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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. Horizontal polarization of ground motion in the Hayward fault zone at Fremont, California: dominant fault-high-angle polarization and fault-induced cracks

    NASA Astrophysics Data System (ADS)

    Pischiutta, M.; Salvini, F.; Fletcher, J.; Rovelli, A.; Ben-Zion, Y.

    2012-03-01

    We investigate shear wave polarization in the Hayward fault zone near Niles Canyon, Fremont, CA. Waveforms of 12 earthquakes recorded by a seven-accelerometer seismic array around the fault are analysed to clarify directional site effects in the fault damage zone. The analysis is performed in the frequency domain through H/V spectral ratios with horizontal components rotated from 0° to 180°, and in the time domain using the eigenvectors and eigenvalues of the covariance matrix method employing three component records. The near-fault ground motion tends to be polarized in the horizontal plane. At two on-fault stations where the local strike is N160°, ground motion polarization is oriented N88 ± 19° and N83 ± 32°, respectively. At a third on-fault station, the motion is more complex with horizontal polarization varying in different frequency bands. However, a polarization of N86 ± 7°, similar to the results at the other two on-fault stations, is found in the frequency band 6-8 Hz. The predominantly high-angle polarization from the fault strike at the Hayward Fault is consistent with similar results at the Parkfield section of the San Andreas Fault and the Val d'Agri area (a Quaternary extensional basin) in Italy. In all these cases, comparisons of the observed polarization directions with models of fracture orientation based on the fault movement indicate that the dominant horizontal polarization is near-orthogonal to the orientation of the expected predominant cracking direction. The results help to develop improved connections between fault mechanics and near-fault ground motion.

  5. 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.

  6. 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.

  7. Hayward fault: Large earthquakes versus surface creep

    USGS Publications Warehouse

    Lienkaemper, James J.; Borchardt, Glenn

    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

  8. Inferred depth of creep on the Hayward Fault, central California

    USGS Publications Warehouse

    Savage, J.C.; Lisowski, M.

    1993-01-01

    A relation between creep rate at the surface trace of a fault, the depth to the bottom of the creeping zone, and the rate of stress accumulation on the fault is derived from Weertman's 1964 friction model of slip on a fault. A 5??1 km depth for the creeping zone on the Hayward fault is estimated from the measured creep rate (5mm/yr) at the fault trace and the rate of stress increase on the upper segment of the fault trace inferred from geodetic measurements across the San Francisco Bay area. Although fault creep partially accommodates the secular slip rate on the Hayward fault, a slip deficit is accumulating equivalent to a magnitude 6.6 earthquake on each 40 km segment of the fault each century. Thus, the current behavior of the fault is consistent with its seismic history, which includes two moderate earthquakes in the mid-1800s. -Authors

  9. 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

  10. Gravity and Magnetic Expression of the San Leandro Gabbro with Implications for the Geometry and Evolution of the Hayward Fault Zone, Northern California

    NASA Astrophysics Data System (ADS)

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

    2002-12-01

    The Hayward Fault, one of the most hazardous faults in northern California, trends NNW and extends for about 90 km along the eastern margin of the 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 75-80o 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, that extends to a depth of about 12 km, 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 by Late Cretaceous to early Tertiary, a low-angle roof thrust related to the tectonic wedging of the Franciscan Complex. After repeated episodes of extension and attenuation, the strike-slip Hayward Fault probably reactivated or preferentially followed this pre-existing feature in the late Tertiary. Because earthquakes concentrate near the edge of the San Leandro gabbro but tend to avoid its interior, 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 Hayward Fault will provide additional constraints on seismic

  11. Three-dimensional Geology of the Hayward Fault and its Correlation with Fault Behavior, Northern California

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

    Relationships between fault behavior and geology along the Hayward Fault were investigated using a three-dimensional geologic model of the Hayward fault and vicinity. The three-dimensional model, derived from geologic, geophysical, and seismicity data, allowed the construction of a `geologic map' of east- and west-side surfaces, maps that show the distribution of geologic units on either side of the fault that truncate against the fault surface. These two resulting geologic maps were compared with seismicity and creep along the Hayward Fault using three-dimensional visualization software. The seismic behavior of the Hayward Fault correlates with rock unit contacts along the fault, rather than in rock types across the fault. This suggests that fault activity is, in part, controlled by the physical properties of the rocks that abut the fault and not by properties of the fault zone itself. For example, far fewer earthquakes occur along the northern part of the fault where an intensely sheared Franciscan mélange on the west side abuts the fault face, compared to the region to the south where more coherent rocks of other Franciscan terranes or the Coast Range Ophiolite are present. More locally, clusters of earthquakes correlate spatially with some of the contacts between Franciscan terranes as well as mafic rocks of the Coast Range Ophiolite. Steady creep rates along the fault correlate with the lateral extent of the San Leandro gabbro, and changes in creep rate correlate with changes in geology. Although preliminary, the results of comparing fault behavior with the inferred three-dimensional geology adjacent to the Hayward Fault suggest that any attempt to understand the detailed distribution of earthquakes or creep along the fault should include consideration of the rock types that abut the fault surface. Such consideration would benefit greatly from incorporating into the three-dimensional geologic model the physical properties of the rock types along the fault.

  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

    NASA Astrophysics Data System (ADS)

    Waldhauser, Felix; Ellsworth, William L.

    2002-03-01

    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 suggests 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

  14. 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

  15. 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.

  16. New evidence doubles the seismic potential of the Hayward Fault

    USGS Publications Warehouse

    Lienkaemper, J.J.; Galehouse, J.S.

    1998-01-01

    The Hayward Fault produced its last major (M7) earthquake in 1868 (Figure 1). It is widely considered to be the most hazardous fault in the San Francisco Bay region. In large part, this is because it lies so close to a densely populated urban corridor that has an abundance of old structures highly vulnerable to seismic hazard. The probability of a major earthquake on this fault was estimated to be 45% in thirty years (Working Group on California Earthquake Probabilities, 1990). In 1991, Lienkaemper et al. (hereinafter referred to as L91) estimated the potential for seismic slip along the entire length and depth of the fault zone. Recent studies have provided new information relevant to the seismic potential of the fault, which results in markedly larger estimates of its present potential for producing major earthquakes. Here we define the seismic potential as the total seismic moment on all parts of the fault accumulated since the time of the last major earthquake that has not been released by fault creep. Principal reasons for the change in potential are (1) a deeper locking zone and better characterization of the creeping zone, and (2) better information on the extent of the 'southern' 1868 earthquake and the timing of the most recent 'northern' earthquake.

  17. Seismic Velocity Structure and Seismotectonics of the Hayward Fault System, East San Francisco Bay, California

    NASA Astrophysics Data System (ADS)

    Hardebeck, J. L.; Michael, A. J.; Brocher, T. M.

    2004-12-01

    The Hayward Fault is considered the most likely fault in the San Francisco Bay Area, California, to have a major earthquake in the next 30 years, posing a serious earthquake risk to more than 2 million people. In order to accurately evaluate various earthquake scenarios for this fault, it is important to understand its structure, kinematics, and physical properties. We present a new seismological study of the Hayward Fault system, including a new 3D seismic velocity model for the East San Francisco Bay, relocated earthquake hypocenters, and improved focal mechanisms. We use these new constraints on structure and seismicity to study the geometry and kinematics of the Hayward Fault. The new East Bay 3D tomography model, based on travel times from earthquakes and controlled-source experiments, reveals a clear velocity contrast across the Hayward Fault. In the upper 10 km, the P-wave velocity in the Franciscan rocks to the west are up to 0.8 km/s faster than in the Great Valley sequence rocks to the east. Below 10 km, where Franciscan rocks are thought to be present on both sides of the fault, there is negligible contrast. The observed P-wave velocities are comparable with velocities observed in deep boreholes in the East Bay. Anomalously low S-wave velocities are observed east of the Hayward Fault, near the Livermore Basin. We relocated more than 20,000 East Bay earthquakes, 1967-2004, with the 3D model. The events illuminate the Hayward Fault at depth, shifting from near-vertical in the north to steeply east-dipping in the south. New focal mechanisms were also computed, using take-off angles from ray tracing in the 3D seismic velocity model. Previous authors found heterogeneous focal mechanisms along the Hayward Fault near San Leandro, interpreted it as a zone of complex fracturing, and speculated that San Leandro marks a probable boundary for major Hayward Fault earthquakes. We find, however, that our high-quality focal mechanisms for events all along the Hayward

  18. Slip-parallel seismic lineations on the Northern Hayward Fault, California

    USGS Publications Warehouse

    Waldhauser, F.; Ellsworth, W.L.; Cole, A.

    1999-01-01

    A high-resolution relative earthquake location procedure is used to image the fine-scale seismicity structure of the northern Hayward fault, California. The seismicity defines a narrow, near-vertical fault zone containing horizontal alignments of hypocenters extending along the fault zone. The lineations persist over the 15-year observation interval, implying the localization of conditions on the fault where brittle failure conditions are met. The horizontal orientation of the lineations parallels the slip direction of the fault, suggesting that they are the result of the smearing of frictionally weak material along the fault plane over thousands of years.

  19. 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.

  20. 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.

  1. Geophysical Investigations Along the Hayward Fault, Northern California, and Their Implications on Earthquake Hazards

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    Geophysical studies indicate that the Hayward Fault follows a pre-existing basement structure and that local geologic features play an important role in earthquake seismicity. The recent creeping trace of the Hayward Fault extends for about 90 km from San Pablo Bay in the northwest to Fremont in the southeast, and together with its northern extension, the Rodgers Creek Fault, is regarded as one of the most hazardous faults in northern California. The Hayward Fault is predominantly a right-lateral strike-slip fault that forms the western boundary of the East Bay Hills and separates Franciscan Complex rocks on the southwest from Coast Range Ophiolite and Great Valley Sequence basement rocks on the northeast. The Hayward Fault is characterized by distinct linear gravity and magnetic anomalies that correlate with changes in geology, structural trends, creep rates, and clusters of seismicity. These correlations indicate the existence of fault-zone discontinuities that probably reflect changes in mechanical properties. These fault-zone discontinuities may play a role in defining fault segments--locations where recurring seismic ruptures may tend to nucleate or terminate. Along the central part of the Hayward Fault, a prominent gravity and magnetic anomaly correlates with an exposed gabbro body, the San Leandro gabbro. Modeling of these anomalies reveals that the San Leandro gabbro is much more extensive in the subsurface than the outcrop pattern suggests, extending to a depth of about 6-8 km. The inferred extent of the San Leandro gabbro, it's geologic setting, and associated seismicity suggest that the Hayward Fault evolved from a pre-existing basement feature, similar to the ancestral Coast Range Fault. Combined modeling and relocated double-difference seismicity data indicate that the dip of the fault surface varies from near vertical in the north to about 75 degrees in the central part to about 50 degrees in the south near Fremont and ultimately connects with the

  2. Gravity, magnetic, and high-precision relocated seismicity profiles suggest a connection between the Hayward and Calaveras Faults, northern California

    NASA Astrophysics Data System (ADS)

    Ponce, D. A.; Simpson, R. W.; Graymer, R. W.; Jachens, R. C.

    2004-07-01

    Gravity, magnetic, and seismicity data profiled across the Hayward Fault Zone were generated as part of ongoing studies to help determine the geologic and tectonic setting of the San Francisco Bay region. These data, combined with previous geophysical studies that indicate that the Hayward Fault Zone dips 75°NE near San Leandro and follows a preexisting structure, reveal a possible direct connection between the seismogenic portion of the Hayward and Calaveras Faults at depth. Although the relocated seismicity data are regional in nature, they suggest that the dip of the Hayward Fault Zone may vary from near vertical in the northwestern part of the fault to about 75°NE at San Leandro in the central part of the fault to about 50°NE in the southeastern part of the fault. Gravity and magnetic data, profiled across the Hayward Fault Zone, were processed using standard geophysical techniques. Cross sections of high-precision relocated hypocenters were constructed along each profile from the northwestern to the southeastern end of the Hayward Fault Zone. Profiles and cross sections are referenced to Pinole Point, where the Hayward Fault enters San Pablo Bay, and are spaced 2.5 km apart. Topographic profiles shown on the seismicity cross sections were generated using U.S. Geological Survey (USGS) 7.5-min, 30-m digital elevation models. Relocation of seismicity data was accomplished using a regional double-difference method. The double-difference method incorporates ordinary travel time measurements and cross correlation of P and S wave differential travel time measurements. Relative locations between earthquakes have hypocentral errors of about 100 m horizontally and 250 m vertically. Absolute location uncertainties were not determined but are probably dramatically improved compared to the USGS's Northern California Seismic Network catalog data.

  3. New Airborne LiDAR Survey of the Hayward Fault, Northern California

    NASA Astrophysics Data System (ADS)

    Brocher, T. M.; Prentice, C. S.; Phillips, D. A.; Bevis, M.; Shrestha, R. L.

    2007-12-01

    We present a digital elevation model (DEM) constructed from newly acquired high-resolution LIght Detection and Ranging (LIDAR) data along the Hayward Fault in Northern California. The data were acquired by the National Center for Airborne Laser Mapping (NCALM) in the spring of 2007 in conjunction with a larger regional airborne LIDAR survey of the major crustal faults in northern California coordinated by UNAVCO and funded by the National Science Foundation as part of GeoEarthScope. A consortium composed of the U. S. Geological Survey, Pacific Gas & Electric Company, the San Francisco Public Utilities Commission, and the City of Berkeley separately funded the LIDAR acquisition along the Hayward Fault. Airborne LIDAR data were collected within a 106-km long by 1-km wide swath encompassing the Hayward Fault that extended from San Pablo Bay on the north to the southern end of its restraining stepover with the Calaveras Fault on the south. The Hayward Fault is among the most urbanized faults in the nation. With its most recent major rupture in 1868, it is well within the time window for its next large earthquake, making it an excellent candidate for a "before the earthquake" DEM image. After the next large Hayward Fault event, this DEM can be compared to a post-earthquake LIDAR DEM to provide a means for a detailed analysis of fault slip. In order to minimize location errors, temporary GPS ground control stations were deployed by Ohio State University, UNAVCO, and student volunteers from local universities to augment the available continuous GPS arrays operated in the study area by the Bay Area Regional Deformation (BARD) Network and the Plate Boundary Observatory (PBO). The vegetation cover varies along the fault zone: most of the vegetation is non-native species. Photographs from the 1860s show very little tall vegetation along the fault zone. A number of interesting geomorphic features are associated with the Hayward Fault, even in urbanized areas. Sag ponds and

  4. Dipping San Andreas and Hayward faults revealed beneath San Francisco Bay, California

    USGS Publications Warehouse

    Parsons, T.; Hart, P.E.

    1999-01-01

    The San Francisco Bay area is crossed by several right-lateral strike-slip faults of the San Andreas fault zone. Fault-plane reflections reveal that two of these faults, the San Andreas and Hayward, dip toward each other below seismogenic depths at 60?? and 70??, respectively, and persist to the base of the crust. Previously, a horizontal detachment linking the two faults in the lower crust beneath San Francisco Bay was proposed. The only near-vertical-incidence reflection data available prior to the most recent experiment in 1997 were recorded parallel to the major fault structures. When the new reflection data recorded orthogonal to the faults are compared with the older data, the highest, amplitude reflections show clear variations in moveout with recording azimuth. In addition, reflection times consistently increase with distance from the faults. If the reflectors were horizontal, reflection moveout would be independent of azimuth, and reflection times would be independent of distance from the faults. The best-fit solution from three-dimensional traveltime modeling is a pair of high-angle dipping surfaces. The close correspondence of these dipping structures with the San Andreas and Hayward faults leads us to conclude that they are the faults beneath seismogenic depths. If the faults retain their observed dips, they would converge into a single zone in the upper mantle -45 km beneath the surface, although we can only observe them in the crust.

  5. 3D Image Tour of the Hayward Fault in the East Bay, San Francisco Bay Region, California

    NASA Astrophysics Data System (ADS)

    Stoffer, P.

    2007-12-01

    A 3D image tour of the Hayward Fault begins at its northern land-based terminus at Point Pinole from where it continues northward under the waters of San Pablo Bay. From Point Pinole, the Hayward Fault extends southward for about 90 kilometers through the urbanized landscape of the East Bay region, passing through the cities of Richmond, Berkeley, Oakland, San Leandro, Hayward, Fremont, and other communities. At its southern end, the fault forms a series of oblique reverse faults, but at depth it connects with the Calaveras Fault as a through-going structure along the western foothills of the Diablo Range east of the greater San Jose area. This presentation focuses on access to the Hayward Fault in public places where features impacted by active fault creep can be viewed. Features include offset curbs, fractures in sidewalks, parking areas, buildings, and damage to other infrastructure in the active fault zone. Additional images highlight landscape features and historic landmarks along the fault, including those that were impacted by the 1868 Hayward earthquake, and those that were or were engineered both with and without consideration of the location of the fault. Earthquake data and geologic interpretations of the subsurface along the fault zone are also presented. This presentation, and an associated website, is for educational audiences with the intent of promoting public awareness and earthquake preparedness. This work is part of the ongoing outreach and public education efforts by the U.S. Geological Survey in cooperation with the 1868 Hayward Earthquake Alliance in anticipation of the 140th anniversary of the great earthquake. The use of 3D imagery enhances the educational value of the presentation and provides a unique perspective on the subject matter. Red-and-cyan 3D viewing glasses will be available at the presentation.

  6. 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.

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

    PubMed

    Bilham, R; Bodin, P

    1992-10-01

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

  8. Subsurface Structure of San Leandro From the San Francisco Bay to the Hayward Fault

    NASA Astrophysics Data System (ADS)

    Goldman, M. R.; Catching, R. D.; Rymer, M. J.; Gandhok, G.; Steedman, C. E.

    2003-12-01

    The city of San Leandro, California is located in the eastern San Francisco Bay area between the Bay and the East Bay hills (Diablo Mountains). The major known tectonic structures in the immediate San Leandro area are the Hayward fault to the east and the San Leandro basin, a deep sedimentary basin, beneath the western side of the city. To better understand the San Leandro basin, its subsurface fault structures, and the effect of these structures on ground water and earthquake hazards, the U.S. Geological Survey acquired an approximately 10-km-long, high-resolution, combined reflection and refraction seismic imaging profile across the city in June 2002. The seismic profile originated within the waters of the San Francisco Bay and ended at the Hayward fault. Seismic sources were generated by a combination of 400-grain, Betsy-Seisgun blanks in 0.3-m-deep holes and 0.25-to-0.5-kg, buried explosions in 1.5-m-deep holes. The combined spacing of seismic sources was 5 m. The seismic data were recorded on an array of four 60-channel Geometrics Strataview seismographs, with 40-Hz single-element, vertical sensors spaced at 5 m. P-wave velocities range from about 800 m/s at the surface to greater than 2000 m/s at about 100 m depth. Prominent lateral low-velocity areas are evident at several locations along the profile. Reflection images show that the low-velocity areas are largely related to zones of faulting. Near-surface faults are observed on the reflection images, including southwest-dipping faults at the edge of the bay and near-vertical faults within the Hayward fault zone, but the most prominent fault occurs approximately 1 km east of the bay, where it bounds the ~1-km-deep San Leandro basin. Because the near-surface faults are observed within a few meters of the surface and because epicenters of small-magnitude earthquakes correlate with these faults, it is likely that they are active and represent potential hazards. The reflection and velocity images show that some

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  16. 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

  17. 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.

  18. Geophysical Anomalies and Seismicity Suggest a Connection Between the Hayward and Calaveras Faults, Eastern San Francisco Bay Area, Northern California

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

    Gravity, magnetic, and seismicity data of the eastern San Francisco Bay Area are used to reveal the three-dimensional subsurface geologic structure of the eastern San Francisco Bay Area and its relationship to ongoing seismicity. Combined, these data suggest a connection between the Hayward and Calaveras Faults. Gravity and magnetic modeling of a tabular gabbro body near San Leandro and relocated, double-difference seismicity data along the Hayward Fault (Ellsworth et al., 2000) suggest that the Hayward Fault dips to the northeast. Further southeast, double-difference seismicity data indicate that the fault dip becomes shallower, possibly connecting the creeping surface trace of the Hayward Fault with the diverging Mission seismicity trend at depth as suggested by Manaker and Michael (2003). In the stepover region, the southern extension of the Hayward Fault is parallel to the active central Calaveras Fault for about 25 km and the 4-km wide area in between is characterized by en echelon reverse (oblique?) faults. At depths below about 5 km, seismicity appears to be continuous, connecting the Hayward fault to the left-stepping central Calaveras Fault along the Mission seismicity trend. Geophysical interpretation of offset magnetic rock units also suggests that the northern Calaveras Fault has at most a few tens of kilometers of total offset and that most slip may be transferred from the southern Calaveras Fault, with a total offset of about 175 km, along the central Calaveras, Silver Creek, Hayward, and other faults west of the northern Calaveras Fault, consistent with present seismicity. Cross-sectional and 3D visualizations of these data are used to illustrate the proposed geometry of the connection between the Hayward and Calaveras Faults.

  19. Inversion of InSAR Data for the Aseismic Slip-Rate on the Hayward Fault

    NASA Astrophysics Data System (ADS)

    Schmidt, D. A.; Bürgmann, R.; Nadeau, R.; D'Alessio, M.

    2002-12-01

    The Hayward fault is a major strand of the San Andreas fault system, and has received considerable attention because of the seismic hazard it poses to the San Francisco Bay Area. We perform a least-squares inversion of multiple geodetic and seismic data sets to determine the strike-slip distribution of the aseismic slip-rate on the fault. The analysis focuses on the northern 60 km of the fault where surface creep rates appear to be constant over the past several decades. InSAR data from 24 independent ERS interferograms are stacked to obtain range-change rates from 1992 to 2000. Surface displacement rates at 43 sites are observed using GPS from 1994 to 2002. Surface creep observations and estimates of deep slip rates determined from characteristic repeating earthquake sequences are also incorporated in the inversion. The densely spaced InSAR data require a non-planar fault surface to adequately model the near-fault data. The fault is discretized into 283 triangular dislocation elements that approximate the non-planar attributes of the fault surface. South of Hayward, a steeply, east-dipping fault geometry accommodates the divergence of the surface trace and the micro-seismicity at depth. Laplacian smoothing and a positivity constraint are included in the inversion. The InSAR data provide the greatest resolution on the shallow portion of the fault. The additional data sets help to complement the InSAR data and improve the model resolution. The inversion result suggests a heterogeneous distribution of aseismic slip-rate that is characterized by both locked and freely slipping patches. A seismic cluster beneath San Leandro coincides with a creeping patch as resolved by the geodetic data. A locked region at depth coincides with the source region of the 1868 earthquake (M 6.8) on the southern Hayward fault.

  20. 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.

  1. 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.

  2. The Hayward Fault Exposed! 20,000 Visitors Made it a Success

    NASA Astrophysics Data System (ADS)

    Stenner, H.; Zoback, M.; Schwartz, D.

    2007-12-01

    Last year, as part of the commemoration of the anniversary of the 1906 earthquake, an exhibit was built that gave the public a chance to better understand earthquakes and the faults that create them, and how to be prepared for a major earthquake. Open for six months, the exhibit in Fremont Central Park attracted more than 20,000 visitors from throughout the San Francisco Bay area and beyond. The main draw was the opportunity to descend into a 12-foot-deep excavation that provided up-close views of the Hayward fault itself. Visitors came to see the fault but stayed to hear its story and view displays about being prepared for the coming quake and the science behind it. The Hayward fault is an excellent subject to spark public interest. The large 1868 earthquake, which was known as "the great San Francisco earthquake" until 1906, caused the Hayward fault to slip up to 6 feet in areas that are now densely urbanized with homes and town centers. Further, the fault has been researched extensively, revealing that we are currently in the time window during which the next big earthquake, perhaps a repeat of the 1868 earthquake, is likely to occur along the Hayward fault. And to top it off, the fault experiences tectonic creep that provides fairly dramatic evidence of fault movement by cracking and offsetting curbs, parking lots, and streets near the exhibit site. Visitor feedback was overwhelmingly positive. Local groups came en masse and were spurred into developing plans for responding to a large earthquake in their community. School children came on field trips, saw what a fault looks like and how fault movement affects what they think of as static features of their world. Many visitors mentioned that such an exhibit should be a permanent Bay Area attraction. Two years in planning, the event required large amounts of volunteer time, sponsorship funds, agreement from the local government, and dedication from its developers. A permanent exhibit would undoubtedly be

  3. 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.

  4. The Hayward Fault in the East San Francisco Bay Region, California: A Regional Geophysical and Geological Perspective

    NASA Astrophysics Data System (ADS)

    Jachens, R. C.; Ponce, D. A.; Graymer, R. W.; Wentworth, C. M.; Hildenbrand, T. G.

    2003-12-01

    Regional gravity, magnetic, and geologic data, together with sparse seismic reflection and refraction data, and drill hole logs, provide a regional tectonic perspective and context of the Hayward fault. The fault is at least 85 km long and terminates at both ends at pull-apart basins. The southeastern terminus falls near the northeastern tip of the NW-SE Evergreen basin, which likely formed in the wake of a right step between the Silver Creek and Hayward Faults as a result of large right slip. The northwestern terminus lies along the southwestern edge of the deep basin that lies beneath eastern San Pablo Bay and extends, as the East Bay Trough, both southeast and northwest. Here, a structural manifestation of the Hayward Fault (the southwestern edge of the deep basin) steps right to about trace of the Tolay thrust Fault whereas seismicity and recent movement step farther right to the Rodgers Creek Fault. The deep basin under San Pablo Bay is three times wider than the right step from the Hayward fault to the Rodgers Creek fault, suggesting that if this basin is a strike-slip pull-apart basin, then faults farther east of the Rodgers Creek fault must have been involved in its formation. The local basin that formed during the past few million years in the wake of the Hayward-Rodgers Creek right step probably is no more than 500 m deep, according to a seismic reflection profile. A continuous magnetic anomaly probably reflecting a buried volcanic body lies between the Rodgers Creek Fault and the western deep basin margin north of San Pablo Bay, continues southward to truncate against the Hayward fault beneath most of San Pablo Bay. This body is not dismembered, precluding a simple strike-slip connection between the Rodgers Creek and Hayward Faults with more than about 10 km of offset (compared to the estimated roughly 100 km of total offset across the Hayward fault). The Hayward fault separates two distinctly different crustal blocks. The Bay block to the southwest

  5. 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.

  6. Bounding Ground Motions for Hayward Fault Scenario Earthquakes Using Suites of Stochastic Rupture Models

    NASA Astrophysics Data System (ADS)

    Rodgers, A. J.; Xie, X.; Petersson, A.

    2007-12-01

    The next major earthquake in the San Francisco Bay area is likely to occur on the Hayward-Rodgers Creek Fault system. Attention on the southern Hayward section is appropriate given the upcoming 140th anniversary of the 1868 M 7 rupture coinciding with the estimated recurrence interval. This presentation will describe ground motion simulations for large (M > 6.5) earthquakes on the Hayward Fault using a recently developed elastic finite difference code and high-performance computers at Lawrence Livermore National Laboratory. Our code easily reads the recent USGS 3D seismic velocity model of the Bay Area developed in 2005 and used for simulations of the 1906 San Francisco and 1989 Loma Prieta earthquakes. Previous work has shown that the USGS model performs very well when used to model intermediate period (4-33 seconds) ground motions from moderate (M ~ 4-5) earthquakes (Rodgers et al., 2008). Ground motions for large earthquakes are strongly controlled by the hypocenter location, spatial distribution of slip, rise time and directivity effects. These are factors that are impossible to predict in advance of a large earthquake and lead to large epistemic uncertainties in ground motion estimates for scenario earthquakes. To bound this uncertainty, we are performing suites of simulations of scenario events on the Hayward Fault using stochastic rupture models following the method of Liu et al. (Bull. Seism. Soc. Am., 96, 2118-2130, 2006). These rupture models have spatially variable slip, rupture velocity, rise time and rake constrained by characterization of inferred finite fault ruptures and expert opinion. Computed ground motions show variability due to the variability in rupture models and can be used to estimate the average and spread of ground motion measures at any particular site. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No.W-7405-Eng-48. This is

  7. 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.

  8. Fault damage zones

    NASA Astrophysics Data System (ADS)

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

    2004-03-01

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

  9. 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.

  10. 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

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

    NASA Astrophysics Data System (ADS)

    Williams, Robert A.; Simpson, Robert W.; Jachens, Robert C.; Stephenson, William J.; Odum, Jack K.; Ponce, David A.

    2005-07-01

    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.

  12. 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.

  13. 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

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

    NASA Astrophysics Data System (ADS)

    Schmidt, D. A.; Bürgmann, R.; Nadeau, R. M.; D'Alessio, M.

    2005-08-01

    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.

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. 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

  20. 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.

  1. 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.

  2. 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

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

    NASA Astrophysics Data System (ADS)

    Allam, Amir A.

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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. The Dynamics of Fault Zones

    NASA Astrophysics Data System (ADS)

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

    2006-05-01

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

  16. 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.

  17. Seismic fault zone trapped noise

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  18. 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.

  19. Relationships between sliding behavior and internal geometry of laboratory fault zones and some creeping and locked strike-slip faults of California

    USGS Publications Warehouse

    Moore, Diane E.; Byerlee, J.

    1992-01-01

    Moore, D.E. and Byerlee, J., 1992. Relationships between sliding behavior and internal geometry of laboratory fault zones and some creeping and locked strike-slip faults of California. In: T. Mikumo, K. Aki, M. Ohnaka, L.J. Ruff and P.K.P. Spudich (Editors), Earthquake Source Physics and Earthquake Precursors. Tectonophysics, 211: 305-316. In order to relate fault geometries to sliding behavior, maps of recently active breaks within the Hayward fault of central California, which is characterized by fault creep, have been examined and compared to maps of the San Andreas fault. The patterns of recent breaks of the Hayward fault are consistent with those found within the creeping section of the San Andreas, and they appear to have plausible physical explanations in the findings of laboratory experiments. The distinguishing geometric features of the examined locked and creeping faults are: (1) P-type second-order traces predominate over R(Riedel)-type traces in creeping sections; and (2) R-type second-order traces make smaller angles to the local fault strike in creeping sections than they do in locked sections. Two different maps of the Hayward fault gave similar results, supporting the inference that the patterns identified are basic characteristics of the fault rather than artifacts of a particular mapping procedure. P shears predominate over R shears under laboratory conditions that allow dilation within the fault zone. In our own experiments, P-shear development was favored by the generation of excess pore-fluid pressures. We propose that creep in California faults also is the result of fluid overpressures that are maintained in a low-permeability gouge zone and that significantly lower effective stresses, thus helping to stabilize slip and producing high values of the ratio P/R. Small R-trace angles may also be an indicator of low effective stresses, but the evidence for this is not conclusive because other factors can also affect the size of the angles. ?? 1992.

  20. Simulation of Fault Zone Dynamics

    NASA Astrophysics Data System (ADS)

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

    2002-12-01

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

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. Granular packings and fault zones

    PubMed

    Astrom; Herrmann; Timonen

    2000-01-24

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  8. 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

  9. Transfer zones in listric normal fault systems

    NASA Astrophysics Data System (ADS)

    Bose, Shamik

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

  10. 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

  11. 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

  12. 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.

  13. Reactivation mechanisms of heterogeneous, complex fault zones

    NASA Astrophysics Data System (ADS)

    Heesakkers, Vincent

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

  14. Delineation of fault zones using imaging radar

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  15. 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

  16. 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.

  17. 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

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  19. 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).

  20. 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

  1. 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

  2. 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).

  3. 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

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

    SciTech Connect

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

    1989-11-01

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

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  10. 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.

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

    NASA Astrophysics Data System (ADS)

    Knipe, Robert J.; Lloyd, Geoffrey E.

    1994-03-01

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

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

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

    PubMed

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

    2014-12-12

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

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

    NASA Astrophysics Data System (ADS)

    Caglayan, A.; ISIK, V.

    2012-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  17. 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

  18. 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

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. Fluid-rock reaction weakening of fault zones

    SciTech Connect

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

    1995-07-10

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

  4. 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.

  5. 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

  6. 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.

  7. Kumano Seismogenic Zone Imaging and Splay Fault Property

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

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

  8. 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

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

    NASA Astrophysics Data System (ADS)

    Ujiie, Kohtaro; Kimura, Gaku

    2014-12-01

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

  10. 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.

  11. Influence of carbonate facies on fault zone architecture

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

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

    SciTech Connect

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

    1991-03-29

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

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

    PubMed

    Ben-Zion, Y; Malin, P

    1991-03-29

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

  14. 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.

  15. 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

  16. 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

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

    NASA Astrophysics Data System (ADS)

    Bjornerud, M.

    2010-12-01

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

  18. 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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Martel, Stephen J.; Pollard, David D.

    1989-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  2. 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.

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

    NASA Astrophysics Data System (ADS)

    Yang, Hongfeng

    2015-04-01

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

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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

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

    NASA Astrophysics Data System (ADS)

    Mizoguchi, K.; Ueta, K.

    2011-12-01

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

  10. Orientations of faults determined by premonitory shear zones

    NASA Astrophysics Data System (ADS)

    Johnson, Arvid M.

    1995-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  13. 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.

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

    NASA Astrophysics Data System (ADS)

    Masuda, Koji

    2015-12-01

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

  15. 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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Sibson, R. H.

    2005-12-01

    Syntectonic hydrothermal veining is widespread in ancient fault zones exhibiting mixed brittle-ductile behavior that are exhumed from subgreenschist to greenschist environments. The hydrothermal material (predominantly quartz ± carbonate) commonly occurs as fault-veins developed along principal slip surfaces, with textures recording intermittent deposition, sometimes in the form of repeated episodes of brecciation and recementation. Systematic sets of extension veins with histories of incremental dilation often occur in adjacent wallrocks. Conspicuous for their size and continuity among these fault-hosted vein systems are mesozonal Au-quartz lodes, which are most widespread in Archean granite-greenstone belts but also occur throughout the geological record. Most of these lode gold deposits developed at pressures of 1-5 kbar and temperatures of 200-450°C within the lower continental seismogenic zone. A notable characteristic is their vertical continuity: many `ribbon-texture' fault veins with thicknesses of the order of a meter extend over depth ranges approaching 2 km. The largest lodes are usually hosted by reverse or reverse- oblique fault zones with low finite displacement. Associated flat-lying extension veins in the wallrock may taper away from the shear zones over tens or hundreds of meters, and demonstrate repeated attainment of the ~lithostatic fluid overpressures needed for hydraulic extension fracturing. Where hosted by extensional-transtensional fault systems, lode systems tend to be less well developed. Mesozonal vein systems are inferred to be the product of extreme fault-valve behavior, whereby episodic accumulation of pore-fluid pressure to near-lithostatic values over the interseismic period leads to fault rupture, followed by postseismic discharge of substantial fluid volumes along the freshly permeable rupture zone inducing hydrothermal precipitation that seals the fracture permeability. Aqueous mineralizing fluids were generally low

  18. 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.

  19. 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.

  20. Paradoxical pseudotachylyte - Fault melt outside the seismogenic zone

    NASA Astrophysics Data System (ADS)

    White, Joseph Clancy

    2012-05-01

    Fault generated melt, pseudotachylyte, is an established indicator of palaeoseismic faulting. The existing consensus that frictionally induced melting occurs within the classic seismogenic zone contrast the contention over how pseudotachylyte forms within the ductile regime. Central to this issue is whether all pseudotachylyte originates as pressure-dependent frictional melt along slip surfaces, or if pressure-independent processes have roles in its formation. Propagation of high-velocity slip into deeper crustal levels provides a satisfactory explanation for pseudotachylyte at depth, but does not of itself rationalize earthquake nucleation outside the classic seismogenic zone. Pseudotachylyte from the Minas Fault Zone, Nova Scotia, Canada is used to demonstrate the formation and preservation of fault-related melt under lower crustal conditions. Microstructures retain evidence of intense dislocation glide with minimal climb, and ductile disaggregation of the host; the latter are consistent with intracrystalline deformation in the Peierls stress-controlled glide regime. It remains unclear whether the crystal plasticity serves only as a precursory stage to rupture and high-velocity slip or is itself responsible for both instability and the thermal transient. There are similarities between accelerating plastic slip leading to rupture and aseismic creep bursts (tremor) that emphasize the mechanistic complexity of deep faulting, and the need to extend consideration beyond that of a simple brittle-ductile response. The occurrence of tremor bursts fall within the depth range of "paradoxical" pseudotachylyte and provides a circumstantial link between active tectonics and the geologic record that merits examination.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  3. 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.

  4. Fault-Tolerant, Multiple-Zone Temperature Control

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

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

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

  7. Triggered tremors beneath the seismogenic zone of an active fault zone, Kyushu, Japan

    NASA Astrophysics Data System (ADS)

    Miyazaki, Masahiro; Matsumoto, Satoshi; Shimizu, Hiroshi

    2015-11-01

    Non-volcanic tremors were induced by the surface waves of the 2012 Sumatra earthquake around the Hinagu fault zone in Kyushu, Japan. We inferred from dense seismic observation data that the hypocenters of these tremors were located beneath the seismogenic zone of the Hinagu fault. Focal mechanisms of the tremors were estimated using S-wave polarization angles. The estimated focal mechanisms show similarities to those of shallow earthquakes in this region. In addition, one of the nodal planes of the focal mechanisms is almost parallel to the strike direction of the Hinagu fault. These observations suggest that the tremors were triggered at the deeper extension of the active fault zone under stress conditions similar to those in the shallower seismogenic region. A low-velocity anomaly beneath the hypocentral area of the tremors might be related to the tremor activity.

  8. 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.

  9. 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

  10. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  12. 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.

  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. 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

  15. 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.

  16. 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.

  17. 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.

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

    USGS Publications Warehouse

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

    1991-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  20. 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

  1. 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.

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

    NASA Astrophysics Data System (ADS)

    Kang, Jingqian; Duan, Benchun

    2014-02-01

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

  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. 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

  6. Transformations in shallow fault zones; evidence from fault rocks in young strike-slip systems.

    NASA Astrophysics Data System (ADS)

    van der Pluijm, B. A.; Schleicher, A. M.; Warr, L. N.

    2008-12-01

    cataclasis creates nucleation sites for neomineralization or produces localized melting in upper-crustal strike-slip fault systems (< 5 km depth), which is coupled to slip rate. Transformations in shallow fault rock involve the localization of clay neomineralization along slip surfaces in creeping segments, controlling strength in the shallowest segment of fault zones. During sudden, large displacements, the energy can be sufficient to produce friction melts that are similarly generated at small slip surfaces. Thus, shallow faults rocks preserve mineral and state transformations during faulting, and provide information on the history of fluid activity, mass transport and mechanical behavior. Additionally, dating of neocrystallized mineral phases by radiogenic techniques provides the age of faulting and can constrain rates of crustal deformation.

  7. 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

  8. 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.

  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. 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.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

    Kerrich, R.

    1986-01-01

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

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  15. 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

  16. 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.

  17. Multiscale seismic signature of a small fault zone in a carbonate reservoir: Relationships between VP imaging, fault zone architecture and cohesion

    NASA Astrophysics Data System (ADS)

    Jeanne, Pierre; Guglielmi, Yves; Cappa, Frédéric

    2012-07-01

    The seismic (P-waves velocity, VP) signature of a small fault zone intersecting carbonate reservoir layers with contrasted properties of the southeastern French sedimentary basin was studied from the micro-scale to the fault zone pluri-meter scale architecture. VP measurements were done both at the meter scale, at 250-m depth in a gallery within the LSBB-URL, and at the centimeter scale (laboratory scale), on samples collected through boreholes. Results were compared to a VP tomography at the reservoir scale and to the fault rock mechanical properties. Our investigations indicated that P-wave velocity variations across the fault zone are strongly correlated to some key parameters, such as the uniaxial compressive strength (σc) of the fault core, the intact rock porosity (ϕ) and the fracturation intensity (RQD) of the damage zone. The seismic visibility of the fault zone depends on the contrasts between the porosity and the fracturation density of the sedimentary layers. In porous layers the fault induced deformations are mainly accommodated at the micro-scale (grain scale) with few macroscopic fractures, and the damage zone is thin leading to a high VP contrast with the fault core. In the low-porosity layers where deformations are mainly accommodated through brittle fractures, the seismic visibility of the fault is moderate, characterized by a decrease in the VP value which remains within the magnitude of the VP variations within the layers outside the fault zone. Interestingly, the fault seismic signature in the highly fractured layers appears clearly in the frequency domain at 3 dominant frequencies (2000, 9000 and 28,000 Hz), each of which exhibiting different spectral amplitudes for each components of the fault zone. Finally, the seismic signature of a relatively small fault zone included in a layered sedimentary series appears discontinuous, characterized by more or less thick high velocity patches more or less extended within the stratigraphic layers. We

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

    USGS Publications Warehouse

    Orndorff, Randall C.

    2012-01-01

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

  19. 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

  20. 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

  1. Slip on 'weak' faults by the rotation of regional stress in the fracture damage zone.

    PubMed

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

    2006-12-14

    Slip on unfavourably oriented faults with respect to a remotely applied stress is well documented and implies that faults such as the San Andreas fault and low-angle normal faults are weak when compared to laboratory-measured frictional strength. If high pore pressure within fault zones is the cause of such weakness, then stress reorientation within or close to a fault is necessary to allow sufficient fault weakening without the occurrence of hydrofracture. From field observations of a major tectonic fault, and using laboratory experiments and numerical modelling, here we show that stress rotation occurs within the fractured damage zone surrounding faults. In particular, we find that stress rotation is considerable for unfavourably oriented 'weak' faults. In the 'weak' fault case, the damage-induced change in elastic properties provides the necessary stress rotation to allow high pore pressure faulting without inducing hydrofracture. PMID:17167484

  2. 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.

  3. 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.

  4. 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

  5. Fault zone rheology and length scales of frictional failure

    NASA Astrophysics Data System (ADS)

    Fagereng, A.

    2011-12-01

    Faults have a finite thickness and commonly contain fault rocks of heterogeneous composition, leading to rheological contrasts between intermingled lithologies (at the macroscale) and minerals (at the microscale) within the fault zone. The distribution and volumetric ratio of materials with different viscosity, frictional behavior, and preferred deformation mechanism, may therefore be a critical factor controlling the bulk rheology of heterogeneous fault zones. For example, at subgreenschist facies metamorphic conditions, fine-grained phyllosilicate-dominated mudstones tend to experience viscous shearing flow by dissolution-precipitation creep, whereas coarse grained quartz-dominated sandstones tend to act like competent, brittle volumes. In the rock record, deformation of mixed lithologies is well represented in tectonic mélanges. The subgreenschist facies (P < 550 MPa, T ~ 300°C) Chrystalls Beach Complex accretionary mélange, New Zealand, is an example of a well-exposed shear zone where relatively competent lenses of chert, sandstone, and basalt are distributed within a cleaved pelitic matrix. Whereas the pelitic matrix deformed predominantly by viscous shearing flow accommodated by dissolution-precipitation creep, the more competent lenses commonly contain extension fractures. The complex is cross-cut by an anastomosing fault-fracture mesh, defined by slickenfibre-coated shear surfaces linked by quartz-calcite extension veins. The frequency-size distribution of competent lenses (phacoids) in the Chrystalls Beach Complex follows a power-law distribution and is scale-invariant. The exponent of the power-law distribution varies with dominant deformation style, and is high in zones of dominantly continuous deformation - relating to a high matrix fraction, predominance of small phacoids, and small phacoid aspect ratios, whereas a low power-law exponent relates to a small matrix fraction and localized deformation accommodated on shear discontinuities. This

  6. Seismic imaging constraints on megathrust fault zone properties

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  7. Fault zones and seismicity in western Connecticut and southeastern New York

    NASA Astrophysics Data System (ADS)

    Tillman, J. E.

    1981-10-01

    Two previously unmapped, major fault zones were identified and investigated in southeastern New York and western Connecticut. These fault zones were clearly active in the Paleozoic and Mesozoic and probably also in the Cenozoic. Although surface rupture has not been associated with historic events along these zones, their locations do coincide with alignments of historic and instrumentally measured seismicity. Multiple episodes of epigenetic mineralization that occur on these faults indicate that their faulting and circulation histories are indeed complex and that a detailed record of their stress release history from the Paleozoic to the present can be obtained for each fault zone.

  8. 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.

  9. 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.

  10. Modeling the Permeability Anisotropy due to Reservoir-Scale Fault Damage Zones Using Dynamic Rupture Propagation: Applications to a Faulted Hydrocarbon Reservoir and the Nojiima Fault

    NASA Astrophysics Data System (ADS)

    Paul, P. K.; Zoback, M. D.; Hennings, P. H.

    2007-12-01

    Secondary fractures and faults associated with reservoir scale faults affect both permeability and permeability anisotropy and hence may play an important role in controlling production from a faulted reservoir. It is well known from geologic studies that there is a concentration of secondary fractures and faults in a damage zone adjacent to larger-scale faults. Because there is usually inadequate data to incorporate permeability anisotropy due to these damage zone fractures and faults into reservoir flow models, in this study we utilize the principles of dynamic rupture propagation from earthquake seismology to predict the nature of fractured/damage zones associated with reservoir scale faults. We discuss the concepts of dynamic rupture propagation and propose a workflow to model damage zones on the real field scale faults. The model we propose calculates the extent of the damage zone along the fault plane by estimating the stress perturbation associated with dynamic rupture propagation. To verify this technique we compare the modeling results of damage zone width for a reservoir scale fault with field observations. Also, we model the damage zone width associated with the Nojima Fault for the rupture that occurred in the 1996 Kobe earthquake and compare the results with the measurements on core samples from a scientific borehole drilled through the fault after the earthquake. In both the cases this technique gives a reasonable first order approximation of the damage zone width. Using fine scale simulations we show that the fractures associated with the damage zone effects the permeability distribution in both horizontal and vertical directions and defines the permeability anisotropy of the reservoir.

  11. 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

  12. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Caine, Jonathan Saul; Forster, Craig B.

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

  15. Distributed Anelastic Strain and its Relationship to Compliant Zones Surrounding Active Faults of the Eastern California Shear Zone

    NASA Astrophysics Data System (ADS)

    Shelef, E.; Oskin, M.; Fialko, Y.

    2006-12-01

    Geologic measurements of distributed anelastic strain (DAS) adjacent to active strike slip faults of the Mojave Desert portion of the Eastern California shear zone quantify the magnitude, mechanism, temporal evolution, and relationship of DAS to fault compliant zones imaged via InSAR. Prefaulting markers (mylonitic lineation, dikes, and faults assumed linear prior to dextral faulting) in crystalline rocks next to the Harper Lake fault and Calico fault indicate that DAS accounts for 6 to 23 percent of total displacement and that this displacement scales with fault slip. We conclude that DAS is a significant, active process that is not restricted to the initial fault propagation stage. We find that the width of the zone of DAS is 400-700 m on each side of the faults studied, irrespective of total fault slip. 60 percent of the displacement due to DAS occurs within 100 m of the Calico fault. A similar zone of more intense deformation occurs adjacent to the Harper Lake fault. These 100m- wide-zones are of the same extent but much less intensely deformed compared to the damage zones surrounding the San Andreas fault. Based on these relationships, we hypothesize that damage feedback progressively focuses DAS into a stable, approximately 100-m-wide-zone where its intensity can increase proportionally to fault slip. Disruption of linear markers supports that DAS in crystalline rocks occurs via slip along secondary faults and small-scale block rotation with block sizes decreasing with proximity to faults. The widths of the geologically documented zones of DAS in the Eastern California shear zone are similar to the approximately 1 km width of compliant zones modeled from InSAR observations of surface deformation due to stress changes caused by nearby earthquakes. This correlation suggests a relationship between damage- reduction of shear modulus and displacement via DAS. Paleomagnetic measurements of prefaulting and syntectonically emplaced volcanic rocks in sedimentary

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  17. 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

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

    SciTech Connect

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

    1987-05-01

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

  19. Forced Gradient Tracer Tests In A Highly Permeable Fault Zone

    NASA Astrophysics Data System (ADS)

    Himmelsbach, T.; Hötzl, H.; Maloszewski, P.

    1994-03-01

    In the area of a planned dam site in the southern Black Forest, an observation tunnel with boreholes drilled into an adjacent vertically orientated ore body offered nearly ideal conditions to investigate transport phenomena in a highly permeable fault and fracture zone. The experimental array, consisting of horizontal and inclined boreholes lying within distances of ten to twelve meters apart, gave the opportunity to perform forced gradient tracer tests over varying distances under fixed hydraulic boundary conditions. The breakthrough curves of the tracer experiments were analyzed using an adequate transport model. The fitting procedure yielded hydraulic parameters such as fissure and matrix porosities and first estimations of the average fracture aperture.

  20. 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 (

  1. 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.

  2. Low effective fault strength due to frictional-viscous flow in phyllonites, Karakoram Fault Zone, NW India

    NASA Astrophysics Data System (ADS)

    Wallis, David; Lloyd, Geoffrey E.; Phillips, Richard J.; Parsons, Andrew J.; Walshaw, Richard D.

    2015-08-01

    Phyllosilicate-rich fault rocks are common in large-scale fault zones and can dramatically impact fault rheology. Experimental evidence suggests that multi-mechanism frictional-viscous flow (FVF) may operate in such lithologies, potentially significantly weakening mature fault cores. We report microstructures indicative of FVF in exhumed phyllonites of the Karakoram Fault Zone (KFZ), NW India. These include interconnected muscovite foliae, lack of quartz/feldspar crystal preferred orientations, and sutured grains and overgrowths indicative of fluid-assisted diffusive mass transfer. FVF microphysical modelling, using microstructural observations from the natural fault rock and experimentally-derived friction and diffusion coefficients, predicts low peak shear strengths of <20 MPa within the frictional-viscous transition zone. Chlorite geothermometry indicates that synkinematic chlorites grew at 351 ± 34 °C (c. 10 km depth) during FVF, immediately above the transition to quartz crystal plasticity. The deformation processes and interpreted low shear strength of the exhumed KFZ fault rocks provide analogues for processes operating currently at depth in active faults of similar scale. If similar lithologies are present at depth, then the Quaternary seismic characteristics of the KFZ support faults with phyllonitic cores being able to accommodate large seismic ruptures. The results also provide rare rheological constraints for mechanical models of the India-Asia collision zone.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  4. Dilational fault zone architecture in a welded ignimbrite: The importance of mechanical stratigraphy

    NASA Astrophysics Data System (ADS)

    Soden, Aisling M.; Shipton, Zoe K.

    2013-06-01

    Analysis of a population of dilational faults within a densely welded ignimbrite layer reveals fault zone geometries that vary greatly within a single fault and between faults, but does not correlate with displacement. Within an individual fault the thickness of the fault core can differ by up to an order of magnitude along dip. Similarly, joint density adjacent to faults varies along fault dip but does not increase with displacement. A correlation does exist however, between joint density and the degree of ignimbrite welding, which can vary vertically within an ignimbrite layer. Previous work has shown that welding increases ignimbrite strength: non-welded ignimbrites form deformation bands and densely welded ignimbrites form discrete fractures. We observe zones of densely welded ignimbrite with high joint density, while less-welded zones have lower joint density. In turn, high joint densities correlate with narrow fault cores and low joint densities with wide fault cores. We propose a joint based model for dilational fault initiation and growth. Faults initiate on precursory joints and grow by entraining joint bound slabs, hence the correlation between high and low joint density (thin and thick slabs) and narrow and wide fault cores respectively. Ultimately joint density and consequently fault zone architecture are controlled by subtle variations in mechanical strength within the ignimbrite layer.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  7. 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.

  8. Elastic and inelastic responses of compliant fault zones to nearby earthquakes in three dimensions: a parameter-space study

    NASA Astrophysics Data System (ADS)

    Kang, Jingqian; Duan, Benchun

    2015-05-01

    Using dynamic rupture models of a right-lateral fault embedded in an elastic or elastoplastic 3-D medium, we investigate elastic and inelastic responses of compliant fault zones to nearby earthquake ruptures. We particularly examine effects of fault zone depth, width, shape and rigidity reduction on the surface displacement field. Our results from elastic models show that deeper and wider fault zones generally result in larger residual displacements. However, for shallow fault zones, the vertical residual displacement is insensitive to or even decreases with fault zone width. The width of horizontal displacement anomalies across a fault zone is only indicative of the fault zone width near the Earth's surface. There are trade-off effects among fault zone depth, width, shape and rigidity reduction on the amplitude of surface residual displacements. Our elastoplastic models show that plastic strain can occur along the entire fault zone near the Earth's surface and in the extensional quadrant at depth, if fault zone rocks are close to failure before a nearby earthquake happens. Compared with results from elastic models, plastic strain near the Earth's surface generally enhances surface displacements of a fault zone and does not change the trend of effects of fault zone depth and width, while plastic strain at depth can result in reduced retrograde motion or sympathetic motion across the fault zone, and introduce complexities in effects of fault zone depth and width. Sympathetic horizontal motion more likely occurs across a narrow fault zone with inelastic response at depth. Vertical motion in the extensional quadrant may actually decrease with fault zone width in elastoplastic models. Sympathetic horizontal motion, or small retrograde horizontal motion in conjunction with large vertical motion above a fault zone is indicative of inelastic response of a fault zone at depth.

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Marshak, Stephen; Paulsen, Timothy

    1996-02-01

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

  13. Evolution of the Sorong fault zone, northeast Indonesia

    SciTech Connect

    Charlton, T.R.

    1991-03-01

    The Sorong fault zone (SFZ) of northeast Indonesia is a broad zone of inferred left-lateral shear at the triple junction of the Indo-Australian, Eurasian, and Pacific plates. It is widely believed that fragments of the northern Australian continental margin in New Guinea are being detached and translated westward in this shear zone until they collide with the eastern margin of Eurasia (Sundaland) in the region of Sulawesi Island. However, the details of terrane translation, amalgamation, and docking remain poorly documented. In particular, the timing of events is very poorly constrained, with estimates for the commencement of the SFZ ranging from early Miocene or older to Pleistocene. Recent investigations of the SFZ and the adjacent regions of Sulawesi and Irian Jaya (Indonesian New Guinea), including new fieldwork in several of the SFZ island-terranes (Waigeo, Halmahera, Bacon, Obi, and Sula), suggest a less mobilist interpretation of the region than previous reconstructions. In general, the closest interisland geological correlations are between the geographically closest islands. This would seem to favor rather conservative reconstructions, and a new interpretation of the region based on this tenet is proposed. Although arc-continent collision commented in New Guinea during the mid-Oligocene and only slightly later in Sulaswesi, the SFZ did not begin to develop in its present form before the late Miocene.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  15. 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

  16. 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.

    2016-03-01

    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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. Shallow fault-zone dilatancy recovery after the 2003 Bam earthquake in Iran.

    PubMed

    Fielding, Eric J; Lundgren, Paul R; Bürgmann, Roland; Funning, Gareth J

    2009-03-01

    Earthquakes radiate from slip on discrete faults, but also commonly involve distributed deformation within a broader fault zone, especially near the surface. Variations in rock strain during an earthquake are caused by heterogeneity in the elastic stress before the earthquake, by variable material properties and geometry of the fault zones, and by dynamic processes during the rupture. Stress changes due to the earthquake slip, both dynamic and static, have long been thought to cause dilatancy in the fault zone that recovers after the earthquake. Decreases in the velocity of seismic waves passing through the fault zone due to coseismic dilatancy have been observed followed by postseismic seismic velocity increases during healing. Dilatancy and its recovery have not previously been observed geodetically. Here we use interferometric analysis of synthetic aperture radar images to measure postseismic surface deformation after the 2003 Bam, Iran, earthquake and show reversal of coseismic dilatancy in the shallow fault zone that causes subsidence of the surface. This compaction of the fault zone is directly above the patch of greatest coseismic slip at depth. The dilatancy and compaction probably reflects distributed shear and damage to the material during the earthquake that heals afterwards. Coseismic and postseismic deformation spread through a fault zone volume may resolve the paradox of shallow slip deficits for some strike-slip fault ruptures. PMID:19262670

  5. 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.

  6. Ductile shear zones beneath strike-slip faults: Implications for the thermomechanics of the San Andreas Fault Zone

    NASA Astrophysics Data System (ADS)

    Thatcher, Wayne; England, Philip 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

  7. 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

  8. Fault zone hydraulic properties provide an independent estimate of coseismic fracturing at 8 km depth (Gole Larghe Fault Zone, Italian Southern Alps)

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    The Gole Larghe Fault Zone (GLFZ, Italian S Alps) was exhumed from c. 8 km, 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). The fault zone has previously been quantitatively characterized (Bistacchi 2011, PAGEOPH; Smith 2013, JSG) providing a rich dataset to generate 3D Discrete Fracture Network (DFN) models and simulate fault hydraulic properties. A fundamental parameter that cannot be directly evaluated in the field is the fraction of fractures-faults that were open over a certain time period in the evolution of the fault zone. 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 post-seismic period, when the largest number of fractures was (re)opened by off-fault deformation, then permeability dropped due to fracture cementation. Postseismic permeability has been evaluated in a few cases in the world thanks to seismological evidence of fluid migration along active fault systems. Therefore, we were able to develop a parametric hydraulic model of the GLFZ and calibrate it to obtain the fraction of faults-fractures that were open in the postseismic period to obtain realistic fluid flow and permeability values. This fraction is very close to the percolation threshold of the DFN, and it can be converted to fracture intensity (fracture surface per unit volume in the fault zone), which could be integrated to obtain the fracture energy due to off-fault fracturing. Since the fracture energy due to on-fault processes has already been estimated for the GLFZ (Pittarello, 2008, EPSL), this also allows us to estimate the total fracture energy.

  9. 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

  10. 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.