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John E Vidale - One of the best experts on this subject based on the ideXlab platform.
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healing of the shallow Fault Zone from 1994 1998 after the 1992 m7 5 landers california earthquake
Geophysical Research Letters, 2001Co-Authors: John E VidaleAbstract:We conducted seismic surveys at the Johnson Valley Fault in 1994, 1996, and 1998. We found that the shear velocity of the Fault Zone rock increased by ∼1.2% between 1994 and 1996, and increased further by ∼0.7% between 1996 and 1998. This trend indicates the Landers rupture Zone has been healing by strengthening after the mainshock, most likely due to the closure of cracks that opened during the 1992 earthquake. The observed Fault-Zone strength recovery is consistent with a decrease of ∼0.03 in the apparent crack density within the Fault Zone. The ratio of decrease in travel time for P to S waves changed from 0.75 in the earlier two years to 0.65 in the later two years between 1994 and 1998, suggesting that cracks near the Fault Zone are partially fluid-filled and have became more fluid saturated with time.
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depth dependent structure of the landers Fault Zone from trapped waves generated by aftershocks
Journal of Geophysical Research, 2000Co-Authors: John E Vidale, Keiiti AkiAbstract:We delineate the internal structure of the Johnson Valley and Kickapoo Faults (Landers southern rupture) at seismogenic depth using Fault Zone trapped waves generated by aftershocks. Trapped waves recorded at the dense linear seismic arrays deployed across and along the surface breaks of the 1992 M7.5 Landers earthquake show large amplitudes and dispersive wave trains following the S waves. Group velocities of trapped waves measured from multiple band-pass-filtered seismograms for aftershocks occurring at different depths between 1.8 km and 8.2 km show an increase in velocity with depth. Velocities range from 1.9 km/s at 4 Hz to 2.6 km/s at 1 Hz for shallow events, while for deep events, velocities range from 2.3 km/s at 4 Hz to 3.1 km/s at 1 Hz. Coda-normalized amplitude spectra of trapped waves peak in amplitudes at 3–4 Hz for stations located close to the Fault trace. The amplitude decays rapidly with the station offset from the Fault Zone. Normalized amplitudes also decrease with distance along the Fault, giving an apparent Q of 30 for shallow events and 50 for deep events. We evaluated depth-dependent Fault Zone structure and its uncertainty from these measurements plus our previous results from near-surface explosion-excited trapped waves [Li et al., 1999] in a systematic model parameter-searching procedure using a three-dimensional (3-D) finite difference computer code [Graves, 1996]. Our best model of the Landers Fault Zone is 250 m wide at the surface, tapering to 100–150 m at 8.2 km depth. The shear velocity within the Fault Zone increases from 1.0 to 2.5 km/s and Q increases from 20 to 60 in this depth range. Fault Zone shear velocities are reduced by 35 to 45% from those of the surrounding rock and also vary along the Fault Zone with an increase of ∼10% near ends of the southern rupture Zone.
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evidence of shallow Fault Zone strengthening after the 1992 m7 5 landers california earthquake
Science, 1998Co-Authors: John E Vidale, Keiiti Aki, Thomas BurdetteAbstract:Repeated seismic surveys of the Landers, California, Fault Zone that ruptured in the magnitude (M) 7.5 earthquake of 1992 reveal an increase in seismic velocity with time. P, S, and Fault Zone trapped waves were excited by near-surface explosions in two locations in 1994 and 1996, and were recorded on two linear, three-component seismic arrays deployed across the Johnson Valley Fault trace. The travel times of P and S waves for identical shot-receiver pairs decreased by 0.5 to 1.5 percent from 1994 to 1996, with the larger changes at stations located within the Fault Zone. These observations indicate that the shallow Johnson Valley Fault is strengthening after the main shock, most likely because of closure of cracks that were opened by the 1992 earthquake. The increase in velocity is consistent with the prevalence of dry over wet cracks and with a reduction in the apparent crack density near the Fault Zone by approximately 1.0 percent from 1994 to 1996.
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low velocity Fault Zone guided waves numerical investigations of trapping efficiency
Bulletin of the Seismological Society of America, 1996Co-Authors: John E VidaleAbstract: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 sedi- ments 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 pro- vide dramatic improvements in our knowledge of Fault-Zone structure.
Yehuda Benzion - One of the best experts on this subject based on the ideXlab platform.
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ten kilometer vertical moho offset and shallow velocity contrast along the denali Fault Zone from double difference tomography receiver functions and Fault Zone head waves
Tectonophysics, 2017Co-Authors: A A Allam, Yehuda Benzion, Vera Schultepelkum, Carl Tape, Natalia A Ruppert, Zachary E RossAbstract:We examine the structure of the Denali Fault system in the crust and upper mantle using double-difference tomography, P-wave receiver functions, and analysis (spatial distribution and moveout) of Fault Zone head waves. The three methods have complementary sensitivity; tomography is sensitive to 3D seismic velocity structure but smooths sharp boundaries, receiver functions are sensitive to (quasi) horizontal interfaces, and Fault Zone head waves are sensitive to (quasi) vertical interfaces. The results indicate that the Mohorovicic discontinuity is vertically offset by 10 to 15 km along the central 600 km of the Denali Fault in the imaged region, with the northern side having shallower Moho depths around 30 km. An automated phase picker algorithm is used to identify ~ 1400 events that generate Fault Zone head waves only at near-Fault stations. At shorter hypocentral distances head waves are observed at stations on the northern side of the Fault, while longer propagation distances and deeper events produce head waves on the southern side. These results suggest a reversal of the velocity contrast polarity with depth, which we confirm by computing average 1D velocity models separately north and south of the Fault. Using teleseismic events with M ≥ 5.1, we obtain 31,400 P receiver functions and apply common-conversion-point stacking. The results are migrated to depth using the derived 3D tomography model. The imaged interfaces agree with the tomography model, showing a Moho offset along the central Denali Fault and also the sub-parallel Hines Creek Fault, a suture Zone boundary 30 km to the north. To the east, this offset follows the Totschunda Fault, which ruptured during the M7.9 2002 earthquake, rather than the Denali Fault itself. The combined results suggest that the Denali Fault Zone separates two distinct crustal blocks, and that the Totschunda and Hines Creeks segments are important components of the Fault and Cretaceous-aged suture Zone structure.
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ground motion prediction equations in the san jacinto Fault Zone significant effects of rupture directivity and Fault Zone amplification
Pure and Applied Geophysics, 2014Co-Authors: I Kurzon, Yehuda Benzion, Frank L Vernon, Gail M AtkinsonAbstract:We present a new set of Ground Motion Prediction Equations (GMPEs) for horizontal Peak Ground Acceleration, Peak Ground Velocity, and 5 % damped pseudo-spectral acceleration (PSA), developed for the San Jacinto Fault Zone (SJFZ) area. Besides using these equations to quantify seismic shaking in the area, the results allow us to examine the physics and local properties controlling the observed ground motions. The analyzed dataset includes ~30,000 observations from ~800 events spanning a magnitude range of 1.5 < M < 6.0 and recorded by up to 140 stations at epicentral distances ranging from essentially zero to 150 km. The local GMPE is developed for the SJFZ by applying classical regression techniques with predictive variables that include first distance and magnitude, and then site characteristics, rupture directivity, and Fault Zone amplification. The significance of these effects is determined by measuring the uncertainty-reduction of the GMPE due to each factor. The results show that, in contrast to many regional studies, traditional site characteristic has a relatively minor effect on peak amplitudes in our study area. However, rupture directivity is a significant factor controlling the amplitudes of ground motion even for small events. The dense seismic network and newly developed directivity tool enable us to extract efficiently directivity effects with statistical significance, using the ground-motion dataset during the regression analysis process. The obtained rupture directivities are consistent with the main focal mechanism orientations and surface trace orientations, known from other studies, and predictions for bimaterial ruptures in the trifurcation area of the SJFZ. Fault Zone amplification is a second important factor, showing strong impact on the peak ground motion values, with increasing role for the lower frequency range (<10 Hz) examined in the 5 % damped PSA values. We also observe signatures of large amplitude-variances, which indicate additional source-related control on the distribution of amplitudes (besides rupture directivity) for aftershocks close in time and location to the ML 5.1 earthquake of March 2013. Using the full set of records we present the most complete set of GMPEs for the SJFZ area, including a higher-amplitude prediction for regions in the direction of rupture.
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shallow seismic trapping structure in the san jacinto Fault Zone near anza california
Geophysical Journal International, 2005Co-Authors: M A Lewis, Yehuda Benzion, Zhigang Peng, Frank L VernonAbstract:SUMMARY We analyse Fault Zone trapped waves, generated by ∼500 small earthquakes, for high-resolution imaging of the subsurface structure of the Coyote Creek, Clark Valley and Buck Ridge branches of the San Jacinto Fault Zone near Anza, California. Based on a small number of selected trapped waves within this data set, a previous study concluded on the existence of a lowvelocity waveguide that is continuous to a depth of 15‐20 km. In contrast, our systematic analysis of the larger data set indicates a shallow trapping structure that extends only to a depth of 3‐5 km. This is based on the following lines of evidence. (1) Earthquakes clearly outside these Fault branches generate Fault Zone trapped waves that are recorded by stations within the Fault Zones. (2) A traveltime analysis of the difference between the direct S arrivals and trapped wave groups shows no systematic increase (moveout) with increasing hypocentral distance or event depth. Estimates based on the observed average moveout values indicate that the propagation distances within the low-velocity Fault Zone layers are 3‐5 km. (3) Quantitative waveform inversions of trapped wave data indicate similar short propagation distances within the low-velocity Fault Zone layers. The results are compatible with recent inferences on shallow trapping structures along several other Faults and rupture Zones. The waveform inversions also indicate that the shallow trapping structures are offset to the northeast from the surface trace of each Fault branch. This may result from a preferred propagation direction of large earthquake ruptures on the San Jacinto Fault.
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a shallow Fault Zone structure illuminated by trapped waves in the karadere duzce branch of the north anatolian Fault western turkey
Geophysical Journal International, 2003Co-Authors: Yehuda Benzion, Zhigang Peng, D A Okaya, L Seeber, John G Armbruster, Naside Ozer, Andrew J Michael, Serif Baris, Mustafa AktarAbstract:SUMMARY We discuss the subsurface structure of the Karadere‐Duzce branch of the North Anatolian Fault based on analysis of a large seismic data set recorded by a local PASSCAL network in the 6 months following the Mw = 7.4 1999 Izmit earthquake. Seismograms observed at stations located in the immediate vicinity of the rupture Zone show motion amplification and long-period oscillations in both P- and S-wave trains that do not exist in nearby off-Fault stations. Examination of thousands of waveforms reveals that these characteristics are commonly generated by events that are well outside the Fault Zone. The anomalous features in Fault-Zone seismograms produced by events not necessarily in the Fault may be referred to generally as Fault-Zone-related site effects. The oscillatory shear wave trains after the direct S arrival in these seismograms are analysed as trapped waves propagating in a low-velocity Fault-Zone layer. The time difference between the S arrival and trapped waves group does not grow systematically with increasing source‐receiver separation along the Fault. These observations imply that the trapping of seismic energy in the Karadere‐Duzce rupture Zone is generated by a shallow Fault-Zone layer. Traveltime analysis and synthetic waveform modelling indicate that the depth of the trapping structure is approximately 3‐4 km. The synthetic waveform modelling indicates further that the shallow trapping structure has effective waveguide properties consisting of thickness of the order of 100 m, a velocity decrease relative to the surrounding rock of approximately 50 per cent and an S-wave quality factor of 10‐15. The results are supported by large 2-D and 3-D parameter space studies and are compatible with recent analyses of trapped waves in a number of other Faults and rupture Zones. The inferred shallow trapping structure is likely to be a common structural element of Fault Zones and may correspond to the top part of a flower-type structure. The motion amplification associated with Fault-Zone-related site effects increases the seismic shaking hazard near Fault-Zone structures. The effect may be significant since the volume of sources capable of generating motion amplification in shallow trapping structures is large.
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properties of seismic Fault Zone waves and their utility for imaging low velocity structures
Journal of Geophysical Research, 1998Co-Authors: Yehuda BenzionAbstract:A two-dimensional solution for the scalar wave equation in a model of two vertical layers between two quarter spaces is used to study properties of seismic waves in a laterally heterogeneous low-velocity structure. The waves, referred to as seismic Fault Zone waves, include head waves, internal Fault Zone reflections, and trapped waves. The analysis aims to clarify the dependency of the waves on media velocities, media attenuation coefficients, layer widths, and source-receiver geometry. Additional calculations with extreme low-velocity layers provide examples that may be relevant for volcanic and geothermal domains. The interference patterns controlling seismic Fault Zone waves change with the number of internal reflections in the low-velocity structure. This number increases with propagation distance along the structure, decreases with Fault Zone width, and increases (for given length scales) with the velocity contrast. The relative lateral position of the source within the low-velocity layer modifies die length scales associated with internal reflections and influences the resulting interference pattern. Low values of Q affect considerably the dominant period and overall duration of the waves. Thus there are significant tradeoffs between propagation distance along the structure, Fault Zone width, velocity contrast, source location within the Fault Zone, and Q. The lateral and depth receiver coordinates determine the particular point where the interference pattern is sampled and observed motion is a strong function of both coordinates. The Zone connecting sources generating Fault Zone waves and observation points with appreciable wave amplitude can be over an order of magnitude larger than the Fault Zone width. Calculations for cases with layer P wave velocity of ∼200 m s−1, modeling a vertical dike or crack with fluid and gas, show conspicuous persisting oscillations. The results resemble aspects of seismic data in volcanic domains. If these waves exist in observed records, their explicit recognition and modeling will help to separate source and structural effects and aid in the interpretation of volcano-seismology signals. Although the tradeoffs in parameters governing seismic Fault Zone waves are significant, each variable has its own signature, and the parameters may be constrained by additional geophysical data. Simultaneous modeling of many waveforms with an appropriate solution can resolve the various parameters and provide a high-resolution structural image.
James P Evans - One of the best experts on this subject based on the ideXlab platform.
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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
Journal of Geophysical Research, 2010Co-Authors: Tamara Jeppson, Kelly K Bradbury, James P EvansAbstract:[1] 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.
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composition microstructures and petrophysics of the mozumi Fault japan in situ analyses of Fault Zone properties and structure in sedimentary rocks from shallow crustal levels
Journal of Geophysical Research, 2008Co-Authors: James P Evans, Angela J Isaacs, Peter T Kolesar, Tsuyoshi NoharaAbstract:[1] We characterize the chemical, microstructural, and geophysical properties of Fault-related rock samples from the 80–100 m wide Mozumi Fault Zone, north central Honshu, Japan. The Fault is exposed in a research tunnel 300–400 m below the ground, and we combine geological data with borehole geophysical logs to determine the elastic and seismic properties of the Fault Zone. Detailed mapping within the tunnel reveals that the Fault Zone consists of two Zones of breccia to foliated cataclasites 20 and 50 m thick. Two narrow (tens of centimeters wide) principal slip Zones on which most of the slip occurred bound the central Fault Zone. The dominant deformation mechanisms within the Fault Zone were brittle fracture, brecciation, slip localization, plastic deformation, and vein formation in a sericite-calcite rich matrix. Clay alteration patterns are complex within the Fault Zone, with clay-rich Fault breccia enriched in smectite, illite, and kaolinite relative to the kaolinite and illite dominant in the host rock. Whole rock geochemical analyses show that the Fault-related rocks are depleted in Fe, Na, K, Al, Mg, and Si relative to the host rock. The Fault Zone exhibits depressed electrical resistivity values by 10–100 ohm m relative to the wall rock, values of Vp and Vs values that are ∼0.30 and ∼0.40 km/s (10–20%) less than protolith values. The spontaneous potential logs indicate that the Fault Zone has increased freshwater content relative to formation waters. Wellbore-based measurements of Vp and Vs in Fault-related rocks to enable us to calculate values of Young's modulus from 16.2 to 44.9 GPa and Poisson's ratio for the Fault Zone of 0.263 to 0.393. The protolith has Young's modulus of 55.4 GPa and a Poisson's ratio of 0.242. Lowest calculated values of Young's modulus and highest calculated values of Poisson's ratio correspond to Fault breccia with increased porosity, high fluid content, and low resistivity values. Taken together, these data show that the shallow portion of the Mozumi Fault consists of a complex Zone of anastomosing narrow slip Zones that bound broad Zones of damage. Fluid-rock alteration and deformation created altered Fault-related rocks, which have resulted in overall reduced interval velocities of the Fault Zone. These data indicate that seismic waves traveling along the interface or internally reflected in the Fault Zone would encounter rocks of differing and reduced elastic properties relative to the host rocks but that in detail, material properties within the Fault may vary.
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Fault Zone architecture and permeability structure
Geology, 1996Co-Authors: Jonathan Saul Caine, James P Evans, Craig B. ForsterAbstract:Fault Zone architecture and related permeability structures form primary controls on fluid flow in upper-crustal, brittle Fault Zones. We develop qualitative and quantitative schemes for evaluating Fault-related permeability structures by using results of field investigations, laboratory permeability measurements, and numerical models offlow within andnearFaultZones.ThequalitativeschemecomparesthepercentageofthetotalFaultZone width composed of Fault core materials (e.g., anastomosing slip surfaces, clay-rich gouge, cataclasite,andFaultbreccias)tothepercentageofsubsidiarydamageZonestructures(e.g., kinematically related fracture sets, small Faults, and veins). A more quantitative scheme is developed to define a set of indices that characterize Fault Zone architecture and spatial variability.TheFaultcoreanddamageZonearedistinctstructuralandhydrogeologicunits that reflect the material properties and deformation conditions within a Fault Zone. Whether a Fault Zone will act as a conduit, barrier, or combined conduit-barrier system is controlled by the relative percentage of Fault core and damage Zone structures and the inherent variability in grain scale and fracture permeability. This paper outlines a frameworkforunderstanding,comparing,andcorrelatingthefluidflowpropertiesofFaultZones in various geologic settings.
Thomas K. Rockwell - One of the best experts on this subject based on the ideXlab platform.
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Interseismic Strain Localization in the San Jacinto Fault Zone
Pure and Applied Geophysics, 2014Co-Authors: Eric O. Lindsey, Valerie J. Sahakian, Yuri Fialko, Yehuda Bock, Sylvain Barbot, Thomas K. RockwellAbstract:We investigate interseismic deformation across the San Jacinto Fault at Anza, California where previous geodetic observations have indicated an anomalously high shear strain rate. We present an updated set of secular velocities from GPS and InSAR observations that reveal a 2–3 km wide shear Zone deforming at a rate that exceeds the background strain rate by more than a factor of two. GPS occupations of an alignment array installed in 1990 across the Fault trace at Anza allow us to rule out shallow creep as a possible contributor to the observed strain rate. Using a dislocation model in a heterogeneous elastic half space, we show that a reduction in shear modulus within the Fault Zone by a factor of 1.2–1.6 as imaged tomographically by Allam and Ben-Zion (Geophys J Int 190:1181–1196, 2012 ) can explain about 50 % of the observed anomalous strain rate. However, the best-fitting locking depth in this case (10.4 ± 1.3 km) is significantly less than the local depth extent of seismicity (14–18 km). We show that a deep Fault Zone with a shear modulus reduction of at least a factor of 2.4 would be required to explain fully the geodetic strain rate, assuming the locking depth is 15 km. Two alternative possibilities include Fault creep at a substantial fraction of the long-term slip rate within the region of deep microseismicity, or a reduced yield strength within the upper Fault Zone leading to distributed plastic failure during the interseismic period.
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Fault Zone architecture of the san jacinto Fault Zone in horse canyon southern california a model for focused post seismic fluid flow and heat transfer in the shallow crust
Earth and Planetary Science Letters, 2012Co-Authors: Nissa Morton, Gary H Girty, Thomas K. RockwellAbstract:Abstract We report results of a new study of the architecture of the San Jacinto Fault Zone in Horse Canyon, California, where stream incision has exposed a nearly continuous outcrop of the Fault Zone at ~ 0.4 km depth. The Fault Zone at this location consists of a Fault core, transition Zone, damage Zone, and tonalitic wall rocks. We collected and analyzed samples for their bulk and grain density, geochemical data, clay mineralogy, and textural and modal mineralogy. Progressive deformation within the Fault Zone is characterized by mode I cracking, subsequent shearing of already fractured rock, and cataclastic flow. Grain comminution advances towards the strongly indurated cataclasite Fault core. Damage progression towards the core is accompanied by a decrease in bulk and grain density, and an increase in porosity and dilational volumetric strain. Palygorskite and mixed-layer illite/smectite clay minerals are present in the damage and transition Zones and are the result of hydrolysis reactions. The estimated percentage of illite in illite/smectite increases towards the Fault core where the illite/smectite to illite conversion is complete, suggesting elevated temperatures that may have reached 150 °C. Chemical alteration and elemental mass changes are observed throughout the Fault Zone and are most pronounced in the Fault core. We conclude that the observed chemical and mineralogical changes can only be produced by the interaction of fractured wall rocks and chemically active fluids that are mobilized through the Fault Zone by thermo-pressurization during and after seismic events. Based on the high element mobility and absence of illite/smectite in the Fault core, we expect that the greatest water/rock ratios occur within the Fault core. These results indicate that hot pore fluids circulate upwards through the fractured Fault core and into the surrounding damage Zone. Though difficult to constrain, we speculate that the site studied during this investigation may represent the top of a narrow, ephemeral hydrothermal circulation cell that dissipates heat generated from rupture events at deeper levels (> 4 km).
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Pulverized rocks in the Mojave section of the San Andreas Fault Zone
Earth and Planetary Science Letters, 2006Co-Authors: O. Dor, Yehuda Ben-zion, Thomas K. Rockwell, Jim BruneAbstract:We present mapping of pulverized Fault Zone rocks along a 140 km long section of the San Andreas Fault in the Mojave Desert. The results show that almost every outcrop of crystalline rock within about 100 m wide belt along this Fault section is pulverized and lacks significant shear. We find structural similarities between the San Andreas Fault Zone and exhumed Faults of the San Andreas system, although pulverized rocks are not common in all of them. About 70% of the pulverized Fault Zone rocks appear on the northeast side of the principal slip Zone of the San Andreas Fault, possibly reflecting an asymmetric structure of the damage Zone. Detailed mapping at selected sites, as well as previous mapping of rock damage at smaller scales, are consistent with the large-scale asymmetric pattern of the pulverized rocks. A possible pulverization of sedimentary rocks, inferences from regional uplift indicators, and theoretical considerations imply that pulverization along this portion of the Fault occurred in the top few km of the crust. The width of the pulverized Fault Zone rocks and inferred depth extent of pulverization are similar to the dimensions of imaged low velocity Fault Zone layers that act as waveguides for seismic trapped waves. The side of the Fault that appears to sustain more damage is the block with faster seismic velocities at seismogenic depth. This correlation and the inferred shallow depth for pulverization are compatible with predictions for wrinkle-like ruptures along a material interface, with a preferred northwest propagation direction of large earthquakes on the Mojave section of the Fault.
J. Trampert - One of the best experts on this subject based on the ideXlab platform.
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The deep structure of the North Anatolian Fault Zone
Earth and Planetary Science Letters, 2013Co-Authors: A. Fichtner, E. Saygin, T. Taymaz, P. Cupillard, Y. Capdeville, J. TrampertAbstract:Multi-scale full waveform inversion of complete continental- and regional-scale seismograms reveals the crustal and upper-mantle signature of the North Anatolian Fault Zone which shapes the neotectonics of Turkey and the eastern Mediterranean. Within the crust, the Fault Zone is mostly bounded by several high-velocity blocks, suggesting that it developed along the edges of continental fragments with high rigidity. Below the crust, the surface expression of the eastern and central parts of the North Anatolian Fault Zone correlate with a pronounced low-velocity band that extends laterally over 600 km. Around 100 km depth, the low-velocity band merges into the shallow Anatolian asthenosphere, thereby providing a link to the Kirka-Afyon-Isparta Volcanic Field and the Central Anatolian Volcanics. We interpret the low-velocity band beneath the North Anatolian Fault Zone as the upper-mantle expression of the Tethyan sutures that formed 60-15 Ma ago as a result of Africa-Eurasian convergence. The structurally weak suture facilitated the formation of the younger (less than 10 Ma) crustal Fault Zone. In this sense, the North Anatolian Fault Zone is not only a crustal feature, but a narrow Zone of weakness that extends into the upper mantle.
