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Sample records for hayward fault zone

  1. Tectonic creep in the Hayward fault zone, California

    USGS Publications Warehouse

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

    1966-01-01

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

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

    USGS Publications Warehouse

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

    1995-01-01

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

  3. Hayward Fault, California Interferogram

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This image of California's Hayward fault is an interferogram created using a pair of images taken by Synthetic Aperture Radar(SAR) combined to measure changes in the surface that may have occurred between the time the two images were taken.

    The images were collected by the European Space Agency's Remote Sensing satellites ERS-1 and ERS-2 in June 1992 and September 1997 over the central San Francisco Bay in California.

    The radar image data are shown as a gray-scale image, with the interferometric measurements that show the changes rendered in color. Only the urbanized area could be mapped with these data. The color changes from orange tones to blue tones across the Hayward fault (marked by a thin red line) show about 2-3centimeters (0.8-1.1 inches) of gradual displacement or movement of the southwest side of the fault. The block west of the fault moved horizontally toward the northwest during the 63 months between the acquisition of the two SAR images. This fault movement is called a seismic creep because the fault moved slowly without generating an earthquake.

    Scientists are using the SAR interferometry along with other data collected on the ground to monitor this fault motion in an attempt to estimate the probability of earthquake on the Hayward fault, which last had a major earthquake of magnitude 7 in 1868. This analysis indicates that the northern part of the Hayward fault is creeping all the way from the surface to a depth of 12 kilometers (7.5 miles). This suggests that the potential for a large earthquake on the northern Hayward fault might be less than previously thought. The blue area to the west (lower left) of the fault near the center of the image seemed to move upward relative to the yellow and orange areas nearby by about 2 centimeters (0.8 inches). The cause of this apparent motion is not yet confirmed, but the rise of groundwater levels during the time between the images may have caused the reversal of a small portion of the subsidence that

  4. Three-Dimensional Geologic Map of the Hayward Fault Zone, San Francisco Bay Region, California

    USGS Publications Warehouse

    Phelps, G.A.; Graymer, R.W.; Jachens, R.C.; Ponce, D.A.; Simpson, R.W.; Wentworth, C.M.

    2008-01-01

    A three-dimensional (3D) geologic map of the Hayward Fault zone was created by integrating the results from geologic mapping, potential field geophysics, and seismology investigations. The map volume is 100 km long, 20 km wide, and extends to a depth of 12 km below sea level. The map volume is oriented northwest and is approximately bisected by the Hayward Fault. The complex geologic structure of the region makes it difficult to trace many geologic units into the subsurface. Therefore, the map units are generalized from 1:24,000-scale geologic maps. Descriptions of geologic units and structures are offered, along with a discussion of the methods used to map them and incorporate them into the 3D geologic map. The map spatial database and associated viewing software are provided. Elements of the map, such as individual fault surfaces, are also provided in a non-proprietary format so that the user can access the map via open-source software. The sheet accompanying this manuscript shows views taken from the 3D geologic map for the user to access. The 3D geologic map is designed as a multi-purpose resource for further geologic investigations and process modeling.

  5. Seismic Imaging of a Bimaterial Interface Along the Hayward Fault, CA, with Fault Zone Head Waves and Direct P Arrivals

    NASA Astrophysics Data System (ADS)

    Allam, A. A.; Ben-Zion, Y.; Peng, Z.

    2014-11-01

    We observe fault zone head waves (FZHW) that are generated by and propagate along a roughly 80 km section of the Hayward fault in the San Francisco Bay area. Moveout values between the arrival times of FZHW and direct P waves are used to obtain average P-wave velocity contrasts across different sections of the fault. The results are based on waveforms generated by more than 5,800 earthquakes and recorded at up to 12 stations of the Berkeley digital seismic network (BDSN) and the Northern California seismic network (NCSN). Robust identification of FZHW requires the combination of multiple techniques due to the diverse instrumentation of the BDSN and NCSN. For single-component short-period instruments, FZHW are identified by examining sets of waveforms from both sides of the fault, and finding on one (the slow) side emergent reversed-polarity arrivals before the direct P waves. For three-component broadband and strong-motion instruments, the FZHW are identified with polarization analysis that detects early arrivals from the fault direction before the regular body waves which have polarizations along the source-receiver backazimuth. The results indicate average velocity contrasts of 3-8 % along the Hayward fault, with the southwest side having faster P wave velocities in agreement with tomographic images. A systematic moveout between the FZHW and direct P waves for about a 80 km long fault section suggests a single continuous interface in the seismogenic zone over that distance. We observe some complexities near the junction with the Calaveras fault in the SE-most portion and near the city of Oakland. Regions giving rise to variable FZHW arrival times can be correlated to first order with the presence of lithological complexity such as slivers of high-velocity metamorphic serpentinized rocks and relatively distributed seismicity. The seismic velocity contrast and geological complexity have important implications for earthquake and rupture dynamics of the Hayward fault

  6. SEISMOLOGY: Watching the Hayward Fault.

    PubMed

    Simpson, R W

    2000-08-18

    The Hayward fault, located on the east side of the San Francisco Bay, represents a natural laboratory for seismologists, because it does not sleep silently between major earthquakes. In his Perspective, Simpson discusses the study by Bürgmann et al., who have used powerful new techniques to study the fault. The results indicate that major earthquakes cannot originate in the northern part of the fault. However, surface-rupturing earthquakes have occurred in the area, suggesting that they originated to the north or south of the segment studied by Bürgmann et al. Fundamental questions remain regarding the mechanism by which plate tectonic stresses are transferred to the Hayward fault.

  7. Features and dimensions of the Hayward Fault Zone in the Strawberry and Blackberry Creek Area, Berkeley, California

    SciTech Connect

    Williams, P.L.

    1995-03-01

    This report presents an examination of the geometry of the Hayward fault adjacent to the Lawrence Berkeley Laboratory and University of California campuses in central Berkeley. The fault crosses inside the eastern border of the UC campus. Most subtle geomorphic (landform) expressions of the fault have been removed by development and by the natural processes of landsliding and erosion. Some clear expressions of the fault remain however, and these are key to mapping the main trace through the campus area. In addition, original geomorphic evidence of the fault`s location was recovered from large scale mapping of the site dating from 1873 to 1897. Before construction obscured and removed natural landforms, the fault was expressed by a linear, northwest-tending zone of fault-related geomorphic features. There existed well-defined and subtle stream offsets and beheaded channels, fault scarps, and a prominent ``shutter ridge``. To improve our confidence in fault locations interpreted from landforms, we referred to clear fault exposures revealed in trenching, revealed during the construction of the Foothill Housing Complex, and revealed along the length of the Lawson Adit mining tunnel. Also utilized were the locations of offset cultural features. At several locations across the study area, distress features in buildings and streets have been used to precisely locate the fault. Recent published mapping of the fault (Lienkaemper, 1992) was principally used for reference to evidence of the fault`s location to the northwest and southeast of Lawrence Berkeley Laboratory.

  8. Interseismic coupling and refined earthquake potential on the Hayward-Calaveras fault zone

    NASA Astrophysics Data System (ADS)

    Chaussard, E.; Bürgmann, R.; Fattahi, H.; Johnson, C. W.; Nadeau, R.; Taira, T.; Johanson, I.

    2015-12-01

    Interseismic strain accumulation and fault creep is usually estimated from GPS and alignment arrays data, which provide precise but spatially sparse measurements. Here we use interferometric synthetic aperture radar to resolve the interseismic deformation associated with the Hayward and Calaveras Faults (HF and CF) in the East San Francisco Bay Area. The large 1992-2011 SAR data set permits evaluation of short- and long-wavelength deformation larger than 2 mm/yr without alignment of the velocity field to a GPS-based model. Our time series approach in which the interferogram selection is based on the spatial coherence enables deformation mapping in vegetated areas and leads to refined estimates of along-fault surface creep rates. Creep rates vary from 0 ± 2 mm/yr on the northern CF to 14 ± 2 mm/yr on the central CF south of the HF surface junction. We estimate the long-term slip rates by inverting the long-wavelength deformation and the distribution of shallow slip due to creep by inverting the remaining velocity field. This distribution of slip reveals the locations of locked and slowly creeping patches with potential for a M6.8 ± 0.3 on the HF near San Leandro, a M6.6 ± 0.2 on the northern CF near Dublin, a M6.5 ± 0.1 on the HF south of Fremont, and a M6.2 ± 0.2 on the central CF near Morgan Hill. With cascading multisegment ruptures the HF rupturing from Berkeley to the CF junction could produce a M6.9 ± 0.1, the northern CF a M6.6 ± 0.1, the central CF a M6.9 ± 0.2 from the junction to Gilroy, and a joint rupture of the HF and central CF could produce a M7.1 ± 0.1.

  9. Interseismic coupling on the Hayward-Calaveras fault zone from InSAR

    NASA Astrophysics Data System (ADS)

    Chaussard, E.; Burgmann, R.; Fattahi, H.; Johnson, C. W.; Nadeau, R. M.; Taira, T.; Johanson, I. A.

    2015-12-01

    Evaluation of interseismic deformation traditionally relies on GPS and alignment arrays (AA) providing precise but spatially sparse measurements. Here, we resolve with a high spatial resolution interseismic strain accumulation and fault creep associated with the Hayward and Calaveras Faults (HF and CF) in the Eastern San Francisco Bay Area using InSAR. The large 1992-2011 ascending and descending ERS-Envisat dataset enables characterization of short- and long-wavelength horizontal and vertical deformation as small as 2 mm/yr without alignment to a GPS-based model. A comparison between independent InSAR, GPS, and AA datasets shows that the remaining noise is negligible in mean velocity maps and that the creep rates are mostly constant between 1992-2011. Creep rates vary from 0±2 mm/yr on the northern CF to 14±2 mm/yr on the central CF south of the HF surface junction. The high spatial resolution velocity map also highlights the southernmost occurrence of creep on the HF, located ~15 km farther south than prior determinations based on AA and field mapping. We remove the long-wavelength deformation using a deep-dislocation model and estimate the shallow slip due to creep by inverting the remaining InSAR fault-parallel motion. We confirm a good agreement between our model and surface slip rates measured with AA and slip at depth from characteristically repeating earthquakes. The distribution of aseismic slip is comparable to previous models focused on the HF, confirming that the distribution of creeping and locked patches is stable. We find that the northern CF is mostly locked, explaining the absence of seismicity and that most of the aseismic slip is limited to the shallowest 5 km on the HF and CF, suggesting partial or full locking at deeper levels. Considering the time since the last earthquakes and the difference between the long-term slip rates and the shallow aseismic slip, we infer that a joint rupture of the HF and central CF could currently produce a M7.1

  10. Hayward fault: Large earthquakes versus surface creep

    USGS Publications Warehouse

    Lienkaemper, James J.; Borchardt, Glenn; Borchardt, Glenn; Hirschfeld, Sue E.; Lienkaemper, James J.; McClellan, Patrick H.; Williams, Patrick L.; Wong, Ivan G.

    1992-01-01

    The Hayward fault, thought a likely source of large earthquakes in the next few decades, has generated two large historic earthquakes (about magnitude 7), one in 1836 and another in 1868. We know little about the 1836 event, but the 1868 event had a surface rupture extending 41 km along the southern Hayward fault. Right-lateral surface slip occurred in 1868, but was not well measured. Witness accounts suggest coseismic right slip and afterslip of under a meter. We measured the spatial variation of the historic creep rate along the Hayward fault, deriving rates mainly from surveys of offset cultural features, (curbs, fences, and buildings). Creep occurs along at least 69 km of the fault's 82-km length (13 km is underwater). Creep rate seems nearly constant over many decades with short-term variations. The creep rate mostly ranges from 3.5 to 6.5 mm/yr, varying systemically along strike. The fastest creep is along a 4-km section near the south end. Here creep has been about 9mm/yr since 1921, and possibly since the 1868 event as indicated by offset railroad track rebuilt in 1869. This 9mm/yr slip rate may approach the long-term or deep slip rate related to the strain buildup that produces large earthquakes, a hypothesis supported by geoloic studies (Lienkaemper and Borchardt, 1992). If so, the potential for slip in large earthquakes which originate below the surficial creeping zone, may now be 1/1m along the southern (1868) segment and ≥1.4m along the northern (1836?) segment. Substracting surface creep rates from a long-term slip rate of 9mm/yr gives present potential for surface slip in large earthquakes of up to 0.8m. Our earthquake potential model which accounts for historic creep rate, microseismicity distribution, and geodetic data, suggests that enough strain may now be available for large magnitude earthquakes (magnitude 6.8 in the northern (1836?) segment, 6.7 in the southern (1868) segment, and 7.0 for both). Thus despite surficial creep, the fault may be

  11. Gravity and magnetic expression of the San Leandro gabbro with implications for the geometry and evolution of the Hayward Fault zone, northern California

    USGS Publications Warehouse

    Ponce, D.A.; Hildenbrand, T.G.; Jachens, R.C.

    2003-01-01

    The Hayward Fault, one of the most hazardous faults in northern California, trends north-northwest and extends for about 90 km along the eastern San Francisco Bay region. At numerous locations along its length, distinct and elongate gravity and magnetic anomalies correlate with mapped mafic and ultramafic rocks. The most prominent of these anomalies reflects the 16-km-long San Leandro gabbroic block. Inversion of magnetic and gravity data constrained with physical property measurements is used to define the subsurface extent of the San Leandro gabbro body and to speculate on its origin and relationship to the Hayward Fault Zone. Modeling indicates that the San Leandro gabbro body is about 3 km wide, dips about 75??-80?? northeast, and extends to a depth of at least 6 km. One of the most striking results of the modeling, which was performed independently of seismicity data, is that accurately relocated seismicity is concentrated along the western edge or stratigraphically lower bounding surface of the San Leandro gabbro. The western boundary of the San Leandro gabbro block is the base of an incomplete ophiolite sequence and represented at one time, a low-angle roof thrust related to the tectonic wedging of the Franciscan Complex. After repeated episodes of extension and attenuation, the roof thrust of this tectonic wedge was rotated to near vertical, and in places, the strike-slip Hayward Fault probably reactivated or preferentially followed this pre-existing feature. Because earthquakes concentrate near the edge of the San Leandro gabbro but tend to avoid its interior, we qualitatively explore mechanical models to explain how this massive igneous block may influence the distribution of stress. The microseismicity cluster along the western flank of the San Leandro gabbro leads us to suggest that this stressed volume may be the site of future moderate to large earthquakes. Improved understanding of the three-dimensional geometry and physical properties along the

  12. Frictional Strength of Hayward Fault Gouge

    NASA Astrophysics Data System (ADS)

    Morrow, C.; Moore, D.; Lockner, D.

    2007-12-01

    A recent 3-D geologic model of the Hayward fault in the San Francisco Bay Region shows that a number of different rock units are juxtaposed across the fault surface as a result of lateral displacement. The fault gouge formed therein is likely a mixture of these various rock types. To better model the mechanical behavior of the Hayward fault, which is known to both creep and have large earthquakes, frictional properties of mixtures of the principal rock types were determined in the laboratory. Room temperature triaxial shearing tests were conducted on binary and ternary mixtures of Great Valley Sequence graywacke, Franciscan jadeite-bearing metagraywacke, Franciscan pumpellyite-bearing metasandstone, Franciscan melange matrix, serpentinite and two-pyroxene gabbro. The gouge samples were crushed and sieved (<150 μm grains), then applied in a 1-mm layer between saw-cut sliding blocks. Each sample assemblage was saturated and sheared at constant pore water pressure of 1 MPa and normal stress of 51 MPa. Coefficients of friction, μ, ranged from a low of 0.38 for the serpentinite to a maximum of 0.85 for the gabbro. While the serpentinite and the Franciscan melange matrix were relatively weak, all other rock types obeyed Byerlee's Law. The friction coefficient of mixtures could be reliably predicted by a simple average based on dry weight percent of the end member strengths. This behavior is in contrast to some mixtures of common gouge materials such as montmorillonite+quartz, which exhibit non- linear frictional strength trends with varying weight percent of constituents. All materials tested except serpentinite were velocity strengthening, therefore promoting creeping behavior. The addition of serpentinite decreased a-b values of the gouge and increased the characteristic displacement, dc, of strength evolution. Because temperature strongly influences the mechanical properties of fault gouge as well as speeding chemical reactions between the constituents, elevated

  13. Fault structure and mechanics of the Hayward Fault, California from double-difference earthquake locations

    USGS Publications Warehouse

    Waldhauser, F.; Ellsworth, W.L.

    2002-01-01

    The relationship between small-magnitude seismicity and large-scale crustal faulting along the Hayward Fault, California, is investigated using a double-difference (DD) earthquake location algorithm. We used the DD method to determine high-resolution hypocenter locations of the seismicity that occurred between 1967 and 1998. The DD technique incorporates catalog travel time data and relative P and S wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events. The relocated seismicity reveals a narrow, near-vertical fault zone at most locations. This zone follows the Hayward Fault along its northern half and then diverges from it to the east near San Leandro, forming the Mission trend. The relocated seismicity is consistent with the idea that slip from the Calaveras Fault is transferred over the Mission trend onto the northern Hayward Fault. The Mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the Calaveras Fault at Calaveras Reservoir. In some locations, discrete structures adjacent to the main trace are seen, features that were previously hidden in the uncertainty of the network locations. The fine structure of the seismicity suggest that the fault surface on the northern Hayward Fault is curved or that the events occur on several substructures. Near San Leandro, where the more westerly striking trend of the Mission seismicity intersects with the surface trace of the (aseismic) southern Hayward Fault, the seismicity remains diffuse after relocation, with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation. The seismicity is highly organized in space, especially on the northern Hayward Fault, where it forms horizontal, slip-parallel streaks of hypocenters of only a few tens of meters width, bounded by areas almost absent of seismic activity. During the interval from 1984 to 1998, when digital

  14. Mapping the 3D Geometry of the San Leandro Block of the Hayward Fault Zone Using Geologic, Geophysical and Remote Sensing Data, California State University, East Bay Campus

    NASA Astrophysics Data System (ADS)

    McEvilly, A.; Abimbola, A.; Chan, J. H.; Strayer, L. M.

    2015-12-01

    California State University, East Bay (CSUEB), located in Hayward, California, lies atop the San Leandro block (SLB) in the Hayward fault zone. The SLB is a J-K aged lithotectonic assemblage dominated by gabbro and intercalated with minor volcanics and sediments. It is bound by the subparallel northwest-trending western Hayward and eastern Chabot (CF) faults and pervasively cut by anastomosing secondary faults. The block itself is ~30 km along strike and 2-3 km wide. Previous studies suggest the block dips steeply to the northeast and extends to a depth of at least 7 km. In May of 2015, as part of an ongoing collaborative effort led by the USGS to create a 3D velocity model of the San Francisco Bay Area, researchers from CSUEB and the USGS conducted a seismic survey on the CSUEB campus. The primary goal of this pilot study was to locate the trace of the CF on the CSUEB campus and to determine bedrock depth. We deployed a 60-channel, 300m profile using 4.5Hz sensors spaced at 5m intervals. Active seismic sources were used at each geophone location. A 226kg accelerated weight-drop was used to generate P and Rayleigh waves for P-wave tomography and multichannel analysis of surface waves (MASW), and a 3.5kg sledgehammer and block were used to generate S and Love waves for S-wave tomography and multichannel analysis of Love waves (MALW). Preliminary P-wave tomography, MASW, and MALW results from this pilot study suggest the location of an eastward-dipping CF as well as the presence of a high-velocity unit at about 20m depth, presumably an unmapped sliver of bedrock from the San Leandro block. Further studies planned for the fall of 2015 include additional seismic lines and surface mapping along the Chabot fault on and near the CSUEB campus. These new geophysical, GPS, and field geological data will be integrated with LiDAR imagery and existing geological, gravity and magnetic maps to create a 3-dimensional model of the portion of the SLB that contains the CSUEB campus.

  15. Missing link between the Hayward and Rodgers Creek faults

    PubMed Central

    Watt, Janet; Ponce, David; Parsons, Tom; Hart, Patrick

    2016-01-01

    The next major earthquake to strike the ~7 million residents of the San Francisco Bay Area will most likely result from rupture of the Hayward or Rodgers Creek faults. Until now, the relationship between these two faults beneath San Pablo Bay has been a mystery. Detailed subsurface imaging provides definitive evidence of active faulting along the Hayward fault as it traverses San Pablo Bay and bends ~10° to the right toward the Rodgers Creek fault. Integrated geophysical interpretation and kinematic modeling show that the Hayward and Rodgers Creek faults are directly connected at the surface—a geometric relationship that has significant implications for earthquake dynamics and seismic hazard. A direct link enables simultaneous rupture of the Hayward and Rodgers Creek faults, a scenario that could result in a major earthquake (M = 7.4) that would cause extensive damage and loss of life with global economic impact. PMID:27774514

  16. Where's the Hayward Fault? A Green Guide to the Fault

    USGS Publications Warehouse

    Stoffer, Philip W.

    2008-01-01

    This report describes self-guided field trips to one of North America?s most dangerous earthquake faults?the Hayward Fault. Locations were chosen because of their easy access using mass transit and/or their significance relating to the natural and cultural history of the East Bay landscape. This field-trip guidebook was compiled to help commemorate the 140th anniversary of an estimated M 7.0 earthquake that occurred on the Hayward Fault at approximately 7:50 AM, October 21st, 1868. Although many reports and on-line resources have been compiled about the science and engineering associated with earthquakes on the Hayward Fault, this report has been prepared to serve as an outdoor guide to the fault for the interested public and for educators. The first chapter is a general overview of the geologic setting of the fault. This is followed by ten chapters of field trips to selected areas along the fault, or in the vicinity, where landscape, geologic, and man-made features that have relevance to understanding the nature of the fault and its earthquake history can be found. A glossary is provided to define and illustrate scientific term used throughout this guide. A ?green? theme helps conserve resources and promotes use of public transportation, where possible. Although access to all locations described in this guide is possible by car, alternative suggestions are provided. To help conserve paper, this guidebook is available on-line only; however, select pages or chapters (field trips) within this guide can be printed separately to take along on an excursion. The discussions in this paper highlight transportation alternatives to visit selected field trip locations. In some cases, combinations, such as a ride on BART and a bus, can be used instead of automobile transportation. For other locales, bicycles can be an alternative means of transportation. Transportation descriptions on selected pages are intended to help guide fieldtrip planners or participants choose trip

  17. Hayward Fault rocks: porosity, density, and strength measurements

    USGS Publications Warehouse

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

    2001-01-01

    Porosity, density and strength measurements were conducted on rock samples collected from the Hayward Fault region in Northern California as part of the Hayward Fault Working Group’s efforts to create a working model of the Hayward Fault. The rocks included in this study were both fine and coarse grained gabbros, altered keratophyre, basalt, sandstone, and serpentinite from various rock formations adjacent to the Hayward Fault. Densities ranged from a low of 2.25 gm/cc (altered keratophyre) to 3.05 gm/cc (fine gabbro), with an average of 2.6 gm/cc, typical of many other rocks. Porosities were generally around 1% or less, with the exception of the sandstone (7.6%) and altered keratophyre (13.5%). Failure and frictional sliding tests were conducted on intact rock cylinders at room temperature under effective pressure conditions of up to 192 MPa, simulating depths of burial to 12 km. Axial shortening of the samples progressed at a rate of 0.1 µm/sec (fine samples) or 0.2 µm/sec (porous samples) for 6 mm of displacement. Velocity stepping tests were then conducted for an additional 2 mm of displacement, for a total of 8 mm. Both peak strength (usually failure strength) and frictional strength, determined at 8 mm of displacement, increased systematically with effective pressure. Coefficients of friction, based on the observed fracture angles, ranged from 0.6 to 0.85, consistent with Byerlee’s Law. Possible secondary influences on the strength of the Hayward rock samples may be surface weathering, or a larger number of pre-existing fractures due to the proximity to the Hayward Fault. All samples showed velocity strengthening, so that the average a-b values were all strongly positive. There was no systematic relation between a-b values and effective pressure. Velocity strengthening behavior is associated with stable sliding (creep), as observed in the shallow portions of the Hayward Fault.

  18. Developing a Hayward Fault Greenbelt in Fremont, California

    NASA Astrophysics Data System (ADS)

    Blueford, J. R.

    2007-12-01

    The Math Science Nucleus, an educational non-profit, in cooperation with the City of Fremont and U.S. Geological Survey has concluded that outdoor and indoor exhibits highlighting the Hayward Fault is a spectacular and educational way of illustrating the power of earthquakes. Several projects are emerging that use the Hayward fault to illustrate to the public and school groups that faults mold the landscape upon which they live. One area that is already developed, Tule Ponds at Tyson Lagoon, is owned by Alameda County Flood Control and Conservation District and managed by the Math Science Nucleus. This 17 acre site illustrates two traces of the Hayward fault (active and inactive), whose sediments record over 4000 years of activity. Another project is selecting an area in Fremont that a permanent trench or outside earthquake exhibit can be created that people can see seismic stratigraphic features of the Hayward Fault. This would be part of a 3 mile Earthquake Greenbelt area from Tyson Lagoon to the proposed Irvington BART Station. Informational kiosks or markers and a "yellow brick road" of earthquake facts could allow visitors to take an exciting and educational tour of the Hayward Fault's surface features in Fremont. Visitors would visually see the effects of fault movement and the tours would include preparedness information. As these plans emerge, an indoor permanent exhibits is being developed at the Children's Natural History Museum in Fremont. This exhibit will be a model of the Earthquake Greenbelt. It will also allow people to see a scale model of how the Hayward Fault unearthed the Pleistocene fossil bed (Irvingtonian) as well as created traps for underground aquifers as well as surface sag ponds.

  19. Creep rate estimation along the Hayward fault using polarimetric SAR interferometry

    NASA Astrophysics Data System (ADS)

    Alipour, S.; Tiampo, K. F.; Samsonov, S. V.; Gonzalez, P. J.

    2011-12-01

    The Hayward fault running through eastern San Francisco Bay represents a significant seismic hazard in northern California. Surface geodetic measurements, including those from creepmeters and continuous GPS, manifest aseismic creep equivalent to 4-9 mm/yr along this fault. Comparison with the long-term slip rate estimates of ~9 mm/yr suggest that up to several meters of slip potential has accumulated since the last large event, making the Hayward fault now capable of M>6.5 earthquakes. Here we apply polarimetric Synthetic Aperture Radar interferometry (PolInSAR) on quad-pol Radarsat-2 images acquired from 2008 to 2011 in order to map the surface creep along the northern thirty km of the Hayward fault. In addition to quantifying aseismic creep across the fault, the polInSAR data depict another sharp discontinuity in range change to the northeast of the fault, an indication of ongoing creep along a second fault in that region. Comparison of the recent creep rate estimates along the Hayward fault with the previous measurements proves that there is consistency in the right-lateral aseismic slip. However, vertical movements corresponding to landslides on slopes near Berkeley display a lower mean velocity for the period 2008-2011 than 1992-2000. Modeling of the slip distribution using the polInSAR data in conjunction with creepmeter and GPS data provides additional insights into the depth of the creeping zone and the locking segments of the fault, an indicator of the extent of any probable rupture and the magnitude of the potential future event.

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

    USGS Publications Warehouse

    Lienkaemper, James J.

    2006-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  2. Log of Trench 04A Across the Hayward Fault at Tyson's Lagoon (Tule Pond), Fremont, Alameda County, California

    USGS Publications Warehouse

    Lienkaemper, James J.; Williams, Patrick L.; Sickler, Robert R.; Fumal, Thomas E.

    2005-01-01

    This publication makes available a detailed trench log (sheets 1 and 2) of a 110-m trench we excavated in 2004 across a tectonic sag pond in the Hayward fault zone. Also included are revised stratigraphic unit descriptions from this fifth field season of subsurface investigation of the Hayward fault at Tyson's Lagoon (Tule Pond). Preliminary findings based on fieldwork done in 2000 have been published (Lienkaemper and others: data archive, 2002a; report, 2002b), as were the logs and data for 2001-2003 (Lienkaemper and others, 2003, L03). A continuous exposure of the geologic section across the entire pond made in 2004 (Fig. 1, 04A) has revealed some critical miscorrelations of units made in the original on-line version of L03, hence users of these earlier trench data should only use the 2005 revised version 2.0 of L03 for correlation purposes. Lienkaemper, Williams, and Sickler interpreted the geology and logged the trenches. Fumal did most of the trench photography. The Hayward fault is recognized to be among the most hazardous in the United States (Working Group on California Earthquake Probabilities, 2003). Establishing a chronology of prehistoric or paleoearthquakes is of immediate use in resolving the likelihood of future large earthquakes Hayward fault. This document makes available geologic evidence for historical and prehistoric surface-rupturing earthquakes preserved at the site. A second, formal report on our conclusions based on these data is in preparation.

  3. Geodetic constraints on San Francisco Bay Area fault slip rates and potential seismogenic asperities on the partially creeping Hayward fault

    NASA Astrophysics Data System (ADS)

    Evans, Eileen L.; Loveless, John P.; Meade, Brendan J.

    2012-03-01

    The Hayward fault in the San Francisco Bay Area (SFBA) is sometimes considered unusual among continental faults for exhibiting significant aseismic creep during the interseismic phase of the seismic cycle while also generating sufficient elastic strain to produce major earthquakes. Imaging the spatial variation in interseismic fault creep on the Hayward fault is complicated because of the interseismic strain accumulation associated with nearby faults in the SFBA, where the relative motion between the Pacific plate and the Sierra block is partitioned across closely spaced subparallel faults. To estimate spatially variable creep on the Hayward fault, we interpret geodetic observations with a three-dimensional kinematically consistent block model of the SFBA fault system. Resolution tests reveal that creep rate variations with a length scale of <15 km are poorly resolved below 7 km depth. In addition, creep at depth may be sensitive to assumptions about the kinematic consistency of fault slip rate models. Differential microplate motions result in a slip rate of 6.7 ± 0.8 mm/yr on the Hayward fault, and we image along-strike variations in slip deficit rate at ˜15 km length scales shallower than 7 km depth. Similar to previous studies, we identify a strongly coupled asperity with a slip deficit rate of up to 4 mm/yr on the central Hayward fault that is spatially correlated with the mapped surface trace of the 1868 MW = 6.9-7.0 Hayward earthquake and adjacent to gabbroic fault surfaces.

  4. 3D Spontaneous Rupture Models of Large Earthquakes on the Hayward Fault, California

    NASA Astrophysics Data System (ADS)

    Barall, M.; Harris, R. A.; Simpson, R. W.

    2008-12-01

    We are constructing 3D spontaneous rupture computer simulations of large earthquakes on the Hayward and central Calaveras faults. The Hayward fault has a geologic history of producing many large earthquakes (Lienkaemper and Williams, 2007), with its most recent large event a M6.8 earthquake in 1868. Future large earthquakes on the Hayward fault are not only possible, but probable (WGCEP, 2008). Our numerical simulation efforts use information about the complex 3D fault geometry of the Hayward and Calaveras faults and information about the geology and physical properties of the rocks that surround the Hayward and Calaveras faults (Graymer et al., 2005). Initial stresses on the fault surface are inferred from geodetic observations (Schmidt et al., 2005), seismological studies (Hardebeck and Aron, 2008), and from rate-and- state simulations of the interseismic interval (Stuart et al., 2008). In addition, friction properties on the fault surface are inferred from laboratory measurements of adjacent rock types (Morrow et al., 2008). We incorporate these details into forward 3D computer simulations of dynamic rupture propagation, using the FaultMod finite-element code (Barall, 2008). The 3D fault geometry is constructed using a mesh-morphing technique, which starts with a vertical planar fault and then distorts the entire mesh to produce the desired fault geometry. We also employ a grid-doubling technique to create a variable-resolution mesh, with the smallest elements located in a thin layer surrounding the fault surface, which provides the higher resolution needed to model the frictional behavior of the fault. Our goals are to constrain estimates of the lateral and depth extent of future large Hayward earthquakes, and to explore how the behavior of large earthquakes may be affected by interseismic stress accumulation and aseismic slip.

  5. Dependence of frictional strength on compositional variations of Hayward fault rock gouges

    USGS Publications Warehouse

    Morrow, Carolyn A.; Moore, Diane E.; Lockner, David A.

    2010-01-01

    The northern termination of the locked portion of the Hayward Fault near Berkeley, California, is found to coincide with the transition from strong Franciscan metagraywacke to melange on the western side of the fault. Both of these units are juxtaposed with various serpentinite, gabbro and graywacke units to the east, suggesting that the gouges formed within the Hayward Fault zone may vary widely due to the mixing of adjacent rock units and that the mechanical behavior of the fault would be best modeled by determining the frictional properties of mixtures of the principal rock types. To this end, room temperature, water-saturated, triaxial shearing tests were conducted on binary and ternary mixtures of fine-grained gouges prepared from serpentinite and gabbro from the Coast Range Ophiolite, a Great Valley Sequence graywacke, and three different Franciscan Complex metasedimentary rocks. Friction coefficients ranged from 0.36 for the serpentinite to 0.84 for the gabbro, with four of the rock types having coefficients of friction ranging from 0.67-0.84. The friction coefficients of the mixtures can be predicted reliably by a simple weighted average of the end-member dry-weight percentages and strengths for all samples except those containing serpentinite. For the serpentinite mixtures, a linear trend between end-member values slightly overestimates the coefficients of friction in the midcomposition ranges. The range in strength for these rock admixtures suggests that both theoretical and numerical modeling of the fault should attempt to account for variations in rock and gouge properties.

  6. Hayward Fault rate constraints at Berkeley: Evaluation of the 335-meter Strawberry Creek offset

    NASA Astrophysics Data System (ADS)

    Williams, P. L.

    2007-12-01

    At UC Berkeley the active channel of Strawberry Creek is offset 335 meters by the Hayward fault and two abandoned channels of Strawberry Creek are laterally offset 580 and 730 meters. These relationships record the displacement of the northern Hayward fault at Berkeley over a period of tens of millennia. The Strawberry Creek site has a similar geometry to the central San Andreas fault's Wallace Creek site, which arguably provides the best geological evidence of "millennial" fault kinematics in California (Sieh and Jahns, 1984). Slip rate determinations are an essential component of overall hazard evaluation for the Hayward fault, and this site is ripe to disclose a long-term form of this parameter, to contrast with geodetic and other geological rate evidence. Large offsets at the site may lower uncertainty in the rate equation relative to younger sites, as the affect of stream abandonment age, generally the greatest source of rate uncertainty, is greatly reduced. This is helpful here because it more-than-offsets uncertainties resulting from piercing projections to the fault. Strawberry Creek and its ancestral channels suggest west-side-up vertical deformation across the Hayward fault at this location. The development of the vertical deformation parameter will complement ongoing geodetic measurements, particularly InSAR, and motivate testing of other geological constraints. Up-to-the-west motion across the Hayward fault at Berkeley has important implications for the partitioning of strain and kinematics of the northern Hayward fault, and may explain anomalous up-on-the-west landforms elsewhere along the fault. For example, geological features of the western Berkeley Hills are consistent with rapid and recent uplift to the west of the fault. On the basis of a preliminary analysis of the offset channels of Strawberry Creek, up-to-the-west uplift is about 0.5mm/yr across the Hayward fault at Berkeley. If this is in fact the long-term rate, the 150 m height of the Hills

  7. Multi-scale InSAR analysis of aseismic creep across the San Andreas, Calevaras,and Hayward Fault systems

    NASA Astrophysics Data System (ADS)

    Agram, P. S.; Simons, M.

    2011-12-01

    We apply the Multi-scale Interferometric Time-series (MInTS) technique, developed at Caltech,to study spatial variations in aseismic creep across the San Andreas, Calaveras and Hayward Faultsystems in Central California.Interferometric Synthetic Aperture Radar (InSAR) Time-series methods estimate the spatio-temporal evolution of surface deformation using multiple SAR interferograms. Traditional time-series analysis techniques like persistent scatterers and short baseline methods assume the statistical independence of InSAR phase measurements over space and time when estimating deformation. However, existing atmospheric phase screen models clearly show that noise in InSAR phase observations is correlated over the spatial domain. MInTS is an approach designed to exploit the correlation of phase observations over space to significantly improve the signal-to-noise ratio in the estimated deformation time-series compared to the traditional time-series InSAR techniques. The MInTS technique reduces the set of InSAR observations to a set of almost uncorrelated observations at various spatial scales using wavelets. Traditional inversion techniques can then be applied to the wavelet coefficients more effectively. Creep across the Central San Andreas Fault and the Hayward Fault has been studied previously using C-band (6 cm wavelength) ERS data, but detailed analysis of the transition zone between the San Andreas and Hayward Faults was not possible due to severe decorrelation. Improved coherence at L-band (24 cm wavelength) significantly improves the spatial coverage of the estimated deformation signal in our ALOS PALSAR data set. We analyze 450 ALOS PALSAR interferograms processed using 175 SAR images acquired between Dec 2006 and Dec 2010 that cover the area along the San Andreas Fault System from Richmond in the San Francisco Bay Area to Maricopa in the San Joaquin Valley.We invert the InSAR phase observations to estimate the constant Line-of-Sight (LOS) deformation

  8. The 1868 Hayward fault, California, earthquake: Implications for earthquake scaling relations on partially creeping faults

    USGS Publications Warehouse

    Hough, Susan E.; Martin, Stacey

    2015-01-01

    The 21 October 1868 Hayward, California, earthquake is among the best-characterized historical earthquakes in California. In contrast to many other moderate-to-large historical events, the causative fault is clearly established. Published magnitude estimates have been fairly consistent, ranging from 6.8 to 7.2, with 95% confidence limits including values as low as 6.5. The magnitude is of particular importance for assessment of seismic hazard associated with the Hayward fault and, more generally, to develop appropriate magnitude–rupture length scaling relations for partially creeping faults. The recent reevaluation of archival accounts by Boatwright and Bundock (2008), together with the growing volume of well-calibrated intensity data from the U.S. Geological Survey “Did You Feel It?” (DYFI) system, provide an opportunity to revisit and refine the magnitude estimate. In this study, we estimate the magnitude using two different methods that use DYFI data as calibration. Both approaches yield preferred magnitude estimates of 6.3–6.6, assuming an average stress drop. A consideration of data limitations associated with settlement patterns increases the range to 6.3–6.7, with a preferred estimate of 6.5. Although magnitude estimates for historical earthquakes are inevitably uncertain, we conclude that, at a minimum, a lower-magnitude estimate represents a credible alternative interpretation of available data. We further discuss implications of our results for probabilistic seismic-hazard assessment from partially creeping faults.

  9. Historic creep rate and potential for seismic slip along the Hayward Fault, California

    USGS Publications Warehouse

    Lienkaemper, J.J.; Borchardt, G.; Lisowski, M.

    1991-01-01

    The Hayward fault is considered the most likely source of one or more major earthquakes in the San Francisco Bay area in the next few decades. Historically, at least one, and probably two, major earthquakes (about M 6.8) occurred along the Hayward fault, one in 1836 and another in 1868. Little is known about the 1836 event, but the 1868 earthquake was accompanied by a surface rupture that extended as much as 41 km along the southern part of the fault. Although the amount of surface slip in 1868 is uncertain, right slip (including afterslip) reached at least several centimeters, and possibly several decimeters in places. This paper documents the spatial variation of creep rate along the Hayward fault since the 1868 earthquake. Creep (aseismic fault slip) occurs over at least 66 km and may extend over the fault's entire 82-km length, of which about 13 km lies underwater. Creep rate seems nearly constant over decades, but short-term variations occur. We derive creep rate mainly from our own systematic surveying of offset cultural features (curbs, fences, and buildings). On each feature we solve directly for accumulated creep by using multiple linear regression. Creep rate mostly falls in the range of 3.5–6.5 mm/yr; but systematic variation occurs along strike. Fault segments with distinctly higher and lower rates generally correspond to parts of the fault most salient from the overall average alinement of the fault. Most distinctive is a 4-km-long section near the south end of the fault that creeps at about 9 mm/yr. Such a high rate has occurred there at least since the 1920s and probably since the 1868 earthquake, as indicated by an offset railroad track built in 1869. We suggest that this 9 mm/yr slip rate may approach the long-term or deep slip rate that controls average recurrence interval between major earthquakes. If so, assuming an elastic rebound model, the potential for slip in large earthquakes below the surficial creeping zone is now ∼1.1 m in the

  10. High-Resolution Seismic Reflection and Refraction Imaging of the Hayward Fault in Fremont, Alameda County, California

    NASA Astrophysics Data System (ADS)

    Everson, E. D.; Rymer, M. J.; Goldman, M. R.; Catchings, R. D.

    2007-12-01

    In July 2007, the U.S. Geological Survey acquired a 60-m-long seismic reflection and refraction profile across the main trace of the Hayward fault in Fremont Central Park, Fremont, California. The profile was designed to determine the geometry, seismic velocities, and possible structural complexities of the fault. The study was along a part of the surface rupture of the 1868 M 7.0 Hayward earthquake. We used single-element, 40-Hz vertical geophones placed at 1-m intervals along the profile with 0.5-m lateral offset from the shot points, also with 1-m intervals. Seismic sources were generated by multiple sledgehammer blows at each shot point. Data were recorded unfiltered in the field on a Geometrics Strataview RX-60 seismograph at a sampling rate of 0.5 ms for 2 s. Geophone locations were measured in 3D using differential GPS. We developed a velocity model using the Hole (1992) code to invert P-wave first arrivals of the refraction data. Seismic P-wave velocities range from about 200 m/s near the surface to approximately 800 m/s at a depth of 13 to 16 m. The velocity model was then applied to the reflection data to develop an unmigrated common depth point (CDP) stack. The reflection data indicate the presence of at least three fault strands in an approximately 20-m-wide zone. We believe the three strands define an upwardly flaring 'flower structure', with the central strand being the main strand of the Hayward fault. The three strands project to merge at a depth of about 150 m; the overall dip of the fault zone in the upper 100 m is to the northeast, at about 88 degrees.

  11. Earthquake recurrence on the south Hayward fault is most consistent with a time dependent, renewal process

    USGS Publications Warehouse

    Parsons, T.

    2008-01-01

    Elastic rebound and stress renewal are important components of earthquake forecasting because if large earthquakes can be shown to be periodic, then rupture probability is time dependent. While renewal models are used in formal forecasts, it has not been possible to exclude the alternate view that repeated large earthquakes can happen in rapid succession without requiring time for stress regeneration. Here a consistency test between time dependent and time independent recurrence distributions is made using a Monte Carlo method to replicate the paleoseismic series on the south Hayward fault. Time dependent distributions with recurrence interval of 210 years and coefficient of variation of 0.6 reproduce the event series on the south Hayward 5 times more often than any exponential distribution: a highly significant difference as determined using a two-tailed Z-test for relative proportions. Therefore large Hayward fault earthquakes are quasi-periodic and are most consistent with a stress renewal process.

  12. Timing of paleoearthquakes on the northern Hayward Fault: preliminary evidence in El Cerrito, California

    USGS Publications Warehouse

    Lienkaemper, J.J.; Schwartz, D.P.; Kelson, K.I.; Lettis, W.R.; Simpson, Gary D.; Southon, J.R.; Wanket, J.A.; Williams, P.L.

    1999-01-01

    The Working Group on California Earthquake Probabilities estimated that the northern Hayward fault had the highest probability (0.28) of producing a M7 Bay Area earthquake in 30 years (WGCEP, 1990). This probability was based, in part, on the assumption that the last large earthquake occurred on this segment in 1836. However, a recent study of historical documents concludes that the 1836 earthquake did not occur on the northern Hayward fault, thereby extending the elapsed time to at least 220 yr ago, the beginning of the written record. The average recurrence interval for a M7 on the northern Hayward is unknown. WGCEP (1990) assumed an interval of 167 years. The 1996 Working Group on Northern California Earthquake Potential estimated ~210 yr, based on extrapolations from southern Hayward paleoseismological studies and a revised estimate of 1868 slip on the southern Hayward fault. To help constrain the timing of paleoearthquakes on the northern Hayward fault for the 1999 Bay Area probability update, we excavated two trenches that cross the fault and a sag pond on the Mira Vista golf course. As the site is on the second fairway, we were limited to less than ten days to document these trenches. Analysis was aided by rapid C-14 dating of more than 90 samples which gave near real-time results with the trenches still open. A combination of upward fault terminations, disrupted strata, and discordant angular relations indicates at least four, and possibly seven or more, surface faulting earthquakes occurred during a 1630-2130 yr interval. Hence, average recurrence time could be <270 yr, but is no more than 710 yr. The most recent earthquake (MRE) occurred after AD 1640. Preliminary analysis of calibrated dates supports the assumption that no large historical (post-1776) earthquakes have ruptured the surface here, but the youngest dates need more corroboration. Analyses of pollen for presence of non-native species help to constrain the time of the MRE. The earthquake

  13. The Hayward Fault - Is It Due for a Repeat of the Powerful 1868 Earthquake?

    USGS Publications Warehouse

    Brocher, Thomas M.; Boatwright, Jack; Lienkaemper, James J.; Prentice, Carol S.; Schwartz, David P.; Bundock, Howard

    2008-01-01

    On October 21, 1868, a magnitude 6.8 earthquake struck the San Francisco Bay region. Although the region was then sparsely populated, this quake on the Hayward Fault was one of the most destructive in California?s history. Recent studies show that such powerful Hayward Fault quakes have repeatedly jolted the region in the past. U.S. Geological Survey (USGS) scientists describe this fault as a tectonic time bomb, due anytime for another magnitude 6.8 to 7.0 earthquake. Because such a quake could cause hundreds of deaths, leave thousands homeless, and devastate the region?s economy, the USGS and other organizations are working together with new urgency to help prepare Bay Area communities for this certain future quake.

  14. Variations in creep rate along the Hayward Fault, California, interpreted as changes in depth of creep

    USGS Publications Warehouse

    Simpson, R.W.; Lienkaemper, J.J.; Galehouse, J.S.

    2001-01-01

    Variations ill surface creep rate along the Hayward fault are modeled as changes in locking depth using 3D boundary elements. Model creep is driven by screw dislocations at 12 km depth under the Hayward and other regional faults. Inferred depth to locking varies along strike from 4-12 km. (12 km implies no locking.) Our models require locked patches under the central Hayward fault, consistent with a M6.8 earthquake in 1868, but the geometry and extent of locking under the north and south ends depend critically on assumptions regarding continuity and creep behavior of the fault at its ends. For the northern onshore part of the fault, our models contain 1.4-1.7 times more stored moment than the model of Bu??rgmann et al. [2000]; 45-57% of this stored moment resides in creeping areas. It is important for seismic hazard estimation to know how much of this moment is released coseismically or as aseismic afterslip.

  15. Earthquake stress drops and inferred fault strength on the Hayward Fault, east San Francisco Bay, California

    USGS Publications Warehouse

    Hardebeck, J.L.; Aron, A.

    2009-01-01

    We study variations in earthquake stress drop with respect to depth, faulting regime, creeping versus locked fault behavior, and wall-rock geology. We use the P-wave displacement spectra from borehole seismic recordings of M 1.0-4.2 earthquakes in the east San Francisco Bay to estimate stress drop using a stack-and-invert empirical Green's function method. The median stress drop is 8.7 MPa, and most stress drops are in the range between 0.4 and 130 MPa. An apparent correlation between stress drop and magnitude is entirely an artifact of the limited frequency band of 4-55 Hz. There is a trend of increasing stress drop with depth, with a median stress drop of ~5 MPa for 1-7 km depth, ~10 MPa for 7-13 km depth, and ~50 MPa deeper than 13 km. We use S=P amplitude ratios measured from the borehole records to better constrain the first-motion focal mechanisms. High stress drops are observed for a deep cluster of thrust-faulting earthquakes. The correlation of stress drops with depth and faulting regime implies that stress drop is related to the applied shear stress. We compare the spatial distribution of stress drops on the Hayward fault to a model of creeping versus locked behavior of the fault and find that high stress drops are concentrated around the major locked patch near Oakland. This also suggests a connection between stress drop and applied shear stress, as the locked patch may experience higher applied shear stress as a result of the difference in cumulative slip or the presence of higher-strength material. The stress drops do not directly correlate with the strength of the proposed wall-rock geology at depth, suggesting that the relationship between fault strength and the strength of the wall rock is complex.

  16. Evidence for a twelfth large earthquake on the southern hayward fault in the past 1900 years

    USGS Publications Warehouse

    Lienkaemper, J.J.; Williams, P.L.; Guilderson, T.P.

    2010-01-01

    We present age and stratigraphic evidence for an additional paleoearthquake at the Tyson Lagoon site. The acquisition of 19 additional radiocarbon dates and the inclusion of this additional event has resolved a large age discrepancy in our earlier earthquake chronology. The age of event E10 was previously poorly constrained, thus increasing the uncertainty in the mean recurrence interval (RI), a critical factor in seismic hazard evaluation. Reinspection of many trench logs revealed substantial evidence suggesting that an additional earthquake occurred between E10 and E9 within unit u45. Strata in older u45 are faulted in the main fault zone and overlain by scarp colluviums in two locations.We conclude that an additional surfacerupturing event (E9.5) occurred between E9 and E10. Since 91 A.D. (??40 yr, 1??), 11 paleoearthquakes preceded the M 6:8 earthquake in 1868, yielding a mean RI of 161 ?? 65 yr (1??, standard deviation of recurrence intervals). However, the standard error of the mean (SEM) is well determined at ??10 yr. Since ~1300 A.D., the mean rate has increased slightly, but is indistinguishable from the overall rate within the uncertainties. Recurrence for the 12-event sequence seems fairly regular: the coefficient of variation is 0.40, and it yields a 30-yr earthquake probability of 29%. The apparent regularity in timing implied by this earthquake chronology lends support for the use of time-dependent renewal models rather than assuming a random process to forecast earthquakes, at least for the southern Hayward fault.

  17. Probabilistic estimates of surface coseismic slip and afterslip for Hayward fault earthquakes

    USGS Publications Warehouse

    Aagaard, Brad T.; Lienkaemper, James J.; Schwartz, David P.

    2012-01-01

    We examine the partition of long‐term geologic slip on the Hayward fault into interseismic creep, coseismic slip, and afterslip. Using Monte Carlo simulations, we compute expected coseismic slip and afterslip at three alinement array sites for Hayward fault earthquakes with nominal moment magnitudes ranging from about 6.5 to 7.1. We consider how interseismic creep might affect the coseismic slip distribution as well as the variability in locations of large and small slip patches and the magnitude of an earthquake for a given rupture area. We calibrate the estimates to be consistent with the ratio of interseismic creep rate at the alinement array sites to the geologic slip rate for the Hayward fault. We find that the coseismic slip at the surface is expected to comprise only a small fraction of the long‐term geologic slip. The median values of coseismic slip are less than 0.2 m in nearly all cases as a result of the influence of interseismic creep and afterslip. However, afterslip makes a substantial contribution to the long‐term geologic slip and may be responsible for up to 0.5–1.5 m (median plus one standard deviation [S.D.]) of additional slip following an earthquake rupture. Thus, utility and transportation infrastructure could be severely impacted by afterslip in the hours and days following a large earthquake on the Hayward fault that generated little coseismic slip. Inherent spatial variability in earthquake slip combined with the uncertainty in how interseismic creep affects coseismic slip results in large uncertainties in these slip estimates.

  18. Petrography and physical properties of selected rock types associated with the Hayward Fault, California

    USGS Publications Warehouse

    Moore, Diane E.; Ponce, David A.

    2001-01-01

    A larger group of samples, most of them 1"-diameter cores, on which density and magnetic susceptibility measurements were made as part of gravity and magnetic surveys of the Hayward Fault. Because this second group of samples received less extensive laboratory study, examination of them was limited to standard petrographic microscope examination of covered thin sections. The density and susceptibility measurements of this second group of samples are included in this report.

  19. Long-term monitoring of creep rate along the Hayward fault and evidence for a lasting creep response to 1989 Loma Prieta earthquake

    USGS Publications Warehouse

    Lienkaemper, J.J.; Galehouse, J.S.; Simpson, R.W.

    2001-01-01

    We present results from over 30 yr of precise surveys of creep along the Hayward fault. Along most of the fault, spatial variability in long-term creep rates is well determined by these data and can help constrain 3D-models of the depth of the creeping zone. However, creep at the south end of the fault stopped completely for more than 6 years after the M7 1989 Loma Prieta Earthquake (LPEQ), perhaps delayed by stress drop imposed by this event. With a decade of detailed data before LPEQ and a decade after it, we report that creep response to that event does indeed indicate the expected deficit in creep.

  20. A record of large earthquakes on the southern Hayward fault for the past 500 years

    USGS Publications Warehouse

    Lienkaemper, J.J.; Dawson, T.E.; Personius, S.F.; Seitz, G.G.; Reidy, L.M.; Schwartz, D.P.

    2002-01-01

    The Hayward fault, a major branch of the right-lateral San Andreas fault system, traverses the densely populated eastern San Francisco Bay region, California. We conducted a paleoseismic investigation to better understand the Hayward fault's past earthquake behavior. The site is near the south end of Tyson's Lagoon, a sag pond formed in a right step of the fault in Fremont. Because the Hayward fault creeps at the surface, we identified paleoseismic events using features that we judge to be unique to ground ruptures or the result of strong ground motion, such as the presence of fault-scarp colluvial deposits and liquefaction. We correlate the most recent event evidence (E1) to the historical 1868 M 6.9 earthquake that caused liquefaction in the pond and recognize three additional paleoruptures since A.D. 1470 ?? 110 yr. Event ages were estimated by chronological modeling, which incorporated historical and stratigraphic information and radiocarbon and pollen data. Modeled, mean age and 95-percentile ranges of the three earlier events are A.D. 1730 (1650-1790) yr (E2), A.D. 1630 (1530-1740) yr (E3), and A.D. 1470 (1360-1580) (E4). The ages of these paleoearthquakes yield a mean recurrence of 130 ?? 40 yr. Although the mean recurrence is well determined for the period A.D. 1470-1868, individual intervals are less well determined: E1-E2, 140 + 80/ - 70 yr; E2-E3, 100 + 90/ - 100 yr; and E3-E4, 150 + 130/ - 110 yr.

  1. Correlation Between Radon Outgassing and Seismic Activity Along the Hayward Fault Near Berkeley, California

    NASA Astrophysics Data System (ADS)

    Holtmann-Rice, D.; Cuff, K.

    2003-12-01

    Results from previous studies indicate that radon concentration values are significantly higher over selected sections of the Hayward fault than adjacent areas. This phenomenon is believed to be attributed to the presence of abundant fractures in rock associated with the fault, which act as pathways for radon as it migrates from depth towards the earth?s surface. In an attempt to determine whether or not a relationship exists between seismicity along the fault, the production of microfractures, and emanation of radon, a radon outgassing monitoring study was conducted along an active section of the Hayward fault in Berkeley, California. The study was carried out by using an alphaMETER 611, which is a device capable of accurately measuring radon concentrations every 15 minutes. The alphaMETER was placed at the bottom of a sealed one meter deep well, in close proximity to a section of the Hayward fault located along the northwestern face of the Berkeley Hills. Once per week for several months data collected by the alphaMETER was downloaded into a laptop computer. Data from the alphaMETER was then compared with seismic data recorded by local seismometers to see if any correlation existed. A general correlation between variation in radon concentration and the occurrence of small earthquakes was found. Significant peaks in radon concentration were observed within an approximately one week period before the occurrence of small earthquakes. Concentration values then decreased dramatically just prior to and during periods when the earthquakes occurred. Such correlation is very similar to that recently observed in association with a magnitude five earthquake along the Anatolian Fault, reported by geoscientists working in Turkey using similar instrumentation (Inan, 2003, personal communication). The most plausible explanation for the observed correlation is as follows: 1) prior to a given earthquake, stress build up within a particular fault region leads to the formation of

  2. Results for aseismic creep on the Hayward fault using polarization persistent scatterer InSAR

    NASA Astrophysics Data System (ADS)

    Tiampo, Kristy F.; González, Pablo J.; Samsonov, Sergey S.

    2013-04-01

    We present new results for shallow aseismic creep on the Hayward fault in California using a new DInSAR technique. This method not only provides, for the first time, the ability to map the displacement field on both sides of the fault, it does so over a much shorter time period than earlier results. The results provide a good match in the near-field to both the regional continuous GPS velocities and data from an alinement network that measures long-term creep along the fault. The average slip rate for the northern segment of the Hayward fault is ˜4.4 mm/yr between 2008 and 2011, slightly less than that estimated for longer time periods, suggesting that the slip rate may not be constant. If the slip rate along the fault is variable on the decadal or longer scale, current estimates of its earthquake potential and the associated hazard associated with the slip rate deficit may need to be revised from previous estimates. We demonstrate the potential impact of this method to better define the spatial and temporal complexity of aseismic slip and estimate the accumulated elastic strain along one of the most significant sources of seismic hazard in the San Francisco Bay area.

  3. Seismic reflection evidence for a northeast-dipping Hayward fault near Fremont, California: Implications for seismic hazard

    USGS Publications Warehouse

    Williams, R.A.; Simpson, R.W.; Jachens, R.C.; Stephenson, W.J.; Odum, J.K.; Ponce, D.A.

    2005-01-01

    A 1.6-km-long seismic reflection profile across the creeping trace of the southern Hayward fault near Fremont, California, images the fault to a depth of 650 m. Reflector truncations define a fault dip of about 70 degrees east in the 100 to 650 m depth range that projects upward to the creeping surface trace, and is inconsistent with a nearly vertical fault in this vicinity as previously believed. This fault projects to the Mission seismicity trend located at 4-10 km depth about 2 km east of the surface trace and suggests that the southern end of the fault is as seismically active as the part north of San Leandro. The seismic hazard implication is that the Hayward fault may have a more direct connection at depth with the Calaveras fault, affecting estimates of potential event magnitudes that could occur on the combined fault surfaces, thus affecting hazard assessments for the south San Francisco Bay region.

  4. Characterizing Slow Slip Events on the Hayward Fault from Two Decades of SBAS-InSAR Data

    NASA Astrophysics Data System (ADS)

    Johanson, I. A.; Burgmann, R.

    2011-12-01

    In the San Francisco Bay Area (SFBA), two million people live in a geologically complex, tectonically active region that has experienced several historic earthquakes, including the 1868 Hayward, the 1906 San Francisco, and 1989 Loma Prieta earthquakes. The Uniform California Earthquake Rupture Forecast (2008) puts a 63% probability of a M6.7 or greater in the SFBA before 2038 and a 31% probability for the Hayward fault alone, the highest for any fault in the SFBA. The Hayward fault along the eastern side of San Francisco Bay is arguably one of the most hazardous faults in the world when one combines the probability of an earthquake with proximity to urban centers. Assessment of earthquake potential along Bay Area faults is complicated by the recognition that the system is not static and, in particular, that creep rates vary through time. Hayward fault monitoring by creepmeter, strainmeter and alinement array has detected a number of variations in creep rate on the Hayward fault. The largest in 1996, when an alinement array survey detected a SSE that produced 18 mm of fault creep within at most 63 days. The SSE also marked a change in longer-term creep rate, from nearly zero post-Loma Prieta to 3.9 mm/yr, still lower than the pre-Loma Prieta rate of ~9 mm/yr. More recent alinement array surveys (since 2006) show an increase in creep rates on the southern Hayward fault by ~2-5 mm/yr over the long-term average. The Small Baseline Subset (SBAS) approach is a method for extracting time series of range change at certain locations from a large set of InSAR data and is well suited to reveal time varying deformation without a known functional form. This project incorporates time series processing of InSAR data spanning 18 years and three satellites, together with 17 years of GPS acquisitions. In particular, we use these data to investigate slow slip events (SSEs) on the Hayward fault. The spatial density of SBAS-InSAR gives us more information on the spatial extent of the

  5. Ground-Motion Simulations of Scenario Earthquakes on the Hayward Fault

    SciTech Connect

    Aagaard, B; Graves, R; Larsen, S; Ma, S; Rodgers, A; Ponce, D; Schwartz, D; Simpson, R; Graymer, R

    2009-03-09

    We compute ground motions in the San Francisco Bay area for 35 Mw 6.7-7.2 scenario earthquake ruptures involving the Hayward fault. The modeled scenarios vary in rupture length, hypocenter, slip distribution, rupture speed, and rise time. This collaborative effort involves five modeling groups, using different wave propagation codes and domains of various sizes and resolutions, computing long-period (T > 1-2 s) or broadband (T > 0.1 s) synthetic ground motions for overlapping subsets of the suite of scenarios. The simulations incorporate 3-D geologic structure and illustrate the dramatic increase in intensity of shaking for Mw 7.05 ruptures of the entire Hayward fault compared with Mw 6.76 ruptures of the southern two-thirds of the fault. The area subjected to shaking stronger than MMI VII increases from about 10% of the San Francisco Bay urban area in the Mw 6.76 events to more than 40% of the urban area for the Mw 7.05 events. Similarly, combined rupture of the Hayward and Rodgers Creek faults in a Mw 7.2 event extends shaking stronger than MMI VII to nearly 50% of the urban area. For a given rupture length, the synthetic ground motions exhibit the greatest sensitivity to the slip distribution and location inside or near the edge of sedimentary basins. The hypocenter also exerts a strong influence on the amplitude of the shaking due to rupture directivity. The synthetic waveforms exhibit a weaker sensitivity to the rupture speed and are relatively insensitive to the rise time. The ground motions from the simulations are generally consistent with Next Generation Attenuation ground-motion prediction models but contain long-period effects, such as rupture directivity and amplification in shallow sedimentary basins that are not fully captured by the ground-motion prediction models.

  6. Hayward Fault: A 50-km-long Locked Patch Regulates Its Large Earthquake Cycle (Invited)

    NASA Astrophysics Data System (ADS)

    Lienkaemper, J. J.; Simpson, R. W.; Williams, P. L.; McFarland, F. S.; Caskey, S. J.

    2010-12-01

    We have documented a chronology of 11 paleoearthquakes on the southern Hayward fault (HS) preceding the Mw6.8, 1868 earthquake. These large earthquakes were both regular and frequent, as indicated by a 0.40 coefficient of variation and mean recurrence interval (MRI) of 161 ± 65 yr (1σ of recurrence intervals). Furthermore, the Oxcal-modeled probability distribution for the average interval resembles a Gaussian rather than a more irregular Brownian passage time distribution. Our revised 3D-modeling of subsurface creep, using newly updated long-term creep rates, now suggests there is only one ~50-km-long locked patch (instead of two), confined laterally between two large patches of deep creep (≥9 km), with an extent consistent with evidence for the 1868 rupture. This locked patch and the fault’s lowest rates of surface creep are approximately centered on HS’s largest bend and a large gabbro body, particularly where the gabbro forms both east and west faces of the fault. We suggest that this locked patch serves as a mechanical capacitor, limiting earthquake size and frequency. The moment accumulation over 161 yr summed on all locked elements of the model reaches Mw6.79, but if half of the moment stored in the creeping elements were to fail dynamically, Mw could reach 6.91. The paleoearthquake histories for nearby faults of the San Francisco Bay region appear to indicate less regular and frequent earthquakes, possibly because most lack the high proportion (40-60%) of aseismic release found on the Hayward fault. The northernmost Hayward fault and Rodgers Creek fault (RCF) appear to rupture only half as frequently as the HS and are separated from the HS by a creep buffer and 5-km wide releasing bend respectively, both tending to limit through-going ruptures. The paleoseismic record allows multi-segment, Hayward fault-RCF ruptures, but does not require it. The 1868 HS rupture preceded the 1906 multi-segmented San Andreas fault (SAF) rupture, perhaps because the HS

  7. Distribution of aseismic slip rate on the Hayward fault inferred from seismic and geodetic data

    USGS Publications Warehouse

    Schmidt, D.A.; Burgmann, R.; Nadeau, R.M.; d'Alessio, M.

    2005-01-01

    We solve for the slip rate distribution on the Hayward fault by performing a least squares inversion,of geodetic and seismic data sets. Our analysis focuses on the northern 60 km of the fault. Interferometric synthetic aperture radar (InSAR) data from 13 independent ERS interferograms are stacked to obtain range change rates from 1992 to 2000. Horizontal surface displacement rates at 141 bench marks are measured using GPS from 1994 to 2003. Surface creep observations and estimates of deep slip rates determined from characteristic repeating earthquake sequences are also incorporated in the inversion. The fault is discretized into 283 triangular dislocation elements that approximate the nonplanar attributes of the fault surface. South of the city of Hayward, a steeply, east dipping fault geometry accommodates the divergence of the surface trace and the microseismicity at depth. The inferred slip rate distribution is consistent with a fault that creeps aseismically at a rate of ???5 mm/yr to a depth of 4-6 km. The interferometric synthetic aperture radar (InSAR) data require an aseismic slip rate that approaches the geologic slip rate on the northernmost fault segment beneath Point Pinole, although the InSAR data might be complicated by a small dip-slip component at this location. A low slip rate patch of <1 mm/yr is inferred beneath San Leandro consistent with the source location of the 1868 earthquake. We calculate that the entire fault is accumulating a slip rate deficit equivalent to a Mw = 6.77 ?? 0.05 per century. However, this estimate of potential coseismic moment represents an upper bound because we do not know how much of the accumulated strain will be released through aseismic processes such as afterslip. Copyright 2005 by the American Geophysical Union.

  8. Status and needs for seismic instrumentation of structures along the Hayward fault

    USGS Publications Warehouse

    Kalkan, Erol; Çelebi, Mehmet

    2008-01-01

    The inventory of structures in heavily urbanized communities within the greater San Francisco (SF) Bay area that will experience strong ground motions from the rupture of the Hayward Fault includes a variety of types of recent and older structures built with a variety of materials and to different code standards. Those who remember the effects of the 1989 Loma Prieta earthquake on structures in the San Francisco Bay area also remember the collapse of one upper-deck segment of the Bay Bridge that halted transportation for approximately five weeks. In order to understand how these structures respond to earthquake motions and to improve building practices to resist these strong motions it is imperative that owners of these structures as well as governmental organizations acquire shaking response data from instrumented (or yet to be instrumented structures) during the forecast events. Within California, such data are acquired mainly by California Geological Survey and the United States Geological Survey. A small number of private owners contribute to this effort. The inventory of existing instrumented structures is much less than 0.1% of the total, and thus statistically it is not sufficient. For example, some of the existing important regular or lifeline structures are not instrumented(e.g. Bart Trans-Bay Tunnel, many segments of the Bart elevated structures in the proximity of the Hayward Fault, the yet to be completed eastern part of San Francisco Bay Bridge, Hetch-Hetchy pipeline system crossing the Hayward Fault)even though attempts and proposals have been developed to do so in the past. This paper presents a critical assessment of the status quo and the future needs for instrumentation of structures in the greater SF Bay area that includes the Hayward Fault. There are many new attempts and successes in instrumentation of structures in this region. Two successful examples are provided here, but more needs to be done. The paper does not present new research results

  9. Fault zone hydrogeology

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  10. Principal facts for gravity data along the Hayward fault and vicinity, San Francisco Bay area, northern California

    USGS Publications Warehouse

    Ponce, David A.

    2001-01-01

    The U.S. Geological Survey (USGS) established over 940 gravity stations along the Hayward fault and vicinity. The Hayward fault, regarded as one of the most hazardous faults in northern California (Working Group on California Earthquake Probabilities, 1999), extends for about 90 km from Fremont in the southeast to San Pablo Bay in the northwest. The Hayward fault is predominantly a right-lateral strike-slip fault that forms the western boundary of the East Bay Hills. These data and associated physical property measurement were collected as part of on-going studies to help determine the earthquake hazard potential of major faults within the San Francisco Bay region. Gravity data were collected between latitude 37°30' and 38°15' N and longitude 121°45' and 122°30' W. Gravity stations were located on the following 7.5 minute quadrangles: Newark, Niles, San Leandro, Hayward, Dublin, Oakland West, Oakland East, Las Trampas Ridge, Diablo, Richmond, Briones Valley, Walnut Creek, and Clayton. All data were ultimately tied to primary gravity base station Menlo Park A, located on the campus of the U.S. Geological Survey in Menlo Park, Calif. (latitude 37°27.34' N, longitude 122°10.18' W, observed gravity value 979944.27 mGal).

  11. Potential for larger earthquakes in the East San Francisco Bay Area due to the direct connection between the Hayward and Calaveras Faults

    NASA Astrophysics Data System (ADS)

    Chaussard, E.; Bürgmann, R.; Fattahi, H.; Nadeau, R. M.; Taira, T.; Johnson, C. W.; Johanson, I.

    2015-04-01

    The Hayward and Calaveras Faults, two strike-slip faults of the San Andreas System located in the East San Francisco Bay Area, are commonly considered independent structures for seismic hazard assessment. We use Interferometric Synthetic Aperture RADAR to show that surface creep on the Hayward Fault continues 15 km farther south than previously known, revealing new potential for rupture and damage south of Fremont. The extended trace of the Hayward Fault, also illuminated by shallow repeating micro-earthquakes, documents a surface connection with the Calaveras Fault. At depths greater than 3-5 km, repeating micro-earthquakes located 10 km north of the surface connection highlight the 3-D wedge geometry of the junction. Our new model of the Hayward and Calaveras Faults argues that they should be treated as a single system with potential for earthquake ruptures generating events with magnitudes greater than 7, posing a higher seismic hazard to the East San Francisco Bay Area than previously considered.

  12. Subsurface structure and kinematics of the Calaveras-Hayward fault stepover from three-dimensional Vp and seismicity, San Francisco Bay region, California

    USGS Publications Warehouse

    Manaker, David M.; Michael, Andrew J.; Burgmann, Roland

    2005-01-01

    We perform a joint inversion for hypocenters and the 3D P-wave velocity structure of the stepover region using 477 earthquakes. We find strong velocity contrasts across the Calaveras and Hayward faults, corroborated by geologic, gravity, and aeromagnetic data. Detailed examination of two seismic lineaments in conjunction with the velocity model and independent geologic and geophysical evidence suggests that they represent the southern extension of a northeasterly dipping Hayward fault that splays off the Calaveras fault, directly accounting for the deep slip transfer. The Mission fault appears to be accommodating deformation within the block between the Hayward and Calaveras faults. Thus, the Calaveras and Hayward faults need to be considered as a single system for developing rupture scenarios for seismic hazard assessments.

  13. Structure and mechanics of the Hayward-Rodgers Creek Fault step-over, San Francisco Bay, California

    USGS Publications Warehouse

    Parsons, T.; Sliter, R.; Geist, E.L.; Jachens, R.C.; Jaffe, B.E.; Foxgrover, A.; Hart, P.E.; McCarthy, J.

    2003-01-01

    A dilatational step-over between the right-lateral Hayward and Rodgers Creek faults lies beneath San Pablo Bay in the San Francisco Bay area. A key seismic hazard issue is whether an earthquake on one of the faults could rupture through the step-over, enhancing its maximum possible magnitude. If ruptures are terminated at the step-over, then another important issue is how strain transfers through the step. We developed a combined seismic reflection and refraction cross section across south San Pablo Bay and found that the Hayward and Rodgers Creek faults converge to within 4 km of one another near the surface, about 2 km closer than previously thought. Interpretation of potential field data from San Pablo Bay indicated a low likelihood of strike-slip transfer faults connecting the Hayward and Rodgers Creek faults. Numerical simulations suggest that it is possible for a rupture to jump across a 4-km fault gap, although special stressing conditions are probably required (e.g., Harris and Day, 1993, 1999). Slip on the Hayward and Rodgers Creek faults is building an extensional pull-apart basin that could contain hazardous normal faults. We investigated strain in the pull-apart using a finite-element model and calculated a ???0.02-MPa/yr differential stressing rate in the step-over on a least-principal-stress orientation nearly parallel to the strike-slip faults where they overlap. A 1- to 10-MPa stress-drop extensional earthquake is expected on normal faults oriented perpendicular to the strike-slip faults every 50-500 years. The last such earthquake might have been the 1898 M 6.0-6.5 shock in San Pablo Bay that apparently produced a small tsunami. Historical hydrographic surveys gathered before and after 1898 indicate abnormal subsidence of the bay floor within the step-over, possibly related to the earthquake. We used a hydrodynamic model to show that a dip-slip mechanism in north San Pablo Bay is the most likely 1898 rupture scenario to have caused the tsunami

  14. Revised long-term creep rates on the Hayward Fault, Alameda and Contra Costa Counties, California

    USGS Publications Warehouse

    Lienkaemper, James J.; Galehouse, Jon S.

    1997-01-01

    Although the Hayward fault is a source of major earthquakes, it also creeps or slips aseismically, and has done so steadily for several decades (certainly since 1921 and probably since 1869). Most of the fault creeps between 3 and 6 mm/yr, except for a 4- to 6-km-long segment near its south end that creeps at about 9 mm/yr. We present results of our recent surveys to recover angles and deflection lines established across the fault in the 1960s and 1970s, but unmonitored since. We have added data from more offset cultural features to the long-term creep rate data set and made substantial improvements to the analytical method used to compute offsets. The revised creep rate values improve our knowledge of spatial and temporal variation along the fault. The more accurate revised data has reduced the estimate of the average creep rate along most of the fault from 5.1 mm/yr to 4.6 mm/yr. Creep rates in the 9 mm/yr section near the south end have remained the same.

  15. Ground-motion modeling of Hayward fault scenario earthquakes, part I: Construction of the suite of scenarios

    USGS Publications Warehouse

    Aagaard, Brad T.; Graves, Robert W.; Schwartz, David P.; Ponce, David A.; Graymer, Russell W.

    2010-01-01

    We construct kinematic earthquake rupture models for a suite of 39 Mw 6.6-7.2 scenario earthquakes involving the Hayward, Calaveras, and Rodgers Creek faults. We use these rupture models in 3D ground-motion simulations as discussed in Part II (Aagaard et al., 2010) to provide detailed estimates of the shaking for each scenario. We employ both geophysical constraints and empirical relations to provide realistic variation in the rupture dimensions, slip heterogeneity, hypocenters, rupture speeds, and rise times. The five rupture lengths include portions of the Hayward fault as well as combined rupture of the Hayward and Rodgers Creek faults and the Hayward and Calaveras faults. We vary rupture directivity using multiple hypocenters, typically three per rupture length, yielding north-to-south rupture, bilateral rupture, and south-to-north rupture. For each rupture length and hypocenter, we consider multiple random distributions of slip. We use two approaches to account for how aseismic creep might reduce coseismic slip. For one subset of scenarios, we follow the slip-predictable approach and reduce the nominal slip in creeping regions according to the creep rate and time since the most recent earthquake, whereas for another subset of scenarios we apply a vertical gradient to the nominal slip in creeping regions. The rupture models include local variations in rupture speed and use a ray-tracing algorithm to propagate the rupture front. Although we are not attempting to simulate the 1868 Hayward fault earthquake in detail, a few of the scenarios are designed to have source parameters that might be similar to this historical event.

  16. Time-dependent model of creep on the Hayward fault from joint inversion of 18 years of InSAR and surface creep data

    NASA Astrophysics Data System (ADS)

    Shirzaei, M.; Bürgmann, R.

    2013-04-01

    Spatial and temporal variations of aseismic fault creep influence the size and timing of large earthquakes along partially coupled faults. To solve for a time-dependent model of creep on the Hayward fault, we invert 18 years of surface deformation data (1992-2010), obtained by interferometric processing of 52 and 50 SAR images acquired by the ERS1/2 and Envisat satellites, respectively, and surface creep data obtained at 19 alinement and 4 creepmeter stations. For multi-temporal analysis of the SAR data we developed a method for identifying stable pixels using wavelet multi-resolution analysis. We also implement a variety of wavelet-based filters for reducing the effects of environmental artifacts. Using a reweighted least squares approach, we inverted the interferometric data to generate a time series of surface deformation over the San Francisco Bay Area with a precision of better than a few millimeters. To jointly invert the InSAR displacement time series and the surface creep data for a time-dependent model of fault creep, we use a robust inversion approach combined with a Kalman filter. The time-dependent model constrains a zone of high slip deficit that may represent the locked rupture asperity of past and future M≈7 earthquakes. We identify several additional temporal variations in creep rate along the Hayward fault, the most important one being a zone of accelerating slip just northwest of the major locked zone. We estimate that a slip-rate deficit equivalent to Mw 6.3-6.8 has accumulated on the fault, since the last event in 1868.

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

    NASA Astrophysics Data System (ADS)

    Allam, Amir A.

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

  18. Shipborne Magnetic Survey of San Pablo Bay and Implications on the Hayward-Rodgers Creek Fault Junction

    NASA Astrophysics Data System (ADS)

    Ponce, D. A.; Athens, N. D.; Denton, K.

    2012-12-01

    A shipborne magnetic survey of San Pablo Bay reveals a steep magnetic gradient as well as several prominent magnetic anomalies along the offshore extension of the Hayward Fault. The Hayward Fault enters San Pablo Bay at Pinole Point and potentially extends beneath San Pablo Bay for 15 km. About 1,000 line-km of shipborne magnetometer data were collected in San Pablo Bay along approximately north-east and north-west trending traverses. Shiptrack lines were spaced 200-m apart in a N55oE direction and tie-lines were spaced 500- and 1,000-m apart in a N145oE direction. Magnetometer and Geographic Positioning System (GPS) data were collected simultaneously at one-second intervals using a Geometrics G858 cesium vapor magnetometer with the sensor attached to a nonmagnetic pole extended about 2 m over the bow. Diurnal variations of the Earth's magnetic field were recorded at a ground magnetic base station and shipborne data were corrected for diurnal variations, International Geomagnetic Reference Field, cultural noise, heading errors, and leveling errors. The heading correction applied to the shipborne magnetic data accounts for a systematic shift in the magnetic readings due to the magnetic field produced by the boat and the orientation of the boat. The heading correction was determined by traversing several shiptrack lines in various azimuths in opposite directions. Magnetic measurements off the main survey lines (e.g., turns) were removed from the survey. After applying the heading correction, crossing values or the difference in values where two survey lines intersect were compared and the survey was leveled. Shipborne magnetic data reveal a prominent magnetic anomaly immediately offshore of Point Pinole that probably reflects ultramafic rocks (e.g. serpentinite), similar to those exposed in the northern part of the onshore Hayward Fault. Further to the northwest, shipborne magnetic data enhance two prominent aeromagnetic anomalies along the Hayward Fault in the

  19. Evidence for surface rupture in 1868 on the Hayward fault in north Oakland and major rupturing in prehistoric earthquakes

    USGS Publications Warehouse

    Lienkaemper, J.J.; Williams, P.L.

    1999-01-01

    WGCEP90 estimated the Hayward fault to have a high probability (0.45 in 30 yr) of producing a future M7 Bay Area earthquake. This was based on a generic recurrence time and an unverified segmentation model, because there were few direct observations for the southern fault and none for the northern Hayward fault. To better constrain recurrence and segmentation of the northern Hayward fault, we trenched in north Oakland. Unexpectedly, we observed evidence of surface rupture probably from the M7 1868 earthquake. This extends the limit of that surface rupture 13 km north of the segmentation boundary used in the WGCEP90 model and forces serious re-evaluation of the current two-segment paradigm. Although we found that major prehistoric ruptures have occurred here, we could not radiocarbon date them. However, the last major prehistoric event appears correlative with a recently recognized event 13 km to the north dated AD 1640-1776. Copyright 1999 by the American Geophysical Union.

  20. A Double-difference Earthquake location algorithm: Method and application to the Northern Hayward Fault, California

    USGS Publications Warehouse

    Waldhauser, F.; Ellsworth, W.L.

    2000-01-01

    We have developed an efficient method to determine high-resolution hypocenter locations over large distances. The location method incorporates ordinary absolute travel-time measurements and/or cross-correlation P-and S-wave differential travel-time measurements. Residuals between observed and theoretical travel-time differences (or double-differences) are minimized for pairs of earthquakes at each station while linking together all observed event-station pairs. A least-squares solution is found by iteratively adjusting the vector difference between hypocentral pairs. The double-difference algorithm minimizes errors due to unmodeled velocity structure without the use of station corrections. Because catalog and cross-correlation data are combined into one system of equations, interevent distances within multiplets are determined to the accuracy of the cross-correlation data, while the relative locations between multiplets and uncorrelated events are simultaneously determined to the accuracy of the absolute travel-time data. Statistical resampling methods are used to estimate data accuracy and location errors. Uncertainties in double-difference locations are improved by more than an order of magnitude compared to catalog locations. The algorithm is tested, and its performance is demonstrated on two clusters of earthquakes located on the northern Hayward fault, California. There it colapses the diffuse catalog locations into sharp images of seismicity and reveals horizontal lineations of hypocenter that define the narrow regions on the fault where stress is released by brittle failure.

  1. A record of large earthquakes on the southern Hayward fault for the past 1800 years

    USGS Publications Warehouse

    Lienkaemper, J.J.; Williams, P.L.

    2007-01-01

    This is the second article presenting evidence of the occurrence and timing of paleoearthquakes on the southern Hayward fault as interpreted from trenches excavated within a sag pond at the Tyson's Lagoon site in Fremont, California. We use the information to estimate the mean value and aperiodicity of the fault's recurrence interval (RI): two fundamental parameters for estimation of regional seismic hazard. An earlier article documented the four most recent earthquakes, including the historic 1868 earthquake. In this article we present evidence for at least seven earlier paleoruptures since about A.D. 170. We document these events with evidence for ground rupture, such as the presence of blocky colluvium at the base of the main trace fault scarp, and by corroborating evidence such as simultaneous liquefaction or an increase in deformation immediately below event horizons. The mean RI is 170 ?? 82 yr (1??, standard deviation of the sample), aperiodicity is 0.48, and individual intervals may be expected to range from 30 to 370 yr (95.4% confidence). The mean RI is consistent with the recurrence model of the Working Group on California Earthquake Probabilities (2003) (mean, 161 yr; range, 99 yr [2.5%]; 283 yr [97.5%]). We note that the mean RI for the five most recent events may have been only 138 ?? 58 yr (1??). Hypothesis tests for the shorter RI do not demonstrate that any recent acceleration has occurred compared to the earlier period or the entire 1800-yr record, principally because of inherent uncertainties of the event ages.

  2. Seismic-reflection evidence that the hayward fault extends into the lower crust of the San Francisco Bay Area, California

    USGS Publications Warehouse

    Parsons, T.

    1998-01-01

    This article presents deep seismic-reflection data from an experiment across San Francisco Peninsula in 1995 using large (125 to 500 kg) explosive sources. Shot gathers show a mostly nonreflective upper crust in both the Franciscan and Salinian terranes (juxtaposed across the San Andreas fault), an onset of weak lower-crustal reflectivity beginning at about 6-sec two-way travel time (TWTT) and bright southwest-dipping reflections between 11 and 13 sec TWTT. Previous studies have shown that the Moho in this area is no deeper than 25 km (~8 to 9 sec TWTT). Three-dimensional reflection travel-time modeling of the 11 to 13 sec events from the shot gathers indicates that the bright events may be explained by reflectors 15 to 20 km into the upper mantle, northeast of the San Andreas fault. However, upper mantle reflections from these depths were not observed on marine-reflection profiles collected in San Francisco Bay, nor were they reported from a refraction profile on San Francisco Peninsula. The most consistent interpretation of these events from 2D raytracing and 3D travel-time modeling is that they are out-of-plane reflections from a high-angle (dipping ~70??to the southwest) impedance contrast in the lower crust that corresponds with the surface trace of the Hayward fault. These results suggest that the Hayward fault truncates the horizontal detachment fault suggested to be active beneath San Francisco Bay.

  3. Anomalously low strength of serpentinite sheared against granite and implications for creep on the Hayward and Calaveras Faults

    USGS Publications Warehouse

    Moore, Diane E.; Lockner, David A.; Ponce, David A.

    2010-01-01

    Serpentinized ophiolitic rocks are juxtaposed against quartzofeldspathic rocks at depth across considerable portions of the Hayward and Calaveras Faults. The marked compositional contrast between these rock types may contribute to fault creep that has been observed along these faults. To investigate this possibility, we are conducting hydrothermal shearing experiments to look for changes in frictional properties resulting from the shear of ultramafic rock juxtaposed against quartzose rock units. In this paper we report the first results in this effort: shear of bare-rock surfaces of serpentinite and granite, and shear of antigorite-serpentinite gouge between forcing blocks of granitic rock. All experiments were conducted at 250°C. Serpentinite sheared against granite at 50 MPa pore-fluid pressure is weaker than either rock type separately, and the weakening is significantly more pronounced at lower shearing rates. In contrast, serpentinite gouge sheared dry between granite blocks is as strong as the bare granite surface. We propose that the weakening is the result of a solution-transfer process involving the dissolution of serpentine minerals at grain-to-grain contacts. Dissolution of serpentine is enhanced by modifications to pore-fluid chemistry caused by interaction of the fluid with the quartz-bearing rocks. The compositional differences between serpentinized ultramafic rocks of the Coast Range Ophiolite and quartzofeldspathic rock units such as those of the Franciscan Complex may provide the mechanism for aseismic slip (creep) in the shallow crust along the Hayward, Calaveras, and other creeping faults in central and northern California.

  4. Three-dimensional geologic map of the Hayward fault, northern California: Correlation of rock unites with variations in seismicity, creep rate, and fault dip

    USGS Publications Warehouse

    Graymer, R.W.; Ponce, D.A.; Jachens, R.C.; Simpson, R.W.; Phelps, G.A.; Wentworth, C.M.

    2005-01-01

    In order to better understand mechanisms of active faults, we studied relationships between fault behavior and rock units along the Hayward fault using a three-dimensional geologic map. The three-dimensional map-constructed from hypocenters, potential field data, and surface map data-provided a geologic map of each fault surface, showing rock units on either side of the fault truncated by the fault. The two fault-surface maps were superimposed to create a rock-rock juxtaposition map. The three maps were compared with seismicity, including aseismic patches, surface creep, and fault dip along the fault, by using visuallization software to explore three-dimensional relationships. Fault behavior appears to be correlated to the fault-surface maps, but not to the rock-rock juxtaposition map, suggesting that properties of individual wall-rock units, including rock strength, play an important role in fault behavior. Although preliminary, these results suggest that any attempt to understand the detailed distribution of earthquakes or creep along a fault should include consideration of the rock types that abut the fault surface, including the incorporation of observations of physical properties of the rock bodies that intersect the fault at depth. ?? 2005 Geological Society of America.

  5. In search of earthquake-related hydrologic and chemical changes along Hayward Fault

    USGS Publications Warehouse

    King, C.-Y.; Basler, D.; Presser, T.S.; Evans, William C.; White, L.D.; Minissale, A.

    1994-01-01

    Flow and chemical measurements have been made about once a month, and more frequently when required, since 1976 at two springs in Alum Rock Park in eastern San Jose, California, and since 1980 at two shallow wells in eastern Oakland in search of earthquake-related changes. All sites are on or near the Hayward Fault and are about 55 km apart. Temperature, electric conductivity, and water level or flow rate were measured in situ with portable instruments. Water samples were collected for later chemical and isotopic analyses in the laboratory. The measured flow rate at one of the springs showed a long-term decrease of about 40% since 1987, when a multi-year drought began in California. It also showed several increases that lasted a few days to a few months with amplitudes of 2.4 to 8.6 times the standard deviations above the background rate. Five of these increases were recorded shortly after nearby earthquakes of magnitude 5.0 or larger, and may have resulted from unclogging of the flow path and increase of permeability caused by strong seismic shaking. Two other flow increases were possibly induced by exceptionally heavy rainfalls. The water in both wells showed seasonal temperature and chemical variations, largely in response to rainfall. In 1980 the water also showed some clear chemical changes unrelated to rainfall that lasted a few months; these changes were followed by a magnitude 4 earthquake 37 km away. The chemical composition at one of the wells and at the springs also showed some longer-term variations that were not correlated with rainfall but possibly correlated with the five earthquakes mentioned above. These correlations suggest a common tectonic origin for the earthquakes and the anomalies. The last variation at the affected well occurred abruptly in 1989, shortly before a magnitude 5.0 earthquake 54 km away. ?? 1993.

  6. Logs and data from trenches across the Hayward Fault at Tyson's Lagoon (Tule Pond), Fremont, Alameda County, California

    USGS Publications Warehouse

    Linenkaemper, James J.; Dawson, Timothy E.; Personius, Stephen F.; Seitz, Gordon G.; Reidy, Liam M.; Schwartz, David P.

    2002-01-01

    INTRODUCTION The purpose of this publication is to make available detailed trench logs (sheets 1, 2), radiocarbon dates (table 1) and pollen data (fig. 1) obtained as a result of an intensive subsurface investigation of the Hayward Fault at Tyson's Lagoon (Tule Pond) from August to November 2000 (figs. 1, 2 on sheet 1). The Hayward Fault is recognized to be among the most hazardous in the United States (Working Group on California Earthquake Probabilities, 1999). This document makes available geologic evidence for historical and prehistoric surfacerupturing earthquakes that were recorded at the site. Prehistoric earthquakes deduced from geologic evidence are called paleoearthquakes. Establishing a chronology of paleoearthquakes is of immediate use in resolving the level of hazard posed by the Hayward Fault for producing large earthquakes in the future. Preliminary findings of this investigation have been presented in Lienkaemper and others (2001). A formal report on our conclusions based on these data is in preparation. The investigation at Tyson's Lagoon is ongoing, so these products should not be considered final. Lienkaemper, Dawson, and Personius interpreted the geology and logged the trenches. Seitz and Reidy performed analyses on radiocarbon and pollen samples, respectively. Schwartz led the critical-review field team. Previous trenching work was done at Tyson's Lagoon (figs. 2, 3 on sheet 1). Lienkaemper (1992) references the location of most of those trenches. The earlier trenching was generally for the evaluation of local faultrupture hazard, except for the study of Williams (1993), which was a paleoearthquake investigation. An unpublished study by J.N. Alt in 1998 (shown on our site map as trenches 98A and 98B, fig. 3, on sheet 1), also sought evidence of paleoearthquakes. Alt's study and one by Woodward-Clyde and Associates (1970; trenches 70A to 70G, fig. 3) were located south of Walnut Avenue in one of the few areas that still remain undisturbed and

  7. Ground-motion modeling of Hayward fault scenario earthquakes, part II: Simulation of long-period and broadband ground motions

    USGS Publications Warehouse

    Aagaard, Brad T.; Graves, Robert W.; Rodgers, Arthur; Brocher, Thomas M.; Simpson, Robert W.; Dreger, Douglas; Petersson, N. Anders; Larsen, Shawn C.; Ma, Shuo; Jachens, Robert C.

    2010-01-01

    We simulate long-period (T>1.0–2.0 s) and broadband (T>0.1 s) ground motions for 39 scenario earthquakes (Mw 6.7–7.2) involving the Hayward, Calaveras, and Rodgers Creek faults. For rupture on the Hayward fault, we consider the effects of creep on coseismic slip using two different approaches, both of which reduce the ground motions, compared with neglecting the influence of creep. Nevertheless, the scenario earthquakes generate strong shaking throughout the San Francisco Bay area, with about 50% of the urban area experiencing modified Mercalli intensity VII or greater for the magnitude 7.0 scenario events. Long-period simulations of the 2007 Mw 4.18 Oakland earthquake and the 2007 Mw 5.45 Alum Rock earthquake show that the U.S. Geological Survey’s Bay Area Velocity Model version 08.3.0 permits simulation of the amplitude and duration of shaking throughout the San Francisco Bay area for Hayward fault earthquakes, with the greatest accuracy in the Santa Clara Valley (San Jose area). The ground motions for the suite of scenarios exhibit a strong sensitivity to the rupture length (or magnitude), hypocenter (or rupture directivity), and slip distribution. The ground motions display a much weaker sensitivity to the rise time and rupture speed. Peak velocities, peak accelerations, and spectral accelerations from the synthetic broadband ground motions are, on average, slightly higher than the Next Generation Attenuation (NGA) ground-motion prediction equations. We attribute much of this difference to the seismic velocity structure in the San Francisco Bay area and how the NGA models account for basin amplification; the NGA relations may underpredict amplification in shallow sedimentary basins. The simulations also suggest that the Spudich and Chiou (2008) directivity corrections to the NGA relations could be improved by increasing the areal extent of rupture directivity with period.

  8. Ground motion modeling of Hayward fault scenario earthquakes II:Simulation of long-period and broadband ground motions

    SciTech Connect

    Aagaard, B T; Graves, R W; Rodgers, A; Brocher, T M; Simpson, R W; Dreger, D; Petersson, N A; Larsen, S C; Ma, S; Jachens, R C

    2009-11-04

    We simulate long-period (T > 1.0-2.0 s) and broadband (T > 0.1 s) ground motions for 39 scenarios earthquakes (Mw 6.7-7.2) involving the Hayward, Calaveras, and Rodgers Creek faults. For rupture on the Hayward fault we consider the effects of creep on coseismic slip using two different approaches, both of which reduce the ground motions compared with neglecting the influence of creep. Nevertheless, the scenario earthquakes generate strong shaking throughout the San Francisco Bay area with about 50% of the urban area experiencing MMI VII or greater for the magnitude 7.0 scenario events. Long-period simulations of the 2007 Mw 4.18 Oakland and 2007 Mw 4.5 Alum Rock earthquakes show that the USGS Bay Area Velocity Model version 08.3.0 permits simulation of the amplitude and duration of shaking throughout the San Francisco Bay area, with the greatest accuracy in the Santa Clara Valley (San Jose area). The ground motions exhibit a strong sensitivity to the rupture length (or magnitude), hypocenter (or rupture directivity), and slip distribution. The ground motions display a much weaker sensitivity to the rise time and rupture speed. Peak velocities, peak accelerations, and spectral accelerations from the synthetic broadband ground motions are, on average, slightly higher than the Next Generation Attenuation (NGA) ground-motion prediction equations. We attribute at least some of this difference to the relatively narrow width of the Hayward fault ruptures. The simulations suggest that the Spudich and Chiou (2008) directivity corrections to the NGA relations could be improved by including a dependence on the rupture speed and increasing the areal extent of rupture directivity with period. The simulations also indicate that the NGA relations may under-predict amplification in shallow sedimentary basins.

  9. Cross-sections and maps showing double-difference relocated earthquakes from 1984-2000 along the Hayward and Calaveras faults, California

    USGS Publications Warehouse

    Simpson, Robert W.; Graymer, Russell W.; Jachens, Robert C.; Ponce, David A.; Wentworth, Carl M.

    2004-01-01

    We present cross-section and map views of earthquakes that occurred from 1984 to 2000 in the vicinity of the Hayward and Calaveras faults in the San Francisco Bay region, California. These earthquakes came from a catalog of events relocated using the double-difference technique, which provides superior relative locations of nearby events. As a result, structures such as fault surfaces and alignments of events along these surfaces are more sharply defined than in previous catalogs.

  10. Development of Characterization Technology for Fault Zone Hydrology

    SciTech Connect

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

    2010-08-06

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

  11. Spatiotemporal model of aseismic slip on the Hayward fault inferred from joint inversion of geodetic and seismic data time series

    NASA Astrophysics Data System (ADS)

    Shirzaei, M.; Burgmann, R.

    2011-12-01

    Interferometric synthetic aperture radar (InSAR) provides valuable spatiotemporal observations of surface deformation in volcanic and tectonic areas. In this study we generate a long time series of InSAR-measured deformation over the San Francisco Bay Area by combining over 100 ERS1/2 and Envisat SAR acquisitions from 1992 through 2011. We apply an advanced multitemporal processing algorithm that uses multiple-master interferometry and generate about 700 interferograms (ERS-ERS, Envisat-Envisat and ERS-Envisat pairs) with temporal and perpendicular baseline smaller than 4 years and 300 m, respectively. The systematic errors (such as DEM error and atmospheric delay) are estimated and reduced by using a variety of wavelet based filters. The differential displacement measured in each unwrapped interferogram is inverted by using an L1-norm minimization approach to generate time series of the surface displacement for identified stable pixels. Using a Kalman filter, the line-of-sight velocity is estimated, temporal random noise is reduced and the displacement variance-covariance matrix is refined. To solve for the time dependent model of aseismic slip on the Hayward fault, the upper-crustal fault plane is discretized into triangular patches. The size of these patches is optimized in a way that allows estimating the fault slip with maximum precision. Then, we apply an iterated inversion approach, combining static slip inversion and Kalman filtering to model temporal behavior of the slip. For the static inversion we expand the slip to the wavelet base functions and truncate noisy coefficients, which provide a solution equivalent to implementation of the Laplace smoothing operator in conventional slip inversion. This novel approach, however, overcomes the need of choosing a smoothing operator and allows automating the whole inversion step. Since we aim to integrate seismic and creepmeter data sets, the issue of relative weighting of these data sets becomes important, which

  12. Long‐term creep rates on the Hayward Fault: evidence for controls on the size and frequency of large earthquakes

    USGS Publications Warehouse

    Lienkaemper, James J.; McFarland, Forrest S.; Simpson, Robert W.; Bilham, Roger; Ponce, David A.; Boatwright, John; Caskey, S. John

    2012-01-01

    The Hayward fault (HF) in California exhibits large (Mw 6.5–7.1) earthquakes with short recurrence times (161±65 yr), probably kept short by a 26%–78% aseismic release rate (including postseismic). Its interseismic release rate varies locally over time, as we infer from many decades of surface creep data. Earliest estimates of creep rate, primarily from infrequent surveys of offset cultural features, revealed distinct spatial variation in rates along the fault, but no detectable temporal variation. Since the 1989 Mw 6.9 Loma Prieta earthquake (LPE), monitoring on 32 alinement arrays and 5 creepmeters has greatly improved the spatial and temporal resolution of creep rate. We now identify significant temporal variations, mostly associated with local and regional earthquakes. The largest rate change was a 6‐yr cessation of creep along a 5‐km length near the south end of the HF, attributed to a regional stress drop from the LPE, ending in 1996 with a 2‐cm creep event. North of there near Union City starting in 1991, rates apparently increased by 25% above pre‐LPE levels on a 16‐km‐long reach of the fault. Near Oakland in 2007 an Mw 4.2 earthquake initiated a 1–2 cm creep event extending 10–15 km along the fault. Using new better‐constrained long‐term creep rates, we updated earlier estimates of depth to locking along the HF. The locking depths outline a single, ∼50‐km‐long locked or retarded patch with the potential for an Mw∼6.8 event equaling the 1868 HF earthquake. We propose that this inferred patch regulates the size and frequency of large earthquakes on HF.

  13. Subsurface structure of the East Bay Plain ground-water basin: San Francisco Bay to the Hayward fault, Alameda County, California

    USGS Publications Warehouse

    Catchings, R.D.; Borchers, J.W.; Goldman, M.R.; Gandhok, G.; Ponce, D.A.; Steedman, C.E.

    2006-01-01

    The area of California between the San Francisco Bay, San Pablo Bay, Santa Clara Valley, and the Diablo Ranges (East Bay Hills), commonly referred to as the 'East Bay', contains the East Bay Plain and Niles Cone ground-water basins. The area has a population of 1.46 million (2003 US Census), largely distributed among several cities, including Alameda, Berkeley, Fremont, Hayward, Newark, Oakland, San Leandro, San Lorenzo, and Union City. Major known tectonic structures in the East Bay area include the Hayward Fault and the Diablo Range to the east and a relatively deep sedimentary basin known as the San Leandro Basin beneath the eastern part of the bay. Known active faults, such as the Hayward, Calaveras, and San Andreas pose significant earthquake hazards to the region, and these and related faults also affect ground-water flow in the San Francisco Bay area. Because most of the valley comprising the San Francisco Bay area is covered by Holocene alluvium or water at the surface, our knowledge of the existence and locations of such faults, their potential hazards, and their effects on ground-water flow within the alluvial basins is incomplete. To better understand the subsurface stratigraphy and structures and their effects on ground-water and earthquake hazards, the U.S. Geological Survey (USGS), in cooperation with the East Bay Municipal Utility District (EBMUD), acquired a series of high-resolution seismic reflection and refraction profiles across the East Bay Plain near San Leandro in June 2002. In this report, we present results of the seismic imaging investigations, with emphasis on ground water.

  14. Arrest and recovery of frictional creep on the southern Hayward fault triggered by the 1989 Loma Prieta, California, earthquake and implications for future earthquakes

    NASA Astrophysics Data System (ADS)

    Kanu, Chinaemerem; Johnson, Kaj

    2011-04-01

    Theodolite measurements across the right-lateral Hayward fault, San Francisco Bay, California, show a dramatic reduction in surface creep rate from 5 to 10 mm/yr before the 1989 Loma Prieta earthquake to nearly zero creep rate after the earthquake. A ˜6 year period of nearly zero surface creep was followed by sudden fault creep that accumulated about 20-25 mm of right-lateral displacement followed by an eventual return to a steady creep by year ˜2000. This creep behavior can be explained as a result of a sudden shear stress reduction on the fault and is consistent with model predictions for a fault imbedded in an elastic medium with slip governed by laboratory-derived friction laws. We infer friction parameters on the fault using a spring-slider model and a boundary element model with the rate- and state-dependent friction laws. The state (healing) term in the friction law is critical for reproducing the observed evolution of surface creep; a popular simplified rate-dependent friction law is insufficient. Results suggest that the creep event extended to a depth of ˜4-7.5 km. The inferred critical slip distance, dc, is 1-2 orders of magnitude larger than lab values, and inferred aσ values imply low effective fault-normal stresses of 5-30 MPa. This range of effective normal stress and inversion results for (a - b)σ imply very small values for a - b of 10-5 to 10-3, suggesting the fault has nearly velocity-neutral frictional properties. Earthquake simulations with such small a - b values show that creeping areas on the Hayward fault may be capable of rupturing during earthquakes.

  15. Probable origin of the Livingston Fault Zone

    NASA Astrophysics Data System (ADS)

    Monroe, Watson H.

    1991-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  17. Mantle fault zone beneath Kilauea Volcano, Hawaii.

    PubMed

    Wolfe, Cecily J; Okubo, Paul G; Shearer, Peter M

    2003-04-18

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

  18. Mantle fault zone beneath Kilauea Volcano, Hawaii

    USGS Publications Warehouse

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

    2003-01-01

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

  19. Predicted liquefaction in the greater Oakland area and northern Santa Clara Valley during a repeat of the 1868 Hayward Fault (M6.7-7.0) earthquake

    USGS Publications Warehouse

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

    2010-01-01

    Probabilities of surface manifestations of liquefaction due to a repeat of the 1868 (M6.7-7.0) earthquake on the southern segment of the Hayward Fault were calculated for two areas along the margin of San Francisco Bay, California: greater Oakland and the northern Santa Clara Valley. Liquefaction is predicted to be more common in the greater Oakland area than in the northern Santa Clara Valley owing to the presence of 57 km2 of susceptible sandy artificial fill. Most of the fills were placed into San Francisco Bay during the first half of the 20th century to build military bases, port facilities, and shoreline communities like Alameda and Bay Farm Island. Probabilities of liquefaction in the area underlain by this sandy artificial fill range from 0.2 to ~0.5 for a M7.0 earthquake, and decrease to 0.1 to ~0.4 for a M6.7 earthquake. In the greater Oakland area, liquefaction probabilities generally are less than 0.05 for Holocene alluvial fan deposits, which underlie most of the remaining flat-lying urban area. In the northern Santa Clara Valley for a M7.0 earthquake on the Hayward Fault and an assumed water-table depth of 1.5 m (the historically shallowest water level), liquefaction probabilities range from 0.1 to 0.2 along Coyote and Guadalupe Creeks, but are less than 0.05 elsewhere. For a M6.7 earthquake, probabilities are greater than 0.1 along Coyote Creek but decrease along Guadalupe Creek to less than 0.1. Areas with high probabilities in the Santa Clara Valley are underlain by young Holocene levee deposits along major drainages where liquefaction and lateral spreading occurred during large earthquakes in 1868 and 1906.

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

    NASA Astrophysics Data System (ADS)

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

    2004-02-01

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

  1. Long-term Creep Behavior (1928-2002) of the Hayward Fault at Depth in the Claremont Water Tunnel, Berkeley, CA

    NASA Astrophysics Data System (ADS)

    Cain, W. J.; Hampton, J. L.

    2003-12-01

    The Claremont Tunnel, a nine foot horseshoe shaped water tunnel conveying up to 175 million gallons per day (mgd) of treated drinking water to 800,000 residents on the east side of San Francisco Bay, crosses the Hayward Fault approximately 850 feet from the west portal of the tunnel. Creep along the fault has offset the tunnel at a depth of about 130 feet below the ground surface. Completed in 1928, the tunnel has undergone two inspections (1966 and 2002) in which detailed survey measurements have been made of the creep movements of the fault. There have been few opportunities to secure creep measurements below the ground surface. This paper will present the results of the two surveys showing the creep that has occurred at a depth of 130 feet and give time-based creep rates based on survey measurements. It will compare these measured creep rates with the tectonic creep model developed by NOAA. Due to the large time interval between the two surveys, surveying technology has dramatically changed. A discussion of the techniques used in each survey will be presented with discussions of how current technology compares with historical methods and what impact this has on the results.

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

    SciTech Connect

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

    2009-03-31

    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

  3. Characterising the Alpine Fault Damage Zone using Fault Zone Guided Waves, South Westland, New Zealand

    NASA Astrophysics Data System (ADS)

    Eccles, J. D.; Gulley, A.; Boese, C. M.; Malin, P. E.; Townend, J.; Thurber, C. H.; Guo, B.; Sutherland, R.

    2015-12-01

    Fault Zone Guided Waves (FZGWs) are observed within New Zealand's transpressional continental plate boundary, the Alpine Fault, which is late in its typical seismic cycle. Distinctive dispersive seismic coda waves (~7-35 Hz), trapped within the low-velocity fault damage zone, have been recorded on three component 2 Hz borehole seismometers installed within 20 m of the principal slip zone in the shallow (< 150 m deep) DFDP-1 boreholes. Near the central Alpine Fault, known for low background seismicity, FZGW-generating microseismic events are located beyond the catchment-scale strike-slip and thrust segment partitioning of the fault indicating lateral connectivity of the low-velocity zone immediately below the near-surface segmentation. Double-difference earthquake relocation of events using the dense SAMBA and WIZARD seismometer arrays allows spatio-temporal patterns of 2013 events to be analysed and the segmentation and low velocity zone depth extent further explored. Three layer, dispersion modeling of the low-velocity zone indicates a waveguide width of 60-200 m with a 10-40% reduction in S-wave velocity, similar to that inferred for the fault core of other mature plate boundary faults such as the San Andreas and North Anatolian Faults.

  4. Caldecott 4th bore tunnel project: influence of ground water flows and inflows triggered by tectonic fault zones?

    NASA Astrophysics Data System (ADS)

    Neuhuber, G.; G. Neuhuber1, W. Klary1, A. Nitschke1, B. Thapa2, Chris Risden3, T. Crampton4, D. Zerga5

    2011-12-01

    The 4th Bore is a highway tunnel on California State Route 24 currently under construction. The 4th Bore is undertaken by the California State Department of Transportation (CALTRANS) and the Contra Costa County Transportation Commission (CCTC) to alleviate traffic congestion on SR24 connecting the cities of Oakland and Orinda in the San Francisco East Bay Area. The cost for the 4th Bore is estimated at $ 390.8 Mill. The 3,249 ft long 4th Bore tunnel will have excavated dimensions of approximately 40 ft height and 49 ft width. A total of 7 cross passages will run between the 3rd and the new 4th bore. Geology and Hydrogeology: The project is located in the Oakland Berkeley Hills of the SF Bay Area. The Caldecott Tunnels lie within the easterly assemblage of the Hayward fault zone province which consists of a sequence of sedimentary and volcanic rocks that accumulated in the interval between about 16 and 8.4 Ma (Miocene). The basal rocks of these Tertiary deposits consist of deep marine basin sediments of the Monterey Group. These rocks are overlain uncomfortably by an interbedded sequence of terrestrial sediments (Orinda Formation) and volcanic rocks (Moraga Formation). The Tertiary rocks have been folded into large amplitude, NW trending folds that are cut by N trending strike and slip faults. The SF Bay Region, which is crossed by 4 major faults (San Gregorio, San Andreas, Hayward, and Calaveras), is considered one of the more seismically active regions of the world. The active Hayward fault lies 0.9mi to the west of the Caldecott Tunnels and is the closest major fault to the project area. The tunnel is at the moment under top heading construction: West Portal (360ft) and East Portal (1,968.5ft). While major faults typically influence groundwater flow, characterization of such influences is extremely difficult because of the heterogeneity of the hydraulic systems and the different lithological parameters and influences. Four major inactive fault zones striking

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  6. Examining Communities at Risk: Physical and Socioeconomic Impacts of an Earthquake Scenario on the Hayward Fault (The HayWired Scenario)

    NASA Astrophysics Data System (ADS)

    Dinitz, L.; Wein, A. M.; Johnson, L. A.; Jones, J. L.

    2015-12-01

    This research led by the U.S. Geological Survey aims to inform and stimulate the development of plans and policies in disaster management and hazard mitigation that will help improve the capacity of residents, businesses and communities to rebound from disasters. As was evidenced in the 1994 Northridge earthquake, "ghost towns" emerged in neighborhoods with high concentrations of damaged rental housing. Also, rental properties that served predominantly lower income households had more difficulty financing repairs which led to blight and other long-term community recovery challenges. Our approach is to develop a framework for identifying and spatially analyzing communities at risk of long-term displacement and recovery challenges for an earthquake scenario. The HayWired scenario postulates a M7.05 earthquake on the Hayward Fault in the San Francisco Bay Area with surface fault rupture, liquefaction, landslides, and fires, as well as subsequent aftershocks. The analytical framework relies on the literature and prior disaster experience to identify and systematically combine physical and socioeconomic impacts of the earthquake sequence with pre-existing socioeconomic conditions to identify areas where housing and building damage, lifeline service disruption, and socioeconomic challenges intersect and can potentially lead to long-term displacements of people, businesses, and jobs. Hazus analyses estimate $46 billion in building damage from the HayWired main shock, which increases by 10-25% due to aftershocks. Heavy damage to large apartment buildings exceeds many other housing types, and preliminary analyses identify neighborhoods where these damage concentrations also intersect with concentrations of low income households. Also, in some counties, the estimated population displaced from severely damaged housing far exceeds the number of vacant housing units, which means residents may be forced to move well away from former neighborhoods and even outside the region

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  8. The 1868 Hayward Earthquake Alliance: A Case Study - Using an Earthquake Anniversary to Promote Earthquake Preparedness

    NASA Astrophysics Data System (ADS)

    Brocher, T. M.; Garcia, S.; Aagaard, B. T.; Boatwright, J. J.; Dawson, T.; Hellweg, M.; Knudsen, K. L.; Perkins, J.; Schwartz, D. P.; Stoffer, P. W.; Zoback, M.

    2008-12-01

    Last October 21st marked the 140th anniversary of the M6.8 1868 Hayward Earthquake, the last damaging earthquake on the southern Hayward Fault. This anniversary was used to help publicize the seismic hazards associated with the fault because: (1) the past five such earthquakes on the Hayward Fault occurred about 140 years apart on average, and (2) the Hayward-Rodgers Creek Fault system is the most likely (with a 31 percent probability) fault in the Bay Area to produce a M6.7 or greater earthquake in the next 30 years. To promote earthquake awareness and preparedness, over 140 public and private agencies and companies and many individual joined the public-private nonprofit 1868 Hayward Earthquake Alliance (1868alliance.org). The Alliance sponsored many activities including a public commemoration at Mission San Jose in Fremont, which survived the 1868 earthquake. This event was followed by an earthquake drill at Bay Area schools involving more than 70,000 students. The anniversary prompted the Silver Sentinel, an earthquake response exercise based on the scenario of an earthquake on the Hayward Fault conducted by Bay Area County Offices of Emergency Services. 60 other public and private agencies also participated in this exercise. The California Seismic Safety Commission and KPIX (CBS affiliate) produced professional videos designed forschool classrooms promoting Drop, Cover, and Hold On. Starting in October 2007, the Alliance and the U.S. Geological Survey held a sequence of press conferences to announce the release of new research on the Hayward Fault as well as new loss estimates for a Hayward Fault earthquake. These included: (1) a ShakeMap for the 1868 Hayward earthquake, (2) a report by the U. S. Bureau of Labor Statistics forecasting the number of employees, employers, and wages predicted to be within areas most strongly shaken by a Hayward Fault earthquake, (3) new estimates of the losses associated with a Hayward Fault earthquake, (4) new ground motion

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

    NASA Astrophysics Data System (ADS)

    Reyer, Dorothea; Philipp, Sonja L.

    2010-05-01

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

  10. Anisotropy of Resisitiviy Distributions and Fault Rock Microstructures in Fault Zones -Two Case Studies of Hatagawa and Atotsugawa Fault, Japan-

    NASA Astrophysics Data System (ADS)

    Omura, K.

    2015-12-01

    Structure and physical characteristics in a fault zone are not homogeneous. The inhomogeneity should be related to earthquake generation mechanism. However, main features of the inhomogeneity in fault zones are not yet sufficiently understood. It is considered to be effective to compare geophysical data of geophysical survey and/or downhole logging with physical properties, microstructures and mineral compositions of fault rocks in the fault zone. In this presentation, results of the comparisons are introduced in the case of two fault zones; Hatagawa and Atotsugawa fault, in north-east and central Japan, respectively, and factors affecting the inhomogeneity of fault structure are suggested.Anisotropic resistivity measurements in laboratory were compared with microscopic observations of fault rocks recovered from outcrops of Hatagawa fault. In the case of Atotsugawa fault, the anisotropic resistivity profiles by physical survey across the fault zones were compared with microscopic observations and mineral composition analysis of fault rocks provided by drilling into the fault zone. As a result, the anisotropic resistivity profiles are strongly related to foliation structure of fault rocks. It is suggested that fault slip at the earthquake and shear deformation during the earthquake recurrence time develope foliation fabrics of fault rocks, and that the resistivity profile becomes anisotropic progressively in the fault zone.

  11. The Bocono Fault Zone, Western Venezuela

    SciTech Connect

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

    1993-02-01

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

  12. Fault zone roughness controls slip stability

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  14. Liquefaction Scenarios in the Northern Santa Clara Valley for a Repeat of the 1868 Hayward Fault (M6.7-7.0) Earthquake

    NASA Astrophysics Data System (ADS)

    Holzer, T. L.; Noce, T. E.; Bennett, M. J.

    2007-12-01

    The spatial distribution of the probability of liquefaction in the northern Santa Clara Valley, California, was predicted for a repeat of an earthquake like the 1868 Hayward Fault (M6.7-7.0) earthquake. Probabilities were computed with the methodology for probabilistic liquefaction hazard mapping that was developed by Holzer and others (USGS OFR 02-296, 2006). The methodology relies on field-based plots of cumulative frequency of the liquefaction potential index (LPI) for spatially homogenous surficial geologic units. LPI, which is a scalar parameter that integrates the liquefaction potential of the entire soil column, was computed for 164 seismic cone penetration tests (SCPT) that were conducted in Holocene and Pleistocene geologic units. The plots of cumulative frequency were used to estimate the liquefaction probability distribution for each surficial geologic unit given peak ground acceleration (PGA) and earthquake magnitude. Scenario maps were produced with ArcGIS Model Builder. PGA at each node in a 50-m grid was estimated with the new attenuation relation proposed by Boore and Atkinson (2007, v. 3.04). Regional averages of VS30 values, which were based on the SCPT, were used to account for local site amplification. The probability of liquefaction was estimated at each node using the liquefaction probability distribution appropriate for the surficial geology at the node. For a M7 earthquake and an assumed water-table depth of 1.5 m in the central part of the valley, liquefaction probabilities range from 0.1 to 0.2 along Coyote and Guadalupe Creeks, but are less than 0.05 elsewhere. For an M6.7 earthquake, probabilities remain greater than 0.1 along Coyote Creek but decrease along Guadalupe Creek to less than 0.1. For assumed water-table depths greater than 5 m, liquefaction probabilities are less than 0.05 throughout the valley. The probability of lateral spreading is less than 0.05 throughout the valley for both water table depths and both earthquakes

  15. QUANTIFYING UNCERTAINTIES IN GROUND MOTION SIMULATIONS FOR SCENARIO EARTHQUAKES ON THE HAYWARD-RODGERS CREEK FAULT SYSTEM USING THE USGS 3D VELOCITY MODEL AND REALISTIC PSEUDODYNAMIC RUPTURE MODELS

    SciTech Connect

    Rodgers, A; Xie, X

    2008-01-09

    This project seeks to compute ground motions for large (M>6.5) scenario earthquakes on the Hayward Fault using realistic pseudodynamic ruptures, the USGS three-dimensional (3D) velocity model and anelastic finite difference simulations on parallel computers. We will attempt to bound ground motions by performing simulations with suites of stochastic rupture models for a given scenario on a given fault segment. The outcome of this effort will provide the average, spread and range of ground motions that can be expected from likely large earthquake scenarios. The resulting ground motions will be based on first-principles calculations and include the effects of slip heterogeneity, fault geometry and directivity, however, they will be band-limited to relatively low-frequency (< 1 Hz).

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

    SciTech Connect

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

    1993-04-01

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

  17. High-resolution imaging of earthquake rupture process for Hayward microearthquakes

    NASA Astrophysics Data System (ADS)

    Taira, Taka'aki; Dreger, Douglas; Nadeau, Robert

    2014-05-01

    The Hayward fault (HF) in the San Francisco Bay Area is one of the major strands of the San Andreas fault system, extending for about 70 km. Crustal deformation along the HF is characterized by a wide variety of fault slip behaviors from aseismic creep to stick-slip earthquake including a Mw~6.8 earthquake in 1868. The high stress drop earthquakes have been observed near a geodetically-imaged locked zone that might be responsible for past and future M > 6.7 HF earthquakes, which suggests the stronger fault zone material associated with this locked zone. To further explore the spatial heterogeneities of stress drop, we determine finite-fault rupture models for Hayward microearthquakes (3 < M < 4) by using an empirical Green's function approach (Mori & Hartzell, 1990, BSSA). We make use of high-quality borehole seismograms from the Hayward Fault Network (HFN). The HFN is an array of borehole instrumentation deployed along the HF, with the aim of improving monitoring of spatial and temporal evolution of microseismicity. The stations are typically equipped with three-component geophones and accelerometers at a depth of 30-200 m. The HFN was initially deployed with 10 borehole stations in 1995-1996, and the 20 stations are currently in operation. Recently two borehole sites were installed by the Plate Boundary Observatory, which improves the azimuthal coverage for the finite-fault modeling. Our analysis finds a variety of slip distributions from the Hayward microearthquakes that includes multiple subevents, strong directivity, and high stress drop. One of the high stress drop earthquakes is the 2011 Mw 4.0 Berkeley event. The location of this event is about 5 km distance from the geodetically-imaged locked zone. The estimated peak stress drop is about 150 MPa while the stress drop averaged over the asperity is about 30 MPa. Our result indicates the strong small patch with the rupture area that is able to sustain shear stress up to the order of 100 MPa.

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

    USGS Publications Warehouse

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

    1996-01-01

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

  19. Earthquake ruptures modulated by waves in damaged fault zones

    NASA Astrophysics Data System (ADS)

    Huang, Yihe; Ampuero, Jean-Paul; Helmberger, Don V.

    2014-04-01

    Faults are usually surrounded by damaged zones of lower elastic moduli and seismic wave velocities than their host rocks. If the interface between the damaged rocks and host rocks is sharp enough, earthquakes happening inside the fault zone generate reflected waves and head waves, which can interact with earthquake ruptures and modulate rupture properties such as rupture speed, slip rate, and rise time. We find through 2-D dynamic rupture simulations the following: (1) Reflected waves can induce multiple slip pulses. The rise time of the primary pulse is controlled by fault zone properties, rather than by frictional properties. (2) Head waves can cause oscillations of rupture speed and, in a certain range of fault zone widths, a permanent transition to supershear rupture with speeds that would be unstable in homogeneous media. (3) Large attenuation smears the slip rate function and delays the initial acceleration of rupture speed but does not affect significantly the rise time or the period of rupture speed oscillations. (4) Fault zones cause a rotation of the background stress field and can induce plastic deformations on both extensional and compressional sides of the fault. The plastic deformations are accumulated both inside and outside the fault zone, which indicates a correlation between fault zone development and repeating ruptures. Spatially periodic patterns of plastic deformations are formed due to oscillating rupture speed, which may leave a permanent signature in the geological record. Our results indicate that damaged fault zones with sharp boundaries promote multiple slip pulses and supershear ruptures.

  20. The width of fault zones in a brittle-viscous lithosphere: Strike-slip faults

    NASA Technical Reports Server (NTRS)

    Parmentier, E. M.

    1991-01-01

    A fault zone in an ideal brittle material overlying a very weak substrate could, in principle, consist of a single slip surface. Real fault zones have a finite width consisting of a number of nearly parallel slip surfaces on which deformation is distributed. The hypothesis that the finite width of fault zones reflects stresses due to quasistatic flow in the ductile substrate of a brittle surface layer is explored. Because of the simplicity of theory and observations, strike-slip faults are examined first, but the analysis can be extended to normal and thrust faulting.

  1. Spatiotemporal evolution of a fault shear stress patch due to viscoelastic interseismic fault zone rheology

    NASA Astrophysics Data System (ADS)

    Sone, Hiroki; Uchide, Takahiko

    2016-08-01

    We conducted numerical studies to explore how shear stress anomalies on fault planes (shear stress patches) evolve spatiotemporally during the interseismic period under the influence of viscoelastic rheology assigned to fault zones of finite thickness. 2-D viscoelastic models consisting of a fault zone and host rock were sheared to simulate shear stress accumulation along fault zones due to tectonic loading. No fault slip along a distinct fault planes is implied in the model, thus all fault shear motion is accommodated by distributed deformation in the viscoelastic fault zone. Results show that magnitudes of shear stress patches evolve not only temporally, but also spatially, especially when the stress anomaly is created by a geometrical irregularity (asperity) along the interface of an elastic host rock and viscoelastic fault zone. Such shear stress anomalies diffuse spatially so that the spatial dimension of the shear stress patch appears to grow over time. Models with varying fault zone viscoelastic properties and varying fault zone viscosity both show that such spatial diffusion of shear stress is enhanced by increasing the contribution of the viscous behavior. The absolute rate at which shear stress patches grow spatially is generally not influenced by the size of the shear stress patch. Therefore shear stress patches with smaller dimensions will appear to grow quicker, in the relative sense, compared to larger stress patches. These results suggest that the minimum dimensions of shear stress patches that can exist along a fault could be governed by the effective viscosity of the fault zone. Therefore patterns of accumulated shear stress could vary along faults when viscous properties are heterogeneous, for instance due to depth or material heterogeneity, which has implications on how earthquake rupture behavior could vary along faults.

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  4. Characteristics of faults and shear zones in deep mines

    USGS Publications Warehouse

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

    1986-01-01

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

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

    PubMed

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

    2014-12-12

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

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

    USGS Publications Warehouse

    Sharp, R.V.

    1989-01-01

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

  7. Development of Hydrologic Characterization Technology of Fault Zones

    SciTech Connect

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

    2008-03-31

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

  8. 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

    USGS Publications Warehouse

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

    2013-01-01

    extensional stresses on built structures within the fault zone. Such differential movement and resulting distortion of built structures appear to have occurred between fault traces at the gatewell near the southern end of San Andreas Lake during the 1906 San Francisco earthquake (Schussler, 1906). In addition to the three fault traces within the main 1906 surface rupture zone, our data indicate at least one additional fault trace (or zone) about 80 meters northeast of the main 1906 surface rupture zone. Because ground shaking also can damage structures, we used fault-zone guided waves to investigate ground shaking within the fault zones relative to ground shaking outside the fault zones. Peak ground velocity (PGV) measurements from our guided-wave study indicate that ground shaking is greater at each of the surface fault traces, varying with the frequency of the seismic data and the wave type (P versus S). S-wave PGV increases by as much as 5–6 times at the fault traces relative to areas outside the fault zone, and P-wave PGV increases by as much as 3–10 times. Assuming shaking increases linearly with increasing earthquake magnitude, these data suggest strong shaking may pose a significant hazard to built structures that extend across the fault traces. Similarly complex fault structures likely underlie other strike-slip faults (such as the Hayward, Calaveras, and Silver Creek Faults) that intersect structures of the water delivery system, and these fault structures similarly should be investigated.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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. The effects of lateral property variations on fault-zone reactivation by fluid pressurization: Application to CO2 pressurization effects within major and undetected fault zones

    NASA Astrophysics Data System (ADS)

    Jeanne, Pierre; Guglielmi, Yves; Cappa, Frédéric; Rinaldi, Antonio P.; Rutqvist, Jonny

    2014-05-01

    In this study, we performed in situ multidisciplinary analyses of two different fault zones in carbonate formations. One is a seismically active fault zone several kilometers long (the Roccasseira Fault Zone); the other is a small fault zone a few hundred meters long (the GAS Fault Zone). The smaller, "immature" fault zone displays a discontinuous damage zone, because tectonic deformations have been accommodated differently according to the initial properties of the host rock. The larger, "mature" fault zone displays a continuous damage zone caused by the presence of secondary fault cores embedded in a heavily fractured area inside the damage zone. These markedly different fault-zone architectures were reflected in two hydraulic and geomechanical fault models, both generated from a coupled fluid-flow and geomechanical simulator, to examine the impact of hydromechanical property distribution on fault stability when the faults are reactivated by CO2 injection. In the smaller fault zone, marked differences in hydromechanical properties (Young's modulus and permeability) favor fluid accumulation, inducing high pressurization in parts of the damage zone, potentially resulting in small seismic events. On the other hand in the mature fault zone, fluid flows more easily and thus fluid-induced earthquakes may not readily occur, because the fault-zone pressurization is much lower, insufficient for triggering a seismic event.

  11. Seismic measurements of the internal properties of fault zones

    USGS Publications Warehouse

    Mooney, W.D.; Ginzburg, A.

    1986-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Choi, J.; Kim, Y.

    2013-12-01

    Surface ruptures associated with earthquake faulting commonly comprise a number of segments, and the discontinuities form tip and linking damage zones, which are deformed regions consisting of secondary features. Stress transferring or releasing, when seismic waves pass through the discontinuities, could produce different slip features depending on rupture propagation or termination. Thus, slip patterns at fault damage zones can be one of the key factors to understand fault kinematics, fault evolution and, hence, earthquake hazard. In some previous studies (e.g. Peacock and Sanderson, 1991; Kim and Sanderson, 2005), slip distribution along faults to understand the connectivity or maturity of segmented faults system have commonly been analyzed based on only the main slip components (dip-slip or strike-slip). Secondary slip components, however, are sometimes dominant at fault damage zones, such as linkage and tip zones. In this study, therefore, we examine slip changes between both main and secondary slip components along unilaterally propagated coseismic strike-slip ruptures. Horizontal and vertical components of slip and the slip compensation patterns at tip and linking damage zones are various from slip deficit (decrease in both slip components) through slip compensation (increase of vertical slip with horizontal slip decrease) to slip neutral. Front and back tip zones, which are classified depending on main propagation direction of earthquake ruptures, show different slip patterns; slip compensation is observed at the frontal tip whilst slip deficit occurs at the back tip zone. Average values of the two slip components and their compensative patterns at linking damage zones are closely related with the ratio of length to width (L/W) of linkage geometry; the horizontal slip is proportional to the ratio of L/W, whilst the vertical slip shows little dependence on the value L/W. When the L/W is greater than ~2, average values of two slip components are almost similar

  13. Continuity of the West Napa Fault Zone Inferred from Aftershock Recordings on Fault-Crossing Arrays

    NASA Astrophysics Data System (ADS)

    Catchings, R.; Goldman, M.; Slad, G. W.; Criley, C.; Chan, J. H.; Fay, R. P.; Fay, W.; Svitek, J. F.

    2014-12-01

    In an attempt to determine the continuity and lateral extent of the causative fault(s) of the 24 August 2014 Mw 6.0 Napa earthquake and possible interconnections with other mapped faults, we recorded aftershocks on three closely spaced (100 m) seismograph arrays that were positioned across the coseismic rupture zone and across mapped faults located north and south of coseismic rupture. Array 1 was located in northwest Napa, between Highway 29 and the intersection of Redwood and Mt. Veeder roads, array 2 was located southwest of Napa, ~1 km north of Cuttings Wharf, and array 3 was located south of San Pablo Bay, within the town of Alhambra. Our intent was to record high-amplitude guided waves that only travel within the causative fault zone and its extensions (Li and Vidale, 1996). Preliminary analysis of seismic data from an M 3.2 aftershock shows high-amplitude (up to 1 cm/s) seismic waves occurred on seismographs within 100 m of mapped surface ruptures and fault zones. Northwest of Napa, the high amplitudes along array 1 coincide with zones of structural damage and wide spread surface ground cracking, and along array 2 near Cuttings Wharf, the high amplitudes occur slightly east of surface ruptures seen along Los Amigas Road. We also observe relatively high-amplitude seismic waves across the Franklin Fault (array 3), approximately 32 km southeast of the mainshock epicenter; this observation suggests the West Napa and the Franklin faults may be continuous or connected. Existing fault maps show that the Franklin Fault extends at least 15 km southward to the Calaveras Fault zone and the West Napa Fault extends at least 25 km north of our array 1. Collectively, the mapped faults, surface ruptures, and guided waves suggest that the West Napa- Franklin Fault zone may extend more than 85 km before it merges with the Calaveras Fault. Assuming a continuous fault zone, the West Napa - Franklin Fault zone may be capable of generating a much larger magnitude earthquake that

  14. The deep structure of the North Anatolian Fault Zone

    NASA Astrophysics Data System (ADS)

    Fichtner, Andreas; Saygin, Erdinc; Taymaz, Tuncay; Cupillard, Paul; Capdeville, Yann; Trampert, Jeannot

    2013-07-01

    Multi-scale full waveform inversion of complete continental- and regional-scale seismograms reveals the crustal and upper-mantle signature of the North Anatolian Fault Zone which shapes the neotectonics of Turkey and the eastern Mediterranean. Within the crust, the fault zone is mostly bounded by several high-velocity blocks, suggesting that it developed along the edges of continental fragments with high rigidity. Below the crust, the surface expression of the eastern and central parts of the North Anatolian Fault Zone correlate with a pronounced low-velocity band that extends laterally over 600 km. Around 100 km depth, the low-velocity band merges into the shallow Anatolian asthenosphere, thereby providing a link to the Kırka-Afyon-Isparta Volcanic Field and the Central Anatolian Volcanics. We interpret the low-velocity band beneath the North Anatolian Fault Zone as the upper-mantle expression of the Tethyan sutures that formed 60-15 Ma ago as a result of Africa-Eurasian convergence. The structurally weak suture facilitated the formation of the younger (less than 10 Ma) crustal fault zone. In this sense, the North Anatolian Fault Zone is not only a crustal feature, but a narrow zone of weakness that extends into the upper mantle.

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

    USGS Publications Warehouse

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

    2015-01-01

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

  16. Fault-Zone Maturity Defines Maximum Earthquake Magnitude

    NASA Astrophysics Data System (ADS)

    Bohnhoff, M.; Bulut, F.; Stierle, E.; Ben-Zion, Y.

    2014-12-01

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

  17. Kinematics at Death Valley-Garlock fault zone junction

    SciTech Connect

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

    1987-08-01

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

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

    NASA Astrophysics Data System (ADS)

    Lambert, Valere; Barbot, Sylvain

    2016-04-01

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

  19. Imaging Faults and Shear Zones Using Receiver Functions

    NASA Astrophysics Data System (ADS)

    Schulte-Pelkum, Vera; Mahan, Kevin H.

    2014-11-01

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

  20. Some Recent Laboratory Measurements of Fault Zone Permeability

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

    The permeability of fault zone material is key to understanding fluid circulation and the role of pore fluids in earthquake generation and rupture dynamics. Permeability results of core samples from several scientific drillholes are presented, including new results from the SAFOD drillsite in California and the Chelungpu Fault in Taiwan. Permeability values at simulated in situ pressures range from 10-18 to 10-23 m2, a broad range reflecting differences in rock type, proximity to the fault (i.e., fault core, damage zone or country rock), and degree of interseismic healing and sealing. In addition to these natural characteristics, stress-relief and thermal cracking damage resulting from core retrieval will tend to increase the permeability of some of the deepest crystalline rock samples, although testing under in situ conditions can reduce these errors. Recently active fault rocks, with an interconnected network of fractures, tend toward the higher end of the permeability range, whereas fault rocks that have had time to heal through hydrothermal processes tend to have lower permeabilities. In addition, the permeability of borehole-derived core samples was found to be more sensitive to applied pressure than equivalent rocks obtained from surface outcrops because of weathering and other processes. Thus, permeability values of surface samples can not be adequately extrapolated to depth, highlighting the importance of deep drilling studies in determining in situ transport properties. Permeability studies also reveal the storage capacity of the fault rocks, an important parameter in the determination of excess fluid pressure potential. Storage capacity was found to be 10-10 to 10-11/Pa in the Chelungpu Fault cores. Typical down-hole permeability measurements are generally 1-2 orders of magnitude higher than laboratory-derived values because they sample joints and fractures in the damage zone that are larger in scale than the core samples. Consequently, most fluid flow at

  1. The internal structure of fault zones in basaltic sequences

    NASA Astrophysics Data System (ADS)

    Holland, M.; Urai, J. L.; Martel, S.

    2005-12-01

    In contrary to most sedimentary rocks that need burial for consolidation, effusive basalts solidify quickly thus imposing a different mechanical behavior at the surface. Extensional stresses due to gravitational failure, caldera collapse or general tectonic forces generate prominent morphologies and large dilatant structures with impacts for hydraulic, mechanical and also bionomic aspects. In this study we present insights of field work on the Koa`e fault zone on Kilauea volcano/Hawai`i combined with the analysis of a scaled analogue model of normal faults in cohesive sequences. The Koa`e fault zone is a 12 km long normal fault zone connecting sections of the two rift zones. Unlike the predominantly mode-I cracks of the rift zones, the Koa`e faults show up to 20 m high sub-vertical fault scarps accompanied with footwall fissures. Open fractures, broken or buckled ramp structures and sub-vertical walls are the key elements in what is considered to be a volcanic growth fault system. Our analogue model visualizes the deformation of brittle flow units on top of a buried fault. The model uses dry hemihydrate powder with a tensional strength of 33 Pa, and a curved yield envelope. Depending on the rock prototype a scaling relationship of 1:5000-40000 is apparent. The faults initiate as sub-vertical mode-I fissuring at the surface propagating downward. Some of the open fissures on the footwall are deactivated; others evolve into faults producing the morphological scarps. A shallow antithetic fracture decouples a surface slap on the hanging wall producing the morphological ramps seen in the field. Its rotation is responsible for cavities and buckling. The internal structure of the shallow faults is open and filled partly with collapsing wall fragments that are progressively milled down at deeper levels. The model implies that normal faults in basalt are largely dilatant systems with a prominent mode-I component up to several meters magnitude. If the insights of the work are

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

    NASA Astrophysics Data System (ADS)

    Peacock, D. C. P.

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

  3. Independent seismic evaluation of the 24-580-980 south connector ramps response to the south connector ramps to a magnitude 7.25 Hayward Fault earthquake. Volume 3

    SciTech Connect

    McCallen, D. B.; Gerhard, M. A.; Trummer, D. J.; Murray, R. C.

    1996-11-01

    The 24/580/980 interchange is located near Oakland California on the Eastern perimeter of the San Francisco Bay (Fig. 1 and Fig. 2). This interchange is a major artery in the Eastern San Francisco Bay area and provides a critical link between major bay area highways. The main Concord line of the Bay Area Rapid Transit System (BART), with ridership of approximately 270,000 per day, runs underneath the interchange. The interchange site is approximately 4 Km from the Hayward fault and 16 Km from the San Andreas fault. The reinforced concrete interchange was designed and constructed in the mid 1960`s and thus the asphalt structure has many of the vulnerabilities associated with typical pre-1970`s concrete structures (Roberts [1], Zefinski [2], Chai et. al. [3], Priestly and Seible [4]). In 1980 some of the seismic vulnerabilities were addressed as the interchange was retrofit with deck hinge restrainers as part of the California Department of Transportation (Caltrans) state-wide seismic retrofit of bridge expansion joints. The interchange was subjected to earthquake motion during the 1989 Loma Prieta earthquake and sustained minor damage in some of the concrete diaphragms which support the hinge restrainer forces [5]. Caltrans engineers, working together with their external consultants Imbsen and Associates, have recently completed a seismic retrofit design for portions of the interchange. The retrofit is primarily intended to fix inadequacies in many of the 1960`s vintage reinforced concrete elements which constitute the bridge superstructure and foundations.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  5. Internal Structure of Taiwan Chelungpu Fault Zone Gouges

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

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

    PubMed

    Berquist Jr; Bailey

    1999-11-01

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

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

    PubMed

    Berquist Jr; Bailey

    1999-11-01

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

  8. Late Quaternary Faulting along the San Juan de los Planes Fault Zone, Baja California Sur, Mexico

    NASA Astrophysics Data System (ADS)

    Busch, M. M.; Coyan, J. A.; Arrowsmith, J.; Maloney, S. J.; Gutierrez, G.; Umhoefer, P. J.

    2007-12-01

    As a result of continued distributed deformation in the Gulf Extensional Province along an oblique-divergent plate margin, active normal faulting is well manifest in southeastern Baja California. By characterizing normal-fault related deformation along the San Juan de los Planes fault zone (SJPFZ) southwest of La Paz, Baja California Sur we contribute to understanding the patterns and rates of faulting along the southwest gulf-margin fault system. The geometry, history, and rate of faulting provide constraints on the relative significance of gulf-margin deformation as compared to axial system deformation. The SJPFZ is a major north-trending structure in the southern Baja margin along which we focused our field efforts. These investigations included: a detailed strip map of the active fault zone, including delineation of active scarp traces and geomorphic surfaces on the hanging wall and footwall; fault scarp profiles; analysis of bedrock structures to better understand how the pattern and rate of strain varied during the development of this fault zone; and a gravity survey across the San Juan de los Planes basin to determine basin geometry and fault behavior. The map covers a N-S swath from the Gulf of California in the north to San Antonio in the south, an area ~45km long and ~1-4km wide. Bedrock along the SJPFZ varies from Cretaceous Las Cruces Granite in the north to Cretaceous Buena Mujer Tonalite in the south and is scarred by shear zones and brittle faults. The active scarp-forming fault juxtaposes bedrock in the footwall against Late Quaternary sandstone-conglomerate. This ~20m wide zone is highly fractured bedrock infused with carbonate. The northern ~12km of the SJPFZ, trending 200°, preserves discontinuous scarps 1-2km long and 1-3m high in Quaternary units. The scarps are separated by stretches of bedrock embayed by hundreds of meters-wide tongues of Quaternary sandstone-conglomerate, implying low Quaternary slip rate. Further south, ~2 km north of the

  9. Complex Faulting within the New Madrid Seismic Zone

    NASA Astrophysics Data System (ADS)

    Deshon, H. R.; Powell, C. A.; Magnani, M.; Bisrat, S. T.

    2010-12-01

    Relative relocations derived using double-difference tomography techniques reveal a complex sequence of faulting within the New Madrid Seismic Zone (NMSZ) and upper Mississippi Embayment. The majority of NMSZ seismicity recorded over the last 30 years occurs along four limbs: 1) a NE-SW trending dextral strike-slip fault, termed the Axial fault, coincident with the central valley of the Cambrian Reelfoot Rift system; 2) the SE-NW trending Reelfoot thrust fault; 3) a E-W trending left lateral strike-slip fault extending off of the northern terminus of the Reelfoot fault, here termed New Madrid west; and 4) a NE-SW dextral strike-slip fault also extending off of the northern terminus of the Reelfoot fault, here termed New Madrid north. Each of these segments is thought to have ruptured during the 1811-1812 large earthquake sequence. A fifth segment, the Bootheel lineament, is marked by 1811-1812 related liquefaction features but appears largely aseismic, though we suggest there are at least five events in the catalog associated with this feature. Geological and geophysical evidence across the embayment suggests that the region is crossed by additional faults at shallow depths (<1-2 km), while seismicity is generally confined to the 3-20 km depth range. Here we present relative relocations derived using catalog and waveform cross-correlation differential times of the 1989-1992 local PANDA network and the 1995-2010 Cooperative New Madrid Seismic Network. We show that the four known seismic lineations exhibit internal complexity. For example, New Madrid north is composed of two parallel faults rather then a single fault, and seismicity associated with the Axial lineation exhibits temporal changes along strike and becomes spatially more diffuse south of the Axial fault/Bootheel lineament intersection. Seismicity along the southern Reelfoot fault does not define a dipping plane consistent with thrust faulting, unlike the northern Reelfoot fault, and is associated with

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

    USGS Publications Warehouse

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

    1996-01-01

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

  11. Geophysical investigation of the Hockai Fault Zone, Eastern Belgium

    NASA Astrophysics Data System (ADS)

    Havenith, Hans-Balder; Nguyen, Frédéric; Halleux, Lucien; Hölz, Sebastian; Camelbeeck, Thierry

    2015-04-01

    In the frame of a regional project evaluating the geothermal potential of the Wallonian Region of Belgium, the Hockai Fault Zone has been identified as one of the most interesting targets. It is a seismically active fault zone that hosted the largest historical earthquake in Northwestern Europe, the M6-6.5 Verviers event in 1692 as well as a swarm of small earthquakes that was recorded in 1989-90. On the surface, the presence of the fault zones is marked by a series of geomorphic features, such as several landslides near the borders in the northern part, repeated NW-SE oriented scarps all along the Eastern border (over a distance of 40 km), river diversions and captures with formation of paleo-valleys. Along the most prominent paleo-valley, the Paleo-Warche Valley crossing the fault zone over a distance of 5 km, a geophysical survey has been organized by several teams to better characterize the shallow (<150 m) subsurface of the fault zone. It included electro-magnetic sounding (frequency-based and TEM), shallow seismics (refraction, walk-away, surface waves analysis), electrical resistivity tomography as well as ambient noise recordings. To support an integrated interpretation of all geophysical results in combination with geomorphic and seismo-tectonic aspects, surface morphology, soundings and profiles were represented in a 3D model. This model clearly reveals low-resistivity and low-velocity zones near the Eastern border of the fault zone, vertically above the hypocenters of the 1989-90 earthquake swarm. Across the structure, low-resistivity zones have a limited extent while they are repeatedly identified all along Eastern border.

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

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

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

  13. Damage, permeability and sealing processes of an exhumed seismic fault zone; The Gole Larghe Fault Zone, Italian Alps

    NASA Astrophysics Data System (ADS)

    Mitchell, Thomas; Rempe, Marieke; Smith, Steven; Renner, Joerg; Di Toro, Giulio

    2013-04-01

    The Gole Larghe Fault Zone (GLFZ) in the Italian Southern Alps has been extensively studied as a natural laboratory for seismic faulting. Ancient seismicity is attested by the widespread occurrence of cataclasites associated with pseudotachylytes (solidified frictional melts) formed at 9 - 11 km depth in tonalite host rock at ambient temperatures of 250 - 300° C. Here we sythesise systematic meso- and micro-structural data with permeability and ultrasonic velocity laboratory measurements from samples collected along fault transects, in order to define the damage structure, fluid flow properties and sealing history of a seismogenic source in the crystalline basement. The GLFZ (~600m wide) and surrounding tonalite wall rocks have a broadly symmetric damage structure and can be divided in to five distinct zones, distinguished by large variations in fracture density, distribution of pseudotachylyte, volume of fault rock materials, and microfracture sealing characteristics. The ~80 m wide central zone has pervasive fracture damage in the form of dense cataclastic fault-fracture networks, and is bordered by two unusually (2 m) thick and continuous cataclastic horizons. This central zone is flanked by outer damage zones ~250 m wide where the fracture density is lower, and individual fault surfaces surround relatively intact blocks of tonalite. In the southern damage zone, macroscopic fracture density (faults + joints) increases gradually from background wall-rock values towards the central zone where it remains relatively high throughout. The boundary between the wall rocks and the southern damage zone is defined by an abrupt transition from joints to cataclasite- and pseudotachylyte-bearing faults. Fracture density drops off sharply within the northern damage zone. Within and immediately surrounding the central zone, the syn-tectonic sealing of both micro- and macro-fractures by epidote, K-feldspar, and chlorite minerals was pervasive, resulting in low permeabilities

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

    SciTech Connect

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

    2004-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  18. The deep structure of the North Anatolian Fault Zone (Invited)

    NASA Astrophysics Data System (ADS)

    Fichtner, A.; Cupillard, P.; Saygin, E.; Trampert, J.; Taymaz, T.; Capdeville, Y.

    2013-12-01

    Multi-scale full waveform inversion of complete continental- and regional-scale seismograms reveals the crustal and upper-mantle signature of the North Anatolian Fault Zone which shapes the neotectonics of Turkey and the eastern Mediterranean. Within the crust, the fault zone is mostly bounded by several high-velocity blocks, suggesting that it developed along the edges of continental fragments with high rigidity. Below the crust, the surface expression of the eastern and central parts of the North Anatolian Fault Zone correlate with a pronounced low-velocity band that extends laterally over 600 km. Around 100 km depth, the low-velocity band merges into the shallow Anatolian asthenosphere, thereby providing a link to the Kirka-Afyon-Isparta Volcanic Field and the Central Anatolian Volcanics. We interpret the low-velocity band beneath the North Anatolian Fault Zone as the upper-mantle expression of the Tethyan sutures that formed 60-15 Ma ago as a result of Africa-Eurasian convergence. The structurally weak suture facilitated the formation of the younger (less than 10 Ma) crustal fault zone. In this sense, the North Anatolian Fault Zone is not only a crustal feature, but a narrow zone of weakness that extends into the upper mantle. Horizontal slices through the isotropic S velocity, vS, at 20 km (a) and 40 km (b) depth. Indicated are the surface expressions of the North Anatolian Fault Zone (NAFZ). The North Anatolian Fault (NAF) marks the northern boundary of the NAFZ. Dashed rectangles mark regions that are amplified in the two leftmost panels of the figure. Dotted ellipses indicate thin (20-30 km) crust as inferred from receiver function analysis (Vanacore et al., GJI 2013). Key to marked features: ATB: Anatolide-Tauride Block, IZ: Istanbul Zone, KM: Krsehir Massif, SZ: Sakarya Zone. Horizontal slices through the isotropic S velocity, vs, at 70 km and 150 km depth beneath Europe and western Asia. The Anatolian region where shorter-period data have been

  19. Fracturing and rock pulverization along an exhumed seismogenic fault zone in dolostones: The Foiana Fault Zone (Southern Alps, Italy)

    NASA Astrophysics Data System (ADS)

    Fondriest, Michele; Aretusini, Stefano; Di Toro, Giulio; Smith, Steven A. F.

    2015-07-01

    The Foiana Fault Zone (FFZ) is a major sinistral transpressive fault zone exhumed from < 2 km depth in the Italian Southern Alps. The fault zone crosscuts thick sequences of sedimentary dolostones and shows increasing cumulative throw (0.3-1.8 km) moving from south to north along fault strike. The FFZ consists of variably fractured and fragmented dolostones locally cut by small-displacement (< 0.5 m) faults containing discrete, highly-reflective (so-called "mirror-like") slip surfaces. The mirror-like slip surfaces are typically embedded within fine-grained cataclasite layers up to a few centimeters thick. Preservation of bedding planes in the fragmented dolostones indicates a lack of significant shear strain. Instead, the fragmented dolostones are affected by in-situ shattering from the centimeter down to the micrometer scale, resembling pulverized rocks in crystalline lithologies. Detailed field and aerial structural mapping reveals significant changes in the structure of the FFZ along strike. In particular, the fault zone exhibits large variations in thickness (from c. 100 m in the north to more than 300 m in the south) and changes in mean fault orientation and fault kinematics (from dominant oblique- and strike-slip in the north to dip-slip reverse in the south), together with the reactivation of preexisting anisotropies (i.e. bedding). Overall, the structure of the FFZ, when considered together with possible variable exhumation levels along strike, compares favorably to the predicted damage distribution in three-dimensional earthquake rupture simulations on strike-slip faults, as well as to the characteristics of active seismic sources hosted in carbonate rocks as illuminated by recent seismological studies.

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

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

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

    SciTech Connect

    Neuhaus, D. )

    1993-09-01

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

  2. Constraints on the Rupture of the October 21, 1868, Hayward Earthquake Determined From the Distribution of Modified Mercalli Intensity

    NASA Astrophysics Data System (ADS)

    Boatwright, J.; Bundock, H.

    2007-12-01

    The October 21, 1868, Hayward earthquake was the most damaging earthquake to occur in California in the half- century following the 1848 annexation. The earthquake shattered the city centers of Oakland and San Francisco, and cracked brick buildings as far away as Santa Rosa and Gilroy. We have re-evaluated MMI intensites at the 124 sites with damage or felt reports compiled by Toppozada et al. (1981), and added 26 sites where we obtained reports from newspapers and historical narratives. We used the 1878 Thompson and West Atlas of Alameda County to locate most of the specific buildings that were reported as damaged. The resulting ShakeMap interpolates the distribution of intensity along the Hayward fault, and the extent of shaking throughout the greater Bay Area and the San Joaquin Delta. Surprisingly, the highest intensities (MMI 8-9 to 9) are clustered near the middle of the fault rupture, in Hayward, San Leandro, and San Lorenzo. The intensities are lower (MMI 7- 8) at the ends of the fault rupture, in Berkeley and Warm Springs. The lack of strong shaking at either end of the fault rupture makes it hard to discern the rupture direction: the intensities observed at regional distances suggest that the rupture was stronger to the northwest towards Petaluma (MMI 7) and Martinez (MMI 7) than to the southeast towards Calaveras Valley (MMI 6-7) and Gilroy (MMI 6-7). The relatively low intensities in Oakland and Berkeley (MMI 7-8) suggest that the shallow locked zone near Piedmont, which Simpson et al. (2001) infer from the distribution of fault creep, did not rupture in the earthquake. This result appears to contradict Yu and Segall's (1996) conclusion that the fault slipped > 1 m in Berkeley. Given the large proportion of aseismic slip on Hayward fault, both observed geologically at the surface and inferred geodetically at depth, it is natural to propose that the rupture process of the 1868 earthquake comprised a series of disjoint asperity ruptures with variable

  3. Reconnaissance study of late quaternary faulting along cerro GoDen fault zone, western Puerto Rico

    USGS Publications Warehouse

    Mann, P.; Prentice, C.S.; Hippolyte, J.-C.; Grindlay, N.R.; Abrams, L.J.; Lao-Davila, D.

    2005-01-01

    The Cerro GoDen fault zone is associated with a curvilinear, continuous, and prominent topographic lineament in western Puerto Rico. The fault varies in strike from northwest to west. In its westernmost section, the fault is ???500 m south of an abrupt, curvilinear mountain front separating the 270- to 361-m-high La CaDena De San Francisco range from the Rio A??asco alluvial valley. The Quaternary fault of the A??asco Valley is in alignment with the bedrock fault mapped by D. McIntyre (1971) in the Central La Plata quadrangle sheet east of A??asco Valley. Previous workers have postulated that the Cerro GoDen fault zone continues southeast from the A??asco Valley and merges with the Great Southern Puerto Rico fault zone of south-central Puerto Rico. West of the A??asco Valley, the fault continues offshore into the Mona Passage (Caribbean Sea) where it is characterized by offsets of seafloor sediments estimated to be of late Quaternary age. Using both 1:18,500 scale air photographs taken in 1936 and 1:40,000 scale photographs taken by the U.S. Department of Agriculture in 1986, we iDentified geomorphic features suggestive of Quaternary fault movement in the A??asco Valley, including aligned and Deflected drainages, apparently offset terrace risers, and mountain-facing scarps. Many of these features suggest right-lateral displacement. Mapping of Paleogene bedrock units in the uplifted La CaDena range adjacent to the Cerro GoDen fault zone reveals the main tectonic events that have culminated in late Quaternary normal-oblique displacement across the Cerro GoDen fault. Cretaceous to Eocene rocks of the La CaDena range exhibit large folds with wavelengths of several kms. The orientation of folds and analysis of fault striations within the folds indicate that the folds formed by northeast-southwest shorTening in present-day geographic coordinates. The age of Deformation is well constrained as late Eocene-early Oligocene by an angular unconformity separating folDed, Deep

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  5. An algorithm for automated identification of fault zone trapped waves

    NASA Astrophysics Data System (ADS)

    Ross, Z. E.; Ben-Zion, Y.

    2015-08-01

    We develop an algorithm for automatic identification of fault zone trapped waves in data recorded by seismic fault zone arrays. Automatic S picks are used to identify time windows in the seismograms for subsequent search for trapped waves. The algorithm calculates five features in each seismogram recorded by each station: predominant period, 1 s duration energy (representative of trapped waves), relative peak strength, arrival delay and 6 s duration energy (representative of the entire seismogram). These features are used collectively to identify stations in the array with seismograms that are statistical outliers. Applying the algorithm to large data sets allows for distinguishing genuine trapped waves from occasional localized site amplification in seismograms of other stations. The method is verified on a test data set recorded across the rupture zone of the 1992 Landers earthquake, for which trapped waves were previously identified manually, and is then applied to a larger data set with several thousand events recorded across the San Jacinto fault zone. The developed technique provides an important tool for systematic objective processing of large seismic waveform data sets recorded near fault zones.

  6. Hydrothermal alteration in an exhumed crustal fault zone: geochemical mobility in the Caleta Coloso Fault, Atacama Fault System, Northern Chile

    NASA Astrophysics Data System (ADS)

    Arancibia, G.; Fujita, K.; Hoshino, K.; Mitchell, T. M.; Cembrano, J. M.; Gomila, R.; Morata, D.; Faulkner, D. R.; Rempe, M.

    2013-12-01

    Fault zones must be considered as complex and heterogeneous systems, with areas of high permeability that alternate with very low permeability bands. Strike-slip fault zones play an important role in fluid migration in the crust, and exhumed faults can provide insights into the interrelationships of deformation mechanisms, fluid-rock interactions and bulk chemical redistributions. We determined the mineral chemistry and whole-rock geochemistry of the damage zone and fault core of the Caleta Coloso Fault, a complex major crustal scale strike-slip fault in Northern Chile, in order to constrain the physical and chemical conditions of fluids that lead to strong hydrothermal alteration. Caleta Coloso Fault consists of variably altered protocataclasites, cataclasites and discrete bands of ultracataclasite derived from a protolith of Jurassic tonalite. Hydrothermal alteration associated with fault-related fluid flow is characterized by a very low-grade association composed by chlorite, epidote, albite, quartz and calcite. Chlorite thermometry indicates T-values in the range of 284 to 352 °C (average temperature of 323 °C) and no differences in mineral composition or T-values were observed among different cataclastic rock types. Mass balance and volume change calculations document that the major chemical mobility was observed in protocataclasite, whereas cataclasite and ultracataclasite show smaller changes. This suggests that fluid flow and chemical alteration post-dated the faulting, when the protocataclasite was relatively permeable and the cataclasite and ultracataclasite acted as a barrier for fluid flow having a very low permeability due to extreme grain size reduction during cataclasis.

  7. Fault zone amplified waves as a possible seismic hazard along the Calaveras fault in central California

    USGS Publications Warehouse

    Spudich, P.; Olsen, K.B.

    2001-01-01

    The Calaveras fault lies within a low velocity zone (LVZ) 1-2 km wide near Gilroy, California. Accelerographs G06, located in the LVZ 1.2 km from the Calaveras fault, and G07, 4 km from G06, recorded both the M 6.2 1984 Morgan Hill and the M 6.9 1989 Loma Prieta earthquakes. Comparison of the ground motions shows that a large 0.6-1.0 Hz velocity pulse observed at G06 during the Morgan Hill event may be amplified by focussing caused by the LVZ. Such amplified waves might be a mappable seismic hazard, and the zone of increased hazard can extend as much as 1.2 km from the surface trace of the fault. Finite-difference simulations of ground motions in a simplified LVZ model show a zone of amplified motion similar to the observations.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    USGS Publications Warehouse

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

    2005-01-01

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

  10. Late Holocene earthquakes on the Toe Jam Hill fault, Seattle fault zone, Bainbridge Island, Washington

    USGS Publications Warehouse

    Nelson, A.R.; Johnson, S.Y.; Kelsey, H.M.; Wells, R.E.; Sherrod, B.L.; Pezzopane, S.K.; Bradley, L.-A.; Koehler, R. D.; Bucknam, R.C.

    2003-01-01

    Five trenches across a Holocene fault scarp yield the first radiocarbon-measured earthquake recurrence intervals for a crustal fault in western Washington. The scarp, the first to be revealed by laser imagery, marks the Toe Jam Hill fault, a north-dipping backthrust to the Seattle fault. Folded and faulted strata, liquefaction features, and forest soil A horizons buried by hanging-wall-collapse colluvium record three, or possibly four, earthquakes between 2500 and 1000 yr ago. The most recent earthquake is probably the 1050-1020 cal. (calibrated) yr B.P. (A.D. 900-930) earthquake that raised marine terraces and triggered a tsunami in Puget Sound. Vertical deformation estimated from stratigraphic and surface offsets at trench sites suggests late Holocene earthquake magnitudes near M7, corresponding to surface ruptures >36 km long. Deformation features recording poorly understood latest Pleistocene earthquakes suggest that they were smaller than late Holocene earthquakes. Postglacial earthquake recurrence intervals based on 97 radiocarbon ages, most on detrital charcoal, range from ???12,000 yr to as little as a century or less; corresponding fault-slip rates are 0.2 mm/yr for the past 16,000 yr and 2 mm/yr for the past 2500 yr. Because the Toe Jam Hill fault is a backthrust to the Seattle fault, it may not have ruptured during every earthquake on the Seattle fault. But the earthquake history of the Toe Jam Hill fault is at least a partial proxy for the history of the rest of the Seattle fault zone.

  11. Anatomy of a Complex Fault Zone: Land Seismic Reflection Imaging of the Tacoma Fault Zone, Washington State

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

    Preliminary interpretations of new land-based seismic reflection images across the Tacoma fault zone in western Washington State document a complex pattern of faulting and folding. The Tacoma fault zone bounds gravity and aeromagnetic anomalies for 50 km across the central Puget Lowland west of the city of Tacoma, and tomography data suggest there is as much as 6 km of post-Eocene uplift of the hanging wall relative to Tacoma basin sediments to the south. We acquired four north-south seismic reflection profiles to define the character and tectonic history of the Tacoma fault zone. The 6-km long Powerline Road profile, located west of Case Inlet, perpendicularly crosses the 4-km-long Catfish Lake scarp discerned from Lidar data and trenching. The profile shows flat-lying strata on the south, but the north part of the profile is dominated by south-dipping Tertiary and older strata that appear to form the limb of an anticline. There appears to be at least one, and likely two faults in the Tertiary and older strata, although it is not clear these faults penetrate the shallowest Pleistocene strata. The 8.5-km long Carney Lake profile is located east of Case Inlet and spans two scarps imaged on Lidar data. This profile shows a similar geometry to the Powerline Road profile, folded and faulted Tertiary and older strata adjacent to flat-lying marine sediments of the Tacoma Basin. The 9-km long Bethel-Burley profile across the east portion of the Tacoma fault near Gig Harbor shows a significantly different reflector geometry than the profiles to the west. The Bethel-Burley profile is dominated by a strong, south-dipping reflection that becomes a prominent arch near the north end of the section. The strength of the reflector suggests that it marks the top of the Eocene basement rocks. South-dipping strata on this profile match those imaged on marine profiles from Carr Inlet. The new seismic reflection data support an interpretation in which the north edge of the Tacoma basin

  12. Significance of brittle deformation in the footwall of the Alpine Fault, New Zealand: Smithy Creek Fault zone

    NASA Astrophysics Data System (ADS)

    Lund Snee, J.-E.; Toy, V. G.; Gessner, K.

    2014-07-01

    The Smithy Creek Fault represents a rare exposure of a brittle fault zone within Australian Plate rocks that constitute the footwall of the Alpine Fault zone in Westland, New Zealand. Outcrop mapping and paleostress analysis of the Smithy Creek Fault were conducted to characterize deformation and mineralization in the footwall of the nearby Alpine Fault, and the timing of these processes relative to the modern tectonic regime. While unfavorably oriented, the dextral oblique Smithy Creek thrust has kinematics compatible with slip in the current stress regime and offsets a basement unconformity beneath Holocene glaciofluvial sediments. A greater than 100 m wide damage zone and more than 8 m wide, extensively fractured fault core are consistent with total displacement on the kilometer scale. Based on our observations we propose that an asymmetric damage zone containing quartz-carbonate-chlorite-epidote veins is focused in the footwall. Damage zone asymmetry likely resulted from the fact that the hanging wall was mostly deformed at greater depth than the footwall, rather than resulting from material contrasts across the fault plane. Kinematic inversions on mineralized fractures within the damage zone suggest veins formed in the current stress regime, from fluids comparable to those now circulating in the footwall. The Smithy Creek Fault zone is therefore a rare exhumed example of the modern footwall hydrothermal system, and of a structure actively accommodating footwall deformation near the Alpine Fault zone. Two significantly less mature, subvertical faults having narrow (20 cm or less) damage zones and similar orientations to nearby strike-slip segments of the Alpine Fault crosscut the mineralized zone at Smithy Creek. We envisage that hydrothermal mineralization strengthened the fault core, causing it to widen as later slip was partitioned into the (now) weaker surrounding damage zone. With progressive alteration, formation of favorably oriented faults became

  13. Fault-related clay authigenesis along the Moab Fault: Implications for calculations of fault rock composition and mechanical and hydrologic fault zone properties

    USGS Publications Warehouse

    Solum, J.G.; Davatzes, N.C.; Lockner, D.A.

    2010-01-01

    The presence of clays in fault rocks influences both the mechanical and hydrologic properties of clay-bearing faults, and therefore it is critical to understand the origin of clays in fault rocks and their distributions is of great importance for defining fundamental properties of faults in the shallow crust. Field mapping shows that layers of clay gouge and shale smear are common along the Moab Fault, from exposures with throws ranging from 10 to ???1000 m. Elemental analyses of four locations along the Moab Fault show that fault rocks are enriched in clays at R191 and Bartlett Wash, but that this clay enrichment occurred at different times and was associated with different fluids. Fault rocks at Corral and Courthouse Canyons show little difference in elemental composition from adjacent protolith, suggesting that formation of fault rocks at those locations is governed by mechanical processes. Friction tests show that these authigenic clays result in fault zone weakening, and potentially influence the style of failure along the fault (seismogenic vs. aseismic) and potentially influence the amount of fluid loss associated with coseismic dilation. Scanning electron microscopy shows that authigenesis promotes that continuity of slip surfaces, thereby enhancing seal capacity. The occurrence of the authigenesis, and its influence on the sealing properties of faults, highlights the importance of determining the processes that control this phenomenon. ?? 2010 Elsevier Ltd.

  14. Fault-related clay authigenesis along the Moab Fault: Implications for calculations of fault rock composition and mechanical and hydrologic fault zone properties

    NASA Astrophysics Data System (ADS)

    Solum, John G.; Davatzes, Nicholas C.; Lockner, David A.

    2010-12-01

    The presence of clays in fault rocks influences both the mechanical and hydrologic properties of clay-bearing faults, and therefore it is critical to understand the origin of clays in fault rocks and their distributions is of great importance for defining fundamental properties of faults in the shallow crust. Field mapping shows that layers of clay gouge and shale smear are common along the Moab Fault, from exposures with throws ranging from 10 to ˜1000 m. Elemental analyses of four locations along the Moab Fault show that fault rocks are enriched in clays at R191 and Bartlett Wash, but that this clay enrichment occurred at different times and was associated with different fluids. Fault rocks at Corral and Courthouse Canyons show little difference in elemental composition from adjacent protolith, suggesting that formation of fault rocks at those locations is governed by mechanical processes. Friction tests show that these authigenic clays result in fault zone weakening, and potentially influence the style of failure along the fault (seismogenic vs. aseismic) and potentially influence the amount of fluid loss associated with coseismic dilation. Scanning electron microscopy shows that authigenesis promotes that continuity of slip surfaces, thereby enhancing seal capacity. The occurrence of the authigenesis, and its influence on the sealing properties of faults, highlights the importance of determining the processes that control this phenomenon.

  15. Permeability of the San Andreas Fault Zone at Depth

    NASA Astrophysics Data System (ADS)

    Rathbun, A. P.; Song, I.; Saffer, D.

    2010-12-01

    Quantifying fault rock permeability is important toward understanding both the regional hydrologic behavior of fault zones, and poro-elastic processes that affect fault mechanics by mediating effective stress. These include long-term fault strength as well as dynamic processes that may occur during earthquake slip, including thermal pressurization and dilatancy hardening. Despite its importance, measurements of fault zone permeability for relevant natural materials are scarce, owing to the difficulty of coring through active fault zones seismogenic depths. Most existing measurements of fault zone permeability are from altered surface samples or from thinner, lower displacement faults than the SAF. Here, we report on permeability measurements conducted on gouge from the actively creeping Central Deformation Zone (CDZ) of the San Andreas Fault, sampled in the SAFOD borehole at a depth of ~2.7 km (Hole G, Run 4, sections 4,5). The matrix of the gouge in this interval is predominantly composed of particles <10 µm, with ~5 vol% clasts of serpentinite, very fine-grained sandstone, and siltstone. The 2.6 m-thick CDZ represents the main fault trace and hosts ~90% of the active slip on the SAF at this location, as documented by repeated casing deformation surveys. We measured permeability in two different configurations: (1) in a uniaxial pressure cell, in which a sample is placed into a rigid steel ring which imposes a zero lateral strain condition and subjected to axial load, and (2) in a standard triaxial system under isostatic stress conditions. In the uniaxial configuration, we obtained permeabilities at axial effective stresses up to 90 MPa, and in the triaxial system up to 10 MPa. All experiments were conducted on cylindrical subsamples of the SAFOD core 25 mm in diameter, with lengths ranging from 18mm to 40mm, oriented for flow approximately perpendicular to the fault. In uniaxial tests, permeability is determined by running constant rate of strain (CRS) tests up

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

    USGS Publications Warehouse

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

    2004-01-01

    The behavior of apparent stress for normal-fault earthquakes at subduction zones is derived by examining the apparent stress (?? a = ??Es/Mo, where E s is radiated energy and Mo is seismic moment) of all globally distributed shallow (depth, ?? 1 MPa) are also generally intraslab, but occur where the lithosphere has just begun subduction beneath the overriding plate. They usually occur in cold slabs near trenches where the direction of plate motion across the trench is oblique to the trench axis, or where there are local contortions or geometrical complexities of the plate boundary. Lower ??a (< 1 MPa) is associated with events occurring at the outer rise (OR) complex (between the OR and the trench axis), as well as with intracrustal events occurring just landward of the trench. The average apparent stress of intraslab-normal-fault earthquakes is considerably higher than the average apparent stress of interplate-thrust-fault earthquakes. In turn, the average ?? a of strike-slip earthquakes in intraoceanic environments is considerably higher than that of intraslab-normal-fault earthquakes. The variation of average ??a with focal mechanism and tectonic regime suggests that the level of ?? a is related to fault maturity. Lower stress drops are needed to rupture mature faults such as those found at plate interfaces that have been smoothed by large cumulative displacements (from hundreds to thousands of kilometres). In contrast, immature faults, such as those on which intraslab-normal-fault earthquakes generally occur, are found in cold and intact lithosphere in which total fault displacement has been much less (from hundreds of metres to a few kilometres). Also, faults on which high ??a oceanic strike-slip earthquakes occur are predominantly intraplate or at evolving ends of transforms. At subduction zones, earthquakes occurring on immature faults are likely to be more hazardous as they tend to generate higher amounts of radiated energy per unit of moment than

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

    SciTech Connect

    Donald Sweetkind; Ronald M. Drake II

    2007-11-27

    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.

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

    USGS Publications Warehouse

    Sweetkind, Donald S.; Drake II, Ronald M.

    2007-01-01

    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.

  19. Scaling of the critical slip distance for seismic faulting with shear strain in fault zones

    USGS Publications Warehouse

    Marone, C.; Kilgore, B.

    1993-01-01

    THEORETICAL and experimentally based laws for seismic faulting contain a critical slip distance1-5, Dc, which is the slip over which strength breaks down during earthquake nucleation. On an earthquake-generating fault, this distance plays a key role in determining the rupture nucleation dimension6, the amount of premonitory and post-seismic slip7-10, and the maximum seismic ground acceleration1,11. In laboratory friction experiments, Dc has been related to the size of surface contact junctions2,5,12; thus, the discrepancy between laboratory measurements of Dc (??? 10-5 m) and values obtained from modelling earthquakes (??? 10-2 m) has been attributed to differences in roughness between laboratory surfaces and natural faults5. This interpretation predicts a dependence of Dc on the particle size of fault gouge 2 (breccia and wear material) but not on shear strain. Here we present experimental results showing that Dc scales with shear strain in simulated fault gouge. Our data suggest a new physical interpretation for the critical slip distance, in which Dc is controlled by the thickness of the zone of localized shear strain. As gouge zones of mature faults are commonly 102-103 m thick13-17, whereas laboratory gouge layers are 1-10 mm thick, our data offer an alternative interpretation of the discrepancy between laboratory and field-based estimates of Dc.

  20. Nature of Subduction Megathrust Faults at the Ryukyu Subduction Zone

    NASA Astrophysics Data System (ADS)

    Arai, R.; Kaiho, Y.; Takahashi, T.; Nakanishi, A.; Fujie, G.; Nakamura, Y.; Miura, S.; Kodaira, S.; Kaneda, Y.

    2015-12-01

    The Ryukyu subduction zone (RSZ) has been intensively examined in terms of seismic coupling along the plate boundary and tsunami potentials. On the contrary to other subduction zones nearby, such as the Nankai Trough and the Japan Trench, the RSZ has lacked clear evidence of great interplate earthquakes (M>8) for the last few hundred years and thus the overall interplate coupling is thought to be weak (Peterson and Seno, 1984). Correspondingly, geodetic observation implies that a possible coupled zone is narrow and limited to a shallow portion of the plate boundary near the trench (Ando et al., 2009). Recent seismic studies show that very low frequency earthquakes (VLFEs) are ubiquitously distributed in the forearc region of the Ryukyu arc, implying a variety of slip behaviors along the subduction faults related to fluid distribution (Nakamura and Sunagawa, 2015). However, these findings were derived from land station network and did not have sufficient resolution near the trench to determine spatial relationship of megathrust faults to the seismic activity. Since 2013 we JAMSTEC have been carrying out marine active- and passive-source seismic experiments in the Ryukyu subduction zone to reveal the fine-scale geometry and nature of subduction faults. Here we present integrated seismological evidence for megathrust fault structure and its relation to VLFEs at the southern Ryukyu Trench. Active-source seismic data consistently reveal that the plate boundary and backstop interface form a 40-km-wide frontal prism where low-velocity sedimentary rocks fill in. We find VLFEs occur around the low-velocity wedge where fluids are distributed as suggested by negative polarity in the reflection data. This forearc structure is also coincident with the source region of Yaeyama earthquake tsunami in 1771 (Nakamura, 2009), the most devastating disaster known in this region. Slow ruptures enhanced by the fluid-rich condition at the plate boundary and/or surrounding faults may be a

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

    NASA Astrophysics Data System (ADS)

    de Joussineau, G.; Aydin, A.

    2006-12-01

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

  2. Earthquake rupture extents and coseismic slips promoted by damaged fault zones

    NASA Astrophysics Data System (ADS)

    Weng, Huihui; Yang, Hongfeng; Zhang, Zhenguo; Chen, Xiaofei

    2016-06-01

    Here we investigate the effects of damage fault zones on rupture propagation by conducting a series of 3-D dynamic rupture simulations on a planar vertical strike-slip fault. We find that damage fault zones can promote rupture extent and increase earthquake potency. The waves reflected from the bottom of shallow damage fault zones can increase shear stress on the fault and thus promote rupture propagation. In addition, the promotional effects increase with the width and depth extent of damage fault zones. The overall effects of the waves reflected from the fault-parallel side boundaries of damage fault zones are unfavorable for rupture propagation. Therefore, rupture propagation is promoted with the increased width of fault zones due to geometrical spreading effects. Moreover, nonground-breaking ruptures may reach the ground surface with the effects of damage fault zones. Furthermore, along-strike segmented fault zones as suggested by observations could also promote ruptures and may lead to preferred rupture directions if epicenters are close to fault zones. The effects of damage fault zones on rupture propagation hold important implications on assessing earthquake risk.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  4. Slip zone structure and processes in seismogenic carbonate faults

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Nanfito, A.; Karson, J. A.

    2009-12-01

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

  6. Static versus dynamic fracturing in shallow carbonate fault zones

    NASA Astrophysics Data System (ADS)

    Fondriest, M.; Doan, M. L.; Aben, F. M.; Fusseis, F.; Mitchell, T. M.; Di Toro, G.

    2015-12-01

    Moderate to large earthquakes often nucleate within and propagate through carbonates in the shallow crust, therefore several field and experimental studies were recently aimed to constrain earthquake-related deformation processes within carbonate fault rocks. In particular, the occurrence of thick belts (10-100s m) of low-strain fault-related breccias (average size of rock fragments >1 cm), which is relatively common within carbonate damage zones, was generally interpreted as resulting from the quasi-static growth of fault zones rather than from the cumulative effect of multiple earthquake ruptures. Here we report the occurrence of up to hundreds of meters thick belts of intensely fragmented dolostones along the major transpressive Foiana Fault Zone (Italian Southern Alps) which was exhumed from < 2 km depth. Such dolostones are reduced into fragments ranging from few centimeters down to few millimeters in size with ultrafine-grained layers in proximity to the principal slip zones. Preservation of the original bedding indicates a lack of significant shear strain in the fragmented dolostones which seem to have been shattered in situ. To investigate the origin of the in-situ shattered rocks, the host dolostones were deformed in uniaxial compression both under quasi-static loading (strain rate ~10-3 s-1) and dynamic loading (strain rate >50 s-1). Dolostones deformed up to failure under low-strain rate were affected by single to multiple discrete (i.e. not interconnected) extensional fractures sub-parallel to the loading direction. Dolostones deformed under high-strain rate were shattered above a strain rate threshold of ~200 s-1(strain >1.2%) while they were split in few fragments or were macroscopically intact for lower strain rates. Experimentally shattered dolostones were reduced into a non-cohesive material with most rock fragments a few millimeters in size and elongated parallel to the loading direction. Fracture networks were investigated by X

  7. Seismicity around the Cimandiri fault zone, West Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Febriani, Febty

    2016-02-01

    We analyzed the seismicity activity around the Cimandiri fault zone, West Java, Indonesia by using the earthquake catalogs listed by Indonesian Meteorological Climatological and Geophysical (BMKG) and International Seismological Centre (ISC) from 1973 to 2013 (M>=1 and depth ≤ 0-50 km), along with the focal mechanism data from National Research Institute of Earth Science and Disaster Prevention (NIED) from 2007 to 2014 (M>4; depth ≤ 50 km) and Global CMT catalog from 1976 to 2014 (M=0-10 and depth ≤ 50 km). The result from earthquake catalogs suggest that there are earthquake activities around the Cimandiri fault zone in the recent years, which is also supported by the results of focal mechanism data analysis from NIED data and Global CMT catalog.

  8. Brecciation processes in fault zones: Inferences from earthquake rupturing

    NASA Astrophysics Data System (ADS)

    Sibson, Richard H.

    1986-01-01

    Surface-rupture patterns and aftershock distributions accompanying moderate to large shallow earthquakes reveal a residual brittle infrastructure for established crustal fault zones, the complexity of which is likely to be largely scale-invariant. In relation to such an infrastructure, continued displacement along a particular master fault may involve three dominant mechanical processes of rock brecciation: (a) attrition brecciation, from progressive frictional wear along principal slip surfaces during both seismic and aseismic sliding, (b) distributed crush brecciation, involving microfracturing over broad regions when slip on the principal slip surfaces is impeded by antidilational jogs or other obstructions, and (c) implosion brecciation, associated with the sudden creation of void space and fluid-pressure differentials at dilational fault jogs during earthquake rupture propagation. These last, high-dilation breccias are particularly favorable sites for hydrothermal mineral deposition, forming transitory low-pressure channels for the rapid passage of hydrothermal fluids. Long-lived fault zones often contain an intermingling of breccias derived from all three processes.

  9. Heat flow and energetics of the San Andreas fault zone.

    USGS Publications Warehouse

    Lachenbruch, A.H.; Sass, J.H.

    1980-01-01

    Approximately 100 heat flow measurements in the San Andreas fault zone indicate 1) there is no evidence for local frictional heating of the main fault trace at any latitude over a 1000-km length from Cape Mendocino to San Bernardino, 2) average heat flow is high (ca.2 HFU, ca.80 mW m-2) throughout the 550-km segment of the Coast Ranges that encloses the San Andreas fault zone in central California; this broad anomaly falls off rapidly toward the Great Valley to the east, and over a 200-km distance toward the Mendocino Triple Junction to the northwest. As others have pointed out, a local conductive heat flow anomaly would be detectable unless the frictional resistance allocated to heat production on the main trace were less than 100 bars. Frictional work allocated to surface energy of new fractures is probably unimportant, and hydrologic convection is not likely to invalidate the conduction assumption, since the heat discharge by thermal springs near the fault is negligible. -Authors

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

    SciTech Connect

    Wills, C.J.

    1989-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Iacopini, David; Butler, Rob; Purves, Steve

    2013-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  13. Syn-collisional transform faulting of the Tan-Lu fault zone, East China

    NASA Astrophysics Data System (ADS)

    Zhu, Guang; Liu, Guo Sheng; Niu, Man Lan; Xie, Cheng Long; Wang, Yong Sheng; Xiang, Biwei

    2009-02-01

    Origin of the continental-scale Tan-Lu fault zone (TLFZ), East China, remains controversial. About 550 km sinistral offset of the Dabie orogenic belt (DOB) and Sulu orogenic belt (SOB) is shown along the NE-NNE-striking TLFZ. Syn-collisional, sinistral ductile shear belts in the TLFZ have been identified. Thirteen phengite bulk separates from the mylonites were dated by the 40Ar/39Ar method. They gave cooling ages of the 198-181 Ma for the shear belts along the eastern margin of the DOB and 221-210 Ma from the western margin of the SOB. Distribution of the foreland basin deposits suggests that sinistral offset of the DOB and SOB by the TLFZ took place prior to deposition of the Upper Triassic strata. The marginal structures around the DOB and SOB support syn-collisional faulting, and indicate anticlockwise rotation of the DOB during the displacement. The folding and thrust faulting related to crustal subduction, coeval with the Tan-Lu faulting, is older than the foreland basin deposition related to the orogenic exhumation. Several lines of evidence demonstrate that the TLFZ was developed as a syn-collisional transform fault during latest Middle to earliest Late Triassic time when the DOB and SOB experienced crustal subduction of the South China Block (SCB). Eastward increase of the crustal subduction rates is believed to be responsible for the sinistral transform faulting.

  14. Fault-zone guided waves from explosions in the San Andreas fault at Parkfield and Cienega Valley, California

    USGS Publications Warehouse

    Li, Y.-G.; Ellsworth, W.L.; Thurber, C.H.; Malin, P.E.; Aki, K.

    1997-01-01

    Fault-zone guided waves were successfully excited by near-surface explosions in the San Andreas fault zone both at Parkfield and Cienega Valley, central California. The guided waves were observed on linear, three-component seismic arrays deployed across the fault trace. These waves were not excited by explosions located outside the fault zone. The amplitude spectra of guided waves show a maximum peak at 2 Hz at Parkfield and 3 Hz at Cienega Valley. The guided wave amplitude decays sharply with observation distance from the fault trace. The explosion-excited fault-zone guided waves are similar to those generated by earthquakes at Parkfield but have lower frequencies and travel more slowly. These observations suggest that the fault-zone wave guide has lower seismic velocities as it approaches the surface at Parkfield. We have modeled the waveforms as S waves trapped in a low-velocity wave guide sandwiched between high-velocity wall rocks, resulting in Love-type fault-zone guided waves. While the results are nonunique, the Parkfield data are adequately fit by a shallow wave guide 170 m wide with an S velocity 0.85 km/sec and an apparent Q ??? 30 to 40. At Cienega Valley, the fault-zone wave guide appears to be about 120 m wide with an S velocity 0.7 km/sec and a Q ??? 30.

  15. Structural styles of Paleozoic intracratonic fault reactivation: A case study of the Grays Point fault zone in southeastern Missouri, USA

    USGS Publications Warehouse

    Clendenin, C.W.; Diehl, S.F.

    1999-01-01

    A pronounced, subparallel set of northeast-striking faults occurs in southeastern Missouri, but little is known about these faults because of poor exposure. The Commerce fault system is the southernmost exposed fault system in this set and has an ancestry related to Reelfoot rift extension. Recent published work indicates that this fault system has a long history of reactivation. The northeast-striking Grays Point fault zone is a segment of the Commerce fault system and is well exposed along the southeast rim of an inactive quarry. Our mapping shows that the Grays Point fault zone also has a complex history of polyphase reactivation, involving three periods of Paleozoic reactivation that occurred in Late Ordovician, Devonian, and post-Mississippian. Each period is characterized by divergent, right-lateral oblique-slip faulting. Petrographic examination of sidwall rip-out clasts in calcite-filled faults associated with the Grays Point fault zone supports a minimum of three periods of right-lateral oblique-slip. The reported observations imply that a genetic link exists between intracratonic fault reactivation and strain produced by Paleozoic orogenies affecting the eastern margin of Laurentia (North America). Interpretation of this link indicate that right-lateral oblique-slip has occurred on all of the northeast-striking faults in southeastern Missouri as a result of strain influenced by the convergence directions of the different Paleozoic orogenies.

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

    USGS Publications Warehouse

    Orndorff, Randall C.

    2012-01-01

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

  17. High-velocity frictional properties and microstructures of clay-rich fault gouge in megasplay fault zone, Nankai subduction zone

    NASA Astrophysics Data System (ADS)

    Ujiie, K.; Tsutsumi, A.

    2010-12-01

    In accretionary margins, a large out-of-sequence fault system (the megasplay fault) commonly branches from the megathrust and intersects the seafloor along the lower slope of the margin. Detailed seismic reflection surveys and theoretical studies have suggested that the propagation of earthquake rupture occurred repeatedly along the megasplay fault during great subduction earthquakes. Recently, IODP Expedition 316 drilled into the shallow portion of the megasplay fault zone in the Nankai subduction zone offshore the Kii Peninsula, southwest Japan and found the evidence for the slip localization and past frictional heating along ~10-mm-thick dark gouges in the microbreccia. Thus, high-velocity frictional properties of the megasplay fault material are crucial for understanding whether the megasplay fault efficiently transfers displacement toward the seafloor and fosters a tsunami genesis during a subduction earthquake. We conducted high-velocity friction experiments on clay-rich fault gouge taken from the Nankai megasplay fault zone at a slip rate of 1.3 m/s and normal stresses of 0.6-2.0 MPa under dry and wet conditions. After the experiments, the microstructures of the fault gouges were examined by optical microscope and SEM. In the dry tests, dehydration of clay minerals occurred by frictional heating, and the slip weakening is related to the fault gouge expansion due to a water phase transition from liquid to vapor. The water is derived from the dehydration of clay minerals by frictional heating. The resulting microstructure in the gouge layer is a random distribution of spherical clay-clast aggregates (CCA) in the optically isotropic, dark matrix. In the wet tests, the slip weakening is caused by pore-fluid pressurization resulting from shear-enhanced compaction of the water-saturated gouge and frictional heating. Compared to the dry tests, the wet tests show smaller dynamic stress drops and slip weakening distance. The steady-state shear stress in the wet tests

  18. Fault-zone structure and weakening processes in basin-scale reverse faults: The Moonlight Fault Zone, South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Alder, S.; Smith, S. A. F.; Scott, J. M.

    2016-10-01

    The >200 km long Moonlight Fault Zone (MFZ) in southern New Zealand was an Oligocene basin-bounding normal fault zone that reactivated in the Miocene as a high-angle reverse fault (present dip angle 65°-75°). Regional exhumation in the last c. 5 Ma has resulted in deep exposures of the MFZ that present an opportunity to study the structure and deformation processes that were active in a basin-scale reverse fault at basement depths. Syn-rift sediments are preserved only as thin fault-bound slivers. The hanging wall and footwall of the MFZ are mainly greenschist facies quartzofeldspathic schists that have a steeply-dipping (55°-75°) foliation subparallel to the main fault trace. In more fissile lithologies (e.g. greyschists), hanging-wall deformation occurred by the development of foliation-parallel breccia layers up to a few centimetres thick. Greyschists in the footwall deformed mainly by folding and formation of tabular, foliation-parallel breccias up to 1 m wide. Where the hanging-wall contains more competent lithologies (e.g. greenschist facies metabasite) it is laced with networks of pseudotachylyte that formed parallel to the host rock foliation in a damage zone extending up to 500 m from the main fault trace. The fault core contains an up to 20 m thick sequence of breccias, cataclasites and foliated cataclasites preserving evidence for the progressive development of interconnected networks of (partly authigenic) chlorite and muscovite. Deformation in the fault core occurred by cataclasis of quartz and albite, frictional sliding of chlorite and muscovite grains, and dissolution-precipitation. Combined with published friction and permeability data, our observations suggest that: 1) host rock lithology and anisotropy were the primary controls on the structure of the MFZ at basement depths and 2) high-angle reverse slip was facilitated by the low frictional strength of fault core materials. Restriction of pseudotachylyte networks to the hanging-wall of the

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  2. Measuring Transient Signals in Plate Boundary Faults Zones with Strainmeters

    NASA Astrophysics Data System (ADS)

    Hodgkinson, Kathleen; Mencin, Dave; Phillips, David; Henderson, Brent; Gottlieb, Mike; Gallaher, Warren; Johnson, Wade; Pyatt, Chad; Van Boskirk, Elizabeth; Fox, Otina; Mattioli, Glen; Meertens, Chuck

    2014-05-01

    One of the fundamental goals the U.S. National Science Foundation (NSF) funded Earthscope program was to provide a high-quality, continuous geodetic data set that would allow the scientific community to study the evolution of plate boundary zones. Of particular importance was enabling investigation of the role aseismic transient deformation plays in the release of accumulated stress. For example, to allow the comparison of the amount of strain released through Episodic Tremor and Slip (ETS) events to that released in subduction zone earthquakes or, provide the ability to geodetically illuminate the kinematics of fault creep in strike-slip fault zones. The ability to easily integrate these measurements with compatible geophysical data sets was also an essential objective. With goals such as these in mind NSF funded the Plate Boundary Observatory (PBO) to record the continuous deformation field across the western US Plate Boundary. PBO, built and operated by UNAVCO, now consists of over 1100 GPS stations, 76 co-located borehole strain and seismic sites, 6 long baseline strainmeters, Depending on the scientific questions being addressed sites may also have tiltmeter, meteorological, pore pressure and meteorological instrumentation. This presentation will focus on the transient deformation signals recorded by the PBO strainmeter network. PBO strainmeters, which excel in recording signals on the order of nanostrain over hours, have provided unprecedented temporal resolution of aseismic transients such as ETS events in the Cascadia subduction zone, creep signals along the central section of the San Andreas fault system and tsunami generated strain waves. UNAVCO is responsible not only for the ongoing operation of PBO but also the generation of data products associated with each instrument type. In this presentation we will highlight some of the transient signals these instruments have captured, outline the processing steps required to extract these signals data and

  3. Subsurface geometry and evolution of the Seattle fault zone and the Seattle Basin, Washington

    USGS Publications Warehouse

    ten Brink, U.S.; Molzer, P.C.; Fisher, M.A.; Blakely, R.J.; Bucknam, R.C.; Parsons, T.; Crosson, R.S.; Creager, K.C.

    2002-01-01

    The Seattle fault, a large, seismically active, east-west-striking fault zone under Seattle, is the best-studied fault within the tectonically active Puget Lowland in western Washington, yet its subsurface geometry and evolution are not well constrained. We combine several analysis and modeling approaches to study the fault geometry and evolution, including depth-converted, deep-seismic-reflection images, P-wave-velocity field, gravity data, elastic modeling of shoreline uplift from a late Holocene earthquake, and kinematic fault restoration. We propose that the Seattle thrust or reverse fault is accompanied by a shallow, antithetic reverse fault that emerges south of the main fault. The wedge enclosed by the two faults is subject to an enhanced uplift, as indicated by the boxcar shape of the shoreline uplift from the last major earthquake on the fault zone. The Seattle Basin is interpreted as a flexural basin at the footwall of the Seattle fault zone. Basin stratigraphy and the regional tectonic history lead us to suggest that the Seattle fault zone initiated as a reverse fault during the middle Miocene, concurrently with changes in the regional stress field, to absorb some of the north-south shortening of the Cascadia forearc. Kingston Arch, 30 km north of the Seattle fault zone, is interpreted as a more recent disruption arising within the basin, probably due to the development of a blind reverse fault.

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

    NASA Astrophysics Data System (ADS)

    Qu, Dongfang; Røe, Per; Tveranger, Jan

    2015-08-01

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

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

    USGS Publications Warehouse

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

    2004-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  7. On the Origin and Distribution of Fracture Damage Surrounding Strike-Slip Fault Zones

    NASA Astrophysics Data System (ADS)

    Mitchell, T. M.; Faulkner, D. R.

    2006-12-01

    Fault damage zones are represented by both microfracturing of the rock matrix and by macroscopic fracture networks. The spatial distribution and geometric characterization of fracture patterns at various scales help to predict fault growth processes, subsequent mechanics and bulk hydraulic properties of a fault zone. We studied strike-slip faults of various displacements that cut crystalline rock (granodiorite) within the excellently exposed and passively exhumed Atacama Fault Zone, Northern Chile. Micro- and macroscale fracture densities within the damage zones of faults with well-constrained displacements ranging over 3 orders of magnitude (~0.12 m 5000 m) have been characterized. These faults can be compared and contrasted as they all cut the same rock type. Multiple generations of microfractures indicating deformation at different crustal depths and times are represented by fluid inclusion planes (FIPs), partially healed, and open microfractures. The FIPs show a log- linear decrease in density with perpendicular distance from the fault plane on all faults studied. Recent work has shown that the damage zone surrounding faults is largely developed in the process zone that precedes the fault tip. As the fault tip propagates through the process zone, microfracture damage is left flanking either side of the fault. These FIPs are in a predominantly mode I orientation and we interpret them to record a snapshot of fault history related to the passage of a migrating fault tip process zone. Microfracture densities fall to background levels at ~150 m for the 5000 m offset fault, ~115 m for the 220 m offset fault, ~18 m for the 35 m fault, ~0.06 m for the 2 m offset fault, ~0.09 m for the 1.2 m offset fault and ~0.05mm for the 0.13 m offset fault. All faults appear to have a critical microfracture density independent of displacement. However, fault damage zone widths scale with displacement. Later microfractures do not show a clear relationship of microfracture density

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

    SciTech Connect

    Reheis, M. )

    1993-04-01

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

  9. Structure of a normal seismogenic fault zone in carbonates: The Vado di Corno Fault, Campo Imperatore, Central Apennines (Italy)

    NASA Astrophysics Data System (ADS)

    Demurtas, Matteo; Fondriest, Michele; Balsamo, Fabrizio; Clemenzi, Luca; Storti, Fabrizio; Bistacchi, Andrea; Di Toro, Giulio

    2016-09-01

    The Vado di Corno Fault Zone (VCFZ) is an active extensional fault cutting through carbonates in the Italian Central Apennines. The fault zone was exhumed from ∼2 km depth and accommodated a normal throw of ∼2 km since Early-Pleistocene. In the studied area, the master fault of the VCFZ dips N210/54° and juxtaposes Quaternary colluvial deposits in the hangingwall with cataclastic dolostones in the footwall. Detailed mapping of the fault zone rocks within the ∼300 m thick footwall-block evidenced the presence of five main structural units (Low Strain Damage Zone, High Strain Damage Zone, Breccia Unit, Cataclastic Unit 1 and Cataclastic Unit 2). The Breccia Unit results from the Pleistocene extensional reactivation of a pre-existing Pliocene thrust. The Cataclastic Unit 1 forms a ∼40 m thick band lining the master fault and recording in-situ shattering due to the propagation of multiple seismic ruptures. Seismic faulting is suggested also by the occurrence of mirror-like slip surfaces, highly localized sheared calcite-bearing veins and fluidized cataclasites. The VCFZ architecture compares well with seismological studies of the L'Aquila 2009 seismic sequence (mainshock MW 6.1), which imaged the reactivation of shallow-seated low-angle normal faults (Breccia Unit) cut by major high-angle normal faults (Cataclastic Units).

  10. Laboratory and Numerical Observations of the Spectrum of Fault Slip Behaviors: Implications for Fault Zone Properties

    NASA Astrophysics Data System (ADS)

    Marone, C.

    2015-12-01

    Slow earthquakes, tectonic fault tremor and other modes of quasi-dynamic slip represent an important enigma. In the standard earthquake model, elastic energy is released catastrophically as the fault weakens and dynamic rupture expands at speeds measured in km/s. The spectral content of the resulting seismic waves is understood in terms of a source model based on elastodynamic rupture propagation. However, faults also fail in slow earthquakes and there is no such understanding of rupture dynamics, seismic spectra, or source scaling relations in these cases. The mechanics of slow earthquakes are poorly understood in part because there are few systematic laboratory observations that can be used to identify the underlying mechanics. Here, I summarize and discuss results from numerical models of slow slip using rate/state friction laws and recent lab studies showing slow slip and the full spectrum of stick-slip behaviors. Early lab studies saw slow slip during frictional sliding or in association with dehydration or ductile flow; however, they did not include systematic measurements that could be used to isolate the underlying mechanics. Numerical studies based on rate/state friction also document slow slip and chaotic forms of stick-slip, however they require special conditions including two state variable frictional behavior. Recent lab work sheds new light on slow earthquakes by showing: 1) that repetitive, slow stick-slip can occur if the fault friction-velocity relation becomes positive during slip acceleration, and 2) that slow slip and the full spectrum of fault slip modes can occur if loading stiffness k matches the fault zone critical rheologic stiffness kc given by the frictional weakening rate and the critical frictional distance. These data show that the key control parameter for stress drop, slip speed, and slip duration is the non dimensional stiffness k' = k/kc, with the spectrum of fast to slow slip mode occurring in a narrow range around k'=1. I

  11. Three-dimensional characterization of a crustal-scale fault zone: The Pusteria and Sprechenstein fault system (Eastern Alps)

    NASA Astrophysics Data System (ADS)

    Bistacchi, Andrea; Massironi, Matteo; Menegon, Luca

    2010-12-01

    The characterization and representation of fault zones is of paramount importance for studies of fault and earthquake mechanics, since their rheological and geometric complexity controls seismic/aseismic behaviour and fluid circulation at depth. We present a 3D geological model of a fault system, created by integrating borehole and surface structural data, which allows us to bridge the gap between outcrop-scale descriptions and large-scale geophysical models. The model integrates (i) fault geometry and topology, (ii) fault-rock distribution, and (iii) characterization of fracturing in damage zones at the km scale. The dextral-reverse Pusteria and Sprechenstein-Mules Faults (Italian Eastern Alps) provide an opportunity to study fault rocks and damage distribution as a function of host-rock lithology and fabric, and of fault geometry. A first-order control is exerted by the composition of protoliths (quartzo-feldspathic vs. phyllosilicate-rich) and/or by the presence of an inherited anisotropic fabric (massive vs. foliated), resulting in a marked asymmetry of damage zones. Interestingly, the pervasive foliation typical of some protoliths may explain both this asymmetry and the relative weakness of one of the faults. The importance of geometrical factors is highlighted when the damage zone thickness increases five times in proximity to a km-scale contractional jog. On the other hand, the type of fault rock present within the fault core does not show a direct relationship with damage intensity. In addition, the thickness of damage zones along planar fault segments does not appear to grow indefinitely with displacement, as might be envisaged from some scaling laws. We interpret both of these observations as reflecting the maturity of these large-displacement faults.

  12. The search for creep on the faults of northern California

    NASA Astrophysics Data System (ADS)

    Funning, Gareth; Jin, Lizhen

    2013-04-01

    Shallow aseismic fault creep is a behaviour exhibited by very few faults in the world. Instead of the stick-slip frictional regime that most faults follow, creeping faults move, steadily or episodically, throughout the interseismic period of the earthquake cycle. Creep effectively reduces the fault surface area capable of rupture in earthquakes, and thus knowledge of its extent is critical for the correct assessment of seismic hazard. In addition, by comparing the geographical locations of creeping fault areas with mapped lithologies, we may be able to better understand the underlying causes or mechanisms. We present here the results of our ongoing research into the distribution of creeping fault areas in northern California, where the majority of reported cases are located. We map the surface deformation field of the plate boundary system south and north of the San Francisco Bay Area using persistent scatterer InSAR, which provides a dense spatial coverage of surface deformation measurements across the region, and 'ground truth' these, where possible, with additional surface deformation measurements from GPS. In so doing, we identify deformation consistent with right-lateral shallow creep on sections of five major faults (the Hayward, Calaveras, San Andreas, Rodgers Creek and Concord faults). On the Hayward fault, we are able to map both the extent and distribution of creep rates at depth, constraining the location of a locked zone that is presumably the source of major earthquakes on the fault. We are not able to identify a consistent lithological control for the creep behaviour.

  13. Rheological Control of Interbedded Siliciclastic Strata on Damage Zone Evolution During Fault Growth

    NASA Astrophysics Data System (ADS)

    Wightman, R. H.; Imber, J.; Healy, D.; Holdsworth, R. E.; McCaffrey, K. J.; Jones, R. R.

    2006-12-01

    Fault damage zones can have a major impact on fluid flow through sub-surface reservoirs. The typical resolution of seismic reflection data is such that faults with throws <15m are not imaged, and those with throws >15 m are imaged as discrete planes, revealing none of the smaller scale architecture of the fault damage zones. Previous field studies show that damage zone width scales with fault throw, which suggests that a relationship exists between fault growth and increasing damage zone width. However, this hypothesis remains largely untested and the factors controlling damage zone evolution are poorly understood. This study develops kinematic models to describe the evolution of damage zones during fault growth. The predictions of these models are tested against quantitative geometric attributes of natural fault damage zones preserved in siliciclastic sand/shale sequences from the Carboniferous Northumberland Basin, NE England. These data, obtained from faults with throws spanning 0.1-20 m, were measured from detailed (cm-resolution) digital outcrop models captured using terrestrial laser scanning techniques. Study locations include areas of active open-cast coal mining that provide good 3D exposure of faults during progressive coal extraction. The damage zones comprise complex arrays of structural elements including: fault splays and oversteps; drag folds; rotated fault-bound blocks; sub-parallel fracture sets and ductile shear zones; cataclasite lenses; and intensely deformed scaly gouge. We propose two complimentary kinematic models to explain the structural relationships observed within these damage zones. The first model predicts the development of cataclasite lenses from fault-bounded blocks in contractional oversteps with increasing fault throw. In this scenario, the damage zone width remains approximately constant, defined by the initial fault separation. The second model describes the space incompatibility that develops between discrete fault planes in

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Ampuero, Jean Paul; Mao, Xiaolin

    2016-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  17. 2013 East Bay Seismic Experiment (EBSE): implosion data, Hayward, Calif

    USGS Publications Warehouse

    Catchings, Rufus D.; Strayer, Luther M.; Goldman, Mark R.; Criley, Coyn J.; Garcia, Susan; Sickler, Robert R.; Catchings, Marisol K.; Chan, Joanne; Gordon, Leslie C.; Haefner, Scott; Blair, James Luke; Gandhok, Gini; Johnson, Michaela R.

    2015-01-01

    In August 2013, the California State University, East Bay (CSUEB) in Hayward, California imploded a 13-story building (Warren Hall) that was deemed unsafe because of its immediate proximity to the active trace of the Hayward Fault. The U.S. Geological Survey (USGS) and the CSUEB collaborated on a program to record the seismic waves generated by the collapse of the building. We refer to this collaboration as the East Bay Seismic Experiment (EBSE). The principal objective of recording the seismic energy was to observe ground shaking as it radiated from the source, but the data also may be useful for other purposes. For example, the seismic data may be useful in evaluating the implosion process as it relates to structural engineering purposes. This report provides the metadata needed to utilize the seismic data.

  18. Evolution of elastic wave speed during shear-induced damage and healing within laboratory fault zones

    NASA Astrophysics Data System (ADS)

    Kaproth, Bryan M.; Marone, Chris

    2014-06-01

    Earthquake faults fail and restrengthen repeatedly during the seismic cycle. Faults restrengthen via a set of processes known collectively as fault healing, which is well documented in the laboratory but less well understood in tectonic fault zones. Recent observations of fault zone wave speed following earthquakes suggest opportunities to connect laboratory and field observations of fault healing. However, existing laboratory data lack detail necessary to identify specific processes linking elastic wave speed to fault damage and healing. Here we document changes in elastic properties during laboratory seismic cycles, simulated via periods of nonshear and quasistatic fault slip. Experiments were conducted on brine-saturated halite under conditions favoring pressure solution, analogous to healing processes within and at the base of the seismogenic zone. We find that elastic wave speed (V) and amplitude (A) correlate with porosity. For each percent of porosity lost during compaction, VP increases by ~3%, VS by ~2%, AP by ~10%, and AS by ~7%. Moreover, V and A decrease with granular dilation during fault slip. With increasing shear strain, fabric formation dominates the ultrasonic signals. We find that fault strength depends on fault porosity, making VP and VS potential proxies for fault strength evolution. Our data show that a 1% change in VP or VS results in a friction increase of 0.01 or 0.02, respectively. Within natural fault zones, advances in monitoring elastic wave speed may provide critical information on the evolution of fault strength and seismic hazard throughout the seismic cycle.

  19. Three dimensional elastoplastic response of compliant fault zones to nearby earthquakes: A theoretic study

    NASA Astrophysics Data System (ADS)

    Kang, J.; Duan, B.

    2012-12-01

    Response of compliant fault zone to the nearby dynamic rupture is detected by seismic and InSAR observations. Seismic observations of damage to the Landers fault zone by the Hector Mine earthquake suggest that response of fault zones can be inelastic. Recent two dimensional theoretical studies reveal that inelastic response of fault zones results in distinguished features in the surface residual displacement field that can be detected by InSAR images. In this study, we extend the recent theoretical studies to three dimensions, so that we may compare modeling results with InSAR observations in the future. We use a Drucker-Prager criterion to characterize elastoplastic response of rocks to nearby spontaneous dynamic rupture in an inhomogeneous medium that contains a compliant fault zone. A finite element method is used to simulate dynamic rupture and seismic wave propagations in the model. Preliminary results show that 1) depth dependence of plastic strain within the fault zone may have important effects on the surface deformation field, 2) plastic strain near the Earth's surface within the fault zone can occur in both extensional and compressive quadrants of the rupture, which is different from previous two dimensional studies, and 3) the vertical surface residual displacement is enhanced within the fault zone, while is reduced outside of the fault zone.

  20. From accommodation zones to metamorphic core complexes: Tracking the progressive development of major normal fault systems

    SciTech Connect

    Faulds, J.E. . Dept. of Geology)

    1992-01-01

    The along-strike dimension in rifted continental crust is critical to assessing models of continental extension because individual normal faults or fault systems can potentially be traced from their tips in accommodation zones to their culminations in metamorphic core complexes. Accommodation zones and the linkages between the zones and core complexes have not been thoroughly studied or incorporated extensively into models of continental extension. Regionally extensive, gently dipping normal faults (i.e., detachment faults) that surface in metamorphic core complexes terminate and flip polarity in accommodation zones. Diametrical lateral transport of upper-plate rocks in positively dipping detachment terranes should presumably induce strike-slip faulting on segments of accommodation zones paralleling the extension direction. Most accommodation zones correspond, however, to belts of intermeshing conjugate normal faults with little strike-slip faulting. Normal faults simply terminate along-strike in the zones with little, if any, transfer of slip to strike-slip faults. Decreases in cumulative strain within individual normal fault systems toward some accommodation zones cannot alone account for the lack of strike-slip faulting. These findings pose a serious challenge to generally accepted notions of large-magnitude, lateral motion of parts of detachment terranes. Large-scale lateral translations of rifted continental crust may be governed more by discrete axes of extension than by detachment geometries. The dovetail-like interfingering of conjugate normal fault systems and attendant tilt-block domains observed in some accommodation zones (e.g., Colorado River extensional corridor, US) does suggest, however, that at least some major normal faults projecting into the zones from metamorphic core complexes have listric geometries that flatten out at relatively shallow depths.

  1. Geodetic Investigation of Compliant Fault Zones on the San Francisco Peninsula segment of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Materna, K.; Burgmann, R.

    2015-12-01

    At many places along the San Andreas Fault, geodetic and seismic studies have suggested the presence of near-field compliant fault zones (CFZs). These zones of damaged rock display reduced elastic moduli compared to intact rock, resulting in both higher geodetic strain rates and lower seismic velocities within the fault zones. In this study, we investigate the CFZ surrounding the San Andreas Fault in the San Francisco Peninsula by examining interseismic deformation over the past several decades. We use new and existing survey GPS measurements, as well as older electronic distance measurements, to characterize the deformation of the CFZ. The data come from networks at Black Mountain and Lake San Andreas, both small-aperture geodetic networks on the San Francisco Peninsula with survey GPS occupations spanning at least 15 years. We compare the inferred fault zone properties between the two networks, which are separated by less than 40 kilometers but which represent different geologic boundaries and show different fault ages. We also compare patterns in seismicity between the two regions. The differences in inferred fault parameters between these two regions may be related to differences in fault age and development, giving clues into how CFZs develop over time.

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

    NASA Astrophysics Data System (ADS)

    Myers, Rodrick; Aydin, Atilla

    2004-05-01

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

  3. Fault zone architecture, San Jacinto fault zone, southern California: evidence for focused fluid flow and heat transfer in the shallow crust

    NASA Astrophysics Data System (ADS)

    Morton, N.; Girty, G. H.; Rockwell, T. K.

    2011-12-01

    We report results of a new study of the San Jacinto fault zone architecture in Horse Canyon, SW of Anza, California, where stream incision has exposed a near-continuous outcrop of the fault zone at ~0.4 km depth. The fault zone at this location consists of a fault core, transition zone, damage zone, and lithologically similar wall rocks. We collected and analyzed samples for their bulk and grain density, geochemical data, clay mineralogy, and textural and modal mineralogy. Progressive deformation within the fault zone is characterized by mode I cracking, subsequent shearing of already fractured rock, and cataclastic flow. Grain comminution advances towards the strongly indurated cataclasite fault core. Damage progression towards the core is accompanied by a decrease in bulk and grain density, and an increase in porosity and dilational volumetric strain. Palygorskite and mixed-layer illite/smectite clay minerals are present in the damage and transition zones and are the result of hydrolysis reactions. The estimated percentage of illite in illite/smectite increases towards the fault core where the illite/smectite to illite conversion is complete, suggesting elevated temperatures that may have reached 150°C. Chemical alteration and elemental mass changes are observed throughout the fault zone and are most pronounced in the fault core. We conclude that the observed chemical and mineralogical changes can only be produced by the interaction of fractured wall rocks and chemically active fluids that are mobilized through the fault zone by thermo-pressurization during and after seismic events. Based on the high element mobility and absence of illite/smectite in the fault core, we expect that greatest water/rock ratios occur within the fault core. These results indicate that hot pore fluids circulate upwards through the fractured fault core and into the surrounding damage zone. Though difficult to constrain, the site studied during this investigation may represent the top

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

    USGS Publications Warehouse

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

    2004-01-01

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

  5. Characterizing Fault Damage Zones in the Field and Laboratory; Scaling and Physical Properties

    NASA Astrophysics Data System (ADS)

    Faulkner, D. R.; Armitage, P. J.; Blake, O. O.; Mitchell, T. M.

    2011-12-01

    Fault damage zones are a key component of faults as they control the fluid flow, rupture and seismological properties of faults. Fracturing around faults occurs on a range of scales, from small scale (microfracturing) to larger scale (macrofracturing), with varying intensities ranging from background levels to pervasive pulverization of the country rock. Fracturing generally results in permeability increases in crystalline rocks. Fracturing in the damage zone during earthquake rupture leads to energy loss, and pre-existing fracture damage and associated modifications of elastic properties may control rupture properties such as directivity. Despite their importance, the full characterization of the spatial extent of damage zones and their associated physical properties is still at an early stage. Recent field measurements of the width of damage zones suggest that they scale positively with fault displacement, although this relationship is masked by other parameters such as depth of faulting, lithology, mode of faulting and tectonic environment. The well-established exponential decay of fracture damage with distance from the fault likely relates to elastic decay of stress. Determining the physical properties of natural fault damage zones has proved problematic, as fault-related fractures in the damage zones are commonly modified by healing and sealing, and the rocks are generally affected by exhumation. Another approach is to mimic the level of fracture damage on the small scale in laboratory experiments on initially intact rocks. Here, experiments have been completed under triaxial stresses. Variably fractured samples are produced by stress cycling, and the seismic velocity, crack surface area and permeability have been measured. These physical properties can be mapped onto natural fault damage zones by relating the fracture damage in laboratory samples with that in natural faults. The results give insights into the transport properties of faults and the energy

  6. Upper crustal fault zones: Constraining structure and dynamics using electrical conductivity

    NASA Astrophysics Data System (ADS)

    Hoffmann-Rothe, A.; Ritter, O.; Janssen, C.

    2003-04-01

    Upper crustal fault zones, either fossil or active, are often connected with electrical conductivity anomalies. These anomalies depend on properties such as the porosity/permeability of the fault zone material, the fluid content or the state of healing/cementation of the fault-fracture mesh; properties that moreover control the ability of a fault to accumulate strain. Structural heterogeneities caused by the faulting process are therefore believed to either increase or decrease the electrical conductivity in the fault's vicinity. We show results of two combined magnetotelluric and structural studies of large scale strike-slip dominated fault zones. The trench-linked West Fault (WF) in Northern Chile shows a pronounced anomaly of high conductivity confined to the central region of the fault. The zone of high conductivity is approximately 400 m wide and 1.5 km deep. Structural mapping reveals that this conductivity enhancement is closely related to a mesh of faults and fractures ('damage zone') that most likely provides a pathway for fluids. In contrast to this, the Dead Sea Transform Fault (DST) in Jordan shows no obvious evidence of such a fault zone conductor as the DST is expressed as the boundary between two different domains of conductivity on either side of the fault. Correspondingly, a marked macroscopic fault-fracture mesh in the fault core region is not developed. Comparison of the results from the WF with published data from the San Andreas Fault suggests generally a positive correlation of fault activity with geometric extent and conductivity of the fault zone conductor. However, the Dead Sea Transform Fault apparently does not comply with this scheme although it is active. It is possible that intense localisation of deformation caused the formation of a very narrow fault gouge, which cannot be resolved with the MT experiments. This result could suggest that the existence or non-existence of high conductivity in the central parts of large scale strike

  7. Hydromechanical heterogeneities of a mature fault zone: impacts on fluid flow.

    PubMed

    Jeanne, Pierre; Guglielmi, Yves; Cappa, Frédéric

    2013-01-01

    In this paper, fluid flow is examined for a mature strike-slip fault zone with anisotropic permeability and internal heterogeneity. The hydraulic properties of the fault zone were first characterized in situ by microgeophysical (VP and σc ) and rock-quality measurements (Q-value) performed along a 50-m long profile perpendicular to the fault zone. Then, the local hydrogeological context of the fault was modified to conduct a water-injection test. The resulting fluid pressures and flow rates through the different fault-zone compartments were then analyzed with a two-phase fluid-flow numerical simulation. Fault hydraulic properties estimated from the injection test signals were compared to the properties estimated from the multiscale geological approach. We found that (1) the microgeophysical measurements that we made yield valuable information on the porosity and the specific storage coefficient within the fault zone and (2) the Q-value method highlights significant contrasts in permeability. Fault hydrodynamic behavior can be modeled by a permeability tensor rotation across the fault zone and by a storativity increase. The permeability tensor rotation is linked to the modification of the preexisting fracture properties and to the development of new fractures during the faulting process, whereas the storativity increase results from the development of micro- and macrofractures that lower the fault-zone stiffness and allows an increased extension of the pore space within the fault damage zone. Finally, heterogeneities internal to the fault zones create complex patterns of fluid flow that reflect the connections of paths with contrasting properties.

  8. Slip on 'Weak' Faults by the Rotation of Regional Stress in the Fracture Damage Zone

    NASA Astrophysics Data System (ADS)

    Faulkner, D. R.; Mitchell, T. M.; Healy, D.; Heap, M. J.

    2006-12-01

    The concept of stress rotation within fault zones is important in order to understand the strength of fault zones that are unfavourably oriented with respect to the remotely-applied driving stress. The San Andreas 'stress-heat flow paradox' and slip on low-angle normal faults imply that fault zone weakening must occur. Possible explanations for this weakening include weak fault materials, dynamic slip weakening and elevated pore fluid pressures. Stress rotation within the fault zone must accompany high pore fluid pressures, or effective σ3 will be pushed well into the tensile field, resulting in hydrofracture, pore fluid pressure loss and fault strengthening. Here we show from field observations of a major tectonic fault, laboratory experiments and numerical modelling, that stress rotation is significant within the fractured damage zone surrounding a fault. We characterize the microfracture damage surrounding a major strike-slip fault within the Atacama fault system in northern Chile, which shows an exponential decrease with distance from the fault core. We then relate the microfracture damage to changes in elastic properties as measured in laboratory experiments. The field and laboratory data are then used in a two-dimensional plane strain model to show how the remotely applied stress field is affected as the fault core is approached. We show that greatest principal stress orientations of 80° with respect to the fault plane can be rotated to less than 45° within the damage zone. The damage-induced change in elastic properties provide the necessary stress rotation to allow high pore pressure faulting, without resulting in hydrofracture.

  9. Inferred fluid flow through fault damage zones based on the observation of stalactites in carbonate caves

    NASA Astrophysics Data System (ADS)

    Kim, Young-Seog; Sanderson, David J.

    2010-09-01

    Faults and fractures are important factors that control fluid flow in rock masses in hydrothermal, groundwater, and hydrocarbon systems. In this paper we examine local variations in fluid flow as evidenced by the distribution patterns and sizes of stalactites in fractured limestone. We observe that the size and distribution of stalactites relate to fluid flow and is strongly controlled by the fracture apertures, intersection of fractures, and development of damage zones around a fault. Fault damage zones are the volumes of deformed wall rocks around a fault surface that result from the initiation, propagation, interaction, termination, and build-up of slip along the fault. They are divided into tip-, wall-, and linkage damage zones depending on their location along the fault. The pattern of deformation within a damage zone mainly depends on fault tip modes (mode II or III), the 3-D locations around a fault surface, and the evolutionary stage of the fault. The development of different structures within damage zones gives valuable information about fault initiation and termination, fault propagation and growth, and fluid flow. Stalactites indicate fluid flow variation within a fault in that fluid flow is high in dilational jogs, variable along the main fault traces, and low in contractional jogs. Variation in ore fluid flow within faults is also important in controlling the position of ore shoots in structurally-controlled hydrothermal mineral deposits. Thus, the characteristics of fluid flow in fractured carbonate rocks can be related to patterns of damage around faults. Hence, the mapping of damage zones can be applied to the study of fracture-controlled fluid flow in the fields of petroleum geology, hydrogeology, and ore deposits.

  10. Hydrogeological properties of fault zones in a karstified carbonate aquifer (Northern Calcareous Alps, Austria)

    NASA Astrophysics Data System (ADS)

    Bauer, H.; Schröckenfuchs, T. C.; Decker, K.

    2016-08-01

    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. Cataclastic rocks and sheared, strongly cemented breccias form low-permeability (<1 mD) domains along faults. Fractured rocks with fracture densities varying by a factor of 10 and fracture porosities varying by a factor of 3, and dilation breccias with average porosities >3 % and permeabilities >1,000 mD form high-permeability domains. With respect to fault-zone architecture and rock content, which is demonstrated to be different for dolostone and limestone, four types of faults are presented. Faults with single-stranded minor fault cores, faults with single-stranded permeable fault cores, and faults with multiple-stranded fault cores are seen as conduits. Faults with single-stranded impermeable fault cores are seen as conduit-barrier systems. Karstic carbonate dissolution occurs along fault cores in limestones and, to a lesser degree, dolostones and creates superposed high-permeability conduits. On a regional scale, faults of a particular deformation event have to be viewed as forming a network of flow conduits directing recharge more or less rapidly towards the water table and the springs. Sections of impermeable fault cores only very locally have the potential to create barriers.

  11. Fault Zone Drainage, Heating and Melting During Earthquake Slip

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  13. Wasatch fault zone, Utah - segmentation and history of Holocene earthquakes

    USGS Publications Warehouse

    Machette, Michael N.; Personius, Stephen F.; Nelson, Alan R.; Schwartz, David P.; Lund, William R.

    1991-01-01

    The Wasatch fault zone (WFZ) forms the eastern boundary of the Basin and Range province and is the longest continuous, active normal fault (343 km) in the United States. It underlies an urban corridor of 1.6 million people (80% of Utah's population) representing the largest earthquake risk in the interior of the western United States. The authors have used paleoseismological data to identify 10 discrete segments of the WFZ. Five are active, medial segments with Holocene slip rates of 1-2 mm a-1, recurrence intervals of 2000-4000 years and average lengths of about 50 km. Five are less active, distal segments with mostly pre-Holocene surface ruptures, late Quaternary slip rates of <0.5 mm a-1, recurrence intervals of ???10,000 years and average lengths of about 20 km. Surface-faulting events on each of the medial segments of the WFZ formed 2-4-m-high scarps repeatedly during the Holocene. Paleoseismological records for the past 6000 years indicate that a major surface-rupturing earthquake has occurred along one of the medial segments about every 395 ?? 60 years. However, between about 400 and 1500 years ago, the WFZ experienced six major surface-rupturing events, an average of one event every 220 years, or about twice as often as expected from the 6000-year record. Evidence has been found that surface-rupturing events occurred on the WFZ during the past 400 years, a time period which is twice the average intracluster recurrence interval and equal to the average Holocene recurrence interval.

  14. Coupled fragmentation and silicification processes in fault zones.

    NASA Astrophysics Data System (ADS)

    Ord, Alison; Seybold, Lina; Hobbs, Bruce; Kruhl, Jörn; Heuss, Soraya; Blenkinsop, Tom

    2015-04-01

    We explore some possible interactions of mechanical and chemical processes which may have led to the patterns of fragmentation and quartz precipitation observed at the Fountain Range Fault at Fountain Springs. Seybold et al. (this session) describe features which indicate a multiphase fragmentation and quartz precipitation history of the Fountain Range Fault (Mt Isa Inlier, Australia). They infer that intense fragmentation, together with fluid infiltration and quartz crystallization in pore space, led to fine-grained cataclastic and silicified masses, followed by numerous events of quartz-vein formation and, again, cataclasis probably leading to flow of particle-fluid suspensions. They proposed the macro- and microstructures to reflect the interaction of repeated processes of fragmentation, fluid flux, quartz precipitation and cataclastic flow during the long-lasting history of the fault zone. We compare and contrast the patterns arising from the modelled interactions with the observed patterns in a quantitative manner through the application of wavelets. There are all sorts of wavelets, each useful for different patterns. The point is that all of them are localised wave packets of some kind the wavelet is scanned across the image with different magnifications and we look to see how closely the wavelet matches the image at a particular scale. It is a "fabric microscope" that enables one to zoom into the details of any deformation fabric and extract information on the ways in which the geometry of every part of the fabric scales with size. This enables a scalogram to be constructed and from that the singularity spectrum with its many measures of features of the geometry. The wavelet analysis enables us to compare in a quantitative manner the results of numerical modeling based on a coupled damage quartz precipitation model with field observations.

  15. Fault segmentation: New concepts from the Wasatch Fault Zone, Utah, USA

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    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 (<3 ka) and best-constrained earthquakes, differences in earthquake timing across prominent primary 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.

  16. Fault segmentation: New concepts from the Wasatch Fault Zone, Utah, USA

    USGS Publications Warehouse

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

    2016-01-01

    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 (<3 ka) and best-constrained earthquakes, differences in earthquake timing across prominent primary 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.

  17. KONOCTI BAY FAULT ZONE, LAKE COUNTY, CALIFORNIA: A REEVALUATION.

    USGS Publications Warehouse

    Thompson, J. Michael

    1984-01-01

    The Konocti Bay Fault Zone (KBFZ), initially regarded by some as a promising liquid-dominated hydrothermal system, has been a disappointment as a geothermal prospect. Five exploratory wells have been drilled in the vicinity of the KBFZ, but none of them are producing thermal fluids; in fact, three have been abandoned. This may be because hydrothermal fluid discharges along the KBFZ are low. The Na-K-Ca and Na-Li geothermometers indicate that the waters discharging around Howard and Seigler Springs may have equilibrated at temperatures above 200 degree C. If boiling has occurred or is occurring, a chloride-enthalpy diagram may be appropriate. Such a diagram for the KBFZ shows that a water in excess of 250 degree C existed or may exist in the area. However, because currently measured temperatures rarely exceed 50 degree C and magnesium concentration in the water is high, very little deep high temperature water may be present. Refs.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Berg, Silje S.; Skar, Tore

    2005-10-01

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

  20. CO2/Brine transport into shallow aquifers along fault zones.

    PubMed

    Keating, Elizabeth H; Newell, Dennis L; Viswanathan, Hari; Carey, J W; Zyvoloski, G; Pawar, Rajesh

    2013-01-01

    Unintended release of CO(2) from carbon sequestration reservoirs poses a well-recognized risk to groundwater quality. Research has largely focused on in situ CO(2)-induced pH depression and subsequent trace metal mobilization. In this paper we focus on a second mechanism: upward intrusion of displaced brine or brackish-water into a shallow aquifer as a result of CO(2) injection. Studies of two natural analog sites provide insights into physical and chemical mechanisms controlling both brackish water and CO(2) intrusion into shallow aquifers along fault zones. At the Chimayó, New Mexico site, shallow groundwater near the fault is enriched in CO(2) and, in some places, salinity is significantly elevated. In contrast, at the Springerville, Arizona site CO(2) is leaking upward through brine aquifers but does not appear to be increasing salinity in the shallow aquifer. Using multiphase transport simulations we show conditions under which significant CO(2) can be transported through deep brine aquifers into shallow layers. Only a subset of these conditions favor entrainment of salinity into the shallow aquifer: high aspect-ratio leakage pathways and viscous coupling between the fluid phases. Recognition of the conditions under which salinity is favored to be cotransported with CO(2) into shallow aquifers will be important in environmental risk assessments. PMID:22799449

  1. The Honey Lake fault zone, northeastern California: Its nature, age, and displacement

    SciTech Connect

    Wagner, D.L.; Saucedo, G.J.; Grose, T.L.T.

    1990-01-01

    The Honey Lake fault zone of northeastern California is composed of en echelon, northwest trending faults that form the boundary between the Sierra Nevada and the Basin Ranges provinces. As such the Honey Lake fault zone can be considered part of the Sierra Nevada frontal fault system. It is also part of the Walker Lane of Nevada. Faults of the Honey Lake zone are vertical with right-lateral oblique displacements. The cumulative vertical component of displacement along the fault zone is on the order of 800 m and right-lateral displacement is at least 10 km (6 miles) but could be considerably more. Oligocene to Miocene (30 to 22 Ma) age rhyolite tuffs can be correlated across the zone, but mid-Miocene andesites do not appear to be correlative indicating the faulting began in early to mid-Miocene time. Volcanic rocks intruded along faults of the zone, dated at 16 to 8 Ma, further suggest that faulting in the Honey Lake zone was initiated during mid-Miocene time. Late Quaternary to Holocene activity is indicated by offset of the 12,000 year old Lake Lahontan high stand shoreline and the surface rupture associated with the 1950 Fort Sage earthquake.

  2. Imaging the Seattle Fault Zone with high-resolution seismic tomography

    USGS Publications Warehouse

    Calvert, A.J.; Fisher, M.A.

    2001-01-01

    The Seattle fault, which trends east-west through the greater Seattle metropolitan area, is a thrust fault that, around 1100 years ago, produced a major earthquake believed to have had a magnitude greater than 7. We present the first high resolution image of the shallow P wave velocity variation across the fault zone obtained by tomographic inversion of first arrivals recorded on a seismic reflection profile shot through Puget Sound adjacent to Seattle. The velocity image shows that above 500 m depth the fault zone extending beneath Seattle comprises three distinct fault splays, the northernmost of which dips to the south at around 60??. The degree of uplift of Tertiary rocks within the fault zone suggests that the slip-rate along the northernmost splay during the Quaternary is 0.5 mm a-1, which is twice the average slip-rate of the Seattle fault over the last 40 Ma.

  3. Ductile shear zones beneath strike-slip faults: Implications for the thermomechanics of the San Andreas fault zone

    USGS Publications Warehouse

    Thatcher, W.; England, P.C.

    1998-01-01

    We have carried out two-dimensional (2-D) numerical experiments on the bulk flow of a layer of fluid that is driven in a strike-slip sense by constant velocities applied at its boundaries. The fluid has the (linearized) conventional rheology assumed to apply to lower crust/upper mantle rocks. The temperature dependence of the effective viscosity of the fluid and the shear heating that accompanies deformation have been incorporated into the calculations, as has thermal conduction in an overlying crustal layer. Two end-member boundary conditions have been considered, corresponding to a strong upper crust driving a weaker ductile substrate and a strong ductile layer driving a passive, weak crust. In many cases of practical interest, shear heating is concentrated close to the axial plane of the shear zone for either boundary condition. For these cases, the resulting steady state temperature field is well approximated by a cylindrical heat source embedded in a conductive half-space at a depth corresponding to the top of the fluid layer. This approximation, along with the application of a theoretical result for one-dimensional shear zones, permits us to obtain simple analytical approximations to the thermal effects of 2-D ductile shear zones for a range of assumed rheologies and crustal geotherms, making complex numerical calculations unnecessary. Results are compared with observable effects on heat flux near the San Andreas fault using constraints on the slip distribution across the entire fault system. Ductile shearing in the lower crust or upper mantle can explain the observed increase in surface heat flux southeast of the Mendocino triple junction and match the amplitude of the regional heat flux anomaly in the California Coast Ranges. Because ductile dissipation depends only weakly on slip rate, faults moving only a few millimeters per year can be important heat sources, and the superposition of effects of localized ductile shearing on both currently active and now

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

    NASA Astrophysics Data System (ADS)

    Hillers, Gregor; Campillo, Michel

    2016-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  6. Hydraulic characteristics of fault zones and their impact on groundwater flow

    NASA Astrophysics Data System (ADS)

    Banks, E.; Cook, P. G.

    2014-12-01

    An important source of groundwater recharge to sedimentary basin aquifers is from mountain block recharge and in many instances the rate and direction of groundwater flow is controlled by regional scale fault systems. Vertical faults may act as either barriers to horizontal groundwater flow perpendicular to the fault, conduits to horizontal flow along the fault or a combination of both. Faults can also provide conduits for vertical flow. There are very few evaluations of the impact of fault zones on groundwater flow. This study investigated groundwater flow characteristics across a fault zone between a fractured rock and sedimentary aquifer system. Hydrogeological and hydrogeophysical techniques were used to design a drilling program whereby multi-level observation wells were constructed at 3 field sites either side of the Willunga fault in the Willunga Basin, South Australia, up to 300 metres below ground level. The observed hydraulic gradients across the fault zone were very significant (2.5), with a head difference of 80 metres over a horizontal distance of less than 30 metres. Despite the high hydraulic gradient, calculating the groundwater flux across the fault was more complicated. A 3D numerical model was developed to determine the relative proportion of groundwater flow across the fault and flow parallel to the fault. This model was also used to assess the impact of the fault zone permeability on the hydraulic gradients across the fault and evaluate the mechanisms and behaviour of these conduit-barrier systems to groundwater flow. Groundwater age dating and hydrochemical analyses were conducted to examine and constrain the contributing end members of the different aquifer systems and trace groundwater movement and residence time across the fault zone.

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

    USGS Publications Warehouse

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

    2010-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  9. 3D modeling of fault-zone architecture and hydraulic structure along a major Alpine wrench lineament: the Pusteria Fault

    NASA Astrophysics Data System (ADS)

    Bistacchi, A.; Massironi, M.; Menegon, L.

    2007-05-01

    The E-W Pusteria (Pustertal) line is the eastern segment of the Periadriatic lineament, the > 600 km tectonic boundary between the Europe and Adria-vergent portions of the Alpine Collisional Orogen. The lithospheric-scale Periadriatic lineament is characterized by a transcurrent polyphase activity of Tertiary age, and is marked by an array of calcalkaline to shoshonitic magmatic bodies. At the map scale, the western edge of the Pusteria line is characterized by a complex network of generally transcurrent brittle fault zones, interconnected by a full spectrum of transtensional and transpressional features related to releasing and restraining bands respectively. An older ductile/brittle sinistral activity can be recognized in some segments of the fault thanks to their relationships with a strongly tectonized Oligocene tonalite/diorite body (Mules tonalitic "lamella"), emplaced along the Pusteria line, and minor related dikes. A late dextral activity involved the whole Pusteria Fault network and is consistent with the Eastward escape of a major lithospheric block of the Eastern Alps towards the Pannonian basin. During its polyphase activity, the fault network developed a complex architecture, showing different kinds of damage and core zones. Here we report the first results of a detailed mapping project in which, in addition to a traditional structural geology work, the spatial distribution of fault rocks in core zones and the degree and characteristics of fracturing (e.g. joint spacing and number of joint sets) in damage zones are taken into account. As regards the quantitative characterization of damage zones, a new description schema, partly inspired by engineering geology classifications, is proposed. The results of this work are implemented in a 3D structural model (developed with gOcad), allowing the study of the complex relationships among the various structural, mechanical and lithological parameters which concur in the development of the fault-zone

  10. Fault zone architecture of a major oblique-slip fault in the Rawil depression, Western Helvetic nappes, Switzerland

    NASA Astrophysics Data System (ADS)

    Gasser, D.; Mancktelow, N. S.

    2009-04-01

    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

  11. Shoreline and Oceano Fault Zones' Intersection Geometry, San Luis Obispo Bay, Offshore South Central Coastal California

    NASA Astrophysics Data System (ADS)

    Hogan, P. J.; Nishenko, S. P.; Greene, H. G.; Bergkamp, B.

    2015-12-01

    As part of the Central Coastal California Seismic Imaging Project, high-resolution 3D low energy marine seismic-reflection data were acquired within San Luis Obispo Bay in 2011 and 2012. Mapping of the sediment-buried bedrock surface using 2D and 3D data clearly reveals that the trace of the Shoreline fault zone bifurcates at Souza Rock. The eastern strand is a reverse fault that trends toward the east-southeast, connecting with the Oceano fault zone onshore. The Shoreline fault is a vertical dextral fault with a very linear geometry that continues south to near the Santa Maria river mouth, and may intersect the Casmalia fault onshore. Both of these fault strands are crossed by Pleistocene low-stand paleochannels eroded into bedrock, and are buried by marine and non-marine sediment. The 3D data show that both the Oceano and Shoreline faults are narrow, well defined fault zones. The reverse slip rate for the Oceano fault (~0.1 mm/y.) falls within published slip rate estimates for the Oceano fault onshore (0.01-0.20 mm/y). The dextral slip rate for the Shoreline fault southeast of Souza Rock is estimated to be 0.06 mm/y. Souza Rock is located on the hanging wall of the Oceano Fault, north of the point of intersection between the Shoreline and Oceano faults. Water depths shoal from 60 m on the surrounding seafloor to 5 m on top of Souza Rock. This structure is interpreted as a structural popup in a restraining bend where the N65°W-trending Oceano fault intersects the N25°W-trending Shoreline fault. The structural geometry near the point of intersection has several minor secondary fault strands, but is remarkably simple.

  12. How can fluid overpressures be developed and maintained in crustal fault zones ?

    NASA Astrophysics Data System (ADS)

    LECLÈRE, H.; Cappa, F.; Faulkner, D. R.; Armitage, P. J.; Blake, O. O.; Fabbri, O.

    2013-12-01

    The presence of fluid overpressure in crustal fault zones is known to play a key role on the stability of faults and it has often been invoked to explain the triggering of earthquakes and the apparent weakness of misoriented faults. However, the mechanisms allowing the development and maintenance of fluid overpressures in fault remain unresolved. We investigate how fluid overpressures can be developed and maintained in complex fault zones with hydraulic and elastic heterogeneities. Here we address this question combining geological observations, laboratory experiments and hydromechanical models of an active crustal fault zone in the Ubaye-Argentera area (southeastern France). The fault zone studied is located in the Argentera external crystalline massif and is connected to regional NW-SE steeply-dipping dextral strike-slip faults with an offset of several kilometers. The fault zone cuts through migmatitic gneisses composed of quartz, K-feldspar, plagioclase, biotite and muscovite. It exposes several anastomosing core zones surrounded by damage zones with a pluri-decametric total width. The core zones are made up of centimetric to pluridecimetric phyllosilicate-rich gouge layers while the damage zones are composed of pluri-metric phyllonitic rock derived from mylonite. The determination of fault structure in the field and its hydraulic and mechanical properties in the lab are key aspects to improve our understanding of the role of fluids in fault mechanics and earthquake triggering. Here, the permeability and elastic moduli of the host rock, damage zone and fault core were measured from natural plugs with a diameter of 20 mm and lengths between 26 to 51 mm, using a high-pressure hydrostatic fluid-flow apparatus. Measurements were made with confining pressures ranging from 30 to 210 MPa and using argon pore fluid pressure of 20 MPa. Data show a reduction of the permeability values of one order of magnitude between host rock and fault damage zone and a decrease of 50

  13. Style of deformation along the Death Valley-Furnace Creek fault zone and other faults in the southern Walker Lane, Nevada and California

    SciTech Connect

    Noller, J.S. ); Reheis, M.C. )

    1993-04-01

    Quaternary normal and right-lateral faults and associated lineaments in the southern part of the Walker Lane are anomalous with respect to the north-striking normal faults in most of the central Great Basin. The authors identify and characterize many faults and lineaments that were previously unmapped, with the exception of faults in the Death Valley-Furnace Creek fault zone (DVFCFZ) and some faults in and near the Nevada Test Site. Faults and associated lineaments in deposits of late Cenozoic age are distinguished on the basis of age of most recent activity and orientation, and are grouped into two domains. One domain is characterized by northwest-striking faults and lineaments and associated north-striking en echelon structures within the DVFCFZ and the Pahrump fault zone; the other domain is characterized by north- to northeast-striking faults and linearments within a broad region east of the DVFCFZ that narrows southward toward the Pahrump fault zone. Preliminary observations of faults and linearments suggest dominantly right-oblique slip in the first domain and dominantly dip-slip in the second domain. The DVFCFZ is a regional right-lateral strike-slip system that shows changes in style of deformation along strike. Numerous normal faults at the northern end of the DVFCFZ in northern fish Lake Valley and the Volcanic Hills form an extensional right step that links the DVFCFZ with northwest-striking right-lateral faults of the northern part of the Walker Lane. South of this extensional step, the DVFCFZ trends southeast along strike-slip faults from central Fish Lake Valley to the latitude of Furnace Creek. From Furnace Creek, the fault zone apparently steps left to the Pahrump fault zone in the area of Ash Meadows where a complex zone of folds and faults of diverse orientation suggest local compression. This stepover coincides with east-northeast-striking faults that appear to be an extension of the left-lateral Rock Valley fault zone.

  14. Deep rock damage in the San Andreas Fault revealed by P- and S-type fault-zone-guided waves

    USGS Publications Warehouse

    Ellsworth, William L.; Malin, Peter E.

    2011-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Bauer, Helene; Decker, Kurt

    2014-05-01

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

  17. Geometry and kinematics of adhesive wear in brittle strike-slip fault zones

    NASA Astrophysics Data System (ADS)

    Swanson, Mark T.

    2005-05-01

    Detailed outcrop surface mapping in Late Paleozoic cataclastic strike-slip faults of coastal Maine shows that asymmetric sidewall ripouts, 0.1-200 m in length, are a significant component of many mapped faults and an important wall rock deformation mechanism during faulting. The geometry of these structures ranges from simple lenses to elongate slabs cut out of the sidewalls of strike-slip faults by a lateral jump of the active zone of slip during adhesion along a section of the main fault. The new irregular trace of the active fault after this jump creates an indenting asperity that is forced to plow through the adjoining wall rock during continued adhesion or be cut off by renewed motion along the main section of the fault. Ripout translation during adhesion sets up the structural asymmetry with trailing extensional and leading contractional ends to the ripout block. The inactive section of the main fault trace at the trailing end can develop a 'sag' or 'half-graben' type geometry due to block movement along the scallop-shaped connecting ramp to the flanking ripout fault. Leading contractional ramps can develop 'thrust' type imbrication and forces the 'humpback' geometry to the ripout slab due to distortion of the inactive main fault surface by ripout translation. Similar asymmetric ripout geometries are recognized in many other major crustal scale strike-slip fault zones worldwide. Ripout structures in the 5-500 km length range can be found on the Atacama fault system of northern Chile, the Qujiang and Xiaojiang fault zones in western China, the Yalakom-Hozameen fault zone in British Columbia and the San Andreas fault system in southern California. For active crustal-scale faults the surface expression of ripout translation includes a coupled system of extensional trailing ramps as normal oblique-slip faults with pull-apart basin sedimentation and contractional leading ramps as oblique thrust or high angle reverse faults with associated uplift and erosion. The

  18. Smoothing and re-roughening processes: The geometric evolution of a single fault zone

    NASA Astrophysics Data System (ADS)

    Shervais, Katherine A. H.; Kirkpatrick, James D.

    2016-10-01

    The geometry of a fault zone exerts a major control on earthquake rupture processes and source parameters. Observations previously compiled from multiple faults suggest that fault surface shape evolves with displacement, but the specific processes driving the evolution of fault geometry within a single fault zone are not well understood. Here, we characterize the deformation history and geometry of an extraordinarily well-exposed fault using maps of cross-sectional exposures constructed with the Structure from Motion photogrammetric method. The La Quinta Fault, located in southern California, experienced at least three phases of deformation. Multiple layers of ultracataclasite formed during the most recent phase. Crosscutting relations between the layers define the evolution of the structures and demonstrate that new layers formed successively during the deformation history. Wear processes such as grain plucking from one layer into a younger layer and truncation of asperities at layer edges indicate that the layers were slip zones and the contacts between them slip surfaces. Slip surfaces that were not reactivated or modified after they were abandoned exhibit self-affine geometry, preserving the fault roughness from different stages of faulting. Roughness varies little between surfaces, except the last slip zone to form in the fault, which is the smoothest. This layer contains a distinct mineral assemblage, indicating that the composition of the fault rock exerts a control on roughness. In contrast, the similar roughness of the older slip zones, which have comparable mineralogy but clearly crosscut one another, suggests that as the fault matured the roughness of the active slip surface stayed approximately constant. Wear processes affected these layers, so for roughness to stay constant the roughening and smoothing effects of fault slip must have been approximately balanced. These observations suggest fault surface evolution occurs by nucleation of new surfaces and

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

    NASA Astrophysics Data System (ADS)

    Scibek, J.

    2015-12-01

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

  20. Tectonic controls on fault-zone permeability in a geothermal reservoir at Dixie Valley, Nevada

    USGS Publications Warehouse

    Hickman, Stephen; Zoback, Mark; Benoit, Richard

    1998-01-01

    To determine factors controlling permeability variations within and adjacent to a fault-hosted geothermal reservoir at Dixie Valley, Nevada, we conducted borehole televiewer observations of wellbore failure (breakouts and cooling cracks) together with hydraulic fracturing stress measurements in six wells drilled into the Stillwater fault zone at depths of 2 to 3 km. Measurements in highly permeable wells penetrating the main geothermal reservoir indicate that the local orientation of the least horizontal principal stress, Shmin, is nearly optimal for normal faulting on the Stillwater fault. Hydraulic fracturing tests from these wells further show that the magnitude of Shmin is low enough to lead to frictional failure on the Stillwater and nearby subparallel faults, suggesting that fault slip is responsible for the high reservoir productivity. Similar measurements were conducted in two wells penetrating a relatively impermeable segment of the Stillwater fault zone, located approx. 8 and 20 km southwest of the geothermal reservoir (wells 66-21 and 45-14, respectively). The orientation of Shmin in well 66-21 is near optimal for normal faulting on the nearby Stillwater fault, but the magnitude of Shmin is too high to result in incipient frictional failure. In contrast, although the magnitude of Shmin in well 45-14 is low enough to lead to normal faulting on optimally oriented faults, the orientation of the Stillwater fault near this well is rotated by approx. 40?? from the optimal orientation for normal faulting. This misorientation, coupled with an apparent increase in the magnitude of the greatest horizontal principal stress in going from the producing to nonproducing wells, acts to inhibit frictional failure on the Stillwater fault zone in proximity to well 45-14. Taken together, data from the nonproducing and producing wells thus suggest that a necessary condition for high reservoir permeability is that the Stillwater fault zone be critically stressed for

  1. Fault segment linkage and growth of the Polopos transpressive fault zone and its influence on Pleistocene drainage captures (southeastern Betics).

    NASA Astrophysics Data System (ADS)

    Giaconia, F.; Booth-Rea, G.; Martínez-Martínez, J. M.; Azañón, J. M.; Villegas, I.

    2012-04-01

    The Polopos fault zoneis a dextral-reverse fault-system that developed under Neogene to Quaternary N/S to NNW/SSE convergence between Africa and Iberia. This fault zone is formed by three main fault segments, the North and South Gafarillos dextral strike-slip faults, and the North Alhamilla reverse fault. The whole fault zone with an approximate length of 30 km has an E/W to ESE/WNW orientation and helicoidal geometry that permits the transfer of oblique SE-directed shortening in Sierra Cabrera to NW-directed shortening along the North Alhamilla reverse fault via vertical dextral Gafarillos fault segments, in between. The north Alhamilla reverse fault to the west of the system produces a fault-propagation fold in the hangingwall and an overturned fold in the footwall cutting through early Tortonian turbidites and folded Quaternary alluvial fans at the north Alhamilla mountain front. The Quaternary paleo-topographic surface formed by the alluvial fan has been displaced approximately 100 m by reverse faulting after 400 - 70 ky with a slip rate ranging between 0.25 and 1.4 mm yr-1. The South Gafarillos fault includes several N90°-110°E-striking segments with dextral and reverse-dextral kinematics. This fault cuts through the southeastern limb of the Alhamilla anticline by a fault segment that separates the basement from Messinian sediments, meanwhile other segments in the Nijar basin further south cut through Pleistocene river strath-terraces.. During the late Miocene the locus of dextral displacement occurred along the North Gafarillos fault segment that linked to a reverse fault segment at the northeast of the Sierra Alhamilla . The North Gafarillos fault segment and its associated mountain front was sealed by Messinian reefs. Since the Messinian, recent fault activity migrated towards the south forming the South Gafarillos fault segments. Fault segment migration displaced the active oblique strike-slip-related mountain fronts from the north towards the southeast

  2. Mountain front migration and drainage captures related to fault segment linkage and growth: The Polopos transpressive fault zone (southeastern Betics, SE Spain)

    NASA Astrophysics Data System (ADS)

    Giaconia, Flavio; Booth-Rea, Guillermo; Martínez-Martínez, José Miguel; Azañón, José Miguel; Pérez-Romero, Joaquín; Villegas, Irene

    2013-01-01

    The Polopos E-W- to ESE-WNW-oriented dextral-reverse fault zone is formed by the North Alhamilla reverse fault and the North and South Gafarillos dextral faults. It is a conjugate fault system of the sinistral NNE-SSW Palomares fault zone, active from the late most Tortonian (≈7 Ma) up to the late Pleistocene (≥70 ky) in the southeastern Betics. The helicoidal geometry of the fault zone permits to shift SE-directed movement along the South Cabrera reverse fault to NW-directed shortening along the North Alhamilla reverse fault via vertical Gafarillos fault segments, in between. Since the Messinian, fault activity migrated southwards forming the South Gafarillos fault and displacing the active fault-related mountain-front from the north to the south of Sierra de Polopos; whilst recent activity of the North Alhamilla reverse fault migrated westwards. The Polopos fault zone determined the differential uplift between the Sierra Alhamilla and the Tabernas-Sorbas basin promoting the middle Pleistocene capture that occurred in the southern margin of the Sorbas basin. Continued tectonic uplift of the Sierra Alhamilla-Polopos and Cabrera anticlinoria and local subsidence associated to the Palomares fault zone in the Vera basin promoted the headward erosion of the Aguas river drainage that captured the Sorbas basin during the late Pleistocene.

  3. Neogene Structural Basins Beneath Santa Rosa Plain: Strike-Slip Basins Formed in Wake of the Mendocino Triple Junction During Initiation of the Rodgers Creek-Healdsburg Fault Zone

    NASA Astrophysics Data System (ADS)

    McLaughlin, R. J.; Sarna-Wojcicki, A. M.; Fleck, R. J.; Langenheim, V. E.; McPhee, D. K.; Jachens, R. C.; Wagner, D. L.; McCabe, C. A.

    2006-12-01

    Located on the Humboldt Plate, just N of the San Francisco Bay block, the Santa Rosa Plain (SRP) is a NW- oriented dissected lowland ~60 km long by 12 km wide, underlain by fault bounded Neogene basins containing syntectonic sedimentary and volcanic fills up to 2.5 km-thick. In response to lengthening of the transform margin ~7 to 5 Ma, Neogene strata now beneath the plain were dropped into extensional basins in a SE-tapered wedge-shaped block bounded on the SW by ~N 50° W-oriented faults of a proto-Hayward fault zone, and on the NE by newly initiated ~N 35°- 40°W-oriented faults of the Rodgers Creek-Healdsburg fault zone. Comparisons of the geologic, chronostratigraphic and geophysical frameworks of SRP with well constrained datasets used for Neogene reconstructions of the northern San Andreas Fault system indicates to us that the SRP and its buried basins are firmly tied to a strike-slip basin formational setting in the wake of the Mendocino triple junction (MTJ). Onshore and offshore datasets that integrate the geology and chronostratigraphy with geophysical data show that the MTJ at ~7 to 5 Ma was situated between the present latitudes of ~38.5° and ~39° N, opposite SRP. The SRP formed the delta of a large river that flowed toward the WNW, around a proto-Hayward fault-bounded bedrock promontory, into an estuary that adjoined the adjacent near shore and shelf of the margin. The modern Eel River basin, a deformed and uplifted remnant of the Cascadia Forearc margin just north of the present position of the MTJ, lies in a setting similar to the paleogeographic setting of the SRP. Closer examination, however, reveals two important differences between the SRP and MTJ settings. First, the ~6 to 9 Ma fluvial system that flowed NW across the Hayward fault from the east San Francisco Bay region onto SRP, also flowed across the San Andreas fault into submarine canyons of the Delgada Fan on the Pacific Plate, south of the MTJ. In contrast, sediment transported by the

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

    NASA Astrophysics Data System (ADS)

    Marliyani, G. I.; Arrowsmith, R.

    2014-12-01

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

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

    USGS Publications Warehouse

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

    1985-01-01

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

  6. Determining fault zone structure and examining earthquake early warning signals using large datasets of seismograms

    NASA Astrophysics Data System (ADS)

    Lewis, Michael Antony

    Seismic signals associated with near-fault waveforms are examined to determine fault zone structure and scaling of earthquake properties with event magnitude. The subsurface structure of faults is explored using fault zone head and/or trapped waves, while various signals from the early parts of seismograms are investigated to find out the extent to which they scale with magnitude. Fault zone trapped waves are observed in three arrays of instruments across segments of the San Jacinto fault. Similarly to previous fault zone trapped wave studies, the low velocity damage zones are found to be 100-200m wide and extend to a depth of ˜3-5km. Observation and modeling indicate that the damage zone was asymmetric around the fault trace. A similar sense of damage asymmetry was observed using detailed geological mapping by Dor et al. (2006) nearby on the San Jacinto fault at Anza. Travel time analysis and arrival time inversions of fault zone head waves were used to produce high resolution images of the fault structure of the San Andreas fault south of Hollister. The contrast of P wave velocities across the fault was found to be ˜50% in the shallow section, lowering to 10-20% below 3 km, with the southwest side having faster velocities. Inversions making use of different subsets of stations suggest that a low velocity damage zone also exists in this area and that it is more prominent on the faster velocity side of the fault. The patterns of damage from these studies of fault zone head waves and trapped waves are consistent (Ben-Zion and Shi, 2005) with the theoretical prediction that earthquake ruptures on these fault sections have statistically-preferred propagation directions. The early parts of P waveforms are examined for signals that have previously been proposed to scale with the final event magnitude. Data from Turkey and a deep South African gold mine show that scaling is present in signals related to the maximum displacement amplitude and frequency content. The high

  7. Preseismic, Postseismic and Slow Faulting in Subduction Zones

    NASA Astrophysics Data System (ADS)

    Melbourne, T. I.; Webb, F. H.; Miller, M. M.

    2002-12-01

    The last several years have witnessed a broad reappraisal of our understanding of the energy budgets of subduction zones. Due primarily to the deployment of continuous geodetic instrumentation along convergent margins worldwide, we now recognize that fault rupture commonly occurs over rates ranging from kilometers per second to millimeters per day. Along with transient postseismic slip, both isolated and episodic slow slip events have now been recorded along convergent margins offshore Japan, Alaska, Mexico, Cascadia and Peru, and thus would appear to constitute a fundamental mode of strain release only observable through geodetic methods. In many instances, postseismic creep along the deeper plate interface is triggered by seismogenic rupture up-dip. Continuous GPS measurements from three earthquakes in México (Mw=8.0,1995), Peru (Mw=8.4,2001) and Japan (Mw=7.7, 1994) show that deep postseismic creep was triggered by local Coulomb stress increases of the order of one half bar produced by their mainshock ruptures. For these three events, afterslip along their primary coseismic asperities is significantly less important than triggered deep creep. Deeper slow faulting does not have to be triggered by adjacent seismogenic rupture. In Cascadia, eight episodic slow slip events since 1991 have been recognized to have an astonishingly regular 14.5-month onset period, the most recent of which began in February of 2002. For these events, time dependent inversion of GPS data map the propagation of creep fronts and show they released moment with magnitudes in excess of Mw=6.5. If they occur throughout the Cascadia interseismic period, then cumulatively they rival the moment release of the infrequent Mw=9.0 megathrust events. Most recently, an 18-hour precursor to an Mw=7.6 aftershock of the 2001 Mw=8.4 Peru earthquake was detected at Arequipa, Peru. This precursor appears as a ~3 cm departure from a continuous time series broken only by the coseismic displacements of the

  8. A Virtual Tour of the 1868 Hayward Earthquake in Google EarthTM

    NASA Astrophysics Data System (ADS)

    Lackey, H. G.; Blair, J. L.; Boatwright, J.; Brocher, T.

    2007-12-01

    The 1868 Hayward earthquake has been overshadowed by the subsequent 1906 San Francisco earthquake that destroyed much of San Francisco. Nonetheless, a modern recurrence of the 1868 earthquake would cause widespread damage to the densely populated Bay Area, particularly in the east Bay communities that have grown up virtually on top of the Hayward fault. Our concern is heightened by paleoseismic studies suggesting that the recurrence interval for the past five earthquakes on the southern Hayward fault is 140 to 170 years. Our objective is to build an educational web site that illustrates the cause and effect of the 1868 earthquake drawing on scientific and historic information. We will use Google EarthTM software to visually illustrate complex scientific concepts in a way that is understandable to a non-scientific audience. This web site will lead the viewer from a regional summary of the plate tectonics and faulting system of western North America, to more specific information about the 1868 Hayward earthquake itself. Text and Google EarthTM layers will include modeled shaking of the earthquake, relocations of historic photographs, reconstruction of damaged buildings as 3-D models, and additional scientific data that may come from the many scientific studies conducted for the 140th anniversary of the event. Earthquake engineering concerns will be stressed, including population density, vulnerable infrastructure, and lifelines. We will also present detailed maps of the Hayward fault, measurements of fault creep, and geologic evidence of its recurrence. Understanding the science behind earthquake hazards is an important step in preparing for the next significant earthquake. We hope to communicate to the public and students of all ages, through visualizations, not only the cause and effect of the 1868 earthquake, but also modern seismic hazards of the San Francisco Bay region.

  9. Timing of Surface-Rupturing Earthquakes on the Philippine Fault Zone in Central Luzon Island, Philippines

    NASA Astrophysics Data System (ADS)

    Tsutsumi, H.; Daligdig, J. A.; Goto, H.; Tungol, N. M.; Kondo, H.; Nakata, T.; Okuno, M.; Sugito, N.

    2006-12-01

    The Philippine fault zone is an arc-parallel left-lateral strike-slip fault zone related to oblique subduction of the Philippine Sea plate beneath the Philippine island arc. The fault zone extends for about 1300 km from the Luzon Island southward to the Mindanao Island. This fault zone has been seismically active with more than 10 earthquakes greater than M7 in the last century. The July 16, 1990, Luzon earthquake was the largest event that produced 120-km-long surface rupture along the Digdig fault. The coseismic displacement was predominantly left-lateral strike-slip with maximum slip of about 6 m. The Philippine fault zone in the Luzon Island consists of four left-stepping en echelon faults: the San Manuel, San Jose, Digdig, and Gabaldon faults from north to south. Historical documents and geomorphic data suggest that the San Manuel and Gabaldon faults ruptured most recently during historical earthquakes in 1796 and 1645, respectively. However, paleoseismic activities and slip rates for these faults were poorly constrained. In order to reconstruct chronology of surface-rupturing earthquakes, we excavated multiple trenches across these faults in the past three years. We have excavated two sites, San Gregorio and Puncan sites, across the Digdig fault. At the both sites, we identified near vertical fault zones that contain evidence for four surface-rupturing earthquakes during the past 2000 years, including the 1990 rupture. The timing of the penultimate earthquake is constrained to prior to 1400 AD, suggesting that the Digdig fault did not rupture during the 1645 earthquake. The average recurrence interval of the Digdig fault is about 600 years. A left-lateral slip rate of 8-13 mm/yr was obtained for the Digdig fault based on stream offsets and age of alluvial fan at San Juan in the central portion of the fault. For the San Jose fault, we excavated two trenches north of downtown San Jose. The sediments exposed on the trench walls were warped into a monocline by

  10. Fault-related amorphous materials and their influence on the rheological behavior of fault zones (Invited)

    NASA Astrophysics Data System (ADS)

    Pec, M.; Stunitz, H.; Heilbronner, R.; Drury, M. R.

    2013-12-01

    Identification of fault-related amorphous materials in both nature as well as experiment has significantly increased over the last years. Amorphous materials provide new possibilities for our understanding of the rheological behavior of fault zones and the seismic cycle. We performed a series of experiments on granitoid fault rocks under a range of temperatures (T ≈ 300 to 600°C), confining pressures (Pc ≈ 300 to 1500 MPa) and slow displacement rates of (10-8 ms-1 < ddot < 10-6 ms-1). Granitoid powder (d ≤ 200 μm), with 0.2 wt% water added was sheared in a solid medium deformation apparatus to a range of finite shear strains (γ = 0 - 5). Samples reach peak shear strengths of (0.56 GPa < τ < 1.6 GPa) then weaken slightly (10 MPa < τ < 190 MPa) and continue to deform at approximately constant stress. A clear temperature and a weak rate dependence of steady-state stress is observed. Only at the fastest displacement rates (10-6 ms-1), and lowest temperatures (300°C) the samples fail abruptly and audibly shortly after reaching peak strength. Microstructural observations show the development of an S-C-C' fabric with C' slip zones being the dominant feature. At peak strength (γ ≈ 2 - 2.5), deformation partitions in several C' - C slip zones which cover 5-10 vol% of the sample. TEM observations show small, highly strained nanocrystalline fragments with an average grain size of ~ 35 nm surrounded by up to ~90% of TEM-amorphous material (partly amorphous material - PAM). During higher strain deformation (γ > 2.5) some C' - C slip zones continue to accommodate strain and further change their microstructure. Up to 25 vol% of the sample consists of PAM as well as fully TEM-amorphous material (AM). This material shows injection veins, flow structures and contains quartz clasts surrounded by a thin layer of different z-contrast material. At highest stresses (> 1.1 GPa) and lowest temperatures (300°C) stretched bubbles, and bubble trains following the local flow

  11. Ductile creep and compaction: A mechanism for transiently increasing fluid pressure in mostly sealed fault zones

    USGS Publications Warehouse

    Sleep, N.H.; Blanpied, M.L.

    1994-01-01

    A simple cyclic process is proposed to explain why major strike-slip fault zones, including the San Andreas, are weak. Field and laboratory studies suggest that the fluid within fault zones is often mostly sealed from that in the surrounding country rock. Ductile creep driven by the difference between fluid pressure and lithostatic pressure within a fault zone leads to compaction that increases fluid pressure. The increased fluid pressure allows frictional failure in earthquakes at shear tractions far below those required when fluid pressure is hydrostatic. The frictional slip associated with earthquakes creates porosity in the fault zone. The cycle adjusts so that no net porosity is created (if the fault zone remains constant width). The fluid pressure within the fault zone reaches long-term dynamic equilibrium with the (hydrostatic) pressure in the country rock. One-dimensional models of this process lead to repeatable and predictable earthquake cycles. However, even modest complexity, such as two parallel fault splays with different pressure histories, will lead to complicated earthquake cycles. Two-dimensional calculations allowed computation of stress and fluid pressure as a function of depth but had complicated behavior with the unacceptable feature that numerical nodes failed one at a time rather than in large earthquakes. A possible way to remove this unphysical feature from the models would be to include a failure law in which the coefficient of friction increases at first with frictional slip, stabilizing the fault, and then decreases with further slip, destabilizing it. ?? 1994 Birkha??user Verlag.

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

    USGS Publications Warehouse

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

    1998-01-01

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

  13. Fracture systems in normal fault zones crosscutting sedimentary rocks, Northwest German Basin

    NASA Astrophysics Data System (ADS)

    Reyer, Dorothea; Bauer, Johanna F.; Philipp, Sonja L.

    2012-12-01

    Field studies of fracture systems associated with 58 normal fault zones crosscutting sedimentary rocks were performed in the Northwest German Basin. Fracture orientations, densities, apertures and lengths, as well as fault zone structural indices, were analysed separately for fault damage zones and host rocks. The results show a pronounced difference between carbonate and clastic rocks: mainly in carbonate rocks we found presence of clear damage zones, characterized by higher fracture densities than in the host rocks. While the maximum aperture is similar for both units, the percentage of fractures with large apertures is much higher in the damage zones than in the host rocks. Based on laboratory measurements of Young's moduli and field measurements of fracture densities, we calculate effective stiffnesses Ee, that is the Young's moduli of the in situ rock masses, within the normal fault zones. Compared with carbonate rocks, Ee computed for clastic-rock damage zones decreases significantly less due to lower fracture densities. We conclude that normal fault zones in carbonate rocks have more profound effects on enhancing permeability in fluid reservoirs than those in clastic rocks. The results are of great importance for modelling the hydromechanical behaviour of normal fault zones in subsurface fluid reservoirs.

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

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

    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

  15. Discovery of amorphous carbon veins in the 2008 Wenchuan earthquake fault zone: implications for the fault weakening mechanism

    NASA Astrophysics Data System (ADS)

    Liu, J.; Zhang, J.; Zhang, B.; Li, H.

    2013-12-01

    The 2008 Wenchuan earthquake generated 270- and 80-km-long surface ruptures along Yingxiu-Beichuan fault and Guanxian-Anxian fault, respectively. At the outcrop near Hongkou village, southwest segment of Yingxiu-Beichuan rupture, network black amorphous carbon veins were discovered near fault planes in the 190-m-wide earthquake fault zone. These veins are mainly composed of ultrafine- and fine-grained amorphous carbon, usually narrower than 5mm and injected into faults and cracks as far as several meter. Flowage structures like asymmetrical structures around few stiff rock fragments indicate materials flew when the veins formed. Fluidization of cataclastic amorphous carbon and the powerful driving force in the veins imply high pore pressure built up during earthquakes. High pore pressure solution and graphite reported in the fault gouge (Togo et al., 2011) can lead very low dynamic friction during the Wenchuan earthquake. This deduction hypothesis is in accordance with the very low thermal abnormal measured on the principle fault zone following the Wenchuan earthquake (Mori et al., 2010). Furthermore, network amorphous carbon veins of different generations suggest similar weakening mechanism also worked on historical earthquakes in Longmenshan fault zone. Reference: Brodsky, E. E., Li, H., Mori, J. J., Kano, Y., and Xue, L., 2012, Frictional Stress Measured Through Temperature Profiles in the Wenchuan Scientific Fault Zone Drilling Project. American Geophysical Union, Fall Meeting. San Francisco, T44B-07 Li, H., Xu, Z., Si, J., Pei, J., Song, S., Sun, Z., and Chevalier, M., 2012, Wenchuan Earthquake Fault Scientific Drilling program (WFSD): Overview and Results. American Geophysical Union, Fall Meeting. San Francisco, T44B-01 Mori, J. J., Li, H., Wang, H., Kano, Y., Pei, J., Xu, Z., and Brodsky, E. E., 2010, Temperature measurements in the WFSD-1 borehole following the 2008 Wenchuan earthquake (MW7.9). American Geophysical Union, Fall Meeting. San Francisco, T53E

  16. Vertical tectonic deformation associated with the San Andreas fault zone offshore of San Francisco, California

    USGS Publications Warehouse

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

    2008-01-01

    A new fault map of the shelf offshore of San Francisco, California shows that faulting occurs as a distributed shear zone that involves many fault strands with the principal displacement taken up by the San Andreas fault and the eastern strand of the San Gregorio fault zone. Structures associated with the offshore faulting show compressive deformation near where the San Andreas fault goes offshore, but deformation becomes extensional several km to the north off of the Golden Gate. Our new fault map serves as the basis for a 3-D finite element model that shows that the block between the San Andreas and San Gregorio fault zone is subsiding at a long-term rate of about 0.2-0.3??mm/yr, with the maximum subsidence occurring northwest of the Golden Gate in the area of a mapped transtensional basin. Although the long-term rates of vertical displacement primarily show subsidence, the model of coseismic deformation associated with the 1906 San Francisco earthquake indicates that uplift on the order of 10-15??cm occurred in the block northeast of the San Andreas fault. Since 1906, 5-6??cm of regional subsidence has occurred in that block. One implication of our model is that the transfer of slip from the San Andreas fault to a fault 5??km to the east, the Golden Gate fault, is not required for the area offshore of San Francisco to be in extension. This has implications for both the deposition of thick Pliocene-Pleistocene sediments (the Merced Formation) observed east of the San Andreas fault, and the age of the Peninsula segment of the San Andreas fault.

  17. Vertical tectonic deformation associated with the San Andreas fault zone offshore of San Francisco, California

    NASA Astrophysics Data System (ADS)

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

    2008-10-01

    A new fault map of the shelf offshore of San Francisco, California shows that faulting occurs as a distributed shear zone that involves many fault strands with the principal displacement taken up by the San Andreas fault and the eastern strand of the San Gregorio fault zone. Structures associated with the offshore faulting show compressive deformation near where the San Andreas fault goes offshore, but deformation becomes extensional several km to the north off of the Golden Gate. Our new fault map serves as the basis for a 3-D finite element model that shows that the block between the San Andreas and San Gregorio fault zone is subsiding at a long-term rate of about 0.2-0.3 mm/yr, with the maximum subsidence occurring northwest of the Golden Gate in the area of a mapped transtensional basin. Although the long-term rates of vertical displacement primarily show subsidence, the model of coseismic deformation associated with the 1906 San Francisco earthquake indicates that uplift on the order of 10-15 cm occurred in the block northeast of the San Andreas fault. Since 1906, 5-6 cm of regional subsidence has occurred in that block. One implication of our model is that the transfer of slip from the San Andreas fault to a fault 5 km to the east, the Golden Gate fault, is not required for the area offshore of San Francisco to be in extension. This has implications for both the deposition of thick Pliocene-Pleistocene sediments (the Merced Formation) observed east of the San Andreas fault, and the age of the Peninsula segment of the San Andreas fault.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  19. Magnetic fabrics induced by dynamic faulting reveal damage zone sizes in soft rocks, Dead Sea basin

    NASA Astrophysics Data System (ADS)

    Levi, T.; Weinberger, R.; Marco, S.

    2014-11-01

    The anisotropy of magnetic susceptibility (AMS) of soft rocks was measured in order to distinguish between the effect of remote and local strain fields, determine the size of the related inelastic damage zone and resolve the fault-plane solutions of past earthquakes. The AMS fabrics were explored next to late Pleistocene syndepositional normal faults (total displacement up to ˜3.5 m) that cross soft lacustrine rocks within the seismically active Dead Sea basin. `Deposition fabrics' prevail meters away from the fault planes and are characterized by scattered maximum and intermediate principal AMS axes. `Deformation fabrics' are detected up to tens of centimetres from the fault planes and are characterized by well-grouped AMS axes, in which one of the principal axes is parallel to the strike of the nearby fault. Variations in the AMS fabrics and magnetic lineations define the size of the inelastic damage zone around the faults. The results demonstrate that the deformation-driven magnetic fabrics and the associated inelastic damage zones are compatible with coseismic dynamic faulting and the effects of the local strain field during earthquakes. Most of the AMS fabrics show a conspicuous similarity to that of the fault-plane solutions, i.e., the principal AMS axes and instantaneous strain ellipsoids are coaxial. These results suggest a novel application of the AMS method for defining the shape and size of the damage zones surrounding dynamic faults and determining the full tensor of the local strain field.

  20. Sources, Fluxes, and Effects of Fluids in the Alpine Fault Zone, South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Menzies, C. D.; Teagle, D. A. H.; Niedermann, S.; Cox, S.; Craw, D.; Zimmer, M.; Cooper, M. J.; Erzinger, J.

    2015-12-01

    Historic ruptures on some plate boundary faults occur episodically. Fluids play a key role in modifying the chemical and physical properties of fault zones, which may prime them for repeated rupture by the generation of high pore fluid pressures. Modelling of fluid loss rates from fault zones has led to estimates of fluid fluxes required to maintain overpressure (Faulkner and Rutter, 2001), but fluid sources and fluxes, and permeability evolution in fault zones remain poorly constrained. High mountains in orogenic belts can drive meteoric water to the middle crust, and metamorphic water is generated during rock dehydration. Additionally, fluids from the mantle are transported into the crust when fluid pathways are created by tectonism or volcanism. Here we use geochemical tracers to determine fluid flow budgets for meteoric, metamorphic and mantle fluids at a major compressional tectonic plate boundary. The Alpine Fault marks the transpressional Pacific-Australian plate boundary through South Island of New Zealand, it has historically produced large earthquakes (Mw ~8) and is late in its 329±68 year seismic cycle, having last ruptured in 1717. We present strontium isotope ratios of hot springs and hydrothermal minerals that trace fluid flow paths in and around the Alpine Fault to illustrate that the fluid flow regime is restricted by low cross-fault permeability. Fluid-rock interaction limits cross-fault fluid flow by the precipitating clays and calcite that infill pore spaces and fractures in the Alpine Fault alteration zone. In contrast, helium isotopes ratios measured in hot springs near to the fault (0.15-0.81 RA) indicate the fault acts as a conduit for mantle fluids from below. Mantle fluid fluxes are similar to the San Andreas Fault (<1x10-5 m3m-2/yr) and insufficient to promote fault weakening. The metamorphic fluid flux is of similar magnitude to the mantle flux. The dominant fluid throughout the seismogenic zone is meteoric in origin (secondary mineral

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

    NASA Astrophysics Data System (ADS)

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

    2004-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2005-09-01

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

  3. Abrupt along-strike change in tectonic style: San Andreas Fault zone, San Francisco Peninsula

    NASA Astrophysics Data System (ADS)

    Zoback, Mary Lou; Jachens, Robert C.; Olson, Jean A.

    1999-05-01

    Seismicity and high-resolution aeromagnetic data are used to define an abrupt change from compressional to extensional tectonism within a 10- to 15-km-wide zone along the San Andreas fault on the San Francisco Peninsula and offshore from the Golden Gate. This 100-km-long section of the San Andreas fault includes the hypocenter of the Mw = 7.8 1906 San Francisco earthquake as well as the highest level of persistent microseismicity along that ˜470-km-long rupture. We define two distinct zones of deformation along this stretch of the fault using well-constrained relocations of all post-1969 earthquakes based a joint one-dimensional velocity/hypocenter inversion and a redetermination of focal mechanisms. The southern zone is characterized by thrust- and reverse-faulting focal mechanisms with NE trending P axes that indicate "fault-normal" compression in 7- to 10-km-wide zones of deformation on both sides of the San Andreas fault. A 1- to 2-km-wide vertical zone beneath the surface trace of the San Andreas is characterized by its almost complete lack of seismicity. The compressional deformation is consistent with the young, high topography of the Santa Cruz Mountains/Coast Ranges as the San Andreas fault makes a broad restraining left bend (˜10°) through the southernmost peninsula. A zone of seismic quiescence ˜15 km long separates this compressional zone to the south from a zone of combined normal-faulting and strike-slip-faulting focal mechanisms (including a ML = 5.3 earthquake in 1957) on the northernmost peninsula and offshore on the Golden Gate platform. Both linear pseudogravity gradients, calculated from the aeromagnetic data, and seismic reflection data indicate that the San Andreas fault makes an abrupt ˜3-km right step less than 5 km offshore in this northern zone. A similar right-stepping (dilatational) geometry is also observed for the subparallel San Gregorio fault offshore. Persistent seismicity and extensional tectonism occur within the San Andreas

  4. Abrupt along-strike change in tectonic style: San Andreas fault zone, San Francisco Peninsula

    USGS Publications Warehouse

    Zoback, M.L.; Jachens, R.C.; Olson, J.A.

    1999-01-01

    Seismicity and high-resolution aeromagnetic data are used to define an abrupt change from compressional to extensional tectonism within a 10- to 15-km-wide zone along the San Andreas fault on the San Francisco Peninsula and offshore from the Golden Gate. This 100-km-long section of the San Andreas fault includes the hypocenter of the Mw = 7.8 1906 San Francisco earthquake as well as the highest level of persistent microseismicity along that ???470-km-long rupture. We define two distinct zones of deformation along this stretch of the fault using well-constrained relocations of all post-1969 earthquakes based a joint one-dimensional velocity/hypocenter inversion and a redetermination of focal mechanisms. The southern zone is characterized by thrust- and reverse-faulting focal mechanisms with NE trending P axes that indicate "fault-normal" compression in 7- to 10-km-wide zones of deformation on both sides of the San Andreas fault. A 1- to 2-km-wide vertical zone beneath the surface trace of the San Andreas is characterized by its almost complete lack of seismicity. The compressional deformation is consistent with the young, high topography of the Santa Cruz Mountains/Coast Ranges as the San Andreas fault makes a broad restraining left bend (???10??) through the southernmost peninsula. A zone of seismic quiescence ???15 km long separates this compressional zone to the south from a zone of combined normal-faulting and strike-slip-faulting focal mechanisms (including a ML = 5.3 earthquake in 1957) on the northernmost peninsula and offshore on the Golden Gate platform. Both linear pseudo-gravity gradients, calculated from the aeromagnetic data, and seismic reflection data indicate that the San Andreas fault makes an abrupt ???3-km right step less than 5 km offshore in this northern zone. A similar right-stepping (dilatational) geometry is also observed for the subparallel San Gregorio fault offshore. Persistent seismicity and extensional tectonism occur within the San

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

    NASA Astrophysics Data System (ADS)

    Vho, Alice; Bistacchi, Andrea

    2015-04-01

    A quantitative analysis of fault-rock distribution is of paramount importance for studies of fault zone architecture, fault and earthquake mechanics, and fluid circulation along faults at depth. Here we present a semi-automatic workflow for fault-rock mapping on a Digital Outcrop Model (DOM). This workflow has been developed on a real case of study: the strike-slip Gole Larghe Fault Zone (GLFZ). It consists of a fault zone exhumed from ca. 10 km depth, hosted in granitoid rocks of Adamello batholith (Italian Southern Alps). Individual seismogenic slip surfaces generally show green cataclasites (cemented by the precipitation of epidote and K-feldspar from hydrothermal fluids) and more or less well preserved pseudotachylytes (black when well preserved, greenish to white when altered). First of all, a digital model for the outcrop is reconstructed with photogrammetric techniques, using a large number of high resolution digital photographs, processed with VisualSFM software. By using high resolution photographs the DOM can have a much higher resolution than with LIDAR surveys, up to 0.2 mm/pixel. Then, image processing is performed to map the fault-rock distribution with the ImageJ-Fiji package. Green cataclasites and epidote/K-feldspar veins can be quite easily separated from the host rock (tonalite) using spectral analysis. Particularly, band ratio and principal component analysis have been tested successfully. The mapping of black pseudotachylyte veins is more tricky because the differences between the pseudotachylyte and biotite spectral signature are not appreciable. For this reason we have tested different morphological processing tools aimed at identifying (and subtracting) the tiny biotite grains. We propose a solution based on binary images involving a combination of size and circularity thresholds. Comparing the results with manually segmented images, we noticed that major problems occur only when pseudotachylyte veins are very thin and discontinuous. After

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  7. Stress orientations in subduction zones and the strength of subduction megathrust faults

    USGS Publications Warehouse

    Hardebeck, Jeanne L.

    2015-01-01

    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.

  8. Uranium-series nuclides in the Golden fault, Colorado, U.S.A.: dating latest fault displacement and measuring recent uptake of radionuclides by fault-zone materials

    USGS Publications Warehouse

    Szabo, B. J.; Rosholt, J.N.

    1989-01-01

    Concentrations and isotopic ratios of U, Th and Ra were measured in a fault zone near Golden, Colorado where major displacement occurred between about 190 and 615 ka. Faulting created new surfaces for leaching and provided the pathways for U-rich ground water. Uranium and 230Th, the latter produced by the decay of dissolved 234U, are adsorbed by fault gouge, hematite-stained sand and brecciated sand- and claystones. The observed U enrichment is as much as six times baseline value and the simultaneous enrichment of 230Th is estimated at about ninefold relative to 238U. The adsorption of radionuclides chemically analogous to Th, such as Pu (IV) and Np, and 237Np decay products, on fault-zone materials would contribute to the immobilization of high-level radioactive waste in the vicinity of a repository in the event of leakage from engineered barriers into fractured rock-mass. ?? 1989.

  9. Fault zone regulation, seismic hazard, and social vulnerability in Los Angeles, California: Hazard or urban amenity?

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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.

  10. Paleofluid evolution of strike-slip compartmentalized extensional fault zones in the Jabal Qusaybah anticline, Salakh Arc, Oman

    NASA Astrophysics Data System (ADS)

    Balsamo, Fabrizio; Clemenzi, Luca; Storti, Fabrizio; Mozafari, Mahtab; Solum, John; Swennen, Rudy; Taberner, Conxita; Tueckmantel, Christian

    2015-04-01

    The E-W-trending Jabal Qusaybah anticline, developed in layered Cretaceous carbonates, is located at the western termination of the Salakh Arc, Oman Mountains. The anticline is 10 km long and is characterized by a complex fault pattern which mainly includes NE-SW left-lateral strike-slip and N-S extensional fault zones. The N-S striking extensional fault zones are best developed in the central sector of the anticlinal crest, likely due to along-strike outer-arc extension associated with positive fault inversion and salt migration. Extensional fault zones are perpendicular to the fold axis and geometrically confined within major NE-SW left-lateral strike-slip fault zones. They have trace lengths ranging from a few m up to ~800 m, and displacements ranging from a few dm up to ~60 m. Fault zones consist of cataclastic fault cores (~1-15 cm thick) surrounded by vein-dominated damage zones. Overall, fault zones show significant volumes of dilation breccia texture, m-thick infillings of calcite crystals, and cm- to m-thick veins localized at fault tip zones, areas of fault overlap, and zones of interaction between strike-slip and extensional fault segments. By analyzing fault abutting geometries, detailed vein relative chronology, delta13C and delta18O signatures and fluid inclusion data from calcite veins and calcite fault infillings, we propose a model where a deep seated left-lateral strike-slip fault system, active during the growth of the anticline, inhibited the lateral propagation of late-stage transversal extensional fault zones. Our findings show that, in this geological setting, the structural position, rather than fault throw, is the parameter controlling the location of the more dilatant fault segments.

  11. The influence of changing plate kinematics on a continental transform fault; the example of the Dead Sea Fault Zone

    NASA Astrophysics Data System (ADS)

    Smit, J.; Brun, J. P.; Cloetingh, S.

    2003-04-01

    The Dead Sea Fault Zone forms the boundary between the Sinai and Arabian plates and links the Red Sea spreading center in the South to the Taurus Mountains in the North. From field observations along the Southern part of the Dead Sea Fault zone (DSFZ) and investigations in the Red Sea area it has been suggested that the Arabian plate moves northward along the DSFZ by a rotation along an Euler pole that for the last 4 Ma years is located at 33°N23°E. It has also been suggested that this Euler pole was located about 5° more to the West during the first episode of movement. This change in motion of the Arabian plate coincides with the initiation of the main subsidence in the Dead Sea basin and the Gulf of Aqaba. The geometry and timing of deformation along the Northern segment of the DSFZ is much less constrained and different models have been proposed for the history of this segment. To study the influence of the change in plate motion on the DSFZ, a series of laboratory experiments has been performed. Special attention is being paid to the influence of rheologies on the system, the development of the fault zones geometry in time and with depth and wether a new rotational pole forces the initiation of a new fault or that the movement is accommodated by trenspression-transtension along the old fault.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  13. Tectonic history of the northern Nabitah fault zone, Arabian Shield, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Quick, J.E.; Bosch, Paul S.

    1990-01-01

    Based on the presence of similar lithologies, similar structure, and analogous tectonic setting, the Mother Lode District in California is reviewed as a model for gold occurrences near the Nabitah fault zone in this report.

  14. An Inexpensive Device for Modelling Strike-Slip and Oblique-Slip Fault Zones.

    ERIC Educational Resources Information Center

    Larter, Richard C. L.; Allison, Iain

    1983-01-01

    Describes construction/use of a device to simulate structures produced in fault zones of dominantly strike-dip motion. Apparatus modifications allow simulation of transtension and transpression as well as pure strike-slip fault motion. Illustrates formation of several structures using the apparatus, comparing them with natural examples. Includes…

  15. Shallow, old, and hydrologically insignificant fault zones in the Appalachian orogen

    NASA Astrophysics Data System (ADS)

    Malgrange, Juliette; Gleeson, Tom

    2014-01-01

    The permeability of fault zones impacts diverse geological processes such as hydrocarbon migration, hydrothermal fluid circulation, and regional groundwater flow, yet how fault zones affect groundwater flow at a regional scale (1-10 km) is highly uncertain. The objective of this work is to determine whether faults affect regional patterns of groundwater flow, by using radioactive radon and chloride to quantify groundwater discharge to lakes underlain by faults and not underlain by faults. We sampled lakes overlying the Paleozoic Appalachian fold and thrust belt in the Eastern Townships in Québec, and compared our results to a previous study in a crystalline watershed in the Canadian Shield. The field data was analyzed with an analytical geochemical mixing model. The uncertainties of model parameters were assessed in a sensitivity analysis using Monte Carlo simulation, and the difference between lakes tested with statistical analysis. While the model results indicate non-negligible groundwater discharge for most of the lakes in the Paleozoic orogen, the difference between the groundwater discharge rate into the lakes located on faults and the other lakes is not statistically significant. However, the groundwater discharge rate to lakes in the Paleozoic orogeny is significantly higher than lakes that overlay crystalline bedrock, which is consistent with independent estimates of permeability. The rate of groundwater discharge is not significantly enhanced or diminished around the thrust fault zones, suggesting that in a regional scale, permeability of fault zones is not significantly different from the bedrock permeability at shallow depth in this old, tectonically- inactive orogen.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

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

    SciTech Connect

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

    1994-12-31

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

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

    SciTech Connect

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

    1994-04-01

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

  19. Weak ductile shear zone beneath a major strike-slip fault: Inferences from earthquake cycle model constrained by geodetic observations of the western North Anatolian Fault Zone

    NASA Astrophysics Data System (ADS)

    Yamasaki, Tadashi; Wright, Tim J.; Houseman, Gregory A.

    2014-04-01

    GPS data before and after the 1999 İzmit/Düzce earthquakes on the North Anatolian Fault Zone (Turkey) reveal a preseismic strain localization within about 25 km of the fault and a rapid postseismic transient. Using 3-D finite element calculations of the earthquake cycle in an idealized model of the crust, comprising elastic above Maxwell viscoelastic layers, we show that spatially varying viscosity in the crust can explain these observations. Depth-dependent viscosity without lateral variations can reproduce some of the observations but cannot explain the proximity to the fault of maximum postseismic velocities. A localized weak zone beneath the faulted elastic lid satisfactorily explains the observations if the weak zone extends down to midcrustal depths, and the ratio of relaxation time to earthquake repeat time ranges from ~0.005 to ~0.01 (for weak-zone widths of ~24 and 40 km, respectively) in the weakened domain and greater than ~1.0 elsewhere, corresponding to viscosities of ~1018 ± 0.3 Pa s and greater than ~1020 Pa s. Models with sharp weak-zone boundaries fit the data better than those with a smooth viscosity increase away from the fault, implying that the weak zone may be bounded by a relatively abrupt change in material properties. Such a change might result from lithological contrast, grain size reduction, fabric development, or water content, in addition to any effects from shear heating. Our models also imply that viscosities inferred from postseismic studies primarily reflect the rheology of the weak zone and should not be used to infer the mechanical properties of normal crust.

  20. Hydrothermal fault zone mapping using seismic and electrical measurements

    NASA Astrophysics Data System (ADS)

    Onacha, Stephen Alumasa

    This dissertation presents a new method of using earthquakes and resistivity data to characterize permeable hydrothermal reservoirs. The method is applied to field examples from Casa Diablo in the Long Valley Caldera, California; Mt. Longonot, Kenya; and Krafla, Iceland. The new method has significant practical value in the exploration and production of geothermal energy. The method uses P- and S-wave velocity, S-wave polarization and splitting magnitude, resistivity and magnetotelluric (MT) strike directions to determine fracture-porosity and orientation. The conceptual model used to characterize the buried, fluid-circulating fault zones in hydrothermal systems is based on geological and fracture models. The method has been tested with field earthquake and resistivity data; core samples; temperature measurements; and, for the case of Krafla, with a drilled well. The use of resistivity and microearthquake measurements is based on theoretical formulation of shared porosity, anisotropy and polarization. The relation of resistivity and a double porosity-operator is solved using a basis function. The porosity-operator is used to generate a correlation function between P-wave velocity and resistivity. This correlation is then used to generate P-wave velocity from 2-D resistivity models. The resistivity models are generated from magnetotelluric (MT) by using the Non-Linear Conjugate Gradient (NLCG) inversion method. The seismic and electrical measurements used come from portable, multi station microearthquake (MEQ) monitoring networks and multi-profile, MT and transient electromagnetic (TEM) observation campaigns. The main conclusions in this dissertation are listed below: (1) Strong evidence exists for correlation between MT strike direction and anisotropy and MEQ S-wave splitting at sites close to fluid-filled fracture zones. (2) A porosity operator generated from a double porosity model has been used to generate valid P-wave velocity models from resistivity data. This

  1. Model for episodic flow of high-pressure water in fault zones before earthquakes

    USGS Publications Warehouse

    Byerlee, J.

    1993-01-01

    In this model for the evolution of large crustal faults, water originally from the country rock saturates the porous and permeable fault zone. During shearing, the fault zone compacts and water flows back into the country rock, but the flow is arrested by silicate deposition that forms low permeability seals. The fluid will be confined to seal-bounded fluid compartments of various sizes and porosity that are not hydraulically connected with each other. When the seal between two compartments is ruptured, an electrical streaming potential will be generated by the sudden movement of fluid from the high-pressure compartment to the low-pressure compartment. During an earthquake the width of the fault zone will increase by failure of the geometric irregularities on the fault. This newly created, porous and permeable, wider fault zone will fill with water, and the process described above will be repeated. Thus, the process is episodic with the water moving in and out of the fault zone, and each large earthquake should be preceded by an electrical and/or magnetic signal. -from Author

  2. Improved characterization of fault zones by quantitative integration of seismic and production data

    NASA Astrophysics Data System (ADS)

    Ali, Aamir; Shahraini, Ali; Jakobsen, Morten

    2011-06-01

    This paper proposes a method for the parameterization and characterization of fault facies models including a fault core and a fault damage zone containing either fractures or deformation bands, typically associated with carbonate and sandstone reservoirs, respectively. We represent the faulted reservoir models with a relatively small number of parameters and focus on the inverse problem; that is, how to estimate transmissibility of the fault core and the parameters of the fractures or deformation bands that determine the effective stiffness and permeability tensors in the damage zone. Our workflow is based on a consistent stiffness-permeability model for the fractured or composite porous media in the damage zone, and a Bayesian (Monte Carlo Markov chain) method of inversion, which provides information about uncertainties as well as the most likely values of the model parameters. For simplicity, we have assumed that the damage zone consists of a single set of fractures or deformation bands that are parallel with the (vertical) fault core, but the forward modelling part of our workflow can easily be extended to deal with more complex situations involving multiple sets of fractures and/or deformation bands that are characterized by different shapes and orientations. The results of our numerical experiments suggest that one can indeed obtain an improved characterization of fault zones by quantitative integration of seismic AVAZ and production data using the workflow presented in this paper.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  4. Delineation of Active Basement Faults in the Eastern Tennessee and Charlevoix Intraplate Seismic Zones

    NASA Astrophysics Data System (ADS)

    Powell, C. A.; Langston, C. A.; Cooley, M.

    2013-12-01

    Recognition of distinct, seismogenic basement faults within the eastern Tennessee seismic zone (ETSZ) and the Charlevoix seismic zone (CSZ) is now possible using local earthquake tomography and datasets containing a sufficiently large number of earthquakes. Unlike the New Madrid seismic zone where seismicity clearly defines active fault segments, earthquake activity in the ETSZ and CSZ appears diffuse. New arrival time inversions for hypocenter relocations and 3-D velocity variations using datasets in excess of 1000 earthquakes suggest the presence of distinct basement faults in both seismic zones. In the ETSZ, relocated hypocenters align in near-vertical segments trending NE-SW, parallel to the long dimension of the seismic zone. Earthquakes in the most seismogenic portion of the ETSZ delineate another set of near-vertical faults trending roughly E-ESE. These apparent trends and steep dips are compatible with ETSZ focal mechanism solutions. The solutions are remarkably consistent and indicate strike-slip motion along the entire length of the seismic zone. Relocated hypocenter clusters in the CSZ define planes that trend and dip in directions that are compatible with known Iapitan rift faults. Seismicity defining the planes becomes disrupted where the rift faults encounter a major zone of deformation produced by a Devonian meteor impact. We will perform a joint statistical analysis of hypocenter alignments and focal mechanism nodal plane orientations in the ETSZ and the CSZ to determine the spatial orientations of dominant seismogenic basement faults. Quantifying the locations and dimensions of active basement faults will be important for seismic hazard assessment and for models addressing the driving mechanisms for these intraplate zones.

  5. Fluid-rock Interaction and Episodic Fluid Flow within the Hurricane Fault-zone

    NASA Astrophysics Data System (ADS)

    Koger, J.; Newell, D. L.

    2015-12-01

    The Hurricane Fault is an active 250-km long, west dipping, Basin and Range bounding normal fault in SW Utah and NW Arizona. Fault rock alteration and mineralization is common in the damage zone along strike, indicating that this structure has influenced past groundwater flow. Multiple Quaternary basaltic centers are located proximal to the fault. This study tests the hypothesis that fault-zone diagenesis is being driven by deeply circulated meteoric groundwater infiltration and associated rock-water interaction that is punctuated by periods of hydrothermal alteration associated with local magmatism. Fault-parallel/oblique fractures and small-offset antithetic and synthetic normal faults have been found within fault-zone rocks. The intensity of fracturing and associated evidence of fluid-rock interaction progressively decreases away from the main fault trace into the footwall. Host rock alteration, hematite mineralized fault surfaces, and calcite and hematite cemented deformation bands and veins are observed. These features are focused in 1 - 2 m wide zones of fracturing with densities of 6 - 18 m-1 located within the footwall damage zone. Host rock alteration in the form of both "bleaching" and oxidation along fractures provides evidence for past redox reactions. Mineralization in deformation bands suggests that some fluid flow and diagenesis was penecontemporaneous with deformation. Laminations and cross-cutting relationships in veins indicate periodic mineralization that could be controlled by episodic fluid flow, or fracturing and degassing leading to calcite precipitation. Stable isotopic results from calcite veins show δ13CPDB values of -7 to 3 ‰ and δ18OPDB values of -19 to -9 ‰. Carbon stable isotope ratios suggest multiple carbon sources such as marine carbonates, organic sedimentary rocks, and mantle derived CO2. Temperature differences in paleofluids and associated fluid-rock interaction may explain the observed range in δ18O values. Fluid

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The Alpine Fault of the South Island, New Zealand marks the active transpressional boundary between the Australian and Pacific plates. Phase one of the Deep Fault Drilling Project (DFDP1) drilled two holes that sample the Alpine Fault zone (DFDP1A and DFDP1B) in the near surface. Two distinct principal slip zones (PSZ) were recovered in these cores (one in DFDP1A and two in DFDP1B) enabling investigation of chemical and mineralogical changes throughout the fault's hangingwall and footwall rocks. Here we use geochemical analyses to identify fault rock protoliths, alteration styles, and mass changes in the fault zone to test the control of chemical alteration on fault rock material properties and compare with distal parts of the fault zone sampled in the second phase of DFDP (DFDP2). 87Sr/86Sr and 143Nd/144Nd isotopes, and immobile trace element ratios identify protolith lithology contributions. We show that cataclasites above the upper principal slip zone in holes DFDP1A and DFDP1B contain a mixture of hangingwall Alpine Schist and radiogenic granitic and metasedimentary footwall lithologies indicating physical mixing of material up to ~25 m above the PSZ. In DFDP1B between upper and lower PSZs cataclasites distinctly resemble granitic footwall rocks, and below the lower PSZ radiogenic strontium isotope ratios identify porphyroclastic ultramylonite breccias as Australian plate Palaeozoic metasediments. Lithological mixing is overprinted by alteration of primary minerals to clays and infilling of pore spaces and fractures by calcite and chlorite. As proximity to the upper PSZ increases permeability decreases corresponding to an increase in volatile content (LOI). LOI peaks in the PSZ where permeability is lowest and clay content and carbonate cementation are greatest. Local, meteoric-derived spring waters are saturated in secondary minerals documented in the Alpine Fault zone and fault zone secondary mineral δD compositions indicate formation from meteoric waters

  7. Hydrological and Hydrochemical Characterization of Fault Zones in Crystalline Media: Implications for Groundwater Fluxes

    NASA Astrophysics Data System (ADS)

    Roques, C.; Aquilina, L.; Bour, O.; Dewandel, B.

    2014-12-01

    Fault zones are heterogeneities that may greatly influence groundwater flow in crystalline regions. The quantification of fluxes, the origin of water and geochemical processes associated to groundwater flow in such context remain not well understood. This study mainly concerns a large-scale multidisciplinary field experiments performed on a specific site in Brittany (Saint-Brice en Coglès, France) where a permeable fault zone was identified at depth (200 m). The main objectives here are to constrain both fluxes dynamic and water sources involved during different seasonal regimes. We demonstrate that the fault zone allows the discharge of regional groundwater at the watershed outlet. Using specific hydro-geophysical measurements (Heat Pulse Flow Meter), we estimate a natural discharge rate between 150 and 200 m3/d. The fault zone presents different geochemical signatures related to changes in hydrologic regime. They are linked to transient fluxes enhancement from different reservoirs. During the low hydrologic regimes, water with high resident time flows along the fault zone, with a contribution of inter-glacial origin (recharge temperature of 7°C deduced from noble gases interpretation). Water trapped in a low-permeability domain is mobilized to the fault zone and/or large-scale circulation loops are involved. During the high hydrologic regimes, modern water predominantly ensures the recharge of the system at a local scale. Results are compared to regional observations in the Armoricain Massif in order to establish mechanisms responsible for recharge and migration of groundwater at the basement scale.

  8. 3D insight into fault geometries, deformation, and fluid-migration within the Hosgri Fault Zone offshore central California: Results from high-resolution 3D seismic data

    NASA Astrophysics Data System (ADS)

    Kluesner, J.; Brothers, D. S.; Johnson, S. Y.; Watt, J. T.

    2015-12-01

    High-resolution 3D seismic P-Cable data and advanced seismic attribute analyses were used to detect and interpret complex strike-slip fault geometries, deformation patterns, and fluid-pathways across a portion of the Hosgri Fault Zone (HFZ) offshore central California. Combination of the fault attribute results with structural analysis provides 3D insight into the geometry and internal structure of restraining and releasing bends, step-over zones, fault convergence zones, and apparent paired fault bends. The 3D seismic volume covers a 13.7 km2 region along the HFZ offshore of Point Sal and was collected in 2012 as part of the PG&E Central California Seismic Imaging Project (PG&E, 2014). Application of the fault attribute workflow isolated and delineated fault strands within the 3D volume. These results revealed that the northern and southern edges of the survey region are characterized by single fault strands that exhibit an approximate 6° change in strike across the 3D volume. Between these single faults strands is a complex network of fault splays, bends, stepovers, and convergence zones. Structural analysis reveals that the southern portion of the HFZ in the region is characterized by transtensional deformation, whereas transpressional-related folding dominates the central and northern portions of the HFZ. In the central region, convergence of the Lions Head Fault from the southeast results in an apparent impinging block, leading to development of a "paired fault bend" to the west. Combination of the fault and "chimney" attribute results indicates a strong connection between faults and fluid-migration pathways. Fluid-pathways are concentrated along discrete faults in the transtensional zones, but appear to be more broadly distributed amongst fault bounded anticlines and structurally controlled traps in the transpressional zones.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  10. Structure and kinematics of the Livingstone Mountains border fault zone, Nyasa (Malawi) Rift, southwestern Tanzania

    NASA Astrophysics Data System (ADS)

    Wheeler, Walter H.; Karson, Jeffrey A.

    Reconnaissance mapping of the Livingstone Mountains border fault zone (LMBFZ) at the northern end of the Nyasa (Malawi) Rift in SW Tanzania constrains the geometry and movement history of this typical rift border fault. The fault is a narrow zone of complex brittle deformation, striking 320°, that overprints and reactivates an older ductile shear zone. Long, straight, NW-trending border fault segments are offset by minor NE-trending faults. These two orthogonal fault sets integrate along strike to produce an overall curved fault trace that is concave towards a major depositional basin in the rift. A typical section through the fault zone shows an E to W progression from gneissic country rock through ductilely deformed country rock, into a zone overprinted by closely spaced fractures and grading into an intensely fractured, massive, flinty, aphanitic mylonite band at the lakeshore. Pseudotachylite veins, probably generated during seismic movement on the border fault, are common within and near the aphanitic mylonite. Slickensides indicate dextral oblique-slip, whereas shear belts and rolled porphyroclasts with complex tails in the older ductile shear zone indicate sub-horizontal sinistral motion. The adjacent rift basin is typical of other East African Rift Basins, and contains at least 4 km of Recent to perhaps Mesozoic sediment. Whereas the minimum net slip on the LMBFZ, in the dominant slickenside direction, is on the order of 10 km, regional geologic considerations suggest that dominantly strike-slip motion preceded the oblique-slip phase that produced the LMBFZ and the adjacent rift basin.

  11. The Olmsted fault zone, southernmost Illinois: A key to understanding seismic hazard in the northern new Madrid seismic zone

    USGS Publications Warehouse

    Bexfield, C.E.; McBride, J.H.; Pugin, Andre J.M.; Nelson, W.J.; Larson, T.H.; Sargent, S.L.

    2005-01-01

    Geological deformation in the northern New Madrid seismic zone, near Olmsted, Illinois (USA), is analyzed using integrated compressional-wave (P) and horizontally polarized-wave (SH) seismic reflection and regional and dedicated borehole information. Seismic hazards are of special concern because of strategic facilities (e.g., lock and dam sites and chemical plants on the Ohio River near its confluence with the Mississippi River) and because of alluvial soils subject to high amplification of earthquake shock. We use an integrated approach starting with lower resolution, but deeper penetration, P-wave reflection profiles to identify displacement of Paleozoic bedrock. Higher resolution, but shallower penetration, SH-wave images show deformation that has propagated upward from bedrock faults into Pleistocene loess. We have mapped an intricate zone more than 8 km wide of high-angle faults in Mississippi embayment sediments localized over Paleozoic bedrock faults that trend north to northeast, parallel to the Ohio River. These faults align with the pattern of epicenters in the New Madrid seismic zone. Normal and reverse offsets along with positive flower structures imply a component of strike-slip; the current stress regime favors right-lateral slip on northeast-trending faults. The largest fault, the Olmsted fault, underwent principal displacement near the end of the Cretaceous Period 65 to 70 million years ago. Strata of this age (dated via fossil pollen) thicken greatly on the downthrown side of the Olmsted fault into a locally subsiding basin. Small offsets of Tertiary and Quaternary strata are evident on high-resolution SH-wave seismic profiles. Our results imply recent reactivation and possible future seismic activity in a critical area of the New Madrid seismic zone. This integrated approach provides a strategy for evaluating shallow seismic hazard-related targets for engineering concerns. ?? 2005 Elsevier B.V. All rights reserved.

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

    USGS Publications Warehouse

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

    2013-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  14. Fault zone identification in the eastern part of the Persian Gulf based on combined seismic attributes

    NASA Astrophysics Data System (ADS)

    Mirkamali, M. S.; Keshavarz FK, N.; Bakhtiari, M. R.

    2013-02-01

    Faults, as main pathways for fluids, play a critical role in creating regions of high porosity and permeability, in cutting cap rock and in the migration of hydrocarbons into the reservoir. Therefore, accurate identification of fault zones is very important in maximizing production from petroleum traps. Image processing and modern visualization techniques are provided for better mapping of objects of interest. In this study, the application of fault mapping in the identification of fault zones within the Mishan and Aghajari formations above the Guri base unconformity surface in the eastern part of Persian Gulf is investigated. Seismic single- and multi-trace attribute analyses are employed separately to determine faults in a vertical section, but different kinds of geological objects cannot be identified using individual attributes only. A mapping model is utilized to improve the identification of the faults, giving more accurate results. This method is based on combinations of all individual relevant attributes using a neural network system to create combined attributes, which gives an optimal view of the object of interest. Firstly, a set of relevant attributes were separately calculated on the vertical section. Then, at interpreted positions, some example training locations were manually selected in each fault and non-fault class by an interpreter. A neural network was trained on combinations of the attributes extracted at the example training locations to generate an optimized fault cube. Finally, the results of the fault and nonfault probability cube were estimated, which the neural network applied to the entire data set. The fault probability cube was obtained with higher mapping accuracy and greater contrast, and with fewer disturbances in comparison with individual attributes. The computed results of this study can support better understanding of the data, providing fault zone mapping with reliable results.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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

  16. Origin and formation of carbonaceous material veins in the 2008 Wenchuan earthquake fault zone

    NASA Astrophysics Data System (ADS)

    Liu, Jiang; Li, Haibing; Zhang, Jinjiang; Zhang, Bo

    2016-02-01

    This paper establishes a reference data set of carbonaceous materials (CMs) from the active fault zone of the Longmen Shan fault belt that ruptured in the 2008 Mw7.9 Wenchuan earthquake and presents an application of these data for studies of both other exhumed carbonaceous-rich fault zones and deep-drilling cores. The CMs distributed in the active fault zone are found as narrow veins and located along the slip surfaces. Microstructural observation shows that the carbonaceous material veins (CMVs) are located along slip surfaces in the fault gouge zones. Some CMVs have a cataclastic fabric, and their branches intrude into voids around the slip surfaces. Raman spectra of the CMVs show a wide (full width at half maximum >200 cm-1) D-peak at ~1345 cm-1 (defect peak), which is much lower than the O-peak at ~1595 cm-1 (ordered peak), indicating a metamorphic temperature of zeolite facies or lower than 250 °C. In addition, the stable carbon isotopic compositions (δ13C values) of the CMVs, ranging from -23.4 to -26.4‰, are very similar to that of the kerogen collected from the Late Triassic Xujiahe Formation in Sichuan Basin. Given the data at which it may be formed, the Xujiahe Formation is the most likely origin of CMs for the CMVs, and it seems that some CMVs in the fault zone were crushed and intruded into the voids during coseismic events, possibly driven by an enhanced pore fluid pressure. Since graphitization is suggested as an indicator of transient frictional heating in this area, our study providing a reference data set of CMs would help future CM-rich fault-zone research to retrieve seismic signatures presumably occurring in the Longmen Shan fault zone belt.

  17. 1-D and 2-D Probabilistic Inversions of Fault Zone Guided Waves

    NASA Astrophysics Data System (ADS)

    Gulley, A.; Eccles, J. D.; Kaipio, J. P.; Malin, P. E.

    2015-12-01

    Fault Zone Guided Waves (FZGWs) are seismic coda that are trapped by the low velocity damage zone of faults. Inversions of these phases can be carried out using their measured dispersion and a Bayesian probability approach. This method utilises a Markov chain Monte Carlo which allows uncertainties and trade-offs to be quantified. Accordingly we have developed a scheme that estimates the dispersion curve and amplitude response variability from a FZGW record. This method allows the computation of both the point estimates and the covariance of the dispersion curve. The subsequent estimation of fault zone parameters is then based on a Gaussian model for the dispersion curve. We then show that inversions using FZGW dispersion data can only resolve fault zone velocity contrast and fault zone width - it leaves densities, absolute country rock velocities and the earthquake location unresolved. We show that they do however significantly affect the estimated fault zone velocities and widths. As these parameters cannot be resolved, we allow for their effects on the estimates of fault zone width and velocity contrast by using the Bayesian approximation error method. We show that using this method reduces computational time from days to minutes and the associated loss of accuracy is insignificant compared to carrying out the inversion on all parameters. We have extended our scheme to 2-D using 1-D slices. The Bayesian approximation error methodology is further employed to provide a 'correction term' with uncertainty for the 1-D slice approximation. We investigate these features with both synthetic data and FZGW data from the Alpine Fault of New Zealand.

  18. Geologic structure of Middle Mountain within the San Andreas Fault zone near Parkfield, California

    NASA Astrophysics Data System (ADS)

    Thayer, M. R.; Arrowsmith, R.; Young, J.; Fayon, A.; Rymer, M.

    2004-12-01

    Knowledge of the geometry and history of motion of rock bodies within fault zones such as the San Andreas fault (SAF) is essential input into mechanical models of earthquake rupture dynamics and fault evolution. The Parkfield segment of the SAF is the focus of significant geophysical characterization and borehole studies. In order to enhance the geologic information about the SAF structure in this area, we undertook an intensive high-resolution geologic mapping effort (1:6000 scale) of the Middle Mountain area (about 40 km^2). The geologic structure differs dramatically across the San Andreas fault zone. The northeast side contains numerous sub-parallel faults that likely accommodated significant strike slip motion. These high-angle faults bound granite, marble, and sedimentary rock slivers. The density and complexity of these faults increases toward the center of the fault zone. The Gold Hill reverse fault on the northeast side of the SAF is a low-angle southwest-dipping fault that locally displaces the older Tertiary Monterey Formation over the younger Tertiary Etchegoin Formation. Folds with axes trending parallel to the strike of the Gold Hill reverse fault are present within the hanging wall. The Plio-Pleistocene Paso Robles Formation dominates the southwest side of the SAF and is a formidable cover. Fault-bounded granitoid slivers are also present within the southwest terrain. One fault striking nearly normal to the SAF cuts rock units near the mid-section of Middle Mountain. To the northwest of this fault, older Tertiary formations are present. The folds within the hanging wall of the Gold Hill reverse fault and the reverse fault itself indicate SAF-normal shortening near the SAF zone. The Gold Hill fault most likely cuts the numerous high-angle sub-parallel faults at depth. With the northeastward-verging nature of this fault, the cross-section on the northeast side is a roughly hewn half-flower structure. The sedimentary basin into which the Paso Robles

  19. Rheological transitions in high-temperature volcanic fault zones

    NASA Astrophysics Data System (ADS)

    Okumura, Satoshi; Uesugi, Kentaro; Nakamura, Michihiko; Sasaki, Osamu

    2015-05-01

    Silicic magma experiences shear-induced brittle fracturing during its ascent, resulting in the formation of a magmatic fault at the conduit margin. Once the fault is formed, frictional behavior of the fault controls the magma ascent process. We observed torsional deformation of a magmatic fault gouge in situ at temperatures of 800 and 900°C using synchrotron radiation X-ray radiography. The torsional deformation rate was set at 0.1-10 rpm, corresponding to equivalent slip velocities of 2.27 × 10-5-1.74 × 10-3 m s-1 and shear strain rates of 0.014-1.16 s-1. The normal stresses used were 1, 5, and 10 MPa. The magmatic fault showed frictional sliding as well as viscous flow even above the glass transition temperature. The transition between frictional sliding and viscous flow depends on temperature, deformation rate, and normal stress on the fault. At 900°C, the fault showed viscous deformation at a normal stress of 10 MPa, while frictional sliding was predominant at 800°C. We propose the ratio of timescales of fault healing and deformation as a criterion for transition between frictional sliding and viscous flow. The experimentally calibrated criterion infers that frictional sliding is predominant from ~500 m in depth during explosive eruption; this may explain rapid magma ascent without efficient outgassing. Frictional heating would in turn enhance fault healing, resulting in the reverse transition from frictional sliding to viscous flow, followed by deceleration of magma ascent. Therefore, cyclic transitions between frictional sliding and viscous flow are a possible explanation for the cyclic behavior of lava effusion.

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

    SciTech Connect

    Nadeau, R.M.

    1995-10-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  2. High-Resolution Fault Zone Monitoring and Imaging Using Long Borehole Arrays

    NASA Astrophysics Data System (ADS)

    Paulsson, B. N.; Karrenbach, M.; Goertz, A. V.; Milligan, P.

    2004-12-01

    Long borehole seismic receiver arrays are increasingly used in the petroleum industry as a tool for high--resolution seismic reservoir characterization. Placing receivers in a borehole avoids the distortion of reflected seismic waves by the near-surface weathering layer which leads to greatly improved vector fidelity and a much higher frequency content of 3-component recordings. In addition, a borehole offers a favorable geometry to image near-vertically dipping or overturned structure such as, e.g., salt flanks or faults. When used for passive seismic monitoring, long borehole receiver arrays help reducing depth uncertainties of event locations. We investigate the use of long borehole seismic arrays for high-resolution fault zone characterization in the vicinity of the San Andreas Fault Observatory at Depth (SAFOD). We present modeling scenarios to show how an image of the vertically dipping fault zone down to the penetration point of the SAFOD well can be obtained by recording surface sources in a long array within the deviated main hole. We assess the ability to invert fault zone reflections for rock physical parameters by means of amplitude versus offset or angle (AVO/AVA) analyzes. The quality of AVO/AVA studies depends on the ability to illuminate the fault zone over a wide range of incidence angles. We show how the length of the receiver array and the receiver spacing within the borehole influence the size of the volume over which reliable AVO/AVA information could be obtained. By means of AVO/AVA studies one can deduce hydraulic properties of the fault zone such as the type of fluids that might be present, the porosity, and the fluid saturation. Images of the fault zone obtained from a favorable geometry with a sufficient illumination will enable us to map fault zone properties in the surrounding of the main hole penetration point. One of the targets of SAFOD is to drill into an active rupture patch of an earthquake cluster. The question of whether or not

  3. Regional stress field around the Taigu fault zone in Shanxi Province, China

    NASA Astrophysics Data System (ADS)

    Li, Bin; Li, Zihong; Sørensen, Mathilde B.; Løvlie, Reidar; Liu, Liqiang; Atakan, Kuvvet

    2015-12-01

    A comprehensive study on regional stress field around the Taigu fault zone in Shanxi Province, China, was performed in this study. To get a better understanding of the present-day stress status in this area, 31 focal mechanisms of M L ≥3 earthquakes since 1965 were compiled, and the best stress tensor was then inverted based on the database. Additionally, magnetic fabrics along the Taigu fault zone were investigated to get an indication of the regional stress field in the past. Our results show that the present-day stress field around the Taigu fault zone is characterized by astable NW-SE extension with a strike-slip component, consistent with the geological surveys and recent GPS data. Results from magnetic fabrics indicate that the orientations of principal stress axes from magnetic fabrics of sedimentary rocks in Neogene coincide to the orientations of principal stress axes from focal mechanisms. The south segment of the Taigu fault displays more complicated magnetic fabrics and more activity of moderate earthquakes. It is connected with the Mianshan west fault and intersects with NW-SE striking Fenyang fault and the north fault of the Lingshi uplift at the south edge of Taiyuan basin. This may be the area needing more attention in terms of seismic risk along the Taigu fault.

  4. Fault-tolerant control for a class of non-linear systems with dead-zone

    NASA Astrophysics Data System (ADS)

    Chen, Mou; Jiang, Bin; Guo, William W.

    2016-05-01

    In this paper, a fault-tolerant control scheme is proposed for a class of single-input and single-output non-linear systems with the unknown time-varying system fault and the dead-zone. The non-linear state observer is designed for the non-linear system using differential mean value theorem, and the non-linear fault estimator that estimates the unknown time-varying system fault is developed. On the basis of the designed fault estimator, the observer-based fault-tolerant tracking control is then developed using the backstepping technique for non-linear systems with the dead-zone. The stability of the whole closed-loop system is rigorously proved via Lyapunov analysis and the satisfactory tracking control performance is guaranteed in the presence of the unknown time-varying system fault and the dead-zone. Numerical simulation results are presented to illustrate the effectiveness of the proposed backstepping fault-tolerant control scheme for non-linear systems.

  5. Style and rate of quaternary deformation of the Hosgri Fault Zone, offshore south-central coastal California

    USGS Publications Warehouse

    Hanson, Kathryn L.; Lettis, William R.; McLaren, Marcia; Savage, William U.; Hall, N. Timothy; Keller, Mararget A.

    2004-01-01

    The Hosgri Fault Zone is the southernmost component of a complex system of right-slip faults in south-central coastal California that includes the San Gregorio, Sur, and San Simeon Faults. We have characterized the contemporary style of faulting along the zone on the basis of an integrated analysis of a broad spectrum of data, including shallow high-resolution and deep penetration seismic reflection data; geologic and geomorphic data along the Hosgri and San Simeon Fault Zones and the intervening San Simeon/Hosgri pull-apart basin; the distribution and nature of near-coast seismicity; regional tectonic kinematics; and comparison of the Hosgri Fault Zone with worldwide strike-slip, oblique-slip, and reverse-slip fault zones. These data show that the modern Hosgri Fault Zone is a convergent right-slip (transpressional) fault having a late Quaternary slip rate of 1 to 3 mm/yr. Evidence supporting predominantly strike-slip deformation includes (1) a long, narrow, linear zone of faulting and associated deformation; (2) the presence of asymmetric flower structures; (3) kinematically consistent localized extensional and compressional deformation at releasing and restraining bends or steps, respectively, in the fault zone; (4) changes in the sense and magnitude of vertical separation both along trend of the fault zone and vertically within the fault zone; (5) strike-slip focal mechanisms along the fault trace; (6) a distribution of seismicity that delineates a high-angle fault extending through the seismogenic crust; (7) high ratios of lateral to vertical slip along the fault zone; and (8) the separation by the fault of two tectonic domains (offshore Santa Maria Basin, onshore Los Osos domain) that are undergoing contrasting styles of deformation and orientations of crustal shortening. The convergent component of slip is evidenced by the deformation of the early-late Pliocene unconformity. In characterizing the style of faulting along the Hosgri Fault Zone, we assessed

  6. Modeling Activity of Very-Low-Frequency Earthquakes in Shallow Subduction Zone Considering Splay Faults and High Pore Pressure Zones

    NASA Astrophysics Data System (ADS)

    Shibazaki, B.; Ito, Y.; Ujiie, K.

    2010-12-01

    Recent observations reveal that very-low-frequency (VLF) earthquakes occur in the shallow subduction zones in the Nankai trough, Hyuganada, and off the coast of Tokachi, Japan (Obara and Ito, 2005; Asano et al., 2008; Obana and Kodaira, 2009). The ongoing super drilling project, Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), involves sampling the core of seismogenic faults and conducting analyses, experiments, and in-situ borehole measurements at the Nankai trough where VLF earthquakes occur. The data obtained in this project will be used to develop a model of VLF earthquakes that integrates seismological observations, laboratory experimental results, and geological observations. In the present study, first, we perform 2D quasi-dynamic modeling of VLF earthquakes in an elastic half-space on the basis of a rate- and state-dependent friction law. We set a local unstable zone in a shallow stable zone. To explain very low stress drops and short recurrence intervals of VLF earthquakes, the effective stress is assumed to be around 0.2 MPa. The results indicate that VLF earthquakes are unstable slips that occur under high pore pressure conditions. The probable causes for the high pore pressure along the faults of VLF earthquakes are the sediment compaction and dehydration that occur during smectite-to-illite transition in the shallow subduction zone. Then, we model the generation process of VLF earthquakes by considering splay faults and the occurrences of large subduction earthquakes. We set the local unstable zones with high pore pressure in the stable splay fault zones. We assume the long-term average slip velocity of the splay faults, and that the shear stress is accumulated by the delay of the fault slip from the long-term slip motion. Depending on the frictional properties of the shallow splay faults, two types of VLF earthquakes can occur. When the effective stress is low all over the splay faults, the rupture of large earthquakes propagates to the

  7. Evaluating Temporal Variations in Fault Slip-Rate and Fault Interaction in the Eastern California Shear Zone

    NASA Astrophysics Data System (ADS)

    Amos, C. B.; Jayko, A.; Burgmann, R.

    2008-12-01

    Delineating spatiotemporal patterns of strain accumulation and release within plate boundaries remains fundamental to our understanding of the dynamics of active crustal deformation. The timescales at which active strain varies or remains constant for individual fault systems, however, are often poorly resolved. The origin of large-magnitude strain transients in the Eastern California shear zone remains enigmatic and underpins the importance of quantifying active deformation at multiple geologic timescales along this tectonic boundary. Here, we focus on the Late Pleistocene- Holocene record of slip on the NW-striking Little Lake fault zone, one of the primary structures responsible for transferring Pacific-North American plate motion between the northern Mojave Desert and the east side of the Sierra Nevada block north of the Garlock fault. Discrepancies between geologic and geodetically determined rates of motion along the Little Lake fault zone in the China Lake-Indian Wells Valley area suggest a potentially complex temporal history of slip on this structure with some slip stepping eastward onto structures bounding the west side of the Coso Range. Preliminary reconstruction of a slip-rate history on the Little Lake fault from multiple generations of displaced Quaternary geomorphic features suggests potential variation in fault-slip rates at timescales of 104- 105 years. Two paleochannel margins on a basalt strath in the Little Lake spillway represent the youngest of these features. Each margin exhibits ~30 m of right-lateral displacement and suggests a minimum slip rate of ~1.4 mm/yr during Holocene-Late Pleistocene time. Additionally, a prominent fluvial escarpment or terrace riser along the east side of Little Lake wash is offset at least ~150 to 700 m, depending on how the initial geometry of this feature is reconstructed. Pending geochronologic constraints on the age of this feature, such an offset potentially suggests higher rates of slip averaged over longer

  8. A methodology for incorporating geomechanically-based fault damage zones models into reservoir simulation

    NASA Astrophysics Data System (ADS)

    Paul, Pijush Kanti

    In the fault damage zone modeling study for a field in the Timor Sea, I present a methodology to incorporate geomechanically-based fault damage zones into reservoir simulation. In the studied field, production history suggests that the mismatch between actual production and model prediction is due to preferential fluid flow through the damage zones associated with the reservoir scale faults, which is not included in the baseline petrophysical model. I analyzed well data to estimate stress heterogeneity and fracture distributions in the reservoir. Image logs show that stress orientations are homogenous at the field scale with a strike-slip/normal faulting stress regime and maximum horizontal stress oriented in NE-SW direction. Observed fracture zones in wells are mostly associated with well scale fault and bed boundaries. These zones do not show any anomalies in production logs or well test data, because most of the fractures are not optimally oriented to the present day stress state, and matrix permeability is high enough to mask any small anomalies from the fracture zones. However, I found that fracture density increases towards the reservoir scale faults, indicating high fracture density zones or damage zones close to these faults, which is consistent with the preferred flow direction indicated by interference and tracer test done between the wells. It is well known from geologic studies that there is a concentration of secondary fractures and faults in a damage zone adjacent to larger faults. Because there is usually inadequate data to incorporate damage zone fractures and faults into reservoir simulation models, in this study I utilized the principles of dynamic rupture propagation from earthquake seismology to predict the nature of fractured/damage zones associated with reservoir scale faults. The implemented workflow can be used to more routinely incorporate damage zones into reservoir simulation models. Applying this methodology to a real reservoir utilizing

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Ishii, Eiichi

    2016-08-01

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

  12. Structure of the eastern Seattle fault zone, Washington state: New insights from seismic reflection data

    USGS Publications Warehouse

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

    2008-01-01

    We identify and characterize the active Seattle fault zone (SFZ) east of Lake Washington with newly acquired seismic reflection data. Our results focus on structures observed in the upper 1 km below the cities of Bellevue, Sammamish, Newcastle, and Fall City, Washington. The SFZ appears as a broad zone of faulting and folding at the southern boundary of the Seattle basin and north edge of the Seattle uplift. We interpret the Seattle fault as a thrust fault that accommodates north-south shortening by forming a fault-propagation fold with a forelimb breakthrough. The blind tip of the main fault forms a synclinal growth fold (deformation front) that extends at least 8 km east of Vasa Park (west side of Lake Sammamish) and defines the south edge of the Seattle basin. South of the deformation front is the forelimb break-through fault, which was exposed in a trench at Vasa Park. The Newcastle Hills anticline, a broad anticline forming the north part of the Seattle uplift east of Lake Washington, is interpreted to lie between the main blind strand of the Seattle fault and a backthrust. Our profiles, on the northern limb of this anticline, consistently image north-dipping strata. A structural model for the SFZ east of Lake Washington is consistent with about 8 km of slip on the upper part of the Seattle fault, but the amount of motion is only loosely constrained.

  13. The role of fault zones in affecting multiphase flow at Yucca Mountain

    SciTech Connect

    Tsang, Y.W.; Pruess, K.; Wang, J.S.Y.

    1993-01-01

    Within Yucca Mountain, the potential High Level Nuclear-Waste Repository site, there are large scale fault zones, most notably the Ghost Dance Fault. The effect of such high-permeability, large scale discontinuities on the flow and transport is a question of concern in assessing the ability of the site to isolate radio-nuclides from the biosphere. In this paper, we present a numerical study to investigate the role of the fault in affecting both the liquid and gas phase flows in the natural state at Yucca Mountain prior to waste emplacement, as well as after the waste emplacement when the fluid flow is strongly heat-driven. Our study shows that if the characteristic curves of the Ghost Dance Fault obey the same relationship between saturated permeability and capillary scaling parameter, as is observed from the measured data of Yucca Mountain welded and nonwelded tuffs. Apache Leap tuffs, and Las Cruces soil, then a large saturated permeability of the Ghost Dance Fault will play little role in channeling water into the fault, or inenhancing the flow of water down the fault. However, the Fault may greatly enhance the upward gas flow after emplacement of waste. This may have implications on the transport of gaseous radio-nuclides such as C{sup 14}. The results of this study also focus attention on the need for field measurements of fluid flow in the fault zones.

  14. Quaternary faulting of basalt flows on the Melones and Almanor fault zones, North Fork Feather River, northeastern California

    SciTech Connect

    Wakabayashi, J. , Hayward, CA ); Page, W.D. . Geosciences Dept.)

    1993-04-01

    Field relations indicate multiple sequences of late Cenozoic basalt flowed down the canyon of the North Fork Feather River from the Modoc Plateau during the Pliocene and early Quaternary. Remnants of at least three flow sequences are exposed in the canyon, the intermediate one yielding a K/Ar plagioclase date of 1.8 Ma. Topographic profiling of the remnants allows identification of Quaternary tectonic deformation along the northern Plumas trench, which separates the Sierra Nevada from the Diamond Mountains. The authors have identified several vertical displacements of the 1.8-Ma unit in the North Fork canyon and the area NE of Lake Almanor. NE of the lake, three NW-striking faults, each having down-to-the-west displacements of up to 35 m, are related to faulting along the east side of the Almanor tectonic depression. Analysis of the displaced basalt flows suggests that uplift of the Sierra Nevada occurred with canyon development prior to 2 Ma, and has continued coincident with several subsequent episodes of basalt deposition. Quaternary faulting of the basalt is associated with the Melones fault zone and the Plumas trench where they extend northward from the northern Sierra Nevada into the Modoc Plateau and southern Cascades. In contrast to the Mohawk Valley area, where the Plumas trench forms a 5-km-wide graben, faulting in the Almanor region is distributed over a 15-km-wide zone. A change in the strike of faulting occurs at Lake Almanor, from N50W along the Plumas trench to N20W north of the lake. The right-slip component on the fault of the Plums trench may result in a releasing bend at the change in strike and explain the origin of the Almanor depression.

  15. Fault slip rates and initiation age based on diffusion equation modeling: Wasatch Fault Zone and eastern Great Basin

    NASA Astrophysics Data System (ADS)

    Mattson, Ann; Bruhn, Ronald L.

    2001-01-01

    Models of the evolution of fault scarp morphology provide time elapsed since slip initiated on a faulted surface and may therefore provide more accurate estimates of slip rate than the rate calculated by dividing scarp offset by the age of the ruptured surface. To accomplish this task, linear and nonlinear models of sediment transport are calibrated from the morphology of Lake Bonneville shoreline scarps and fault scarps formed by multiple, surface-rupturing earthquakes along the Wasatch Fault Zone (WFZ). Profile modeling of scarps formed by several events distributed through time is done using a constant slip rate (CSR) solution and yields a value of A/κ (1/2 slip rate/diffusivity). Time elapsed since slip initiated on a fault is determined by establishing a value for κ and measuring total scarp offset. CSR nonlinear modeling (κ0 = 2.8 ± 1.1 m2/kyr, WFZ) of faults along the west slope of the Oquirrh Mountains indicates a slip rate of ˜0.1 mm/yr since 50 to 65 ka, which is corroborated by cosmogenic dating (10Be/26Al age = 75 ka). The slip rate along the west flank of the Stansbury Mountains varies from 0.04 to 0.2 mm/yr for time frames of 10 to >100 ka, with the most recent rupture on the northern portion of the fault zone ˜10 ka. Scarp analysis of the southern end of the Nephi segment, WFZ, suggests either temporal clustering or variable slip rate as indicated by differences in the short-term (1.3 mm/yr for 4.3 ka) versus long-term (0.4 mm/yr for 70 ka) slip rates.

  16. Scientific drilling into the San Andreas Fault Zone - an overview of SAFOD's first five years

    USGS Publications Warehouse

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

    2011-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    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.

  18. Experimental determination of the long-term strength and stability of laterally bounding fault zones in CO2 storage reservoirs based on kinetic modeling of fault zone evolution

    NASA Astrophysics Data System (ADS)

    Samuelson, J. E.; Koenen, M.; Tambach, T.

    2011-12-01

    Long-term sequestration of CO2, harvested from point sources such as coal burning power plants and cement manufactories, in depleted oil and gas reservoirs is considered to be one of the most attractive options for short- to medium-term mitigation of anthropogenic forcing of climate change. Many such reservoirs are laterally bounded by low-permeability fault zones which could potentially be reactivated either by changes in stress state during and after the injection process, and also by alterations in the frictional strength of fault gouge material. Of additional concern is how the stability of the fault zones will change as a result of the influence of supercritical CO2, specifically whether the rate and state frictional constitutive parameters (a, b, DC) of the fault zone will change in such a way as to enhance the likelihood of seismic activity on the fault zone. The short-term influence of CO2 on frictional strength and stability of simulated fault gouges prepared from mixtures of cap rock and reservoir rock has been analyzed recently [Samuelson et al., In Prep.], concluding that CO2 has little influence on frictional constitutive behavior on the timescale of a typical experiment (< 24 hours). Because of the time constraints of experimental work, and the long durations over which CO2 is intended to be sequestered, we have chosen to model the long-term mineralogical alteration of a fault zone with a simple starting mineralogy of 33% quartz, 33% illite, and 33% dolomite by weight using the geochemical modeling program PHREEQC and the THERMODDEM database, assuming instantaneous mixing of the CO2 with the fault gouge. The geochemical modeling predicts that equilibrium will be reached between fault gouge, reservoir brine, and CO2 in approximately 440 years, assuming an average grain-size (davg) of 20 μm, and ~90 years assuming davg =4 μm, a reasonable range of grain-sizes for natural fault gouges. The main change to gouge mineralogy comes from the complete

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  20. Stretching lineations, shear zone kinematics and dextral transpression along the Flying Point/Norumbega fault zone, Casco Bay, Maine

    SciTech Connect

    Swanson, M.T. . Dept. of Geosciences)

    1993-03-01

    Stretching lineations (L2) throughout the high-grade metamorphic rocks of the Casco Bay area are defined by the alignment of grain aggregates and elongate minerals generally parallel to subhorizontal upright F2 fold hinges. L2 lineations were developed due to regional layer-parallel shear related to dextral transpression along the Flying Point segment of the Norumbega Fault Zone during the later Paleozoic. The reorientation of boudin partings, quartz veins and pegmatite intrusions, the asymmetry of boudin pods, late vein folds and crenulations as well as a range of microscopic kinematic indicators within these rocks clearly indicate an overall dextral shear sense and a variable dip-slip component with local transport directions parallel to L2 during deformation. The distribution of L2 lineations about the trace of the NE- trending Flying Point Fault Zone shows: (a) E-plunging L2 in a broad zone on the NW side within SE-dipping, locally, pegmatite-injected, porphyroclastic schists and gneisses and; (c) sub-horizontal L2 within subordinate fault slices of folded Casco Bay Group lithologies to the SE. The Flying Point Fault zone itself consists of the straight planar gneisses and related rocks as a 2 km wide corridor of high shear strain reflected in the development of quartz-vein sheath folds parallel to L2. Variably-deformed mafic and felsic intrusions preserved as asymmetric pods and lenses within the flanking lithologies have been obliterated within this zone of high shear strain. This kinematic pattern and distribution of lineations is interpreted as an asymmetric transpressional uplift dominated by a broad NW front suffering oblique escape toward the west under dextral reverse motions and a major near-vertical zone of decoupling that developed at a restraining bend at the southwest end of the Norumbega Fault Zone.

  1. Evolution of the Permeability Architecture of the Baton Rouge Fault Zone, Louisiana Gulf Coastal Plain

    NASA Astrophysics Data System (ADS)

    Hanor, J. S.; Chamberlain, E. L.; Tsai, F. T.

    2011-12-01

    The Baton Rouge fault is a west-east trending, south-dipping listric fault in Louisiana, which offsets a thick sequence of unconsolidated siliciclastic sediments, the upper kilometer of which includes the Baton Rouge aquifer system. The Baton Rouge aquifer system consists of a series of complexly interbedded fluvial-deltaic sands and mudstones ranging in age from the late Miocene to the Pleistocene and dipping to the south. The high proportion of mudstones in the stratigraphic section, approximately 55 percent, reflects deposition in a rapidly aggrading setting. The fault was reactivated in the early Pleistocene, and the aquifer sands are offset by the same slip, 120 m. The fault is of significant hydrogeologic and environmental importance because it marks a sharp boundary between fresh water sands to the north and brackish water sands to the south. Large withdrawal of fresh water has resulted in the migration of brackish waters to the north from the fault and the progressive salinization of the groundwater supply. Migration of salt water up the fault and/or across the fault have been proposed as causes. Understanding the permeability architecture of the fault zone is of critical importance in developing strategies for controlling salinization. We have made an evaluation of the possible present permeability of the fault zone using an algorithm developed by Bense and Person [2006] which is based on the amount of slip on a fault and the clay-content of the sedimentary units flanking a fault. The algorithm provides an estimation of the present width and permeability of the fault zone and how the permeability architecture has evolved with time as offset on the fault has progressively increased. The basic geologic input is lithostratigraphy derived from SP-resistivity logs from wells immediately north and south of the fault over a 425 m high by 34 km wide area of the fault plane. The results of our calculations are as follows: the average fault zone width increases as a

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2005-05-01

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

  4. Kinematics and Fault Interaction of the Marmara Segment of the North Anatolian Fault Zone from Fault-Plane Solutions Based on a Refined High Precision Hypocenter Catalogue

    NASA Astrophysics Data System (ADS)

    Wollin, C.; Bohnhoff, M.; Küpperkoch, L.

    2015-12-01

    The North Anatolian Fault Zone (NAFZ) is separating the Eurasian and Anatolian plates representing a right-lateral transform plate boundary accommodating 20-30 mm annual slip. During the last seismic cycle the NAFZ has produced a series of large earthquakes that started in 1939 in Eastern Anatolia and has propagated westward towards the Istanbul-Marmara region. Here an up to 150 km long segment below the Sea of Marmara remains the only NAFZ segment that was not activated since 1766 representing a seismic gap hosting the potential for a magnitude up to 7.5 earthquake.Here we present a hypocenter catalogue for the Marmara section of the NAFZ which is a challenge since the fault is located offshore permitting no long-term on- or near fault stations. Using the Akaike Information Criterion applied on a characteristic function derived from higher order statistics as well as autoregressive forward prediction to automatically pick P- and S-onset times, we consistently analyze extensive waveform data provided by permanent seismic broadband stations of a combined regional seismic network with unprecedented station distribution.The quality of automatically determined travel times is carefully examined by comparing them to manual reference picks which were determined with a scheme emphasizing highest possible consistency and precision. The high accuracy obtained for the travel times results in an improved hypocenter catalog with fewer but well-located events that allow to image the major fault branches of the NAFZ below the Sea of Marmara.The large network aperture with lacking stations immediately above the seismicity along the fault and insufficient azimuthal station density prevents inversion for focal mechanisms of most single events. Therefore we form spatial seismicity clusters and calculate composite fault plane solutions. Resolving fault-zone geometry and kinematics allow to identify the currently active fault branches and to determine the currently ongoing processes

  5. Fault Scarp Detection Beneath Dense Vegetation Cover: Airborne Lidar Mapping of the Seattle Fault Zone, Bainbridge Island, Washington State

    NASA Technical Reports Server (NTRS)

    Harding, David J.; Berghoff, Gregory S.

    2000-01-01

    The emergence of a commercial airborne laser mapping industry is paying major dividends in an assessment of earthquake hazards in the Puget Lowland of Washington State. Geophysical observations and historical seismicity indicate the presence of active upper-crustal faults in the Puget Lowland, placing the major population centers of Seattle and Tacoma at significant risk. However, until recently the surface trace of these faults had never been identified, neither on the ground nor from remote sensing, due to cover by the dense vegetation of the Pacific Northwest temperate rainforests and extremely thick Pleistocene glacial deposits. A pilot lidar mapping project of Bainbridge Island in the Puget Sound, contracted by the Kitsap Public Utility District (KPUD) and conducted by Airborne Laser Mapping in late 1996, spectacularly revealed geomorphic features associated with fault strands within the Seattle fault zone. The features include a previously unrecognized fault scarp, an uplifted marine wave-cut platform, and tilted sedimentary strata. The United States Geologic Survey (USGS) is now conducting trenching studies across the fault scarp to establish ages, displacements, and recurrence intervals of recent earthquakes on this active fault. The success of this pilot study has inspired the formation of a consortium of federal and local organizations to extend this work to a 2350 square kilometer (580,000 acre) region of the Puget Lowland, covering nearly the entire extent (approx. 85 km) of the Seattle fault. The consortium includes NASA, the USGS, and four local groups consisting of KPUD, Kitsap County, the City of Seattle, and the Puget Sound Regional Council (PSRC). The consortium has selected Terrapoint, a commercial lidar mapping vendor, to acquire the data.

  6. Motion on upper-plate faults during subduction zone earthquakes: Case of the Atacama Fault System, northern Chile

    NASA Astrophysics Data System (ADS)

    Loveless, J. P.; Pritchard, M. E.

    2008-12-01

    Motion on the Atacama Fault System (AFS) in northern Chile is driven by Andean subduction zone processes. We use two approaches, observational and theoretical, to evaluate how the AFS and other forearc faults responded to coseismic stress induced by one well-studied megathrust earthquake, the 1995 Mw = 8.1 Antofagasta event. We use synthetic aperture radar interferometry (InSAR) to search for small-scale coseismic and postseismic deformation on individual faults. The InSAR data are ambiguous: some images show offset consistent with coseismic faulting on the Paposo segment of the AFS and others lack such signal. The fact that we do not observe the fault-like displacement in all coseismic interferograms suggests that atmospheric contamination, not tectonic deformation, is responsible for the signal. To explore the capacity of the earthquake to trigger motion on upper plate faults, we use seven published slip maps constrained by geodetic and/or seismic data to calculate static and dynamic Coulomb stress change (CSC) on faults in the Antofagasta region. The static CSC field varies between models and depends on the distribution of coseismic interplate slip. On the basis of the CSC distribution predicted by our preferred model constrained by all available data, we suggest it was unlikely that the Antofagasta earthquake directly triggered normal motion on the AFS, and the InSAR data are consistent with this null result. Field reports of normal faulting related to the earthquake may reflect recent (but not coseismic) motion or highly localized behavior not representative of the regional coseismic stress field.

  7. Late Neogene kinematics of intra-arc oblique shear zones: The Petilia-Rizzuto Fault Zone (Calabrian Arc, Central Mediterranean)

    NASA Astrophysics Data System (ADS)

    van Dijk, J. P.

    1994-10-01

    The kinematics of intra-arc shear zones play a key role in the secondary shaping of orogenic arcs such as the Calabrian Arc (central Mediterranean). Comparison of the Neogene structural development of the Petilia-Rizzuto Fault Zone and the basement structure of the bordering Sila massif reveals that the fault zone is the surface expression of a deep NW-SE trending sinistral crustal oblique shear zone. This shear zone continues over a length of more than 130 km across the northern segment of the Calabrian Arc and shows a post-Eocene sinistral displacement of about 50 km. The late Neogene forearc basin development and syndepositional tectonics along the fault zone are reconstructed in great detail by analyzing the middle Miocene-Recent tectonic sequence stratigraphy. A strike-slip cycle can be recognized whereby the subsequent activity of Riedel shears, tensional faults, and P shears, positive flower structures and principle displacement wrench faults, can accurately be traced in time. Observed phenomena are discussed in terms of the activity of a conjugate system of oblique thrust zones within the growing accretionary complex. The evolution of special types of thrust belt basins is illustrated. These include oblique thin-skinned pull-apart basins, oblique rhomboidal "harmonica" basins, and "detached slab" basins (new terms introduced here), evolving one into the other. A new feature illustrated is the recurrent basin inversion which generated passive roof duplexes through back-shear motion and out-of-sequence thrusting along the wedge. The fault patterns and the style of inversion tectonics imply an E-W directed axis of effective compressive stress in this part of the arc. This resulted from an interaction of (1) local E-W directed compression related to a differential displacement of two parallel segments of the arc (generated by the migration to the southeast of the Calabrian Arc and opening of the Tyrrhenian backarc basin); (2) alternating NW-SE directed

  8. Variscan granitoids related to shear zones and faults: examples from the Central Sudetes (Bohemian Massif) and the Middle Odra Fault Zone

    NASA Astrophysics Data System (ADS)

    Oberc-Dziedzic, T.; Kryza, R.; Pin, C.

    2015-07-01

    The granitoid intrusions of the Central Sudetes (CS) and of the Middle Odra Fault Zone (MOFZ), NE part of the Bohemian Massif, are both spatially and temporally related to large-scale shear zones and faults (including possible terrane boundaries) that provided effective channels for melt migration. Summarizing common features of the CS and MOFZ granitoids, we have delineated a set of characteristics of the fault-related and shear zone-related granitoids: (1) they are mainly generated by partial melting of crustal sources, with variable contribution (or no contribution) of mantle materials; (2) the sheet-like, steeply inclined, narrow and rather small granitoid intrusions are emplaced within shear zones at mid-crustal level (c. 20 km depth), whereas the larger, flat-lying plutons intrude into the upper crust, outside or above these shear zones; (3) the magmatic foliation and lineation in granitoids of the deeper, sheet-like intrusions are concordant with those in the surrounding metamorphic rocks, suggesting that the solidification of granitoids was coeval with the deformation in the shear zones; instead, the magmatic foliation in the shallower and larger dome-like plutons reflects magma flow; (4) ductile, transcurrent movements along the shear zones postdate medium-pressure regional metamorphism and are accompanied by an increase in the local thermal gradient, as documented by the crystallization of cordierite, andalusite and sillimanite; (5) the increase in the thermal gradient precedes the emplacement of granitoids and their concomitant thermal influence on the country rocks. The granitoids related to the final stages of tectonothermal activity of the shear zones are good-time markers of their evolutionary path.

  9. Holocene activity of the Rose Canyon fault zone in San Diego, California

    NASA Astrophysics Data System (ADS)

    Lindvall, Scott C.; Rockwell, Thomas K.

    1995-12-01

    The Rose Canyon fault zone in San Diego, California, has many well-expressed geomorphic characteristics of an active strike-slip fault, including scarps, offset and deflected drainages and channel walls, pressure ridges, a closed depression, and vegetation lineaments. Geomorphic expression of the fault zone from Mount Soledad south to Mission Bay indicates that the Mount Soledad strand is the most active. A network of trenches excavated across the Mount Soledad strand in Rose Creek demonstrate a minimum of 8.7 m of dextral slip in a distinctive early to middle Holocene gravel-filled channel that crosses the fault zone. The gravel-filled channel was preserved within and east of the fault but was removed west of the fault zone by erosion or possibly grading during development. Consequently, the actual displacement of the channel could be greater than 8.7 m. Radiocarbon dates on detrital charcoal recovered from the sediments beneath the channel yield a maximum calibrated age of about 8.1±0.2 kyr. The minimum amount of slip along with the maximum age yield a minimum slip rate of 1.07±0.03 mm/yr on this strand of the Rose Canyon fault zone for much of Holocene time. Other strands of the Rose Canyon fault zone, which are east and west of our site, may also have Holocene activity. Based on an analysis of the geomorphology of fault traces within the Rose Canyon fault zone, along with the results of our trenching study, we estimate the maximum likely slip rate at about 2 mm/yr and a best estimate of about 1.5 mm/yr. Stratigraphie evidence of at least three events is present during the past 8.1 kyr. The most recent surface rupture displaces the modern A horizon (topsoil), suggesting that this event probably occurred within the past 500 years. Stratigraphie and structural relationships also indicate the occurrence of a scarp-forming event at about 8.1 kyr, prior to deposition of the gravel-filled channel that was used as a piercing line. A third event is indicated by the

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  11. Temporal variations in slip rate of the White Mountain Fault Zone, Eastern California

    USGS Publications Warehouse

    Kirby, E.; Burbank, D.W.; Reheis, M.; Phillips, F.

    2006-01-01

    The evolution of fault slip through time may yield insight into the geodynamics of deforming lithosphere. Precise determination of temporal variations in fault slip is often hindered, however, by a dearth of markers of varying age from which to reconstruct fault slip. Here we determine slip rates across the White Mountain Fault Zone over the past ca. 0.8??Ma from displaced alluvial deposits preserved along the flank of the White Mountains. Displacement histories inferred from deposits containing the ??? 760??ka Bishop Tuff contrast strongly with those inferred from Late Pleistocene alluvial fans dated by cosmogenic 36Cl, indicating that the fault has experienced significant temporal variations in slip rate. Oblique-slip rates over the past ??? 760??ky are determined to have been > 0.9??m/ky parallel to a net slip vector plunging shallowly ( ca. 70??ky, yet occurred on a well-established fault system. Moreover, the timing and magnitude of slip rate variation mimics behavior documented for the northern Fish Lake Valley fault zone. Together, our data provide evidence for coordinated slip rate variations across the Eastern California Shear Zone during the Pleistocene. ?? 2006 Elsevier B.V. All rights reserved.

  12. Deformation and fluid flow during fault zone development in granitic rocks

    SciTech Connect

    Pollard, D.D.; Buergmann, R.; Christiansen, P.P. . Geology Dept.); Martel, S.J. )

    1992-01-01

    Fault zone development in crystalline rock of the Lake Edison granodiorite, Sierra Nevada, California, is characterized by five stages with distinct physical mechanisms, each identified by outcrop mapping, and understood through mechanical analysis. Because fluid flow through the developing fault system can influence the rock properties and loading, and because rock fracturing can influence the fluid pathways, the phenomena of deformation and fluid flow are closely coupled. Both the faulting mechanisms and the evolution of permeability in crystalline rocks are demonstrably different from fault zones in porous sedimentary rocks. The paper describes the five stages of fault development. Deformation of the adjacent granodiorite at each stage of growth for a particular fault zone depended on the distribution of slip. This distribution is a function of the remote stress state, the constitutive rock properties, the geometry of the fault surfaces, and their frictional properties. Simple forward models, using elasticity theory, illustrate how the displacement distributions can vary with remote loading, friction, and geometry. Inverse methods provide the analytical tools to deduce these variables from outcrop data, but their implementation awaits a credible model that couples the fluid flow and rock deformation.

  13. Insights into the damage zones in fault-bend folds from geomechanical models and field data

    NASA Astrophysics Data System (ADS)

    Ju, Wei; Hou, Guiting; Zhang, Bo

    2014-01-01

    Understanding the rock mass deformation and stress states, the fracture development and distribution are critical to a range of endeavors including oil and gas exploration and development, and geothermal reservoir characterization and management. Geomechanical modeling can be used to simulate the forming processes of faults and folds, and predict the onset of failure and the type and abundance of deformation features along with the orientations and magnitudes of stresses. This approach enables the development of forward models that incorporate realistic mechanical stratigraphy (e.g., the bed thickness, bedding planes and competence contrasts), include faults and bedding-slip surfaces as frictional sliding interfaces, reproduce the geometry of the fold structures, and allow tracking strain and stress through the whole deformation process. In this present study, we combine field observations and finite element models to calibrate the development and distribution of fractures in the fault-bend folds, and discuss the mechanical controls (e.g., the slip displacement, ramp cutoff angle, frictional coefficient of interlayers and faults) that are able to influence the development and distribution of fractures during fault-bend folding. A linear relationship between the slip displacement and the fracture damage zone, the ramp cutoff angle and the fracture damage zone, and the frictional coefficient of interlayers and faults and the fracture damage zone was established respectively based on the geomechanical modeling results. These mechanical controls mentioned above altogether contribute to influence and control the development and distribution of fractures in the fault-bend folds.

  14. Magnetic fabrics induced by dynamic faulting reveal damage zone sizes in soft rocks, Dead Sea basin

    NASA Astrophysics Data System (ADS)

    Levi, Tsafrir; Weinberger, Rami; Marco, Shmulik

    2015-04-01

    Distinguishing between the effect of remote versus local strain fields, determining the size of the related inelastic damage zone, and resolving the fault-plane solutions of past earthquakes are of fundamental importance to neotectonic reconstructions and paleoseismic studies. In order to shad lights on these issues, we measured the anisotropy of magnetic susceptibility (AMS) of soft rocks within a seismically active region. The AMS fabrics were explored next to late Pleistocene syndepositional normal faults (total displacement up to ~3.5 m) that cross soft lacustrine rocks in the Dead Sea basin. 'Deposition fabrics' prevail meters away from the fault planes and are characterized by scattered maximum and intermediate principal AMS axes. 'Deformation fabrics' are detected up to tens of centimeters from the fault planes and are characterized by well-grouped AMS axes, in which one of the principal axes is parallel to the strike of the nearby fault. Variations in the AMS fabrics and magnetic lineations define the size of the inelastic damage zone around the faults. The results demonstrate that the deformation-driven magnetic fabrics and the associated inelastic deformation zones are compatible with coseismic dynamic faulting and the effects of the local strain field during earthquakes. Most of the AMS fabrics show a conspicuous similarity to that of the fault-plane solutions, i.e. the principal AMS axes and instantaneous strain ellipsoids are coaxial. These results suggest a novel application of the AMS method for defining the shape and size of the damage zones surrounding the paleo- dynamic faults and determining the principal axes of the local strain field.

  15. Paleoearthquake recurrence on the East Paradise fault zone, metropolitan Albuquerque, New Mexico

    USGS Publications Warehouse

    Personius, Stephen F.; Mahan, Shannon

    2000-01-01

    A fortuitous exposure of the East Paradise fault zone near Arroyo de las Calabacillas has helped us determine a post-middle Pleistocene history for a long-forgotten Quaternary fault in the City of Albuquerque, New Mexico. Mapping of two exposures of the fault zone allowed us to measure a total vertical offset of 2.75 m across middle Pleistocene fluvial and eolian deposits and to estimate individual surface-faulting events of about 1, 0.5, and 1.25 m. These measurements and several thermoluminescence ages allow us to calculate a long-term average slip rate of 0.01 ± 0.001 mm/yr and date two surface-faulting events to 208 ± 25 ka and 75 ± 7 ka. The youngest event probably occurred in the late Pleistocene, sometime after 75 ± 7 ka. These data yield a single recurrence interval of 133 ± 26 ka and an average recurrence interval of 90 ± 10 ka. However, recurrence intervals are highly variable because the two youngest events occurred in less than 75 ka. Offsets of 0.5-1.25 m and a fault length of 13-20 km indicate that surface-rupturing paleoearthquakes on the East Paradise fault zone had probable Ms or Mw magnitudes of 6.8-7.0. Although recurrence intervals are long on the East Paradise fault zone, these data are significant because they represent some of the first published slip rate, paleoearthquake magnitude, and recurrence information for any of the numerous Quaternary faults in the rapidly growing Albuquerque-Rio Rancho metropolitan area.

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  18. Frictional melting experiments investigate coseismic behaviour of pseudotachylyte-bearing faults in the Outer Hebrides Fault Zone, UK.

    NASA Astrophysics Data System (ADS)

    Campbell, L.; De Paola, N.; Nielsen, S. B.; Holdsworth, R.; Lloyd, G. E. E.; Phillips, R. J.; Walcott, R.

    2015-12-01

    Recent experimental studies, performed at seismic slip rates (≥ 1 m/s), suggest that the friction coefficient of seismic faults is significantly lower than at sub-seismic (< 1 mm/s) speeds. Microstructural observations, integrated with theoretical studies, suggest that the weakening of seismic faults could be due to a range of thermally-activated mechanisms (e.g. gel, nanopowder and melt lubrication, thermal pressurization, viscous flow), triggered by frictional heating in the slip zone. The presence of pseudotachylyte within both exhumed fault zones and experimental slip zones in crystalline rocks suggests that lubrication plays a key role in controlling dynamic weakening during rupture propagation. The Outer Hebrides Fault Zone (OHFZ), UK contains abundant pseudotachylyte along faults cutting varying gneissic lithologies. Our field observations suggest that the mineralogy of the protolith determines volume, composition and viscosity of the frictional melt, which then affects the coseismic weakening behaviour of the fault and has important implications for the magnitudes and distribution of stress drops during slip episodes. High velocity friction experiments at 18 MPa axial load, 1.3 ms-1 and up to 10 m slip were run on quartzo-feldspathic, metabasic and mylonitic samples, taken from the OHFZ in an attempt to replicate its coseismic frictional behaviour. These were configured in cores of a single lithology, or in mixed cores with two rock types juxtaposed. All lithologies produce a general trend of frictional evolution, where an initial peak followed by transient weakening precedes a second peak which then decays to a steady state. Metabasic and felsic single-lithology samples both produce sharper frictional peaks, at values of μ = 0.19 and μ= 0.37 respectively, than the broader and smaller (μ= 0.15) peak produced by a mixed basic-felsic sample. In addition, both single-lithology peaks occur within 0.2 m slip, whereas the combined-lithology sample displays a

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

    USGS Publications Warehouse

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

    1994-01-01

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

  20. Evidence of shallow fault zone strengthening after the 1992 M7.5 landers, california, earthquake

    PubMed

    Li; Vidale; Aki; Xu; Burdette

    1998-01-01

    Repeated seismic surveys of the Landers, California, fault zone that ruptured in the magnitude (M) 7.5 earthquake of 1992 reveal an increase in seismic velocity with time. P, S, and fault zone trapped waves were excited by near-surface explosions in two locations in 1994 and 1996, and were recorded on two linear, three-component seismic arrays deployed across the Johnson Valley fault trace. The travel times of P and S waves for identical shot-receiver pairs decreased by 0.5 to 1.5 percent from 1994 to 1996, with the larger changes at stations located within the fault zone. These observations indicate that the shallow Johnson Valley fault is strengthening after the main shock, most likely because of closure of cracks that were opened by the 1992 earthquake. The increase in velocity is consistent with the prevalence of dry over wet cracks and with a reduction in the apparent crack density near the fault zone by approximately 1.0 percent from 1994 to 1996.

  1. Fine structure of the landers fault zone: segmentation and the rupture process.

    PubMed

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

    1994-07-15

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

  2. San Andreas fault zone drilling project: scientific objectives and technological challenges

    USGS Publications Warehouse

    Hickman, Stephen; Younker, Leland; Zobeck, Mark; Cooper, George

    1994-01-01

    We are leading a new international initiative to conduct scientific drilling within the San Andreas fault zone at depths of up to 10 km. This project is motivated by the need to understand the physical and chemical processes operating within the fault zone and to answer fundamental questions about earthquake generation along major plate-boundary faults. Through an integrated program of coring, fluid sampling, in-situ and laboratory experimentation and long-term monitoring, we hope to provide fundamental constraints on the structure, composition, mechanical behavior and physical state of the San Andreas fault system at depths comparable to the nucleation zones of great earthquakes. The drilling, sampling and observational requirements needed to ensure the success of this project are stringent. These include: 1) drilling stable vertical holes to depths of about 9 km in fractured rock at temperatures of up to 300??C; 2) continuous coring of inclined holes branched off these vertical boreholes to intersect the fault at depths of 3, 6 and 9 km; 3) conducting sophisticated borehole geophysical measurements and fluid/rock sampling at high temperatures and pressures; and 4) instrumenting some or all of these inclined core holes for continuous monitoring of seismicity and a broad range of physical and chemical properties over periods of up to several decades. For all of these tasks, because of the overpressured clay-rich formations anticipated within the fault zone at depth, we expect to encounter difficult drilling, coring and hole-completion conditions in the regions of greatest scientific interest.

  3. San Andreas fault zone drilling project: scientific objectives and technological challenges

    USGS Publications Warehouse

    Hickman, S.H.; Younker, L.W.; Zoback, M.D.

    1995-01-01

    We are leading a new international initiative to conduct scientific drilling within the San Andreas fault zone at depths of up to 10 km. This project is motivated by the need to understand the physical and chemical processes operating within the fault zone and to answer fundamental questions about earthquake generation along major plate-boundary faults. Through a comprehensive program of coring, fluid sampling, downhole measurements, laboratory experimentation, and long-term monitoring, we hope to obtain critical information on the structure, composition, mechanical behavior and physical state of the San Andreas fault system at depths comparable to the nucleation zones of great earthquakes. The drilling, sampling and observational requirements needed to ensure the success of this project are stringent. These include: 1) drilling stable vertical holes to depths of about 9 km in fractured rock at temperatures of up to 300°C; 2) continuous coring and completion of inclined holes branched off these vertical boreholes to intersect the fault at depths of 3, 6, and 9 km; 3) conducting sophisticated borehole geophysical measurements and fluid/rock sampling at high temperatures and pressures; and 4) instrumenting some or all of these inclined core holes for continuous monitoring of earthquake activity, fluid pressure, deformation and other parameters for periods of up to several decades. For all of these tasks, because of the overpressured clay-rich formations anticipated within the fault zone at depth, we expect to encounter difficult drilling, coring and hole-completion conditions in the region of greatest scientific interest.

  4. Evidence of shallow fault zone strengthening after the 1992 M7.5 Landers, California, earthquake

    USGS Publications Warehouse

    Li, Y.-G.; Vidale, J.E.; Aki, K.; Xu, Fei; Burdette, T.

    1998-01-01

    Repeated seismic surveys of the Landers, California, fault zone that ruptured in the magnitude (M) 7.5 earthquake of 1992 reveal an increase in seismic velocity with time. P, S, and fault zone trapped waves were excited by near-surface explosions in two locations in 1994 and 1996, and were recorded on two linear, three-component seismic arrays deployed across the Johnson Valley fault trace. The travel times of P and S waves for identical shot-receiver pairs decreased by 0.5 to 1.5 percent from 1994 to 1996, with the larger changes at stations located within the fault zone. These observations indicate that the shallow Johnson Valley fault is strengthening after the main shock, most likely because of closure of cracks that were opened by the 1992 earthquake. The increase in velocity is consistent with the prevalence of dry over wet cracks and with a reduction in the apparent crack density near the fault zone by approximately 1.0 percent from 1994 to 1996.

  5. Continuity, segmentation and faulting type of active fault zones of the 2016 Kumamoto earthquake inferred from analyses of a gravity gradient tensor

    NASA Astrophysics Data System (ADS)

    Matsumoto, Nayuta; Yoshihiro, Hiramatsu; Sawada, Akihiro

    2016-10-01

    We analyze Bouguer anomalies in/around the focal region of the 2016 Kumamoto earthquake to examine features, such as continuity, segmentation and faulting type, of the active fault zones related to the earthquake. Several derivatives and structural parameters calculated from a gravity gradient tensor are applied to highlight the features. First horizontal and vertical derivatives, as well as a normalized total horizontal derivative, characterize well the continuous subsurface fault structure along the Futagawa fault zone. On the other hand, the Hinagu fault zone is not clearly detected by these derivatives, especially in the case of the Takano-Shirahata segment, suggesting a difference of cumulative vertical displacement between the two fault zones. The normalized total horizontal derivative and the dimensionality index indicate a discontinuity of the subsurface structure of the Hinagu fault zone, that is, a segment boundary between the Takano-Shirahata and the Hinagu segments. The aftershock distribution does not extend beyond this segment boundary. In other words, this segment boundary controls the southern end of the rupture area of the foreshock. We also recognize normal fault structures dipping to the northwest in some areas of the fault zones from estimations of dip angles.[Figure not available: see fulltext.

  6. Fault damage zones in mechanically layered rocks: The effects of planar anisotropy

    NASA Astrophysics Data System (ADS)

    Misra, Santanu; Ellis, Susan; Mandal, Nibir

    2015-08-01

    This study shows how inherited strength anisotropy influences damage localization at both the tip and wall regions of a fault or fracture. We performed analogue and numerical compression experiments on transversely isotropic models with single and multiple cuts of finite length, simulating the propagation of preexisting faults and cracks in layered rock. The stress-strain curves from the analogue experiments show a change in bulk yield behavior with fault inclination and anisotropy orientation with respect to the stress direction. Earlier isotropic models demonstrated a brittle (wing fracturing) to ductile (shear-zone formation) transition as the fault angle (α) to the principal compression direction increased. The experiments with anisotropic models show patterns of damage localization change dramatically with the orientation of transversely isotropic planes (θ, measured with respect to principal extension direction). Under layer-normal (θ = 0°) and layer-parallel compression (θ = 90°), preexisting faults undergo significant reactivation when 0 < α < 90°, and fault slip eventually leads to mechanical instabilities within the anisotropic layering, causing damage zones in the tip regions. For layer-normal (θ = 0°) compression, the damage processes involve intense extensional shear localization, whereas for layer-parallel compression, contractional shear localization and tensile opening result in characteristic internal shear-band structures. In contrast, for 0 < θ < 90°, the faults undergo little or no reactivation, irrespective of α. In this case, bulk compression leads to an interlayer slip-mediated global deformation. Obliquely anisotropic models thus produce weak or no fault damage zones. We also show that the fault-parallel principal damage localized at the tips can be coupled with transversely oriented, antithetic secondary damage in the wall regions. However, secondary damage develops predominantly when θ = 90°. Field examples of fault damage

  7. Frictional resistance of a fault zone with strong rotors

    NASA Astrophysics Data System (ADS)

    Brune, James N.; Anooshehpoor, A.

    1997-08-01

    As a possible mechanism to explain the lack of a heat flow anomaly along the creeping section of the San Andreas Fault, we have determined the effect of placing hard rotors along a surface between two deformable media, in this case styrofoam balls between two blocks of foam rubber. The probable presence of Franciscan rocks at depth along the creeping section of the San Andreas Fault suggested this mechanism, since the Franciscan is characterized not only by basic serpentinous rocks which are weak, but also by embedded, more or less equidimensional, blocks of very strong rocks (knockers), e.g., high grade blueschists and eclogites, which might act as rotors. The results suggest that knocker rotation may be a viable mechanism for reduction of friction on the creeping section of the San Andreas fault, and thus be at least a partial explanation of the lack of any observed frictional heat flow anomaly there.

  8. Forearc deformation and megasplay fault system of the Ryukyu subduction zone

    NASA Astrophysics Data System (ADS)

    Hsu, S.; Yeh, Y.; Sibuet, J.; Tsai, C.; Doo, W.

    2011-12-01

    A great tsunami caused by a subduction earthquake had struck south Ryukyu islands and killed ~12000 people in 1771. Here we report the existence of a megasplay fault system along the south Ryukyu forearc. Analyses of deep multi-channel seismic reflection profiles indicate that the megasplay fault system is rising from the summit of a ~1 km high mount sitting on a ~5° landward dipping subducted plate interface. The fault system has accumulated large strain as evidenced by the active and widespread normal faults in the inner wedge. The along-trench length of the megasplay fault system is estimated to be ~450 km. The origin of this south Ryukyu megasplay fault system is linked to the subduction of elevated ridges parallel to the fracture zones. In contrast, no similar splay fault system is found in the west of 125. 5°E where the oblique subduction has produced shear zones along the south Ryukyu forearc. We infer that the megasplay fault system is responsible for the 1771 south Ryukyu tsunami. Likewise, after a quiescence of ~240 years, a near-future great earthquake and tsunami is anticipated as the extensional feature is strongly widespread over the south Ryukyu forearc.

  9. Quantifying Morphologic Changes in a Low Gradient River Crossing Southeast Louisiana Fault Zones

    NASA Astrophysics Data System (ADS)

    Fischer, G.; Gasparini, N. M.; Dawers, N. H.

    2011-12-01

    This study investigates the signature of faulting in low gradient, alluvial rivers crossing the Baton Rouge fault zone (BRFZ) and Denham Springs-Scotlandville fault zone (DSSFZ), which encompass a set of East-West striking normal faults in southeast Louisiana. These faults exhibit surface expressions associated with up to a few meters of vertical displacement of Late Pleistocene sediments, but little is known about their activity during the Holocene. Our study aims to quantify geomorphic changes in a number of rivers that cross these fault zones and to use these changes to gain insight into the history of faulting in the region. We hypothesize that fault movement will be evident in patterns of river sinuosity, slope, and width to depth ratio. We focus on four subparallel channels of various discharges that cross either or both the BRFZ and the DSSFZ. Information on local fault scarp heights and channel reaches are extracted by GIS analysis of the LA LiDAR 5 m DEM, as well as flow modeling using the HEC-RAS software program. On the Tickfaw River, we conducted field surveys using differential GPS to record contemporary water surface slopes and channel location. Historic channel features on the Tickfaw are characterized using a series of aerial photographs dating back to 1952. Over the past 50 years, the Tickfaw River has shortened its course through the study area significantly (~4.9%) by means of meander cutoffs. Since 1952, sinuosity (P) has decreased in all of the Tickfaw channel reaches that cross fault segments. Currently, the sinuosity is extremely low (average P = 1.14) where the river crosses the DSSFZ and slightly higher where the river crosses the BRFZ (average P = 1.9). We use the LiDAR data to quantify offset on the faults that the river crosses. These values will be compared with the average lateral migration rate of the river in order to better understand the time scales over which both processes operate. If the faults appear to have little morphologic

  10. Stress and strain around a multiply reactivated deep-seated fault zone and its impact on a potential geothermal reservoir - The Freiburg-Bonndorf-Bodensee fault zone

    NASA Astrophysics Data System (ADS)

    Egli, Daniel; Madritsch, Herfried; Ibele, Tobias; Mosar, Jon; Vietor, Tim

    2014-05-01

    The Swiss and German Molasse Basin is generally of high geo-economical interest as it is considered to host potential reservoirs for natural gas and geothermal energy production, as well as sites for radioactive waste disposal and CO2 storage. Its successful exploration and eventually exploitation requires detailed understanding of its deep underground in particular its structural characteristics. Information of the rocks underlying the up to km thick Molasse sediments is mainly available from drillhole and seismic data. Outcrops of Mesozoic and Paleozoic sediments as well as the crystalline basement that could provide additional information on structural geological characteristics are very rare and mostly restricted to the borders of the basin. This study focuses on the eastern part of the Freiburg-Bonndorf-Bodensee Fault Zone (FBBFZ; e.g. Paul 1948, Carlé 1955), a roughly 100 km long fault system, which runs approximately from the Kaiserstuhl in the Upper Rhein Graben across the Black Forest Massif to the Lake Constance. Its extensive present day surface trace allows to study the fault zone as it cuts through a wide range of lithologies from the Variscan basement of the Black Forest to the Tertiary sediments of the Molasse west of Lake Constance. As such, it can serve as natural analogue for the characterization of fault structures in the subsurface of the Molasse Basin. The Randen Fault is a well-exposed NW-SE trending fault segment of the FBBFZ, situated in NE Switzerland and SW Germany. In the field, as well as in seismic sections the structure shows the characteristics of a normal fault but there are indications for a dextral transcurrent overprint. We presents a kinematic analysis of outcrop scale fracture systems collected along the various segments of the FBBFZ with a focus on the Randen Fault segment. The results indicate a perturbation of the regional fracture characteristics and the paleostress pattern in the vicinity of the fault zone. A recently

  11. Seismic Imaging of the San Jacinto Fault Zone Area From Seismogenic Depth to the Surface

    NASA Astrophysics Data System (ADS)

    Ben-Zion, Y.

    2015-12-01

    I review multi-scale multi-signal seismological results on structural properties within and around the San Jacinto Fault Zone (SJFZ). The results are based on data of the regional southern California and ANZA networks, additional near-fault seismometers and linear arrays with instrument spacing 25-50 m that cross the SJFZ at several locations, and a spatially-dense rectangular array with 1108 vertical-component sensors separated by 10-30 m centered on the fault. The studies utilize earthquake data to derive Vp and Vs velocity models with horizontal resolution of 1-2 km over the depth section 2-15 km, ambient noise with frequencies up to 1 Hz to image with similar horizontal resolution the depth section 0.5-7 km, and high-frequency seismic noise from the linear and rectangular arrays for high-resolution imaging of the top 0.5 km. Pronounced damage regions with low seismic velocities and anomalous Vp/Vs ratios are observed around the SJFZ, as well as the San Andreas and Elsinore faults. The damage zones follow generally a flower-shape with depth. The section of the SJFZ from Cajon pass to the San Jacinto basin has a faster SW side, while the section farther to the SE has an opposite velocity contrast with faster NE side. The damage zones and velocity contrasts produce at various locations fault zone trapped and head waves that are utilized to obtain high-resolution information on inner fault zone components (bimaterial interfaces, trapping structures). Analyses of high-frequency noise recorded by the fault zone arrays reveal complex shallow material with very low seismic velocities and strong lateral and vertical variations.

  12. Fault zone hydrogeologic properties and processes revealed by borehole temperature monitoring

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    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.

  13. Using Novel Earthquake Early Warning (EEW) with Optimized Sensor Model to Determine How Establishments Will Be Affected in a 7.0 Hayward Earthquake Scenario

    NASA Astrophysics Data System (ADS)

    Munnangi, P.

    2015-12-01

    The Bay Area is one of the world's most vulnerable places to earthquakes, and being ready is vital to survival. The purpose of this study was to determine the distribution of places affected in a 7.0 Hayward Earthquake and the effectiveness of earthquake early warning (EEW) in this scenario. We manipulated three variables: the location of the epicenter, the station placement, and algorithm used for early warning. To compute the blind zone and warning times, we calculated the P and S wave velocities by using data from the Northern California Earthquake Catalog and the radius of the blind zone using appropriate statistical models. We came up with a linear regression model directly relating warning time and distance from the epicenter. We used Google Earth to plot three hypothetical epicenters on the Hayward Fault and determine which establishments would be affected. By varying the locations, the blind zones and warning times changed. As the radius from the epicenter increased, the warning times also increased. The intensity decreased as the distance from the epicenter grew. We determined which cities were most vulnerable. We came up with a list of cities and their predicted warning times in this hypothetical scenario. For example, for the epicenter in northern Hayward, the cities at most risk were San Pablo, Richmond, and surrounding cities, while the cities at least risk were Gilroy, Modesto, Lincoln, and other cities within that radius. To find optimal station placement, we chose two cities with stations placed variable distances apart from each other. There was more variability in scattered stations than dense stations, suggesting stations placed closer together are more effective since they provide precise warnings. We compared the algorithms ElarmS, which is currently used in the California Integrated Seismic Network (CISN) and Onsite, which is a single-sensor approach that uses one to two stations, by calculating the blind zone and warning times for each

  14. The Influence of a Local Fault Zone on High Energy Tremor Occurrence during Longwall Mining of a Coal Seam

    NASA Astrophysics Data System (ADS)

    Wojtecki, Łukasz; Knopik, Małgorzata; Zuberek, Wacław Marian

    2016-08-01

    Underground mining of coal seams in the Upper Silesian Coal Basin in Poland is accompanied by seismic activity of varying magnitude. The investigations which have been performed for several years distinguished high energy mine tremors connected directly with mining or coupled with geological structures, such as large faults. In mined seams, local fault zones occur. Faults in these zones are usually small, with throws comparable with coal seams thicknesses. Local fault zone may be responsible for the occurrence of high energy tremors as well as large faults, as presented in this article. An analysis of source mechanism of high energy tremors generated during longwall mining of the coal seam No. 510, with presence of a local fault zone, in one of the Polish hard coal mines in the Upper Silesian Coal Basin was performed. For this purpose, the seismic moment tensor inversion method was used. In most of foci, the process of shear predominated. Determined nodal plane parameters were correlated with parameters of faults forming the local fault zone. High energy tremors were generated mostly by dislocations on faults of the local fault zone. Weakening of roof rocks in the neighborhood of local fault zone takes an important role too, and was responsible for share of implosion in the focal mechanism.

  15. Seismic reflection images of shallow faulting, northernmost Mississippi embayment, north of the New Madrid seismic zone

    USGS Publications Warehouse

    McBride, J.H.; Nelson, W.J.

    2001-01-01

    High-resolution seismic reflection surveys document tectonic faults that displace Pleistocene and older strata just beyond the northeast termination of the New Madrid seismic zone, at the northernmost extent of the Mississippi embayment. These faults, which are part of the Fluorspar Area fault complex in southeastern Illinois, are directly in line with the northeast-trending seismic zone. The reflection data were acquired using an elastic weight-drop source recorded to 500 msec by a 48-geophone array (24-fold) with a 10-ft (??3.0m) station interval. Recognizable reflections were recorded to about 200 msec (100-150 m). The effects of multiple reflections, numerous diffractions, low apparent velocity (i.e., steeply dipping) noise, and the relatively low-frequency content of the recorded signal provided challenges for data processing and interpreting subtle fault offsets. Data processing steps that were critical to the detection of faults included residual statics, post-stack migration, deconvolution, and noise-reduction filtering. Seismic migration was crucial for detecting and mitigating complex fault-related diffraction patterns, which produced an apparent 'folding' of reflectors on unmigrated sections. Detected individual offsets of shallow reflectors range from 5 to 10 m for the top of Paleozoic bedrock and younger strata. The migrated sections generally indicate vertical to steeply dipping normal and reverse faults, which in places outline small horsts and/or grabens. Tilting or folding of stratal reflectors associated with faulting is also locally observed. At one site, the observed faulting is superimposed over a prominent antiformal structure, which may itself be a product of the Quaternary deformation that produced the steep normal and reverse faults. Our results suggest that faulting of the Paleozoic bedrock and younger sediments of the northern Mississippi embayment is more pervasive and less localized than previously thought.

  16. Paleoseismic results of the east strand of the Lower Tagus Valley Fault Zone, Central Portugal.

    NASA Astrophysics Data System (ADS)

    Canora, Carolina; Vilanova, Susana; Besana-Ostman, Glenda; Heleno, Sandra; Fonseca, Joao; Domingues, Ana; Pinheiro, Patricia; Pinto, Luis

    2014-05-01

    The Lower Tagus Valley Fault Zone (LTVFZ) is a northeast-southwest trending tectonic structure located within the Lower Tagus Valley (LTV), in central Portugal associated with at least two historical events: the 1909 Mw 6.0-6.2 Benavente earthquake and the 1531 Mw 6.9 earthquake. Recent investigations indicate that the relatively linear valley associated with the Lower Tagus River is controlled by active faults in varying geometry and slip rates. Based on mapped traces, LTVFZ is about 80 kilometers long and transects Miocene to Holocene deposit. The east and west strands of the fault zone may have different level of activity based on the variable clarity of mapped morphological expressions. In recent studies new fault strands were identified using aerial photos and field survey on eastern side of LTV. These eastern faults have a trend that almost parallel those active traces previously mapped by Besana-Ostman et al., 2012 on the western side of the valley. Quaternary activity of this fault deforms fluvial terraces and produces morphological features related to left-lateral strike-slip movement like river offsets. In this work we present the results of the first paleoseismic analysis carried out on this strand of the fault. Trenching studies shows that surface rupture events have occurred affecting Tagus fluvial terraces. The geometry of faulting exposed in the trench provides valuable insights into the kinematics of the fault, and provides a preliminary minimum net slip rate. New relative ages of the deformation are established on preliminary trenching results, and recurrence intervals will be determined upon receipt of results of sample processing for C14 dating. 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 the future seismic hazard assessments. Further studies are proposed and underway to characterize the LTVFZ, including high-resolution LIDAR images analysis, more

  17. Paleoearthquakes and Eolian-dominated fault sedimentation along the Hubbell Spring fault zone near Albuquerque, New Mexico

    USGS Publications Warehouse

    Personius, S.F.; Mahan, S.A.

    2003-01-01

    The Hubbell Spring fault zone forms the modern eastern margin of the Rio Grande rift in the Albuquerque basin of north-central New Mexico. Knowledge of its seismic potential is important because the fault zone transects Kirtland Air Force Base/Sandia National Laboratories and underlies the southern Albuquerque metropolitan area. No earthquakes larger than ML 5.5 have been reported in the last 150 years in this region, so we excavated the first trench across this fault zone to determine its late Quaternary paleoseismic history. Our trench excavations revealed a complex, 16-m-wide fault zone overlain by four tapered blankets of mixed eolian sand and minor colluvium that we infer were deposited after four large-magnitude, surface-rupturing earthquakes. Although the first (oldest) rupture event is undated, we used luminescence (thermoluminescence and infrared-stimulated luminescence) ages to determine that the subsequent three rupture events occurred about 56 ?? 6, 29 ?? 3, and 12 ?? 1 ka. These ages yield recurrence intervals of 27 and 17 k.y. between events and an elapsed time of 12 k.y. since the latest surface-rupturing paleoearthquake. Slip rates are not well constrained, but our preferred average slip rate since rupture event 2 (post-56 ka) is 0.05 mm/yr, and interval slip rates between the last three events are 0.06 and 0.09 mm/yr, respectively. Vertical displacements of 1-2 m per event and probable rupture lengths of 34-43 km indicate probable paleoearthquake magnitudes (Ms or Mw) of 6.8-7.1. Future earthquakes of this size likely would cause strong ground motions in the Albuquerque metropolitan area.

  18. The Relationship Between Fault Zone Processes and Physical-Transport Properties: The carbonate-bearing Monte Maggio Fault (Central Italy)

    NASA Astrophysics Data System (ADS)

    Trippetta, F.; Mollo, S.; Carpenter, B. M.; Collettini, C.

    2013-12-01

    The physical properties of fault zones vary with time and space making their characterization challenging. Here we investigate the physical properties of the Monte Maggio Fault (MMF), a normal fault with 500m of displacement where the hangingwall (HW) block is made of bedded pelagic limestone (Bugarone fm) and the footwall (FW) block is a massive limestone (Calcare Massiccio fm). In the HW block, fault rock is represented by a carbonate-rich cataclasite whereas in the footwall block, fault rock evolves from a cemented cataclasite (CC) to a fault breccia (FB) with increasing distance from the principal slipping zone (PSZ). Micro and meso-scale observations show that the predominant deformation mechanisms are: fracturing for the FB, cataclasis with grain size reduction for the CC, and cataclasis, pressure solution and hydrofracturing for the HW fault rocks. After preliminary porosity measurements, we performed laboratory measurements of permeability, Vp and Vs, at effective confining pressures up to 100 MPa on samples cored along the fault zone. The FW protolith has a primary porosity of about 7 %, formed predominantly by isolated pores that result in a connected porosity of 1%. FB samples are characterized by 10% and 5% of bulk and connected porosity respectively, whereas CC and HW samples show lower bulk porosity (7-8%), and a connected porosity of 2%. At a confining pressure of 100 MPa, P-wave velocity is ~6.0 km/s for FB, CC and protolith samples, whereas it is 5.7 km/s for HW samples. Permeability of FB samples is pressure dependent, ranging from 10-17 m2 to 10-18 m2 with increasing pressure up to 100 MPa. In contrast, for CC samples, permeability is about 10-19 m2 and is pressure independent. HW samples exhibit the lowest permeability (10-20 m2) that is also pressure independent. Our dataset suggests a heterogeneous fault-zone evolution. In the footwall, made of massive limestone, initial fracturing would increase both the total (from 7% to 10%) and connected

  19. Physical and Transport Properties of the carbonate-bearing faults: experimental insights from the Monte Maggio Fault zone (Central Italy)

    NASA Astrophysics Data System (ADS)

    Trippetta, Fabio; Scuderi, Marco Maria; Collettini, Cristiano

    2015-04-01

    Physical properties of fault zones vary with time and space and in particular, fluid flow and permeability variations are strictly related to fault zone processes. Here we investigate the physical properties of carbonate samples collected along the Monte Maggio normal Fault (MMF), a regional structure (length ~10 km and displacement ~500 m) located within the active system of the Apennines. In particular we have studied an exceptionally exposed outcrop of the fault within the Calcare Massiccio formation (massive limestone) that has been recently exposed by new roadworks. Large cores (100 mm in diameter and up to 20 cm long) drilled perpendicular to the fault plane have been used to: 1) characterize the damage zone adjacent to the fault plane and 2) to obtain smaller cores, 38 mm in diameter both parallel and perpendicular to the fault plane, for rock deformation experiments. At the mesoscale two types of cataclastic damage zones can be identified in the footwall block (i) a Cemented Cataclasite (CC) and (ii), a Fault Breccia (FB). Since in some portions of the fault the hangingwall (HW) is still preserved we also collected HW samples. After preliminary porosity measurements at ambient pressure, we performed laboratory measurements of Vp, Vs, and permeability at effective confining pressures up to 100 MPa in order to simulate crustal conditions. The protolith has a primary porosity of about 7 %, formed predominantly by isolated pores since the connected porosity is only 1%. FB samples are characterized by 10% and 5% of bulk and connected porosity respectively, whilst CC samples show lower bulk porosity (7%) and a connected porosity of 2%. From ambient pressure to 100 MPa, P-wave velocity is about 5,9-6,0 km/s for the protolith, ranges from 4,9 km/s to 5,9 km/s for FB samples, whereas it is constant at 5,9 km/s for CC samples and ranges from 5,4 to 5,7 for HW sample. Vs shows the same behaviour resulting in a constant Vp/Vs ratio from 0 to 100 MPa that ranges from 1

  20. Near-surface location, geometry, and velocities of the Santa Monica Fault Zone, Los Angeles, California

    USGS Publications Warehouse

    Catchings, R.D.; Gandhok, G.; Goldman, M.R.; Okaya, D.; Rymer, M.J.; Bawden, G.W.

    2008-01-01

    High-resolution seismic-reflection and seismic-refraction imaging, combined with existing borehole, earthquake, and paleoseismic trenching data, suggest that the Santa Monica fault zone in Los Angeles consists of multiple strands from several kilometers depth to the near surface. We interpret our seismic data as showing two shallow-depth low-angle fault strands and multiple near-vertical (???85??) faults in the upper 100 m. One of the low-angle faults dips northward at about 28?? and approaches the surface at the base of a topographic scarp on the grounds of the Wadsworth VA Hospital (WVAH). The other principal low-angle fault dips northward at about 20?? and projects toward the surface about 200 m south of the topographic scarp, near the northernmost areas of the Los Angeles Basin that experienced strong shaking during the 1994 Northridge earthquake. The 20?? north-dipping low-angle fault is also apparent on a previously published seismic-reflection image by Pratt et al. (1998) and appears to extend northward to at least Wilshire Boulevard, where the fault may be about 450 m below the surface. Slip rates determined at the WVAH site could be significantly underestimated if it is assumed that slip occurs only on a single strand of the Santa Monica fault or if it is assumed that the near-surface faults dip at angles greater than 20-28??. At the WVAH, tomographic velocity modeling shows a significant decrease in velocity across near-surface strands of the Santa Monica fault. P-wave velocities range from about 500 m/sec at the surface to about 4500 m/sec within the upper 50 m on the north side of the fault zone at WVAH, but maximum measured velocities on the south side of the low-angle fault zone at WVAH are about 3500 m/sec. These refraction velocities compare favorably with velocities measured in nearby boreholes by Gibbs et al. (2000). This study illustrates the utility of com- bined seismic-reflection and seismic-refraction methods, which allow more accurate

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

    NASA Astrophysics Data System (ADS)

    Mittempergher, Silvia; Vho, Alice; Bistacchi, Andrea

    2016-04-01

    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

  2. Paleoseismicity and neotectonics of the Cordillera Blanca fault zone, Northern Peruvian Andes.

    USGS Publications Warehouse

    Schwartz, D.P.

    1988-01-01

    The Cordillera Blanca fault zone is a major W dipping normal fault that bounds the W side of a 120- 170-km wide zone of active extension along the crest of the N Peruvian Andes. The fault is approximately 210 km long and exhibits continuous geomorphic evidence of repeated late Pleistocene and Holocene displacements but has not been the source of historical or teleseismically recorded earthquakes. Trenching and mapping of fault scarps provide new information on earthquake recurrence, slip rate, timing of the most recent events and Andean neotectonics. At Quebrada Queroccocha, 55 km from valley fill lacustrine and fluvial deposits are displaced 7.5-8 m. Scarp profiles, tectonic terraces, and trench exposures indicate 5 to 7 scarp-forming earthquakes of 2-3 m per event during the past 11 000-14 000 yrs at this location.-from Author

  3. The kinematic and geodynamic significance of the Atacama fault zone, northern Chile

    NASA Astrophysics Data System (ADS)

    Scheuber, Ekkehard; Andriessen, Paul A. M.

    The Atacama fault zone (AFZ) is the dominant feature in the structure of the North Chilean Coastal Cordillera. Left lateral displacement took place along its system of longitudinal faults during the Jurassic and early Cretaceous. This development was contemporaneous with arc magmatism and was later reactivated, resulting in a steep normal fault. Strike-slip movements along the AFZ consist of two sets of ductile shear zones of different ages: one Jurassic, formed under amphibolite-facies conditions; the other early Cretaceous, with greenschist-facies mylonites. Structural asymmetries point to a sinistral sense of shear in both sets. The AFZ can be interpreted as a magmatic arc structure which accommodated the oblique subduction of an oceanic plate (trench-linked strike-slip fault). The sinistral sense of shear is consistent with reconstructions of late Jurassic to early Cretaceous plate configurations in the SE Pacific.

  4. Structural and fluid-chemical properties of fault zones

    SciTech Connect

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

    1992-01-01

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

  5. The Damage and Geochemical Signature of a Crustal Scale Strike-Slip Fault Zone

    NASA Astrophysics Data System (ADS)

    Gomila, R.; Mitchell, T. M.; Arancibia, G.; Jensen Siles, E.; Rempe, M.; Cembrano, J. M.; Faulkner, D. R.

    2013-12-01

    Fluid-flow migration in the upper crust is strongly controlled by fracture network permeability and connectivity within fault zones, which can lead to fluid-rock chemical interaction represented as mineral precipitation in mesh veins and/or mineralogical changes (alteration) of the host rock. While the dimensions of fault damage zones defined by fracture intensity is beginning to be better understood, how such dimensions compare to the size of alteration zones is less well known. Here, we show quantitative structural and chemical analyses as a function of distance from a crustal-scale strike-slip fault in the Atacama Fault System, Northern Chile, to compare fault damage zone characteristics with its geochemical signature. The Jorgillo Fault (JF) is a ca. 18 km long NNW striking strike-slip fault cutting Mesozoic rocks with sinistral displacement of ca. 4 km. In the study area, the JF cuts through orthogranulitic and gabbroic rocks at the west (JFW) and the east side (JFE), respectively. A 200 m fault perpendicular transect was mapped and sampled for structural and XRF analyses of the core, damage zone and protolith. The core zone consists of a ca. 1 m wide cataclasite zone bounded by two fault gouge zones ca. 40 cm. The damage zone width defined by fracture density is ca. 50 m wide each side of the core. The damage zone in JFW is characterized by NW-striking subvertical 2 cm wide cataclastic rocks and NE-striking milimetric open fractures. In JFE, 1-20 mm wide chlorite, quartz-epidote and quartz-calcite veins, cut the gabbro. Microfracture analysis in JFW reveal mm-wide cataclasitic/ultracataclasitic bands with clasts of protolith and chlorite orientated subparallel to the JF in the matrix, calcite veins in a T-fractures orientation, and minor polidirectional chlorite veins. In JFE, chlorite filled conjugate fractures with syntaxial growth textures and evidence for dilational fracturing processes are seen. Closest to the core, calcite veins crosscut chlorite veins

  6. Maximum earthquake magnitudes along different sections of the North Anatolian fault zone

    NASA Astrophysics Data System (ADS)

    Bohnhoff, Marco; Martínez-Garzón, Patricia; Bulut, Fatih; Stierle, Eva; Ben-Zion, Yehuda

    2016-04-01

    Constraining the maximum likely magnitude of future earthquakes on continental transform faults has fundamental consequences for the expected seismic hazard. Since the recurrence time for those earthquakes is typically longer than a century, such estimates rely primarily on well-documented historical earthquake catalogs, when available. Here we discuss the maximum observed earthquake magnitudes along different sections of the North Anatolian Fault Zone (NAFZ) in relation to the age of the fault activity, cumulative offset, slip rate and maximum length of coherent fault segments. The findings are based on a newly compiled catalog of historical earthquakes in the region, using the extensive literary sources that exist owing to the long civilization record. We find that the largest M7.8-8.0 earthquakes are exclusively observed along the older eastern part of the NAFZ that also has longer coherent fault segments. In contrast, the maximum observed events on the younger western part where the fault branches into two or more strands are smaller. No first-order relations between maximum magnitudes and fault offset or slip rates are found. The results suggest that the maximum expected earthquake magnitude in the densely populated Marmara-Istanbul region would probably not exceed M7.5. The findings are consistent with available knowledge for the San Andreas Fault and Dead Sea Transform, and can help in estimating hazard potential associated with different sections of large transform faults.

  7. Mechanical and lithological controls on the development of heterogeneous fault zones: an example from the southern Dead Sea Fault System, Israel

    NASA Astrophysics Data System (ADS)

    Evans, Siân; Holdsworth, Bob; Imber, Jonny; de Paola, Nicola; Marco, Shmuel; Weinberger, Rami

    2014-05-01

    The mechanical weakening processes involved in the development of major crustal fault systems have been widely documented, and it is recognised that clay-bearing fault rocks frequently have a significant influence on fault strength and slip behaviour in the upper crust. It is less well-understood how mechanical processes, such as cataclasis and the mechanical entrainment of fault rock materials along fault zones (e.g. "smearing"), interact with chemical processes, such as clay mineral transformations and phyllonitisation during fault rock development. These processes can combine to form fault zones that may be both lithologically and mechanically heterogeneous, and which may also evolve over time, changing the nature of observed heterogeneities. We present here data from exhumed sections of the southern Dead Sea Fault System, Israel, an active continental transform fault that has accumulated 105 km of sinistral displacement since the mid-Miocene. These faults are estimated to have been active at shallow depths (<5 km, but potentially significantly less. The so-called "fault cores" of these sections are highly heterogeneous and are comprised of material formed by a variety of processes: fault gouges formed by cataclasis; coarser-grained, variably crushed crystalline basement rocks; mechanically entrained highly mobile units, derived from shale in adjacent cover sequence wall rocks; and growth of authegenic mineral phases through alteration and pressure solution. Through operation of grain-size reduction and diffusive mass transfer processes, we see a bulk change from fault rocks dominated by relatively strong phases displaying no obvious fabric, such as feldspars and calcite, through to foliated phyllosilicate-rich (illite, chlorite, smectite) fault rocks which likely have much lower frictional strengths. Mechanically entrained shale that has not undergone significant brittle deformation can also efficiently introduce large volumes of relatively weak material into

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

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

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

  9. Talc friction in the temperature range 25°–400 °C: relevance for fault-zone weakening

    USGS Publications Warehouse

    Moore, Diane E.; Lockner, David A.

    2008-01-01

    Talc has a temperature–pressure range of stability that extends from surficial to eclogite-facies conditions, making it of potential significance in a variety of faulting environments. Talc has been identified in exhumed subduction zone thrusts, in fault gouge collected from oceanic transform and detachment faults associated with rift systems, and recently in serpentinite from the central creeping section of the San Andreas fault. Typically, talc crystallized in the active fault zones as a result of the reaction of ultramafic rocks with silica-saturated hydrothermal fluids. This mode of formation of talc is a prime example of a fault-zone weakening process. Because of its velocity-strengthening behavior, talc may play a role in stabilizing slip at depth in subduction zones and in the creeping faults of central and northern California that are associated with ophiolitic rocks.

  10. Transfer zones and fault reactivation in inverted rift basins: Insights from physical modelling

    NASA Astrophysics Data System (ADS)

    Konstantinovskaya, Elena A.; Harris, Lyal B.; Poulin, Jimmy; Ivanov, Gennady M.

    2007-08-01

    Lateral transfer zones of deformation and fault reactivation were investigated in multilayered silicone-sand models during extension and subsequent co-axial shortening. Model materials were selected to meet similarity criteria and to be distinguished on CT scans; this approach permitted non-destructive visualisation of the progressive evolution of structures. Transfer zones were initiated by an orthogonal offset in the geometry of a basal mobile aluminium sheet and/or by variations of layer thickness or material rheology in basal layers. Transfer zones affected rift propagation and fault kinematics in models. Propagation and overlapping rift culminations occurred in transfer zones during extension. During shortening, deviation in the orientation of frontal thrusts and fold axes occurred within transfer zones in brittle and ductile layers, respectively. CT scans showed that steep (58-67°) rift-margin normal faults were reactivated as reverse faults. The reactivated faults rotated to shallower dips (19-38°) with continuing shortening after 100% inversion. Rotation of rift phase faults appears to be due to deep level folding and uplift during the inversion phase. New thrust faults with shallow dips (20-34°) formed outside the inverted graben at late stages of shortening. Frontal ramps propagated laterally past the transfer structure during shortening. During inversion, the layers filling the rift structures underwent lateral compression at the depth, the graben fill was pushed up and outwards creating local extension near the surface. Sand marker layers in inverted graben have showed fold-like structures or rotation and tilting in the rifts and on the rift margins. The results of our experiments conform well to natural examples of inverted graben. Inverted rift basins are structurally complex and often difficult to interpret in seismic data. The models may help to unravel the structure and evolution of these systems, leading to improved hydrocarbon exploration

  11. Map of the Rinconada and Reliz Fault Zones, Salinas River Valley, California

    USGS Publications Warehouse

    Rosenberg, Lewis I.; Clark, Joseph C.

    2009-01-01

    The Rinconada Fault and its related faults constitute a major structural element of the Salinas River valley, which is known regionally, and referred to herein, as the 'Salinas Valley'. The Rinconada Fault extends 230 km from King City in the north to the Big Pine Fault in the south. At the south end of the map area near Santa Margarita, the Rinconada Fault separates granitic and metamorphic crystalline rocks of the Salinian Block to the northeast from the subduction-zone assemblage of the Franciscan Complex to the southwest. Northwestward, the Rinconada Fault lies entirely within the Salinian Block and generally divides this region into two physiographically and structurally distinct areas, the Santa Lucia Range to the west and the Salinas Valley to the east. The Reliz Fault, which continues as a right stepover from the Rinconada Fault, trends northwestward along the northeastern base of the Sierra de Salinas of the Santa Lucia Range and beyond for 60 km to the vicinity of Spreckels, where it is largely concealed. Aeromagnetic data suggest that the Reliz Fault continues northwestward another 25 km into Monterey Bay, where it aligns with a high-definition magnetic boundary. Geomorphic evidence of late Quaternary movement along the Rinconada and Reliz Fault Zones has been documented by Tinsley (1975), Dibblee (1976, 1979), Hart (1976, 1985), and Klaus (1999). Although definitive geologic evidence of Holocene surface rupture has not been found on these faults, they were regarded as an earthquake source for the California Geological Survey [formerly, California Division of Mines and Geology]/U.S. Geological Survey (CGS/USGS) Probabilistic Seismic Hazards Assessment because of their postulated slip rate of 1+-1 mm/yr and their calculated maximum magnitude of 7.3. Except for published reports by Durham (1965, 1974), Dibblee (1976), and Hart (1976), most information on these faults is unpublished or is contained in theses, field trip guides, and other types of reports

  12. Kinematic vicissitudes and the spatial distribution of the alteration zone related to the Byobuyama fault, central Japan. (Implication; Influence of another faults.)

    NASA Astrophysics Data System (ADS)

    Katori, T.; Kobayashi, K.

    2015-12-01

    The central Japan is one of the most concentrated area of active faults (Quaternary fault). These are roughly classified into two orthogonally-oriented fault sets of NE-SW and NW-SE strikes. The study area is located in Gifu prefecture, central Japan. In there, the basement rocks are composed mainly of Triassic-Jurassic accretionary prism (Mino belt), Cretaceous Nohi Rhyolite and Cretaceous granitic rocks. Miocene Mizunami G. and Pliocene-Pleistocene Toki Sand and Gravel F. unconformably cover the basement rocks. The Byobuyama fault, 32 km in length, is NE-SW strike and displaces perpendicularly the Toki Sand and Gravel F. by 500 m. The northeastern terminal of the fault has contact with the southern terminal of the Atera fault of NW-SE strike and offset their displacements each other. It is clear that the activity of the Byobuyama fault plays a role of the development of the complicated fault geometry system in the central Japan. In this study, we performed a broad-based investigation along the Byobuyama fault and collected samples. Actually, we observed 400 faults and analyzed 200 fault rocks. Based on these results, we obtained the following new opinion. 1. The Byobuyama fault has experienced following activities that can be divided to 3 stages at least under different stress field. 1) Movement with the sinisterly sense (preserved in cataclasite zone). 2) Dextral movement (preserved in fault gouge zone). 3) Reverse fault movement (due to the aggressive rise of mountains). In addition, the change from Stage 2 to Stage 3 is a continuous. 2. There is a relationship between the distance from the trace of the Byobuyama fault and the combination of alteration minerals included in the fault rocks. 3. In the central part of the Byobuyama fault (CPBF), fault plane trend and combination of alteration minerals shows specific features. The continuous change is considered to mean the presence of factors that interfere with the dextral movement of the Byobuyama fault. What is

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  14. Dynamic fracturing by successive coseismic loadings leads to pulverization in active fault zones

    NASA Astrophysics Data System (ADS)

    Aben, F. M.; Doan, M.-L.; Mitchell, T. M.; Toussaint, R.; Reuschlé, T.; Fondriest, M.; Gratier, J.-P.; Renard, F.

    2016-04-01

    Previous studies show that pulverized rocks observed along large faults can be created by single high-strain rate loadings in the laboratory, provided that the strain rate is higher than a certain pulverization threshold. Such loadings are analogous to large seismic events. In reality, pulverized rocks have been subject to numerous seismic events rather than one single event. Therefore, the effect of successive "milder" high-strain rate loadings on the pulverization threshold is investigated by applying loading conditions below the initial pulverization threshold. Single and successive loading experiments were performed on quartz-monzonite using a Split Hopkinson Pressure Bar apparatus. Damage-dependent petrophysical properties and elastic moduli were monitored by applying incremental strains. Furthermore, it is shown that the pulverization threshold can be reduced by successive "milder" dynamic loadings from strain rates of ~180 s-1 to ~90 s-1. To do so, it is imperative that the rock experiences dynamic fracturing during the successive loadings prior to pulverization. Combined with loading conditions during an earthquake rupture event, the following generalized fault damage zone structure perpendicular to the fault will develop: furthest from the fault plane, there is a stationary outer boundary that bounds a zone of dynamically fractured rocks. Closer to the fault, a pulverization boundary delimits a band of pulverized rock. Consecutive seismic events will cause progressive broadening of the band of pulverized rocks, eventually creating a wider damage zone observed in mature faults.

  15. Remote sensing analysis for fault-zones detection in the Central Andean Plateau (Catamarca, Argentina)

    NASA Astrophysics Data System (ADS)

    Traforti, Anna; Massironi, Matteo; Zampieri, Dario; Carli, Cristian

    2015-04-01

    Remote sensing techniques have been extensively used to detect the structural framework of investigated areas, which includes lineaments, fault zones and fracture patterns. The identification of these features is fundamental in exploration geology, as it allows the definition of suitable sites for the exploitation of different resources (e.g. ore mineral, hydrocarbon, geothermal energy and groundwater). Remote sensing techniques, typically adopted in fault identification, have been applied to assess the geological and structural framework of the Laguna Blanca area (26°35'S-66°49'W). This area represents a sector of the south-central Andes localized in the Argentina region of Catamarca, along the south-eastern margin of the Puna plateau. The study area is characterized by a Precambrian low-grade metamorphic basement intruded by Ordovician granitoids. These rocks are unconformably covered by a volcano-sedimentary sequence of Miocene age, followed by volcanic and volcaniclastic rocks of Upper Miocene to Plio-Pleistocene age. All these units are cut by two systems of major faults, locally characterized by 15-20 m wide damage zones. The detection of main tectonic lineaments in the study area was firstly carried out by classical procedures: image sharpening of Landsat 7 ETM+ images, directional filters applied to ASTER images, medium resolution Digital Elevation Models analysis (SRTM and ASTER GDEM) and hill shades interpretation. In addition, a new approach in fault zone identification, based on multispectral satellite images classification, has been tested in the Laguna Blanca area and in other sectors of south-central Andes. In this perspective, several prominent fault zones affecting basement and granitoid rocks have been sampled. The collected fault gouge samples have been analyzed with a Field-Pro spectrophotometer mounted on a goniometer. We acquired bidirectional reflectance spectra, from 0.35μm to 2.5μm with 1nm spectral sampling, of the sampled fault rocks

  16. [Characteristics of Raman spectra of minerals in the veins of Wenchuan earthquake fault zone].

    PubMed

    Xie, Chao; Zhou, Ben-gang; Liu, Lei; Zhou, Xiao-cheng; Yi, Li; Chen, Zhi; Cui, Yue-ju; Li, Jing; Chen, Zheng-wei; Du, Jian-guo

    2015-01-01

    Quartz in the veins at the Shenxigou section of Wenchuan earthquake fault zone was investigated by micro-Raman spectroscopic measurement, and the distribution of compressive stress in the fault zone was estimated by the frequency shifts of the 464 cm-1 vibrational mode of quartz grains in the veins. It was showed that the 464 cm-1 peak arising from the quartz grains in the veins near the fault plane shifts by 3. 29 cm-1 , and the corresponding compressive stress is 368. 63 MPa, which is significantly lower than the stress accumulation on both sides due to multi-stage events. Stress accumulation increased with moving away from the fault plane in the footwall with the offset of the 464 cm-1 peak arising from the quartz grains in the veins increasing, which can reach 494. 77 MPa at a distance of 21 m with a high offset of 4. 40 cm-1 of the 464 cm-1 peak. The compressive stress gets the maximum value of 519.87 MPa at a distance of 10 m from the fault plane in the hanging wall with the offset of the 464 cm-1 peak arising from the quartz grains in the veins being 4. 62 cm-1, followed by a sudden drop in stress accumulation, and it drops to 359. 59 MPa at a distance of 17 m. Because of moving away from the foult plane at the edge of the foult zone, the stress drops to 359. 59 MPa with a small value of 464 cm-1 peak offset 3. 21 cm-1 at a distance of 27 m from the fault plane in the hanging wall due to the little effect by the fault activity. Therefore, the stress of Wenchuan earthquake fault zone is partially released, but the rest of the stress distribution is uneven, and there is also a high stress accumulation in somewhere in the fault zone, which reflects that the mechanical properties of the rocks in the fault zone have a characteristic of unevenness in space.

  17. [Characteristics of Raman spectra of minerals in the veins of Wenchuan earthquake fault zone].

    PubMed

    Xie, Chao; Zhou, Ben-gang; Liu, Lei; Zhou, Xiao-cheng; Yi, Li; Chen, Zhi; Cui, Yue-ju; Li, Jing; Chen, Zheng-wei; Du, Jian-guo

    2015-01-01

    Quartz in the veins at the Shenxigou section of Wenchuan earthquake fault zone was investigated by micro-Raman spectroscopic measurement, and the distribution of compressive stress in the fault zone was estimated by the frequency shifts of the 464 cm-1 vibrational mode of quartz grains in the veins. It was showed that the 464 cm-1 peak arising from the quartz grains in the veins near the fault plane shifts by 3. 29 cm-1 , and the corresponding compressive stress is 368. 63 MPa, which is significantly lower than the stress accumulation on both sides due to multi-stage events. Stress accumulation increased with moving away from the fault plane in the footwall with the offset of the 464 cm-1 peak arising from the quartz grains in the veins increasing, which can reach 494. 77 MPa at a distance of 21 m with a high offset of 4. 40 cm-1 of the 464 cm-1 peak. The compressive stress gets the maximum value of 519.87 MPa at a distance of 10 m from the fault plane in the hanging wall with the offset of the 464 cm-1 peak arising from the quartz grains in the veins being 4. 62 cm-1, followed by a sudden drop in stress accumulation, and it drops to 359. 59 MPa at a distance of 17 m. Because of moving away from the foult plane at the edge of the foult zone, the stress drops to 359. 59 MPa with a small value of 464 cm-1 peak offset 3. 21 cm-1 at a distance of 27 m from the fault plane in the hanging wall due to the little effect by the fault activity. Therefore, the stress of Wenchuan earthquake fault zone is partially released, but the rest of the stress distribution is uneven, and there is also a high stress accumulation in somewhere in the fault zone, which reflects that the mechanical properties of the rocks in the fault zone have a characteristic of unevenness in space. PMID:25993832

  18. Deep view of the Subduction-Transform Edge Propagator (STEP) fault in the Calabrian Subduction Zone

    NASA Astrophysics Data System (ADS)

    Maesano, Francesco Emanuele; Tiberti, Mara Monica; Basili, Roberto

    2016-04-01

    The Calabrian Subduction Zone plays a key role in the evolution of the central Mediterranean in the framework of the convergence between Africa and Europe. Here, the remnants of the World's oldest oceanic crust form a narrow NW-dipping slab passively subducting beneath the Calabrian Arc. Recently published high-resolution seismic profiles and bathymetric data of the western Ionian Sea highlight the presence of a NNW-SSE faulting system connected with a series of Plio-Pleistocene syn-tectonic basins. These features are correlated with the recent activity of a major NNW-SSE deformation zone confining the active subduction to the SW and interpreted as a Subduction-Transform Edge Propagator (STEP) fault. The goal of this work is to jointly reconstruct the geometry of the STEP fault and the subduction interface in its surroundings. We use multichannel seismic profiles acquired in the southwestern part of the Calabrian accretionary wedge to focus on the STEP fault geometry at depth and to analyse its relationships with shallow deformation features. The quantitative analysis and enhancement of seismic data provided an accurate image of the internal structure of the accretionary wedge at various depths, showing growth strata in the Plio-Pleistocene succession and major discontinuities in the lower crust. Our results depict a main subvertical, slightly east-dipping, lithospheric fault cutting the oceanic crust down to the Moho, and a rich set of associated secondary synthetic and antithetic faults. This picture also provides new insights on the STEP fault propagation mechanism. In addition, the tridimensional correlation of the STEP fault occurrences in various seismic profiles provides a preliminary scheme of its segmentation and highlights the relationships of this master fault with other main structural elements of the Calabrian Arc and Eastern Sicily, including some of the faults deemed to be responsible for major historical earthquakes in the area.

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

    NASA Astrophysics Data System (ADS)

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

    2007-06-01

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

  20. Towards quantifying the matrix permeability of fault damage zones in low porosity rocks

    NASA Astrophysics Data System (ADS)

    Mitchell, T. M.; Faulkner, D. R.

    2012-07-01

    In nature, permeability is enhanced in the damage zone of faults in crystalline rocks, where fracturing occurs on a wide range of scales. Understanding this permeability structure is paramount for predicting crustal fluid flow. We combine quantitative field and laboratory measurements to predict microfracture damage zone permeability in low-porosity granitic rocks as a function of distance from the fault core and displacement. Microfracture controlled matrix permeability exerts an increasingly dominant role on fluid flow with increasing depth. In the field we analysed the scaling relationships of microfracture densities surrounding strike-slip faults developed in granodiorite within the Atacama fault system in northern Chile. Displacements ranging over 5 orders of magnitude (˜0.012-5000 m), allow the variation of microfracture damage with increasing distance from faults to be determined empirically as a function of displacement. We reproduce microfracture damage in the laboratory in a suite of triaxial deformation experiments by inducing cyclic damage in initially intact samples while continuously measuring permeability. Combining field and laboratory datasets through the microfracture density allows the permeability profile with distance from the fault to be predicted from fault displacement.

  1. A 3-D view of field-scale fault-zone cementation from geologically ground-truthed electrical resistivity

    NASA Astrophysics Data System (ADS)

    Barnes, H.; Spinelli, G. A.; Mozley, P.

    2015-12-01

    Fault-zones are an important control on fluid flow, affecting groundwater supply, hydrocarbon/contaminant migration, and waste/carbon storage. However, current models of fault seal are inadequate, primarily focusing on juxtaposition and entrainment effects, despite the recognition that fault-zone cementation is common and can dramatically reduce permeability. We map the 3D cementation patterns of the variably cemented Loma Blanca fault from the land surface to ~40 m depth, using electrical resistivity and induced polarization (IP). The carbonate-cemented fault zone is a region of anomalously low normalized chargeability, relative to the surrounding host material. Zones of low-normalized chargeability immediately under the exposed cement provide the first ground-truth that a cemented fault yields an observable IP anomaly. Low-normalized chargeability extends down from the surface exposure, surrounded by zones of high-normalized chargeability, at an orientation consistent with normal faults in the region; this likely indicates cementation of the fault zone at depth, which could be confirmed by drilling and coring. Our observations are consistent with: 1) the expectation that carbonate cement in a sandstone should lower normalized chargeability by reducing pore-surface area and bridging gaps in the pore space, and 2) laboratory experiments confirming that calcite precipitation within a column of glass beads decreases polarization magnitude. The ability to characterize spatial variations in the degree of fault-zone cementation with resistivity and IP has exciting implications for improving predictive models of the hydrogeologic impacts of cementation within faults.

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

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

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

  3. Interseismic deformation and moment deficit along the Manila subduction zone and the Philippine Fault system

    NASA Astrophysics Data System (ADS)

    Hsu, Y. J.; Yu, S. B.; Loveless, J. P.; Bacolcol, T.; Woessner, J.; Solidum, R., Jr.

    2015-12-01

    The Sunda plate converges obliquely with the Philippine Sea plate with a rate of ~100 mm/yr and results in the sinistral slip along the 1300 km-long Philippine fault. Using GPS data from 1998 to 2013 as well as a block modeling approach, we decompose the crustal motion into multiple rotating blocks and elastic deformation associated with fault slip at block boundaries. Our preferred model composed of 8 blocks, produces a mean residual velocity of 3.4 mm/yr at 93 GPS stations. Estimated long-term slip rates along the Manila subduction zone show a gradual southward decrease from 66 mm/yr at the northwest tip of Luzon to 60 mm/yr at the southern portion of the Manila Trench. We infer a low coupling fraction of 11% offshore northwest Luzon and a coupling fraction of 27% near the subduction of Scarborough Seamount. The accumulated strain along the Manila subduction zone at latitudes 15.5°~18.5°N could be balanced by earthquakes with composite magnitudes of Mw 8.7 and Mw 8.9 based on a recurrence interval of 500 years and 1000 years, respectively. Estimates of sinistral slip rates on the major splay faults of the Philippine fault system in central Luzon increase from east to west: sinistral slip rates are 2 mm/yr on the Dalton fault, 8 mm/yr on the Abra River fault, and 12 mm/yr on the Tubao fault. On the southern segment of the Philippine fault (Digdig fault), we infer left-lateral slip of ~20 mm/yr. The Vigan-Aggao fault in northwest Luzon exhibits significant reverse slip of up to 31 mm/yr, although deformation may be distributed across multiple offshore thrust faults. On the Northern Cordillera fault, we calculate left-lateral slip of ~7 mm/yr. Results of block modeling suggest that the majority of active faults in Luzon are fully locked to a depth of 15-20 km. Inferred moment magnitudes of inland large earthquakes in Luzon fall in the range of Mw 7.0-7.5 based on a recurrence interval of 100 years. Using the long-term plate convergence rate between the Sunda plate

  4. Microstructural evidence for northeastward movement on the Chocolate Mountains fault zone, southeastern California

    SciTech Connect

    Simpson, C. )

    1990-01-10

    Microstructural analysis of rocks from the Chocolate Mountains fault zone, Gavilan Hills area, southeastern California, show unequivocal evidence for northeast directed transport of the upper plate gneisses over lower plate Orocopia schists. Samples were taken from transects through the fault zone. Prefaulting fabrics in upper plate gneisses show a strong component of northeast directed rotational deformation under lower amphibolite facies conditions. In contrast, prefaulting lower plate Orocopia schists show strongly coaxial fabrics (minimum stretch value of 2.2) formed at greenschist grade. Mylonitic fabrics associated with the Chocolate Mountains fault are predominantly northeast directed shear bands that are unidirectional (northeastward) in the gneisses but bi-directional in the schists, suggesting a significant component of nonrotational deformation occurred in the Orocopia schists during and after emplacement of the upper plate. The kinematic findings are in agreement with Dillon et al. (1989), who found that the vergence of asymmetrical folds within the fault zone indicates overthrusting to the northeast, toward the craton, in this region. The available evidence favors a single protracted northeastward movement on the Chocolate Mountains fault zone with temperatures waning as deformation proceeded.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  7. Loading Rate-Dependent Elastoviscoplasticity in San Andreas Fault Observatory at Depth (SAFOD) Fault Gouge: Implications for Repeating Earthquakes and Fault Zone-Guided Waves

    NASA Astrophysics Data System (ADS)

    Kohli, A. H.; Lockner, D. A.

    2015-12-01

    Deformation experiments on phyllosilicate-rich fault gouges reveal velocity-strengthening behavior and monotonic strength evolution in response to perturbations in slip velocity below ~10-4 ms-1. Fault gouge from the actively creeping zones at the San Andreas Fault Observatory at Depth (SAFOD) exhibits similar monotonic strength evolution and has been described in terms of rate-state friction-velocity dependence and ageing behavior. While these parameters provide phenomenological descriptions of gouge rheology on relatively short timescales, they are commonly applied in numerical simulations of repeating earthquakes within the SAF creeping section, often being adjusted arbitrarily in order to match seismological observations. With first assuming a deformation constitutive law, we performed comprehensive microstructural and mechanical characterization of