spatial distribution of focal mechanisms for interplate and intraplate earthquakes associated with the subducting pacific plate beneath the northeastern japan arc a triple planed deep seismic zone the northeastern japan arc is located in one of the most seismically active subduction zones in the world in this study we relocated hypocenters and determined focal mechanisms of small earthquakes m 5 beneath the arc in order to investigate in detail the stress distribution in and around the descending oceanic plate in the hypocenter relocation we adopted a source region station correction method in which station corrections vary with hypocenter locations we have developed a new focal mechanism determination technique named master solution method which is analogous to the master event method in hypocenter determination we applied the method to p and sh wave amplitude data to obtain 1106 focal mechanism solutions from the new mechanism solutions and relocated hypocenters we found that there occur both low angle thrust fault lt type and downdip compression dc type earthquakes at depths from 40 to 70 km near the aseismic front the dc type events are underlying the lt type events almost all the earthquake clusters are composed of lt type events the western limit of the region where lt type events have occurred is subparallel to the trench axis although it undulates considerably it delineates the westernend of the active region of interplate seismicity furthermore we found that normal fault nf type events also occur at depths from 70 km in the upper plane of the double planed deep seismic zone which is characterized mainly by dc type event these nf type events are distributed only in a thin uppermost portion of the slab close to the plate boundary below these in the lower plane are downdip extension de type events this result indicates that the deep seismic zone in the northeastern japan arc is not double planed but triple planed even beneath the land area which cannot be explained by any simple models

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

earthquake sequence simulations with measured properties for jfast core samples since the 2011 tohoku oki earthquake multi disciplinary observational studies have promoted our understanding of both the coseismic and long term behaviour of the japan trench subduction zone we

scaling of the critical slip distance for seismic faulting with shear strain in fault zones theoretical and experimentally based laws for seismic faulting contain a critical slip distance1 5 dc which is the slip over which strength breaks down during earthquake nucleation on an earthquake generating fault this distance plays a key role in determining the rupture nucleation dimension6 the amount of premonitory and post seismic slip7 10 and the maximum seismic ground acceleration1 11 in laboratory friction experiments d c has been related to the size of surface contact junctions2 5 12 thus the discrepancy between laboratory measurements of dc 10 5m and values obtained from modelling earthquakes 10 2m has been attributed to differences in roughness between laboratory surfaces and natural faults5 this interpretation predicts a dependence of dc on the particle size of fault gouge2 breccia and wear material but not on shear strain here we present experimental results showing that dc scales with shear strain in simulated fault gouge our data suggest a new physical interpretation for the critical slip distance in which dc is controlled by the thickness of the zone of localized shear strain as gouge zones of mature faults are commonly 102 103 m thick12 17 whereas laboratory gouge layers are 1 10 mm thick our data offer an alternative interpretation of the discrepancy between laboratory and field based estimates of dc

stressing of locked patches along a creeping fault an analysis is presented of the stressing of locked patches along a fault zone which is creeping elsewhere the model consists of strike slip faulted elastic lithospheric plates loaded in a manner equivalent to imposition of a remotely uniform tectonic shear stress the fault zone has an inhomogeneous strength distribution both depth wise and along strike it is modeled as being composed of locked patches and freely slipping parts treated as cracks the solution is given with the use of the line spring model which analyzes the problem by thickness averaged plane stress theory for lithospheric plates which slip along a discontinuity cut at the plate boundary as a boundary condition thickness averaged stress and slip at each local section along the cut was related to one another by the result of an antiplane strain analysis of slip for the crack or crack pair which describes the slipping and locked depth ranges at that section the analysis indicates that the slip distribution along creeping parts of the fault as well as the stress distribution along locked patches depends strongly on the geometry of these zones the model is used to examine stress concentrations associated with a slip deficient seismic gap along strike and to study the effect of local irregularities in the margin of a locked region it is also used to simulate slip and stressing processes associated with the creeping portion of the san andreas fault in central california between the presently locked zones of the great 1906 and 1857 ruptures and to constrain the nature of an apparently locked zone at the southeastern end which ruptures in characteristic parkfield earthquakes near fault creep and broadscale displacement data along the fault since the 1966 parkfield earthquake and inferences from seismicity distributions are used limitations of the modeling procedure at short spatial wavelengths prohibit an accurate description of the parkfield locked patch but results suggest that it may be localized and occupy a small fraction of area of the normal seismogenic zone an effective remote stressing rate of order 0 3 10 6 shear modulus yr is inferred together with a less well constrained 30 to 40 km lithospheric thickness for consistency with the displacement data results enable estimates of stress accumulation along the locked 1857 rupture zone and the build up of fracture energy release capability of order 107 j m2 in 150 yr at its lower margin

a model for possible crustal deformation prior to a coming large interplate earthquake in the tokai district central japan we perform numerical simulations of a seismic cycle by applying a laboratory derived friction law to evaluate possible crustal deformations prior to the hypothesized tokai earthquake which is expected to occur in the near future along the suruga trough central japan the frictional force obeying a rate and state dependent friction law is assumed to act on the plate interface in a 2d model of the subduction zone we test two versions of the friction law the so called slowness version and the slip version we select model parameters on the basis of historical documents about past large earthquakes in the tokai district and the present coupling state of the plate interface beneath the tokai district estimated by gps observations simulation results for both the slowness and the slip version are as follows 1 the coupling region of the plate interface becomes narrower with time in the interseismic period 2 the inland crust contracts at a nearly constant rate for most of the interseismic period the contraction rate decreases or a change from contraction to extension takes place before the occurrence of a large interplate earthquake 3 significant abnormal crustal deformation precedes the earthquake and maximum amplitudes about one day before the earthquake exceed the noise levels in the case of clear weather of borehole strainmeters installed in the tokai district 4 the spatiotemporal variation of aseismic sliding on the plate interface perturbs the regional stress field around the source volume of the coming earthquake leading possibly to precursory seismic quiescence in the overriding plate and a change in focal mechanisms of small earthquakes in the subducting slab the most significant difference in the results between the slowness version and the slip version of the friction law is that amplitudes of preslip and crustal deformation just before earthquakes are several times larger for the slowness version than for the slip version although some ambiguity remains in the present model mainly because of the incompleteness of the friction law and the deficiency of observational data constraining model parameters the physical model can be improved through the comparison of predicted crustal deformation with observations continuous and concentrated observations of crustal deformation and seismic activity are thus important in the tokai district to understand quantitatively the sliding process preceding a large interplate earthquake there

contribution of radar interferometry to a two step inversion of the kinematic process of the 1992 landers earthquake we study the rupture process of the 1992 landers earthquake to limit the trade off between slip amplitude and rupture time that affects solutions using only seismological data we adopt a two step approach we first constrain the slip distribution and its uncertainty by independent geodetic data to recover in the second step the temporal details of the rupture propagation the first step consists of an inversion of interferometric data and global positioning system measurements both independently and together to constrain slip distribution on a three segment fault model along both strike and dip direction we use a genetic algorithm to test the uniqueness of the solution and a least squares formulation to find the model which best fits the data we conclude from the results of these geodetic inversions that interferometric data are rich enough to access the slip distribution in the case of the landers earthquake since the surface deformations are more sensitive to shallow slip in our configuration the slip amplitude is better resolved near the surface than at depth the resulting slip distribution is in agreement with geological observations at the surface and confirms the heterogeneous nature of the landers earthquake most of the slip occurs at shallow depths on the homestead valley fault second segment with a maximum value of around 7 m another high slip zone is observed on the johnson valley fault first segment at 8 km depth in the second step we invert strong motion data with the a priori final slip amplitude and its uncertainty deduced from geodetic data to constrain the time history of the rupture process this second step emphasizes a strong variation of the temporal development of the earthquake fast rupture front velocities appear within high slip zones and the rupture slows when it encounters a resistance along the fault on average the rupture front propagates with velocities close to the s wave velocity and terminates about 20 s after initiation the large variations in both slip amplitude and rupture velocity suggest that the rupture process is better described by successively breaking asperities than by a pulse propagating with constant velocity

the 2000 tottori earthquake a shallow earthquake with no surface rupture and slip properties controlled by depth the m w 6 8 tottori earthquake japan does not exhibit any surface trace but was particularly well instrumented strong motion displacement records and gps coseismic data are used to constrain the evolution of the slip on the fault plane in time and space we adopt in this study a two plane fault geometry based on aftershock distributions and analysis of close station records in a first step our inversion allowed surface slip the model obtained has a significant surface slip which contradicts the absence of clear surface slip reported by geologists in a second step models with no slip at the surface buried faults compatible with geological observations have been tested the tests with different fault depths show that when slip is allowed to occur close to the surface the fit to seismological and geodetic data is increased these tests confirm that slip actually occurred at shallow depth despite the nonuniqueness of the solution all the inverted source models show 1 a large slip amplitude patch at a depth of about 4 5 km and 2 relatively small slip in the hypocentral area the rupture velocity is about 2750 m s in the asperity region the total rupture duration is about 8 s the slip distribution seems to be controlled by the variation of fault properties with depth another feature that could control the rupture of this earthquake is a fault plane almost perpendicular to the main fault nw of the epicenter which apparently inhibits further rupture propagation

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

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

initiation and arrest of earthquake ruptures due to elongated overstressed regions the initiation of natural and induced earthquakes is promoted in fault areas where the shear stress is close to fault strength in many important situations these overstressed fault areas or asperities are very elongated for example in the case of a fault intersecting a reservoir subject to fluid injection or the stress concentration along the bottom of a seismogenic zone induced by deep fault creep theoretical estimates of the minimum overstressed asperity size leading to runaway rupture and of the final size of self arrested ruptures are only available for 2d problems and for 3d problems with an asperity aspect ratio close to one in this study we determine how the nucleation of ruptures on elongated asperities and their ensuing arrest depend on the size and aspect ratio of the asperity and on the background stress based on a systematic set of 3d dynamic rupture simulations assuming linear slip weakening friction we find that if the shortest asperity side is smaller than the 2d critical length the problem effectively reduces to a 2d problem in which rupture nucleation and arrest are controlled by the shortest length of the asperity otherwise nucleation and rupture arrest are controlled by the asperity area with a minor exception for asperities with shortest side slightly larger than the 2d critical length arrested ruptures are smaller than predicted by the asperity area the fact that rupture arrest is dominantly controlled by area even for elongated asperities corroborates the finding that observed maximum magnitudes of earthquakes induced by fluid injection are consistent with the theoretical relation between the magnitude of the largest self arrested rupture and the injected volume galis et al 2017 in context of induced seismicity our simulations provide plausible scenarios that could be either favourable or challenging for traffic light systems and provide mechanical insights into the conditions leading to these situations

coseismic fault related folding during the south golbaf earthquake of november 20 1989 in southeast iran the south golbaf earthquake of november 20 1989 m s 5 7 m b 5 6 i vii in southeast iran was associated with coseismic surface faulting and folding surface faults 11 km west dipping and 8 km east dipping long with oblique reverse mechanisms developed on both sides of a small holocene playa apparently repeated coseismic fault related folding was responsible for the holocene 20 tilting of the playa deposits above the active fault tip at the ground surface this study provided the first evidence of earthquake folding of holocene playa deposits in iran

collection and three dimensional modeling of gps and tilt data at merapi volcano java we study here the deformations associated with the november 1996 to march 1997 eruption period at mount merapi central java one of the most active volcanoes in indonesia this activity period includes a vertical explosion on january 17 and an increase of the lava dome volume by about 3 106 m3 two global positioning system gps campaigns have been carried out on a six benchmark network at the beginning and at the end of the period relative displacements with respect to the reference point show an average subsidence of 6 5 cm a multicomponent tilt station installed on the southeast flank 3 km from the summit recorded a tilt of 11 1 0 7 rad in the tangential direction and 0 9 0 4 rad in the radial direction these data are interpreted using a three dimensional 3 d elastic model based on the mixed boundary element method and a near neighbor monte carlo inversion interpretation of tilt data requires an accurate mesh for discretizing the 3 d topography the final result supports a horizontal elliptic magma source located 8 5 0 4 km below the summit and 2 0 4 km to the east of it in particular the data cannot be consistent with the location of a magma chamber determined from seismic activity analysis i e 2 km below the summit the computed depth depends strongly on the source shape and cannot be constrained properly because of the small amount of data the computed deflation of 11 2 106 m3 is about 3 times larger than the observed increase in the lava dome volume this difference is attributed to rock avalanches and pyroclastic flows on the flanks of the volcano

fluid transport properties in sediments and their role in large slip near the surface of the plate boundary fault in the japan trench abstract fluid transport properties such as permeability and porosity are significant parameters that affect earthquake generation we measured the transport properties of shallow sediments sampled around the plate boundary near the japan trench during iodp expedition 343 at confining pressures up to 40 mpa the permeabilities of samples from the shallow plate boundary fault were very low at 10 20 m 2 equivalent to a hydraulic diffusivity of 10 10 m 2 s 1 permeability and porosity in the core of the fault zone at the plate boundary were lower than those in the immediately overlying sediments and the surrounding intact sediment suggesting that the plate boundary fault can act as a barrier for fluid flow low permeability and high pore compressibility in the shallow plate boundary fault create a strong potential for dynamic fault weakening due to fluid pressurization with frictional heating even when the initial shear stress is low our investigation supports the hypothesis that thermal pressurization on the fault plane helped facilitate the extremely large slip in the shallow part of the subduction zone during the tohoku earthquake as the fault zone has a lower permeability than the surrounding sediments and a higher clay content pore pressure generation at depth by dehydration of clay minerals can explain formation of the shallow strong patch on the fault more reasonably than continuous fluid influx from the subducting oceanic crust which does not affect pore pressure at depth in the fault zone although there are many possible mechanisms of fault weakening thermal pressurization can act relatively efficiently as slip begins even at shallow depths therefore our results support the role of thermal pressurization in shallow slip during the tohoku earthquake

rupture dynamics with energy loss outside the slip zone 1 energy loss in a fault damage zone outside the slip zone contributes to the fracture energy that determines rupture velocity of an earthquake a nonelastic two dimensional dynamic calculation is done in which the slip zone is modeled as a fault plane and material off the fault is subject to a coulomb yield condition in a mode 2 crack like solution in which an abrupt uniform drop of shear traction on the fault spreads from a point coulomb yielding occurs on the extensional side of the fault plastic strain is distributed with uniform magnitude along the fault and it has a thickness normal to the fault proportional to propagation distance energy loss off the fault is also proportional to propagation distance and it can become much larger than energy loss on the fault specified by the fault constitutive relation the slip velocity function could be produced in an equivalent elastic problem by a slip weakening friction law with breakdown slip dc increasing with distance fracture energy g and equivalent dc will be different in ruptures with different initiation points and stress drops so they are not constitutive properties they are determined by the dynamic solution that arrives at a particular point peak slip velocity is however a property of a fault location nonelastic response can be mimicked by imposing a limit on slip velocity on a fault in an elastic medium

thermal constraints on the seismogenic portion of the southwestern japan subduction thrust for coastal cities an important factor in earthquake hazard from subduction zone earthquakes is the landward extent of the seismogenic portion of the subduction thrust fault in this study we test the hypothesis that the maximum downdip extent is defined by a critical temperature we have developed a transient thermal model for the nankai subduction zone of southwest japan to allow comparison of the thermally estimated downdip extent of the seismogenic zone with that from 1 seismicity and tsunami data for two great subduction earthquakes 2 the coseismic faulting extent of these events estimated from geodetic deformation data and 3 the interseismic locked zone determined from interseismic geodetic data the nankai margin has extensive heat flow and heat production data to control thermal models and thus crustal temperatures it has earthquake tsunami and geodetic data that constrain the coseismic rupture portion of the subduction thrust fault for past great earthquakes and the portion of the thrust fault that is locked and storing interseismic elastic strain on the nankaido margin off shikoku island the thermal model indicates that a temperature of 350 c taken to be the limit for seismic initiation from laboratory and field data is reached on the subduction thrust fault 150 km from the trench a transition zone into which rupture may extend with decreasing offset taken to be 450 c extends an additional 45 km downdip the thermal model results are in excellent agreement with the maximum downdip extent of coseismic displacement for the 1946 nankaido ms 8 2 earthquake off shikoku island and with the downdip extent of the present locked zone in the region of the 1944 tonankai ms 8 2 earthquake to the northeast the subduction angle is much steeper and the thermal models indicate a narrower downdip seismogenic extent the seismogenic locked zone from earthquake and geodetic data is also narrower thus our analysis of the southwest japan margin indicates that all three constraints on the downdip extent of the seismogenic zone thermal coseismic and interseismic geodetic data are in general agreement the study also supports the hypothesis that the seismogenic portion of subduction thrust faults is limited primarily by temperature the thermal control implies that subduction thrust faults with shallow dip have wider seismogenic zones compared to those with steep dip the subducting plate age and thus heat flow and the thickness of the insulating sediments on the incoming plate are also very important to the thermal regime and thus to the seismogenic width the relation of the maximum seismic rupture area to the interseismic locked zone is particularly important for earthquake hazard estimation on subduction margins such as cascadia where there have been no great historical events

a shallow strong patch model for the 2011 great tohoku oki earthquake a numerical simulation 1 a numerical simulation is conducted for understanding the mechanics of the 2011 great tohoku oki earthquake mw 9 0 which widely broke the plate interface at the pacific plate subducting beneath northern honshu tohoku japan in the model frictional stress on the plate interface is assumed to obey a rate and state dependent friction law a strong patch asperity with higher effective normal stress and a large value of characteristic slip distance is assumed at a shallower part of the plate interface this strong patch controls the occurrence of great earthquakes that broke the entire seismogenic plate interface with recurrence intervals of several hundred years the present model explains large coseismic slip at a shallower part of the 2011 great earthquake and accumulation of slip deficit at deeper parts where smaller m7 class earthquakes repeatedly occurred before the great earthquake

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

the 2003 december 26 bam earthquake iran mw 6 6 aftershock sequence summary from 2003 december 29 to 2004 january 30 a dense seismological network of 23 stations was installed in the epicentral area of the 2003 december 26 bam earthquake to study the aftershock seismicity we select the 331 earthquakes recorded at a minimum of 10 stations with rms less than 0 1 s and uncertainties less than 1 km to infer the precise geometry of the seismicity in the fault region we also process the data with the double difference technique to confirm the results the aftershock cluster is 25 km long trends north south and is located 5 km west of the bam baravat escarpment exactly beneath the observed surface breaks at depth aftershocks are concentrated between 6 and 20 km beneath the upper layer of relatively low velocity that experienced the maximum slip and they dip slightly westward the southernmost part of the aftershock cluster is narrow and defines the rupture zone that is likely the bam baravat fault at depth however it is unlikely that it is connected at surface to the bam baravat escarpment but more likely to the co seismic ruptures south of bam on the contrary the distribution of the northernmost aftershocks spread into a more complex pattern which is consistent with a northward propagation of the rupture along the fault plane the focal mechanisms are consistent with right lateral strike slip faulting on n s trending faults parallel to the bam baravat escarpment

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

fracture energies at the rupture nucleation points of large interplate earthquakes abstract numerical simulations of recurrence of interplate earthquakes in a subduction zone are conducted using a rate and state dependent friction law to estimate the fracture energies at the rupture nucleation points during an interseismic period shear stress is concentrated near the downdip of the locked portion of the plate boundary and seismic rupture initiates when the energy release rate by rupture extension exceeds the fracture energy the simulation results indicate that the fracture energy is proportional to the square of the amount of slip in the deep aseismic zone during the preceding interseismic period this suggests that the fracture energy at the nucleation point can be estimated from the recurrence interval of earthquakes and the relative plate velocity the fracture energies at the rupture nucleation points of great m w 8 nankai earthquakes in southwestern japan are estimated to be 0 1 1 mj m 2 and that of the 2011 m w 9 tohoku oki earthquake to be of the order of 10 mj m 2 the results suggest that fracture energy tends to increase with earthquake magnitude

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

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

spatial relation between main earthquake slip and its aftershock distribution 1 we examine where aftershocks occur relative to the spatial distribution of the main shock slip using data from several recent large earthquakes no universal relation between high and low moment regions and high or low aftershock occurrence or vice versa is found we generally find that few and usually the smaller aftershocks occur in the high slip regions of the fault a notable exception to this being the great 1996 biak indonesia subduction zone earthquake in all cases aftershocks occur on favorably oriented planes of weakness in regions of increased postseismic stress generally they are clustered at both ends of faults but examples where aftershocks occur only at one end or where there is no clustering at the ends are found aftershock clusters are also found at the edge of unbroken barriers and regions of rapid transition from high to low slip within the main fault area we identify examples of geometrical and inhomogeneous barriers and sharp and dull stress concentrations rupture in the main shock is generally found to nucleate in the region of low slip or at the edge of high slip regions the 1996 biak earthquake again being the only exception nucleating in a very high slip region off fault aftershocks are found for all earthquakes in this study and they sometimes rupture the nodal plane conjugate to the main shock fault plane

scaling of small repeating earthquakes explained by interaction of seismic and aseismic slip in a rate and state fault model because of short recurrence times and known locations small repeating earthquakes present a rare predictable opportunity for detailed field observations they are used to study fault creeping velocities earthquake nucleation stress drops and other aspects of tectonophysics earthquake mechanics and seismology an intriguing observation about repeating earthquakes is their scaling of recurrence time with seismic moment which is significantly different from the scaling based on a simple conceptual model of circular ruptures with stress drop independent of seismic moment and no aseismic slip here we show that a model of repeating earthquakes based on laboratory derived rate and state friction laws reproduces the observed scaling in the model a small fault patch governed by steady state velocity weakening friction is surrounded by a much larger velocity strengthening region long term slip behavior of the fault is simulated using a methodology that fully accounts for both aseismic slip and inertial effects of occasional seismic events the model results in repeating earthquakes with typical stress drops and sizes comparable with observations for a fixed set of friction parameters the observed scaling is reproduced by varying the size of the velocity weakening patch in simulations a significant part of slip on the velocity weakening patches is accumulated aseismically even though the patches also produce seismic events the proposed model supplies a laboratory based framework for interpreting the wealth of observations about repeating earthquakes provides indirect evidence that rate and state friction acts on natural faults and has important implications for possible scenarios of slip partition into seismic and aseismic parts

hypocenter depths of large interplate earthquakes and their relation to seismic coupling we examine locations of hypocenters of large interplate earthquakes mv 7 5 at subduction zones relative to their rupture areas to obtain a relation between the hypocentral depth and the seismic coupling coefficient which is the ratio of the long term slip rate estimated from cumulative seismic moment of large earthquakes to the relative plate motion we find 1 that the hypocentral depth is close to the bottom of the depth extent of the rupture area when the seismic coupling coefficient is nearly equal to 1 0 and 2 that the hypocentral depth relative to the depth extent of the rupture area shows a large scatter from shallow to deep when the seismic coupling coefficient is smaller than about 0 5 to interpret these observations we conduct a numerical simulation of seismic cycles of interplate earthquakes where the frictional stress on the plate boundary is assumed to obey a laboratory derived rate and statedependent friction law the observed result 1 is reproduced in the simulation when the critical fault length which is the size of the fault where the slip nucleation process takes place is much shorter than the seismogenic zone of the plate boundary in this case the plate boundary is strongly locked during an interseismic period and accordingly the calculated seismic coupling coefficient is close to 1 0 seismic slip starts near the bottom of the seismogenic zone because the maximum shear stress concentration is generated near the bottom of the seismogenic zone due to deeper steady plate motion on the other hand when the critical fault length is large appreciable aseismic sliding occurs in the seismogenic zone and therefore the calculated seismic coupling coefficient becomes significantly smaller than 1 0 the hypocentral depths of simulated large earthquakes tend to be shallow for large critical fault lengths heterogeneous frictional properties on the plate boundary may produce non uniform aseismic sliding during an interseismic period in this case the seismic coupling is small and seismic slip starts in various portions of the seismogenic zone this can explain the observed result 2 2 2003 elsevier science b v all rights reserved

mapping active fault associated with the 2003 mw 6 6 bam se iran earthquake with aster 3d images abstract satellite images reveal the geomorphology and geometry of an active fault associated with an earthquake that caused over 40 000 deaths in southeast iran this earthquake of moment magnitude mw 6 6 occurred at 01 56 52 utc on december 26 2003 near the towns of bam and baravat an active fault that ruptured during the earthquake can be seen on three dimensional 3d pre and post earthquake images generated from advanced spaceborne thermal emission and reflection radiometer aster visible and near infrared vnir data the interpretation and analysis of satellite images suggest that a dextral fault extends for 65 km through the bam baravat region it strikes north northwest and steps leftward at a segment boundary between two towns transpressional stress at this step over bend probably triggered the 2003 earthquake rupture as suggested also by source mechanism solution of the bam earthquake and by landforms observed in the field in the past 2000 years bam has had no earthquake as destructive as the one in 2003 the potential for this catastrophe could have been identified through a combination of satellite remote sensing technique and field reconnaissance

geodetic predictions of a strike slip fault model implications for intermediate and short term earthquake prediction mechanical models of faulting during an earthquake cycle now exist that are based on laboratory derived constitutive laws for rock friction such models allow calculation of geodetic changes as a function of depth distance from the fault and time and are useful for gaining insight on the magnitude and timing of geodetic changes that might occur prior to an earthquake we have used the tse and rice 1986 model of a crustal strike slip fault to study the sensitivity of surface deformation to changes in the values of the friction constitutive parameters and the amount of dynamic overshoot during an earthquake models were examined with values of the characteristic decay distance dc in the constitutive law ranging from 5 to 80 mm with near surface values of the steady state velocity dependence a b of 0 0015 and 0 003 and with either zero or 30 dynamic overshoot the time variations of the predicted displacement velocity strain and strain rate distributions are strongly affected by changes in dc and a b and only slightly affected by the amount of dynamic overshoot the larger values of dc and the less negative value of a b i e large ratios of dc to b a produce larger and earlier precursory signals the most useful signals for predicting the model earthquakes are strain changes near the fault because for nearly all model parameters studied the predicted strain changes are considerably larger than the detectability limits of existing borehole strain meters in the presence of earth noise detectable changes occur a few minutes to a month prior to the earthquake depending on parameter values premonitory increases in velocity also occur a pattern of larger velocities at distances a few kilometers away from the fault trace is a diagnostic indication of accelerating slip at depth that would be useful for predictive purposes unfortunately these velocity changes are detectable with creep meters and two color laser electronic distance measuring devices only for the largest ratios of dc to b a in agreement with recent measurements for several earthquakes the predicted amount of preseismic moment release is 0 5 of the earthquake moment for most simulations and the postseismic moment release is a significant fraction of the earthquake moment this two dimensional model suggests that earthquakes of magnitude 6 or greater on strike slip faults that cut the earth s surface could be predicted using existing instrumentation unless the ratio of dc to b a for natural faults is equal to or smaller than the smallest values investigated by tse and rice 1986 study of three dimensional models is needed since premonitory signals will be smaller if along strike variation is considered

fracture energy of stick slip events in a large scale biaxial experiment the concept of apparent fracture energy for the shear failure process is employed by many authors in modeling earthquake sources as dynamically extending shear cracks using records of shear strain and relative displacement from stick slip events generated along a simulated prepared fault surface in a large 1 5m x 1 5m x 0 4m granite block and a slip weakening model for the fault direct estimates of the apparent shear fracture energy of the stick slip events have been obtained for events generated on a finely ground fault surface apparent fracture energy ranges from 0 06 j m sup 2 at a normal stress of 1 1 mpa to 0 8 j m sup 2 at a normal stress of 4 6 mpa in contrast to estimates for tensile crack formation we find that the apparent fracture energy of stick slip events increases linearly with normal stress the results for the slip weakening model for the stick slip events are generally consistent with constitutive fault models suggested by observations of stable sliding in smaller scale experiments

offset and evolution of the gowk fault s e iran a major intra continental strike slip system abstract we use drainage reconstructions to estimate long term offsets on the gowk fault an oblique right lateral strike slip fault in eastern iran on which there have been a number of recent large earthquakes a 3 km horizontal offset is inferred from well preserved geomorphology we further identify a total cumulative offset of 12 km which produces a simple reconstruction of geomorphology across the fault filling in pull apart basins restoring rivers to linear courses across the fault trace and aligning structural and bed rock features the probable age of the gowk fault and k ar dating of offset basalts north of the study region suggest an overall slip rate of 1 5 2 4 mm year this is small compared with the overall 10 20 mm year of shear expected between central iran and afghanistan and the deficit is likely to have been accommodated on other faults east of the gowk fault drainage displaced by dextral movement leads to the development of a series of basins along the fault and a longitudinal topographic profile that resembles an asymmetric saw tooth the geomorphic evolution of the fault zone at the surface includes both normal and reverse faulting components reflecting a probable ramp and flat structure in cross section this interpretation is consistent with evidence from the analysis of seismological radar and surface rupture data in recent earthquakes

simple crack models explain deformation induced by subduction zone megathrust earthquakes following the 2010 maule and 2011 tohoku earthquakes many studies have examined the relation between megathrust earthquakes and subsequent deformation here we apply simple models based on mode ii shear cracks including approximated effects of the free surface to study induced deformation during coseismic and early postseismic stages we distinguish between buried and surface ruptures represented by a full crack and a half crack model respectively we adopt an analogy based approach to interpret the half crack model from well known results of the full crack model which is also validated by our numerical simulations with transferable knowledge between the two models we provide easy ways to understand 1 the contrasting deformation patterns in the frontal wedge of the overriding plate between buried ruptures and surface ruptures 2 the correlation between triggered outer rise normal faulting and surface ruptures and 3 the similar deformation patterns for both buried and surface ruptures toward the down dip end with a preference for normal faulting in the overriding plate and for reverse faulting in the subducting plate these model outcomes are consistent with several recent observations on aftershocks and veins in a paleoaccretionary wedge we further investigate some important transient features during rupture propagation which show that a transition from compressional to extensional deformation in the frontal wedge of the overriding plate is possible even during a single rupture event our work provides alternative views for understanding various aspects of subduction zone megathrust earthquakes and raises the issue of important transient features that were typically ignored in previous studies

megaquake cycle at the tohoku subduction zone with thermal fluid pressurization near the surface abstract for the 2011 tohoku earthquake we propose a mechanical model to explain rare giant m9 class and frequent large m7 class earthquakes on a thrust fault in the subduction zone observations implied in the m9 tohoku earthquake that extremely large slip on the order of tens of meters occurs in a shallower part to release a slip deficit as well as substantial slip about ten meters or so in a deeper part including the source area of the m7 class earthquakes here we present a model in which the extremely large slip is caused by hydrothermal weakening dynamic thermal pressurization of pore fluid on the fault plane not by contrast of frictional properties in terms of rate and state dependent friction the model explains that the tohoku earthquake followed a m7 class earthquake in two days but m7 class earthquakes are not always followed by a giant earthquake in a giant event large coseismic slip can occur over an area where quasistatic slip namely afterslip of m7 class earthquakes or spontaneous slow slip events takes place slight differences of stress state in the shallow part can result in drastically different coseismic slips we further perform numerical experiments varying hydraulic parameters and the length of effective hydrothermal weakening area the experiments imply that observations for monitoring the effective hydrothermal weakening area need spatial resolution on the order of 10 km or finer

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

fracture energies at the rupture nucleation points of large strike slip earthquakes on the xianshuihe fault southwestern china abstract earthquake cycles along a pure strike slip fault were numerically simulated using a rate and state dependent friction law to obtain the fracture energies at the rupture nucleation points in the model deep aseismic slip is imposed on the fault which generates recurrent earthquakes in the shallower velocity weakening friction region the fracture energy at the rupture nucleation point for each simulated earthquake was calculated using the relation between shear stress and slip which indicates slip weakening behavior the simulation results show that the relation between the fracture energy at the nucleation point and other source parameters is consistent with a theoretical approach based on fracture mechanics in that an earthquake occurs when the energy release rate at the tip of the aseismic slip zone first exceeds the fracture energy because the energy release rate is proportional to the square of the amount of deep aseismic slip during the interseismic period which can be estimated from the recurrence interval of earthquakes and the deep aseismic slip rate the fracture energies for strike slip earthquakes can be calculated using this result we estimated the fracture energies at the nucleation points of large earthquakes on selected segments of the xianshuihe fault southwestern china we find that the estimated fracture energies at the rupture nucleation points are generally smaller than the values of average fracture energy for developed ruptures as estimated in previous studies suggesting that the fracture energy tends to increase with the rupture propagation distance

can observations of earthquake scaling constrain slip weakening summary we use observations of earthquake source parameters over a wide magnitude range m w 0 7 to place constraints on constitutive fault weakening the data suggest a scale dependence of apparent stress and stress drop both may increase slightly with earthquake size we show that this scale dependence need not imply any difference in fault zone properties for different sized earthquakes we select 30 earthquakes well recorded at 2 5 km depth at cajon pass california we use individual and empirical green s function spectral analysis to improve the resolution of source parameters including static stress drop and total slip s we also measure radiated energy e s w ecompare the cajon pass results with those from larger california earthquakes including aftershocks of the 1994 northridge earthquake and confirm the results of abercrombie 1995 e s m 0 where rigidity and both e s m 0 and increase as m 0 and s increases uncertainties remain large due to model assumptions and variations between possible models and earthquake scale independence is possible within the resolution assuming that the average trends are real we define a quantity g 2 es m 0 s 2w hich is the total energy dissipation in friction and fracture minus 1 s w here 1 is the final static stress if 1 d the dynamic shear strength during the last increments of seismic slip then g g the fracture energy in a slip weakening interpretation of dissipation

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

earthquake fracture energy inferred from kinematic rupture models on extended faults 1 we estimate fracture energy on extended faults for several recent earthquakes by retrieving dynamic traction evolution at each point on the fault plane from slip history imaged by inverting ground motion waveforms we define the breakdown work wb as the excess of work over some minimum traction level achieved during slip wb is equivalent to seismological fracture energy g in previous investigations our numerical approach uses slip velocity as a boundary condition on the fault we employ a three dimensional finite difference algorithm to compute the dynamic traction evolution in the time domain during the earthquake rupture we estimate wb by calculating the scalar product between dynamic traction and slip velocity vectors this approach does not require specifying a constitutive law and assuming dynamic traction to be collinear with slip velocity if these vectors are not collinear the inferred breakdown work depends on the initial traction level we show that breakdown work depends on the square of slip the spatial distribution of breakdown work in a single earthquake is strongly correlated with the slip distribution breakdown work density and its integral over the fault breakdown energy scale with seismic moment according to a power law with exponent 0 59 and 1 18 respectively our estimates of breakdown work range between 4 105 and 2 107 j m2 for earthquakes having moment magnitudes between 5 6 and 7 2 we also compare our inferred values with geologic surface energies this comparison might suggest that breakdown work for large earthquakes goes primarily into heat production

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

large nucleation before large earthquakes is sometimes skipped due to cascade up implications from a rate and state simulation of faults with hierarchical asperities 1 does a large earthquake have a large quasi static preparation a hierarchical asperity model in which a large tough patch patch l contains smaller fragile patches patch s enables a large earthquake to start with only small preparation because of cascade up rupture growth we realized such a model in a rate and state framework by heterogeneous distributions of the state evolution distance and its consequences are investigated by earthquake sequence simulations focus is put on elementary processes the interaction between two scales one patch l containing one patch s is simulated with their size ratio as a parameter if patch s is larger than the nucleation size of patch l the system falls into a limit cycle consisting of only one earthquake that starts with patch s nucleation and grows dynamically to rupture entire patch l if patch s is considerably smaller than the nucleation size of patch l small earthquakes never dynamically cascade up and the large earthquakes are initiated by large quasi static nucleation in between large earthquakes start in various ways by large nucleation dynamic cascade up or delayed cascade up in the final stage of quasi static nucleation the preseismic moment release rate increases roughly inversely proportional to the time to failure tf with its amplitude depending on the nucleation size for a patch s rupture to cascade up strength in the adjacent region must have been reduced manifested by a higher creep velocity before the patch s nucleation starts following 1 tf acceleration large nucleation sometimes has a precursory small earthquake characterized by larger afterslip than nonprecursory ones