structure and mechanical properties of faults in the north anatolian fault system from insar observations of coseismic deformation due to the 1999 izmit turkey earthquake 1 we study the structure and mechanical properties of faults in the north anatolian fault system by observing near fault deformation induced by the 1999 mw 7 4 izmit earthquake turkey we use interferometric synthetic aperture radar insar and global positioning system observations to analyze the coseismic surface deformation in the near field of the izmit rupture the overall observed coseismic deformation is consistent with deformation predicted by a dislocation model assuming a uniform elastic crust previous insar studies revealed small scale changes in the radar range across the nearby faults of the north anatolian fault system in particular the mudurnu valley and iznik faults e g wright et al 2001 we demonstrate that these anomalous range changes are consistent with an elastic response of compliant fault zones to the stress perturbation induced by the izmit earthquake we examine the spatial variations and mechanical properties of fault zones around the mudurnu valley and iznik faults using three dimensional finite element models in these models we include compliant fault zones having various geometries and elastic properties and apply stress changes deduced from a kinematic slip model of the izmit earthquake the best fitting models suggest that the inferred fault zones have a characteristic width of a few kilometers depth in excess of 10 km and reductions in the effective shear modulus of about a factor of 3 compared to the surrounding rocks the characteristic width of the best fitting fault zone models is consistent with field observations along the north anatolian fault system ambraseys 1970 our results are also in agreement with insar observations of small scale deformation on faults in the eastern california shear zone in response to the 1992 landers and 1999 hector mine earthquakes fialko et al 2002 fialko 2004 the inferred compliant fault zones likely represent intense damage and may be quite commonly associated with large crustal faults

shallow slip deficit due to large strike slip earthquakes in dynamic rupture simulations with elasto plastic off fault response summary slip inversions of geodetic data from several large magnitude 7 strike slip earthquakes point to coseismic slip deficit at shallow depths 3 4 km that is coseismic slip appears to decrease towards the earth surface while the inferred slip distribution may be consistent with laboratory derived rate and state friction laws suggesting that the uppermost brittle crust may be velocity strengthening there remains a question of how the coseismic slip deficit is accommodated throughout the earthquake cycle the consequence of velocity strengthening fault friction at shallow depths is that the deficit of coseismic slip is relieved by post seismic afterslip and interseismic creep however many seismic events with inferred shallow slip deficit were not associated with either resolvable shallow interseismic creep or robust shallow afterslip hence the origin of shallow slip deficit remains uncertain in this study we investigate whether inelastic failure in the shallow crust due to dynamic earthquake rupture can explain the inferred deficit of shallow slip evidence for such failure is emerging from geologic seismic and geodetic observations we find that the amount of shallow slip deficit is proportional to the amount of inelastic deformation near the earth surface such deformation occurs under a wide range of parameters that characterize rock strength in the upper crust however the largest magnitude of slip deficit in models accounting for off fault yielding is 2 4 times smaller than that inferred from kinematic inversions of geodetic data to explain this discrepancy we further explore to what extent assumptions in the kinematic inversions may bias the inferred slip distributions inelastic deformation in the shallow crust reduces coseismic strain near the fault introducing an additional artificial deficit of up to 10 per cent of the maximum slip in inversions of geodetic data that are based on purely elastic models the largest magnitude of slip deficit in our models combined with the bias in inversions accounts for up to 25 per cent of shallow slip deficit which is comparable but still smaller than 30 60 per cent deficit inferred from kinematic inversions we discuss potential mechanisms that may account for the remaining discrepancy between slip deficit predicted by elasto plastic rupture models and that inferred from inversions of space geodetic data

fine structure of the landers fault zone segmentation and the rupture process observations and modeling of 3 to 6 hertz seismic shear waves trapped within the fault zone of the 1992 landers earthquake series allow the fine structure and continuity of the zone to be evaluated the fault to a depth of at least 12 kilometers is marked by a zone 100 to 200 meters wide where shear velocity is reduced by 30 to 50 percent this zone forms a seismic waveguide that extends along the southern 30 kilometers of the landers rupture surface and ends at the fault bend about 18 kilometers north of the main shock epicenter another fault plane waveguide disconnected from the first exists along the northern rupture surface these observations in conjunction with surface slip detailed seismicity patterns and the progression of rupture along the fault suggest that several simple rupture planes were involved in the landers earthquake and that the inferred rupture front hesitated or slowed at the location where the rupture jumped from one to the next plane reduction in rupture velocity can tentatively be attributed to fault plane complexity and variations in moment release can be attributed to variations in available energy

three dimensional models of elastostatic deformation in heterogeneous media with applications to the eastern california shear zone summary we present a semi analytic iterative procedure for evaluating the 3 d deformation due to faults in an arbitrarily heterogeneous elastic half space spatially variable elastic properties are modelled with equivalent body forces and equivalent surface traction in a homogenized elastic medium the displacement field is obtained in the fourier domain using a semi analytic green function we apply this model to investigate the response of 3 d compliant zones cz around major crustal faults to coseismic stressing by nearby earthquakes we constrain the two elastic moduli as well as the geometry of the fault zones by comparing the model predictions to synthetic aperture radar inferferometric insar data our results confirm that the cz models for the rodman calico and pinto mountain faults in the eastern california shear zone ecsz can explain the coseismic insar data from both the landers and the hector mine earthquakes for the pinto mountain fault zone insar data suggest a 50 per cent reduction in effective shear modulus and no significant change in poisson s ratio compared to the ambient crust the large wavelength of coseismic line of sight displacements around the pinto mountain fault requires a fairly wide 1 9 km cz extending to a depth of at least 9 km best fit for the calico cz north of galway dry lake is obtained for a 4 km deep structure with a 60 per cent reduction in shear modulus with no change in poisson s ratio we find that the required effective rigidity of the calico fault zone south of galway dry lake is not as low as that of the northern segment suggesting along strike variations of effective elastic moduli within the same fault zone the ecsz insar data is best explained by cz models with reduction in both shear and bulk moduli these observations suggest pervasive and widespread damage around active crustal faults

reconciling patterns of interseismic strain accumulation with thermal observations across the carrizo segment of the san andreas fault article i nfo the carrizo segment of the san andreas fault separates rocks of the salinian block southwest of the fault characterized by high heat flow 75 95 mw m 2 and shallow seismicity b 10 km depth from rocks of the franciscancomplexandgreatvalleygroupnortheastofthefaultassociatedwithlowheat flow 50 60 mw m 2 and deeper seismicity b 20 km depth gps data from this region suggest that the northeast side of the fault accommodates more interseismic strain than the southwest side we show that by incorporating variations in depthtothebrittleductiletransitioninferredbasedonheat flowandseismicitydata we fitthegeodeticdatawell and achieve agreement with geologically accepted long term average slip rates with a 20 km wide zone with lowyoung smodulusneofthefault thiswidecompliantzoneisconsistentwithobservationssuggestingthatthe presence of large overpressures may be decreasing the elastic moduli in this region

fracture surface energy of the punchbowl fault san andreas system the energetics of earthquake rupture slip weakening and rupture surface formation are poorly understood by measuring the energy associated with fracture damage along the punchbowl fault in the devil s punchbowl los angeles county park part of the san andreas system chester et al show that the fracture surface energy for rupture along a mature fault of this type accounts for only a small fraction of the energy released during large earthquakes as determined by seismologists this suggests that mechanisms such as melt lubrication and thermal pressurization are responsible for slip weakening fracture energy is a form of latent heat required to create an earthquake rupture surface and is related to parameters governing rupture propagation and processes of slip weakening1 2 3 fracture energy has been estimated from seismological and experimental rock deformation data4 5 6 7 8 yet its magnitude mechanisms of rupture surface formation and processes leading to slip weakening are not well defined8 9 10 here we quantify structural observations of the punchbowl fault a large displacement exhumed fault11 12 in the san andreas fault system and show that the energy required to create the fracture surface area in the fault is about 300 times greater than seismological estimates would predict for a single large earthquake if fracture energy is attributed entirely to the production of fracture surfaces then all of the fracture surface area in the punchbowl fault could have been produced by earthquake displacements totalling 1 km but this would only account for a small fraction of the total energy budget and therefore additional processes probably contributed to slip weakening during earthquake rupture

contribution of viscoelastic flow in earthquake cycles within the lithosphere asthenosphere system faults slip relaxes lithospheric stress imposed by mantle flow and in turn transfers stress to the ductile regions the interplay of these systems governs the style of deformation at plate boundaries including the recurrence of seismic events however such deep processes remain challenging to incorporate in numerical simulations of earthquake cycles here we propose a model that couples fault slip and viscoelastic deformation to simulate fault dynamics in the lithosphere asthenosphere system our method resolves all phases of the earthquake cycle including dynamic rupture propagation afterslip slow slip events and the modulation of strain rate incurred in the ductile regions transient strain accelerations in the asthenosphere may follow both earthquakes and slow slip events shortly after the rupture depending on the rheology of the upper mantle and the magnitude of the event this study opens the door to greater insight into the variability of earthquake cycles by incorporating the dynamics of distributed deformation

micro and macroscopic models of rock fracture summary the anelastic deformation of solids is often treated using continuum damage mechanics an alternative approach to the brittle failure of a solid is provided by the discrete fiber bundle model here we show that the continuum damage model can give exactly the same solution for material failure as the fiber bundle model we compare both models with laboratory experiments on the time dependent failure of chipboard and fiberglass the power law scaling obtained in both models and in the experiments is consistent with the power law seismic activation observed prior to some earthquakes

low frequency sound speed and attenuation in sandy seabottom from long range broadband acoustic measurements a joint china u s underwater acoustics experiment was conducted in the yellow sea with a very flat bottom and a strong and sharp thermocline broadband explosive sources were deployed both above and below the thermocline along two radial lines up to 57 2 km and a quarter circle with a radius of 34 km two inversion schemes are used to obtain the seabottom sound speed one is based on extracting normal mode depth functions from the cross spectral density matrix the other is based on the best match between the calculated and measured modal arrival times for different frequencies the inverted seabottom sound speed is used as a constraint condition to extract the seabottom sound attenuation by three methods the first method involves measuring the attenuation coefficients of normal modes in the second method the seabottom sound attenuation is estimated by minimizing the difference between the theoretical and measured modal amplitude ratios the third method is based on finding the best match between the

rapid determination of near fault earthquake deformation using differential lidar improved near field measurements of earthquake slip and deformation patterns have the potential for expanding our understanding of fault behavior and the relationship of active faulting to topography current techniques for obtaining these measurements including field observation global navigation satellite systems displacement estimation and optical or radar remote sensing have limitations that can be mitigated by the inclusion of results from differential airborne light detection and ranging lidar analysis of the rupture zone the 2005 airborne lidar survey of the southern san andreas san jacinto and banning faults the b4 survey mapped 1100 km of the most seismically active fault systems in southern california for the purpose of providing a baseline for determining slip from a future earthquake we used the b4 survey to develop a processing algorithm that yields rapid estimates of near fault ground deformation using simultaneous cross correlation of both topography and backscatter intensity from pre earthquake and simulated postearthquake lidar datasets we show robust recovery of the direction and magnitude of an applied synthetic slip of 5 m in the horizontal and 0 5 m in the vertical within our area of study with clear discrimination between areas with and without applied slip we also successfully recovered more complex deformation from a modeled fault stepover in the same study area our results indicate that we should be able to recover slip to accuracies of better than 20 cm in the horizontal and 1 cm in the vertical at a spatial resolution of 15 m for lidar datasets with sample densities as low as 0 5 points m2

probing the mechanical properties of seismically active crust with space geodesy study of the coseismic deformation due to the 1992 mw7 3 landers southern california earthquake 1 the coseismic deformation due to the 1992 m w 7 3 landers earthquake southern california is investigated using synthetic aperture radar sar and global positioning system gps measurements the ers 1 satellite data from the ascending and descending orbits are used to generate contiguous maps of three orthogonal components east north up of the coseismic surface displacement field the coseismic displacement field exhibits symmetries with respect to the rupture plane that are suggestive of a linear relationship between stress and strain in the crust interferometric synthetic aperture radar insar data show small scale deformation on nearby faults of the eastern california shear zone some of these faults in particular the calico rodman and pinto mountain faults were also subsequently strained by the 1999 m w 7 1 hector mine earthquake i test the hypothesis that the anomalous fault strain represents essentially an elastic response of kilometer scale compliant fault zones to stressing by nearby earthquakes fialko et al 2002 the coseismic stress perturbations due to the landers earthquake are computed using a slip model derived from inversions of the insar and gps data calculations are performed for both homogeneous and transversely isotropic half space models the compliant zone model that best explains the deformation on the calico and pinto mountain faults due to the hector mine earthquake successfully predicts the coseismic displacements on these faults induced by the landers earthquake deformation on the calico and pinto mountain faults implies about a factor of 2 reduction in the effective shear modulus within the similar to 2 km wide fault zones the depth extent of the low rigidity zones is poorly constrained but is likely in excess of a few kilometers the same type of structure is able to explain high gradients in the radar line of sight displacements observed on other faults adjacent to the landers rupture in particular the lenwood fault north of the soggy lake has likely experienced a few centimeters of left lateral motion across 1 km wide compliant fault zone having the rigidity reduction of more than a factor of 2 the inferred compliant fault zones are interpreted to be a result of extensive damage due to past earthquakes

deformation on nearby faults induced by the 1999 hector mine earthquake interferometric synthetic aperture radar observations of surface deformation due to the 1999 hector mine earthquake reveal motion on several nearby faults of the eastern california shear zone we document both vertical and horizontal displacements of several millimeters to several centimeters across kilometer wide zones centered on pre existing faults portions of some faults experienced retrograde that is opposite to their long term geologic slip motion during or shortly after the earthquake the observed deformation likely represents elastic response of compliant fault zones to the permanent co seismic stress changes the induced fault displacements imply decreases in the effective shear modulus within the kilometer wide fault zones indicating that the latter are mechanically distinct from the ambient crustal rocks

space geodetic investigation of the coseismic and postseismic deformation due to the 2003 mw7 2 altai earthquake implications for the local lithospheric rheology 1 we use envisat advanced synthetic aperture radar data and spot optical imagery to investigate the coseismic and postseismic deformation due to the 27 september 2003 mw7 2 altai earthquake which occurred in the chuya basin near the russia china mongolia border on the basis of the synthetic aperture radar sar and spot data we determined the rupture location and developed a coseismic slip model for the altai earthquake the inferred rupture location is in a good agreement with field observations and the geodetic moment from our slip model is consistent with the seismic moment determined from the teleseismic data while the epicentral area of the altai earthquake is not optimal for radar interferometry in particular due to temporal decorrelation we were able to detect a transient signal over a time period of 3 years following the earthquake the signal is robust in that it allows us to discriminate among several commonly assumed mechanisms of postseismic relaxation we find that the postearthquake interferometric sar data do not warrant poroelastic rebound in the upper crust the observed deformation also disagrees with linear viscoelastic relaxation in the upper mantle or lower crust giving rise to a lower bound on the dynamic viscosity of the lower crust of the order of 1019 pa s the data can be explained in terms of fault slip within the seismogenic zone on the periphery of areas with high coseismic slip most of the postseismic deformation can be explained in terms of seismic moment release in aftershocks some shallow slip may have also occurred aseismically therefore the observed postseismic deformation due to the altai earthquake is qualitatively different from deformation due to other similarly sized earthquakes in particular the landers and hector mine earthquakes in the mojave desert southern california the observed variations in the deformation pattern may be indicative of different rheologic structure of the continental lithosphere in different tectonically active areas

seismic and geodetic evidence for extensive long lived fault damage zones during earthquakes slip is often localized on preexisting faults but it is not well understood how the structure of crustal faults may contribute to slip localization and energetics growing evidence suggests that the crust along active faults undergoes anomalous strain and damage during large earthquakes seismic and geodetic data from the calico fault in the eastern california shear zone reveal a wide zone of reduced seismic velocities and effective elastic moduli using seismic traveltimes trapped waves and interferometric synthetic aperture radar observations we document seismic velocities reduced by 40 50 and shear moduli reduced by 65 compared to wall rock in a 1 5 km wide zone along the calico fault observed velocity reductions likely represent the cumulative mechanical damage from past earthquake ruptures no large earthquake has broken the calico fault in historic time implying that fault damage persists for hundreds or perhaps thousands of years these fi ndings indicate that faults can affect rock properties at substantial distances from primary fault slip surfaces and throughout much of the seismogenic zone a result with implications for the amount of energy expended during rupture to drive cracking and yielding of rock and development of fault systems

effect of a compliant fault zone on the inferred earthquake slip distribution 1 we present a new semi analytic method to evaluate the deformation due to a screw dislocation in arbitrarily heterogeneous and or anisotropic elastic half plane the method employs integral transformations to reduce the governing partial differential equations to the integral fredholm equation of the second kind dislocation sources as well as spatial perturbations in the elastic properties are modeled using equivalent body forces the solution to the fredholm equation is obtained in the fourier domain using a method of successive over relaxation and is mapped into the spatial domain using the inverse fast fourier transform we apply this method to investigate the effect of a soft damage zone around an earthquake fault on the co seismic displacement field and on the earthquake slip distribution inferred from inversions of geodetic data in the presence of a kilometer wide damage zone with a reduction of the effective shear modulus of a factor of 2 inversions that assume a laterally homogeneous model tend to underestimate the amount of slip in the middle of the seismogenic layer by as much as 20 this bias may accentuate the inferred maxima in the seismic moment release at depth between 3 6 km suggested by previous studies of large strike slip earthquakes

slip accumulation and lateral propagation of active normal faults in afar we investigate fault growth in afar where normal fault systems are known to be currently growing fast and most are propagating to the northwest using digital elevation models we have examined the cumulative slip distribution along 255 faults with lengths ranging from 0 3 to 60 km faults exhibiting the elliptical or bell shaped slip profiles predicted by simple linear elastic fracture mechanics or elastic plastic theories are rare most slip profiles are roughly linear for more than half of their length with overall slopes always 0 035 for the dominant population of nw striking faults and fault systems longer than 2 km the slip profiles are asymmetric with slip being maximum near the eastern ends of the profiles where it drops abruptly to zero whereas slip decreases roughly linearly and tapers in the direction of overall aden rift propagation at a more detailed level most faults appear to be composed of distinct shorter subfaults or segments whose slip profiles while different from one to the next combine to produce the roughly linear overall slip decrease along the entire fault on a larger scale faults cluster into kinematically coupled systems along which the slip on any scale individual fault or fault system complements that of its neighbors so that the total slip of the whole system is roughly linearly related to its length with an average slope again 0 035 we discuss the origin of these quasilinear asymmetric profiles in terms of initiation points where slip starts and barriers where fault propagation is arrested in the absence of a barrier slip apparently extends with a roughly linear profile tapered in the direction of fault propagation

influence of dilatancy on the frictional constitutive behavior of a saturated fault zone under a variety of drainage conditions we use numerical simulations to investigate how fault zone dilatancy and pore fluid decompression influence fault strength and friction constitutive behavior dilatant hardening can change the frictional response and the effective critical stiffness kcr which determines the transition from stable to unstable sliding in velocity weakening fault zones we study the frictional shear strength response to numerical velocity stepping experiments and show that when the duration of pore fluid decompression is long compared to the time necessary for frictional evolution as dictated by rate and state friction both the effective critical slip distance dc and the effective shear strength direct effect a are increased we investigate the role of fault zone permeability k dilatancy coefficient varepsilon and the magnitude of shearing velocity of the fault zone vlp and compare results using the dieterich and ruina state evolution laws over the range from k 10 15 to 10 21 m2 dc increases from 25 m to 2 mm and a increases from 0 15 to 5 mpa we vary varepsilon from 10 5 to 10 3 and the size of the velocity perturbation from 3x to 1000x and find large increases in the values of dc and a which may lead to inhibition of unstable sliding our results indicate that spatial variations with either depth or lateral extent in varepsilon and k could result in significant changes in the drainage state in fault zones such variation may lead to spatial variation of the nucleation and propagation of earthquakes based upon the drainage capabilities of the fault zone

shallow rupture of the 2011 tarlay earthquake mw 6 8 eastern myanmar we use l band advanced land observation satellite palsar data to infer the distribution of subsurface fault slip during the tarlay earthquake m w 6 8 in eastern myanmar we find the total length of surface rupture is approximately 30 km with nearly 2 m maximum surface offset along the westernmost section of the nam ma fault the tarlay segment finite fault inversions constrained by interferometric synthetic aperture radar insar and pixel tracking data suggest that fault slip is concentrated within the upper 10 km of the crust maximum slip exceeds 4 m at a depth between 3 and 5 km comparison between field measurements and near fault deformation obtained from the insar range offset result suggests about 10 80 of displacement occurred within a 1 km wide zone off the main surface fault trace this off fault deformation may explain the shallow slip deficit that we observed during this earthquake we estimate a recurrence interval for tarlay like events to be 1600 6500 yrs at this section of the nam ma fault a detailed paleoseismological study is essential to clarify the slip behavior and the earthquake recurrence interval of the nam ma fault

convection in three dimensions with surface plates generation of toroidal flow this work presents numerical calculations of mantle convection that incorporate some of the basic observational constraints imposed by plate tectonics the model is three dimensional and includes surface plates it allows plate velocity to change dynamically according to the forces which result from convection we show that plates are an effective means of introducing a toroidal component into the flow field after initial transients the plate motion is nearly parallel to transform faults and in the direction that tends to minimizes the toroidal flow field the toroidal field decays with depth from its value at the surface the poloidal field is relatively constant throughout the layer but falls off slightly at the top and bottom boundaries layered viscosity increasing with depth causes the toroidal field to decay more rapidly effectively confining it to the upper low viscosity layer the effect of viscosity layering on the poloidal field is relatively small which we attribute to its generation by temperature variations distributed throughout the system the generation of toroidal flow by surface plates would seem to account for the observed nearly equal energy of toroidal and poloidal fields of plate motions on the earth a low viscosity region in the upper mantle will cause the toroidal flow to decay significantly before reaching the lower mantle the resulting concentration of toroidal flow in the upper mantle may result in more thorough mixing there and account for some of the geochemical and isotopic differences proposed to exist between the upper and lower mantles

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

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

particle size and energetics of gouge from earthquake rupture zones surprisingly considering the forces that we see at the surface not all the energy involved in an earthquake is transformed into ground motion much of it is consumed by frictional heating and rock pulverization an analysis of pulverized rock or gouge collected from the san andreas fault in california and from a rupture zone at 2 km depth in a south african gold mine contradicts the commonly held view that gouge surface energy is a negligible component of earthquake energy balance the analysis reveals unexpected diminutive particles in gouge samples indicating that pulverization not frictional heating is the major consumer of earthquake energy at depth this might explain the heat flow anomaly seen in the san andreas fault system and perhaps some other long standing puzzles in earthquake energetics grain size reduction and gouge formation are found to be ubiquitous in brittle faults at all scales1 2 3 4 and most slip along mature faults is observed to have been localized within gouge zones5 6 this fine grain gouge is thought to control earthquake instability3 6 7 8 and thus understanding its properties is central to an understanding of the earthquake process7 9 here we show that gouge from the san andreas fault california with 160 km slip and the rupture zone of a recent earthquake in a south african mine with only 0 4 m slip display similar characteristics in that ultrafine grains approach the nanometre scale gouge surface areas approach 80 m2 g 1 and grain size distribution is non fractal these observations challenge the common perception that gouge texture is fractal10 11 and that gouge surface energy is a negligible contributor to the earthquake energy budget3 9 12 we propose that the observed fine grain gouge is not related to quasi static cumulative slip but is instead formed by dynamic rock pulverization during the propagation of a single earthquake

revisiting the 1992 landers earthquake a bayesian exploration of co seismic slip and off fault damage existing models for the distribution of subsurface fault slip associated with the 1992 landers ca earthquake m w 7 3 show significant dissimilarities in particular they exhibit different amounts of slip at shallow depths 5 km these discrepancies can be primarily attributed to the ill posed nature of the slip inversion problem and to the use of physically unjustifiable smoothing or regularization constraints in this study we propose a new coseismic model obtained from the joint inversion of multiple observations in a relatively unregularized and fully bayesian framework we use a comprehensive data set including gps terrestrial geodesy multiple sar interferograms and co seismic offsets from correlation of aerial images these observations provide dense coverage of both near and far field deformation to limit the impact of modelling uncertainties we develop a 3 d fault geometry designed from field observations co seismic offsets and the distribution of aftershocks in addition we account for uncertainty in the assumed elastic structure used to compute the green s functions our solution includes the ensemble of all plausible models that are consistent with our prior information and fit the available observations within data and prediction uncertainties using near fault high resolution ground deformation measurements and the density of aftershocks we investigate the properties of the damage zone and its impact on the inferred slip at depth we attribute a part of the inferred slip deficit at shallow depth to our models not including the impact of a damage zone associated with a reduction of shear modulus in the vicinity of the fault

earthquake cycle fault zones and seismicity patterns in a rheologically layered lithosphere we study the coupled evolution of earthquakes and faults in a model consisting of a seismogenic upper crust governed by damage rheology over a viscoelastic substrate the damage rheology has two types of functional coefficients 1 a generalized internal friction separating states associated with material degradation and healing and 2 damage rate coefficients for positive degradation and negative healing changes the evolving damage modifies the effective elastic properties of material in the upper crust as a function of the ongoing deformation this simulates the creation and healing of fault systems in the upper seismogenic zone in addition to the vertically averaged thin sheet approximation we introduce a green function for three dimensional elastic half space for the instantaneous component of deformation the formulation accounts in an internally consistent manner for evolving deformation fields evolving fault structures aseismic energy release and spatiotemporal seismicity patterns these developments allow us to simulate long histories of crustal deformation and to study the simultaneous evolution of regional earthquakes and faults for various model realizations to focus on basic features of a large strike slip fault system we first consider a simplified geometry of the seismogenic crust by prescribing initial conditions consisting of a narrow damage zone in an otherwise damage free plate for this configuration the model generates an earthquake cycle with distinct interseismic preseismic coseismic and postseismic periods model evolution during each period is controlled by a subset of physical properties which may be constrained by geophysical geodetic rock mechanics and seismological data in the more generic case with a random initial damage distribution the model generates large crustal faults and subsidiary branches with complex geometries the simulated statistics depend on the space time window of the observational domain the results indicate that long healing timescale h describing systems with relatively long memory leads to the development of geometrically regular fault systems and the characteristic frequency size earthquake distribution conversely short h relatively short memory leads to the development of a network of disordered fault systems and the gutenberg richter earthquake statistics for intermediate values of h the results exhibit alternating overall switching of response from periods of intense seismic activity and the characteristic earthquake distribution to periods of low seismic activity and gutenberg richter statistics

displacement and stress associated with distributed anelastic deformation in a half space we present a suite of analytical and semianalytical solutions for the displacements strains and stress due to distributed anelastic deformation of finite strain volumes in a half space for cuboid sources we provide the solutions in the cases of antiplane strain plane strain and 3d deformation these expressions represent powerful tools for the analysis of deformation data to image distributed strain in the earth s interior and for the dynamic modeling of distributed deformation off faults including thermoelasticity poroelasticity and viscoelasticity we include computer programs that evaluate these expressions free of major singular points combined with formulas that describe the deformation around faults these solutions represent a comprehensive description of quasi static deformation throughout the earthquake cycle within the lithosphere asthenosphere system electronic supplement 1 animations of displacement and stress 1 http www bssaonline org lookup suppl doi 10 1785 0120160237 dc1

geodetic exploration of the elastic properties across and within the northern san andreas fault zone abstract relying on densely spaced gps data collected between 1996 and 2007 and on insar data spanning the 1992 2001 time period we explore the effects of lateral rheological heterogeneities across the san andreas fault near point reyes on the interseismic velocity field we evaluate heterogeneous elastic dislocation models including an asymmetric model with contrasting rigidities on either side of the san andreas fault and models with a narrow compliant fault zone that lead to high near fault strain rates we show that we cannot resolve a compliant zone from interseismic surface displacement measurements unless independent constraints on the locking depth exist we infer an 18 1 mm yr 1 slip rate on the san andreas fault with a 10 2 km locking depth and a 40 higher rigidity to the sw of the fault at bodega bay gps and edm data suggest a compliant zone on the saf with a 50 to 60 rigidity decrease but 25 km further south we find no evidence for a weak fault zone this suggests substantial variability in fault zone properties along the san andreas fault

a three dimensional semianalytic viscoelastic model for time dependent analyses of the earthquake cycle 1 exploring the earthquake cycle for large complex tectonic boundaries that deform over thousands of years requires the development of sophisticated and efficient models in this paper we introduce a semianalytic three dimensional 3 d linear viscoelastic maxwell model that is developed in the fourier domain to exploit the computational advantages of the convolution theorem a new aspect of this model is an analytic solution for the surface loading of an elastic plate overlying a viscoelastic half space when fully implemented the model simulates 1 interseismic stress accumulation on the upper locked portion of faults 2 repeated earthquakes on prescribed fault segments and 3 the viscoelastic response of the asthenosphere beneath the plate following episodic ruptures we verify both the analytic solution and computer code through a variety of 2 d and 3 d tests and examples on the basis of the methodology presented here it is now possible to explore thousands of years of the earthquake cycle along geometrically complex 3 d fault systems

contrasts in compliant fault zone properties inferred from geodetic measurements in the san francisco bay area author s materna k burgmann r abstract 2016 american geophysical union all rights reserved in crustal fault zones regions of damaged rock characterized by reduced elastic shear modulus can influence patterns of near field interseismic deformation in order to study these compliant fault zones cfzs and how they might develop over the lifetimes of faults we compare two fault segments with contrasting fault age and lithology along the san andreas fault in the san francisco bay area new geodetic measurements of the interseismic velocity fields at each location are used to constrain fault zone parameters through a markov chain monte carlo method at black mountain in the santa cruz mountains of the san francisco peninsula we do not find evidence for a compliant fault zone instead we find that the geodetic data are more consistent with a model of a single fault in a homogeneous elastic half space at lake san andreas a younger fault segment 35nkm farther north we find evidence for a compliant fault zone about 3 4 1 1 1 4nkm wide containing a shear modulus of about 40 of the shear modulus of the surrounding rock we also find that the best fitting cfz model at this location unlike the best fitting homogeneous half space model has a locking depth that agrees well with the observed depth of microseismicity based on differences in fault age cumulative displacement and lithology between black mountain and lake san andreas we infer that lithology plays an important and in this case perhaps a dominant role in the accumulation of fault zone damage structures and the development of cfzs over the lifetime of a fault

thermomechanical evolution of oceanic fracture zones a fracture zone fz model is constructed from existing models of the thermal and mechanical evolution of the oceanic lithosphere as the lithosphere cools by conduction thermal and mechanical boundary layers develop and increase in thickness as age 1 2 surface expressions of this development such as topography and deflection of the vertical i e gravity field are most apparent along major fz s because of the sharp age contrast a simple model including the effects of lateral heat transport but with no elastic layer predicts that variations in seafloor depth and deflection of the vertical will become increasingly smooth and ultimately disappear as the fz ages observations however show that both the fz topography and the deflection of the vertical remain sharp as the fz evolves these two observations as well as the observed asymmetry in deflection of the vertical profiles across the udintsev romanche and mendocino fz s are explained by including a continuous elastic layer in the model the asymmetry in deflection of the vertical is a consequence of elastic thickness variations across the fz modeling also shows that the evolution of the fz topography is extremely sensitive to the initial thermal structure near the ridge transform intersection model geoid steps and their development with age are used to access techniques for measuring geoid offsets across fz s reasonable step estimation techniques will underestimate the overall step amplitude by up to 50 this implies that abnormally thin thermal boundary layers derived from studies of geoid height versus age are not required by the data

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

an iterative spectral solution method for thin elastic plate flexure with variable rigidity s u m m a r y thin plate flexure theory provides an accurate model for the response of the lithosphere to vertical loads on horizontal length scales ranging from tens to hundreds of kilometres examples include flexure at seamounts fracture zones sedimentary basins and subduction zones when applying this theory to real world situations most studies assume a locally uniform plate thickness to enable simple fourier transform solutions however in cases where the amplitude of the flexure is prominent such as subduction zones or there are rapid variations in seafloor age such as fracture zones these models are inadequate here we present a computationally efficient algorithm for solving the thin plate flexure equation for non uniform plate thickness and arbitrary vertical load the iterative scheme takes advantage of the 2 d fast fourier transform to perform calculations in both the spatial and spectral domains resulting in an accurate and computationally efficient solution we illustrate the accuracy of the method through comparisons with known analytic solutions finally we present results from three simple models demonstrating the differences in trench outer rise flexure when 2 d variations in plate rigidity and applied bending moment are taken into account although we focus our analysis on ocean trench flexure the method is applicable to other 2 d flexure problems having spatial rigidity variations such as seamount loading of a thermally eroded lithosphere or flexure across the continental oceanic crust boundary

the effect of elastic layering on inversions of gps data for coseismic slip and resulting stress changes strike slip earthquakes we investigate the effect of depth dependent elasticity on slip inversions and coseismic stress change estimates for large strike slip earthquakes using a series of hypothetical models and the 1999 izmit turkey earthquake as examples slip inversions are performed using both semianalytical and finite element solutions for surface displacements due to a shear dislocation in layered and uniform elastic earth models we find that incorporating realistic increases to shear modulus with depth in our inversions increases recovered centroid depth and seismic potency relative to uniform elastic half space models recovered seismic moment is up to 40 greater for models incorporating depth dependent than it is for uniform elastic half space models incorporating depth dependent also increases our estimate of the maximum slip depth for the izmit turkey earthquake to at least 20 km our estimates of coseismic stress change in the upper crust do not change significantly when we incorporate depth dependent elasticity in our inversions as long as slip at depth is tuned increased to match surface displacements coseismic differential stresses in the lower crust increase by up to a factor of 3 in the near field but further from the fault stresses from layered and uniform elastic models are approximately equal with increasing depth in the mantle the ratio of modeled differential stresses for the layered and uniform elastic models approaches the ratio of mantle values for these two models we conclude that models of postseismic viscoelastic relaxation following large strike slip earthquakes should incorporate depth dependent elasticity but that uniform elastic half space models are adequate to calculate coseismic coulomb stresses in the upper crust for most triggering studies

the muddy bottom of lake pannon a challenge for dreissenid settlement late miocene bivalvia abstract the late miocene dreissenids of lake pannon a long existing eastern central european lake bear witness to two very different modes of life which allowed these bivalves to successfully settle in what appears to be an inhospitable environment one guild is restricted to the genera mytilopsis conrad 1858 and sinucongeria lorenthey 1894 these representatives are extreme r strategists which tend to produce temporal boom and bust populations during time windows of improved ecological conditions these opportunities are interpreted here to correlate with cyclic shifts in the epilimnion hypolimnion relation and the corresponding oxygenation of bottom waters events which are probably triggered by low frequency orbital forcing the second guild is composed solely of congeria partsch 1836 the paradox of the proliferation of a single species characterised by extreme size and weight in a muddy oxygen deficient lake environment avoided by nearly all other molluscs points to a hidden mechanism not accessible to other species we tentatively link this mechanism with chemosymbiosis functional morphology in interplay with a highly sulphidic over saturated interstitial water support an interpretation of the large congeria subglobosa as a successful h2s pump model

mitigation of atmospheric phase delays in insar data with application to the eastern california shear zone we present a method for estimating radar phase delays due to propagation through the troposphere and the ionosphere based on the averaging of redundant interferograms that share a common scene estimated atmospheric contributions can then be subtracted from the radar interferograms to improve measurements of surface deformation inversions using synthetic data demonstrate that this procedure can considerably reduce scatter in the time series of the line of sight displacements we demonstrate the feasibility of this method by comparing the interferometric synthetic aperture radar insar time series derived from ers 1 2 and envisat data to continuous global positioning system data from eastern california we also present results from several sites in the eastern california shear zone where anomalous deformation has been reported by previous studies including the blackwater fault the hunter mountain fault and the coso geothermal plant

postseismic deformation due to the mw 6 0 2004 parkfield earthquake stress driven creep on a fault with spatially variable rate and state friction parameters 1 we investigate the coseismic and postseismic deformation due to the m w 6 0 2004 parkfield california earthquake we produce coseismic and postseismic slip models by inverting data from an array of 14 continuous gps stations from the scign network kinematic inversions of postseismic gps data over a time period of 3 years show that afterslip occurred in areas of low seismicity and low coseismic slip predominantly at a depth of 5 km inversions suggest that coseismic stress increases were relaxed by predominantly aseismic afterslip on a fault plane the kinetics of afterslip is consistent with a velocity strengthening friction generalized to include the case of infinitesimal velocities we performed simulations of stress driven creep using a numerical model that evaluates the time dependent deformation due to coseismic stress changes in a viscoelastoplastic half space starting with a coseismic slip distribution we compute the time dependent evolution of afterslip on a fault plane and the associated displacements at the gps stations data are best explained by a rate strengthening model with frictional parameter a b 7 x 10 3 at a high end of values observed in laboratory experiments we also find that the geodetic moment due to creep is a factor of 100 greater than the cumulative seismic moment of aftershocks the rate of aftershocks in the top 10 km of the seismogenic zone mirrors the kinetics of afterslip suggesting that postearthquake seismicity is governed by loading from the nearby aseismic creep the san andreas fault around parkfield is deduced to have large along strike variations in rate and state frictional properties velocity strengthening areas may be responsible for the separation of the coseismic slip in two distinct asperities and for the ongoing aseismic creep occurring between the velocity weakening patches after the 2004 rupture

earthquake locations and three dimensional fault zone structure along the creeping section of the san andreas fault near parkfield ca preparing for safod 1 arrival time data from 453 local earthquakes and 6 explosions at parkfield ca are inverted for earthquake locations and three dimensional vp and vp vs structure the structure is dominated by the velocity contrast across the saf with the southwest side about 20 25 faster consistent with previous studies nearly all the earthquakes occur almost directly beneath the fault trace we find high vp vs anomalies that correlate with low resistivity features in a magnetotelluric model that are interpreted to represent fluids we locate a magnitude 2 earthquake that is a potential target event for the final stage of safod drilling yielding a depth of 3 1 km below surface and an epicenter 100 m southwest of the fault trace nonlinear analyses indicate 95 confidence relative and absolute uncertainties on the order of 500 700 m vertically and 200 300 m horizontally for this target earthquake

resolving the kinematics and moment release of early afterslip within the first hours following the 2016 mw 7 1 kumamoto earthquake implications for the shallow slip deficit and frictional behavior of aseismic creep continuous measurements of postseismic surface deformation provide insight into variations of the frictional strength of faults and the rheology of the lower crust and upper mantle as stresses following rupture are dissipated however due to the difficulty of capturing the earliest phase of afterslip most analyses have focused on understanding postseismic processes over timescales of weeks to years here we investigate the kinematics moment release and frictional properties of the earliest phase of afterslip within the first hours following the 2016 m w 7 1 kumamoto earthquake using a network of five minute sampled continuous gps stations using independent component analysis to filter the gps data we find that 1 early afterslip contributes only 1 of total moment release within the first hour and 8 after 24 hours this suggests that the slip model of the mainshock which we estimate using standard geodetic datasets e g insar gps and pixel offsets and which span the first four days of the postseismic period is largely reflective of the dynamic rupture process and we can rule out contamination of moment release by early afterslip 2 early afterslip shows no evidence of a delayed nucleation or acceleration phase where instead fault patches transition to immediate deceleration following rupture that is consistent with frictional relaxation under steady state conditions with dependence only on the sliding velocity 3 there is a close correlation between the near field aftershocks and afterslip within the first hours following rupture suggesting afterslip may still be an important possible triggering mechanism during the earliest postseismic period

coseismic deformation from the 1999 mw 7 1 hector mine california earthquake as inferred from insar and gps observations we use interferometric synthetic aperture radar insar and global positioning system gps observations to investigate static deformation due to the 1999 m w 7 1 hector mine earthquake that occurred in the eastern california shear zone interferometric decorrelation phase and azimuth offset measurements indicate regions of surface and near surface slip which we use to constrain the geometry of surface rupture the inferred geometry is spatially complex with multiple strands the southern third of the rupture zone consists of three subparallel segments extending about 20 km in length in a n45 w direction the central segment is the simplest with a single strand crossing the bullion mountains and a strike of n10 w the northern third of the rupture zone is characterized by multiple splays with directions subparallel to strikes in the southern and central the average strike for the entire rupture is about n30 w the interferograms indicate significant along strike variations in strain which are consistent with variations in the ground based slip measurements using a variable resolution data sampling routine to reduce the computational burden we invert the insar and gps data for the fault geometry and distribution of slip we compare results from assuming an elastic half space and a layered elastic space results from these two elastic models are similar although the layered space model predicts more slip at depth than does the half space model the layered model predicts a maximum coseismic slip of more than 5 m at a depth of 3 to 6 km contrary to preliminary reports the northern part of the hector mine rupture accommodates the maximum slip our model predictions for the surface fault offset and total seismic moment agree with both field mapping results and recent seismic models the inferred shallow slip deficit is enigmatic and may suggest that distributed inelastic yielding occurred in the uppermost few kilometers of the crust during or soon after the earthquake