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

dynamics of izmit earthquake postseismic deformation and loading of the duzce earthquake hypocenter we have developed dynamic finite element models of izmit earthquake postseismic deformation to evaluate whether this deformation is better explained by afterslip via either velocity strengthening frictional slip or linear viscous creep or by distributed linear viscoelastic relaxation of the lower crust we find that velocity strengthening frictional afterslip driven by coseismic shear stress loading can reproduce time dependent global positioning system data better than either linear viscous creep on a vertical shear zone below the rupture or lower crustal viscoelastic relaxation our best frictional afterslip model fits the main features of postseismic slip inversions in particular high slip patches at and below the hypocenter and on the western karadere segment and limited afterslip west of the hersek delta burgmann et al 2002 the model requires a weakly velocity strengthening fault that is either low effective normal stress in the slipping regions or a smaller value for the parameter describing rate dependence of friction a b than is indicated by laboratory experiments our best afterslip model suggests that the coulomb stress at the duzce hypocenter increased by 0 14 mpa 1 4 bars during the izmit earthquake assuming right lateral slip on a surface dipping 50 to the north and by another 0 1 mpa during the 87 days between the izmit and duzce earthquakes in the marmara sea region within about 160 km of the izmit earthquake rupture this model indicates that the coulomb stresses increased by 15 25 of the coseismic amount during the first 300 days after the earthquake three hundred days after the earthquake postseismic contributions to coulomb stressing rate on the maramara region faults had fallen to values equal to or less than the inferred secular stress accumulation rate our estimates of postseismic coulomb stress are highly model dependent in the marmara region the linear viscous shear zone and viscoelastic lower crust models predict greater postseismic coulomb stresses than the frictional afterslip model near field stress and fault zone rheology estimates are sensitive to the earth9s elastic structure when a layered elastic structure is incorporated in our model it yields a coulomb stress of 0 24 mpa at the duzce hypocenter significantly more than the 0 14 mpa estimated from the uniform elastic model because of the higher near field coseismic stresses the layered elastic model requires a higher value of velocity strengthening parameter a b a b times effective normal stress r to produce comparable postseismic slip a b is estimated at 0 4 and 0 2 mpa respectively for the layered and uniform elastic models these results highlight the importance of understanding the earth9s elastic structure and the mechanism for postseismic deformation if we wish to accurately model coseismic and postseismic crustal stresses

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

viscoelastic cycle model of interseismic deformation in the northwestern united states summary we apply a viscoelastic cycle model to a compilation of gps velocity fields in order to address the kinematics of deformation in the northwestern united states a viscoelastic cycle model accounts for time dependent deformation following large crustal earthquakes and is an alternative to block models for explaining the interseismic crustal velocity field building on the approach taken in pollitz et al we construct a deformation model for the entire western united states based on combined fault slip and distributed deformation and focus on the implications for the mendocino triple junction mtj cascadia megathrust and western washington we find significant partitioning between strike slip and dip slip motion near the mtj as the tectonic environment shifts from northwest directed shear along the san andreas fault system to east west convergence along the juan de fuca plate by better accounting for the budget of aseismic and seismic slip along the cascadia subduction interface in conjunction with an assumed rheology we revise a previous model of slip for the m 9 1700 cascadia earthquake in western washington we infer slip rates on a number of strike slip and dip slip faults that accommodate northward convergence of the oregon coast block and northwestward convergence of the juan de fuca plate lateral variations in first order mechanical properties e g mantle viscosity vertically averaged rigidity explain to a large extent crustal strain that cannot be rationalized with cyclic deformation on a laterally homogeneous viscoelastic structure our analysis also shows that present crustal deformation measurements particularly with the addition of the plate boundary observatory can constrain such lateral variations

postseismic and interseismic displacements near a strike slip fault a two dimensional theory for general linear viscoelastic rheologies 1 we present an analytic solution for the deformation near an infinite strike slip fault in an elastic layer overlying a linear viscoelastic half space the theory is valid for any linear viscoelastic rheology and any earthquake sequence this is a generalization of the work of j c savage and colleagues which only holds for models with a uniform shear modulus maxwell viscoelastic lower half space and periodic rupture recurrence we demonstrate the theory for models of an elastic layer over a maxwell standard linear solid burgers and triviscous half space for each of these models we calculate example postseismic displacements interseismic displacements in a periodic earthquake sequence and interseismic displacements for a nonperiodic earthquake sequence our solution is for a simple geometry however the model presents an elegant tool to explore the evolution of displacements for relatively complex rheologies and rupture recurrence histories

geodetic slip solutions for the mw 7 4 champerico guatemala earthquake of 2012 november 7 and its postseismic deformation as the first large subduction thrust earthquake off the coast of western guatemala in the past several decades the 2012 november 7 m w 7 4 earthquake offers the first opportunity to study coseismic and postseismic behaviour along a segment of the middle america trench where frictional coupling makes a transition from weak coupling off the coast of el salvador to strong coupling in southern mexico we use measurements at 19 continuous gps sites in guatemala el salvador and mexico to estimate the coseismic slip and postseismic deformation of the november 2012 champerico guatemala earthquake an inversion of the coseismic offsets which range up to 47 mm at the surface near the epicentre indicates that up to 2 m of coseismic slip occurred on a 30 30 km rupture area between 10 and 30 km depth which is near the global cmt centroid the geodetic moment of 13 10 19 n m and corresponding magnitude of 7 4 both agree well with independent seismological estimates transient postseismic deformation that was recorded at 11 gps sites is attributable to a combination of fault afterslip and viscoelastic flow in the lower crust and or mantle modelling of the viscoelastic deformation suggests that it constituted no more than 30 per cent of the short term postseismic deformation gps observations that extend six months after the earthquake are well fit by a model in which most afterslip occurred at the same depth or directly downdip from the rupture zone and released energy equivalent to no more than 20 per cent of the coseismic moment an independent seismological slip solution that features more highly concentrated coseismic slip than our own fits the gps offsets well if its slip centroid is translated 50 km to the west to a position close to our slip centroid the geodetic and seismologic slip solutions thus suggest bounds of 2 7 m for the peak slip along a region of the interface no larger than 30 30 km

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

source parameters for the 1952 kern county earthquake california a joint inversion of leveling and triangulation observations coseismic leveling and triangulation observations are used to determine the faulting geometry and slip distribution of the july 21 1952 mw 7 3 kern county earthquake on the white wolf fault a singular value decomposition inversion is used to assess the ability of the geodetic network to resolve slip along a multisegment fault and shows that the network is sufficient to resolve slip along the surface rupture to a depth of 10 km below 10 km the network can only resolve dip slip near the fault ends the preferred source model is a two segment right stepping fault with a strike of 51 and a dip of 75 sw the epicentral patch has deep 6 27 km left lateral oblique slip while the northeastern patch has shallow 1 12 5 km reverse slip there is nearly uniform reverse slip epicentral 1 6 m northeast 1 9 m with 3 6 m of left lateral strike slip limited to the epicentral patch the seismic moment is m0 9 2 0 5 1019 n m mw 7 2 the signal to noise ratio of the leveling and triangulation data is reduced by 96 and 49 respectively the slip distribution from the preferred model matches regional geomorphic features and may provide a driving mechanism for regional shortening across the comanche thrust and structural continuity with the scodie seismic lineament to the northeast

crustal deformation the earthquake cycle and models of viscoelastic flow in the asthenosphere summary the crustal deformation patterns associated with the earthquake cycle can depend strongly on the rheological properties of subcrustal material substantial deviations from the simple patterns for a uniformly elastic earth are expected when viscoelastic flow of subcrustal material is considered the detailed description of the deformation pattern and in particular the surface displacements displacement rates strains and strain rates depend on the structure and geometry of the material near the seismogenic zone in the past few years various viscoelastic models of crustal deformation have been published these models differ in their predictions concerning the temporal and spatial patterns of crustal deformation in some cases these differences are due to varying choices for the physical mechanism under study in other cases however the differences are the result of the details of the mathematical treatment or the choice of model parameters we seek to resolve the origin of some of these differences by analysing several different linear viscoelastic models with a common finite element computational technique the models involve strike slip faulting and include a thin channel asthenosphere model a model with a varying thickness lithosphere and a model with a viscoelastic inclusion below the brittle slip plane the calculations reveal that the surface deformation pattern is most sensitive to the rheology of the material that lies below the slip plane in a volume whose extent is a few times the fault depth if this material is viscoelastic the surface deformation pattern resembles that of an elastic layer lying over a viscoelastic half space when the thickness or breadth of the viscoelastic material is less than a few times the fault depth then the surface deformation pattern is altered and geodetic measurements are potentially useful for studying the details of subsurface geometry and structure distinguishing among the various models in best accomplished by making geodetic measurements not only near the fault but out to distances equal to several times the fault depth this is where the model differences are greatest these differences will be most readily detected shortly after an earthquake when viscoelastic effects are most pronounced for a thin channel asthenosphere model we have found that the predicted displacements are less than those for a half space asthenosphere this result is contrary to recently published results based on analytical approximations the deficiencies of the latter work result from ignoring material below the asthenosphere and in using thickness averaged deformation parameters although the displacements predicted for a thin channel asthenosphere are less than those for a half space asthenosphere the post seismic strain rates at intermediate distances from the fault are greater in an absolute value sense in the former model

viscoelastic deformation for a clustered earthquake cycle 1 the clustering of earthquakes in time on the same fault affects the rate and pattern of interseismic deformation we develop a simple analytic viscoelastic model of the surface velocity field through a clustered earthquake cycle by superposing the velocities of individual earthquake cycles of constant period but varying phase velocity profiles prior to and after an earthquake show a wider range of behavior than they do for earthquake cycles with constant repeat times these new types of behavior provide possible explanations for discrepancies between geologic estimates of long term fault slip rates and slip rate estimates from geodetic data

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

gps constraints on deformation in northern central america from 1999 to 2017 part 1 time dependent modelling of large regional earthquakes and their post seismic effects we use continuous and campaign measurements from 215 gps sites in northern central america and southern mexico to estimate coseismic and afterslip solutions for the 2009 m w 7 3 swan islands fault strike slip earthquake and the 2012 m w 7 3 el salvador and m w 7 4 guatemala thrust faulting earthquakes on the middle america trench our simultaneous time dependent inversion of more than 350 000 daily gps site positions gives the first jointly consistent estimates of the coseismic slips for all three earthquakes their combined time dependent post seismic effects and secular station velocities corrected for both the co seismic and post seismic deformation our geodetic slip solutions for all three earthquakes agree with previous estimates that were derived via static coseismic offset modelling our time dependent model which attributes all transient post seismic deformation to earthquake afterslip fits nearly all of the continuous gps site position time series within their several millimetre position noise afterslip moments for the three earthquakes range from 35 to 140 per cent of the geodetic coseismic moments with the largest afterslip estimated for the 2012 el salvador earthquake along the weakly coupled el salvador trench segment forward modelling of viscoelastic deformation triggered by all three earthquakes for a range of assumed mantle and lower crustal viscosities suggests that it accounts for under 20 per cent of the observed post seismic deformation and possibly under 10 per cent our results thus point to afterslip as the primary and perhaps dominant mode of post seismic deformation for these c the author s

slip rate of the western garlock fault at clark wash near lone tree canyon mojave desert california the precise tectonic role of the left lateral garlock fault in southern california has been controversial three proposed tectonic models yield significantly different predictions for the slip rate history orientation and total bedrock offset as a function of distance along strike in an effort to test these models we present the first slip rate estimate for the western garlock fault that is constrained by radiocarbon dating a channel referred to here as clark wash incised into a latest pleistocene alluvial fan has been left laterally offset at least 66 6 m and no more than 100 m across the western garlock fault indicating a left lateral slip rate of 7 6 mm yr 95 confidence interval of 5 3 10 7 mm yr using dendrochronologically calibrated radiocarbon dates the timing of aggradational events on the clark wash fan corresponds closely to what has been documented elsewhere in the mojave desert suggesting that much of this activity has been climatically controlled the range front fault located a few hundred meters northwest of the gar lock fault has probably acted primarily as a normal fault with a holocene rate of dip slip of 0 4 0 7 mm yr the record of prehistoric earthquakes on the garlock fault at this site though quite possibly incomplete suggests a longer interseismic interval 1200 2700 yr for the western garlock fault than for the central garlock fault the relatively high slip rate determined here indicates that the western and central segments of the garlock fault show similar rates of movement that are somewhat faster than rates inferred from geodetic data the high rate of motion on the western garlock fault is most consistent with a model in which the western garlock fault acts as a conjugate shear to the san andreas fault other mechanisms involving extension north of the garlock fault and block rotation at the eastern end of the fault may be relevant to the central and eastern sections of the fault but they cannot explain a high rate of slip on the western garlock fault

influence of lithosphere viscosity structure on estimates of fault slip rate in the mojave region of the san andreas fault system 1 it is well known that slip rate estimates from geodetic data are nonunique because they depend on model assumptions and parameters that are often not known a priori estimates of fault slip rate on the mojave segment of the san andreas fault system derived from elastic block models and gps data are significantly lower than estimates from geologic data to determine the extent to which the slip rate discrepancy might be due to the oversimplified models of the rheology of the lithosphere we develop a two dimensional linear maxwell viscoelastic earthquake cycle model and simultaneously estimate fault slip rates and lithosphere viscosity structure in the mojave region the model consists of episodic earthquakes in an elastic crust overlying layers with different viscosities that represent the lower crust uppermost mantle and upper mantle we use gps measurements of postseismic relaxation following the 1992 landers earthquake triangulation measurements spanning 1932 1977 gps measurements of the contemporary velocity field and paleoseismic data along the san andreas fault we infer lower crustal 15 30 km depth viscosity of 1019 10 20 pa s uppermost mantle 30 60 km viscosity of 10 20 22 pa s and underlying upper mantle viscosity of 10 18 10 19 pa s consistent with inferences from laboratory experiments of relatively high viscosity lithospheric mantle and lower viscosity lower crust and underlying asthenospheric mantle we infer a 20 30 mm yr slip rate on the san andreas fault in agreement with the lower end of geologic estimates inversions of geodetic data with models that do not incorporate layered viscosity structure may significantly misestimate slip rates

dynamic models of interseismic deformation and stress transfer from plate motion to continental transform faults thermal regime on geologic timescales 10 6 10 7 years as well as on timescales of the order of the earthquake recurrence 10 2 years strain localization in the viscoelastic medium results from thermomechanical coupling and power law dependence of strain rate on stress for conditions corresponding to the san andreas fault saf the predicted width of the shear zone in the lower crust is 3 5 km this shear zone accommodates more than 50 of the far field plate motion coupled thermomechanical models predict a single layer lithosphere in case of dry composition of the lower crust and upper mantle and a jelly sandwich lithosphere in case of wet composition deviatoric stress in the lithosphere in our models is relatively insensitive to the water content the far field loading rate and the fault strength and is of the order of 10 2 mpa thermomechanical coupling gives rise to an inverse correlation between the fault slip rate and the ductile strength of the lithosphere we show that our models are broadly consistent with geodetic and heat flow constrains from the saf in northern california models suggest that the regionally elevated heat flow around the saf may be at least in part due to viscous dissipation in the ductile part of the lithosphere

can lateral viscosity contrasts explain asymmetric interseismic deformation around strike slip faults abstract geodetic studies have shown that deformation rates around several major strike slip faults are asymmetric this asymmetry is often explained in terms of a crustal scale contrast in elastic properties across the fault motivated by the fact that elasticity variations for different rock types under similar ambient conditions are generally modest whereas effective viscosity may vary over orders of magnitude we have developed earthquake cycle models to evaluate whether contrasts in viscosity structure and effective plate thickness can explain observed asymmetric surface deformation we find that an increased plate thickness contrast results in a more asymmetric surface velocity profile furthermore for the same plate thickness contrast asymmetry of the surface deformation is most pronounced in models with a low viscosity substrate initially velocities relative to a point on the fault are higher on the side with the thin plate however late in the interseismic interval this reverses and these velocities are higher on the side with the thick plate models with a contrast in the substrate viscosity on either side of the fault and a uniform plate thickness show behavior similar to that of the variable thickness plate models in both suites of asymmetric models the surface velocity at the fault varies through the earthquake cycle this is necessary to reconcile symmetric coseismic deformation asymmetric interseismic deformation and the requirement of zero strain in the blocks on either side of the fault over an earthquake cycle given the modest asymmetry in surface deformation for models capable of producing localized interseismic deformation around the fault i e models with high substrate viscosities we conclude that lateral contrasts in viscosity or effective plate thickness cannot produce dramatic asymmetries in global positioning system surface velocity profiles across major strike slip faults

gravitational viscoelastic postseismic relaxation on a layered spherical earth viscoelastic relaxation of a ductile asthenosphere underlying a purely elastic plate is a strong candidate process for explaining anomalous rates of crustal deformation observed following large earthquakes the nongravitational treatment of pollitz 1992 which is valid on a global scale and includes the effects of compressibility is here extended to permit the calculation of gravitational viscoelastic relaxation for a specified spherically layered viscoelastic rheology following an earthquake in an elastic layer the simple approximations we adopt make the resulting treatment particularly suitable for near field calculations for an asthenosphere with a maxwell rheology the effect of gravitational coupling is manifested only many relaxation times after the earthquake as obtained by previous investigators its effect is generally to speed up the long wavelength component of the relaxation process and attenuate the overall vertical displacement pattern several subtle features common to the relaxation behavior from several different fault types thrust rift and strike slip are identified the effect of gravitational coupling on horizontal displacements is consistent with flexure of the upper elastic plate driven by the corresponding effects on the vertical displacement stress diffusion away from the source region generally exhibits pulse like behavior which is dispersive in both space and time if the asthenosphere is confined to a relatively narrow channel then the dispersion branches governing relaxation are radically altered and stress diffusion effects far from the coseismic rupture zone exhibit a complicated time dependence reflecting the competing tendencies of toroidal and spheroidal mode relaxation

slip in the 1857 and earlier large earthquakes along the carrizo plain san andreas fault the moment magnitude mw 7 9 fort tejon earthquake of 1857 with a 350 kilometer long surface rupture was the most recent major earthquake along the south central san andreas fault california based on previous measurements of its surface slip distribution rupture along the 60 kilometer long carrizo segment was thought to control the recurrence of 1857 like earthquakes new high resolution topographic data show that the average slip along the carrizo segment during the 1857 event was 5 3 1 4 meters eliminating the core assumption for a linkage between carrizo segment rupture and recurrence of major earthquakes along the south central san andreas fault earthquake slip along the carrizo segment may recur in earthquake clusters with cumulative slip of 5 meters

a unified analysis of crustal motion in southern california 1970 2004 the scec crustal motion map 1 to determine crustal motions in and around southern california we have processed and combined trilateration data collected from 1970 to 1992 vlbi data from 1979 to 1992 and gps data from 1986 to 2004 a long temporal coverage required in part by the occurrence of several large earthquakes in this region from a series of solutions for station positions we have estimated interseismic velocities coseismic displacements and postseismic motions within the region from 31 n to 38 n and east to 114 w the final product includes estimated horizontal velocities for 1009 gps 190 trilateration and 16 vlbi points with ties between some of these used to stabilize the solution all motions are relative to the stable north american reference frame snarf as realized through the velocities of 20 gps stations this provides a relatively dense set of horizontal velocity estimates with well tested errors for the past quarter century over the plate boundary from 31 n to 36 5 n these velocities agree well with those from the plate boundary observatory which apply to a later time period we also estimated vertical velocities 533 of which have errors below 2 mm yr most of these velocities are less than 1 mm yr but they show 2 4 mm yr subsidence in the ventura and los angeles basins and in the salton trough our analysis also included estimates of coseismic and postseismic motions related to the 1992 landers 1994 northridge 1999 hector mine and 2003 san simeon earthquakes postseismic motions increase logarithmically over time with a time constant of about 10 days and generally mimic the direction and relative amplitude of the coseismic offsets

insights into active tectonics of eastern taiwan from analyses of geodetic and geologic data 1 about 50 mm yr of convergence between the philippine sea and eurasian plates is absorbed in eastern taiwan and it remains unclear how the convergence is partitioned among active faults the longitudinal valley fault lvf the most seismically active fault in eastern taiwan creeps at the surface in the south and not in the north however it is unclear how much of the fault is locked or creeping at depth to address these problems we model holocene and interseismic deformation of elastic lithospheric blocks moving over a viscoelastic asthenosphere in eastern taiwan through a fully probabilistic scheme we invert gps interferometric synthetic aperture radar creepmeter and holocene marine terrace data for block motions fault slip rates and distribution of interseismic creep the data are explained with four blocks separated by three faults central range fault lvf and an offshore fault the model explains the essential features of interseismic and holocene deformation we find that 35 55 mm yr of slip on the offshore fault is necessary to fit marine terrace uplift rates which is a larger fraction of the plate convergence than previously recognized the lvf has a holocene slip rate of 20 30 mm yr with approximately equal magnitudes of reverse slip and left lateral strike slip components only about half of the surface area of the longitudinal valley fault appears to be locked the southern segment of the lvf creeps at a rate of 5 28 mm yr down to a depth of 15 20 km while the northern segment is locked from the surface to a depth of 20 km

reconciling geologic and geodetic model fault slip rate discrepancies in southern california consideration of nonsteady mantle flow and lower crustal fault creep in southern california slip rates derived from geodesy constrained elastic models are lower than geologic rates along the mojave and san bernardino segments of the san andreas fault and the garlock fault in contrast the summed geodetic rate across the mojave eastern california shear zone ecsz is significantly higher than the summed geologic rate we show that geodetic and geologic slip rates in southern california can be reconciled using a viscoelastic earthquake cycle model that explicitly incorporates time dependent deformation due to nonsteady interseismic fault creep in the lower crust and viscous flow in the upper mantle to reconcile geologic and geodetic model rates our model requires that the southern san andreas fault and the garlock fault are in the late stages of the earthquake cycle resulting in lower current deformation rates than the cycle averaged rate our model implies that the ecsz and the san jacinto faults are in the early stages of the earthquake cycle resulting in high current deformation rates

reconciling viscoelastic models of postseismic and interseismic deformation effects of viscous shear zones and finite length ruptures we have developed a suite of earthquake cycle models for strike slip faults to investigate how finite ruptures and lithosphere scale viscous shear zones affect interseismic deformation in particular we assess whether localized and stationary interseismic deformation and large scale rapidly decaying postseismic transients may be explained with models incorporating either or both of these features models incorporating viscous shear zones give more stationary interseismic deformation than layered half space maxwell viscoelastic models producing similar early postseismic deformation in the near field this tendency is accentuated when the effective viscosity per unit width of the shear zone increases either with depth or with interseismic time models with finite 200 km long ruptures produce time dependent deformation similar to that from models with infinitely long ruptures though with smaller magnitude and somewhat more localized surface velocity fluctuations models incorporating a stiff lithosphere a low viscosity mantle asthenosphere and a crust to lithosphere scale viscous shear zone can replicate postseismic and interseismic deformation typical of large strike slip earthquakes such models require depth dependent power law or transient rheologies for the viscous shear zone material in the crust as long as the effective viscosity per unit shear zone width is approximately 1015 pa s m at crustal depths during the postseismic interval below the moho the shear zone effective viscosity per unit width must be higher throughout the seismic cycle at least over a short depth interval for example if shear zone viscosity per unit width is 5 1016 pa s m in the mantle lithosphere a model with a 50 km thick lithosphere and asthenosphere effective viscosities of 1 to 5 1018 pa s can reproduce reference velocity profiles for both postseismic and later interseismic deformation

persistent slip rate discrepancies in the eastern california usa shear zone understanding fault slip rates in the eastern california shear zone ecsz using gps geodesy is complicated by potentially overlapping strain signals due to many sub parallel strike slip faults and by inconsistencies with geologic slip rates the role of fault system geometry in describing ecsz deformation may be investigated with total variation regularization which algorithmically determines a best fitting geometry from an initial model with numerous faults constrained by a western united states gps velocity field the initial dense model 1 enables construction of the first geodetically constrained block model to include all ecsz faults with geologic slip rates allowing direct geologic geodetic slip rate comparisons and 2 permits fault system geometries with many active faults that are analogous to distributed interseismic deformation beginning with 58 ecsz blocks a model containing 10 ecsz blocks is most consistent with geologic slip rates reproducing five of 11 within their reported uncertainties the model fits gps observations with a mean residual velocity of 1 5 mm yr persistent geologic geodetic slip rate discrepancies occur on the calico and garlock faults on which we estimate slip rates of 7 6 mm yr and 2 mm yr respectively indicating that inconsistencies between geology and geodesy may be concentrated on or near these faults and are not due to pervasive distributed deformation in the region discrepancies may in part be due to postseismic relaxation following the a d 1992 mw 7 3 landers and 1999 mw 7 1 hector mine earthquakes otherwise resolving geologic geodetic discrepancies would require as much as 11 4 mm yr of off fault deformation within 10 km of the main ecsz faults with 5 mm yr concentrated near the calico fault

carnivores mammalia carnivora of the urals in the late pleistocene and holocene abstract carnivore assemblages from localities of the late pleistocene and holocene of northern middle and southern urals were studied analysis of species composition of the carnivore fauna was performed for seven chronological periods mis 5e mis 3 mid mis2 lgt late mis 2 baic early mis 1 preboreal boreal mid mis 1 atlantic subboreal late mis 1 subatlantic in the urals changes in carnivore fauna were occurring during the late pleistocene and holocene faunal composition included the species from european siberian and european siberian faunal complexes throughout the late pleistocene and holocene dominated by the species from european siberian faunal complexes the general trend of fauna changes is represented by a decreasing percentage of species from the european faunal complex and an increasing percentage of those from the siberian faunal complex faunal composition has changed due to two main reasons range shifts and extinction sixteen out of 24 species that inhabited the urals during the late pleistocene and holocene underwent range shifts the ranges shifted in different directions reduction increased and fluctuations the ranges of several species have not changed three species became extinct

nonlinear strain buildup and the earthquake cycle on the san andreas fault two contrasting models of the earthquake deformation cycle on strike slip faults predict significant temporal declines in shear strain rate near the fault accompanied by a progressive broadening of the zone of deformation adjacent to it in the thin lithosphere model transient deformation results from flow in the asthenosphere due to stress relaxation following faulting through most or all of the lithosphere for an earth model with a thick elastic lithosphere plate thickness depth of seismic slip transient motions are due to postearthquake aseisrnic slip below the coseismic fault plane data from the san andreas fault indicate a long term temporal decrease in strain rate that persists for at least 30 years and may extend through the entire earthquake cycle observations support a cycle long rate decrease and a temporal spreading of the deformation profile only if movement cycles on the northern and southern locked sections of the fault are basically similar if so the usually lower strain rates and broader deformation zone currently observed on the southern san andreas represent a later evolutionary stage of the northern locked section where a great earthquake is a more recent occurrence although the data allow some extreme models to be discarded no sufficiently strong constraints exist to decide between the thin and thick lithosphere models regardless of the appropriate model the geodetic observations themselves indicate that strain buildup is sufficiently nonlinear to cause significant departures from recurrence estimates based on linear strain accumulation and the time predictable model

origin sedimentary processes and depositional evolution of the agadir turbidite system central eastern atlantic the oligocene to recent agadir turbidite system occurs in the agadir basin abutting against the continental margin off south morocco central eastern atlantic this system is part of the submarine drainage system linking back to the anti and high atlas mountains through the agadir canyon and its sedimentary evolution is shown to comprise lateral shifts of canyon channel overbank and lobe deposits governed by local topography draped palaeorelief seamounts and a contourite ridge and channel avulsions in addition the turbidite system shows an overall retrogradational stacking migrating about 60 km upslope this probably reflects a decrease in gradient on the continental margin gradual basin filling and or a progressive decrease in energy and load of the sediment gravity flows that fed the system the latter change in sediment flux could result from the interplay between the progressive denudation of the source areas together with the climatic change which led to the present arid desertic conditions in the hinterland the seismic features observed with new ultra high resolution seismic tools allow the recognition of the present day sedimentary activity within the agadir turbidite system and this is related among other factors to the active seismicity of the area

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

viscoelastic deformation from north anatolian fault zone earthquakes and the eastern mediterranean gps velocity field 1 we have modeled linear viscoelastic relaxation of a uniform viscosity asthenosphere following large earthquakes in the aegean anatolian region during the 20th century to evaluate whether this process contributes significantly to the regional velocity field we address in particular whether southward motion of the aegean sea region relative to central anatolia and thus extension of western turkey can be attributed to a postseismic strain pulse our models show that postseismic relaxation of a thick 250 km viscoelastic substrate cannot generate the observed extension in western turkey regardless of the choice of viscosity we also find that the asthenosphere viscosity must exceed about 5 1020 pa s at least north of the north anatolian fault zone nafz to be consistent with low gps site velocities in the black sea region and highly localized strain around the fault

localized ductile shear below the seismogenic zone structural analysis of an exhumed strike slip fault austrian alps 1 the miocene salzachtal ennstal mariazell puchberg semp strike slip fault in austria allows study of the internal structure of a fault zone from the near surface to 30 km depth as it enters the tauern window along the rinderkarsee shear zone the semp fault passes from a dominantly brittle to a dominantly ductile structure the shear zone consists of three 1 to 100 m wide zones of brittle ductile and ductile deformation separated by 500 m wide zones of less deformed rocks the southern shear zone is mylonitic with ductile amphibole and plagioclase weak crystal preferred orientations imply that the main deformation mechanism was dislocation accommodated grain boundary sliding the northern and central shear zones are characterized by discrete millimeter wide shear zones with ductile quartz muscovite and biotite and brittle feldspar shear zone nucleation at the grain scale involved dislocation creep and the transformation of plagioclase to muscovite strain then localized in muscovite rich grain boundary shear zones that linked to form throughgoing shear zones

the 1952 kern county california earthquake a case study of issues in the analysis of historical intensity data for estimation of source parameters abstract seismic intensity data based on first hand accounts of shaking give valuable insight into historical and early instrumental earthquakes comparing an observed intensity distribution to intensity prediction models based on modern calibration events allows the magnitude to be estimated for many historic earthquakes magnitude estimates can also potentially be refined for earthquakes for which limited instrumental data are available however the complicated nature of macroseismic data and the methods used to collect and interpret the data introduce significant uncertainties in this paper we illustrate these challenges and possible solutions using the 1952 kern county california earthquake as a case study published estimates of its magnitude vary from mw 7 2 7 5 making it possibly the second largest in california during the 20th century we considered over 1100 first hand reports of shaking supplemented with other data and inferred the magnitude in several ways using intensity prediction equations yielding a preferred intensity magnitude mi 7 2 0 2 where the uncertainty reflects our judgement the revised intensity distribution reveals stronger shaking on the hanging wall south of the surface expression of the white wolf fault than on the footwall characterizing the magnitude and shaking distribution of this early instrumental earthquake can help improve estimation of the seismic hazard of the region such reinterpreted intensities for historic earthquakes combined with u s geological survey usgs did you feel it data for more recent events can be used to produce a uniform shaking dataset with which earthquake hazard map performance can be assessed

new methods for estimating the spatial distribution of locked asperities and stress driven interseismic creep on faults with application to the san francisco bay area california 1 we introduce new forward and inverse methods for inferring long term fault slip rates interseismic fault creep rates and distribution of locked and creeping patches on faults using geodetic and geologic data the forward model consists of fault bounded blocks in an elastic crust overlying a maxwell viscoelastic mantle interseismic elastic distortion of the blocks is modeled due to periodic locking and unlocking of faults throughout the earthquake cycle patches on the fault are assumed to be either locked during the interseismic period or creeping at constant shear stress we utilize a bayesian probabilistic inversion method to infer the posterior probability distribution of long term interseismic fault slip rates distribution of locked and creeping patches and relative weighting of multiple data sets we illustrate the method with an inversion of a synthetic data set we apply the method to estimate fault slip rates and the distribution of interseismic creep on faults in the san francisco bay area ca using gps derived velocities and geologic measurements of fault slip rates we show that the inferred fault slip rates and areas of the locked regions of faults are sensitive to the assumed viscosity of the upper mantle and the timing of past earthquakes and can be significantly different from values inferred from elastic models that do not include viscous flow considering models with different viscosities inferred fault slip rates on major bay area faults can differ by factors of 1 5 4 0 and the inferred moment accumulation rate can differ by factors of 2 13

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

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

strain partitioning along the western margin of north america abstract this paper describes an elastic block model for the interseismic horizontal crustal velocity field occurring in that part of the united states located west of longitude 100 w and between latitudes 31 n and 49 n we developed the model by simultaneously inverting 6873 gps derived velocity vectors and 166 geological fault slip rates for the angular velocities i e the euler poles relative to the north america plate of 46 elastic blocks horizontal strain rate tensors for 38 of these blocks and the spatially variable elastic coupling coefficients on faults that bound adjacent blocks while the model covers all of the western united states located between canada and mexico this paper focuses on the region residing south of cape mendocino where plate boundary deformation is accommodated predominantly by slip on the san andreas fault system block strain rates which account for deformation associated with distributed faults within blocks are systematically higher in blocks located in the western part of the model and adjacent to the plate boundary strain rate magnitudes range from over 10 7 yr for some blocks adjacent to the san andreas fault system to values of about 10 9 yr for blocks located in eastern nevada and western utah blocks adjacent to the san andreas fault system are characterized by strain rate tensors that correspond to uniaxial contraction perpendicular to the local strike of the san andreas the highest rates of fault normal contraction are associated with the northern end of the fault north of san francisco and in the southern end south of los angeles the central san andreas including the creeping segment of the fault is characterized by strain rate tensors more consistent with dextral shear thus the northern and southern ends of the fault are consistent with a transpressional strain partitioning model with strike slip occurring on the san andreas fault system and distributed shortening occurring within the blocks adjacent to this fault system there is no evidence of strain partitioning in the central san andreas

izmit earthquake postseismic deformation and dynamics of the north anatolian fault zone 1 we have modeled postseismic deformation from 1999 to 2003 in the region surrounding the 1999 izmit and duzce earthquake ruptures using a three dimensional viscoelastic finite element method our models confirm earlier findings that surface deformation within the first few months of the izmit earthquake is principally due to stable frictional afterslip on and below the izmit earthquake rupture a second deformation process is required however to fit the surface deformation after several months viscoelastic relaxation of lower crust and or upper mantle with a viscosity of the order of 2 to 5 1019 pa s improves the models fit to later gps site velocities however for a linear viscous rheology this range of values is inconsistent with highly localized interseismic deformation around the north anatolian fault zone nafz that was well observed prior to the earthquake sequence the simplest solution to this problem is to assume that the effective viscosity of the relaxing material increases with time after large earthquakes that is that it has a power law or burger s body transient rheology a burger s body rheology with two characteristic viscosities 2 to 5 1019 pa s and at least 2 1020 pa s in the mantle is consistent with deformation around the nafz throughout the earthquake cycle