Abstract: A method for identifying a seismic event includes extracting a portion of a plurality of seismic data signals based on energy levels in the plurality, comparing the extracted portion to a known pattern and determining a correlation, and identifying the seismic event based on the correlation. A computer program product and devices for implementing the method are provided.

Abstract: System and method for performing anisotropy corrections of post-imaging seismic data for a subsurface formation. The method may receive seismic data, preferably pre-stack seismic data comprising a plurality of traces, e.g., collected from a plurality of source and receiver locations. The seismic data may be imaged/migrated to produce imaged seismic data, which is organized into an arrangement that preserves aspects of the relative seismic propagation angle in the subsurface. One or more anisotropic parameters and corresponding corrections may be determined by analyzing the organized imaged seismic data. The determined parameters or corrections may be used to correct at least a subset of the imaged seismic data, thereby producing corrected seismic data which is useable in analyzing the formation. The corrected data may then optionally be stacked to produce a collection of corrected stacked traces, and/or analyzed as desired. The pre-stack data and/or the corrected seismic data may optionally be displayed.

Abstract: The storage device system comprises: a plurality of signal transmission paths connected respectively to a plurality of installed storage devices; a plurality of system side communications sections for transmitting and receiving signals respectively to and from the plurality of storage devices, via the plurality of signal transmission paths; and one or a plurality of signal correcting sections for inputting a signal exchanged between the plurality of storage devices and the plurality of system side communications sections, correcting the input signal on the basis of a previously established correction parameter, and outputting the corrected signal. The correction parameter is a value set on the basis of at least one of the length of the signal transmission path between the storage device and the system side communications section, the wavelength attribute of the signal input to the signal correcting section, and the storage device attribute relating to the storage device.

Abstract: A new approach is described based on reciprocity for estimating acquisition-related effects, which has several advantages over conventional surface-consistent processing techniques: (i) It can be applied to complete recordings, hence does not require the isolation of primary reflections in the data, (ii) no assumptions are imposed on the subsurface, and (iii) it is applicable to multi-component data. The application of reciprocity requires symmetric data acquisition, i.e. identical source and receiver patterns, identical locations, and the source orientations have to be identical to the receiver components. Besides reciprocity, additional constraints are required to determine the lateral source and receiver amplitude variations fully. Criteria based on minimizing total energy differences between adjacent common source and common receiver gathers, and in common offset panels of the medium response are applied.

Abstract: A system and methods for enhancing an image of post-stack seismic data, with pre-stack seismic data features, and displaying the enhanced image with the image of the post-stack seismic data are disclosed.

Abstract: A technique for calculating traveltime of a seismic wave in three dimensional tilted transversely isotropic (3D TI) media includes determining a wave vector, defining a unit vector, calculating an angle of the wave vector from an axis and performing a slowness determination, wherein a unit vector for a symmetry axis is defined as: (cos ? sin ?, sin ? sin ?, cos ?); where ? represents the azimuth of the symmetry axis measured from the x direction; and, ? represents the dip angle of the symmetry axis measured from the z direction. The technique may be practiced as a computer implemented set of instructions, and may be incorporated into measurement equipment.

Abstract: A method for coding and decoding seismic data acquired, based on the concept of multishooting, is disclosed. In this concept, waves generated simultaneously from several locations at the surface of the earth, near the sea surface, at the sea floor, or inside a borehole propagate in the subsurface before being recorded at sensor locations as mixtures of various signals. The coding and decoding method for seismic data described here works with both instantaneous mixtures and convolutive mixtures. Furthermore, the mixtures can be underdetemined [i.e., the number of mixtures (K) is smaller than the number of seismic sources (I) associated with a multishot] or determined [i.e., the number of mixtures is equal to or greater than the number of sources). When mixtures are determined, we can reorganize our seismic data as zero-mean random variables and use the independent component analysis (ICA) or, alternatively, the principal component analysis (PCA) to decode.

Abstract: Implementations of various technologies for a method for processing seismic data. In one implementation, the method includes (a) selecting a first trace from a first seismic data set and a second trace from a second seismic data set; (b) extracting one or more features of the same types from the first trace and the second trace; (c) matching the extracted features from the first trace with the extracted features from the second trace; and (d) calculating for a displacement field using one or more of the matching features of the first trace and the second trace.

Abstract: Methods for determining the existence and characteristics of a gradational pressurized zone within a subterranean formation are disclosed. One embodiment involves employing an attenuation relationship between a seismic response signal and increasing wavelet wavelength, which relationship may be used to detect a gradational pressurized zone and/or determine characteristics thereof. In another embodiment, a method for analyzing data contained within a response signal for signal characteristics that may change in relation to the distance between an input signal source and the gradational pressurized zone is disclosed. In a further embodiment, the relationship between response signal wavelet frequency and comparative amplitude may be used to estimate an optimal wavelet wavelength or range of wavelengths used for data processing or input signal selection. Systems for seismic exploration and data analysis for practicing the above-mentioned method embodiments are also disclosed.

Abstract: Methods for scanning geophysical data sets to find geological entities with specific geophysical responses entail selecting a focus sub-volume and a background sub-volume proximal to the focus sub-volume. The sub-volumes include discrete sampling locations and are located within at least two geophysical data sets. Each discrete sampling location has associated data values. The background data volume and each data value are normalized. A determination is made to whether a data value is inside or outside of the background data. A distance value is associated with each determination. The distance values are evaluated to find discrete sampling locations with specific geophysical responses. The anomalous data points can be related to the presence of hydrocarbon or water bearing strata at the corresponding depth locations of the data points.

Abstract: The present invention provides a method for harmonic noise attenuation in correlated sweep data in seismic exploration. The method includes forming a plurality of correlation data subsets using a plurality of sweep data sets and a correlation reference sequence. The method further includes estimating a noise level in a correlation data set using the correlation data subsets and subtracting the estimated noise level from the correlation data set.

Abstract: A downhole tool for gathering formation data from inside a borehole includes a substantially tubular housing adapted for axial connection to a drill string and multiple sensors coupled to the tubular housing. The sensors include a first pair of sensors aligned along a first axis and adapted to measure a spatial derivative along the first axis, a second pair of sensors aligned along a second axis and adapted to measure a spatial derivative along the second axis, and a third pair of sensors aligned along a third axis and adapted to measure a spatial derivative along the third axis. In selected embodiments, the spatial derivatives are used to differentiate seismic or sonic compression and shear waves measured in a downhole environment.

Abstract: To calculate information on a relative distance or positional relationship between an interface section and an object by detecting an electromagnetic wave transmitted through the interface section, and using the electromagnetic wave from the object to detect a relative position of the object with respective to the interface section. Information on the relative spatial position of an object 101 with respect to an interface section 102 that has an arbitrary shape and deals with transmission of information or signal from one side to the other side of the interface section 102 is detected with a spatial position detection method. An electromagnetic wave 106 radiated from the object 101 and transmitted through the interface section 102 is detected by an electromagnetic wave detection section 103, and based on the detection result, information on spatial position coordinates of the object 101 is calculated by a position calculation section 104.

Abstract: A method for automated extraction of surface primitives from seismic data is presented. A preferred embodiment of the method includes defining, typically with sub-sample precision, positions of seismic horizons through an extrema representation of a 3D seismic input volume; deriving coefficients that represent the shape of the seismic waveform in the vicinity of the extrema positions; sorting the extrema positions into groups that have similar waveform shapes by applying classification techniques with the coefficients as input attributes using unsupervised or supervised classification based on an underlying statistical class model; and extracting surface primitives as surface segments that are both spatially continuous along the extrema of the seismic volume and continuous in class index in the classification volume.

Abstract: A method of investigating a reservoir region in a subsurface formation by a time-lapse seismic survey. The subsurface formation comprises a further formation region adjacent to the reservoir region. Data are obtained from a time-lapse seismic survey and includes seismic data of the subsurface formation at a first point in time and a later point in time. The seismic data is processed to obtain a seismic representation of change in a predetermined seismic parameter in the further formation region, whereby the seismic parameter is dependent on stress. The seismic representation of change in the seismic parameter in the further formation region is interpreted for an indication of changes of stress distribution in the further formation region, and a property of the reservoir region is derived using the indication of change of stress distribution in the further formation region.

Abstract: The invention provides a method and apparatus by which the direction in or the position at which a signal source such as a sound source is present is estimated. A signal or signals from a signal source or a plurality of signal sources are received by a plurality of reception apparatus, and the received signals are decomposed into signals of different frequency bands by a plurality of band-pass filters. Then, cross correlation functions between the different frequency band signals are calculated for individual combinations of the reception apparatus for the individual corresponding frequency bands. If the power of noise having no directivity is high in some of the frequency bands, then the cross correlation functions of the frequency band do not exhibit a maximum value. Therefore, an influence of the noise can be suppressed effectively when delay times of the individual reception apparatus which depend upon the direction or directions or the position or positions of the signal source or sources are estimated.

Abstract: A method to convert seismic traces to petrophysical properties is disclosed. One embodiment of the method comprises (a) deriving a combined log seismic response from at least one petrophysical log from a well and at least one seismic trace substantially near the well, (b) convolving the combined log seismic response filter with each seismic trace to convert the seismic traces to logs of petrophysical properties, (c) outputting the petrophysical properties. Equations to derive the combined log seismic response and to convolve the combined seismic response filter are disclosed. The method may be used to output the petrophysical data as a two-dimensional cross-section or as a three-dimensional volume cube.

Abstract: A method of determining seismic properties of a layer of the seabed, in particular a surface or near-surface layer (5), comprises directing seismic energy propagating in a first mode at a boundary face of the layer so as to cause partial mode conversion of the seismic energy at the boundary face. For example partial mode conversion may occur when seismic energy propagates upwards through the interface between a surface or near-surface layer (5) and the basement (6), owing to the difference in seismic properties between the surface or near-surface layer (5) and the basement (6). In the invention, the two modes of seismic energy—that is the initial mode and the mode generated by mode conversions at the interface—are received at a receiver. The difference in travel time of the two modes between the interface and the receiver is determined from the seismic data acquired by the receiver.

Abstract: The invention concerns a method for retrieving local near-surface material information including the steps of:—providing a group of receivers comprising at least one buried receiver and at least one surface receiver positioned either at or very near the Earth surface;—recording a seismic wavefield;—estimating a propagator from said recorded seismic wavefield;—inverting said propagator; and—retrieving said near-surface material information.

Abstract: A downhole crystal-based clock that is substantially insensitive to the factors that cause frequency deviation. The clock may be maintained at a predetermined temperature using a temperature sensing device and a heating device, where the predetermined temperature corresponds to the temperature at which the crystal experiences only slight frequency deviation as a function of temperature. A microprocessor may monitor the clock and compensate for long-term aging effects of the crystal according to a predetermined algorithm. The predetermined algorithm may represent long-term aging effects of the crystal which were derived by comparing the crystal clock to a more accurate clock (e.g., an atomic clock) prior to placing the clock downhole. In this manner, the crystal-based clock may be substantially free from the factors that cause frequency, and therefore time variations.

Abstract: A Method for Interpreting Seismic Data Using Duplex Waves is described. Whereas substantially horizontal boundaries are readily identified using conventional processing methods based on primary reflections, it has been difficult or impossible to use such methods for locating substantially vertical events or boundaries. The method of the present invention uses secondary reflections to locate substantially vertical events by gathering common source or receiver traces for processing. Wave fields of these gathers are continued downward to the level of the base boundary, then at each discrete depth level, a seismic image of sub-vertical events is formed. The downward-continued gathers correspond to the travel time of the wave from when it left the source or the receiver point, was reflected from the base boundary, and arrived to the corresponding point of the discrete level of wave-field continuation.

Abstract: An acoustic tool that provides a reduced tool mode and enhanced accuracy for estimating shear wave propagation slowness in slow formations is disclosed. In one embodiment, the acoustic tool comprises: an acoustic source, an array of acoustic receivers, and an internal controller. The acoustic source excites waves that propagate in a quadrupole mode. The internal controller processes signals from the array of acoustic receivers to determine a peak phase semblance having a slowness value that varies with frequency. The minimum slowness value associated with the peak phase semblance provides an accurate estimate of the shear wave propagation slowness. The acoustic source preferably includes four source elements. The elements that are 90° apart are preferably driven in inverse-phase to obtain the quadrupole excitation pattern.

Abstract: A method of seismic data analysis to provide clustering of A.V.O. data into A.V.O. anomaly types, the method comprising: obtaining successive values of a plurality of seismic attributes, each seismic attribute comprising a respective property of a seismic reflection event, grouping said values using a running window of a predetermined size into a plurality of groups, for each group identifying first and second parameters corresponding to said first and second attributes, and plotting each group as a single event based on said group parameters, said group parameters having been selected to cause clustering of said seismic reflection events on said plot according to the presence or absence of A.V.O. anomalies.

Abstract: A method for multipath imaging of three-dimensional volumes of seismic data, given the subsurface velocity distribution. Ray tracing is used to generate the volumes of information needed for migration, but using coarse-scaled grids for computational efficiency. Interpolation methods are disclosed that address the specific shot points and receiver locations and that enable a final image on a grid with the desired resolution. Data storage and retrieval techniques are also disclosed.

Abstract: A method for seismic characterization of subsurface Earth formations includes determining at least one of compressional velocity and shear velocity, and determining reservoir parameters of subsurface Earth formations, at least including density, from data obtained from a wellbore penetrating the formations. A quality factor for the subsurface formations is calculated from the velocity, the density and the water saturation. A synthetic seismogram is calculated from the calculated quality factor and from the velocity and density. The synthetic seismogram is compared to a seismic survey made in the vicinity of the wellbore. At least one parameter is adjusted. The synthetic seismogram is recalculated using the adjusted parameter, and the adjusting, recalculating and comparing are repeated until a difference between the synthetic seismogram and the seismic survey falls below a selected threshold.

Abstract: A method is disclosed for seismic imaging of subsurface diffractors. The method includes performing migration velocity analysis on a seismic time record section and depth migrating the time section for offsets exceeding one-half a distance between a seismic energy source and a seismic receiver most distant from the source during acquisition of seismic data used to generate the time record section.

Abstract: Methods for determining the existence and characteristics of a gradational pressurized zone within a subterranean formation are disclosed. One embodiment involves employing an attenuation relationship between a seismic response signal and increasing wavelet wavelength, which relationship may be used to detect a gradational pressurized zone and/or determine characteristics thereof. In another embodiment, a method for analyzing data contained within a response signal for signal characteristics that may change in relation to the distance between an input signal source and the gradational pressurized zone is disclosed. In a further embodiment, the relationship between response signal wavelet frequency and comparative amplitude may be used to estimate an optimal wavelet wavelength or range of wavelengths used for data processing or input signal selection. Systems for seismic exploration and data analysis for practicing the above-mentioned method embodiments are also disclosed.

Abstract: A method intended to obtain reflection travel times from an interpretation of seismic data in migrated cylindrical waves, for a given value of the parameter defining the slope of these waves, or the superposition of such data associated with various substantially parallel acquisition lines, this parameter possibly taking successively several values. The method comprises the steps: a) defining a slowness vector ({right arrow over (p)}) b) for a given position of a seismic receiver of abscissa (XR) on an acquisition line, seeking, the abscissa (?) of the source; c) determining a travel time (te(XR)) d) repeating steps (b and c) for all the positions of the receivers for which demigration result is wanted; and e) repeating steps (a to d) for all the acquisition lines for which a demigration result is wanted and for all the values taken by parameter (px).

Abstract: A method is disclosed for processing seismic data. The method includes prestack depth migrating the seismic data to generate common image gathers using an initial velocity-depth model. Horizons in the migrated seismic data are selected. Residual migration velocity analysis in the depth-offset domain is performed with respect to each selected horizon, and the velocity-depth model is updated based on the residual migration velocity analysis.

Abstract: A method of obtaining a spatial model of a property of part of a subsurface formation located between underground seismic receivers in which at least two sets of pairs of seismic receivers are utilized and one pair of receivers is used to record a signal from a seimic source and obtaining a response by solving (s11(?t){circle around (x)}s21(t))=r11,21(t){circle around (x)}(s11(?t){circle around (x)}s21(t)), wherein the symbol {circle around (x)} denotes convolution and wherein s11(?t) is the time-reverse of the signal s11(t). A path-related attribute is selected from transmission response r11,21(t) that corresponds to the property of the subsurface formation and a tomographic reconstruction technique is applied to the path-related attribute to obtain the spatial model of the property of part of the subsurface formation.

Abstract: Directional acoustic measurements made in the borehole are used for imaging a near-borehole geological formation structure and determination of its orientation. Four-component cross-dipole data set measured in a deviated borehole in combination with the directionality of the compressional waves in the dipole data give the orientation of bed boundaries crossing the borehole. The low-frequency content (2˜3 kHz) of the data allows for imaging the radial extent of the formation structure up to 15 m, greatly enhancing the penetration depth as compared to that obtained using conventional monopole compressional-wave data. A combination monopole/dipole arrangement of sources and receivers may also be used for imaging of bed boundaries.

Abstract: Representative embodiments provide for a computer including a program code configured to cause a processor to invert and thereafter calibrate first and second data sets, subtract the inverted second data set from the inverted first data set to derive a time-lapse data set, calculate a model including a plurality of parametric values, sort the plurality of parametric values into a plurality of bins, select, map and calibrate a plurality of optimal parametric values from the plurality of bins, and plot the plurality of calibrated optimal parametric values to represent at least one physical characteristic of a subterranean reservoir of hydrocarbons. The method includes deriving a time-lapse data set from a first seismic data set and a second seismic data set, deriving a model, sorting the plurality of values into bins, selecting, mapping and calibrating a plurality of optimal values from the bins, and plotting the calibrated values.

Abstract: A number of seismic stacks are precomputed (20) for known velocity fields. The velocity fields are chosen to span the range of velocities of interest. The stacks are then arranged (21) in the 3D memory of a graphics computer (10–14) using time and position as first dimensions and the index of the velocity field as the last dimension. In such 3D space, any velocity field to be used for stacking appears as a surface (S) within a volume. Projecting the seismic stacks onto that surface provides the seismic line stacked for the velocity field of interest.

Abstract: A method is disclosed for identifying zones anomalously absorptive of seismic energy. The method includes jointly time-frequency decomposing seismic traces, low frequency bandpass filtering the decomposed traces to determine a general trend of mean frequency and bandwidth of the seismic traces, and high frequency bandpass filtering the decomposed traces to determine local variations in the mean frequency and bandwidth of the seismic traces. Anomalous zones are determined where there is difference between the general trend and the local variations.

Abstract: A method of analyzing seismic survey data in which a transfer function for a geological model is derived by ray tracing techniques applied to theoretical data and the transfer function is applied to actual survey data in order to calculate reflection points (50) and/or other attributes for each shot (42)/receiver (44) pair. The number of ray tracing calculations which have to be performed in deriving the model transfer function can thus be controlled. A sufficiently accurate transfer function can be derived using theoretical data representing substantially fewer shot (42)/receiver (44) pairs than are used in the traditional ray tracing solution applied directly to actual survey data. Attribute values for actual source (42)/receiver (44) pairs are estimated by interpolating the transfer function data.

Abstract: A method of determining a fluid property in a subsurface region of interest of an earth formation uses measurements of seismic attributes on seismic data. For a test region, a plurality of realizations of rock properties are specified, and for each of the realizations and a selected value of a fluid property, the seismic attribute is modeled. This defines a probability density function (PDF). Comparison of the PDF of the model output with the PDF on the measured seismic data is used to determine the likelihood of the selected fluid property.

Abstract: A method of applying an effective velocity model to vertical seismic profile (VSP) seismic data comprises correcting for offset using a non-hyperbolic effective velocity model so as to take account of the earth's layering and anisotropy. One preferred non-hyperbolic model for the relationship between offset and travel time is: formula (I) where t is the travel time of seismic energy from the source to the receiver, x is the offset between the source and the receiver, and z is the depth of the receiver.

Abstract: Disclosed is a new method for providing accurate real time predictions of pore pressure and fracture gradient, at the rig site by determining the wave velocity from drill cuttings by a portable continuous wave technology (CWT) tool that measures drill cuttings at high resonant frequency and then using the velocity obtained in combination with the novel method of the present invention to arrive at accurate predictions for pore pressure and fracture gradient. The new technique offers real time pore pressure prediction at the rig site with small error margin that is not otherwise available using seismic, VSP, or check shot velocities in exploration.

Abstract: A method of processing sonic wireline or logging while drilling data acquired in a borehole that includes filtering the sonic data to attenuate tool-borne and borehole-borne arrivals; migrating the filtered sonic data; and beamforming the filtered and migrated sonic data to determine a position of a reflector with respect to the borehole. The sonic data may be processed down-hole, transmitted to the surface, and used for geosteering purposes while drilling. The filter may comprise an adaptive noise-attenuating filter capable of attenuating noise arising from different borehole modes from desired signal and allowing for changes in the source signature.

Abstract: Waveform data, such as reflection seismic data, is filtered by concurrently analyzing various phase angles of the data. The various phase angles of the data are compared to phase rotated background trends and the phase angle producing the maximum deviation from the equivalent background trend is selected as the optimum phase angle for predictive analysis or exclusion filtering.

Abstract: A method of generating a semblance panel comprises summing two or more gathers of traces. The dip of the reflector is taken into account in the summation process, and this prevents semblance peaks from becoming smeared during the summation process and so allows a greater number of gathers to be used to generate the semblance panel. In an embodiment of the invention the dip is determined from the seismic data. Alternatively, the reflector dip used in the summation process may be obtained from pre-existing data acquired at the survey location, or the reflector dip may be already known. The invention can be applied to seismic data containing events from more than one reflector.

Abstract: A method for estimating near-surface material properties in the vicinity of a locally dense group of seismic receivers is disclosed. The method includes receiving seismic data that has been measured by a locally dense group of seismic receivers. Local derivatives of the wavefield are estimated such that the derivatives are centered at a single location preferably using the Lax-Wendroff correction. Physical relationships between the estimated derivatives including the free surface condition and wave equations are used to estimate near-surface material properties in the vicinity of the receiver group. Another embodiment of the invention is disclosed wherein the physical relationships used to estimate material properties are derived from the physics of plane waves arriving at the receiver group, and the group of receivers does not include any buried receivers.

Abstract: Surface seismic sources are used to simulate crosswell data between the two wells, and, using surface receivers, reflection seismic data are obtained over the region between the two wells. Reflection data are preferably obtained from reflectors both above and below the reservoir. Tomographic analysis of the simulated crosswell and reflection data gives a model of the reservoir. Changes in the model are indicative of reservoir fluid changes, pressure changes, or compaction.

Abstract: A method is disclosed for separating energy resulting from actuating at least two different seismic energy sources from seismic signals. The sources are actuated to provide a variable time delay between successive actuations of a first one and a second one of the sources. The method includes sorting the seismic signals such that events therein resulting from actuations of the first source are substantially coherent in all spatial directions, coherency filtering the first source coherency sorted signals, sorting the seismic signals such that events therein resulting from actuations of the second source are substantially coherent in all spatial directions, and coherency filtering the second source coherency sorted signals.

Abstract: A method of monitoring a microseismic event includes detecting the event to produce a first signal dependent on the event. The first signal includes noise at a frequency of, for example 50 Hz. A first sample of the first signal is taken. Then a second sample of the first signal is taken, the second sample occurring n/f seconds after the first sample, where n is an integer (e.g. 1). Subtracting the first and second samples from each other produces a farther signal dependent on the event in which the noise has been at least partly compensated for.

Abstract: A method of determining the sonic slowness of a formation traversed by a borehole comprising generating tracks from sonic waveform peaks received at a plurality of depths wherein the peaks that are not classified prior to tracking is set forth. A method for generating a slowness versus depth log is generated for waveform arrivals by classifying long tracks, classifying small tracks; classifying tracks that overlap; filling in gaps; and creating a final log is disclosed. In further improvements, non-classified tracks and interpolation are used to fill in gaps.

Abstract: A system and method of creating a filter for use with locally dense seismic data is disclosed. The method includes obtaining survey geometry characteristics from a locally dense seismic survey. A filter is designed which uses spatial derivatives of the wavefield of order between (1) and the maximum order of spatial derivatives of the wavefield that can be estimated within a group. The filter can be designed so as to separate up/down going components, p/s components, or both up/down and p/s components. Partial derivatives in space and time of the wavefield can be calculated, using, for example, a taylor series expansion as an approximation. The seismic data is filtered by combining estimated near surface material properties, the seismic data, and the calculated partial derivatives.

Abstract: A method of seismic data analysis to provide clustering of A.V.O. data into A.V.O. anomaly types, the method comprising: obtaining successive values of a plurality of seismic attributes, each seismic attribute comprising a respective property of a seismic reflection event, grouping said values using a running window of a predetermined size into a plurality of groups, for each group identifying first and second parameters corresponding to said first and second attributes, and plotting each group as a single event based on said group parameters, said group parameters having been selected to cause clustering of said seismic reflection events on said plot according to the presence or absence of A.V.O. anomalies.

Abstract: The invention concerns a method for retrieving local near-surface material information including the steps of:—providing a group of receivers comprising at least one buried receiver and at least one surface receiver positioned either at or very near the Earth surface;—recording a seismic wavefield;—estimating a propagator from said recorded seismic wavefield;—inverting said propagator; and—retrieving said near-surface material information.

Abstract: The patent discloses a signal processing technique for determining the fast and slow shear wave polarizations, and their orientation, for acoustic waves in an anisotropic earth formation. The signal processing method decomposes composite received waveforms a number of times using a number of different strike angles. The decomposed signals are used to create estimated source signals. The estimated source signals are compared in some way to obtain an objective function. Locations in a plot where the objective function reaches minimum values are indicative of the acoustic velocity of the fast and slow polarizations within the formation.