further development of a high frequency seismic source for use in boreholes a borehole sparker seismic source enclosed in a semi flexible tube has been developed to produce a short compressional seismic pulse with a frequency content in the range 250 hz to 3 5 khz with a peak power at 570 hz the pulse shape and frequency content are shown to be a function of the input power the diameter of the spark chamber the salinity of the electrolyte the material of the spark chamber and the electrode configuration when in a borehole the source produces a vertically polarized shear wave but being similar to a small explosive charge does not allow phase reversal as a means of identifying the shear wave in the received pulse train the source is shown to be ideal for tomographic imaging surveys because of its repetitive nature high frequency content and reliability very high resolution seismic reflection surveys are also shown to be possible under favourable circumstances

laboratory investigations into wave period effects on sand bed erodibility under the combined action of waves and currents laboratory experimental data on sediment threshold conditions for fine to coarse sands under the combined action of waves and currents are presented higher flows are needed to satisfy threshold under short period waves than for longer period waves the combined threshold velocities indicate that under the shorter 5 s period waves the oscillatory and steady flows are independent of each other but interact to a greater extent as the wave period increases the derived threshold flow conditions are converted into threshold shear stress values using existing linear and non linear models the performance of the models for various periods of oscillation is then examined in view of the assumption that a unique threshold value exists for a particular grain size all models suggest that the critical stress of a particular grain is higher under shorter period waves for the range of grain sizes presented using different models for waves of different periods appears to remove the effect of wave period upon the data it is suggested that theories used by the existing models are insufficient to fully describe the interaction of the steady and oscillatory flows during the experiments

do critical stresses for incipient motion and erosion really exist the concept of critical stress for the initial motion of noncohesive sediment beds under turbulent flow conditions is reviewed observational definitions of incipient motion are many and not entirely compatible some laboratory flume observations of sediment movement suggest that no true threshold exists current understanding of turbulent fluid motion at a sediment bed suggests that some particle movement must occur at all nonzero time mean velocities a combined model for flume flow and sediment transport having no threshold is seen to explain features of data that have been previously used to support the threshold concept

source rupture process of the 2004 chuetsu mid niigata prefecture japan earthquake inferred from waveform inversion with dense strong motion data abstract the kinematic source rupture process of the 2004 chuetsu mid niigata prefecture japan earthquake is estimated from strong motion data by the linear waveform inversion method in order to develop appropriate green s functions one dimensional velocity structure models for each station are constructed by modeling the aftershock waveforms the estimated top of the bedrock is deeper at the western side of the fault and relatively shallow at the eastern side this tendency coincides with other investigations of seismic tomography and microtremor array observations the obtained source model shows large slips in the vicinity of the hypocenter the reverse slipping rupture originated from the deeper part of the fault and propagated toward the up dip and southwest directions the near surface slip is small two tests are demonstrated to check the stability of the obtained source model the first test examines the effects of the number of available stations on the solution and the second test examines how the difference in the target waveform type affects the solution the number of stations affects the variation of slip amount and more than 12 stations appear to be sufficient to obtain a stable solution in this case the difference in the target wave type in the data set does not significantly affect the solution if the number of stations is sufficient and the green s functions are well calibrated the model obtained using calibrated velocity structure models shows clear image of high slip area compared to the model obtained using a single velocity structure model

the variability of critical shear stress friction angle and grain protrusion in water worked sediments the erodibility of a grain on a rough bed is controlled by among other factors its relative projection above the mean bed its exposure relative to upstream grains and its friction angle here we report direct measurements of friction angles grain projection and exposure and small scale topographic structure on a variety of water worked mixed grain sediment surfaces using a simple analytical model of the force balance on individual grains we calculate the distribution of critical shear stress for idealized spherical grains on the measured bed topography the friction angle projection and exposure of single grain sizes vary widely from point to point within a given bed surface the variability within a single surface often exceeds the difference between the mean values of disparate surfaces as a result the critical shear stress for a given grain size on a sediment surface is characterized by a probability distribution rather than a single value on a given bed the crtitical shear stress distributions of different grain sizes have similar lower bounds but above their lower tails they diverge rapidly with smaller grains having substantially higher median critical shear stresses large numbers of fines trapp ed within pockets on the bed or shielded by upstream grains are effectively lost to the flow our calculations suggest that critical shear stress as conventionally measured is defined by the most erodible grains entrained during transient shear stress excursions associated with the turbulent flow this implies a physical basis for the indeterminacy of initial motion these observations suggest that transport rate shear stress relationships may be controlled in part by the increasing numbers of grains that become available for entrainment as mean shear stress increases they also suggest that bed textures and grain size distributions may be controlled within the constraints of an imposed shear stress and sediment supply regime by the influence of each size fraction on the erodibility of other grain sizes present on the bed

laboratory investigations into wave period effects on sand bed erodibility under the combined action of waves and currents by g voulgaris et al comments

bed load transport of sediment mixtures experiments were conducted on alluvial beds of four sediment mixtures having different arithmetic mean diameters and standard deviations the bed load transport rates of individual fractions were measured einstein s method proffitt and sutherland s method and misri s method of calculation of the bed load transport of individual fractions for sediment mixtures were checked with carefully collected laboratory data by analyzing the data on lines similar to those of misri et al their method of calculation of the bed load transport rate for individual fraction is modified to make it applicable over a wide range of parameters the relationship between the dimensionless grain shear stress and the dimensionless bed load transport rate developed by misri et al for uniform sediments was made applicable to sediment mixtures by introducing a multiplying correction factor the parameters affecting this correction factor were identified and a relationship obtained for the same by analysis of an extreme amount of laboratory and river data use of this factor along with the transport law for uniform sediments enables determination of the rate of bed load transport of the individual fractions of a mixture

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

precise aftershock distribution of the 2004 mid niigata prefecture earthquake implication for a very weak region in the lower crust abstract the 2004 mid niigata prefecture earthquake mjma 6 8 occurred in the region of large strain rates 0 1 ppm y contraction in the intraplate region in japan the mainshock was followed by four major aftershocks with mjma 6 0 the hypocenters of the mainshock and two large aftershocks that occurred in the central part of the aftershock region were located near the lower limit of the earthquake distribution while hypocenters of the other two aftershocks near both ends are located near its upper limit furthermore the fault planes of the latter two aftershocks were confined within the upper half of the upper crust also the lower limit of the aftershock distribution is deepest in the central part and becomes shallower toward the nne and ssw ends these data can be explained by the hypothesis that a localized stress concentration occurred near the bottom of the seismogenic region only in the central part the stress concentration may be generated by the deformation in the very weak region of low strength in the lower crust beneath the central part of the aftershock region

relationship between hypocentral distributions and vp vs ratio structures inferred from dense seismic array data a case study of the 1984 western nagano prefecture earthquake central japan

comparison of source areas of m4 8 0 1 repeating earthquakes off kamaishi ne japan are asperities persistent features abstract m4 8 0 1 earthquakes have occurred regularly since 1957 with a recurrence interval of 5 52 0 68 yr at the same location of the plate boundary off kamaishi iwate prefecture the last event m4 7 occurred on 11 13 2001 16 44 jst and the previous one m4 8 on 3 11 1995 10 30 jst waveforms of these events are similar to each other to examine the hypothesis that this characteristic earthquake sequence is caused by repeating ruptures of an asperity frictionally locked patch surrounded by creeping areas we compared the rupture area of the 2001 event with that of the 1995 event by a waveform inversion method estimated spatial extents of the rupture areas of the 2001 and 1995 events are almost the same and are estimated to be about 1 5 1 5 km 2 the rupture area of the 2001 event is almost completely overlapped with that of the 1995 event although the ruptures of the two events were initiated from different points the present observations clearly show that the 1995 and 2001 events are caused by the repeating ruptures of the same asperity patch and support the hypothesis of persistent asperities

seismic structure in and around the source area of the 2004 mid niigata japan earthquake 3 d waveform modelling based on local tomography images summary the seismic velocity structure in and around the source area of the 2004 mid niigata earthquake which featured complicated heterogeneities was investigated by combining waveform modelling and traveltime tomography inversion using low frequency 0 05 f 0 2 hz and high frequency f 1 hz data respectively on the footwall of the main shock that includes multiplanar faults 3 d finite difference waveform modelling using only a previously proposed tomography model was not sufficient to synthesize the observed waveforms in 0 05 f 0 2 hz at most stations thus we derived a final 3 d model 3dm 28 examining body wave amplitudes phases and traveltimes the image produced by model 3dm 28 shows a clearer contrast between low and high velocities than that seen in the original tomography models due to the higher velocity on the footwall this increase in velocity particularly in the seismogenic zone also indicates that short wavelength low velocity anomalies revealed in the revised tomography image may be more localized in the vicinity of the multiplanar faults than that shown in the original one moreover the low velocity anomaly zone within a depth range of 15 20 km beneath the seismogenic zone lower crust appears to be associated with the short wavelength low velocity anomalies at shallower depths upper crust these characteristics may support the hypothesis of infiltration of pressurized fluids from the lower crust into the multiplanar fault system the volumes or distributions of such fluids may be clarified by further examination of unsatisfactory fit waveforms recorded at stations along the strikes of the major faults we suggest that the clear velocity contrasts between the hangingwall and footwall and the upper crust and lower crust including the effects of fluids all seem to be essential characteristics of the seismogenic conditions in this earthquake sequence

initial motion and pivoting characteristics of sand particles in uniform and heterogeneous beds experiments and modelling experiments are described in which the threshold conditions for sediment entrainment are measured for uniform and mixed sand beds beneath both steady and combined steady oscillatory flows derived critical shear stresses are compared with the mixed bed entrainment model of wiberg smith 1987 as predicted by the model coarser grains within a sand mixture are entrained at lower bed shear stresses than progressively finer grains entrainment occurs generally at lower shear stresses than predicted by the model especially under unidirectional flows this may be the result of grains resting in unusually unstable positions during the experiments because the beds are unworked at the start of the experiments the model of wiberg and smith predicts threshold conditions more accurately for the mixed beds if the bed pivoting angle is correctly defined the pivoting angles of the beds used here are measured using a new technique designed specifically for comparison with the threshold data the measured angles repeat the finding that the coarse grains are more mobile than the finer fractions of a mixture the results are poorly described by the pivoting angle model presented by wiberg smith 1987 and are better represented by a model of the form d di d50 after li komar 1986 where and are empirical constants the threshold model is found to be more effective using the improved pivoting relationship the entrainment of grains is found to be easier beneath unidirectional flows than combined flows in accordance with previous authors findings a suggestion that this result is caused by a change in the erosion mechanism beneath wave flows is made wave boundary layers may act as an extended laminar sublayer over bed grains and reduce the erosive efficiency of the overlying current flow the results of the experiment have implications for the natural sorting mechanisms of sediment beds being deposited in near threshold flows

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

a comparison between shields threshold criterion and the movement of loosely packed gravel in a tidal channel observations of the threshold of movement of loosely packed gravel in a tidal current are described for gravel with equivalent spherical diameters d in the range 0 2 d 5 0cm the critical friction velocity u c corresponding to the initiation of sediment transport is given by u c 7 0 d0 2 at large values of d within the quoted range the value u c is significantly lower than would be obtained by a shields experiment u c d0 5 by comparing our values of u c with those obtained under well controlled laboratory conditions the discrepancy with shields is shown to be due to the open spacing between and exposure of individual pebbles on the seabed by comparing our results with those from upland gravel streams and flume experiments it is suggested that shields assumed an excessively large water depth to particle size ratio as a constraint within which the critical sediment entrainment number 0c is valid

applications of grain pivoting and sliding analyses to selective entrapment of gravel and to flow competence evaluations models of sediment threshold by grain pivoting or sliding over underlying particles are examined in order to explore their application to evaluations of selective entrainment of gravel by flowing water of special interest is whether such process based models provide satisfactory evaluations of flow competence and the movement of large clasts by floods a detailed derivation is undertaken focusing first on the fluid flow and forces at the particle level the resulting threshold equation for the particle level velocity is then modified to yield the mean entrainment stress for the flow as a whole this approach is appropriate for considerations of selective entrainment of grains of varying sizes within a deposit the sorting being due to their relative projection distances above the bed and the dependence of their pivoting angles on grain size and shape the resulting threshold equations contain a number of coefficients e g drag and lift whose values are poorly known but can be constrained by requiring agreement with the shields curve for the threshold of grains in uniform deposits if pivoting coefficients based on laboratory measurements with tetrahedral arrangements of particles are used in the models smaller degrees of selective sorting are predicted than found in the field measurements of gravel entrainment however if reasonable modifications of those coefficients are made for expected field conditions then the models yield good agreement with the data sliding models where sorting is due entirely to projection distances of the grains above the bed yield somewhat poorer agreement with the field data however the sliding models may have support from laboratory experiments on gravel entrainment in that the data and theoretical curves have similar concave trends the existing measurements lack documentation of the mechanisms of grain movement so it is not possible to conclusively determine the relative importance of grain pivoting versus sliding in spite of such uncertainties the results are encouraging and it is concluded that pivoting and sliding models for grain entrainment do have potential for field computations of selective entrainment and flow competence

bed load transport of mixed size sediment fractional transport rates bed forms and the development of a coarse bed surface layer fractional transport rates bed surface texture and bed configuration were measured after a mixed size sediment had reached an equilibrium transport state for seven different flow strengths in a recirculating laboratory flume fractional transport rates were also measured at the beginning of each run when the bed was well mixed and planar the start up observations allow us to describe the variation of fractional transport rates with bed shear stress for a constant bed surface texture and bed configuration the start up and equilibrium observations together allow for the first time an unambiguous description of the mutual adjustment among the transport the bed configuration and the bed surface as the transport system moves toward equilibrium we find that a substantial interaction exists among the transport bed surface and bed configuration bed forms and a coarse surface layer coexist over a range of bed shear stress under some flow conditions the size and shape of the bed forms are controlled by the presence of the coarse surface layer at higher flows the coarse surface layer is eliminated by scour in the lee of the bed forms if the bed surface is defined as that over which the bed forms move a coherent relation between the bed surface texture and the transport grain size distribution may be defined at equilibrium the transport rates of all fractions were not equally mobile defined as identical transport and bed grain size distributions although equal mobility was approached for runs in which the bed shear stress was more than twice that for initial motion of the mixture under some flow conditions the transport was observed to adjust away from equal mobility as the bed adjusted from a well mixed start up condition to an equilibrium state development of a partial static armor wherein some individual grains become essentially immobile even though other grains in the same fraction remain in transport is suggested to explain these adjustments between the transport and bed surface grain size distributions constraints on equilibrium mixed size sediment transport are defined the special conditions for which equal mobility must hold and the relevance to natural conditions of flume results and the equal mobility concept are discussed

imaging the source area of the 1995 southern hyogo kobe earthquake m7 3 using double difference tomography abstract to understand the generation process of inland earthquake we determined the seismic velocity structure in and around the source area of the 1995 southern hyogo kobe earthquake m7 3 in sw japan we adopted the double difference dd tomography method zhang h and c thurber double difference tomography the method and its application to the hayward fault california bull seism soc am 93 2003 1875 1889 we inverted arrival times recorded by a dense temporary seismic network for aftershocks and seismic networks routinely operated by japanese universities obtained results are summarized as follows 1 low velocity zones of a few kilometers width are distributed along the fault or along the aftershock alignment suggesting that the fault of the 1995 earthquake is located primarily in a low velocity zone 2 amount of velocity decrease within this low velocity zone varies along the strike of the fault most of large slip areas asperities seem to correspond to higher velocity areas relative to the surroundings on the fault rather than to lower velocity areas

seismic waveform inversion in the frequency domain part 2 fault delineation in sediments using crosshole data a crosshole experiment was carried out in a layered sedimentary environment in which a normal fault is known to cut through the section initial traveltime inversions produced stable but low resolution images from which the fault could be only vaguely inferred to image the fault wavefield inversion was used to produce a velocity model consistent with the detailed phase and amplitude of the data at a number of frequencies our wavefield inversion scheme uses a classical descent type algorithm for decreasing the data misfit by iteratively computing the gradient of this misfit by repeated forward and backward propagations our propagator is a full wave equation frequency domain acoustic finite difference method the use of the frequency space domain yields computational advantages for multisource data and allows an easy incorporation of viscous effects by running wavefield inversion on the field data a quantitative velocity image was produced that yielded a significantly improved image of the fault when compared with the original traveltime inversions because the original field data were noisy and contained a high degree of multiple scattering from the layering of the sediments the transmitted arrivals were selectively windowed to enhance the image the sediments at the site were strongly attenuating we therefore used a viscoacoustic model during the modeling and the inversion that correctly simulated the observed decrease in amplitude with increasing frequency and source receiver offset furthermore since the traveltime inversion indicated a high degree of anisotropy at the site a fixed homogeneous level of anisotropy was used during the inversion tests at varying levels of anisotropy confirmed the improvement in image quality and in data fit when anisotropy was incorporated the final image was verified by examining the distribution of the residuals in the frequency domain by comparing time domain modeled wavefields with the observed data and by direct comparison with borehole logs

application of cross hole seismic measurements in site investigation surveys application of the cross hole seismic method to site investigation surveys for civil engineering developments is illustrated by case histories from the united kingdom using the borehole sparker probe developed in mccann et al 1975 as the seismic source at newborough anglesey it is shown that this source generates both a compressional wave and a vertically polarized shear wave in the borehole the measured velocity values are used to determine the dynamic elastic moduli of the saturated sand deposit at this site at cocking sussex and east fleet dorset the presence of an air filled void between two boreholes is shown to have a significant effect on the velocity of propagation and amplitude of the transmitted seismic signals this work is extended at maidstone kent where the technique is used to confirm the presence of a cavity below the foundation of a house in the hot dry rock geothermal project at rosemanowes cornwall increased fracturing of the granitic rock mass following explosive stimul

threshold of coarse sediment transport in broad and narrow natural streams the threshold of coarse sediment transport has been examined in natural streambeds in an upland pennine u k area threshold values of the total boundary shear stress t0 for a given grain size in a narrow natural stream w d 11 efficiency in the entrainment process is related not only to the overall channel geometry but also varies as a function of discharge in channels characterized by compound roughness empirical curves relating t0 and a mean grain size d5 are presented but are limited in application to streams of similar physical and hydraulic characteristics as the ones examined in this investigation considerable divergence is noted between these empirical functions and a summary empirical function for general application obtained from a published source the reasons for this divergence are discussed the influence of grain shape was found not to be important in the initiation of motion criterion this conclusion may reflect the limited range of natural grain shapes in the study streams but might reasonably apply to other field investigations of similar streams modifications of the shields and yalin diagrams are suggested for practical applications in shallow streams with poorly graded bed material the shields parameter may be regarded as an inverse function of the relative protrusion of individual grains in the shallow flow depth d5 d the increased importance of augmented drag forces in the entrainment process in shallow flows is suggested as the physical explanation for the reduced values of the shields parameter however the relationships presented should not be applied to laboratory experiments concerned with well graded sediments therefore beds with little deviation in level in which the shields parameter may be regarded as constant at high reynolds grain numbers consistent estimated field values of a threshold sediment transport parameter might be used to compare field data to threshold values derived from statistical arguments and laboratory experiments reported in the literature

bed load transport of coarse nonuniform sediment experiments involving measurements of the bed load transport rates of different fractions in a mixture are reported a conceptual model for the effect of a particular size of sediment on the transport rates of other sizes of sediment is proposed the experimental data are analyzed with the dual objectives of assessing the accuracy of existing methods of computation of bed load transport and of proposing a new method of computation

laboratory measurements of pivoting angles for applications to selective entrainment of gravel in a current important to grain entrainment by a flowing fluid is the pivoting angle of the grain about its contact point with an underlying grain a series of experiments has been undertaken to determine how this angle depends on grain shape rollability and angularity on the ratio of the size of the pivoting grain to those beneath and on factors such as imbrication the experiments involved gravel sized spheres ball bearings and marbles natural pebbles selected for their approximately triaxial ellipsoid shapes and angular crushed basalt pebbles the pivoting angles for these grains were measured on an apparatus consisting of a board which can be progressively inclined the angle of the board being equal to the pivoting angle at the instant of grain movement the pivoting angles of spheres showed reasonable agreement with a theoretically derived equation showing much better agreement than in previous studies which utilized sand sized spheres a series of measurements with spheres ranging from sand to gravel sizes reveals that the pivoting angles decrease with increasing particle size our results are therefore consistent with the earlier studies limited to sand size spheres the cause of this size dependence is unknown since moisture and electrostatic binding can be ruled out similar size dependencies are also found for the ellipsoidal pebbles and angular gravel the experiments with ellipsoidal pebbles demonstrated a strong shape dependence for the pivoting angle being a function of the ratio of the pebble s smallest to intermediate axial diameters this ratio controls the grain s ability to roll and pivot with small ratios of these diameters the pebbles tended to slide out of position whereas with ratios closer to unity circular cross section true pivoting took place and the angles were smaller experiments with flat pebbles placed in an imbricated arrangement yielded much larger angles than when the pebbles lay in a horizontal position the pivoting angle being increased approximately by the imbrication angle the angular crushed gravel also required high pivoting angles apparently due to interlocking of the grains resulting from their angularity other factors being equal the measurements of pivoting angles demonstrate that the order of increasing difficulty of entrainment is spheres ellipsoidal grains angular grains and imbricated grains the results obtained here make possible the quantitative evaluation of these shape effects on grain threshold as well as evaluation of the selective entrainment of grains from a bed of mixed sizes

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

three dimensional velocity structure seismicity and fault structure in the parkfield region central california this study examines the three dimensional velocity structure in a 60 by 80 km region containing the parkfield segment of the san andreas fault we use local earthquake and shot p arrival times in an iterative simultaneous inversion for velocity and hypocentral parameters using the three dimensional model we relocated 5251 events that occurred from 1969 to 1991 as well as the 1966 aftershocks and computed 664 fault plane solutions the san andreas fault saf characterized by a sharp across fault velocity gradient is the primary feature in the velocity solution there is a 5 20 lateral change in velocity over a 4 km width the contrast being sharper where there is better resolution the model also shows significant variations in the velocity and in the complexity of the velocity patterns along the saf the largest across fault velocity difference is below middle mountain where a large volume of low velocity material impinges on the saf from the northeast this material is inferred to be overpressured and may be key to understanding the unusual behavior in the parkfield preparation zone a 20 km long high velocity slice is imaged northeast of the saf near gold hill its along fault length corresponds to the length of the maximum slip in 1966 the relocated seismicity shows that the san andreas fault is a planar vertical fault zone at seismogenic depths ninety percent of the fault plane solutions that are on or near the saf were right lateral strike slip on subvertical fault planes that parallel the saf thus the surface fault complexities do not appear to extend to depth and therefore do not explain the rupture character at parkfield at parkfield variations in material properties play a key role in fault segmentation and deformation style our observations suggest that there may be a general relation between increasing velocity and increasing ability of the rocks to store strain energy and release it as brittle failure

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

comparative tomography of reverse slip and strike slip seismotectonic provinces in the northern south island new zealand abstract actively deforming crust and upper mantle around the obliquely convergent pacific australia plate boundary in the northern south island of new zealand have been investigated by seismic tomography using data from a temporary c 50 station network plus geonet the alpine wairau fault principal component of the plate boundary at the surface transects the study area separating the buller nelson bn province of active compressional inversion involving steep reverse faulting to the northwest from the marlborough fault system ma dominated by dextral strike slip faulting to the southeast in the course of this study ma hosted the 2013 seddon earthquake sequence m5 9 6 6 and the 2016 m7 8 kaikoura earthquake active fault structures and present seismicity are associated with a heterogeneous distribution of low velocity and vp vs anomalies elsewhere there is a general association between crustal seismicity and low velocity zones along major fault structures within both the ma and bn seismotectonic provinces along which high vp vs anomalies are locally conspicuous areas of active crustal seismicity are also generally characterized by high vp vs for instance the hypocentre and aftershocks of the 2016 m7 8 kaikoura earthquake overlie a low velocity region with high vp vs the coincidence of anomalously low vp and vs and anomalously high vp vs with zones of high electrical conductivity defined by a previous mt transect is consistent with the notion that upward migration of overpressured hydrothermal fluid from the subducting slab at depth leads to a heterogeneous distribution of overpressured fluid in and around the base of the crustal seismogenic zone weakening the overlying crust and promoting seismic rupture along major fault systems it seems possible that the association of mid crustal low velocity zones with anomalously high vp vs may diagnose rupture preparation zones where frictional strength is being lowered by the build up of fluid overpressure concurrent with accumulating shear stress so that eventual fault failure is dual driven

detailed imaging of the fault planes of the 2004 niigata chuetsu central japan earthquake sequence by double difference tomography abstract imaging of the hypocentral faults of the niigata chuetsu earthquake sequence was performed by double difference tomography using data obtained by a temporary aftershock observation network densely deployed in the hypocentral region two parallel unfavorly oriented fault planes steeply inclined to the wnw are revealed that of the main shock and that of the largest aftershock as well as a zone of velocity change between the high velocity footwall and the low velocity hanging wall for both p and s waves this suggests that the main shock and the largest aftershock are caused by the reactivation of normal faults in the miocene under the current compressional stress regime parts of the fault planes are also found to be located within the low velocity zone this low velocity zone continues to the lower crust which is imaged by an inversion from the regional data and would correspond with highly fractured zone around the fault plane with high fluid pressure which reactivated the unfavorly oriented fault and triggered the present earthquake large coseismic slip area appears to extend to the northeastern portion with relatively high velocity this suggests that the asperity large coseismic slip area of the main shock possibly correspond with a higher velocity region along the fault plane