numerical simulation of seismic cycles with a composite rate and state dependent friction law properties of rate and state dependent friction laws are examined through numerical simulations among several versions of the rate and state dependent friction laws we use the slowness law the slip law and the composite law the last was recently proposed by kato and tullis 2001 for better explaining experimental observations of rock friction in the laboratory two kinds of simulations are done one is for cyclic stick slip motion of a single degree of freedom spring block system the other is for seismic cycles at a subduction zone where a 2d model of uniform elastic half space is used assuming the same values of friction parameters we compare the simulation results for the three friction laws from the two kinds of simulations we find that the recurrence interval of simulated earthquakes is the longest and the magnitude of preseismic sliding is the smallest for the composite law

stress triggering of large earthquakes complicated by transient aseismic slip episodes 1 we investigate how a static stress change caused by a nearby earthquake perturbs sliding processes on a fault and the time to the next earthquake for this purpose we model numerically a reverse fault in a two dimensional semi infinite and elastic medium partly stable and partly unstable under a rate and state dependent friction law when no stress change intervenes steady sliding spreads out of the deep zone of frictional stability and keeps expanding updip during the interseismic period aseismic slip episodes ases develop spontaneously within the region of steady sliding and repeat quasi periodically when steady sliding has spread beyond a certain critical length the nucleation length above the zone of frictional stability one of the ases undergoes rapid buildup and avalanches into high speed seismic sliding when a step like stress change intervenes ases of larger amplitudes arise and evolve similarly to their spontaneous counterparts until one of them avalanches into an earthquake if the stress change arrives not too early nor too late in the seismic cycle the basic picture is as follows delaying the stress step be it positive or negative delays the timing of the ase sequence and thereby postpones the next earthquake when the stress step is delayed to more than a certain extent however an earlier ase gets to evolve into an earthquake advancing its time discontinuously only in the final stage of a seismic cycle does a positive stress step systematically advance the next earthquake and a negative stress step systematically delay it

post seismic and interseismic fault creep ii transient creep and interseismic stress shadows on megathrusts we use idealized subduction megathrust models to examine aseismic frictional fault creep throughout the interseismic period we consider rate dependent and rate and state dependent friction when there is significant post seismic creep surrounding locations of coseismic slip the creep rates surrounding an asperity may be lower than the plate convergence rate late in the seismic cycle this lowering of the creep rates is due to stress shadows forming around the interseismically locked asperities the size of the stress shadows increases as there is more transient post seismic creep larger asperities produce larger interseismic stress shadows and multiple asperities can act together to produce a stress shadow larger than the sum of the effects of the individual asperities for rate state frictional megathrusts there is a wide range of transient post seismic creep that occurs from pulses of post seismic creep with decreasing creep rates through time to delayed post seismic creep delayed post seismic creep may occur well into the interseismic period with transient creep lasting over a significant portion of the seismic cycle delayed post seismic creep is generally favoured in velocity strengthening regions with either a larger magnitude of the frictional direct effect or a larger effective normal stress in addition regions of the fault undergoing delayed post seismic creep must be above steady state following coseismic slip

contrasting hydrological and mechanical properties of clayey and silty muds cored from the shallow nankai trough accretionary prism abstract two mud samples cored from the shallow 1000 mbsf nankai trough accretionary prism at site c0002 of iodp expedition 315 are found to be distinctly different in hydrological and mechanical properties at confining pressures pore water pressures and temperatures close to their in situ conditions a clayey mud sample has lower permeability of 2 92 10 19 m 2 while a silty mud sample has higher permeability of 2 29 10 18 m 2 triaxial compression experiments at these conditions and an axial displacement rate of 10 m s reveal that the clayey mud sample exhibits lower failure strength of 14 2 mpa followed by a slow failure lasting for 40 s while the silty mud sample exhibits higher failure strength of 20 1 mpa followed by a rapid failure within 5 s friction experiments at these conditions and axial displacement rates changed stepwise among 0 1 1 and 10 m s reveal that the clayey mud sample has a much lower steady state friction ss 0 25 than the silty mud sample ss 0 53 although both samples exhibit velocity strengthening the former has more than three times larger velocity dependence of steady state friction than the latter such contrasting hydrological and mechanical properties of the clayey and silty mud samples as revealed in this study suggest the following implications for deformation and faulting in the shallow mud dominant nankai trough accretionary prism deformation results in a possible increase in pore pressure and hence in strength reduction in clayey mud but not in silty mud faulting would preferentially occur in the weaker clayey mud and its slow failure may result in a slow slip faults formed in clayey mud are weak and easily reactivated but stable and not seismogenic in contrast once the stronger silty mud is faulted its rapid failure may become a seismic slip faults formed in silty mud are strong and not easily reactivated but possibly unstable and seismogenic

basin centered asperities in great subduction zone earthquakes a link between slip subsidence and subduction erosion 1 published areas of high coseismic slip or asperities for 29 of the largest circum pacific megathrust earthquakes are compared to forearc structure revealed by satellite free air gravity bathymetry and seismic profiling on average 71 of an earthquake s seismic moment and 79 of its asperity area occur beneath the prominent gravity low outlining the deep sea terrace 57 of an earthquake s asperity area on average occurs beneath the forearc basins that lie within the deep sea terrace in sw japan slip in the 1923 1944 1946 and 1968 earthquakes was largely centered beneath five forearc basins whose landward edge overlies the 350 c isotherm on the plate boundary the inferred downdip limit of the locked zone basin centered coseismic slip also occurred along the aleutian mexico peru and chile subduction zones but was ambiguous for the great 1964 alaska earthquake beneath intrabasin structural highs seismic slip tends to be lower possibly due to higher temperatures and fluid pressures kilometers of late cenozoic subsidence and crustal thinning above some of the source zones are indicated by seismic profiling and drilling and are thought to be caused by basal subduction erosion the deep sea terraces and basins may evolve not just by growth of the outer arc high but also by interseismic subsidence not recovered during earthquakes basin centered asperities could indicate a link between subsidence subduction erosion and seismogenesis whatever the cause forearc basins may be useful indicators of long term seismic moment release the source zone for cascadia s 1700 a d earthquake contains five large basin centered gravity lows that may indicate potential asperities at depth the gravity gradient marking the inferred downdip limit to large coseismic slip lies offshore except in northwestern washington where the low extends landward beneath the coast transverse gravity highs between the basins suggest that the margin is seismically segmented and could produce a variety of large earthquakes

a composite rate and state dependent law for rock friction existing constitutive laws of rock friction cannot describe both observed strengthening in the absence of slip and frictional behavior around steady state sliding combining existing rate and state dependent friction laws we propose a new friction law which expresses logarithmically time dependent healing at sliding velocities smaller than a cut off velocity v c and approaches the so called slip law at velocities larger than v c numerical simulations show that the new friction law adequately explains experimental results of velocity stepping tests and slide hold slide tests which have widely been used to examine velocity time and displacement dependent property of rock friction because the new friction law has a simple form and appears appropriate for a wide range of conditions it is useful for application to numerical modeling of seismic cycles

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

under the hood of the earthquake machine toward predictive modeling of the seismic cycle advances in observational laboratory and modeling techniques open the way to the development of physical models of the seismic cycle with potentially predictive power to explore that possibility we developed an integrative and fully dynamic model of the parkfield segment of the san andreas fault the model succeeds in reproducing a realistic earthquake sequence of irregular moment magnitude m w 6 0 main shocks including events similar to the ones in 1966 and 2004 and provides an excellent match for the detailed interseismic coseismic and postseismic observations collected along this fault during the most recent earthquake cycle such calibrated physical models provide new ways to assess seismic hazards and forecast seismicity response to perturbations of natural or anthropogenic origins

a possible model for large preseismic slip on a deeper extension of a seismic rupture plane abstract i develop a numerical model for preseismic slip and episodic aseismic slip events slow earthquakes on a deeper extension of a seismogenic plate interface using a rate and state dependent friction law the deep preseismic slip and episodic slow slip were indicated by models based on geodetic observations though they cannot be explained by common rate and state dependent laws i investigate whether this incongruity can be removed by including use of additional known constraints on the frictional property the steady state friction on a model fault is taken to be velocity weakening at low velocities and velocity strengthening at high velocities the transition velocity from velocity weakening friction to velocity strengthening is assumed to be the seismic slip velocity at shallow seismic depths and decreases with depth at deeper parts simulation results for a 2d model of interplate earthquakes at a subduction zone are as follows 1 during an interseismic period between successive large earthquakes at shallow seismogenic depths some episodic aseismic slip events with durations of a few years occur on the plate interface just below the seismogenic depths 2 preseismic slip occurs at nearly the same location where the episodic aseismic slip events occur these may explain some characteristics of observed preseismic slip of the 1944 tonankai earthquake m 7 9 along the nankai trough central japan and episodic aseismic slip events in the same area

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

fault friction parameters inferred from the early stages of afterslip following the 2003 tokachi oki earthquake 1 we use subdaily gps time series of positions in the first 5 hours following the 2003 tokachi oki earthquake mw 8 0 located offshore of hokkaido japan to estimate frictional parameters for the afterslip zone on the subduction interface the data show little motion immediately after the earthquake with sudden acceleration at about 1 2 hours after the main shock this coincides with the largest aftershock m 7 4 followed by gradual deceleration we assume that early afterslip is the response of a fault patch to instantaneous stress perturbations caused by the main shock and the largest aftershock early afterslip is modeled with a spring slider system obeying a rate and state dependent friction law we develop and apply an inversion method to estimate friction parameters dc a and a b where is effective normal stress the estimated 95 confidence intervals of dc a and a b are 2 6 10 4 to 1 8 10 3 m 0 29 to 0 43 mpa and 0 214 to 0 220 mpa respectively estimated dc is 10 to 103 times larger than typical laboratory values estimated a and a b values suggest that a and a b are smaller than typical laboratory values and or the pore pressure on the plate boundary is significantly elevated above the hydrostatic value our analyses show that the model can reproduce the observed gps data and that the timing of the rapid acceleration of postseismic deformation is controlled by the frictional properties of the fault and stress change from the main shock not by the timing of the largest aftershock

the 1946 nankai earthquake and segmentation of the nankai trough abstract we perform a simple subevent analysis of seismic p waveforms from historical records of the 1946 nankai earthquake the results of this analysis establish that the earthquake rupture consisted of two main subevents one lying within the 1 day aftershock area off the kii peninsula while the other lies much farther to the west in the area of pronounced crustal deformation of western shikoku these conform to two segments of the nankai trough which have long been referred to in studies of historical earthquakes and geology of the nankai trough but to our knowledge have not previously been established as having distinct megathrust rupture behavior we show that these two subevents are bounded by pronounced features in the geometry of the subducting philippine sea plate psp a tear in the plate to the east beneath the kii peninsula and a subducting seamount farther to the west we speculate that these features may be associated with low strength parts of the upper and or lower plates that may be susceptible to permanent anelastic deformation which prevents the accumulation of the elastic strain energy necessary to sustain seismic rupture

frictional properties of megathrust fault gouges at low sliding velocities new data on effects of normal stress and temperature abstract friction data used in modelling studies of subduction zone seismogenesis are often poorly representative of in situ conditions we investigated the influence of in situ effective stresses and temperatures on the frictional properties of simulated fault gouges prepared either from nankai odp material or illite shale at sliding velocities approaching those relevant for earthquake nucleation and sses biaxial double direct shear experiments were performed at room temperature normal stresses of 5 30 mpa and sliding velocities of 0 16 18 m s all materials exhibited velocity strengthening under these conditions along with an increase in the friction coefficient and slip hardening rate with increasing normal stress illite gouge showed increased velocity strengthening towards higher normal stresses the effect of temperature was investigated by means of ring shear experiments on illite gouge at 200 300 c an effective normal stress of 170 mpa a pore fluid pressure of 100 mpa and sliding velocities of 1 100 m s these experiments showed a transition from velocity strengthening to velocity weakening at 250 c our results provide a possible explanation for the updip seismogenic limit within subduction zone megathrusts and imply an enhanced tendency for earthquake nucleation and sses at low effective normal stresses

towards inferring earthquake patterns from geodetic observations of interseismic coupling ultimately seismotectonic studies seek to provide ways of assessing the timing magnitude and spatial extent of future earthquakes ample observations document the spatial variability in interseismic coupling defined as a degree of locking of a fault during the period of stress build up between seismic events fully or nearly locked fault patches are often surrounded by aseismically creeping areas however it is unclear how these observations could help assess future earthquakes here we simulate spontaneous seismic and aseismic fault slip with a fully dynamic numerical model our simulations establish the dependence of earthquake rupture patterns and interseismic coupling on spatial variations of fault friction we consider the long term evolution of slip on a model fault where two seismogenic locked segments are separated by an aseismically slipping patch where rupture is impeded we find that the probability for a large earthquake to break through the rupture impeding patch is correlated with the interseismic coupling averaged over this patch in addition the probability that an earthquake breaks through the rupture impeding patch and interseismic coupling are both related to fault friction properties through a single non dimensional parameter our study opens the possibility of predicting seismic rupture patterns that a fault system can produce on the basis of observations of its interseismic coupling and suggests that regions of low interseismic coupling may reveal permanent barriers to large earthquakes

proximal depositional facies from a caldera forming eruption the parata grande tuff at ventotene island italy abstract ventotene and s stefano islands form part of the southeastern flank of a pleistocene stratovolcano the products of 27 eruptions the majority of which have never been previously identified comprise the two islands these products consist chiefly of pyroclastic deposits with only three effusive episodes represented the youngest and most prominent deposit hereafter called parata grande tuff was produced by an eruption that represents the culmination of more than 0 5 ma of volcanic evolution and that formed a 3 km wide summit caldera the parata grande tuff is the focus of this study and consists mostly of pyroclastic flow deposits overlying basal pumice and ash fall beds the studied sections crop out as far as 2 km from the caldera rim the flow deposits sequence can be represented by four different lithofacies 1 massive facies originated by rapid sedimentation of grains through a boundary layer 2 coarse tail graded facies formed with a relatively lower fallout rate of particles from the suspension toward the boundary layer 3 inverse graded facies considered to have formed by gradual deposition from the base to the top of a traction carpet when the shear stress dropped below the threshold value to support the weight of the clasts and 4 sand wave facies the product of deposition from an unsteady low concentration flow the base of the pyroclastic flow succession is welded and thickens in topographic depressions the welding of deposits with traction structures and undeformed coarse pumice clasts probably occurred during the final stages of deposition of a formerly paniculate pyroclastic flow the flow deposits that overlie the welded succession show a drastic increase and change of lithic types that are interpreted to reflect the collapse of the roof of the reservoir triggering magma water interaction the uppermost part of the sequence is a succession of layers with dunes and cross stratification alternating with massive beds the stratified and heterogeneous succession of flow deposits could be due to the unsteady nature of the flow during the final phase of the eruption a vertical trend of sedimentary facies from massive to coarse tail graded into sand wave lithofacies is dominant in the pgt sequence and is interpreted as a depositional cycle each cycle is suggestive of deposition from a flow that was progressively diluted with time

a cause of rupture segmentation and synchronization in the nankai trough revealed by seismic imaging and numerical simulation 1 a giant earthquake occasionally occurs in a subduction zone owing to a simultaneous rupture in adjacent segments which have been previously ruptured by large earthquakes however it is still unknown if a giant earthquake coincidentally occurs or if there is a causal factor to control its generation in this study we show a cause and a growth process of a giant earthquake which may occur along southwestern japan on the basis of seismic images obtained from wide angle seismic data and a numerical simulation incorporating the structural images the wide angle seismic data were acquired along three trough parallel profiles crossing the rupture segmentation boundary between the 1944 tonankai moment magnitude mw 8 1 and the 1946 nankai mw 8 4 earthquakes the seismic imaging detected a high seismic velocity body forming a strongly coupled patch at the segmentation boundary the numerical simulation explained the historic rupture patterns and shows the occurrence of a giant earthquake along the entire nankai trough a distance of over 600 km long mw 8 7 the growth process revealed from the simulated slip history in and around the strongly coupled patch is 1 prior to the giant earthquake a small slow event or earthquake occurs near the segmentation boundary 2 this accelerates a very slow slip slower than the plate convergent rate at the strong patch which reduces a degree of coupling and 3 then a rupture easily propagates through the strong patch when the next earthquake is nucleated near the segmentation boundary consequently growing into a giant earthquake

a numerical simulation of earthquake cycles along the nankai trough in southwest japan lateral variation in frictional property due to the slab geometry controls the nucleation position abstract the occurrence pattern of historical great earthquakes along the nankai trough indicates the existence of rupture segments that seem to correlate with 100 km scale lateral variation in the dip angle of the subducting philippine sea plate for instance the latest earthquakes the 1944 tonankai and the 1946 nankai earthquakes initiated their ruptures off kii peninsula where the dip angle of the slab is steeper than in adjacent areas to investigate how such heterogeneity in slab geometry affects the occurrence of earthquakes we conducted a three dimensional 3d numerical simulation of earthquake cycles for a large source area about 700 km long along the trough and 300 km wide in the dip direction based on a rate and state dependent friction law we used a simple flat dipping plane to model the plate boundary frictional parameters and effective normal stress were assumed to depend on the estimated depth of the real plate boundary based on seismic surveys and seismicity data the depth dependent frictional parameters were mapped on the flat model plane this made lateral variation in frictional property due to the variation in the dip angle of the slab the plate convergence rate in the model decreased eastward along the trough consistent with a recent global positioning system gps analysis in the simulation results preslip occurred and rupture started off kii peninsula both effects of a narrower locked area due to the higher dip angle and a higher plate convergence rate caused the highest stress accumulation rate to be in this area promoting slip nucleation our simple simulation suggests that lateral variation in the dip angle of the slab is one of the factors controlling the nucleation position of great interplate earthquakes

on the physical mechanism of silent slip events along the deeper part of the seismogenic zone 1 to investigate the mechanism of recently observed silent slip events we simulated earthquake preparation processes using the dieterich ruina rate and state dependent friction law to ensure realistic modeling of the unstable stable transition we considered small cut off velocity to an evolution effect in the friction law for the transition zone when the cut off velocity to the evolution effect is significantly smaller than that of a direct effect steady state friction behaves as velocity weakening at low slip velocity and velocity strengthening at high slip velocity this frictional behavior was experimentally and theoretically confirmed for the unstable stable transition zone the results of our numerical simulations show that silent slips of which velocity is higher than the velocity of relative plate motion eventually propagates horizontally along the unstable stable transition over a period of several years silent slip events can be interpreted as being caused by the transitional behavior of the fault constitutive law

broadband modeling of the 2002 denali fault earthquake on the earth simulator abstract we use a spectral element method implemented on the earth simulator in japan to simulate broadband seismic waves generated by the 3 november 2002 denali fault earthquake this mw 7 9 event is the largest strike slip earthquake in north america in almost 150 years the source model is constrained by teleseismic body waves and observed surface offsets the earthquake was initiated by a small thrust event and is well characterized by a five segment fault geometry dominated by right lateral rupture along 220 km of the denali fault we perform the three dimensional numerical simulations at unprecedented resolution and reveal significantly enhanced ground motions directivity toward the conterminous united states for both body and surface waves

crustal structure across the coseismic rupture zone of the 1944 tonankai earthquake the central nankai trough seismogenic zone 1 differences in the coseismic rupture process between the 1944 tonankai and the 1946 nankaido earthquakes have been studied by many fault models to understand what factors control coseismic rupture zones it is important to investigate differences in deep crustal structures of the rupture zones between the 1944 and 1946 earthquakes the previously published crustal structure of the rupture zone of the 1946 earthquake shows that the coseismic rupture extends to the neogene quaternary accretionary prism however little is known about the structure of the rupture zone of the 1944 earthquake to obtain a complete image of the seismogenic zone of the 1944 earthquake a wide angle seismic survey was performed across the presumed coseismic rupture zone of the 1944 earthquake from ocean to land our model for the crustal structure is based on ocean bottom seismographic data the crustal structure appears characteristic for subducting oceanic crust and a neogene quaternary accretionary prism bounded by an island arc crust the neogene quaternary accretionary prism reaches a maximum thickness of 7 km at 50 km distance landward from the deformation front the subducting oceanic crust can be traced down to 35 km the subduction angle becomes steeper landward reaching up to 11 beneath the island arc crust the depth of the top of subducting oceanic crust at the downdip limit of the rupture zone is 23 km while the updip limit is located beneath the island arc upper crust similar structures of the updip and downdip limits are also published for several other subduction zones

subducted seamount imaged in the rupture zone of the 1946 nankaido earthquake the nankai trough is a vigorous subduction zone where large earthquakes have been recorded since the seventh century with a recurrence time of 100 to 200 years the 1946 nankaido earthquake was unusual with a rupture zone estimated from long period geodetic data that was more than twice as large as that derived from shorter period seismic data in the center of this earthquake rupture zone we used densely deployed ocean bottom seismographs to detect a subducted seamount 13 kilometers thick by 50 kilometers wide at a depth of 10 kilometers we propose that this seamount might work as a barrier inhibiting brittle seismogenic rupture

dynamic rupture scenarios of anticipated nankai tonankai earthquakes southwest japan 1 we investigated dynamic rupture scenarios of anticipated megathrust earthquakes on the nankai tonankai subduction zone southwest japan to improve the scenario reliability the model parameters should be constrained by available data or derived from their analysis we employed the three dimensional plate interface geometry and the slip deficit rate on the interface accumulated slip deficit was used to obtain the stress drop distribution of anticipated earthquakes the estimated stress drop distribution is consistent with the seismogenic asperity locations known from the analysis of past earthquakes fault friction constitutive parameters however had to be assumed from indirect observations because they cannot be constrained directly by the data based on various geophysical observations we defined three regions where larger fracture energy is required these are the eastern edge of the tonankai area the western edge of the nankai area and the region between the tonankai and nankai areas beneath the kii peninsula such lateral heterogeneity promoted the segmented rupture along the nankai trough with predefined stress drop and constitutive parameters various rupture scenarios for tonankai and nankai asperities were obtained for different initiation locations in some cases a single segment is ruptured while in other cases all the segments are broken due to dynamic linkage at the segment boundary causing a giant earthquake the initiation location is a critical parameter that controls the rupture propagation across the segment boundary these scenarios will be extremely useful to evaluate deterministically the strong ground motions and tsunami hazards caused by the next major earthquakes in southwest japan

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

integration of transient strain events with models of plate coupling and areas of great earthquakes in southwest japan we model the crustal deformation caused by two long term subduction slip transients in southwest japan which we refer to as the 2000 2004 tokai and the 2002 2004 bungo channel slow slip events sses we use re analysed geonet position time series and a kalman filter based network inversion method to image the spatiotemporal slip variation of the two events on the plate interface during the period of 1998 2004 67 and 2000 2005 both events are found to have complex slip histories with multiple subevents in addition to a newly identified slip subevent in 2002 2003 we find that the major event in the bungo channel sse initiated in early 2003 beneath the northeastern corner of the region and expanded southwestward in contrast to the slip characteristics suggested by other studies the re analysed gps data in the tokai region shows a renewed slip activity for the tokai sse in early 2003 2004 at a similar location as in the period of 2001 2002 the equivalent m w for both the tokai and bungo channel sses are about 7 0 our results show that the tokai sse appears to start before the miyaki kozu seismovolcanic event integrating plate coupling and sses shows that the transient slip zones are located in a region between the locked zones and the epicentres of the low frequency earthquakes lfes at least part of the interseismic slip deficit is released by episodic sses beneath the bungo channel region we find excellent temporal correspondence between transient slip and adjacent lfes for both sse suggesting that they are closely related and possibly reflect that long term slow slip may modulate the occurrence of lfes

slow earthquakes and great earthquakes along the nankai trough abstract we have reexamined reports indicating that slow deformation occurred before the great japan earthquakes of 1944 tonankai and 1946 nankaido and find that the observations are well founded although no quantitative models have previously been proposed to explain all of the relevant data we show that they are satisfied by a simple model for both earthquakes the model based on known properties of subduction zones has slow slip on the subduction interface in an area deeper than the seismic rupture if this model is correct and a similar physical situation holds for an anticipated tokai earthquake existing instruments will be able to reveal the pre slip in real time while differences among the deformation time series at different sites will provide strong constraints on the slow rupture propagation these differences could result in delaying the recognition of a coherent event

simulation of recurring earthquakes along the nankai trough and their relationship to the tokai long term slow slip events taking into account the effect of locally elevated pore pressure and subducting ridges 1 many earthquakes of moment magnitudes greater than 8 associated with subduction of the philippine sea plate under japan have occurred along the nankai trough with a recurrence interval of 90 150 years a large scale rupture of the tokai fault segment is believed to be imminent because that segment did not rupture during the most recent tonankai earthquake in 1944 recurring long term slow slip events lsses have recently been observed in the tokai region to investigate the current stress state in the tokai region we numerically simulated earthquake cycles using a three dimensional model consisting of triangular cells based on the rate and state dependent friction law our numerical simulations successfully modeled the tokai segment not ruptured during the 1944 tonankai earthquake as well as the recurring lsses in the tokai region we found that a large characteristic displacement l and effective normal stress in areas of subducted ridges are essential to avoid rupture of the tokai segment during the 1944 tonankai earthquake we also demonstrated that we can reproduce the recurring lsses by assigning low values of and l to the area beneath lake hamana without introducing a velocity strengthening friction law at high slip rate our simulation showed that the amplitudes of the lsses increased following the earthquakes that did not rupture the tokai segment which suggests that the recent lsses may be related to the accumulation of stresses in the tokai segment because it did not rupture during the 1944 earthquake

quasi dynamic versus fully dynamic simulations of earthquakes and aseismic slip with and without enhanced coseismic weakening physics based numerical simulations of earthquakes and slow slip coupled with field observations and laboratory experiments can in principle be used to determine fault properties and potential fault behaviors because of the computational cost of simulating inertial wave mediated effects their representation is often simplified the quasi dynamic qd approach approximately accounts for inertial effects through a radiation damping term we compare qd and fully dynamic fd simulations by exploring the long term behavior of rate and state fault models with and without additional weakening during seismic slip the models incorporate a velocity strengthening vs patch in a velocity weakening vw zone to consider rupture interaction with a slip inhibiting heterogeneity without additional weakening the qd and fd approaches generate qualitatively similar slip patterns with quantitative differences such as slower slip velocities and rupture speeds during earthquakes and more propensity for rupture arrest at the vs patch in the qd cases simulations with additional coseismic weakening produce qualitatively different patterns of earthquakes with near periodic pulse like events in the fd simulations and much larger crack like events accompanied by smaller events in the qd simulations this is because the fd simulations with additional weakening allow earthquake rupture to propagate at a much lower level of prestress than the qd simulations the resulting much larger ruptures in the qd simulations are more likely to propagate through the vs patch unlike for the cases with no additional weakening overall the qd approach should be used with caution as the qd simulation results could drastically differ from the true response of the physical model considered

comparison of characteristic and gutenberg richter models for time dependent m 7 9 earthquake probability in the nankai tokai subduction zone japan summary earthquake forecasts are usually underinformed and can be plagued by uncertainty in terms of the most appropriate model and parameter values used in that model in this paper we explore the application of two different models to the same seismogenic area the first is a renewal model based on the characteristic earthquake hypothesis that uses historical palaeoseismic recurrence times and fixed rupture geometries the hazard rate is modified by the coulomb static stress change caused by nearby earthquakes that occurred since the latest characteristic earthquake the second model is a very simple earthquake simulator based on plate motion or fault slip rates and adoption of a gutenberg richter magnitude frequency distribution this information is commonly available even if historical and palaeoseismic recurrence data are lacking the intention is to develop and assess a simulator that has a very limited parameter set that could be used to calculate earthquake rates in settings that are not as rich with observations of large earthquake recurrence behaviour as the nankai trough we find that the use of convergence rate as a primary constraint allows the simulator to replicate much of the spatial distribution of observed segmented rupture rates along the nankai tonankai and tokai subduction zones although we note rate differences between the two forecast methods in the tokai zone we also see enough similarities between simulations and observations to suggest that very simple earthquake rupture simulations based on empirical data and fundamental earthquake laws could be useful forecast tools in information poor settings

detection of short term slow slip events along the nankai trough southwest japan using gnss data 1 we detected short term slow slip events sses previously observable only with tilt and strain data along the nankai trough southwest japan using gnss global navigation satellite system data offsets detected in gnss time series using akaike s information criterion helped automatically identify 207 episodes with a motion direction opposite to that of the relative plate motion from june 1996 to january 2012 by nonlinear inversion of the detected displacement we estimated rectangular fault models for 133 probable and 25 possible short term sses over 15 years the sse moment magnitudes range from 5 5 to 6 3 most sse fault models are located in a narrow band of non volcanic tremors on the interfaces of the subducting philippine sea plate large sses moment magnitude mw 6 often occur in western and central shikoku the cumulative slip is distributed heterogeneously along the strike generally decreasing eastward with the maximum slip 50 cm in western shikoku no definite short term sses were found in the kii channel but several short term sses occurred in ise bay both regions are known as tremor gaps the local maximum of the cumulative slip fills in the tremor gap located in ise bay the long term rate of short term sse cumulative moment increased by threefold around 2003 in eastern shikoku whereas it was almost constant in other regions comparison with short term sse catalogues using tilt data suggests that both this study and previous studies missed some sses along the nankai trough a combination of geodetic data is important in the monitoring of the spatiotemporal distribution of short term sses

present day stress states underneath the kumano basin to 2 km below seafloor based on borehole wall failures at iodp site c0002 nankai accretionary wedge we constrain the state of stress to 2 km below seafloor in the nankai accretionary prism at the integrated ocean drilling program iodp site c0002f southwest japan based on borehole wall failures and rock strengths the logging while drilling resistivity images from 872 5 to 2005 5 meters below seafloor show that drilling mud control in riser drilling worked properly to minimize borehole wall failures available breakouts indicate a consistent maximum compression orientation subparallel to the subducting plate margin breakout analysis with drill logs suggests that breakouts occurred only when borehole pressure was slightly lowered and time lag between hole cutting and image logging was several hours this indicates that the observed breakouts are not immediate stress induced failure but brought up into shape gradually with time due to other mechanisms laboratory investigations on deformation and failure of the cores suggest that the time delayed breakout might be a result of progressive rock spall out in borehole wall damage zones that occur at a stress level close to failure condition we constrain stress magnitudes assuming that the stress state is sufficient to bring about the damage zones at the borehole wall an integrated method utilizing breakouts drilling induced tensile fractures and a leak off test suggests that the stress states are on the boundary between strike slip faulting and normal faulting stress regimes and somewhat variable depending on depth the stress magnitudes in the accretionary wedge appear to be controlled by frictional strength of the rock such that the differential stresses are constrained by the laboratory determined frictional coefficients this article is protected by copyright all rights reserved

earthquake rupture dependence on hypocentral location along the nicoya peninsula subduction megathrust abstract although interseismic locking distributions have been used in qualitatively evaluating the future earthquake potential quantitatively estimating how an earthquake may rupture through the locked interface is a more useful tool for quantifying both seismic and tsunami hazards here we investigate rupture scenarios from interseismic locking models along the megathrust interface below nicoya peninsula costa rica using spontaneous rupture simulations we first estimate initial stress from locking then initiate spontaneous ruptures at different nucleation points and observe the eventual earthquake magnitudes and slip distribution we find that 40 of nucleations tested develop into large earthquakes of m w 7 2 based on present interseismic locking models of these events those nucleated from deeper depths have a tendency for larger amplitude shallow slip suggesting increased tsunami potential furthermore irrespective of the input locking models we do not observe rupture scenarios of earthquakes with intermediate magnitudes between 6 and 7 a result consistent with observations in nicoya the results of hypocentre dependent earthquake magnitudes and tsunamigenic potential not only pose challenges in estimating rupture extents from locking models but also underscore the significance of quantitatively evaluating seismic and tsunami hazard in subduction zones

on behaviour and scaling of small repeating earthquakes in rate and state fault models with abundant seismic data for small repeating earthquakes it is important to construct a dynamic model that can explain various aspects of related observations in this work we study small repeating earthquakes on a fault governed by rate and state dependent friction laws the earthquakes occur on a velocity weakening patch surrounded by a much larger velocity strengthening region the whole fault is subject to long term tectonic loading the model with a circular patch and the aging form of rate and state dependent friction laws has been shown to reproduce the scaling of recurrence time versus seismic moment for small repeating earthquakes in a previous study here we investigate the behaviour of small repeating earthquakes in related models under different scenarios including several forms of the state evolution equations in rate and state dependent friction laws rectangular velocity weakening patch geometries quasi dynamic versus fully dynamic representation of inertial effects and 2 d versus 3 d simulations we find that the simulated scalings between the recurrence time and seismic moment for these different scenarios is similar while differences do exist we propose a theoretical consideration for the scaling between the recurrence time and seismic moment of small repeating earthquakes for patch radii smaller than or comparable to the full nucleation size the scaling is explained by the increase of seismic to aseismic slip ratio with magnitude for patch radii larger than the full nucleation size the scaling is explained by the model in which the recurrence time is determined by the earthquake nucleation time which is in turn determined by the time for aseismic slip to penetrate the distance of the full nucleation size into the patch the obtained theoretical insight is used to find the combinations of fault properties that allow the model to fit the observed scaling and range of the seismic moment and recurrence time

slow slip slow earthquakes period two cycles full and partial ruptures and deterministic chaos in a single asperity fault abstract the assimilation of geological geophysical and laboratory data in physics based models of fault dynamics promises increasingly realistic simulations of the seismic cycle to assist this effort i explore the dynamics of a single velocity weakening asperity to delineate the relationship between a fault physical properties and the style of faulting during the seismic cycle based on a micro physical model of rate and state friction from a dimensional analysis four non dimensional parameters control the characteristics of slip events and the behavior during the interseismic period including the dieterich ruina rice number ru which is proportional to the ratio of asperity to critical nucleation size w h and rb b a b where a and b control the direct and local evolutionary effects respectively for sufficiently large rb the ru number controls the spectrum of fault slip from periodic slow slip events to aperiodic fast ruptures in finite faults but not in semi infinite faults the transition between these end members includes a bifurcation that involves period two period four period six cycles and deterministic chaos with increasing ru macroscopic fault slip is stabilized as rb vanishes even as ru 1 for finite faults but not for semi infinite faults the transition between slow and fast ruptures for increasing rb includes another type of bifurcation with period two and period four cycles of slow and fast ruptures for 0

a three dimensional simulation of crustal deformation accompanied by subduction in the tokai region central japan abstract a great earthquake is expected to occur along the suruga trough where the philippine sea plate subducts beneath the eurasian plate we estimate crustal deformation prior to this hypothetical earthquake called the tokai earthquake based on a simulation model for plate subduction a three dimensional extension of the models by stuart 1988 and kato and hirasawa 1996 in this model the time evolution of a dislocation field in an elastic half space is governed by a quasi static interaction induced by the dislocation field itself as well as by a rate and state dependent friction law acting on the plate interface observed geophysical constraints taken into account are the shapes of the curved subducting plate interface the recurrence interval of past great earthquakes 90 150 years the average seismic coupling coefficient 0 5 the annual rate of level change 5 mm year between the two bench marks at hamaoka and kakegawa and the backslip distribution on the plate interface estimated from the result of gps observation the simulation shows the following the occurrence of great earthquakes is approximately periodic during interseismic times a strongly coupled region is formed in a seismic zone and it shrinks as the next great earthquake approaches the strongly coupled region is confined to an area where the plate inclination is gentle the rupture of the earthquake starts at a point close to the maximum shear stress acting on the plate boundary subsidence of hamaoka relative to kakegawa changes to uplift several years before the earthquake volumetric strain undergoes a change from compression to extension or vice versa at certain observation sites several years before the earthquake changes in volumetric strain accelerate as the occurrence of the earthquake impends the maximum strain change for 1 day observed on the ground surface just before the earthquake is 10 8 to 10 7 a value about one tenth of the value predicted by a related two dimensional model the pattern of shear stress accumulation and the location of the preslip are affected by the shape of the plate interface

deformable backstop as seaward end of coseismic slip in the nankai trough seismogenic zone abstract wide angle seismic surveys performed in the last decade have clarified the 3 d crustal structure along the nankai trough the geometry and velocity structure of the southwestern japan subduction zone are now well constrained comparing these observations with the rupture distribution of historic great thrust earthquakes it appears that the coseismic rupture occurred along plate boundaries deeper than the wedge backstop boundary the boundary between the neogene quaternary accretionary wedge and the crust forming the backstop from the view of spatial relationship both rupture distributions of the last two large events and the crust forming the backstop are considerably retreated from the trough axis in the west and east off the kii peninsula in both areas seamount or ridge subduction is apparent in seismic results geomorphological data and geomagnetic data the landward indentation of the deformable backstop which corresponds to the crustal block of old accreted sediments may be formed by seamount subduction according to published results of sandbox modeling in particular the subducted seamount may be a structural factor affecting the recession of the crustal block forming the backstop

a comparison of seismicity characteristics and fault structure between stick slip experiments and nature fault zones contain structural complexity on all scales this complexity influences fault mechanics including the dynamics of large earthquakes as well as the spatial and temporal distribution of small seismic events incomplete earthquake records unknown stresses and unresolved fault structures within the crust complicate a quantitative assessment of the parameters that control factors affecting seismicity to better understand the relationship between fault structure and seismicity we examined dynamic faulting under controlled conditions in the laboratory by creating saw cut guided natural fractures in cylindrical granite samples the resulting rough surfaces were triaxially loaded to produce a sequence of stick slip events during these experiments we monitored stress strain and seismic activity after the experiments fault structures were imaged in thin sections and using computer tomography the laboratory fault zones showed many structural characteristics observed in upper crustal faults including zones of localized slip embedded in a layer of fault gouge laboratory faults also exhibited a several millimeter wide damage zone with decreasing micro crack density at larger distances from the fault axis in addition to the structural similarities we also observed many similarities between our observed distribution of acoustic emissions aes and natural seismicity the aes followed the gutenberg richter and omori utsu relationships commonly used to describe natural seismicity moreover we observed a connection between along strike fault heterogeneity and variations of the gutenberg richter b value as suggested by natural seismicity studies areas of low b value marked the nucleation points of large slip events and were located at large asperities within the fault zone that were revealed by post experimental tomography scans our results emphasize the importance of stick slip experiments for the study of fault mechanics the direct correlation of acoustic activity with fault zone structure is a unique characteristic of our laboratory studies that has been impossible to observe in nature

fault stability inferred from granite sliding experiments at hydrothermal conditions seismicity on crustal faults is concentrated in the depth interval 1 3 to 12 15km tse and rice 1986 suggested that the lower bound on seismicity is due to a switch with increasing temperature from velocity weakening destabilizing to velocity strengthening stabilizing friction they inferred this transition from friction data for dry granite however pore fluids exist at elevated temperatures throughout the crust and may strongly influence strength and sliding behavior we present new data from sliding experiments on granite at elevated t 23 to 600 plus elevated ph2o 100 mpa our results show velocity strengthening at room temperature but velocity weakening from 100 to 350 c except at 250 from 350 to 600 there are systematic trends from velocity weakening to strong velocity strengthening and from high to low friction neither trend was seen in tests on dry granite the velocity dependence data imply the potential for unstable slip in the interval 100 to 350 using a geotherm to map temperature to depth this interval closely matches the observed earthquake distribution

loading mechanism and scaling relations of large interplate earthquakes we have done a numerical simulation of tectonic loading at transform plate boundaries with a lithosphere asthenosphere coupling model subject to steady relative plate motion in this model a seismic fault is represented by a locked patch with a finite length on an infinitely long vertical dislocation surface cutting the entire lithosphere through the numerical simulation we have obtained the following results stress accumulation on the fault is partly due to viscous drag at the base of the lithosphere base loading and partly due to dislocation pile ups at horizontal edges of the fault edge loading if the viscosity of the asthenosphere is less than 1018 pa s the base loading is not effective since its rate exponentially decays very soon if the viscosity of the asthenosphere is greater than 1020 pa s both types of loading are effective and then the stress accumulation rate in the early stage of loading is formally written as d dt vpl a bl where vpl is a rate of relative plate motion and l is a fault length when the fault length l is small the effect of edge loading the second term is dominant and the stress accumulation rate is in proportion to the inverse of l when the fault length l is large the effect of base loading the first term becomes dominant and the stress accumulation rate is independent of l it is well known that the general l cubed dependence of seismic moment m0 breaks for large interplate earthquakes this break in the moment length relation can be ascribed to difference in loading mechanism between small and large earthquakes from the results of numerical computation if interplate earthquakes have the same stress drop regardless of their fault lengths we may derive a l squared dependence of m0 for large interplate earthquakes and a linear l dependence of m0 for very large interplate earthquakes

modulation of fault strength during the seismic cycle by grain size evolution around contact junctions abstract earthquake prediction is fundamentally hampered by insufficient knowledge of the constitutive behavior of faults laboratory and theoretical work by dieterich 1978 and ruina 1983 formed the basis of rate and state friction a constitutive framework that captures the healing and weakening of frictional contacts the rate and state law successfully explains the frictional behavior of a wide range of rocks and many phenomena associated with fault slip the physics underlying the rate and state friction law is not fully understood but it is generally accepted that several micro mechanisms operate depending on the texture maturity fluid content and other physical and kinematic conditions of the fault here i formulate a constitutive framework that unifies a number of laboratory experiments on silicate rocks and the gouges derived from these rocks that describe the effect of grain size temperature real area of contact gouge thickness and fault roughness fundamental to the model is that fault strength is controlled by the area of the interfacial contact junctions that support the shear and normal loads the curvature of asperities weakly controls the area of their contact junction and the resulting fault strength as a result the dynamics of grain size evolution around micro asperities enables the seismic cycle the model quantitatively explains the correlation between the characteristic weakening distance and the gouge thickness marone and kilgore 1993 the correlation of the static friction coefficient with the rate dependence parameters ikari et al 2011 the dependence of frictional resistance to sub solidus temperatures chester 1994 and predicts a range of grain sizes that is compatible with observations at exposed fault zones however the dynamics of grain size evolution is still challenging to verify experimentally the model features a regularization at vanishing slip speeds that implies distinct dynamics at low strength for friction coefficients lower than 0 1 seismic cycle simulations predict the emergence of frictional instabilities with complex source time functions this is a significant departure from the predictions of rate and state friction that is most relevant to the dynamics of decollements serpentinized shear zones and other low strength faults

estimation of interplate coupling in the nankai trough japan using gps data from 1996 to 2006 we used three component surface velocities in southwest japan to estimate plate coupling on the subducting plate interface at the nankai trough we analyzed continuous gps data from the japanese geonet network from 1996 to 2006 using a consistent analysis strategy that generates bias fixed solutions for the entire network we applied systematic time series analysis methods to estimate common mode error which improved position solutions for the entire network to allow for differences in regional deformation sources we modelled the plate coupling on the plate interface beneath shikoku island to kii peninsula and the tokai suruga trough separately the results show strong coupling at a depth of 10 30 km off shikoku and kii peninsula the spatial variation in plate coupling coincides well with the coseismic rupture zones of the past large earthquakes maximum slip deficit rates of 2 3 cm yr 1 at the depth of 5 25 km are found beneath the tokai area consistent with results from other studies the downdip limits of the highly coupled areas and transition zones beneath shikoku and the kii peninsula correspond approximately to estimates of the 450 c isotherms good correlation is observed between the lateral variations of the slip deficit distribution low frequency earthquakes and coseismic slip this correlation suggests that temperature and possibly fluid variations contribute to such correlation in space the interplate slip deficit derived from the gps velocities over the 10 yr of observations is generally compatible with the results over shorter time spans suggesting that plate coupling in sw japan does not change significantly over the period of these gps measurements

temperature distribution of the upper surface of the subducted philippine sea plate along the nankai trough southwest japan from a three dimensional subduction model relation to large interplate and low frequency earthquakes summary the nankai subduction fault in southwest japan is a plate boundary along which large megathrust earthquakes have repeatedly occurred a previous 2 d thermal model suggested that the updip and downdip limits of the seismogenic zone are closely related to the temperature of the plate interface we estimated a new temperature distribution for the plate interface based on a 3 d thermal convection model that incorporates revised governing equations temporal changes in relative plate motion the shape of the subducted slab temperature variations related to basin evolution and more heat flow data and model regions than have been used in previous models the margin parallel spatial variation in the temperature of the plate interface was caused by spatio temporal changes associated with the cooling of the shikoku basin the updip limit of the thermally delineated seismogenic zone thermal seismogenic zone was approximately parallel to the trough axis due to a spreading rate that increased with distance from a fossil ridge although the margin parallel age dependency of the subducting plate was taken into account the downdip limit of the thermal seismogenic zone was determined by temperature except in eastern kyushu where it was determined by a boundary between the continental moho depth and the upper surface of the subducting plate the maximum coseismic slip associated with the 1944 tonankai m 7 9 and the 1946 nankai m 8 0 earthquakes and a strongly coupled region estimated from gps data inversion obtained by previous studies were both located in the thermal seismogenic zone on the plate interface low frequency earthquakes located at the downdip of the thermal seismogenic zone took place at temperatures of about 400 500 c this may be related to the phase transformation of hydrous minerals in oceanic crust from lawsonite blueschist jadeite to amphibole eclogite and the associated decreases in water content of approximately 2 4 wt the thermal seismogenic zone is narrowest off the kii peninsula where the hypocentres of the tonankai and nankai earthquakes were located the narrow seismogenic zone may have determined the rupture initiation points for these earthquakes as was previously demonstrated by numerical simulations of the earthquake cycle

constitutive properties of clayey fault gouge from the hanaore fault zone southwest japan velocity step tests at a range of slip rates 0 0154 155 54 m s 1 are performed using natural fault gouge containing smectite mica and quartz collected from an outcrop of the hanaore fault southwest japan field and microscopic observations reveal that the shear deformation is localized to a few centimeters or thinner layer of black clayey fault gouge this layer is formed by multiple stages and determining the width of the shear zone due to a single event is difficult to determine the experimental data on the abrupt jumps in the load point velocity are fitted by a rate and state dependent frictional law coupled with the spring slider model the stiffness of which is treated as a fitting parameter this treatment is shown to be essential to determine the constitutive parameters and their errors the velocity steps are successfully fit with typically two state variables larger b 1 with shorter d c1 and smaller b 2 with longer d c2 at slip rates higher than 1 m s 1 negative b 2 is required to fit the data in most of the cases thin gouge layers 200 m in the experiment enables us to simulate large averaged shear strain which is important to recognize the evolution of the state variable associated with negative b 2 and long d c2 observation of microscopic structure after experiments shows poor development of y planes this may be consistent with the mechanical behavior observed weak occurrence of initial peak strength at yielding and displacement hardening throughout the experiments

coseismic slip resolution along a plate boundary megathrust the nankai trough southwest japan geodetic survey measurements are used to estimate the coseismic slip distribution in the 1944 tonankai mw 8 1 and 1946 nankaido mw 8 3 earthquakes and to assess quantitatively the degree to which this slip is resolved on the plate boundary megathrust data used include 798 angle changes from triangulation surveys 328 leveling section differences and 5 coseismic tidal gage offsets many of the nominally coseismic triangulation data span 50 years nearly half the earthquake cycle and correction for interseismic deformation using post 1950 observations is applied microseismicity is used to define the configuration of the plate boundary interface and approximate it with a continuous multisegment fault model because the onshore geodetic data have very limited resolving power for offshore fault segments offshore coseismic slip was constrained by satake s 1993 estimation based on tsunami data the majority of the coseismic slip occurs between 15 and 25 km depth although resolution declines toward the trench axis it is sufficiently good to define two distinct high slip regions one off southeastern shikoku island 11 m maximum and the other offshore of kii peninsula 3 m maximum the slip magnitude off southeastern shikoku coupled with the plate convergence rate would imply an recurrence interval of about 270 years much longer than the average repeat time of 120 years for historical great earthquakes on the nankai trough however the maximum coseismic slip is sensitive to the assumed fault geometry and slippage on trough parallel splay faults could significantly decrease the maximum slip to about 6 m

nucleation process of magnitude 2 repeating earthquakes on the san andreas fault predicted by rate and state fault models with safod drill core data recent laboratory shear slip experiments conducted on a nominally flat frictional interface reported the intriguing details of a two phase nucleation of stick slip motion that precedes the dynamic rupture propagation this behavior was subsequently reproduced by a physics based model incorporating laboratory derived rate and state friction laws however applying the laboratory and theoretical results to the nucleation of crustal earthquakes remains challenging due to poorly constrained physical and friction properties of fault zone rocks at seismogenic depths here we apply the same physics based model to simulate the nucleation process of crustal earthquakes using unique data acquired during the san andreas fault observatory at depth safod experiment and new and existing measurements of friction properties of safod drill core samples using this well constrained model we predict what the nucleation phase will look like for magnitude 2 repeating earthquakes on segments of the san andreas fault at a 2 8 km depth we find that despite up to three orders of magnitude difference in the physical and friction parameters and stress conditions the behavior of the modeled nucleation is qualitatively similar to that of laboratory earthquakes with the nucleation consisting of two distinct phases our results further suggest that precursory slow slip associated with the earthquake nucleation phase may be observable in the hours before the occurrence of the magnitude 2 earthquakes by strain measurements close a few hundreds meters to the hypocenter in a position reached by the existing borehole

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

crustal velocity field of southwest japan subduction and arc arc collision we investigate crustal deformation in southwest japan over a 3 year period revealed by a permanent dense global positioning system gps array southwest japan is a part of the amurian plate a microplate moving about 10 mm yr toward the east with respect to the eurasian plate it overrides the philippine sea plate at the nankai trough and collides with the northeast japan arc in the central part of japan in this paper we first derive gps site velocities relative to the stable part of the amurian plate in order to isolate signals of crustal deformation caused by the subduction and or the collision the velocity field has a conspicuous feature indicating the interseismic elastic loading by the philippine sea plate slab at the nankai trough characterized by the northwestward movements of points throughout the studied area their amplitudes are the largest at the pacific coast and decay toward the japan sea coast with a subtle systematic shift of azimuths a model assuming an elastic half space the convergence rate at the nankai trough based on a refined euler vector and the strength of the coupling inferred from a thermal model could explain the velocity field in the western part of the studied area to a large extent those in the eastern part systematically deviate from them and the residual components there show east west shortening and north south extension this may represent crustal thickening and trenchward extrusion of crustal blocks caused by the collision between southwest and northeast japan this suggests that the collision between southwest and northeast japan gives rise to not only crustal thickening but also trenchward extrusion of crustal block a velocity contrast was found across the median tectonic line the largest inland active fault in japan but the current permanent gps network is not dense enough for us to discuss its coupling depth

reconstruction of multi century flood histories from oxbow lake sediments peace athabasca delta canada floods caused by ice jams on the peace river are considered to be important for maintaining hydro ecological conditions of perched basins in the peace athabasca delta pad canada a highly productive and internationally recognized northern boreal ecosystem concerns over the potential linkages between regulation of the peace river in 1968 for hydroelectric production and low peace river discharge between 1968 and 1971 during the filling of the hydroelectric reservoir absence of a major ice jam flood event between 1975 and 1995 and low water levels in perched basins during the 1980s and early 1990s have sparked numerous environmental studies largely aimed at restoring water levels in the pad lack of sufficient long term hydrological records however has limited the ability to objectively assess the importance of anthropogenic factors versus natural climatic forcing in regulating hydro ecological conditions of the pad here we report results of a paleolimnological study on laminated sediments from two oxbow lakes in the pad which are located adjacent to major flood distributaries of the peace river sediment core magnetic susceptibility measurements supported by results from several other physical and geochemical analyses as well as stratigraphic correspondence with recorded high water events on the peace river provide proxy records of flood history spanning the past 180 and 300 years in these two basins results indicate that inferred flood frequency has been highly variable over the past 300 years but in decline for many decades beginning as early as the late nineteenth century well before peace river regulation additionally several multi decadal intervals without a major flood have occurred during the past 300 years while climate related mechanisms responsible for this variability in flood frequency remain to be determined as does quantifying the relative roles of river regulation and climate variability on hydro ecological conditions in the pad since 1968 these results suggest that ecosystem management strategies for the pad need to explicitly account for natural variations in flood recurrence intervals copyright 2006 john wiley sons ltd

seismicity of the prince william sound region for over thirty years following the 1964 great alaskan earthquake in this paper we present results of body wave form modeling of 19 earthquakes generally m b 5 7 occurring from 1964 to 1983 in the vicinity and down dip of the large asperity within the prince william sound region that ruptured in 1964 these data are supplemented with source parameters from studies of more recent post 1980 events our results suggest that moderate earthquakes which occurred in the region between 1964 and 1984 were predominantly located in the vicinity of the prince william sound asperity and could be assigned to two groups the first group consists of events occurring above the plate interface within prince william sound along reverse faults or low angle thrusts the second group occurs at 35 to 60 km depth in the region north of prince william sound and represents normal to normal oblique faulting within the subducted pacific crust or upper mantle these earthquakes occur below the northern edge of the 1964 asperity in a region where the subducting plate undergoes a rapid change in strike and dip a third group of events occurs in cook inlet well down dip of the 1964 asperity and below the plate interface these events exhibit a variety of mechanisms and many at depths of 50 to 70 km may be associated with complexities in the shape of the downgoing slab most of the cook inlet events occurred after 1984 whereas a few events of similar magnitude have occurred in the vicinity of the prince william sound asperity since 1984

forecast model for great earthquakes at the nankai trough subduction zone an earthquake instability model is formulated for recurring great earthquakes at the nankai trough subduction zone in southwest japan the model is quasistatic two dimensional and has a displacement and velocity dependent constitutive law applied at the fault plane a constant rate of fault slip at depth represents forcing due to relative motion of the philippine sea and eurasian plates the model simulates fault slip and stress for all parts of repeated earthquake cycles including post inter pre and coseismic stages calculated ground uplift is in agreement with most of the main features of elevation changes observed before and after the m 8 1 1946 nankaido earthquake in model simulations accelerating fault slip has two time scales the first time scale is several years long and is interpreted as an intermediate term precursor the second time scale is a few days long and is interpreted as a short term precursor accelerating fault slip on both time scales causes anomalous elevation changes of the ground surface over the fault plane of 100 mm or less within 50 km of the fault trace

the slip distribution of the 1946 nankai earthquake estimated from tsunami inversion using a new plate model abstract a new model for the shape of the philippine sea plate psp subducting beneath southwest japan was constructed by combining marine seismic survey results and seismicity data this resulted in a plate model that is generally 3 5 km shallower than previous estimates and contains new details of plate boundary structure near the nankai trough axis we estimated the slip distribution of the 1946 nankai earthquake by inverting tsunami waveforms using the new plate boundary model and found that the large slip off cape muroto and seismic moment were reduced by about 10 from the previous estimate of tanioka and satake 2001a however we also found reason to suspect the tide gauge closest to the epicenter at shimotsu and this resulted in a much more substantial reduction in the amount of slip in the eastern segment of the rupture area we also find that our new rupture model correlates well with features of the subducting plate boundary such as a large subducting seamount off cape muroto kodaira et al 2000a this suggests that such features have an important effect on either earthquake rupture propagation or the interseismic accumulation of elastic strain energy or both

stress state and its anomaly observations in the vicinity of a fault in nantroseize expedition 322 to better understand the stress state and geological properties within the shallow shikoku basin southwest of japan two sites c0011a and c0011b were drilled in open ocean sediments using logging while drilling lwd and coring respectively resistivity image logging was performed at c0011a from sea floor to 950 m below sea floor mbsf at c0011b the serial coring was obtained in order to determine physical properties from 340 to 880 mbsf for the lwd images a notable breakout anomaly was observed at a depth of 615 m using resistivity images and a stress polygon the potential horizontal principal stress azimuth and its magnitude within the 500 750 mbsf section of the c0011a borehole were constrained borehole breakout azimuths were observed for the variation by the existence of a fault zone at a depth of 615 mbsf out of this fracture zone the breakout azimuth was located at approximately 109 12 subparallel to the nankai trough convergence vector 300 315 our calculations describe a stress drop was determined based on the fracture geometry a close 90 73 12 rotation implied a 100 stress drop defined as a maximum shear stress drop equal to 1 mpa the magnitude of the horizontal principal stresses near the fracture stress anomaly ranged between 49 and 52 mpa and the bearing to the vertical stress sv 52 mpa was found to be within the normal faulting stress regime low rock strength and a low stress level are necessary to satisfy the observations

physics based 3 d simulation for earthquake generation cycles at plate interfaces in subduction zones the generation of interplate earthquakes can be regarded as a process of tectonic stress accumulation and release driven by relative plate motion we completed a physics based simulation system for earthquake generation cycles at plate interfaces in the japan region where the pacific plate is descending beneath the north american and philippine sea plates and the philippine sea plate is descending beneath the north american and eurasian plates the system is composed of a quasi static tectonic loading model and a dynamic rupture propagation model developed on a realistic 3 d plate interface model the driving force of the system is relative plate motion in the quasi static tectonic loading model mechanical interaction at plate interfaces is rationally represented by the increase of tangential displacement discontinuity fault slip across them on the basis of dislocation theory for an elastic surface layer overlying maxwell type viscoelastic half space in the dynamic rupture propagation model stress changes due to fault slip motion on non planar plate interfaces are evaluated with the boundary integral equation method the progress of seismic dynamic or aseismic quasi static fault slip on plate interfaces is governed by a slip and time dependent fault constitutive law as an example we numerically simulated earthquake generation cycles at the source region of the 1968 tokachi oki earthquake on the north american pacific plate interface from the numerical simulation we can see that postseismic stress relaxation in the asthenosphere accelerates stress accumulation in the source region when the stress state of the source region is close to a critical level dynamic rupture is rapidly accelerated and develops over the whole source region when the stress state is much lower than the critical level the rupture is not accelerated this means that the stress state realized by interseismic tectonic loading essentially controls the subsequent dynamic rupture process

in situ stress conditions at iodp site c0002 reflecting the tectonic evolution of the sedimentary system near the seaward edge of the kumano basin offshore from sw japan this paper presents a complete set of in situ stress calculations for depths of 200 1400 mbsf meters below seafloor at iodp site c0002 near the seaward margin of the kumano forearc basin offshore from southwest japan the vertical stress component was obtained by integrating bulk density calculations from moisture and density logging data and the two horizontal components were stochastically optimized by minimizing misfits between a probabilistic model and measured breakout widths for every 30 m vertical segment of the wellbore our stochastic optimization process reveals that the in situ stress regime is decoupled across an unconformity between an accretionary complex and the overlying kumano forearc basin the stress condition above the unconformity is close to the critical condition for normal faulting while below the unconformity the geologic system is stable in a normal to strike slip fault stress regime the critical state of stress demonstrates that the tectonic evolution of the sedimentary system has been achieved mainly by the regionally continuous action of a major out of sequence thrust fault during sedimentation in the forearc basin the stable stress condition in the accretionary prism is interpreted to have resulted from mechanical decoupling by the accommodation of large displacement along the megasplay fault

modeling the activity of short term slow slip events along deep subduction interfaces beneath shikoku southwest japan 1 we developed a model of short term slow slip events sses on the 3 d subduction interface beneath shikoku southwest japan considering a rate and state dependent friction law with a small cutoff velocity for the evolution effect we assume low effective normal stress and small critical displacement at the sse zone on the basis of the hypocentral distribution of low frequency tremors we set three sse generation segments a large segment beneath western shikoku and two smaller segments beneath central and eastern shikoku using this model we reproduce events beneath western shikoku with longer lengths in the along strike direction and with longer recurrence times compared with events beneath central and eastern shikoku the numerical results are consistent with observations in that the events at longer segments have longer recurrence intervals the activity of sses is determined by nonuniform frictional properties at the transition zone we also attempt to model the very low frequency vlf earthquakes that accompany short term sses on a 2 d thrust fault we consider a local patch in which the friction parameters are varied in the case that critical displacement is very small at the patch fast multiple slips occur at the patch in the case that the effective normal stress is high at the patch the patch acts as a barrier to sses when it ruptures however rapid slip occurs because the source time functions of these cases are somewhat different it would be possible in the future to assess if either case is an appropriate model for vlf earthquakes

connecting depth limits of interseismic locking microseismicity and large earthquakes in models of long term fault slip thickness of the seismogenic zone is commonly determined based on the depth of microseismicity or the fault locking depth inferred from geodetic observations the relation between the two estimates and their connection to the depth limit of large earthquakes remain elusive here we explore the seismic and geodetic observables in models of faults governed by laboratory based friction laws that combine quasi static rate and state friction and enhanced dynamic weakening our models suggest that the transition between the locked and fully creeping regions can occur over a broad depth range the effective locking depth d elock associated with concentrated loading and promoting microseismicity is located at the top of this transition zone the geodetic locking depth d glock inverted from surface geodetic observations corresponds to the depth of fault creeping with approximately half of the long term rate following large earthquakes d elock either stays unchanged or becomes shallower due to creep penetrating into the shallower locked areas whereas d glock deepens as the slip deficit region expands compensating for the afterslip as the result the two locking depths diverge in the late interseismic period consistent with available seismic and geodetic observations from several major fault segments in southern california we find that d glock provides a bound on the depth limit of large earthquakes in our models however the assumed layered distribution of fault friction and simple depth estimates are insufficient to characterize more heterogeneous faults e g ones with significant along strike variations improved observations and models are needed to illuminate physical properties and seismic potential of fault zones

detailed coseismic slip distribution of the 1944 tonankai earthquake estimated from tsunami waveforms coseismic slip distribution on the fault plane of the 1944 tonankai earthquake is estimated from inversion of tsunami waveforms three improvements from a previous study satake 1993 are made these are 1 smaller subfaults are used to resolve detailed slip distribution 2 the sub faults fit better to the plate interface geometry and 3 finer and more accurate bathymetry data is used the inversion result shows that a maximum slip of about 3 m occurred on the plate interface off shima peninsula the total seismic moment is estimated to be 2 0 1021 nm mw 8 2 the result confirms that the 1944 tonankai earthquake did not rupture the plate interface beneath the tokai region and supports the existence of the seismic gap in the tokai region suggested by ishibashi 1981 the slip of about 1 5 m on the plate interface beneath atsumi peninsula northeast of the large slip area is necessary to explain the observed tsunami waveforms although no seismic moment release was estimated from strong motion data by kikuchi et al 1999 this may suggest that the rupture beneath atsumi peninsula was slow

plate convergence and long term crustal deformation in central japan surveys by continuous global positioning system in and around japan revealed that the amurian plate collides with the north american plate in central japan by 2 cm yr long term crustal deformation seems to be influenced mainly by this collision although subduction of oceanic plates governs short term elastic deformation over the arc here we study the long term deformation field by carefully removing the short term signals inferred from a priori plate convergence vectors and coupling strengths predicted by a thermal model the obtained field shows that the change in velocities occurs along the longitude 135 137 and there exist a relatively rigid block and zones accommodating strains characteristic compressional deformation is found northwest of izu due possibly to the collision of the izu bonin arc with honshu plate convergence rate along the nankai suruga trough is considerably smaller in eastern parts due partly to the transition from the amurian to the north american plate of the landward side and partly to the motion of the izu microplate relative to the philippine sea plate this accounts for longer recurrence intervals of interplate earthquakes in the suruga trough where the tokai earthquake is anticipated to occur

modeling earthquake sequences along the manila subduction zone effects of three dimensional fault geometry abstract to assess the potential of catastrophic megathrust earthquakes m w 8 along the manila trench the eastern boundary of the south china sea we incorporate a 3d non planar fault geometry in the framework of rate state friction to simulate earthquake rupture sequences along the fault segment between 15 n 19 n of northern luzon our simulation results demonstrate that the first order fault geometry heterogeneity the transitional segment possibly related to the subducting scarborough seamount chain connecting the steeper south segment and the flatter north segment controls earthquake rupture behaviors the strong along strike curvature at the transitional segment typically leads to partial ruptures of m w 8 3 and m w 7 8 along the southern and northern segments respectively the entire fault occasionally ruptures in m w 8 8 events when the cumulative stress in the transitional segment is sufficiently high to overcome the geometrical inhibition fault shear stress evolution represented by the s ratio is clearly modulated by the width of seismogenic zone w at a constant plate convergence rate a larger w indicates on average lower interseismic stress loading rate and longer rupture recurrence period and could slow down or sometimes stop ruptures that initiated from a narrower portion moreover the modeled interseismic slip rate before whole fault rupture events is comparable with the coupling state that was inferred from the interplate seismicity distribution suggesting the manila trench could potentially rupture in a m8 earthquake

three dimensional boundary integral modeling of spontaneous earthquake sequences and aseismic slip 1 fault processes involve complex patterns of seismic events and aseismic slip this work develops a three dimensional 3 d methodology for simulating long term history of spontaneous seismic and aseismic slip on a vertical planar strike slip fault subjected to slow tectonic loading our approach reproduces all stages of earthquake cycles from accelerating slip before dynamic instability to rapid dynamic propagation of earthquake rupture to postseismic slip and to interseismic creep including aseismic transients we use the developed 3 d methodology to study interaction of fault slip with a small patch of higher normal stress over long term slip history for uniform initial prestress dynamic rupture is significantly affected by the stronger patch in the first simulated event but not in subsequent ones the change in behavior is due to redistribution of shear stress by prior slip which demonstrates that distributions of fault strength and stress are related and illustrates the importance of simulating long slip histories even in studies of dynamic rupture despite no long term effect on dynamic rupture the small patch of higher normal stress influences nucleation processes and hence long term slip patterns in the model comparison of the fully dynamic simulations and a widely used quasi dynamic approach shows that the quasi dynamic approach modifies long term slip patterns in addition to resulting in much smaller slip velocities and rupture speeds during dynamic events we show that the response of quasi dynamic formulations with reduced radiation damping terms can be scaled to match the results of the standard quasi dynamic formulation and hence cannot improve the comparison