internal structure of the san jacinto fault zone in the trifurcation area southeast of anza california from data of dense seismic arrays we image the internal structure of the san jacinto fault zone sjfz in the trifurcation area southeast of anza california with seismic records from dense linear and rectangular arrays the examined data include recordings from more than 20 000 local earthquakes and nine teleseismic events automatic detection algorithms and visual inspection are used to identify p and s body waves along with p and s types fault zone trapped waves fztw the location at depth of the main branch of the sjfz the clark fault is identified from systematic waveform changes across lines of sensors within the dense rectangular array delay times of p arrivals from teleseismic and local events indicate damage asymmetry across the fault with higher damage to the ne producing a local reversal of the velocity contrast in the shallow crust with respect to the large scale structure a portion of the damage zone between the main fault and a second mapped surface trace to the ne generates p and s types fztw inversions of high quality s type fztw indicate that the most likely parameters of the trapping structure are width of 70 m s wave velocity reduction of 60 per cent q value of 60 and depth of 2 km the local reversal of the shallow velocity contrast across the fault with respect to large scale structure is consistent with preferred propagation of earthquake ruptures in the area to the nw

archean gold mineralization in the wabigoon subprovince a product of crustal accretion evidence from u pb geochronology in the lake of the woods area superior province canada within the lake of the woods greenstone terrain in the wabigoon subprovince of northwest ontario gold is in faults shears and tension veins that developed in response to a late archean northwest directed contraction and emplacement of contemporaneous plutons nine rocks in this area have been dated using u pb analyses of zircon in order to obtain precise time constraints on gold mineralization and to compare its timing with the age of major crustal events in the region a mineralized dike at the duport mine shoal lake is 2716 pm 2 ma old whereas a later dike that cuts mineralized rocks has an age of 2709 pm 2 ma gold mineralization is therefore distinctly younger than calc alkaline and tholeiitic rocks dated at 2724 pm 2 ma in the shoal lake area and 2727 pm 2 ma in the high lake area to the north hydrothermal activity associated with mineralization at the duport mine overprints the amphibolite facies contact metamorphic aureole of the snowshoe bay batholith 2708 pm 7 ma

ground motion prediction equations in the san jacinto fault zone significant effects of rupture directivity and fault zone amplification 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 m l 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

velocity contrast across the 1944 rupture zone of the north anatolian fault east of ismetpasa from analysis of teleseismic arrivals 1 we use differences between arrival times of teleseismic events at sets of stations crossing the north anatolian fault east of ismetpasa where shallow creep has been observed to detect and quantify a contrast of seismic velocities across the fault waveform cross correlations are utilized to calculate phase delays of p waves with respect to expected teleseismic arrivals with incident angles corresponding to the generating events compiled delay times associated with 121 teleseismic events indicate about 4 3 average p wave velocity contrast across the fault over the top 36 km with faster velocity on the north side the estimated contrast is about 8 3 if the velocity contrast is limited to the top 18 km the sense of velocity contrast is consistent with the overall tectonic setting and inference made for the examined fault section based on theoretical expectations for bimaterial ruptures and observed asymmetry of rock damage across the fault our data indicate lack of significant microseismicity near the fault suggesting that creep in the area is limited to the depth section above the seismogenic zone

geological observations of damage asymmetry in the structure of the san jacinto san andreas and punchbowl faults in southern california a possible indicator for preferred rupture propagation direction we present new in situ observations of systematic asymmetry in the pattern of damage expressed by fault zone rocks along sections of the san andreas san jacinto and punchbowl faults in southern california the observed structural asymmetry has consistent manifestations at a fault core scale of millimeters to meters a fault zone scale of meters to tens of meters and related geomorphologic features the observed asymmetric signals are in agreement with other geological and geophysical observations of structural asymmetry in a damage zone scale of tens to hundreds of meters in all of those scales more damage is found on the side of the fault with faster seismic velocities at seismogenic depths the observed correlation between the damage asymmetry and local seismic velocity structure is compatible with theoretical predictions associated with preferred propagation direction of earthquake ruptures along faults that separate different crustal blocks the data are consistent with a preferred northwestward propagation direction for ruptures on all three faults if our results are supported by additional observations asymmetry of structural properties determined in field studies can be utilized to infer preferred propagation direction of large earthquake ruptures along a given fault section the property of a preferred rupture direction can explain anomalous behavior of historic rupture events and may have profound implications for many aspects of earthquake physics on large faults

a shallow fault zone structure illuminated by trapped waves in the karadere duzce branch of the north anatolian fault western turkey 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

a 21 event 4 000 year history of surface ruptures in the anza seismic gap san jacinto fault and implications for long term earthquake production on a major plate boundary fault paleoseismic work completed at hog lake on the san jacinto fault sjf near anza california indicates that at least 21 surface ruptures have occurred in the anza seismic gap over the past 4 000 years the ages of the ruptures are constrained by 111 radiocarbon dates 97 of which fall in stratigraphic order the average recurrence interval for all ruptures for this period is about 185 105 years although some ruptures such as occurred in the april 1918 earthquake caused only minor displacement we rate the expression of each interpreted event in each of the twelve developed field exposures presented in this work by assigning numeric values for the presence of different criteria that indicate rupture to a paleo ground surface weakly expressed ruptures for example the deformation we interpret to be the result of the historical 1918 earthquake received low scores and are interpreted as smaller earthquakes from this analysis we infer that at least fifteen of the identified ruptures are indicative of large earthquakes similar to the penultimate earthquake inferred to be the m w 7 3 22 november 1800 earthquake the adjusted recurrence interval for large earthquakes lengthens to approximately 254 years comparison with the rupture history at the mystic lake paleoseismic site on the claremont strand indicates that it is plausible that several of the large ruptures identified at hog lake could have jumped the hemet step over at mystic lake and continued on the claremont strand or vice versa but most of the event ages do not match between the two sites indicating that most ruptures do not jump the step finally comparison with san andreas fault ruptures both to the north and south of its juncture with the sjf suggest that some northern sjf ruptures identified at mystic lake may correlate with events identified at wrightwood but that these northern ruptures have no match at hog lake and can not indicate rupture of the entire sjf onto the saf

properties of seismic fault zone waves and their utility for imaging low velocity structures 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

dynamic rupture on a material interface with spontaneous generation of plastic strain in the bulk abstract we discuss 2d simulations of in plane ruptures on a fault between different solids in a model that includes dynamic generation of plastic strain off the fault the fault is governed by a regularized friction with a gradual response to abrupt changes of normal stress while plastic strain in the bulk is governed by a coulomb yielding criterion the occurrence of off fault damage stabilizes the slip velocity on the fault stable self sustaining ruptures propagate on the material interface as narrow unidirectional pulses in the direction of slip on the more compliant side of the fault plastic strain is generated only on the stiffer side of the fault the tensional quadrant in the direction of rupture propagation in a strip of approximately constant width that is correlated with the slip velocity on the fault simulations for various values of confining normal stress material contrast and cohesion in the bulk suggest that significant generation of off fault damage is limited to conditions that correspond to the top few kilometers of the crust the results are compatible with field observations of shallow asymmetric damage patterns in the structure of several large faults

shallow seismic trapping structure in the san jacinto fault zone near anza california 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

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

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

age and source of colluvial sediments at vaihingen enz germany abstract colluvial sediments accumulated on the lower slopes of a ridge as a result of past and present soil erosion were dated by optical 14 c and archaeological methods this allowed us to reconstruct the depositional history of the colluvium and also to identify temporary sedimentary sinks in its transportational pathway a cascade model of colluvium formation is developed colluvial sediments resulting from early soil erosion in the neolithic to iron age periods were mainly deposited on the upper slopes significant deposition on the lower slope occurred for the first time during the iron age and roman period since then deposition rates have increased because of more intensive land use

the response of two joined quarter spaces to sh line sources located at the material discontinuity interface summary exact analytical solutions to problems of sh line force and line dislocation operating at the interface between two quarter spaces are derived and discussed it is shown that the resulting fields differ from that of a homogeneous half space in the distribution of travel times wave amplitudes and polarity of first motions these effects are documented in the literature it is therefore suggested that when constructing theoretical seismic displacement fields from source path and site effects it is important to use response functions that account for material heterogeneity in the source region an extension of the formulation used in the case of sh line dislocation leads to a 3 d representation theorem which gives the displacement field in terms of the displacement discontinuities along the rupture area the resulting overall sue scaling parameter is the potency which does not suffer from an ambiguity associated with seismic moment in the case of heterogeneous source region

examining tendencies of in plane rupture to migrate to material interfaces summary we perform a numerical parameter space study of 2 d in plane ruptures in a model consisting of two different half spaces separated by a low velocity layer and possible simultaneous slip along multiple faults ruptures are nucleated by a bilateral expanding stress drop in a limited source region and may continue to propagate spontaneously or not along one or several faults most calculations are done for purely elastic media and faults governed by coulomb friction but some simulations employ prakash clifton friction and kelvin voigt viscosity the faults two of which are material interfaces are situated equidistant and parallel to each other using different nucleation locations different initial stress different velocity contrasts different frictional fault separations different widths of a low velocity zone and different number of faults we examine the range of conditions for which ruptures migrate to other faults and continue to propagate in a self sustaining manner the model produces diverse migration and propagation phenomena represented by several phase diagrams however a general result of the study is that ruptures tend to migrate to the material interfaces and become self sustained wrinkle like pulses for wide ranges of conditions the wrinkle like pulses propagate along each material interface unilaterally in the direction of motion on the more compliant side of the interface referred to as the positive direction the existence of a large number of faults produces like viscosity distributed deformation that reduces the divergent behaviour of the wrinkle like pulses in many cases ruptures migrate to the interface with the stronger contrast and propagate unilaterally in the positive direction associated with that interface and the overall contrast across the fault zone in smaller number of cases ruptures migrate to the interface with the weaker contrast and propagate unilaterally in the opposite positive direction associated with that interface for various parameter combinations self sustained unilateral pulses travel simultaneously in the two opposite positive directions along the interfaces on the opposite sides of the low velocity layer a low resolution imaging of these ruptures would lead to an inference on bilateral propagation the m6 2004 september parkfield california earthquake may provide a natural example of such a case

low velocity zones along the san jacinto fault southern california from body waves recorded in dense linear arrays we derive high resolution information on low velocity fault zone fz structures along the san jacinto fault zone sjfz southern california using waveforms of local earthquakes that are recorded at multiple linear cross fault arrays we observe clear across fault delays of direct p and s waves indicating damage zones at different segments of the sjfz we then compute synthetic traveltimes and waveforms using generalized ray theory and perform forward modeling to constrain the fz parameters at the southern section near the trifurcation area the low velocity zone lvz of the clark branch has a width of 200 m 30 45 reduction in vp and 50 reduction in vs from array data across the anza seismic gap we find a lvz with 200 m width and 50 reduction in both vp and vs nearly as prominent as that on the southern section we only find prominent lvzs beneath three out of the five arrays indicating along strike variations of the fault damage fz reflected phases are considerably less clear than those observed above the rupture zone of the 1992 landers earthquake shortly after the event this may reflect partially healed lvzs with less sharp boundaries at the sjfz given the relatively long lapse time from the last large surface rupturing event alternatively the lack of observed fz reflected phases could be partially due to the relatively small aperture of the arrays nevertheless the clear signatures of damage zones at anza and other locations indicate very slow healing process at least in the top few kilometers of the crust

seismic tomography of the southern california plate boundary region from noise based rayleigh and love waves we use cross correlations of ambient seismic noise between pairs of 158 broadband and short period sensors to investigate velocity structure over the top 5 10 km of the crust in the southern california plate boundary region around the san jacinto fault zone sjfz from the 9 component correlation tensors associated with all station pairs we derive dispersion curves of rayleigh and love wave group velocities the dispersion results are inverted first for rayleigh and love waves group velocity maps on a 1 5 1 5 km2 grid that includes portions of the sjfz the san andreas fault saf and the elsinore fault we then invert these maps to 3d shear wave velocities in the top 7 km of the crust the distributions of the rayleigh and love group velocities exhibit 2 azimuthal anisotropy with fast directions parallel to the main faults and rotations in complex areas the reconstructed 3d shear velocity model reveals complex shallow structures correlated with the main geological units and strong velocity contrasts across various fault sections along with low velocity damage zones and basins the sjfz is marked by a clear velocity contrast with higher v s values on the ne block for the section se of the san jacinto basin and a reversed contrast across the section between the san jacinto basin and the saf velocity contrasts are also observed along the southern parts on the saf and the elsinore fault with a faster southwest block in both cases the region around the salton trough is associated with a significant low velocity zone strong velocity reductions following flower shape with depth are observed extensively around both the sjfz and the saf and are especially prominent in areas of geometrical complexity in particular the area between the sjfz and the saf is associated with an extensive low velocity zone correlated with diffuse seismicity at depth and a similar pattern including correlation with deep diffuse seismicity is observed on a smaller scale in the trifurcation area of the sjfz these results augment local earthquake tomography images that have low resolution in the top few km of the crust and provide important constraints for studies concerned with behavior of earthquake ruptures generation of rock damage and seismic shaking hazard in the region

diversity of fault zone damage and trapping structures in the parkfield section of the san andreas fault from comprehensive analysis of near fault seismograms summary we perform comprehensive analyses of trapped waves and signals of damaged fault zone rocks associated with time delays of body waves along the parkfield section of the san andreas fault saf waveforms generated by thousands of earthquakes and recorded by near fault stations in several permanent and temporary deployments are examined with attention to the possible influence of a lithology contrast across the fault on signals of the low velocity damage zone clear candidate trapped waves are identified at only three stations mmnb and two of the other near fault stations flip and pies further to the nw clear candidate trapped waves are not seen at any of the near fault stations to the se of mmnb the locations of the events generating good candidate trapped waves at mmnb and the other two stations are not distributed broadly in space but clustered in a small number of locations moreover events that generate clear candidate trapped waves at one station do not typically generate trapped waves at the other two stations these observations imply that the damage zone is highly variable along strike and that a coherent connected waveguide does not exist for distances along strike larger than at most 3 5 km the distance between stations synthetic waveform fits for observed trapped waves at stations mmnb and flip indicate that the most likely parameters of the trapping structures at these locations are widths of about 150 m depths of about 3 km velocity reductions of 30 40 per cent and q values of 10 40 synthetic calculations of trapped waves demonstrate that if there is a contrast of seismic velocity across the fault the trapped waves are delayed relative to the s wave arrival trapped waves at station mmnb and to a lesser extent also at stations flip and pies in the nw section show this characteristic this suggests a lithology contrast in the top few km at these locations in agreement with results from tomography and studies of head waves in the parkfield area at several mini across fault arrays where trapped waves are not observed a low velocity damage zone is detected from the delay in the arrival time of body wave phases relative to a nearby off fault station the observed delay of the s wave is greater than the p wave delay consistent with the existence of a damage zone with poisson ratio of about 0 33 the observations of time delays without trapped waves indicate that parts of the damage zone are insufficiently coherent to generate trapped waves a broader damage zone may exist in the region between the saf and the south west fracture zone the results highlight the diversity of damage structures along the 40 km of the saf examined in this study and imply that fault imaging based on data at single sites does not necessarily apply to a larger section

lidar and field observations of slip distribution for the most recent surface ruptures along the central san jacinto fault we measured offsets on tectonically displaced geomorphic features along 80 km of the clark strand of the san jacinto fault sjf to estimate slip per event for the past several surface ruptures we identify 168 offset features from which we make over 490 measurements using b4 light detection and ranging lidar imagery and field observations our results suggest that lidar technology is an exemplary supplement to traditional field methods in slip per event studies displacement estimates indicate that the most recent surface rupturing event mre produced an average of 2 5 2 9 m of right lateral slip with maximum slip of nearly 4 m at anza a m w 7 2 7 5 earthquake average multiple event offsets for the same 80 kms are 5 5 m with maximum values of 3 m at anza for the penultimate event cumulative displacements of 9 10 m through anza suggest the third event was also similar in size paleoseismic work at hog lake dates the most recent surface rupture event at ca 1790 a poorly located large earthquake occurred in southern california on 22 november 1800 we relocate this event to the clark fault based on the mre at hog lake we also recognize the occurrence of a younger rupture along 15 20 km of the fault in blackburn canyon with 1 25 m of average displacement we attribute these offsets to the 21 april 1918 m w 6 9 event these data argue that much or all of the clark fault and possibly also the casa loma fault fail together in large earthquakes but that shorter sections may fail in smaller events online material topographic contour maps and hillshades generated from b4 lidar data corresponding field photographs and data tables comparing lidar based and field based slip measurements for individual geomorphic features along the clark fault

waveform relocated earthquake catalog for southern california 1981 to june 2011 we determine a new relocated catalog hys catalog 2011 for southern california from 1981 through june 2011 about 75 3 of the hypocenters are calculated with absolute and differential travel time picks and 24 7 could be relocated only by using absolute travel time picks with 3d or 1d velocity models the total catalog consists of more than 502 000 earthquakes in the region extending from baja california in the south to coalinga and owens valley in the north the catalog consists of three m 7 1 m 7 2 and m 7 3 mainshocks their foreshocks and aftershocks and background seismicity caused by tectonic and other processes in the southern california crust hypocenters in the new relocated catalog exhibit tighter spatial clustering of seismicity than does the routinely generated catalog and the depth distribution is tighter and reflects the thickness of the seismogenic zone more accurately compared to the standard catalog the relocated hypocenters are more easily related to other data sets such as mapped late quaternary faults

guided waves from sources outside faults an indication for shallow fault zone structure using 3 d numerical modeling of seismic wave propagation we investigate the possibility of generating fault zone fz trapped wave energy from sources well outside a fault the fz is represented by a o 200 m wide vertical low velocity layer in a half space we find that fz trapped waves can be excited from sources well outside the fault if 1 the low velocity structure extemds only to shallow depth and the source is located at greater depth or 2 the structure of the low velocity zone is such that only the shallow part of the fz traps energy fz trapped waves are not excited from sources well outside a fz continuous with depth the results support in conjunction with recent observational evidence a model for natural faults with shallow trapping structures rather than ones that span the entire seismogenic zone this may have implications for fault mechanics as well as for aspects of shaking hazard near faults

structure of the san andreas fault at safod from p wave tomography and fault guided wave mapping 1 fault guided waves reveal a low velocity fault segment a few hundred meters southwest of the main strand of the san andreas fault saf system in 2004 the san andreas fault observatory at depth safod main hole was drilled 2 5 km underground and 0 7 km west of the saf surface trace a 3 component 4 5 hz seismograph was installed near the bottom of this hole this instrument recorded fault zone guided fg waves originating from earthquakes along the main saf 2 km north and 3 km south of the safod site this 5 km length corresponds to a distinctive low velocity structure imaged in 2003 using microearthquakes recorded on the pilot hole array because this structure transmits fg waves from the main fault it is probably connected to the main saf and is most likely a major unmapped fault

asymmetric distribution of aftershocks on large faults in california summary we examine the relations between spatial symmetry properties of earthquake patterns along faults in california ca and local velocity structure images to test the hypothesis that ruptures on bimaterial faults have statistically preferred propagation directions the analysis employs seismic catalogues for 25 fault zones in ca we distinguish between clustered and homogeneous parts of each catalogue using a recently introduced earthquake cluster analysis and examine asymmetry of offspring with respect to parent events within the clustered portion of each catalogue the results indicate strong asymmetric patterns along large faults with prominent bimaterial interfaces e g sections of the san andreas fault with enhanced activities in the directions predicted for the local velocity contrasts and absence of significant asymmetry along most other faults assuming the observed asymmetric properties of seismicity reflect the properties of the parent earthquake ruptures the discussed methodology and results can be used to develop refined estimates of seismic shaking hazard associated with individual fault zones

three dimensional calculations of fault zone guided waves in various irregular structures summary the detailed structure of fault zones fzs plays an important role in problems related to fault mechanics earthquake rupture wave propagation and seismic hazard fzs are thought to consist of an o 10 100 m wide region of decreased seismic velocity but structural details such as their depth extent lateral and vertical variations etc are elusive the small spatial scales involved make such structures difficult to image with ray theoretical methods such as tomography however seismic energy trapped inside fz layers can provide dispersive wave trains that carry information on the fz structure these waves can travel many kilometres inside the fz before reaching the surface and are therefore strongly altered by its properties candidate trapped waves have been observed above several active faults inversion algorithms exist that can model these observations in terms of planar fault zone structures however at present it is not clear how reliable these estimates are as the effects of even small 3 d variations on trapped waves are not well understood the goal of this study is to distinguish 3 d structures that do and do not significantly affect fz waves to achieve this we perform numerical calculations of wave propagation in various fz geometries and analyse the waveforms spectra and envelopes of the synthetic seismograms the main results are that 1 moderate changes of the shape of fz or 2 small scale heterogeneities or 3 depth dependent properties do not strongly affect the observed fz waves in contrast strong effects are to be expected from 4 breaks in the continuity of fz structure e g offsets which may at some point allow imaging of such features at depth