a rheologic model for wet crust applied to strike slip faults the strength and stability of crustal faults are not adequately addressed by the widely used two mechanism rheologic models of the crust based on byerlee s law and power law creep the models neglect the fluid assisted mechanisms of deformation that are important to strength of the crust and do not describe the variation in rate dependence of friction that governs the stability of fault slip several distinct mechanisms of frictional slip are defined on the basis of variations in frictional behavior and microfabric of simulated fault gouge in laboratory experiments state variable constitutive relations are used in a multiple mechanism formulation to describe the rate and temperature dependence of three friction mechanisms in wet quartz gouge at elevated temperatures this multimechanism description of friction is substituted for byerlee s law in the two mechanism models to generate a multimechanism rheologic model for the crust the multimechanism model is used to predict the rate and temperature dependence of crustal strength and the slip rate and depth temperature conditions over which each mechanism dominates application of the model to strike slip faults in the crust illustrates that the thickness of the actively shearing zone within faults is a critical parameter governing fault strength and stability the model predicts that frictional strength at midcrustal depths is significantly reduced relative to byerlee s law only for thick fault zones the reduction in strength is due to the operation of a strain rate sensitive friction mechanism involving combined cataclasis and solution transfer the rheologic model predicts that only very thin faults display the rate dependent characteristics necessary for initiation of seismic slip to any significant depth in the crust

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

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

active deformation in the bolivian andes south america a method is described for determining the horizontal field of velocity and velocity gradients in the bolivian andes in the vicinity of the bolivian orocline using the following data 1 space geodetic measurements of crustal motions 2 the style distribution and rate of late miocene quaternary folding and faulting and 3 paleomagnetic measurements of rigid body rotations about a vertical axis these data were analyzed in a network of 26 triangles which spanned the bolivian andes by solving the velocity gradient compatibility equations between adjacent triangles subject to the input data constraints this yielded 120 140 linear equations to constrain 108 unknowns making the problem moderately overdetermined a series of experiments were carried out with different combinations of the input data to determine the best fit in the least squares sense field of quaternary horizontal velocities and velocity gradients the azimuths of velocity vectors in the high andes are subparallel to both the relative plate convergence vector and the symmetry axis of the bolivian orocline with magnitudes relative to stable south america in the range 7 17 mm yr 1 accommodating up to 30 of the relative plate convergence however the azimuths of velocities along the range front are nearly orthogonal to the range with a component of distributed range parallel dextral or sinistral shear within the eastern cordillera and altiplano the horizontal velocity field requires bending about a vertical axis of both limbs of the bolivian orocline the field of horizontal dilatation assuming homogeneous deformation of the entire crustal thickness requires vertical velocities of material points up to 2 5 mm yr in the sub andean zone decreasing to 0 1 mm yr farther east in the eastern cordillera and altiplano the direction of maximum gradients of buoyancy stress determined from the field of gradients of appropriate combinations of velocity gradients using a thin sheet model of viscous flow are broadly parallel to the direction of maximum topographic gradients in the eastern cordillera providing support for the idea that the bulk behaviour of the bolivian lithosphere is fluid like a comparison of these gradients with buoyancy stress gradients calculated from crustal thickness contrasts suggest that the bulk lithospheric viscosity is in the range 0 5 1 0 1022 pa s gradients of velocity gradients along the eastern margin of the bolivian andes can be interpreted in terms of marked gradients of viscosity with viscosity increasing toward the brazilan shield in the cratonic core of south america buoyancy stresses calculated from crustal thickness contrasts calibrated with the crustal thicknesses at the changeovers from thrust to strike slip or normal faulting suggest that the average lithosphericscale deviatoric stresses are in the range 7 15 mpa

current shortening across the himalayas of nepal summary underthrusting of the indian lithosphere beneath the himalayas occurs during the quaternary period along a gently north dipping main basal detachment main himalayan thrust mht from which the southernmost emergent ramp main frontal thrust mft branches historical seismicity shows that slip on the mht is frequently accommodated through m 8 shallow earthquakes but shows a seismic gap in western nepal this absence of major historical earthquakes in western nepal can be explained either by an aseismic slip on the mht or a longlived elastic strain accumulation to test these hypotheses the present day displacement field has been measured for a gps network formed of 35 sites the updated solution presented in this paper combines data from 1995 1997 1998 and 2000 measurements the lack of deformation less than 3 10 8 yr 1 through the outer belt does not fit with a regional aseismic slip along the southern part of mht a less than 3 mm yr 1 aseismic slip could nonetheless affect restricted areas of the outer belt in contrast a strain accumulation of more than 30 10 8 yr 1 is measured south of the higher himalayas in a zone where an intense microseismicity reflects a stress build up it is presumably generated by locking of the aseismic creep that occurs along the mht beneath the higher himalayas and tibet the displacement field is simulated by a dual dislocation model that takes into account the pattern of microseismicity and particularly a segmentation between central and western nepal the best fit between the measured and simulated displacement fields is obtained with 19 mm yr 1 thrust and 0 1 mm yr 1 dextral strike slip components along a 117 ne dislocation locked to a depth of 20 21 km beneath western nepal and 19 20 mm yr 1 thrust and 0 2 mm yr 1 dextral strike slip components along a 108 ne dislocation locked to a depth of 17 21 km beneath central nepal the width of the locked zone between the main frontal thrust and the creeping zone is of the same order but rather greater in western nepal than in central nepal therefore it is expected that m 8 earthquakes could occur in western nepal

geodetic displacements and aftershocks following the 2001 mw 8 4 peru earthquake implications for the mechanics of the earthquake cycle along subduction zones we analyzed aftershocks and postseismic deformation recorded by the continuous gps station areq following the m w 8 4 23 june 2001 peru earthquake this station moved by 50 cm trenchward in a n235 e direction during the coseismic phase and continued to move in the same direction for an additional 15 cm over the next 2 years we compare observations with the prediction of a simple one dimensional 1 d system of springs sliders and dashpot loaded by a constant force meant to simulate stress transfer during the seismic cycle the model incorporates a seismogenic fault zone obeying rate weakening friction a zone of deep afterslip the brittle creep fault zone bcfz obeying rate strengthening friction and a zone of viscous flow at depth the ductile fault zone dfz this simple model captures the main features of the temporal evolution of seismicity and deformation our results imply that crustal strain associated with stress accumulation during the interseismic period is probably not stationary over most of the interseismic period the bcfz appears to control the early postseismic response afterslip and aftershocks although an immediate increase by a factor of about 1 77 of ductile shear rate is required placing constraints on the effective viscosity of the dfz following a large subduction earthquake displacement of inland sites is trenchward in the early phase of the seismic cycle and reverse to landward after a time t i for which an analytical expression is given this study adds support to the view that the decay rate of aftershocks may be controlled by reloading due to deep afterslip given the ratio of preseismic to postseismic viscous creep we deduce that frictional stresses along the subduction interface account for probably 70 of the force transmitted along the plate interface

numerical studies of the heat and mass transport in the cerro prieto geothermal field mexico numerical simulation techniques are employed in studies of the natural flow of heat and mass through the cerro prieto reservoir mexico and of the effects of exploitation on the field s behavior the reservoir model is a two dimensional vertical east to west southwest cross section which is based on a recent hydrogeologic model of this geothermal system the numerical code mulkom is used in the simulation studies the steady state pressure and temperature distributions are computed and compared against observed preproduction pressures and temperatures a reasonable match is obtained a natural hot water recharge rate of about 1 x 10 sup 2 kg s per meter of field length measured in a north south direction is obtained the model is then used to simulate the behavior of the field during the 1973 1978 production period the response of the model to fluid extraction agrees to what has been observed in the field or postulated by other authors there is a decrease in temperatures and pressures in the produced region no extensive two phase zone develops in the reservoir because of the strong fluid recharge most of the fluid recharging the system comes from colder regions located above and west of the produced reservoir 34 references 22 figures more 5 tables less

on the mechanics of earthquake afterslip we propose a model for earthquake afterslip based on rate and state variable friction laws in the model afterslip is attributed to the interaction of a velocity weakening region at depth within which earthquakes nucleate with an upper region of velocity strengthening frictional behavior the existence of this upper region is supported by independent seismologic observations and the results of laboratory friction experiments in our model afterslip is the result of relaxation of a stress perturbation within the velocity strengthening region which arises when an earthquake propagates into that region from below we derive the stress perturbation and its decay from the friction constitutive law using a simple 1 degree of freedom approximation for the elastic interaction between the fault and its surroundings this approximation is based on thickness averaged displacements and slip velocities within the velocity strengthening region which is assumed to slip as a rigid block coseismic and postseismic slip are coupled through the thickness averaged stiffness k of the velocity strengthening region we assume k to be inversely proportional to the thickness of this region which means that thicker velocity strengthening regions have a greater tendency to arrest coseismic slip we model the afterslip time histories of the 1966 parkfield and 1987 superstition hills earthquakes and relate the model parameters to physical parameters which may govern the rheologic behavior of the faults in accord with field observations our model predicts 1 that afterslip on some faults scales with the thickness of the unconsolidated sedimentary cover and 2 that proportionally more afterslip occurs for earthquakes in which coseismic surface slip is small compared with coseismic slip at depth velocity strengthening frictional behavior is to be expected for faults within poorly consolidated sediments and for those that contain significant gouge zones about 500 m within their shallow regions 3 5 km combining our results with those of recent laboratory friction studies indicates that relatively young faults with little accumulated fault gouge should exhibit little afterslip

controls of shear zone rheology and tectonic loading on postseismic creep 1 postseismic deformation is well documented in geodetic data collected in the aftermath of large earthquakes in the postseismic time interval gps is most sensitive to creep in the lower crust or upper mantle activated by earthquake generated stress perturbations in these regions deformation may be localized on an aseismic frictional surface or on a ductile shear zone these two hypotheses imply specific rheologies and therefore time dependence of postseismic creep hence postseismic creep constitutes a potential probe into the rheology of aseismic regions of the lithosphere i present a simple shear zone model of postseismic creep in which the rheology of the creeping element can be varied in the absence of tectonic loading during the postseismic time interval the displacement history of the shear zone obeying a power law rheology with stress exponent n follows an analytical relaxation curve parameterized by 1 n for a frictional surface postseismic creep follows the same relaxation law in the limit 1 n 0 a rough estimate of the apparent stress exponent can be obtained from continuous gps records application to data collected after the 1994 sanriku earthquake yields 1 n 0 1 which is consistent with dislocation creep mechanisms however the records of two other subduction zone events the 2001 peru event and the 1997 kronotski earthquake and a continental strike slip earthquake the 1999 izmit earthquake require negative 1 n rather than characterizing the shear zone rheology these negative exponents indicate that reloading of the shear zone by tectonic forces is important numerical simulations of postseismic deformation with nonnegligible reloading produce curves that are well fit by the generalized relaxation law with 1 n 0 although the actual stress exponent of the rheology is positive while this prevents rheology from being tightly constrained by the studied gps records it indicates that reloading is important in the postseismic time interval in other words the stress perturbation induced by an earthquake is comparable to the stress supported by ductile shear zones in the interseismic period

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

tide gage measurements of uplift along the south coast of alaska annual mean sea levels along the south coast of alaska are used to measure uplift along the alaska aleutian subduction zone oceanographic effects are removed from the observed annual mean sea levels by subtracting a correction that is proportional to the sea level fluctuations observed in southeast alaska that correction is effective in reducing fluctuations in the observed annual mean sea level as far west as the tip of alaska peninsula additional corrections to remove the eustatic rise in sea level and the apparent fall in sea level due to postglacial isostatic rebound of the land are introduced this corrected sea level record should provide a measure of tectonic subsidence in the area affected by the 1964 alaska earthquake postseismic uplift occurs where coseismic subsidence was observed and postseismic subsidence occurs where coseismic uplift was observed the immediate postseismic response is damped out within the first decade and the subsequent uplift rates appear to be steady over the 1974 1989 interval however some of those rates seem to be too high to be sustained over the 1000 year earthquake recurrence interval appropriate to this area if the interseismic deformation is only to recover the coseismic displacement thus a long term 100 years relaxation in uplift rates is postulated the immediate time constant 5 years postseismic relaxation is attributed to postseismic slip on the plate interface directly downdip from the coseismic rupture the long term time constant 100 years relaxation is attributed to flow in the asthenosphere

rapid afterslip following the 1999 chi chi taiwan earthquake 1 postseismic displacements of as much as 14 cm were recorded by gps measurements in the 3 months following the mw 7 6 1999 chi chi taiwan earthquake data from 35 continuous and 90 campaign surveyed stations which show continued east over west thrusting are analyzed to estimate the postseismic slip distribution and fault geometry assuming the shallow fault dips 24 e as determined by numerous studies of the mainshock we invert for the deeper fault structure our results show that the fault dip shallows with depth below the hypocenter merging into a nearly horizontal decollement at a depth of 8 12 km the afterslip distribution shows a maximum slip of 25 cm in the hypocentral region at 7 12 km depth as well as significant slip on the lower decollement afterslip is notably absent in the region of maximum coseismic slip consistent with the afterslip being driven by the mainshock stress change

rapid postseismic transients in subduction zones from continuous gps 1 continuous gps time series from three of four recently measured large subduction earthquakes document triggered rapid postseismic fault creep representing an additional moment release upward of 25 over the weeks following their main shocks data from two mw 8 0 and mw 8 4 events constrain the postseismic centroids to lie down dip from the lower limit of coseismic faulting and show that afterslip along the primary coseismic asperities is significantly less important than triggered deep creep time series for another mw 7 7 event show 30 postseismic energy release but here we cannot differentiate between afterslip and triggered deeper creep a fourth mw 8 1 event which occurred in the broad chilean seismogenic zone shows no postseismic deformation despite coseismic offsets in excess of 1 m for the three events which are followed by postseismic deformation stress transferred to the inferred centroids at 34 60 and 36 km depths by their respective main shock asperities increased reverse shear stress by 0 5 0 8 and 0 2 bar with a comparatively small decrease in normal stress 0 01 bar constraining the coulomb stress increase required to force slip along the metastable plate interface deep triggered slip of this nature is invisible without continuous geodesy but on the basis of these earthquakes would appear to constitute an important mode of strain release from beneath the seismogenic zones of convergent margins these events captured by some of the first permanent gps networks show that deep moment release is often modulated by seismogenic rupture updip and underscore the need for continuous geodesy to fully quantify the spectrum of moment release in great earthquakes index terms 7209 seismology earthquake dynamics and mechanics 3040 marine geology and geophysics plate tectonics 8150 8155 8157 8158 8150 tectonophysics plate boundary general 3040 7230 seismology seismicity and seismotectonics keywords subduction zone earthquake postseismic moment release

spatial variations in present day deformation kenai peninsula alaska and their implications from four years of global positioning system gps measurements we find significant spatial variations in present day deformation between the eastern and western kenai peninsula alaska sites in the eastern kenai peninsula and prince william sound move to the nnw relative to north america in the direction of pacific north america relative plate motion velocities decrease in magnitude from nearly the full plate rate in southern prince william sound to about 30 mm yr at seward and to about 5 mm yr near anchorage in contrast sites in the western kenai peninsula move to the sw in a nearly trenchward direction with a velocity of about 20 mm yr the data are consistent with the shallow plate interface offshore and beneath the eastern kenai and prince william sound being completely locked or nearly so with elastic strain accumulation resulting in rapid motion in the direction of relative plate motion of sites in the overriding plate the velocities of sites in the western kenai along strike to the southwest are opposite in sign with those predicted from elastic strain accumulation these data are incompatible with a significant locked region in this segment of the plate boundary trenchward velocities are found also for some sites in the anchorage area we interpret the trenchward velocities as being caused by a continuing postseismic transient from the 1964 great alaska earthquake there may be significant along strike differences in the long term behavior of the plate interface between the western and eastern kenai based on roughly coincident boundaries in the coseismic slip distribution cumulative postseismic uplift present day plate coupling and stress field the present postseismic response appears to generate purely trenchward motion suggesting a creep process that is purely dip slip our observations suggest that postseismic processes after the largest earthquakes can influence patterns of deformation for decades after the event

stress transfer and strain rate variations during the seismic cycle 1 the balance of forces implies stress transfers during the seismic cycle between the elastobrittle upper crust and the viscoelastic lower crust this could induce observable time variations of crustal straining in the interseismic period we simulate these variations using a one dimensional system of springs sliders and dashpot loaded by a constant force the seismogenic zone and the zone of afterslip below are modeled from rate and state friction the ductile deeper fault zone is modeled from a viscous slider with newtonian viscosity n the force per unit length f must exceed a critical value fc to overcome friction resistance of the fault system this simple system produces periodic earthquakes the recurrence period tcycle and the duration of the postseismic relaxation phase which is driven dominantly by afterslip then both scale linearly with n between two earthquakes interseismic strain buildup across the whole system is nonstationary with the convergence rates vi just after each earthquake being systematically higher than the value vf at the end of the interseismic period we show

consistency of geologic and geodetic displacements during andean orogenesis displacement and convergence rates inferred from gps and marine magnetic data suggest that this trend may be continuing at present hence an increasing fraction of convergence is being absorbed by mountain building this change may reflect increased plate coupling due to decreased sediment supply younger subducting lithosphere or increased normal stress at the interface from the effects of uplift index terms 8102 tectonophysics continental contract orogenic belts 8157 evolution of the earth plate motions past 3040 8158 evolution of the earth plate motions present and recent 3040 8099 structural geology general or miscellaneous

space time distribution of afterslip following the 2003 tokachi oki earthquake implications for variations in fault zone frictional properties 1 gps time series following the september 25 2003 ut tokachi oki earthquake m w 8 0 reveal significant deformation we use the network inversion filter to invert for the spatial and temporal evolution of afterslip in the 30 days following the earthquake afterslip is concentrated adjacent to the coseismic rupture zone between the 2003 rupture and the inferred source regions of the 1968 tokachi oki and the 1973 nemuro oki earthquakes the inversion shows a rapid decay of slip rate in the 2003 rupture zone with slower deceleration in the surrounding regions the stress velocity paths for the afterslip regions approximately follow d d in v 0 6 mpa suggestive of steady state velocity strengthening friction the complementary spatial pattern of coseismic rupture and afterslip may indicate along strike spatial variations of frictional properties although other interpretations can not be ruled out

precursory transient slip during the 2001 mw 8 4 peru earthquake sequence from continuous gps 1 two hour position estimates from a continuous gps station located at arequipa peru document precursory deformation beginning 18 hours prior to an mw 7 6 aftershock of the june 23rd 2001 mw 8 4 earthquake this preseismic signal appears on the north and east components as a slow displacement with an amplitude twice that of the subsequent coseismic analysis of three years of 18 hour rate measurement shows this signal to be unprecedented and beyond four standard deviations from the mean rate the best fitting centroid is directionally consistent with slow slip along the plate interface and suggests the preseismic deformation arises from creep near the aftershock rupture this implies the nazca south american plate interface slipped slowly prior to seismogenic faulting these observations indicate the mw 7 6 earthquake grew out of slow slip along the plate interface and clearly demonstrate the breadth of slip rates accommodated by subduction zone plate interfaces

frictional slip of granite at hydrothermal conditions sliding on faults in much of the continental crust likely occurs at hydrothermal conditions i e at elevated temperature and elevated pressure of aqueous pore fluids yet there have been few relevant laboratory studies to measure the strength sliding behavior and friction constitutive properties of faults at hydrothermal conditions we slid laboratory granite faults containing a layer of granite powder simulated gouge velocity stepping experiments were performed at temperatures of 23 to 600 c pore fluid pressures ph2o of 0 dry and 100 mpa wet effective normal stress of 400 mpa and sliding velocities v of 0 01 to 1 m s 0 32 to 32 m yr conditions were similar to those in earlier tests on dry granite to 845 c by lockner et al 1986 the mechanical results define two regimes the first regime includes dry granite up to at least 845 and wet granite below 250 c in this regime the coefficient of friction is high 0 7 to 0 8 and depends only modestly on temperature slip rate and ph2o the second regime includes wet granite above 350 c in this regime friction decreases considerably with increasing temperature temperature weakening and with decreasing slip rate velocity strengthening these regimes correspond well to those identified in sliding tests on ultrafine quartz we infer that one or more fluid assisted deformation mechanisms are activated in the second hydrothermal regime and operate concurrently with cataclastic flow slip in the first cool and or dry regime is characterized by pervasive shearing and particle size reduction slip in the second hot and wet regime is localized primarily onto narrow shear bands adjacent to the gouge rock interfaces weakness of these boundary shears may result either from an abundance of phyllosilicates preferentially aligned for easy dislocation glide or from a dependence of strength on gouge particle size major features of the granite data set can be fit reasonably well by a rate and temperature dependent three regime friction constitutive model chester this issue we extrapolate the experimental data and model fit in order to estimate steady state shear strength versus depth along natural slipping faults for sliding rates as low as 31 mm yr we do this for two end member cases in the first case pore pressure is assumed hydrostatic at all depths shallow crustal strength in this case is similar to that calculated in previous work from room temperature friction data while at depths below about 9 13 km depending on slip rate strength becomes less sensitive to depth but sensitive to slip rate in the second case pore pressure is assumed to be near lithostatic at depths below 5 km strength is low at all depths in this case 20 mpa in agreement with observations of weak faults such as the san andreas the predicted depth of transition from velocity weakening to velocity strengthening lies at about 13 km depth for a slip rate of 31 mm yr in rough agreement with the seismic aseismic transition depth observed on mature continental faults these results highlight the importance of fluid assisted deformation processes active in faults at depth and the need for laboratory studies on the roles of additional factors such as fluid chemistry large displacements higher concentrations of phyllosilicates and time dependent fault healing

the role of evaporating showers in the transfer of sting jet momentum to the surface the most damaging winds in a severe extratropical cyclone often occur just ahead of the evaporating ends of cloud filaments emanating from the so called cloud head these winds are associated with low level jets lljs sometimes occurring just above the boundary layer the question then arises as to how the high momentum is transferred to the surface an opportunity to address this question arose when the severe st jude s day windstorm travelled across southern england on 28 october 2013 we have carried out a mesoanalysis of a network of 1 min resolution automatic weather stations and high resolution doppler radar scans from the sensitive s band chilbolton advanced meteorological radar camra along with satellite and radar network imagery and numerical weather prediction products we show that although the damaging winds occurred in a relatively dry region of the cyclone there was evidence within the llj of abundant precipitation residues from shallow convective clouds that were evaporating in a localized region of descent we find that pockets of high momentum were transported towards the surface by the few remaining actively precipitating convective clouds within the llj and also by precipitation free convection in the boundary layer that was able to entrain evaporatively cooled air from the llj the boundary layer convection was organized in along wind rolls separated by 500 to about 3000 m the spacing varying according to the vertical extent of the convection the spacing was greatest where the strongest winds penetrated to the surface a run with a medium resolution version of the weather research and forecasting wrf model was able to reproduce the properties of the observed llj it confirmed the llj to be a sting jet which descended over the leading edge of a weaker cold conveyor belt jet

stress loading from viscous flow in the lower crust and triggering of aftershocks following the 1994 northridge california earthquake following the m w 6 7 northridge earthquake significant postseismic displacements were resolved with gps using a three dimensional viscoelastic model we suggest that this deformation is mainly driven by viscous flow in the lower crust such flow can transfer stress to the upper crust and load the rupture zone of the main shock at a decaying rate most aftershocks within the rupture zone especially those that occurred after the first several weeks of the main shock may have been triggered by continuous stress loading from viscous flow the long term decay time of aftershocks about 2 years approximately matches the decay of viscoelastic loading and thus is controlled by the viscosity of the lower crust our model provides a physical interpretation of the observed correlation between aftershock decay rate and surface heat flow

crustal deformation and fault slip during the seismic cycle in the north chile subduction zone from gps and insar observations summary the different phases of the earthquake cycle can produce measurable deformation of the earth s surface this work is aimed at describing the evolution of that deformation in space and time as well as the distribution of causal slip on the fault at depth we have applied gps and synthetic aperture radar sar interferometry insar techniques to northern chile where fast plate convergence rates are associated with large subduction earthquakes and extensive crustal deformation the region of northern chile between 18 s and 23 s is one of the most important seismic gaps in the world with no rupture having occurred since 1877 in 1995 the mw 8 1 antofagasta earthquake ruptured the subduction interface over a length of 180 km in the region immediately to the south of this 450 km long gap the coseismic deformation associated with this event has been documented previously here we use gps position time series for 40 benchmarks measured between 1996 and 2000 and ers sar interferograms for the interval between 1995 and 1999 to map both the post seismic deformation following the 1995 event and the ongoing interseismic deformation in the adjacent gap region in the seismic gap the interseismic velocities of 20 30 mm yr 1 to the east with respect to south america are mapped both the gps and the insar measurements can be modelled with 100 per cent coupling of the thrust interface of the subduction to a depth of 35 km with a transition zone extending down to 55 km depth the slip rate in that zone increases linearly from zero to the plate convergence rate south of the gap the interferometric map shows interseismic deformation superimposed with deformation following the 1995 earthquake and covering the same area as the coseismic deformation some 40 per cent of this deformation is related to seismic activity in the 3 3 yr following the 1995 event in particular slip during a mw 7 1 earthquake in 1998 however most of the signal 60 per cent corresponds to post seismic deformation resulting from widespread aseismic slip in the subduction interface the afterslip appears to have occurred down dip in the transition zone at 35 55 km depth and to have propagated laterally northwards at 25 45 km depth under the mejillones peninsula which is a prominent geomorphological feature at the boundary between the 1877 and 1995 rupture zones we propose a simple slip model for the seismic cycle associated with the antofagasta earthquake where the transition zone alternates between aseismic shear and seismic slip

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

on the mechanism of seismic decoupling and back arc spreading at subduction zones to address the problem of the great variability of the mechanical state of subduction zones we investigate the mechanics of back arc spreading and seismic decoupling back arc spreading is assumed to be due to rifting of the upper plate and hence occurs when trench normal tension reaches a critical value seismic decoupling is assumed to occur when the normal stress at the frictional interface is decreased by an amount sufficient to cross the friction stability transition two forces are important in this problem the first is a small component of the slab pull force which remains unbalanced by the subduction resistance and exerts a vertical suction force at the trench the second is a sea anchor force exerted on the slab that resists its lateral motion assumed to occur at the upper plate velocity both forces contribute to the coupling problem only the sea anchor force is responsible for back arc spreading the unbalanced slab pull force is determined from a force balance for subduction the sea anchor force is computed as the hydrodynamic resistance to the facewise translation of an elliptical disc through a viscous fluid the model predicts three regimes seismically coupled compressional arcs with advancing upper plates seismically decoupled extensional arcs with retreating upper plates and strongly extensional arcs which also have back arc spreading this model is applied in detail to the izu bonin marianas system it shows that back arc spreading occurs when the integrated tension in the upper plate exceeds a value of about 1 1013 n m 1 and requires a residual tension of about a third that to drive the back arc spreading once rifting is completed it shows why the plate interface near guam is seismically coupled while the plate boundary everywhere farther north is decoupled when applied globally it successfully predicts the state of seismic coupling and back arc spreading in more than 80 of the world s subduction zones of the remaining half can be seen to contain additional complications not included in the model about 10 of cases remain unexplained but some of these may have incorrectly determined seismic coupling coefficients

joint estimation of afterslip rate and postseismic relaxation following the 1989 loma prieta earthquake global positioning system gps data from campaigns carried out over the 5 years following the 1989 loma prieta earthquake and leveling data measured in 1990 and 1992 define the postseismic velocity field around the loma prieta rupture zone subtraction of a background velocity field yields a residual velocity pattern which we interpret as the product of two physical processes 1 slow afterslip along distinct planes in the upper cru st and 2 viscoelastic relaxation of the lower crust and upper mantle biirgmann et al 1997 previously derived an afterslip model involving uniform afterslip on two optimally determined planes in cluding oblique reverse slip on the coseismic rupture and reverse slip on a shallow thrust fault to the northeast of the san andreas fault we further consider models of distributed slip on these two fault planes plus a viscoelastic relaxation pattern which depends on a suitable cose ismic rupture model and crust and mantle viscosities several fault models from the literature were considered for the 1989 coseismic rupture with nearly identical impact on the results simultaneous maximum likelihood inversion of the gps and leveling data for afterslip distri bution and viscosity yields the following results 1 a good fit to the data is obtained by smooth afterslip distributions without any viscoelastic relaxation being required 2 tangible broad scale viscoelastic relaxation of the lower crust and upper mantle are present in this data set at 97 confidence and a lower crustal viscosity of 1029 pa s is obtained however the viscosity of both the lower crust and upper mantle are poorly constrained 3 for a given misfit 20 less integrated afterslip and smoother afterslip distributions result when viscoelas tic relaxation is included 4 maximum slip rates on the slip distributed models are 3 5 crn yr the dominant patches estimated on the two planes fill in the entire depth range 4 13 km without significant overlap and deeper afterslip is not required the afterslip distribution on the coseismic rupture plane is strongly dominated by reverse slip immediately southeast of the main center of coseismic reverse slip

crustal motion north and south of the arica deflection comparing recent geodetic results from the central andes 1 an intercomparison of recent velocity solutions for the global positioning system gps networks constructed by the south american nazca plate project snapp based in bolivia and peru and our central andes gps project cap based in chile and argentina indicates a velocity discontinuity of order 10 mm yr near the boundary between these networks we suggest that this velocity jump manifests measurement bias in the snapp velocity field our results indicate that no major slip partioning occurs within the forearc of northern chile in response to the obliquity of subduction but that nazca south america plate convergence is partitioned between the forearc and the backarc regions the present rate of shortening across the southern part of the sub andean belt in argentina is 8 9 1 6 mm yr

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

prolonged post seismic deformation of the 1960 great chile earthquake and implications for mantle rheology 1 contemporary crustal deformation of the southern andean margin shows an interesting feature while nearly all coastal gps sites move landward consistent with inter seismic deformation near a locked subduction fault sites 300 400 km landward of the rupture region of the mw9 5 1960 chile earthquake are moving in the opposite direction we attribute the seaward motion of these inland sites to a prolonged crustal deformation due to mantle stress relaxation following the 1960 great earthquake in order to reproduce the observed seaward motion using a three dimensional finite element model we need to incorporate a mantle viscosity of about 3 1019 pa s the possibility that the seaward motion is caused by a silent slip event on the plate interface at large depths cannot be completely excluded and our analysis provides a working model for future field tests

time dependent triggered afterslip following the 1989 loma prieta earthquake we employ a modified version of the network inversion filter to investigate time dependent slip following the 1989 loma prieta earthquake previous analysis of global positioning system gps and leveling data suggests afterslip on the loma prieta rupture as well as aseismic slip on a thrust fault northeast of the san andreas fault which we identify with the foothills thrust belt we analyzed 173 daily gps solution files at 62 stations collected from 1989 8 to 1998 3 a total of 1 134 three dimensional relative baseline determinations the observed position changes are assumed to result from secular deformation random benchmark motions and temporally varying fault slip the data reveal temporal variations in slip rate but poorly resolve spatial variations in fault slip the amount of temporal smoothing is estimated by maximum likelihood conditional on this estimate reverse slip on the foothills thrust decays from 45 12 mm yr immediately after the earthquake to zero by 1992 reverse slip on the loma prieta rupture surface decays from 57 11 mm yr to zero by 1994 right lateral slip on the loma prieta rupture surface decays monotonically from 30 10 mm yr to zero by 1994 these results suggest that 1 triggered afterslip can occur off the main rupture zone on adjacent faults 2 shallow afterslip dominated the postseismic deformation for the 8 years following the earthquake and 3 postseismic slip on the foothills thrust may account for a significant portion of its total slip budget

strong interseismic coupling fault afterslip and viscoelastic flow before and after the oct 9 1995 colima jalisco earthquake continuous gps measurements from colima mexico 1 continuous gps measurements from colima mexico during 4 93 6 01 bracketing the oct 9 1995 m 8 0 colima jalisco earthquake provide new constraints on rivera plate subduction mechanics modeling of margin normal strain accumulation before the earthquake suggests the rivera north america subduction interface was fully locked transient postseismic motion from 10 95 6 97 is well fit by a model that includes logarithmically decaying fault afterslip elastic strain from shallow fault relocking and possibly a minor viscoelastic response but is fit poorly by models that assume a dominant maxwell viscoelastic response of the lower crust and upper mantle independent of the assumed viscosities landward margin normal motion since mid 1997 is parallel to but 75 slower than the pre seismic velocity afterslip alone fails to account for this slowdown the viscoelastic response predicted by a fem correctly resolves the remaining velocity difference within the uncertainties both processes thus offset elastic strain accumulating from the relocked subduction interface

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

aftershocks and pore fluid diffusion following the 1992 landers earthquake 1 we model the evolution of regional stress following the 1992 landers earthquake in order to test the importance of pore fluid flow in producing aftershocks rising fluid pressure due to pore fluid flow and the resulting coulomb stress changes were found to be strongly correlated with the time and location of aftershock events regional aftershock frequencies computed by integrating pore pressure decay rates also agreed quite well with aftershock data calculations show that regions of rising postseismic poroelastic coulomb stress overlap considerably with regions of positive coseismic coulomb stress thus pore fluid flow which affects pore pressure within faults and causes regional poroelastic stress evolution following earthquakes gradually evolves the initial coseismic stress changes together these changes provide a reasonable physical mechanism for aftershock triggering which agrees with data for the 1992 landers earthquake

on the rapid postseismic uplift along turnagain arm alaska following the 1964 prince william sound earthquake an analysis of leveling data obtained along turnagain arm alaska in the aftermath of the 1964 prince william sound earthquake shows that the postseismic uplift rate was constant during the first year following the earthquake the maximum 1 yr peak to trough uplift was about 15 cm while the maximum uplift relative to a tide gauge site in anchorage was about 9 cm there is some evidence for a modest decrease in the uplift rate between may and october of 1965 although the evidence is weakened by the lack of an appropriate reference point the longer term temporal evolution of uplift rates as compiled from leveling gps tide gauge and vlbi observations by cohen 1996 can be modeled by an omori like or exponential transient decay curve with a time constant of several years the geodetic data taken in conjunction with seismological constraints can be explained by aseismic slip at depth along the tectonic plate interface with an initial slip rate of 35 cm yr and a slip depth of 25 37 km

viscosity estimates for the crust and upper mantle from patterns of lacustrine shoreline deformation in the eastern great basin the deformed shorelines of lake bonneville constitute a classic source of information on lithospheric elastic thickness and upper mantle viscosity we describe and apply a new model to a recently augmented data set new data better constrain both the complex spatio temporal pattern of the lake load and the crustal deformation response to that load the history of lake level fluctuations has been significantly refined and somewhat modified this is due to both more radiocarbon dates from within the bonneville basin and to an improved calibration of the radiocarbon timescale itself the data which constrain the crustal deformation pattern consist of ages and shoreline elevations from several hundred points which sample three major levels of lake bonneville and corresponding elevations from the high stands of three smaller lakes situated to the west of lake bonneville the data from the smaller lakes help elucidate the pattern of deflection which occurred beyond the edge of the big lake the geometry of the earth model incorporates an arbitrary number of layers overlying a half space and the rheology of each level can accommodate an arbitrary number of maxwell viscoelastic elements in parallel the inverse modeling comprises three complementary approaches for the simplest configurations we performed a direct search of the parameter space and delineated the irregular boundary of the subspace of acceptable models for more complex configurations we constrained the elastic parameters to their seismically determined values and then solved for viscosity versus depth profiles by either expressing the log viscosity versus log depth profile as a series of specially constructed orthogonal polynomials or by allowing each of 8 10 layers plus the half space to have an independently determined viscosity we found that the data do not strongly support nor can they conclusively exclude a more complex rheology than simple maxwell viscoelasticity the orthogonal polynomial solution exhibits an essentially monotonic decrease in viscosity with depth the most rapid change occurs at shallow depths decreasing from 1023 pa s at 3 km to 102o pa s at 30 km the decrease is much more gradual below with only another factor of 5 decrease between 30 and 300 km depth the unconstrained solution exhibits a rapid decrease in viscosity with depth from 2x 10 24 pa s in the top 10 km to 4x 1017 pa s at a depth of 40 km a nearly isoviscous asthenospheric region extends from 40 to 150 km and is underlain by a mantle lithospheric region with increased viscosity 2x 102o pa s extending from 150 to 300 km depth and by a uniform viscosity 1019 pa s half space below

analysis of the 23 june 2001 mw 8 4 peru underthrusting earthquake and its aftershocks on 23 june 2001 a m w 8 4 underthrusting earthquake occurred in the southern peru subduction zone followed by several large aftershocks including 26 june m w 6 7 and 7 july m w 7 5 broadband analyses of seismic data for the largest of these earthquakes show southeastward rupture of 180 km along the portion of the subduction zone previously ruptured in 1868 m w 8 8 9 moment release distributions determined are consistent with aftershock location patterns earthquake rupture mode varies along southern peru from larger multi segment rupture in 1868 to several smaller segment ruptures in 2001 similar to rupture variation observed in northern peru and other subduction zones based on models of subduction zone segment interaction the 2001 earthquake sequence may suggest a shorter recurrence time for future earthquakes along this portion of the peru chile subduction zone

a modelling study of vertical surface displacements at convergent plate margins summary during the evolution of a subduction zone system variations are likely to occur in for example surface plate velocities and buoyancy of the subducting lithosphere we quantify vertical surface displacements at convergent plate margins resulting from such imposed variations for this purpose we use a 2 d numerical model in which the lithospheric plates have an effective elastic thickness we first define a model in which the subducting plate is driven by its negative buoyancy and a velocity at its surface side boundary its equilibrium topography after around 2 myr is the reference level for examination of surface displacements resulting from variations in buoyancy velocity of the surface plates friction along the interplate contact and subduction zone roll back we find that a decrease increase in buoyancy of the subducting material leads to a deepening uplift of the plate margins an increase in friction along the subduction fault deepens the overriding plate margin subduction zone roll back due to sinking of the negatively buoyant subducting plate induces subsidence of the overriding plate margin this subsidence is reduced when roll back takes place in a land locked basin setting trench retreat forced by the motion of the overriding plate is characterized by higher topography of the overriding plate margin than the case of retreat due to the sinking of the negatively buoyant slab in the first case in plane stress in the back arc region is compressive while it is tensional for roll back due to the sinking of the slab we conclude that vertical surface displacements during ongoing subduction may reach a magnitude of a few kilometres on the overriding and subducting plate margins

slip kinematics and dynamics during and after the 1995 october 9 mw 8 0 colima jalisco earthquake mexico from gps geodetic constraints we use horizontal and vertical crustal displacements derived from gps measurements at 26 sites in western mexico to study the coseismic and post seismic kinematics and dynamics of the 1995 october 9 m w 8 0 colima jalisco earthquake along the middle america trench the measurements bracket the entire landward edge of the approximately 150 km long rupture zone and span a 4 yr period for most sites we solve for the temporal evolution of slip along the subduction interface by inverting gps displacements for the coseismic and four post seismic intervals march 1995 march 1999 subject to the assumption that the crust responds elastically to slip along a shallow dipping curved subduction interface coseismic rupture of up to 5 m was largely focused above depths of 20 km and was limited to a 120 140 km long segment of the subduction zone within one week of the earthquake post seismic slip migrated downdip to depths of 16 35 km where it has since decayed logarithmically we also find evidence for shallow aseismic slip during 1996 or early 1997 northwest of the coseismic rupture zone and increasingly widespread relocking of shallow regions of the subduction interface after early 1997 the relative lack of afterslip in shallow regions of the subduction interface suggests that the interface lies in the unstable frictional regime and hence is strongly coupled between earthquakes by 1999 the cumulative slip moment associated with post seismic slip equaled 70 per cent of the coseismic moment with nearly all of this slip occurring downdip from the coseismic rupture zone the migration of slip after the earthquake to a deeper and presumably velocity strengthening area of the subduction interface and the logarithmic decay of afterslip conform to the qualitative and quantitative predictions of a model in which the fault kinematics are prescribed by rate and state variable frictional laws however misfits to the geodetic displacements exceed the average displacement uncertainties for all epochs implying one or more of the following 1 the elastic response is heterogeneous due to slip along unmodelled upper crustal faults or variations in the elastic properties of the crust 2 other post seismic mechanisms such as viscoelastic or poroelastic effects contribute to or possibly dominate the post seismic response 3 we have underestimated the uncertainties in the gps displacements