accelerated pacific plate subduction following interplate thrust earthquakes at the japan trench interplate thrust earthquakes are usually followed by afterslips and they let the fore arc move slowly trenchward however we do not know if the subducting oceanic plate is accelerated landward after such earthquakes the westward velocity of global positioning system gps stations in ne japan show gradient decreasing from east to west reflecting the e w contractional strain built up by the inter plate coupling here we show that such coupling significantly enhanced 1 5 times after the 2003 tokachi oki earthquake mw 8 0 hokkaido in the segments adjacent to the ruptured fault the coupling seems to be further enhanced 3 times after the 2011 tohoku oki earthquake mw 9 0 it is unlikely that interplate friction suddenly increased over such a large region and relatively strong pre 2003 coupling there would not allow such enhancements even if full coupling is attained hence they are attributable to the temporary acceleration of the pacific plate subduction we propose a simple 2 dimensional model in which down dip acceleration of the slab let the force balance rapidly recover promoted by a thin low viscosity layer on the slab surface the accelerated subduction would account for temporary activations of regional interplate seismicity after megathrust earthquakes

an elastic plate model for interseismic deformation in subduction zones geodetic observations of interseismic surface deformation in the vicinity of subduction zones are frequently interpreted using simple kinematic elastic dislocation models edm in this theoretical study we develop a kinematic edm that simulates plate subduction over the interseismic period the elastic subducting plate model espm having only 2 more degrees of freedom than the well established back slip model bsm an elastic plate thickness and the fraction of flexural stresses due to bending at the trench that are released continuously unlike the bsm in which steady state deformation in both plates is assumed to be negligible the espm includes deformation in the subducting and overriding plates owing to plate thickness while still preserving the correct sense of convergence velocity between the subducting and overriding plates as well as zero net steady state vertical offset between the two plates when integrated over many seismic cycles the espm links elastic plate flexure processes to interseismic deformation and helps clarify under what conditions the bsm is appropriate for fitting interseismic geodetic data at convergent margins we show that the espm is identical to the bsm in the limiting case of zero plate thickness thereby providing an alternative motivation for the bsm the espm also provides a consistent convention for applying the bsm to any megathrust interface geometry even in the case of nonnegligible plate thickness the deformation field predicted by the espm reduces to that of the bsm if stresses related to plate flexure at the trench are released either continuously and completely at shallow depths during the interseismic period or deep in the subduction zone below 100 km however if at least a portion of these stresses are not continuously released in the shallow portion of the subduction zone via seismic or aseismic events then the predicted surface velocities of these two models can differ significantly at horizontal distances from the trench equivalent to a few times the effective interseismic locking depth

haskell 1935 revisited the haskell 1935 value of 1021 pa s for mantle viscosity is a classic and enduring constraint on the rheology of the earth s interior we revisit this inference using spherically symmetric self gravitating maxwell viscoelastic earth models our inference is based on both forward and inverse analyses of decay times associated with uplift at two sites considered by haskell angerman river sweden and oslo norway rather than the raw relative sea level rsl data at these sites we demonstrate that predictions of the decay time associated with the angerman river data are insensitive to variations in both the late pleistocene ice load history and the lithospheric thickness of the earth model the predictions at oslo are sensitive to both these inputs and hence decay times at this site provide a remarkably robust constraint on mantle viscosity we derive a constraint on the average viscosity of the mantle of 0 65 1 10 1021 pa s where the average resolved by the data encompasses a region which extends from the base of the lithosphere to a depth of near 1400 km this indicates that many previous analyses which have invoked the haskell value of 1021 pa s as a constraint on the average upper mantle i e above 670 km depth viscosity alone have misinterpreted the resolving power of the inference furthermore our analysis indicates that a number of apparently contradictory inferences of viscosity based on fennoscandian data satisfy the new rigorous interpretation of the haskell constraint finally we demonstrate how the ambiguity in the upper mantle lower mantle viscosity contrast associated with the haskell average may be reduced by invoking decay time constraints estimated from rsl curves in hudson bay a preliminary inversion of decay times at angerman river and richmond gulf in hudson bay suggests a contrast of approximately an order of magnitude between the average viscosities of the upper mantle and the top 1000 km of the lower mantle however a conclusive analysis in this regard must await the determination of consistent decay time estimates for the hudson bay region

a high resolution time variable afterslip model for the 2010 maule mw 8 8 chile megathrust earthquake the excellent spatial coverage of continuous gps stations in the region affected by the maule mw 8 8 2010 earthquake combined with the proximity of the coast to the seismogenic zone allows us to model megathrust afterslip on the plate interface with unprecedented detail we invert post seismic observations from continuous gps sites to derive a time variable model of the first 420 d of afterslip we also invert co seismic gps displacements to create a new co seismic slip model the afterslip pattern appears to be transient and non stationary with the cumulative afterslip pattern being formed from afterslip pulses changes in static stress on the plate interface from the co and post seismic slip cannot solely explain the aftershock patterns suggesting that another process perhaps fluid related is controlling the lower magnitude aftershocks we use aftershock data to quantify the seismic coupling distribution during the post seismic phase comparison of the post seismic behaviour to interseismic locking suggests that highly locked regions do not necessarily behave as rate weakening in the post seismic period by comparing the inter seismic locking co seismic slip afterslip and aftershocks we attempt to classify the heterogeneous frictional behaviour of the plate interface

separating rapid relocking afterslip and viscoelastic relaxation an application of the postseismic straightening method to the maule 2010 cgps the postseismic deformation captured with continuous global positioning system cgps monitoring following many recent mega thrust events has been shown to be a signal composed of two dominant processes afterslip on the plate interface and viscoelastic relaxation of the continental and oceanic mantles in response to the coseismic stress perturbation following the south central chile 2010 maule mw 8 8 earthquake the time series from the regional cgps network show a distinct curvature in the pathway of the horizontal motion that is not easily fit by a stationary decaying pattern of afterslip in combination with viscoelastic relaxation here we show that with realistic assumptions about the long term decay of the afterslip signal the postseismic signal can be decomposed into three first order contributing processes plate interface re locking plate interface afterslip and mantle viscoelastic relaxation from our analyses we conclude that the plate interface recovers its interseismic locking state rapidly model space ranges between an instant recovery and a period of 1 year a finding that supports laboratory experimental evidence as well as some recent studies of aftershocks and postseismic surface deformation furthermore re locking is the main cause of the curvature in the cgps signal and this study presents a plausible range of geodetic re locking rates following a megathrust earthquake

stress dependent power law flow in the upper mantle following the 2002 denali alaska earthquake abstract far field continuous global positioning system gps time series data following the 2002 m7 9 denali alaska earthquake imply that mantle viscoelastic rheology is stress dependent a linear viscous mantle cannot explain fast early displacement rates at the surface that rapidly decay with time whereas a power law rheology where strain rate is proportional to stress raised to the power of 3 5 0 5 provides decay rates and spatial patterns in agreement with observations this is consistent with laboratory measurements for hot wet olivine implying a hydrated mantle and a relatively thin 60 km thick lithosphere beneath south central alaska these results suggest that the viscous strength of the lithosphere varies both spatially and temporally and that effective viscosities inferred from different loading events or observational time periods can differ by up to several orders of magnitude thus the very conditions that enable the inference of rheologic strength transient loading and unloading events significantly alter the effective viscosity

granular mass flows and coulomb s friction in shear cell experiments implications for geophysical flows 1 granular mass flows of rock fragments are studied in the lab by means of a high speed video camera at 2000 frames per second these granular flows are generated using beds of pumice fragments positioned on a rough rotating disk whose angular velocity is controlled by a motor the experimental apparatus allows an understanding of the arrangement of the particles in granular mass flows with relatively small and relatively large values of the savage number the savage number represents the ratio between grain collision stresses and gravitational grain contact stresses in particular these flows develop a basal layer of agitated and colliding particles underneath a relatively rigid upper layer our experimental results suggest the validity on average of the coulomb s relationship between shear and normal forces at the base of granular mass flows irrespective of their savage number value in coulomb s equation the shear stresses do not depend on the shear rate we expect the coulomb friction law to be valid also in moving pyroclastic flows our experiments suggest that the collisions and subsequent comminution of pumice fragments in moving pyroclastic flows could provide ash for the overriding ash clouds in our experiments the amount of ash generated by particle particle and particle boundary interactions increases as the value of the savage number increases in nature part of this ash may also simply move toward the base of the flows because of kinetic sieving

numerical modeling of self channeling granular flows and of their levee channel deposits when not laterally confined in valleys pyroclastic flows create their own channel along the slope by selecting a given flowing width furthermore the lobe shaped deposits display a very specific morphology with high parallel lateral levees a numerical model based on saint venant equations and the empirical variable friction coefficient proposed by pouliquen and forterre 2002 is used to simulate unconfined granular flow over an inclined plane with a constant supply numerical simulations successfully reproduce the self channeling of the granular lobe and the levee channel morphology in the deposits without having to take into account mixture concepts or polydispersity numerical simulations suggest that the quasi static shoulders bordering the flow are created behind the front of the granular material by the rotation of the velocity field due to the balance between gravity the two dimensional pressure gradient and friction for a simplified hydrostatic model competition between the decreasing friction coefficient and increasing surface gradient as the thickness decreases seems to play a key role in the dynamics of unconfined flows the description of the other disregarded components of the stress tensor would be expected to change the balance of forces the front s shape appears to be constant during propagation the width of the flowing channel and the velocity of the material within it are almost steady and uniform numerical results suggest that measurement of the width and thickness of the central channel morphology in deposits in the field provides an estimate of the velocity and thickness during emplacement citation mangeney a f bouchut n thomas j p vilotte and m o bristeau 2007 numerical modeling of self channeling granular flows and of their levee channel deposits

very long baseline interferometry and active rotations of crustal blocks in the western transverse ranges california changes in baseline vectors between very long baseline interferometry vlbi receiving stations in the western transverse ranges imply that east west blocks of crust in this region rotate clockwise about vertical axes with respect to the pacific and north american plates minimum apparent rotations given by the ratios between components of velocity perpendicular to baseline vectors and the lengths of the baselines imply minimum current rotation rates of a few degrees per million years the relevant vlbi receivers lie on different crustal blocks that are separated by major active faults both geologic and other geodetic observations imply north south convergence between such blocks at several millimeters per year corrections to perpendicular components of velocity for such relative movements between blocks yield likely clockwise rotation rates of 6 m y 2 m y which are indistinguishable from the average rate inferred from paleomagnetic declinations of rocks in the western transverse ranges with ages less than 15 m y thus rotation seems to have occurred continuously and apparently with only small variations in rate during a period when the tectonics of southern california changed dramatically this apparent independence of the rotation rate on the changing surface kinematics is consistent 1 with such rotation being a manifestation of continuous deformation at depth in the lower crust and upper mantle 2 with weak faults separating upper crustal blocks and 3 with the important resistance to continental deformation lying in the upper mantle and or lower crust

randomness of megathrust earthquakes implied by rapid stress recovery after the japan earthquake the 2011 tohoku oki earthquake released stress within a subduction zone analysis of seismic data shows that stresses returned to pre quake levels within a few years implying that large quakes could occur more often than previously thought

the 2015 illapel earthquake central chile a type case for a characteristic earthquake on 16 september 2015 the mw 8 2 illapel megathrust earthquake ruptured the central chilean margin combining inversions of displacement measurements and seismic waveforms with high frequency hf teleseismic backprojection we derive a comprehensive description of the rupture which also predicts deep ocean tsunami wave heights we further determine moment tensors and obtain accurate depth estimates for the aftershock sequence the earthquake nucleated near the coast but then propagated to the north and updip attaining a peak slip of 5 6 m in contrast hf seismic radiation is mostly emitted downdip of the region of intense slip and arrests earlier than the long period rupture indicating smooth slip along the shallow plate interface in the final phase a superficially similar earthquake in 1943 with a similar aftershock zone had a much shorter source time function which matches the duration of hf seismic radiation in the recent event indicating that the 1943 event lacked the shallow slip

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

toward understanding tectonic control on the mw 8 8 2010 maule chile earthquake the maule earthquake of 27th february 2010 m w 8 8 affected similar to 500 km of the nazca south america plate boundary in south central chile producing spectacular crustal deformation here we present a detailed estimate of static coseismic surface offsets as measured by survey and continuous gps both in near and far field regions earthquake slip along the megathrust has been inferred from a joint inversion of our new data together with published gps insar and land level changes data using green s functions generated by a spherical finite element model with realistic subduction zone geometry the combination of the data sets provided a good resolution indicating that most of the slip was well resolved coseismic slip was concentrated north of the epicenter with up to 16 m of slip whereas to the south it reached over 10 m within two minor patches a comparison of coseismic slip with the slip deficit accumulated since the last great earthquake in 1835 suggests that the 2010 event closed a mature seismic gap slip deficit distribution shows an apparent local overshoot that highlight cycle to cycle variability which has to be taken into account when anticipating future events from interseismic observations rupture propagation was obviously not affected by bathymetric features of the incoming plate instead splay faults in the upper plate seem to have limited rupture propagation in the updip and along strike directions additionally we found that along strike gradients in slip are spatially correlated with geometrical inflections of the megathrust our study suggests that persistent tectonic features may control strain accumulation and release along subduction megathrusts c 2012 elsevier b v all rights reserved

spatial and temporal evolution of a long term slow slip event the 2006 guerrero slow slip event summary the guerrero 2006 slow slip event sse mexico one of the world s largest observed sses was recorded at 15 continuous gps stations this event provides the opportunity to analyse in detail the spatial and temporal evolution of slip at depth and to constrain the characteristics of a large sse we perform an inversion in two steps first we invert the cumulative gps displacements to retrieve the total slip amplitude second we invert for the initiation time and duration of the slip using a linearized least squares inversion procedure and assuming a functional form for the slip function our results show that the slip is located on a patch of 300 km 150 km parallel and perpendicular to the coast respectively and extends from the bottom of the seismogenic zone to the transition zone this slow slip event has an equivalent moment magnitude of 7 5 the maximum slip over a length scale of 25 km is 15 cm and the mean slip is 5 5 cm its lateral extension coincides with the segmentation of the subduction our inversion scheme allows us to analyse the spatial variability of the rise time rupture velocity and slip function we obtain a continuous image of the spatial and temporal variations of slip on the fault plane the rupture initiated at a depth of 40 km transition zone in the western part of the guerrero gap the rupture then propagated from the western to the eastern part of the guerrero segment with an average velocity of 0 8 km d 1 our results show that a slip dislocation pulse characterized by a symmetric ramp function can model the 2006 sse the rise time local duration of slip does not show large spatial variations and is equal to about 185 d the local slip duration is compared to the total duration 11 12 months of the event suggesting a large interaction of a large part of the fault during the dynamic process we find that our inverted slip model is well resolved on the shallow part of the fault and in the central section of the fault

pressures at the base of dry flows of angular rock fragments as a function of grain size and flow volume experimental results geophysical granular flows such as pyroclastic flows and rock avalanches kill people and damage properties worldwide the pressures exerted at their base affect the retarding forces that act on them and for this reason affect also their mobility that is important to foresee when assessing natural hazards in mountain regions here we present the results of experiments obtained by measuring with a load cell the basal pressures exerted by dry and cohesionless granular flows that descend a curved chute in the laboratory the interaction between these flows and the chute surface on which they travel is dominated by collisions of particles and or clusters of particles a dimensional analysis suggests that the energy dissipation of these flows increases as grain size increases and as flow volume decreases all the other features equal therefore the smaller the grain size and the larger the volume the larger is expected to be flow mobility although the longer travel distances of the centre of mass of finer grain size flows are easily discernible in our experiments the effect of volume is probably hidden by additional phenomena such as the deposition first of the frontal portion of longer flows on the less steep more distal part of the slope that prevents the rear portion and the centre of mass of the flows to travel further downhill

heterogeneous plate locking in the south central chile subduction zone building up the next great earthquake abstract we use global positioning system gps velocities and kinematic finite element models fe models to infer the state of locking between the converging nazca and south america plates in south central chile 36 s 46 s and to evaluate its spatial and temporal variability gps velocities provide information on earthquake cycle deformation over the last decade in areas affected by the megathrust events of 1960 m w 9 5 and 2010 m w 8 8 our data confirm that a change in surface velocity patterns of these two seismotectonic segments can be related to their different stages in the seismic cycle accordingly the northern 2010 segment was in a final stage of interseismic loading whereas the southern 1960 segment is still in a postseismic stage and undergoes a prolonged viscoelastic mantle relaxation after correcting the signals for mantle relaxation the residual gps velocity pattern suggests that the plate interface accumulates slip deficit in a spatially and presumably temporally variable way towards the next great event though some similarity exist between locking and 1960 coseismic slip extrapolating the current decadal scale slip deficit accumulation towards the 300 yr recurrence times of giant events here does neither yield the slip distribution nor the moment magnitude of the 1960 earthquake this suggests that either the locking pattern is evolving in time to reconcile a slip deficit distribution similar to the 1960 earthquake or that some asperities are not persistent over multiple events the accumulated moment deficit since 1960 suggests that highly locked patches in the 1960 segment are already capable of producing a m 8 event if triggered to fail by stress transfer from the 2010 event

geodetic imaging of coseismic slip and postseismic afterslip sparsity promoting methods applied to the great tohoku earthquake 1 geodetic observations of surface displacements during and following earthquakes such as the march 11 2011 great tohoku earthquake can be used to constrain the spatial extent of coseismic slip and postseismic afterslip and characterize the spectrum of earthquake cycle behaviors slip models are often regularized by assuming that slip on the fault varies smoothly in space which may result in the artificial smearing of fault slip beyond physical boundaries alternatively it may be desirable to estimate a slip distribution that is spatially compact and varies sharply here we show that sparsity promoting state vector regularization methods can be used to recover slip distributions with sharp boundaries representing an alternative end member result to very smooth slip distributions using onshore gps observations at 298 stations during and in the 2 weeks following the tohoku earthquake we estimate a band of coseismic slip between 30 and 50 km depth extending 500 km along strike with a maximum slip of 64 m corresponding to a minimum magnitude estimate of mw 8 8 our estimate of afterslip is located almost exclusively down dip of the coseismic rupture with a transition between 40 and 50 km depth and an equivalent moment magnitude mw 8 2 this depth may be interpreted as coincident with the transition from velocity strengthening to velocity weakening frictional behavior consistent with the upper limit of cold subduction estimates of the thermal structure of the japan trench

tsunami earthquake generation by the release of gravitational potential energy earthquakes that generate large tsunamis share a number of unusual features they commonly have long source time functions involve large displacements of 10 m or more of the prisms of poorly consolidated sediment that form the accretionary wedge and have many aftershocks with normal faulting mechanisms on the landward side of the trench these features are not easily understood if the only source of the energy involved is the stored elastic strain the observations especially those from the tohoku japan 2011 earthquake instead suggest that the observed behaviour results from the release of gravitational potential energy as well as elastic strain a simple model of this process can account for these and other observations

rapid aseismic moment release following the 5 december 1997 kronotsky kamchatka earthquake model inversions of displacements of continuously operating gps stations in kamchatka show that aseismic afterslip during 2 months following the mw 7 8 5 december 1997 kronotsky subduction earthquake released as much moment as the earthquake itself the rapidly decaying transient slip on the subduction underthrust occurred near the downdip edge of the coseismic rupture and extended laterally away from it including a region of vigorous foreshock activity a logarithmic decay function fit to the cumulative afterslip curve has a relaxation time of about 3 days rapid afterslip can contribute significantly to the moment release of partially coupled subduction zones

the 2010 mw 8 8 maule chile earthquake nucleation and rupture propagation controlled by a subducted topographic high knowledge of seismic properties in an earthquake rupture zone is essential for understanding the factors controlling rupture dynamics we use data from aftershocks following the maule earthquake to derive a three dimensional seismic velocity model of the central chile forearc at 36 s we find a high v p 7 0 km s and high v p v s 1 89 anomaly lying along the megathrust at 25 km depth which coincides with a strong forearc bouguer gravity signal we interpret this as a subducted topographic high possibly a former seamount on the nazca slab the maule earthquake nucleated at the anomaly s updip boundary yet high co seismic slip occurred where the megathrust is overlain by lower seismic velocities sparse aftershock seismicity occurs within this structure suggesting that it disrupts normal interface seismogenesis these findings imply that subducted structures can be conducive to the nucleation of large megathrust earthquakes even if they subsequently hinder co seismic slip and aftershock activity

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

evolution of strength recovery and permeability during fluid rock reaction in experimental fault zones abstract physical and chemical fluid rock interactions are implicated in controlling earthquake nucleation and recurrence in particular interseismic compaction sealing and healing of fractured fault rocks can lead to strength recovery and stabilisation of fault zones in contrast these same processes can also assist increases in pore fluid pressures and consequent destabilisation of faults here we present high temperature hydrothermal experiments designed to assess the evolution of strength of fault zones in previously intact rock and also characterise the associated changes to porosity and permeability cores of fontainebleau sandstone were initially loaded to failure in a high pressure gas medium apparatus the failed specimens were then hydrothermally reacted at 927 c for variable duration under isostatic conditions and subsequently re fractured to determine the interseismic strength recovery in the most extreme case hydrothermally induced gouge compaction cementation and crack healing resulted in 75 strength recovery after reaction for 6 h isostatic hydrothermal treatment also resulted in dramatic reduction in porosity and permeability strength of the fault zone following hydrothermal reaction appears to be closely correlated to porosity consistent with previous studies on brittle failure of porous aggregates the experimental results show how hydrothermal reactions in fault zones may lead to two competing time dependent effects fault strengthening due to increased cohesion in the fault zone and fault weakening arising from elevated pore pressures within a well cemented low permeability gouge layer

seismic evidence for rock damage and healing on the san andreas fault associated with the 2004 m 6 0 parkfield earthquake we deployed a dense linear array of 45 seismometers across and along the san andreas fault near parkfield a week after the m 6 0 parkfield earthquake on 28 september 2004 to record fault zone seismic waves generated by aftershocks and explosions seismic stations and explosions were co sited with our previous exper iment conducted in 2002 the data from repeated shots detonated in the fall of 2002 and 3 months after the 2004 m 6 0 mainshock show 1 0 1 5 decreases in seismic wave velocity within an 200 m wide zone along the fault strike and smaller changes 0 2 0 5 beyond this zone most likely due to the coseismic damage of rocks during dynamic rupture in the 2004 m 6 0 earthquake the width of the damage zone characterized by larger velocity changes is consistent with the low velocity waveguide model on the san andreas fault near parkfield that we derived from fault zone trapped waves li et al 2004 the damage zone is not symmetric but extends farther on the southwest side of the main fault trace waveform cross correlations for repeated aftershocks in 21 clusters with a total of 130 events located at different depths and distances from the array site show 0 7 1 1 increases in s wave velocity within the fault zone in 3 months starting a week after the earthquake the velocity recovery indicates that the damaged rock has been healing and regaining the strength through rigidity recovery with time most likely due to the closure of cracks opened during the mainshock we estimate that the net decrease in seismic velocities within the fault zone was at least 2 5 caused by the 2004 m 6 0 parkfield earthquake the healing rate was largest in the earlier stage of the postmainshock healing process the magnitude of fault healing varies along the rupture zone being slightly larger for the healing beneath middle mountain correlating well with an area of large mapped slip the fault healing is most promi nent at depths above 7 km

the 2011 magnitude 9 0 tohoku oki earthquake mosaicking the megathrust from seconds to centuries geophysical observations from the 2011 moment magnitude m w 9 0 tohoku oki japan earthquake allow exploration of a rare large event along a subduction megathrust models for this event indicate that the distribution of coseismic fault slip exceeded 50 meters in places sources of high frequency seismic waves delineate the edges of the deepest portions of coseismic slip and do not simply correlate with the locations of peak slip relative to the m w 8 8 2010 maule chile earthquake the tohoku oki earthquake was deficient in high frequency seismic radiation a difference that we attribute to its relatively shallow depth estimates of total fault slip and surface secular strain accumulation on millennial time scales suggest the need to consider the potential for a future large earthquake just south of this event

afterslip and viscoelastic relaxation model inferred from the large scale post seismic deformation following the 2010 mw 8 8 maule earthquake chile

troposphere mapping functions for gps and very long baseline interferometry from european centre for medium range weather forecasts operational analysis data 1 in the analyses of geodetic very long baseline interferometry vlbi and gps data the analytic form used for mapping of the atmosphere delay from zenith to the line of site is most often a three parameter continued fraction in 1 sin elevation using the 40 years reanalysis era 40 data of the european centre for medium range weather forecasts for the year 2001 the b and c coefficients of the continued fraction form for the hydrostatic mapping functions have been redetermined unlike previous mapping functions based on data from numerical weather models isobaric mapping functions niell 2000 and vienna mapping functions vmf boehm and schuh 2004 the new c coefficients are dependent on the day of the year and unlike the niell mapping functions niell 1996 they are no longer symmetric with respect to the equator apart from the opposite phase for the two hemispheres compared to vmf this causes an effect on the vlbi or gps station heights that is constant and as large as 2 mm at the equator and that varies seasonally between 4 mm and 0 mm at the poles the updated vmf based on these new coefficients and called vmf1 hereinafter yields slightly better baseline length repeatabilities for vlbi data the hydrostatic and wet mapping functions are applied in various combinations with different kinds of a priori zenith delays in the analyses of all vlbi international vlbi service for geodesy and astrometry ivs r1 and ivs r4 24 hour sessions of 2002 and 2003 the investigations concentrate on baseline length repeatabilities as well as on absolute changes of station heights

the 2010 mw 8 8 maule megathrust earthquake of central chile monitored by gps large earthquakes produce crustal deformation that can be quantified by geodetic measurements allowing for the determination of the slip distribution on the fault we used data from global positioning system gps networks in central chile to infer the static deformation and the kinematics of the 2010 moment magnitude m w 8 8 maule megathrust earthquake from elastic modeling we found a total rupture length of 500 kilometers where slip up to 15 meters concentrated on two main asperities situated on both sides of the epicenter we found that rupture reached shallow depths probably extending up to the trench resolvable afterslip occurred in regions of low coseismic slip the low frequency hypocenter is relocated 40 kilometers southwest of initial estimates rupture propagated bilaterally at about 3 1 kilometers per second with possible but not fully resolved velocity variations

effect of grain size on mobility of dry granular flows of angular rock fragments an experimental determination abstract rapid mass movements of rock fragments are among the most hazardous natural phenomena they are too dangerous to be approached and studied directly and for this reason experiments are necessary to understand their flow mechanisms here we present the results of experiments on granular flow mobility obtained releasing batches of angular rock fragments down a curved chute our experiments demonstrate that the finer the grain size of the flow the larger its mobility this is accompanied by a decrease of fragments agitation when grain size decreases as shown by particle image velocimetry measurements of high speed video camera images the smaller the agitation the smaller is also the energy dissipated by flows per unit of travel distance this explains the effect of finer grain size on flow mobility these results are an important step towards the prediction of runout distances as a function of the features that characterize the different geophysical flows

rapid postseismic strength recovery of pingxi fault gouge from the longmenshan fault system experiments and implications for the mechanisms of high velocity weakening of faults 1 slide hold slide tests were conducted on gray blackish gouge gbg and yellowish gouge yg from pingxi fault zone to see how rapidly the strength of longmenshan fault recovers after the 2008 wenchuan earthquake twenty dry runs were made at a normal stress of 0 8 mpa at a seismic slip rate of 1 4 m s and with hold time th ranging 0 3 105 s results exhibit very rapid healing by more than 0 4 in friction coefficient in less than 5 10 s followed by gradual healing in proportion to log th healing rates increase in log th during rapid and slow healing are 0 188 and 0 015 for gbg and 0 154 and 0 016 for yg respectively the average temperature in the outer half of a 5 m thick slip zone decreases from 260 300 c to 110 170 c in 5 10 s and hence temperature drop appears to be correlated with the rapid healing previously reported rapid healing at subseismic slip rates 85 90 mm s begins to occur in 10 300 s after the stop of sliding and this cannot be explained by the cooling of gouge the difference in healing between subseismic slip rates delayed and rapid healing and seismic slip rates immediate and rapid healing suggests that the dominant weakening mechanism shifts from tribochemical processes at subseismic slip rates to frictional heating at seismic slip rates slip zone structures are too complex and variable from run to run to reveal microscopic mechanisms for the strength recovery rapid healing following seismic slip can be a cause for reduced aftershocks along major coseismic faults

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

2010 maule earthquake slip correlates with pre seismic locking of andean subduction zone analysis of seismic data and global positioning system gps observations from the region around the site of the recent magnitude 8 8 maule earthquake in chile have been combined with modelling of the andean subduction zone to build up a detailed image of the event the earthquake occurred at a seismic gap part of the fault that has not experienced a major earthquake since 1835 and it seems to have released most of the stress accumulated since that time the observations suggest that coseismic slip heterogeneity at the scale of single asperities and therefore the seismic potential of future great earthquakes might be anticipated by geodetic observations these authors show evidence for a high coherence between the slip distribution inferred from the 2010 maule earthquake chile and the patchwork of interseismic locking distribution derived from global positioning system observations during the previous decade their work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future earthquakes which thus might be anticipated by geodetic observations the magnitude 8 8 maule chile earthquake of 27 february 2010 ruptured a segment of the andean subduction zone megathrust that has been suspected to be of high seismic potential1 2 3 4 5 6 it is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space geodetic network before the event this provides an image of the pre seismically locked state of the plate interface of unprecedentedly high resolution allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip pre seismic locking might be used to anticipate future ruptures in many seismic gaps6 7 8 9 10 11 12 given the fundamental assumption that locking and slip are similar this hypothesis however could not be tested without the occurrence of the first gap filling earthquake here we show evidence that the 2010 maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system gps observations during the previous decade the earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835 two regions of high seismic slip asperities appeared to be nearly fully locked before the earthquake between these asperities the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip the rupture stopped in areas that were highly locked before the earthquake but where pre stress had been significantly reduced by overlapping twentieth century earthquakes our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes which thus might be anticipated by geodetic observations

comparison of postseismic afterslip models with aftershock seismicity for three subduction zone earthquakes nias 2005 maule 2010 and tohoku 2011 we focus on the relation between seismic and total postseismic afterslip following the maule mw 8 8 earthquake on 2010 february 27 in central chile first we calculate the cumulative slip released by aftershock seismicity we do this by summing up the aftershock regions and slip estimated from scaling relations comparing the cumulative seismic slip with afterslip models we show that seismic slip of individual aftershocks exceeds locally the inverted afterslip model from geodetic constraints as the afterslip model implicitly contains the displacements from the aftershocks this reflects the tendency of afterslip models to smear out the actual slip pattern however it also suggests that locally slip for a number of the larger aftershocks exceeds the aseismic slip in spite of the fact that the total equivalent moment of the afterslip exceeds the cumulative moment of aftershocks by a large factor this effect seen weakly for the maule 2010 and also for the tohoku 2011 earthquake can be explained by taking into account the uncertainties of the seismicity and afterslip models in spite of uncertainties the hypocentral region of the nias 2005 earthquake is suggested to release a large fraction of moment almost purely seismically therefore these aftershocks are not driven solely by the afterslip but instead their slip areas have probably been stressed by interseismic loading and the mainshock rupture in a second step we divide the megathrust of the maule 2010 rupture into discrete cells and count the number of aftershocks that occur within 50 km of the centre of each cell as a function of time we then compare this number to a time dependent afterslip model by defining the afterslip to aftershock ratio asar for each cell as the slope of the best fitting line when the afterslip at time t is plotted against aftershock count although we find a linear relation between afterslip and aftershocks for most cells there is significant variability in asar in both the downdip and along strike directions of the megathrust we compare the spatial distribution of asar with the spatial distribution of seismic coupling coseismic slip and bouguer gravity anomaly and in each case we find no significant correlation

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

surface microscopic examination of quartz grains from rock avalanche basal facies the wenchuan earthquake which occurred on 12 may 2008 triggered many rock avalanches that presented abundant fractured surface textures the surface textures of the rock avalanche clasts bear abundant characteristic signatures that are significant for understanding the mechanical behavior of rock avalanche dynamic fragmentation to study this mechanism of rock avalanche basal facies further two large rock avalanches were investigated using microscopic surface texture examination of quartz grains sampled from their basal facies with a scanning electron microscope after the morphological and statistical analyses of the surface textures on the quartz grains the following features are noted i surface textures on the quartz grains are all fresh with obvious irregular shapes and very sharp edges ii the display of brittle fractures including conchoidal fractures step fractures concavities and v depressions or marks is very common iii cracks or fissures are also visible on the quartz grains t

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

anatomy of the andean subduction zone three dimensional density model upgraded and compared against global scale models summary we present an upgraded version of a previously published 3 d density model of the andean subduction zone between 18 s and 45 s this model consists of 3 d bodies of constant density which geometry is constrained by independent seismic data and is triangulated from vertical cross sections these bodies define the first order morphology and internal structure of the subducted nazca slab and south american plate the new version of the density model results after forward modelling the bouguer anomaly as computed from the most recent version of the earth gravitational model egm2008 the 3 d density model incorporates new seismic information to better constrain the geometry of the subducted slab and continental moho cmh and has a trench parallel resolution doubling the resolution of the previous model as an example of the potential utility of our model we compare the geometry of the subducted slab and cmh against the corresponding global models slab1 0 and crust2 0 respectively this exercise demonstrates that although global models provide a good first order representation of the slab and upper plate crustal geometries they show large discrepancies up to 40 km with our upgraded model for some well constrained areas the geometries of the slab lithosphere asthenosphere boundary below the continent cmh and intracrustal density discontinuity that we present here as supporting information can be used to study andean geodynamic processes from a wide range of quantitative approaches

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

slip distribution of the february 27 2010 mw 8 8 maule earthquake central chile from static and high rate gps insar and broadband teleseismic data 1 the shallow depth underthrust earthquake of february 27 2010 mw 8 8 ruptured the subduction plate interface in central chile between 34 s and 38 s we retrieve the spatial and temporal distribution of slip during this mega earthquake through a joint inversion of teleseismic records insar and high rate gps hrgps data additionally our model is shown to agree with broadband surface waves rupture initiated at about 32 km depth and propagated bilaterally resulting in two main slip zones located ssw and nne of the hypocenter nucleation did not take place within or at the edge of one of these main asperities but in between during the first 30s slip propagated predominantly southwards later on the rupture evolved more slowly and more symmetrically eventually the northern asperity became predominant with maximum slip reaching about 20 m most of the seismic moment was released within 110s a relatively short time explained by the bilateral propagation the overall average rupture velocity is 2 6 km s but propagation occurred initially faster towards the south 3 2 km s large slip did not reach the trench a result consistent with the moderate size of the tsunami down dip rupture stopped at about 50 km depth in agreement with the lower limit of the locked zone inferred by ruegg et al 2009 from pre seismic gps data

the constitucion earthquake of 25 march 2012 a large aftershock of the maule earthquake near the bottom of the seismogenic zone abstract the mw 7 0 constitucion earthquake of march 2012 is one of the largest interplate aftershocks of the maule 2010 mw 8 8 mega thrust earthquake this event was recorded by high rate gps stations local seismometers and accelerometers the global seismographic network and sar acquisitions by the envisat satellite we have used these data to perform a kinematic inversion and back projection to identify the principal characteristics of this event the constitucion earthquake nucleated at 39 km depth and then propagated up dip at subshear speed towards its centroid with an unusually long initiation phase that lasted almost 6 s the largest slip of this event was located in the deeper part of the subduction interface between the region of maximum co seismic slip of the 2010 maule earthquake and the area where rapid afterslip occurred following that event features of the constitucion earthquake may suggest that larger interplate aftershocks of the maule event preferentially occur in the deeper part of the plate interface where ruptures are complex produce high frequencies and involve numerous asperities

revisiting viscoelastic effects on interseismic deformation and locking degree a case study of the peru north chile subduction zone viscoelastic effects potentially play an important role during all phases of the earthquake cycle in subduction zones however most current models neglect such effects in the interseismic deformation pattern here we use finite element method fem models to investigate the control of viscoelasticity on interseismic deformation and to highlight the pitfalls of interpreting the data with purely elastic models for both the forward and inverse problems our results confirm that elastic models are prone to overestimating the interseismic locking depth a crucial parameter for estimating the maximum possible earthquake magnitude the application of the viscoelastic model improves the fit to the interseismic deformation especially in the inland area additionally we construct 3 d fem models constrained by geophysical and gps data and apply our methodology to the peru north chile subduction zone our results indicate that viscoelastic effects contribute significantly to the observed gps data the signals interpreted as back arc shortening in the elastic model can be alternatively explained by viscoelastic deformation which in turn dramatically refines the interseismic locking pattern in both dip and strike directions our viscoelastic locking map exhibits excellent correlation with the slip distributions of previous earthquakes especially the recent 2014 mw 8 1 iquique earthquake the incorrect elastic assumptions affect the analysis of interseismic deformation with respect to slip deficit calculations our results thus suggest that it is necessary to thoroughly reevaluate existing locking models that are based on purely elastic models some of which attribute viscoelastic deformation to different sources such as microplate sliver motions

viscoelastic relaxation following subduction earthquakes and its effects on afterslip determination afterslip is commonly thought to be the controlling process in postseismic deformation immediately following a great megathrust earthquake and is usually inferred from geodetic observations using purely elastic models however observed motion reversal of the near trench area right after the 2011 mw 9 tohoku oki earthquake demonstrates the dominance of viscoelastic relaxation of coseismically induced stresses to understand the importance of incorporating viscoelasticity in afterslip determination we employ biviscous burgers mantle rheology and use finite element models to explore how viscoelastic relaxation in short term postseismic deformation is controlled by various geometrical and rheological factors our results indicate that immediately after large megathrust earthquakes mw 8 0 viscoelastic deformation should always cause opposing motion of inland and trench areas and subsidence around landward termination of the rupture although the rate of such postseismic motion depends on local conditions such as the age and hence thickness of the slab and transient mantle viscosity values while elastic models may be adequate for afterslip estimation for earthquakes of mw 7 5 neglect of viscoelasticity for larger events leads to overestimate of afterslip downdip of the rupture and underestimate of afterslip at shallower depths reassessing shallow afterslip following the 2005 mw 8 7 nias earthquake using 2 d viscoelastic models suggests that the actual afterslip may be greater than that estimated using an elastic model by more than 50 similarly interpreting trenchward motion of some seafloor gps sites following the tohoku oki earthquake using a viscoelastic model suggests large shallow afterslip outside of the main rupture area

granular pressure at the base of dry flows of angular rock fragments as a function of grain size and flow volume a relationship from laboratory experiments 1 experiments are carried out by releasing angular rock fragments down a curved chute and by measuring the basal pressures that are exerted by the granular flows on the basal containing surface the substrate the purpose of these experiments is to understand the mechanisms of energy dissipation and interaction with the ground of rock avalanches and dense pyroclastic flows our data show that collisions due to particle agitation affect significantly the basal interaction of granular flows in particular our experiments reveal that particle agitation per unit of flow mass increases as grain size increases or as flow volume decreases with all the other features the same this is so because as grain size increases or as flow volume decreases with all the other features the same there are fewer particles in the flows and the agitation due to the interaction with the rough containing boundary surfaces penetrates relatively more inside the flows the analysis of the experimental data generates a linear relationship between particle agitation expressed as a dimensionless basal pressure deviation and a parameter which is directly proportional to the square of grain size and inversely proportional to the cube root of flow volume this relationship shows the intrinsic ability of the granular flows to dissipate more energy larger particle agitation per unit of flow mass or less energy smaller particle agitation per unit of flow mass as a function of flow volume and grain size

dynamics of the 2008 earthquake triggered wenjiagou creek rock avalanche qingping sichuan china abstract the wenjiagou creek rock avalanche was triggered by the 2008 wenchuan earthquake it traveled 4 6 km and left a granular deposit of 1 5 108 m3 in wenjiagou creek valley the dynamics of the rock avalanche were studied through field and laboratory investigations and remote sensing the dynamic course was divided into three segments 1 failing the original slope failed due to the huge earthquake ground accelerations acting on a rock mass weakened by severe karstification 2 falling the rock mass experienced several drops due to abrupt changes in slope and broke into granular debris during collisions with the ground and mountain flanks and 3 flow the broken granular mass flowed approximately 3 km down the valley of wenjiagou creek the transport mechanism of the granular mass of debris was studied by analyzing the structure of the deposit and through ring shear tests a gully incised into the deposit by rainfall runoff and debris flows enabled the internal structure of the deposit to be examined and sampled in cross section the exposed deposit was finest near the base and gradually became coarser towards the surface inverse grading in longitudinal section deposits near the base and on the surface both became finer with increasing travel distance near the base the granular debris experienced the maximum normal and shear stresses and fragmented into the finest grains both normal and shear stresses between the grains gradually decreased from near the base to the surface samples were sheared in a ring shear apparatus to simulate the shearing within the granular debris shear resistance between grains was found to decrease as grains became finer due to pervasive fragmentation which is one of the possible mechanisms by which the granular debris was able to travel a long distance at a high speed

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

evaluating titan2d mass flow model using the 1963 little tahoma peak avalanches mount rainier washington the titan2d geophysical mass flow model is evaluated by comparing its simulation results and those obtained from another flow model flow3d with published data on the 1963 little tahoma peak avalanches on mount rainier washington the avalanches totaling approximately 10 10 6 m 3 of broken lava blocks and other debris traveled 6 8 km horizontally and fell 1 8 km vertically h l 0 246 velocities calculated from runup range from 24 to 42 m s and may have been as high as 130 m s while the avalanches passed over emmons glacier titan2d is a code for an incompressible coulomb continuum it is a depth averaged dshallow watert granular flow model the conservation equations for mass and momentum are solved with a coulomb type friction term at the basal interface the governing equations are solved on multiple processors using a parallel adaptive mesh godunov scheme adaptive gridding dynamically concentrates computing power in regions of special interest mesh refinement and coarsening key on the perimeter of the moving avalanche the model flow initiates as a pile defined as an ellipsoid by a height z and an elliptical base defined by radii in the x and y planes flow parameters are the internal friction angle and bed friction angle results from the model are similar in terms of velocity history lateral spreading location of runup areas and final distribution of the little tahoma peak deposit the avalanches passed over the emmons glacier along their upper flow paths but lower in the valley they traversed stream gravels and glacial outwash deposits this presents difficulty in assigning an appropriate bed friction angle for the entire deposit incorporation of variable bed friction angles into the model using gis will help to resolve this issue d 2004 elsevier b v all rights reserved

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

contrasting amount of fluids along the megathrust ruptured by the 2010 maule earthquake as revealed by a combined analysis of aftershocks and afterslip abstract we present a novel approach combining time variable computations of b value and afterslip to study the postseismic activity following the mw 8 8 maule 2010 earthquake we subdivided the first 392 days after the mainshock into overlapping windows for which we compared maps of b value computed from neic seismicity and afterslip computed from continuous gps stations the correlation between both parameters is weak during the first 2 months when the aftershocks magnitude of completeness decreases and the number of gps stations increased after this early stage a correlation between both parameters emerges we interpret this correlated spatiotemporal pattern combining factors proposed to control each parameter separately this exercise suggests a segmentation of the maule megathrust the northern segment is characterized by an increase of afterslip and b value during the early postseismic phase and then a simultaneous decrease of both parameters which we interpret as the effect of an ingression of fluids into the megathrust and its subsequent consumption during fault healing in contrast the southern segment is characterized by a central region with minimum afterslip and low b value surrounded by areas that experience mostly seismic afterslip as a consequence of large static stress loaded by the mainshock suggesting a drier and stronger megathrust where healing was active earlier interpreted along with features of the pre and coseismic phases our results allow us to propose the existence of two contrasting types of seismic asperities classical strong stick slip patches that we link with dry regions of the megathrust versus weak wet and conditionally stable frictional patches that could have a range of seismogenic behaviors from creeping and or locking during the interseismic period largely contributing with coseismic slip and concentrating afterslip at their borders the application of our novel method to other great earthquakes could reveal whether this is a common or anomalous feature of megathrusts

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

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