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Sample records for fault zone structure

  1. Fault damage zones

    NASA Astrophysics Data System (ADS)

    Kim, Young-Seog; Peacock, David C. P.; Sanderson, David J.

    2004-03-01

    Damage zones show very similar geometries across a wide range of scales and fault types, including strike-slip, normal and thrust faults. We use a geometric classification of damage zones into tip-, wall-, and linking-damage zones, based on their location around faults. These classes can be sub-divided in terms of fault and fracture patterns within the damage zone. A variety of damage zone structures can occur at mode II tips of strike-slip faults, including wing cracks, horsetail fractures, antithetic faults, and synthetic branch faults. Wall damage zones result from the propagation of mode II and mode III fault tips through a rock, or from damage associated with the increase in slip on a fault. Wall damage zone structures include extension fractures, antithetic faults, synthetic faults, and rotated blocks with associated triangular openings. The damage formed at the mode III tips of strike-slip faults (e.g. observed in cliff sections) are classified as wall damage zones, because the damage zone structures are distributed along a fault trace in map view. Mixed-mode tips are likely to show characteristics of both mode II and mode III tips. Linking damage zones are developed at steps between two sub-parallel faults, and the structures developed depend on whether the step is extensional or contractional. Extension fractures and pull-aparts typically develop in extensional steps, whilst solution seams, antithetic faults and synthetic faults commonly develop in contractional steps. Rotated blocks, isolated lenses or strike-slip duplexes may occur in both extensional and contractional steps. Damage zone geometries and structures are strongly controlled by the location around a fault, the slip mode at a fault tip, and by the evolutionary stage of the fault. Although other factors control the nature of damage zones (e.g. lithology, rheology and stress system), the three-dimensional fault geometry and slip mode at each tip must be considered to gain an understanding of

  2. Internal Structure of Taiwan Chelungpu Fault Zone Gouges

    NASA Astrophysics Data System (ADS)

    Song, Y.; Song, S.; Tang, M.; Chen, F.; Chen, Y.

    2005-12-01

    Gouge formation is found to exist in brittle faults at all scale (1). This fine-grain gouge is thought to control earthquake instability. And thus investigating the gouge textures and compositions is very important to an understanding of the earthquake process. Employing the transmission electron microscope (TEM) and a new transmission X-ray microscope (TXM), we study the internal structure of fault zone gouges from the cores of the Taiwan Chelungpu-fault Drilling Project (TCDP), which drilled in the fault zone of 1999 Chi-Chi earthquake. This X-ray microscope have installed at beamline BL01B of the Taiwan Light Source, National Synchrotron Radiation Research Center (NSRRC). It provides 2D imaging and 3D tomography at energy 8-11 keV with a spatial resolution of 25-60 nm, and is equipped with the Zernike-phase contrast capability for imaging light materials. In this work, we show the measurements of gouge texture, particle size distribution and 3D structure of the ultracataclasite in fault gouges within 12 cm about 1111.29 m depth. These characterizations in transition from the fault core to damage zone are related to the comminuting and the fracture energy in the earthquake faulting. The TXM data recently shows the particle size distributions of the ultracataclasite are between 150 nm and 900 nm in diameter. We will keep analyzing the characterization of particle size distribution, porosity and 3D structure of the fault zone gouges in transition from the fault core to damage zone to realize the comminuting and fracture surface energy in the earthquake faulting(2-5).The results may ascertain the implication of the nucleation, growth, transition, structure and permeability of the fault zones(6-8). Furthermore, it may be possible to infer the mechanism of faulting, the physical and chemical property of the fault, and the nucleation of the earthquake. References 1) B. Wilson, T. Dewerw, Z. Reches and J. Brune, Nature, 434 (2005) 749. 2) S. E. Schulz and J. P. Evans

  3. Multi-Scale Imaging of the Fault Zone Velocity Structure: Double-difference Tomography, Inversion of Fault Zone Headwaves, and Fault Zone Sensitivity Kernels

    NASA Astrophysics Data System (ADS)

    Allam, Amir A.

    In spite of the close relationship between fault zone structure and earthquake mechanics, fault zone structure at seismogenic depths remains poorly understood. How does localization of the primary slip zone vary with depth? Is there a signature of broad persistent damage zones at seismogenic depths? How does fault zone structure merge with regional structure? To answer these questions, we utilize multiple imaging techniques. We apply high-resolution double-difference tomography to the San Jacinto fault zone, invert for velocity structure along the Hayward fault using fault zone head waves, and use analytical results for idealized geometries to validate sensitivity kernels of fault zone phases for use in adjoint tomographic inversions. Double-difference tomography uses the arrival times of P and S waves to invert simultaneously for compressional velocity, shear wave velocity, and source location in three dimensions. We present results in the southern California plate-boundary area, with a focus on the San Jacinto fault zone, which incorporate arrival times of 247,472 P- and 105,448 S-wave picks for 5493 earthquakes recorded at 139 stations. Starting with a layered 1D model, and continuing in later iterations with various updated initial models, we invert the data for Vp and Vs in a 270 km long, 105 km wide and 35 km deep volume using a spatially variable grid with higher density around the San Jacinto. Our final velocity results show zones of low-velocity and high Vp/Vs ratios associated with various fault strands and sedimentary basins, along with clear velocity contrasts across the San Jacinto. While both features are limited to the upper 10km, the low velocity zones generally have higher amplitude and broader distribution in geometrically complex areas, while the velocity contrasts are more pronounced for Vp than Vs. Along the Hayward fault in the San Francisco Bay region, we identify fault zone head waves at eight stations on the northeastern side of the fault

  4. The tectonic structure of the Song Ma fault zone, Vietnam

    NASA Astrophysics Data System (ADS)

    Wen, Strong; Yeh, Yu-Lien; Tang, Chi-Cha; Phong, Lai Hop; Toan, Dinh Van; Chang, Wen-Yen; Chen, Chau-Huei

    2015-08-01

    Indochina area is a tectonic active region where creates complex topographies and tectonic structures. In particular, the Song Ma fault zone plays an important role in understanding the mechanism and revolution of the collision between the Indian plate and Eurasian plate. In order to have better understanding the seismotectonic structures of the Song Ma fault zone, a three-year project is proposed to study the seismotectonic structures of crust in this region. The main goal of this project is to deploy temporary broad-band seismic stations around/near the shear zone to record high quality microearthquakes. By using the data recorded by the temporary array and the local seismic network, we are able to conduct seismological studies which include using waveform inversion to obtain precise fault plane solutions of microearthquakes, one-dimensional (1-D) velocity structure of the crust in the region as well as the characteristics of seismogeneric zone. From the results of earthquake relocation and focal mechanisms, we find that the spatial distribution of events occurred in Song Ma fault zone forms in several distinct groups which are well correlated local geological structures and further use to gain insights on tectonic evolution.

  5. 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.

  6. Hydraulic structure of a fault zone at seismogenic depths (Gole Larghe Fault Zone, Italian Southern Alps)

    NASA Astrophysics Data System (ADS)

    Bistacchi, Andrea; Mittempergher, Silvia; Di Toro, Giulio; Smith, Steve; Garofalo, Paolo; Vho, Alice

    2016-04-01

    The Gole Larghe Fault Zone (GLFZ, Italian Southern Alps) was exhumed from c. 8 km depth, where it was characterized by seismic activity (pseudotachylytes), but also by hydrous fluid flow (alteration halos and precipitation of hydrothermal minerals in veins and cataclasites). Thanks to glacier-polished outcrops exposing the fault zone over a continuous area > 1 km2, the fault zone architecture has been quantitatively described with an unprecedented detail (Bistacchi 2011, PAGEOPH; Smith 2013, JSG; Mittempergher 2016, this meeting), providing a rich dataset to generate 3D Discrete Fracture Network (DFN) models and simulate the fault zone hydraulic properties. Based on field and microstructural evidence, we infer that the opening and closing of fractures resulted in a toggle-switch mechanism for fluid flow during the seismic cycle: higher permeability was obtained in the syn- to early post-seismic period, when the largest number of fractures was (re)opened by off-fault deformation, then permeability dropped due to hydrothermal mineral precipitation and fracture sealing. Since the fracture network that we observe now in the field is the result of the cumulative deformation history of the fault zone, which probably includes thousands of earthquakes, a fundamental parameter that cannot be directly evaluated in the field is the fraction of fractures-faults that were open immediately after a single earthquake. Postseismic permeability has been evaluated in a few cases in the world thanks to seismological evidences of fluid migration along active fault systems. Therefore, we were able to develop a parametric hydraulic model of the GLFZ and calibrate it, varying the fraction of faults/fractures that were open in the postseismic period, to obtain on one side realistic fluid flow and permeability values, and on the other side a flow pattern consistent with the observed alteration/mineralization pattern. The fraction of open fractures is very close to the percolation threshold

  7. Fault zone hydrogeology

    NASA Astrophysics Data System (ADS)

    Bense, V. F.; Gleeson, T.; Loveless, S. E.; Bour, O.; Scibek, J.

    2013-12-01

    Deformation along faults in the shallow crust (< 1 km) introduces permeability heterogeneity and anisotropy, which has an important impact on processes such as regional groundwater flow, hydrocarbon migration, and hydrothermal fluid circulation. Fault zones have the capacity to be hydraulic conduits connecting shallow and deep geological environments, but simultaneously the fault cores of many faults often form effective barriers to flow. The direct evaluation of the impact of faults to fluid flow patterns remains a challenge and requires a multidisciplinary research effort of structural geologists and hydrogeologists. However, we find that these disciplines often use different methods with little interaction between them. In this review, we document the current multi-disciplinary understanding of fault zone hydrogeology. We discuss surface- and subsurface observations from diverse rock types from unlithified and lithified clastic sediments through to carbonate, crystalline, and volcanic rocks. For each rock type, we evaluate geological deformation mechanisms, hydrogeologic observations and conceptual models of fault zone hydrogeology. Outcrop observations indicate that fault zones commonly have a permeability structure suggesting they should act as complex conduit-barrier systems in which along-fault flow is encouraged and across-fault flow is impeded. Hydrogeological observations of fault zones reported in the literature show a broad qualitative agreement with outcrop-based conceptual models of fault zone hydrogeology. Nevertheless, the specific impact of a particular fault permeability structure on fault zone hydrogeology can only be assessed when the hydrogeological context of the fault zone is considered and not from outcrop observations alone. To gain a more integrated, comprehensive understanding of fault zone hydrogeology, we foresee numerous synergistic opportunities and challenges for the discipline of structural geology and hydrogeology to co-evolve and

  8. Evolution of the internal structure of fault zones in three-dimensional numerical models of normal faults

    NASA Astrophysics Data System (ADS)

    Schöpfer, Martin P. J.; Childs, Conrad; Walsh, John J.; Manzocchi, Tom

    2016-01-01

    Fault zone internal structure is characterised by heterogeneous distributions of both continuous (drag, lens rotation) and discontinuous (joints, faults) deformation which cannot be easily modelled using continuum numerical methods. Distinct element method (DEM) models, that exhibit bulk rheologies comparable to rock, demonstrate emergent behaviours that make them ideal for modelling both the nucleation and growth of fault zones. The ability to model fault zones numerically allows extant conceptual models for fault zone evolution based on outcrop studies to be tested, and controls on fault zone structure to be analysed. Three-dimensional DEM models of faults zones in mechanically layered sequences demonstrate that internal fault zone structure is predominantly controlled by the geometry of the initial fault. Whether the initial fault is a segmented array or an irregular surface determines the complexity of structure it will develop as displacement increases. Confining pressure at the time of faulting determines the irregularity of the initial fault array and also the efficiency with which irregularities are incorporated into a fault and subsequently comminuted, leading to a relationship whereby brittle faulting at high confining pressure results in less complex internal fault zone structure than at low confining pressure.

  9. Structural evolution of fault zones in sandstone by multiple deformation mechanisms: Moab fault, southeast Utah

    USGS Publications Warehouse

    Davatzes, N.C.; Eichhubl, P.; Aydin, A.

    2005-01-01

    Faults in sandstone are frequently composed of two classes of structures: (1) deformation bands and (2) joints and sheared joints. Whereas the former structures are associated with cataclastic deformation, the latter ones represent brittle fracturing, fragmentation, and brecciation. We investigated the distribution of these structures, their formation, and the underlying mechanical controls for their occurrence along the Moab normal fault in southeastern Utah through the use of structural mapping and numerical elastic boundary element modeling. We found that deformation bands occur everywhere along the fault, but with increased density in contractional relays. Joints and sheared joints only occur at intersections and extensional relays. In all locations , joints consistently overprint deformation bands. Localization of joints and sheared joints in extensional relays suggests that their distribution is controlled by local variations in stress state that are due to mechanical interaction between the fault segments. This interpretation is consistent with elastic boundary element models that predict a local reduction in mean stress and least compressive principal stress at intersections and extensional relays. The transition from deformation band to joint formation along these sections of the fault system likely resulted from the combined effects of changes in remote tectonic loading, burial depth, fluid pressure, and rock properties. In the case of the Moab fault, we conclude that the structural heterogeneity in the fault zone is systematically related to the geometric evolution of the fault, the local state of stress associated with fault slip , and the remote loading history. Because the type and distribution of structures affect fault permeability and strength, our results predict systematic variations in these parameters with fault evolution. ?? 2004 Geological Society of America.

  10. Detailed Northern Anatolian Fault Zone crustal structure from receiver functions

    NASA Astrophysics Data System (ADS)

    Cornwell, D. G.; Kahraman, M.; Thompson, D. A.; Houseman, G. A.; Rost, S.; Turkelli, N.; Teoman, U.; Altuncu Poyraz, S.; Gülen, L.; Utkucu, M.

    2013-12-01

    We present high resolution images derived from receiver functions of the continental crust in Northern Turkey that is dissected by two fault strands of the Northern Anatolian Fault Zone (NAFZ). The NAFZ is a major continental strike-slip fault system that is comparable in length and slip rate to the San Andreas Fault Zone. Recent large earthquakes occurred towards the western end of the NAFZ in 1999 at Izmit (M7.5) and Düzce (M7.2). As part of the multi-disciplinary Faultlab project, we aim to develop a model of NAFZ crustal structure and locate deformation by constraining variations in seismic properties and anisotropy in the upper and lower crust. The crustal model will be an input to test deformation scenarios in order to match geodetic observations from different phases of the earthquake loading cycle. We calculated receiver functions from teleseismic earthquakes recorded by a rectangular seismometer array spanning the NAFZ with 66 stations at a nominal inter-station spacing of 7 km and 7 additional stations further afield. This Dense Array for North Anatolia (DANA) was deployed from May 2012 until September 2013 and we selected large events (Mw>5.5) from the high quality seismological dataset to analyze further. Receiver functions were calculated for different frequency bands then collected into regional stacks before being inverted for crustal S-wave velocity structure beneath the entire DANA array footprint. In addition, we applied common conversion point (CCP) migration using a regional velocity model to construct a migrated 3D volume of P-to-S converted and multiple energy in order to identify the major crustal features and layer boundaries. We also performed the CCP migration with transverse receiver functions in order to identify regions of anisotropy within the crustal layers. Our preliminary results show a heterogeneous crust above a flat Moho that is typically at a depth of 33 km. We do not observe a prominent step in the Moho beneath the surface

  11. Geophysical properties within the San Andreas Fault Zone at the San Andreas Fault Observatory at Depth and their relationships to rock properties and fault zone structure

    NASA Astrophysics Data System (ADS)

    Jeppson, Tamara N.; Bradbury, Kelly K.; Evans, James P.

    2010-12-01

    We examine the relationships between borehole geophysical data and physical properties of fault-related rocks within the San Andreas Fault as determined from data from the San Andreas Fault Observatory at Depth borehole. Geophysical logs, cuttings data, and drilling data from the region 3- to 4-km measured depth of the borehole encompass the active part of the San Andreas Fault. The fault zone lies in a sequence of deformed sandstones, siltstone, shale, serpentinite-bearing block-in-matrix rocks, and sheared phyllitic siltstone. The borehole geophysical logs reveal the presence of a low-velocity zone from 3190 to 3410 m measured depth with Vp and Vs values 10-30% lower than the surrounding rocks and a 1-2 m thick zone of active shearing at 3301-3303 m measured depth. Seven low-velocity excursions with increased porosity, decreased density, and mud-gas kick signatures are present in the fault zone. Geologic data on grain-scale deformation and alteration are compared to borehole data and reveal weak correlations and inverse relationships to the geophysical data. In places, Vp and Vs increase with grain-scale deformation and alteration and decrease with porosity in the fault zone. The low-velocity zone is associated with a significant lithologic and structural transition to low-velocity rocks, dominated by phyllosilicates and penetratively foliated, sheared rocks. The zone of active shearing and the regions of low sonic velocity appear to be associated with clay-rich rocks that exhibit fine-scale foliation and higher porosities that may be a consequence of the fault-related shearing of foliated and fine-grained sedimentary rocks.

  12. Structural character of Hosgri fault zone and adjacent areas in offshore central California

    SciTech Connect

    Crouch, J.K.; Bachman, S.B.

    1987-05-01

    The Hosgri fault zone extends from the east-west Transverse Ranges structures near Point Arguello northward for more than 150 km to the offshore area near San Simeon Point. The fault zone is seismically active and consists chiefly of a continuous series of eastside-up thrust and high-angle reverse faults. East of the fault zone, Miocene Monterey and volcanic rocks, along with underlying pre-Miocene strata, have been tightly folded as a result of low-angle imbricate thrust faulting during post-Miocene time. These highly deformed strata have been uplited and truncated along the inner shelf. Immediately west of the Hosgria fault zone, similar Monterey and older rocks, which are less folded, conformably underlie Pliocene and younger basinal strata at structural levels that are generally 1200 to 2000 m deeper than correlative strata east of the Hosgri fault zone. Following its discovery in 1971, the Hosgri fault zone was characterized by subsequent investigators as a northwest-trending fault that was part of the San Andreas system of strike-slip faults, with disagreements on the timing and amount of right-lateral offset along the fault zone. However, modern offshore seismic-reflection data, earthquake focal-mechanism studies, and recently available offshore well information suggest that the Hosgri fault zone is instead a major imbricate thrust zone. Detailed structural analyses along part of the Hosgri fault zone suggest that little, if any, strike-slip offset has occurred along this structural trend since its post-Miocene inception. Nevertheless, the Hosgri fault zone itself can be interpreted to be a product of the larger overall San Andreas transform system in that compression has developed because the San Andreas is not parallel to the Pacific-North American plate motion.

  13. 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.

  14. 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 Wenchuan earthquake (Ms 8.0) struck the Longmen Shan area, the eastern margin of the Tibetan Plateau in Sichuan, China.It produced a large co-seismic surface rupture zone along the Yingxiu-Beichuan and Guanxian-Anxian fault zones. Our research focuses on the central fault of the Longmuanshan fault belt: the Yingxiu-Beichuan fault zone. Detailed studies were done on the coseismic surface rupture in Bajiaomiao village, Hongkou town. Combining with analyses of the cores from the No.1 Well of the Wenchuan Earthquake Fault Scientific Drilling (WFSD-1) Project, the composition features and structures of the Longmenshan fault belt are discussed. Our research indicates that the Yingxiu-Beichuan fault zone is composed of many small sub-faults (damage zone), which consist of fault breccia, cataclasite and/or fault gouge, and small amounts pseudotachylite in some faults. The thickness of the gouge in the fault zone ranges from several millimeters to 25 centimeters, which is consistent with the fault characteristics recorded in the cores of WFSD-1. Gouge is the product of the frictional effect during the earthquake, representing the principal slip zone (PSZ). The width of the Yingxiu-Beichuan fault zone is about 120 m viewed from outcrops in Bajiaomiao village. More than 80 small sub-faults that contain gouge are distributed in this area. Only several millimeters to approximately 2 centimeters gouge can be formed in one earthquake, from the results of the Taiwan Chelungpu-fault Drilling Project (TCDP) and Wenchuan Earthquake Fault Scientific Drilling (WFSD) Project, so we can infer that each layer of gouge in Yingxiu-Beichuan fault zone might be produced by at least 1 to 13 large earthquakes. The total thickness of the gouge in this area is about 150 cm, indicating at least 183 earthquake events, and suggesting that strong earthquakes repeatedly occurred along the Yingxiu-Beichuan fault zone. Each earthquake does not completely slip along the principal slip zone (PSZ) of

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  16. Slip zone structure and processes in seismogenic carbonate faults

    NASA Astrophysics Data System (ADS)

    Bullock, R. J.; De Paola, N.

    2011-12-01

    High velocity rotary shear experiments performed at seismic slip velocities (>1 m/s) have shown that experimental faults are weak; with increasing displacement, friction coefficient values decrease from Byerlee's values (μ = 0.6-0.85) to values of ~0.1. In carbonate rocks, experimental studies have shown that fault lubrication is due to the operation of multiple dynamic weakening mechanisms (e.g., flash heating, thermal pressurization, nanoparticle lubrication), which are thermally activated due to the frictional heat generated along localized slip surfaces during rapid slip. This study has set out to investigate whether evidence for the operation of these weakening mechanisms can be found in naturally occurring carbonate fault zones. Field studies were carried out on the active Gubbio fault zone (1984, Mw = 5.6) in the northern Apennines of Italy. Jurassic-Oligocene carbonates in the footwall are heavily deformed within a fault core of ~15 m thickness, which contains a number of very well exposed, highly localized principal slip surfaces (PSSs). Fault rocks are predominantly breccias and foliated cataclasites. Microstructural analyses of the PSSs reveal that slip is localized within very narrow principal slip zones (PSZs), ranging from 10-85 μm in thickness, with sub-millimetre scale asperities. PSZs are composed of very fine-grained, orange-brown ultracataclasite gouge containing a high proportion of nano-sized particles. The ultracataclasite commonly displays a foliated texture and sub-micron scale zones of extreme shear localization. A broader slip zone, up to 1.5 mm wide and containing multiple slip surfaces, is associated with the most evolved PSSs; it is located on the opposite side of the PSS to the PSZ. Here, the host rock material is heavily fractured, abraded and altered, sometimes with an ultracataclasite matrix. The surrounding wall rock often appears to have a porous texture, and calcite crystals within the slip zone have altered rims with lobate

  17. Surface and subsurface structural analysis of a part of Washita Valley fault zone, southern Oklahoma

    SciTech Connect

    Palladino, D.L.

    1984-04-01

    The Washita Valley fault zone is one of the major northwest-trending structures in southern Oklahoma. This fault system is believed to have originated as a series of normal faults during the formation of the southern Oklahoma aulacogen by late Precambrian or early Cambrian time and to have been reactivated during the Arbuckle orogeny in the Pennsylvanian. Descriptions of movement along the Washita Valley fault zone during Pennsylvanian deformation include numerous interpretations, the most common being left-lateral strike slip with 30-40 mi (50-65 km) of displacement. Structures in the area, however, suggest an alternate model. A detailed field study of small folds, faults, fracture arrays, slickensides, and drainage patterns was conducted along the southeastern half of the Washita Valley fault zone. An attempt has been made to relate these small-scale features to the major structures in the area to determine the orientation of the major compressive stress during deformation and the relative amounts of strike-slip vs. reverse dip-slip movement along the fault zone. Exploration for oil and gas along the Washita Valley fault zone has identified several overturned folds and repeated sections. Field observations in the study area include small drag folds and thrust faults parallel to the trend of the Washita Valley fault zone. The two major anticlines in the area, the Arbuckle and the Tishomingo, are both nearly parallel to the trend of the fault zone. These data suggest a model of deformation involving a large component of reverse dip-slip faulting with major duplication of strata.

  18. CRUSTAL STRUCTURE OF THE SOUTHERN CALAVERAS FAULT ZONE, CENTRAL CALIFORNIA, FROM SEISMIC REFRACTION INVESTIGATIONS.

    USGS Publications Warehouse

    Blumling, Peter; Mooney, Walter D.; Lee, W.H.K.

    1985-01-01

    A magnitude 5. 7 earthquake on August 6, 1979, within the Calaveras fault zone, near Coyote Lake of west-central California, motivated a seismic-refraction investigation in this area. A northwest-southeast profile along the fault, as well as two fan profiles across the fault were recorded to examine the velocity structure of this region. The analysis of the data reveals a complicated upper crustal velocity structure with strong lateral variations in all directions. Velocities within the fault zone were determined from the fan profiles. Near Anderson Lake, a pronounced delay of first arrivals on the fan records indicates a vertical 1- to 2-km-wide near-surface, low-velocity zone along the fault. Near Coyote Lake, the delays observed in the fan records correlate with two subsurface en-echelon fault planes which have been previously identified from lineations in the seismicity pattern. Refs.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  20. Electrical Structure of the Shallow Part of the Atotsugawa Fault, Central Japan: Detecting en Echelon Structure in the Fault Zone

    NASA Astrophysics Data System (ADS)

    Yamashita, F.; Kubo, A.; Yamada, R.; Omura, K.

    2005-12-01

    Dense VLF-MT and TDEM surveys were carried out to image the electrical structure of a region interpreted as a creeping segment of the Atotsugawa Fault, central Japan. The Atotsugawa Fault is an active fault with a length of 60-70 km and a strike of approximately N60°E. The fault type is a right-lateral strike-slip. The most significant characteristic of this fault is a possible existence of creeping segment. In the central region, the stable slip with a rate of 1.5 mm/year was found by the observation of baseline change (Geographical Survey Institute, 1997). However, such slip has not been found at the southwestern region. Therefore, the central region is considered to be a creeping segment. In the creeping segment, many fault outcrops were found on the right bank of the Atotsu-gawa River that runs along the fault. Strikes of shear planes in outcrops were observed to be N30°-47°E, which is apparently different from that of the Atotsugawa fault. This observation suggested the existence of en echelon structure, which is the cluster of small shear zones oblique to main fault. Investigation of the nature of the en echelon structure will help us to understand the growth history of the Atotsugawa fault and the mechanisms of creeping phenomenon. Because a fracture zone usually includes much water, we can detect it as a low resistivity zone. In order to image the detailed structure of echelon, we carried out the electromagnetic surveys; VLF-MT and TDEM survey as a preliminary and main investigation, respectively. The results of VLF-MT survey has been reported by Yamashita et al. (2005), and therefore we don_ft refer to the results here. We acquired data at 10000 points with airborne TDEM survey, and over 4000 data were selectively used for modeling the subsurface structure. Apparent resistivity at each point was modeled assuming 1-D structure that consists of 30 and 70 m thick layers on a semi-infinite basement (three layers in total). Because over 4000 survey points

  1. Controls on fault damage zone width, structure, and symmetry in the Bandelier Tuff, New Mexico

    NASA Astrophysics Data System (ADS)

    Riley, Paul R.; Goodwin, Laurel B.; Lewis, Claudia J.

    2010-06-01

    We studied welded and glassy nonwelded ignimbrites of the Bandelier Tuff cut by the Pajarito fault system to examine the influence of primary lithology and structure on fault damage-zone characteristics. Our work supports previous studies that indicate welding and resulting rock strength are first-order controls on the type of fault-zone structure that forms in high porosity ignimbrites. However, inherited mechanical anisotropy is the most significant control on spatial variations in fault-zone width and orientation of structures for a given throw. Cooling joints in welded ignimbrite localize strain, producing a narrower damage zone than that in glassy nonwelded ignimbrite. The joints also control the orientations of discrete fractures formed during faulting, so fractures show the same patterns inside and outside damage zones, which we attribute to local reorientation of stresses adjacent to joints. In contrast, deformation bands formed in relatively isotropic, glassy nonwelded ignimbrite exhibit conjugate sets oblique to the Pajarito fault, consistent with left-lateral extension across a pre-existing structure. Where footwall and hanging wall damage-zone widths can be compared in welded ignimbrite, they reflect greater hanging wall deformation, consistent with near-surface faulting. These observations collectively record 3D strain of a physically heterogeneous system.

  2. Multi-scale compressional wave velocity structure of the San Gregorio Fault zone

    NASA Astrophysics Data System (ADS)

    Gettemy, G. L.; Tobin, H. J.; Hole, J. A.; Sayed, A. Y.

    2004-03-01

    Understanding fault architecture at multiple scales is crucial to delineate in situ fault zone physical properties and rupture dynamics through modeling and geophysical imaging/monitoring. An exposure of the active large-offset, strike-slip San Gregorio Fault at Moss Beach, CA provides a unique field site to relate the well-mapped fault zone architecture with compressional wave velocity (Vp) structure measured at centimeter to meter scales. Laboratory ultrasonic velocities of fault zone samples, adjusted for fluid-related frequency and structural dispersion, indicate that (i) a seismic velocity reduction of ~30% characterizes the central smectite-rich clay gouge relative to the rocks 100 m away in the relatively undeformed host rocks, and (ii) the across-fault velocity profile trends for the seismic to ultrasonic bandwidth correlate almost exactly to the previously mapped macroscale fault zone structure. These results highlight the value of conducting multiscaled investigations when measuring fault zone properties defined by physical elements at multiple scale lengths.

  3. Shallow seismic trapping structure in the San Jacinto fault zone near Anza, California

    NASA Astrophysics Data System (ADS)

    Lewis, M. A.; Peng, Z.; Ben-Zion, Y.; Vernon, F. L.

    2005-09-01

    We analyse fault zone trapped waves, generated by ~500 small earthquakes, for high-resolution imaging of the subsurface structure of the Coyote Creek, Clark Valley and Buck Ridge branches of the San Jacinto fault zone near Anza, California. Based on a small number of selected trapped waves within this data set, a previous study concluded on the existence of a low-velocity waveguide that is continuous to a depth of 15-20 km. In contrast, our systematic analysis of the larger data set indicates a shallow trapping structure that extends only to a depth of 3-5 km. This is based on the following lines of evidence. (1) Earthquakes clearly outside these fault branches generate fault zone trapped waves that are recorded by stations within the fault zones. (2) A traveltime analysis of the difference between the direct S arrivals and trapped wave groups shows no systematic increase (moveout) with increasing hypocentral distance or event depth. Estimates based on the observed average moveout values indicate that the propagation distances within the low-velocity fault zone layers are 3-5 km. (3) Quantitative waveform inversions of trapped wave data indicate similar short propagation distances within the low-velocity fault zone layers. The results are compatible with recent inferences on shallow trapping structures along several other faults and rupture zones. The waveform inversions also indicate that the shallow trapping structures are offset to the northeast from the surface trace of each fault branch. This may result from a preferred propagation direction of large earthquake ruptures on the San Jacinto fault.

  4. The shallow velocity structure of the Carboneras fault zone from high-resolution seismic investigations

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Understanding and characterizing fault zone structure at depth is vital to predicting the slip behaviour of faults in the brittle crust. The CFZ is a large offset (10s of km) strike-slip fault that constitutes part of the diffuse plate boundary between Africa and Iberia. It has been largely passively exhumed from ca. 4 to 6 km depth. The friable fault zone components are excellently preserved in the region’s semi-arid climate, and consist of multiple strands of phyllosilicate-rich fault gouge ranging from 1 to 20 m in thickness. We conducted four high-resolution seismic refraction tomography lines. Two of these lines crossed the entire width of the fault zone (~1km long) while the remaining lines concentrated on individual fault strands and associated damage zones (~100m long). For each line a combination of seismic sources (accelerated drop weight, sledgehammer and 100g explosives) was used, with 2m-geophone spacing. First breaks have been picked for each of the shot gathers and inputted into a 2D travel time inversion and amplitude-modeling package (Zelt & Smith, 1992) to obtain first break tomography images down to a depth 100m for the longer lines. The fault zone is imaged as a series of low velocity zones associated with the gouge strands, with Vp=1.5-1.75 km/s a velocity reduction of 40-60% compared to the wall-rock velocities (Vp=2.8-3.2km/s). These velocities are consistent with first break tomographic observations across the Dead Sea Transform fault (Haberland et al., 2007), but lower than the velocities imaged along the Punchbowl fault zone (part of the San Andreas system). Along the longer profiles we image multiple fault strands that exhibit a variety of thicknesses (~20-80m).

  5. Internal structure of fault zones in geothermal reservoirs: Examples from palaeogeothermal fields and potential host rocks

    NASA Astrophysics Data System (ADS)

    Leonie Philipp, Sonja; Reyer, Dorothea; Meier, Silke; Bauer, Johanna F.; Afşar, Filiz

    2014-05-01

    Fault zones commonly have great effects on fluid transport in geothermal reservoirs. During fault slip all the pores and small fractures that meet with the slip plane become interconnected so that the inner part of the fault, the fault core, consisting of breccia or gouge, may suddenly develop a very high permeability. This is evidenced, for example by networks of mineral veins in deeply eroded fault zones in palaeogeothermal fields. Inactive faults, however, may have low permeabilities and even act as flow barriers. In natural and man-made geothermal reservoirs, the orientation of fault zones in relation to the current stress field and their internal structure needs be known as accurately as possible. One reason is that the activity of the fault zone depends on its angle to the principal stress directions. Another reason is that the outer part of a fault zone, the damage zone, comprises numerous fractures of various sizes. Here we present field examples of faults, and associated joints and mineral veins, in palaeogeothermal fields, and potential host rocks for man-made geothermal reservoirs, respectively. We studied several localities of different stratigraphies, lithologies and tectonic settings: (1) 58 fault zones in 22 outcrops from Upper Carboniferous to Upper Cretaceous in the Northwest German Basin (siliciclastic, carbonate and volcanic rocks); (2) 16 fault zones in 9 outcrops in Lower Permian to Middle Triassic (mainly sandstone, limestone and granite) in the Upper Rhine Graben; and (3) 74 fault zones in two coastal sections of Upper Triassic and Lower Jurassic age (mudstones and limestone-marl alternations) in the Bristol Channel Basin, UK. (1) and (2) are outcrop analogues of geothermal reservoir horizons, (3) represent palaeogeothermal fields with mineral veins. The field studies in the Northwest German Basin (1) show pronounced differences between normal-fault zones in carbonate and clastic rocks. In carbonate rocks clear damage zones occur that are

  6. Using Fault-Zone Trapped Waves from Teleseismic Earthquakes to Document Deep Structure of the Calico Fault in Mojave Desert

    NASA Astrophysics Data System (ADS)

    Li, Y. G.; Chen, P.; Lee, E. J.

    2014-12-01

    Fault-zone trapped waves (FZTWs) are observed at a square seismic array consisting of 40 intermediate-period stations deployed adjacent to the Calico Fault (CF) in Mojave Desert, California for teleseismic earthquakes and used to characterize the deep structure of fault damage zone. In the previous study, traveltimes inverse, FZTWs generated by explosions and local earthquakes, and InSAR observations have been used to document the seismic velocity structure of the CF zone, within which velocities are reduced to ~40% in the center of a 1.5-km-wide compliant zone along the fault strike and extending to 5-6 km depth at the array site [Cochran, et al., 2009]. In order to better address the deep portion of the CF beyond the depth coverage of local earthquakes, we use FZTWs recorded at this array atop the CF for teleseismic earthquakes which have great promise for providing unprecedented constrains of the depth extension of fault-zone damage structure because the FZTWs arise from teleseismic waves incident at the fault bottom at deep level. We examined the data from 72 M≥6 teleseismic earthquakes recorded at the Calico array, and identified significant FZTWs with much larger amplitudes and longer wavetrains starting ~5-s after the first-arrivals at stations located within the compliant zone along the CF strike than those registered at farther stations for teleseismic earthquakes occurring at great depths with less surface wave affect. We interpret observed FZTWs being formed by S-waves converted from P waves at the Moho (~30-km depth) and entering the bottom of the CF. The FZTWs from teleseismic earthquakes show consistent longer wavetrains (~12-s) than those (3-8-s) recorded at same stations for local earthquakes at shallow depths, indicating that the CF low-velocity compliant zone likely extends throughout much of the seismogenic zone as a result of the portion of energy expended during rupture in historical earthquakes to drive cracking and yielding of rock and

  7. Developing Advanced Seismic Imaging Methods For Characterizing the Fault Zone Structure

    NASA Astrophysics Data System (ADS)

    Zhang, Haijiang

    2015-04-01

    Here I present a series of recent developments on seismic imaging of fault zone structure. The goals of these advanced methods are to better determine the physical properties (including seismic velocity, attenuation, and anisotropy) around the fault zone and its boundaries. In order to accurately determine the seismic velocity structure of the fault zone, we have recently developed a wavelet-based double-difference seismic tomography method, in which the wavelet coefficients of the velocity model, rather than the model itself, are solved using both the absolute and differential arrival times. This method takes advantage of the multiscale nature of the velocity model and the multiscale wavelet representation property. Because of the velocity model is sparse in the wavelet domain, a sparsity constraint is applied to tomographic inversion. Compared to conventional tomography methods, the new method is both data- and model-adaptive, and thus can better resolve the fault zone structure. In addition to seismic velocity property of the fault zone, seismic anisotropy and attenuation properties are also important to characterize the fault zone structure. For this reason, we developed the seismic anisotropy tomography method to image the three-dimensional anisotropy strength model of the fault zone using shear wave splitting delay times between fast and slow shear waves. The applications to the San Andreas fault around Parkfield, California and north Anatolian fault in Turkey will be shown. To better constrain the seismic attenuation structure, we developed a new seismic attenuation tomography method using measured t* values for first arrival body waves, in which the structures of attenuation and velocity models are similar through the cross-gradient constraint. Seismic tomography can, however, only resolve the smooth variations in elastic properties in Earth's interior. To image structure at length scales smaller than what can be resolved tomographically, including

  8. Large-scale hydraulic structure of a seismogenic fault at 10 km depth (Gole Larghe Fault Zone, Italian Southern Alps)

    NASA Astrophysics Data System (ADS)

    Bistacchi, Andrea; Di Toro, Giulio; Smith, Steve; Mittempergher, Silvia; Garofalo, Paolo

    2014-05-01

    The definition of hydraulic properties of fault zones is a major issue in structural geology, seismology, and in several applications (hydrocarbons, hydrogeology, CO2 sequestration, etc.). The permeability of fault rocks can be measured in laboratory experiments, but its upscaling to large-scale structures is not straightforward. For instance, typical permeability of fine-grained fault rock samples is in the 10-18-10-20 m2 range, but, according to seismological estimates, the large-scale permeability of active fault zones can be as high as 10-10 m2. Solving this issue is difficult because in-situ measurements of large-scale permeability have been carried out just at relatively shallow depths - mainly in oil wells and exceptionally in active tectonic settings (e.g. SAFOD at 3 km), whilst deeper experiments have been performed only in the stable continental crust (e.g. KTB at 9 km). In this study, we apply discrete fracture-network (DFN) modelling techniques developed for shallow aquifers (mainly in nuclear waste storage projects like Yucca Mountain) and in the oil industry, in order to model the hydraulic structure of the Gole Larghe Fault Zone (GLFZ, Italian Southern Alps). This fault, now exposed in world-class glacier-polished outcrops, has been exhumed from ca. 8 km, where it was characterized by a well-documented seismic activity, but also by hydrous fluid flow evidenced by alteration halos and precipitation of hydrothermal minerals in veins and along cataclasites. The GLFZ does not show a classical seal structure that in other fault zones corresponds to a core zone characterized by fine-grained fault rocks. However, permeability is heterogeneous and the permeability tensor is strongly anisotropic due to fracture preferential orientation. We will show with numerical experiments that this hydraulic structure results in a channelized fluid flow (which is consistent with the observed hydrothermal alteration pattern). This results in a counterintuitive situation

  9. Towards "realistic" fault zones in a 3D structure model of the Thuringian Basin, Germany

    NASA Astrophysics Data System (ADS)

    Kley, J.; Malz, A.; Donndorf, S.; Fischer, T.; Zehner, B.

    2012-04-01

    3D computer models of geological architecture are evolving into a standard tool for visualization and analysis. Such models typically comprise the bounding surfaces of stratigraphic layers and faults. Faults affect the continuity of aquifers and can themselves act as fluid conduits or barriers. This is one reason why a "realistic" representation of faults in 3D models is desirable. Still so, many existing models treat faults in a simplistic fashion, e.g. as vertical downward projections of fault traces observed at the surface. Besides being geologically and mechanically unreasonable, this also causes technical difficulties in the modelling workflow. Most natural faults are inclined and may change dips according to rock type or flatten into mechanically weak layers. Boreholes located close to a fault can therefore cross it at depth, resulting in stratigraphic control points allocated to the wrong block. Also, faults tend to split up into several branches, forming fault zones. Obtaining a more accurate representation of faults and fault zones is therefore challenging. We present work-in-progress from the Thuringian Basin in central Germany. The fault zone geometries are never fully constrained by data and must be extrapolated to depth. We use balancing of serial, parallel cross-sections to constrain subsurface extrapolations. The structure sections are checked for consistency by restoring them to an undeformed state. If this is possible without producing gaps or overlaps, the interpretation is considered valid (but not unique) for a single cross-section. Additional constraints are provided by comparison of adjacent cross-sections. Structures should change continuously from one section to another. Also, from the deformed and restored cross-sections we can measure the strain incurred during deformation. Strain should be compatible among the cross-sections: If at all, it should vary smoothly and systematically along a given fault zone. The stratigraphic contacts and

  10. Connecting onshore structures in the Algarve with the southern Portuguese continental margin: The Carcavai fault zone

    NASA Astrophysics Data System (ADS)

    Carvalho, João; Matias, Hugo; Rabeh, Taha; Menezes, Paulo T. L.; Barbosa, Valeria C. F.; Dias, Ruben; Carrilho, Fernando

    2012-10-01

    The Algarve is located a few hundred kilometres north of the crossing of the E-W Eurasia-Africa plate boundary and is characterised by a moderate seismicity, with some important historical and instrumental earthquakes causing loss of lives and significant material damages. The area is affected not only by plate boundary generated earthquakes but also by local events capable of generating moderate to large earthquakes. The assessment of onshore local sources and its connections with the plate border is therefore of vital importance for an evaluation of the regional seismic hazard. This paper discusses the application of geophysical data to study a large fault zone which is the offshore prolonging of the Carcavai fault zone (CF), an onshore outcropping structure more than 20 km long which is seen to deform sediments of Plio-Quaternary age. Offshore and onshore aeromagnetic data, offshore gravimetric and seismic reflection data shows the existence of a long (over 200 km) WSW-ENE trending fault zone affecting the Palaeozoic basement with a normal geometry which is probably segmented by NNW-SSE to N-S faults. Seismic data shows that this fault zone has been reactivated as a left-lateral strike-slip fault and inverted in the Cenozoic with the upthrust of the northwestern block, in agreement with the onshore CF characteristics. Recent work carried out onshore and offshore near the coastline that shows deformation of Plio-Quaternary sediments suggests that this is an active fault. Some of the faults segments have instrumental seismicity associated. Though faults very rarely rupture along its entire length, several fault segments have a length of about 30 km and may produce an earthquake of magnitude about7. The proximity of the onshore segment to the city of Faro and of the offshore segments to the main population centres of the Algarve makes it a serious threat to the Algarve.

  11. Rheological structure of the lithosphere in plate boundary strike-slip fault zones

    NASA Astrophysics Data System (ADS)

    Chatzaras, Vasileios; Tikoff, Basil; Kruckenberg, Seth C.; Newman, Julie; Titus, Sarah J.; Withers, Anthony C.; Drury, Martyn R.

    2016-04-01

    How well constrained is the rheological structure of the lithosphere in plate boundary strike-slip fault systems? Further, how do lithospheric layers, with rheologically distinct behaviors, interact within the strike-slip fault zones? To address these questions, we present rheological observations from the mantle sections of two lithospheric-scale, strike-slip fault zones. Xenoliths from ˜40 km depth (970-1100 ° C) beneath the San Andreas fault system (SAF) provide critical constraints on the mechanical stratification of the lithosphere in this continental transform fault. Samples from the Bogota Peninsula shear zone (BPSZ, New Caledonia), which is an exhumed oceanic transform fault, provide insights on lateral variations in mantle strength and viscosity across the fault zone at a depth corresponding to deformation temperatures of ˜900 ° C. Olivine recrystallized grain size piezometry suggests that the shear stress in the SAF upper mantle is 5-9 MPa and in the BPSZ is 4-10 MPa. Thus, the mantle strength in both fault zones is comparable to the crustal strength (˜10 MPa) of seismogenic strike-slip faults in the SAF system. Across the BPSZ, shear stress increases from 4 MPa in the surrounding rocks to 10 MPa in the mylonites, which comprise the core of the shear zone. Further, the BPSZ is characterized by at least one order of magnitude difference in the viscosity between the mylonites (1018 Paṡs) and the surrounding rocks (1019 Paṡs). Mantle viscosity in both the BPSZ mylonites and the SAF (7.0ṡ1018-3.1ṡ1020 Paṡs) is relatively low. To explain our observations from these two strike-slip fault zones, we propose the "lithospheric feedback" model in which the upper crust and lithospheric mantle act together as an integrated system. Mantle flow controls displacement and the upper crust controls the stress magnitude in the system. Our stress data combined with data that are now available for the middle and lower crustal sections of other transcurrent fault

  12. Fine structure of the landers fault zone: Segmentation and the rupture process

    USGS Publications Warehouse

    Li, Y.-G.; Vidale, J.E.; Aki, K.; Marone, C.J.; Lee, W.H.K.

    1994-01-01

    Observations and modeling of 3- to 6-hertz seismic shear waves trapped within the fault zone of the 1992 Landers earthquake series allow the fine structure and continuity of the zone to be evaluated. The fault, to a depth of at least 12 kilometers, is marked by a zone 100 to 200 meters wide where shear velocity is reduced by 30 to 50 percent. This zone forms a seismic waveguide that extends along the southern 30 kilometers of the Landers rupture surface and ends at the fault bend about 18 kilometers north of the main shock epicenter. Another fault plane waveguide, disconnected from the first, exists along the northern rupture surface. These observations, in conjunction with surface slip, detailed seismicity patterns, and the progression of rupture along the fault, suggest that several simple rupture planes were involved in the Landers earthquake and that the inferred rupture front hesitated or slowed at the location where the rupture jumped from one to the next plane. Reduction in rupture velocity can tentatively be attributed to fault plane complexity, and variations in moment release can be attributed to variations in available energy.

  13. Structural and fluid-chemical properties of fault zones

    SciTech Connect

    Bruhn, R.L. . Dept. of Geology and Geophysics)

    1992-01-01

    Fault fluids are mostly NaCl-CO[sub 2]-H[sub 2]O mixtures that originate by metamorphism, escape of connate water from wall rock, circulation of meteoric water, and perhaps contain components derived form igneous and subcrustal sources. Rupturing extends downward into metamorphic terrains undergoing greenschist and amphibolite facies metamorphism, where mineral alteration triggered by fluid pressure transients may extend several hundred meters to perhaps several kilometers into the wall rock. Fluid flowing into regions of lower temperature and/or pressure causes retrograde metamorphic alteration of fault and wall rock, and cementation of fractures. Fault permeability is heterogeneous because irregular, discontinuous lenses of cataclastic and gouge are encased in a heterogeneous damage layer characterized by intense fracturing and hydrothermal alteration. Permeability is also controlled by the geometry of corrugated slip surfaces which create anisotropic flow channels with greatest permeability parallel to long-axes of corrugations. Mineral assemblages and fluid inclusions provide evidence for fluid pressure cycling. Fluid pressure drops when permeability is enhanced by rupturing and subsequently increases as fractures deform, heal and become cemented with alteration minerals. Rates of hydrothermal alteration are comparable to, and sometimes faster, than those of mechanically induced permeability reduction. Effects of fluid chemistry on fault mechanics are not as well understood as fluid pressure effects. Frictional properties of fault surfaces are changed by chemical corrosion, cementation, and pressure solution. Strengthening by fluid pressure drop during dilatant fracturing may be partially offset by a decrease in fluid bulk modulus triggered by effervescence of CO[sub 2].

  14. Fault zone structure: insights from high resolution seismological data of the 2009 MW 6.1 L'Aquila causative fault.

    NASA Astrophysics Data System (ADS)

    Valoroso, Luisa; Chiaraluce, Lauro; Collettini, Cristiano

    2013-04-01

    Fault zone structure characterization is of paramount importance for our understanding of fault zone evolution, earthquake mechanics and crustal permeability. Most of our knowledge of fault zones is achieved by field studies of ancient faults now exposed at the Earth's surface. We use earthquake locations in order to provide a seismological image of a (high-angle normal) fault zone structure and to investigate the role of earthquakes in the fault damage zone generation and evolution. The extraordinary dataset is composed by ~13k aftershocks nucleated during the 2009 L'Aquila earthquake along the MW 6.1 mainshock causative fault that activated the whole upper crust, from 12 km of depth up to the surface. We generally observe an amazing similarity in between the seismological and geological fault zone architecture. We detect horsetail structures (2x2 km) in the shallower crustal portion (<3km) of the hanging-wall block of the main fault plane. Fault bending, dilation jogs (<1 km wide) and parallel slipping planes (<1 km long) are imaged at greater depths. Small (< 0.5 km) synthetic and antithetic structures are widespread along the entire fault plane both in the hanging-wall and footwall blocks. The total fault zone thickness as measured in terms of area interested by aftershocks activity, ranges from 0.5 to 1 km, in agreement with the observations made by field geologists. Fracture (50 to 200 m long) density decays as r*exp-n, where r is distance from the fault plane. n is in the range of 0.8-2 with variation induced by along strike and in depth fault complexities. Fracture densities seem to be related also with coseismic slip, showing with fault portions affected by larger slip and higher rupture velocity.

  15. Architecture, fracture system, mechanical properties and permeability structure of a fault zone in Lower Triassic sandstone, Upper Rhine Graben

    NASA Astrophysics Data System (ADS)

    Bauer, Johanna F.; Meier, Silke; Philipp, Sonja L.

    2015-04-01

    Close to the western Upper Rhine Graben Main Fault, Alsace, a NNE-SSW-striking fault zone, crosscutting porous, thick bedded Lower Triassic Bunter sandstone was investigated in detail, including its architecture, discontinuity system, mechanical rock properties and implications on its permeability structure and fault zone type. Field observations indicate a three-part fault zone structure including core-, transition- and damage zone. The at least 14 m thick fault core is composed of various slip surfaces and deformation bands, which encompass fractured host rock lenses. When connected, host rock lenses may transport fluids through the core zone. Adjacent transition zones are highly fractured in R1-orientation, show folded beds and contain P1-oriented deformation bands. R1 and P1-fractures are synthetic shear fractures and project with an acute angle (10-20°) toward the fault plane. Only in the damage zone, fault-parallel striking fractures occur. Here, increasing fracture apertures and connectivity may increase the permeability toward the fault core. Mechanical rock properties from 12 rock samples (Young's modulus, uniaxial compressive strength, tensile strength) measured in all the parts of the fault zone, show highest values within the transition zone. In-situ measurements of rebound-hardnesses with a Schmidt-Hammer and analytical approaches, however, indicate that effective Young's moduli are two to sixteen times lower than the Young's moduli of intact rock. Values clearly decrease toward the fault core, even in the transition zone and are in average lower than effective Young's moduli in the damage zone. Although many fault zones in sandstone are sealing structures these field study show, that fault zones in porous sandstone may allow fluid flow.

  16. The Dynamics of Fault Zones

    NASA Astrophysics Data System (ADS)

    Mooney, W. D.; Beroza, G.; Kind, R.

    2006-05-01

    Geophysical studies of the Earth's crust, including fault zones, have developed over the past 80 years. Among the first methods to be employed, seismic refraction and reflection profiles were recorded in the North American Gulf Coast to detect salt domes which were known to trap hydrocarbons. Seismic methods continue to be the most important geophysical technique in use today due to the methods' relatively high accuracy, high resolution, and great depth of penetration. However, in the past decade, a much expanded repertoire of seismic and non-seismic techniques have been brought to bear on studies of the Earth's crust and uppermost mantle. Important insights have also been obtained using seismic tomography, measurements of seismic anisotropy, fault zone guided waves, borehole surveys, and geo-electrical, magnetic, and gravity methods. In this presentation, we briefly review recent geophysical progress in the study of the structure and internal properties of faults zones, from their surface exposures to their lower limit. We focus on the structure of faults within continental crystalline and competent sedimentary rock rather than within the overlying, poorly consolidated sedimentary rocks. A significant body of literature exists for oceanic fracture zones, however, due to space limitations we restrict this review to faults within and at the margins of the continents. We also address some unanswered questions, including: 1) Does fault-zone complexity, as observed at the surface, extend to great depth, or do active faults become thin simple planes at depth? and 2) How is crustal deformation accommodated within the lithospheric mantle?

  17. Pulse-Like Rupture Induced by Three-Dimensional Fault Zone Flower Structures

    NASA Astrophysics Data System (ADS)

    Pelties, Christian; Huang, Yihe; Ampuero, Jean-Paul

    2015-05-01

    Faults are often embedded in low-velocity fault zones (LVFZ) caused by material damage. Previous 2D dynamic rupture simulations (H uang and A mpuero, 2011; H uang et al., 2014) showed that if the wave velocity contrast between the LVFZ and the country rock is strong enough, ruptures can behave as pulses, i.e. with local slip duration (rise time) much shorter than whole rupture duration. Local slip arrest (healing) is generated by waves reflected from the LVFZ-country rock interface. This effect is robust against a wide range of fault zone widths, absence of frictional healing, variation of initial stress conditions, attenuation, and off-fault plasticity. These numerical studies covered two-dimensional problems with fault-parallel fault zone structures. Here, we extend previous work to 3D and geometries that are more typical of natural fault zones, including complexities such as flower structures with depth-dependent velocity and thickness, and limited fault zone depth extent. This investigation requires high resolution and flexible mesh generation, which are enabled here by the high-order accurate arbitrary high-order derivatives discontinuous Galerkin method with an unstructured tetrahedral element discretization (P elties et al., 2012). We show that the healing mechanism induced by waves reflected in the LVFZ also operates efficiently in such three-dimensional fault zone structures and that, in addition, a new healing mechanism is induced by unloading waves generated when the rupture reaches the surface. The first mechanism leads to very short rise time controlled by the LVFZ width to wave speed ratio. The second mechanism leads to generally longer, depth-increasing rise times, is also conditioned by the existence of an LVFZ, and persists at some depth below the bottom of the LVFZ. Our simulations show that the generation of slip pulses by these two mechanisms is robust to the depth extent of the LVFZ and to the position of the hypocenter. The first healing

  18. Fault zone structure and seismic reflection characteristics in zones of slow slip and tsunami earthquakes

    NASA Astrophysics Data System (ADS)

    Bell, Rebecca; Henrys, Stuart; Sutherland, Rupert; Barker, Daniel; Wallace, Laura; Holden, Caroline; Power, William; Wang, Xiaoming; Morgan, Joanna; Warner, Michael; Downes, Gaye

    2015-04-01

    Over the last couple of decades we have learned that a whole spectrum of different fault slip behaviour takes place on subduction megathrust faults from stick-slip earthquakes to slow slip and stable sliding. Geophysical data, including seismic reflection data, can be used to characterise margins and fault zones that undergo different modes of slip. In this presentation we will focus on the Hikurangi margin, New Zealand, which exhibits marked along-strike changes in seismic behaviour and margin characteristics. Campaign and continuous GPS measurements reveal deep interseismic coupling and deep slow slip events (~30-60 km) at the southern Hikurangi margin. The northern margin, in contrast, experiences aseismic slip and shallow (<10-15 km) slow slip events (SSE) every 18-24 months with equivalent moment magnitudes of Mw 6.5-6.8. Updip of the SSE region two unusual megathrust earthquakes occurred in March and May 1947 with characteristics typical of tsunami earthquakes. The Hikurangi margin is therefore an excellent natural laboratory to study differential fault slip behaviour. Using 2D seismic reflection, magnetic anomaly and geodetic data we observe in the source areas of the 1947 tsunami earthquakes i) low amplitude interface reflectivity, ii) shallower interface relief, iii) bathymetric ridges, iv) magnetic anomaly highs and in the case of the March 1947 earthquake v) stronger geodetic coupling. We suggest that this is due to the subduction of seamounts, similar in dimensions to seamounts observed on the incoming Pacific plate, to depths of <10 km. We propose a source model for the 1947 tsunami earthquakes based on geophysical data and find that extremely low rupture velocities (c. 300 m/s) are required to model the observed large tsunami run-up heights (Bell et al. 2014, EPSL). Our study suggests that subducted topography can cause the nucleation of moderate earthquakes with complex, low velocity rupture scenarios that enhance tsunami waves, and the role of

  19. Structure and early kinematic history of the Great Glen Fault Zone, Scotland

    NASA Astrophysics Data System (ADS)

    Stewart, M.; Strachan, R. A.; Holdsworth, R. E.

    1999-04-01

    The Great Glen Fault Zone (GGFZ) is a major, reactivated strike-slip fault within the lower Paleozoic Caledonian orogenic belt of the British Isles. The Late Devonian to Tertiary reactivation history is well documented, but the early history is poorly known and controversial. New analysis of early structures and fabrics shows that the GGFZ comprises a 3-km-wide belt of fault rocks ranging from rare mylonite and quartz blastomylonite to common cataclasite, hydrated cataclasite, and phyllonite. Kinematic indicators demonstrate a sinistral sense of displacement with a southeasterly component of downthrow. Microstructural analysis indicates that presently exposed levels of the GGFZ developed initially at depths of about 9-16 km, within the frictional-viscous creep transition zone. Deformation continued during exhumation and was associated with pervasive syntectonic infiltration of hydrous fluids which resulted in widespread retrogression along the GGFZ. Strong protolith mineral phases were progressively replaced by secondary fine-grained aggregates of phyllosilicates leading to a permanent weakening of the fault zone. Relationships between fault zone structures, dated igneous intrusions, and posttectonic (Devonian/Old Red Sandstone) sedimentary rocks constrain sinistral displacement to a late stage in the Caledonian orogeny, between about 428 Ma and 390 Ma. Early displacements probably overlapped crustal-scale, foreland-directed thrusting which resulted from the oblique collision of the Scottish segment of Laurentia with Baltica. There is no geological evidence that these late Caledonian displacements involved reactivation of an older structure at the current exposure level. However, the Caledonian structural architecture of the GGFZ exerted a fundamental influence on the upper crustal Late Devonian to Tertiary reactivation history during which microfracturing and development of discrete fault planes were localized either within or along the boundaries of preexisting

  20. Crustal Structure across The Southwest Longmenshan Fault Zone from Seismic Wide Angle Reflection/Refraction Profile

    NASA Astrophysics Data System (ADS)

    Tian, Xiaofeng; Wang, Fuyun; Wang, Shuaijun; Duan, Yonghong

    2014-05-01

    The Lushan eathquake, which epicenter and focal depth were at 30.308° N, 102.888° E, and 14.0 km, is the latest intense earthquake occurring in the southwest section of the Longmenshan fault zone after the Ms 8.0 Wenchuan earthquake in 2008. According to the emergency field observations, the slip distribution of the Lushan earthquake was concentrated at the hypocenter, and did not rupture to the surface(Chen et al, 2013). The rupture history constrained by inverting waveforms showed that the causative fault plane of the Lushan event is apparently not a simple extension of either the Pengguan fault or the Beichuan fault that ruptured during the 2008 Mw 8.0 Wenchuan earthquake. The focal mechanism using the Cut and Paste algorithm showed this event occurred on a high dip-angle fault, but its dip angle is not steep enough to rupture the surface. All these research is not independent on the heterogeneous crust structure of the Longmenshan fault zone. A 450 km-long wide-angle reflection/refraction profile executed during September and October 2013. This experiment have provided the best opportunities to obtain better knowledge of seismic structure and properties of crust and uppermost mantle beneath the Southwest Longmenshan fault zone. This seismic profile extends from the west Sichuan Plain, through the Longmenshan Fault zone, and into the west Sichuan Plateau. We observed clear Pg, refraction Phase from the upper crust, Pi1/Pi2/Pi3, reflection/refraction Phase from intra-crust, PmP, reflection from the Moho boundary, and the Pn phase, refraction Phase from uppermost mantle. We present a hybrid tomographic and layered velocity model of the crust and uppermost mantle along the profile. The final velocity model reveals large variations both in structure and velocity, and is demonstrated that a particular model has minimum structure. The model shows the crustal thickness of the region is very variable. The Moho topography varies more than 10km in the southwest

  1. Crustal Structure across The Southwest Longmenshan Fault Zone from Seismic Controlled Source Seismic Data

    NASA Astrophysics Data System (ADS)

    Tian, X.; Wang, F.; Liu, B.

    2014-12-01

    The Lushan eathquake, which epicenter and focal depth were at 30.308° N, 102.888° E, and 14.0 km, is the latest intense earthquake occurring in the southwest section of the Longmenshan fault zone after the Ms 8.0 Wenchuan earthquake in 2008. According to the emergency field observations, the slip distribution of the Lushan earthquake was concentrated at the hypocenter, and did not rupture to the surface(Chen et al, 2013). The rupture history constrained by inverting waveforms showed that the causative fault plane of the Lushan event is apparently not a simple extension of either the Pengguan fault or the Beichuan fault that ruptured during the 2008 Mw 8.0 Wenchuan earthquake. The focal mechanism using the Cut and paste algorithm showed this event occurred on a high dip-angle fault, but its dip angle is not steep enough to rupture the surface. All these research is not independent on the heterogeneous crust structure of the Longmenshan fault zone. A 450 km-long wide-angle reflection/refraction profile executed during September and October 2013. This experiment have provided the best opportunities to obtain better knowledge of seismic structure and properties of crust and uppermost mantle beneath the Southwest Longmenshan fault zone. This seismic profile extends from the west Sichuan Plain, through the Longmenshan Fault zone, and into the west Sichuan Plateau. We observed clear Pg, refraction Phase from the upper crust, Pi1/Pi2/Pi3, reflection/refraction Phase from intra-crust, PmP, reflection from the Moho boundary, and the Pn phase, refraction Phase from uppermost mantle. We present a hybrid tomographic and layered velocity model of the crust and uppermost mantle along the profile. The final velocity model reveals large variations both in structure and velocity, and is demonstrated that a particular model has minimum structure. The model shows the crustal thickness of the region is very variable. The Moho topography varies more than 10km in the southwest

  2. Evaluation of soft sediment deformation structures along the Fethiye-Burdur Fault Zone, SW Turkey

    NASA Astrophysics Data System (ADS)

    Ozcelik, Mehmet

    2016-03-01

    Burdur city is located on lacustrine sedimentary deposits at the northeastern end of the Fethiye-Burdur Fault Zone (FBFZ) in SW Turkey. Fault steps were formed in response to vertical displacement along normal fault zones in these deposits. Soft sediment deformation structures were identified at five sites in lacustrine sediments located on both sides of the FBFZ. The deformed sediments are composed of unconsolidated alternations of sands, silts and clay layers and show different morphological types. The soft sediment deformation structures include load structures, flame structures, slumps, dykes, neptunian dykes, drops and pseudonodules, intercalated layers, ball and pillow structures, minor faults and water escape structures of varying geometry and dimension. These structures are a direct response to fluid escape during liquefaction and fluidization mechanism. The driving forces inferred include gravitational instabilities and hydraulic processes. Geological, tectonic, mineralogical investigations and age analysis were carried out to identify the cause for these soft sediment deformations. OSL dating indicated an age ranging from 15161±744 to 17434±896 years for the soft sediment deformation structures. Geological investigations of the soft sediment deformation structures and tectonic history of the basin indicate that the main factor for deformation is past seismic activity.

  3. Dynamic rupture simulations on complex fault zone structures with off-fault plasticity using the ADER-DG method

    NASA Astrophysics Data System (ADS)

    Wollherr, Stephanie; Gabriel, Alice-Agnes; Igel, Heiner

    2015-04-01

    In dynamic rupture models, high stress concentrations at rupture fronts have to to be accommodated by off-fault inelastic processes such as plastic deformation. As presented in (Roten et al., 2014), incorporating plastic yielding can significantly reduce earlier predictions of ground motions in the Los Angeles Basin. Further, an inelastic response of materials surrounding a fault potentially has a strong impact on surface displacement and is therefore a key aspect in understanding the triggering of tsunamis through floor uplifting. We present an implementation of off-fault-plasticity and its verification for the software package SeisSol, an arbitrary high-order derivative discontinuous Galerkin (ADER-DG) method. The software recently reached multi-petaflop/s performance on some of the largest supercomputers worldwide and was a Gordon Bell prize finalist application in 2014 (Heinecke et al., 2014). For the nonelastic calculations we impose a Drucker-Prager yield criterion in shear stress with a viscous regularization following (Andrews, 2005). It permits the smooth relaxation of high stress concentrations induced in the dynamic rupture process. We verify the implementation by comparison to the SCEC/USGS Spontaneous Rupture Code Verification Benchmarks. The results of test problem TPV13 with a 60-degree dipping normal fault show that SeisSol is in good accordance with other codes. Additionally we aim to explore the numerical characteristics of the off-fault plasticity implementation by performing convergence tests for the 2D code. The ADER-DG method is especially suited for complex geometries by using unstructured tetrahedral meshes. Local adaptation of the mesh resolution enables a fine sampling of the cohesive zone on the fault while simultaneously satisfying the dispersion requirements of wave propagation away from the fault. In this context we will investigate the influence of off-fault-plasticity on geometrically complex fault zone structures like subduction

  4. Internal structure of Longmenshan fault zone at Hongkou outcrop, Sichuan, China, that caused the 2008 Wenchuan earthquake

    NASA Astrophysics Data System (ADS)

    Togo, Tetsuhiro; Shimamoto, Toshihiko; Ma, Shengli; Wen, Xueze; He, Honglin

    2011-06-01

    This paper reports the internal structures of the Beichuan fault zone of Longmenshan fault system that caused the 2008 Wenchuan earthquake, at an outcrop in Hongkou, Sichuan province, China. Present work is a part of comprehensive project of Institute of Geology, China Earthquake Administration, trying to understand deformation processes in Longmenshan fault zones and eventually to reproduce Wenchuan earthquake by modeling based on measured mechanical and transport properties. Outcrop studies could be integrated with those performed on samples recovered from fault zone drilling, during the Wenchuan Earthquake Fault Scientific Drilling (WFSD) Project, to understand along-fault and depth variation of fault zone properties. The hanging wall side of the fault zone consists of weakly-foliated, clayey fault gouge of about 1 m in width and of several fault breccia zones of 30-40 m in total width. We could not find any pseudotachylite at this outcrop. Displacement during the Wenchuan earthquake is highly localized within the fault gouge layer along narrower slipping-zones of about 10 to 20 mm in width. This is an important constraint for analyzing thermal pressurization, an important dynamic weakening mechanism of faults. Overlapping patterns of striations on slickenside surface suggest that seismic slip at a given time occurred in even narrower zone of a few to several millimeters, so that localization of deformation must have occurred within a slipping zone during coseismic fault motion. Fault breccia zones are bounded by thin black gouge layers containing amorphous carbon. Fault gouge contains illite and chlorite minerals, but not smectite. Clayey fault gouge next to coseismic slipping zone also contains amorphous carbon and small amounts of graphite. The structural observations and mineralogical data obtained from outcrop exposures of the fault zone of the Wenchuan earthquake can be compared with those obtained from the WFSD-1 and WFSD-2 boreholes, which have been

  5. Multi-Scale Structure and Earthquake Properties in the San Jacinto Fault Zone Area

    NASA Astrophysics Data System (ADS)

    Ben-Zion, Y.

    2014-12-01

    I review multi-scale multi-signal seismological results on structure and earthquake properties within and around the San Jacinto Fault Zone (SJFZ) in southern California. The results are based on data of the southern California and ANZA networks covering scales from a few km to over 100 km, additional near-fault seismometers and linear arrays with instrument spacing 25-50 m that cross the SJFZ at several locations, and a dense rectangular array with >1100 vertical-component nodes separated by 10-30 m centered on the fault. The structural studies utilize earthquake data to image the seismogenic sections and ambient noise to image the shallower structures. The earthquake studies use waveform inversions and additional time domain and spectral methods. We observe pronounced damage regions with low seismic velocities and anomalous Vp/Vs ratios around the fault, and clear velocity contrasts across various sections. The damage zones and velocity contrasts produce fault zone trapped and head waves at various locations, along with time delays, anisotropy and other signals. The damage zones follow a flower-shape with depth; in places with velocity contrast they are offset to the stiffer side at depth as expected for bimaterial ruptures with persistent propagation direction. Analysis of PGV and PGA indicates clear persistent directivity at given fault sections and overall motion amplification within several km around the fault. Clear temporal changes of velocities, probably involving primarily the shallow material, are observed in response to seasonal, earthquake and other loadings. Full source tensor properties of M>4 earthquakes in the complex trifurcation area include statistically-robust small isotropic component, likely reflecting dynamic generation of rock damage in the source volumes. The dense fault zone instruments record seismic "noise" at frequencies >200 Hz that can be used for imaging and monitoring the shallow material with high space and time details, and

  6. Structure of a seismogenic fault zone in dolostones: the Foiana Line (Italian Southern Alps)

    NASA Astrophysics Data System (ADS)

    Di Toro, G.; Fondriest, M.; Smith, S. A.; Aretusini, S.

    2012-12-01

    clasts (resulting from force chains) oriented at 60-80 degrees to the slip surfaces. Similar features have been reported in natural and experimental pulverized rocks, the latter produced under dynamic stress wave loading conditions. 3-Dimensional rupture simulations along strike-slip faults predict (1) off-fault damage distributions with "flower-like" shapes (broad damage zone near the surface that rapidly narrows with increasing confining pressure, e.g., Ma and Andrews, 2010) and (2) formation of secondary faults/fractures with disperse attitudes and kinematics near the surface, with horizontal slip at depth. Qualitatively, these theoretical results compare favorably with increasing strain localization and a switch in fault kinematics recognized along the FL moving from the southern, shallower portion of the fault zone to the northern, deeper portion. Observations along the FL suggest that the association of shattered dolostones and mirror-like slip surfaces might be a potential indicator of seismic rupture propagation. Further detailed structural mapping along the FL coupled with experimental work on rock pulverization will be necessary to understand rupture dynamics in dolostones.

  7. Structural and Petrophysical Characterization of Fault Zones in Shales: Example from the Tournemire Url (sw, France)

    NASA Astrophysics Data System (ADS)

    DICK, P.; Du Peloux de Saint Romain, A.; Moreno, E.; Homberg, C.; Renel, F.; Dauzères, A.; Wittebroodt, C.; Matray, J.

    2013-12-01

    The Tournemire Underground Research Laboratory (URL) operated by IRSN (French Institute for Radiological Protection and Nuclear Safety) is located on the western border of the Mesozoic sedimentary Causses Basin (SW France). The URL crosses a thick Toarcian shale formation (≈250 m) and is interbedded between two aquiferous limestone formations. In addition to the 250 m thick overlying limestones, the geotechnical and hydrogeological characteristics of this site exhibit similarities with those measured by the French National Agency for Radioactive Waste Management (Andra) in the Callovo-Oxfordian formation of Bure (Meuse/Haute Marne, France). The Tournemire site is marked by numerous minor shear bands that affect not only the shale formation but also the over- and underlying limestone units. Since analogous discontinuities in an underground deep geological repository could act as a preferential pathway for radionuclide migration, the Tournemire site appears as an ideal location to understand the internal and permeability structures of such clay-based faults. In this study, we investigate the structural and petrophysical variations observed in a 10-15 m thick, subvertical, strike-slip shear band. For this, eight fully cored and logged horizontal boreholes were drilled normal to the fault's direction. The internal architecture and permeability of the fault was revealed through a combination of different tools (AMS, SEM, XRD and helium pycnometer) used on samples, as well as optical, induction and neutron porosity logging used in boreholes. The analysis of core samples from the different boreholes indicates that the studied fault zone is divided into a fault core (gouge), surrounded by a damaged zone (e.g., kinematically related fracture sets, small faults, and veins). Porosity and hydraulic conductivity values are low in the undisturbed shale (respectively, 9% and 10-14 m.s-1) and increase progressively towards the fault core (respectively, 15-20% and 5.10-12 m.s-1

  8. A shallow fault-zone structure illuminated by trapped waves in the Karadere-Duzce branch of the North Anatolian Fault, western Turkey

    USGS Publications Warehouse

    Ben-Zion, Y.; Peng, Z.; Okaya, D.; Seeber, L.; Armbruster, J.G.; Ozer, N.; Michael, A.J.; Baris, S.; Aktar, M.

    2003-01-01

    We discuss the subsurface structure of the Karadere-Duzce branch of the North Anatolian Fault based on analysis of a large seismic data set recorded by a local PASSCAL network in the 6 months following the Mw = 7.4 1999 Izmit earthquake. Seismograms observed at stations located in the immediate vicinity of the rupture zone show motion amplification and long-period oscillations in both P- and S-wave trains that do not exist in nearby off-fault stations. Examination of thousands of waveforms reveals that these characteristics are commonly generated by events that are well outside the fault zone. The anomalous features in fault-zone seismograms produced by events not necessarily in the fault may be referred to generally as fault-zone-related site effects. The oscillatory shear wave trains after the direct S arrival in these seismograms are analysed as trapped waves propagating in a low-velocity fault-zone layer. The time difference between the S arrival and trapped waves group does not grow systematically with increasing source-receiver separation along the fault. These observations imply that the trapping of seismic energy in the Karadere-Duzce rupture zone is generated by a shallow fault-zone layer. Traveltime analysis and synthetic waveform modelling indicate that the depth of the trapping structure is approximately 3-4 km. The synthetic waveform modelling indicates further that the shallow trapping structure has effective waveguide properties consisting of thickness of the order of 100 m, a velocity decrease relative to the surrounding rock of approximately 50 per cent and an S-wave quality factor of 10-15. The results are supported by large 2-D and 3-D parameter space studies and are compatible with recent analyses of trapped waves in a number of other faults and rupture zones. The inferred shallow trapping structure is likely to be a common structural element of fault zones and may correspond to the top part of a flower-type structure. The motion amplification

  9. Seismic fault zone trapped noise

    NASA Astrophysics Data System (ADS)

    Hillers, G.; Campillo, M.; Ben-Zion, Y.; Roux, P.

    2014-07-01

    Systematic velocity contrasts across and within fault zones can lead to head and trapped waves that provide direct information on structural units that are important for many aspects of earthquake and fault mechanics. Here we construct trapped waves from the scattered seismic wavefield recorded by a fault zone array. The frequency-dependent interaction between the ambient wavefield and the fault zone environment is studied using properties of the noise correlation field. A critical frequency fc ≈ 0.5 Hz defines a threshold above which the in-fault scattered wavefield has increased isotropy and coherency compared to the ambient noise. The increased randomization of in-fault propagation directions produces a wavefield that is trapped in a waveguide/cavity-like structure associated with the low-velocity damage zone. Dense spatial sampling allows the resolution of a near-field focal spot, which emerges from the superposition of a collapsing, time reversed wavefront. The shape of the focal spot depends on local medium properties, and a focal spot-based fault normal distribution of wave speeds indicates a ˜50% velocity reduction consistent with estimates from a far-field travel time inversion. The arrival time pattern of a synthetic correlation field can be tuned to match properties of an observed pattern, providing a noise-based imaging tool that can complement analyses of trapped ballistic waves. The results can have wide applicability for investigating the internal properties of fault damage zones, because mechanisms controlling the emergence of trapped noise have less limitations compared to trapped ballistic waves.

  10. Complex fragmentation and silicification structures in fault zones: quartz crystallization and repeated fragmentation in the Rusey fault zone (Cornwall/UK)

    NASA Astrophysics Data System (ADS)

    Yilmaz, Tim I.; Blenkinsop, Tom; Duschl, Florian; Kruhl, Jörn H.

    2015-04-01

    Silicified fault rocks typically show structures resulting from various stages of fragmentation and quartz crystallization. Both processes interact episodically and result in complex structures on various scales, which require a wide spectrum of analysis tools. Based on field and microstructural data, the spatial-temporal connection between deformation, quartz crystallization and fluid and material flow along the Rusey fault zone was investigated. The fault can be examined in detail in three dimensions on the north Cornwall coast, UK. It occurs within Carboniferous sandstones, siltstones, mudstones and slates of the Culm basin, and is likely to have had a long history. The fault rocks described here formed during the younger events, possibly due to Tertiary strike-slip reactivation. Frequent fragmentation, flow and crystallization events and their interaction led to various generations of complex-structured quartz units, among them quartz-mantled and partly silicified wall-rock fragments, microcrystalline quartz masses of different compositions and structures, and quartz vein patterns of various ages. Lobate boundaries of quartz masses indicate viscous flow. Fragments are separated by quartz infill, which contains cm-sized open pores, in which quartz crystals have pyramidal terminations. Based on frequent occurrence of feathery textures and the infill geometry, quartz crystallization from chalcedony appears likely, and an origin from silica gel is discussed. Fragmentation structures are generally fractal. This allows differentiation between various processes, such as corrosive wear, wear abrasion and hydraulic brecciation. Material transport along the brittle shear zone, and displacement of the wall-rocks, were at least partly governed by flow of mobile fluid-quartz-particle suspensions. The complex meso- to microstructures were generated by repeated processes of fragmentation, quartz precipitation and grain growth. In general, the brittle Rusey fault zone

  11. Combined structural and magnetotelluric investigation across the West Fault Zone in northern Chile

    NASA Astrophysics Data System (ADS)

    Hoffmann-Rothe, Arne

    2002-08-01

    The characterisation of the internal architecture of large-scale fault zones is usually restricted to the outcrop-based investigation of fault-related structural damage on the Earth's surface. A method to obtain information on the downward continuation of a fault is to image the subsurface electrical conductivity structure. This work deals with such a combined investigation of a segment of the West Fault, which itself is a part of the more than 2000 km long trench-linked Precordilleran Fault System in the northern Chilean Andes. Activity on the fault system lasted from Eocene to Quaternary times. In the working area (22°04'S, 68°53'W), the West Fault exhibits a clearly defined surface trace with a constant strike over many tens of kilometers. Outcrop condition and morphology of the study area allow ideally for a combination of structural geology investigation and magnetotelluric (MT) / geomagnetic depth sounding (GDS) experiments. The aim was to achieve an understanding of the correlation of the two methods and to obtain a comprehensive view of the West Fault's internal architecture. Fault-related brittle damage elements (minor faults and slip-surfaces with or without striation) record prevalent strike-slip deformation on subvertically oriented shear planes. Dextral and sinistral slip events occurred within the fault zone and indicate reactivation of the fault system. Youngest deformation increments mapped in the working area are extensional and the findings suggest a different orientation of the extension axes on either side of the fault. Damage element density increases with approach to the fault trace and marks an approximately 1000 m wide damage zone around the fault. A region of profound alteration and comminution of rocks, about 400 m wide, is centered in the damage zone. Damage elements in this central part are predominantly dipping steeply towards the east (70-80°). Within the same study area, the electrical conductivity image of the subsurface was

  12. Local structural controls on outer-rise faulting, hydration, and seismicity in the Alaska subduction zone

    NASA Astrophysics Data System (ADS)

    Shillington, D. J.; Becel, A.; Nedimovic, M. R.; Kuehn, H.; Webb, S. C.; Li, J.; Keranen, K. M.; Abers, G. A.

    2013-12-01

    We present evidence from marine geophysical data that pre-existing structures in the incoming oceanic plate off the Alaska Peninsula control bending faulting and hydration at the outer rise, which in turn correlate to changes in the abundance of interplate and intermediate-depth earthquakes within the subduction zone. Thus, pre-existing heterogeneities in the downgoing plate can result in significant variations in plate hydration over relatively small distances and may in part explain the observed global diversity of seismicity in subduction zones. ALEUT MCS and bathymetry data reveal large changes in the style and amount of bending in the incoming plate. To the west, outboard of the Shumagin Gap, there is significant bending faulting, with fault offsets up to ~250 m at the seafloor and larger offsets at depth. Faults create rugged topography at the seafloor, and sediment cover is thin (~0.5 km). Most faults have strikes within ~25 degrees of the trench. In contrast, the downgoing plate outboard of the Semidi segment to the east exhibits less dramatic bending faulting, with maximum offsets at the seafloor of 30 m, and the sediment cover is thicker (>1 km). These along-strike changes in faulting correlate with changes in the expected orientation of pre-existing structures in the incoming oceanic crust, which is nearly parallel to the trench near the Shumagin Gap, but highly oblique to the trench near the Semidi segment. This implies that more favorably-oriented pre-existing structures may facilitate bending faulting. P-wave velocity models from wide-angle seismic data reveal that along-strike changes in faulting are accompanied by variations in the velocity structure of the incoming plate. Mantle velocities are reduced by ~0.5 km/s at the outer rise off the Shumagin Gap, where significant bending faulting is observed. We interpret decreased velocities to represent serpentinization of the upper mantle. In contrast, the velocity structure is more variable off the

  13. Geochemistry, mineralization, structure, and permeability of a normal-fault zone, Casino mine, Alligator Ridge district, north central Nevada

    NASA Astrophysics Data System (ADS)

    Hammond, K. Jill; Evans, James P.

    2003-05-01

    We examine the geochemical signature and structure of the Keno fault zone to test its impact on the flow of ore-mineralizing fluids, and use the mined exposures to evaluate structures and processes associated with normal fault development. The fault is a moderately dipping normal-fault zone in siltstone and silty limestone with 55-100 m of dip-slip displacement in north-central Nevada. Across-strike exposures up to 180 m long, 65 m of down-dip exposure and 350 m of along-strike exposure allow us to determine how faults, fractures, and fluids interact within mixed-lithology carbonate-dominated sedimentary rocks. The fault changes character along strike from a single clay-rich slip plane 10-20 mm thick at the northern exposure to numerous hydrocarbon-bearing, calcite-filled, nearly vertical slip planes in a zone 15 m wide at the southern exposure. The hanging wall and footwall are intensely fractured but fracture densities do not vary markedly with distance from the fault. Fault slip varies from pure dip-slip to nearly pure strike-slip, which suggests that either slip orientations may vary on faults in single slip events, or stress variations over the history of the fault caused slip vector variations. Whole-rock major, minor, and trace element analyses indicate that Au, Sb, and As are in general associated with the fault zone, suggesting that Au- and silica-bearing fluids migrated along the fault to replace carbonate in the footwall and adjacent hanging wall rocks. Subsequent fault slip was associated with barite and calcite and hydrocarbon-bearing fluids deposited at the southern end of the fault. No correlation exists at the meter or tens of meter scale between mineralization patterns and fracture density. We suggest that the fault was a combined conduit-barrier system in which the fault provides a critical connection between the fluid sources and fractures that formed before and during faulting. During the waning stages of deposit formation, the fault behaved as

  14. Characteristics of the Lithology, Fault-related Rocks and Fault Zone Structures in the TCDP Hole-A

    NASA Astrophysics Data System (ADS)

    Song, S.; Kou, L.; Yeh, E.

    2005-12-01

    Probing a fault zone of recently major activity at depth to study the physical, mechanical and chemical properties is the one of main purposes of the Taiwan Chelungpu-fault Drilling Project (TCDP). We have finished drilling the hole-A which it has the cuttings from 0 to 430 m and cores from 430 to 2003.67 m deep in the end of 2004. Stratigraphically, from surface to 1029 m deep is the Pliocene to Pleistocene Cholan Formation which is dominantly composed of sandstone and sandstone-siltstone alternation with weak to heavy bioturbations. The Pliocene Chinshui Shale occurs from 1029 to 1303 m deep and predominantly consists of siltstone with weak bioturbation. From 1303 to 1712 m deep is the late Miocene to early Pliocene Kueichulin Formation and is dominantly composed of massive sandstone with minor siltstone. Below the 1712 m deep, the Formation is back to the younger Cholan Formation with mollusca-rich thick layered shale and heavy bioturbated sandstone. Four kinds of fault rocks can be identified in the cores. They are the fault breccia, gouge, foliated and non-foliated cataclasites and pseudotachylyte. At least six major fault zones can be found in the cores: FZ1111, FZ1153, FZ1222, FZ1580, FZ1712 and FZ1818. In those fault zones, the FZ1111 may be correlative to the surface rupture of Chi-Chi earthquake,1999, while the FZ1712 may be the Sanyi fault.

  15. Sedimentary record of relay zone evolution, Central Corinth Rift (Greece): Role of fault propagation and structural inheritance.

    NASA Astrophysics Data System (ADS)

    Hemelsdaël, Romain; Ford, Mary; Meyer, Nicolas

    2013-04-01

    Relay zones along rift border fault systems form topographic lows that are considered to allow the transfer of sediment from the footwall into hanging wall depocentres. Present knowledge focuses on the modifications of drainage patterns and sediment pathways across relay zones, however their vertical motion during growth and interaction of faults segments is not well documented. 3D models of fault growth and linkage are also under debate. The Corinth rift (Greece) is an ideal natural laboratory for the study of fault system evolution. Fault activity and rift depocentres migrated northward during Pliocene to Recent N-S extension. We report on the evolution of a relay zone in the currently active southern rift margin fault system from Pleistocene to present-day. The relay zone lies between the E-W East Helike (EHF) and Derveni faults (DF) that lie just offshore and around the town of Akrata. During its evolution the relay zone captured the antecedent Krathis river which continued to deposit Gilbert-type deltas across the relay zone during fault interaction, breaching and post linkage phases. Moreover our work underlines the role that pre-existing structure in the location of the transfer zone. Offshore fault geometry and kinematics, and sediment distribution were defined by interpretation and depth conversion of high resolution seismic profiles (from Maurice Ewing 2001 geophysical survey). Early lateral propagation of the EHF is recorded by synsedimentary fault propagation folds while the DF records tilted block geometries since initiation. Within the relay zone beds are gradually tilted toward the basin before breaching. These different styles of deformation highlight mechanical contrasts and upper crustal partition associated with the development of the Akrata relay zone. Onshore detailed lithostratigraphy, structure and geomorphological features record sedimentation across the subsiding relay ramp and subsequent footwall uplift after breaching. The area is

  16. Shallow Seismic Trapping Structure in the San Jacinto Fault Zone, California

    NASA Astrophysics Data System (ADS)

    Lewis, M. A.; Peng, Z.; Ben-Zion, Y.; Vernon, F.

    2003-12-01

    We analyze a waveform data set generated by 385 events and recorded by linear seismic arrays across the Clark Valley and Coyote Creek faults in the trifurcation area of the San Jacinto fault zone (FZ). The goal is to obtain structural information from a comprehensive analysis of FZ trapped waves in the data. A previous work based on selected waveforms suggested a low-velocity waveguide continuous to a depth of at least 18 km (Li and Vernon, JGR, 2001). If so, events located clearly outside the FZ proper should not generate any FZ trapped waves. On the other hand, a shallow FZ waveguide can produce (Fohrmann et al., PAGEOPH, 2003) trapped waves for events clearly off the fault. Our analysis of trapped waves in the larger considered data set is compatible with the existence of shallow non continuous waveguide layers along both the Clark Valley and Coyote Creek faults. Ben-Zion et al. (GJI, 2003) found in the context of the North Anatolian fault that many events off the fault produce FZ trapped waves and suggested that a better term for such data may be FZ related site effects. Within a distance of roughly 90 km, a subset of 159 events including many off the fault are suitably recorded by the arrays for analysis. A spectral ratio method is used to calculate the concentration of seismic energy within the FZ stations, producing a systematic measure of the quality of trapped waves or FZ related site effects. We find that FZ site effects are observed at FZ stations for the majority of the earthquakes, with the generating events located at various distances from the fault trace and various angles and distances from the receivers. The distribution of the events implies that the trapping structures are not continuous along the strike of either fault branch and do not extend bellow the depth of the shallowest events (e.g., 5 km). A travel time analysis of the difference between the direct S and trapped wave group arrivals shows no systematic increase with hypocentral distance

  17. Morphology and structure of the Camarinal Sill from high-resolution bathymetry: evidence of fault zones in the Gibraltar Strait

    NASA Astrophysics Data System (ADS)

    Luján, María; Crespo-Blanc, Ana; Comas, Menchu

    2011-06-01

    The Gibraltar Strait is the very narrow neck which connects the Atlantic Ocean and the Mediterranean Sea. The causes and mode of its opening at the end of the Messinian Salinity Crisis are still a matter of debate, and models based on eustatic rise and/or topographic lowering due to either erosion or faulting are generally evoked. We investigated the presence of faults based on a morphological and structural analysis of the Camarinal Sill, the shallowest passage in the Gibraltar Strait (<100 m water depth in places). This sill connects the Spanish and Moroccan shelves, and probably represents a structural high inherited from the Miocene compressive tectonics which took place in the external zones of the Betic-Rif orogenic arc. Our high-resolution bathymetric data enabled us to identify and interpret the origin of major morphological features in the area, including canyons, channels and a landslide, which we name the Tarifa landslide. Topographic arguments suggest that the Camarinal Sill is crossed by two main E-W- to ENE-WSW-directed fault zones which bound areas with different distribution, orientation and slopes of both scarps and crests. We name these the Hercules and Tarik fault zones, north and south of the sill respectively. The Hercules fault zone probably incorporates a normal movement component, whereas kinematic indicators are poor along the Tarik fault zone. The age of faulting is poorly constrained in both cases. Together with existing evidence of faults onland, the presence of these fault zones implies that they could be responsible for, or have contributed to, the opening of the Gibraltar Strait.

  18. Fault zone structure from topography: signatures of en echelon fault slip at Mustang Ridge on the San Andreas Fault, Monterey County, California

    USGS Publications Warehouse

    DeLong, Stephen B.; Hilley, George E.; Rymer, Michael J.; Prentice, Carol

    2010-01-01

    We used high-resolution topography to quantify the spatial distribution of scarps, linear valleys, topographic sinks, and oversteepened stream channels formed along an extensional step over on the San Andreas Fault (SAF) at Mustang Ridge, California. This location provides detail of both creeping fault landform development and complex fault zone kinematics. Here, the SAF creeps 10–14 mm/yr slower than at locations ∼20 km along the fault in either direction. This spatial change in creep rate is coincident with a series of en echelon oblique-normal faults that strike obliquely to the SAF and may accommodate the missing deformation. This study presents a suite of analyses that are helpful for proper mapping of faults in locations where high-resolution topographic data are available. Furthermore, our analyses indicate that two large subsidiary faults near the center of the step over zone appear to carry significant distributed deformation based on their large apparent vertical offsets, the presence of associated sag ponds and fluvial knickpoints, and the observation that they are rotating a segment of the main SAF. Several subsidiary faults in the southeastern portion of Mustang Ridge are likely less active; they have few associated sag ponds and have older scarp morphologic ages and subdued channel knickpoints. Several faults in the northwestern part of Mustang Ridge, though relatively small, are likely also actively accommodating active fault slip based on their young morphologic ages and the presence of associated sag ponds.

  19. Gravity field and structure of the Sorong Fault Zone, eastern Indonesia

    NASA Astrophysics Data System (ADS)

    Sardjono

    free-air gravity were observed in south of Mangole (about 13 mGal/km) and west of Obi (about 15 mGal/km) but elsewhere were gentler. Analyses of gravity data along the Sorong Fault Zone in the region of Barggal-Sula Islands controlled in part by geological, reflection seismic and sidescan sonar data, have produced four models which suggest that the crustal structures beneath the zone consist predominantly of attenuated continental fragments, juxtaposed to thick layer of tectonic melange and anomalous oceanic crusts. The continental fragments appear to be severely attenuated and limited in extent in the east but thicker and wider towards the west. The tectonic melange is underlain by deep seated oceanic crust in the Molucca Sea region. The anomalously thin North Banda Sea crust appears to underlie a very thin layer of sediments and to have suffered some degree of arching. The deep seated oceanic crust and the thick layer of tectonic melange are interpreted as the result of the sinking of the lithospheric plate of the Molucca Sea. The descent of this plate may have produced bending forces which may have initiated flexure which propagates through the surrounding region. Depending on the rigidity of the crustal slab, arching and fracturing may have occurred in the crustal rocks. The arching of the oceanic crust of the North Banda Sea may have been one result of this process. The continental fragments of the Banggai-Sula region appear to dip northwards and this may, in addition to the effect of shear tectonics along the Sorong Fault Zone, also be interpreted as the response of the continental fragments to the sinking of the lithospheric plate of the Molucca Sea. In the Obi region, the gravity data suggest that most of the island is underlain by peridotitic and basaltic rocks. Continental crust appears to form the basement in the south and extend offshore south of the island and juxtaposed to oceanic rock. The ultramafic and basic rocks appear to be emplaced on Obi by a high

  20. Regional Survey of Structural Properties and Cementation Patterns of Fault Zones in the Northern Part of the Albuquerque Basin, New Mexico - Implications for Ground-Water Flow

    USGS Publications Warehouse

    Minor, Scott A.; Hudson, Mark R.

    2006-01-01

    Motivated by the need to document and evaluate the types and variability of fault zone properties that potentially affect aquifer systems in basins of the middle Rio Grande rift, we systematically characterized structural and cementation properties of exposed fault zones at 176 sites in the northern Albuquerque Basin. A statistical analysis of measurements and observations evaluated four aspects of the fault zones: (1) attitude and displacement, (2) cement, (3) lithology of the host rock or sediment, and (4) character and width of distinctive structural architectural components at the outcrop scale. Three structural architectural components of the fault zones were observed: (1) outer damage zones related to fault growth; these zones typically contain deformation bands, shear fractures, and open extensional fractures, which strike subparallel to the fault and may promote ground-water flow along the fault zone; (2) inner mixed zones composed of variably entrained, disrupted, and dismembered blocks of host sediment; and (3) central fault cores that accommodate most shear strain and in which persistent low- permeability clay-rich rocks likely impede the flow of water across the fault. The lithology of the host rock or sediment influences the structure of the fault zone and the width of its components. Different grain-size distributions and degrees of induration of the host materials produce differences in material strength that lead to variations in width, degree, and style of fracturing and other fault-related deformation. In addition, lithology of the host sediment appears to strongly control the distribution of cement in fault zones. Most faults strike north to north-northeast and dip 55? - 77? east or west, toward the basin center. Most faults exhibit normal slip, and many of these faults have been reactivated by normal-oblique and strike slip. Although measured fault displacements have a broad range, from 0.9 to 4,000 m, most are <100 m, and fault zones appear to

  1. Structure of the North Anatolian Fault Zone from the Autocorrelation of Ambient Seismic Noise

    NASA Astrophysics Data System (ADS)

    Taylor, George; Rost, Sebastian; Houseman, Gregory

    2016-04-01

    In recent years the technique of cross-correlating the ambient seismic noise wavefield at two seismometers to reconstruct empirical Green's Functions for the determination of Earth structure has been a powerful tool to study the Earth's interior without earthquakes or man-made sources. However, far less attention has been paid to using auto-correlations of seismic noise to reveal body wave reflections from interfaces in the subsurface. In principle, the Green's functions thus derived should be comparable to the Earth's impulse response to a co-located source and receiver. We use data from a dense seismic array (Dense Array for Northern Anatolia - DANA) deployed across the northern branch of the North Anatolian Fault Zone (NAFZ) in the region of the 1999 magnitude 7.6 Izmit earthquake in western Turkey. The NAFZ is a major strike-slip system that extends ~1200 km across northern Turkey and continues to pose a high level of seismic hazard, in particular to the mega-city of Istanbul. We construct body wave images for the entire crust and the shallow upper mantle over the ~35 km by 70 km footprint of the 70-station DANA array. Using autocorrelations of the vertical component of ground motion, P-wave reflections can be retrieved from the wavefield to constrain crustal structure. We show that clear P-wave reflections from the crust-mantle boundary (Moho) can be retrieved using the autocorrelation technique, indicating topography on the Moho on horizontal scales of less than 10 km. Offsets in crustal structure can be identified that seem to be correlated with the surface expression of the northern branch of the fault zone, indicating that the NAFZ reaches the upper mantle as a narrow structure. The southern branch has a less clear effect on crustal structure. We also see evidence of several discontinuities in the mid-crust in addition to an upper mantle reflector that we interpret to represent the Hales discontinuity.

  2. Rapid mapping of ultrafine fault zone topography with structure from motion

    USGS Publications Warehouse

    Johnson, Kendra; Nissen, Edwin; Saripalli, Srikanth; Arrowsmith, J. Ramón; McGarey, Patrick; Scharer, Katherine M.; Williams, Patrick; Blisniuk, Kimberly

    2014-01-01

    Structure from Motion (SfM) generates high-resolution topography and coregistered texture (color) from an unstructured set of overlapping photographs taken from varying viewpoints, overcoming many of the cost, time, and logistical limitations of Light Detection and Ranging (LiDAR) and other topographic surveying methods. This paper provides the first investigation of SfM as a tool for mapping fault zone topography in areas of sparse or low-lying vegetation. First, we present a simple, affordable SfM workflow, based on an unmanned helium balloon or motorized glider, an inexpensive camera, and semiautomated software. Second, we illustrate the system at two sites on southern California faults covered by existing airborne or terrestrial LiDAR, enabling a comparative assessment of SfM topography resolution and precision. At the first site, an ∼0.1 km2 alluvial fan on the San Andreas fault, a colored point cloud of density mostly >700 points/m2 and a 3 cm digital elevation model (DEM) and orthophoto were produced from 233 photos collected ∼50 m above ground level. When a few global positioning system ground control points are incorporated, closest point vertical distances to the much sparser (∼4 points/m2) airborne LiDAR point cloud are mostly 530 points/m2 and a 2 cm DEM and orthophoto were produced from 450 photos taken from ∼60 m above ground level. Closest point vertical distances to existing terrestrial LiDAR data of comparable density are mostly <6 cm. Each SfM survey took ∼2 h to complete and several hours to generate the scene topography and texture. SfM greatly facilitates the imaging of subtle geomorphic offsets related to past earthquakes as well as rapid response mapping or long-term monitoring of faulted landscapes.

  3. San Andreas fault zone velocity structure at SAFOD at core, log, and seismic scales

    NASA Astrophysics Data System (ADS)

    Jeppson, Tamara N.; Tobin, Harold J.

    2015-07-01

    The San Andreas Fault (SAF), like other mature brittle faults, exhibits a zone of low seismic velocity hypothesized to result from fluid pressure effects and/or development of a damage zone. To address the relative contributions of these mechanisms in developing low-velocity zones, we measured P and S wave velocities ultrasonically at elevated confining and pore pressures on core samples from the San Andreas Fault Observatory at Depth (SAFOD). We compared those data to wireline and seismic-scale velocities to examine the scale dependence of acoustic properties of the fault core and damage zone. Average laboratory P and S wave velocities of the fault gouge at estimated in situ conditions are 3.1 and 1.5 km/s, respectively, consistent with the sonic log from the same intervals. These data show that fault core has intrinsically low velocity, even if no anomalous pore pressure is assumed, due to alteration and mechanical damage. In contrast, laboratory average P and S wave velocities for the damage zone are 4.7 and 2.5 km/s, up to 41% greater than the sonic log in the damage zone. This scale dependence indicates that stress conditions or macroscale features dominate the damage zone's acoustic properties, although velocity dispersion could play a role. Because no pressure anomaly was detected while drilling the SAFOD borehole, we infer that damage at a scale larger than core samples controls the elastic properties of the broader damage zone. This result bolsters other independent lines of evidence that the SAF does not contain major pore fluid overpressure at SAFOD.

  4. Deep resistivity structure along the Longmen Mountain fault zone in the eastern Tibetan plateau of China

    NASA Astrophysics Data System (ADS)

    Wang, X.; Zhang, G.; Luo, W.; Luo, H.; Cai, X.; Zhou, Y.; Zhang, W.; Qin, Q.

    2012-12-01

    1.Introduction Many researchers (e.g.,Wang et al.,2009) have proposed the relevant knowledge of tectonic evolution and dynamic characteristics of the Longmen Mountain belt as well as the Songpan-Ganzi and Yangtze blocks in the past few decades, the knowledge of shallow thrust nappe tectonic along the belt has then been generally recognized. It's, however, still difficult to image the deep crust and mantle structures and reveal the dynamic mechanism of the crustal formation under the Longmen Mountain. In this study, we carried out the MT experiments along and across the Longmen mountain region and investigated the relationships between the crust structure and seismic activity basing on the latest MT geological results. 2. Field observations We conducted three MT experiment profiles in the eastern Tibetan Plateau. One is along the Mingshan-Guangyuan profile parallel with the structural direction, and another two profiles (Maqu-Gaoliangzhen and Luqu-Hechuan) perpendicular to the Longmen Mountain fault zone. In this study, we use the conventional magnetotelluric (MT) data combine with the long-period magnetotelluric (LMT) data to observe electromagnetic response. The MT and LMT data was observed by using the V8 instrument and LEMI-417, respectively. 3. Conclusion (1) According to the results of MT inversion, we find that the high concentration of stress process along the Songpan-Ganzi block and the Yangtze block colliding zone might result from the deep crust-mantle tough shear Zone of Longmen Mountain expanded to mid-upper crust, and finally leads to a new rupture. This could be one of the focal mechanisms of the Wenchuan earthquake (Ms 8.0) generating. The deep resistivity structure along the Longmen Mountain fault zone can be divided into southern,middle and northern segments from southwest to northeast. The total resistivity of southern segment is lower than the middle and northern portions. We suggest that the upper crust of the Longmen Mountain, south of Dayi

  5. Location and Shallow Structure of the Frijoles Strand of the San Gregorio Fault Zone, Pescadero, California

    NASA Astrophysics Data System (ADS)

    Fox-Lent, C.; Catchings, R. D.; Rymer, M. J.; Goldman, M. R.; Steedman, C. E.; Prentice, C. S.

    2003-12-01

    The San Gregorio fault is one of the principal faults of the San Andreas fault system in the San Francisco Bay area. Located west of the active trace of the San Andreas fault and near the coast, the San Gregorio fault zone consists of at least two northwest-southeast-trending strands, the Coastways and Frijoles faults. Little is known about the slip history on the San Gregorio, and information for the Frijoles fault is especially scarce, as it lies mostly offshore. To better understand the contribution of the San Gregorio fault zone to slip along the San Andreas fault system, we conducted a high-resolution, seismic imaging investigation of the Frijoles fault to locate near-surface, onshore, branches of the fault that may be suitable for paleoseismic trenching. Our seismic survey consisted of a 590-meter-long, east-west-trending, combined seismic reflection and refraction profile across Butano Creek Valley, in Pescadero, California. The profile included 107 shot points and 120 geophones spaced at 5-m increments. Seismic sources were generated by a Betsy Seisgun in 0.3-m-deep holes. Data were recorded on two Geometrics Strataview RX-60 seismographs at a sampling rate of 0.5 ms. Seismic p-wave velocities, determined by inverting first-arrival refractions using tomographic methods, ranged from 900 m/s in the shallow subsurface to 5000 m/s at 200 m depth, with higher velocities in the western half of the profile. Migrated seismic reflection images show clear, planar layering in the top 100-200 meters on the eastern and western ends of the seismic profile. However, to within the shallow subsurface, a 200-m-long zone near the center of the profile shows disturbed stratigraphic layers with several apparent fault strands approaching within a few meters of the surface. The near-surface locations of the imaged strands suggest that the Frijoles fault has been active in the recent past, although further paleoseismic study is needed to detail the slip history of the San Gregorio

  6. Cretaceous to Miocene fault zone evolution in the Eastern Alps constrained by multi-system thermochronometry and structural data.

    NASA Astrophysics Data System (ADS)

    Wölfler, Andreas; Frisch, Wolfgang; Danišík, Martin; Fritz, Harald; Wölfler, Anke

    2015-04-01

    Fault zones that display both, ductile and brittle deformation stages offer perfect sites to study the evolution of the earth's crust over a wide range of temperatures and possibly over long time spans. This study combines structural- geo- and thermochronologcial data to evaluate the tectonic evolution of a fault zone to the southeast of the Tauern Window in the Eastern Alps. This fault zone comprises a mylonitic part, the so-called "Main Mylonitic Zone" (MMZ) that has been reworked by brittle faulting, the so-called "Ragga-Teuchl fault" (RTF). Structural data of the MMZ demonstrate ductile deformation with top-to-the NW transport in the Late Cretaceous under greenschist facies conditions. Subsequent SE-directed extension occurred under semi-brittle to brittle conditions during the Late Cretaceous and Paleocene. The Polinik Block to the north of the RTF revealed Late Cretaceous Ar/Ar ages, which reflect cooling subsequent to the thermal peak of Eo-alpine metamorphism. In contrast, the Kreuzeck Block to the south of the RTF shows early Permian Ar/Ar ages that reflect cooling related to both, late Variscan collapse in the late Carboniferous and post-Variscan extension in the Permian. Zircon and apatite fission track ages and thermal history modeling results suggest that the Polinik Block cooled rapidly to near surface temperatures in the middle Miocene. The Kreuzeck Block, in contrast, cooled and exhumed to near surface conditions already in the Oligocene and early Miocene. Thermal history modeling and apatite fission track ages of 23.3±0.8 and 11.5±1.0 suggest that brittle deformation along the RTF occurred in the middle- and late Miocene. Our results demonstrate that one single fault zone may comprise information about the evolution of the Eastern Alps from Late Cretaceous to Miocene time and that low-temperature thermochronology is a viable tool to resolve the timing of brittle faulting and accompanied fluid activity.

  7. Disturbed zones; indicators of deep-seated subsurface faults in the Valley and Ridge and Appalachian structural front of Pennsylvania

    USGS Publications Warehouse

    Pohn, Howard A.; Purdy, Terri L.

    1982-01-01

    Field studies of geologic structures in the Valley and Ridge and adjacent parts of the Appalachian Plateau provinces in Pennsylvania have shown a new type of structure, formerly poorly understood and frequently unmapped, is a significant indicator of deep-seated subsurface faulting. These structures, herein called disturbed zones, are formed by movement between closely spaced pairs of thrust faults. Disturbed zones are characterized at the surface by long, narrow, intensely folded and faulted zones of rocks in a relatively undisturbed stratigraphic sequence. These zones are frequently kilometers to tens of kilometers long and tens to hundreds of meters wide. Although disturbed zones generally occur in sequences of alternating siltstone and shale beds, they can also occur in other lithologies including massively-bedded sandstones and carbonates. Disturbed zones are not only easily recognized in outcrop but their presence can also be inferred on geologic maps by disharmonic fold patterns, which necessitates a detachment between adjacent units that show the disharmony. A number of geologic problems can be clarified by understanding the principles of the sequence of formation and the method of location of disturbed zones, including the interpretation of some published geologic cross sections and maps. The intense folding and faulting which accompanies the formation of a typical disturbed zone produces a region of fracture porosity which, if sealed off from the surface, might well serve as a commercially-exploitable hydrocarbon trap. We believe that the careful mapping of concentrations of disturbed zones can serve as an important exploration method which is much less expensive than speculation seismic lines.

  8. Subsurface structure along the eastern marginal fault zone of Yokote Basin by Seismic reflection profiling studies, Northeast Japan

    NASA Astrophysics Data System (ADS)

    Kagohara, K.; Imaizumi, T.; Echigo, T.; Miyauchi, T.; Sato, H.

    2005-12-01

    Typical reverse faults, which are known as Senya earthquake faults appeared along the western foot of the Mahiru Mountains, associated with The Rikuu Earthquake (Mj7.2) of 1896 in Northeast Japan. Eastern marginal fault zone of the Yokote Basin consist of four main surface ruptures, about 35 km long, Obonai fault, Shiraiwa fault, Ota fault and Senya fault, depending on their continuity and strike (Matsuda et al., 1980). We carried out the seismic reflection profiling across these faults (Kawaguchi03 Seismic line, Unjono04 Seismic line and Kotaki05 Seismic line) to clarify the subsurface structure of these reverse fault system based on the data of tectonic geomorphology and structural geology and furthermore, to discuss the timing of migration of the thrusting from the range front to the basin margin. The seismic source was mini-vibrator trucks, with 20seconds of 10-100Hz signals at 10m or 5m intervals. The sweep signals were recorded by a digital telemetry system (GDAPS-4a) with 10 Hz geophones. The obtained seismic reflection data were processed by conventional Common mid-point (CMP) methods, including post-stack migration and depth conversion. The resulting seismic reflection profile reveals a thrust structure beneath these areas. At the Center of Senya hills there are two thrusts and one high angle reverse fault (1997 Seismic Line). Senya fault is an active frontal emergent thrust with flat and ramp structure. Although, the high angle reverse fault, located along the foot of the range is a short-cut branching fault from the Senya fault in the central part of the Senya hill (Sato et al., 1998), in the Unjono04 seismic line, the depth of the flat and ramp structure gradually shallow in the north part of the Senya hill, where the flexure scarp accompanied with antithetic faults formed on the fluvial terraces. In the Kawaguchi03 seismic line, the concealed fault, 0.5km below the surface, branched from the master Ota fault, form a flexure scarplet on the alluvial fan

  9. Imaging the internal structure of the San Jacinto Fault Zone with high Frequency noise

    NASA Astrophysics Data System (ADS)

    Zigone, D.; Ben-Zion, Y.; Campillo, M.; Hillers, G.; Roux, P.; Vernon, F.

    2014-12-01

    Regional tomography studies in the SJFZ area gives detailed images up to the top 500 meters or so of the crust (Zigone et al., 2014; Allam et al., 2014). To obtain additional high resolution information on local structures at the shallower crust, we use cross correlation of ambient seismic noise between 10 Hz and 70 Hz recorded by several linear arrays that cross the SJFZ with typical inter-station distances around 40 m. Pre-processing techniques involving earthquakes removal and whitening on 15 minutes time windows are used to obtained the 9-component correlation tensors associated with all station pairs. The obtained cross correlations exhibit coherent waves up to 30-40 Hz that travel between the station pairs. Polarization and dispersion analysis show that both body and surface waves are reconstructed with Rayleigh group velocity around 400-500 m/s. The results likely include also body waves and trapped fault zone signals. After rejecting paths without sufficient signal to noise ratios, we invert the Rayleigh group velocity measurements using the Barmin et al. (2001) approach on a 20m grid size. The obtained group velocity maps reveal complex structures with very low velocity damage zones around the surface traces of the SJFZ. The group velocities are inverted to 3D images of shear wave speeds using the linear inversion method of Hermann & Ammon (2002). The results show local flower-type damage structures in the top 200m, with Vs values at 30m depths around 250-300 m/s in agreement with the available Vs30 values in the literature. This high-resolution study will be complemented with a more detailed analysis using a dense rectangular array with 1108 vertical-component seismometers separated by 10-30 m centered on the fault. This geometry allows the use of very high frequency seismic noise up to 200 Hz that can be used to image the small-scale features (~10-20 m) in the top few hundred m of the crust. Updated results will be presented in the meeting.

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

    USGS Publications Warehouse

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

    2003-01-01

    We analyse quantitatively a waveform data set of 238 earthquakes recorded by a dense seismic array across and along the rupture zone of the 1992 Landers earthquake. A grid-search method with station delay corrections is used to locate events that do not have catalogue locations. The quality of fault zone trapped waves generated by each event is determined from the ratios of seismic energy in time windows corresponding to trapped waves and direct S waves at stations close to and off the fault zone. Approximately 70 per cent of the events with S-P times of less than 2 s, including many clearly off the fault, produce considerable trapped wave energy. This distribution is in marked contrast with previous claims that trapped waves are generated only by sources close to or inside the Landers rupture zone. The time difference between the S arrival and trapped waves group does not grow systematically with increasing hypocentral distance and depth. The dispersion measured from the trapped waves is weak. These results imply that the seismic trapping structure at the Landers rupture zone is shallow and does not extend continuously along-strike by more than a few kilometres. Synthetic waveform modelling indicates that the fault zone waveguide has depth of approximately 2-4 km, a width of approximately 200 m, an S-wave velocity reduction relative to the host rock of approximately 30-40 per cent and an S-wave attenuation coefficient of approximately 20-30. The fault zone waveguide north of the array appears to be shallower and weaker than that south of the array. The waveform modelling also indicates that the seismic trapping structure below the array is centred approximately 100 m east of the surface break.

  11. Architecture of small-scale fault zones in the context of the Leinetalgraben Fault System

    NASA Astrophysics Data System (ADS)

    Reyer, Dorothea; Philipp, Sonja L.

    2010-05-01

    Understanding fault zone properties in different geological settings is important to better assess the development and propagation of faults. In addition this allows better evaluation and permeability estimates of potential fault-related geothermal reservoirs. The Leinetalgraben fault system provides an outcrop analogue for many fault zones in the subsurface of the North German Basin. The Leinetalgraben is a N-S-trending graben structure, initiated in the Jurassic, in the south of Lower Saxony and as such part of the North German Basin. The fault system was reactivated and inverted during Alpine compression in the Tertiary. This complex geological situation was further affected by halotectonics. Therefore we can find different types of fault zones, that is normal, reverse, strike-slip an oblique-slip faults, surrounding the major Leinetalgraben boundary faults. Here we present first results of structural geological field studies on the geometry and architecture of fault zones in the Leinetalgraben Fault System in outcrop-scale. We measured the orientations and displacements of 17 m-scale fault zones in limestone (Muschelkalk) outcrops, the thicknesses of their fault cores and damage zones, as well as the fracture densities and geometric parameters of the fracture systems therein. We also analysed the effects of rock heterogeneities, particularly stiffness variations between layers (mechanical layering) on the propagation of natural fractures and fault zones. The analysed fault zones predominantly show similar orientations as the major fault zones they surround. Other faults are conjugate or perpendicular to the major fault zones. The direction of predominant joint strike corresponds to the orientation of the fault zones in the majority of cases. The mechanical layering of the limestone and marlstone stratification obviously has great effects on fracture propagation. Already thin layers (mm- to cm-scale) of low stiffness - here marl - seem to suffice to change the

  12. Complex fragmentation and silicification structures in fault zones: quartz mineralization and repeated fragmentation along the Fountain Range Fault (Mt. Isa Inlier, Australia)

    NASA Astrophysics Data System (ADS)

    Seybold, Lina; Blenkinsop, Tom; Heuss, Soraya; Ord, Alison; Kruhl, Jörn H.

    2015-04-01

    In large-scale fault zones fracture networks are commonly generated by high volumes of pressurized fluids, followed by quartz precipitation. In this way large amounts of quartz are formed as microcrystalline masses and as complex vein systems, with partly highly different textures, as a result of different formation processes. Based on field and microstructural data and the quantification of vein patterns, the spatial and temporal connection between fragmentation, quartz crystallization and fluid and material flow along the Fountain Range Fault at Fountain Springs was investigated. Dextral strike-slip led to up to 25 km horizontal displacement along the fault. Due to various fragmentation and quartz formation processes, a ca. 100 m high, 80 - 100 m wide and km-long quartz ridge with numerous vein systems and variable microfabrics was formed. Locally, lenses of highly altered metamorphic wall-rocks occur in the quartz zone. Where exposed, the contact to wall rocks is sharp. Millimetre- to decimetre-thick quartz veins penetrate the wall-rocks only within metre distance from the contact. Several clearly distinguishable fine-grained reddish, brownish to dark and pigment-rich quartz masses form up to 50 m wide and up to several 100 m long steep lenses that build the major part of the silicified fault zone. A chronology can be established. Some of these lenses are oriented slightly oblique to the general trend of the quartz zone, in agreement with the supposed dextral strike slip along the fault. Numerous generations of typically µm-cm thick quartz veins transect the microcrystalline quartz masses and, locally, form anisotropic networks. In the quartz masses, angular fragments often composed of quartz with, again, internal fragmentation structures, indicate earlier fracturing and silicification events. Within the veins, quartz forms geodes, locally filled with fine-grained reddish quartz and palisade structures with feathery textures and fluid-inclusion zoning

  13. Structure of the Melajo clay near Arima, Trinidad and strike-slip motion in the El Pilar fault zone

    NASA Technical Reports Server (NTRS)

    Robertson, P.; Burke, K.; Wadge, G.

    1985-01-01

    No consensus has yet emerged on the sense, timing and amount of motion in the El Pilar fault zone. As a contribution to the study of this problem, a critical area within the zone in North Central Trinidad has been mapped. On the basis of the mapping, it is concluded that the El Pilar zone has been active in right-lateral strike-slip motion during the Pleistocene. Recognition of structural styles akin to those of the mapped area leads to the suggestion that the El Pilar zone is part of a 300 km wide plate boundary zone extending from the Orinoco delta northward to Grenada. Lateral motion of the Caribbean plate with respect to South America has been suggested to amount to 1900 km in the last 38 Ma. Part of this displacement since the Miocene can be readily accommodated within the broad zone identified here. No one fault system need account for more than a fraction of the total motion and all faults need not be active simultaneously.

  14. 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

  15. Preliminary Results on Seismicity and Fault Zone Structure Along the 1944 Rupture of the North Anatolian Fault East of Ismetpasa

    NASA Astrophysics Data System (ADS)

    Ozakin, Y.; Ben-Zion, Y.; Aktar, M.; Karabulut, H.; Peng, Z.

    2010-12-01

    The North Anatolian Fault (NAF), a continental plate boundary similar in some respects to the San Andreas Fault (SAF), is of great importance to Turkey in terms of seismic hazard. The geological history, lithology & topography suggest that the NAF is generally a bimaterial interface separating different rock bodies. Theoretical and observational studies suggest that there may be fundamental differences between properties of earthquakes and seismic radiation generated by ruptures along interfaces that separate similar and dissimilar solids (e.g., Weertman 1980; Ben-Zion 2001; Dor et al. 2008; Ampuero & Ben-Zion 2008; Zaliapin & Ben-Zion 2010). High-resolution imaging of the internal fault structure in various locations can be used to test hypotheses associated with bimaterial ruptures, and estimate expected shaking hazard based on the results. It is also important to clarify the geometry and seismic potential of various sections through high-resolution studies of seismicity. To begin such studies, we conducted a pilot seismic experiment east of Ismetpasa on the 1944 rupture of the NAF with a line of 6-11 seismometers that cross the fault. The location was chosen because it is within the area where Dor et al. (2008) found strong asymmetry of rock damage that may reflect repeating ruptures on a bimaterial fault interface. The location also coincides with a section of the NAF that is partially creeping at least at shallow depth. The creep rate decayed from a maximum of 4-5 cm/yr following the 1994 earthquake to a present value of to 0.7 cm/yr (Cakir et al. 2005). The small local network has been operating for ~2.5 yr. Earthquake detection was done by a manual inspection of automatic identification of candidate events. To date we were able to detect only ~235 events in the magnitude range -1 to 2.5 within a radius of 45 km from the center of the network. Using template earthquakes for detecting more events was not successful so far, as the signals produced by the

  16. A re-evaluation of the Eskişehir Fault Zone as a recent extensional structure in NW Turkey

    NASA Astrophysics Data System (ADS)

    Ocakoğlu, Faruk

    2007-10-01

    The Eskişehir Fault Zone (EFZ), one of the major active structures within the Anatolian platelet, is investigated in a 100 km long sector between Bozüyük and Alpu, in vicinity of Eskişehir. The morphotectonic observations indicate that throughout the studied area the EFZ extends WNWwards as a ca. 15 km wide belt, and is composed of some 21 fault segments, 5-25 km long. These segments form a north-dipping southern set and two south-dipping northern sets, all together working both sides of the Eskişehir graben. The faults are dominantly normal in character with a slight right-lateral component in the westernmost areas. The estimated total vertical displacement on certain northern and southern fault segments exceeds 450 m. In order to estimate the initiation age of the EFZ a brief stratigraphic review is given. The generally horizontal Pliocene terrestrial deposits are separated from the Miocene succession by a low-angular unconformity, and are cut in turn by the EFZ. Sedimentological data show that neither the distribution of the Pliocene depositional environments and their paleocurrent directions, nor the preserved Pliocene basal unconformity surface have a genetic relation to the EFZ. These data strongly suggest that the EFZ is a younger post-Pliocene active normal fault zone with low rates of deformation.

  17. Deformation of Sedimentary Rock Across the San Andreas Fault Zone: Mesoscale and Microscale Structures Displayed in Core From SAFOD

    NASA Astrophysics Data System (ADS)

    Chester, J. S.; Chester, F. M.; Kirschner, D. L.; Almeida, R.; Evans, J. P.; Guillemette, R. N.; Hickman, S.; Zoback, M.; Ellsworth, W.

    2007-12-01

    Sedimentary rocks captured in cores taken at the San Andreas Fault Observatory at Depth (SAFOD) provide an unparalleled sampling of deformation in the transition zone between creeping and locked segments of a major transform fault at 2.5-3.1 km vertical depth. These samples provide the unique opportunity to study deformation processes and the development of brittle structures within porous and granular rocks that have been subjected to variable loading rates and chemically reactive fluids while residing at the top of the seismogenic zone. The samples provide a transect from relatively undeformed host rock through highly fractured and sheared rock, and capture the two prominent zones of active, aseismic slip. Core recovery was almost complete. Wrap-around 1:1 map tracings of the outer surfaces of all cores characterize the lithology and mesoscale deformation. Cores from 3056-3067 m and 3141-3153 m measured depth (MD) sample moderately deformed rock at the western boundary of the fault zone. The cores display massive to finely laminated, pebbly arkosic sandstones with lesser amounts of fine-grained sandstone and siltstone. Numerous shear fractures and cm-thick cataclastic shear zones form a conjugate geometry indicating contraction at high angles to the San Andreas fault. Both intervals display minor faults that juxtapose different lithologies consistent with meters or greater of slip. Fracture density is variable but tends to increase with proximity to the minor faults. Cross-cutting relationships between shear fractures and cataclastic zones indicate a general progression from early faulting along thicker shear zones to later, more localized slip within shear zones and along fractures. Microstructures provide ample evidence for densification of the sandstones through grain-scale fracture and crushing, as well as fluid assisted processes of crack-sealing, dissolution-precipitation, and alteration-neocrystallization. Grain-scale features are consistent with these

  18. 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.

  19. 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.

  20. Petrophysical Properties of Sandstones Containing Deformation Bands Versus Those With Fractures: the Importance of Grain Contact Strength to Fault-Zone Structure

    NASA Astrophysics Data System (ADS)

    Schneider, J. R.; Tobin, H. J.; Goodwin, L. B.

    2010-12-01

    In upper crustal fault zones, the majority of slip accumulates within a fault core, which is surrounded by a less deformed damage zone. Both the width and structural character of the damage zone affect its mechanical and hydrologic properties. Fault-related deformation can change rock mechanical properties, causing stress orientations to rotate in fault damage zones, and affecting seismicity over time. In addition, the types, densities, and orientations of structures in fault zones exert a first-order control on fault-zone permeability structure, permeability anisotropy, and flow pathways. For example, open-fracture damage zones enhance fault-parallel flow, whereas cataclastic deformation band networks slow flow in every direction except parallel to the line of intersection between bands. To improve our understanding of controls on damage zone character, we explored relationships between fault-zone structure and lithologic characteristics such as porosity and cement mineralogy in faulted quartz-rich sandstones. The sandstones chosen from fault sites in the Jurassic Navajo and Entrada sandstones in Utah, and the Cretaceous Mesaverde sandstone in Wyoming, exhibit a wide range in porosity. Samples collected include even greater variability in cements, from clay coatings on grains to patchy carbonate cement to grain-bridging quartz overgrowths and iron oxide cements. These variables demonstrably influence damage zone character, resulting in fractures in some locations and deformation bands in others (even within a single fault zone) and affecting deformation-band damage zone width. They likely influenced grain-contact strength also. Because ultrasonic velocity and related elastic moduli also vary with grain-contact strength, we measured P and S wave velocities as a function of confining pressure to 20 MPa as a sensitive proxy for grain-contact strength. More than 40 samples, including both host rock and rock with deformation bands, have been analyzed. Samples

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

    USGS Publications Warehouse

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

    2009-01-01

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

  2. Decimeter-resolution fault zone topography mapped with Structure-From-Motion

    NASA Astrophysics Data System (ADS)

    Nissen, E.; Saripalli, S.; Arrowsmith, R.

    2012-12-01

    We describe an affordable and accessible new system for generating decimeter resolution, textured topographic maps along active faults using a digital camera mounted on the underside of an autonomous helicopter. Point elevations of target pixels are determined using Structure-From-Motion (SFM), whereby movement between sequential photographs creates enough parallax to infer 3D structure. We showcase DEMs generated at sites on the southern San Andreas Fault and the 1992 Landers earthquake rupture, and compare these to airborne and terrestrial LiDAR DEMs from the same locations. The spacing of ground returns is finer than is typical for airborne laser scanning, allowing us to image offsets generated in previous ground-rupturing earthquakes that are too small or too subtle to be detected with LiDAR. However, observed footprints are much narrower than airborne LiDAR swaths, so the system is suited to the rapid collection of imagery for known targets rather than to reconnaissance missions of unmapped areas.

  3. Variable deep structure of a midcontinent fault and fold zone from seismic reflection: La Salle deformation belt, Illinois basin

    USGS Publications Warehouse

    McBride, J.H.

    1997-01-01

    Deformation within the United States mid-continent is frequently expressed as quasilinear zones of faulting and folding, such as the La Salle deformation belt, a northwest-trending series of folds cutting through the center of the Illinois basin. Seismic reflection profiles over the southern La Salle deformation belt reveal the three-dimensional structural style of deformation in the lower Paleozoic section and uppermost Precambrian(?) basement. Individual profiles and structural contour maps show for the first time that the folds of the La Salle deformation belt are underlain at depth by reverse faults that disrupt and offset intrabasement structure, offset the top of interpreted Precambrian basement, and accommodate folding of overlying Paleozoic strata. The folds do not represent development of initial dips by strata deposited over a preexisting basement high. Rather, the structures resemble subdued "Laramide-style" forced folds, in that Paleozoic stratal reflectors appear to be flexed over a fault-bounded basement uplift with the basement-cover contact folded concordantly with overlying strata. For about 40 km along strike, the dominant faults reverse their dip direction, alternating between east and west. Less well expressed antithetic or back thrusts appear to be associated with the dominant faults and could together describe a positive flower structure. The overall trend of this part of the La Salle deformation belt is disrupted by along-strike discontinuities that separate distinct fold culminations. Observations of dual vergence and along-strike discontinuities suggest an original deformation regime possibly involving limited transpression associated with distant late Paleozoic Appalachian-Ouachita mountain building. Moderate-magnitude earthquakes located west of the western flank of the La Salle deformation belt have reverse and strike-slip mechanisms at upper trustai depths, which might be reactivating deep basement faults such as observed in this study

  4. Complex permeability structure of a fault zone crosscutting a sequence of sandstones and shales and its influence on hydraulic head distribution

    NASA Astrophysics Data System (ADS)

    Cilona, A.; Aydin, A.; Hazelton, G.

    2013-12-01

    Characterization of the structural architecture of a 5 km-long, N40°E-striking fault zone provides new insights for the interpretation of hydraulic heads measured across and along the fault. Of interest is the contaminant transport across a portion of the Upper Cretaceous Chatsworth Formation, a 1400 m-thick turbidite sequence of sandstones and shales exposed in the Simi Hills, south California. Local bedding consistently dips about 20° to 30° to NW. Participating hydrogeologists monitor the local groundwater system by means of numerous boreholes used to define the 3D distribution of the groundwater table around the fault. Sixty hydraulic head measurements consistently show differences of 10s of meters, except for a small area. In this presentation, we propose a link between this distribution and the fault zone architecture. Despite an apparent linear morphological trend, the fault is made up of at least three distinct segments named here as northern, central and southern segments. Key aspects of the fault zone architecture have been delineated at two sites. The first is an outcrop of the central segment and the second is a borehole intersecting the northern segment at depth. The first site shows the fault zone juxtaposing sandstones against shales. Here the fault zone consists of a 13 meter-wide fault rock including a highly deformed sliver of sandstone on the northwestern side. In the sandstone, shear offset was resolved along N42°E striking and SE dipping fracture surfaces localized within a 40 cm thick strand. Here the central core of the fault zone is 8 m-wide and contains mostly shale characterized by highly diffuse deformation. It shows a complex texture overprinted by N30°E-striking carbonate veins. At the southeastern edge of the fault zone exposure, a shale unit dipping 50° NW towards the fault zone provides the key information that the shale unit was incorporated into the fault zone in a manner consistent with shale smearing. At the second site, a

  5. Fault-related structural permeability: Qualitative insights of the damage-zone from micro-CT analysis.

    NASA Astrophysics Data System (ADS)

    Gomila, Rodrigo; Arancibia, Gloria; Nehler, Mathias; Bracke, Rolf; Stöckhert, Ferdinand

    2016-04-01

    Fault zones and their related structural permeability play a leading role in the migration of fluids through the continental crust. A first approximation to understanding the structural permeability conditions, and the estimation of its hydraulic properties (i.e. palaeopermeability and fracture porosity conditions) of the fault-related fracture mesh is the 2D analysis of its veinlets, usually made in thin-section. Those estimations are based in the geometrical parameters of the veinlets, such as average fracture density, length and aperture, which can be statistically modelled assuming penny-shaped fractures of constant radius and aperture within an anisotropic fracture system. Thus, this model is related to fracture connectivity, its length and to the cube of the fracture apertures. In this way, the estimated values presents their own inaccuracies owing to the method used. Therefore, the study of the real spatial distribution of the veinlets of the fault-related fracture mesh (3D), feasible with the use of micro-CT analyses, is a first order factor to unravel both, the real structural permeability conditions of a fault-zone, together with the validation of previous estimations made in 2D analyses in thin-sections. This early contribution shows the preliminary results of a fault-related fracture mesh and its 3D spatial distribution in the damage zone of the Jorgillo Fault (JF), an ancient subvertical left-lateral strike-slip fault exposed in the Atacama Fault System in northern Chile. The JF is a ca. 20 km long NNW-striking strike-slip fault with sinistral displacement of ca. 4 km. The methodology consisted of the drilling of vertically oriented plugs of 5 mm in diameter located at different distances from the JF core - damage zone boundary. Each specimen was, then, scanned with an x-ray micro-CT scanner (ProCon X-Ray CTalpha) in order to assess the fracture mesh. X-rays were generated in a transmission target x-ray tube with acceleration voltages ranging from 90

  6. Transfer zones in listric normal fault systems

    NASA Astrophysics Data System (ADS)

    Bose, Shamik

    Listric normal faults are common in passive margin settings where sedimentary units are detached above weaker lithological units, such as evaporites or are driven by basal structural and stratigraphic discontinuities. The geometries and styles of faulting vary with the types of detachment and form landward and basinward dipping fault systems. Complex transfer zones therefore develop along the terminations of adjacent faults where deformation is accommodated by secondary faults, often below seismic resolution. The rollover geometry and secondary faults within the hanging wall of the major faults also vary with the styles of faulting and contribute to the complexity of the transfer zones. This study tries to understand the controlling factors for the formation of the different styles of listric normal faults and the different transfer zones formed within them, by using analog clay experimental models. Detailed analyses with respect to fault orientation, density and connectivity have been performed on the experiments in order to gather insights on the structural controls and the resulting geometries. A new high resolution 3D laser scanning technology has been introduced to scan the surfaces of the clay experiments for accurate measurements and 3D visualizations. Numerous examples from the Gulf of Mexico have been included to demonstrate and geometrically compare the observations in experiments and real structures. A salt cored convergent transfer zone from the South Timbalier Block 54, offshore Louisiana has been analyzed in detail to understand the evolutionary history of the region, which helps in deciphering the kinematic growth of similar structures in the Gulf of Mexico. The dissertation is divided into three chapters, written in a journal article format, that deal with three different aspects in understanding the listric normal fault systems and the transfer zones so formed. The first chapter involves clay experimental models to understand the fault patterns in

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  8. Fault zones in Triassic Muschelkalk limestones of the Upper Rhine Graben: Infrastructure characterization and permeability structure analyses

    NASA Astrophysics Data System (ADS)

    Meier, Silke; Bauer, Johanna F.; Philipp, Sonja L.

    2014-05-01

    The characterization of fault zones is of particular importance in geothermal reservoirs since there may be great effects on fluid flow. Fault zones generally consist of two major hydromechanical units: the fault core and the damage zone, surrounded by the unaffected host rock. To improve predictions of fracture system parameters for each unit and resulting estimations of reservoir permeabilities at depths, we perform outcrop analogue studies. We analyze Middle Triassic Muschelkalk limestones that form one potential geothermal reservoir formation in the Upper Rhine Graben (URG), in quarries on its eastern graben shoulder. We measure the orientations and displacements of various fault zones and characterize the fracture systems within the fault zone units and the host rock. Important features in terms of reservoir permeability are the fracture aperture, the fracture connectivity and the fracture vertical extension. Fractures have to be connected to create a hydraulically relevant flow path and non-stratabound fractures could create a hydraulic connectivity between multiple layers. We observed a decreasing fracture length with increasing distance to the fault core but a better connectivity between shorter fractures in the well-developed damage zones. Our studies show, however, that the differing mechanical properties in the analyzed limestone-marl alternations are significant for the fracture propagation, even in the fault zones. Based on the field data we use analytical models to estimate the permeabilities of the analyzed fracture systems. Results show increased fracture frequencies in the fault zone damage zones and larger fracture apertures parallel or subparallel to fault zone strike and to the URG that lead to enhanced permeabilities compared with other fracture orientations. Mineralized fractures accumulated in directions parallel or subparallel to fault zone strike as well as observed mineralizations in some fault cores indicate a fluid flow along the fault

  9. Role of structural inheritances and major transfer fault-zones in the tectonic history of the Alboran Basin (Western Mediterranean)

    NASA Astrophysics Data System (ADS)

    Comas, Menchu; Crespo-Blanc, Ana; Balanya, Juan Carlos

    2014-05-01

    reorganization (N-S shortening) of the basin, which encompass wrench tectonics, margin rotations, sub-basin inversions, bending of former extensional structures, and further shale-tectonics. The recent NW-SE and NE-SW trending conjugate wrench-fault system that bound the actual structural domains observed offshore locates over major transfer-faults zones from the Miocene extension. The rotated segments of basin-margins and concomitant structural bending, as well as changes in the tectonic regimen of the transfer-fault systems are expressive of the aftermath of superimposed extensional and compressional processes in the Alboran Basin. The spatial and temporary evolution of the tectonic deformation documented by geological and geophysical observables in the Alboran Sea basin provides new insights into the critical role of the tectonic heritage and major transfer fault-zones in the geodynamic history of the GAS. Acknowledgements: This study was supported by projects RNM-3713, RNM-215, CTM2009-07715 and CGL2009-11384 (MINECO, JA, and FEDER founds, Spain).

  10. Palaeopermeability structure within fault-damage zones: A snap-shot from microfracture analyses in a strike-slip system

    NASA Astrophysics Data System (ADS)

    Gomila, Rodrigo; Arancibia, Gloria; Mitchell, Thomas M.; Cembrano, Jose M.; Faulkner, Daniel R.

    2016-02-01

    Understanding fault zone permeability and its spatial distribution allows the assessment of fluid-migration leading to precipitation of hydrothermal minerals. This work is aimed at unraveling the conditions and distribution of fluid transport properties in fault zones based on hydrothermally filled microfractures, which reflect the ''frozen-in'' instantaneous advective hydrothermal activity and record palaeopermeability conditions of the fault-fracture system. We studied the Jorgillo Fault, an exposed 20 km long, left-lateral strike-slip fault, which juxtaposes Jurassic gabbro against metadiorite belonging to the Atacama Fault System in northern Chile. Tracings of microfracture networks of 19 oriented thin sections from a 400 m long transect across the main fault trace was carried out to estimate the hydraulic properties of the low-strain fault damagezone, adjacent to the high-strain fault core, by assuming penny-shaped microfractures of constant radius and aperture within an anisotropic fracture system. Palaeopermeability values of 9.1*10-11 to 3.2*10-13 m2 in the gabbro and of 5.0*10-10 to 1.2*10-13 m2 in the metadiorite were determined, both decreasing perpendicularly away from the fault core. Fracture porosity values range from 40.00% to 0.28%. The Jorgillo Fault has acted as a left-lateral dilational fault-bend, generating large-scale dilation sites north of the JF during co-seismic activity.

  11. Geophysical and isotopic mapping of preexisting crustal structures that influenced the location and development of the San Jacinto fault zone, southern California

    USGS Publications Warehouse

    Langenheim, V.E.; Jachens, R.C.; Morton, D.M.; Kistler, R.W.; Matti, J.C.

    2004-01-01

    We examine the role of preexisting crustal structure within the Peninsular Ranges batholith on determining the location of the San Jacinto fault zone by analysis of geophysical anomalies and initial strontium ratio data. A 1000-km-long boundary within the Peninsular Ranges batholith, separating relatively mafic, dense, and magnetic rocks of the western Peninsular Ranges batholith from the more felsic, less dense, and weakly magnetic rocks of the eastern Peninsular Ranges batholith, strikes north-northwest toward the San Jacinto fault zone. Modeling of the gravity and magnetic field anomalies caused by this boundary indicates that it extends to depths of at least 20 km. The anomalies do not cross the San Jacinto fault zone, but instead trend northwesterly and coincide with the fault zone. A 75-km-long gradient in initial strontium ratios (Sri) in the eastern Peninsular Ranges batholith coincides with the San Jacinto fault zone. Here rocks east of the fault are characterized by Sri greater than 0.706, indicating a source of largely continental crust, sedimentary materials, or different lithosphere. We argue that the physical property contrast produced by the Peninsular Ranges batholith boundary provided a mechanically favorable path for the San Jacinto fault zone, bypassing the San Gorgonio structural knot as slip was transferred from the San Andreas fault 1.0-1.5 Ma. Two historical M6.7 earthquakes may have nucleated along the Peninsular Ranges batholith discontinuity in San Jacinto Valley, suggesting that Peninsular Ranges batholith crustal structure may continue to affect how strain is accommodated along the San Jacinto fault zone. ?? 2004 Geological Society of America.

  12. Delineation of fault zones using imaging radar

    NASA Technical Reports Server (NTRS)

    Toksoz, M. N.; Gulen, L.; Prange, M.; Matarese, J.; Pettengill, G. H.; Ford, P. G.

    1986-01-01

    The assessment of earthquake hazards and mineral and oil potential of a given region requires a detailed knowledge of geological structure, including the configuration of faults. Delineation of faults is traditionally based on three types of data: (1) seismicity data, which shows the location and magnitude of earthquake activity; (2) field mapping, which in remote areas is typically incomplete and of insufficient accuracy; and (3) remote sensing, including LANDSAT images and high altitude photography. Recently, high resolution radar images of tectonically active regions have been obtained by SEASAT and Shuttle Imaging Radar (SIR-A and SIR-B) systems. These radar images are sensitive to terrain slope variations and emphasize the topographic signatures of fault zones. Techniques were developed for using the radar data in conjunction with the traditional types of data to delineate major faults in well-known test sites, and to extend interpretation techniques to remote areas.

  13. Reactivation mechanisms of heterogeneous, complex fault zones

    NASA Astrophysics Data System (ADS)

    Heesakkers, Vincent

    Fault reactivation occurs on a short-term cycle of tens to thousands of years between infrequent earthquakes, and on long-term cycles of fault inactivity for 106 -- 107 years. During long-term cycles, faults may heal and renew their strength. The objective of the present work is to study the mechanisms of fault reactivation after a long dormant period, when the pre-existing fault is not necessarily "weak". The study is conducted along the Pretorius fault, TauTona mine, South Africa. The deep gold mines in South Africa provide access to earthquake processes at focal depth, which was motivation for the NELSAM (Natural Earthquake Laboratory in South African Mines) project to develop an underground earthquake laboratory at ˜3.5 km depth within TauTona mine (Ch. 1). The present study is conducted within the NELSAM site that includes the 2.7 Ga Pretorius fault, which has been inactive for at least 2.0 Ga and is currently being reactivated due to nearby mining activity. I characterize the fault zone by 3D underground mapping within mining tunnels at 3.6 km depth (Ch. 2). The structural analysis is accompanied by fracture analysis from borehole image logs and micro-structural studies. I find that the Pretorius fault is structurally complex, with a 20-30 m wide zone of anastomosing, dominantly steep fault segments that contain a strong cohesive sintered cataclasite. Despite the size of the Pretorius fault, a few km long with ˜200m horizontal and 30-60 m vertical displacement, its complexity reflects the fault zone immaturity. The exposed rupture zone of the M2.2 of December 12, 2004, was mapped in detail at focal depth (Ch. 3). It reactivated three to four quasi-planar, non-parallel segments of the Pretorius fault, with characteristic generation of fresh fine grained rock powder along the contact of the quartzitic host rock and the cataclasite, indicating localization of slip during the event. To investigate the mechanism responsible for such localization, rock mechanics

  14. Modelling Fault Zone Evolution: Implications for fluid flow.

    NASA Astrophysics Data System (ADS)

    Moir, H.; Lunn, R. J.; Shipton, Z. K.

    2009-04-01

    Flow simulation models are of major interest to many industries including hydrocarbon, nuclear waste, sequestering of carbon dioxide and mining. One of the major uncertainties in these models is in predicting the permeability of faults, principally in the detailed structure of the fault zone. Studying the detailed structure of a fault zone is difficult because of the inaccessible nature of sub-surface faults and also because of their highly complex nature; fault zones show a high degree of spatial and temporal heterogeneity i.e. the properties of the fault change as you move along the fault, they also change with time. It is well understood that faults influence fluid flow characteristics. They may act as a conduit or a barrier or even as both by blocking flow across the fault while promoting flow along it. Controls on fault hydraulic properties include cementation, stress field orientation, fault zone components and fault zone geometry. Within brittle rocks, such as granite, fracture networks are limited but provide the dominant pathway for flow within this rock type. Research at the EU's Soultz-sous-Forệt Hot Dry Rock test site [Evans et al., 2005] showed that 95% of flow into the borehole was associated with a single fault zone at 3490m depth, and that 10 open fractures account for the majority of flow within the zone. These data underline the critical role of faults in deep flow systems and the importance of achieving a predictive understanding of fault hydraulic properties. To improve estimates of fault zone permeability, it is important to understand the underlying hydro-mechanical processes of fault zone formation. In this research, we explore the spatial and temporal evolution of fault zones in brittle rock through development and application of a 2D hydro-mechanical finite element model, MOPEDZ. The authors have previously presented numerical simulations of the development of fault linkage structures from two or three pre-existing joints, the results of

  15. Metamorphic and structural evidence for significant vertical displacement along the Ross Lake fault zone, a major orogen-parallel shear zone in the Cordillera of western North America

    USGS Publications Warehouse

    Baldwin, J.A.; Whitney, D.L.; Hurlow, H.A.

    1997-01-01

    Results of an investigation of the petrology and structure of the Skymo complex and adjacent terranes constrain the amount, timing, and sense of motion on a segment of the > 600-km-long Late Cretaceous - early Tertiary Ross Lake fault zone (RLFZ), a major orogen-parallel shear zone in the Cordillera of western North America. In the study area in the North Cascades, Washington state, the RLFZ accommodated significant pre-middle Eocene vertical displacement, and it juxtaposes the Skymo complex with upper amphibolite facies (650??-690??C and 6-7 kbar) Skagit Gneiss of the North Cascades crystalline core to the SW and andalusite-bearing phyllite of the Little Jack terrane (Intermontane superterrane) to the NE. The two main lithologic units of the Skymo complex, a primitive mafic intrusion and a fault-bounded block of granulite facies metasedimentary rocks, are unique in the North Cascades. Granulite facies conditions were attained during high-temperature (> 800??C), low pressure (??? 4 kbar) contact metamorphism associated with intrusion of the mafic magma. P-T estimates and reaction textures in garnet-orthopyroxene gneiss suggest that contact metamorphism followed earlier, higher pressure regional metamorphism. There is no evidence that the Skagit Gneiss experienced high-T - low-P contact metamorphism. In the Little Jack terrane, however, texturally late cordierite ?? spinel and partial replacement of andalusite by sillimanite near the terrane's fault contact with Skymo gabbro suggest that the Little Jack terrane experienced high-T (??? 600??C) - low-P (??? 4 kbar) contact metamorphism following earlier low-grade regional metamorphism. Similarities in the protoliths of metasedimentary rocks in the Skymo and Little Jack indicate that they may be part of the same terrane. Differences in pressure estimates for the Little Jack versus Skymo for regional metamorphism that preceded contact metamorphism indicate vertical displacement of ??? 10 km (west side up) on the strand

  16. Mesozoic reactivated transpressional structures and multi-stage tectonic deformation along the Hong-Che fault zone in the northwestern Junggar Basin, NW China

    NASA Astrophysics Data System (ADS)

    Yu, Yangli; Wang, Xin; Rao, Gang; Wang, Renfu

    2016-06-01

    The recognition of paleo-strike-slip faulting is often difficult, particularly when the associated structures are presently inactive and covered by thick sediments. Fortunately, high-resolution 3D seismic reflection data can provide a powerful tool to solve this problem. In this study, we focus on the structural features and tectonic evolution of Hong-Che fault system, a paleo-strike-slip fault zone recognized in the NW margin of Junggar Basin by using the 2D and 3D seismic data. The results of our analysis demonstrate that: 1) The Middle Triassic to Jurassic dextral transpressional structures were developed along Hong-Che fault zone, which are characterized by the restraining bend on the southern segment, the highly localized shearing deformation on the central segment, and the horsetail splay faulting of a fault tip zone on the northern segment; 2) The Hong-Che fault zone had also experienced the Early Permian rifting and the Late Permian-Early Triassic tectonic inversion, which probably played important roles in controlling the subsequent tectonic deformation; and 3) The demonstrated dextral strike-slip faulting is consistent with the Middle Triassic-Jurassic deformation in the Ke-Bai, Wu-Xia, and Irtysh fault zones, and therefore supports the counterclockwise rotation of Junggar Basin, which might be the far-field effect of the collision between Qiangtang block and Songpan-Ganzi terrane in the Triassic. The results of this study also prove that high-resolution seismic reflection data can serve as a useful tool for investigating the buried paleo-structures.

  17. Velocity Structure of the Alpine Fault Zone, New Zealand: Laboratory and Log-Based Fault Rock Acoustic Properties at Elevated Pressures

    NASA Astrophysics Data System (ADS)

    Jeppson, T.; Graham, J. L., II; Tobin, H. J.; Paris Cavailhes, J.; Celerier, B. P.; Doan, M. L.; Nitsch, O.; Massiot, C.

    2015-12-01

    The elastic properties of fault zone rocks at seismogenic depth play a key role in rupture nucleation, propagation, and damage associated with fault slip. In order to understand the seismic hazard posed by a fault we need to both measure these properties and understand how they govern that particular fault's behavior. The Alpine Fault is the principal component of the active transpressional plate boundary through the South Island of New Zealand. Rapid exhumation along the fault provides an opportunity to study near-surface rocks that have experienced similar histories to those currently deforming at mid-crustal depths. In this study, we examine the acoustic properties of the Alpine Fault in Deep Fault Drilling Project (DFDP)-1 drill core samples and borehole logs from the shallow fault zone, DFDP-2 borehole logs from the hanging wall, and outcrop samples from a number of field localities along the central Alpine Fault. P- and S-wave velocities were measured at ultrasonic frequencies on saturated 2.5 cm-diameter core plugs taken from DFDP-1 core and outcrops. Sampling focused on mylonites, cataclasites, and fault gouge from both the hanging and foot walls of the fault in order to provide a 1-D seismic velocity transect across the entire fault zone. Velocities were measured over a range of effective pressures between 1 and 68 MPa to determine the variation in acoustic properties with depth and pore pressure. When possible, samples were cut in three orthogonal directions and S-waves were measured in two polarization directions on all samples to constrain velocity anisotropy. XRD and petrographic characterization were used to examine how fault-related alteration and deformation change the composition and texture of the rock, and to elucidate how these changes affect the measured velocities. The ultrasonic velocities were compared to sonic logs from DFDP to examine the potential effects of frequency dispersion, brittle deformation, and temperature on the measured

  18. Rapid, decimeter-resolution fault zone topography mapped with Structure from Motion

    NASA Astrophysics Data System (ADS)

    Johnson, K. L.; Nissen, E.; Saripalli, S.; Arrowsmith, R.; McGarey, P.; Scharer, K. M.; Williams, P. L.

    2013-12-01

    Recent advances in the generation of high-resolution topography have revolutionized our ability to detect subtle geomorphic features related to ground-rupturing earthquakes. Currently, the most popular topographic mapping methods are airborne Light Detection And Ranging (LiDAR) and terrestrial laser scanning (TLS). Though powerful, these laser scanning methods have some inherent drawbacks: airborne LiDAR is expensive and can be logistically complicated, while TLS is time consuming even for small field sites and suffers from patchy coverage due to its restricted field-of-view. An alternative mapping technique, called Structure from Motion (SfM), builds upon traditional photogrammetry to reproduce the topography and texture of a scene from photographs taken at varying viewpoints. The improved availability of cheap, unmanned aerial vehicles (UAVs) as camera platforms further expedites data collection by covering large areas efficiently with optimal camera angles. Here, we introduce a simple and affordable UAV- or balloon-based SfM mapping system which can produce dense point clouds and sub-decimeter resolution digital elevation models (DEMs) registered to geospatial coordinates using either the photograph's GPS tags or a few ground control points across the scene. The system is ideally suited for studying ruptures of prehistoric, historic, and modern earthquakes in areas of sparse or low-lying vegetation. We use two sites from southern California faults to illustrate. The first is the ~0.1 km2 Washington Street site, located on the Banning strand of the San Andreas fault near Thousand Palms. A high-resolution DEM with ~700 point/m2 was produced from 230 photos collected on a balloon platform flying at 50 m above the ground. The second site is the Galway Lake Road site, which spans a ~1 km strip of the 1992 Mw 7.3 Landers earthquake on the Emerson Fault. The 100 point/m2 DEM was produced from 267 photos taken with a balloon platform at a height of 60 m above the ground

  19. Low-velocity fault-zone guided waves: Numerical investigations of trapping efficiency

    USGS Publications Warehouse

    Li, Y.-G.; Vidale, J.E.

    1996-01-01

    Recent observations have shown that shear waves trapped within low-velocity fault zones may be the most sensitive measure of fault-zone structure (Li et al., 1994a, 1994b). Finite-difference simulations demonstrate the effects of several types of complexity on observations of fault-zone trapped waves. Overlying sediments with a thickness more than one or two fault-zone widths and fault-zone step-overs more than one or two fault widths disrupt the wave guide. Fault kinks and changes in fault-zone width with depth leave readily observable trapped waves. We also demonstrate the effects of decreased trapped wave excitation with increasing hypocentral offset from the fault and the effects of varying the contrast between the velocity in the fault zone and surrounding hard rock. Careful field studies may provide dramatic improvements in our knowledge of fault-zone structure.

  20. Structure and evolution of the seismically active Ostler Fault Zone (New Zealand) based on interpretations of multiple high resolution seismic reflection profiles

    NASA Astrophysics Data System (ADS)

    Campbell, Fiona M.; Ghisetti, Francesca; Kaiser, Anna E.; Green, Alan G.; Horstmeyer, Heinrich; Gorman, Andrew R.

    2010-12-01

    To improve our understanding of active faulting away from the main plate boundary on New Zealand's South Island, we have acquired high resolution seismic data across the Ostler Fault Zone Twelve 1.2 km long lines perpendicular to fault strike and a 1.6 km long crossline were collected in a region of the MacKenzie Basin where surface mapping delineates significant complexity in the form of two non-overlapping reverse fault strands separated by a transfer zone characterised by multiple smaller strands and increased folding. Interpretation of the resultant images includes a 45-55° west-dipping principal fault and two 25-30° west-dipping subsidiary faults, one in the hanging wall and one in the footwall of the principal fault. The geologically mapped complexities are shown to be caused by shallow variations in the structure of the principal fault, which breaks the surface in the north and south but not within the transfer zone, where it forms a triangle zone with associated backthrusting and minor faulting. These complexities only extend to ~ 300 m depth. Structures below this level are markedly simpler and much more 2D in nature, with the principal fault strand extending over a much longer distance than the individual strands observed at the surface. Since longer faults are susceptible to larger earthquakes than shorter ones, seismic hazard at the study site may be higher than previously thought. Multiple surface fault strands that give way to a single more major stand at relatively shallow depths may be a common feature of segmented fault systems. The deepest layered reflections at our site are consistent with the presence of a Late Cretaceous (?)-Tertiary basin underlying the present-day MacKenzie Basin. Structural restoration of the seismic images back to the base of Quaternary fluvioglacial terraces and back to the top of a Late Pliocene-Pleistocene fluviolacustrine unit indicate that compression was initiated prior to the Late Pliocene and that it has continued

  1. Fault Zones from Top to Bottom: A Geophysical Perspective

    NASA Astrophysics Data System (ADS)

    Mooney, W.; Beroza, G.; Kind, R.

    2006-12-01

    Geophysical studies of the Earth's crust, including fault zones, have greatly developed over the past 80 years. Among the first methods to be employed, seismic refraction and reflection profiles were recorded in the North American Gulf Coast to detect salt domes which were known to trap hydrocarbons. Seismic methods continue to be the most important geophysical technique in use today due to the methods' relatively high accuracy, high resolution, and great depth of penetration. However, in the past decade, a much expanded repertoire of seismic and non-seismic techniques have been brought to bear on studies of the Earth's crust and uppermost mantle. Important insights have also been obtained using seismic tomography, measurements of seismic anisotropy, fault zone guided waves, borehole surveys, and geo-electrical, magnetic, and gravity methods. In this paper we briefly review recent geophysical progress in the study of the structure and internal properties of faults zones, from their surface exposures to their lower limit. We focus on the structure of faults within continental crystalline and competent sedimentary rock rather than within the overlying, poorly consolidated sedimentary rocks. We find that 1) The width of the fault damage zone is proportional to total fault offset, 2) Large strike-slip faults have vertical low-velocity, high-conductivity zones, 3) Anomalous fault zone properties undergo temporal "healing" after a large earthquake, and 4) Fault zones can either act as a fluid conduit or an impermeable barrier, depending on composition and history.

  2. Geophysical data reveal the crustal structure of the Alaska Range orogen within the aftershock zone of the Mw 7.9 Denali fault earthquake

    USGS Publications Warehouse

    Fisher, M.A.; Ratchkovski, N.A.; Nokleberg, W.J.; Pellerin, L.; Glen, J.M.G.

    2004-01-01

    Geophysical information, including deep-crustal seismic reflection, magnetotelluric (MT), gravity, and magnetic data, cross the aftershock zone of the 3 November 2002 Mw 7.9 Denali fault earthquake. These data and aftershock seismicity, jointly interpreted, reveal the crustal structure of the right-lateral-slip Denali fault and the eastern Alaska Range orogen, as well as the relationship between this structure and seismicity. North of the Denali fault, strong seismic reflections from within the Alaska Range orogen show features that dip as steeply as 25?? north and extend downward to depths between 20 and 25 km. These reflections reveal crustal structures, probably ductile shear zones, that most likely formed during the Late Cretaceous, but these structures appear to be inactive, having produced little seismicity during the past 20 years. Furthermore, seismic reflections mainly dip north, whereas alignments in aftershock hypocenters dip south. The Denali fault is nonreflective, but modeling of MT, gravity, and magnetic data suggests that the Denali fault dips steeply to vertically. However, in an alternative structural model, the Denali fault is defined by one of the reflection bands that dips to the north and flattens into the middle crust of the Alaska Range orogen. Modeling of MT data indicates a rock body, having low electrical resistivity (>10 ??-m), that lies mainly at depths greater than 10 km, directly beneath aftershocks of the Denali fault earthquake. The maximum depth of aftershocks along the Denali fault is 10 km. This shallow depth may arise from a higher-than-normal geothermal gradient. Alternatively, the low electrical resistivity of deep rocks along the Denali fault may be associated with fluids that have weakened the lower crust and helped determine the depth extent of the after-shock zone.

  3. Fault zone Q values derived from Taiwan Chelungpu Fault borehole seismometers (TCDPBHS)

    NASA Astrophysics Data System (ADS)

    Wang, Yu-Ju; Lin, Yen-Yu; Lee, Meng-Chieh; Ma, Kuo-Fong

    2012-11-01

    The attenuation factor, Q, at a fault zone is an important parameter for understanding the physical properties. In this study, we investigated the Q value of the Chelungpu Fault, the main rupture of the Mw 7.6 Chi-Chi earthquake, using the 7-level TCDP borehole seismometer array (TCDPBHS). The TCDPBHS was deployed at depths from 945 to 1270 m throughout the 1999 ruptured slip zone at 1111 m. Three borehole seismometers (BHS1-BHS3) were placed in the hanging wall, and the remaining three (BHS5-BHS7) were placed in the foot wall, with BHS4 near the slip zone. The configuration allowed us to estimate the Q-structure of the recent ruptured fault zone. In this study, we estimated Q values between BHS1 and BHS4, Qs1 (Qp1) at the fault zone and between BHS4 to 2 km in depth, Qs4 (Qp4) beneath the fault zone. We utilized two independent methods, the spectral ratio and spectral fitting analyses, for calculating the Q value of Qs1 (Qp1) in order to provide a reliability check. After analyzing 26 micro-events for Qs and 17 micro-events for Qp, we obtained consistent Q values from the two independent methods. The values of Qs1 and Qp1 were 21-22 and 27-35, respectively. The investigation for the value of Qs4 was close to 45, and Qp4 was 85. These Qp and Qs values are quiet consistent with observations obtained for the San Andreas Fault at the corresponding depth. A low Qs1 value for the recent Chelungpu Fault zone suggests that this fault zone has been highly fractured. Qs values within the Chelungpu Fault, similar to those within the San Andreas Fault, suggest that the Q structure within the fault zone is sedimentary rock independent. However, the possible existence of fluids, fractures, and cracks dominates the attenuation feature in the fault zone.

  4. Distribution and structure of active strike-slip faults in the Enshu forearc basin of the eastern Nankai subduction zone

    NASA Astrophysics Data System (ADS)

    Ojima, T.; Ashi, J.; Nakamura, Y.

    2010-12-01

    Accretionary prisms and forearc basins are developed in the Nankai Trough, SW Japan. Many active faults are recognized and classified into five fault systems in the eastern Nankai Trough. The Enshu Faults System, the most landward one, runs over 200 km along the northern edge of the Tokai, Enshu and Kumano forearc basins. Swath bathymetry and side-scan sonar surveys indicate a general fault trend of ENE-WSW and dextral displacement of submarine canyons across the landward-most fault. Seismic reflection profiles partly exhibit landward dipping fault planes and flower structures suggesting that the Enshu fault system is affected by oblique subduction of the Philippines Sea Plate. Structural investigation of this area is important for earthquake disaster mitigation as well as understanding of oblique subduction tectonics. However, activity of faults has not been clarified. Japan Oil, Gas and Metal National Corporation (JOGMEC) conducted dense seismic reflection survey at the Tokai-Kumano area in 2001. Seismic reflection profiles clearly show depositional sequences and deformation structures such as faults and folds. This study examined deformation styles and fault activities based on detailed interpretation of seismic reflection profiles. Sediment thickness mapped from seismic profiles clearly changes with age. Sediment thickness is almost homogeneous from the acoustic basement (probably Paleogene Shimanto Complex) to a Pliocene horizon in the survey area. In contrast, thickness between a Pliocene horizon and present seafloor shows large variations from east to west. It is suggested that sedimentary environments change drastically at this period. There are also small-scale variations in sediment thickness for all horizons. Some distinct changes are distributed along linear boundaries. It seems that they correspond to the faults recognized as lineaments on the sidescan sonar images. We estimated activities of faulting based on such sediment thickness changes and their

  5. Mechanics of slip and fracture along small faults and simple strike-slip fault zones in granitic rock

    NASA Astrophysics Data System (ADS)

    Martel, Stephen J.; Pollard, David D.

    1989-07-01

    We exploit quasi-static fracture mechanics models for slip along pre-existing faults to account for the fracture structure observed along small exhumed faults and small segmented fault zones in the Mount Abbot quadrangle of California and to estimate stress drop and shear fracture energy from geological field measurements. Along small strike-slip faults, cracks that splay from the faults are common only near fault ends. In contrast, many cracks splay from the boundary faults at the edges of a simple fault zone. Except near segment ends, the cracks preferentially splay into a zone. We infer that shear displacement discontinuities (slip patches) along a small fault propagated to near the fault ends and caused fracturing there. Based on elastic stress analyses, we suggest that slip on one boundary fault triggered slip on the adjacent boundary fault, and that the subsequent interaction of the slip patches preferentially led to the generation of fractures that splayed into the zones away from segment ends and out of the zones near segment ends. We estimate the average stress drops for slip events along the fault zones as ˜1 MPa and the shear fracture energy release rate during slip as 5 × 102 - 2 × 104 J/m2. This estimate is similar to those obtained from shear fracture of laboratory samples, but orders of magnitude less than those for large fault zones. These results suggest that the shear fracture energy release rate increases as the structural complexity of fault zones increases.

  6. How fault zones impact regional permeability and groundwater systems: insights from global database of fault zone studies.

    NASA Astrophysics Data System (ADS)

    Scibek, J.; McKenzie, J. M.; Gleeson, T.

    2014-12-01

    Regional and continental scale groundwater flow models derive aquifer permeability distributions from datasets based on hydraulic tests and calibrated local and regional flow models, however, much of this data does not account for barrier/conduit effects of fault zones, local and regional geothermal flow cells, and other fault-controlled flow systems. In this study we researched and compiled fault zone permeability and conceptual permeability models in different geologic settings from published multidisciplinary literature (structural- and hydro-geology, engineering geology of tunnels and mines, and geothermal projects among others). The geospatial database focuses on data-rich regions such as North America, Europe, and Japan. Regionalization of the dominant conceptual models of fault zones was regionalized based on geological attributes and tested conceptually with simple numerical models, to help incorporate the effect of fault zones on regional to continental flow models. Results show that for large regional and continental scale flow modeling, the fault zone data can be generalized by geology to determine the relative importance of fault conduits vs fault barriers, which can be converted to effective anisotropy ratios for large scale flow, although local fault-controlled flow cells in rift zones require appropriate upscaling. The barrier/conduit properties of fault zones are present in all regions and rock types, and the barrier effect must be properly conceptualized in large scale flow models. The fault zone data from different geologic disciplines have different biases (e.g. outcrop studies, deep drillhole tests, tunnels, etc.) depending on scale of hydraulic tests. Finally, the calibrated recharge estimates for fault controlled flow systems may be lower than for unfaulted flow systems due to predominant barrier (regional anisotropy or permeability reduction), suggesting a "scaling effect" on recharge estimates.

  7. Simulation of Fault Zone Dynamics

    NASA Astrophysics Data System (ADS)

    Mora, P.; Abe, S.; Place, D.

    2002-12-01

    Particle models such as the discrete element model for granular assemblies and the lattice solid model provide a means to study the dynamics of fault zones. The lattice solid model was developed with the aim of progressively building up the capacity to simulate all relevent physical processes in fault zones. The present implementation of the model is able to simulate the dynamics of a granular lattice consisting of bonded or unbonded circular (2D) or spherical (3D) particles. Thermal effects (frictional hear generation, thermal expansion, heat flow) and pore fluid effects (heat induced pore pressure gradients and the consequent Darcian flow and impact on effective friction) can be modelled. Past work involving both circular particles and non-circular grains constructed as groups of bonded particles have demonstrated that grain shape has a fundamental impact on zero-th order behaviour. When circular particles are used, rolling is the most efficient means to accomodate slip of a simulated fault gouge layer leading to unrealistically low friction, typically around 0.2. This is consistent with laboratory results by Mair and Marone which have demonstrated that gouge consisting entirely of spherical beads shows a lower coefficient of friction than gouge containing irregular shaped particles. Recent work comparing quasi-2D laboratory results using pasta (Marone) with 2D numerical results (Morgan) have confirmed that numerical and laboratory results with circular ``particles'' are in agreement. When irregular grains are modelled at the lowest scale, the friction of simulated gouge layers matches with laboratory observations of rock friction (μ ~ 0.6) and is insentitive to the value used for interparticle friction (Mora et al, 2000). This indicates a self-regulation mechanism is occurring in which the group behaviour of the gouge layer remains constant at around 0.6 by balancing the amount of slip and rolling of grains within the gouge layer. A limitation of these studies

  8. Mechanical and Microstructural Evolution of Ductile Shear Zones: Implications for the Deep Structure of Lithospheric Faults

    NASA Astrophysics Data System (ADS)

    Platt, J. P.; Behr, W. M.

    2010-12-01

    We offer three new concepts that help place constraints on the mechanics and width of plate-boundary shear zones below the brittle-ductile transition. 1. Lithospheric shear zones operate at approximately constant stress at any given depth (temperature). This is because shear zones form by microstructural changes that cause weakening and hence strain localization. These changes occur when the ambient stress reaches the yield strength σy of intact rock. As a result, the cumulative width w of shear zones reaches a value such that they can accommodate plate motion at a flow stress equal to σy. 2. Exhuming shear zones preserve a record of the stress-temperature profile through the deforming crust. Increasing strain localization as the rocks cool, and quenching of the microstructure outside the narrowing shear zone, allow preservation of the microstructure and mineral chemistry at various stages in their evolution. If the flow stress in the shear zone at any depth is a measure of the yield strength of the surrounding rock, we can use this information to construct strength-depth profiles through the lithosphere. 3. Dislocation creep causes dynamic recrystallization and grainsize reduction. This may result in a switch to grainsize-sensitive creep, which is the main cause of weakening and strain localization in shear zones. At constant strain-rate, this results in a stress drop, which may be followed by grain growth, preventing a permanent switch in mechanism. If shear zones operate at constant stress, however, dislocation density in the deforming grains remains the same after the switch, so that dynamic recrystallization and grain-boundary migration driven by dislocation strain energy continue at the same rate as before. This inhibits grain growth driven by surface energy, so that the deformation mechanism switch is permanent. We calculate shear zone widths at depth in the lithosphere based on these concepts. We use a stress-temperature profile obtained from the Whipple

  9. Probable origin of the Livingston Fault Zone

    NASA Astrophysics Data System (ADS)

    Monroe, Watson H.

    1991-09-01

    Most faulting in the Coastal Plain is high angle and generally normal, but the faults in the Livingston Fault Zone are all medium-angle reverse, forming a series of parallel horsts and grabens. Parallel to the fault zone are a number of phenomena all leading to the conclusion that the faults result from the solution of a late Cretaceous salt anticline by fresh groundwater, which then migrated up to the Eutaw and perhaps Tuscaloosa aquifers, causing an anomalous elongated area of highly saline water. The origin of the Livingston Fault Zone and the association of salt water in underlying aquifers is of particular importance at this time in relation to environmental concerns associated with hazardous waste management in the area.

  10. Fault intersections along the Hosgri Fault Zone, Central California

    NASA Astrophysics Data System (ADS)

    Watt, J. T.; Johnson, S. Y.; Langenheim, V. E.

    2011-12-01

    It is well-established that stresses concentrate at fault intersections or bends when subjected to tectonic loading, making focused studies of these areas particularly important for seismic hazard analysis. In addition, detailed fault models can be used to investigate how slip on one fault might transfer to another during an earthquake. We combine potential-field, high-resolution seismic-reflection, and multibeam bathymetry data with existing geologic and seismicity data to investigate the fault geometry and connectivity of the Hosgri, Los Osos, and Shoreline faults offshore of San Luis Obispo, California. The intersection of the Hosgri and Los Osos faults in Estero Bay is complex. The offshore extension of the Los Osos fault, as imaged with multibeam and high-resolution seismic data, is characterized by a west-northwest-trending zone (1-3 km wide) of near vertical faulting. Three distinct strands (northern, central, and southern) are visible on shallow seismic reflection profiles. The steep dip combined with dramatic changes in reflection character across mapped faults within this zone suggests horizontal offset of rock units and argues for predominantly strike-slip motion, however, the present orientation of the fault zone suggests oblique slip. As the Los Osos fault zone approaches the Hosgri fault, the northern and central strands become progressively more northwest-trending in line with the Hosgri fault. The northern strand runs subparallel to the Hosgri fault along the edge of a long-wavelength magnetic anomaly, intersecting the Hosgri fault southwest of Point Estero. Geophysical modeling suggests the northern strand dips 70° to the northeast, which is in agreement with earthquake focal mechanisms that parallel this strand. The central strand bends northward and intersects the Hosgri fault directly west of Morro Rock, corresponding to an area of compressional deformation visible in shallow seismic-reflection profiles. The southern strand of the Los Osos

  11. Mantle fault zone beneath Kilauea Volcano, Hawaii

    USGS Publications Warehouse

    Wolfe, C.J.; Okubo, P.G.; Shearer, P.M.

    2003-01-01

    Relocations and focal mechanism analyses of deep earthquakes (???13 kilometers) at Kilauea volcano demonstrate that seismicity is focused on an active fault zone at 30-kilometer depth, with seaward slip on a low-angle plane, and other smaller, distinct fault zones. The earthquakes we have analyzed predominantly reflect tectonic faulting in the brittle lithosphere rather than magma movement associated with volcanic activity. The tectonic earthquakes may be induced on preexisting faults by stresses of magmatic origin, although background stresses from volcano loading and lithospheric flexure may also contribute.

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

    USGS Publications Warehouse

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

    2002-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2001-12-01

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

  14. Laboratory evidence of strength recovery of a healed fault: implications for a mechanism responsible for creating wide fault zones

    NASA Astrophysics Data System (ADS)

    Masuda, Koji

    2015-12-01

    Fault zones consist of a high-strain fault core and a surrounding damage zone of highly fractured rock. The close, reciprocal relationship between fault zones and earthquake rupture evolution demands better understanding of the processes that create and modify damage zones. This study modeled the evolution of a damage zone in the laboratory by monitoring seismic signals (acoustic emissions) in a specimen of ultramylonite stressed to failure. The result provided evidence supporting the strength recovery of parts of the healed surface. A new fault initiated in an area of heterogeneous structure a short distance from the preexisting fault plane. Repeated cycles of fracture and healing may be one mechanism responsible for wide fault zones with multiple fault cores and damage zones.

  15. Seismic measurements of the internal properties of fault zones

    USGS Publications Warehouse

    Mooney, W.D.; Ginzburg, A.

    1986-01-01

    The internal properties within and adjacent to fault zones are reviewed, principally on the basis of laboratory, borehole, and seismic refraction and reflection data. The deformation of rocks by faulting ranges from intragrain microcracking to severe alteration. Saturated microcracked and mildly fractured rocks do not exhibit a significant reduction in velocity, but, from borehole measurements, densely fractured rocks do show significantly reduced velocities, the amount of reduction generally proportional to the fracture density. Highly fractured rock and thick fault gouge along the creeping portion of the San Andreas fault are evidenced by a pronounced seismic low-velocity zone (LVZ), which is either very thin or absent along locked portions of the fault. Thus there is a correlation between fault slip behavior and seismic velocity structure within the fault zone; high pore pressure within the pronounced LVZ may be conductive to fault creep. Deep seismic reflection data indicate that crustal faults sometimes extend through the entire crust. Models of these data and geologic evidence are consistent with a composition of deep faults consisting of highly foliated, seismically anisotropic mylonites. ?? 1986 Birkha??user Verlag, Basel.

  16. Widening of normal fault zones due to the inhibition of vertical propagation

    NASA Astrophysics Data System (ADS)

    Roche, Vincent; Homberg, Catherine; van der Baan, Mirko; Rocher, Muriel

    2015-04-01

    Fault zones structures are the result of a progressive development and are largely controlled by fault geometry inherited from the early stage of faulting. In this paper, we document this early stage, based on detailed observations on mesocale faults in layered rocks in two outcrops. Study includes analyses of fault structures, along-planes displacement profiles, and far-field displacement profiles. This last profile take into account the total strain induced by fault zones including folding and segmentation. The vertical propagation of the studied faults is stopped by layer-parallel faults. This restriction involves a flat-topped displacement profile along the fault plane. Far from the restricted tip, fault structures correspond to simple planar slip surfaces exhibiting dip refraction due to layering. Near the restricted tips, their structures range from planar structures to complex fault zone characterized by abundant parallel fault segment. In one site, fault-related folding also occurs at the fault tips. Unlike the segmentation, fault-related folding is not restricted by the layer-parallel fault. Far-field displacement profiles have therefore flat topped shape along the restricted faults exhibiting segmentation, whereas profiles become more triangular when folding take place. Based on the observations, we developed a model of fault zone evolution in which the complexities and the width of fault zone are inherited during the fault restriction period. In this model fault propagation alternates between periods of vertical restriction and vertical propagation. In the course of restriction, faults form first as simple isolated planar structures, then, fault zone complexity, specifically the number of sub parallel segments, increases to accommodate increasing strain. Eventually the fault should finally propagate through the layer-parallel faults with a complex geometry. This model implies that fault widening is controlled by the fault capacity to propagate vertically

  17. Slip compensation at fault damage zones along earthquake surface ruptures

    NASA Astrophysics Data System (ADS)

    Choi, J.; Kim, Y.

    2013-12-01

    to those of the main traces. In contrast, when the L/W < 2, the vertical slip is either increased or decreased as the horizontal slip is decreased, depending on the maturity of the linking zone. Thus, we argue that slip patterns at linking damage zones may be controlled by the LW-ratio of linking damage zones and hence structural maturities of the segmented fault systems. In conclusion, slip patterns at fault damage zones along earthquake surface ruptures are various depending on the maturity of linkage zones and/or the rupture propagation direction. Therefore, the consideration of slip compensation as well as damage structures along surface ruptures must be very useful to understand fault evolution and, hence, to assess seismic hazards around active fault systems.

  18. 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.

  19. Kumano Seismogenic Zone Imaging and Splay Fault Property

    NASA Astrophysics Data System (ADS)

    Kuramoto, S.; Okano, T.; Hashimoto, T.; Tanaka, H.; Taira, A.

    2003-12-01

    Splay faults or out-of-sequence thrusts (OOSTs) are prominent structure in the Nankai accretionary prism. The splay faults merging to the plate interface between the subducting Philippine Sea plate and the overriding Eurasian plate. The contact area of the splay faults and decollement plane may be a possible up-dip limit of the seismogenic zone from geological interpretation point of view. The splay faults are not continuously traced nearly parallel to the trough axis. The discontinuity of splay fault system coincides with the basement structure from magnetic anomaly map. The faults are recognized as the outer-arc-high in the Kumano accretionary wedge. The splay fault system has an important scientific target that will be clarified by drilling. A new bathymetric survey and dive observations by manned submersible are carried out in the Kumano accretionary wedge. Basic morphological interpretation and dive observations give a new insight of tectonic framework of the Kumano area. Prominent splay fault system shows transpressional fault system and associated by active folding and faulting structures. One of the splay faults shows dextral slip phenomena from en-echelon structural interpretation. Several seepage sites are discovered along the splay faults. Preliminary chemical analysis of sediment pore fluids on the splay fault shows up to 10 % depletion of chloride concentration compare with bottom seawater and extremely high methane concentration of more than 600 umol/kg (Toki et al., in prep.). A significant gamma-ray anomaly also discovered from the same site (Ashi et al.). These data suggest that the origin of fluid is significantly deep and the fluid may flow along the splay fault. A recent Tsunami inversion study suggests that the rupture area during the last large earthquake (Tonankai, 1944) spread over even the splay fault system area. The splay faults show significant differences of activities from structural interpretation of each fault. The lower fault is cut

  20. Granular packings and fault zones

    PubMed

    Astrom; Herrmann; Timonen

    2000-01-24

    The failure of a two-dimensional packing of elastic grains is analyzed using a numerical model. The packing fails through formation of shear bands or faults. During failure there is a separation of the system into two grain-packing states. In a shear band, local "rotating bearings" are spontaneously formed. The bearing state is favored in a shear band because it has a low stiffness against shearing. The "seismic activity" distribution in the packing has the same characteristics as that of the earthquake distribution in tectonic faults. The directions of the principal stresses in a bearing are reminiscent of those found at the San Andreas Fault. PMID:11017335

  1. Seismic velocity structure in the Hot Springs and Trifurcation areas of the San Jacinto fault zone, California, from double-difference tomography

    NASA Astrophysics Data System (ADS)

    Allam, A. A.; Ben-Zion, Y.; Kurzon, I.; Vernon, F.

    2014-08-01

    We present tomographic images of crustal velocity structures in the complex Hot Springs and Trifurcation areas of the San Jacinto Fault Zone (SJFZ) based on double-difference inversions of earthquake arrival times. We invert for VP, VS and hypocentre location within 50 × 50 × 20 km3 volumes, using 266 969 P and 148 249 S arrival times. We obtain high-fidelity images of seismic velocities with resolution on the order of a few kilometres from 2 to 12 km depth and validate the results using checkerboard tests. Due to the relatively large proportion of S-wave arrival times, we also obtain stable maps of VP/VS ratios in both regions. The velocity of the Trifurcation Area as a whole is lower than adjacent unfaulted material. We interpret a 4-km-wide low velocity zone with high VP/VS ratio in the trifurcation itself as related to fault zone damage. We also observe clear velocity contrasts across the Buck Ridge, Clark and Coyote Creek segments of the SJFZ. The Anza segment of the SJFZ, to the NW of the trifurcation area, displays a strong (up to 27 per cent) contrast of VS from 2 to 9 km depth. In the Hot Springs area, a low velocity zone between the Claremont and Casa Loma Strands narrows with depth, with clear velocity contrasts observed across both segments. A roughly 10-km-wide zone of low velocity and low VP/VS ratio at the NW tip of the Hot Springs fault is indicative of either unconsolidated sediments associated with the San Jacinto basin, or fluid-filled cracks within a broad deformation zone. High VP/VS ratios along the Anza segment could indicate a preferred nucleation location for future large earthquakes, while the across-fault velocity contrast suggests a preferred northwest rupture propagation direction for such events.

  2. Seismic velocity structure in the Hemet Stepover and Trifurcation Areas of the San Jacinto Fault Zone from double-difference earthquake tomography

    NASA Astrophysics Data System (ADS)

    Allam, A. A.; Ben-Zion, Y.; Vernon, F.; Kurzon, I.

    2013-12-01

    We present tomographic images of crustal velocity structures in the Hemet Stepover and Trifurcation areas of the San Jacinto Fault Zone (SJFZ) based on double-difference inversions of earthquake arrival times. We discretize both regions with a horizontal 250m grid spacing and a vertical 500m spacing within 50km by 50km by 20km volumes. We invert for VP, VS, and hypocenter location using data from 16064 earthquakes recorded at 136 stations. In total, we use 266,969 P and 148,249 S arrivals to constrain the seismic velocity structures in the two regions. With large numbers of both arrivals, we are able to obtain images of VP and VS at similar resolutions, enabling us to make spatial maps of and interpret the VP/VS ratios. Though ray coverage is limited at shallow depths, we obtain high-fidelity images of seismic velocities from 2 to 12 km, and validate the results using checkerboard tests. The tomographic images indicate that the velocity of the trifurcation area as a whole is lower than adjacent unfaulted material. We interpret a 4km-wide low velocity zone in the trifurcation itself as fault zone damage related due to high VP/VS ratio. We also observe clear velocity contrasts across the Buck Ridge, Clark, and Coyote Creek segments of the SJFZ. The Anza segment of the SJFZ, to the NW of the trifurcation area, displays a strong (up to 27%) contrast of VS from 2km to 9km. In the Hemet Stepover, a low velocity zone between the Claremont and Casa Loma Strands narrows with depth, with clear velocity contrasts observed across both segments. A roughly 10km-wide zone of low velocity and low VP/VS ratio at the NW tip of the Hot Springs fault is indicative of either unconsolidated sediments associated with the San Jacinto basin, or fluid-filled cracks within a broad deformation zone. Relocated seismicity tends to align with the surface traces of the various fault strands, though it is offset to the northeast of the Casa Loma-Clark strand and to the southwest of the Hot Springs

  3. Recent advances in imaging crustal fault zones: a review

    NASA Astrophysics Data System (ADS)

    Yang, Hongfeng

    2015-04-01

    Crustal faults usually have a fault core and surrounding regions of brittle damage, forming a low-velocity zone (LVZ) in the immediate vicinity of the main slip interface. The LVZ may amplify ground motion, influence rupture propagation, and hold important information of earthquake physics. A number of geophysical and geodetic methods have been developed to derive high-resolution structure of the LVZ. Here, I review a few recent approaches, including ambient noise cross-correlation on dense across-fault arrays and GPS recordings of fault-zone trapped waves. Despite the past efforts, many questions concerning the LVZ structure remain unclear, such as the depth extent of the LVZ. High-quality data from larger and denser arrays and new seismic imaging technique using larger portion of recorded waveforms, which are currently under active development, may be able to better resolve the LVZ structure. In addition, effects of the along-strike segmentation and gradational velocity changes across the boundaries between the LVZ and the host rock on rupture propagation should be investigated by conducting comprehensive numerical experiments. Furthermore, high-quality active sources such as recently developed large-volume air-gun arrays provide a powerful tool to continuously monitor temporal changes of fault-zone properties, and thus can advance our understanding of fault zone evolution.

  4. Influence of carbonate facies on fault zone architecture

    NASA Astrophysics Data System (ADS)

    Michie, E. A. H.; Haines, T. J.; Healy, D.; Neilson, J. E.; Timms, N. E.; Wibberley, C. A. J.

    2014-08-01

    Normal faults on Malta were studied to analyse fault propagation and evolution in different carbonate facies. Deformation of carbonate facies is controlled by strength, particle size and pore structure. Different deformation styles influence the damage characteristics surrounding faults, and therefore the fault zone architecture. The carbonates were divided into grain- and micrite-dominated carbonate lithofacies. Stronger grain-dominated carbonates show localised deformation, whereas weaker micrite-dominated carbonates show distributed deformation. The weaker micrite-dominated carbonates overlie stronger grain-dominated carbonates, creating a mechanical stratigraphy. A different architecture of damage, the ‘Fracture Splay Zone’ (FSZ), is produced within micrite-dominated carbonates due to this mechanical stratigraphy. Strain accumulates at the point of juxtaposition between the stronger grain-dominated carbonates in the footwall block and the weaker micrite-dominated carbonates in the hanging wall block. New slip surfaces nucleate and grow from these points, developing an asymmetric fault damage zone segment. The development of more slip surfaces within a single fault zone forms a zone of intense deformation, bound between two slip surfaces within the micrite-dominated carbonate lithofacies (i.e., the FSZ). Rather than localisation onto a single slip surface, allowing formation of a continuous fault core, the deformation will be dispersed along several slip surfaces. The dispersed deformation can create a highly permeable zone, rather than a baffle/seal, in the micrite-dominated carbonate lithofacies. The formation of a Fracture Splay Zone will therefore affect the sealing potential of the fault zone. The FSZ, by contrast, is not observed in the majority of the grain-dominated carbonates.

  5. Displacements and segment linkage in strike-slip fault zones

    NASA Astrophysics Data System (ADS)

    Peacock, D. C. P.

    Small-scale, well exposed strike-slip fault zones near Kirkcudbright, Scotland, cut sub-vertical bedding, so that mapped bed separations allow the displacements, linkage and evolution of fault segments to be assessed. Displacement variations along the segments can be related to lithologic variations, conjugate relationships, offsets, segment linkage and fault bends. High displacement gradients at the tips of conjugate and offset faults produce convex-upwards ( E-type) displacement-distance ( d-x) profiles. Contractional fault bends and linkage points are marked by a decrease in fault displacement, producing partially concave-upwards ( D-type) d-x profiles. Where fault displacement gradients are steep, wallrocks are marked by structures such as synthetic faults, normal drag folding, ductile strain and veining, which transfer displacement. The faults studied tend to have lower r/ dMAX ratios (where r = distance between the point of maximum displacement and the fault tip on a particular profile, and dMAX = maximum displacement on the profile) than are shown by normal faults in map view. This may be because r is measured parallel to the displacement direction and/or because of lithologic variations.

  6. A method for generating volumetric fault zone grids for pillar gridded reservoir models

    NASA Astrophysics Data System (ADS)

    Qu, Dongfang; Røe, Per; Tveranger, Jan

    2015-08-01

    The internal structure and petrophysical property distribution of fault zones are commonly exceedingly complex compared to the surrounding host rock from which they are derived. This in turn produces highly complex fluid flow patterns which affect petroleum migration and trapping as well as reservoir behavior during production and injection. Detailed rendering and forecasting of fluid flow inside fault zones require high-resolution, explicit models of fault zone structure and properties. A fundamental requirement for achieving this is the ability to create volumetric grids in which modeling of fault zone structures and properties can be performed. Answering this need, a method for generating volumetric fault zone grids which can be seamlessly integrated into existing standard reservoir modeling tools is presented. The algorithm has been tested on a wide range of fault configurations of varying complexity, providing flexible modeling grids which in turn can be populated with fault zone structures and properties.

  7. Late Cenozoic Reverse Faulting in the Fall Zone, Southeastern Virginia.

    PubMed

    Berquist Jr; Bailey

    1999-11-01

    A set of en-echelon reverse faults cut Paleozoic metamorphosed igneous rocks of the Piedmont and overlying late Cenozoic sediments at the Old Hickory Heavy Mineral Deposit in the Fall Zone of southeastern Virginia. Diorite of the eastern Slate Belt was faulted over nearshore to shore-face deposits of the Pliocene Yorktown Formation. These NW-SE-striking faults experienced oblique dip-slip movement with a maximum displacement of up to 6 m on individual faults. Faults tip out along strike and are overlain by distinct cobble beds, suggesting that sediment deposition and faulting were contemporaneous. Deformation at Old Hickory may have been formed by reactivation of existing Paleozoic structures under a regionally extensive compressional stress field parallel to the modern one. PMID:10517887

  8. Some Recent Laboratory Measurements of Fault Zone Permeability

    NASA Astrophysics Data System (ADS)

    Morrow, C. A.; Lockner, D. A.

    2005-12-01

    depth is likely to occur through these larger-scale features rather than through the matrix of the rock. Then a `typical' fault structure might consist of a narrow, low-permeability fault zone surrounded by a higher permeability damage zone, in which the damage zone acts as a conduit for fluids parallel to the fault. The low-permeability, often clay-rich shear zone will impede flow across the fault. Quartzo-feldspathic lithologies such as those of the Nojima Fault in Japan, fit this scenario. However, such a fault model may not be appropriate in many cases, particularly in sedimentary sequences. For instance, there may be little difference in the permeability of the fault-rock and surrounding rock in clay-rich sandstones or siltstones, such as those of the Chelungpu Fault in Taiwan. For interbedded sandstones and siltstones sequences such as the Moab Fault in Utah, clay-rich layers may be entrained in the fault zone, forming a continuous barrier to fluid flow (fault gouge) across the fault, but with very different damage zone/country rock evolution and hydrologic properties.

  9. 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

    surface along fractures associated with groundwater flow. Therefore, it will be possible to estimate the groundwater flow pathways from deep underground in fracture zones around a fault by measurement of the hydrogen gas. From this standpoint, we have obtained multipoint hydrogen gas measurements across an exposed fault zone in the Atera Fault System, an active, major strike-slip fault in Central Japan and provide a continuous cross-section from fault core to damage zone. The distribution of hydrogen gas emissions, corresponding to the microscopic structure of fracture zones, have shown that large volumes of hydrogen gas emission occur where open micro-fractures are dominant and emissions were not observed in the central part of faults with abundant clay minerals. Using these simple methods, we have obtained information on the qualitative permeability of fracture zones. A rapid evaluation of the spatial heterogeneity of hydrogen gas emissions along the faults probably increase knowledge of hydrogeological structure around faults. Reference Sugisaki et al., 1983, Jour. Geol. 91, 239-258. Kita et al., 1982, JGR 87, 10789-10795. Shimada et al., 2008, Resource Geol. 58, 196-202.

  10. Inelastic response of compliant fault zones to nearby earthquakes in three dimensions

    NASA Astrophysics Data System (ADS)

    Kang, Jingqian; Duan, Benchun

    2014-02-01

    Using dynamic modeling of earthquake rupture on a strike-slip fault and seismic wave propagation in a three dimensional inhomogeneous elastoplastic medium, we investigate the inelastic response of compliant fault zones to nearby earthquakes. We primarily examine the plastic strain distribution within the fault zone and the displacement field that characterizes the effects of the presence of the fault zone. We find that when the fault zone rocks are close to failure in the prestress field, plastic strain occurs along the entire fault zone near the Earth's surface and some portions of the fault zone in the extensional quadrant at depth, while the remaining portion deforms elastically. Plastic strain enhances the surface displacement of the fault zone, and the enhancement in the extensional quadrant is stronger than that in the compressive quadrant. Inelastic response may be distinguished from elastic response by sympathetic motion (or reduced retrograde motion) exhibited in the fault-parallel horizontal surface displacement in conjunction with enhanced vertical surface displacement in a strike-slip faulting environment. These findings suggest that taking into account both elastic and inelastic deformation of fault zones to nearby earthquakes may improve our estimations of fault zone structure and properties from small-scale surface deformation signals. Furthermore, identifying the inelastic response of nearby fault zones to large earthquakes may allow us to place some constraints on the absolute stress level in the crust.

  11. Porosity variations in and around normal fault zones: implications for fault seal and geomechanics

    NASA Astrophysics Data System (ADS)

    Healy, David; Neilson, Joyce; Farrell, Natalie; Timms, Nick; Wilson, Moyra

    2015-04-01

    Porosity forms the building blocks for permeability, exerts a significant influence on the acoustic response of rocks to elastic waves, and fundamentally influences rock strength. And yet, published studies of porosity around fault zones or in faulted rock are relatively rare, and are hugely dominated by those of fault zone permeability. We present new data from detailed studies of porosity variations around normal faults in sandstone and limestone. We have developed an integrated approach to porosity characterisation in faulted rock exploiting different techniques to understand variations in the data. From systematic samples taken across exposed normal faults in limestone (Malta) and sandstone (Scotland), we combine digital image analysis on thin sections (optical and electron microscopy), core plug analysis (He porosimetry) and mercury injection capillary pressures (MICP). Our sampling includes representative material from undeformed protoliths and fault rocks from the footwall and hanging wall. Fault-related porosity can produce anisotropic permeability with a 'fast' direction parallel to the slip vector in a sandstone-hosted normal fault. Undeformed sandstones in the same unit exhibit maximum permeability in a sub-horizontal direction parallel to lamination in dune-bedded sandstones. Fault-related deformation produces anisotropic pores and pore networks with long axes aligned sub-vertically and this controls the permeability anisotropy, even under confining pressures up to 100 MPa. Fault-related porosity also has interesting consequences for the elastic properties and velocity structure of normal fault zones. Relationships between texture, pore type and acoustic velocity have been well documented in undeformed limestone. We have extended this work to include the effects of faulting on carbonate textures, pore types and P- and S-wave velocities (Vp, Vs) using a suite of normal fault zones in Malta, with displacements ranging from 0.5 to 90 m. Our results show a

  12. A new conceptual model for damage zone evolution with fault growth

    NASA Astrophysics Data System (ADS)

    de Joussineau, G.; Aydin, A.

    2006-12-01

    Faults may either impede or enhance fluid flow in the subsurface, which is relevant to a number of economic issues (hydrocarbon migration and entrapment, formation and distribution of mineral deposits) and environmental problems (movement of contaminants). Fault zones typically comprise a low-permeability core made up of intensely deformed fault rock and a high-permeability damage zone defined by fault-related fractures. The geometry, petrophysical properties and continuity of both the fault core and the damage zone have an important influence on the mechanical properties of the fault systems and on subsurface fluid flow. Information about fault components from remote seismic methods is limited and is available only for large faults (slip larger than 20-100m). It is therefore essential to characterize faults and associated damage zones in field analogues, and to develop conceptual models of how faults and related structures form and evolve. Here we present such an attempt to better understand the evolution of fault damage zones in the Jurassic Aztec Sandstone of the Valley of Fire State Park (SE Nevada). We document the formation and evolution of the damage zone associated with strike-slip faults through detailed field studies of faults of increasing slip magnitudes. The faults initiate as sheared joints with discontinuous pockets of damage zone located at fault tips and fault surface irregularities. With increasing slip (slip >5m), the damage zone becomes longer and wider by progressive fracture infilling, and is organized into two distinct components with different geometrical and statistical characteristics. The first component of the damage zone is the inner damage zone, directly flanking the fault core, with a relatively high fracture frequency and a thickness that scales with the amount of fault slip. Parts of this inner zone are integrated into the fault core by the development of the fault rock, contributing to the core's progressive widening. The second

  13. Subsurface Rock Damage Structure of the Mw7.1 Darfield and Mw6.3 Christchurch Earthquake Sequence Viewed with Fault-Zone Trapped Waves

    NASA Astrophysics Data System (ADS)

    Li, Y.; De Pascale, G. P.; Quigley, M. C.; Gravley, D.

    2012-12-01

    In order to document the subsurface structure of the damage zones caused by multiple slips in the 2010 Mw7.1 Darfield - 2011 Mw6.3 Christchurch earthquake sequence in NZ's South Island, we deployed two short linear seismic arrays in the Canterbury region to record aftershocks in middle 2011. Array 1 was deployed across the central Greendale fault (GF) where right-lateral slip of ~4.5 m was measured across the surface rupture of the 2010 Darfield mainshock. Array 2 was located at the surface projection of an aftershock zone along the blind Port Hills fault (PHF) which ruptured in the 2011 Christchurch earthquake. We have examined the data for 853 aftershocks and identified prominent fault-zone trapped waves (FZTWs) with large amplitude and long wavetrains following S-arrivals at stations of Array 1 within the ~200-m-wide rupture zone for aftershocks occurring along the GF and the PHF. The post-S durations of these FZTWs increase as event depth and epicentral distance increase, showing an effective low-velocity waveguide formed by severely damaged rocks extending along the GF and PHF at seismogenic depth, but with variations in its geometry and velocity reduction along multiple rupture segments. The FZTWs suggest that the Darfield rupture zone extends eastward as bifurcating blind fault segments an additional ~5-8 km beyond the mapped ~30-km extent of the GF surface rupture, consistent with aftershock distributions and geodetic models. On the other hand, the main rupture of the Mw6.3 Christchurch earthquake is ~15-km in length on the blind PHF dipping to SSE, but it likely extends westward along the aftershock lineament approaching the east blind extension of the GF/Darfield rupture. These two main rupture segments might connect through a weak portion of the low-velocity waveguide formed by rocks along blind faults that experienced milder damage beneath the dilatational fault step-over where accumulated seismic energy release was lower than adjacent rupture zones in

  14. The Maradi fault zone: 3-D imagery of a classic wrench fault in Oman

    SciTech Connect

    Neuhaus, D. )

    1993-09-01

    The Maradi fault zone extends for almost 350 km in a north-northwest-south-southeast direction from the Oman Mountain foothills into the Arabian Sea, thereby dissecting two prolific hydrocarbon provinces, the Ghaba and Fahud salt basins. During its major Late Cretaceous period of movement, the Maradi fault zone acted as a left-lateral wrench fault. An early exploration campaign based on two-dimensional seismic targeted at fractured Cretaceous carbonates had mixed success and resulted in the discovery of one producing oil field. The structural complexity, rapidly varying carbonate facies, and uncertain fracture distribution prevented further drilling activity. In 1990 a three-dimensional (3-D) seismic survey covering some 500 km[sup 2] was acquired over the transpressional northern part of the Maradi fault zone. The good data quality and the focusing power of 3-D has enabled stunning insight into the complex structural style of a [open quotes]textbook[close quotes] wrench fault, even at deeper levels and below reverse faults hitherto unexplored. Subtle thickness changes within the carbonate reservoir and the unconformably overlying shale seal provided the tool for the identification of possible shoals and depocenters. Horizon attribute maps revealed in detail the various structural components of the wrench assemblage and highlighted areas of increased small-scale faulting/fracturing. The results of four recent exploration wells will be demonstrated and their impact on the interpretation discussed.

  15. Pseudotachylyte-bearing faults and shear zones along the Norumbega fault system in Maine

    NASA Astrophysics Data System (ADS)

    West, D. P.; Price, N. A.; Swanson, M.; Pollock, S. G.

    2012-12-01

    The Norumbega fault system represents the eroded roots of a >400 km long fault system that records a Middle Paleozoic through Mesozoic history of superimposed deformational processes. The Paleozoic history is dominated by right lateral shearing that evolved from a wide zone of regional scale dextral transpression to more highly focused and in many cases seismogenic slip along relatively narrow faults and shear zones. The Mesozoic history, largely deduced through geochronological studies, likely involved localized reactivation in association with the transition between Late Paleozoic dextral transpression and Early Mesozoic extension in the northern Appalachians. Pseudotachylyte, found in a variety of structural settings, has been identified on numerous fault strands along the southern 250 km of the fault system in Maine and provides an excellent opportunity to evaluate evolving seismogenic processes, at a variety of depths, along a regional scale fault system. The oldest pseudotachylyte (Late Devonian-Early Carboniferous) formed at frictional-to-viscous transitional depths during dextral deformation and is most commonly characterized by multiple generations of foliation-parallel frictional melt veins that were subsequently deformed through viscous shearing and transformed into thin ultramylonite layers. While this variety of pseudotachylyte has only been positively identified along three ~25 km long fault segments within the central portion of the Norumbega (e.g., Sandhill Corner), we speculate it may be more widespread in the fault system owing to difficulties in recognition in the field and a lack of detailed imaging and laboratory studies of mylonite-hosted pseudotachylyte-bearing rocks in the fault system. Younger (Permian-Early Triassic) undeformed pseudotachylyte-bearing faults have been found discontinuously along much of the Norumbega and presumably these occurrences reflect countless high velocity coseismic slip events at shallower depths. Spectacularly

  16. A neotectonic tour of the Death Valley fault zone, Inyo County

    SciTech Connect

    Wills, C.J.

    1989-09-01

    The Death Valley fault zone has recently been evaluated by the Division of Mines and Geology for zoning under the Alquist-Priolo Special Studies Zones Act of 1972. This act requires the State Geologist to zone for special studies those faults that are sufficiently active and well defined as to constitute a potential hazard to structures from surface faulting or fault creep. The Death Valley fault zone is part of a system of faults that extends over 180 miles (300 km) from Fish Lake Valley in Nevada to the Garlock fault. The northern part of this system, the Northern Death Valley-Furnace Creek fault zone, is an active right-lateral fault zone. The southern part of the system, the Death Valley fault zone, is a right-lateral oblique-slip fault between Furnace Creek and Shoreline Butte. From Shoreline Butte to the Garlock fault, it is a right-lateral strike-slip fault. Landforms along this fault indicate that it is the source of many earthquakes and that it has been active in Holocene time. The heights of the scarps and magnitude of the smallest right-lateral offsets (4 feet; 1.2 m) suggest that the most recent of these events was M 6.5 or larger. The freshness of the geomorphic features and the youth of the offset materials suggest that event occurred late in the Holocene, and that multiple Holocene earthquakes have occurred.

  17. The permeability of fault zones: a case study of the Dead Sea rift (Middle East)

    NASA Astrophysics Data System (ADS)

    Ran, Gabay; Eyal, Shalev; Yoseph, Yechieli; Amir, Sagy; Noam, Weisbrod

    2014-03-01

    Fault zone architecture plays an important role in flow regimes of hydrological systems. Fault zones can act as conduits, barriers, or conduits/barrier systems depending on their spatial architecture. The goal of this study is to determine the fault-zone permeability structure and its effect on the local hydrogeological system in the Dead Sea fault system. Permeability was measured on small-scale outcrop plug samples at four faults along the Dead Sea fault system, and large-scale slug tests in four boreholes, in different parts of the fault, at Yair fault in Israel. The research results show that values in the damage zone are two to five orders of magnitude higher than those of the fault core (~3.5 × 10-10, 1 × 10-15 m2 respectively), resulting in an anisotropic permeability structure for the overall fault zone and preferable flow parallel to the fault. A set of injection tests in the Yair fault damage zone revealed a water-pressure-dependent behavior. The permeability of this zone increases when employing a higher water pressure in the fault fracture-dominated damage zone, due to the reopening of fractures.

  18. Influence of syn-sedimentary faults on orogenic structures in a collisional belt: Insights from the inner zone of the Northern Apennines (Italy)

    NASA Astrophysics Data System (ADS)

    Brogi, Andrea

    2016-05-01

    This paper discusses the possible influence of syn-sedimentary structures on the development of orogenic structures during positive tectonic inversion in the inner Northern Apennines (Italy). Examples from key areas located in southern Tuscany provided original cartographic, structural and kinematics data for Late Oligocene-Early Miocene thrusts, organized in duplex systems, verging in the opposite direction of the foreland propagation (back-thrusts), which affected the Late Triassic-Oligocene sedimentary succession of the Tuscan Domain, previously affected by pre-orogenic structures. These latter consist of mesoscopic-to cartographic-scale Jurassic syn-sedimentary normal faults and extensional structures, which gave rise to effective stratigraphic lateral variation and mechanical heterogeneities. Structural analysis of both syn-sedimentary faults and back-thrusts were therefore compared in order to discuss the possible role of the pre-existing anisotropies in influencing the evolution of the back-thrusts. As a result, it can be reasonably proposed that back-thrusts trajectories and stacking pattern were controlled by relevant syn-sedimentary normal faults; these latter were reactivated, in some cases, if properly oriented. Such an issue adds new inputs for discussing the potential role of structural inheritance during tectonic inversions, and helps to better understand the processes suitable for the development of back-thrusts in the inner zones of orogenic belts, as it is the case of the inner Northern Apennines.

  19. 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.

  20. Structural and petrographic analysis of hypabyssal rocks in the central Menderes Massif: implications for the role of transfer zones during detachment faulting

    NASA Astrophysics Data System (ADS)

    Erkül, Fuat; Gürboǧa, Şule; Tatar Erkul, Sibel; Deveci, Zehra

    2014-05-01

    Structural and petrographic analysis of hypabyssal rocks in the central Menderes Massif: implications for the role of transfer zones during detachment faulting Fuat ERKÜL(1), Şule GÜRBOǧA(2), Sibel TATAR ERKÜL(3), Zehra DEVECİ(4) The central Menderes Massif is formed by complex assemblages of transfer zones, detachment faults and associated syn-extensional granitoids in western Turkey. Syn-extensional Salihli and Turgutlu granitoids were widely recognized in the footwall rocks of the Gediz detachment fault, but their hypabyssal equivalents were not described in detail. Hypabyssal rocks discovered during this study include substantial structural data that may shed light into the development of transfer zones during detachment faulting. Hypabyssal rocks are mafic and felsic in compositions. Mafic rocks, which are located to the SW of the Turgutlu granitoid, were emplaced into the phyllites as sills and dykes that were surrounded by a narrow hornfelsic halo. Dykes are subvertical and trend N20oW, intersecting the phyllites of the Menderes Massif. They include abundant xenoliths of phyllite and gneiss and are mainly characterized by ophitic texture formed by plagioclase, tremolite/actinolite, biotite, and pyroxene crystals. Felsic dykes, which are located in the SE of the Salihli granitoid, are defined as three subparallel, N10oW-trending dykes that intrude into the mica schists. Felsic dykes consist of quartz, sanidine and plagioclase and zircon, apatite and allanite as accessory phases. They display holocrystalline hypidiomorphic porphyritic texture, suggesting their typical shallow-seated and hypabyssal emplacement. Microcrystalline matrix surrounds embayed quartz and locally corroded crystals. Alteration mineral assemblages of chlorite, epidote and sericite and carbonatization are also common. Their mineral constituents appear to be similar to those of the Salihli granitoid. Felsic dykes have well-preserved two sets of slip surfaces striking NE and NW in

  1. 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.

  2. Fault zone connectivity: slip rates on faults in the san francisco bay area, california.

    PubMed

    Bilham, R; Bodin, P

    1992-10-01

    The slip rate of a fault segment is related to the length of the fault zone of which it is part. In turn, the slip rate of a fault zone is related to its connectivity with adjoining or contiguous fault zones. The observed variation in slip rate on fault segments in the San Francisco Bay area in California is consistent with connectivity between the Hayward, Calaveras, and San Andreas fault zones. Slip rates on the southern Hayward fault taper northward from a maximum of more than 10 millimeters per year and are sensitive to the active length of the Maacama fault. PMID:17835127

  3. Complex Rift-Parallel, Strike-Slip Faulting in Iceland: Kinematic Analysis of the Gljúfurá Fault Zone

    NASA Astrophysics Data System (ADS)

    Nanfito, A.; Karson, J. A.

    2009-12-01

    The N-S striking Gljúfurá Fault Zone is an anomalous, dextral, strike-slip fault cutting Tertiary basaltic lavas in west-central Iceland. The fault zone is nearly parallel to structures formed at extinct spreading centers that were active from ~15 to 7 Ma ago in this region, suggesting ridge-parallel strike-slip faulting. The fault zone is well exposed in a river gorge for ~2 km along a well-defined regional lineament. The combined damage zone and fault core are about 50 m wide revealing an especially intense and complex style of deformation compared to other Icelandic fault zones. Basaltic lava flows on either side of the fault zone are cut by numerous closely spaced (10s of cm to m) Riedel shear fractures that grade into a fault core of progressively more intensely fractured lava and strongly altered and mineralized fault breccias, cataclasite and fault gouge. Riedel shears are frequently rotated or bend into the main fault zone. Distinctive bands of fault breccia derived from lava flow interiors, flow tops and dike rock are mapped for tens of meters along strike and reach thicknesses of several meters wide. Breccias contain angular basaltic fragments that range from few meters to millimeters. Fault breccias are typically clast supported with a matix of finely comminuted basalt clasts to clay gouge. 'Jigsaw' breccias are supported by a calcite matrix. Discrete faults and shear fractures show dominantly gently plunging slickenlines and abundant kinematic indicators showing dextral>normal oblique slip. Zeolite and calcite veins show multiple episodes of extension. Local left steps in fault zone are marked by extensional duplex structures with vertical separations of tens of meters bounded by major strike-slip fault strands. The overall architecture of the fault zone in interpreted as an exhumed flower structure. Numerous deformed and undeformed basaltic dikes sub-parallel the deformation structures, suggesting synkinematic intrusion. Some dikes deviate from the

  4. A Geophysical Study of the Carcavai Fault Zone, Portugal

    NASA Astrophysics Data System (ADS)

    Carvalho, J.; Ramalho, E.; Dias, R.; Pinto, C.; Ressurreição, R.

    2012-01-01

    The Algarve province is located a few hundred kilometres north of the crossing of the E-W Eurasia-Africa plate boundary in an area of diffuse seismicity and broad deformation. It is characterised by a moderate seismicity, with some important historical and instrumental earthquakes causing loss of lives and significant material damages. The area is affected not only by plate boundary earthquakes but also by moderate to large events generated by local sources. The assessment of onshore local sources is, therefore, of vital importance for an evaluation of the regional seismic hazard. This paper discusses the application of geophysical data to the study of the Carcavai fault zone, an outcropping structure more than 20 km long which is seen to deform sediments of the Plio-Quaternary age. The location of some sectors of the fault zone, as well as the vertical offsets of the structure, are still to be confirmed. In order to estimate these and to study the geometry of the fault zone at depth, geophysical data were acquired together with new geological data. Where the location of the fault was less certain, EM and seismic reflection profiles with coarse spatial sampling were carried out. After the detailed location of the fault zone, seismic reflection profiles with a more dense spatial resolution were acquired. The integrated interpretation of the geological and geophysical data confirmed the presence of a large fault zone. The total fault length is still unknown as its extension offshore is still being studied. Together with estimated values of the throw obtained, this data set has improved understanding the seismic hazard in the area by providing more refined estimates of co-seismic rupture, maximum expected earthquake and return periods.

  5. Characterization of the Hosgri Fault Zone and adjacent structures in the offshore Santa Maria Basin, south-central California: Chapter CC of Evolution of sedimentary basins/onshore oil and gas investigations - Santa Maria province

    USGS Publications Warehouse

    Willingham, C. Richard; Rietman, Jan D.; Heck, Ronald G.; Lettis, William R.

    2013-01-01

    The Hosgri Fault Zone trends subparallel to the south-central California coast for 110 km from north of Point Estero to south of Purisima Point and forms the eastern margin of the present offshore Santa Maria Basin. Knowledge of the attributes of the Hosgri Fault Zone is important for petroleum development, seismic engineering, and environmental planning in the region. Because it lies offshore along its entire reach, our characterizations of the Hosgri Fault Zone and adjacent structures are primarily based on the analysis of over 10,000 km of common-depth-point marine seismic reflection data collected from a 5,000-km2 area of the central and eastern parts of the offshore Santa Maria Basin. We describe and illustrate the along-strike and downdip geometry of the Hosgri Fault Zone over its entire length and provide examples of interpreted seismic reflection records and a map of the structural trends of the fault zone and adjacent structures in the eastern offshore Santa Maria Basin. The seismic data are integrated with offshore well and seafloor geologic data to describe the age and seismic appearance of offshore geologic units and marker horizons. We develop a basin-wide seismic velocity model for depth conversions and map three major unconformities along the eastern offshore Santa Maria Basin. Accompanying plates include maps that are also presented as figures in the report. Appendix A provides microfossil data from selected wells and appendix B includes uninterpreted copies of the annotated seismic record sections illustrated in the chapter. Features of the Hosgri Fault Zone documented in this investigation are suggestive of both lateral and reverse slip. Characteristics indicative of lateral slip include (1) the linear to curvilinear character of the mapped trace of the fault zone, (2) changes in structural trend along and across the fault zone that diminish in magnitude toward the ends of the fault zone, (3) localized compressional and extensional structures

  6. Fault-Zone Maturity Defines Maximum Earthquake Magnitude: The case of the North Anatolian Fault Zone

    NASA Astrophysics Data System (ADS)

    Bohnhoff, Marco; Bulut, Fatih; Stierle, Eva; Martinez-Garzon, Patricia; Benzion, Yehuda

    2015-04-01

    Estimating the maximum likely magnitude of future earthquakes on transform faults near large metropolitan areas has fundamental consequences for the expected hazard. Here we show that the maximum earthquakes on different sections of the North Anatolian Fault Zone (NAFZ) scale with the duration of fault zone activity, cumulative offset and length of individual fault segments. The findings are based on a compiled catalogue of historical earthquakes in the region, using the extensive literary sources that exist due to the long civilization record. We find that the largest earthquakes (M~8) are exclusively observed along the well-developed part of the fault zone in the east. In contrast, the western part is still in a juvenile or transitional stage with historical earthquakes not exceeding M=7.4. This limits the current seismic hazard to NW Turkey and its largest regional population and economical center Istanbul. Our findings for the NAFZ are consistent with data from the two other major transform faults, the San Andreas fault in California and the Dead Sea Transform in the Middle East. The results indicate that maximum earthquake magnitudes generally scale with fault-zone evolution.

  7. Structure of the North Anatolian Fault Zone from the Auto-Correlation of Ambient Seismic Noise Recorded at a Dense Seismometer Array

    NASA Astrophysics Data System (ADS)

    Taylor, D. G.; Rost, S.; Houseman, G.

    2015-12-01

    In recent years the technique of cross-correlating the ambient seismic noise wavefield at two seismometers to reconstruct empirical Green's Functions for the determination of Earth structure has been a powerful tool to study the Earth's interior without earthquake or man-made sources. However, far less attention has been paid to using auto-correlations of seismic noise to reveal body wave reflections from interfaces in the subsurface. In principle, the Green's functions thus derived should be comparable to the Earth's impulse response to a co-located source and receiver. We use data from a dense seismic array (Dense Array for Northern Anatolia - DANA) deployed across the northern branch of the North Anatolian Fault Zone (NAFZ) in the region of the 1999 magnitude 7.6 Izmit earthquake in western Turkey. The NAFZ is a major strike-slip system that extends ~1200 km across northern Turkey and continues to pose a high level of seismic hazard, in particular to the mega-city of Istanbul. We construct reflection images for the entire crust and upper mantle over the ~35 km by 70 km footprint of the 70-station DANA array. Using auto-correlations of vertical and horizontal components of ground motion, both P- and S-wave velocity information can be retrieved from the wavefield to constrain crustal structure further to established methods. We show that clear P-wave reflections from the crust-mantle boundary (Moho) can be retrieved using the autocorrelation technique, indicating topography on the Moho on horizontal scales of less than 10 km. Offsets in crustal structure can be identified that seem to be correlated with the surface expression of the fault zone in the region. The combined analysis of auto-correlations using vertical and horizontal components will lead to further insight into the fault zone structure throughout the crust and upper mantle.

  8. Fault zone architecture and fluid flow: Insights from field data and numerical modeling

    NASA Astrophysics Data System (ADS)

    Caine, Jonathan Saul; Forster, Craig B.

    Fault zones in the upper crust are typically composed of complex fracture networks and discrete zones of comminuted and geochemically altered fault rocks. Determining the patterns and rates of fluid flow in these distinct structural discontinuities is a three-dimensional problem. A series of numerical simulations of fluid flow in a set of three-dimensional discrete fracture network models aids in identifying the primary controlling parameters of fault-related fluid flow, and their interactions, throughout episodic deformation. Four idealized, but geologically realistic, fault zone architectural models are based on fracture data collected along exposures of the Stillwater Fault Zone in Dixie Valley, Nevada and geometric data from a series of normal fault zones in east Greenland. The models are also constrained by an Andersonian model for mechanically compatible fracture networks associated with normal faulting. Fluid flow in individual fault zone components, such as a fault core and damage zone, and full outcrop scale model domains are simulated using a finite element routine. Permeability contrasts between components and permeability anisotropy within components are identified as the major controlling factors in fault-related fluid flow. Additionally, the structural and hydraulic variations in these components are also major controls of flow at the scale of the full model domains. The four models can also be viewed as a set of snapshots in the mechanical evolution of a single fault zone. Changes in the hydraulic parameters within the models mimic the evolution of the permeability structure of each model through a single deformation cycle. The model results demonstrate that small changes in the architecture and hydraulic parameters of individual fault zone components can have very large impacts, up to five orders of magnitude, on the permeability structure of the full model domains. Closure of fracture apertures in each fault zone magnifies the magnitude and

  9. Development of Characterization Technology for Fault Zone Hydrology

    SciTech Connect

    Karasaki, Kenzi; Onishi, Tiemi; Gasperikova, Erika; Goto, Junichi; Tsuchi, Hiroyuki; Miwa, Tadashi; Ueta, Keiichi; Kiho, Kenzo; MIyakawa, Kimio

    2010-08-06

    Several deep trenches were cut, and a number of geophysical surveys were conducted across the Wildcat Fault in the hills east of Berkeley, California. The Wildcat Fault is believed to be a strike-slip fault and a member of the Hayward Fault System, with over 10 km of displacement. So far, three boreholes of ~;; 150m deep have been core-drilled and borehole geophysical logs were conducted. The rocks are extensively sheared and fractured; gouges were observed at several depths and a thick cataclasitic zone was also observed. While confirming some earlier, published conclusions from shallow observations about Wildcat, some unexpected findings were encountered. Preliminary analysis indicates that Wildcat near the field site consists of multiple faults. The hydraulic test data suggest the dual properties of the hydrologic structure of the fault zone. A fourth borehole is planned to penetrate the main fault believed to lie in-between the holes. The main philosophy behind our approach for the hydrologic characterization of such a complex fractured system is to let the system take its own average and monitor a long term behavior instead of collecting a multitude of data at small length and time scales, or at a discrete fracture scale and to ?up-scale,? which is extremely tenuous.

  10. Fault zone characterization using P- and S-waves

    NASA Astrophysics Data System (ADS)

    Wawerzinek, Britta; Buness, Hermann; Polom, Ulrich; Tanner, David C.; Thomas, Rüdiger

    2014-05-01

    Although deep fault zones have high potential for geothermal energy extraction, their real usability depends on complex lithological and tectonic factors. Therefore a detailed fault zone exploration using P- and S-wave reflection seismic data is required. P- and S-wave reflection seismic surveys were carried out along and across the eastern border of the Leinetal Graben in Lower Saxony, Germany, to analyse the structural setting, different reflection characteristics and possible anisotropic effects. In both directions the P-wave reflection seismic measurements show a detailed and complex structure. This structure was developed during several tectonic phases and comprises both steeply- and shallowly-dipping faults. In a profile perpendicular to the graben, a strong P-wave reflector is interpreted as shallowly west-dipping fault that is traceable from the surface down to 500 m depth. It is also detectable along the graben. In contrast, the S-waves show different reflection characteristics: There is no indication of the strong P-wave reflector in the S-wave reflection seismic measurements - neither across nor along the graben. Only diffuse S-wave reflections are observable in this region. Due to the higher resolution of S-waves in the near-surface area it is possible to map structures which cannot be detected in P-wave reflection seismic, e.g the thinning of the uppermost Jurassic layer towards the south. In the next step a petrophysical analysis will be conducted by using seismic FD modelling to a) determine the cause (lithological, structural, or a combination of both) of the different reflection characteristics of P- and S-waves, b) characterize the fault zone, as well as c) analyse the influence of different fault zone properties on the seismic wave field. This work is part of the gebo collaborative research programme which is funded by the 'Niedersächsisches Ministerium für Wissenschaft und Kultur' and Baker Hughes.

  11. Fault weakening across the frictional-viscous transition zone, Karakoram Fault Zone, NW Himalaya

    NASA Astrophysics Data System (ADS)

    Wallis, David; Phillips, Richard J.; Lloyd, Geoffrey E.

    2013-09-01

    fault rocks formed in the frictional-viscous transition zone (FVTZ) provide test material that can be used to assess the strength of natural fault zones. In the Karakoram Fault Zone (KFZ), such rocks contain evidence of several long-term weakening mechanisms associated with reduced coefficients of friction (<0.4). The Nubra, Tangtse, and Arganglas strands of the KFZ are focused along metavolcano-sedimentary formations indicating weakness relative to the bounding granitoids. Synkinematic retrogression suggests that reaction softening has weakened the margins of granitoids along the Nubra and Tangtse strands and the Nubra Formation within the Nubra strand. The resultant phyllosilicates have formed well-developed interconnected weak layers within phyllonites and granitic mylonites. Micaceous foliae with increased proportions of opaque minerals in granitic mylonites suggest that fluid-assisted diffusive mass transfer aided deformation within the Nubra and Tangtse strands. Microstructures within Nubra strand phyllonites suggest that frictional-viscous flow accommodated deformation at low shear stresses in the FVTZ. Multiple generations of veining within each strand indicate overpressured pore fluids within the fault zone across a range of depths. Active springs and travertines along the fault indicate ongoing suprahydrostatic fluid flow within the KFZ. Despite such evidence for weakening mechanisms, the KFZ is currently locked and most likely generates moment magnitude 7.5+ earthquakes. Evidence for multiple fault weakening mechanisms reduces potential for shear heating within the KFZ and suggests that the long-term strength of the lithosphere must reside below the depth of penetration of the fault.

  12. Detailed Shallow Structure and Seismic Catalog Based on Data of a Spatially-Dense Array on the San Jacinto Fault Zone

    NASA Astrophysics Data System (ADS)

    Ben-Zion, Y.

    2015-12-01

    I review results on imaging the shallow structure of San Jacinto fault zone and detection/location of seismic energy sources using data of a spatially-dense Nodal array centered on the Clark branch of the fault. The array operated at the Sage Brush site south of Anza for about 4 weeks in 2014 with 1108 vertical (10 Hz) geophones in about 650 m x 700 m box configuration. Continuous waveforms with signals generated by the ambient seismic noise, earthquakes, and Betsy gunshots were recorded with useable frequencies up to 200 Hz. Imaging the shallow structure is done with surface and body waves extracted from the ambient noise, arrivals from local and teleseismic earthquakes, and waves generated by the gunshots. The results reveal shallow material with very low seismic velocities and attenuation coefficients, strong lateral and vertical variations, seismic trapping structure, local sedimentary basin, and overall lithology contrast across the fault. The detection/location techniques include stacking, beamforming, matched field processing, and templates generated by these methods. The analysis uncovers many hundred of daily earthquakes not detected by the regional networks and several different types of surface noise sources.

  13. Earthquake faulting as a structural process

    NASA Astrophysics Data System (ADS)

    Sibson, Richard H.

    Structural geology is concerned with the history of movement in the Earth's crust and the processes by which displacements occur. In the upper one third to one half of deforming continental crust, displacement is accommodated largely by seismic slip increments on existing faults. It follows that earthquakes and related processes are an integral part of structural geology. Traditionally, structural geologists have been preoccupied with the complexity of the finite deformation within fault zones and with the stress states prevailing at the initiation of faults in intact crust. Future structural work should be directed more towards understanding the dynamic character of fault reactivation during incremental slip, and related effects. Questions of interest include rheological and geometrical controls on the initiation, perturbation and termination of ruptures; directivity effects associated with rupture propagation; the recognition of structures resulting from repeated stress cycling within seismogenic crust; and identification of structural features diagnostic of shear stress levels during faulting. Structures arising from the inter-relationships between slip episodes and induced fluid flow are of special importance, because these dynamic fault processes appear influential in the development of much fault-hosted mineralization. Mesothermal gold-quartz lodes hosted in high-angle reverse shear zones of mixed brittle-ductile character form illustrative examples of structures that, arguably, can only be interpreted by seismo-structural analysis embodying the concepts listed above.

  14. Seismic velocity models for the Denali fault zone along the Richardson Highway, Alaska

    USGS Publications Warehouse

    Brocher, T.M.; Fuis, G.S.; Lutter, W.J.; Christensen, N.I.; Ratchkovski, N.A.

    2004-01-01

    Crustal-scale seismic-velocity models across the Denali fault zone along the Richardson Highway show a 50-km-thick crust, a near vertical fault trace, and a 5-km-wide damage zone associated with the fault near Trans-Alaska Pipeline Pump Station 10, which provided the closest strong ground motion recordings of the 2002 Denali fault earthquake. We compare models, derived from seismic reflection and refraction surveys acquired in 1986 and 1987, to laboratory measurements of seismic velocities for typical metamorphic rocks exposed along the profiles. Our model for the 1986 seismic reflection profile indicates a 5-km-wide low-velocity zone in the upper 1 km of the Denali fault zone, which we interpret as fault gouge. Deeper refractions from our 1987 line image a 40-km wide, 5-km-deep low-velocity zone along the Denali fault and nearby associated fault strands, which we attribute to a composite damage zone along several strands of the Denali fault zone and to the obliquity of the seismic line to the fault zone. Our velocity model and other geophysical data indicate a nearly vertical Denali fault zone to a depth of 30 km. After-shocks of the 2002 Denali fault earthquake and our velocity model provide evidence for a flower structure along the fault zone consisting of faults dipping toward and truncated by the Denali fault. Wide-angle reflections indicate that the crustal thickness beneath the Denali fault is transitional between the 60-km-thick crust beneath the Alaska Range to the south, and the extended, 30-km-thick crust of the Yukon-Tanana terrane to the north.

  15. Cyclical Fault Permeability in the Lower Seismogenic Zone: Geological Evidence

    NASA Astrophysics Data System (ADS)

    Sibson, R. H.

    2005-12-01

    -salinity and rich in CO2. Analysis of fluid inclusions suggests that cycling of fluid pressure, in at least some instances, spanned much of the lithostatic-hydrostatic range. While the mesozonal lodes appear to represent an extreme form of fault-valve behavior, minor valving action involving smaller fluid discharges seems likely to be widespread at this structural level in seismogenic crust. The vein systems themselves represent permeability barriers allowing accumulation of fluid overpressure in subseismogenic shear zones, and may occupy part or all of the transition zone between hydrostatic and lithostatic fluid pressure regimes.

  16. The Bocono Fault Zone, Western Venezuela

    SciTech Connect

    Schubert, C. ); Estevez, R. ); Henneberg, H.G. )

    1993-02-01

    The Bocono Fault Zone, the western part of the Bocono Moron-El Pilar Fault System of the southern Caribbean plate boundary, consists of aligned valleys, linear depressions, pull-apart basins and other morphological features, which extend for about 500 km in a N45[degrees]E direction, between the Tachira depression (Venezuela-Colombia border) and the Caribbean Sea. It crosses obliquely the Cordillera de Merida and cuts across the Caribbean Mountains, two different geologic provinces of Late Tertiary-Quaternary and Late Cretaceous-Early Tertiary age, respectively. Therefore, the maximum age that can be assigned to the Bocono Fault Zone is Late Tertiary (probably Pliocene). A total maximum right-lateral offset rate of 3.3 mm/a. The age of the sedimentary fill o[approximately] the La Gonzalez pull-apart basin suggests that the 7-9 km right-lateral offset necessary to produce it took place in Middle to Late Pleistocene time. The majority of seismic events are well aligned with the main fault trace; minor events are distributed in a belt several kilometers wide. Focal depth is typically 15 km and focal mechanisms indicate an average east-west compression across the zone. Return periods of 135-460 a (Richter M = 8), 45-70 a (M = 7), and 7-15 a (M = 6) have been calculated. Geodetic studies of several sites along the zone indicate compressive and right-lateral components; at Mucubaji the rate of right-lateral displacement observed is about 1 mm every 5 months (15 a of measurements).

  17. Fluids in the damage zone: Insights from clumped isotope thermometry of fault-hosted carbonate cements

    NASA Astrophysics Data System (ADS)

    Crider, Juliet G.; Hodson, Keith R.; Huntington, Katharine W.

    2015-04-01

    Carbonate cements in fault zone rocks contain both chemical and physical information about the interaction and coevolution of their source fluids with surrounding fault rock. In this work, we present an analysis of textural relationships and isotopic compositions of carbonate cements in sandstone, within a well-characterized upper-crustal fault intersection zone, 'Courthouse Junction' along the Moab Fault in southeast Utah, USA. Structures exposed at the outcrop record several phases of overprinting brittle deformation, including cataclastic deformation bands, fracturing and faulting. Carbonate diagenesis is thought to be a later stage, possibly facilitated by an increase in fault parallel permeability. Calcite is hosted within joints and concretions associated with both deformation-band faults and fracture-based faults. We have used cathodoluminescence, oxygen and carbon isotopes, and clumped isotope paleothermometry to differentiate two populations of calcite cement in the fault intersection zone: cool (

  18. Fault zone roughness controls slip stability

    NASA Astrophysics Data System (ADS)

    Harbord, Christopher; Nielsen, Stefan; De Paola, Nicola

    2016-04-01

    Fault roughness is an important control factor in the mechanical behaviour of fault zones, in particular the frictional slip stability and subsequent earthquake nucleation. Despite this, there is little experimental quantification as to the effects of varying roughness upon rate- and state-dependant friction (RSF). Utilising a triaxial deformation apparatus and a novel adaptation of the direct shear methodology to simulate initially bare faults in Westerly Granite, we performed a series of velocity step frictional sliding experiments. Initial root mean square roughnesses (Sq) was varied in the range 6x10‑7 ‑ 2.4x10‑5 m. We also investigated the effects upon slip stability of normal stress variation in the range σn = 30 ‑ 200 MPa, and slip velocity between 0.1 ‑ 10 μm s‑1. A transition from stable sliding to unstable slip (manifested by stick-slip and slow slip events) was observed, depending on the parameter combination, thus covering the full spectrum of fault slip behaviours. At low normal stress (σn = 30MPa) smooth faults (Sq< 1x10‑6 m) are conditional unstable (stress drops on slow slip events upon velocity increase), with strongly velocity weakening friction. When normal stress is increased to intermediate values (σn = 100 ‑ 150 MPa), smooth faults (Sq< 1x10‑6 m) are fully unstable and generate seismic stick-slip behaviour. However at higher normal stress (σn = 200 MPa) a transition from unstable to stable sliding is observed for smooth faults, which is not expected using RSF stability criteria. At all conditions sliding is stable for rough faults (Sq> 1x10‑6 m). We find that instability can develop when the ratio of fault to critical stiffness kf kc > 10, or, alternatively, even when a ‑ b > 0 at σn = 150MPa, suggesting that bare surfaces may not strictly obey the R+S stability condition. Additionally we present white light interferometry and SEM analysis of experimentally deformed samples which provide information about the

  19. Constraints on Shallow Crustal Structure across the San Andreas Fault Zone, Coachella Valley, Southern California: Results from the Salton Seismic Imaging Project (SSIP)

    NASA Astrophysics Data System (ADS)

    Hernandez, A.; Persaud, P.; Bauer, K.; Stock, J. M.; Fuis, G. S.; Hole, J. A.; Goldman, M.

    2015-12-01

    The strong influence of basin structure and crustal heterogeneities on seismic wave propagation suggests that these factors should be included in calculations of strong ground shaking. Knowledge of the shallow subsurface is thus essential for an accurate seismic hazard estimate for the densely populated Coachella Valley, the region north of the potential M7.8 rupture near the Salton Sea. Using SSIP data, we analyzed first arrivals from nine 65-911 kg explosive shots recorded along a profile in the Coachella Valley in order to evaluate the interpretation of our 2D tomographic results and give added details on the structural complexity of the shallow crust. The line extends 37 km from the Peninsular Ranges to the Little San Bernardino Mountains crossing the major strands of the San Andreas Fault Zone. We fit traveltime curves to our picks with forward modeling ray tracing, and determined 1D P-wave velocity models for traveltime arrivals east and west of each shot, and a 2D model for the line. We also inferred the geometry of near-vertical faults from the pre-stack line migration method of Bauer et al. (2013). In general, the 1D models east of individual shots have deeper basement contacts and lower apparent velocities, ~5 km/s at 4 km depth, whereas the models west of individual shots have shallower basement and velocities up to 6 km/s at 2 km depth. Mismatches in basement depths (assuming 5-6 km/s) between individual 1D models indicate a shallowly dipping basement, deepening eastward towards the Banning Fault and shoaling abruptly farther east. An east-dipping structure in the 2D model also gives a better fit than horizontal layers. Based on high velocity zones derived from traveltimes at 9-20 km from the western end of the line, we included an offset from ~2 km to 4 km depth near the middle of the line, which significantly improved the 2D model fit. If fault-related, this offset could represent the Garnet Hill Fault if it continues southward in the subsurface.

  20. Fine-scale structure of the San Andreas fault zone and location of the SAFOD target earthquakes

    USGS Publications Warehouse

    Thurber, C.; Roecker, S.; Zhang, H.; Baher, S.; Ellsworth, W.

    2004-01-01

    We present results from the tomographic analysis of seismic data from the Parkfield area using three different inversion codes. The models provide a consistent view of the complex velocity structure in the vicinity of the San Andreas, including a sharp velocity contrast across the fault. We use the inversion results to assess our confidence in the absolute location accuracy of a potential target earthquake. We derive two types of accuracy estimates, one based on a consideration of the location differences from the three inversion methods, and the other based on the absolute location accuracy of "virtual earthquakes." Location differences are on the order of 100-200 m horizontally and up to 500 m vertically. Bounds on the absolute location errors based on the "virtual earthquake" relocations are ??? 50 m horizontally and vertically. The average of our locations places the target event epicenter within about 100 m of the SAF surface trace. Copyright 2004 by the American Geophysical Union.

  1. A three-dimensional study of fault zone architecture: Results from the SEMP fault system, Austria.

    NASA Astrophysics Data System (ADS)

    Frost, E. K.; Dolan, J. F.; Sammis, C. G.; Hacker, B.; Cole, J.; Ratschbacher, L.

    2008-12-01

    One of the most exciting frontiers in earthquake science is the linkage between the internal structure and mechanical behavior of fault zones. Little is known about how fault-zone structure varies as a function of depth, yet such understanding is vital if we are to understand the mechanical instabilities that control the nucleation and propagation of seismic ruptures. This has led us to the Salzach-Ennstal-Mariazell-Puchberg [SEMP] fault system in Austria, a major left-lateral strike-slip fault that has accommodated ~ 60 km of displacement during Oligo-Miocene time. Differential exhumation of the SEMP has resulted in a fault zone that reveals a continuum of structural levels along strike. This provides us with a unique opportunity to directly observe how fault-zone properties change with depth, from near-surface levels, down through the seismogenic crust, across the brittle-ductile transition, and into the uppermost part of the lower crust in western Austria. Here we present results from four key outcrops and discuss the mechanical implications of these new data. Our brittle outcrop at Gstatterboden has been exhumed from at least 4 km depth. Here the SEMP juxtaposes limestone of the Wettersteinkalk on the south against Rauwacken dolomite to the north. Faulting has produced extremely asymmetric damage, extensively shattering and shearing the dolomite while leaving the limestone largely intact. Measurements of outcrop-scale faults and fractures in the dolomite, combined with analysis of grain-size-distributions, suggest that strain has progressively localized to a zone ~ 10 m wide. These findings are compared to those from two outcrops (Kitzlochklamm and Liechtensteinklamm) that bracket the brittle-ductile transition, exhumed from depths of = 10 km. Here, the SEMP juxtaposes Greywacke Zone rocks on the north against carbonate mylonites of the Klammkalk to the south. We calculate the strain gradient in the ductile Klammkalk rocks by analyzing the lattice preferred

  2. The offshore Palos Verdes fault zone near San Pedro, Southern California

    USGS Publications Warehouse

    Fisher, M.A.; Normark, W.R.; Langenheim, V.E.; Calvert, A.J.; Sliter, R.

    2004-01-01

    High-resolution seismic-reflection data are combined with a variety of other geophysical and geological data to interpret the offshore structure and earthquake hazards of the San Pedro shelf, near Los Angeles, California. Prominent structures investigated include the Wilmington graben, the Palos Verdes fault zone, various faults below the west part of the San Pedro shelf and slope, and the deep-water San Pedro basin. The structure of the Palos Verdes fault zone changes markedly along strike southeastward across the San Pedro shelf and slope. Under the north part of the shelf, this fault zone includes several strands, with the main strand dipping west. Under the slope, the main fault strands exhibit normal separation and mostly dip east. To the southeast near Lasuen Knoll, the Palos Verdes fault zone locally is low angle, but elsewhere near this knoll, the fault dips steeply. Fresh seafloor scarps near Lasuen Knoll indicate recent fault movement. We explain the observed structural variation along the Palos Verdes fault zone as the result of changes in strike and fault geometry along a master right-lateral strike-slip fault at depth. Complicated movement along this deep fault zone is suggested by the possible wave-cut terraces on Lasuen Knoll, which indicate subaerial exposure during the last sea level lowstand and subsequent subsidence of the knoll. Modeling of aeromagnetic data indicates a large magnetic body under the west part of the San Pedro shelf and upper slope. We interpret this body to be thick basalt of probable Miocene age. This basalt mass appears to have affected the pattern of rock deformation, perhaps because the basalt was more competent during deformation than the sedimentary rocks that encased the basalt. West of the Palos Verdes fault zone, other northwest-striking faults deform the outer shelf and slope. Evidence for recent movement along these faults is equivocal, because we lack age dates on deformed or offset sediment.

  3. Coseismic stresses indicated by pseudotachylytes in the Outer Hebrides Fault Zone, UK.

    NASA Astrophysics Data System (ADS)

    Campbell, Lucy; Lloyd, Geoffrey; Phillips, Richard; Holdsworth, Robert; Walcott, Rachel

    2015-04-01

    During the few seconds of earthquake slip, dynamic behaviour is predicted for stress, slip velocity, friction and temperature, amongst other properties. Fault-derived pseudotachylyte is a coseismic frictional melt and provides a unique snapshot of the rupture environment. Exhumation of ancient fault zones to seismogenic depths can reveal the structure and distribution of seismic slip as pseudotachylyte bearing fault planes. An example lies in NW Scotland along the Outer Hebrides Fault Zone (OHFZ) - this long-lived fault zone displays a suite of fault rocks developed under evolving kinematic regimes, including widespread pseudotachylyte veining which is distributed both on and away from the major faults. This study adds data derived from the OHFZ pseudotachylytes to published datasets from well-constrained fault zones, in order to explore the use of existing methodologies on more complex faults and to compare the calculated results. Temperature, stress and pressure are calculated from individual fault veins and added to existing datasets. The results pose questions on the physical meaning of the derived trends, the distribution of seismic energy release across scattered cm-scale faults and the range of earthquake magnitudes calculated from faults across any given fault zone.

  4. Midcontinent U.S. fault and fold zones: A legacy of Proterozoic intracratonic extensional tectonism?

    NASA Astrophysics Data System (ADS)

    Marshak, Stephen; Paulsen, Timothy

    1996-02-01

    The U.S. continental interior (midcontinent) contains numerous fault and fold zones. Seismic and drilling data indicate that some of these zones first formed as Proterozoic-Eocambrian rift faults, but the origin of most remains enigmatic. We propose that the enigmatic fault and fold zones also began as Proterozoic-Eocambrian normal faults. We base our hypothesis on the following: (1) enigmatic zones parallel known rifts, (2) the structural style of enigmatic zones mirrors the structural style of known rifts, (3) the map pattern of some enigmatic zones (e.g., the La Salle deformation belt of Illinois) resembles the map pattern of contemporary rifts, and (4) it is easier to rupture an intact craton by normal faulting than by reverse or strike-slip faulting. These zones, along with known rifts, represent the legacy of widespread extensional tectonism that brittlely broke up the craton into fault-bounded blocks prior to deposition of Phanerozoic platform cover. Once formed, midcontinent fault and fold zones remained weak, allowing cratonic blocks to jostle relative to one another during the Phanerozoic, thereby inverting faults (and creating transpressional or transtensional structural assemblages), localizing seismicity, and channeling (or releasing) ore-generating fluids.

  5. Structure of the 1906 near-surface rupture zone of the San Andreas Fault, San Francisco Peninsula segment, near Woodside, California

    USGS Publications Warehouse

    Rosa, C.M.; Catchings, R.D.; Rymer, M.J.; Grove, Karen; Goldman, M.R.

    2016-01-01

    High-resolution seismic-reflection and refraction images of the 1906 surface rupture zone of the San Andreas Fault near Woodside, California reveal evidence for one or more additional near-surface (within about 3 meters [m] depth) fault strands within about 25 m of the 1906 surface rupture. The 1906 surface rupture above the groundwater table (vadose zone) has been observed in paleoseismic trenches that coincide with our seismic profile and is seismically characterized by a discrete zone of low P-wave velocities (Vp), low S-wave velocities (Vs), high Vp/Vs ratios, and high Poisson’s ratios. A second near-surface fault strand, located about 17 m to the southwest of the 1906 surface rupture, is inferred by similar seismic anomalies. Between these two near-surface fault strands and below 5 m depth, we observed a near-vertical fault strand characterized by a zone of high Vp, low Vs, high Vp/Vs ratios, and high Poisson’s ratios on refraction tomography images and near-vertical diffractions on seismic-reflection images. This prominent subsurface zone of seismic anomalies is laterally offset from the 1906 surface rupture by about 8 m and likely represents the active main (long-term) strand of the San Andreas Fault at 5 to 10 m depth. Geometries of the near-surface and subsurface (about 5 to 10 m depth) fault zone suggest that the 1906 surface rupture dips southwestward to join the main strand of the San Andreas Fault at about 5 to 10 m below the surface. The 1906 surface rupture forms a prominent groundwater barrier in the upper 3 to 5 m, but our interpreted secondary near-surface fault strand to the southwest forms a weaker barrier, suggesting that there has been less or less-recent near-surface slip on that strand. At about 6 m depth, the main strand of the San Andreas Fault consists of water-saturated blue clay (collected from a hand-augered borehole), which is similar to deeply weathered serpentinite observed within the main strand of the San Andreas Fault at

  6. Crustal heterogeneity and earthquake generating properties in and around the Yamasaki fault zone, Southwest Japan

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    We have been estimating crustal heterogeneous structure and earthquake generating properties in and around the Yamasaki fault zone, which is a left-lateral strike-slip active fault with a total length of ~80 km in southwest Japan. We deployed dense seismic observation network, composed of 32 stations with average spacing of ~10 km around the Yamasaki fault zone. We will estimate detailed fault structure such as fault dip and shape, segmentation, and possible location of asperities and rupture initiation point, as well as generating properties of earthquakes in the fault zone, through analyses of accurate hypocenter distribution, focal mechanism, 3-D velocity tomography, coda wave inversion, and other waveform analyses. We also deployed a linear seismic array across the fault, composed of 20 stations with ~20 m spacing, in order to delineate the fault-zone structure in more detail using the seismic waves trapped inside the low velocity zone. We also estimate detailed resistivity structure of the fault zone by AMT (audio-frequency magnetotelluric) and MT surveys. In the scattering analysis of coda waves, we used 1,762 wave traces from 106 earthquakes that occurred in 2002, 2003, and 2008, recorded at 60 stations, including dense temporary and routine stations. We estimated 3-D distribution of relative scattering coefficients along the Yamasaki fault zone. Microseismicity is high and scattering coefficient is relatively larger in the upper crust along the entire fault zone. The distribution of strong scatterers suggests that the Ohara and Hijima faults, which are the segments in the northwestern part of the Yamasaki fault zone, have almost vertical fault plane from surface to a depth of ~15 km. We used seismic network data operated by Universities, NIED, AIST, and JMA. This study has been carried out as a part of the project "Study on evaluation of earthquake source faults based on surveys of inland active faults" by Japan Nuclear Energy Safety Organization (JNES

  7. Fault-zone attenuation of high-frequency seismic waves

    SciTech Connect

    Blakeslee, S.; Malin, P.; Alvarez, M. )

    1989-11-01

    The authors have developed a technique to measure seismic attenuation within an active fault-zone at seismogenic depths. Utilizing a pair of stations and pairs of earthquakes, spectral ratios are performed to isolate attenuation produced by wave-propagation within the fault-zone. The empirical approach eliminates common source, propagation, instrument and near-surface site effects. The technique was applied to a cluster of 19 earthquakes recorded by a pair of downhole instruments located within the San Andreas fault-zone, at instruments located within the San Andreas fault-zone, at Parkfield, California. Over the 1-40 Hz bandwidth used in this analysis, amplitudes are found to decrease exponentially with frequency. Furthermore, the fault-zone propagation distance correlates with severity of attenuation. Assuming a constant Q attenuation operator, the S-wave quality factor within the fault-zone at a depth of 5-6 kilometers is 31 (+7,{minus}5). If fault-zones are low-Q environments, then near-source attenuation of high-frequency seismic waves may help to explain phenomenon such as f{sub max}. Fault-zone Q may prove to be a valuable indicator of the mechanical behavior and rheology of fault-zones. Specific asperities can be monitored for precursory changes associated with the evolving stress-field within the fault-zone. The spatial and temporal resolution of the technique is fundamentally limited by the uncertainty in earthquake location and the interval time between earthquakes.

  8. Comparative geometry of the San Andreas Fault, California, and laboratory fault zones

    USGS Publications Warehouse

    Moore, Diane E.; Byerlee, J.D.

    1991-01-01

    Textural examination of fault gouge deformed in triaxial friction experiments has revealed differences in the orientations of secondary shear sets between the stably sliding and stick-slip samples. In order to determine whether such differences can be identified in natural faults, maps of recently active breaks along the San Andreas fault were examined to compare the types and orientations of secondary structures mapped in the creeping and locked sections. The fault zone was divided into 52 geometrically defined segments of uniform strike, which were then grouped into 7 sections: 4 straight and two curved sections, and Cholame Valley. Many of the gross geometric characteristics of the individual segments, such as length, width, and stepover size, reflect their position in either a straight or a curved section. In contrast, with respect to the orientations of the recent breaks within the segments, the single creeping section differs from all of the locked sections, both straight and curved. -from Authors

  9. Recurrent late Quaternary surface faulting along the southern Mohawk Valley fault zone, NE California

    SciTech Connect

    Sawyer, T.L.; Hemphill-Haley, M.A. ); Page, W.D. )

    1993-04-01

    The Mohawk Valley fault zone comprises NW- to NNW-striking, normal and strike-slip( ) faults that form the western edge of the Plumas province, a diffuse transitional zone between the Basin and Range and the northern Sierra Nevada. The authors detailed evaluation of the southern part of the fault zone reveals evidence for recurrent late Pleistocene to possibly Holocene, moderate to large surface-faulting events. The southern Mohawk fault zone is a complex, 6-km-wide zone of faults and related features that extends from near the crest of the Sierra Nevada to the middle of southern Sierra Valley. The fault zone has two distinct and generally parallel subzones, 3 km apart, that are delineated by markedly different geomorphic characteristics and apparently different styles of faulting. Paleoseismic activity of the western subzone was evaluated in two trenches: one across a fault antithetic to the main range-bounding fault, and the other across a splay fault delineated by a 3.7-m-high scarp in alluvium. Stratigraphic relations, soil development, and radiocarbon dates indicate that at least four mid- to late-Pleistocene surface-faulting events, having single-event displacements in excess of 1.6 to 2.6 m, occurred along the splay fault prior to 12 ka. The antithetic fault has evidence of three late Pleistocene events that may correspond to event documented on the splay fault, and a Holocene event that is inferred from youthful scarplets and small closed depressions.

  10. Distributed transpressive continental deformation: The Varto Fault Zone, eastern Turkey

    NASA Astrophysics Data System (ADS)

    Sançar, Taylan; Zabcı, Cengiz; Akyüz, H. Serdar; Sunal, Gürsel; Villa, Igor M.

    2015-10-01

    The convergence between the Eurasian and Arabian plates has created a complicated structural setting in the Eastern Turkish high plateau (ETHP), particularly around the Karlıova Triple Junction (KTJ) where the Eurasian, Arabian, and Anatolian plates intersect. This region of interest includes the junction of the North Anatolian Shear Zone (NASZ) and the East Anatolian Shear Zone (EASZ), which forms the northern border of the westwardly extruding Anatolian Scholle and the western boundary of the ETHP, respectively. In this study, we focused on a poorly studied component of the KTJ, the Varto Fault Zone (VFZ), and the adjacent secondary structures, which have complex structural settings. Through integrated analyses of remote sensing and field observations, we identified a widely distributed transpressional zone where the Varto segment of the VFZ forms the most northern boundary. The other segments, namely, the Leylekdağ and Çayçatı segments, are oblique-reverse faults that are significantly defined by uplifted topography along their strikes. The measured 515 and 265 m of cumulative uplifts for Mt. Leylek and Mt. Dodan, respectively, yield a minimum uplift rate of 0.35 mm/a for the last 2.2 Ma. The multi-oriented secondary structures were mostly correlated with "the distributed strike-slip" and "the distributed transpressional" in analogue experiments. The misfits in strike of some of secondary faults between our observations and the experimental results were justified by about 20° to 25° clockwise restoration of all relevant structures that were palaeomagnetically measured to have happened since ~ 2.8 Ma ago. Our detected fault patterns and their true nature are well aligned as being part of a transpressional tectonic setting that supports previously suggested stationary triple junction models.

  11. Mesoscopic structure of the Punchbowl Fault, Southern California and the geologic and geophysical structure of active strike-slip faults

    NASA Astrophysics Data System (ADS)

    Schulz, Steven E.; Evans, James P.

    2000-07-01

    We examine the distribution, density, and orientation of outcrop-scale structures related to the Punchbowl Fault, an exhumed ancient trace of the San Andreas Fault, southern California, in order to determine the structure of the fault zone. The Punchbowl Fault has 44 km of right-lateral slip, and cuts the Cretaceous Pelona Schist in the study area. The mesoscopic structures examined include fractures, small faults, and veins; they were inventoried using scan lines at closely spaced stations along three strike-perpendicular traverses 200-250 m long across the fault. The fault zone thickness is a function of the type of structure measured. Slip along narrow (<2 m wide) ultracataclasite cores of the faults results in foliation reorientation over a distance of 50 m from the cores: fracture and fault densities appear to increase 50-80 m from the fault cores, and vein densities are highly variable across the fault zone. Fractures and faults in the damaged zone have a variety of orientations, but most are at high angles to the main fault zone. When coupled with previous geochemical and microstructural data, these data show that large-displacement faults of the San Andreas system, are up to 200-250 m thick, and enclose zones of mineralogic and geochemical alteration that are 20-30 m thick. Extreme slip localization occurs over zones 1-5 m thick. When reconciled with geophysical imaging, our data suggest that trapped headwaves travel in the damaged zone, and that some aftershock events produce slip on faults and fractures, which often have orientations very different from the principal slip surfaces.

  12. Fault Zone Guided Wave generation on the locked, late interseismic Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Eccles, J. D.; Gulley, A. K.; Malin, P. E.; Boese, C. M.; Townend, J.; Sutherland, R.

    2015-07-01

    Fault Zone Guided Waves (FZGWs) have been observed for the first time within New Zealand's transpressional continental plate boundary, the Alpine Fault, which is late in its typical seismic cycle. Ongoing study of these phases provides the opportunity to monitor interseismic conditions in the fault zone. Distinctive dispersive seismic codas (~7-35 Hz) have been recorded on shallow borehole seismometers installed within 20 m of the principal slip zone. Near the central Alpine Fault, known for low background seismicity, FZGW-generating microseismic events are located beyond the catchment-scale partitioning of the fault indicating lateral connectivity of the low-velocity zone immediately below the near-surface segmentation. Initial modeling of the low-velocity zone indicates a waveguide width of 60-200 m with a 10-40% reduction in S wave velocity, similar to that inferred for the fault core of other mature plate boundary faults such as the San Andreas and North Anatolian Faults.

  13. Geophysical investigation of landslides and fault scarps in the Hockai Fault Zone, Belgium

    NASA Astrophysics Data System (ADS)

    Mreyen, Anne-Sophie; Havenith, Hans-Balder; Fernandez-Steeger, Tomas

    2016-04-01

    During several years, a series of geophysical surveys have been carried out in East Belgium to study the seismically active Hockai Fault Zone (HFZ). The most prominent earthquake that occurred in that fault zone is the 1692 Verviers Earthquake with a magnitude of M6-6.5; it is also the largest historical seismic event in NW Europe. The geomorphic impact of the fault zone is expressed by several landslides, NW-SE orientated scarps and paleo-valleys generated by river diversions. The NW part of the HFZ (near Battice, Belgium) is also known as the Graben de la Minerie; here, geophysical measurements confirmed the presence of a series of fault scarps and helped imaging the general basin structure related to vertical offsets of coal seams that had been found during former mining works. In the southern part of the HFZ, the ENE-SWS orientated Paleo-Warche-Valley (that was formed before upstream capturing of the Warche River) crosses the fault zone over a distance of 5 km. The shallow subsurface of this area was further investigated by geophysics to identify fault structures. The work presented here is focused on the SE prolongation of the HFZ (region of Malmedy, Belgium). Two new clear morphological markers unknown before were detected through analysis of a LiDAR-DEM recently published by the Walloon Region. The following geological-geomorphic survey confirmed the presence of a NNW-SSE oriented, 100 m long and 20 m high, scarp and an associated landslide (about 8 ha) with minimum age of 300 years. The landslide was formed in the Poudingue de Malmedy, a local Permian conglomerate lying on top of a quartz-phyllite bedrock. Different geophysical methods were applied to investigate the subsurface: microseismic measurements (H/V method), seismic refraction tomography (combined with surface wave analysis) and electrical resistivity tomography. To establish the structural relationship between the fault scarp and the landslide and to estimate the offset of the Poudingue de

  14. The evolution of faults formed by shearing across joint zones in sandstone

    NASA Astrophysics Data System (ADS)

    Myers, Rodrick; Aydin, Atilla

    2004-05-01

    The evolution of strike-slip and normal faults formed by slip along joint zones is documented by detailed field studies in the Jurassic Aztec Sandstone in the Valley of Fire State Park, Nevada, USA. Zones of closely spaced planar sub-parallel joints arranged en échelon are sheared, forming faults. Fracturing occurs as a result of shearing, forming new joints. Later shearing along these joints leads to successively formed small faults and newer joints. This process is repeated through many generations of fracturing with increasing fault slip producing a hierarchical array of structures. Strain localization produced by shearing of joint zones at irregularities in joint traces, fracture intersections, and in the span between adjacent sheared joints results in progressive fragmentation of the weakened sandstone, which leads to the formation of gouge along the fault zone. The length and continuity of the gouge and associated slip surfaces is related to the slip magnitude and fault geometry with slip ranging from several millimeters to about 150 m. Distributed damage in a zone surrounding the gouge core is related to the original joint zone configuration (step sense, individual sheared joint overlaps and separation), shear sense, and slip magnitude. Our evolutionary model of fault development helps to explain some outstanding issues concerning complexities in faulting such as, the variability in development of fault rock and fault related fractures, and the failure processes in faults.

  15. The Bear River Fault Zone, Wyoming and Utah: Complex Ruptures on a Young Normal Fault

    NASA Astrophysics Data System (ADS)

    Schwartz, D. P.; Hecker, S.; Haproff, P.; Beukelman, G.; Erickson, B.

    2012-12-01

    The Bear River fault zone (BRFZ), a set of normal fault scarps located in the Rocky Mountains at the eastern margin of Basin and Range extension, is a rare example of a nascent surface-rupturing fault. Paleoseismic investigations (West, 1994; this study) indicate that the entire neotectonic history of the BRFZ may consist of two large surface-faulting events in the late Holocene. We have estimated a maximum per-event vertical displacement of 6-6.5 m at the south end of the fault where it abuts the north flank of the east-west-trending Uinta Mountains. However, large hanging-wall depressions resulting from back rotation, which front scarps that locally exceed 15 m in height, are prevalent along the main trace, obscuring the net displacement and its along-strike distribution. The modest length (~35 km) of the BRFZ indicates ruptures with a large displacement-to-length ratio, which implies earthquakes with a high static stress drop. The BRFZ is one of several immature (low cumulative displacement) normal faults in the Rocky Mountain region that appear to produce high-stress drop earthquakes. West (1992) interpreted the BRFZ as an extensionally reactivated ramp of the late Cretaceous-early Tertiary Hogsback thrust. LiDAR data on the southern section of the fault and Google Earth imagery show that these young ruptures are more extensive than currently mapped, with newly identified large (>10m) antithetic scarps and footwall graben. The scarps of the BRFZ extend across a 2.5-5.0 km-wide zone, making this the widest and most complex Holocene surface rupture in the Intermountain West. The broad distribution of Late Holocene scarps is consistent with reactivation of shallow bedrock structures but the overall geometry of the BRFZ at depth and its extent into the seismogenic zone are uncertain.

  16. Scaling Between Fault Length, Damaged Zone Thickness and Width of Secondary Fault Fans Derived from Fracture Mechanics

    NASA Astrophysics Data System (ADS)

    Ampuero, Jean Paul; Mao, Xiaolin

    2016-04-01

    The interaction between earthquakes, fault network geometry and fault zone structure is a key question motivating the integration of dynamic rupture and long-term crustal deformation modeling. Here, we address the scaling between fault structural properties from the perspective of dynamic and quasi-static processes involved in fault system evolution. Faults are surrounded by materials damaged through quasi-static and dynamic processes, forming damaged zones whose thickness and damage intensity may vary as a function of fault maturity and length. In the vicinity (typically less than a few hundred meters) of their principal slip surface, faults develop an "inner damage zone", usually characterized by micro-fracture observations. At a larger scale, faults develop an "outer damage zone" of secondary macroscopic fault branches at their tips, which organize into fans of splay faults. Inner damage zones can significantly affect earthquake ruptures, enhance near-field ground motions and facilitate fluid transport in the crust. Fault zone trapped waves can generate pulse-like rupture and oscillatory rupture speed, facilitate supershear rupture transition and allow for steady rupture propagation at speeds that are unstable or inadmissible in homogeneous media. The effects of a fault damage zone crucially depend on its thickness. Field observations of inner damage zone thickness as a function of cumulated slip show linear scaling at small slip but saturation at large slip, with maximum damage zone thickness of a few hundred meters. We previously developed fracture mechanics theoretical arguments and dynamic rupture simulations with off-fault inelastic deformation that predict saturation of the thickness of co-seismic damage zone controlled by the depth extent of the seismogenic zone. In essence, the stress intensity factor at the front of a rupture, which controls the distance reached by the large off-fault stresses that cause damage, scales with the shortest characteristic

  17. Interplay between magmatic accretion, spreading asymmetry and detachment faulting at a segment end: Crustal structure south of the Ascension Fracture Zone

    NASA Astrophysics Data System (ADS)

    Bialas, Jörg; Dannowski, Anke; Reston, Timothy J.

    2015-12-01

    A wide-angle seismic section across the Mid-Atlantic Ridge just south of the Ascension transform system reveals laterally varying crustal thickness, and to the east a strongly distorted Moho that appears to result from slip along a large-offset normal fault, termed an oceanic detachment fault. Gravity modelling supports the inferred crustal structure. We investigate the interplay between magmatism, detachment faulting and the changing asymmetry of crustal accretion, and consider several possible scenarios. The one that appears most likely is remarkably simple: an episode of detachment faulting which accommodates all plate divergence and results in the westward migration of the ridge axis, is interspersed with dominantly magmatic and moderately asymmetric (most on the western side) spreading which moves the spreading axis back towards the east. Following the runaway weakening of a normal fault and its development into an oceanic detachment fault, magma both intrudes the footwall to the fault, producing a layer of gabbro (subsequently partially exhumed).

  18. The internal deformation of the Peridotite Nappe of New Caledonia: A structural study of serpentine-bearing faults and shear zones in the Koniambo Massif

    NASA Astrophysics Data System (ADS)

    Quesnel, Benoît; Gautier, Pierre; Cathelineau, Michel; Boulvais, Philippe; Couteau, Clément; Drouillet, Maxime

    2016-04-01

    We present a structural analysis of serpentine-bearing faults and shear zones in the Koniambo Massif, one of the klippes of the Peridotite Nappe of New Caledonia. Three structural levels are recognized. The upper level is characterized by a dense network of fractures. Antigorite and polygonal serpentine form slickenfibers along fault planes with distinct kinematics. As a result, the upper level keeps the record of at least two deformation events, the first associated with the growth of antigorite (WNW-ESE extension), the second with the growth of polygonal serpentine (NW-SE compression). The lower level coincides with the 'serpentine sole' of the nappe, which consists of massive tectonic breccias overlying a layer of mylonitic serpentinites. The sole records pervasive tangential shear with top-to-SW kinematics and represents a décollement at the base of the nappe. The intermediate level is characterized by the presence of several meters-thick conjugate shear zones accommodating NE-SW shortening. Like the sole, these shear zones involve polygonal serpentine and magnesite as the main syn-kinematic mineral phases. The shear zones likely root into the basal décollement, either along its roof or, occasionally, around its base. Compared to top-to-SW shearing along the sole, the two deformation events recorded in the upper level are older. The three structural levels correlate well with previously recognized spatial variations in the degree of serpentinization. It is therefore tempting to consider that the intensity of serpentinization played a major role in the way deformation has been distributed across the Peridotite Nappe. However, even the least altered peridotites, in the upper level, contain so much serpentine that, according to theoretical and experimental work, they should be nearly as weak as pure serpentinite. Hence, no strong vertical gradient in strength due to variations in the degree of serpentinization is expected within the exposed part of the nappe

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

    NASA Astrophysics Data System (ADS)

    Iacopini, David; Butler, Rob; Purves, Steve

    2013-04-01

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

  20. Observation and Modeling of Fault Damage Zones at Reservoir Depths

    NASA Astrophysics Data System (ADS)

    Johri, M.; Zoback, M. D.; Dunham, E. M.; Hennings, P.

    2011-12-01

    We report a study of sub-surface fault damage zones adjacent to the San Andreas Fault in central California and series of first- and second-order faults in a gas field in Southeast Asia. We compare the observations with theoretically-predicted damage zones from dynamic rupture propagation modeling. The importance of characterizing damage zones arises from the important role that damage zones and natural fractures play in governing fluid flow in low permeability rocks. While there are many published studies of exposed damage zones, there is an absence of studies utilizing subsurface data that characterizes damage zones at depth. Damage zones associated with second-order faults adjacent to the San Andreas Fault are studied in well-cemented arkosic sandstones immediately southwest of the fault at the SAFOD site using electrical image logs and physical property measurements. The peak fracture intensity is between three and six fractures per meter in thee damage zones which persist about 50-80 meters from the second-order faults. Fracture intensity in these damage zones in both the regions of study decreases according to a power law where the rate of decrease is approximately -0.8 . The gas reservoir in Southeast Asia is associated with a large, basement master fault and twenty-seven seismically resolvable second-order faults. Four to seven fractures per meter are observed in electrical image logs from five wells in the 50-80m wide damage zones of the second-order faults. The second part of this work involves predicting damage zone widths utilizing two-dimensional plane-strain dynamic rupture models with strong rate-weakening fault friction and off-fault Drucker-Prager plasticity. The number of induced third-order faults and fractures are calculated by assuming that the dilatational plastic strain is manifested in the form of discrete fault planes. The theoretical results suggest that the damage zones are approximately 60-100 meters wide and the fracture intensity

  1. Comparing Biases of Fault Zone Permeability Magnitudes and Inferred Conceptual Models - Global Multidisciplinary Compilation and Mapping

    NASA Astrophysics Data System (ADS)

    Scibek, J.

    2015-12-01

    Although fault zones have been studied worldwide, there have been no global mapping, compilation and meta-analysis of interpretations of the fault zone permeability structures and/or methodological biases. To investigate biases in data collection sources we review ~2000 published studies and reports and summarize categorical data from over 600 cases, including ~200 studies with reported fault zone permeability, transmissivity, or diffusivity estimates from the fault damage zone, fault core, whole fault zone, and protolith. The data are categorized into fault zone permeability structures (e.g. barrier, conduit, barrier-conduit, etc.) and are evaluated with respect to the type of fluid flow or permeability observation, the data collection source (e.g. studies in structural geology, hydrogeology, tunneling, mining, engineering, etc.), and on the scale of measurement. Our results show that the combined conduit-barrier fault zone structure is observed in only 15-20% of the cases (but up to 60% of structural geology cases if paleo-conduit studies are included). The barrier structure is observed in ~30% of the faults in structural geology, hydrogeology, and mining studies, and in over 40% petroleum engineering studies, but in less than 10% in tunnel engineering and rarely in geothermal engineering. The barrier nature of faults is detected primarily with qualitative observations (water levels and pressures, water geochemistry), and is difficult to measure in the subsurface. Some hydrogeological observations favour the detection of hydraulic barriers or conduits, but not both equally. Therefore, the frequency of fault zone conceptual models (barriers/conduits) globally or within a region may be a result of measurement bias and not of actual conditions. We also compare reported permeability values at three scales of measurement: matrix permeability, small scale fractured bulk permeability, and whole fault zone permeability. The quantitative permeability anisotropy or scaling

  2. Geometric and kinematic controls on the internal structure of a large normal fault in massive limestones: The Maghlaq Fault, Malta

    NASA Astrophysics Data System (ADS)

    Bonson, C. G.; Childs, C.; Walsh, J. J.; Schöpfer, M. P. J.; Carboni, V.

    2007-02-01

    The Maghlaq Fault is a large, left-stepping normal fault (displacement >210 m) cutting the Oligo-Miocene pre- to syn-rift carbonates of SW Malta. Two principal slip zones separate the deformed rocks of the fault zone from the undeformed wall rocks. Fault rocks derived from fully lithified, pre- to early syn-rift sediments comprise relatively continuous fine-grained veneers of cataclasite and localised fault-bound lenses of wall rock, occurring over a range of scales, which are commonly brecciated. The lenses result from the linkage of slip surfaces, the inclusion of asperities and the formation of Riedel shears within the fault zone. In contrast, fault rock incorporated from unlithified syn-rift sediments comprise relatively continuous veils of rock that deformed in a ductile manner. Anomalously thick parts of the fault zone with highly complex structure and content are associated with breached relay zones, branch-lines and bends; these structures represent progressive stages of fault segment linkage. The progressive evolution and bypassing of fault zone complexities to form a smoother and more continuous active fault surface, results in complex fault rock distributions within the fault zone. Segment linkage structures have high fracture densities which combined with their significant vertical extents suggest they are potentially important up-fault fluid flow conduits.

  3. Fault zone reverberations from cross-correlations of earthquake waveforms and seismic noise

    NASA Astrophysics Data System (ADS)

    Hillers, Gregor; Campillo, Michel

    2016-03-01

    Seismic wavefields interact with low-velocity fault damage zones. Waveforms of ballistic fault zone head waves, trapped waves, reflected waves and signatures of trapped noise can provide important information on structural and mechanical fault zone properties. Here we extend the class of observable fault zone waves and reconstruct in-fault reverberations or multiples in a strike-slip faulting environment. Manifestations of the reverberations are significant, consistent wave fronts in the coda of cross-correlation functions that are obtained from scattered earthquake waveforms and seismic noise recorded by a linear fault zone array. The physical reconstruction of Green's functions is evident from the high similarity between the signals obtained from the two different scattered wavefields. Modal partitioning of the reverberation wavefield can be tuned using different data normalization techniques. The results imply that fault zones create their own ambiance, and that the here reconstructed reverberations are a key seismic signature of wear zones. Using synthetic waveform modelling we show that reverberations can be used for the imaging of structural units by estimating the location, extend and magnitude of lateral velocity contrasts. The robust reconstruction of the reverberations from noise records suggests the possibility to resolve the response of the damage zone material to various external and internal loading mechanisms.

  4. Structural and geomorphic fault segmentations of the Doruneh Fault System, central Iran

    NASA Astrophysics Data System (ADS)

    Farbod, Yassaman; Bellier, Olivier; Shabanian, Esmaeil; Abbassi, Mohammad Reza

    2010-05-01

    The active tectonics of Iran results from the northward Arabia-Eurasia convergence at a rate of ~22±2 mm/yr at the longitude of Bahrain (e.g., Sella et al., 2002). At the southwestern and southern boundaries of the Arabia-Eurasia collision zone, the convergence is taken up by the continental collision in the Zagros Mountains, and the active subduction of Makran, respectively. Further north, the northward motion not absorbed by the Makran subduction is expressed as the N-trending right lateral shear between central Iran and Eurasia at a rate of ~16 mm/yr (e.g., Regard et al., 2005; Vernant et al, 2004). This shear involves N-trending right-lateral fault systems, which are extended at both sides of the Lut block up to the latitude of 34°N. North of this latitude, about 35°N, the left-lateral Doruneh Fault separates the N-trending right-lateral fault systems from the northern deformation domains (i.e., the Alborz, Kopeh Dagh and Binalud mountain ranges). At the Iranian tectonic scale, the Doruneh Fault represents a curved-shape, 600-km-long structure through central Iran, which runs westward from the Iran-Afghanistan boundary (i.e., the eastern boundary of the Arabia-Eurasia collision zone) to the Great Kavir desert. Nevertheless, east of the longitude of 56°45'E, the fault is expressed as an E-trending ~360-km-long fault (hereinafter the Doruneh Fault System - DFS) having a geological evolution history different from the western part (the Great Kavir Fault System). In this study, we look for characterizing geomorphic and structural features of active faulting on the DFS. Detailed structural and geomorphic mapping based on satellite Imageries (SPOT5 and Landsat ETM+) and SRTM digital topographic data, complemented with field surveys allowed us to establish structural and geomorphic segmentations along the DFS. According to our observations, the DFS is comprised of three distinct fault zones: (1) The 100-km-long, N75°E-trending western fault zone, which is

  5. Geomorphic and Structural Analysis of the Verona-Williams-Pleasanton fault zone and implications for seismic hazard, eastern San Francisco Bay Area, California

    NASA Astrophysics Data System (ADS)

    Sawyer, T. L.; Unruh, J. R.; Hoirup, D. F.; Barry, G.; Pearce, J. T.

    2012-12-01

    Folds and thrust faults adjacent to and beneath the Livermore Valley have accommodated Quaternary crustal shortening between major dextral faults of the eastern San Andreas fault system. The Verona and Williams faults are NE-dipping thrust or reverse faults that have uplifted the Pliocene-Pleistocene Livermore gravels along the western and southern margins of the valley. The Williams fault extends ~13 km northwest from the Mt. Lewis seismic trend to the sinistral Las Positas fault, which forms the southern margin of the valley. A 3-km left step along the Las Positas fault separates the surface traces of the Verona and Williams faults. The Verona fault extends ~8 km northwest from the stepover to southwestern Livermore Valley. It is possible that the Las Positas fault extends to the base of the seismogenic crust and separates the Verona and Williams faults into two kinematically independent structures. Alternatively, the Verona and Williams faults may merge downdip into a common thrust fault plane, with the Las Positas fault confined to the hanging wall as a tear fault. The Verona and Williams faults exhibit geomorphic evidence for late Quaternary fault rupture propagating to or very near the ground surface. The Williams fault tightly folds and overturns the Livermore gravels, and appears to form scarps that impound late Quaternary alluvium and cross Holocene landslide deposits. Many Holocene(?) alluvial fans exhibit distinct convex longitudinal profiles across the fault trace suggesting active folding above the Verona fault. The geomorphic position of a stream-terrace remnant suggests that >7 m of tectonic uplift is possible across the Verona fault during the late Quaternary. Surficial geologic mapping and geomorphic analysis of the ancestral Arroyo Valle drainage system reveals numerous paleochannels that generally decrease in elevation (age) to the northwest, and provide useful isochronous markers delineating a subtle tectonic uplift in western Livermore Valley

  6. Kinematics of the Eastern California shear zone: Evidence for slip transfer from Owens and Saline Valley fault zones to Fish Lake Valley fault zone

    USGS Publications Warehouse

    Reheis, M.C.; Dixon, T.H.

    1996-01-01

    Late Quaternary slip rates and satellite-based geodetic data for the western Great Basin constrain regional fault-slip distribution and evolution. The geologic slip rate on the Fish Lake Valley fault zone (the northwest extension of the Furnace Creek fault zone) increases northward from about 3 to 5 mm/yr, in agreement with modeled geodetic data. The increase coincides with the intersections of the Deep Springs fault, connected to the Owens Valley fault zone, and of other faults connected to the Saline Valley fault. The combined geologic and geodetic data suggest that (1) the northwest-striking faults of the Eastern California shear zone north of the Garlock fault are connected by north- to northeast-striking normal faults that transfer slip in a series of right steps, and (2) the amount and distribution of slip among the many faults of this broad, complex plate boundary have changed through time.

  7. Geomorphological and Paleoseismological Studies of the Malatya Fault (Malatya-Ovacık Fault Zone, Turkey)

    NASA Astrophysics Data System (ADS)

    Sançar, Taylan; Zabcı, Cengiz; Karabacak, Volkan; Akyüz, Hüsnü Serdar

    2016-04-01

    The Malatya-Ovacık Fault Zone (MOFZ is about 240 km-long sinistral strike-slip tectonic structure within the Anatolian Scholle. Although the MOFZ is claimed to be an inactive structure since 3 Ma (Westaway and Arger, 2001), recent GPS measurements, morphotectonic studies and micro seismicity strongly suggest considerable amount of strain accumulation along this tectonic feature. The GPS-based elastic block model results yield horizontal slip rates of about 1.2 and 1.6 mm/a, for the northeastern and southwestern sections of this fault zone, respectively (Aktuǧ et al., 2013). In order to understand the seismic potential of the southwestern section, Malatya Fault (MF), of the MOFZ, we carried out paleoseismological trenching and morphometric analyses in the frame of the TÜBİTAK project no. 114Y580. The preliminary results of morphometric analyses, including the hypsometric curve and channel longitudinal profiles, suggest that the northernmost part of the MF accommodate more deformation than the southern part, where the fault zone bifurcates into several discrete segments. Relatively high values of hypsometric integral and the shape of hypsometric curves and the longitudinal channel profiles, indicate youthful topography at northern part of the MF. In the northern section of the MF, Kızık Basin is one of the most remarkable fault-related landforms, which is 9 km long and 2 km wide, and is directly controlled by the extensional step-over of the fault segments. On the northern parts of this relatively narrow depression, a linear scarp prolongs between Kızık and Ahlas villages for about 150 m. In summer 2015, we excavated a single trench on this straight lineament, where mostly braided river-related gravels and sands were exposed. Although we could not observe any evidence of surface faulting inside the erosional channel systems, the bedrock has very well-developed shear fabric at the toe of the observed scarp. We sampled the most bottom section of the undeformed

  8. Fluid infiltration into fault zones: Chemical, isotopic, and mechanical effects

    NASA Astrophysics Data System (ADS)

    Kerrich, R.

    1986-01-01

    Fluid infiltration into fault zones and their deeper-level counterparts, brittle-ductile shear zones, is examined in diverse tectonic environments. In the 2.7 Ga Abitibi greenstone belt, major tectonic discontinuities, with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism. During reverse motion on the structures, accommodating shortening of the belt, these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids. Such fluids were characterised by δ18O=+6±2, δD=-50±20, δ13C=-4±4, and temperatures of 270 to 450°C, probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism. Hydrothermal fluids were more radiogenic (87Sr/86Sr=0.7010 to 0.7040) and possessed higher μ than did contemporaneous mantle, komatiites or tholeiites, and thus carried a contribution from older sialic basement. A provinciality of87Sr/86Sr and δ13C is evident, signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres. Mineralised faults possess enrichments of large ion lithophile (LIL), LIL elements, including K, Rb, Ba, Cs, B, and CO2, and rare elements, such as Au, Ag, As, Sb, Se, Te, Bi, and W. Fluids were characterised by XCO 2≈0.1, neutral to slightly acidic pH, low salinity ≤3 wt-%, K/Na=0.1, they carried minor CH4, CO, and N2, and they underwent transient effervescence of CO2 during decompression. Clastic sediments occupy graben developed at fault flexures. The40Ar/39Ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years. At the Grenville front, translation was accommodated along two mylonite zones and an intervening

  9. Damaged beyond repair? Characterising the damage zone of a fault late in its interseismic cycle, the Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Williams, Jack N.; Toy, Virginia G.; Massiot, Cécile; McNamara, David D.; Wang, Ting

    2016-09-01

    X-ray computed tomography (CT) scans of drill-core, recovered from the first phase of the Deep Fault Drilling Project (DFDP-1) through New Zealand's Alpine Fault, provide an excellent opportunity to study the damage zone of a plate-bounding continental scale fault, late in its interseismic cycle. Documentation of the intermediate-macro scale damage zone structures observed in the CT images show that there is no increase in the density of these structures towards the fault's principal slip zones (PSZs), at least within the interval sampled, which is 30 m above and below the PSZs. This is in agreement with independent analysis using borehole televiewer data. Instead, we conclude the density of damage zone structures to correspond to lithology. We find that 72% of fractures are fully healed, by a combination of clays, calcite and quartz, with an additional 24% partially healed. This fracture healing is consistent with the Alpine Fault's late interseismic state, and the fact that the interval of damage zone sampled coincides with an alteration zone, an interval of extensive fluid-rock interaction. These fractures do not impose a reduction of P-wave velocity, as measured by wireline methods. Outside the alteration zone there is indirect evidence of less extensive fracture healing.

  10. Microstructural analysis of faulting in quartzite, Assynt, NW Scotland: Implications for fault zone evolution

    NASA Astrophysics Data System (ADS)

    Knipe, Robert J.; Lloyd, Geoffrey E.

    1994-03-01

    Macroscopic fracture arrays, microstructures and interpreted deformation mechanisms are used to assess the development of a minor reverse fault (backthrust) in quartzite from the Moine Thrust Zone, Assynt, NW Scotland. Fracturing dominates the faulting via the progression: intragranular extension microcracks; transgranular, cataclasite absent extension fractures; through-going, cataclasite filled shear microfaults, within which fracturing and particulate flow operate. However, both diffusive mass transfer (DMT) and intracrystalline plasticity (low temperature plasticity, LTP) processes also contribute to the fault zone deformation and lead to distinct associations of deformation mechanisms (e.g., DMT-fracture and LTP-fracture or low-temperature ductile fracture, LTDF). Over a large range of scales the fault zone consists of blocks of relatively intact rock separated by narrow zones of intense deformation where fracture processes dominate. The populations of fragments/blocks of different sizes in the fault zone have a power-law relationship which is related to the dimension of the fault zone. These observations are used to develop a general model for fault zone evolution based on the distribution of deformation features as a function of either time or space. A systematic variation in the deformation rate: time histories is recognised, associated with different positions within the fault zone. Thus, the fault zone preserves elements of the “birth, life and death” sequences associated with the displacement history and strain accommodation.

  11. Location, structure, and seismicity of the Seattle fault zone, Washington: Evidence from aeromagnetic anomalies, geologic mapping, and seismic-reflection data

    USGS Publications Warehouse

    Blakely, R.J.; Wells, R.E.; Weaver, C.S.; Johnson, S.Y.

    2002-01-01

    A high-resolution aeromagnetic survey of the Puget Lowland shows details of the Seattle fault zone, an active but largely concealed east-trending zone of reverse faulting at the southern margin of the Seattle basin. Three elongate, east-trending magnetic anomalies are associated with north-dipping Tertiary strata exposed in the hanging wall; the magnetic anomalies indicate where these strata continue beneath glacial deposits. The northernmost anomaly, a narrow, elongate magnetic high, precisely correlates with magnetic Miocene volcanic conglomerate. The middle anomaly, a broad magnetic low, correlates with thick, nonmagnetic Eocene and Oligocene marine and fluvial strata. The southern anomaly, a broad, complex magnetic high, correlates with Eocene volcanic and sedimentary rocks. This tripartite package of anomalies is especially clear over Bainbridge Island west of Seattle and over the region east of Lake Washington. Although attenuated in the intervening region, the pattern can be correlated with the mapped strike of beds following a northwest-striking anticline beneath Seattle. The aeromagnetic and geologic data define three main strands of the Seattle fault zone identified in marine seismic-reflection profiles to be subparallel to mapped bedrock trends over a distance of >50 km. The locus of faulting coincides with a diffuse zone of shallow crustal seismicity and the region of uplift produced by the M 7 Seattle earthquake of A.D. 900-930.

  12. Tectonic creep in the Hayward fault zone, California

    USGS Publications Warehouse

    Radbruch-Hall, Dorothy H.; Bonilla, M.G.

    1966-01-01

    Tectonic creep is slight apparently continuous movement along a fault. Evidence of creep has been noted at several places within the Hayward fault zone--a zone trending northwestward near the western front of the hills bordering the east side of San Francisco Bay. D. H. Radbruch of the Geological Survey and B. J. Lennert, consulting engineer, confirmed a reported cracking of a culvert under the University of California stadium. F. B. Blanchard and C. L. Laverty of the East Bay Municipal Utility District of Oakland studied cracks in the Claremont water tunnel in Berkeley. M. G. Bonilla of the Geological Survey noted deformation of railroad tracks in the Niles district of Fremont. Six sets of tracks have been bent and shifted. L. S. Cluff of Woodward-Clyde-Sherard and Associates and K. V. Steinbrugge of the Pacific Fire Rating Bureau noted that the concrete walls of a warehouse in the Irvington district of Fremont have been bent and broken, and the columns forced out of line. All the deformations noted have been right lateral and range from about 2 inches in the Claremont tunnel to about 8 inches on the railroad tracks. Tectonic creep almost certainly will continue to damage buildings, tunnels, and other structures that cross the narrow bands of active movement within the Hayward fault zone.

  13. Controls on damage zone asymmetry of a normal fault zone: outcrop analyses of a segment of the Moab fault, SE Utah

    NASA Astrophysics Data System (ADS)

    Berg, Silje S.; Skar, Tore

    2005-10-01

    Outcrop data has been used to examine the spatial arrangement of fractures in the damage zones of a segment of the large-scale Moab Fault (45 km in length), SE Utah. The characteristics of the footwall and hanging wall damage zones show pronounced differences in the deformation pattern: (1) there is a well-developed syncline in the hanging wall, as opposed to sub-horizontal bedding of the footwall; (2) the footwall damage zone is sub-divided into an inner zone (0-5 m from fault core) and an outer zone (>5 m) based on differences in deformation band frequency, whereas no clear sub-division can be made in the hanging wall; (3) the hanging wall damage zone is more than three times wider than the footwall damage zone; (4) there is a higher abundance of antithetic fractures and deformation bands in the hanging wall than in the footwall; and (5) the antithetic structures generally have more gentle dips in the hanging wall than in the footwall. The main conclusion is that the structural pattern across the fault zone is strongly asymmetric. The deformation pattern is partly influenced by lithology and/or partly by processes associated with the development of the fault core. We suggest, however, that the most important cause for the asymmetric strain distribution is the development of the hanging wall syncline and the resulting asymmetric stress pattern expected to exist during fault propagation.

  14. Rigidity of the fault zones in the Earth's crust estimated from seismic data

    NASA Astrophysics Data System (ADS)

    Spivak, A. A.

    2011-07-01

    Nonlinear effects in seismic wave propagation are analyzed to determine the mechanical rigidity of different-order faults that thread the tectonic structures in the central part of the East European platform (Moscow syneclise and Voronezh Crystalline Massif) and the fault zones of the Balapan and Degelen mountain regions in Kazakhstan (the Degelen magmatic node in the Central Chingiz zone). The dependency of the rigidity of the fault zone on the fault's length is obtained. The rigidity of the tectonic structures is found to experience well-expressed temporal variations with periods of 13-15 days, 27-32 days, and about one year. In the different-order fault zones, the amplitudes of both normal k n and the shear k s rigidity for semimonthly, monthly, and annual variations can span a factor of 1.3, 1.5, and 2.5, respectively.

  15. Characteristics of faults and shear zones in deep mines

    USGS Publications Warehouse

    Wallace, R.E.; Morris, H.T.

    1986-01-01

    The characteristics of fault and shear zones to depths of 2.5 km are well documented in deep mines in North America. The characteristics may be summarized as follows. (a) Fault zones usually are irregular, branched, anastomosed, and curved rather than simple and planar. (b) Faults are generally composed of one or more clay or clay-like gouge zones in a matrix of sheared and foliated rock bordered by highly fractured rock. (c) The widths of fault zones appear to be greater when faults have greater displacement, probably as a result of a long history of repeated minor movements. Fault zones with kilometers of displacement tend to be 100 m or more wide, whereas those with only a few hundred meters of displacement commonly are only 1 m or less wide. (d) Some zones represent shear distributed across hundreds of meters without local concentration in a narrow gouge zone. (e) Many fault zones are wet even above the water table, and water moves along them at various rates, but some also serve as subsurface dams, ponding ground water as much as several hundred meters higher on one side than on the other. No striking differences in the characteristics of faults over the vertical range of 2.5 km are documented. ?? 1986 Birkha??user Verlag.

  16. Imaging the Carboneras fault zone at depth: preliminary results from reflection/refraction seismic tomography

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    Understanding and characterizing fault zone structure at depth is vital to predicting the slip behaviour of faults in the brittle crust. We aim to combine detailed field mapping and laboratory velocity/physical property determinations with seismic measurements on the Carboneras fault zone (S.E. Spain) to improve our knowledge of how fault zone structure affects seismic signals. The CFZ is a large offset (10s of km) strike-slip fault that constitutes part of the diffuse plate boundary between Africa and Iberia. It has been largely passively exhumed from ca. 4 to 6 km depth. The friable fault zone components are excellently preserved in the region’s semi-arid climate, and consist of multiple strands of phyllosilicate-rich fault gouge ranging from 1 to 20 m in thickness. In May 2009 we conducted 4 high-resolution seismic reflection and refraction/first break tomography lines. Two of these lines (~1km long) crossed the entire fault zone while the remaining lines (~150 and ~300m long) concentrated on individual fault strands and associated damage zones. For each of the lines a 2 m-geophone spacing was used with a combination of accelerated drop weight, sledgehammer and 100g explosives as seismic sources. Initial seismic reflection processing has been carried out on each of the 4 lines. First breaks have been picked for each of the shot gathers and inputted into a 2D traveltime inversion and amplitude-modeling package (Zelt & Smith, 1992) to obtain first break tomography images. During this field campaign we also carried out numerous fault zone guided wave experiments on two of the dense seismic lines. At the larger offsets (~600-700m) we observe low frequency guided waves. These experiments will capture the various length scales involved in a mature fault zone and will enable the surface mapping and petrophysical studies to be linked to the seismic field observations.

  17. Fault zone characteristics, fracture systems and permeability implications of Middle Triassic Muschelkalk in Southwest Germany

    NASA Astrophysics Data System (ADS)

    Meier, Silke; Bauer, Johanna F.; Philipp, Sonja L.

    2015-01-01

    Fault zone structure and lithology affect permeability of Triassic Muschelkalk limestone-marl-alternations in Southwest Germany, a region characterized by a complex tectonic history. Field studies of eight fault zones provide insights into fracture system parameters (orientation, density, aperture, connectivity, vertical extension) within fault zone units (fault core, damage zone). Results show decreasing fracture lengths with distances to the fault cores in well-developed damage zones. Fracture connectivity at fracture tips is enhanced in proximity to the slip surfaces, particularly caused by shorter fractures. Different mechanical properties of limestone and marl layers obviously affect fracture propagation and thus fracture system connectivity and permeability. Fracture apertures are largest parallel and subparallel to fault zones and prominent regional structures (e.g., Upper Rhine Graben) leading to enhanced fracture-induced permeabilities. Mineralized fractures and mineralizations in fault cores indicate past fluid flow. Permeability is increased by the development of hydraulically active pathways across several beds (non-stratabound fractures) to a higher degree than by the formation of fractures interconnected at fracture tips. We conclude that there is an increase of interconnected fractures and fracture densities in proximity to the fault cores. This is particularly clear in more homogenous rocks. The results help to better understand permeability in Muschelkalk rocks.

  18. Rock mechanics. Superplastic nanofibrous slip zones control seismogenic fault friction.

    PubMed

    Verberne, Berend A; Plümper, Oliver; de Winter, D A Matthijs; Spiers, Christopher J

    2014-12-12

    Understanding the internal mechanisms controlling fault friction is crucial for understanding seismogenic slip on active faults. Displacement in such fault zones is frequently localized on highly reflective (mirrorlike) slip surfaces, coated with thin films of nanogranular fault rock. We show that mirror-slip surfaces developed in experimentally simulated calcite faults consist of aligned nanogranular chains or fibers that are ductile at room conditions. These microstructures and associated frictional data suggest a fault-slip mechanism resembling classical Ashby-Verrall superplasticity, capable of producing unstable fault slip. Diffusive mass transfer in nanocrystalline calcite gouge is shown to be fast enough for this mechanism to control seismogenesis in limestone terrains. With nanogranular fault surfaces becoming increasingly recognized in crustal faults, the proposed mechanism may be generally relevant to crustal seismogenesis. PMID:25504714

  19. Geometry of the Gerede Segment, North Anatolian Fault Zone, Turkey

    NASA Astrophysics Data System (ADS)

    Caglayan, A.; ISIK, V.

    2012-12-01

    The North Anatolian Fault Zone (NAFZ) is an active dextral strike-slip fault zone in northern Turkey. The NAFZ is approximately 1200 km in length which extends from Karliova in the east and to reach as far as the Gulf of Saros in the west. The NAFZ becomes wider geometry from east to west which are characterized by 9 destructive earthquake of Ms>7 in the 20th century. An earthquake on 1944 February 1 (Ms 7,3) caused 180 km long surface rupture associated with 2-6.5 m of right-lateral slip between Bayramören in the east and Abant Lake in the west along the NAFZ, which is called the Gerede Segment. This study describes internal geometrical characteristics and deformation mechanism of faults with fault surfaces in the Gerede Segment. The faults along the segment variously cut across Mesozoic-Cenozoic basement rocks and Quaternary alluvium deposits. They juxtapose not only different units of basement but also basement rocks and alluvium. We select typical fault surface that have been formed the best exposures in limestone in different locality, which define exhumed main faults along the segment. These faults strike N70°-80°E and dip 50°-85°NW. Slickenlines on these fault surface plunge shallowly to the NE and/or SW. Fault surface include brittle kinematic indicators indicating right-lateral strike-slip displacements. Some typical Riedel shear fractures (R- and P-fractures) around the main faults also show dextral displacements. Along the main faults two main architectural elements including fault core and fault damage zone is typical. The fault damage zones of these faults are characterized by both fault-related fracturing and fluid-assisted deformation processes. Although breccia is common fault rock in fault zones, gouge and cataclasite are seen in variable exposures. We have defined crackle, mosaic and chaotic type breccias using clast-size and clast proportion. Rock fragments within breccias have occurred mm-cm scale from angular to rounded clast. Sub

  20. Late Neogene structural inversion around the northern Gulf of Tonkin, Vietnam: Effects from right-lateral displacement across the Red River fault zone

    NASA Astrophysics Data System (ADS)

    Fyhn, Michael B. W.; Phach, Phung V.

    2015-02-01

    Continental extrusion may take up much of the deformation involved in continental collisions. Major strike-slip zones accommodate the relative extrusion displacement and transfer deformation away from the collision front. The Red River fault zone (RRFZ) accommodated left- and right-lateral displacements when Indochina and South China were extruded during the Indian-Eurasian collision. The northern Song Hong basin onshore and offshore in the Gulf of Tonkin delineates the direct extension of the RRFZ and thus records detailed information on the collision-induced continental extrusion. We assess the rapidly evolving kinematics of the fault zone buried within the basin based on seismic analysis. Contrary to previous studies, we do not identify indications for latest Miocene left-lateral motion across the RRFZ. We tentatively consider the shift from left- to right-lateral motion to have occurred already during the middle Late Miocene as indicated by inversion of NE-SW-striking faults in the Bach Long Vi area. Right-lateral displacement terminated around the end of the Miocene in the Song Hong basin. However, continued inversion in the Bach Long Vi area and NNW-SSE-striking normal faulting suggests a stress regime compatible with right-lateral motion across the onshore part of the RRFZ continuing to the present. Inversion around the Bach Long Vi Island may have accommodated up to a few kilometers of right-lateral displacement between the Indochina and South China blocks. Comparable NE-SW-striking fault zones onshore may have accommodated a larger fraction of the right-lateral slip across the RRFZ, thus accounting for the restricted transfer of lateral displacement to the offshore basins.

  1. Surface faulting along the Superstition Hills fault zone and nearby faults associated with the earthquakes of 24 November 1987

    USGS Publications Warehouse

    Sharp, R.V.

    1989-01-01

    The M6.2 Elmore Desert Ranch earthquake of 24 November 1987 was associated spatially and probably temporally with left-lateral surface rupture on many northeast-trending faults in and near the Superstition Hills in western Imperial Valley. Three curving discontinuous principal zones of rupture among these breaks extended northeastward from near the Superstition Hills fault zone as far as 9km; the maximum observed surface slip, 12.5cm, was on the northern of the three, the Elmore Ranch fault, at a point near the epicenter. Twelve hours after the Elmore Ranch earthquake, the M6.6 Superstition Hills earthquake occurred near the northwest end of the right-lateral Superstition Hills fault zone. We measured displacements over 339 days at as many as 296 sites along the Superstition Hills fault zone, and repeated measurements at 49 sites provided sufficient data to fit with a simple power law. The overall distributions of right-lateral displacement at 1 day and the estimated final slip are nearly symmetrical about the midpoint of the surface rupture. The average estimated final right-lateral slip for the Superstition Hills fault zone is ~54cm. The average left-lateral slip for the conjugate faults trending northeastward is ~23cm. The southernmost ruptured member of the Superstition Hills fault zone, newly named the Wienert fault, extends the known length of the zone by about 4km. -from Authors

  2. Influence of fault trend, fault bends, and fault convergence on shallow structure, geomorphology, and hazards, Hosgri strike-slip fault, offshore central California

    NASA Astrophysics Data System (ADS)

    Johnson, S. Y.; Watt, J. T.; Hartwell, S. R.

    2012-12-01

    We mapped a ~94-km-long portion of the right-lateral Hosgri Fault Zone from Point Sal to Piedras Blancas in offshore central California using high-resolution seismic reflection profiles, marine magnetic data, and multibeam bathymetry. The database includes 121 seismic profiles across the fault zone and is perhaps the most comprehensive reported survey of the shallow structure of an active strike-slip fault. These data document the location, length, and near-surface continuity of multiple fault strands, highlight fault-zone heterogeneity, and demonstrate the importance of fault trend, fault bends, and fault convergences in the development of shallow structure and tectonic geomorphology. The Hosgri Fault Zone is continuous through the study area passing through a broad arc in which fault trend changes from about 338° to 328° from south to north. The southern ~40 km of the fault zone in this area is more extensional, resulting in accommodation space that is filled by deltaic sediments of the Santa Maria River. The central ~24 km of the fault zone is characterized by oblique convergence of the Hosgri Fault Zone with the more northwest-trending Los Osos and Shoreline Faults. Convergence between these faults has resulted in the formation of local restraining and releasing fault bends, transpressive uplifts, and transtensional basins of varying size and morphology. We present a hypothesis that links development of a paired fault bend to indenting and bulging of the Hosgri Fault by a strong crustal block translated to the northwest along the Shoreline Fault. Two diverging Hosgri Fault strands bounding a central uplifted block characterize the northern ~30 km of the Hosgri Fault in this area. The eastern Hosgri strand passes through releasing and restraining bends; the releasing bend is the primary control on development of an elongate, asymmetric, "Lazy Z" sedimentary basin. The western strand of the Hosgri Fault Zone passes through a significant restraining bend and

  3. An Attempt of Hydrogeological Classification of Fault Zones in Karst Areas

    NASA Astrophysics Data System (ADS)

    Bauer, Helene; Decker, Kurt

    2014-05-01

    Around 60% of Vienna`s drinking water originates in the Hochschwab plateau (Eastern Alps, Austria). The hydrogeology (groundwater storage and flow) of the Hochschwab is essentially governed by karstified, large-scale faults. Previous work has shown that faults that formed during the Oligocene/L. Miocene lateral extrusion of the Eastern Alps act as groundwater pathways draining the karst massif preferably in E-W-direction. However, further analysis of flow processes in karstified aquifers requires hydrogeological relevant data from natural fault zones. We investigated E- to ENE- striking strike-slip faults in limestones and dolomites of the Wetterstein Fm. in terms of potential permeability properties that result from structural composition and fault rock content. Using the standard fault core-damage zone model, we analyzed fault rock characteristics and volumes at the fault cores and connective fracture networks surrounding faults in the damage zones. Special attention has been drawn to fracture densities and the spatial extent of fracture networks. Small-scale fractures are generally assumed to carry most of the effective porosity and have a great influence on the permeability of a fault zone. Therefore, we established a classification scheme and measuring method that provides semi-quantitative estimates of the density and abundance of small-scale fractures by using scanning line techniques to quantify the total joint surface in a volume of rock (m² joint surfaces per m³ rock). This easily applicable method allows to generate fracture density data for the entire damage zones (over tens of meters) and thus to enhance the understanding of permeability properties of damage zones. The field based data is supported by effective porosity and permeability measurements of fractured wall rock and fault rock samples. Different fault rock categories turned out to have complex poro/perm properties due to differences in grain sizes, matrix content, cementation and fracturing

  4. Distribution of faults in a transition zone: Bimodal faulting in the Pit River region, Shasta County, California

    NASA Astrophysics Data System (ADS)

    Austin, L. J.; Weldon, R. J.; Paulson, K. T.

    2012-12-01

    Northern California marks a zone of transition between oblique subduction in Cascadia, dextral transtension in Walker Lane, and north-south compression of the Klamath Mountains. Because of its unique location, the region between Mt. Shasta and Lassen Peak provides insight into the distribution of deformation in regions of transitional tectonic regimes. In particular, the Pit River region provides several excellent exposures of faults in a diatomite quarry and in larger regional structures. We present information on the distribution, amount of slip, and orientation of local faults, and demonstrate how these data reflect the interaction of multiple regional stress fields. We have measured and compiled the orientations of many small faults to evaluate the distribution of deformation in a complex zone of oblique extension and compression. A ~0.5 km2 diatomite quarry near the Pit River and Lake Britton exposes hundreds of faults with small amounts of displacement. Two main faulting patterns emerge: 1) high angle NW/SE-striking faults characterized by normal, oblique normal, or strike slip kinematic indicators; and 2) lower angle E/W-striking faults with evidence of reverse to oblique reverse motion. We find that the regional landscape reflects a dominant mode of faulting that is NW/SE-striking normal, oblique normal, or strike slip; the Hat Creek and Rocky Ledge faults, each with tens of meters of oblique normal offset, exemplify this. Observations of numerous smaller faults in the diatomite quarry also show a dominant pattern of NW/SE-striking faults. E/W-striking compressional structures are present, but are less abundant. Faults of differing orientations occur together in the quarry and occasionally cross cut one another. Many faults cross but do not offset each other, indicating that they formed simultaneously. Where cross-cutting faults do exhibit offset, the NW/SE-striking faults offset E/W-striking faults, which suggests that NW/SE oriented faults have been

  5. Development of Hydrologic Characterization Technology of Fault Zones

    SciTech Connect

    Karasaki, Kenzi; Onishi, Tiemi; Wu, Yu-Shu

    2008-03-31

    Through an extensive literature survey we find that there is very limited amount of work on fault zone hydrology, particularly in the field using borehole testing. The common elements of a fault include a core, and damage zones. The core usually acts as a barrier to the flow across it, whereas the damage zone controls the flow either parallel to the strike or dip of a fault. In most of cases the damage zone isthe one that is controlling the flow in the fault zone and the surroundings. The permeability of damage zone is in the range of two to three orders of magnitude higher than the protolith. The fault core can have permeability up to seven orders of magnitude lower than the damage zone. The fault types (normal, reverse, and strike-slip) by themselves do not appear to be a clear classifier of the hydrology of fault zones. However, there still remains a possibility that other additional geologic attributes and scaling relationships can be used to predict or bracket the range of hydrologic behavior of fault zones. AMT (Audio frequency Magneto Telluric) and seismic reflection techniques are often used to locate faults. Geochemical signatures and temperature distributions are often used to identify flow domains and/or directions. ALSM (Airborne Laser Swath Mapping) or LIDAR (Light Detection and Ranging) method may prove to be a powerful tool for identifying lineaments in place of the traditional photogrammetry. Nonetheless not much work has been done to characterize the hydrologic properties of faults by directly testing them using pump tests. There are some uncertainties involved in analyzing pressure transients of pump tests: both low permeability and high permeability faults exhibit similar pressure responses. A physically based conceptual and numerical model is presented for simulating fluid and heat flow and solute transport through fractured fault zones using a multiple-continuum medium approach. Data from the Horonobe URL site are analyzed to demonstrate the

  6. The Sundance fault: A newly recognized shear zone at Yucca Mountain, Nevada

    SciTech Connect

    Spengler, R.W.; Braun, C.A.; Martin, L.G.; Weisenberg, C.W.

    1994-12-31

    Ongoing detailed mapping at a scale of 1:240 of structural features within the potential repository area indicates the presence of several previously unrecognized structural features. Minor north-trending west-side-down faults occur east and west of the Ghost Dance fault and suggest a total width of the Ghost Dance fault system of nearly 366 m (1200 ft). A zone of near-vertical N30{degrees}-40{degrees} W-trending faults, at least 274 m (900 ft) wide, has been identified in the northern part of our study area and may traverse across the potential repository area. On the basis of a preliminary analysis of available data, we propose to name this zone the {open_quotes}Sundance fault system{close_quotes} and the dominant structure, occurring near the middle of the zone, the {open_quotes}Sundance fault{close_quotes}. Some field relations suggest left-stepping deflections of north-trending faults along a pre-existing northwest-trending structural fabric. Other field observations suggest that the {open_quotes}Sundance fault system{close_quotes} offsets the Ghost Dance fault system in an apparent right lateral sense by at least 52 m (170 ft). Additional detailed field studies are needed to better understand structural complexities at Yucca Mountain.

  7. The Sundance fault: A newly recognized shear zone at Yucca Mountain, Nevada

    SciTech Connect

    Spengler, R.W.; Braun, C.A.; Martin, L.G.; Weisenberg, C.W.

    1994-04-01

    Ongoing detailed mapping at a scale of 1:240 of structural features within the potential repository area indicates the presence of several previously unrecognized structural features. Minor north-trending west-side-down faults occur east and west of the Ghost Dance fault and suggest a total width of the Ghost Dance fault system of nearly 366 m (1200 ft). A zone of near-vertical N30{degrees} {minus} 40{degrees}W {minus} trending faults, at least 274 m (900 ft) wide, has been identified in the northern part of our study area and may traverse across the proposed repository area. On the basis of a preliminary analysis of available data, we propose to name this zone the ``Sundance fault system`` and the dominant structure, occurring near the middle of the zone, the ``Sundance fault.`` Some field relations suggest left-stepping deflections of north-trending faults along a preexisting northwest-trending structural fabric. Other field observations suggest that the ``Sundance fault system`` offsets the Ghost Dance fault system in an apparent right lateral sense by at least 52 m (170 ft). Additional detailed field studies, however, are needed to better understand structural complexities at Yucca Mountain.

  8. Continental strike slip fault zones in geologically complex lithosphere: the North Anatolian Fault, Turkey.

    NASA Astrophysics Data System (ADS)

    Cornwell, David; Thompson, David; Papaleo, Elvira; Rost, Sebastian; Houseman, Gregory; Kahraman, Metin; Turkelli, Niyazi; Teoman, Ugur; Altuncu Poyraz, Selda; Gulen, Levent; Utkucu, Murat

    2016-04-01

    As part of the multi-disciplinary Faultlab project, we present new detailed images in a geologically complex region where the crust and upper mantle is bisected by a major continental strike-slip fault system. Our study region samples the north Anatolian fault zone (NAFZ) near the epicentres of two large earthquakes that occurred in 1999 at Izmit (M7.5) and Düzce (M7.2) and where estimates of present day slip rate are 20-25 mm/yr. Using recordings of teleseismic earthquakes from a rectangular seismometer array spanning the NAFZ with 66 stations at a nominal inter-station spacing of 7 km and 7 additional stations further afield, we build a detailed 3-D image of structure and anisotropy using receiver functions, tomography and shear wave splitting and illuminate major changes in the architecture and properties of the upper crust, lower crust and upper mantle, both across and along the two branches of the NAFZ, at length scales of less than 20 km. We show that the northern NAFZ branch depth extent varies from the mid-crust to the upper mantle and it is likely to be less than 10 km wide. A high velocity lower crust and a region of crustal underthrusting appear to add strength to a heterogeneous crust and play a role in dictating the variation in faulting style and postseismic deformation. Sharp changes in lithospheric mantle velocity and anisotropy are constrained as the NAFZ is crossed, whereas crustal structure and anisotropy vary considerably both parallel and perpendicular to the faulting. We use our observations to test current models of the localisation of strike-slip deformation and develop new ideas to explain how narrow fault zones develop in extremely heterogeneous lithosphere.

  9. When did movement begin on the Furnace Creek fault zone

    SciTech Connect

    Reheis, M. )

    1993-04-01

    About 50 km of post-Jurassic right-lateral slip has occurred on the northern part of the Furnace Creek fault zone (FCFZ). The sedimentology, stratigraphy, and structure of Tertiary rocks suggest that movement on the fault began no earlier than 12--8 Ma and possibly as late as 5--4 Ma. Large remnants of erosion surfaces occur on both sides of the FCFZ in the southern White Mountains and Fish Lake Valley and are buried by rhyolite and basalt, mostly 12--10 Ma; the ash flows and welded tuffs were likely erupted from sources at least 40 km to the east. Thus, the area probably had gentle topography, suggesting a lengthy period of pre-late Miocene tectonic stability. On the west side of the FCFZ, Cambrian sedimentary rocks are buried by a fanglomerate with an [sup [minus

  10. Geologic map of the Hayward fault zone, Contra Costa, Alameda, and Santa Clara counties, California: a digital database

    USGS Publications Warehouse

    Graymer, R.W.; Jones, D.L.; Brabb, E.E.

    1995-01-01

    The Hayward is one of three major fault zones of the San Andreas system that have produced large historic earthquakes in the San Francisco Bay Area (the others being the San Andreas and Calaveras). Severe earthquakes were generated by this fault zone in 1836 and in 1868, and several large earthquakes have been recorded since 1868. The Hayward fault zone is considered to be the most probable source of a major earthquake in the San Francisco Bay Area, as much as 28% chance for a magnitude 7 earthquake before the year 2021 (Working Group on California Earthquake Probabilities, 1990). The Hayward fault zone, as described in this work, is a zone of highly deformed rocks, trending north 30 degrees west and ranging in width from about 2 to 10 kilometers. The historic earthquake generating activity has been concentrated in the western portion of the zone, but the zone as a whole reflects deformation derived from oblique right-lateral and compressive tectonic stress along a significant upper crustal discontinuity for the past 10 million or more years. The Hayward fault zone is bounded on the east by a series of faults that demarcate the beginning of one or more structural blocks containing rocks and structures unrelated to the Hayward fault zone. The eastern bounding faults are, from the south, the Calaveras, Stonybrook, Palomares, Miller Creek, and Moraga faults. These faults are not considered to be part of the Hayward fault zone, although they are shown on the map to demarcate its boundary. The western boundary of the zone is less clearly defined, because the alluvium of the San Francisco Bay and Santa Clara Valley basins obscures bedrock and structural relationships. Although several of the westernmost faults in the zone clearly project under or through the alluvium, the western boundary of the fault is generally considered to be the westernmost mapped fault, which corresponds more or less with the margin of thick unconsolidated surficial deposits. The Hayward fault

  11. Tectonic Geomorphology of the Hanging Wall Blocks of the Cimandiri Fault Zone, West Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Marliyani, G. I.; Arrowsmith, R.

    2014-12-01

    In areas where regional strain is accommodated by broad zones of short and low slip-rate faults, geomorphic and paleoseismic characterization of faults is difficult because of poor surface expression and long earthquake recurrence intervals. In humid areas, faults can be buried by thick sediments and undetectable until the next earthquake. In Java, despite the frequency of damaging shallow earthquakes, active faults are diffuse and their characterization is challenging. Among them is the ENE-trending Cimandiri fault. Cumulative displacement along the fault produces prominent ENE-oriented ranges with the east side moving relatively upward and to the north. Along its length, the few hundred meter wide fault zone is expressed in the bedrock by numerous NE, E and NW-trending thrust- and strike slip faults and folds. However, it is unclear which of these structures are active, as the diffuse nature of the fault zone has so far stymied conventional paleoseismic study. To address this, we performed a tectonic geomorphology analysis of the fault zone. We used the 30-m resolution SRTM-DEM to construct longitudinal profiles of 601 bedrock rivers along the ranges and calculated the normalized channel steepness index (ksn). Our preliminary results rely on the assumption that ksn is a reasonable proxy for relative rock uplift rate in a region, assuming variations in rock type and climate are insignificant. While the active traces of the Cimandiri fault are obscured, the spatial variation in ksn allows us to delineate 4 discontinuous hanging wall blocks that vary between E and NE striking along the zone. The largest ksn values are along the central-western block (Cibeber area). The longest block is in the central eastern portion of the fault zone and comprises 45 km of the 100 km long fault zone. The fault bifurcates at its eastern termination and steps into the Lembang fault. The distribution of ksn suggests that reverse motion is more dominant than lateral because of a lack of

  12. Seismic imaging constraints on megathrust fault zone properties

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  13. Counter-intuitive Behavior of Subduction Zones: Weak Faults Rupture, Strong Faults Creep

    NASA Astrophysics Data System (ADS)

    Wang, K.; Gao, X.; Bilek, S. L.; Brown, L. N.

    2014-12-01

    Subduction interfaces that produce great earthquakes are often said to be "strongly coupled", and those that creep are said to be "weakly coupled". However, the relation between the strength and seismogenic behavior of subduction faults is far from clear. Seismological and geodetic observations of earthquake rupture usually provide information only on stress change, not fault strength. In this study, we infer fault strength by calculating frictional heating along megathrusts and comparing results with heat flow measurements. We find that stick-slip megathrusts that have produced great earthquakes such as at Japan Trench and northern Sumatra have very low apparent friction coefficients (~ 0.02 - 0.03), but megathrusts that creep such as at Northern Hikurangi and Manila Trench have higher values (up to ~0.13). The differnce cannot be explained by coseismic dynamic weakening of the stick-slip megathrusts, because the average stress drop in great earthquakes is usually less than 5 MPa, equivalent to a coseismic reduction of apparent friction coefficient by less than ~0.01. Therefore our results indicate differences in the static strength of different subduction faults. Why are the creeping faults stronger? We think it is related to their creeping mechanism. Very rugged subducting seafloor tends to cause creep and hinder great earthquake rupture (Wang and Bilek, 2014). In contrast, all giant earthquakes have occurred at subduction zones with relatively smooth subducting seafloor. Large geometrical irregularities such as seamounts generate heterogeneous structure and stresses that promote numerous small and medium size earthquakes and aseismic creep. The creeping is a process of breaking and wearing of geometrical irregularities in a deformation zone and is expected to be against relatively large resistance (strong creep). This is different from the creeping of smooth faults due to the presence of weak fault gouge (weak creep) such as along the creeping segment of the

  14. Fluid-rock reaction weakening of fault zones

    SciTech Connect

    Wintsch, R.P.; Christoffersen, R.; Kronenberg, A.K.

    1995-07-10

    The presence of weak phyllosilicates may explain the low shear strengths of fault zones if they define well-developed fabrics. The growth of phyllosilicates is favored in meteoric water-dominated granitic fault systems, where mineral-aqueous fluid equilibria predict that modal phyllosilicate will increase via feldspar replacement reactions. In deeper, more alkaline, rock-dominated regimes, the reactions reverse, and feldspars tend to replace phyllosilicates. In Mg-rich mafic rocks, however, phyllosilicates (chlorite, biotite) can replace stronger framework and chain silicates in both shallower (<{approximately}10 km) meteoric H{sub 2}O-dominated and in deeper, alkaline, rock-dominated regimes. Where these phyllosilicates precipitate in active fault zones, they contribute directly to reaction softening. Because low-temperature deformation of phyllosilicates is not governed by frictional processes alone but can occur by pressure-independent dislocation glide, the strength of phyllosilicate-rich fault rocks can be low at all depths. Low strain rate creep during interseismic periods can align phyllosilicate grains in foliated gouge and phyllonites. Where preferred orientations are strong and contiguity of phyllosilicates is large, strengths of rocks within fault zones may approach minimum strengths defined by single phyllosilicate crystals. Fault zones containing localized high concentrations of phyllosilicates with strong preferred orientations in well-defined folia can exhibit aseismic slip, especially where mafic Mg-rich rocks occur along the fault (like parts of the San Andreas Fault). 104 refs., 6 figs., 1 tab.

  15. Kinematics at Death Valley-Garlock fault zone junction

    SciTech Connect

    Abrams, R.B.; Verosub, K.; Finnerty, A.

    1987-08-01

    The Garlock and Death Valley fault zones in southeast California are two active strike-slip faults that come together on the east side of the Avawatz Mountains. The kinematics of this intersection, and the possible continuation of either fault zone, is being investigated using a combination of detailed field mapping, and processing and interpretation of remotely sensed image data from satellite and aircraft platforms. Regional and local relationships are derivable from the thematic Mapper data (30 m resolution), including discrimination and relative age dating of alluvial fans, bedrock mapping, and fault mapping. Aircraft data provide higher spatial resolution data over more limited areas. Hypotheses that are being considered are (1) the Garlock fault extends east of the intersection; (2) the Garlock fault terminates at the intersection and the Death Valley fault continues southeastward; and (3) the Garlock fault has been offset right laterally by the Death Valley fault that continues to the southeast. Preliminary work indicates that the first hypothesis is invalid. Kinematic considerations, image analysis, and field work results favor the third hypothesis. The projected continuation of the Death Valley zone defines the boundary between the Mojave crustal block and the Basin and Range block.

  16. Arshan palaeoseismic feature of the Tunka fault (Baikal rift zone, Russia)

    NASA Astrophysics Data System (ADS)

    Smekalin, Oleg P.; Shchetnikov, Alexander A.; White, Dustin

    2013-01-01

    The traditional concept of the rift development of flank depressions in the Baikal rift zone is now doubted in view of some indicators for compression deformations identified by the seismogeological and geodetic methods. Besides, the paleoseismological investigations revealed seismogenic strike-slips and reverse faults in the Tunka fault zone that is a major structure-controlling element of the Tunka rift depression. However, a detailed study of the upslope-facing scarp in the Arshan paleoseismogenic structure zone has shown that its formation might be due to rift mechanism of basin formation. Age estimation has been made for the previously unknown pre-historic earthquake whose epicentral area coincides with the western flank of the Arshan paleoseismogenic structure. Judging from previously determined ages of paleoearthquakes, the mean recurrence period for faulting events on the central Tunka fault is 2780-3440 years.

  17. Crustal imaging across the North Anatolian Fault Zone from the autocorrelation of ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Taylor, George; Rost, Sebastian; Houseman, Gregory

    2016-03-01

    Seismic images of active fault zones can be used to examine the structure of faults throughout the crust and upper mantle and give clues as to whether the associated deformation occurs within a narrow shear zone or is broadly distributed through the lower crust. Limitations on seismic resolution within the crust and difficulties imaging shallow structures such as the crust-mantle boundary (Moho) place constraints on the interpretation of seismic images. In this study we retrieve body wave reflections from autocorrelations of ambient seismic noise. The instantaneous phase coherence autocorrelations allow unprecedented ambient noise images of the North Anatolian Fault Zone (NAFZ). Our reflection profiles show a Moho reflected P wave and additional structure within the crust and upper mantle. We image a distinct vertical offset of the Moho associated with the northern branch of the NAFZ indicating that deformation related to the fault remains narrow in the upper mantle.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  19. Imaging Faults and Shear Zones Using Receiver Functions

    NASA Astrophysics Data System (ADS)

    Schulte-Pelkum, Vera; Mahan, Kevin H.

    2014-11-01

    The geometry of faults at seismogenic depths and their continuation into the ductile zone is of interest for a number of applications ranging from earthquake hazard to modes of lithospheric deformation. Teleseismic passive source imaging of faults and shear zones can be useful particularly where faults are not outlined by local seismicity. Passive seismic signatures of faults may arise from abrupt changes in lithology or foliation orientation in the upper crust, and from mylonitic shear zones at greater depths. Faults and shear zones with less than near-vertical dip lend themselves to detection with teleseismic mode-converted waves (receiver functions) provided that they have either a contrast in isotropic shear velocity ( V s), or a contrast in orientation or strength of anisotropic compressional velocity ( V p). We introduce a detection method for faults and shear zones based on receiver functions. We use synthetic seismograms to demonstrate common features of dipping isotropic interfaces and contrasts in dipping foliation that allows determination of their strike and depth without making further assumptions about the model. We proceed with two applications. We first image a Laramide thrust fault in the western U.S. (the Wind River thrust fault) as a steeply dipping isotropic velocity contrast in the middle crust near the surface trace of the fault; further downdip and across the range, where basin geometry suggests the fault may sole into a subhorizontal shear zone, we identify a candidate shear zone signal from midcrustal depths. The second application is the use of microstructural data from exhumed ductile shear zones in Scotland and in the western Canadian Shield to predict the character of seismic signatures of present-day deep crustal shear zones. Realistic anisotropy in observed shear fabrics generates a signal in receiver functions that is comparable in amplitude to first-order features like the Moho. Observables that can be robustly constrained without

  20. Thermo-mechanical coupling of faults and mantle shear zones

    NASA Astrophysics Data System (ADS)

    Lambert, Valere; Barbot, Sylvain

    2016-04-01

    Paleo-seismological records suggest non-steady and potentially periodic trends in slip rates over time scales of the order of millennia. It is unclear whether the variability of recurrence times is due to fault processes alone or if they are modulated by off-fault deformation. Theoretical and numerical modeling of fault kinematics from geodetic data have enabled an explosion of new findings about the mechanics of the earthquake cycle. However, these models have been mostly confined to processes along the interface of a fault. Therefore many sources of off-fault deformation, such as thermoelasticity and viscoelasticity, cannot yet be accounted for in the earthquake cycle. Here, we couple fault kinematics and viscoelastic deformation within shear zones using the integral method to simulate unified earthquake cycles that combine fault and off-fault processes. We consider the modulation of slip rates along a fault within the brittle layer due to strain in a viscoelastic substrate beneath the brittle-ductile transition. By implementing a thermally-activated rheology accounting for thermal diffusion, we investigate the thermo-mechanical coupling of faults and mantle shear zones and its implications for earthquake recurrence.

  1. Fault zone development and strain partitioning in an extensional strike-slip duplex: A case study from the Mesozoic Atacama fault system, Northern Chile

    NASA Astrophysics Data System (ADS)

    Cembrano, J.; González, G.; Arancibia, G.; Ahumada, I.; Olivares, V.; Herrera, V.

    2005-05-01

    Upper crustal strike-slip duplexes provide an excellent opportunity to address the fundamental question of fault zone development and strain partitioning in an evolving system. Detailed field mapping of the Mesozoic Atacama fault system in the Coastal Cordillera of Northern Chile documents the progressive development of second- and third-order faults forming a duplex at a dilational jog between two overstepping master faults: the sinistral strike-slip, NNW-striking, Jorgillo and Bolfin faults. These are constituted by a meter-wide core of foliated S-C ultracataclasite and cataclasite, flanked by a damage zone of protocataclasite, splay faults and veins. Lateral separation of markers along master faults is on the order of a few kilometers. Second-order, NW-striking, oblique-slip subsidiary fault zones do not show foliated ultracataclasite; lateral sinistral separations are in the range of ˜ 10 to 200 m with a relatively minor normal dip-slip component. In turn, third-order, east-west striking normal faults exhibit centimetric displacement. Oblique-slip (sinistral-normal) fault zones located at the southern termination of the Bolfin fault form a well-developed imbricate fan structure. They exhibit a relatively simple architecture of extensional and extensional-shear fractures bound by low displacement shear fractures. Kinematic analysis of fault slip data from mesoscopic faults within the duplex area, document that the NW-striking and the EW-striking faults accommodate transtension and extension, respectively. Examination of master and subsidiary faults of the duplex indicates a strong correlation between total displacement and internal fault structure. Faults started from arrays of en echelon extensional/extensional-shear fractures that then coalesced into throughgoing strike-slip faults. Further displacement leads to the formation of discrete bands of cataclasite and ultracataclasite that take up a significant part of the total displacement. We interpret that the

  2. 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

  3. Earthquake faulting in subduction zones: insights from fault rocks in accretionary prisms

    NASA Astrophysics Data System (ADS)

    Ujiie, Kohtaro; Kimura, Gaku

    2014-12-01

    Subduction earthquakes on plate-boundary megathrusts accommodate most of the global seismic moment release, frequently resulting in devastating damage by ground shaking and tsunamis. As many earthquakes occur in deep-sea regions, the dynamics of earthquake faulting in subduction zones is poorly understood. However, the Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) and fault rock studies in accretionary prisms exhumed from source depths of subduction earthquakes have greatly improved our understanding of earthquake faulting in subduction zones. Here, we review key advances that have been made over the last decade in the studies of fault rocks and in laboratory experiments using fault zone materials, with a particular focus on the Nankai Trough subduction zone and its on-land analog, the Shimanto accretionary complex in Japan. New insights into earthquake faulting in subduction zones are summarized in terms of the following: (1) the occurrence of seismic slip along velocity-strengthening materials both at shallow and deep depths; (2) dynamic weakening of faults by melt lubrication and fluidization, and possible factors controlling coseismic deformation mechanisms; (3) fluid-rock interactions and mineralogical and geochemical changes during earthquakes; and (4) geological and experimental aspects of slow earthquakes.

  4. San Andreas fault zone head waves near Parkfield, California

    SciTech Connect

    Ben-Zion, Y.; Malin, P. Univ. of California, Santa Barbara, CA )

    1991-03-29

    Microearthquakes seismograms from the borehole seismic network on the San Andreas Fault near Parkfield, California, provide three lines of evidence that first P arrivals are head waves refracted along the cross-fault material contrast. First, the travel time difference between these arrivals and secondary phases identified as direct P waves scales linearly with the source-receiver distance. Second, these arrivals have the emergent wave character associated in theory and practice with refracted head waves instead of the sharp first breaks associated with direct P arrivals. Third, the first motion polarities of the emergent arrivals are reversed from those of the direct P waves as predicted by the theory of fault zone head waves for slip on the San Andreas fault. The presence of fault zone head waves in local seismic network data may help account for scatter in earthquake locations and source mechanisms. The fault zone head waves indicate that the velocity contrast across the San Andreas fault near Parkfield is approximately 4 percent. Further studies of these waves may provide a way of assessing changes in the physical state of the fault system.

  5. San andreas fault zone head waves near parkfield, california.

    PubMed

    Ben-Zion, Y; Malin, P

    1991-03-29

    Microearthquake seismograms from the borehole seismic network on the San Andreas fault near Parkfield, California, provide three lines of evidence that first P arrivals are "head" waves refracted along the cross-fault material contrast. First, the travel time difference between these arrivals and secondary phases identified as direct P waves scales linearly with the source-receiver distance. Second, these arrivals have the emergent wave character associated in theory and practice with refracted head waves instead of the sharp first breaks associated with direct P arrivals. Third, the first motion polarities of the emergent arrivals are reversed from those of the direct P waves as predicted by the theory of fault zone head waves for slip on the San Andreas fault. The presence of fault zone head waves in local seismic network data may help account for scatter in earthquake locations and source mechanisms. The fault zone head waves indicate that the velocity contrast across the San Andreas fault near Parkfield is approximately 4 percent. Further studies of these waves may provide a way of assessing changes in the physical state of the fault system. PMID:17793143

  6. 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

  7. The Longriqu fault zone, eastern Tibetan Plateau: Segmentation and Holocene behavior

    NASA Astrophysics Data System (ADS)

    Ansberque, Claire; Bellier, Olivier; Godard, Vincent; Lasserre, Cécile; Wang, Mingming; Braucher, Régis; Talon, Brigitte; Sigoyer, Julia; Xu, Xiwei; Bourlès, Didier L.

    2016-03-01

    The dextral Longriba fault system (LFS), ~300 km long and constituting of two fault zones, has recently been recognized as an important structure of the eastern Tibetan plateau (Sichuan province), as it accommodates a significant amount of the deformation induced by the ongoing Indo-Asian collision. Although previous paleoseismological investigations highlighted its high seismogenic potential, no systematic quantification of the dextral displacements along the fault system has been undertaken so far. As such information is essential to appraise fault behavior, we propose here a first detailed analysis of the segmentation of the Longriqu fault, the northern fault zone of the LFS, and an offset inventory of morphological features along the fault, using high-resolution Pleiades satellite images. We identify six major segments forming a mature fault zone. Offsets inventory suggests a characteristic coseismic displacement of ~4 m. Two alluvial fans, with minimum ages of 6.7 and 13.2 ka, respectively displaced by 23 ± 7 m and 40 ± 5 m, give an estimate of the maximal horizontal slip rate on the Longriqu fault of 3.2 ± 1.1 mm yr-1. As a result, a minimum ~1340 year time interval between earthquakes is expected.

  8. 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

  9. The Internal Structure of Fault Zones in Carbonates Deformed at Shallow Crustal Level - Evidence From Scaled Physical Models Using Cohesive Powder.

    NASA Astrophysics Data System (ADS)

    van Gent, H. W.; Holland, M.; Urai, J. L.; Loosveld, R.

    2006-12-01

    In cohesive carbonates deformed at shallow depth the ratio of the rock's compressive stress and the in-situ mean effective stress is usually large and faults are highly dilatant. This makes it difficult to do detailed studies outcrop or core, because the structures are fragile and easily damaged. We present scaled physical models of these structures made from fine-grained, cohesive Hemihydrate powder. Extensive deformation experiments characterize the material's properties to allow scaling with respect to the natural prototypes. Uniaxial consolidation test shows void ratio linearly dependent on pressure and a coefficient of compressibility (change of void ratio over change of normal load) of 0.0001/Pa. Compression and shear tests show that tensile strength of the powder is between 5 and 50 Pa, and cohesion varies between 50 and 250 Pa. Cohesion and tensile strength are inversely proportional to void ratio whereas the friction angle remains virtually constant. The powder's properties can be described by a Cam-Clay type constitutive relation, where the cohesion and tensile strength of the powder changes with depth in the model. We studied the evolution of normal faults in a graben above a rigid basement containing a fault with a dip of 60 DEG, in homogeneous or layered models with sand or graphite-gypsum mixtures to represent the weaker layers. The structural evolution and displacement field was analyzed by time-lapse digital photography and Particle Imaging Velocimetry (PIV). The initial displacement field is continuous: we interpret this as elastic strain prior to brittle failure. Localization of deformation produces both mode I and mode II fractures depending on the depth in the model. Characteristic structures are dilational jogs, fragmentation and fault gouge formation by gravity-driven mass transport along the open sections. The model show good correspondence with what is known from the structures in naturally occurring dilatant fault systems in carbonates.

  10. Fluids, fault zone permeability and two distinct types of pseudotachylyte

    NASA Astrophysics Data System (ADS)

    Bjornerud, M.

    2010-12-01

    The comparative rarity of pseudotachylyte in ancient fault zones is surprising in light of estimates that ca. 90% of the energy budget of an earthquake is expended in frictional heating. One explanation is that frictional melting (pseudotachylyte generation) is suppressed after the initial rupture on a fault zone because fluids infiltrate the zone and thermal pressurization of these fluids inhibits melting in subsequent seismic events. While this seems plausible for many of the iconic occurrences of pseudotachylyte in otherwise undamaged crystalline rocks, some pseudotachylytes clearly formed in host rocks in which permeability was apparently high and fluids were present at the time of frictional melting. In these fault zones, cataclasites and pseudotachylyte commonly have mutually cross cutting relationships, and both types of fault rock have been complexly intruded into the surrounding damage zone. In contrast, cataclasites associated with pseudotachylyte in pristine crystalline rocks occur in smaller volumes and have simpler geometries, typically limited to the margins of fault veins or in dilational jogs. These observations suggest that there may be two distinct physical circumstances under which frictional melting may occur and thus two distinct genetic types of pseudotachylyte. Classic “dry” pseudotachylytes (e.g., Holsnøy, Bergen Arcs, Norway; Gole Larghe Fault, Italy) probably represent the initial seismic rupture of intact, low-permeability rock at high effective stress in the absence of fluids. When fluids are present, however (e.g., central Otago, New Zealand; Nojima fault, Japan), the potential for frictional melting depends on the relative rates at which heat and fluids can escape from a fault zone. Geophysical models of dynamic weakening mechanisms during earthquakes (Rempel and Rice, JGR, 2006) show that thermal pressurization occurs when the hydraulic diffusivity is effectively less than thermal diffusivity, while melting occurs when thermal

  11. Transient Deformation at the Seismic-Aseismic Transition in a Mature Plate Boundary Fault Zone - New Zealand's Alpine Fault

    NASA Astrophysics Data System (ADS)

    Toy, V. G.; Norris, R. J.; Prior, D. J.

    2008-12-01

    During the seismic cycle, stresses and strain rates fluctuate in the viscously-deforming zones down-dip of large faults. These transient events produce geological records that can be preserved in exhumed fault zones that have experienced single ruptures (e.g. Sesia Zone, European Western Alps). On the other hand, in major faults that have not experienced a simple, single rupture history, coseismic structures are likely to be destroyed during subsequent cycles of postseismic creep. New Zealand's active Alpine Fault has likely experienced upwards of 20,000 Mw~8 earthquakes, on average one every 200-300 years, over the last ≥5 million years of dextral-reverse slip. Fault rocks generated during these events are exhumed in the hangingwall, exposing materials deformed throughout the seismogenic zone at the surface. We have recognised a structural record of transient events in these rocks that differs from that previously reported elsewhere. Mylonites were formed by viscous shearing of a metasedimentary protolith downdip of the seismogenic structure. Rheological models predict these mylonites should have passed through a crustal strength peak (τ ≥100 MPa) around the brittle-viscous transition. Immediately prior to passing through this transition, they should have developed a small recrystallised grainsize (~10-15μm) and a crystallographic preferred orientation (CPO) indicating slip on the basal system during quartz dislocation creep, as well as a retrograde greenschist-facies mineralogy. However, the high-strain mylonites preserve a large recrystallised grainsize (>~30μm), amphibolite-facies mineralogy and CPO characteristic of prism slip. This suggests they were not significantly deformed at temperatures below ~450°C, significantly above the lower temperature limit for quartz crystal-plasticity at steady-state strain rates in the fault zone Microstructural observations and textural data indicate variable deformation style through the seismic cycle. Large fault

  12. Fault pattern at the northern end of the Death Valley - Furnace Creek fault zone, California and Nevada

    NASA Technical Reports Server (NTRS)

    Liggett, M. A. (Principal Investigator); Childs, J. F.

    1974-01-01

    The author has identified the following significant results. The pattern of faulting associated with the termination of the Death Valley-Furnace Creek Fault Zone in northern Fish Lake Valley, Nevada was studied in ERTS-1 MSS color composite imagery and color IR U-2 photography. Imagery analysis was supported by field reconnaissance and low altitude aerial photography. The northwest-trending right-lateral Death Valley-Furnace Creek Fault Zone changes northward to a complex pattern of discontinuous dip slip and strike slip faults. This fault pattern terminates to the north against an east-northeast trending zone herein called the Montgomery Fault Zone. No evidence for continuation of the Death Valley-Furnace Creek Fault Zone is recognized north of the Montgomery Fault Zone. Penecontemporaneous displacement in the Death Valley-Furnace Creek Fault Zone, the complex transitional zone, and the Montgomery Fault Zone suggests that the systems are genetically related. Mercury mineralization appears to have been localized along faults recognizable in ERTS-1 imagery within the transitional zone and the Montgomery Fault Zone.

  13. Spatial variability of time-constant slip rates on the San Jacinto fault zone, southern California

    NASA Astrophysics Data System (ADS)

    Blisniuk, K.; Oskin, M. E.; Sharp, W. D.; Meriaux, A. B.; Rockwell, T. K.; Fletcher, K.; Owen, L. A.

    2011-12-01

    In southern California, the San Andreas (SAF) and San Jacinto fault (SJF) zones account for 70-80% of the relative dextral motion between the Pacific and North American plates, with some studies suggesting that the SJF zone may be the dominant structure. However, few slip rate measurements are available for the SJF zone, making it difficult to evaluate the partitioning of deformation across the plate boundary. To more reliably constrain the late Quaternary slip history of the SJF zone, we measured the displacement of well-preserved alluvial fans along the Clark and Coyote Creek fault strands of the SJF zone using field mapping and high-resolution LiDAR topographic data, and dated the fans using U-series on pedogenic carbonate clast-coatings and in situ cosmogenic 10Be. Our results from four sites along the Clark fault strand and two sites along the Coyote Creek fault strand indicate that late Quaternary slip rates have fluctuated along their length but have remained constant since the late Pleistocene. Slip rates along the Clark fault strand over the past 50-30 kyr decrease southward over a distance of ~60 km from ~13 mm/yr at Anza, to 8.9 ± 2.0 mm/yr at Rockhouse Canyon, and 1.5 ± 0.4 mm/yr near the SE end of the Santa Rosa Mountains, probably due to transfer of slip from the Clark fault strand to the Coyote Creek fault strand and nearby zones of distributed deformation. Slip rates of up to ~14 to 18 mm/yr summed across the southern SJF zone suggest that since the latest Pleistocene, the SJF zone may rival the southern SAF zone in accommodating deformation across the Pacific-North America Plate boundary.

  14. Low resistivity and permeability in actively deforming shear zones on the San Andreas Fault at SAFOD

    NASA Astrophysics Data System (ADS)

    Morrow, C.; Lockner, D. A.; Hickman, S.

    2015-12-01

    The San Andreas Fault Observatory at Depth (SAFOD) scientific drill hole near Parkfield, California, crosses the San Andreas Fault at a depth of 2.7 km. Downhole measurements and analysis of core retrieved from Phase 3 drilling reveal two narrow, actively deforming zones of smectite-clay gouge within a roughly 200 m wide fault damage zone of sandstones, siltstones, and mudstones. Here we report electrical resistivity and permeability measurements on core samples from all of these structural units at effective confining pressures up to 120 MPa. Electrical resistivity (~10 Ω-m) and permeability (10-21 to 10-22 m2) in the actively deforming zones were 1 to 2 orders of magnitude lower than the surrounding damage zone material, consistent with broader-scale observations from the downhole resistivity and seismic velocity logs. The higher porosity of the clay gouge, 2 to 8 times greater than that in the damage zone rocks, along with surface conduction were the principal factors contributing to the observed low resistivities. The high percentage of fine-grained clay in the deforming zones also greatly reduced permeability to values low enough to create a barrier to fluid flow across the fault. Together, resistivity and permeability data can be used to assess the hydrogeologic characteristics of the fault, key to understanding fault structure and strength. The low resistivities and strength measurements of the SAFOD core are consistent with observations of low resistivity clays that are often found in the principal slip zones of other active faults making resistivity logs a valuable tool for identifying these zones.

  15. Geochemical Characterisation of the Alpine Fault Zone from the DFDP Boreholes

    NASA Astrophysics Data System (ADS)

    Menzies, C. D.; Teagle, D. A. H.; Boulton, C. J.; Toy, V.; Townend, J.; Sutherland, R.

    2015-12-01

    . These findings imply that chemical alteration resulting from the circulation of meteoric waters modifies the fault zone's permeability structure by redistributing mass and changing the material properties of the plate boundary, and therefore plays an important role in the evolution of the fault zone which may prime it for repeated rupture.

  16. Spatial analysis of hypocenter to fault relationships for determining fault process zone width in Japan.

    SciTech Connect

    Arnold, Bill Walter; Roberts, Barry L.; McKenna, Sean Andrew; Coburn, Timothy C. (Abilene Christian University, Abilene, TX)

    2004-09-01

    Preliminary investigation areas (PIA) for a potential repository of high-level radioactive waste must be evaluated by NUMO with regard to a number of qualifying factors. One of these factors is related to earthquakes and fault activity. This study develops a spatial statistical assessment method that can be applied to the active faults in Japan to perform such screening evaluations. This analysis uses the distribution of seismicity near faults to define the width of the associated process zone. This concept is based on previous observations of aftershock earthquakes clustered near active faults and on the assumption that such seismic activity is indicative of fracturing and associated impacts on bedrock integrity. Preliminary analyses of aggregate data for all of Japan confirmed that the frequency of earthquakes is higher near active faults. Data used in the analysis were obtained from NUMO and consist of three primary sources: (1) active fault attributes compiled in a spreadsheet, (2) earthquake hypocenter data, and (3) active fault locations. Examination of these data revealed several limitations with regard to the ability to associate fault attributes from the spreadsheet to locations of individual fault trace segments. In particular, there was no direct link between attributes of the active faults in the spreadsheet and the active fault locations in the GIS database. In addition, the hypocenter location resolution in the pre-1983 data was less accurate than for later data. These pre-1983 hypocenters were eliminated from further analysis.

  17. Dissecting Oceanic Detachment Faults: Fault Zone Geometry, Deformation Mechanisms, and Nature of Fluid-Rock Interactions

    NASA Astrophysics Data System (ADS)

    Bonnemains, D.; Escartin, J.; Verlaguet, A.; Andreani, M.; Mevel, C.

    2015-12-01

    To understand the extreme strain localization at long-lived oceanic detachment faults rooting deeply below the axis, we present results of geological investigations at the 13°19'N detachment along the Mid-Atlantic Ridge, conducted during the ODEMAR cruise (Nov-Dec13, NO Pourquoi Pas?) with ROV Victor6000 (IFREMER). During this cruise we investigated and sampled the corrugated fault to understand its geometry, nature of deformation, and links to fluid flow. We identified and explored 7 fault outcrops on the flanks of microbathymetric striations subparallel to extension. These outcrops expose extensive fault planes, with the most prominent ones extending 40-90m laterally, and up to 10 m vertically. These fault surfaces systematically show subhorizontal striations subparallel to extension, and define slabs of fault-rock that are flat and also striated at sample scale. Visual observations show a complex detachment fault zone, with anastomosing fault planes at outcrop scale (1-10 m), with a highly heterogeneous distribution of deformation. We observe heterogeneity in fault-rock nature at outcrop scale. In situ samples from striated faults are primarily basalt breccias with prior green-schist facies alteration, and a few ultramafic fault-rocks that show a complex deformation history, with early schistose textures, brittlely reworked as clasts within the fault. The basalt breccias show variable silicification and associated sulfides, recording important fluid-rock interactions during exhumation. To understand the link between fluid and deformation during exhumation, we will present microstructural observation of deformation textures, composition, and distribution and origin of quartz and sulfides, as well as constraints on the temperature of silicifying fluids from fluid inclusions in quartz. These results allow us to characterize in detail the detachment fault zone geometry, and investigate the timing of silicification relative to deformation.

  18. 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.

  19. Fault zone exploration in a geothermal context using P- and S-wave measurements

    NASA Astrophysics Data System (ADS)

    Wawerzinek, Britta; Buness, Hermann; Musmann, Patrick; Tanner, David C.; Krawczyk, Charlotte M.; Thomas, Rüdiger

    2015-04-01

    In the framework of the collaborative research programme gebo ('Geothermal Energy and High Performance Drilling') we applied seismic P- and S-wave measurements to analyse and characterise fault zones. Fault zones have a high potential for geothermal energy extraction, but their usability depends on complex factors (structure, lithology, tectonics), underlining the need for detailed fault zone exploration and the deeper understanding of the factors' interplay. In this study, we carried out both P- and S-wave reflection seismic surveys parallel and perpendicular to the eastern border of the Leinetal Graben, Lower Saxony, to explore the fault system. The seismic data reveal a high-resolution image of the complex graben structure which comprises both steeply-dipping normal faults and shallowly west-dipping normal faults, which cause a roll-over structure. In addition halokinesis is observed. The structural image of the graben structure indicates independent tectonic development of the uppermost (<500 m) and deeper (>500 m) depth levels. One of the shallowly west-dipping normal faults is traceable from the surface down to 500 m depth. To further investigate this fault zone which shows different reflection characteristics of P- and S-waves, a petrophysical analysis was conducted, including elastic parameter derivation and seismic modelling. Elastic parameters change strongly in the near-surface area, e.g., vs increases from 300 m/s at the surface to 900 m/s at 100 m depth, leading to a decrease in vp/vs from 6 to approx. 2.5. Changes in elastic parameters correlate with the geological interpretation and are in correspondence to literature values for the given lithologies. However, the fault zone itself shows no significant changes in elastic parameters due to the low resolution of the derived seismic velocities. Seismic modelling is a helpful tool to check elastic parameters which are assigned to the fault zone in the model. A comparison between synthetic and field data

  20. Fault roughness evolution with slip (Gole Larghe Fault Zone, Italian Alps)

    NASA Astrophysics Data System (ADS)

    Bistacchi, A.; Spagnuolo, E.; Di Toro, G.; Nielsen, S. B.; Griffith, W. A.

    2011-12-01

    Fault surface roughness is a principal factor influencing fault and earthquake mechanics. However, little is known on roughness of fault surfaces at seismogenic depths, and particularly on how it evolves with accumulating slip. We have studied seismogenic fault surfaces of the Gole Larghe Fault Zone, which exploit precursor cooling joints of the Adamello tonalitic pluton (Italian Alps). These faults developed at 9-11 km and 250-300°C. Seismic slip along these surfaces, which individually accommodated from 1 to 20 m of net slip, resulted in the production of cm-thick cataclasites and pseudotachylytes (solidified melts produced during seismic slip). The roughness of fault surfaces was determined with a multi-resolution aerial and terrestrial LIDAR and photogrammetric dataset (Bistacchi et al., 2011, Pageoph, doi: 10.1007/s00024-011-0301-7). Fault surface roughness is self-affine, with Hurst exponent H < 1, indicating that faults are comparatively smoother at larger wavelengths. Fault surface roughness is inferred to have been inherited from the precursor cooling joints, which show H ≈ 0.8. Slip on faults progressively modified the roughness distribution, lowering the Hurst exponent in the along-slip direction up to H ≈ 0.6. This behaviour has been observed for wavelengths up to the scale of the accumulated slip along each individual fault surface, whilst at larger wavelengths the original roughness seems not to be affected by slip. Processes that contribute to modify fault roughness with slip include brittle failure of the interacting asperities (production of cataclasites) and frictional melting (production of pseudotachylytes). To quantify the "wear" due to these processes, we measured, together with the roughness of fault traces and their net slip, the thickness and distribution of cataclasites and pseudotachylytes. As proposed also in the tribological literature, we observe that wearing is scale dependent, as smaller wavelength asperities have a shorter

  1. 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

  2. Ground Penetrating Radar Imaging of the Emigrant Peak Fault Zone and Alluvial Fan

    NASA Astrophysics Data System (ADS)

    Christie, M. W.; Tsoflias, G. P.

    2006-12-01

    Near-surface geophysical studies at the University of Kansas are investigating active faulting in the Eastern California Shear Zone. The Emigrant Peak Fault, in Fish Lake Valley, Nevada, is a normal fault that aids in the transfer of right-lateral deformation associated with the Furnace Creek/Fish Lake/Death Valley fault system of the Walker Lane Belt/Eastern California Shear Zone. During the spring and summer of 2006 we collected ground penetrating radar (GPR) across the deformed alluvial fan associated with the Emigrant Peak Fault. The GPR study is conducted in conjunction with high resolution shallow seismic and geologic investigations underway to more fully characterize the fault zone. The GPR data crosses the surface expression of the Emigrant Peak Fault and it is comprised of a 50 MHz 3-D grid and 25 MHz 2-D lines. The 3-D grid covers an area of 115m X 500m at 1m trace spacing, 5m in-line spacing and intersecting cross-lines at 50, 100, 150, 250, and 450m across the in-lines. 2-D GPR lines were acquired at coincident locations with the shallow seismic data and along a 1500m regional line over the fault and alluvial fan deposits. Depth of imaging ranged between 17m for the 50 MHz data and 25m for the 25 MHz data. GPR imaging aids in the characterization of the fault zone structurally as well as characterizing alluvial fan stratigraphy. Data shows stratigraphic reflectors on a 1m scale. Reflector geometries are quite complex, showing continuous coherent events, as well as areas that are less coherent which appear to signal a change to more boulder/cobble-rich deposition, a common characteristic in debris-flow dominated alluvial fans. The reflectors are also heavily influenced by the structural components that are imaged. The GPR shows a number of west-dipping faults that seem to migrate towards the basin. The faults are not imaged merely as interrupted reflectors, but the fault surfaces are actually imaged. Stratigraphic reflectors truncate at the faults in

  3. Oblique strike-slip faulting of the Cascadia submarine forearc: The Daisy Bank fault zone off central Oregon

    NASA Astrophysics Data System (ADS)

    Goldfinger, Chris; Kulm, LaVerne D.; Yeats, Robert S.; Hummon, Cheryl; Huftile, Gary J.; Niem, Alan R.; McNeill, Lisa C.

    The Cascadia submarine forearc off Oregon and Washington is deformed by numerous active WNW-trending, left-lateral strike-slip faults. The kinematics of this set of sub-parallel left-lateral faults suggests clockwise block rotation of the forearc driven by oblique subduction. One major left-lateral strike-slip fault, the 94 km-long Daisy Bank fault, located off central Oregon, was studied in detail using high-resolution AMS 150 kHz and SeaMARC-lA sidescan sonar, swath bathymetry, multichannel seismic reflection profiles and a submersible. The Daisy Bank fault zone cuts the sediments and basaltic basement of the subducting Juan de Fuca plate, and the overriding North American plate, extending from the abyssal plain to the upper slope-outer shelf region. The Daisy Bank fault, a near-vertical left-lateral fault striking 292°, is a wide structural zone with multiple scarps observed in high-resolution sidescan images. From a submersible, we observe that these scarps offset late Pleistocene gray clay and overlying olive green Holocene mud, dating fault activity as post-12 ka on the upper slope. Vertical separation along individual fault scarps ranges from a few centimeters to 130 meters. Using a retrodeformation technique with multichannel reflection records, we calculate a net slip of 2.2±0.5 km. Fault movement commenced at about 380±50 ka near the western fault tip, based upon an analysis of growth strata and correlation with deep-sea drill hole biostratigraphy. We calculate a slip rate of 5.7±2.0 mm/yr. for the Daisy Bank fault at its western end on the Juan de Fuca plate. The motion of the set of oblique faults, including the Daisy Bank fault, may accommodate a significant portion of the oblique component of plate motion along the central Cascadia margin. We propose a block rotation model by which the seawardmost part of the forearc rotates clockwise and translates northward.

  4. Structure and Particle Size Distribution of Non-tectonic Faults - Difference from Tectonic Faults

    NASA Astrophysics Data System (ADS)

    Yamasaki, S.; Chigira, M.

    2009-04-01

    Non-tectonic faults are commonly formed by mass movements but their structures and formative processes have been scarcely studied in spite of their importance in slope development and slope stability. We observed structures of non-tectonic faults and analyzed particle size distribution of the material from the shear zones of non-tectonic faults and compared these results with those of tectonic faults. We clarified the structures of non-tectonic faults in pelitic schist by observing X-ray computer tomography images and cross-sections of paraffin-impregnated core samples that have been recovered from the subsurface by the hybrid drilling technique. We identified structures at various stages of non-tectonic fault development. Shearing within black layers, which are rich in graphite, dominates at an incipient stage. Then, rotation, fracturing, and pulverization of rock proceed, forming breccias and fine fractions in a fracture zone. Fracture zone at an early stage have many open fractures, which indicates a low confining pressure during deformation. With the development of a fracture zone, open fractures decrease and fine fractions increase in amount. Finally shearing deformation would be dominated by cataclastic flow in fine fractions. This stage is at a mature stage, where the structure becomes very similar to that of tectonic faults so that it cannot be distinguished from a tectonic fault by structure only. However, particle size distribution could indicate the formative condition of fine fractions in a fracture zone. We sampled "gauge" from several mature fracture zones in two landslide sites of pelitic schist, and analyzed their particle size distributions from 20 nm to 1 mm by using a laser diffraction particle size analyzer. The ultra micro particles in the fracture zone of a non-tectonic fault can be assumed to be primary particles which are less affected by alteration, and their particle size distributions could reflect the conditions of fracturing. The

  5. Porosity and Connectivity Anisotropy of The Pyrgaki Fault Zone, South Part of The Corinth Rift.

    NASA Astrophysics Data System (ADS)

    Géraud, Y.; Diraison, M.

    Quantitatively assessing the impact of fault zone on fluid flow in seismically active area requires an accurate conceptual model of fractures, matrix porosity, chemical and physical properties. Three main volumes compose a fault zone: the gouge, the damage zone and the protolith. As a fault zone evolves, its structure and properties, especially hydraulic, thermal and mechanical vary on time and space in value and anisotropy. This behavior depends as well as on the fracture network than the matrix transforma- tion. Indeed, multi-scalar approach becomes necessary to develop a coherent numeri- cal model. In the aim to contribute to the model development, characterization of the porous network is performed using mercury porosimetry and SEM observations. The Pyrgaki fault zone is twenty kilometers in the South of Aigion (Greece) in the south part of the corinth rift, fault zones have limestone in the both hanging wall and foot- wall. A cross section through the fault zone samples 5 meters in the footwall and 4 meters in the hanging wall. Two material types compose the gouge, the first has low grain size and low macroporosity value, and the second material has large grain size and high macroporosity value. Mercury injection gives data about different porosity volumes; the connectivity anisotropy defined using a new is procedure of mercury test. The porous network is mainly formed by tubes in the gouge zone and by cracks in the damage zone. In the gouge zone the crack content is higher in the second types of material than in the first one. Porosity volumes, connectivity anisotropy and void shapes are used to build a porous network usable to modeling hydraulic, mechanical and chemical properties.

  6. Orientations of faults determined by premonitory shear zones

    NASA Astrophysics Data System (ADS)

    Johnson, Arvid M.

    1995-07-01

    The postulate of premonitory shear zones that the orientations of many faults are controlled by previously formed shear zones is a combination of theoretical analysis and the concept that faulting is the result of a group of hereditary processes. The hereditary nature of faulting processes is evinced by detailed observations of faulting in several, quite different materials in which the faults are end products of irreversible, localized deformation sequences such as pressure solution, particle rearrangement, layer reorientation, plastic flow or grain fracturing. The localized deformation is concentrated within shear zones that premonish the formation of faults. Thus, the problem of determining the orientations of faults becomes one of determining the preferred orientations of shear zones, which is the focus of the postulate of premonitory shear zones. The postulate is based on one definition and two assumptions: by definition, deformation becomes localized within a shear zone (the reason need not be specified); by assumption, the virtual shearing and dilation within the shear zone are coupled and the orientation that develops corresponds to the preferred orientation. The preferred orientation of the shear zone is defined as that which satisfies the mechanical and kinematical boundary conditions and maximizes, in some sense, the virtual work accomplished by the shearing and dilation. With the exception of coupling of the shearing and dilation through a coefficient of dilation, the analysis is only implicitly dependent on rheology; the only rheological requirement is that the properties allow localization. Although the postulate is based on very simple assumptions, and so its predictions are necessarily simple, it has a power that belies its simplicity. The preferred orientations of premonitory shear zones are consistent with orientations of shear zones and faults in laboratory specimens of Chelmsford granite. The coefficient of dilatancy in granite specimens about

  7. Spatiotemporal patterns of fault slip rates across the Central Sierra Nevada frontal fault zone

    NASA Astrophysics Data System (ADS)

    Rood, Dylan H.; Burbank, Douglas W.; Finkel, Robert C.

    2011-01-01

    Patterns in fault slip rates through time and space are examined across the transition from the Sierra Nevada to the Eastern California Shear Zone-Walker Lane belt. At each of four sites along the eastern Sierra Nevada frontal fault zone between 38 and 39° N latitude, geomorphic markers, such as glacial moraines and outwash terraces, are displaced by a suite of range-front normal faults. Using geomorphic mapping, surveying, and 10Be surface exposure dating, mean fault slip rates are defined, and by utilizing markers of different ages (generally, ~ 20 ka and ~ 150 ka), rates through time and interactions among multiple faults are examined over 10 4-10 5 year timescales. At each site for which data are available for the last ~ 150 ky, mean slip rates across the Sierra Nevada frontal fault zone have probably not varied by more than a factor of two over time spans equal to half of the total time interval (~ 20 ky and ~ 150 ky timescales): 0.3 ± 0.1 mm year - 1 (mode and 95% CI) at both Buckeye Creek in the Bridgeport basin and Sonora Junction; and 0.4 + 0.3/-0.1 mm year - 1 along the West Fork of the Carson River at Woodfords. Data permit rates that are relatively constant over the time scales examined. In contrast, slip rates are highly variable in space over the last ~ 20 ky. Slip rates decrease by a factor of 3-5 northward over a distance of ~ 20 km between the northern Mono Basin (1.3 + 0.6/-0.3 mm year - 1 at Lundy Canyon site) to the Bridgeport Basin (0.3 ± 0.1 mm year - 1 ). The 3-fold decrease in the slip rate on the Sierra Nevada frontal fault zone northward from Mono Basin is indicative of a change in the character of faulting north of the Mina Deflection as extension is transferred eastward onto normal faults between the Sierra Nevada and Walker Lane belt. A compilation of regional deformation rates reveals that the spatial pattern of extension rates changes along strike of the Eastern California Shear Zone-Walker Lane belt. South of the Mina Deflection

  8. Spatiotemporal Patterns of Fault Slip Rates Across the Central Sierra Nevada Frontal Fault Zone

    NASA Astrophysics Data System (ADS)

    Rood, D. H.; Burbank, D.; Finkel, R. C.

    2010-12-01

    We examine patterns in fault slip rates through time and space across the transition from the Sierra Nevada to the Eastern California Shear Zone-Walker Lane belt. At each of four sites along the eastern Sierra Nevada frontal fault zone between 38-39° N latitude, geomorphic markers, such as glacial moraines and outwash terraces, are displaced by a suite of range-front normal faults. Using geomorphic mapping, surveying, and Be-10 surface exposure dating, we define mean fault slip rates, and by utilizing markers of different ages (generally, ~20 ka and ~150 ka), we examine rates through time and interactions among multiple faults over 10-100 ky timescales. At each site for which data are available for the last ~150 ky, mean slip rates across the Sierra Nevada frontal fault zone have probably not varied by more than a factor of two over time spans equal to half of the total time interval (~20 ky and ~150 ky timescales): 0.3 ± 0.1 mm/yr (mode and 95% CI) at both Buckeye Creek in the Bridgeport basin and Sonora Junction; and 0.4 +0.3/-0.1 mm/yr along the West Fork of the Carson River at Woodfords. Our data permit that rates are relatively constant over the time scales examined. In contrast, slip rates are highly variable in space over the last ~20 ky. Slip rates decrease by a factor of 3-5 northward over a distance of ~20 km between the northern Mono Basin (1.3 +0.6/-0.3 mm/yr at Lundy Canyon site) and the Bridgeport Basin (0.3 ± 0.1 mm/yr). The 3-fold decrease in the slip rate on the Sierra Nevada frontal fault zone northward from Mono Basin reflects a change in the character of faulting north of the Mina Deflection as extension is transferred eastward onto normal faults between the Sierra Nevada and Walker Lane belt. A compilation of regional deformation rates reveal that the spatial pattern of extension rates changes along strike of the Eastern California Shear Zone-Walker Lane belt. South of the Mina Deflection, extension is accommodated within a diffuse zone of

  9. The role of bedding in the evolution of meso- and microstructural fabrics in fault zones

    NASA Astrophysics Data System (ADS)

    Ishii, Eiichi

    2016-08-01

    To investigate the role of bedding in the evolution of meso- and microstructural fabrics in fault zones, detailed microscopic, mineralogical, and geochemical analyses were conducted on bedding-oblique and bedding-parallel faults that cut a folded Neogene siliceous mudstone that contains opal-CT, smectite, and illite. An analysis of asymmetric structures in the fault gouges indicates that the secondary fractures associated with each fault exhibit contrasting characteristics: those of the bedding-oblique fault are R1 shears, whereas those of the bedding-parallel fault are reactivated S foliation. The bedding-oblique fault shows the pervasive development of S foliation, lacks opal-CT, and has low SiO2/TiO2 ratios only in gouge, whereas the bedding-parallel fault exhibits these characteristics in both gouge and wall rocks. The development of S foliation and the lack of silica can result from local ductile deformation involving the sliding of phyllosilicates, coupled with pressure solution of opal-CT. Although such deformation can occur in gouge, the above results indicate that it may occur preferentially along bedding planes, preceding the formation of a gouge/slip surface. Thus, in sedimentary rocks that contain phyllosilicates and soluble minerals, bedding can influence the rheological evolution of meso- and microstructural fabrics in fault zones.

  10. Architecture of a low-angle normal fault zone, southern Basin and Range (SE California)

    NASA Astrophysics Data System (ADS)

    Goyette, J. A.; John, B. E.; Campbell-Stone, E.; Stunitz, H.; Heilbronner, R.; Pec, M.

    2009-12-01

    Exposures of the denuded Cenozoic detachment fault system in the southern Sacramento Mountains (SE California) delimit the architecture of a regional low-angle normal fault, and highlight the evolution of these enigmatic faults. The fault was initiated ~23 Ma in quartzo-feldspathic basement gneiss and granitoids at a low-angle (<20 degrees); isostatic accommodation due to unloading and doming of the footwall continued until ~16 Ma, leading to initiation of a secondary breakaway accommodating up to 5km of additional ENE-directed slip. Minimum-relief structure contours define the fault as a continuous low-angle structure with both slip-parallel (NE) and slip-normal (NW) corrugations. Fault dip of the secondary breakaway is ~7° based on the contour map, and 10-15° measured at outcrop, flattening to <2° down dip. Slip-parallel corrugations plunge NE with wavelengths between 600m and >2km, and amplitudes up to 100m. These corrugations are continuous along their hinges for up to 3.6 km. Damage zone fracture intensity varies both laterally, and perpendicular to the fault plane (over an area of 25km2), decreasing with depth in the footwall, and varies as a function of lithology and proximity to corrugation walls. Deformation is concentrated into narrow damage zones (<4m) where gouge is developed. In contrast, thick damage zones (>100m) are found in areas where low-fracture intensity horses are corralled by sub-horizontal zones of cataclasite (up to 8m) and thick zones of epidote (up to 20cm) and silica-rich alteration (up to 1m). Sub-vertical shear and extension fractures, and sub-horizontal shear fractures/zones dominate the NE side of the core complex. In all cases, sub-vertical fractures verge into or are truncated by low-angle fractures that dominate the top of the damage zone. These low-angle fractures have an antithetic dip to the detachment fault plane. Some sub-vertical fractures become curviplanar close to the fault, where they are folded into parallelism with