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

imaging subduction from the trench to 300 km depth beneath the central north island new zealand with vp and vp vs summary recent dense deployments of portable digital seismographs have provided excellent control on earthquakes beneath the central north island of new zealand here we use a subset of the best recorded earthquakes in an inversion for the 3 d vp and vp vs structure the data set includes 39 123 p observations and 18 331 s observations from 1239 earthquakes and nine explosions the subducted plate is imaged as a high vp low vp vs feature vp within the mantle of the subducted slab is almost always 8 5 km s 1 which requires the ca 120 myr slab to be unusually cold the low vp vs within the subducted plate closely parallels the lower plane of the dipping seismic zone it most likely indicates fluid resulting from dehydration of serpentine in the slab mantle and the earthquakes themselves are likely to be promoted by dehydration embrittlement we identify a region with vp 8 0 km s 1 directly above the dipping seismic zone can be interpreted as sinking entrained with the motion of the subducted slab and forming a viscous blanket that insulates the slab from the high temperature mantle wedge material in the overlying low vp region can be interpreted as rising within a return flow within the wedge the volcanic front appears to be controlled by where this dipping low vp region meets the base of the crust the thickness of the backarc crust also shows significant variation along strike in the central taupo volcanic zone tvz the crust is ca 35 km thick while southwest of mt ruapehu the crust thickens by ca 10 km there is no significant low vp zone in the mantle wedge in this southwestern region suggesting that this thicker crust has choked off mantle return flow the seismic tomography results when combined with constraints on mantle flow from previous shear wave splitting results provide a plausible model for both the distribution of volcanism in the central north island and the exceptional magmatic productivity of the central tvz

a new map of the geographic extent of the socorro mid crustal magma body for 35 years strong reflected phases from the sill like mid crustal socorro magma body smb have been observed on microearthquake seismograms recorded in the central rio grande rift new mexico in 1979 the lateral extent of the smb was estimated at 1700 km2 by mapping reflection points for 220 observed szs arrivals we have remapped the magma body using 697 pzp 2169 szp and 2589 szs reflections observed on seismograms recorded between 1975 and 1995 by new mexico tech seismic networks these data indicate that the smb covers an area greater than 3400 km2 by comparing the distribution of observed reflection points with the distribution of all possible reflection points limits can be set for the northern and southern boundaries of the smb the 80 km north south extent of the smb falls just inside a 100 km north south range of enhanced seismicity near socorro this area the socorro seismic anomaly ssa covers 5000 km2 and has the same elliptical shape as the outline of the smb based on observed reflection points the close spatial relation between the ssa and the mid crustal magma body along their northern and southern boundaries suggests that the observed seismicity can be used to place limits on the eastern and western boundaries of the magma body using the distribution of earthquakes within the ssa over the last 34 years the maximum east west extent of the smb is 60 km our reflection based value is 50 km our data indicates that the upper surface of the magma body displays no regional dip considering timing errors maximum possible relief on the magma body surface is 0 50 km

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

strong shaking in los angeles expected from southern san andreas earthquake 1 the southernmost san andreas fault has a high probability of rupturing in a large greater than magnitude 7 5 earthquake sometime during the next few decades new simulations show that the chain of sedimentary basins between san bernardino and downtown los angeles form an effective waveguide that channels love waves along the southern edge of the san bernardino and san gabriel mountains earthquake scenarios with northward rupture in which the guided wave is efficiently excited produce unusually high long period ground motions over much of the greater los angeles region including intense localized amplitude modulations arising from variations in waveguide cross section

site amplification in the los angeles basin from three dimensional modeling of ground motion it is well established that sedimentary basins can significantly amplify earthquake ground motion however the amplification at any given site can vary with earthquake location to account for basin response in probabilistic seismic hazard analysis therefore we need to know the average amplification and intrinsic variability standard deviation at each site given all earthquakes of concern in the region due to a dearth of empirical ground motion observations theoretical simu lations constitute our best hope of addressing this issue here 0 0 5 hz finite difference finite fault simulations are used to estimate the three dimensional 3d response of the los angeles basin to nine different earthquake scenarios amplifi cation is quantified as the peak velocity obtained from the 3d simulation divided by that predicted using a regional one dimensional 1d crustal model average ampli fication factors are up to a factor of 4 with the values from individual scenarios typically differing by as much as a factor of 2 5 the average amplification correlates with basin depth with values near unity at sites above sediments with thickness less than 2 km and up to factors near 6 above the deepest 9 km and steepest dipping parts of the basin there is also some indication that amplification factors are greater for events located farther from the basin edge if the 3d amplification factors are divided by the 1d vertical sh wave amplification below each site they are lowered by up to a factor of 1 7 the duration of shaking in the 3d model is found to be longer by up to more than 60 seconds relative to the 1d basin response the simu lation of the 1994 northridge earthquake reproduces recorded 0 0 5 hz particle velocities relatively well in particular at near source stations the synthetic and observed peak velocities agree within a factor of two and the log standard deviation of the residuals is 0 36 this is a reduction of 54 and 51 compared to the values obtained for the regional 1d model and a 1d model defined by the velocity and density profile below a site in the middle of the basin dow respectively this result suggests that long period ground motion estimation can be improved consid erably by including the 3d basin structure however there are uncertainties con cerning accuracy of the basin model model resolution the omission of material with shear velocities lower than 1 km s and the fact that only nine scenarios have been considered therefore the amplification factors reported here should be used with caution until they can be further tested against observations however the results do serve as a guide to what should be expected particularly with respect to increased amplification factors at sites located above the deeper parts of the basin

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

seismic structure of the northeastern japan convergent margin a synthesis many studies recently made on the basis of seismic observations have revealed a detailed structure of the crust and the upper mantle beneath the northeastern japan arc and its relationship to seismic and volcanic activity spatial distributions of the depths to the conrad and the moho discontinuities estimated from shallow earthquake data and seismic explosion data show that both discontinuities are deep in the middle of the land area and shallow toward the coastlines of the japan sea and the pacific ocean the pn velocity has a lateral variation it is as low as 7 5 km s beneath the land area while that beneath the japan sea and the pacific ocean is 8 0 8 2 km s it changes abruptly at the transition zones which are located along the coastlines precise structure and location of the subducted pacific plate beneath the land area is inferred from converted or reflected seismic waves at the top or bottom of the plate the pacific plate is composed of a thin 5 km low velocity upper layer and a thick high velocity lower layer its total thickness being 80 90 km the upper plane seismicity of the double seismic zone is confined to the thin low velocity upper layer which probably corresponds to the subducted former oceanic crust the lower plane seismicity lies at the middle of the high velocity lower layer and the lower half of the plate below it is incapable of generating earthquakes the shallower portion of the upper surface of the plate beneath the pacific ocean along which major seismicity with low angle thrust faultings is actually occurring is also located by seismic observations on land and in the sea the pacific plate subducts at an extremely low angle of 5 for the first 25 km depth and then the dip steepens rather abruptly to 30 normal fault type events at the top of the plate have not been detected in the portion where the downward bending is the largest but have been ditected near the trench axis where it is rather small tomographic inversions for seismic velocity structure clearly delineate the inclined high velocity pacific plate with a thickness of 80 90 km and low velocity zones in the crust and the mantle wedge beneath active volcanoes seismic attenuation tomography also shows similar zones of low q value beneath active volcanoes although its spatial resolution is much lower the low velocity zones with 2 6 velocity lows are continuously distributed from the upper crust just beneath active volcanoes to a depth of 100 150 km in the mantle wedge and are approximately parallel to the dip of the underlying pacific plate these low velocity zones probably reflect the pathway of magma ascent from a depth in the mantle wedge to the earth s surface corresponding to a portion of the subduction induced secondary mantle wedge flow

morphology of the subducting slab boundary in the northeastern japan arc abstract the detection and location of the subducting slab boundary is crucial for a better understanding of the mechanical coupling between the subducting oceanic plate and the overlying continental plate and of the occurrence of large and destructive earthquakes on the main thrust zone in the forearc region of subduction zones it is also important for the understanding of the dehydration of the subducting slab and the genesis of island arc magmatism and volcanism in this study we have estimated the morphology of the upper surface of the subducting pacific plate under northeastern ne japan by using 1372 sp converted waves at the slab boundary and 666 earthquakes beneath the pacific ocean that are well located with sp depth phases we found that the pacific slab beneath ne japan subducts at a small dip angle of less than 10 for the first descent to about 20 km depth and has a steeper dip angle of 15 25 at 30 50 km depth and about 30 at deeper areas the slab depth is approximately 50 km under the pacific coast 150 km under the japan sea coast and nearly 100 km beneath the volcanic front at 60 150 km depths earthquakes in the lower plane of the double seismic zone occur in the central part of the slab while the upper plane events occur within 10 15 km beneath the slab boundary there is a change in the slab surface geometry around 38 n which corresponds to the landward extension of an oceanic fracture zone the strike of the slab is nne in the north and becomes ne in the south the southern part of the slab has a steeper dip angle than the northern part we believe that these features are related to the different patterns of interplate seismicity and mechanical coupling between the northern and southern parts of ne japan many great m8 0 8 5 interplate earthquakes have occured in northern ne japan during recorded history 830 1995 and microearthquakes show a wide distribution in the forearc region from the japan trench to the pacific coast suggesting strong interplate seismic coupling in that region in contrast only a few m7 0 7 5 class earthquakes have occurred in southern ne japan in the same period and microearthquakes tend to cluster in many small areas suggesting weaker interplate coupling there the subducted slab may be segmented by the oceanic fracture zones and the degree of seismic coupling changes from segment to segment the behavior of the segment in southern ne japan might be affected by the subducted seamounts so that the slab subducts at a steeper dip angle this interpretation is supported by geomagnetic topographic and geological studies which show that many small sized seamounts were subducted in the past from the southern part of the japan trench but almost no seamounts were subducted beneath the northern part

semi empirical estimation of peak ground acceleration from large earthquakes abstract a simplified method is proposed for synthesizing ground acceleration from a large earthquake the present method is based on the semi empirical method of irikura 1986 which is consistent with the square source model but is much simplified for engineering use in this method the fault of the large earthquake is divided into small elements and the acceleration envelope waveforms instead of the time histories from the elements are simply determined using the empirical relations the envelope waveforms from the elements are summed to synthesize the envelope waveform of a large earthquake the peak acceleration of the large earthquake is obtained from the maximum value of the summed envelope to test the present method the peak accelerations are calculated for the 1985 central chile earthquake ms 7 8 during which a considerable number of the strong motion records were obtained close to the source the calculated accelerations are in good agreement with the observed ones the attenuation characteristics of the calculated peak accelerations for earthquakes of different magnitudes are examined the results show that 1 1 the shortest distance from the fault plane is an appropriate definition for source distance 2 2 the peak acceleration becomes independent of magnitude in the near field and 3 3 the source direction effect on the peak acceleration is not negligible

earthquake ground motion amplification for surface waves surface waves from earthquakes are known to cause strong damage especially for larger structures such as skyscrapers and bridges however common practice in characterizing seismic hazard at a specific site considers the effect of near surface geology on only vertically propagating body waves here we show that surface waves have a unique and different frequency dependent response to known geologic structure and that this amplification can be analytically calculated in a manner similar to current hazard practices applying this framework to amplification in the los angeles basin we find that peak ground accelerations for certain large regional earthquakes are underpredicted if surface waves are not properly accounted for and that the frequency of strongest ground motion amplification can be significantly different including surface wave amplification in hazards calculations is therefore essential for accurate predictions of strong ground motion for future san andreas fault ruptures

strong ground motion modelling of causative fault for the 2002 avaj earthquake iran abstract the suitability of a very fast method for obtaining synthesizing accelerograms has been demonstrated for a hybrid simulation technique of source wavelet and acceleration envelope waveform for the 2002 avaj earthquake this method is based on the amplitude modeled white noise and envelope waveform the estimation of peak acceleration from a preliminary simulated record is based on using modeling parameters of rupture plane instead of empirical relations for peak acceleration based on comparison between observed and simulated strong ground motion data a fair agreement is observed between simulated and observed records up to distances 40 km for peak acceleration and duration the most important feature of the recorded strong motion is decay up to a distance of 40 km which is due to direct upgoing shear waves at distance of 50 to 60 km peak acceleration increase which is due to postcritical reflection from velocity gradient in the lower crust a flat trend is observed for peak acceleration at distance of 60 to 100 km the simulation indicates that the rupture is started at depth of 8 km and propagated from northwest to southeast the causative fault for the 2002 avaj earthquake shows similar mechanism to the 1962 buin zahra earthquake

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

regional seismic characteristics of the 9 october 2006 north korean nuclear test we investigate the regional seismic signature of the 9 october 2006 north korean nuclear test broadband regional data for the nuclear test and a group of earthquakes close to the test site were obtained between december 2000 and no vember 2006 epicentral distances from the stations to the test site are between 371 and 1153 km we first use these regional events to calibrate the lg wave magnitude in the network then the network is used to calculate mblg 3 93 for the north ko rean nuclear explosion using a modified fully coupled magnitude yield relation the yield of the north korean nuclear test is estimated to be 0 48 kt because of large uncertainties in the source depth the estimate is preliminary the p s type spectral ratios pg lg pn lg and pn sn are calculated for the nuclear explosion and a group of earthquakes close to the test site at frequencies above 2 hz the network averaged p s spectral ratios clearly separate the 9 october 2006 explosion from the regional earthquakes our result indicates that a single blast explosion in the north korea re gion shows different seismic characteristics from an earthquake any well coupled single blast explosion detonated in this region with yield similar to that for the north korean nuclear test has a large probability of being identified by a regional seismic network such as the one adopted in this study

seismic reflector alignment along the volcanic front in northeastern honshu japan 1 we found seismic reflectors aligned along the east side of the volcanic front in northeastern honshu japan by analyzing seismograms of intermediate depth earthquakes recorded at high sensitivity seismograph network japan stations we identified an unusual high frequency later phase on the seismograms which arrives after the direct s waves and continues for 5 s the characteristics of the waveforms suggest that this later phase is an s wave incidence we plotted envelope waveforms and identified later phase arrivals on envelope waveforms to estimate the location of the source of the later phases we defined an event group that consisted of six to eight events distributed in a region of 50 km 3 the source of the later phases was located by a combination of a station and an event group using later phase travel times if we assume that later phases arriving at a station from an event group are generated by a common source then we can use the observed travel times in a grid search to obtain the source location the sources of the later phase were found to be aligned along the east side of a volcanic front at a depth of 20 30 km the averaged ratio of the amplitudes of the later phases to the amplitudes of the incident waves on the later phase source was estimated to be 0 6 this result suggests the existence of unusual reflectors spread in the lower crust beneath the fore arc region it may be possible that the later phase sources are steeply inclined bodies filled with fluid

how the development of magma chambers affects collapse calderas insights from an overview here we review the studies of pluton emplacement and caldera collapse proposing a model linking the two processes the shallow rise of magma occurs by dyking and its emplacement occurs along major anisotropies many plutons are emplaced at subhorizontal discontinuities forming sills these will eventually grow forming laccoliths the most common mechanism to store shallow magma calderas are a surface expression of these reservoirs and can be approximated by a piston cylinder which sinks due to 1 underpressure in the reservoir producing outward dipping reverse faults 2 overpressure within a silllike chamber undergoing doming and 3 overpressure within a laccolith generating apical tensile stresses in the latter two cases inward dipping normal faults form we suggest that collapse calderas are the surface expression of pressure variations within laccoliths or tabular intrusions their geometric relationships depend on the shape and aspect ratio of the intrusion and its pressure conditions tabular intrusions generating ring faults mainly at their tips form calderas with a similar width to the intrusion laccoliths may generate ring faults along the intrusion roof forming calderas narrower than the intrusion the outward or inward dip of the caldera faults results from the underpressure or overpressure conditions within the

a 3 d model of the crust and uppermost mantle beneath the central and western us by joint inversion of receiver functions and surface wave dispersion 1 rayleigh wave phase velocity maps from ambient noise and earthquake data are inverted jointly with receiver functions observed at 828 stations from the usarray transportable array west of 100 w longitude for data recorded in the years 2005 through 2010 to produce a 3 d model of shear wave speeds beneath the central and western us to a depth of 150 km eikonal tomography is applied to ambient noise data to produce about 300 000 rayleigh wave phase speed curves and helmholtz tomography is applied to data following 1550 ms 5 0 earthquakes so that rayleigh wave dispersion maps are constructed from 8 to 80 s period with associated uncertainties across the region harmonic stripping generates back azimuth independent receiver functions with uncertainty estimates for each of the stations a nonlinear bayesian monte carlo method is used to estimate a distribution of shear wave speed vs models beneath each station by jointly interpreting surface wave dispersion and receiver functions and their uncertainties the assimilation of receiver functions improves the vertical resolution of the model by reducing the range of estimated moho depths improving the determination of the shear velocity jump across moho and improving the resolution of the depth of anomalies in the uppermost mantle a great variety of geological and tectonic features are revealed in the 3 d model that form the basis for future detailed local to regional scale analysis and interpretation

imaging the heterogeneous source area of the 2003 m6 4 northern miyagi earthquake ne japan by double difference tomography abstract a shallow m6 4 inland earthquake occurred on 26 july 2003 in the northern part of miyagi prefecture northeastern japan this earthquake was a typical inland thrust earthquake a type that is common in ne japan we obtained a detailed seismic velocity structure in the focal area of this earthquake by the double difference tomography method arrival time data came from temporary seismic stations deployed above the mainshock fault plane both the p wave and s wave velocities in the hanging wall were lower than those in the footwall aftershocks were aligned along a zone where the seismic velocity changes rapidly this is consistent with the interpretation that the 2003 northern miyagi earthquake occurred along a fault that acted as a normal fault in the miocene and has been reactivated as a reverse fault under the present compressional stress regime the large slip area by the main shock rupture asperity corresponds to an area with relatively high p and s wave velocities a zone with low vp vs was detected along the aftershock area one of the possible causes of this low vp vs zone is the existence of high aspect ratio pores that contain water hypocenters of the main shock largest foreshock and largest aftershock are also located within the low vp vs zone

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

attenuation tomography of the western united states from ambient seismic noise 1 we show that the spatial coherency of the ambient seismic field can be used for attenuation tomography in the western united states we evaluate the real portion of the spatial coherency with an elastic geometric spreading term a bessel function and a distance dependent decay an attenuation coefficient in order to invert the spatial coherency a weight stack inversion technique is applied we recover phase velocity and attenuation coefficient maps at periods of 8 32s which correspond to the elastic and anelastic structure at crustal and upper mantle depths the phase velocity maps obtained by this method are of similar resolution to more standard two station methods the attenuation results provide an important complement to the information extracted from earthquake based tomography several geological features are easily identifiable in the attenuation coefficient maps such as the highly attenuating sedimentary basins along the west coast of the united states and the highly attenuating yellowstone region and the boundaries of the snake river plains

on the robustness of global radially anisotropic surface wave tomography a number of recent global tomographic studies have modeled three dimensional variations in the parameters of radial anisotropy as yet there is limited agreement among such studies suggesting significant uncertainties in the models which could lead to divergent geodynamical interpretations in this study we assess the robustness of lateral variations in radial anisotropy globally in the upper mantle and in the transition zone to determine the extent to which anisotropic parameters are constrained by a data set of over 10 000 000 fundamental and higher mode surface wave dispersion measurements we carry out inversions for isotropic and radially anisotropic shear wave velocity systematically changing regularization and using three different crustal models to remove the effects of the crust on the data using crustal corrections from different crustal models has an impact on the data fit comparable or larger than that obtained by including lateral variations of radial anisotropy in the modeling moreover the use of crustal corrections from different a priori crustal models may lead to different images of radial anisotropy suggesting divergent geodynamical interpretations this work suggests that the three dimensional determination of global radial anisotropy in the earth s mantle using surface wave dispersion data is still an ongoing experiment

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

imaging of vp vs and poisson s ratio anomalies beneath kyushu southwest japan implications for volcanism and forearc mantle wedge serpentinization abstract we determine detailed 3 d vp and vs structures of the crust and uppermost mantle beneath the kyushu island southwest japan using a large number of arrival times from local earthquakes from the obtained vp and vs models we further calculate poisson s ratio images beneath the study area by using this large data set we successfully image the 3 d seismic velocity and poisson s ratio structures beneath kyushu down to a depth of 150 km with a more reliable spatial resolution than previous studies our results show very clear low vp and low vs anomalies in the crust and uppermost mantle beneath the northern volcanoes such as abu kujyu and unzen low velocity anomalies are seen in the mantle beneath most other volcanoes in contrast there are no significant low velocity anomalies in the crust or in the upper mantle between aso and kirishima the subducting philippine sea slab is imaged generally as a high velocity anomaly down to a depth of 150 km with some patches of normal to low seismic wave velocities the poisson s ratio is almost normal beneath most volcanoes the crustal seismicity is distributed in both the high and low velocity zones but most distinctly in the low poisson s ratio zone a high poisson s ratio region is found in the forearc crustal wedge above the slab in the junction area with shikoku and honshu this high poisson s ratio could be caused by fluid filled cracks induced by dehydration from the philippine sea slab the poisson s ratio is normal to low in the forearc mantle in middle south kyushu this is consistent with the absence of low frequency tremors and may indicate that dehydration from the subducting crust is not vigorous in this region

global models of surface wave attenuation 1 a large data set of fundamental mode rayleigh wave amplitudes is analyzed to derive global models of surface wave attenuation 1 q the data set consists of measurements of rayleigh wave amplitude anomalies in the period range 50 250 s for 347 earthquakes observed at 179 seismic stations the amplitude anomalies are considered to depend on four factors intrinsic attenuation along the ray path elastic focusing effects along the ray path a source factor accounting for uncertainties in the strength of excitation and a receiver factor accounting for uncertainties in the response at the station the amplitude data are inverted simultaneously for global maps of attenuation expanded in spherical harmonics up to degree 12 global maps of phase velocity expanded to degree 20 and source and receiver correction factors all four variable types are shown to be important in explaining the amplitude anomalies a data set of phase delay measurements provides additional constraints on velocity structure the maps of attenuation obtained by simultaneous inversion for elastic and anelastic models contain important features that are not robustly imaged when the effect of focusing on wave amplitude is ignored these include high attenuation along western north america and along the east pacific rise and other ridge systems and low attenuation associated with stable continental interiors the global attenuation maps exhibit a strong correlation with phase velocity maps corrected for the effect of the crust particularly for periods 200 s the correlation suggests that the variability in both q and velocity in the shallow upper mantle is primarily thermal in origin

distinct s wave reflector in the midcrust beneath nikko shirane volcano in the northeastern japan arc distinct s waves reflected from a midcrustal seismic velocity discontinuity are detected beneath nikko shirane volcano in the southernmost part of the northeastern japan arc a detailed travel time analysis of the reflected s waves by using data acquired through a dense seismic network temporarily set up in this region shows that this unusual s wave reflector is distributed over an area of 15 15 km2 at depths ranging from 8 to 15 km the reflector has a conical shape becoming shallow toward the summit of nikko shirane volcano observed amplitude spectral ratios of reflected s waves to direct s waves show that the reflector body has a strong velocity contrast to the surrounding medium and its thickness is of the order of 100 m at most the reflector body is approximated by two thin layers probably filled with partially molten materials cutoff depth for shallow seismicity in this area is 3 5 km above the reflector and becomes shallow toward nikko shirane volcano nearly parallel to the reflector the depth to brittle ductile transition zone seems to be prescribed by the existence of the reflector body which is perhaps a thin magma body

tomographic imaging of seismic velocity structure in and around the onikobe volcanic area northeastern japan implications for fluid distribution abstract we estimated three dimensional p vp and s wave velocity vs and vp vs structures in and around the onikobe volcanic area northeastern japan by local travel time tomography we used travel time data from source and receiver pairs located within and outside the study area which plays an important role in obtaining the optimum ray coverage and in elucidating the deeper structure more accurately detailed information on deeper structures is essential for imaging the complete volcanic system from the magmatic source zone through areas of shallow hydrothermal circulation more than 50 000 travel time data for the p waves and 35 000 for the s waves were used to image the velocity structure our results show the following dominant features 1 two conduits in the upper crust with low vp and low vs indicative of h2o rich fluid pathways one lying beneath naruko volcano the other beneath the focal area of the 1962 northern miyagi earthquake m6 5 2 an underlying broad region in the lower crust with low vp low vs and high vp vs suggestive of a zone of partial melt from which the fluids in 1 are derived and 3 low vp vs areas near the surface of the sanzugawa and onikobe calderas suggesting a diffuse vapor saturated cap

effect of h2o released by dehydration of serpentine and chlorite on compressional wave velocities of peridotites at 1 gpa and up to 1000 c abstract compressional wave velocities v p of serpentine bearing wehrlite 0 2 wt h 2 o serpentinized dunite 4 1 wt h 2 o chlorite bearing websterite 1 3 wt h 2 o and chlorite bearing dunite 0 6 wt h 2 o were measured at 1 gpa and up to 1000 c during heating to and cooling from 1000 c during heating the serpentine bearing rocks showed a sudden decrease in v p at 600 700 c when serpentine dehydration took place similarly the chlorite bearing rocks exhibited a sharp change in v p at 800 900 c due to chlorite dehydration during cooling experiments on both serpentine and chlorite bearing rocks v p showed a linear increase down to room temperature suggesting that no rehydration reaction took place with decreasing temperature the decrease in v p due to dehydration reactions was relatively small 1 5 in rocks with low h 2 o content 0 2 1 3 wt whereas the dehydration reaction of serpentinized dunite with higher 4 1 wt h 2 o led to a marked decrease in v p 5 1 which is comparable to the degree of v p reduction reported from the low velocity anomaly regions in subducting slabs the effect of h 2 o fluid on the v p of peridotite is evaluated by assessing the ratio of v p values v p v p 0 under both wet and dry conditions the v p v p 0 ratio was 0 97 0 99 in rocks with 0 2 1 3 wt h 2 o but was markedly lower in rocks with 4 1 wt h 2 o 0 87 the run products showed variable geometries of fluid filled pores which clearly depended on the h 2 o content of the rock studied the run products with 0 2 1 3 wt h 2 o had relatively small and isolated fluid filled pores whereas run products with 4 1 wt h 2 o contained relatively large fluid filled pores that were interconnected our results suggest that connected fluid filled pores cause a significant decrease in v p but that isolated fluid pores have little effect on v p

mapping the basement of the ebro basin in spain with seismic ambient noise autocorrelations this work is funded by the spanish project misterios cgl2013 48601 c2 1 r we also acknowledge support and discussion through tides cost action es1401

the effect of crustal structure on strong ground motion attenuation relations in eastern north america strong ground motion attenuation relations are usually described by smoothly decreasing functions of distance however consideration of wave propagation in the crust suggests that attenuation relations should be more complex such complexity may be present in strong ground motion data for eastern north american earthquakes which show amplitudes in the distance range of 60 to 150 km that lie above the trends at smaller and greater distances using a wavenumber integration method to compute green s functions and close in recordings of several earthquakes as empirical source functions we have generated synthetic seismograms that are in good agreement with regional and strong motion recordings of eastern north american earthquakes from these synthetic seismograms we have shown that the observed interval of relatively high amplitudes may be attributable to postcritically reflected s waves from the moho the presence and location of the interval of relatively high amplitudes is highly dependent on the crustal velocity structure and may therefore be expected to show regional variation however for any realistic structure model there will be a transition in the attenuation relation from an interval at shorter distances less than about 100 km that is dominated by direct waves to an interval at greater distances that is dominated by postcritically reflected waves the synthetic seismograms have response spectral velocities that match those of the recorded data and their m blg values are in good agreement with observed values

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

a magma hydrothermal system beneath hakone volcano central japan revealed by highly resolved velocity structures high resolution images of subsurface structures are necessary to understand the transport processes of crustal fluids from deep magma sources and their relationship to earthquake swarms in active volcanic regions based on a seismic tomography approach we have developed a new model for the magma hydrothermal system beneath hakone volcano central japan where shallow earthquake swarms and crustal deformation associated with inflation of an open crack source are often observed by applying travel time data for local earthquakes to a tomographic inversion we obtained highly resolved seismic velocity structures that show a region of low p wave velocity vp low s wave velocity vs and high vp vs ratios at depths of 10 20 km beneath the volcano corresponding to the location of the open crack source we suggest that the high vp vs ratios represent a deep magma chamber with a high concentration of melt and or fluids deep low frequency earthquakes located just beneath this high vp vs zone may indicate that magmatic fluids are supplied from below above the high vp vs zone a region of low vp low vs and low vp vs ratios exists at depths of 3 10 km suggesting the presence of crack filled water or co2 supplied from the inferred deep magma chamber many earthquake swarms occur in this low vp vs zone indicating that crustal fluids play an important role in generating the swarms similar relationships between magma reservoirs overlying hydrothermal systems and swarm activity have been reported from other volcanic areas and thus may be a ubiquitous feature beneath active volcanoes

three dimensional simulation of a magnitude 7 75 earthquake on the san andreas fault simulation of 2 minutes of long period ground motion in the los angeles area with the use of a three dimensional finite difference method on a parallel supercomputer provides an estimate of the seismic hazard from a magnitude 7 75 earthquake along the 170 kilometer section of the san andreas fault between tejon pass and san bernardino maximum ground velocities are predicted to occur near the fault 2 5 meters per second and in the los angeles basin 1 4 meters per second where large amplitude surface waves prolong shaking for more than 60 seconds simulated spectral amplitudes for some regions within the los angeles basin are up to 10 times larger than those at sites outside the basin at similar distances from the san andreas fault

regional observations of the second north korean nuclear test on 2009 may 25 summary the suspicious seismic event that occurred in the northern korean peninsula on 2009 may 25 was declared to be the second underground nuclear test nk2nd by north korea we investigated the characteristics of nk2nd using seismic signals recorded at regional distance stations in south korea and china the pn lg ratios of nk2nd definitely discriminate this event from two nearby natural earthquakes at frequencies above 4 hz full moment tensor inversion of full waveform data shows that nk2nd had a very large isotropic component pure isotropic moment tensor inversion also resulted in good recovery of observed waveforms with clear indication that nk2nd was explosive in origin the moment magnitude mw from the full moment tensor inversion was estimated to be 4 5 and network averaged values of 4 6 and 3 6 were calculated for rms mb lg and ms vmax respectively although mb ms signature has been considered one of the most reliable discriminants for separating explosions and earthquakes this signature showed poor discrimination in the case of nk2nd the pn lg ratios and moment tensor inversion give more reliable evidence than does the mb ms for classifying the suspicious event in the northern korean peninsula as a possible explosion the characteristics of nk2nd are also quite similar to those of the first north korean nuclear test on 2006 october 9

role of fluids in the initiation of the 2008 iwate earthquake m7 2 in northeast japan 1 seismic velocity vp vs and poisson s ratio images show that the hypocenter of the 2008 iwate miyagi earthquake m7 2 is located in a distinctive zone with low vp slightly low vs and low within the upper 10 km depths where the mechanical strength might be weaker than the normal seismogenic layer with high velocity and low poisson s ratio immediate below a prominent low vp low vs and high zone is revealed in the lower crust and uppermost mantle under the iwate mainshock hypocenter which may reflect fluids resulting from the dehydration of the subducting pacific slab under northeast japan the aqueous component of fluids intruded into the source region may have reduced the mechanical strength of the rock matrix and so triggered the iwate earthquake our results indicate that crustal fluids beneath the seismogenic layer can play an important role in the initiation of large crustal earthquakes

determination of causative fault parameters for some recent iranian earthquakes using near field sh wave data abstract a method based on a point source representation and non linear least square formulation which estimates the strike dip and rake of the causative fault has been used to infer the causative fault plane parameters using strong ground motion data for the some recent earthquakes in iran this study indicates that the analysis of sh waves of near field accelerographs can distinguish the fault plane from the auxiliary plane this method is especially helpful when lack of information such as surface rupture aftershock data and isoseismal maps makes it difficult to identify causative fault plane in the fault plane solution the estimated fault plane parameters from inversion of the near field data based on the point source model for these earthquakes are in fair agreement with solutions given by hrv and neic

automated detection extraction and measurement of regional surface waves our goal is to develop and test an effective method to detect identify extract and quantify surface wave signals for weak events observed at regional stations we describe an automated surface wave detector and extractor designed to work on weak surface wave signals across eurasia at intermediate periods 8 s 40 s the method is based on phase matched filters defined by the rayleigh wave group travel time predictions from the broadband group velocity maps presented by ritzwoller and levshin 1998 and ritzwoller et al 1998 and proceeds in three steps signal compression signal extraction or cleaning and measurement first the dispersed surface wave signals are compressed in time by applying an anti dispersion or phase matched filter defined from the group velocity maps we refer to this as the compressed signal second the surface wave is then extracted by filtering noise temporally isolated from the time compressed signal this filtered signal is then redispersed by applying the inverse of the phase matched filter finally we adaptively estimate spectral amplitude as well as group and phase velocity on the filtered signal the method is naturally used as a detector by allowing origin time to slide along the time axis we describe preliminary results of the application of this method to a set of nuclear explosions and earthquakes that occurred on or near the chinese lop nor test site from 1992 through 1996 and one explosion on the indian rajasthan test site that occurred in may of 1998

upper mantle velocity structure estimated from ps converted wave beneath the north eastern japan arc summary the upper boundary of the descending oceanic plate is located by using ps waves converted from p to s at the boundary in the tohoku district the north eastern part of honshu japan the observed ps p time data are well explained by a two layered oceanic plate model composed of a thin low velocity upper layer whose thickness is less than 10 km and a thick high velocity lower layer the upper and lower layers respectively have 6 per cent lower and 6 per cent higher velocity than the overriding mantle the estimated location of the upper boundary is just above the upper seismic plane of the double planed deep seismic zone this result indicates that events in the upper seismic plane at least in the depth range from 60 to 150 km occur within the thin low velocity layer on the surface of the oceanic plate

shear wave splitting vp vs and gps during a time of enhanced activity at aso caldera kyushu 1 we performed shear wave splitting analyses and calculated vp vs ratios on local earthquakes recorded at seven stations around aso volcano japan between 2001 and 2008 the mean vp vs of 1 61 0 01 from all stations is among the lowest average values found anywhere in the world a temporal change of shear wave splitting fast polarization is observed at one station additionally spatial variations of shear wave splitting delay times and vp vs ratios show a correlation at three stations we suggest that stress controlled anisotropy dominates at these stations gps baselines and 2d strain reveal extension in the caldera in 2003 and compression before and after 2003 strain shortening axes indicate either a variation in regional stress or a local stress source that overprints the regional field in 2003 baseline changes correlate with periods of increased low frequency seismic activity located deeper than 15 km compaction and degassing of a previously reported sill at approximately 15 km depth could lead to constantly high pressure of volcanic gases over a wide area and explain the generally low vp vs ratios and the observed compression in the caldera we propose that a small volume of magma intruded into the sill in 2003 caused extension at the surface and triggered ash eruptions between 2003 and 2005 associated localized migration of gases in overpressured cracks with aspect ratios potentially 0 5 in the upper crust with porosities 0 1 could be the source of changes in seismic anisotropy and explain the slight variations observed in vp vs

simultaneous high p t measurements of ultrasonic compressional and shear wave velocities in ichino megata mafic xenoliths their bearings on seismic velocity perturbations in lower crust of northeast japan arc 1 simultaneous measurements of ultrasonic compressional vp and shear wave velocities vs were conducted under pressures and temperatures representative of the lower crust on five mafic xenoliths derived from the northeast japan arc crust for comparison with the observed seismic heterogeneity of the lower crust of the northeast japan arc the velocity deviations dvp and dvs of the xenoliths were calculated using the average reference vp 6 61 0 1 km s and vs 3 76 0 1 km s the dvp and dvs values of the xenoliths at 700 c and 0 8 gpa are 0 8 and 1 2 for hornblende gabbro 4 8 and 4 0 for hornblende pyroxene gabbro 0 9 and 1 5 for amphibolite 2 5 and 1 7 for pyroxene amphibolite and 0 9 and 5 6 for hornblendite respectively we compared the velocity perturbations in the lower crust determined by seismic tomography with dvp and dvs of the xenoliths using vp vs vp vs deviation diagrams on the basis of our measurements we suggest that 1 the seismically high vp and vs regions beneath the tobishima basin consist of hornblende pyroxene gabbro 2 hornblende gabbro is a predominant rock type beneath the dewa hills and ou backbone range 3 the low velocity anomalies beneath the active volcano areas may be caused by the existence of partial melts of hornblende gabbro and 4 the low vp and high vs regions beneath the kitakami mountains consist of quartz plagioclase bearing rocks our data demonstrate that the seismic heterogeneity in the lower crust of the northeast japan arc reflects variations in rock composition and temperature that are related to the regional geological history

moho depth variation in the central part of northeastern japan estimated from reflected and converted waves abstract we detected reflected p and s waves at the moho in seismograms of shallow crustal earthquakes in the central part of northeastern ne japan p to s and s to p mode converted waves at the moho are also detected in seismograms of intermediate depth earthquakes in the subducted pacific slab the depth distribution of the moho in the central part of ne japan is estimated by using travel time differences between these later phases and the first p and s arrivals we collected travel time data of 496 reflected waves from 67 shallow earthquakes and 200 converted waves from 65 intermediate depth earthquakes the depth to the moho estimated is deep beneath the land and becomes shallower toward the eastern and western coastlines the moho depth is about 34 km in the middle of the land area about 30 km under the coastline of the japan sea and 27 29 km under the coastline of the pacific ocean

a composite source model for computing realistic synthetic strong ground motions a composite source model is presented for convolution with synthetic green s functions in order to synthesize strong ground motions due to a complex rupture process of a large earthquake subevents with a power law distribution of sizes are located randomly on the fault each subevent radiates a displacement pulse with the shape of a brune s pulse in the far field at a time determined by a constant rupture velocity propagating from the hypocenter thus all the input parameters have a physical basis we simulate strong ground motions for event station pairs that correspond to records obtained in mexico by the guerrero accelerograph network the synthetic accelerations velocities and displacements have realistic amplitudes durations and fourier spectra

evidence for water filled cracks in earthquake source regions 1 we identify lowered vp vs ratios near earthquake source regions in southern california using observations from a seismic tomography model and high resolution local vp vs estimates using waveform cross correlation data from within similar event clusters the median tomographic vp vs ratio is 1 716 0 008 at all the relocated crustal earthquake locations compared to the background median value of 1 729 0 007 for the tomography model although the error estimates overlap slightly the median in situ vp vs ratio of 1 673 0 022 within the similar event clusters suggests that tomographic studies are overestimating vp vs at source regions interpretation of vp vs anomalies is complicated by the scatter in values obtained for individual clusters and in comparisons to absolute vp and vs velocities in the tomography model however the low vp vs ratios measured for the seismicity clusters are hard to explain with known rocks and suggest the presence of water filled cracks with several percent porosity in earthquake source regions in southern california which likely has an effect on faulting and earthquake activity

spatial distribution of scattering loss and intrinsic absorption of short period s waves in the lithosphere of japan on the basis of the multiple lapse time window analysis of hi net data summary propagation of short period s waves through the crust is strongly controlled by scattering loss and intrinsic absorption scattering loss controls the shape of the seismic envelope and the spatial distribution of the energy while intrinsic absorption produces an exponential decay as a function of time which is independent of the coordinates since both parameters have a different effect it is possible to compute them by means of the multiple lapse time window analysis mltwa in this paper high resolution maps of japan for both seismic s wave attenuation parameters are obtained by using the mltwa with data provided by the hi net seismic network the maps show strong regional variation of the parameters the variations depend mainly on the tectonic setting of each region and volcanism mechanisms in the scattering loss maps in the 1 2 hz map there is a very different behaviour between the northeast stronger scattering loss and the southwest much weaker scattering loss in the northeast of japan areas with strong scattering loss correspond mainly to the location of the volcanic arcs in southwest japan chugoku region and the west side of kii peninsula show strong scattering levels for the 4 8 hz and higher frequency bands in hokkaido strong scattering loss and intrinsic absorption can be observed for the lower frequency bands in the sendai plain we find strong scattering loss for all the frequency bands under all these areas low velocity anomalies have been detected in previous works in tohoku area the east side shows lower intrinsic attenuation than the west side this characteristic seems to extend to the southern part of hokkaido and to central japan in kanto area the values of intrinsic absorption are lower than in the surrounding areas but in the region around the itoigawa shizuoka tectonic line and in its western side strong absorption areas are observed the behaviour of each area for intrinsic absorption is similar to the behaviour observed in the q 1c maps the mltwa is based on the hypothesis of multiple isotropic scattering in a medium with the homogeneous distribution of scattering mean free path and intrinsic absorption although these hypotheses are very simple the results are very informative on the characteristics of each region and show the usefulness of studying the properties of scattered seismic waves in the understanding of the properties of the crust

3 d seismic velocity structure of the crust and the uppermost mantle in the northeastern japan arc 3 d seismic velocity structure of the crust and the uppermost mantle beneath the northeastern japan arc is investigated by using arrival time data from local earthquakes we use a velocity model composed of three layers corresponding to the upper crust the lower crust and the uppermost mantle respectively taking into account the observed regional variation of pn velocity the uppermost mantle is further divided into three parts by two pn velocity boundaries near the coasts of the japan sea and the pacific ocean the velocities within the upper crust the lower crust and the three parts of the uppermost mantle are assumed to be constant locations of two pn velocity boundaries and depth distributions of the conrad and the moho discontinuities are expressed by continuous functions of unknown parameters station corrections and hypocenters are also introduced to be unknowns these unknown parameters are determined by inverting arrival time data of p and s wave first arrivals and clear later arrivals of pg and p waves the pn velocity boundary between the land and the pacific ocean is located approximately along the pacific coastline and that between the land and the japan sea is nearly along the japan sea coastline the conrad and the moho discontinuities are at depths ranging from 14 to 20 km and from 27 to 36 km respectively the conrad and the moho depths have similar spatial distributions they are deep beneath the land and become shallower toward the western and the eastern coastlines beneath the land they are shallow in the central part of the tohoku district and become deeper toward both the north and the south directions in the north they become shallow again

evaluation of models for earthquake source spectra in eastern north america there have been several relations proposed in the last few years to describe the amplitudes of ground motion in eastern north america ena these relations differ significantly in their assumptions concerning the amplitude and shape of the spectrum of energy radiated from the earthquake source in this article we compare ground motions predicted for these source models against the sparse ena ground motion database the source models evaluated include the two comer models of boatwright and choy 1992 atkinson 1993a haddon 1996 and joyner 1997a b and the one comer model of brune as independently implemented by frankel et al 1996 and by toro et al 1997 the database includes data from ena mainshocks of m 4 and historical ena earthquakes of m 5 5 for a total of 110 records from 11 events of 4 m 7 3 all recorded on rock we also include 24 available rock records from 4 large earthquakes in other intraplate regions con clusions are checked to determine whether they are sensitive to the addition of these non ena data the atkinson source model as implemented in the ground motion relations of atkinson and boore 1995 is the only model that provides unbiased ground motion predictions over the entire period band of interest from 0 1 to 10 sec the source models of frankel et al 1996 toro et al 1997 and joyner 1997a b all provide unbiased ground motion estimates in the period range from 0 1 to 0 5 sec but over estimate motions at periods of 1 to 10 sec the haddon 1996 source model over predicts motions at all periods by factors of 2 to 10 these conclusions do not change significantly if data from non ena intraplate regions are excluded although the ten dency of all models toward overprediction of long period amplitudes becomes more pronounced the tendency of most proposed ena source models to overestimate long period motions is further confirmed by an evaluation of the relationship between ms a measure of the spectrum at 20 sec period and moment magnitude a worldwide catalog of shallow continental earthquakes triep and sykes 1996 is compared to the ms m relations implied by each of the source models the atldnson source model is consistent with these data while other proposed ena models overpredict the average ms for a given m the implications of mmi data from historical earthquakes are also addressed by exploiting the correlation between felt area and high frequency source spectral level high frequency spectral amplitudes as specified by the atkinson and boore 1995 frankel et al 1996 toro et al 1997 and joyner 1997a b source models equal or exceed the levels inferred from the felt areas of most of the large ena events with the noteable exception of the saguenay earthquake by contrast high frequency spectral amplitudes specified by the haddon 1996 source model agree with the felt area of the saguenay earthquake but overpredict the felt areas of nearly all other large events in general models that fit the saguenay data be it intensity data strong ground motion data regional seismographic data or teleseismic data will not fit the data from the remaining earthquakes a source model derived from the california database suitably modified for re gional differences in crustal properties is also evaluated this model is not signifi

adaptive regularization of earthquake slip distribution inversion abstract regularization is a routine approach used in earthquake slip distribution inversion to avoid numerically abnormal solutions to date most slip inversion studies have imposed uniform regularization on all the fault patches however adaptive regularization where each retrieved parameter is regularized differently has exhibited better performances in other research fields such as image restoration in this paper we implement an investigation into adaptive regularization for earthquake slip distribution inversion it is found that adaptive regularization can achieve a significantly smaller mean square error mse than uniform regularization if it is set properly we propose an adaptive regularization method based on weighted total least squares wtls this approach assumes that errors exist in both the regularization matrix and observation and an iterative algorithm is used to solve the solution a weight coefficient is used to balance the regularization matrix residual and the observation residual an experiment using four slip patterns was carried out to validate the proposed method the results show that the proposed regularization method can derive a smaller mse than uniform regularization and resolution based adaptive regularization and the improvement in mse is more significant for slip patterns with low resolution slip patches in this paper we apply the proposed regularization method to study the slip distribution of the 2011 mw 9 0 tohoku earthquake the retrieved slip distribution is less smooth and more detailed than the one retrieved with the uniform regularization method and is closer to the existing slip model from joint inversion of the geodetic and seismic data

fine structure beneath the tohoku district northeastern japan arc as derived by an inversion of p wave arrival times from local earthquakes abstract three dimensional p wave velocity structure beneath the tohoku district northeastern japan arc is investigated by an inversion of arrival times from local earthquakes using the method originally due to aki and lee 1976 in the crust 0 32 km depth a low velocity region is found along the volcanic front and its vicinity velocities at depths of 32 65 km are low beneath the regions where many quaternary volcanoes and geothermal areas are distributed in the region deeper than 65 km the subduction of the pacific plate is clearly revealed and the mantle structure above the descending plate is rather uniform these features suggest that volcanic activities have relation to the upper mantle structure the results obtained in this study will be helpful in investigating the mechanism of magma generation in a subduction zone

a wave equation migration method for receiver function imaging 2 application to the japan subduction zone 1 the newly developed wave equation poststack depth migration method for receiver function imaging is applied to study the subsurface structures of the japan subduction zone using the fundamental research on earthquakes and earth s interior anomalies freesia broadband data three profiles are chosen in the subsurface imaging two in northeast ne japan to study the subducting pacific plate and one in southwest sw japan to study the philippine sea plate the descending pacific plate in ne japan is well imaged within a depth range of 50 150 km the slab image exhibits a little more steeply dipping angle 32 in the south than in the north 27 although the general characteristics between the two profiles in ne japan are similar the imaged philippine sea plate in eastern sw japan in contrast exhibits a much shallower subduction angle 19 and is only identifiable at the uppermost depths of no more than 60 km synthetic tests indicate that the top 150 km of the migrated images of the pacific plate is well resolved by our seismic data but the resolution of deep part of the slab images becomes poor due to the limited data coverage synthetic tests also suggest that the breakdown of the philippine sea plate at shallow depths reflects the real structural features of the subduction zone rather than caused by insufficient coverage of data comparative studies on both synthetics and real data images show the possibility of retrieval of fine scale structures from high frequency contributions if high frequency noise can be effectively suppressed and a small bin size can be used in future studies the derived slab geometry and image feature also appear to have relatively weak dependence on overlying velocity structure the observed seismicity in the region confirms the geometries inferred from the migrated images for both subducting plates moreover the deep extent of the pacific plate image and the shallow breakdown of the philippine sea plate image are observed to correlate well with the depth extent of the seismicity beneath ne and sw japan such a correlation supports the inference that the specific appearance of slabs and intermediate depth earthquakes are a consequence of temperature dependent dehydration induced metamorphism occurring in the hydrated descending oceanic crust

lens effect in santa monica we used finite difference simulations of 10 hz p sv and sh waves to estimate the contribution from the deep basin structure to the large ground motion amplification in santa monica california observed for seismic waves incident from the north our simulations of a 17 km deep northridge aftershock with epicenter 30 km north of santa monica show that focusing at the lens shaped boundary of the sediments can only account for less than half the amplification observed in the area that was heavily damaged during the 1994 m 6 7 northridge earthquake the focusing in the simulations caused amplification of up to 1 6 times in a zone 0 65 2 4 km south of the santa monica fault and de amplification at sites just south of the fault where some of the largest amplification is observed in the data

adjoint analysis of the source and path sensitivities of basin guided waves summary simulations of earthquake rupture on the southern san andreas fault saf reveal large amplifications in the san gabriel and los angeles basins sgb and lab apparently associated with long range path effects geometrically similar excitation patterns can be recognized repeatedly in different saf simulations e g love wave like energy with predominant period around 4 s channelled southwestwardly from the sgb into lab yet the amplitudes with which these distinctive wavefield patterns are excited change depending upon source details slip distribution direction and velocity of rupture we describe a method for rapid calculation of the sensitivity of such predicted wavefield features to perturbations of the source kinematics using a time reversed adjoint wavefield simulation the calculations are analogous to those done in adjoint tomography and the same time reversed calculation also yields path sensitivity kernels that give further insight into the excitation mechanism for rupture on the southernmost 300 km of saf lab excitation is greatest for slip concentrated between the northern coachella valley and the transverse ranges propagating to the ne and with rupture velocities between 3250 and 3500 m s 1 along that fault segment that is within or slightly above the velocity range between rayleigh and s velocities that is energetically precluded in the limit of a sharp rupture front highlighting the potential value of imposing physical constraints such as from spontaneous rupture models on source parametrizations lab excitation is weak for rupture to the sw and for ruptures in either direction located north of the transverse transverse ranges whereas ventura basin vtb is preferentially excited by ne ruptures situated north of the transverse ranges path kernels show that lab excitation is mediated by surface waves deflected by the velocity contrast along the southern margin of the transverse ranges having most of their energy in basement rock until they impinge on the eastern edge of sgb through which they are then funnelled into lab vtb amplification is enhanced by a similar waveguide effect

seismological evidence for compositional variations at the base of the mantle transition zone under japan islands abstract temperature and water content anomalies just above the 660 km discontinuity under the japan islands are estimated from seismological observations two sets of seismological observations of p wave velocity perturbations and depth variations of the 660 km discontinuity are used which are 1 long wavelength 500 km variations from seismic tomography based on a grid parameterization and waveform analysis of scs reverberations and 2 moderate wavelength 150 km variations from seismic tomography with a block parameterization and receiver function analysis to estimate temperature and water content anomalies partial derivatives of velocity and depth variations with respect to temperature and water content determined by mineral physics studies are used under southwest japan low temperature and high water content anomalies are obtained from both sets of seismological observations which have already been found by a previous study under northeast japan however there are discrepancies between the results estimated from the two data sets possibly due to the different resolution scales this discrepancy is dismissed when examining distributions of the temperature and water content anomalies these anomalies can be grouped into two geographical locations one group under southwest japan the other under northeast japan the two groups are clearly separated and exhibit common features in both sets of the seismological observations the grouping is interpreted by a compositional difference between the subducting pacific slab under southwest japan and a normal mantle under northeast japan

metastable olivine wedge in the subducting pacific slab and its relation to deep earthquakes abstract a metastable olivine wedge mow is detected in the subducting pacific slab under the japan sea by applying a forward modeling approach with 3 d ray tracing to high quality arrival time data from 78 well located deep earthquakes the data were recorded by the dense and high quality seismic networks on the japan islands the double difference earthquake location technique is improved and used to relocate the 78 deep earthquakes precisely our results show that the mow does exist in the pacific slab and it has a p wave velocity 3 lower than the normal mantle or 4 lower than the surrounding slab velocity the top and bottom depths of the mow are 400 and 570 km respectively and the mow is located in the central portion of the slab after precise relocation all the 78 deep earthquakes are found to occur within the mow or along its edges within the slab the cut off depth of deep seismicity under the japan sea is consistent with the estimated mow bottom depth our results favor the transformational faulting as the mechanism of deep earthquakes in the pacific slab under the japan sea

geometric effects of global lateral heterogeneity on long period surface wave propagation long period rayleigh waves from iranian earthquakes have large amplitude asymmetries between minor arc and major arc arrivals e g r 2 and r 3 at digital stations in the azimuth range n20 w to n60 e these asymmetries are as large as a factor of 2 at a period of 256 s and persist to periods greater than 300 s in some cases the entire rayleigh wave group arrival spanning periods from 100 to 300 s is either uniformly enhanced in amplitude or diminished to such a degree that the group arrival appears to be missing the amplitude anomalies are generally not accompanied by significant phase anomalies the irregular azimuthal distribution of the amplitude asymmetries and their occurrence for events with different focal mechanisms and epicentral separations of several hundred kilometers preclude an explanation of these observations by source complexity events in the mediterranean and nepal do not produce similar amplitude asymmetries at the same stations the anomalies are thus most likely due to focusing and defocusing propagation effects as a preliminary investigation of the effects of lateral heterogeneity of upper mantle velocity structure on long period surface wave amplitudes surface wave ray tracing calculations are performed using recently proposed global phase velocity distributions dramatic deviations from great circle paths are predicted for long propagation paths e g r 3 the particular spatial distribution of lateral velocity gradients around a given source location determines whether substantial amplitude asymmetries will be observed between minor arc and major arc arrivals and whether these will persist for sequential great circle orbits the 200 s period amplitude asymmetry observed at kip for the iranian source region r 2 4 r 3 is well predicted by the ray tracing results the absence of this anomaly for the other source regions is also predicted other observed anomalies are not all well predicted but it is clear that geometric effects can contribute significantly to the observed variations of rayleigh and love wave amplitudes this is the probable explanation for the instability of q estimates made from surface waves other source regions producing large surface wave amplitude anomalies include japan and southeastern alaska

extension of the basin rayleigh wave amplification theory to include basin edge effects the presence of sediments near the earth s surface can significantly amplify the strength of shaking during earthquakes such basin or site amplification effects have been well documented in numerous regions yet the complex and often situational dependence of competing reasons for this amplification makes it hard to quantify in a general sense or to determine the most significant contributions simple 1d seismic profiles can be used to estimate the amplitude differences between a basin site and a hard rock reference site but this ignores any reflections or conversions at the basin edge or a resonance effect depending on the basin s geometry in this article we explore an analytic model based on coupling coefficients for surface rayleigh waves to account for the lateral discontinuities at a basin s edge datta 2018 we use this simple tool to explore the relationship between the basin s rayleigh wave amplification spectrum and various parameters such as basin depth edge slope angle and impedance contrast the step by step construction of the model allows us to quantify the contributions from various wave propagation effects with the goal of identifying situations under which various basin edge effects must be considered in addition to purely 1d estimates for the most velocity contrasts less than a factor of 5 the error made by the 1d theory in predicting maximum rayleigh wave basin amplification is under 35 for both the horizontal and the vertical components for simple basins the vertical amplification dominates at larger high frequencies and the horizontal at lower frequencies finally we demonstrate from comparisons with spectral element wavefield simulations that realistic velocity structures can be reduced to a simpler box shape for the semi analytic formulation used here with reasonable results for the purposes of estimating site amplification or microzonation an improved model that accounts for basin edge effects can be implemented without high computational cost

melting features along the western ryukyu slab edge northeast taiwan tomographic evidence 1 behind the sedimentary ryukyu arc lies the okinawa trough whose termination is located at the tip of the ilan plain northern taiwan just above the ryukyu slab edge the present day active volcanic front is located 80 100 km above the ryukyu slab and extends from japan to kueishantao island an islet situated 10 km offshore the ilan plain between december 1990 and may 1999 3370 earthquakes recorded in northern taiwan by 65 seismic land stations were used to determine the three dimensional vp and vs velocity structures and vp vs ratios a low vs but high vp vs sausage like body 30 km in diameter lies within the eurasian mantle wedge on top of the western ryukyu slab extremity at depths ranging between 20 and 100 km we suggest that the h2o rich component formed by dehydration processes from subducting sediments oceanic crust and serpentinized mantle above the ryukyu slab and along the vertical portion of the slab edge might explain the presence of the sausage like body a low vs but high vp vs channel rises obliquely from the sausage like body at a depth of 40 km in direction of the andesitic kueishantao island we propose that the h2o rich component and or melt rise up from the sausage like body and interfere with the okinawa trough back arc basin magmas formed in the upper mantle lower crust then magmas propagate upward within the upper brittle crust through veins and or narrow conduits

subducting plate boundary beneath the northeastern japan arc estimated from sp converted waves abstract in the tohoku district the northeastern part of honshu japan a conspicuous phase is frequently observed between p and s phases in seismograms for events in the lower seismic plane of the double planed deep seismic zone this phase is dominant in the vertical component and has an apparent velocity almost equal to or slightly smaller than the p phase we have never found this phase in seismograms for events in the upper seismic plane from these characteristics the phase is interpreted as sp converted from s to p at the upper boundary of the descending oceanic plate ubp using the travel times of the sp waves we estimated the location of the ubp beneath the tohoku district to be just above the upper seismic plane of the double planed deep seismic zone this position is consistent with those determined from the analyses of the travel times of the scsp and ps waves which are respectively the seismic wave converted from scs to p and that from p to s at the ubp

inhomogeneous crustal structure beneath northern miyagi prefecture northeastern japan imaged by coda envelope inversion implication for fluid distribution 1 three dimensional 3 d distribution of scattering coefficients in the crust beneath northern miyagi prefecture of northeastern japan is estimated using an envelope inversion method in order to investigate the short wavelength inhomogeneous structure that cannot be imaged by conventional travel time tomography the inversion revealed two large scattering coefficient zones lszs which are distributed beneath active volcanoes and around the mainshock fault of the 1962 m 6 5 northern miyagi earthquake these lszs merge in the lower crust and the characteristic distribution correlates well with the previously reported seismic low velocity zones which are perhaps caused by fluids we inferred that fluids are supplied from the lower crust to the upper crust along the lszs resulting in inhomogeneous structures such as localized distribution of fluid filled cracks it is expected that this distribution of fluids will cause strain and stress accumulation affecting seismic activity in this region index terms 7205 seismology continental crust 1242 7218 seismology lithosphere and upper mantle 7230 seismology seismicity and seismotectonics 8180 tectonophysics tomography citation asano y k obara j nakajima and a hasegawa 2004 inhomogeneous crustal structure beneath northern miyagi prefecture northeastern japan imaged by coda envelope inversion implication for fluid distribution geophys res lett 31 l24615 doi 10 1029 2004gl021261

anelastic earth structure from the coherency of the ambient seismic field 1 cross correlation of the ambient seismic field is now routinely used to measure seismic wave travel times however relatively little attention has been paid to other information that could be extracted from these signals in this paper we demonstrate the relationship between the spatial coherency of the ambient field and the elastodynamic green s function in both time and frequency domains through measurement of the frequency domain coherency as a function of distance we sequentially recover phase velocities and attenuation coefficients from these measurements we generate 1 d shear wave velocity and attenuation models for southern california the ambient field measurements of attenuation and the exceptional path coverage that results from the many possible interstation measurements allow us to extend q estimates over a range of frequencies that has previously been difficult to analyze using earthquake data measurements from paths that cross major sedimentary basins show both lower wave speeds and lower quality factors than other paths as expected our results indicate that there is a wealth of information available in the spatial coherency of the ambient seismic field

three dimensional velocity structures of mount fuji and the south fossa magna central japan 1 we present the three dimensional structures of the p wave velocity vp s wave velocity vs as well as the p wave to s wave velocity ratio vp vs beneath mount fuji and the south fossa magna japan using arrival time data collected from 2002 to 2005 by a dense seismograph array the high resolution data set and improved methodology reveal not only several velocity features that are consistent with previous studies but also important new details that clarify the velocity structures associated with volcanic processes beneath mount fuji and the collision tectonics of the south fossa magna one such particular feature is a low vp low vs and low vp vs anomaly at depths of 7 17 km beneath mount fuji that corresponds with the locations of deep low frequency dlf earthquakes the coincidence of the velocity anomaly and the dlf locations suggests that supercritical volatile fluid such as h2o and co2 may be abundant in the low vp vs region and may play an important role in generating dlf earthquakes this anomaly overlies a deeper low vp low vs and high vp vs anomaly at depths of 15 25 km that may represent a zone of basaltic partial melt a low vp low vs and low vp vs anomaly is seen at depths of 6 14 km beneath mount hakone isovelocity surfaces vp 6 0 km s and vs 3 5 km s corresponding to the upper limit of hypocenter distribution below mount fuji may define the upper surface of the philippine sea plate whose existence in a seismic gap beneath mount fuji has been controversial

quantitative analysis of the inclined low velocity zone in the mantle wedge of northeastern japan a systematic change of melt filled pore shapes with depth and its implications for melt migration abstract travel time tomography beneath the northeastern japan arc reveals that an inclined low velocity zone exists in the mantle wedge sub parallel to the down dip direction of the slab this zone distributed continuously along the arc as a single inclined sheet has been considered as the main source of arc magma a quantitative interpretation of both p and s wave velocity structures precisely determined from the recent travel time tomography is done in terms of thermal heterogeneity and fluid content the combined analysis of both p and s wave velocity structures makes it possible to independently derive the information on the shape and volume fraction of the fluid filled pores the reference p and s wave velocities representing the host rock velocities at reference temperature t 0 are estimated from the tomographic data while an alternative method based on high temperature and high pressure elasticity of upper mantle minerals is used to confirm the validity of the present method the calculated velocity anomalies are corrected for the thermal effect using the three dimensional thermal structure estimated from the p wave attenuation data showing that the observed low velocity anomalies cannot be explained by the thermal effect alone the remaining velocity anomalies are explained by the existence of melt filled pores and effective aspect ratio and volume fraction of the pores are determined the results show a systematic change in melt filled pore shapes with depth suggesting the existence of 3 6 vol melts as grain boundary tubules at a depth of 90 km 0 04 0 05 vol melts as thin cracks or dikes with aspect ratio of 0 001 at a depth of 65 km and 1 2 vol melts as cracks or dikes with aspect ratio of 0 02 0 04 at a depth of 40 km

temporal changes of medium properties during explosive volcanic eruption volcanic evolutions typically accompany significant changes in medium properties monitoring the seismic properties may be useful in identifying the state of volcanic evolution temporal variation of shallow crustal vp vs ratios before and during the 2009 eruption of redoubt volcano alaska is investigated using the p and s traveltimes of local earthquakes high vp vs ratios of 1 9 are observed over a wide region in the precursory phase suggesting the presence of partial melts in the medium at least several months before explosive eruptions the high v p v s ratios decrease until the early effusive phase with rates of 0 179 year 1 in the precursory phase 65 days and 2 147 year 1 in the explosive phase 40 days which is equivalent to a decrease in the bulk modulus of fluids by 1 1 and 7 9 gpa respectively the decreasing v p v s ratios in the precursory phase may be due to increasing amounts of overpressurized gas and water vapor in the medium the rapid decrease in vp vs ratios during the explosive phase may be caused by melt eruption and gas emission the vp vs ratios were observed to be nearly stationary since the early effusive phase suggesting rare presence of melts and low levels of pore pressures with degassing these observations suggest that monitoring vp vs ratios may be useful to identify the eruption state

midperiod rayleigh wave attenuation model for asia 1 we present an attenuation model for midperiod rayleigh waves in central asia and surrounding regions this model is defined by maps of attenuation coefficient across the region of study in the period band 14 24 s the model is constructed to characterize the regional variations in attenuation of seismic waves in the crust which are related to the tectonic history of the studied territory to calibrate the regional surface wave magnitude scale and to extend the teleseismic surface wave magnitude body wave magnitude ms mb discriminant to regional distances the construction of the model proceeds in three stages the first stage in model construction is the measurement of rayleigh wave spectral amplitudes we collected and processed waveform data for 200 earthquakes occurring from 2003 to 2006 inside and around eurasia and used records of about 135 broadband permanent and temporary stations this data set provided a sufficient number of spectral amplitude measurements between 14 and 24 s periods for the construction of two dimensional tomographic maps of attenuation coefficients at the second stage of the work the integral of attenuation coefficients along given paths is estimated using both inter station measurements and single station measurements corrected for source and receiver terms the third stage includes the refining of source parameters recalculation of attenuation coefficient integrals after this refinement grooming of resulting coefficients and multistage tomographic inversion of the data tomographic maps for the set of periods from 14 to 24 s which exhibit clear correlation with geology and tectonics of the territory under study were obtained validation of these maps using the inter station measurements confirms their accuracy in predicting the observations

study of the propagation and amplification of seismic waves in caracas valley with reference to the 29 july 1967 earthquake sh waves the antiplane response of a 2 d model of the valley of caracas venezuela a ns cross section through the palos grandes district to seismic excitations such as those due to antiplane line point sources and incident plane sh waves is investigated it is found that the steeply sloped northern edge of the valley is a more efficient generator and reflector of surface waves than the midly sloped southern edge also the spectral amplification and time response characteristics of this asymmetric wedge shaped valley are a function of the direction of incidence of the excitation waves e g incidence from the north versus incidence from the south versus vertical incidence the same 2 d model of the valley is used to simulate also the antiplane response of the valley to synthetic strong motions equivalent in amplitude frequency content and duration to those that most likely were generated by the 29 july 1967 caracas earthquake this event has been found to consist of four subevents of which the second subevent located at a distance of 25 km from the valley caused the damage in caracas the source spectrum of each of the subevents used in the generation of the synthetic time histories was assumed to be a simple square model the locations relative times of occurrence seismic moments and mechanisms of the subevents were available from an inversion study of teleseismic data it is found that peak acceleration was fairly uniform across the valley varying from 0 15 to 0 21 g on the contrary peak velocities and peak rotational torsional strains varied considerably factor of 2 to 3 across the valley with the maximum values being 25 cm sec for velocity and 1 5 10 4 for rotational strain for sites in palos grandes spectral accelerations sa reached values as high as 0 4 g for periods in the range 0 4 t 1 4 sec and damping ratio 5 our estimates of the intensity of motion on rock and on the sediments are higher by a factor of 3 compared with estimates proposed by previous investigators who assumed that all the seismic energy was released from a point located at a distance of 55 km from caracas various pieces of evidence e g seismoscope response recorded on rock are presented that suggest that the intensity of motion was at least as high as estimated in this paper

the global attenuation structure of the upper mantle 1 a large data set of fundamental mode rayleigh wave amplitudes is analyzed to derive a new global three dimensional model of shear wave attenuation in the upper mantle the amplitude observations span a range of periods between 50 and 250 s and are derived from earthquakes with mw 6 0 that occurred between 1993 and 2005 four separate factors may influence an amplitude anomaly intrinsic attenuation along the raypath elastic focusing effects along the raypath uncertainties in the strength of excitation and uncertainties in the response at the station in an earlier paper dalton and ekstrom 2006a dependence of the retrieved attenuation structure on these terms was shown to be significant and an approach was developed to invert the amplitudes simultaneously for each term the new three dimensional attenuation model qrfsi12 which is the subject of this paper is derived using this method the model contains large lateral variations in upper mantle attenuation 60 to 100 and exhibits strong agreement with surface tectonic features at depths shallower than 200 km at greater depth qrfsi12 is dominated by high attenuation in the southeastern pacific and eastern africa and low attenuation along many subduction zones in the western pacific resolution tests confirm that the change in pattern of attenuation above and below 200 km depth can be determined with confidence using the fundamental mode data set the new model is highly correlated with global models of shear wave velocity particularly in the uppermost mantle suggesting that the same factors may control both seismic attenuation and velocity in this depth range however forcing the lateral perturbations in attenuation to match those found in global velocity models decreases the data variance reduction which suggests that subtle differences between patterns of attenuation and velocity are robust

deep structure of the northeastern japan arc and its implications for crustal deformation and shallow seismic activity abstract seismic tomography studies in the northeastern japan arc have revealed the existence of an inclined sheet like seismic low velocity and high attenuation zone in the mantle wedge at depths shallower than about 150 km this sheet like low velocity high attenuation zone is oriented sub parallel to the subducted slab and is considered to correspond to the upwelling flow portion of the subduction induced convection the low velocity high attenuation zone reaches the moho immediately beneath the volcanic front or the ou backbone range running through the middle of the arc nearly parallel to the trench axis which suggests that the volcanic front is formed by this hot upwelling flow aqueous fluids supplied by the subducted slab are probably transported upward through this upwelling flow to reach shallow levels beneath the backbone range where they are expelled from solidified magma and migrate further upward the existence of aqueous fluids may weaken the surrounding crustal rocks resulting in local contractive deformation and uplift along the backbone range under the compressional stress field of the volcanic arc a strain rate distribution map generated from gps data reveals a notable concentration of east west contraction along the backbone range consistent with this interpretation shallow inland earthquakes are also concentrated in the upper crust of this locally large contraction deformation zone based on these observations a simple model is proposed to explain the deformation pattern of the crust and the characteristic shallow seismic activity beneath the northeastern japan arc

deep structure of the northeastern japan arc and its relationship to seismic and volcanic activity evidence for possible deep seated magmatic activity beneath northeastern japan can be obtained from seismic observations tomographic inversions of p wave velocity data show low velocity zones distributed in the crust and upper mantle beneath active volcanoes in or around these zones anomalously low frequency micro earthquakes perhaps caused by magmatic activity are found at depths of 25 40 km distinct s wave reflectors corresponding to the upper surfaces of magma bodies are found at depths of 10 18 km large crustal earthquakes also occur around the low velocity zones these observations reveal the distribution of magma reservoirs at depths and elucidate its relation with shallow seismicity beneath volcanic arcs

the role of fluids in lower crustal earthquakes near continental rifts earthquakes in the lower continental crust of the earth are rare as the lower crust is thought to be too hot to allow brittle failure so it is surprising that they occasionally occur where continental crust is rifting apart a study of three dimensional crustal structure and seismicity in the taupo volcanic zone an active continental rift in new zealand has now provided insight into how these earthquakes arise the crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones seismic velocities within the band are consistent with the presence of fluids and the linking of upper and lower crust seismicity to crustal structure point to a common explanation for all of the seismicity probably the weakening of faults on the periphery of an otherwise dry crust by hot fluids a report on three dimensional tomographic imaging of seismic velocities and attenuation in the taupo volcanic zone an active continental rift where earthquakes are known to occur in the lower crust finds that crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones the occurrence of earthquakes in the lower crust near continental rifts has long been puzzling as the lower crust is generally thought to be too hot for brittle failure to occur1 2 such anomalous events have usually been explained in terms of the lower crust being cooler than normal3 4 but if the lower crust is indeed cold enough to produce earthquakes then the uppermost mantle beneath it should also be cold enough2 and yet uppermost mantle earthquakes are not observed5 numerous lower crustal earthquakes occur near the southwestern termination of the taupo volcanic zone tvz an active continental rift in new zealand6 here we present three dimensional tomographic imaging of seismic velocities and seismic attenuation in this region using data from a dense seismograph deployment7 we find that crustal earthquakes accurately relocated with our three dimensional seismic velocity model form a continuous band along the rift deepening from mostly less than 10 km in the central tvz to depths of 30 40 km in the lower crust 30 km southwest of the termination of the volcanic zone these earthquakes often occur in swarms suggesting fluid movement in critically loaded fault zones8 seismic velocities within the band are also consistent with the presence of fluids and the deepening seismicity parallels the boundary between high seismic attenuation interpreted as partial melt within the central tvz and low seismic attenuation in the crust to the southwest this linking of upper and lower crustal seismicity and crustal structure allows us to propose a common explanation for all the seismicity involving the weakening of faults on the periphery of an otherwise dry mafic crust by hot fluids including those exsolved from underlying melt such fluids may generally be an important driver of lower crustal seismicity near continental rifts

estimation of causative fault parameters of the rudbar earthquake of june 20 1990 from near field sh wave data abstract we analyze the strong motion accelerograms recorded for the large m s 7 7 m w 7 3 m b 6 4 rudbar earthquake of june 20 1990 the earthquake had a complex source process we have identified the imprints of rupture of three localized asperities on the major causative fault on the accelerograms these asperities are interpreted to correspond to i the main shock that initiated the rupture process and was located in the domino block between the kabateh and zard goli faults ii a foreshock that occurred about 10 s earlier in the kabateh fault and iii a later shock on the western end of the baklor fault which terminated the bilateral rupture process at the western end we estimate the strike dip and slip of these causative sub event rupture planes using the sh spectral amplitudes based on a point source representation of sub events and a non linear least square formulation for inversion of the amplitude data the results of our inversion of the near field data are comparable to other studies based on teleseismic data

three dimensional crustal s wave velocity structure in japan using microseismic data recorded by hi net tiltmeters 1 we developed a three step method for three dimensional 3 d s wave velocity tomography by fitting synthetic cross spectra to the observed ones of ambient seismic noise we applied this method to the recording of hi net tiltmeters in japan at 679 stations from june 2004 to december 2004 first we calculated normalized cross spectra between radial components and those between transverse components for every pair of stations the first step is local 1 d s wave velocity inversion for each station assuming small lateral heterogeneity under a 100 km circle of a station we measured the dispersion curves of fundamental rayleigh waves fundamental love waves and first overtone of love waves by fitting the synthetic cross spectra to the observed ones between pairs of stations within the circle we inverted the measured dispersion curves for obtaining a 1 d s wave velocity model the second step is the inversion of the observed cross spectra for obtaining path averaged 1 d s wave velocity structure the third step is the inversion of the resultant path averaged structures for obtaining 3 d s wave velocity structure 0 1 0 1 1 km grid from the surface to a depth of 50 km using ray approximation the resultant s wave velocity structures show clear low velocity anomalies along tectonic lines from the surface to a depth of 20 km in particular along the hidaka mountain range we observed s wave perturbation more extreme than 20 they also show low velocity anomalies under volcanoes in kyusyu and tohoku in the southwestern part of shikoku our results show a clear low velocity anomaly corresponding to an accretional belt shimanto belt below 20 km we observe a low velocity anomaly in the center of japan which suggests a thick crust citation nishida k h kawakatsu and k obara 2008 three dimensional crustal s wave velocity structure in japan using microseismic data recorded by hi net tiltmeters j geophys res 113 b10302 doi 10 1029 2007jb005395

mapping p wave anisotropy of the honshu arc from japan trench to the back arc abstract we determined a 3 d p wave anisotropic tomography beneath the entire honshu arc using about 448 000 high quality p wave arrival times from 18 335 local earthquakes that occurred beneath the northeast ne japan land area and the fore arc area under the pacific ocean our results show that low velocity low v zones exist beneath the active arc volcanoes in the crust and in the central portion of the mantle wedge above the subducting pacific slab the low v anomalies are related to the arc magmatism low v zones are also revealed in the fore arc area which are probably caused by large volumes of water releasing upwards from dehydration of the subducting oceanic crust and sediments the anisotropic amplitude in the upper crust is weaker than that in other portions under ne japan in the mantle wedge the fast velocity direction fvd is generally trench normal in back arc area which may reflect that the olivine a axis aligns with the transport direction induced by the slab driven corner flow the fvd becomes trench parallel in the central portion of the fore arc mantle wedge which is possibly induced by the olivine of b type fabric in the slab driven corner flow the fvd shows trench parallel in the low v zones in the fore arc mantle wedge close to the upper boundary of the pacific slab which may reflect the b type olivine fabric dominating in those areas or it may be induced by the dextral shearing of the overlying crust the trench parallel fvd is also revealed beneath the volcanic front indicating complex 3 d mantle flows in the mantle wedge the fvd in the subducting pacific slab is mostly trench parallel which may reflect one or more of the following possibilities 1 the original fossil anisotropy of the pacific plate formed at the mid ocean ridge 2 cracks within the slab and 3 the olivine fabric transition due to the changes in water content stress and temperature

coseismic and postseismic deformation of the 2011 tohoku oki earthquake constrained by grace gravimetry 1 spaceborne gravimetry data from the gravity recovery and climate experiment grace are processed using spatio spectral slepian localization analysis enabling the high resolution detection of permanent gravity change associated with both coseismic and postseismic deformation resulting from the great 11 march 2011 mw 9 0 tohoku oki earthquake the grace observations are then used in a geophysical inversion to estimate a new slip model containing both coseismic slip and after slip the grace estimated moment for the total slip up to the end of july 2011 is estimated as 4 59 0 49 1022 n m equivalent to a composite mw of 9 07 0 65 if the moment for the tohoku oki main shock is assumed to be 3 8 1022 n m the contribution from the after slip is estimated to be 3 0 1021 12 8 1021 n m in good agreement with a postseismic slip model inverted from gps data we conclude that grace data provide an independent constraint to quantify co and post seismic deformation for the tohoku oki event

deep slab subduction and dehydration and their geodynamic consequences evidence from seismology and mineral physics abstract we present new pieces of evidence from seismology and mineral physics for the existence of low velocity zones in the deep part of the upper mantle wedge and the mantle transition zone that are caused by fluids from the deep subduction and deep dehydration of the pacific and philippine sea slabs under western pacific and east asia the pacific slab is subducting beneath the japan islands and japan sea with intermediate depth and deep earthquakes down to 600 km depth under the east asia margin and the slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant pacific slab is roughly coincident with the ne sw daxing anling taihangshan gravity lineament located west of beijing approximately 2000 km away from the japan trench the upper mantle above the stagnant slab under east asia forms a big mantle wedge bmw corner flow in the bmw and deep slab dehydration may have caused asthenospheric upwelling lithospheric thinning continental rift systems and intraplate volcanism in northeast asia the philippine sea slab has subducted down to the mantle transition zone depth under western japan and ryukyu back arc though the seismicity within the slab occurs only down to 200 300 km depths combining with the corner flow in the mantle wedge deep dehydration of the subducting pacific slab has affected the morphology of the subducting philippine sea slab and its seismicity under southwest japan slow anomalies are also found in the mantle under the subducting pacific slab which may represent small mantle plumes or hot upwelling associated with the deep slab subduction slab dehydration may also take place after a continental plate subducts into the mantle

pb sr isotopic evidence for contribution of deep crustal fluid to the hishikari epithermal gold deposit southwestern japan abstract the gold bearing quartz adularia veins of the world class hishikari mine in southwestern japan occur in a geological regime where the rocks of the upper to middle crust are simple and their chemical and sr nd pb isotopic compositions are well studied detailed comparison of pb and sr isotopic data of the hishikari veins with those of all possible source materials demonstrates that metals in the veins were essentially derived from a mixture of magmatic fluid with a deep crustal fluid that originated near the boundary between the shimanto middle crust and the underlying subcontinental crustal materials we propose that the release of the deep crustal fluid was triggered by intrusion of the shishimano rhyodacite magma related to timing of the mineralization this fluid mixture carried metals to the brittle upper crust along fissures created by extensional stress forming the ore deposits although the deep crustal fluid has not been paid much attention it may be distributed over a large scale in the deep crust from the continent to the arc system and play an important role in the genesis of magmatic hydrothermal ore deposits and in the generation of flow induced deep tremor