empirical relationships among seismic velocity effective pressure porosity and clay content in sandstone we use a multivariate analysis to investigate the influence of effective pressure pe porosity and clay content c on the compressional velocity vp and shear velocity vs of sandstones laboratory measurements on water saturated samples of 64 different sandstones provide a large data set that was analyzed statistically for each sample relationships between effective pressure and vp and vs have been determined all samples were well fit by relationships that have an exponential increase in velocity at low pe tapering to a linear increase with pe for pe greater than 0 2 kbar there are differences in the pressure dependences of velocity for different rocks particularly at very low pressures however the differences cannot be attributed to or c for the combined set of measurements from all samples the best fitting formulations are vp 5 77 6 94 1 73c 0 446 pe e 16 7pe and vs 3 70 4 94 1 57c 0 361 pe e 16 7pe while this is admittedly a very simplified parameterization it is remarkable how well

geothermal structure of the miura boso plate subduction margin central japan abstract we have constrained the geothermal structure of the miura boso plate subduction margin located in central japan using maximum paleo temperature data derived from vitrinite reflectance measurements we established that higher maximum paleo temperatures are restricted to the western part of the early miocene hota accretionary complex hota and hayama groups indicating a spatial difference in the amount of slip upon the out of sequence thrust potentially associated with the izu bonin island arc collision the weakly deformed sedimentary sequences overlying the highly deformed hota group strata have much lower vitrinite reflectance values than the latter this variation indicates that the sedimentary sequences of the trench slope experienced a markedly lower maximum burial depth than the relatively deep buried and uplifted hota accretionary complex conversely maximum paleo temperatures obtained for tectonic blocks hosted by the neighboring mineoka ophiolite complex are very high ca 140 c for the large early miocene haccho formation blocks and 65 90 c for the other blocks this result suggests that the individual tectonic blocks enclosed in the ophiolite complex were subjected exhumation from depths of 3 5 km

high frequency source radiation during the 2011 tohoku oki earthquake japan inferred from kik net strong motion seismograms 1 to investigate source processes of the 2011 tohoku oki earthquake we utilized a source location method using high frequency 5 10 hz seismic amplitudes in this method we assumed far field isotropic radiation of s waves and conducted a spatial grid search to find the best fitting source locations along the subducted slab in each successive time window our application of the method to the tohoku oki earthquake resulted in artifact source locations at shallow depths near the trench caused by limited station coverage and noise effects we then assumed various source node distributions along the plate and found that the observed seismograms were most reasonably explained when assuming deep source nodes this result suggests that the high frequency seismic waves were radiated at deeper depths during the earthquake a feature which is consistent with results obtained from teleseismic back projection and strong motion source model studies we identified three high frequency subevents and compared them with the moment rate function estimated from low frequency seismograms our comparison indicated that no significant moment release occurred during the first high frequency subevent and the largest moment release pulse occurred almost simultaneously with the second high frequency subevent we speculated that the initial slow rupture propagated bilaterally from the hypocenter toward the land and trench the landward subshear rupture propagation consisted of three successive high frequency subevents the trenchward propagation ruptured the strong asperity and released the largest moment near the trench

elevated pore pressure and anomalously low stress in regions of low frequency earthquakes along the nankai trough subduction megathrust 1 recent seismic reflection and ocean bottom seismometer obs studies reveal broad regions of low seismic velocity along the nankai subduction plate boundary megathrust offshore sw japan these low velocity zones lvz s extend 55 km landward from the trench corresponding to depths of 10 km below sea floor here we estimate the in situ pore pressure and stress state within these lvz s by combining p wave velocities obtained from the geophysical surveys with new well constrained empirical relations between p wave velocity porosity and effective mean stress defined by laboratory deformation tests on drill core samples of the incoming oceanic sediment we document excess pore pressures of 17 87 mpa that extend 55 km into the subduction zone indicating that trapped pore fluids support 45 91 of the overburden stress along the base of the upper plate and surrounding major fault zones the resulting effective stresses in the lvz are limited to 1 3 of the values expected for non overpressured conditions these low effective stresses should lead to a mechanically weak and predominantly aseismic plate boundary the region of lowest effective stress coincides with precisely located very low frequency earthquakes providing the first quantitative evidence linking these anomalous slip events to low stress and high pore pressure

smectite swelling in the miura boso accretionary prism possible cause for incipient decollement zone formation abstract an analysis of the mineralogy of the miura boso accretionary prism which consists of off scraped upper miocene strata exposed on the southern parts of the miura and boso peninsulas in central japan revealed homogeneous mineral composition throughout all levels of silt layers hosting deformation structures associated with sediment accretion xrd analyses showed that the sediment consists of randomly ordered mixed layer illite smectite i s with low illite content 40 wt quartz 30 wt illite 10 20 wt plagioclase 10 wt kaolinite chlorite 5 wt and calcite 0 10 wt the observed mineralogical assemblage indicates that location of the decollement formation was not constrained by mechanical heterogeneities associated with mineralogical variations but was controlled by spatial variations in effective pressure within the over consolidated sediment located above the incipient decollement zone the occurrence of abundant smectite with a shape preferred orientation gave rise to smectite swelling producing pressures in the order of 3 0 mpa the combined effect of high swelling pressure and high pore pressure resulted in an overpressured zone at the base of the over consolidated zone facilitating the development of a decollement zone within the prism

influence of thermal and mechanical cracks on permeability and elastic wave velocities in a basalt from mt etna volcano subjected to elevated pressure abstract we report simultaneous laboratory measurements of seismic velocities and fluid permeability on lava flow basalt from etna italy results were obtained for dry and saturated samples deformed under triaxial compression during each test the effective pressure was first increased up to 190 mpa to investigate the effect of pre existing crack closure on seismic properties then the effective pressure was unloaded down to 20 mpa a pressure which mirrors the stress field acting under a lava pile of approximately 1 5 2 km thick and deviatoric stress was increased until failure of the specimens using an effective medium model the measured elastic wave velocities were inverted in terms of two crack densities i the crack density of the pre existing thermal cracks and v the crack density of the stress induced cracks in addition a link was established between elastic properties elastic wave velocities vp and vs and permeability using a statistical permeability model our results show that the velocities increase with increasing hydrostatic pressure up to 190 mpa due to the closure of the pre existing thermal cracks this is interpreted by a decrease of the crack density i from 1 to 0 2 the effect of pre existing cracks closure is also highlighted by the permeability evolution which decreases of more than two orders of magnitude under deviatoric loading the velocities signature is interpreted in the first stage of the loading by the closure of the pre existing thermal cracks however with increasing deviatoric loading newly formed vertical cracks nucleate and propagate this is clearly seen from the velocity signature and its interpretation in term of crack density from the location of the acoustic emission sources and from microstructural observations this competition between pre existing cracks closure and propagation of vertical cracks is also seen from the permeability evolution and our study shows that mechanically induced cracks has lesser influence on permeability change than pre existing thermal cracks

compaction in the nankai and barbados accretionary prisms new insights from logging while drilling data 1 sediment deformation changes in physical properties and fluid migration can be studied under well defined conditions in accretionary prisms our investigations focused on the accretionary prisms of barbados caribbean and nankai japan to interpret the effects of compaction on different lithologies during accretion the interpretation is based on very good quality logging while drilling data statistical data analysis is used to determine sediment composition and its specific physical properties finally the sediments are decompacted to determine the initial compaction before accretion and thus to quantify both the lateral and the vertical compaction components this investigation shows that different lithologies undergo similar compaction and porosity reduction the porosity differences of selected sediment layers between adjacent sites are significantly lower in nankai than in barbados which implies higher fluid expulsion in nankai decompaction of these sediment layers proves that the lateral compaction component is higher than the vertical compaction component

source amplitudes of volcano seismic signals determined by the amplitude source location method as a quantitative measure of event size article i nfo the amplitude source location asl method which uses high frequency amplitudes under the assumption of isotropic s wave radiation has been shown to be useful for locating the sources of various types of volcano seismic signals we tested the asl method by using synthetic seismograms and examined the source amplitudes determined by this method for various types of volcano seismic signals observed at different volcanoes our synthetic tests indicated that although asl results are not strongly influenced by velocity structure and noise they do depend on site amplification factors at individual stations we first applied the asl method to volcano tectonic vt earthquakes at taal volcano philippines our asl results for the largest vt earthquake showed that a frequency range of 7 12 hz and a q value of 50 were appropriate for the source location determination using these values we systematically estimated source locations and amplitudes of vt earthquakes at taal we next applied the asl method to long period events at cotopaxi volcano and to explosions at tungurahua volcano in ecuador we proposed a practical approach to minimize the effects of site amplifications among different volcano seismic networks and compared the source amplitudes of these various volcano seismic events with their seismic magnitudes we found a proportional relation between seismic magnitude and the logarithm of the source amplitude the asl method can be used to de termine source locations of small events for which onset measurements are difficult and thus can estimate the sizes of events over a wider range of sizes compared with conventional hypocenter determination ap proaches previously there has been no parameter widely used to quantify the sources of volcano seismic signals this study showed that the source amplitude determined by the asl method may be a useful quan titative measure of volcano seismic event size

structural characteristics of shallowly buried accretionary prism rapidly uplifted neogene accreted sediments on the miura boso peninsula central japan 1 the upper miocene misaki and nishizaki formations on the miura and boso peninsulas in central japan preserve the deformation features of an off scraped accretionary prism the spatial distribution geometry and style of accretion related deformation with paleotemperature and burial depth estimation are elucidated in this study the deformation structures and textures are similar to those of modern accretionary prisms the low maximum paleotemperature 50 c and high preserved porosity of the sediments 30 50 imply a maximum burial depth of less than 1000 m on the basis of the mode of deformation this off scraped body is divided into an imbricate thrust a thrust unit and an upper coherent unit in ascending order the imbricate thrust corresponds to a branch from the basal decollement zone and is subdivided into a brecciated zone a main gouge zone and a shear band zone the thrust unit hosts a concentration of thrust systems that form various orders of duplex structures while the upper coherent unit is characterized by gravitational instability and earthquake induced deformation without thrust faulting the duplex distribution shear strain and fluid migration associated with the off scraping processes are clearly localized within the imbricate thrust and thrust unit this accretion related deformation occurred before lithification of the sediment and under high fluid pressure induced by shear deformation thickening of the sedimentary sequence and earthquake induced liquefaction these processes are inferred to control the effect on the mode of deformation and the location of thrusting during early deformation of the accretionary prism

modeling of multicomponent reactive transport in groundwater 2 metal mobility in aquifers impacted by acidic mine tailings discharge the mobility of potentially toxic dissolved metals discharged from a mine tailings source into an aquifer is investigated by using the multicomponent reactive transport model mintran a generic aquifer resembling a site in northern ontario is used as a basis and a scenario analysis is performed to determine the effect of terminating the source input of acidity and dissolved metals after a finite time it is found that for most metals the buffering reactions in the carbonate aquifer lower the dissolved metal concentrations substantially often by several orders of magnitude in the case of a 12 year source duration most metals are effectively immobilized by precipitation and the concentrations of metals remaining in solution are well below drinking water limits the risk of contamination of water resources by toxic metals can thus be controlled

systematic variation of shear induced physical properties and fabrics in the miura boso accretionary prism the earliest processes during off scraping abstract the interrelations between deformation and variations in the physical properties and fabrics of a shallow level accretionary prism have been clarified using measurements of porosity pore size distribution and the anisotropy of magnetic susceptibility ams within the miura boso accretionary prism central japan based on the mode of deformation this onland example of an off scraped body can be divided into three parts from bottom to top imbricate thrusts corresponding to a decollement zone a thrust unit in the lower part of the off scraped body and an upper coherent unit in the top part of the off scraped body physical properties and fabrics are quite variable in each of the three parts even within a particular lithology these observations reflect each structural unit s individual strain history during shallow off scraping and accretion prior to the accretion the sediments underwent vertical compaction when horizontal compressional stresses subsequently began to deform the sediments precursory shear disturbed the previous compaction fabric accompanied by a pervasive porosity decrease over a zone several tens to hundreds of meters in thickness the porosity decrease occurred by large pore collapse which led to the development of an impermeable over consolidated horizon and inevitable high pore fluid pressures below that controlled the position of the subsequent decollement zone displacement along imbricate thrusts within the decollement zone took place just below the over consolidated horizon where high fluid pressure had been generated here a flattening fabric parallel to the imbricate thrust and associated further porosity and pore size reductions occurred in association with the fault movement these findings imply unrecoverable pre fractured strain information of sediments before being included in the decollement zone and suggest that the precursory formation of an over consolidated zone via grain rearrangement and pore size reduction is an essential control on subsequent large deformation i e within a decollement zone in the shallow part of an accretionary prism especially within lithologically homogeneous material

evidence for a weak and overpressured decollement beneath sediment dominated accretionary prisms we present structural data from several underthrust sequences in southwest alaska that suggest that the deformation regime beneath accretionary prisms is characterized by a subvertical 1 and regionally extensive layer parallel shearing these results contrast markedly with the results obtained from the more shallow parts of accretionary prisms and fold and thrust belts where 1 plunges gently seaward or toward the deformation front on the basis of mohr circle diagrams we propose that these different stress directions are consistent only with a model in which the two regimes are separated by a very weak decollement and calculate coefficient of friction values that range from 0 25 to 0 08 these values are significantly lower than coefficient of friction values calculated for the basal decollement in the taiwan fold and thrust belt e g 0 2 barr and dahlen 1989a and they are also lower than laboratory friction measurements for most rocks e g 0 6 0 8 byerlee 1978 consequently these low values suggest the presence of rocks with unusual material properties e g montmorillonite logan and rauenzahn 1987 or anomalous fluid pressures along the decollement on the basis of the occurrence of shale diapirs the distribution of early veins and the absence of montmorillonite in the underthrust sequences we propose that there was an anomalously high fluid pressure along the decollement fault instead of there being such a low coefficient of friction these results emphasize the importance of dewatering and fluid flow in controlling the position of the decollement which in turn determines how the accretionary prism grows in essence it is the development of a weak overpressured decollement within a thick sediment pile that allows plate convergence to be partitioned into offscraping and underthrusting regimes

water flow in the barbados accretionary complex we present a simple analytic kinematic model of the barbados accretionary complex assuming a porosity depth law and deformation by pure vertical shear the model is applied to two sections a northern one with a 900 m thick basin sedimentary column near 16 n and a southern one with a 4 5 km thick one to the south this simple model is compatible with growth of the barbados accretionary complex since 50 ma assuming a constant subduction rate and a constant basin sedimentary column equal to the present one this conclusion is not affected by reasonable changes in the porosity depth law it suggests that the totality of the entering sedimentary column is either accreted or subcreted to the wedge the accretion velocity decreases dramatically with age and its variation should be taken into account in any quantitative model the average strain rates show remarkably different distributions between the two sections the thinner wedge having a much higher rate in a narrow area at the toe we then use the model to compute the sediment grains flow the fluid flow and their thermal effects these effects are small and do not exceed 5 of the heat flow in the absence of other internal flows in contrast the thermal effect of the burial of the slab can result in a lowering of the surface heat flow by as much as 40 the temperature at the base of the wedge on its arc side is close to 300 c on the southern section and half that amount on the northern one this high temperature could account for the absence of large earthquakes to the south and their presence to the north the amount of water discharged if collected by faults over the whole toe area is unable to account for some of the manifestations observed over the toe or seaward of the toe in the barbados area we suggest two possible other sources one for the southern section is the orinoco fan area the other for the northern section might be seismic pumping at the limit of the seismogenic zone along the backthrusts between the accretionary wedge and the forearc basin

porosity of sediments in accretionary prisms and some implications for dewatering processes rapid dewatering largely through loss of porosity is one of the most striking changes affecting deformed sediments in accretionary prisms analysis of porosity from sample and seismic data confirms that porosity in accretionary prisms is significantly less than that in basinal strata of similar lithology more specifically the porosity depth gradient increases arcward across the prism until porosities less than 10 occur within a few kilometers of the surface in deeper parts of the prism dewatering and volume reduction occur not only during loss of porosity but also during dehydration and metamorphic reactions calculations involving volume change lead us to define a function which reflects total volume reduction the distribution of the relative intensity of dewatering within the prism can be calculated from the porosity contours and trajectories of sediment elements an initial attempt indicates that in the toe region the rate of dewatering is accelerated at depth relative to the basinal section and may be greatest near the base of the prism toward the rear of the prism the maximum rate of dewatering occurs at progressively shallower depths several lines of evidence suggest that in addition to gradual diffuse dewatering localized zones of strong dewatering are associated with zones of intense shear this model of shear dewatering based on critical state soil mechanics suggests that sediments adjacent to the basal decollement should be strongly dewatered

location of tremor sources and estimation of lava output using tremor source amplitude on the piton de la fournaise volcano 2 estimation of lava output abstract we propose several relations for estimating the amounts of lava emitted during eruptions of the piton de la fournaise volcano based on the use of tremor source amplitude sources for eruption tremor are located in several frequency bands with a location method based on the use of seismic amplitudes corrected for recording site effects sources are usually found at shallow depth and close to the eruptive vents suggesting that tremor is directly generated by the eruptive activity simultaneously with the location of the tremor sources our program gives the source amplitude of the phenomenon we assume a linear or a quadratic relation between the lava output and the tremor source amplitude both relations are calibrated using data for the march 1998 eruption and tested using the volumes emitted during the july and september 1999 and february 2000 eruptions we found that the 5 10 hz frequency band gives lava output much higher than for lower frequencies suggesting that for that band the tremor generation depends on the eruption site in addition to the lava output or that tremor at those frequencies is not directly caused by the outflow of lava but maybe rather by gas the best estimations are obtained using the quadratic relation for frequencies below 5 hz with an agreement better than 15 with the field observations for the july and september 1999 eruptions and 30 for the february 2000 eruption our results show that the cumulative amplitude of tremor recorded during eruptions of the piton de la fournaise is directly related to the amounts of lava erupted

fluid accumulation and channeling along the northern barbados ridge decollement thrust a volume of three dimensional seismic reflection data acquired in 1992 imaged the decollement beneath the northern barbados ridge accretionary prism revealing reflection amplitude and waveform variations attributed to fluid accumulations along the plate boundary fault we model the seismic reflection by inversion for seismic impedance the product of velocity and density throughout the 5 x 25 km survey area and thus map physical property variations in 1997 ocean drilling program leg 171a penetrated the protodecollement and decollement at five sites with a logging while drilling lwd tool to log density and other physical properties of the decollement we construct a regional map of density and inferred porosity within the decollement from seismic models calibrated with lwd density data in the sediments out in front of the trench the protodecollement forms in a radiolarian rich miocene mudstone with an anomalously high porosity 70 75 that appears as a pervasive inherent characteristic of this interval seaward of the deformation front in the decollement beneath the wedge a consolidation trend of decreasing porosity runs perpendicular to the deformation front with porosity decreasing from 70 at the wedge toe to 50 4 km from the wedge toe a second distinct trend also forms along a 10 km long 1 to 2 km wide ne sw zone in which porosity is 70 as high as it is in the protodecollement this zone can be explained as an area of the decollement where fluid accumulations develop by maintaining high fluid content we postulate that high fluid content is maintained by continuous recharge flowing into and along this channel this porosity distribution within the decollement also strongly influences fluid migration into the overlying accretionary wedge and is directly associated with fluid charging of ramps and out of sequence thrusts above the decollement

location of long period events below kilauea volcano using seismic amplitudes and accurate relative relocation 1 we present methods for improving the location of long period lp events deep and shallow recorded below kilauea volcano by the permanent seismic network lp events might be of particular interest to understanding eruptive processes as their source mechanism is assumed to directly involve fluid transport however it is usually difficult or impossible to locate their source using traditional arrival time methods because of emergent wave arrivals at kilauea similar lp waveform signatures suggest the existence of lp multiplets the waveform similarity suggests spatially close sources while catalog solutions using arrival time estimates are widely scattered beneath kilauea s summit caldera in order to improve estimates of absolute lp location we use the distribution of seismic amplitudes corrected for station site effects the decay of the amplitude as a function of hypocentral distance is used for inferring lp location in a second stage we use the similarity of the events to calculate their relative positions the analysis of the entire lp seismicity recorded between january 1997 and december 1999 suggests that a very large part of the lp event population both deep and shallow is generated by a small number of compact sources deep events are systematically composed of a weak high frequency onset followed by a low frequency wave train aligning the low frequency wave trains does not lead to aligning the onsets indicating the two parts of the signal are dissociated this observation favors an interpretation in terms of triggering and resonance of a magmatic conduit instead of defining fault planes the precise relocation of similar lp events based on the alignment of the high energy low frequency wave trains defines limited size volumes

three dimensional p and s wave velocity structure of redoubt volcano alaska the three dimensional p and s wave structure of redoubt volcano alaska and the underlying crust to depths of 7 8 km is determined from 6219 p wave and 4008 s wave first arrival times recorded by a 30 station seismograph network deployed on and around the volcano first arrival times are calculated using a finite difference technique which allows for flexible parameterization of the slowness model and easy inclusion of topography and source receiver geometry the three dimensional p wave velocity structure and hypocenters are determined simultaneously while the three dimensional s wave velocity model is determined using the relocated seismicity and an initial s wave velocity model derived from the p wave velocity model assuming an average vp vs ratio of 1 78 convergence is steady with approximately 73 and 52 reduction in p and s wave arrival time rms respectively after 10 iterations the most prominent feature observed in the three dimensional velocity models derived for both p and s waves is a relative low velocity near vertical pipelike structure approximately 1 km in diameter that extends from 1 to 6 km beneath sea level this feature aligns axially with the bulk of seismicity and is interpreted as a highly fractured and altered zone encompassing a magma conduit the velocity structure beneath the north flank of the volcano between depths of 1 and 6 km is characterized by large lateral velocity variations high velocities within this region are interpreted as remnant dikes and sills and low velocities as regions along which magma migrates no large low velocity body suggestive of a magma chamber is resolved in the upper 7 8 km of the crust

characterization of scattered seismic wavefields simulated in heterogeneous media with topography 1 we performed numerical simulations of seismic waveforms with frequencies up to 10 hz in heterogeneous media with topography to investigate the effects of topography and structural heterogeneity on seismic scattering we used the simulated waveforms to test the source location method assuming isotropic radiation of s waves for long period events and tremor at volcanoes the assumption of isotropic radiation has been shown previously to be valid in a high frequency band because of the path effect caused by the scattering of seismic waves our simulation results showed that distortion of the wavefields increased as the correlation distance of structural heterogeneity a decreased as the frequency increased and as the travel distance increased topography alone considerably distorted the wavefields however we found that strong scattering due to topography was suppressed if the correlation distance of structural heterogeneity was longer than the s wave wavelength isotropic radiation of s waves by scattering due to topography was not achieved in our simulations our results indicated that scattering due to structural heterogeneity becomes stronger than that due to topography at ka 1 and a 50 m where k is the wave number of the s waves this suggests that strong short scale structural heterogeneity is required to achieve isotropic radiation of s waves although we could not reproduce isotropic radiation our results support the validity of the assumption of isotropic radiation in the source location method

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

mechanical properties and processes of deformation in shallow sedimentary rocks from subduction zones an experimental study to better constrain the mechanical behavior of sediments accreted to accretionary prism we conducted triaxial mechanical tests on natural samples from the miura boso paleo accretionary prism japan in drained conditions with confining pressures up to 200 mpa as well as postexperiments p wave velocity vp measurements during experiments deformation is principally noncoaxial and accommodated by two successive modes of deformation both associated with strain hardening and velocity strengthening behavior 1 compaction assisted shearing distributed in a several mm wide shear zone and 2 faulting localized within a few tens of m wide dilatant fault zone deformation is also associated with 1 a decrease in young s modulus all over the tests 2 anomalously low vp in the deformed samples compared to their porosity and 3 an increase in sensitivity of vp to effective pressure we interpret this evolution of the poroelastic properties of the material as reflecting the progressive breakage of intergrain cement and the formation of microcracks along with macroscopic deformation when applied to natural conditions these results suggest that the deformation style localized versus distributed of shallow z a few km sediments is mainly controlled by the variations in stress strain rate during the seismic cycle and is therefore independent of the porosity of sediments finally we show that the effect of strain through cement breakage and microcracks formation may lower vp for effective pressure up to 40 mpa as a consequence the low vp anomalies observed in nankai accretionary prisms by seismic imaging between 2 and 4 km depth could reflect sediment deformation rather than porosity anomalies

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

broadband seismic monitoring of active volcanoes using deterministic and stochastic approaches 1 we systematically used two approaches to analyze broadband seismic signals for monitoring active volcanoes one is waveform inversion of very long period vlp signals assuming possible source mechanisms the other is a source location method of long period lp events and tremor using their amplitudes the deterministic approach of the waveform inversion is useful to constrain the source mechanism and location but is basically only applicable to vlp signals with periods longer than a few seconds the source location method assumes isotropic radiation of s waves and uses seismic amplitudes corrected for site amplifications this simple approach provides reasonable source locations for various seismic signals such as a vlp event accompanying lp signals an explosion event and tremor associated with lahars and pyroclastic flows observed at five or fewer stations our results indicate that a frequency band of about 5 12 hz and a q factor of about 60 are appropriate for the determination of the source locations in this frequency band the assumption of isotropic radiation may become valid because of the path effect caused by the scattering of seismic waves the source location method may be categorized as a stochastic approach based on the nature of scattering waves systematic use of these two approaches provides a way to better utilize broadband seismic signals observed at a limited number of stations for improved monitoring of active volcanoes

locking of the chile subduction zone controlled by fluid pressure before the 2010 earthquake large subduction zone earthquakes are thought to occur where the down going and overriding tectonic plates are strongly locked analysis of geodetic and seismic data collected in the decade before the 2010 chile earthquake shows that variations in pore fluid pressure correlate with the degree of plate interface locking and may therefore control earthquake rupture

acoustic and mechanical properties of nankai accretionary prism core samples we studied undeformed sediment and accreted strata recently recovered by ocean drilling program integrated ocean drilling program odp iodp drilling in nankai trough convergent margin to unravel the changes in physical properties from initial deposition to incipient deformation we have derived acoustic vp and mechanical uniaxial poroelastic compliance compaction amplitude properties of samples from various drill sites along the muroto odp 1173 and kii transects iodp c0001 c0002 c0006 and c0007 from isotropic loading tests where confining and pore pressure were independently applied we quantified the dependence of vp on both effective peff and confining pc pressure which can be used to correct atmospheric pressure measurements of vp experimental vp obtained on core samples extrapolated to in situ conditions are slightly higher than logging derived velocities which can be attributed either to velocity dispersion or to the effect of large scale faults and weak zones on waves with longer wavelength in the high porosity 30 60 tested sediments velocities are controlled at first order by porosity and not by lithology which is in agreement with our static measurements of drained framework incompressibility much smaller than fluid incompressibility rather than framework incompressibility shear modulus is probably the second order control on vp accounting for most of the difference between actual vp and the prediction by wood s 1941 suspension model we also quantified the mechanical state of nankai samples in terms of anisotropy diagenesis and consolidation both acoustic and mechanical parameters reveal similar values in vertical and horizontal directions attesting to the very low anisotropy of the tested material when considering the porous samples of the upper shikoku basin sediments site 1173 as examples of diagenetically cemented material several mechanical and acoustic attributes appeared as reliable experimental indicators of the presence of intergrain cementation we also detected incipient cementation in samples from iodp site c0001 accretionary prism unit in terms of consolidation we distinguished two classes of material response shallow deformable samples and deep hardly deformable ones based on the amount of compaction upon application of a peff large with respect to the inferred in situ value with a transition that might be related to a critical porosity

velocity porosity relationships for water saturated siliciclastic sediments seeking a global empirical relationship between compressional wave velocity and porosity for siliciclastic sediments we have brought together an extensive suite of both new and published log and core based data we undertook a detailed statistical analysis of ocean drilling program data from amazon fan to examine variables affecting compressional velocity in shallow unconsolidated sediments we identify three dominant variables porosity shale fraction and consolidation history and present two empirically determined boundary curves one for normally consolidated sediments and a second for highly consolidated environments e g accretionary prisms these two empirical relationships predict the compressional velocity of siliciclastic sedimentary rocks with water filled pores as a function of porosity and clay content for the full range of observed porosities velocities of siliciclastic sedimentary rocks decrease rapidly with both increasing porosity and increasing clay content at fractional porosities higher than about 0 4 fluid dominates the elastic properties and velocity exhibits a subtle dependence on porosity remarkably the amazon fan data show that clay content has no direct influence on velocity at high porosities both clay content and sorting do indirectly affect velocity through their control of porosity burial affects velocity not only by compaction related porosity decrease but also by pressure induced increase of intergrain coupling because of the sensitivity of velocity to consolidation history particularly at intermediate fractional porosities of about 0 30 0 40 no single velocity porosity relationship can apply to all high porosity sediments the two proposed relationships fit the majority of published and new data they are applicable however only for normally pressured in situ conditions and water filled pores

how cracks modify permeability and introduce velocity dispersion examples of glass and basalt the porosity of igneous rocks is usually very small although for some basalts it can be nonnegligible due to gas exsolution in the case of glass it is vanishingly small why is it of any interest to look at this kind of material from the point of view of rock physics two series of reasons indeed motivate such investigations

broad weak regions of the nankai megathrust and implications for shallow coseismic slip abstract deep within the nankai trough subduction zone the plate boundary thrust slips along a well imaged megasplay fault system during the megathrust earthquakes that regularly strike southwest japan the routing of the active plate boundary thrust along an upward branching splay fault causes deep underthrusting of an unusually thick section of material attached to the subducting ocean crust here we present three dimensional seismic reflection data that shows this unusually thick section is fluid rich sediment that results in broad weakly coupled regions of the megathrust down into the updip end of the seismogenic zone the weakly coupled regions lie above an underthrust low seismic impedance presumed to be low velocity and low density sediment section that is between one and two kilometers thick and covers 3300 km2 at least one eighth of the total rupture area of the 1944 mw 8 1 tonankai earthquake this underthrust sediment section is broader and much deeper than inferred at other margins sediment underthrusting into the normally well coupled seismogenic zone likely releases fluids and elevates fluid pressure which reduces inter plate coupling along portions of the megasplay fault and allows coseismic rupture to propagate to unusually shallow depths and generate large tsunami as inferred for the 1944 tonankai event splay faults may be a common yet transient mechanism for developing weak subduction zone thrusts

the role of acids in electrical conduction through ice 1 electrical conduction through meteoric polar ice is controlled by soluble impurities that originate mostly from sea salt biomass burning and volcanic eruptions the strongest conductivity response is to acids yet the mechanism causing this response has been unclear here we elucidate conduction mechanisms in ice using broadband dielectric spectroscopy of meteoric polar ice cores we find that conduction through polycrystalline polar ice is consistent with jaccard theory for migration of charged protonic point defects through single ice crystals except that bulk dc conduction is impeded by grain boundaries neither our observations nor modeling using archie s law support the hypothesis that grain boundary networks of unfrozen acids cause significant electrolytic conduction common electrical logs of ice cores by electrical conductivity measurement ecm or dielectric profiling dep and the attenuation of radio waves in ice sheets thus respond to protonic point defects only this response implies that joint interpretation of electrical and chemical logs can determine impurity partitioning between the lattice and grain boundaries or inclusions for example in the greenland ice core project grip ice core from central greenland on average more than half of the available lattice soluble impurities h cl nh4 create defects understanding this partitioning could help further resolve the nature of past changes in atmospheric chemistry