esr dating of fault movement using various defect centres in quartz the case in the western south fossa magna japan the dates of movements of the itoigawa shizuoka tectonic line i s t l and minobu fault in the western south fossa magna have been obtained by esr dating measurements were made on various lattice defects of the ohc ge al and e centres in quartz grains of fault clay and quartz veins intruded at the time of movement all the dates obtained from these centres in quartz grains from two localities of the i s t l and iwo localities of the minobu fault fall in the range of 0 30 0 55 ma this suggests that all the centres were annihilated completely and that the obtained age can be admitted as the actual data of the latest fault movement meanwhile esr dates of quartz vein and fault clay in other localities locations 3 6 7 are divided into 0 30 0 55 ma and 1 5 2 0 ma which suggest incomplete resetting the dates of 0 30 0 55 and 1 5 2 0 ma might correspond to the clino unconformities observed in plio pleistocene sequence of this region

anatomy of the chesapeake bay impact structure revealed by seismic imaging delmarva peninsula virginia usa 1 a 30 km long radial seismic reflection and refraction survey completed across the northern part of the late eocene chesapeake bay impact structure cbis on the delmarva peninsula virginia usa confirms that the cbis is a complex central peak crater we used a tomographic p wave velocity model and low fold reflection images constrained by data from two deep boreholes located on the profile to interpret the structure and composition of the upper 5 km of crust the seismic images exhibit well defined structural features including with increasing radial distance a collapsed central uplift a breccia filled moat and a collapsed transient crater margin which collectively constitute a 40 km wide collapsed transient crater and a shallowly deformed annular trough these seismic images are the first to resolve the deep structure of the crater 1 km and the boundaries between the central uplift moat and annular trough several distinct seismic signatures distinguish breccia units from each other and from more coherent crystalline rocks below the central uplift moat and annular trough within the moat breccia extends to a minimum depth of 1 5 km or a maximum of 3 5 km depending upon the interpretation of the deepest layered materials the images show 350 to 500 m of postimpact sediments above the impactites the imaged structure of the cbis indicates a complex sequence of events during the cratering process that will provide new constraints for numerical modeling

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

wavefield tomography using reverse time migration backscattering abstractreverse time migration backscattering contains kinematic information that can be used to constrain velocity models the backscattering results from the correlation between forward scattered and backscattered wavefields from sharp interfaces i e sediment salt interfaces the synchronization between these wavefields depends on the velocity of the sediment section and the correct interpretation of the sharp boundary we have developed an optimization workflow in which the sediment velocity and the sharp boundary are updated iteratively the presence of sharp boundaries in the model lead to high and low wavenumber components in the objective function gradient the high wavenumber components correspond to the correlation of wavefields traveling in opposite directions whereas the low wavenumber components correspond to the correlation of wavefields traveling in the same direction this behavior is similar to reverse time migration in which the high wavenumber components represent the reflectors th

full traveltime inversion abstractmany previously published wave equation based methods which attempt to automatically invert traveltime or kinematic information in seismic data or migrated gathers for smooth velocities suffer a common and severe problem the inversions are involuntarily and unconsciously hijacked by amplitude information to overcome this problem we have developed a new wave equation based traveltime inversion methodology referred to as full traveltime i e fully dependent on traveltime inversion fti to automatically estimate a kinematically accurate velocity model from seismic data the key idea of fti is to make the inversion fully dependent on traveltime information and thus prevent amplitude interference during inversion under the assumption that velocity perturbations cause only traveltime changes we have derived the fti method in the data and image domains which are applicable to transmitted arrivals and reflected waves respectively fti does not require an accurate initial velocity model or

automated velocity model building with wavepath tomography wavefield continuation migration generally is recognized as superior to kirchhoff methods in complex velocity models such as below rugose salt bodies it accounts for multipathing sharp velocity contrasts and the limited bandwidth of seismic wave propagation wavepath tomography builds the velocity model in a way that is consistent with the wavefield migration operator traveltime residuals are back projected along a wavepath instead of rays the actual wavefield continuation operator is used to represent the wave propagation between surface source receiver pairs and subsurface reflection points a wavepath is obtained by multiplying impulse responses from a surface location and a reflection point the inversion matrix is kept to a manageable size by restricting the wavepath to the first fresnel zone the considerable expense of computing a single wavepath kernel in comparison to ray tomography is partially offset by the smaller number of back projections necessary to sample the velocity model adequately we have used wavepath tomography to build subsalt velocity models using 2d synthetic data wavepath tomography was implemented in 3d

attenuation of specular and diffracted 2d multiples in image space in complex areas the attenuation of specular and diffracted multiples in image space is an attractive alternative to surface related multiple elimination srme and to data space radon filtering we present the equations that map via wave equation migration 2d diffracted and specular water bottom multiples from data space to image space we show the equations for both subsurface offset domain common image gathers sodcigs and angle domain common image gathers adcigs we demonstrate that when migrated with sediment velocities the over migrated multiples map to predictable regions in both sodcigs and adcigs specular multiples focus similarly to primaries whereas diffracted multiples do not in particular the apex of the residual moveout curve of diffracted multiples in adcigs is not located at the zero aperture angle we use our equation of the residual moveout of the multiples in adcigs to design an apex shifted radon transform that maps the 2d adcigs into a 3d model space cube whose dimensions are depth curvature and apex shift distance well corrected primaries map to or near the zero curvature plane and specularly reflected multiples map to or near the zero apex shift plane diffracted multiples map elsewhere in the cube according to their curvature and apex shift distance thus specularly reflected as well as diffracted multiples can be attenuated simultaneously we show the application of our apex shifted radon transform to a 2d seismic line from the gulf of mexico diffracted multiples originate at the edges of the salt body and we show that we can successfully attenuate them along with the specular multiples in the image radon domain

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

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

spectral features of dual frequency multibeam echosounder data for benthic habitat mapping abstract automatic methods of seafloor mapping are still in their early stage of development despite the technical progress made in recent years a serious imperfection is the limited types of predictor features available for seabed classification it is therefore desirable to introduce new class of spectral features to benthic habitat mapping in this study we introduced eight spectral features of a rough seafloor surface that were indicative of better seabed classification we compared them with traditional secondary features like terrain variables and textural features the suitability of 48 variables was tested and the most important features were identified the selected variables were used to perform a supervised object based image analysis using four machine learning algorithms we found that backscatter was the strongest predictor followed by several spectral features from bathymetry that appeared more predictive than bathymetry itself the highest overall accuracy of predictive model reached approximately 86 using the support vector machine classifier the innovative results of this study suggest further application of the spectral features for predictive benthic habitat mapping including research based on multi frequency multibeam echosounder datasets the utilisation of spectral features derived from bathymetry provide an important step towards more accurate maps of benthic habitats and seabed sediments composition

interferometric imaging condition for wave equation migration the fidelity of depth seismic imaging depends on the accuracy of the velocity models used for wavefield reconstruction models can be decomposed in two components corresponding to large scale and small scale variations in practice the large scale velocity model component can be estimated with high accuracy using repeated migration tomography cycles but the small scale component cannot when the earth has significant small scale velocity components wavefield reconstruction does not completely describe the recorded data and migrated images are perturbed by artifacts there are two possible ways to address this problem 1 improve wavefield reconstruction by estimating more accurate velocity models and image using conventional techniques e g wavefield crosscorrelation or 2 reconstruct wavefields with conventional methods using the known background velocity model but improve the imaging condition to alleviate the artifacts caused by the imprecise reconstruction wedescribe the unknown component o

kinematic artifacts in prestack depth migration strong refraction of waves in the migration velocity model introduces kinematic artifacts coherent events not corresponding to actual reflectors into the image volumes produced by prestack depth migration applied to individual data bins because individual bins are migrated independently the migration has no access to the bin component of slowness this loss of slowness information permits events to migrate along multiple incident reflected ray pairs thus introducing spurious coherent events into the image volume this pathology occurs for all common binning strategies including common source common offset and common scattering angle since the artifacts move out with bin parameter their effect on the final stacked image is minimal provided that the migration velocity model is kinematically correct however common image gathers may exhibit energetic primary events with substantial residual moveout even with the kinematically accurate migration velocity model

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

reply to comment on near surface location geometry and velocities of the santa monica fault zone los angeles california by r d catchings g gandhok m r goldman d okaya m j rymer and g w bawden by t l pratt and j f dolan in a comment on our 2008 paper catchings gandhok et al 2008 on the santa monica fault in los angeles california pratt and dolan 2010 herein referred to as p d cite numerous objections to our work inferring that our study is flawed however as shown in our reply their objections contradict their own published works published works of others and proven seismic methodologies rather than responding to each repeated invalid objection we address their objections by topic in the subsequent sections in catchings gandhok et al 2008 we presented high resolution seismic reflection images that showed two near surface faults in the upper 50 m beneath the grounds of the wadsworth veterans administration hospital wvah although p d suggest we effectively duplicated their seismic acquisition our survey was not a duplication of their efforts rather we conducted a seismic imaging survey over a similar profile as pratt et al 1998 but used a different data acquisition system and different data processing methods to evaluate methods of seismically imaging blind faults in the wake of the 17 january 1994 m 6 7 northridge earthquake we used an acquisition method that provides both tomographic seismic velocities and reflection images our combined data approach allowed for shallower imaging 2 5 m minimum than the 20 m minimum of pratt et al 1998 clearer images of the fault zone and more accurate depth determinations rather than time images in processing the reflection images we used prestack depth migration which is generally accepted as the only proper imaging method for imaging subsurface structures with strong lateral velocity variations versteeg 1993 a condition shown to exist at the wvah site we correlated our reflection images with refraction tomography images borehole lithology and velocity data interferometric synthetic aperture radar images and changes in groundwater depths except for some minor differences our seismic reflection images coincide with previously published seismic reflection

angle dependent reflectivity by means of prestack migration most present day seismic migration schemes determine only the zero offset reflection coefficient for each grid point depth point in the subsurface in matrix notation the zero offset reflection coefficient is found on the diagonal of a reflectivity matrix operator that transforms the illuminating source wave field into a reflected wave field however angle dependent reflectivity information is contained in the full reflectivity matrix our objective is to obtain angle dependent reflection coefficients from seismic data by means of prestack migration multisource multioffset after downward extrapolation of source and reflected wave fields to one depth level the rows of the reflectivity matrix representing angle dependent reflectivity information for each grid point at that depth level are recovered by deconvolving the reflected wave fields with the related source wave fields this process is carried out in the space frequency domain in order to preserve the angle dependent reflectivity in the im

evaluation of seabed mapping methods for fine scale classification of extremely shallow benthic habitats application to the venice lagoon italy abstract recent technological developments of multibeam echosounder systems mbes allow mapping of benthic habitats with unprecedented detail mbes can now be employed in extremely shallow waters challenging data acquisition as these instruments were often designed for deeper waters and data interpretation honed on datasets with resolution sometimes orders of magnitude lower with extremely high resolution bathymetry and co located backscatter data it is now possible to map the spatial distribution of fine scale benthic habitats even identifying the acoustic signatures of single sponges in this context it is necessary to understand which of the commonly used segmentation methods is best suited to account for such level of detail at the same time new sampling protocols for precisely geo referenced ground truth data need to be developed to validate the benthic environmental classification this study focuses on a dataset collected in a shallow 2 10 m deep tidal channel of the lagoon of venice italy using 0 05 m and 0 2 m raster grids we compared a range of classifications both pixel based and object based approaches including manual maximum likelihood classifier jenks optimization clustering textural analysis and object based image analysis through a comprehensive and accurately geo referenced ground truth dataset we were able to identify five different classes of the substrate composition including sponges mixed submerged aquatic vegetation mixed detritic bottom fine and coarse and unconsolidated bare sediment we computed estimates of accuracy namely overall user producer accuracies and the kappa statistic by cross tabulating predicted and reference instances overall pixel based segmentations produced the highest accuracies and the accuracy assessment is strongly dependent on the number of classes chosen for the thematic output tidal channels in the venice lagoon are extremely important in terms of habitats and sediment distribution particularly within the context of the new tidal barrier being built however they had remained largely unexplored until now because of the surveying challenges the application of this remote sensing approach combined with targeted sampling opens a new perspective in the monitoring of benthic habitats in view of a knowledge based management of natural resources in shallow coastal areas

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

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

equivalence of source receiver migration and shot profile migration at first glance shot profile migration jacobs 1982 and source receiver survey sinking migration claerbout 1985 seem to be substantially different algorithms the basic principles used by the two schemes are different shot profile migration is performed by independently propagating the source wavefield and the receiver wavefield the image is obtained by crosscorrelating the two wavefields possibly normalized by the amplitude of the source wavefield source receiver migration is based on the concept of survey sinking by which we recursively synthesize equivalent data sets at increasing depth at each depth step imaging is performed by extracting the wavefield at zero time recently the issue of the relation between shot profile migration and source receiver migration has become more relevant because of two important developments 1 the increase in the practical applications of 3d prestack migration by wavefield continuation for imaging complex structures and 2 the introduction of methods for computing angle domain common image gathers adcig both for velocity estimation biondi and sava 1999 prucha et al 1999 clapp and biondi 2000 and for amplitude variation with angle ava analysis de bruin et al 1990 wapenaar et al 1999 sava et al 2001

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

target oriented velocity analysis using marchenko redatumed data abstractimaging a target zone and analyzing its corresponding velocities using seismic surface data can be challenging in particular if the target zone is located below a highly scattering overburden marchenko redatuming enables the redatuming of the surface reflection response to an arbitrary new datum level below such an overburden the obtained reflection response is free of internal multiples originating in the overburden and thus such data can be the starting point for target oriented analyses we develop the first application of marchenko redatumed data for target oriented velocity analysis marchenko redatumed data are used as the input for a conventional migration method to create angle domain common image gathers using incorrect velocities for redatuming or migration leads to residual moveout of reflections in such angle gathers thus semblance analysis of the angle gathers allows us to correct an erroneous velocity profile by combining events occurring at different depths in the angle gat

a review of least squares inversion and its application to geophysical problems geophysical inversion involves the estimation of the parameters of a postulated earth model from a set of observations since the associated model responses can be nonlinear functions of the model parameters nonlinear least squares techniques prove to be useful for performing the inversion a common type of inversion applies iterative damped linear least squares through use of the marquardt levenberg method traditionally this method has been implemented by solving the associated normal equations in conventional ways however singular value decomposition svd produces significant improvements in computational precision when applied to the same system of normal equations iterative least squares modeling finds application in a wide variety of geophysical problems two examples illustrate the approach 1 seismic wavelet deconvolution and 2 the location of a buried wedge from surface gravity data more generally nonlinear least squares inversion can be used to estimate earth models for any set of geophysical observations for which an appropriate mathematical description is available

influence of structural dip angles on interval velocity analysis common scattering angle and traditional common offset gathers can be of limited use for interval velocity analysis in regions with complex geologic structures in the summation process which occurs when generating each trace in the common image gather vital information about structural dip is lost during prestack depth migration this inadvertently lost data can provide important input to moveout based velocity updating algorithms maintaining this crucial dip information can improve the quality of the velocity analysis and imaging processes

habitat mapping of the maltese continental shelf using acoustic textures and bathymetric analyses abstract the uneven mapping of the maltese continental shelf precludes a full assessment of its marine habitats important for their monitoring and conservation in line with the eu marine strategy framework directive and local initiatives from 2009 to 2012 high resolution multibeam echosounder mbes surveys offshore the nw and e coasts of the maltese archipelago were carried out covering a total area of 1408 3 km2 with a maximum resolution of 1 m at depths from 1 5 to 263 m the types of benthic habitats occurring on the continental shelf often showed subtle acoustic variations this article aims at 1 integrating analyses of the bathymetry and acoustic textures with ground truthing grab samples in key areas 2 validating this combined approach by rewriting an existing benthic habitat map of the eastern continental shelf of malta 3 exploiting this ground truthed classification to calibrate an unsupervised classification of a dataset acquired with a different sonar the main results obtained from these analyses are i a sediment map of the continental shelf of nw malta and east of the maltese archipelago classifying in detail bedrock rocky blocks coarse sand and gravel fine to medium sand and maerl sand and gravel that supports the geomorphological interpretation of the seabed features ii an automatic classification of the seafloor morphology highlighting a very gentle sloping seabed crossed by the shelf break and by palaeo river valleys iii the first full benthic habitat map of the continental shelf offshore e and nw coast of malta obtained with a semi automatic classification in this work we highlight and explain the main differences in seafloor sediment coverage its morphology and the relative occurrences of benthic habitats between the nw and e sides of the maltese archipelago

esr dating of north anatolian turkey and nojima japan faults abstract electron spin resonance esr ages were obtained on al e and oh centres in quartz extracted from fault gouge from the north anatolian fault naf in turkey and the nojima fault nf in japan the data were used to test two contradictory criteria which have been used for the recognition of complete signal resetting during the fault movement the grain size plateau and the isochron models the grain size plateau method predicts decreasing ages with decreasing gain sizes because the fine grains are more intensely stressed during the faulting process for those grains that were completely reset a plateau of constant age is obtained and esr ages derived from centres with different stress sensitivity converge the isochron method is based on the fact that newly formed fracture surfaces are exposed to external alpha and beta radiation thus smaller grains ought to accumulate larger dose values the plot of grain size versus external dose rate yields an isochron which gives the age of the fracturing process it was found that most samples yielded smaller doses with decreasing grain sizes thus confirming the underlying principles of the grain size plateau method however only one sample yielded an extended plateau over a wider particle size range and converging ages for the different centres the e centre of the sample from the nf yielded the only result that indicated that the isochron method might work the results derived from the e centre of the other samples may have been interferred with by the so called counterfeit e signal which may render those results unreliable the esr ages obtained on the naf burdigalian to pliocene agree with those derived from geological estimates sample b which gave the extended plateaux and an age estimate of 2 54 0 58 ma indicates the time when faulting began the youngest age of 0 59 0 1 ma may indicate the last major faulting episode of the naf the minimum age of 1 56 0 22 ma obtained on the sample from the nf coincides with the commencement of the uplift of awaji island at about 1 2 ma ago which was caused by movements of the nf as well as a range of other fault systems in the area

a low frequency multibeam assessment spatial mapping of shallow gas by enhanced penetration and angular response anomaly this study highlights the potential of using a low frequency multibeam echosounder for detection and visualization of shallow gas occurring several meters beneath the seafloor the presence of shallow gas was verified in the bornholm basin baltic sea at 80 m water depth with standard geochemical core analysis and hydroacoustic subbottom profiling successively this area was surveyed with a 95 khz and a 12 khz multibeam echosounder mbes the bathymetric measurements with 12 khz provided depth values systematically deeper by several meters compared to 95 khz data this observation was attributed to enhanced penetration of the low frequency signal energy into soft sediments consequently the subbottom geoacoustic properties contributed highly to the measured backscattered signals those appeared up to 17 db higher inside the shallow gas area compared to reference measurements outside and could be clearly linked to the shallow gas front depth down to 5 meter below seafloor no elevated backscatter was visible in 95 khz mbes data which in turn highlights the superior potential of low frequency mbes to image shallow sub seafloor features small gas pockets could be resolved even on the outer swath up to 65 strongly elevated backscattering from gassy areas occurred at large incidence angles and a high gas sensitivity of the mbes is further supported by an angular response analysis presented in this study we conclude that the mbes together with subbottom profiling can be used as an efficient tool for spatial subbottom mapping in soft sediment environments

sensitivity kernel based tomographic migration velocity analysis using reverse time migration angle image gathers abstractsensitivity kernel based tomographic migration velocity analysis tmva provides a means to better update the migration velocity model in complex media for actual seismic data with finite frequency bandwidth migration velocity updated from wave equation based tomography is more suitable and robust than ray based tomography for images obtained from reverse time migration rtm depth residuals in the rtm extracted angle image gathers offer a reliable source of velocity information we have developed cost effective means of calculating the angle domain sensitivity kernel and incorporated it into the tmva approach using rtm angle image gathers the angle domain sensitivity kernels are used to convert the depth residuals from rtm angle image gathers into velocity perturbations which were then used to refine the velocity model we derived an approximate analytical residual moveout function for measuring depth residuals of the rtm angle image gather in isotropic media and also devised a workflow for

dating of a volcanic rock by electron spin resonance the age of a volcanic rock has been determined by esr dating using the ge center in quartz the total dose of natural radiation and the age obtained from the ge center are 460 krad and 2 07 0 50 ma respectively and those from the unidentified defect at g 2 011 are 484 krad and 2 16 0 21 ma respectively these dates agree well with the age of 2 0 0 5 ma determined by the fission track method high stress or temperature destroy these accumulated defects but in the same time produce a lot of new diamagnetic precursors which enable us to observe the clear esr signal

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

scattering and dip angle decomposition based on subsurface offset extended wave equation migration abstractan angle dependent reflection coefficient is recovered by seismic migration in the angle domain we have developed a postmigration technique for computing scattering and dip angle common image gathers cigs from seismic images extended by the subsurface offset based on wave equation migration methods our methodology suggests a system of radon transform operators by introducing local transform relations between the subsurface offset image and the angle domain components in addition to the commonly used decomposition of the scattering angle the methodology associates the wave equation migration with dip domain images as well the same postmigration subsurface offset image is used to decompose scattering and dip angle cigs individually or to decompose a multiangle cig by showing simultaneously both angles on the gather s axis we show that the dip angle response of seismic reflections is a spot like signature focused at the specular dip of the subsurface reflector it differs from the well stu

wave equation migration velocity analysis for vti models abstractanisotropic models are needed for wave simulation and inversion where a complex geologic environment exists we extended the theory of wave equation migration velocity analysis to build vertical transverse isotropic models because of the ambiguity between depth and in the acoustic regime we assumed can be accurately obtained from other sources of information and inverted for the nmo slowness and the anellipticity parameter we combined the differential semblance optimization objective function with the stacking power maximization to evaluate the focusing of the prestack image in the subsurface offset domain to regularize the multiparameter inversion we built a framework to adapt the geologic and the rock physics information to guide the updates in nmo slowness and this regularization step was crucial to stabilize the inversion and to produce geologically meaningful results we tested the proposed approach on a synthetic data set and a 2d gulf of mexico data set starting with a fairly

offset and angle domain common image point gathers for shot profile migration prestack depth migration of shot profiles by downward continuation is a practical imaging algorithm that is especially cost effective for sparse shot wide azimuth geometries the interpretation of offset as the displacement between the downward propagating shot wavefield and upward propagating receiver wavefield enables us to extract offset domain common image point cip gathers during shot profile migration the offset domain gathers can then be transformed to the angle domain with a radial trace mapping originally introduced for shot geophone migration the computational implications of this procedure include both the additional cost of multioffset imaging and an implicit transformation from shot geophone to midpoint offset coordinates although this algorithm provides a mechanism for imaging angle dependent reflectivity via shot profile migration for sparse shot geometries the fundamental problem of shot aliasing may severely impact the quality of cip gathers

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

angle domain common image gathers for migration velocity analysis by wavefield continuation imaging we analyze the kinematic properties of offset domain common image gathers cigs and angle domain cigs adcigs computed by wavefield continuation migration our results are valid regardless of whether the cigs were obtained by using the correct migration velocity they thus can be used as a theoretical basis for developing migration velocity analysis mva methods that exploit the velocity information contained in adcigs we demonstrate that in an adcig cube the image point lies on the normal to the apparent reflector dip that passes through the point where the source ray intersects the receiver ray the image point position on the normal depends on the velocity error when the velocity is correct the image point coincides with the point where the source ray intersects the receiver ray starting from this geometric result we derive an analytical expression for the expected movements of the image points in adcigs as functions of the traveltime perturbation caused by velocity errors by applying this ana

velocity estimation by image focusing analysis migration velocity can be estimated from seismic data by analyzing focusing and defocusing of residual migrated images the accuracy of these velocity estimates is limited by the inherent ambiguity between velocity and reflector curvature however velocity resolution improves when reflectors with different curvatures are present image focusing is measured by evaluating coherency across structural dips in addition to coherency across aperture azimuth angles the inherent ambiguity between velocity and reflector curvature is directly tackled by introducing a curvature correction into the computation of the semblance functional that estimates image coherency the resulting velocity estimator provides velocity estimates that are 1 unbiased by reflector curvature and 2 consistent with the velocity information that is routinely obtained by measuring coherency over aperture azimuth angles applications to a 2d synthetic prestack data set and a 2d field prestack data set confirm that the proposed method provides consistent and unbiased velocity information they also suggest that velocity estimates based on the new image focusing semblance may be more robust and have higher resolution than estimates based on conventional semblance functionals applying the proposed method to zero offset field data recorded in new york harbor yields a velocity function that is consistent with available geologic information and clearly improves the focusing of the reflectors

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

high frequency bottom backscatter measurements in shallow water bottom backscatter measurements have been made at six shallow water sites over the frequency range 20 85 khz for bottom types including silt sand and gravel bottom samples were taken at all experimental sites and some sites are well characterized in terms of seabed acoustic parameters and roughness a slight frequency dependence was observed and scattering strength was generally found to decrease as grazing angle decreased backscatter measurements in four azimuthal directions showed no measurable anisotropy for grazing angles between 10 and 40 spatial variability of backscatter strength was measured along two tracks approximately 35 and 75 km long

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

wide azimuth angle gathers for wave equation migration extended common image point cip gathers contain all of the necessary information for decomposition of reflectivity as a function of the reflection and azimuth angles at selected locations in the subsurface this decomposition operates after the imaging condition applied to wavefields reconstructed by any type of wide azimuth migration method e g using downward continuation or time reversal the reflection and azimuth angles are derived from the extended images using analytic relations between the space lag and time lag extensions the transformation amounts to a linear radon transform applied to the cips obtained after applying the extended imaging condition if information about the reflector dip is available at the cip locations then only two components of the space lag vectors are required thus reducing computational cost and increasing the affordability of the method applications of this method include the study of subsurface illumination in areas of complex geology where ray based methods are

detailed investigation of continental shelf morphology using a high resolution swath sonar survey the eel margin northern california abstract the eel shelf northern california lies within an active compressional tectonic margin subject to abundant terrigenous sediment input from the eel river a recent high resolution swath sonar survey provides us with the opportunity to investigate seafloor morphology and acoustic backscatter patterns within this dynamic region our analysis of the statistical character of bathymetry demonstrates a clear separation into large and small scale morphologies at a 3 10 km scale with smaller scale morphology heavily damped relative to large scale morphology the eel shelf bathymetry is subtle but several structures can be readily discerned in a residual bathymetry formed by removal of the downslope gradient some shelf structures are evidently related to depositional processes as evidenced by correlation with 100 yr sediment accumulation rates whereas others appear related to tectonic processes as evidenced by correlation with subsurface synclines and anticlines the sidescan structure of the shelf is dominated by the low backscatter over the eel and mad river subaqueous deltas evidently associated with the sand to mud transition however contrary to usual correlations between backscatter and grain size in this situation higher backscatter is associated with the muddy sediments in addition we observe a series of shore perpendicular striations or ribbons spaced 0 2 1 0 km apart which extend northward from the eel river subaqueous delta and lie at or near the sand to mud transition some aspects of ribbon morphology suggest that they may be associated with down slope flows

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

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

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

stochastic modeling of seafloor morphology inversion of sea beam data for second order statistics at scale lengths less than 100 km or so statistical descriptions of seafloor morphology can be usefully employed to characterize ridge crest processes off ridge tectonics and vulcanism sedimentation and postdepositional transport we seek to develop methods for the estimation of seafloor statistics that take into account the finite precision resolution and sampling obtained by actual echo sounding systems in this initial paper we restrict our attention to the problem of recovering second order statistics from data sets collected by multibeam devices such as sea beam the seafloor is modeled as a stationary zero mean gaussian random field completely specified by its two point covariance function we introduce an anisotropic two point covariance function that has five free parameters describing the amplitude orientation characteristic wave numbers and hausdorff fractal dimension of seafloor topography we formulate the general forward problem relating this model to the statistics of an ideal multibeam echo sounder in particular the along track autocovariance functions of individual beams and the cross covariance functions between beams of arbitrary separation using these second moments as data functionals we then pose the inverse problem of estimating the seafloor parameters from realistic noisy data sets with finite sampling and beamwidth and we solve this inverse problem by an iterative linearized least squares method the inversion method is applied to sea beam transit data from both the pacific and atlantic oceans sea beam system noise stands out as a sharp spike on the along track autocovariance function and can be modeled as a white noise process whose amplitude generally increases with beam angle the five parameters in our second order model can be estimated from the inversion of data sets comprising 100 200 km of track length in general the cross track wave number is the most poorly determined although uncertainties in the assumed sea beam response may bias the values of the fractal dimension using the assumed beamwidth the measured noise values and the seafloor parameters recovered from the inversion we generate sea beam synthetics whose statistical character can be directly compared with raw sea beam data for most of the track segments we have processed thus far the synthetics are similar to the data in the case of one atlantic profile however the comparison clearly indicates the necessity of incorporating higher order statistics the space domain procedures described in this paper can be extended for this purpose

angle domain common image gathers from anisotropic migration i present a general methodology for computing angle domain common image gathers adcigs in conjunction with anisotropic wavefield continuation migration the method is based on transforming the prestack image from the subsurface offset domain to the angle domain using slant stacks the processing sequence is the same as that for computing adcigs for the isotropic case though the interpretation of the relationship between the slopes measured in the prestack image and the aperture angles is more complex i demonstrate that the slopes measured by performing slant stacks along the subsurface offset axis of the prestack image provide a good approximation of the phase aperture angles and they are exactly equal to the phase aperture angles for flat reflectors in vertical transversly isotropic vti media in the general case of dipping reflectors the angles computed using slant stacks can be easily corrected by applying the relationships that i present in this paper and the accurate aperture angles can be determined as a function of the reflector dip and anisotropic slowness at the reflector i derive these relationships from both plane wave and ray viewpoints this theoretical development links the kinematics in adcigs with migration velocity errors i apply the proposed method to compute adcigs from the prestack image obtained by anisotropic migration of a 2d line recorded in the gulf of mexico i analyze the error introduced by neglecting the difference between the true phase aperture angle and the angle computed through slant stacks showing that at least for this data set these errors are negligible and can be safely ignored in contrast group aperture angles can be quite different from phase aperture angles thus ignoring the distinction between these two angles can be detrimental to practical applications

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

kirchhoff modeling inversion for reflectivity and subsurface illumination because of its computational efficiency prestack kirchhoff depth migration is currently one of the most popular algorithms used in 2 d and 3 d subsurface depth imaging nevertheless kirchhoff algorithms in their typical implementation produce less than ideal results in complex terranes where multipathing from the surface to a given image point may occur and beneath fast carbonates salt or volcanics through which ray theoretical energy cannot penetrate to illuminate underlying slower velocity sediments to evaluate the likely effectiveness of a proposed seismic acquisition program we could perform a forward modeling study but this can be expensive we show how kirchhoff modeling can be defined as the mathematical transpose of kirchhoff migration the resulting kirchhoff modeling algorithm has the same low computational cost as kirchhoff migration and unlike expensive full acoustic or elastic wave equation methods only models the events that kirchhoff migration can image kirchhoff modeling is also

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

microseismic imaging using a source function independent full waveform inversion method we thank kaust for sponsoring this research we also thank to the team of swag for their help during the research

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

residual moveout in anisotropic angle domain common image gathers i develop the fundamental concepts for quantitatively relating perturbations in anisotropic parameters to the corresponding reflector movements in angle domain common image gathers adcigs after anisotropic wavefield continuation migration the proposed theory potentially enables the application of residual moveout rmo analysis of adcigs to velocity estimation in realistic anisotropic conditions i demonstrate that linearization of the relationship between anisotropic velocity parameters and reflector movements can be derived by assuming stationary raypaths this assumption leads to a fairly simple analytical derivation i then apply the general method to the particular case of rmo analysis of reflections from flat reflectors in a vertical transverse isotropic vti medium this analysis yields expressions to predict rmo curves in migrated adcigs these rmo expressions are functions of both the phase aperture angle and the group aperture angle several numerical examples demonstrate the accuracy of the rmo curves predicted by my kinematic analysis the synthetic examples also show that approximating the group angles with the phase angles in the application of the rmo expressions may lead to substantial errors for events reflected at wide aperture angles the results obtained by migrating a 2d line extracted from a gulf of mexico 3d data set confirm the accuracy of the proposed method the rmo curves predicted by the theory match the rmo function observed in the adcigs computed from the real data

esr dating of ancient flints natural radioactivity can produce measurable amounts of radiation damage in rocks and glasses and the gradual accumulation of this damage with time provides a built in clock that can be used as a dating tool for geology and archaeology although a studied technique for estimating this damage involves measurements of stored thermoluminescent tl activity1 4 several authors have reported the direct observation of natural radiation damage by esr5 7 we describe here esr measurements on a damage signal which we have found to be present without exception in a wide variety of natural flints the point defect responsible for the signal is identified and the samples are calibrated with an artificial damage simulation preliminary age determinations are presented for several natural flints flint artefacts heated in antiquity will have their clock reset to zero and measurements on one sample suggest that the esr technique may have applications in the study of early cultures

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

azimuth preserved local angle domain prestack time migration in isotropic vertical transversely isotropic and azimuthally anisotropic media conventional prestack migration does not preserve local directional information of the seismic waves at the image points new attempts such as sectored migration of azimuth limited or common offset vector data only concern source receiver azimuth and offset on the surface which can be poor representation of subsurface wavepath direction moreover they could result in inaccurate imaging because they do not account for the energy propagation between azimuths or offset vectors in the past decade local angle domain seismic imaging has been highly advocated to avoid migration artifacts and to improve velocity estimation in complex media considering prestack time migration pstm is still widely used in seismic imaging and seismic data preconditioning for amplitude variations with offset or incident angle avo ava analysis fracture detection and reservoir characterization we present an azimuth preserved local angle domain kirchhoff pstm approach for such purposes we apply a seismic imaging condition i

use of rtm full 3d subsurface angle gathers for subsalt velocity update and image optimization case study at shenzi field various reverse time migration rtm angle gather generation techniques have been developed to address poor subsalt data quality and multiarrival induced problems in gathers from kirchhoff migration but these techniques introduce new problems such as inaccuracies in 2d subsurface angle gathers and edge diffraction artifacts in 3d subsurface angle gathers the unique rich azimuth data set acquired over the shenzi field in the gulf of mexico enabled the generally artifact free generation of 3d subsurface angle gathers using this data set we carried out suprasalt tomography and salt model building steps and then produced 3d angle gathers to update the subsalt velocity we used tilted transverse isotropy rtm with extended image condition to generate full 3d subsurface offset domain common image gathers which were subsequently converted to 3d angle gathers the angle gathers were substacked along the subsurface azimuth axis into azimuth sectors residual moveout analysis was carried out and ray based tom

stereographic imaging condition for wave equation migration imaging under the single scattering approximation consists of two steps wavefield reconstruction of source and receiver wavefields from simulated and recorded data respectively andimagingfromtheextrapolatedwavefieldsoflocations where reflectors occur conventionally the imaging condition indicates the presence of reflectors when propagationtimesofreflectionsinthesourceandreceiverwavefields match the main drawback of a conventional crosscorrelation imaging condition is that it ignores the local spatial coherence of reflection events and relies only on their propagationtime thisleadstointerferencebetweenunrelatedevents thatoccuratthesametime sourcesofcrosstalkincludeseismic events corresponding to different seismic experiments propagation paths types of reflectionsprimary or multiple orwavemodespors analternativeimagingconditionoperates on the same extrapolated wavefields but crosscorrelationtakesplaceinahigher dimensiondomainwhereseismic events are separated based on their local space time slope events are matched based on two parameters time and local slope thus justifying the name stereographic for this imagingcondition stereographicimagingattenuateswavefield crosstalk and reduces imaging artifacts compared with conventional imaging applications of the stereographic imagingconditionincludesimultaneousimagingofmultipleseismic experiments multiple attenuation in the imaging condition andattenuationofcrosstalkbetweenmultiplewavefield branchesormultiplewavemodes