separation of coseismic and postseismic gravity changes for the 2004 sumatra andaman earthquake from 4 6 yr of grace observations and modelling of the coseismic change by normal modes summation eodspatiale grgs for comparison the release 04 solutions of the center for space research csr are also inves tigated after a spectral windowing or a gaussian spatial smoothing results are shown both in terms of geoid height changes and gravity variations coseismic and postseismic gravitational changes estimated from the different gravity solutions are globally similar although their spa tial extent and amplitude depend on the type of filter used in the processing of grace fields the highest signal to noise ratio is found with the grgs solutions the postseismic signature has a spectral content closer to the grace bandwidth than the coseismic signature and is therefore better detected by grace the coseismic signature consists mainly of a strong gravity decrease east of the sunda trench in the andaman sea a gravity increase is also detected at a smaller scale west of the trench the model for the coseismic gravity changes agrees well with the coseismic signature estimated from grace regarding the overall shape and orientation location with respect to the trench and order of magnitude coseismic gravity changes are followed by a postseismic relaxation that are well fitted by an increasing expo nential function with a mean relaxation time of 0 7 yr the total postseismic gravity change consists of a large scale positive anomaly centred above the trench and extending over 15 of latitude along the subduction after 26 months the coseismic gravity decrease has been partly compensated by the postseismic relaxation but a negative anomaly still remains south of phuket a dominant gravity increase extends over 15 of latitude west of the trench being maximal south of the epicentre area by investigating analyses of two global hydrology models and one ocean general circulation model we show that our grace estimates of the coseismic and postseismic gravitational changes are almost not biased by interannual variations originat ing from continental hydrology and ocean circulation in the subduction area and in the central part of the andaman sea while they are biased by several gal in the malay peninsula

investigation on afterslip and steady state and transient rheology based on postseismic deformation and geoid change caused by the sumatra 2004 earthquake the commonly used rheological model for the earth s mantle when considering geological time scales mantle convection is the viscoelastic maxwell model which assumes a steady state creep process however application of this model to phenomena on shorter time scales such as postglacial rebound or postseismic relaxation leads to difficulties in finding a consistent interpretation of obtained viscosities using standard maxwell viscosity of 1e19 pa s to analyze postseismic near field gps time series from the 2004 sumatra andaman earthquake requires large time dependent afterslip with a relaxation time of about 1 year we show that using linear biviscous burgers rheology for the asthenosphere together with a refined coseismic slip model we can drastically reduce the amount of apparent afterslip comparison of predicted geoid change to observations by the grace satellite mission shows that a univiscous maxwell model with afterslip is not compatible with observations since even large afterslip has a more localized effect than transient relaxation due to the main earthquake which in turn is in agreement with observations thus a combination of ground and space based geodetic observations is very useful in differentiating between rheological models an additional independent discrimination between afterslip and biviscous relaxation could be obtained by installing ocean bottom pressure gauges close to the trench

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

relating viscosities from postseismic relaxation to a realistic viscosity structure for the lithosphere summary models of geodetic observations of postseismic relaxation most often represent the lithosphere with only a few layers with constant viscosity this is surpr ising because rock mechanical experiments consistently demonstrate that we should expect a profound vertical gradient in lithospheric viscosities due to the geothermal gradient i n this thermal boundary layer we isolate the effect of lower crustal flow where the effect of visc osity gradients has the largest impact on surface deformation we therefore explore postseismic deformation in models with realistic vertical viscosity gradients and seek to illustrate th e differences between these models and those with idealized uniform viscosity layers by means of synthetic experiments with a semianalytical viscoelastic relaxation model we show how for a given earthquake the averaged viscosity value obtained for a thick viscoelastic layer is d ependent on both the layout of the geodetic network and on the observation time window

post glacial rebound and transient lower mantle rheology summary although post glacial rebound data have been conventionally interpreted as being governed by the steady state component of the mantle viscosity spectrum the radial profile of this parameter which is then inferred by fitting a model to observations is characterized by the fact that it exhibits rather slight variation with depth this disagrees with expectations based upon microphysical models of the solid state creep process it also disagrees with very recent inferences of the viscosity stratification based on isostatic geoid anomalies expected on the basis of the internal lateral heterogeneity of mantle density obtained from seismic tomographic analyses the new calculations of the signatures of post glacial rebound reported here show that these two types of information are easily reconciled if the previously inferred value of the lower mantle viscosity is interpreted as a transient value as originally suggested by weertman on the basis of qualitative considerations in these new models considered here the steady state creep resistance of the lower mantle is not constrained at all by post glacial rebound observations it can be futed only by an appeal to other geophysical data whether such models are actually required by the data should become clear in the very near future

two dimensional viscosity structure of the northeastern japan islands arc trench system 1 two dimensional viscosity profiles were constructed for the northeastern japan islands arc trench system covering the source area of the 2011 tohoku oki earthquake from seismologically determined models of lithospheric structure experimentally derived constitutive laws of various rocks and densely measured geothermal gradient data we have predicted the steady state effective viscosity across the subduction zone the profile reveals strong lateral viscosity gradients both parallel and normal to the trench axis the detailed viscosity structures presented here contribute to accurate evaluation of viscoelastic relaxation components when modeling geodetically measured postseismic deformation at high spatial and temporal resolution

steady state laboratory flow laws alone fail to explain postseismic observations abstract we test whether laboratory derived steady state flow laws for wet olivine can be used to explain postseismic relaxation in the upper mantle following the 1999 hector mine earthquake this is accomplished using rate changes in gps observed displacement time series at far field stations as constraints on the parameters associated with laboratory derived temperature and stress dependent flow laws for diffusion and dislocation creep of olivine we primarily concentrate on the influences of temperature grain size and background strain rate to explain observed fast early displacement rates that slow rapidly in the 7 years of postseismic observations we find that a reasonable fit to the observed time series cannot be achieved by any combination of flow law parameters and plausible assumptions for the tectonic environment of the mantle beneath the mojave desert we conclude that postseismic relaxation within the mantle following the hector mine earthquake likely includes an initial transient weakening phase suggesting that steady state flow laws by themselves are insufficient to characterize the flow of mantle rocks when stress conditions evolve

high temperature arc parallel normal faulting and transtension at the roots of an obliquely convergent orogen structural and kinematic data from northern coastal british columbia 54 5 n document intra arc deformation patterns at mid crustal levels during and after emplacement of the coast mountains batholith major arc parallel displacements occurred along high temperature 700 c ductile normal faults and steep sinistral transtensional shear zones within an obliquely convergent margin strain patterns and pluton emplacement were controlled by 1 structural anisotropies in host rocks that predate batholith emplacement and 2 kinematic compatibility requirements created by simultaneous motion on curved pluton bounding shear zones these controls superseded a partitioning of the arc parallel and arc normal components of oblique plate convergence onto strike slip and thrust faults respectively

tide model errors and grace gravimetry towards a more realistic assessment summary the manner in which errors in tide models affect monthly gravity solutions from grace satellite data is re examined we perform a complete simulation of grace gravity estimation including allowance for accelerometer calibrations and satellite state vector adjustment errors in monthly geoid estimates are for most regions of a order of 0 5 mm or roughly 1 cm of equivalent water height when smoothed over radii of 600 km in polar regions where ocean tide models are suspect errors can grow significantly larger over 2 mm in geoid height although over very localized regions errors from diurnal tides tend to cancel but they are not completely eliminated inducing geoid errors of the order of 0 3 mm the currently accepted grace total error budget is roughly an order of magnitude larger than the component arising from tide modelling errors

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

grace detects coseismic and postseismic deformation from the sumatra andaman earthquake 1 we show that spherical harmonic sh solutions of the gravity recovery and climate experiment grace are now of sufficient quality to observe effects of co seismic and post seismic deformation due to the rupture from the mw 9 3 sumatra andaman earthquake on december 26 2004 and its companion nias earthquake mw 8 7 on march 28 2005 the improved ggm 03 sh level 2 solutions and improved filtering methods provide estimates with spatial resolution comparable to earlier estimates from range rate level 1 grace data the gravityfield disturbance extends over 1800 km along andaman and sunda subduction zones and changes with time following events gravity changes may be due to afterslip viscoelastic relaxation or other processes associated with dilatation satellite gravity measurements from grace provide a unique new measure of deformation and post seismic processes associated with major earthquakes especially in areas which are primarily oceanic citation chen j l c r wilson b d tapley and s grand 2007 grace detects coseismic and postseismic deformation from the sumatraandaman earthquake geophys res lett 34 l13302

prevalence of viscoelastic relaxation after the 2011 tohoku oki earthquake seafloor global positioning system observations immediately after the great 2011 tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than just afterslip on the fault as is commonly assumed this paper presents revised estimates of the afterslip following the 2011 tohoku oki earthquake based on seafloor gps observations made immediately after the earthquake tianhaozhe sun et al obtain unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than elastic afterslip on the fault as is commonly assumed they conclude that models which erroneously assume an elastic earth substantially overestimate afterslip downdip of the rupture zone and underestimate afterslip updip after a large subduction earthquake crustal deformation continues to occur with a complex pattern of evolution1 this postseismic deformation is due primarily to viscoelastic relaxation of stresses induced by the earthquake rupture and continuing slip afterslip or relocking of different parts of the fault2 3 4 5 6 when postseismic geodetic observations are used to study earth s rheology and fault behaviour it is commonly assumed that short term a few years deformation near the rupture zone is caused mainly by afterslip and that viscoelasticity is important only for longer term deformation6 7 however it is difficult to test the validity of this assumption against conventional geodetic data here we show that new seafloor gps global positioning system observations immediately after the great tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation these data reveal fast landward motion of the trench area opposing the seaward motion of gps sites on land using numerical models of transient viscoelastic mantle rheology we demonstrate that the landward motion is a consequence of relaxation of stresses induced by the asymmetric rupture of the thrust earthquake a process previously unknown because of the lack of near field observations our findings indicate that previous models assuming an elastic earth will have substantially overestimated afterslip downdip of the rupture zone and underestimated afterslip updip of the rupture zone our knowledge of fault friction based on these estimates therefore needs to be revised

postseismic relaxation driven by brittle creep a possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks application to the chi chi earthquake taiwan we evaluate the effect of coseismic stress changes on the fault slip at midcrustal depth assuming a velocity strengthening brittle creep rheology we show that this model can help reconcile the time evolution of afterslip as measured from geodesy with aftershocks decay we propose an analytical expression for slip of the brittle creeping fault zone bcfz that applies to any dynamic or static stress perturbation including shear stress and normal stress changes the model predicts an initial logarithmic increase of slip with time postseismic slip rate decays over a characteristic time t r a that does not depend on the amplitude of the stress perturbation and it asymptotically joins the long term creep imposed by interseismic stress buildup given that the seismicity rate might be considered proportional to the sliding velocity of the bcfz the model predicts a decay rate of aftershocks that follows omori s law with a mathematical formalism identical to that of dieterich 1994 although based on a different mechanical rationale our model also differs from dieterich s model in that it requires that aftershock sequences and deep afterslip as constrained from geodetic measurements should follow the same temporal evolution we test this for the 1999 chi chi earthquake m w 7 6 and find that both sets of data are consistent with a model of afterslip due to the response of the bcfz the inferred relaxation time t r 8 5 years requires a value for a log v being the coefficient of friction in the range between 1 3 10 3 and 10 2

effect of 3 d viscoelastic structure on post seismic relaxation from the 2004 m 9 2 sumatra earthquake summary the 2004 m 9 2 sumatra andaman earthquake profoundly altered the state of stress in a large volume surrounding the 1400 km long rupture induced mantle flow fields and coupled surface deformation are sensitive to the 3 d rheology structure to predict the post seismic motions from this earthquake relaxation of a 3 d spherical viscoelastic earth model is simulated using the theory of coupled normal modes the quasi static deformation basis set and solution on the 3 d model is constructed using a spherically stratified viscoelastic earth model with a linear stress strain relation an aspherical perturbation in viscoelastic structure a static mode basis set consisting of earth s spheroidal and toroidal free oscillations a viscoelastic mode basis set and interaction kernels that describe the coupling among viscoelastic and static modes application to the 2004 sumatra andaman earthquake illustrates the profound modification of the post seismic flow field at depth by a slab structure and similarly large effects on the near field post seismic deformation field at earth s surface comparison with postseismic gps observations illustrates the extent to which viscoelastic relaxation contributes to the regional post seismic deformation

coseismic slip and afterslip of the great mw 9 15 sumatra andaman earthquake of 2004 we determine coseismic and the first month postseismic deformation associated with the sumatra andaman earthquake of 26 december 2004 from near field global positioning system gps surveys in northwestern sumatra and along the nicobar andaman islands continuous and campaign gps measurements from thailand and malaysia and in situ and remotely sensed observations of the vertical motion of coral reefs the coseismic model shows that the sunda subduction mega thrust ruptured over a distance of about 1500 km and a width of less than 150 km releasing a total moment of 6 7 7 0 10 22 n m equivalent to a magnitude m w 9 15 the latitudinal distribution of released moment in our model has three distinct peaks at about 4 n 7 n and 9 n which compares well to the latitudinal variations seen in the seismic inversion and of the analysis of radiated t waves our coseismic model is also consistent with interpretation of normal modes and with the amplitude of very long period surface waves the tsunami predicted from this model fits rela tively well the altimetric measurements made by the jason and topex satellites neither slow nor delayed slip is needed to explain the normal modes and the tsunami wave the near field geodetic data that encompass both coseismic deformation and up to 40 days of postseismic deformation require that slip must have continued on the plate interface after the 500 sec long seismic rupture the postseismic geodetic moment of about 2 4 10 22 nm mw 8 8 is equal to about 30 5 of the coseismic moment release evolution of postseismic deformation is consistent with rate strengthening frictional afterslip online material summary of geodetic data used in this study

postseismic deformation following the 2010 m 7 2 el mayor cucapah earthquake observations kinematic inversions and dynamic models due to its location on a transtensional section of the pacific north american plate boundary the salton trough is a region featuring large strike slip earthquakes within a regime of shallow asthenosphere high heat flow and complex faulting and so postseismic deformation there may feature enhanced viscoelastic relaxation and afterslip that is particularly detectable at the surface the 2010 m 7 2 el mayor cucapah earthquake was the largest shock in the salton trough since 1892 and occurred close to the us mexico border and so the postseismic deformation recorded by the continuous gps network of southern california provides an opportunity to study the rheology of this region three year postseismic transients extracted from gps displacement time series show four key features 1 1 2 cm of cumulative uplift in the imperial valley and sim 1 cm of subsidence in the peninsular ranges 2 relatively large cumulative horizontal displacements 150 km from the rupture in the peninsular ranges 3 rapidly decaying horizontal displacement rates in the first few months after the earthquake in the imperial valley and 4 sustained horizontal velocities following the rapid early motions that were still visibly ongoing 3 years after the earthquake kinematic inversions show that the cumulative 3 year postseismic displacement field can be well fit by afterslip on and below the coseismic rupture though these solutions require afterslip with a total moment equivalent to at least a m 7 2 earthquake and higher slip magnitudes than those predicted by coseismic stress changes forward modeling shows that stress driven afterslip and viscoelastic relaxation in various configurations within the lithosphere can reproduce the early and later horizontal velocities in the imperial valley while newtonian viscoelastic relaxation in the asthenosphere can reproduce the uplift in the imperial valley and the subsidence and large westward displacements in the peninsular ranges we present two forward models of dynamically coupled deformation mechanisms that fit the postseismic transient well a model combining afterslip in the lower crust newtonian viscoelastic relaxation in a localized zone in the lower crust beneath areas of high heat flow and geothermal activity and newtonian viscoelastic relaxation in the asthenosphere and a second model that replaces the afterslip in the first model with viscoelastic relaxation with a stress dependent viscosity in the mantle the rheology of this high heat flow high strain rate region may incorporate elements of both these models and may well be more complex than either of them

long and short term postseismic gravity changes of megathrust earthquakes from satellite gravimetry using monthly satellite gravimetry data we studied time variable gravity field after three m9 class earthquakes the 2004 sumatra andaman 2010 chile maule and 2011 tohoku oki earthquakes the observations showed that the gravity typically 1 decreases coseismically 2 continues to decrease for a few months and 3 increases over a longer period therefore postseismic gravity changes have two components with different time constants and polarities the mechanisms of short and long term postseismic gravity changes are not as clear as coseismic changes at the moment but might be explained to some extent with afterslip and the maxwell viscoelasticity respectively these two components are difficult to discriminate with surface velocity measurements because the forearc area moves trenchward at both stages they appear in different polarities in gravity making satellite gravimetry a unique tool to separate them

using short term postseismic displacements to infer the ambient deformation conditions of the upper mantle 1 to interpret short term postseismic surface displacements in the context of key ambient conditions e g temperature pressure background strain rate water content creep mechanism we combined steady state and transient flow into a single constitutive relation that can explain the response of a viscoelastic material to a change in stress the flow law is then used to investigate mantle deformation beneath the eastern california shear zone following the 1999 m7 1 hector mine earthquake the flow law parameters are determined using finite element models of relaxation processes constrained by surface displacement time series recorded by 55 continuous gps stations for 7 years following the earthquake results suggest that postseismic flow following the hector mine earthquake occurs below a depth of 50 km and is controlled by dislocation creep of wet olivine diffusion creep models can also explain the data but require a grain size 3 5 mm that is smaller than the inferred grain size 10 20 mm based on the mantle conditions at these depths in addition laboratory flow laws predict dislocation creep would dominate at the stress grain size conditions that provide the best fit to diffusion creep models model results suggest a transient creep phase that lasts 1 year and has a viscosity 10 times lower than subsequent steady state flow in general agreement with laboratory observations the postseismic response is best explained as occurring within a relatively hot upper mantle e g 1200 1300 c at 50 km depth with a long term background mantle strain rate of 0 1 0 2 mstrain yr consistent with the observed surface strain rate long term background shear stresses at the top of the mantle are 4 mpa then decrease with depth to a minimum of 0 1 0 2 mpa at 70 km depth before increasing slowly with depth due to the pressure dependence of viscosity these conditions correspond to a background viscosity of 10 21 pa s within a thin mantle lid that decreases to 5 10 19 pa s within the underlying asthenosphere this study shows the utility of using short term postseismic observations to infer long term mantle conditions that are not readily observable by other means

source parameter inversion for recent great earthquakes from a decade long observation of global gravity fields we quantify gravity changes after great earthquakes present within the 10 year long time series of monthly gravity recovery and climate experiment grace gravity fields using spherical harmonic normal mode formulation the respective source parameters of moment tensor and double couple were estimated for the 2004 sumatra andaman earthquake the gravity data indicate a composite moment of 1 2 1023 n m with a dip of 10 in agreement with the estimate obtained at ultralong seismic periods for the 2010 maule earthquake the grace solutions range from 2 0 to 2 7 1022 n m for dips of 12 24 and centroid depths within the lower crust for the 2011 tohoku oki earthquake the estimated scalar moments range from 4 1 to 6 1 1022 n m with dips of 9 19 and centroid depths within the lower crust for the 2012 indian ocean strike slip earthquakes the gravity data delineate a composite moment of 1 9 1022 n m regardless of the centroid depth comparing favorably with the total moment of the main ruptures and aftershocks the smallest event we successfully analyzed with grace was the 2007 bengkulu earthquake with m0 5 0 1021 n m we found that the gravity data constrain the focal mechanism with the centroid only within the upper and lower crustal layers for thrust events deeper sources i e in the upper mantle could not reproduce the gravity observation as the larger rigidity and bulk modulus at mantle depths inhibit the interior from changing its volume thus reducing the negative gravity component focal mechanisms and seismic moments obtained in this study represent the behavior of the sources on temporal and spatial scales exceeding the seismic and geodetic spectrum

postseismic deformation of the andaman islands following the 26 december 2004 great sumatra andaman earthquake 1 two years after the great sumatra andaman earthquake the 3 1 m wsw coseismic displacement at port blair andaman islands had increased by 32 cm postseismic uplift initially exceeded 1 cm per week and decreased to 1 mm week by 2007 points near port blair had risen more than 20 cm a 24 reversal of coseismic subsidence uplift at eight gps sites suggests a gradual eastward shift of the coseismic neutral axis separating subsidence from uplift simulations of the gps postseismic displacements as viscoelastic relaxation of coseismic stress change and as slip on the plate interface indicate that slip down dip of the seismic rupture dominates near field deformation during the first two years postseismic slip beneath the andaman islands released moment equivalent to a magnitude mw 7 5 earthquake and the distribution suggests deep slip in the stable frictional regime accelerated to catch up to the coseismic rupture

post seismic relaxation following the great 2004 sumatra andaman earthquake on a compressible self gravitating earth summary the mw 9 0 2004 december 26 sumatra andaman and mw 8 7 2005 march 28 nias earthquakes which collectively ruptured approximately 1800 km of the andaman and sunda subduction zones are expected to be followed by vigorous viscoelastic relaxation involving both the upper and lower mantle because of these large spatial dimensions it is desirable to fully account for gravitational coupling effects in the relaxation process we present a stable method of computing relaxation of a spherically stratified compressible and self gravitating viscoelastic earth following an impulsive moment release event the solution is cast in terms of a spherical harmonic expansion of viscoelastic normal modes for simple layered viscoelastic models which include a low viscosity oceanic asthenosphere we predict substantial post seismic effects over a region several 100s of km wide surrounding the eastern indian ocean we compare observed gps time series from ten regional sites mostly in thailand and indonesia beginning in 2004 december with synthetic time series that include the coseismic and post seismic effects of the 2004 december 26 and 2005 march 28 earthquakes a viscosity structure involving a biviscous burgers body rheology in the asthenosphere explains the pattern and amplitude of post seismic offsets remarkably well

first evidence for locomotion in the ediacara biota from the 565 ma mistaken point formation newfoundland evidence for locomotion in the precambrian fossil record is scant reliable ediacaran trace fossils are all younger than 560 ma and consist of relatively simple horizontal burrows and trails from shallow water deposits here we describe an assemblage of macroscopic locomotory traces from deep water environments at mistaken point southeastern newfoundland canada dated to ca 565 ma these trails extend the record of complex trace fossils back into the earliest avalonian biota our new evidence for large motile organisms on the seafloor at this time suggests that at least some of these early ediacaran organisms whose biological affinities are widely debated could have been muscular and of metazoan grade

frictional afterslip following the 2005 nias simeulue earthquake sumatra continuously recording global positioning system stations near the 28 march 2005 rupture of the sunda megathrust moment magnitude m w 8 7 show that the earthquake triggered aseismic frictional afterslip on the subduction megathrust with a major fraction of this slip in the up dip direction from the main rupture eleven months after the main shock afterslip continues at rates several times the average interseismic rate resulting in deformation equivalent to at least a m w 8 2 earthquake in general along strike variations in frictional behavior appear to persist over multiple earthquake cycles aftershocks cluster along the boundary between the region of coseismic slip and the up dip creeping zone we observe that the cumulative number of aftershocks increases linearly with postseismic displacements this finding suggests that the temporal evolution of aftershocks is governed by afterslip

ocean contribution to seismic gravity changes the sea level equation for seismic perturbations revisited during megathrust earthquakes great ruptures are accompanied by large scale mass redistribution inside the solid earth and by ocean mass redistribution due to bathymetry changes these large scale mass displacements can be detected using the monthly gravity maps of the grace satellite mission in recent years it has become increasingly common to use the long wavelength changes in the earth s gravity field observed by grace to infer seismic source properties for large megathrust earthquakes an important advantage of space gravimetry is that it is independent from the availability of land for its measurements this is relevant for observation of megathrust earthquakes which occur mostly offshore such as the mw 9 2004 sumatra andaman 2010 maule chile and 2011 tohoku oki japan events in broerse et al we examined the effect of the presence of an ocean above the rupture on long wavelength gravity changes and showed it to be of the first order here we revisit the implementation of an ocean layer through the sea level equation and compare the results with approximated methods that have been used in the literature one of the simplifications usually lies in the assumption of a globally uniform ocean layer we show that especially in the case of the 2010 maule earthquake due to the closeness of the south american continent the uniform ocean assumption is not valid and causes errors up to 57 per cent for modelled peak geoid height changes expressed at a spherical harmonic truncation degree of 40 in addition we show that when a large amount of slip occurs close to the trench horizontal motions of the ocean floor play a mayor role in the ocean contribution to gravity changes using a slip model of the 2011 tohoku oki earthquake that places the majority of slip close to the surface the peak value in geoid height change increases by 50 per cent due to horizontal ocean floor motion furthermore we test the influence of the maximum spherical harmonic degree at which the sea level equation is performed for sea level changes occurring along coastlines which shows to be important for relative sea level changes occurring along the shore finally we demonstrate that ocean floor loading self gravitation of water and conservation of water mass are of second order importance for coseismic gravity changes when grace observations are used to determine earthquake parameters such as seismic moment or source depth the uniform ocean layer method introduces large biases depending on the location of the rupture with respect to the continent the same holds for interpreting shallow slip when horizontal motions are not properly accounted for in the ocean contribution in both cases the depth at which slip occurs will be underestimated

the viscoelastic relaxation of a realistically stratified earth and a further analysis of postglacial rebound summary we discuss the isostatic adjustment of the earth in response to pleistocene deglaciation and derive constraints on the earth s viscosity profile we model the earth as viscoelastic self gravitating realistically stratified and spherically symmetric it is shown that the earth s relaxation eigenspectrum besides possessing a small set of well known discrete modes also includes infinitely dense sets of modes a continuous spectrum which separate into classes that depend on the principal restoring force of the mode methods for estimating the continuous spectrum are discussed and the effects on the predicted uplift are assessed we find that the effects of the continuous spectrum are far less important than those of the discrete modes though the presence of the continuous spectrum can make the discrete modes more difficult to identify the continuous spectrum does become important when computing the rebound due to more recent loading such as might be associated with present day changes in polar ice we use our model to refine predictions of the earth s response to pleistocene glacial loading with particular emphasis on implications for mantle viscosity we have used time histories that are consistent with the recently recalibrated 14c time scale a special effort is made to match the geologic records of sea level at sites in the vicinity of hudson bay we find consistent with the results of other authors that the curvatures of the records are sensitive indicators of lower mantle viscosity but that there are inconsistencies between the records at different sites however we find we are also able to change the predicted curvatures by modifying the temporal and spatial distribution of the ice loads if we assume a factor of 50 increase in viscosity between the upper and lower mantles and if we assume that the ice on the eastern side of hudson bay melted a few thousand years later than the ice on the western side a result consistent with recent geologic evidence we are able to match the observed sea level data about as well as we are able to if we use instead a uniform mantle viscosity profile a model with a factor of 50 jump in viscosity predicts a large free air gravity anomaly over northern canada that is reasonably consistent with what is observed whereas a uniform viscosity model does not though some authors have argued that the observed north american gravity anomaly may be mostly a consequence of mantle convection and largely unrelated to postglacial rebound our objective here is not to present a preferred ice model or viscosity profile rather we conclude only that the interpretation of the data is ambiguous and that the mantle viscosity profile can not yet be uniquely inferred from them

a low viscosity wedge in subduction zones geochemical petrologic and seismological observations indicate that there may be high concentrations of water in the region above a subducting slab the mantle wedge which could decrease the viscosity of the mantle locally by several orders of magnitude using numerical models we demonstrate that a low viscosity wedge has a dramatic influence on the force balance in a subduction zone and leads to an observable signal in the topography gravity and geoid a regional dynamic model of the tonga kermadec subduction zone shows that the viscosity of the wedge is at least a factor of 10 smaller than surrounding mantle lithosphere and asthenosphere consistent with estimates from seismic dissipation and deformation experiments

postseismic grace and gps observations indicate a rheology contrast above and below the sumatra slab more than 7 years of observations of postseismic relaxation after the 2004 sumatra andaman earthquake provide an improving view on the deformation in the wide vicinity of the 2004 rupture we include both gravity recovery and climate experiment grace gravity field data that show a large postseismic signal over the rupture area and gps observations in the back arc region with increasing time gps and grace show contrasting relaxation styles that were not easily discernible on shorter time series we investigate whether mantle creep can simultaneously explain the far field surface displacements and the long wavelength gravity changes we interpret contrasts in the temporal behavior of the gps grace observations in terms of lateral variations in rheological properties of the asthenosphere below and above the slab based on 1 d viscoelastic models our results support an almost order of magnitude contrast between oceanic lithosphere viscosity and continental viscosity which likely means that the low viscosities frequently found from postseismic deformation after subduction earthquakes are valid only for the mantle wedge next to mantle creep we also consider afterslip as an alternative mechanism for postseismic deformation we investigate how the combination of grace and gps data can better discriminate between different mechanisms of postseismic relaxation distributed deformation mantle creep versus localized deformation afterslip we conclude that the grace observed gravity changes rule out afterslip as the dominant mechanism explaining long wavelength deformation even over the first year after the event

postseismic deformation following the 1999 chi chi earthquake taiwan implication for lower crust rheology on 1999 september 21 the mw 7 6 chi chi earthquake ruptured a segment of the chelungpu fault a frontal thrust fault of the western foothills of taiwan the stress perturbation induced by the rupture triggered a transient deformation across the island which was well recorded by a wide network of continuously operating gps stations the analysis of more than ten years of these data reveals a heterogeneous pattern of postseismic displacements with relaxation times varying by a factor of more than ten and large cumulative displacements at great distances in particular along the longitudinal valley in eastern taiwan where relaxation times are also longer we show that while afterslip is the dominant relaxation process in the epicentral area viscoelastic relaxation is needed to explain the pattern and time evolution of displacements at the larger scale we model the spatiotemporal behavior of the transient deformation as the result of afterslip on the decollement that extends downdip of the chelungpu thrust and viscoelastic flow in the lower crust and in the mid crust below the central range we construct a model of deformation driven by coseismic stress change where afterslip and viscoelastic flow are fully coupled the model is compatible with the shorter relaxation times observed in the near field which are due to continued fault slip and the longer characteristic relaxation times and the reversed polarity of vertical displacements observed east of the central range our preferred model shows a viscosity of 0 5 1 x 10 19 pa s at lower crustal depths and 5 x 10 17 pa s in the mid crust below the central range between 10 and 30 km depth the low viscosity zone at mid crustal depth below the central range coincides with a region of low seismicity where rapid advection of heat due to surface erosion coupled with underplating maintain high temperatures estimated to be between 300 c and 600 c from the modeling of thermo chronology and surface heat flow data

three dimensional viscoelastic finite element model for postseismic deformation of the great 1960 chile earthquake 2 5 10 19 pa s for the continental upper mantle the model well explains the gps observations numerical tests suggest that the continental mantle viscosity value is reasonably well constrained the model shows the prolonged postseismic seaward motion of the inland area to be a unique feature of earthquakes with very long rupture along strike and large coseismic fault slip for short rupture and small coseismic slip the motion will stop very quickly after the earthquake explaining why this phenomenon is not more commonly observed with an oceanic mantle viscosity of 10 20 pa s the model also provides an explanation for tide gauge constrained postseismic uplift 200 km from the trench that had previously been explained using a model of prolonged afterslip of a deep segment of the chile subduction fault index terms 1236 geodesy and gravity rheology of the lithosphere and mantle 8160 1242 geodesy and gravity seismic deformations 7205 3230 mathematical geophysics numerical solutions 7209 seismology earthquake dynamics and mechanics 7260 seismology theory and modeling keywords postseismic deformation viscoelastic stress relaxation gps finite element modeling chile subduction zone upper mantle viscosity

itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters 1 unlike the past international terrestrial reference frame itrf versions where global long term solutions were combined the itrf2005 uses as input data time series weekly from satellite techniques and 24 h session wise from very long baseline interferometry of station positions and daily earth orientation parameters eops the advantage of using time series of station positions is that it allows to monitor station non linear motion and discontinuities and to examine the temporal behavior of the frame physical parameters namely the origin and the scale the itrf2005 origin is defined in such a way that it has zero translations and translation rates with respect to the earth center of mass averaged by the satellite laser ranging slr time series spanning 13 years of observations its scale is defined by nullifying the scale and its rate with respect to the very long baseline interferometry vlbi time series spanning 26 years of observations the itrf2005 orientation at epoch 2000 0 and its rate are aligned to the itrf2000 using 70 stations of high geodetic quality the estimated level of consistency of the itrf2005 origin at epoch 2000 0 and its rate with respect to the itrf2000 is respectively 0 1 0 8 5 8 mm and 0 2 0 1 1 8 mm yr along the x yand z axis we estimate the formal errors on these components to be 0 3 mm and 0 3 mm yr we believe that this low level of agreement between the two frame origins is most probably due to the poor slr network geometry and its degradation over time the itrf2005 combination involving 84 co location sites revealed a scale inconsistency of 1 ppb 6 3 mm at the equator at epoch 2000 0 and 0 08 ppb yr between the slr and vlbi long term solutions as obtained by the stacking of their respective time series possible causes of this inconsistency may include the poor slr and vlbi networks and their co locations local tie uncertainties systematic effects and possible inconsistent model corrections used in the data analysis of both techniques for the first time of the itrf history the itrf2005 rigorous combination provides self consistent series of eops including polar motion from vlbi and satellite techniques and universal time and length of day from vlbi only a velocity field of 152 sites with an error less than 1 5 mm yr is used to estimate absolute rotation poles of 15 tectonic plates that are consistent with the itrf2005 frame this new absolute plate motion model supersedes and significantly improves that of the itrf2000 which involved six major tectonic plates citation altamimi z x collilieux j legrand b garayt and c boucher 2007 itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters j geophys res 112 b09401

preceding coseismic and postseismic slips of the 2011 tohoku earthquake japan 1 we estimated the spatial and temporal evolution of the preceding aseismic slip from january 2003 to january 2011 the coseismic slip of the tohoku earthquake and the postseismic slip after the earthquake based on global positioning system gps data time dependent analysis indicates aseismic slip offshore of miyagi and fukushima prefectures from 2004 associated with a series of subduction earthquakes that overlap the aseismic slip area these preceding aseismic and coseismic slip areas are centered between the centers of the coseismic and afterslip areas of the tohoku earthquake offshore of miyagi prefecture while they overlap the coseismic and afterslip areas of the tohoku earthquake off fukushima prefecture the timing of moment magnitude nine mw9 class earthquakes appears to be controlled by multiple preceding slip events smaller earthquakes and their afterslip the preceding aseismic and coseismic slip decreased the coupling rate off the tohoku coast suggesting the possibility that the preceding slip represented a precursive stage of the tohoku earthquake the afterslip of the tohoku earthquake occurred in an area where the coseismic slip was not large complementing the large coseismic slip zone the afterslip along iwate miyagi extends up to 80 km in depth and is currently the sole mechanism of strain release in this depth range the source region of the anticipated miyagi oki earthquake shows small postseismic slip after the tohoku earthquake reflecting the energy release at the time of the earthquake aftershock activity is roughly governed by an afterslip process

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

deformation cycles of subduction earthquakes in a viscoelastic earth subduction zones produce the largest earthquakes over the past two decades space geodesy has revolutionized our view of crustal deformation between consecutive earthquakes the short time span of modern measurements necessitates comparative studies of subduction zones that are at different stages of the deformation cycle piecing together geodetic snapshots from different subduction zones leads to a unifying picture in which the deformation is controlled by both the short term years and long term decades and centuries viscous behaviour of the mantle traditional views based on elastic models such as coseismic deformation being a mirror image of interseismic deformation are being thoroughly revised snapshots of subduction zones using space geodesy reveal that the viscous behaviour of the mantle controls crustal deformation requiring the revision of traditional elastic models for earthquake risk assessment space geodesy the use of satellites to monitor earth has revolutionized our view of crustal deformation between consecutive earthquakes however the brevity of such measurements means that studies must be done by comparing multiple subduction zones at different stages of the earthquake cycle by piecing together geodetic snapshots from the sumatra chile and cascadia subduction zones this review presents a unifying picture in which deformation is controlled by the viscous behaviour of the mantle in both the short term years and the long term decades to centuries

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

constraints on 2004 sumatra andaman earthquake rupture from gps measurements in andaman nicobar islands the 26 december 2004 sumatra andaman earthquake mw 9 0 9 3 is the greatest earthquake of the modern seismological era the rupture characteristics of the earthquake particularly in the andaman nicobar region are not well resolved from seismological or far field geodetic data here in this article we present campaign mode global positioning system gps measurements of coseismic displacements at 13 sites in the andaman nicobar islands before and after the 2004 sumatra andaman earthquake these measurements provide improved estimates of rupture characteristics in the region coseismic horizontal ground displacement of 1 5 6 5 m towards the southwest and coseismic vertical displacement mostly subsidence of 0 5 2 8 m occurred along the andaman nicobar islands with maximum displacements in the nicobar islands we estimate coseismic slip under the andaman and nicobar islands as 3 8 7 9 m and 11 15 m respectively the length of the rupture is estimated to be about 1500 km with a width varying from 120 km under middle andaman island to 160 km under great nicobar island gps measurements during january 11 22 2005 from port blair suggest rapid afterslip in the postseismic period limited gps data available from 1995 measurements at two sites in andaman provide evidence of strain accumulation that varied significantly in the 10 yr preceding the earthquake d 2005 elsevier b v all rights reserved

afterslip and aftershocks in the rate and state friction law istituto nazionale di geofisica e vulcanologia italy ingv centre national de la recherche scientifique cnrs exxonmobil upstream research company

andaman postseismic deformation observations still slipping after all these years more than six years after the great m w 9 2 sumatra andaman earthquake postevent processes responsible for relaxation of the coseismic stress change remain controversial modeling of andaman islands global positioning system gps displacements indicated early near field motions were dominated by slip down dip of the rupture but various researchers ascribe elements of relaxation to dominantly poroelastic dominantly viscoelastic and dominantly fault slip processes depending primarily on their measurement sampling and modeling tools used after subtracting a pre 2004 interseismic velocity significant transient motion during the 2008 5 2010 5 epoch confirms that postseismic relaxation processes continue in andaman modeling three component velocities as viscoelastic flow yields a weighted root mean square wrms misfit that always exceeds the wrms of the measured signal 26 3 mm yr the best fitting models are those that yield negligible deformation indicating the model parameters have no real physical meaning gps velocities are well fit wrms 4 0 mm yr by combining a viscoelastic flow model that best fits the horizontal velocities with 50 cm yr thrust slip down dip of the coseismic rupture both deep slip and flow respond to stress changes and each can significantly change stress in the realm of the other it therefore is reasonable to expect that both transient deep slip and viscoelastic flow will influence surface deformation long after a great earthquake

slow postseismic recovery of geoid depression formed by the 2004 sumatra andaman earthquake by mantle water diffusion 1 earthquakes are accompanied with mass redistributions and cause changes in gravity field and shape of geoid an equipotential surface coincident with the mean sea surface such coseismic changes were detected by satellite gravimetry after the 2004 sumatra andaman earthquake but little has been known on what happens on geoid after the earthquake here we report slow postseismic recovery of coseismic geoid depression from satellite measurements this cannot be explained with simple afterslip or viscous relaxation of maxwellian upper mantle it suggests the relaxation of coseismic dilatation and compression by the diffusion of supercritical h2o abundant in the upper mantle such a self healing system of coseismic geoid undulations a brand new role of water in mantle would significantly reduce the amount of permanent shifts of the earth s rotation axis by earthquakes

insight into the 2004 sumatra andaman earthquake from gps measurements in southeast asia data collected at 60 global positioning system gps sites in southeast asia show the crustal deformation caused by the 26 december 2004 sumatra andaman earthquake at an unprecedented large scale small but significant co seismic jumps are clearly detected more than 3 000 km from the earthquake epicentre the nearest sites still more than 400 km away show displacements of 10 cm or more here we show that the rupture plane for this earthquake must have been at least 1 000 km long and that non homogeneous slip is required to fit the large displacement gradients revealed by the gps measurements our kinematic analysis of the gps recordings indicates that the centroid of released deformation is located at least 200 km north of the seismological epicentre it also provides evidence that the rupture propagated northward sufficiently fast for stations in northern thailand to have reached their final positions less than 10 min after the earthquake hence ruling out the hypothesis of a silent slow aseismic rupture data culled from gps stations in indonesia malaysia singapore thailand india and china have answered more questions relating to the 26 december sumatra andaman megathrust earthquake permanent displacements were seen 3 000 km away final displacements occurred within 10 minutes of the earthquake ruling out slow aseismic slip on the fault

high temperature transient creep in olivine rocks abstract the transient creep behaviour of two natural dunites has been investigated at temperatures between 1373 and 1573 k and a confining pressure of 300 mpa in a high resolution gas medium deformation apparatus the specimens were deformed in constant stress experiments in the presence of an aqueous phase and were oriented perpendicular to foliation the results confirm the finding of earlier workers that the high temperature transient flow properties of olivine rocks can be effectively modelled in terms of a burgers body rheology observations of time dependent strain recovery after unloading further support this model the viscosity in the transient regime 1 is found to have the same sensitivity to temperature and stress within the errors of each estimate as has been found previously for steady state creep viscosity 2 thus the ratio 2 1 is found to be relatively insensitive to temperature and stress with values between 0 17 and 0 67 these values are higher than the 2 1 0 1 that has generally been assumed in geophysical modelling of upper mantle transient deformation but are similar to the results of previous experiments with olivine single crystals the ratio of the shear moduli in the transient and steady state regimes 2 1 is found to be weakly sensitive to temperature at 250 mpa stress and 300 mpa confining pressure the value of 2 1 decreases slowly as temperature increases for the present experiments 0 05 2 1 which is comparable to the range of values reported in previous studies

upper mantle rheology from grace and gps postseismic deformation after the 2004 sumatra andaman earthquake 1 mantle rheology is one of the essential yet least understood material properties of our planet controlling the dynamic processes inside the earth s mantle and the earth s response to various forces with the advent of grace satellite gravity measurements of mass displacements associated with many processes are now available in the case of mass displacements related to postseismic deformation these data may provide new constraints on the mantle rheology we consider the postseismic deformation due to the m w 9 2 sumatra 26 december 2004 and m w 8 7 nias 28 march 2005 earthquakes applying wavelet analyses to enhance those local signals in the grace time varying geoids up to september 2007 we detect a clear postseismic gravity signal we supplement these gravity variations with gps measurements of postseismic crustal displacements to constrain postseismic relaxation processes throughout the upper mantle the observed gps displacements and gravity variations are well explained by a model of visco elastic relaxation plus a small amount of afterslip at the downdip extension of the coseismically ruptured fault planes our model uses a 60 km thick elastic layer above a viscoelastic asthenosphere with burgers body rheology the mantle below depth 220 km has a maxwell rheology assuming a low transient viscosity in the 60 220 km depth range the grace data are best explained by a constant steady state viscosity throughout the ductile portion of the upper mantle e g 60 660 km this suggests that the localization of relatively low viscosity in the asthenosphere is chiefly in the transient viscosity rather than the steady state viscosity we find a 8 10 18 pa s mantle viscosity in the 220 660 km depth range this may indicate a transient response of the upper mantle to the high amount of stress released by the earthquakes to fit the remaining misfit to the grace data larger at the smaller spatial scales cumulative afterslip of about 75 cm at depth should be added over the period spanned by the grace models it produces only small crustal displacements our results confirm that satellite gravity data are an essential complement to ground geodetic and geophysical networks in order to understand the seismic cycle and the earth s inner structure

postseismic relaxation and aftershocks 1 perfettini et al 2005 suggested that the temporal dependence of surface displacements u t measured in the epicentral area following an earthquake is related to n t the cumulative number of aftershocks by the equation u t a bt cn t d 1 e t where a b c d and are constants chosen to fit the data and t is the postearthquake time n t appears in the expression for u t because both the aftershocks and a portion of u t are thought to be driven by the same source postseismic fault creep at subseismogenic depths on the downdip extension of the coseismic rupture we show that this equation with the actually observed n t fits the postseismic displacements recorded on several baselines following each of five earthquakes 1999 m7 6 chi chi taiwan 1999 m7 1 hector mine southern california 2002 m7 9 denali central alaska 2003 m6 5 san simeon central california and 2004 m6 0 parkfield central california earthquakes although there are plausible physical interpretations for each of the terms in the expression for u t the large number of adjustable constants a b c d and involved in fitting the rather simple postseismic displacements diminishes the significance of the fit because the observed n t is well fit by the modified omori s law fault creep at depth presumably exhibits the same temporal dependence that dependence could be explained if the rheology of the fault downdip from the coseismic rupture is consistent with ordinary transient creep montesi 2004 demonstrated that power law creep across a shear zone at depth would also produce that temporal signal

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

grace gravity data help constraining seismic models of the 2004 sumatran earthquake 1 the analysis of gravity recovery and climate experiment grace level 2 data time series from the center for space research csr and geoforschungszentrum gfz allows us to extract a new estimate of the co seismic gravity signal due to the 2004 sumatran earthquake owing to compressible self gravitating earth models including sea level feedback in a new self consistent way and designed to compute gravitational perturbations due to volume changes separately we are able to prove that the asymmetry in the co seismic gravity pattern in which the north eastern negative anomaly is twice as large as the south western positive anomaly is not due to the previously overestimated dilatation in the crust the overestimate was due to a large dilatation localized at the fault discontinuity the gravitational effect of which is compensated by an opposite contribution from topography due to the uplifted crust after this localized dilatation is removed we instead predict compression in the footwall and dilatation in the hanging wall the overall anomaly is then mainly due to the additional gravitational effects of the ocean after water is displaced away from the uplifted crust as first indicated by de linage et al 2009 we also detail the differences between compressible and incompressible material properties by focusing on the most robust estimates from grace data consisting of the peak to peak gravity anomaly and an asymmetry coefficient that is given by the ratio of the negative gravity anomaly over the positive anomaly we show that they are quite sensitive to seismic source depths and dip angles this allows us to exploit space gravity data for the first time to help constraining centroid momentum tensor cmt source analyses of the 2004 sumatran earthquake and to conclude that the seismic moment has been released mainly in the lower crust rather than the lithospheric mantle thus grace data and cmt source analyses as well as geodetic slip distributions aided by gps complement each other for a robust inference of the seismic source of large earthquakes particular care is devoted to the spatial filtering of the gravity anomalies estimated both from observations and models to make their comparison significant

implications of postseismic gravity change following the great 2004 sumatra andaman earthquake from the regional harmonic analysis of grace intersatellite tracking data 1 we report gravity recovery and climate experiment grace satellite observations of coseismic displacements and postseismic transients from the great sumatra andaman islands thrust event mw 9 2 earthquake in december 2004 instead of using global spherical harmonic solutions of monthly gravity fields we estimated the gravity changes directly using intersatellite range rate data with regionally concentrated spherical slepian basis functions every 15 day interval we found significant step like coseismic and exponential like postseismic behavior in the time series of estimated coefficients from may 2003 to april 2007 for the spherical slepian functions after deriving coseismic slip estimates from seismic and geodetic data that spanned different time intervals we estimated and evaluated postseismic relaxation mechanisms with alternate asthenosphere viscosity models the large spatial coverage and uniform accuracy of our grace solution enabled us to clearly delineate a postseismic transient signal in the first 2 years of postearthquake grace data our preferred interpretation of the long wavelength components of the postseismic gravity change is biviscous viscoelastic flow we estimated a transient viscosity of 5 1017 pa s and a steady state viscosity of 5 1018 1019 pa s additional years of the grace observations should provide improved steady state viscosity estimates in contrast to our interpretation of coseismic gravity change the prominent postearthquake positive gravity change around the nicobar islands is accounted for by seafloor uplift with less postseismic perturbation in intrinsic density in the region surrounding the earthquake

modeling afterslip and aftershocks following the 1992 landers earthquake one way to probe the rheology of the lithosphere and fault zones is to analyze the temporal evolution of deformation following a large earthquake in such a case the lithosphere responds to a known stress change that can be assessed from earthquake slip models constrained from seismology and geodesy here we model the postseismic response of a fault zone that is assumed to obey a rate strengthening rheology where the frictional stress varies as a ln e e being the deformation rate and a 0 a rheological parameter the model is simple enough that these parameters can be estimated by inversion of postseismic geodetic data we apply this approach to the analysis of geodetic displacements following the m w 7 3 1992 landers earthquake the model adjusts well the measured displacements and implies a 0 47 0 53 mpa in addition we show that aftershocks and afterslip follow the same temporal evolution and that the spatiotemporal distribution of aftershocks is consistent with the idea that they are driven by reloading of the seismogenic zone resulting from frictional afterslip

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

poroelastic stress triggering of the 2005 m8 7 nias earthquake by the 2004 m9 2 sumatra andaman earthquake abstract the m9 2 sumatra andaman earthquake sae occurred three months prior to the m8 7 nias earthquake ne we propose that the ne was mechanically triggered by the sae and that poroelastic effects were a major component of this triggering this study uses 3d finite element models fems of the sumatra andaman subduction zone sasz to predict the deformation stress and pore pressure fields of the sae the coseismic slip distribution for the sae is calibrated to near field gps data using fem generated green s functions and linear inverse methods the calibrated fem is then used to predict the postseismic poroelastic contribution to stress triggering along the rupture surface of the ne which is adjacent to the southern margin of the sae the coseismic deformation of the sae combined with the rheologic configuration of the sasz produces two transient fluid flow regimes having separate time constants sae coseismic pore pressures in the relatively shallow forearc and volcanic arc regions within a few km depth dissipate within one month after the sae however pore pressures in the oceanic crust of the down going slab persist several months after the sae predictions suggest that the sae initially induced mpa scale negative pore pressure near the hypocenter of the ne this pore pressure slowly recovered increased during the three month interval separating the sae and ne due to lateral migration of pore fluids driven by coseismic pressure gradients within the subducting oceanic crust because pore pressure is a fundamental component of coulomb stress the mpa scale increase in pore pressure significantly decreased stability of the ne fault during the three month interval after the sae and prior to rupture of the ne a complete analysis of stress triggering due to the sae must include a poroelastic component failure to include poroelastic mechanics will lead to an incomplete model that cannot account for the time interval between the sae and ne our transient poroelastic model explains both the spatial and temporal characteristics of triggering of the ne by the sae