lateral velocity resolution from three dimensional seismic refraction data summary a method for estimating the lateral velocity resolution from 3 d seismic refraction traveltimes is presented the method is non linear in that synthetic data calculated from checkerboard models are inverted using an iterative tomographic approach incorporating smoothness constraints and updated ray paths at each iteration two applications are presented 1 real data from the faeroe basin experiment using the ray coverage and noise level of approximately 50 000 picks and 2 ideal data from the same experiment corresponding to 100 per cent data recovery equivalent to about three times as many ray paths the refraction data constrain the sedimentary and basement structure to approximately 12 km depth a comparison of the results from the two data sets provides a qualitative check on the resolution method illustrates the pitfalls of using ray coverage as an indicator of resolution and demonstrates the potential resolution of currently feasible 3 d refraction experiments 32 checkerboard models consisting of alternating positive and negative velocity anomalies superimposed on the preferred final model of the basin were tested each with a diverent cell size position or orientation the problem of ray bending associated with the 5 per cent checkerboard anomalies is shown to be small using models with four cell sizes allowed for resolution estimates from 3 to 15 km this range being imposed by the frequency content of the data and the areal dimensions of the study area 44 26 km an operator centred on each model node measures the local semblance between the known and recovered checkerboard models a determination of the smallest well resolved cell size at each model node is then made using a 0 7 semblance threshold to provide a spatially dependent lateral resolution estimate resolution for the real data set varies from an average of just over 3 km at 2 km depth to 10 km at 10 km depth where there is a local maximum in ray coverage due to a concentration of ray bottoming points for the ideal data set the average lateral resolution drops ov roughly linearly from better than 3 km at 2 km depth to 6 3 km at 10 km depth the largest diverence between the resolution associated with the ideal and real data occurs at 7 2 km depth where it averages 4 6 km for the former and 10 8 km for the latter due to the near absence of ray bottoming points between 7 and 9 km the results show that the final model for the faeroe basin obtained by regularized inversion with smoothness constraints is consistent with the resolution estimates in the sense that the model does not contain structure with a wavelength smaller than the resolution estimate at any point the results for the ideal data show that good quality 3 d refraction experiments can provide a lateral resolution of no worse than the receiver spacing shot spacing for land data throughout most of the sampled volume

the 23 19 aftershock of the 15 october 1979 imperial valley earthquake more evidence for an asperity the well recorded strong ground motion data for the 23 19 aftershock of the 15 october 1979 imperial valley earthquake provide a good opportunity to study the high frequency source characteristics and the path effects at near source distances the best fitting point source model has a strike slip mechanism n40 w which is nearly identical to the main event the estimated stress drop is extremely high roughly 500 bars with a triangular time history 0 1 0 1 sec but with a moment of 1 0 10 24 dyne cm a double source model found by inversion fits the high frequency data better but indicates complex faulting the first source with strike n319 e dip 42 ne and slip angle 165 has a moment of 0 7 10 24 dyne cm the second source with strike n324 e dip 82 sw and slip angle 181 lies about 0 5 km to the north and has a seismic moment twice that of the first source source dimensions appear very small for this amount of energy release many of the anomalous behaviors observed at certain stations for the main event are also present in the aftershock data these features are examined in terms of path effects

ground motion prediction from tremor 1 the widespread occurrence of tremor coupled with its frequency content and location provides an exceptional opportunity to test and improve strong ground motion attenuation relations for subduction zones we characterize the amplitude of thousands of individual 5 min tremor events in cascadia during three episodic tremor and slip events to constrain the distance decay of peak ground acceleration pga and peak ground velocity pgv we determine the anelastic attenuation parameter for ground motion prediction equations gmpes to a distance of 150 km which is sufficient to place important constraints on ground motion decay tremor pga and pgv show a distance decay that is similar to subduction zone specific gmpes developed from both data and simulations however the massive amount of data present in the tremor observations should allow us to refine distance amplitude attenuation relationships for use in hazard maps and to search for regional variations and intrasubduction zone differences in ground motion attenuation

the burgess shale and associated cambrian formations west of the fossil gully fault zone on mount stephen british columbia west of the fossil gully fault zone on mount stephen the three lowest members only of the burgess shale formation are preserved the kicking horse shale the yoho river limestone and the campsite cliff shale the formation rests unconformably upon the takakkaw tongue formation whose dark basinal limestones conformably overlie paler shelf like limestones of the mount whyte formation mapping has resolved a long standing problem and shown that the stratigraphical position of the famous mount stephen trilobite beds lies within the campsite cliff shale it has also revealed some of the complexities of the fossil gully fault zone among which different periods and directions of component fault movements are indicated faunal evidence shows that the plagiura kochaspis to albertella and albertella to glossopleura zonal boundaries lie within the takakkaw tongue sequence within the burgess shale three distinct soft bodied communities occur at different stratigraphical levels on this mountain slope the oldest

early cambrian priapulid worms buried with their lined burrows five specimens of the priapulid maotianshania cylindrica preserved inside their lined burrows were described from the lower cambrian chengjiang deposits near kunming southern china the exceptional preservation suggests that this worm made a dwelling tube by lining within the uppermost sediment layers this seems to be unique among priapulids in comparison with the cambrian selkirkia and paraselkirkia as well as some modern priapulid larvae and loriciferans taphonomic evidence indicates that the burrow and worm specimens are not buried in situ but were moved by storm tsunami or turbidity generated currents that are thought to have brought sedimentary material intermittently

bioturbation in burgess shale type lagerstatten case study of trace fossil body fossil association from the kaili biota cambrian series 3 guizhou china abstract cruziana gordia planolites rusophycus and trichophycus are common ichnological elements of the kaili biota new discoveries based on the examination of 323 specimens include eldoniids echinoderms trilobites monoplacophorans and non biomineralizing arthropods that are associated with trace fossils based on the observed effects of bioturbation on the preservation of five different animal groups it is clear that infaunal scavengers deposit feeders were periodically active on the kaili sea floor and were able to reach historic layers yielding exceptionally preserved fossils in general the average level of infaunal activity is absent to moderate ichnofabric index i i 1 to 3 in the kaili substrate by contrast the phycodes beds are completely disturbed by infaunal activity i i 5 observed burrow diameter ranges from diminutive 0 2 mm to normal up to 4 2 mm computed tomography allows us to visualize the precise geometry of the trace fossil body fossil association in three dimensions we concluded that although some kaili infaunal animals could bore through the biomineralized echinoderms they did not appear to have scavenged upon these echinoderms based on our three dimensional reconstruction furthermore kaili burrowers can reach the historic layers containing exceptionally preserved fossils without altering soft tissue preservation on the other hand we used conventional techniques to reveal that one burrow is filled with fecal pellets 100 200 m at its terminal end because most burrows are filled with yellow brown coarse sediment and because there is no compositional difference between the fecal pellets and the surrounding coarse sediment within the burrow the origin of the yellow brown coarse sediment is interpreted here as parautochthonous and or autochthonous and as a result of sediment reworking by deposit or suspension feeders the relative scarcity of soft part preservation in the kaili biota compared to the older chengjiang biota and the younger burgess shale biota may be the result of post burial bio disturbance due to the relatively high intensity of local bioturbation it is plausible that oxygenation in deeper sediments facilitated by bioturbation allowed carcasses in the kaili biota to undergo a more extensive period of normal decay prior to final burial than in other cambrian konservat lagerstatten

seismic wave attenuation determined from tectonic tremor in multiple subduction zones abstract tectonic tremor provides a new source of observations that can be used to constrain the seismic attenuation parameter for ground motion prediction and hazard mapping traditionally recorded earthquakes of magnitude 3 8 are used to develop ground motion prediction equations however typical earthquake records may be sparse in areas of high hazard in this study we constrain the distance decay of seismic waves using measurements of the amplitude decay of tectonic tremor which is plentiful in some regions tectonic tremor occurs in the frequency band of interest for ground motion prediction i e 2 8 hz and is located on the subducting plate interface at the lower boundary of where future large earthquakes are expected we empirically fit the distance decay of peak ground velocity from tremor to determine the attenuation parameter in four subduction zones nankai japan cascadia united states canada jalisco mexico and southern chile with the large amount of data available from tremor we show that in the upper plate the lower crust is less attenuating than the upper crust we apply the same analysis to intraslab events in nankai and show the possibility that waves traveling from deeper intraslab events experience more attenuation than those from the shallower tremor due to ray paths that pass through the subducting and highly attenuating oceanic crust this suggests that high pore fluid pressure is present in the tremor source region these differences imply that the attenuation parameter determined from intraslab earthquakes may underestimate ground motion for future large earthquakes on the plate interface

crustal density structure across the central indian shear zone from gravity data abstract the central indian shear zone is a distinct tectonic feature in the central part of india that separates the central indian tectonic zone from the bastar craton the complete bouguer anomaly map of the region encompassing central indian shear zone is characterised by a broad relative gravity high over central indian tectonic zone as compared to the bastar craton the paired gravity anomaly across the two crustal domains signifies that the central indian shear zone is a locus of density discontinuity along which the two crustal domains accreted horizontal gravity gradient analysis further demonstrates the northward subduction of the bastar craton beneath the bundelkhand craton 2 d gravity modelling along mungwani rajnandgaon profile constrained by seoni kalimati seismic section delineates a thick crust beneath the bastar craton as compared to the central indian tectonic zone northward dipping contact of the two crustal domains when projected on the surface coincides with the central indian shear zone with a well defined moho offset and crustal density discontinuity central indian shear zone represents a suture zone that separates the bastar craton from the central indian tectonic zone a low velocity 6 4 km s density 2 90 g cm 3 layer at the base of the crust and relatively lower density 3 21 g cm 3 subcrustal mantle may be the imprint of thermal remobilization beneath the central indian tectonic zone

nied seismic moment tensor catalogue for regional earthquakes around japan quality test and application abstract we have examined the quality of the national research institute for earth science and disaster prevention nied seismic moment tensor mt catalogue obtained using a regional broadband seismic network freesia first we examined using synthetic waveforms the robustness of the solutions with regard to data noise as well as to errors in the velocity structure and focal location then to estimate the reliability robustness and validity of the catalogue we compared it with the harvard centroid moment tensor cmt catalogue as well as the japan meteorological agency jma focal mechanism catalogue we found out that the nied catalogue is consistent with harvard and jma catalogues within the uncertainty of 0 1 in moment magnitude 10 km in depth and 15 in direction of the stress axes the nied mt catalogue succeeded in reducing to 3 5 the lower limit of moment magnitude above which the moment tensor could be reliably estimated finally we estimated the stress tensors in several different regions by using the nied mt catalogue this enables us to elucidate the stress deformation field in and around the japanese islands to understand the mode of deformation and applied stress moreover we identified a region of abnormal stress in a swarm area from stress tensor estimates

visualization of 3d wave propagation from the 2000 tottori ken seibu japan earthquake observation and numerical simulation the dense networks of strong ground motion instruments in japan k net and kik net provide a means of direct visualization of regional wave propa gation during large earthquakes for the 2000 tottori ken seibu earthquake mw 6 6 in western japan snapshots of ground motion derived directly from interpolation of a large number of array observations demonstrate clearly the nature of the source radiation and the character of the seismic wave field propagating to regional dis tances in western japan the wave field from the earthquake is characterized in most parts by the dominance of high frequency 0 2 5 hz lg waves on three component acceleration records and longer period t 10 sec fundamental mode love waves in tangential displacement the presence of strong lateral variations in the crust and upper mantle structures such as the low velocity superficial layer and the high velocity philippine sea plate with shallow subduction into the mantle impose sig nificant modifications on the regional wave field further insight into the nature of the seismic wave field is gained by comparison of the observations with numerical simulation for a 3d model including sedimentary basins by an embedded submesh a multigrid parallel computation using a hybrid pseudospectral finite difference method allows the inclusion of a realistic model of the source process for the 2000 tottori ken seibu earthquake there is good agreement in the dominant features of the regional wave field propagating through the complex structure of western japan however the differences between the observations and the computer simulations indicates the need for further refinement of the source and structural models the inclusion of amplification effects for the population centers in sedimentary basins means that the modeling procedure is already suitable for estimating the main pattern of ground motion for future earthquake scenarios

diminishing high frequency directivity due to a source effect empirical evidence from small earthquakes in the abruzzo region italy the aim of this study is to investigate the directivity effects of 250 aftershocks magnitudes 3 5 5 of the mw 6 1 2009 l aquila earthquake central italy to this end we estimate the apparent source spectra at each station removing path and site effects inferred by standard generalized inversion technique then we evaluate the residuals between the apparent source spectra and the event mean source spectrum at selected frequencies we investigate azimuthal and frequency dependence of the residuals for 40 events with the best station coverage for most of events with the strongest directivity effect mw 3 4 4 0 we observe a remarkable decrease of the directivity amplification at high frequencies which has not yet been documented for such relatively small magnitude events since there is negligible distance dependence we ascribe this observation to a source phenomenon such as significant small scale rupture propagation complexity

ground motion in the presence of complex topography ii earthquake sources and 3d simulations abstract eight seismic stations were placed in a linear array with a topographic relief of 222 m over mission peak in the east san francisco bay region for a period of one year to study topographic effects seventy two well recorded local earthquakes are used to calculate spectral amplitude ratios relative to a reference site a well defined fundamental resonance peak is observed with individual station amplitudes following the theoretically predicted progression of larger amplitudes in the upslope direction favored directions of vibration are also seen that are related to the trapping of shear waves within the primary ridge dimensions spectral peaks above the fundamental one are also related to topographic effects but follow a more complex pattern theoretical predictions using a 3d velocity model and accurate topography reproduce many of the general frequency and time domain features of the data shifts in spectral frequencies and amplitude differences however are related to deficiencies of the model and point out the importance of contributing factors including the shear wave velocity under the topographic feature near surface velocity gradients and source parameters electronic supplement figures of recorded and simulated acceleration response spectra and earthquake ground motion directional response

post cambrian closure of the deep water slope basin taphonomic window exceptional faunas konservat lagerstatten that preserve traces of volatile nonmineralized tissues are statistically overabundant in the cambrian period almost all examples preserved in continental slope and shelf basin environments are of this age the hypothesis that an increase in the amount and complexity of bioturbation was an important agent in the elimination of this deep water slope basin taphonomic window is supported post cambrian ichnofaunal assemblages contain a higher proportion of pascichnia and agrichnia ethologies produced by a mobile infauna they also illustrate the lateral partitioning of organisms into different environmental niches both opportunistic and equilibrium infaunas occur in low oxygen environments in which the preservation of nonbiomineralized tissues was favored direct consumption of carcasses by bioturbating organisms was less important than changes to sediment properties as a result of bioturbation notably enhanced microbial degradation of reactive organic matter increased permeability and the disruption of geochemical gradients necessary for mineral authigenesis

magnitudes and moment duration scaling of low frequency earthquakes beneath southern vancouver island we employ 130 low frequency earthquake lfe templates representing tremor sources on the plate boundary below southern vancouver island to examine lfe magnitudes each template is assembled from hundreds to thousands of individual lfes representing over 269 000 independent detections from major episodic tremor and slip ets events between 2003 and 2013 template displacement waveforms for direct p and s waves at near epicentral distances are remarkably simple at many stations approaching the zero phase single pulse expected for a point dislocation source in a homogeneous medium high spatiotemporal precision of template match filtered detections facilitates precise alignment of individual lfe detections and analysis of waveforms upon correction for 1 d geometrical spreading attenuation free surface magnification and radiation pattern we solve a large sparse linear system for 3 d path corrections and lfe magnitudes for all detections corresponding to a single ets template the spatiotemporal distribution of magnitudes indicates that typically half the total moment release occurs within the first 12 24 h of lfe activity during an ets episode when tidal sensitivity is low the remainder is released in bursts over several days particularly as spatially extensive rapid tremor reversals rtrs during which tidal sensitivity is high rtrs are characterized by large magnitude lfes and are most strongly expressed in the updip portions of the ets transition zone and less organized at downdip levels lfe magnitude frequency relations are better described by power law than exponential distributions although they exhibit very high b values 5 we examine lfe moment duration scaling by generating templates using detections for limiting magnitude ranges mw 1 5 mw 2 0 lfe duration displays a weaker dependence upon moment than expected for self similarity suggesting that lfe asperities are limited in fault dimension and that moment variation is dominated by slip this behavior implies that lfes exhibit a scaling distinct from both large scale slow earthquakes and regular seismicity

the middle cambrian burgess shale and its relationship to the stephen formation in the southern canadian rocky mountains the burgess shale has been an anomalous geologic unit ever since walcott named it in 1911 as the geographic equivalent of the ogygopsis shale in the middle cambrian stephen formation of southeastern british columbia but it has never been recognized outside of its type locality so its status relative to the stephen formation remained uncertain the geologic setting of the burgess shale was determined by aitken and fritz in 1968 when they recognized the cathedral escarpment and divided the stephen formation into a thin platformal succession on top of the escarpment and a thick basinal succession which included walcott s burgess shale in front fieldwork by royal ontario museum parties between 1982 and 1997 has now demonstrated that the thin and thick stephen successions lie within different facies belts and should be regarded as separate formations the stephen shale formation is part of the middle carbonate belt succession whereas the name burgess shale formation is applied to the thick basinal

sedimentation of the phyllopod bed within the cambrian burgess shale formation of british columbia we provide the most detailed sedimentological log to date through the phyllopod bed of the mid cambrian burgess shale formation of british columbia based on millimetre scale logging of a suite of thin sections the sedimentary facies is dominated by alternations of homogeneous mudstone and a coarser grained laminated variably sandy and shelly mudstone that is locally micronodular most boundaries between these two lithologies are gradational and discrete fining upwards turbidite units were rarely recognized such a pattern is interpreted to indicate rapid sedimentation of up to decimetre thick units at this location from pulsatory quasi continuous density currents consistent with earlier proposals of exceptional preservation through rapid burial the density currents responsible were probably largely akin to mud rich slurries helping explain the transport and entombment of the fossils the homogeneous mudstone units are characterized by numerous distinctive lenses of pyrite framboids or subeuhedral crystals previously interpreted as small ripples their 3d shape however suggests an origin as subspherical early diagenetic aggregates their present morphology is consistent with the high levels of compaction inferred from the preservation of fossils

evidence for widespread aqueous sedimentation in the northern plains of mars high resolution imaging data sets were used to identify and investigate a discrete stratigraphic unit exposed in the walls of impact craters throughout chryse and acidalia planitiae mars the unique morphology and spectral signatures observed in this unit which include fine scale layering lensing pinching and elevated hydration signatures all indicate that this material was deposited in a suite of aqueous environments furthermore this unit s widespread distribution and relationship to regional topography suggests an origin from the circum chryse outflow channels while earlier studies have suggested that large quantities of outflow channel effluents are located throughout this region this analysis is the first to identify and characterize the outcrop scale morphology and spatial distribution of this extensive unit these observations imply that the northern plains of mars served as a global depocenter for immense volumes of water and sediment early in martian history

configuration of the moho discontinuity beneath the japanese islands derived from three dimensional seismic tomography abstract the mohorovicic discontinuity moho is defined on the basis of an abrupt increase in seismic velocity in the lithosphere which has been observed using seismic refraction and receiver function analysis methods worldwide moho depth varies regionally and remains a fundamental parameter of crustal structure we present a new method of mapping the moho using a 3d seismic tomography model since the tomographic method cannot locate discontinuities we treat the moho as a zone of high velocity gradient maximum lower crust minimum upper mantle p wave velocities in japan are known to be 7 0 km s and 7 5 km s respectively we map the residual between isovelocity surfaces of 7 0 km s and 7 5 km s to find areas where the residual is small the separation between the surfaces is narrow and the velocity gradient is high the moho is best constrained where the isovelocity surfaces are close together and under much of japan they are 10 km apart we chose an isovelocity surface of 7 2 km s as a representative moho proxy in these areas our resulting moho map under japan compares favorably with existing regional moho models that were obtained from controlled source seismic investigations the moho varies from shallow 25 30 km to deep 30 km and this variability relates to the structural evolution of the japanese islands the opening of the sea of japan back arc ongoing arc arc collisions at the hidaka and izu collision zones ongoing back arc extension in kyushu and a possible failed back arc extensional event of mesozoic age it is apparent that the moho is less well constrained in areas where the crustal structure has been modified by magmatic activity or thickened due to arc arc collision

greenschist facies metamorphism of the burgess shale and its implications for models of fossil formation and preservation metamorphosed silty mudstones of the burgess shale and stephen shale formations record a poly metamorphic history an early greenschist facies event associated with burial by paleozoic strata produced a nearly ubiquitous bedding parallel cleavage s1 tectonic exhumation during the formation of the southern canadian rocky mountains produced a domainal subgreenschist facies retrograde overprint in which a high angle crenulation cleavage s2 was developed whereas all rocks have experienced these two events the degree of deformation and fossil pre servation varies with position relative to the cathedral escarpment this paleosubmarine cliff resulted in a zone of reduced deformation within adjacent strata by buttressing them during burial and deflecting deformation during orogenesis fossil bearing strata are composed of a typical greenschist assemblage of muscovite chlorite quartz albite are devoid of clays and contain an average of 0 28 organic carbon this typical metamudstone assemblage is consiste

basement configuration of the jhagadia rajpipla profile in the western part of deccan syneclise india from travel time inversion of seismic refraction and wide angle reflection data abstract 2 d velocity structure up to the basement is derived by travel time inversion of the first arrival seismic refraction and wide angle reflection data along the sw ne trending jhagadia rajpipla profile located on the western part of deccan syneclise in the narmada tapti region the study region is mostly covered by alluvium inversion of refraction and wide angle reflection data reveals four layered velocity structure above the basement the first two layers with p wave velocities of 1 95 2 3 km s 1 and 2 7 3 05 km s 1 represent the recent and quaternary sediments respectively the thickness of these sediments varies from 0 15 km to 3 4 km the third layer with a p wave velocity of 4 8 5 1 km s 1 corresponds to the deccan volcanics whose thickness varies from 0 5 km to 1 0 km presence of a low velocity zone lvz below the high velocity volcanic rocks in the study area is inferred from the travel time skip and amplitude decay of the first arrival refraction data and the wide angle reflection from top of the lvz present immediately after the first arrival refraction from deccan trap layer the thickness of the low velocity mesozoic sediments varies from 0 3 km to 1 7 km the basement with a p wave velocity of 5 9 6 15 km s 1 lies at a depth of 4 9 km near jhagadia and shallows to 1 2 km towards northeast near rajpipla the results indicate presence of low velocity mesozoic sediments hidden below the deccan trap layer in the western part of the deccan syneclise

assessment of crustal velocity models using seismic refraction and reflection tomography two tomographic methods for assessing velocity models obtained from wide angle seismic traveltime data are presented through four case studies the modelling inversion of wide angle traveltimes usually involves some aspects that are quite subjective for example 1 identifying and including later phases that are often difficult to pick within the seismic coda 2 assigning specific layers to arrivals 3 incorporating pre conceived structure not specifically required by the data and 4 selecting a model parametrization these steps are applied to maximize model constraint and minimize model non uniqueness however these steps may cause the overall approach to appear ad hoc and thereby diminish the credibility of the final model the effect of these subjective choices can largely be addressed by estimating the minimum model structure required by the least subjective portion of the wide angle data set the first arrival times for data sets with moho reflections the tomographic velocity model can be used to invert the pmp times for a minimum structure moho in this way crustal velocity and moho models can be obtained that require the least amount of subjective input and the model structure that is required by the wide angle data with a high degree of certainty can be differentiated from structure that is merely consistent with the data the tomographic models are not intended to supersede the preferred models since the latter model is typically better resolved and more interpretable this form of tomographic assessment is intended to lend credibility to model features common to the tomographic and preferred models four case studies are presented in which a preferred model was derived using one or more of the subjective steps described above this was followed by conventional first arrival and reflection traveltime tomography using a finely gridded model parametrization to derive smooth minimum structure models the case studies are from the se canadian cordillera across the rocky mountain trench central india across the narmada son lineament the iberia margin across the galicia bank and the central chilean margin across the valparaiso basin and a subducting seamount these case studies span the range of modern wide angle experiments and data sets in terms of shot receiver spacing marine and land acquisition lateral heterogeneity of the study area and availability of wide angle reflections and coincident near vertical reflection data the results are surprising given the amount of structure in the smooth tomographically derived models that is consistent with the more subjectively derived models the results show that exploiting the complementary nature of the subjective and tomographic approaches is an effective strategy for the analysis of wide angle traveltime data

interference of long period seismic wavefield observed by the dense hi net array in japan 1 in order to recover small signals of long period ground motions recorded by a short period seismometer we designed a time domain recursive filter that simulates seismic waves recorded with broadband seismometers we applied the time domain filter to seismograms recorded by the dense hi net array which consists of 800 stations at intervals of approximately 20 km the effectiveness of the time domain filter is demonstrated through the comparison of broadband waveforms obtained by the filter and sts 2 true broadband seismograms from the f net at the same site good agreement is observed between filtered and true broadband waveforms with high correlation coefficients for periods of up to 100 s for waveforms from the 2007 sumatra earthquake m7 9 which occurred approximately 5000 5800 km away from japan the applicability of the time domain filter to the recovery of long period signals from the record of a short period seismometer depends on the signal to noise ratio as a result a limited bandwidth of broadband signal is recovered for smaller earthquake from the spatiotemporal variation of the long period t 20 100 s wavefield obtained by the time domain filter we newly found an anomalous phase pattern of splitting of polarity along the wavefront particularly for the relatively short period band of from 20 50 s array analysis of the dense broadband waveforms revealed multipathing of the rayleigh waves which propagated toward central japan from two directions with slightly different slowness vectors the interference of two rayleigh waves caused such splitting of wavefield

deep seismic soundings along hirapur mandla profile central india summary the crustal depth section along hirapur mandla profile has been computed in two steps from deep seismic sounding dss data the shallow section up to the crystalline basement is derived by inverting first arrival refraction travel times the upper vindhyan sediments velocity 4 5 km s have a maximum thickness of about 1 5 km at bakshaho the lower vindhyan sediments velocity 5 4 km s were deposited north of narmadason lineament between katangi and narsinghgarh in a graben developed in crystalline basement the thickness of the lower vindhyans increases from north to south towards katangi and the depth to the basement reaches 5 5 km near jabera the depth to the moho boundary varies from 39 5 km near tikaria to 45 km at narsinghgarh the narrow block between katangi and jabalpur forms a horst feature which represents the narmada son lineament forming the southern boundary of the vindhyan basin two dimensional ray tracing was performed generating travel time curves from various shot points which were matched with observed travel time data

interpretation of first arrival travel times in seismic refraction work the necessary condition for the seismic refraction method to succeed is that the refracted first arrivals from each layer in a multilayered earth system should be detected on a seismogram as first arrivals and this is possible only when velocities of all underlying layers are successively greater the usual procedure to interpret the refraction travel times is to fit such a data set with several intersecting straight lines by employing a visual technique which may lead to errors of subjective judgment as the velocity model depends on the selection of various line segments through the data to remove the visual fit we propose here a layer stripping method based on minimum intercept time apparent velocity rms residual and maximum data points by least squares fitting to yield several intersecting straight lines once data are segmented out the conventional equations can be used to determine the velocity structure

invariant geodynamical information in geometric geodetic measurements summary repeated geodetic measurements have been used to extract geodynamical quantities such as displacements velocities of movement and crustal strains historical geodetic networks especially those established before the space geodetic era were and still are very important in providing a unique insight into the local or regional historical deformation state of the earth for the geodetic network without a tie to an external reference frame free network adjustment methods have been widely applied to derive geodynamical quantities currently it is commonly accepted that absolute displacements cannot be uniquely determined from triangulation trilateration measurements but relative displacements can be found uniquely if the geodetic network is geometrically overdetermined see e g segall matthews 1988 strain tensors were derived using the coordinate method and were reported to be uniquely determined we have carried out a theoretical analysis of invariant geodynamical information in geometric geodetic observations and concluded 1 that relative displacements are not invariant quantities and thus cannot be uniquely determined from the geodetic network without a tie to an external reference frame and 2 the components of the strain tensors are not all invariant and thus cannot individually be determined uniquely from the network however certain combinations of strain components are indeed invariant and can be uniquely determined from geometric geodetic measurements the theory of invariant information is then applied to the analysis of the tokai first order triangulation trilateration network spanning an interval of more than 100 yr the results show that the normal and principal strains are significantly affected by the unknown scaling biases and orientation differences thus any attempt at geophysical interpretation of these quantities must be exercised with great care if the scaling bias and the orientation difference are small the shear strain is shown to be practically invariant the invariant analysis of the tokai network has also shown that a belt near shizuoka has been significantly deformed in the past 100 yr this has not been seen in any previous analysis of displacements and or strains

delineation of subtrappean mesozoic sediments in deccan syneclise india using travel time inversion of seismic refraction and wide angle reflection data 2 d shallow velocity structure is derived by travel time inversion of the first arrival seismic refraction and wide angle reflection data along the e w trending narayanpur nandurbar and n s kothar sakri profiles located in the narmada tapti region of the deccan syneclise deccan volcanic trap rocks are exposed along the two profiles inversion of seismic data reveals two layered velocity structures above the basement along the two profiles the first layer with a p wave velocity of 5 15 5 25 km s 1 and thickness varying from 0 7 1 5 km represents the deccan trap formation along the narayanpur nandurbar profile the trap layer velocity ranges from 4 5 to 5 20 km s 1 and the thickness varies from 0 95 to 1 5 km along the kothar sakri profile the second layer represents the low velocity mesozoic sediments with a p wave velocity of 3 5 km s 1 and thickness ranging from about 0 70 to 1 6 km and 0 55 to 1 1 km along the e w and n s profiles respectively presence of a low velocity zone lvz below the volcanic rocks in the study area is inferred from the travel time skip and amplitude decay of the first arrival refraction data together with the prominent wide angle reflection phase immediately after the first arrivals from the deccan trap formation the basement with a p wave velocity of 5 8 6 05 km s 1 lies at a depth ranging from 1 5 to 2 45 km along the profiles the velocity models of the profiles are similar to each other at the intersection point the results indicate the existence of a mesozoic basin in the narmada tapti region of the deccan syneclise

burgess shale type biotas were not entirely burrowed away burgess shale type biotas occur globally in the cambrian record and offer unparalleled insight into the cambrian explosion the initial phanerozoic radiation of the metazoa deposits bearing except

taphonomic study of ediacaran organic walled fossils confirms the importance of clay minerals and pyrite in burgess shale type preservation burgess shale type bst macrofossils and organic walled microfossils are preserved as carbonaceous compressions and may share similar taphonomic processes previous taphonomic investigations of carbonaceous compressions have primarily focused on the microchemistry of cambrian bst fossils but comparative data from organic walled microfossils were not available to address these issues we analyzed two organic walled taxa from the yangtze gorges area of the south china block chuaria an acritarch and vendotaenia a ribbon shaped fossil their abundance offers the opportunity for destructive microanalysis including petrography electron microscopy and elemental mapping on both bedding planes and in cross sections our data suggest that chuaria preservation is remarkably similar to bst fossils in that its vesicle walls are closely associated with clay minerals in addition like many bst macrofossils chuaria and vendotaenia are also closely associated with pyrite chuaria vesicles are often filled with framboidal pyrite and vendotaenia fossils are associated with sulfate partly derived from pyrite oxidation the comparative taphonomy of chuaria and vendotaenia and bst macrofossils indicates that the preservation of organic walled acritarchs may be aided by clay and pyrite mineralization and that these abundant microfossils may serve as proxies for uncovering in more detail the taphonomic histories of bst preservation

diminutive trace fossils in the chengjiang lagerstatte diminutive trace fossils described here have been well preserved in connection with certain pliable carapaces or skeletons of the chengjiang animals taphonomic evidence suggests that these traces were formed in situ the peculiar preservation indicates that some bilaterians of uncertain affinities seem to have been active at the burial site constituting an important group of the hidden majority of cambrian marine community this may be an essential feature closely associated with the palaeoecology and exceptional preservation of the cambrian fossil lagerstatten the rare preservation of such millimetre sized trace fossils raises further doubts about the timing of the initial benthic bilaterians by applying trace fossil evidence

crustal velocity inhomogeneities along the hirapur mandla profile central india and its tectonic implications abstract wide angle seismic and gravity data across the narmada son lineament nsl in central india are analyzed to determine crustal structure velocity inhomogeneities and hence constrain the tectonics of the lineament we present the 2 d crustal velocity structure from deep wide angle reflection data by using a ray trace inverse approach the main result of the study is the delineation of fault bounded horst raised to a subsurface depth 1 5 km and the moho upwarp beneath the nsl the crust below the basement consists of three layers with velocities of 6 45 6 7 6 2 6 5 and 6 7 6 95 km s and interface depths of about 5 5 8 7 14 17 and 18 23 km along the profile the low velocity 6 2 6 5 km s layer goes up to a depth of 5 km and becomes the thickest part 13 km while the overlying high velocity 6 45 6 7 km s layer becomes the thinnest 3 km and upper boundary lies at a depth of 1 5 km beneath the nsl the overall uncertainties of various velocity and boundary nodes are of the order of 0 12 km s and 1 40 km respectively the up lifted crustal block and the up warping moho beneath the nsl indicate that the north and south faults bounding the nsl are deeply penetrated through which mafic materials from upper mantle have been intruded into the upper crust gravity modeling was also undertaken to assess the seismically derived crustal features and to fill the seismic data gap the lateral and vertical heterogeneous nature of the structure and velocity inhomogeneities in the crust cause instability to the crustal blocks and played an important role in reactivation of the narmada south fault during the 1997 jabalpur earthquake

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

modeling of long period ground motions in the nankai subduction zone model simulation using the accretionary prism derived from oceanfloor local s wave velocity structures the accretionary prism in the subduction zone which consists of thick low velocity oceanic sediments significantly affects the propagation of seismic waves for shallow offshore earthquakes including large interplate earthquakes in order to simulate long period 5 s ground motions in the nankai subduction zone we constructed a three dimensional 3d seismic velocity structure model of the accretionary prism by interpolation extrapolation of local s wave velocity structures beneath 46 oceanfloor seismic stations donet which are deployed just above the accretionary prism off the southern kii and eastern shikoku regions we modeled local s wave velocity structures using a simple two parameter depth varying velocity function to investigate the effects of the accretionary prism on ground and seafloor motions we conducted numerical simulations of seismic wave propagation for three local earthquakes that occurred in southwestern japan the simulations reasonably reproduced the observed seismograms not only for the period ranges of the moment tensor inversion 50 s but also for the strong long period ground motions in the sedimentary basins 5 s especially in the region where donet stations are densely deployed since depth varying local s wave structures significantly improve the reproducibility of long period ground motions our modeling procedure is useful for modeling long period ground motions of local and regional offshore subduction zone earthquakes

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

evidence of underplating from seismic and gravity studies in the mahanadi delta of eastern india and its tectonic significance 1 we have imaged the crustal configuration of the mahanadi delta of eastern india by modeling both wide angle seismic and bouguer gravity data this delta has undergone several stages of rifting subsidence sedimentation and uplift it is one of the important gondwana sedimentary basins of india where widespread volcanic activity occurred during the early cretaceous along the rift zones this volcanic activity corresponds to the breakup of greater india from east gondwana e g present antarctica and australia we have derived a five layer crustal model with velocities of 6 0 6 5 6 0 7 0 and 7 5 km s having estimated densities of 2 7 2 8 2 65 2 9 and 3 05 g cm3 respectively the velocity density relation along with heat flux and other geological geochronological information indicates typical rift related evolution of the delta with a midcrustal low velocity 6 0 km s and low density 2 65 g cm3 zone and a 10 km thick high velocity 7 5 km s and high density 3 05 g cm3 layer at the base of the crust presumably due to underplating the moho upwarping or crustal thinning in the rift zone and emplacement of thick high velocity material at the base of the crust strongly suggests basaltic underplating probably due to the kerguelen hot spot activity these activities are synchronous with 117 ma rajmahal volcanism in northeast india and the lambert graben in east antarctica and are closely associated with the gondwana breakup in the india antarctica sector the rifting stages are closely correlated with the sedimentation phases of the lower and upper gondwana deposits in the mahanadi delta which evolved parallel to the lambert graben in east antarctica

a general inversion scheme for source site and propagation characteristics using multiply recorded sets of moderate sized earthquakes abstract we derive an inversion scheme that fits the logarithms of seismic body wave spectra to 2 source shapes conditioned by anelastic attenuation with a frequency independent q the residuals from this fit are then projected onto the set of sources and sites with the source terms damped to estimate residual source spectra and site response spectra this two part inversion process is iterated until the square of the residuals summed over frequency for all recordings is minimized the absolute amplitudes of the source and site spectra are determined by fitting the site response spectra to estimates of the site amplification derived from geotechnical data we apply this inversion process to three sets of recordings of loma prieta aftershocks the first data set contains s waves recorded both in the marina district and at nearby hard rock stations we constrain the site response using the s wave velocity measured in a nearby borehole the absolute site amplifications for the marina stations are 15 to 20 at 1 hz and 10 at 2 5 hz the other two data sets comprise the p and s wave recordings from 28 aftershocks ranging in size from m d 2 1 to 4 6 obtained at accelerograph sites near the epicentral area the p and s wave attenuations determined from the inversions are q 414 and 380 while the average near site attenuations are t 0 012 and 0 026 sec respectively the average ratio of the s to p wave seismic moments is 1 1 0 1 the ratio of the p to s wave corner frequencies is 1 24 0 11 and the ratio of s to p wave radiated energy is 13 9 3 2 the brune stress drops for these aftershocks range from 8 to 800 bars the largest earthquakes exhibit the largest stress drops but there is no apparent dependence of stress drop on seismic moment for earthquakes with 10 19 m 0 21 dyne cm

the evolution of the vindhyan basin vis a vis the narmada son lineament central india from deep seismic soundings abstract the evolution of the vindhyan basin has been studied from deep seismic soundings block tectonics appear to be active throughout the geological history in this region the crust is divided into four major blocks by deep faults at narsinghgarh katangi and jabalpur the crustal block between narsinghgarh and katangi forms a graben in the crystalline basement giving rise to the great vindhyan basin in which precambrian vindhyan sediments of about 5 5 km thickness are deposited the crustal block between katangi and jabalpur is a horst block which represents the narmada son lineament a crustal depth section obtained from wide angle reflections shows a large number of reflector segments up to the mono boundary indicating crustal heterogeneity the boundary faults at the northern and the southern ends of the vindhyan basin extend up to the moho the crustal thickness varies from 39 5 to 45 km

preservational modes in the ediacaran gaojiashan lagerstatte pyritization aluminosilicification and carbonaceous compression abstract burgess shale type bst fossils often are preserved as two dimensional carbonaceous compressions sometimes aided by two mineralization processes pyritization and aluminosilicification defined by a thin and sometimes localized coating of authigenic pyrite or aluminosilicate minerals on the carbonaceous materials here we report similar mineralization modes within the late ediacaran gaojiashan lagerstatte of southern shaanxi province south china examination of two common gaojiashan fossils conotubus hemiannulatus and gaojiashania cyclus hereafter referred by generic names only indicates that pervasive pyritization is the primary taphonomic pathway in this deposit responsible for the preservation of 80 of the collected fossils pervasive pyritization of gaojiashan fossils results in their three dimensional preservation as opposed to two dimensional carbonaceous compression with thin pyrite coatings seen in some bst lagerstatte however microscale investigation using environmental scanning electron microscopy esem and energy dispersive x ray spectroscopy eds shows that some flattened specimens of conotubus and gaojiashania are preserved as carbonaceous compressions which are in some cases associated with aluminosilicate minerals rare compressed specimens of conotubus are replicated by greenish clay minerals which are interpreted as diagenetic products of aluminosilicate precursors our taphonomic analysis shows that pervasive authigenic pyritization tends to replicate more labile tissues than aluminosilicate aided carbonaceous compression but both pyritization and aluminosilicification processes can facilitate the replication and preservation of soft bodied organisms in siliciclastic sediments building upon this conclusion we propose that multiple taphonomic processes including kerogenization or polymerization of organic molecules pyritization and aluminosilicification can contribute to the mode of bst preservation viewed in this light various siliciclastic hosted lagerstatten that are facilitated by kerogenization pyritization and aluminosilicification can be plotted on a ternary diagram based on the relative importance of these taphonomic processes

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

in situ benthos and paleo oxygenation in the middle cambrian burgess shale british columbia canada the middle cambrian burgess shale was deposited under variable levels of oxygenation during periods of oxygenation low diversity shell beds were formed and the muds were colonized by infauna under these circumstances pyrite was restricted to anoxic microenvironments and formed small 1 mm discrete aggregated masses soft bodied organisms were preserved under low oxygen conditions typified by evenly dispersed pyrite and an absence of trace fossils and shell beds

geochemical evidence for oxygenated bottom waters during deposition of fossiliferous strata of the burgess shale formation abstract deciphering the oxygenation potential of bottom waters during deposition of the fossiliferous strata of the burgess shale is key to understanding the paleoecology of the organisms preserved as fossils and the processes involved in their preservation methods of paleo redox determination that are based upon trace fossils organic carbon content or size analysis of pyrite framboids are problematic when applied to the burgess shale fortunately patterns in redox sensitive trace elements hold great potential for determining paleo redox conditions for these greenschist facies rocks because they are independent of both age and metamorphic grade four burgess shale type bst fossil bearing sections were studied three lie within the burgess shale formation whereas one lies within the slightly younger duchesnay unit of the middle chancellor formation the geochemical proxies of seawater redox conditions that were used are mo u th v cr v v ni ni co and v sc each of these redox sensitive indices suggests that oxygenated conditions prevailed in the overlying seawater during deposition of beds within which bst preservation developed non fossiliferous beds at the base of the mt stephen trilobite beds yield three geochemical indices v v ni v sc ni co that indicate deposition under dysoxic to anoxic conditions thus the only beds to have been deposited under anoxic conditions are barren of fossils of soft bodied taxa further contradicting the notion that bottom water anoxia is a factor in bst preservation the laminated nature of the burgess shale and evidence for subsurface anoxia coupled with evidence for oxygenated bottom waters presence of bacterial mats and surficial trace fossils suggest that the burgess shale was deposited in the exaerobic zone oxic anoxic boundary at the water sediment interface implications of this reinterpretation of the depositional environment of the burgess shale include 1 taphonomic models for bst preservation must account for the presence of oxygen in bottom waters 2 paleoecological interpretations of the burgess shale need to account for a probable autochthonous benthic component in what is a complex assemblage of fossils that includes elements derived from the platform and 3 the possibility of burgess shale communities based upon chemosynthesis and or bacteria grazing must be considered

the paleoredox setting of burgess shale type deposits abstract burgess shale type bst biotas occur globally in lower and middle cambrian shales and were preserved under specific and exceptional circumstances among the circumstances surrounding fossilization benthic redox conditions have been the subject of particular disagreement while most authors have assumed that the sites of preservation were anoxic and therefore inhospitable to metazoans several have recently argued that bst assemblages were preserved in situ under habitable benthic conditions here we use field and laboratory intensive fine scale methods to investigate the paleoredox settings of fossil assemblages in two burgess shale type deposits the wheeler and marjum formations of western utah cambrian series 3 and review recently published data for other principal burgess shale type deposits in the wheeler and marjum formations fossil assemblages and ichnofabrics were evaluated at the millimeter scale an ichnological model was then applied to reconstruct relative paleo oxygen content of bottom waters at a bed to bed scale through multiple intervals sampled continuously this approach permits fine scale evaluation of the relationships of discrete fossil assemblages to paleoredox conditions over 7800 individual beds were logged in this study these data demonstrate that the wheeler and marjum formations were deposited under dynamic benthic redox conditions in both deposits beds representing deposition under dysoxic conditions may be interbedded at the millimeter centimeter scale with those representing deposition under anoxic conditions although the beds deposited under both types of redox conditions may be richly fossiliferous the distribution of fossil assemblages within the wheeler and marjum formations was regulated by dissolved oxygen content of bottom waters as a first order control bst preservation occurs within a microfacies inferred to represent deposition under anoxic conditions and contains transported fossils along a recognizable proximal distal gradient under dysoxic benthic conditions assemblages of skeletonized body fossils dominated by trilobites occur in both formations in the wheeler formation the junction of these two benthic redox environments is characterized by dense monospecific associations of the opportunistic trilobite elrathia kingii but a comparable exaerobic taxon does not appear to be present in the marjum formation these results demonstrate the control of near bottom anoxia over preservation of bst assemblages in both formations and are consistent with the findings from the burgess shale and the chengjiang

seismic attenuation structure associated with episodic tremor and slip zone beneath shikoku and the kii peninsula southwestern japan in the nankai subduction zone the three dimensional seismic attenuation structure frequency independent q beneath southwestern japan was analyzed using t estimated by applying the s coda wave spectral ratio method to the waveform data from a dense permanent seismic network the seismic attenuation qp 1 structure is clearly imaged for the region beneath shikoku the kii peninsula and eastern kyushu at depths down to approximately 50 km at depths of 5 to 35 km the seismic attenuation structure changes at the median tectonic line and other geological boundaries beneath shikoku and the southwestern kii peninsula high qp zones within the lower crust of the overlying plate are found just above the slip regions at the centers of the long term slow slip events sses beneath the bungo and kii channels and central shikoku beneath central shikoku within the overlying plate a high qp zone bounded by low qp zones is located from the land surface to the plate interface of the subducting plate the high qp zone and low qp zones correspond to high vp and low vp zones of previous study respectively the boundaries of the high and low qp zones are consistent with the segment boundaries of tremors segment boundaries of short term sses these results indicated that the locations of the long and short term sses could be limited by the inhomogeneous distribution of the materials and or condition of the overlying plate which is formed due to geological and geographical process the heterogeneity of materials and or condition within the fore arc crust possibly makes an effect on inhomogeneous rheological strength distribution on the interface

mechanism for burgess shale type preservation exceptionally preserved fossil biotas of the burgess shale and a handful of other similar cambrian deposits provide rare but critical insights into the early diversification of animals the extraordinary preservation of labile tissues in these geographically widespread but temporally restricted soft bodied fossil assemblages has remained enigmatic since walcott s initial discovery in 1909 here we demonstrate the mechanism of burgess shale type preservation using sedimentologic and geochemical data from the chengjiang burgess shale and five other principal burgess shale type deposits sulfur isotope evidence from sedimentary pyrites reveals that the exquisite fossilization of organic remains as carbonaceous compressions resulted from early inhibition of microbial activity in the sediments by means of oxidant deprivation low sulfate concentrations in the global ocean and low oxygen bottom water conditions at the sites of deposition resulted in reduced oxidant availability subsequently rapid entombment of fossils in fine grained sediments and early sealing of sediments by pervasive carbonate cements at bed tops restricted oxidant flux into the sediments a permeability barrier provided by bed capping cements that were emplaced at the seafloor is a feature that is shared among burgess shale type deposits and resulted from the unusually high alkalinity of cambrian oceans thus burgess shale type preservation of soft bodied fossil assemblages worldwide was promoted by unique aspects of early paleozoic seawater chemistry that strongly impacted sediment diagenesis providing a fundamentally unique record of the immediate aftermath of the cambrian explosion

the persistence of directivity in small earthquakes abstract we derive a simple inversion of peak ground acceleration pga or peak ground velocity pgv for rupture direction and rupture velocity and then test this inversion on the peak motions obtained from seven 3 5 m 4 1 earthquakes that occurred in two clusters in november 2002 and february 2003 near san ramon california these clusters were located on two orthogonal strike slip faults so that the events share the same approximate focal mechanism but not the same fault plane three earthquakes exhibit strong directivity but the other four earthquakes exhibit relatively weak directivity we use the residual pgas and pgvs from the other six events to determine station corrections for each earthquake the inferred rupture directions unambiguously identify the fault plane for the three earthquakes with strong directivity and for three of the four earthquakes with weak directivity the events with strong directivity have fast rupture velocities 0 63 v 0 87 the events with weak directivity either rupture more slowly 0 17 v 0 35 or bilaterally the simple unilateral inversion cannot distinguish between slow and bilateral ruptures adding a bilateral rupture component degrades the fit of the rupture directions to the fault planes by comparing pgas from the events with strong and weak directivity we show how an up dip rupture in small events can distort the attenuation of peak ground motion with distance when we compare the rupture directions of the earthquakes to the location of aftershocks in the two clusters we find than almost all the aftershocks of the three earthquakes with strong directivity occur within 70 of the direction of rupture

a mesoproterozoic supercontinent evidence from the indian shield abstract geophysical signatures of late paleoproterozoic collisional sutures fold belts between the deccan protocontinent and bundelkhand craton and between the bundelkhand and mewar cratons of the north indian shield are presented the aravalli and satpura orogenies evolved during these continent continent collision episodes both the orogenic episodes are associated with granulite facies metamorphism and metallogeny serpentinised ultramafic breccia in ophiolitic melange is present in both regions structural discontinuities and oppositely dipping reflection fabrics with high conductivity anomalies are the characteristic features of these collision zones a major gravity high is also observed all along the strike of these fold belts to a distance of 700 1000 km paleoproterozoic 1 8 2 1 ma ages corresponding to compressional activity have also been observed in the southern granulite terrain and other gondwana fragments extensive granites and gneisses of 1900 ma age are observed in the lower himalayas and nanga parbat ranges late paleoproterozoic orogenic activity is also observed in all of the earth s shields intense orogenic activity of this period observed in various widely separated cratonic blocks is related to global plate tectonic processes and supercontinental episodes the available geophysical evidences in various parts of the globe suggest the presence of a supercontinent referred to as columbia during the early mesoproterozoic period

shallow velocity structure along the hirapur mandla profile using traveltime inversion of wide angle seismic data and its tectonic implications summary in order to investigate the velocity structure and hence shed light on the related tectonics across the narmada son lineament traveltimes of wide angle seismic data along the 240 km long hirapur mandla profile in central india have been inverted a blocky laterally heterogeneous three layer velocity model down to a depth of 10 km has been derived the first layer shows a maximum thickness of the upper vindhyans 4 5 km s1 of about 1 35 km and rests on top of normal crystalline basement represented by the 5 9 km s1 velocity layer the anomalous feature of the study is the absence of normal granitic basement in the great vindhyan graben where lower vindhyan sediments 5 3 km s1 were deposited during the precambrian on high velocity 6 3 km s1 metamorphic rock the block beneath the narmada son lineament represents a horst feature in which high velocity 6 5 km s1 lower crustal material has risen to a depth of less than 2 km south of the lineament the deccan traps were deposited on normal basement during the upper cretaceous period and attained a maximum thickness of about 800 m

nonbiomineralized carapaces in cambrian seafloor landscapes sirius passet greenland opening a new window into early phanerozoic benthic ecology widespread microbial mats and the absence of significant bioturbation resulted in a poorly developed mixed layer and extensive cohesive substrates during the ediacaran cambrian transition large nonbiomineralized arthropod carapaces overprinted with trails interconnected burrow systems narrow caliber structures with dendritic terminations and annulated burrows are abundant in the early cambrian sirius passet lagerstatte greenland taphonomic controls were partially responsible for the pronounced association of these structures and carapaces but ecologic conditions are envisioned as playing a significant role although some trace fossils e g annulated structures may be related to scavenging and or deposit feeding morphologic evidence suggests that this is not always the case interconnected burrow systems provide evidence for re use of structures suggesting grazing on or farming of bacteria sulfur bacteria were probably abundant in cambrian sediments requiring a source of sulfur or sulfide and limited quantities of oxygen anoxic sediment provided a source of hydrogen sulfide whereas burrow outlets connected to the oxygenated sediment water interface carcasses and molds of nonbiomineralized organisms may have acted as attractors supporting a community of small invertebrates carapaces created a sharp boundary further decreasing oxygen diffusion into the sediment this steep oxygen gradient at the organic surface of the carapace promoted the growth of sulfur bacteria that could have served as the primary food for small macrofauna and meiofauna

diversity of fault zone damage and trapping structures in the parkfield section of the san andreas fault from comprehensive analysis of near fault seismograms summary we perform comprehensive analyses of trapped waves and signals of damaged fault zone rocks associated with time delays of body waves along the parkfield section of the san andreas fault saf waveforms generated by thousands of earthquakes and recorded by near fault stations in several permanent and temporary deployments are examined with attention to the possible influence of a lithology contrast across the fault on signals of the low velocity damage zone clear candidate trapped waves are identified at only three stations mmnb and two of the other near fault stations flip and pies further to the nw clear candidate trapped waves are not seen at any of the near fault stations to the se of mmnb the locations of the events generating good candidate trapped waves at mmnb and the other two stations are not distributed broadly in space but clustered in a small number of locations moreover events that generate clear candidate trapped waves at one station do not typically generate trapped waves at the other two stations these observations imply that the damage zone is highly variable along strike and that a coherent connected waveguide does not exist for distances along strike larger than at most 3 5 km the distance between stations synthetic waveform fits for observed trapped waves at stations mmnb and flip indicate that the most likely parameters of the trapping structures at these locations are widths of about 150 m depths of about 3 km velocity reductions of 30 40 per cent and q values of 10 40 synthetic calculations of trapped waves demonstrate that if there is a contrast of seismic velocity across the fault the trapped waves are delayed relative to the s wave arrival trapped waves at station mmnb and to a lesser extent also at stations flip and pies in the nw section show this characteristic this suggests a lithology contrast in the top few km at these locations in agreement with results from tomography and studies of head waves in the parkfield area at several mini across fault arrays where trapped waves are not observed a low velocity damage zone is detected from the delay in the arrival time of body wave phases relative to a nearby off fault station the observed delay of the s wave is greater than the p wave delay consistent with the existence of a damage zone with poisson ratio of about 0 33 the observations of time delays without trapped waves indicate that parts of the damage zone are insufficiently coherent to generate trapped waves a broader damage zone may exist in the region between the saf and the south west fracture zone the results highlight the diversity of damage structures along the 40 km of the saf examined in this study and imply that fault imaging based on data at single sites does not necessarily apply to a larger section

residence time of diffuse waves in the crust as a physical interpretation of coda q application to seismograms recorded in mexico summary we consider a simple model for elastic wave propagation in the earth s litho sphere consisting of a heterogeneous and scattering crust overlying a homogeneous mantle that is we neglect backscattering from the upper mantle this rough condition is not strictly valid everywhere but this model allows us to investigate the effects of variations of diffracting properties between crust and mantle on the coda decay the free parameters describing the wave propagation are the mean free path of the waves and the intrinsic absorption in the crust in the framework of the radiative transfer theory we treat accurately jumps in s wave speed and the mean free path at the moho without intrinsic absorption this configuration yields a synthetic coda decay 1 texp 2 ft qc a form similar to that proposed by aki chouet 1975 to parametrize the observations the exponential decay in our purely elastic model is due to the partial leakage of diffuse energy into the mantle in order to test the applicability of our model we have determined the coda q parameter qc in the 1 15 hz frequency band from data recorded at four stations in mexico in the low frequency regime around 1 hz we suggest that the energy leakage significantly affects coda q whilst at higher frequencies around 10 hz the anelastic attenuation dominates a weak intrinsic absorption expressed by a frequency independent parameter qi of about 1000 accounts satisfactorily for the observed qc values in the whole frequency range our very simple model has only two free parameters and offers an attractive alternative physical interpretation of coda q in mexico this model is sufficient to interpret the coda observations according to our model in regions where the mean free path is much larger than the crustal thickness weakly heterogeneous crust the leakage effect should be small and the observed qc will mainly be due to the intrinsic absorption on the other hand when the mean free path is of the order of the crustal thickness strongly heterogeneous crust we predict a strong sensitivity of the decay rate of the coda to the crustal thickness this dependence may be important for the interpretation of the regional variations of coda q we propose introducing a new parameter d the residence time of diffuse energy in the crust which is physically more meaningful than a quality factor to quantify the leakage effect

a genetic link between konzentrat and konservat lagerstatten in the fezouata shale lower ordovician morocco abstract in the central anti atlas morocco zagora region the fezouata shale has yielded an extraordinary fossil lagerstatte documenting the initial stages of the great ordovician biodiversification event this lagerstatte contains abundant and exceptionally well preserved fossils epf exhibiting soft bodied preservation as well as hard mineralized parts of extinct organisms while soft bodied preservation in the fezouata shale is confined to a few stratigraphic intervals other fossiliferous intervals contain only shelly fossils in sandstone lenses sl placed in the context of a previously established depositional model epf are interpreted as autochthonous assemblages buried by storm deposits close to storm wave base there the current component of storms is reduced compared to proximal settings and weak oscillation is dominant resulting in the record of oscillation ripples in contrast bioclastic accumulations were generated upslope in shallower more proximal lower shoreface environments there the current component of storms was significant as suggested by the disarticulation of skeletal remains bioclastic materials are localized in sl which are lenses a few tens of centimeters in thickness and a few meters in width and length these lenses commonly display erosive bases and convex tops resulting in a lobate or a channel lobe morphology a large amount of sediment was thus rapidly deposited resulting in the rapid burial of allochthonous material across a strongly localized surface of the sea floor integrating both sedimentological and paleontological evidence intervals yielding epf are considered as konservat lagerstatten ksl in contrast with bioclastic accumulations defined as konzentrat lagerstatten kzl thus ksl assemblages are interpreted to approximate biocenoses in which organisms experienced rapid burial by distal tempestites while kzl assemblages more likely correspond to thanatocenoses locally deposited by storm back currents here a genetic link between ksl and kzl is suggested within the fezouata shale both types of lagerstatten were related to storm activity but at different depths

distortion of the apparent s wave radiation pattern in the high frequency wavefield tottori ken seibu japan earthquake of 2000 summary the distortion properties of the apparent s wave radiation pattern in the high frequency seismic wavefield of over f 2 hz is investigated using a large number of waveform records of the main shock and 29 aftershocks of the tottori ken seibu japan magnitude mw 6 6 earthquake in 2000 the dense seismic records from the kik net strong motion network show a clear four lobe pattern in the apparent s wave radiation pattern in the low frequency wavefield of f 2 hz and shows an almost isotropic distribution in all directions as the frequency increases above 5 hz the distortion of the apparent s wave radiation pattern in the high frequency wavefield increases as travel distance increases therefore the path effect caused by the scattering of seismic waves due to small scale heterogeneities in the crust is a major cause of distortion of the radiation pattern this hypothesis is examined by a 2 d finite difference method simulation of seismic waves in heterogeneous structure models the results of simulations clearly demonstrate the collapse of the s wave front due to seismic wave scattering in the heterogeneous structure by comparing the observed wavefield and the results of simulations using different sorts of stochastic heterogeneous models the most preferable model that can explain the observation is described by a von karman autocorrelation function with correlation distance of a 3 5 km order of 0 5 and rms value of e 0 07 however our simple stochastic random heterogeneity model proposed herein somewhat overestimates the scattering of low frequency signals below 2 hz

ground motion in the presence of complex topography earthquake and ambient noise sources to study the influence of topography on ground motion eight seismic recorders were deployed for a period of one year over poverty ridge on the east side of the san francisco bay area california this location is desirable because of its proximity to local earthquake sources and the significant topographic relief of the array 439 m topographic amplification is evaluated as a function offrequency using a variety of methods including reference site based spectral ratios and single station horizontal to vertical spectral ratios using both shear waves from earthquakes and ambient noise field observations are compared with the predicted ground motion from an accurate digital model of the topography and a 3d local velocity model amplification factors from the theoretical calculations are consistent with observa tions the fundamental resonance of the ridge is prominently observed in the spectra of data and synthetics however higher frequency peaks are also seen primarily for sources in line with the major axis of the ridge perhaps indicating higher resonant modes excitations of lateral ribs off of the main ridge are also seen at frequencies consistent with their dimensions the favored directions of resonance are shown to be transverse to the major axes of the topographic features

a new burgess shale type assemblage from the thin stephen formation of the southern canadian rockies a new burgess shale type assemblage from the stephen formation of the southern canadian rocky mountains is described herein it occurs near stanley glacier in kootenay national park 40 km southeast of the type area near field british columbia while at least a dozen burgess shale localities are known from the thick stephen formation the stanley glacier locality represents the first discovery of burgess shale type fossils from the thin stephen formation the cathedral escarpment an important regional paleotopographic feature has been considered important to the paleoecologic set ting and the preservation of the burgess shale biota however the stanley glacier assemblage was preserved in a distal ramp setting in a region where no evidence of an escarpment is present the low diversity assemblage contains eight new soft bodied taxa including the anomalocaridid stanleycaris hirpex n gen n sp new genus new species pelagic or nektobenthic predators represent the most diverse group whereas in relative abundance the assemblage is dominated by typical cambrian shelly benthic taxa the low diversity of both the benthic taxa and the ichnofauna which includes diminutive trace fossils associated with carapaces of soft bodied arthropods suggests a paleoenvironment with restrictive conditions the stanley glacier assemblage expands the temporal and geographic range of the burgess shale biota in the southern canadian rockies and suggests that burgess shale type assemblages may be common in the thin ste phen formation which is regionally widespread

sequence stratigraphy cyclic facies and lagerstatten in the middle cambrian wheeler and marjum formations great basin utah abstract recurrent taphofacies including conservation lagerstatten are identified within a spectrum of facies in fourth order sequences in the middle cambrian wheeler and marjum formations of the drum mountains and house range west central utah these sequences are 3 20 m thick and commence with sharply based compact oncolitic oolitic or pelletal pack and grainstones with sharply defined corroded and mineralized upper contacts that record drowning discontinuities and early transgressive systems tracts tsts overlying intervals of calcareous shale and thin bedded wacke to packstones with abundant disarticulated polymerid and agnostoid trilobites represent late tsts these are commonly followed by lavender gray mudstones rich in sponge spicules and comminuted fossil debris that reflect condensed maximum flooding zones the overlying early highstand hst intervals of black fissile shales are typically barren except for indistinct circular carbonized algae but in rare instances include soft bodied animal remains a combination of lower dysoxic anoxic conditions with a fluctuating oxycline and relatively rapid episodic influx of fine grained detrital sediment favored repeated burial and preservation of abundant organic detritus and rarely soft bodied animals interbedded dark gray shales include abundant articulated agnostoid trilobites and diminutive polymerids e g jenkinsonia overlying platy calcareous bedding planes covered with articulated bodies and molts of the polymerid elrathia indicate rapid blanketing of undisturbed seafloors by calcareous mud layers these beds grade upward successively into interbedded sparsely fossiliferous platy to flaggy shale and thin pale gray weathering calcisiltites and burrow mottled to nodular limestones recording late hst to falling stage fsst carbonate shedding thin calcisiltites include fossil debris and articulated larger polymerid trilobites and the eocrinoid gogia preserved by obrutionary deposits the repeated recurrence of these patterns provides the rudiments of a predictive model that not only explains the differing modes of preservation but may also aid in prospecting for new lagerstatten

upper crust of the archean dharwar craton in southern india as revealed by seismic refraction tomography and its geotectonic implications s u m m a r y imaging shallow crustal structure is essential to extend the geological information from surface mapping to a depth and to develop tectonic models we applied seismic tomography modelling to refraction data acquired along a 200 km long line in the dharwar craton of the indian shield and we derived a crustal velocity model that was evaluated with checkerboard tests to demonstrate the reliability of the model we also tested the model for artefacts upper crustal velocities vary between 5 7 and 6 4 km s 1 and are determined to 10 km depth probably due to very low velocity gradients in the upper crust undulating high and low velocities in the top layers of the crust are terminated at a depth of 7 8 km consistent with a probable detachment we interpret the undulating upper crustal velocity layers to represent a fold thrust belt structure that developed during a collision in a transpressional tectonic regime consistent with themodel of chadwick et al which suggests oblique convergence and accretion of two crustal blocks in the region the velocity structure also correlates reasonably well with the distinct geological units we interpret relatively low velocities between the undulating layers as representative of faults that bound various tectonic domains

taphonomic traits of clay hosted early cambrian burgess shale type fossil lagerstatten in south china abstract the chengjiang and guanshan fossil lagerstatten of yunnan represent key fossil deposits to understand and reconstruct early metazoan evolution despite extensive studies on the systematics of taxa from these lagerstatten the major mechanisms of exceptional soft tissue preservation at these fossil lagerstatten have remained controversial the chengjiang and guanshan fossil lagerstatten represent typical burgess shale type deposits influenced by late alteration and weathering that led to some major transformations in clay and iron minerals as well as dissolution of dolomite and skeletal biominerals the detailed geochemical screening of various fossil groups such as brachiopods priapulids arthropods and sponges indicates a more complex preservational history than hitherto supposed besides oxidation processes during sub recent recent weathering clay mineral formation and or alteration carbonization phosphatization and pyritization played key roles in the preservation of various metazoans the chengjiang fossil lagerstatte is characterized by the existence of clay dominated background beds bgbs and event beds ebs fossil preservation varies considerably in the two different depositional settings with soft tissue preservation occurring preferentially in ebs whereas skeletal accumulations are typical of bgbs the samples were analyzed and classified into three groups with different degrees of alteration and fundamentally different chemistries the specific clay mineral composition shows increasing chlorite and goethite decreasing kaolinite 2m1 mica and dolomite and a rise in the chemical alteration of mudstones it also indicates slight variations between the primary types of beds eb bgb hinting at variations in the source of clastics or the hydrochemical environment during the deposition of strata furthermore the geochemical paleoredox proxy data indicate that dysoxic or anoxic conditions were not permanently present during the deposition of ebs and bgbs in the chengjiang and guanshan fossil lagerstatten we consider that rapid deposition in finest claystones had a greater influence on the preservation of highly volatile tissues than the presence of bottom water anoxia even though bottom water anoxia and microbial sealing may further increase the probability of soft tissue preservation using different geochemical proxies such as various redox indicators and iron speciation statistics on framboid sizes classical geological observation and clay mineralogy we show that iron mineral precipitation onto organic carcasses of the chengjiang type fossils is mostly confined to later diagenetic processes and thus is not crucial for the early fixation of easily decayable tissues in burgess shale type faunas

nature of continental crust along the narmada son lineament inferred from gravity and deep seismic sounding data abstract the narmada son lineament nsl is a very prominent feature on the tectonic map of india and divides the indian peninsula into two parts the northern part characterised by lower elevations and more positive bouguer gravity anomalies as compared to the southern part the lineament is characterised by a gravity high practically all along its length four published deep seismic sounding dss profiles across the nsl give vital information concerning its origin an analysis of the bouguer gravity field along these profiles has been carried out using all available geological and velocity density information the analysis reveals that the areas immediately south of the nsl are characterised by higher density crust in comparison to the areas north of it this increase in density could have taken place during mesozoic to tertiary times when major tectonic volcanic activity took place over peninsular india the presence of deep seated faults sediments and anomalous crust shows that the lineament has some characteristics of a rift valley

three dimensional attenuation structure of intrinsic absorption and wide angle scattering of s waves in northeastern japan summary intrinsic absorption and random velocity inhomogeneities are important medium properties for studies on wave propagation at high frequency 1 hz in the lithosphere recent studies have shown that the spatial distribution of random velocity inhomogeneities can be estimated by an inversion analysis of peak delay times where the peak delay time is the time lag between direct wave onset and its maximal amplitude arrival this study estimates the 3 d structure of the s wave attenuation quality factor q 1 after we corrected the maximal amplitude attenuation due to multiple forward scattering on the basis of the markov approximation for parabolic wave equation even though this estimate of q 1 includes both intrinsic absorption and wide angle scattering the contribution of wide angle scattering can be identified by taking into account random inhomogeneities estimated in the peak delay time analysis the estimated q 1 structure in northeastern japan shows weak attenuation q 1 f 10 2 5f 0 5 on the forearc side of the volcanic front and strong attenuation q 1 f 10 2 3f 0 3 beneath the quaternary volcanoes and near the collision zone between the honshu and kuril arcs according to the born approximation the estimated q 1 at 0 40 km depth consists mainly of the intrinsic absorption if the characteristic scale of random inhomogeneities is 5 km or longer beneath the quaternary volcanoes of northeastern japan q 1 f shows weak frequency dependence and the power spectral density functions of random velocity inhomogeneities are characterized by a weak spectral gradient that means rich in small scale inhomogeneities these results demonstrate the importance of the frequency dependence of wave propagation in the lithosphere that is the scale dependence of velocity fluctuation or small scale inhomogeneities is an important property of the lithosphere underlying quaternary volcanoes

imaging the fault zones of the 2000 western tottori earthquake by a new inversion method to estimate three dimensional distribution of the scattering coefficient 1 we developed an inversion method to estimate the spatial variation of scattering coefficient from observed envelopes of s coda waves synthetic envelopes are calculated on the basis of the single scattering theory assuming double couple sources and a one dimensional depth dependent velocity structure in our algorithm we evaluated scattering attenuation taking spatial variation of scattering coefficient into consideration in order to model energy attenuation by passing through the localized anomalous zones with high scattering coefficients the inversion method was applied to the seismograms in and around the focal area of the 2000 western tottori earthquake with m 7 3 obtained results show that there exist several zones with large scattering coefficient zones lszs one of the most predominant lsz is located along and around the fault zone of the m 7 3 earthquake in the upper crust this lsz suggests the existence of damaged zones in the main shock fault within this lsz an exceptionally small scattering coefficient area was detected this area corresponds to an asperity with a large amount of coseismic slip of the main shock other prominent lszs are detected in the mid to lower crust below the northwestern part of the main shock fault in addition lszs are distributed in a seismic low velocity zone near quaternary volcanoes and near hypocenters of deep low frequency microearthquakes some of the imaged lszs are probably related to local concentration of fluid in the crust

moho depth variation beneath southwestern japan revealed from the velocity structure based on receiver function inversion abstract the philippine sea plate is subducting under the eurasian plate beneath the chugoku shikoku region southwestern japan we have constructed depth contours for the continental and oceanic mohos derived from the velocity structure based on receiver function inversion receiver functions were calculated using teleseismic waveforms recorded by the high density seismograph network in southwestern japan in order to determine crustal velocity structure we first improved the linearized time domain receiver function inversion method the continental moho is relatively shallow 30 km at the coastline of the sea of japan and at the seto inland sea and becomes deeper greater than 40 km around 35 n and 133 8 e near the seto inland sea a low velocity layer of thickness 10 km lies under the continental moho this low velocity layer corresponds to the subducting oceanic crust of the philippine sea plate the oceanic moho continues to descend from south to northwest and exhibits complicated ridge and valley features the oceanic moho runs around 25 km beneath the pacific coast and 45 km beneath the seto inland sea and it extends to at least to 34 5 n the depth variation of the moho discontinuities is in good qualitative agreement with the concept of isostasy from the configurations of both the continental and oceanic mohos we demonstrate that the continental lower crust and the subducting oceanic crust overlap beneath the southern and central part of shikoku and that a mantle wedge may exist beneath the western and eastern part of shikoku the southern edge of the overlapping region coincides with the downdip limit of the slip area of a megathrust earthquake

spatial distribution of seismic energy rate of tectonic tremors in subduction zones the sizes of deep tectonic tremors have never been accurately evaluated as a physical quantity here we estimate tremor size as the band limited seismic energy rate at 2 8 hz with accurate evaluation of the path attenuation and site amplification of seismic waves in four subduction zones nankai cascadia jalisco and south chile the size frequency statistics of seismic energy rate which are characterized by the median measure for each subregion are spatially variable the spatial variations are categorized into three types with each type corresponding to a different tremor migration behavior in type a regions where tremor zone is wider seismic energy rates are highly variable in the dip direction and tremor activities are usually initiated in the less energetic tremor zone some of them further penetrate into the energetic tremor zone and subsequently migrate for long distances in the strike direction type b regions are characterized by relatively narrow tremor zones minor variations in energy rates in the dip direction and long distance migration in the strike direction type c regions are characterized by isolated clusters of tremor activities without migration and by independent failure of each small tremor cluster given that the spatial distributions of tremor energy rates reflect heterogeneities in the strength of the plate interface such distributions which would be controlled by the width of tremor zone may determine the regional style of slow earthquake behavior some energetic tremor regions act as switches that trigger large slow slip events especially in type a regions

seismic and tsunami wave propagation of the 2011 off the pacific coast of tohoku earthquake as inferred from the tsunami coupled finite difference simulation abstract the 2011 tohoku earthquake m 9 0 caused significant hazards including strong ground motion coseismic ground deformation and tsunamis for a deeper understanding of these phenomena we conducted a large scale parallel computer simulation by means of the finite difference method fdm with newly developed tsunami coupled equations of motion this method is based on the equations of motion for an elastic medium treating seawater as elastic material having zero s wave velocity tsunami waves are included by taking into account gravity and their equilibrium with the pressure gradient an effective method of fdm simulation using the state of the art massively parallelized k computer is also studied with the use of a 3d layered velocity structure that includes topography and bathymetry basement structure moho depth and plate boundaries and use of the appropriate source rupture model based on joint inversion of seismic waves and geodetic observations the simulated seismic waves demonstrate anomalous seismic wave propagation by the thick 3d basin structure inland we also found that the sea column acts as a strong absorber of seismic waves for shallow up dip slip on the ocean side coseismic deformation and tsunamis are dynamically generated in this simulation tsunami attacks on the subsided pacific coast are simulated without any additional assumptions we also modeled the tsunami and seismic records of ocean bottom pressure gauges above the fault because sea bottom tsunami and seismic observation is powerful but very complex recording both seismic and tsunami waves the use of these coupled numerical simulations has great potential for resolving complex source fault rupture processes in a 3d heterogeneous structure online material mpeg movies of fault slip seismic wave propagation seafloor and ground displacement and tsunamic propagation

detailed fault structure of the 2000 western tottori japan earthquake sequence we investigate the faulting process of the aftershock region of the 2000 western tottori earthquake m w 6 6 by combining aftershock hypocenters and moment tensor solutions aftershock locations were precisely determined by the double difference method using p and s phase arrival data of the japan meteorological agency unified catalog by combining the relocated hypocenters and moment tensor solutions of aftershocks by broadband waveform inversion of freesia f net we successfully resolved very detailed fault structures activated by the mainshock the estimated fault model resolves 15 individual fault segments that are consistent with both aftershock distribution and focal mechanism solutions rupture in the mainshock was principally confined to the three fault elements in the southern half of the zone which is also where the earliest aftershocks concentrate with time the northern part of the zone becomes activated which is also reflected in the postseismic deformation field from the stress tensor analysis of aftershock focal mechanisms we found a rather uniform stress field in the aftershock region although fault strikes were scattered the maximum stress direction is n107 e which is consistent with the tectonic stress field in this region in the northern part of the fault where no slip occurred during the mainshock but postseismic slip was observed the maximum stress direction of n130 e was possible as an alternative solution of stress tensor inversion

slip history and dynamic implications of the 1999 chi chi taiwan earthquake we investigate the rupture process of the 1999 chi chi taiwan earthquake using extensive near source observations including three component velocity waveforms at 36 strong motion stations and 119 gps measurements a three plane fault geometry derived from our previous inversion using only static data ji et al 2001 is applied the slip amplitude rake angle rupture initiation time and risetime function are inverted simultaneously with a recently developed finite fault inverse method that combines a wavelet transform approach with a simulated annealing algorithm ji et al 2002b the inversion results are validated by the forward prediction of an independent data set the teleseismic p and sh ground velocities with notable agreement the results show that the total seismic moment release of this earthquake is 2 7 10 20 n m and that most of the slip occurred in a triangular shaped asperity involving two fault segments which is consistent with our previous static inversion the rupture front propagates with an average rupture velocity of 2 0 km s 1 and the average slip duration risetime is 7 2 s several interesting observations related to the temporal evolution of the chi chi earthquake are also investigated including 1 the strong effect of the sinuous fault plane of the chelungpu fault on spatial and temporal variations in slip history 2 the intersection of fault 1 and fault 2 not being a strong impediment to the rupture propagation and 3 the observation that the peak slip velocity near the surface is in general higher than on the deeper portion of the fault plane as predicted by dynamic modeling

scattering of trapped p and s waves in the hydrated subducting crust of the philippine sea plate at shallow depths beneath the kanto region japan

high resolution geochemical evidence for oxic bottom waters in three cambrian burgess shale type deposits abstract the cambrian radiation of complex animals is a fundamental event in the history of life on earth much of our understanding of this event is made possible through the study of exceptionally preserved fossils in burgess shale type bst deposits based on bioturbation levels in bst deposits they are often interpreted as representing restricted oxygen settings this study tests the low oxygen interpretation through analysis of geochemical paleoredox proxies and bioturbation levels in three bst deposits the early cambrian maotianshan shale china the middle cambrian wheeler shale usa and the middle cambrian spence shale usa results from 96 samples show fine scale geochemical evidence for oxic bottom water conditions during the deposition of these three bst deposits trace element paleoredox indices pi give consistent oxic signals in all three shales in addition total organic carbon toc and total sulfur ts levels in the spence shale are extremely low the average c s ratio is 3 1 comparable to values for modern oxic marine water bioturbation levels in all three shales are low with rare development of minimal to moderate horizontal bioturbation while short term oxygen fluctuations or poikiloaerobic conditions could still have sporadically existed in these settings this study shows that these bst deposits were deposited in a dominantly oxic paleoredox setting evidence for low bioturbation levels coupled with paleoredox geochemistry indicative of oxic bottom waters suggests that pervasive exaerobic conditions with an oxic water column positioned above oxygen depleted sediment pore waters may have existed in many cambrian bst deposit paleoenvironments