the key frictional parameters controlling spatial variations in the speed of postseismic slip propagation on a subduction plate boundary abstract we investigate relations between the postseismic slip process effective normal stress and friction parameters for a rate and state dependent law using 3 d numerical simulations of a subduction zone the results show that the postseismic propagation speed largely depends on a a rather than a b a b or d c where a and b are the frictional parameters describing the friction law is the effective normal stress and d c is the characteristic slip distance the duration of the postseismic slip is found to depend on d c and a b considering that postseismic slip propagates faster in shallower regions than in deeper regions for both our numerical simulations and observation off sanriku and that frictional parameter a is not likely to be several times smaller than that estimated from rock laboratory experiments we conclude that effective normal stress mainly controls the spatial variations in the speed of postseismic slip propagation for large earthquakes off sanriku moreover the effective normal stress much lower than lithostatic stress due to high pore pressure may explain the speed of aseismic slip propagation in other subduction zones as well as off sanriku

transfer of basal sliding variations to the surface of a linearly viscous glacier on etudie pour une plaque a faces paralleles d epaisseur h et de viscosite lineaire l effet en surface des fluctuations de la vitesse de derapage

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

dynamics of a velocity strengthening fault region implications for slow earthquakes and postseismic slip we consider the effect of permanent stress changes on a velocity strengthening rate and state fault through numerical simulations and analytical results on 1 d 2 d and 3 d models we show that slip transients can be triggered by perturbations of size roughly larger than lb gdc b where g is the shear modulus dc and b are the characteristic slip distance and the coefficient of the evolution effect of rate and state friction respectively and is the effective normal stress perturbations that increase the coulomb stress lead to the strongest transients but creep bursts can also be triggered by perturbations that decrease the coulomb stress in the latter case peak slip velocity is attained long after the perturbation so that it may be difficult in practice to identify their origin the evolution of slip in a creep transient shares many features with the nucleation process of a rate and state weakening fault slip initially localizes over a region of size not smaller than lb and then accelerates transiently and finally expands as a quasi static propagating crack the characteristic size lb implies a constraint on the grid resolution of numerical models even on strengthening faults that is more stringent than classical criteria in the transition zone between the velocity weakening and strengthening regions the peak slip velocity may be arbitrarily large and may approach seismic slip velocities postseismic slip may represent the response of the creeping parts of the fault to a stress perturbation of large scale comparable to the extent of the main shock rupture and high amplitude while slow earthquakes may represent the response of the creeping zones to a more localized stress perturbation our results indicate that superficial afterslip observed at usually seismogenic depths is governed by a rate strengthening rheology and is not likely to correspond to stable weakening zones the predictions of the full rate and state framework reduce to a pure velocity strengthening law on a timescale longer than the duration of the acceleration transient only when the triggering perturbation extends over length scales much larger than lb

interseismic deformation and creep along the central section of the north anatolian fault turkey insar observations and implications for rate and state friction properties 1 we present high resolution measurements of interseismic deformation along the central section of the north anatolian fault naf in turkey using interferometric synthetic aperture radar data from the advanced land observing satellite and envisat missions we generated maps of satellite line of sight velocity using five ascending advanced land observing satellite tracks and one descending envisat track covering the naf between 31 2 e and 34 3 e the line of sight velocity reveals discontinuities of up to 5 mm yr across the ismetpasa segment of the naf implying surface creep at a rate of 9 mm yr this is a large fraction of the inferred slip rate of the naf 21 25 mm yr the lateral extent of significant surface creep is about 75 km we model the inferred surface velocity and shallow fault creep using numerical simulations of spontaneous earthquake sequences that incorporate laboratory derived rate and state friction our results indicate that frictional behavior in the ismetpasa segment is velocity strengthening at shallow depths and transitions to velocity weakening at a depth of 3 6 km the inferred depth extent of shallow fault creep is 5 5 7 km suggesting that the deeper locked portion of the partially creeping segment is characterized by a higher stressing rate smaller events and shorter recurrence interval we also reproduce surface velocity in a locked segment of the naf by fault models with velocity weakening conditions at shallow depth our results imply that frictional behavior in a shallow portion of major active faults with little or no shallow creep is mostly velocity weakening

theoretical limitations to englacial velocity calculations to study the dynamics of ice sheets and glaciers velocities at the bed of a glacier must be measured directly or calculated using data gathered from boreholes and surface surveys boreholes to the bed are expensive and time consuming to drill so the determination of basal velocity is almost exclusively by numerical inversion of velocities observed at the surface for non linearly viscous glaciers a perturbation analysis demonstrates that inversions for englacial velocities will magnify measurement errors at an exponential rate with depth the rate at which calculation errors grow is proportional to a lyapunov exponent a measure of information loss which is shown to be a simple linear function of spatial frequency with a coefficient depending on glen s flow law exponent n the coefficient decreases with increasing non linearity demonstrating that inversions with non linearly viscous ice have smaller calculation errors than inversions with linearly viscous ice in both the linear and nonlinear cases the lyapunov exponent and rate of error growth increases with decreasing wavelength which limits velocity calculations at the bed to wavelengths on the order of one ice thickness or greater this limitation is theoretical and cannot be countered by more accurate survey data or special numerical techniques

spatial variations in fault friction related to lithology from rupture and afterslip of the 2014 south napa california earthquake following earthquakes faults are often observed to continue slipping aseismically it has been proposed that this afterslip occurs on parts of the fault with rate strengthening friction that are stressed by the main shock but our understanding has been limited by a lack of immediate high resolution observations here we show that the behavior of afterslip following the 2014 south napa earthquake in california varied over distances of only a few kilometers this variability cannot be explained by coseismic stress changes alone we present daily positions from continuous and survey gps sites that we remeasured within 12 h of the main shock and surface displacements from the new sentinel 1 radar mission this unique geodetic data set constrains the distribution and evolution of coseismic and postseismic fault slip with exceptional resolution in space and time we suggest that the observed heterogeneity in behavior is caused by lithological controls on the frictional properties of the fault plane

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

force budget i theory and numerical methods a practical method is developed for calculating stresses and velocities at depth using field measurements of the geometry and surface velocity of glaciers to do this it is convenient to partition full stresses into lithostatic and resistive components the horizontal gradient in vertically integrated lithostatic stress is the driving stress and it describes the horizontal action of gravity the horizontal resistive stress gradients describe the reactions resistive stresses are simply related to deviatoric stresses and hence to strain rates through a constitutive relation a numerical scheme can be used to calculate stresses and velocities from surface velocities and slope and from ice thickness there is no mathematical requirement that the variations in these quantities be small

spatial variability in the flow of a valley glacier deformation of a large array of boreholes measurements of the deformation of a dense array of boreholes in worthington glacier alaska show that the glacier moves with generally bed parallel motion strain in the 200 m deep valley glacier is constant near the surface but follows a nonlinear vertical profile below a depth of about 120 m by a depth of 180 m the octahedral strain rate reaches 0 35 yr 1 the three dimensional velocity field shows spatial complexity with significant deviations from plane strain despite relatively simple valley geometry in the vicinity of the 6 10 6 m 3 study volume no evidence was found for time varying deformation or movement along localized shear planes observations were made by repeatedly measuring the long axis geometry of 31 closely spaced boreholes over a 70 day period and three additional holes after 1 full year of deformation the holes were spaced 15 to 30 m apart installation and measurement of such a large number of boreholes required the development of a semiautomated hot water drilling system that creates straight and vertical boreholes with uniform walls the equipment and procedures enables borehole profiles to be measured without the use of hole casing inclinometry measurements collected in the holes were processed analyzed for error and visualized as a fully three dimensional data set the new methods offer unique insight into small scale spatial and temporal variations in the pattern of flow in a valley glacier

modelling of short interval silent slip events in deeper subduction interfaces considering the frictional properties at the unstable stable transition regime summary recent high resolution observations of crustal movements have revealed silent slip events sses with propagation velocities of around 10 15 km d 1 and with intervals of 3 14 months along the deeper parts of the cascadia and nankai subduction zones this study develops 2 d and 3 d models of these short interval sses considering the frictional behaviour that was confirmed experimentally by shimamoto for the unstable stable transition regime to represent this frictional behaviour a small cut off velocity to an evolution effect is introduced in a rate and state dependent friction law when the cut off velocity to the evolution effect is significantly smaller than that to a direct effect steady state friction exhibits velocity weakening at low slip velocities and velocity strengthening at high slip velocities at the deeper cascadia and nankai subduction interfaces the pore pressure is inferred to be high because of the dehydration of materials in the descending plate under conditions where the pore fluid pressure is nearly equal to the lithostatic pressure and the critical weakening displacement is very small short interval sses with propagation velocities and slip velocities of 4 8 km d 1 and 2 4 10 7 m s 1 respectively can be reproduced the propagation velocity of short interval sses is in proportion to the slip velocity the results also show that during the nucleation process of large earthquakes the occurrence of short interval sses becomes irregular because of the accelerated slips that occur at the bottom of the seismogenic zone our results suggest that monitoring of short interval sses might be useful for forecasting the main earthquakes

the nature of complex ice flow in shirase glacier catchment east antarctica the transition of inlandto complex ice flow is investigated inthedown stream area of shirase glaciercatchment east antarctica the 250km long mizuhotri angulation chain mtc naruse 1978 230kmupstreamof the grounding line of shirase glacier is re analyzed by a force balance analysis in combination with balance velocity estimates numerical model experiments were carried out with a two dimensional ther momechanical higher order ice sheet model along a central flowline extending from the ice divide dome fuji to the grounding line of shirase glacier passing through the mtc results show that complex flow originates near the mtc where longitudinal normal stresses and normal drag in particular play a decisive role in the force balance the fast flow area however is geologically controlled and confined to the bottleneck or ice flow convergence area a few tens of kilometres upstream of the grounding line in between the mtc and the grounding zone longitudinal normal stress and basal sliding are dominant features of the ice flow regime

frictional constraints on crustal faulting we consider how variations in fault frictional properties affect the phenomenology of earthquake faulting in particular we propose that lateral variations in fault friction produce the marked heterogeneity of slip observed in large earthquakes we model these variations using a rate and state dependent friction law where we differentiate velocity weakening behavior into two fields the strong seismic field is very velocity weakening and the weak seismic field is slightly velocity weakening similarly we differentiate velocity strengthening behavior into two fields the compliant field is slightly velocity strengthening and the viscous field is very velocity strengthening the strong seismic field comprises the seismic slip concentrations or asperities the two intermediate fields weak seismic and compliant have frictional velocity dependences that are close to velocity neutral these fields modulate both the tectonic loading and the dynamic rupture process during the interseismic period the weak seismic and compliant regions slip aseismically while the strong seismic regions remain locked evolving into stress concentrations that fail only in main shocks the weak seismic areas exhibit most of the interseismic activity and aftershocks but can also creep seismically this mixed frictional behavior can be obtained from a sufficiently heterogeneous distribution of the critical slip distance the model also provides a mechanism for rupture arrest dynamic rupture fronts decelerate as they penetrate into unloaded complaint or weak seismic areas producing broad areas of accelerated afterslip aftershocks occur on both the weak seismic and compliant areas around a fault but most of the stress is diffused through aseismic slip rapid afterslip on these peripheral areas can also produce aftershocks within the main shock rupture area by reloading weak fault areas that slipped in the main shock and then healed we test this frictional model by comparing the seismicity and the coseismic slip for the 1966 parkfield 1979 coyote lake and 1984 morgan hill earthquakes the interevent seismicity and aftershocks appear to occur on fault areas outside the regions of significant slip these regions are interpreted as either weak seismic or compliant depending on whether or not they manifest interevent seismicity

spatial and temporal evolution of stress and slip rate during the 2000 tokai slow earthquake 1 we investigate an ongoing silent thrust event in the tokai seismic gap along the suruga nankai trough central japan prior to the event continuous gps data from april 1996 to the end of 1999 show that this region displaced 2 cm yr to the northwest relative to the landward plate the gps time series show an abrupt change in rate in mid june 2000 that continues as of mid 2005 we model this transient deformation which we refer to as the tokai slow thrust slip event as caused by slip on the interface between the philippine sea and amurian plates the spatial and temporal distribution of slip rate is estimated with kalman filter based inversion methods our inversions reveal two slow subevents the first initiated in late june 2000 slightly before the miyake jima eruption the locus of slip then propagated southeast in the second half of 2000 with maximum slip rates of about 15 cm yr through 2001 a second locus of slip initiated to the northeast in early 2001 the depth of the slip zone is about 25 km which may correspond to the transition zone from a seismogenic to a freely sliding zone the cumulative moment magnitude of the slow slip event up to november 2002 is mw 6 8 we calculate shear stress changes on the plate interface from the slip histories stress change as a function of slip rate shows trajectories similar to that inferred for high speed ruptures however the maximum velocity is 8 orders of magnitude less than in normal earthquakes

a 3 d quasi static model for a variety of slip behaviors on a subduction fault earthquake faultings have a wide variety of slip behaviors such as a log linear frequency magnitude relation characteristic earthquakes slow slip events and so on we report a model which can reproduce a certain variety of observed complex slip behaviors on a fault our 3 d model simulates the seismic cycle on a shallow dipping subduction fault in a homogeneous elastic half space on which frictional sliding is controlled by a rate and state dependent friction law we find that the behaviors of reproduced seismic cycles depend on a lateral dimension of a seismogenic zone h with respect to a constant seismogenic width in dip direction w the following three domains appear in the seismic cycle behaviors 1 regular periodic behaviors when h is comparable to w 2 transitional quasi periodic behaviors when h w 3 and 3 complex behaviors when h w is larger than about 4 the slip behavior in the domain 1 is characterized by a periodical recurrence of a characteristic earthquake which is centered in strike direction in the domain 2 although earthquakes are still centered these recurrence intervals and the sizes are modulated within a certain range also in the domain 3 earthquakes occur not only at the center but at various lateral positions on the seismogenic zone in this domain the log linear frequency magnitude relations like the gutenberg richter relation are produced slow slip events also occur at source areas of the earthquakes it is suggested that a heterogeneous stress distribution at a source region is important as well as heterogeneities in friction properties on the fault for understanding the wide variety of slip behaviors in faultings

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

detection and monitoring of ongoing aseismic slip in the tokai region central japan analysis of global positioning system data shows that the rate of crustal deformations in the tokai region of japan a seismic gap area changed over the past 18 months kalman filtering analysis shows aseismic slip on the plate boundary in the western tokai region centered on lake hamana adjacent to the anticipated tokai earthquake source area the cumulative moment magnitude reaches 6 7 in june 2002 with a relative slip increase northeast of lake haman from january 2002 an existence of aseismic slip in the western tokai supports the hypothesis of a silent event as the cause of uplifting several days before the 1944 tonankai earthquake

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

earthquake nucleation on rate and state faults aging and slip laws we compare 2 d quasi static earthquake nucleation on rate and state faults under both aging and slip versions of the state evolution law for both versions mature nucleation zones exhibit 2 primary regimes of growth well above and slightly above steady state corresponding respectively to larger and smaller fault weakening rates well above steady state aging law nucleation takes the form of accelerating slip on a patch of fixed length this length is proportional to b 1 and independent of a where a and b are the constitutive parameters relating changes in slip speed and state to frictional strength under the slip law the nucleation zone is smaller and continually shrinks as slip accelerates the nucleation zone is guaranteed to remain well above steady state only for values of a b that are low by laboratory standards near steady state for both laws the nucleation zone expands the propagating front remains well above steady state giving rise to a simple expression for its effective fracture energy g c this fracture energy controls the propagation style for the aging law g c increases approximately as the square of the logarithm of the velocity jump this causes the nucleation zone to undergo quasi static crack like expansion to a size asymptotically proportional to b b a 2 for the slip law g c increases only as the logarithm of the velocity jump and crack like expansion is not an option instead the nucleation zone grows as an accelerating unidirectional slip pulse under both laws the nucleation front propagates at a velocity larger than the slip speed by roughly b divided by the logarithm of the velocity jump where is the effective elastic shear modulus for this prediction to be consistent with observed propagation speeds of slow slip events in subduction zones appears to require effective normal stresses as low as 1 mpa

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

quantitative relationship between aseismic slip propagation speed and frictional properties recent observations show evidence of propagation of postseismic slip which may contain information about the mechanical properties of faults here we develop a new analytical relationship between the propagation speed of aseismic slip transients and fault frictional properties modeled by a rate and state dependent friction law the relationship explains the propagation speed of afterslip in 3 d numerical simulations to first order based on this relationship we identify systematic dependencies of afterslip propagation speed on effective normal stress and frictional properties the coefficients a and a b which quantify the instantaneous and the steady state velocity dependence of friction respectively and the characteristic slip distance l of fault state evolution lower values of the parameter a a cause faster propagation in areas where the passage of the postseismic slip front induces large shear stress changes compared to a which are typically located near the mainshock rupture in areas where a is small typically more distant from the mainshock afterslip propagation speed is more sensitive to a b the propagation speed is proportional to initial slip velocity and under the condition that loading span is significantly shorter than the passage of postseismic slip inversely proportional to l the relationship developed here should be useful to constrain the frictional properties of faults based on observed propagation speeds independently of rock laboratory experiments which can then be used in predictive numerical simulations of aseismic slip phenomena

stress gradient coupling in glacier flow ii longitudinal averaging of the flow response to small perturbations in ice thickness and surface slope as a result of the coupling effects of longitudinal stress gradients the perturbations u in glacier flow velocity that result from longitudinally varying perturbations in ice thickness h and surface slope are determined by a weighted longitudinal average of h h and where h and are influence coefficients that control the size of the contributions made by local h and to the flow increment in the longitudinal average the values of h and depend on effects of longitudinal stress and velocity gradients in the unperturbed datum state if the datum state is an inclined slab in simple shear flow the longitudinal averaging solution for the flow perturbation is essentially that obtained previously kamb and echelmeyer 1985 with equivalent values for the longitudinal coupling length l and with h n l and n where n is the flow law exponent calculation of the influence coefficients from flow data for blue glacier washington indicates that in practice differs little from n whereas h can differ considerably from n 1 the weighting function in the longitudinal averaging integral which is the green s function for the longitudinal coupling equation for flow perturbations can be approximated by an asymmetric exponential whose asymmetry depends on two asymmetry parameters and where is the longitudinal gradient of l dl dx the asymmetric exponential has different coupling lengths l and l for the influences from up stream and from down stream on a given point of observation if is in the range 1 5 2 2 as expected for flow perturbations in glaciers or ice sheets in which the ice flux is not a strongly varying function of the longitudinal coordinate x then when dl dx 0 the down stream coupling length l is longer than the up stream coupling length l and vice versa when dl dx 0 flow thickness and slope perturbation data for blue glacier obtained by comparing the glacier in 1957 58 and 1977 78 require longitudinal averaging for reasonable interpretation analyzed on the basis of the longitudinal coupling theory with 4l 1 6 km up stream decreasing toward the terminus the data indicate n to be about 2 5 if interpreted on the basis of a response factor 0 85 derived theoretically by echelmeyer unpublished for the flow response to thickness perturbations in a channel of finite width the data contain an apparent indication that the flow response to slope perturbations is distinctly smaller in relation to the response to thickness perturbations than is expected on a theoretical basis i e h n n 1 for a slab this probably indicates that the effective l is longer than can be tested directly with the available data set owing to its limited range in x

ice volume and subglacial topography for western canadian glaciers from mass balance fields thinning rates and a bed stress model abstracta method is described to estimate the thickness of glacier ice using information derived from the measured ice extent surface topography surface mass balance and rate of thinning or thickening of the ice column shear stress beneath an ice column is assumed to be simply related to ice thickness and surface slope as for an inclined slab but this calculation is cast as a linear optimization problem so that a smoothness regularization can be applied assignment of bed stress is based on the flow law for ice and a mass balance calculation but must be preceded by delineation of the ice flow drainage basin validation of the method is accomplished by comparing thickness estimates to the known thickness generated by a numerical ice dynamics model once validated the method is used to estimate the subglacial topography for all glaciers in western canada that lie south of 60 n adding the present ice volume of each glacier gives the estimated total volume as 2320 km3 equivalent to 5 8 mm of sea leve

episodic slow slip events and rate and state friction 1 there are several ways of generating episodic slow slip events in models of rate and state friction here i explore the possibility that they arise on velocity weakening faults whose length is tuned in some sense unlike spring block sliders which have a unique critical stiffness for instability elastically deformable faults have multiple length scales stiffnesses relevant to nucleation slow slip events occur when the fault is large enough to initiate an event but too small for that event to reach dynamic instability the available window of lengths depends upon the effective fracture energy of the growing nucleation zone for the aging evolution law this fracture energy increases rapidly with slip speed and the range of permissible lengths increases nearly as b b a where a and b are the coefficients of the velocity and state dependence of the frictional strength this range becomes very large for faults that are near velocity neutral a b however existing lab data firmly favor the slip law as a predictor of nucleation style and for this law the effective fracture energy increases much less rapidly with slip speed the range of fault lengths capable of hosting slow slip events in this case seems too small to explain why they are common to so many subduction zones slow slip can be stabilized over an exceedingly large range of fault lengths if the fracture energy increases with slip speed much more rapidly than for the aging law an appealing mechanism is inelastic dilation of the fault zone coupled with pore pressure reduction and diffusive recovery

geodetic observations of postseismic creep in the decade after the 1999 izmit earthquake turkey implications for a shallow slip deficit the relationship between aseismic slip and tectonic loading is important for understanding both the pattern of strain accumulation along a fault and its ability to generate large earthquakes we investigate the spatial distribution and temporal evolution of aseismic creep on the western north anatolian fault naf using time series analysis of envisat interferometric synthetic aperture radar insar data covering the full extent of the 1999 izmit and duzce earthquake ruptures and spanning 2002 2010 discontinuities in the line of sight velocity across the fault imply that fault creep reaches the earth s surface at an average fault parallel rate of 5 mm yr along an 80 km section of the naf by combining insar and published gps velocities we are able to extract the vertical and east west components of motion and show that the adapazari basin is subsiding at a rate of 6 mm yr vertical motions have biased previous estimates of creep in this region the displacement time series close to the fault is consistent with an afterslip model based on rate and state friction which predicts a rapid deceleration in fault creep rate after the izmit earthquake to a near steady state 5 mm yr after 5 years projecting our model 200 years into the future we find that the cumulative displacement of 1 1 3 m is insufficient to account for the shallow coseismic slip deficit observed in previous studies distributed off fault deformation in the shallow crust or transient episodes of faster slip are likely required to release some of the long term strain during the earthquake cycle

expansion of aftershock areas caused by propagating post seismic sliding summary it is known that the aftershock areas of large earthquakes often expand over time this expansion indicates that the stress increase associated with a main shock gradually propagates outward from the main shock rupture area it is likely that this propagating stress increase is caused by the propagation of post seismic sliding which has been detected for many large earthquakes from geodetic observations mainly global positioning system gps in the present study i perform a numerical simulation of the expansion of the aftershock area caused by the propagation of post seismic sliding the model fault exists within an infinite elastic medium and is loaded at a constant displacement rate the frictional stress on the fault obeys a laboratory derived rate and state dependent friction law non uniformity of the frictional constitutive parameters is introduced to the model fault plane to represent a large asperity for a large earthquake main shock and many possible nucleus sites for aftershocks around the main shock asperity negative values of a b are assigned to areas of seismic slip for the main shock and aftershocks while positive values of a b are assigned to regions where aseismic sliding occurs here a b is defined by d ss d ln v that describes the velocity v dependence of steady state friction stress ss seismic slip may be nucleated for negative a b and aseismic slip occurs for positive a b slip histories on the model fault plane are simulated through numerical integration of the friction law under the condition of uniform shear loading of a constant velocity the simulation can reproduce aftershocks triggered by stress increases related to postseismic sliding and expansion of the aftershock area the rate of expansion of the aftershock area decreases with increasing distance from the main shock asperity or increasing value of a b in the velocity strengthening region this finding suggests that the a b value for a plate interface can be estimated from aftershock data the simulation indicates that the 7 day and 30 day aftershock areas are 14 22 and 24 39 per cent larger respectively than the 1 day aftershock area these numbers are approximately consistent with observations from large earthquakes at subduction zones

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

numerical simulation of recurrence of asperity rupture in the sanriku region northeastern japan 1 a numerical simulation study is presented for the recurrence of great earthquakes and aseismic sliding in the sanriku region northeastern japan where the pacific plate subducts beneath northern honshu and m8 class earthquakes have occurred approximately every 100 years the friction on the plate interface is assumed to obey a rate and state dependent friction law and the spatial distribution of constitutive parameters of the friction law is estimated so that the simulated slip histories mimic those estimated from seismic and geodetic observations by introducing two large asperities that have velocity weakening frictional properties earthquakes similar to the 1968 tokachi oki earthquake mw 8 2 and the 1994 sanriku oki earthquake mw 7 7 can be modeled the former broke both the large asperities and the latter broke one of them the ruptures of the two simulated large earthquakes started from almost the same location and their nucleation processes are similar to each other two smaller asperities were introduced to represent smaller earthquakes one of the small asperities is for the largest aftershock mw 6 9 of the 1994 sanriku oki earthquake which was located westward from the 1994 main shock area and took place 10 d after the main shock the present simulation suggests that the largest aftershock was triggered by stress caused by propagation of postseismic sliding in the simulation the area of greatest intensity of postseismic sliding is located in the region between the main shock slip area and the largest aftershock area which is consistent with the estimation from gps data analyses for the postseismic sliding of the 1994 sanriku oki earthquake some important characteristics of seismic and aseismic processes as estimated from observations are reproduced in the model this suggests that spatially nonuniform frictional properties on the plate interface can be estimated to some extent by comparison between model results and observed data

partial rupture of a locked patch of the sumatra megathrust during the 2007 earthquake sequence the great sumatra andaman earthquake and tsunami of 2004 was a dramatic reminder of the importance of understanding the seismic and tsunami hazards of subduction zones 1 2 3 4 in march 2005 the sunda megathrust ruptured again producing an event 5 of moment magnitude mw 8 6 south of the 2004 rupture area which was the site of a similar event in 1861 ref 6 concern was then focused on the mentawai area where large earthquakes had occurred in 1797 mw 8 8 and 1833 mw 9 0 6 7 two earthquakes one of mw 8 4 and twelve hours later one of mw 7 9 indeed occurred there on 12 september 2007 here we show that these earthquakes ruptured only a fraction of the area ruptured in 1833 and consist of distinct asperities within a patch of the megathrust that had remained locked in the interseismic period this indicates that the same portion of a megathrust can rupture in different patterns depending on whether asperities break as isolated seismic events or cooperate to produce a larger rupture this variability probably arises from the influence of non permanent barriers zones with locally lower pre stress due to the past earthquakes the stress state of the portion of the sunda megathrust that had ruptured in 1833 and 1797 was probably not adequate for the development of a single large rupture in 2007 the moment released in 2007 amounts to only a fraction both of that released in 1833 and of the deficit of moment that had accumulated as a result of interseismic strain since 1833 the potential for a large megathrust event in the mentawai area thus remains large

re examination of possible great interplate earthquake scenarios in the nankai trough southwest japan based on recent findings and numerical simulations abstract great earthquakes have occurred repeatedly along the nankai trough in southwestern japan with recurrence intervals of 100 200 years the magnitudes of nankai earthquakes have historically varied with many studies to date asserting that an event s magnitude is controlled only by the number of broken segments arranged along the trough recent evidence suggests that large tsunami with recurrence intervals of several hundred years have occurred along the nankai trough therefore it is now essential to reconsider the scenario of the nankai earthquakes including the possibility of seismic slip on the shallow subduction interface recently model calculations of interplate seismic cycles have been conducted using rate and state dependent friction in these calculations assuming heterogeneous distribution of fracture energy in the seismogenic zone and its shallower extension both massive earthquakes with slips up to the trough and ordinary earthquakes in the seismogenic zone can occur here we apply a heterogeneous distribution of fracture energy in the shallow plate interface of the nankai trough in the model we represent the difference in fracture energy by the difference in the characteristic slip distance l to model the conventional seismogenic zone as a zone of low fracture energy we set l to be 5 cm at depths of 10 20 km conversely the shallow plate boundary near the trough is modeled as a zone of high fracture energy by setting l to 5 m as a result two types of earthquake with different moment magnitude occur alternately the recurrence interval of the larger type is about 370 years which is comparable to the recurrence of larger tsunami deduced from geological findings large coseismic slip extends to the trough during the larger types in contrast the smaller one whose seismic slip is distributed along the seismogenic zone occurs after 200 years of the larger one

locking of the chile subduction zone controlled by fluid pressure before the 2010 earthquake large subduction zone earthquakes are thought to occur where the down going and overriding tectonic plates are strongly locked analysis of geodetic and seismic data collected in the decade before the 2010 chile earthquake shows that variations in pore fluid pressure correlate with the degree of plate interface locking and may therefore control earthquake rupture

propagation of a glacier surge into stagnant ice the propagation of the surge of variegated glacier into its terminal lobe was observed by daily surveying of a longitudinal line of closely spaced markers extending up glacier from a stagnant zone of thin 40 m nearly motionless ice near the terminus across a front zone to a surge zone of thicker 100 m rapidly moving 20 m d 1 ice above within the front zone there were large angles of upward motion 30 compressive longitudinal strain rates 0 1 d 1 and upward vertical velocities 5 m d 1 within the surge zone the ice motion was nearly parallel to the ice surface and longitudinal gradients were small the deformation pattern produced microcracking exfoliation and buckling of surface ice longitudinal cracking longitudinal chasms and an increase in glacier volume the front zone propagated at an average speed of about 40 m d 1 or roughly twice the surge speed of the ice above the front this factor is determined by the thickness jump across the front finite element modeling constrained by measured geometry and surface velocity was used to deduce the velocity and stress at depth the velocity in the surging zone occurs almost entirely by sliding the sliding rate drops abruptly beneath the center of the front zone to zero in the stagnant zone a comparison of basal velocity and shear stress distributions indicates a highly lubricated area beneath the upper part of the front zone and a locked area beneath the lower part of the front zone normal stress at the bed is not significantly different from overburden and there is no high compressive normal stress on the bed to act as a pressure dam to obstruct water flow through the front zone

modeling high stress drops scaling interaction and irregularity of repeating earthquake sequences near parkfield repeating earthquake sequences have been actively investigated to clarify many aspects of earthquake physics the two particularly well studied sequences known as the los angeles and san francisco repeaters have several intriguing observations including their long for the seismic moment recurrence times that would suggest stress drops of 300 mpa based on typical assumptions near syncronized timing prior to 2004 and higher than typical inferred stress drops of 25 to 65 mpa up to 90 mpa locally but not as high as the recurrence times suggest here we show that all these observations are self consistent in the sense that they can be reproduced in a single fault model the suitable models build on the standard rate and state fault models with velocity weakening patches imbedded into a velocity strengthening region by adding either enhanced dynamic weakening during seismic slip or elevated normal stress on the patches or both to allow for the higher stress drops such models are able to match the observed average properties of the san francisco and los angeles repeaters as well as the overall nontrivial scaling between the recurrence time and seismic moment exhibited by many repeating sequences as a whole for reasonable parameter choices based on experiments and theoretical studies these models are characterized by the occurrence of substantial and variable aseismic slip at the locations of the repeating sources which explains their atypical relation between recurrence interval and seismic moment induces variability in the repeating source properties as observed and results in their neither slip nor time predictable behavior

weathering and vegetation controls on nickel isotope fractionation in surface ultramafic environments albania abstract the dissolved nickel ni isotopic composition of rivers and oceans presents an apparent paradox even though rivers represent a major source of ni in the oceans seawater is more enriched in the heavier isotopes than river water additional sources or processes must therefore be invoked to account for the isotopic budget of dissolved ni in seawater weathering of continental rocks is thought to play a major role in determining the magnitude and sign of isotopic fractionation of metals between a rock and the dissolved product we present a study of ni isotopes in the rock soil plant systems of several ultramafic environments the results reveal key insights into the magnitude and the control of isotopic fractionation during the weathering of continental ultramafic rocks this study introduces new constraints on the influence of vegetation during the weathering process which should be taken into account in interpretations of the variability of ni isotopes in rivers the study area is located in a temperate climate zone within the ophiolitic belt area of albania the serpentinized peridotites sampled present a narrow range of heavy ni isotopic compositions ni 60 0 25 0 16 2sd n 2 at two locations horizons within two soil profiles affected by different degrees of weathering all presented light isotopic compositions compared to the parent rock 60nisoil rock up to 0 63 this suggests that the soil pool takes up the light isotopes while the heavier isotopes remain in the dissolved phase by combining elemental and mineralogical analyses with the isotope compositions determined for the soils the extent of fractionation was found to be controlled by the secondary minerals formed in the soil the types of vegetation growing on ultramafic derived soils are highly adapted and include both ni hyperaccumulating species which can accumulate several percent per weight of ni and non accumulating species whole plant isotopic compositions were found to be isotopically heavier than the soil 60niwhole plant soil up to 0 40 fractions of ni extracted by dtpa diethylenetriaminepentaacetic acid presented isotopically heavy compositions compared to the soil 60nidtpa soil up to 0 89 supporting the hypothesis that the dissolved ni fraction controlled by weathering has a heavy isotope signature the non hyperaccumulators n 2 were inclined to take up and translocate light ni isotopes with a large degree of fractionation 60nileaves roots up to 0 60 for ni hyperaccumulators n 7 significant isotopic fractionation was observed in the plants in their early growth stages while no fractionation occurred during later growth stages when plants are fully loaded with ni this suggests that i the high efficiency translocation process involved in hyperaccumulators does not fractionate ni isotopes and ii the root uptake process mainly controls the isotopic composition of the plant in ultramafic contexts vegetation composed of hyperaccumulators can significantly influence isotopic compositions through its remobilization in the upper soil horizon thereby influencing the isotopic balance of ni exported to rivers

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

triggered non similar slip events on repeating earthquake asperities results from 3d numerical simulations based on a friction law 1 we investigated the changes in slip rate and recurrence interval of repeating earthquakes using 3 d numerical simulations of a subduction zone involving large and small asperities and based on a rate and state dependent friction law our results reveal that the postseismic slip of a large earthquake can trigger an event at a nearby small asperity although the event may differ to other repeating earthquakes at the asperity because the slip velocity of the event tends to be slower than that of other repeaters the slip distribution also differs these results probably explain the observation that the slip amount estimated from repeating earthquake analyses tends to be smaller than that estimated from gps analyses for large amounts of postseismic slip as observed for postseismic activity following the 2003 tokachi oki earthquake

seismic and aseismic slip on the central peru megathrust slip on a subduction megathrust can be seismic or aseismic with the two modes of slip complementing each other in time and space to accommodate the long term plate motions although slip is almost purely aseismic at depths greater than about 40 km heterogeneous surface strain suggests that both modes of slip occur at shallower depths with aseismic slip resulting from steady or transient creep in the interseismic and postseismic periods thus active faults seem to comprise areas that slip mostly during earthquakes and areas that mostly slip aseismically the size location and frequency of earthquakes that a megathrust can generate thus depend on where and when aseismic creep is taking place and what fraction of the long term slip rate it accounts for here we address this issue by focusing on the central peru megathrust we show that the pisco earthquake with moment magnitude m w 8 0 ruptured two asperities within a patch that had remained locked in the interseismic period and triggered aseismic frictional afterslip on two adjacent patches the most prominent patch of afterslip coincides with the subducting nazca ridge an area also characterized by low interseismic coupling which seems to have repeatedly acted as a barrier to seismic rupture propagation in the past the seismogenic portion of the megathrust thus appears to be composed of interfingering rate weakening and rate strengthening patches the rate strengthening patches contribute to a high proportion of aseismic slip and determine the extent and frequency of large interplate earthquakes aseismic slip accounts for as much as 50 70 of the slip budget on the seismogenic portion of the megathrust in central peru and the return period of earthquakes with m w 8 0 in the pisco area is estimated to be 250 years

earthquake triggering by migrating slow slip initiated by m8 earthquake along kuril trench japan 1 evidence of a slow slip temporally ahead of the m7 earthquake doublet that occurred in november december 2004 offshore of eastern hokkaido japan was registered in continuous gps measurements the gps data suggest that a slow slip around a forthcoming rupture zone on the plate boundary triggered these earthquakes this slow slip episode was itself triggered by the m8 tokachi earthquake of september 2003 this is a demonstration of the geodetic visualization of the mechanism of a triggering of a subsequent earthquake caused by a preceding large earthquake the geodetic data will improve the reliability of the warning of an occurrence of a subsequent earthquake after a large one that is currently dependent on only co seismic static stress increase

a model for complex slip behavior on a large asperity at subduction zones 1 3 d numerical simulations for rupture process of a large asperity on a subduction fault are carried out in order to examine whether the whole area of an asperity always breaks at once or not during an earthquake our quasi static simulation in an elastic half space includes a rate and state dependent friction we examine the effect of lateral dimension of an asperity which extends the whole seismogenic width in dip direction on the slip behavior in cases of the asperity with comparable dimension to the seismogenic width the whole area of the asperity can break at once and its seismic cycle shows a regular periodic behavior however in cases with much larger lateral dimension the asperity does not break its whole area at once in addition its slip behavior becomes complex within a certain range this suggests that the slip complexity in earthquake fault may be an intrinsic property in the system

a trial estimation of frictional properties focusing on aperiodicity off kamaishi just after the 2011 tohoku earthquake motivated by the fact that temporal earthquake aperiodicity was observed off kamaishi just after the 2011 tohoku earthquake we performed numerical simulations of chain reactions due to the postseismic slip of large earthquakes by applying rate and state dependent friction laws if the repeater is composed of single asperity our results show that i a mixture of partial and whole rupturing of a single asperity can explain some of the observed variability in timing and size of the repeating earthquakes off kamaishi ii the partial rupturing can be reproduced with moderate frictional instability with the aging law and not the slip or nagata laws iii the perturbation of the activated earthquake hypocenters observed mostly in the ese wnw direction may reflect the fact that the large postseismic slip of the 2011 tohoku earthquake propagated from ese to wnw off kamaishi iv the observed region of repeating earthquake quiescence may reflect the strong plate coupling of megathrust earthquakes

evolving force balance at columbia glacier alaska during its rapid retreat 1 changes in driving and resistive stresses play an essential role in governing the buoyancy forces that are important controls on the speed and irreversibility of tidewater glacier retreats we describe changes in geometry velocity and strain rate and present a top down force balance analysis performed over the lower reach of columbia glacier our analysis uses new measurements and estimates of basal topography and photogrammetric surface velocity measurements made between 1977 and 2001 while assuming depth independent strain sensitivity tests show that the method is robust and insensitive to small changes in the calculation parameters spatial distributions of ice speed show little correspondence with driving stress instead spatial patterns of ice speed exhibit a nonlinear correspondence with basal drag primary resistance to flow comes from basal drag but lateral drag becomes increasingly more important throughout the retreat which may account for observed increases in speed maximum basal drag is always located in a prominent constriction located 12 km upstream from the preretreat terminus once the terminus retreated into deep water off the terminal moraine marking the modern maximum extent the upstream location of this maximum basal drag helped to promote thinning and decrease effective pressure in the lower region by limiting replenishing ice flow from upstream an increase in both ice velocity and calving resulted initiating what appears to be an irreversible retreat

bed topography and lubrication inferred from surface measurements on fast flowing ice streams observations of surface elevation s and horizontal velocity components u and v are inverted to infer the topography b and lubrication c at the bed of an ice stream based on a linearized perturbation theory of the transmission of flow disturbances through the ice thickness synthetic data are used to illustrate non uniqueness in the inversion but also demonstrate that effects of b and c can be separated when s u and v are specified even with added noise to simulate measurement errors we have analyzed prominent short horizontal scale 2 km features in topography and velocity pattern in a local 64 km by 32 km area of the surface of ice stream e west antarctica our preferred interpretation of bed conditions beneath the most prominent features on the surface identifies a deep trough in the basal topography with low lubrication in the base of the trough

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

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

interaction of slip on asperities numerical simulation of seismic cycles on a two dimensional planar fault with nonuniform frictional property 1 numerical simulation is conducted to understand the variety of frictional sliding on a plate interface and complex recurrence of earthquakes a planar square fault in an infinite uniform elastic medium is considered and the frictional stress on the fault is assumed to obey a rate and state dependent friction law nonuniformity in a frictional constitutive parameter is introduced on the model fault on the fault plane one or two circular patches with velocity weakening frictional property are surrounded by velocity strengthening areas unstable slip may occur for velocity weakening friction and aseismic sliding occurs for velocity strengthening friction velocity weakening patches correspond to asperities because intense seismic slip may occur there simulation results indicate that episodic aseismic slip events slow earthquakes occur when the velocity weakening patch size is close to the critical size of earthquake nucleation propagation of postseismic sliding on the velocity strengthening region follows an earthquake at a velocity weakening patch when the postseismic sliding reaches another velocity weakening patch an earthquake may be triggered at the patch resulting in a double earthquake the time delay between two events of the double earthquake increases with the distance between the two velocity weakening patches or the degree of velocity strengthening in the region between the patches when the distance between the two velocity weakening patches is long an earthquake at one patch does not directly cause an earthquake at the other patch in these cases complex earthquake recurrence may appear due to the interaction between ruptures at the two patches and the recurrence interval of earthquakes and coseismic slip is not constant at each velocity weakening patch

interactions and triggering in a 3 d rate and state asperity model we present a 3 d continuous quasi dynamic rate and state model of multiple seismic asperities forced by surrounding aseismic creep and motivated by observations of coplanar multiplets our model allows to study the physics of interactions among a set of asperities first we show that the amount of interactions and clustering characterized by the omori law and interevent time distribution depends on how far the system is from a critical density of asperities which is related to the friction properties of the barriers separating the sources this threshold controls the ability of a population of asperities to destabilize the creeping barriers between them and therefore determines whether dynamic sequences including several asperities in the same event might occur in agreement with what is expected from observed magnitude frequency distributions therefore the concept of critical density of asperity provides a mechanical interpretation of statistical properties of seismicity as an illustration we used our numerical results in the specific case of parkfield in the period preceding the mw 6 2004 earthquake in order to infer the steady state friction parameter a b characterizing the creep of this part of the san andreas fault we estimate a value of a b that locally exceeds 0 001 which is in the upper range of what has already been proposed for the postseimic period of the mw 6 2004 parkfield earthquake

on fundamental limits to glacier flow models computational theory and implications no single flow model can simulate all possible glaciers and ice sheets without violating fundamental tenets of computational science the root cause is not one of numerical sophistication precision or accurate initial conditions instead using flow and transport as data transmission glaciers inadvertently function as information processors this computational capability confers a level of complexity that inherently limits our ability to accurately and efficiently predict glacier flow and therefore for example to forecast those aspects of climate systems that depend on glaciers in particular even with considerable future advancements in glacier physics computational theory shows that no dramatic improvements in numerical speed are likely when compared to today s glacier models therefore to increase speed and resolution the next generation of climate and sea level models must rely on simulations tailored to specific ice sheet geometries rather than general purpose glacier flow models however because glaciers process information entirely new computation theoretic advances in glaciology are possible and concepts from information entropy may help to define new glacier scaling relationships and identify which geometries will be most problematic for modeling

stress release process along an intraplate fault analogous to the plate boundary a case study of the 2017 m5 2 akita daisen earthquake ne japan stress accumulation and release in the crust remains poorly understood compared to that at the plate boundaries spatiotemporal variations in foreshock and aftershock activities can provide key con