true amplitude elastic gaussian beam imaging of multicomponent walkaway vertical seismic profiling data we develop the true amplitude prestack migration of multicomponent data based on the use of elastic gaussian beams for walkaway vertical seismic profile vsp acquisition systems it consists in a weighted summation of multishot data with specific weights computed by tracing elastic gaussian beams from each imaging point of the target area towards the sources and receivers each pair of beams may be connected with either a pair of p rays pp image or the p ray towards sources and the s ray to receivers ps image and is uniquely determined by dip the angle of the bisector between the rays and the vertical direction and opening the angle between the rays angles shooting from the bottom towards the acquisition system helps to avoid well known troubles in particular multipathing for the imaging conditions in complex velocity models the ability to fix the dip angle and implement summation over opening angles leads to the so called selective images that contain mostly interfaces with desired slopes on the other hand a set of images computed for a range of opening angles by summation over all available dip angles is used as input of an avo like inversion procedure for the recovery of elastic parameters the feasibility of this imaging procedure is verified by synthetic data for 2d realistic elastic models

least squares reverse time migration with a wavefield separation imaging condition and updated source wavefields abstractdirectly imaging steeply dipping fault zones is difficult for conventional migration including reverse time migration rtm we developed a new least squares rtm lsrtm method to directly image steeply dipping fault zones the method uses a wavefield separation imaging condition and updated source wavefields during each iteration our new imaging method produces horizontal looking images that show mostly steeply dipping fault zones conventional least squares rtm does not update source wavefields and cannot directly image vertical fault zones we numerically determined that it is crucial to update source wavefields to image steeply dipping fault zones using synthetic seismic data we proved that our new lsrtm method can directly image steeply dipping fault zones with dipping angles up to 90 compared with conventional lsrtm our lsrtm method was less sensitive to the smoothness and the velocity error of the initial migration velocity model

an overview of depth imaging in exploration geophysics prestack depth migration is the most glamorous step of seismic processing because it transforms mere data into an image and that image is considered to be an accurate structuraldescriptionoftheearth thus ourexpectationsofitsaccuracy robustness and reliability are high amazingly seismic migration usually delivers the past few decades have seen migration move from its heuristic roots to mathematically sound techniques that using relatively few assumptions render accurate pictures of the interior of the earth interestingly theearthandthesubjectswewanttoimageinside itarevariedenoughthat sofar nosinglemigrationtechnique has dominated practical application all techniques continually improve and borrow from each other so one technique mayneverdominate despitetheprogressinstructuralimaging wehavenotreachedthepointwhereseismicimagesprovide quantitatively accurate descriptions of rocks and fluids nor have we attained the goal of using migration as part of a purelycomputationalprocesstodeterminesubsurfacevelocity in areas where images have the highest quality we might be nearing those goals collectively called inversion where data are more challenging the goals seem elusive we describe the progress made in depth migration to the present and the most significant barriers to attaining its inversion goalsinthefuture wealsoconjectureonprogresslikelytobe made in the years ahead and on challenges that migration mightnotbeabletomeet

structural geometry and evolution of the ku zaap and maloob structures campeche bay mexico the ku zaap and maloob structures consist of an arcuate series of fold thrust structures which change orientation from approximately east west to north northwest south southeast along a structural salient in the offshore campeche bay mexico the structures are related to a series of thrust faults which merge into the maloob thrust the ku zaap and maloob fields located on these structures together constitute an important complex of fields with proven remaining reserves of approximately 1850 mmboe the structures formed during three main periods of deformation 1 a jurassic cretaceous extensional episode 2 a miocene compressive phase during which the main trap forming structures were formed and 3 a pliocene to holocene extensional episode resulting in several listric growth faults three dimensional 3 d models of the main reservoir unit upper cretaceous breccia and other prospective reservoir units eocene and kimmeridgian constructed by integrating 3 d seismic interpretation well data and a series of balanced structural cross sections provide an understanding of the geometry and evolution of the structures the zaap maloob and sub maloob structures are interpreted as a series of faulted detachment folds detaching within salt and other jurassic ductile units the front limbs of these structures are typically cut by thrust faults with small displacements terminating in the lower tertiary section the ku and pakal structures also originated as a detachment fold but was faulted relatively early in its deformational history the frontal zone of this structure is marked by a closely spaced thrust system consisting of the ku pakal 1 and maloob thrusts the 3 d models provide an accurate picture of the structural geometry of the principal reservoir units which will be useful for future production from the fields and for exploration in adjacent areas in the basin

acoustic elastic coupled equation for ocean bottom seismic data elastic reverse time migration abstractconventionally multicomponent geophones used to record the elastic wavefields in the solid seabed are necessary for ocean bottom seismic obs data elastic reverse time migration rtm particle velocity components are usually injected directly as boundary conditions in the elastic wave equation in the receiver side wavefield extrapolation step which causes artifacts in the resulting elastic images we have deduced a first order acoustic elastic coupled equation aece by substituting pressure fields into the elastic velocity stress equation evse aece has three advantages for obs data over evse when performing elastic rtm first the new equation unifies wave propagation in acoustic and elastic media second the new equation separates p waves directly during wavefield propagation third three approaches are identified when using the receiver side multicomponent particle velocity records and pressure records in elastic rtm processing 1 particle velocity components are set as boundary cond

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

late mesozoic gravity sliding and oxfordian hydrocarbon reservoir potential of the northern yucatan margin abstract the stratigraphy and structural evolution of the western florida margin is much better understood than its northern yucatan conjugate because previous hydrocarbon exploration has been more extensive on the florida margin in the deep water northeastern gom the post salt section records late jurassic cretaceous gravity sliding of rafted blocks along a basinward dipping layer of callovian salt this study uses approximately 31 000 line km of 2d seismic data to describe a coeval area of widespread gravity sliding along the less studied northern yucatan margin we define three structural domains based on their distinctive salt structures and associated deformation 1 a region in the northeastern study area consists of relatively undeformed late jurassic cretaceous section underlain by 0 300 m thick salt 2 areas in the central and southwestern study area contain late mesozoic gravity slides defined by 300 600 m thick salt rollers and normal faults rooted onto a 1 4 basinward dipping salt detachment and 3 the distal margin of the western and central study area exhibits large salt diapirs up to 6 km tall that deform quaternary stratigraphic units in the central yucatan study area containing late mesozoic gravity slides a stratigraphic unit equivalent to the productive oxfordian norphlet sandstone of the deep water northeastern gom is identified based on its similar seismic character reconstructing the extent of this norphlet equivalent unit along the yucatan margin to its location during oxfordian deposition places it adjacent to an extensive area of norphlet sandstone mapped in the deep water northeastern gom by previous authors our reconstruction suggests a 48 000 km2 fairway of potential aeolian late jurassic reservoirs on the yucatan and campeche margins that includes productive reservoirs in the southeastern bay of campeche which previous authors correlated with the norphlet formation

real data results of kirchhoff elastic wave migration although kirchhoff integral migration has attracted considerable attention for seismic data processing since the early 1970s it like all other seismic migration methods is only applicable to compressional p waves because of a recent surge of interest in shear s waves kuo and dai 1984 developed the kirchhoff elastic p and s wave migration kewm formulation and migration principle for the case of source and receiver noncoincidence they obtained encouraging results using two dimensional 2 d synthetic surface data from various geometric elastic models including a dipping layer a composite dipping and horizontal layer and two layers over a half space

topographic elastic least squares reverse time migration based on vector p and s wave equations in the curvilinear coordinates elastic least squares reverse time migration has been applied to multi component seismic data to obtain high quality images however the final images may suffer from artefacts caused by p and s wave crosstalk and severe spurious diffractions caused by complex topographic surface conditions to suppress these crosstalk artefacts and spurious diffractions we have developed a topographic separated wavefield elastic least squares reverse time migration algorithm in this method we apply p and s wave separated elastic velocity stress wave equations in the curvilinear coordinates to derive demigration equations and gradient formulas with respect to p and s velocity for the implementation of topographic separated wavefield elastic least squares reverse time migration the wavefields gradient directions and step lengths are all calculated in the curvilinear coordinates numerical experiments conducted with the two component data synthetized by a three topographic layer with anomalies model and the canadian foothills model are considered to verify our method the results reveal that compared with the conventional method our method promises imaging results with higher resolution and has a faster residual convergence speed finally we carry out numerical examples on noisy data imperfect migration velocity and inaccurate surface elevation to analyse its sensitivity to noise migration velocity and surface elevation error the results prove that our method is less sensitive to noise compared with the conventional elastic least squares reverse time migration and needs good migration velocities as other least squares reverse time migration methods in addition when implementing the proposed method an accurate surface elevation should be obtained by global positioning system to yield high quality images

upper regime parallel lamination as the result of turbulent sediment transport and low amplitude bed forms a series of laboratory experiments has been carried out in which parallel laminated deposits were produced from an upper regime plane bed the laminae had thicknesses of a few mm and could be traced continuously over distances up to the length and width of the depositional area 0 3 m by 1 5m fluctuations in bed elevation were measured both during deposition and at equilibrium much of the bed fluctuation occurs at time scales that are too long to be due directly to turbulence as most theories for lamina formation would require we suggest instead that extremely low amplitude bed forms are present even on apparently flat beds and that the migration of these bed forms produces laterally continuous lamination all the lamination produced in the laboratory experiments was normally graded using high speed photography it was observed that the normal grading results from rapid deposition of a layer of loosely packed coarse sand several grain diameters thick followed by the slow sieving out of a well packed surface layer of finer sand the initial deposition is the result of small scale turbulent fluctuations in boundary shear stress the sieving out that follows results in a smooth surface whose low friction coefficient temporarily inhibits further deposition we term this process glazing the alignment of small scale turbulent scour and fill structures along the paths traced by migrating bedform troughs produces laterally continuous parallel lamination

elastic reverse time migration elastic prestack reverse time finite difference migration of two component seismic surface data requires data extrapolation and application of an imaging condition data extrapolation involves synchronous driving of the vertical component and horizontal component finite difference meshes with the time reverse of the recorded vertical and horizontal traces respectively extrapolation uses the coupled elastic wave equation for variable velocity solved with a second order explicit finite difference scheme the imaging condition at any point in the grid is the one way traveltime from the source to that point elastic migrations of both synthetic test data and real two component common source gathers produce simpler images than acoustic migrations because of the coalescing of double reflections compressional waves and shear waves into single loci

least squares migration of incomplete reflection data a least squares migration algorithm is presented that reduces the migration artifacts i e recording footprint noise arising from incomplete data instead of migrating data with the adjoint of the forward modeling operator the normal equations are inverted by using a preconditioned linear conjugate gradient scheme that employs regularization the modeling operator is constructed from an asymptotic acoustic integral equation and its adjoint is the kirchhoff migration operator we tested the performance of the least squares migration on synthetic and field data in the cases of limited recording aperture coarse sampling and acquisition gaps in the data numerical results show that the least squares migrated sections are typically more focused than are the corresponding kirchhoff migrated sections and their reflectivity frequency distributions are closer to those of the true model frequency distribution regularization helps attenuate migration artifacts and provides a sharper better frequency distribution of estimated reflectivity the least squares migrated sections can be used to predict the missing data traces and interpolate and extrapolate them according to the governing modeling equations several field data examples are presented a ground penetrating radar data example demonstrates the suppression of the recording footprint noise due to a limited aperture a large gap and an undersampled receiver line in addition better fault resolution was achieved after applying least squares migration to a poststack marine data set and a reverse vertical seismic profiling example shows that the recording footprint noise due to a coarse receiver interval can be suppressed by least squares migration

three dimensional structural model of the cantarell and sihil structures campeche bay mexico the cantarell and sihil fields are located in a complex system of compressive structures in the offshore campeche bay province in mexico the geometry of the cantarell sihil structure varies along trend from a simple fault related structure in the south to a duplex consisting of the cantarell and sihil structures in the central part to a more complex system consisting of compressive blocks separated by tertiary normal faults in the north the cantarell sihil structures formed during three main episodes of deformation 1 jurassic to early cretaceous extension resulting in the formation of normal faults that displace tithonian kimmeridgian and lower cretaceous units 2 miocene compression during which the cantarell sihil thrust system was formed and 3 pliocene to holocene extension during which several of the preexisting jurassic normal faults were reactivated the cantarell field produces out of three separate fault bounded allochthonous blocks the akal nohoch and kutz blocks the main field is located in the akal structure secondary fields in the allochthonous block include kutz which formed on the crest of a downthrown fault block and nohoch which formed above a west vergent backthrust the recently discovered sihil field is located in a subthrust compressive structure and consists of two structural lobes formed above the sub sihil fault the chac structure is formed at the updip edge of a tilted fault block in the autochthonous block the detailed three dimensional structural model is being used for future production of the remaining reserves in the cantarell field as well as for the delineation of the sihil field

three dimensional seismo tectonics in the po valley basin northern italy the po valley northern italy is a composite foreland foredeep basin caught in between the southern alps and northern apennine mountain belts by integrating the 3d structural model of the region with the public earthquake dataset the seismo tectonics of the basin is shown at different scales of observation the three dimensional geo volumeis used to reviewthe seismicity around the region and validate the structure earthquake association for such a complex tectonic framework despite the overall uncertainty due to the original data distribution quality as well as the crustal scale model dimension the direct correlation between structures and seismicity a confirms the po valley region as an active tectonic system and b allows the whole structural architecture to be revised by a unique three dimensional perspective and approach this study also indicates that 3d methodology is a powerful tool for better understanding of highly complex seismo tectonic situations at both regional and local scales

ek balam field a structure related to multiple stages of salt tectonics and extension the ek balam field is a major oil and gas field in the offshore campeche bay mexico the structure was formed as a result of multiple episodes of salt tectonics and associated extension salt movement into the core of the structure initiated in the jurassic early cretaceous and continued until the miocene the most prominent normal faults are of jurassic early cretaceous age and detach in the jurassic salt these faults mostly dip to the west although in the vicinity of the ek balam structure some east dipping faults are also present some of these faults were subsequently reactivated in the late cretaceous and tertiary separating the ek and balam structures is a set of upper cretaceous faults which drop the eastern part of the structure down tertiary faults are related to continued uplift of the salt and are symmetrically distributed with respect to the central uplift seismic time maps three dimensional depth models of the top of the cretaceous breccia and the kimmeridgian and balanced structural cross sections provide accurate details of the structural geometry and fault patterns in the ek balam structure at the level of the cretaceous breccia many of the faults have small throws and are discontinuous along trend the top of the kimmeridgian however is cut by faults of different ages many of which have significant throw and extend for longer distances the detailed structural geometry and fault patterns will be useful for identifying compartments within the ek balam field and for identifying secondary traps within kimmeridgian and oxfordian reservoirs

kirchhoff elastic wave migration for the case of noncoincident source and receiver in taking into account both compressional p and shear s waves more geologic information can likely be extracted from the seismic data the presence of shear and converted shear waves in both land and marine seismic data recordings calls for the development of elastic wave migration methods the migration method presently developed consists of simultaneous migration of p and s waves for offset seismic data based on the kirchhoff helmholtz type integrals for elastic waves a new principle of simultaneously migrating both p and s waves is introduced the present method named the kirchhoff elastic wave migration has been tested using the 2 d synthetic surface data calculated from several elastic models of a dipping layer including a horizontal layer a composite dipping and horizontal layer and two layers over a half space the results of these tests not only assure the feasibility of this migration scheme but also demonstrate that enhanced images in the migrated sections are well formed moreove