stress transfer and its implication for earthquake hazard on the kunlun fault tibet abstract the 1600 km long kunlun fault striking e w to wnw ese had long been recognized as one of the major left lateral strike slip faults bounding the tibetan plateau and ranked one of the most active faults in china continent during the past hundred years over twenty strong earthquakes occurred along and near the kunlun fault including six large earthquakes m 7 since some major highly populated and industrialized cities are close to the kunlun fault understanding of stress transfer and earthquakes migration along the kunlun fault is most important for assessing seismic hazard in this region in this study by integrating coseismic effect viscoelastic relaxation and tectonic loading we studied the evolution of the regional coulomb stress field by analyzing a sequence of strong earthquakes along the kunlun fault we studied the stress evolution over one century by analysing a sequence of five earthquakes m 7 that occurred along the kunlun fault since 1937 the model of dislocation sources embedded in a mixed elastic inelastic layered half space was used and the layered model and relevant parameters were constrained by seismic studies fault rupture locations and geometry as well as slip distribution of earthquakes were taken from field observations and seismic studies numerical results showed a good correlation between stress transfer accumulation and earthquakes occurrence all four studied earthquakes occurred after the 1937 tuosuo lake quake were encouraged by the preceding earthquakes with positive stress loading in subject to the choice of the earthquake source parameter two or three out of four events occurred in regions that experienced previous coseismic and postseismic stress changes of at least 0 01 mpa suggesting that earthquake triggering due to stress transfer has occurred along the kunlun fault the total stress change since 1937 of the kunlun fault region has lead to high levels of stress accumulated on the xidatan dongdatan segment and maqin maqu segment which have not experienced any significant large earthquake over at least several hundred or several thousand years the accumulated stress raises the potential earthquake hazard in these areas our study demonstrated the crucial importance of postseismic viscoelastic relaxation in the stress transfer and accumulation following large earthquakes

space geodetic observations of nazca south america convergence across the central andes space geodetic data recorded rates and directions of motion across the convergent boundary zone between the oceanic nazca and continental south american plates in peru and bolivia roughly half of the overall convergence about 30 to 40 millimeters per year accumulated on the locked plate interface and can be released in future earthquakes about 10 to 15 millimeters per year of crustal shortening occurred inland at the sub andean foreland fold and thrust belt indicating that the andes are continuing to build little 5 to 10 millimeters per year along trench motion of coastal forearc slivers was observed despite the oblique convergence

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

a multilayer model of time dependent deformation following an earthquake on a strike slip fault a multilayer half space model of the earth is used in finite element calculations of time dependent deformation and stress following an earthquake on an infinitely long strike slip fault the model involves shear properties of an elastic upper lithosphere a standard viscoelastic linear solid lower lithosphere a maxwell viscoelastic asthenosphere and an elastic mesosphere time dependent displacements strains and stresses are computed both at the surface of the earth and at depth the analysis includes both systematic variations of fault and layer depths and comparisons with simpler elastic lithosphere over viscoelastic asthenosphere calculations for conditions which may be appropriate for the earth the creep of both the lower lithosphere and the asthenosphere can contribute to the postseismic deformation the magnitude of the deformation is enhanced by a short distance between the bottom of the fault slip zone and the top of the creep layer but is less sensitive to the thickness of the creeping layer furthermore postseismic restressing is increased as the lower lithosphere becomes more viscoelastic but the tendency for the width of the restressed zone to grow with time is retarded

fossil strain from the 1811 1812 new madrid earthquakes observations of postseismic deformation generally suggest that the effects of postseismic viscoelastic relaxation may persist for many decades after an earthquake in particular strain effects from the three great earthquakes that occurred in the new madrid seismic zone in 1811 1812 may influence present day measurements of ground deformation in this active seismic region of the central united states forward calculations using an earth rheology that may be appropriate for a continental intraplate region and a simple fault model for the 1811 1812 sequence suggest that postseismic relaxation may be an important factor in driving the unexpectedly high rate of shear deformation recently observed in the southern new madrid seismic zone

a sea level equation for seismic perturbations summary large earthquakes are a potentially important source of relative sea level variations since they can drive global deformation and simultaneously perturb the gravity field of the earth for the first time we formalize a gravitationally self consistent integral sea level equation suitable for earthquakes in which we account both for direct effects by the seismic dislocation and for the feedback from water loading associated with sea level changes our approach builds upon the well established theory first proposed in the realm of glacio isostatic adjustment modelling the seismic sea level equation is numerically implemented to model sea level signals following the 2004 sumatra andaman earthquake showing that surface loading from ocean water redistribution so far ignored in post seismic deformation modelling may account for a significant fraction of the total computed post seismic sea level variation

transient creep of a composite lower crust 1 constitutive theory a composite model is proposed to describe the time dependent response of the earth s lower crust the motivation for such a model is twofold first new observations of widespread postseismic deformation indicate that the deep continental crust responds viscoelastically having both long and short term decay times second by any number of observationally based rationales the lower crust is compositionally and structurally heterogeneous over many length scales for heterogeneities that have much smaller characteristic lengths than the minimum deformation wavelength of interest the aggregate rheology can be described by composite media theory for wavelengths of the order of the thickness of the lower crust 25 40 km and larger composite theory may be applied to heterogeneities that are smaller than about several hundred meters or equivalent to the vertical extent of a thick lower crustal mylonitic shear zone the composite media theory developed here is constructed using both eshelby mori tanaka theory for aligned generalized spheroidal inclusions and a generalized self consistent method the inclusions and matrix are considered to be maxwellian viscoelastic a rheology that is consistent with past homogeneous models of postseismic stress relaxation the composite theory presented here introduces a transient response to a suddenly imposed stress field which does not appear in homogeneous maxwell models analytic expressions for the amplitude and duration of the transient and for the effective long and short term viscosities of the composite are given which describe the sensitivity to inclusion concentration to shape and to ratio of inclusion to matrix viscosity r

on the effects of thermally weakened ductile shear zones on postseismic deformation 1 we present three dimensional 3 d numerical models of postseismic deformation following repeated earthquakes on a vertical strike slip fault our models use linear maxwell burgers and temperature dependent power law rheology for the lower crust and upper mantle we consider effects of viscous shear zones that result from thermomechanical coupling and investigate potential kinematic similarities between viscoelastic models incorporating shear zones and elastic models incorporating rate strengthening friction on a deep aseismic fault root we find that the thermally activated shear zones have little effect on postseismic relaxation in particular the presence of shear zones does not change the polarity of vertical displacements in cases of rheologies that are able to generate robust postseismic transients stronger rheologies can give rise to an opposite polarity of vertical displacements but the amplitude of the predicted transient deformation is generally negligible we conclude that additional to thermomechanical coupling mechanisms of strain localization are required for a viscoelastic model to produce a vertical deformation pattern similar to that due to afterslip on a deep extension of a fault we also investigate the discriminating power of models incorporating burgers and power law rheology these rheologies were proposed to explain postseismic transients following large m7 earthquakes in the mojave desert eastern california numerical simulations indicate that it may be difficult to distinguish between these rheologies even with high quality geodetic observations for observation periods less than a decade longer observations however may potentially allow discrimination between the competing models as illustrated by the model comparisons with available gps and interferometric synthetic aperture radar data

a note on adding viscoelasticity to earthquake simulators abstract here i describe how time dependent quasi static stress transfer can be implemented in an earthquake simulator code that is used to generate long synthetic seismicity catalogs most existing seismicity simulators use precomputed static stress interaction coefficients to rapidly implement static stress transfer in fault networks with typically tens of thousands of fault patches the extension to quasi static deformation which accounts for viscoelasticity of earth s ductile lower crust and mantle involves the precomputation of additional interaction coefficients that represent time dependent stress transfer among the model fault patches combined with defining and evolving additional state variables that track this stress transfer the new approach is illustrated with application to a california wide synthetic fault network

coseismic deformation from earthquake faulting on a layered spherical earth summary a method for calculating the static displacement field following earthquake faulting in a layered spherical earth is presented at shallow levels the earth s layering is characterized by sharp jumps in bulk and shear moduli at the conrad discontinuity and the moho and is therefore important to consider when evaluating crustal deformation the solution to the equations of static equilibrium is represented as a superposition of spheroidal and toroidal components that each depend on spherical harmonic degree and the moment tensor a method that has recently been applied to the problem of wave propagation on a layered spherical earth is here applied to the static deformation field by representing the point source in terms of discontinuities in the displacement stress vector the green s function for a particular source geometry is derived directly numerical tests are presented to verify the accuracy of the method and to illustrate the effects of sphericity and layering on the calculated deformation fields the effect of sphericity is generally less than about 2 per cent of maximum deformation within 100 km of an earthquake source at crustal depths comparisons between the deformation calculated on a spherical homogeneous earth and spherical layered earth show that up to 20 per cent errors would be introduced if the earth s layered structure were ignored the effect of layering is strongest for sources with a strong horizontal slip component

the 1995 kobe japan earthquake a long delayed aftershock of the offshore 1944 tonankai and 1946 nankaido earthquakes the 1995 kobe earthquake produced predominantly right lateral slip along the northeast southwest trending nojima fault approximately 200 km landward of the nankai trough southwest japan the last major earthquakes along the nankai trough the m 8 0 1944 tonanakai and m 8 2 1946 nankaido earthquakes involved about 4 m of interplate slip each releasing about 100 years of accumulated stress from the northwest southeast convergence of the philippine sea phs plate by calculating the change in coulomb failure stress on the nojima fault due to 1944 46 to 1995 postseismic relaxation of a thin low viscosity channel beneath southwest japan we show that stress diffusion from the 1940s interplate earthquakes increased the likelihood of future failure on the nojima fault by slowly but progressively unloading the normal stress on the fault over a 50 yr period

geodetic and seismic constraints on some seismogenic zone processes in costa rica new seismic and geodetic data from costa rica provide insight into seismogenic zone processes in central america where the cocos and caribbean plates converge seismic data are from combined land and ocean bottom deployments in the nicoya peninsula in northern costa rica and near the osa peninsula in southern costa rica in nicoya inversion of gps data suggests two locked patches centered at 14 2 and 39 6 km depth interplate microseismicity is concentrated in the more freely slipping intermediate zone suggesting that small interseismic earthquakes may not accurately outline the updip limit of the seismogenic zone the rupture zone for future large earthquakes at least over the short 1 year observation period we also estimate northwest motion of a coastal sliver block at 8 3 mm yr probably related to oblique convergence in the osa region to the south convergence is orthogonal to the trench cocos caribbean relative motion is partitioned here with 8 cm yr on the cocos panama block boundary including a component of permanent shortening across the fila costena fold and thrust belt and 1 cm yr on the panama block caribbean boundary the gps data suggest that the cocos plate panama block boundary is completely locked from 10 50 km depth this large locked zone as well as associated forearc and back arc deformation may be related to subduction of the shallow cocos ridge and or younger lithosphere compared to nicoya with consequent higher coupling and compressive stress in the direction of plate convergence

on the resolution of shallow mantle viscosity structure using postearthquake relaxation data application to the 1999 hector mine california earthquake 1 most models of lower crust mantle viscosity inferred from postearthquake relaxation assume one or two uniform viscosity layers a few existing models possess apparently significant radially variable viscosity structure in the shallow mantle e g the upper 200 km but the resolution of such variations is not clear we use a geophysical inverse procedure to address the resolving power of inferred shallow mantle viscosity structure using postearthquake relaxation data we apply this methodology to 9 years of gps constrained crustal motions after the 16 october 1999 m 7 1 hector mine earthquake after application of a differencing method to isolate the postearthquake signal from the background crustal velocity field we find that surface velocities diminish from 20 mm yr in the first few months to 2 mm yr after 2 years viscoelastic relaxation of the mantle with a time dependent effective viscosity prescribed by a burgers body provides a good explanation for the postseismic crustal deformation capturing both the spatial and temporal pattern in the context of the burgers body model which involves a transient viscosity and steady state viscosity a resolution analysis based on the singular value decomposition reveals that at most two constraints on depth dependent steady state mantle viscosity are provided by the present data set uppermost mantle viscosity depth 60 km is moderately resolved but deeper viscosity structure is poorly resolved the simplest model that explains the data better than that of uniform steady state mantle viscosity involves a linear gradient in logarithmic viscosity with depth with a small increase from the moho to 220 km depth however the viscosity increase is not statistically significant this suggests that the depth dependent steady state viscosity is not resolvably different from uniformity in the uppermost mantle

viscoelastic gravitational deformation by a rectangular thrust fault in a layered earth previous papers in this series have been concerned with developing the numerical techniques required for the evaluation of vertical displacements which are the result of thrust faulting in a layered elastic gravitational earth model this paper extends these methods to the calculation of fully time dependent vertical surface deformation from a rectangular dipping thrust fault in an elastic gravitational layer over a viscoelastic gravitational half space the elastic gravitational solutions are used together with the correspondence principle of linear viscoelasticity to give the solution in the laplace transform domain the technique used here to invert the displacements into the time domain is the prony series technique wherein the transformed solution is fit to the transformed representation of a truncated series of decaying exponentials purely viscoelastic results obtained are checked against results found previously using a different inverse transform method and agreement is excellent the major advantage in using the prony series technique is that deformations can be computed for arbitrary time intervals a series of results are obtained for a rectangular 30 dipping thrust fault in an elastic gravitational layer over viscoelastic gravitational half space time dependent displacements are calculated out to 50 half space relaxation times a or 100 maxwell times 2 m a significant effects due to gravity are shown to exist in the solutions as early as several a the difference between the purely viscoelastic solution and the viscoelastic gravitational solutions grows as time progresses typically the solutions with gravity reach an equilibrium value after 10 20 relaxation times when the purely viscoelastic solutions are still changing significantly additionally the length scaling which was apparent in the purely viscoelastic problem breaks down in the viscoelastic gravitational problem two independent length scales one of which changes with time are now seen to characterize the problem

postseismic deformation following the 1994 northridge earthquake identified using the localized hartley transform filter here we present a new mathematical tool the localized hartley hl transform hartley 1942 bracewell 1990 that allows for the filtering of 1 d time series through the identification of the power at various spatial and temporal wavelengths its application to and the associated results are presented from its application to continuous global positioning system gps data from southern california for the time period 1994 through 2006 the hl transform filter removes the high frequency components of the data and effectively isolates the longer period signal this long period signal is modeled as time dependent postseismic deformation using the viscoelastic gravitational model of fernandez and rundle 2004 for six stations selected for their proximity to the northridge earthquake the x y and z components of the postseismic deformation are compared to the filtered data results suggest that this long period deformation is a result of postseismic relaxation and that the hl transform filter provides an important new technique for the filtering of geophysical data consisting of the superposition of the effects of numerous complex sources at a variety of spatial and temporal scales

viscosity structure beneath northeast iceland the dynamics of crustal rifting in iceland depend strongly on the lower crustal rheology which controls the intensity of upper crustal stress concentration and scale time of heat diffusion from the underlying mantle plume while magnetotelluric surveys suggest the presence of a pervasive hot and highly ductile lowermost crust with possibly high fraction of partial melt observations of low seismic attenuation and strong shear wave transmission suggest a much cooler lower crust and upper mantle since viscosity is also sensitive to the degree of partial melt present viscosity estimates for these regions could shed light on the factors responsible for these observations in this study we utilize horizontal and vertical displacement vectors determined in gps campaigns in northeast iceland since 1986 these are modeled in terms of steady state tectonic loading plus postseismic postdiking relaxation following the 1975 1984 krafla rifting episode as first proposed by foulger and others with the elastic part of the model fixed by external constraints these data have a high sensitivity to the viscosity structure beneath iceland lower crust and upper mantle viscosities of about 3 1019 pa s and 3 1018 pa s respectively yield the closest agreement with the data our lower crustal viscosity estimate is consistent with the low attenuation and low subsolidus temperature for the lower crust inferred in recent studies inversions for fissure opening during the krafla rifting episode yield about 7 m of opening centered on the krafla rift as is observed allowing for contemporaneous deep rifting on vertical faults along the askja segment partially accounts for the observed increase in separation across the rift during 1987 1992 but does not account for large displacements in the southeastern part of the network or the large relative subsidence around the askja rift during 1987 1990 recent deep normal faulting beneath the askja rift and further south might explain all of these remaining features

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

global post seismic deformation summary we quantify the effects of post seismic deformation on the radial and horizontal components of the displacement in the near and far field of strike and dip slip point dislocations these sources are embedded in the elastic top layer of a spherical self gravitating stratified viscoelastic earth within the scheme of the normal mode technique we derive the explicit analytical expression of the fundamental matrix for the toroidal component of the field equations this component is propagated together with its spheroidal counterpart from the core mantle boundary to the earth s surface viscosity stratification at 670km depth influences the radial and horizontal deformation accompanying viscoelastic relaxation in the mantle over time scales of 103 104 yr both in the near field ranging from 100 to 500 km and in the far field from 103 to 5 x 103 km if the upper mantle is differentiated into a low viscosity zone beneath the lithosphere and a normal upper mantle faster relaxation is obtained for an asthenospheric viscosity of 1020 pa s we obtain for a strike slip dislocation and a seismic moment of 1022 n m characteristic of an average large earthquake horizontal rates of 1 4 mm yr 1 in the near field and 0 05 0 4 mm yr 1 in the far field these values are maintained over time scales of 10 103 yr larger rates with shorter duration are obtained if the viscosity is reduced in the low viscosity channel as expected strike slip dislocations are the most effective in driving horizontal deformation in the far field in comparison with dip slip ones it is noteworthy that horizontal velocities are maintained longer in the far field in comparison with radial ones which is not surprising since momentum is propagated in far regions essentially in the horizontal direction radial deformation is generally lower in the far field vlbi techniques with a precision of a few parts per billion over distances of 103 km can detect global post seismic deformation induced by large earthquakes our results affect the interpretation of the transfer of stress and seismic activity among different plate boundaries

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

the effect of global seismicity on the polar motion of a viscoelastic earth we evaluate the polar drift of a stratified viscoelastic earth generated by 20 years of global seismicity from the centroid moment tensor catalog 1977 1997 our estimate is better than that of soldati and spada 1999 because it accounts for the effects previously neglected of earthquakes at depths larger than 80 km in fact we show that deep focus and intermediate depth focus seismic events tend to affect the earth s inertia tensor more significantly than shallow ones specifically we find that the mean rate of polar drift evaluated over a 6 year time interval immediately following the seismic event due to a vertical dip slip source at the bottom of the asthenosphere 280 km depth in our model is 5 times larger than that generated by an analogous source located at the boundary between lithosphere and asthenosphere 80 km depth we conclude nevertheless that global seismic activity is not able to alter significantly the rotational parameters of the earth according to our computations the changes that it induces in the inertia tensor result in an average polar drift that is still significantly smaller than the observed one

probabilistic seismic hazard in the san francisco bay area based on a simplified viscoelastic cycle model of fault interactions 1 we construct a viscoelastic cycle model of plate boundary deformation that includes the effect of time dependent interseismic strain accumulation coseismic strain release and viscoelastic relaxation of the substrate beneath the seismogenic crust for a given fault system time averaged stress changes at any point not on a fault are constrained to zero that is kinematic consistency is enforced for the fault system the dates of last rupture mean recurrence times and the slip distributions of the assumed repeating ruptures are key inputs into the viscoelastic cycle model this simple formulation allows construction of stress evolution at all points in the plate boundary zone for purposes of probabilistic seismic hazard analysis psha stress evolution is combined with a coulomb failure stress threshold at representative points on the fault segments to estimate the times of their respective future ruptures in our psha we consider uncertainties in a four dimensional parameter space the rupture peridocities slip distributions time of last earthquake for prehistoric ruptures and coulomb failure stress thresholds we apply this methodology to the san francisco bay region using a recently determined fault chronology of area faults assuming single segment rupture scenarios we find that future rupture probabilities of area faults in the coming decades are the highest for the southern hayward rodgers creek and northern calaveras faults this conclusion is qualitatively similar to that of working group on california earthquake probabilities but the probabilities derived here are significantly higher given that fault rupture probabilities are highly model dependent no single model should be used to assess to time dependent rupture probabilities we suggest that several models including the present one be used in a comprehensive psha methodology as was done by working group on california earthquake probabilities

effects of source model variations on coulomb stress analyses of a multi fault intraplate earthquake sequence abstract fault models are quickly produced and iteratively improved over weeks to years following a major earthquake to characterise the dynamics of rupture evaluate the role of stress transfer and contribute to earthquake forecasting we model coulomb stress transfer cfs between the largest foreshock mw 5 4 1 year prior to first mainshock and three mw 6 1 to 6 5 earthquakes that occurred in a 12 hour period on january 22 1988 in central australia tennant creek earthquake sequence to investigate the role of static stress transfer in earthquake triggering relative to progressive source model development the effects of fault model variance are studied using cfs modelling of five different fault source model sequences 27 total models using different inputs from seismic and geospatial data some initial models do not yield positive cfs changes proximal to hypocentres but in all models preceding earthquakes generate positive cfs 0 1 bar on 10 to 30 of the forthcoming receiver fault rupture areas the most refined and data integrative model reveals cfs 0 7 to 13 bars within 2 km of impending hypocentres and large 30 to 99 areas of positive cfs when compared to global compilations of threshold cfs prior to impending ruptures average 3 71 bar median 1 bar this suggests that coulomb stress change theory adequately explains the tennant creek rupture sequence in the most refined model earthquake inter event times decrease as cfs increases suggesting that higher stress magnitudes may have more rapidly within hours triggered successive events thus accounting for some temporal aspects of this sequence cfs analyses provide a useful framework for understanding the spatiotemporal aspects of some intraplate earthquakes the progressive refinement of source models using emergent data may reduce epistemic uncertainties in the role of stress transfer that result from different model inputs approaches and results

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

evidence for and implications of a bering plate based on geodetic measurements from the aleutians and western alaska 1 global positioning system gps measurements are used to examine the hypothesis of a clockwise rotating bering plate originally proposed on the basis of seismicity the bering plate encompasses the bering sea western alaska and the aleutian islands gps measurements from the bering plate s interior show south to southwest motions of 3 5 mm a where a is years we construct elastic dislocation models to determine the spatial distribution and intensity of locked patches on the aleutian subduction interface we use these to remove interseismic strain from the gps observation and determine an arc translation velocity for each region of the aleutians revealing south and southwest motions of 4 8 mm a we combine the arc translation rates with measurements from the bering plate s interior sites and estimate the euler pole for the bering plate relative to north america to be located at 42 5 n 121 3 e with an angular speed of 6 0 ma the clockwise rotation of the bering plate may cause left lateral faulting in interior alaska the bering plate s interaction with south central alaska may be responsible for the decreased slip rate on the western denali fault and for contraction across the central alaska range we analyze slip partitioning along the aleutian arc on the basis of both gps measurements and slip azimuths of thrust earthquakes and find a systematic discrepancy between plate convergence direction and slip azimuths we conclude that slip partitioning in the back arc only develops west of amchitka pass whereas slip partitioning in the fore arc is present throughout the arc

modeling the holocene slip history of the wasatch fault utah coseismic and postseismic coulomb stress changes and implications for paleoseismicity and seismic hazard

surface deformation due to a strike slip fault in an elastic gravitational layer overlying a viscoelastic gravitational half space we extend a technique previously used to model surface displacements resulting from thrust faulting in an elastic gravitational layer over a viscoelastic gravitational half space to the case of strike slip faulting the method involves the calculation of the green s functions for a strike slip point source contained in an elastic gravitational layer over a viscoelastic gravitational half space the correspondence principle of linear viscoelasticity is applied to introduce time dependence the resulting green s functions are then integrated over the source region to obtain the near field displacements several sample calculations are presented involving 90 o and 30 o dipping faults and ruptures completely and partially through the elastic layer we also illustrate the time dependent deformation due to a buried fault results show that the use of a viscoelastic half space underlying an elastic layer introduces a long wavelength component into the deformation field cohen and kramer 1984 even in cases of non vertical strike slip fault and inclusion of gravitational effect that cannot be modeled by purely elastic techniques calculations have shown that vertical postseismic displacement is insignificant and that the horizontal movement is about the same magnitude as the coseismic strike slip displacement the inclusion of gravity affects the horizontal displacement due to vertical strike slip faulting in far field and the vertical displacement for dipping strike slip faulting in near field the computed results have been fit to the global positioning system measurements of the landers earthquake taken shortly after the main shock assuming a relaxation time of the order of days this relaxation time is considerably shorter than times of the order of years to decades found in previous studies the major differences between this detailed three dimensional and simplified two dimensional model are the decay of magnitude in displacement field and the distinct displacement pattern in the regions beyond the fault tip the displacement field due to the cyclic earthquakes was constructed by considering the finite fault length and inclusion of gravity it is found that the displacement field is dominated by the plate motion in the case of short recurrence time on the other hand a looping and migrating pattern in the displacement field is found in the case of very long recurrence time which is not seen in those 2d simplified models

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

analysis of the crustal thickness and poisson s ratio in eastern tibet from teleseismic receiver functions summary crustal thickness and poisson s ratio are two key parameters for investigating tectonic setting and evolution the h k technique has become popular to determinate their values in recent years however ifacomplexstructureexistsinthecrust thereverberatedphasesfromdifferent depths may interfere with each other resulting in reduction or even absence of the ppps phase from the moho such that the h k algorithm may not reveal unambiguous estimates of these two parameters in this paper the h k technique is applied to process a synthetic receiver function for a test case the result of which is compared with that from direct picking of the time delays of the converted and reverberated phases then we process the observational data recorded at two stations in eastern tibet determine the crustal thickness and the velocity ratio using the two methods compare the result with that obtained by xu et al a t the same location and analyse the potential causes for discrepancy as well as the reliability of the two methods finally the crustal thickness and the poisson s ratio in eastern tibet and sichuan basin are determined from the receiver functions recorded at 51 broad band stations using the two different methods the results indicate that the crustal thickness from the time delays is thicker than that from the h k algorithm near the eastern himalayan syntaxis and the crustal poisson s ratio in the rigid sichuan basin from the time delays ranges from 0 26 to 0 28 which are more reasonable than that from the h k 0 28 to 0 34 additionally the poisson s ratio under the faults from the time delays is found to be higher than those on the two sides which is consistent with the tectonic background and previous study

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

effects of lithospheric viscoelastic relaxation on the contemporary deformation following the 1959 mw 7 3 hebgen lake montana earthquake and other areas of the intermountain seismic belt 1 the 1959 mw 7 3 hebgen lake mt normal faulting earthquake occurred in an extensional stress regime near the yellowstone volcanic field time dependent crustal deformation data following this major earthquake were acquired by precise trilateration and gps surveys from 1973 to 2000 around the hebgen lake fault zone modeling the changes of baseline lengths across and near the fault reveals a lateral variation of transient rheology in which the lithosphere is stronger near the hebgen lake fault zone than in the vicinity of the yellowstone volcano system the models also imply that the lower crust is stronger than the upper mantle in agreement with results from studies of postseismic and post lake filling relaxations 100 years in addition evaluations of the postseismic motion produced by the hebgen lake and the 1983 mw 6 9 borah peak id earthquakes indicate that horizontal transient motion of up to 1 mm yr contribute significantly to the contemporary regional crustal deformation near the epicentral areas for the eastern basin and range 500 km south of the hebgen lake fault similar rheologic models were derived from the observed uplift associated with the lake bonneville rebound and were used to evaluate the postseismic deformation associated with six most recent paleoearthquakes of the wasatch fault zone and three m 5 6 historic earthquakes of northern utah the results show 0 1 mm yr of horizontal postseismic motion at present time that are within the horizontal uncertainties of continuous gps velocity from the basin and range and significantly smaller than the contemporary extension of 1 3 mm yr in the wasatch front

estimation of intraplate strain accumulation in the new madrid seismic zone from repeat gps surveys the new madrid seismic zone nmsz a region within the eastern portion of the north american plate where great earthquakes occurred in 1811 1812 provides a type example of large earthquakes within a relatively stable continental interior assessing the scale and causes of deformation in such regions as well estimation of the recurrence interval for the large earthquakes within them has long been recognized as an important but challenging issue for which the advent of space based geodesy provides an important new tool here we report initial results from two global positioning system gps surveys of a geodetic network spanning the new madrid seismic zone because the expected strain signal is small the data were analyzed in three different ways first site velocities were estimated and analyzed for spatial gradients parallel and perpendicular to the trend of the major strike slip faults inferred from seismicity this analysis suggests but does not require a few millimeters per year of right lateral shear across the southern portion of the seismic zone consistent with the earthquake focal mechanisms second we divided the network into near field subnetworks and found possibly significant shear associated with approximately e w shortening within the southern nmsz and possible n s shortening across the left step connecting the presumed strike slip faults third we compared the strain observed along individual baselines to that predicted from the results of earlier near field surveys which combined gps and triangulation data in the southern part of the seismic zone we found general agreement with the earlier study although our data suggest lower strain rates hence after only 2 years of measurements the gps data suggest but do not yet require detectable strain accumulation however given that great earthquakes occur in the area and that our results are reasonably consistent with the results of other geodetic studies using different data and with earthquake mechanisms it seems likely that we are seeing strain accumulation in the southern nmsz a simple interpretation of the data as showing about 3 to 5 mm yr 1 of right lateral fault parallel motion implies a 1000 to 3300 year recurrence for great earthquakes with 5 to 10 m slip assuming all the accumulating strain is released seismically this recurrence interval may be an underestimate if the observed strains are largely postseismic effects of the 1811 1812 earthquakes a possibility suggested by the observation that plate wide data show less motion across the nmsz future surveys should resolve this issue as the longer measurement spans yield more precise velocity estimates

viscosity of oceanic asthenosphere inferred from remote triggering of earthquakes a sequence of large interplate earthquakes from 1952 to 1965 along the aleutian arc and kurile kamchatka trench released accumulated stresses along nearly the entire northern portion of the pacific plate boundary the postseismic stress evolution across the northern pacific and arctic basins calculated from a viscoelastic coupling model with an asthenospheric viscosity of 5 x 10 17 pascal seconds is consistent with triggering of oceanic intraplate earthquakes temporal patterns in seismicity at remote plate boundaries and space based geodetic measurements of anomalous velocity over an area 7000 by 7000 kilometers square during the 30 year period after the sequence

asthenospheric viscosity inferred from correlated land sea earthquakes in north east japan the viscosity of the earth s mantle has been estimated from studies of post glacial rebound1 2 post seismic deformations of the ground following large earthquakes3 4 and aftershock sequences5 7 here we derive a value for the viscosity of the asthenosphere from a correlation found in the historical catalogue of subduction induced seismicity between the intraplate land and interplate sea earthquakes in north east japan the correlation persists since the time of reliably reported earthquakes in ad 1600 land events precede sea events by 36 yr with a mean distance between land sea pairs of 200 km because of the visocoelastic coupling of the lithosphere to the asthenosphere a plausible mechanism to explain the correlation is stress migration governed by the viscosity of the asthenosphere large land shocks generate diffuse like stress pulses which sweep past and unlock the thrust fault in the subduction zone thus triggering the sea events the correlation time and distance provide a measure of the speed of diffusion 5 6 km yr 1 and hence an estimate of the viscosity 7 1018 pa s

lithospheric rheology in southern italy inferred from postseismic viscoelastic relaxation following the 1980 irpinia earthquake 1 postseismic relaxation is modeled for the irpinia earthquake which struck southern italy in 1980 our goal is to understand the mechanism of surface deformation due to stress relaxation in the deep portion of the crust lithosphere system for a shallow normal fault source and to infer the rheological properties of the lithosphere in the extensional environment of peninsular italy the modeling is carried out within the framework of our normal mode viscoelastic theory at high spatial resolution in order to accurately resolve the vertical surface displacements for a seismic source the slip distribution over the faults is first inverted from coseismic leveling data the misfit between observed and modeled vertical displacements being minimized by means of the l2 norm slip distribution is then used within the viscoelastic model to invert for the viscosities of the lower crust and generally of the lithosphere inversion is based on leveling data sampled along three lines crossing the epicentral area postseismic deformation in the irpinia area is characterized by a broad region of crust upwarping in the footwall of the major fault and downwarping in the hanging wall that is responsible for the long wavelength features of the vertical displacement pattern the 2 analysis indicates that the irpinia earthquake cannot constrain the rheology of the upper mantle but only of the crust a full search in the viscosity spaces makes it possible to constrain the crustal viscosity to values of the order of 1019 pa s in agreement with previous studies carried out in different tectonic environments

a physical model for strain accumulation in the san francisco bay region summary strain accumulation in tectonically active regions is generally a superposition of the effects of background tectonic loading steady state dislocation processes such as creep and transient deformation in the san francisco bay region sfbr the most uncertain of these processes is transient deformation which arises primarily in association with large earthquakes as such it depends upon the history of faulting and the rheology of the crust and mantle which together determine the pattern of longer term decade scale post seismic response to earthquakes we utilize a set of 102 gps velocity vectors in the sfbr in order to characterize the strain rate field and construct a physical model of its present deformation we first perform an inversion for the continuous velocity gradient field from the discrete gps velocity field from which both tensor strain rate and rotation rate may be extracted the present strain rate pattern is well described as a nearly uniform shear strain rate oriented approximately n34 w 140 nanostrain yr 1 plus a n56 e uniaxial compression rate averaging 20 nanostrain yr 1 across the shear zone we fit the velocity and strain rate fields to a model of time dependent deformation within a 135 km wide arcuate shear zone bounded by strong pacific plate and sierra nevada block lithosphere to the sw and ne respectively driving forces are purely lateral consisting of shear zone deformation imposed by the relative motions between the thick pacific plate and sierra nevada block lithospheres assuming a depth dependent viscoelastic structure within the shear zone we account for the effects of steady creep on faults and viscoelastic relaxation following the 1906 san francisco and 1989 loma prieta earthquakes subject to constant velocity boundary conditions on the edges of the shear zone fault creep is realized by evaluating dislocations on the creeping portions of faults in the fluid limit of the viscoelastic model a priori plate boundary pb parallel motion is set to 38 mm yr 1 ag rid search based on fitting the observed strain rate pattern yields a mantle viscosity of 1 2 10 19 p as and a pb perpendicular convergence rate of 3m m yr 1 most of this convergence appears to be uniformly distributed in the pacific sierra nevada plate boundary zone

the interpretation of gravity changes and crustal deformation in active volcanic areas simple models like the well known point source of dilation mogi s source in an elastic homogeneous and isotropic half space are widely used to interpret geodetic and gravity data in active volcanic areas this approach appears at odds with the real geology of volcanic regions since the crust is not a homogeneous medium and magma chambers are not spheres in this paper we evaluate several more realistic source models that take into account the influence of self gravitation effects vertical discontinuities in the earth s density and elastic parameters and non spherical source geometries our results indicate that self gravitation effects are second order over the distance and time scales normally associated with volcano monitoring for an elastic model appropriate to long valley caldera we find only minor differences between modeling the 1982 1999 caldera unrest using a point source in elastic homogeneous half spaces or in elasto gravitational layered half spaces a simple experiment of matching deformation and gravity data from an ellipsoidal source using a spherical source shows that the standard approach of fitting a center of dilation to gravity and uplift data only excluding the horizontal displacements may yield estimates of the source parameters that are not reliable the spherical source successfully fits the uplift and gravity changes overestimating the depth and density of the intrusion but is not able to fit the radial displacements

postseismic relaxation across the central nevada seismic belt 1 two gps geodetic surveys across the basin and range br province of western north america have detected an anomalous compression east of the central nevada seismic belt cnsb the first network installed by the u s geological survey along an east west trending transect across the br at approximately 40 n consisted of 63 monuments observed campaign style in 1992 1996 and 1998 the second network installed by the california institute of technology consisted of 50 continuously operating gps receivers 18 of which were roughly along the same transect as the campaign survey we have used a viscoelastic postseismic relaxation model of the four largest earthquakes in the cnsb on the pleasant valley fault in 1915 the cedar mountain fault in 1932 and on the fairview peak and dixie valley faults in 1954 to interpret the geodetic velocities observed across the cnsb a model of postseismic relaxation with a lower crustal maxwell viscosity of 5 50 1018 pa s can explain the apparent compression regardless of the assumed mantle viscosity the geodetic velocities that we determined after removing the postseismic contribution indicate that within current gps detection limits the br is stable east of the cnsb and is undergoing rapid right lateral shear west of the cnsb

rheology of the lithosphere inferred from postseismic uplift following the 1959 hebgen lake earthquake 1 we have modeled the broad postseismic uplift measured by geodetic leveling in the epicentral area of the 1959 mw 7 3 hebgen lake montana earthquake a normal faulting event in the northern basin and range province to fit the observed uplift we calculate synthetic postseismic deformation using the relaxation response of a gravitational viscoelastic earth to the earthquake for a model with an elastic plate overlying a viscoelastic half space we find that the elastic thickness is 38 8 km which is close to the local crustal thickness the half space viscosity is estimated at 4 1018 0 5 pa s the leveling data do not require a viscous lower crust but permit a lower bound viscosity of 1020 pa s the observed broad uplift cannot be explained by physically plausible afterslip on and below the coseismic fault however local deformation across the coseismic surface rupture requires shallow afterslip reaching the surface the postseismic deformation induced by the estimated viscoelastic structure decays exponentially with a time constant of 15 years because of coupling between the elastic layer and the viscoelastic substrate this relaxation time is significantly longer than the 2 year maxwell relaxation time of the viscous half space itself our result suggests the importance of postseismic relaxation in interpreting high precision global positioning system velocities for example our model results suggest that postseismic transient velocities from both the 1959 hebgen lake and the 1983 mw 6 9 borah peak earthquakes are currently as large as 1 2 mm yr

migration of large earthquakes along the san jacinto fault stress diffusion from the 1857 fort tejon earthquake abstract historic and modern catalogs of seismicity in california suggest a migration of earthquakes m 5 6 along the san jacinto fault these events appear to travel down the fault with a migration speed of 1 7 krn year sanders 1993 this migration is explained by postseismic strain diffusion due to viscoelastic relaxation from the great fort tejon earthquake in 1857 we model this postseismic effect and find that significant stress diffuses down the san jacinto fault for distances in excess of 200 km and the corresponding migration may be a result of coulomb triggering from this stress perturbation the level of postseismic stress that seems to be the trigger level for most of the events is of order 1 bar since the temporal evolution of the postseismic strain field is mainly dependent on the inelastic properties of the lower crust and uppermost mantle the observed migration enables a viscosity estimate of 4x10 8 pas for this region of california introduction sanders 1993 has presented evidence that suggests large earthquakes on the san andreas fault zone safz can influence the seismicity on neighboring faults such as the san jacinto fault zone sjfz of particular interest it was shown that from 1899 to 1987 larger magnitude earthquakes m 5 6 along the sjfz appear to migrate in a southeast direction with a migration rate of 1 7 krn yr this led sanders to

surface coseismic gravity changes caused by dislocations in a 3 d heterogeneous earth summary this study describes an examination of surface gravity changes caused by dislocations within a 3 d heterogeneous earth this new theory is described using six independent dislocations a vertical strike slip two vertical dip slips perpendicular to each other and three tensile openings on three perpendicular planes a combination of the six independent dislocations is useful to compute coseismic gravity changes resulting from an arbitrary seismic source at an arbitrary position based on the 3 d lateral inhomogeneous p wave velocity model we deduce the 3 d density and s wave velocity models using the relation of karato finally numerical computations are performed for a location south of japan 30 n 135 e we calculate the coseismic gravity changes resulting from the six independent dislocations for source depths of 100 300 and 637 km respectively numerical results show that the maximum 3 d effect varies concomitantly with the dislocation type and the source depth for seismic problems the effect of elastic parameter is dominant

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

postseismic deformation following the june 2000 earthquake sequence in the south iceland seismic zone 1 we observe postseismic deformation on two spatiotemporal scales following mw 6 5 earthquakes in the south iceland seismic zone on 17 and 21 june 2000 we see a rapidly decaying deformation transient lasting no more than 2 months and extending about 5 km away from the two main shock ruptures this local month scale transient is captured by several radar interferograms and is also observed at a few campaign gps sites located near the faults a slower transient with a characteristic timescale of about a year is detected only by gps measurements the month scale deformation pattern has been explained by poroelastic rebound due to postearthquake pore pressure changes in contrast the year scale deformation can be explained by either afterslip at 8 14 km depth or viscoelastic relaxation of the lower crust and upper mantle in response to the coseismic stress changes the optimal viscoelastic models have lower crustal viscosities of 0 5 1 1019 pa s and upper mantle viscosity of 3 1018 pa s because of the limitations of our gps campaign data we consider both afterslip and viscoelastic relaxation as plausible mechanisms explaining the deformation field both types of postseismic deformation models suggest that the areas of large coseismic stress increase east of the 17 june and west of the 21 june ruptures continue to be loaded by the postseismic deformation

coseismic and postseismic subsurface displacements and strains for a dip slip normal fault in a three layer elastic gravitational medium a three layer elastic gravitational fault displacement model has been developed using elastic dislocation and employed to examine the effects of rigidity layering gravity and stress relaxation on surface and subsurface displacements fields for a dip slip normal fault within our three layer model layer 1 represents the upper crust layer 2 the lower crust and layer 3 the upper mantle the fault is embedded in the upper crust horizontal as well as vertical displacement components have been determined displacement field changes due to postseismic stress relaxation have been calculated using both the correspondence principle and relaxed rigidity moduli and results are in close agreement the relaxed rigidity method provides an accurate and computationally efficient method of examining postseismic relaxation postseismic relaxation within the lower two layers only gives surface uplift increasing footwall uplift and decreasing hangingwall subsidence and also increases the wavelength of surface vertical displacement postseismic stress relaxation within all three layers i e uniform half space produces a shorter wavelength of surface vertical deformation with respect to the coseismic response moho topography created during coseismic deformation is initially amplified during postseismic relaxation the relaxed moho topography is dependent on the strength of the upper crust as well as the strength of the lower crust and mantle gravity has a significant influence on displacements only at the postseismic stage when the effective rigidity of the lower layers is small coseismic and postseismic normal strains associated with dip slip normal faulting have been examined for a large normal basement fault intersecting the free surface the coseismic horizontal surface strain perpendicular to fault strike is compressive adjacent to the fault and in the footwall and tensile in the hangingwall away from the fault coseismic stress redistribution may generate significant tensile brittle failure of the upper crust adjacent to large basement faults

poroelastic rebound along the landers 1992 earthquake surface rupture maps of surface displacement following the 1992 landers california earthquake generated by interferometric processing of ers 1 synthetic aperture radar sar images reveal effects of various postseismic deformation processes along the 1992 surface rupture the large scale pattern of the postseismic displacement field includes large lobes mostly visible on the west side of the fault comparable in shape with the lobes observed in the coseismic displacement field this pattern and the steep displacement gradient observed near the emerson camp rock fault cannot be simply explained by afterslip on deep sections of the 1992 rupture models show that horizontal slip occurring on a buried dislocation in a poisson s material produces a characteristic quadripole pattern in the surface displacement field with several centimeters of vertical motion at distances of 10 20 km from the fault yet this pattern is not observed in the postseismic interferograms as previously proposed to explain local strain in the fault step overs peltzer et al 1996b we argue that poroelastic rebound caused by pore fluid flow may also occur over greater distances from the fault compensating the vertical ground shift produced by fault afterslip such a rebound is explained by the gradual change of the crustal rocks poisson s ratio value from undrained coseismic to drained postseismic conditions as pore pressure gradients produced by the earthquake dissipate using the poisson s ratio values of 0 27 and 0 31 for the drained and undrained crustal rocks respectively elastic dislocation models show that the combined contributions of afterslip on deep sections of the fault and poroelastic rebound can account for the range change observed in the sar data and the horizontal displacement measured at global positioning system gps sites along a 60 km long transect across the emerson fault savage and svarc 1997 using a detailed surface slip distribution on the homestead valley kickapoo and johnson valley faults we modeled the poroelastic rebound in the homestead valley pull apart a poisson s ratio value of 0 35 for the undrained gouge rocks in the fault zone is required to account for the observed surface uplift in the 3 5 years following the earthquake this large value implies a seismic velocity ratio vp vs of 2 1 consistent with the observed low vs values of fault zone guided waves at shallow depth li et al 1997 the sar data also reveal postseismic creep along shallow patches of the eureka peak and burnt mountain faults with a characteristic decay time of 0 8 years coseismic dilatant hardening locking process followed by post seismic pore pressure controlled fault creep provide a plausible mechanism to account for the decay time of the observed slip rate along this section of the fault

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

what can gps data tell us about the dynamics of post seismic deformation summary this paper describes differences in time varying post seismic deformation due to after slip and viscoelastic relaxation following large strike slip earthquakes and how these differences may be exploited to characterize the configuration and rheology of aseismically deforming material in the subsurface the analysis involves two steps first near field time dependent post seismic deformation characteristics of a typical mw 7 4 strike slip earthquake is defined based on analysis of gps data from three recent earthquakes secondly this earthquake is modelled assuming uniform slip along a rectangular surface and several classes of after slip and viscoelastic relaxation models that can reproduce the evolution of early post seismic displacements with time at a near field reference point are developed postseismic displacements and velocities away from the reference point where the differences are greatest and thus most likely to be distinguished with gps are compared i find that displacements from a judiciously designed network of continuous or frequently occupied campaign mode gps sites are sufficiently precise to distinguish linear viscoelastic relaxation from after slip on a vertical surface extending the coseismic rupture furthermore both the thickness and viscosity of a relaxing linearly viscoelastic layer may be identified to maximize what post seismic gps surveys can tell us particularly concerning potential relaxation of low viscosity layers in the crust and or upper mantle some gps sites should be located along strike beyond the rupture tip also far field gps sites should be occupied as frequently as sites close to the rupture

crustal deformation in great california earthquake cycles periodic crustal deformation associated with repeated strike slip earthquakes is computed for the following model a depth l h extending downward from the earth s surface at a transform boundary between uniform elastic lithospheric plates of thickness h is locked between earthquakes it slips an amount consistent with remote plate velocity vpl after each lapse of earthquake cycle time tcy lower portions of the fault zone at the boundary slip continuously so as to maintain constant resistive shear stress the plates are coupled at their base to a maxwellian viscoelastic asthenosphere through which steady deep seated mantle motions compatible with plate velocity are transmitted to the surface plates the coupling is described approximately through a generalized elsasser model we argue that the model gives a more realistic physical description of tectonic loading including the time dependence of deep slip and crustal stress buildup throughout the earthquake cycle than do simpler kinematic models in which loading is represented as imposed uniform dislocation slip on the fault below the locked zone parameters of the model are chosen to fit seismic and geologic constraints and the apparent time dependence of surface strain rates along presently locked traces of the 1857 and 1906 san andreas ruptures we fix vpl 35 mm yr tcy 160 years and l 9 11 km based on earthquake nucleation depths the geodetic data are then found to be described reasonably within the context of a model that is locally uniform along strike and symmetric about a single san andreas fault strand by lithosphere thickness h 20 30 km and elsasser relaxation time tr 10 16 years we therefore suggest that the asthenosphere appropriate to describe crustal deformation on the earthquake cycle time scale lies in the lower crust and perhaps crust mantle transition zone and has an effective viscosity between about 2 1018 and 1019 pa s depending on the thickness assigned to the asthenospheric layer predictions based on the chosen set of parameters are also consistent with data on variations of contemporary surface strain and displacement rates as a function of distance from the 1857 and 1906 rupture traces although the fit is degraded by asymmetry relative to the fault and by slip on adjacent fault strands

broadscale postseismic gravity change following the 2011 tohoku oki earthquake and implication for deformation by viscoelastic relaxation and afterslip the analysis of grace gravity data revealed postseismic gravity increase by 6 gal over a 500 km scale within a couple of years after the 2011 tohoku oki earthquake which is nearly 40 50 of the coseismic gravity change it originates mostly from changes in the isotropic component corresponding to the mrr moment tensor element the exponential decay with rapid change in a year and gradual change afterward is a characteristic temporal pattern both viscoelastic relaxation and afterslip models produce reasonable agreement with the grace free air gravity observation while their bouguer gravity patterns and seafloor vertical deformations are distinctly different the postseismic gravity variation is best modeled by the biviscous relaxation with a transient and steady state viscosity of 1018 and 1019 pa s respectively for the asthenosphere our calculated higher resolution viscoelastic relaxation model underlying the partially ruptured elastic lithosphere yields the localized postseismic subsidence above the hypocenter reported from the gps acoustic seafloor surveying

ongoing deformation of antarctica following recent great earthquakes antarctica s secular motion is thought to be almost everywhere governed by horizontal rigid plate rotation plus three dimensional deformations due to past and present changes in ice ocean loading known as glacial isostatic adjustment gia we use geodetic data to investigate deformation following the 1998 m 8 2 antarctic intraplate earthquake and show sustained three dimensional deformation along east antarctica s coastline 600 km from the rupture location using a model of viscoelastic deformation we are able to match observed northward velocity changes and either east or height but not all three directions simultaneously apparently partly due to lateral variations in mantle rheology our modeling predicts that much of antarctica may still be deforming with further deformation possible from the 2004 m 8 macquarie ridge earthquake this previously unconsidered mode of antarctic deformation affects geodetic estimates of plate motion and gia its viscous nature raises the prospect of further present day deformation due to earlier great earthquakes

coseismic displacements caused by point dislocations in a three dimensional heterogeneous spherical earth model summary we present a method to study the coseismic displacements caused by point dislocations in a 3 d heterogeneous spherical earth model specifically first we express the solutions by the sum of unperturbed displacements on a spherically symmetric earth model and the effects of the earth s laterally inhomogeneous structures 3 d effect then we deliberately decompose the 3 d effect into two contributions the effect of seismic sources and the effect of the earth s lateral increments which are obtainable respectively by perturbation of seismic source functions and perturbation of equilibrium equation next we present new formulations for six point seismic sources a vertical strike slip two vertical dip slips perpendicular to each other and three tensile openings on three perpendicular planes a combination of the six dislocations is useful to compute the 3 d effect resulting from an arbitrary seismic source at an arbitrary position finally based on a 3 d earth model we calculate the coseismic displacements resulting from three types of point dislocations results show that the maximum 3 d effect on coseismic displacements which varies concomitantly with the dislocation type and the source depth is about 1 2 per cent of the corresponding unperturbed solutions among those parameters the effect due to the heterogeneities in s wave velocity is biggest

mobility of continental mantle evidence from postseismic geodetic observations following the 1992 landers earthquake the crust around the rupture zone of the 1992 landers earthquake has continued to deform in the years following the earthquake at rates 3 times greater than pre earthquake rates we use a combination of global positioning system gps and synthetic aperture radar insar data collected during a 3 year epoch following the earthquake in order to investigate postseismic mechanisms responsible for the high transient velocities in order to maximize the potential signal from viscoelastic relaxation we evaluate and model postseismic relaxation following the first few months of documented accelerated deformation the combination of gps and insar data allows us to establish viscoelastic relaxation of the lower crust and upper mantle as the dominant postseismic process and to discriminate among possible viscoelastic models the data particularly require the presence of a highly ductile uppermost mantle beneath the central mojave domain with temperature between the wet and dry basalt solidus this is consistent with independent seismic and geochemical inferences of a regionally warm uppermost mantle further consideration of seismic velocity variations in conjunction with faulting patterns within the mojave desert suggests that the primary faulting characteristics of the mojave desert namely the pervasive late cenozoic deformation within the eastern california shear zone versus the near absence of faults in the western mojave domain are controlled by the rheology of the uppermost mantle

the relationship between the instantaneous velocity field and the rate of moment release in the lithosphere summary instantaneous velocity gradients within the continental lithosphere are often related to the tectonic driving forces this relationship is direct if the forces are secular as for the case of loading of a locked section of a subduction interface by the downgoing plate if the forces are static as for the case of lateral variations in gravitational potential energy then velocity gradients can be produced only if the lithosphere has on average zero strength the static force model may be related to the long term velocity field but not the instantaneous velocity field typically measured geodetically over a period of several years because over short time intervals the upper lithosphere behaves elastically in order to describe both the short and long term behaviour of an elastic lithosphere viscoelastic asthenosphere system in a selfconsistent manner i construct a deformation model termed the expected interseismic velocity eiv model assuming that the lithosphere is populated with faults that rupture continually each with a definite mean recurrence time and that the earth is well approximated as a linear elastic viscoelastic coupled system i derive a simple relationship between the instantaneous velocity field and the average rate of moment release in the lithosphere examples with synthetic fault networks demonstrate that velocity gradients in actively deforming regions may to a large extent be the product of compounded viscoelastic relaxation from past earthquakes on hundreds of faults distributed over large 10 6 km 2 areas

coseismic compression dilatation and viscoelastic uplift subsidence following the 2012 indian ocean earthquakes quantified from satellite gravity observations the 2012 indian ocean earthquake sequence mw 8 6 8 2 is a rare example of great strike slip earthquakes in an intraoceanic setting with over a decade of gravity recovery and climate experiment grace data we were able to measure and model the unanticipated large coseismic and postseismic gravity changes of these events using the approach of normal mode decomposition and spatial localization we computed the gravity changes corresponding to five moment tensor components our analysis revealed that the gravity changes are produced predominantly by coseismic compression and dilatation within the oceanic crust and upper mantle and by postseismic vertical motion our results suggest that the postseismic positive gravity and the postseismic uplift measured with gps within the coseismic compressional quadrant are best fit by ongoing uplift associated with viscoelastic mantle relaxation our study demonstrates that the grace data are suitable for analyzing strike slip earthquakes as small as mw 8 2 with the noise characteristics of this region

global postseismic rebound of a viscoelastic earth theory for finite faults and application to the 1964 alaska earthquake a spherically symmetric earth model with viscoelastic rheology is used to study the postseismic rebound associated with finite lithospheric dislocations we perform a systematic study of surface deformations due to sources characterized by two and three dimensional faults modeled by a linear and planar distribution of point sources our approach is based on the normal mode technique for a layered earth with linear viscoelastic rheology and allows for a self consistent description of the time evolution of postseismic displacements due to strike and dip slip faults as a case study we compare the predicted horizontal displacements due to the 1964 alaska earthquake with very long baseline interferometry vlbi baselines changes observed in this region in the period 1984 1989 although subduction and postglacial isostatic adjustment are expected to contribute significantly to present day velocities our results show that the postseismic rebound due to the 1964 alaska earthquake plays a relevant role in the changes of several vlbi baselines the last section is devoted to the analysis of the evolution of other north american baselines as suggested by recent investigations based on forward approaches isostatic readjustment of the earth s crust in response to the melting of the last pleistocene ice sheets is a major contributor to baseline variations in this area our results indicate that a correct interpretation of vlbi baseline changes in north america should account also for the effects of postseismic deformation

transient rheology of the upper mantle beneath central alaska inferred from the crustal velocity field following the 2002 denali earthquake the m7 9 2002 denali earthquake alaska is one of the largest strike slip earthquakes ever recorded the postseismic gps velocity field around the 300 km long rupture is characterized by very rapid horizontal velocity up to 300 mm yr for the first 0 1 years and slower but still elevated horizontal velocity up to 100 mm yr for the succeeding 1 5 years i find that the spatial and temporal pattern of the displacement field may be explained by a transient mantle rheology representing the regional upper mantle as a burghers body 1 infer steady state and transient viscosities of 1 2 8 x 10 18 pa s and 2 1 0 x 10 17 pa s respectively corresponding to material relaxation times of 1 3 and 0 05 years the lower crustal viscosity is poorly constrained by the considered horizontal velocity field and the quoted mantle viscosities assume a steady state lower crust viscosity that is 7 1 systematic bias in predicted versus observed velocity vectors with respect to a fixed north america during the first 3 6 months following the earthquake is reduced when all velocity vectors are referred to a fixed site this suggests that the post denali gps time series for the first 1 63 years are shaped by a combination of a common mode noise source during the first 3 6 months plus viscoelastic relaxation controlled by a transient mantle rheology

postseismic relaxation theory on the spherical earth abstract postseismic displacements and strains observed at the earth9s surface can be explained through the relaxation of a viscoelastic asthenosphere underlying a purely elastic crust a theory is presented for modeling the effects of postseismic relaxation on a spherically symmetric earth for an earthquake point source located in the upper elastic layer the displacement field is decomposed into its toroidal and spheroidal components a linear maxwell rheology in the viscoelastic layers is assumed enabling the use of the correspondence principle for the solutions of the equations of static equilibrium displacement and strain fields are then calculated using normal mode summation computational results are presented for two simple earthquake sources a strike slip fault and a uniaxial thrust fault the patterns of postseismic displacements and strains are found to depend strongly on both the earth model and earthquake source geometry in particular the elastic plate thickness asthenosphere thickness fault type and fault length each play a major role in determining the spatial pattern of postseismic relaxation effects asthenospheric viscosity controls the temporal pattern of relaxation

viscous gravitational relaxation summary this paper is concerned with a detailed examination of the response of maxwell models of the planet to surface mass loads particular attention is devoted to an examination of the factors which determine the isostatic response since the understanding of this response is crucial in a number of different geodynamic problems one particular example which we discuss in detail is concerned with the prediction of free air gravity anomalies produced by large scale deglaciation events using the methods developed here we are able to provide the first direct assessment of the importance of initial isostatic disequilibrium on the observed relative sea level variations and free air gravity anomalies forced by the melting of the laurentide ice sheet we are therefore able to estimate the extent to which such initial disequilibrium might influence the inference of mantle viscosity from isostatic adjustment data our calculations establish that free air gravity data although they are sensitive to the degree of initial disequilibrium provide an extremely high quality constraint upon the viscosity of the lower mantle

a possible dependence of tectonic strength on the age of the crust in asia in asia the intensity and style of active tectonics appears to depend on the age of the last orogenic activity the shields have remained essentially undeformed during the india eurasian collision but paleozoic and mesozoic orogenic belts apparently have been reactivated by this collision with a suggestion of greater reactivation and more diffuse deformation of the younger belts if the greater observed heat flow in regions of more recent orogenic activity reflects at least in part a greater heat flow from the mantle beneath the younger belts then the temperatures in the mantle beneath the younger belts should be higher than beneath older belts and shields because of the strong dependence on temperature of the creep strength of minerals particularly of olivine the crust and mantle beneath the hotter younger belts should be much weaker than those beneath older belts this difference in temperature and consequent difference in strength may be the cause of the greater reactivation of younger belts

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

asthenospheric viscosity and stress diffusion a mechanism to explain correlated earthquakes and surface deformations in ne japan summary a significant correlation is found in both space and time between the intraplate land and interplate sea thrust zone only earthquakes in tohoku ne japan that has persisted since the times of reliably reported events in ad 1600 the correlation peaks at a land lead of about 36 yr with an average correlation distance of 200km with the implication of an average strain migration rate of 5 6 km yr 1 the correlation is highly significant 99 per cent both from formal statistics and from tests of random shuffles of the data additional analysis of the data as a point process confirms the results of the correlation analysis the sharpness of the correlation peak when compared to the individual times of occurrence of the land and sea events suggests a trigger mechanism to explain the correlation the general model ofsubduction rupture rebound is extended to include additional features the buckling of the land plate from the force of the subducting slab and the viscoelastic coupling of the plate to the underlying asthenosphere a buckle produces a high stress region in the continental plate where earthquakes are more prone to occur thus producing the spatial correlation in the data this may also explain the preferred location on land for the smaller modern day seismic events in ne japan the viscoelastic coupling controls the interaction between the land and sea events resulting in the temporal correlation in the data because of viscosity the model equations are diffuse like with strain pulses as solutions thus from the inferred strain migration rate it is possible to estimate asthenospheric viscosity 7 1018pa s using this model a large land shock generates a strain pulse that affects the locked fault at the thrust zone several decades later as the continental plate tends to pull away from the subducting slab the frictional force arising from the overburden pressure is reduced thus unlocking the fault and triggering a sea earthquake the viscoelastic model is also used to explain surface deformations measured by triangulation surveys in japan in 1904 and 1964 horizontal displacements which we believe are surface manifestations of the strain pulse from the large 1896 riku u land shock m 7 5 in ne japan are fit well by the model and provide a viscosity estimate 13 1018 pa s

def3d a fem simulation tool for computing deformation near active faults and volcanic centers abstracts most analytical solutions of deformation near active and volcanic centers are limited to simple geometries and homogeneous media to solve more complex problems we have developed a fem software package called def3d for modeling deformation caused by earthquakes or magma chambers in laterally inhomogeneous media features presently available include modeling of split node technique equivalent body forces and surface tractions def3d presently supports the isotropic elastic and viscoelastic materials behaving as a maxwell body the program has been verified in various test cases by strict comparison with analytical solutions displacements following the 2008 wenchuan earthquake and magma induced surface deformation near changbaishan volcano are used to test the reliability of the software package

effect of viscoelastic postseismic relaxation on estimates of interseismic crustal strain accumulation at yucca mountain nevada 1 we estimate the long term crustal strain rate at yucca mountain ym nevada from gps velocities taking into account viscoelastic relaxation following recent earthquakes to remove bias associated with transient deformation the ym data reveal postseismic relaxation in time series non linearity and geographic variation of the transient signal from the data we estimate best fitting lower crust and upper mantle viscosities of 1019 5 pa s and 1018 5 pa s respectively once the relaxation model predictions are subtracted from the data the long term shear strain accumulation rate is between 16 3 and 25 1 nanostrains year ns yr to 99 confidence a range much larger than the formal uncertainties from gps measurement we conclude that 1 a maxwell viscoelastic model cannot explain all the deformation observed at ym 2 uncertainty in viscosities dominates uncertainty in ym strain rates and 3 the effects of large recent earthquakes must be accounted for in seismic hazard studies using gps

spectral finite element approach to post seismic relaxation in a spherical compressible earth application to gravity changes due to the 2004 sumatra andaman earthquake

interaction of the san jacinto and san andreas fault zones southern california triggered earthquake migration and coupled recurrence intervals two lines of evidence suggest that large earthquakes that occur on either the san jacinto fault zone sjfz or the san andreas fault zone safz may be triggered by large earthquakes that occur on the other first the great 1857 fort tejon earthquake in the safz seems to have triggered a progressive sequence of earthquakes in the sjfz these earthquakes occurred at times and locations that are consistent with triggering by a strain pulse that propagated southeastward at a rate of 1 7 kilometers per year along the sjfz after the 1857 earthquake second the similarity in average recurrence intervals in the sjfz about 150 years and in the mojave segment of the safz 132 years suggests that large earthquakes in the northern sjfz may stimulate the relatively frequent major earthquakes on the mojave segment analysis of historic earthquake occurrence in the sjfz suggests little likelihood of extended quiescence between earthquake sequences

cathodoluminescence fluid inclusion and stable c o isotope study of tectonic breccias from thrusting plane of a thin skinned calcareous nappe basal hydraulic breccias of alpine thin skinned mura nappe were investigated by means of cathodoluminescence petrography stable isotope geochemistry and fluid inclusions analysis our study reveals an unusual dynamic fluid regime along basal thrust plane during final episode of the nappe emplacement over its metamorphic substratum basal thrusting fluids enriched in 18o silica alumina alkalies and phosphates were generated in the underlying metamorphosed basement at epizonal conditions corresponding to the temperatures of 400 450 c the fluids fluxed the tectonized nappe base leached evaporite bearing formations in hangingwall whereby becoming oversaturated with sulphates and chlorides the fluids further modified their composition by dedolomitization and isotopic exchange with the host carbonatic cataclasites newly formed mineral assemblage of quartz phlogopite albite potassium feldspar apatite dravite tourmaline and anhydrite precipitated from these fluids on cooling down to 180 200 c finally the cataclastic mush was cemented by calcite at ambient anchizonal conditions recurrent fluid injections as described above probably enhanced the final motion of the mura nappe

stress evolution before and after the 2008 wenchuan china earthquake abstract we examine the distribution of coulomb stress before and following the m 7 9 wenchuan earthquake and model the time dependent components of the stress field into the future our modelling shows that the combined coseismic plus postseismic viscoelastic stress change due to the preceding large events m 6 7 at the hypocentral area of the wenchuan earthquake is negative which may have led to a delay on its occurrence between 16 and 95 yr depending on the rake of the rupture on the other hand coseismic stress modelling of the wenchuan earthquake shows strong interaction particularly with the faults close to its sw and ne ends such interactions have previously been shown to trigger further large earthquakes in addition redistribution of stresses due to continuing postseismic deformation will potentially increase the stress levels not only on these faults but also on the distant faults such as the xianshuihe kunlun and tazang faults postseismic viscoelastic stress load on these distant faults over the next 22 yr since the earthquake could be up to 2 5 times larger than that of the coseismic stress increase alone this would potentially advance these faults in their seismic cycle and thereby encourage future earthquakes resulting in clustering of large earthquakes in the region this behaviour however strongly depends on the stage that these faults are in their seismic cycle which is not known currently given the high density of population in the area with several cities chengdu guangyuan and hanzhong of more than 1 million inhabitants our results indicate a need for detailed paleoseismic studies to help elucidate the state of the stressed faults

post seismic relaxation and earthquake triggering in the southern adriatic region summary an attempt at quantifying post seismic relaxation triggered by decoupling earthquakes along the eastern thrusting border of the adriatic plate southern dinarides is carried out by finite element modelling with a model constituted by an elastic lithosphere riding on a viscous asthenosphere in particular it is investigated the possibility that the above phenomenon is responsible for the fact that in the last two centuries most major earthquakes in the southern dinarides ms 6 have been followed within a few years by intense mainly tensional earthquakes in southern italy i e the zone lying on the opposite margin of the adriatic plate this analysis has been applied to the last example of the supposed seismic interrelation i e the triggering 1979 april 15 montenegro event ms 6 7 and the presumably induced 1980 november 23 irpinia earthquake in the southern apennines ms 6 9 results indicate that the strain induced in the southern apennines by the triggering event has significant amplitude since it largely exceeds the effect of earth tides and the principal stress axes are consistent with those of southern apenninic earthquakes the order of magnitude of the time delay between the montenegro and irpinia events 1 6 yr could be explained by assuming that earthquake triggering is most probable when the highest values of the induced strain rate reach the southern apennines in particular this interpretation predicts the observed time delay when a model diffusivity of 400 m2 s 1 is assumed the constraints that this diffusivity value may pose on the structural and rheological features of the crust upper mantle system in the study area are discussed it is shown that the effects of the montenegro event on the present velocity field are comparable to though systematically lower than the velocities suggested by geodetic observations in the italian region this suggests that geodynamic interpretations of geodetic data given without taking into account possible transient effects on the kinematic pattern as those related to post seismic relaxation may be incorrect experiments carried out by tentatively simulating the presence of subducted lithosphere along the western margin of the adriatic plate as a lateral variation of diffusivity have shown that this structural feature may emphasize e w tensional strains in the southern apennines

a new method for the computation of global viscoelastic post seismic deformation in a realistic earth model i vertical displacement and gravity variation summary we introduce a new method by which to compute global post seismic deformation psd in a spherically symmetric self gravitating viscoelastic earth model previous methods are based on simplified earth models that neglect compressibility and or the continuous variation of the radial structure of earth this is because the previous mode summation technique cannot avoid intrinsic numerical difficulties caused by the innumerable poles that appear in a realistic earth model that considers such effects in contrast the proposed method enables both of these effects to be taken into account simultaneously we carry out numerical inverse laplace integration which allows evaluation of the contribution from all of the innumerable modes of the realistic earth model using this method a complete set of green s functions is obtained including functions of the time variation of the displacement gravity change and the geoid height change at the surface for strike slip dip slip horizontal and vertical tensile point dislocations as an earth model we employ the preliminary reference earth model prem and a convex viscosity profile further we investigate the effects of fine layering of the viscoelastic structure and compressibility on a time series of psd using the green s function for a dip slip fault the result indicates that the effect of increasing number of layers is saturated at several tens of layers even when compressibility is taken into account and that the effect of compressibility is detectable with modern observational techniques for a shallower large earthquake mw 8 as an application the psd due to the sumatra andaman islands earthquake mw 9 3 is estimated we show that the rate of post seismic vertical displacement and gravity change is possibly detected in the far field where the epicentral distance exceeds 400 km

spherical earth finite element model of short term postseismic deformation following the 2004 sumatra earthquake 1 decadal scale postseismic deformation of subduction earthquakes has been widely modeled using a maxwell viscoelastic earth with a mantle wedge viscosity of about 1019 pa s short term postseismic deformation within a few years after the earthquake remains a more challenging problem because of the predominance of afterslip of the megathrust and the potentially more complex mantle rheology questions include the necessity of invoking the transient rheology and the relative importance of contributions from afterslip and viscoelastic relaxation in this work we address these questions by developing a spherical earth viscoelastic finite element model for the short term postseismic deformation following the magnitude 9 2 sumatra earthquake of 2004 the model consists of elastic overriding and subducting plates and a viscoelastic mantle of bi viscous burgers rheology with the continental mantle mantle wedge being less viscous than the oceanic mantle by a factor of ten primary observational constraints for the short term postseismic deformation include 1 year net displacements of nine near field gps sites and 3 year time series from three far field sites several hundred kilometers from the 2004 rupture zone model results indicate that the afterslip of the fault must be at work within the first few years after the earthquake the observed deformation is best explained with a model that includes both the afterslip and transient rheology in the preferred model the transient and steady state viscosities of the mantle wedge are 5 1017 pa s and 1019 pa s respectively

postseismic deformation following the 2 july 2013 mw 6 1 aceh indonesia earthquake estimated using gps data abstract gps data after the 2 july 2013 mw 6 1 aceh earthquake provide valuable information for understanding the postseismic behavior of a strike slip fault in northern sumatra indonesia the analysis of postseismic deformation following the 2004 sumatra andaman earthquake and the 2012 indian ocean earthquake suggest that the ongoing deformation affected northern sumatra between july and december 2013 the postseismic deformation of the 2013 aceh earthquake is herein investigated with the contribution of poroelastic rebound and viscoelastic relaxation evaluated the results suggest that the model displacement of those two mechanisms failed to estimate the data the afterslip analysis of the 2013 aceh earthquake on the contrary fits the data very well with a seismic slip occurring at multiple fault segments of the sumatran fault in northern sumatra indonesia

a hybrid spectral and finite element method for coseismic and postseismic deformation abstract we investigate the elastic and viscoelastic responses of the earth to a sudden slip along a fault firstly equations describing the earth s infinitesimal deformations for elastic and viscoelastic rheological models are introduced within the weak formulation and the theorems of existence and uniqueness of solutions are demonstrated three dimensional numerical method which combines the 2d finite element method in a plane perpendicular to the fault with application of the fourier transform in the direction along the fault is described we then discuss several numerical benchmarks at the end the coseismic deformation and the coulomb stress for the august 14 2003 earthquake on the lefkada island in greece are computed incorporating also the influence of topography we demonstrate that the results are sensitive to both source interpretations and the epicenter area topography