Accurate Velocity Model Research Articles

Data-driven tomographic velocity analysis in tilted transversely isotropic media: A 3D case history from the Canadian Foothills

We evaluated how velocity and anisotropy model-building strategies affect seismic imaging in the Canadian Foothills Thrust Belt by comparing the results of a model-driven approach with those of a data-driven approach. Two independently run Kirchhoff prestack depth-imaging projects were initiated using different static corrections for near-surface weathering layers and using different velocity and anisotropy model-building strategies. We observed that an isotropic data-driven reflection tomography velocity model-building approach resulted in a significantly better stack image than did a highly interpretive anisotropic model-driven velocity model-building approach. By carefully introducing anisotropy into the former, data-driven approach, we achieved significant improvements in positioning, including more accurate depth ties between the seismic image and well tops and better definition of structural geometries. The differences in the imaging observed at the various stages of this case history illustrate the sensitivity of the final depth images to the treatment of the near-surface velocity field, the macrointerval velocity model-building technique, and the choices of [Formula: see text] and [Formula: see text], which are the Thomsen anisotropy parameters for tilted transverse isotropy. The data-driven approach successfully challenged the historical idea that we must perform a geologic interpretation of the seismic data to derive an accurate depth velocity model in a complex geologic setting.

Practical approaches for subsalt velocity model building

Imaging sediments below salt bodies is challenging because of the inherent difficulty of estimating accurate velocity models. These models can be estimated in a variety of ways with varying degrees of expense and effectiveness. Two methods are commercially viable trade-offs. In the first method, residual-moveout analysis is performed in a layer-stripping mode. The models produced with this method can be used as a first approximation of the subsalt velocity field. A wave-equation migration scanning technique is more suitable for fine-tuning the velocity model below the salt. Both methods can be run as part of a sophisticated interactive velocity interpretation software package that makes velocity interpretation efficient. Performance of these methods has been tested on synthetic and field data examples.

Finite‐frequency tomography in a crustal environment: Application to the western part of the Gulf of Corinth

ABSTRACTIn this paper we investigate finite‐frequency effects in crustal tomography. We developed an inversion procedure based on an exact numerical computation of the sensitivity kernels. In this approach we compute the 3D travel‐time sensitivity kernels by using (1) graph theory and an additional bending to estimate accurately both rays and travel‐times between source/receiver and diffraction points and (2) paraxial ray theory to estimate the amplitude along theses rays. We invert both the velocity and the hypocentre parameters, using these so‐called banana‐doughnut kernels and the LSQR iterative solver. We compare the ray‐theoretical and the finite‐frequency tomography to image the intermediate structures beneath the Gulf of Corinth (Greece), which has long been recognized as the most active continental rifting zone in the Mediterranean region. Our dataset consists of 451 local events with 9233 P‐ first‐arrival times recorded in the western part of the Gulf (Aigion area) in the framework of the 3F‐Corinth European project. Previous tomographic images showed a complex velocity crustal model and a low‐dip surface that may accommodate the deformation. Accurate velocity models will help to better constrain the rifting process, which is still a subject of debate. The main results of this study show that finite‐frequency tomography improves crustal tomographic images by providing better resolved images of the 3D complicated velocity structure. Because the kernels spread the information over a volume, finite‐frequency tomography results in a sharpening of layer boundaries as we observed for the shallower part of the crust (down to 5 km depth) beneath the Gulf of Corinth.

Interferometric imaging condition for wave-equation migration

The fidelity of depth seismic imaging depends on the accuracy of the velocity models used for wavefield reconstruction. Models can be decomposed in two components, corresponding to large-scale and small-scale variations. In practice, the large-scale velocity model component can be estimated with high accuracy using repeated migration/tomography cycles, but the small-scale component cannot. When the earth has significant small-scale velocity components, wavefield reconstruction does not completely describe the recorded data, and migrated images are perturbed by artifacts. There are two possible ways to address this problem: (1) improve wavefield reconstruction by estimating more accurate velocity models and image using conventional techniques (e.g., wavefield crosscorrelation) or (2) reconstruct wavefields with conventional methods using the known background velocity model but improve the imaging condition to alleviate the artifacts caused by the imprecise reconstruction. Wedescribe the unknown component of the velocity model as a random function with local spatial correlations. Imaging data perturbed by such random variations is characterized by statistical instability, i.e., various wavefield components image at wrong locations that depend on the actual realization of the random model. Statistical stability can be achieved by preprocessing the reconstructed wavefields prior to the imaging condition. We use Wigner distribution functions to attenuate the random noise present in the reconstructed wavefields, parameterized as a function of image coordinates. Wavefield filtering using Wigner distribution functions and conventional imaging can be lumped together into a new form of imaging condition that we call an interferometric imaging condition because of its similarity to concepts from recent work on interferometry. The interferometric imaging condition can be formulated both for zero-offset and for multioffset data, leading to robust, efficient imaging procedures that effectively attenuate imaging artifacts caused by unknown velocity models.

2D PP/PS‐stereotomography: Application to a real 2D‐OBC dataset

ABSTRACTIt has been shown on an ‘ideal’ synthetic dataset that PP/PS‐stereotomography can estimate an accurate velocity model without any pairing of PP‐ and PS‐events. The P‐wave velocity model is first estimated using PP data and then, fixing this velocity field, the S‐wave velocity is estimated using the PS data. This method needed to be evaluated further and we present here the first application of PP/PS‐stereotomography to a real dataset: the 2D East‐West Mahogany OBC line (Gulf of Mexico). We are here confronted with data which do not fit our working assumptions: coherent noise (due to an approximate separation of PP‐ and PS‐events and some remaining multiples), probably some anisotropy and 3D effects. With a careful selection of the stereotomographic picks, which allows one to decrease the effect of the picked coherent noise by the automatic picker, our application can demonstrate the relevance of our approach in the upper part of the profile, where anisotropy and 3D effects might be low. We can thus estimate, without any pairing of PP‐ and PS‐events, a velocity field which provides not only flat common image gathers, but also PP‐ and PS‐depth migrated images located at the same positions. For the deeper part of the profile, a significant shift in depth appears. In addition to possible anisotropy, 3D effects and a more complex velocity field (‘salt body’), this is due to the quality of the PZ‐ and X‐components profiles: The PZ‐component profile where the PP‐stereotomographic picking is performed, is polluted by conflicting converted or multiple events and the X‐component profile, where the PS‐stereotomographic picking is performed, is highly noisy. This study emphasizes the need to develop accurate selection criteria for the stereotomographic picks.

Common reflection surface stack, new method in seismic reflection data processing: A synthetic data example.

The NMO/DMO/stack method is a traditional and well-known method in the oil industry that needs an accurate macro velocity model to image the subsurface structures. Making such a macro velocity model is a time consuming process that is error prone. New introduced common-reflection-surface (CRS) stack is a data driven method which is independent of velocity information apart from the surface velocity. It comes from common reflection point (CRP) trajectory concept for finite offset. In NMO/DMO/stack, the stacked data are obtained from a summation over a curve along the offset coordinate but the principal of CRS stack is to sum along a surface of specular contributions from a segment of a reflector instead of reflection point. The summation over a segment of a coherent reflector drastically improves the signal/noise (S/N) ratio as the stacked data will show. An important aspect of the method is that the estimated parameters provide us with significant information on the subsurface structure. These are three new parameters called kinematic wavefield attributes; a, RN and RNIP. The parameter a is the emergence angle of normal-ray which will be used later for a normal-ray map migration. RN is the curvature of the exploding reflector wavefield measured at the surface and RNIP is the curvature of normal-incidence-point wave which could be used later to yield information on the propagation velocity and inversion NIP tomography. Here we processed a synthetic data to derive zero offset or CRS stacked section with high S/N ratio and better continuity on the reflection events.

From time to depth imaging with ‘Beyond Dix’

In many parts of the world, pre-stack time migration (PSTM) still represents the majority of seismic imaging activity in the industry. The reason for this is the simple efficiency and robustness of time imaging and its ability to focus seismic reflectors for many geological settings. Limitations of PSTM appear in the case of strong lateral velocity variations, where the more rigorous imaging and more accurate velocity models offered by Pre-Stack Depth Migration (PSDM) are required. In areas of moderate complexity, where PSTM begins to struggle we introduce a new, accurate method, ‘Beyond Dix’, to help bridge the gap between PSTM and PSDM. Beyond Dix provides an accurate fast-track PSDM from PSTM outputs. It takes full advantage of the efficiency, good focusing, and high signal-to-noise ratio available from time imaging to jump-start the PSDM process. The name comes from the fact that we are going beyond the limitations of the 1D Dix inversion commonly used to derive depth interval velocities from the PSTM velocities. It uses the full kinematic information available in the time migrated domain to directly build an accurate depth velocity model and bypass the 1D Dix inversion altogether. Not only does this approach extract the maximum value from time imaging, it also adds great flexibility to imaging projects by allowing a seamless and fast transition from PSTM to PSDM and thus avoiding the need to choose at an early stage between a time or depth approach. It is clear that in addition to providing a fast-track PSDM, Beyond Dix has a range of possible applications, including building more accurate initial models for full depth imaging projects. In this paper we explain how the detailed information freely available within the time migrated domain can be used directly to build an accurate depth velocity model. We also illustrate the application of Beyond Dix with two examples from different geological settings. In particular, we demonstrate that the resulting PSDM images converted back to time exhibit significantly improved focusing and structural delineation compared to equivalent PSTM images. Depth velocity model building The estimation of an accurate 3D depth velocity model certainly remains one of the greatest challenges in seismic imaging. Depth velocity model building typically involves: N Initial PSDM N Residual moveout (RMO) picking on common image point (CIP) gathers N Structural dip picking in the migrated domain N Update of the depth velocity model by ray-based tomographic inversion Starting from an initial velocity model, an initial PSDM is performed to build CIP gathers for RMO picking. The objective of the velocity model building/update is to minimize the observed RMO (related to the velocity error) in the migrated domain, flattening the events on the CIP gathers. From the knowledge of the RMO and the structural dip one can implement a linearized solution to tomographically update the velocity model with the objective of reducing RMO in the next PSDM run (Al-Yahya, 1989; Liu and Bleistein, 1995). The tomography is usually repeated through several iterations to solve for complex non-linear effects. To avoid the extra delay involved in running a full PSDM and re-picking RMO and dip after each tomographic update iteration, Guillaume et al. (2001) proposed an efficient kinematic approach. This same kinematic approach is used by Beyond Dix.

Efficient waveform tomography for lithospheric imaging: implications for realistic, two-dimensional acquisition geometries and low-frequency data

We provide a series of numerical experiments designed to test waveform tomography under (i) a reduction in the number of input data frequency components (‘efficient’ waveform tomography), (ii) sparse spatial subsampling of the input data and (iii) an increase in the minimum data frequency used. These results extend the waveform tomography results of a companion paper, using the same third-party, 2-D, wide-angle, synthetic viscoelastic seismic data, computed in a crustal geology model 250 km long and 40 km deep, with heterogeneous P-velocity, S-velocity, density and Q-factor structure. Accurate velocity models were obtained using efficient waveform tomography and only four carefully selected frequency components of the input data: 0.8, 1.7, 3.6 and 7.0 Hz. This strategy avoids the spectral redundancy present in ‘full’ waveform tomography, and yields results that are comparable with those in the companion paper for an 88 per cent decrease in total computational cost. Because we use acoustic waveform tomography, the results further justify the use of the acoustic wave equation in calculating P-wave velocity models from viscoelastic data. The effect of using sparse survey geometries with efficient waveform tomography were investigated for both increased receiver spacing, and increased source spacing. Sampling theory formally requires spatial sampling at maximum interval of one half-wavelength (2.5 km at 0.8 Hz): For data with receivers every 0.9 km (conforming to this criterion), artefacts in the tomographic images were still minimal when the source spacing was as large as 7.6 km (three times the theoretical maximum). Larger source spacings led to an unacceptable degradation of the results. When increasing the starting frequency, image quality was progressively degraded. Acceptable image quality within the central portion of the model was nevertheless achieved using starting frequencies up to 3.0 Hz. At 3.0 Hz the maximum theoretical sample interval is reduced to 0.67 km due to the decreased wavelengths; the available sources were spaced every 5.0 km (more than seven times the theoretical maximum), and receivers were spaced every 0.9 km (1.3 times the theoretical maximum). Higher starting frequencies than 3.0 Hz again led to unacceptable degradation of the results.

Physical modeling and analysis of P-wave attenuation anisotropy in transversely isotropic media

Anisotropic attenuation can provide sensitive attributes for fracture detection and lithology discrimination. This paper analyzes measurements of the P-wave attenuation coefficient in a transversely isotropic sample made of phenolic material. Using the spectral-ratio method, we estimate the group (effective) attenuation coefficient of P-waves transmitted through the sample for a wide range of propagation angles (from [Formula: see text] to [Formula: see text]) with the symmetry axis. Correction for the difference between the group and phase angles and for the angular velocity variation help us to obtain the normalized phase attenuation coefficient [Formula: see text] governed by the Thomsen-style attenuation-anisotropy parameters [Formula: see text] and [Formula: see text]. Whereas the symmetry axis of the angle-dependent coefficient [Formula: see text] practically coincides with that of the velocity function, the magnitude of the attenuation anisotropy far exceeds that of the velocity anisotropy. The quality factor [Formula: see text] increases more than tenfold from the symmetry axis (slow direction) to the isotropy plane (fast direction). Inversion of the coefficient [Formula: see text] using the Christoffel equation yields large negative values of the parameters [Formula: see text] and [Formula: see text]. The robustness of our results critically depends on several factors, such as the availability of an accurate anisotropic velocity model and adequacy of the homogeneous concept of wave propagation, as well as the choice of the frequency band. The methodology discussed here can be extended to field measurements of anisotropic attenuation needed for AVO (amplitude-variation-with-offset) analysis, amplitude-preserving migration, and seismic fracture detection.

Early arrival waveform tomography on near-surface refraction data

We develop a waveform-tomography method for estimating the velocity distribution that minimizes the waveform misfit between the predicted and observed early arrivals in space-time seismograms. By fitting the waveforms of early arrivals, early arrival waveform tomography (EWT) naturally takes into account more general wave-propagation effects compared to the high-frequency method of traveltime tomography, meaning that EWT can estimate a wider range of slowness wavenumbers. Another benefit of EWT is more reliable convergence compared to full-waveform tomography, because an early-arrival misfit function contains fewer local minima. Synthetic test results verify that the waveform tomogram is much more accurate than the traveltime tomogram and that this algorithm has good convergence properties. For marine data from the Gulf of Mexico, the statics problem caused by shallow, gassy muds was attacked by using EWT to obtain a more accurate velocity model. Using the waveform tomogram to correct for statics, the stacked section was significantly improved compared to using the normal move-out (NMO) velocity, and moderately improved compared to using the traveltime tomogram. Inverting high-resolution land data from Mapleton, Utah, showed an EWT velocity tomogram that was more consistent with the ground truth (trench log) than the traveltime tomogram. Our results suggest that EWT can provide supplemental, shorter-wavelength information compared to the traveltime tomogram for both shallow and moderately deep seismic data.

Velocity-independent layer stripping of PP and PS reflection traveltimes

Building accurate interval velocity models is critically important for seismic imaging and AVO (amplitude variation with offset) analysis. Here, we adapt the [Formula: see text] method to develop an exact technique for constructing the interval traveltime-offset function in a target zone beneath a horizontally layered overburden. All layers in the model can be anisotropic, with an essential assumption that the overburden has a horizontal symmetry plane (i.e., up-down symmetry). Our layer-stripping algorithm is entirely data-driven and, in contrast to the generalized Dix equations, does not require knowledge of the velocity field anywhere in the medium. Important advantages of our approach compared to the Dix-style formalism also include the ability to handle mode-converted waves, long-offset data, and laterally heterogeneous target layers with multiple, curved reflectors. Numerical tests confirm the high accuracy of the algorithm in computing the interval traveltimes of both PP- and PS-waves in a dipping, transversely isotropic layer with a tilted symmetry axis (TTI medium) beneath an anisotropic overburden. In combination with the inversion techniques developed for homogeneous TTI models, the proposed layer stripping of PP and PS data can be used to estimate the interval parameters of TTI formations in such important exploration areas as the Canadian Foothills. Potential applications of this methodology also include the dip-moveout inversion for the P-wave time-processing parameter [Formula: see text] and stable computation of the interval long-spread (nonhyperbolic) moveout for purposes of anisotropic velocity analysis.

Straight-rays redatuming: A fast and robust alternative to wave-equation-based datuming

Wave-equation-based redatuming is expensive and requires a detailed knowledge of the shallow velocity field. We derive the analytical expression of a new prestack wavefield extrapolation operator, the Topographic Datuming Operator (TDO), which applies redatuming based on straight-rays approximation above and below a chosen datum. This redatuming operator is directly applied to common-source gathers to downward continue the source and the receivers, simultaneously, to the datum level without resorting to common-receiver gathers. As a result, the method is far more efficient and robust than the conventional wave-equation-based redatuming and does not require an accurate depth-domain interval velocity model. In addition, TDO, unlike wave-equation-based redatuming, requires effective velocities above datum, and thus can be applied using attributes valid for static correction methods. Effective velocities beneath the datum permit us to replace the surface integral, which is needed for wave-equation redatuming with a line integral. In the particular case of infinite (in practice, very high with respect to the shallow layers) velocity beneath the datum, the TDO impulse response collapses to a point, and TDO redatuming is equivalent to conventional static correction, which may, therefore, be regarded as a special case of the newly derived operator. The computational cost of applying TDO is slightly larger than static corrections, yet provides higher quality results partially attributable to the ability of TDO to suppress diffractions emanating from anomalies above datum. Since TDO is an operation based on geometrical optics approximation, velocity after TDO is not biased by the vertical shift correction associated with conventional static correction. Application to a synthetic data set demonstrates the features of the method.

Velocity-porosity relationships, 1: Accurate velocity model for clean consolidated sandstones, GEOPHYSICS, 68, 1822–1834.

The empirical equation of Arns et al., 2002a, is reproduced incorrectly in this paper as equation 22. The correct nonlinear empirical equation for the Poisson's ratio of a dry porous rock should read

The Global Offset seismic approach: advantages and limitations

Seismic acquisition and processing in thrust belt areas represent challenging tasks in geophysics. Rough topography, geological complexity and sharp velocity variations increase the difficulties of recording seismic data of good quality and decrease the possibility of obtaining satisfactory imaging. In these circumstances, application of pre-stack depth migration (PSDM) can help in improving the imaging. However, the success of PSDM depends on the range of offset used and on the accuracy of the adopted background velocity model (Jin and Madariaga, 1994). When significant lateral velocity variations are predominant (Lynn and Claerbout, 1982), the derivation of an accurate velocity model by standard velocity analysis can fail. In these cases, accurate tomographic techniques can be extremely helpful, especially if applied to redundant data sets recorded in an extended range of offsets. In this framework, the advantages and difficulties of recording useful data at offsets larger than 15-20 km, or more, are well known from refraction seismic widely applied for studies of the middle-deep portion of the terrestrial crust. Super-critical reflections and long offset turning rays generally contain a lot of information about the elastic properties of the investigated medium. On the other hand, the risk of introducing artefacts when stacking and migrating wide angle reflections can be high, especially in the case of complex geological settings. Typical artefacts can be produced by lateral events introduced in the final migrated section, or by reflected energy migrated in the wrong position due to wrong velocity field definition. Other artefacts can be created when the wide angle reflections are not properly distinguished and separated from refracted energy. How to reduce these risks without renouncing the benefits offered by long offset data is still an open question. During the last decade many experiments have been performed using the Global Offset seismic approach (Buia et al., 2002; Colombo et al., 2004a; Colombo et al., 2004b; Colombo et al., 2003; Dell’Aversana, 2003), in order to verify the contribution offered by this methodology for improving the velocity field definition and seismic imaging. The Global Offset acquisition layout is set in order to guarantee the same shot and receiver spacing typical of the standard near-vertical reflection seismic, but for an extended range of offsets. Experiments with offsets larger than 30 km and shotreceiver density comparable with that of the industrial reflection seismic have been performed in the last few years (Dell’Aversana et al., 2001). In this sense Global Offset bridges the gap between commercial reflection seismic (commonly used for exploration in the hydrocarbon industry) and long offset refraction seismic (often applied for academic studies, focused mainly on the middle-deep portions of the terrestrial crust). Near-critical and post-critical reflections and long-offset turning rays are included in the Global Offset data set. The advantage is that the wide-angle reflections can show a high signal-to-noise ratio even in those cases where complex overburden can prevent to record good near-vertical reflection data. Moreover, using long offsets, it is possible to undershoot high velocity ‘shallow’ layers that can produce a shield effect for the propagating wave-field (Dell’Aversana et al. 2003). In general, massive application of transmission-reflection tomography is the first step aimed at producing a reliable velocity model (Dell’Aversana et al., 2003; Improta et al., 2000a, 2000b; Operto et al., 2004; Ravaut et al., 2004;). This can be successively used for improving the pre-stack depth migration process (Dell’Aversana et al, 2002). In this paper we show, with real examples, how including high-fold long offset data can really improve the seismic imaging and interpretation process. At the same time we also discuss the pitfalls that can be caused if long offset data are used indiscriminately without the necessary limitations. Finally, we explain how these problems can be controlled and avoided using a series of ‘consistency’ criteria.

Near-surface velocity and static model estimation from downgoing VSP multiples

Processing land walkaway or 3D VSP data often requires the application of source static corrections. Because of the effect of statics on the final image, the determination of an accurate near-surface velocity model and statics are critical, especially in desert areas such as in Saudi Arabia.

Seismic angle tomography

One of the main challenges in seismic imaging is the estimation of sufficiently accurate background velocity models in the presence of complex geology. In this paper we show the use of a differential semblance in angle or DSA (Symes and Carazzone, 1991; Brandsberg-Dahl et al., 2003) misfit function to perform ray-based angle tomography on PP and its extension to PS reflection events. This measure is optimal as it is the only measure that depends smoothly on the velocity model.

Orientation of Three-Component Geophones in the San Andreas Fault Observatory at Depth Pilot Hole, Parkfield, California

To identify and constrain the target zone for the planned safod Main Hole through the San Andreas Fault (saf) near Parkfield, California, a 32-level three-component (3C) geophone string was installed in the Pilot Hole (ph) to monitor and improve the locations of nearby earthquakes. The orientation of the 3C geophones is essential for this purpose, because ray directions from sources may be determined directly from the 3D particle motion for both P and S waves. Due to the complex local velocity structure, rays traced from explosions and earthquakes to the ph show strong ray bending. Observed azimuths are obtained from P -wave polarization analysis, and ray tracing provides theoretical estimates of the incoming wave field. The differences between the theoretical and the observed angles define the calibration azimuths. To investigate the process of orientation with respect to the assumed velocity model, we compare calibration azimuths derived from both a homogeneous and 3D velocity model. Uncertainties in the relative orientation between the geophone levels were also estimated for a cluster of 36 earthquakes that was not used in the orientation process. The comparison between the homogeneous and the 3D velocity model shows that there are only minor changes in these relative orientations. In contrast, the absolute orientations, with respect to global North, were significantly improved by application of the 3D model. The average data residual decreased from 13° to 7°, supporting the importance of an accurate velocity model. We explain the remaining residuals by methodological uncertainties and noise and with errors in the velocity model.

Multiscale imaging of complex structures from multifold wide-aperture seismic data by frequency-domain full-waveform tomography: application to a thrust belt

An application of full-waveform tomography to dense onshore wide-aperture seismic data recorded in a complex geological setting (thrust belt) is presented. The waveform modelling and tomography are implemented in the frequency domain. The modelling part is solved with a finite-difference method applied to the visco-acoustic wave equation. The inversion is based on a local gradient method. Only the P-wave velocity is involved in the inversion. The inversion is applied iteratively to discrete frequency components by proceeding from low to high frequencies. This defines a multiscale imaging in the sense that high wavenumbers are progressively incorporated in images. The linearized waveform tomography requires an accurate starting velocity model that has been developed by first-arrival traveltime tomography. After specific pre-processing of the data, 16 frequency components ranging between 5.4 and 20 Hz were inverted. Ten iterations were computed per frequency component leading to 160 tomographic models. The waveform tomography has successfully imaged southwest-dipping structures previously identified from other geophysical data as being associated with high-resistivity bodies. The relevance of the tomographic images is locally demonstrated by comparison of a velocity–depth function extracted from the waveform tomography models with a coincident vertical seismic profiling (VSP) log available on the profile. Moreover, comparison between observed and synthetic seismograms computed in the (starting) traveltime and waveform tomography models demonstrates unambiguously that the waveform tomography successfully predicts for wide-angle reflections from southwest-dipping geological structures. This study demonstrates that the combination of first-arrival traveltime and frequency-domain full-waveform tomographies applied to dense wide-aperture seismic data is a promising approach to quantitative imaging of complex geological structures. Indeed, wide-aperture acquisition geometries offer the opportunity to develop an accurate background velocity model for the subsequent waveform tomography. This is critical, because the building of the macromodel remains an open question when only near-vertical reflection data are considered.

Application of deterministic deconvolution of ground-penetrating radar data in a study of carbonate strata

We successfully applied deterministic deconvolution to real ground-penetrating radar (GPR) data by using the source wavelet that was generated in and transmitted through air as the operator. The GPR data were collected with 400-MHz antennas on a bench adjacent to a cleanly exposed quarry face. The quarry site is characterized by horizontally bedded carbonate strata with shale partings. In order to provide groundtruth for this deconvolution approach, 23 conductive rods were drilled into the quarry face at key locations. The steel rods provided critical information for: (1) correlation between reflections on GPR data and geologic features exposed in the quarry face, (2) GPR resolution limits, (3) accuracy of velocities calculated from common midpoint data and (4) identifying any multiples. Comparing the results of deconvolved data with non-deconvolved data demonstrates the effectiveness of deterministic deconvolution in low dielectric-loss media for increased accuracy of velocity models (improved at least 10–15% in our study after deterministic deconvolution), increased vertical and horizontal resolution of specific geologic features and more accurate representation of geologic features as confirmed from detailed study of the adjacent quarry wall.

Application of deterministic deconvolution of ground-penetrating radar data in a study of carbonate strata

We successfully applied deterministic deconvolution to real ground-penetrating radar (GPR) data by using the source wavelet that was generated in and transmitted through air as the operator. The GPR data were collected with 400-MHz antennas on a bench adjacent to a cleanly exposed quarry face. The quarry site is characterized by horizontally bedded carbonate strata with shale partings. In order to provide groundtruth for this deconvolution approach, 23 conductive rods were drilled into the quarry face at key locations. The steel rods provided critical information for: (1) correlation between reflections on GPR data and geologic features exposed in the quarry face, (2) GPR resolution limits, (3) accuracy of velocities calculated from common midpoint data and (4) identifying any multiples. Comparing the results of deconvolved data with non-deconvolved data demonstrates the effectiveness of deterministic deconvolution in low dielectric-loss media for increased accuracy of velocity models (improved at least 10–15% in our study after deterministic deconvolution), increased vertical and horizontal resolution of specific geologic features and more accurate representation of geologic features as confirmed from detailed study of the adjacent quarry wall.