a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

dislocation models of interseismic deformation in the western united states 1 the gps derived crustal velocity field of the western united states is used to construct dislocation models in a viscoelastic medium of interseismic crustal deformation the interseismic velocity field is constrained by 1052 gps velocity vectors spanning the 2500 km long plate boundary zone adjacent to the san andreas fault and cascadia subduction zone and extending 1000 km into the plate interior the gps data set is compiled from u s geological survey campaign data plate boundary observatory data and the western u s cordillera velocity field of bennett et al 1999 in the context of viscoelastic cycle models of postearthquake deformation the interseismic velocity field is modeled with a combination of earthquake sources on 100 known faults plus broadly distributed sources models that best explain the observed interseismic velocity field include the contributions of viscoelastic relaxation from faulting near the major plate margins viscoelastic relaxation from distributed faulting in the plate interior as well as lateral variations in depth averaged rigidity in the elastic lithosphere resulting rigidity variations are consistent with reduced effective elastic plate thickness in a zone a few tens of kilometers wide surrounding the san andreas fault saf system primary deformation characteristics are captured along the entire saf system eastern california shear zone walker lane the mendocino triple junction the cascadia margin and the plate interior up to 1000 km from the major plate boundaries

dislocation pileup as a representation of strain accumulation on a strike slip fault 1 the conventional model of strain accumulation on a vertical transform fault is a discrete screw dislocation in an elastic half space with the burgers vector of the dislocation increasing at the rate of relative plate motion it would be more realistic to replace that discrete dislocation by a dislocation distribution presumably a pileup in which the individual dislocations are in equilibrium the length of the pileup depends upon the applied stress and the amount of slip that has occurred at depth i argue here that the dislocation pileup the transition on the fault from no slip to slip at the full plate rate occupies a substantial portion of the lithosphere thickness a discrete dislocation at an adjustable depth can reproduce the surface deformation profile predicted by a pileup so closely that it will be difficult to distinguish between the two models the locking depth dislocation depth of that discrete dislocation approximation is substantially 30 larger than that depth to top of the pileup in the pileup model thus in inverting surface deformation data using the discrete dislocation model the locking depth in the model should not be interpreted as the true locking depth although dislocation pileup models should provide a good explanation of the surface deformation near the fault trace that explanation may not be adequate at greater distances from the fault trace because approximating the expected horizontally distributed deformation at subcrustal depths by uniform slip concentrated on the fault is not justified

inference of postseismic deformation mechanisms of the 1923 kanto earthquake 1 coseismic slip associated with the m7 9 1923 kanto earthquake is fairly well understood involving slip of up to 8 m along the philippine sea honshu interplate boundary under sagami bay and its onland extension postseismic deformation after the 1923 earthquake however is relatively poorly understood we revisit the available deformation data in order to constrain possible mechanisms of postseismic deformation and to examine the consequences for associated stress changes in the surrounding crust data from two leveling lines and one tide gage station over the first 7 8 years postseismic period are of much greater amplitude than the corresponding expected interseismic deformation during the same period making these data suitable for isolating the signal from postseismic deformation we consider both viscoelastic models of asthenosphere relaxation and afterslip models a distributed coseismic slip model presented by pollitz et al 2005 combined with prescribed parameters of a viscoelastic earth model yields predicted postseismic deformation that agrees with observed deformation on mainland honshu from tokyo to the izu peninsula elsewhere southern miura peninsula boso peninsula the considered viscoelastic models fail to predict observed deformation and a model of 1 m shallow afterslip in the offshore region south of the boso peninsula with equivalent moment magnitude mw 7 0 adequately accounts for the observed deformation using the distributed coseismic slip model layered viscoelastic structure and a model of interseismic strain accumulation we evaluate the post 1923 stress evolution including both the coseismic and accumulated postseismic stress changes and those stresses contributed by interseismic loading we find that if account is made for the varying tectonic regime in the region the occurrence of both immediate first month post 1923 crustal aftershocks as well as recent regional crustal seismicity is consistent with the predicted stress pattern this suggests that the influence of the 1923 earthquake on regional seismicity is fairly predictable and has persisted for at least seven decades following the earthquake

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

viscoelastic coupling model for the earthquake cycle driven from below in a linear system the earthquake cycle can be represented as the sum of a solution which reproduces the earthquake cycle itself viscoelastic coupling model and a solution that provides the driving force we consider two cases one in which the earthquake cycle is driven by stresses transmitted along the schizosphere and a second in which the cycle is driven from below by stresses transmitted along the upper mantle i e the schizosphere and upper mantle respectively act as stress guides in the lithosphere in both cases the driving stress is attributed to steady motion of the stress guide and the upper crust is assumed to be elastic the surface deformation that accumulates during the interseismic interval depends solely upon the earthquake cycle solution viscoelastic coupling model not upon the driving source solution thus geodetic observations of interseismic deformation are insensitive to the source of the driving forces in a linear system in particular the suggestion of bourne et al 1998 that the deformation that accumulates across a transform fault system in the interseismic interval is a replica of the deformation that accumulates in the upper mantle during the same interval does not appear to be correct for linear systems

seven years of postseismic deformation following the 1999 m 7 4 and m 7 2 izmit duzce turkey earthquake sequence 1 we report the results of nearly 7 years of postseismic deformation measurements using continuously recorded and survey mode gps observations for the 1999 izmit duzce earthquake sequence resolvable time dependent postseismic changes to the preearthquake interseismic velocity field extend at least as far as the continuous gps station in ankara 200 km southeast of the izmit rupture seven years after the earthquake sequence the relative postseismic velocity across the north anatolian fault naf reaches 10 12 mm a roughly 50 of the steady state interseismic rate with the highest postseismic velocities within 40 km of the coseismic ruptures we use a sequence of logarithmic time functions to fit gps site motions up to three logarithmic terms with decay constants of 1 150 and 3500 days are necessary to fit all the transient motion observed at the continuous gps stations the first term is required for the component of site motion parallel to the naf at near field sites strongly implicating rapid shallow afterslip the intermediate and longer term postseismic velocity components reflect more broadly distributed strain with a symmetric double couple pattern suggestive of either localized deep afterslip or viscoelastic relaxation of the upper mantle and or lower crust in two areas including the marmara sea this pattern is superimposed on north south extension centered on the naf we speculate that this extension may result from aseismic dip slip along coseismically weakened faults driven by the background tectonic stress

interseismic strain localization in the san jacinto fault zone we investigate interseismic deformation across the san jacinto fault at anza california where previous geodetic observations have indicated an anomalously high shear strain rate we present an updated set of secular velocities from gps and insar observations that reveal a 2 3 km wide shear zone deforming at a rate that exceeds the background strain rate by more than a factor of two gps occupations of an alignment array installed in 1990 across the fault trace at anza allow us to rule out shallow creep as a possible contributor to the observed strain rate using a dislocation model in a heterogeneous elastic half space we show that a reduction in shear modulus within the fault zone by a factor of 1 2 1 6 as imaged tomographically by allam and ben zion geophys j int 190 1181 1196 2012 can explain about 50 of the observed anomalous strain rate however the best fitting locking depth in this case 10 4 1 3 km is significantly less than the local depth extent of seismicity 14 18 km we show that a deep fault zone with a shear modulus reduction of at least a factor of 2 4 would be required to explain fully the geodetic strain rate assuming the locking depth is 15 km two alternative possibilities include fault creep at a substantial fraction of the long term slip rate within the region of deep microseismicity or a reduced yield strength within the upper fault zone leading to distributed plastic failure during the interseismic period

paleoseismology of the palu lake hazar segment of the east anatolian fault zone turkey the east anatolian fault zone eafz is among the most important active continental transform fault zones in the world as testified by major historical and minor instrumental seismicity the first paleoseismological exploratory trenching study on the eafz was done on the palu lake hazar segment plhs which is one of the six segments forming the fault zone in order to determine its past activity and to assess its earthquake hazard the results of trenching indicate that the latest surface rupturing earthquakes on this segment may be the ms 7 1 1874 and ms 6 7 1875 events and there were other destructive earthquakes prior to these events the recurrence interval for a surface rupturing large m 7 earthquake is estimated as minimum 100 35 and maximum 360 years estimates for the maximum possible paleoearthquake magnitude are mw 7 1 7 7 for the palu lake hazar segment based on empirical magnitude fault rupture relations an alluvial fan dated 14 475 15 255 cal years bp as well as another similar age fan with an abandoned stream channel on it are offset in a left lateral sense 175 and 160 5 m respectively indicating an average slip rate of 11 mm year because 127 years have elapsed since the last surface rupturing event this slip rate suggests that 1 4 m of left lateral strain has accumulated along the segment ignoring possible creep effects folding and other inelastic deformation a 2 5 ma age for the start of left lateral movement on the segment and in turn the eafz is consistent with a slip rate of 11 mm year and a previously reported 27 km total left lateral offset the cumulative 5 6 mm year vertical slip rate near lake hazar suggests a possible age of 148 178 ka for the lake our trenching results indicate also that a significant fraction of the slip across the eafz zone is likely to be accommodated seismically the present seismic quiescence compared with the past activity paleoseismic and historic indicate that the eafz may be locked and accumulating elastic strain energy but could move in the near future

modern and ancient seismogenic out of sequence thrusts in the nankai accretionary prism comparison of laboratory derived physical properties and seismic reflection data 1 to investigate characteristics of a seismogenic out ofsequence thrust oost imaged as a strong reflection on seismic profiles in the nankai accretionary prism we determined acoustic properties of discrete samples from an fossil nobeoka oost outcrop under confining pressures and compared the acoustic properties with those of an active oost in the nankai accretionary prism we observed anisotropy of velocity and attenuation in the hanging wall of nobeoka oost attributed to foliation of pelitic phyllite in contrast the footwall is composed of brittlely deformed chaotic shales and fine sandstones and velocities in the footwall are lower than those in the hanging wall amplitude variation with offset avo modeling utilizing contrasts in p and s wave velocities and densities between the hanging wall and footwall of the nobeoka oost indicates that fractures filled with overpressured fluid likely account for angle dependent reflection amplitudes of the active oost in the nankai trough citation tsuji t g kimura s okamoto f kono h mochinaga t saeki and h tokuyama 2006 modern and ancient seismogenic out ofsequence thrusts in the nankai accretionary prism comparison of laboratory derived physical properties and seismic reflection data geophys res lett 33 l18309 doi 10 1029 2006gl027025

kinematics of active left lateral faulting in se turkey from offset pleistocene river gorges improved constraint on the rate and history of relative motion between the turkish and arabian plates in the arabian platform of se turkey abundant evidence exists of fluvial incision by c 110 10 m since the late early pleistocene starting in or around marine oxygen isotope stage 22 at 870 ka this incision which has accompanied regional surface uplift as the isostatic response to regional erosion has progressively locked rivers into their gorges in landscape that formerly had much lower relief we use this effect to estimate 4 44 0 06 km of left lateral slip on this time scale on the golbasi turkoglu fault a segment of the east anatolian fault zone from offset river gorges giving a slip rate of 5 10 0 07 mm a 1 piercing points indicate that this fault has slipped a total of 19 km making its age 3 73 0 05 ma a total of 33 km of relative motion between the turkish and arabian plates is documented on this time scale in the vicinity of golbasi at an overall time averaged rate of 8 85 0 12 mm a 1 the estimated euler vector for relative motion between these plates being 0 89 0 01 ma 1 about 33 4 n 42 3 e this method can be readily applied to determine slip rates time averaged since the late early pleistocene on other strike slip fault zones worldwide

magnitude of late quaternary left lateral displacements along the north edge of tibet images taken by the earth observation satellite spot of the quaternary morphology at 18 sites on the 2000 kilometer long altyn tagh fault at the north edge of tibet demonstrate that it is outstandingly active long term left lateral strike slip offsets of stream channels alluvial terrace edges and glacial moraines along the fault cluster between 100 and 400 meters the high elevation of the sites mostly above 4000 meters in the periglacial zone suggests that most offsets resulted from slip on the fault since the beginning of the holocene these data imply that slip rates are 2 to 3 centimeters per year along much of the fault length and support the hypothesis that the continuing penetration of india into asia forces tibet rapidly toward the east

deformation processes adjacent to active faults examples from eastern california 1 major seismogenic faults are embedded within narrow zones of inelastic off fault deformation ofd where both distributed displacement and modification of rock properties occur active distributed displacement may affect slip rate estimates seismic energy radiation and geodynamic models this study addresses the role of ofd in the displacement history and mechanical behavior of seismogenic faults by multisite study of deformed geologic features adjacent to 30 60 km long active strike slip faults of 10 km of dextral displacement in the mojave desert eastern california we find that distributed displacement accommodates 0 to 25 of the total displacement over zones of one to two kilometers width displacement occurs mostly within 100 200 m of faults and decreases nonlinearly away from the main fault we show evidence for distributed displacement through simple shear in the form of parallel secondary faults and progressive deformation of linear markers adjacent to the calico fault we also find evidence for shear via rotation and progressive fragmentation adjacent to the harper lake fault analysis of block dimensions show that blocks tend to decrease in size toward faults and that cumulative length of secondary faults is longer than the main fault by at least a factor of 10 based on crosscutting relationships and the relationship of ofd to geophysically imaged compliant zones around active faults we argue that distributed displacement is an active process and suggest that zones of diminished rigidity near faults may be at least in part driven by secondary faulting during the rupture propagation along the main fault

influence of the earthquake cycle and lithospheric rheology on the dynamics of the eastern california shear zone the eastern california shear zone is bounded by the high heat flow region of the basin and range province and the low heat flow region of the sierra nevada block this difference in thermal state influences the rheology of the lower crust upper mantle resulting in a viscosity contrast between the two regions we analyze the effect of such a contrast on the kinematics and dynamics of the shear zone with numerical models this viscosity contrast drives asymmetric strain accumulation in the upper crust producing an asymmetric surface velocity field an additional consequence of this strain pattern is the potential for asymmetric co seismic displacement during an earthquake

first global positioning system results in northern myanmar constant and localized slip rate along the sagaing fault we present the first recorded global positioning system gps data from myanmar measured at the northern tip of the sagaing fault this area is in a very complex geodynamic context where rigid and semirigid plates interact the 12 gps sites measured in 2005 and 2008 in northern myanmar show that the slip rate is 18 mm yr and is localized along a single active narrow fault trace 20 km wide the same rate was previously demonstrated and remeasured 500 km southward in central myanmar despite the geodynamic regional complexity induced by interaction between the sunda and india plates the burma microplate and the highly deformable eastern himalayan syntaxis the slip rate remains surprisingly constant along this fault however the modeled locking depth varies from 20 km in central myanmar to 5 km in the north

the rachaya serghaya fault system lebanon evidence of coseismic ruptures and the ad 1759 earthquake sequence 1 the rachaya and serghaya faults are the easternmost fault branches of the dead sea transform fault within the lebanese restraining bend they lie east of the yammouneh fault the main strand of the dead sea transform fault within the restraining bend extend along the western and eastern flanks of the anti lebanon range respectively and show left lateral strike slip movement manifested as offset drainage we studied both faults through combined field investigations in geomorphology and paleoseismology young fault scarps mole tracks pressure ridges and offset streams detected along the faults traces attest to recent coseismic ruptures two paleoseismic investigations highlight their seismogenic potential and indicate earthquake recurrence along them the rachaya and serghaya faults are active and the sources of recent historical earthquakes the last of which might be the 30 october 25 november 1759 ms 6 6 and 7 4 earthquake sequence that caused severe damage in the eastern mediterranean region such a possible correlation suggests that the two faults are probably structurally interconnected as movement on one fault may stimulate movement on the other fault in addition both faults may define together an active seismogenic fault system that accommodates some of the regional displacement that takes place within the lebanese restraining bend our results highlight that the seismogenic potential of the rachaya and serghaya faults must be included in any seismic hazard assessment of the region

viscoelastic coupling model of the san andreas fault along the big bend southern california the big bend segment of the san andreas fault is the 300 km long segment in southern california that strikes about n65 w roughly 25 counterclockwise from the local tangent to the small circle about the pacific north america pole of rotation the broad distribution of deformation of trilateration networks along this segment implies a locking depth of at least 25 km as interpreted by the conventional model of strain accumulation continuous slip on the fault below the locking depth at the rate of relative plate motion whereas the observed seismicity and laboratory data on fault strength suggest that the locking depth should be no greater than 10 to 15 km the discrepancy is explained by the viscoelastic coupling model which accounts for the viscoelastic response of the lower crust thus the broad distribution of deformation observed across the big bend segment can be largely associated with the san andreas fault itself not subsidiary faults distributed throughout the region the working group on california earthquake probabilities 1995 in using geodetic data to estimate the seismic risk in southern california has assumed that strain accumulated off the san andreas fault is released by earthquakes located off the san andreas fault thus they count the san andreas contribution to total seismic moment accumulation more than once leading to an overestimate of the seismicity for magnitude 6 and greater earthquakes in their type c zones

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

structure and tectonic development of the ghab basin and the dead sea fault system syria we examine the structure and evolution of the ghab basin that formed on the active yet poorly understood northern segment of the dead sea transform fault system the basin formed in plio quaternary time at a complex step over zone on the fault subsidence occurred along cross basin and transform parallel faults in two asymmetric depocentres the larger depocentre in the south of the basin is asymmetric towards the east the margin along which most active transform displacement apparently occurs the syrian coastal ranges located directly west of the ghab basin are a consequence of late cretaceous and cenozoic regional compression heavily modified by the dead sea fault system and ghab basin formation we prefer a model whereby the dead sea fault system in northwest syria developed in plio quaternary time consistent with previously proposed models of two phase dead sea fault system movement and red sea spreading

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

geodetic evidence for a low slip rate in the altyn tagh fault system the collision between india and asia has been simulated with a variety of computational models that describe or predict the motions of the main faults of east asia geological slip rate estimates of 20 30 mm yr 1 suggest that the largest of these faults the 2 000 km long altyn tagh fault system on the northern edge of the tibetan plateau absorbs as much of the indo asian convergence signal as do the himalayas partly by oblique slip and partly by contraction and mountain growth however the predictions of dynamic models for asian deformation and the lower bounds of some geological slip rates estimates 3 9 mm yr 1 refs 7 8 suggest that the altyn tagh system is less active here we report geodetic data from 89 91 degrees e that indicate left lateral shear of 9 5 mm yr 1 and contraction of 3 1 mm yr 1 across the altyn tagh system this result combined with our finding that at 90 degrees e tibet contracts north south at 9 1 mm yr 1 supports the predictions of dynamic models of asian deformation

evidence for 830 years of seismic quiescence from palaeoseismology archaeoseismology and historical seismicity along the dead sea fault in syria an edited version of this paper was published in earth and planetary science letters by elsevier science elsevier science retains the copyright to this paper copyright 2003 see also http dx doi org 10 1016 s0012 821x 03 00144 4 http atlas geo cornell edu deadsea publications meghraoui2003 epsl htm

active deformation of asia from kinematics to dynamics using estimated strain rates across the actively deforming region of asia to infer variations in viscous stress it is shown that gradients of stress point uphill toward the center of tibet where gravitational potential energy per unit surface area reaches a maximum thus the dynamics of the deformation seem to obey the equation of creeping flow which expresses a balance between gradients in stress and the gravitational body force this balance in the region of the tibetan plateau yields an estimate of 10 22 pascal second for the average viscosity of the tibetan lithosphere which is only about 10 to 100 times greater than the viscosity of the convecting upper mantle

active faulting and natural hazards in armenia eastern turkey and northwestern iran active fault zones of armenia se turkey and nw iran present a diverse set of interrelated natural hazards three regional case studies in this cross border zone are examined to show how earthquakes interact with other hazards to increase the risk of natural disaster in northern armenia a combination of several natural and man made phenomena earthquakes landslides and unstable dams with toxic wastes along the pambak sevan sunik fault pssf zone lowers from 0 4 to 0 2 0 3g the maximum permissible level mpl of seismic hazard that may induce disastrous destruction and loss of life in the adjacent vanadzor depression in the ararat depression a large active fault bounded pull apart basin at the junction of borders of armenia turkey iran and azerbaijan an earthquake in 1840 was accompanied by an eruption of ararat volcano lahars landslides floods soil subsidence and liquefaction the case study demonstrates that natural hazards that are secondary with respect to earthquakes may considerably increase the damage and the casualties and increase the risk associated with the seismic impact the north tabriz gailatu fault system poses a high seismic hazard to the border areas of nw iran eastern turkey nakhichevan azerbaijan and southern armenia right lateral strike slip motions along the north tabriz fault have given rise to strong earthquakes which threaten the city of tabriz with its population of 1 2 million the examples illustrate how the concentration of natural hazards in active fault zones increases the risk associated with strong earthquakes in armenia eastern turkey and nw iran this generally occurs across the junctions of international borders hence the transboundary character of active faults requires transboundary cooperation in the study and mitigation of the natural risk

seismic hazard in the marmara sea region following the 17 august 1999 izmit earthquake on 17 august 1999 a destructive magnitude 7 4 earthquake occurred 100 km east of istanbul near the city of izmit on the north anatolian fault this 1 600 km long plate boundary 1 2 slips at an average rate of 2 3 cm yr 1 refs 3 5 and historically has been the site of many devastating earthquakes 6 7 this century alone it has ruptured over 900 km of its length 6 models of earthquake induced stress change 8 combined with active fault maps 9 had been used to forecast that the epicentral area of the 1999 izmit event was indeed a likely location for the occurrence of a large earthquake 9 10 here we show that the 1999 event itself significantly modifies the stress distribution resulting from previous fault interactions 9 10 our new stress models take into account all events in the region with magnitudes greater than 6 having occurred since 1700 ref 7 as well as secular interseismic stress change constrained by gps data 11 these models provide a consistent picture of the long term spatio temporal behaviour of the north anatolian fault and indicate that two events of magnitude equal to or greater than the izmit earthquake are likely to occur within the next decades beneath the marmara sea south of istanbul

dislocation model for aseismic crustal deformation at hollister california geodetic observations at many active plate margins reveal relatively steady aseismic motion during the time between major earthquakes we model the aseismic motion by the relative motion between several blocks that suffer frictional resistance in the upper crust frictional drag is represented by uniform dislocation on a fault surface we assume that friction occurs only on the upper brittle zone of each block boundary and that frictionless sliding occurs below this zone using a bayesian inversion procedure we invert geodetic data to determine the parameters of the block and dislocation model parameters to be estimated include the two horizontal components of velocity for each block and the dislocation rate dip angle slip angle and width of each rectangular fault patch for hollister we assume five blocks and nine rectangular fault patches rates of length change on 92 lines observed by trilateration make up the data triangulation leveling very long baseline interferometry satellite ranging and global positioning system data can also be easily included in our model our inversion procedure uses prior estimates of all block and fault parameters based on geological and seismological data the block parameters are estimated from geological observations of fault displacement rates while the widths of the fault patches are estimated from earthquake hypocentral depths we choose prior estimates of the dislocation rate to match observed creep rates the estimated block motion is well resolved by the geodetic data and agrees well with the geological estimates this suggests that the block motion is steady on time scales from 10 years to 1 m y the net motion across the san andreas calaveras fault system is 38 3 mm yr oriented s38 e thus some additional displacement possibly offshore is needed to match the rate of 56 mm yr predicted by plate tectonic models the depth of the transition from frictional to free sliding varies considerably from 0 4 km on the southern calaveras to 11 km on the central san andreas fault two segments of the san andreas north of 36 50 and south of 36 40 have the greatest potential for moderate to large earthquakes

geochemistry and origin of sour gas accumulations in the northeastern sichuan basin sw china significant natural gas reserves have recently been discovered in the lower triassic oolitic reservoirs from northeastern sichuan basin sw china in the wake of the december 2003 sour gas well blow out this study presents an overview on the petroleum geology and geochemistry of the sour gas accumulations in the study area two types of natural gas accumulations were identified in the lower triassic oolitic reservoirs both containing highly mature thermogenic gases with their hydrocarbon source rocks in upper permian strata natural gases from the area south of the ancient kaijiang liangping seaway are generally sweet gases formed as the result of thermal maturation whereas those discovered from north of the seaway are products of both thermal maturation and thermochemical sulfate reduction of early accumulated oils in the feixianguan formation reservoirs the proposed origins of the gases are supported by their chemical and stable carbon isotope compositions as well as the presence or absence of pyrobitumens in the reservoir the distribution of gas accumulations is controlled predominantly by the combination of lithologic and structural factors the regional variation in the concentrations of h2s in the gases appears related to the presence and thickness of anhydrite bearing evaporitic rocks interbedded or intercalated with the oolitic reservoirs

measurement of interseismic strain across the haiyuan fault gansu china by insar the haiyuan fault is part of a major left lateral fault system at the northeastern edge of the tibet qinghai plateau two m8 earthquakes 1920 and 1927 occurred along the fault bracketing an unbroken section of the fault identified as the tianzhu seismic gap we use interferometric synthetic aperture radar data from descending orbits of the ers satellites acquired between 1993 and 1998 along two adjacent tracks covering the gap to measure the current surface movements and better understand the present day mechanical behavior of this fault section the analysis of the radar data involves first the combined correction of orbital errors and errors associated with the phase delay through the troposphere a subset of the data is then selected based on the analysis of the residual noise spectra for each pair of data the selected interferograms are stacked and the average phase change rate is converted in fault parallel velocity assuming that the ground movement is horizontal and parallel to the fault velocity maps from both tracks show a zone of high velocity gradient across the fault a few kilometers wide consistent with left lateral slip on the haiyuan fault the average velocity field from the two tracks in their overlapping area is well fit with a single screw dislocation model in an elastic half space the derived fault slip rate at depth 4 2 8 mm yr is consistent with recent gps results the corresponding shallow apparent locking depth 0 4 2 km can be explained by a current low stress accumulation on the fault due to creep almost on the entire fault plane however unless it is transient this creep would be paradoxical with the occurrence of past large earthquakes along this fault section as revealed by paleoseismology an alternative model implying both shallow creep in the brittle upper crust and deep aseismic slip beneath the seismogenic layer separated by a locked section would be consistent with insar observations and with the potential for large earthquakes on the fault as well a two dislocation model with slip at 5 mm yr beneath 15 km and a transient creep rate of 11 mm yr between 2 and 7 km fits the insar data however the width and creep rate of the shallow creeping zone and their possible along strike variations are still poorly resolved with the present data set

oblique plate convergence slip vectors and forearc deformation slip vectors from thrust earthquakes at subduction zones where convergence is oblique to the trench often point between the directions of relative plate convergence and normal to the trench axis suggesting that oblique convergence is taken up by partial decoupling decoupling means that a component of arc parallel motion of the leading edge of the upper plate results in less oblique thrusting at the trench partial decoupling is modeled by partitioning of oblique convergence into slip on thrust and strike slip faults that are parallel to the trench and to each other and starting with a force equilibrium condition a relationship between the obliquity and the earthquake slip vector orientation is derived assuming that either fault slips when shear stress on it reaches a yield stress oblique slip parallel to the plate vector should occur on the thrust fault when obliquity is smaller than a critical angle for obliquity at or greater than this angle the stress on the strike slip fault is large enough to start it slipping and when both faults are active the arc parallel motion of the forearc deflects the slip vector back toward the trench normal if we assume that continued slip on either fault occurs at constant stress but the two faults can be at different stresses the slip vector will maintain a constant angle relative to the trench normal even when obliquity is larger than the critical angle this limiting angle of the slip vector called max measured relative to the trench normal is simply the arcsine of the ratio of the shear forces resisting slip on the strike slip and thrust faults a consequence is that when the obliquity exceeds max the slip vectors on the thrust fault are sensitive only to the thrust fault orientation and contain no information about the convergence direction between the plates slip vectors at the java trench southwest of sumatra show the relationship clearly with max 20 5 while slip vectors at the aleutian trench show the relationship less clearly with max 25 to 45 the greater angle at the aleutian trench suggests that the upper plate is stronger in the aleutian arc relative to the thrust fault than in the sumatran arc consistent with the sumatran arc being continental and having a well developed strike slip fault while the aleutian arc is oceanic and without a clear transcurrent fault slip vectors at the philippine trench which like sumatra has a large strike slip fault inboard of it tend to stay within 25 of the trench normal when obliquity is as large as 50 if obliquity exceeds max and continues to increase along a subduction zone the rate of motion of the forearc relative to the upper plate will vary with obliquity in which case the forearc sliver should extend or contract parallel to the arc from the geometry of modern island arcs arc parallel extension should be the more common and has been hypothesized for both sumatra and the aleutians on the basis of earthquake slip vectors and for these and other arcs from geological observations from estimates of max and the arc parallel gradients in obliquity arc parallel strain rates are estimated to be 1 to 3 10 8 yr for the sumatran forearc 2 to 6 10 8 yr for the aleutian forearc and 0 3 to 3 10 8 yr for the philippine forearc oblique convergence and subsequent arc parallel extension if accompanied by crustal thinning may provide an important yet little appreciated mechanism for bringing high grade metamorphic rocks to the surface of subduction complexes

southern san andreas san jacinto fault system slip rates estimated from earthquake cycle models constrained by gps and interferometric synthetic aperture radar observations we use ground geodetic and interferometric synthetic aperture radar satellite observations across the southern san andreas saf san jacinto sjf fault systems to constrain their slip rates and the viscosity structure of the lower crust and upper mantle on the basis of periodic earthquake cycle maxwell viscoelastic finite element models key questions for this system are the saf and sjf slip rates the slip partitioning between the two main branches of the sjf and the dip of the saf the best fitting models generally have a high viscosity lower crust 10 21 pa s overlying a lower viscosity upper mantle 10 19 pa s we find considerable trade offs between the relative time into the current earthquake cycle of the san jacinto fault and the upper mantle viscosity with reasonable assumptions for the relative time in the earthquake cycle the partition of slip is fairly robust at around 24 26 mm a for the san jacinto fault system and 16 18 mm a for the san andreas fault models for two subprofiles across the saf sjf systems suggest that slip may transfer from the western coyote creek branch to the eastern clark superstition hills branch of the sjf from nw to se across the entire system our best fitting model gives slip rates of 2 3 12 9 12 9 and 17 3 mm a for the elsinore coyote creek clark and san andreas faults respectively where the large uncertainties in the slip rates for the sjf branches reflect the large uncertainty in the slip rate partitioning within the sjf system

asymmetry in elastic properties and the evolution of large continental strike slip faults 1 we use geodetic studies to quantify several cases of significant asymmetry in interseismic and coseismic effects along large continental strike slip faults using simple two dimensional edge dislocation models we first show that asymmetric elastic loading characterizes the present main marmara fault a portion of the north anatolian fault along the northern margin of the sea of marmara the ratio of asymmetry there is about 10 this ratio is even larger about 30 along the northern sumatra fault near lake toba caldera we then examine two profiles near point reyes and point arena across the northern san andreas fault that have been previously proposed as affected by asymmetry both in interseismic and coseismic effects we show that an asymmetry ratio of 1 6 in interseismic loading exists near point arena with the southwest side of the fault being more rigid than the northeast one on the other hand we do not find significant asymmetry for the point reyes profile that was previously described as highly asymmetric we examine coseismic motion during the 1906 earthquake along the same two profiles ratios of 1 2 and 1 7 are found for the point arena and point reyes profiles respectively we discuss the possible causes of asymmetry contrasts in seismic velocity in the brittle portion suggest ratios generally not exceeding 2 5 for the dynamic rigidity in the upper brittle section larger ratios may involve other complex causes such as differences between static and dynamic rigidities contrasts in rheology in the deeper creeping sections and postseismic transients we conclude that asymmetry should be systematically included within the parameters to be inverted when dealing with the mechanics of large scale strike slip faults

equivalent strike slip earthquake cycles in half space and lithosphere asthenosphere earth models by virtue of the images used in the dislocation solution the deformation at the free surface produced throughout the earthquake cycle by slippage on a long strike slip fault in an earth model consisting of an elastic plate lithosphere overlying a viscoelastic half space asthenosphere can be duplicated by prescribed slip on a vertical fault embedded in an elastic half space for the case in which each earthquake ruptures the entire lithosphere thickness h the half space equivalent slip rate is as follows depth interval 0 h slip identical to that in lithosphere asthenosphere model i e abrupt coseismic slip and no subsequent slip depth interval 2n 1 h to 2n 1 h n 1 2 slip rate uniform in space and dependent upon time as fn t exp t a where fn is a n 1 degree polynomial in t a is twice the asthenosphere relaxation time and t is measured from the instant after the preceding earthquake the slip rate averaged over the seismic cycle in each depth interval equals the secular rate of relative plate motion for reasonable values of a slip rates below 5h do not vary much from that mean value and can be treated as constant thus the surface deformation due to the earthquake cycle in the lithosphere asthenosphere model can be calculated very simply from the half space model with time dependent slip in the two depth intervals h 3h and 3h 5h and uniform slip at a rate equal to the secular relative plate velocity below depth 5h inversion of 1973 1988 geodetic measurements of deformation across the segment of the san andreas fault in the transverse ranges north of los angeles for the half space equivalent slip distribution suggests no significant slip on the fault above 30 km and a uniform slip rate of 36 mm yr below 30 km one equivalent lithosphere asthenosphere model would have a 30 km thick lithosphere and an asthenosphere relaxation time greater than 33 years but other models are possible

is the slip rate variation on the great sumatran fault accommodated by fore arc stretching in oblique convergent subduction areas an obliquity increase should produce a slip rate increase on trench parallel strike slip faults and thus the fore arc platelet should be stretched along the great sumatran fault gsf that is associated with the oblique convergent sunda arc a northward increase of the gsf slip rate occurs parallel with the convergence obliquity transpressional back arc deformation accommodates part of the gsf slip rate variation while no significant fore arc stretching is observed the sumatran case shows that oblique convergence may be accommodated by deformation of a 500 km wide zone from the fore arc to the back arc domains

interseismic strain accumulation spin up cycle invariance and irregular rupture sequences using models of infinite length strike slip faults in an elastic layer above linear viscoelastic regions we investigate interseismic deformation in the models we investigate interseismic strain accumulation on mature faults is the result of the cumulative effects of all previous ruptures and is independent of the fault loading conditions the time for a fault to spin up to a mature state depends on the rheologies and the fault loading conditions after the model has spun up the temporal variation of shear stresses is determined by the fault slip rate and model rheologies the change in stress during spin up depends on the slip rate rheologies and fault loading conditions but is independent of the magnitude of the initial stress over enough cycles such that the cumulative deformation is block like the average mature interseismic velocities are equal to the interseismic velocities of an elastic model with the same geometry and distribution of shear moduli in a model that has spun up with the fault rupturing periodically the cumulative deformation is block like at the end of each seismic cycle and the interseismic deformation is cycle invariant i e the same in all cycles when the fault ruptures nonperiodically the fault spins up to a mature state that is the same as if the fault had ruptured periodically with the mean slip rate when the fault slip rate within each cycle varies the interseismic deformation evolves toward the cycle invariant deformation determined by the most recent fault slip rate around a fault whose slip rate has been faster slower than average interseismic velocities are larger smaller than the cycle invariant velocities and increase decrease from cycle to cycle

a 48 kyr long slip rate history for the jordan valley segment of the dead sea fault abstract we investigate the late quaternary active deformation along the jordan valley segment of the left lateral dead sea fault and provide new insights on the behaviour of major continental faults the 110 km long fault segment shows systematic offsets of drainage systems surveyed at three sites along its southern section the isotopic dating of six paleoclimatic events yields a precise chronology for the onset of six generations of gully incisions at 47 5 ka bp 37 5 ka bp 13 ka bp 9 ka bp 7 ka bp and 5 ka bp additionally detailed mapping and reconstructions provide cumulative displacements for 20 dated incisions along the fault trace the individual amounts of cumulative slip consistently fall into six distinct classes this yields i an average constant slip rate of 4 7 to 5 1 mm yr for the last 47 5 kyr and ii a variable slip rate ranging from 3 5 mm yr to 11 mm yr over 2 kyr to 24 kyr long intervals taking into account that the last large earthquake occurred in ad 1033 we infer 3 5 to 5 m of present day slip deficit which corresponds to a mw 7 4 earthquake along the jordan valley fault segment the timing of cumulative offsets reveals slip rate variations critical to our understanding of the slip deficit and seismic cycle along major continental faults

westward propagation of the north anatolian fault into the northern aegean timing and kinematics we present new evidence for the propagation processes of the north anatolian fault folding in the dardanelles straits region allows us to document the timing of the deformation preceding and the finite displacement after the passage of the propagating tip of the fault the accuracy of the observations is due to interplay between deformation and the sea level changes in the mediterranean the well known messinian regression followed by the pliocene transgression the long term kinematics around the sea of marmara pull apart total displacement of about 85 km over the past 5 m y is similar to the present day kinematics deduced from space geodesy at a larger scale westward propagation of the north anatolian fault over nearly 2000 km in the past 10 m y appears to be associated with strain recovery suggesting that the continental lithosphere retains long term elasticity

does interseismic strain localization near strike slip faults result from boundary conditions or rheological structure summary geodetic observations across most of the major strike slip faults show an interseismic strain rate which presents a sharp localization of elastic shear strain in the fault vicinity 20 60km the screw dislocation model of savage burford is commonly used to fit these geodetic data and to retrieve the far field velocity and the locking depth this model is very popular because of its inherent simplicity to derive fault slip rates and mostly because it predicts locking depths which are of the same order of magnitude as the base of the seismogenic zone 5 20km a first issue with the screw dislocation model is that localization is paradoxically introduced by imposing a step function in the velocity field at a depth where the crust is otherwise recognized to behave following a viscous rheology a second issue with this model is that it is not consistent with the rheological model of the crust that is valid for both postseismic 1 10yr interseismic several thousand years and long term geodynamic several thousand to several million years timescales here we use numerical models to study how alternative and more geologically realistic boundary conditions and rheological structures can lead to the localization of elastic strain at the earth s surface during the interseismic period we find that simple elastic models resembling the savage burford model but driven by far field plate velocity are inefficient at localizing strain unless this driving velocity is transmitted by a rigid indentor we also find that models including a weak viscous heterogeneity beneath the fault zone are able to produce appropriate localization of the deformation near the fault this alternative class of model is shown to be pertinent in regards to the boundary conditions and geological observations along exhumed ductile strike slip shear zone

neotectonics of the sumatran fault indonesia the 1900 km long trench parallel sumatran fault accommodates a significant amount of the right lateral component of oblique convergence between the eurasian and indian australian plates from 10 n to 7 s our detailed map of the fault compiled from topographic maps and stereographic aerial photographs shows that unlike many other great strike slip faults the sumatran fault is highly segmented cross strike width of step overs between the 19 major subaerial segments is commonly many kilometers the influence of these step overs on historical seismic source dimensions suggests that the dimensions of future events will also be influenced by fault geometry geomorphic offsets along the fault range as high as 20 km and may represent the total offset across the fault if this is so other structures must have accommodated much of the dextral component of oblique convergence during the past few million years our analysis of stretching of the forearc region near the southern tip of sumatra constrains the combined dextral slip on the sumatran and mentawai faults to be no more than 100 km in the past few million years the shape and location of the sumatran fault and the active volcanic arc are highly correlated with the shape and character of the underlying subducting oceanic lithosphere nonetheless active volcanic centers of the sumatran volcanic arc have not influenced noticeably the geometry of the active sumatran fault on the basis of its geologic history and pattern of deformation we divide the sumatran plate margin into northern central and southern domains we support previous proposals that the geometry and character of the subducting investigator fracture zone are affecting the shape and evolution of the sumatran fault system within the central domain the southern domain is the most regular the sumatran fault there comprises six right stepping segments this pattern indicates that the overall trend of the fault deviates 4 clockwise from the slip vector between the two blocks it separates the regularity of this section and its association with the portion of the subduction zone that generated the giant m w 9 earthquake of 1833 suggest that a geometrically simple subducting slab results in both simple strike slip faulting and unusually large subduction earthquakes

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

late holocene slip rate for the north anatolian fault turkey from cosmogenic 36cl geochronology implications for the constancy of fault loading and strain release rates geomorphologic mapping and cosmogenic radionuclide 36cl dating of an offset fluvial terrace yield a preferred late holocene slip rate of 20 5 5 5 mm yr for the central part of the north anatolian fault turkey an independent slip rate constrained by 14c ages is 20 5 8 5 mm yr these rates are generally similar to but possibly slightly slower than the short term rate of elastic strain storage of 25 1 measured geodetically across this major strike slip fault reilinger et al 2006 1 suggesting that loading and strain release on this part of the north anatolian fault have been relatively constant when averaged over the past 2 2 5 k y we attribute this consistency to the relatively simple structure of the anatolia eurasia plate boundary in north central turkey where almost all plate boundary strain is accommodated along the north anatolian fault the absence of other moderate to high slip rate faults and the earthquakes they produce leads to a relatively simple stress evolution for the fault dominated by steady tectonic loading 1 ref 10

nailing down the slip rate of the altyn tagh fault 1 previous estimates of the geodetic and geologic slip rates of the 1500 km long altyn tagh fault bordering the northern edge of the tibetan plateau vary by a factor of five proposed reasons for these discrepancies include poor gps geometry interpretative errors in terrace morphology and changes in fault slip rate over time here we present results from a new dense gps array orthogonal to the fault at 86 2 e that indicates a velocity of 9 0 3 2 4 4 mm yr in close agreement with geomorphologic estimates at the same location our estimated geodetic slip rate is consistent with recent geological slip rates based on terrace offsets the resulting mean combined geological and geodetic slip rate 9 0 4 0 mm yr is remarkably uniform for the central 800 km of the altyn tagh fault significantly lower than early kinematic estimates and consistent with deformation elsewhere in tibet and central asia

progressive strain localization in a major strike slip fault exhumed from midseismogenic depths structural observations from the salzach ennstal mariazell puchberg fault system austria 1 analysis of a strike slip fault exhumed from midseismogenic depths reveals that the fault experienced progressive strain localization toward a high strain fault core we focus on the ennstal segment of the 400 km long salzach ennstal mariazell puchberg semp strike slip fault system in the eastern alps which accommodated 60 km of left lateral displacement during oligo miocene time macroscopic and microscopic observations reveal a zoned fault featuring a high strain core at least 10 m wide within a fault zone that is at least 150 m wide grain size distribution analysis shows how the ennstal segment of the semp evolved our data reveal a 10 m wide high strain fault core characterized by a power law relationship of grain sizes d2 2 0 bordered by a 54 m wide transition zone where the largest and smallest grains are characterized by two power law relationships d2 2 0 and 1 6 respectively this zone is in turn bordered by a region with grain sizes that show a single low strain power law relationship of d2 1 6 we interpret these relationships to be the result of concentrated shear overprinting an initial low strain power law grain size distribution before strain localized to the core this is consistent with the theory that faults mature by smoothing geometrical complexities forming a highly localized high strain fault core the data do not support the idea that damage forms primarily in response to dynamic stresses during seismic rupture although they do suggest that this mechanism may operate within tens of meters of the fault once it has developed its zoned structure

slip rate and locking depth from gps profiles across the southern dead sea transform 1 the dead sea transform is a major strike slip fault bounding the arabia plate and the sinai subplate on the basis of two gps campaign measurements 6 years apart at 17 sites distributed in israel and jordan complemented by israeli permanent stations we compute the present day deformation across the southern segment of the dead sea transform the wadi araba fault elastic locked fault modeling of fault parallel velocities provides a slip rate of 4 9 1 4 mm a and a best fit locking depth of 12 km this slip rate is slightly higher than previous results based only on israeli permanent gps stations data which are located west of the fault it is in good agreement with results based on offset geomorphologic and geologic features that average longer periods of time 10 ka to 1 ma projection in itrf2000 reference frame allows using our data combined with results published earlier to further study the kinematics between arabia nubia and sinai systematic combination of euler poles available in the literature in addition to our new set of data shows that a wide range of arabia sinai pole positions and angular velocities predict reasonable slip rate on the dead sea fault we highlight uncertainties of calculating such poles due to the small size of the blocks and their slow relative motion along a short and almost straight strand of the transform fault which lead to a large trade off between pole location and angular velocity

time dependent distributed afterslip on and deep below the izmit earthquake rupture surface deformation transients measured with the global positioning system during the 87 days between the 17 august 1999 izmit earthquake and the 12 november 1999 duzce earthquake indicate rapidly decaying aseismic fault slip on and well below the coseismic rupture elastic model inversions for time dependent distributed fault slip using a network inversion filter approach show that afterslip was highest between and below the regions of maximum coseismic slip and propa gated downward to or even below the base of the crust maximum afterslip rates decayed from greater than 2 m yr immediately after the i zmit earthquake to about 1 2 m yr just prior to the duzce earthquake maximum afterslip occurred below the eastern karadere rupture segment and near the i zmit hypocenter afterslip in the upper 16 km decayed more rapidly than that below the seismogenic zone these observations are consistent with a phase of rapid aseismic fault slip concentrated near the base of the seismogenic zone continued loading from the rapid deep afterslip along the eastern rupture zone is a plausible mechanism that helped trigger the nearby mw 7 2 12 november duzce earthquake

reconciling rapid strain accumulation with deep seismogenic fault planes in the ventura basin california global positioning system measurements across the east central ventura basin transverse ranges southern california before the nearby 1994 northridge earthquake show high strain rates interpreting this rapid strain accumulation using the usual model of deep slip on a dislocation in a uniform elastic half space requires slip to extend to within 5 km of the surface such shallow slip is difficult to reconcile with the substantial coseismic displacement at depths from 7 to 19 km during the northridge earthquake here we model the displacement and velocity fields throughout the earthquake cycle using a two dimensional finite element model with a viscoelastic rheology displacements are driven by far field and basal velocity boundary conditions and by imposed periodic earthquakes on the thrust faults bounding the basin the thrust faults rupture through an elastic upper crust to a depth of 15 km after a transient stage during which stresses and strains build up to quasi equilibrium values the behavior of the model becomes periodic the sum of the coseismic displacement divided by the repeat interval plus the average interseismic velocity is equal to the geologic velocity the temporal variation in surface velocity depends mainly on the elsasser relaxation time proportional to the product of the maxwell time of the lower crust and the ratio of the thicknesses of the entire crust and viscoelastic lower crust we are able to match the observed high strain rate only if we include the observed variations in elastic modulus associated with the deep basin sediments the model reconciles geologic geodetic and seismological observations of deformation there are trade offs among the far field convergence rate the elsasser time the earthquake repeat time and the time into the earthquake cycle acceptable convergence rates range from 8 mm yr for a relaxation time of the lower crust of 300 years to 12 mm yr for a 30 year relaxation time

how well do surface slip measurements track slip at depth in large strike slip earthquakes the importance of fault structural maturity in controlling on fault slip versus off fault surface deformation abstract comparisons of observed surface displacements with geodetically inferred slip at depth in six large m w 7 1 strike slip earthquakes reveal a correlation between the structural maturity of the fault and the ratio of deep slip to surface slip that occurs on localized zones of surface rupture specifically structurally immature faults 25 km of total displacement manifest only 50 60 of total slip on narrow fault surface traces versus 85 95 for structurally mature faults 85 km total slip the same pattern holds when structurally simple parts of a surface rupture are analyzed separately from parts that exhibit obvious structural complexity e g discontinuous or multiple traces or significant dip slip these results imply that geologic measurements of surface slip along structurally immature faults are likely to significantly underestimate the true slip at depth in large earthquakes this observation has implications for a number of important problems including determination of fault slip rates which are based on surface offsets earthquake probability assessments which are based on geologic fault slip rates comparisons of geologic and geodetic rate data in the search for strain transients the structural evolution of fault zones estimation of paleo earthquake magnitudes based on geomorphic offsets analyses of the relative importance of faulting vs distributed deformation in accommodating relative plate motions in continental crust the design and construction of infrastructure built near active faults and possibly for the prediction of strong ground motions which may at least partially depend on the degree of slip localization to the surface

precise tremor source locations and amplitude variations along the lower crustal central san andreas fault 1 we precisely locate 88 tremor families along the central san andreas fault using a 3d velocity model and numerous p and s wave arrival times estimated from seismogram stacks of up to 400 events per tremor family maximum tremor amplitudes vary along the fault by at least a factor of 7 with by far the strongest sources along a 25 km section of the fault southeast of parkfield we also identify many weaker tremor families which have largely escaped prior detection together these sources extend 150 km along the fault beneath creeping transitional and locked sections of the upper crustal fault depths are mostly between 18 and 28 km in the lower crust epicenters are concentrated within 3 km of the surface trace implying a nearly vertical fault a prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6 0 parkfield earthquake

rapid slip along the central altyn tagh fault morphochronologic evidence from cherchen he and sulamu tagh consistent with the d 18 o record from the guliya ice cap in the west kunlun the features of interest were all formed by glacial and fluvial processes subsequent to marine isotope stage 5e with the youngest features having formed during the early holocene optimum this near field morphochronological slip rate is averaged over many earthquake cycles and is hence little affected by interseismic strain it is kinematically consistent with other somewhat lower geomorphic slip rate measurements to the east the average rate and lower bounds obtained from alternate interpretational models 18 4 mm yr cannot be reconciled with the most rece geodetic measurements 7 mm yr suggesting that interseismic strain and interactions with adjacent faults may lead to disparate geologic and geodetic rate estimates this late pleistocene holocene morphochronologic rate would imply that at this longitude the altyn tagh fault on the north edge of tibet might absorb almost as much of india s convergence relative to siberia as the himalayan main frontal thrust does on the southern edge of the plateau index terms 1035 geochemistry geochronology 1208 geodesy and gravity crustal movements intraplate 8110 8102 tectonophysics continental contractional orogenic belts 8107 tectonophysics continental neotectonics keywords slip rates cosmogenic dating indo asian collision

constraints on arabian plate motion and extensional history of the red sea analysis of the geologic and geophysical data from the western and northern margin of the arabian plate combined with data from the red sea gulf of aden leads to an interpretation of arabian plate motion that supports an episodic extensional history in the red sea and gulf of aden phase 1 extension began in medial to late eocene and was caused by the nw propagation of the reoriented central indian ridge spreading center it stretched and thinned continental crust along numerous wrench and normal faults that reactivated preexisting structures first phase extension stopped when the arabian plate terminally sutured to eurasia in the medial miocene and halted northward movement of arabia relative to africa the combined african arabian plates moved north more slowly constricting and thickening continental crust in the bitlis zagros sutures while the red sea remained technically quiescent and accumulated salt by the early pliocene continued northward movement was accommodated by lateral extrusion of large continental wedges north of the bitlis zagros sutures this allowed arabia to move northward faster than africa and reopen the red sea where phase 2 extension was expressed by seafloor spreading extension within the red sea gulf of aden rift system has been controlled by the interactions and effects of two factors 1 convergent processes between the north margin of the arabian plate and the eurasian plate to the north and 2 northwest propagation of extension associated with the medial eocene reorganization of the central indian spreading center

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

active tectonics of the adriatic region from gps and earthquake slip vectors 1 to investigate the kinematics of the adriatic region we integrate continuous and episodic gps measurements with mw 4 5 earthquake slip vectors selected from the regional centroid moment tensor catalogue coherent motion of gps sites in the po valley in apulia and in the hyblean plateau allows us to estimate geodetically constrained angular velocities for these regions the predictions of the gps inferred angular velocities are compared with the earthquake slip vectors showing that the seismically expressed deformation at the microplate boundaries is consistent with the observed geodetic motion the remarkable consistency between geodetic seismological and geological evidence of active tectonics suggests that active deformation in the central adriatic is controlled by the relative motion between the adria and apulia microplates the microplates angular rotation rates are then compared with the rotation rates calculated with a simple block model supporting the hypotheses 1 that apulia forms a single microplate with the ionian sea and possibly with the hyblean region and 2 that adria and apulia rotate in such a way as to accommodate the eurasia nubia relative motion we suggest that the present day microplate configuration follows a recent fragmentation of the adriatic promontory that during the neogene rigidly transferred the africa motion to the orogenic belts that now surround the adriatic region

low quaternary slip rate reconciles geodetic and geologic rates along the altyn tagh fault northwestern tibet for more than two decades the slip rate along the active left slip altyn tagh fault of northwestern tibet has been disputed with millennial rates reported to be as much as three times faster than those determined geodetically this problem is significant because the total offset plate boundary length and age of the altyn tagh fault make it the most important single structure accommodating india asia convergence north of the himalayas here we show that the central altyn tagh fault slipped at only 14 9 mm a over the past 4 6 ka by tightly bracketing the age of a displaced fluvial terrace riser at yuemake 88 51 e 38 19 n this result contradicts previous latest quaternary rates and is consistent with those derived from geodetic paleoseismic and geologic measurements and thus resolves the long standing dispute over the latest quaternary slip rate along the longest active strike slip fault in tibet

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

new gps constraints on active deformation along the africa iberia plate boundary abstract we use velocities from 65 continuous stations and 31 survey mode gps sites as well as kinematic modeling to investigate present day deformation along the africa iberia plate boundary zone in the western mediterranean region the gps velocity field shows southwestward motion of the central part of the rif mountains in northern morocco with respect to africa varying between 3 5 and 4 0 mm yr consistent with prior published results stations in the southwestern part of the betic mountains of southern spain move west southwest with respect to eurasia 2 3 mm yr the western component of betics motion is consistent with partial transfer of nubia eurasia plate motion into the southern betics the southward component of betics motion with respect to iberia is kinematically consistent with south to southwest motion of the rif mountains with respect to africa we use block modeling constrained by mapped surface faults and seismicity to estimate the geometry and rates of strain accumulation on plate boundary structures our preferred plate boundary geometry includes one block between iberia and africa including the sw betics alboran sea and central rif this geometry provides a good fit to the observed motions suggesting a wide transpressive boundary in the westernmost mediterranean with deformation mainly accommodated by the gloria azores fault system to the west and the rif tell lineament to the east block boundaries encompass aspects of earlier interpretations suggesting three main deformation styles i extension along the ne sw trending trans alboran shear zone ii dextral strike slip in the betics corresponding to a well defined e w seismic lineament and iii right lateral strike slip motion extending west to the azores and right lateral motion with compression extending east along the algerian tell we interpret differential motion in the rif alboran betic system to be driven both by surface processes related the africa eurasia oblique convergence and sub crustal dynamic processes associated with the long history of subduction of the neotethys ocean lithosphere the dextral slip identified in the betic mountains in southern spain may be related to the offshore fault that produced the great 1755 lisbon earthquake and as such may represent a significant seismic hazard for the west mediterranean region

morphotectonic and geodetic evidence for a constant slip rate over the last 45 kyr along the tabriz fault iran iran is an active continental domain accommodating the convergence between the arabia and eurasia plates in northwestern iran deformation between the central iranian block and the caucasus domain is mainly accommodated by right lateral strike slip on the tabriz fault cities and villages including the city of tabriz have been destroyed by several strong historical earthquakes m similar to 7 in this study we compare the slip rates estimated from geodetic measurements radar interferometry and ups with those determined by dating a geomorphological offset of an alluvial fan along the tabriz fault the gps measurements along two profiles normal to the tabriz fault suggest a slip rate of 7 3 1 3 mm yr 1 the persistent scatterer radar interferometry analysis of envisat satellite archives from 2003 to 2010 shows a velocity gradient 6 3 mm yr 1 across the tabriz fault in agreement with gps results moreover it reveals that most of the area located south of the tabriz fault is affected by subsidence and that some sections of the fault probably act as barriers to fluid migration which may have an impact on its mechanical behaviour west of tabriz morphotectonic investigations on an alluvial fan surface show a right lateral cumulative offset of 320 40 m luminescence analyses of the coarse matrix alluvial fan deposits provide an age of 46 3 ka this yields a slip rate comprised between 6 5 and 7 3 mm yr 1 along this segment these results suggest that the late quaternary slip rate is in agreement with the present day slip rate estimated by geodetic measurements showing no slip rate changes during the past 45 000 yr short term variations within the 45 000 yr related to temporal earthquake clustering over few seismic cycles cannot be ruled out but if they exist they do not affect the geodetic and the geomorphological estimates this study is in agreement with previous ones suggesting that long term slip rates i e averaged over several tens of seismic cycles are consistent with geodetic estimated slip rates i e extrapolated from few years of interseismic observations and suggests that perturbations of fault slip rates are related to variations over few seismic cycles

nw iran eastern turkey present day kinematics results from the iranian permanent gps network abstract a network of continuous gps stations has been installed in nw iran since 2005 to complement the survey gps network already existing in the region we present the 1999 2009 gps derived velocity field for this region based on the continuous and survey mode observations the results confirm a right lateral slip of 7 1 mm yr for the north tabriz fault in agreement with previous studies this rate is consistent with earthquakes of magnitude 7 7 3 and recurrence times of 250 300 yr the higher spatial coverage of the new network shows that deformation is localized in the vicinity of the chalderan south gailatu siah cheshmeh khoy fault and the north tabriz fault however the eastern end of the north tabriz fault appears to cross mount bozgush rather than following its southern foothills this new velocity field does not indicate the 8 mm yr of nne ssw extension suggested earlier for the region but rather shows lower extension of 1 2 1 mm yr across the eastern segment of the north tabriz fault and the talesh to the west the chalderan and the western north tabriz fault segment act like pure strike slip faults without significant extension or compression the denser network in the rudbar earthquake region ms 7 3 1992 shows no significant motion across the fault suggesting that the recurrence time of earthquakes like the rudbar event must be very long the lack of substantial compressive strain and the sharp azimuth change of the velocity vectors in the transition zone from arabia to lesser caucasus motion imply that processes other than extrusion possibly related to old subduction or delamination contribute to active deformation

insar observations of low slip rates on the major faults of western tibet two contrasting views of the active deformation of asia dominate the debate about how continents deform i the deformation is primarily localized on major faults separating crustal blocks or ii deformation is distributed throughout the continental lithosphere in the first model western tibet is being extruded eastward between the major faults bounding the region surface displacement measurements across the western tibetan plateau using satellite radar interferometry insar indicate that slip rates on the karakoram and altyn tagh faults are lower than would be expected for the extrusion model and suggest a significant amount of internal deformation in tibet

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

global positioning system constraints on fault slip rates in southern california and northern baja mexico we use global positioning system gps estimates of horizontal site velocity to constrain slip rates on faults comprising the pacific north america plate boundary in southern california and northern mexico we enlist a simple elastic block model to parameterize the distribution and sum of deformation within and across the plate boundary we estimate a pacific north america relative plate motion rate of 49 3 mm yr one standard deviation consistent with nuvel 1a estimates we are able to resolve robust slip rate estimates for the southernmost san andreas san jacinto and elsinore faults 26 2 9 2 and 6 2 mm yr respectively and for the imperial and cerro prieto faults 35 2 and 42 1 mm yr respectively accounting for about 86 of the total plate motion the remaining 14 appears to be accommodated to the west of these fault systems probably via slip along the san clemente fault and or the san miguel vallecitos rose canyon and newport inglewood fault systems these results are highly consistent with paleoseismic estimates for slip rates implying that off fault strain accumulation within the deforming zone of the plate boundary is largely elastic we estimate that the seismically quiescent southernmost san andreas fault has incurred about 8 2 m of slip deficit over the last few hundred years presumably to be recovered during a future large earthquake

inescapable slow slip on the altyn tagh fault 1 gps surveys conducted in 1994 1998 and 2002 on the central portion of the altyn tagh fault confirm left lateral slip rates of 9 4 mm yr significantly slower than geological estimates of slip rate for the past several thousand years the measurements were obtained on a 300 km long profile between 88 and 91 e within one fault dimension of the mw 7 6 and mw 7 8 kunlun earthquakes of 1997 and 2001 the inferred elastic displacements from these events are incorporated into the interpreted 1994 2002 velocity field the recent serendipitous occurrence of these two large earthquakes on a sub parallel fault system suggests that slip on the kunlun fault may have recently accelerated thereby reducing the slip rate on the altyn tagh fault however geodetic data from northern tibet prior to the 2001 earthquake indicate present day rates similar to long term rates this suggests that systematic errors may be present in published geologic slip rate estimates for the altyn tagh fault

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

global imaging of polar cap patches with dual airglow imagers during a 2 h interval from 2240 to 2440 ut on 12 november 2012 regions of increased 630 0 nm airglow emissions were simultaneously detected by dual all sky imagers in the polar cap one at longyearbyen norway 78 1 n 15 5 e and the other at resolute bay canada 74 7 n 265 1 e the resolute bay incoherent scatter radar observed clear enhancements of the f region electron density up to 1012 m 3 within these airglow structures which indicates that these are optical manifestations of polar cap patches propagating across the polar cap during this interval of simultaneous airglow imaging the nightside dawnside dayside duskside half of the patches was captured by the imager at longyearbyen resolute bay this unique situation enabled us to estimate the dawn dusk extent of the patches to be around 1500 km which was at least 60 70 of the width of the antisunward plasma stream seen in the super dual auroral radar network convection maps in contrast to the large extent in the dawn dusk direction the noon midnight thickness of each patch was less than 500 km these observations demonstrate that there exists a class of patches showing cigar shaped structures such patches could be produced in a wide range of local time on the dayside nearly simultaneously and spread across many hours of local time soon after their generation

a test of present day plate geometries for northeast asia and japan alternative geometries for the present day configuration of plate boundaries in northeast asia and japan are tested using nuvel 1 and 256 horizontal earthquake slip vectors from the japan and northern kuril trenches statistical analysis of the slip vectors is used to determine whether the north american eurasian or okhotsk plate overlies the trench along the northern kuril trench sup vectors are well fit by the nuvel 1 pacific north america euler pole but are poorly fit by the pacific eurasia euler pole results for the japan trench are less conclusive but suggest that much of honshu and hokkaido are also part of the north american plate the simplest geometry consistent with the trench slip vectors is a geometry in which the north american plate extends south to 41 n and possibly includes northern honshu and southern hokkaido although these results imply that the diffuse seismicity that connects the lena river delta to sakhalin island and the eastern sea of japan records motion between eurasia and north america onshore geologic and seismic data define an additional belt of seismicity in siberia that cannot be explained with this geometry assuming that these two seismic belts constitute evidence for an okhotsk block two published kinematic models for motion of the okhotsk block are tested the first model which predicts motion of up to 15 mm yr 1 relative to north america is rejected because kuril and japan trench slip vectors are fit more poorly than for the simpler geometry described above the second model gives a good fit to the trench slip vectors but only if okhotsk north america motion is slower than 5 mm yr 1

what can we learn from 20 years of interseismic gps measurements across strike slip faults i use gps interseismic velocities and classic 2d elastic half space models with a screw dislocation to estimate the long term fault slip rate locking depth and the offset between the surface fault trace and the location of the dislocation below the seismogenic zone for 13 segments along 8 major strike slip faults using deduced strike slip rates and the position of the dislocation to normalize the interseismic velocities to facilitate comparison of spatial patterns of deformation i show that no substantial differences can be detected ruling out a large asymmetry in interseismic velocities across the 8 faults used in this study only the carrizo plain segment of the san andreas fault shows a significant asymmetry that cannot be explained by shifting the position of the dislocation at depth relative to the fault trace however the resulting perturbation is less than 10 of total strike slip rate fault traces are usually curved defining a concave side when the dislocation at depth is significantly offset from the fault trace the shift is always toward the block on the concave side of the fault trace this suggests that the fault zone in the lower crust may develop a simpler geometry more consistent with relative motion across the fault than its upper seismogenic part constrained by the structural complexity of the brittle crust since the faults used in this study are at different times in their interseismic period comparing the interseismic velocity fields across them allows identification of possible variations of the interseismic velocities with time when normalized by slip rate and dislocation location all the faults show the same interseismic strain with no significant differences between deduced locking depths these comparisons suggest that if temporal variations occur as suggested by some dynamic earthquake cycle models they are small and below the accuracy of the available geodetic measurements

the velocity field along the san andreas fault in central and southern california the velocity field within a 100 km broad zone centered on the san andreas fault between the mexican border and san francisco bay has been inferred from repeated surveys of trilateration networks in the 1973 1989 interval the velocity field has the appearance of a shear flow that remains parallel to the local strike of the fault even through such major deflections as the big bend of the san andreas fault in the transverse ranges of southern california across strike profiles of the fault parallel component of velocity exhibit the expected sigmoidal shape whereas across strike profiles of the fault normal component of velocity are flat and featureless no significant convergence upon the fault is observed even along the big bend sector of the fault simple dislocation models can explain most of the features of the observed velocity field but those explanations are not unique about 35 mm yr of relative plate motion is accounted for within the span of the trilateration networks geologic studies indicate that the secular slip rate on the san andreas fault is about 35 mm yr the agreement between these two estimates implies that most of the strain accumulation is elastic and will be recovered in subsequent earthquakes the relative motion observed across the san andreas fault 35 mm yr plus that observed across the eastern california shear zone 8 mm yr accounts for most 43 mm yr of the observed north america pacific relative plate motion 47 mm yr