comparison of prestack stereotomography and nip wave tomography for velocity model building instances from the messinian evaporites velocity model determination during seismic data processing is crucial for any kind of depth imaging we compared two approaches of grid tomography prestack stereotomography and normal incidence point nip wave tomography whereas nip wave tomography is based on wavefield attributes obtained during the common reflection surface stack and thus on the underlying hyperbolic second order traveltime approximation prestack stereotomography describes traveltimes by local slopes i e linearly in the prestack data domain to analyze the impact of the different traveltime approximations and the different input data domains on velocity model building we applied two implementations of these techniques to two profiles of a field marine data set from the levante basin eastern mediterranean because ofthe presence of a thick tabular mobile unit of the messinian evaporites strong vertical and lateral velocity contrasts had been expected the velocity models revealed the reconstruction of high velocity contrasts

inside baleen exceptional microstructure preservation in a late miocene whale skeleton from peru exceptionally preserved delicate baleen microstructures have been found in association with the skeleton of a late miocene balaenopteroid whale in a dolomite concretion of the pisco formation peru microanalytical data scanning electron microscopy electron probe microanalysis x ray diffraction on fossil baleen are provided and the results are discussed in terms of their taphonomic and paleoecological implications baleen fossilization modes at this site include molding of plates and tubules and phosphatization a rapid formation of the concretion was fundamental for fossilization we suggest that the whale foundered in a soft sediment chemically favorable to rapid dolomite precipitation allowing the preservation of delicate structures morphometric considerations on the baleen plates and bristles coupled with the reconstructed calcification of the latter permit speculation on the trophic preferences of this balaenopteroid whale the densely spaced plates and the fine and calcified bristles provide evidence for feeding on small sized plankton as does the modern sei whale

image ray tomography abstract seismic tomography is a well established approach to invert smooth macro velocity models from kinematic parameters such as traveltimes and their derivatives which can be directly estimated from data tomographic methods differ more with respect to data domains than in the specifications of inverse problem solving schemes typical examples are stereotomography which is applied to prestack data and normal incidence point wave tomography which is applied to common midpoint stacked data one of the main challenges within the tomographic approach is the reliable estimation of the kinematic attributes from the data that are used in the inversion process estimations in the prestack domain weak and noisy signals as well as in the post stack domain occurrence of triplications and diffractions leading to numerous conflicting dip situations may lead to parameter inaccuracies that will adversely impact the resulting velocity models to overcome the above limitations a new tomographic procedure applied in the time migrated domain is proposed we call this method image incident point wave tomography the new scheme can be seen as an alternative to normal incidence point wave tomography the latter method is based on traveltime attributes associated with normal rays whereas the image incidence point wave technique is based on the corresponding quantities for the image rays compared to normal incidence point wave tomography the proposed method eases the selection of the tomography attributes which is shown by synthetic and field data examples moreover the method provides a direct way to convert time migration velocities into depth migration velocities without the need of any dix style inversion

3d tomographic velocity model estimation with kinematic wavefield attributes a tomographic inversion method is presented that uses kinematic information in the form of zero offset traveltimes and kinematic wavefield attributes first and second spatial traveltime derivatives to determine smooth laterally inhomogeneous 3d subsurface velocity models for depth imaging the kinematic wavefield attributes can be extracted from the seismic prestack data by means of the common reflection surface crs stack the input for the tomography is then taken from the resulting attribute volumes at a number of pick locations in the crs stacked zero offset volume as a smooth model description based on b splines is used and reflection points are treated independently of each other only locally coherent events in the stacked volume are required and very few picks are needed thus picking is considerably simplified during the iterative inversion process the required forward modelled quantities are obtained by dynamic ray tracing along normal rays pertaining to the input data points frechet derivatives for the tomographic matrix are calculated with ray perturbation theory the inversion algorithm is demonstrated on a 3d synthetic data example where the kinematic wavefield attributes have directly been obtained by forward modelling

a comparative study of different pga attenuation and error models case of 1999 chi chi earthquake abstract in order to evaluate the horizontal peak ground acceleration hpga during earthquakes the author studies the respective efficiency of two existing attenuation models mebarki a 2003a risques sismiques aleas vulnerabilite et aide a la decision par cartes sig proceedings of international conference on risks vulnerability and reliability in construction towards a reduction of disasters isbn 9961 891 01 5 pp 82 97 algiers october 11 12 mebarki a 2003b proposal of a parametric attenuation model and comparison with some worldwide earthquakes viio congreso venezolano de sismologia y ingenieria sismica barquisimeto venezuela november 12 13 cd rom mebarki a 2004 modele d attenuation sismique prediction probabiliste des pics d acceleration rfgc revue francaise de genie civil hermes ed 8 9 10 1071 1086 a comparative study of their performances is done in the case of 1999 chi chi earthquake taiwan the reported pga peak ground accelerations values correspond to hypocentral distances ranging from 15 up to 180 km with observed acceleration peaks ranging from 0 04 g up to 1 16 g the author considers two kinds of probabilistic distributions for the error model in order to describe the uncertainty and the variability that affect the values of the pga a gamma distribution and a log normal distribution the adopted error models assume that the variability of the pga is such that its coefficient of variation is equal to 55 mebarki a 2003a risques sismiques aleas vulnerabilite et aide a la decision par cartes sig proceedings of international conference on risks vulnerability and reliability in construction towards a reduction of disasters isbn 9961 891 01 5 pp 82 97 algiers october 11 12 mebarki a 2003b proposal of a parametric attenuation model and comparison with some worldwide earthquakes viio congreso venezolano de sismologia y ingenieria sismica barquisimeto venezuela november 12 13 cd rom mebarki a 2004 modele d attenuation sismique prediction probabiliste des pics d acceleration rfgc revue francaise de genie civil hermes ed 8 9 10 1071 1086 the obtained results show that both attenuation models provide adequate values of the pga when a gamma distribution is adopted for the error model the attenuation models efficiency decreases slightly when a log normal distribution is adopted for the error model

fast velocity analysis by wave path migration iterative migration velocity analysis is computationally expensive where most of the computation time is used for generating prestack depth images by using a reduced form of kirchhoff migration denoted as wave path migration we can significantly speed up the depth imaging process and reduce the entire velocity analysis expense accordingly our results with 2d synthetic and field data show that wave path migration velocity analysis can efficiently improve the velocity model and the wave path migration velocity analysis updated velocity correlates well with that from the kirchhoff migration velocity analysis the central processing unit comparison shows that for a 2d synthetic and field data set wave path migration velocity analysis is six times faster than kirchhoff migration velocity analysis this efficiency should be even greater for 3d data

two dimensional pp ps stereotomography p and s waves velocities estimation from obc data summary we present the extension of stereotomography to p and s wave velocity estimation from pp and ps reflected diffracted waves in this new context we greatly benefit from the use of locally coherent events by stereotomography in particular when applied to s wave velocity estimation from ps data no pairing of pp and ps events is a priori required in our procedure the p wave velocity model is obtained first using stereotomography on pp arrivals then the s wave velocity model is obtained using ps stereotomography on ps arrivals fixing the pwave velocity model we present an application to an ideal synthetic data set demonstrating the relevance of the approach which allows us to recover depth consistent p and s waves velocity models even if no pairing of pp and ps events is introduced finally results to a real data set from the gulf of mexico are presented demonstrating the potential of the method in a noisy data context

velocity analysis by iterative profile migration in conventional seismic processing velocity analysis is performed by using the normal moveout nmo equation which is based on the assumption of flat horizontal reflectors imaging by migration either before or after stack is done normally in a subsequent step using these velocities in this paper velocity analysis and imaging are combined in one step and migration itself is used as a velocity indicator because unlike nmo migration can be formulated for any velocity function migration based velocity analysis methods are capable of handling arbitrary structures i e those with lateral velocity variations in the proposed scheme each shot gather profile is migrated with an initial depth velocity model profile migration is implemented in the x domain but the actual implementation of profile migration is not critical as long as it is not done in a spatial wavenumber domain which would preclude handling of lateral velocity variations after migration with an initial velocity model the

fault imaging in sparsely sampled 3d seismic data using common reflection surface processing and attribute analysis a study in the upper rhine graben abstract cost reduction in seismic reconnaissance is an issue in geothermal exploration and can principally be achieved by sparse acquisition to address the adherent decrease in signal noise ratio the common reflection surface method has been proposed we reduced the data density of an existing 3d dataset and evaluated the results of common reflection surface processing using seismic attributes the application of the common reflection surface method leads in all cases to an improvement of the signal noise ratio the most distinct improvement can be seen in the low fold regions the improvement depends strongly on the midpoint aperture and there is a tradeoff between reflector continuity and horizontal resolution if small scale targets are to be imaged a small aperture size is necessary which may be far below the fresnel zone for a specific reflector the substantial reduction of the data density leads in our case to an irrecoverable information loss

joint interpretation of geophysical field experiments in the danube deep sea fan black sea abstract gas hydrates are naturally occurring solid compounds of gas and water within almost all sediment rich continental margins due to the large amounts of methane stored in submarine gas hydrates they might serve as future reservoirs for offshore marine gas production assessing the reservoir characteristics requires reliable estimates of both the gas and gas hydrate concentration which can be best addressed using geophysical and geological investigations here we demonstrate the power of joint interpretation of interdisciplinary geophysical techniques and geological laboratory experiments regional 2d multichannel seismic data provide the broad overview of a hydrate bearing area high resolution 2d and 3d seismic reflection data provide detailed images of two working areas the buried s1 channel levee system at 1500 m water depth well within the gas hydrate stability zone and a slope failure location located at 665 m water depth top limit of the hydrate formation next to the s2 channel detailed compressional and shear wave vs velocity depth models were derived from four component ocean bottom seismic data the latter from p to s conversion upon reflection due to their steep reflection angles shear wave events result in less resolved vs models nevertheless in case of a change in elasticity of the sediment matrix due to gas hydrate cementation shear wave events can be used as an indicator as such vs can give insight into the nature of hydrate formation throughout the ghsz we present new developments in the application of common reflection surface normal incidence point tomography and full waveform inversion techniques to enhance model resolution for the seismic data sets 2d and 3d controlled source electromagnetic measurements provide volume information of the resistivity depth distribution models electrical resistivity of the sediment formation depends on its porosity and the resistivity of the pore fluid gas hydrate and free gas generally have much higher electrical resistivities than saline pore fluid and can be assessed using empirical relationships if the porosity and pore fluid salinity are known calibration with logging data laboratory experiments on hydrate or ice bearing sediments and resulting velocity and resistivity values guide the joint interpretation into more accurate saturation estimations beyond that a joint inversion framework supporting forward calculation of specialized geophysical methods at distributed locations is under development in this paper we summarize these individual components of a multi parameter study and their joint application to investigate gas hydrate systems their equilibrium conditions and preservation of bottom simulating reflectors we analyze data from two working areas at different locations and depth levels along the slope of the danube fan which are both characterized by multiple bottom simulating reflectors indicating the presence of gas hydrate in the first working area we located two depth windows with indications for moderate 16 24 gas hydrate formation but no vertical gas migration in the second working area we observed fluid migration pathways and active gas seepage limiting gas hydrate formation to less than 10 at the bsr some discrepancies remain between seismic based and electromagnetic based models of gas and gas hydrate distribution and saturation estimates indicating that further in situ investigations are likely required to better understand the gas hydrate systems at our study areas and to calibrate the inversion processes which will be required for a joint inversion framework as well

crustal scale pop up structure in cratonic lithosphere dobre deep seismic reflection study of the donbas fold belt ukraine the dobre project investigated the interplay of geologic and geodynamic processes that controlled the evolution of the donbas fold belt ukraine as an example of an inverted intracratonic rift basin a deep seismic reflection profile provides an excellent image of the structure of the donbas fold belt which is the uplifted and compressionally deformed part of the late paleozoic pripyat dniepr donets basin both the effects of rifting and those of later structural inversion are recognized in the seismic and geologic data the interpretation of the reflection data shows that the inversion of the donbas fold belt occurred at the crustal scale as a mega pop up which involved a major detachment fault through the entire crust and an associated back thrust the dobreflection image provides a simple concept of intracratortic basin inversion the crustal pop up being uplifted and internally deformed the association of such a structure with inverted intracratonic basins such as the donbas fold belt implies brittle deformation of relatively cold crust

the dolomite nodules enclosing fossil marine vertebrates in the east pisco basin peru field and petrographic insights into the lagerstatte formation abstract the mio pliocene pisco formation peru is a world famous marine vertebrate lagerstatte several fossil specimens are wrapped up in dolomitic nodules some others lie in the sediment displaying dolomite only in bone cavities e g mesorostral canal and endocranium with the aim to understand whether the precipitation of the dolomitic nodules influenced the formation of the lagerstatte we collected field data on a high number of fossil vertebrates and conducted petrographic and mineralogical analyses on samples representative of the variable development of concretions our results revealed positive relationships between size completeness and articulation of skeletons and the presence of an external nodule clear evidence of chemoautotrophic communities that thrived on the carcasses is scarce microborings are often found in the cortical bone tissues together with iron oxides the former are left by microorganisms feeding on the carcass the latter are traces of former fe sulphides a product of organic matter degradation we suggest that an early burial of the skeletons was a determinant factor in the development of dolomite concretions since it allowed methanogenesis and anaerobic sulphate reduction exploiting the lipids in the bones and the organic matter dispersed in the sediments dolomite precipitation was driven by the same bacteria operating during the suphophilic stage of whale fall communities textural observations imply that dolomite precipitated shortly after the burial of carcasses the increase of alkalinity generated by sulphate reduction and methanogenesis caused a rapid precipitation of the dolomite within skeletal cavities and prevented the degradation of the bones and diagenetic compression of skeletons the nodules themselves prevented erosion of fossils after exhumation therefore nodule formation had a crucial role in the development of the pisco lagerstatte

migration velocity analysis from locally coherent events in 2 d laterally heterogeneous media part i theoretical aspects we present a new method based on migration velocity analysis mva to estimate 2 d velocity models from seismic reflection data with no assumption on reflector geometry or the background velocity field classical approaches using picking on common image gathers cigs must consider continuous events over the whole panel this interpretive step may be difficult particularly for applications on real data sets we propose to overcome the limiting factor by considering locally coherent events a locally coherent event can be defined whenever the imaged reflectivity locally shows lateral coherency at some location in the image cube in the prestack depth migrated volume obtained for an a priori velocity model locally coherent events are picked automatically without interpretation and are characterized by their positions and slopes tangent to the event even a single locally coherent event has information on the unknown velocity model carried by the value of the slope measured in the cig the velocity is e

seismic wave equation demigration migration reverse time migration is a well known method based on a single scattering approximation it is designed to obtain seismic images in the case of a complex subsurface it can however be a very time consuming task because the number of computations is directly proportional to the number of processed sources in the context of velocity model building iterative approaches require that one derives a series of migrated sections for different velocity models we propose to replace the summation over sources by a summation over depth offsets or time delays defined in the subsurface for that we have developed a new relationship between two migrated sections obtained for two different velocity models starting from one of the two images we obtain a second section correctly and efficiently for each time delay we compute a generalized source term by extending the concept of exploding reflector to nonzero offset we obtain the final migrated section by solving the same wave equation in the perturbed model with the modified source term our work included testing the methodology on 2d synthetic data sets particularly when the initial and perturbed velocity models differ greatly

new insights into the crustal structure of the north german basin from reprocessing of seismic reflection data using the common reflection surface stack the influence of deep crustal processes on basin formation and evolution and its relation to current morphology is not well understood yet a key feature to unravel these issues is a detailed seismic image of the crust a part of the data recorded by the hydrocarbon industry in the late 1970s and 1980s in the north german basin were released to the public recently the seismic reflection data were recorded down to 15 s two way travel time the mean common midpoint fold of about 20 is relatively low compared to contemporary seismic acquisitions the processing of the 1980s focussed on the sedimentary structures to explore the hydrocarbon potential of this area we applied the common reflection surface stack technique to the data sets which is well suited for low fold data the reprocessing was focussed on the imaging of the subsedimentary crustal range the reprocessed images show enhanced reflections especially in the mid and lower crustal part also the image of the salt structures in the graben area was improved furthermore the reprocessed images indicate an almost flat moho topography in the area of the gluckstadt graben and an additional lower crustal structure which can be correlated with a high density body found in recent gravity modeling studies

taphonomy and palaeoecology of the lower miocene marine vertebrate assemblage of ullujaya chilcatay formation east pisco basin southern peru the taphonomy and palaeoecology of the early miocene burdigalian vertebrate assemblage of ullujaya east pisco basin peru is here described vertebrate remains are concentrated in marine facies ct1a association of the exposed chilcatay formation dated 19 18 ma deposited within a 30 40 m deep semi enclosed offshore environment coupled with ichnological observations the size distribution of pyrite framboid relics reveals fluctuation of euxinic and oxic dysoxic conditions at the seafloor the assemblage is dominated by toothed cetaceans kentriodontids squalodelphinids physeteroids and the eurhinodelphinid like chilcacetus together with a large dermochelyid turtle some bony fish and diverse elasmobranchs mostly juveniles of carcharhinus brachyurus and cosmopolitodus hastalis the vertebrate assemblage comprises a coastal community dominated by mesopredators representative of a warm temperate sheltered embayment connected with riverine and open ocean environments vertebrate skeletons are typically disarticulated and incomplete and some bone elements display shark bite marks microborings are observed at the bone surface bones exhibit a good degree of apatite mineralisation and bone cavities are locally filled by ca mg carbonates our taphonomic observations suggest prolonged flotation of carcasses during which they were subject to biogenic and physical processes of partial destruction including scavenging by sharks before final deposition on a soft compact substrate preservation was favoured by the oxygen deficient bottom conditions that inhibited the action of benthic macro scavengers

enabling affordable omnidirectional subsurface extended image volumes via probing image gathers as a function of subsurface offset are an important tool for the inference of rock properties and velocity analysis in areas of complex geology traditionally these gathers are thought of as multidimensional correlations of the source and receiver wavefields the bottleneck in computing these gathers lies in the fact that one needs to store compute and correlate these wavefields for all shots in order to obtain the desired image gathers therefore the image gathers are typically only computed for a limited number of subsurface points and for a limited range of subsurface offsets which may cause problems in complex geological areas with large geologic dips we overcome increasing computational and storage costs of extended image volumes by introducing a formulation that avoids explicit storage and removes the customary and expensive loop over shots found in conventional extended imaging as a result we end up with a matrix vector formulation from which different image gathers can be formed and with which amplitude versus angle and wave equation migration velocity analysis can be performed without requiring prior information on the geologic dips aside from demonstrating the formation of two way extended image gathers for different purposes and at greatly reduced costs we also present a new approach to conduct automatic wave equation based migration velocity analysis instead of focusing in particular offset directions and preselected subsets of subsurface points our method focuses every subsurface point for all subsurface offset directions using a randomized probing technique as a consequence we obtain good velocity models at low cost for complex models without the need to provide information on the geologic dips

reprocessing of deep seismic reflection data from the north german basin with the common reflection surface stack abstract the common reflection surface crs stack is a promising alternative stacking technique for reflection data this technique is an automatic multi parameter stack that does not require the explicit knowledge of a stacking velocity model furthermore it significantly improves the signal to noise ratio as it considers more traces during the zero offset stacking than the conventional cmp stack especially for low fold data in heterogeneous settings the crs stack is able to further enhance reflections recently the crs stack was applied to reflection data from sedimentary basins for oil and gas exploration purposes it was not yet applied to crustal and deeper reflection data we used the crs stack for deep reflection data from the north german basin the data were acquired in the late 1970 s and early 1980 s with recording times down to 15 s twt and mean cmp folds of about 20 we reprocessed the data focusing on lower crustal and deeper structures compared to the conventional cmp processing of the 1980 s the reprocessed sections show an improved image quality at all time levels i e from the sedimentary cover down to the crust and upper mantle especially the reflections from the salt structures and moho events are enhanced further a constrained crs stack was applied to the data using a stacking velocity model from conventional velocity analysis the latter further improved the coherency and visibility of the reflections especially in the area of the salt plugs and in the upper crust where multiples were suppressed the data examples demonstrate that the crs stack is a suitable tool for improving the quality of seismic images especially for deep reflection data from low low fold data acquisitions

vast amount of accommodation space controlled evolution of a continuous pliocene pleistocene mixed cool water carbonate siliciclastic prograding wedge in the bay of oran western mediterranean abstract the bay of oran is part of the northern algerian continental margin located in the western mediterranean sea between europe and northern africa a regional terrace in ca 320 m water depth described in earlier studies and a second deeper located one 1200 m water depth provide an unusually vast amount of accommodation space for an observed prograding wedge seismo stratigraphic interpretation of high resolution reflection seismic data show different phases of mixed cool water carbonate siliciclastic deposition ia initial aggradation with low dipping foreset deposition during early pliocene relative sea level highstand ib deposition transitions to progradation when aggradation reaches the base level iia once progradation reaches the shelf break terrace deposition is reduced to coarse fraction foreset deposits until it ceases entirely iib finer sediments are bypassed and start to aggrade on the lower slope terrace until deposits reach the shelf terrace depth iii due to accommodation space prolongation progradation recommences phase iia and phase iii deposits are separated by a hiatus a drop in mean sea level during the mid pleistocene will have caused the base level to fall below the upper strata hence causing some reworking and redeposition however sea level variations are not considered to be a main controlling factor of the depositional sequences the evolution of this continuous pliocene pleistocene mixed cool water carbonate siliciclastic prograding wedge is instead attributed to the controlling factor of this unusually vast amount of accommodation space in closest proximity to the sea floor sparse recent sedimentation in form of 5 10 m thick sediment lobes can be observed in subbottom profiler data only from a tectonic point of view a prolongation of the yusuf fault into the survey area though expected by other authors could not be supported with the available dataset

common reflection surface stack image and attributes the common reflection surface stack provides a zero offset simulation from seismic multicoverage reflection data whereas conventional reflection imaging methods e g the nmo dip moveout stack or prestack migration require a sufficiently accurate macrovelocity model to yield appropriate results the common reflection surface crs stack does not depend on a macrovelocity model we apply the crs stack to a 2 d synthetic seismic multicoverage dataset we show that it not only provides a high quality simulated zero offset section but also three important kinematic wavefield attribute sections which can be used to derive the 2 d macrovelocity model we compare the multicoverage data derived attributes with the model derived attributes computed by forward modeling we thus confirm the validity of the theory and of the data derived attributes for 2 d acquisition the crs stack leads to a stacking surface depending on three search parameters the optimum stacking surface needs to be determined for each point

crs stack based seismic imaging considering top surface topography in this case study we consider the seismic processing of a challenging land data set from the arabian peninsula it suffers from rough top surface topography a strongly varying weathering layer and complex near surface geology we aim at establishing a new seismic imaging workflow well suited to these specific problems of land data processing this workflow is based on the common reflection surface stack for topography a generalized high density velocity analysis and stacking process it is applied in a non interactive manner and provides an entire set of physically interpretable stacking parameters that include and complement the conventional stacking velocity the implementation introduced combines two different approaches to topography handling to minimize the computational effort after initial values of the stacking parameters are determined for a smoothly curved floating datum using conventional elevation statics the final stack and also the related residual static correction are applied to the original prestack data considering the true source and receiver elevations without the assumption of nearly vertical rays finally we extrapolate all results to a chosen planar reference level using the stacking parameters this redatuming procedure removes the influence of the rough measurement surface and provides standardized input for interpretation tomographic velocity model determination and post stack depth migration the methodology of the residual static correction employed and the details of its application to this data example are discussed in a separate paper in this issue in view of the complex near surface conditions the imaging workflow that is conducted i e stack residual static correction redatuming tomographic inversion prestack and post stack depth migration leads to a significant improvement in resolution signal to noise ratio and reflector continuity

crp based seismic migration velocity analysis a new migration velocity analysis is developed by combining the speed of parsimonious prestack depth migration with velocity adjustments estimated within and across common reflection point crp gathers the proposed approach is much more efficient than conventional tomographic velocity analysis because only the traces that contribute to a series of crp gathers are depth migrated at each iteration the local interval velocity adjustments for each crp are obtained by maximizing the stack amplitude over the predicted nonhyperbolic moveout in each crp gather this does not involve retracing rays at every iteration the velocity in each pixel is updated by averaging over all the predicted velocity updates finally crp positions and orientations are updated by parsimonious migration and rays are retraced to define new crp gathers for the next iteration this ensures internal consistency between the updated velocity model and the crp gather because the algorithm has a gridded model parameterization no explicit representation or fitting of reflectors is involved strong lateral velocity variations such as those found at salt flanks can be handled application to synthetic and field data sets show that the proposed algorithm works effectively and efficiently

velocity and interface depth determination by tomography of depth migrated gathers a method for velocity and interface depth determination based on tomography of migrated common reflecting point crp gathers is presented the method is derived from the tomographic principle that relates traveltime change along a given ray to perturbations in slowness and layer depths the tomographic principle is used to convert depth errors in migrated crp gathers to time errors along a crp ray pair and thus enable use of conventional traveltime tomography it is also used to affect a very fast prestack migration and set up the tomography matrix the velocity depth determination method uses the available offsets of all crps and inverts for the parameters of all layers simultaneously hand picking of depth errors on crp gathers is avoided by a method where the tomography matrix operates directly on the migrated gathers the velocity depth determination method is demonstrated on a synthetic example and on a field example from the north sea

velocity estimation by the common reflection surface crs method using ground penetrating radar data in this paper we describe the use of the common reflection surface crs method to estimate velocities from ground penetrating radar gpr data applied to multicoverage data the crs method provides as one of its outputs the time domain rms velocity map which is then converted to depth by the familiar dix algorithm combination of the obtained depth converted velocity map with electrical resistivity in situ measurements enables us to estimate both water content and water conductivity these quantities are essential to delineate infiltration of contaminants from the surface after industrial or agricultural activities the method was applied to gpr data and compared with the classical nmo approach the results show that the crs method provides a physically more meaningful velocity field thus improving the potential of gpr as an investigation tool for environmental studies

fossil whale preservation implies high diatom accumulation rate in the miocene pliocene pisco formation of peru diatomaceous deposits in the miocene pliocene pisco for mation contain abundant whales preserved in pristine condition bones articulated or at least closely associated in some cases in cluding preserved baleen the well preserved whales indicate rapid burial the 346 whales within 1 5 km 2 of surveyed surface were not buried as an event but were distributed uninterrupted through an 80 m thick sedimentary section the diatomaceous sediment lacks repeating primary laminations but instead is mostly massive with irregular laminations and speckles there is no evidence for bioturbation by invertebrates in the whale bearing sediment cur rent depositional models do not account for the volume of diato maceous sediments or the taphonomic features of the whales these taphonomic and sedimentary features suggest that rapid burial due to high diatom accumulation in part by lateral advection into pro tected shallow embayments is responsible for the superb preser vation of these whales leading to a higher upper limit on phyto plankton accumulation rates than previously documented

operator oriented crs interpolation in common reflection surface imaging the reflection arrival time field is parameterized by operators that are of higher dimension or order than in conventional methods using the common reflection surface approach locally in the unmigrated prestack data domain opens a potential for trace regularization and interpolation in most data interpolation methods based on local coherency estimation a single operator is designed for a target sample and the output amplitude is defined as a weighted average along the operator this approach may fail in presence of interfering events or strong amplitude and phase variations in this paper we introduce an alternative scheme in which there is no need for an operator to be defined at the target sample itself instead the amplitude at a target sample is constructed from multiple operators estimated at different positions in this case one operator may contribute to the construction of several target samples vice versa a target sample might receive contributions from different operators operators are determined on a grid which can be sparser than the output grid this allows to dramatically decrease the computational costs in addition the use of multiple operators for a single target sample stabilizes the interpolation results and implicitly allows several contributions in case of interfering events due to the considerable computational expense common reflection surface interpolation is limited to work in subsets of the prestack data we present the general workflow of a common reflection surface based regularization interpolation for 3d data volumes this workflow has been applied to an obc common receiver volume and binned common offset subsets of a 3d marine data set the impact of a common reflection surface regularization is demonstrated by means of a subsequent time migration in comparison to the time migrations of the original and dmo interpolated data the results show particular improvements in view of the continuity of reflections events this gain is confirmed by an automatic picking of a horizon in the stacked time migrations

pliocene stratigraphic paleobiology in tuscany and the fossil record of marine megafauna abstract tuscany has a rich pliocene record of marine megafauna mm including mysticetes odontocetes sirenians and seals among the mammals and six orders of sharks among the elasmobranchs this is reviewed with respect to paleogeography and sequence stratigraphy in six different basins conditions at the ancient seafloor are explored by means of sedimentary facies analysis taphonomy and multivariate techniques applied to a large quantitative dataset of benthic molluscs mm is rare or absent in most basins during the zanclean except in one basin and most abundant in piacenzian deposits in all six basins mm occurs preferentially in fine grained shelfal highstand deposits of small scale depositional sequences or at condensed horizons of the maximum flooding interval it is rare in shallow marine paleonvironments and nearly absent in bathyal paleosettings paleogeographic and paleoecological evidence and a comparison with modern patterns of marine upwelling suggest that a wedge of nutrient rich waters sustained in the offshore during the pliocene a high biomass of primary producers and a community of apex consumers and mesopredators similarly to the modern northwestern mediterranean sea with a species richness higher than the modern and a more complex trophic structure the highest mm diversity coincides with the mid piacenzian warm period suggesting that facies control does not obscure a link between climate and diversity we underline however that not all marine environments were suitable for marine mammal preservation buoyant carcasses were preferentially dismembered and destroyed in high energy shallow waters with the possible exception of delta front deposits where sudden sediment input occasionally buried pristine carcasses we hypothesise that carcasses sunken on the seafloor below the shelf break underwent destruction through the activity of a whale fall biota of modern type specialised in the consumption of decomposing tissues both soft and mineralised a taphonomic window was left between storm wave base and the shelf break here water pressure is high enough to prevent the formation of decomposing gases and the resurfacing of carcasses while the lack of a specialised whale fall biota slows down bone degradation with respect to deeper settings sedimentation rate was high enough to cover skeletal material before its complete destruction an estimate of paleobathymetries based on multivariate techniques suggests that the preferential depth for the inclusion of mm in the fossil record was 30 300 m the results are compared with major mesozoic and cenozoic mm records worldwide available evidence suggests that the late neogene radiation of large whales true ecosystem engineers and their size increase triggered the radiation of a bone eating fauna that hampered and hampers mm preservation in the deep sea stratigraphic paleobiology and an ecosystem level approach deliver useful insights to the nature of the fossil record

exceptional occurrence of fossil baleen in shallow marine sediments of the neogene pisco formation southern peru abstract fossil baleen is rare in the sedimentary record this paper documents the exceptional occurrence of thirty seven fossil whale specimens with preserved baleen in the neogene pisco formation during a transect survey in a limited area west of the ica river valley near the town of ocucaje in southern peru the sedimentary layers consist of tuffaceous and diatomaceous sandstones diatomaceous mudstones and dolomites deposited in a shallow marine embayment observations of modern whale carcasses on the seafloor and stranded individuals indicate that baleen detaches from the mouth of the whales very rapidly after death and that bones deteriorate very rapidly as a result of scavenging activity and abrasion in contrast the bones of the pisco formation whales are exceptionally well preserved and their baleen is often found in life position suspended from the rostrum sedimentary structures found associated with some skeletons indicate tidal and storm processes suggesting that the environment was not anoxic this exceptional occurrence of fossil baleen suggests early mineralization of the baleen attachment to the rostrum or rapid burial of the skeletons before any detachment or loss could occur

slowness driven gaussian beam prestack depth migration for low fold seismic data subsurface images based on low fold seismic reflection data or data with geometry acquisition limitations such as obtained from ocean bottom seismography obs are often corrupted by migration swing artifacts incorporating prestack instantaneous slowness information into the imaging condition can significantly reduce these migration swing artifacts and improve image quality especially for areas with poor illumination we combine the horizontal surface slowness information of observed seismic data with gaussian beam depth migration to implement a new slowness driven gaussian beam prestack depth migration whereby fresnel weighting is combined naturally with beam summation the prestack instantaneous slowness information is extracted from the original obs or shot gathers using local slant stacks and is combined with a local semblance analysis during migration we propagate the seismic energy downward knowing its instantaneous slowness information at each image location the beam summation is localized in a resolution dependent fresnel zone the instantaneous slowness information controls the beam summation synthetic and real data examples confirm that slowness driven gaussian beam migration can suppress most noise from inadequate stacking and give a clearer migration result

velocity model estimation for depth imaging comparison of three tomography methods on a 2d real data set the estimation of velocity models is still crucial in seismic reflection imaging as it controls the quality of the depth migrated image which is the basis of geological interpretation among the numerous existing methods for velocity determination tomographic methods are very attractive for their efficiency and ability to retrieve heterogeneities of the medium we present three tomographic methods in order to estimate heterogeneous velocity models from 2d prestack pp reflection data a traveltime tomography in the time migrated domain a traveltime and slope tomography in the non migrated time domain and a slope tomography in the depth migrated domain the first method traveltime tomography in the time domain is based on continuous picked events whereas the two slope tomographic methods one in the time domain and the other in the depth domain are based on locally coherent events with no assumptions about reflector geometry or the unknown velocity field the purpose of this paper is not to describe in detail the theoretical basis and implementation of the methods but to apply and compare their output using the same marine real data set based on the estimated velocity models the migrated images and the common image gathers from the three processing routes the relative strengths and weaknesses of the methods are discussed finally similarities are indicated and potential alternative approaches are proposed

multifocusing revisited inhomogeneous media and curved interfaces we review the multifocusing method for traveltime moveout approximation of multicoverage seismic data multifocusing constructs the moveout based on two notional spherical waves at each source and receiver point respectively these two waves are mutually related by a focusing quantity we clarify the role of this focusing quantity and emphasize that it is a function of the source and receiver location rather than a fixed parameter for a given multicoverage gather the focusing function can be designed to make the traveltime moveout exact in certain generic cases that have practical importance in seismic processing and interpretation the case of a plane dipping reflector planar multifocusing has been the subject of all publications so far we show that the focusing function can be generalized to other surfaces most importantly to the spherical reflector spherical multifocusing at the same time the generalization implies a simplification of the multifocusing method the exact traveltime moveout on spherical surfaces is a very versatile and robust formula which is valid for a wide range of offsets and locations of source and receiver even on rugged topography in two dimensional surveys it depends on the same three parameters that are commonly used in planar multifocusing and the common reflection surface crs stack method the radii of curvature of the normal and normal incidence point waves and the emergence angle in three dimensions the exact traveltime moveout on spherical surfaces depends on only one additional parameter the inclination of the plane containing the source receiver and reflection point comparison of the planar and spherical multifocusing with the crs moveout expression for a range of reflectors with increasing curvature shows that the planar multifocusing can be remarkably accurate but the crs becomes increasingly inaccurate this can be attributed to the fact that the crs formula is based on a taylor expansion whereas the multifocusing formulae are double square root formulae as a result planar and spherical multifocusing are better suited to model the moveout of diffracted waves

nonlinear 3d tomographic least squares inversion of residual moveout in kirchhoff prestack depth migration common image gathers velocity model estimation with seismic reflection tomographyisanonlinearinverseproblem wepresentanewmethodforsolvingthenonlineartomographicinverseproblemusing 3d prestack depth migrated reflections as the input data i e our method requires that prestack depth migration psdmbeperformedbeforetomography themethodisapplicable to any type of seismic data acquisition that permits seismic imaging with kirchhoff psdm afundamental conceptofthemethodisthatwedissociatethepossiblyincorrect initialmigrationvelocitymodelfromthetomographicvelocity model we take the initial migration velocity model and the residual moveout in the associated psdm common image gathers as the reference data this allows us to consider themigrateddepthoftheinitialpsdmastheinvariantobservation for the tomographic inverse problem we can therefore formulate the inverse problem within the general framework of inverse theory as a nonlinear least squares data fitting between observed and modeled migrated depth the modeledmigrateddepthiscalculatedbyraytracinginthetomographic model followed by a finite offset map migration in the initial migration model the inverse problem is solved iteratively with a gauss newton algorithm we applied the method to a north sea data set to build an anisotropic layer velocitymodel

high resolution seismic imaging in complex environments a comparison among common reflection surface stack common midpoint stack and prestack depth migration at the ilva bagnoli brownfield site campi flegrei italy abstracti used the common reflection surface crs stack technique together with conventional common midpoint processing and prestack depth migration psdm to process three parallel high resolution seismic reflection lines acquired in a closed industrial plant this brownfield site now undergoing remediation is located within the bagnoli district of the city of naples italy near the southeastern border of campi flegrei caldera compared with the other results the crs stack followed by poststack depth migration produced a seismic image more consistent with the expected subsurface structures and with outcropping units present in the area the survey confirmed the presence under the brownfield site of some buried steps of coroglio fault a main structure formed approximately 15 ky ago during the neapolitan yellow tuff supereruption results have important implications for hazard assessment and geothermal exploration because the imaged faults certainly are preferential passageways for geothermal flu

3d seismic survey for geothermal exploration in crystalline rocks in saxony germany a 3d seismic survey was recorded in 2012 to explore a petrothermal reservoir in a late variscan granitic pluton within the erzgebirge ore mountains in saxony germany the main objective was to test this area in the context of the enhanced geothermal system concept and to test the 3d seismic technique as an exploration tool the intention and challenge are to image and characterize potentially permeable fracture zones at target depths of 5 6 km with temperatures above 150 c unconventional methods were applied for field acquisition and data processing the vibroseis technique was used in the core experiment accompanied by a special explosive seismic experiment field acquisition was characterized by severe noise conditions and a highly irregular layout these conditions required extensive preprocessing and data conditioning the imaging started with conventional common midpoint processing for quality control and for a first reference better images were obtained by common reflection surface processing with subsequent post stack time migration prestack time migration was also used for comparison outstanding results were obtained by the operator oriented version of the common reflection surface technique a rich repertoire of structures within the granite pluton was imaged including steeply dipping fault zones and conjugate faults images and indications of fracture and crack porosity of a prominent fault zone provide the background to define an optimum drill path this is considered as the next stage for a possible geothermal plant if a decision is taken to drill a research well in the future the 3d seismic reflection technique was shown to be an indispensable tool for geothermal exploration even in crystalline basement rocks

stereotomography of seismic data acquired on undulant topography stereotomography is a robust method for building velocity models from seismic reflection data and has been applied to offshore seismic data but there is almost no stereotomographic study with rugged topographic conditions we study the topographic effects on the slopes of locally coherent events of seismic data and propose an approach to calculating the slopes on an undulant observation surface using the horizontal and vertical components of slowness vectors estimated then we present an extended stereotomography with undulant observation surface based on the conventional one tests on synthetic data validate the extended stereotomography application to the field seismic data in a foothill belt in xinjiang of the west china shows that the extended stereotomography is an effective tool to build velocity models for prestack depth migration of seismic data acquired on rugged topography

time migration velocity analysis by image wave propagation of common image gathers image wave propagation or velocity continuation describes the variation of the migrated position of a seismic event as a function of migration velocity image wave propagation in the common image gather cig domain can be combined with residual moveout analysis for iterative migration velocity analysis mva velocity continuation of cigs leads to a detection of those velocities in which events flatten although image wave continuation is based on the assumption of a constant migration velocity the procedure can be applied in inhomogeneous media for this purpose cigs obtained by migration with an inhomogeneous macrovelocity model are continued starting from a constant reference velocity the interpretation of continued cigs as if they were obtained from residual migrations leads to a correction formula that translates residual flattening velocities into absolute time migration velocities in this way the migration velocity model can be improved iteratively until a satisfactory result is reached wi

estimation of peak ground accelerations of the malay peninsula due to distant sumatra earthquakes the low seismicity malay peninsula has never experienced any earthquake damage thus earthquake resistant design has not been specifically required in the building codes however it has been realized that urban areas located rather distantly from earthquake sources may also be affected by tremors in this article the potential ground motion in terms of the peak ground accelerations pgas due to long distance sumatra earthquakes is investigated for singapore and kuala lumpur following a probabilistic seismic hazard assessment approach earthquakes that have occurred in sumatra in the last 37 yr are used for which m s and m w catalogs are constructed from the available m b catalog the analysis is then carried out using the m w catalog based on the pgas of 52 recent sumatra earthquakes recorded in singapore the attenuation relationship of fukushima and tanaka 1992 is found to correlate well with the high rate attenuation characteristic of the region the predicted design basis pgas i e pga with 10 probability of being exceeded in a 50 yr exposure time on rock outcrop sites are 12 7 and 29 5 gal for singapore and kuala lumpur respectively the predicted maximum credible pgas i e pga with 2 probability of being exceeded in 50 yr are 24 3 and 55 1 gal for the two cities current building design codes in the region require that buildings be capable of resisting a notional ultimate horizontal design load equal to 1 5 of the characteristic dead weight applied at each floor simultaneously to ensure structural robustness the base shear forces resulting from the predicted design basis pgas and the maximum credible pgas at rock site in singapore and kuala lumpur are therefore comparable to or higher than the capacity required by the current building codes manuscript received 27 february 2001

migration moveout analysis and depth focusing prestack depth migration still suffers from the problems associated with building appropriate velocity models the two main after migration before stack velocity analysis techniques currently used depth focusing and residual moveout correction have found good use in many applications but have also shown their limitations in the case of very complex structures to address this issue we have extended the residual moveout analysis technique to the general case of heterogeneous velocity fields and steep dips while keeping the algorithm robust enough to be of practical use on real data our method is not based on analytic expressions for the moveouts and requires no a priori knowledge of the model but instead uses geometrical ray tracing in heterogeneous media layer stripping migration and local wavefront analysis to compute residual velocity corrections these corrections are back projected into the velocity model along raypaths in a way that is similar to tomographic reconstruction while this approa

3d angle domain common image gathers for migration velocity analysis angle domain common image gathers adcigs are an essential tool for migration velocity analysis mva we present a method for computing adcigs in 3d from the results of wavefield continuation migration the proposed methodology can be applied before or after the imaging step in a migration procedure when computed before imaging 3d adcigs are functions of the offset ray parameters we derive the geometric relationship that links the offset ray parameters to the aperture angle and the reflection azimuth when computed after imaging 3d adcigs are directly produced as functions of and the mapping of the offset ray parameters into the angles depends on both the local dips and the local interval velocity therefore the transformation of adcigs computed before imaging into adcigs that are functions of the actual angles is difficult in complex structure by contrast the computation of adcigs after imaging is efficient and accurate even in the presence of complex structure and a heterogeneous velocity function on the other hand the estimation of the offset ray parameters is less sensitive to velocity errors than the estimation of the angles when adcigs that are functions of the offset ray parameters are adequate for the application of interest e g ray based tomography the computation of adcigs before imaging might be preferable errors in the migration velocity cause the image point in the angle domain to shift along the normal to the apparent geological dip by assuming stationary rays i e small velocity errors we derive a quantitative relationship between this normal shift and the traveltime perturbation caused by velocity errors this relationship can be directly used in an mva procedure to invert depth errors measured from adcigs into migration velocity updates in this paper we use it to derive an approximate 3d residual moveout rmo function for measuring inconsistencies between the migrated images at different and we tested the accuracy of our kinematic analysis on a 3d synthetic data set with steeply dipping reflectors and a vertically varying propagation velocity the tests confirm the accuracy of our analysis and illustrate the limitations of the straight ray approximation underlying our derivation of the 3d rmo function

deep seismic image enhancement with the common reflection surface crs stack method evidence from the aravalli delhi fold belt of northwestern india summary imaging of deep crustal features from narrow angle deep seismic reflection data especially from fold belt region has been a challenging task the common reflection surface crs stack is an alternative seismic imaging technique for multicoverage reflection data it is an automatic stacking process which does not require explicit knowledge of stacking velocity this crs stack is especially useful when the data quality is poor and foldage is low in this paper we demonstrate an application of the crs stack to a deep seismic reflection data set acquired across the aravalli delhi fold belt of the northwestern india which provides a seismic stack section with much improved signal to noise ratio comparing the conventional common midpoint cmp stack with the crs stack we find that the moho and other crustal reflections have been resolved clearly and the continuity of the reflectors has also been enhanced with the crs stack method the major findings from our crs processing include clear image of the moho discontinuity below the marwar basin and sandmata complex and prominent upper and mid crustal reflections our study for the first time images an extension of crustal scale jahazpur thrust below the sandmata complex which becomes listric at the moho some of the crustal features derived in this study were not identified in the earlier investigations using the cmp stack our study clearly demonstrates that the crs stacking method is more appropriate for imaging the crustal and subcrustal structures of the thrust fold belt region than the conventional cmp method where limited velocity information is available crustal thickness across the proterozoic orogenic aravalli delhi fold belt varies between 38 and 50km global correlation of the seismic results suggests no relation between crustal thickness and age of the crustal block but it depends on the thermorheological and tectonic history of the region palaeosignatures of the proterozoic subduction and collision processes are still preserved in major portion of the crust in this study area as well as in several parts of the world

a differential semblance criterion for inversion of multioffset seismic reflection data mean square error leading to least squares inversion of multioffset reflection seismograms is insensitive to velocity trend information except in the immediate vicinity of a kinematically correct model in contrast differential semblance retains sensitivity to velocity trend changes over a wide range of models the differential semblance criterion combines mean square error with the mean square differences of inverted models from data sets at neighboring shot positions or offsets or slownesses differential semblance compares model estimates at nearby acquisition parameters which are similar even when the model velocity trends are incorrect because the method inverts the data so that the estimated model amplitudes are meaningful simple differences between the unstacked model estimates give a reliable measure of velocity error a mathematical investigation indicates that the differential semblance criterion is smooth and convex over a large range of velocity models numerical simulation using synthetic data sets verifies this contention

seismic demigration migration in the curvelet domain curvelets can represent local plane waves they efficiently decompose seismic images and possibly imaging operators we study how curvelets are distorted after demigration followed by migration in a different velocity model we show that for small local velocity perturbations the demigration migration is reduced to a simple morphing of the initial curvelet the derivation of the expected curvature of the curvelets shows that it is easier to sparsify the demigration migration operator than the migration operator an application on a 2d synthetic data set generated in a smooth heterogeneous velocity model and with a complex reflectivity demonstrates the usefulness of curvelets to predict what a migrated image would become in a locally different velocity model without the need for remigrating the full input data set curvelets are thus well suited to study the sensitivity of a prestack depth migrated image with respect to the heterogeneous velocity model used for migration

prestack migration velocity estimation using nonlinear methods we describe here methods of estimating interval velocities based on two nonlinear optimization methods very fast simulated annealing vfsa and a genetic algorithm ga the objective function is defined using prestack seismic data after depth migration this inverse problem involves optimizing the lateral consistency of reflectors between adjacent migrated shot records in effect the normal moveout correction in velocity analysis is replaced by prestack depth migration when the least squared difference between each pair of migrated shots is at a minimum the true velocity model has been found our model is parameterized using cubic b splines distributed on a rectangular grid the main advantages of using migrated data are that they do not require traveltime picking knowledge of the source wavelet and expensive computation of synthetic waveform data to assess the degree of data model fit nonlinear methods allow automated determination of the global minimum without relying on estimates of the gradien

noise removal by migration of time shift images abstractwhen using seismic data to image complex structures the reverse time migration rtm algorithm generally provides the best results when the velocity model is accurate with an inexact model moveouts appear in common image gathers cigs which are either in the surface offset domain or in subsurface angle domain thus the stacked image is not well focused in extended image gathers the strongest energy of a seismic event may occur at non zero lag in time shift or offset shift gathers based on the operation of rtm images produced by the time shift imaging condition the non zero lag time shift images exhibit a spatial shift we propose an approach to correct them by a second pass of migration similar to zero offset depth migration the proposed approach is based on the local poststack depth migration assumption after the proposed second pass migration the time shift cigs appear to be flat and can be stacked the stack enhances the energy of seismic events that are defocused at zero time lag

velocity inversion by differential semblance optimization differential semblance optimization dso is an approach to inversion of reflection seismograms which avoids the severe convergence difficulties associated with nonlinear least squares inversion the method exploits both moveout and amplitude characteristics of reflections we have implemented a version appropriate to plane wave p tau seismograms and layered constant density acoustic earth models theoretical and numerical analyses of this version of dso indicate that stable and reasonably accurate estimates of both velocity trend and reflectivity can be derived to test dso further we applied it to a marine data set from the gulf of mexico where the method produced results which compare favorably to well log information the method can be extended to incorporate laterally heterogeneous velocity models

3d angle gathers from reverse time migration reverse time migration rtm based on directly solving the two way wave equation provides a natural way to deal with large lateral velocity variations and imposes no dip limitations on the seismic images it has become a standard migration tool for subsalt imaging in the gulf of mexico in addition the adoption of wide azimuth waz data acquisition provides better subsurface illumination and more azimuthal information which significantly aids imaging beneath complex overburdens because waz data are richer in the propagation directions of the waves recorded rtm and waz acquisition go hand in hand

a combined seismic and geoelectrical monitoring approach for co2 storage using a synthetic field site this paper presents an approach to assess the methods of 2d elastic seismic full waveform inversion fwi and electrical resistivity tomography ert for monitoring storage of co2 in deep saline formations as at a real site the subsurface is not fully known this approach uses a synthetic field site densities and saturations are obtained from a numerical simulation of the injection process and are introduced into geophysical forward models which simulate the geophysical data acquisition from the surface fwi and boreholes ert these synthetic geophysical data are then evaluated with respect to changes in co2 saturation and are compared to the fully known co2 saturation of the numerical process model to verify the geophysical monitoring methods results show that both methods are capable of detecting a thin co2 phase body in about 2 200 m depth for a synthetic site in the north german basin inverted co2 saturations are in good agreement however both methods cannot resolve the co2 phase edges of less than 4 m saturated thickness the maximum error of estimated co2 saturation is 10 for the fwi method and 15 for the ert method if accurate baseline models are available the fwi method sensitivity on the baseline model is tested by a sensitivity analysis demonstrating high sensitivity on bulk density but low sensitivity on fluid densities and porosity ert results are considerably improved using structural information from the fwi as constraint

seismic hazard map of turkey using the deterministic approach abstract because the instrumental records of turkey are far from being satisfactory for modeling the seismic hazard using the probabilistic approach an attempt was made in this study to accomplish it through the deterministic way in this regard all active faults of turkey small and large were evaluated together to obtain major fault systems then the procedure suggested by wells and coppersmith bull seismol soc am 4 1994 975 applied to those faults to obtain the maximum magnitude earthquake that they can generate to do this it was assumed that 1 3 of the total fault length would rupture to yield the maximum earthquake following that seven different attenuation relationships of the strong ground motion were utilized to calculate the maximum horizontal ground accelerations for the whole turkey at 0 2 intervals using the computer model tumdes written in basic programming language the computed peak ground acceleration pga values were contoured and the iso acceleration map based on sadigh et al seismol res lett 1 1997 180 relationship was selected as the new seismic hazard map of turkey on which the seismic zonations were determined as following pga 0 3 g zone 1 0 3 g

migration velocity analysis from locally coherent events in 2 d laterally heterogeneous media part ii applications on synthetic and real data we demonstrate a method for estimating 2 d velocity models from synthetic and real seismic reflection data in the framework of migration velocity analysis mva no assumption is required on the reflector geometry or on the unknown background velocity field provided that the data only contain primary reflections diffractions in the prestack depth migrated volume locations where the reflectivity exhibits local coherency are automatically picked without interpretation in two panels common image gathers cigs and common offset gathers cogs they are characterized by both their positions and two slopes the velocity is estimated by minimizing all slopes picked in the cigs we test the applicability of the method on a real data set showing the possibility of an efficient inversion using 1 the migration of selected cigs and cogs 2 automatic picking on prior uncorrelated locally coherent events 3 efficient computation of the gradient of the cost function via paraxial ray tracing from the picked events to the surface and 4 a gradient type optimization algorithm for convergence

residual stereotomographic inversion depth migration requires highly accurate knowledge of the subsurface velocity field different traveltime tomographic methods are used for this purpose stereotomography is a tomographic method that uses local dip estimates in addition to traveltimes for velocity model estimation we present a new methodology for velocity model updating it combines poststack stereotomography and residual moveout velocity inversion the former is used for initial model construction and the latter for updating the velocity model residual inversion is a kind of stereotomographic inversion applied to common reflection point crp gathers after model based moveout correction velocity analysis can be made more efficient by preselecting the traces that contribute to a series of crp gathers and using only these traces for inversion the algorithm is defined in a two step procedure first ray tracing from the reflection point for nonzero reflection offsets defines the source and receiver locations of the data traces in the crs gather then these traces are moveout corrected according to the calculated traveltimes and residual moveout is estimated the interval velocity model is updated by fitting the velocity that minimizes estimated residuals application of the proposed technique demonstrates its robustness and reliability for fast and automatic velocity model estimation

a critical examination of near field accelerograms from the sea of marmara region earthquakes in 1999 turkey was struck by two major earthquakes that occurred 86 days apart on the north anatolian fault system both earthquakes had right lateral strike slip mechanisms with moment magnitudes greater than 7 the number of strong motion records obtained from the kocaeli earthquake 17 august 1999 m w 7 4 was 34 the second event designated as the bolu duzce earthquake 12 november 1999 m w 7 2 triggered 20 instruments among the records that we have from these earthquakes seven are from near source ground motion data these records were obtained from the cities of gebze gbz yarimca ypt izmit izt capital city of the province of kocaeli adapazari skr capital of the province of sakarya duzce dzc shaken strongly in both the events and bolu bol in many of these urban centers extensive structural damage was observed although these near field data have greatly expanded the strike slip near source ground motion database worldwide for m w 7 earthquakes they represent a blurred image of the actual severity of the ground motions in the epicentral area because of the sparseness of the national strong motion network and the unrepresentative geologic conditions at the recording sites we examine the records to determine whether they provide clues about the extensive damage on the housing stock in the epicentral region the goal is tackled with earthquake structural engineering criteria in mind using the drift spectrum as the primary yardstick there appears to be conflicting evidence that the fault normal fn direction should represent a greater damage causing potential when this potential is based on ground story drift spectra the component with larger ground velocity does correlate better with the component with larger drift demand but this does not always coincide with the fn direction the period of the peak velocity pulse matches the structural period where the drift demand is the largest further refinements of code requirements that consider this effect are in order manuscript received 20 august 2000