imaging diffraction points using the local image matrices generated in prestack migration energy angle distributions in the local image matrix which is a function of local incident and receiving angles at a subsurface point are different for a planar reflector and a diffraction point the former exhibits a linear distribution along a certain dip direction whereas the latter shows a scattered distribution in the entire matrix therefore the singular values of the local image matrix in the local angle domain indicate the energy distribution along different dip directions the difference between the auto and crosscorrelation coefficients of the sets of singular values between adjacent image points can be used to distinguish these two types of targets and obtain prestack images which contain only diffraction points using three synthetic examples we found that the method can effectively image diffraction points seismic images of diffraction points may provide important information about geological discontinuities and diffraction points can be taken as secondary sources for potential applications in imaging subsalt structures which are poorly illuminated by primary waves

mass flux and undertow in a surf zone abstract the mass of water carried shoreward by the breaking waves in a surf zone will in a two dimensional situation be compensated by a seaward return flow the undertow it is shown that the undertow is driven by the local difference between radiation stress and the set up pressure gradient which only balance each other in average over the depth turbulent shear stresses are required to maintain a steady situation comparison with measurements confirms the theoretical results

nonlinear and 3d effects in leaky infragravity waves abstract in this paper infragravity ig waves forced by normally and obliquely incident wave groups are studied using the quasi 3d q3d nearshore circulation model shorecirc van dongeren a r i a svendsen 1997b quasi 3 d modeling of nearshore hydrodynamics research report cacr 97 04 center for applied coastal research university of delaware newark 243 pp which includes the q3d effects the governing equations that form the basis of the model as well as the numerical model and the boundary conditions are described the model is applied to the case of leaky ig waves it is shown that the q3d terms have a significant effect on the cross shore variation of the surface elevation envelope especially around the breakpoint and in the inner surf zone the effect of wave groupiness on the temporal and spatial variation of all q3d terms is shown after which their contribution to the momentum equations is analyzed this reveals that only those q3d coefficients which appear in combination with the largest horizontal velocity shears make a significant contribution to the momentum equations as a result of the calculation of the q3d coefficients the ig wave velocity profiles can be determined this shows that in the surf zone the velocity profiles exhibit a large curvature and time variation in the cross shore direction and a small but essential depth variation in the longshore direction

3d diffraction imaging of linear features and its application to seismic monitoring many subsurface features such as faults fractures cracks or fluid content terminations are defined by geological discontinuities the seismic response from such features is encoded in diffractions we develop an algorithm for imaging such discontinuities by detecting edge diffractions the algorithm exploits phase reversal phenomena of edge diffractions and uses them as a criterion to separate these diffractions from specular reflections and diffractions produced by a leaner object the performance of the method is demonstrated on both synthetic and real 3d seismic data the output image focuses the diffracted energy back to its origin and shows high semblance values at the edge of the object the method is applied on conventionally stacked data producing an image that contains only diffraction events called the d volume we also reveal the potential of diffractions to image and track the changes of a co2 plume using time lapse analysis and detect any possible co2 seepage from its primary containment

anisotropy parameter inversion in vertical axis of symmetry media using diffractions diffractions play a vital role in seismic processing as they can be utilized for high resolution imaging applications and analysis of subsurface medium properties like velocity they are particularly valuable for anisotropic media as they inherently possess a wide range of dips necessary to resolve the angular dependence of velocity however until recently the focus of diffraction imaging or inversion algorithms have been only on the isotropic approximation of the subsurface using diffracted waves we develop a framework to invert for the effective model this effective model is obtained through scanning over possible effective values and selecting the one that best fits the observed moveout curve for each diffractor location the obtained effective model is then converted to an interval model using a dix type inversion formula the inversion methodology holds the potential to reconstruct the true model with sufficiently high accuracy and resolution properties however it relies on an accurate estimation of diffractor locations which in turn requires good knowledge of the background velocity model we test the effectiveness and applicability of our method on the vertical transverse isotropic marmousi model the inversion results yield a reasonable match even for the complex marmousi model

remote sensing of breaking wave phase speeds with application to non linear depth inversions abstract a number of existing models for surface wave phase speeds linear and non linear breaking and non breaking waves are reviewed and tested against phase speed data from a large scale laboratory experiment the results of these tests are utilized in the context of assessing the potential improvement gained by incorporating wave non linearity in phase speed based depth inversions the analysis is focused on the surf zone where depth inversion accuracies are known to degrade significantly the collected data includes very high resolution remote sensing video and surface elevation records from fixed in situ wave gages wave phase speeds are extracted from the remote sensing data using a feature tracking technique and local wave amplitudes are determined from the wave gage records and used for comparisons to non linear phase speed models and for non linear depth inversions a series of five different regular wave conditions with a range of non linearity and dispersion characteristics are analyzed and results show that a composite dispersion relation which includes both non linearity and dispersion effects best matches the observed phase speeds across the domain and hence improves surf zone depth estimation via depth inversions incorporating non linearity into the phase speed model reduces errors to o 10 which is a level previously found for depth inversions with small amplitude waves in intermediate water depths using linear dispersion considering the controlled conditions and extensive ground truth this appears to be a practical limit for phase speed based depth inversions finally a phase speed sensitivity analysis is performed that indicates that typical nearshore sand bars should be resolvable using phase speed depth inversions however increasing wave steepness degrades the sensitivity of this inversion method

measurements of seismic anisotropy and fracture compliances in synthetic fractured media ultrasonic velocities were measured on a stack of synthetic material plexiglass at low 90 120 khz long wavelength range and high 480 khz short wavelength range frequencies plates were pressed together with uniaxial normal stress these measurements were repeated under different uniaxial pressures for two cases 1without circular rubber inclusions between synthetic fractures and 2with circular rubber inclusions between fractures calculation of anisotropy parameters and also normal and shear interface fracture compliances using linear calculus show reasonable variations anisotropy and compliances decreases as overburden pressure increases suggesting that anisotropy is caused by compliances at higher frequencies synthetic fractures seem to be stiffer than at lower frequencies for the long and short wavelength ranges similar variations were observed for anisotropy parameters and fracture compliances vs measurements in different directions show that for the case without rubber inclusions there is a good approximation of vti medium whereas for the case with inclusions there is a significant difference between vs travelling in directions parallel and perpendicular to the plates

modelling waves and currents at the lstf and other laboratory facilities the main objective of the paper is to use the detailed measurements of wave and current motions in the large scale sediment transport facility lstf at the coastal and hydraulics laboratory chl erdc vicksburg to compare with model simulations and particularly to investigate the accuracy of two wave models used for driving nearshore circulation computations the major questions asked are how accurate are the models and how do the inevitable inaccuracies in the prediction of the wave quantities influence the current predictions the lstf is one of a few large scale facilities around the world designed to accurately reproduce the 2 d horizontal flow and sediment conditions in the nearshore region of a littoral coast the measurements include all relevant wave data such as wave heights setup variations 2 d current distributions across the basin and a detailed cross shore array of measurements of the 3 d current structures the two wave model formulations used for the comparisons are versions of the kinematic wave model one using sinusoidal the other using non sinusoidal wave shapes both before and after wave breaking as wave drivers in the quasi 3 d model shorecirc sc the comparisons with the measurements are aimed at providing an overall picture of both the flow conditions and the model performance the discussions provide insight into the mechanisms behind the complex nearshore dynamics and demonstrate the strengths and weaknesses of the two methods in a comprehensive comparison of available wave and current data the comparisons also reveal that an essential requirement for a wave driver is its capability to represent the phase motion of the wave and its capability to correctly predict the phase speed of waves

shallow diffraction imaging in an sh wave crosshole configuration abstractimaging shallow subsurface voids such as karsts sinkholes pinch outs dikes and man made voids is an important task in near surface geophysics we have developed a new diffraction based methodology for void detection and imaging due to the low signal to noise ratio of the diffracted signal in surface acquisition setups we advocate the use of an sh wave multicomponent crosshole acquisition naturally the same setup can be used for velocity model building using tomography and for void imaging the sh wave data are migrated using a model based image point dependent automatic muting function that separates direct arrivals from diffracted events in the migration process for the purpose of location and velocity analysis data are migrated to the depth imaging offset domain only when the velocity model and imaging locations are correct will the diffracted energy be coherently focused to the void location and the diffracted event moveout in the migrated gather will be flat we found that the re

tomography of diffraction based focusing operators diffractions carry the same kinematic information provided by common focus point operators cfpos thus cfpo and diffraction time trajectories may be used separately or combined into a single unified tomography for velocity analysis velocity estimation by tomography of cfpos reduces the depth velocity ambiguity compared to two way time tomography cfpo estimation is complicated where there are event discontinuities and diffractions this problem is overcome by using the kinematic information in diffractions in near offset common offset gathers the procedure is illustrated using synthetic data and a single channel field seismic profile from the blake ridge off the east coast of the united states the results show the effectiveness of the proposed method for estimation of velocity from single channel seismic data and for refinement of the velocity field from multichannel data both applications are costcompetitive

prestack time migration velocity analysis using remigration trajectories abstractwe have developed a prestack time migration tool for local improvement of the seismic migration velocity model the method is based on remigration trajectories that describe the position of an image point in the image domain for different source receiver offsets as a function of the migration velocity it determines kinematic migration parameters using local slope information of migrated seismic reflection events these parameters in turn are used to locally correct the velocity model the main advantage of this technique is that it allows us to carry out a moveout correction not just at a fixed point in a zero offset poststack time migrated gather but varying through all offsets of a common image gather taking into account the reflection point displacement in the midpoint direction in other words it provides for time migration velocity analysis from prestack data we have tested the feasibility of the method on synthetic data from four simple models and the sigsbee2b data our tests deter

interpolating wide aperture ground penetrating radar beyond aliasing abstractmost of the data acquisition in ground penetrating radar is done along fixed offset profiles in which velocity is known only at isolated points in the survey area at the locations of variable offset gathers such as a common midpoint we have constructed sparse heavily aliased variable offset gathers from several fixed offset collinear profiles we interpolated those gathers to produce properly sampled counterparts thus pushing data beyond aliasing the interpolation methodology estimated nonstationary adaptive filter coefficients at all trace locations including at the missing traces corresponding positions filled with zeroed traces this is followed by an inversion problem that uses the previously estimated filter coefficients to insert the new interpolated traces between the original ones we extended this two step strategy to data interpolation by employing a device in which we used filter coefficients from a denser variable offset gather to interpolate the missing traces on a few

seismic monitoring of diffraction images for detection of local heterogeneities diffracted waves contain valuable information regarding both the structure and composition of the media they are in in seismic data processing however these waves are usually regarded as noise in this paper we present an attempt to use scattered diffracted waves for the detection of local heterogeneities the method is based on the detection of diffracted waves by concentrating the signal amplitudes from diffracting points on the seismic section this is done using a correlation procedure that enhances the amplitude of the seismic signal at the location of the diffractors on the common diffraction point section d section the new local time correction for diffraction traveltime curve parameterization is based on the radius of curvature of the diffracted wavefront and near surface velocity we use the idea of seismic monitoring for detection and delineating local objects which may occur within the subsurface resulting from human activity or fast geological processes the method consists of continuou

poststack velocity analysis by separation and imaging of seismic diffractions small geologic features manifest themselves in seismic data in the form of diffracted waves which are fundamentally different from seismic reflections using two field data examples and one synthetic example we demonstrate the possibility of separating seismic diffractions in the data and imaging them with optimally chosen migration velocities our criteria for separating reflection and diffraction events are the smoothness and continuity of local event slopes that correspond to reflection events for optimal focusing we develop the local varimax measure the objectives of this work are velocity analysis implemented in the poststack domain and high resolution imaging of small scale heterogeneities our examples demonstrate the effectiveness of the proposed method for high resolution imaging of such geologic features as faults channels and salt boundaries

wave setup and setdown generated by obliquely incident waves an analytical theory is developed for the wave setup and setdown induced by obliquely incident waves on an impermeable swell built beach profile the wave setup and setdown are found to decrease as wave obliquity increases the incorporation of wave obliquity in wave setup and setdown formulation offers the physical reality in engineering applications the general solutions presented in this paper yield the limiting case of normal wave incidence and the result is consistent with the classical theories published the present theory is primarily applicable to the spilling and plunging breaker across the surf zone within which wave amplitude is assumed to be linearly related to the local water depth experiments were conducted in a large scale wave basin to compare with theoretical results and especially to investigate the applicability of this assumption to the case of obliquely incident waves the dimensionless setup versus the distance offshore within the surf zone is found to depend on wave breaking angle and the shape of the beach profile and it has a non zero value at the original shoreline position this implies that the original shoreline will advance landwards and that the extent of this movement can be related to wave angle at breaking and the beach profile under consideration the results of the present theory are in good agreement with experimental data and field measurements available

diffraction imaging by uniform asymptotic theory and double exponential fitting seismic diffracted waves carry valuable information for identifying geological discontinuities unfortunately the diffraction energy is generally too weak and standard seismic processing is biased to imaging reflection in this paper we present a dynamic diffraction imaging method with the aim of enhancing diffraction and increasing the signal to noise ratio the correlation between diffraction amplitudes and their traveltimes generally exists in two forms with one form based on the kirchhoff integral formulation and the other on the uniform asymptotic theory however the former will encounter singularities at geometrical shadow boundaries and the latter requires the computation of a fresnel integral therefore neither of these methods is appropriate for practical applications noting the special form of the fresnel integral we propose a least squares fitting method based on double exponential functions to study the amplitude function of diffracted waves the simple form of the fitting function has no singularities and can accelerate the calculation of diffraction amplitude weakening coefficients by considering both the fitting weakening function and the polarity reversal property of the diffracted waves we modify the conventional kirchhoff imaging conditions and formulate a diffraction imaging formula the mechanism of the proposed diffraction imaging procedure is based on the edge diffractor instead of the idealized point diffractor the polarity reversal property can eliminate the background of strong reflection and enhance the diffraction by samephase summation moreover the fitting weakening function of diffraction amplitudes behaves like an inherent window to optimize the diffraction imaging aperture by its decaying trend synthetic and field data examples reveal that the proposed diffraction imaging method can meet the requirement of high resolution imaging with the edge diffraction fully reinforced and the strong reflection mostly eliminated

3 d seismic attributes using a semblance based coherency algorithm seismic coherency is a measure of lateral changes in the seismic response caused by variation in structure stratigraphy lithology porosity and the presence of hydrocarbons unlike shaded relief maps that allow 3 d visualization of faults and channels from horizon picks seismic coherency operates on the seismic data itself and is therefore unencumbered by interpreter or automatic picker biases we present a more robust multitrace semblance based coherency algorithm that allows us to analyze data of lesser quality than our original three trace cross correlation based algorithm this second generation semblance based coherency algorithm provides improved vertical resolution over our original zero mean crosscorrelation algorithm resulting in reduced mixing of overlying or underlying stratigraphic features in general we analyze stratigraphic features using as narrow a temporal analysis window as possible typically determined by the highest usable frequency in the input seismic data in the limit one may confidently apply our new semblance based algorithm to a one sample thick seismic volume extracted along a conventionally picked stratigraphic horizon corresponding to a peak or trough whose amplitudes lie sufficiently above the ambient seismic noise in contrast near vertical structural features such as faults are better enhanced when using a longer temporal analysis window corresponding to the lowest usable frequency in the input data the calculation of reflector dip azimuth throughout the data volume allows us to generalize the calculation of conventional complex trace attributes including envelope phase frequency and bandwidth to the calculation of complex reflector attributes generated by slant stacking the input data along the reflector dip within the coherency analysis window these more robust complex reflector attribute cubes can be combined with coherency and dip azimuth cubes using conventional geostatistical clustering and segmentation algorithms to provide an integrated multiattribute analysis

poststack diffraction imaging using reverse time migration abstract we propose a method for imaging small scale diffraction objects in complex environments in which kirchhoff based approaches may fail the proposed method is based on a separation between the specular reflection and diffraction components of the total wavefield in the migrated surface angle domain reverse time migration was utilized to produce the common image gathers this approach provides stable and robust results in cases of complex velocity models the separation is based on the fact that in surface angle common image gathers reflection events are focused at positions that correspond to the apparent dip angle of the reflectors whereas diffracted events are distributed over a wide range of angles the high resolution radon based procedure is used to efficiently separate the reflection and diffraction wavefields in this study we consider poststack diffraction imaging the advantages of working in the poststack domain are its numerical efficiency and the reduced computational time the numerical results show that the proposed method is able to image diffraction objects in complex environments the application of the method to a real seismic dataset illustrates the capability of the approach to extract diffractions

observation of undertow and turbulence in a laboratory surf zone abstract undertow and turbulence in the surf zone have been studied in a wave flume for a spilling breaker and a plunging breaker fluid velocities across a 1 on 35 sloped false bottom were measured using a fiber optic laser doppler anemometer and wave decay and set up were measured using a capacitance wave gage the characteristics of mean flow and turbulence in spilling versus plunging breakers were studied the mean flow is the organized wave induced flow defined as the phase average of the instantaneous velocity while the turbulence is taken as the deviations from the phase average it was found that under the plunging breaker turbulence levels are much higher and vertical variations of undertow and turbulence intensity are much smaller in comparison with the spilling breaker it was also found that turbulent kinetic energy is transported seaward under the spilling breaker and landward under the plunging breaker by the mean flow the study indicates that there are fundamental differences in the dynamics of turbulence between spilling and plunging breakers which can be related to the processes of wave breaking and turbulence production it is suggested that the types of beach profile produced by storm and swell waves may be the results of different relationships between mean flow and turbulence in these waves

undertow over a barred beach the spatial distribution of the mean cross shore flow undertow over a barred beach is examined with field data obtained on three energetic wave days during the duck94 experiment the vertical structure of the undertow is modeled using a turbulent eddy viscosity closure and includes the important effects of wave breaking described using the roller concept and convective acceleration of the current other than a more realistic description of observed turbulence variations a depth dependent eddy viscosity compared with a constant does not improve the agreement between predicted and observed undertow profiles the effect of using different boundary conditions is investigated by extending the formulations of stive and wind 1986 and svendsen et al 1987 to include random waves by ensemble averaging over the wave height distribution the contribution of breaking wave rollers to the surface mass flux can be of the same order or greater than the contribution associated with the organized wave motion the largest discrepancies between model predictions and observations occur over the sandbar where the mass transport of the breaking waves appears to be underestimated

transition zone width and implications for modeling surfzone hydrodynamics the surfzone associated with a wave breaking on a plane slope may be subdivided into three regions the transition zone the inner zone and the swash zone the transition zone is the region just shoreward of the point of wave breaking and is characterised by rapid wave decay and also by constant wave setdown and thus constant radiation stress in this paper an empirical expression for the width of this zone is developed from monochromatic wave data two techniques are proposed for the consideration of this phenomenon in the numerical modelling of surfzone hydrodynamics for random waves the implications of a zone of nearly constant radiation stress inside the breakpoint are examined with respect to wave induced current generation both cross shore and longshore and sediment transport prediction comparisons are made to both field and laboratory data from plane and undulating profiles

enhancing the detection of small coal structures by seismic diffraction imaging abstract faults are the most important geological structures that need to be detected in any modern underground coal mining project even a fault with a throw of a few metres can create safety issues and lead to costly delays in mine production while seismic surveys are usually successful at locating faults with throws greater than 5 10 m reliable techniques for resolving more subtle faults dykes and other minor features are yet to be developed in seismic data there are two types of seismic energy signatures that can be used for subsurface imaging specular reflections and diffractions specular reflections are created by relatively smooth surfaces between layers of differing impedance contrasts such as at coal rock interfaces specular reflections are used in conventional seismic reflection surveys diffractions are generated by local discontinuities caused by surface roughness faults dykes and fractures in this paper we describe the use of a moving average error filter which along with a process of reflection event flattening for accommodation of dips and undulations of coal seam reflections can be used to effectively extract diffraction signals from post stack reflection seismic data by identifying diffractions small faults and other minor features that are elusive using conventional seismic reflection processing can be detected suggesting that diffraction imaging may be a superior method to seismic reflection imaging both synthetic and real 2d and 3d coal seismic data are used to illustrate the feasibility of diffraction imaging for small fault detection it is demonstrated from synthetic examples that the extracted diffractions can be used to detect faults with a throw of 1 m while a real data example shows that it is possible to detect igneous dykes with widths of just 4 m

diffraction imaging by multifocusing correct identification of geologic discontinuities such as faults pinch outs and small size scattering objects is a primary challenge of the seismic method seismic response from these objects is encoded in diffractions our method images local heterogeneities of the subsurface using diffracted seismic events the method is based on coherent summation of diffracted waves arising in media that include interface discontinuities and local velocity heterogeneities this is done using a correlation procedure that coherently focuses diffraction energy on a seismic section by flattening diffraction events using a new local time correction formula to parameterize diffraction traveltime curves this time correction which is based on the multifocusing method depends on two parameters the emergent angle and the radius of curvature of the diffracted wavefront these parameters are estimated directly from prestack seismic traces the diffraction multifocusing stack dmfs can separate diffracted and reflected energy on a stacked section by focusing diffractions to the diffraction location and defocusing the reflection energy over a large area

suspended sand transport in surf zones 1 three tests were conducted in a wave flume to investigate time averaged suspended sediment transport processes under irregular breaking waves on equilibrium beaches consisting of fine sand free surface elevations were measured at ten locations for each test velocities and concentrations were measured in the vicinity of the bottom at 94 elevations along 17 vertical lines the relations among the three turbulent velocity variances are found to be similar to those for the boundary layer flow the vertical variation of the mean velocity which causes offshore transport is fitted by a parabolic profile fairly well the vertical variation of the mean concentration is fitted by the exponential and power form distributions equally well the ratio between the concentration standard deviation c and the mean varies little vertically the correlation coefficient uc between the horizontal velocity and concentration which results in onshore transport is of the order of 0 1 and decreases upward linearly the offshore and onshore transport rates of suspended sediment are estimated and expressed in terms of the suspended sediment volume per unit area a time averaged numerical model is developed to predict as well as the mean and standard deviation of the free surface elevation and horizontal velocity the bottom slope effect on the wave energy dissipation rate db due to wave breaking is included in the model the computation can be made well above the still water shoreline with no numerical difficulty reflected waves from the shoreline are estimated from the wave energy flux remaining at the shoreline the numerical model is in agreement with the statistical data except that the undertow current is difficult to predict accurately the measured turbulent velocities are found to be more related to the turbulent velocity estimated from the energy dissipation rate df due to bottom friction the suspended sediment volume expressed in terms of db and df can be predicted only within a factor of about 2 the roller effect represented by the roller volume flux does not necessarily improve the agreement for the three tests

diffraction imaging by prestack reverse time migration in the dip angle domain prestack image volumes may be decomposed into specular and non specular parts by filters defined in the dip angle domain for space shift extended image volumes the dip angle decomposition is derived via local radon transform in depth and midpoint coordinates followed by an averaging over space shifts we propose to employ prestack space shift extended reverse time migration and dip angle decomposition for imaging small scale structural elements considered as seismic diffractors in models with arbitrary complexity a suitable design of a specularity filter in the dip angle domain rejects the dominant reflectors and enhances diffractors and other non specular image content the filter exploits a clear discrimination in dip between specular reflections and diffractions the former are stationary at the specular dip whereas the latter are non stationary without a preferred dip direction while the filtered image volume features other than the diffractor images for example noise and truncation artifacts are also present synthetic and field data examples suggest that diffractors tend to dominate and are readily recognizable averaging over space shifts in the filter construction makes the reflectors rejection robust against migration velocity errors another consequence of the space shift extension and its angle domain transforms is the possibility of exploring the image in a multiple set of common image gathers the filtered diffractions may be analyzed simultaneously in space shift scattering angle and dip angle image gathers by means of a single migration job the deliverables of our method obviously enrich the processed material on the interpreter s desk we expect them to further supplement our understanding of the earth s interior this article is protected by copyright all rights reserved

automatic detection and imaging of diffraction points using pattern recognition hydrocarbon reservoirs are generally located beneath complex geological structures frequently such areas contain seismic diffractors that carry detailed structure information in the order of the seismic wavelength therefore the development of computational facilities capable of detecting diffractor points with a good resolution is desirable but has been a challenge in the area of seismic processing in this work we present a method for the detection of diffraction points in the common offset gather domain the method applies a two class k nearest neighbours knn pattern recognition technique to amplitudes along diffraction traveltime curves to distinguish between diffractions and reflections or noise while the method in principle requires knowledge of the migration velocity field it is very robust with respect to an erroneous model numerical examples using synthetic seismic and field ground penetrating radar gpr data demonstrate the feasibility of the technique and show its usefulness for automatically mapping diffraction points in a seismic section in our applications the method was able to detect all diffractions present in the data and did not produce any false positives

post stack velocity analysis in the dip angle domain using diffractions interval velocity analysis in complex geological areas is often considered as an unresolved problem a novel approach to improve the velocity analysis process is to perform the analysis in a non conventional domain and to use seismic events that are usually ignored during standard data processing and imaging in this study a method to analyse diffraction data for migration velocity analysis in the time or depth domain is presented the method is based on the clear distinction between diffractions and reflections in the post migration dip angle domain the attractive possibility to perform the analysis using only stacked data as an input is demonstrated on synthetic and real data examples

diffraction imaging by focusing defocusing an outlook on seismic superresolution diffractions always need more advertising it is true that conventional seismic processing and migration are usually successful in using specular reflections to estimate subsurface velocities and reconstruct the geometry and strength of continuous and pronounced reflectors however correct identification of geological discontinuities such as faults pinch outs and small size scattering objects is one of the main objectives of seismic interpretation the seismic response from these structural elements is encoded in diffractions and diffractions are essentially lost during the conventional processing migration sequence hence we advocate a diffraction based data oriented approach to enhance image resolution as opposed to the traditional image oriented techniques which operate on the image after processing and migration even more it can be shown that at least in principle processing of diffractions can lead to superresolution and the recovery of details smaller than the seismic wavelength the so called reflection stack is capable of effectively separating diffracted and reflected energy on a prestack shot gather by focusing the reflection to a point while the diffraction remains unfocused over a large area muting the reflection focus and defocusing the residual wavefield result in a shot gather that contains mostly diffractions diffraction imaging applies the classical isotropic diffraction stack to these diffraction shot gathers this focusingmuting defocusing approach can successfully image faults small size scattering objects and diffracting edges it can be implemented both in model independent and modeldependent contexts the resulting diffraction images can greatly assist the interpreter when used as a standard supplement to full wave images

nonstationary phase estimation a tool for seismic interpretation spectral decomposition is a standard tool in seismic interpretation to highlight variations in layer thicknesses e g in sand channels and turbidites this is done by examining changes in peak frequencies in extracted horizon slices partyka et al 1999 variations in peak frequencies occur due to constructive interference between reflections from the top and bottom of a layer with lower peak frequencies indicating thicker layers

seismic rock physics of steam injection in bituminous oil reservoirs this case study explores rock physics properties of heavy oil reservoirs subject to the steam assisted gravity drainage sagd thermal enhanced recovery process butler 1998 butler and stephens 1981 previous measurements e g wang et al 1990 and eastwood 1993 of the temperature dependant properties of heavy oil saturated sands are extended by fluid substitution modeling and wireline data to assess the effects of pore fluid composition and pressure and temperature changes on the seismic velocities of unconsolidated sands rock physics modeling is applied to a typical shallow mcmurray formation reservoir depth of 135 160 m within the bituminous athabasca oil sands deposit in western canada to construct a rock physics based velocity model of the sagd process although the injected steam pressure and temperature control the fluid bulk moduli within the pore space the effective stress dependant elastic frame moduli are the most poorly known yet most important factors governing the changes of

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

fracture detection by gaussian beam imaging of seismic data and image spectrum analysis localization of fractured areas is of primary interest in the study of oil and gas geology in carbonate environments hydrocarbon reservoirs in these environments are embedded within an impenetrable rock matrix but possess a rich system of various microheterogeneities i e cavities cracks and fractures cavities accumulate oil but its flow is governed by a system of fractures a distinctive feature of wave propagation in such media is the excitation of the scattered diffracted waves by the microheterogeneities this scattering could be a reliable attribute for characterization of the fine structure of reservoirs but it has extremely low energy and any standard data processing renders them practically invisible in comparison with images produced by specular reflections therefore any attempts to use these waves for image congestion of microheterogeneities should first have a preliminary separation of the scattering and specular reflections in this paper the approach to performing this separation is based on the asymmetric summation it is implemented by double focusing of gaussian beams to do this the special weights are computed by propagating gaussian beams from the target area towards the acquisition system separately for sources and receivers the different mutual positioning of beams in each pair introduces a variety of selective images that are destined to represent some selected singular primitives of the target objects such as fractures cavities and edges in this way one can construct various wave images of a target reservoir particularly in scattered diffracted waves additional removal of remnants of specular reflections is done by means of spectral analysis of the scattered diffracted waves images to recognize and cancel extended lineaments numerical experiments with sigsbee 2a synthetic seismic data and some typical structures of the yurubcheno tokhomskoye oil field in east siberia are presented and discussed

a laboratory study of longshore currents over barred and non barred beaches abstract a detailed description is given of the results of laboratory experiments on wave driven longshore currents on both barred and non barred beaches the objective is to examine the cross shore distribution of the longshore current velocities for purely wave driven currents with emphasis on the position of maximum current velocity with respect to areas where wave energy is dissipated unidirectional obliquely incident waves both regular and random were used the measurements were performed in a large wave basin with a pump recirculation system to create spatially homogeneous longshore currents the experiments yielded information on wave transformation set up of the mean water level and the cross shore distribution of wave driven longshore current velocity a number of cases are presented and compared with each other the measurements show that in the case of purely wave driven longshore currents the maximum current velocities occur close to areas where wave breaking is most intense the effect of mixing bottom friction and wave rollers on the longshore current velocity profile are examined in more detail with help of numerical modelling existing model equations based on the assumption of alongshore uniformity are used the results for the mean longshore current profile on a barred beach are in close agreement with the measurements

energy dissipation in the inner surf zone new insights from lidar based roller geometry measurements the spatial and temporal variation of energy dissipation rates in breaking waves controls the mean circulation of the surf zone as this circulation plays an important role in the morphodynamics of beaches it is vital to develop better understanding of the energy dissipation processes in breaking and broken waves in this paper we present the first direct field measurements of roller geometry extracted from a lidar data set of broken waves to obtain new insights into wave energy dissipation in the inner surf zone we use a roller model to show that most existing roller area formulations in the literature lead to considerable overestimation of the wave energy dissipation which is found to be close to but smaller than the energy dissipation in a hydraulic jump of the same height the role of the roller density is also investigated and we propose that it should be incorporated into modified roller area formulations until better knowledge of the roller area and its link with the mean roller density is acquired finally using previously published results from deepwater wave breaking studies we propose a scaling law for energy dissipation in the inner surf zone which achieves satisfactory results at both the time averaged and wave by wave scales

2d common offset traveltime based diffraction enhancement and imaging the diffracted energy in a seismic recording contains key information about small scale inhomogeneities or discontinuities of the subsurface diffractions can therefore lead to high resolution imaging of subsurface structures associated with hydrocarbon traps however seismic diffracted signals are often much weaker than specular reflections and consequently require enhancement before they can be utilized in this paper diffractions are enhanced relative to reflections based on two traveltime techniques namely the modified common reflection surface approach which uses the common reflection surface technique with some modification to tailor it for diffractions and the replacement media approach derived here for the purpose of a simplified parametrization of diffraction traveltimes both approaches are implemented in the common offset domain with the use of a finite offset central ray unlike the zero or small offset diffraction enhancement techniques that use a zero offset central ray the validity of the two moveout expressions is tested using velocity data taken from a smooth isotropic marmousi model a feasibility test was also carried out with respect to the new replacement media traveltime approximation addressing the various effects of signal to noise ratio depth and lateral displacement of the diffractor location finally diffraction enhancement and imaging was performed on 2d seismic data from the jequitinhonha basin offshore brazil diffractions were significantly enhanced and a high resolution image of the discontinuities of the subsurface was obtained

3d seismic reflection imaging of volcanic hosted massive sulfide deposits insights from reprocessing halfmile lake data new brunswick canada three dimensional seismic reflection data from the halfmile lake area new brunswick canada was reprocessed over an 18 km2 grid to improve the seismic signatures of a 5 million ton volcanic hosted massive sulfide vhms deposit located at 1200 m depth known as the deep zone as well as key host rock structures we chose a prestack dip moveout dmo and poststack migration processing sequence to preserve the possible diffraction signature of the deep vhms zone despite the high level of source generated noise and large statics caused by near surface conditions our processing results revealed improved 3d seismic images for shallow and deep structures many of the imaged structures were easily correlated with known lithological con tacts constrained by boreholes and petrophysical measurements a short flat lying segment of high amplitude reflection at about 800 m depth in the unmigrated cube was interpreted to originate from a small portion of the lower vhms zone the dmo stack was characterized by a l

three dimensional simulation of wave induced circulation comparison of three radiation stress formulations 1 a three dimensional current wave modeling system curvilinear grid hydrodynamics 3d ch3d simulating waves nearshore swan has been used to simulate wave induced circulation and compare the performances of three radiation stress rs formulations two depth dependent formulations m08 by mellor 2008 and x04 by xia et al 2004 and one depth independent formulation lhs by longuet higgins and stewart 1964 while all are based on linear wave theory lhs uses the vertically integrated equations of motion and m08 and x04 consider the three dimensional equations of motion results of ch3d swan with three rs formulations are compared with steady state wave setup observed data in an undertow experiment by ting and kirby 1994 tk94 and observed data in a laboratory fringing reef all three rs formulations reproduce the analytical solution of wave setup very well simulated wave induced currents and turbulence for tk94 are the best when m08 is used and worst when x04 is used apparently due to the errors in the x04 formulation all three rs formulations give good simulation of wave setup in the fringing reef wave induced currents in the fringing reef simulated by the three rs formulations are quite different m08 produces a single large clockwise gyre in the x z plane lhs produces a weaker gyre and x04 produces a clockwise gyre plus a counterclockwise gyre inside the surf zone using the ch3d storm surge modeling system and m08 storm surge and currents in the outer banks and chesapeake bay during hurricane isabel are simulated compared to the earlier simulation obtained with the lhs m08 produces similar storm surge but slightly improved the wave induced currents

on the use of the radon transform in studying nearshore wave dynamics in the nearshore describing the complex individual wave dynamics remains a key challenge in this paper we test the ability of the radon transform to produce estimates of individual wave celerities and to separate incoming and outgoing waves conserving the temporal characteristics the radon transform is a projection of a two dimensional field into polar space oblique features such as propagating crests in a spatio temporal space are identified with density peaks in the polar space in this paper the radon transform is applied to synthetic test cases including a wide range of beach slopes and wave conditions the radon transform shows good skills at estimating individual celerity and separating incoming and outgoing components with a relative rms error lower than 10 even a standing wave node the accuracy is fairly insensitive to wave characteristics whereas the main limitations rise from the sampling scheme and are the number and density of wave gauges the distance between gauges should be less than one third of the shortest wavelength while the set of gauges should cover more than one third of the longest wavelength

full azimuth subsurface angle domain wavefield decomposition and imaging part i directional and reflection image gathers we present a new subsurface angle domain seismic imaging systemforgeneratingandextractinghigh resolutioninformation about subsurface angle dependent reflectivity the system enables geophysicists to use all recorded seismic data in a continuousfashiondirectlyinthesubsurfacelocalangledomainlad resulting in two complementary full azimuth common imageangle gather systems directional and reflection the complete setofinformationfrombothtypesofanglegathersleadstoaccurate high resolution reliable velocity model determination and reservoir characterization the directional angle decomposition enables the implementation of specular and diffraction imaging in real 3d isotropic anisotropic geological models leading to simultaneous emphasis on continuous structural surfaces and discontinuous objects such as faults and small scale fractures structural attributes at each subsurface point e g dip azimuth andcontinuity canbederiveddirectlyfromthedirectionalangle gathers the reflection angle gathers display reflectivity as a function of the opening angle and opening azimuth these gathers are most meaningful in the vicinity of actual local reflecting surfaces wherethereflectionanglesaremeasuredwithrespectto the derived background specular direction the reflection angle gathers are used for automatic picking of full azimuth angle domainresidualmoveoutsrmowhich togetherwiththederived background orientations of the subsurface reflection horizons provide a complete set of input data to isotropic anisotropic tomography the full azimuth angle dependent amplitude variations are used for reliable and accurate amplitude versus angle andazimuthavazanalysisandreservoircharacterization the proposed system is most effective for imaging and analysis below complex structures such as subsalt and subbasalt high velocity carbonate rocks shallow low velocity gas pockets and others in addition it enables accurate azimuthal anisotropic imaging and analysis providing optimal solutions for fracture detectionandreservoircharacterization

vertical profiles of longshore currents and related bed shear stress and bottom roughness the vertical structure of the mean wave driven longshore current over a barred beach is examined on three strong current days during the duck94 experiment and it is found that the bottom boundary layer is well described by a logarithmic profile mean correlation coefficient for all 22 profiles 0 98 the logarithmic profile fits better in the trough where turbulent bottom boundary layer processes predominate than over the bar where breaking wave induced turbulence generated at the surface modifies the profile the surface layer in the presence of waves is well described by adjusting the logarithmic profile for the intermittent presence of water and adding the alongshore component of the mass transport velocity slope of the least squares linear regression between model predictions and observations 1 005 and root mean square rms error of 7 bed shear stresses calculated from logarithmic velocity profiles are equated to a quadratic bottom shear stress formulation the associated bed shear stress coefficients vary by more than an order of magnitude across the surf zone 0 0006 0 012 bottom roughness was measured throughout the nearshore using a sonic altimeter mounted on a moving platform the bed shear stress coefficients are positively correlated with bottom roughness linear correlation coefficient 0 6 a higher linear correlation coefficient 0 8 is obtained by subtracting skin friction from the total bed shear stress

periodic waves in the surf zone analysis of experimental data abstract the paper discusses observed characteristics of some basic integral parameters for regular waves essential for the determination of the energy flux the radiation stress and the energy dissipation throughout the surf zone the paper further indicates a connection to the parameters at the breaking point and hence a connection to the wave shoaling area prior to the waves breaking on a beach the variation of the integral mainly time averaged wave parameters within the surf zone is in general given as a parametric description calling for further theoretical work in this field

diffraction imaging of sub vertical fractures and karst with full resolution 3d ground penetrating radar abstract vertical fractures with openings of less than one centimetre and irregular karst cause abundant diffractions in ground penetrating radar gpr records gpr data acquired with half wavelength trace spacing are uninterpretable as they are dominated by spatially undersampled scattered energy to evaluate the potential of high density 3d gpr diffraction imaging a 200 mhz survey with less than a quarter wavelength grid spacing 0 05 m 0 1 m was acquired at a fractured and karstified limestone quarry near the village of cassis in southern france after 3d migration processing diffraction apices line up in sub vertical fracture planes and cluster in locations of karstic dissolution features the majority of karst is developed at intersections of two or more fractures and is limited in depth by a stratigraphic boundary such high resolution 3d gpr imaging offers an unprecedented internal view of a complex fractured carbonate reservoir model analogue as seismic and gpr wave kinematics are similar improvements in the imaging of steep fractures and irregular voids at the resolution limit can also be expected from high density seismic diffraction imaging

bar generating cross shore flow mechanisms on a beach random waves normally incident on a dissipative beach induce a variety of cross shore flows such as asymmetric oscillatory flow wave grouping induced long wave flow breaking induced turbulent flow and momentum decay induced undertow these flows are identified analyzed and hindcasted in a set of laboratory experiments with the aim of revealing the role of each of the flow mechanisms in the two dimensional case of bar generation on a beach

3 d seismic discontinuity for faults and stratigraphic features the coherence cube seismic data are usually acquired and processed for imaging reflections this paper describes a method of processing seismic data for imaging discontinuities e g faults and stratigraphic features one application of this nontraditional process is a 3 d volume or cube of coherence coefficients within which faults are revealed as numerically separated surfaces figure 1 compares a traditional 3 d reflection amplitude time slice with the results of the new method to our knowledge this is the first published method of revealing fault surfaces within a 3 d volume for which no fault reflections have been recorded

predictive painting of 3d seismic volumes predictive painting is a numerical algorithm that spreads information in 3d volumes according to the local structure of seismic events the algorithm consists of two steps first local spatially variable inline and crossline slopes of seismic events are estimated by the plane wave destruction method next a seed trace is inserted in the volume and the information contained in that trace is spread inside the volume thus automatically painting the data space immediate applications of this technique include automatic horizon picking and flattening in applications to both prestack and poststack seismic data analysis synthetic and field data tests demonstrate the effectiveness of predictive painting

establishing uniform longshore currents in a large scale sediment transport facility a large scale laboratory facility for conducting research on surf zone sediment transport processes has been constructed at the u s army engineer research and development center successful execution of sediment transport experiments which attempt to replicate some of the important coastal processes found on long straight beaches requires a method for establishing the proper longshore current an active pumping and recirculation system comprised of 20 independent pumps and pipelines is used to control the cross shore distribution of the mean longshore current pumping rates are adjusted in an iterative manner to converge toward the proper settings based on measurements along the beach two recirculation criteria proposed by visser coastal eng 15 1991 563 were also used and they provided additional evidence that the proper total longshore flow rate in the surf zone was obtained the success of the external recirculation system and its operational procedure and the degree of longshore uniformity achieved along the beach are the subjects of this paper to evaluate the performance of the recirculation system and as a precursor to sediment transport experiments two comprehensive test series were conducted on a concrete beach with straight and parallel contours 1 30 slope one using regular waves and the other using irregular waves in the regular wave case the wave period was 2 5 s and the average wave height at breaking was approximately 0 25 m in the irregular wave case the peak wave period was 2 5 s and the significant breaking wave height was approximately 0 21 m the longshore current recirculation system proved to be very effective in establishing uniform mean longshore currents along the beach in both cases this facility and the data presented here are unique for the following reasons 1 the high cross shore resolution of the recirculation system and the ease with which changes can be made to the longshore current distribution 2 the degree of longshore uniformity achieved as a percentage of the length of the basin even near the downdrift boundary 3 the scale of the wave conditions generated and 4 the relatively gentle beach slope used in the experiments compared to previous laboratory studies of the longshore current measured data are provided in an appendix for use in theoretical studies and numerical model development and validation

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

calcareous nannofossil age constraints on miocene flysch sedimentation in the outer dinarides slovenia croatia bosnia herzegovina and montenegro flysch deposits are associated with the outer dinaride nappe front they overlie eocene platform carbonate to bathyal marl successions that subsequently cover cretaceous plat form carbonates of apulia and the dinaride nappes planktonic foraminifer biostratigraphy indi cates eocene age of flysch sedimentation new calcareous nannofossil data reveal that several assemblages are present besides the dominant mid eocene species cretaceous paleocene oligocene and miocene taxa were also identified throughout the entire flysch belt widespread occurrence of nannofossil species of zone nn4 6 indicates that flysch deposition lasted up to at least the mid miocene ubiquitous occurrence of various pre miocene taxa demonstrates that extensive possibly submarine sediment recycling has occurred in the cenozoic as flysch remnants are typically sandwiched between thrust sheets these new stratigraphic ages give a lower bracket on deformation age of the coastal range the data provide a link between cretaceous compression in the bosnian flysch and recent deformation in the adriatic offshore area

a boussinesq model for waves breaking in shallow water abstract a simple description of wave breaking in shallow water is incorporated in the boussinesq equations by using the concept of surface rollers the roller is considered as a volume of water being carried by the wave with the wave celerity the effect of the roller is included in the vertical distribution of the horizontal velocity which leads to an additional convective momentum term the breaking criterion is related to the local slope of water surface and the thickness of the roller is determined from simple geometrical considerations although the model is simple it is capable of representing a variety of processes such as the initiation and cessation of wave breaking the evolution of wave profiles before during and after wave breaking the initial conversion of potential energy into forward momentum flux and the associated horizontal shift between the break point and the point where the setup in mean water level is initiated results are presented for regular and irregular wave trains and comparison with measurements shows good agreement

numerical modeling of infragravity wave response during delilah 1 the nearshore circulation model shorecirc is applied to simulate the infragravity wave conditions at two intervals during the 1990 delilah campaign at duck n c the model has been extended to solve the energy equation for random short waves on the timescale of the wave groups which acts as a wave driver for the long wave model to simulate the wave conditions an algorithm has been derived which synthesizes a directional offshore wavefield from measured data including the bound directional low frequency components the model data comparison shows that the mean short wave transformation and mean longshore current are predicted well the structure of the infragravity spectrum as measured in the nearshore array is correctly represented albeit that the energy levels are underpredicted in most locations the 2 d frequency longshore wavenumber spectra show that the infragravity wave energy consists mostly of edge waves and that the computations qualitatively resemble the measurements it is shown that for 1 day bar trapped edge waves are present the model is also used to show that the influence of the longshore variability is small for this particular beach and that the directional spreading in the offshore wave field is critical in predicting the nearshore infragravity wave conditions correctly edge waves which propagate against the current are generated by the directionally broad short wave forcing and to a lesser extent by back scattering the nonlinear terms are relatively unimportant for the prediction of the infragravity wave climate the cross shore gradient of the onshore directed radiation stress is the most important of the forcing terms

separation and imaging of seismic diffractions using migrated dip angle gathers abstractcommon reflection angle migration can produce migrated gathers either in the scattering angle domain or in the dip angle domain the latter reveals a clear distinction between reflection and diffraction events we derived analytical expressions for events in the dip angle domain and found that the shape difference can be used for reflection diffraction separation we defined reflection and diffraction models in the radon space the radon transform allowed us to isolate diffractions from reflections and noise the separation procedure can be performed after either time migration or depth migration synthetic and real data examples confirmed the validity of this technique

a comparison of diffraction imaging to incoherence and curvature detecting small subsurface features such as faults fracture swarms steep reef edges and channel edges is a routine task in seismic interpretation common seismic attributes used for this task such as curvature and incoherence are derived from conventional images containing both reflections and diffractions an emerging alternative approach is to interpret these edge features using the diffraction imaging technique which images diffracted energy separately a diffraction imaging volume is generated by separating specular reflections from diffractions in an unmigrated volume followed by migration of those diffractions different methods can be used to separate diffractions from reflections on unmigrated data in a case history they are separated with a plane wave destruction pwd filter an evaluation of diffraction imaging performance is applied to a 3d seismic data set from the cooper basin of australia diffraction imaging horizon maps are compared with corresponding maps made from incoherence and curvature volumes the resolution and the ability to detect faults fractures and channel edge features are compared the results show that diffraction imaging provides superior vertical and spatial resolution over conventional incoherence and curvature attributes for mapping faults and stratigraphy