seismic imaging of salt structures in the gulf of mexico in this article we discuss seismic imaging of salt structures in the gulf of mexico with emphasis on the recognition preservation and migration of salt signals we describe three salt imaging technologies

shallow structure characterization by 2d elastic full waveform inversion assessing the effectiveness of elastic full waveform inversion fwi algorithms when applied to shallow 2d structures in the presence of a complex topography is critically important by using fwi we overcome inherent limitations of conventional seismic methods used for near surface prospecting acoustic tomography and multichannel spectral analysis of surface waves the elastic forward problem formulated in the frequency domain is based on a mixed finite element p0p1 discontinuous galerkin method to ensure accurate modeling of complex topography effects at a reasonable computing cost the inversion problem uses an fwi algorithm to minimize the misfit between observed and calculated data based on results from a numerical experiment performed on a realistic landslide model inspired from the morphostructure of the super sauze earthflow we analyzed the effect of using a hierarchical preconditioning strategy based on a simultaneous multifrequency inversion of damped data to mitigate the strong nonlinearities coming from the surface waves this strategy is a key point in alleviating the strong near surface effects and avoiding convergence toward a local minimum using a limited memory quasi newton method improved the convergence level these findings are analogous to recent applications on large scale domains although limited sourcereceiver offset ranges low frequency content of the source and domination of surface waves on the signal led to some difficulties regarding the impact of data decimation on the inversion results we have learned that an inversion restricted to the vertical data component can be successful without significant loss in terms of parameter imagery resolution in our investigations of the effect of increased source spacing we found that a sampling of 4 m less than three times the theoretical maximum of one half wavelength led to severe aliasing

near surface velocity estimation using source domain full traveltime inversion and early arrival waveform inversion accurate estimation of near surface velocity is a key step for imaging deeper targets we present a new workflow to invert complex early arrivals in land seismic data for near surface velocities this workflow is composed of two methods source domain full traveltime inversion fti and early arrival waveform inversion ewi source domain fti automatically generates the background velocity that kinematically matches the reconstructed plane wave sources from early arrivals with true plane wave sources this method does not require picking first arrivals for inversion which is one of the most challenging and labor intensive steps in ray based first arrival traveltime tomography especially when the subsurface medium contains low velocity zones that cause shingled multi value arrivals moreover unlike conventional born based method source domain fti can determine if the initial velocity is slower or faster than the true one according to the gradient sign in addition the computational cost is reduced co

quantitative imaging of the permo mesozoic complex and its basement by frequency domain waveform tomography of wide aperture seismic data from the polish basin in this study we present the workflow and results of 2d frequency domain waveform tomography applied to the global offset seismic data acquired in central poland along a 50 km long profile during the grundy 2003 experiment the waveform tomography method allows full exploitation of the wide aperture content of these data and produces in a semi automatic way both the detailed p wave velocity model and the structural image i e perturbations in respect to the starting model thirteen frequencies ranging from 4 to 16 hz were inverted sequentially gradually introducing higher wavenumbers and more details into the velocity models although the data were characterised by relatively large shot spacings 1 5 km we obtained clear images both of the mesozoic and permian sedimentary cover velocity patterns indicated facies changes within the jurassic and zechstein strata a high velocity layer ca 5500 m s was found near the base of triassic scythian which made the imaging of a deeper layer difficult nevertheless we were able to delineate the base of the permian i e base of the rotliegend which was not possible to derive from conventional common depth point processing as well as some deeper events attributed to the carboniferous the sub permian events formed a syn form which favoured our previous interpretation of a depression filled with upper carboniferous molasse the validity of the waveform tomography derived model was confirmed by well log data forward ray tracing modelling and synthetic seismograms calculations provided another justification for the key structures present in the waveform tomography model

elastic wave equation traveltime and waveform inversion of crosswell data a method is presented for reconstructing p and s velocity distributions from elastic traveltimes and waveforms the input data consist of crosswell hydrophone records generated by a piezoelectric borehole source borehole effects are partially accounted for by using a low frequency green s function to simulate the pressure generated in the fluid filled receiver well the tube waves in the borehole are ignored on the assumption that they can be removed from the field data by median filtering in addition the source radiation pattern is partially taken into account by inverting for the equivalent stress components acting on the earth at the source location the elastic wave equation traveltime and waveform inversion wtw method is applied to both synthetic crosswell data and the mcelroy field crosswell data as predicted by theory results show that elastic wtw tomograms provide a sharper interface image than delineated in the traveltime tomograms the spatial resolution of the mcelroy traveltime tomogr

tomographic imaging of velocity and q with application to crosswell seismic data from the gypsy pilot site oklahoma the centroid frequency shift method is implemented tested with synthetic data and applied to field data from three contiguous crosswell seismic experiments at the gypsy pilot in northern oklahoma the similtaneous iterative reconstruction technique is used for tomographic estimations of both p wave velocity and q no amplitude corrections or spreading loss corrections are needed for the q estimation the estimated in situ velocity and q distributions correlate well with log data and local lithology the q velocity ratio appears to correlate with the sand shale ratio ranging from an average of 15 s km for the sand dominated lithologies to an average of 8 5 s km for the shale dominated ones with the result that new information is provided on interwell connectivity

atmospheric boundary layer studies in fife challenges and advances in a brief review and introduction of 13 other articles concerning the atmospheric boundary layer abl attention is focused on challenges and advances in experimental design and analysis represented by those studies which are part of the first international satellite land surface climatology project islscp field experiment fife the articles not only address problems posed by the experimental site itself size inhomogeneity of terrain and vegetation but also examine relationships between the abl and remote sensing measurements they also scrutinize various abl data for internal consistency for example in budget studies and for comparisons with other abl results and with data from surface measurements finally new and existing analysis techniques are presented and evaluated for example for abl self preservation extraction of wind velocities from lidar reflectivity data estimation of surface heat flux from doppler lidar data two dimensional maps of abl and surface variables sensitivity of aircraft data to surface variations and contribution of individual abl structures to flight level fluxes besides adding to our understanding of abl processes the studies point out several problems that need to be addressed by the measurement and modeling communities

colluvial wedge imaging using traveltime and waveform tomography along the wasatch fault near mapleton utah summary four high resolution seismic surveys were conducted across the wasatch fault zone near mapleton utah the objective was twofold 1 to use velocity tomograms and reflection images to delineate fault structures and colluvial wedges to more than twice the depth of the mapleton megatrench excavated by urs personnel 2 to assess the strengths and limitations of traveltime and waveform tomography by synthetic studies and comparison of the tomogram to the ground truth seen in the megatrench log four out of the five faults within the trench area are accurately identified in the migrated image and in the tomograms and the main fault s dip angle is estimated to be between 71 and 80 two additional faults are interpreted outside the trench the faults can be delineated down to 30 m below the surface which is 20 m deeper than the excavated trench five out of six colluvial wedges found in the trench log were seen as low velocity zones lvzs in the tomogram however the biggest colluvial wedge could not be identified by either tomography method waveform tomography prevailed over ray based traveltime tomography by more clearly recovering the faults and lvzs a newly discovered lvz at a depth of 18 21 m below the surface possibly represents a colluvial wedge and is estimated to be less than 21 000 years old if this lvz is a colluvial wedge the earthquake history obtained by trenching can be extended from 13 500 to 21 000 yr with seismic tomography our results further demonstrate the capability of tomography in identifying faults and show that waveform tomography more accurately resolves colluvial wedges compared to traveltime tomography however despite the successful recovery of most faults and some but not all colluvial wedges both tomography methods show many more lvzs besides the wedges so that an unambiguous interpretation cannot be made a major part of the ambiguity in the tomograms is due to the many major faults which result in an uneven raypath coverage as our synthetic studies show hence seismic trenching will be more successful at simple fault geometries however even under optimal conditions there will be some ambiguity in the interpretation so that detected lvzs should be drilled cored and dated to determine the history of the ancient earthquakes

focus on land seismic technology the near surface challenge a new era in land seismic is at hand growing energy demand will spur greater efforts in exploration and development into regions of the world where hydrocarbons occur in land environments interpreters will require accurate near surface solutions for mapping low relief structures and stratigraphic traps and to improve data quality for placing horizontal wells this will require solutions to near surface challenges such as energy penetration scattering source generated noise surface generated multiples statics and source and receiver coupling solutions to these problems will become possible due to advances in seismic acquisition including simultaneous source acquisition and wireless seismic driven ultrahigh channel systems additionally advances in seismic processing technology for processing the resulting huge data volumes will be made possible by continual growth in computational capability these advances will for the first time allow acquisition of true 3d seismic data this will not only re

high resolution near surface velocity model building using full waveform inversion a case study from southwest sweden full waveform inversion fwi is an iterative optimization technique that provides high resolution models of subsurface properties frequency domain acoustic fwi was applied to seismic data acquired over a known quick clay landslide scar in southwest sweden we inverted data from three 2 d seismic profiles 261 572 m long two of them shot with small charges of dynamite and one with a sledgehammer to our best knowledge this is the first published application of fwi to sledgehammer data both sources provided data suitable for waveform inversion the sledgehammer data containing even wider frequency spectrum inversion was performed for frequency groups between 27 5 and 43 1 hz for the explosive data and 27 5 51 0 hz for the sledgehammer the lowest inverted frequency was limited by the resonance frequency of the standard 28 hz geophones used in the survey high velocity granitic bedrock in the area is undulated and very shallow 15 100 m below the surface and exhibits a large p wave velocity contrast to the overlying normally consolidated sediments in order to mitigate the non linearity of the inverse problem we designed a multiscale layer stripping inversion strategy obtained p wave velocity models allowed to delineate the top of the bedrock and revealed distinct layers within the overlying sediments of clays and coarse grained materials models were verified in an extensive set of validating procedures and used for pre stack depth migration which confirmed their robustness

nonlinear elastic waveform inversion of land seismic reflection data data from 53 shot records collected in a conventional land seismic reflection survey are inverted to obtain subsurface maps of short wavelength variations in elastic parameters impedance the inversion method employs a robust nonlinear iterative gradient algorithm which inverts waveform data thus there is no picking of travel times or amplitudes the algorithm is also computationnally expensive as it relies heavily upon elastic finite difference modeling in addition because a gradient search is employed to minimize the misfit between observed and modeled data we attempt to solve only the weakly nonlinear problem associated with the short wavelenghts of imedance information on the short wavelengths of impedance is mainly derived from amplitude variations of the data resolving the long wavelengths of velocity background is thought to be a highly nonlinear problem at least for waveform inversion and is not attempted herein for the inversion of this data set long wavelenghts have been derived from well logs located along the seismic reflection profile although the data set is dominated by unconverted p wave arrivals we obtain maps of the short wavelenghts of both p impedance and s impedance three well logs in the survey area confirm the validity of the p impedance map however no s velocity well log are available from this area there are channel sands of economic interest which have a thickness of approximately 10 m in one well and are very thin or absent in the other two wells the 10 m occurrence of channel sands is quite visible in both impedance maps we note that because inversion in three dimensions of a realistically sized data set is simply not possible on present day computers all modeling was performed in two dimensions and a rather crude conversion from spherical to cylindrical energy spreading was applied to the original field data before inversion other seismic reflection data in the survey area suggest that there is little lateral variation in the subsurface except for the channel sands thus we feel that a two dimensional inversion with energy compensation is justified

on the role of reflections refractions and diving waves in full waveform inversion full waveform inversion suffers from local minima due to a lack of low frequencies in data a reflector below the zone of interest may however help in recovering the long wavelength components of a velocity perturbation as demonstrated in a paper by mora with the born approximation for a perturbation in a reference model consisting in two homogeneous isotropic acoustic half spaces and the assumption of infinitely large apertures available in the data analytic expressions can be found that describe the spatial spectrum of the recorded seismic signal as a function of the spatial spectrum of the inhomogeneity diving waves can be included if the deeper part of the homogeneous model is replaced by one that has a vertical velocity gradient we study this spectrum in more detail by separately considering scattering of direct reflected and head waves as well as singly and multiply reflected diving waves for a gradient model taking the reflection coefficient of the deeper reflector into account we obtain sensitivity estimates for each wavetype although the head waves have a relatively small contribution to the reconstruction of the velocity perturbation compared to the other waves they contain reliable long wavelength information that can be beneficial for full waveform inversion if the deeper part has a constant positive velocity gradient with depth all the energy eventually returns to the source receiver line given a sufficiently large acquisition aperture this will improve the sensitivity of the scattered reflected and refracted wavefields to perturbations in the background model the same happens for a zero velocity gradient but with a very high impedance contrast between the two half spaces which results in a large reflection coefficient

joint inversion of seismic traveltime and frequency domain airborne electromagnetic data for hydrocarbon exploration geophysical joint inversion requires setting of few parameters for the optimum performance of the process however there are yet no known detailed procedures for selecting the various parameters for performing the joint inversion previous works on the joint inversion of em and seismic data have reported parameter applications for both data sets acquired from the same dimensional geometry either both in 2d or in 3d and few on variant geometry but none has discussed the parameter selections for the joint inversion of methods from variant geometry for example a 2d seismic travel and pseudo 2d frequency domain em data with the advantage of affordable computational cost and the sufficient approximation of 1d em model in a horizontally layered sedimentary environment we are able to set optimum joint inversion parameters to perform structurally constrained joint 2d seismic traveltime and pseudo 2d em data for hydrocarbon exploration from the synthetic experiments even in the presence of noise we are a

traveltime tomographic inversion with simultaneous static corrections well worth the effort we have developed a first arrival traveltime inversion scheme that jointly solves for seismic velocities and source and receiver static time terms the static time terms are included to compensate for varying time delays introduced by the near surface low velocity layer that is too thin to be resolved by tomography results on a real data set consisting of picked first arrival times from a seismic reflection 2d 3d experiment in a crystalline environment show that the tomography static time terms are very similar in values and distribution to refraction static corrections computed using standard refraction statics software when applied to 3d seismic reflection data tomography static time terms produce similar or more coherent seismic reflection images compared to the images using corrections from standard refraction static software furthermore the method provides a much more detailed model of the near surface bedrock velocity than standard software when the static time terms are included in the inversion low velocity zones in this model correlate with other geologic and geophysical data suggesting that our method results in a reliable model in addition to generally being required in seismic reflection imaging static corrections are also necessary in traveltime tomography to obtain high fidelity velocity images of the subsurface

nonlinear refraction and reflection travel time tomography we develop a rapid nonlinear travel time tomography method that simultaneously inverts refraction and reflection travel times on a regular velocity grid for travel time and ray path calculations we apply a wave front method employing graph theory the first arrival refraction travel times are calculated on the basis of cell velocities and the later refraction and reflection travel times are computed using both cell velocities and given interfaces we solve a regularized nonlinear inverse problem a laplacian operator is applied to regularize the model parameters cell slownesses and reflector geometry so that the inverse problem is valid for a continuum the travel times are also regularized such that we invert travel time curves rather than travel time points a conjugate gradient method is applied to minimize the nonlinear objective function after obtaining a solution we perform nonlinear monte carlo inversions for uncertainty analysis and compute the posterior model covariance in numerical experiments we demonstrate that combining the first arrival refraction travel times with later reflection travel times can better reconstruct the velocity field as well as the reflector geometry this combination is particularly important for modeling crustal structures where large velocity variations occur in the upper crust we apply this approach to model the crustal structure of the california borderland using ocean bottom seismometer and land data collected during the los angeles region seismic experiment along two marine survey lines details of our image include a high velocity zone under the catalina ridge but a smooth gradient zone between catalina ridge and san clemente ridge the moho depth is about 22 km with lateral variations

wave equation traveltime inversion this paper presents a new traveltime inversion method based on the wave equation in this new method designated as wave equation traveltime inversion wt seismograms are computed by any full wave forward modeling method we use a finite difference method the velocity model is perturbed until the traveltimes from the synthetic seismograms are best fitted to the observed traveltimes in a least squares sense a gradient optimization method is used and the formula for the frechet derivative perturbation of traveltimes with respect to velocity is derived directly from the wave equation no traveltime picking or ray tracing is necessary and there are no high frequency assumptions about the data body wave diffraction reflection and head wave traveltimes can be incorporated into the inversion in the high frequency limit wt inversion reduces to ray based traveltime tomography it can also be shown that wt inversion is approximately equivalent to full wave inversion when the starting velocity model is

finite frequency tomography in a crustal environment application to the western part of the gulf of corinth in this paper we investigate finite frequency effects in crustal tomography we developed an inversion procedure based on an exact numerical computation of the sensitivity kernels in this approach we compute the 3d travel time sensitivity kernels by using 1 graph theory and an additional bending to estimate accurately both rays and travel times between source receiver and diffraction points and 2 paraxial ray theory to estimate the amplitude along theses rays we invert both the velocity and the hypocentre parameters using these so called banana doughnut kernels and the lsqr iterative solver we compare the ray theoretical and the finite frequency tomography to image the intermediate structures beneath the gulf of corinth greece which has long been recognized as the most active continental rifting zone in the mediterranean region our dataset consists of 451 local events with 9233 p first arrival times recorded in the western part of the gulf aigion area in the framework of the 3f corinth european project previous tomographic images showed a complex velocity crustal model and a low dip surface that may accommodate the deformation accurate velocity models will help to better constrain the rifting process which is still a subject of debate the main results of this study show that finite frequency tomography improves crustal tomographic images by providing better resolved images of the 3d complicated velocity structure because the kernels spread the information over a volume finite frequency tomography results in a sharpening of layer boundaries as we observed for the shallower part of the crust down to 5 km depth beneath the gulf of corinth

inverse theory applied to multi source cross hole tomography part 1 acoustic wave equation method1 frequency domain methods are well suited to the imaging of wide aperture cross hole data however although the combination of the frequency domain with the wavenumber domain has facilitated the development of rapid algorithms such as diffraction tomography this has also required linearization with respect to homogeneous reference media this restriction and association restrictions on source receiver geometries are overcome by applying inverse techniques that operate in the frequency space domain in order to incorporate the rigorous modelling technique of finite differences into the inverse procedure a nonlinear approach is used to reduce computational costs the method of finite differences is applied directly to the frequency domain wave equation the use of high speed high capacity vector computers allow the resultant finite difference equations to be factored in place in this way wavefields can be computed for additional source positions at minimal extra cost allowing inversions to be generated using data from a very large number of source positions synthetic studies show that where weak scatter approximations are valid diffraction tomography performs slightly better than a single iteration of non linear inversion however if the background velocities increase systematically with depth diffraction tomography is ineffective whereas non linear inversion yields useful images from one frequency component of the data after a single iteration further synthetic studies indicate the efficacy of the method in the time lapse monitoring of injection fluids in tertiary hydrocarbon recovery projects

two dimensional full wavefield inversion of wide aperture marine seismic streamer data summary a 2 d full wavefield inversion method is presented for the processing of wide aperture data the diversity of information contained within such datasets may be handled in a complete manner by first matching the traveltimes of the main events and then progressing to waveform fitting of the data through explicit full wavefield modelling our wavefield inversion scheme is based upon a finite difference solution of the 2 d elastic wave equation in the time distance domain the strength of adopting such an approach is the ability to generate all possible wave types within a given 2 d model multiples converted waves etc and thus to simulate and accurately model complex seismic wavefields the aim of the inversion is to find the 2 d p wave velocity model that minimizes the least squared difference between the observed and synthetic data across the full range of offsets following extensive testing on synthetic data the wavefield inversion scheme has been applied to wide aperture real marine seismic streamer datasets we present results from the synthetic testing and the wavefield inversion of wide aperture real data out to 12 km offset that was recorded on a single streamer even though current computational restrictions allow only a small subsection of the data to be analysed these examples demonstrate the potential value of wide aperture 2 d full wavefield inversion

tomostatics turning ray tomography static corrections applications of tomographic velocities to static corrections have drawn much attention recently in computing field statics with the help of seismic tomography geophysical prospecting 1987 w n de amorin et al showed that the waves refracted at the base of a low velocity layer can be used successfully for computing and refining field static corrections in tomographic inversion for velocity plus statics seg expanded abstracts 1991 livia squires et al pointed out that velocity variations and static shifts caused by near surface effects and positional uncertainties can be solved simultaneously using constraint tomography

two dimensional velocity models from wide angle seismic data by wavefield inversion summary modern wide angle surveys are often multi fold and multi channel with densely sampled source and receiver spacings such closely spaced data are potentially amenable to multi channel techniques involving wavefield propagation methods such as those commonly used in reflection data processing however the wide angle configuration requires techniques capable of handling very general wave types including those not commonly used in reflection seismology this is a situation analogous to that faced in cross borehole seismics where similar wave types are also recorded in a real cross borehole example we compare pre stack migration traveltime tomography and wavefield inversion we find that wavefield inversion produces images that are quantitative in velocity as are the tomograms but are of significantly higher resolution the wavefield inversion results have a resolution comparable to that of the qualitative pre stack migration images we seek to extend this novel development to the larger scale problem of crustal imaging an essential element of the approach we adopt is its formulation entirely within the temporal frequency domain this has three principal advantages 1 we can choose to decimate the data by selecting only a limited number of frequency components to invert thus making inversion of data from large numbers of source positions feasible 2 we can mitigate the notorious non linearity of the seismic inverse problem by progressing from low frequency components in the data to high frequency components and 3 we can include in the model any arbitrary frequency dependence of inelastic attenuation factors q and indeed solve for the spatial distribution of q an initial synthetic test with an anomaly located within the middle crust yields a velocity image with the correct structural features of the anomaly and the correct magnitude of velocity anomaly this is related to the fact that the reconstruction is obtained from forward scattered waves under these conditions the method thus behaves much like tomography a second test with a deeper more extensive anomaly yields an image with the correct velocity polarity and the correct location but with a deficiency in low and high wavenumbers in this case this is because the reconstruction is obtained from backscattered waves under these conditions the method behaves not like tomography but like migration a more extensive test based on a large wide angle survey in south eastern california and western arizona demonstrates a real potential for high resolution imaging of crustal structures although our results are limited by the acoustic approximation and by the relatively low frequencies that we can model today the images are sufficiently encouraging to warrant future research the problem of local minima in the objective function is the most significant practical problem with our method but we propose that appropriate layer stripping methods can handle this problem

velocity model building by waveform inversion of early arrivals and reflections a 2d case study with gas cloud effects joint full waveform inversion jfwi combines reflection waveform inversion rwi and early arrival waveform inversion ewi to build a large scale velocity model of the subsurface from long offset data the misfit function of jfwi requires an explicit separation between the short spread reflections and early arrivals the feasibility of which is illustrated with a real data case study jfwi is alternated with a waveform inversion migration of short spread reflections to provide a short scale impedance model this model is needed for building the sensitivity kernel of rwi along the two way reflection paths the large scale velocity macromodel built by jfwi can be used as the initial model for classical fwi to enrich the high wavenumber content of the subsurface model we present an application of this workflow to a real 2d obc profile across a gas cloud in the north sea to review its main promises and pitfalls viscoacoustic vti seismic modeling allows us to account for attenuation and anisotropy effects

acoustic wave equation traveltime and waveform inversion of crosshole seismic data a hybrid wave equation traveltime and waveform inversion method is presented that reconstructs the interwell velocity distribution from crosshole seismic data this inversion method designated as wtw retains the advantages of both full wave inversion and traveltime inversion i e it is characterized by reasonably fast convergence which is somewhat independent of the initial model and it can resolve detailed features of the velocity model in principle no traveltime picking is required and the computational cost of the wtw method is about the same as that for full wave inversion we apply the wtw method to synthetic data and field crosshole data collected by exxon at their friendswood texas test site results show that the wtw tomograms are much richer in structural information relative to the traveltime tomograms subtle structural features in the wtw friendswood tomogram are resolved to a spatial resolution of about 1 5 m yet are smeared or completely absent in the traveltime tomogram this sugg

palaeoseismicity of the oquirrh fault utah from shallow seismic tomography the magnitude and frequency of normal fault palaeoearthquakes are usually determined by trenching studies that ascertain the size and number of colluvial wedges along the fault such information can be invaluable in predicting the seismic hazard and potential for a future earthquake in that region digging trenches across normal faults however is environmentally intrusive expensive and limited in the penetration depth to overcome these problems we propose the use of 3 d seismic tomography as a means to identify the shapes and sizes of colluvial wedges along normal faults as an example 2 d and 3 d seismic surveys were conducted across the oquirrh fault utah with the purpose of imaging the normal fault structure to a depth of about 10 m results show that the 3 d tomogram clearly delineates the fault zone and a colluvial wedge both of which correlate extremely well with the geological cross section interpreted from an adjacent trench the thickness of the colluvial wedge image is used in conjunction with a seismic section to compute an estimate of a 6 8 moment magnitude earthquake for the most recent event on this fault which is in close agreement with the 7 0 estimate based on a nearby trenching study these tomographic results demonstrate for the first time that seismic imaging methods can be used in some cases to estimate unambiguously the shapes of colluvial wedges and the sizes of prehistoric earthquakes thus seismic tomography has the possibility of providing cheaper deeper and wider but less resolved images of fault systems than the intrusive excavation of trenches across faults

applications of multiscale waveform inversion to marine data using a flooding technique and dynamic early arrival windows a recently developed time domain multiscale waveform tomography mwt method is applied to synthetic and field marine data although the mwt method was already applied to synthetic data the synthetic data application leads to a development of a hybrid method between waveform tomography and the salt flooding technique commonly use in subsalt imaging this hybrid method can overcome a convergence problem encountered by inversion with a traveltime velocity tomogram and successfully provides an accurate and highly resolved velocity tomogram for the 2d seg eage salt model in the application of mwt to the field data the inversion process is carried out using a multiscale method with a dynamic early arrival muting window to mitigate the local minima problem of waveform tomography and elastic effects with the modified mwt method reasonably accurate results as verified by comparison of migration images and common image gathers were obtained the hybrid method with the salt flooding technique is not used in this field data example because there is no salt in the subsurface according to our interpretation however we believe it is applicable to field data applications

2 d seismic trenching of colluvial wedges and faults abstract images of the depth and shape of colluvial wedges by 3 d travel time tomography can be valuable in estimating the past history of ancient earthquakes and assessing the earthquake hazard of a fault unfortunately 3 d seismic surveys can be both costly and time consuming in this paper we report our first successful results of detecting the shapes and depths of colluvial wedges with 2 d travel time tomography the locations of the colluvial wedges are along the oquirrh fault and the salt lake city segment of the wasatch fault we also report that the tomogram from one of our 2 d surveys suggests the possibility of detecting multiple colluvial wedges at depth using both reflection and tomographic images at another site clearly reveals the presence of a known shallow fault and the contact between native soil and recent fill our results suggest the synergistic use of both seismic tomography and reflection imaging we denote as seismic trenching as a means of detecting shallow colluvial wedges and faults seismic trenching has the potential to significantly expand the lateral extent and depth of investigation of paleoseismology

early arrival waveform tomography on near surface refraction data we develop a waveform tomography method for estimating the velocity distribution that minimizes the waveform misfit between the predicted and observed early arrivals in space time seismograms by fitting the waveforms of early arrivals early arrival waveform tomographyewt naturally takes into account more general wave propagation effects compared to the high frequency method of traveltime tomography meaning that ewt can estimate a wider range of slowness wavenumbers another benefit of ewt is more reliable convergence compared to full waveform tomography because an early arrival misfit function contains fewer local minima synthetic test results verify that the waveform tomogram is much more accurate than the traveltime tomogram and that this algorithm has good convergence properties for marine data from the gulf of mexico the statics problem caused by shallow gassy muds was attacked by using ewt to obtain a more accurate velocity model using the waveform tomogram to correct for statics the stacked section was significantly improved compared to using the normal moveout nmo velocity and moderately improved compared to using the traveltime tomogram inverting high resolution land data from mapleton utah showed an ewt velocity tomogram that was more consistent with the ground truth trench log than the traveltime tomogram our results suggest that ewt can provide supplemental shorter wavelength information compared to the traveltime tomogram for both shallow and moderately deep seismic data

ers 1 scatterometer measurements i the relationship between radar cross section and buoy wind in two oceanic regions extensive european remote sensing satellite ers 1 spacecraft scatterometer measurements were collocated within spl plusmn 25 km of buoy measurements at midlatitudes and in the equatorial pacific during 1992 1994 two different directional functional forms for the geophysical model were fit to these measurements described by cross section maxima aligned and offset with respect to the mean wind direction the two models exhibit fits with similar residuals for each of three years in the equatorial region thus neither of these two model functions can convincingly be identified as more accurate than the other unless additional factors are considered nevertheless the offset model results in an average directional offset near 10 spl deg for each season during the three year period whereas no such offset was inferred at midlatitudes the cross section dependence on wind direction also exhibits another unexpected average property a larger downwind compared to upwind cross section a sub 10 spl ap 0 25 db in the equatorial pacific this characteristic could be caused by a concentration of the short bragg waves on the backside of the long wave crests both of these unexpected characteristics are likely related to a dominant systematic swell traveling nearly perpendicular to the prevailing easterly winds across the equatorial pacific ocean the possible cross section dependence on wind stress and wind speed is due to long waves when adjusting the buoy measurements to a common height are discussed