earthquake activity related to seismic cycles in a model for a heterogeneous strike slip fault we investigate the evolution of seismicity within large earthquake cycles in a model of a discrete strike slip fault in elastic solid the model dynamics is governed by realistic boundary conditions consisting of constant velocity motion of regions around the fault static kinetic friction and dislocation creep along the fault and 3d elastic stress transfer the fault consists of brittle parts which fail during earthquakes and undergo small creep deformation between events and aseismic creep cells which are characterized by high ongoing creep motion this mixture of brittle and creep cells is found to generate realistic aftershock sequences which follow the modified omori law and scale with the mainshock size furthermore we find that the distribution of interevent times of the simulated earthquakes is in good agreement with observations the temporal occurrence however is magnitude dependent in particular the small events are clustered in time whereas the largest earthquakes occur quasiperiodically averaging the seismicity before several large earthquakes we observe an increase of activity and a broadening scaling range of magnitudes when the time of the next mainshock is approached these results are characteristics of a critical point behavior the presence of critical point dynamics is further supported by the evolution of the stress field in the model which is compatible with the observation of accelerating moment release in natural fault systems

oblique convergence and deformation along the kuril and japan trenches the hypothesis that present day deformation within the southern kuril forearc is driven by oblique subduction of the pacific plate is tested using 397 horizontal slip directions derived from shallow thrust earthquakes from the kuril and japan trenches for the period 1963 1991 a simple two plate model fits the 397 slip vectors significantly worse than a model that permits strike slip motion of the southern kuril forearc relative to the overlying plate weighted mean slip directions along the southern kuril trench are systematically rotated toward the direction orthogonal to the trench which implies that the net convergence is partitioned into less oblique subduction and trench parallel displacement of the southern kuril forearc the angular discrepancy between the observed slip direction and the direction predicted by the nuvel 1 pacific north america euler vector implies that the southern kuril forearc translates 6 11 mm yr 1 to the southwest relative to the overlying north american plate these results are consistent with geologically geodetically and seismologically observed convergence at the leading edge of the forearc sliver in southern hokkaido and with previously inferred extension at the trailing edge of the sliver which is located at the bussol strait at 46 n the percentage of the oblique component of the rigid plate convergence vector that is transferred into forearc strike slip motion is only 30 which may be evidence that the hokkaido honshu bend in the trench hinders southwest forearc motion or that the greater strength of oceanic forearcs impedes motion along forearc strike slip faults

morphology of the distorted subducted pacific slab beneath the hokkaido corner japan abstract the intersection of the japan and kurile arcs is expressed as a cuspate feature at the trench a bend in the japanese islands and a complex lithospheric structure and is known as the hokkaido corner the pacific plate is subducting beneath the two arcs in the northwest pacific at different velocities which has resulted in an arc arc collision and distortion of the subducting oceanic lithosphere using p and s wave tomographic images and seismicity the distorted shape of the subducted pacific plate beneath the hokkaido corner can be interpreted in three dimensions the pacific plate is imaged as continuous along the japan kurile arc with dip angle increasing from south to north but at the arc arc junction the geometry is complex and appears crumpled beneath the hokkaido corner there are two features in the tomography that are clearly imaged a region of low velocity at approximately 50 150 km depth between 142 5 145 e and 41 43 n and a distorted buckled lower slab boundary these two unusual characteristics in the slab morphology are likely to be related to deformation of the subducted pacific plate at the arc arc junction

tomography of the 1995 kobe earthquake area comparison of finite frequency and ray approaches summary we determined a detailed 3 d crustal model in the 1995 kobe earthquake m 7 2 area in southwest japan using both finite frequency and ray tomography methods our finite frequency tomography technique is based on the single scattering theory the finite frequency sensitivity kernel derived in this study reflects correctly the sensitivity of the heterogeneity off the geometrical ray path and the existence of fresnel volume and the kernel depends on the dominant frequency of the observed wave the dominant frequency is estimated directly from the earthquake magnitude based on a relation that is obtained by regressively analyzing the displacement spectra of 20 earthquakes in the study area we used 141 118 p wave and 133 648 s wave high quality arrival time data from 2813 kobe aftershocks and 3140 other local earthquakes during 1995 2010 the tomographic images obtained with the finite frequency and ray tomography methods show a high level of similarity which is verified quantitatively by adopting the structural similarity index our results show that the kobe main shock hypocentre is located in a distinctive zone characterized by a high poisson s ratio and a low product vp vs of p and s wave velocities which is interpreted as a fluid filled fractured rock matrix that may have triggered the 1995 kobe earthquake

deep low frequency microearthquakes in or around seismic low velocity zones beneath active volcanoes in northeastern japan abstract precise hypocenter relocations have been made for shallow intraplate microearthquakes beneath northeastern japan by applying source region station corrections the relocated hypocenter distribution shows that most of the events are confined to the upper 15 km of the crust which forms the brittle seismogenic zone in this volcanic arc it also shows that exceptionally deep microearthquakes well below the base of the seismic aseismic boundary occur at twelve locations of northeastern japan they occur in the lowermost crust or in the uppermost mantle where rheological properties of rocks are presumed to be in the ductile regime all the 153 events presently detected in the lowermost crust or in the uppermost mantle have anomalously low predominant frequencies 1 5 5 hz both for p and s waves in contrast to those 8 20 hz of normal shallow events in the brittle seismogenic zone the magnitudes of these events are small m 2 2 moreover all of these events are located beneath active volcanoes and or near p wave low velocity zones in the uppermost mantle the proximity of these events to the active volcanoes and other anomalous features suggest that these deep low frequency events are generated by magmatic activity of mantle diapirs in the uppermost mantle

geological and industrial implications of extensive dilatancy anisotropy extensive dilatancy anisotropy is the hypothesized distribution of stress aligned fluid filled microcracks pervading most rocks in the earth s crust the geometry of the cracks and the aligning stress field can be monitored by analysing the waveforms of shear waves propagating through the rockmass the ability to estimate some of the parameters of the crack and stress geometry by analysing shear wave particle displacements has widespread implications

investigating transport properties and turbidity dynamics of a karst aquifer using correlation spectral and wavelet analyses in many places throughout the world drinking water is frequently contaminated by turbidity such turbidity however as representative of particle transport can be used as to trace certain features of particle transport properties in order to investigate the relation between particle and dissolved species transport and hydrodynamics in karst systems correlation and spectral analyses were performed on time series of rainfall input signal and water level specific conductance and turbidity output signals at a karst spring system in the chalk aquifer of the lower seine valley france this system is composed of a spring connected to a sinkhole on the chalk plateau where a small creek enters the subsurface the autocorrelation functions for water level and turbidity showed a short memory effect demonstrating the short duration of the influence of flood events on these two parameters whereas specific conductance representing less mineralized storm derived water had a much longer memory effect these results were interpreted as reflecting the rapid reactivity of the spring to rain events with storage of water in the fissured chalk explaining the longer memory effect for specific conductance than for particles energy spectra computed by fast fourier transform of autocorrelation functions showed a strong structure in the output signals whereas the input signal rainfall was random thus allowing assessment and comparison of system behaviour regarding dissolved and solid transport as well as hydraulics cross correlation functions which allow an assessment of impulse response functions confirmed the low inertia of the system for water level and turbidity and the much higher inertia for specific conductance in addition to the main peak two secondary peaks in the cross correlation functions suggest the existence of additional flowpaths that might involve the contribution of other point source recharge and or delayed infiltration through the clayey surficial formation and solution pipes which could act as epikarst analysis using continuous wavelet spectra allowed a better investigation of the rainfall signal structure and highlighted a strong relationship between turbidity and rainfall which could not be deduced from the energy spectra specific spectral components in water level were isolated and a time domain reconstruction using inverse wavelet transform allowed separation of quick flow and slow flow components

newly imaged shape of the deep seismic zone within the subducting pacific plate beneath the hokkaido corner japan kurile arc arc junction 1 the geometry of the deep seismic zone associated with the subducting pacific plate beneath the north american plate in the hokkaido corner japan kurile arc arc junction has been investigated based on the hypocenters accurately relocated by a dense local seismographic network with three dimensional p and s wave velocity structures the model suggests that the lateral changes in the dip of the subduction zone are more rapid than previously believed we found that the deep seismic zone in the pacific plate dips at 20 to 30 on the side of the japan arc the dip angle increased in a narrow region around 143 144 e by 10 to 20 and the dip was 40 to 50 on the side of the kurile arc in the transitional zone around 143 144 e an unusual distribution of microearthquakes has been discovered within the pacific plate which was located on a near vertical plane with an area of 50 100 km2 with strike that was perpendicular to the kurile trench axis this feature was named the tokachi oki slab cracking zone we suggest that this is a slab cracking zone torn by the extensional stress due to the rapid lateral changes in the dip of the subduction zone the slab cracking zone may possibly grow into the large disruption or tear of the slab in the future

accretion and exhumation structures formed by deeply subducted seamounts in the kamuikotan high pressure temperature zone hokkaido japan 1 the lower cretaceous iwashimizu complex in the southern kamuikotan zone japan was formed by accretion of seamounts which subducted to the lawsonite albite to blueschist facies the complex is a pile of four nappe units each unit comprises a duplex with horses of seamount volcanics sedimentary rocks and ramp shear zones suggesting a thin skinned peeling of subducted seamounts each unit bounded fault is regarded as the floor thrust of an overlying duplex and the roof thrust of an underlying duplex reflecting a downward progression of underplating accretion the structurally upper pirashuke unit was metamorphosed at higher pressure than the structurally lower units this inverted arrangement of metamorphic grade can be explained by shallowing of progressively younging subducted slab structurally upper units were exhumed synchronously with growth of the structurally lower units this synaccretionary exhumation can be explained by repetition of undercritical duplex forming compression and overcritical extensional unroofing during seamounts subduction

mineralogy and composition of the upper mantle seismic velocities are calculated for two petrological models of the upper mantle an olivine rich assemblage pyrolite and a garnet clinopyroxene rich olivine bearing assemblage piclogite these are compared with recent seismic profiles for various tectonic provinces the shield data is most consistent with a cold olivine and orthopyroxene rich lid the seismic lithosphere extending to 150 km followed by a high temperature gradient and or a change in mineralogy that serves to decrease the velocity from 200 to 400 km the velocities follow a 1400 c adiabat the rise tectonic mantle is much slower presumably hotter and is likely to be above the solidus to depths of at least 300 km the high v p v s ratio of the lower oceanic lithosphere in the western pacific is most consistent with eclogite

p wave anisotropic tomography of the crust and upper mantle under hokkaido japan abstract we determined a 3 d anisotropic velocity structure beneath hokkaido in northern japan using a large number of first p wave arrival times the travel time inversion is parameterized with an isotropic component and two anisotropic parameters for each grid node by assuming p wave azimuthal anisotropy with hexagonal symmetry axis distributed horizontally the geometries of the conrad and moho discontinuities and the upper boundary of the subducting pacific plate are taken into account in the model our results show that low velocity zones exist beneath active arc volcanoes in the crust and in the central portion of mantle wedge above the high velocity pacific slab which are similar to the previous tomographic images p wave anisotropy is revealed in the crust mantle wedge and the subducting pacific slab in the upper crust the anisotropy is possibly caused by microcracks and cracks in the lower crust the anisotropic structure is different from that in the upper crust and it may be affected considerably by the plastic flow deformation in the mantle wedge the fast velocity direction fvd is generally trench normal in most of the study area while it becomes trench parallel in the pacific coast areas close to the trench which agrees with the shear wave splitting results beneath the volcanic front the fvd is also trench parallel which may suggest the existence of complex 3 d mantle flow in the mantle wedge the fvd in the subducting pacific slab is nearly north south which likely keeps the original fossil anisotropy of the pacific plate formed at the mid ocean ridge or is affected by the olivine fabric transition from a type to b type fabric due to the changes in water content stress and temperature

tectonic volcanic and semi volcanic deep low frequency earthquakes in western japan abstract in western japan relatively small m the present paper characterizes the seismicity of the three types of lfes in five regions based on a more complete catalog thanks to automated event detection and precise relocation using waveform correlation the results show that isolated intraplate lfes are more similar to volcanic lfes than to tectonic lfes the volcanic and isolated intraplate lfes are insensitive to tidal stress are characterized by power law magnitude frequency statistics such as the gutenberg richter relation and are distributed mainly in small vertical clusters while the tectonic lfes are modulated by tidal stress are limited in size and are distributed along the plate boundary hence we propose that isolated intraplate lfes should be named semi volcanic lfes since tectonic lfes and volcanic lfes are thought to be related to the fluid existence and fluid movements respectively isolated intraplate semi volcanic lfes may be related to crustal fluid movements in the source area

laboratory measurements of elastic anisotropy parameters for the exposed crustal rocks from the hidaka metamorphic belt central hokkaido japan summary to study crustal rock seismic anisotropy and its effect on seismic wave propagation we measure the seismic velocity anisotropy of two amphibolites one biotite gneiss and one biotite schist from the hidaka metamorphic belt in central hokkaido japan under confining pressures up to 150 mpa the rock microstructures show foliation and lineation characterized by lattice preferred orientation lpo of hornblende or biotite p and two s wave velocities are measured along the direction perpendicular to the foliation plane and two directions in the foliation plane perpendicular and parallel to the lineation we assume orthorhombic symmetry based on the rock microstructures and obtain tsvankin s anisotropic parameters an extension of thomsen s parameters for orthorhombic symmetry p and s wave phase velocity surfaces are calculated from anisotropy parameters and compared with the measured velocities along particular directions and with the velocity contour maps calculated from the voigt averages of singlecrystal elastic constants based on the orientation of measured lpo data qualitatively the measured velocity anisotropy agrees with the velocity contour calculated from the lpo data although large quantitative differences exist between them all anisotropy patterns can be approximated as transverse isotropy or its modification appearing as orthorhombic symmetry biotite schist containing 30 per cent volume ratio biotite shows strong s wave anisotropy and the phase velocity surfaces of p waves show a large deviation from ellipticity in the plane perpendicular to the foliation and parallel to the lineation in the same plane s waves show a singularity due to a large bulge of the sv velocity surface

seismic structure beneath the tonga arc and lau back arc basin determined from joint vp vp vs tomography the tonga arc and associated lau basin exhibit many geologically important processes that link subduction and mantle flow with plate separation and crustal production we create seismic tomograms of the tonga lau region by jointly inverting for vp and vp vs structure using data from the labatts ocean bottom seismograph experiment and several island deployments to better constrain dynamic processes in the mantle wedge jointly using p and s data can help distinguish between the various mechanisms responsible for seismic velocity anomalies such as temperature and the presence of melt and or volatiles because high attenuation in the wedge limits the s wave data set we focus on 2 d inversions beneath the linear obs array where resolution is best and also parameterize the solution in terms of the vp vs ratio as expected the subducting slab has fast vp and vs and a low vp vs ratio consistent with the cold downgoing plate the central lau spreading center clsc exhibits stronger anomalies in vp vs than in vp with the anomalies larger than would be predicted purely by temperature variations the clsc anomaly extends 100 km to the west of the axis suggesting a broad region of melt production driven by passive upwelling from plate separation rather than active upwelling mechanisms the anomaly is asymmetric about the axis suggesting that slab induced corner flow possibly influences mantle dynamics several hundred kilometers away from the arc there is a strong anomaly beneath the volcanic arc that gradually deepens as it trends toward the back arc likely outlining a hydrated region of melt production that feeds the volcanic front hydration possibly continues throughout the wedge to at least 400 km depth the lau ridge exhibits a thicker lithosphere relative to the rest of the basin while the fiji platform likely has a thinner lithosphere than the lau ridge from more recent extension there is also a reasonable likelihood of a small degree of partial melt in the uppermost mantle beneath the platform

anisotropic tomography of hokkaido reveals delamination induced flow above a subducting slab we present a new 3 d anisotropic seismic model for the crust and upper mantle beneath hokkaido japan based on tomographic inversion of p and s arrival times from a regional seismic database the p model is parameterized with three parameters at each point that describe the azimuthal anisotropy the s model is represented isotropically the isotropic p and s velocity anomalies match nearly perfectly in the crust they show a prominent linear anomaly in central hokkaido along the kamuikotan and hidaka belts which represents the area of eastward underthrusting of the japan block underneath the kuril fore arc we interpret the high velocity anomaly beneath the hidaka zone as being delaminated mafic crust and entrained mantle lithosphere which developed due to crustal shortening in the collision zone one of our vertical sections shows a very unusual configuration for a subduction zone a low velocity slab is overlain by a high velocity body in the mantle wedge we propose that the high velocity delaminated material sinking along the slab surface prevents the escape of fluids and melts from the upper part of the slab where they are generated due to phase transitions as a result a large portion of the fluids is entrained downward and lowers the seismic velocities in the slab the azimuthal anisotropy in the crust clearly corresponds to the major tectonic units and delineates the major suture zones in the mantle the anisotropy has a fan shaped configuration and most likely represents the deviating of flows starting in southern hokkaido and splitting into three directions the western and eastern flows proceed toward the two volcanic groups on hokkaido and they may carry with them additional material to trigger the characteristic caldera forming eruptions in these groups

shear wave anisotropy in the crust mantle wedge and subducting pacific slab under northeast japan to study the anisotropic structure beneath northeast ne japan we made 4366 shear wave splitting measurements using high quality seismograms of many earthquakes occurring in the crust and the subducting pacific slab our results provide important new information on the s wave anisotropy in the upper crust lower crust mantle wedge and subducting pacific slab in the upper crust the anisotropy is mainly caused by the stress aligned fluid saturated microcracks the measured delay times dts increase to 0 10 s at 10 11 km depth the fast velocity directions fvds are parallel to either the tectonic stress or the strike of active faults the maximum dts for the low frequency earthquakes near the moho are 0 15 0 17 s suggesting strong anisotropy at the base of the crust or in the uppermost mantle the measurements for the intermediate depth earthquakes in the pacific slab show dominant e w trench normal fvds in the back arc area and n s trench parallel fvds in the fore arc area the trench normal fvds in the back arc area are caused by the corner flow in the mantle wedge as a result of the subduction of the pacific plate the maximum dts for the slab earthquakes reach 0 30 0 32 s at 100 km depth but only half of the total dts are produced in the mantle wedge the small dts in the mantle wedge may result from an isotropic or weak anisotropic zone in the middle of the mantle wedge in the fore arc the dominant trench parallel fvds for the slab earthquakes are consistent with those for the upper crust earthquakes and 80 of the total dts can be accounted for by the anisotropy in the crust in the subducting pacific slab the trench parallel fvds may reflect either the original fossil anisotropy in the pacific plate when the plate was produced in the mid ocean ridge or the preferred orientations of the crystals and cracks in the upper part of the subducting slab

detailed seismic attenuation structure beneath hokkaido northeastern japan arc arc collision process arc magmatism and seismotectonics in this study we imaged a detailed seismic attenuation structure frequency independent q 1 beneath hokkaido japan by merging waveform data from a dense permanent seismic network with those from a very dense temporary network corner frequency of each event used for t estimation was determined by the s coda wave spectral ratio method the seismic attenuation qp 1 structure is clearly imaged at depths down to about 120 km for the fore arc side of hokkaido high qp zones are imaged at depths of 10 to 80 km in the crust and mantle wedge above the pacific slab low qp zones are clearly imaged in the mantle wedge beneath the back arc areas of eastern and southern hokkaido these low qp zones extending from deeper regions extend to the moho beneath volcanoes the locations of which are consistent with those of seismic low velocity regions these results suggest that the mantle wedge upwelling flow occurs beneath hokkaido except in the area where there is a gap in the volcano chain in contrast an inhomogeneous seismic attenuation structure is clearly imaged beneath the hokkaido corner a broad low qp zone is located at depths of 0 60 km to the west of the hidaka main thrust the location almost corresponds to that of the seismic low velocity zone in the collision zone the fault planes of the 1970 m6 7 and 1982 m7 1 earthquakes are located at the edges of this broad low qp zone observations in this study indicate that our findings contribute to understanding the detailed arc arc collision process magmatism and seismotectonics beneath hokkaido

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

seismic anisotropy due to preferred mineral orientation observed in shallow crustal rocks in southern alaska laboratory velocity measurements and structural field relations explain the observation of a significant seismic anisotropy within highly foliated rocks in southern alaska the orientation of the principal compressive stress indicates that this anisotropy is not related to extensive dilatancy but can be satisfactorily explained by the foliation of the metasedimentary rocks laboratory measurements indicate a significant anisotropy within these rocks even at pressures well above those thought to close microcracks these observations document that anisotropy related to preferred mineral orientation may be widespread in continental rocks thus pervasive foliation can play a more important role in causing anisotropy than dilatancy and inferences of principal stress orientations solely from anisotropy may be erroneous

tomographic imaging of the alaska subduction zone the alaska subduction zone is characterized by the pacific plate descending beneath the north american plate causing abundant seismic activity in the crust and along the wadati benioff zone down to a depth of approximately 200 km we have used 142 908 p wave arrival times from 12 237 shallow and intermediate depth earthquakes recorded by the alaska earthquake information center jointly run by the geophysical institute university of alaska fairbanks and u s geological survey in the period from january 1977 to november 1991 to investigate the three dimensional 3 d p wave velocity structure beneath central and southern alaska travel times and ray paths are accurately calculated by using an efficient 3 d ray tracing technique the nonlinear tomographic problem is solved by iteratively conducting linear inversions and the velocity structure and hypocentral locations are simultaneously determined we conducted two types of inversions one is an inversion with a laterally homogeneous starting model the others are what we call slab inversions in which we introduce into the initial model the high velocity subducting pacific plate as a priori information we found that the slab inversions gave a seismologically more plausible result and a final root mean square travel time residual significantly smaller than that of the inversion with the homogeneous starting model detailed p wave tomographic images are obtained for the crust and upper mantle down to a depth of 200 km with spatial resolutions of 30 60 km the tomographic image of the upper crust correlates well with the major surface geological features such as slow sedimentary basins and fast ultramafic bodies prominent low velocity anomalies exist in the crust and upper mantle beneath active volcanoes in the mantle wedge the low velocity anomalies dip toward the continental side and extend to a depth of about 150 km which are considered to be associated with the active volcanism in the alaska subduction zone the results suggest that the subducting pacific plate has a thickness of 45 55 km and a p wave velocity 3 6 higher than that of the surrounding mantle

upper and middle crustal deformation of an arc arc collision across hokkaido japan inferred from seismic refraction wide angle reflection experiments abstract the hidaka collision zone hcz central hokkaido japan is a good target for studies of crustal evolution and deformation processes associated with an arc arc collision the collision of the kuril arc ka with the northeast japan arc nja which started in the middle miocene is considered to be a controlling factor for the formation of the hidaka mountains the westward obduction of middle lower crustal rocks of the ka the hidaka metamorphic belt hmb and the development of the foreland fold and thrust belt on the nja side the hokkaido transect project undertaken from 1998 to 2000 was a multidisciplinary effort intended to reveal structural heterogeneity across this collision zone by integrated geophysical geological research including seismic refraction reflection surveys and earthquake observations an e w trending 227 km long refraction wide angle reflection profile found a complicated structural variation from the ka to the nja across the hcz in the east of the hcz the hinterland region is covered with 4 4 5 km thick highly undulated neogene sedimentary layers beneath which two eastward dipping reflectors were imaged in a depth range of 10 25 km probably representing the layer boundaries of the obducting middle lower crust of the ka the hmb crops out on the westward extension of these reflectors with relatively high vp 6 0 km s and vp vs 1 80 consistent with middle lower crustal rocks beneath these reflectors more flat and westward dipping reflector sequences are situated at the 25 27 km depth forming a wedge like geometry this distribution pattern indicates that the ka crust has been delaminated into more than two segments under our profile in the western part of the transect the structure of the fold and thrust belt is characterized by a very thick 5 8 km sedimentary package with a velocity of 2 5 4 8 km s this package exhibits one or two velocity reversals in paleogene sedimentary layers probably formed by imbrication associated with the collision process from the horizontal distribution of these velocity reversals and other geophysical geological data the rate of crustal shortening in this area is estimated to be greater than 3 4 mm year which corresponds to 40 50 of the total convergence rate between the nja and the eurasian plate this means that the fold and thrust belt west of the hcz is absorbing a large amount of crustal deformation associated with plate interaction across hokkaido island

high resolution seismic velocity structure beneath the hokkaido corner northern japan arc arc collision and origins of the 1970 m 6 7 hidaka and 1982 m 7 1 urakawa oki earthquakes 1 using travel time data from both a nationwide dense seismic network and a dense temporary seismic network we obtain a high resolution three dimensional seismic velocity structure beneath the hokkaido corner considerable inhomogeneity in the seismic velocity structure is clearly imaged above the subducting pacific slab our results indicate that a broad low velocity zone of p and s waves with velocities consistent for crustal rocks is observed west of the hidaka main thrust at depths of 35 90 km the images also indicate that several smaller scale high velocity zones are located at depths of 0 35 km striking approximately north south and inclined to the east northeastward at 40 60 all of these anomalous high velocity zones are located at the deeper extension of neogene thrust faults the clearest high velocity zone is located beneath the hidaka metamorphic belt and is in contact with the eastern edge of the broad low velocity zone moreover the boundary between the clearest high velocity and the broad low velocity zones corresponds to the fault plane of the 1970 mj magnitude determined by the japan meteorological agency 6 7 hidaka earthquake the western boundary of another small high velocity zone at depths of 20 to 30 km within the broad low velocity zone corresponds to the fault plane of the 1982 mj 7 1 urakawa oki earthquake these observations suggest that these two large and anomalously deep inland earthquakes occurred at sharp material boundaries under a northeast southwest compressional stress field caused by ongoing arc arc collision process

correlation of paleotectonic fracture and microfracture orientations in cores with seismic anisotropy at cajon pass drill hole southern california fractures and microfractures in oriented cores from the cajon pass drill hole southern california have strong preferred orientations there are two major sets of extensional fractures and microfractures that have northwest and northeast strikes and vertical dips relative and absolute densities of both sets vary greatly within a single core the regional tectonic history implies that these fractures and microfractures probably formed before late miocene pliocene vertical seismic profiling experiments in the drill hole show shear wave splitting with polarization directions parallel to the fracture and microfracture orientations the measured seismic anisotropy is due to these inherited deformation fabrics and does not appear to be caused by the current local stress field

continuous gps array and present day crustal deformation of japan a gps array with about 1 000 permanent stations is under operation in japan the gps array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the japanese islands based on daily coordinate data of the gps stations strain rate distribution is estimated most regions with a large strain rate are related to plate boundaries and active volcanoes in addition the niigata kobe tectonic zone nktz is recognized as a region of large strain rate along the japan sea coast and in the northern chubu and kinki districts this newly found tectonic zone may be related to a hypothetical boundary between the eurasian or amurian and the okhotsk or north america plates precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations

complex layered deformation within the aegean crust and mantle revealed by seismic anisotropy continental lithosphere can undergo pervasive internal deformation often distributed over broad zones near plate boundaries however because of the paucity of observational constraints on three dimensional movement at depth patterns of flow within the lithosphere remain uncertain endmember models for lithospheric flow invoke deformation localized on faults or deep shear zones or alternatively diffuse viscous fluid like flow here we determine seismic rayleigh wave anisotropy in the crust and mantle of the aegean region an archetypal example of continental deformation our data reveal a complex depth dependent flow pattern within the extending lithosphere beneath the northern aegean sea fast shear wave propagation is in a north south direction within the mantle lithosphere parallel to the extensional component of the current strain rate field in the south central aegean where deformation is weak at present anisotropic fabric in the lower crust runs parallel to the direction of palaeo extension in the miocene the close match of orientations of regional scale anisotropic fabric and the directions of extension during the last significant episodes of deformation implies that at least a large part of the extension in the aegean has been taken up by distributed viscous flow in the lower crust and lithospheric mantle

p wave anisotropic tomography beneath northeast japan we determined a 3 d p wave anisotropic tomography beneath northeast japan by using first p arrival times the travel time inversion is parameterized with an isotropic component and two anisotropic parameters for each grid node by assuming p wave azimuthal anisotropy with hexagonal symmetry axis distributed horizontally the geometries of the conrad and moho discontinuities and the upper boundary of the subducting pacific plate are taken into account in the model our extensive synthetic tests show that the anisotropic velocity inversion method is reliable our results show that low velocity zones exist below active volcanoes in the crust in the fore arc mantle wedge and in the central portion of the mantle wedge above the high velocity pacific slab which are similar to the previous tomographic images anisotropic velocity variations are revealed in the crust mantle wedge and the subducting pacific slab the anisotropic patterns are complex and different in the upper and lower crust in the mantle wedge the fast direction of p velocity is generally trench parallel in the fore arc area while it becomes trench normal in the back arc area which agree well with the shear wave splitting results the trench parallel fast direction is revealed beneath the volcanic front which may suggest the existence of complex 3 d mantle flows in the mantle wedge the fast velocity direction in the subducting pacific slab is mostly n s which is likely due to the original fossil anisotropy of the pacific plate formed at the mid ocean ridge our result also suggests that the anisotropy is weak in the upper crust and the average amplitude of the velocity anisotropy in the mantle is no larger than 4

depth of the moho discontinuity beneath the japanese islands estimated by traveltime analysis 1 the crustal structure beneath the japanese islands including depth distributions of the conrad and moho discontinuities was estimated using a tomographic inversion of regional body wave arrival times depth distributions of the bottom of the surface layer the conrad and the moho were modeled with two dimensional b spline functions while velocity distributions in layers were expressed by three dimensional b spline functions the depth of the discontinuities and the velocity in the layers were estimated simultaneously by the least squares method the velocity structure was sequentially estimated from shallower parts to deeper parts to avoid correlation between them this sequential analysis provided improved depth resolution the deepest region of the moho discontinuity was located in central honshu reaching about 40 km the moho discontinuity was generally deep in the central part of the islands whereas it was relatively shallow in the kanto southwestern chubu and chugoku districts in honshu and in northern kyushu some of the shallow moho regions would be related to graben formation due to tensile tectonic stress since the miocene the results were compared with those of seismic refraction surveys and receiver function analyses and it was found that the obtained model was consistent with many of these studies

oblique subduction and collision forearc tectonics of the kuril arc the tectonics of the southwestern kuril arc are a result of the oblique subduction of the pacific plate at the kuril trench in association with forearc sliver migration caused by the oblique subduction collision tectonics occur at the leading margin of the sliver and tensional tectonics take place at the tapering margin as a result of the collision a deep crustal section of island arc is observed at the leading margin of the forearc sliver tectonics of the kuril arc related to oblique subduction are different from those of the western sunda arc where backarc spreading occurs at the leading margin this difference is due to margin morphology of the oblique subduction zone