroo

    2013-07-01

    A pair of large earthquakes ruptured within the Pacific plate below the Japan Trench about 14 s apart on December 7, 2012. The doublet began with an Mw 7.2 thrust event 50-70 km deep, followed by an Mw 7.1-7.2 normal-faulting event in the range 10-30 km deep about 27 km to the south-southwest. The deep lithosphere thrust earthquake is the largest such event to be recorded seaward of the rupture zone of the great March 11, 2011 Tohoku Mw 9.0 earthquake. It follows an extensive intraplate normal-faulting aftershock sequence since 2011 extending up to 100 km east of the trench. Many small normal faulting aftershocks of the doublet occurred along a 60 km-long trench-parallel-trend beneath the inner trench slope. The complex overlapping signals produced by the doublet present challenges for routine long-period moment tensor inversion procedures, but the inadequacy of any single point-source inversion was readily evident from comparisons of different data sets and solutions using different frequency bands. We use a two double-couple inversion of W-phase signals to quantify the doublet characteristics, along with an iterative deconvolution of P-wave signals that extracts a compatible three sub-event sequence. The occurrence of a large deep compressional event near the trench several years subsequent to a great megathrust event is similar to a sequence that occurred in the central Kuril Islands between 2006 and 2009, and appears to be associated with stress changes caused by the preceding interplate thrusting and intraplate normal faulting. Recent large deep compressional events in the Philippine Trench and northern Kermadec Trench regions may be influenced by strain accumulation on adjacent locked interplate megathrusts. Regions having more pronounced curvature of the subducting plate may have unrelaxed bending stresses, facilitating occurrence of large deep thrust faulting in advance of future megathrust failures, as was observed in 1963 in the central Kuril Islands

  8. Faulting structure above the Main Himalayan Thrust as shown by relocated aftershocks of the 2015 Mw7.8 Gorkha, Nepal, earthquake

    NASA Astrophysics Data System (ADS)

    Bai, Ling; Liu, Hongbing; Ritsema, Jeroen; Mori, James; Zhang, Tianzhong; Ishikawa, Yuzo; Li, Guohui

    2016-01-01

    The 25 April 2015, Mw7.8 Gorkha, Nepal, earthquake ruptured a shallow section of the Indian-Eurasian plate boundary by reverse faulting with NNE-SSW compression, consistent with the direction of current Indian-Eurasian continental collision. The Gorkha main shock and aftershocks were recorded by permanent global and regional arrays and by a temporary local broadband array near the China-Nepal border deployed prior to the Gorkha main shock. We relocate 272 earthquakes with Mw>3.5 by applying a multiscale double-difference earthquake relocation technique to arrival times of direct and depth phases recorded globally and locally. We determine a well-constrained depth of 18.5 km for the main shock hypocenter which places it on the Main Himalayan Thrust (MHT). Many of the aftershocks at shallower depths illuminate faulting structure in the hanging wall with dip angles that are steeper than the MHT. This system of thrust faults of the Lesser Himalaya may accommodate most of the elastic strain of the Himalayan orogeny.

  9. 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.

  10. Estimation of active faulting in a slow deformation area: Culoz fault as a case study (Jura-Western Alps junction).

    NASA Astrophysics Data System (ADS)

    de La Taille, Camille; Jouanne, Francois; Crouzet, Christian; Jomard, Hervé; Beck, Christian; de Rycker, Koen; van Daele, Maarten; Lebourg, Thomas

    2014-05-01

    The north-western Alps foreland is considered as still experiencing distal effects of Alpine collision, resulting in both horizontal and vertical relative displacements. Based on seismological and geodetic surveys, detailed patterns of active faulting (including subsurface décollements, blind ramps and deeper crustal thrusts have been proposed (Thouvenot et al., 1998), underlining the importance of NW-SE left-lateral strike-slip offsets as along the Vuache and Culoz faults (cf. the 1996 Epagny event: M=5.4; Thouvenot et al., 1998 and the 1822 Culoz event I=VII-VIII; Vogt, 1979). In parallel to this tectonic evolution, the last glaciation-deglaciation cycles contributed to develop large and over-deepened lacustrine basins, such as Lake Le Bourget (Perrier, 1980). The fine grain, post LGM (ie post 18 ky), sedimentary infill gives a good opportunity to evidence late quaternary tectonic deformations. This study focuses on the Culoz fault, extending from the Jura to the West, to the Chautagne swamp and through the Lake Le Bourget to the East. Historical earthquakes are known nearby this fault as ie the 1822 Culoz event. The precise location and geometry of the main fault is illustrated but its Eastern termination still needs to be determined. High resolution seismic sections and side-scan sonar images performed in the 90's (Chapron et al., 1996) showed that the Col du Chat and Culoz faults have locally deformed the quaternary sedimentary infill of the lake. These studies, mainly devoted to paleo-climate analysis were not able to determine neither the geometry of the fault, or to quantify the observed deformations. A new campaign devoted to highlight the fault geometry and associated deformation, has been performed in October 2013. Very tight profiles were performed during this high resolution seismic survey using seistec boomer and sparker sources. In several places the rupture reaches the most recent seismic reflectors underlying that these faults were active during

  11. Geophysical characterization of buried active faults: the Concud Fault (Iberian Chain, NE Spain)

    NASA Astrophysics Data System (ADS)

    Pueyo Anchuela, Óscar; Lafuente, Paloma; Arlegui, Luis; Liesa, Carlos L.; Simón, José L.

    2015-12-01

    The Concud Fault is a ~14-km-long active fault that extends close to Teruel, a city with about 35,000 inhabitants in the Iberian Range (NE Spain). It shows evidence of recurrent activity during Late Pleistocene time, posing a significant seismic hazard in an area of moderate-to-low tectonic rates. A geophysical survey was carried out along the mapped trace of the southern branch of the Concud Fault to evaluate the geophysical signature from the fault and the location of paleoseismic trenches. The survey identified a lineation of inverse magnetic dipoles at residual and vertical magnetic gradient, a local increase in apparent conductivity, and interruptions of the underground sediment structure along GPR profiles. The origin of these anomalies is due to lateral contrast between both fault blocks and the geophysical signature of Quaternary materials located above and directly south of the fault. The spatial distribution of anomalies was successfully used to locate suitable trench sites and to map non-exposed segments of the fault. The geophysical anomalies are related to the sedimentological characteristics and permeability differences of the deposits and to deformation related to fault activity. The results illustrate the usefulness of geophysics to detect and map non-exposed faults in areas of moderate-to-low tectonic activity where faults are often covered by recent pediments that obscure geological evidence of the most recent earthquakes. The results also highlight the importance of applying multiple geophysical techniques in defining the location of buried faults.

  12. The role of pressure solution seam and joint assemblages in the formation of strike-slip and thrust faults in a compressive tectonic setting; The Variscan of south-western Ireland

    NASA Astrophysics Data System (ADS)

    Nenna, Filippo; Aydin, Atilla

    2011-11-01

    The Ross Sandstone in County Clare, Ireland, was deformed by an approximately north-south compression during the end-Carboniferous Variscan orogeny. The initial assemblage consists of mutually abutting orthogonal arrays of 170° oriented set 1 joints/veins (JVs) and approximately 75° oriented set 1 pressure solution seams (PSSs) formed under the same stress conditions. Orientations of splay JVs and PSSs (set 2) suggest a clockwise remote stress rotation of about 35° responsible for the contemporaneous shearing of the set 1 arrays. Among these nearly orthogonal strike-slip faults, the prominent set is sub-parallel to set 1 JVs. These faults are formed by the linkage of en-echelon segments with broad damage zones responsible for right-lateral offsets of hundreds of meters. Thrust faults with up to 30 m of offset initiate within shale horizons and follow either the PSSs in the sandstones or high-angle shales within tilted sequences. Within the large thrust fault zones, compartmentalised blocks of rocks are bounded by thrust faults segments with various dip angles. Strike-slip and thrust faults are contemporaneous and owe their existence to initial weaknesses in the form of JVs and PSSs rather than by switching relative stress magnitudes and orientations associated with Andersonian models of faults and related stress orientations.

  13. 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

  14. Active fault creep variations at Chihshang, Taiwan, revealed by creep meter monitoring, 1998-2001

    NASA Astrophysics Data System (ADS)

    Lee, Jian-Cheng; Angelier, Jacques; Chu, Hao-Tsu; Hu, Jyr-Ching; Jeng, Fu-Shu; Rau, Ruey-Juin

    2003-11-01

    The daily creep meter data recorded at Chihshang in 1998-2001 are presented. The Chihshang creep meter experiment was set up across the Chihshang thrust fault, the most active segment of the Longitudinal Valley Fault, which is the present-day plate suture between the Eurasian and the Philippine Sea plates in eastern Taiwan. Near-continuous data recording at two sites revealed different surface fault motions yet similar annual shortening rates: 16.2 mm at the Tapo site (comprising two connected creep meters) and 15.0 mm at the Chinyuan site (three creep meters straddling parallel fault branches). Four of the five creep meters showed a seasonal variation, with the fault moving steadily during the rainy season from April to October, and remaining quiescent during the rest of the year. The only exception was recorded by the creep meter located on a mélange-composed hillslope, where local gravitational landsliding played an additional role other than tectonic faulting. Through comparison with daily precipitation data, we inferred that moderate rainfall suffices to trigger or facilitate slippage on the surface fault, during the transition period of the dry/wet season. During the observation period from 1998 to 2001, the subsurface seismicity exhibited clusters of microearthquakes on the Chihshang Fault at depths of 10-25 km. Recurrent earthquakes occurred regardless of whether the season was wet or dry, indicating that the stress relaxation associated with seismicity in the seismogenic zone did not transfer immediately up to the surface. The accumulated strain on the Chihshang Fault at shallow surface levels was released through creep during the wet season. In addition to these short-term seasonal variations, an apparent decrease in the annual slipping rate on the Chihshang Fault during the last few years deserves further investigation in order to mitigate against seismic hazard.

  15. 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

  16. Accommodation of Large Displacement along Thin Principal Slip Layer of a Fault: An Example of the Garam Thrust in the Paleozoic Taebaeksan Basin

    NASA Astrophysics Data System (ADS)

    Kim, S.; Ree, J.

    2009-12-01

    The principal slip layer (PSL) along which most of the shear displacement within a fault zone occurs is very narrow (less than 1-5 mm) and it is not so clear how this narrow layer accommodates a large (several m to several km) displacement. The NNW-striking and WSW-dipping Garam Thrust puts the Cambrian Wagok Formation on top of the Ordovician Mungok Formation in the Paleozoic Taebaeksan Basin of Korea. The Wagok Formation of the hanging wall is a massive dolostone consisting of euhedral dolomite grains (0.1-1 mm) and some fossil fragments. In contrast, the Mungok Formation of the footwall is a bedded limestone composed of calcite (20-150 μm) with some fossil fragments and dolomite. The estimated minimum displacement of the thrust is about 120 m. The principal slip zone between the two formations is only 3-10 mm thick and filled by vein calcites (100-500 μm in size) with foam texture. The hanging wall dolostone is highly fractured or “pulverized” while the footwall limestone is almost intact except a micro shear zone near the principal slip layer. In and adjacent to the principal slip layer, there are no fault rocks such as gouge or cataclasite. Prismatic euhedral quartz grains (100-200 μm long) occurs within and around the principal slip layer suggesting infiltration of fluid rich in silica as well as carbonate along the principal slip layer. In view of the absence of fault rocks within and adjacent to the principal slip layer, the possible accommodation processes of the large displacement along the thin layer may include fault lubrication by nano-crystalline decomposition products of carbonate minerals and fluid effect. To test these possibilities, textural analyses on the principal slip zone and micro shear zone using scanning electron microscopy are under way and we will discuss these results.

  17. Feedback between erosion and active deformation: geomorphic constraints from the frontal Jura fold-and-thrust belt (eastern France)

    NASA Astrophysics Data System (ADS)

    Madritsch, Herfried; Fabbri, Olivier; Hagedorn, Eva-Marie; Preusser, Frank; Schmid, Stefan M.; Ziegler, Peter A.

    2010-10-01

    A regional tectono-geomorphic analysis indicates a Pliocene to recent rock uplift of the outermost segment of the Jura fold-and-thrust belt, which spatially coincides with the intra-continental Rhine-Bresse Transfer Zone. Elevated remnants of the partly eroded Middle Pliocene Sundgau-Forêt de Chaux Gravels identified by heavy mineral analyses allow for a paleo-topographic reconstruction that yields minimum regional Latest Pliocene to recent rock uplift rates of 0.05 ± 0.02 mm/year. This uplift also affected the Pleistocene evolution of the Ognon and Doubs drainage basins and is interpreted as being tectonically controlled. While the Ognon River was deflected from the uplifted region the Doubs deeply incised into it. Focused incision of the Doubs possibly sustained ongoing deformation along anticlines which were initiated during the Neogene evolution of the thin-skinned Jura fold-and-thrust belt. At present, this erosion-related active deformation is taking place synchronously with thick-skinned tectonics, controlling the inversion of the Rhine-Bresse Transfer Zone. This suggests local decoupling between seismogenic basement faulting and erosion-related deformation of the Mesozoic cover sequences.

  18. Fold and thrust belt structures and strike-slip faulting at the SE margin of the Salar de Atacama basin, Chilean Andes

    NASA Astrophysics Data System (ADS)

    Kuhn, Dirk

    2002-07-01

    A tectonic reinterpretation is reported for the southeastern margin of the Salar de Atacama basin of northern Chile. Detailed structural mapping revealed the presence of an east vergent thin-skinned fold and thrust belt affecting Oligocene-Miocene Paciencia Group rocks and the overlying Plio-Pleistocene volcanic rocks. Along-strike segmentation of the main fold implies local foreland influence on footwall ramp geometry leading to local thrust sheet rotation. To the east the adjacent western slope of the Western Cordillera displays two different structural domains, probably controlled by preexisting basement structures. The southern domain comprises two N-S oriented sigmoidal belts of linear arranged pressure ridges, indicating left-lateral transpression. In contrast, the northern domain is characterized by east vergent fold and thrust belt structures and reactivated NW-SE striking sinistral strike-slip faults, governing clockwise block rotations. An indenter-driven deformation model is proposed to explain sinistral transpression and clockwise block rotations around vertical axes. This variant of a small-block rotation mechanism is discussed in the context of oroclinal bending of the central Andes, emphasizing the significance of ancient structures in controlling rotations.

  19. 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

  20. Bubble mass center and fluid feedback force fluctuations activated by constant lateral impulse with variable thrust

    NASA Technical Reports Server (NTRS)

    Hung, R. J.; Long, Y. T.

    1995-01-01

    Sloshing dynamics within a partially filled rotating dewar of superfluid helium 2 are investigated in response to constant lateral impulse with variable thrust. The study, including how the rotating bubble of superfluid helium 2 reacts to the constant impulse with variable time period of thrust action in microgravity, how amplitudes of bubble mass center fluctuates with growth and decay of disturbances, and how fluid feedback forces fluctuates in activating on the rotating dewar through the dynamics of sloshing waves are investigated. The numerical computation of sloshing dynamics is based on the non-inertial frame spacecraft bound coordinate with lateral impulses actuating on the rotating dewar in both inertial and non-inertial frames of thrust. Results of the simulations are illustrated.

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. 300-km-long co-seismic surface rupture produced by the 2008 Mw 7.9 Wenchuan earthquake along the active Longmen Shan Thrust Belt, China

    NASA Astrophysics Data System (ADS)

    Lin, A.; Rao, G.; Yan, B.

    2012-12-01

    The magnitude (Mw) 7.9 (Ms 8.1) Wenchuan earthquake occurred on 12 May 2008 and ruptured active faults of the Longmen Shan Thrust Belt (LSTB), which marks the boundary between the eastern margin of the Tibetan Plateau and the Sichuan Basin. Although many studies of the 2008 Mw 7.9 Wenchuan earthquake have described the ground deformation features, rupture mechanism, and structural features of the seismogenic fault zone associated with this event, debate remains concerning the total length of the co-seismic surface rupture zone and whether the earthquake ruptured the Qingchuan Fault in the northeastern segment of the Longmen Shan Thrust Belt (LSTB), China. Based on our initial fieldwork carried out 2 days after the 2008 Wenchuan earthquake, we reported that the earthquake produced a ~285-km-long surface rupture zone along the LSTB, at the eastern margin of the Tibetan Plateau, dominated by thrust slip and right-lateral displacement along the central and northeastern segments of the zone, and by left-lateral displacement along the southeastern segment (Lin et al., 2009, 2010). However, other field-based studies have reported that the total length of the co-seismic surface rupture zone is 200-240 km and that the Qingchuan Fault was not ruptured by the Wenchuan earthquake (e.g., Liu-Zeng et al., 2009; Xu et al., 2009; Yin, 2010; Zhang et al., 2010). The length of surface rupture produced by large, individual earthquakes is a key parameter in assessing the seismic moment, the rupture mechanism, the degree of seismic hazard, and the activity of a seismogenic fault, including the recurrence interval of large earthquakes and the long-term slip rate. Therefore, additional work is needed to constrain the length of the co-seismic surface rupture and the location of rupture termination at the northeastern segment of the LSTB, in order to accurately assess the nature of the seismic hazard in the densely populated Sichuan region of China. In this study, we present new field

  6. 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.

  7. 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)

  8. 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

  9. 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

  10. 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.

  11. Extreme Hydrothermal Conditions Near an Active Geological Fault, DFDP-2B Borehole, Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Sutherland, R.; Townend, J.; Toy, V.; Allen, M.; Baratin, L. M.; Barth, N. C.; Beacroft, L.; Benson, A.; Boese, C. M.; Boles, A.; Boulton, C. J.; Capova, L.; Carpenter, B. M.; Celerier, B. P.; Chamberlain, C. J.; Conze, R.; Cooper, A.; Coussens, J.; Coutts, A.; Cox, S.; Craw, L.; Doan, M. L.; Eccles, J. D.; Faulkner, D.; Grieve, J.; Grochowski, J.; Gulley, A.; Henry, G.; Howarth, J. D.; Jacobs, K. M.; Jeppson, T.; Kato, N.; Keys, S.; Kirilova, M.; Kometani, Y.; Lukács, A.; Langridge, R.; Lin, W.; Little, T.; Mallyon, D.; Mariani, E.; Marx, R.; Massiot, C.; Mathewson, L.; Melosh, B.; Menzies, C. D.; Moore, J.; Morales, L. F. G.; Morgan, C.; Mori, H.; Niemeijer, A. R.; Nishikawa, O.; Nitsch, O.; Paris Cavailhes, J.; Pooley, B.; Prior, D. J.; Pyne, A.; Sauer, K. M.; Savage, M. K.; Schleicher, A.; Schmitt, D. R.; Shigematsu, N.; Taylor-Offord, S.; Tobin, H. J.; Upton, P.; Valdez, R. D.; Weaver, K.; Wiersberg, T.; Williams, J. N.; Yeo, S.; Zimmer, M.; Broderick, N.

    2015-12-01

    The DFDP-2B borehole sampled rocks above and within the upper part of the Alpine Fault, New Zealand, to a depth of 893 m in late 2014. The experiment was the first to drill a major geological fault zone that is active and late in its earthquake cycle. We determined ambient fluid pressures 8-10% above hydrostatic and a geothermal gradient of 130-150 °C/km in rocks above the fault. These unusual ambient conditions can be explained by a combination of: rock advection that transports heat from depth by uplift and oblique slip on the fault; and fluid advection through fractured rock, driven by topographic forcing, which concentrates heat and causes fluid over-pressure in the valley. Highly-anomalous ambient conditions can exist in the vicinity of active faults, and earthquake and mineralization processes occur within these zones.

  12. 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

  13. Gravimetric evidences of active faults and underground structure of the Cheliff seismogenic basin (Algeria)

    NASA Astrophysics Data System (ADS)

    Abtout, A.; Boukerbout, H.; Bouyahiaoui, B.; Gibert, D.

    2014-11-01

    The Cheliff basin (ex El Asnam) is known as one of the most seismic active zone in Algeria and the West Mediterranean region. We can cite the El Asnam earthquake which occurred in 10.10.01980 with magnitude of 7.3. It was generated by a thrust fault with NE-SW sinistral component. Until now, there is a little information about existence of deep active faults, which generate this strong activity. The gravity field is an important resource of information on crustal structure. The aim of this work is giving a reliable geometry of the major faults relative to the kinematics of this region. The results obtained from various filtered maps (derivatives, upward continuation) of the gravity data, were used to generate a structural map of the studied area. Whilst the continuous wavelet transform method can help in automatic detection of elongated structures in 3-D, to estimate their strike direction, shape and depth. It gives a 3-D image or a model of the region and confirms the existence of several faults, localized or inferred, from former geological studies.

  14. Hydrogen Gas Emissions from Active Faults and Identification of Flow Pathway in a Fault Zone

    NASA Astrophysics Data System (ADS)

    Ishimaru, T.; Niwa, M.; Kurosawa, H.; Shimada, K.

    2010-12-01

    It has been observed that hydrogen gas emissions from the subsurface along active faults exceed atmospheric concentrations (e.g. Sugisaki et. al., 1983). Experimental studies have shown that hydrogen gas is generated in a radical reaction of water with fractured silicate minerals due to rock fracturing caused by fault movement (e.g. Kita et al., 1982). Based on such research, we are studying an investigation method for an assessment of fault activity using hydrogen gas emissions from fracture zones. To start, we have devised portable equipment for rapid and simple in situ measurement of hydrogen gas emissions (Shimada et al., 2008). The key component of this equipment is a commercially available and compact hydrogen gas sensor with an integral data logger operable at atmospheric pressure. In the field, we have drilled shallow boreholes into incohesive fault rocks to depths ranging from 15 to 45 cm using a hand-operated drill with a 9mm drill-bit. Then, we have measured the hydrogen gas concentrations in emissions from active faults such as: the western part of the Atotsugawa fault zone, the Atera fault zone and the Neodani fault in central Japan; the Yamasaki fault zone in southwest Japan; and the Yamagata fault zone in northeast Japan. In addition, we have investigated the hydrogen gas concentrations in emissions from other major geological features such as tectonic lines: the Butsuzo Tectonic Line in the eastern Kii Peninsula and the Atokura Nappe in the Northeastern Kanto Mountains. As a result of the investigations, hydrogen gas concentration in emissions from the active faults was measured to be in the approximate range from 6,000 ppm to 26,000 ppm in two to three hours after drilling. A tendency for high concentrations of hydrogen gas in active faults was recognized, in contrast with low concentrations in emissions from tectonic lines that were observed to be in the range from 730 ppm to 2,000 ppm. It is inferred that the hydrogen gas migrates to ground

  15. Structural geometry of Raplee Ridge monocline and thrust fault imaged using inverse Boundary Element Modeling and ALSM data

    NASA Astrophysics Data System (ADS)

    Hilley, G. E.; Mynatt, I.; Pollard, D. D.

    2010-01-01

    We model the Raplee Ridge monocline in southwest Utah, where Airborne Laser Swath Mapping (ALSM) topographic data define the geometry of exposed marker layers within this fold. The spatial extent of five surfaces were mapped using the ALSM data, elevations were extracted from the topography, and points on these surfaces were used to infer the underlying fault geometry and remote strain conditions. First, we compare elevations extracted from the ALSM data to the publicly available National Elevation Dataset 10-m DEM (Digital Elevation Model; NED-10) and 30-m DEM (NED-30). While the spatial resolution of the NED datasets was too coarse to locate the surfaces accurately, the elevations extracted at points spaced ˜50 m apart from each mapped surface yield similar values to the ALSM data. Next, we used a Boundary Element Model (BEM) to infer the geometry of the underlying fault and the remote strain tensor that is most consistent with the deformation recorded by strata exposed within the fold. Using a Bayesian sampling method, we assess the uncertainties within, and covariation between, the fault geometric parameters and remote strain tensor inferred using the model. We apply these methods to the Raplee Ridge monocline, and find that the resolution and precision of the ALSM data are unnecessary for inferring the fault geometry and remote strain tensor using our approach. However, the ALSM data were necessary for the mapping of the spatial distribution of surface outcrops. Our models considered two scenarios: one in which fault geometry and remote strains were inferred using a single deformed stratum, and another in which all mapped strata were used in the inversion. Modeled elevations match those observed to within a root-mean-squared error of 16-18 m, and show little bias with position along the fold. Both single- and multilayer inversions image a fault that is broadly constrained to be ˜4.5-14 km in down-dip height, 13-30 km in along-strike width, with a tip-line 2

  16. Assessing active faulting by hydrogeological modeling and superconducting gravimetry: A case study for Hsinchu Fault, Taiwan

    NASA Astrophysics Data System (ADS)

    Lien, Tzuyi; Cheng, Ching-Chung; Hwang, Cheinway; Crossley, David

    2014-09-01

    We develop a new hydrology and gravimetry-based method to assess whether or not a local fault may be active. We take advantage of an existing superconducting gravimeter (SG) station and a comprehensive groundwater network in Hsinchu to apply the method to the Hsinchu Fault (HF) across the Hsinchu Science Park, whose industrial output accounts for 10% of Taiwan's gross domestic product. The HF is suspected to pose seismic hazards to the park, but its existence and structure are not clear. The a priori geometry of the HF is translated into boundary conditions imposed in the hydrodynamic model. By varying the fault's location, depth, and including a secondary wrench fault, we construct five hydrodynamic models to estimate groundwater variations, which are evaluated by comparing groundwater levels and SG observations. The results reveal that the HF contains a low hydraulic conductivity core and significantly impacts groundwater flows in the aquifers. Imposing the fault boundary conditions leads to about 63-77% reduction in the differences between modeled and observed values (both water level and gravity). The test with fault depth shows that the HF's most recent slip occurred in the beginning of Holocene, supplying a necessary (but not sufficient) condition that the HF is currently active. A portable SG can act as a virtual borehole well for model assessment at critical locations of a suspected active fault.

  17. Active Fault Topography and Fault Outcrops in the Central Part of the Nukumi fault, the 1891 Nobi Earthquake Fault System, Central Japan

    NASA Astrophysics Data System (ADS)

    Sasaki, T.; Ueta, K.; Inoue, D.; Aoyagi, Y.; Yanagida, M.; Ichikawa, K.; Goto, N.

    2010-12-01

    It is important to evaluate the magnitude of earthquake caused by multiple active faults, taking into account the simultaneous effects. The simultaneity of adjacent active faults are often decided on the basis of geometric distances except for known these paleoseismic records. We have been studied the step area between the Nukumi fault and the Neodani fault, which appeared as consecutive ruptures in the 1891 Nobi earthquake, since 2009. The purpose of this study is to establish innovation in valuation technique of the simultaneity of adjacent active faults in addition to the paleoseismic record and the geometric distance. Geomorphological, geological and reconnaissance microearthquake surveys are concluded. The present work is intended to clarify the distribution of tectonic geomorphology along the Nukumi fault and the Neodani fault by high-resolution interpretations of airborne LiDAR DEM and aerial photograph, and the field survey of outcrops and location survey. The study area of this work is the southeastern Nukumi fault and the northwestern Neodani fault. We interpret DEM using shaded relief map and stereoscopic bird's-eye view made from 2m mesh DEM data which is obtained by airborne laser scanner of Kokusai Kogyo Co., Ltd. Aerial photographic survey is for confirmation of DEM interpretation using 1/16,000 scale photo. As a result of topographic survey, we found consecutive tectonic topography which is left lateral displacement of ridge and valley lines and reverse scarplets along the Nukumi fault and the Neodani fault . From Ogotani 2km southeastern of Nukumi pass which is located at the southeastern end of surface rupture along the Nukumi fault by previous study to Neooppa 9km southeastern of Nukumi pass, we can interpret left lateral topographies and small uphill-facing fault scarps on the terrace surface by detail DEM investigation. These topographies are unrecognized by aerial photographic survey because of heavy vegetation. We have found several new

  18. Quaternary Uplift of Coral Terraces from Active Folding and Thrusting Along the Northern Coast of Timor-Leste

    NASA Astrophysics Data System (ADS)

    Cox, N. L.; Harris, R.; Merritts, D.

    2006-12-01

    Emergent coral terraces along the northern coast of Timor-Leste, reveal differential vertical strain along the strike of the active Banda arc-continent collision complex. The number of major coral terraces in surveyed profiles increases from 2 to 25 along a coastal distance of 150 km from central to eastern Timor-Leste. Comparison of 8 separate terrace profiles with sea level curves predicts vertical displacement rates that increase eastward from <0.3 to 1.0-1.5 mm/year. This pattern is corroborated by U-series age analyses that document non-linear increases in vertical strain eastward with the uplift rates ranging from <.04 to 2.0 mm/year. U-series ages also indicates the occurrence of both erosional (regressional) and depositional terraces. Two profiles, dominated by erosional terraces, have associated local lower depositional terraces. The erosional terraces are more abundant, but yield apparent lower uplift rates in comparison with the depositional terraces. This occurrence questions the validity of uplift rates obtained by age analysis for the errosional terraces and/or aids in the conclusion that differential vertical strain not only exists with distance between profiles but with time for each profile. We associate active uplift with northward movement along retro- wedge thrust faults that are well documented in seismic reflection profiles adjacent to the north coast of Timor- Leste.

  19. 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.

  20. 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.

  1. 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.

  2. Active and inactive faults in southern California viewed from Skylab

    NASA Technical Reports Server (NTRS)

    Merifield, P. M.; Lamar, D. L.

    1977-01-01

    A number of prominent linears in basement terrane of the Peninsular Ranges appeared on Skylab images. In most cases, they were represented by straight or gently curved valleys; however, detailed field investigations have shown that several of these linears mark previously unmapped faults which form two distinct fault sets; one set trends northeast, the other west-northwest. No indications of recent movement were present on these faults which were truncated by seismically active, northwest trending fault zones such as the Elsinore and San Jacinto. Right-lateral separation is demonstrable on the northeast trending set.

  3. 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

  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. Tertiary structural evolution of the Gangdese thrust system southeastern Tibet

    SciTech Connect

    Yin, An; Harrison, M.; Ryerson, F.J.; Wenji, Chen; Kidd, W.S.F.; Copeland, P.

    1994-09-10

    Structural and thermochronological investigations of southern Tibet (Xizang) suggest that intracontinental thrusting has been the dominant cause for formation of thickened crust in the southernmost Tibetan plateau since late Oligocene. Two thrust systems are documented in this study: the north dipping Gangdese system (GTS) and the younger south dipping Renbu-Zedong system (RZT). West of Lhasa, the Gangdese thrust juxtaposes the Late Cretaceous forearc basin deposits of the Lhasa Block (the Xigaze Group) over the Tethyan sedimentary rocks of the Indian plate, whereas east of Lhasa, the fault juxtaposes the Late Cretaceous-Eocene, Andean-type arc (the Gangdese batholith) over Tethyan sedimentary rocks. Near Zedong, 150 km southeast of Lhasa, the Gangdese thrust is marked by a >200-m-thick mylonitic shear zone that consists of deformed granite and metasedimentary rocks. A major south dipping backthrust in the hanging wall of the Gangdese thrust puts the Xigaze Group over Tertiary conglomerates and the Gangdese plutonics north of Xigaze and west of Lhasa. A lower age bound for the Gangdese thrust of 18.3{+-}0.5 Ma is given by crosscutting relationships. The timing of slip on the Gangdese thrust is estimate to be 27-23 Ma from {sup 40}Ar/{sup 39}Ar thermochronology, and a displacement of at least 46{+-}9 km is indicated near Zedong. The age of the Gangdese thrust (GT) is consistent with an upper age limit of {approximately}24 Ma for the initiation of movement on the Main Central thrust. In places, the younger Renbu-Zedong fault is thrust over the trace of the GT, obscuring its exposure. The RZT appears to have been active at circa 18 Ma but had ceased movement by 8{+-}1 Ma. The suture between India and Asia has been complexely modified by development of the GTS, RZT, and, locally, strike-slip and normal fault systems. 64 refs., 14 figs., 2 tabs.

  6. 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

  7. 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

  8. The Mendocino triple junction: Active faults, episodic coastal emergence, and rapid uplift

    NASA Astrophysics Data System (ADS)

    Merritts, Dorothy J.

    1996-03-01

    A complex zone of rapid Holocene surface uplift and deformation occurs at the Mendocino triple junction, the juncture of three plate-bounding faults: the Cascadia subduction zone, San Andreas fault, and Mendocino fault. Within this mountainous structural knot, up to 1.4 m of coastal emergence occurred during the 1992 Cape Mendocino MS 7.1 earthquake. Surveying and radiometric dating of ancient marine strandlines (<8000 years) along the trace of the southernmost Cascadia subduction zone indicate that the Holocene pattern of net surface uplift is very similar to the 1992 coseismic uplift pattern. Results of this investigation also indicate that episodic emergence occurred at least four times between about 600 and 7000 years ago and that some past events might have resulted in larger amounts of uplift (˜2.5 m) than the 1992 earthquake, perhaps during great earthquakes (M>7.5) along the Cascadia subduction zone megathrust. However, another plausible interpretation of the data is that multiple earthquakes resulting in smaller amounts of net surface uplift per event (similar to the 1992 earthquake) occurred closely spaced in time, giving the appearance in the geologic record of less frequent and larger events. Regardless of the number and timing of paleoearthquakes, the number of platforms is a minimum of the number of events that resulted in sudden, rapid uplift, because platform preservation is also a function of rising Holocene sea level. At present, rates and patterns of net surface uplift are better constrained than the timing and magnitude of paleoearthquakes. Periods of rapid Holocene emergence also are identified as far south of the area of 1992 uplift and the Mendocino fault as ˜30 km, along the unlocated San Andreas fault. These also might be associated with coseismic uplift. Based on new mapping of active faults in the region, it is proposed here that this uplift is the result of multiple discontinuous thrust and strike-slip fault segments which distribute

  9. 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.

    2016-01-01

    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.

  10. Spatial distribution of microfractures in damage zone along active faults

    NASA Astrophysics Data System (ADS)

    Mizoguchi, K.; Ueta, K.

    2011-12-01

    For basement faults without overlying quaternary sediments, there are few methods to determine whether the fault is active or not. Recently, we focus on microfracture characteristics of damage zone along active faults as used for the assessment of seismic activity of basement faults. In this study, we examined a newly-found active fault (Sasaki et al., 2011) located to the east of the epicentral area of 1943 Tottori earthquake, southwest Japan. The fault zone consists of the 75 cm thick fault core of the purple-colored clayey fault gouge and the fault breccia with cataclastic foliation, and the surrounding damage zone developed in Cretaceous Kyushozan granite. A subsidiary fault accompanying a fault core of white clayey fault gouge that ranges from 3 to 5 mm thickness is located at about 110 m from the main fault. We collected ten orientated samples 9 m to 180 m from the main fault. The samples were coated with epoxy and then thin sections were cut perpendicular to the fault plane and parallel to a horizontal plane because the slip direction is unknown. Microfracture density data were collected from 40 quartz grains per thin section (per sample). A thin section is marked with a square grid at 3 mm intervals and we picked one grain up in each square of the grid marked on the thin section to reduce operator sampling bias resulting from the selection of quartz grains. Quartz is suitable to estimate the damage that the rock sample has sustained because quartz without cleavage acts as an isotropic medium for fracturing and it is physically and chemically resistant to weathering than other minerals constituting the granite. We counted the number of microfractures that intersected a line which was drawn from the edge of each quartz grain, through the center point, to the other edge of the grain. The linear microfracture density for each sample is calculated to be the total number of microfractures intersecting the lines divided by the total counting line length. Under the

  11. Seismic images of the active fault system in the Yunlin and Chiayi area of Taiwan.

    NASA Astrophysics Data System (ADS)

    Sun, Wei-Hsiang; Shih, Ruey-Chyuan

    2015-04-01

    The Yunlin and Chiayi area in western Taiwan are well known of having a higher risk of earthquake disaster. The main fault system that controls the structure deformation in this area consists of the Chiuchiungkeng fault, the Meishan fault, and the Gukeng fault. According to historical records, the 1906 Meishan earthquake, magnitude 7.1, was triggered by the right-lateral strike-slip fault Meishan fault. Previous Seismic surveys showed that the Meishan fault is a high angle fault with flower structure. The Chiuchiungkeng fault is a thrust fault, located at front of the western foothills. Formations on the hanging wall and foot wall of the fault, both dipping to the east with different angles, can be identified from seismic images. The Gukeng fault was never been studied before. From the recent study of GPS monitoring, we may found that the velocity field near the Gukeng fault had a significant difference at both side of the fault. In addition, there is other information showed that there exists an aseismic gap around the fault. The above phenomena could be considered as a stress accumulation along the Gukeng fault. In the other words, the Gukeng fault could be playing an important role of controlling the regional surface deformation and seismicity distribution in this area. In this case, it will be worthwhile of knowing where the Gukeng fault is, and its subsurface structure. In this presentation, we will show our study of the subsurface structure of the Gukeng fault by using the seismic exploration method. The data consist of the shallow seismic reflection images those conducted by ourselves and the deeper seismic profiles acquired by CPC. Three dimensional relationships between the Gukeng fault, the Meishan fault, the Chiuchiungkeng fault, and other structures such as the Hsiaomei anticline will be illustrated as well.

  12. ALBANIA: Thrust and backthrust systems of external Albanides: Examples

    SciTech Connect

    Bega, Z.; Janopulli, V.

    1995-08-01

    External Albanides have proved as an oil/gas province in a certain limited area. Better understanding of thrusting and backthrusting systems and how both systems work, could improve objectives for exploration beyond actual discoveries. Backthrusting is not seen any more typical for Cenozoic sediments, where buried front of thrust faulted belts are very active. Mesozoic rocks, that are dominated by westward thrust propagation are also affected by backthrusting, thus leaving more space for other units accommodation. New concepts postulated are based on Deep Holes, Seismic Data, Outcrops and Spot Imagery. Among onshore examples, some of them cross existing fields.

  13. 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

  14. Evidence against Late Quaternary activity along the Northern Karakoram Fault

    NASA Astrophysics Data System (ADS)

    Robinson, A. C.; Owen, L. A.; Hedrick, K.; Blisniuk, K.; Sharp, W. D.; Chen, J.; Schoenbohm, L. M.; Imrecke, D. B.; Yuan, Z.; Li, W.

    2012-12-01

    Although the entire 1000 km long Karakoram fault has long been interpreted to be active, recent work based primarily on interpretation of satellite imagery suggests that the northern end of the fault, where it enters the Pamir mountains, is inactive. We present field observations and geochronologic data from the southern end of the Tashkurgan valley, in the Pamir, on the Karakoram fault where it splits into two identifiable strands; an eastern strand which is the main trace of the Karakoram fault, and a western strand called the Achiehkopai fault. These results support the interpretation that the northern Karakoram fault is currently inactive, and has been for at least 200 ka: 1) Near the village of Dabudaer in the southern Tashkurgan valley the main trace of the Karakoram fault is orthogonally cut by a narrow incised valley with no observed lateral offset across the fault. Within this valley, a strath terrace ~50 m above the active drainage which overlies the main trace of the Karakoram fault which is capped by a carbonate cemented conglomerate. U-series analyses of carbonate cement from a correlative deposit located several km away yields a minimum depositional age of 76±12 ka. This age is coeval with the local Tashkurgan glacial stage we dated using Be-10 surface exposure dating (66±10 ka; Owen et al., 2012, Quaternary Science Reviews) suggesting both the conglomerate and strath terrace formed during this glacial stage. 2) ~25 km south of Dabudar, the main trace of the Karakoram projects beneath Tashkurgan glacial stage moraine and fluvial-glacial deposits which similarly show no evidence of disturbance by strike-slip deformation. Both of the above results demonstrate the main trace of the Karakoram fault has been inactive since at least ~70 ka. 3) Both the Karakoram and Achiehkopai faults are overlain by older Dabudaer glacial stage moraine deposits which are interpreted to be at least as old as the penultimate glacial, but may be >200 ka based on our Be-10

  15. Anatomy of a microearthquake sequence on an active normal fault.

    PubMed

    Stabile, T A; Satriano, C; Orefice, A; Festa, G; Zollo, A

    2012-01-01

    The analysis of similar earthquakes, such as events in a seismic sequence, is an effective tool with which to monitor and study source processes and to understand the mechanical and dynamic states of active fault systems. We are observing seismicity that is primarily concentrated in very limited regions along the 1980 Irpinia earthquake fault zone in Southern Italy, which is a complex system characterised by extensional stress regime. These zones of weakness produce repeated earthquakes and swarm-like microearthquake sequences, which are concentrated in a few specific zones of the fault system. In this study, we focused on a sequence that occurred along the main fault segment of the 1980 Irpinia earthquake to understand its characteristics and its relation to the loading-unloading mechanisms of the fault system. PMID:22606366

  16. Anatomy of a microearthquake sequence on an active normal fault

    PubMed Central

    Stabile, T. A.; Satriano, C.; Orefice, A.; Festa, G.; Zollo, A.

    2012-01-01

    The analysis of similar earthquakes, such as events in a seismic sequence, is an effective tool with which to monitor and study source processes and to understand the mechanical and dynamic states of active fault systems. We are observing seismicity that is primarily concentrated in very limited regions along the 1980 Irpinia earthquake fault zone in Southern Italy, which is a complex system characterised by extensional stress regime. These zones of weakness produce repeated earthquakes and swarm-like microearthquake sequences, which are concentrated in a few specific zones of the fault system. In this study, we focused on a sequence that occurred along the main fault segment of the 1980 Irpinia earthquake to understand its characteristics and its relation to the loading-unloading mechanisms of the fault system. PMID:22606366

  17. 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

  18. Active faults and minor plates in NE Asia

    NASA Astrophysics Data System (ADS)

    Kozhurin, Andrey I.; Zelenin, Egor A.

    2014-05-01

    Stated nearly 40 yr ago the uncertainty with plate boundaries location in NE Asia (Chapman, Solomon, 1976) still remains unresolved. Based on the prepositions that a plate boundary must, first, reveal itself in linear sets of active structures, and, second, be continuous and closed, we have undertaken interpretation of medium-resolution KH-9 Hexagon satellite imageries, mostly in stereoscopic regime, for nearly the entire region of NE Asia. Main findings are as follows. There are two major active fault zones in the region north of the Bering Sea. One of them, the Khatyrka-Vyvenka zone, stretches NE to ENE skirting the Bering Sea from the Kamchatka isthmus to the Navarin Cape. Judging by the kinematics of the Olyutorsky 2006 earthquake fault, the fault zones move both right-laterally and reversely. The second active fault zone, the Lankovaya-Omolon zone, starts close to the NE margin of the Okhotsk Sea and extends NE up to nearly the margin of the Chukcha Sea. The fault zone is mostly right-lateral, with topographically expressed cumulative horizontal offsets amounting to 2.5-2.6 km. There may be a third NE-SW zone between the major two coinciding with the Penzhina Range as several active faults found in the southern termination of the Range indicate. The two active fault zones divide the NE Asia area into two large domains, which both could be parts of the Bering Sea plate internally broken and with uncertain western limit. Another variant implies the Khatyrka-Vyvenka zone as the Bering Sea plate northern limit, and the Lankovaya-Omolon zone as separating an additional minor plate from the North-American plate. The choice is actually not crucial, and more important is that both variants leave the question of where the Bering Sea plate boundary is in Alaska. The Lankovaya-Omolon zone stretches just across the proposed northern boundary of the Okhorsk Sea plate. NW of the zone, there is a prominent left-lateral Ulakhan fault, which is commonly interpreted to be a

  19. 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.

  20. 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

  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. Three-dimensional finite-element modelling of horizontal surface velocity and strain patterns near thrust and normal faults during the earthquake cycle: implications for interpreting geological and geodetic data

    NASA Astrophysics Data System (ADS)

    Hampel, Andrea; Hetzel, Ralf

    2015-04-01

    In recent years, more and more geological and space-geodetic data on the surface deformation associated with earthquakes on intra-continental normal and thrust faults have become available. Here we use three-dimensional finite-element models that account for gravity, far-field ("regional") extension/shortening and postseismic relaxation in a viscoelastic lower crust to quantify the surface deformation caused by an Mw ~7 earthquake on a dip-slip fault. The coseismic deformation is characterized by horizontal shortening in the footwall of the normal fault and extension in the hanging wall of the thrust fault - consistent with elastic dislocation models, geological field observations and GPS data from earthquakes in Italy and Taiwan. During the postseismic phase, domains of extensional and contractional strain exist next to each other near both fault types. The spatiotemporal evolution of these domains as well as the postseismic velocities and strain rates strongly depend on the viscosity of the lower crust. For viscosities of 1e18-1e20 Pa s, the signal from postseismic relaxation is detectible for 20-50 years after the earthquake. If GPS data containing a postseismic relaxation signal are used to derive regional rates, the stations may show rates that are too high or too low or even an apparently wrong tectonic regime. By quantifying the postseismic deformation through space and time, our models help to interpret GPS data and to identify the most suitable locations for GPS stations.

  3. New GPS Network on the Active Fault System in Taiwan

    NASA Astrophysics Data System (ADS)

    Hou, C.; Chen, Y.; Hu, J.; Lin, C.; Chen, C.; Wang, J.; Chung, L.; Chung, W.; Hsieh, C.; Chen, Y.

    2004-12-01

    According to the historical records, disastrous earthquakes occurred in Taiwan were caused by reactivations of active faults. In last century, there were five with the surface rupture: 1906 Meishan Eq. (the Meishan F.), 1935 Hsihchu Eq. (the Shihtan and the Tuntzuchiao F.), 1946 Hsinhua Eq. (Hsinhua F.), 1951 Hualien-Taitung Eq. (Longitudinal Valley F.), and 1999 Chi-Chi Eq. (the Chelungpu F.). In order to identify earthquake associated surface rupture and further to mitigate potential hazards, the investigation and monitoring on the active fault system are of great urgency. Central Geological Survey (CGS) of Taiwan is currently executing a 5-year (2002-2006) project, integrating geological and geodetic data to better characterize short-term and long-term spatial and temporal variations in deformation across major already-known active faults of Taiwan. For the former, we use field survey, drilling, geophysical exploration, and trenching to recognize the long-term slip rate and recurrence interval of each fault. For the latter, we deploy near-fault campaign-style GPS and leveling monitoring networks. Here we further combine the result of other GPS networks including continuous-mode. This project is actually concentrated on fault-specific investigation.. Until Dec. 2004, we have set up 756 GPS stations and 27 precise leveling lines including 1024 leveling benchmarks. For the purpose of understanding temporal variability and receive continuous record, the CGS began to deploy 6~10 new GPS stations of continuous mode since 2004. Upon the completion of the geodetic project, we are supposed to provide information on short-term slip rates of major active faults. By integrating other geological datasets we will also evaluate the short-term and long-term behavior of the active faults, and further offer insight into spatial and temporal variability in deformation processes.

  4. Activity of faults observed in caves of the Eastern Alps

    NASA Astrophysics Data System (ADS)

    Baroň, Ivo; Plan, Lukas; Grasemann, Bernhard; Mitrovič, Ivanka; Stemberk, Josef

    2015-04-01

    Major recent tectonic process in the Eastern Alps involves the Neogene and Quaternary lateral extrusion of parts of the Eastern Alps towards the Pannonian Basin coeval with north-south shortening of the collision realm between the Adriatic Plate and the Bohemian Massif (European Plate). Within the framework of the FWF project "Speleotect" (2013-2017), we observe recent activity of the major fault systems of the Eastern Alps, such as the (1) Salzach-Ennstal-Mariazell-Puchberg (SEMP), (2) Mur-Mürz, (3) Periadriatic, (4) Lavanttal, and (5) Vienna Basin marginal Faults. Totally seven high-accuracy 3D crack-gauges TM71 with automated reading devices were installed in five selected karst caves with faults younger than the particular caves and correlated to one of these fault zones. The recorded micro-displacement events have been compared to known regional fault kinematics and to regional seismic activity (seismic data provided by the ZAMG). Already within the first year of observation, several micro displacement events were registered; these events sometimes revealed the same mechanisms as the geologically documented kinematics of the particular active faults, but in some cases performed completely opposite kinematics. These micro displacement events occurred in seismically rather quiet periods, however, usually about 1 - 10 days prior to local seismic events of different magnitudes (varying between ML 0.1 and 3.3). Further, in some caves gravitational mass movements were recorded that accompanied the tectonic moments.

  5. Fault mirrors of seismically active faults: A fossil of small earthquakes at shallow depths

    NASA Astrophysics Data System (ADS)

    Kuo, L.; Song, S.; Suppe, J.

    2013-12-01

    Many faults are decorated with naturally polished and glossy surfaces named fault mirrors (FMs) formed during slips. The characterization of FMs is of paramount importance to investigate physico-chemical processes controlling dynamic fault mechanics during earthquakes. Here we present detailed microstructural and mineralogical observations of the FMs from borehole cores of seismically active faults. The borehole cores were recovered from 600 to 800 m depth located in the hanging wall of the Hsiaotungshi fault in Taiwan which ruptured during 1935 Mw7.1 Hsinchu-Taichung earthquake. Scanning electron microscope (SEM) images of FMs show that two distinct textural domains, fault gouge and coated materials (nanograins, melt patchs, and graphite), were cut by a well-defined boundary. Melt patches and graphite, determined by X-ray diffraction (XRD), Transmission electron microscope (TEM), and SEM-EDS analysis, were found to be distributed heterogeneously on the slip surfaces. On the basis of the current kinematic cross section of the Hsiaotungshi fault, all the FMs were exhumed less than 5 km, where ambient temperatures are less than 150°C. It seems that the amorphous materials on the FMs were generated by seismic slips. The sintering nanograins coating the slip surfaces was also suggested to be produced at high slip rates from both natural observation and recent rock deformation experiments. In addition, graphite could be produced by seismic slips and lubricate the fault based on the rock deformation experiments. Our observation suggests that the FMs were composed of several indicators of coseismic events (melt patches, sintering nanograins, and graphite) corresponding to small thermal perturbation generated by seismic slips. Although the contribution of these coseismic indicators on frictional behavior remains largely unknown, it suggests that multiple dynamic weakening mechanisms such as flash heating, powder lubrication and graphitization may be involved during

  6. 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).

  7. Fold-thrust dislocations in sedimentary cover of the Sea of Azov

    NASA Astrophysics Data System (ADS)

    Popkov, V. I.

    2009-07-01

    As follows from geological and geophysical data, tectonic deformations formed under lateral compression are widespread in the sedimentary cover at the bottom of the Sea of Azov. Fold-thrust dislocations are established in the North Azov Trough on the southern slope of the Ukrainian Shield, in the Azov Swell of the young Scythian Plate, and in the Indol-Kuban Foredeep. The transregional Main Azov Thrust Fault and smaller thrust faults of listric morphology tens of kilometers in extent are known. Asymmetric anticlines are related to their fronts. In plan view, the crests of these anticlines are displaced down the dip of the controlling faults. Folds and thrusts developed in pulsatory manner in the regime of periodically acting tangential compression are recorded in the thickness of the plate complex and stratigraphic and angular unconformities. Some of these dislocations are active and accompanied by anomalously high formation pressure, temperature and hydrochemical anomalies, tectonic brecciation, and mud volcanoes.

  8. 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

  9. Study on the Late Quaternary Activity of Niyang River Fault

    NASA Astrophysics Data System (ADS)

    Fangtou, T.

    2015-12-01

    Niyang River fault with north-west trending is located on the west side of the Eastern Himalayan Syntaxis. It dislocated the eastern segment of Brahmaputra fault zone. We study the late Quaternary activity of the Niyang River fault by the high-resolution image data in combination with detailed field investigation, GPS observation, trenching and radiocarbon dating of charcoal samples. The GPS observation data shows that the movement characteristics of Niyang River fault is dextral strike-slip with extrusion at present, its strike-slip rate is 3~4mm/a and its extrusion rate is 2~3mm/a. The trench at Bayi town revealed that the first terraces of Niyang River was dislocated 50cm by the fault and it is dated to be 1220±40cal.a BP.. We found that third Lake terraces of the Linzhi ancient lakes was dislocated about 1.5m at Mirui town and it is dated to be 18060±60cal.a BP.. By the fault influence, there are different elevations at the same level terraces of Niyang river and the Linzhi ancient lakes both sides of Niyang river near Bayi town. The altitude of the second terraces of Niyang River is about 20 meters at eastern side higher than western side and it is dated to be between 8860±40cal.a BP. and 9870±50cal.a BP., the altitude of the third lake terraces of the Linzhi ancient lakes is about 60 meters at eastern side higher than western side. So, the average vertical slip rate of Niyang River fault was about 2mm/a since Holocene and its average vertical slip rate was about 3mm/a since late period of the late Pleistocene. This is consistent with GPS observation data. All these data suggest that Niyang River fault is active since Holocene. So further detailed research will be necessary to determine the range of the latest activity of this fault, movement characteristics and velocity and recurrence intervals of major earthquakes. These data will be a great significance for earthquake zonation and assessment of seismic risk in this region. Keywords:Niyang River fault

  10. 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.

  11. 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

  12. Controls on thrust belt curvature, Wyoming-Idaho thrust belt

    SciTech Connect

    Montgomery, J.M. Jr. . Dept. of Geological Sciences)

    1993-04-01

    Structural curvature in the northern part of the Wyoming-Idaho thrust belt (WITB) may be the result of either along-strike variations in pre-thrust stratigraphy or a buttress which physically concentrated shortening, or possibly both. Most thrust sheets of the WITB strike northward and were translated eastward, but in the Snake River Range (SRR) (the northernmost range in the WITB), structural strike curves from northward to nearly westward. Structural cross sections of the SRR are generally drawn in a radial pattern creating a volumetric imbalance in regional palinspastic restorations. Stratigraphic separation diagrams of major, through-going thrust faults in the SRR show extensive cut off in upper Paleozoic strata. New measured sections of upper Paleozoic stratigraphy at locations in several major thrust sheets of the WITB and in the foreland, new structural cross sections and mapping, and existing paleomagnetic data are used in a new interpretation of the origin of structural curvature in the WITB. Published paleomagnetic data require counterclockwise rotation of frontal thrust sheets along the northern boundary of the WITB, but no rotation of eastward-translated thrust sheets farther south along most of the WITB. Evidence for both a pre-existing west-trending depositional margin and rotation of frontal thrust sheets suggests that buttressing and modification of structural strike occurred along an oblique ramp where differences in stratigraphic thickness and possible pre-existing fault partitioning of the Paleozoic strata are localized.

  13. Structural Discordance Between Neogene Detachments and Frontal Sevier Thrusts, Central Mormon Mountains, Southern Nevada

    NASA Astrophysics Data System (ADS)

    Wernicke, Brian; Walker, J. Douglas; Beaufait, Mark S.

    1985-02-01

    Detailed geologic mapping in the Mormon Mountains of southern Nevada provides significant insight into processes of extensional tectonics developed within older compressional orogens. A newly discovered, WSW-directed low-angle normal fault, the Mormon Peak detachment, juxtaposes the highest levels of the frontal most part of the east-vergent, Mesozoic Sevier thrust belt with autochthonous crystalline basement. Palinspastic analysis suggests that the detachment initially dipped 20-25° to the west and cut discordantly across thrust faults. Nearly complete lateral removal of the hanging wall from the area has exposed a 5 km thick longitudinal cross-section through the thrust belt in the footwall, while highly attenuated remnants of the hanging wall (nowhere more than a few hundred meters thick) structurally veneer the range. The present arched configuration of the detachment resulted in part from progressive "domino-style" rotation of a few degrees while it was active, but is largely due to rotation on younger, structurally lower, basement-penetrating normal faults that initiated at high-angle. The geometry and kinematics of normal faulting in the Mormon Mountains suggest that pre-existing thrust planes are not required for the initiation of low-angle normal faults, and even where closely overlapped by extensional tectonism, need not function as a primary control of detachment geometry. Caution must thus be exercised in interpreting low-angle normal faults of uncertain tectonic heritage such as those seen in the COCORP west-central Utah and BIRP's MOIST deep-reflection profiles. Although thrust fault reactivation has reasonably been shown to be the origin of a very few low-angle normal faults, our results indicate that it may not be as fundamental a component of orogenic architecture as it is now widely perceived to be. We conclude that while in many instances thrust fault reactivation may be both a plausible and attractive hypothesis, it may never be assumed.

  14. Deep geometry and evolution of the northern part of Itoigwa-Shizuoka Tectonic Line active fault system, Central Japan, revealed by Seismic profiling

    NASA Astrophysics Data System (ADS)

    Sato, H.; Ikeda, Y.; Iwasaki, T.; Matsuta, N.; Takeda, T.; Kawasaki, S.; Kozawa, T.; Elouai, D.; Hirata, N.; Kawanaka, T.

    2003-12-01

    -related folds on their hanging wall. Westward migration of thrusting is recognized by shallow high-resolution seismic section and tectonic geomorphology. The ISTL active fault is an emergent thrust dipping 30 degrees to the east and no evidence is observed showing late Quaternary faulting along the fault, runs parallel to the ISTL and located east of it. Based on the balanced geologic cross-section, the total amount of Miocene extension is ca. 45 km and the total amount of shortening is ca. 25 km. If we assume that the shortening deformation has continued since 5 Ma at constant rate, the horizontal slip rate is calculated as 5 mm/y. The late Quaternary slip rate in the northern part of the ISTL active fault system based on very shallow seismic profiling and drilling shows similar value. The 7-km-long seismic section (Matsumoto 2002) across the middle part of ISTL active fault system also suggests that east-dipping fault geometry at gentle dip. To summarize deep geometry of the ISTL active fault system is strongly controlled by the Miocene extensional structure.

  15. 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).

  16. Active control of surge in centrifugal compressors using magnetic thrust bearing actuation

    NASA Astrophysics Data System (ADS)

    Sanadgol, Dorsa

    This research presents a new method for active surge control in centrifugal compressors with unshrouded impellers using a magnetic thrust bearing to modulate the impeller tip clearance. Magnetic bearings offer the potential for active control of flow instabilities. This capability is highly dependent on the sensitivity of the compressor characteristics to blade tip clearance. If the position of the shaft can be actuated with sufficient authority and speed, the induced pressure modulation makes control of surge promising. The active nature of the magnetic bearing system makes the real-time static and dynamic positioning of the rotor and therefore modulation of the impeller tip clearance possible. A theoretical model is first established that describes the sensitivity of the centrifugal compressor characteristic curve to tip clearance variations induced by axial motion of the rotor. Results from simulation of the nonlinear model for a single stage high-speed centrifugal compressor show that using the proposed control method, mass flow and pressure oscillations associated with compressor surge are quickly suppressed with acceptable tip clearance excursions, typically less than 20% of the available clearance. It is shown that it is possible to produce adequate axial excursions in the clearance between the impeller blades and the adjacent stationary shroud using a magnetic thrust bearing with practical levels of drive voltage. This surge control method would allow centrifugal compressors to reliably and safely operate with a wider range than is currently done in the field. The principal advantage of the proposed approach over conventional surge control methods lies in that, in machines already equipped with magnetic bearing, the method can potentially be implemented by simply modifying controller software. This dispenses with the need to introduce additional hardware, permitting adaptation of existing machinery at virtually no cost. In addition, since the controller is

  17. Sliding mode fault detection and fault-tolerant control of smart dampers in semi-active control of building structures

    NASA Astrophysics Data System (ADS)

    Yeganeh Fallah, Arash; Taghikhany, Touraj

    2015-12-01

    Recent decades have witnessed much interest in the application of active and semi-active control strategies for seismic protection of civil infrastructures. However, the reliability of these systems is still in doubt as there remains the possibility of malfunctioning of their critical components (i.e. actuators and sensors) during an earthquake. This paper focuses on the application of the sliding mode method due to the inherent robustness of its fault detection observer and fault-tolerant control. The robust sliding mode observer estimates the state of the system and reconstructs the actuators’ faults which are used for calculating a fault distribution matrix. Then the fault-tolerant sliding mode controller reconfigures itself by the fault distribution matrix and accommodates the fault effect on the system. Numerical simulation of a three-story structure with magneto-rheological dampers demonstrates the effectiveness of the proposed fault-tolerant control system. It was shown that the fault-tolerant control system maintains the performance of the structure at an acceptable level in the post-fault case.

  18. The 1994 Sefidabeh earthquakes in eastern Iran: blind thrusting and bedding-plane slip on a growing anticline, and active tectonics of the Sistan suture zone

    NASA Astrophysics Data System (ADS)

    Berberian, M.; Jackson, J. A.; Qorashi, M.; Talebian, M.; Khatib, M.; Priestley, K.

    2000-08-01

    In 1994 a sequence of five earthquakes with Mw 5.5-6.2 occurred in the Sistan belt of eastern Iran, all of them involving motion on blind thrusts with centroid depths of 5-10km. Coseismic ruptures at the surface involved bedding-plane slip on a growing hanging-wall anticline displaying geomorphological evidence of uplift and lateral propagation. The 1994 earthquakes were associated with a NW-trending thrust system that splays off the northern termination of a major N-S right-lateral strike-slip fault. Elevation changes along the anticline ridge suggest that displacement on the underlying thrust dies out to the NW, away from its intersection with the strike-slip fault. This is a common fault configuration in eastern Iran and accommodates oblique NE-SW shortening across the N-S deforming zone, probably by anticlockwise rotations about a vertical axis. This style of fault kinematics may be transitional to a more evolved state that involves partitioning of the strike-slip and convergent motion onto separate subparallel faults.

  19. High Frequency Monitoring of the Aigion Fault Activity

    NASA Astrophysics Data System (ADS)

    Cornet, Francois; Bourouis, Seid

    2013-04-01

    In 2007, a high frequency monitoring system was deployed in the 1000 m deep AIG10 well that intersects the Aigion fault at a depth of 760 m. This active 15 km long fault is located on the south shore of the Corinth rift, some 40 km east from Patras, in western central Greece. The borehole intersects quaternary sediments down to 495 m, then cretaceous and tertiary heavily tectonized deposits from the Pindos nappe. Below the fault encountered at 760 m, the borehole remains within karstic limestone of the Gavrovo Tripolitza nappe. The monitoring system involved two geophones located some 15 m above the fault, and two hydrophones located respectively at depths equal to 500 m and 250 m. The frequency domain for the data acquisition system ranged from a few Hz to 2500 Hz. The seismic velocity structure close to the borehole was determined through both sonic logs and vertical seismic profiles. This monitoring system has been active during slightly over six months and has recorded signals from microseismic events that occurred in the rift, the location of which was determined thanks to the local 11 stations, three components, short period (2 Hz), monitoring system. In addition, the borehole monitoring system has recorded more than 1000 events not identified with the regional network. Events were precisely correlated with pressure variations associated with two human interventions. These extremely low magnitude events occurred at distances that reached at least up to 1500 m from the well. They were associated, some ten days later, with some local rift activity. A tentative model is proposed that associates local short slip instabilities in the upper part of the fault close to the well, with a longer duration pore pressure diffusion process. Results demonstrate that the Aigion fault is continuously creeping down to a depth at least equal to 5 km but probably deeper.

  20. Fault Activity, Seismicity and GPS Deformation of the Seismic Gap along the Red River Fault Zone (RRFZ) in Yunnan, China

    NASA Astrophysics Data System (ADS)

    Xue-Ze, Wen; Shengli, Ma; Fang, Du; Feng, Long

    2016-04-01

    Along the middle segment of the NW-trending and dextral-slip Red River fault zone (RRFZ), also the Honghe fault zone, Yunnan, China, there has been little of modern seismicity since the 1970's. Some Chinese researchers believed that this fault segment is inactive in the late Quaternary. However, more and more evidence shows that the middle segment of RRFZ is geologically-active in the late Quaternary, even is a Holocene-active one with evidence of paleo-earthquakes occurring. Our study suggests that along the fault segment there has been no any major earthquake occurring for over 500 years at least, and a large-scale seismic gap, the Honghe seismic gap, have formed there. On the modern seismicity, the middle segment of RRFZ has presented as a fault portion without or with very few small earthquakes occurring since the 1980's, but surrounded by several areas with low b-values, suggesting relatively high stress having built-up there. Also, GPS deformation analysis suggests that this fault segment has tightly locked already. Such tight locking would be associated with the fault geometry: A large-scale restraining bend of about 30°over a distance of ~100 km exists along the main fault trace along RRFZ between Yuanjiang and Yuanyang. However, how such a restraining bend makes the middle segment of RRFZ have tightly locked? How much strain has built up there? Moreover, how about the long-term seismic potential of major earthquake on the middle segment of RRFZ, and on some secondary active faults of the two sides of the segment, especially on the parallel faults Chuxiong, Qujiang and Shiping. All these are issues we want to study further. Keywords: Red River Fault Zone, Seismic Gap, Fault Activity, Seismicity, GPS Deformation

  1. 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.

  2. Testing Damage Scenarios. From Historical Earthquakes To Silent Active Faults

    NASA Astrophysics Data System (ADS)

    Galli, P.; Orsini, G.; Bosi, V.; di Pasquale, G.; Galadini, F.

    Italy is rich with historical scenarios of disruption and death that arrived up to us through the insight descriptions of hundreds of manuscripts, reports, treatises, letters and epigraphs. All these historical data constitute today one of the most powerful data-base of earthquake-induced effects. Moreover, it is now possible to relate many of these earthquakes to geological structures, the seismogenetic behavior of which has been investigated by means of paleoseismological studies. On the basis of these information and of those gathered through the national census (performed on popu- lation and dwellings by ISTAT, Italian Institute of Statistics in 1991) we developed a methodology (FaCES, Fault-Controlled Earthquake Scenario) which reproduce the damage scenario caused by the rupture of a defined fault, providing an estimate of the losses in terms of damages to building and consequences to population. The reliabil- ity of scenarios has been tested by comparing the historical damage distribution of an earthquake with that obtained applying FaCES to the responsible fault. Finally, we hypothesize the scenario related to three historically-silent faults of central Apennines (Mt. Vettore, Mt. Gorzano and Gran Sasso faults), the Holocene activity of which has been recently ascertained though paleoseimological analyses.

  3. Horizontal surface velocity and strain patterns near thrust and normal faults during the earthquake cycle: The importance of viscoelastic relaxation in the lower crust and implications for interpreting geodetic data

    NASA Astrophysics Data System (ADS)

    Hampel, Andrea; Hetzel, Ralf

    2015-04-01

    In recent years, more and more space-geodetic data on the surface deformation associated with earthquakes on intracontinental normal and thrust faults have become available. However, numerical models investigating the coseismic and postseismic deformation near such faults in a general way, i.e., not focused on a particular earthquake, are still sparse. Here we use three-dimensional finite element models that account for gravity, far-field ("regional") extension/shortening and postseismic relaxation in a viscoelastic lower crust to quantify the surface deformation caused by an Mw ~7 earthquake on a dip-slip fault. The coseismic deformation is characterized by horizontal shortening in the footwall of the normal fault and extension in the hanging wall of the thrust fault—consistent with elastic dislocation models, geological field observations, and GPS data from earthquakes in Italy and Taiwan. During the postseismic phase, domains of extensional and contractional strain exist next to each other near both fault types. The spatiotemporal evolution of these domains as well as the postseismic velocities and strain rates strongly depend on the viscosity of the lower crust. For viscosities of 1018-1020 Pa s, the signal from postseismic relaxation is detectible for 20-50 years after the earthquake. If GPS data containing a postseismic relaxation signal are used to derive regional rates, the stations may show rates that are too high or too low or even an apparently wrong tectonic regime. By quantifying the postseismic deformation through space and time, our models help to interpret GPS data and to identify the most suitable locations for GPS stations.

  4. 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.

  5. Inferring Earthquake Physics from Deep Drilling Projects of Active Faults

    NASA Astrophysics Data System (ADS)

    Di Toro, G.; Smith, S. A. F.; Kuo, L. W.; Mittempergher, S.; Remitti, F.; Spagnuolo, E.; Mitchell, T. M.; Gualtieri, A.; Hadizadeh, J.; Carpenter, B. M.

    2014-12-01

    Deep drilling projects of active faults offer the opportunity to correlate physical and chemical processes identified in core samples with experiments reproducing the seismic cycle in the laboratory and with high-resolution seismological and geophysical data. Here we discuss the constraints about earthquakes source processes at depth gained by fault cores retrieved from the deep drilling projects SAFOD (2.7 km depth, San Andreas Fault), J-FAST (0.9 km depth, following the Mw 9.0 Tohoku 2011 earthquake), TCDP (1.1 km depth, following the Mw 7.6 Chi-Chi 1999 earthquake) and WFSD (1.2 km depth, following the Mw 7.9 Wenchuan 2008 earthquake). Recovered samples were tested at room temperature with the rotary shear apparatus SHIVA installed in Rome (INGV, Italy). All the tested samples were made by clay-rich gouges (usually including smectite/illite), though their bulk mineralogy and modal composition were different (e.g., SAFOD samples included saponite, WFSD carbonaceous materials). The gouges were investigated before and after the experiments with scanning and transmission electron microscopy, X-Ray diffraction, micro-Raman spectroscopy, etc. A common behavior of all the tested gouges was that their friction coefficient was low (often less than 0.1) under room-humidity and wet conditions when sheared at slip rates of ca. 1 m/s (seismic deformation conditions). Moreover, when the natural fault rocks next to the principal slipping zones were sheared from sub-seismic (few micrometers/s) to seismic slip rates, the experimental products had similar microstructures to those found in the principal slipping zones of the drilled faults. This included the formation of mirror-like surfaces, graphite-rich materials, foliated gouges, nanograins, amorphous materials, etc. In most cases the mechanical data were consistent with several seismological (> 50 m of seismic slip for the fault zone drilled by J-FAST) and geophysical observations (absence of a thermal anomaly in the fault

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

    NASA Astrophysics Data System (ADS)

    Besstrashnov, V. M.; Strom, A. L.

    2011-05-01

    Assessment of seismic strong motion hazard produced by earthquakes originating within causative fault zones allows rather low accuracy of localisation of these structures that can be provided by indirect evidence of fault activity. In contrast, the relevant accuracy of localisation and characterisation of active faults, capable of surface rupturing, can be achieved solely by the use of direct evidence of fault activity. This differentiation requires strict definition of what can be classified as "active fault" and the normalisation of methods used for identification and localisation of active faults crossing oil and natural gas trunk pipelines.

  7. 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.

  8. Frictional properties of the active San Andreas Fault at SAFOD: Implications for fault strength and slip behavior

    NASA Astrophysics Data System (ADS)

    Carpenter, B. M.; Saffer, D. M.; Marone, C.

    2015-07-01

    We present results from a comprehensive laboratory study of the frictional strength and constitutive properties for all three active strands of the San Andreas Fault penetrated in the San Andreas Observatory at Depth (SAFOD). The SAFOD borehole penetrated the Southwest Deforming Zone (SDZ), the Central Deforming Zone (CDZ), both of which are actively creeping, and the Northeast Boundary Fault (NBF). Our results include measurements of the frictional properties of cuttings and core samples recovered at depths of ~2.7 km. We find that materials from the two actively creeping faults exhibit low frictional strengths (μ = ~0.1), velocity-strengthening friction behavior, and near-zero or negative rates of frictional healing. Our experimental data set shows that the center of the CDZ is the weakest section of the San Andreas Fault, with μ = ~0.10. Fault weakness is highly localized and likely caused by abundant magnesium-rich clays. In contrast, serpentine from within the SDZ, and wall rock of both the SDZ and CDZ, exhibits velocity-weakening friction behavior and positive healing rates, consistent with nearby repeating microearthquakes. Finally, we document higher friction coefficients (μ > 0.4) and complex rate-dependent behavior for samples recovered across the NBF. In total, our data provide an integrated view of fault behavior for the three active fault strands encountered at SAFOD and offer a consistent explanation for observations of creep and microearthquakes along weak fault zones within a strong crust.

  9. 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.

  10. 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.

  11. Finding Active Faults in a Glaciated and Forested Landscape: the Southern Whidbey Island Fault, Washington

    NASA Astrophysics Data System (ADS)

    Blakely, R. J.; Sherrod, B. L.; Wells, R. E.; Weaver, C. S.

    2004-12-01

    The Puget Lowland, Washington, lies within the Cascadia forearc and is underlain by at least six seismically active and regionally significant crustal faults that together accommodate several mm/yr of net north-south shortening. The surface expression of pre-15-ka slip on Puget Lowland faults has been largely scoured away or covered by glacial deposits, and younger fault geomorphology is often concealed by vegetation and urban development. High-resolution aeromagnetic and lidar surveys, followed by geologic site investigations, have identified and confirmed late Holocene deformation on each of these mostly concealed but potentially hazardous faults. Most geomorphic features identified in lidar data are closely associated with linear magnetic anomalies that reflect the underlying basement structure of the fault and help map its full extent. The southern Whidbey Island fault (SWIF) is a case in point. The northwest-striking SWIF was mapped previously using borehole data and potential-field anomalies on Whidbey Island and marine seismic-reflection surveys beneath surrounding waterways. Gravity inversions and aeromagnetic mapping suggest that the SWIF extends at least 50 km southeast, from Vancouver Island to the Washington mainland, and transitions along its length from northeast-side-down beneath Puget Sound to northeast-side-up on the mainland. Abrupt subsidence at a coastal marsh on south-central Whidbey Island suggests that the SWIF experienced a MW 6.5 to 7.0 earthquake about 3 ka. Southeast of Whidbey Island, a hypothesized southeastward projection of the SWIF makes landfall between the cities of Seattle and Everett. Linear, northwest-striking magnetic anomalies in this mainland region do coincide with this hypothesized projection, are low in amplitude, and are best illuminated in residual magnetic fields. The most prominent of the residual magnetic anomalies extends at least 16 km, lies approximately on strike with the SWIF on Whidbey Island, and passes within

  12. Active thrusting offshore Mount Lebanon: Source of the tsunamigenic A.D. 551 Beirut-Tripoli earthquake

    NASA Astrophysics Data System (ADS)

    Elias, Ata; Tapponnier, Paul; Singh, Satish C.; King, Geoffrey C. P.; Briais, Anne; Daëron, Mathieu; Carton, Helene; Sursock, Alexander; Jacques, Eric; Jomaa, Rachid; Klinger, Yann

    2007-08-01

    On 9 July A.D. 551, a large earthquake, followed by a tsunami, destroyed most of the coastal cities of Phoenicia (modern-day Lebanon). Tripoli is reported to have “drowned,” and Berytus (Beirut) did not recover for nearly 1300 yr afterwards. Geophysical data from the Shalimar survey unveil the source of this event, which may have had a moment magnitude (Mw) of 7.5 and was arguably one of the most devastating historical submarine earthquakes in the eastern Mediterranean: rupture of the offshore, hitherto unknown, ˜100-150-km-long active, east-dipping Mount Lebanon thrust. Deep-towed sonar swaths along the base of prominent bathymetric escarpments reveal fresh, west-facing seismic scarps that cut the sediment-smoothed seafloor. The Mount Lebanon thrust trace comes closest (˜8 km) to the coast between Beirut and Enfeh, where, as 13 14C-calibrated ages indicate, a shoreline-fringing vermetid bench suddenly emerged by ˜80 cm in the sixth century A.D. At Tabarja, the regular vertical separation (˜1 m) of higher fossil benches suggests uplift by three more earthquakes of comparable size since the Holocene sea level reached a maximum ca. 7-6 ka, implying a 1500-1750 yr recurrence time. Unabated thrusting on the Mount Lebanon thrust likely drove the growth of Mount Lebanon since the late Miocene.

  13. 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

  14. 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

  15. Transient fluvial incision as an indicator of active faulting and surface uplift in the Moroccan High Atlas.

    NASA Astrophysics Data System (ADS)

    Boulton, Sarah; Stokes, Martin; Mather, Anne

    2013-04-01

    Quantifying the extent to which geomorphic features can be used to extract tectonic signals is a key challenge for the Earth Sciences. Here, we analyse the long profiles of rivers that drain southwards across the Southern Atlas Fault (SAF), a segmented thrust fault that forms the southern margin of the High Atlas Mountains in Morocco, with the aim of deriving new data on the recent activity of this little known fault system. River long profiles were extracted for the 32 major rivers that drain southwards into the Ouarzazate foreland basin. Of these, twelve exhibit concave-up river profiles with a mean concavity (Θ) of 0.61 and normalized steepness indices (Ksn) in the range 42-219; these are interpreted as rivers at or near steady-state. By contrast, 20 rivers are characterised by the presence of at least one knickpoint upstream of the thrust front. Knickzone height (the vertical distance between the knickpoint and the fault) varies from 100 - 1300 m, with calculated amounts of uplift at the range bounding fault ranging from 1040 - 80 m. In map view, knickpoint locations generally plot along sub-parallel lines to the thrust front and there are no obvious relationships with specific lithological units or boundaries. Furthermore, drainage areas upstream of the knickpoints range over several orders of magnitude indicating that they are not pinned at threshold drainage areas. Therefore, these features are interpreted as a transient response to base-level change. However, three distinct populations of knickpoints can be recognised based upon knickpoint elevation, these are termed K1, K2 and K3 and channel reaches are universally steeper below knickpoints than above. K1 and K2 knickpoints share common characteristics in that the elevation of the knickpoints, calculated incision and ksn all increase from west to east. Whereas, K3 knickpoints show little systematic variation along the range front, are observed at the lowest altitudes with calculated incision of < 200 m

  16. 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.

  17. Fault Mechanics and Active Strain Along the Garlock Fault in SE California

    NASA Astrophysics Data System (ADS)

    Rittase, W.; Walker, D.; Taylor, M.; Kirby, E.

    2008-12-01

    We report here results from new geologic mapping along a 38 km segment of the Garlock Fault (GF) between US 395 and the Slate Range, and an 8 km segment at the northern terminus of the Blackwater- Calico fault (BCF) in the Lava Mountains. This study area lies within the ENE-striking central segment of the sinistral GF. NNW-striking faults of the dextral Eastern California shear zone approach the GF, but do not offset it: exact mechanisms of strain transfer across the GF from the Mojave Desert to the Basin and Range is enigmatic. Field mapping reveals that the GF is complex with numerous sub-parallel strands both north and south of the mapped fault. Holocene slip on the GF is dominantly sinistral, but a major zone to the north adjacent to the bedrock of the southern Slate Range is dip-slip. The mapped portion of the northern BCF is expressed as a bedrock scarp and does not cut Holocene sediments. Significant N-S shortening is superimposed along the GF adjacent to the southern Slate Range, in the Christmas Canyon area, and the Lava Mountains. Pliocene- Pleistocene sediments are uplifted and deformed into E-W open to chevron folds in the Christmas Canyon and Slate Range areas. Cretaceous quartz-monzonite and overlying Miocene strata are deformed by similar structures in the northern Lava Mountains. In general, areas of topographic uplifts are disjointed and spatially restrictive in comparison to the more continuous GF and the BCF. These observations suggest several possibilities for the region. (1) Active slip on the GF and the Eastern California shear zone are driven by a single, Mojave-wide stress field with sigma-1 oriented roughly N-S. (2) The GF may be a weak zone in the lithosphere and crust with sigma-1 oriented nearly perpendicular to strike as evidenced by ENE- to East-trending fold hinges in Pliocene-Pleistocene sediments. (3) The continuous trace of the GF rupture through the 38-km-long study area suggests that it, at least locally, poses a mechanical

  18. 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.

  19. 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

  20. First paleoseismological assessment of active deformation along the eastern front of the southern Alps (NE Italy, Friuli). Insights on the 1511 earthquake causative fault.

    NASA Astrophysics Data System (ADS)

    Falcucci, Emanuela; Eliana Poli, Maria; Galadini, Fabrizio; Paiero, Giovanni; Scardia, Giancarlo; Zanferrari, Adriano

    2014-05-01

    The study area belongs to the Julian Prealps that represent the easternmost portion of the Plio-Quaternary front of the eastern Southalpine Chain (ESC), a south-verging polyphase fold and thrust belt, in evolution from the Middle Miocene to the Present. Here, the WSW-ENE trending, SW- verging thrusts of the ESC join the NW-SE trending, right-lateral strike slip Idrija fault system, which develops along the Italian-Slovenian boundary. The area is characterized by medium/high seismicity testified by both large historical and instrumental earthquakes. The DBMI11 (Locati et al., 2011) records the 1348 Carinzia earthquake (Mw= 7.02), the 1511 Idrija earthquake (Mw=6.98), and the 1976 Friuli earthquakes on May (Mw=6.46) and September (Mw=5.98) We studied a segment of the Susans-Tricesimo thrust system, namely the Colle Villano (CV) thrust, identified by means of geological and geophysical investigations (Galadini et al., 2005). New geological and geomorphological analyses allowed identifying the surficial geomorphic evidence of recent blind thrusting along the structure, represented by gentle scarps and surface warping. In order to characterise the Late Pleistocene-Holocene activity of this blind thrust, paleoseismological investigations were performed along one of CV thrust-related fault scarps. We dug three trenches ~1 km to the north of the Magredis village. The analysis of the trench walls allowed identifying deformation events induced by the fault activity. Two subsequent episodes of deformation are distinguished by localised warping (few metres in wave length) of the sedimentary sequences exposed by the excavations and secondary extrados faulting. One event occurred between 544-646 AD (radiocarbon cal. age, 2σ) and 526-624 AD the other - probably the last one - occurred close to 1485-1604 AD. The last displacement event is consistent with the aforementioned 1511 earthquake both in terms of chronology of the deformation and location of the causative fault. This

  1. 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

  2. Paleomagnetic Data From the Rinconada Fault in Central California: Evidence for Off-fault Deformation

    NASA Astrophysics Data System (ADS)

    Crump, S.; Titus, S.; McGuire, Z.; Housen, B. A.

    2009-12-01

    The Rinconada fault is one of three major sub-parallel faults of the San Andreas fault system in central California. The fault has 18 km of dextral displacement since the Pliocene and up to 60 km of total displacement for the Tertiary. A fold and thrust best is well developed in Miocene and younger sedimentary rocks on either side of the Rinconada fault. We sampled ~150 sites from the Miocene Monterey Formation within this fold and thrust belt, a unit that is often used in regional paleomagnetic studies. The sites were located within 15 km of the fault trace along a segment of the Rinconada fault that stretches from Greenfield to Paso Robles. Because this unit was deposited while the San Andreas fault system was active at this latitude, any deformation recorded by these rocks is related to plate boundary deformation. Unlike the large (>90°) rotations observed in the Transverse Ranges to the south, vertical axis rotations adjacent to the Rinconada fault are smaller (<15°) and vary with distance from the fault as well as along strike. Thus, the model for rotations from the Transverse Ranges, where large fault-bound panels rotate within a system of conjugate strike-slip faults, does not apply for this region in central California. Instead, we believe rotations occur in small fault blocks and the magnitude of rotation may be affected by local parameters such as fault geometries, specific rock types, and structural complexities. One implication of these vertical axis rotations adjacent to the Riconada fault is that off-fault regions are accommodating some of the fault-parallel plate motion. This is important for our understanding of the partitioning of plate boundary deformation in California.

  3. 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.

  4. Growth and interaction of active faults within a nascent shear zone, central Mojave Desert, California

    NASA Astrophysics Data System (ADS)

    Oskin, M.; Strane, M.

    2006-12-01

    Compilation of new slip-distribution and slip-rate data from the Mojave Desert portion of the Eastern California shear zone (ECSZ) lends insight into the role of fault growth and interaction of conjugate fault systems in accommodating shear. Dextral faults of the Mojave Desert ECSZ approach but do not appear to cut the bounding ENE-striking sinistral Pinto Mountain and Garlock faults. Differing styles of accommodation of these bounding faults occur at opposite ends of the 140 km-long NW-striking Hidalgo-Calico-Blackwater dextral fault system. Total slip and slip rate of the Blackwater fault gradually diminish northward. The fault terminates as a single strand with a zero-slip fault tip before intersecting the Garlock fault. In contrast, the Calico and Hidalgo faults spread displacement southward onto multiple fault strands spaced several kilometers apart. Active folding further distributes displacement onto the adjacent Bullion and Mesquite Lake faults. These mechanisms appear to maintain a uniform gradient of displacement approaching the Pinto Mountain fault. The highest displacement (9.8 ± 0.2 km) and slip rate (1.8 ± 0.3 mm/yr) occur in the central part of the Hidalgo-Calico-Blackwater fault system where strain is concentrated onto a single fault strand. A significant drop in total displacement and slip rate occurs along the northern Calico fault. Strain appears to be transferred here onto ENE-striking sinistral faults that separate domains of clockwise rotation in the central Mojave Desert. The kinematically incompatible intersection of sinistral and dextral faults is accommodated, at least in part, by active folding and uplift of the Calico Mountains and Mud Hills. Total slip and slip rate are not correlative for dextral faults of the Mojave ECSZ, indicating ongoing evolution of the fault network. For example, the Lenwood fault is a highly segmented, immature dextral fault with only 1.0 ± 0.1 km of total displacement yet its slip rate (1.5 ± 0.4 mm/yr) is

  5. 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.

  6. 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.

  7. Thrust-type focal mechanisms of tectonic tremors in Taiwan: Evidence of subduction

    NASA Astrophysics Data System (ADS)

    Ide, Satoshi; Yabe, Suguru; Tai, Hsin-Ju; Chen, Kate Huihsuan

    2015-05-01

    Unlike tectonic tremors in subduction zones and along transform faults, the hosting structure for tremors in Taiwan remains debated. Tectonic tremors in Taiwan have been discovered at ~30 km depth beneath the southern Central Range, which is a young and active collisional mountain belt. Here we provide the first evidence for the focal mechanism of tremor using moment tensor inversion in the very low frequency band, employing broadband seismograms stacked relative to the hypocentral time of tremor. The best solution corresponds to low-angle thrust faulting, suggesting the subduction of the Eurasian plate. This mechanism is consistent with strong tidal modulation of tremor activity but differs from the normal-type faulting that dominates regional shallow earthquakes. This result suggests vertical variations in the tectonic stress regime. Thrust faulting may be facilitated by a decrease in normal stress due to the buoyant roots of the mountain belt and local high fluid pressure.

  8. 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: ...

  9. 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.

  10. 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.

  11. 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.

  12. The Yakima Fold and Thrust Belt - a paradigm for active shortening in the Columbia embayment from Pasco to the Pacific Ocean (Invited)

    NASA Astrophysics Data System (ADS)

    Wells, R. E.; Blakely, R. J.; Sherrod, B. L.; Weaver, C. S.

    2009-12-01

    The Yakima Fold Belt (YFB), a series of nearly east-west trending folds and associated thrusts, accommodates N-S shortening in the 16-6 Ma Columbia River Basalt Group (CRBG) and younger strata in the western Columbia Plateau. The folds are commonly asymmetric and north verging, with broad, south dipping back limbs and short, steep, fore-limbs. The YFB lies within the Columbia embayment, an oroclinal bend in the Mesozoic orogen between the Klamath Mountains and the North Cascades, long considered to be the result of northwest motion of California in late Cenozoic time. YFB-style deformation is not restricted to the YFB; it fans westward across the Cascades and is superimposed on the subduction-related arc, Puget-Willamette trough, and Coast Range. New geophysical data link the YFB across the Cascades to the active South Whidbey Island and Seattle Faults in the Puget Lowland, generally along the broadly defined Olympic-Wallowa Lineament (OWL). South of Puget Sound, the east-west Doty Fault, the Columbia River Syncline (controlling the location of the Columbia River across the Coast Range), and the post-CRBG folding in the northern Willamette Valley are all late Cenozoic YFB-related structures accommodating N-S shortening in the forearc. This geologic evidence indicates that the Columbia embayment is the locus of extensive post middle Miocene shortening, and there is abundant paleoseismic evidence for large Holocene earthquakes on these structures in Puget Lowland and in the YFB. Seismicity in the embayment is characterized by thrust and strike slip focal mechanisms, with P axes oriented approximately N-S. GPS results of McCaffrey et al. (2007) indicate that folding in the embayment is driven by the clockwise rotation of Oregon about a pole near the OR-WA-ID border, compressing Washington against slow-moving Canada. The folds fan westward from this pole of rotation, and shortening increases to the west to about 7.1 mm/yr between Astoria and Penticton, BC. Shortening

  13. Continuous monitoring of an active fault in a plate suture zone: a creepmeter study of the Chihshang Fault, eastern Taiwan

    NASA Astrophysics Data System (ADS)

    Lee, J.-C.; Angelier, J.; Chu, H.-T.; Hu, J.-C.; Jeng, F.-S.

    2001-04-01

    Data from continuously monitored creepmeters across the active Chihshang Fault in eastern Taiwan are presented. The Chihshang Fault is an active segment of the Longitudinal Valley Fault, the main suture between the converging Philippine and Eurasian plates in Taiwan. Since the 1951 earthquake (Mw=7.0), no earthquake larger than magnitude 6.0 occurred in the Chihshang area. At least during the last 20 years, the Chihshang Fault underwent a steady creep movement, resulting in numerous fractures at the surface. Five creepmeters were installed in 1998 at two sites, Tapo and Chinyuan, within the Chihshang active fault zone. One-year results (from August 1998 to July 1999) show a horizontal shortening of 19.4±0.3 mm and 17.3±0.7 mm, at Tapo and Chinyuan, respectively. These annual shortening rates are in a good agreement with other estimates of strain rate independently obtained from geodetic measurements and geological site investigation. The creepmeter measurements were made on a daily basis, providing accurate information on the previously unknown evolution of creep during the year. The records of fault creep at the Tapo site thus revealed close seasonal correlation with average rainfall: the period of high creep rate coincides with the wet season, whereas that of low creep rate coincides with the dry season. Also, in comparison with the Tapo site, the creep behaviour as a function of time is complex at the Chinyuan site. Possible factors of irregularity are under investigation (thermal effect acting on the concrete basement of the creepmeters, earth tide effect, water table variations in a nearby rice field, and rainfall). The comparison between GPS measurements across the Longitudinal Valley (31 mm/year of horizontal displacement) and the creepmeter measurement across the Chihshang Fault zone (17-19 mm/year of horizontal displacement) suggests that there exists other shortening deformation across the active fault zone in addition to those we have measured from the

  14. 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

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. Offshore active faults of the Mikata fault zone in Fukui, Japan, revealed by high-resolution seismic profiles

    NASA Astrophysics Data System (ADS)

    Inoue, T.; Sugiyama, Y.; Sakamoto, I.; Takino, Y.; Murakami, F.; Hosoya, T.; Usami, T.

    2014-12-01

    The Mikata fault zone are located in coastal and shallow sea area off Fukui Prefecture, West Japan. National Institute of Advanced Industrial Science and Technology (AIST) and Tokai University conducted, as part of MEXT 2013 nearshore active fault survey project, a high-resolution multi-channel seismic survey using Boomer and a 12-channel streamer cable, acoustic profiling survey using parametric sub-bottom profiler and shallow-sea offshore drilling, in order to clarify distribution and activity of the Mikata fault zone. The seismic reflection surveys identified four reflection surfaces as vertical displacement markers in the post-glacial deposits at a depth ranging from ca. 4.5m to ca. 17m below the sea bottom on the downthrown side. We estimated the age of each marker reflection surface by using the C14 age and others from 4m-long core obtained on the downthrown side of fault and the sea level change in the latest Pleistocene and early Holocene around Japan. The results of these surveys have revealed that the fault system was reactivated three times since the latest Pleistocene. The vertical slip rate and average recurrence interval of the fault system are estimated at ca. 0.8-1.0 m/ky and 2,000-3,800 years, respectively.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Fault detection and isolation for an active wheelset control system

    NASA Astrophysics Data System (ADS)

    Mirzapour, Mohammad; Mei, T. X.; Xuesong, Jin

    2014-05-01

    Active control for railway wheelsets in the primary suspension has been shown to offer a number of performance gains, and especially it can be used to stabilise the wheelsets without compromising the vehicle's performance on curves. However, the use of actuators, sensors and data processors to replace the traditional passive suspension raises the issue of system safety in the event of a failure of the active control, which could result in the loss of stability (i.e. wheelset hunting), and in more severe cases, derailment. This paper studies the key issue of condition monitoring for an actively controlled railway system, with a focus on actuator failures to detect and isolate failure modes in such a system. It seeks to establish the necessary basis for fault detection to ensure system reliability in the event of malfunction in one of the two actuators. Computer simulations are used to demonstrate the effectiveness of the method.

  8. 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.

  9. 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

  10. Fault kinematics and active tectonics at the southeastern boundary of the eastern Alborz (Abr and Khij fault zones): Geodynamic implications for NNE Iran

    NASA Astrophysics Data System (ADS)

    Javidfakhr, Bita; Bellier, Olivier; Shabanian, Esmaeil; Siame, Lionel; Léanni, Laëtitia; Bourlès, Didier; Ahmadian, Seiran

    2011-10-01

    The Alborz is a region of active deformation within the Arabia-Eurasia collision zone. The Abr and the Khij Faults are two NE-trending left-lateral strike-slip faults in the eastern Alborz that correspond to the Shahrud fault system extended through an area of about 95 km × 55 km. Tectonic landforms typically associated with active strike-slip faults, such as deflected stream channels, offset ridges and fault scarps are documented along the mentioned faults. Detailed analyses of satellite images and digital topographic data accompanied by field surveys allowed us to measure horizontal offsets of about 420 ± 50 m and 400 ± 50 m for the Abr and Khij Faults, respectively. A total of 8 quartz-rich samples were sampled and dated from two different fan surfaces using in situ-produced 10Be cosmogenic dating method. Minimum exposure ages for the abandonment of the alluvial fan surfaces of 115 ± 14 kyr along the Abr Fault and of 230 ± 16 kyr along the Khij Fault imply that both faults are active with slip rates of about 3-4 mm yr -1 and 1-3 mm yr -1, respectively. The results of our study provide the first direct quantitative geological estimates of slip rate along these two active faults and place a new constraint on slip distribution between the faults in the eastern Alborz. Fault kinematic studies (from fault slip data) indicate a N35°E-trending maximum stress axis comprising a dominant strike-slip regime in agreement with the geomorphological analyses. The left-lateral strike-slip faulting along the Abr and Khij Faults and their associated fault zones in the eastern Alborz can be due to the westward component of motion of the South Caspian Basin with respect to Eurasia and Central Iran.

  11. 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.

  12. 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.

  13. Neotectonic faulting in northern Norway; the Stuoragurra and Nordmannvikdalen postglacial faults

    NASA Astrophysics Data System (ADS)

    Dehls, John F.; Olesen, Odleiv; Olsen, Lars; Harald Blikra, Lars

    2000-10-01

    A systematic compilation and characterisation of many reports of neotectonic crustal deformation in Norway (both on local and regional scales) has identified two neotectonic faults in northern Norway. The Stuoragurra Fault is a large reverse fault in Finnmark County. The Nordmannvikdalen fault is a much smaller normal fault in Troms County. The Stuoragurra postglacial fault can be followed, in several discontinuous sections, for 80 km, in a NE-SW direction. The fault has up to 10 m of displacement. During 1998, two trenches were made across the fault. The hanging wall was seen to be thrust upwards over the footwall, with 7 m vertical displacement evident from displaced glacial contacts. The fault did not penetrate the overlying glacial materials, but rather folded them, forming a blind thrust. Large liquefaction and other deformation structures were found in the glaciofluvial sediments in both trenches. Veins of angular and subangular pebbles from the local bedrock penetrate more than 10 m laterally from the thrust plane and into the sediments in the footwall. It is thought that these veins were injected during the fault activity. The major deformation of the sediments has a décollement plane that continues laterally in the E/B horizon contact of the modern soil on top of the footwall. This may indicate that an initial pedogenesis had taken place before the fault activity occurred, however no macro plant fossils to support this were found in the possible buried soil. Deformational structures seen in the trench can be explained as a result of one major fault event. The Nordmannvikdalen postglacial fault is a NW-SE trending normal fault, dipping to the NE. The fault offsets till on the NW slope of Nordmannvikdalen. The escarpment varies in height from 0.5 to 1.5 m, with a trench often present between the hanging wall and the footwall. The fault locally splits into two subparallel branches, however this is probably only in the glacial overburden. Ground penetrating

  14. 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.

  15. 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

  16. Strike-slip fault geometry in Turkey and its influence on earthquake activity

    NASA Technical Reports Server (NTRS)

    Barka, A. A.; Kadinsky-Cade, K.

    1988-01-01

    The geometry of Turkish strike-slip faults is reviewed, showing that fault geometry plays an important role in controlling the location of large earthquake rupture segments along the fault zones. It is found that large earthquake ruptures generally do not propagate past individual stepovers that are wider than 5 km or bends that have angles greater than about 30 degrees. It is suggested that certain geometric patterns are responsible for strain accumulation along portions of the fault zone. It is shown that fault geometry plays a role in the characteristics of earthquake behavior and that aftershocks and swarm activity are often associated with releasing areas.

  17. 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

  18. Fault control on the hydrogeological setting of the Sibillini Mountains aquifers (Central Apennines, Italy): an example of hydrogeological structures in thrust-belt contexts

    NASA Astrophysics Data System (ADS)

    Tarragoni, C.

    2012-04-01

    This work is aimed at highlighting the importance of fault control on the hydrogeological setting in orogenic areas. In Sibillini Montains, Umbrian-Marchean pelagic succession outcrops. This succession, characterized by calcareous, calcareous-marly and silicate could presents condensed succession and is involved in fold and overthrust deformation, followed by a development of normal faults. The lithostratigraphical and structural study allowed defining the aquifer settings. Several cross-sections have been drawn to identify the three-dimensional geological setting and aquifer's boundaries that consist on: lithological limit between permeable and very low permeable complexes and structural features (groundwater divide and faults). The analyses of principals structural features (e.g. overthrust) have allowed to identify the prominent groundwater flow direction: the Sibillini Montains, Monte Val di Fibbia-P.ta Bambucerta and Visso overthrusts represent three important inverse faults oriented NNW-SSE having aquiclude role due to the high displacement. The altitude gradual decrease forward N of aquiclude handing aquifers combined to Apennine orientation of overthrusts induce a SSE-NNW groundwater flow. A detailed analysis of base flow has allowed to: 1) define the river's base flow; 2) recognize the punctual, diffused and linear springs; 3) quantify the water resource on average drained; and 4) determine the discharge regime of springs and rivers. The geologic-structural analyses with the quantitative hydrogeological studies have allowed to prepare the Conceptual Hydrogeological Model (CHM) and to calculate the hydrogeological balance for each aquifer. This double approach let to carry out a detailed study and make out hypotheses about groundwater circulation for each aquifer. These hypotheses represent the bases for the groundwater modelling that could give an important contribute to confirm or not them. The CHM of main aquifer has been adopted to carry out the

  19. Fold Thrust Belt Kinematics from 3D Seismic Imaging along the NanTroSEIZE Transect, Nankai Accretionary Prism, Japan.

    NASA Astrophysics Data System (ADS)

    Kington, J. D.; Tobin, H.; Moore, G.

    2008-12-01

    The accretionary prism of the Nankai Trough, Japan provides an excellent location to study the kinematics of a fold and thrust belt developed primarily in low permeability units. Recently acquired 3D reflection seismic data covering a 12 x 56 km area from the Kumano basin seaward to the deformation front reveals three structural domains within the frontal accretionary prism. The farthest seaward domain of the prism consists closely-spaced, apparently in-sequence thrust sheets forming a steep critical taper angle. The primary decollement beneath these thrusts ramps upsection above a topographic high within the oceanic basement. The farthest landward domain within the study area consists of the hanging wall of an apparently out of sequence megasplay thrust fault that dips landward to the top of the oceanic crust. The central structural domain within the prism consists of thrust sheets formed above a decollement approximately 2 km above the top of the oceanic crust, above the decollement associated with the more seaward thrusts. These thrusts are more widely spaced than those nearer the deformation front and are blanketed with syn and post kinematic sediments. Synkinematic sediments indicate that thrusts in the most seaward and most landward structural domains within the prism are the most active, though some reactivation of structures in the middle domain has occurred. Additionally, gas hydrate bottom simulating reflectors (BSRs) in the lowermost portions of the prism are present as discrete bands striking parallel to thrusts. These BSRs occur primarily along the most active thrusts, and are only present as small patches within the central structural domain of the prism. As these are expected to be the result of fluid migration along faults and permeable structures, they provide insight into the hydrologic controls on thrusting within the accretionary prism.

  20. The Jura Mountains — an active foreland fold-and-thrust belt?

    NASA Astrophysics Data System (ADS)

    Becker, Arnfried

    2000-06-01

    Recently completed in situ stress measurements using the borehole slotter at 33 new test sites within the Swiss and French Jura Mountains, combined with previously published stress data, allow a detailed description of the contemporary state of stress in this fold-and-thrust belt and the adjacent foreland. Five stress provinces can be recognized, with two different general orientations of maximum horizontal stress SH: (1) the Central and Southwest Provinces with a NNW-SSE to NNE-SSW orientation; (2) the East, Northwest and Southeast Provinces with an E-W to NW-SE orientation. Stress magnitudes are in general higher in the southern than in the northern Jura Mountains. Characteristic of the northern Jura is an E-W-trending zone of low stress magnitudes which can be traced from the Bresse Depression south of Besançon to the eastern end of the Jura northwest of Zurich. Boundaries of stress provinces show poor agreement with boundaries of tectonic units in the Jura. In addition, stress provinces extend beyond the boundaries of the Jura Mountains into their foreland. Furthermore, palaeo-stress orientations show large discrepancies with respect to the contemporary stress orientation. These findings are considered to indicate a termination of Jura thin-skinned foreland tectonics, which probably took place some time between 9 and 4 Ma according to palaeontological and tectonic evidence. It is suggested that a new style of tectonics has commenced in the Jura Mountains, deforming both the basement directly below the Jura fold-and-thrust belt and the cover rocks in a similar mode.

  1. 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.

  2. 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.

  3. Fault Population Analyses in the Eastern California Shear Zone: Insights into the Development of Young, Actively Evolving Plate Boundary Structures

    NASA Astrophysics Data System (ADS)

    Zhou, X.; Dawers, N. H.; Amer, R. M.

    2014-12-01

    Relationships between cumulative fault displacement, slip rate and length, along with fault population statistics are analyzed for faults located within the Eastern California Shear Zone (ECSZ), focusing on areas north of the Garlock fault. Here many faults are geologically young and in an early stage of evolution, while many older and larger faults are also still active. We analyze scaling relationships for both strike-slip and normal faults in order to determine whether the two fault populations share the same properties or not. Cumulative displacement, slip rate and length data are collected from published maps and literature sources. The dataset spans fault lengths from tens of meters to hundreds of kilometers. Results of fault scaling analyses indicate that displacement has a linear relationship with fault length for normal faults in this area over the entire length span, whereas strike-slip faults do not have a clear displacement-length scaling relation. For a given length, the subset of strike-slip faults typically exhibits a much larger displacement than that for the normal faults. The slip rate versus length trends are similar but are considerably more scattered. In addition, we define a subpopulation of normal faults that are kinematically related to the right-lateral strike-slip faults; these have a maximum length set by the spacing between the right-lateral faults. Fault size-frequency distributions also indicate differences between the normal and strike-slip fault populations. Overall, the normal faults have higher ratios of cumulative number to fault length than the strike-slip population does, which we relate to different patterns of localization of faulting. We interpret these trends as reflecting different tectonic histories, with the majority of normal faults being intraplate faults associated with Basin and Range extension and the strike-slip faults being kinematically connected with plate boundary.

  4. 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

  5. Contribution of high resolution PLEIADES imagery to active faults analysis. Case study of the Longriba Fault System, eastern Tibet.

    NASA Astrophysics Data System (ADS)

    Ansberque, Claire; Bellier, Olivier; Godard, Vincent; Lasserre, Cécile; Wang, Mingming; Xu, Xiwei; Tan, Xibin

    2015-04-01

    High resolution imagery has largely developed during those two last decades allowing the possibility to observe and quantify geological and geomorphological features ranging from meter to few centimeters. Active tectonic and geomorphological studies have greatly benefited from the systematic use of such data. For that reason, we tested the contribution of PLEAIDES images to the analysis of an active strike-slip fault system in eastern Tibet. We used 50 cm resolution panchromatic PLEIADES images in order to map active fault segmentation, localize offsets of geomorphic markers and quantify vertical and horizontal displacements. We propose a preliminary study using PLEIADES images along the Longriba Fault System (LFS). The LFS, located at the eastern Tibetan Plateau margin, is constituted of two NW-SE dextral strike-slip and parallel fault zones: Longriqu and Maoergai, 80 and 120 km-long, respectively. It accommodates ~4 mm/yr dextral slip and very few vertical motion. We used stereo-pairs to build relative Digital Elevation Models (DEMs) (without ground control points) with a horizontal resolution ranging from 2 to 5 m, in order to understand the geometry of the system. We measured fault segments with lengths ranging from a hundred meters to several kilometers which are relatively close from each others, and several offsets of geomorphic markers (alluvial fans, ridges, rivers) ranging from a few meters to ~40 m. According to the segmentation deduced from those results we suggest that the fault has a high seismic potential (>Mw7.0) and that probably many surface rupturing earthquakes occurred along the LFS over the Holocene.

  6. 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

  7. Relationship between normal faulting and volcanic activity in the Taranaki backarc basin, New Zealand

    NASA Astrophysics Data System (ADS)

    Giba, M.; Walsh, J. J.; Nicol, A.

    2009-04-01

    Volcanoes and normal faults are, by definition, both present within volcanic rifts. Despite this association the causal relationships between volcanism and normal faulting can be unclear and are poorly understood. One of the principal challenges for investigations of the links between faulting and volcanic activity, is the definition of the detailed temporal relationships between these two processes. The northern Taranaki Basin, which benefits from excellent seismic (2D and 3D) and drillhole coverage, provides the basis for a detailed study of volcanism and faulting over the last ca 15 Myr. Most of the basin is characterised by sedimentation rates which exceed fault displacement rates, a condition which permits displacement backstripping of these syn-sedimentary growth faults. The timing of a suite of mostly andesitic submarine volcanoes has been constrained by interdigitation of the volcanic cones with basinal sedimentary rocks. Eleven dated horizons within the ca 15 Myr and younger stratigraphy together with mapping provide a means of examining the temporal and spatial links between fault and volcanic activity within the basin. The northern Taranaki Basin has a multiphase deformation history, with extension during the Late Cretaceous to Mid Eocene (ca 80-45 Ma), followed by contraction in the Late Eocene to Early Miocene (ca 40-18 Ma) and then by Mid Miocene to recent back arc extension (ca 15-0 Ma). The youngest phase of extensional faulting initiated in the north and west of the basin and migrated to the southeast where present activity is focused. Volcanic activity also commenced in the north during the Mid Miocene and migrated towards the south and east. Volcanism and backarc extension are driven by subduction of the Pacific plate along the Hikurangi margin. The southward and eastward migration of both faulting and volcanic activity is attributed to the steepening and rotation of the subducting slab beneath the Taranaki Basin. Despite the common origin of

  8. Nature of thrusting along western flank of Bighorn Mountains, Wyoming

    SciTech Connect

    Noggle, K.S.

    1986-08-01

    The northern portion of the Bighorn Mountains is characterized by opposed mountain-front thrusts, of which the southwest direction is dominant. Blind basement thrusts along the northeastern flank do not pierce the folded Paleozoic cover; whereas on the western flank, southwest-directed thrust segments expose Precambrian rocks along a 24-km (14-mi) extent. Field studies on the western flank show evidence of four major southwest-directed thrust segments delineated by tear-fault boundaries, which include from northwest to southeast: (1) the Five Springs thrust, a low-angle, out-of-the-syncline fault mainly involving the sedimentary sequence; (2) the Bear Creek thrust, a continuation of the Five Springs out-of-the-syncline fault; (3) the South Beaver Creek thrust, which juxtaposes Precambrian rocks against a tectonically thinned, overturned anticlinal limb of Mississippian through Jurassic rocks and which is inward from an out-of-the-syncline thrust involving little displacement of Jurassic formations; and (4) a mountain-front reentrant that coincides with the zone where the South Beaver Creek thrust continues beneath Paleozoic cover, causing the upper flexure of a double monocline. The central portion of the Bighorn Mountains is thrust eastward, whereas the northern portion is thrust southwestward with much less displacement. The segmented association of southwest-directed basement thrusts along the western flank of the northern Bighorns is indicative of the major transport direction for that portion of the Bighorn uplift.

  9. Development of the Himalayan frontal thrust zone: Salt Range, Pakistan

    SciTech Connect

    Baker, D.M.; Lillie, R.J.; Yeats, R.S.; Johnson, G.D.; Yousuf, M.; Zamin, A.S.H.

    1988-01-01

    The Salt Range is the active frontal thrust zone of the Himalaya in Pakistan. Seismic reflection data show that a 1 km offset of the basement acted as a buttress that caused the central Salt Range-Potwar Plateau thrust sheet to ramp to the surface, exposing Mesozoic and Paleozoic strata. The frontal part of the thrust sheet was folded passively as it overrode the subthrust surface on a ductile layer of Eocambrian salt. Lack of internal deformation of the rear part of the thrust sheet is due to decoupling of sediments from the basement along this salt layer. Early to middle Pliocene (approx. 4.5 Ma) conglomerate deposition in the southern Potwar Plateau, previously interpreted in terms of compressional deformation, may instead document uplift related to basement normal faulting. Stratigraphic evidence, paleomagnetic dating of unconformities, and sediment-accumulation rates suggest that the thrust sheet began to override the basement offset from 2.1 to 1.6 Ma. Cross-section balancing demonstrates at least 20 to 23 km of shortening across the ramp. The rate of Himalayan convergence that can be attributed to underthrusting of Indian basement beneath sediments in the Pakistan foreland is therefore at least 9-14 mm/yr, about 20-35% of the total plate convergence rate.

  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. Geological and tectonic implications obtained from first seismic activity investigation around Lembang fault

    NASA Astrophysics Data System (ADS)

    Afnimar; Yulianto, Eko; Rasmid

    2015-12-01

    The Lembang fault located at northern part of populated Bandung basin is the most conspicuous fault that potentially capable in generating earthquakes. The first seismic investigation around Lembang fault has been done by deploying a seismic network from May 2010 till December 2011 to estimate the seismic activities around that fault. Nine events were recorded and distributed around the fault. Seven events were likely to be generated by the Lembang fault and two events were not. The events related to the Lembang fault strongly suggest that this fault has left-lateral kinematic. It shows vector movement of Australian plate toward NNE might have been responsible for the Lembang fault kinematic following its initial vertical gravitational movement. The 1-D velocity model obtained from inversion indicates the stratigraphy configuration around the fault composed at least three layers of low Vp/Vs at the top, high Vp/Vs at the middle layer and moderate Vp/Vs at the bottom. In comparison with general geology of the area, top, mid and bottom layers may consecutively represent Quaternary volcanic layer, pre-Quaternary water-filled sedimentary layer and pre-Quaternary basement. Two eastern events related to minor faults and were caused by a gravitational collapse.

  12. Geometry and evolution of the frontal part of the Magallanes foreland thrust and fold belt (Vicuna Area), Tierra del Fuego, southern Chile

    SciTech Connect

    Alvarez-Marron, J.; McClay, K.R. ); Harambour, S.; Rojas, L.; Skarmeta, J. )

    1993-11-01

    The Magallanes foreland thrust and fold belt is a thin-skinned foreland thrust and fold belt of Paleocene to Oligocene age that deforms Upper Jurassic through Tertiary volcanic, volcaniclastic, and siliciclastic strata of the Magallanes basin, southern Andean Cordillera, Chile. This paper is a detailed description and analysis of the geology and structural evolution of the thrust front (Vicuna area of southern Tierra del Fuego). Reflection seismic and well data, together with 1:50,000 scale geological mapping, have been used in the analysis. In the southern part of the Vicuna area, two different thrust systems have been found: an upper imbricate fan that deforms Upper Jurassic and Cretaceous strata, and a younger, lower duplex composed of Cretaceous and probably Upper Jurassic rocks. The imbricate fan is characterized by fault-propagation folding in which listric thrust faults merge downward into a sole thrust that probably is located within the Upper Jurassic stratigraphy. The sole thrust of the upper imbricates forms the roof thrust of the underlying duplex. In the northern part of the Vicuna area, the syntectonic sedimentary wedge of the foredeep consists of Late Cretaceous through Tertiary siliciclastics that have been deformed and uplifted by passive back thrusting at the triangle zone. The structural style in the foreland region shows three main subhorizontal detachment levels located within the sedimentary wedge as a result of the progressive transfer of slip from the thrust belt to the foreland. Minor blind thrusts produce stacked [open quotes]pop up[close quotes] and triangle structures that result in complex geometries in the cores of anticlines. A forward-breaking sequence of thrusting is interpreted. During deformation, the active foredeep wedge migrated at least 10 km northward. Balanced geological cross sections indicate approximately 60% (-30 km) shortening for this part of the Magallanes thrust belt.

  13. 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.

  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. 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.

  16. Experimental Fault Reactivation on Favourably and Unfavourably Oriented Faults

    NASA Astrophysics Data System (ADS)

    Mitchell, T. M.; Sibson, R. H.; Renner, J.; Toy, V. G.; di Toro, G.; Smith, S. A.

    2010-12-01

    In this study, we introduce work which aims assess the loading of faults to failure under different stress regimes in a triaxial deformation apparatus. We explore experimentally the reshear of an existing fault in various orientations for particular values of (σ1 - σ3) and σ3' for contrasting loading systems - load-strengthening (equivalent to a thrust fault) with σ1' increasing at constant σ3', versus load-weakening (equivalent to a normal fault) with reducing σ3' under constant σ1'. Experiments are conducted on sawcut granite samples with fault angles at a variety of orientations relative to σ1 , ranging from an optimal orientation for reactivation to lockup angles where new faults are formed in preference to reactivating the existing sawcut orientation. Prefailure and postfailure behaviour is compared in terms of damage zone development via monitoring variations in ultrasonic velocity and acoustic emission behaviour. For example, damage surrounding unfavourably oriented faults is significantly higher than that seen around favourably orientated faults due to greater maximum stresses attained prior to unstable slip, which is reflected by the increased acoustic emission activity leading up to failure. In addition, we also experimentally explore the reshear of natural pseudotachylytes (PSTs) from two different fault zones; the Gole Larghe Fault, Adamello, Italy in which the PSTs are in relatively isotropic Tonalite (at lab sample scale) and the Alpine Fault, New Zealand in which the PSTs are in highly anisotropic foliated shist. We test whether PSTs will reshear in both rock types under the right conditions, or whether new fractures in the wall rock will form in preference to reactivating the PST (PST shear strength is higher than that of the host rock). Are PSTs representative of one slip event?

  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. The mechanism of post-rift fault activities in Baiyun sag, Pearl River Mouth basin

    NASA Astrophysics Data System (ADS)

    Sun, Zhen; Xu, Ziying; Sun, Longtao; Pang, Xiong; Yan, Chengzhi; Li, Yuanping; Zhao, Zhongxian; Wang, Zhangwen; Zhang, Cuimei

    2014-08-01

    Post-rift fault activities were often observed in deepwater basins, which have great contributions to oil and gas migration and accumulation. The main causes for post-rift fault activities include tectonic events, mud or salt diapirs, and gravitational collapse. In the South China Sea continental margin, post-rift fault activities are widely distributed, especially in Baiyun sag, one of the largest deepwater sag with its main body located beneath present continental slope. During the post-rift stage, large population of faults kept active for a long time from 32 Ma (T70) till 5.5 Ma (T10). Seismic interpretation, fault analysis and analogue modeling experiments indicate that the post-rift fault activities in Baiyun sag between 32 Ma (T70) and 13.8 Ma (T30) was mainly controlled by gravity pointing to the Main Baiyun sag, which caused the faults extensive on the side facing Main Baiyun sag and the back side compressive. Around 32 Ma (T70), the breakup of the continental margin and the spreading of the South China Sea shed a combined effect of weak compression toward Baiyun sag. The gravity during post-rift stage might be caused by discrepant subsidence and sedimentation between strongly thinned sag center and wing areas. This is supported by positive relationship between sedimentation rate and fault growth index. After 13.8 Ma (T30), fault activity shows negative relationship with sedimentation rate. Compressive uplift and erosion in seismic profiles as well as negative tectonic subsiding rates suggest that the fault activity from 13.8 Ma (T30) to 5.5 Ma (T10) might be controlled by the subductive compression from the Philippine plate in the east.

  19. Mapping Active Fault Zones in Southern California Using Master Multispectral Imagery Data

    NASA Astrophysics Data System (ADS)

    Harvey, J. C.; Peltzer, G. F.; Hook, S. J.; Alley, R.; Myers, J.; Coffland, B.; Dominguez, R.; Fitzgerald, M.

    2004-12-01

    Recent studies of active fault zones using the GPS and InSAR techniques have revealed slip rates that often differ from the slip rates determined from geological observations. This discrepancy is principally due to the different time windows over which surface movements are integrated in both approaches. If surface velocities near faults vary over cycles of several hundreds of years, it becomes important to document the slip history along faults over various time scales as it has been recorded in the Quaternary deposits along the fault. To this endeavor, we have acquired sets of images of the major active faults in Southern California using the MODIS/ASTER airborne simulator (MASTER) instrument. The lines are flown at low altitude above the ground to provide 4 to 5 m spatial resolution in the 50 spectral bands (0.5 to 13 microns) of the instrument. A preliminary set of data was acquired in the summer 2003 over the Garlock and the Blackwater faults in the Mojave. A more extensive campaign carried out in September 2004 covered more than 1000 km of fault lines from the central section of the San Andreas fault to the Salton Sea area. The data are being processed to extract reflectance and emissivity information. Preliminary analysis of the 2003 data confirmed the strong potential of the MASTER thermal bands to identify changes in surface emissivity due to subtle variations of the mineral composition of the deposits. Additional information on the near surface structure of the fault zones can be obtained by combining day and night surface temperature maps, as buried sections of faults are revealed by thermal capacity contrasts between the two sides of a given fault. The paper will present the data set acquired during the 2003 and 2004 campaigns and the status of the raw data processing into geo-referenced emissivity and reflectivity maps of the fault zones.

  20. 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.

  1. 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.

  2. 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.

  3. Finding concealed active faults: Extending the southern Whidbey Island fault across the Puget Lowland, Washington

    NASA Astrophysics Data System (ADS)

    Sherrod, Brian L.; Blakely, Richard J.; Weaver, Craig S.; Kelsey, Harvey M.; Barnett, Elizabeth; Liberty, Lee; Meagher, Karen L.; Pape, Kristin

    2008-05-01

    The southern Whidbey Island fault zone (SWIF), as previously mapped using borehole data, potential field anomalies, and marine seismic reflection surveys, consists of three subparallel, northwest trending strands extending ˜100 km from near Vancouver Island to the northern Puget Lowland. East of Puget Sound, the SWIF makes landfall between the cities of Seattle and Everett but is concealed beneath a thick mantle of young glacial deposits and vegetation. A ˜20-km-wide, northwest trending swath of subparallel, low-amplitude aeromagnetic anomalies crosses this region of the Puget Lowland and is on strike with the SWIF. The most prominent aeromagnetic anomaly, the Cottage Lake lineament, extends at least 18 km and lies approximately on strike with the SWIF on Whidbey Island. Subtle scarps and topographic lineaments on Pleistocene surfaces, visible on high-resolution lidar topography at a number of locations along the SWIF, lie on or near these magnetic anomalies. In the field, scarps exhibit northeast-side-up and vertical relief of 1 to 5 m. Excavations across several lidar scarps lying on or near magnetic anomalies show evidence for multiple folding and faulting events since deglaciation, most likely above buried reverse/oblique faults. Excavations in areas away from magnetic anomalies do not show evidence of tectonic deformation. In total, paleoseismological evidence suggests that the SWIF produced at least four earthquakes since deglaciation about 16,400 years ago, the most recent less than 2700 years ago.

  4. 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.

  5. 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.

  6. High-Resolution Seismic Reflection Studies of Active Faults: a Case Study from Washington State

    NASA Astrophysics Data System (ADS)

    Liberty, L. M.; Pratt, T. L.

    2007-12-01

    In the past five years, new high-resolution seismic surveys have filled in gaps in our understanding of active structures beneath the Puget Lowland region of Washington State. The extensive forests have made recognition of active faults difficult, but new Light Distance and Ranging (LIDAR) detailed topographic data have made a major breakthrough in mapping active faults. Extensive regional and high-resolution marine seismic surveys have been fundamental to understanding the tectonic framework of the area. These marine profiles, however, lack coverage beneath water bodies that large ships cannot navigate and beneath city streets underlain by late Pleistocene glacial deposits that are missing from the waterways. Recent land surveys and profiles in restricted waterways can therefore bridge the gap between paleoseismic and marine geophysical studies, and test elements of models proposed by regional-scale geophysical studies. We have also been venturing into more congested areas to seismically image faults in key urban locations. Results from recent surveys have: 1) documented new faults that had long been suspected in the Olympia area; 2) clarified the relationship between the LIDAR scarps and observed structures across the Tacoma fault zone; 3) provided a window into structures beneath the north and eastern portions of the western Tacoma fault zone; 4) documented deformation along the Seattle fault near a paleoseismic trench; 5) mapped the eastern part the Seattle fault zone beyond its previously mapped limits; and 6) documented multiple fault strands in the Seattle fault zone in the cities of Bellevue and Seattle. The results better constrain interpretations of paleoseismic data collected on these faults, and provide targets for future paleoseismic studies.

  7. 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.

  8. Structure and paleoearthquake records of active submarine faults, Cook Strait, New Zealand: Implications for fault interactions, stress loading, and seismic hazard

    NASA Astrophysics Data System (ADS)

    Pondard, Nicolas; Barnes, Philip M.

    2010-12-01

    A new interpretation of active faulting in central Cook Strait, New Zealand, reveals tectonic structures associated with the spatial transition from subduction to continental transform faulting. Marine seismic reflection profiles and multibeam bathymetric data indicate that there are no throughgoing crustal faults connecting the North Island Dextral Fault Belt and the Marlborough Fault System in South Island. The major faults terminate offshore, associated with 5-20 km wide step-overs and a change in regional fault strike. This structure implies that propagation of strike-slip earthquake ruptures across the strait is not probable. Faulted sedimentary sequences in the Wairau Basin (Marlborough shelf), correlated to glacioeustatic sea level cycles, provide a stratigraphic framework for fault analysis. A high-resolution study of the postglacial (<20 ka) vertical displacement history of the Cloudy and Vernon faults reveals up to six and five paleoearthquakes since 18 ka, respectively. These long-timescale records indicate variable recurrence intervals and possibly variable stress drop, thus conforming to the variable slip model of earthquake behavior. Integration of these data with other submarine and terrestrial paleoearthquake records indicates the presence of clustered earthquake sequences involving multiple faults. Different sequences do not always involve the same faults. It appears that earthquake clustering is driven by fault interactions that lead to specific loading conditions favoring the triggering of earthquakes on major faults in relatively short time intervals. Present-day regional Coulomb stress distribution has been calculated in two scenarios considered to represent minimum and maximum loading conditions. The models, incorporating secular tectonic loading and stress changes associated with major crustal earthquakes, indicate high stress loading in a large part of central Cook Strait. These conditions may favor the triggering of future damaging

  9. Variation in Magnitude of Differential Stress Across an Exhumed Continental-scale Thrust Zone

    NASA Astrophysics Data System (ADS)

    Lusk, A. D.; Platt, J. P.

    2015-12-01

    The Moine Thrust Zone (MTZ), located in NW Scotland, formed as a result of the closing of the Iapetus Ocean and docking of various terranes and arcs (Scandian Phase of the Caledonian Orogeny, ca. 445-420 Ma). The MTZ as defined here comprises three major foreland-propagating thrust faults, the latest of which is the Moine Thrust itself, which emplaced Proterozoic Moine Supergroup psammites westward onto Cambro-Ordovician shelf sequence rocks and Lewisian basement gneiss. Presently, the north-south striking Moine Thrust Zone is exposed for more than 200 km along strike, and Scandian deformation can be traced up to 40 km eastward from the Moine Thrust towards the hinterland. The thrust system is thought to have been exhumed while still active, resulting in the exposure of deep structural levels of the MTZ. As part of an ongoing project to study how the stress, rheology, and width of continental-scale faults vary with depth, we use the piezometer based on the grainsize of dynamically recrystallized quartz to determine the variation in magnitude of differential stress across the MTZ. We present a transect from the head of Loch Eriboll in the footwall, eastward to the base of Ben Hope in the hangingwall. Grainsize generally decreases westward and structurally downward to the Moine Thrust, where ultramylonites have grainsizes on the order of 10 μm. Higher stresses towards the foreland likely reflect lower temperatures of deformation in rocks that before thrusting were at higher structural levels, and may have triggered a switch to grainsize sensitive creep, thus resulting in localization of strain and narrowing of shear zone width.

  10. Active displacements recorded along major fault systems in caves (Eastern Alps, Austria)

    NASA Astrophysics Data System (ADS)

    Mitrovic, Ivanka; Plan, Lukas; Baron, Ivo; Grasemann, Bernhard

    2014-05-01

    Seismic data and GPS observations suggest that several major tectonic fault systems in the Eastern Alps are still active. However, direct geological evidences for recent movements along individual fault systems are rather scarce and limited to local observations in the Vienna Basin. Recently, tectonically damaged speleothems have been described from a cave close to the Salzach Ennstal Mariazeller Puchberger (SEMP) strike-slip fault, which accommodated the lateral extrusion of the Eastern Alps towards the Pannonian Basin. The project SPELEOTECT investigates the Quaternary tectonic activity and recent dynamics of micro-displacements along major fault systems of the Eastern Alps recorded in caves. The work focuses on cave passages, which have been displaced by active faulting and on speleothems, which have been damaged by fault movements. In order to bracket the tectonic events, flowstones, which have grown before and after the tectonic event are dated using the U-series disequilibrium method. For the reconstruction of the local stress field during (re)activation of the faults, the paleostress and the active stress field will be calculated from the fault-slip data of the recent micro-dislocations monitored with high-accuracy 3D crack-gauges. Cataclasites and fault gouges from sheared flowstones are investigated with high-resolution electron beam analytical techniques in order to characterize the microstructures caused by various deformation mechanisms within principal slip surfaces. Cathodoluminescense images are combined with electron backscattered diffraction maps in order to discriminating between fault displacements caused by seismic slip or aseismic creep. The major aim of SPELEOTECT is the record of a solid and broad data base of the paleoseismic record of the Eastern Alps for regional earthquake hazard assessment.

  11. Fault and graben growth along active magmatic divergent plate boundaries in Iceland and Ethiopia

    NASA Astrophysics Data System (ADS)

    Trippanera, D.; Acocella, V.; Ruch, J.; Abebe, B.

    2015-11-01

    Recent studies highlight the importance of annual-scale dike-induced rifting episodes in developing normal faults and graben along the active axis of magmatic divergent plate boundaries (MDPB). However, the longer-term (102-105 years) role of diking on the cumulative surface deformation and evolution of MDPB is not yet well understood. To better understand the longer-term normal faults and graben along the axis of MDPB, we analyze fissure swarms in Iceland and Ethiopia. We first focus on the simplest case of immature fissure swarms, with single dike-fed eruptive fissures; these consist of a <1 km wide graben bordered by normal faults with displacement up to a few meters, consistent with theoretical models and geodetic data. A similar structural pattern is found, with asymmetric and multiple graben, within wider mature fissure swarms, formed by several dike-fed eruptive fissures. We then consider the lateral termination of normal faults along these grabens to detect their upward or downward propagation. Most faults terminate as open fractures on flat surface, suggesting downward fault propagation; this is consistent with recent experiments showing dike-induced normal faults propagating downward from the surface. However, some normal faults also terminate as open fractures on monoclines, which resemble fault propagation folds; this suggests upward propagation of reactivated buried faults, promoted by diking. These results suggest that fault growth and graben development, as well as the longer-term evolution of the axis of MDPB, may be explained only through dike emplacement and that any amagmatic faulting is not necessary.

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. 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

  19. 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.

  20. Complex fault interactions in a restraining bend on the San Andreas fault, southern Santa Cruz Mountains, California

    SciTech Connect

    Schwartz, S.Y.; Orange, D.L.; Anderson, R.S. )

    1990-07-01

    The unusual oblique thrust mechanism of the October 18, 1989 Loma Prieta earthquake focused attention on the complex tectonic setting of this segment of the San Andreas Fault. Near the mainshock epicenter, the San Andreas Fault curves to the left defining a restraining bend. The large thrust component of the mainshock focal mechanism is consistent with the horizontal compression expected across restraining bends. However, repeated Loma Prieta type earthquakes cannot exclusively produce the observed topography of the southern Santa Cruz Mountains, the highest point of which experienced subsidence during the 1989 earthquake. In this paper, the authors integrate seismic, geomorphic and tectonic data to investigate the possibility that motions on faults adjacent to the San Andreas Fault play an important role in producing the observed topography. The three-dimensional geometry of active faults in this region is imaged using the Loma Prieta preshock and aftershock sequences. The most conspicuous features of the fault geometries at depth are: (1) the presence of two distinct zones of seismicity corresponding to the San Andreas and the Sargent-Berrocal Fault Zones, (2) the concave upward shape of the Loma Prieta rupture surface, (3) the reduction in dip of the deepest portions of the rupture plane as the mainshock hypocenter is approached, (4) the apparent transfer of shallow slip in some areas from faults in the San Andreas Fault Zone to those in the Sargent-Berrocal Fault Zone, and (5) the presence of a deep northeasterly dipping plane associated with the Sargent-Berrocal Fault Zone. The authors find that a model of fault interactions which involves displacement on faults in both the San Andreas and the Sargent-Berrocal Fault Zones is consistent with Loma Prieta coseismic displacements, preshock and aftershock seismicity and observed topography.

  1. Earthquake location, active faulting, and P-wave velocity structure near a metamorphic massif in the eastern syntaxis of the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Brown, L. E.; Meltzer, A.

    2011-12-01

    Within the core of the eastern syntaxis of the Himalaya, the Namche Barwa - Gyala Peri massif is a site of rapid exhumation where high grade metamorphic rocks from the mid to lower crust are exposed at the surface. Some of the world's highest relief is observed in this massif. The two peaks, standing over 7000m tall, are only 20km apart and are separated by a major river, the Tsangpo, at an elevation of 2500m. This impressive relief is maintained because these mountains constitute an actively forming, localized, antiformal structure, which is rapidly uplifting, while the Tsangpo downcuts through the structure. This tectonic situation is interesting because there appear to be feedbacks between topography and tectonics. As part of an effort to understand the dynamics associated with this localized structure, a temporary seismic network was used to record earthquakes near the massif. In this study approximately 2000 local earthquakes are used to define a 3-D velocity model and the locations of active faulting. The majority of events are part of an impressive spatial cluster which occurred during a series of earthquake swarms. This NW trending cluster has a vertical dip, extending to 15km in depth, and closely correlates to a topographic ridge immediately to the north of Namche Barwa. The Tsangpo takes a sharp turn when it reaches this ridge, flowing parallel to the base of the ridge, and the river then makes a dramatic 180° turn around the ridge. Given that the river's erosional power is thought to be responsible for localizing deformation into this area, it is significant that the Tsangpo's course through this area might be fault controlled. A second cluster of events is located to the west of Gyala Peri and trends to the north. Comparing this cluster to a geologic map shows that the events fall on a mapped thrust fault. This fault extends to the south of the massif, where there were no recorded events. This portion of the fault is interpreted to be locked. The

  2. 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.

  3. 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

  4. Recent high-resolution seismic reflection studies of active faults in the Puget Lowland

    NASA Astrophysics Data System (ADS)

    Liberty, L. M.; Pratt, T. L.

    2005-12-01

    In the past four years, new high-resolution seismic surveys have filled in key gaps in our understanding of active structures beneath the Puget Lowland, western Washington State. Although extensive regional and high-resolution marine seismic surveys have been fundamental to understanding the tectonic framework of the area, these marine profiles lack coverage on land and in shallow or restricted waterways. The recent high-resolution seismic surveys have targeted key structures beneath water bodies that large ships cannot navigate, and beneath city streets underlain by late Pleistocene glacial deposits that are missing from the waterways. The surveys can therefore bridge the gap between paleoseismic and marine geophysical studies, and test key elements of models proposed by regional-scale geophysical studies. Results from these surveys have: 1) documented several meters of vertical displacement on at least two separate faults in the Olympia area; 2) clarified the relationship between the Catfish Lake scarp and the underlying kink band in the Tacoma fault zone; 3) provided a first look at the structures beneath the north portion of the western Tacoma fault zone, north of previous marine profiles; 4) documented that deformation along the Seattle fault extends well east of Lake Sammamish; 5) imaged the Seattle fault beneath the Vasa Park trench; and 6) documented multiple fault strands in and south of the Seattle fault zone south of Bellevue. The results better constrain interpretations of paleoseismic investigations of past earthquakes on these faults, and provide targets for future paleoseismic studies.

  5. 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.

  6. Geomorphological observations of active faults in the epicentral region of the Huaxian large earthquake in 1556 in Shaanxi Province, China

    NASA Astrophysics Data System (ADS)

    Hou, Jian-Jun; Han, Mu-Kang; Chai, Bao-Long; Han, Heng-Yue

    1998-05-01

    The Huaxian magnitude 8 great earthquake of January 23, 1556, is the largest one recorded in the Weihe basin, Shaanxi Province, China and caused 830,000 people either injury or death. The epicenter is located in the southeastern part of the Weihe basin, around Huaxian City. Earthquakes are closely related to active faults and active faults are well developed in the epicentral area of the Huaxian large earthquake. Thus we will discuss the activity of the major faults in the epicentral area by geomorphological observations. There are three major fault sets in the study area: striking approximately east-west, northeast and northwest. These are inhomogeneous in spatial distribution, rates and manners of faulting, as shown by geomorphological observations such as faulted fluvial terraces and alluvial fans. The ages of the second and first terraces are around 20,000 and 5,000 years B.P. by thermoluminescent dating, Carbon-14 dating and archeology. The terraces were faulted by the North Huashan fault (F 1), the main boundary fault of Weihe basin and the Piedmont fault (F 2) after the second and the first terraces formed. The distribution of the displacement shows that the intersections of the North Huashan fault and the Chishui fault (F 4) striking northwest, and the western margin fault (F 5) of Tongguan loess tableland, have the largest in offsets in the area. Perhaps the Huanxian great earthquake in 1556 A.D. had a close relation to the North Huashan fault. The Weihe fault (F 3) striking east-west is also an active fault by analysis of the flood plain structure. Thus we should pay attention to the activities of the faults to take precautions against another possible large earthquake in this region.

  7. New insights on the seismogenic potential of the Eastern Betic Shear Zone (SE Iberia): Quaternary activity and paleoseismicity of the SW segment of the Carrascoy Fault Zone

    NASA Astrophysics Data System (ADS)

    Martín-Banda, Raquel; García-Mayordomo, Julián.; Insua-Arévalo, Juan M.; Salazar, Ángel E.; Rodríguez-Escudero, Emilio; Álvarez-Gómez, Jose A.; Medialdea, Alicia; Herrero, María. J.

    2016-01-01

    The Carrascoy Fault (CAF) is one of the main active faults that form part of the Eastern Betic Shear Zone, a 450 km fault system that accommodates most of the convergence between the Eurasian (Iberia) and Nubian plates in the Betic Cordillera, south Spain. Although the CAF represents a major earthquake threat to the nearby City of Murcia, studies on its Quaternary tectonics and seismogenic potential are scarce to date. We present evidence that supports the division of the CAF into two overlapping segments with contrasting tectonic structure, Quaternary activity, and landform control: a SW segment, characterized by a broad fold-and-thrust zone similar to the forebergs defined in the Gobi-Altai region, and a NE segment, characterized by a sharp mountain front controlled by strike-slip tectonics. We attribute the differentiation into these two segments to the stresses associated with topography, which in turn is a consequence of the shortening component, at the middle Pleistocene, after circa 217.4 ka. For the SW segment we infer the occurrence of 9 to 11, Mw 6.7 paleoearthquakes in the last 30.2 kyr, and a slip rate of 0.37 ± 0.08 m/kyr. We date the occurrence of the last surface rupture event after 2750 B.P., and we estimate an average recurrence period of major events of 3.3 ± 0.7 kyr.

  8. 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.

  9. 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.

  10. 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.

  11. Fluid involvement in normal faulting

    NASA Astrophysics Data System (ADS)

    Sibson, Richard H.

    2000-04-01

    Evidence of fluid interaction with normal faults comes from their varied role as flow barriers or conduits in hydrocarbon basins and as hosting structures for hydrothermal mineralisation, and from fault-rock assemblages in exhumed footwalls of steep active normal faults and metamorphic core complexes. These last suggest involvement of predominantly aqueous fluids over a broad depth range, with implications for fault shear resistance and the mechanics of normal fault reactivation. A general downwards progression in fault rock assemblages (high-level breccia-gouge (often clay-rich) → cataclasites → phyllonites → mylonite → mylonitic gneiss with the onset of greenschist phyllonites occurring near the base of the seismogenic crust) is inferred for normal fault zones developed in quartzo-feldspathic continental crust. Fluid inclusion studies in hydrothermal veining from some footwall assemblages suggest a transition from hydrostatic to suprahydrostatic fluid pressures over the depth range 3-5 km, with some evidence for near-lithostatic to hydrostatic pressure cycling towards the base of the seismogenic zone in the phyllonitic assemblages. Development of fault-fracture meshes through mixed-mode brittle failure in rock-masses with strong competence layering is promoted by low effective stress in the absence of thoroughgoing cohesionless faults that are favourably oriented for reactivation. Meshes may develop around normal faults in the near-surface under hydrostatic fluid pressures to depths determined by rock tensile strength, and at greater depths in overpressured portions of normal fault zones and at stress heterogeneities, especially dilational jogs. Overpressures localised within developing normal fault zones also determine the extent to which they may reutilise existing discontinuities (for example, low-angle thrust faults). Brittle failure mode plots demonstrate that reactivation of existing low-angle faults under vertical σ1 trajectories is only likely if

  12. Late quaternary active characteristics and slip-rate of Pingding-Huama Fault, the eastern segment of Guanggaishan-Dieshan Fault zone ( West Qinlin Mountain )

    NASA Astrophysics Data System (ADS)

    Jingxing, Y.; Wenjun, Z.; Daoyang, Y.; Jianzhang, P.; Xingwang, L.; Baiyun, L.

    2012-12-01

    Stretching along the west QinlinShan in the north Tibet, the Guanggaishan-Dieshanfaultis composed of three sub-parallel faults among which the major one is a fault named Pingding-Huama fault. The Pingding-Huama fault can be further defined as a combination of a western segment and an eastern segment separated by Minjiang river at Dangchang. Along the western segment of the Pingding-Huama fault, significant linear characteristics, scars, and fault scarps cutting several alluvial fans can be easily distinguished, indicating that the western segment is active since the late Quatenary and the elapsed time of the last event should be less than 1ka B.P.. We estimated the slip rates of the western segment through geomorphology analysis and dating the age of the top surface of terraces and the deformed strata (OSL, 14C). The results show that its reverse slip rate ranges from 0.69±0.16 to 1.15±0.28mm/a and the sinistral slip rate is 0.51±0.13mm/a. In contrast to the simple structure of the western segment, the eastern segment consists of several sub-parallel faults as well as oblique intersected faults. On all faults of the eastern segment, no sign of recent movement was discovered. Along these faults, the tectonic topography features a sequence of linear valleys in the west and dominant folds in the east. Only striations in bedrock and geomorphology show that the eastern segment was reversely slipping on the whole with sinistral component. In summary, at present the Pingding-Huama fault is active along its western segment while shows very weak deformation along the eastern segment.

  13. 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

  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. Structural character of Hosgri fault zone and adjacent areas in offshor