systematic comparisons of earthquake source models determined using insar and seismic data abstract robust earthquake source parameters e g location seismic moment fault geometry are essential for reliable seismic hazard assessment and the investigation of large scale tectonics they are routinely estimated using a variety of data and techniques such as seismic data and more recently interferometric synthetic aperture radar insar comparisons between these two datasets are frequently made although not usually in a comprehensive way this review compares source parameters from global and regional seismic catalogues with those from a recent database of insar parameters which has been expanded with 18 additional source models for this study we show that moment magnitude mw estimates agree well between the two datasets with a trend for thrust events modelled using insar to have slightly larger mw estimates earthquake locations determined using insar agree well with those reported in regional catalogues with a median difference of 6 3 km between them which is smaller than for global seismic catalogues we also investigate the consistency of source parameters and source directivity by comparing isc hypocentres with gcmt and icmt centroid locations for earthquakes with mw 6 5 in some cases the source directivity is qualitatively comparable with previous studies especially when comparing isc and icmt locations the average difference between insar determined depths and those in the ehb catalogue is reduced if a layered half space is used in the inversion of insar data overall faulting geometry strike dip and rake angles remain in good agreement with values from the gcmt catalogue and any large discrepancies can be attributed to tradeoffs between parameters with continued investment in satellites for radar interferometry insar is a valuable technique for the estimation of earthquake source parameters the observed trends and discrepancies between insar and seismically determined source parameters are the result of issues with the data different inversion techniques and the assumed earth structure model

the critical slip distance for seismic faulting experimentally based friction laws1 2 have been found to predict virtually the entire range of observed behaviour of natural faults3 4 these laws contain a critical slip distance l which plays a key role in determining the degree of fault instability the size of the zone of earthquake nucleation the frictional breakdown width and the proportion of pre and post seismic slip to co seismic slip in laboratory measurements l is found to be about 10 5m but modelling results show that it must be about 10 2m if natural earthquake behaviour is to be simulated the discovery that fault surfaces are fractal over the scale range 10 5 105 refs 5 6 even for faults with large net slip has confused the problem of scaling this parameter from laboratory experiments to natural faults because fractal surfaces have no characteristic length here i show that geometrically unmated fractal surfaces when in contact under a normal load develop a characteristic length in their contact because long wavelength apertures close under load whereas short wavelength apertures may remain open this critical distance may be identified with l and calculations based on fault topography data show that at seismogenic depths it will be in the range anticipated from the earthquake modelling studies

kinking of shallow dip slip zones a two dimensional crack model is used to investigate the effect of the free surface on the propagation of kink cracks that develop at the tip of dip slip shear zones the slip zones undergo frictional sliding under tectonic loading with the presence of the gravitational force because the numerical scheme incorporates the exact asymptotic form of slip near the end of the shear zone results for the stress intensity factors are accurate the calculations show that crack opening occurs along a portion of the planar slip zone near the kink as well as at the kink itself for a typical shallow reverse dip slip zone the mode i stress intensity factor at the tip of the kink can be 60 greater than that for a full space the effect of free surface is negligible if the ratio of the depth of the shallow end to the length of the slip zone is greater than two the influence of the free surface makes it possible for the kink crack to grow to much greater length under compressive tectonic loading the kink that develops at the shallow end of a shear zone does not move toward the free surface instead the kink curves away from the free surface extends stably parallel to the free surface and is then arrested at a finite length the calculations suggest that rupture termination of a reverse dip slip earthquake may be due to extensive tensile cracking near the free surface and that the growth of long extensional fractures parallel to the free surface dissipate sufficient energy to stop the fault rupture in addition the present calculations demonstrate that the orientation and the length of observed vein sets are consistent with the extensional fractures developed near the tip of the dip slip zone

quantitative estimates of interplate coupling inferred from outer rise earthquakes interplate coupling plays an important role in the seismogenesis of great interplate earthquakes at subduction zones the spatial and temporal variations of such coupling control the patterns of subduction zone seismicity we calculate stresses in the outer rise based on a model of oceanic plate bending and coupling at the interplate contact to quantitatively estimate the degree of interplate coupling for the tonga new hebrides kurile kamchatka and marianas subduction zones depths and focal mechanisms of outer rise earthquakes are used to constrain the stress models we perform waveform modeling of body waves from the gdsn network to obtain reliable focal depth estimates for 24 outer rise earthquakes a propagator matrix technique is used to calculate outer rise stresses in a bending 2 d elastic plate floating on a weak mantle the modeling of normal and tangential loads simulates the total vertical and shear forces acting on the subducting plate we estimate the interplate coupling by searching for an optimal tangential load at the plate interface that causes the corresponding stress regime within the plate to best fit the earthquake mechanisms in depth and location

stress relaxation at the lower dislocation edge of great shallow earthquakes abstract the problem of post seismic stress evolution at the lower dislocation edge of great shallow earthquakes is investigated by a model reproducing a transcurrent boundary zone subject to a constant strain rate dislocation models with frictional stress threshold for slip arrest must be considered in order to study post seismic stress evolution in the proximity of dislocation edges it is found that the boundary zone is vertically divided in two regions an upper region where stress increases with time and a lower region where stress decreases dislocations which are nucleated in the seismogenic region can propagate downward into the aseismic region in this case earthquakes are followed by relaxation of the stress concentration at the lower dislocation edge this may have effects on the space time distribution of aftershocks

effects of subducted seamounts on megathrust earthquake nucleation and rupture propagation 1 subducted seamounts have been linked to interplate earthquakes but their specific effects on earthquake mechanism remain controversial a key question is under what conditions a subducted seamount will generate or stop megathrust earthquakes here we show results from numerical experiments in the framework of rate and state dependent friction law in which a seamount is characterized as a patch of elevated effective normal stress on the thrust interface we find that whether subducted seamounts generate or impede megathrust earthquakes depends critically on their relative locations to the earthquake nucleation zone defined by depth variable friction parameters a seamount may act as a rupture barrier and such barrier effect is most prominent when the seamount sits at an intermediate range of the seamount to trench distances 20 100 of the nucleation zone to trench distance moreover we observe that seamount induced barriers can turn into asperities on which megathrust earthquakes can nucleate at shallow depths and rupture the entire seismogenic zone these results suggest that a strong barrier patch may not necessarily reduce the maximum size of earthquakes instead the barrier could experience large coseismic slip when it is ruptured

crustal structure of the northern margin of the eastern tien shan china and its tectonic implications for the 1906 m 7 7 manas earthquake abstract the tien shan orogenic belt is the most active intracontinental mountain belt in the world we describe an 86 km long n s trending deep seismic reflection profile which passes through the southern junggar basin located on the northeastern tien shan piedmont two distinct anticlines beneath the northern margin of the tien shan are clearly imaged in the seismic section in addition we have imaged two detachment surfaces at depths of 7 and 16 km the detachment surface at 16 km depth corresponds to the main detachment that converges with the steep angle reverse fault the junggar southern marginal fault on which the 1906 m 7 7 manas earthquake occurred a 12 14 km thick sedimentary basin is imaged beneath the southern junggar basin near shihezi the crust beneath the northern margin of the tien shan is 50 55 km thick and decreases beneath the junggar basin to 40 45 km thick the crustal image of the deep seismic reflection profile is consistent with models derived from nearby seismic refraction data and bouguer gravity anomalies in the same region the faulting associated with the 1906 manas earthquake also fits within the structural framework imaged by the seismic reflection profile present day micro seismicity shows a hypocentral depth distribution between 5 and 35 km with a peak at 20 km we hypothesize that the 1906 manas earthquake initiated at a depth of 20 km and propagated upwards causing northward slip on the sub horizontal detachments beneath the southern junggar basin thus in accord with regional geological mapping the current shortening within the eastern tien shan is accommodated both by high angle reverse faulting and detachment faulting that can be clearly imaged at depth in seismic reflection data

paleoseismology and seismic hazards evaluations in extensional volcanic terrains extensional structures in volcanic terrains are the surface expression of shallow dike intrusion and can be misinterpreted as structures associated with major tectonic faults dike induced structures can be distinguished from their tectonic counterparts by their association with cogenetic volcanic rocks and by several geometric relationships tensile fissures with little or no vertical displacement fissure swarms flexural monoclines and normal faults are commonly symmetrically distributed about a central eruptive fissure sometimes forming a graben above shallow dikes the structures typically occur within broad zones not narrow belts near a main fault zone reflecting their origin by repeated dike injection colluvial wedges containing records of single large earthquakes generally do not form instead fault scarps with several meter vertical displacements in volcanic bedrock may reflect the cumulative effects of many decimeter scale displacement events from several dike injection episodes the mechanism of dike intrusion and the nature of cointrusive seismicity have important implications for determination of the maximum magnitude and recurrence of earthquakes in extensional volcanic terrains observational seismicity from volcanic rift zones worldwide suggests the maximum magnitudes of dike induced earthquakes are 3 8 0 8 earthquakes are generally small to moderate because downdip extents of faults and fissures are controlled by the depth to the top of the associated dike usually 5 km permitting only small rupture areas also rupture and displacement on faults and fissures migrate incrementally at about the velocity of propagating dikes 0 5 m s as dike dilation stresses the zone above and ahead of the dike earthquake recurrence is tied to recurrence of volcanic cycles based on the geochronology of the associated volcanic materials based on these concepts innovative approaches have led to estimates of the maximum magnitude and recurrence for magma induced seismicity in eastern snake river plain esrp volcanic rift zones the most conservative approach uses surface length fault width downdip extent and rupture areas of normal faults and fissures produced by dike injection to estimate a maximum m5 5 earthquake for an episode of rift zone volcanism chronology of volcanic rocks suggests annual probabilities of 10 4 to 10 5 for volcanic rift zones near idaho national engineering laboratory facilities probabilistic assessments show that ground motion hazard due to volcanic rift zone seismicity is lower than the hazard from other earthquake sources this is because of the relatively low magnitudes and long recurrence intervals of cointrusive earthquakes in volcanic rift zones

transform fault earthquakes in the north atlantic source mechanisms and depth of faulting we have determined the centroid depths and source mechanisms of 12 large earthquakes on transform faults of the northern mid atlantic ridge from an inversion of long period body waveforms the earthquakes occurred on the gibbs oceanographer hayes kane 15 20 and vema transforms we have also estimated the depth extent of faulting during each earthquake from the centroid depth and the fault width for five of the transforms earthquake centroid depths lie in the range 7 10 km beneath the seafloor and the maximum depth of seismic faulting is 14 20 km on the basis of a comparison with a simple thermal model for transform faults this maximum depth of seismic behavior corresponds to a nominal temperature of 900 100 c in contrast the nominal temperature limiting the maximum depth of faulting during oceanic intraplate earthquakes with strike slip mechanisms is 700 100 c the difference in these limiting temperatures may be attributed to the different strain rates characterizing intraplate and transform fault environments three large earthquakes on the 15 20 transform have shallower centroid depths of 4 5 km and a maximum depth of seismic faulting of 10 km corresponding to a limiting temperature of 600 c the shallower extent of seismic behavior along the 15 20 transform may be related to a recent episode of extension across the transform associated with the northward migration of the triple junction among north american south american and african plates to its present position near the transform the source mechanisms for all events in this study display the strike slip motion expected for transform fault earthquakes slip vector azimuths agree to within 2 3 of the local strike of the zone of active faulting the only anomalies in mechanism were for two earthquakes near the western end of the vema transform which occurred on significantly nonvertical fault planes secondary faulting occurring either precursory to or near the end of the main episode of strike slip rupture was observed for five of the 12 earthquakes for three events the secondary faulting was characterized by reverse motion on fault planes striking oblique to the trend of the transform in all three cases the site of secondary reverse faulting is near a compressional jog in the current trace of the active transform fault zone we find no evidence to support the conclusions of engeln wiens and stein that oceanic transform faults in general are either hotter than expected from simple thermal models or weaker than normal oceanic lithosphere

transition from interplate slip to double seismic zone along the kuril kamchatka arc during subduction the downgoing slab interacts with a strong overriding plate at shallow depths and with the surrounding asthenosphere at intermediate depths thus the transition from earthquakes representing interplate slip to those reflecting intraplate deformation within subducting lithosphere is important for understanding how the mechanics of subduction varies with depth to characterize this transition we studied 44 large to moderate sized earthquakes that occurred between 1964 and 1990 in two regions along the central portion of the kuril kamchatka arc precise earthquake source parameters are determined by analyzing body waveforms recorded at teleseismic distances at depths of 30 50 km our results delineate a transitional thrust zone characterized by earthquakes showing thrust faulting on moderately dipping nodal planes the northwesterly dipping nodal plane dips approximately 40 some 10 15 steeper than the dip of low angle earthquake faulting along the interplate thrust zone at depths shallower than 30 km for earthquakes along the transitional thrust zone secondary features in observed waveforms suggest that either a thick layer of sediments is present in the forearc region or the sources are embedded in materials with crustal seismic wave speeds in the former case the transitional thrust zone is interpreted as the deep seated portion of the plate interface whose dip increases with depth the alternative implies that the transitional thrust zone occurrs below the plate interface within subducted crust of the pacific plate and that the occurrence of earthquakes along the transitional zone may indicate a locked plate interface between depths of 30 and 50 km the inference of a locked plate interface is consistent with the occurrence of compressional earthquakes beneath the outer rise region however a locked interface does not seem to affect the state of strain in the double seismic zone the upper compressional layer of the double seismic zone abuts the transitional thrust zone at a depth of approximately 50 km at this depth the two layers of seismicity in the double seismic zone are separated by as much as 30 40 km too large a distance to be accommodated by models of seismogenesis invoking either the gabbro eclogite transition or dehydration of subducted oceanic crust

the brittle plastic transition and the depth of seismic faulting a simple rheological model of shearing of the lithosphere that has gained wide acceptance is a two layer model with an upper brittle zone in which deformation takes place by frictional sliding on discrete fault surfaces and a lower plastic zone in which deformation takes place by bulk plastic flow the two are separated by an abrupt brittle plastic transition which is assumed to be indicated by the lower limit of seismicity experimental studies however as well as the deformation structures of mylonites indicate that a broad transitional field of semi brittle behavior lies between these extremes this is a field of mixed mode deformation with a strength that can be expected to be considerably higher than that predicted from the extrapolation of high temperature flow laws for quartzofeldspathic rocks the semi brittle field lies between t1 the onset of quartz plasticity at about 300 c and t2 feldspar plasticity at about 450 c a model is presented in which the transition t1 does not correspond to a transition to bulk flow but to a change from unstable velocity weakening friction to stable velocity strengthening friction t1 thus marks the depth limit of earthquake nucleation but large earthquakes can propagate to a greater depth t3 t3 t2 which corresponds to the lower limit of dynamic frictional behavior in the semi brittle field and approximately to the peak in strength the zone between t1 and t3 is one of alternating behavior with flow occurring m the interseismic period and with co seismic dynamic slip occurring during large earthquakes this zone is characterized by mylonites interlaced by pseudotachylytes and other signs of dynamic faulting the transition t1 is also marked by a change in the generation mechanism of fault rocks from abrasive wear above which produces cataclastites to adhesive wear below which is proposed as an important generation mechanism of mylonites in the upper part of the semi brittle field

textures of sheared halite and their implications for the seismogenic slip of deep faults abstract halite exhibits a wide spectrum of behavior from frctional slip in the brittle field to fully ductile shearing flow even at room temperature and the simulated halite shear zone is ideal for studying mechanical properties of large scale faults and plate boundaries with the currently available apparatus thirty nine triaxial experiments were performed on dry cylindrical specimens of tennessee sandstone with a 0 5 mm thick layer of synthetic or natural halite along a 35 precut at room temperature with a constant slip rate along the precut ranging from 3 to 300 m s and at confining pressures up to 200 mpa mechanical data are consistent with those reported previously shimamoto 1985c 1986 this paper reports observations on these and some previous specimens our new data reconfirm the earlier results by shimamoto and logan that 1 nearly homogeneous shearing deformation characterized by the formation of a well developed foliation changes into heterogeneous shearing after a critical shear strain and that 2 the potentially unstable fault motion is associated with this strain localization within the shear zones the nature of this heterogeneous deformation is examined closely in this paper and it is shown that the primary mode of internal slip within the shear zones is slip along y riedel shears interconnected with r 1 riedel shears thus some kind of brittle deformation possibly overlaps the predominantly plastic deformation after strain localization although no direct evidence of cataclastic deformation can be found owing to the nearly complete recrystallization of halite more importantly potentially unstable fault motion occurs only when internal shearing takes place along narrow nearly planar and discrete surfaces at pressures above about 100 mpa the discontinuous zones become wider and irregular and the potentially unstable fault motion disappears seismogenic slip thus extends well into the semiductile regime of deformation and mylonites should receive renewed attention with the view that at least some of them could well be associated with seismogenic fault motion

relative sea level changes in the basque coast northern spain bay of biscay during the holocene and anthropocene the urdaibai estuary case abstract in order to reconstruct the environmental evolution process of the urdaibai estuary in response to sea level changes in the basque coast northern spain bay of biscay during the last 8500 years 10 boreholes were drilled in different estuarine areas using a rotary drill until the pre quaternary basement was reached one manual short core 50 cm was obtained from a salt marsh environment located in the middle part of the estuary micropalaeontological benthic foraminifera sedimentological grain size and geochemical 14 c 210 pb and 137 cs radioisotopes and total pb and zn analyses were performed on these materials aiming to quantify the sea level changes both of natural origin holocene or derived from recent human activities anthropocene based on the obtained results and by comparison with previously published information for this coastal area the holocene environmental evolution of the urdaibai estuary has been interpreted as the result of relative sea level variation that exhibits a rapid rise until 7000 cal bp followed by a moderate rise since then and a stabilization during the last 3000 years until modern rates of sea level rise 20th century 1 7 0 2 mm y 1 were reached

four seismogenic environments in eastern canada abstract although the seismogenic environments in eastern canada have some common features the respective seismotectonic environments are influenced by local features the seismotectonic environment in four seismogenic regions are described in order to illustrate how local features are reacting with the ambient plate tectonic stress a common feature to modify the nature of the seismic activity the charlevoix earthquakes are occurring along steeply dipping planes formed during the opening of lapetus ocean in the proterozoic perturbed by a meteor impact during the paleozoic and reactivated by the opening of the present day atlantic ocean in the mesozoic theoretical curves of maximum shear stress versus depth based on a wet upper crust and a wet quartz rheology in the lower crust for which the heat flow is 1 0 hfu 42 mw m2 can account for the depth distribution of earthquakes in this region potential trigger mechanisms are gravitationally induced stress water infiltration and vertical shear strain changes approximately 3 10 8 yr due to post glacial rebound the unusually deep focus 29 km of the m 5 9 saguenay earthquake of 1988 could be due in part to the lower heat flow in this region as compared with that in the charlevoix region which is about 70 km to the east the miramichi earthquake sequence is occurring on conjugate faults within an intrusion at depths shallower than 10 km theoretical curves of maximum shear stress versus depth based on a wet quartz rheology in the lower crust for which the heat flow is 1 5 hfu can account for this depth distribution the steep gradient in the vertical ground movement rate 5 10 8 yr in the epicentral area which is probably due to post glacial rebound is a potential trigger mechanism for favorably oriented faults the normal fault seismic regime along northeastern baffin island can be explained by a combination of topography and post glacial rebound which can generate horizontal extensional stresses capable of overcoming the ambient compressional plate tectonic stress post glacial rebound stress can act as a trigger mechanism for the ne dipping faults in this region in the grand banks region there is seismic evidence indicating that the slump that caused the destructive tsunami also generated the strong seismic m 7 2 signals but double couple solutions that satisfy certain criteria are not ruled out the absence of surface faulting especially in the epicentral regions of large earthquakes is not properly understood but several possibilities are near surface layering that could mask the underlying fault offsets and a spatiotemporal variation in the ambient plate tectonic stress field as knowledge of the causative factors of eastern canada earthquakes and also the data base for empirical earthquake scaling relations increase an overview of the seismotectonics of these mid plate earthquakes should be enhanced

internal structure of the median tectonic line fault zone sw japan revealed by borehole analysis abstract the internal structure of the median tectonic line mtl fault zone and the processes that prevailed at depths are described based on an analysis of a borehole the fault plane which defines the boundary between the ryoke and sanbagawa derived rocks dips at 56 to the north immediately beneath the boundary approximately 40 m thick fractured rocks form the major strand of the mtl fault zone the hanging wall above the boundary comprises variably deformed ryoke granitoids including several mylonite zones and cataclasite zones the fault zone has evolved through a series of faulting events under temperatures ranging from 400 to 200 c the mineral assemblages of the mylonites and cataclasites immediately above the boundary indicate that these fault rocks were formed at temperatures of about 300 c these mylonites and cataclasites represent therefore fault rocks that formed immediately below and above the brittle plastic transition respectively development of dissolution seams in these cataclasites suggests that the cataclasite has low strength the presence of pseudotachylytes in the cataclasite indicates the occurrence of seismicity immediately above the brittle plastic transition on the other hand the very fine grain size of recrystallised quartz in the mylonites indicates high differential stress immediately below the brittle plastic transition it is therefore likely that the differential stresses immediately below the brittle plastic transition are much higher than those immediately above the transition formation of laumontite in the major strand of the mtl fault zone occurred at temperatures of around 200 c the central slip zone of the major strand is about 30 cm thick and is surrounded by thick gouge zones this situation is favourable for thermal pressurisation during earthquake slips

earthquake depths and the relation to strain accumulation and stress near strike slip faults in southern california earthquakes in the major fault zones are predominantly deep earthquakes in the crustal blocks bounding the fault zones are predominantly shallow in the san jacinto fault zone maximum earthquake depths correlate with surface heat flow these relations together with focal mechanisms geodetic strain measurements and fault zone models are consistent with the following ideas 1 interseismic plate motion is accommodated by aseismic slip along an extension of the major fault zone below a brittle zone that is locked between large earthquakes 2 the aseismic slip in a narrow fault zone in the brittle plastic transition region concentrates strain at the base of the brittle fault zone 3 deep earthquakes occur in thelower part of the brittle fault zone due to stick slip failure of highly stressed patches 4 background earhtquakes and aftershocks that occur several kilometers deeper than large earthquake hypocenters suggest that a zone of mixed slip behavior may exist between the stable sliding deep and stick slip shallow regions of the fault zone furthermore the difference in seismicity between the san jacinto and southern san andreas faults suggests that the nature of this mixed zone may evolve as total displacement in the fault zone increases 5 shear stress may be lessmore in the crustal blocks than in the deep brittle fault zones and generally at a level sufficient to cause brittle failure only shallow in the crustal blocks 6 in the stress field produced by plate motion and slip in the deep fault zone the upper brittle fault zone is not oriented favorably for shear failure lack of shallow earthquakes in the fault zones and the predominance of shallow earthquakes on favorably oriented fractures in the adjacent crustal blocks suggest that either stress in the upper brittle fault zone is relatively low or the upper fault zone is effectively strong due to its orientation less

an assessment of source parameters of earthquakes in the cordillera of the western united states abstract source parameters for 50 earthquakes occurring between 1915 and 1988 have been used to examine the faulting characteristics of magnitude 5 5 to 7 8 earthquakes within the western u s cordillera an area extending from the eastern sierra nevada to the great plains and from northwestern montana to trans pecos texas source parameters used in this study include seismic information from first motion analyses body and surface waveform modeling geodetic studies and geological studies of surface faulting the principal results of this analysis include 1 all earthquakes occurred on faults dipping 38 or more and no evidence for listric of low angle planar faulting was found 2 all m 7 0 earthquakes occurred at depths 12 km and were composed of multiple subevents 3 most earthquakes 70 per cent had unilateral ruptures and 4 no individual subevent had a rupture length 21 km

far field pressurization likely caused one of the largest injection induced earthquakes by reactivating a large preexisting basement fault structure the mw 5 1 fairview oklahoma earthquake on 13 february 2016 and its associated seismicity produced the largest moment release in the central and eastern united states since the 2011 mw 5 7 prague oklahoma earthquake sequence and is one of the largest earthquakes potentially linked to wastewater injection this energetic sequence has produced five earthquakes with mw 4 4 or larger almost all of these earthquakes occur in precambrian basement on a partially unmapped 14 km long fault regional injection into the arbuckle group increased approximately sevenfold in the 36 months prior to the start of the sequence january 2015 we suggest far field pressurization from clustered high rate wells greater than 12 km from this sequence induced these earthquakes as compared to the fairview sequence seismicity is diffuse near high rate wells where pressure changes are expected to be largest this points to the critical role that preexisting faults play in the occurrence of large induced earthquakes

frictionless shear at great depth and other paradoxes of hard rocks shearing with very low friction is regarded as responsible for the high energy release from deep seated earthquakes and rock bursts in deep underground mines but in spite of considerable attention to the problem no consensus of opinion has been reached regarding the physical explanation for the low friction alternative hypotheses include melting lubrication excess pore pressure velocity effects and vibration at the interface here however we propose that under high confining stresses shear fractures developing in pristine hard rocks can exhibit dramatically low shear resistance over a certain displacement range before the residual frictional strength is mobilized due to the intrinsic nature of the fault structure this feature is due to a special fault structure formed during the fault development the proposed phenomenon can explain a number of anomalies observed in the field and laboratory conditions but in particular the very high energy released from deep seated earthquakes and rockbursts

implications of an elastic analysis of in situ stress measurements near the san andreas fault twenty nine measurements of in situ stress obtained with the hydraulic fracturing technique near palmdale california are the basis of an elastic analysis of the state of stress in the mojave desert adjacent to the san andreas fault the measurements were made at depths extending from 80 to 849 m and at distances from the fault between 2 and 34 km the elastic solution indicates a state of deviatoric stress typical for continents in that the inferred depth gradient of the maximum shear stress is about 7 9 mpa km extrapolation yields an average shear stress in the upper 14 km of the crust of about 56 mpa a result that is higher than estimates of the average shear stress on the san andreas fault based on the analysis of heat flow data this finding is consistent however with estimates of fault strength based on laboratory determinations of the coefficient of friction for samples of san andreas fault gouge if the regional state of deviatoric stress is limited by the strength of the fault zone if so then the coefficient of friction of the san andreas fault zone inferred from the stress field results is about 0 45 the state of stress does not appear to vary systematically with distance from the san andreas fault although considerable localized variation is observed the observations suggest an upper bound of about 0 1 mpa km for the horizontal gradient of the maximum shear stress in the direction perpendicular to the san andreas fault a result that implies a corresponding limit of about 1 4 mpa on the shear traction applied to the base of the seismogenic layer finally we demonstrate the potential application of in situ stress data to the direct assessment of accumulated slip which could be released in a large earthquake we show that on the basis of a model involving a locked fault extending to about 22 km the total fault slip below the locked portion is less than 13 m a more comprehensive set of stress data could permit the estimation of an even lower bound

ductile fracture of fine grained plagioclase in the brittle plastic transition regime implication for earthquake source nucleation abstract crush zones along strain localized zones of plastic deformation were found in a small natural brittle plastic shear zone in the abukuma mountains ne japan the optical microstructures indicate that crush zones are developed where plastic deformation is strong scanning electron microscopy sem revealed the presence of microvoids which connect together to form intergranular fractures in fine grained plagioclase layers in strain localized zones with crush zones this suggests that the microvoids coalesce in the fine grained plagioclase layers allowed ductile fracture to form crush zones during plastic deformation transmission electron microscopy tem revealed that the dislocation densities of all grains in fine grained plagioclase layers in strain localized zones with crush zones are high while evidence for grain boundary migration and dynamic recrystallization is found away from crush zones during plastic deformation of plagioclase in the brittle plastic transition regime strong plastic deformation with insufficient recrystallization may have resulted in the nucleation of microvoids which link together to form intergranular fractures this process may be an important mechanism during earthquake source nucleation

seismic domains within the gissar kokshal seismic zone soviet central asia by evaluating seismological data from the belt of shallow intraplate seismicity known as the gissar kokshal seismic zone in soviet central asia in conjunction with recent data on the shallow crustal structure and longer term geologic deformation we show that certain size classes of earthquakes are characteristic of adjacent and in some places overlapping geologic tectonic settings we call these settings seismic domains they are both geologically and seismologically distinct i e they contain different rocks and structures and have different frequency magnitude relationships for example in terms of number of events gissar kokshal seismicity is dominated by the microearthquakes that have occurred within the sedimentary rocks of the vakhsh fold thrust belt these are all shallow and have occurred mostly within the frontal portions of the thrust sheets more rarely moderate size m 5 5 earthquakes have ruptured the thrust ramps on the other hand the major strain release in this region has accompanied the large 5 5 m 8 1 shallow earthquakes on basement faults in the southern gissar range adjacent to the fold thrust belt within these ranges there is relatively little microearthquake activity that dichotomy indicates that a significantly different seismic hazard is associated with each of these areas but the seismological distinction is obscured along the front of the fold thrust belt where the domain of small shocks in the sedimentary rocks overlaps the domain of large earthquakes on basement faults to explain the localization of the large basement events along the southern flank of the fold thrust belt adjacent to the fold thrust belt we hypothesize a mechanism of thrust sheet loading thrust loads are greatest in this region since thrust sheets have overridden large basement block uplifts beneath the illiac and peter the first range faults

the 2011 mw 6 8 burma earthquake fault constraints provided by multiple sar techniques we used two tracks of alos palsar images to investigate the focal mechanism and slip distribution of the 2011 march 24 m w 6 8 burma strike slip earthquake three different sar techniques namely conventional interferometry sar pixel offsets spo and multiple aperture insar mai were employed to obtain the coseismic surface deformation fields along the 30 km length of the fault rupture along track measurements from spo and mai techniques show a high correlation and were subsequently used to precisely determine the location and extent of the surface fault trace the best fitting fault model geometry derived from an iterative inversion technique suggests that the rupture occurred on a near vertical sinistral strike slip fault west of the nam ma fault with a strike of 70 a maximum slip of 4 2 m occurs at a depth of 2 5 km with significant slip constrained only to the upper 10 km of the crust

why large earthquakes do not nucleate at shallow depths although by definition tectonic earthquakes may nucleate anywhere within the seismogenic layer in almost all cases those earthquakes that become large nucleate near the base of the seismogenic layer because frictional strength and stress drop should increase with depth and in situ stress measurements suggest that the ambient stress increases with depth we have examined spontaneous rupture models with gradients of both average stress drop and average strength relative to ambient stress to determine whether this explains the observed phenomena we report here that ruptures that are nucleated with in the low stress drop shallow regions of the model are inhibited from propagating but those that are nucleated within the high stress drop regions can propagate over the entire fault plane

stress triggering of conjugate normal faulting late aftershocks of the 1983 ms 7 3 borah peak idaho earthquake the 1984 devil canyon sequence was a late aftershock sequence of the 28 october 1983 ms 7 3 borah peak idaho earthquake the sequence began on 22 august 1984 with the ml 5 8 devil canyon earthquake which nucleated at a depth of 12 8 0 7 km between the surface traces of two normal faults the challis segment of the lost river fault and the lone pine fault two hundred thirty seven aftershocks were recorded by a temporary array during a 3 week period their focal mechanisms and hypocenter distribution define a cross sectional v pattern whose base corresponds to the ml 5 8 event whose tips correspond to the exposed fault traces and whose sides define two planar fault zones oriented n25 w 75 sw challis fault segment and n39 w 58 ne lone pine fault this pattern describes a graben bounded by conjugate normal faults temporal aspects of the devil canyon sequence provide strong evidence that slip on conjugate normal faults occurs sequentially aftershocks occurred primarily along the challis segment until the occurrence of the 8 september 1984 ml 5 0 earthquake along the lone pine fault after which aftershocks primarily occurred along this fault these observations are consistent with worldwide seismologic and geologic observations and with physical andmore numerical models of conjugate normal faulting aftershocks of the devil canyon sequence occurred immediately northwest of the ml 5 8 devils canyon earthquake which itself was immediately northwest of the thousand springs segment of the lost river fault the fault that slipped in association with the ms 7 3 borah peak earthquake coulomb failure stress analysis indicates that stress increases resulting from both the borah peak mainshock and devil canyon ml 5 8 earthquake were sufficient to induce failure on the lone pine fault these space time patterns suggest that conjugate normal faults may transfer stress or accommodate stress changes at the terminations of major normal faults in the basin and range province less

the seismic cycle at subduction thrusts 1 insights from laboratory models 1 subduction megathrust earthquakes occur at the interface between the subducting and overriding plates these hazardous phenomena are only partially understood because of the absence of direct observations the restriction of the instrumental seismic record to the past century and the limited resolution completeness of historical to geological archives to overcome these restrictions modeling has become a key tool to study megathrust earthquakes we present a novel model to investigate the seismic cycle at subduction thrusts using complementary analog paper 1 and numerical paper 2 approaches here we introduce a simple scaled gelatin on sandpaper setup including realistic tectonic loading spontaneous rupture nucleation and viscoelastic response of the lithosphere particle image velocimetry allows to derive model deformation and earthquake source parameters analog earthquakes are characterized by quasi periodic recurrence consistent with elastic theory the interseismic stage shows rearward motion subsidence in the outer wedge and uplift of the coastal area as a response of locked plate interface at shallow depth the coseismic stage exhibits order of magnitude higher velocities and reversal of the interseismic deformation pattern in the seaward direction subsidence of the coastal area and uplift in the outer wedge like natural earthquakes analog earthquakes generally nucleate in the deeper portion of the rupture area and preferentially propagate upward in a crack like fashion scaled rupture width slip proportionality and seismic moment duration scaling verifies dynamic similarities with earthquakes experimental repeatability is statistically verified comparing analog results with natural observations we conclude that this technique is suitable for investigating the parameter space influencing the subduction interplate seismic cycle

geometry of continental normal faults seismological constraints teleseismic body waves from large earthquakes are used to study the downdip geometry of continental normal faults in the aegean waveform modeling techniques together with rigorous statistical tests are applied to put firm bounds on the amount of downdip curvature of these faults and the role of coseismic slip on a basal detachment synthetic modeling shows that good azimuthal station coverage and inclusion of sh waves are necessary to resolve fault curvature the data indicate ruptures of the aegean events occurred on planar faults extending across the entire brittle portion of the crust no seismogenic low angle detachment faulting at the base of the upper crust was detected for these events decoupling of the brittle upper crust from the plastic lower crust probably occurs aseismically in a ductile fashion

crustal structure around the eastern end of coseismic rupture zone of the 1944 tonankai earthquake abstract the high potential for a major earthquake to occur in the suruga trough tokai earthquake has been recognized since 1969 and is closely related to how far the coseismic rupture during the 1944 tonankai earthquake propagated eastward to understand what kind of structure might have interrupted the rupture of the 1944 event it is necessary to obtain the crustal structure around the eastern end of its rupture zone the crustal model deduced from a wide angle seismic survey shows characteristics of the subducting oceanic crust and the neogene quaternary accretionary sediments bounded by the crustal block of the island arc around the eastern end of the rupture zone of the 1944 event this model shows that the subduction oceanic crust has a particularly irregular geometry 40 km landward from the deformation front comparing our crustal models with a recently published coseismic rupture distribution of the 1944 event deduced from tsunami waveforms there is no slip in the east of the irregularity of the slab moreover it seems that coseismic rupture propagated northeastward avoiding this irregularity the spatial relationship between the irregularity of the slab found in this study and the rupture distribution is analogous to that between the subducted seamount found off the shikoku island and the rupture distribution of the 1946 nankai earthquake although the existence of a subducted ridge parallel to the nankai trough off the tokai district has been suggested based on published geomagnetic data and seafloor topography our crustal models may support the existence of a slab irregularity more suggestive of a subducted seamount at least at the eastern end of the coseismic rupture zone of the 1944 event such irregular geometry of the subducting oceanic crust in particular subducted seamounts may be one of the causes that control the rupture process of great earthquakes along the nankai trough

14 february 1983 earthquake sequence in the shumagin islands alaska abstract two moderate events m s 6 3 and 5 6 occurred just outside a local network in the shumagin islands alaska on 14 february 1983 these were the first events of magnitude greater than 5 5 in the region since 1979 they occurred within the subduction zone at a depth of 26 km of the more than 50 aftershocks that were recorded at one or more stations 12 events ranging from m b 2 5 to 4 0 were recorded digitally and located focal mechanisms were calculated for the two main events from first motion polarities and teleseismic body wave modeling the mechanisms for both events show similar nodal planes with p axes in the approximate direction of plate convergence and nearly vertical t axes the plane of motion is not constrained by the aftershocks but the shallowly dipping plane parallel to the subduction zone interface is the preferred solution dynamic stress drops of 80 and 70 bars are calculated from local strong motion records these events occurred in a mature seismic gap they nucleated in a shallow portion of the main thrust zone that apparently has a relatively low state of stress and thus were not capable of rupturing into the higher strength region at the base of the main thrust zone

a 667 year record of coseismic and interseismic coulomb stress changes in central italy reveals the role of fault interaction in controlling irregular earthquake recurrence intervals current studies of fault interaction lack sufficiently long earthquake records and measurements of fault slip rates over multiple seismic cycles to fully investigate the effects of interseismic loading and co seismic stress changes on the surrounding fault network we model elastic interactions between 97 faults from 30 earthquakes since 1349 ad in central italy to investigate the relative importance of co seismic stress changes versus interseismic stress accumulation for earthquake occurrence and fault interaction this region has an exceptionally long 667 year record of historical earthquakes and detailed constraints on the locations and slip rates of its active normal faults of 21 earthquakes since 1654 20 events occurred on faults where combined co seismic and interseismic loading stresses were positive even though 20 of all faults are in stress shadows at any one time furthermore the coulomb stress on the faults that experience earthquakes is statistically different from a random sequence of earthquakes in the region we show how co seismic coulomb stress changes can alter earthquake inter event times by c 103 years and fault length controls the intensity of this effect static coulomb stress changes cause greater inter event perturbations on shorter faults in areas characterized by lower strain or slip rates the exceptional duration and number of earthquakes we model enable us to demonstrate the importance of combining long earthquake records with detailed knowledge of fault geometries slip rates and kinematics to understand the impact of stress changes in complex networks of active faults

ultramylonite bands derived from cataclasite and pseudotachylyte in granites northeast japan abstract small scale ultramylonite and cataclasite bands millimeters to tens of centimeters thick are developed in granitic rocks west of the hatagawa fault zone hfz in the abukuma belt northeast japan they occur as single or paired bands with sharp planar boundaries trending nne ssw and often form networks and conjugate sets the very small s c angle and the high displacement thickness ratio of the bands suggest that the shear strain is high the ultramylonite bands are commonly associated with cataclasite bands and mineral veins and rarely with pseudotachylyte some cataclasite bands contain mylonitized layers in which quartz fragments are strongly deformed and dynamically recrystallized on the other hand some ultramylonites are fractured producing fragments that have rotated during later cataclasis the major element content of the ultramylonite bands is similar to that of the surrounding granitic rocks strongly suggesting that the ultramylonite bands have formed through in situ deformation of the granitic protolith without significant mass transfer mineralogy and microstructures of some ultramylonites suggest the strong possibility that they are derived from pseudotachylyte the ultramylonite bands are interpreted as forming in the 10 15 km deep cataclastic plastic transition zone under greenschist facies conditions where co seismic fracturing and aseismic plastic flow have alternated

source scaling of earthquakes in the shumagin region alaska time domain inversions of regional waveforms the scaling of pulse duration to seismic moment is estimated for earthquakes along an interplate thrust zone from digital waveforms recorded by short period and broad band instruments of the east aleutian shumagin seismic network we measure pulse duration using an empirical green s function technique based on damped time domain deconvolution from several thousand events 22 earthquakes with magnitudes 3 0 7 0 and depths 23 56 km are found to give reliable estimates of pulse duration durations are also determined directly from one parameter nonlinear inversions for a variety of simple functional forms of source time functions symmetric source pulses boxcar or triangle shapes fit waveforms better than an asymmetric model t exp 2t d for most 62 per cent of the waveform pairs while the asymmetric model fits best for only 8 per cent of the data pulse duration increases with the size of events from 0 1 to 10s over the seismic moment m0 range of 1014 to 3 1019 nm when normalized by the cube root of seismic moment pulse durations show 8 x variation comparable static stress drop estimates range from 0 2 to 135 mpa contrary to predictions of some laboratory and theoretical studies earthquakes at the deepest part of the thrust zone do not show significantly higher stress drops than do shallower events rupture properties however show a strong dependence on earthquake size the three largest events m0 5 1018nm have the three longest normalized durations on average 3 8 times longer than those for smaller events the durations require smaller events to have 10 100 x larger static stress drops or 4 x faster rupture velocities or some combination of the two possibly the largest events rupture both strong and weak patches while smaller events just rupture strong patches on the fault surface the characteristic dimension that separates large from small events 3 15 km is comparable to characteristic wavelengths of pacific basin bathymetry and may reflect the influence of the subducted sea floor upon fault zone heterogeneity

three dimensional spontaneous rupture propagation and implications for the earthquake source mechanism summary we consider spontaneous cracks spreading out areally over a fault plane in an infinite medium as a realistic earthquake source model the boundary integral equation technique described in das is used to determine the displacements and stresses everywhere on the crack plane for faults spreading out symmetrically in all four quadrants over infinite planes of constant yield strength we find that the terminal rupture velocity viiicr in the direction of purely anti plane rupture is given by viiicr in the purely in plane direction of rupture propagation we find the terminal rupture velocity viicr to be given by viicr or viicr 0 5 depending on the yield strength we also find that crack propagation in the purely antiplane direction does not influence crack propagation in the purely in plane direction and vice versa for infinitely long shear cracks of finite width the slip at a point is found to grow more slowly after the arrival of a shear wave diffracted from the nearer crack edge the slip virtually ceases after the shear arrival from the further crack edge this implies that for such faults the slip is controlled by the fault width for a rectangular fault in an infinite medium our final dynamic solution is in closer agreement with the static elliptical crack solution of eshelby than with the static rectangular dislocation model solution of chinnery we find the relationship between the average slip and average dynamic stress drop e on such a rectangular fault of half width w to be e c w where c 0 7 the slip at an interior point is again controlled by the fault width for faults that are much longer than wide so that the slip may stop in the region where the fault initiated before the completion of the rupture process this implies that two rectangular faults of varying lengths but of the same width have the same slip for the same average stress drop a fact clearly contradicted by observations that fault slip increases with earthquake size for great earthquakes occurring along the same fault this contradiction is resolved if stress drops are also bigger for bigger earthquakes

effects of frictional behavior and geometry of subduction fault on coseismic seafloor deformation abstract the seismogenic zone of subduction faults appears to have an updip limit seaward of which the fault exhibits velocity strengthening behavior we use a two dimensional finite element model including a frictional subduction fault to explore how coseismic strengthening of the updip segment affects seafloor deformation for a stress drop of a few mpa along the seismogenic zone strengthening of the updip segment by a comparable amount can prevent the rupture from breaking the trench the resultant seafloor uplift is much larger than that predicted by a model of equal seismic moment or maximum fault slip in which the seismogenic zone extends to the trench with a curved fault geometry although a lower degree of coseismic strengthening of the updip segment leads to greater slip in the shallowest part of the fault it produces smaller seafloor uplift contrary to a popular belief given the paucity of direct observations of the coseismic behavior of the updip segment the models yield important information for understanding rupture mechanics of subduction faults and tsunami generation we also illustrate how the results may be used to guide fault slip parameterization in analytical dislocation models

scaling of ground motion parameters state of stress and focal depth the ground motion parametersrv and ra where r is hypocentral distance v is peak velocity is density and a is peak acceleration are found observationally to be strong functions of stress state and linearly related to focal depth z if the stress state and focal depth are properly taken into account then the ground motion parameters depend on the seismic moment m0 as expected from basic scaling principles that is rv m01 3 and ra is independent of earthquake size regression lines fitted to observations covering broad ranges in seismic moment and focal depth indicate that for extensional and compressional tectonic regimes corresponding to normal and thrust or reverse faulting earthquakes respectively peak acceleration is given by ra 1 08 mpa 3 06 mpa km z normal and ra 5 65 mpa 8 76 mpa km z thrust and for peak velocity rv m01 3 10 4 m2 s n m 1 3 3 00 0 69 km 1 z normal and rv m01 3 10 4 m2 s n m 1 3 4 63 1 82 km 1 z thrust for strike slip earthquakes the data currently are insufficient to define regression fits but such lines would definitely lie between those for the normal and thrust stress regimes these equations are appropriate for ground motion at small hypocentral distance as recorded in a whole space it follows that for comparable hypocentral depth peak acceleration in a compressional tectonic regime for example much of the eastern united states is a factor of about 3 greater than in an extensional regime such as nevada and for peak velocity a similar comparison yields a factor of 2 difference the similarity in behavior of the peak acceleration parameter to crustal strength estimated from byerlee s law of friction with respect to depth and stress state indicates that crustal strength is probably the factor governing the seismic source processes that give rise to the high frequency peak ground motion analysis of the peak acceleration data in the context of crustal strength suggests bounds on this ground motion parameter as recorded at a typical surface site that depend on stress state specifically a normal 0 5 g and a thrust 1 9 g thus the state of stress as well as the focal depth clearly is an important factor to be taken into account in the prediction of seismic ground motion

localisation of plastic flow in the mid crust along a crustal scale fault insight from the hatagawa fault zone ne japan abstract this study examines plastic flow in fault rocks exposed along the hatagawa fault zone hfz of ne japan the fault zone developed in 110 ma granitoids ceased activity by 98 1 2 5 ma three different fault rocks mylonites with microstructures a and b and cataclasite are exposed along the fault microstructure a formed at the brittle plastic transition the temperature conditions for microstructure b were higher than those for microstructure a those for the cataclasite were lowest microstructure a is exposed in limited areas maximum length extent of approximately 6 km along the hfz the distribution of microstructure a is considered to represent the latest stage localised zones of plastic flow associated with strain weakening accompanied by dynamic recrystallisation of feldspar suggesting the restriction of plastic displacement to certain intervals at depth ranges with p t conditions of the brittle plastic transition many zones of localised deformation containing crush zones are observed in rocks with microstructure a suggesting that numerous fractures nucleated due to the ductile fracturing of highly deformed fine grained feldspar in the outcrop extent of microstructure a the nucleation of large earthquakes was possibly promoted by interaction between fractures that nucleated by ductile fracture and stress concentrations associated with the restricted development of plastic displacement

a model of interseismic stress evolution in a transcurrent shear zone abstract it has been observed that most shallow earthquakes occur in a seismogenic layer which extends to a depth of a few tens of kilometres while at greater depths the relative plate motion must take place aseismically such behaviour is reproduced by a model where a wide deformed fault region is encompassed by two transcurrent plates and subjected to a constant strain rate the shear zone is treated as a viscoelastic body for which a power law constitutive relation is employed temperature and therefore rheology depend on depth z also rigidity depends on depth the model determines a maximum depth h for earthquake nucleation on the faults in the shear zone if a frictional resistance linearly increasing with depth is assumed the interseismic shear stress evolution on a vertical fault is obtained analytically for n 1 2 3 and 4 where n is the power law exponent it is found that the rate of stress increase does not change appreciably as a function of n for z h while the effect of non linearity becomes more sensible at larger z moreover for z h the state of stress as obtained from this model is very different from estimates obtained from purely viscous models even for much longer times than are considered in seismology

the seismic cycle at subduction thrusts 2 dynamic implications of geodynamic simulations validated with laboratory models 1 the physics governing the seismic cycle at seismically active subduction zones remains poorly understood due to restricted direct observations in time and space to investigate subduction zone dynamics and associated interplate seismicity we validate a continuum visco elasto plastic numerical model with a new laboratory approach paper 1 the analogous laboratory setup includes a visco elastic gelatin wedge underthrusted by a rigid plate with defined velocity weakening and strengthening regions our geodynamic simulation approach includes velocity weakening friction to spontaneously generate a series of fast frictional instabilities that correspond to analog earthquakes a match between numerical and laboratory source parameters is obtained when velocity strengthening is applied in the aseismic regions to stabilize the rupture spontaneous evolution of absolute stresses leads to nucleation by coalescence of neighboring patches mainly occurring at evolving asperities near the seismogenic zone limits consequently a crack or occasionally even pulse like rupture propagates toward the opposite side of the seismogenic zone by increasing stresses ahead of its rupture front until it arrests on a barrier the resulting surface displacements qualitatively agree with geodetic observations and show landward and from near the downdip limit upward interseismic motions these are rebound and reversed coseismically this slip increases adjacent stresses which are relaxed postseismically by afterslip and thereby produce persistent seaward motions the wide range of observed physical phenomena including back propagation and repeated slip and the agreement with laboratory results demonstrate that visco elasto plastic geodynamic models with rate dependent friction form a new tool that can greatly contribute to our understanding of the seismic cycle at subduction zones

lateral structure variations and transient swarm revealed by seismicity along the main himalayan thrust north of kathmandu abstract the midcrustal seismicity along the main himalayan thrust in nepal presents lateral variations along the rupture of the 2015 gorkha earthquake in order to resolve these variations we relocate the seismicity north of kathmandu during a period well covered by the nepal national seismological network using a double difference algorithm the 550 relocated events highlight a complex pattern of clustered seismicity within the unstable stable transition zone part of the seismicity is densely clustered on a southward dipping plane which ruptured on january 31st 1997 ml 5 8 activating a backthrust with a geometry consistent with the centroid moment tensor of this event calculated in this study at its eastern end the midcrustal cluster is offset by 20 km to the south suggesting the presence of a tear fault the analysis of the time sequence allows constraining a scenario involving stress transfer between these local midcrustal structures beginning more than one month before the 1997 main shock the temporal evolution of the seismicity is strikingly similar for two other transient seismic swarm episodes which developed hundreds of kilometers apart along the main himalayan thrust at the same time the local stress field appears responsible for the higher sensitivity of these regions to subtle strain transients developing along the main himalayan thrust

numerical study of ground motion differences between buried rupturing and surface rupturing earthquakes recent ground motion observations suggest that surface rupturing earth quakes generate weaker near fault ground motion than buried earthquakes this dif ference is significant in the period range of 0 3 3 sec contributing factors to this phenomenon may include the effect of fault zone weakness at shallow depth on rup ture dynamics and rupture directivity during earthquakes we present results from numerical experiments of spontaneous dynamic rupture and near source ground motion simulations of surface rupturing and buried earth quakes and discuss mechanisms for the observed ground motion differences the surface rupturing earthquake is modeled with a shallow zone of 5 km thickness con taining areas of negative stress drop within the framework of the slip weakening fric tion model and lower rigidity surface rupturing models with this weak zone generate lower amplitude ground velocity than do models without this modification observed ground motion differences between surface and buried events are qual itatively reproduced by imposing higher stress drop in the buried earthquakes than in the surface earthquakes combined with introducing a deeper rupture initiation for buried rupture enhancing upward rupture directivity effects for the latter events in the context of our simplified model parameterization then the observed differences in ground motion could arise from combined effects of relative weakness of the shal low layer of faults the relatively larger stress drops of buried ruptures and a tendency of near fault sites to record strong upward directivity from buried ruptures

deterministic frequency wavenumber methods and direct measurements of rupture propagation during earthquakes using a dense array data analysis data recorded by the smart 1 array in taiwan are used to make the first direct measurements of two dimensional earthquake rupture propagation using frequency wavenumber techniques and ray theory we obtain estimates of the spatial extent duration and directions of rupture propagation during two earthquakes located offshore taiwan our estimates include uncertainties due to errors in fault plane location and orientation velocity structure and slowness ray parameter measured at the array we find that the january 29 1981 ml 6 3 taiwan earthquake ruptured unilaterally updip and toward the west on a 60 dipping 109 striking reverse fault using p waves we find its fault length and duration to be 25 18 km and 7 4 3 4 s respectively s waves indicate a fault length and duration of 27 15 km and 9 4 3 6 s respectively we suggest that the november 14 1986 ml 7 0 hualien taiwan earthquake was triggered by a shallow h 14 km foreshock ml 5 4 which occurred on a subparallel or splay fault approximately 5 s before the mainshock based on p waves rupture propagation during the foreshock is unilateral towards the northeast and slightly downdip on a 58 dipping 38 striking reverse fault its spatial extent and duration are approximately 23 km and 5 4 s the mainshock initiated at greater depth h 34 km than the foreshock with its primary direction of rupture unilateral toward the northeast and slightly updip on a 57 dipping 43 striking reverse fault using p waves we found a spatial extent and duration of 68 15 km and 12 4 2 2 s s waves indicate a similar extent duration and direction of propagation for the mainshock however we found it difficult to distinguish the foreshock and mainshock 5 waves we show by example that these results represent an improvement over what can be obtained using long period t 5 s teleseismic methods comparison of our results with those obtained using teleseismic data suggests either a short duration slip time function or that most slip occurs near the rupture front our results indicate that much of the complexity in the seismograms recorded during these events by the smart 1 array is due to spatial and temporal variations of the source this suggests that at least in some cases predictions of both the phase and amplitude of strong ground motion as a function of time would require a priori knowledge of source properties finally we recommend siting small 10 station dense arrays on land above offshore subduction zones which are considered seismic gaps because they can provide more detailed measurements of rupture propagation than is presently possible

a reappraisal of large earthquake scaling abstract twelve years ago i pointed out that observations indicate that the slip in large earthquakes scales with their length rather than their width as expected from the canonical model romanowicz 1992 has recently argued that more recent data show that the opposite is true which has obliged me to re examine the question i point out here a defining flaw in her analysis in that she allowed mo the moment at the cross over from small to large earthquakes to be a free variable in her curve fitting whereas this parameter can be defined independently when this parameter is independently fixed i find that the up dated data set confirms my earlier conclusion that for large crustal earthquakes m0 scales with l 2 a little over a decade ago i pointed out that obser vations indicate that the slip in large earthquakes scales with their rupture length scholz 1982 several sub sequent papers provided additional data supportive of this view chen and molnar 1983 shimazaki 1986 scholz et al 1986 large earthquakes are defined in this con text as those that rupture the entire seismogenic thick ness w0 and are thus constrained to propagate farther in a horizontal direction only for crustal earthquakes w0 is nearly constant 15 km so this scaling conflicts with conventional models of earthquakes such as dislocation models because they predict that slip scales with width which is invariant for these earthquakes i offered two alternative ways to interpret these observations one is that such conventional w models are correct but that stress drop could no longer be regarded as scale invariant but must scale with fault length as an alternative i sug gested the possibility of what i termed an l model in which slip intrinsically scales with fault length this created a minor crisis in seismology which has yet to be resolved it is no exaggeration to say that my l model suggestion has not attracted a noticeable coterie of admirers nor has my other suggestion and there has been no other model proposed in the interim that ex plains the observed l scaling although heaton 1990 has suggested a way in which length may scale with stress drop a variation of my w model scaling alternative in the face of this an alternative is to question the obser vations which is what romanowicz 1992 has recently chosen to do in her interpretation of an updated data set she concluded that seismic moment m0 scales lin early with rupture length l for large earthquakes which is consistent with w models and implies that slip u is scale invariant for large crustal earthquakes this great discrepancy with the earlier result she implies is due to the presence of superior modern measurements in the updated data set this issue has major implications both practical and theoretical and merits some debate here i present my own reappraisal of the data in which the conclusions are very different reappraisal of the data romanowicz s conclusions were based on a log log plot of m0 versus l for a data set of strike slip earth quakes she showed that the data in this figure could be better fit by two straight lines one with slope 3 in the lower scale range and one with slope 1 in the upper scale range than with a single line of slope 2 for small earth quakes which grow in both dimensions with l w m0 should scale with l 3 for large earthquakes where w has saturated at w0 and growth only occurs in the l di rection m0 should scale with l according to conven tional models hence the problem produced by my ob servation that m0 scales with l 2 for those events superficially then it appears that she has resolved the issue the problem however is that she has allowed the cross over length l which separates small from large earthquakes to be a free variable in her curve fitting ex ercise she thus obtains a cross over moment of 0 6 to 0 8 x 1020 n m which is appropriate for a rupture length of 60 to 70 km by adding an additional free parameter to the curve fitting one would expect a much better fit to be achieved the question is whether such a step is justified if small earthquakes grow with l w then the transition to large earthquakes defined as an event that ruptures the entire seismogenic thickness would be l w0 10 to 20 km for the data being studied this may be checked observationally because large earth quakes almost invariably nucleate near the base of the seismogenic layer das and scholz 1983 it follows that the transition to large earthquakes is at the length at which one begins to consistently see surface ruptures inspec tion of the earthquakes in romanowicz s 1992 figure 215

3d geometry of the strain field at transform plate boundaries implications for seismic rupture we examine the amplitude and distribution of slip on vertical frictionless faults in the zone of concentrated shear strain that is characteristic of transform plate boundaries we study both a 2d and a 3d approximation to this strain field mean displacements on ruptures within the zone of concentrated shear strain are proportional to the shear strain at failure when they are short and are limited by plate displacements since the last major earthquake when they are long the transition between these two behaviors occurs when the length of the dislocation approaches twice the thickness of the seismogenic crust approximately the breadth of the zone of concentrated shear strain observed geodetically at transform plate boundaries this result explains the observed non linear scaling relation between seismic moment and rupture length a geometrical consequence of the 3d model in which the strain field tapers downward is that moderate earthquakes with rupture lengths similar to the thickness of the crust tend to slip more at depth than near the surface seismic moments estimated from surface slip in moderate earthquakes m less than or equal to 7 will thus be underestimated shallow creep if its along strike dimension is extensive can reduce a surface slip deficit thatmore would otherwise develop on faults on which m less than 7 events are typical in the absence of surface creep or other forms of off fault deformation great earthquakes may be necessary features of transform boundaries with downward tapering strain fields less

an objective method for the assessment of fluid injection induced seismicity and application to tectonically active regions in central california changes in seismicity rates whether of tectonic or of induced origin can readily be identified in regions where background rates are low but are difficult to detect in seismically active regions we present a novel method to identify likely induced seismicity in tectonically active regions based on short range spatiotemporal correlations between changes in fluid injection and seismicity rates the method searches through the entire parameter space of injection rate thresholds and determines the statistical significance of correlated changes in injection and seismicity rates applying our method to kern county central california we find that most earthquakes within the region are tectonic however fluid injection contributes to seismicity in four different cases three of these are connected to earthquake sequences with events above m4 each of these sequences followed an abrupt increase in monthly injection rates of at least 15 000 m 3 the probability that the seismicity sequences and the abrupt changes in injection rates in kern county coincide by chance is only 4 the identified earthquake sequences display low gutenberg richter b values of 0 6 0 7 and at times systematic migration patterns characteristic for a diffusive process our results show that injection induced pressure perturbations can influence seismic activity at distances of 10 km or more triggering of earthquakes at these large distances may be facilitated by complex local geology and faults in tectonically active regions our study provides the first comprehensive statistically robust assessment of likely injection induced seismicity within a large tectonically active region

fennoscandian earthquakes whole crustal rupturing related to postglacial rebound local and regional earthquake locations provide seismic evidence that large shield earthquakes have occurred in northern fennoscandia these paleoearthquakes with fault lengths of up to 160 kilometers and average displacements of up to 15 meters were triggered by nonisostatic compressive stresses caused by the removal of the ice at the end of the last deglaciation the fennoscandian faults were probably formed by single events that ruptured through most of the crust the largest event moment magnitude mw 8 2 was larger than other known stable continent earthquakes outside failed rifts or extended crust

reconstruction of changes in the weddell sea sector of the antarctic ice sheet since the last glacial maximum the weddell sea sector is one of the main formation sites for antarctic bottom water and an outlet for about one fifth of antarctica s continental ice volume over the last few decades studies on glacial geological records in this sector have provided conflicting reconstructions of changes in ice sheet extent and ice sheet thickness since the last glacial maximum lgm at ca 23 19 calibrated kiloyears before present cal ka bp terrestrial geomorphological records and exposure ages obtained from rocks in the hinterland of the weddell sea ice sheet thickness constraints from ice cores and some radiocarbon dates on offshore sediments were interpreted to indicate no significant ice thickening and locally restricted grounding line advance at the lgm other marine geological and geophysical studies concluded that subglacial bedforms mapped on the weddell sea continental shelf subglacial deposits and sediments over compacted by overriding ice recovered in cores and the few available radiocarbon ages from marine sediments are consistent with major ice sheet advance at the lgm reflecting the geological interpretations different ice sheet models have reconstructed conflicting lgm ice sheet configurations for the weddell sea sector consequently the estimated contributions of ice sheet build up in the weddell sea sector to the lgm sea level low stand of 130 m vary considerably in this paper we summarise and review the geological records of past ice sheet margins and past ice sheet elevations in the weddell sea sector we compile marine and terrestrial chronological data constraining former ice sheet size thereby highlighting different levels of certainty and present two alternative scenarios of the lgm ice sheet configuration including time slice reconstructions for post lgm grounding line retreat moreover we discuss consistencies and possible reasons for inconsistencies between the various reconstructions and propose objectives for future research the aim of our study is to provide two alternative interpretations of glacial geological datasets on antarctic ice sheet history for the weddell sea sector which can be utilised to test and improve numerical ice sheet models

reconciling seismicity and geodetic locking depths on the anza section of the san jacinto fault observations from the anza section of the san jacinto fault in southern california reveal that microseismicity extends to depths of 15 18 km while the geodetically determined locking depth is less than 10 km this contrasts with observations from other major faults in the region and also with predictions of fault models assuming a simple layered distribution of frictional properties with depth we suggest that an anomalously shallow geodetic fault locking may result from a transition zone at the bottom of seismogenic layer with spatially heterogeneous frictional properties numerical models of faults that incorporate stochastic heterogeneity at transitional depths successfully reproduce the observed depth relation between seismicity and geodetic locking as well as complex spatio temporal patterns of microseismicity with relatively scarce repeating earthquakes our models predict propagation of large earthquakes to the bottom of the transition zone and ubiquitous aseismic transients below the locked zone potentially observable using high precision geodetic techniques

shallow earthquakes in a viscoelastic shear zone with depth dependent friction and rheology summary most crustal earthquakes of the world are observed to occur within a seismogenic layer which extends from the earth s surface to a depth of a few tens of kilometres at most a model is proposed in which the shear zone along a transcurrent plate margin is represented as a viscoelastic medium with depth dependent power law rheology a frictional resistance linearly increasing with depth is assumed on a vertical transcurrent fault within the shear zone such a model is able to reproduce a continuous transition from the brittle behaviour of the upper crust to the ductile behaviour at depth assuming that the shear zone is subjected to a constant strain rate from the opposite motions of the two adjacent plates it is found that there exists a maximum depth h below which tectonic stress can never reach the frictional threshold this may be identified as the maximum depth of earthquake nucleation the value of h is consistent with observations for plausible values of the model parameters the stress evolution in the shear zone is calculated in the linear approximation of the constitutive equation a change in rigidity with depth which is also introduced in the model may reproduce the high vertical gradient of shear stress which has been measured across the san andreas fault and the fact that most earthquakes are nucleated at some depth in the seismogenic layer a crack which drops the ambient stress to the dynamic frictional level is then introduced in the model to this aim a crack solution is employed without a stress singularity at its edges which is compatible with a frictional stress threshold criterion for fracture a constraint on the vertical friction gradient is obtained if such cracks are assumed to be entirely confined within the seismogenic layer

locking depths estimated from geodesy and seismology along the san andreas fault system implications for seismic moment release 1 the depth of the seismogenic zone is a critical parameter for earthquake hazard models independent observations from seismology and geodesy can provide insight into the depths of faulting but these depths do not always agree here we inspect variations in fault depths of 12 segments of the southern san andreas fault system derived from over 1000 gps velocities and 66 000 relocated earthquake hypocenters geodetically determined locking depths range from 6 to 22 km while seismogenic thicknesses are largely limited to depths of 11 20km theseseismogenicdepthsbestmatchthegeodeticlockingdepthswhenestimated at the 95 cutoff depth in seismicity and most fault segment depths agree to within 2 km however the imperial coyote creek and borrego segments have significant discrepancies in these cases the geodetically inferred locking depths are much shallower than the seismogenic depths we also examine variations in seismic moment accumulation rate per unit fault length as suggested by seismicity and geodesy and find that both approaches yield high rates 1 5 1 8 1 0 13 nm yr km along the mojave and carrizo segments and low rates 0 2 10 13 nm yr km along several san jacinto segments the largest difference in seismic moment between models is calculated for the imperial segment where the moment rate from seismic depths is a factor of 2 5 larger than that from geodetic depths such variability has important implications for the accuracy to which future major earthquake magnitudes can be estimated

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

shocks in a box an analogue model of subduction earthquake cycles with application to seismotectonic forearc evolution 1 we introduce and test an experimental approach to simulate elastoplastic megathrust earthquake cycles using an analogue model and apply it to study the seismotectonic evolution of subduction zones the quasi two dimensional analogue model features rate and state dependent elastic frictional plastic and viscoelastic material properties and is scaled for gravity inertia elasticity friction and viscosity the experiments are monitored with a high resolution strain analysis tool based on digital image correlation particle imaging velocimetry piv providing deformation time series comparable to seismologic geodetic and geologic observations in order to separate elastic and nonelastic effects inherent the experimental deformation patterns we integrate elastic dislocation modeling edm into a hybrid approach we use the analogue earthquake slip and interseismic locking distribution as edm dislocation input and forward model the coseismic and interseismic elastic response the residual which remains when the edm prediction is subtracted from the experimental deformation pattern highlights the accumulation of permanent deformation in the model the setup generates analogue earthquake sequences with realistic source mechanisms and elastic forearc response and recurrence patterns and reproduces principal earthquake scaling relations by applying the model to an accretionary type plate margin we demonstrate how strain localization at the rupture peripheries may lead to a seismotectonically segmented forearc including a tectonically stable shelf and coastal high 20 plate convergence accommodated by internal shortening overlying the area of large megathrust earthquake slip fifty to 75 of plate convergence is accommodated by internal shortening in the slope region where earthquake slip tapers out toward the trench the inner forearc region remains undeformed and represents a basin

dynamic fault rupture and stress recovery processes in continental crust under depth dependent shear strength and frictional parameters abstract mikumo t 1992 dynamic fault rupture and stress recovery processes in continental crust under depth dependent shear strength and frictional parameters in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 201 222 the dynamic rupture process of large earthquakes in continental crust and the post seismic stress recovery process due to visco plastic behaviour are investigated by three and two dimensional numerical modelling taking into account the possible depth variations of the shear strength tectonic stress expected stress drop and of the critical weakening slip which are suggested by recent laboratory experiments on frictional parameters it was found that dynamic rupture can initiate at any depth in a brittle zone if high stress is concentrated with a dimensionless stress ratio s less than a certain limit but that the rupture cannot nucleate in a semi brittle zone with negative stress drop this suggests that the boundary between the fully brittle and semi brittle zones delineates the base of the seismogenic zone of background seismicity and aftershock distribution however the dynamic rupture of large earthquakes originating from the brittle zone can propagate into the semi brittle zone after some temporary arrest or with decelerated velocities which could generate low frequency seismic waves the depth extent of dynamic faulting and the maximum fault displacement are affected by the depth to the brittle semi brittle boundary and hence by the geothermal state within the crust the stress recovery due to visco plastic behaviour in the semi brittle and plastic regimes suggests that the rupture for eventual earthquakes tends to be nucleated near the upper boundary of the semi brittle zone

absolute location of 2019 ridgecrest seismicity reveals a shallow mw 7 1 hypocenter migrating and pulsing mw 7 1 foreshocks and duplex mw 6 4 ruptures

aftershocks of the western argentina caucete earthquake of 23 november 1977 some tectonic implications an aftershock survey using a network of eight portable and two permanent seismographs was conducted for the western argentina caucete earthquake ms 7 3 of november 23 1977 monitoring began december 6 almost 2 weeks after the main shock and continued for 11 days the data set includes 185 aftershock hypocenters that range in the depth from near surface to more than 30 km the spatial distribution of those events occupied a volume of about 100 km long 50 km wide 30 km thick the volumnar nature of the aftershock distribution is interpreted to be a result of a bimodal distribution of foci that define east and west dipping planar zones efforts to select which of those zones was associated with the causal faulting include special attention to the determination of the mainshock focal depth and dislocation theory modeling of the coseismic surface deformation in the epicentral region our focal depth 25 35 km and modeling studies lead us to prefer an east dipping plane as causal a previous interpretation by other investigators used a shallower focal depth 17 km and similar modeling calculations in choosing a west dipping plane our selection of the east dipping plane is physically more appealing because it places fault initiation at the base of the crustal seismogenic layer rather than in the middle of that layer which requires fault propagation to be updip rather than downdip

lateral variation of the cutoff depth of shallow earthquakes beneath the japan islands and its implications for seismogenesis abstract we estimated the spatial distribution of the cut off depth of shallow seismicity beneath the japan islands based on data from a recently constructed nationwide dense seismic network in order to avoid the effect of heterogeneous seismic velocity structure we determined the 3d seismic velocity structure for the whole of japan which was then used to relocate the hypocenters the cut off depth was determined by calculating d90 the depth above which 90 of the earthquakes occur a spatial distribution of estimated d90 values shows a considerable lateral variation ranging from about 5 km to about 40 km the d90 s are deep along the pacific coast of eastern japan locally shallow d90 s extend along belt like stretches of volcanic areas heat flow is low along the pacific coast in eastern japan and high in the volcanic areas this indicates that the lateral variation of d90 s is formed mainly by lateral geotherm variation cooling by the subducting old very cold pacific plate may cause the deep d90 s along the pacific coast in eastern japan heating by magma supplied from the mantle wedge below is considered to be the main cause of the shallow d90 s in the volcanic areas magma and or aqueous fluids derived from solidified magma contribute not only to locally shallow d90 s but also to the weakening of ambient rocks in the lower crust resulting in stress concentrations in the upper crust just above them large shallow inland earthquakes tend to occur in such areas suggesting that a model of shallow earthquake generation applied to tohoku can be used in other areas in japan as well

cyclic ductile and brittle deformation related to coseismic thrust fault propagation structural record at the base of a basement nappe preveli crete 1 the structural record at the base of a basement nappe preveli nappe crete greece thrust upon sedimentary rocks is investigated aimed on understanding mechanisms which result in decoupling of the thrust sheet from its original substratum we identify several superimposed deformation stages each with characteristic structural style and indications of episodic deformation at initially high differential stress the final stage involves formation of a matrix supported breccia transected by pseudotachylytes comprising the lowermost 30 m of the nappe brecciation and pseudotachylyte formation occurred in a single event and structures were not modified afterward complete induration of breccia and composition of phengite crystallized during devitrification of pseudotachylytes place the sequence of events into the middle crust we propose a model relating episodic deformation and cyclic stress history to propagation of a thrust fault in a limited number of seismic events terminal brecciation and frictional fusion record passage of the fault front beneath the site of observation and decoupling of the thrust sheet absence of discernible further deformation is consistent with negligible basal friction during transport as a nappe brecciation and pseudotachylyte formation mark the switch from a history of repeated coseismic loading and postseismic stress relaxation in the plastosphere driven by seismic events on the approaching thrust fault to passive transport with deformation localized in a weak thrust plane for a sequence of superimposed ductile to brittle structures our model provides an alternative to progressive cooling and exhumation concomitant with deformation over millions of years

seismological constraints on the down dip shape of normal faults this work forms part of the nerc and esrc funded project earthquakes without frontiers and was partially supported by the nerc large grant looking inside the continents from space

depth of the brittle ductile transition in a transcurrent boundary zone a model is proposed which describes the boundary zone between two transcurrent plates as a viscoelastic body with rheological properties changing with depth in this model the brittle ductile transition is defined as the depth at which the time derivative of shear stress changes from positive to negative values variations of this depth are studied as functions of geothermal gradient rheological parameters and strain rate using a power law rheology with exponent ranging from 1 to 4 stress relaxation in the ductile zone is controlled by a local characteristic time which depends on petrology temperature and in the case of non newtonian rheology on strain rate the composition and the hydration degree of crustal rocks may also sensibly influence the depth of the brittle ductile transition the model predictions are compared with observations regarding the san andreas imperial valley and north anatolian faults it is found that values ofn from 1 to 3 are more appropriate to reproduce the transition depth inferred by the seismicity distribution

spatiotemporal evolution of the 2011 prague oklahoma aftershock sequence revealed using subspace detection and relocation the 6 november 2011 mw 5 7 earthquake near prague oklahoma is the second largest earthquake ever recorded in the state a mw 4 8 foreshock and the mw 5 7 mainshock triggered a prolific aftershock sequence utilizing a subspace detection method we increase by fivefold the number of precisely located events between 4 november and 5 december 2011 we find that while most aftershock energy is released in the crystalline basement a significant number of the events occur in the overlying arbuckle group indicating that active meeker prague faulting extends into the sedimentary zone of wastewater disposal although the number of aftershocks in the arbuckle group is large comprising 40 of the aftershock catalog the moment contribution of arbuckle group earthquakes is much less than 1 of the total aftershock moment budget aftershock locations are sparse in patches that experienced large slip during the mainshock

aftershocks of the 1988 january 22 tennant creek australia intraplate earthquakes evidence for a complex thrust fault geometry summary on 1988 january 22 three earthquakes of ms 6 3 6 7 occurred in a 12 hr period near tennant creek northern territory in the proterozoic north australian craton and produced 32 km of surface rupture on two main scarps the lake surprise scarp is shaped like a boomerang with the east arm trending ese and the west arm wsw the kunayungku scarp lies 7 km to the northwest and trends ese locations of 211 aftershocks determined using data from portable seismograph arrays define a 10 km by 40 km aftershock zone elongated parallel to the trend of the surface ruptures in the western and eastern part of the fault zone aftershocks occur only south of the kunayungku and eastern lake surprise scarps respectively in the central section in contrast aftershocks lie primarily to the north of the western arm of the lake surprise scarp focal depths range from the surface to 8km in all sections the shallowest earthquakes lie closest to the scarps whereas deeper events lie further away in cross section the aftershocks lie in three distinct inclined zones which delineate fault surfaces ruptured by the main shocks aftershocks are concentrated near the edges of the inferred fault surfaces suggesting that stress was relieved in the centre of the faults by rupture during the main shocks the inferred fault plane dips are 45 to the ssw for the kunayungku fault 55 to the nnw for the western lake surprise fault and 35 to the ssw for the eastern lake surprise fault these dip directions are consistent with the sense of thrust movement inferred from surface deformation the reversal of fault dip and sense of movement between the central and end segments requires a complicated fault geometry the aftershock data would allow a second south dipping plane in the central section that does not intersect the surface this blind fault may be responsible for much of the moment release interpreted from the modelling of broad band teleseismic waveforms choy bowman 1989 rupture of the north dipping plane may have been controlled by a pre existing fault marked at the surface by a quartz ridge 5 km long and may be of secondary importance although the quartz ridge suggests previous faulting the absence of significant topographic relief together with estimates of erosion rates suggest an average repeat time in excess of 104yr preliminary interpretation of water withdrawal histories and water level data from a borefield adjacent to the eastern lake surprise scarp does not support a causal relationship between the borefield and the occurrence of the earthquakes the nearby warramunga wra seismic array provides a record of local earthquake activity from 1965 to the present the fault area was essentially aseismic until two small earthquakes in 1986 february and a series of six magnitude 4 5 earthquakes in 1987 january which were followed by more than 1000 aftershocks the frequency of occurrence of aftershocks declined very slowly in 1987 with p 0 2 in the modified omori formula whereas for the 1988 aftershock sequence p 1 the low p during 1987 may have been diagnostic of high stress in the source and water authority provided partial financial support for j r b and g g

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

depth dependence of earthquake frequency magnitude distributions in california implications for rupture initiation statistics of earthquakes in california show linear frequency magnitude relationships in the range of m2 0 to m5 5 for various data sets assuming gutenberg richter distributions there is a systematic decrease in b value with increasing depth of earthquakes we find consistent results for various data sets from northern and southern california that both include and exclude the larger aftershock sequences we suggest that at shallow depth 0 to 6 km conditions with more heterogeneous material properties and lower lithospheric stress prevail rupture initiations are more likely to stop before growing into large earthquakes producing relatively more smaller earthquakes and consequently higher b values these ideas help to explain the depth dependent observations of foreshocks in the western united states the higher occurrence rate of foreshocks preceding shallow earthquakes can be interpreted in terms of rupture initiations that are stopped before growing into the mainshock at greater depth 9 15 km any rupture initiation is more likely to continue growing into a larger event so there are fewer foreshocks if one assumes that frequency magnitude statistics can be used to estimate probabilities of a small rupture initiation growing into a larger earthquake then a small m2 rupture initiation at 9 to 12 km depth is 18 times more likely to grow into a m5 5 or larger event compared to the same small rupture initiation at 0 to 3 km

spatial variation of seismogenic depths of crustal earthquakes in the taiwan region implications for seismic hazard assessment abstract this paper presents the first whole taiwan scale spatial variation of the seismogenic zone using a high quality crustal seismicity catalog the seismicity onset and cutoff depths i e seismogenic depths are determined by the earthquake depth moment distribution and used to define the upper and lower boundaries of the seismogenic zone respectively together with the published fault geometries and fault area moment magnitude relations the depth difference in the onset and cutoff depths i e seismogenic thickness is used as the fault width to determine the moment magnitudes of potential earthquakes for the major seismogenic faults results show that the largest mw7 9 8 0 potential earthquake may occur along the changhua fault in western taiwan where the seismic risk is relatively high and seismic hazard mitigation should be a matter of urgent concern in addition the first motion focal mechanism catalog is used to examine the relation between the seismogenic depths and earthquake source parameters for crustal earthquakes 50 km the shallowest onset and cutoff depths are observed for normal and strike slip events respectively this observation is different from the prediction of the conventional continental rheology model which states that thrust events have the shallowest cutoff depth thus a more sophisticated rheology model is necessary to explain our observed dependence of the seismogenic depths on faulting types meanwhile for intermediate to large crustal mw 4 depth 50 km earthquakes thrust events tend to occur at the bottom region of the seismogenic zone but normal and strike slip events distribute at a large depth range

mechanical interaction between neighboring active faults an application to the atera fault central japan abstract static stress changes across the atera fault central japan due to the neighboring large earthquakes are examined several large earthquakes in the past 100 yrs which might have dominantly affected the fault are selected in order to calculate coseismic changes in the fracture stress the result suggests that the stress increased at both the northern and southern ends of the fault which amounted to as much as 6 bar in total among these earthquakes the nagano seibu earthquake m 6 8 of 14 september 1984 seems to have most seriously affected the atera fault in such a sense as to increase the fracture stress

recent research on the physical aspects of earthquakes abstract recent developments in the field of physical aspects of earthquakes which encompasses in present day terminology the analysis of focal dynamics and of catastrophic effects of earthquakes are reviewed in particular individual sections of this review deal with the earthquake source effects of earthquakes on the ground the geographic and temporal distribution of earthquakes the characterization of seismic risk earthquake prediction and with the artificial release of earthquakes in this instance the review supplements earlier information by the author 1975 by new data published mainly between 1975 and 1984

influence of fault plane heterogeneity on the seismic behavior in the southern kurile islands arc the seismic behavior in the southern kurile islands arc is strongly influenced by spatial heterogeneity in the mechanical properties of the plate interface maps showing sites of maximum seismic moment release for the great underthrusting earthquakes of 1958 1963 1969 and 1973 provide a first order image of the major regions of enhanced strength or asperities hypocenters of these and an additional 83 smaller earthquakes with mb 5 3 and known underthrusting mechanisms were recomputed using the method of joint hypocenter determination in order to assess better the influence that the strength distribution exerts on the interplate seismicity patterns nearly all of the smaller magnitude earthquakes locate outside of the principal asperities of the great earthquakes this observation is consistent with substantial release of accumulated strain energy in asperity regions during the great earthquakes and a redistribution of stress in adjacent areas following their rupture an along dip depth dependent component of strength heterogeneity appears to influence the seismicity patterns the asperities of the 1958 and 1973 great earthquakes and hypocenters of most of the ms 7 earthquakes occur near the downdip edge of the 100 km wide seismically active plate interface this would be expected if shear resistance on the interface increases monotonically with lithostatic pressure up to the brittle ductile or stick slip stable slip transition that defines the base of the seismogenic zone the asperities of the 1963 and 1969 earthquakes however appear to be located well above the downdip edge of the coupled plate interface the occurrence of large asperities in middepth ranges of the seismogenic interface suggests the influence of along dip changes in other parameters besides lithostatic pressure that control shear resistance along strike segmentation of the kurile islands thrust zone may be a consequence of along strike alternation in the location of the largest asperities between the deep interface and the midinterface

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

nucleation and growth of dip slip faults in a stable craton we analyze the conditions for nucleation of a dip slip fault in intact crust and its subsequent growth using linear elastic fracture mechanics and the finite element method we assume a fault can be modeled as a mode ii shear crack in a layered elastic crust and we investigate fault behavior under conditions of a variable dip and shear fracture energy two shear fracture energy gradients gc were evaluated both have surface values of 1 105 j m2 and increase linearly to values of 1 106 or 1 107 j m2 at 15 km depth the base of the seismogenic zone we assume that the vertical and horizontal components of the gravitational stress are both equal to the lithostatic load effectively removing them from the calculation of shear stress on the fault strain required for failure varied with respect to shear fracture energy gradient and rupture direction but not with dip rupture upward from the base of the seismogenic zone required more than twice the initial strain to cause fault growth and would result in very large earthquakes rupture downward in models associated with the higher gc gradient resulted in stable growth of the fault that is additional strain was needed to allow for continuous fault growth from the surface to the base of the seismogenic zone we suggest that fault nucleation and growth are a stable process which would preferentially occur by rupturing downward under stable conditions rerupturing of an established fault may initiate at depth or the surface depending on the degree of healing between rupture events and the tectonic stress available a vast majority of shallow crustal earthquakes nucleate at the base of the seismogenic zone and rupture upwards this suggests that most events are a reactivation of an old established fault and not growth of a new or developing fault