investigating the role of the itoigawa shizuoka tectonic line towards the evolution of the northern fossa magna rift basin abstract the itoigawa shizuoka tectonic line istl fault system is considered to have one of the highest probabilities for a major inland earthquake occurrence in the whole of japan it is a complex fault system with the dip directions of the local fault segments changing from north to south between an east dipping low angle thrust fault a strike slip fault and a west dipping thrust fault the tectonic relations between the different parts of the fault system and the surrounding geological units are yet to be fully explained this study aims to reveal the juncture of the northern and central parts of the istl and investigate its contribution towards the shaping of the northern fossa magna rift basin we conducted 3 deployments of 1 or 2 linear arrays of seismic stations across the central and northern istl regions and observed local micro earthquakes for a period of 3 years each deployment recorded continuous waveform data for approximately 3 months using arrival times of 1193 local earthquakes we jointly determined earthquake locations and a 3d velocity model applying the tomography method we were able to image the regional crustal structures from the surface to a depth of 20 km with a spatial resolution of 5 km subsequently we used the obtained 3d velocity model to relocate the background local seismicity from 2003 to 2009 the juncture of the northern and central parts of the istl was well constrained by our results the depth extension of the northern parts of the istl fault segments follows the bottom of the miocene northern fossa magna rift basin nfm and forms an east dipping low angle fault in contrast the central parts of the istl fault segments are estimated to lie along the eastern boundary of the matsumoto basin forming an oblique strike slip fault fig 1

seismic imaging of arc magma and fluids under the central part of northeastern japan abstract a dense seismic network was temporarily deployed during 1997 1999 in the central part of northeastern japan by japanese university research groups using the local earthquake arrival time data recorded by the network we have determined high resolution three dimensional images of p wave velocity vp s wave velocity vs and vp vs ratio in this area our results show that low vp low vs and high vp vs areas are extensively distributed in the uppermost mantle along the volcanic front in the lower crust low vp low vs and high vp vs areas are visible but they are confined to the individual volcanic areas in contrast the upper crust of volcanic areas shows low vp low vs and low vp vs rather than high vp vs these observations suggest that partial melting materials exist in the uppermost mantle along the volcanic front and they spread up to the midcrust of the volcanic areas low vp low vs and low vp vs in the upper crust of the volcanic areas suggest the presence of h2o rather than melt there deep low frequency microearthquakes perhaps caused by the rapid movement of fluids are located mostly at the edge of partial melting zones particularly at their upper surface distinct s wave reflectors bright spots with large reflection coefficients are distributed in the midcrust with slightly low vp vs suggesting that most of them are filled with h2o

paleomagnetic evidence for the miocene counter clockwise rotation of northeast japan rifting process of the japan arc paleomagnetic results have been obtained from more than 700 oriented samples in igneous rocks of cretaceous to miocene age from northeast japan the remanent magnetizations of welded tuffs with age between 32 ma and 21 ma old from 17 widely distributed sampling sites in northeast japan are fairly well grouped with a mean ofd 41 2 i 56 5 95 7 2 the remanent magnetization of welded tuffs of 14 ma and 11 ma from 4 sites shows a northerly direction d 11 7 i 60 5 95 15 3 these data imply that northeast japan was apparently subjected to a counter clockwise rotation through 47 14 about a vertical axis on the representative point of northeast japan 141 e 39 n during the past 21 ma comparing with the period of the clockwise rotation of southwest japan the differential rotation between northeast japan and southwest japan is concluded to have occurred concurrently during the period between 21 ma and 12 ma a rifting model of the japan arc is proposed northeast japan rotated counter clockwise through 50 about a northern pivot at 146 e 44 n while southwest japan rotated clockwise through 54 about a southern pivot at 129 e 34 n the differential rotation about different rotation pivots gives rise to the opening of a diamond shaped back arc basin the japan sea

active nappe with a high slip rate seismic and gravity profiling across the southern part of the itoigawa shizuoka tectonic line central japan abstract nappe structures at different scales have been reported from many orogenic belts in the world but almost all the examples are old inactive structures under conditions of low erosion rate and or high tectonic strain rate active nappes are expected to grow with time we report in this paper an example of active nappe from central japan the itoigawa shizuoka tectonic line istl in central japan is a fault zone with a very high slip rate in pliocene quaternary time we carried out seismic reflection refraction and gravity surveys along a 30 km line across the shimotsuburai ichinose fault sif a main active strand of istl west of the kofu basin seismic and gravity data indicate that the fault is a west dipping low angle 15 thrust which separates horizontally layered basin fill sediments total thickness 1 5 km on the east from highly deformed miocene and older rocks on the west on the hanging wall side of the fault the seismic line is located in a deeply incised valley we precisely determined the surface projection of the fault in this valley by analyzing closely spaced gravity data and found that the fault emerges 1 35 0 10 km west of the mountain front this indicates that the frontmost 1 35 km of the hanging wall lies horizontally over pliocene quaternary basin fill forming an active nappe fault bend folding is associated with the nappe formation a fluvial terrace which is tephrochronologically dated at 50 60 ka is involved in this deformation the amount of slip during the past 50 60 kyr is estimated from tectonic landforms yielding an average slip rate as high as 7 5 11 mm yr it is likely that the front of the nappe on sif is nearly at a dynamic equilibrium between erosive and tectonic forces because the present day width 1 35 km of the nappe in the valley is only a fraction of the total amount of thrust front advance a comparison is made with the miocene main central thrust mct in the central himalaya which evolved under climatic conditions similar to those in central japan but at a slip rate twice as high as that on the istl the high himalayan nappe front after the mct became inactive has been retreating due to head ward erosion by small tributaries of ganges cooling ages of crystalline klippen in the lesser himalaya give an estimate of the retreating rate 10 mm yr this value is about a half of the present day convergence rate 20 mm yr between india and tibet it is therefore likely that in early to middle miocene time when the mct was active the high himalayan nappe had been growing laterally at a rate as high as 10 mm yr

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

intra arc deformations with vertical rotation axes the case of the pre middle miocene terranes of southwest japan abstract various folds bends with vertical or subvertical rotation axes occur in the pre middle miocene terranes of southwest japan they are variable in shape conical folds accordion folds megakink bands and so on and some are accompanied with strike slip faults they range from several kilometers to more than 100 km in width and some of their hinge surfaces are traceable more than a few tens of kilometers their shapes which resemble megakink band or buckle folds indicate that they were produced by horizontal compression with vertical or subvertical 2 axes in a shallow level of the crust they were superimposed on the pre middle miocene fold and thrust structures or nappe melange complexes and are regarded to have been formed mostly during the middle miocene contemporaneous with the clockwise rotation of southwest japan related to the fan shaped opening of the sea of japan geometrical analysis clearly suggests that the drifting southwest japan behaved as a non rigid body and the formation of these structures resulted from the differential rotation of the terranes and the collision of the izu bonin arc with eastern southwest japan

tectonic evolution of the japanese island arc system abstract growth of the japanese arc system which has mainly taken place along the continental margin of asia since the permian is the result of subduction of the ancient pacific ocean floor backarc basin formation in the tertiary shaped the present day arc configuration the neotectonic regime which is characterized by strong east west compression has been triggered by the eastward motion of the amur plate in the quaternary the tectonic evolution of the japanese arc system includes formation of rock assemblages common in most orogenic belts because the origin and present day tectonics of these assemblages are better defined in the case of the japanese arc system study of the system provides useful insight into orogenesis and continental crust evolution

three dimensional structure of vp vs and vp vs beneath northeastern japan implications for arc magmatism and fluids we estimated both p v p and s wave velocity v s structures beneath northeastern japan by applying a tomographic method to 169 712 p and 103 993 s wave arrival time data from 4338 local events the average value of v p v s ratio is 1 69 in the upper crust 1 75 in the lower crust and 1 77 in the uppermost mantle these differences in v p v s ratio may mainly reflect the lithological variations with depth low v p low v s and high v p v s zones are extensively distributed along the volcanic front in the uppermost mantle and are downward to the back arc side in the mantle wedge here the low v p low v s and high v p v s values are interpreted because of partial melting materials which imply the presence of a vast amount of melt in the uppermost mantle in the lower crust low v p low v s and high v p v s zones are not continuously visible along the volcanic front but are confined to individual volcanic areas which suggests that melting of lower crustal materials occurs just beneath each active volcano in contrast the upper crust beneath active volcanoes exhibits low v p low v s and low v p v s these results suggest that the partial melting zones under northeastern japan spread out from the uppermost mantle along the volcanic front up to the midcrust right beneath active volcanoes the low v p low v s and low v p v s features in the upper crust suggest the existence of h 2 o rather than melt right beneath active volcanoes

rapid intra arc rifting in miocene northeast japan although life times of major continental rifts are tens of millions of years intra arc rifting in miocene ne japan lasted for only about 3 m y before back arc spreading began the rate of initial subsidence was over 1 km m y much faster than that in major continental rifts thus this intra arc rift evolved 10 times as fast as major intracontinental rifts the large temperature dependence of lithosphere rheology and the hot thermal regime of island arc lithosphere account for the rapid rifting less than 1 m y before the rifting spreading transition the inner ne japan arc subsided from shallow marine depths to middle or lower bathyal depths 1 0 2 5 km the average total basement subsidence was 2 3 km during the rifting the rapid submergence occurred during one third of the duration of rifting but accounts for two thirds of the total subsidence during rifting namely the initial subsidence rate accelerated toward the time of breakup of the arc crust at the same time the region along the present pacific coast remained only shallow marine or terrestrial throughout presumably influenced by global eustacy

seismological evidence of an active footwall shortcut thrust in the northern itoigawa shizuoka tectonic line derived by the aftershock sequence of the 2014 m 6 7 northern nagano earthquake abstract a destructive m 6 7 earthquake struck northern nagano prefecture on november 22 2014 the main shock occurred on the kamishiro fault segment of the northern itoigawa shizuoka tectonic line istl we used data recorded at 41 stations of the local seismographic network in order to locate 2118 earthquakes that occurred between november 18 and november 30 2014 to estimate hypocenters we assigned low vp models to stations within the northern fossa magna nfm basin thus accounting for large lateral crustal heterogeneities across the kamishiro fault in order to further improve accuracy the final hypocenter locations were recalculated inside a 3d velocity model using the double difference method we used the aftershock activity distribution and focal mechanism solutions of major events in order to estimate the source fault area of the main shock our analysis suggests that the shallow part of the source fault corresponds to the surface trace of the kamishiro fault and dips 30 45 se while the deeper part of the source fault corresponds to the downdip portion of the otari nakayama fault a high angle fault dipping 50 65 se that formed during the opening of the nfm basin in the miocene along its surface trace the otari nakayama fault has been inactive during the late quaternary we verified the validity of our model by calculating surface deformation using a simple homogeneous elastic half space model and comparing it to observed surface deformation from satellite interferometry assuming large coseismic slip in the areas of low seismicity and small coseismic slip in the areas of high seismicity shallowing of the source fault from 50 65 to 30 45 in the upper 4 km in the areas where both surface fault traces are visible is a result of footwall shortcut thrusting by the kamishiro fault off the otari nakayama fault

thickness variation of the descending philippine sea slab and its relationship to volcanism beneath the kanto tokai district central japan 1 we use an iterative nonlinear travel time tomography technique to determine three dimensional p wave and s wave seismic velocity models for the region beneath the kanto tokai district of central japan salient points of the models are the following 1 the subducting philippine sea slab has thickness variation with a stepwise offset east of the izu peninsula the eastern beneath the kanto district and western beneath the area north of izu peninsula and the tokai district regions have respective thicknesses of 60 and 25 km the slab clearly subducts continuously to a depth of 100 km from the sagami trough beneath the kanto district although the tokai slab is indistinct at depths of 50 70 km 2 the oceanic crust at the top of the descending philippine sea slab transforms into eclogite at a depth of about 70 km beneath the kanto district 3 low velocity anomalies are associated with present and past volcanism they are located on the west of a 110 km depth contour of the wadati benioff zone rather than only on the backarc side of the volcanic front deflection of the volcanic front might result from the subducting philippine sea slab which shifts the dehydration reaction deeper as it subducts deeper

water concentration profiles in natural mantle orthopyroxenes a geochronometer for long annealing of xenoliths within magma both mantle derived clinopyroxene and orthopyroxene are generally homogeneous in water concentration while water content in the coexisting olivine is affected by partial or complete loss during the ascent of the hosting magma here we report the first record of water content profiles higher water in the cores than in the rims in natural orthopyroxene grains in peridotite xenoliths hosted by cenozoic alkali basalts in tianchang volcano eastern china the water contents of the coexisting clinopyroxene grains are homogeneous and are twice that measured in the cores of orthopyroxene grains confirming previous chemical equilibrium between the two pyroxenes the olivines ol are nearly dry 0 ppm these observations demonstrate that h diffusion in mantle orthopyroxene opx is faster than in clinopyroxene cpx and the relative mobility of h in each mineral phase could be quantified as dol 10dopx 1000dcpx where d is the chemical diffusion coefficient of hydrogen combining this with experimental diffusion coefficients from the literature we infer that 1 the xenoliths remained in contact with the magma below 900 c for several months and 2 clinopyroxene remains the more reliable recorder of water from depth and orthopyroxene should be used more cautiously but can be considered with olivine for tracing slow transport and cooling of magma

configuration of subducting philippine sea plate and crustal structure in the central japan region a seismic experiment with six explosive sources and 391 seismic stations was conducted in august 2001 in the central japan region the crustal velocity structure for the central part of japan and configuration of the subducting philippine sea plate were revealed a large lateral variation of the thickness of the sedimentary layer was observed and the p wave velocity values below the sedimentary layer obtained were 5 3 5 8 km s p wave velocity values for the lower part of upper crust and lower crust were estimated to be 6 0 6 4 and 6 6 6 8 km s respectively the reflected wave from the upper boundary of the subducting philippine sea plate was observed on the record sections of several shots the configuration of the subducting philippine sea slab was revealed for depths of 20 35 km the dip angle of the philippine sea plate was estimated to be 268 for a depth range of about 20 26 km below this depth the upper boundary of the subducting philippine sea plate is distorted over a depth range of 26 33 km a large variation of the reflected wave amplitude with depth along the subducting plate was observed at a depth of about 20 26 km the amplitude of the reflected wave is not large and is explained by the reflected wave at the upper boundary of the subducting oceanic crust however the reflected wave from reflection points deeper than 26 km showed a large amplitude that cannot be explained by several reliable velocity models some unique seismic structures have to be considered to explain the observed data such unique structures will provide important information to know the mechanism of inter plate earthquakes d 2004 elsevier b v all rights reserved

rock lithology and porosity determination from shear and compressional wave velocity data examined in this study are previously published laboratory shear s and compressional p wave velocity measurements on water saturated sandstone calcareous sandstone dolomite and limestone cores as well as laboratory porosity measurements on the sandstone and limestone cores sandstone and limestone porosities range from 092 to 299 and from 006 to 229 respectively differential pressure was varied from 500 to 6000 psi corresponding to approximate burial depths from 290 to 3460 m respectively sandstone limestone and dolomite are effectively separated by poisson s ratio or equivalently by the ratio of p to s wave velocity separation of sandstone and limestone appears to result from the difference in of the matrix material namely quartz 056 and calcite 316 respectively an empirical function 1 v a b was fit by regression analysis to sandstone and limestone velocity vs and vp versus porosity values at each differential pressure in this equation a and b are const

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

formation and shortening deformation of a back arc rift basin revealed by deep seismic profiling central japan abstract the northern fossa magna nfm basin is a miocene rift system produced in the final stages of the opening of the sea of japan it divides the major structure of japan into two regions with north trending geological structures to the ne of the basin and ew trending structures to the west of the basin the itoigawa shizuoka tectonic line istl bounds the western part of the northern fossa magna and forms an active fault system that displays one of the largest slip rates 4 9 mm year in the japanese islands deep seismic reflection and refraction wide angle reflection profiling were undertaken in 2002 across the northern part of istl in order to delineate structures in the crust and the deep geometry of the active fault systems the seismic images are interpreted based on the pattern of reflectors the surface geology and velocities derived from refraction analysis the 68 km long seismic section suggests that the miocene nfm basin was formed by an east dipping normal fault with a shallow flat segment to 6 km depth and a deeper ramp penetrating to 15 km depth this low angle normal fault originated as a comparatively shallow brittle ductile detachment in a high thermal regime present in the miocene the nfm basin was filled by a thick 6 km accumulation of sediments shortening since the late neogene is accommodated along ns to ne se trending thrust faults that previously accommodated extension and produce fault related folds on their hanging wall based on our balanced geologic cross section the total amount of miocene extension is ca 42 km and the total amount of late neogene to quaternary shortening is ca 23 km

palaeomagnetic and chronological study of miocene welded tuffs in the northern part of central japan tectonic implications for the latest stage of arc formation of japan abstract kinematical adjustment of tectonic blocks has occurred in the latest stage of arc formation of japan within central japan miocene welded tuffs have been sampled for chronological and palaeomagnetic studies from the northern part of central japan zircon fission track dating confirms middle to late miocene ages 13 7 5 0 ma for the yatakezawa shiobara kawaji kinugawa katashinagawa okkai and ashio formations characteristic directions with high unblocking temperature component above 560 c are isolated from 36 sites palaeomagnetic directions after tilt correction provide a miocene characteristic palaeomagnetic direction of the northern part of central japan 36 8 n 139 3 e d 7 3 i 50 3 95 6 6 presence of normal and reversed polarities and a fairly long time average exclude the effect of geomagnetic field secular variation comparison with the miocene palaeomagnetic poles of the neighbouring blocks indicates that the northern part of central japan and northeast japan behaved as a unified block since 15 ma whereas the kanto mountain region moved kinematically as an independent block from the northern block comprised of central japan and northeast japan at least between 16 ma and 12 ma the boundary between the northern part of central japan and the kanto mountain was in a convergent regime with dextral strike slip a southward force exerted from the northern part of central japan as well as a northward force by the izu bonin ridge induced the clockwise rotation of the kanto mountain region the northern part of central japan had welded completely with the kanto mountain region by 6 ma

the 3 d tectonic stress fields in and around japan inverted from centroid moment tensor data of seismic events 1 we can regard the occurrence of earthquakes as the partial release of tectonic stress by sudden brittle rupture in the framework of linear elasticity any indigenous source including earthquake rupture is represented by a moment tensor the moment tensor is mathematically equivalent to the volume integral of stress release over the whole elastic region surrounding the source and so we can quantitatively relate the centroid moment tensor cmt of seismic events with an unknown tectonic stress field on the basis of such an idea and bayesian statistical inference theory we developed an inversion method to estimate the 3 d pattern of tectonic stress from cmt data applying the cmt data inversion method to 12 500 seismic events in and around japan we obtained precise 3 d tectonic stress patterns that illuminate the present day quaternary complex tectonic motion of japanese islands the stress pattern of the kuril japan nankai arc is basically e w compression but the direction of intermediate principal stress changes from n s reverse faulting type in northeast japan to vertical strike slip faulting type in southwest japan on the other hand the stress pattern of the ryukyu and izu bonin back arc regions is basically trench perpendicular tension normal faulting type in addition to these basic stress patterns governed by mechanical interaction between the eurasian north american pacific and philippine sea plates we can recognize several characteristic local stress patterns corresponding to the horizontal motion of the kuril fore arc sliver the collision of the izu peninsula with the mainland of japan and the opening of the beppu shimabara rift zone

the relationship between late cenozoic tectonic events and stress field and basin development in northeast japan the regional tectonic stress field basin development and crustal deformation of the ne japan arc in the interval between 32 ma to the quaternary can be synthesized based on dike vein and fault orientation data as well as on the compilation of the regional geology an extensional stress field became prevalent from 32 ma and major normal faulting started at 25 20 ma which resulted from back arc rifting normal faulting trending nearly parallel to the arc propagated from the present japan sea coast to the forearc side following the trenchward migration of the main volcanic field from 20 to 15 ma normal faults with an oblique trend to the arc developed due to the counterclockwise rotation of ne japan the rapid clockwise rotation of sw japan since 16 ma produced a nw se directed transtensional stress regime in the ne japan arc due to crustal stretching associated with this pull apart movement the back arc side of the ne japan arc subsided rapidly to middle bathyal environments after the termination of the opening of the japan sea at about 14 ma a neutral stress regime prevailed which included phases of both weak extension and compression lithospheric cooling eventually led to thermal subsidence of the back arc region and igneous underplating caused uplift of the axial zone of the volcanic arc the increase in velocity of the westward motion of the pacific plate at around 4 ma produced strong compression across the arc reactivating most of the miocene normal faults and uplifting the volcanic arc the greatest crustal shortening occurred in areas that were stretched the most in the miocene within the volcanic arc which implies tectonic inversion

reactivation of ancient rift systems triggers devastating intraplate earthquakes 1 large historical and recent intraplate earthquakes have been concentrated along a contractional zone at the eastern margin of the japan sea back arc basin here we present high resolution three dimensional tomographic imaging of seismic velocities in this zone using data from a dense seismograph deployment we discover that stepwise and tilted block structures of the basement which are geophysical evidence of a miocene rift system are widely distributed beneath the thick sedimentary basin most aftershocks following recent intraplate earthquakes align roughly along the tilted block boundaries and are controlled by weaknesses associated with buried rift systems furthermore slow anomalies are localized beneath the seismogenic zones suggesting that fluids may have locally weakened the strength of the lower crust we propose that stress loading through ductile creeping of the weak lower crust reactivates pre existing weak faults within ancient rift systems leading to devastating intraplate earthquakes

a fault scarp in an urban area identified by lidar survey a case study on the itoigawa shizuoka tectonic line central japan abstract a light detection and ranging lidar survey was conducted in a densely built up area to generate a high resolution digital elevation model dem to look for active faults the urban district of matsumoto city in central japan is located in a 3 km 2 basin along the itoigawa shizuoka tectonic line active fault system one of japanese onshore fault systems with the highest earthquake probability a high resolution dem at a 0 5 m grid interval was obtained after removing the effects of laser returns from buildings clouds and vegetation it revealed a continuous scarp up to 2 m in height borehole data and archaeological studies indicate the scarp was formed during the most recent faulting event associated with historical earthquakes in addition the fault scarp strongly supports that the urban district is in a pull apart basin related to a fault step over between two left lateral strike slip faults consequently accurate interpretation of fault geometry is crucial to provide estimates of future surface deformation and to allow modeling of basin structure and strong ground motion thus the lidar mapping survey in urban districts is effective for detailed active fault mapping in order to constrain basin structure and to forecast the exact location of surface rupturing associated with large earthquakes

three dimensional p and s wave velocity structures beneath the japan islands obtained by high density seismic stations by seismic tomography abstract we construct fine scale 3d p and s wave velocity structures of the crust and upper mantle beneath the whole japan islands with a unified resolution where the pacific pac and philippine sea phs plates subduct beneath the eurasian eur plate we can detect the low velocity low v oceanic crust of the pac and phs plates at their uppermost part beneath almost all the japan islands the depth limit of the imaged oceanic crust varies with the regions high vp vs zones are widely distributed in the lower crust especially beneath the volcanic front and the high strain rate zones are located at the edge of the extremely high vp vs zone however vp vs at the top of the mantle wedge is not so high beneath northern japan we can image the high v subducting pac plate using the tomographic method without any assumption of velocity discontinuities we also imaged the heterogeneous structure in the pac plate such as the low v zone considered as the old seamount or the highly seismic zone within the double seismic zone where the seismic fault ruptured by the earthquake connects the upper and lower layer of the double seismic zone beneath central japan thrust type small repeating earthquakes occur at the boundary between the eur and phs plates and are located at the upper part of the low v layer that is considered to be the oceanic crust of the phs plate in addition to the low v oceanic crust the subducting high v pac plate is clearly imaged to depths of approximately 250 km and the subducting high v phs zone to depths of approximately 180 km is considered to be the phs plate beneath southwestern japan the iso depth lines of the moho discontinuity in the phs plate derived by the receiver function method divide the upper low v layer and lower high v layer of our model at depths of 30 50 km beneath kyushu the steeply subducting phs plate is clearly imaged to depths of approximately 250 km with high velocities the high vp vs zone is considered as the lower crust of the eur plate or the oceanic crust of the phs plate at depths of 25 35 km and the partially serpentinized mantle wedge of the eur plate at depths of 30 45 km beneath southwestern japan the deep low frequency nonvolcanic tremors occur at all parts of the high vp vs zone within the zone the seaward side and the landward side where the phs plate encounters the mantle wedge of the eur plate we prove that we can objectively obtain the fine scale 3d structure with simple constraints such as only 1d initial velocity model with no velocity discontinuity

v p v s and lithology published laboratory investigations suggest an association exists between the ratio of seismic compressional and shear wave velocities vp vs and sedimentary rock lithology comparisons of some theoretical models with these laboratory studies suggest that crack or pore geometry has a stronger effect on observed vp vs values than elastic constants of the minerals comprising the matrix further it can be inferred that the observed association between lithology and vp vs is a result of an association between lithology and distribution of pore and crack shapes direct observation of crack shapes for a variety of lithologies is a next step in strengthening these inferences the present study reviews the empirical relations between vp vs and lithology and examines two published theoretical models of cracked elastic media the models suggest that seismic velocities of sandstones may be controlled by cracks and pores with aspect ratios in the range of 10 1 to 1 dolomite in the range of 10 2 to 10 1 and dens

crustal structure of central japan and its petrological implications the crustal structure of central honshu japan has been influenced by several tectonic events a series of collision processes during the late tertiary extensive faulting highly compressive deformation and quaternary volcanism the southern part of the study area is covered by various granitic rocks which intrude into old palaeozoic formations quaternary volcanoes occupy the northern part and cover the basement which is mainly composed of granitic rocks and tertiary formations a traveltime inversion for velocity and interface depth was applied to the seismic data together with constraints from amplitude forward modelling to produce a seismic velocity model of the crust in central honshu in this experiment both refracted p and s waves are clearly recorded along a 110 km profile these provide constraints on the 2 d p and s wave velocity structure down to a depth of about 10 km moreover clear p wave reflections from intracrustal interfaces provide constraints on deeper parts of the crust down to about 25 km for the p wave velocity model the velocities of near surface layers show large lateral variations from 3 7 to 4 4 km s 1 increasing towards the south underlying layers have velocities ranging from 4 85 to 5 6 km s 1 velocities in the range 5 85 6 2 km s 1 characterize the upper crust that extends to a depth of about 15 km for the s wave velocity model the near surface layer velocities change from 1 7 to 2 55 km s 1 showing remarkable lateral heterogeneity whilst the upper crust is characterized by velocities of 3 4 3 6 km s 1 the deeper parts are modelled by two prominent reflectors in the mid crust the shallower one which delineates the bottom of the upper crust dips southwards from 14 to 16 km the deeper reflector lies between 20 and 24 km depth and dips northwards the velocity in this mid crustal layer is 6 35 km s 1 at the top and 6 7 km s 1 at the bottom the crustal thickness under the profile could not be determined because of a lack of pn and or pm p phases this study also presents the vp vs ratio and the poisson s ratio distribution and gives the probable composition of the upper crust poisson s ratio varies from 0 29 to 0 34 which can be ascribed to a porous and water saturated structure for the near surface layers in the northern part of the region poisson s ratios of about 0 24 0 25 in the southern part and 0 22 0 24 in the upper crust together with the geological data show that the upper crust has a felsic content and is formed by granite granodioritic rocks with a high quartz content the changes in the quartz content explain the lateral variations of vp vs and poisson s ratio in the model the higher velocities in the middle crust suggest a more mafic structure probably composed of diorites

case study finite element method and artificial neural network models for flow through jeziorsko earthfill dam in poland a finite element method fem and an artificial neural network ann model were developed to simulate flow through jeziorsko earthfill dam in poland the developed fem is capable of simulating two dimensional unsteady and nonuniform flow through a nonhomogenous and anisotropic saturated and unsaturated porous body of an earthfill dam for jeziorsko dam the fem model had 5 497 triangular elements and 3 010 nodes with the fem network being made denser in the dam body and in the neighborhood of the drainage ditches the ann model developed for jeziorsko dam was a feedforward three layer network employing the sigmoid function as an activator and the back propagation algorithm for the network learning the water levels on the upstream and downstream sides of the dam were input variables and the water levels in the piezometers were the target outputs in the ann model the two models were calibrated and verified using the piezometer data collected on a section of the jeziorsko dam the water levels computed by the models satisfactorily compared with those measured by the piezometers the model results also revealed that the ann model performed as good as and in some cases better than the fem model this case study offers insight into the adequacy of ann as well as its competitiveness against fem for predicting seepage through an earthfill dam body