irregular recurrence of paleoearthquakes along the central garlock fault near el paso peaks california 1 new investigations at the el paso peaks paleoseismic site have refined and extended the record of paleoearthquakes for the central garlock fault event evidence in the form of buried fissures scarps folds and upward terminations has allowed us to identify six well resolved earthquakes designated as events w u r q k and f within the last 7000 years the exposures that we excavated did not reveal additional evidence for three poorly resolved events reported by mcgill and rockwell 1998 evidence for event y identified in the previous study was reexamined and found not to be a paleoearthquake radiocarbon dates of detrital charcoal combined with a method of interpolating the event ages with revised sedimentation rates provide our preferred constraints on the timing of faulting events the most recent surface rupturing earthquake event w occurred between a d 1450 and 1640 the penultimate event u occurred between a d 675 and 950 event r which was unrecognized in the previous study occurred between a d 250 and 475 event q occurred relatively shortly before event r between a d 25 and 275 event k occurred between 3340 and 2930 b c the oldest identified paleoearthquake event f occurred between 5300 and 4670 b c the event ages indicate that earthquake recurrence is highly irregular at the el paso peaks site with individual preferred intervals ranging from as little as 215 years to as many as 3300 years the irregular recurrence of surface rupturing earthquakes along the central garlock fault may be related to temporal and spatial clustering of earthquakes proposed for faults in the eastern california shear zone

constancy of geologic slip rate along the central garlock fault implications for strain accumulation and release in southern california summary we present new slip rate estimates for the central garlock fault the incised edge of an alluvial fan deposit with a 10be cosmogenic radionuclide age of 13 3 5 9 1 1 ka is offset 70 7 m yielding a slip rate of 5 3 1 0 2 5 mm yr 1 a stream thalweg that is deeply incised into this surface is offset a lesser amount 58 4 m providing the lower bound for this rate climate considerations however suggest that the deep incision of this thalweg may have occurred at a younger date specifically at the end of the younger dryas period at 11 5 ka or at the onset of a summer monsoon rainfall pattern at 8 10 ka if the deep incision was related to one of these climate events then the resulting slip rate would be 5 1 0 3 and 6 6 1 2 mm yr 1 respectively all of the slip rates are consistent with previous geologic slip rates most of which suggest a latest pleistocene holocene slip rate of 5 7 mm yr 1 these geologic slip rates however contrast markedly with much slower at most half as fast short term rates of elastic strain accumulation constrained by geodesy the new slip rate thus adds to a growing body of evidence indicating that the garlock fault is experiencing a period of transient lack of strain accumulation in which the lower crust and mantle beneath the fault is deforming at a rate that is much slower than its long term average rate these observations suggest that the garlock fault experiences two modes of strain accumulation the current slow mode in which strain accumulates very slowly along the fault and fast mode during which the fault must store and release elastic strain energy at much faster rates than the long term average to account for the relatively rapid geologic slip rates measured along the central part of the fault

seismological evidence on characteristic time of crack healing in the shallow crust 1 a continuous observation of shear wave splitting for 17 years reveals a unique temporal variation in seismic anisotropy in the shallow crust induced by a larger earthquake mw5 7 beneath the tokai region japan the delay time between the fast and slow wavelets coseismically increased and then decreased back to the pre event value the duration of the decreasing stage is about two years the decrease may indicate crack healing in the upper 10 km of the crust we approximate the temporal variation in the delay time as a function of logarithm of time which is concordant with healing phenomena of cracks reported by laboratory experiments the observation indicates that healing of cracks in crustal rocks is complete in approximately two years

the architecture of an anisotropic elastic plastic sea ice mechanics constitutive law the architecture for a new large scale anisotropic constitutive law intended for use in a sea ice dynamics model is presented here this architecture accounts directly for refrozen lead systems in the pack ice strength with an anisotropic failure surface and in the ice thickness distribution with an oriented thickness distribution the lower limit 5 km of the model resolution is controlled by the fracture spacing of old thicker ice and the maximum lead width the upper limit of the model resolution 100 km is controlled by curvature in the lead directions and variations in the lead width these in turn are controlled by the variations in internal ice stress due to driving forces winds and currents which set the time resolution this architecture features abrupt changes in the failure surface and the associated flow rule that cannot be averaged over a time step in addition the principal stress normal to a new lead must be zero as it opens this model has subscale simulations that allow for the inclusion of phenomena such as ridging rafting buckling and fracture on the behavior of the ice with this new ice constitutive law it is possible to test directly the ice failure strength plastic flow rule and ice thickness distribution the data most useful for this testing come from ice stress and position buoys together with synthetic aperture radar deformation data some data comparisons have already been made

strain accumulation in southern california 1973 1980 frequent surveys of seven trilateration networks in southern california over the interval 1973 1980 suggest that a regional increment in strain may have occurred in 1978 1979 prior to 1978 and after late 1979 the strain accumulation has been predominantly a uniaxial north south compression this secular trend was interrupted sometime in 1978 1979 by an increment in both north south and east west extension in five of the seven networks the onset of this change appears to have occurred first in the networks farthest south the changes occurred without any unusual seismicity within the networks but the overall seismicity in southern california was unusually low prior to and has been unusually high since the occurrence the average principal strain rates for the seven networks in the 1973 1980 interval are 0 17 mu strain yr north south contraction and 0 08 mu strain yr east west extension although the observed increment in strain could be related to unidentifed systematic error in the measuring system a careful review of the measurements and comparison with three other measuring systems reveal no appreciable cumulative systematic error

seismic waveform attributes before and after the loma prieta earthquake scattering change near the earthquake and temporal recovery during 1987 1995 several clusters of nearly identical seismic events multiplets occurred near the loma prieta source region these multiplets allow us to investigate and demonstrate spatial and temporal changes in seismic wave character associated with the 1989 loma prieta main shock for seismogram pairs we use a moving window technique to compute coherencies depending on lapse time and frequency post loma prieta events have reduced coherencies with pre loma prieta events in a spatially limited region close to the loma prieta hypocenter while other paths remain nearly unaffected these changes gradually recover within a time interval of 5 years after the loma prieta earthquake a possible explanation for the time dependence is coseismically opened cracks which cause scattering increase for wavefields after the loma prieta event postseismic relaxation processes such as crack healing fluid diffusion or after deformations lead to progressive closure of these cracks with time after the main shock thus the scattering properties of the local crust approach the pre main shock state

temporal changes in coda q 1 and b value due to the static stress change associated with the 1995 hyogo ken nanbu earthquake the seismicity in the tamba region northeast of the hyogo ken nanbu earthquake in japan january 17 1995 mjma 7 2 increased significantly following this earthquake this increase suggests that the static stress change due to a large earthquake causes a change in the crustal condition or dynamics in order to reveal the changes quantitatively we investigate the temporal variation in coda q l and b value in the tamba region we analyze the waveform data of many shallow microearthquakes m 1 5 3 0 in the region recorded in a period from 1987 to 1996 coda q 1 is estimated in 10 frequency bands in a range of 1 5 24 hz based on the single isotropic scattering model at frequencies between 1 5 and 4 0 hz the temporal variation in coda q 1 shows significant correlation with the occurrence of the hyogo ken nanbu earthquake coda q l increases after the event a variation in b value whose sign is opposite to that of coda q 1 is recognized the fracture dimensions of microearthquakes that contribute to the variation in b value are estimated to be 400 m this scale length is consistent with the characteristic scale length of scatterer 300 600 m which contributes effectively to a temporal variation in coda q 1 the crustal activity in the tamba region is possibly controlled by the heterogeneity with dominant scale of 102 m the stress sensitivity of the coda q 1 change is estimated to be 10 mpa 1 this value is an order of magnitude larger than the stress sensitivity of seismic velocity reported before

deriving fault slip histories to test for secular variation in slip with examples from the kunlun and awatere faults abstract although offset and age data from displaced landforms are essential for identifying earthquake clusters and thus testing whether faults slip at uniform or secularly varying rates it is not clear how the uncertainties in such measurements should be propagated so as to yield a robust fault slip history i e record of fault displacement over time here we develop a monte carlo approach for estimating the distribution of geologically reasonable fault slip histories that fit the offset and age data from a population of dated and displaced landforms the model assumes that the landforms share common faulting histories the offset and age constraints are correct and the fault has not reversed shear sense analysis of the model results yields both a precise average slip rate in the case where a linear fit is applied to the data and a best fit fault slip history in the case where the linear constraint is removed the method can be used to test for secular variation in slip because the uncertainty on this best fit history is quantified by applying the method to previously published morphochronologic data from faulted late quaternary terrace risers along the kunlun fault in china and the awatere fault in new zealand we have assessed the extent to which our modeled average slip rates match previously reported values and the data support previous interpretations of uniform slip rate the kunlun data set yields average slip rates of 8 7 3 6 2 1 mm yr and 5 1 1 6 1 2 mm yr 68 27 confidence for the central and eastern reaches of the fault respectively both of which match previously published slip rates our analysis further indicates that these fault reaches have both slipped uniformly over the latest quaternary in contrast analysis of data from the saxton river site along the awatere fault reveals a mid holocene deceleration in slip rate from 6 2 1 6 1 4 mm yr to 2 8 1 0 0 6 mm yr this result contradicts previous interpretations of uniform slip along the awatere fault the monte carlo method we present here for quantifying fault slip histories using the offset and age data from a population of faulted landforms provides an important tool for distinguishing temporally uniform from secularly varying fault slip

present day kinematics of the eastern california shear zone from a geodetically constrained block model we use global positioning system gps data from 1993 2000 to determine horizontal velocities of 65 stations in eastern california and western nevada between 35 and 37 n we relate the geodetic velocities to fault slip rates using a block model that enforces path integral constraints over geologic and geodetic time scales and that includes the effects of elastic strain accumulation on faults locked to a depth of 15 km the velocity of the sierra nevada block with respect to nevada is 11 1 0 3 mm yr with slip partitioned across the death valley 2 8 0 5 mm yr panamint valley 2 5 0 8 mm yr and airport lake owens valley 5 3 0 7 4 6 0 5 mm yr faults the western mojave block rotates at 2 1 0 8 my clockwise with 3 7 0 7 mm yr of left lateral motion across the western garlock fault we infer 11 2 mm yr of right lateral motion across the mojave region of the eastern california shear zone

interseismic strain accumulation and anthropogenic motion in metropolitan los angeles 1 we use global positioning system gps geodesy and synthetic aperture radar sar interferometry to distinguish between interseismic strain accumulation and anthropogenic motion in metropolitan los angeles we establish a relationship between horizontal and vertical seasonal oscillations of the santa ana aquifer use this relationship to infer cumulative horizontal anthropogenic motions from cumulative vertical motions caused by water and oil resource management and estimate horizontal interseismic velocities corrected for anthropogenic effects vertical anthropogenic rates from 1992 to 1999 are slower than 3 mm yr 1 in the santa ana and san gabriel aquifers and faster than 5 mm yr 1 in the chino aquifer and in many oil fields inferred horizontal anthropogenic velocities are faster than 1 mm yr 1 at 18 of 46 gps sites northern metropolitan los angeles is contracting with the 25 km south of the san gabriel mountains shortening at 4 5 1 mm yr 1 95 confidence limits the thrust fault in an elastic edge dislocation model of the observed strain is creeping at 9 2 mm yr 1 beneath and north of a position 6 2 km deep and 8 8 km north of downtown los angeles the model fault is near the los angeles segment of the puente hills thrust but south of the sante fe springs segment of the thrust disagreement between the 6 km locking depth in the model and the 15 km seismogenic depth inferred from earthquakes suggests that the elastic continuum model may be unsatisfactory models with different stiffnesses of sedimentary basin and crystalline basement must be investigated

spatial and temporal correlation between coda q 1 and seismicity and its physical mechanism from the analysis of local earthquake coda waves recorded by the benioff short period vertical seismograph at riverside california we found a surprisingly large and systematic temporal variation in coda q 1 in the southern california during the 55 year period from 1933 to 1987 comparison of the coda q 1 variation with the b value obtained for earthquakes with m 3 occurred in the area within 180 km from riverside corresponding to the area for which q 1 is estimated by the coda method led to an extraordinary result that coda q 1 correlates positively with b value with the correlation coefficient of 0 79 the significance of correlation cannot be rejected at the confidence level of 0 974 since the data used for measuring q 1 namely the coda part of seismograms and the data used for measuring b namely the seismicity catalog are totally independent the observed correlation supports strongly the physical reality of temporal change in both coda q 1 and b value the correlation between coda q 1 and b value has been reported for several other cases but the correlation was positive in some cases and negative in others our current preferred model for explaining the observed correlation is the following aseismic creep is going on from time to time over various sizes of cracks in the ductile part and in some cases in the brittle part of lithosphere at and near the plate boundary creep activities tend to increase the crack density and coda q 1 observed in the region if the creek occurs over distributed cracks with a certain predominant scale length spatial stress concentration may enhance seismicity for earthquakes with a similar size if this characteristic size is in the lower part of the magnitude range for which the b value is estimated the enhanced seismicity will increase b on the other hand if it is in the upper part of the magnitude range it will decrease b thus we can explain the observed strong correlation between coda q 1 and b value for both positive and negative cases the existence of such a characteristic crack size in a seismic region has been supported by various observations on earthquake scaling

healing of the shallow fault zone from 1994 1998 after the 1992 m7 5 landers california earthquake 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

surficial offsets on the central and eastern garlock fault associated with prehistoric earthquakes geomorphic features offset along the central and eastern garlock fault record the amount of surface slip associated with prehistoric earthquakes along the easternmost 90 km of the fault the smallest offsets cluster around 2 3 m of left lateral slip apparently associated with the most recent earthquake on this portion of the fault larger offsets along this part of the fault especially in pilot knob valley cluster around values consistent with 2 4 m of slip in each of the past several events farther west south of el paso mountains offset geomorphic features suggest that each of the past two earthquakes on this stretch of the garlock fault was produced by about 7 m of slip whereas the third event back was produced by about 4 m of slip vertical displacements of geomorphic features range from 0 to 30 of the left lateral offsets within pilot knob valley along the southern side of the slate range vertical displacements are consistently up on the northern side whereas within the avawatz mountains both north and south side up vertical displacements are present on the basis of the geomorphic offsets the geometry of the garlock fault and the precedents set by historical strike slip earthquakes elsewhere a number of different rupture patterns are plausible these range from rupture of the entire garlock fault in a single event with a maximum magnitude of about mw 7 8 to separate rupture of the western segment and of the central and eastern segments combined with approximate magnitudes mw 1 1 and mw 7 5 respectively to separate rupture of even shorter segments producing earthquakes of magnitudes mw 6 6 to mw 7 5 in conjunction with available slip rates for the garlock fault the geomorphic offsets suggest that average recurrence intervals are probably within the range of 600 1200 years south of el paso mountains about 200 750 years in searles valley about 200 1300 years in pilot knob valley and about 200 3000 years near leach lake and in the avawatz mountains

numerical analysis of the relationship between time variant coda q and the variation in crustal stress summary coda q is a stochastic parameter reflecting the heterogeneities of medium that seismic waves travel through we confirmed that coda q would vary with the stress loaded to an elastic medium using numerical simulations of seismic wave propagation when the stress is loaded cracks in the crust could either close or newly open the closure and opening of the cracks are not random but depending on the magnitude and the direction of the stress and the crack aspect ratio the cracks in the medium after loading stress could be aligned in a specific orientation and elastic wave velocity field would become anisotropic due to the alignment of specific crack orientations elastic wave velocity is in general faster along the direction corresponding with the crack orientation while slower along the perpendicular direction in the numerical simulation the effect of anisotropy in elastic wave velocity field due to the selective closure and opening of the cracks is calculated using a 2 d finite difference method assuming elastic wave velocity to be a function of the magnitude of loaded stress the coda q calculated from seismic waves simulated for a model varies when the averaged normal stress changes our simulation indicated that the sensitivity of coda q 1 that is the reciprocal of the coda q would be 1 0 10 2 1 0mpa 1 against the magnitude of the confining pressure and 1 0 10 3 1 0 deg 1 against the direction of principal stress we would like to conclude that coda q a stochastic parameter reflecting heterogeneities of subsurface medium could become a quantitative state indicator of the stress field of the medium where seismic waves propagate through spatiotemporal variation of coda q reflects change in the stress field in the crust

rates of active faulting during late quaternary fluvial terrace formation at saxton river awatere fault new zealand a flight of faulted fluvial terraces at saxton river on the awatere fault northeast south island new zealand preserves the incremental slip history and detailed paleoearthquake chronology of this major strike slip fault here six fluvial terraces have been progressively displaced across the inland molesworth section of the fault with horizontal displacements ranging from 6 m for an ephemeral channel on the youngest terrace to 81 m for the riser above the oldest terrace new optically stimulated luminescence ages for abandonment of the two oldest terrace treads are 14 5 1 5 and 6 7 0 7 ka when combined with new measurements of incremental horizontal displacements and previous age data these new ages indicate that strike slip on this part of the awatere fault has been occurring at a near constant rate of 5 6 0 8 mm yr since ca 15 ka this rate is similar to recent slip rate estimates for an adjoining section of the same fault to the east which suggests that there is near complete slip transfer across the junction between the two fault strands comparison of the magnitudes and ages of the terrace riser displacements to the timing of paleoearthquakes on the molesworth section allows the mean per event horizontal displacement over the eight most recent surface rupture events to be estimated at 4 4 0 8 m between ca 5 ka and ca 2 ka surface rupturing earthquakes increased in frequency and decreased in their mean coseismic displacements to 2 6 m during this time the sense of local dip slip also shifted from north side up to south side up rapid incision of saxton river in the mid holocene may have caused a perturbation in the near surface stress directions acting on the fault plane beneath the saxton river valley forcing a change in the near surface fault geometry that resulted in the shift in sense of dip slip

long term earthquake clustering a 50 000 year paleoseismic record in the dead sea graben the temporal distribution of earthquakes in the dead sea graben is studied through a 50 000 year paleoseismic record recovered in laminated sediments of the late pleistocene lake lisan paleo dead sea the lisan represents more than 10 times the 4000 years of historical earthquake records it is the longest and most complete paleoseismic record along the dead sea transform and possibly the longest continuous record on earth it includes unique exposures of seismite beds earthquake induced structures associated with slip events on syndepositional faults the seismites are layers consisting of mixtures of fragmented and pulverized laminae the places where the seismites abut syndepositional faults are interpreted as evidence for their formation at the sediment water interface during slip events on these faults thicker sediment accumulation above the seismites in the downthrown blocks indicates that a seismite formed at the water sediment interface on both sides of the fault scarps modern analogs and the association with surface ruptures suggest that each seismite formed during a m l 5 5 earthquake the 230 th 234 u ages of a columnar section obtained by thermal ionization mass spectrometry give a mean recurrence time of 1600 years of m l 5 5 earthquakes in the dead sea graben the earthquakes cluster in 10 000 year periods separated by quiet periods of similar length this distribution implies that a long term behavior of the dead sea transform should be represented by a mean recurrence of at least 20 000 year record this observation has ramifications for seismic hazard assessment based on shorter records

how do ghost transients from past earthquakes affect gps slip rate estimates on southern california faults 1 in this study we investigate the extent to which viscoelastic velocity perturbations or ghost transients from individual fault segments can affect elastic block model based inferences of fault slip rates from gps velocity fields we focus on the southern california gps velocity field exploring the effects of known large earthquakes for two end member rheological structures our approach is to compute at each gps site the velocity perturbation relative to a cycle average for earthquake cycles on particular fault segments we then correct the scec cmm4 0 velocity field for this perturbation and invert the corrected field for fault slip rates we find that if asthenosphere viscosities are low 3 1018 pa s the current gps velocity field is significantly perturbed by viscoelastic earthquake cycle effects associated with the san andreas fault segment that last ruptured in 1857 mw 7 9 correcting the gps velocity field for this perturbation or ghost transient adds about 5 mm a to the saf slip rate along the mojave and san bernardino segments the gps velocity perturbations due to large earthquakes on the garlock fault most recently events in the early 1600s and the white wolf fault most recently the mw 7 3 1952 kern county earthquake are smaller and do not influence block model inverted fault slip rates this suggests that either the large discrepancy between geodetic and geologic slip rates for the garlock fault is not due to a ghost transient or that un modeled transients from recent mojave earthquakes may influence the gps velocity field

continuous gps array and present day crustal deformation of japan a gps array with about 1 000 permanent stations is under operation in japan the gps array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the japanese islands based on daily coordinate data of the gps stations strain rate distribution is estimated most regions with a large strain rate are related to plate boundaries and active volcanoes in addition the niigata kobe tectonic zone nktz is recognized as a region of large strain rate along the japan sea coast and in the northern chubu and kinki districts this newly found tectonic zone may be related to a hypothetical boundary between the eurasian or amurian and the okhotsk or north america plates precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations

temporal change in site response caused by earthquake strong motion as revealed from coda spectral ratio measurement 1 the spectral ratios of coda waves of local earthquakes have been often used as measures of relative amplification factors of different sites applying this method to coda waves registered by seismometers installed on the surface and at the bottom of a borehole we succeeded in stably measuring the temporal change in site response associated with the occurrence of a large earthquake strong motion a remarkable drop of coda spectral ratio and a shift of the peak frequency were observed during strong shake at two sites by the 2000 western tottori earthquake and at a site by the 2003 tokachi oki earthquake in japan the reduction of the peak frequency reached 30 70 at all the sites after that the peak frequency logarithmically recovered to the value before the strong motions for a few years at two sites whereas the other one quickly recovered in a few tens of minutes

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

evidence for post early miocene initiation of movement on the garlock fault from offset of the cudahy camp formation east central california the cudahy camp formation located in the el paso basin east central california consists of a 350 m thick volcanic and sedimentary sequence of early miocene age previous investigators determined from paleocurrent indicators that the source for these rocks was to the south and southeast but failed to suggest a specific location for that source restoration of 64 km of left slip on the garlock fault places cudahy camp rocks north and northwest of the early miocene eagle crags volcanic field the unique geochemical nature of basalts found in both locations coincident ages of volcanic rocks identical clast content of volcanic tuffs and identical stratigraphic sequence indicate that the source for the cudahy camp formation was the eagle crags volcanic field this is the first documented occurrence of miocene rocks offset by the garlock fault because the cudahy camp rocks and their sources appear to be offset by the full displacement on the garlock fault we conclude that movement on the garlock started after earliest middle miocene time further constraining initiation of movement on the garlock fault adds significantly to fully understanding the evolution of the western north american plate boundary in the middle to late cenozoic

deformation across the western united states a local estimate of pacific north america transform deformation we obtain a locally based estimate of pacific north america relative motion and an uncertainty in this estimate by integrating deformation rate along three different paths leading west across southwestern north america from east of the rio grande rift to near the continental escarpment data are primarily quaternary geologic slip rate estimates and resulting deformation determinations therefore are instantaneous in a geologic sense but long term with respect to earthquake cycles we deduce a rate of motion of the pacific plate relative to north america that is 48 2 mm yr a rate indistinguishable from that predicted by the global kinematic models rm2 and nuvel 1 however we obtain an orientation that is 5 9 counterclockwise of these models a more westerly motion of the pacific plate with respect to north america is calculated from all three paths the relatively westerly motion of the pacific plate is accommodated by deformation in the north american continent that includes slip on relatively counterclockwise oriented strike slip faults including the san andreas fault which is especially relevant in and south of the transverse ranges and a margin normal component of net extension across the continent which is especially relevant north of the transverse ranges deformation of the sw united states occurs in regionally coherent domains within which the style of deformation is approximately uniform in the vicinity of the transverse ranges two important shear systems splay from the san andreas fault the eastern california shear zone trending nnw from the eastern transverse ranges and the trans peninsular faults trending sse from the western and central transverse ranges within the transverse ranges the right lateral san andreas fault steps left seemingly requiring large amounts of convergence there however most of this convergence is avoided through a funneling flow of the crust toward the western transverse ranges and into the relatively narrow central california coast ranges and the northern motion of the mojave the former process involves an alternation of rotation direction from counterclockwise in and south of the central transverse ranges to clockwise in the western transverse ranges

the 3 d distribution of random velocity inhomogeneities in southwestern japan and the western part of the nankai subduction zone 1 seismic waves at high frequencies 1 hz show collapsed and broadened wave trains caused by multiple scattering in the lithosphere this study analyzed the envelopes of direct s waves in southwestern japan and on the western side of the nankai trough and estimated the spatial distribution of random inhomogeneities by assuming a von karman type power spectral density function psdf strongly inhomogeneous media have been mostly imaged at shallow depth 0 20 km depth in the onshore area of southwestern japan and their psdf is represented as p m 0 05m 3 7 km3 with m being the spatial wave number whereas most of the other area shows weak inhomogeneities of which psdf is p m 0 005m 4 5 km3 at hyuga nada in nankai trough there is an anomaly of inhomogeneity of which psdf is estimated as p m 0 01m 4 5 km3 this psdf has the similar spectral gradient with the weakly inhomogeneous media but has larger power spectral density than other offshore areas this anomalous region is broadly located in the subducted kyushu palau ridge which was identified by using velocity structures and bathymetry and it shows no clear correlation with the fault zones of large earthquakes in past decades these spatial correlations suggest that possible origins of inhomogeneities at hyuga nada are ancient volcanic activity in the oceanic plate or deformed structures due to the subduction of the kyushu palau ridge

extreme multi millennial slip rate variations on the garlock fault california strain super cycles potentially time variable fault strength and implications for system level earthquake occurrence abstract pronounced variations in fault slip rate revealed by new measurements along the garlock fault have basic implications for understanding how faults store and release strain energy in large earthquakes specifically dating of a series of 26 0 3 5 2 5 m fault offsets with a newly developed infrared stimulated luminescence method shows that the fault was slipping at 14 0 2 2 1 8 mm yr approximately twice as fast as the long term average rate during a previously documented cluster of four earthquakes 0 5 2 0 ka this elevated late holocene rate must be balanced by periods of slow or no slip such as that during the ca 3300 yr long seismic lull preceding the cluster moreover whereas a comparison of paleoseismic data and stress modeling results suggests that individual garlock earthquakes may be triggered by periods of rapid san andreas fault slip or very large slip events the on off behavior of the garlock suggests a longer term mechanism that may involve changes in the rate of elastic strain accumulation on the fault over millennial time scales this inference is consistent with most models of the geodetic velocity field which yield slip deficit rates that are much slower than the average latest pleistocene early holocene post 8 13 ka garlock slip rate of 6 5 1 5 mm yr these observations indicate the occurrence of millennia long strain super cycles on the garlock fault that may be associated with temporal changes in elastic strain accumulation rate which may in turn be controlled by variations in relative strength of the various faults in the garlock san andreas eastern california shear zone fault system and or changes in relative plate motion rates

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

deep crustal heterogeneity along and around the san andreas fault system in central california and its relation to the segmentation the three dimensional distribution of scatterers in the crust along and around the san andreas fault system in central california is estimated using an inversion analysis of coda envelopes from local earthquakes i analyzed 3801 wave traces from 157 events recorded at 140 stations of the northern california seismic network the resulting scatterer distribution shows a correlation with the san gregorio san andreas hayward and calaveras faults these faults seem to be almost vertical from the surface to 15 km depth some of the other scatterers are estimated to be at shallow depths 0 5 km below the diablo range and these may be interpreted as being generated by topographic roughness the depth distribution of scatterers shows relatively stronger scattering in the lower crust at 15 25 km depth especially between the san andreas fault and the hayward calaveras faults this suggests a subhorizontal detachment structure connecting these two faults in the lower crust several clusters of scatterers are located along the san andreas fault at intervals of 20 30 km from south of san francisco to the intersection with the calaveras fault this part of the san andreas fault appears to consist of partially locked segments also 20 30 km long which rupture during m6 7 events and segment boundaries characterized by stronger scattering and stationary microseismicity the segment boundaries delineated by the present analysis correspond with those estimated from the slip distribution of the great 1906 san francisco earthquake and from the fault geometry as reported by the working group on california earthquake probabilities 1990 although the segment boundaries along the san andreas fault in and around the san francisco bay area are still uncertain

temporally constrained tectonic rotations derived from magnetostratigiraphic data implications for the initiation of the garlock fault california examination of declination anomalies within a well controlled chronologic framework can permit precise delineation of the progression of a tectonic rotation in the past declination anomalies from numerous spatially separated and individually dated localities have been synthesized in order to define regional progressive rotations rarely however have magneto stratigraphic data from a single locality been used successfully to chronicle a sequential rotation that resulted from movement along a nearby fault magnetostratigraphic studies from the el paso basin in southern california reveal progressively smaller amounts of counterclockwise rotation for strata dated between 11 and 7 ma two tests indicate that this is a temporally controlled rather than a spatially controlled rotation this rotation is interpreted to have resulted from sinistral shear along the garlock fault as such it appears to delimit the initiation of miocene movement along the western segment of this major strike slip fault

coseismic change and recovery of scattering environment in the crust after the 1995 hyogo ken nanbu earthquake japan we observe a unique temporal variation in crustal heterogeneity from the analysis of coda q 1 for 14 years in the tamba region northeast to the rupture zone of the 1995 hyogo ken nanbu earthquake m jma 7 3 in southwest japan the values of graphic 1 at lower frequencies 1 5 4 0 hz that increased coseismically due to the static stress change decreased back to the preevent values in about two years no such variations are found at higher frequencies 5 0 24 0 hz we confirm that no tectonic events that cause a significant stress change occurred during the recovery period the time required for the recovery of the scattering environment observed here such as the number density of cracks and cracks opened by the stress change is consistent with those of previous studies focused on the brittle shallower crust this suggests a possibility that a similar mechanism of the recovery operates in both the brittle and the ductile parts of the crust 1 embed inline graphic 1 gif

evidence for rapid fault healing derived from temporal changes in s wave splitting 1 tadokoro et al 1999 had made an s wave splitting analysis on the nojima fault zone that ruptured during the 1995 hyogo ken nanbu earthquake for a period 9 12 months after the mainshock the direction of faster shear wave polarization had been parallel to the fault strike suggesting fractures of shear fault origin in this study we made an additional s wave splitting analysis for a period 33 45 months after the mainshock and detected the rotation of that is the direction was parallel to the regional maximum horizontal compressional stress which is oblique to the fault strike this temporal change suggests that all the fractures of shear fault origin had completely healed and cracks of tectonic stress origin recovered between the two periods this is strong evidence for rapid fault healing which completed within 33 months after the mainshock

slip rates and off fault deformation in southern california inferred from gps data and models 1 in southern california fault slip rate estimates along the san andreas fault saf and garlock fault from geodetically constrained kinematic models are systematically at the low end or lower than geologic slip rate estimates the sum of geodetic model slip rates across the eastern california shear zone is higher than the geologic sum however the ranges of reported model and geologic slip rate estimates in the literature are sufficiently large that it remains unclear whether these apparent discrepancies are real or attributable to epistemic uncertainties in the two types of estimates we further examine uncertainties in geodetically derived slip rate estimates on major faults in southern california by conducting a suite of inversions with four kinematic models long term rigid elastic block models constrained by the geologic slip rates cannot fit the present day gps derived velocity field deforming permanent off fault strain elastic block models and viscoelastic earthquake cycle block models constrained by geologic slip rates can fit the present day gps derived velocity field with 28 33 of the total geodetic moment rate occurring as distributed deformation off of the major faults models incorporating viscoelastic mantle flow predict systematically higher slip rates than purely elastic models on many of the major southern california faults with ranges of elastic viscoelastic 29 34 30 37 mm yr for the carrizo saf segment 20 24 20 32 mm yr for the mojave saf segment 14 17 18 22 mm yr for the coachella saf segment 13 19 14 22 mm yr for the san jacinto fault and 5 11 5 11 mm yr for the western garlock fault