Sample records for subparallel fault zones

  1. Cataclastic faults along the SEMP fault system (Eastern Alps, Austria) — A contribution to fault zone evolution, internal structure and paleo-stresses (United States)

    Hausegger, Stefan; Kurz, Walter


    In this study three different sites along the ENE-trending, sinistral Salzach-Ennstal-Mariazell-Puchberg [SEMP] fault zone were investigated with respect to brittle fault zone evolution and fault re-activation. All sites crop out in Triassic carbonates (Ladinian Wetterstein limestone/-dolomite). Simultaneously (re-) activated faults were investigated with focus on fault-slip data and structural inventory of each individual fault zone. Configuration of (internal) structural elements, fault core thickness, strike direction and slip sense in addition to particle analysis of fault core cataclasites add up to three different fault types (Fault Types I, II and III). Fault Type I is classified by a complex internal fault core structure with thicknesses up to several 10s of meters and generally evolve in a strike direction of maximum shear stress (τmax). Type II faults, characterized by cataclastic fault cores with thicknesses up to 1 m, as well as Type III faults (thin solitary cataclastic layers) evolve sub-parallel to the main fault direction and in orientation according to R, R' or X shear fractures with variable (σn/τ) ratio. Progressive development from Type III to Type II and Type I faults is consistent with increasing displacement and increasing fault core width. Fault type classification and related paleostress analysis provide evidence from field observation compared to theoretical and analog models of Mohr-Coulomb fracture evolution.

  2. Fethiye-Burdur Fault Zone (SW Turkey): a myth? (United States)

    Kaymakci, Nuretdin; Langereis, Cornelis; Özkaptan, Murat; Özacar, Arda A.; Gülyüz, Erhan; Uzel, Bora; Sözbilir, Hasan


    Fethiye Burdur Fault Zone (FBFZ) is first proposed by Dumont et al. (1979) as a sinistral strike-slip fault zone as the NE continuation of Pliny-Strabo trench in to the Anatolian Block. The fault zone supposed to accommodate at least 100 km sinistral displacement between the Menderes Massif and the Beydaǧları platform during the exhumation of the Menderes Massif, mainly during the late Miocene. Based on GPS velocities Barka and Reilinger (1997) proposed that the fault zone is still active and accommodates sinistral displacement. In order to test the presence and to unravel its kinematics we have conducted a rigorous paleomagnetic study containing more than 3000 paleomagnetic samples collected from 88 locations and 11700 fault slip data collected from 198 locations distributed evenly all over SW Anatolia spanning from Middle Miocene to Late Pliocene. The obtained rotation senses and amounts indicate slight (around 20°) counter-clockwise rotations distributed uniformly almost whole SW Anatolia and there is no change in the rotation senses and amounts on either side of the FBFZ implying no differential rotation within the zone. Additionally, the slickenside pitches and constructed paleostress configurations, along the so called FBFZ and also within the 300 km diameter of the proposed fault zone, indicated that almost all the faults, oriented parallel to subparallel to the zone, are normal in character. The fault slip measurements are also consistent with earthquake focal mechanisms suggesting active extension in the region. We have not encountered any significant strike-slip motion in the region to support presence and transcurrent nature of the FBFZ. On the contrary, the region is dominated by extensional deformation and strike-slip components are observed only on the NW-SE striking faults which are transfer faults that accommodated extension and normal motion. Therefore, we claim that the sinistral Fethiye Burdur Fault (Zone) is a myth and there is no tangible

  3. The evolution of faults formed by shearing across joint zones in sandstone (United States)

    Myers, Rodrick; Aydin, Atilla


    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.

  4. The implications of fault zone transformation on aseismic creep: Example of the North Anatolian Fault, Turkey (United States)

    Kaduri, Maor; Gratier, Jean-Pierre; Renard, François; ćakir, Ziyadin; Lasserre, Cécile


    Aseismic creep is observed at surface along several segments of the North Anatolian right-lateral active fault in Turkey, a major plate boundary between Eurasia and Anatolia. Identifying the mechanisms that control creep and their temporal and spatial change represents a major challenge for predicting the mechanical evolution of active faults, the interplay between creep and earthquakes, and the link between short-term observations from geodesy and the long-term fault zone evolution. We combine geological observations, laboratory analyses, and imaging techniques, shedding new light on the mechanism of fault creep along the North Anatolian Fault (NAF) and its time-dependent change. A clear correlation is shown between shallow creep and near-surface fault gouge composition: locked segments of the NAF are mostly composed of massive limestones without clay gouges, whereas creeping segments comprise clay gouges that contain low-friction minerals. Such fault gouges appear to result from a progressive change of initial volcanic host rocks during their deformation. Anastomosing cleavage develops during the first stage of displacement, leading to layering, oblique at first and then subparallel to the fault, which accommodates part of the aseismic creep by pressure solution. Soluble minerals are dissolved, leading to passive concentration of phyllosilicates in the gouges where alteration transformations by fluid flow produce low friction minerals. At the same time damage zones are fractured and fractures are sealed by carbonates. As a result, these mineralogical and structural transformations weaken the gouge and strengthen the damage zone leading to the change from diffuse to localized seismic-aseismic zones.

  5. Ten kilometer vertical Moho offset and shallow velocity contrast along the Denali fault zone from double-difference tomography, receiver functions, and fault zone head waves (United States)

    Allam, A. A.; Schulte-Pelkum, V.; Ben-Zion, Y.; Tape, C.; Ruppert, N.; Ross, Z. E.


    We examine the structure of the Denali fault system in the crust and upper mantle using double-difference tomography, P-wave receiver functions, and analysis (spatial distribution and moveout) of fault zone head waves. The three methods have complementary sensitivity; tomography is sensitive to 3D seismic velocity structure but smooths sharp boundaries, receiver functions are sensitive to (quasi) horizontal interfaces, and fault zone head waves are sensitive to (quasi) vertical interfaces. The results indicate that the Mohorovičić discontinuity is vertically offset by 10 to 15 km along the central 600 km of the Denali fault in the imaged region, with the northern side having shallower Moho depths around 30 km. An automated phase picker algorithm is used to identify 1400 events that generate fault zone head waves only at near-fault stations. At shorter hypocentral distances head waves are observed at stations on the northern side of the fault, while longer propagation distances and deeper events produce head waves on the southern side. These results suggest a reversal of the velocity contrast polarity with depth, which we confirm by computing average 1D velocity models separately north and south of the fault. Using teleseismic events with M ≥ 5.1, we obtain 31,400 P receiver functions and apply common-conversion-point stacking. The results are migrated to depth using the derived 3D tomography model. The imaged interfaces agree with the tomography model, showing a Moho offset along the central Denali fault and also the sub-parallel Hines Creek fault, a suture zone boundary 30 km to the north. To the east, this offset follows the Totschunda fault, which ruptured during the M7.9 2002 earthquake, rather than the Denali fault itself. The combined results suggest that the Denali fault zone separates two distinct crustal blocks, and that the Totschunda and Hines Creeks segments are important components of the fault and Cretaceous-aged suture zone structure.

  6. Gravity Modeling of the Cerro Goden fault zone, NW Puerto Rico (United States)

    Mattei, G. A.; Keranen, K. M.; Asencio, E.


    The 2010 M7.0 Haiti earthquake served as a reminder of potential earthquake hazards on upper-crustal fault systems along the northern boundary of the Carribean plate. In this study we modeled the structure of the Cerro Goden and subparallel fault zones in northwestern Puerto Rico, which cross through densely populated areas, using existing and newly collected gravity data. The fault zone had previously been mapped at the surface, but the details of the fault zone in the subsurface and the detailed structure remain poorly constrained. We used our gravity data to extend surface geologic models to greater depth. Specifically, we modeled and interpreted a north-to-south 2-D model perpendicular to the Cerro Goden fault zone. We used horizontal derivative and residual anomaly maps to emphasize edges of subsurface bodies and shallow structures of interest. Our preliminary 2D model constrains the width and depth extent of serpentinite bodies along the fault zones, the relationship of the faults with the Cerro Goden anticline in central Puerto Rico, and confirms the steep NE dip of the faults extrapolated from surface data. Additional data will be collected in the future across the Cerro Goden fault zone to laterally extend our models of subsurface structural features.

  7. Fault zone fabric and fault weakness

    NARCIS (Netherlands)

    Collettini, C.; Niemeijer, A.; Viti, C.; Marone, C.


    Geological and geophysical evidence suggests that some crustal faults are weak1–6 compared to laboratory measurements of frictional strength7. Explanations for fault weakness include the presence of weak minerals4, high fluid pressures within the fault core8,9 and dynamic processes such as

  8. Shear zones formed along long, straight traces of fault zones during the 28 June 1992 Landers, California, earthquake (United States)

    Johnson, Arvid M.; Fleming, Robert W.; Cruikshank, Kenneth M.


    Surface rupturing during the 28 June 1992 Landers, California, earthquake, east of Los Angeles, accommodated right-lateral offsets up to about 6 m along segments of distinct, en-echelon fault zones with a total length of 80 km. The offsets were accommodated generally not by faults—distinct slip surfaces—but rather by shear zones, tabular bands of localized shearing. Along simple stretches of fault zones at Landers the rupture is characterized by telescoping of shear zones and intensification of shearing: broad shear zones of mild shearing, containing narrow shear zones of more intense shearing, containing even narrower shear zones of very intense shearing, which may contain a fault. Thus the ground ruptured across broad belts of shearing with clearly defined, subparallel walls, oriented NW. Each broad belt consists of a broad zone of mild shearing, extending across its entire width (50 to 200 m), and much narrower (a few meters wide) shear zones that accommodate most of the offset of the belt and are portrayed by en-echelon tension cracks. In response to right-lateral shearing, the slices of ground bounded by the tension cracks rotated in a clockwise sense, producing left-lateral shearing, and the slices were forced against the walls of the shear zone, producing thrusting. Even narrower shear zones formed within the narrow shear zones. Although these probably are guides to right-lateral fault segments below, the surface rupturing during the earthquake is characterized not by faulting, but by the formation of shear zones at various scales.

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

    DEFF Research Database (Denmark)

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


    We locate the concealed Carlsberg Fault zone along a 12-km-long trace in the Copenhagen city centre by seismic refraction, reflection and fan profiling. The Carlsberg Fault is located in a NNW-SSE striking fault system in the border zone between the Danish Basin and the Baltic Shield. Recent...... the fault zone. The fault zone is a shadow zone to shots detonated outside the fault zone. Finite-difference wavefield modelling supports the interpretations of the fan recordings. Our fan recording approach facilitates cost-efficient mapping of fault zones in densely urbanized areas where seismic normal...

  10. Oblique strike-slip faulting of the Cascadia submarine forearc: The Daisy Bank fault zone off central Oregon (United States)

    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.

  11. Fault zones in Triassic Muschelkalk limestones of the Upper Rhine Graben: Infrastructure characterization and permeability structure analyses (United States)

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


    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

  12. Paleoseismology of the 1966 Varto Earthquake (Ms 6.8) and Structure of the Varto Fault Zone, Eastern Turkey (United States)

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


    Turkey is a region of active faulting and contains several strike-slip fault zones, which have generated both historical and recent large earthquakes. Two active fault zones in Turkey, the North Anatolian Fault Zone (NAFZ) and the East Anatolian Fault Zone (EAFZ), divide the area into the Anatolian micro-plate accommodating WSW-directed movement. The southeastern continuation of the NAFZ is often referred to the Varto Fault Zone (VFZ). The VFZ cuts mainly Pliocene volcano-sedimentary units and/or Quaternary deposits and is characterized by multiple fault strands and multiple, closely spaced, active seismogenic zones. Fault motions in the zone are primarily right-lateral, with a subordinate component of NNW-SSE shortening. Study area is Varto region in which indications of active faulting are very well preserved. We recognized three coseismic ruptures from five trench exposures. It is referred to these as events 1 (youngest) through 3 (oldest). The best evidence of event 3 comes from fault traces and its upward terminations. The major components of this fault are fault core and damage zone. The fault is not just one plane of discontinuity and bifurcates and creates additional slip surfaces, which propagate out of the plane of the original fault. Event 2 and event 1, referring to 1946 and 1966 earthquakes, are characterized primarily by discrete, regularly spaced normal faults with and 55-80 cm and 105-270 cm throws, respectively and geometry of growth strata. The VFZ in the study area include typical structures of strike-slip fault zone. It forms a number of parallel and slightly sub-parallel strands striking N50°-72°W including contractional and extensional brittle structures. Several meters to tens of meters wavelength active folds with ENE-WSW and WNW-ESE trending fold axis. These folds deform the Plio-Quaternary units and show classic asymmetry associated with both a south- and north-vergent fault propagation fold. Meso-scale normal faults are also well

  13. Fault Zones in the Gulf Coast [gcfltzoneg (United States)

    U.S. Geological Survey, Department of the Interior — These data represent major fault zones as indicated on Plate 2, Principal structural features, Gulf of Mexico Basin (compiled by T.E. Ewing and R.F. Lopez) in volume...

  14. Integrated seismic interpretation of the Carlsberg Fault zone, Copenhagen, Denmark (United States)

    Nielsen, Lars; Thybo, Hans; Jørgensen, Mette I.


    We locate the concealed Carlsberg Fault zone along a 12-km-long trace in the Copenhagen city centre by seismic refraction, reflection and fan profiling. The Carlsberg Fault is located in a NNW-SSE striking fault system in the border zone between the Danish Basin and the Baltic Shield. Recent earthquakes indicate that this area is tectonically active. A seismic refraction study across the Carlsberg Fault shows that the fault zone is a low-velocity zone and marks a change in seismic velocity structure. A normal incidence reflection seismic section shows a coincident flower-like structure. We have recorded seismic signals in a fan geometry from shots detonated both inside the low-velocity fault zone and up to ~500 m away from the fault zone. The seismic energy was recorded on three receiver arrays (1.5- to 2.4-km-long arcs) across the expected location of the ~400- to 700-m-wide fault zone at distances of up to ~7 km from the shots. Shots detonated inside the fault zone result in (1) weak and delayed first arrivals on the receivers located inside the fault zone compared to earlier and stronger first arrivals outside the fault zone; (2) strong guided P and S waves as well as surface waves inside the fault zone. The fault zone is a shadow zone to shots detonated outside the fault zone. Finite-difference wavefield modelling supports the interpretations of the fan recordings. Our fan recording approach facilitates cost-efficient mapping of fault zones in densely urbanized areas where seismic normal incidence and refraction profiling are not feasible.

  15. Fault damage zone origin of the Teufelsmauer, Subhercynian Cretaceous Basin, Germany (United States)

    Klimczak, Christian; Schultz, Richard A.


    Recognition of fractures as porosity-reducing deformation bands pervading all sandstone segments of the Teufelsmauer, Subhercynian Creatceous Basin, Germany, motivates a study relating the observed macroscopic and microscopic deformation to the damage zone of the nearby Harz border fault. Deformation bands, confirmed and documented by several porosity-reducing micro-mechanisms, such as cataclasis, particulate flow, pressure solution and a heavy quartz cementation, were mapped and analyzed in terms of the kinematics and deformation intensities expressed by them. Deformation band kinematics are uniform throughout the entire basin and consistent with the large-scale tectonic structures of the area. A strain intensity study highlights two narrow but long zones of deformation bands, sub-parallel to the Harz border fault. Deformation band kinematics, strain intensity, as well as micro-mechanisms are all consistent with a continuous but internally diverse deformation band damage zone of the entire Teufelsmauer structure along the Harz border fault, bringing new insights into the tectonic evolution and the origin of the heavy quartz cementation of the sandstones in the Subhercynian Cretaceous Basin.

  16. The East Anatolian Fault Zone: Seismotectonic setting and spatiotemporal characteristics of seismicity based on precise earthquake locations (United States)

    Bulut, F.; Bohnhoff, M.; Eken, T.; Janssen, C.; Kilic, T.; Dresen, G. H.


    The East Anatolian Fault Zone (EAFZ) represents a plate boundary extending over approx. 500 km between the Arabian and Anatolian plates. Relative plate motion occurs with slip rates ranging from 6 to 10 mm/yr and has resulted in destructive earthquakes in eastern Turkey as documented by historical records. In this study, we investigate the seismic activity along the EAFZ and fault kinematics based on recordings from a densified regional seismic network providing the best possible azimuthal coverage for the target region. We optimize a reference 1-D velocity model using a grid-search approach and re-locate hypocenters using the Double-Difference earthquake relocation technique. The refined hypocenter catalog provides insights into the kinematics and internal deformation of the fault zone down to a resolution ranging typically between 100 and 200 m. The distribution of hypocenters suggests that the EAFZ is characterized by NE-SW and E-W oriented sub-segments that are sub-parallel to the overall trend of the fault zone. Faulting mechanisms are predominantly left-lateral strike-slip and thus in good correlation with the deformation pattern derived from regional GPS data. However, we also observe local clusters of thrust and normal faulting events, respectively. While normal faulting events typically occur on NS-trending subsidiary faults, thrust faulting is restricted to EW-trending structures. This observation is in good accordance with kinematic models proposed for evolving shear zones. The observed spatiotemporal evolution of hypocenters indicates a systematic migration of micro- and moderate-sized earthquakes from the main fault into adjacent fault segments within several days documenting progressive interaction between the major branch of the EAFZ and its secondary structures. Analyzing the pre versus post-seismic phase for M > 5 events we find that aftershock activities are initially spread to the entire source region for several months but start to cluster at

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

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


    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

  18. Numerical modelling of the mechanical and fluid flow properties of fault zones - Implications for fault seal analysis

    NARCIS (Netherlands)

    Heege, J.H. ter; Wassing, B.B.T.; Giger, S.B.; Clennell, M.B.


    Existing fault seal algorithms are based on fault zone composition and fault slip (e.g., shale gouge ratio), or on fault orientations within the contemporary stress field (e.g., slip tendency). In this study, we aim to develop improved fault seal algorithms that account for differences in fault zone

  19. The Geomorphological Developments Along the East Anatolian Fault Zone, Turkey (United States)

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


    The collision of Eurasia with Arabia has given rise to intracontinental shortening in SE Turkey and development of large scale fault zones. The East Anatolian Fault Zone (EAFZ), a major active fault zone over 700 km in length with NE-striking, defines the boundary zone between Eurasia plate and Anatolian micro-plate. Although the northeastern continuation of the zone merges into the North Anatolian Fault Zone at Karliova region, the southwestern continuation has been the subject of some debate. The zone is characterized by numerous, complex faults and segmented surface ruptures. It cuts and offsets several distinctive units in east and southeast Turkey. The portion of the EAFZ examined in this study extends from Celikhan to Turkoglu. Active fault strands in this portion of the EAFZ is termed the Erkenek and Golbasi segments. The zone is made of several NE-SW closely spaced strands cut across Mesozoic-to-Tertiary variable rock units and structures, indicating inception of strike-slip motion in Quaternary and characterized by a series of basins. Fault-related several morphological features have been mapped are within the study area, suggesting the left-lateral motion of fault strands along this part of the EAFZ. Offset streams, beheaded channels, pressure and shutter ridges, linear valleys and ridges and sag ponds are prominent morpho-tectonic features. Offset streams have been measured as few meters to hundreds of meters and show sinistral displacement along the fault zone. Fault scarps, several tens of metres high, are developed in fan deposits along the length of the fault strands. Forming the set of linear sag ponds in Golbasi reveals extentional activity of the EAFZ in this area. Motion of fault strands formed linear valleys and ridges parallel to the faults which is most remarkable features. Our geomorphic studies demonstrated the ongoing activity of the the EAFZ between Celikhan to Turkoglu regions.

  20. Active faulting on the Wallula fault zone within the Olympic-Wallowa lineament, Washington State, USA (United States)

    Sherrod, Brian; Blakely, Richard J.; Lasher, John P.; Lamb, Andrew P.; Mahan, Shannon; Foit, Franklin F.; Barnett, Elizabeth


    The Wallula fault zone is an integral feature of the Olympic-Wallowa lineament, an ∼500-km-long topographic lineament oblique to the Cascadia plate boundary, extending from Vancouver Island, British Columbia, to Walla Walla, Washington. The structure and past earthquake activity of the Wallula fault zone are important because of nearby infrastructure, and also because the fault zone defines part of the Olympic-Wallowa lineament in south-central Washington and suggests that the Olympic-Wallowa lineament may have a structural origin. We used aeromagnetic and ground magnetic data to locate the trace of the Wallula fault zone in the subsurface and map a quarry exposure of the Wallula fault zone near Finley, Washington, to investigate past earthquakes along the fault. We mapped three main packages of rocks and unconsolidated sediments in an ∼10-m-high quarry exposure. Our mapping suggests at least three late Pleistocene earthquakes with surface rupture, and an episode of liquefaction in the Holocene along the Wallula fault zone. Faint striae on the master fault surface are subhorizontal and suggest reverse dextral oblique motion for these earthquakes, consistent with dextral offset on the Wallula fault zone inferred from offset aeromagnetic anomalies associated with ca. 8.5 Ma basalt dikes. Magnetic surveys show that the Wallula fault actually lies 350 m to the southwest of the trace shown on published maps, passes directly through deformed late Pleistocene or younger deposits exposed at Finley quarry, and extends uninterrupted over 120 km.

  1. Electrical conductivity images of active and fossil fault zones


    Oliver Ritter; A. Hoffmann-Rothe; P. A. Bedrosian; Ute Weckmann; V. Haak;  ;  


    We compare recent magnetotelluric investigations of four large fault systems: (i) the actively deforming, ocean-continent interplate San Andreas Fault (SAF), (ii) the actively deforming, continent-continent interplate Dead Sea Transform (DST), (iii) the currently inactive, trench-linked intraplate West Fault (WF) in northern Chile, and (iv) the Waterberg Fault/Omaruru Lineament (WF/OL) in Namibia, a fossilized intraplate shear zone formed during early Proterozoic continental collision. These ...

  2. Paleoseismic evidence for late Holocene tectonic deformation along the Saddle mountain fault zone, Southeastern Olympic Peninsula, Washington (United States)

    Barnett, Elizabeth; Sherrod, Brian; Hughes, Jonathan F.; Kelsey, Harvey M.; Czajkowski, Jessica L.; Walsh, Timothy J.; Contreras, Trevor A.; Schermer, Elizabeth R.; Carson, Robert J.


    Trench and wetland coring studies show that northeast‐striking strands of the Saddle Mountain fault zone ruptured the ground about 1000 years ago, generating prominent scarps. Three conspicuous subparallel fault scarps can be traced for 15 km on Light Detection and Ranging (LiDAR) imagery, traversing the foothills of the southeast Olympic Mountains: the Saddle Mountain east fault, the Saddle Mountain west fault, and the newly identified Sund Creek fault. Uplift of the Saddle Mountain east fault scarp impounded stream flow, forming Price Lake and submerging an existing forest, thereby leaving drowned stumps still rooted in place. Stratigraphy mapped in two trenches, one across the Saddle Mountain east fault and the other across the Sund Creek fault, records one and two earthquakes, respectively, as faulting juxtaposed Miocene‐age bedrock against glacial and postglacial deposits. Although the stratigraphy demonstrates that reverse motion generated the scarps, slip indicators measured on fault surfaces suggest a component of left‐lateral slip. From trench exposures, we estimate the postglacial slip rate to be 0.2  mm/yr and between 0.7 and 3.2  mm/yr during the past 3000 years. Integrating radiocarbon data from this study with earlier Saddle Mountain fault studies into an OxCal Bayesian statistical chronology model constrains the most recent paleoearthquake age of rupture across all three Saddle Mountain faults to 1170–970 calibrated years (cal B.P.), which overlaps with the nearby Mw 7.5 1050–1020 cal B.P. Seattle fault earthquake. An earlier earthquake recorded in the Sund Creek trench exposure, dates to around 3500 cal B.P. The geometry of the Saddle Mountain faults and their near‐synchronous rupture to nearby faults 1000 years ago suggest that the Saddle Mountain fault zone forms a western boundary fault along which the fore‐arc blocks migrate northward in response to margin‐parallel shortening across the Puget Lowland.

  3. Geochemical characteristics of fault core and damage zones of the Hong-Che Fault Zone of the Junggar Basin (NW China) with implications for the fault sealing process (United States)

    Liu, Yin; Wu, Kongyou; Wang, Xi; Pei, Yangwen; Liu, Bo; Guo, Jianxun


    Faults may have a complex internal structure, including fault core and damage zone, and can act as major conduits for fluid migration. The migration of fluids along faults is generally associated with strong fluid-rock interaction, forming large amounts of cement that fill in the fractures. The cementation of the fault fractures is considered to be one of the important parameters of fault sealing. The different components of faults have diverse geochemical features because of varying physical characteristics. The investigation of the geochemical characteristics of the fault and damage zones could provide important information about the fault sealing process, which is very important in oil and gas exploration. To understand the fault-cemented sealing process, detailed geochemical studies were conducted on the fault and damage zones of the Hong-Che Fault of the northwestern Junggar Basin in China. The major and trace element data of our study suggest that the fault core is characterized by higher loss on ignition (LOI), potassium loss, Chemical Index of Alteration (CIA), and Plagioclase Index of Alteration (PIA) values and lower high field strength element (HFSE), large-ion lithosphile element (LILE), and rare earth element (REE) concentrations compared with the damage zone, implying more serious elemental loss and weathering of the fault core compared with the damage zone during faulting. The carbon and oxygen isotope data reveal that the cement of the Hong-Che Fault Zone formed due to multiple sources of fluids. The fault core was mainly affected by deep sources of hydrothermal fluids. In combination with previous studies, we suggest a potential fault-cemented sealing process during the period of fault movement. The fault core acts as the fluid conduit during faulting. After faulting, the fault core is cemented and the damage zone becomes the major conduit for fluid migration. The cementation firstly occurs on two sides of the damage zone in the upper part of the

  4. 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 (United States)

    Minor, Scott A.; Hudson, Mark R.


    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 host the greatest concentrations

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

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


    ). An AMS study on 205 samples indicates a progressive variation in the magnetic fabric from a strongly oblate fabric (>95%) in the damaged and undisturbed zone, to a moderately oblate fabric (≈83%) in the fault gouge. These results are consistent with the structural data observed in the URL: development of a magnetic foliation (sub-parallel to bedding) in the undisturbed zone and a NNW-SSE trending magnetic lineation in the fault gouge. A systematic decrease in the mass-normalized magnetic susceptibility is also observed within the fault gouge. The lower magnetic susceptibility might be the result of cemented portions of the fault zone or dissolution of magnetic minerals due to fluid circulation concentrated in the fault core. Preliminary results indicate a correlation between magnetic susceptibility and porosity-permeability variations within the Tournemire clay-based shear zones.

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

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


    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. Location of the Carlsberg Fault zone from seismic controlled-source fan recordings (United States)

    Nielsen, Lars; Thybo, Hans


    We locate the concealed Carlsberg Fault zone in the city of Copenhagen from seismic fan recordings. The fault is part of a fault system close to the border between the Danish Basin and the Baltic Shield. Recent earthquakes indicate that this area is tectonically active. The fault zone is a seismic low-velocity zone. Fan shots were recorded on three receiver arrays (1.5-2.4 km long arcs) across the fault. Sources were placed inside and up to ~500 m away from the ~400-700 m wide fault zone at offsets of up to ~7 km. Shots inside the fault zone show: 1) weak, delayed first arrivals inside the fault zone; 2) stronger first arrivals outside the fault zone; 3) guided waves inside the fault zone. The fault is a shadow zone for shots detonated outside the fault zone. Our approach facilitates fault mapping in densely urbanized areas where seismic profiling is not feasible.

  8. Development of Hydrologic Characterization Technology of Fault Zones

    Energy Technology Data Exchange (ETDEWEB)

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


    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

  9. Fault Zone Architecture and Mineralogy: Implications in Fluid Flow and Permeability in Crustal Scale Fault Zones in the Southern Andes. (United States)

    Roquer, T.; Terrón, E.; Perez-Flores, P.; Arancibia, G.; Cembrano, J. M.


    Fluid flow in the upper crust is controlled by the permeability and interconnection of fractures in the fault zones. The permeability within the fault zone is determined by its activity, architecture and, in particular, by the mineralogy of the core and the damage zone. Whereas the permeability structure of a fault zone can be defined by the volume proportion of the core with respect to the damage zone, the relationship between the mineralogy and permeability along fault zones still remains obscure. This work examines structural and mineralogical data to show the relationship between the mineral composition of the fault zone with its permeability in the Liquiñe-Ofqui Fault System (LOFS) and the Arc-oblique Long-lived Fault Systems (ALFS), Southern Chile. The LOFS is an active ca. 1200 km long strike-slip Cenozoic intra-arc structure that strikes NNE in its master traces and NE in its subsidiary traces, with dextral and dextral-normal movement mostly developed in the last 6 My. Although the LOFS and the ALFS cross-cut each other, the ALFS is an apparently older basement fault system where seismic and field evidences record sinistral, sinistral-normal and sinistral-reverse movements. One 22-m-long NE transect was mapped orthogonal to a segment of the ALFS, where host rocks are Miocene andesitic rocks. Structural and XRD sampling were conducted in the core and damage zone. Structural mapping shows a multiple core, NW-striking fault zone with foliated gouge and an asymmetric damage zone, where the hanging wall has significantly higher mesoscopic fracture density than the footwall. The hanging wall is characterized by NW-striking, steeply dipping veins. Preliminary XRD results indicate the presence of homogenously distributed Ca-rich zeolite (mainly laumontite) in the core and the veins of the damage zone, which could indicate that the core acted as a conduit for low-temperature (ca. 220°C) fluids.

  10. Quaternary basin formation along the Dien Bien Phu fault zone and its neotectonic implication of northwestern Vietnam (United States)

    Lai, K.; Chen, Y.; Chung, L.; Li, P.; Lam, D.


    The Dien Bien Phu (DBP) fault zone is one of the most conspicuous fault systems in the Indochina, extending over a distance of 150 km from Yunnan, China through the NW Vietnam into Laos. Recent Global Positioning system (GPS) data in China yielded that the present clockwise rotation of the southeastern Tibet block geologically corresponds to a region of left-lateral strike-slip faults, such as the Xianshuihe-Xiaojang fault and Dien Bien Phu fault, which appear to have accommodated clockwise rotation; whereas other GPS data from the network of Southeast Asia proposed that Indochina constitutes a stable tectonic block moving approximately east with respect to Eurasia. Although above GPS data show insignificant differential motion along DBP fault, active sinistral slip can be identified by clear geomorphic features, focal solutions and seismicity distribution in a NNE-striking zone parallel to the fault zone. Mapping of surface fault traces along the DBP fault zone using field outcrops, geophysical data, and geomorphologic features recognized by the aerial photos, SRTM, ASTER imageries and derived digital elevation models shows that virtually all active faults are reactivated structures sub-parallel to chronostratigraphic boundary. Along the DBF fault, three larger basins have been developed by different kinematics from north to south. The northern one at Chan Nua is rhomboidal in shape with a dimension of 2.5 km?.5 km, which can be defined as a pull-apart basin resulted by the strike-slip motion of the DBP fault. The fault configuration associated with the central one changes to two parallel sinistral and sinistral-normal faults forming a narrow subsiding weak zone (10 km?.5 km) filled with Quaternary deposits. The southern one is, however, created by that the main DBP fault bends the strike from NNE to NE where branches out a sinistral- normal fault with N-striking controlling a half-graben basin (17 km? km) filled with Quaternary deposits about 200 m in depth above

  11. The Finne fault zone (central Germany): structural analysis of a partially inverted extensional fault zone by balanced cross-sections (United States)

    Malz, Alexander; Kley, Jonas


    The Finne fault zone, located in central Germany to the southwest of the Harz mountains, was studied by means of detailed map analysis, investigations of fault displacement and balanced cross-sections for the most strongly deformed area in the center of the fault zone (ca. 50 % of total fault zone length). The system of the Finne fault zone shows a nearly 100-km-long straight flexure that symbolizes the morphological and geological northeastern border of the Thuringian basin. In the central part, which should be surveyed here, the fault zone corresponds to a distinctive narrow band of highly deformed Triassic sedimentary rocks. The northwestern and especially the southeastern parts of the research area are developed as several parallel branch faults. In the southeastern elongation of the fault zone, which is not part of our survey, the sedimentary cover is missing. Here, it is possible to gain insight to the fact that the basement is also involved to the kinematics of the fault zone. Based on our results, we propose a subdivision of the fault zone into four sectors. From the northwest to the southeast, we interpret the structure of these sectors to reflect (1) a compressional flexure, (2) an overthrust graben, and (3) a partially inverted and folded half graben. In the extreme southeast (4), the fault zone is characterized by an anticline with some strike-slip movement parallel to the fold axis. This segmentation is caused by a thrust fault system whose strike direction deviates slightly from that of the earlier formed graben system. The structural configuration can be explained by a two-phase deformation, in which the contractional strain exceeded the preceding extensional deformation. In the investigated area, the horizontal shortening attains a maximum of ca. 1 km. The present study confirms many earlier hypotheses, presents new results on the deformation history of the fault zone, and attempts to evaluate the deformation in a regional geological context. The

  12. Structural Analysis of the Exhumed SEMP Fault Zone, Austria: Towards an Understanding of Fault Zone Architecture Throughout the Seismogenic Crust (United States)

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


    One of the most exciting and important frontiers in earthquake science is the linkage between the internal structure and the mechanical behavior of fault zones. In particular, little is known about how fault-zone structure varies as a function of depth, from near-surface conditions down through the seismogenic crust and into the ductile lower crust. Such understanding is vital if we are to understand the mechanical instabilities that control the nucleation and propagation of seismic ruptures. This imperative has led us to the Oligo-Miocene Salzach-Ennstal-Mariazell-Puchberg [SEMP] fault zone in Austria, a major left-lateral strike-slip fault that has been exhumed differentially such that it exposes a continuum of structural levels along strike. This exhumed fault system provides a unique opportunity to systematically examine depth-dependent changes in fault-zone geometry and structure along a single fault. In order to establish the structure of the fault zone in the seismogenic crust, we are studying exposures of this fault at a variety of exhumation levels, from <1 km near the eastern end of the fault, downward through the seismogenic crust, across the brittle-ductile transition, and into the uppermost part of the lower crust in western Austria. Here we present our results from one of these study sites, a spectacular exposure of the fault zone near the town of Gstatterboden in central Austria. The fault, which at this location has been exhumed from a depth of ~ 2-3 km, juxtaposes limestone of the Wettersteinkalk on the south with dolomite of the Ramsaudolomit on the north. We conducted two detailed structural traverses over a fault-perpendicular width of over 200 m. Analysis of the density and orientation of outcrop scale features, such as faults and fractures, reveals a highly asymmetric pattern of fault zone damage. Dolomite to the north of the fault is extensively shattered, while the limestone unit to the south shows only minor evidence of fault damage

  13. Landforms along transverse faults parallel to axial zone of folded ...

    Indian Academy of Sciences (India)

    -4. Landforms along transverse faults parallel to axial zone of folded mountain front, north-eastern Kumaun. Sub-Himalaya, India. Khayingshing Luirei∗. , S S Bhakuni and Sanjay S Negi. Wadia Institute of Himalayan Geology, Dehradun, India.

  14. Fault zone architecture within Miocene–Pliocene syn-rift sediments ...

    Indian Academy of Sciences (India)

    The fault zones are associated with sliver fault blocks, clay smear, segmented faults and fault lenses' structural features. These features are mechanically related to the growth and linkage of the fault arrays. The structural features may represent a neotectonic and indicate that the architecture of the fault zones is developed ...

  15. Fluid flow and permeabilities in basement fault zones (United States)

    Hollinsworth, Allan; Koehn, Daniel


    Fault zones are important sites for crustal fluid flow, specifically where they cross-cut low permeability host rocks such as granites and gneisses. Fluids migrating through fault zones can cause rheology changes, mineral precipitation and pore space closure, and may alter the physical and chemical properties of the host rock and deformation products. It is therefore essential to consider the evolution of permeability in fault zones at a range of pressure-temperature conditions to understand fluid migration throughout a fault's history, and how fluid-rock interaction modifies permeability and rheological characteristics. Field localities in the Rwenzori Mountains, western Uganda and the Outer Hebrides, north-west Scotland, have been selected for field work and sample collection. Here Archaean-age TTG gneisses have been faulted within the upper 15km of the crust and have experienced fluid ingress. The Rwenzori Mountains are an anomalously uplifted horst-block located in a transfer zone in the western rift of the East African Rift System. The north-western ridge is characterised by a tectonically simple western flank, where the partially mineralised Bwamba Fault has detached from the Congo craton. Mineralisation is associated with hydrothermal fluids heated by a thermal body beneath the Semliki rift, and has resulted in substantial iron oxide precipitation within porous cataclasites. Non-mineralised faults further north contain foliated gouges and show evidence of leaking fluids. These faults serve as an analogue for faults associated with the Lake Albert oil and gas prospects. The Outer Hebrides Fault Zone (OHFZ) was largely active during the Caledonian Orogeny (ca. 430-400 Ma) at a deeper crustal level than the Ugandan rift faults. Initial dry conditions were followed by fluid ingress during deformation that controlled its rheological behaviour. The transition also altered the existing permeability. The OHFZ is a natural laboratory in which to study brittle fault

  16. Splay fault branching along the Nankai subduction zone. (United States)

    Park, Jin-Oh; Tsuru, Tetsuro; Kodaira, Shuichi; Cummins, Phil R; Kaneda, Yoshiyuki


    Seismic reflection profiles reveal steeply landward-dipping splay faults in the rupture area of the magnitude (M) 8.1 Tonankai earthquake in the Nankai subduction zone. These splay faults branch upward from the plate-boundary interface (that is, the subduction zone) at a depth of approximately 10 kilometers, approximately 50 to 55 kilometers landward of the trough axis, breaking through the upper crustal plate. Slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion.

  17. Are quartz LPOs predictably oriented with respect to the shear zone boundary?: A test from the Alpine Fault mylonites, New Zealand (United States)

    Little, Timothy A.; Prior, David J.; Toy, Virginia G.


    The Alpine fault self-exhumes its own ductile shear zone roots and has a known slip kinematics. Within ˜1 km of the fault, the mylonitic foliation is subparallel to the boundary of the amphibolite-facies ductile shear zone in which it formed. Using EBSD, we analyzed quartz Lattice Preferred Orientations [LPOs) of mylonites along a central part of the Alpine Fault. All LPOs feature a strongest girdle of [c]-axes that is forward-inclined ˜28 ± 4° away from the pole to the fault. A maximum of axes is inclined at the same angle relative the fault. The [c]-axis girdle is perpendicular to extensional (C') shear bands and the maximum is parallel to their slip direction. [c]-axis girdles do not form perpendicular to the SZB. Schmid factor analysis suggests that σ1 was arranged at 60-80° to the Alpine Fault. These observations indicate ductile transpression in the shear zone. The inclined arrangement of [c]-axis girdles, axes, and C' planes relative to the fault can be explained by their alignment relative to planes of maximum shear-strain-rate in a general shear zone, a significant new insight regarding shear zones and how LPO fabrics may generally develop within them. For the Alpine mylonite zone, our data imply a kinematic vorticity number (Wk) of ˜0.7 to ˜0.85. Inversions of seismic focal mechanisms in the brittle crust of the Southern Alps indicate that σ1 is oriented ˜60° to the Alpine Fault; that shear bands form at ˜30° to this direction, and that σ2 and σ3 flip positions between the brittle and ductile parts of the crust.

  18. Low-velocity fault-zone guided waves: Numerical investigations of trapping efficiency (United States)

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


    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.

  19. Orientations of faults determined by premonitory shear zones (United States)

    Johnson, Arvid M.


    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

  20. The hydrogeological structure of fault zones in poorly lithified sediment, Gulf of Corinth rift


    Loveless, Sian


    Often, the structure of fault zones cutting poorly lithified sediment examined in outcrop indicate such fault zones should behave as hydraulic barriers, but hydrological observations indicate they behave as conduit-barriers. This thesis investigates the hydrogeological structure of fault zones cutting poorly lithified sediment to better understand the observed conduit-barrier behaviour. The macro- and micro-structure of fault zones was investigated at outcrops of five fault arrays cutting...

  1. San Andreas tremor cascades define deep fault zone complexity (United States)

    Shelly, David R.


    Weak seismic vibrations - tectonic tremor - can be used to delineate some plate boundary faults. Tremor on the deep San Andreas Fault, located at the boundary between the Pacific and North American plates, is thought to be a passive indicator of slow fault slip. San Andreas Fault tremor migrates at up to 30 m s-1, but the processes regulating tremor migration are unclear. Here I use a 12-year catalogue of more than 850,000 low-frequency earthquakes to systematically analyse the high-speed migration of tremor along the San Andreas Fault. I find that tremor migrates most effectively through regions of greatest tremor production and does not propagate through regions with gaps in tremor production. I interpret the rapid tremor migration as a self-regulating cascade of seismic ruptures along the fault, which implies that tremor may be an active, rather than passive participant in the slip propagation. I also identify an isolated group of tremor sources that are offset eastwards beneath the San Andreas Fault, possibly indicative of the interface between the Monterey Microplate, a hypothesized remnant of the subducted Farallon Plate, and the North American Plate. These observations illustrate a possible link between the central San Andreas Fault and tremor-producing subduction zones.

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

    Directory of Open Access Journals (Sweden)

    Prinya Putthapiban


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

  3. Integrated Near-Surface Seismic and Geoelectrical Mapping of the Concealed Carlsberg Fault zone, Copenhagen, Denmark (United States)

    Nielsen, L.; Thybo, H.; Jorgensen, M. I.


    The Carlsberg Fault is located in a NNW-SSE striking fault system in the border zone between the Danish Basin and the Baltic Shield. Recent earthquakes indicate that this area is tectonically active. We locate the concealed Carlsberg Fault zone along a 12 km long trace in the Copenhagen city center by seismic refraction, reflection and fan profiling. We supplement our seismic investigations with multi-electrode geoelectrical profiling. The seismic refraction study shows that the Carlsberg Fault zone is a low-velocity zone and marks a change in seismic velocity structure. A normal-incidence reflection seismic section shows a coincident flower structure. We have recorded seismic signals in a fan geometry from shots detonated both inside the low-velocity fault zone and up to about 500 m away from the fault zone. The seismic energy was recorded on three receiver arrays (1.5-2.4 km long arcs) across the expected location of the 400-700 m wide fault zone at distances of up to 7 km from the shots. Shots detonated inside the fault zone result in: 1) weak and delayed first arrivals on the receivers located inside the fault zone compared to earlier and stronger first arrivals outside the fault zone; 2) strong guided P- and S-waves as well as surface waves inside the fault zone. The fault zone is a shadow zone to shots detonated outside the fault zone. Finite-difference wavefield modeling supports the interpretations of the fan recordings. Our fan recording approach facilitates cost-efficient mapping of fault zones in densely urbanized areas where seismic normal-incidence and refraction profiling are not feasible. The geoelectrical measurements show that the fault zone is characterized by low resistivities (lower than 5 ohmm), indicating that the fault zone is fractured and water-filled. This interpretation is supported by hydrological measurements conducted by others, which show that the Carlsberg Fault zone is highly permeable.

  4. Evidence for cyclical fault zone sealing and strengthening, Alpine Fault, New Zealand (United States)

    Allen, M. J.; Mariani, E.; Boulton, C. J.; Faulkner, D.


    The Alpine Fault, a transpressional plate boundary fault between the Australia-Pacific plates, ruptures periodically ( 300yr) with large magnitude earthquakes (Mw 8) and is currently locked and nearing the end of its interseismic period. Using temporal and fine-scale spatial variations in carbonate deformation microstructures and geochemistry, this study investigates the influential role of calcite in sealing and restrengthening the Alpine Fault. Phase 1 of the Deep Fault Drilling Project (DFDP-1) at Gaunt Creek revealed a fault zone structure with 1m fault core and associated damage zone, overprinted by a zone of alteration (AZ) in the hanging wall, formed through enhanced fluid-rock interaction on a fault which currently has very low permeability. Carbonate is one of the primary authigenic minerals in this AZ, with mineralisation concentrated within fault core fractures. Through Electron Backscatter Diffraction, Cathodoluminescence (CL) and Secondary Ion Mass Spectrometry multiple episodes of fracture generation and mineralisation have been recognised. Early carbonate veins exhibit dull CL and high Fe concentrations; these generations have accommodated extensive deformation including intense mechanical e-twinning and dynamic recrystallization, indicating formation at temperatures of >250°C. Younger generations, attributed to more recent seismicity exhibit bright CL and greater Mn concentrations and lack deformation microstructures, supporting the absence of stable creep between rupture events on the central Alpine Fault. Variations in trace elements highlight fluctuations in ambient conditions/fluid source between generations of calcite veining. Variation within a single generation indicates multiple pulses of fluid were required to fully seal some voids. Older calcite generations and those closer to the principal slip zone contain greater amounts of Fe and Mg, while younger generations and recrystallized regions contain more Mn. The precipitation of secondary

  5. Lineations and faults in the Texas Coastal Zone

    Energy Technology Data Exchange (ETDEWEB)

    Kreitler, C.W.


    Over 7000 miles of lineations have been observed on aerial photographic mosaics of the Texas Coastal Zone. These lineations, in part, represent the surface traces of faults originating in the Tertiary sediments and propagating through the Quaternary sediments. The extrapolation of subsurface faults from specific oil and gas reservoirs are commonly coincident to lineations in those areas. Some extrapolated fault traces weave back and forth across lineations for 10 to 20 miles and then coincide with another lineation and follow it for 20 miles. They also may partially represent fracture-joint systems within the sedimentary deposits of the Gulf basin. Land subsidence and fault activation can be expected in areas of the Texas Coastal Zone other than the Houston-Galveston area if in these areas there is extensive ground-water withdrawal from shallow (less than 3000 ft) fresh-water artesian aquifers. In these areas surface faulting and/or differential subsidence would be expected to occur in part within the zones defined by the lineations.

  6. Kinematics of the quaternary fault zones in the Kyeongju area of the southeastern Korean Peninsula

    Energy Technology Data Exchange (ETDEWEB)

    Kim, In Seob; Lee, Byeong Hyui; Kwon, Hyeok Sang [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)] (and others)


    The purposes of this study are to interpret the kinematics of the Quaternary fault zones in the Kyeongju area, to determine deformation mechanisms during faulting by analyzing micorstrucutres of fault rocks from the fault zones, and to unravel the technic evaluation of the regional fault structures in the Kyeongju-Wolsung area. The scope of this study consists of ; collection and interpretation of structural elements through a detailed geologic investigation on the Quaternary faults in the Kyeongju-Wolsung area, interpretation of fault-rock microstructures from the fault zones using oriented samples of faults rocks, determination of deformation processes and mechanisms of the fault rocks and, interpretation of faulting kinematics and evaluation of the fault zones.

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

    Sboras, Sotiris; Chatzipetros, Alexandros; Pavlides, Spyros; Karastathis, Vassilis; Papadopoulos, Gerassimos


    The 2014 seismic sequence in Cephalonia and the following 2015 earthquake in Lefkada Islands, Greece, showed that the Cephalonia Transfer Fault Zone (CTFZ), which runs along the western coasts of both islands, comprises a wide fault zone of parallel to sub-parallel fault segments. The January-February 2014 sequence of Cephalonia consisted of three moderate to strong events. According to published focal mechanisms, the first strongest shock (January 26, Mw 6.1) was produced by a W-dipping, oblique (right-lateral reverse) fault, the second (January 26, Mw 5.3) by a ENE-dipping, pure reverse fault and the third by a ESE-dipping, almost pure right-lateral strike slip fault. The November 17 2015 (Mw 6.4) Lefkada earthquake was produced by a WNW-dipping, roughly vertical, almost pure right-lateral strike-slip fault. None of the shocks above produced any direct coseismic ground rupture, while published relocated hypocentral locations for the Cephalonia sequence revealed various depths indicating a complex fault pattern. Based on published seismological, geological and satellite data (i.e. InSAR), the respective seismic sources were modelled in order to calculate the static stress changes i) during the Cephalonia and Lefkada sequences, and ii) after the sequences for the surrounding faults from the Greek Database of Seismogenic Sources (GreDaSS). Results showed that the February 3 2014 Cephalonia fault was variously affected by the rupture of the two January 26 faults. Stress change distribution on the fault plane showed that both stress drop and rise occurred. The November 17 2015 Lefkada fault was slightly loaded after the rupture of the whole Cephalonia fault system due to the great distance. The post-sequence stress changes variously affect the surrounding faults: the southern segment of the CTFZ is relieved from stresses, while the central ones show a mixed situation. The large northern segment, offshore from Lefkada Island, is mainly under stress drop. Stress drop is

  8. Deformation of Sedimentary Rock Across the San Andreas Fault Zone: Mesoscale and Microscale Structures Displayed in Core From SAFOD (United States)

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


    processes having operated concurrently and cyclically. The microstructure of wear product along some slip surfaces, and associated mobilization and injections of wear microbreccia, are consistent with dynamic slip and local pore fluid pressurization. Cores from the actively creeping segments at 3194 m and 3301 m MD display a variety of moderately to highly sheared rocks. Disrupted bedding and cataclastic foliations oriented subparallel to the macroscopic orientation of the San Andreas fault are common. Protoliths of the fault rocks include interbedded sandstone, siltstone, shale, and serpentinite. Mesoscale calcite veins are abundant locally, yet are rare in the other cores. Zones of foliated cataclasites record a distributed shear within meters-thick zones, but sharp contacts between different types of cataclasite are also consistent with extremely localized slip having occurred at various stages of deformation. Zones of incohesive cataclasite and scaly fabrics could correlate with current locations of active, aseismic creep.

  9. Fault-Tolerant, Multiple-Zone Temperature Control (United States)

    Granger, James; Franklin, Brian; Michalik, Martin; Yates, Phillip; Peterson, Erik; Borders, James


    A computer program has been written as an essential part of an electronic temperature control system for a spaceborne instrument that contains several zones. The system was developed because the temperature and the rate of change of temperature in each zone are required to be maintained to within limits that amount to degrees of precision thought to be unattainable by use of simple bimetallic thermostats. The software collects temperature readings from six platinum resistance thermometers, calculates temperature errors from the readings, and implements a proportional + integral + derivative (PID) control algorithm that adjusts heater power levels. The software accepts, via a serial port, commands to change its operational parameters. The software attempts to detect and mitigate a host of potential faults. It is robust to many kinds of faults in that it can maintain PID control in the presence of those faults.

  10. Experimental tests of truncated diffusion in fault damage zones (United States)

    Suzuki, Anna; Hashida, Toshiyuki; Li, Kewen; Horne, Roland N.


    Fault zones affect the flow paths of fluids in groundwater aquifers and geological reservoirs. Fault-related fracture damage decreases to background levels with increasing distance from the fault core according to a power law. This study investigated mass transport in such a fault-related structure using nonlocal models. A column flow experiment is conducted to create a permeability distribution that varies with distance from a main conduit. The experimental tracer response curve is preasymptotic and implies subdiffusive transport, which is slower than the normal Fickian diffusion. If the surrounding area is a finite domain, an upper truncated behavior in tracer response (i.e., exponential decline at late times) is observed. The tempered anomalous diffusion (TAD) model captures the transition from subdiffusive to Fickian transport, which is characterized by a smooth transition from power-law to an exponential decline in the late-time breakthrough curves.

  11. Geology of the Elephanta Island fault zone, western Indian rifted ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Earth System Science; Volume 126; Issue 1. Geology of the Elephanta Island fault zone, western Indian rifted margin, and its significance for understanding the Panvel flexure. Hrishikesh Samant Ashwin Pundalik Joseph D'souza Hetu Sheth Keegan Carmo Lobo Kyle D'souza Vanit Patel. Volume ...

  12. Landforms along transverse faults parallel to axial zone of folded ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Earth System Science; Volume 126; Issue 1. Landforms along transverse faults parallel to axial zone of folded mountain front, north-eastern Kumaun Sub-Himalaya, India. Khayingshing ... Keywords. Himalayan Frontal Thrust; outer Kumaun Himalaya; transverse structure; folded mountain front.

  13. Influence of fault slip on mining-induced pressure and optimization of roadway support design in fault-influenced zone


    Wang, Hongwei; Jiang, Yaodong; Xue, Sheng; Mao, Lingtao; Lin, Zhinan; Deng, Daixin; Zhang, Dengqiang


    This paper presents an investigation on the characteristics of overlying strata collapse and mining-induced pressure in fault-influenced zone by employing the physical modeling in consideration of fault structure. The precursory information of fault slip during the underground mining activities is studied as well. Based on the physical modeling, the optimization of roadway support design and the field verification in fault-influenced zone are conducted. Physical modeling results show that, du...

  14. A three-dimensional study of fault zone architecture: Results from the SEMP fault system, Austria. (United States)

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


    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

  15. Width of surface rupture zone for thrust earthquakes: implications for earthquake fault zoning

    Directory of Open Access Journals (Sweden)

    P. Boncio


    Full Text Available The criteria for zoning the surface fault rupture hazard (SFRH along thrust faults are defined by analysing the characteristics of the areas of coseismic surface faulting in thrust earthquakes. Normal and strike–slip faults have been deeply studied by other authors concerning the SFRH, while thrust faults have not been studied with comparable attention. Surface faulting data were compiled for 11 well-studied historic thrust earthquakes occurred globally (5.4 ≤ M ≤ 7.9. Several different types of coseismic fault scarps characterize the analysed earthquakes, depending on the topography, fault geometry and near-surface materials (simple and hanging wall collapse scarps, pressure ridges, fold scarps and thrust or pressure ridges with bending-moment or flexural-slip fault ruptures due to large-scale folding. For all the earthquakes, the distance of distributed ruptures from the principal fault rupture (r and the width of the rupture zone (WRZ were compiled directly from the literature or measured systematically in GIS-georeferenced published maps. Overall, surface ruptures can occur up to large distances from the main fault ( ∼ 2150 m on the footwall and  ∼  3100 m on the hanging wall. Most of the ruptures occur on the hanging wall, preferentially in the vicinity of the principal fault trace ( >   ∼  50 % at distances  <   ∼  250 m. The widest WRZ are recorded where sympathetic slip (Sy on distant faults occurs, and/or where bending-moment (B-M or flexural-slip (F-S fault ruptures, associated with large-scale folds (hundreds of metres to kilometres in wavelength, are present. A positive relation between the earthquake magnitude and the total WRZ is evident, while a clear correlation between the vertical displacement on the principal fault and the total WRZ is not found. The distribution of surface ruptures is fitted with probability density functions, in order to define a criterion to

  16. Characteristics of Fault Zones in Volcanic Rocks Near Yucca Flat, Nevada Test Site, Nevada

    Energy Technology Data Exchange (ETDEWEB)

    Donald Sweetkind; Ronald M. Drake II


    During 2005 and 2006, the USGS conducted geological studies of fault zones at surface outcrops at the Nevada Test Site. The objectives of these studies were to characterize fault geometry, identify the presence of fault splays, and understand the width and internal architecture of fault zones. Geologic investigations were conducted at surface exposures in upland areas adjacent to Yucca Flat, a basin in the northeastern part of the Nevada Test Site; these data serve as control points for the interpretation of the subsurface data collected at Yucca Flat by other USGS scientists. Fault zones in volcanic rocks near Yucca Flat differ in character and width as a result of differences in the degree of welding and alteration of the protolith, and amount of fault offset. Fault-related damage zones tend to scale with fault offset; damage zones associated with large-offset faults (>100 m) are many tens of meters wide, whereas damage zones associated with smaller-offset faults are generally a only a meter or two wide. Zeolitically-altered tuff develops moderate-sized damage zones whereas vitric nonwelded, bedded and airfall tuff have very minor damage zones, often consisting of the fault zone itself as a deformation band, with minor fault effect to the surrounding rock mass. These differences in fault geometry and fault zone architecture in surface analog sites can serve as a guide toward interpretation of high-resolution subsurface geophysical results from Yucca Flat.

  17. Detection of Interphase Fault Zone in Overhead Power Distribution Networks

    Directory of Open Access Journals (Sweden)

    E. Kalentionok


    Full Text Available Parametric methods have been recommended on the basis of current and voltage value recording in normal and emergency modes at a sub-transmission substation in order to detect two- and three-phase short circuits in overhead power distribution networks. The paper proposes to detect an inspection zone in order to locate an interphase fault with the help of analytical calculation of distance up to the fault point using 3–4 expressions on the basis of data obtained as a result of multiple metering pertaining to emergency mode parameters  with their subsequent statistical processing.

  18. Active faulting and folding along the Jumilla Fault Zone, northeastern Betics, Spain (United States)

    Van Balen, R. T.; Forzoni, A.; Van Dam, J. A.


    The Jumilla Fault Zone (JFZ) is an ENE-WSW topographic lineament in the external part of the eastern Betic Cordillera. It represents an active fault. Three small basins are aligned along the JFZ, the La Celia-, Alqueria- and Jumilla basins. The tectonic geomorphology of the La Celia- and Alqueria basins consists of folds, a set of normal fault scarps, strike-slip lineaments, fault-springs, tectonically-modified drainage lines and elevated gypsum/anhydrite diapirs. Two of the scarps are normal faults generated by the extensional collapse of one of the folds. The other scarps are secondary normal faults generated by transtensional left-lateral motions along the JFZ. Normal fault scarps that developed on conglomerates are considerably steeper (~ 30°) than those affecting softer marly materials (post-Messinian deposits in the studied basins. The discrepancy between the age of the tectonic landforms and the late Neogene age of the basin infill can be explained by an endo- to exhorheic change in the drainage system, due to the capture of the ancient basin lake system by tributaries of the nearby Segura river. The cessation of sedimentation in the basins resulted in the preservation of tectonic landforms.

  19. A new conceptual model for damage zone evolution with fault growth (United States)

    de Joussineau, G.; Aydin, A.


    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

  20. Microstructural investigations on carbonate fault core rocks in active extensional fault zones from the central Apennines (Italy) (United States)

    Cortinovis, Silvia; Balsamo, Fabrizio; Storti, Fabrizio


    The study of the microstructural and petrophysical evolution of cataclasites and gouges has a fundamental impact on both hydraulic and frictional properties of fault zones. In the last decades, growing attention has been payed to the characterization of carbonate fault core rocks due to the nucleation and propagation of coseismic ruptures in carbonate successions (e.g., Umbria-Marche 1997, L'Aquila 2009, Amatrice 2016 earthquakes in Central Apennines, Italy). Among several physical parameters, grain size and shape in fault core rocks are expected to control the way of sliding along the slip surfaces in active fault zones, thus influencing the propagation of coseismic ruptures during earthquakes. Nevertheless, the role of grain size and shape distribution evolution in controlling the weakening or strengthening behavior in seismogenic fault zones is still not fully understood also because a comprehensive database from natural fault cores is still missing. In this contribution, we present a preliminary study of seismogenic extensional fault zones in Central Apennines by combining detailed filed mapping with grain size and microstructural analysis of fault core rocks. Field mapping was aimed to describe the structural architecture of fault systems and the along-strike fault rock distribution and fracturing variations. In the laboratory we used a Malvern Mastersizer 3000 granulometer to obtain a precise grain size characterization of loose fault rocks combined with sieving for coarser size classes. In addition, we employed image analysis on thin sections to quantify the grain shape and size in cemented fault core rocks. The studied fault zones consist of an up to 5-10 m-thick fault core where most of slip is accommodated, surrounded by a tens-of-meters wide fractured damage zone. Fault core rocks consist of (1) loose to partially cemented breccias characterized by different grain size (from several cm up to mm) and variable grain shape (from very angular to sub

  1. Detailed Northern Anatolian Fault Zone crustal structure from receiver functions (United States)

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


    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

  2. Motion in the north Iceland volcanic rift zone accommodated by bookshelf faulting (United States)

    Green, Robert G.; White, Robert S.; Greenfield, Tim


    Along mid-ocean ridges the extending crust is segmented on length scales of 10-1,000km. Where rift segments are offset from one another, motion between segments is accommodated by transform faults that are oriented orthogonally to the main rift axis. Where segments overlap, non-transform offsets with a variety of geometries accommodate shear motions. Here we use micro-seismic data to analyse the geometries of faults at two overlapping rift segments exposed on land in north Iceland. Between the rift segments, we identify a series of faults that are aligned sub-parallel to the orientation of the main rift. These faults slip through left-lateral strike-slip motion. Yet, movement between the overlapping rift segments is through right-lateral motion. Together, these motions induce a clockwise rotation of the faults and intervening crustal blocks in a motion that is consistent with a bookshelf-faulting mechanism, named after its resemblance to a tilting row of books on a shelf. The faults probably reactivated existing crustal weaknesses, such as dyke intrusions, that were originally oriented parallel to the main rift and have since rotated about 15° clockwise. Reactivation of pre-existing, rift-parallel weaknesses contrasts with typical mid-ocean ridge transform faults and is an important illustration of a non-transform offset accommodating shear motion between overlapping rift segments.

  3. Fault zone architecture within Miocene–Pliocene syn-rift sediments ...

    Indian Academy of Sciences (India)

    The present study focusses on field description of small normal fault zones in Upper Miocene–Pliocene sedimentary rocks on the northwestern side of the Red Sea, Egypt. The trend of these fault zones is mainly NW–SE. Paleostress analysis of 17 fault planes and slickenlines indicate that the tension direction is NE–SW.

  4. Counter-intuitive Behavior of Subduction Zones: Weak Faults Rupture, Strong Faults Creep (United States)

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


    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

  5. Continental strike slip fault zones in geologically complex lithosphere: the North Anatolian Fault, Turkey. (United States)

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


    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.

  6. Fault Rock Zones Characterisation - Final report. TRUE-1 Continuation Project

    Energy Technology Data Exchange (ETDEWEB)

    Winberg, Anders (ed.) (Conterra AB (Sweden))


    At the conclusion of the TRUE-1 and TRUE Block Scale experimental programmes at the Aespoe Hard Rock Laboratory one remaining identified uncertainty was the in situ internal structure of conductive structures, and in particular the in situ material properties of unconsolidated fault gouge of such conductive structures. With the aim of reducing these uncertainties an experimental program has been conducted at depth in the Aespoe Hard Rock Laboratory. Four conductive structures in the immediate vicinity of the Aespoe tunnel were identified for further study. Following basic geometrical and geological modelling based on tunnel observations, geological/ mineralogical and hydrogeological investigations in four boreholes at each site, epoxy resin was injected in selected packed off borehole sections containing the structure. Following a sufficient time for curing of the epoxy, the injected borehole 72 mm sections were overcored with a 300 mm core barrel. Customised techniques were employed to section the core in the borehole and for its retrieval out of the borehole. Following basic geological mapping, selected overcores were sectioned and were subject to image analysis to assess the pore structure using a variety of different descriptive geometrical attributes. In addition, an attempt was made to infer the porosity of the fault rock (including fault gouge) using binary images. Since analysis has been made on multiple slices of impregnated rock it is also possible to crudely map the 3D variability of a given entity. It was furthermore identified that porosity estimates, which range from some 10-70% are, apart from being dependent on the penetration of the epoxy, dependent on the resolution of the given image, the size of the averaging window, and the porosity components contained therein. The obtained quantifications of porosity can therefore only be regarded as ball-park relative porosities of a complete fault rock zones. It does not, however, provide firm

  7. Influence of fault slip on mining-induced pressure and optimization of roadway support design in fault-influenced zone

    Directory of Open Access Journals (Sweden)

    Hongwei Wang


    Full Text Available This paper presents an investigation on the characteristics of overlying strata collapse and mining-induced pressure in fault-influenced zone by employing the physical modeling in consideration of fault structure. The precursory information of fault slip during the underground mining activities is studied as well. Based on the physical modeling, the optimization of roadway support design and the field verification in fault-influenced zone are conducted. Physical modeling results show that, due to the combined effect of mining activities and fault slip, the mining-induced pressure and the extent of damaged rock masses in the fault-influenced zone are greater than those in the uninfluenced zone. The sharp increase and the succeeding stabilization of stress or steady increase in displacement can be identified as the precursory information of fault slip. Considering the larger mining-induced pressure in the fault-influenced zone, the new support design utilizing cables is proposed. The optimization of roadway support design suggests that the cables can be anchored in the stable surrounding rocks and can effectively mobilize the load bearing capacity of the stable surrounding rocks. The field observation indicates that the roadway is in good condition with the optimized roadway support design.

  8. Direct observation of fault zone structure and mechanics in three-dimensions: A study of the SEMP fault system, Austria (United States)

    Frost, Erik Karl

    Outcrops of the Salzach-Ennstal-Mariazell-Puchberg (SEMP) fault system exhumed from depths of ˜4--17 km allow for the direct observation of fault zone structures throughout the crust, and provide insights into the way this fault, and perhaps others, distributes strain in three dimensions. At Gstatterboden, exhumed from ˜4--8 km, grain size distributions and small fault data reveal the presence of a 10-m-wide high-strain core towards which strain localized during fault evolution. Brittle fracture was accommodated via constrained comminution, which only occurs in strain-weakening rheologies and favors localization. Exposures of the SEMP at Lichtensteinklamm and Kitzlochklamm, exhumed from ˜12 km depth, bracket the brittle ductile transition. At these outcrops, the SEMP is characterized by a ˜70-m-wide, cataclastic fault core that has been altered to clays that transitions downward into a wide, ductile shear zone that has accommodated only minor amounts of strain, placing the majority of displacement on the razor-sharp fault contact. Deformation mechanisms transition from cataclasis and minor amounts of dislocation creep in calcite, to dislocation creep in quartz and calcite occurring against a background of fault-normal solution mass transfer. The ductile/ductile-brittle Rinderkarsee shear zone, exhumed from ˜17 km, marks the SEMP's continuation into the Tauern Window and is composed of three distinct shear zones. The southern, 100-m-wide shear zone has accommodated the most strain, and shows evidence for creep-accommodated grain boundary sliding in feldspar and quartz, while incipient shear zones contain ductile quartz and brittle-feldspars that undergo dislocation creep as fluids alter Kspar to muscovite, which localizes strain along felspar grain boundaries, encouraging ductility. These findings are compared to results from other faults exhumed from similar depth ranges, highlighting fundamental fault zone structures and characteristics.

  9. Fault-zone trapped waves at Muyu in Wenchuan earthquake region

    Directory of Open Access Journals (Sweden)

    Lai Xiaoling


    Full Text Available Trapped waves in the Qingchuan fault zone were observed at Muyu near the northeastern end of the fractured zone of the Wenchuan Ms8. 0 earthquake. The results indicate a fault-zone width of about 200 m and a great difference in physical property of the crust on different sides of the fault. The inferred location of crustal changes is consistent with land-form boundary on the surface.

  10. Incremental Slip Along Dilatant Faults in Ancient Fluid-Rich Subduction Zones (United States)

    Remitti, F.; Fagereng, A.; Sibson, R. H.; Vannucchi, P.; Bettelli, G.


    At a variety of depths in subduction zones a proportion of relative plate motion is accommodated by episodic tremor and slow slip events. These events are accompanied by distinct low frequency seismic signals and/or high levels of micro-seismic activity. Based on theoretical studies and seismic attributes of the source region, fluids overpressured to near-lithostatic values seem likely to be involved in the mechanism behind episodic tremor. Ancient crust surrounding paleoseismic zones, especially if rich in overpressured fluids, should contain widespread relics of this kind of activity. Here we present microstructural observations from two ancient subduction thrust analogues where brittle deformation was accommodated by repeating micro-movements along dilatant faults. The first example is a mélange formed during Triassic-Jurassic tectonic accretion of ocean floor sediments now exposed in the Chrystalls Beach Complex, South Island, NZ. The mélange comprises competent sandstone and chert lenses set in a cleaved mudstone matrix deformed in a continuous-discontinuous style under subgreenschist conditions. Deformation is characterized by a pervasive anastomosing fault-fracture mesh of multiple shearing surfaces, subparallel to cleavage and coated with incrementally developed quartz-calcite slickenfibres. Microstructural observations reveal that slickenfibres grew by 'crack-seal' increments of 10-100 μm. Incremental slip transfer was constant over a single slickenfiber and accommodated by opening of extension fractures that link en echelon slip surfaces. The characteristic spacing of inclusion bands indicates relatively constant growth increments, possibly occurring into regular size cracks. Increments of non-constant growth and, instead, fractures significantly wider than 100 μm, are represented by local veins of euhedral quartz and carbonate. Similar structures are present in the shallow part of an ancient plate interface, now exposed in the Northern Apennines of

  11. Coda Wave Attenuation Characteristics for North Anatolian Fault Zone, Turkey (United States)

    Sertcelik, Fadime; Guleroglu, Mehmet


    North Anatolian Fault Zone, on which large earthquakes have occurred in the past, migrates regularly from east to west, and it is one of the most active faults in the world. The purpose of this study is to estimate the coda wave quality factor (Qc) for each of the five sub regionsthat were determined according to the fault rupture of these large earthquakes and along the fault. 978 records have been analyzed for 1.5, 3, 6, 9, 12 and 18 Hz frequencies by Single Backscattering Method. Along the fault, the variations in the Qc with lapse time are determined via, Qc = (136±25)f(0.96±0.027), Qc = (208±22)f(0.85±0.02) Qc = (307±28)f(0.72±0.025) at 20, 30, 40 sec lapse times, respectively. The estimated average frequency-dependence quality factor for all lapse time are; Qc(f) = (189±26)f(0.86±0.02) for Karliova-Tokat region; Qc(f) = (216±19)f(0.76±0.018) for Tokat-Çorum region; Qc(f) = (232±18)f(0.76±0.019) for Çorum-Adapazari region; Qc(f) = (280±28)f(0.79±0.021) for Adapazari-Yalova region; Qc(f) = (252±26)f(0.81±0.022) for Yalova-Gulf of Saros region. The coda wave quality factor at all the lapse times and frequencies is Qc(f) = (206±15)f(0.85±0.012) in the study area. The most change of Qc with lapse time is determined at Yalova-Saros region. The result may be related to heterogeneity degree of rapidly decreases towards the deep crust like compared to the other sub region. Moreover, the highest Qc is calculated between Adapazari - Yalova. It was interpreted as a result of seismic energy released by 1999 Kocaeli Earthquake. Besides, it couldn't be established a causal relationship between the regional variation of Qc with frequency and lapse time associated to migration of the big earthquakes. These results have been interpreted as the attenuation mechanism is affected by both regional heterogeneity and consist of a single or multi strands of the fault structure.

  12. Slow Active Intraplate Faults: The Paleoseismology Of The Irtysh Fault Zone, Eastern Kazakhstan (United States)

    Baize, S.; Reicherter, K. R.; Avagyan, A.; Belyashov, A.; Pestov, E.; Eutizio, V.; Arakelyan, A.


    The Asian plate interiors are known to host strong earthquakes with magnitudes up to M 8, especially around the border area between Mongolia, Russia, Kazakhstan and China. Their recurrence times are long, because of the low slip rates of faults smaller than 1 mm/yr. Geodynamically, our study region in eastern Kazakhstan is set in the frame of the Indian-Eurasian collision zone situated on the Eurasian craton. Major plate tectonic forces are induced by the indentation of the Indian plate into Eurasia. As a consequence, in the foreland a set of very long and large strike-slip fault zones developed, the western of which all have in common a dextral sense of shear. The more than 250 km long Irtysh Fault Zone (IFZ) marks a major tectonic block boundary separating two different units with granitoid intrusions, Silurian-Devonian magmatic rocks, and, thick deposits of Late Paleozoic age with coal measures of the Carboniferous and Permian. The formation of the IFZ probably dates back into Paleozoic times, it was repeatedly reactivated in later times. The IFZ is one potential source of large earthquakes in easternmost Kazakhstan. Tectonic-morphological analyses revealed the occurrence of a set of lineaments offsetting or deflecting streamlets and lithology. Geophysical data (GPR and seismics) helped to identify fault strands and trenching sites. Across three main segments, all longer than 50 km, a series of paleoseismic trenches was excavated. Within the trenches, faulted Holocene-Late Pleistocene deposits with organic soils, loess layers and colluvium directly overlying the Paleozoic rocks were encountered and 14C-dated. Astonishingly, no older Pleistocene rocks have been found suggesting complete erosion during/after glacial periods. Our findings lead to the conclusions that the IFZ and all segments are clearly active during the Holocene with surface ruptures displacements of around 2.0±0.2 meters, suggesting events with a magnitude around M≈7 along the individual

  13. Determination of the relationship between major fault and zinc mineralization using fractal modeling in the Behabad fault zone, central Iran (United States)

    Adib, Ahmad; Afzal, Peyman; Mirzaei Ilani, Shapour; Aliyari, Farhang


    The aim of this study is to determine a relationship between zinc mineralization and a major fault in the Behabad area, central Iran, using the Concentration-Distance to Major Fault (C-DMF), Area of Mineralized Zone-Distance to Major Fault (AMZ-DMF), and Concentration-Area (C-A) fractal models for Zn deposit/mine classification according to their distance from the Behabad fault. Application of the C-DMF and the AMZ-DMF models for Zn mineralization classification in the Behabad fault zone reveals that the main Zn deposits have a good correlation with the major fault in the area. The distance from the known zinc deposits/mines with Zn values higher than 29% and the area of the mineralized zone of more than 900 m2 to the major fault is lower than 1 km, which shows a positive correlation between Zn mineralization and the structural zone. As a result, the AMZ-DMF and C-DMF fractal models can be utilized for the delineation and the recognition of different mineralized zones in different types of magmatic and hydrothermal deposits.

  14. 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 (United States)

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


    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

  15. Is there really an active fault (Cibyra Fault?) cutting the Stadion of the ancient city of Cibyra? (Burdur-Fethiye Fault Zone, Turkey) (United States)

    Elitez, İrem; Yaltırak, Cenk


    The Cibyra segment of the Burdur-Fethiye Fault Zone (BFFZ) is in a tectonically very active region of southwestern Anatolia. The presence of the Cibyra Fault was firstly suggested by Akyüz and Altunel (1997, 2001). Researchers identified traces of historical earthquakes in Cibyra by taking into account the collapsed seat rows on the east side of the stadion as reference. They claimed that the NNE-SSW left lateral fault Cibyra Fault (related to Burdur-Fethiye Fault Zone) continues through Pliocene sediments on both eastern and western sides of the stadion of Cibyra. The questionable left-lateral fault had been examined in detail by ourselves during our 60-days accommodation in the ancient city of Cibyra excavations for the Burdur-Fethiye Fault Zone Project in 2008, 2009 and 2012. A left-lateral offset on the Stadion was firstly mentioned in a study whose aim is to find the traces of Burdur-Fethiye Fault (Akyüz and Altunel, 2001) and many researchers accepted this fault by reference (for example Alçiçek et al. 2002, 2004, 2005, 2006 and Karabacak, 2011). However as a result of the field observations it is understood that there is no fault cutting the Stadion. By the reason of the fact that there are a lot of faults in the region, however the fault that devastated the ancient city is unknown. The deformation traces on the ruins of the ancient city display a seismic movement occured in the region. It is strongly possible that this movement is related to the NE-SW left lateral oblique normal fault named as Cibyra Fault at the northwestern side of the city. Especially the ravages in the eastern part of the city indicate that the deformations are related to ground properties. If the rotation and overturn movement are considered and if both movements are the product of the same earthquake, the real Cibyra Fault is compatible with normal fault with left lateral compenent. After the 2011 excavations and 2012 field studies, the eastern wall of the Stadion showed that

  16. Active tectonics west of New Zealand's Alpine Fault: South Westland Fault Zone activity shows Australian Plate instability (United States)

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


    The 300 km long South Westland Fault Zone (SWFZ) is within the footwall of the Central Alpine Fault (Holocene sediments and gentle hanging wall anticlinal folding. Cone penetration test (CPT) stratigraphy shows repeated sequences within the fault scarp (consistent with thrusting). Optically stimulated luminescence (OSL) dating constrains the most recent rupture post-12.1 ± 1.7 ka with evidence for three to four events during earthquakes of at least Mw 6.8. This study shows significant deformation is accommodated on poorly characterized Australian Plate structures northwest of the Alpine Fault and demonstrates that major active and seismogenic structures remain uncharacterized in densely forested regions on Earth.

  17. Detecting Possible Fault Zone Head Waves Along the Longmenshan Fault Zone Using Aftershocks of the 2013 Mw6.7 Lushan Earthquake (United States)

    Daniels, C.; Peng, Z.; Li, Z.; Ross, Z. E.; Wu, J.; Su, J.; Zhang, H.; Pei, S.


    Fault zone head waves (FZHWs) are subtle refracted waves propagated along bi-material fault interfaces and recorded at stations at slower side of the fault. FZHWs are typically observed in association with mature strike-slip faults or subduction zones, where two sides exhibit a noticeable P-wave velocity difference. So far FZHWs have not been observed along continental thrust faults. In this study we search for possible FZHWs using abundant aftershock observations following the 2013 Mw6.7 Lushan earthquake. This event occurred along the southern portion of the Longmenshan Fault Zone that separated the Tibetan Plateau and Sichuan Basin in Western China. Recent P-wave tomographic studies have found clear velocity contrasts along this fault, suggesting that events occurred at the fault boundary are capable of producing FZHW-like signals. We are in the process of analyzing 4100 aftershocks recorded by 28 temporary stations deployed between April 24 to May 19 2013. We use both visual inspections and automatic FZHW pickers to identify weak precursory-type signals before sharp direct P wave arrivals. Next, we align them on the P-wave onset, and examine the moveout between the time delays of P and weak arrivals and distance along the fault strike. So far we find that many stations on both sides of the fault recorded possible evidence of FZHWs, but we do not find clear moveout with along-strike distances. Our next step is to combine this dataset with another larger dataset recorded by both permanent and temporary stations, and use automatic FZHW pickers to quantify the existences of FZHWs in this region. A systematic detection of FZHW along continental thrust faults could provide new insights on the fault geometry and high-resolution fault interface properties at seismogenic depth.

  18. Fault segmentation: New concepts from the Wasatch Fault Zone, Utah, USA (United States)

    Duross, Christopher; Personius, Stephen F.; Crone, Anthony J.; Olig, Susan S.; Hylland, Michael D.; Lund, William R.; Schwartz, David P.


    The question of whether structural segment boundaries along multisegment normal faults such as the Wasatch fault zone (WFZ) act as persistent barriers to rupture is critical to seismic hazard analyses. We synthesized late Holocene paleoseismic data from 20 trench sites along the central WFZ to evaluate earthquake rupture length and fault segmentation. For the youngest (segment boundaries, especially for the most recent earthquakes on the north-central WFZ, are consistent with segment-controlled ruptures. However, broadly constrained earthquake times, dissimilar event times along the segments, the presence of smaller-scale (subsegment) boundaries, and areas of complex faulting permit partial-segment and multisegment (e.g., spillover) ruptures that are shorter (~20–40 km) or longer (~60–100 km) than the primary segment lengths (35–59 km). We report a segmented WFZ model that includes 24 earthquakes since ~7 ka and yields mean estimates of recurrence (1.1–1.3 kyr) and vertical slip rate (1.3–2.0 mm/yr) for the segments. However, additional rupture scenarios that include segment boundary spatial uncertainties, floating earthquakes, and multisegment ruptures are necessary to fully address epistemic uncertainties in rupture length. We compare the central WFZ to paleoseismic and historical surface ruptures in the Basin and Range Province and central Italian Apennines and conclude that displacement profiles have limited value for assessing the persistence of segment boundaries but can aid in interpreting prehistoric spillover ruptures. Our comparison also suggests that the probabilities of shorter and longer ruptures on the WFZ need to be investigated.

  19. Fault Zone Drainage, Heating and Melting During Earthquake Slip (United States)

    Rempel, A. W.; Rice, J. R.; Jacques, L. M.


    The expansion of pore water caused by frictional heating during large crustal events provides a powerful weakening mechanism (Sibson, 1973; Lachenbruch, 1980). It may explain the magnitude of seismically inferred fracture energy and aspects of its variation with increased slip (Abercrombie and Rice, 2003; Rice et al., 2003; Rice, this section, 2003). The weakening is mediated by the effects of fluid transport, which are sensitive to the permeability structure of the fault zone and its modification by damage induced by the passing rupture front (Poliakov et al., 2002), as well as by the increase in pore pressure itself. Higher permeabilities allow partial drainage to occur, so that enough strength remains for the heat generated to cause partial melting of the fault gouge at large enough slip. We use recent field and laboratory data for fluid transport through pressurized fault gouge (e.g. Lockner et al., 2000; Wibberley and Shimamoto, 2003) to motivate models for drainage and melting during earthquake slip. A dramatic illustration of the role of drainage is provided by an idealized model in which we assume that a freshly damaged, highly permeable region extends right up to a localized shear zone of thickness ho=5 mm, with fixed porosity n and much lower permeability k. At 7 km depth, for n=0.02 and k=10-19 m2, the slip distance required to reach the onset of melting at 750oC is approximately 0.4 m for a constant friction coefficient of f=0.6. At 14 km depth, for n=0.01 and k=10-20 m2, the same temperature is reached after only 0.1 m of slip. Yet more efficient drainage might occur due to the permeability increases that accompany reductions in the effective stress, so that even more rapid temperature increases would be predicted. For example, with ten times higher k, melting begins after 0.1 m slip at 7 km depth and just 0.05 m at 14 km. At onset of melting the high melt viscosity impedes further drainage and, with increasing melt fraction, inter-particle contact is

  20. Phase mixing and the spatial distribution of material heterogeneities in a crustal fault zone: Insights from New Zealand's Alpine Fault (United States)

    Sauer, Katrina M.; Renard, Francois; Toy, Virginia G.


    Large-scale continental faults represent zones of inherent weakness and focused deformation in the crust. Heterogeneities in fault zone rocks, such as grain-boundary pores, fine-grained secondary phases, and fluid inclusions can provide nucleation points for deformation instabilities, which are required for strain localisation. However, these heterogeneities are not uniformly distributed at any scale within fault zones. Therefore, a systematic characterisation of the nature and distribution of fault rock heterogeneities will improve our understanding of the mechanisms of strain localisation and fault zone dynamics. The Alpine Fault is the main Pacific-Australian plate-boundary structure on the South Island of New Zealand, with rapidly exhumed hangingwall mylonite and cataclasite sequences that are equivalent to the fault rocks currently deforming at depth. We have sampled across the ductile strain gradient of the Alpine Fault zone to examine how microstructures and material heterogeneities evolve with increasing strain. Synchrotron micro-computed x-ray tomography (Sµ-CT), electron microprobe analyses (EPMA), and scanning electron microscopy (SEM) imaging reveal that at lower strains, pure quartz domains are common and grain-boundary pores are concentrated on monophase quartz boundaries, while with increasing strain phase mixing is more prominent and pores are progressively found on boundaries between different phases. Electron backscatter diffraction (EBSD) is used to evaluate the evolution of fabric anisotropy, such as crystallographic preferred orientations (CPO) across the strain gradient. Using both the J-index and M-index to quantify quartz CPO strength, we find a decrease in the CPO intensity with increasing strain in polyphase rocks. We infer this is due to a switch in the dominant deformation mechanism associated with increased phase mixing. Here we explore the relationship between phase mixing, microstructural evolution, and the spatial distribution of

  1. Fault zone architecture of a major oblique-slip fault in the Rawil depression, Western Helvetic nappes, Switzerland (United States)

    Gasser, D.; Mancktelow, N. S.


    The Helvetic nappes in the Swiss Alps form a classic fold-and-thrust belt related to overall NNW-directed transport. In western Switzerland, the plunge of nappe fold axes and the regional distribution of units define a broad depression, the Rawil depression, between the culminations of Aiguilles Rouge massif to the SW and Aar massif to the NE. A compilation of data from the literature establishes that, in addition to thrusts related to nappe stacking, the Rawil depression is cross-cut by four sets of brittle faults: (1) SW-NE striking normal faults that strike parallel to the regional fold axis trend, (2) NW-SE striking normal faults and joints that strike perpendicular to the regional fold axis trend, and (3) WNW-ESE striking normal plus dextral oblique-slip faults as well as (4) WSW-ENE striking normal plus dextral oblique-slip faults that both strike oblique to the regional fold axis trend. We studied in detail a beautifully exposed fault from set 3, the Rezli fault zone (RFZ) in the central Wildhorn nappe. The RFZ is a shallow to moderately-dipping (ca. 30-60˚) fault zone with an oblique-slip displacement vector, combining both dextral and normal components. It must have formed in approximately this orientation, because the local orientation of fold axes corresponds to the regional one, as does the generally vertical orientation of extensional joints and veins associated with the regional fault set 2. The fault zone crosscuts four different lithologies: limestone, intercalated marl and limestone, marl and sandstone, and it has a maximum horizontal dextral offset component of ~300 m and a maximum vertical normal offset component of ~200 m. Its internal architecture strongly depends on the lithology in which it developed. In the limestone, it consists of veins, stylolites, cataclasites and cemented gouge, in the intercalated marls and limestones of anastomosing shear zones, brittle fractures, veins and folds, in the marls of anastomosing shear zones, pressure

  2. Reactivation of normal faults as high-angle reverse faults due to low frictional strength: Experimental data from the Moonlight Fault Zone, New Zealand (United States)

    Smith, S. A. F.; Tesei, T.; Scott, J. M.; Collettini, C.


    Large normal faults are frequently reactivated as high-angle reverse faults during basin inversion. Elevated fluid pressure is commonly invoked to explain high-angle reverse slip. Analogue and numerical modeling have demonstrated that frictional weakening may also promote high-angle reverse slip, but there are currently no frictional strength measurements available for fault rocks collected from large high-angle reverse faults. To test the hypothesis that frictional weakening could facilitate high-angle reverse slip, we performed single- and double-direct friction experiments on fault rocks collected from the Moonlight Fault Zone in New Zealand, a basin-bounding normal fault zone that was reactivated as a high-angle reverse fault (present-day dip angle 60°-75°). The fault core is exposed in quartzofeldspathic schists exhumed from c. 4-8 km depth and contains a <20 m thick sequence of breccias, cataclasites and foliated cataclasites that are enriched in chlorite and muscovite. Friction experiments on water-saturated, intact samples of foliated cataclasite at room temperature and normal stresses up to 75 MPa yielded friction coefficients of 0.19<μ < 0.25. On the assumption of horizontal maximum compressive stress, reactivation analysis indicates that a friction coefficient of <0.25 will permit slip on high-angle reverse faults at hydrostatic (or even sub-hydrostatic) fluid pressures. Since foliated and phyllosilicate-rich fault rocks are common in large reactivated fault zones at basement depths, long-term frictional weakening is likely to act in concert with episodic build-ups of fluid pressure to promote high-angle reverse slip during basin inversion.

  3. Finite-frequency sensitivity kernels of seismic waves to fault zone structures (United States)

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


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

  4. Deep rock damage in the San Andreas Fault revealed by P- and S-type fault-zone-guided waves (United States)

    Ellsworth, William L.; Malin, Peter E.


    Damage to fault-zone rocks during fault slip results in the formation of a channel of low seismic-wave velocities. Within such channels guided seismic waves, denoted by Fg, can propagate. Here we show with core samples, well logs and Fg-waves that such a channel is crossed by the SAFOD (San Andreas Fault Observatory at Depth) borehole at a depth of 2.7 km near Parkfield, California, USA. This laterally extensive channel extends downwards to at least half way through the seismogenic crust, more than about 7 km. The channel supports not only the previously recognized Love-type- (FL) and Rayleigh-type- (FR) guided waves, but also a new fault-guided wave, which we name FF. As recorded 2.7 km underground, FF is normally dispersed, ends in an Airy phase, and arrives between the P- and S-waves. Modelling shows that FF travels as a leaky mode within the core of the fault zone. Combined with the drill core samples, well logs and the two other types of guided waves, FF at SAFOD reveals a zone of profound, deep, rock damage. Originating from damage accumulated over the recent history of fault movement, we suggest it is maintained either by fracturing near the slip surface of earthquakes, such as the 1857 Fort Tejon M 7.9, or is an unexplained part of the fault-creep process known to be active at this site.

  5. Exploration of fault-zone trapped waves at Pingtong Town, in Wenchuan earthquake region

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    Xiaoling Lai


    Full Text Available Pingtong Town is located on the fractured zone of the Wenchuan 8.0 earthquake, and is seriously damaged by the earthquake. Our observation line is centered at an earthquake exploration trench across the fractured zone in the NW-SE direction, and is about 400 m long. The results reveal trapped waves in the ruptured fault zone of the earthquake, and indicate a great difference in physical property between the media inside and outside the fault zone. The predominant frequency of the fault-zone trapped waves is about 3 – 4 Hz. The wave amplitudes are larger near the exploration trench. The width of the fault zone in the crust at this location is estimated to be 200 m. In some records, the waveforms and the arrival times of S waves are quite different between the two sides of the trench. The place of change coincides with the boundary of uplift at the surface.

  6. Transpressional inversion in an extensional transfer zone (the Saltacaballos fault, northern Spain) (United States)

    Quintana, Luís; Alonso, Juan Luís; Pulgar, Javier A.; Rodríguez-Fernández, Luís Roberto


    This paper deals with an extensional transfer zone and its main structure, the Saltacaballos fault, developed during Early Cretaceous times, and obliquely inverted during the Alpine shortening. Geological mapping and structural analysis were carried out to determine the kinematic history of the deformation. The Saltacaballos ridge is the relay zone between two major and conjugate normal fault systems: the Bilbao and the La Granja-Samano fault systems. Three distinct phases in the structural evolution of this transfer zone can be identified. (1) During the initial stages of extensional deformation, shallow-water marine limestones were deposited on the relay ridge and deep-water marls on the flanking depocenters. At the same time, submarine landslides developed on paleoslope generated either by normal drag or by a fault-propagation fold related to the Saltacaballos normal fault. (2) With increasing displacement, normal faults antithetic to the Saltacaballos fault were developed probably in response to the collapse of its hanging-wall. (3) During the subsequent Alpine compressional stage, these normal faults were reactivated as dextral strike-slip faults as a result of transpressional inversion, whereas previous extensional fault-related folds were tightened. At the same time, some normal faults were overturned as a consequence of passive rotation in fold limbs.

  7. Active faults and related Late Quaternary deformation along the Northwestern Himalayan Frontal Zone, India

    Directory of Open Access Journals (Sweden)

    T. Nakata


    Full Text Available Numerous newly-identified traces of active faults in the Himalayan foothill zone along the HFF around Chandigarh, in Pinjore Dun, along the piedmont zone of the Lower Siwalik hill front and within the Lower Tertiary hill range reveal the pattern of thrust and strike-slip faulting, striking parallel to the principal structural trend (NNW-SSE of the orogenic belt. The active Chandigarh Fault, Pinjore Garden Fault and Barsar thrust have vertically dislocated, warped and backtilted fluvial and alluvial-fan surfaces made up of Late Pleistocene-Holocene sediments. West- and southwest-facing fault scarplets with heights ranging from 12 to 50 m along these faults suggest continued tectonic movement through Late Pleistocene to recent times. Gentle warping and backtilting of the terraces on the hanging wall sides of the faults indicate fault-bend folding. These active faults are the manifestation of north-dipping imbricated thrust faults branching out from the major fault systems like the Main Boundary Fault (MBF and Himalayan Frontal Fault (HFF, probably merging down northward into a décollement. The Taksal Fault, striking NNW-SSE, shows prominent right-lateral movement marked by lateral offset of streams and younger Quaternary terraces and occupies a narrow deep linear valley along the fault trace. Right stepping along this fault has resulted in formation of a small pull-apart basin. Fault scarplets facing ENE and WSW are the manifestation of dip-slip movement. This fault is an example of slip-partitioning between the strike-slip and thrust faults, suggesting ongoing oblique convergence of the Indian plate and northward migration of a tectonic sliver. Slip rate along the Taksal Fault has been calculated as 2.8 mm/yr. Preliminary trench investigation at the base of the Chandigarh Fault Scarp has revealed total displacement of 3.5 m along a low angle thrust fault with variable dip of 20° to 46° due northeast, possibly the result of one

  8. Possible Connections Between the Coronado Bank Fault Zone and the Newport-Inglewood, Rose Canyon, and Palos Verdes Fault Zones Offshore San Diego County, California. (United States)

    Sliter, R. W.; Ryan, H. F.


    High-resolution multichannel seismic-reflection and deep-tow Huntec data collected by the USGS were interpreted to map the Coronado Bank fault zone (CBFZ) offshore San Diego County, California. The CBFZ is comprised of several major strands (eastern, central, western) that change in both orientation and degree of deformation along strike. Between Coronado Bank and San Diego, the CBFZ trends N25W and occupies a narrow 7 km zone. Immediately north of La Jolla submarine canyon (LJSC), the easternmost strand changes orientation to almost due north and appears to be offset in a right-lateral sense across the canyon axis. The strand merges with a prominent fault that follows the base of the continental slope in about 600 m water depth. The central portion of the CBFZ is mapped as a negative flower structure and deforms seafloor sediment as far north as 15 km north of LJSC. Farther north, this structure is buried by more than 400 m of basin sediment. Along the eastern edge of the Coronado Bank, the western portion of the CBFZ is characterized by high angle normal faults that dip to the east. North of the Coronado Bank, the western segment follows the western edge of a basement high; it cuts through horizontal basin reflectors and in places deforms the seafloor. We mapped an additional splay of the CBFZ that trends N40W; it is only observed north and west of LJSC. Although the predominant trend of the CBFZ is about N40W, along strike deviations from this orientation of some of the strands indicate that these strands connect with other offshore fault zones in the area. Based on the limited data available, the trend of the CBFZ south of Coronado Bank suggests that it might connect with the Rose Canyon fault zone (RCFZ) that has been mapped in San Diego Bay. North of Coronado Bank, the CBFZ is a much broader fault zone (about 25 km wide) composed of diverging fault strands. The westernmost strand may merge with the western strand of the Palos Verdes fault zone (PVFZ) south of

  9. Incremental Holocene slip rates from the Hope fault at Hossack Station, Marlborough fault zone, South Island, New Zealand (United States)

    Hatem, A. E.; Dolan, J. F.; Langridge, R.; Zinke, R. W.; McGuire, C. P.; Rhodes, E. J.; Van Dissen, R. J.


    The Marlborough fault system, which links the Alpine fault with the Hikurangi subduction zone within the complex Australian-Pacific plate boundary zone, partitions strain between the Wairau, Awatere, Clarence and Hope faults. Previous best estimates of dextral strike-slip along the Hope fault are ≤ ~23 mm/yr± 4 mm/year. Those rates, however, are poorly constrained and could be improved using better age determinations in conjunction with measurements of fault offsets using high-resolution imagery. In this study, we use airborne lidar- and field-based mapping together with the subsurface geometry of offset channels at the Hossack site 12 km ESE of Hanmer Springs to more precisely determine stream offsets that were previously identified by McMorran (1991). Specifically, we measured fault offsets of ~10m, ~75 m, and ~195m. Together with 65 radiocarbon ages on charcoal, peat, and wood and 25 pending post-IR50-IRSL225 luminescence ages from the channel deposits, these offsets yield three different fault slip rates for the early Holocene, the late Holocene, and the past ca. 500-1,000 years. Using the large number of age determinations, we document in detail the timing of initiation and abandonment of each channel, enhancing the geomorphic interpretation at the Hossack site as channels deform over many earthquake cycles. Our preliminary incremental slip rate results from the Hossack site may indicate temporally variable strain release along the Hope fault. This study is part of a broader effort aimed at determining incremental slip rates and paleo-earthquake ages and displacements from all four main Marlborough faults. Collectively, these data will allow us to determine how the four main Marlborough faults have work together during Holocene-late Pleistocene to accommodate plate-boundary deformation in time and space.

  10. Groundwater flow through anisotropic fault zones in multiaquifer systems

    NARCIS (Netherlands)

    Anderson, E.I.; Bakker, M.


    Vertical faults through the shallow crust are commonly believed to act as either barriers to horizontal groundwater flow normal to the fault, conduits to horizontal flow tangential to the fault, or a combination of both. In addition, enhanced vertical permeability has been identified as a common

  11. New active faults on Eurasian-Arabian collision zone: Tectonic activity of Özyurt and Gülsünler faults (Eastern Anatolian Plateau, Van-Turkey)

    Energy Technology Data Exchange (ETDEWEB)

    Dicle, S.; Üner, S.


    The Eastern Anatolian Plateau emerges from the continental collision between Arabian and Eurasian plates where intense seismicity related to the ongoing convergence characterizes the southern part of the plateau. Active deformation in this zone is shared by mainly thrust and strike-slip faults. The Özyurt thrust fault and the Gülsünler sinistral strike-slip fault are newly determined fault zones, located to the north of Van city centre. Different types of faults such as thrust, normal and strike-slip faults are observed on the quarry wall excavated in Quaternary lacustrine deposits at the intersection zone of these two faults. Kinematic analysis of fault-slip data has revealed coeval activities of transtensional and compressional structures for the Lake Van Basin. Seismological and geomorphological characteristics of these faults demonstrate the capability of devastating earthquakes for the area.

  12. The Role of Thermal Processes in Defining the Seismogenic Zone: The Interplay Between Faults and Shear Zones (United States)

    Lambert, V.; Barbot, S.


    The extent of the seismogenic zone is thought to be controlled by lithological, pressure, and thermal gradients. Thermodynamic considerations indicate a temperature dependence of frictional parameters that may control the up-dip limit of the seismogenic zone. However, there is no consensus on what determines the down-dip limit. In addition, recent observations of through-lithospheric ruptures, such as the 2012 Wharton Basin earthquake, or tsunami earthquakes (Hubbard et al. 2015) that rupture regions normally up-dip of the typical seismogenic zone, indicate that the width of the seismogenic zone varies throughout the earthquake cycle over long time-scales. Here, we propose a competition of strengthening and weakening mechanisms where fault slip during earthquakes is enhanced by thermal weakening and mitigated by off-fault thermally-activated viscous strain. We couple fault kinematics and off-fault viscoelastic deformation using the integral method to simulate earthquake cycles combining fault and off-fault processes. We seek a physical framework for thermal weakening in rate and state friction whereby increasing temperatures reduce frictional stability. We then couple frictional sliding to a thermally-activated rheology and thermal diffusion to investigate the thermo-mechanical coupling of faults and their surrounding volume. Thermal effects are mediated by the geothermal gradient, which enhances dynamic frictional weakening by melt lubrication near the base of the lithosphere. The strong weakening of peridotite by melt lubrication may reduce the strength of the lithosphere and create more favorable conditions for plate tectonics to occur.

  13. Geomorphic evidence of Quaternary tectonics within an underlap fault zone of southern Apennines, Italy (United States)

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


    A composite seismic source, the Irpinia - Agri Valley Fault zone, located in the axial sector of the fold-and-thrust belt of southern Apennines, Italy, is investigated. This composite source is made up of a series of nearly parallel, NW-striking normal fault segments which caused many historical earthquakes. Two of these fault segments, known as the San Gregorio Magno and Pergola-Melandro, and the fault-related mountain fronts, form a wedge-shaped, right-stepping, underlap fault zone. This work is aimed at documenting tectonic geomorphology and geology of this underlap fault zone. The goal is to decipher the evidence of surface topographic interaction between two bounding fault segments and their related mountain fronts. In particular, computation of geomorphic indices such as mountain front sinuosity (Smf), water divide sinuosity (Swd), asymmetry factor (AF), drainage basin elongation (Bs), relief ratio (Rh), Hypsometry (HI), normalized steepness (Ksn), and concavity (θ) is integrated with geomorphological analysis, the geological mapping, and structural analysis in order to assess the recent activity of the fault scarp sets recognized within the underlap zone. Results are consistent with the NW-striking faults as those showing the most recent tectonic activity, as also suggested by presence of related slope deposits younger than 38 ka. The results of this work therefore show how the integration of a multidisciplinary approach that combines geomorphology, morphometry, and structural analyses may be key to solving tectonic geomorphology issues in a complex, fold-and-thrust belt configuration.

  14. Strain localisation within ductile shear zones beneath active faults: The Alpine Fault contrasted with the adjacent Otago fault system, New Zealand (United States)

    Norris, Richard J.


    The Alpine Fault accommodates around 60-70% of the 37 mm/yr oblique motion between the Australian and Pacific plates in the South Island of New Zealand. Uplift on the fault over the past 5 Ma has led to the exhumation of the deep-seated mylonite zone alongside the present surface trace. Shear strain estimates in the mylonites reach 200-300 in the most highly strained rocks, and provide an integrated displacement across the zone of 60-120 km. This is consistent with the amount of displacement during the last 5 Ma, suggesting that displacement on the fault is localised within a 1-2 km wide ductile shear zone to depths of 25-30 km. Existing geodetic data, together with Late Quaternary slip rate and paleoseismic data, are consistent with the steady build-up and release of elastic strain in the upper crust driven by ductile creep within a narrow mylonite zone at depth. Faults of the Otago Fault System form a parallel array east of the Alpine Fault and accommodate c. 2 mm/yr contraction. Long periods of quiescence on individual structures suggest episodic, or "intermittently characteristic", behaviour. This is more consistent with failure on faults within an elastico-frictional upper crust above a ductile lower crust. Localisation of crustal deformation may be initiated by inherited weaknesses in the upper crust, with downward propagation of slip causing strain weakening within the ductile zone immediately beneath. Inherited structures of great length focus a greater amount of displacement and hence more rapidly develop underlying zones of ductile shear.

  15. Thermochronometric and textural evidence for seismicity via asperity flash heating on exhumed hematite fault mirrors, Wasatch fault zone, UT, USA (United States)

    McDermott, Robert G.; Ault, Alexis K.; Evans, James P.; Reiners, Peter W.


    Exhumed faults record the temperatures produced by earthquakes. We show that transient elevated fault surface temperatures preserved in the rock record are quantifiable through microtextural analysis, fault-rock thermochronometry, and thermomechanical modeling. We apply this approach to a network of mirrored, minor, hematite-coated fault surfaces in the exhumed, seismogenic Wasatch fault zone, UT, USA. Polygonal and lobate hematite crystal morphologies, coupled with hematite (U-Th)/He data patterns from these surfaces and host rock apatite (U-Th)/He data, are best explained by friction-generated heat at slip interface geometric asperities. These observations inform thermomechanical simulations of flash heating at frictional contacts and resulting fractional He loss over generated fault surface time-temperature histories. Temperatures of >∼700-1200 °C, depending on asperity size, are sufficient to induce 85-100% He loss from hematite within 200 μm of the fault surface. Spatially-isolated, high-temperature microtextures imply spatially-variable heat generation and decay. Our results reveal that flash heating of asperities and associated frictional weakening likely promote small earthquakes (Mw ≈ - 3 to 3) on Wasatch hematite fault mirrors. We suggest that similar thermal processes and resultant dynamic weakening may facilitate larger earthquakes.

  16. Structure of the Newport-Inglewood/Rose Canyon and Palos Verdes Fault Zones and Implications for Current Fault Models (United States)

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


    Faulting in the Inner California Borderlands is complex. In the past, this region has undergone various deformational events such as extensional and rotational deformation to variable strike-slip deformation; this has imparted the geomorphology and fault structures observed offshore Southern California. Several hypotheses have been proposed to explain the current fault structures and the hazards they pose to populated coastal regions. The geometry and architecture of these structures can have significant implications for ground motions in the event of a rupture, and therefore impact working models of hazard assessment. Here, focusing on the Newport-Inglewood/Rose Canyon (NI/RC) and Palos Verdes (PV) fault zones, we use new and existing multibeam, CHIRP and Multi-Channel Seismic (MCS) data to describe the geometry of the fault system. We interpret reprocessed (prestack time migration) MCS data collected in 1979, 1986, and 2006 as well as newly acquired high-res MCS datasets collected offshore San Diego County. Combining these high and intermediate resolution datasets with very high resolution CHIRP data, we define structures that show distinct changes in the style of deformation through time, and place constraints on the segmentation of faults in this system. The timing of the most recent deformation on the NI/RC appears to vary along-strike. Likewise, the NI/RC fault's dip direction and angle appears to vary along-strike, and these changes in dip seem to mark the boundaries of restraining and releasing bends. Additionally, the NI/RC fault appears to die away to the north, possibly partitioning its strain on to the PV fault. We will present interpretations of the faults' current deformational activity as well as likelihood of rupture propagating across releasing/restraining bends, and discuss how this impacts current fault models that are employed for hazard assessment for Los Angeles and San Diego counties.

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

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


    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

  18. Stress orientations in subduction zones and the strength of subduction megathrust faults. (United States)

    Hardebeck, Jeanne L


    Subduction zone megathrust faults produce most of the world's largest earthquakes. Although the physical properties of these faults are difficult to observe directly, their frictional strength can be estimated indirectly by constraining the orientations of the stresses that act on them. A global investigation of stress orientations in subduction zones finds that the maximum compressive stress axis plunges systematically trenchward, consistently making an angle of 45° to 60° with respect to the subduction megathrust fault. These angles indicate that the megathrust fault is not substantially weaker than its surroundings. Together with several other lines of evidence, this implies that subduction zone megathrusts are weak faults in a low-stress environment. The deforming outer accretionary wedge may decouple the stress state along the megathrust from the constraints of the free surface. Copyright © 2015, American Association for the Advancement of Science.

  19. Stress orientations in subduction zones and the strength of subduction megathrust faults (United States)

    Hardebeck, Jeanne L.


    Subduction zone megathrust faults produce most of the world’s largest earthquakes. Although the physical properties of these faults are difficult to observe directly, their frictional strength can be estimated indirectly by constraining the orientations of the stresses that act on them. A global investigation of stress orientations in subduction zones finds that the maximum compressive stress axis plunges systematically trenchward, consistently making a 45°-60° angle to the subduction megathrust fault. These angles indicate that the megathrust fault is not substantially weaker than its surroundings. Together with several other lines of evidence, this implies that subduction zone megathrusts are weak faults in a low-stress environment. The deforming outer accretionary wedge may decouple the stress state along the megathrust from the constraints of the free surface.

  20. Geological modeling of a fault zone in clay rocks at the Mont-Terri laboratory (Switzerland) (United States)

    Kakurina, M.; Guglielmi, Y.; Nussbaum, C.; Valley, B.


    Clay-rich formations are considered to be a natural barrier for radionuclides or fluids (water, hydrocarbons, CO2) migration. However, little is known about the architecture of faults affecting clay formations because of their quick alteration at the Earth's surface. The Mont Terri Underground Research Laboratory provides exceptional conditions to investigate an un-weathered, perfectly exposed clay fault zone architecture and to conduct fault activation experiments that allow explore the conditions for stability of such clay faults. Here we show first results from a detailed geological model of the Mont Terri Main Fault architecture, using GoCad software, a detailed structural analysis of 6 fully cored and logged 30-to-50m long and 3-to-15m spaced boreholes crossing the fault zone. These high-definition geological data were acquired within the Fault Slip (FS) experiment project that consisted in fluid injections in different intervals within the fault using the SIMFIP probe to explore the conditions for the fault mechanical and seismic stability. The Mont Terri Main Fault "core" consists of a thrust zone about 0.8 to 3m wide that is bounded by two major fault planes. Between these planes, there is an assembly of distinct slickensided surfaces and various facies including scaly clays, fault gouge and fractured zones. Scaly clay including S-C bands and microfolds occurs in larger zones at top and bottom of the Mail Fault. A cm-thin layer of gouge, that is known to accommodate high strain parts, runs along the upper fault zone boundary. The non-scaly part mainly consists of undeformed rock block, bounded by slickensides. Such a complexity as well as the continuity of the two major surfaces are hard to correlate between the different boreholes even with the high density of geological data within the relatively small volume of the experiment. This may show that a poor strain localization occurred during faulting giving some perspectives about the potential for

  1. Fault zone regulation, seismic hazard, and social vulnerability in Los Angeles, California: Hazard or urban amenity? (United States)

    Toké, Nathan A.; Boone, Christopher G.; Arrowsmith, J. Ramón


    Public perception and regulation of environmental hazards are important factors in the development and configuration of cities. Throughout California, probabilistic seismic hazard mapping and geologic investigations of active faults have spatially quantified earthquake hazard. In Los Angeles, these analyses have informed earthquake engineering, public awareness, the insurance industry, and the government regulation of developments near faults. Understanding the impact of natural hazards regulation on the social and built geography of cities is vital for informing future science and policy directions. We constructed a relative social vulnerability index classification for Los Angeles to examine the social condition within regions of significant seismic hazard, including areas regulated as Alquist-Priolo (AP) Act earthquake fault zones. Despite hazard disclosures, social vulnerability is lowest within AP regulatory zones and vulnerability increases with distance from them. Because the AP Act requires building setbacks from active faults, newer developments in these zones are bisected by parks. Parcel-level analysis demonstrates that homes adjacent to these fault zone parks are the most valuable in their neighborhoods. At a broad scale, a Landsat-based normalized difference vegetation index shows that greenness near AP zones is greater than the rest of the metropolitan area. In the parks-poor city of Los Angeles, fault zone regulation has contributed to the construction of park space within areas of earthquake hazard, thus transforming zones of natural hazard into amenities, attracting populations of relatively high social status, and demonstrating that the distribution of social vulnerability is sometimes more strongly tied to amenities than hazards.


    Directory of Open Access Journals (Sweden)

    M. G. Mel’nikov


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

  3. Soil-gas helium and surface-waves detection of fault zones in ...

    Indian Academy of Sciences (India)

    gas helium; surface-waves; faults and fractures; groundwater; granite basement. ... Soil-gas helium emanometry has been utilized in Wailapally watershed,near Hyderabad in southern India,for the detection of fracture and fault zones in a granite ...

  4. Frictional behaviour of megathrust fault gouges under in-situ subduction zone conditions

    NARCIS (Netherlands)

    den Hartog, S.A.M.


    Subduction zone megathrusts generate the largest earthquakes and tsunamis known. Understanding and modelling “seismogenesis” on such faults requires an understanding of the frictional processes that control nucleation and propagation of seismic slip. However, experimental data on the frictional

  5. Geological and geomorphological evidence for the southwestern extension of the East Anatolian Fault Zone, Turkey (United States)

    Yönlü, Önder; Altunel, Erhan; Karabacak, Volkan


    The left lateral strike slip East Anatolian Fault Zone (EAFZ) is the main structural link between the North Anatolian Fault Zone (NAFZ) in north and subduction in the Mediterranean Sea and the transform Dead Sea Fault Zone (DSFZ) in south. We studied the southwestern continuation of the EAFZ using combined field investigations including geomorphology, geology and paleoseismology. Mapping of offset drainages, lineaments, shutter ridges and fault planes in young geological units suggests existence of active faults between the Mediterranean coast and Türkoğlu where it intersects with the DSFZ. Yumurtalık and Toprakkale faults are the main tectonic structures and detailed examination of geological and geomorphological evidences suggest their Quaternary activity. Paleoseismic trenching on these faults provided evidence for at least two surface rupturing events in the last 9,000 yr. Detailed examination of paleo-valleys of the Ceyhan River suggests that the course of the river migrated due to the activity of the Toprakkale Fault. Obtained geological and geomorphological data indicates that the EAFZ continues across the Amanos Mountains and the slip transfer is mainly accommodated by the Toprakkale and Yumurtalık faults.

  6. Assessment of the geothermal potential of fault zones in Germany by numerical modelling (United States)

    Kuder, Jörg


    Fault zones with significantly better permeabilities than host rocks can act as natural migration paths for ascending fluids that are able to transport thermal energy from deep geological formations. Under these circumstances, fault zones are interesting for geothermal utilization especially those in at least 7 km depth (Jung et al. 2002, Paschen et al. 2003). One objective of the joint project "The role of deep rooting fault zones for geothermal energy utilization" supported by the Federal Ministry for Economic Affairs and Energy was the evaluation of the geothermal potential of fault zones in Germany by means of numerical modelling with COMSOL. To achieve this goal a method was developed to estimate the potential of regional generalized fault zones in a simple but yet sophisticated way. The main problem for the development of a numerical model is the lack of geological and hydrological data. To address this problem the geothermal potential of a cube with 1 km side length including a 20 meter broad, 1000 m high and 1000 m long fault zone was calculated as a unified model with changing parameter sets. The properties of the surrounding host rock and the fault zone are assumed homogenous. The numerical models were calculated with a broad variety of fluid flow, rock and fluid property parameters for the depths of 3000-4000 m, 4000-5000 m, 5000-6000 m and 6000-7000 m. The fluid parameters are depending on temperature, salt load and initial pressure. The porosity and permeability values are provided by the database of the geothermal information system (GeotIS). The results are summarized in a table of values of geothermal energy modelled with different parameter sets and depths. The geothermal potential of fault zones in Germany was then calculated on the basis of this table and information of the geothermal atlas of Germany (2016).

  7. The northwest trending north Boquerón Bay-Punta Montalva Fault Zone; A through going active fault system in southwestern Puerto Rico (United States)

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


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

  8. Structure of a shear zone at the base of the seismogenic zone, Norumbega fault system, Maine; Potential for comparison with upper-crustal fault structure (United States)

    Price, N. A.; Johnson, S. E.; Gerbi, C. C.; Koons, P. O.


    Studies of large strike-slip faults provide a detailed picture of the upper crustal structure of a seismogenic fault system (e.g. Chester et al., 1993; Ben-Zion and Sammis, 2003; Wibberley et al., 2008). Few studies have provided that same degree of detail for such faults at greater depths. Because of this, it is not well understood how the structure of the fault at the surface correlates with the structure of a fault with depth, particularly across the frictional-to-viscous transition. Our study of the Sandhill Corner shear zone (SCSZ) within the Norumbega fault system (a long-lived, subvertical, seismogenic fault system in Maine, USA) focuses on this depth level and provides an informative view of across and along strike variations within a shear zone from the base of the seismogenic zone. We suggest that the structure of this shear zone correlates with the structure of modern strike slip faults like the San Andreas. The SCSZ is a 300-500m wide shear zone exhumed from depths of ~10-15km that preserves mutually-overprinting pseudotachylyte and mylonite. Using over 100 samples from 6 transects, we considered the spatial variation in (1) quartz fabric intensity, grain size, and CPO data; (2) the prevalence of mineral-filled fractures and shattered porphyroclasts; and (3) the amount of pseudotachylyte (deformed and undeformed). We find a focused shear zone core (1-7m) that contains ultramylonite and phyllonite nearly devoid of porphyroclasts and rich in deformed pseudotachylyte with the finest sizes of quartz new grains. This core region is comparable to the focused core region of upper crustal faults rich in foliated gauge where most of the slip is thought to occur. The core of the SCSZ is surrounded by a wider zone of quartzofeldspathic mylonite and protomylonite, mylonitized calc-silicates, and sheared schist (~100-500m). There is an increased incidence of shattered porphyroclasts and deformed pseudotachylyte in these rocks with proximity to the fault core but

  9. Pinpoint core sampling at active faults in the Nankai subduction zone by new ROV "NSS" (United States)

    Ashi, J.; Shirai, M.; Tokuyama, H.; Soh, W.; Kinoshita, M.; Machiyama, H.; Kanamatsu, T.; Hirono, T.; Ikehara, K.; Arai, K.; Omura, A.


    Piston coring across active faults in shallow water depth, as well as drilling or trenching of fault zone on land, provides us with information about earthquake timing, recurrence of fault activity and fault displacement. In contrast, it is not easy to take samples from deep-sea with pinpoint accuracy. In order to identify the position of the core sampler and approach the target for sampling, a transponder is recently installed on the cable just above the sampler. The pilot vehicle of new ROV "NSS" (Navigable Sampling System) can move by four thrusters, observe seafloor by video cameras, release samplers and measurement tools by command from a mother ship, and real time geophysical or geochemical monitoring through an armored cable. The whole system including winches is removal. The ship with large deck can be equipped with NSS system. Depth capability of the pilot vehicle is 4000m and maximum payload weight is 1.5 Tons. First cruise using NSS was conducted in the Nankai Trough and the Sagami Trough using JAMSTEC R/V "Kaiyo" in 2003. Piston cores were taken from active faults off the Central Japan in the Nankai Trough, and the cold seep sites along the blind fault off Hatsushima, Sagami Bay. NSS using seafloor video camera and thrusters has accuracy of pinpoint sampling within 2m, and allows us to take samples from narrow fault zone or small clam colony. Core samples derived from active fault zones show different sedimentation histories; lack of strata and differences of layer thickness across dip-slip faults and lithological changes with time across strike-slip faults near submarine canyon, and provide information about recurrence time and fault displacement. NSS is one of tools that break through difficulties of pinpoint sampling in deep-sea and will proceed studies of active submarine faults.

  10. Evolving seismogenic plate boundary megathrust and mega-splay faults in subduction zone (Invited) (United States)

    Kimura, G.; Hamahashi, M.; Fukuchi, R.; Yamaguchi, A.; Kameda, J.; Kitamura, Y.; Hashimoto, Y.; Hamada, Y.; Saito, S.; Kawasaki, R.


    Understanding the fault mechanism and its relationship to the sesimo-tsunamigenesis is a key of the scientific targets of subduction zone and therefore NantroSEIZE project of IODP and future new drilling project of International Ocean Discovery Program keeps focusing on that. Mega-splay fault branched from plate boundary megathrust in subduction zone is located around the border between outer and inner wedges and is considered to cause great earthquake and tsunami such as 1960 Alaska earthquake, 1944 and 1946 Nankai-Tonankai earthquakes, and 2004 Sumatra earthquakes. Seismic reflection studies for the mega-splay fault in 2D and 3D in the Nankai forearc present the reflector with negative or positive polarities with various amplitudes and suggest complicated petrophysical properties and condition of the fault and its surroundings. The Nankai mega-splay fault at a depth of ~5km is going to be drilled and cored by NantroSEIZE experiments and is expected for great progress of understanding of the fault mechanics. Before drilling the really targeted seismogenic fault, we are conducting many exercises of geophysical and geological observations. The core-log-seismic integrated exercise for the exhumed mega-splay fault by drilling was operated for the Nobeoka thrust in the Shimanto Belt, Kyushu, Japan. The Nobeoka thrust was once buried in the depth >~10km and suffered maximum temperature >~300 dgree C. As the core recovery is ~99%, perfect correlation between the core and logging data is possible. Thickness of the fault zone is >200 m with a ~50 cm thick central fault core dividing the phyllitic hanging wall and the footwall of broken-melange like cataclasite. A-few-meter-thick discrete damage zones with fault cores are recognized by difference in physical properties and visual deformation textures at several horizons in the fault zone. Host rocks for those damaged zones are completely lithified cataclasites with abundant mineral veins, which record the older and deeper

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

    Energy Technology Data Exchange (ETDEWEB)

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


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

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

    Directory of Open Access Journals (Sweden)

    Sheng-Rong Song


    Full Text Available The main objective of the Taiwan Chelungpu-fault Drilling Project (TCDP was to conduct an in-depth probe into a fault zone of recent major activity so as to gain a better understanding of and more insight into the physical, mechanical and chemical properties involved. By the end of 2004, with the completion of the drilling of Hole-A, cuttings from 0 to 431.34 m and cores from a 431.34- to 2003.26-m depth had been obtained. Stratigraphically, the Pliocene to Pleistocene Cholan Formation is found from the surface to a 1029-m depth and is predominantly composed of sandstone and sandstone-siltstone alternations with weak to intense bioturbation. The Pliocene Chinshui Formation is observed from a depth of 1029- to 1303-m and predominantly consists of siltstone with weak bioturbation. From 1303- to 1712-m down there is the late Miocene to early Pliocene Kueichulin Formation which is predominantly composed of massive sandstone with minor siltstone. Below 1712 m, the Formation again resembles the younger Cholan Formation with mollusca-rich, thick, layered shale and heavy bioturbated sandstone. Four types of fault-related rocks are identified in the cores. They are the fault breccia, gouges, foliated and non-foliated cataclasites and pseudotachylytes. At least six major fault zones are found in the cores: FZ1111, FZ1153, FZ1220, FZ1580, FZ1712, and FZ1812. Among these, FZ1111 most probably corresponds to the slip surface of the Chi-Chi earthquake, the Chelungpu fault, while FZ1712 very likely represents the Sanyi fault.

  13. Low resistivity and permeability in actively deforming shear zones on the San Andreas Fault at SAFOD (United States)

    Morrow, Carolyn A.; Lockner, David A.; Hickman, Stephen H.


    The San Andreas Fault Observatory at Depth (SAFOD) scientific drillhole 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 ohm-m) and permeability (10-21 to 10-22 m2) in the actively deforming zones were one to two 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.

  14. Quantification of Fault-Zone Plasticity Effects with Spontaneous Rupture Simulations (United States)

    Roten, D.; Olsen, K. B.; Day, S. M.; Cui, Y.


    Previous studies have shown that plastic yielding in crustal rocks in the fault zone may impose a physical limit to extreme ground motions. We explore the effects of fault-zone non-linearity on peak ground velocities (PGVs) by simulating a suite of surface-rupturing strike-slip earthquakes in a medium governed by Drucker-Prager plasticity using the AWP-ODC finite-difference code. Our simulations cover magnitudes ranging from 6.5 to 8.0, three different rock strength models, and average stress drops of 3.5 and 7.0 MPa, with a maximum frequency of 1 Hz and a minimum shear-wave velocity of 500 m/s. Friction angles and cohesions in our rock models are based on strength criteria which are frequently used for fractured rock masses in civil and mining engineering. For an average stress drop of 3.5 MPa, plastic yielding reduces near-fault PGVs by 15-30% in pre-fractured, low strength rock, but less than 1% in massive, high-quality rock. These reductions are almost insensitive to magnitude. If the stress drop is doubled, plasticity reduces near-fault PGVs by 38-45% and 5-15% in rocks of low and high strength, respectively. Because non-linearity reduces slip rates and static slip near the surface, plasticity acts in addition to, and may partially be emulated by, a shallow velocity-strengthening layer. The effects of plasticity are exacerbated if a fault damage zone with reduced shear-wave velocities and reduced rock strength is present. In the linear case, fault-zone trapped waves result in higher near-surface peak slip rates and ground velocities compared to simulations without a low-velocity zone. These amplifications are balanced out by fault-zone plasticity if rocks in the damage zone exhibit low-to-moderate strength throughout the depth extent of the low-velocity zone (˜5 km). We also perform dynamic non-linear simulations of a high stress drop (8 MPa) M 7.8 earthquake rupturing the southern San Andreas fault along 250 km from Indio to Lake Hughes. Non-linearity in the

  15. Scientific drilling into the San Andreas Fault Zone - an overview of SAFOD's first five years (United States)

    Zoback, Mark; Hickman, Stephen; Ellsworth, William; ,


    The San Andreas Fault Observatory at Depth (SAFOD) was drilled to study the physical and chemical processes controlling faulting and earthquake generation along an active, plate-bounding fault at depth. SAFOD is located near Parkfield, California and penetrates a section of the fault that is moving due to a combination of repeating microearthquakes and fault creep. Geophysical logs define the San Andreas Fault Zone to be relatively broad (~200 m), containing several discrete zones only 2–3 m wide that exhibit very low P- and S-wave velocities and low resistivity. Two of these zones have progressively deformed the cemented casing at measured depths of 3192 m and 3302 m. Cores from both deforming zones contain a pervasively sheared, cohesionless, foliated fault gouge that coincides with casing deformation and explains the observed extremely low seismic velocities and resistivity. These cores are being now extensively tested in laboratories around the world, and their composition, deformation mechanisms, physical properties, and rheological behavior are studied. Downhole measurements show that within 200 m (maximum) of the active fault trace, the direction of maximum horizontal stress remains at a high angle to the San Andreas Fault, consistent with other measurements. The results from the SAFOD Main Hole, together with the stress state determined in the Pilot Hole, are consistent with a strong crust/weak fault model of the San Andreas. Seismic instrumentation has been deployed to study physics of faulting—earthquake nucleation, propagation, and arrest—in order to test how laboratory-derived concepts scale up to earthquakes occurring in nature.

  16. Fluid Flow and Fault Zone Damage in Crystalline Basement Rocks (Ore Mountains Saxony) (United States)

    Achtziger-Zupančič, P.; Loew, S.; Hiller, A.; Mariethoz, G.


    Groundwater flow in fractured basement rocks on aquifer scale and processes involved in the creation of fracture network permeability are poorly understood even though they have been studied for decades. A unique hydrogeological dataset consisting of 1030 discrete inflows (corresponding to preferential groundwater pathways) to the Poehla Ore Mine (Ore Mountains) of the SDAG Wismut has been compiled and quantitatively interpreted. Transmissivities and permeabilities were calculated from discrete and cumulative inflows using analytical equations and numerical groundwater flow models. The Variscan basement at Poehla Mine was modelled in 3-D, covering a volume of 14x4x1 km3 with 14 metamorphosed litho-stratigraphic units and 131 faults separated in 6 main strike directions. Mesoscale fractures mapped at inflows points, i.e. locally conductive fractures, show a weak correlation with fault orientation, and a large orientation scattering, which could be related to small scale stress heterogeneities. Inflow points were spatially correlated with major faults considering two distance criteria. This correlation suggests that mainly NW-SE and NE-SW striking faults are transmissive, which should be critically stressed considering all available data about the regional stress field. The trace length (extent) and width of the core and damage zones of the modelled faults were compiled in order to investigate the flow distribution and permeability profiles in directions perpendicular to fault strike. It can be shown that 90% of all inflows are located in damage zones. The inflows are usually situated within multiple fault zones which overlap each other. Cumulative flow distribution functions within damage zones are non-linear and vary between faults with different orientation. 75-95% of the flow occurs in the inner 50% of the damage zone. Significantly lower flow rates were recognized within most fault cores.

  17. Dynamic rupture simulations on complex fault zone structures with off-fault plasticity using the ADER-DG method (United States)

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


    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

  18. Direct Observation of Depth Variation in Fault Zone Structure Through and Below the Seismogenic Crust: Preliminary Results From the SEMP Fault System in Austria (United States)

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


    One of the most exciting and important frontiers in earthquake science is the linkage between the internal structure and the mechanical behavior of fault zones. In particular, little is known about how fault-zone structure varies as a function of depth, from near-surface conditions down through the seismogenic crust and into the ductile lower crust. Such understanding is vital if we are to understand the mechanical instabilities that control the nucleation and propagation of seismic ruptures. This imperative has led us to the Oligo-Miocene Salzach-Ennstal-Mariazell-Puchberg [SEMP] fault zone in Austria. The SEMP system is an extremely rare example of a major strike-slip fault that has been exhumed differentially such that it exposes a continuum of structural levels along strike. This exhumed fault system thus provides a unique opportunity to systematically examine depth-dependent changes in fault-zone geometry and structure along a single fault. Our ongoing field studies focus on structural transects across the SEMP fault zone at exhumation levels ranging from the near-surface at the eastern end of the fault (Vienna pull-apart basin), within the seismogenic crust (central Austria), and down into the ductile lower crust exposed in the Tauern window of western Austria. In addition to detailed field mapping of structural fabrics, fluid-rock interactions, relative timing relationships, and variations in fault geometry, we are also conducting detailed analyses of fault-zone rocks designed to explore deformation at a wide range of scales using petrographic microscopy, cathodoluminescence microscopy, fluid-inclusion studies, scanning-electron microscopy, and transmission/analytical-electron microscopy. Preliminary results from one of our first detailed study sites, at Gesäuse in central Austria, reveal strikingly asymmetric damage across the fault. The limestones exposed south of the fault are fractured, but relatively coherent to within a few meters of the main fault

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


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


    Abstract The Alborz is a region of active deformation within the Arabia-Eurasia collision zone. The Abr and the Khij Faults are two NE-trending left-lateral strike-slip faults in the eastern Alborz that correspond to the Shahrud fault system extended through an area of about 95?55 km2. Tectonic landforms typically associated with active strike-slip faults, such as deflected stream channels, offset ridges and fault scarps are documented along the mentioned faults. Detailed analyses ...

  20. Fault-Zone Deformation and Strain Partitioning at the Brittle-Ductile Transition, SEMP Fault, Austrian Alps. (United States)

    Cole, J. N.; Hacker, B. R.; Ratschbacher, L.; Dolan, J. F.; Frost, E.; Barth, N.


    The differentially exhumed Miocene strike-slip Salzachtal-Ennstal-Mariazell-Puchberg (SEMP) fault in Eastern Austria allows one to study fault structure from Earth's surface to ~30km depth, simply by moving along strike from the Vienna basin to the Tauern Window. Coincident with its entry into the Tauern Window, the SEMP fault passes from a dominantly brittle to a dominantly ductile structure. It is these kinds of brittle-ductile transitions that represent major mechanical discontinuities in the crust and may represent the base of the seismogenic zone. The Tauern segment of the SEMP fault therefore represents a key location for studying earthquake nucleation and mid-crustal rheology. Previous studies (e.g. Behrmann, 1990; Ratschbacher et al., 1991a; Linzer et al., 2002) suggested that the SEMP fault splayed down-section into the Tauern Window into a series of ductile shear zones, including the Olperer, Griener, and Ahrntal shear zones. At each of these locations, however, outcrop-scale structures (e.g. cross-cutting dikes) demonstrate that the main shear-zone fabrics are pre-Alpine, and thus largely unrelated to the SEMP. In contrast, a brittle-ductile shear zone in the northeastern edge of the Tauern Window (near Rinderkarsee south of Krimml) is a probable deeper level portion of the SEMP. The Rinderkarsee shear zone is localized along the contact between the tonalitic Zentral Gneiss and the metasedimentary/meta-igneous rocks of the Habach Group, but extends at least 1300m into the Zentral Gneiss. Shear strain is partitioned into separate discrete zones of sinistral and dextral shear, and both structures have the same slip plane mineralogy and are thus interpreted as coeval. Generally, sinistral shear zones are subvertical and strike NE-SW, while dextral shear zones are steeply dipping and strike NW-SE. At Rinderkarsee there exists a continuum of deformation from high to low temperature. High-temperature deformation shows dominantly sinistral amphibolite


    Directory of Open Access Journals (Sweden)

    K. Zh. Seminsky


    Full Text Available Long-term studies of shear zones have included collection of data on fractures showing no indication of displacement which are termed as 'blank' fractures. A method aimed at mapping fault structures and stress fields has been developed on the basis of results of paragenetic analysis of measurements of abundant fractures. The method is termed as 'specialized mapping', firstly, due to its specific structural goal so that to distinguish it from the conventional geological mapping of regions in nature, and, secondly, because of the specific procedure applied to refer to fractures as references to decipher fault-block patterns of natural regions. In Part 1, basic theoretical concepts and principles of specialized mapping are described. Part 2 is being prepared for publication in one of the next issues of the journal; it will cover stages of the proposed method and describe some of the cases of its application.In terms of general organizational principles, specialized mapping is similar to other methods based on structural paragenetic analysis and differs from such methods in types of paragenesises viewed as references to reveal crustal fault zones. Such paragenesises result from stage-by-stage faulting (Fig 2 and Fig. 7 during which stress fields of the 2nd order are regularly changeable within the shear zone. According to combined experimental and natural data, a complete paragenesis of fractures in the shear zone includes a major (1st order fault plane and fractures of other seven types, R, R’, n, n’, t, t’ and T (2nd order (Fig. 4 and Fig 8. At the fracture level, each of them corresponds to a paragenesis including three nearly perpendicular systems of early ruptures (Fig. 1, which are based on two classical patterns of conjugated fractures, one of which is consistent with the position of the fault plane (Fig. 3. Taking into account that strike-slip, reverse and normal faults are similar in terms of mechanics (i.e. they are formed due to


    Directory of Open Access Journals (Sweden)

    K. Zh. Seminsky


    Full Text Available Long-term studies of shear zones have included collection of data on fractures showing no indication of displacement which are termed as 'blank' fractures. A method aimed at mapping fault structures and stress fields has been developed on the basis of results of paragenetic analysis of measurements of abundant fractures. The method is termed as 'specialized mapping', firstly, due to its specific structural goal so that to distinguish it from the conventional geological mapping of regions in nature, and, secondly, because of the specific procedure applied to refer to fractures as references to decipher fault-block patterns of natural regions. In Part 1, basic theoretical concepts and principles of specialized mapping are described. Part 2 is being prepared for publication in one of the next issues of the journal; it will cover stages of the proposed method and describe some of the cases of its application.In terms of general organizational principles, specialized mapping is similar to other methods based on structural paragenetic analysis and differs from such methods in types of paragenesises viewed as references to reveal crustal fault zones. Such paragenesises result from stage-by-stage faulting (Fig 2 and Fig. 7 during which stress fields of the 2nd order are regularly changeable within the shear zone. According to combined experimental and natural data, a complete paragenesis of fractures in the shear zone includes a major (1st order fault plane and fractures of other seven types, R, R’, n, n’, t, t’ and T (2nd order (Fig. 4 and Fig 8. At the fracture level, each of them corresponds to a paragenesis including three nearly perpendicular systems of early ruptures (Fig. 1, which are based on two classical patterns of conjugated fractures, one of which is consistent with the position of the fault plane (Fig. 3. Taking into account that strike-slip, reverse and normal faults are similar in terms of mechanics (i.e. they are formed due to


    Directory of Open Access Journals (Sweden)

    K. Zh. Seminsky


    Full Text Available The article is to complete the description of the special mapping method which theoretical basis and principles were published in [Seminsky, 2014]. With reference to data on the Ulirba site located in Priolkhonie (Western Pribaikalie, the content of special mapping is reviewed in detail. The method is based on paragenetical analysis of abundant jointing which specific feature is the lack of any visible displacement indicators. There are three stages in the special mapping method (Fig. 3 as follows:Stage I: Preparation and analysis of previously published data on the regional fault structure (Fig. 1, А–Г, establishment of a networks of stations to conduct structural geological monitoring and mass measurements of joints, re­cord of rock data (Fig. 2, А, general state of the fault network (Fig. 1, Д–З, fracture density (Fig. 2, Б and, if any, structures of the above-jointing level (Fig. 1, Е, З; Fig. 2, А.Stage II is aimed at processing of field data and includes activities in four groups (II.1–II.4 as follows: Group II.1: construction of circle diagrams, specification of characteristics of joint systems and their typical scatters (Fig. 4, А, identification of simple (generally tipple paragenesises, and determination of dynamic settings of their formation (translocal rank (Table 1, evaluation of densities and complexity of the joint networks, analysis of their spacial patterns within the site under mapping, and identification of the most intensively destructed zones in the rock massif (Fig. 2, Б–В. Group II.2: comparison of jointing diagrams with reference ones showing joint poles (Fig. 4, Б–В; Е–З; Л–Н, and, in case of their satisfactory correlation, making a conclusion of potential formation of a specific joint pattern in the local zone of strike-slip, normal faulting or reverse faulting (Fig. 4,  Г–Д, И–К, О–П; Fig. 5; Fig. 7, Б, and determination of relative age relationships between such zones on

  4. Morphotectonics of the Padul-Nigüelas Fault Zone, southern Spain

    Directory of Open Access Journals (Sweden)

    Jochen Hürtgen


    Full Text Available The Padul-Nigüelas Fault Zone (PNFZ is situated at the south-western mountain front of the Sierra Nevada (southern Spain in the Internal Zone of the Betic Cordilleras and belongs to a NW-SE trending system of normal faults dipping SW. The PNFZ constitutes a major tectonic and lithological boundary in the Betics, and separates the metamorphic units of the Alpujárride Complex from Upper Tertiary to Quaternary deposits. Due to recent seismicity and several morphological and geological indicators, such as preserved fault scarps, triangular facets, deeply incised valleys and faults in the colluvial wedges, the PNFZ is suspected to be a tectonically active feature of the south-eastern Granada Basin. We performed morphotectonic GIS analyses based on digital elevation models (DEM, cell size: 10 m to obtain tectonic activity classes for each outcropping segment of the PNFZ. We have determined the following geomorphic indices: mountain front sinuosity, stream-length gradient index, concavity index and valley floor width to height ratio. The results show a differentiation in the states of activity along the fault zone strike. The western and eastern segments of the PNFZ indicate a higher tectonic activity compared to the center of the fault zone. We discuss and critically examine the comparability and reproducibility of geomorphic analyses, concluding that careful interpretation is necessary, if no ground-truthing can be performed.

  5. Lithospheric Structure of the Western North Anatolian Fault Zone from 3-D Teleseismic Tomography (United States)

    Papaleo, E.


    The North Anatolian Fault Zone (NAFZ) is a 1500 km long active strike-slip fault that spans northern Turkey. During the past century a series of migrating earthquakes have sequentially activated different segments of the fault. The last major events of this sequence are the 1999 Izmit and Düzce earthquakes, which are consistent with a gradual westward migration in seismicity. The next active segment of the fault may be close to the city of Istanbul, posing a major risk for its population. Historically, the NAFZ exhibits a recurrent migrating sequence of high magnitude earthquakes along the fault zone, suggesting that it accommodates most of the plate motion between Anatolian and Eurasian plates in a narrow shear zone. From GPS studies following the Izmit and Düzce events, this motion does not appear to be constrained to the upper crust, and may extend at least to the lower crust. However, the geometry of the fault in the lower crust and upper mantle is at present poorly understood and previous tomographic studies do not provide a consistent picture of the velocity structure in this region. To better constrain the geometry of the shear zone at depth, in particular beneath the most recently active segment of the fault, an array of 70 temporary seismic stations with a 7 km spacing was deployed for 18 months as part of the FaultLab project. Amongst all the events recorded, those of magnitude ≥ 5 and situated between 27 and 98 degrees from the centre of the array were selected to perform 3D teleseismic tomography. Synthetic resolution tests indicate that structures as small as the average station spacing can be recovered to a depth of approximately 80 km. The work aims to provide a higher resolution image of the velocity structure beneath the western segment of the NAFZ, leading to a better understanding of the shear zone in the lower crust and upper mantle.

  6. Distribution of Subsurface Flexure zone caused by Uemachi Fault, Japan and its activity (United States)

    Kitada, N.; Inoue, N.; Takemura, K.; Ito, H.; Mitamura, M.


    In Osaka, Uemachi Fault is one of the famous active faults. It across the center of Osaka and lies in N-S direction mainly and is more than 40 km in length. The faults bound sedimentary basins, where thick sedimentary deposits of the Pliocene-Quaternary Osaka Group have accumulated. The deposits consist primarily of sand and marine and non-marine clay, and the clay layers are key markers for the interpretation of glacial and interglacial cycles. In this study, we estimate the width of the flexure zone using a geotechnical borehole database. GI database collects more than 40,000 boreholes and includes both geological information and soil properties around Osaka by the Geo-database Information Committee of Kansai Area. Our results indicate that the deformation associated with the flexure zone is distributed primarily along the splay fault (NE-SW) and not along the main fault, suggesting that the splay fault might be the primary fault at present. We first examined the borehole data along the seismic reflection line and then considered the surrounding area. An Upper Pleistocene marine clay (Ma12) is a good indicator of the flexure zone. We constructed many cross sections in and around the fault zone and classified the deformation form into three categories around the flexure zone. The results of this study allowed us to map the distribution of folding in a zone in the west of the Osaka area. Folding can be classified into three types: (1) Ma12 folding, (2) Ma12 folding that does not continue toward the hanging wall, and (3) folding or displacement of old marine clay. These folding zone trends are N-W strike however these trace are serpentine. These folding zone information are not in worth to estimate the source fault, however these zone will be more serious damaged when the earthquake occurred. Our result agrees well with the average displacement speed of about 0.4 m/ka that was derived by the Headquarters for Earthquake Research Promotion of the Ministry of Education

  7. Fault zone hydrogeologic properties and processes revealed by borehole temperature monitoring (United States)

    Fulton, P. M.; Brodsky, E. E.


    High-resolution borehole temperature monitoring can provide valuable insight into the hydrogeologic structure of fault zones and transient processes that affect fault zone stability. Here we report on results from a subseafloor temperature observatory within the Japan Trench plate boundary fault. In our efforts to interpret this unusual dataset, we have developed several new methods for probing hydrogeologic properties and processes. We illustrate how spatial variations in the thermal recovery of the borehole after drilling and other spectral characteristics provide a measure of the subsurface permeability architecture. More permeable zones allow for greater infiltration of cool drilling fluids, are more greatly thermally disturbed, and take longer to recover. The results from the JFAST (Japan Trench Fast Drilling Project) observatory are consistent with geophysical logs, core data, and other hydrologic observations and suggest a permeable damage zone consisting of steeply dipping faults and fractures overlays a low-permeability clay-rich plate boundary fault. Using high-resolution time series data, we have also developed methods to map out when and where fluid advection occurs in the subsurface over time. In the JFAST data, these techniques reveal dozens of transient earthquake-driven fluid pulses that are spatially correlated and consistently located around inferred permeable areas of the fault damage zone. These observations are suspected to reflect transient fluid flow driven by pore pressure changes in response to dynamic and/or static stresses associated with nearby earthquakes. This newly recognized hydrologic phenomenon has implications for understanding subduction zone heat and chemical transport as well as the redistribution of pore fluid pressure which influences fault stability and can trigger other earthquakes.

  8. Pumping-Test Evaluation of Fault-Zone Hydraulic Properties in a Fractured Sandstone (United States)

    Johnson, N. M.


    Subzones of both reduced and enhanced permeability are often ascribed to fault zones, consistent with a fault-core/damage-zone conceptualization, with associated implications for assessing potential contaminant transport. Within this context, a 31-day pumping test was conducted in relation to a relatively minor, 2000 m long fault zone cutting fractured Cretaceous sandstone interbedded with siltstone and shale at a groundwater remediation site in the Simi Hills of southern California during March-April 2013. Our objective was to evaluate the potential hydrogeologic influence of the fault zone on groundwater movement across and along it by observing the spatial patterns of drawdown and estimated hydraulic properties. A 122 m deep open borehole was pumped at a constant rate of approximately 112 L/min while monitoring hydraulic heads in 14 observation wells, two completed with multi-level systems, within 750 m of the pumping well. Hydraulic heads were monitored for more than 9 months before, during, and after the test. Prior to the test, we used the site's three-dimensional, equivalent-porous-media groundwater flow model to anticipate the potential response of alternative fault-zone permeability structures. The results suggest that the fault zone may be slightly more permeable (by a factor of about 2 or less) and less confined than the fractured sandstone away from the fault, and is not a significant barrier to groundwater flow across it. Within the areal extent of observed drawdown, the site's hydrostratigraphic structures exhibited a relatively greater hydraulic influence. The pattern and magnitude of observed drawdown lie within the range of pre-test model simulations, and the test results are now being used to revise and recalibrate the model.

  9. Semi-automatic mapping of fault rocks on a Digital Outcrop Model, Gole Larghe Fault Zone (Southern Alps, Italy) (United States)

    Mittempergher, Silvia; Vho, Alice; Bistacchi, Andrea


    A quantitative analysis of fault-rock distribution in outcrops of exhumed fault zones is of fundamental importance for studies of fault zone architecture, fault and earthquake mechanics, and fluid circulation. We present a semi-automatic workflow for fault-rock mapping on a Digital Outcrop Model (DOM), developed on the Gole Larghe Fault Zone (GLFZ), a well exposed strike-slip fault in the Adamello batholith (Italian Southern Alps). The GLFZ has been exhumed from ca. 8-10 km depth, and consists of hundreds of individual seismogenic slip surfaces lined by green cataclasites (crushed wall rocks cemented by the hydrothermal epidote and K-feldspar) and black pseudotachylytes (solidified frictional melts, considered as a marker for seismic slip). A digital model of selected outcrop exposures was reconstructed with photogrammetric techniques, using a large number of high resolution digital photographs processed with VisualSFM software. The resulting DOM has a resolution up to 0.2 mm/pixel. Most of the outcrop was imaged using images each one covering a 1 x 1 m2 area, while selected structural features, such as sidewall ripouts or stepovers, were covered with higher-resolution images covering 30 x 40 cm2 areas.Image processing algorithms were preliminarily tested using the ImageJ-Fiji package, then a workflow in Matlab was developed to process a large collection of images sequentially. Particularly in detailed 30 x 40 cm images, cataclasites and hydrothermal veins were successfully identified using spectral analysis in RGB and HSV color spaces. This allows mapping the network of cataclasites and veins which provided the pathway for hydrothermal fluid circulation, and also the volume of mineralization, since we are able to measure the thickness of cataclasites and veins on the outcrop surface. The spectral signature of pseudotachylyte veins is indistinguishable from that of biotite grains in the wall rock (tonalite), so we tested morphological analysis tools to discriminate

  10. Geology of the Elephanta Island fault zone, western Indian rifted ...

    Indian Academy of Sciences (India)

    ... Madagascar (Storey et al. 1995;. Pande et al. 2001) and at ∼63 Ma between India and Seychelles (Collier et al. 2008; Bhattacharya and Yatheesh 2015). The Panvel flexure in the. ∼65 Ma Deccan flood basalts runs along the. Keywords. Flood volcanism; Deccan traps; Panvel flexure; Mumbai; Elephanta Island; faulting.

  11. Joint development in perturbed stress fields near faults (United States)

    Rawnsley, K. D.; Rives, T.; Petti, J.-P.; Hencher, S. R.; Lumsden, A. C.


    Field evidence is presented for complex spatial and temporal perturbations of an otherwise systematic joint pattern around faults from well exposed faulted rock platforms. Joints propagating in perturbed stress fields will curve to follow the directions of the stress field trajectories. A progressive change in joint direction is observed from unperturbed regions away from faults, to strongly perturbed zones adjacent to faults. This indicates that the joint pattern can reflect perturbations of the regional stress field around faults. In the examples, the stress field perturbations are probably due to points of high friction on the fault plane which concentrate stress and distort the stress field in the surrounding rock. The corresponding joints converge at these points and are sub-parallel to the fault along the remainder of the fault plane. The possibility that a fault plane acts as a free surface contained within an elastic body is considered. In this situation the fault plane induces a rotation of the principal stress axes to become either perpendicular or parallel to the fault. The free surface model seems to explain the metre-scale curvature of joints in the vicinity of existing joints, but at the kilometre scale of a large fault plane the model becomes unrealistic unless the fault is open at the Earth's surface. Two examples are investigated from the Lias of Great Britain; at Nash Point and Robin Hood's Bay. Both comprise sub-horizontal strata of relatively homogeneous lithology and bed thickness, which provide striking examples of joints developed near faults.

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

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


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

  13. The southern Sierra Nevada Frontal Fault Zone: what longitudinal stream profiles tell us about fault evolution and the presence of relay zone structures (United States)

    Koehler, K.; Krugh, W. C.


    The mechanical linkage of normal faults can result in spatial variations in fault displacement. In this study we use ArcGIS®, Matlab®, and software from to perform stream profile analysis along the southern Sierra Nevada Frontal Fault Zone (SNFFZ). This work aims to constrain the pattern of rock uplift and identify potential relay zone structures associated with fault evolution. Stream profile analysis is suitable for this investigation since the fluvial network upholds a continuous connection to the driving forces of tectonics. For this study we expect to find higher channel steepness indices and rates of rock uplift where the processes of mechanical fault linkage have occurred most recently. Using a 10m digital elevation model from the USGS, watershed boundaries and longitudinal stream profiles were extracted for divide reaching, and select non-divide reaching, drainages along the footwall of the southern SNFFZ. The relationship between channel slope and contributing drainage area for each watershed was then used to determine an average channel concavity, and to specify a regional reference concavity of θref = 0.695. This information was used to calculate the normalized steepness index for each watershed. Preliminary findings, using an initial θref = 0.45, indicated that the max channel steepness occurs at Cottonwood Creek, which drains much of the relay zone, with ksn values decreasing in both directions along strike. With further analyses using θref = 0.695, it is evident that anomalous values of ksn are present around the Cottonwood Creek drainage, and near Sawmill Creek to the north. Knickpoint examination shows that a prominent trend exists within the southern catchments, while north of Cottonwood Creek knickpoint elevations are highly erratic. Interpretation of this suggests that the southern knickpoints hold greater value for tectonic analyses. The findings of this study provide evidence that relay zone structures are potentially

  14. A Low Velocity Zone along the Chaochou Fault in Southern Taiwan: Seismic Image Revealed by a Linear Seismic Array

    Directory of Open Access Journals (Sweden)

    Hsin-Chieh Pu


    Full Text Available The Chaochou fault is one of the major boundary faults in southern Taiwan where strong convergence has taken place between the Eurasian and Philippine Sea plates. The surface fault trace between the Pingtung plain and the Central Range follows a nearly N-S direction and stretches to 80 km in length. In order to examine the subsurface structures along the Chaochou fault, a linear seismic array with 14 short-period stations was deployed across the fault to record seismic data between August and December 2001. Detailed examination of seismic data generated by 10 local earthquakes and recorded by the linear array has shown that the incidence angles of the first P-waves recorded by several seismic stations at the fault zone were significantly larger than those located farther away from the fault zone. This difference might reflect the lateral variation of velocity structures across the Chaochou fault. Further examination of ray-paths of seismic wave propagation indicates that a low-velocity zone along the Chaochou fault is needed to explain the significant change in incidence angles across the fault zone. Although we do not have adequate information to calculate the exact geometry of the fault zone well, the variation in incidence angles across the fault can be explained by the existence of a low-velocity zone that is about 3 km in width on the surface and extends downward to a depth of 5 km. The low-velocity zone along the Chaochou fault might imply that the fault system consists of several splay faults on the hanging wall in the Central Range.

  15. Structural and hydraulic properties of a small fault zone in a layered reservoir

    Directory of Open Access Journals (Sweden)

    Jeanne P.


    Full Text Available This paper focuses on a small fault zone (too small to be detected by geophysical imaging affecting a carbonate reservoir composed of porous and low-porous layers. In a gallery located at 250-m depth in the Underground Low Noise Laboratory, hydraulic properties of a 20-m thick section of the reservoir affected by the studied fault are characterized by structural measurements and by a hydraulic injection in boreholes. Main result is that the damage zone displays contrasted permeability values (up to two orders of magnitude inherited from the differential alteration of the intact rock layers. To characterize the impact of these hydraulic properties variations on the flow of fluids, numerical simulations of supercritical CO2 injections were performed with the TOUGH2 code. It appears, the permeability variations inside the fault zone favor the appearance of high fluid overpressure located in the layers having the highest permeability and storativity.

  16. Radon concentration distributions in shallow and deep groundwater around the Tachikawa fault zone. (United States)

    Tsunomori, Fumiaki; Shimodate, Tomoya; Ide, Tomoki; Tanaka, Hidemi


    Groundwater radon concentrations around the Tachikawa fault zone were surveyed. The radon concentrations in shallow groundwater samples around the Tachikawa fault segment are comparable to previous studies. The characteristics of the radon concentrations on both sides of the segment are considered to have changed in response to the decrease in groundwater recharge caused by urbanization on the eastern side of the segment. The radon concentrations in deep groundwater samples collected around the Naguri and the Tachikawa fault segments are the same as those of shallow groundwater samples. However, the radon concentrations in deep groundwater samples collected from the bedrock beside the Naguri and Tachikawa fault segments are markedly higher than the radon concentrations expected from the geology on the Kanto plane. This disparity can be explained by the development of fracture zones spreading on both sides of the two segments. The radon concentration distribution for deep groundwater samples from the Naguri and the Tachikawa fault segments suggests that a fault exists even at the southern part of the Tachikawa fault line. Copyright © 2017 Elsevier Ltd. All rights reserved.

  17. Structural Analysis of the Exhumed SEMP Fault Zone, Austria: Towards an Understanding of the Mechanics of Shear Zone Localization (United States)

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


    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 Oligo-Miocene Salzach-Ennstal-Mariazell-Puchberg [SEMP] fault zone in Austria, a major left-lateral strike-slip fault that has been exhumed differentially such that it exposes a continuum of structural levels along strike. In order to establish the structure of this fault zone, we are studying outcrops at a variety of exhumation levels, from <1 km near the eastern end of the fault, downward through the seismogenic crust, across the brittle- ductile transition, and into the uppermost part of the lower crust in western Austria. Here we present new results and discuss the mechanical implications of these new data from two key outcrops at Gstatterboden and Taxenbach, where the SEMP has experienced 40-60 km of displacement. The outcrop at Gstatterboden has been exhumed from 2-3 km depth. Here the SEMP juxtaposes limestone of the Wettersteinkalk on the south with dolomite of the Ramsaudolomit on the north. Faulting has produced extremely asymmetric damage, extensively shattering and shearing the dolomite while leaving the limestone largely intact. We interpret this brittle damage using both mesoscopic calculations of damage intensity and microscopic grain size distribution analysis, which suggests that shear has localized to a zone approximately 10 m wide. These findings are compared to the brittle-ductile outcrop at Taxenbach, which has been exhumed from depths of up to 10 km. Here, the SEMP juxtaposes Greywacke Zone rocks with carbonate mylonites of the Klammkalk. Microstructural observations of grain size and lattice preferred orientation suggest a marked increase in strain within

  18. Final Project Report: Imaging Fault Zones Using a Novel Elastic Reverse-Time Migration Imaging Technique

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Lianjie [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Chen, Ting [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Tan, Sirui [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Lin, Youzuo [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Gao, Kai [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)


    Imaging fault zones and fractures is crucial for geothermal operators, providing important information for reservoir evaluation and management strategies. However, there are no existing techniques available for directly and clearly imaging fault zones, particularly for steeply dipping faults and fracture zones. In this project, we developed novel acoustic- and elastic-waveform inversion methods for high-resolution velocity model building. In addition, we developed acoustic and elastic reverse-time migration methods for high-resolution subsurface imaging of complex subsurface structures and steeply-dipping fault/fracture zones. We first evaluated and verified the improved capabilities of our newly developed seismic inversion and migration imaging methods using synthetic seismic data. Our numerical tests verified that our new methods directly image subsurface fracture/fault zones using surface seismic reflection data. We then applied our novel seismic inversion and migration imaging methods to a field 3D surface seismic dataset acquired at the Soda Lake geothermal field using Vibroseis sources. Our migration images of the Soda Lake geothermal field obtained using our seismic inversion and migration imaging algorithms revealed several possible fault/fracture zones. AltaRock Energy, Inc. is working with Cyrq Energy, Inc. to refine the geologic interpretation at the Soda Lake geothermal field. Trenton Cladouhos, Senior Vice President R&D of AltaRock, was very interested in our imaging results of 3D surface seismic data from the Soda Lake geothermal field. He planed to perform detailed interpretation of our images in collaboration with James Faulds and Holly McLachlan of University of Nevada at Reno. Using our high-resolution seismic inversion and migration imaging results can help determine the optimal locations to drill wells for geothermal energy production and reduce the risk of geothermal exploration.

  19. Dependence of residual displacements on the width and depth of compliant fault zones: a 3D study (United States)

    Kang, J.; Duan, B.


    Compliant fault zones have been detected along active faults by seismic investigations (trapped waves and travel time analysis) and InSAR observations. However, the width and depth extent of compliant fault zones are still under debate in the community. Numerical models of dynamic rupture build a bridge between theories and the geological and geophysical observations. Theoretical 2D plane-strain studies of elastic and inelastic response of compliant fault zones to nearby earthquake have been conducted by Duan [2010] and Duan et al [2010]. In this study, we further extend the experiments to 3D with a focus on elastic response. We are specifically interested in how residual displacements depend on the structure and properties of complaint fault zones, in particular on the width and depth extent. We conduct numerical experiments on various types of fault-zone models, including fault zones with a constant width along depth, with decreasing widths along depth, and with Hanning taper profiles of velocity reduction. . Our preliminary results suggest 1) the width of anomalous horizontal residual displacement is only indicative of the width of a fault zone near the surface, and 2) the vertical residual displacement contains information of the depth extent of compliant fault zones.

  20. Hydrogeological properties of fault zones in a karstified carbonate aquifer and their impact on groundwater circulation (Northern Calcareous Alps, Austria) (United States)

    Bauer, Helene; Schröckenfuchs, Theresa Christina; Decker, Kurt


    This study presents a comparative, field-based hydrogeological characterization of exhumed, inactive fault zones in low porosity Triassic dolostones and limestones of the Hochschwab massif, a carbonate unit of high economic importance supplying 60% of the drinking water of Austria`s capital Vienna. The hydrogeology (groundwater storage and flow) of the massif has been reported to be essentially governed by karstified, large-scale faults. Previous work has shown that faults that formed during the Oligocene to Miocene lateral extrusion of the Eastern Alps act as groundwater pathways draining the karst massif preferably in E-W-direction. We present hydrogeological relevant data from these types of fault zones and a conceptual model, which supports the idea that fault-zone networks also have the potential to contribute significantly to the storage capacity of the aquifer. With respect to fault zone architecture and rock content, four types of faults are presented: (1) faults with single stranded, minor fault cores, (2) faults with single stranded, permeable fault cores, (3) faults with single stranded, impermeable fault cores, and (4) faults with multiple stranded, permeable fault cores. Within these faults cataclastic rocks and strongly cemented cataclastic breccias form low-permeability ( 3%) with respect to the country rock ( 3% and permeabilities > 1000 mD form high-permeability domains. Our data illustrates significant differences in the architectural build-up of fault zones in dolostone (multiple-stranded cataclastic fault cores of weak lateral continuity, high volumes of intensely fractured rock) and limestone (laterally distinct, single-stranded fault cores, Riedel-shear fractures dominating fracture patterns). Karstic carbonate dissolution occurs preferentially along faults cores in limestones and, to a lesser degree, dolostones creating superposed high-permeability conduits. All faults contain domains of brecciated and highly fractured rocks along their

  1. Audio-Magnetotelluric Modeling of Cimandiri Fault Zone at Cibeber, Cianjur


    Lina Handayani; Maryati Maryati; Kamtono Kamtono; M. Ma’ruf Mukti; Yayat Sudrajat


    DOI: 10.17014/ijog.4.1.39-47The characteristic of Cimandiri Fault Zone has not been completely defined despite plenty of studies had already been accomplished. Therefore, an audio-magnetotelluric modeling was carried out. An audiomagnetotelluric survey was conducted at two parallel lines (N166oE) that intersected Cimandiri Fault Zone in Cibeber area, Cianjur. The distance between those two lines was 4.5 km and each line consisted of twenty-one stations with the distance between stations was 5...

  2. Structural character of the Ghost Dance Fault, Yucca Mountain, Nevada

    Energy Technology Data Exchange (ETDEWEB)

    Spengler, R.W. [Geological Survey, Denver, CO (United States); Braun, C.A.; Linden, R.M.; Martin, L.G.; Ross-Brown, D.M.; Blackburn, R.L. [SAIC, Golden, CO (United States)


    Detailed structural mapping of an area that straddles the southern part of the Ghost Dance Fault has revealed the presence of several additional subparallel to anastomosing faults. These faults, mapped at a scale of 1:240, are: (1) dominantly north-trending, (2) present on both the upthrown and downthrown sides of the surface trace of the Ghost Dance fault, (3) near-vertical features that commonly offset strata down to the west by 3 to 6 m (10 to 20 ft), and (4) commonly spaced 15 to 46 m (50 to 150 ft) apart. The zone also exhibits a structural fabric, containing an abundance of northwest-trending fractures. The width of the zone appears to be at least 213 m (700 ft) near the southernmost boundary of the study area but remains unknown near the northern extent of the study area, where the width of the study area is only 183 m (600 ft).

  3. Audio-Magnetotelluric Modeling of Cimandiri Fault Zone at Cibeber, Cianjur

    Directory of Open Access Journals (Sweden)

    Lina Handayani


    Full Text Available DOI: 10.17014/ijog.4.1.39-47The characteristic of Cimandiri Fault Zone has not been completely defined despite plenty of studies had already been accomplished. Therefore, an audio-magnetotelluric modeling was carried out. An audiomagnetotelluric survey was conducted at two parallel lines (N166oE that intersected Cimandiri Fault Zone in Cibeber area, Cianjur. The distance between those two lines was 4.5 km and each line consisted of twenty-one stations with the distance between stations was 500 m. From the acquired forty-two apparent resistivity curves, inversion was executed to obtain two models. The models indicate layers with resistivity value of > 1000 ohm.m at about 500 m depth at both lines, which are associated to the basement layer. Columns of low resistivity zones in about the middle of each model represent fault zones as the weak zones of the area, and both models displayed them slightly dip southward as thrust faults.

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

    KAUST Repository

    Pelties, Christian


    © 2014, Springer Basel. Faults are often embedded in low-velocity fault zones (LVFZ) caused by material damage. Previous 2D dynamic rupture simulations (Huang and Ampuero, 2011; Huang 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 (Peltieset 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

  5. Kinematics of the East Anatolian Fault Zone between Turkoglu (Kahramanmaras) and Celikhan (Adiyaman), eastern Turkey (United States)

    Yilmaz, H.; Over, S.; Ozden, S.


    In this study we determined the stress regime acting along the East Anatolian Fault Zone between Turkoglu (Kahramanmaras) and Celikhan (Adiyaman), from the Neocene to present-day, based on the inversion of striations measured on faults and on the focal mechanisms of earthquakes having magnitudes greater than 5.0. The inversions yield a strike-slip stress regime with a reverse component (i.e., transpression) operative in the Neocene to present with a consistent N-to NW-trending σ1 axis 156 ± 11° and an E- to NE-trending σ3 axis, 67 ± 9°σ3, producing left-lateral motion along the East Anatolian Fault Zone. The inversions of focal mechanisms yield a strike-slip stress deviator characterized by an approximately N-S (N1°W)-trending σ1 and an approximately E-W (N89°E)-trending σ3 axis. Both the kinematic analysis and structural observations indicate that the stress regime operating in the study area has had a transpressional character, giving rise to the Mio-Pliocene compressive structures (reverse faults, thrusts and folds) observed in the study area. Field observations allow estimation of a Pliocene age for the strike-slip East Anatolian Fault Zone.

  6. Crustal Structure across The Southwest Longmenshan Fault Zone from Seismic Wide Angle Reflection/Refraction Profile (United States)

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


    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

  7. Development of Hydrologic Characterization Technology of Fault Zones -- Phase I, 2nd Report

    Energy Technology Data Exchange (ETDEWEB)

    Karasaki, Kenzi; Onishi, Tiemi; Black, Bill; Biraud, Sebastien


    This is the year-end report of the 2nd year of the NUMO-LBNL collaborative project: Development of Hydrologic Characterization Technology of Fault Zones under NUMO-DOE/LBNL collaboration agreement, the task description of which can be found in the Appendix 3. Literature survey of published information on the relationship between geologic and hydrologic characteristics of faults was conducted. The survey concluded that it may be possible to classify faults by indicators based on various geometric and geologic attributes that may indirectly relate to the hydrologic property of faults. Analysis of existing information on the Wildcat Fault and its surrounding geology was performed. The Wildcat Fault is thought to be a strike-slip fault with a thrust component that runs along the eastern boundary of the Lawrence Berkeley National Laboratory. It is believed to be part of the Hayward Fault system but is considered inactive. Three trenches were excavated at carefully selected locations mainly based on the information from the past investigative work inside the LBNL property. At least one fault was encountered in all three trenches. Detailed trench mapping was conducted by CRIEPI (Central Research Institute for Electric Power Industries) and LBNL scientists. Some intriguing and puzzling discoveries were made that may contradict with the published work in the past. Predictions are made regarding the hydrologic property of the Wildcat Fault based on the analysis of fault structure. Preliminary conceptual models of the Wildcat Fault were proposed. The Wildcat Fault appears to have multiple splays and some low angled faults may be part of the flower structure. In parallel, surface geophysical investigations were conducted using electrical resistivity survey and seismic reflection profiling along three lines on the north and south of the LBNL site. Because of the steep terrain, it was difficult to find optimum locations for survey lines as it is desirable for them to be as

  8. Pore fluid chemistry of the North Anatolian Fault Zone in the Sea of Marmara: A diversity of sources and processes


    Tryon, M. D.; Henry, P.; Cagatay, M. N.; Zitter, T. A. C.; Geli, Louis; Gasperini, L.; Burnard, P.; Bourlange, S.; Grall, Celine


    As part of the 2007 Marnaut cruise in the Sea of Marmara, an investigation of the pore fluid chemistry of sites along the Main Marmara Fault zone was conducted. The goal was to define the spatial relationship between active faults and fluid outlets and to determine the sources and evolution of the fluids. Sites included basin bounding transtensional faults and strike-slip faults cutting through the topographic highs. The basin pore fluids are dominated by simple mixing of bottom water with a ...

  9. Modeling of fault activation and seismicity by injection directly into a fault zone associated with hydraulic fracturing of shale-gas reservoirs (United States)

    LBNL, in consultation with the EPA, expanded upon a previous study by injecting directly into a 3D representation of a hypothetical fault zone located in the geologic units between the shale-gas reservoir and the drinking water aquifer.

  10. Structural characteristics of the Yilan-Yitong and Dunhua-Mishan faults as northern extensions of the Tancheng-Lujiang Fault Zone: New deep seismic reflection results (United States)

    Xu, Ming; Li, Yalin; Hou, Hesheng; Wang, Chengshan; Gao, Rui; Wang, Haiyan; Han, Zhongpeng; Zhou, Aorigele


    The Tancheng-Lujiang Fault Zone (TLFZ) can be subdivided into three segments that exhibit sharp contrasts in their deep structures. A deep seismic reflection profile (length 600 km) across the north part of the TLFZ, which provides new constraints on the structural styles of the northern TLFZ, was recently completed by the Chinese Sinoprobe Project. Here, the TLFZ branches into the Yilan-Yitong Fault (YYF) to the west and the Dunhua-Mishan Fault (DMF) to the east. The YYF developed as an internal fault in the Songnen-Zhangguangcai massif, while the DMF serves as the tectonic boundary between the Nadanhada terrane and the Khanka massif. Both faults developed large-scale flower structures, with that of the YYF being negative and that of the DMF being positive with reverse faults. The Moho in the profile is at a depth of 25-39 km and is offset by the faults. The north part of the TLFZ extends into the upper mantle as thin shear zones with the reflectors truncated in the middle/lower crust. This feature differs from most crustal-scale strike-slip faults that distribute over a discrete shear zone in the lower crust, such as the San Andreas Fault.

  11. Gouge-zone or solid-rock: An experimental view on fault frictional behavior (United States)

    Reches, Z.


    Natural faults always include zone(s) of breccia, gouge or cataclasite that localize the slip. In contrast, many rock mechanics experiments are conducted on experimental faults made of rough, solid blocks without fault-rock zones. We experimentally compare the frictional strength of solid experimental faults with fault-zones made of granular material in high-velocity/long-distance runs. The frictional evolution of solid and granular dolomite fault was tested in a rotary apparatus at slip velocity up to 1 m/s and normal stress up to 7 MPa. The granular samples were composed of the 125-250 microns fraction of the crushed dolomite. They were sheared in a confined, rotary cell with continuous monitoring of CO2 and H2O and mechanical data. The tests showed that the granular samples required longer slip-distances and higher velocities to evolve to a frictional strength similar to the solid samples. Yet, both sample types display similar evolution trends, including slip-weakening at velocities above ~0.05 m/s, and drastic velocity-weakening as slip velocity approached 1 m/s. At velocity above 0.3 m/s, a shining principal-slip-zone developed spontaneously with identical microstructure in both solid and granular sample: thickness friction evolution of granular granite from the San-Andreas fault-zone at Tejon-Pass, CA. These samples remained strong, μ =0.8-0.9, at velocities up to 0.8 m/s and slip-distances up to 3 m, in contrast to known frictional evolution of solid faults made of granite and tonalite. We envision that at the present slip-velocity/normal-stress, the dolomite samples reached a stage of thermally activated phase-transition and associated weakening, whereas the granitic samples were below such transition. Fig. 1. Evolotion of slip-velocity, friction, temperature and CO2 emission in run 3165 with granular Kasota dolomite. Normal stress is 3.3 MPa. The time delay of CO2 data reflect gas flow from shear chamber to gas analyzer.

  12. Geophysical and geochemical tracing of fault-zone slip and seal mechanisms through diagenetic evolution (United States)

    Matonti, Christophe; Guglielmi, Yves; Viseur, Sophie; Leonide, Phlippe; Floquet, Marc; Garambois, Stéphane


    Fault and fractures properties are responsible of a large part of the fluid transfer properties at all scales, especially in tight rocks. Fault reactivations increase the complexity of the fault zone structure and cause slip reactivation on previously formed fractures. Multiple fracture reactivations can deeply modify the initial fracture properties all along the rocks diagenetic history, leading to alternate periods of fractures sealing and seismic instability. For instance, each slip step may be associated with cementation/dissolution that can be traced through combined geophysical and geochemical analyses. To that end, we studied a polyphased fault-zone outcropping on a quarry presenting a very smooth surface due to diamond wire saw exploitation of rock blocks. The quarry is composed of carbonates displaying non-porous inner-platform rudist facies of Late Cenomanian. Inside the fault zone, the rock is affected by two en-échelon fracture clusters, the first one being simply formed in mode 1 and cemented, the second one being polyphased (multiple reactivations, cementation and karstification phases). We performed a detailed structural and diagenetical characterization (fractures, karsts and stylolites digitalization on Gocad software; thin section and plug porosity), along with geochemical analyses of carbon and oxygen isotopes ratios on fracture fillings/cements and geophysical measurements at two scales. First, 1298 ultrasonic P-wave velocity measurements using a piezoelectric source were performed on a rock block (2.4x1.5x1.1m parallelepiped sampled in the fault zone border), along a vertical cross section. Then, more than 200 seismic measurements using hammer source across the decameter scale outcrop. Source and receivers were precisely located using a LIDAR 3D model of the fault-zone outcrop. First key results from ultrasonic measurements show that the fracture diagenetical/temporal evolution induces an anisotropic Vp variation regarding the dip angle of the

  13. Quaternary layer anomalies around the Carlsberg Fault zone mapped with high-resolution shear-wave seismics south of Copenhagen (United States)

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


    The Carlsberg Fault zone is located in the N-S striking Höllviken Graben and traverses the city of Copenhagen. The fault zone is a NNW-SSE striking structure in direct vicinity to the transition zone of the Danish Basin and the Baltic Shield. Recent small earthquakes indicate activity in the area, although none of the mapped earthquakes appear to have occurred on the Carlsberg Fault. We examined the fault evolution by a combination of very high resolution onshore shear-wave seismic data, one conventional onshore seismic profile and marine reflection seismic profiles. The chalk stratigraphy and the localization of the fault zone at depth was inferred from previous studies by other authors. We extrapolated the Jurassic and Triassic stratigraphy from the Pomeranian Bay to the area of investigation. The fault zone shows a flower structure in the Triassic as well as in Cretaceous sediments. The faulting geometry indicates strong influence of Triassic processes when subsidence and rifting prevailed in the Central European Basin System. Growth strata within the 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. This finding contrasts the Late Cretaceous to Paleogene inversion tectonics in neighbouring structures, as the Tornquist Zone. The high-resolution shear-wave seismic method was used to image structures in Quaternary layers in the Carlsberg Fault zone. 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 30 m of the upward continuation of the Carlsberg Fault zone. In our area of investigation, the fault zone appears to comprise

  14. Geology of the Elephanta Island fault zone, western Indian rifted margin, and its significance for understanding the Panvel flexure (United States)

    Samant, Hrishikesh; Pundalik, Ashwin; D'souza, Joseph; Sheth, Hetu; Lobo, Keegan Carmo; D'souza, Kyle; Patel, Vanit


    The Panvel flexure is a 150-km long tectonic structure, comprising prominently seaward-dipping Deccan flood basalts, on the western Indian rifted margin. Given the active tectonic faulting beneath the Panvel flexure zone inferred from microseismicity, better structural understanding of the region is needed. The geology of Elephanta Island in the Mumbai harbour, famous for the ca. mid-6th century A.D. Hindu rock-cut caves in Deccan basalt (a UNESCO World Heritage site) is poorly known. We describe a previously unreported but well-exposed fault zone on Elephanta Island, consisting of two large faults dipping steeply east-southeast and producing easterly downthrows. Well-developed slickensides and structural measurements indicate oblique slip on both faults. The Elephanta Island fault zone may be the northern extension of the Alibag-Uran fault zone previously described. This and two other known regional faults (Nhava-Sheva and Belpada faults) indicate a progressively eastward step-faulted structure of the Panvel flexure, with the important result that the individual movements were not simply downdip but also oblique-slip and locally even rotational (as at Uran). An interesting problem is the normal faulting, block tectonics and rifting of this region of the crust for which seismological data indicate a normal thickness (up to 41.3 km). A model of asymmetric rifting by simple shear may explain this observation and the consistently landward dips of the rifted margin faults.

  15. Development of a Hydrologic Characterization Technology for Fault Zones Phase II 2nd Report

    Energy Technology Data Exchange (ETDEWEB)

    Karasaki, Kenzi [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Doughty, Christine [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Gasperikova, Erika [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Peterson, John [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Conrad, Mark [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Cook, Paul [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Tiemi, Onishi [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)


    This is the 2nd report on the three-year program of the 2nd phase of the NUMO-LBNL collaborative project: Development of Hydrologic Characterization Technology for Fault Zones under NUMO-DOE/LBNL collaboration agreement. As such, this report is a compendium of the results by Kiho et al. (2011) and those by LBNL.

  16. Fabric transition with dislocation creep of a carbonate fault zone in the brittle regime (United States)

    Kim, Sungshil; Ree, Jin-Han; Han, Raehee; Kim, Nahyeon; Jung, Haemyeong


    Fabric transition by a switch in the dominant slip system of minerals in the plastic regime can be induced by changes in temperature, strain rate, or water content. We propose here this fabric transition by frictional heating in seismogenic fault zones in the brittle regime. The Garam Thrust in the Taebaeksan Basin of South Korea has a hanging wall of Cambrian dolostone juxtaposed against a footwall of Ordovician limestone and records a minimum displacement of 120 m. In a 10 cm thick plastically deformed layer adjacent to the principal slip layer of the fault zone, the lattice preferred orientation of calcite grains suggests that the dominant slip system changes, approaching the principal slip layer, from r 〈02-21〉 and e-twinning, through r 〈02-21〉 and basal 〈a〉, to basal 〈a〉. This fabric transition requires a high temperature-gradient of 40 °C/cm, which we infer to result from frictional heating of the seismic fault zone. We suggest that fabric transition within a thin plastically deformed layer adjacent to the principal slip layer of a fault zone indicates an unusually steep temperature gradient and provides strong evidence of seismic slip.

  17. Tectonic phase separation applied to the Sudetic Marginal Fault Zone (NE part of the Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Nováková, Lucie


    Roč. 12, č. 2 (2015), s. 251-267 ISSN 1672-6316 R&D Projects: GA ČR GA205/09/1244 Institutional support: RVO:67985891 Keywords : Sudetic Marginal Fault Zone * paleostress reconstruction * active tectonics * frequency analysis Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 1.017, year: 2015

  18. Slip zone and energetics of a large earthquake from the Taiwan Chelungpu-fault Drilling Project. (United States)

    Ma, Kuo-Fong; Tanaka, Hidemi; Song, Sheng-Rong; Wang, Chien-Ying; Hung, Jih-Hao; Tsai, Yi-Ben; Mori, Jim; Song, Yen-Fang; Yeh, Eh-Chao; Soh, Wonn; Sone, Hiroki; Kuo, Li-Wei; Wu, Hung-Yu


    Determining the seismic fracture energy during an earthquake and understanding the associated creation and development of a fault zone requires a combination of both seismological and geological field data. The actual thickness of the zone that slips during the rupture of a large earthquake is not known and is a key seismological parameter in understanding energy dissipation, rupture processes and seismic efficiency. The 1999 magnitude-7.7 earthquake in Chi-Chi, Taiwan, produced large slip (8 to 10 metres) at or near the surface, which is accessible to borehole drilling and provides a rare opportunity to sample a fault that had large slip in a recent earthquake. Here we present the retrieved cores from the Taiwan Chelungpu-fault Drilling Project and identify the main slip zone associated with the Chi-Chi earthquake. The surface fracture energy estimated from grain sizes in the gouge zone of the fault sample was directly compared to the seismic fracture energy determined from near-field seismic data. From the comparison, the contribution of gouge surface energy to the earthquake breakdown work is quantified to be 6 per cent.

  19. Investigations into early rift development and geothermal resources in the Pyramid Lake fault zone, Western Nevada

    Energy Technology Data Exchange (ETDEWEB)

    Eisses, A.; Kell, A.; Kent, G.; Driscoll, N. [UCSD; Karlin, R.; Baskin, R. [USGS; Louie, J. [UNR; Pullammanappallil, S. [Optim


    A. K. Eisses, A. M. Kell, G. Kent, N. W. Driscoll, R. E. Karlin, R. L. Baskin, J. N. Louie, S. Pullammanappallil, 2010, Investigations into early rift development and geothermal resources in the Pyramid Lake fault zone, Western Nevada: Abstract T33C-2278 presented at 2010 Fall Meeting, AGU, San Francisco, Calif., 13-17 Dec.

  20. The history of late holocene surface-faulting earthquakes on the central segments of the Wasatch fault zone, Utah (United States)

    Duross, Christopher; Personius, Stephen; Olig, Susan S; Crone, Anthony J.; Hylland, Michael D.; Lund, William R; Schwartz, David P.


    The Wasatch fault (WFZ)—Utah’s longest and most active normal fault—forms a prominent eastern boundary to the Basin and Range Province in northern Utah. To provide paleoseismic data for a Wasatch Front regional earthquake forecast, we synthesized paleoseismic data to define the timing and displacements of late Holocene surface-faulting earthquakes on the central five segments of the WFZ. Our analysis yields revised histories of large (M ~7) surface-faulting earthquakes on the segments, as well as estimates of earthquake recurrence and vertical slip rate. We constrain the timing of four to six earthquakes on each of the central segments, which together yields a history of at least 24 surface-faulting earthquakes since ~6 ka. Using earthquake data for each segment, inter-event recurrence intervals range from about 0.6 to 2.5 kyr, and have a mean of 1.2 kyr. Mean recurrence, based on closed seismic intervals, is ~1.1–1.3 kyr per segment, and when combined with mean vertical displacements per segment of 1.7–2.6 m, yield mean vertical slip rates of 1.3–2.0 mm/yr per segment. These data refine the late Holocene behavior of the central WFZ; however, a significant source of uncertainty is whether structural complexities that define the segments of the WFZ act as hard barriers to ruptures propagating along the fault. Thus, we evaluate fault rupture models including both single-segment and multi-segment ruptures, and define 3–17-km-wide spatial uncertainties in the segment boundaries. These alternative rupture models and segment-boundary zones honor the WFZ paleoseismic data, take into account the spatial and temporal limitations of paleoseismic data, and allow for complex ruptures such as partial-segment and spillover ruptures. Our data and analyses improve our understanding of the complexities in normal-faulting earthquake behavior and provide geological inputs for regional earthquake-probability and seismic hazard assessments.

  1. Geochemistry, mineralization, structure, and permeability of a normal-fault zone, Casino mine, Alligator Ridge district, north central Nevada (United States)

    Hammond, K. Jill; Evans, James P.


    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

  2. Hydrothermal fault zones in the lower oceanic crust: An example from the Samail ophiolite, Oman (United States)

    Zihlmann, Barbara; Müller, Samuel; Koepke, Juergen; Teagle, Damon


    Hydrothermal circulation is a key process for the exchange of chemical elements between the oceans and the solid Earth and particularly for the extraction of heat from newly accreted crust at mid-ocean ridges. However, due to a dearth of samples from intact oceanic crust, or continuous samples from ophiolites, there remain major short comings in our understanding of hydrothermal circulation in the oceanic crust, especially in the deeper part. In particular, it is unknown whether fluid recharge and discharge occurs pervasively or if it is mainly channeled onto discrete zones such as faults. Here, we present a description of a hydrothermal fault zone that crops out in the layered gabbro section, of Wadi Gideah in the Samail ophiolite in Oman, which might be a channel of enhanced fluid flow. Field observations reveal an approximately one meter-thick chlorite - epidote normal fault with heavily altered gabbro clasts in the center. In places there is copper mineralization within the chlorite - epidote zone. In both, the hanging and the footwall the gabbro is heavily altered and veined, mainly with amphibole, epidote, prehnite and zeolite veins. Even though the fault zone is within the layered gabbro section, and perhaps only 1 km above the crust-mantle boundary, the gabbro around the fault zone shows highly variable textures. Preliminary strontium isotope whole rock data yield 87Sr/86Sr ratios of ˜ 0.7046, which are considerably more radiogenic than "fresh" gabbro from the Oman ophiolite (87Sr/86Sr = 0.7026 - 0.7030), and similar to black smoker hydrothermal signatures based on epidote, measured elsewhere in the ophiolite.

  3. Infrastructure and mechanical properties of a fault zone in sandstone as an outcrop analogue of a potential geothermal reservoir (United States)

    Bauer, J. F.; Meier, S.; Philipp, S. L.


    Due to high drilling costs of geothermal projects, it is economically sensible to assess the potential suitability of a reservoir prior to drilling. Fault zones are of particular importance, because they may enhance fluid flow, or be flow barriers, respectively, depending on their particular infrastructure. Outcrop analogue studies are useful to analyze the fault zone infrastructure and thereby increase the predictability of fluid flow behavior across fault zones in the corresponding deep reservoir. The main aims of the present study are to 1) analyze the infrastructure and the differences of fracture system parameters in fault zones and 2) determine the mechanical properties of the faulted rocks. We measure fracture frequencies as well as orientations, lengths and apertures and take representative rock samples for each facies to obtain Young's modulus, compressive and tensile strengths in the laboratory. Since fractures reduce the stiffnesses of in situ rock masses we use an inverse correlation of the number of discontinuities to calculate effective (in situ) Young's moduli to investigate the variation of mechanical properties in fault zones. In addition we determine the rebound hardness, which correlates with the compressive strength measured in the laboratory, with a 'Schmidt-Hammer' in the field because this allows detailed maps of mechanical property variations within fault zones. Here we present the first results for a fault zone in the Triassic Lower Bunter of the Upper Rhine Graben in France. The outcrop at Cleebourg exposes the damage zone of the footwall and a clear developed fault core of a NNW-SSE-striking normal fault. The approximately 15 m wide fault core consists of fault gouge, slip zones, deformation bands and host rock lenses. Intensive deformation close to the core led to the formation of a distal fault core, a 5 m wide zone with disturbed layering and high fracture frequency. The damage zone also contains more fractures than the host rock

  4. The January 25th, 2014 Kebumen earthquake: A normal faulting in subduction zone of Southern Java (United States)

    Serhalawan, Yopi Ruben; Sianipar, Dimas; Suardi, Iman


    Normal faulting mechanism of earthquake in subduction zone is quite interested to study further. We investigated the Kebumen, January 25, 2014 earthquake sequences by retrieving focal mechanisms using full moment tensor inversion. We used BMKG seismic data from stations in the vicinity of Central Java region for these inversions. Then we correlated the static coulomb stress change by the mainshock to the aftershocks. We found that mainshock is a normal faulting earthquake with nodal plane 1; strike 283, dip 22 and rake -100; nodal plane 2 with strike 113, dip 68 and rake -86. Using distribution analysis of high precision aftershocks after relocated; we considered that the reliable fault plane was nodal plane 1 with strike trending SE-NW. The focal mechanisms provide an estimate of the local stress field in the Wadati-Beniof Zone of Southern Java subduction zone. There is also conclution stating that the mainshock may trigger the aftershocks mainly in three zones, i.e. in continental crustal, upper mantle and on the oceanic slab. This is visually showed that the high quality aftershocks located in positive zones of static coulomb stress change.

  5. Spatiotemporal earthquake clusters along the North Anatolian fault zone offshore Istanbul (United States)

    Bulut, Fatih; Ellsworth, William L.; Bohnhoff, Marco; Aktar, Mustafa; Dresen, Georg


    We investigate earthquakes with similar waveforms in order to characterize spatiotemporal microseismicity clusters within the North Anatolian fault zone (NAFZ) in northwest Turkey along the transition between the 1999 ??zmit rupture zone and the Marmara Sea seismic gap. Earthquakes within distinct activity clusters are relocated with cross-correlation derived relative travel times using the double difference method. The spatiotemporal distribution of micro earthquakes within individual clusters is resolved with relative location accuracy comparable to or better than the source size. High-precision relative hypocenters define the geometry of individual fault patches, permitting a better understanding of fault kinematics and their role in local-scale seismotectonics along the region of interest. Temporal seismic sequences observed in the eastern Sea of Marmara region suggest progressive failure of mostly nonoverlapping areas on adjacent fault patches and systematic migration of microearthquakes within clusters during the progressive failure of neighboring fault patches. The temporal distributions of magnitudes as well as the number of events follow swarmlike behavior rather than a mainshock/aftershock pattern.

  6. The Suckling Hills Fault, Kayak Island Zone, and accretion of the Yakutat microplate, Alaska (United States)

    Chapman, James B.; Worthington, Lindsay L.; Pavlis, Terry L.; Bruhn, Ronald L.; Gulick, Sean P.


    The Suckling Hills and Kayak Island are isolated mountain blocks located along strike from each other within the foreland of the St. Elias orogen in southern Alaska. These blocks preserve an erosional surface that was deformed by slip on northwest-dipping reverse faults in the Pleistocene. We suggest that the Suckling Hills Fault and Kayak Island Zone form a segmented fault network that links with the Bering Glacier structure to the north. This fault network separates the central Yakataga fold and thrust belt from complex, multiply deformed structures in the western syntaxis. Ongoing accretion of the Yakutat microplate to North America results in translation of structures of the fold and thrust belt into the western syntaxis. The composite Suckling Hills Fault, Kayak Island Zone, and Bering Glacier structure may have formed because the older structures of the fold and thrust belt were unfavorably oriented within the western syntaxis region. This pattern of deformation provides a template for understanding the complex deformation within the core of the western syntaxis and predicts refolding and straightening of the western syntaxis margin with continued accretion. This study provides an analog for structural overprinting and changing deformation patterns through time in orogenic corners.

  7. Tomography of the Chukou Fault Zone, Southwest Taiwan: Insights from Microearthquake Data

    Directory of Open Access Journals (Sweden)

    Yu-Lien Yeh


    Full Text Available The vigorous collision between the Eurasian plate and Philippine Sea plate in Taiwan causes a series of imbricate fold and thrust belts to develop at the deformation front. The Chukou Fault (CKF, characterized by a thrust type fault, located in Chiayi County, southwest (SW Taiwan, is a prominent boundary between the fold-thrust belts and the Western Coastal Plain. Most of the seismicity in SW Taiwan is associated with this fault and its neighboring fault systems. The seismotectonic structures in the CKF zone, especially in the east, are complex due to the interactions among fault systems with distinct slip motions. To gain better insights into the seismogenic characteristics in the CKF zone, we used 1661 microearthquakes recorded by a temporary dense broadband seismic network and the Central Weather Bureau Seismic Network (CWBSN between 2003 and 2004 to investigate the physical properties of the crust in the CKF zone. A waveform cross-correlation technique was applied to 143086 pairs of waveform data to determine the relative differential travel time between the P- and S-waves. By combining both the absolute and relative differential travel time data, we were able to obtain a new 3-D crustal P-wave velocity structure and Vp/Vs ratios. This study suggests that by using both absolute and relative differential travel time data in tomographic inversion can obtain precise 3-D velocity images and also gain better correlation between seismic events and fault structures, which is crucial for understanding the seismogenic process in our study area.

  8. Adaptive Fault-Tolerant Control of Uncertain Nonlinear Large-Scale Systems With Unknown Dead Zone. (United States)

    Chen, Mou; Tao, Gang


    In this paper, an adaptive neural fault-tolerant control scheme is proposed and analyzed for a class of uncertain nonlinear large-scale systems with unknown dead zone and external disturbances. To tackle the unknown nonlinear interaction functions in the large-scale system, the radial basis function neural network (RBFNN) is employed to approximate them. To further handle the unknown approximation errors and the effects of the unknown dead zone and external disturbances, integrated as the compounded disturbances, the corresponding disturbance observers are developed for their estimations. Based on the outputs of the RBFNN and the disturbance observer, the adaptive neural fault-tolerant control scheme is designed for uncertain nonlinear large-scale systems by using a decentralized backstepping technique. The closed-loop stability of the adaptive control system is rigorously proved via Lyapunov analysis and the satisfactory tracking performance is achieved under the integrated effects of unknown dead zone, actuator fault, and unknown external disturbances. Simulation results of a mass-spring-damper system are given to illustrate the effectiveness of the proposed adaptive neural fault-tolerant control scheme for uncertain nonlinear large-scale systems.

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

    DEFF Research Database (Denmark)

    Kammann, Janina; Hübscher, Christian; Nielsen, Lars

    The Carlsberg Fault zone is located in the N-S striking Höllviken Graben and traverses the city of Copenhagen. The fault zone is a NNW-SSE striking structure in direct vicinity to the transition zone of the Danish Basin and the Baltic Shield. Recent small earthquakes indicate activity in the area......, although none of the mapped earthquakes appear to have occurred on the Carlsberg Fault. We examined the fault evolution by a combination of very high resolution onshore shear-wave seismic data, one conventional onshore seismic profile and marine reflection seismic profiles. The chalk stratigraphy....... In the Upper Cretaceous growth faulting documents continued rifting. This finding contrasts the Late Cretaceous to Paleogene inversion tectonics in neighboring structures, as the Tornquist Zone. The high-resolution shear-wave seismic method was used to image structures in Quaternary layers in the Carlsberg...

  10. Enriquillo–Plantain Garden fault zone in Jamaica: paleoseismology and seismic hazard (United States)

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


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

  11. Application of electric and electromagnetic prospection methods for the investigation of geological fault zones (United States)

    Schaumann, G.; Günther, T.; Musmann, P.; Grinat, M.


    Electric and electromagnetic prospection methods are applied in combination and investigated concerning their ability to image geological fault zones with depths up to a few km. Faults are prominent targets to explore because they bear possible flow paths for hydrothermal fluids. Therefore resistivity can become a valuable key parameter. Within the German Research Association gebo (Geothermal Energy and High Performance Drilling, the electric/electromagnetic methods are operated alongside with the seismic exploration method. While seismic investigations yield information about the subsurface structure, electric and electromagnetic methods supplement these results with their ability to provide information about the resistivity distribution. Commonly used survey setups are analysed with respect to their investigation depth. Non-standard large-scale DC resistivity measurements in a dipole-dipole configuration energized by a high current source were applied in the field. Furthermore, Transient electromagnetic (TEM) soundings with a high transmitter moment were carried out. The setup in the field was modified in order to reach greater investigation depths. The course of seismic reflectors was incorporated into the inversion of the DC resistivity data by structural constraints. Especially thin low-resistive layers, detected by a 1D interpretation of the TEM data show a correlation to the seismic reflectors. While the 2D DC results give information about the resistivity structure of the fault zone, layers of low resistivity that are poorly determined with the DC measurements can be observed with an adapted TEM survey setup. After an initial investigation of known shallow fault zones more emphasis will be attached to the exploration of deeper structures in the subsurface, significant for geothermal tasks. A concept for a suitable field survey design is under development, especially adapted to the specific geological features in the sedimentary basin of

  12. Deformation of conjugate compliant fault zones induced by the 2013 Mw7.7 Baluchistan (Pakistan) earthquake (United States)

    Dutta, Rishabh; Wang, Teng; Feng, Guangcai; Harrington, Jonathan; Vasyura-Bathke, Hannes; Jónsson, Sigurjón


    Strain localizations in compliant fault zones (with elastic moduli lower than the surrounding rocks) induced by nearby earthquakes have been detected using geodetic observations in a few cases in the past. Here we observe small-scale changes in interferometric Synthetic Aperture Radar (InSAR) measurements along multiple conjugate faults near the rupture of the 2013 Mw7.7 Baluchistan (Pakistan) earthquake. After removing the main coseismic deformation signal in the interferograms and correcting them for topography-related phase, we observe 2-3 cm signal along several conjugate faults that are 15-30 km from the mainshock fault rupture. These conjugate compliant faults have strikes of N30°E and N45°W. The sense of motion indicates left-lateral deformation across the N30°E faults and right-lateral deformation across the N45°W faults, which suggests the conjugate faults were subjected to extensional coseismic stresses along the WSW-ENE direction. The spacing between the different sets of faults is around 5 to 8 km. We explain the observed strain localizations as an elastic response of the compliant conjugate faults induced by the Baluchistan earthquake. Using 3D Finite Element models (FEM), we impose coseismic static displacements due to the earthquake along the boundaries of the FEM domain to reproduce the coseismic stress changes acting across the compliant faults. The InSAR measurements are used to constrain the geometry and rigidity variations of the compliant faults with respect to the surrounding rocks. The best fitting models show the compliant fault zones to have a width of 0.5 km to 2 km and a reduction of the shear modulus by a factor of 3 to 4. Our study yields similar values as were found for compliant fault zones near the 1992 Landers and the 1999 Hector Mine earthquakes in California, although here the strain localization is occurring on more complex conjugate sets of faults.

  13. Faults (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Through the study of faults and their effects, much can be learned about the size and recurrence intervals of earthquakes. Faults also teach us about crustal...

  14. Investigating the possible effects of salt in the fault zones on rates of seismicity - insights from analogue and numerical modeling (United States)

    Urai, Janos; Kettermann, Michael; Abe, Steffen


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

  15. Deformation bands in normal fault damage zones, Southwestern Sinai, Suez rift, Egypt (United States)

    Zaky, Kh. S.


    The present study provides evidence that the NW-SE normal faults in Nubian Sandstone reservoirs (Malha and Naqus formations) are surrounded by damage zones in which the rocks are affected by cataclastic deformation bands and small scale faults. The paleostress analysis of the small faults indicates that σ3 has NE-SW direction while σ1 is sub-vertical. The thickness of the bands is ranging from 3 mm to 1 cm. The density and thickness of the bands increase toward the faults and decrease backward. The deformation bands form two prominent sets. The first set is running in the NW-SE direction parallel to the main faults and dip towards the northeast and southwest, i.e. synthetic and antithetic conjugate sets. The second set has NE-SW direction and dip mainly in the NW in the Malha Formation and in the SE in Naqus Formation. The two sets of deformation bands mutually crosscut each other, suggesting that both sets developed during the same deformation event. The deformation bands are planar features and occur singly or form braided clusters. The microscopic studies indicate that the host rock is mainly quartz arenite and composed of fine to very fine, well sorted quartz grains which weakly fractured and cemented by calcite. The microscopic studies of the bands indicate that they composed of strong grain crushing (cataclasis) and clay minerals. This composition is probably causes reduction of porosity and permeability within the deformation bands. The reservoir rocks in the damage zones of the normal faults are divided into polygonal areas by the deformation bands.

  16. Testing the time dependence of slip on the West Klamath Lake fault zone (United States)

    Speth, G.; Amos, C. B.; Amidon, W. H.; Meigs, A.


    Detailed inventories of fault slip over multiple time intervals are critical to our understanding of strain accumulation and release during the earthquake cycle, as well as for resolving potential variability in slip rates over time. Such variations are potentially associated with spatially or temporally clustered earthquakes and possible time-dependent changes in shear zone strength. The West Klamath Lake fault zone (WKLFZ) in southern Oregon provides an excellent opportunity to study incremental fault slip rates because it displaces multiple generations of datable landforms and has remarkable surface expression in airborne lidar imagery. There, we utilize these lidar data and new 3He cosmogenic exposure dating to reconstruct fault slip rates over intervals ranging from 103 - 105 years. Our surficial geologic mapping along the northern extent of the WKLFZ reveals at least two generations of late-Pleistocene glacial landforms as well as several Holocene fan surfaces, all of which are progressively offset by an array of predominately down-to-the-east normal fault scarps. Dating of these features relies on 3He exposure dating of basaltic andesite boulders and depth profiles from glacial outwash terraces. Preliminary exposure dating of an offset moraine along Sevenmile Creek reveals ages consistent with the last glacial maximum ( 15 - 25 ka), suggesting normal fault slip rates of 0.1 mm/yr over this period. This estimate is consistent with slip rates determined from K-Ar dating of offset lava flows near Crater Lake, 20 km to the north. Two dozen additional samples will focus on older glacial moraines and outwash surfaces, as well as debris-flow boulders on Holocene fans. These data will test the constancy of this preliminary slip rate over time. Taken together, our results will provide a detailed slip inventory for the WKLFZ over the last 105 years, and elucidate the role of this structure in accommodating active deformation at the eastern edge of the Oregon Coast

  17. Fault Zone Resistivity Structure and Monitoring at the Taiwan Chelungpu Drilling Project (TCDP

    Directory of Open Access Journals (Sweden)

    Chih-Wen Chiang


    Full Text Available The Taiwan Chelungpu-fault drilling project (TCDP has undertaken scientific drilling and directly sampled the sub-surface rupture of the 1999 Chi-Chi earthquake. Audio-magnetotelluric (AMT measurements were used to investigate electrical resistivity structure at the TCDP site from 2004 - 2006. These data show a geoelectric strike direction of N15°E to N30°E. Inversion and forward modeling of the AMT data were used to generate a 1-D resistivity model that has a prominent low resistivity zone (< 10 ohm-m between depths of 1100 and 1500 m. When combined with porosity measurements, theAMT measurements imply that the ground water has a resistivity of 0.55 ohm-m at the depth of the fault zone.

  18. In situ stress and fracture permeability along the Stillwater fault zone, Dixie Valley Nevada (United States)

    Hickman, S.H.; Barton, C.A.; Zoback, M.D.; Morin, R.; Sass, J.; Benoit, R.


    Borehole televiewer and hydrologic logging and hydraulic fracturing stress measurements were carried out in a 2.7-km-deep geothermal production well (73B-7) drilled into the Stillwater fault zone. Precision temperature and spinner flowmeter logs were also acquired in well 73B-7, with and without simultaneously injecting water into the well. Localized perturbations to well-bore temperature and flow were used to identify hydraulically conductive fractures. Comparison of these data with fracture orientations from the televiewer log indicates that permeable fractures within and adjacent to the Stillwater fault zone are critically stressed, potentially active shear planes in the current west-northwest extensional stress regime at Dixie Valley.

  19. Finite-frequency wave propagation through outer rise fault zones and seismic measurements of upper mantle hydration (United States)

    Miller, Nathaniel; Lizarralde, Daniel


    Effects of serpentine-filled fault zones on seismic wave propagation in the upper mantle at the outer rise of subduction zones are evaluated using acoustic wave propagation models. Modeled wave speeds depend on azimuth, with slowest speeds in the fault-normal direction. Propagation is fastest along faults, but, for fault widths on the order of the seismic wavelength, apparent wave speeds in this direction depend on frequency. For the 5–12 Hz Pn arrivals used in tomographic studies, joint-parallel wavefronts are slowed by joints. This delay can account for the slowing seen in tomographic images of the outer rise upper mantle. At the Middle America Trench, confining serpentine to fault zones, as opposed to a uniform distribution, reduces estimates of bulk upper mantle hydration from ~3.5 wt % to as low as 0.33 wt % H2O.

  20. Stability of Deep Underground Openings through Large Fault Zones in Argillaceous Rock

    Directory of Open Access Journals (Sweden)

    Deyu Qian


    Full Text Available The stability of underground openings is pivotal to sustainable safe mining in underground coal mines. To determine the stability and tunneling safety issues in 800-m-deep underground openings through large fault zones in argillaceous rocks in the Guqiao Coal Mine in East China, the pilot industrial test, laboratory experimentation, and field measurements were used to analyze the large deformations and failure characteristics of the surrounding rock, the influence factors of safe excavation and stability of underground openings, and to study the stability control countermeasures. The main factors influencing the stability and tunneling safety include large fault zones, high in situ stress, poor mechanical properties and engineering performance of the argillaceous rock mass, groundwater inrush and gas outburst. According to the field study, the anchor-ability of cables and the groutability of cement-matrix materials in the argillaceous rock in the large fault zones were extremely poor, and deformations and failure of the surrounding rock were characterized by dramatic initial deformation, high long-term creep rate, obviously asymmetric deformations and failure, rebound of roof displacements, overall loosened deformations of deep surrounding rock on a large scale, and high sensitivity to engineering disturbance and water immersion. Various geo-hazards occurred during the pilot excavation, including roof collapse, groundwater inrush, and debris flow. Control techniques are proposed and should be adopted to ensure tunneling safety and to control the stability of deep underground openings through large fault zones, including regional strata reinforcement technique such as ground surface pre-grouting, primary enhanced control measures, floor grouting reinforcement technique, and secondary enclosed support measures for long-term stability, which are critical for ensuring the sustainable development of the coal mine.

  1. Fault zone characteristics and basin complexity in the southern Salton Trough, California (United States)

    Persaud, Patricia; Ma, Yiran; Stock, Joann M.; Hole, John A.; Fuis, Gary S.; Han, Liang


    Ongoing oblique slip at the Pacific–North America plate boundary in the Salton Trough produced the Imperial Valley (California, USA), a seismically active area with deformation distributed across a complex network of exposed and buried faults. To better understand the shallow crustal structure in this region and the connectivity of faults and seismicity lineaments, we used data primarily from the Salton Seismic Imaging Project to construct a three-dimensional P-wave velocity model down to 8 km depth and a velocity profile to 15 km depth, both at 1 km grid spacing. A VP = 5.65–5.85 km/s layer of possibly metamorphosed sediments within, and crystalline basement outside, the valley is locally as thick as 5 km, but is thickest and deepest in fault zones and near seismicity lineaments, suggesting a causative relationship between the low velocities and faulting. Both seismicity lineaments and surface faults control the structural architecture of the western part of the larger wedge-shaped basin, where two deep subbasins are located. We estimate basement depths, and show that high velocities at shallow depths and possible basement highs characterize the geothermal areas.

  2. Numerical modeling of fracking fluid migration through fault zones and fractures in the North German Basin (United States)

    Pfunt, Helena; Houben, Georg; Himmelsbach, Thomas


    Gas production from shale formations by hydraulic fracturing has raised concerns about the effects on the quality of fresh groundwater. The migration of injected fracking fluids towards the surface was investigated in the North German Basin, based on the known standard lithology. This included cases with natural preferential pathways such as permeable fault zones and fracture networks. Conservative assumptions were applied in the simulation of flow and mass transport triggered by a high pressure boundary of up to 50 MPa excess pressure. The results show no significant fluid migration for a case with undisturbed cap rocks and a maximum of 41 m vertical transport within a permeable fault zone during the pressurization. Open fractures, if present, strongly control the flow field and migration; here vertical transport of fracking fluids reaches up to 200 m during hydraulic fracturing simulation. Long-term transport of the injected water was simulated for 300 years. The fracking fluid rises vertically within the fault zone up to 485 m due to buoyancy. Progressively, it is transported horizontally into sandstone layers, following the natural groundwater flow direction. In the long-term, the injected fluids are diluted to minor concentrations. Despite the presence of permeable pathways, the injected fracking fluids in the reported model did not reach near-surface aquifers, either during the hydraulic fracturing or in the long term. Therefore, the probability of impacts on shallow groundwater by the rise of fracking fluids from a deep shale-gas formation through the geological underground to the surface is small.

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

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


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

  4. Strike-slip and extensional tectonics of the Tan-Lu fault zone (eastern China) from the Cretaceous to Cenozoic (United States)

    Zhang, Y. Q.; Shi, W.; Dong, S. W.


    The Tan-Lu fault zone which extends NNE-SSW more than 3000 km forms conspicuous geological feature along the northeastern margin of the Asia continent. Since its recognition by air-magnetic anomaly in 1957, this fault zone has become the subject of live debate. Most studies were mainly focused on the amount and age of the sinistral offsets along its middle and southern segments. It has been generally thought that the Tan-Lu fault zone was initiated as a transform fault during the Triassic collision between the South and North China Blocks and that it was strongly activated during the Cretaceous and Cenozoic time period. Some authors proposed that the Tan-Lu fault is part of a wide wrench fault system along the north-eastern Asia continent and that sinistral movement along this fault system accommodated oblique convergence between the Pacific oceanic plate and the Asia continent. Some others considered that the Tan-Lu fault belongs to the rifting system of eastern China. Based on field analysis of slip vector data from different rock units of the Cretaceous basins along the middle Tan-Lu fault zone (Shandong Province, eastern China), we document polyphase tectonic stress fields and address the changes in the sense of motion of the Tan-Lu fault zone during the Cretaceous and Cenozoic. The Cretaceous deformation history of the Tan-Lu fault zone can be divided into four main stages. The first stage during the lowermost Cretaceous was dominated by N-S extension, which is responsible for the formation of the Jiaolai basin. We interpret this extension to be related to dextral strike-slip pull-apart opening guided by the Tan-Lu fault zone. The second stage during the middle Early Cretaceous was overwhelmingly rift-dominated, and characterized by widespread intermediate volcanism, normal faulting and basin subsidence. It was at this stage that the Tan-Lu-parallel Yi-Shu Rift was initiated by E-W to WNW-ESE extension. The tectonic regime changed during the late Early

  5. Numerical modeling of fluid flow in a fault zone: a case of study from Majella Mountain (Italy). (United States)

    Romano, Valentina; Battaglia, Maurizio; Bigi, Sabina; De'Haven Hyman, Jeffrey; Valocchi, Albert J.


    The study of fluid flow in fractured rocks plays a key role in reservoir management, including CO2 sequestration and waste isolation. We present a numerical model of fluid flow in a fault zone, based on field data acquired in Majella Mountain, in the Central Apennines (Italy). This fault zone is considered a good analogue for the massive presence of fluid migration in the form of tar. Faults are mechanical features and cause permeability heterogeneities in the upper crust, so they strongly influence fluid flow. The distribution of the main components (core, damage zone) can lead the fault zone to act as a conduit, a barrier, or a combined conduit-barrier system. We integrated existing information and our own structural surveys of the area to better identify the major fault features (e.g., type of fractures, statistical properties, geometrical and petro-physical characteristics). In our model the damage zones of the fault are described as discretely fractured medium, while the core of the fault as a porous one. Our model utilizes the dfnWorks code, a parallelized computational suite, developed at Los Alamos National Laboratory (LANL), that generates three dimensional Discrete Fracture Network (DFN) of the damage zones of the fault and characterizes its hydraulic parameters. The challenge of the study is the coupling between the discrete domain of the damage zones and the continuum one of the core. The field investigations and the basic computational workflow will be described, along with preliminary results of fluid flow simulation at the scale of the fault.

  6. 3D multi-scale velocity structure of an active seismogenic normal fault zone (Central Apennines, Italy) (United States)

    Fondriest, Michele; Mitchell, Tom; Vassallo, Maurizio; Di Giulio, Giuseppe; Balsamo, Fabrizio; Passelegue, Francois; Pischiutta, Marta; Di Toro, Giulio


    The characterization of physical properties of fault zones (e.g., ultrasonic velocities, elastic moduli, porosity and fracture intensity of the fault zone rocks) is a relevant topic in reservoir geology (exploration and exploitation) and fault mechanics, for the modelling of both long-term quasi-static and fast dynamic fault zone evolution with time. Here we characterized the shallow subsurface velocity-elastic structure of the active Vado di Corno normal fault zone (Campo Imperatore, Central Apennines, Italy) which is up to > 300 m thick. Based on a detailed structural mapping of the fault footwall block covering a 2 km long fault segment, four main structural units separated by principal fault strands were recognized: (i) cataclastic unit, (ii) breccia unit, (iii) high-strain damage zone, (iv) low-strain damage zone. The single units were systematically sampled along a transect ( 200 m) orthogonal to the average strike of the fault and characterized in the laboratory in terms of petrophysical properties (i.e., Vp, Vs, static and dynamic elastic moduli, porosity). The cataclastic and breccia units (Vp = 4.68±0.43 kms-1, Vs = 2.68±0.24 kms-1) were significantly "slower" compared to the damage zone units (Vp = 5.43±0.53 kms-1, Vs = 3.20±0.29 kms-1). A general negative correlation between ultrasonic velocity and porosity values was reported. Moreover three dimensional acoustic anisotropy was quantified within the different units with respect to the mapped fault strands, and related to the deformation fabrics (i.e., open fractures, veins) observed at the sample scale. A Vp - Vs seismic refraction tomography was then performed in the field along a profile ( 90 m) across the fault zone. The tomographic results clearly illuminated fault-bounded rock bodies characterized by different velocities (i.e., elastic properties) and geometries which match with the ones deduced from the structural analysis of the fault zone exposures. Fracture intensity measurements (both at

  7. Rock Geochemistry and Mineralogy from Fault Zones and Polymetallic Fault Veins of the Central Front Range, Colorado (United States)

    Caine, Jonathan S.; Bove, Dana J.


    ideas regarding the genetic processes associated with ore-deposit formation. The central part of the eastern Front Range has excellent exposures of fault zones and polymetallic fault veins, subsequently resulting in some of the most detailed mapping and associated data sets in the region. Thus, the area was chosen for detailed data compilation, new sample and data collection, and a variety of structural and geochemical analyses. The data presented in this report come from samples of fault-related exposures in the Front Range and include elemental chemistry and mineralogy from the outcrop-scale study localities within the larger CCAP study area.

  8. Palaeo-stress fleld and tectonic evolution of the Mazhan graben area in the Yi-Shu fault zone of the Tan-Lu fault belt, East China


    Zhang, Yan; Uemura, Takeshi


    The Mazhan graben is located in the Yi-Shu fault zone, which is the middle segment of the Tan-Lu fault belt, one of the oldest and famous large fault belt in China. As a result of the structural analyses on the change of stress field and basin formation, it is clarified that tectonic evolution of the Manzhan graben can be divided into three stages, namely the pre-graben first stage in Palaeozoic to middle Jurassic, the graben-forming second stage in Cretaceous and the post-graben third stage ...

  9. VNIR reflectance spectroscopy of natural carbonate rocks: implication for remote sensing identification of fault damage zones (United States)

    Traforti, Anna; Mari, Giovanna; Carli, Cristian; Demurtas, Matteo; Massironi, Matteo; Di Toro, Giulio


    Reflectance spectroscopy in the visible and near-infrared (VNIR) is a common technique used to study the mineral composition of Solar System bodies from remote sensed and in-situ robotic exploration. In the VNIR spectral range, both crystal field and vibrational overtone absorptions can be present with spectral characteristics (i.e. albedo, slopes, absorption band with different positions and depths) that vary depending on composition and texture (e.g. grain size, roughness) of the sensed materials. The characterization of the spectral variability related to the rock texture, especially in terms of grain size (i.e., both the size of rock components and the size of particulates), commonly allows to obtain a wide range of information about the different geological processes modifying the planetary surfaces. This work is aimed at characterizing how the grain size reduction associated to fault zone development produces reflectance variations in rock and mineral spectral signatures. To achieve this goal we present VNIR reflectance analysis of a set of fifteen rock samples collected at increasing distances from the fault core of the Vado di Corno fault zone (Campo Imperatore Fault System - Italian Central Apennines). The selected samples had similar content of calcite and dolomite but different grain size (X-Ray Powder Diffraction, optical and scanning electron microscopes analysis). Consequently, differences in the spectral signature of the fault rocks should not be ascribed to mineralogical composition. For each sample, bidirectional reflectance spectra were acquired with a Field-Pro Spectrometer mounted on a goniometer, on crushed rock slabs reduced to grain size <800, <200, <63, <10 μm and on intact fault zone rock slabs. The spectra were acquired on dry samples, at room temperature and normal atmospheric pressure. The source used was a Tungsten Halogen lamp with an illuminated spot area of ca. 0.5 cm2and incidence and emission angles of 30˚ and 0˚ respectively

  10. Quantification of Ground Motion Reductions by Fault Zone Plasticity with 3D Spontaneous Rupture Simulations (United States)

    Roten, D.; Olsen, K. B.; Cui, Y.; Day, S. M.


    We explore the effects of fault zone nonlinearity on peak ground velocities (PGVs) by simulating a suite of surface rupturing earthquakes in a visco-plastic medium. Our simulations, performed with the AWP-ODC 3D finite difference code, cover magnitudes from 6.5 to 8.0, with several realizations of the stochastic stress drop for a given magnitude. We test three different models of rock strength, with friction angles and cohesions based on criteria which are frequently applied to fractured rock masses in civil engineering and mining. We use a minimum shear-wave velocity of 500 m/s and a maximum frequency of 1 Hz. In rupture scenarios with average stress drop (~3.5 MPa), plastic yielding reduces near-fault PGVs by 15 to 30% in pre-fractured, low-strength rock, but less than 1% in massive, high quality rock. These reductions are almost insensitive to the scenario earthquake magnitude. In the case of high stress drop (~7 MPa), however, plasticity reduces near-fault PGVs by 38 to 45% in rocks of low strength and by 5 to 15% in rocks of high strength. Because plasticity reduces slip rates and static slip near the surface, these effects can partially be captured by defining a shallow velocity-strengthening layer. We also perform a dynamic nonlinear simulation of a high stress drop M 7.8 earthquake rupturing the southern San Andreas fault along 250 km from Indio to Lake Hughes. With respect to the viscoelastic solution (a), nonlinearity in the fault damage zone and in near-surface deposits would reduce long-period (> 1 s) peak ground velocities in the Los Angeles basin by 15-50% (b), depending on the strength of crustal rocks and shallow sediments. These simulation results suggest that nonlinear effects may be relevant even at long periods, especially for earthquakes with high stress drop.

  11. Influence of host lithofacies on fault rock variation in carbonate fault zones: A case study from the Island of Malta (United States)

    Michie, E. A. H.


    Relatively few studies have examined fault rock microstructures in carbonates. Understanding fault core production helps predict the hydraulic behaviour of faults and the potential for reservoir compartmentalisation. Normal faults on Malta, ranging from fracture networks that develop into breccias. Alternatively, this lithofacies is commonly recrystallised. In contrast, in the coarse-grained, heterogeneous grain-dominated carbonates the development of faulting is characterised by localised deformation, creating protocataclasite and cataclasite fault rocks. Cementation also occurs within some grain-dominated carbonates close to and on slip surfaces. Fault rock variation is a function of displacement as well as juxtaposed lithofacies. An increase in fault rock variability is observed at higher displacements, potentially creating a more transmissible fault, which opposes what may be expected in siliciclastic and crystalline faults. Significant heterogeneity in the fault rock types formed is likely to create variable permeability along fault-strike, potentially allowing across-fault fluid flow. However, areas with homogeneous fault rocks may generate barriers to fluid flow.

  12. Seismic-wave attenuation associated with crustal faults in the new madrid seismic zone. (United States)

    Hamilton, R M; Mooney, W D


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

  13. Numerical modeling of fracking fluid and methane migration through fault zones in shale gas reservoirs (United States)

    Taherdangkoo, Reza; Tatomir, Alexandru; Sauter, Martin


    Hydraulic fracturing operation in shale gas reservoir has gained growing interest over the last few years. Groundwater contamination is one of the most important environmental concerns that have emerged surrounding shale gas development (Reagan et al., 2015). The potential impacts of hydraulic fracturing could be studied through the possible pathways for subsurface migration of contaminants towards overlying aquifers (Kissinger et al., 2013; Myers, 2012). The intent of this study is to investigate, by means of numerical simulation, two failure scenarios which are based on the presence of a fault zone that penetrates the full thickness of overburden and connect shale gas reservoir to aquifer. Scenario 1 addresses the potential transport of fracturing fluid from the shale into the subsurface. This scenario was modeled with COMSOL Multiphysics software. Scenario 2 deals with the leakage of methane from the reservoir into the overburden. The numerical modeling of this scenario was implemented in DuMux (free and open-source software), discrete fracture model (DFM) simulator (Tatomir, 2012). The modeling results are used to evaluate the influence of several important parameters (reservoir pressure, aquifer-reservoir separation thickness, fault zone inclination, porosity, permeability, etc.) that could affect the fluid transport through the fault zone. Furthermore, we determined the main transport mechanisms and circumstances in which would allow frack fluid or methane migrate through the fault zone into geological layers. The results show that presence of a conductive fault could reduce the contaminant travel time and a significant contaminant leakage, under certain hydraulic conditions, is most likely to occur. Bibliography Kissinger, A., Helmig, R., Ebigbo, A., Class, H., Lange, T., Sauter, M., Heitfeld, M., Klünker, J., Jahnke, W., 2013. Hydraulic fracturing in unconventional gas reservoirs: risks in the geological system, part 2. Environ Earth Sci 70, 3855

  14. Predicting the width and average fracture frequency of damage zones using a partial least squares statistical analysis: Implications for fault zone development (United States)

    O'Hara, Alex P.; Jacobi, Robert D.; Sheets, H. David


    We introduce the partial least squares (PLS) statistical analysis that quantifies and predicts the observed relationships among normal fault slip, fracturing associated with the fault, and lithology. We describe the systematic process for constructing a multivariate PLS model that predicts the average fracture frequency and the width of fracture-dominated fault damage zones from fault, lithologic and fracture data. Conversely, the model can also predict normal fault net slip for a defined lithology given the average fracture frequency and width of a fracture-dominated fault damage zone, hereafter defined as a fracture intensification domain (FID). Fracture, fault and lithologic data were collected in the Mohawk Valley of New York State from outcrops in the Upper Ordovician Utica Group and Lorraine Group. Data collection was focused on faults with observable slip, associated FIDs, and no observable lateral restriction. Our statistical analysis used three variables to describe the geometry of the FID: FID width (FIDw), average fracture frequency within the FID (FIDƒ), and the power law regression exponent (FIDR) of the least squares trend line. We incorporated additional data from literature and tested multiple PLS models in order to refine the analysis using quality indicators provided by the PLS summary statistics output. Variables included in the final predictive model included FIDw, FIDƒ, fault slip, grain size and clay percent. Fault slip and grain size were found to have a positive covariance with FIDw while clay percent had a negative covariance. Fault slip, grain size and clay percent all showed a negative covariance with FIDƒ. Results from this research indicate that increasing fault slip leads to wider FIDs and lower average fracture frequency within the FID. The lower average fracture frequency in wider FIDs is primarily attributed to an increase in the length of the low-frequency FID tail away from the associated fault. A possible secondary influence

  15. Kinematics of the Eastern Part of the North Anatolian Fault Zone (United States)

    Haluk, Ozener; Esen, Arpat; Semih, Ergintav; Asli, Dogru; Rahsan, Cakmak; Bulent, Turgut; Ugur, Dogan


    The North Anatolian Fault Zone (NAFZ), which marks the boundary between Anatolia and the Eurasian plate, is one of the world's most seismically active structures. Although the eastern part of NAFZ has high seismic hazard, there is a lack of geodetic information about the present tectonics of this region. Even though many scientists would like to study this area, geographical and logistical problems make performing scientific research difficult. In order to investigate contemporary neotectonic deformation on the eastern NAFZ and in its neighborhood, a relatively dense Global Positioning System (GPS) monitoring network was established in 2003. Geodetic observations were performed in three GPS campaigns in an area of 350 × 200 km square with 12-month intervals. In addition, 14 new GPS stations were measured far from the deforming area. Since this region includes the intersection of the NAFZ and the East Anatolian Fault Zone (EAFZ), deformation is complex and estimating seismic hazard is difficult. One important segment is the Yedisu segment and it has not broken since the 1784 earthquake. After the 1992 Erzincan and 2003 Pulumur earthquakes, the Coulomb stress loading on the Yedisu segment of the NAFZ has increased significantly, emphasizing the need to monitor this region. We computed the horizontal velocity field with respect to Eurasia and strain rates field as well. GPS-derived velocities relative to Eurasia are in the range of 16-24 mm/yr, which are consistent with the regional tectonics. The principal strains rates were derived from the velocity field. Results show that strain is accumulating between the NAFZ and EAFZ along small secondary fault branches such as the Ovacık Fault (OF).

  16. Dynamics of intraoceanic subduction initiation : 1. Oceanic detachment fault inversion and the formation of supra-subduction zone ophiolites

    NARCIS (Netherlands)

    Maffione, Marco; Thieulot, Cedric|info:eu-repo/dai/nl/270177493; van Hinsbergen, Douwe J.J.|info:eu-repo/dai/nl/269263624; Morris, Antony; Plümper, Oliver|info:eu-repo/dai/nl/37155960X; Spakman, Wim|info:eu-repo/dai/nl/074103164

    Subduction initiation is a critical link in the plate tectonic cycle. Intraoceanic subduction zones can form along transform faults and fracture zones, but how subduction nucleates parallel to mid-ocean ridges, as in e.g., the Neotethys Ocean during the Jurassic, remains a matter of debate. In

  17. Western frontal fault of the Canyon Range: is it the breakaway zone of the Sevier Desert detachment? (United States)

    Otton, J.K.


    Geologic evidence developed from surface exposures demonstrates that the western frontal fault of the Canyon Range is a major structure representing the eastern Breakaway zone of the Sevier Desert detachment. Maximum upper plate displacement for the entire Sevier Desert detachment cannot be determined from these breakaway-zone exposures. -from Author

  18. Landform development in a zone of active Gedi Fault, Eastern Kachchh rift basin, India (United States)

    Kothyari, Girish Ch.; Rastogi, B. K.; Morthekai, P.; Dumka, Rakesh K.


    An earthquake of 2006 Mw 5.7 occurred along east-west trending Gedi Fault (GF) to the north of the Kachchh rift basin in western India which had the epicenter in the Wagad upland, which is approximately 60 km northeast of the 2001 Mw 7.7 earthquake site (or epicenter). Development of an active fault scarp, shifting of a river channel, offsetting of streams and uplift of the ground indicate that the terrain is undergoing active deformation. Based on detailed field investigations, three major faults that control uplifts have been identified in the GF zone. These uplifts were developed in a step-over zone of the GF, and formed due to compressive force generated by left-lateral motion within the segmented blocks. In the present research, a terrace sequence along the north flowing Karaswali river in a tectonically active GF zone has been investigated. Reconstructions based on geomorphology and terrace stratigraphy supported by optical chronology suggest that the fluvial aggradation in the Wagad area was initiated during the strengthening (at ~ 8 ka) and declining (~ 4 ka) of the Indian Summer Monsoon (ISM). The presence of younger valley fill sediments which are dated ~ 1 ka is ascribed to a short lived phase of renewed strengthening of ISM before present day aridity. Based on terrace morphology two major phases of enhanced uplift have been estimated. The older uplift event dated to 8 ka is represented by the Tertiary bedrock surfaces which accommodated the onset of valley-fill aggradation. The younger event of enhanced uplift dated to 4 ka was responsible for the incision of the older valley fill sediments and the Tertiary bedrock. These ages suggest that the average rate of uplift ranges from 0.3 to 1.1 mm/yr during the last 9 ka implying active nature of the area.

  19. Development of a Hydrologic Characterization Technology for Fault Zones Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Karasaki, Kenzi [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Onishi, Celia Tiemi [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Doughty, Christine [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Conrad, Mark [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Gasperikova, Erika [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Cook, Paul [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Ulrich, Craig [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)


    This is the final report for the five-year program of the NUMO-LBNL collaborative project (hereafter called the Project): Development of Hydrologic Characterization Technology for Fault Zones, under a NUMO-DOE/LBNL collaboration agreement. Detailed results from the past four years of study can be found in the each year’s year-end report (Karasaki et al., 2008, 2009, 2010, and 2011; Kiho et al., 2008, 2009, 2010, and 2011). In this report, we discuss the results of the studies conducted in FY2011. We also give a summary of the overall results and findings, as well as the lessons learned during the course of the Project.

  20. Gravity field and structure of the Sorong Fault Zone, eastern Indonesia (United States)


    Gravity surveys along coastlines of islands in the region Banggai-Sula, Eastern Sulawesi, Halmahera, Bacan and Obi were carried out as part of the Sorong Fault Zone Project. Results of the Surveys were integrated with gravity data previously acquired by other projects, including on-land gravity data from the Bird Head area Irian Jaya (Dow et al 1986), Seram Island (Milsom 1977), Buru Island (Oemar and Reminton 1993) and Central Sulawesi (Silver et al. 1983) as well as marine gravity information within and surrounding the Sorong Fault Zone (Bowin et al. 1980). Gravity expeditions of the Sorong Fault Zone Project also include measurements in Mayu Island and the island group of Talaud, situated further north in the Central Molucca Sea region. A total of one hundred and forty two gravity data were acquired in the region of Banggai-Sula islands, forty seven in eastern part of Central Sulawesi, about four hundred in Halmahera, Bacan and Obi, and seventy nine in Mayu and Talaud. Surveys in the eastern part of Central Sulawesi were carried out for the purpose of tieing the older gravity data obtained from Silver et al. (1983) and the more recent data of the Sorong Fault Zone Project. About one thousand thirty hundred and thirty gravity data were acquired as part of the Irian Jaya Geological Mapping Project (IJGMP) in the period of 1978-1983, a project commissioned by the Indonesian Geological Research and Development Centre (GRDC) and the Australian Bureau of Mineral Resources (BMR). The remoteness of the survey areas of the Sorong Fault Zone Project necessitated a careful planning for travel arrangements and provision of logistics. A wide range of magnitude of gravity field was observed in the Sorong Fault Zone, extending from values below -250 mGal recorded in the southern part of the Molucca Sea to values in excess of +320 mGal measured near to sea level in the coastal areas south of Mangole and north of Sulabesi, the two islands of the Sula Group. Steep gradients of

  1. Paleoseismology of the Palu-Lake Hazar segment of the East Anatolian Fault Zone, Turkey (United States)

    Cetin, Hasan; Güneyli, Hakan; Mayer, Larry


    The East Anatolian Fault Zone (EAFZ) is among the most important active continental transform fault zones in the world as testified by major historical and minor instrumental seismicity. The first paleoseismological exploratory trenching study on the EAFZ was done on the Palu-Lake Hazar segment (PLHS), which is one of the six segments forming the fault zone, in order to determine its past activity and to assess its earthquake hazard. The results of trenching indicate that the latest surface rupturing earthquakes on this segment may be the Ms=7.1+ 1874 and Ms=6.7 1875 events, and there were other destructive earthquakes prior to these events. The recurrence interval for a surface rupturing large ( M>7) earthquake is estimated as minimum 100±35 and maximum 360 years. Estimates for the maximum possible paleoearthquake magnitude are (Mw) 7.1-7.7 for the Palu-Lake Hazar segment based on empirical magnitude fault rupture relations. An alluvial fan dated 14,475-15,255 cal years BP as well as another similar age fan with an abandoned stream channel on it are offset in a left-lateral sense 175 and 160.5 m, respectively, indicating an average slip rate of 11 mm/year. Because 127 years have elapsed since the last surface rupturing event, this slip rate suggests that 1.4 m of left-lateral strain has accumulated along the segment, ignoring possible creep effects, folding and other inelastic deformation. A 2.5 Ma age for the start of left-lateral movement on the segment, and in turn the EAFZ, is consistent with a slip rate of 11 mm/year and a previously reported 27 km total left-lateral offset. The cumulative 5-6 mm/year vertical slip rate near Lake Hazar suggests a possible age of 148-178 ka for the lake. Our trenching results indicate also that a significant fraction of the slip across the EAFZ zone is likely to be accommodated seismically. The present seismic quiescence compared with the past activity (paleoseismic and historic) indicate that the EAFZ may be "locked" and

  2. Late Quaternary Activity and Seismogenic Potential of the Gonave Microplate: Plantain Garden Strike-Slip Fault Zone of Eastern Jamaica (United States)

    Mann, P.; Prentice, C.; King, W.; Demets, C.; Wiggins-Grandison, M.; Benford, B.


    At the longitude of Jamaica, Caribbean (Carib)-North America (Noam) plate motion of 19 ± 2 mm/a is carried by two parallel, left-lateral strike-slip faults, the Oriente fault zone, immediately south of Cuba, and the Enriquillo-Plantain Garden fault zone (EPGFZ), which lies 100-150 km further south. It has been postulated that the lithosphere between these faults constitutes an independent Gonave microplate that has formed in response to the ongoing collision between the leading edge of Carib in Hispaniola and the Bahama carbonate platform. GPS measurements in Jamaica and Hispanola is supportive of the microplate hypothesis and indicates that roughly half of Carib-Noam plate motion (8-14 mm/a) is carried by the EPGFZ of southern Hispaniola and eastern Jamaica. This study applies geomorphic and paleoseismic methods as a direct test of the activity and amount of microplate motion carried on the Plantain Garden fault segment of eastern Hispaniola and how this motion is distributed across a large restraining bend that has formed the island of Jamaica since the late Miocene. The EPFZ curves gently to the northeast and forming a steep mountain front to the Blue Mountains restraining bend with elevations up to 2200 m. Geomorphic fault-related features along the mountain front fault zone include left-laterally deflected rivers and streams, but no small scale features indicative of Holocene activity. River and stream deflections range from 0.1 to 0.5 km. We identified and trenched the most active trace of the mountain front fault at the Morant River where the fault is characterized by a 1.5-m-wide sub-vertical fault zone juxtaposing sheared alluvium and fault Cretaceous basement rocks This section is overlain by a 6-m-thick fluvial terrace. Trenching in the unfaulted terrace immediately overlying the fault trace revealed radiocarbon and OSL ages ranging from 20 to 21 ka that are consistent with a prominent unfaulted alluvial fan along the projection of this fault 1.5 km to

  3. Heterogeneous slip and rupture models of the San Andreas fault zone based upon three-dimensional earthquake tomography

    Energy Technology Data Exchange (ETDEWEB)

    Foxall, William [Univ. of California, Berkeley, CA (United States)


    Crystal fault zones exhibit spatially heterogeneous slip behavior at all scales, slip being partitioned between stable frictional sliding, or fault creep, and unstable earthquake rupture. An understanding the mechanisms underlying slip segmentation is fundamental to research into fault dynamics and the physics of earthquake generation. This thesis investigates the influence that large-scale along-strike heterogeneity in fault zone lithology has on slip segmentation. Large-scale transitions from the stable block sliding of the Central 4D Creeping Section of the San Andreas, fault to the locked 1906 and 1857 earthquake segments takes place along the Loma Prieta and Parkfield sections of the fault, respectively, the transitions being accomplished in part by the generation of earthquakes in the magnitude range 6 (Parkfield) to 7 (Loma Prieta). Information on sub-surface lithology interpreted from the Loma Prieta and Parkfield three-dimensional crustal velocity models computed by Michelini (1991) is integrated with information on slip behavior provided by the distributions of earthquakes located using, the three-dimensional models and by surface creep data to study the relationships between large-scale lithological heterogeneity and slip segmentation along these two sections of the fault zone.

  4. Landslide susceptibility mapping for a part of North Anatolian Fault Zone (Northeast Turkey) using logistic regression model (United States)

    Demir, Gökhan; aytekin, mustafa; banu ikizler, sabriye; angın, zekai


    The North Anatolian Fault is know as one of the most active and destructive fault zone which produced many earthquakes with high magnitudes. Along this fault zone, the morphology and the lithological features are prone to landsliding. However, many earthquake induced landslides were recorded by several studies along this fault zone, and these landslides caused both injuiries and live losts. Therefore, a detailed landslide susceptibility assessment for this area is indispancable. In this context, a landslide susceptibility assessment for the 1445 km2 area in the Kelkit River valley a part of North Anatolian Fault zone (Eastern Black Sea region of Turkey) was intended with this study, and the results of this study are summarized here. For this purpose, geographical information system (GIS) and a bivariate statistical model were used. Initially, Landslide inventory maps are prepared by using landslide data determined by field surveys and landslide data taken from General Directorate of Mineral Research and Exploration. The landslide conditioning factors are considered to be lithology, slope gradient, slope aspect, topographical elevation, distance to streams, distance to roads and distance to faults, drainage density and fault density. ArcGIS package was used to manipulate and analyze all the collected data Logistic regression method was applied to create a landslide susceptibility map. Landslide susceptibility maps were divided into five susceptibility regions such as very low, low, moderate, high and very high. The result of the analysis was verified using the inventoried landslide locations and compared with the produced probability model. For this purpose, Area Under Curvature (AUC) approach was applied, and a AUC value was obtained. Based on this AUC value, the obtained landslide susceptibility map was concluded as satisfactory. Keywords: North Anatolian Fault Zone, Landslide susceptibility map, Geographical Information Systems, Logistic Regression Analysis.

  5. A New Paradigm For Modeling Fault Zone Inelasticity: A Multiscale Continuum Framework Incorporating Spontaneous Localization and Grain Fragmentation. (United States)

    Elbanna, A. E.


    The brittle portion of the crust contains structural features such as faults, jogs, joints, bends and cataclastic zones that span a wide range of length scales. These features may have a profound effect on earthquake nucleation, propagation and arrest. Incorporating these existing features in modeling and the ability to spontaneously generate new one in response to earthquake loading is crucial for predicting seismicity patterns, distribution of aftershocks and nucleation sites, earthquakes arrest mechanisms, and topological changes in the seismogenic zone structure. Here, we report on our efforts in modeling two important mechanisms contributing to the evolution of fault zone topology: (1) Grain comminution at the submeter scale, and (2) Secondary faulting/plasticity at the scale of few to hundreds of meters. We use the finite element software Abaqus to model the dynamic rupture. The constitutive response of the fault zone is modeled using the Shear Transformation Zone theory, a non-equilibrium statistical thermodynamic framework for modeling plastic deformation and localization in amorphous materials such as fault gouge. The gouge layer is modeled as 2D plane strain region with a finite thickness and heterogeenous distribution of porosity. By coupling the amorphous gouge with the surrounding elastic bulk, the model introduces a set of novel features that go beyond the state of the art. These include: (1) self-consistent rate dependent plasticity with a physically-motivated set of internal variables, (2) non-locality that alleviates mesh dependence of shear band formation, (3) spontaneous evolution of fault roughness and its strike which affects ground motion generation and the local stress fields, and (4) spontaneous evolution of grain size and fault zone fabric.

  6. Late Quaternary strike-slip along the Taohuala Shan-Ayouqi fault zone and its tectonic implications in the Hexi Corridor and the southern Gobi Alashan, China (United States)

    Yu, Jing-xing; Zheng, Wen-jun; Zhang, Pei-zhen; Lei, Qi-yun; Wang, Xu-long; Wang, Wei-tao; Li, Xin-nan; Zhang, Ning


    The Hexi Corridor and the southern Gobi Alashan are composed of discontinuous a set of active faults with various strikes and slip motions that are located to the north of the northern Tibetan Plateau. Despite growing understanding of the geometry and kinematics of these active faults, the late Quaternary deformation pattern in the Hexi Corridor and the southern Gobi Alashan remains controversial. The active E-W trending Taohuala Shan-Ayouqi fault zone is located in the southern Gobi Alashan. Study of the geometry and nature of slip along this fault zone holds crucial value for better understanding the regional deformation pattern. Field investigations combined with high-resolution imagery show that the Taohuala Shan fault and the E-W trending faults within the Ayouqi fault zone (F2 and F5) are left-lateral strike-slip faults, whereas the NW or WNW-trending faults within the Ayouqi fault zone (F1 and F3) are reverse faults. We collected Optically Stimulated Luminescence (OSL) and cosmogenic exposure age dating samples from offset alluvial fan surfaces, and estimated a vertical slip rate of 0.1-0.3 mm/yr, and a strike-slip rate of 0.14-0.93 mm/yr for the Taohuala Shan fault. Strata revealed in a trench excavated across the major fault (F5) in the Ayouqi fault zone and OSL dating results indicate that the most recent earthquake occurred between ca. 11.05 ± 0.52 ka and ca. 4.06 ± 0.29 ka. The geometry and kinematics of the Taohuala Shan-Ayouqi fault zone enable us to build a deformation pattern for the entire Hexi Corridor and the southern Gobi Alashan, which suggest that this region experiences northeastward oblique extrusion of the northern Tibetan Plateau. These left-lateral strike-slip faults in the region are driven by oblique compression but not associated with the northeastward extension of the Altyn Tagh fault.

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

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


    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

  8. Structural analysis of the Gachsar sub-zone in central Alborz range; constrain for inversion tectonics followed by the range transverse faulting (United States)

    Yassaghi, A.; Naeimi, A.


    Analysis of the Gachsar structural sub-zone has been carried out to constrain structural evolution of the central Alborz range situated in the central Alpine Himalayan orogenic system. The sub-zone bounded by the northward-dipping Kandovan Fault to the north and the southward-dipping Taleghan Fault to the south is transversely cut by several sinistral faults. The Kandovan Fault that controls development of the Eocene rocks in its footwall from the Paleozoic-Mesozoic units in the fault hanging wall is interpreted as an inverted basin-bounding fault. Structural evidences include the presence of a thin-skinned imbricate thrust system propagated from a detachment zone that acts as a footwall shortcut thrust, development of large synclines in the fault footwall as well as back thrusts and pop-up structures on the fault hanging wall. Kinematics of the inverted Kandovan Fault and its accompanying structures constrain the N-S shortening direction proposed for the Alborz range until Late Miocene. The transverse sinistral faults that are in acute angle of 15° to a major magnetic lineament, which represents a basement fault, are interpreted to develop as synthetic Riedel shears on the cover sequences during reactivation of the basement fault. This overprinting of the transverse faults on the earlier inverted extensional fault occurs since the Late Miocene when the south Caspian basin block attained a SSW movement relative to the central Iran. Therefore, recent deformation in the range is a result of the basement transverse-fault reactivation.

  9. Is the Vincent fault in southern California the Laramide subduction zone megathrust? (United States)

    Xia, H.; Platt, J. P.


    The Vincent fault (VF) in the San Gabriel Mountains, southern California separates a Meso-Proterozoic gneiss complex and Mesozoic granitoid rocks in the upper plate from the ocean-affiliated Late Cretaceous Pelona schist in the lower plate, and it has been widely interpreted as the original Laramide subduction megathrust. A 500 to 1000 m thick mylonite zone, consisting of a low-stress (LS) section at the bottom, a high-stress (HS) section at the top, and a weakly deformed section in between, is developed above the VF. Our kinematic, thermobarometric and geochronological analysis of the mylonite zone indicates that the VF is a normal fault. Shear sense indicators including asymmetric porphyroblasts, quartz new grain fabric, mineral fish, and quartz CPO from the HS and the LS sections exhibit a top-to-SE sense of shear on the SW-dipping mylonitic foliation, which is contrary to what one would expect for the Laramide subduction megathrust. A few samples from the LS section were overprinted by HS microstructure, implying that the LS mylonites predate the HS mylonites. TitaniQ thermometer and Si-in-muscovite barometer show that the P-T conditions are 389 ± 6 °C, 5 kbar for the LS mylonites and 329 ± 6 °C, 2.4 kbar for HS mylonites. Considering the temporal sequence of HS and LS mylonites, they are likely to be formed during exhumation. A comparison with the lower plate leads to the same conclusion. The top 80-100 m of the Pelona schist underneath the VF is folded and also mylonitized, forming the Narrows synform and S3 simultaneously. Our previous study found that S3 of the Pelona schist has a top-to-SE sense of shear and similar P-T conditions as the LS mylonite in the upper plate, so S3 of the Pelona schist is likely to be formed together with the LS mylonites in the upper plate. While mylonitization of Pelona schist (S3) overprinted both the subduction-related S1 fabric and the return-flow-related S2 fabric, it is reasonable to argue that the mylonite zone above

  10. The Terminology of Fault Zones in the Brittle Regime: Making Field Observations More Useful to the End User (United States)

    Shipton, Z.; Caine, J. S.; Lunn, R. J.


    Geologists are tiny creatures living on the 2-and-a-bit-D surface of a sphere who observe essentially 1D vanishingly small portions (boreholes, roadcuts, stream and beach sections) of complex, 4D tectonic-scale structures. Field observations of fault zones are essential to understand the processes of fault growth and to make predictions of fault zone mechanical and hydraulic properties at depth. Here, we argue that a failure of geologists to communicate their knowledge effectively to other scientists/engineers can lead to unrealistic assumptions being made about fault properties, and may result in poor economic performance and a lack of robustness in industrial safety cases. Fault zones are composed of many heterogeneously distributed deformation-related elements. Low permeability features include regions of intense grain-size reduction, pressure solution, cementation and shale smears. Other elements are likely to have enhanced permeability through fractures and breccias. Slip surfaces can have either enhanced or reduced permeability depending on whether they are open or closed, and the local stress state. The highly variable nature of 1) the architecture of faults and 2) the properties of deformation-related elements demonstrates that there are many factors controlling the evolution of fault zone internal structures (fault architecture). The aim of many field studies of faults is to provide data to constrain predictions at depth. For these data to be useful, pooling of data from multiple sites is usually necessary. This effort is frequently hampered by variability in the usage of fault terminologies. In addition, these terms are often used in ways as to make it easy for 'end-users' such as petroleum reservoir engineers, mining geologists, and seismologists to mis-interpret or over-simplify the implications of field studies. Field geologists are comfortable knowing that if you walk along strike or up dip of a fault zone you will find variations in fault rock type

  11. Rapid mapping of ultrafine fault zone topography with structure from motion (United States)

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


    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.

  12. Megathrust splay faults, forearc basins, and segment boundaries related to the Kodiak Islands segment of the Alaska subduction zone (United States)

    Ramos, M. D.; Liberty, L. M.


    We have compiled and interpreted a comprehensive upper-crustal seismic reflection dataset revealing spatiotemporal Cenozoic deformation across the Kodiak forearc and accretionary prism. Pervasive splay faults and forearc basin growth and positioning with respect to the prism record both accreting and eroding margin episodes through time. Seafloor bathymetry, in conjunction with seismic reflection data, show that post-glacial splay fault motion can exceed 40 meters offshore Kodiak Island. We observe considerable differences in splay fault uplift rates and activation spanning the near-shore region to the continental shelf, with significant tsunamigenic fault motion from the 1964 Great Alaska Earthquake concentrated along the Kodiak Island shelf fault zone system. We utilize potential fields data to highlight the continuity of megathrust splay faults that span the southern Gulf of Alaska and to identify geophysical signatures of segment boundaries that represent subducting Pacific plate morphology which may define megathrust rupture limits. Constraints on interseismic deformation from compiled geodetic GPS, focal mechanism, and earthquake datasets reveal the seismotectonic character of the Kodiak segment and are consistent with the structural heterogeneity at both the plate interface and upper plate. Upper plate geometry of the Kodiak segment shows Holocene fault motion has been accommodated along distinct fault zone segments. This knowledge informs tsunami risk modelers to allow for different alternatives of coseismic splay fault uplift during megathrust rupture. Our results suggest growth of forearc structures is contemporaneous with the subduction of major Pacific plate morphologies and provide clear geophysical evidence that can explain the persistence of the Kodiak segment, which is a major step towards a composite Alaska subduction zone deformation model.

  13. Investigations into the Fish Lake Valley Fault Zone (FLVFZ) and its interactions with normal faulting within Eureka and Deep Springs Valleys (United States)

    Lawson, M. J.; Rhodes, E.; Yin, A.


    In most textbooks, the San Andreas Fault is stated to be the plate boundary between the North American and the Pacific plates, as plate tectonics assumes that boundaries are essentially discrete. In the Western United States this is not the case, as up to 25% of relative plate motion is accommodated on other structures within the Walker Lane Shear Zone (WLSZ) in a diffuse 100 km margin (Faulds et al., 2005; Oldow et al., 2001). Fish Lake Valley Fault Zone (FLVFZ), situated at the northern border of Death Valley National Park, is the northern continuation of the Furnace Creek Fault Zone (FCFZ), and is an important transfer structure within the Walker Lane Shear Zone. Though the FLVFZ has a long term rate (since 10 Ma) of 5 mm/yr (Reheis and Sawyer, 1997), it has a highly variable slip rate. In the middle Pleistocene, the rate has a maximum of up to 11 mm/yr which would accommodate nearly the entirety of slip within the Walker Lane, and yet this rate decreases significantly ( 2.5 to 3 mm/yr) by the late Pleistocene due to unknown causes (Frankel et al. 2007). This variation in slip rate has been proposed by previous workers to be due to strain transience, an increase in the overall strain rate, or due to other unknown structures (Lee et al., 2009). Currently, we are investigating the cause of this variation, and the possibility of the transfer of slip to faults south of the FLVFZ on oblique normal faults within Eureka and Deep Springs Valleys. Preliminary data will be shown utilizing scarp transects, geomorphic scarp modeling, and Optically Stimulated Luminescence (OSL) dating techniques.

  14. The transtensional offshore portion of the northern San Andreas fault: Fault zone geometry, late Pleistocene to Holocene sediment deposition, shallow deformation patterns, and asymmetric basin growth (United States)

    Beeson, Jeffrey W.; Johnson, Samuel Y.; Goldfinger, Chris


    We mapped an ~120 km offshore portion of the northern San Andreas fault (SAF) between Point Arena and Point Delgada using closely spaced seismic reflection profiles (1605 km), high-resolution multibeam bathymetry (~1600 km2), and marine magnetic data. This new data set documents SAF location and continuity, associated tectonic geomorphology, shallow stratigraphy, and deformation. Variable deformation patterns in the generally narrow (∼1 km wide) fault zone are largely associated with fault trend and with transtensional and transpressional fault bends.We divide this unique transtensional portion of the offshore SAF into six sections along and adjacent to the SAF based on fault trend, deformation styles, seismic stratigraphy, and seafloor bathymetry. In the southern region of the study area, the SAF includes a 10-km-long zone characterized by two active parallel fault strands. Slip transfer and long-term straightening of the fault trace in this zone are likely leading to transfer of a slice of the Pacific plate to the North American plate. The SAF in the northern region of the survey area passes through two sharp fault bends (∼9°, right stepping, and ∼8°, left stepping), resulting in both an asymmetric lazy Z–shape sedimentary basin (Noyo basin) and an uplifted rocky shoal (Tolo Bank). Seismic stratigraphic sequences and unconformities within the Noyo basin correlate with the previous 4 major Quaternary sea-level lowstands and record basin tilting of ∼0.6°/100 k.y. Migration of the basin depocenter indicates a lateral slip rate on the SAF of 10–19 mm/yr for the past 350 k.y.Data collected west of the SAF on the south flank of Cape Mendocino are inconsistent with the presence of an offshore fault strand that connects the SAF with the Mendocino Triple Junction. Instead, we suggest that the SAF previously mapped onshore at Point Delgada continues onshore northward and transitions to the King Range thrust.

  15. Constraining geometrical, hydrodynamical and mechanical properties of a fault zone at hourly time scales from ground surface tilt data (United States)

    Schuite, Jonathan; Longuevergne, Laurent; Bour, Olivier; Burbey, Thomas J.; Boudin, Frédéric


    Flow through reservoirs such as fractured media is powered by pressure gradients which also generate measurable poroelastic deformation of the rock body. The combined analysis of ground surface deformation and sub-surface fluid pressure provides valuable insights of a reservoir's structure and hydromechanical properties, which are of interest for deep-seated CO2 or nuclear waste storage for instance. Amongst all surveying tools, surface tiltmeters offer the possibility to grasp hydraulically-induced deformation over a broad range of time scales with a remarkable precision (1 nanoradian). Here, we investigate the information content of transient surface tilt generated by flow in a kilometer scale sub-vertical fault zone and its surrounding fractured rock matrix. Our approach involves the combined analysis of field data and results of a fully coupled poroelastic model, where fault and matrix are represented as equivalent homogeneous domains. The signature of pressure changes in the fault zone due to pumping cycles is clearly recognizable in field tilt data and we aim to explain the peculiar features that appear in: 1) tilt time series alone from a set of 4 instruments; 2) the ratio of tilt over pressure. With the model, we evidence that the shape of tilt measurements on both sides of a fault zone is sensitive to its diffusivity and its elastic modulus. In particular, we show a few well placed tiltmeters (on each side of a fault) give more information on the medium's properties than well spatialized surface displacement maps. Furthermore, the ratio of tilt over pressure predominantly encompasses information about the system's dynamic behavior and extent of the fault zone, and allows separating contributions of flow in the different compartments. Hence, tiltmeters are well suited to characterize hydromechanical processes associated to fault zone hydrogeology at short time scales, where space-borne surveying methods fail to seize any deformation signal.

  16. Cretaceous to Miocene fault zone evolution in the Eastern Alps constrained by multi-system thermochronometry and structural data. (United States)

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


    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.

  17. Carlsbad, San Onofre, and San Mateo Fault Zones: Possible Right-Lateral Offset Along the Slope-Basin Transition, Offshore Southern California (United States)

    Conrad, J. E.; Dartnell, P.; Sliter, R. W.; Ryan, H. F.; Maier, K. L.; Brothers, D. S.


    Several poorly understood faults are exposed along the mid- and lower slope offshore southern California from Encinitas to San Clemente. From south to north, these faults have been referred to as the Carlsbad, San Onofre, and San Mateo fault zones, which are generally characterized as nearly vertical to steeply east-dipping faults with a reverse slip component. The U.S. Geological Survey collected high-resolution seismic reflection and bathymetric data from 2009-2012 to better characterize these faults. From offshore Encinitas to Oceanside, these data reveal a complex and variable fault zone that structurally controls the slope-basin transition. In this area, the faults show both reverse as well as normal offset, but may also include an unknown amount of strike-slip offset. North of Oceanside, however, faulting shows clear evidence of right-lateral slip, offsetting submarine channels near the base of the slope by approximately 60 m. North of these offset channels, the base of the slope bends about 30° to the west, following the trend of the San Mateo fault zone, but fault strands on strike with those that offset the channels trend obliquely up slope, appearing to merge with the Newport-Inglewood fault zone (NIFZ) on the shelf. These fault strands consist of several en echelon left-stepping segments separated by "pop-up" structures, which imply a significant component of right-lateral offset along this fault zone, and thus may serve to transfer right-lateral slip from faults along the base of the slope to the NIFZ. This fault zone also separates structures associated with the San Mateo fold and thrust belt to the west from undeformed slope sediments to the east. The existence of significant right-lateral slip on faults along the slope and slope-basin transition has implications for assessing seismic hazards associated with the NIFZ, and also provides constraints on possible reverse motion on the hypothesized Oceanside Thrust.

  18. Internal structure of the San Jacinto fault zone at Jackass Flat from data recorded by a dense linear array (United States)

    Qiu, H.; Ben-Zion, Y.; Ross, Z. E.; Share, P.-E.; Vernon, F. L.


    The internal structure of the Clark fault in the trifurcation area of the San Jacinto fault zone is imaged using seismograms recorded by a dense linear array (Jackass Flat, JF) crossing the surface trace of the fault and an adjacent array (TR) to the SW. Delay times between phase arrivals associated with ∼3500 local earthquakes and nine teleseismic events are used to estimate velocity variations within the arrays. The teleseismic P waves travel faster beneath the TR than the JF array, in contrast to larger scale tomographic results. Statistical analysis of local P-wave delay times indicates that the entire JF array, with an aperture of ∼400 m, is inside a low-velocity damage zone. This low-velocity zone is bounded on the NE side by a shallow bimaterial interface generating fault zone head waves, and it contains an inner zone of more intense damage generating fault zone trapped waves. The P-wave velocity contrast across the local bounding bimaterial interface is 10-15 per cent. The trapping structure is associated with a width of ∼200 m, S-wave velocity reduction of ∼35 per cent with respect to the surrounding rock, Q-value of ∼20 and depth of ∼3.5 km. The imaging results suggest that the main seismogenic fault is near the SW end of the JF array, in agreement with a prominent geomorphologic feature. The existence of intense local damage on the crustal block with faster larger scale velocity at depth is consistent with common propagation of earthquake ruptures in the area to the NW.

  19. Subsurface fault damage zone of the 2014 Mw 6.0 South Napa, California, earthquake viewed from fault‐zone trapped waves (United States)

    Li, Yong-Gang; Catchings, Rufus D.; Goldman, Mark R.


    The aftershocks of the 24 August 2014 Mw 6.0 South Napa earthquake generated prominent fault‐zone trapped waves (FZTWs) that were recorded on two 1.9‐km‐long seismic arrays deployed across the northern projection (array 1, A1) and the southern part (A2) of the surface rupture of the West Napa fault zone (WNFZ). We also observed FZTWs on an array (A3) deployed across the intersection of the Franklin and Southampton faults, which appear to be the southward continuations of the WNFZ. A1, A2, and A3 consisted of 20, 20, and 10 L28 (4.5 Hz) three‐component seismographs. We analyzed waveforms of FZTWs from 55 aftershocks in both time and frequency to characterize the fault damage zone associated with this Mw 6.0 earthquake. Post‐S coda durations of FZTWs increase with epicentral distances and focal depths from the recording arrays, suggesting a low‐velocity waveguide along the WNFZ to depths in excess of 5–7 km. Locations of the aftershocks showing FZTWs, combined with 3D finite‐difference simulations, suggest the subsurface rupture zone having an S‐wave speed reduction of ∼40%–50% between A1 and A2, coincident with the ∼14‐km‐long mapped surface rupture zone and at least an ∼500‐m‐wide deformation zone. The low‐velocity waveguide along the WNFZ extends further southward to at least A3, but with a more moderate‐velocity reduction of 30%–35% at ray depth. This last FZTW observation suggests continuity between the WNFZ and Franklin fault. The waveguide effect may have localized and amplified ground shaking along the WNFZ and the faults farther to the south (see a companion paper by Catchings et al., 2016).

  20. Dating deformation - Lifetimes of phases vs. lifetimes of crystals and pulsed motion along fault zones (United States)

    Chakraborty, Sumit


    The timing of movement in a fault zone may be obtained either by dating minerals that grow in these zones or by determining the pressure - temperature - time history of the blocks lying on either side of the zone. Interpreting dates of minerals in the fault zone itself requires the assumption that the minerals grew during or close to the timing of movement, that there was a single pulse of movement, or that the ages have not been reset by later pulses of movement. Determining the P-T-t history of the overlying and underlying blocks, on the other hand, may provide a more comprehensive history but it is essential to determine exactly what stage of a P-T history is dated by a given isotopic system. In addition, information on lateral contiguity is missing from such data. Strengths and weaknesses of both approaches may be illustrated using a case study from the MCT zone in the Sikkim Himalaya. Lu-Hf dates of garnets from the underlying lesser Himalayan (LH) and overlying higher Himalayan (HH) rocks yield a systematic picture (Anczkiewicz et al., 2015), but the significance of these dates using the same isotopic system and same mineral are different in the two blocks. In the lower grade lesser Himalayan rocks, fractionated trace element patterns formed during growth of garnet are preserved. As a result, bulk of the Lu occurs at the cores of garnets and the well-defined ages mark the initiation of garnet growth along the prograde path rather than the peak of metamorphism in these rocks. In the higher grade HH rocks, although metamorphic temperatures were higher (750 - 800 °C) they did not cross the closure temperature of Lu and/or Hf diffusion in garnet. In these pelitic bulk compositions, growth of garnet is expected to have occurred at garnet grade conditions (~ 500 °C). Nevertheless, in the presence of melt and deformation, there is evidence that the garnet grains recrystallized and Lu was more homogeneously distributed within the grain. Therefore, the ages from

  1. Preliminary assessment of a previously unknown fault zone beneath the Daytona Beach sand blow cluster near Marianna, Arkansas (United States)

    Odum, Jackson K.; Williams, Robert; Stephenson, William J.; Tuttle, Martitia P.; Al-Shukri, Hadar


    We collected new high‐resolution P‐wave seismic‐reflection data to explore for possible faults beneath a roughly linear cluster of early to mid‐Holocene earthquake‐induced sand blows to the south of Marianna, Arkansas. The Daytona Beach sand blow deposits are located in east‐central Arkansas about 75 km southwest of Memphis, Tennessee, and about 80 km south of the southwestern end of the New Madrid seismic zone (NMSZ). Previous studies of these sand blows indicate that they were produced between 10,500 and 5350 yr B.P. (before A.D. 1950). The sand blows are large and similar in size to those in the heart of the NMSZ produced by the 1811–1812 earthquakes. The seismic‐reflection profiles reveal a previously unknown zone of near‐vertical faults imaged in the 100–1100‐m depth range that are approximately coincident with a cluster of earthquake‐induced sand blows and a near‐linear surface lineament composed of air photo tonal anomalies. These interpreted faults are expressed as vertical discontinuities with the largest displacement fault showing about 40 m of west‐side‐up displacement at the top of the Paleozoic section at about 1100 m depth. There are about 20 m of folding on reflections within the Eocene strata at 400 m depth. Increasing fault displacement with depth suggests long‐term recurrent faulting. The imaged faults within the vicinity of the numerous sand blow features could be a causative earthquake source, although it does not rule out the possibility of other seismic sources nearby. These newly located faults add to a growing list of potentially active Pleistocene–Holocene faults discovered over the last two decades that are within the Mississippi embayment region but outside of the historical NMSZ.

  2. Numerical reconstruction of Late-Cenosoic evolution of normal-fault scarps in Baikal Rift Zone (United States)

    Byzov, Leonid; San'kov, Vladimir


    Numerical landscape development modeling has recently become a popular tool in geo-logic and geomorphic investigations. We employed this technique to reconstruct Late-Cenosoic evolution of Baikal Rift Zone mountains. The objects of research were Barguzin Range and Svyatoy Nos Upland. These structures are formed under conditions of crustal extension and bounded by active normal faults. In our experiments we used instruments, engineered by Greg Tucker (University of Colo-rado) - CHILD (Channel-Hillslope Integrated Landscape Development) and 'Bedrock Fault Scarp'. First program allowed constructing the complex landscape model considering tectonic uplift, fluvial and hillslope processes; second program is used for more accurate simulating of triangular facet evolution. In general, our experiments consisted in testing of tectonic parameters, and climatic char-acteristic, erosion and diffusion properties, hydraulic geometry were practically constant except for some special runs. Numerous experiments, with various scenarios of development, showed that Barguzin range and Svyatoy Nos Upland has many common features. These structures characterized by internal differentiation, which appear in height and shape of slopes. At the same time, individual segments of these objects are very similar - this conclusion refers to most developing parts, with pronounced facets and V-shaped valleys. Accordingly modelling, these landscapes are in a steady state and are undergoing a uplift with rate 0,4 mm/yr since Early Pliocene (this solution accords with AFT-dating). Lower segments of Barguzin Range and Svyatoy Nos Upland also have some general fea-tures, but the reasons of such similarity probably are different. In particular, southern segment of Svyatoy Nos Upland, which characterized by relative high slope with very weak incision, may be formed as result very rapid fault movement or catastrophic landslide. On the other hand, a lower segment of Barguzin Range (Ulun segment, for example

  3. Fleeing to Fault Zones: Incorporating Syrian Refugees into Earthquake Risk Analysis along the East Anatolian and Dead Sea Rift Fault Zones (United States)

    Wilson, B.; Paradise, T. R.


    The influx of millions of Syrian refugees into Turkey has rapidly changed the population distribution along the Dead Sea Rift and East Anatolian Fault zones. In contrast to other countries in the Middle East where refugees are accommodated in camp environments, the majority of displaced individuals in Turkey are integrated into cities, towns, and villages—placing stress on urban settings and increasing potential exposure to strong shaking. Yet, displaced populations are not traditionally captured in data sources used in earthquake risk analysis or loss estimations. Accordingly, we present a district-level analysis assessing the spatial overlap of earthquake hazards and refugee locations in southeastern Turkey to determine how migration patterns are altering seismic risk in the region. Using migration estimates from the U.S. Humanitarian Information Unit, we create three district-level population scenarios that combine official population statistics, refugee camp populations, and low, median, and high bounds for integrated refugee populations. We perform probabilistic seismic hazard analysis alongside these population scenarios to map spatial variations in seismic risk between 2011 and late 2015. Our results show a significant relative southward increase of seismic risk for this period due to refugee migration. Additionally, we calculate earthquake fatalities for simulated earthquakes using a semi-empirical loss estimation technique to determine degree of under-estimation resulting from forgoing migration data in loss modeling. We find that including refugee populations increased casualties by 11-12% using median population estimates, and upwards of 20% using high population estimates. These results communicate the ongoing importance of placing environmental hazards in their appropriate regional and temporal context which unites physical, political, cultural, and socio-economic landscapes. Keywords: Earthquakes, Hazards, Loss-Estimation, Syrian Crisis, Migration

  4. Intermittent tremor migrations beneath Guerrero, Mexico, and implications for fault healing within the slow slip zone (United States)

    Peng, Yajun; Rubin, Allan M.


    Slow slip events exhibit significant complexity in slip evolution and variations in recurrence intervals. Behavior that varies systematically with recurrence interval is likely to reflect different extents of fault healing between these events. Here we use high-resolution tremor catalogs beneath Guerrero, Mexico, to investigate the mechanics of slow slip. We observe complex tremor propagation styles, including rapid tremor migrations propagating either along the main tremor front or backward, reminiscent of those in northern Cascadia. We also find many migrations that originate well behind the front and repeatedly occupy the same source region during a tremor episode, similar to those previously reported from Shikoku, Japan. These migrations could be driven by slow slip in the surrounding regions, with recurrence intervals possibly modulated by tides. The propagation speed of these migrations decreases systematically with time since the previous migration over the same source area. Tremor amplitudes seem consistent with changes in the propagation speeds being controlled primarily by changes in the slip speeds. One interpretation is that the high propagation speeds and inferred high slip speeds during the migrations with short recurrence intervals are caused by incomplete healing within the host rock adjacent to the shear zone, which could lead to high permeability and reduced dilatant strengthening of the fault gouge. Similar processes may operate in other slow slip source regions such as Cascadia.

  5. Comparision of the different probability distributions for earthquake hazard assessment in the North Anatolian Fault Zone (United States)

    Yilmaz, Şeyda; Bayrak, Erdem; Bayrak, Yusuf


    In this study we examined and compared the three different probabilistic distribution methods for determining the best suitable model in probabilistic assessment of earthquake hazards. We analyzed a reliable homogeneous earthquake catalogue between a time period 1900-2015 for magnitude M ≥ 6.0 and estimated the probabilistic seismic hazard in the North Anatolian Fault zone (39°-41° N 30°-40° E) using three distribution methods namely Weibull distribution, Frechet distribution and three-parameter Weibull distribution. The distribution parameters suitability was evaluated Kolmogorov-Smirnov (K-S) goodness-of-fit test. We also compared the estimated cumulative probability and the conditional probabilities of occurrence of earthquakes for different elapsed time using these three distribution methods. We used Easyfit and Matlab software to calculate these distribution parameters and plotted the conditional probability curves. We concluded that the Weibull distribution method was the most suitable than other distribution methods in this region.

  6. Comparision of the different probability distributions for earthquake hazard assessment in the North Anatolian Fault Zone

    Energy Technology Data Exchange (ETDEWEB)

    Yilmaz, Şeyda, E-mail:; Bayrak, Erdem, E-mail: [Karadeniz Technical University, Trabzon (Turkey); Bayrak, Yusuf, E-mail: [Ağrı İbrahim Çeçen University, Ağrı (Turkey)


    In this study we examined and compared the three different probabilistic distribution methods for determining the best suitable model in probabilistic assessment of earthquake hazards. We analyzed a reliable homogeneous earthquake catalogue between a time period 1900-2015 for magnitude M ≥ 6.0 and estimated the probabilistic seismic hazard in the North Anatolian Fault zone (39°-41° N 30°-40° E) using three distribution methods namely Weibull distribution, Frechet distribution and three-parameter Weibull distribution. The distribution parameters suitability was evaluated Kolmogorov-Smirnov (K-S) goodness-of-fit test. We also compared the estimated cumulative probability and the conditional probabilities of occurrence of earthquakes for different elapsed time using these three distribution methods. We used Easyfit and Matlab software to calculate these distribution parameters and plotted the conditional probability curves. We concluded that the Weibull distribution method was the most suitable than other distribution methods in this region.

  7. Application of chaos analyses methods on East Anatolian Fault Zone fractures

    Energy Technology Data Exchange (ETDEWEB)

    Kamışlıoğlu, Miraç, E-mail:; Külahcı, Fatih, E-mail: [Nuclear Physics Division, Department of Physics, Faculty of Science, Fırat University, Elazig, TR-23119 (Turkey)


    Nonlinear time series analysis techniques have large application areas on the geoscience and geophysics fields. Modern nonlinear methods are provided considerable evidence for explain seismicity phenomena. In this study nonlinear time series analysis, fractal analysis and spectral analysis have been carried out for researching the chaotic behaviors of release radon gas ({sup 222}Rn) concentration occurring during seismic events. Nonlinear time series analysis methods (Lyapunov exponent, Hurst phenomenon, correlation dimension and false nearest neighbor) were applied for East Anatolian Fault Zone (EAFZ) Turkey and its surroundings where there are about 35,136 the radon measurements for each region. In this paper were investigated of {sup 222}Rn behavior which it’s used in earthquake prediction studies.


    Directory of Open Access Journals (Sweden)

    V. Ya. Medvedev


    Full Text Available The article presents results of petrophysical laboratory experiments in studies of decompression phenomena associated with consequences of abrupt displacements in fault zones. Decompression was studied in cases of controlled pressure drop that caused sharp changes of porosity and permeability parameters, and impacts of such decompression were analyzed. Healing of fractured-porous medium by newly formed phases was studied. After experiments with decompression, healing of fractures and pores in silicate rock samples (3×2×2 cm, 500 °C, 100 MPa took about 800–1000 hours, and strength of such rocks was restored to 0.6–0.7 of the original value. In nature, fracture healing is influenced by a variety of factors, such as size of discontinuities in rock masses, pressure and temperature conditions, pressure drop gradients, rock composition and saturation with fluid. Impacts of such factors are reviewed.

  9. Application of natural isotope tracers to geothermal research in the Maechan fault zone (N Thailand) (United States)

    Yongprawat, Monthon; Kamdee, Kiatipong; Sauter, Martin; Wiegand, Bettina


    Previous geothermal research in Thailand has mainly focused on high-potential geothermal systems such as the active Maechan fault zone, which is located in the northern part of the country. Fang and Maechan hot springs have been the primary targets for power generation and agricultural applications (Apollaro et al. 2015). Here we present a comprehensive survey of chemical and isotopic compositions of thermal waters from six hot springs, well water, and cold surface water samples. This study aims to identify sources of the geothermal waters, hydrodynamic processes and the thermal capacity of the hot springs along the Maechan fault zone. Field parameters, major ions, stable isotopes of hydrogen, oxygen, and carbon, as well as radiocarbon and tritium were investigated. The chemical composition of both thermal waters and cold surface waters is dominated by the Na-HCO3 type. δ2HSMOW and δ18OSMOW data of thermal water and cold surface water plot along a local meteoric water line, suggesting local precipitation as the source of thermal water in the area. δ13CPDB values between -4 to -16 ‰ indicate that dissolved carbon in the thermal water samples is mainly from inorganic carbon sources but some mixture with organic carbon may occur. Radiocarbon analyses (10-20 pMC) suggest ages of more than 10,000 years for the formation of the thermal waters. Tritium concentrations range between 0-0.2 TU. Bibliography Apollaro, C., Vespasiano, G., De Rosa, R., Marini, L. Use of Mean Residence Time and Flowrate of Thermal Waters to Evaluate the Volume of Reservoir Water Contributing to the Natural Discharge and the Related Geothermal Reservoir Volume. Application to Northern Thailand Hot Springs." Geothermics 58: 62-74. 2015.

  10. Fine-scale delineation of the location of and relative ground shaking within the San Andreas Fault zone at San Andreas Lake, San Mateo County, California (United States)

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


    The San Francisco Public Utilities Commission is seismically retrofitting the water delivery system at San Andreas Lake, San Mateo County, California, where the reservoir intake system crosses the San Andreas Fault (SAF). The near-surface fault location and geometry are important considerations in the retrofit effort. Because the SAF trends through highly distorted Franciscan mélange and beneath much of the reservoir, the exact trace of the 1906 surface rupture is difficult to determine from surface mapping at San Andreas Lake. Based on surface mapping, it also is unclear if there are additional fault splays that extend northeast or southwest of the main surface rupture. To better understand the fault structure at San Andreas Lake, the U.S. Geological Survey acquired a series of seismic imaging profiles across the SAF at San Andreas Lake in 2008, 2009, and 2011, when the lake level was near historical lows and the surface traces of the SAF were exposed for the first time in decades. We used multiple seismic methods to locate the main 1906 rupture zone and fault splays within about 100 meters northeast of the main rupture zone. Our seismic observations are internally consistent, and our seismic indicators of faulting generally correlate with fault locations inferred from surface mapping. We also tested the accuracy of our seismic methods by comparing our seismically located faults with surface ruptures mapped by Schussler (1906) immediately after the April 18, 1906 San Francisco earthquake of approximate magnitude 7.9; our seismically determined fault locations were highly accurate. Near the reservoir intake facility at San Andreas Lake, our seismic data indicate the main 1906 surface rupture zone consists of at least three near-surface fault traces. Movement on multiple fault traces can have appreciable engineering significance because, unlike movement on a single strike-slip fault trace, differential movement on multiple fault traces may exert compressive and

  11. Constraining deformation history and recent activity along the Tuz Gölü fault zone, Central Anatolia, Turkey (United States)

    Krystopowicz, N. J.; Schoenbohm, L. M.; Cosca, M. A.


    The 200 km long, dextral, transtensive Tuz Gölü fault zone is a prominent northwest-striking feature in Central Anatolia. It is one of the most significant structures in Central Anatolia in that it lies within the transition zone between the Western Anatolian Extensional Province and the Eastern Anatolian Contractional Province; its study therefore offers valuable insight into how Central Anatolia is affected by lateral extrusion related to collision in the east, and gravitational pull forces associated with subduction in the west. Proposals for the initiation of the Tuz Gölü fault zone range from Cretaceous to Neogene times, and the amount of recent activity along this fault system remains poorly constrained. Furthermore, potential basinward migration of deformation into the Tuz Gölü basin poses the question as to whether or not this fault system is active in the Holocene. Previous work suggests that migration of deformation towards the basin interior may be related to lithospheric-scale processes such as plateau development, microplate extrusion, or the onset of crustal thinning associated with slab-tear propagation in subducting African lithosphere. In this study, we use a combination of paleostress and morpho-tectonic analysis to further delineate the segmentation and present activity of the Tuz Gölü fault zone. Paleostress analysis offers insight into the deformation history of the region as well as the modern-day stress regime. We conducted a morphometric analysis of over 300 drainage basins along the range-front, which reveal variations that characterize the unique development of numerous fault strands in the region. Statistical analysis of hypsometric curves, systematic variation in basin morphology and orientation, as well as changes in mountain-front sinuosity reveal fault segmentation. Additionally, field mapping and Ar-Ar dating of offset lava flows from the Hasan Dag Volcano quantitatively constrain slip-rates in the southeastern portion of the

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

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, A.M.; Johnson, N.A.; Johnson, K.M.; Wei, W. [Purdue Univ., West Lafayette, IN (United States). Dept. of Earth and Atmospheric Sciences; Fleming, R.W. [Geological Survey, Denver, CO (United States); Cruikshank, K.M. [Portland State Univ., OR (United States). Dept. of Geology; Martosudarmo, S.Y. [BPP Technologi, Jakarta (Indonesia)


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

  13. Paleoseismology of the Southern Section of the Black Mountains and Southern Death Valley Fault Zones, Death Valley, United States (United States)

    Sohn, Marsha S.; Knott, Jeffrey R.; Mahan, Shannon


    The Death Valley Fault System (DVFS) is part of the southern Walker Lane–eastern California shear zone. The normal Black Mountains Fault Zone (BMFZ) and the right-lateral Southern Death Valley Fault Zone (SDVFZ) are two components of the DVFS. Estimates of late Pleistocene-Holocene slip rates and recurrence intervals for these two fault zones are uncertain owing to poor relative age control. The BMFZ southernmost section (Section 1W) steps basinward and preserves multiple scarps in the Quaternary alluvial fans. We present optically stimulated luminescence (OSL) dates ranging from 27 to 4 ka of fluvial and eolian sand lenses interbedded with alluvial-fan deposits offset by the BMFZ. By cross-cutting relations, we infer that there were three separate ground-rupturing earthquakes on BMFZ Section 1W with vertical displacement between 5.5 m and 2.75 m. The slip-rate estimate is ∼0.2 to 1.8 mm/yr, with an earthquake recurrence interval of 4,500 to 2,000 years. Slip-per-event measurements indicate Mw 7.0 to 7.2 earthquakes. The 27–4-ka OSL-dated alluvial fans also overlie the putative Cinder Hill tephra layer. Cinder Hill is offset ∼213 m by SDVFZ, which yields a tentative slip rate of 1 to 8 mm/yr for the SDVFZ.

  14. Monitoring in situ deformation induced by a fluid injection in a fault zone in shale using seismic velocity changes (United States)

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


    We monitor seismic velocity changes during an experiment at decametric scale aimed at artificially reactivate a fault zone by a high-pressure hydraulic injection in a shale formation of the underground site of Tournemire, South of France. A dense and a multidisciplinary instrumentation, with measures of pressure, fluid flow, strain, seismicity, seismic properties and resistivity allow for the monitoring of this experiment. We couple hydromechanical and seismic observations of the fault and its adjacent areas to better understand the deformation process preceding ruptures, and the role played by fluids. 9 accelerometers recorded repeated hammers shots on the tunnel walls. For each hammer shot we measured small travel time delays on direct P and S waves. We then located the seismic velocity perturbations using a tomography method. At low injection pressure, i.e. P< 15 Bars, we observe an increase of P-waves velocity around the injection, while we measure no change in S waves velocity. When the pressure overcomes 15 Bars, velocity perturbations dramatically increase with both P and S waves affected. A decrease of velocity is observed close to the injection point and is surrounded by regions of increasing velocity. Our observations are consistent with hydromechanical measures. Below 15 Bars, we interpret the P-wave velocity increase to be related to the compression of the fault zone around the injection chamber. Above 15 Bars, we measure a shear and dilatant fault movement, and a rapid increase in the injected fluid flow. At this step, our measures are coherent with a poroelastic opening of the fault with velocities decrease at the injection source and velocities increase related to stress transfer in the far field. Velocity changes prove to be efficient to monitor stress/strain variation in an activated fault, even if these observations might produce complex signals due to the highly contrasted hydromechanical responses in a heterogeneous media such as a fault zone.

  15. Evidence of Coseismic Subsidence Along the Newport-Inglewood Fault Zone During the Late Holocene (United States)

    Leeper, R. J.; Rhodes, B. P.; Kirby, M. E.; Scharer, K. M.; Starratt, S.; Hemphill-Haley, E.; Bonuso, N.; Balmaki, B.; Garcia, D. J.; Creager, D. O.


    The Seal Beach wetlands (SBW) are located along strike of the Newport-Inglewood fault zone (NIFZ), where fault geometry is poorly understood. However, the fault steps to the right in the SBW, and oil well and seismological studies indicate that the northeast segment of the fault is down-dropped as a result of oblique-normal slip. The location is significant because coseismic subsidence could alter tidal and/or fluvial processes within the SBW. Such a change should be recorded in the stratigraphy by sudden changes in grain size, magnetic susceptibility, and/or diatom assemblages. Based on field observations of 48 reconnaissance gouge cores and multi-proxy analyses of three vibracores and one piston core, we identify four stratigraphic units in the SBW: (1) very fine to fine sand from 426-350 cm; (2) organic-rich mud from 350-225 cm; (3) fine to coarse silt and clay from 225-100 cm; and (4) organic-rich mud with interbedded mud laminae from 100-0 cm. We interpret unit 2 to represent a relic marsh surface that subsided coseismically and was preserved under unit 3. We analyzed 38 sediment samples for diatoms from vibracore SB002VC to test this idea and characterize the depositional environment of stratigraphic units 4, 3, and 2. The diatom data suggest unit 4 is an intertidal deposit, unit 3 is a fresh/slightly brackish water deposit, and unit 2 is an intertidal deposit. Units 2 and 3 are separated by a sharp, irregular contact. Thus, the diatom data and depositional contact from vibracore SB002VC are consistent with a relic marsh surface subsiding abruptly during an earthquake on the NIFZ. As a result of the earthquake, the intertidal environment abruptly changed to an environment dominated by fresh to slightly brackish water. We hypothesize that the earthquake did not result in flooding by seawater because coseismic uplift of the southwest segment of the NIFZ temporarily isolated the SBW from tidal influence. Radiocarbon dates constrain this event to no more than

  16. Assessment and geomodelling of site effects along the eastern Enriquillo Plantain Garden Fault Zone in Haiti (United States)

    Ulysse, S. M. J.; Havenith, H. B.; Boisson, D.


    The last 2010 earthquake which hits Haiti killed more than 230,000 people, caused nearly 300,000 wounded and material damage of more than 8 billion dollars. This event whose epicenter was located in Léogâne, to the west of Port-au-Prince was triggered by a north dipping fault, the "Léogâne fault", near and to the north of the Enriquillo Plantain Garden Fault (EPGF), a very hazardous fault system crossing the southern part of the country. Several large international projects were carried out in Port-au-Prince and Léogâne. Our work which is done in the frame of a Belgian-Haitian collaboration project rather focused on an eastern region of Port-au-Prince, Fonds-Parisien and a site called Gros-Morne in the southeast of the city. The Fonds-Parisien area is crossed by the eastern part of EPGF. The north of the area is bordered by a sedimentary basin hosting the Azuei Lake and to the south it is bounded by the foothills of a mountain range, the "Massif de la Selle". The Gros-Morne zone is also situated nearby the EPGF and is limited to the north by the Cul-de-Sac plain, a sedimentary basin and to the south, by the foothills of the "Massif de la Selle". We performed local geophysical investigations to assess site effects 1) in areas relatively far from the epicenter, not intensively hit by the 2010 event, to see if they may fit for future construction projects, 2) on a hill in the southeastern part of Port-au-Prince that was affected by important destruction and secondary effects. Multichannel Analysis of Surface Waves (MASW), Horizontal to Vertical Spectral Ratio (HVSR) measurements as well as some Electrical Resistivity Tomography (ERT) were applied. The results were integrated to outline areas that are affected by site amplification and then combined into a 3D geomodel. For Fonds-Parisien, HVSR recordings show sharp and double amplitude peaks for sites located in the northern sedimentary basin along the shores of Azuei Lake, and consequently denotes a high

  17. Landforms along transverse faults parallel to axial zone of folded mountain front, north-eastern Kumaun Sub-Himalaya, India (United States)

    Luirei, Khayingshing; Bhakuni, S. S.; Negi, Sanjay S.


    The shape of the frontal part of the Himalaya around the north-eastern corner of the Kumaun Sub-Himalaya, along the Kali River valley, is defined by folded hanging wall rocks of the Himalayan Frontal Thrust (HFT). Two parallel faults (Kalaunia and Tanakpur faults) trace along the axial zone of the folded HFT. Between these faults, the hinge zone of this transverse fold is relatively straight and along these faults, the beds abruptly change their attitudes and their widths are tectonically attenuated across two hinge lines of fold. The area is constituted of various surfaces of coalescing fans and terraces. Fans comprise predominantly of sandstone clasts laid down by the steep-gradient streams originating from the Siwalik range. The alluvial fans are characterised by compound and superimposed fans with high relief, which are generated by the tectonic activities associated with the thrusting along the HFT. The truncated fan along the HFT has formed a 100 m high-escarpment running E-W for ˜5 km. Quaternary terrace deposits suggest two phases of tectonic uplift in the basal part of the hanging wall block of the HFT dipping towards the north. The first phase is represented by tilting of the terrace sediments by ˜30 ∘ towards the NW; while the second phase is evident from deformed structures in the terrace deposit comprising mainly of reverse faults, fault propagation folds, convolute laminations, flower structures and back thrust faults. The second phase produced ˜1.0 m offset of stratification of the terrace along a thrust fault. Tectonic escarpments are recognised across the splay thrust near south of the HFT trace. The south facing hill slopes exhibit numerous landslides along active channels incising the hanging wall rocks of the HFT. The study area shows weak seismicity. The major Moradabad Fault crosses near the study area. This transverse fault may have suppressed the seismicity in the Tanakpur area, and the movement along the Moradabad and Kasganj

  18. South Pole Fault Zone, 900 km long and almost through the pole (United States)

    Wise, D. U.; Cianfarra, P.; Salvini, F.


    The most prominent feature of snow and ice topography of the East Antarctic Plateau is the 850 x 1100 km Pensacola Basin, named for the mountain range at its mouth. The basin's headwall is a remarkably linear 900 km-long, 100 -200 km-wide zone wherein snow surface slopes of 3 m/km contrast with values of 1 m/km on either side, a total relief of 200 to 400 meters. About 700 km of this slope lies along the 35th meridian, the remainder continuing through the pole for another 200 km. Satellite images show an easily mapped zebra-striped snow unit occurs throughout the basin and beyond. The stripes are well-known from other areas as megadunes, enigmatic, upwind climbing dunes of alternating snow and ice bands with 2 km wavelength and only 1-4 m amplitude. Superposition relationships show this unit is the bottom member of a four-unit snow stratigraphy, the basis for the first geologic map of the youngest snow units of the South Pole region. The megadune stripes are draped obliquely down over the headwall slope to disappear beneath younger snow fill of the Recovery Basin at its foot before cropping out again on the floor of the main basin. Nearer the pole, the slope forms the edge of a 15,000 km2 triangular plateau, the pole located half-way down the slope. Megadune stripes from higher elevations disappear beneath younger snows of the small basin and the pole to reappear on the floor of the main basin as ghosts of megadune stripes. Farther out on the floor they emerge from beneath this thin cover as fully exposed megadune stripes. An overlay of the snow- geologic map across the relatively low resolution maps of bedrock topography shows the surface slope separates two domains of contrasting bedrock topography, the lower elevation domain corresponding to the basin floor. The most likely explanation for this remarkably linear snow slope is flow of ice over a previously unrecognized 200-400 m-high, 900 km-long bedrock fault-line scarp. Along its distal end, the surface slope

  19. Paleo-asperities frozen along a major fault zone in Alpine Corsica ophiolites: Implications on present-day subduction zone intermediate-depth seismicity (United States)

    Fabbri, Olivier; Magott, Rémi; Fournier, Marc


    In an ophiolitic thrust sheet of Alpine Corsica, a major fault zone called PHI2 separates oceanic gabbros from variably serpentinized peridotites. Along and near PHI2, abundant pseudotachylytes testify to ancient seismic ruptures. A mineralogical and structural analysis of the pseudotachylyte veins shows that seismic ruptures occurred at various stages before, during or after the subduction process. Due to the lack of index minerals, P-T conditions of formation of peridotite-hosted pseudotachylyte remain undetermined. Conversely, two populations of gabbro-hosted pseudotachylyte veins can be distinguished: veins formed under blueschist to eclogite facies conditions (containing glaucophane and omphacite) and veins formed under greenschist facies conditions (containing tremolite, clinochlore and clinozoisite). Various kinematic indicators show that the blueschist to eclogite facies pseudotachylyte veins formed within the subducting Piemonte-Liguria oceanic lithosphere at depths of about 60 km, while the greenschist facies veins formed during syn- to post-collisional crustal extension. Detailed mapping indicates that the internal structure of PHI2 fault zone is spatially heterogeneous. A-type damage zones, which are located between gabbro and fresh (not serpentinized) peridotite, are characterized by pseudotachylyte accumulations and are interpreted as ancient fully locked asperities. To the opposite, type C damage zones, observed between gabbro and fully serpentinized peridotites, are characterized by the lack of pseudotachylytes and the presence of cataclasite and mineralized veins, and are regarded as creeping, aseismic, domains. B type damage zones, found between gabbro and moderately serpentinized peridotites, are outlined by pseudotachylytes, but in significantly less amounts than along A-type zones. These zones, intermediate between the other two types, could correspond to partially locked (conditionally stable) portions of the fault zone. The distribution of

  20. Coulomb stress interactions among M≥5.9 earthquakes in the Gorda deformation zone and on the Mendocino Fracture Zone, Cascadia megathrust, and northern San Andreas fault (United States)

    Rollins, John C.; Stein, Ross S.


    The Gorda deformation zone, a 50,000 km2 area of diffuse shear and rotation offshore northernmost California, has been the site of 20 M ≥ 5.9 earthquakes on four different fault orientations since 1976, including four M ≥ 7 shocks. This is the highest rate of large earthquakes in the contiguous United States. We calculate that the source faults of six recent M ≥ 5.9 earthquakes had experienced ≥0.6 bar Coulomb stress increases imparted by earthquakes that struck less than 9 months beforehand. Control tests indicate that ≥0.6 bar Coulomb stress interactions between M ≥ 5.9 earthquakes separated by Mw = 7.3 Trinidad earthquake are consistent with the locations of M ≥ 5.9 earthquakes in the Gorda zone until at least 1995, as well as earthquakes on the Mendocino Fault Zone in 1994 and 2000. Coulomb stress changes imparted by the 1980 earthquake are also consistent with its distinct elbow-shaped aftershock pattern. From these observations, we derive generalized static stress interactions among right-lateral, left-lateral and thrust faults near triple junctions.

  1. Comparative mineral chemistry and textures of SAFOD fault gouge and damage-zone rocks (United States)

    Moore, Diane E.


    Creep in the San Andreas Fault Observatory at Depth (SAFOD) drillhole is localized to two foliated gouges, the central deforming zone (CDZ) and southwest deforming zone (SDZ). The gouges consist of porphyroclasts of serpentinite and sedimentary rock dispersed in a foliated matrix of Mg-smectite clays that formed as a result of shearing-enhanced reactions between the serpentinite and quartzofeldspathic rocks. The CDZ takes up most of the creep and exhibits differences in mineralogy and texture from the SDZ that are attributable to its higher shearing rate. In addition, a ∼0.2-m-wide sector of the CDZ at its northeastern margin (NE-CDZ) is identical to the SDZ and may represent a gradient in creep rate across the CDZ. The SDZ and NE-CDZ have lower clay contents and larger porphyroclasts than most of the CDZ, and they contain veinlets and strain fringes of calcite in the gouge matrix not seen elsewhere in the CDZ. Matrix clays in the SDZ and NE-CDZ are saponite and corrensite, whereas the rest of the CDZ lacks corrensite. Saponite is younger than corrensite, reflecting clay crystallization under declining temperatures, and clays in the more actively deforming portions of the CDZ have better equilibrated to the lower-temperature conditions.

  2. Deep postseismic viscoelastic relaxation excited by an intraslab normal fault earthquake in the Chile subduction zone (United States)

    Bie, Lidong; Ryder, Isabelle; Métois, Marianne


    The 2005 Mw 7.8 Tarapaca earthquake was the result of normal faulting on a west-dipping plane at a depth of 90 km within the subducting slab down-dip of the North Chilean gap that partially ruptured in the 2014 M 8.2 Iquique earthquake. We use Envisat observations of nearly four years of postseismic deformation following the earthquake, together with some survey GPS measurements, to investigate the viscoelastic relaxation response of the surrounding upper mantle to the coseismic stress. We constrain the rheological structure by testing various 3D models, taking into account the vertical and lateral heterogeneities in viscosity that one would expect in a subduction zone environment. A viscosity of 4-8 × 1018 Pa s for the continental mantle asthenosphere fits both InSAR line-of-sight (LOS) and GPS horizontal displacements reasonably well. In order to test whether the Tarapaca earthquake and associated postseismic relaxation could have triggered the 2014 Iquique sequence, we computed the Coulomb stress change induced by the co- and postseismic deformation following the Tarapaca earthquake on the megathrust interface and nodal planes of its M 6.7 foreshock. These static stress calculations show that the Tarapaca earthquake may have an indirect influence on the Iquique earthquake, via loading of the M 6.7 preshock positively. We demonstrate the feasibility of using deep intraslab earthquakes to constrain subduction zone rheology. Continuing geodetic observation following the 2014 Iquique earthquake may further validate the rheological parameters obtained here.

  3. Stratigraphic record of Pliocene-Pleistocene basin evolution and deformation within the Southern San Andreas Fault Zone, Mecca Hills, California (United States)

    McNabb, James C.; Dorsey, Rebecca J.; Housen, Bernard A.; Dimitroff, Cassidy W.; Messé, Graham T.


    A thick section of Pliocene-Pleistocene nonmarine sedimentary rocks exposed in the Mecca Hills, California, provides a record of fault-zone evolution along the Coachella Valley segment of the San Andreas fault (SAF). Geologic mapping, measured sections, detailed sedimentology, and paleomagnetic data document a 3-5 Myr history of deformation and sedimentation in this area. SW-side down offset on the Painted Canyon fault (PCF) starting 3.7 Ma resulted in deposition of the Mecca Conglomerate southwest of the fault. The lower member of the Palm Spring Formation accumulated across the PCF from 3.0 to 2.6 Ma during regional subsidence. SW-side up slip on the PCF and related transpressive deformation from 2.6 to 2.3 Ma created a time-transgressive angular unconformity between the lower and upper members of the Palm Spring Formation. The upper member accumulated in discrete fault-bounded depocenters until initiation of modern deformation, uplift, and basin inversion starting at 0.7 Ma. Some spatially restricted deposits can be attributed to the evolution of fault-zone geometric complexities. However, the deformation events at ca. 2.6 Ma and 0.7 Ma are recorded regionally along 80 km of the SAF through Coachella Valley, covering an area much larger than mapped fault-zone irregularities, and thus require regional explanations. We therefore conclude that late Cenozoic deformation and sedimentation along the SAF in Coachella Valley has been controlled by a combination of regional tectonic drivers and local deformation due to dextral slip through fault-zone complexities. We further propose a kinematic link between the 2.6-2.3 Ma angular unconformity and a previously documented but poorly dated reorganization of plate-boundary faults in the northern Gulf of California at 3.3-2.0 Ma. This analysis highlights the potential for high-precision chronologies in deformed terrestrial deposits to provide improved understanding of local- to regional-scale structural controls on basin

  4. Raman spectra of carbonaceous materials in a fault zone in the Longmenshan thrust belt, China; comparisons with those of sedimentary and metamorphic rocks (United States)

    Kouketsu, Yui; Shimizu, Ichiko; Wang, Yu; Yao, Lu; Ma, Shengli; Shimamoto, Toshihiko


    We analyzed micro-Raman spectra of carbonaceous materials (CM) in natural and experimentally deformed fault rocks from Longmenshan fault zone that caused the 2008 Wenchuan earthquake, to characterize degree of disordering of CM in a fault zone. Raman spectral parameters for 12 samples from a fault zone in Shenxigou, Sichuan, China, all show low-grade structures with no graphite. Low crystallinity and δ13C values (-24‰ to -25‰) suggest that CM in fault zone originated from host rocks (Late Triassic Xujiahe Formation). Full width at half maximum values of main spectral bands (D1 and D2), and relative intensities of two subbands (D3 and D4) of CM were variable with sample locations. However, Raman parameters of measured fault rocks fall on established trends of graphitization in sedimentary and metamorphic rocks. An empirical geothermometer gives temperatures of 160-230 °C for fault rocks in Shenxigou, and these temperatures were lower for highly sheared gouge than those for less deformed fault breccia at inner parts of the fault zone. The lower temperature and less crystallinity of CM in gouge might have been caused by the mechanical destruction of CM by severe shearing deformation, or may be due to mixing of host rocks on the footwall. CM in gouge deformed in high-velocity experiments exhibits slight changes towards graphitization characterized by reduction of D3 and D4 intensities. Thus low crystallinity of CM in natural gouge cannot be explained by our experimental results. Graphite formation during seismic fault motion is extremely local or did not occur in the study area, and the CM crystallinity from shallow to deep fault zones may be predicted as a first approximation from the graphitization trend in sedimentary and metamorphic rocks. If that case, graphite may lower the friction of shear zones at temperatures above 300 °C, deeper than the lower part of seismogenic zone.

  5. Advanced Seismic Imaging Techniques Characterize the Alpine Fault at Whataroa (New Zealand) (United States)

    Lay, V.; Buske, S.; Lukács, A.; Gorman, A. R.; Bannister, S. C.


    The plate-bounding Alpine Fault in New Zealand is a large transpressive continental fault zone that is late in its earthquake cycle. The Deep Fault Drilling Project (DFDP) aims to deliver insight into the geological structure of this fault zone and its evolution by drilling and sampling the Alpine Fault at depth. We have acquired and processed reflection seismic data to image the subsurface around the drill site. The resulting velocity models and seismic images of the upper 5 km show complex subsurface structures around the Alpine Fault zone. The most prominent feature is a strong reflector at depths of 1.2-2.2 km with a dip of ~40° to the southeast below the DFDP-2 borehole, which we assume to be the main trace of the Alpine Fault. The reflector exhibits varying lateral reflectivity along its extent. Additionally, subparallel reflectors are imaged that we interpret as secondary branches of the main fault zone. The derived P-wave velocity models reveal a 400-600 m thick sedimentary layer with velocities of ~2.3 km/s above a schist basement with velocities of 4.5-5.5 km/s. A pronounced low-velocity layer with velocities of approximately 3.5 km/s can be observed within the basement at 0.8-2 km depth. Small-scale low-velocity anomalies appear at the top of the basement and can be correlated to the fault zone. The results provide a reliable basis for a seismic site characterization at the DFDP-2 drill site that can be used for further structural and geological investigations of the architecture of the Alpine Fault in this area.

  6. Reconstruction of the Earthquake History of Limestone Fault Scarps in Knidos Fault Zone Using in-situ Chlorine-36 Exposure Dating and "R" Programming Language (United States)

    Sahin, Sefa; Yildirim, Cengiz; Akif Sarikaya, Mehmet; Tuysuz, Okan; Genc, S. Can; Ersen Aksoy, Murat; Ertekin Doksanalti, Mustafa


    Cosmogenic surface exposure dating is based on the production of rare nuclides in exposed rocks, which interact with cosmic rays. Through modelling of measured 36Cl concentrations, we might obtain information of the history of the earthquake activity. Yet, there are several factors which may impact production of rare nuclides such as geometry of the fault, topography, geographic location of the study area, temporal variations of the Earth's magnetic field, self-cover and denudation rate on the scarp. Recently developed models provides a method to infer timing of earthquakes and slip rates on limited scales by taking into account these parameters. Our study area, the Knidos Fault Zone, is located on the Datça Peninsula in Southwestern Anatolia and contains several normal fault scarps formed within the limestone, which are appropriate to generate cosmogenic chlorine-36 (36Cl) dating models. Since it has a well-preserved scarp, we have focused on the Mezarlık Segment of the fault zone, which has an average length of 300 m and height 12-15 m. 128 continuous samples from top to bottom of the fault scarp were collected to carry out analysis of cosmic 36Cl isotopes concentrations. The main purpose of this study is to analyze factors affecting the production rates and amount of cosmogenic 36Cl nuclides concentration. Concentration of Cl36 isotopes are measured by AMS laboratories. Through the local production rates and concentration of the cosmic isotopes, we can calculate exposure ages of the samples. Recent research elucidated each step of the application of this method by the Matlab programming language (e.g. Schlagenhauf et al., 2010). It is vitally helpful to generate models of Quaternary activity of the normal faults. We, however, wanted to build a user-friendly program through an open source programing language "R" (GNU Project) that might be able to help those without knowledge of complex math programming, making calculations as easy and understandable as

  7. The Iceland Plate Boundary Zone: Propagating Rifts, Migrating Transforms, and Rift-Parallel Strike-Slip Faults (United States)

    Karson, J. A.


    Unlike most of the Mid-Atlantic Ridge, the North America/Eurasia plate boundary in Iceland lies above sea level where magmatic and tectonic processes can be directly investigated in subaerial exposures. Accordingly, geologic processes in Iceland have long been recognized as possible analogs for seafloor spreading in the submerged parts of the mid-ocean ridge system. Combining existing and new data from across Iceland provides an integrated view of this active, mostly subaerial plate boundary. The broad Iceland plate boundary zone includes segmented rift zones linked by transform fault zones. Rift propagation and transform fault migration away from the Iceland hotspot rearrange the plate boundary configuration resulting in widespread deformation of older crust and reactivation of spreading-related structures. Rift propagation results in block rotations that are accommodated by widespread, rift-parallel, strike-slip faulting. The geometry and kinematics of faulting in Iceland may have implications for spreading processes elsewhere on the mid-ocean ridge system where rift propagation and transform migration occur.

  8. Regional variation of coda Q in Kopili fault zone of northeast India and its implications (United States)

    Bora, Nilutpal; Biswas, Rajib; Dobrynina, Anna A.


    Kopili fault has been experiencing higher seismic and tectonic activity during the recent years. These kind of active tectonics can be inspected by examining coda-wave attenuation and its dependence with frequency. Exploiting single back-scattering model, we have endeavored to measure coda Q and its associated parameters such as frequency dependent factor (n) and attenuation coefficient (γ) covering seven lapse-time windows spanning from 30 to 90 s and central frequencies 1.5, 3.5, 6, 9 and 12 Hz. The average estimated values of QC increase with frequency and lapse time window from 114 at frequency 1.5 Hz to 1563 at frequency 12 Hz for 30 s window length, and from 305 at frequency 1.5 Hz to 2135 at frequency 12 Hz for 90 s window length. The values of Q0 and n are also estimated for the entire Kopili fault zone. For this study region, the Q0 values vary from 62 to 348 and n varies from 0.57 to 1.51 within the frequency range 1.5 to 12 Hz. Furthermore, depth variation of attenuation of this region reveals that there is velocity anomaly at depth 210-220 km as there arises sharp changes in γ and n which are supported by available data, reported by other researcher for this region. Finally, we have tried to separate the intrinsic and scattering attenuation for this area. It is observed that the entire region is dominated by mainly scattering attenuation, but we can see an increase in intrinsic attenuation with depths in two stations namely TZR and BKD. Furthermore, the obtained results are comparable with the available global data.

  9. Fault linkages and activities in a transition zone of compression to transpression in Hsinchu area, northwestern Taiwan based on 3-D structural geometry (United States)

    Huang, H.; Hu, J.; Huang, S.; Huang, C.


    The Taiwan orogenic belt is resulted from the convergence between Philippine Sea plate and Eurasian plate. Serious earthquakes occurred in west and northwest flanks of main mountain belt of the island in 1935 and 1999, caused more than 5000 deaths in total. In addition, Hsinchu Science and Industrial Park (HSIP) located in northwest Taiwan is one of the world's most important areas for semiconductor manufacturing. There are more than 400 technology companies in this park, and accounted for 10% of Taiwan's GDP. Consequently, active Hsincheng and Hsinchu faults in study area become the major threat of the industrial park, thus the understanding of complex subsurface seismogenic structures are crucial issue of earthquake hazard assessment and mitigation in Hsinchu area. Several geological cross sections have been constructed and discussed to suggest possible deep structures of these two major faults in previous study. However, how subsurface fault system and folding intersect still remains unclear and the evolution of fault and fold geometry in Hsinchu area is not fully understood. The main purpose of this study is to clarify the spatial linkage between the major thrust faults, folds, and adjacent transverse structures. In this study, we first construct the NW-SE trending cross-section which is sub-parallel to the regional shortening direction, and then balance this cross section to derive the structure evolution in Hsinchu area. We also incorporate several cross-sections and relocated seismicity to get detail 3D fault geometry for the numerical modeling in order to assess the interseismic strain accumulation and seismic potential based on geodetic measurements.

  10. Fluid-Fault rock interaction during progressive deformation in Pelling-Munsiari thrust fault zone: A preliminary study from Darjeeling-Sikkim Himalayan fold thrust belt (United States)

    Singh, Akanksha; Ghosh, Pritam; Bhattacharyya, Kathakali


    In a fold thrust belt,the dominant thrust fault rocks generally record strong overprinting of dislocation-controlled deformation mechanisms by frictional mechanisms during progressive deformation. Fluids play an integral role during evolution of such fault zones by opening channels by fracturing or by sealing existing fractures by forming veins, or by a combination of both. In the Sikkim Himalayan fold thrust belt (FTB), the Pelling-Munsiari thrust (PT) is one of the dominant thrusts that is the roof thrust of the Lesser Himalayan Duplex. Growth of the duplex has folded the overlying PT sheet, exposing it at various structural positions. We focus this study along the hinterlandmost (Mangan) and forelandmost (Suntaleykhola) exposures of the PT zone. We attempt to develop a temporal sequence of fracture growth by studying offsets recorded along fractures of different orientations, and also quantifing the variation in fracture population from hinterland to foreland. Additionally, we probe the role of fluids during the different stages of progressive deformation by studying fractures versus filled in fractures (veins). We examine the sources and temperature of the fluids as a function of the structural position of the exposed PT zones. The PT fault rocks are dominantly quartz-mica mylonite. At the hinterlandmost exposure, three dominant fracture orientations are recorded at 0°-30° ( 46%), 30°-70° ( 37%), and 70°-90° ( 17%) with respect to the mylonitic foliation. Low-angle fractures are offset by the younger, high-angle fractures. Vein population study reveals that the early-formed fractures are filled in by fluids while the later ones are independent of it.The same fault zone records a higher fracture population in the forelandmost exposure with orientations of 0°-30° ( 16%), 30°-70° ( 47%) and 70°-90° ( 37%) with respect to the mylonitic foliation. In this outcrop, fluids are present in both low-angle and high-angle fractures. Based on recrystallized

  11. Geomechanical effects on CO2 leakage through fault zones during large-scale underground injection

    Energy Technology Data Exchange (ETDEWEB)

    Rinaldi, Antonio P. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Rutqvist, Jonny [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Cappa, Frédéric [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of Nice Sophia-Antipolis, Nice (France). Cote d' Azur Observatory. GeoAzur


    The importance of geomechanics—including the potential for faults to reactivate during large-scale geologic carbon sequestration operations—has recently become more widely recognized. However, notwithstanding the potential for triggering notable (felt) seismic events, the potential for buoyancy-driven CO2 to reach potable groundwater and the ground surface is actually more important from public safety and storage-efficiency perspectives. In this context, this paper extends the previous studies on the geomechanical modeling of fault responses during underground carbon dioxide injection, focusing on the short-term integrity of the sealing caprock, and hence on the potential for leakage of either brine or CO2 to reach the shallow groundwater aquifers during active injection. We consider stress/strain-dependent permeability and study the leakage through the fault zone as its permeability changes during a reactivation, also causing seismicity. We analyze several scenarios related to the volume of CO2 injected (and hence as a function of the overpressure), involving both minor and major faults, and analyze the profile risks of leakage for different stress/strain-permeability coupling functions. We conclude that whereas it is very difficult to predict how much fault permeability could change upon reactivation, this process can have a significant impact on the leakage rate. Moreover, our analysis shows that induced seismicity associated with fault reactivation may not necessarily open up a new flow path for leakage. Results show a poor correlation between magnitude and amount of fluid leakage, meaning that a single event is generally not enough to substantially change the permeability along the entire fault length. Finally, and consequently, even if some changes in permeability occur, this does not mean that the CO2 will migrate up along the entire fault, breaking through the caprock to enter the overlying aquifer.

  12. High-resolution shear-wave seismics across the Carlsberg Fault zone south of Copenhagen - Implications for linking Mesozoic and late Pleistocene structures (United States)

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


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

  13. Imaging of the Deep Structure and Extension of the North Anatolian Fault Zone by Magnetotelluric Method Beneath the Marmara Sea (United States)

    Kaya, T.; Ogawa, Y.; Kasaya, T.; Tank, B.; Honkura, Y.; Tuncer, M. K.; Oshiman, N.; Matsushima, M.


    Relative motions of the Arabian and African plates with respect to stable Eurasian plate resulted in westward movement of the Anatolian block and produced two main fault zones in Turkey. The most active one, the North Anatolian Fault Zone (NAFZ), hosted destructive earthquakes during the history causing not only damage in the buildings but also thousands of causalities. The migration of large earthquakes along the NAFZ from east to west in 20th century, occurrence of the last earthquakes (1999 Izmit and Duzce) by the side of Marmara Sea, and owning the fault segment which has not ruptured since 1766 made the Marmara Sea a potential location for the next large rupture on the NAFZ. Seismic, geodetic and other studies showed complexity of the structure suggesting various estimates about the extension of the NAFZ through the Marmara Sea. In this study, we benefit from the high depth resolution of the Magnetotelluric (MT) method to resolve the electrical resistivity structure beneath the Marmara Sea and disclose its relation with the geologic structure. In order to investigate extension of the NAFZ beneath the Marmara Sea we deployed long period ocean bottom electromagnetic data at 16 sites which form 4 profiles perpendicular to the possible traces of the NAFZ. Variation of the geoelectric strike from east to west demonstrates different oriented faults in the Marmara Sea. The highly conductive anomaly in electrical resistivity models extends from crustal depths to the lithosphere and merges with the melted mantle material. This conductive anomaly is surrounded by relatively resistive anomalies which imply continuation of the fault structure from land to the Marmara Sea. Our results clear the location of the highly conductive and resistive anomalies that has crucial implications in two aspects; conductive anomaly may trigger the micro-seismic activity and resistive anomalies may refer to the asperity zones where stress accumulation result in large earth quakes.

  14. A new relevant seismic source of the Eastern Betic Shear Zone with Holocene activity: Los Tollos Fault (Murcia, SE Spain). (United States)

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


    The NW-SE convergence between the Nubian and Eurasian plates in the western Mediterranean (4-5mm/yr) produces a crustal deformation of the southeastern Iberian Peninsula where Late Neogene and Quaternary faulting activity is dominated by a large NE-SW left-lateral strike-slip fault system: the Eastern Betic Shear Zone (EBSZ). The EBSZ is a cortical structure in NNE to NE direction and sigmoid trace that stretches for more than 450 km, and includes, from north to south, the well-known faults of Bajo Segura, Carrascoy, Alhama de Murcia, Palomares and Carboneras. Historically, several of the most destructive seismic events in the Iberian Peninsula, reaching intensities up to IX-X (MSK), have occurred in the area. Those events have been related to the main faults belonging to the EBSZ. Recently, one of the most damaging earthquakes recorded in recent times in Spain, the Lorca earthquake (11/05/2011, Mw 5.2. IEMS98 VII), has been related to the Alhama de Murcia Fault. In this work, we present Los Tollos Fault (LTF) as a new relevant tectonic feature belonging to the Eastern Betic Shear Zone. LTF is located southwest of the Carrascoy Fault, close to densely populated villages (eg: Alhama de Murcia, Totana) and less than 30 km away from downtown Murcia, the largest city of the region with almost half a million inhabitants. This fact highlights the importance of studying the LTF seismogenic potential in order to gain a better picture of the local seismic hazard and risk in the region. The aim of this work is to contribute with new data to parameterize the paleoseismic activity of this active fault in order to be included in future seismic hazard assessments of the area. LTF has been previously mapped as normal fault dipping to the NW. Furthermore, it has also been interpreted as the possible SW extension of the Carrascoy Fault. However, we show that LTF is actually a left-lateral reverse fault dipping to the SE and that it has no apparent connection to the Carrascoy Fault

  15. EEG reactions of the human brain in the gradient magnetic field zone of the active geological fault (pilot study) (United States)

    Pobachenko, S. V.; Shitov, A. V.; Grigorjev, P. E.; Sokolov, M. V.; Zubrilkin, A. I.; Vypiraylo, D. N.; Solovjev, A. V.


    This paper presents the results of experimental studies of the dynamics of the functional state of a person within the zone of an active geological fault characterized by abnormal spatial distribution of the magnetic- field vector values. It is shown that these geophysical modifications have a pronounced effect on the fluctuations of the electrical activity of the human brain. When the person gets into a zone with abnormal levels of gradient magnetic field in the absence of any subjective sensations, a nonspecific orientation activation reaction is observed, which is characterized by a significant increase in the levels of peak performance in key functional EEG frequency bands.

  16. Effects of fluid-rock interactions on faulting within active fault zones - evidence from fault rock samples retrieved from international drilling projects (United States)

    Janssen, C.; Wirth, R.; Kienast, M.; Yabe, Y.; Sulem, J.; Dresen, G. H.


    Chemical and mechanical effects of fluids influence the fault mechanical behavior. We analyzed fresh fault rocks from several scientific drilling projects to study the effects of fluids on fault strength. For example, in drill core samples on a rupture plane of an Mw 2.2 earthquake in a deep gold mine in South Africa the main shock occurred on a preexisting plane of weakness that was formed by fluid-rock interaction (magnesiohornblende was intensively altered to chlinochlore). The plane acted as conduit for hydrothermal fluids at some time in the past. The chemical influence of fluids on mineralogical alteration and geomechanical processes in fault core samples from SAFOD (San Andreas Fault Observatory at Depth) is visible in pronounced dissolution-precipitation processes (stylolites, solution seams) as well as in the formation of new phases. Detrital quartz and feldspar grains are partially dissolved and replaced by authigenic illite-smectite (I-S) mixed-layer clay minerals. Transmission Electron Microscopy (TEM) imaging of these grains reveals that the alteration processes and healing were initiated within pores and small intra-grain fissures. Newly formed phyllosilicates growing into open pore spaces likely reduced the fluid permeability. The mechanical influence of fluids is indicated by TEM observations, which document open pores that formed in-situ in the gouge material during or after deformation. Pores were possibly filled with formation water and/or hydrothermal fluids suggesting elevated fluid pressure preventing pore collapse. Fluid-driven healing of fractures in samples from SAFOD and the DGLab Gulf of Corinth project is visible in cementation. Cathodoluminescence microscopy (CL) reveals different generations of calcite veins. Differences in CL-colors suggest repeated infiltration of fluids with different chemical composition from varying sources (formation and meteoric water).

  17. (U-Th)/He thermochronometry reveals Pleistocene punctuated deformation and synkinematic hematite mineralization in the Mecca Hills, southernmost San Andreas Fault zone (United States)

    Moser, Amy C.; Evans, James P.; Ault, Alexis K.; Janecke, Susanne U.; Bradbury, Kelly K.


    The timing, tempo, and processes of punctuated deformation in strike-slip fault systems are challenging to resolve in the rock record. Faults in the Mecca Hills, adjacent to the southernmost San Andreas Fault, California, accommodate active deformation and exhumation in the Plio-Pleistocene sedimentary rocks and underlying crystalline basement. We document the spatiotemporal patterns of San Andreas Fault-related deformation as recorded in crystalline basement rocks of the Mecca Hills using fault microstructural observations, geochemical data, and hematite (n = 24) and apatite (n = 44) (U-Th)/He (hematite He, apatite He) thermochronometry data. Reproducible mean hematite He dates from minor hematite-coated fault surfaces in the Painted Canyon Fault damage zone range from ∼0.7-0.4 Ma and are younger than ∼1.2 Ma apatite He dates from adjacent crystalline basement host rock. These data reveal concomitant Pleistocene pulses of fault slip, fluid flow, and synkinematic hematite mineralization. Hematite textures, crystal morphology, and hematite He data patterns imply some damage zone deformation occurred via cyclic crack-seal and creep processes. Apatite He data from crystalline basement define distinct date-eU patterns and indicate cooling across discrete fault blocks in the Mecca Hills. Uniform ∼1.2 Ma apatite He dates regardless of eU are located exclusively between the Painted Canyon and Platform faults. Outside of this fault block, samples yield individual apatite He dates from ∼30-1 Ma that define a positive apatite He date-eU correlation. These patterns reveal focused exhumation away from the main trace of the San Andreas Fault at ∼1.2 Ma. Low-temperature thermochronometry of fault-related rocks provides an unprecedented window into the 105-106-yr record of San Andreas Fault-related deformation in the Mecca Hills and documents hematite deformation mechanisms that may be operative in other strike-slip faults world-wide.

  18. Geochemistry of soil gas in the seismic fault zone produced by the Wenchuan Ms 8.0 earthquake, southwestern China. (United States)

    Zhou, Xiaocheng; Du, Jianguo; Chen, Zhi; Cheng, Jianwu; Tang, Yi; Yang, Liming; Xie, Chao; Cui, Yueju; Liu, Lei; Yi, Li; Yang, Panxin; Li, Ying


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

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

    Directory of Open Access Journals (Sweden)

    B. Baier


    Full Text Available The first deep seismic sounding experiment in Northwestern Anatolia was carried out in October 1991 as part of the "German - Turkish Project on Earthquake Prediction Research" in the Mudurnu area of the North Anatolian Fault Zone. The experiment was a joint enterprise by the Institute of Meteorology and Geophysics of Frankfurt University, the Earthquake Research Institute (ERI in Ankara, and the Turkish Oil Company (TPAO. Two orthogonal profiles, each 120 km in length with a crossing point near Akyazi, were covered in succession by 30 short period tape recording seismograph stations with 2 km station spacing. 12 shots, with charge sizes between 100 and 250 kg, were fired and 342 seismograms out of 360 were used for evaluation. By coincidence an M b = 4.5 earthquake located below Imroz Island was also recorded and provided additional information on Moho and the sub-Moho velocity. A ray tracing method orginally developed by Weber (1986 was used for travel time inversion. From a compilation of all data two generalized crustal models were derived, one with velocity gradients within the layers and one with constant layer velocities. The latter consists of a sediment cover of about 2 km with V p » 3.6 km/s, an upper crystalline crust down to 13 km with V p » 5.9 km/s, a middle crust down to 25 km depth with V p » 6.5 km/s, a lower crust down to 39 km Moho depth with V p » 7.0 km/s and V p » 8.05 km/s below the Moho. The structure of the individual profiles differs slightly. The thickest sediment cover is reached in the Izmit-Sapanca-trough and in the Akyazi basin. Of particular interest is a step of about 4 km in the lower crust near Lake Sapanca and probably an even larger one in the Moho (derived from the Imroz earthquake data. After the catastrophic earthquake of Izmit on 17 August 1999 this significant heterogeneity in crustal structure appears in a new light with regard to the possible cause of the Izmit earthquake. Heterogeneities in

  20. The damage is done: Low fault friction recorded in the damage zone of the shallow Japan Trench décollement (United States)

    Keren, Tucker T.; Kirkpatrick, James D.


    Fault damage zones record the integrated deformation caused by repeated slip on faults and reflect the conditions that control slip behavior. To investigate the Japan Trench décollement, we characterized the damage zone close to the fault from drill core recovered during Integrated Ocean Drilling Program Expedition 343 (Japan Trench Fast Drilling Project (JFAST)). Core-scale and microscale structures include phyllosilicate bands, shear fractures, and joints. They are most abundant near the décollement and decrease in density sharply above and below the fault. Power law fits describing the change in structure density with distance from the fault result in decay exponents (n) of 1.57 in the footwall and 0.73 in the hanging wall. Microstructure decay exponents are 1.09 in the footwall and 0.50 in the hanging wall. Observed damage zone thickness is on the order of a few tens of meters. Core-scale structures dip between ~10° and ~70° and are mutually crosscutting. Compared to similar offset faults, the décollement has large decay exponents and a relatively narrow damage zone. Motivated by independent constraints demonstrating that the plate boundary is weak, we tested if the observed damage zone characteristics could be consistent with low-friction fault. Quasi-static models of off-fault stresses and deformation due to slip on a wavy, frictional fault under conditions similar to the JFAST site predict that low-friction fault produces narrow damage zones with no preferred orientations of structures. These results are consistent with long-term frictional weakness on the décollement at the JFAST site.

  1. Holocene surface-faulting earthquakes at the Spring Lake and North Creek Sites on the Wasatch Fault Zone: Evidence for complex rupture of the Nephi Segment (United States)

    Duross, Christopher; Hylland, Michael D.; Hiscock, Adam; Personius, Stephen; Briggs, Richard; Gold, Ryan D.; Beukelman, Gregg; McDonald, Geg N; Erickson, Ben; McKean, Adam; Angster, Steve; King, Roselyn; Crone, Anthony J.; Mahan, Shannon


    The Nephi segment of the Wasatch fault zone (WFZ) comprises two fault strands, the northern and southern strands, which have evidence of recurrent late Holocene surface-faulting earthquakes. We excavated paleoseismic trenches across these strands to refine and expand their Holocene earthquake chronologies; improve estimates of earthquake recurrence, displacement, and fault slip rate; and assess whether the strands rupture separately or synchronously in large earthquakes. Paleoseismic data from the Spring Lake site expand the Holocene record of earthquakes on the northern strand: at least five to seven earthquakes ruptured the Spring Lake site at 0.9 ± 0.2 ka (2σ), 2.9 ± 0.7 ka, 4.0 ± 0.5 ka, 4.8 ± 0.8 ka, 5.7 ± 0.8 ka, 6.6 ± 0.7 ka, and 13.1 ± 4.0 ka, yielding a Holocene mean recurrence of ~1.2–1.5 kyr and vertical slip rate of ~0.5–0.8 mm/yr. Paleoseismic data from the North Creek site help refine the Holocene earthquake chronology for the southern strand: at least five earthquakes ruptured the North Creek site at 0.2 ± 0.1 ka (2σ), 1.2 ± 0.1 ka, 2.6 ± 0.9 ka, 4.0 ± 0.1 ka, and 4.7 ± 0.7 ka, yielding a mean recurrence of 1.1–1.3 kyr and vertical slip rate of ~1.9–2.0 mm/yr. We compare these Spring Lake and North Creek data with previous paleoseismic data for the Nephi segment and report late Holocene mean recurrence intervals of ~1.0–1.2 kyr for the northern strand and ~1.1–1.3 kyr for the southern strand. The northern and southern strands have similar late Holocene earthquake histories, which allow for models of both independent and synchronous rupture. However, considering the earthquake timing probabilities and per-event vertical displacements, we have the greatest confidence in the simultaneous rupture of the strands, including rupture of one strand with spillover rupture to the other. Ultimately, our results improve the surface-faulting earthquake history of the Nephi segment and enhance our understanding of how structural barriers

  2. Polyphase neotectonic movements in the Gavilgarh Fault Zone, central Indian craton: evidences from geomorpho-tectonic analysis (United States)

    Bhattacharjee, Dipanjan; Chattopadhyay, Anupam; Jain, Vikrant


    The central part of Indian craton is believed to be a stable continental region with low strain build-up and long earthquake recurrence periods. It comprises two major Archean cratonic fragments (i.e. the Bundelkhand and the Bastar Cratons) and a Proterozoic mobile belt called Central Indian Tectonic Zone (CITZ), along which the cratonic fragments were amalgamated in the Proterozoic. Gavilgarh Fault Zone (GFZ) is an important component of CITZ and is represented by a >250 km long, ENE-WSW trending fault line which demarcates the southern boundary of the Satpura mountains. Although the eastern part of the lineament shows evidences of polyphase tectonic movements in the Meso-Neoproterozic (Chattopadhyay and Khasdeo, 2011), there is no focussed analysis of neotectonic activity in this fault zone although a number of earthquakes have been recorded within the CITZ in last 100 years or so. The present study comprises structural mapping and geomorphological analysis of a 200 km long stretch of the GFZ lineament. GFZ shows evidences of reverse fault-slip movements that possibly resulted in an uplift of the northern side, as deeper level rocks (e.g. Paleozoic Gondwana sandstones) are juxtaposed against the overlying Deccan Trap basalts of Mesozoic age along the fault line. Crushing of basalts along the lineament, asymmetric folds within Gondwana sandstone, inclination of Anisotropic Magnetic Susceptibility (AMS) axes etc. provide evidences for fault-drag folding related to the post-Deccan reverse faulting. Drainages crosscutting the lineament adjusted with the tectonic uplift either by incising their own sediments and bed rock or by increasing their sinuosity, only in the northern side, as seen in the satellite images. Hypsometric Integral values suggest that the immature/in-equilibrated drainage basins were restricted in the north while mature/equilibrated basins developed in the south of the lineament. Longitudinal profiles and S-L Index of the river profiles, prepared

  3. Thermal waters along the Konocti Bay fault zone, Lake County, California: a re-evaluation (United States)

    Thompson, J. M.; Mariner, R. H.; White, L. D.; Presser, T. S.; Evans, W. C.


    The Konocti Bay fault zone (KBFZ), initially regarded by some as a promising target for liquid-dominated geothermal systems, has been a disappointment. At least five exploratory wells were drilled in the vicinity of the KBFZ, but none were successful. Although the Na-K-Ca and Na-Li geothermometers indicate that the thermal waters discharging in the vicinity of Howard and Seigler Springs may have equilibrated at temperatures greater than 200°C, the spring temperatures and fluid discharges are low. Most thermal waters along the KBFZ contain >100 mg/l Mg. High concentrations of dissolved magnesium are usually indicative of relatively cool hydrothermal systems. Dissolution of serpentine at shallow depths may contribute dissolved silica and magnesium to rising thermal waters. Most thermal waters are saturated with respect to amorphous silica at the measured spring temperature. Silica geothermometers and mixing models are useless because the dissolved silica concentration is not controlled by the solubility of either quartz or chalcedony. Cation geothermometry indicates the possibility of a high-temperature fluid (> 200°C) only in the vicinity of Howard and Seigler Springs. However, even if the fluid temperature is as high as that indicated by the geothermometers, the permeability may be low. Deuterium and oxygen-18 values of the thermal waters indicate that they recharged locally and became enriched in oxygen-18 by exchange with rock. Diluting meteoric water and the thermal water appear to have the same deuterium value. Lack of tritium in the diluted spring waters suggest that the diluting water is old.

  4. Petrophysical, Geochemical, and Hydrological Evidence for Extensive Fracture-Mediated Fluid and Heat Transport in the Alpine Fault's Hanging-Wall Damage Zone (United States)

    Townend, John; Sutherland, Rupert; Toy, Virginia G.; Doan, Mai-Linh; Célérier, Bernard; Massiot, Cécile; Coussens, Jamie; Jeppson, Tamara; Janku-Capova, Lucie; Remaud, Léa.; Upton, Phaedra; Schmitt, Douglas R.; Pezard, Philippe; Williams, Jack; Allen, Michael John; Baratin, Laura-May; Barth, Nicolas; Becroft, Leeza; Boese, Carolin M.; Boulton, Carolyn; Broderick, Neil; Carpenter, Brett; Chamberlain, Calum J.; Cooper, Alan; Coutts, Ashley; Cox, Simon C.; Craw, Lisa; Eccles, Jennifer D.; Faulkner, Dan; Grieve, Jason; Grochowski, Julia; Gulley, Anton; Hartog, Arthur; Henry, Gilles; Howarth, Jamie; Jacobs, Katrina; Kato, Naoki; Keys, Steven; Kirilova, Martina; Kometani, Yusuke; Langridge, Rob; Lin, Weiren; Little, Tim; Lukacs, Adrienn; Mallyon, Deirdre; Mariani, Elisabetta; Mathewson, Loren; Melosh, Ben; Menzies, Catriona; Moore, Jo; Morales, Luis; Mori, Hiroshi; Niemeijer, André; Nishikawa, Osamu; Nitsch, Olivier; Paris, Jehanne; Prior, David J.; Sauer, Katrina; Savage, Martha K.; Schleicher, Anja; Shigematsu, Norio; Taylor-Offord, Sam; Teagle, Damon; Tobin, Harold; Valdez, Robert; Weaver, Konrad; Wiersberg, Thomas; Zimmer, Martin


    Fault rock assemblages reflect interaction between deformation, stress, temperature, fluid, and chemical regimes on distinct spatial and temporal scales at various positions in the crust. Here we interpret measurements made in the hanging-wall of the Alpine Fault during the second stage of the Deep Fault Drilling Project (DFDP-2). We present observational evidence for extensive fracturing and high hanging-wall hydraulic conductivity (˜10-9 to 10-7 m/s, corresponding to permeability of ˜10-16 to 10-14 m2) extending several hundred meters from the fault's principal slip zone. Mud losses, gas chemistry anomalies, and petrophysical data indicate that a subset of fractures intersected by the borehole are capable of transmitting fluid volumes of several cubic meters on time scales of hours. DFDP-2 observations and other data suggest that this hydrogeologically active portion of the fault zone in the hanging-wall is several kilometers wide in the uppermost crust. This finding is consistent with numerical models of earthquake rupture and off-fault damage. We conclude that the mechanically and hydrogeologically active part of the Alpine Fault is a more dynamic and extensive feature than commonly described in models based on exhumed faults. We propose that the hydrogeologically active damage zone of the Alpine Fault and other large active faults in areas of high topographic relief can be subdivided into an inner zone in which damage is controlled principally by earthquake rupture processes and an outer zone in which damage reflects coseismic shaking, strain accumulation and release on interseismic timescales, and inherited fracturing related to exhumation.

  5. Structural analysis of superposed fault systems of the Bornholm horst block, Tornquist Zone, Denmark

    DEFF Research Database (Denmark)

    Graversen, Ole


    Baltica platform is correlated with early-middle Carboniferous deformation in the Variscan foreland and with faulting associated with dolerite dyke injection in Skåne in the Late Carboniferous-Early Permian. The Palaeozoic fault systems are striking NW-SE and WNW-ESE and the platform series are dipping...

  6. Hydrogeological aspects of fault zones on various scales in the Roer Valley Rift System.

    NARCIS (Netherlands)

    Bense, V.F.; van Balen, R.T.


    The impact of faults on the groundwater flow system in the Roer Valley Rift System (RVRS) is demonstrated with examples from outcrop scale to regional scale. Faults in the RVRS can form strong barriers to horizontal groundwater flow as well as enhanced vertical groundwater flow paths at the same

  7. Signature of fault zone deformation in near-surface soil visible in shear wave seismic reflections

    NARCIS (Netherlands)

    Ghose, R.; Carvalho, J.; Loureiro, A.


    Small-throw seismogenic fault segments hidden in the Holocene sediments are crucial but difficult targets in seismic exploration. We report here the detection of the deformation pattern and a concealed fault segment in the unconsolidated sediments at Vila Franca Xira, Portugal, through

  8. Combined UAVSAR and GPS Estimates of Fault Slip for the M 6.0 South Napa Earthquake (United States)

    Donnellan, A.; Parker, J. W.; Hawkins, B.; Hensley, S.; Jones, C. E.; Owen, S. E.; Moore, A. W.; Wang, J.; Pierce, M. E.; Rundle, J. B.


    Combined UAVSAR and GPS Estimates of Fault Slip for the M 6.0 South Napa Earthquake Andrea Donnellan, Jay Parker, Brian Hawkins, Scott Hensley, Cathleen Jones, Susan Owen, Angelyn Moore Jet Propulsion Laboratory, California Institute of Technology Marlon Pierce, Jun Wang Indiana University John Rundle University of California, Davis The South Napa to Santa Rosa area has been observed with NASA's UAVSAR since late 2009 as part of an experiment to monitor areas identified as having a high probability of an earthquake. The M 6.0 South Napa earthquake occurred on 24 August 2014. The area was flown 29 May 2014 preceeding the earthquake, and again on 29 August 2014, five days after the earthquake. The UAVSAR results show slip on a single fault at the south end of the rupture near the epicenter of the event. The rupture branches out into multiple faults further north near the Napa area. A combined inversion of rapid GPS results and the unwrapped UAVSAR interferogram indicate nearly pure strike slip motion. Using this assumption, the UAVSAR data show horizontal right-lateral slip across the fault of 19 cm at the south end of the rupture and increasing to 70 cm northward over a distance of 6.5 km. The joint inversion indicates slip of ~30 cm on a network of sub-parallel faults is concentrated in a zone about 17 km long. The lower depths of the faults are 5-8.5 km. The eastern two sub-parallel faults break the surface, while three faults to the west are buried at depths ranging from 2-6 km with deeper depths to the north and west. The geodetic moment release is equivalent to a M 6.1 event. Additional ruptures are observed in the interferogram, but the inversions suggest that they represent superficial slip that does not contribute to the overall moment release.

  9. Seismogenic faulting in the Meruoca granite, NE Brazil, consistent with a local weak fracture zone. (United States)

    Moura, Ana Catarina A; De Oliveira, Paulo H S; Ferreira, Joaquim M; Bezerra, Francisco H R; Fuck, Reinhardt A; Do Nascimento, Aderson F


    A sequence of earthquakes occurred in 2008 in the Meruoca granitic pluton, located in the northwestern part of the Borborema Province, NE Brazil. A seismological study defined the seismic activity occurring along the seismically-defined Riacho Fundo fault, a 081° striking, 8 km deep structure. The objective of this study was to analyze the correlation between this seismic activity and geological structures in the Meruoca granite. We carried out geological mapping in the epicentral area, analyzed the mineralogy of fault rocks, and compared the seismically-defined Riacho Fundo fault with geological data. We concluded that the seismically-defined fault coincides with ∼E-W-striking faults observed at outcrop scale and a swarm of Mesozoic basalt dikes. We propose that seismicity reactivated brittle structures in the Meruoca granite. Our study highlights the importance of geological mapping and mineralogical analysis in order to establish the relationships between geological structures and seismicity at a given area.

  10. Seismogenic faulting in the Meruoca granite, NE Brazil, consistent with a local weak fracture zone

    Directory of Open Access Journals (Sweden)



    Full Text Available A sequence of earthquakes occurred in 2008 in the Meruoca granitic pluton, located in the northwestern part of the Borborema Province, NE Brazil. A seismological study defined the seismic activity occurring along the seismically-defined Riacho Fundo fault, a 081° striking, 8 km deep structure. The objective of this study was to analyze the correlation between this seismic activity and geological structures in the Meruoca granite. We carried out geological mapping in the epicentral area, analyzed the mineralogy of fault rocks, and compared the seismically-defined Riacho Fundo fault with geological data. We concluded that the seismically-defined fault coincides with ∼E–W-striking faults observed at outcrop scale and a swarm of Mesozoic basalt dikes. We propose that seismicity reactivated brittle structures in the Meruoca granite. Our study highlights the importance of geological mapping and mineralogical analysis in order to establish the relationships between geological structures and seismicity at a given area.

  11. Seismogenic faulting in the Meruoca granite, NE Brazil, consistent with a local weak fracture zone. (United States)

    Moura, Ana Catarina A; Oliveira, Paulo H S DE; Ferreira, Joaquim M; Bezerra, Francisco H R; Fuck, Reinhardt A; Nascimento, Aderson F DO


    A sequence of earthquakes occurred in 2008 in the Meruoca granitic pluton, located in the northwestern part of the Borborema Province, NE Brazil. A seismological study defined the seismic activity occurring along the seismically-defined Riacho Fundo fault, a 081° striking, 8 km deep structure. The objective of this study was to analyze the correlation between this seismic activity and geological structures in the Meruoca granite. We carried out geological mapping in the epicentral area, analyzed the mineralogy of fault rocks, and compared the seismically-defined Riacho Fundo fault with geological data. We concluded that the seismically-defined fault coincides with ∼E-W-striking faults observed at outcrop scale and a swarm of Mesozoic basalt dikes. We propose that seismicity reactivated brittle structures in the Meruoca granite. Our study highlights the importance of geological mapping and mineralogical analysis in order to establish the relationships between geological structures and seismicity at a given area.

  12. The influence of joint parameters on normal fault evolution and geometry: a parameter study using analogue modeling (United States)

    Kettermann, Michael; von Hagke, Christoph; Urai, Janos L.


    Dilatant faults often form in rocks containing pre-existing joints, but the effects of joints on fault segment linkage and fracture connectivity is not well understood. Studying evolution of dilatancy and influence of fractures on fault development provides insights into geometry of fault zones in brittle rocks and will eventually allow for predicting their subsurface appearance. In an earlier study we recognized the effect of different angles between strike direction of vertical joints and a basement fault on the geometry of a developing fault zone. We now systematically extend the results by varying geometric joint parameters such as joint spacing and vertical extent of the joints and measuring fracture density and connectivity. A reproducibility study shows a small error-range for the measurements, allowing for a confident use of the experimental setup. Analogue models were carried out in a manually driven deformation box (30x28x20 cm) with a 60° dipping pre-defined basement fault and 4.5 cm of displacement. To produce open joints prior to faulting, sheets of paper were mounted in the box to a depth of 5 cm at a spacing of 2.5 cm. We varied the vertical extent of the joints from 5 to 50 mm. Powder was then sieved into the box, embedding the paper almost entirely (column height of 19 cm), and the paper was removed. During deformation we captured structural information by time-lapse photography that allows particle imaging velocimetry analyses (PIV) to detect localized deformation at every increment of displacement. Post-mortem photogrammetry preserves the final 3-dimensional structure of the fault zone. A counterintuitive result is that joint depth is of only minor importance for the evolution of the fault zone. Even very shallow joints form weak areas at which the fault starts to form and propagate. More important is joint spacing. Very large joint spacing leads to faults and secondary fractures that form subparallel to the basement fault. In contrast, small

  13. The seismogenic Gole Larghe Fault Zone (Italian Southern Alps): quantitative 3D characterization of the fault/fracture network, mapping of evidences of fluid-rock interaction, and modelling of the hydraulic structure through the seismic cycle (United States)

    Bistacchi, A.; Mittempergher, S.; Di Toro, G.; Smith, S. A. F.; Garofalo, P. S.


    The Gole Larghe Fault Zone (GLFZ) was exhumed from 8 km depth, where it was characterized by seismic activity (pseudotachylytes) and hydrous fluid flow (alteration halos and precipitation of hydrothermal minerals in veins and cataclasites). Thanks to glacier-polished outcrops exposing the 400 m-thick fault zone over a continuous area > 1.5 km2, the fault zone architecture has been quantitatively described with an unprecedented detail, providing a rich dataset to generate 3D Discrete Fracture Network (DFN) models and simulate the fault zone hydraulic properties. The fault and fracture network has been characterized combining > 2 km of scanlines and semi-automatic mapping of faults and fractures on several photogrammetric 3D Digital Outcrop Models (3D DOMs). This allowed obtaining robust probability density functions for parameters of fault and fracture sets: orientation, fracture intensity and density, spacing, persistency, length, thickness/aperture, termination. The spatial distribution of fractures (random, clustered, anticlustered…) has been characterized with geostatistics. Evidences of fluid/rock interaction (alteration halos, hydrothermal veins, etc.) have been mapped on the same outcrops, revealing sectors of the fault zone strongly impacted, vs. completely unaffected, by fluid/rock interaction, separated by convolute infiltration fronts. Field and microstructural evidence revealed that higher permeability was obtained in the syn- to early post-seismic period, when fractures were (re)opened by off-fault deformation. We have developed a parametric hydraulic model of the GLFZ and calibrated it, varying the fraction of faults/fractures that were open in the post-seismic, with the goal of obtaining realistic fluid flow and permeability values, and a flow pattern consistent with the observed alteration/mineralization pattern. The fraction of open fractures is very close to the percolation threshold of the DFN, and the permeability tensor is strongly anisotropic

  14. Hydraulic properties of a low permeable rupture zone on the Yingxiu-Beichuan Fault activated during the Wenchuan earthquake, China: Implications for fluid conduction, fault sealing, and dynamic weakening mechanisms (United States)

    Duan, Qingbao; Yang, Xiaosong; Chen, Jianye


    Fluid transport properties of fault rocks are crucial parameters that affect earthquake nucleation and rupture propagation. In this study, we examined the internal structure, mineral composition and fluid transport properties of fault rocks collected from two shallow boreholes penetrating a granitic rupture zone on the Yingxiu-Beichuan Fault (YBF) that was activated during the 2008 Wenchuan earthquake. Fluid transport properties were measured using water as pore fluid at effective pressures (Pe) ranging from 10 MPa to 165 MPa. Permeabilities of fault rocks exhibit a wide variation from 2.1 × 10- 22 m2 to 4.6 × 10- 17 m2, strongly depending on rock types and overburden pressure. Specifically, at Pe of 165 MPa, the damage zone samples have permeabilities from 5.0 × 10- 21 m2 to 1.2 × 10- 17 m2, and the fault gouges are between 2.1 × 10- 22 m2 and 3.1 × 10- 19 m2. Thus, the YBF consists of a low-permeability fault core acting as fluid barrier, and surrounding high-permeability damage zones acting as fluid conduits. Combining the structural and compositional results and transport data together, we propose that the interplay between cataclasis and fluid-rock interactions controls the hydraulic properties and their response to the fault zone evolution. It is noteworthy that we measured extremely low permeabilities but high porosities and high specific storages for the gouges. The cemented cataclasites, which are inferred to be equivalent to the rocks in which the Wenchuan earthquake nucleated also have low permeabilities, suggesting the fault zone is a potential area for fluid storage and capable of generating high pore pressure at depths. According to our laboratory data, we found fluid pressurization could occur at depths below 2.7 km. We suggest thermal pressurization has played an important role in causing the dynamic weakening of the Wenchuan earthquake.

  15. Estimation of recurrence interval of large earthquakes on the central Longmen Shan fault zone based on seismic moment accumulation/release model. (United States)

    Ren, Junjie; Zhang, Shimin


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

  16. Association of coal metamorphism and hydrothermal mineralization in Rough Creek fault zone and Fluorspar District, Western Kentucky

    Energy Technology Data Exchange (ETDEWEB)

    Hower, J.C.; Fiene, F.L.; Trinkle, E.J.


    The ambient coal rank (metamorphism) of the Carboniferous coals in the Western Kentucky coalfield ranges from high volatile A bituminous (vitrinite maximum reflectance up to 0.75% R/sub max/) in the Webster syncline (Webster and southern Union Counties) to high volatile C bituminous (0.45 to 0.60% R/sub max/) over most of the remainder of the area. Anomalous patterns of metamorphism, however, have been noted in coals recovered from cores and mines in fault blocks of the Rough Creek fault zone and Fluorspar District. Coals in Gil-30 borehole (Rough Creek faults, Bordley Quadrangle, Union County) vary with no regard for vertical position, from high volatile C(0.55% R/sub max/) to high volatile A (0.89%R/sub max) bituminous. Examination of the upper Sturgis Formation (Missourian/Virgilian) coals revealed that the higher rank (generally above 0.75% R/sub max/) coals had vein mineral assemblages of sphalerite, twinned calcite, and ferroan dolomite. Lower rank coals had only untwinned calcite. Several sites in Webster County contain various coals (Well (No. 8) to Coiltwon (No. 14)) with vitrinite reflectances up to 0.83% R/sub max/ and associated sphalerite mineralization. Mississippian and Lower Pennsylvanian (Caseyville Formation Gentry coal) coals in the mineralized Fluorspar District have ranks to nearly medium volatile bituminous (1.03% R/sub max/). The regional rank trend exhibited by the fualt zones is generally higher rank than the surrounding areas. Sphalerite mineralization in itself is not unique within Illinois basin coals, but if it was partly responsible for the metamorphism of these coals, then the fluid temperature must have been higher within the above mentioned fault complexes.

  17. Structural analysis of S-wave seismics around an urban sinkhole: evidence of enhanced dissolution in a strike-slip fault zone

    Directory of Open Access Journals (Sweden)

    S. H. Wadas


    Full Text Available In November 2010, a large sinkhole opened up in the urban area of Schmalkalden, Germany. To determine the key factors which benefited the development of this collapse structure and therefore the dissolution, we carried out several shear-wave reflection-seismic profiles around the sinkhole. In the seismic sections we see evidence of the Mesozoic tectonic movement in the form of a NW–SE striking, dextral strike-slip fault, known as the Heßleser Fault, which faulted and fractured the subsurface below the town. The strike-slip faulting created a zone of small blocks ( < 100 m in size, around which steep-dipping normal faults, reverse faults and a dense fracture network serve as fluid pathways for the artesian-confined groundwater. The faults also acted as barriers for horizontal groundwater flow perpendicular to the fault planes. Instead groundwater flows along the faults which serve as conduits and forms cavities in the Permian deposits below ca. 60 m depth. Mass movements and the resulting cavities lead to the formation of sinkholes and dissolution-induced depressions. Since the processes are still ongoing, the occurrence of a new sinkhole cannot be ruled out. This case study demonstrates how S-wave seismics can characterize a sinkhole and, together with geological information, can be used to study the processes that result in sinkhole formation, such as a near-surface fault zone located in soluble rocks. The more complex the fault geometry and interaction between faults, the more prone an area is to sinkhole occurrence.

  18. High Resistant Sand Injected Marl and Low Resistant Damaged Marl to Locate and Characterize the Thénia Fault Zone in Boumerdes City (North-Central Algeria) (United States)

    Moulouel, Hakim; Bensalem, Rabah; Machane, Djamel; Bendaoud, Abderrahmane; Gharbi, Sofiane; Oubaiche, El-Hadi; Ousalem, Hassane; Skendri, Walid


    The purpose of this study was to locate and characterize the Thénia Fault Zone (TFZ) in the urban area of Boumerdes city; geological and electrical resistivity tomography surveys have targeted the Plaisancian marl and its Quaternary cover. As a whole, data indicate a complex near-vertical fault zone with an asymmetric and zoned internal structure of at least 150 m wide and with a straight N120° overall trending. The fault zone is traversed with two elongated parallel fault branches (FB1 and FB2), generally, 70 m distant from each other. These fault branches locate two intense damage zones (IDZs) of 10-15 m thick each, situated at the margin of two damage zones each having a thickness of several tens of meters. Downward sand injections into IDZs during Pleistocene epoch, possible pulverization of Plaisancian marl rocks, systematic deflection of actual stream channels, and vertical displacement of at least 30 m affecting Quaternary alluvial deposits show that the area would have undergone active tectonic driven by the TFZ.

  19. Core-Log-Seismic Integrative Study of a Subduction Zone Megasplay Fault -An Example from the Nobeoka Thrust, Shimanto Belt, Southwest Japan (United States)

    Hamahashi, M.; Tsuji, T.; Saito, S.; Tanikawa, W.; Hamada, Y.; Hashimoto, Y.; Kimura, G.


    Investigating the mechanical properties and deformation patterns of megathrusts in subduction zones is important to understand the generation of large earthquakes. The Nobeoka Thrust, a fossilized megasplay fault in Kyushu Shimanto Belt, southwest Japan, exposes foliated fault rocks that were formed under the temperature range of 180-350° (Kondo et al., 2005). During the Nobeoka Thrust Drilling Project (2011), core samples and geophysical logging data were obtained recovering a continuous distribution of multiple fault zones, which provide the opportunity to examine their structure and physical properties in various scales (Hamahashi et al., 2013; 2015). By performing logging data analysis, discrete sample physical property measurements, and synthetic modeling of seismic reflections along the Nobeoka Thrust, we conducted core-log-seismic integrative study to characterize the effects of damage zone architecture and structural anisotropy towards the physical properties of the megasplay. A clear contrast in physical properties across the main fault core and surrounding damage zones were identified, where the fault rocks preserve the porosity of 4.8% in the hanging wall and 7.6% in the footwall, and P-wave velocity of 4.8 km/s and 4.2 km/s, respectively. Multiple sandstone-rich- and shale-rich damage zones were found from the drilled cores, in which velocity decreases significantly in the brecciated zones. The internal structure of these foliated fault rocks consist of heterogeneous lithology and texture, and velocity anisotropy ranges 1-18% (P-wave) and 1.5-80% (S-wave), affected by structural dip angle, foliation density, and sandstone/mudstone ratio. To evaluate the fault properties at the seismogenic depth, we developed velocity/earth models and synthetic modeling of seismic reflection using acoustic logs across the thrust and parameterized lithological and structural elements in the identified multiple damage zones.

  20. Paleoseismologic data and seismic tomographic images of the 1992 Erzincan Earthquake along the North Anatolian Fault Zone, Turkey (United States)

    Caglayan, A.; Kaypak, B.; Isik, V.; Saber, R.; Yasar, I.


    The North Anatolian Fault Zone (NAFZ), spanning over 1200 km from Karliova in eastern Turkey to the Aegean Sea, defines complex active fault zone. The zone consists of network of subfaults, each of varying geometry, and associated failure properties. The Erzincan basin, one of a series basins along the NAFZ, is active basin surrounding bedrock which is Mesozoic and Tertiary units. Available geophysical data constrain the total thickness of Pliocene and Quaternary sediments in the Erzincan basin to more than 2 km. The basin was affected by the 1992 March 13 Erzincan earthquake (Ms=6.8) showing weakly developed surface ruptures. We excavated 6 paleoseismic trenches along the southeastern termination of the 1992 rupture in Üzümlü area. A total of trenches is 294 m long and trends N20°-30°E. Exposed lithology in trenches is made up of alluvial fan deposites and fluvial facies with rare flood-plain sediments, which are characterized by stratified and/or lens-shaped pebble gravel to coarse-grained sand, silt, and clay. Our preliminary interpretation of trenches reveals evidence of 1992 earthquake features. Trench logs showing structural elements including normal faults, which are parallel to the strike of the trace of the NAFZ and dipping 40°-75° to the northeast and the southwest, and network of almost vertical fractures with a few centimeters displacement. Some of trenches contain well-developed flame structures, suggesting liquefaction of water-saturated sediments during earthquake. Seismic velocity (VP and VP/VS) images obtained from the 3-D local earthquake tomography using the arrival time data of aftershocks of the 13 March 1992 Erzincan earthquake show several anomalies related to geological features of the Erzincan basin. The tomographic results indicate that (1) the major fault zones control the regional tectonics and the geometry of the Erzincan basin, (2) sediments of the basin show low seismic velocity, and (3) The high velocity units characterized by

  1. Simulating Spatio-Temporal Slip Evolution of Fault Zones at Different Evolutionary Stages (United States)

    Hillers, G.; Mai, M.; Ben-Zion, Y.


    Previous studies of spatio-temporal evolution of slip on a fault governed by rate-and-state friction (e.g., Rice, 1993; Ben-Zion and Rice, 1995, 1997; Tullis, 1996; Lapusta et al., 2000) employed frictional properties corresponding to fairly homogeneous faults. In most cases, the only types of heterogeneities were the lab-based depth-variations of the parameters a and b that produce transitions between stable velocity-strengthening and unstable velocity-weakening regimes. In this study we use a constant a-b profile and a depth-dependent distribution of the critical slip distance parameter L. In addition, correlated heterogeneities of L along strike are used to model geometrical heterogeneities on faults related to roughness. More specifically, we will perform 3D quasi-static and quasi-dynamic simulations of slip on a strike-slip fault using a family of 2D anisotropic correlated distributions of L having different correlation lengths along strike and downdip. The depth-variation of L over the depth range 3km histories. The 3D code with various cases of anisotropic correlated distributions of L will be used to study many issues related to observed complex behavior of seismogenic faults including: (1) Nucleation and arrest properties of failure episodes on a heterogeneous fault governed by RSD friction. (2) Comparison between properties of final simulated slip histories and those of the inverted slip histories. (3) Frequency-size and temporal statistics of simulated earthquakes on a heterogeneous fault governed by rate-and-state friction.

  2. Pulverization Texturein Fault Damage Zones: A result of Implosion Damage or Dynamic Compressive Stresses? (United States)

    Rockwell, T. K.; Girty, G.; Whearty, J.; Mitchell, T. M.


    Micro-brecciation, or pulverization, is recognized as a fundamental component of the architecture and damage products of many large faults, although the precise mechanisms to produce this damage are debated, with both compressive and tensile mechanisms proposed. We characterized several sites along the San Jacinto fault, southern California, where the total depth of exhumation for the life history of the fault can be determined, to study the confining stresses required for pulverization. In basement rock near Anza, where exhumation is less than 100 m, granitic dikes injected into schist of the Burnt Valley Complex are pulverized out to several meters from the fault core, whereas the schist is brecciated at the macro-scale and contains narrow centimeter-thick seams of black cataclasite. Similar relationships are observed in Horse Canyon, which is exhumed about 400 m below a regional Tertiary erosion surface, where granitic dikes emplaced into schist are pulverized out to distances of several tens of meters from the fault core. These observations imply that very low confining stress is required for micro-brecciation in granitic rock. Unconsolidated sandstones (alluvial fan deposits) along the SJF in Rock House Canyon are undeformed where the deposits are exhumed by about 70 m, but show incipient pulverization (high-density, sub-grain cracking) at 120 m depth of exhumation. Cracks oriented perpendicular to the fault formed in individual quartz and feldspar grains out to a few meters from the fault core. These observations suggest that the confining stress required for onset of pulverization in unconsolidated deposits is on the order of 2-2.5 MPa. As the tensile strength of quartz is an order of magnitude higher than these confining stresses, the most likely mechanism that is producing this damage is dynamic compressive stresses during passage of the rupture front.

  3. Winnetka deformation zone: Surface expression of coactive slip on a blind fault during the Northridge earthquake sequence, California. Evidence that coactive faulting occurred in the Canoga Park, Winnetka, and Northridge areas during the 17 January 1994, Northridge, California earthquake

    Energy Technology Data Exchange (ETDEWEB)

    Cruikshank, K.M. [Portland State Univ., OR (United States). Dept. of Geology; Johnson, A.M. [Purdue Univ., West Lafayette, IN (United States). Dept. of Earth and Atmospheric Sciences; Fleming, R.W. [Geological Survey, Denver, CO (United States); Jones, R.L. [City of Los Angeles, CA (United States). Dept. of Public Works


    Measurements of normalized length changes of streets over an area of 9 km{sup 2} in San Fernando Valley of Los Angeles, California, define a distinctive strain pattern that may well reflect blind faulting during the 1994 Northridge earthquake. Strain magnitudes are about 3 {times} 10{sup {minus}4}, locally 10{sup {minus}3}. They define a deformation zone trending diagonally from near Canoga Park in the southwest, through Winnetka, to near Northridge in the northeast. The deformation zone is about 4.5 km long and 1 km wide. The northwestern two-thirds of the zone is a belt of extension of streets, and the southeastern one-third is a belt of shortening of streets. On the northwest and southeast sides of the deformation zone the magnitude of the strains is too small to measure, less than 10{sup {minus}4}. Complete states of strain measured in the northeastern half of the deformation zone show that the directions of principal strains are parallel and normal to the walls of the zone, so the zone is not a strike-slip zone. The magnitudes of strains measured in the northeastern part of the Winnetka area were large enough to fracture concrete and soils, and the area of larger strains correlates with the area of greater damage to such roads and sidewalks. All parts of the pattern suggest a blind fault at depth, most likely a reverse fault dipping northwest but possibly a normal fault dipping southeast. The magnitudes of the strains in the Winnetka area are consistent with the strains produced at the ground surface by a blind fault plane extending to depth on the order of 2 km and a net slip on the order of 1 m, within a distance of about 100 to 500 m of the ground surface. The pattern of damage in the San Fernando Valley suggests a fault segment much longer than the 4.5 km defined by survey data in the Winnetka area. The blind fault segment may extend several kilometers in both directions beyond the Winnetka area. This study of the Winnetka area further supports

  4. Crustal Anisotropy Beneath the Western Segment of North Anatolian Fault Zone from Local Shear-Wave Splitting (United States)

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


    Shear-wave splitting from local earthquakes provides valuable knowledge on anisotropy of the upper crust. Upper-crustal anisotropy is widely interpreted as due to aligned fluid-filled cracks or pores. Differential stress is thought to close cracks aligned perpendicular to the maximum principal stress and leaves cracks open that are aligned perpendicular to the minimum horizontal compressional stress. In other cases local shear-wave splitting has been found to be aligned with regional faulting. Temporal variations in local splitting patterns might provide hints of changes in stress orientation related to earthquakes or volcanoes. North Anatolian Fault Zone (NAFZ) is a large-scale continental strike slip fault system originating at the Karlıova Junction in the east where it intersects the East Anatolian Fault (EAF) and extends west cutting across the entire Northern Turkey towards the Aegean Sea and the mainland Greece. Our primary focus is to provide constraints on the crustal anisotropy beneath the western segment of the North Anatolian Fault Zone with the use of a data set collected from a dense temporary seismic network consisting of 70 stations that was deployed in early May 2012 and operated for 18 months in the Sakarya region and the surroundings during the Faultlab experiment. For the local shear wave splitting analysis, out of 1344 events, we extracted 90 well located earthquakes with magnitudes greater than 2.0. Local shear-wave splitting makes use of earthquakes close to and nearly directly below the recording station. Incidence angles of less than 45 degrees were used to avoid the free-surface effect and resulting non-linear particle motion. Basically, two essential parameters for each station-event pair is needed for shear wave splitting calculations. One of them is fast polarization direction (ɸ) and the other is delay time (δt) between the fast and slow components of the shear wave. In this study, delay times vary between 0,02 and 0,25 seconds

  5. Age and isotopic systematics of Cretaceous borehole and surface samples from the greater Los Angeles Basin region: Implications for the types of crust that might underlie Los Angeles and their distribution along late Cenozoic fault systems (United States)

    Premo, Wayne R.; Morton, Douglas M.; Kistler, Ronald W.


    Nine U-Pb zircon ages were determined on plutonic rocks sampled from surface outcrops and rock chips of drill core from boreholes within the greater Los Angeles Basin region. In addition, lead-strontium-neodymium (Pb-Sr-Nd) whole-rock isotopic data were obtained for eight of these samples. These results help to characterize the crystalline basement rocks hidden in the subsurface and provide information that bears on the tectonic history of the myriad of fault systems that have dissected the Los Angeles region over the past 15 m.y. Seven of the nine samples have U-Pb ages ranging from 115 to 103 Ma and whole-rock Pb-Sr-Nd isotopic characteristics that indicate the crystalline basement underneath the greater Los Angeles Basin region is mostly part of the Peninsular Ranges batholith. Furthermore, these data are interpreted as evidence for (1) the juxtaposition of mid-Cretaceous, northern Peninsular Ranges batholith plutonic rocks against Late Cretaceous plutonic rocks of the Transverse Ranges in the San Fernando Valley, probably along the Verdugo fault; (2) the juxtaposition of older northwestern Peninsular Ranges batholith rocks against younger northeastern Peninsular Ranges batholith rocks in the northern Puente Hills, implying transposition of northeastern Peninsular Ranges batholith rocks to the west along unrecognized faults beneath the Chino Basin; and (3) juxtaposition of northern Peninsular Ranges batholith plutonic rocks against Late Cretaceous plutonic rocks of the Transverse Ranges along the San Jose fault in the northern San Jose Hills at Ganesha Park. These mainly left-lateral strike-slip faults of the eastern part of the greater Los Angeles Basin region could be the result of block rotation within the adjacent orthogonal, right-lateral, Elsinore-Whittier fault zone to the west and the subparallel San Jacinto fault zone to the east. The San Andreas fault system is the larger, subparallel, driving force further to the east.

  6. VLF-EM prospecting for the characterization of a fault zone and the evaluation of its permeability conditions. (United States)

    Fais, Silvana; Ligas, Paola; Cuccuru, Francesco; Maggio, Enrico; Plaisant, Alberto; Pettinau, Alberto; Pala, Antonio


    An electromagnetic VLF survey was carried out to characterize a fault zone in south-western Sardinia (Italy) and to investigate its permeability conditions. The VLF method is passive because instead of a transmitter-receiver system, as in an active electromagnetic method, it uses signals from distant radio stations operating in the very low 15-25 kHz frequency range used for military transmissions. In this survey the station UMS (Moscow - Russia) operating at 17.1 kHz was used to perform four NW-SE electromagnetic profiles at 10m station intervals over the study area where a NE-SW fault zone was supposed. A WADI-ABEM system was used for the VLF data acquisition survey. The VLF-EM data were first interpreted using the Karous-Hjelt linear filter (Karous-Hjelt, 1983; Ogilvy and Lee, 1991) which allows the generation of apparent current density pseudosections by filtering the in-phase data. The pseudosections provide a representation of the depth of the various current concentrations and hence the spatial arrangement of subsurface geological features such as faults, fracture zones and geological contacts. However, on analyzing the Karous-Hjelt current density pseudosections, VLF data are useful to produce a qualitative view of the subsurface structure. The quantitative interpretation of the VLF data was done with a 2-D code for the VLF data inversion. The initial model was constrained considering the results of previous resistivity laboratory measurements carried out on samples from the main geological formations outcropping in the survey area. In all the Karous-Hjelt pseudosections as also in the 2D resistivity models many conductive zones are present (resistivity lower than 440 Ωm in good agreement with the results obtained from the previous laboratory measurements). Some of the conductive zones are located along an ideal alignment that can be linked with a structural discontinuity whose presence was hypothesized in the area. The conductive zones detected with the

  7. Latest Quaternary paleoseismology and evidence of distributed dextral shear along the Mohawk Valley fault zone, northern Walker Lane, California (United States)

    Gold, Ryan D.; Briggs, Richard W.; Personius, Stephen F.; Crone, Anthony J.; Mahan, Shannon A.; Angster, Stephen J.


    The dextral-slip Mohawk Valley fault zone (MVFZ) strikes northwestward along the eastern margin of the Sierra Nevada in the northern Walker Lane. Geodetic block modeling indicates that the MVFZ may accommodate ~3 mm/yr of regional dextral strain, implying that it is the highest slip-rate strike-slip fault in the region; however, only limited geologic data are available to constrain the system's slip rate and earthquake history. We mapped the MVFZ using airborne lidar data and field observations and identified a site near Sulphur Creek for paleoseismic investigation. At this site, oblique dextral-normal faulting on the steep valley margin has created a closed depression that floods annually during spring snowmelt to form an ephemeral pond. We excavated three fault-perpendicular trenches at the site and exposed pond sediment that interfingers with multiple colluvial packages eroded from the scarp that bounds the eastern side of the pond. We documented evidence for four surface-rupturing earthquakes on this strand of the MVFZ. OxCal modeling of radiocarbon and luminescence ages indicates that these earthquakes occurred at 14.0 ka, 12.8 ka, 5.7 ka, and 1.9 ka. The mean ~4 kyr recurrence interval is inconsistent with slip rates of ~3 mm/yr; these rates imply surface ruptures of more than 10 m per event, which is geologically implausible for the subdued geomorphic expression and 60 km length of the MVFZ. We propose that unidentified structures not yet incorporated into geodetic models may accommodate significant dextral shear across the northern Walker Lane, highlighting the role of distributed deformation in this region.

  8. Influence of subduction zone conditions and gouge composition on frictional slip stability of megathrust faults

    NARCIS (Netherlands)

    den Hartog, S.A.M.; Spiers, C.J.


    To understand the temperature/depth distribution of destructive earthquakes in subduction megathrusts, and the mechanisms of nucleation of these events, data on the frictional behaviour of phyllosilicate/quartz-rich megathrust fault gouges under in-situ conditions are needed. We performed rotary

  9. Mapping the geothermal potential of fault zones in the Belgium-Netherlands border region

    NARCIS (Netherlands)

    Loveless, S.; Pluymaekers, M.P.D.; Lagrou, D.; Boever, E. de; Doornenbal, H.; Laenen, B.


    Faults can determine the success or failure of low enthalpy geothermal projects. This is due to their capacity to behave as pathways or baffles to geothermal water (or both simultaneously) and their prevalence throughout the subsurface. Here we present an initial assessment of the possibility for

  10. Progressive Evolution of the Valles Marineris Fault Zone and its Role in Controlling Interior Layered Deposits and Outflow Channels (United States)

    Watkins, J.; Yin, A.


    Most recent studies of Valles Marineris concluded that its interior layered deposits (ILDs) were accumulated after the formation of the Valles Marineris trough system. Some workers also suggest that the ILDs originated from sedimentation in lakes within the Valles Marineris troughs, and that the sudden release of lake waters to the northern lowlands created the spectacular outflow channels at the eastern end of the Valles Marineris trough zone, leaving mounds of ILD sediments exposed within the troughs. The sudden release of water has been commonly related to erosion of damming of the troughs induced by glacial or mass-wasting depositional processes. In all existing models linking the ILDs to the outflow channels, the shape of the Valles Marineris trough system upon deposition of the ILDs was regarded to be constant. However, this notion is at odds with the new observation that the development of the Valles Marineris fault zone, a left-slip transtensional structure, continued to be dynamic throughout at least part of the sedimentation of the ILDs. This conflict prompts analysis of the role of the progressive opening of the Valles Marineris trough system in controlling the spatial and temporal evolution of ILDs and their relationship to the formation of the circum-Chryse outflow channels. Here, we test the hypothesis that the Valles Marineris trough system was a single intra-canyon lake and its outlet was progressively opened by normal faulting at the eastern end of the trough zone, releasing the floodwaters that formed the equatorial outflow channels. Our model sharply contrasts alternative mechanisms for producing the outflow channels such as progressive overtopping of structurally isolated lakes, rapid release of a subsurface groundwater aquifer, rapid release of stored ice, and episodic flooding. This tectonic damming makes specific predictions on the spatial relationships among (1) the evolution of the Valles Marineris fault zone, (2) the deposition and

  11. Lithostratigraphic development and neotectonic significance of the Quaternary sediments along the Kachchh Mainland Fault (KMF) zone, western India (United States)

    Chowksey, V.; Maurya, D. M.; Joshi, Parul; Khonde, N.; Das, Archana; Chamyal, L. S.


    The Kachchh Mainland Fault (KMF) is a major E-W trending seismically active fault of the Kachchh palaeorift basin whose neotectonic evolution is not known. The present study deals with the eastern part of the KMF zone where the fault is morphologically expressed as steep north facing scarps and is divisible into five morphotectonic segments. The Quaternary sediments occurring in a narrow zone between the E-W trending KMF scarps and the flat Banni plain to the north are documented. The sediments show considerable heterogeneity vertically as well as laterally along the KMF zone. (The Quaternary sediments for a northward sloping and are exposed along the north flowing streams which also show rapid decrease in the depth of incision in the same direction.) The deposits, in general, comprise coarse as well as finer gravelly deposits, sands and aeolian and fluvial miliolites. The Quaternary sediments of the KMF zone show three major aggradation phases. The oldest phase includes the colluvio-fluvial sediments occurring below the miliolites. These deposits are strikingly coarse grained and show poor sorting and large angular clasts of Mesozoic rocks. The sedimentary characteristics indicate deposition, dominantly by debris flows and sediment gravity flows, as small coalescing alluvial fans in front of the scarps. These deposits suggest pre-miliolite neotectonic activity along the KMF. The second aggradation phase comprises aeolian miliolites and fluvially reworked miliolites that have been previously dated from middle to late Pleistocene. The youngest phase is the post-miliolite phase that includes all deposits younger than miliolite. These are represented by comparatively finer sandy gravels, gravelly sands and sand. The sediment characteristics suggest deposition in shallow braided stream channels under reduced level of neotectonic activity along the KMF during post-miliolite time evidenced by vertical dips of miliolites and tilting of gravels near the scarps. The

  12. New insights into the distribution and evolution of the Cenozoic Tan-Lu Fault Zone in the Liaohe sub-basin of the Bohai Bay Basin, eastern China (United States)

    Huang, Lei; Liu, Chi-yang; Xu, Chang-gui; Wu, Kui; Wang, Guang-yuan; Jia, Nan


    As the largest strike-slip fault system in eastern China, the northeast-trending Tan-Lu Fault Zone (TLFZ) is a significant tectonic element contributing to the Mesozoic-Cenozoic regional geologic evolution of eastern Asia, as well as to the formation of ore deposits and oilfields. Because of the paucity of data, its distribution and evolutionary history in the offshore Liaohe sub-basin of the northern Bohai Bay Basin (BBB) are still poorly understood. Investigations of the strike-slip fault system in the western portion of the offshore Liaohe sub-basin via new seismic data provide us with new insights into the characteristics of the Cenozoic TLFZ. Results of this study show that Cenozoic dextral strike-slip faults occurred near the center of the Liaoxi graben in the offshore Liaohe sub-basin; these strike-slip faults connect with their counterparts to the north, the western part of the onshore Liaohe sub-basin, and have similar characteristics to those in other areas of the BBB in terms of kinematics, evolutionary history, and distribution; consequently, these faults are considered as the western branch of the TLFZ. All strike-slip faults within the Liaoxi graben merge at depth with a central subvertical basement fault induced by the reactivation of a pre-existing strike-slip basement fault, the pre-Cenozoic TLFZ. Data suggest that the TLFZ across the whole Liaohe sub-basin comprises two branches and that the Cenozoic distribution of this system was inherited from the pre-Cenozoic TLFZ. This characteristic distribution might be possessed by the whole TLFZ, thus the new understandings about the distribution and evolutionary model of the TLFZ in this study can be inferred in many research fields along the whole fault zone, such as regional geology, ore deposits, petroleum exploration and earthquake hazard.

  13. Geoelectrical behavior of a Fault Zone: the meaning of the electrical resistivity of metric-scale segments of the Liquiñe-Ofqui and the Arc-oblique Long-lived Fault Systems, Southern Andes (United States)

    Roquer, T.; Arancibia, G.; Yanez, G. A.; Estay, N.; Rowland, J. V.; Figueroa, R.; Iturrieta, P. C.


    The geoelectrical behavior of blind fault zones has been studied by different authors at decametric-to-kilometric scales, and inferred to reveal the dimensions of the main structural domains of a fault zone (core vs. damage zone). However, there is still a lack in the application of electrical methods in exposed fault zones, despite the importance of validating the inferences based on electrical measurements with direct geologic observation. In this study we correlate the results of structural mapping and geoelectrical measurements in two metric-scale, very well exposed segments of the Liquiñe-Ofqui Fault System (LOFS) and the Arc-oblique Long-lived Fault System (ALFS), Southern Andes. The LOFS is an active dextral and dextral-normal ca. 1200-km-long Cenozoic intra-arc structure that strikes NNE to NE. Although the LOFS and the ALFS cross-cut each other, the ALFS is an apparently older basement NW-striking fault system where mainly sinistral movement is recorded. Two 22-m-long transects were mapped revealing in both examples a simple core and an assymetric damage zone with more frequency of fractures in the hanging wall than in the footwall. The LOFS outcrop showed a WNW-striking, 65°S-dipping core; the ALFS, a NW-striking, 60°SW-dipping core. A 2D direct-current electrical survey was made at each locality, orthogonal to the respective strike of the core. The field installation of the electrical survey used two electrode configurations for each outcrop: (1) electrodes were put in a vertical wall of rock, which gives a resistivity profile in plan view; and (2) electrodes were put in the ground, which gives a cross-section resistivity profile. The combined structural and electrical results suggest that: (1) it is possible to discriminate the geoelectrical response of the main metric-scale structural domains: the core and the fractured damage zones are relative conductors (20-200 ohm-m), whereas the less fractured damage zones are relative resistive volumes (500

  14. Microstructural and fabric characterization of brittle-ductile transitional deformation of middle crustal rocks along the Jinzhou detachment fault zone, Northeast China (United States)

    Zhang, Juyi; Jiang, Hao; Liu, Junlai


    Detachment fault zones (DFZs) of metamorphic core complexes generally root into the middle crust. Exhumed DFZs therefore generally demonstrate structural, microstructural and fabric features characteristic of middle to upper crustal deformation. The Jinzhou detachment fault zone from the Liaonan metamorphic core complex is characterized by the occurrence of a sequence of fault rocks due to progressive shearing along the fault zone during exhumation of the lower plate. From the exhumed fabric zonation, cataclastic rocks formed in the upper crust occur near the Jinzhou master detachment fault, and toward the lower plate gradually changed to mylonites, mylonitic gneisses and migmatitic gneisses. Correspondingly, these fault rocks have various structural, microstructural and fabric characteristics that were formed by different deformation and recrystallization mechanisms from middle to upper crustal levels. At the meanwhile, various structural styles for strain localization were formed in the DFZ. As strain localization occurs, rapid changes in deformation mechanisms are attributed to increases in strain rates or involvement of fluid phases during the brittle-ductile shearing. Optical microscopic studies reveal that deformed quartz aggregates in the lower part of the detachment fault zone are characterized by generation of dynamically recrystallized grains via SGR and BLG recrystallization. Quartz rocks from the upper part of the DFZ have quartz porphyroclasts in a matrix of very fine recrystallized grains. The porphyroclasts have mantles of sub-grains and margins grain boundary bulges. Electron backscattered diffraction technique (EBSD) quartz c-axis fabric analysis suggests that quartz grain aggregates from different parts of the DFZ possess distinct fabric complexities. The c-axis fabrics of deformed quartz aggregates from mylonitic rocks in the lower part of the detachment fault zone preserve Y-maxima which are ascribed to intermediate temperature deformation (500

  15. Deep underground recording of induced and natural earthquakes to investigate rupture processes and fault-zone strength (United States)

    McGarr, A.; Boettcher, M. S.; Fletcher, J. B.; Johnston, M. J.


    Seismic recording systems, installed at deep levels in mines or boreholes, yield seismograms from nearby earthquakes that are relatively free of ambient noise and secondary arrivals. This makes it straightforward to determine moment tensors and other source parameters of interest. The maximum slip within an earthquake rupture zone, inferred from the velocity pulse of the S wave, is combined with the seismic moment to define a laboratory stick-slip friction experiment that has the same maximum slip rate and yield stress as the earthquake. Ground motions from mining-induced earthquakes, of about M2, recorded using broadband stations installed at depths between 2 and 3.6 km in two of the deepest gold mines in South Africa were analyzed in this way to infer peak slip rates ranging up to about 10 m/s and yield stresses of as much as 150 MPa. Because the near-fault peak ground velocity is about half of the maximum slip rate, this result indicates that underground support should be capable of withstanding peak ground velocities of 5 m/s. Analysis of 11 mine tremors resulted in a median maximum slip rate of 3.8 m/s and a median yield stress of 62 MPa. The same analysis of ground motion from a M2.1 repeating earthquake near Parkfield, California, recorded in October 2003 using an extensive string of seismometers installed at depth in the SAFOD pilot hole, revealed similar results, a maximum slip rate of 4 m/s and a yield stress of 64 MPa. This similarity is somewhat unexpected in view of tectonic settings and pore pressures that are quite different. Whereas the mining-induced earthquakes occur in a stable tectonic setting and zero pore pressure environment, repeating earthquakes along the San Andreas are due to active plate-boundary faulting at hydrostatic pore pressure, at least near SAFOD. Analyses of heat flow data indicate that the shear strength of the San Andreas fault near SAFOD is less than 20 MPa and in situ stress measurements there show that the regional shear

  16. Investigation of long period crustal deformation on the inactive branch of the North Anatolian Fault Zone (United States)

    Akay, G.; Ozener, H.


    The western part of North Anatolian Fault (NAF) bifurcates around Mudurnu into two fault segments: northern and southern branch. The latter bifurcates again at west of Pamukova and creates middle strand. This study aimed to analyze crustal movement along the middle strand near Iznik which is considered as inactive fault. We focused on a microgeodetic network called General Command of Mapping-Istanbul Technical University (GCM-ITU) network around this segment. In order to obtain displacement values, five campaigns performed on the network which were used in the study. The displacements of the stations were estimated relative to the fixed stations located at the south of the network. The coordinates of the stations were calculated from the triangulation measurements realized in 1941 and 1963, trilateration measurements in 1981, and GPS campaigns in 2004 and 2007. Then, mean displacements of the network ranging between 7 mm/yr and 18 mm/yr were obtained for these years. In the second part of the study, the GPS data were re-processed by adding three stations from Marmara Continuous GPS Network (MAGNET). Details of MAGNET can be found Ergintav et al. (2002). Estimated displacements were ranging between 3 mm/yr and 13 mm/yr for 2004 and 2007. TUBI station of IGS network was taken as stable.

  17. Investigation of long period crustal deformation on the inactive branch of the North Anatolian Fault Zone

    Directory of Open Access Journals (Sweden)

    G. Akay


    Full Text Available The western part of North Anatolian Fault (NAF bifurcates around Mudurnu into two fault segments: northern and southern branch. The latter bifurcates again at west of Pamukova and creates middle strand. This study aimed to analyze crustal movement along the middle strand near Iznik which is considered as inactive fault. We focused on a microgeodetic network called General Command of Mapping-Istanbul Technical University (GCM-ITU network around this segment. In order to obtain displacement values, five campaigns performed on the network which were used in the study. The displacements of the stations were estimated relative to the fixed stations located at the south of the network. The coordinates of the stations were calculated from the triangulation measurements realized in 1941 and 1963, trilateration measurements in 1981, and GPS campaigns in 2004 and 2007. Then, mean displacements of the network ranging between 7 mm/yr and 18 mm/yr were obtained for these years.

    In the second part of the study, the GPS data were re-processed by adding three stations from Marmara Continuous GPS Network (MAGNET. Details of MAGNET can be found Ergintav et al. (2002. Estimated displacements were ranging between 3 mm/yr and 13 mm/yr for 2004 and 2007. TUBI station of IGS network was taken as stable.

  18. A Uniform Fault Zone Diffusivity Structure in the Simi Valley Based on Water Level Tidal and Barometric Response (United States)

    Xue, L.; Brodsky, E. E.; Allègre, V.; Parker, B. L.; Cherry, J. A.


    measurement and there is no major fault-guided hydrogeological channel at the site. Such homogenous by fault zone damage is possible in a region of multiple strands and copious secondary faulting.

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

    KAUST Repository

    Wu, Guangliang


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

  20. Experimental constraints on the relationship between clay abundance, clay fabric, and frictional behavior for the Central Deforming Zone of the San Andreas Fault (United States)

    Wojatschke, Jasmaria; Scuderi, Marco M.; Warr, Laurence N.; Carpenter, Brett M.; Saffer, Demian; Marone, Chris


    The presence of smectite (saponite) in fault gouge from the Central Deforming Zone of the San Andreas Fault at Parkfield, CA has been linked to low mechanical strength and aseismic slip. However, the precise relationship between clay mineral structure, fabric development, fault strength, and the stability of frictional sliding is not well understood. We address these questions through the integration of laboratory friction tests and FIB-SEM analysis of fault rock recovered from the San Andreas Fault Observatory at Depth (SAFOD) borehole. Intact fault rock was compared with experimentally sheared fault gouge and different proportions of either quartz clasts or SAFOD clasts extracted from the sample. Nano-textural measurements show the development of localized clay particle alignment along shear folia developed within synthetic gouges; such slip planes have multiples of random distribution (MRD) values of 3.0-4.9. The MRD values measured are higher than previous estimates (MRD 1.5) that show lower degrees of shear localization and clay alignment averaged over larger volumes. The intact fault rock exhibits less well-developed nano-clay fabrics than the experimentally sheared materials, and MRD values decrease with smectite content. We show that the abundance, strength, and shape of clasts all influence fabric evolution via strain localization: quartz clasts yield more strongly developed clay fabrics than serpentine-dominated SAFOD clasts. Our results suggest that (1) both clay abundance and the development of nano-scale fabrics play a role in fault zone weakening and (2) aseismic creep is promoted by slip along clay shears with >20 wt % smectite content and MRD values ≥2.7.

  1. Fault Coupling, Slip Rate Deficit and Strain Accumulation of the Haiyuan-Liupanshan Fault Zone in the Northeastern Margin of the Tibetan Plateau (United States)

    Li, Y.; Shan, X.; Qu, C.; Song, X.; Jiang, Y.; Gong, W.; Zhang, G.; Zhang, Y.


    The Haiyuan-Liupanshan fault is one of the main left-lateral fault system in the northeastern edge of the Tibetan Plateau, which contributes to the rising and eastward extrusion of lithospheric blocks. It is a particularly well-suited area to understand the mechanisms of deformation which led to the growth and rise of the Tibet. Besides, the unbroken section (the Tianzhu seismic gap), which was bracketed by two M8 earthquakes (1920 and 1927), was interpreted with high seismic potential. Based on the GPS and geology (slip rate and fault slip vector azimuth) data, we invert for the fault coupling, the slip rate deficit and the strain rate accumulation along the Haiyuan-Liupanshan fault. It's of great importance for a better understanding of interseismic deformation, strain loading and seismic potential assessment. Along the Haiyuan fault, the results show 3.2-6.2 mm/yr of left-lateral strike-slip, and the strike-slip transformed into thrusting deformation (2.8-3.5 mm/yr) along the Liupanshan fault. The results suggest full coupling down to 10 km along the Haiyuan fault. Significant portions from the Jinqianghe fault to the Maomaoshan fault, however, are locked to 23 km depth. The abrupt change in fault coupling coincides with the Tianzhu seismic gap. High slip rate deficit (3.0-4.5 mm/yr) and seismic moment accumulation rate are also interpreted along the seismic gap. The Liupanshan fault is locked to 15-20 km depth. A high seismic moment accumulation rate but low slip rate deficit (2.0-3.2 mm/yr) are inverted along the fault. The fault locking depth is negatively correlated with the coulomb stress accumulation rate and the second invariant of the strain rate tensor. That is, low strain accumulation rates are inverted along the seismic gap and the Liupanshan fault. A possible explanation is that the total amount of the elastic strain along the fault may have reached a high level, but with a low accumulation rate. High seismic hazard are interpreted considering the

  2. Stability of zircon u-pb systematics in a greenschist-grade mylonite - an example from the rockfish valley fault zone, central Virginia, USA


    Wayne, D. M.; Sinha, A. K.


    The mid-Paleozoic, greenschist-grade Rockfish Valley Fault Zone (RVFZ) of central Virginia cuts the Grenville-aged Pedlar River Charnockite Suite (PRCS) and contains zircons that underwent brittle failure during ductile deformation. Electron microprobe analyses and scanning electron microscope (SEM) backscattered electron (BSE) imaging show that zircons from the protolith PRCS are concentrically zoned (with alternating U-Hf-rich and U-Hf-poor bands), and contain numerous radial microcracks. Z...

  3. Carbon monoxide degassing from seismic fault zones in the Basin and Range province, west of Beijing, China (United States)

    Sun, Yutao; Zhou, Xiaocheng; Zheng, Guodong; Li, Jing; Shi, Hongyu; Guo, Zhengfu; Du, Jianguo


    Degassing of carbon monoxide (CO), which plays a significant role in the contribution of deep carbon to the atmosphere, commonly occurs within active fault zones. CO degassing from soil to the atmosphere in the Basin and Range province, west of Beijing (BRPB), China, was investigated by in-situ field measurements in the active fault zones. The measured concentrations of CO in soil gas in the BRPB ranged from 0.29 × 10-6 to 1.1 × 10-6 with a mean value of 0.6 × 10-6, which is approximately twice as large as that in the atmosphere. Net fluxes of CO degassing ranged from -48.6 mg m-2 d-1 to 12.03 mg m-2 d-1. The diffusion of CO from soil to the atmosphere in the BRPB was estimated to be at least 7.6 × 103 ton/a, which is comparable to the corresponding result of about 1.2 × 104 ton/a for CO2. CO concentrations were spatially heterogeneous with clearly higher concentrations along the NE-SW trending in the BRPB. These elevated values of CO concentrations were also coincident with the region with low-velocity and high conductivity in deep mantle, and high Poisson's ratio in the crust, thereby suggesting that CO degassing from the soil might be linked to upwelling of the asthenospheric mantle. Other sources of CO in the soil gas are suggested to be dominated by chemical reactions between deep fluids and carbonate minerals (e.g., dolomite, limestone, and siderite) in country rocks. Biogenic processes may also contribute to the CO in soil gas. The spatial distribution patterns of CO concentrations are coincident with the stress field, suggesting that the concentrations of CO could be a potential indicator for crustal stress field and, hence is potential useful for earthquake monitoring in the BRPB.

  4. Investigation of late Pleistocene and Holocene activity in the San Gregorio fault zone on the continental slope north of Monterey Canyon, offshore central California (United States)

    Maier, Katherine L.; Paull, Charles K.; Brothers, Daniel; Caress, David W.; McGann, Mary; Lundsten, Eve M.; Anderson, Krystle; Gwiazda, Roberto


    We provide an extensive high‐resolution geophysical, sediment core, and radiocarbon dataset to address late Pleistocene and Holocene fault activity of the San Gregorio fault zone (SGFZ), offshore central California. The SGFZ occurs primarily offshore in the San Andreas fault system and has been accommodating dextral strike‐slip motion between the Pacific and North American plates since the mid‐Miocene. Our study focuses on the SGFZ where it has been mapped through the continental slope north of Monterey Canyon. From 2009 to 2015, the Monterey Bay Aquarium Research Institute collected high‐resolution multibeam bathymetry and chirp sub‐bottom profiles using an autonomous underwater vehicle (AUV). Targeted samples were collected using a remotely operated vehicle (ROV) to provide radiocarbon age constraints. We integrate the high‐resolution geophysical data with radiocarbon dates to reveal Pleistocene seismic horizons vertically offset less than 5 m on nearly vertical faults. These faults are buried by continuous reflections deposited after ∼17.5  ka and likely following erosion during the last sea‐level lowstand ∼21  ka, bracketing the age of faulting to ∼32–21  ka. Clearly faulted horizons are only detected in a small area where mass wasting exhumed older strata to within ∼25  m of the seafloor. The lack of clearly faulted Holocene deposits and possible highly distributed faulting in the study area are consistent with previous interpretations that late Pleistocene and Holocene activity along the SGFZ may decrease to the south. This study illustrates the complexity of the SGFZ, offshore central California, and demonstrates the utility of very high‐resolution data from combined AUV (geophysical)–ROV (seabed sampling) surveys in offshore studies of fault activity.

  5. ANN reconstruction of geoelectrical parameters of the Minou fault zone by scalar CSAMT data (United States)

    Spichak, V.; Fukuoka, K.; Kobayashi, T.; Mogi, T.; Popova, I.; Shima, H.


    Scalar controlled source AMT data collected in a northern part of the Minou fault area (Kyushu Island, Japan) are interpreted by means of the ANN Expert System MT-NET in terms of 3-D earth macro-parameters. A number of synthetic responses created in advance by means of forward modeling in typical 3-D geoelectrical models (conductive and resistive local bodies, fault, dyke, etc.) formed sequences for teaching an artificial neural network (ANN). MT-NET, once taught to the correspondence between the data images and the model parameters, is able to recognize unknown parameters given even incomplete and noisy data. The results of ANN reconstruction are compared with the resistivity distribution obtained for the same area using fast 3-D imaging based on synthesis of 1-D Bostick transforms of the apparent resistivities beneath each site as well as on 2-D TM mode inversion along four profiles. The best-fitting model reconstructed by ANN belongs to the guessed model class formed by "dykes buried in the two-layered earth", on the one hand, and to the equivalence class formed by all models giving rms misfit less than the noise level in the data, on the other hand.

  6. Coseismic brecciation at fault stepovers and transient fluid pathways in a mid-crustal San Andreas analogue: The Pofadder Shear Zone, Namibia and South Africa (United States)

    Melosh, B. L.; Rowe, C. D.; Gerbi, C. C.


    Fluid transport along faults is important throughout the seismic cycle due to the effects on fault strength. Rheological boundaries in the crust such as the quartz brittle-plastic transition coincide with permeability changes, and play an important role in controlling fluid distribution. Here we present a newly recognized mechanism for fluid migration through the brittle-plastic transition in an ancient San Andreas Fault analogue: The Pofadder Shear Zone in Namibia and South Africa. Breccias formed in elongate pods during the passage of an earthquake rupture through a fault stepover. These breccias form subvertical fluid pathways (perpendicular to the slip direction). Over time, many overprinting or adjacent ruptures could have allowed fluid migration over a large (~ kms) scale, facilitating fluid flow through a low porosity region of the crust. These pathways were subsequently closed during breccia compaction by crystal plastic flow, facilitated by the presence of fluids. Thus, fluid migration within and across the brittle-plastic transitional zone is time and rate dependent and can both cause fault weakening and strengthening. We observed breccias formed in slip events with displacements between ~1-15 cm, consistent with small to moderate magnitude earthquakes and/or tectonic tremor, which occurs at similar depths in the San Andreas Fault. In addition to providing a new way of identifying paleo-seismic slip in the rock record, these observations may help explain co- post-seismic fluid advection in mid-crustal faults. This process of local brecciation in stepovers may be the origin of cryptic geophysical signals such as tremor bursts in continental faults.

  7. Definition and Paleoseismology of the Active, Left-Lateral Enriquillo-Plantain Garden Fault Zone Based on High-Resolution Chirp Profiles: Lakes Azuey and Mirogoane, Haiti (United States)

    Wang, J.; Mann, P.; von Lignau, A. V.


    In July 2014, we obtained a total of 94 km of high-resolution Chirp profiles from the 129 km2, brackish Lake Azuey and 37 km of profiles from the 14 km2, fresh water Lake Mirogoane that both straddle the active trace of the Enriquillo-Plantain Garden fault zone (EPGFZ) of Haiti. 80% of the grid on Azuey and 85% on Mirogoane was dedicated to north-south profiles of the EPGFZ. In Azuey we defined the linear and east-west-striking fault trace in deformed Holocene sediments along with its landfalls west of Lake Azuey in Haiti and east of Lake Azuey in the Dominican Republic. All profiles showed the fault to be a sub-vertical flower structure whose active traces could be traced on Chirp data to a depth of 30 m below the lake floor. Previous workers have suggested that this fault ruptured during a large November, 1751, earthquake with a parallel and elongate felt zone. We hypothesize the most recent break of the fault several meters below the lake floor to have formed during the 1751 event but plan a coring program to precisely constrain the timing of historical and prehistorical events based on syn-faulting colluvial wedges observed on Chirp profiles. Our survey of Mirogoane confirmed its rhomboidal pull-apart structure with the basin center at a depth of 42-8 m making this basin the deepest lake in the Caribbean region. Deformational features include active folds at the lake bottom, large oblique-slip normal faults at an angle to the bounding east-west faults, and 30 m of recognizable stratigraphy. The 7 m of Holocene cored in the basin center in 1988 is observed to be highly deformed and locally folded and overlies with angular unconformity a well stratified and more folded lower basinal unit. Historical events are proposed to have ruptured on or near this segment of the EPGFZ in 1701 and 1770.

  8. Rapid, decimeter-resolution fault zone topography mapped with Structure from Motion (United States)

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


    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

  9. An exceptionally long paleoseismic record of a slow-moving fault: The Alhama de Murcia fault (Eastern Betic shear zone, Spain)

    DEFF Research Database (Denmark)

    Ortuño, María.; Masana, Eulalia.; García-Meléndez, Eduardo.


    Most catastrophic earthquakes occur along fast-moving faults, although some of them are triggered by slow-moving ones. Long paleoseismic histories are infrequent in the latter faults. Here, an exceptionally long paleoseismic record (more than 300 k.y.) of a slow-moving structure is presented for ...

  10. Rheological weakening of high-grade mylonites during low-temperature retrogression: The exhumed continental Ailao Shan-Red River fault zone, SE Asia (United States)

    Cao, Shuyun; Neubauer, Franz; Liu, Junlai; Bernroider, Manfred; Cheng, Xuemei; Li, Junyu; Yu, Zunpu; Genser, Johann


    We present a detailed case study of an exhumed continental strike-slip fault zone, the Ailao Shan-Red River (ASRR) strike-slip fault zone, to investigate how deformation promotes strain localization, and how the weak second phases and fluids trigger rheological weakening during retrogression near the ductile to brittle transition during exhumation. Along the ASRR strike-slip fault zone, in the Diancang Shan (DCS) metamorphic massif, high-temperature ductile deformation (D1) pervasively occurred during shearing and exhumation since late Oligocene. The high-temperature microstructures and textures are in part or entirely altered by subsequent low-temperature shearing (D2) since late Miocene, which is under the conditions of frictional-viscous transition of K-feldspar (ca. 450 °C) during further exhumation to the upper crustal levels. The formation of D2 microstructures and shear bands overprinted high-temperature intracrystalline plasticity phases (D1) in mylonitic rocks. Depending on the main rock-forming minerals, the results also demonstrate that the brittle-ductile transition involves a combination of different deformation mechanisms and possible rheological paths. In quartz-rich rocks, quartz was deformed in the dislocation creep regime and records transition of microfabrics and slip systems during decreasing temperature, which lasted until retrogression related to exhumation. As a result, grain-size reduction associated with fluids circulating within the ASRR strike-slip fault zone at brittle-ductile transition leads to reaction and texture weakening. Rheological weakening is the consequence of the syntectonic deformation, fluid flow, reaction softening, reaction creep and textural softening. The hydrous fluids resulted in hydration of silicates. Decompression occurred during shearing and as a result of tectonic exhumation. All these results demonstrate that the exhumation through the ductile to ductile-brittle transition involves a combination of different

  11. Superimposed basin formation during Neogene-Quaternary extensional tectonics in SW-Anatolia (Turkey): Insights from the kinematics of the Dinar Fault Zone (United States)

    Alçiçek, M. Cihat; Brogi, Andrea; Capezzuoli, Enrico; Liotta, Domenico; Meccheri, Marco


    In the extensional province of SW-Anatolia, the cross-cutting relationship between the NW- and NE-oriented Neogene and Quaternary basins is an ongoing debate in the understanding of the tectonic evolution of this area. In order to contribute to this issue, we carried out a structural and kinematic study along the seismogenic NW-trending Dinar Fault Zone (DFZ). This structure was initially controlled by the sedimentary and tectonic evolution of the NE-oriented Neogene Baklan, Acıgöl and Burdur basins and, later, by the NW-oriented Quaternary Dinar Basin. On the basis of > 1000 structural and kinematic data, in conjunction with basin stratigraphy, the DFZ can be divided into three almost parallel and continuous bands, that are: (a) the Hangingwall where Quaternary sediments are deformed by normal faults with mechanical striations; (b) the Inner Zone, corresponding to the present Dinar fault scarp, where NW-trending normal faults with mechanical striations are dominant, and (c) the Outer Zone, located in the footwall of the structure comprising the area between the fault scarp and undeformed bedrock, where faults exhibit variable orientation and kinematics, from strike-slip to normal dip-slip. These kinematics are mainly indicated by calcite shear veins and superimposed mechanical striations, respectively. This suggests that the DFZ changed kinematics over time, i.e., the DFZ initiated as dominant dextral strike-slip to oblique-slip fault system and continued with a dominant normal movement. Therefore, we hypothesize that the NW-trending DFZ was initially a transfer zone during the late Miocene-Pliocene, coeval to the sedimentary and structural evolution of the NE-trending Baklan, Acigöl and Burdur basins. During the Quaternary the DFZ, representing an already weakened crustal sector, played the role of a normal fault system providing the accommodation space for the Quaternary Dinar Basin. Hydrothermal circulation and volcanism at NE-/NW-trending faults

  12. Continuity of the West Napa–Franklin fault zone inferred from guided waves generated by earthquakes following the 24 August 2014 Mw 6.0 South Napa earthquake (United States)

    Catchings, Rufus D.; Goldman, Mark R.; Li, Yong-Gang; Chan, Joanne


    We measure peak ground velocities from fault‐zone guided waves (FZGWs), generated by on‐fault earthquakes associated with the 24 August 2014 Mw 6.0 South Napa earthquake. The data were recorded on three arrays deployed across north and south of the 2014 surface rupture. The observed FZGWs indicate that the West Napa fault zone (WNFZ) and the Franklin fault (FF) are continuous in the subsurface for at least 75 km. Previously published potential‐field data indicate that the WNFZ extends northward to the Maacama fault (MF), and previous geologic mapping indicates that the FF extends southward to the Calaveras fault (CF); this suggests a total length of at least 110 km for the WNFZ–FF. Because the WNFZ–FF appears contiguous with the MF and CF, these faults apparently form a continuous Calaveras–Franklin–WNFZ–Maacama (CFWM) fault that is second only in length (∼300  km) to the San Andreas fault in the San Francisco Bay area. The long distances over which we observe FZGWs, coupled with their high amplitudes (2–10 times the S waves) suggest that strong shaking from large earthquakes on any part of the CFWM fault may cause far‐field amplified fault‐zone shaking. We interpret guided waves and seismicity cross sections to indicate multiple upper crustal splays of the WNFZ–FF, including a northward extension of the Southhampton fault, which may cause strong shaking in the Napa Valley and the Vallejo area. Based on travel times from each earthquake to each recording array, we estimate average P‐, S‐, and guided‐wave velocities within the WNFZ–FF (4.8–5.7, 2.2–3.2, and 1.1–2.8  km/s, respectively), with FZGW velocities ranging from 58% to 93% of the average S‐wave velocities.

  13. A Controllable Earthquake Rupture Experiment on the Homestake Fault (United States)

    Germanovich, L. N.; Murdoch, L. C.; Garagash, D.; Reches, Z.; Martel, S. J.; Gwaba, D.; Elsworth, D.; Lowell, R. P.; Onstott, T. C.


    Fault-slip is typically simulated in the laboratory at the cm-to-dm scale. Laboratory results are then up-scaled by orders of magnitude to understand faulting and earthquakes processes. We suggest an experimental approach to reactivate faults in-situ at scales ~10-100 m using thermal techniques and fluid injection to modify in situ stresses and the fault strength to the point where the rock fails. Mines where the modified in-situ stresses are sufficient to drive faulting, present an opportunity to conduct such experiments. During our recent field work in the former Homestake gold mine in the northern Black Hills, South Dakota, we found a large fault present on multiple mine levels. The fault is subparallel to the local foliation in the Poorman formation, a Proterozoic metamorphic rock deformed into regional-scale folds with axes plunging ~40° to the SSE. The fault extends at least 1.5 km along strike and dip, with a center ~1.5 km deep. It strikes ~320-340° N, dips ~45-70° NE, and is recognized by a ~0.3-0.5 m thick distinct gouge that contains crushed host rock and black material that appears to be graphite. Although we could not find clear evidence for fault displacement, secondary features suggest that it is a normal fault. The size and distinct structure of this fault make it a promising target for in-situ experimentation of fault strength, hydrological properties, and slip nucleation processes. Most earthquakes are thought to be the result of unstable slip on existing faults, Activation of the Homestake fault in response to the controlled fluid injection and thermally changing background stresses is likely to be localized on a crack-like patch. Slow patch propagation, moderated by the injection rate and the rate of change of the background stresses, may become unstable, leading to the nucleation of a small earthquake (dynamic) rupture. This controlled instability is intimately related to the dependence of the fault strength on the slip process and has been

  14. Field Evidences for Fault Surface Lubrication by Friction-Induced Melts During Coseismic Slip (United States)

    di Toro, G.; Teza, G.


    Lubrication by friction-induced melts has been proposed as a mechanism for fault weakening during earthquakes. Field evidence for melt lubrication of the fault surfaces is lacking, however, although the andesitic/basaltic composition (i.e. low-viscosity melts) of the matrix of many tectonic pseudotachylytes (solidified friction-induced melts) suggests low dynamic shear strength during coseismic slip. The Gole Larghe Fault Zone is an exhumed seismic source crosscutting the Adamello tonalites (Italian Southern Alps) and is exposed in a glacially polished area. In the fault zone, displacement is partitioned in more than 100 subparallel faults. Fault rocks are an association of pseudotachylytes and cataclasites produced at 6-8 km depth and 250-300 oC. Given the large extent of the outcrop and the large number of structural markers within the tonalites, it has been possible to reproduce the 2D profile (i.e. intersection of the fault surface with the outcrop surface) of 25 different pseudotachylyte-bearing faults and to relate the fault profile with the displacement accommodated by each fault. Two lines of field evidence suggest that shear strength is low during coseismic slip: 1) A maximum shear stress of only 20 MPa has been estimated from the amount of mechanical work converted to heat during coseismic slip to produce the measured volume of pseudotachylyte in single-jerk faults. Although a shear strength of 20 MPa is a minimum estimate since part of the displacement has been accommodated without production of pseudotachylytes, such strengths are very small considering the depth where seismic faulting has occurred. 2) The fractal dimension (measured with a box-counting method) of the 2D profile of pseudotachylyte-bearing faults increases from 1.0 to a constant value of 1.15 with increasing displacement. In experimentally generated friction melts, the fractal dimension of molten surfaces increases from 1.0 to 1.1 when, with increasing slip, a steady state value for the

  15. 3D features of delayed thermal convection in fault zones: consequences for deep fluid processes in the Tiberias Basin, Jordan Rift Valley (United States)

    Magri, Fabien; Möller, Sebastian; Inbar, Nimrod; Siebert, Christian; Möller, Peter; Rosenthal, Eliyahu; Kühn, Michael


    It has been shown that thermal convection in faults can also occur for subcritical Rayleigh conditions. This type of convection develops after a certain period and is referred to as "delayed convection" (Murphy, 1979). The delay in the onset is due to the heat exchange between the damage zone and the surrounding units that adds a thermal buffer along the fault walls. Few numerical studies investigated delayed thermal convection in fractured zones, despite it has the potential to transport energy and minerals over large spatial scales (Tournier, 2000). Here 3D numerical simulations of thermally driven flow in faults are presented in order to investigate the impact of delayed convection on deep fluid processes at basin-scale. The Tiberias Basin (TB), in the Jordan Rift Valley, serves as study area. The TB is characterized by upsurge of deep-seated hot waters along the faulted shores of Lake Tiberias and high temperature gradient that can locally reach 46 °C/km, as in the Lower Yarmouk Gorge (LYG). 3D simulations show that buoyant flow ascend in permeable faults which hydraulic conductivity is estimated to vary between 30 m/yr and 140 m/yr. Delayed convection starts respectively at 46 and 200 kyrs and generate temperature anomalies in agreement with observations. It turned out that delayed convective cells are transient. Cellular patterns that initially develop in permeable units surrounding the faults can trigger convection also within the fault plane. The combination of these two convective modes lead to helicoidal-like flow patterns. This complex flow can explain the location of springs along different fault traces of the TB. Besides being of importance for understanding the hydrogeological processes of the TB (Magri et al., 2015), the presented simulations provide a scenario illustrating fault-induced 3D cells that could develop in any geothermal system. References Magri, F., Inbar, N., Siebert, C., Rosenthal, E., Guttman, J., Möller, P., 2015. Transient

  16. Iowa Bedrock Faults (United States)

    Iowa State University GIS Support and Research Facility — This fault coverage locates and identifies all currently known/interpreted fault zones in Iowa, that demonstrate offset of geologic units in exposure or subsurface...

  17. A multidisciplinary approach for the characterisation of fault zones in geothermal areas in central Mexico (United States)

    Comina, Cesare; Ferrero, Anna Maria; Mandrone, Giuseppe; Vinciguerra, Sergio


    There are more than 500 geothermal areas in the Trans-Mexican Volcanic Belt of central Mexico. Of these, two are presently object of a transnational project between EU and Mexico (GEMex): Acoculco, where there is already a commercial exploitation, and Los Humeros, at present not developed yet. The GEMex project aims to improve the resource assessment and the reservoir characterization using novel geophysical and geological methods and interpretations. One of the main issues controlling the geothermal system is the presence of pervasive fracture systems affecting the carbonatic basements underlying the volcanic complex (basalts and andesites). We propose the characterization of rock masses (rock and fractures) using a multiscale analysis, from the field to the outcrop up to the micro scale integrating a number of techniques. In detail, the University of Torino unit will take care of: 1) Technical field studies aimed to the characterization of the mechanical transitions throughout brittle deformation zones, from the intact rock, to the damage zone to the shear/slip zone; moreover, key geophysical parameters (seismic and electrical properties) will be measured; 2) Petrophysical and minero-petrographic detailed studies on representative samples will be performed at room temperature; verification of the mechanical properties of the samples subjected to cycles of heating up to the temperatures of the reservoir (> 400 °C) will be done; measurements of the geophysical properties of the samples will be done in comparison with the measures in place. 3) Numerical modeling to estimate the petrophysical, geophysical and geomechanical properties of the rock mass under the P and T conditions of the reservoir (i.e., using Comsol, VGeST, UDEC, 3DEC, ...). Detailed geological field studies and photogrammetry/laser scanner imaging of studied outcrops are supposed to be available soon: multiscale analysis will benefis from these new data. Results will be shared between EU and Mexican

  18. Upper crustal structure of the North Anatolian Fault Zone from ambient seismic noise Rayleigh and Love wave tomography (United States)

    Taylor, George; Rost, Sebastian; Houseman, Gregory; Hillers, Gregor


    By utilising short period surface waves present in the noise field, we can construct images of shallow structure in the Earth's upper crust: a region that is usually poorly resolved in earthquake tomography. Here, we use data from a dense seismic array (Dense Array for Northern Anatolia - DANA) deployed across 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 obtain maps of group velocity variation using surface wave tomography applied to short period (1- 6 s) Rayleigh and Love waves to construct high-resolution images of the upper 5 km of a 70 km x 35 km region centred on the eastern end of the fault segment that ruptured in the 1999 Izmit earthquake. The average Rayleigh wave group velocities in the region vary between 1.8 km/s at 1.5 s period, to 2.2 km/s at 6 s period. The NAFZ bifurcates into northern and southern strands in this region; both are active but only the northern strand moved in the 1999 event. The signatures of both the northern and southern branches of the NAFZ are clearly associated with strong gradients in surface wave group velocity. To the north of the NAFZ, we observe low Rayleigh wave group velocities ( 1.2 km/s) associated with the unconsolidated sediments of the Adapazari basin, and blocks of weathered terrigenous clastic sediments. To the south of the northern branch of the NAFZ, we detect high velocities ( 2.5 km/s) associated with a shallow crystalline basement, in particular a block of metamorphosed schists and marbles that bound the northern branch of the NAFZ.

  19. 3-D magnetotelluric imaging of the Phayao Fault Zone, Northern Thailand: Evidence for saline fluid in the source region of the 2014 Chiang Rai earthquake (United States)

    Boonchaisuk, Songkhun; Noisagool, Sutthipong; Amatyakul, Puwis; Rung-Arunwan, Tawat; Vachiratienchai, Chatchai; Siripunvaraporn, Weerachai


    Seismicity in Thailand had been relatively low for decades prior to the Mw 6.5 earthquake of 5 May 2014 which came as a surprise and was followed by thousands of aftershocks. Most of the epicenters were located in the transition region between the Mae Lao Segment (MLS) and the Pan Segment (PS) of the Phayao Fault Zone (PFZ). We conducted a 3-D magnetotelluric (MT) survey (31 sites) to image the deep PFZ structure. The shallow 3-D resistivity structure matches very well with the surface geology, while the deeper structures disclose many interesting resistive and conductive anomalies. However, the most interesting feature of this study is the large conductive anomaly (ML) located at a depth of 4 km to the mid-crust beneath the MLS near the seismogenic zone. Our current hypothesis is that the ML conductor has a highly interconnected aqueous fluid content and also plays crucial role in the earthquake sequence of the 5 May 2014 event. As our previous seismic waveform study revealed that the MLS has a relatively high fault plane instability, the fluid within the fractured fault would further reduce the fault strength. The accumulated pre-existing tectonic stress from the north can therefore overcome the maximum frictional strength of the MLS, and hence cause it to slip and produce the main shock. With the local structural heterogeneities and fluid in the fractured fault zones, the aftershocks then occurred on both the PS and MLS. This is in contrast to the Mae Chan Fault Zone (MCFZ) in the north which many scientists expected to generate a larger magnitude earthquake than any other faults. Since instrumental record, it has only generated a few Mw 4 earthquakes. Some of our MT stations were located within the MCFZ. However, there is no deep conductor as the conductor lies beneath the MLS. A lack of interconnected fluid within the deep fault beneath the MCFZ might be one of the reasons for the lower seismic activity from the MCFZ. Other geophysical methods, such as seismic

  20. A missing-link in the tectonic configuration of the Almacık Block along the North Anatolian Fault Zone (NW Turkey): Active faulting in the Bolu plain based on seismic reflection studies (United States)

    Seyitoğlu, Gürol; Ecevitoğlu, Berkan; Kaypak, Bülent; Esat, Korhan; Çağlayan, Ayşe; Gündoğdu, Oğuz; Güney, Yücel; Işık, Veysel; Pekkan, Emrah; Tün, Muammer; Avdan, Uğur


    The North Anatolian Fault Zone (NAFZ) starts to branch off in the western Bolu plain. The branches of the NAFZ in this location create the Almacık block which is surrounded by the latest surface ruptures of significant earthquakes that occurred between 1944 and 1999, but its northeastern part remains unruptured. The most recently formed rupture, that was a result of the 1999 November 12 Düzce earthquake, ended to the northwest of the Bakacak Fault. The connection between the Bakacak Fault and the main branch of the NAFZ via the Bolu plain has until now remained unknown. This paper establishes that the route of the missing link runs through the Dağkent, Kasaplar and Bürnük faults, a finding achieved with the help of seismic reflection studies. The paper also argues that the cross cutting nature of these newly determined faults and a stress analysis based on focal mechanism solutions of recent earthquakes demonstrate the termination of the suggested pull-apart nature of the Bolu plain.

  1. An L-band interferometric synthetic aperture radar study on the Ganos section of the north Anatolian fault zone between 2007 and 2011: Evidence for along strike segmentation and creep in a shallow fault patch. (United States)

    de Michele, Marcello; Ergintav, Semih; Aochi, Hideo; Raucoules, Daniel


    We utilize L-band interferometric synthetic aperture radar (InSAR) data in this study to retrieve a ground velocity map for the near field of the Ganos section of the north Anatolian fault (NAF) zone. The segmentation and creep distribution of this section, which last ruptured in 1912 to generate a moment magnitude (Mw)7.3 earthquake, remains incompletely understood. Because InSAR processing removes the mean orbital plane, we do not investigate large scale displacements due to regional tectonics in this study as these can be determined using global positioning system (GPS) data, instead concentrating on the close-to-the-fault displacement field. Our aim is to determine whether, or not, it is possible to retrieve robust near field velocity maps from stacking L-band interferograms, combining both single and dual polarization SAR data. In addition, we discuss whether a crustal velocity map can be used to complement GPS observations in an attempt to discriminate the present-day surface displacement of the Ganos fault (GF) across multiple segments. Finally, we characterize the spatial distribution of creep on shallow patches along multiple along-strike segments at shallow depths. Our results suggest the presence of fault segmentation along strike as well as creep on the shallow part of the fault (i.e. the existence of a shallow creeping patch) or the presence of a smoother section on the fault plane. Data imply a heterogeneous fault plane with more complex mechanics than previously thought. Because this study improves our knowledge of the mechanisms underlying the GF, our results have implications for local seismic hazard assessment.

  2. Factors controlling the permeability distribution in fault vein zones surrounding granitic intrusions (Ore Mountains/Germany) (United States)

    Achtziger-Zupančič, P.; Loew, S.; Hiller, A.


    An outstanding legacy data set has been compiled from underground excavations mostly prospected and mined by the former Soviet (German) Stock Company Wismut describing the hydrology of faulted basement rocks in the Ore Mountains (SE Germany). It consists of more than 5000 detailed descriptions of groundwater inflows to about 660 km of tunnels and 57 km of drillings measured during or shortly after excavation. Inflow measurements (recorded between 1E-8 and 4E-2 m3/s) have been converted to fracture transmissivities using a simplified analytical solution. Discarding site specific effects, the median log transmissivity decreases from 1E-7 to 1E-10 m2/s within the studied depth interval of 0-2000 meters below ground surface (mbgs), and the spacing of conductive fracture increases from 0.1 to 2500 m. This general trend is overprinted at three mining sites by a clear reversal of fracture transmissivity which correlates with contact metamorphic aureoles around Variscan granite intrusions (327-295 Ma). We hypothesize that this transmissivity increase is caused by processes accompanying granite intrusion and contact metamorphism. The thickness of these hydraulically active aureoles is greater in lower-grade metamorphic schist than in higher-grade metamorphic gneisses. Rock mass equivalent continuum conductivities have been estimated by arithmetic averaging of fracture and matrix transmissivities over 100 m intervals and have been converted to permeabilities. The median equivalent continuum permeability decreases with depth according to log(k) = - 1.7 * log(z) - 17.3 (k in m2 and increasing depth z in kilometer being positive). Matrix conductivity controls the bulk conductivity below about 1000 mbgs and is less sensitive to the occurrence of contact metamorphic aureoles.

  3. Structural analysis of the Valence basin (SE France) based on kriging and borehole data: implications for hercynian fault zone behaviour in geothermic reservoirs. (United States)

    Chabani, Arezki; Mehl, Caroline; Bruel, Dominique; Cojan, Isabelle


    The Valence basin is a 130 km-long and 60 km-wide Tertiary sub-basin situated north to the SE basin of France, in the central part of the European Cenozoic RIft System (ECRIS). That structural key position in a naturally fractured hostrock associated with a favorable thermal regime make that basin a good target for geothermal exploitation in France. The structure and kinematics of the Valence basin is controlled by a several kilometer-scale hercynian fault system that may have a strong influence on fluid flows and thermal anomalies within the basin. This study aimed to constrain the geometry of deposits and the way they fracture regards to the major faults, to determine their diagenetic evolution and to characterize the hydraulic behavior of the major faults. We thus performed a structural model of the basin and analyzed the Montoison borehole. Kriging on data pointed on 348 boreholes from BSS, synthetic boreholes calculated from two seismic lines and isohypses from existing models allowed modeling the geometry of basement and the ceno-mesozoic unconformity. Basement is structured by two pluri-kilometer long fault corridors striking N/S to NE/SW. The central extends laterally on around 1 kilometer and has been identified as a segment of the Cevennes fault. The maximum depth of the basement is around 6000 m and is situated between the two corridors. Interpretations on seismic lines highlight a westward migration of Cenozoic depocenters within time. A structural analysis of the Montoison borehole confirms it is affected by a major fault interpreted as the Cevennes fault. Fault zone cuts across the Keuper and is characterized by an heterometric breccia within marly layers. The entire sedimentary pile recorded 2 sets of fractures: perpendicular and parallel to the borehole axis. Both sets are recrystallized. Nature of recrystallization (quartz, calcite and dolomite) strongly depends on the hostrock. An important thread of barite is located under the fault zone, putting

  4. Surface creep and slip-behavior segmentation along the northwestern Xianshuihe fault zone of southwestern China determined from decades of fault-crossing short-baseline and short-level surveys (United States)

    Zhang, Jing; Wen, Xue-ze; Cao, Jian-ling; Yan, Wei; Yang, Yong-lin; Su, Qin


    This study examines the 200-km-long northwestern Xianshuihe fault zone (NWXFZ), southwestern China, using more than three decades of geodetic observations from fault-crossing short-baseline and short-leveling surveys at seven sites. These data enable estimates of creep rates and depths, and examination of the long-term slip behavior. The surface motion of the NWXFZ is dominated by sinistral creep, although sinistral, transverse, and vertical slip components show spatio-temporal variations. Combining these slip variations with data of earthquake rupture, coseismic slip, seismicity, fault geometry, and far-fault movement velocity, and using the velocity-and-state friction theory, our analysis indicates that the surface slip behavior of the NWXFZ is segmented along strike. The 1973 rupture section of this fault zone exhibits spatio-temporally variable slip behavior, showing time-decaying post-1973 afterslip on the northwestern and southeastern parts of the rupture at depths above 5.8 - 7.0 km with average sinistral-creep rates of 1.3 and 3.5 mm/yr, respectively, but being relocked in the central part of the rupture. The 1923/1981 rupture section is generally in locking state, with postseismic and interseismic sinistral-creep at 1.1 mm/yr on its central part at depths above 2.0-2.8 km. The 1893 rupture section has been tightly locked without creep since at least the early 1980s. The thickness of the shallow velocity-strengthening (or creep) layer and the restraining bend geometry of the NWXFZ are the key factors that control spatio-temporal variations in surface creep rates. Two surface-observed locked fault portions are located within two different restraining bends in the NWXFZ, both of which act as compressive asperities and hence have enabled the long-term locking of these portions. Creep along the NWXFZ has also been affected to varying degrees by M6.5 - Mw9.2 earthquakes at distances of 50 - 3800 km from the fault zone. Most of these effects have been removed

  5. Post-Late Glacial calcareous tufas from the Kurai fault zone (Southeastern Gorny Altai, Russia) (United States)

    Kokh, Svetlana N.; Sokol, Ella V.; Deev, Evgeny V.; Ryapolova, Yuliya M.; Rusanov, Gennady G.; Tomilenko, Anatoliy A.; Bul'bak, Taras A.


    Calcareous tufa deposits have been discovered in the Chibitka River valley near Lake Cheybek-Kohl, at the junction of the Kurai and Teletsk-Kurai large active faults in the southeastern Gorny Altai, Russia, at an altitude of 1800-2000 m. Fossil tufa is composed of calcite and cements Holocene grey colluvium and glacial till deposited by the Late Glacial Chibitka Glacier. Current tufa precipitation has been observed from a low-flow spring with cold (10 °C) HCO3-SO4-Ca-Mg water, pH = 6.86. The stable isotope composition of spring water is - 5.8‰ VPDB δ13C of dissolved inorganic carbon and - 14.5‰ VSMOW δ18O. Modern tufa consists of thin laminated Mg-calcite and Sr-aragonite crusts, with abundant algae and biofilms on their surfaces. Both modern and fossil tufas are depleted in REE (a total of 0.40-16.4 ppm and 0.40-3.80 ppm, respectively) and share similar PAAS-normalised REE + Y spectra with HREE enrichment and slight progressive LREE depletion. The modern tufas show positive δ13C values of 0.1‰ to 0.9‰ VPDB while the fossil ones have an isotopically lighter composition of δ13C = - 4.1‰ to - 1.9‰ VPDB; the δ18O range is very narrow (- 13.0 to - 13.8‰ VPDB). Both stable isotope and trace-element signatures (including REE patterns) of the tufas indicate precipitation from cold groundwaters subjected to prolonged interaction with a carbonate aquifer (the Baratal Group of limestone and dolostone) in a cold continental climate similar to the present conditions. Tufa deposition in the Lake Cheybek-Kohl area began with the onset of post-Late Glacial global warming and permafrost degradation. Unlike the fossil tufa formation, current precipitation of freshwater carbonates has been microbially mediated. The discovered tufa deposits provide new palaeoclimatic and active tectonic proxies in the southeastern Gorny Altai.

  6. Overpressure generation and episodic dewatering in the Delaware basin, western Texas: The dual nature of a fault zone (United States)

    Hansom, J.; Lee, M.; Wolf, L. W.; Kosuwan, T.


    This study combines numerical modeling techniques with field data to investigate overpressure development and episodic dewatering processes in the Delaware Basin and the Central Basin Platform (CBP). Low-permeability shales in the eastern Delaware Basin are characterized by elevated pore fluid pressures that are much greater than hydrostatic pressures. Observed geophysical anomalies such as low resistivity, high conductivity, and high seismic transit time are consistent with the presence of fluid-filled, fractured and mechanically weak rocks in the eastern Delaware Basin. Our new geophysical analyses also indicate that the overpressures likely extend further into the shallower western basin in Culberson County near the sulfur mineralization area. The predicted present-day gas window is located within the overpressure zone, suggesting that overpressure may be maintained by active oil-to-gas conversion. A basin hydrology model Basin2 is modified to evaluate the pore pressure increases by oil-gas conversion from the equation of state (EOS) for the CH4-CO2-H2O system. Our modeling shows that source beds in CBP have been rather shallowly buried and did not become thermally mature to generate gas directly. Overpressure and episodic dewatering processes appear to be the most plausible mechanism to move deep-basin hydrocarbons eastward into the CBP and westward into the shallow margin of the Delaware Basin. The model of long-distance fluid migration from the eastern Delaware across the fault zone into the CBP is supported by the geochemical similarities of oils from the two basins. A model that invokes episodic release of overpressured fluids by hydrofracturing processes can simultaneously provide mechanisms for achieving transient overpressure preservation and substantial, episodic fluid movement. The episodic dewatering through hydrofracturing processes thus can better explain the observed overpressure preservation, long-distance fluid migration, and related

  7. Displacement and dynamic weakening processes in smectite-rich gouge from the Central Deforming Zone of the San Andreas Fault (United States)

    French, M. E.; Kitajima, H.; Chester, J. S.; Chester, F. M.; Hirose, T.


    The strength of clay-rich gouge from the Central Deforming Zone (CDZ) of the San Andreas Fault (SAF) was measured using a high-speed rotary shear apparatus to evaluate the potential for unstable slip along the creeping segment of the SAF. Wet and dry gouge was sheared at 0.1-1.3 m/s, 0.5-1.5 MPa normal stress, and 1-20 m displacement. CDZ gouge is weaker wet than dry and exhibits displacement strengthening to peak friction followed by weakening to steady state strength that decreases with increasing velocity. A clay foliation (Unit 2) develops from the initial microstructure (Unit 1) during the first 1.5 m of slip coincident with increasing strength. Subsequent weakening occurs during shear within Unit 2, and subsequently with development of a localized foliated slip zone (Unit 4) and fluidized material (Unit 3). Displacement and dynamic weakening result from slip along clay foliation assisted by shear-heating pressurization of pore fluid in wet gouge and additional grain-size reduction and possible clay dehydration in dry gouge. Peak strength is proportional to normal stress, but steady state strength is insensitive to normal stress probably because pore pressure approaches the normal stress. As such, CDZ gouge is weak at coseismic rates relative to interseismic creep strength. The potential for sustaining rupture propagation into the CDZ from an adjacent seismic segment is sensitive to the relationship used to extrapolate the critical weakening displacement from experimental to in situ conditions. Rupture propagation from a microseismic patch within the CDZ is unlikely, but sustained propagation from a large earthquake (e.g., Parkfield event) may be possible.

  8. A Poisson method application to the assessment of the earthquake hazard in the North Anatolian Fault Zone, Turkey

    Energy Technology Data Exchange (ETDEWEB)

    Türker, Tuğba, E-mail: [Karadeniz Technical University, Department of Geophysics, Trabzon/Turkey (Turkey); Bayrak, Yusuf, E-mail: [Ağrı İbrahim Çeçen University, Ağrı/Turkey (Turkey)


    North Anatolian Fault (NAF) is one from the most important strike-slip fault zones in the world and located among regions in the highest seismic activity. The NAFZ observed very large earthquakes from the past to present. The aim of this study; the important parameters of Gutenberg-Richter relationship (a and b values) estimated and this parameters taking into account, earthquakes were examined in the between years 1900-2015 for 10 different seismic source regions in the NAFZ. After that estimated occurrence probabilities and return periods of occurring earthquakes in fault zone in the next years, and is being assessed with Poisson method the earthquake hazard of the NAFZ. The Region 2 were observed the largest earthquakes for the only historical period and hasn’t been observed large earthquake for the instrumental period in this region. Two historical earthquakes (1766, M{sub S}=7.3 and 1897, M{sub S}=7.0) are included for Region 2 (Marmara Region) where a large earthquake is expected in the next years. The 10 different seismic source regions are determined the relationships between the cumulative number-magnitude which estimated a and b parameters with the equation of LogN=a-bM in the Gutenberg-Richter. A homogenous earthquake catalog for M{sub S} magnitude which is equal or larger than 4.0 is used for the time period between 1900 and 2015. The database of catalog used in the study has been created from International Seismological Center (ISC) and Boğazici University Kandilli observation and earthquake research institute (KOERI). The earthquake data were obtained until from 1900 to 1974 from KOERI and ISC until from 1974 to 2015 from KOERI. The probabilities of the earthquake occurring are estimated for the next 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 years in the 10 different seismic source regions. The highest earthquake occur probabilities in 10 different seismic source regions in the next years estimated that the region Tokat-Erzincan (Region 9) %99

  9. Detection of small earthquakes with dense array data: example from the San Jacinto fault zone, southern California (United States)

    Meng, Haoran; Ben-Zion, Yehuda


    We present a technique to detect small earthquakes not included in standard catalogues using data from a dense seismic array. The technique is illustrated with continuous waveforms recorded in a test day by 1108 vertical geophones in a tight array on the San Jacinto fault zone. Waveforms are first stacked without time-shift in nine non-overlapping subarrays to increase the signal-to-noise ratio. The nine envelope functions of the stacked records are then multiplied with each other to suppress signals associated with sources affecting only some of the nine subarrays. Running a short-term moving average/long-term moving average (STA/LTA) detection algorithm on the product leads to 723 triggers in the test day. Using a local P-wave velocity model derived for the surface layer from Betsy gunshot data, 5 s long waveforms of all sensors around each STA/LTA trigger are beamformed for various incident directions. Of the 723 triggers, 220 are found to have localized energy sources and 103 of these are confirmed as earthquakes by verifying their observation at 4 or more stations of the regional seismic network. This demonstrates the general validity of the method and allows processing further the validated events using standard techniques. The number of validated events in the test day is >5 times larger than that in the standard catalogue. Using these events as templates can lead to additional detections of many more earthquakes.

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

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


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

  11. Late Quaternary eruption of the Ranau Caldera and new geological slip rates of the Sumatran Fault Zone in Southern Sumatra, Indonesia (United States)

    Natawidjaja, Danny Hilman; Bradley, Kyle; Daryono, Mudrik R.; Aribowo, Sonny; Herrin, Jason


    Over the last decade, studies of natural hazards in Sumatra have focused primarily on great earthquakes and associated tsunamis produced by rupture of the Sunda megathrust. However, the Sumatran Fault and the active volcanic arc present proximal hazards to populations on mainland Sumatra. At present, there is little reliable information on the maximum magnitudes and recurrence intervals of Sumatran Fault earthquakes, or the frequency of paroxysmal caldera-forming (VEI 7-8) eruptions. Here, we present new radiocarbon dates of paleosols buried under the voluminous Ranau Tuff that constrain the large caldera-forming eruption to around 33,830-33,450 calender year BP (95% probability). We use the lateral displacement of river channels incised into the Ranau Tuff to constrain the long-term slip rate of two segments of the Sumatran Fault. South of Ranau Lake, the Kumering segment preserves isochronous right-lateral channel offsets of approximately 350 ± 50 m, yielding a minimum slip rate of 10.4 ± 1.5 mm/year for the primary active fault trace. South of Suoh pull-apart depression, the West Semangko segment offsets the Semangko River by 230 ± 60 m, yielding an inferred slip rate of 6.8 ± 1.8 mm/year. Compared with previous studies, these results indicate more recent high-volume volcanism in South Sumatra and increased seismic potency of the southernmost segments of the Sumatran Fault Zone.

  12. Sensitivity Analysis of Impacts of Natural Internal Fault Zones and Well Design on Fluid Flow and Heat Transfer in a Deep Geothermal Reservoir (United States)

    Wong, Li Wah; Watanabe, Norihiro; Fuchs, Sven; Bauer, Klaus; Cacace, Mauro; Blöcher, Guido; Kastner, Oliver; Zimmermann, Günter


    In order to show the impacts of natural internal fault zones and well design on geothermal energy production, two main deep geothermal reservoir sites in Germany, Groß Schönebeck (GrSk) and Berlin Tempelhof which are part of the North German Basin (NGB) are investigated. Groß Schönebeck is located at about 40km away from the Berlin centre whereas Berlin Tempelhof is situated in the south-central Berlin. Hydrothermal power plant shows complex coupling between four major components, the deep geothermal reservoir, the boreholes, the heat exchangers of the primary thermal water cycle and the power plant unit. In order to study the lifetime behavior of the overall Enhanced Geothermal System (EGS), it is mandatory to develop a combined transient model representing all relevant components as whole and their inter-relations. In this regards, the framework of Groß Schönebeck (GrSk) project is posed as the first scenario. The hydrothermal power plant is subdivided logically into components modeled separately and subsequently a standalone 3D transient hydro-thermal FEM (finite element method) reservoir model which consists of reservoir, fractures, wells and fault zones is weighted in the first place and its hydro-thermal processes are simulated for a period of 35 years. Using COMSOL Multiphysics, two significant objectives are achieved. Deviated geometries such as the production well and dipping geometries such as natural internal fault zones are successfully implemented into the 3D transient reservoir model which is constructed with the integration of hydraulically induced fractures and reservoir rock layers which are conducive to geothermal power production. Using OpenGeoSys (OGS), sensitivity analysis of varied conductivity of natural internal fault zones due to different permeability and apertures, on current fluid flow and heat transfer pattern is carried out. Study shows that natural internal fault zones play a significant role in the generation of production

  13. A Possible Source Mechanism of the 1946 Unimak Alaska Far-Field Tsunami: Uplift of the Mid-Slope Terrace Above a Splay Fault Zone (United States)

    von Huene, Roland; Miller, John J.; Klaeschen, Dirk; Dartnell, Peter


    In 1946, megathrust seismicity along the Unimak segment of the Alaska subduction zone generated the largest ever recorded Alaska/Aleutian tsunami. The tsunami severely damaged Pacific islands and coastal areas from Alaska to Antarctica. It is the charter member of "tsunami" earthquakes that produce outsized far-field tsunamis for the recorded magnitude. Its source mechanisms were unconstrained by observations because geophysical data for the Unimak segment were sparse and of low resolution. Reprocessing of legacy geophysical data reveals a deep water, high-angle reverse or splay thrust fault zone that leads megathrust slip upward to the mid-slope terrace seafloor rather than along the plate boundary toward the trench axis. Splay fault uplift elevates the outer mid-slope terrace and its inner area subsides. Multibeam bathymetry along the splay fault zone shows recent but undated seafloor disruption. The structural configuration of the nearby Semidi segment is similar to that of the Unimak segment, portending generation of a future large tsunami directed toward the US West coast.

  14. A possible source mechanism of the 1946 Unimak Alaska far-field tsunami, uplift of the mid-slope terrace above a splay fault zone (United States)

    von Huene, Roland E.; Miller, John J.; Klaeschen, Dirk; Dartnell, Peter


    In 1946, megathrust seismicity along the Unimak segment of the Alaska subduction zone generated the largest ever recorded Alaska/Aleutian tsunami. The tsunami severely damaged Pacific islands and coastal areas from Alaska to Antarctica. It is the charter member of “tsunami” earthquakes that produce outsized far-field tsunamis for the recorded magnitude. Its source mechanisms were unconstrained by observations because geophysical data for the Unimak segment were sparse and of low resolution. Reprocessing of legacy geophysical data reveals a deep water, high-angle reverse or splay thrust fault zone that leads megathrust slip upward to the mid-slope terrace seafloor rather than along the plate boundary toward the trench axis. Splay fault uplift elevates the outer mid-slope terrace and its inner area subsides. Multibeam bathymetry along the splay fault zone shows recent but undated seafloor disruption. The structural configuration of the nearby Semidi segment is similar to that of the Unimak segment, portending generation of a future large tsunami directed toward the US West coast.

  15. Structural Overview and Morphotectonic Evolution of a Strike-Slip Fault in the Zone of North Almora Thrust, Central Kumaun Himalaya, India

    Directory of Open Access Journals (Sweden)

    Lalit M. Joshi


    Full Text Available The aim of the present research is to provide the base line details of the NNW-SSE trending Raintoli fault (RF which is running parallel to the North Almora Thrust (NAT along the Saryu valley from Seraghat-Naichun to Seri in the central sector of the Uttarakhand Himalaya, India. The RF is characterized as dextral strike slip fault and behaves as a ductile shear zone within the zone of NAT. The dextral sense of shear movement of RF is delineated by the fabric of the shear zone rocks including microscopically observed indicators such as sigma and delta porphyroclasts, quartz c-axis, and the field structural data. Additionally, in the quaternary period the dextral strike slip fault is reactivated with oblique slip component as characterized by various geomorphic indicators, for example, triangular facets, abandoned river channels, unpaired fluvial terraces, and V-shaped valleys with recurrent seismicity. Further, the morphometric parameters including Valley Floor Width to Valley Height (Vf, asymmetry factor (AF, and gradient index (GI further prove active nature of RF as suggested by low values of hypsometric integration, V-shaped valley, higher gradient index, and tilting of Saryu basin.

  16. Robust model reference adaptive output feedback tracking for uncertain linear systems with actuator fault based on reinforced dead-zone modification. (United States)

    Bagherpoor, H M; Salmasi, Farzad R


    In this paper, robust model reference adaptive tracking controllers are considered for Single-Input Single-Output (SISO) and Multi-Input Multi-Output (MIMO) linear systems containing modeling uncertainties, unknown additive disturbances and actuator fault. Two new lemmas are proposed for both SISO and MIMO, under which dead-zone modification rule is improved such that the tracking error for any reference signal tends to zero in such systems. In the conventional approach, adaption of the controller parameters is ceased inside the dead-zone region which results tracking error, while preserving the system stability. In the proposed scheme, control signal is reinforced with an additive term based on tracking error inside the dead-zone which results in full reference tracking. In addition, no Fault Detection and Diagnosis (FDD) unit is needed in the proposed approach. Closed loop system stability and zero tracking error are proved by considering a suitable Lyapunov functions candidate. It is shown that the proposed control approach can assure that all the signals of the close loop system are bounded in faulty conditions. Finally, validity and performance of the new schemes have been illustrated through numerical simulations of SISO and MIMO systems in the presence of actuator faults, modeling uncertainty and output disturbance. Copyright © 2015 ISA. Published by Elsevier Ltd. All rights reserved.

  17. The historical and recent destructive earthquakes along the Sumatran fault zone: The March 6th, 2007 doublet event in west Sumatra. (United States)

    Natawidjaja, D. H.


    The Sumatran fault zone is a major transcurrent fault accommodating most of the dextral component of the Sumatran oblique convergence. Its 1900-km-long strand runs along the backbone of Sumatra bisecting the volcanic arch. The Sumatran fault is highly segmented, consists of 20 major geometrically defined segments, which range in length from about 60 to 200 km, which constraint seismic source dimensions and have limited the magnitudes of major historical fault ruptures to between Mw 6.3 and 7.7. In average, major earthquakes occur one or twice every decade. As the obliquity increases, slip rates along the fault increase northwestward, from about 5 mm/yr around the Sunda Strait to 27 mm/yr around Toba Lake. These sliprate values together with fault-segment lengths provide a quantitative basis for calculating level of earthquake hazard of each segment. Most recent destructive earthquake occurred on March 6th, 2007. Two earthquakes (Mw 6.4 & Mw6.3), separated by two hours, ruptured two major segments of the Sumatran fault south and north of the Singkarak Lake in west Sumatra. This earthquake doublet killed more than 70 inhabitants and destroyed many houses and other constructions on and near the fault ruptures. The shaking was strongly felt in Padang, the capital city of west Sumatra on the west coast, and even in Singapore, especially in high-rise buildings. The surface ruptures of the first event were observed south of the lake with a total length up to 15 km and slips varies up to 25 cm right lateral and 25 cm vertical movements. The second event ruptured a 22 km fault strand north of the lake and produce dextral slip up to 25 cm. Timing and locations of the first and the second ruptures were consistent with the shake intensity felt by people in the north and south of the Singkarak region. People who live south of the lake felt the first event the strong shake and destroyed their houses, but people live north of lake witnessed that the second event produced the

  18. Fault and fluid systems in supra-subduction zones: The Troodos ophiolite (United States)

    Quandt, Dennis; Micheuz, Peter; Kurz, Walter; Krenn, Kurt


    The Troodos massif on the island of Cyprus represents a well-preserved and complete supra-subduction zone (SSZ) ophiolite. It includes an extrusive sequence that is subdivided into Upper (UPL) and Lower Pillow Lavas (LPL). These volcanic rocks contain mineralized fractures (veins) and vesicles that record fluid availability probably related to slab dehydration and deformation subsequent to a period of subduction initiation in the framework of a SSZ setting. Here, we present electron microprobe element mappings and cathodoluminescence studies of vein minerals as well as analyses of fluid inclusions entrapped in zeolite, calcite and quartz from veins and vesicles of the Pillow Lavas of the Troodos ophiolite. Two different zeolite type assemblages, interpreted as alteration products of compositional varying volcanic glasses, occur: (1) Na-zeolites analcime and natrolite from the UPL that require lower formation temperatures, higher Na/Ca ratios and pH values than (2) Ca-zeolites heulandite and mordenite from the LPL which indicate temporal or spatial varying fluid compositions and conditions. Calcite represents a late stage phase in incompletely sealed blocky type (1) assemblage and in syntaxial quartz veins. Additionally, calcite occurs as major phase in syntaxial and blocky veins of UPL and LPL. These syntaxial quartz and calcite veins are assumed to be related to tectonic extension. Chalcedony is associated with quartz and occurs in typical veins and vesicles of the LPL. In addition, the presence of neptunian dykes in veins suggests that seawater penetrated fractures throughout the extrusive sequence. Thus, circulation in an open system via advective transport is favored while diffusion in a closed system is a subordinate, local and late stage phenomenon. Calcite veins and quartz vesicles contain primary, partly re-equilibrated two phase (liquid, vapor) fluid inclusions. The chemical system of all studied inclusions in both host minerals is restricted to aqueous

  19. Investigation of giant mass movements in the Lesser Caucasus and assessment of the spatial relationship between landslides and major fault zones and volcanoes (United States)

    Ofélia Matossian, Alice; Mreyen, Anne-Sophie; Karakhanian, Arkady; Havenith, Hans-Balder


    Two landslides of assumed seismic origin in the vicinity of Garni, Armenia, were investigated during a geophysical field campaign in September 2016. On the basis of geophysical prospecting (microseismic ambient noise measurements, i.e. H/V method), the thickness of the landslide deposits has been estimated and a trigger scenario model was developed. The original trigger of those landslides is not known - but one major reactivation by an earthquake in 1679 has been proved (see below). Additionally, the spatial distribution of landslides was analysed with respect to the location of major fault zones and volcanic areas. For that, a spatial analysis with GIS has been carried out on the basis of two landslide catalogues. The catalogue that was generated during this work covers the areas of including the Pambak-Sevan-Syunik and the Garni Faults as well as several volcanic areas. These NW-SE faults are mainly marked dextral strike-slip movements locally combined with reverse mechanisms. Along these fault zones strong historical earthquakes occurred, as for example one major event in 1139 (M 7.5 - 7.7). The 1679 Garni earthquake caused widespread destruction and also reactivated landslides located near the Garni Fault, including the two investigated landslides. According to historical sources, the event reached a magnitude of M=5.5-7 with an intensity between VIII and X. The volcanic areas on the other hand include the NNW-SSE-oriented Ghegham and the NW-SE Vardeniss ridges. Some of the ridges' volcanoes erupted during the Holocene, i.e. 2090 ± 70 BP for the Ghegham ridge. Nowadays, more than 80% of Armenia is covered by Quaternary volcanic formations or friable deposits which are favourable to the formation of landslides. Nevertheless, our first analysis showed that the faults have a stronger influence on landslide distribution than the volcanoes. This is also due to the indirect fact that many volcanic areas are marked by more gentle slopes than the valleys hosting the

  20. Submarine earthquake rupture, active faulting and volcanism along the major Liquiñe-Ofqui Fault Zone and implications for seismic hazard assessment in the Patagonian Andes Ruptura sísmica submarina, tectónica y volcanismo activo a lo largo de la Falla Liquiñe-Ofqui e implicancias para el peligro sísmico en los Andes patagónicos


    Gabriel Vargas; Sofía Rebolledo; Sergio A Sepúlveda; Alfredo Lahsen; Ricardo Thiele; Brian Townley; Cristóbal Padilla; Rodrigo Rauld; Maria José Herrera; Marisol Lara


    The Liquiñe-Ofqui fault zone (LOFZ) in the Patagonian Andes is an active major transpressional intra-arc fault system along which Quaternary faulting and volcanism develop. Subaerial and submarine geomorphologic and structural characterization of latest Pleistocene-Holocene faults and monogenetic volcanoes allows us to assess geological cartography of active faults and the kinematic model for recent tectonics during postglacial times, since 12,000 cal. years BP. This allows increasing the bas...

  1. Modelling of Earthquake History of the Knidos Fault Zone SW Turkey Using in-situ 36Cl Surface Exposure Dating by R (United States)

    Sahin, S.; Yıldırım, C.; Sarıkaya, M. A.; Tuysuz, O.; Genç, S. C.; Aksoy, M. E.; Doksanaltı, M. E.; Benedetti, L.


    Cosmogenic surface exposure dating is based on the production of rare nuclides in exposed rocks, which interact with cosmic rays. Through modelling of measured 36Cl concentrations, we might obtain information of the history of the earthquake activity. Yet, there are several factors which may impact production of rare nuclides such as geometry of fault, topography, geographic location of study area, temporal variations of the Earth's magnetic field, self-cover and denudation rate on the scarp. Our study area, the Knidos Fault Zone, is located on the Datça Peninsula in the Southwestern Anatolia and contains several normal fault scarps formed within the limestone, which are appropriate to apply cosmogenic chlorine-36 dating. Since it has a well-preserved scarp, we have focused on the Mezarlık Segment of the fault zone, which has an average length of 300 m and height 12-15 m. 128 continuous samples from top to bottom of the fault scarp were collected to carry out analysis of cosmic 36Cl isotopes concentrations. Recent research elucidated each step of the application of this method by the Matlab (e.g. Schlagenhauf et al., 2010). It is vitally helpful to generate models activity of normal faults. We, however, wanted to build a user-friendly program through an open source programing language R that might be able to help those without knowledge of complex math, programming, making calculations as easy as possible. We have set out to obtain accurate conclusions to compare and contrast our results with synthetic profiles and previous studies of limestone fault scarps. The preliminary results indicate at least three major or more earthquakes/earthquakes cluster events occurred on the Mezarlık fault within the past 20 kyr; over 10 meters of displacement took place between early Holocene and late Pleistocene. Estimated ages of those three large slip events are 18.7, 15.1 and 10.8 ka respectively. This study was conducted with the Decision of the Council of Ministers with No

  2. First palaeoseismological data on the Santa Marta Fault System, Northern Colombia (United States)

    Idárraga, J.


    The Santa Marta Fault System (SMFS) is a NNW-striking major structural feature that controls the western foothills of the Sierra Nevada of Santa Marta (northern Colombia), the world's highest coastal relief. Morphotectonically, the SMFS exhibits an arrangement of parallel to subparallel fault traces. These traces are associated with a set of offset streams indicating a left-lateral component for displacement. NE-trending compressive structures as reverse faults (e.g. the Orihueca and San Pedro faults) and folds (the Fundación Anticline), and NW-trending distensive structures as normal faults are present too. These structures are consistent with a left-lateral shear zone striking NNW. An unlitified ruditic deposit with tectonic deformation crops out at the Riofrío site; this deposit consists of a series of debris slope layers linked to a deyection cone. The documented deformation in this outcrop is characterized by a tilting of the sequence to NE (against the direction of deposition) and by the presence of inverse faulting in which the coseismic displacement could have been distributed across distensive structures (normal faults and opened fractures). A magnitude (Mw) of 6.4 was calculated for the compressive event based on the displacement measured on the outcrop; this value corresponds to a minimum magnitude. Unfortunately, it has not been possible to date the deposits to constrain the tectonic events in time. The results of this research constitute the first data on the palaeoseismology of the SMFS, and are an important basis for future paleoseismic studies that allow calculating the seismic hazard of the region and giving an approximation of the Plio-Quaternary evolution of the South American northwestern corner.

  3. Geometry and kinematics of the eastern Lake Mead fault system in the Virgin Mountains, Nevada and Arizona (United States)

    Beard, Sue; Campagna, David J.; Anderson, R. Ernest


    The Lake Mead fault system is a northeast-striking, 130-km-long zone of left-slip in the southeast Great Basin, active from before 16 Ma to Quaternary time. The northeast end of the Lake Mead fault system in the Virgin Mountains of southeast Nevada and northwest Arizona forms a partitioned strain field comprising kinematically linked northeast-striking left-lateral faults, north-striking normal faults, and northwest-striking right-lateral faults. Major faults bound large structural blocks whose internal strain reflects their position within a left step-over of the left-lateral faults. Two north-striking large-displacement normal faults, the Lakeside Mine segment of the South Virgin–White Hills detachment fault and the Piedmont fault, intersect the left step-over from the southwest and northeast, respectively. The left step-over in the Lake Mead fault system therefore corresponds to a right-step in the regional normal fault system.Within the left step-over, displacement transfer between the left-lateral faults and linked normal faults occurs near their junctions, where the left-lateral faults become oblique and normal fault displacement decreases away from the junction. Southward from the center of the step-over in the Virgin Mountains, down-to-the-west normal faults splay northward from left-lateral faults, whereas north and east of the center, down-to-the-east normal faults splay southward from left-lateral faults. Minimum slip is thus in the central part of the left step-over, between east-directed slip to the north and west-directed slip to the south. Attenuation faults parallel or subparallel to bedding cut Lower Paleozoic rocks and are inferred to be early structures that accommodated footwall uplift during the initial stages of extension.Fault-slip data indicate oblique extensional strain within the left step-over in the South Virgin Mountains, manifested as east-west extension; shortening is partitioned between vertical for extension-dominated structural

  4. The role of fault zone fabric and lithification state on frictional strength, constitutive behavior, and deformation microstructure

    NARCIS (Netherlands)

    Ikari, M.; Niemeijer, A.R.; Marone, C.


    We examine the frictional behavior of a range of lithified rocks used as analogs for fault rocks, cataclasites and ultracataclasites at seismogenic depths and compare them with gouge powders commonly used in experimental studies of faults. At normal stresses of ∼50 MPa, the frictional strength of

  5. Aseismic Slip Events along the Southern San Andreas Fault System Captured by Radar Interferometry

    Energy Technology Data Exchange (ETDEWEB)

    Vincent, P


    A seismic slip is observed along several faults in the Salton Sea and southernmost Landers rupture zone regions using interferometric synthetic aperture radar (InSAR) data spanning different time periods between 1992 and 1997. In the southernmost Landers rupture zone, projecting south from the Pinto Mountain Fault, sharp discontinuities in the interferometric phase are observed along the sub-parallel Burnt Mountain and Eureka Peak Faults beginning three months after the Landers earthquake and is interpreted to be post-Landers after-slip. Abrupt phase offsets are also seen along the two southernmost contiguous 11 km Durmid Hill and North Shore segments of the San Andreas Fault with an abrupt termination of slip near the northern end of the North Shore Segment. A sharp phase offset is seen across 20 km of the 30 km-long Superstition Hills Fault before phase decorrelation in the Imperial Valley along the southern 10 km of the fault prevents coherent imaging by InSAR. A time series of deformation interferograms suggest most of this slip occurred between 1993 and 1995 and none of it occurred between 1992 and 1993. A phase offset is also seen along a 5 km central segment of the Coyote Creek fault that forms a wedge with an adjoining northeast-southwest trending conjugate fault. Most of the slip observed on the southern San Andreas and Superstition Hills Faults occurred between 1993 and 1995--no slip is observed in the 92-93 interferograms. These slip events, especially the Burnt Mountain and Eureka Peak events, are inferred to be related to stress redistribution from the June, 1992 M{sub w} = 7.3 Landers earthquake. Best-fit elastic models of the San Andreas and Superstition Hills slip events suggest source mechanisms with seismic moments over three orders of magnitude larger than a maximum possible summation of seismic moments from all seismicity along each fault segment during the entire 4.8-year time interval spanned by the InSAR data. Aseismic moment releases of this

  6. Expression of Lithospheric Shear Zones in Rock Elasticity Tensors and in Anisotropic Receiver Functions and Inferences on the Roots of Faults and Lower Crustal Deformation (United States)

    Schulte-Pelkum, V.; Condit, C.; Brownlee, S. J.; Mahan, K. H.; Raju, A.


    We investigate shear zone-related deformation fabric from field samples, its dependence on conditions during fabric formation, and its detection in situ using seismic data. We present a compilation of published rock elasticity tensors measured in the lab or calculated from middle and deep crustal samples and compare the strength and symmetry of seismic anisotropy as a function of location within a shear zone, pressure-temperature conditions during formation, and composition. Common strengths of seismic anisotropy range from a few to 10 percent. Apart from the typically considered fabric in mica, amphibole and quartz also display fabrics that induce seismic anisotropy, although the interaction between different minerals can result in destructive interference in the total measured anisotropy. The availability of full elasticity tensors enables us to predict the seismic signal from rock fabric at depth. A method particularly sensitive to anisotropy of a few percent in localized zones of strain at depth is the analysis of azimuthally dependent amplitude and polarity variations in teleseismic receiver functions. We present seismic results from California and Colorado. In California, strikes of seismically detected fabric show a strong alignment with current strike-slip motion between the Pacific and North American plates, with high signal strength near faults and from depths below the brittle-ductile transition. These results suggest that the faults have roots in the ductile crust; determining the degree of localization, i.e., the width of the fault-associated shear zones, would require an analysis with denser station coverage, which now exists in some areas. In Colorado, strikes of seismically detected fabric show a broad NW-SE to NNW-SSE alignment that may be related to Proterozoic fabric developed at high temperatures, but locally may also show isotropic dipping contrasts associated with Laramide faulting. The broad trend is punctuated with NE-SW-trending strikes

  7. Holocene faulting in the Bellingham forearc basin: upper-plate deformation at the northern end of the Cascadia subduction zone (United States)

    Kelsey, Harvey M.; Sherrod, Brian L.; Blakely, Richard J.; Haugerud, Ralph A.


    The northern Cascadia forearc takes up most of the strain transmitted northward via the Oregon Coast block from the northward-migrating Sierra Nevada block. The north-south contractional strain in the forearc manifests in upper-plate faults active during the Holocene, the northern-most components of which are faults within the Bellingham Basin. The Bellingham Basin is the northern of four basins of the actively deforming northern Cascadia forearc. A set of Holocene faults, Drayton Harbor, Birch Bay, and Sandy Point faults, occur within the Bellingham Basin and can be traced from onshore to offshore using a combination of aeromagnetic lineaments, paleoseismic investigations and scarps identified using LiDAR imagery. With the recognition of such Holocene faults, the northernmost margin of the actively deforming Cascadia forearc extends 60 km north of the previously recognized limit of Holocene forearc deformation. Although to date no Holocene faults are recognized at the northern boundary of the Bellingham Basin, which is 15 km north of the international border, there is no compelling tectonic reason to expect that Holocene faults are limited to south of the international border.

  8. Subsurface Constraints on Late Cenozoic Basin Geometry in Northern Fish Lake Valley and Displacement Transfer Along the Northern Fish Lake Valley Fault Zone, Western Nevada (United States)

    Mueller, N.; Kerstetter, S. R.; Katopody, D. T.; Oldow, J. S.


    The NW-striking, right-oblique Fish Lake Valley fault zone (FLVFZ) forms the northern segment of the longest active structure in the western Great Basin; the Death Valley - Furnace Creek - Fish Lake Valley fault system. Since the mid-Miocene, 50 km of right-lateral displacement is documented on the southern FLVFZ and much of that displacement was and is transferred east and north on active WNW left-lateral faults. Prior to the Pliocene, displacement was transferred east and north on a low-angle detachment. Displacement on the northern part of the FLVFZ continues and is transferred to a fanned array of splays striking (west to east) WNW, NNW, ENE and NNE. To determine the displacement budget on these structures, we conducted a gravity survey to determine subsurface basin morphology and its relation to active faults. Over 2450 stations were collected and combined with existing PACES and proprietary data for a total of 3388 stations. The data were terrain corrected and reduced to a 2.67 g/cm3 density to produce a residual complete Bouguer anomaly. The eastern part of northern Fish Lake Valley is underlain by several prominent gravity lows forming several sub-basins with maximum RCBA values ranging from -24 to -28 mGals. The RCBA was inverted for depth using Geosoft Oasis Montaj GM-SYS 3D modeling software. Density values for the inversion were constrained by lithologic and density logs from wells that penetrate the entire Cenozoic section into the Paleozoic basement. Best fitting gravity measurements taken at the wellheads yielded an effective density of 2.4 g/cm3 for the basin fill. Modeled basement depths range between 2.1 to 3 km. The sub-basins form an arc opening to the NW and are bounded by ENE and NNE faults in the south and NS to NNW in the north. At the northern end of the valley, the faults merge with ENE left-lateral strike slip faults of the Mina deflection, which carries displacement to NW dextral strike-slip faults of the central Walker Lane.

  9. Deformation rates across the San Andreas Fault system, central California determined by geology and geodesy (United States)

    Titus, Sarah J.

    The San Andreas fault system is a transpressional plate boundary characterized by sub-parallel dextral strike-slip faults separating internally deformed crustal blocks in central California. Both geodetic and geologic tools were used to understand the short- and long-term partitioning of deformation in both the crust and the lithospheric mantle across the plate boundary system. GPS data indicate that the short-term discrete deformation rate is ˜28 mm/yr for the central creeping segment of the San Andreas fault and increases to 33 mm/yr at +/-35 km from the fault. This gradient in deformation rates is interpreted to reflect elastic locking of the creeping segment at depth, distributed off-fault deformation, or some combination of these two mechanisms. These short-term fault-parallel deformation rates are slower than the expected geologic slip rate and the relative plate motion rate. Structural analysis of folds and transpressional kinematic modeling were used to quantify long-term distributed deformation adjacent to the Rinconada fault. Folding accommodates approximately 5 km of wrench deformation, which translates to a deformation rate of ˜1 mm/yr since the start of the Pliocene. Integration with discrete offset on the Rinconada fault indicates that this portion of the San Andreas fault system is approximately 80% strike-slip partitioned. This kinematic fold model can be applied to the entire San Andreas fault system and may explain some of the across-fault gradient in deformation rates recorded by the geodetic data. Petrologic examination of mantle xenoliths from the Coyote Lake basalt near the Calaveras fault was used to link crustal plate boundary deformation at the surface with models for the accommodation of deformation in the lithospheric mantle. Seismic anisotropy calculations based on xenolith petrofabrics suggest that an anisotropic mantle layer thickness of 35-85 km is required to explain the observed shear wave splitting delay times in central

  10. Mapping the b-values along the Longmenshan fault zone before and after the 12 May 2008, Wenchuan, China, MS 8.0 earthquake

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    Y. Z. Zhao


    Full Text Available The b-value in the Gutenberg-Richter frequency-magnitude distribution, which is assumed to be related to stress heterogeneity or asperities, was mapped along the Longmenshan fault zone which accommodated the 12 May 2008, Wenchuan, MS 8.0 earthquake. Spatial distributions of b-value before and after the Wenchuan earthquake, respectively, were compared with the slip distribution of the mainshock. It is shown that the mainshock rupture nucleated near to, but not within, the high-stress (low b-value asperity in the south part of the Longmenshan fault, propagating north-eastward to the relatively low stress (high b-value region. Due to the significant difference between the rupture process results from different sources, the comparison between slip distribution and pre-seismic b-value distribution leads to only conclusion of the rule-of-thumb. The temporal change of b-value before the mainshock shows a weak trend of decreasing, being hard to be used as an indicator of the approaching of the mainshock. Distribution of b-values for the aftershocks relates the termination of the mainshock rupture to the harder patch along the Longmenshan fault to the north.

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

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    A. O. Öncel


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

  12. Extensional Detachment faulting in melange rocks. Plurikilometres migration by W the External Zone (Cordillera Bética, Spain) (United States)

    Roldán, Francisco Javier; Azañon, Jose Miguel; Rodríguez, Jose; Mateos, Rosa Maria


    The synthesis and correlation of units carried out in the continuous geological map (Roldán et al., 2012), has revealed a fragmentation of the carbonate outcrops belong to the Subbetic Domain (García-Hernández et al., 1980). Subbetic NW verging thrust and fold axial traces have not lateral continuity and Jurassic carbonate outscrops appear as klippes on the olistotromic unit. These ductile structures that can be observed in the internal structure of these jurassic blocks are unrelated to the brittle-ductile deformation bands observed at the basal pelitic levels. Basal detachments are rooted in: a) the Olistostromic unit, a Upper Langhian-Lower Serravallian breccia constituted by gypsum-bearing clay and marls; b) Cretaceous-Tertiary marly sedimentary rocks (Rodríguez-Fernández, et al., 2013) . In both kind of rocks, cataclastic structures allows to infer a top-to-the WSW displacement. Paleostress measurements, made on these detachments levels, are compatible with a extensional regime (Roldán et al., 2012). At the same time, the analysis and interpretation of subsurface data (seismic surveys and borehole testing) shows that the Subbetic Domain (External Subbetic, Molina 1987) are affected by westward low-angle normal faults. A balanced cross-section, based on morphological and cartographic data in the area between Sierra de Cabra and Sierra de Alta Coloma (Valdepeñas de Jaén), shows plurikilometric displacements which has been produced during Late Serravallian-Early Tortonian times. References: García-Hernández, M., López-Garrido, A.C., Rivas, P., Sanz de Galdeano, C., Vera, J.A. (1980): Mesozoic paleogeographic evolution of the zones of the Betic Cordillera. Geol. Mijnb. 59 (2). 155-168. Molina, J.M. (1987). Análisis de facies del Mesozoico en el Subbético. Tesis Doctoral, Univ. Granada. 518 p. Rodríguez-Fernández, J., Roldán, F. J., Azañón, J.M. y García-Cortés, A. (2013). El colapso gravitacional del frente orogénico a lpino en el Dominio Subb

  13. Crustal Variations in the Axial Low Velocity Zone Between the Siqueiros and Clipperton Transform Faults, East Pacific Rise (United States)

    Wilcock, W. S.; Toomey, D. R.; Detrick, R. S.


    As part of the 1997 UNDERSHOOT seismic experiment, three rise-perpendicular profiles were collected across the East Pacific Rise between the Siqueiros and Clipperton transform faults. The southern line at 8°42'N lies at the center of an inflated segment south of the 9°03'N overlapping spreading center (OSC); the middle line at 9°18'N coincides with anomalously thick crust just to the north of the OSC; and the northern line at 9°50'N overlies a bathymetrically shallow segment near the site of recent eruptions. The lines extend at least 55 km off-axis and each comprises 200-400 airgun shots that were recorded by 6-7 seafloor receivers. We have used a two-dimensional tomography algorithm to invert crustal phases and Moho reflections for models of the P-wave velocity structure. For each line, we first inverted the non-rise crossing paths for off-axis structure and crustal thickness. We then interpolated the results to derive a starting model for axial inversions. Using a creeping method, we successively incorporated crustal phases that pass above the axial magma chamber (AMC), crustal phases that pass below the AMC, and Moho reflections. Since the ray geometry is two-dimensional, the width of the axial low velocity zone (LVZ) is not well resolved. We chose to squeeze the solutions by damping velocity perturbations at nodes that are more than 4-6 km off-axis. The root mean squared residuals are about 0.025 s for rise-crossing crustal phases and 0.03-0.04 s for sub-axial Moho reflections. The structure of the LVZ appears substantially different in the three models. Immediately beneath the AMC, the LVZ has the highest amplitude along the 9°50'N profile. In contrast, the LVZ in the lowermost crust has its largest amplitude along the 9°18'N profile where the crustal thickness requires that the melt supply is highest. The lower crustal LVZ beneath the 9°50'N profile is less pronounced than at the other two sites and is significantly skewed to the east. The differences

  14. Geologic map of the Bartlett Springs Fault Zone in the vicinity of Lake Pillsbury and adjacent areas of Mendocino, Lake, and Glenn Counties, California (United States)

    Ohlin, Henry N.; McLaughlin, Robert J.; Moring, Barry C.; Sawyer, Thomas L.


    The Lake Pillsbury area lies in the eastern part of the northern California Coast Ranges, along the east side of the transform boundary between the Pacific and North American plates (fig. 1). The Bartlett Springs Fault Zone is a northwest-trending zone of faulting associated with this eastern part of the transform boundary. It is presently active, based on surface creep (Svarc and others, 2008), geomorphic expression, offset of Holocene units (Lienkaemper and Brown, 2009), and microseismicity (Bolt and Oakeshott, 1982; Dehlinger and Bolt, 1984; DePolo and Ohlin, 1984). Faults associated with the Bartlett Springs Fault Zone at Lake Pillsbury are steeply dipping and offset older low to steeply dipping faults separating folded and imbricated Mesozoic terranes of the Franciscan Complex and interleaved rocks of the Coast Range Ophiolite and Great Valley Sequence. Parts of this area were mapped in the late 1970s and 1980s by several investigators who were focused on structural relations in the Franciscan Complex (Lehman, 1978; Jordan, 1975; Layman, 1977; Etter, 1979). In the 1980s the U.S. Geological Survey (USGS) mapped a large part of the area as part of a mineral resource appraisal of two U.S. Forest Service Roadless areas. For evaluating mineral resource potential, the USGS mapping was published at a scale of 1:62,500 as a generalized geologic summary map without a topographic base (Ohlin and others, 1983; Ohlin and Spear, 1984). The previously unpublished mapping with topographic base is presented here at a scale of 1:30,000, compiled with other mapping in the vicinity of Lake Pillsbury. The mapping provides a geologic framework for ongoing investigations to evaluate potential earthquake hazards and structure of the Bartlett Springs Fault Zone. This geologic map includes part of Mendocino National Forest (the Elk Creek Roadless Area) in Mendocino, Glenn, and Lake Counties and is traversed by several U.S. Forest Service Routes, including M1 and M6 (fig. 2). The study

  15. Holocene and latest Pleistocene paleoseismology of the Salt Lake City segment of the Wasatch Fault Zone, Utah, at the Penrose Drive Trench Site (United States)

    DuRoss, Christopher B.; Hylland, Michael D.; McDonald, Greg N.; Crone, Anthony J.; Personius, Stephen F.; Gold, Ryan D.; Mahan, Shannon


    The Salt Lake City segment (SLCS) of the Wasatch fault zone (WFZ) and the West Valley fault zone (WVFZ) compromise Holocene-active normal faults that bound a large intrabasin graben in northern Salt Lake Valley and have evidence of recurrent, large-magnitude (M ~6-7) surface-faulting earthquakes. However, at the time of this investigation, questions remained regarding the timing, displacement, and recurrence of latest Pleistocene and Holocene earthquakes on the northern SLCS and WVFZ , and whether the WVFZ is seismically independent of, or moves coseismically with, the SLCS. To improve paleoseismic data for the SLCS, we conducted a fault-trench investigation at the Penrose Drive site on the northern SLCS. Two trenches, excavated across an 11-m-high scarp near the northern end of the East Bench fault, exposed colluvial-wedge evidence for fize of six (preferred) surface-faulting earthquakes postdating to Provo-phase shoreline of Lake Bonneville (~14-18 ka). Radiocarbon and luminescence ages support earthquake times at 4.0 ± 0.5 ka (2σ) (PD1), 5.9 ± 0.7 ka (PD2), 7.5 ± 0.8 ka (PD3a), 9.7 ± 1.1 ka (PD3b), 10.9 ± 0.2 ka (PD4), and 12.1 ± 1.6 ka (PD5). At least one additional earthquake occurred at 16.5 ± 1.9 ka (PD6) based on an erosional unconformity that separates deformed Lake Bonneville sily and flat-lying Provo-phase shoreline gravel. Earthquakes PD5-PD1 yield latest Pleistocene (post-Provo) and Holocene mean recurrence intervals of ~1.6 kyr and ~1.7-1.9 kyr, respectively. Using 1.0-1.4 m of per-event vertical displacement for PD5-PD3b corroborate previously identified SLCS earthquakes at 4-10 ka. PD4 and PD5 occurred within an ~8-kyr *17-9 ka) time interval on the SLCS previously interpreted as a period of seismic quiescence, and PD6 possibly corresponds with a previously identified earthquake at ~17 ka (although both events have large timing uncertainties). The Penrose data, when combined with previous paleoseismic results, improve the latest Pleistocene

  16. Investigation of the fluid flow dynamic parameters for Newtonian and non-Newtonian materials: an approach to understanding the fluid flow-like structures within fault zones (United States)

    Tanaka, H.; Shiomi, Y.; Ma, K.-F.


    To understand the fault zone fluid flow-like structure, namely the ductile deformation structure, often observed in the geological field (e.g., Ramsay and Huber The techniques of modern structure geology, vol. 1: strain analysis, Academia Press, London, 1983; Hobbs and Ord Structure geology: the mechanics of deforming metamorphic rocks, Vol. I: principles, Elsevier, Amsterdam, 2015), we applied a theoretical approach to estimate the rate of deformation, the shear stress and the time to form a streak-line pattern in the boundary layer of viscous fluids. We model the dynamics of streak lines in laminar boundary layers for Newtonian and pseudoplastic fluids and compare the results to those obtained via laboratory experiments. The structure of deformed streak lines obtained using our model is consistent with experimental observations, indicating that our model is appropriate for understanding the shear rate, flow time and shear stress based on the profile of deformed streak lines in the boundary layer in Newtonian and pseudoplastic viscous materials. This study improves our understanding of the transportation processes in fluids and of the transformation processes in fluid-like materials. Further application of this model could facilitate understanding the shear stress and time history of the fluid flow-like structure of fault zones observed in the field.[Figure not available: see fulltext.

  17. Tracer-/Heat transfer decoupling in a heterogenous, fault zone based hydrothermal reservoir in the Upper Rhine Basin; Tracer-/Waermetrnasportentkopplung in einem heterogenen, stoerungszonengepraegten Hydrothermalreservoir im Oberrheingraben

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    Ghergut, I.; Licha, T.; Maier, F.; Nottebohm, M.; Sauter, M. [Goettingen Univ. (Germany). Abt. Angewandte Geologie; Meixner, J.; Rettenmaier, D. [Karlsruher Institut fuer Technologie (KIT) (Germany). Abt. Hydrogeologie


    Heat transport processes and tracer transport processes probe the boundaries of a tracer based prognosis of the thermal lifetime for a geothermal borehole doublet in a heterogeneous hydrothermal reservoir in the Upper Rhine Basin whose behaviour is characterized by two or three large-scale not bored fault zones. A hydro-geologic structure model of the reservoir is the fundament for the identification of decisive fluid transport processes. The thermal breakdown is a rather abstract threatening with a large time distance for the geothermal borehole doublet. Nearby dangers of hydro-geochemical and hydro-mechanical nature require tracer tests for their quantification. Long dwell times are expected in a circulation test, while interpretation difficulties are expected in early tracer signals. Heat-push-shut-in tests or tracer-push-flowback tests at the geothermal re-injection drilling can supply information on transport effective aquifer parameters in an even more appropriate time. A fluid transport based characterization of the fault zones is only imaginable by means of long-term circulation tests with conservative and thermo-sensitive tracers.

  18. Result of alpha track detection of radon in soil gas in the Khlong Marui Fault Zone, Southern Thailand: A possible earthquake precursor

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    Tripob Bhongsuwan


    Full Text Available Measurements of radon concentration in soil gas were conducted at ten stations (ST1-ST10, located mainly in theKhlong Marui Fault Zone, Thap Put District, Phang Nga Province over a period from 28 January to 25 April, 2007. The resultsof the radon concentration were presented as the variation of cumulative alpha track over a week period. At Station ST10 theradon concentrations are in general higher than those at other stations for every week. Two significant radon anomalies werefound to have the concentration above the mean value plus one standard deviation. During the period of monitoring thelocal and regional earthquake activities were observed showing patterns consistent with the occurrence of the radon anomalies.The maximum radon concentration is interpreted to be related to a possible influence of the pressure and stress increasedin the subsurface. An increase in the number of earthquakes is observed correlating to a lower radon concentration when thesubsurface pressure dropped due to tectonic stress release by seismic activities. Therefore, it would be possible to use thevariation of soil gas radon concentration as an earthquake precursor in the Khlong Marui Fault Zone.

  19. Gravity and Magnetic Anomaly Interpretations and 2.5D Cross-Section Models over the Border Ranges Fault System and Aleutian Subduction Zone, Alaska (United States)

    Mankhemthong, N.; Doser, D. I.; Baker, M. R.; Kaip, G.; Jones, S.; Eslick, B. E.; Budhathoki, P.


    Quaternary glacial covers and lack of dense geophysical data on the Kenai Peninsula cause a location and geometry of the Border Ranges fault system (BRFS) within a recent forearc-accretionary boundary of Aleutian subduction zone in southern Alaska are unclear. Using new ~1,300 gravity collections within the Anchorage and Kenai Peninsula regions complied with prior 1997 gravity and aeromagnetic data help us better imaging these fault and the subduction structures. Cook Inlet forearc basin is corresponded by deep gravity anomaly lows; basin boundaries are characterized by a strong gravity gradient, where are considered to be traces of Border Ranges fault system on the east and Castle Mountain and Bruin Bay fault system on the west and northwest of the forearc basin respectively. Gravity anomaly highs over accreted rocks generally increase southeastward to the Aleutian trench, but show a gravity depression over the Kenai Mountains region. The lineament between gravity high and low in the same terrenes over the Kenai Peninsula is may be another evidence to determine the Southern Edge of the Yakutat Microplate (SEY) as inferred by Eberhart-Phillips et al. (2006). Our 2.5-D models illustrate the main fault of the BRFS dips steeply toward the west with a downslip displacement. Gravity and Magnetic anomaly highs, on the east of the BRFS, probably present a slice of the ultramafic complex emplaced by faults along the boundary of the forearc basin and accretionary wedge terranes. Another magnetic high beneath the basin in the southern forearc basin support a serpentiznied body inferred by Saltus et al. (2001), with a decreasing size toward the north. Regional density-gravity models show the Pacific subducting slab beneath the foreacre-arc teranes with a gentle and flatted dip where the subducting plate is located in north of SEY and dips more steeply where it is located on the south of SEY. The gravity depression over the accreted terrene can be explained by a density low

  20. Reconstructing the magnitude and timing of late Pleistocene and Holocene strike-slip events within the Marlborough Fault Zone, New Zealand (United States)

    Rhodes, Ed; Dolan, James; Van Dissen, Russ; Langridge, Rob; Zinke, Rob; Hatem, Alex; McGuire, Chris; Brown, Nathan


    In most instances, information about the timing of pre-historic earthquake events comes from palaeoseismic trenches located within sediments that were deposited gradually and are close to the fault. Earthquake events are recognised by disturbed stratigraphy, and the timing provided by radiocarbon dating of organic materials that constrain the youngest disturbances for each event. In contrast, fault slip rates are typically derived from the dating of geomorphic features that are offset by one or more slip events. In this latter case, it is often hard to locate suitable organic material for dating these features which often comprise fluvial terraces or channels, and a variety of alternative chronological approaches has been taken including the use of terrestrial cosmogenic nuclides (TCNs; 10Be, 36Cl), U-series dating of carbonate overgrowths on pebbles, and/or luminescence dating of sediments. Using luminescence dating based on single grains of K-feldspar and a post-IR IRSL (Infra-Red Stimulated Luminescence) measurement protocol, we have been able to control the age of several offset terrace units from a number of major strike slip faults of the Marlborough Fault Zone, New Zealand. In the past, arguments concerning the selection of which geomorphic terrace feature to date have been presented, and typically a single age estimate, or small number of dates were used to constrain the derived slip rate. In the Marlborough region, we have sampled several locations characterised by multiple fluvial terraces dating from the late Glacial period (c. 16,000 years ago) through the Holocene. By using a high sampling density involving multiple age estimates within each terrace, dating each one of the terraces, and applying a Bayesian statistical approach to constrain the age of deposition and incision events, we are able to approach a situation where we can derive slip-per-event data and event timing from the same dataset. This can overcome problems of relating observed slip

  1. Seismotectonic setting at the North Anatolian Fault Zone after the 1999 Mw=7.4 Izmit earthquake based on high-resolution aftershock locations

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    M. Bohnhoff


    Full Text Available The most recent devastating earthquakes that occurred along the North Anatolian Fault Zone (NAFZ in northwestern Turkey were the 1999 Izmit (Mw=7.4 and Düzce (Mw=7.1 events. In this study we present a catalog of Izmit aftershock hypocenters that was deduced from a network covering the entire 140 km long rupture of the mainshock. 7348 events with a location accuracy better than 5 km are analysed. Aftershocks were observed along the entire ruptured segment along a 20 km wide band of activity. Events are clustered in distinct regions and dominantly occur at 5 to 15 km depth. The eastern termination of the Izmit rupture is characterized by a sharp and steeply dipping boundary exactly where the Düzce mainshock initiated 87 days after the Izmit event. Relocation of the events using double-difference technology results in 4696 high-resolution hypocenters that allow resolving the internal structure of the seismically active areas with a resolution of 300 m (horizontal and 400m (vertical. Below the Akyazi Plain, representing a small pull-apart structure at a triple junction of the NAFZ, we identify planes of activity that can be correlated with nodal planes of EW extensional normal faulting aftershocks. Along the easternmost Karadere-Düzce segment we identify the down-dip extension of the Karadere fault that hosted about 1 m of right-lateral coseismic slip. At the easternmost rupture we correlate a cloud-type distribution of seismic activity with the largest aftershocks in this area, a subevent of the Izmit mainshock and the Düzce mainshock that all have an almost identical focal mechanism. This part of the NAFZ is interpreted as a classical example of a seismic barrier along the fault.

  2. Natural Radiation for Identification and Evaluation of Risk Zones for Affectation of Activated Faults in Aquifer Overexploited. (United States)

    Ramos-Leal, J.; Lopez-Loera, H.; Carbajal-Perez, N.


    In basins as Mexico, Michoacán, Guanajuato, Queretaro, Aguascalientes and San Luis Potosi, the existence of faults and fractures have affected the urban infrastructure, lines of conduction of drinkable water, pipelines, etc., that when not being identified and considered, they don't reflect the real impact that these cause also to the aquifer system, modifying the permeability of the means and in occasions they work as preferential conduits that communicate hydraulically potentially to the aquifer with substances pollutants (metals, fertilizers, hydrocarbons, waste waters, etc.) located in the surface. In the Valley of San Luis Potosi, Villa of Reyes, Arista, Ahualulco and recently The Huizache-Matehuala is being strongly affected by faulting and supposedly due cracking to subsidence, however, the regional tectonic could also be the origin of this phenomenon. To know the origin of the faults and affectation to the vulnerability of the aquifer few works they have been carried out in the area. A preliminary analysis indicates that it is possible that a tectonic component is affecting the area and that the vulnerability of the aquifer in that area you this increasing. Before such a situation, it is necessary to carry out the isotopic study of the same one, for this way to know among other things, isotopic characterization, recharge places and addresses of flow of the groundwater; quality of waters and the behavior hydrochemistry with relationship to the faults. High radon values were measured in San Luis Potosi Valley, the natural source of radon could be the riolites and however, these are located to almost a once thousand meters deep for what the migration of the gas is not very probable. The anomalies radiometrics was not correlation with the faults in this case. In some areas like the Valley of Celaya, the origin of the structures and the tectonic activity in the area was confirmed, identifying the structural arrangement of the faulting, the space relationships

  3. Geophysical evidence for wedging in the San Gorgonio Pass structural knot, southern San Andreas fault zone, southern California (United States)

    Langenheim, V.E.; Jachens, R.C.; Matti, J.C.; Hauksson, E.; Morton, D.M.; Christensen, A.


    Geophysical data and surface geology define intertonguing thrust wedges that form the upper crust in the San Gorgonio Pass region. This picture serves as the basis for inferring past fault movements within the San Andreas system, which are fundamental to understanding the tectonic evolution of the San Gorgonio Pass region. Interpretation of gravity data indicates that sedimentary rocks have been thrust at least 5 km in the central part of San Gorgonio Pass beneath basement rocks of the southeast San Bernardino Mountains. Subtle, long-wavelength magnetic anomalies indicate that a magnetic body extends in the subsurface north of San Gorgonio Pass and south under Peninsular Ranges basement, and has a southern edge that is roughly parallel to, but 5-6 km south of, the surface trace of the Banning fault. This deep magnetic body is composed either of upper-plate rocks of San Gabriel Mountains basement or rocks of San Bernardino Mountains basement or both. We suggest that transpression across the San Gorgonio Pass region drove a wedge of Peninsular Ranges basement and its overlying sedimentary cover northward into the San Bernardino Mountains during the Neogene, offsetting the Banning fault at shallow depth. Average rates of convergence implied by this offset are broadly consistent with estimates of convergence from other geologic and geodetic data. Seismicity suggests a deeper detachment surface beneath the deep magnetic body. This interpretation suggests that the fault mapped at the surface evolved not only in map but also in cross-sectional view. Given the multilayered nature of deformation, it is unlikely that the San Andreas fault will rupture cleanly through the complex structures in San Gorgonio Pass. ?? 2005 Geological Society of America.

  4. Mesoscopic Structural Observations of Cores from the Chelungpu Fault System, Taiwan Chelungpu-Fault Drilling Project Hole-A, Taiwan

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    Hiroki Sone


    Full Text Available Structural characteristics of fault rocks distributed within major fault zones provide basic information in understanding the physical aspects of faulting. Mesoscopic structural observations of the drilled cores from Taiwan Chelungpu-fault Drilling Project Hole-A are reported in this article to describe and reveal the distribution of fault rocks within the Chelungpu Fault System. The Chelungpu Fault System in Hole-A was encountered at a depth of between 1050 - 1250 m where deformation structures increased. Three major fault zone structures were found at approximate depths of 1111, 1153, and 1221 m. The presence of wide fault rock regions were mostly concentrated in these 3 fault zones. The fault zone at 1111 m mainly consists of a nearly brecciated fracture zone and a clayey fault gouge zone of about 1.05 m in thickness. Fault rocks from the fault zone at 1153 m are characterized by the presence of sand grains in the matrix content, consisting of a 1.1-m thick fault breccia zone and a 0.35-m thick fault gouge zone. The fault zone at 1221 m consists of fault breccia and fault gouge of 1.15 m in total thickness. These are relatively harder and darker in color than the previous 2 fault zones. Each of the 3 fault zones contains a few layers of dark colored rocks of approximately 5 - 80 mm in thickness within the fault breccia and fault gouge zones. These dark colored rocks were found distinctively within the fault rocks. However, there relation to the process of faulting is not clearly understood and shall be discussed in detail with the aid of microscopic observations.

  5. Structure and flow properties of syn-rift border faults: The interplay between fault damage and fault-related chemical alteration (Dombjerg Fault, Wollaston Forland, NE Greenland) (United States)

    Kristensen, Thomas B.; Rotevatn, Atle; Peacock, David C. P.; Henstra, Gijs A.; Midtkandal, Ivar; Grundvåg, Sten-Andreas


    Structurally controlled, syn-rift, clastic depocentres are of economic interest as hydrocarbon reservoirs; understanding the structure of their bounding faults is of great relevance, e.g. in the assessment of fault-controlled hydrocarbon retention potential. Here we investigate the structure of the Dombjerg Fault Zone (Wollaston Forland, NE Greenland), a syn-rift border fault that juxtaposes syn-rift deep-water hanging-wall clastics against a footwall of crystalline basement. A series of discrete fault strands characterize the central fault zone, where discrete slip surfaces, fault rock assemblages and extreme fracturing are common. A chemical alteration zone (CAZ) of fault-related calcite cementation envelops the fault and places strong controls on the style of deformation, particularly in the hanging-wall. The hanging-wall damage zone includes faults, joints, veins and, outside the CAZ, disaggregation deformation bands. Footwall deformation includes faults, joints and veins. Our observations suggest that the CAZ formed during early-stage fault slip and imparted a mechanical control on later fault-related deformation. This study thus gives new insights to the structure of an exposed basin-bounding fault and highlights a spatiotemporal interplay between fault damage and chemical alteration, the latter of which is often underreported in fault studies. To better elucidate the structure, evolution and flow properties of faults (outcrop or subsurface), both fault damage and fault-related chemical alteration must be considered.

  6. A multi-tracer approach for the exploration of deep geothermal energy potential and fault zone characterisation, applied in the Upper Rhine Graben (United States)

    Freundt, Florian; Najem, Sami Al; Aeschbach-Hertig, Werner; Isenbeck-Schröter, Margot; Schmidt, Gerhard; Grobe, René; Kraml, Michael


    Current methods of geothermal exploration rely on various expensive geophysical methods (e.g. 3D reflection seismics) to identify permeable fault zones and the geometry of geothermal aquifers. However this analysis alone does not allow for an estimation of an active fault's hydraulic permeability nor provides a characterisation of the chemical properties of the deep aquifer fluid. Both factors play an important role in optimising siting of geothermal wells and operation of a geothermal power plant. This work presents a low cost strategy characterizing deep hydrogeochemical reservoirs using a combination of methods from hydrogeochemistry and isotope hydrology in hot springs and near surface groundwater. The main goal is to confine the area of interest for further, indirect geophysical investigation. For this purpose natural geochemical and isotopical tracers as well as rare earth elements, 3He/4He ratios, and radiogenic isotopes (Sr and Pb) are investigated. Data from the first sampling campaign in the northern Upper Rhine Graben, close to Groß-Gerau, Germany, shows promising results, indicating an area of increased interest where elevated helium ratios coincide with characteristic geochemical data, fault location and a previously known saltwater anomaly. Geochemical analyses exhibit three different types of fluids and various mixtures. CaHCO3-dominated waters represent Quaternary aquifer conditions whereas MgSO4-dominated waters are characterised by a Tertiary aquifer rock. Higher saline NaCl-dominated waters show an impact of mantle fluids revealed by 3He/4He isotope analysis. The ratio is highest where the main fault of the northern Upper Rhine Graben crosses the Rhine river. This suggests that the fault is hydraulically active and connects ascending deep fluids with the shallow aquifer. Further investigations of rare earth element patterns as well as radiogenic isotopes will identify the origin, the ascent as well as the retention time of the deep fluids more

  7. Pulverized granite at the brittle-ductile transition: An example from the Kellyland fault zone, eastern Maine, U.S.A. (United States)

    Sullivan, Walter A.; Peterman, Emily M.


    Granite from a 50-200-m-wide damage zone adjacent to the brittle-ductile Kellyland Fault Zone contains healed fracture networks that exhibit almost all of the characteristics of dynamically pulverized rocks. Fracture networks exhibit only weak preferred orientations, are mutually cross-cutting, separate jigsaw-like interlocking fragments, and are associated with recrystallized areas likely derived from pervasively comminuted material. Fracture networks in samples with primary igneous grain shapes further indicate pulverization. Minimum fracture densities in microcline are ∼100 mm/mm2. Larger fractures in microcline and quartz are sometimes marked by neoblasts, but most fractures are optically continuous with host grains and only visible in cathodoluminescence images. Fractures in plagioclase are crystallographically controlled and typically biotite filled. Petrologic observations and cross-cutting relationships between brittle structures and mylonitic rocks show that fracturing occurred at temperatures of 400 °C or more and pressures of 200 MPa. These constraints extend the known range of pulverization to much higher temperature and pressure conditions than previously thought possible. The mutually cross-cutting healed fractures also provide the first record of repeated damage in pulverized rocks. Furthermore, pulverization must have had a significant but transient effect on wall-rock porosity, and biotite-filled fracture networks in plagioclase form weak zones that could accommodate future strain localization.

  8. Normal faulting of the Daiichi-Kashima Seamount in the Japan Trench revealed by the Kaiko I cruise, Leg 3 (United States)

    Kobayashi, K.; Cadet, J.-P.; Aubouin, J.; Boulegue, J.; Dubois, J.; von, Huene R.; Jolivet, L.; Kanazawa, T.; Kasahara, J.; Koizumi, K.-i.; Lallemand, S.; Nakamura, Y.; Pautot, G.; Suyehiro, K.; Tani, S.; Tokuyama, H.; Yamazaki, T.


    A detailed topographic and geophysical survey of the Daiichi-Kashima Seamount area in the southern Japan Trench, northwestern Pacific margin, clearly defines a high-angle normal fault which splits the seamount into two halves. A fan-shaped zone was investigated along 2-4 km spaced, 100 km long subparallel tracks using narrow multi-beam (Seabeam) echo-sounder with simultaneous measurements of gravity, magnetic total field and single-channel seismic reflection records. Vertical displacement of the inboard half was clearly mapped and its normal fault origin was supported. The northern and southern extensions of the normal fault beyond the flank of the seamount were delineated. Materials on the landward trench slope are displaced upward and to sideways away from the colliding seamount. Canyons observed in the upper landward slope terminate at the mid-slope terrace which has been uplifted since start of subduction of the seamount. Most of the landward slope except for the landward walls aside the seamount comprises only a landslide topography in a manner similar to the northern Japan Trench wall. This survey was conducted on R/V "Jean Charcot" as a part of the Kaiko I cruise, Leg 3, in July-August 1984 under the auspices of the French-Japanese scientific cooperative program. ?? 1987.

  9. Abrupt variations in brittle-ductile transition depth and lower crustal properties beneath two branches of the north Anatolian fault zone, Turkey. (United States)

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


    As part of the multi-disciplinary Faultlab project, we present new detailed images of the crust and upper mantle beneath 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 current slip rate are 20-25 mm/yr. We calculated receiver functions from teleseismic earthquakes that were 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. We use a combination of H-K stacking, common conversion point migration and non-linear inversion of receiver function stacks to constrain the subsurface velocity structure and illuminate major changes in the architecture and properties of the upper crust, lower crust and upper mantle, both across the two NAFZ branches and along 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 5 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. Furthermore, we show a direct relationship between crustal terrane, seismicity rate and seismicity depth, indicating that the brittle-ductile transition is likely to vary over horizontal length scales of less than 10 km.

  10. The Wenquan ultramafic rocks in the Central East Kunlun Fault zone, Qinghai-Tibet Plateau—crustal relics of the Paleo-Tethys ocean (United States)

    Jia, Lihui; Meng, Fancong; Feng, Huibin


    The Wenquan ultramafic rocks, located in the East Kunlun Orogenic belt in the northeastern part of the Qinghai-Tibet Plateau, consist of dunite, wehrlite, olivine-clinopyroxenite and clinopyroxenite, and exhibit cumulate textures. Olivine from dunite has high Fo (forsterite, 90.0-91.8 wt%) and NiO content (0.15-0.42 wt%). Cr-spinels from all of the rocks in this suite are characterized by high Cr# (100×[Cr/(Cr + Al)], 67-91), low Mg# (100×[Mg/(Mg + Fe2+)], 17-35) and low TiO2 contents (mostly 80) and low-CaO (Proterozoic ophiolites. The Wenquan ophiolite might be a relict of the Paleotethyan ocean, indicating that there were two cycles of oceanic-continental evolution along the Central East Kunlun Fault zone.

  11. Late Quaternary alluvial fans of Emli Valley in the Ecemiş Fault Zone, south central Turkey: Insights from cosmogenic nuclides (United States)

    Akif Sarıkaya, M.; Yıldırım, Cengiz; Çiner, Attila


    Alluvial fans within the paraglacial Ecemiş River drainages on the Aladağlar Mountains in south central Turkey were studied using geomorphological, sedimentological, and chlorine-36 terrestrial cosmogenic nuclide (TCN) surface exposure dating methods to examine the timing of alluvial fan abandonment/incision, and to understand the role of climatic and tectonic processes in the region. These alluvial fan complexes are among the best-preserved succession of alluvial fans in Turkey and they were offset by the major strike-slip Ecemiş Fault of the Central Anatolian Fault Zone. The alluvial fans are mostly composed of well-lithified limestone cobbles (5 to 25 cm in size), and comprise crudely stratified thick beds with a total thickness reaching up to about 80 m. TCN surface exposure dating indicates that the oldest alluvial fan surface (Yalak Fan) was likely formed and subsequently abandoned latest by 136.0 ± 23.4 ka ago, largely on the transition of the Penultimate Glaciation (Marine Isotope Stage 6, MIS 6) to the Last Interglacial (MIS 5) (i.e. Termination II). The second set of alluvial fan (Emli Fan) was possibly developed during the Last Interglacial (MIS 5), and incised twice by between roughly 97.0 ± 13.8 and 81.2 ± 13.2 ka ago. A younger alluvial fan deposit placed on relatively older erosional terraces of the Emli Fan suggests that it may have been produced during the Last Glacial Cycle (MIS 2). These events are similar to findings from other fluvial and lacustrine deposits throughout central Anatolia. The incision times of the Ecemiş alluvial fan surfaces largely coincide with major climatic shifts from the cooler glacial periods to warmer interglacial/interstadial conditions. This indicates that alluvial fans were produced by outwash sediments of paleoglaciers during cooler conditions, and, later, when glaciers started to retreat due to a major warming event, the excess water released from the glaciers incised the pre-existing fan surfaces. An

  12. Cyclical shear fracture and viscous flow during transitional ductile-brittle deformation in the Saddlebag Lake Shear Zone, California (United States)

    Compton, Katharine E.; Kirkpatrick, James D.; Holk, Gregory J.


    Exhumed shear zones often contain folded and/or dynamically recrystallized structures, such as veins and pseudotachylytes, which record broadly contemporaneous brittle and ductile deformation. Here, we investigate veins within the Saddlebag Lake Shear Zone, central Sierra Nevada, California, to constrain the conditions and processes that caused fractures to form during ductile deformation. The shear zone mylonites contain compositional banding at centimeter- to meter- scales, and a ubiquitous, grain-scale, continuous- to spaced-foliation defined by aligned muscovite and chlorite grains. Veins of multiple compositions formed in two predominant sets: sub-parallel to the foliation and at high angle to the foliation. Some foliation sub-parallel veins show apparent shear offset consistent with the overall kinematics of the shear zone. These veins are folded with the foliation and are commonly boudinaged, showing they were rigid inclusions after formation. Quartz microstructures and fluid inclusion thermobarometry measurements indicate the veins formed by fracture at temperatures between 400-600 °C. Quartz, feldspar and tourmaline δ18O values (+ 2.5 to + 16.5) suggest extended fluid-rock interaction that involved magmatic, metamorphic, and meteoric-hydrothermal fluids. The orientation and spatial distribution of the veins shows that shear fractures formed along mechanically weak foliation planes. We infer fracture was promoted by perturbations to the strain rate and/or pore pressure during frictional-viscous deformation in a low effective stress environment. Evidence for repeated fracture and subsequent flow suggest both the stress and pore pressure varied, and that the tendency to fracture was controlled by the rates of pore pressure recovery, facilitated by fracture cementation. The tectonic setting and inferred phenomenological behavior were similar to intra-continental transform faults that host triggered tectonic tremor, suggesting the mechanisms that caused

  13. Mesoscopic Structural Observations of Cores from the Chelungpu Fault System, Taiwan Chelungpu-Fault Drilling Project Hole-A, Taiwan

    Directory of Open Access Journals (Sweden)

    Hiroki Sone


    Full Text Available Structural characteristics of fault rocks distributed within major fault zones provide basic information in understanding the physical aspects of faulting. Mesoscopic structural observations of the drilledcores from Taiwan Chelungpu-fault Drilling Project Hole-A are reported in this article to describe and reveal the distribution of fault rocks within the Chelungpu Fault System.

  14. Absolute age determination of quaternary faults

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    Cheong, Chang Sik; Lee, Seok Hoon; Choi, Man Sik [Korea Basic Science Institute, Seoul (Korea, Republic of)] (and others)


    To constrain the age of neotectonic fault movement, Rb-Sr, K-Ar, U-series disequilibrium, C-14 and Be-10 methods were applied to the fault gouges, fracture infillings and sediments from the Malbang, Ipsil, Wonwonsa faults faults in the Ulsan fault zone, Yangsan fault in the Yeongdeog area and southeastern coastal area. Rb-Sr and K-Ar data imply that the fault movement of the Ulan fault zone initiated at around 30 Ma and preliminary dating result for the Yang san fault is around 70 Ma in the Yeongdeog area. K-Ar and U-series disequilibrium dating results for fracture infillings in the Ipsil fault are consistent with reported ESR ages. Radiocarbon ages of quaternary sediments from the Jeongjari area are discordant with stratigraphic sequence. Carbon isotope data indicate a difference of sedimentry environment for those samples. Be-10 dating results for the Suryum fault area are consistent with reported OSL results.

  15. The 1996 Mw 6.6 Lijiang earthquake: Application of JERS-1 SAR interferometry on a typical normal-faulting event in the northwestern Yunnan rift zone, SW China (United States)

    Ji, Lingyun; Wang, Qingliang; Xu, Jing; Feng, Jiangang


    The northwestern Yunnan rift zone in the Yunnan Province of China is a seismically active region located along the western boundary of the Sichuan-Yunnan Block on the eastern margin of the Qinghai-Tibetan Plateau. An earthquake with a magnitude of 6.6 (Mw) occurred in this region on February 3, 1996. The Lijiang earthquake was the largest normal-faulting event to occur along the western boundary of the Sichuan-Yunnan Block in the last 40 years. In this study, we used L-band JERS-1 (Japanese Earth Resources Satellite-1) SAR data sets from two descending orbits to detect surface deformation signals surrounding the epicentral region in order to estimate the source parameters through an inversion of the displacement fields. The results indicated that the earthquake can be explained by slip along two segments of the ∼N-S trending listric normal fault, named the Lijiang-Daju fault. Coseismic deformation patterns and slip distributions revealed that the earthquake consisted of two sub-events, which were also suggested by seismological results. Based on an analysis of the static Coulomb stress change, the second sub-event was likely triggered by the first sub-event. The central segment of the Lijiang-Daju fault, which has an eastward-convex geometry, did not rupture during the earthquake. This phenomenon was probably related to a geometrical discontinuity at the fault-bend area of the Lijiang-Daju fault.

  16. Surface breakthrough of a basement fault by repeated seismic slip episodes: The Ostler Fault, South Island, New Zealand (United States)

    Ghisetti, Francesca C.; Gorman, Andrew R.; Sibson, Richard H.


    The Ostler Fault is one of the major active reverse faults in the piedmont of the Southern Alps, SE of the Alpine Fault. We present a new geological and morphotectonic map of the southern Ostler Fault, integrated with two seismic reflection profiles across the active central segments of the fault. Segmented, subparallel scarps define a N-S belt (˜40 km long and 2-3 km wide) of pure reverse faults, which upthrow and back-tilt a panel of Plio-Pleistocene terrestrial units (2.4-1.0 Ma) plus the overlying glacial outwash (chronology of newly faulted markers, and tectonically controlled diversion of paleodrainages, all indicate progressive S to N breakthrough of the surface trace of the Ostler Fault in the last 2.4 Ma. The new seismic data define a main fault segment dipping 50°-60°W to depths of ˜1.5 km, with a vertical throw of 800 m, and a shortening of ˜30%. The fault geometry and kinematics and the subsurface data favor the interpretation that the Ostler Fault propagated updip across the Plio-Quaternary terrestrial sequence as the emerging, high-angle splay of an inherited Late Cretaceous-Paleocene normal fault, that underwent repeated cycles of compressional reactivation in the last 2.4 Ma.

  17. The Cotoncello Shear Zone (Elba Island, Italy): The deep root of a fossil oceanic detachment fault in the Ligurian ophiolites (United States)

    Frassi, Chiara; Musumeci, Giovanni; Zucali, Michele; Mazzarini, Francesco; Rebay, Gisella; Langone, Antonio


    The ophiolite sequences in the western Elba Island are classically interpreted as a well-exposed ocean-floor section emplaced during the Apennines orogeny at the top of the tectonic nappe-stack. Stratigraphic, petrological and geochemical features indicate that these ophiolite sequences are remnants of slow-ultraslow spreading oceanic lithosphere analogous to the present-day Mid-Atlantic Ridge and Southwest Indian Ridge. Within the oceanward section of Tethyan lithosphere exposed in the Elba Island, we investigated for the first time a ​10s of meters-thick structure, the Cotoncello Shear Zone (CSZ), that records high-temperature ductile deformation. We used a multidisciplinary approach to document the tectono-metamorphic evolution of the shear zone and its role during spreading of the western Tethys. In addition, we used zircon U-Pb ages to date formation of the gabbroic lower crust in this sector of the Apennines. Our results indicate that the CSZ rooted below the brittle-ductile transition at temperature above 800 °C. A high-temperature ductile fabric was overprinted by fabrics recorded during progressive exhumation up to shallower levers under temperature work.

  18. Deep-water turbidites as Holocene earthquake proxies: the Cascadia subduction zone and Northern San Andreas Fault systems

    Directory of Open Access Journals (Sweden)

    J. E. Johnson


    Full Text Available New stratigraphic evidence from the Cascadia margin demonstrates that 13 earthquakes ruptured the margin from Vancouver Island to at least the California border following the catastrophic eruption of Mount Mazama. These 13 events have occurred with an average repeat time of ?? 600 years since the first post-Mazama event ?? 7500 years ago. The youngest event ?? 300 years ago probably coincides with widespread evidence of coastal subsidence and tsunami inundation in buried marshes along the Cascadia coast. We can extend the Holocene record to at least 9850 years, during which 18 events correlate along the same region. The pattern of repeat times is consistent with the pattern observed at most (but not all localities onshore, strengthening the contention that both were produced by plate-wide earthquakes. We also observe that the sequence of Holocene events in Cascadia may contain a repeating pattern, a tantalizing look at what may be the long-term behavior of a major fault system. Over the last ?? 7500 years, the pattern appears to have repeated at least three times, with the most recent A.D. 1700 event being the third of three events following a long interval of 845 years between events T4 and T5. This long interval is one that is also recognized in many of the coastal records, and may serve as an anchor point between the offshore and onshore records. Similar stratigraphic records are found in two piston cores and one box core from Noyo Channel, adjacent to the Northern San Andreas Fault, which show a cyclic record of turbidite beds, with thirty- one turbidite beds above a Holocene/.Pleistocene faunal «datum». Thus far, we have determined ages for 20 events including the uppermost 5 events from these cores. The uppermost event returns a «modern» age, which we interpret is likely the 1906 San Andreas earthquake. The penultimate event returns an intercept age of A.D. 1664 (2 ?? range 1505- 1822. The third event and fourth event

  19. A multidisciplinary approach for the study of the effects of active tectonics along the North Anatolian fault zone: possibilities for the application of the electrical self potential method

    Directory of Open Access Journals (Sweden)

    W. Balderer


    Full Text Available The aims of this joint interdisciplinary project “Marmara” of ETH Zurich and the Istanbul Technical University (ITO are to study the effects of active tectonics as evidenced by geology, geodesy and seismology on hydrogeology and geothermics in selected areas along the North Anatolian fault zone. Within the framework of this project thermal water systems in seven different areas have been investigated or are under investigation up to now (SchindIer et al., 1993. For three study areas along the North Anatolian fault zone (from east to west of Kuzuluk/Adapazari, Bursa and of Canakkale the investigations with respect to the geological and hydrogeological features are complete. The now possible hydrogeological characterisation shows encouraging possibilities for the application of new methods like the electrical self potential method for the following reasons: 1 a fully interdisciplinary approach, including seismic survey with especially conceived network, geodetic survey to investigate tectonic movements by the GPS method, geothermic survey combined with geological mapping and hydrogeological investigations of normal mineral and thermal waters; 2 groundwaters of very different chemical and isotopical composition e.g.: Ca-HCO3-type thermal waters of up to 82 °C temperature and total mineralisation of 500 mg/I to 1500 mg/I in the Bursa area, Na-HCO3-type cold mineral waters of up to 2500 mg/I to thermal waters of same mineralisation of up to 80 °C temperature, containing large amounts of CO2 of up to 1 l per 1 kg of water (at surface conditions in the Kuzuluk area and Na-Cl-type waters presenting real thermal brines of up to 65 000 mg/I of total mineralisation and temperatures of up to 100 °C in the Canakkale area; 3 distinct types of hydrodynamic flow regime in areas of different geological and tectonic structure. Based on the results of the investigations within these areas the possibilities of further studies including self potential methods

  20. Melting and dehydration within mantle plumes and the formation of sub-parallel volcanic trends at intra-plate hotspots: Analysis of physical properties on spatial and temporal evolution of viscous plug formation (United States)

    Kundargi, R.; Hall, P. S.


    Recent volcanism associated with the Hawaiian hotspot has long been recognized as occurring along two physically distinct, sub-parallel volcanic chains, known as the Loa and Kea trends [e.g., Jackson, 1972]. Recently, several additional intra-plate hotspots, including Samoa [Workman et al., 2004], Marquesas [Chauvel et al., 2009; Huang et al., 2011], and Societies [Payne et al., in press], have been shown to exhibit dual-chain volcanism similar to that at Hawaii. Despite the prevalence of this pattern of volcanism at hotspots, its cause is not well understood. Previous explanations for the presence of dual-chain volcanism at Hawaii focused on magma migration to explain the spatial distribution of volcanism. In particular, Hieronymus and Bercovici [1999] developed a model in which lithospheric flexure induced by loading from the growth of volcanic edifices alters magma migration pathways through the lithosphere over time. In this model, a perturbation to the magma supply, such as might be expected as the result of a change in plate motion, can result in the surface expression of magmatism being focused into two sub-parallel chains. Here, we investigate an alternative hypothesis for the formation of dual-chain volcanism, in which melting and dehydration of upwelling peridotite within a plume conduit leads to the creation of a plug of viscous, buoyant residuum that inhibits upward flow at the center of the plume conduit near the base of the lithosphere. This suppresses the rate of melt generation above the center of the conduit and results in a bifurcated distribution of melt production. We report on a series of 3-D numerical experiments in which mantle upwelling within a plume conduit impinges on the base of an overriding oceanic plate far from any plate boundaries. The experiments were conducted using CitcomCU. Melting and dehydration were modeled using a Lagrangian particle method, and a diffusion creep rheology that explicitly includes the effects of water on

  1. An Integrated Approach to Resolving Structure Associated with the Monte Vista Fault Zone, Southwest Santa Clara Valley, California, Using Geologic, Potential-field and Seismic Data (United States)

    Langenheim, V. E.; Catchings, R. D.; McLaughlin, R. J.; Jachens, R. C.; Wentworth, C. M.; Stanley, R. G.; Mankinen, E. A.


    We integrate geologic and geophysical information to characterize the upper-plate structure of the Monte Vista fault zone (MVFZ). The MVFZ is part of the larger Foothills thrust fault system and extends 25 km from Los Altos southeast to Los Gatos along the front of the range. At the northwestern end of the MVFZ, Franciscan and Miocene sedimentary rocks are thrust over Quaternary deposits. Upper-plate rocks of the Plio-Quaternary Santa Clara Formation are folded, with Miocene rocks exposed in the core of a hanging-wall anticline. The fold axes parallel the southeast strike of the MVFZ for 5-6 km, then diverge southward from the fault zone and disappear near Saratoga, to be replaced by deeply dissected, nearly flat-lying Santa Clara Formation and/or Pleistocene fan deposits. These relations suggest that there is a structural transition within the upper plate of the MVFZ. North of this transition, the Santa Clara Formation may be as thick as 600-700 m, if its surface distribution and bedding attitudes represent uniform thickness across the axis of a prominent synclinal trough. South of the transition, water wells within the undeformed surficial deposits encountered "blue shale" at a depth of about 120 m. If the drillers' "blue shale" is Franciscan basement, this abrupt change in thickness of the young deposits should produce a 10 mGal anomaly that is not seen on a longitudinal gravity profile across the transition. Given this absence, the blue shale is probably part of the Santa Clara Formation, rather than Franciscan basement. North of the transition, the absence of local gravity lows over the thick, downfolded Santa Clara Formation suggests that the Santa Clara is not as thick as projected from the geologic relations or is denser than similar deposits elsewhere in the region. Thickening of the Plio-Quaternary deposits northeastward across the MVFZ is suggested by a magnetic high that extends basinward to the northeast. The gradient of the edge anomaly is only 500

  2. Thermochronology of a convergent orogen: Constraints on the timing of thrust faulting and subsequent exhumation of the Maladeta Pluton in the Central Pyrenean Axial Zone (United States)

    Metcalf, James R.; Fitzgerald, Paul G.; Baldwin, Suzanne L.; Muñoz, Josep-Anton


    The Pyrenees Mountains of Spain and France are a collisional orogen cored by a south-vergent antiformal stack of Paleozoic basement thrust sheets (the Axial Zone). Thrusting accommodated shortening due to convergence between Iberia and Europe. Granitic plutons, intruded during the Hercynian orogeny, form an important component of the basement units. Thermochronology of granodioritic samples collected from a vertical [age-elevation] profile from the south-central Maladeta pluton provide new constraints on the timing of thrust faulting and rock exhumation of the Pyrenean orogen. The Maladeta massif lies within the Orri thrust sheet, presently occupying the immediate footwall of the Gavarnie thrust, a major Axial Zone Alpine-age thrust fault. New biotite and K-feldspar 40Ar/ 39Ar and apatite (U-Th)/He (AHe) data combined with previous apatite fission track (AFT) thermochronology and structural studies of the Maladeta pluton constrain the thermal evolution of this massif. Biotite weighted mean plateau and K-feldspar maximum 40Ar/ 39Ar ages from the highest elevations of the Maladeta pluton (2850 m) are ˜ 280 Ma, close to the age of intrusion, and are interpreted to date the timing of rapid cooling in the Hercynian. Subsequently the Maladeta massif remained close to the surface as indicated by the presence of unconformable Triassic continental sediments. K-feldspar 40Ar/ 39Ar multiple diffusion domain thermal models from two samples at lower elevations (1780 m and 1400 m) indicate heating initiated at ˜ 65 Ma, reaching maximum temperatures of 270 to 280 °C. These data are interpreted to record thrust burial of the Maladeta pluton to depths of ˜ 6-10 km in the footwall of the Gavarnie thrust. Burial and heating were followed by a period of relatively rapid cooling beginning at ˜ 50 Ma, recorded in three K-feldspar thermal models from samples at different elevations (2850 m, 1780 m, and 1400 m). AFT thermal models, in conjunction with the AFT and apatite AHe age

  3. Seismic Wave Velocity Decrease near the Fault Zone Associated with the 2007 Noto Peninsula Earthquake, Japan, Detected by Using Ambient Noise (United States)

    Ohmi, S.


    this case. We also calculated the cross-correlation functions (CCF) along the baselines in the source region. Frequency range of the CCF's we used is 0.1 Hz - 1.0 Hz band, which also samples the upper crust portion. CCF's indicate the average velocity change along the baselines. Some of the baselines that sample source region exhibit the velocity decrease of up to 1.7 %, which is rather small compared to that indicated by ACF at the immediate vicinity of the fault zone. These analyses probably indicate that the velocity decrease is localized around the source fault region at deeper portion, which may be attributed to not only the strong motion but also some other causes around the fault.

  4. Hydrothermal brecciation in the Jemez Fault zone, Valles Caldera, New Mexico: Results from CSDP (Continental Scientific Drilling Program) corehole VC-1

    Energy Technology Data Exchange (ETDEWEB)

    Hulen, J.B.; Nielson, D.L.


    Paleozoic and Precambrian rocks intersected deep in Continental Scientific Drilling Program corehole VC-1, adjacent to the late Cenozoic Valles caldera complex, have been disrupted to form a spectacular breccia sequence. The breccias are of both tectonic and hydrothermal origin, and probably formed in the Jemez fault zone, a major regional structure with only normal displacement since mid-Miocene. Tectonic breccias are contorted, crushed, sheared, and granulated; slickensides are commmon. Hydrothermal breccias, by contrast, lack these frictional textures, but arej commonly characterized by fluidized matrix foliation and prominent clast rounding. Fluid inclusions in the hydrothermal breccias are dominantly two-phase, liquid-rich at room temperature, principally secondary, and form two distinctly different compositional groups. Older inclusions, unrelated to brecciation, are highly saline and homogenize to the liquid phase in the temperature range 189 to 246/sup 0/C. Younger inclusions, in part of interbreccia origin, are low-salinity and homogenize (also to liquid) in the range 230 to 283/sup 0/C. Vapor-rich inclusions locally trapped along with these dilute liquid-rich inclusions document periodic boiling. These fluid-inclusion data, together with alteration assemblages and textures as well as the local geologic history, have been combined to model hydrothermal brecciation at the VC-1 site.

  5. Evaluating methods used for fission track dating of tephras: examples from the Afar Depression, Ethiopia, and the Denali fault zone, Alaska (United States)

    Blythe, A. E.; Warfel, T. S.; Phillips, D. J.


    Although fission track geochronology has been successfully used to date volcanic glasses and tephras in several studies, a variety of approaches have been used (see Westgate et al., 2013), and no consensus for a standardized methodology has emerged. As a result, this technique is rarely employed, despite having the potential to date tephras and glasses that cannot be dated by other methods, such as K-Ar dating. We have been evaluating the various approaches used to address the technical issues in fission track dating of tephras, by applying them to standards of known ages, including Moldavite tektite, and Huckleberry and Bishop Tuffs. Some of these issues include track etching and counting protocol, and corrections for the effects of track fading at low temperatures. Track etching is generally done in 24% HF for 75 or more seconds, but the time necessary for optimal etching appears to vary according to sample composition and grain size. To correct for track fading, we are using the diameter correction technique of Sandhu and Westgate (1995). We have obtained tephra samples from two regions, the Afar Depression in Ethiopia, an area with significant early hominid fossils, and the Denali fault zone in Alaska, an area with a complicated tectonic evolution. For both of these regions, we have samples that have been dated by other methods for calibration purposes, and we will explore the application of a Zeta correction to the technique. This underutilized technique can provide powerful constraints on studies of timing in diverse geologic environments.

  6. Geometry and kinematics of the fold-thrust belt and structural evolution of the major Himalayan fault zones in the Darjeeling -- Sikkim Himalaya, India (United States)

    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

  7. Eruption-triggered mixing of extra-caldera basalt and rhyolite complexes along the East Gallatin-Washburn fault zone, Yellowstone National Park, WY, USA (United States)

    Pritchard, C. J.; Larson, P. B.; Spell, T. L.; Tarbert, K. D.


    Though mixing and commingling of magmas is common, mixing between rhyolite and basalt magmas is not commonly preserved in volcanic rocks. The presence of at least four mixed magma complexes at Yellowstone National Park suggests that mingling is not due to random intersections of feeder dikes, geochemical analyses also show that though these magmas appear to be commingled, there is mixing between the two disparate end members. Our model combines previous work on the Grizzly Lake, Gardner River, Crystal Spring, and Appolinaris Spring mixed magma complexes with results from new analyses, recent mixing experiments, and regional structural geology. Coeval extensional tectonism, as seen in the East Gallatin-Washburn fault zone, is also present in other areas of basalt and rhyolite mixing/mingling (e.g. Iceland). The central portions, or core, of the complexes contain increased concentrations of emulsion rock, occasional basaltic pillows in a rhyolite matrix, net veining, and mixed magma with highly variable geochemistry (SiO2 ranges from 50 to 78 wt.%). Phenocrysts have been transferred between mafic and felsic portions of the complexes and suggest that these mixed magmas did not have enough time, or energy (e.g. heat), to thoroughly mix into complete hybrid intermediate magmas. This implies that mixing occurred during eruption. Furthermore, analyses at the micron-scale suggest that zones of chaotic mixing between basalt and high-silica rhyolites may be more complete than previously thought during mixing of high silica rhyolites and basalts with greater than 4 wt.% MgO. The temperature of the rhyolitic magmas was approximately 850 °C with a viscosity between 1 × 106 and 3 × 106 Pas. The basalt was approximately 1070 °C with a viscosity of 2 × 102 to 9 × 103 Pas prior to mixing. Mixing of these two extreme end members may have required decompression of the lower basaltic magma chamber during eruption of the overlying rhyolitic magma chamber into through structurally

  8. Assessing the fugitive emission of CH4 via migration along fault zones - Comparing potential shale gas basins to non-shale basins in the UK. (United States)

    Boothroyd, I M; Almond, S; Worrall, F; Davies, R J


    This study considered whether faults bounding hydrocarbon-bearing basins could be conduits for methane release to the atmosphere. Five basin bounding faults in the UK were considered: two which bounded potential shale gas basins; two faults that bounded coal basins; and one that bounded a basin with no known hydrocarbon deposits. In each basin, two mobile methane surveys were conducted, one along the surface expression of the basin bounding fault and one along a line of similar length but not intersecting the fault. All survey data was corrected for wind direction, the ambient CH4 concentration and the distance to the possible source. The survey design allowed for Analysis of Variance and this showed that there was a significant difference between the fault and control survey lines though a significant flux from the fault was not found in all basins and there was no apparent link to the presence, or absence, of hydrocarbons. As such, shale basins did not have a significantly different CH4 flux to non-shale hydrocarbon basins and non-hydrocarbon basins. These results could have implications for CH4 emissions from faults both in the UK and globally. Including all the corrected fault data, we estimate faults have an emissions factor of 11.5±6.3tCH4/km/yr, while the most conservative estimate of the flux from faults is 0.7±0.3tCH4/km/yr. The use of isotopes meant that at least one site of thermogenic flux from a fault could be identified. However, the total length of faults that penetrate through-basins and go from the surface to hydrocarbon reservoirs at depth in the UK is not known; as such, the emissions factor could not be multiplied by an activity level to estimate a total UK CH4 flux. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

  9. East Pacific Rise from Siqueiros to Orozco Fracture Zones: Along-strike continuity of axial neovolcanic zone and structure and evolution of overlapping spreading centers (United States)

    MacDonald, Ken; Sempere, Jean-Christophe; Fox, P. J.


    We have used the Sea Beam multibeam echo-sounding system to survey the East Pacific Rise (EPR) from 8°20'N to 18°30'N, obtaining complete coverage of the EPR axial neovolcanic zone and all intervening transform faults. Here we focus on the EPR neovolcanic zone and the definition of overlapping spreading centers (OCS's) between the Orozco and Siqueiros transform faults. The neovolcanic zone is narrow (0.5-2.0 km) and continuous along strike and occurs within and near a strike-continuous axial summit graben. The neovolcanic zone and summit graben reside along the crest of a volcanic axial high which is 2-10 km wide and which continues uninterrupted along strike for 40-140 km. Within 20-50 km of an intersection with a transform fault the axial neovolcanic zone narrows and deepens, and within only 3-6 km of the intersection the neovolcanic zone turns sharply into the transform valley. At seven locations between the Siqueiros and Orozco transform faults the axial neovolcanic zone is discontinuous and is laterally offset a short distance (1-15 km). In contrast with a classic ridge/transform/ridge plate boundary, however, offset rise terminations overlap each other by a distance approximately 3 times greater than their offset. They curve toward each other, and often one merges into the other along strike. Separating the OSC's is an elliptical overlap basin up to 600 m deep whose long axis is subparallel to the adjacent spreading centers. The overlap basin is characterized by volcanic constructional edifices. A key difference between these offsets and small transform faults in the Atlantic is that there are no transform fault structures in the overlap basin which link the offset rise axes. A continuous axial depth profile reveals a long-wavelength (20-60 km) undulation of the rise axis which may be associated with variations in the magmatic budget along strike. The lowest points in the axial depth profile occur near transform faults and at OSC's, suggesting that these

  10. The 2014 Kefalonia Doublet ( M W6.1 and M W6.0), Central Ionian Islands, Greece: Seismotectonic Implications along the Kefalonia Transform Fault Zone (United States)

    Karakostas, Vassilios; Papadimitriou, Eleftheria; Mesimeri, Maria; Gkarlaouni, Charikleia; Paradisopoulou, Parthena


    The 2014 Kefalonia earthquake sequence started on 26 January with the first main shock ( M W6.1) and aftershock activity extending over 35 km, much longer than expected from the causative fault segment. The second main shock ( M W6.0) occurred on 3 February on an adjacent fault segment, where the aftershock distribution was remarkably sparse, evidently encouraged by stress transfer of the first main shock. The aftershocks from the regional catalog were relocated using a 7-layer velocity model and station residuals, and their distribution evidenced two adjacent fault segments striking almost N-S and dipping to the east, in full agreement with the centroid moment tensor solutions, constituting segments of the Kefalonia Transform Fault (KTF). The KTF is bounded to the north by oblique parallel smaller fault segments, linking KTF with its northward continuation, the Lefkada Fault.

  11. Influence of fault trend, bends, and convergence on shallow structure and geomorphology of the Hosgri strike-slip fault, offshore central California (United States)

    Johnson, Samuel Y.; Watt, Janet T.


    We mapped an ∼94-km-long portion of the right-lateral Hosgri fault zone in offshore central California using a dense network of high-resolution seismic reflection profiles, marine magnetic data, and multibeam bathymetry. These data document the location, length, and continuity of multiple fault strands, highlight fault-zone heterogeneity, and demonstrate the importance of fault trend, fault bends, and fault convergence in the development of shallow structure and tectonic geomorphology along strike-slip faults.

  12. Reply to discussion by M. C. Alçiçek et al. on ;Neogene-Quaternary evolution of the Tefenni basin on the Fethiye-Burdur fault zone, SW Anatolia-Turkey;, Journal of African Earth Sciences, 118, 137-148, by R. Aksoy and S. Aksarı (United States)

    Aksoy, Rahmi; Aksarı, Süleyman


    In their discussion on the Aksoy and Aksarı (2016) article, Alçiçek et al. (2017) claim that our stratigraphic interpretation, age assignment for the rock units and kinematic analysis depended on incorrect data. They also claim that there is no evidence for a NE-trending fault zone (Fethiye-Burdur Fault Zone) from Fethiye to Burdur with left-lateral strike-slip movement. Our opposing views on the above-mentioned issues are given below.

  13. Petrophysical, Geochemical, and Hydrological Evidence for Extensive Fracture-Mediated Fluid and Heat Transport in the Alpine Fault's Hanging-Wall Damage Zone

    NARCIS (Netherlands)

    Townend, John; Sutherland, Rupert; Toy, Virginia G.; Doan, Mai Linh; Célérier, Bernard; Massiot, Cécile; Coussens, Jamie; Jeppson, Tamara; Janku-Capova, Lucie; Remaud, Léa; Upton, Phaedra; Schmitt, Douglas R.; Pezard, Philippe; Williams, Jack; Allen, Michael John; Baratin, Laura May; Barth, Nicolas; Becroft, Leeza; Boese, Carolin M.; Boulton, Carolyn; Broderick, Neil G.R.; Carpenter, Brett M.; Chamberlain, Calum J.; Cooper, Alan; Coutts, Ashley; Cox, Simon C.; Craw, Lisa; Eccles, Jennifer D.; Faulkner, Dan; Grieve, Jason; Grochowski, Julia; Gulley, Anton; Hartog, Arthur; Henry, Gilles; Howarth, Jamie; Jacobs, Katrina; Kato, Naoki; Keys, Steven; Kirilova, Martina; Kometani, Yusuke; Langridge, Rob; Lin, Weiren; Little, Tim; Lukacs, Adrienn; Mallyon, Deirdre; Mariani, Elisabetta; Mathewson, Loren; Melosh, Ben; Menzies, Catriona; Moore, Jo; Morales, Luis; Mori, Hiroshi; Niemeijer, André|info:eu-repo/dai/nl/370832132; Nishikawa, Osamu; Nitsch, Olivier; Paris, Jehanne; Prior, David J.; Sauer, Katrina; Savage, Martha K.; Schleicher, Anja; Shigematsu, Norio; Taylor-Offord, Sam; Teagle, Damon A H; Tobin, Harold; Valdez, Robert; Weaver, Konrad; Wiersberg, Thomas; Zimmer, Martin


    Fault rock assemblages reflect interaction between deformation, stress, temperature, fluid, and chemical regimes on distinct spatial and temporal scales at various positions in the crust. Here we interpret measurements made in the hanging-wall of the Alpine Fault during the second stage of the Deep

  14. Crystallographic control on early stages of cataclasis in carbonate fault gouges (United States)

    Demurtas, Matteo; Smith, Steven A. F.; Fondriest, Michele; Spagnuolo, Elena; Di Toro, Giulio


    Carbonates are a recurring lithology in most of active seismic areas worldwide, such as the Apennines (Italy). Here, typical fault products are gouges and cataclasites made of mixtures of carbonate minerals (i.e., calcite and dolomite) that occasionally exhibit a foliation. Natural fault gouges often contain minerals with strong anisotropies, such as cleavage surfaces in phyllosilicates and carbonates. Therefore, the understanding of the role of such anisotropies during shearing is important to develop realistic microphysical models of brittle fragmentation and grain size reduction. Here we present results of microstructural and coupled EDS-EBSD (Energy Dispersive Spectroscopy - Electron Backscattered Diffraction) analysis on mixtures (50/50wt%) of calcite-dolomite gouges deformed experimentally in a rotary shear apparatus (SHIVA, INGV-Rome) at room temperature under constant normal stress of 17.5 MPa and slip rates of 30 µm/s to 1 m/s. The EDS-EBSD analysis was focused on the gouge layer underlying the slip zone, which has been previously demonstrated to accommodate low finite shear strain during deformation. At all investigated slip rates, calcite develops a crystallographic preferred orientation (CPO) on the (0001) plane, with the c-axis inclined subparallel to the principal stress and the [-1-120] direction forming a girdle perpendicular to it. Texture strength typically increases with slip rate and appears not to be influenced by the presence of water or foliation development in the gouge during deformation. Misorientation analysis suggests twinning as the principal crystallographic active deformation mechanism. Instead, dolomite grains do not develop a CPO. Microfractures are closely spaced, mainly oriented subparallel to the principal stress and rarely exploit calcite twin planes. The latter typically occur at high angle with respect to fractures, are oriented consistently with the sense of shear and almost orthogonal to the principal stress. Calcite grains

  15. Structural controls on Eocene to Pliocene tectonic and metallogenic evolution of the southernmost Lesser Caucasus, Armenia: paleostress field reconstruction and fault-slip analysis (United States)

    Hovakimyan, Samvel; Moritz, Robert; Tayan, Rodrik


    The Cenozoic evolution of the central segment of the Tethyan belt is dominated by oblique convergence and final collision of Gondwana-derived terranes and the Arabian plate with Eurasia, which created a favorable setting for the formation of the highly mineralized Meghri-Ordubad pluton in the southernmost Lesser Caucasus. Regional strike-slip faults played an important role in the control of the porphyry Cu-Mo and epithermal systems hosted by the Meghri-Ordubad pluton. In this contribution we discuss the paleostress and the kinematic environment of the major strike-slip and oblique-slip ore-controlling faults throughout the Eocene subduction to Mio-Pliocene post-collisional tectonic evolution of the Meghri-Ordubad pluton based on detailed structural field mapping of the ore districts, stereonet compilation of ore-bearing fractures and vein orientations in the major porphyry and epithermal deposits, and the paleostress reconstructions. Paleostress reconstructions indicate that during the Eocene and Early Oligocene, the main paleostress axe orientations reveal a dominant NE-SW-oriented compression, which is compatible with the subduction geometry of the Neotethys along Eurasia. This tectonic setting was favorable for dextral displacements along the two major, regional NNW-oriented Khustup-Giratakh and Salvard-Ordubad strike-slip faults. This resulted in the formation of a NS-oriented transrotational basin, known as the Central magma and ore- controlling zone (Tayan, 1998). It caused a horizontal clockwise rotation of blocks. The EW-oriented faults separating the blocks formed as en-échelon antithetic faults (Voghji, Meghrasar, Bughakyar and Meghriget-Cav faults). The Central zone consists of a network of EW-oriented sinistral and NS-oriented subparallel strike-slip faults (Tashtun, Spetry, Tey, Meghriget and Terterasar faults). They are active since the Eocene and were reactivated during the entire tectonic evolution of the pluton, but with different behaviors

  16. Testing the Existence of the South Gobi Microcontinent: U-Pb Zircon Dating of Tectonites within the East Gobi Fault Zone, Southeastern Mongolia (United States)

    Taylor, J. P.; Webb, L. E.; Johnson, C. L.; Heumann, M. J.; Hagen-Peter, G. A.; Gehrels, G. E.


    The East Gobi Fault Zone (EGFZ) is a northeast trending structural corridor in southeastern Mongolia with a polyphase deformation history. Within the EGFZ, high grade and high strain metamorphic tectonites mapped as Precambrian have been interpreted to represent the South Gobi Microcontinent. Field and petrographic evidence, however, support an alternative hypothesis that the protoliths of the tectonites are Paleozoic arc and sedimentary sequences. Moreover, 40Ar/39Ar thermochronology indicates that fabrics in the metamorphic tectonites are the result of Mesozoic deformation. We present new LA-ICPMS, U-Pb zircon ages for rocks mapped as Precambrian within the EGFZ that serve to test the two hypotheses. Some zircons examined are small or exhibit complex zonation. In these cases, a small spot size of 10 μm was used, which excavates ~ 1 ng of material. The high spatial resolution capable with such a small spot size made dating these zircon grains and zones within grains possible. Two samples were dated from Tavan Har in the northern EGFZ. An augen gneiss (O7TH-10A) yielded zircons with dominantly Late Devonian-Early Permian ages. A granitic gneiss (07TH-12A), interpreted as a synkinematic intrusion in a Late Triassic sinistral shear zone based on field and 40Ar/39Ar data, yielded a weighted mean age of 219.4 ± 5.8 Ma. Within the southern EGFZ, samples from the lower plate of the Yagan-Onch Hayrhan metamorphic core complex were analyzed. Three samples (06OH-1-1, 06OH-1-2, 06OH-2-7) each yielded a large population of Late Devonian ages. Sample 06OH-2-7 also yielded a significant number of Early Devonian ages. Migmatite sample 08OH-4D yielded zircons with resorbed cores surrounded by high-U rims. These rims yielded highly discordant ages, however, multiple populations were resolved from analysis of the cores: The largest population consisted of Permian-Carboniferous ages with two additional smaller populations of Silurian-Cambrian ages and Precambrian ages, ca. 2500 Ma

  17. ESR dating of fault rocks

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hee Kwon [Kangwon National Univ., Chuncheon (Korea, Republic of)


    Past movement on faults can be dated by measurement of the intensity of ESR signals in quartz. These signals are reset by local lattice deformation and local frictional heating on grain contacts at the time of fault movement. The ESR signals then grow back as a result of bombardment by ionizing radiation from surrounding rocks. The age is obtained from the ratio of the equivalent dose, needed to produce the observed signal, to the dose rate. Fine grains are more completely reset during faulting, and a plot of age vs. grain size shows a plateau for grains below critical size; these grains are presumed to have been completely zeroed by the last fault activity. We carried out ESR dating of fault rocks collected near the Gori nuclear reactor. Most of the ESR signals of fault rocks collected from the basement are saturated. This indicates that the last movement of the faults had occurred before the Quaternary period. However, ESR dates from the Oyong fault zone range from 370 to 310 ka. Results of this research suggest that long-term cyclic fault activity of the Oyong fault zone continued into the Pleistocene.

  18. Possibility of prediction of strong seismic events in the Middle Odra Fault Zone based on variations of kinematic activity of the Świebodzice Depression (United States)

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


    Książ Geodynamic Laboratory of Space Research Centre is located in the Świebodzice Depression unit. The laboratory was built inside underground corridors made in the castle hill about 50 m below surface. The main instruments which provide us most of information about tectonic activity of Świebodzice Depression are two long water-tubes tiltmeters 65 and 92 meters long (WT). The WT are situated on several rocky blocks which motions provided tectonic signals to WT. The instruments register numerous irregularly occurred epochs of water levels variations in hydrodynamic systems of magnitudes exceeding tidal signals dozens or so times. These observations are interpreted as result of tiltings of foundation and vertical motions of rock blocks. Signals of tiltings of foundation and vertical motions are superposed by the WT registration system. The resultant signals from four channels of WT were defined by us as tectonic activity functions of the massif. Variations of the tectonic activity functions as well as their first derivatives were compared with the seismic activity in Fore-Sudetic Monocline. We found correlation in time and amplitudes domains between extremes and inflection points of the first derivative of the tectonic activi