space time distribution patterns of destructive earthquakes in the inner belt of central japan part 3 seismic hazard assessment abstract on the basis of the strike and sense of active faults the inner belt of central japan can be divided into the chubu and kinki districts the chubu district can be subdivided into four blocks by lines linking major nw se trending active faults a number of inner belt earthquakes of magnitudes m 6 4 or greater m japan meteorological agency scale have been documented or recorded since 599 a d whereas most epicenters of these earthquakes were located along lines linking active faults a few occurred in intra block areas in the first paper of this series the analysis of space time distribution patterns of destructive earthquakes revealed seismic cycles which consist of an active period of earthquakes and a quiet period with no activity seismic gaps were also detected in which no earthquakes have occurred during the present active period the second paper demonstrated that the average rates of seismic moment release calculated from the average slip rates of active faults which constitute the major tectonic or block boundary lines are nearly equal to those released by the historic earthquakes on the basis of the results of the two former papers two seismic maps a hazard map and an earthquake potential map of the inner belt of central japan are constructed since the seismic activity along tectonic and block boundary lines is much greater than that of the intra block areas the lines and intra block areas are separately evaluated in these seismic maps the hazard map shows the seismic activity by making use of the average rate of seismic moment release while the average rates of the lines range from 0 010to0 030 10 26 dyne cm y those of the intra blocks have values of less than 0 005 10 26 dyne cm y with one exception since regions of higher moment release rate experienced historic earthquakes with larger maximum magnitude the moment release rate is a good indicator for estimating the maximum magnitude of future earthquakes during the present active period future earthquakes will probably occur along seismic gaps these seismic gaps are illustrated in the earthquake potential map the two seismic maps are useful in reducing earthquake disasters by designing earthquake resistant buildings and structures in the earthquake prone regions of central japan

temporal variation of seismic b values beneath northeastern japan island arc 1 analysis of a high quality seismic catalog reveals that the average of seismic b values in the crust beneath most part of northeastern japan island arc decreased from 0 86 between 1984 and 1990 to 0 73 between 1991 and 1995 the two areas with the largest decrease are found to be in the same areas where the coupling between the north american and the pacific plates is the highest as suggested by a recent geodetic study in the same time period the annual seismic moment release increased by 10 times in addition there seems to be a corresponding increase in volcanic activities in the same area one of the most likely interpretations for the observations is an increase in the subduction rate starting from 1991 the timing of this possible increase in subduction rate is consistent with an apparent increase in global seismic activity

interaction of parallel strike slip faults and a characteristic distance in the spatial distribution of active faults summary a numerical simulation of the activities of many parallel strike slip faults is performed to explore the effect of the interaction of fault slip on the spatial distribution of active faults in the model a large number of faults with random strengths are embedded in an elastic layer lithosphere over a maxwell type viscoelastic half space asthenosphere and shear loading of a constant strain rate is applied when slip takes place on a model fault shear stress is decreased around the fault and then recovered with time due to the viscoelastic response of the asthenosphere the decrease in shear stress prohibits the occurrence of another earthquake around the slipped fault resulting in the existence of a characteristic distance between active faults this characteristic distance is found to be controlled by the thickness of the elastic layer the strain rate and the viscoelastic relaxation time the density of simulated active faults increases with the strain rate consistent with observations of active faults in japan furthermore the present simulation result may explain the characteristic distance which breaks the fractal structure of the spatial distribution of active faults in japan which was discovered by lei kusunose 1999

deformation of the japanese islands and seismic coupling an interpretation based on gsi permanent gps observations summary the entire area of the japanese islands has been covered by the permanent gps observation network of the geographical survey institute since 1994 in this paper we use a solution for the vectors of motion during 1995 for a selection of 116 stations to discuss the origin of the observed deformation field we refer the displacement field to eurasia using the vlbi determined motion of kashima and demonstrate that other choices such as the okhotsk or north american plates for north japan are not compatible with the data 1 yr gps velocities are much higher than geological constraints would allow because these short term measurements include transient elastic deformation however the good qualitative agreement between the observed geodetic deformation tensors and those inferred from active faults and earthquakes suggests that the quaternary permanent deformation is essentially the result of the transfer of part of the subduction induced elastic deformation into permanent plastic deformation we then compute the elastic deformation of the japanese islands caused by interseismic loading of the pacific and philippine subduction planes the geometry of the coupled zone and its downward extension are determined from the distribution of earthquakes for the pacific slab for the philippine slab we use the geometry proposed by hyndman et al 1995 these elastic models account for most of the observed velocity field if the subduction movement of the philippine sea plate is 100 per cent locked and if that of the pacific plate is 75 85 per cent locked we note that the boundaries of the areas where significant elastic deformation is predicted more than 10 mm yr 1 of motion with respect to eurasia coincide with the main zones of permanent deformation the eastern japan sea deformation zone for the pacific subduction elastic deformation field and the setouchi mtl deformation zone for the nankai field each zone probably accommodates 10 15 mm yr 1 of motion in the long term convergence in the eastern japan sea strike slip in the setouchi mtl zone to account for this deformation the evect of elastic loading from the trench must be combined with 5 10 mm yr 1 of motion of the amur plate with respect to eurasia because loading during the subduction earthquake cycle causes an increase in stress in the eastern japan sea and setouchi mtl deformation zones the probability of earthquake occurrence in these zones may be higher near the end of the cycle

intraplate deformation in the japanese islands a kinematic study of intraplate deformation at a convergent plate margin relative motions within the deforming japanese islands with respect to the sea of japan are determined using earthquake records over the last 414 years slip rates on quaternary faults and angular change rates obtained from triangulation in the last century we use a least squares inversion method to match the strain rates on the surface of the earth with continuous spline functions to recover the velocity gradient tensors the directions of the principal strain axes obtained from seismic geological and geodetic data are in general agreement with each other with the maximum shortening axis oriented in a wnw direction principal strain rate magnitudes obtained from the geodetic data are about 3 5 times larger than the principal strain rates obtained from the seismic and geological data intraplate deformation in southwestern japan determined from the seismic data accommodates a velocity of5 5 2 l mm yr in a direction parallel to the nankai trough which is about 25 of the plate motion velocity component parallel to the nankai trough between the philippine sea and eurasian plates in northern honshu the velocity vectors from the seismic data are nearly parallel to the plate motion vector at the japan trench and the intraplate deformation accommodates about 6 of the total pacific eurasian or north american plate motion velocity the velocity vector at kashima northern honshu calculated from the geodetic data is about 9 12 mm yr in a direction of n55 w n76 w which is about half of the very long baseline interferometry velocity calculated in the eurasian reference frame suggesting that the sea of japan may not be rigidly attached to the assumed rigid eurasian plate

moment tensor summation to derive the active crustal deformation in japan abstract the country of japan and the surrounding area has been divided into 12 seismogenic sources which belong to five belts with an almost uniform orientation of the stress field in each one of these sources the active crustal deformation has been determined using the summation of the seismic moment tensors of mainly post 1964 earthquakes the analysis showed that due to the subduction of the philippine sea plate beneath the eurasian plate the deformation is expressed as compression at a mean direction of n53 w and an average rate of 1 5 cm yr the fault plane solution corresponding to the summed tensor indicates low angle thrust faulting with the following parameters strike 226 dip 21 and rake 98 along the sagami trough dextral strike slip motion is predominant at an average rate of 6 cm yr the summed tensor corresponds to a fault plane solution with strike 291 dip 73 and rake 180 along the districts of fukushima tohoku and the hokkaido island the motion of the pacific plate toward eurasia causes compression at a mean direction of n65 w and an average rate of 4 cm yr the summed tensor corresponds to a fault plane solution with strike 199 dip 18 and rake 81 that is low angle thrust faulting dipping toward the land this pattern resembles the hellenic arc where the deformation is also taken up by motion on low angle 18 thrust faults dipping to the north in the tohoku district the rate of motion reaches a value of 8 cm yr which is the highest calculated in the whole japan area in the inner part of the japanese islands along western honshu and niigata the mean p axis is almost horizontal trending nearly e w in western honshu the deformation is mainly expressed as dextral strike slip motion at an average rate of 5 cm yr in a n59 e direction the representative fault plane solution for this area has strike 240 dip 81 and rake 173 at niigata the western coast of hokkaido and further north at okushiri the deformation is taken up as compression at a mean direction of n96 e at an average rate of 2 cm yr the summed tensor corresponds to a fault plane solution with strike 5 dip 41 and rake 90 the calculated directions and rates of motion along the japanese islands are in good agreement with the expected values from plate motion models

plate tectonics and crustal deformation around the japanese islands we analyze over a century of geodetic data to study crustal deformation and plate motion around the japanese islands using the block fault model for crustal deformation developed by matsu ura et al 1986 in this model crustal deformation corresponds to the sum of relative movement among designated blocks and displacement due to dislocations along the locked parts of designated faults we model the area including the japanese islands with 19 crustal blocks and 104 faults based on the distribution of active faults and seismicity three kinds of data are used rates of change of angles and lengths and average velocities of very long baseline interferometry stations with the inversion of these geodetic data we obtain block motions and average slip rates of faults this geodetic model predicts that the pacific plate moves n69 2 w at about 80 3 mm yr relative to the eurasian plate which is much lower than that predicted in geologic models substantial aseismic slip occurs on the subduction boundaries the block containing the izu peninsula may be separated from the rigid part of the philippine sea plate the faults on the coast of japan sea and the western part of the median tectonic line have slip rates exceeding 4 mm yr while the fossa magna does not play an important role in the tectonics of the central japan the geodetic model requires the division of northeastern japan contrary to the hypothesis that northeastern japan is a part of the north american plate owing to rapid convergence the seismic risk in the nankai trough may be larger than that of the tokai gap

integration of geological and seismological data for the analysis of seismic hazard a case study of japan seismic hazard analyses are associated with large uncertainties when historical data are insufficient to define secular rates of seismicity such uncertainties may be decreased with geological data in areas where seismicity is shallow and produced by quaternary faulting to illustrate we examine intraplate japan large intraplate earthquakes in japan characteristically produce surface ruptures along mappable quaternary faults and show a systematic relation between seismic moment m 0 and rupture length i log m 0 23 5 1 94 log i it is observed that within the bounds placed by geologically assessed slip rates the mean regional moment release rate m 0 resulting from slip on mapped quaternary faults is in accord with estimates of m 0 determined with the 400 yr record of seismicity recent work also shows that when the repeat time t of earthquakes on quaternary faults in southwest japan is assumed to equal m 0 m 0 g where m 0 is estimated for rupture extended over the entire fault length and m 0 g is the geologically assessed moment release rate of each fault the moment frequency distribution of earthquakes predicted from the geologic record is virtually identical to that seen with the 400 yr record of seismicity these observations indicate that the geologic record of quaternary fault offsets contains sufficient information to predict both the spatial and size distribution of intraplate earthquakes in japan a contour map of the average recurrence time of ground shaking of jma intensity v is thus computed using an empirical relation between seismic moment and the areal distribution of seismic intensity and assuming that the repeat time t of earthquakes on each quaternary fault equals m 0 m 0 g the map demonstrates how quaternary fault data may be used to assess long term seismic hazard in areas of active faulting where historical records of seismicity are relatively short or absent another shortcoming of conventional seismic hazard analysis is that hazard is not considered a function of the time since each fault in a region last ruptured a simple procedure is used to demonstrate how the time dependent nature of the earthquake cycle affects the evaluation of seismic hazard the distribution of seismic shaking characteristic of large interplate earthquakes offshore of japan is estimated from published isoseismal maps the observed average repeat times of ruptures along specific segments of the plate boundaries then provide the basis to make probabilistic estimates of the next expected time of seismic shaking due to plate boundary earthquakes when data are too few to document the average repeat times of rupture the estimates of probability are calculated with data relating to the relative coseismic slip during past earthquakes and the rate of interseismic strain accumulation interpreted within the framework of the time predictable model of earthquake occurrence results are displayed as maps of instantaneous seismic hazard the probability that seismic shaking will occur conditional to knowledge of where in time each fault in a region presently resides with respect to the earthquake cycle

earthquake recurrence and magnitude and seismic deformation of the northwestern okhotsk plate northeast russia 1 recorded seismicity from the northwestern okhotsk plate northeast asia is currently insufficient to account for the predicted slip rates along its boundaries due to plate tectonics however the magnitude frequency relationship for earthquakes from the region suggests that larger earthquakes are possible in the future and that events of mw 7 5 which should occur every 100 350 years would account for almost all the slip of the plate along its boundaries due to eurasia north america convergence we use models for seismic slip distribution along the bounding faults of okhotsk to conclude that relatively little aseismic strain release is occurring and that larger future earthquakes are likely in the region our models broadly support the idea of a single okhotsk plate with the large majority of tectonic strain released along its boundaries

an application of the time and magnitude predictable model for the long term prediction of strong shallow earthquakes in the japan area the country of japan and its surrounding area has been divided into 12 seismogenic sources on the basis of certain seismotectonic and geomorphological criteria in each of these sources interevent times between successive mainshocks with magnitudes equal to or larger than certain cutoff magnitudes were considered these interevent times as well as the magnitudes of the mainshocks have been used to determine the following relations log t t 0 30 m min 0 19 m p 0 18 log m 0 2 41 m f 0 88 m min 0 25 m p 0 46 log m 0 9 06 where tt is the interevent time measured in years m min is the surface wave magnitude of the smallest mainshock considered mp is the magnitude of the preceding mainshock mf is the magnitude of the following mainshock and m is the yearly released seismic moment in each source on the basis of these two relations and taking into account the time of occurrence and the magnitude of the last mainshock in each source time dependent conditional probabilities for the occurrence of the next large ms 7 5 shallow mainshocks in the 12 seismogenic sources during the next 10 yrs 1993 to 2002 and the magnitudes of the expected mainshocks are determined for seismogenic sources 5 fukushima 9 western honshu 7 southern hokkaido 1 ryukyu islands and 12 okushiri island relatively high probabilities p 10 0 5 were assigned it is of interest to note that in seismogenic source 12 okushiri for which an expected magnitude of 7 5 was calculated an earthquake with a magnitude of 7 6 national earthquake information center occurred on 12 july 1993

relationship between tectonics volcanism sedimentation and basin development late cenozoic central part of northern honshu japan abstract a pronounced interplay between tectonics volcanism and sedimentation can be established in the volcanic arc region of the central part of northern honshu during the early miocene to quaternary interval four stages are recognized with the type of volcanism and sedimentation varying according to the tectonic stress regime 1 1 rifting stage 22 15 ma ns trending half grabens were formed under an extensional stress regime related to the rifting of the sea of japan basins were rapidly filled by intermediate to felsic volcanic products which are often associated with subaerial fluvial and lacustrine sediments 2 2 back arc basin opening stage 15 13 ma with more advanced stagess of rifting subsidence from crustal stretching resulted in marked marine incursion and an overall transgressive succession developed during this stage the back arc side of northern honshu subsided rapidly to middle bathyal environments at the same time associated with the opening of the sea of japan large volumes of regionally extensive mafic lavas and associated hyaloclastites were erupted within submarine grabens in contrast in the present backbone ranges felsic volcanism occurred within bathyal to shallow marine environments igneous rock types in this stage display a bimodal mafic felsic chemistry 3 3 transitional stage 13 2 4 ma a thermal subsidence substage 13 8 ma an intermediate stress regime developed which included phases of both weak extension and compression consequently grabens along the sea of japan ceased to form later lithospheric cooling eventually led to thermal subsidence of the back arc region and hemipelagic sediments mantled the previously active mafic volcanic apron volcanism at this time was mainly restricted to a narrow zone along the present backbone ranges where felsic to intermediate volcanic products accumulated within shallow marine environments b incipient compressional substage 8 2 4 ma hemipelagic sedimentation continued on the back arc side of northern honshu along the present backbone ranges the intermediate stress regime continued with formation of many large caldera structures associated with subaerial felsic volcanism 4 4 shortening deformation stage 2 4 ma present the change of the absolute direction of motion of the pacific plate at the early to middle pliocene changed the regional stress regime of the volcanic arc from intermediate to compression movement of back arc thrusts along the sea of japan coast began 2 3 ma and led to uplift of the volcanic arc continued compression in the volcanic arc produced narrow uplifted zones with associated basins bounded by reverse faults these basins were filled rapidly by terrestrial sediments containing upward coarsening sequences under this highly compressional tectonic stress regime volcanism became intermediate mafic in composition with large stratovolcanoes becoming prominent

crustal deformation processes and the stability of the gutenberg richter relationship abstract global and regional surveys of earthquakes show that empirically determined b values of the gutenberg richter distribution are remarkably stable generally limited to values of 1 0 2 here i interpret observations from california new zealand and japan to suggest that the stability of the b value is a manifestation of a physical process specifically the tendency of crustal strains to organize along relatively discrete zones given a portion of the earth9s crust subject to a displacement field displacement is accommodated by a system of fault lengths that obey a power law distribution with continued displacement longer faults develop at the expense of shorter faults and take up an increasingly greater portion of the displacement budget shifts in regional displacement directions lead to reversals of these trends the changes in the ratio of long faults to short faults in a region is thus accompanied by changes in the relationship between fault length and fault slip rate because the recurrence of earthquakes on faults is a function of both fault length and fault slip rate the deformation process may result in a system of feedback that inhibits changes in the b value as fault populations change a corollary to the idea is that the magnitude frequency statistics of seismicity may be attributed to the same physical processes that are responsible for the development of plate tectonic boundaries and the gross spatial distribution of seismicity around the globe

crustal deformation measurements in central japan determined by a global positioning system fixed point network a global positioning system gps fixed point network has been operating in the kanto and tokai districts of central japan since april 1988 to detect crustal deformation associated with the convergence of the eurasian pacific north american and philippine sea plates and to monitor the deformation cycles of frequent large interplate and intraplate earthquakes this 10 station network established by the national research institute for earth science and disaster prevention nied is the first continuously monitoring network of its kind we determine deformation within the network using two consecutive days of data every 2 weeks for the first 17 months of operations we use a station and orbit relaxation method which relies exclusively on data collected within the nied network except for 1 week of global gps tracking data which is used to determine initial station positions with respect to the global reference frame we detect relative to a station on the eurasian plate in central japan significant westward motion of 28 mm yr of the northern tip of the philippine sea plate which is subducting beneath the eurasian plate at the suruga trough our results support finite element models of collision of the izu block with the eurasian plate based on earthquake focal mechanisms and plate block motions of the japanese archipelago determined from conventional geodetic measurements over the last century we detect southwestward motion of 18 mm yr of the southeastern tip of the eurasian plate confirming expected surface extension of the subducted plate parallel to the suruga trough axis significant vertical uplift with a velocity of 20 mm yr is suggested at a site inland of the tokai district located in the akaishi uplift zone and at a site on hatsushima island in sagami bay the general tendency of vertical movements of the other sites agrees with vertical velocities obtained from 70 years of geodetic leveling and with quaternary vertical displacements determined from geomorphological and other geological evidence we detect no significant crustal motion across the fossa magna tectonic zone in central japan often considered a plate boundary across the tokyo metropolitan area nor across the sagami trough associated with the subduction of the philippine sea plate beneath northeast japan our results demonstrate the power of regionally based continuously monitoring gps networks for obtaining temporally dense measurements of small horizontal and vertical crustal movements across plate boundary zones

seismic activity and deformation process of the overriding plate in the northeastern japan subduction zone abstract we estimated the temperature distribution within the crust of the northeastern japan arc from p wave velocity perturbations obtained by travel time tomography by comparing the estimated temperature distribution with the focal depth distribution of shallow precisely relocated microearthquakes we found that the brittle to ductile or stick slip to stable sliding transition occurs at the 400 c isotherm and that the transition depth has considerable lateral variations the brittle seismogenic zone the upper portion of the crust becomes locally thin in the p wave low velocity areas where the temperature is estimated to be relatively high concentration of shallow microearthquakes high topography and relatively large contractile deformation of the crust are also observed in these low velocity areas active faults are not distributed in the low velocity areas but lie just along the edge of those areas or outside them all these observations suggest that earthquake occurrence and deformation within the crust is governed to a considerable degree by the thermal regime of this volcanic arc which is characterized by a horizontally inhomogeneous distribution of temperature

seismic moments of earthquakes at the western hellenic arc and their application to the seismic hazard of the area tselentis g a stavrakakis g m o ulos k latousakis j and drakopoulos j 1988 seismic moments of earthquakes at the western hellenic arc and their application to the seismic hazard of the area tectonophysics 148 73 82 seismic moments of 45 large earthquakes m 2 5 2 which occurred in the southwestern part of the hellenic arc trench system between 1950 and 1981 were used to express the frequency of occurrence of earthquakes in terms of the subduction rate and the largest seismic moment likely to occur in the region for this purpose a moment versus magnitude relationship for earthquakes characteristic of the region was derived and the subduction rate was estimated from seismic moment rates the hellenic arc trench system is a subduction zone of about 1000 km where the african lithosphere is subducting under the aegean lithospheric plate in a roughly sw ne direction this motion of the hellenic consuming boundary with respect to africa results from three different processes the northward motion of the african plate the aegean extensional spreading and the westward motion of turkey mckenzie 1970 1978

on the stress dependence of the earthquake b value laboratory experiments have shown that the b value in the size distribution of acoustic emission events decreases linearly with differential stress there have been a number of observations that indicate that this relation may also hold for earthquakes here using a simple frictional strength model for stresses in the continental lithosphere combined with earthquake b values measured as a function of depth in a wide variety of tectonic regions we verify and calibrate that relation finding b 1 23 0 06 0 0012 0 0003 1 3 where the stress difference 1 3 is in megapascal for subduction zones we find that b value correlates linearly with the slab pull force and with the net reduction of plate interface normal force both of which also indicate a negative linear relation between b value and differential stress

simultaneous reactivation of two subparallel inland normal faults during the mw 6 6 11 april 2011 iwaki earthquake triggered by the mw 9 0 tohoku oki japan earthquake the gigantic m w 9 0 11 march 2011 tohoku oki earthquake suddenly changed the overriding inland area to an extensional stress regime and triggered massive seismic swarms in the coastal region the largest earthquake of m w 6 6 struck southern fukushima on 11 april 2011 and ruptured two previously mapped faults the northwest nw trending yunodake fault and the north northwest nnw trending itozawa fault clear 15 km long and 14 km long surface ruptures appeared along both faults respectively exhibiting a predominantly normal sense of slip down to the west the maximum vertical offset on the yunodake fault is 0 8 m whereas that on the itozawa fault is 2 1 m the itozawa fault rupture is in part marked by uphill facing scarps which is discordant with the large scale topography but consistent with saddled ridges and ponded alluvium the yunodake fault which bounds a neogene half graben structure juxtaposing mesozoic metamorphic rocks against neogene sedimentary rocks shows left lateral deflections of streams seismological data and interviews of local residents revealed that the two subparallel faults ruptured simultaneously based on the location of its hypocenter we however interpret that the itozawa rupture was primary and then triggered normal faulting on the yunodake fault under the heightened coulomb stress caused by the preceding tohoku oki earthquake our paleoseismic trench across the itozawa fault exposed evidence for a penultimate earthquake that occurred sometime between 12 620 and 17 410 cal yr b p there is no evidence that the itozawa fault ruptured during or immediately after the a d 869 jogan earthquake which is believed to be the penultimate giant megathrust earthquake along the japan trench

surf beat induced overwash during typhoon haiyan deposited two distinct sediment assemblages on the carbonate coast of hernani samar central philippines abstract wave set up steepened and accentuated the storm surge during typhoon haiyan in november 2013 resulting in bore like flooding with surge heights of 7 m and flow velocities reaching 5 m s 1 on the open sea coastal plain near hernani this study investigates two distinct sediment assemblages left behind by the coastal flooding associated with this surge the first assemblage consists of numerous coastal boulders that now occupy the reef flat and the second pertains to a laterally extensive sand sheet that blanketed the coastal plain up to 300 m inland the majority of the boulders has b axes between 1 and 2 m weigh no 10 t and were originally submerged on the reef edge the boulders found more landwards of the reef edge were potentially lying loosely on the reef flat prior to haiyan in contrast the coarse carbonate sand sheet starts at 10 m inland of the current shoreline and has a maximum thickness of 10 cm and gradually thins to 3 mm at 300 m inland the haiyan sand contains moderate concentrations of foraminifera amphistegina spp baculogypsina sphaerulata and peneroplis spp that were both abraded and unaltered pointing to a reef flat and beach source for the sand sediment transport inverse modeling complements previous flow velocity estimates using numerical modeling which altogether indicate sustained high velocity overland flow despite the presence of coral reefs and mangroves as natural defenses to extreme waves

earthquakes quaternary faults and seismic hazard in california data describing the locations slip rates and lengths of quaternary faults are the primary basis in this work for constructing maps that characterize seismic hazard in california the expected seismic moment m0e and the strength of ground shaking resulting from the entire rupture of each mapped fault or fault segment are estimated using empirical relations between seismic moment m0 rupture length source to site distance and strong ground motions assuming a fault model whereby the repeat time t of earthquakes on each fault equals m0e m0g where the moment rate m0g is proportional to fault slip rate it is observed that the moment frequency distribution of earthquakes predicted from the geologic data agrees well with the distribution determined from a 150 year historical record the agreement is consistent with the argument that the geologic record of quaternary fault offsets contains information sufficient to predict the average spatial and size distribution of earthquakes through time in california the estimates of t for each fault are the foundation for constructing maps that depict the average return period of 0 1g peak horizontal ground accelerations and the horizontal components of peak acceleration peak velocity and the pseudovelocity response at 1 period and 5 damping expected to occur at the level of 0 1 probability during a 50 year period of time a map is also formulated to show the probability that 0 1g horizontal ground accelerations will occur during the next 50 years the maps serve to illustrate the potential value of quaternary fault studies for assessing seismic hazard interpretation of available slip rates indicates that the largest and most frequent occurrence of potentially destructive strong ground motions are associated principally with the san andreas san jacinto calaveras hayward and ventura basin fault zones other regions of similarly high hazard may yet remain unrecognized this inadequacy results primarily from an incomplete data set numerous faults for example are mapped along the coastal region of northern california and within the modoc plateau but relatively few studies relating to fault slip rate are reported a similar problem exists for other stretches of coastal california where marine reflection studies provide evidence of active faulting offshore yet yield little or no information of fault slip rate geological and geophysical field studies can work to remove these deficiencies a concerted effort to locate and define rates of activity on all faults in california is the most promising means to further quantify present levels of seismic hazard in california

individual faults can t produce a gutenberg richter earthquake recurrence abstract individual faults within a region cannot have a gutenberg richter recurrence if the total of earthquakes within the region follow a gutenberg richter recurrence few faults have produced and adequate number of earthquakes to establish the nature of recurrence on them broad seismic regions however for which there is a statistically viable earthquake data set have been shown to obey a gutenberg richter recurrence with a slope of about 1 a gutenberg richter recurrence is often assumed for faults in probabilistic seismic hazard analyses the requirement that individual faults cannot produce earthquakes with this recurrence casts doubt on the validity of such probabilistic methods errors in probabilistic seismic hazard analysis tend to be amplified in the calculation of rare earthquake probabilities and it is these rare earthquakes for which critical facilities must be designed therefore sole use of probabilistic seismic hazard analysis for critical facilities is not recommended

s wave splitting in the aftershock region of the 1995 hyogo ken nanbu earthquake the 1995 hyogo ken nanbu earthquake kobe earthquake m7 2 occurred on january 17 1995 a temporary aftershock observation was carried out by the geophysical research group organized by universities for prediction seismology in 1995 from october 1995 to january 1996 a dense seismic network was deployed in and around the aftershock region and some seismic stations were set directly on the active fault traces we analyze the s wave splitting in and around the aftershock region of the hyogo ken nanbu earthquake we detect a spatial variation of s wave splitting which can be related to crack orientations in an area where a large earthquake has occurred at stations more than 1 km away from the hyogo ken nanbu earthquake fault zone the leading shear wave polarization directions lspd are found to be parallel to the axis of the regional maximum horizontal compressional stress e w suggesting that cracks caused by regional tectonic stress exist in the area however at stations within 500 m of the earthquake fault zones the lspds are parallel to the fault strikes n45 50 e this suggests that new fractures were produced parallel to the faults by shear faulting of the hyogo ken nanbu earthquake and resulted in s wave splitting along the earthquake fault zone nevertheless shear fault origin anisotropy was not evident at stations on the active faults which ruptured in 1596 this implies that healing processes have already closed the fractures produced by shear faulting in 1596 therefore we can expect that s wave splitting can be a useful tool for monitoring healing processes of active faults

strain rates in northwestern italy from spatially smoothed seismicity 1 this work presents seismic strain rate maps for the western alps and northern apennines northern italy as derived from an earthquake catalog collecting both historical and instrumental data strain rates are calculated on the basis of the rate of seismic moment release using the anderson method unlike previous applications which determined the total strain rate associated with specific seismogenic sources we have employed an innovative zoneless approach based on a spatially smoothed seismicity method in addition a monte carlo simulation procedure is applied to allow for uncertainty in the input data e g magnitude to moment conversion seismogenic thickness maximum earthquake magnitude strain rate maps are developed by summing the moments of the earthquakes reported in the catalog and by using two different earthquake recurrence relations our results indicate that deformation rates are quite high ranging from about 2 to 12 10 9 yr 1 in the northern apennines and from 0 5 to 6 10 9 yr 1 in the western alps these values however are 1 order less than those derived from global positioning system measurements suggesting that a portion of the recent deformation in northwestern italy is related to aseismic processes the discrepancies between seismic and geodetic strain rates may also indicate that the record of seismicity may not provide a sufficient time window for assessment of secular rates of moment release or secular deformation rates and rates of recurrence of large magnitude earthquakes in the study area

physical modelling studies of 3 d p wave seismic for fracture detection summary we have carried out two seismic physical experiments to acquire wide azimuth p wave 3d seismic data with a scaled down model 1 10 000 and scaled up frequencies 10 000 1 our aims are to verify the physical basis of using p wave attributes for fracture detection to understand the usage of these attributes and their merits and to investigate the effects of acquisition geometry and structural variations on these attributes the base model consists of a fractured layer sandwiched between two isotropic layers epoxylite inside the fractured layer there is a dome and a fault block for investigating the effects of structural variations the two experiments were carried out using different acquisition geometries the first experiment was conducted to maximize the data quality with an offset depth ratio of only 0 68 to the bottom of the fracture layer for comparison the second experiment was carried out to maximize the anisotropy effects with the offset depth ratio to the bottom of the fracture layer raised to 1 34 for each experiment about 20 km 2 of wide azimuth 3 d data were acquired with a p wave source the physical modelling confirms that the p wave attributes traveltime amplitude and velocity exhibit azimuthal variations diagnostic of fracture induced anisotropy for the first experiment with noise free data the amplitude from the top of the fracture layer yields the best results that agree with the physical model parameters and free of the acquisition footprint the results from other attributes traveltime velocity avo gradient are either contaminated by the structural imprint or by the acquisition footprint due to the lack of offset coverage for the second experiment despite the interferences from multiples and other coherent noise the traveltime attributes yield the best results both the acquisition footprint and the structural imprint are reduced due to the increased offset coverage however the results from the amplitudes are affected by the noise and are less reliable analysis of the two experiments reveals that the offset depth ratio to the target is a key parameter for the success of the p wave techniques smaller offset depth coverage may only be applicable to amplitude attributes with high quality data whilst large offset coverage makes it possible to use traveltime attributes a reliable estimation from traveltime attributes requires an offset depth ratio of 1 0 or more

crustal deformation process in the mid niigata region of the niigata kobe tectonic zone as observed by dense gps network before during and after the tohoku oki earthquake

earthquake rate analysis abstract earthquake rate analysis explores the quantitative relationship between earthquake occurrence rates and geological deformation rates one application is the estimation of tectonic deformation rates from seismicity for comparison with tectonic models another application is the use of geological models to help quantify seismic hazards seismicity is described by a catalog of the largest earthquakes in the region the contribution of small earthquakes towards causing geological deformation is insignificant although the occurrence rate of small events may be predictable from the occurrence rate of large events by a b value relationship the critical information about each earthquake is its seismic moment or better still its seismic moment tensor when moment is not available directly it can be estimated from the earthquake magnitude although this increases uncertainties considerably the average annual moment from all the earthquakes in the catalog is the seismic moment rate uncertainties in seismic estimates of moment rate arise from the short time period of observations from the magnitude moment relationship from the shape of the distribution function giving number of earthquakes as a function of magnitude and from uncertainties in the physical properties of the earth near the source geological models for deformation rates are described by slip rates on individual faults or by regional strain rates a regional strain rate can be derived as a limiting case where there are numerous individual faults such a strain rate is a particularly useful concept where information about each of the faults is limited in the case of either faulting or regional strain the average seismic moment rate is proportional to the deformation rate geological uncertainties arise from difficulties in estimating slip rates or strain rates from fault creep and other aseismic deformation from uncertainty in the part of the fault that fails during earthquakes and boundaries of the deforming region and from uncertainty about the earth s physical properties the seismic moment rate is the critical factor for relating the earthquake occurrence rate and the geological deformation rate using this intermediate parameter one can infer earthquake occurrence rates from deformation rates or infer deformation rates from earthquake occurrence rates generally it is found that deformation rates and earthquake occurrence rates are consistent within uncertainties where both are well constrained they are generally consistent within a factor of two or three

empirical relationships among the convergence rate of plates rollback rate of trench axis and island arc tectonics laws of convergence rate of plates abstract the data on 27 recent arcs which were subducted by normal oceanic lithosphere were compiled among the compression extension rates for island arcs v a compression is defined as positive and the kinematic components of absolute plate motions parallel to the direction of backarc compression extension v on oceanward velocity of the overriding plate v sn continentward velocity of the subducting plate and v tn rollback rate of the trench axis the equations v a v on v sn 7 2 cm y 1 v tn 7 2 cm y v sn 2 are found to hold as for the convergent zones associated with a wadati benioff zone deeper than 200 km equation 1 suggests that backarc spreading and crustal shortening play the role of compensating the deviation of the convergence rate from the critical value of 7 2 cm y the equation 2 means that any subducting oceanic lithosphere has the potentiality of making the trench axis rollback at the rate of 7 2 cm y and that the virtual rollback rate v tn is determined by the balance between the potential rollback rate 7 2 cm y and v sn the present author calls the kinematic relationships represented by equations 1 and 2 laws of convergence rate of plates the convergent zones of plates associated with the wadati benioff zone shallower than 200 km also show a tendency that the greater and smaller values of v on v sn correspond to the backarc compression and extension however the critical value is 3 4 cm y instead of 7 2 cm y

stress estimate for the highest mountain system in japan the hida range the largest mountain system in japan is a contemporary uplifting feature uplifting rate 1 5 mm yr no large earthquakes nor active faults have been located in this mountain range but small earthquakes occur rather frequently often as swarms in its axial portion their focal mechamisms are found to be of strike slip type with the p axes in the nw se to wnw ese direction this direction is perpendicular to the trend of the mountain chain and coincides with the orientation of the tectonic compression now causing intraplate earthquakes in most regions of the japanese islands it also coincides with the convergence direction of the pacific plate and the eurasian plate the bouguer anomaly profile across the hida range suggests an upper crustal root beneath it a buoyancy load associated with this upper crustal root is calculated from the bouguer anomaly profile which is found to be not large enough to sustain the surface topographic load isostatically if any tectonic forces were removed from the mountain system mountains would subside through inelastic deformation a formula is presented to calculate using the known topographic load and buoyancy load the stress differences arising at the virtual instant of removal of tectonic forces the newtonian fluids of uniform viscosity are assumed the calculated stress difference is horizontally tensile about 290 bars at the axial portion of the mountain range this horizontal tension must be overcome tectonically to ensure the mountain uplifting and the earthquake occurrence we suggest that the hida range is now uplifting by horizontal compression of plate tectonic origin with a compressive stress at least of the order of 300 bars during uplifting the mountain system seems to maintain its upper crustal configuration as the one in a fairly close state of minimum stress difference

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

the relationship between the instantaneous velocity field and the rate of moment release in the lithosphere summary instantaneous velocity gradients within the continental lithosphere are often related to the tectonic driving forces this relationship is direct if the forces are secular as for the case of loading of a locked section of a subduction interface by the downgoing plate if the forces are static as for the case of lateral variations in gravitational potential energy then velocity gradients can be produced only if the lithosphere has on average zero strength the static force model may be related to the long term velocity field but not the instantaneous velocity field typically measured geodetically over a period of several years because over short time intervals the upper lithosphere behaves elastically in order to describe both the short and long term behaviour of an elastic lithosphere viscoelastic asthenosphere system in a selfconsistent manner i construct a deformation model termed the expected interseismic velocity eiv model assuming that the lithosphere is populated with faults that rupture continually each with a definite mean recurrence time and that the earth is well approximated as a linear elastic viscoelastic coupled system i derive a simple relationship between the instantaneous velocity field and the average rate of moment release in the lithosphere examples with synthetic fault networks demonstrate that velocity gradients in actively deforming regions may to a large extent be the product of compounded viscoelastic relaxation from past earthquakes on hundreds of faults distributed over large 10 6 km 2 areas

deformation of an island arc rates of moment release and crustal shortening in intraplate japan determined from seismicity and quaternary fault data the historical record of large m 6 9 earthquakes and geologically determined rates of slip on quaternary faults in intraplate japan honshu and shikoku are used to estimate the average rate of seismic moment release m for the last 400 years and during the late quaternary respectively values of m estimated from the two data sets are similar in regions where seismic activity is concentrated on land we interpret this observation to suggest that m in intraplate japan has been constant during the late quaternary and is relatively free from secular variation when averaged over periods of several hundreds of years m in shikoku may be attributed almost solely to right lateral slip of the median tectonic line mtl the easterly strike of the mtl is consistent with a compressive stress field that trends northwest crustal shortening of the izu peninsula taken up on a set of strike slip faults that show north by northwest compression is 1 mm yr northeast honshu is characterized by a set of reverse type faults that trend northerly conversion of m in northeast japan to strain rates suggests that about 5 of the relative plate motion between japan and the pacific plate 9 7 cm yr is accommodated as a permanent east west shortening 5 mm yr of northeast honshu the predominant deformation in central and western honshu takes place as slip on a conjugate system of strike slip faults that strike northeast and southeast and show right lateral and left lateral motion respectively crustal shortening resulting from slip on faults in central and western honshu is 5 and 0 5 mm yr respectively in an easterly direction central and western honshu are in closest proximity to the nankai trough and hence the stress field in these regions cannot simply be attributed to the accommodation of the relative northwesterly convergence of the philippine sea plate the northward impingement of the izu peninsula into honshu may influence stresses in central and western japan but a conclusive explanation of the stress field in central and western honshu remains an enigma

seismicity focal mechanisms and tectonics in the last four years there has been a tremendous increase in the detail of tectonic processes reported in the typical seismotectonic study new data from many local and regional networks of seismographs established during the previous four year period plus the now routine application of improved hypocentral location procedures long period body wave modelling and moment tensor inversion using digitally recorded data have increased resolution of both the hypocentral location and the nature of the faulting process consequently research emphasis has been on local tectonics or those aspects of regional and global tectonics requiring high resolution i briefly describe below some of the highlights of these studies

a test of present day plate geometries for northeast asia and japan alternative geometries for the present day configuration of plate boundaries in northeast asia and japan are tested using nuvel 1 and 256 horizontal earthquake slip vectors from the japan and northern kuril trenches statistical analysis of the slip vectors is used to determine whether the north american eurasian or okhotsk plate overlies the trench along the northern kuril trench sup vectors are well fit by the nuvel 1 pacific north america euler pole but are poorly fit by the pacific eurasia euler pole results for the japan trench are less conclusive but suggest that much of honshu and hokkaido are also part of the north american plate the simplest geometry consistent with the trench slip vectors is a geometry in which the north american plate extends south to 41 n and possibly includes northern honshu and southern hokkaido although these results imply that the diffuse seismicity that connects the lena river delta to sakhalin island and the eastern sea of japan records motion between eurasia and north america onshore geologic and seismic data define an additional belt of seismicity in siberia that cannot be explained with this geometry assuming that these two seismic belts constitute evidence for an okhotsk block two published kinematic models for motion of the okhotsk block are tested the first model which predicts motion of up to 15 mm yr 1 relative to north america is rejected because kuril and japan trench slip vectors are fit more poorly than for the simpler geometry described above the second model gives a good fit to the trench slip vectors but only if okhotsk north america motion is slower than 5 mm yr 1

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

seismic moment assessment of earthquakes in stable continental regions ii historical seismicity summary this part i study in conjunction with part 11 develops a method to determine within specified uncertainty bounds the seismic moment and thus moment magnitude of all earthquakes of stable continental regions scr for which instrumental or intensity data exist its basis is polynomial regression analysis using a database of scr earthquakes with direct seismic moment determination the independent variables include modern teleseismic magnitudes and regional magnitudes part i and isoseismal areas or number of recording stations part 11 part i11 is an application of the methodology of parts i and i1 to several major historical earthquakes all data used in the regressions are assigned individual uncertainties estimated from the literature or from experience formal confidence limits 68 per cent or 95 per cent on both the regression formulas and the predicted seismic moment values are then possible via error propagation analysis the most complete development is for the teleseismic magnitudes m and mb for both the final regression for log m is a quadratic formula that closely emulates the relationship between amplitude magnitudes and log m expected from dislocation theory and source scaling arguments regressions are also derived for the regional magnitudes mlg and m because there are many scr events mainly pre 1964 that have no teleseismic magnitudes prediction uncertainties from teleseismic magnitudes in moment magnitude units are in the ao 18 0 28 range and from regional magnitudes in the ko 23 0 38 range over a wide magnitude band finally the methodology developed here is generic even though the database is specific application to plate boundary oceanic intraplate or active continental intraplate regions should be straightforward

late quaternary crustal shortening rate across the shinjo basin northeast japan 1 the active fault and fold belt in the eastern shinjo basin has contributed to late quaternary crustal shortening of the northeastern japan arc the geometries of several deformed strata and geomorphic surfaces recorded different rates of cumulative shortening fluvial terraces as old as 290 ka were dated by 14c and fission track dating and tephrochronology we used published seismic profiles to constrain the deep structure of the belt vertical offsets of different terrace surfaces show that the slip rate of the chojahara fault in the innermost basin has increased through time on the basis of its seismic profile this fault was interpreted to dip at a high angle the funagata anticline between the chojahara fault and the ou ranges was probably caused by a low angle blind thrust at about a 2 km depth the different geometries between the basin sediments and fluvial terraces caused by the blind thrust indicate downward propagation of the thrust through time synchronous development of the chojahara fault increased slip rate and the blind thrust beneath the funagata anticline downward propagation suggests that these faults form a piggyback fault system connecting to the deep part of the basin bounding kyodanbara fault estimated crustal shortening rates are averaged to be 0 65 1 05 and 0 79 1 42 m kyr over the last 200 260 and 12 28 ka respectively accounting for about 0 7 1 6 of the convergence between the pacific and eurasian plates estimated strain rates are 0 07 0 11 and 0 08 0 14 ppm yr for the last 200 260 and 12 28 ka respectively

tectonic stress state in ne japan as part of the okhotsk plate abstract an existing geodetic flow velocity model obtained by using an internal free network adjustment technique is used to derive estimates for various strain rates parameters in ne japan the greatest shortening rates of the principal strains trending e w are located in regions where much steady internal frame invariant plastic flow deformation is observed to be taking place the internal geodetic adjustment technique yielded the internal deformation in the tohoku arc most of the intraplate deformations including the much folding deformations observed in the inner zone are produced from within an interseismic transient elastic loading at a strongly coupled locked japan trench would not be needed the observed ongoing extensive ductile folding deformation in the inner zone of tohoku may mean that the geodetic strain rates causing shortening at 2 3 cm yr probably reflect the more correct level of the deformation which is steady permanent in ne japan as compared with seismic faulting data which indicate 0 5 cm yr shortening the calculated principal strain rates are used to make an interpretation for the origin of the deviatoric principal stresses within the greater regional plate tectonic framework the tectonic stress state in ne japan as part of the okhotsk plate could mostly be influenced by the okhotsk plate which is extruding southward to lessen the significant accumulated contractional deformation in ne asia in the verkhoyansk cherskii mountains the principal strain rates are n s extensional essentially everywhere in ne japan as a result of the southerly extrusion except in its southernmost leading edge in the uetsu fossa magna province where the japan alps rampart rises in front of the extrusion here an e w compressional stress state prevails a second e w contractional zone is found in north central tohoku extending from the sanriku province in the outer zone to the inner zone in the japan sea side being more prevalent in the latter zone the calculated rotation rates from the geodetic flow model are clockwise cw in both of the e w contractional regions ne japan extruding southward faces buttresses in 1 the oga ojika line ool and or a crustal weakness zone between the northern and the southern halves of tohoku approx at 38 5 n latitude and especially 2 the japanese alps rampart these obstacles cause the northern and southernmost tohoku to veer to its right and rotate cw thereby setting up the e w trending compressional deformation in their respective inner zones between the ool or the 38 5 n boundary and the kanto tectonic line ktl the sense of the differential rotations is counterclockwise ccw towards the ocean to the se the northern tohoku north of the ool and the southernmost tohoku south of the ktl cannot rotate ccw towards the ocean because of the izu block s collision in the south and the relatively strong coupling along the subduction interface beneath the japan trench in the north off sanriku the relatively stronger long term coupling between the northern tohoku and the pacific plate at the sanriku coast with respect to that in off fukushima is due to a flatter subduction of the pacific slab there increasing the plates interface contact area the flattening of the subduction dip angle was caused by ccw rotation and shifting of the northern tohoku along the dextral honjo matsushima line roughly corresponding to the ool towards the pacific and overriding of the subduction zone during the formation of the japan sea

foreshocks and aftershocks of large m 5 5 earthquakes within the western cordillera of the united states source parameters of foreshocks and aftershocks of 27 large m 5 5 earthquake sequences occurring within the western cordillera of the united states between 1915 and 1988 have been used to examine the properties of foreshocks and aftershocks and to determine how foreshocks and aftershocks relate to faulting properties of their main shocks to physiographic province and to heat flow this study examines only the largest foreshocks and aftershocks occurring within 2 months and 40 km of the main shocks results of this study show that nearly 60 per cent of western cordilleran earthquakes have foreshocks and that 58 per cent of the foreshocks occurred within 24 hours of their main shocks most aftershocks appear to be occurring on a fault plane with the same or similar orientation to the fault that ruptured in the main shock at or slightly above the main shock depth the average magnitude difference between main shocks and their largest aftershocks is 1 03 0 47 the difference between main shock and aftershock magnitude appears to decrease with increasing heat flow sixty percent of the aftershocks occurred within 24 hours of their main shocks but nearly one third occurred more than 1 week after their main shocks