a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

neoproterozoic adakitic plutons in the northern margin of the yangtze block china partial melting of a thickened lower crust and implications for secular crustal evolution abstract numerous neoproterozoic felsic and mafic ultramafic intrusions occur in the hannan region at the northern margin of the yangtze block among these the wudumen and erliba plutons consist of granodiorites and have shrimp zircon u pb ages of 735 ma the rocks have high k 2 o 0 8 3 6 wt and na 2 o 4 4 6 4 wt and low mgo 0 4 1 7 wt they also have high sr y 32 209 and la yb n ratios 4 4 38 6 their e nd values range from 0 41 to 0 92 and zircon initial 176 hf 177 hf ratios from 0 282353 to 0 282581 these geochemical features are similar to those of adakitic rocks produced by partial melting of a thickened lower crust our new analytical results combined with the occurrence of voluminous arc related mafic ultramafic intrusions emplaced before 740 ma lead us to propose that the crustal evolution in the northern margin of the yangtze block during neoproterozoic involved 1 rapid crustal growth and thickening by underplating of mafic magmas from the mantle which was modified by materials coming from the subducting oceanic slab from 1 0 to 0 74 ga and 2 partial melting of the thickened lower crust due to a thermal anomaly induced by upwelling of asthenosphere through an oceanic slab window producing the 735 ma adakitic wudumen and erliba plutons our model suggests that the crustal thickness was more than 50 km at the northern margin of the yangtze block at 735 ma and rule out the possibility of a mantle plume impact causing the 735 ma magmatism in the region

modeling of slow slip events along the deep subduction zone in the kii peninsula and tokai regions southwest japan 1 in the subduction zone of southwest japan short term slow slip events sses occur with low frequency tremors lfts at intervals of several months recently lfts have been located with high resolution and their activities have been examined in detail by setting the generation zones of sses such that these zones contain the lft hypocenters we simulate sses on a 3d plate interface beneath the kii peninsula and tokai regions by using a rate and state dependent friction law with a small cut off velocity for the evolution effect our numerical results show that recurrence intervals of sses in the southern and central kii peninsula in the northern kii peninsula and in the tokai region are 2 5 3 0 4 8 5 6 and 3 5 4 5 months respectively which are consistent with observed sse activity our simulation also produces a multisegment event that propagates from the kii to tokai segments at a speed of 10 km day which is consistent with observations the results suggest that generation zones of lfts coincide with sse regions and that these two events are different manifestations of the same slip process along the subduction zone we also perform 3d modeling of faster events accompanied by short term sses by considering local circular patches with a smaller critical displacement surrounded by sse zones with a larger critical displacement local circular patches are set at the observed lft locations the simulation reproduces fast events that propagate at a speed of 100 200 km day during a single sse event

afterslip tremor and the denali fault earthquake we tested the hypothesis that afterslip should be accompanied by tremor using observations of seismic and aseismic deformation surrounding the 2002 m 7 9 denali fault alaska earthquake dfe afterslip happens more frequently than spontaneous slow slip and has been observed in a wider range of tectonic environments and thus the existence or absence of tremor accompanying afterslip may provide new clues about tremor generation we also searched for precursory tremor as a proxy for posited accelerating slip leading to rupture our search yielded no tremor during the five days prior to the dfe or in several intervals in the three months after this negative result and an array of other observations all may be explained by rupture penetrating below the presumed locked zone into the frictional transition zone while not unique such an explanation corroborates previous models of megathrust and transform earthquake ruptures that extend well into the transition zone

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

introduction to special section on phenomenology underlying processes and hazard implications of aseismic slip and nonvolcanic tremor 1 this paper introduces the special section on the phenomenology underlying processes and hazard implications of aseismic slip and nonvolcanic tremor by highlighting key results of the studies published in it many of the results indicate that seismic and aseismic manifestations of slow slip reflect transient shear displacements on the plate interface with the outstanding exception of northern cascadia where tremor sources have been located on and above the plate interface differing models of the plate interface there also need to be reconciled slow slip phenomena appear to result from propagating deformation that may develop with persistent gaps and segment boundaries results add to evidence that when tectonic deformation is relaxed via slow slip most relaxation occurs aseismically but with seismic signals providing higher resolution proxies for the aseismic slip instead of two distinct slip modes as suggested previously lines between fast and slow slip more appropriately may be described as blurry zones results reported also show that slow slip sources do not coincide with a specific temperature or metamorphic reaction their associations with zones of high conductivity and low shear to compressional wave velocity ratios corroborate source models involving pore fluid pressure buildup and release these models and spatial anticorrelations between earthquake and tremor activity also corroborate a linkage between slow slip and frictional properties transitional between steady state and stick slip finally this special section highlights the benefits of global and multidisciplinary studies which demonstrate that slow phenomena are not confined to beneath the locked zone but exist in many settings

aeromagnetic study of the hengshan wutai fuping region unraveling a crustal profile of the paleoproterozoic trans north china orogen abstract an integrated crustal profile of the intervening trans north china orogen tnco is one of the key issues to understanding the tectonic evolution of the north china craton however the existing geological studies focus only on the surface mapping based petrological geochemical and structural analysis but lack subsurface geophysical evidence and thus make the crustal profile interpretations ambiguous in contrast the current geophysical data covers a very large scale lithospheric mantle and fails to image the detailed structural pattern of the orogenic crust to achieve this goal we present high resolution aeromagnetic data for the hengshan wutai fuping region the largest exposure of the central tnco the reduced to pole magnetic anomaly map firstly verifies the regional tectonic subdivision that the high grade metamorphic terranes i e hengshan and fuping complexes are consistent with high magnetic responses and long wavelength anomalies intervened by a low grade terrane wutai complex characterized by low magnetic responses and short wavelength anomalies 3d euler deconvolution reveals that the tendencies of the clustered solutions show large consistence with the major structural pattern of the region which is characterized by a fan shaped doubly vergent orogenic wedge upward continuation further shows that the northwest part of the orogen yields a thicker crust and is most likely located closer to the paleosubduction zone the new aeromagnetic data combined with structural petrological and metamorphic data indicate that an eastward dipping subduction zone was most possibly active before the collision of the western and eastern blocks leading to the formation of the tnco and the final amalgamation of the north china craton

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

constructing constitutive relationships for seismic and aseismic fault slip for the purpose of modeling natural fault slip a useful result from an experimental fault mechanics study would be a physically based constitutive relation that well characterizes all the relevant observations this report describes an approach for constructing such equations where possible the construction intends to identify or at least attribute physical processes and contact scale physics to the observations such that the resulting relations can be extrapolated in conditions and scale between the laboratory and the earth the approach is developed as an alternative but is based on ruina 1983 and is illustrated initially by constructing a couple of relations from that study in addition two example constitutive relationships are constructed these describe laboratory observations not well modeled by ruina s equations the unexpected shear induced weakening of silica rich rocks at high slip speed goldsby and tullis 2002 and fault strength in the brittle ductile transition zone shimamoto 1986 the examples provided as illustration may also be useful for quantitative modeling

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

complex evolution of transient slip derived from precise tremor locations in western shikoku japan transient slip events which occur more slowly than traditional earthquakes are increasingly being recognized as important components of strain release on faults and may substantially impact the earthquake cycle surface based geodetic instruments provide estimates of the overall slip distribution in larger transients but are unable to capture the detailed evolution of such slip either in time or in space accompanying some of these slip transients is a relatively weak extended duration seismic signal known as nonvolcanic tremor which has recently been shown to be generated by a sequence of shear failures occurring as part of the slip event by precisely locating the tremor we can track some features of slip evolution with unprecedented resolution here we analyze two weeklong episodes of tremor and slow slip in western shikoku japan we find that these slip transients do not evolve in a smooth and steady fashion but contain numerous subevents of smaller size and shorter duration in addition to along strike migration rates of 10 km d observed previously much faster migration also occurs usually in the slab dip direction at rates of 25 150 km h over distances of up to 20 km we observe such migration episodes in both the updip and downdip directions these episodes may be most common on certain portions of the plate boundary that generate strong tremor in intermittent bursts the surrounding regions of the fault may slip more continuously driving these stronger patches to repeated failures tremor activity has a strong tidal periodicity possibly reflecting the modulation of slow slip velocity by tidal stresses

structural pattern of the wutai complex and its constraints on the tectonic framework of the trans north china orogen abstract wutai complex is a key to test controversial models for the tectonic evolution of the trans north china orogen tnco along which the eastern and western blocks amalgamated to form the north china craton three stages of deformation d 1 to d 3 were identified in the wutai complex d 1 is characterized by ne sw trending foliations s 1 and nw se orientated lineations l 1 indicating an initial nw se directed compression associated with d 1 was prograde metamorphism m 1 d 2 progressively overprinted d 1 and generated z shaped folds and nee sww trending ductile shear zones d 2 resulted in a fan shaped structural pattern of the complex with top to the nw thrusting in the northwestern part and opposite top to the se thrusting in the southeastern part during d 2 the crust was doubled through thickening leading to peak metamorphism m 2 d 3 developed during post collision exhumation and deformed the early fabrics to be open folds resulting in near isothermal decompression m 3 and late cooling metamorphism m 4 the overall structure of the wutai complex is characterized by a fan shaped pattern with structural divergence structural features of the wutai complex combined with those of the adjacent hengshan and fuping complexes indicate that the tnco is characterized by a fan shaped orogenic wedge with opposite senses of thrust this orogenic wedge could have resulted from an eastward subduction and collision between the western and eastern blocks to finally form the tnco at 1 85 ga

quasi dynamic 3d modeling of the generation and afterslip of a tohoku oki earthquake considering thermal pressurization and frictional properties of the shallow plate boundary the generation of the 2011 tohoku oki earthquake has been modeled by many authors by considering a dynamic weakening mechanism such as thermal pressurization tp because the effects of tp on afterslip have not been investigated this study develops a 3d quasi dynamic model of the earthquake cycle to investigate afterslip of the tohoku oki earthquake considering tp and the geometry of the plate boundary we employ several velocity weakening vw patches for mw 7 class events and two large shallow vw patches the frictional properties are set as velocity strengthening vs outside the vw patches the results show that during megathrust earthquakes fast slip propagates to the surrounding vs regions near the vw patches owing to weakening by tp following mw 9 events large afterslips occur in regions below the northern shallow rupture area in the off fukushima region close to the japan trench which is consistent with observations in the vs region near the vw patches during the early afterslip period frictional behavior exhibits less vs with increasing slip velocity due to pore pressure reduction we also consider the frictional properties of the shallow plate boundary fault off tohoku which exhibits a transition from vw to vs from low to high slip velocities the results show the occurrence of slow slip events sses at intervals of a few decades at the shallow plate boundary during megathrust events the vw property at low slip velocity promotes slip along the shallow sse region more than the case with vs property throughout the entire velocity range

slow slip events controlled by the slab dip and its lateral change along a trench abstract several slow slip events sses have recently been globally detected at subduction zones by analyses of high precision gps data they occur at the transition zone from seismogenic to stable sliding ones but seem to occur at restricted areas though researchers have proposed some generation mechanisms of sse they made no mention of such restricted occurrence areas of sse to explain why sses occur in some restricted area we compile the features of globally detected sses and we find that the slab dip and its lateral change are important factors for controlling their occurrences through simulations of earthquake cycle including sses using a simplified cell model we examine the effect of dip angle at the transition zone on the interseismic sses the remarkable sses occur several times in a seismic cycle at the cell with a smaller dip while at the cell with a larger dip few small sses occur and attenuate in the interseismic term actually sses occur only at the area with the smallest dip at the transition zone moreover in the case where cells are placed at the neighbor of the existing cell in the lateral direction sses are restrained to become smaller if the dips of cells are the same to the contrary the cells with different dips do not restrain sses this result well explains the observed feature that sses occur at the area where the dip of the plate is laterally changing in addition it is also reproduced that a cell with a smaller dip angle has sses with a longer interval and longer duration these simulation results are understood in terms of the frictional condition related to the dip dependent stiffness of plate interface that is the stress accumulation due to the plate subduction relative to the critical stiffness determined by frictional parameters and the stress interaction which is also dependent on the dip angle

fault model for preseismic deformation at parkfield california we construct an earthquake instability model to estimate precursory faulting and ground deformation before the next moderate m 5 5 6 earthquake on the san andreas fault near parkfield california the quasi static model simulates fault slip fault shear stress and ground deformation for all stages of repeated earthquake cycles unstable slip which is the analog of a moderate parkfield mainshock is caused by overall failure of a postulated strong area or patch of the fault zone the brittle patch and surrounding weaker viscous fault are defined by the sign of a spatially varying coefficient of a slip rate dependent fault law stable failure of the patch leading up to mainshock failure causes slip rate to increase at depth amplitudes and timescales of the resulting preseismic deformation anomalies are found for the current earthquake cycle at parkfield starting just after the 1966 mainshock in two ways in the first way we vary parameter values in a sequence of simulations so as to find the simulation giving best agreement with locations moments and recurrence times of past moderate earthquakes and also with fault creep and trilateration line length changes since the 1966 mainshock in the second way we assign values of most parameters from laboratory friction experiments and a temperature depth profile inferred from heat flow data overall agreement between model results and observations is comparable for the two methods in all simulations preseismic deformation anomalies arise from slip rate increase near the model earthquake focus and start several years or less before instability preseismic anomalies in surface fault creep and line length are always too small to detect in current measurements however for some simulations constrained mainly by field data the predicted anomalies in borehole dilatation are large enough to detect

non volcanic tremor resulting from the combined effect of earth tides and slow slip events swarms of non volcanic tremor in southeastern japan are associated with slow slip events and tend to occur with a periodicity of 12 or 24 h this periodicity can be reproduced by a combination of stresses due to earth tides and transient stress changes caused by slow slip events non volcanic tremors may therefore be useful for understanding stress relaxation at the subduction zone interface slow slip events1 are accompanied by swarms of non volcanic tremor2 3 along the subduction zone of the philippine sea plate in southwest japan the swarms often occur with a periodicity of about 12 or 24 h refs 4 5 these episodic events are considered to be a manifestation of stress relaxation at the subducting plate interface1 6 7 here we analyse seismic data to record the locations and durations of non volcanic tremor swarms that occurred in may 2005 and february 2006 we evaluate the magnitude of stress changes produced by slow slip events as well as the effective normal stress on the plate interface where slow slip events occur we find that the observed periodicity in tremor occurrence originates from a combined effect of the periodic stress due to earth tides and the transient stress due to slow slip events our calculations show that non volcanic tremor is sensitive to stress change this phenomenon can therefore be effective in monitoring the process of stress relaxation at subducting plate interfaces

a slow thrust slip event following the two 1996 hyuganada earthquakes beneath the bungo channel southwest japan we report a slow thrust slip event that occurred beneath the bungo channel region southwestern japan on oct and dec 1996 two hyuganada earthquakes both mw 6 7 followed by afterslips occurred in addition a crustal movement characterized by an extremely slow rise was observed around the bungo channel about 200 km north from the epicenters and continued for about 300 days long assuming a slow slip on the plate boundary we estimate its duration and surface displacements from gps time series data by curve fitting and then determine the fault slip distribution we found that a slow slip without any earthquakes continued for nearly one year and released the seismic moment comparable to that of the hyuganada earthquakes occurrence of the slow thrust slip event suggests that this kind of event may be a characteristic mode of stress release at a transition region of interplate coupling

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

evolution of seismic signals and slip patterns along subduction zones insights from a friction lab scale experiment 1 we investigate the influence of the cumulative slip on the frictional and acoustic patterns of a lab scale subduction zone shallow loud earthquakes medium depth slow deeper silent quakes and deepest steady state creep are reproduced by the ageing of contact interface with cumulative displacement the acoustic emission evolves with cumulative displacement and interface ageing following a trend from strong impulsive events similar to earthquake seismic signals to a collection of smaller amplitude and longer duration signals similar to nvt the latter emerge as the local recollection of the unstable behaviour of the contact interface globally evolving towards the stable sliding regime

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

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

earthquakes as multiscale dynamic ruptures with heterogeneous fracture surface energy 1 we propose a model of the wide scale growth of dynamic rupture during an earthquake based on our multiscale simulation of a planar crack in a three dimensional homogeneous elastic space a simple slip weakening law governs the fracture friction processes and its characteristic parameters slip weakening distance and fracture surface energy have multiscale heterogeneous distributions we consider a set of randomly distributed circular patches whose diameter is proportional to the fracture surface energy each patch represents an asperity between irregular fault surfaces and the size number relation of the patches obeys power law statistics we assess rupture propagation from a small instability using a boundary integral equation method with a renormalization technique although most events stop shortly after their initiation some grow triggering neighboring patches of similar size small and large events show statistically self similar properties of rupture growth and stop spontaneously without requiring a special stopping mechanism the rupture velocity locally exceeds the shear wave speed but globally remains subshear speed due to the increase of the average fracture energy as the rupture grows the relation between size and frequency of events is a power law which is explained by the triggering probability between patches as a consequence of statistically self similar random triggering growth we observe a distinct main phase in seismic waves similar to those of natural earthquakes but we cannot estimate the final size of the event from the initial part of the seismic waves if this is true for the real earthquakes predicting the size of a future earthquake would be quite difficult

scaling relationships of source parameters for slow slip events to better understand the physical mechanisms of slow slip events sses detected worldwide we explore the scaling relationships of various source parameters and compare them with similar scaling laws for earthquakes these scaling relationships highlight differences and similarities between slow slip events and earthquakes and hold implications for the degree of heterogeneity and fault healing characteristics the static stress drop remains constant for different sized events as is observed for earthquakes however the static stress drop of slow slip events is within a range of 0 01 1 0 mpa 1 2 orders of magnitude lower than that found for earthquakes which could be related to the low stress state on the fault the average rupture velocity ranging from kilometers per second to kilometers per day decreases linearly with increasing seismic moment in log log space unlike earthquakes that are nearly constant this inverse relationship of rupture velocity with seismic moment could be related to the heterogeneity of fault properties slow slip events typically have ratios of event duration over dislocation rise time less than 3 while earthquakes have ratios greater than 3 this indicates that slow slip events are less pulselike than earthquakes in their mode of propagation and suggests that the healing behind the rupture front is delayed the recurrence statistics of slow slip events on the northern cascadia subduction zone are weakly time predictable and moderately antislip predictable that is the event size and preevent recurrence interval are anticorrelated which may indicate that healing between events strengthens the fault with time online material table of source parameters and data sources

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

phenomenology of deep slow earthquake family in southwest japan spatiotemporal characteristics and segmentation 1 the phenomenology of deep slow earthquakes including low frequency tremors very low frequency earthquakes and short term slow slip events on the subducting plate interface in southwest japan is investigated on the basis of their spatiotemporal characteristics the belt like distribution of tremors is divided into segments bounded by gaps the repetition of tremor episode depends on the magnitude of the episode which is defined by the number of detected tremors within each episode major tremor episodes with a large number of detected tremors recur at an interval of approximately 6 months accompanying the short term slow slip events in large segments in small segments tremor episodes with small numbers of tremors have recurrence intervals of a few months some of them occasionally accompany the slight ground tilting caused by a small size slow slip event even in the same segment there exist different recurrence intervals according to the magnitude of the tremor episode the migration pattern varies greatly in initiation termination direction and speed however the migration direction has a general tendency for each segment on both sides of the gap the tremor starts next to the gap and propagates to the other side assuming all tremor episodes are caused by slow slip events the equivalent moment and slip are estimated from the number of detected tremor counts and the area of each tremor episode the equivalent slip history estimated from all tremor episodes is almost constant in each segment this indicates that tremor activity is a good proxy for slow slips

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

modeling short and long term slow slip events in the seismic cycles of large subduction earthquakes 1 slow slip events sses occur in the deeper extents of areas where large interplate earthquakes are expected in subduction zones such as the nankai region of japan and the cascadia region of north america in the nankai region sses are divided into long and short term sses depending on their duration and recurrence interval we modeled and examined the occurrence of long and short term sses and changes in their behavior during the seismic cycles of large interplate earthquakes in these numerical simulations we adopted a rate and state dependent friction law with cutoff velocities and assumed that the distribution of pore fluid controls the recurrence interval of both long and short term sses the recurrence intervals of reproduced short term sses decrease during a long term sse as observed in western shikoku in the nankai region the recurrence intervals of both types of sses become shorter in the later stages of interseismic periods large interplate earthquakes nucleate between the region where sses occur and the locked region of the large earthquakes as suggested from observations of the 1944 tonankai earthquake our numerical results suggest that the stress buildup process in a seismic cycle affects the recurrence behavior of sses

slow earthquakes and nonvolcanic tremor nonvolcanic tremor is observed in close association with geodetically observed slow slip events in subduction zones accumulating evidence points to these events as members of a family of slow earthquakes that occur as shear slip on the downdip extensions of fault zones in a regime that is transitional between a frictionally locked region above and a freely slipping region below by virtue of their locations and their properties slow earthquakes are certain to provide new insights into the behavior of earthquakes and faulting and into the hazard they embody

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

high pore fluid pressure may cause silent slip in the nankai trough silent slip events have been detected at several subduction zones but the cause of these events is unknown using seismic imaging we detected a cause of the tokai silent slip which occurred at a presumed fault zone of a great earthquake the seismic image that we obtained shows a zone of high pore fluid pressure in the subducted oceanic crust located down dip of a subducted ridge we propose that these structures effectively extend a region of conditionally stable slips and consequently generate the silent slip

dynamic simulations of slip on a smooth fault in an elastic solid we report on numerical simulations of slip evolution along a two dimensional slip varies only with depth vertical strike slip fault in an elastic half space using a framework incorporating full inertial elastodynamics the model is a follow up on earlier quasi static and quasi dynamic simulations of deformations along smooth fault systems in elastic continua the fault is driven below a crustal depth of 24 km by a constant plate velocity of 35 mm yr deformation at each fault location in the crustal zone is the sum of slip rate contributions from rate and state dependent friction and power law creep where both processes have temperature dependent and hence depth varying coefficients and both take place locally under the same stress the simulations employ two versions of rate and state dependent friction a slip law which requires nonzero velocity for state evolution and an ageing slowness law which incorporates state evolution and restrengthening in stationary contact the assumed constitutive laws and distribution of frictional parameters are compatible with laboratory experiments the elastodynamic calculations are based on spectral representations of variables and a new algorithm providing a unified computational framework for calculations of long deformational histories containing short periods of rapid instabilities the simulations show dynamic rupture propagation and wave phenomena not accounted for in the previous quasi static and quasi dynamic works however the results are qualitatively similar to those obtained by corresponding quasi static and quasi dynamic calculations slip histories along a smooth fault simulated here with full elastodynamics for various constitutive laws and model parameters consist mostly of quasi periodic large events this finding indicates that inertial dynamics does not provide a generic mechanism for generating spatio temporal complexities of slip on the other hand calculations done for cases representing approximately strongly disordered systems do show rich slip histories with a range of event sizes this result is compatible with our previous conclusions that the origin of observed broad distributions of earthquake sizes is strong fault zone heterogeneities the fully dynamic calculations illustrate the evolution of nucleation phases of instabilities associated with accelerating and expanding creep final slip values of model earthquakes in full elastodynamic calculations are larger than those of corresponding quasi static and quasi dynamic events the dynamic overshoot in simulations with the slip version of friction is larger than in those employing the ageing slowness law

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

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

laterally propagating slow slip events in a rate and state friction model with a velocity weakening to velocity strengthening transition we investigate the behavior of simulated slow slip events using a rate and state friction model that is steady state velocity weakening at low slip speeds but velocity strengthening at high slip speeds our simulations are on a one dimensional line fault but we modify the elastic interactions to mimic the elongate geometry frequently observed in slow slip events simulations exhibit a number of small events as well as periodic large events the large events propagate approximately steadily along strike and stress and slip rate decay gradually behind the propagating front their recurrence intervals can be determined by considering what is essentially an energy balance requirement for long distance propagation it is possible to choose the model parameters such that the simulated events have the stress drops slip velocities and propagation rates observed in cascadia

foreshocks and pre events associated with the nucleation of large earthquakes we propose a theoretical model which can explain the occurrence of foreshocks and pre events associated with the nucleation of large earthquakes we consider a broad weak zone with a locally strong part asperity on a fault plane in a two dimensional framework and examine the transition process from quasistatic nucleation to high speed rupture propagation through numerical simulations the dynamic rupture of the asperity occurs in three different manners as aseismic slip foreshock or pre event depending on the peak stress of the asperity in all cases the rupture of the asperity accelerates the nucleation of main rupture

large earthquakes initiate by the acceleration of slips on the downward extensions of seismogenic faults abstract in order to examine the relationship between anomalous crustal deformations and subsequent large earthquakes we compiled and examined data on preseismic anomalous crustal deformations for two earthquakes that occurred in and around the japanese islands in recent years we found that the slip on a downward extension of a seismogenic fault accelerates before the main shock and that the average slip velocity is inversely proportional to the time remaining until the main shock occurs

frictional properties of jfast core samples and implications for slow earthquakes at the tohoku subduction zone slow earthquakes occur in the shallow 20 km deep part of the tohoku subduction zone to understand how frictional properties of the plate boundary fault affect the generation of these slow earthquakes we conducted friction experiments using borehole samples retrieved from the plate boundary decollement and footwall during integrated ocean drilling program expedition 343 japan trench fast drilling project jfast the plate boundary fault material exhibits a transition from velocity strengthening to velocity weakening behavior at temperatures between 50 and 150 c which in the framework of rate and state friction laws is a necessary condition for the generation of slow earthquakes whereas the footwall sample mainly shows velocity strengthening behavior except at temperatures of 50 c the downdip temperature limit of slow earthquakes in the japan trench also lies between 100 and 150 c our results suggest that the frictional properties of the plate boundary fault may play a key role in controlling the locations of observed slow earthquakes

aseismic slip transients emerge spontaneously in three dimensional rate and state modeling of subduction earthquake sequences 1 to investigate the possible physical mechanisms of recently observed aseismic slip events in the cascadia japan and mexico subduction zones we apply a dieterich ruina rate and state friction law to a three dimensional model of a shallow subduction fault that is loaded by imposed steady plate slip rate far downdip along the thrust interface friction properties are temperature and hence depth dependent such that sliding is stable at depths below about 30 km the system is perturbed into a significantly nonuniform slip mode along strike by introducing small along strike variations in the constitutive parameters a and a b in addition to large heterogeneous earthquake slip at seismogenic depths and associated postseismic transients we found that slip events which have clearly aseismic slip rates emerge spontaneously around the downdip end of the seismogenic zone both transients which start well after a seismic event and those which are triggered by other transients are observed from the simulations the slip velocity depth range and sometimes along strike migration speed of simulated transients are similar to the observations from natural subduction zones unstable stable transitional friction properties near the downdip end of the seismogenic zone are suggested to be an ingredient allowing such transients simulated transients can weaken the locking intensity of the updip seismogenic zone while enhancing that of the transition zone spatial temporal correlation of aseismic transients and nearby seismicity in the guerrero mexico area suggests that transients may signal a period of increased probability for nucleating their high frequency counterparts as damaging subduction thrust events

high pressure granulites in the sanggan area north china craton metamorphic evolution p t paths and geotectonic significance high pressure basic granulites are widely distributed as enclaves and sheet like blocks in the huaian ttg gneiss terrane in the sanggan area of the central zone of the north china craton four stages of the metamorphic history have been recognised in mineral assemblages based on inclusion exsolution and reaction textures integrated with garnet zonation patterns as revealed by compositional maps and compositional profiles the p t conditions for each metamorphic stage were obtained using thermodynamically and experimentally calibrated geothermobarometers the low ca core of growth zoned garnet along with inclusion minerals defines a prograde assemblage m1 of garnet clinopyroxene plagioclase quartz yielding 700 c and 10 kbar the peak of metamorphism at about 750 870 c and 11 14 5 kbar m2 is defined by high ca domains in garnet interiors and inclusion minerals of clinopyroxene plagioclase and quartz kelyphites or coronas of orthopyroxene plagioclase magnetite around garnet porphyroblasts indicate garnet breakdown reactions m3 at conditions around 770 830 c and 8 5 10 5 kbar garnet exsolution lamellae in clinopyroxene and kelyphites of amphibole plagioclase around garnet formed during the cooling process at about 500 650 c and 5 5 8 kbar m4 these results help define a sequential p t path containing prograde near isothermal decompression itd and near isobaric cooling ibc stages the clockwise hybrid itd and ibc p t paths of the hp granulites in the sanggan area imply a model of thickening followed by extension in a collisional environment furthermore the relatively high pressures 6 14 5 kbar of the four metamorphic stages and the geometry of the p t paths suggest that the hp granulites together with their host huaian ttg gneisses represent the lower plate in a crust thickened during collision the corresponding upper plate might be the tectonically overlying khondalite series which was subjected to medium to low pressure mp lp 7 4 kbar granulite facies metamorphism with a clockwise p t path including an itd segment both the hp and the mp lp granulite facies events occurred contemporaneously at c 1 90 1 85 ga in a collisional environment created by the assembly process of the north china craton

periodic slow earthquakes from the cascadia subduction zone continuous geodetic measurements from convergent margins have shown that deep transient creep events can release large amounts of strain energy without detectable seismic shaking and they are thus known as slow or silent earthquakes because subduction zones generate the largest earthquakes

slow earthquakes coincident with episodic tremors and slow slip events we report on the very low frequency earthquakes occurring in the transition zone of the subducting plate interface along the nankai subduction zone in southwest japan seismic waves generated by very low frequency earthquakes with seismic moment magnitudes of 3 1 to 3 5 predominantly show a long period of about 20 seconds the seismicity of very low frequency earthquakes accompanies and migrates with the activity of deep low frequency tremors and slow slip events the coincidence of these three phenomena improves the detection and characterization of slow earthquakes which are thought to increase the stress on updip megathrust earthquake rupture zones

an early cretaceous carbonate replacement origin for the xinqiao stratabound massive sulfide deposit middle lower yangtze metallogenic belt china stratabound massive sulfide deposits are widespread along the middle lower yangtze metallogenic belt mlymb and serve as an important copper producer in china two contrasting genetic models have been proposed interpreting the stratabound massive sulfide deposits as a carboniferous sedex protore overprinted by cretaceous magmatic hydrothermal system or an early cretaceous carbonate replacement deposit these two contrasting models have been applied to the xinqiao stratabound cu au sulfide deposit which is dominated by massive sulfide ores hosted in marine carbonates of the carboniferous chuanshan and huanglong formations with minor cu au skarn ores localized in the contact zone between the cretaceous diorite jitou stock and the carboniferous carbonate rocks new sims zircon u pb dating suggests that the jitou stock formed at 138 5 1 1 ma 2 mswd 0 6 pyrite re os dating yields an imprecise date of 142 47 ma 2 mswd 7 8 the geochronological data thus constrain the mineralization of the xinqiao deposit at early cretaceous fluid inclusions in prograde skarn diopside have homogenization temperatures of 450 600 c and calculated salinities of 13 58 wt nacl equiv quartz from the stratabound ores and pyrite quartz vein networks beneath the stratabound ores have homogenization temperatures of 290 360 and 200 300 c with calculated salinities of 5 12 and 2 10 wt nacl equiv respectively quartz from the skarn ores and veins beneath the stratabound ores have 18o values of 12 32 0 55 2 sd n 22 and 15 57 1 92 2 sd n 60 respectively corresponding to calculated 18o values of 6 22 1 59 2 and 6 81 2 76 2 for the equilibrated ore forming fluids the fluid inclusion and oxygen isotope data thus support a magmatic hydrothermal origin rather than a sedex system for the stratabound ores with the hydrothermal fluids most likely being derived from the jitou stock or associated concealed intrusion results from this study have broad implications for the genesis and exploration of other stratabound massive sulfide deposits along the mlymb

zircon u pb hf isotopes and geochemistry of two contrasting neoarchean charnockitic rock series in eastern hebei north china craton implications for petrogenesis and tectonic setting abstract the zunhua qinglong microblock in eastern hebei north china craton exposes two contrasting charnockitic rock series in the yuhuzhai taipingzhai and cuizhangzi areas charnockitic plagioclase gneiss series with chemical compositions of dioritic and tonalitic rocks and charnockite series showing tonalitic and granodioritic components petrographic observation reveals that two types of orthopyroxenes are preserved in these rocks medium fine grained anhedral orthopyroxenes are preserved in both series and coarse grained subhedral orthopyroxenes are preserved only in the charnockite series in situ trace element analyses reveal that the coarse grained subhedral orthopyroxenes exhibit typical chemical features of magmatic orthopyroxene whereas the medium fine grained anhedral orthopyroxenes display lower medium to heavy rare earth elements ree and no obvious eu anomalies resulting in left inclined ree patterns combined with petrographic features these new data indicate that the medium fine grained anhedral orthopyroxenes were formed by granulite facies metamorphism caused by dehydration reactions whereas the coarse grained subhedral orthopyroxenes were directly crystallized from their magmatic precursors laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb isotopic dating reveals that the magmatic precursors of the charnockitic plagioclase gneiss series were emplaced between 2530 17 and 2523 12 ma and those of the charnockite series were emplaced between 2527 28 and 2515 22 ma we conclude that these magmatic precursors are contemporaneous emplacements of two neoarchean granitoid magmatic events which were followed by regional granulite facies metamorphism at 2 45 ga the charnockitic plagioclase gneiss series and charnockite series exhibit similar hf t values of 2 4 to 5 3 and 3 2 to 5 5 indicating either depleted mantle or juvenile crust affinity and involvement of ancient crustal components the charnockitic plagioclase gneiss series exhibit relatively low sio2 contents 54 1 65 2 with various mgo contents 1 93 5 36 mg 0 36 0 55 and la yb n values 3 49 56 00 the charnockite series exhibit higher sio2 contents 60 1 69 2 with similar la yb n values 14 61 42 69 mgo contents 2 10 3 99 and mg 0 29 0 52 these geochemical and zircon lu hf isotopic features together with chemical modeling suggest that the magmatic precursors of the charnockitic plagioclase gneiss series may have been primarily derived from the partial melting of a depleted mantle that was metasomatized by slab derived melts fluids and experienced fractional crystallization processes with hornblende and plagioclase as primary fractionated phases the aforementioned features further suggest that the charnockite series originated from a partial melting of the subducted slab and it was strongly contaminated by mantle peridotites these new data combined with the previous studies of neoarchean basement rocks in the zunhua qinglong microblock in eastern hebei suggest that the magmatic precursors of these two contrasting charnockitic rock series were formed in a back arc related tectonic environment at a convergent plate margin

bridging the gap between seismically and geodetically detected slow earthquakes 1 recently observed unusual seismic events deep low frequency earthquakes and tremor very low frequency earthquakes and slow slip events form a family of slow earthquakes that are governed by a scaling law different from ordinary earthquakes guided by this scaling law we have observed previously unknown events with source duration of 20 200 s and moment magnitude of 3 4 under the kii peninsula in western japan these events radiate seismic energy in the 2 8 hz band in direct proportion to their seismic moment rate though the constant of proportionality is 4 5 orders of magnitude smaller than for ordinary earthquakes slow earthquakes in this region may be comprised of numerous shear slip events which in aggregate are manifest seismically as tremor or isolated longer events up to 200 s and geodetically as slow slip events

episodic aseismic slip in a two degree of freedom block spring model 1 we consider a two degree of freedom block spring model in which two blocks block 1 and block 2 are connected by a spring and driven by a slowly moving driver assuming a rate and state dependent friction law we set the friction parameters such that dynamic instability occurs at block 1 episodic aseismic slip occurs at block 2 when its frictional parameters are near the stability transition when the stress has accumulated to approximately a steady state level during an interseismic period block 2 starts a slow slip quasi static oscillation in the stress and slip velocity occurs with decaying fluctuation amplitudes leading to the steady state values the decaying oscillation could be a plausible generation mechanism of the episodic aseismic slip observed in the tokai district japan since 2001 we also consider various slip modes on a plate boundary based on this two block model associated with the interaction between different frictional properties

zircon u pb hf isotope systematics and geochemistry of helong granite greenstone belt in southern jilin province china implications for neoarchean crustal evolution of the northeastern margin of north china craton abstract as one of the major neoarchean granite greenstone belts in china the helong terrane is located at the northeastern margin southern jilin province of the north china craton ncc it is dominated by metamorphic supracrustal rock assemblage and granitoid gneiss the former contains amphibolite hornblende plagioclase gneiss biotite plagioclase gneiss and banded iron formation bif whereas the latter is dominated by the tonalite trondhjemite granodiorite ttg gneisses zircon la icp ms u pb isotopic analyses indicate that the supracrustal rock assemblage was formed at 2683 2654 ma and underwent regional metamorphism lower amphibolite facies at 2614 2553 ma before the widespread emplacement of plutonic granitoids at 2551 2532 ma both greenstone sequence and plutonic granitoid rocks experienced the subsequent regional metamorphism greenschist to lower amphibolite facies at 2508 2400 ma the supracrustal rocks can be divided into three groups based on their lithological and geochemical characteristics detailed petrogenetic and geochemical studies suggest that the group 1 amphibolite samples were derived from partial melting of depleted upper mantle that had been metasomatized by slab derived fluids group 2 amphibolite samples were derived by partial melting of a depleted mantle wedge that was strongly metasomatized by subduction derived fluids or melts and group 3 hornblende biotite plagioclase gneiss samples were derived from partial melting of juvenile basalt and minor amounts of older sediments in the lower crust level the granitoid gneisses in the helong granite greenstone belt can be divided into relatively high magnesium group hmg and low magnesium group lmg the hmg samples were derived from parental magmas generated by partial melting of juvenile basalt and minor amounts of older sediments within the lower crust level whereas magmatic precursors of the lmg samples were generated by partial melting of a metapelite dominated source under lower temperature melting conditions u pb dating of inherited or captured zircons combined with zircon lu hf isotope data indicates a significant 2 9 2 7 ga crustal growth episode whereas the 2 55 2 53 ga magmatism involved crustal recycling in the helong terrane consequently the helong terrane preserves a record of neoarchean tectonic environment of andean type active continental margin

qingyuan high grade granite greenstone terrain in the eastern north china craton root of a neoarchaean arc abstract the qingyuan high grade granite greenstone terrain is one of the first recognized granite greenstone terrains in the eastern north china craton similar to other archaean terrains its tectonic environment is debated was it an intra continental rift or a modern analogy of arc occurrence and petrogenesis of major igneous series the ultramafic mafic and felsic volcanic rocks 2510 ma and the plutons of the quartz diorite 2570 2510 ma ttg 2570 2510 ma and quartz monzodiorite 2510 2490 ma series in xinbin area are investigated the mafic intrusives and volcanic rocks have high mgo content 5 4 7 5 wt and mg number 48 61 they show slightly depleted to flat trace element patterns the ultramafic rocks serpentinite could be genetically related to the mafic rocks the meta dacite rhyolite is adakitic with enriched light and middle rees and liles but significantly depleted hfses the quartz diorite has high mg number 60 64 moderately enriched light and middle rees and liles the ttg shows distinct light but moderate middle ree enrichment prominent nb ta depletion but zr hf enrichment zr sm 100 the quartz monzodiorite has moderate light and middle ree enrichment significant nb ta depletion and negative eu sr anomalies the ttg has more depleted sr nd isotopes endt 2 6 87sr 86srt 0 700 than all the others endt 0 2 87sr 86srt 0 701 703 their petrogenesis can be explained by an archaean style subduction defined as a mantle wedge absent flat hot subduction with significant vertical tectonism in the overriding slab the ultramafic mafic rocks were originated from primitive mantle the meta dacite rhyolite was originated from the eclogite facies overriding crust the quartz diorite was a mixture of melts from mantle and the overriding crust the ttg was from the subducting slab under amphibolite to amphibole bearing eclogite facies and the quartz monzodiorite was from the subducting slab after the derivation of the ttg the qingyuan terrain represents remnants of the root of a neoarchaean arc its anticlockwise p t path recorded the initiation of the arc to its cession and exhumation cratonization at 2480 ma

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

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 of frictional instability caused by fluid pressurization in subducted blueschist pore pressure is an important factor in controlling the slip instability of faults and thus the generation of earthquakes particularly slow earthquakes are widespread in subduction zones and usually linked to the occurrence of high pore pressure yet the influence of fluid pressure and effective stress on the mechanics of earthquakes is poorly understood therefore we performed shear experiments on blueschist fault rocks which likely exist at depth in cold and old subduction zones to investigate the influence of effective stress on frictional behavior our results show potentially unstable behavior at temperatures characterizing the seismogenic zone as well as a transition from stable to unstable behavior with decreasing effective normal stress which is mechanically equivalent to increasing fluid pressure this transition is a prerequisite for generating slow earthquakes our results imply that high pore pressures are a key factor for nucleating slip leading to both megathrust and slow earthquakes

3 d simulation of the occurrence of slow slip events in the tokai region with a rate and state dependent friction law a slow slip event has been progressing on the plate interface in the area near lake hamana western boundary of the estimated focal region of the tokai earthquake since october 2000 ozawa et al 2002 occurrence of the slow slip was revealed by the gps data of the geographical survey institute the aim of this article is to reproduce the slow slip event in a simulation of plate subduction with a rate and state dependent friction law in which 3d configuration of plate interface is taken into consideration by assigning a zone of large l value within the seismic region where a b is negative we succeeded in producing slow slip events here the a b value expresses the rate dependence of steady state frictional strength and the l value represents the characteristic slip distance over which the state evolves they were found to happen five times during one cycle of interplate earthquakes fifth slow slip event finally brings about the catastrophic rupture the moment release rate of the preslip is 10 to 100 times as large as that of the preceding slow slip events on average a seismic moment equivalent to m w 6 7 to 7 0 is released by slow slip events each year while the moment magnitude of the earthquake is m w 8 3 duration of slow slip events is 13 to 15 years except for the last one that starts several years before the earthquake the temporal change of volumetric strain produced by the preslip is significantly different from that of the preceding slow slip events that is the moment release rate accelerates in the preslip while it is almost constant in the preceding slow slip events in the present model slow slips occur in rather large areas this may be caused by an assignment of a large l value in the seismic region both spatial inhomogeneity in l and curvature of the plate interface are considered indispensable to create appropriate inhomogeneous stress fields that generate slow slip events and then eventually a preslip and a great earthquake

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

spontaneous and triggered aseismic deformation transients in a subduction fault model 1 aseismic deformation transients can emerge as a natural outcome of the rate and state friction processes revealed in laboratory fault sliding experiments when that constitutive formulation is applied to model subduction earthquake sequences transients can arise spontaneously for certain effective stress variations with depth we show that if interstitial fluids are present and pore pressure is near lithostatic around and downdip from the frictional stability transition transients with recurrence intervals of 1 year are predicted on the basis of laboratory friction parameters and their temperature hence depth variations the recurrence interval decreases with and reaches 14 months when is 2 3 mpa dimensional analysis and numerical studies show that the fault response primarily depends on a parameter w h here the high pore pressure zone extends distance w updip from the stability transition and h is the stable patch size for steady sliding evidence that such fluid conditions may actually be present is independently provided by the occurrence of nonvolcanic tremors as apparent responses to extremely small stress changes and by petrological constraints on expected regions of dehydration for the shallow dipping subduction zones where transients are observed transient sequences can also be triggered by a modest one time step like interseismic stress perturbation on the subduction fault due to nearby earthquakes or to pore pressure changes e g during episodes of metamorphic fluid release properties of triggered transients and future thrust earthquakes depend on the interseismic time when the perturbation is introduced its relative location along the subduction fault and its magnitude

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

nucleation and early seismic propagation of small and large events in a crustal earthquake model 1 earthquake nucleation and early seismic propagation are studied in a two dimensional strike slip fault model with depth variable properties the fault is governed by the dieterich ruina rate and state friction law we use an efficient and rigorous numerical procedure for elastodynamic analysis of earthquake sequences on slowly loaded faults developed by lapusta et al 2000 we find that for decreasing values of the characteristic slip distance of the friction law small events appear at the transition from the locked to creeping behavior toward the bottom of the seismogenic zone small and large events have very similar nucleation phases in our simulations here by nucleation phase we mean gradually accelerating aseismic slip in a small slowly expanding zone before the breakout of the dynamic seismically detectable event moment acceleration to which velocity seismograms are proportional in early stages of seismic propagation exhibits irregular fluctuations in the form of speedups and slowdowns in the moment release rate consistently with observations as reported by ellsworth and beroza 1995 our simulations show that such irregular moment acceleration can at least in part be due to the heterogeneous stress distribution imprinted on the fault by the arrest of previous small events and by stress concentrations at the borders of creeping regions and to partial arrest of the rupture in velocity strengthening fault regions which inhibit seismic slip index terms 7209 seismology earthquake dynamics and mechanics 7260 seismology theory and modeling 3220 mathematical geophysics nonlinear dynamics 7230 seismology seismicity and seismotectonics 3230 mathematical geophysics numerical solutions 8164 tectonophysics stresses crust and lithosphere keywords earthquake nucleation phase event clustering irregular moment release stress concentrations rate and state friction earthquake sequences

a change in the geodynamics of continental growth 3 billion years ago models for the growth of continental crust rely on knowing the balance between the generation of new crust and the reworking of old crust throughout earth s history the oxygen isotopic composition of zircons for which uranium lead and hafnium isotopic data provide age constraints is a key archive of crustal reworking we identified systematic variations in hafnium and oxygen isotopes in zircons of different ages that reveal the relative proportions of reworked crust and of new crust through time growth of continental crust appears to have been a continuous process albeit at variable rates a marked decrease in the rate of crustal growth at 3 billion years ago may be linked to the onset of subduction driven plate tectonics

time dependent inversion study of the slow thrust event in the nankai trough subduction zone southwestern japan we estimate time variation of interplate coupling between the subducting philippine sea and the overriding continental plates along the western part of the nankai trough japan during the period between 1996 and 1999 after subtracting annual components and average annual velocities deviation from steady crustal deformation in the shikoku and kyushu islands is examined around 15 gps stations facing the bungo channel detected the following three stage ground displacements of up to 3 cm in 1997 with a duration of 1 year 1 increased displacement rate associated with the 1996 hyuga nada earthquakes 2 an increasingly rapid anomalous period of deformation from june 1997 to the end of 1997 and 3 a slowdown period and return to normal rates of deformation after the end of 1997 linearized least squares locate the slip area of this slow event near the plate boundary beneath the bungo channel the estimated slip is opposite the motion of the philippine sea plate these results support the hypothesis that the observed anomalous caistal deformation is due to a rebound process of the philippine sea plate time dependent inversion analysis shows the following slip history during the initial period of increased displacement rate a visible slip area is resolved beneath the coastal area of southwestern shikoku in the next stage of accelerated displacements the slip area expanded southwestward to the bungo channel beginning around june 1997 when postseismic slip of the 1996 hyuga nada earthquakes almost ended after this accelerated period the estimated thrust slip ends with time

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

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

stressing of the new madrid seismic zone by a lower crust detachment fault a new mechanical model for the cause of the new madrid seismic zone in the central united states is analyzed the model contains a subhorizontal detachment fault which is assumed to be near the domed top surface of locally thickened anomalous lower crust rift pillow regional horizontal compression induces slip on the fault and the slip creates a stress concentration in the upper crust above the rift pillow dome in the coseismic stage of the model earthquake cycle where the three largest magnitude 7 8 earthquakes in 1811 1812 are represented by a single model mainshock on a vertical northeast trending fault the model mainshock has a moment equivalent to a magnitude 8 event during the interseismic stage corresponding to the present time slip on the detachment fault exerts a right lateral shear stress on the locked vertical fault whose failure produces the model mainshock the sense of shear is generally consistent with the overall sense of slip of 1811 1812 and later earthquakes predicted rates of horizontal strain at the ground surface are about 10 7 year 1 and are comparable to some observed rates the model implies that rift pillow geometry is a significant influence on the maximum possible earthquake magnitude

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses

new constraints on megathrust slip stability under subduction zone p t conditions abstract to understand and model subduction zone seismogenesis data are needed on the frictional properties of meta pelitic subduction zone materials under in situ megathrust conditions here we report the results of rotary shear friction experiments on simulated illite quartz fault gouge at an effective normal stress of 170 mpa a pore fluid pressure of 100 mpa at 150 500 c and sliding velocities of 1 100 m s the results show three temperature dependent regimes characterized by velocity strengthening at 150 250 c velocity weakening at 250 400 c and velocity strengthening at 400 500 c the regimes are defined by a decrease in the rate and state friction rsf parameter a b at 150 300 c followed by an increase at 300 500 c these trends correlate with systematic changes in other rsf parameters as well as an increase in friction coefficient above 300 c we explain the effects of increasing temperature in terms of a transition from frictional granular flow 150 250 c through granular flow whereby dilatation is balanced by thermally activated compaction involving stress corrosion cracking scc of quartz clasts 250 400 c to non dilatant slip on the phyllosilicates with accommodation at quartz clasts by scc 400 500 c taking into account the effects of sliding velocity the observed velocity weakening regime broadly explains the extent of the seismogenic zone within subduction megathrusts