block models of crustal motion in southern california constrained by gps measurements 1 we estimate slip rates on major active faults in southern california using a block model constrained by global positioning system measurements of interseismic deformation the block model includes the effects of block rotation and elastic strain accumulation consistent with a simple model of the earthquake cycle our estimates of the right lateral strike slip rate on the san andreas fault vary by at least a factor of 5 from a high of 35 9 0 5 mm yr in the carrizo plain to a low of 5 1 1 5 mm yr through the san bernadino segment shortening across the puente hills thrust and left lateral slip on the raymond hill fault are consistent with both thickening and escape tectonics in the los angeles basin discrepancies between geodetic and geologic slip rate estimates along the san andreas and san jacinto faults as well as in the eastern california shear zone may be explained by a temporal change in fault system behavior we find no substantial evidence for long term postseismic relaxation and infer that the viscosity of the lower crust upper mantle may be relatively high 1019 pa s

power law distribution of fault slip rates in southern california 1 the spatial partitioning of deformation in the continental crust and in particular at plate boundary zones is determined by the distribution of fault slip rates analytic and numerical models of strain accumulation in the elastic upper crust have been divided into those that parameterize faulting as localized on a finite length fault system comprised of relatively few fast slip rate faults or as distributed throughout a continuum of relatively slow slip rate faults we demonstrate that in the southern california fault system between the pacific and north american plates both geologically and geodetically constrained fault slip rate catalogs obey a power law frequency distribution using this empirically constrained scaling relationship we derive an analytic expression for the partitioning of potency accumulation rate which determines the distribution and magnitude of slip localization this model describes the kinematics of both micro plate and continuum deformation models and predicts that 97 of the deformation in southern california is accommodated on faults slipping at 1 mm yr which is consistent with models of continental deformation which explicitly represent a large though finite number of deforming structures

present day strain accumulation and slip rates associated with southern san andreas and eastern california shear zone faults 1 we present the first results from a dense network of 36 campaign and 46 continuous gps stations located in the eastern transverse ranges province etr a transition zone between the southernmost san andreas fault ssaf and eastern california shear zone ecsz we analyzed the campaign data together with available data from continuous gps stations for the period 1994 2009 we used the gps velocity estimates to constrain elastic block models to investigate fault loading rates representing four hypotheses characterized by different fault block geometries fault block scenarios include blocks bounded by the east striking left lateral pinto mountain blue cut and chiriaco faults of the etr blocks bounded by a right lateral north northwest striking structure the landers mojave earthquake line that cuts obliquely across the etr and mapped mojave desert faults and combinations of these end member hypotheses each model implies significantly different active fault geometries block rotation rates and slip rates for etr and ecsz structures all models suggest that ssaf slip rate varies appreciably along strike generally consistent with rates derived from tectonic geomorphology and paleoseismology with a maximum of 23 mm yr right lateral along the southernmost coachella valley strand decreasing systematically to 10 mm yr right lateral through the san gorgonio pass region slip rate estimates for the san jacinto fault are 12 mm yr for all models tested all four models fit the data equally well in a statistical sense qualitative comparison among models and consideration of geologic slip rates and other independent data reveals strengths and weaknesses of each model

interseismic strain accumulation and the earthquake potential on the southern san andreas fault system the southern section of the san andreas fault is the only part of the fault that hasn t ruptured in historic times for this reason it is believed to pose the largest seismic risk in california although whether tectonic stress is actually accumulating there is a topic of heated debate using data from radar interferometry satellites yuri fialko has produced a detailed map of surface deformation in the area that shows that elastic stress is accumulating at a fairly high rate during the past 300 years a displacement of 6 to 9 metres has built up this suggests that the southern san andreas fault is nearing the end of the interseismic phase of the earthquake cycle and that increased seismic activity of some kind can be expected the san andreas fault in california is a mature continental transform fault that accommodates a significant fraction of motion between the north american and pacific plates the two most recent great earthquakes on this fault ruptured its northern and central sections in 1906 and 1857 respectively the southern section of the fault however has not produced a great earthquake in historic times for at least 250 years assuming the average slip rate of a few centimetres per year typical of the rest of the san andreas fault the minimum amount of slip deficit accrued on the southern section is of the order of 7 10 metres comparable to the maximum co seismic offset ever documented on the fault1 2 here i present high resolution measurements of interseismic deformation across the southern san andreas fault system using a well populated catalogue of space borne synthetic aperture radar data the data reveal a nearly equal partitioning of deformation between the southern san andreas and san jacinto faults with a pronounced asymmetry in strain accumulation with respect to the geologically mapped fault traces the observed strain rates confirm that the southern section of the san andreas fault may be approaching the end of the interseismic phase of the earthquake cycle

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

block kinematics of the pacific north america plate boundary in the southwestern united states from inversion of gps seismological and geologic data 1 the active deformation of the southwestern united states 30 41 n is represented by a finite number of rotating elastic plastic spherical caps gps derived horizontal velocities geologic fault slip rates transform fault azimuths and earthquake derived fault slip vector azimuths are inverted for block angular velocities creep on block bounding faults permanent strain rates within the blocks and the rotations of 11 published gps velocity fields into to a common north american reference frame gps velocities are considered to be a combination of rigid block rotations recoverable elastic strain rates resulting from friction on block bounding faults and nonrecoverable strain rates resulting from slip on faults within the blocks the resulting pacific north america angular velocity is similar to some published estimates and satisfies transform azimuths and one spreading rate in the gulf of california earthquake slip vectors in the gulf of california and alaska and gps velocities along coastal california and within the pacific basin published fault slip rates are satisfied except in the southern mojave desert where the motion of the mohave block relative to north america is faster than can be explained by mapped faults the largest blocks the sierra nevada great valley and the eastern basin and range show permanent strain rates after removing elastic strain of only a few nanostrain per year demonstrating approximately rigid behavior observed horizontal strain rates correlate strongly with predicted strain rates from known faults suggesting that the short term strains evident in gps velocities are largely elastic in only about 20 of the region is distributed deformation needed to match the data indicating that a plate tectonic style description of the deformation of the western united states is plausible most blocks rotate about vertical axes at approximately the same rate as the pacific relative to north america suggesting that locally spin rates are communicated from block to block arguing against both floating block and ball bearing mechanisms of block rotation the similarities of the blocks spin rates to that of the pacific suggests that the pacific strongly influences their motions through edge tractions however it is shown that the blocks cannot rotate about the pacific north america pole without spinning counter to the sense of pacific north america shear unlike some other broad plate boundaries in the western united states vertical axis rotations take up very little of the slip rate budget across the region

distribution of aseismic slip rate on the hayward fault inferred from seismic and geodetic data 1 we solve for the slip rate distribution on the hayward fault by performing a least squares inversion of geodetic and seismic data sets our analysis focuses on the northern 60 km of the fault interferometric synthetic aperture radar insar data from 13 independent ers interferograms are stacked to obtain range change rates from 1992 to 2000 horizontal surface displacement rates at 141 bench marks are measured using gps from 1994 to 2003 surface creep observations and estimates of deep slip rates determined from characteristic repeating earthquake sequences are also incorporated in the inversion the fault is discretized into 283 triangular dislocation elements that approximate the nonplanar attributes of the fault surface south of the city of hayward a steeply east dipping fault geometry accommodates the divergence of the surface trace and the microseismicity at depth the inferred slip rate distribution is consistent with a fault that creeps aseismically at a rate of 5 mm yr to a depth of 4 6 km the interferometric synthetic aperture radar insar data require an aseismic slip rate that approaches the geologic slip rate on the northernmost fault segment beneath point pinole although the insar data might be complicated by a small dip slip component at this location a low slip rate patch of 1 mm yr is inferred beneath san leandro consistent with the source location of the 1868 earthquake we calculate that the entire fault is accumulating a slip rate deficit equivalent to a mw 6 77 0 05 per century however this estimate of potential coseismic moment represents an upper bound because we do not know how much of the accumulated strain will be released through aseismic processes such as afterslip

slip rates and spatially variable creep on faults of the northern san andreas system inferred through bayesian inversion of global positioning system data fault creep depending on its rate and spatial extent is thought to reduce earthquake hazard by releasing tectonic strain aseismically we use bayesian inversion and a newly expanded gps data set to infer the deep slip rates below assigned locking depths on the san andreas maacama and bartlett springs faults of northern california and for the latter two the spatially variable interseismic creep rate above the locking depth we estimate deep slip rates of 21 5 0 5 13 1 0 8 and 7 5 0 7 mm yr below 16 km 9 km and 13 km on the san andreas maacama and bartlett springs faults respectively we infer that on average the bartlett springs fault creeps from the earth s surface to 13 km depth and below 5 km the creep rate approaches the deep slip rate this implies that microseismicity may extend below the locking depth however we cannot rule out the presence of locked patches in the seismogenic zone that could generate moderate earthquakes our estimated maacama creep rate while comparable to the inferred deep slip rate at the earth s surface decreases with depth implying a slip deficit exists the maacama deep slip rate estimate 13 1 mm yr exceeds long term geologic slip rate estimates perhaps due to distributed off fault strain or the presence of multiple active fault strands while our creep rate estimates are relatively insensitive to choice of model locking depth insufficient independent information regarding locking depths is a source of epistemic uncertainty that impacts deep slip rate estimates

stress modulation on the san andreas fault by interseismic fault system interactions during the interseismic phase of the earthquake cycle between large earthquakes stress on faults evolves in response to elastic strain accumulation driven by tectonic plate motions because earthquake cycle processes induce non local stress changes the interseismic stress accumulation rate on one fault is influenced by the behavior of all nearby faults using a geodetically constrained block model we show that the total interseismic elastic strain field generated by fault interactions within southern california may increase stressing rates on the mojave and san bernardino sections of the san andreas fault within the big bend region by as much as 38 relative to estimates from isolated san andreas models assuming steady fault system behavior since the c e 1857 fort tejon earthquake shear stress accumulated on these sections due only to interaction with faults other than the san andreas reaches 1 mpa 3 times larger than the coseismic and postseismic stress changes induced by recent southern california earthquakes stress increases along big bend sections coincide with the greatest earthquake frequency inferred from a 1500 yr long paleoseismic record and may affect earthquake recurrence intervals within geometrically complex fault systems including the sections of the san andreas fault closest to metropolitan los angeles

creep and quakes on the northern transition zone of the san andreas fault from gps and insar data 1 the san juan bautista sjb segment forms the northern transition zone of the creeping section of the san andreas fault it is an area of moderate seismicity the largest instrumentally recorded earthquakes have been m5 5 however historic records suggest six m 6 earthquakes occurred near the sjb segment between 1840 and 1899 it is also an area that has experienced several slow earthquakes we perform a joint inversion of gps and insar data to determine the current rate and distribution of interseismic creep we find two low slip locked segments at mid seismogenic depths that may represent source regions for the 19th century earthquakes we find that the sjb segment is currently accumulating strain energy at the rate of one m6 3 6 7 earthquake per century at this rate the 1840 1899 sequence released 135 510 years of accumulated moment deficit

aseismic slip and seismogenic coupling along the central san andreas fault we use high resolution synthetic aperture radar and gps derived observations of surface displacements to derive the first probabilistic estimates of fault coupling along the creeping section of the san andreas fault in between the terminations of the 1857 and 1906 magnitude 7 9 earthquakes using a fully bayesian approach enables unequaled resolution and allows us to infer a high probability of significant fault locking along the creeping section the inferred discreet locked asperities are consistent with evidence for magnitude 6 earthquakes over the past century in this area and may be associated with the initiation phase of the 1857 earthquake as creeping segments may be related to the initiation and termination of seismic ruptures such distribution of locked and creeping asperities highlights the central role of the creeping section on the occurrence of major earthquakes along the san andreas fault

block modeling of crustal deformation of the northern walker lane and basin and range from gps velocities 1 we infer rates of crustal deformation in the northern walker lane nwl and western basin and range using data from the mobile array of gps for nevada transtension and other continuous gps networks including the earthscope plate boundary observatory we present 224 new gps velocities correct them for the effects of viscoelastic postseismic relaxation and use them to constrain a block model to estimate fault slip rates the data segregate the nwl into domains based on differences in deformation rate pattern and style deformation is transtensional with highest rates near the western and eastern edges of the nwl some basins e g tahoe experience shear deformation and extension normal slip is distributed throughout the nwl and basin and range where 11 subparallel range bounding normal fault systems have an average horizontal extension rate of 0 1 mm yr comparison between geologic and geodetic slip rates indicates that out of 12 published geologic rates 10 agree with geodetic rates to within uncertainties this suggests that smaller crustal blocks move steadily similar to larger lithospheric plates and that geodetic measurements of slip rates are reliable in zones of complex crustal deformation for the two slip rates that disagree geologic rates are greater the vertical axis rotation rate of the carson domain is 1 3 0 1 my clockwise lower than the 3 to 6 my obtained in paleomagnetic measurements this suggests that vertical axis rotation rates may have decreased over the last 9 13 my as the role of faulting has increased at the expense of rigid rotations

paleoseismology and global positioning system earthquake cycle effects and geodetic versus geologic fault slip rates in the eastern california shear zone published slip rates for the owens valley fault zone in eastern california based on geodetic data and elastic half space models 5 7 mm yr are faster than longer term geologic rates 2 3 mm yr we use global positioning system data spanning the central owens valley a more realistic rheological model with an elastic upper crust over a viscoelastic lower crust and upper mantle and paleoseismic data from adjacent faults to show that this difference could reflect earthquake cycle effects we estimate a long term rate 2 1 0 7 mm yr and earthquake recurrence interval 2750 350 1000 yr from the geodetic data both in agreement with independent geologic estimates

geodetic slip rates in the southern san andreas fault system effects of elastic heterogeneity and fault geometry 1 we use high resolution interferometric synthetic aperture radar and gps measurements of crustal motion across the southern san andreas fault system to investigate the effects of elastic heterogeneity and fault geometry on inferred slip rates and locking depths geodetically measured strain rates are asymmetric with respect to the mapped traces of both the southern san andreas and san jacinto faults two possibilities have been proposed to explain this observation large contrasts in crustal rigidity across the faults or an alternate fault geometry such as a dipping san andreas fault or a blind segment of the san jacinto fault we evaluate these possibilities using a two dimensional elastic model accounting for heterogeneous structure computed from the southern california earthquake center crustal velocity model cvm h 6 3 the results demonstrate that moderate variations in elastic properties of the crust do not produce a significant strain rate asymmetry and have only a minor effect on the inferred slip rates however we find that small changes in the location of faults at depth can strongly impact the results our preferred model includes a san andreas fault dipping northeast at 60 and two active branches of the san jacinto fault zone in this case we infer nearly equal slip rates of 18 1 and 19 2mm yr for the san andreas and san jacinto fault zones respectively these values are in good agreement with geologic measurements representing average slip rates over the last 10 10 years implying steady long term motion on these faults

clustering of velocities in a gps network spanning the sierra nevada block the northern walker lane belt and the central nevada seismic belt california nevada 1 the deformation across the sierra nevada block the walker lane belt and the central nevada seismic belt cnsb between 38 5 n and 40 5 n has been analyzed by clustering gps velocities to identify coherent blocks cluster analysis determines the number of clusters required and assigns the gps stations to the proper clusters the clusters are shown on a fault map by symbols located at the positions of the gps stations each symbol representing the cluster to which the velocity of that gps station belongs fault systems that separate the clusters are readily identified on such a map four significant clusters are identified those clusters are strips separated by from west to east the mohawk valley genoa fault system the pyramid lake wassuk fault system and the central nevada seismic belt the strain rates within the westernmost three clusters approximate simple right lateral shear 13 nstrain a across vertical planes roughly parallel to the cluster boundaries clustering does not recognize the longitudinal segmentation of the walker lane belt into domains dominated by either northwesterly trending right lateral faults or northeasterly trending left lateral faults

interseismic coupling and refined earthquake potential on the hayward calaveras fault zone interseismic strain accumulation and fault creep is usually estimated from gps and alignment arrays data which provide precise but spatially sparse measurements here we use interferometric synthetic aperture radar to resolve the interseismic deformation associated with the hayward and calaveras faults hf and cf in the east san francisco bay area the large 1992 2011 sar data set permits evaluation of short and long wavelength deformation larger than 2 mm yr without alignment of the velocity field to a gps based model our time series approach in which the interferogram selection is based on the spatial coherence enables deformation mapping in vegetated areas and leads to refined estimates of along fault surface creep rates creep rates vary from 0 2 mm yr on the northern cf to 14 2 mm yr on the central cf south of the hf surface junction we estimate the long term slip rates by inverting the long wavelength deformation and the distribution of shallow slip due to creep by inverting the remaining velocity field this distribution of slip reveals the locations of locked and slowly creeping patches with potential for a m6 8 0 3 on the hf near san leandro a m6 6 0 2 on the northern cf near dublin a m6 5 0 1 on the hf south of fremont and a m6 2 0 2 on the central cf near morgan hill with cascading multisegment ruptures the hf rupturing from berkeley to the cf junction could produce a m6 9 0 1 the northern cf a m6 6 0 1 the central cf a m6 9 0 2 from the junction to gilroy and a joint rupture of the hf and central cf could produce a m7 1 0 1

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

the dynamics of circulations within the trailing stratiform regions of squall lines part i the 10 11 june pre storm system abstract a dynamic version of the two dimensional kinematic cloud model of rutledge and houze has been developed to investigate the effects of microphysics on circulations within the stratiform regions of mesoscale convective systems the design of the model allows for specified inputs of hydrometeors water vapor and heat from the convective line the stratiform region of the 10 11 june 1985 pre storm squall line is simulated with initialization based upon appropriate soundings heat budgets and id cumulonimbus model results the model accurately simulates the evolution of the stratiform rain area significant ascent occurs in the stratiform region where in situ condensate production contributes increasingly to the surface rainfall reaching 65 of the total in the mature stage and averaging 44 over the entire simulation the ratio of condensate produced within the mesoscale updraft to that advected from the convective line generally agrees with water budgets from other studies simulated horizontal

influence of fault connectivity on slip rates in southern california potential impact on discrepancies between geodetic derived and geologic slip rates along the san bernardino strand of the san andreas fault saf and across the eastern california shear zone ecsz geologic slip rates differ from those inverted from geodetic measurements which may partly be due to inaccurate fault connectivity within geodetic models we employ three dimensional models that are mechanically compatible with long term plate motion to simulate both fault slip rates and interseismic surface deformation we compare results from fault networks that follow mapped geologic traces and resemble those used in block model inversions which connect the san jacinto fault to the saf near cajon pass and connect distinct faults within the ecsz the connection of the saf with the san jacinto fault decreases strike slip rates along the saf by up to 10 and increases strike slip rates along the san jacinto fault by up to 16 however slip rate changes are still within the large geologic ranges along the saf the insensitivity of interseismic surface velocities near cajon pass to fault connection suggests that inverse models may utilize both an incorrect fault geometry and slip rate and still provide an excellent fit to interseismic geodetic data similarly connection of faults within the ecsz produces 36 greater cumulative strike slip rates but less than 17 increase in interseismic velocity when using overconnected models to invert gps for slip rates the reduced off fault deformation within the models can lead to overprediction of slip rates while the nature of fault intersections at depth remains enigmatic fault geometries should be chosen with caution in crustal deformation models

distribution of interseismic slip rates and the potential for significant earthquakes on the calaveras fault central california 1 the calaveras fault is a major component of the san andreas fault system in the san francisco bay area that generated 13 earthquakes of ml 5 since 1850 in most recent ml 5 events premain shock and postmain shock microseismicity is sparse in the region of coseismic slip these aseismic areas are believed to represent locked patches of the fault that are accumulating strain to be released in ml 5 events we analyze geodetic data to better characterize the spatial distribution of interseismic slip rates on the calaveras fault modeling the slip distribution in the seismogenic zone by inversion of over 25 years of surface deformation data we use a regional fault model with the seismogenic zone of the calaveras fault discretized into 6 km 3 km elements employing a weighted least squares approach with smoothing and positivity constraints our discretized fault slip model consistently identifies regions of slip deficit in the seismogenic zone of the calaveras fault that generally correspond to regions of decreased microseismicity and ruptures of previous moderate earthquakes in particular we find correspondence with the 1979 coyote lake and 1984 morgan hill events as well as regions where historical earthquakes on the coyote and the sunol san ramon segments have occurred moment magnitude calculations based on the estimated slip deficit fault area and recurrence intervals agree with measured magnitudes of modern events and interpreted historical magnitudes the results suggest that a combination of geodetically derived fault slip models and microseismicity distribution can be used to characterize seismic hazard

locking depths estimated from geodesy and seismology along the san andreas fault system implications for seismic moment release 1 the depth of the seismogenic zone is a critical parameter for earthquake hazard models independent observations from seismology and geodesy can provide insight into the depths of faulting but these depths do not always agree here we inspect variations in fault depths of 12 segments of the southern san andreas fault system derived from over 1000 gps velocities and 66 000 relocated earthquake hypocenters geodetically determined locking depths range from 6 to 22 km while seismogenic thicknesses are largely limited to depths of 11 20km theseseismogenicdepthsbestmatchthegeodeticlockingdepthswhenestimated at the 95 cutoff depth in seismicity and most fault segment depths agree to within 2 km however the imperial coyote creek and borrego segments have significant discrepancies in these cases the geodetically inferred locking depths are much shallower than the seismogenic depths we also examine variations in seismic moment accumulation rate per unit fault length as suggested by seismicity and geodesy and find that both approaches yield high rates 1 5 1 8 1 0 13 nm yr km along the mojave and carrizo segments and low rates 0 2 10 13 nm yr km along several san jacinto segments the largest difference in seismic moment between models is calculated for the imperial segment where the moment rate from seismic depths is a factor of 2 5 larger than that from geodetic depths such variability has important implications for the accuracy to which future major earthquake magnitudes can be estimated

is there a discrepancy between geological and geodetic slip rates along the san andreas fault system previous inversions for slip rate along the san andreas fault system safs based on elastic half space models show a discrepancy between the geologic and geodetic slip rates along a few major fault segments in this study we use an earthquake cycle model representing an elastic plate over a viscoelastic half space to demonstrate that there is no significant discrepancy between long term geologic and geodetic slip rates the california statewide model includes 41 major fault segments having steady slip from the base of the locked zone to the base of the elastic plate and episodic shallow slip based on known historical ruptures and geologic recurrence intervals the slip rates are constrained by 1981 secular velocity measurements from gps and l band intereferometric synthetic aperture radar a model with a thick elastic layer 60 km and half space viscosity of 1019pa s is preferred because it produces the smallest misfit to both the geologic and the geodetic data we find that the geodetic slip rates from the thick plate model agrees to within the bounds of the geologic slip rates while the rates from the elastic half space model disagree on specific important fault segments such as the mojave and the north coast segment of the san andreas fault the viscoelastic earthquake cycle models have generally higher slip rates than the half space model because most of the faults along the safs are late in the earthquake cycle so today they are moving slower than the long term cycle averaged velocity as governed by the viscoelastic relaxation process

aseismic slip and fault normal strain along the central creeping section of the san andreas fault 1 we use gps data to measure the aseismic slip along the central san andreas fault csaf and the deformation across adjacent faults comparison of edm and gps data sets implies that except for small scale transients the fault motion has been steady over the last 40 years we add 42 new gps velocities along the csaf to constrain the regional strain distribution shear strain rates are less than 0 083 0 010 strain yr adjacent to the creeping saf with 1 4 5 mm yr of contraction across the coast ranges dislocation modeling of the data gives a deep long term slip rate of 31 35 mm yr and a shallow 0 12 km creep rate of 28 mm yr along the central portion of the csaf consistent with surface creep measurements the lower shallow slip rate may be due to the effect of partial locking along the csaf or reflect reduced creep rates late in the earthquake cycle of the adjoining saf rupture zones

resolving vertical tectonics in the san francisco bay area from permanent scatterer insar and gps analysis using a combination of gps measured horizontal velocities of 200 sites and 115 487 range change rates determined with the permanent scatterer interferometric synthetic aperture radar insar method in the san francisco bay area we resolve vertical motions in the region at sub mm yr precision the highest displacement rates are due to nontectonic processes such as active landslides subsidence and rebound over aquifers and rapid settling of unconsolidated sediments along the bay margins residual displacement rates are determined by removing the contribution of the gps derived horizontal velocity field from the insar range change rates to isolate vertical tectonic rates we use only those insar measurements made on material that was not quaternary substrate which is susceptible to nontectonic and seasonally varying ground motions the insar residuals indicate significant uplift over the southern foothills of the active mount diablo anticlinorium the mission hills stepover region of the hayward and calaveras faults and the central and southern santa cruz mountains located along a restraining bend of the san andreas fault

geodetic constraints on san francisco bay area fault slip rates and potential seismogenic asperities on the partially creeping hayward fault 1 the hayward fault in the san francisco bay area sfba is sometimes considered unusual among continental faults for exhibiting significant aseismic creep during the interseismic phase of the seismic cycle while also generating sufficient elastic strain to produce major earthquakes imaging the spatial variation in interseismic fault creep on the hayward fault is complicated because of the interseismic strain accumulation associated with nearby faults in the sfba where the relative motion between the pacific plate and the sierra block is partitioned across closely spaced subparallel faults to estimate spatially variable creep on the hayward fault we interpret geodetic observations with a three dimensional kinematically consistent block model of the sfba fault system resolution tests reveal that creep rate variations with a length scale of 15 km are poorly resolved below 7 km depth in addition creep at depth may be sensitive to assumptions about the kinematic consistency of fault slip rate models differential microplate motions result in a slip rate of 6 7 0 8 mm yr on the hayward fault and we image along strike variations in slip deficit rate at 15 km length scales shallower than 7 km depth similar to previous studies we identify a strongly coupled asperity with a slip deficit rate of up to 4 mm yr on the central hayward fault that is spatially correlated with the mapped surface trace of the 1868 mw 6 9 7 0 hayward earthquake and adjacent to gabbroic fault surfaces

strain accumulation across the carrizo segment of the san andreas fault california impact of laterally varying crustal properties 1 major strike slip faults juxtapose geologically dissimilar terrain which may vary in mechanical properties leading to an asymmetric pattern of strain accumulation we present new gps data on the carrizo segment of the san andreas fault separating the salinian block southwest of the fault from franciscan terrane northeast of the fault to better quantify asymmetric strain accumulation we also present a series of finite element models to investigate the possible role of variable elastic layer thickness and material properties of the upper crust the geodetic data are well fit with a simple model comprising a weak upper crustal zone 10 25 km wide northeast of the fault this model is also consistent with geologic data on the distribution of major rock types and corresponding laboratory data on their material properties as well as paleoseismic seismic and magnetotelluric data using this model we estimate a long term average over several seismic cycles slip rate for the san andreas fault of 36 1 5 2 mm yr in agreement with the known holocene rate within uncertainties and a viscosity for the combined lower crust upper mantle of 2 5 1019 pa s

long term fault slip rates distributed deformation rates and forecast of seismicity in the western united states from joint fitting of community geologic geodetic and stress direction data sets 1 the long term average velocity field of the western united states is computed with a kinematic finite element code community data sets include fault traces geologic offset rates geodetic velocities principal stress directions and euler poles there is an irreducible minimum amount of distributed permanent deformation which accommodates one third of pacific north america relative motion in california much of this may be due to slip on faults not included in the model all data sets are fit at a common rms level of 1 8 datum standard deviations experiments with alternate weights fault sets and euler poles define a suite of acceptable community models in pseudoprospective tests fault offset rates are compared to 126 additional published rates not used in the computation 44 are consistent another 48 have discrepancies under 1 mm a 1 and 8 have larger discrepancies updated models are then computed novel predictions include dextral slip at 2 3 mm a 1 in the brothers fault zone two alternative solutions for the mendocino triple junction slower slip on some trains of the san andreas fault than in recent hazard models and clockwise rotation of some domains in the eastern california shear zone long term seismicity is computed by assigning each fault and finite element the seismicity parameters coupled thickness corner magnitude and spectral slope of the most comparable type of plate boundary this long term seismicity forecast is retrospectively compared to instrumental seismicity the western united states has been 37 below its long term average seismicity during 1977 2008 primarily because of temporary reduced activity in the cascadia subduction zone and san andreas fault system

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

response of deep sea benthic foraminifera to late quaternary climate changes southeast indian ocean offshore western australia the late quaternary benthic foraminifera of four deep sea cores off western australia odp 122 760a odp122 762b bmr96gc21 and rc9 150 have been examined for evidence of increased surface productivity to explain the anomalously low sea surface paleotemperatures inferred by planktic foraminifera for the last and penultimate glaciations the 13c trends ofcibicidoides wuellerstorfi and differences between the 13c trends of planktics globigerinoides sacculifer and benthicsc wuellerstorfi in the four cores indicate that during stage 6 bottom waters were significantly depleted in 13c and strong 13c gradients were established in the water column while during stage 2 and the last glacial maximum 13c trends did not differ greatly from that of the holocene two main assemblages of benthic foraminifera were identified by principal component analyses one dominated byuvigerina peregrina another dominated byu proboscidea abundance of these uvigerinids and of taxa preferring an infaunal microhabitat and ofepistominella exigua andbulimina aculeata indicate that episodes of high influx of particulate organic matter were established in most sites during glacial episodes and particularly so during stage 6 while evidence for upwelling during the last glacial maximum is less strong the penultimate glaciation upwellings were established within the areas of low sea surface paleotemperature indicated by planktic foraminifera during the last interglacial climax upwelling appears to have been established in an isolated region offshore from a strengthened leeuwin current off north west cape last glacial maximum 13c values ofc wuellerstorfi at waterdepths of less than 2000 m show smaller than global mean glacial interglacial changes suggesting the development of a deep hydrological front a similar vertical stratification bathyal front was also established during the penultimate glaciation

fault network modeling of crustal deformation in california constrained using gps and geologic observations abstract we have developed a kinematic fault network model of crustal deformation in an elastic half space surface deformation is calculated using this model assuming each fault segment slipping beneath a locking depth each fault segment connects to its adjacent elements with slip vector continuity imposed at fault nodes or intersections the degree of the constraints determines whether deformation is block like or not we apply this model to invert gps observations for slip rates on major faults in california with geological rate constraints based on the f test result we find that lesser block like models fit the data significantly better than the strictly block like model our final inversion shows a slip rate varying from 20 to 23 mm yr along the northern san andreas from the santa cruz to the north coast segment slip rates vary from 9 to 13 mm yr along the hayward to the maacama fault segment and from 15 to 3 mm yr along the central calaveras to the west napa fault segment for the central california creeping zone the result suggests a depth dependent creep rate with an average of 22 mm yr over the top 5 km and 32 mm yr underneath from the mojave to san bernardino mountain segments we also find a significant decrease in slip rate along the san andreas in comparison with the geologic rates in contrast to a significant increase in slip rate on faults along the eastern california shear zone along the southern san andreas slip rates vary from 21 to 25 mm yr from the coachella valley to imperial valley segments slip rates range from 0 to 3 mm yr across the western transverse ranges faults which is consistent with the regional crustal thickening overall slip rates derived from geodetic observations correlate strongly with the geologic slip rates statistically suggesting high compatibility between geodetic and geologic observations

inference of multiple earthquake cycle relaxation timescales from irregular geodetic sampling of interseismic deformation abstract characterizing surface deformation throughout a full earthquake cycle is a challenge due to the lack of high resolution geodetic observations of duration comparable to that of characteristic earthquake recurrence intervals 250 10 000 years here we approach this problem by comparing long term geologic slip rates with geodetically derived fault slip rates by sampling only a short fraction 0 001 0 1 of a complete earthquake cycle along 15 continental strike slip faults geodetic observations provide snapshots of surface deformation from different times through the earthquake cycle the timing of the last earthquake on many of these faults is poorly known and may vary greatly from fault to fault assuming that the underlying mechanics of the seismic cycle are similar for all faults geodetic observations from different faults may be interpreted as samples over a significantly larger fraction of the earthquake cycle than could be obtained from the geodetic record along any one fault alone as an ensemble we find that geologically and geodetically inferred slip rates agree well with a linear relation of 0 94 0 09 to simultaneously explain both the ensemble agreement between geologic and geodetic slip rate estimates with observations of rapid postseismic deformation we consider the predictions from simple two layer earthquake cycle models with both maxwell and burgers viscoelastic rheologies we find that a two layer burgers model with two relaxation timescales is consistent with observations of deformation throughout the earthquake cycle whereas the widely used two layer maxwell model with a single relaxation timescale is not suggesting that the earthquake cycle is effectively characterized by a largely stress recoverable rapid postseismic stage and a much more slowly varying interseismic stage

extremal bounds on earthquake movement from geodetic data application to the landers earthquake we present a technique to place quantifiable bounds on the moment of an earthquake from geodetic data assuming known fault geometry application of this technique to the 1992 landers earthquake shows that the moment must have been between 0 84 and 1 15 10 20 nm with 90 confidence m 7 25 to 7 34 we also find that to satisfy the data to this same level of confidence the slip on the fault must have exceeded 7 m in at least one location in good agreement with field mapping of the surface rupture

fault coupling and potential for earthquakes on the creeping section of the central san andreas fault the 150 km long central section of the san andreas fault csaf in central california creeps at the surface and has not produced a large earthquake historically however sections of the san andreas fault to the north and south are known to have ruptured repeatedly in m 7 8 earthquakes it is currently unclear whether the creeping csaf could rupture in large earthquakes either individually or along with earthquakes on the locked sections to the north and south we invert global positioning system and interferometric synthetic aperture radar data with elastic block models to estimate the degree of locking on the csaf and place bounds on the moment accumulation rate on the fault we find that the inferred moment accumulation rate is highly dependent on the long term fault slip rate which is poorly constrained along the csaf the inferred moment accumulation rate normalized by shear modulus ranges from 3 28 104 to 5 85 107 m3 yr which is equivalent to a mw 5 5 7 2 earthquake every 150 years for a long term slip rate of 26 mm yr and mw 7 3 7 65 for a long term slip rate of 34 mm yr the comparisons of slip distributions with microseismicity and repeating earthquakes indicate a possible locked patch between 10 and 20 km depth on the csaf that could potentially rupture with mw 6 5

crustal deformation across the sierra nevada northern walker lane basin and range transition western united states measured with gps 2000 2004 1 global positioning system gps data collected in campaigns in 2000 and 2004 were processed and interpreted with other gps data in the western basin and range province to provide new constraints on the rate style and pattern of deformation of the central and northern walker lane wl which lies near the western boundary of the basin and range across the central wl near 38n latitude the velocities with respect to north america increase westward by 10 mm yr inducing dextral shear farther north between 40 and 41n latitude a western zone of 7 mm yr relative motion undergoes dextral shear and an eastern zone of 3 mm yr relative motion undergoes extension and shear these data show that the northern wl is essentially a dextral shear zone experiencing minor net dilatation ed 2 6 0 8 nstrain yr near most holocene normal faults dilatation inferred from the velocity field is not greater than the uncertainties however near the central nevada seismic belt we detect significant dilatation expressed as extension in a direction approximately normal to the range fronts ed 23 0 3 9 nstrain yr some of which is attributable to transient postseismic deformation following large historic earthquakes a block model constrained by velocities corrected for transient effects shows that the sum of dextral slip rates across the honey lake warm springs east pyramid fault system and mohawk valley faults is 7 mm yr the wl is a zone whose width and dilatation rate increase northwestward consistent with counterclockwise rotation of the sierra nevada microplate and transfer of deformation into the pacific northwest

kinematic modeling of fault slip rates using new geodetic velocities from a transect across the pacific north america plate boundary through the san bernardino mountains california 2015 american geophysical union all rights reserved campaign gps data collected from 2002 to 2014 result in 41 new site velocities from the san bernardino mountains and vicinity we combined these velocities with 93 continuous gps velocities and 216 published velocities to obtain a velocity profile across the pacific north america plate boundary through the san bernardino mountains we modeled the plate boundary parallel horizontal deformation with 5 14 parallel and one obliquely oriented screw dislocations within an elastic half space our rate for the san bernardino strand of the san andreas fault 6 5 3 6mm yr is consistent with recently published latest quaternary rates at the 95 confidence level and is slower than our rate for the san jacinto fault 14 1 2 9mm yr our modeled rate for all faults of the eastern california shear zone ecsz combined 15 7 2 9mm yr is faster than the summed latest quaternary rates for these faults even when an estimate of permanent off fault deformation is included the rate discrepancy is concentrated on faults near the 1992 landers and 1999 hector mine earthquakes the geodetic and geologic rates agree within uncertainties for other faults within the ecsz coupled with the observation that postearthquake deformation is faster than the pre 1992 deformation this suggests that the ecsz geodetic geologic rate discrepancy is directly related to the timing and location of these earthquakes and is likely the result of viscoelastic deformation in the mantle that varies over the timescale of an earthquake cycle rather than a redistribution of plate boundary slip at a timescale of multiple earthquake cycles or longer

slicing up the san francisco bay area block kinematics and fault slip rates from gps derived surface velocities received 26 october 2004 revised 11 february 2005 accepted 10 march 2005 published 16 june 2005 i observations of surface deformation allow us to determine the kinematics of faults in the san francisco bay area we present the bay area velocity unification bavu bay view a compilation of over 200 horizontal surface velocities computed from campaign style and continuous global positioning system gps observations from 1993 to 2003 we interpret this interseismic velocity field using a three dimensional block model to determine the relative contributions of block motion elastic strain accumulation and shallow aseismic creep the total relative motion between the pacific plate and the rigid sierra nevada great valley sngv microplate is 37 9 0 6 mm yr 1 directed toward n30 4 w 0 8 at san francisco 2 fault slip rates from our preferred model are typically within the error bounds of geologic estimates but provide a better fit to geodetic data notable right lateral slip rates in mm yr 1 san gregorio fault 2 4 1 0 west napa fault 4 0 3 0 zone of faulting along the eastern margin of the coast range 5 4 1 0 and mount diablo thrust 3 9 1 0 of reverse slip and 4 0 0 2 of right lateral strike slip slip on the northern calaveras is partitioned between both the west napa and concord green valley fault systems the total convergence across the bay area is negligible poles of rotation for bay area blocks progress systematically from the north america pacific to north america sngv poles the resulting present day relative motion cannot explain the strike of most bay area faults but fault strike does loosely correlate with inferred plate motions at the time each fault initiated

spatial variations in slip deficit on the central san andreas fault from insar summary we use ers insar measurements to record spatial variations in creep rate along the creeping segment of the san andreas fault saf california between 1992 and 2001 inversion of geodetic data yields a slip rate distribution along the creeping segment which is used for firstorder moment release and deficit calculations we present a time averaged spatial picture of surface deformation and associated subsurface creep an interferometric stack is constructed from 12 interferograms that show good coherence for the decade of observation the total right lateral offset spanned by the data is 34 mm yr 1 along most of the length of the creeping segment this offset occurs within a narrow 2 km zone close to the fault trace in the northern part a minor part of the offset is taken up by the nearby calaveras paicines fault in general the observed rates of surface creep are consistent with those obtained by several other studies for a longer and or earlier period of time using different geodetic methods this suggests that the average creep rate has been constant over a period of almost four decades a joint gps insar inversion implies that the shallow creep rate is variable along strike reaching up to 31 5 1m m yr 1 in the central section of the creeping segment tapering off along strike to the south and becoming partitioned across two subparallel faults in the north the deep slip rate beneath the seismogenic layer is 33 3m m yr 1 the difference between shallow and deep slip rates suggests that there is a shallow slip deficit on the creeping segment of the saf csaf moment release rate due to aseismic slip is approximately three orders of magnitude greater than seismic moment release the annual creep on the csaf is equivalent to the moment released in a m 6 earthquake the equivalent moment of the slip deficit relative to the deep slip rate is between 4 1 10 17 and 8 4 10 17 nm yr 1 which is equivalent to a magnitude 5 7 5 9 earthquake over a 150 yr period the deficit is equivalent to a m 7 2 7 4 earthquake this slip deficit may be compensated by intermittent moderate sized events or by accelerated afterslip following large events on nearby fault segments