Journal articles on the topic 'Wave Equation Datuming'
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Gong, Xufei, Qizhen Du, Qiang Zhao, Pengyuan Sun, Jianlei Zhang, and Zhenping Tian. "Elastic wave-equation datuming." GEOPHYSICS 83, no. 5 (September 1, 2018): U51—U61. http://dx.doi.org/10.1190/geo2017-0672.1.
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Wave-equation datuming (WED) techniques have demonstrated superiority when waves occur on the acquisition surface nonvertically, and traditional static corrections based on the time shift become inaccurate. Meanwhile, as for multicomponent data, those scalar techniques can hardly maintain the vector characteristics for the following multicomponent data processing flows. Considering this, we have developed an elastic-wave datuming approach to handle the static corrections for multicomponent data. Different from those existing scalar WED techniques, the multicomponent data are first decomposed into multicomponent P- and S-wave data. Then, the decomposed data are transformed into the [Formula: see text]-[Formula: see text] domain, and they are extrapolated from the acquisition surface to the datum using the one-way elastic-wave continuation. Finally, the datumed multicomponent data are reconstructed at the output datum by adding up the datumed P- and S-wave data. This elastic WED can guarantee that the same wave modes on different components are equally datumed, and the data remain multicomponent so that they are still applicable to multicomponent-joint processing techniques. Finally, several test examples involved in this paper have proved our method’s effectiveness in multicomponent data datuming application.
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Bevc, Dimitri. "Flooding the topography: Wave‐equation datuming of land data with rugged acquisition topography." GEOPHYSICS 62, no. 5 (September 1997): 1558–69. http://dx.doi.org/10.1190/1.1444258.
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Wave‐equation datuming overcomes some of the problems that seismic data recorded on rugged surface topography present in routine image processing. The main problems are that (1) standard, optimized migration and processing algorithms assume data are recorded on a flat surface, and that (2) the static correction applied routinely to compensate for topography is inaccurate for waves that do not propagate vertically. Wave‐based processes such as stacking, dip‐moveout correction, normal‐moveout correction, velocity analysis, and migration after static shift can be severely affected by the nonhyperbolic character of the reflections. To alleviate these problems, I apply wave‐equation datuming early in the processing flow to upward continue the data to a flat datum, above the highest topography. This is what I refer to as “flooding the topography.” This approach does not require detailed a priori knowledge of the near‐surface velocity, and it streamlines subsequent processing because the data are regridded onto a regularly sampled datum. Wave‐equation datuming unravels the distortions caused by rugged topography, and unlike the static shift method, it does not adversely effect subsequent wave‐based processing. The image obtained after wave‐equation datuming exhibits better reflector continuity and more accurately represents the true structural image than the image obtained after static shift.
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Schneider, William A., Lindy D. Phillip, and Ernest F. Paal. "Wave‐equation velocity replacement of the low‐velocity layer for overthrust‐belt data." GEOPHYSICS 60, no. 2 (March 1995): 573–79. http://dx.doi.org/10.1190/1.1443795.
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Seismic land data are commonly plagued by nonhyperbolic distortions induced by a variable near‐surface, low‐velocity layer (LVL). First‐arrival refraction analysis is conventionally employed to estimate the LVL geometry and velocities. Then vertical static time shifts are used to replace the LVL velocities with the more uniform, faster velocities that characterize the underlying refracting layer. This methodology has earned a good reputation as a geophysical data processing tool; however, velocity replacement with static shifts assumes that no ray bending occurred at the LVL base and that waves propagated vertically through the LVL (even though conventional refraction analysis methods, which are used to derive LVL models from seismic data, are less restrictive). These assumptions often are inadequate in thick, complex LVL situations, where resulting errors may considerably hamper a statics‐based velocity replacement procedure. Wave‐equation datuming may be used to perform LVL velocity replacement when statics are inadequate. This method extrapolates the seismic data from the surface to the LVL base with the LVL velocities. Then it extrapolates the data from the LVL base to an arbitrary datum, with the replacement velocity field. The marine analog of such a procedure has been well documented in the geophysical literature, where the object is to remove distortions caused by an irregular water layer. Application of wave‐equation datuming to land data is more difficult because of certain common characteristics of land data (irregular shooting, large data gaps, and crooked line geometry, combined with lower signal/noise) and because the LVL estimation procedure is considerably more difficult. We demonstrate wave‐equation velocity replacement on land data from a western U.S. overthrust belt. The LVL in this region was particularly thick and complicated and ideal for a wave‐theoretical velocity‐replacement procedure. Standard refraction analysis techniques were employed to estimate the LVL, then wave‐equation datuming was used to perform the velocity replacement. Our derived LVL model was not perfect, so some imaging errors were expected because wave‐equation datuming is highly dependent upon the LVL model. Nevertheless, our results show that wave‐equation datuming generally allowed better shallow reflector imaging than could be achieved with conventional statics processing.
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Beresford, G., and C. Hurst. "Wave-Equation Datuming on a Micro-Computer." Exploration Geophysics 22, no. 1 (March 1991): 41–44. http://dx.doi.org/10.1071/eg991041.
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Yang, Kai, Yu-Zhu Liu, Jian-Hua Geng, and Zai-Tian Ma. "Upward continuation with topographic datuming operator: the integrated wave equation datuming scheme revised." Geophysical Prospecting 57, no. 6 (November 2009): 943–56. http://dx.doi.org/10.1111/j.1365-2478.2009.00790.x.
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Tinivella, U., M. Giustiniani, and R. Nicolich. "Wave equation datuming applied to S-wave reflection seismic data." Journal of Applied Geophysics 152 (May 2018): 167–72. http://dx.doi.org/10.1016/j.jappgeo.2018.03.015.
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Liu, Wenge, Bo Zhao, Hua-wei Zhou, Zhenhua He, Hui Liu, and Zengli Du. "Wave-equation global datuming based on the double square root operator." GEOPHYSICS 76, no. 3 (May 2011): U35—U43. http://dx.doi.org/10.1190/1.3555076.
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Current schemes for removing near-surface effects in seismic data processing use either static corrections or wave-equation datuming (WED). In the presence of rough topography and strong lateral velocity variations in the near surface, the WED scheme is the only option available. However, the traditional procedure of WED downward continues the sources and receivers in different domains. A new wave-equation global-datuming method is based on the double-square-root operator, implementing the wavefield continuation in a single domain following the survey sinking concept. This method has fewer approximations and therefore is more robust and convenient than the traditional WED methods. This method is compared with the traditional methods using a synthetic data example.
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Larkin, Steven P., and Alan Levander. "Wave-equation datuming for improving deep crustal seismic images." Tectonophysics 264, no. 1-4 (October 1996): 371–79. http://dx.doi.org/10.1016/s0040-1951(96)00137-0.
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Reshef, Moshe. "Depth migration from irregular surfaces with depth extrapolation methods." GEOPHYSICS 56, no. 1 (January 1991): 119–22. http://dx.doi.org/10.1190/1.1442947.
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Nonflat surface topography introduces a numerical problem for migration algorithms that are based on depth extrapolation. Since the numerically efficient migration schemes start at a flat interface, wave‐equation datuming is required (Berryhill, 1979) prior to the migration. The computationally expensive datuming procedure is often replaced by a simple time shift for the elevation to datum correction. For nonvertically traveling energy this correction is inaccurate. Subsequent migration wrongly positions the reflectors in depth.
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Berryhill, John R. "Submarine canyons: Velocity replacement by wave‐equation datuming before stack." GEOPHYSICS 51, no. 8 (August 1986): 1572–79. http://dx.doi.org/10.1190/1.1442207.
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Submarine canyons incised into the continental slope interfere with the quality of common‐midpoint (CMP) stacked seismic data obtainable from reflectors beneath the sea floor. The interference problem is caused by rough topography in conjunction with the contrast between the acoustic velocity of sea water and the velocity of the exposed rock layers. Geophysicists have long recognized that part of the solution is to replace the traveltimes of raypaths through the water by their traveltimes through an identical thickness of rock. However, use of wave‐equation datuming to effect velocity replacement yields an additional correction for the change in raypath direction that occurs in crossing from rock to sea water; the wave‐equation datuming implementation of velocity replacement is more comprehensive and complete. The wave‐equation datuming method requires an accurate sea‐floor profile as part of the input, along with values of replacement velocity; it does not require knowledge of geology or velocities at depths much greater than the sea floor. Unstacked common‐source and common‐receiver records are processed to appear as if sources and receivers were moved to the water bottom; the velocity of water is replaced; and the sources and receivers are moved back to the sea surface through the replacement medium. The computational method is well‐suited to the irregular surfaces and laterally variable velocities inherent in the problem of submarine canyons. The advantage of this method is that the corrected seismic records accurately emulate the data that would actually be observed if the acoustic velocity of water could be changed physically. The normal‐moveout (NMO) velocity for optimum CMP stacking becomes the root mean square of the layer velocities, including the velocity substituted for that of water. The spurious lateral variation of stacking velocity in the original data is eliminated. Processing of the corrected data through velocity analysis, stacking, migration, and conversion to depth is therefore more reliable.
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Yang, Kai, Hong-Ming Zheng, Li Wang, Yu-Zhu Liu, Fan Jiang, Jiu-Bing Cheng, and Zai-Tian Ma. "Application of an integrated wave-equation datuming scheme to overthrust data: A case history from the Chinese foothills." GEOPHYSICS 74, no. 5 (September 2009): B153—B165. http://dx.doi.org/10.1190/1.3174393.
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An integrated wave-equation datuming scheme improves the imaging quality of seismic data from overthrust areas. It can be regarded as integrated because upward-layer replacement is included. In this scheme, data are downward continued to a nonplanar datum (such as the base of the weathering layer), followed by upward continuation from the nonplanar datum to a final planar datum using a one-way extrapolator. When compared with a Kirchhoff integral, this method can deal better with the strong lateral velocity variation within the near surface. After a test on synthetic data, the scheme is applied successfully to real 2D overthrust data acquired in the Qi-Lian foothills, western China. Compared with results using static corrections, integrated wave-equation datuming results lead to better reconstruction of the diffractions and reflections, more reliable migration-velocity analyses, and stronger stack and final depth images.
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Lubis, Muhammad Husni Mubarak. "The Application of Wave – Equation Datuming to 3D VSP Processing." Jurnal Geofisika 18, no. 2 (December 22, 2020): 60. http://dx.doi.org/10.36435/jgf.v18i2.455.
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Abstrak
Vertical Seismic Profile (VSP) memperluas aplikasi seismik lubang bor dari hubungan 1D antara waktu-kecepatan hingga citra 2D atau 3D di sekitar lubang bor. Citra seismik yang dihasilkan dari VSP diharapkan memiliki resolusi vertikal yang lebih tinggi dari data seismik permukaan karena gelombang seismik direkam di dalam lubang bor. Namun, pengolahan data VSP 2D dan 3D memiliki tantangan karena sifat asimetri dari penjalaran gelombang membatasi untuk diterapkannya pengolahan data berbasis Common Mid Point (CMP) seperti analisis kecepatan, Normal Moveout (NMO), dan koreksi statik. Penelitian ini mendiskusikan sebuah pendekatan baru untuk mentransformasikan rekaman gelombang P pantul atau upgoing wavefields ke sebuah datum datar di permukaan berbasis persamaan gelombang. Transformasi tersebut menghasilkan gelombang seismik yang seolah-olah direkam pada pseudo-reveiver di permukaan bumi sehingga pendekatan penglahan data berbasis CMP dapat diterapkan. Konsep ini kemudian diterapkan pada sebuah data VSP 3D yang diakuisisi dengan geophone yang ditempatkan sangat dekat dengan permukaan. Hasil pemodelan elastik 2D menunjukkan bahwa gelombang seismik pantul sangat dipengaruhi zona kecepatan rendah di dekat permukaan. Jarak yang jauh antara reflektor target dengan geophone menghasilkan rasio sinyal terhadap bising yang rendah. Kondisi desain akuisisi ini sangat mempengaruhi hasil akhir dari citra VSP 3D. Walaupun begitu, citra VSP 3D yang dihasilkan berdasarkan hasil transformasi gelombang P upgoing ini menunjukkan korelasi yang cukup baik dengan data seismik permukaan di zona reservoir.
Kata kunci: 3D VSP, transformasi datum, persamaan gelombang, gelombang pantul, pemodelan
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Zhu, Xianhuai, Burke G. Angstman, and David P. Sixta. "Overthrust imaging with tomo‐datuming: A case study." GEOPHYSICS 63, no. 1 (January 1998): 25–38. http://dx.doi.org/10.1190/1.1444319.
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Through the use of iterative turning‐ray tomography followed by wave‐equation datuming (or tomo‐datuming) and prestack depth migration, we generate accurate prestack images of seismic data in overthrust areas containing both highly variable near‐surface velocities and rough topography. In tomo‐datuming, we downward continue shot records from the topography to a horizontal datum using velocities estimated from tomography. Turning‐ray tomography often provides a more accurate near‐surface velocity model than that from refraction statics. The main advantage of tomo‐datuming over tomo‐statics (tomography plus static corrections) or refraction statics is that instead of applying a vertical time‐shift to the data, tomo‐datuming propagates the recorded wavefield to the new datum. We find that tomo‐datuming better reconstructs diffractions and reflections, subsequently providing better images after migration. In the datuming process, we use a recursive finite‐difference (FD) scheme to extrapolate wavefield without applying the imaging condition, such that lateral velocity variations can be handled properly and approximations in traveltime calculations associated with the raypath distortions near the surface for migration are avoided. We follow the downward continuation step with a conventional Kirchhoff prestack depth migration. This results in better images than those migrated from the topography using the conventional Kirchhoff method with traveltime calculation in the complicated near surface. Since FD datuming is only applied to the shallow part of the section, its cost is much less than the whole volume FD migration. This is attractive because (1) prestack depth migration usually is used iteratively to build a velocity model, so both efficiency and accuracy are important factors to be considered; and (2) tomo‐datuming can improve the signal‐to‐noise (S/N) ratio of prestack gathers, leading to more accurate migration velocity analysis and better images after depth migration. Case studies with synthetic and field data examples show that tomo‐datuming is especially helpful when strong lateral velocity variations are present below the topography.
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YANG, Kai, Jiu-Bing CHENG, Yu-Zhu LIU, Hong-Ming ZHENG, Wei-Ping XUE, and Yang SONG. "A Study on the Application of the 3-D Wave-Equation-Datuming." Chinese Journal of Geophysics 50, no. 4 (July 2007): 1067–76. http://dx.doi.org/10.1002/cjg2.1124.
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Alkhalifah, Tariq, and Claudio Bagaini. "Straight-rays redatuming: A fast and robust alternative to wave-equation-based datuming." GEOPHYSICS 71, no. 3 (May 2006): U37—U46. http://dx.doi.org/10.1190/1.2196032.
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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.
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Dong, Shuqian, Yi Luo, Xiang Xiao, Sergio Chávez-Pérez, and Gerard T. Schuster. "Fast 3D target-oriented reverse-time datuming." GEOPHYSICS 74, no. 6 (November 2009): WCA141—WCA151. http://dx.doi.org/10.1190/1.3261746.
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Imaging of subsalt sediments is a challenge for traditional migration methods such as Kirchhoff and one-way wave-equation migration. Consequently, the more accurate two-way method of reverse-time migration (RTM) is preferred for subsalt imaging, but its use can be limited by high computation cost. To overcome this problem, a 3D target-oriented reverse-time datuming (RTD) method is presented, which can generate redatumed data economically in target areas beneath complex structures such as salt domes. The redatumed data in the target area then can be migrated inexpensively using a traditional migration method. If the target area is much smaller than the acquisition area, computation costs are reduced significantly by the use of a novel bottom-up strategy to calculate the extrapolated Green’s functions. Target-oriented RTD is tested on 2D and 3D SEG/EAGE synthetic data sets and a 3D field data set from the Gulf of Mexico. Results show that target-oriented RTD combined with standard migration can image sediments beneath complex structures accurately with much less calculation effort than full volume RTM. The requirement is that the area over the target zone is smaller than that of the acquisition survey.
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Martini, Francesca, and Christopher J. Bean. "Interface scattering versus body scattering in subbasalt imaging and application of prestack wave equation datuming." GEOPHYSICS 67, no. 5 (September 2002): 1593–601. http://dx.doi.org/10.1190/1.1512750.
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The presence of high‐velocity, highly heterogeneous layers such as basalt have a detrimental effect on imaging below those structures. Internal characteristics of the basalt itself can also degrade the subbasalt image quality. In many cases the boundary surfaces of a basalt sequence are not smooth but contain some roughness at a scale similar to the seismic wavelength. Interface scattering resulting from interface roughness can be a serious problem. In this paper, body and interface scattering problems are addressed through acoustic finite‐difference modeling. Interface scattering seems to have the most detrimental effect on imaging at depth. A wave equation prestack datuming procedure is applied to synthetic acoustic data to remove the effects of rough interfaces. This computational process transforms seismic data to a new datum plane in the subsurface, eliminating propagation effects between the surface and the new datum plane. The technique leads to a much improved image of below the basalt, with the great advantage that accurate knowledge of the velocity field for the overburden only is required as opposed to the entire velocity‐depth model (e.g., for prestack depth migration).
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Bean, Christopher J., and Francesca Martini. "Sub-basalt seismic imaging using optical-to-acoustic model building and wave equation datuming processing." Marine and Petroleum Geology 27, no. 2 (February 2010): 555–62. http://dx.doi.org/10.1016/j.marpetgeo.2009.09.007.
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Barison, Erika, Giuseppe Brancatelli, Rinaldo Nicolich, Flavio Accaino, Michela Giustiniani, and Umberta Tinivella. "Wave equation datuming applied to marine OBS data and to land high resolution seismic profiling." Journal of Applied Geophysics 73, no. 3 (March 2011): 267–77. http://dx.doi.org/10.1016/j.jappgeo.2011.01.009.
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Tinivella, Umberta, Michela Giustiniani, and Ivan Vargas-Cordero. "Wave Equation Datuming Applied to Seismic Data in Shallow Water Environment and Post-Critical Water Bottom Reflection." Energies 10, no. 9 (September 15, 2017): 1414. http://dx.doi.org/10.3390/en10091414.
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Wang, Bin, Volker Dirks, Patrice Guillaume, François Audebert, and Duryodhan Epili. "A 3D subsalt tomography based on wave-equation migration-perturbation scans." GEOPHYSICS 71, no. 2 (March 2006): E1—E6. http://dx.doi.org/10.1190/1.2187720.
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We have developed a simple but practical methodology for updating subsalt velocities using wave-equation, migration-perturbation scans. For the sake of economy and scalability (with respect to full source-receiver migration) and accuracy (with respect to common-azimuth migration), we use shot-profile, wave-equation migration. As input for subsalt-velocity analysis, we provide wave-equation migration scans with velocity scanning limited to the subsalt sediments. Throughout the migration-scan sections, we look for the best focusing or structural positioning of characteristic seismic events. The picking on the migration stacks selects the value of the best perturbation attribute (alpha-scaling factor) along with the corresponding position and local dip for the chosen seismic events. The associated, locally coherent events are then demigrated to the base of the salt horizon. Our key observation is that this process is theoretically equivalent to performing a datuming to a base of salt followed by subsalt migration of the redatumed data perturbed-velocity profiles. Thanks to this implicit redatuming of shot profiles, no ray tracing through the salt body is required. Thus, the events picked on the subsalt-velocity scans only need to be demigrated to the base of salt. For the event demigration we use 3D specular-ray tracing up to the base of the salt horizon within a predefined range of reflection angles. Event demigration produces model-independent data — time and time slope — that are then kinematically migrated using the current tomographic-inversion working model. To find a final-velocity model that will flatten best the remigrated events on common image point (CIP) angle gathers, we use the same set of demigrated observation data as the input data set for several nonlinear iterations of 3D tomographic inversion.
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Bevc, Dimitri. "Imaging complex structures with semirecursive Kirchhoff migration." GEOPHYSICS 62, no. 2 (March 1997): 577–88. http://dx.doi.org/10.1190/1.1444167.
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I present a semirecursive Kirchhoff migration algorithm that is capable of obtaining accurate images of complex structures by combining wave‐equation datuming and Kirchhoff migration. The method is successful because breaking up the complex velocity structure into small depth regions allows traveltimes to be calculated in regions where the computation is well‐behaved and where the computation corresponds to energetic arrivals. The traveltimes computed in such a region are used first for imaging and second for downward continuation of the entire survey (shots and receivers) to the boundary of the next region. This process results in images comparable to those obtained by shot‐profile migration, but at reduced computational cost. Because traveltimes are computed for small depth domains, the adverse effects of caustics, headwaves, and multiple arrivals do not develop. In principle, this method requires only the same number of traveltime calculations as a standard migration. Tests on the Marmousi data set produce excellent results.
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Carroll, Steven, and Greg Beresford. "Combining reflection tomography with layer replacement for velocity analysis of near‐surface reefs." GEOPHYSICS 61, no. 2 (March 1996): 561–69. http://dx.doi.org/10.1190/1.1443982.
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Reefs in the Browse Basin on the Australian North West Shelf typically have strong lateral velocity inhomogeneity on the reef flanks and produce an irregular sea‐floor topography. The combination of these two factors reduces the effectiveness of conventional velocity analysis as moveout on common midpoint (CMP) gathers is no longer hyperbolic. Consequently, the velocity structure on the reef flanks cannot be resolved properly. An accurate velocity structure is needed for these reefs if seismic data acquired in the vicinity are to be migrated correctly. Tomographic velocity analysis, using a simultaneous iterative reconstruction technique (SIRT), was found to improve the velocity analysis of the reef when compared to conventional analysis. However, the reef’s profile and rapid internal velocity gradients prevent accurate raypath determination. This technique can be further improved by preconditioning the data with wave‐equation datuming. The water is replaced with an average reef velocity by downward and upward continuation. This effectively removes most of the raypath distortions resulting from ray bending at the sea floor, thus reducing the nonlinearity of the forward modeling and improving the convergence of an iteratively linearized inversion. The velocities obtained from this method give an accurate picture of the reef’s internal velocity structure, as well as the lower portion of the seismic section below the reef.
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Beasley, Craig, and Walt Lynn. "The zero‐velocity layer: Migration from irregular surfaces." GEOPHYSICS 57, no. 11 (November 1992): 1435–43. http://dx.doi.org/10.1190/1.1443211.
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Seismic data acquired in areas with irregular topography are usually corrected to a flat datum before migration. A time‐honored technique for handling elevation changes is to time shift the data before application of migration. This simple time shift, or elevation‐static correction, cannot properly represent wide‐angle or dipping reflections as they would have been recorded at the datum. As a result, when elevation varies significantly, accuracy in event positioning may be compromised for migration and other wave‐equation processes, such as dip moveout processing (DMO). Traditionally, such over‐ and under‐migration artifacts have been dealt with by increasing or decreasing the migration velocity. However, simple adjustment of the migration velocity cannot undo the wave‐field distortions induced in seismic data acquired over varying elevations. More sophisticated and accurate solutions such as wave‐equation datuming are too computationally demanding for routine use. Here, we propose an efficient and accurate technique for doing migration from irregular surfaces using conventional migration algorithms. As in elevation‐static corrections, surface‐recorded data are time‐shifted to a horizontal datum; for our process, we choose to have that datum elevation lie at or above the highest elevation in the survey. After migration, the datum elevation can always be adjusted to any other level by means of a bulk time shift. In the migration step, the velocity is set to zero (or some very small value) in the layer between the surface and the datum; below the original surface, the interval velocity represents the best estimate of the subsurface geology. By adding a zero‐velocity layer, the migration algorithm is applied to the data from the flat datum and no lateral propagation is allowed until a nonzero velocity is encountered at the recording surface. Synthetic and field data examples demonstrate that use of the “zero‐velocity layer” significantly improves imaging accuracy relative to conventional migration from a flat datum. Moreover, the geologically derived migration‐velocity field need not be adjusted to compensate for shortcomings in the datum‐static procedure. The technique can be extended to prestack processes such as DMO, shot‐ and receiver‐gather downward extrapolation, and migration and thus suggests a unified approach to processing data from irregular surfaces.
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Mazzotti, Alfredo P., Eusebio Stucchi, Gian Luigi Fradelizio, Luigi Zanzi, and Paolo Scandone. "Seismic exploration in complex terrains: A processing experience in the Southern Apennines." GEOPHYSICS 65, no. 5 (September 2000): 1402–17. http://dx.doi.org/10.1190/1.1444830.
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We discuss a data‐processing sequence adopted to reprocess a seismic line that crosses the Italian southern Apennines from the Tyrrhenian Sea to the Adriatic margin and investigate both the overthrust and foreland areas. We first determine the main causes of the very low S/N ratio in the field data and then propose a processing sequence aimed at exploiting the signal content, also making use of a priori geological knowledge of this area. Our work indicates a combination of causes for the very low quality of the seismic data. These include length of the spread (about 20 km) that is unfavorable because of the rapid variation in the near‐surface geology, tectonic complexity, crooked‐line acquisition, and the rough topography associated with outcropping rocks characterized by highly variable velocities. Based on the outcome of this data analysis, we present a processing sequence driven by knowledge of the regional tectonic setting and by knowledge of the shallow subsurface geology. The main effort is in removing the large, near‐surface related noise components. The low S/N ratio makes it impossible or nearly impossible to successfully apply highly sophisticated techniques such as depth migration or wave equation datuming. Thus, we used robust techniques specifically designed to solve each problem that degraded data quality. The most relevant of these techniques were the removal of bad traces where unacceptably low quality was detected by energy and frequency decay criteria; estimation and correction for static time shifts attributable to near‐surface conditions; optimization of common midpoint (CMP) sorting to attenuate the deleterious effects of the crooked‐line acquisition; application of a weighted stacking technique to maximize stack power and application of prestack f-x deconvolution to attenuate uncorrelated noise. The outcome of this processing sequence is compared with the result of a more standard sequence that was previously applied to the same data and is also discussed in terms of the possible geological model it might evidence. The realization of a seismic section showing rather continuous and structured events down to 8 s which, depending on the interpretation, may be related to Moho discontinuity or to very deep sedimentary layers supports the efficacy of the processing approach we propose.
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Giustiniani, M., U. Tinivella, S. Parolai, F. Donda, G. Brancolini, and V. Volpi. "Integrated Geophysical Analyses of Shallow-Water Seismic Imaging With Scholte Wave Inversion: The Northern Adriatic Sea Case Study." Frontiers in Earth Science 8 (November 25, 2020). http://dx.doi.org/10.3389/feart.2020.587898.
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The integrated analysis using different seismic wave types in a record is a very efficient approach for a comprehensive characterization of marine sediments, especially in shallow water conditions. The proposed integrated method to analyze seismic data in post-critical conditions consists of: 1) the inversion of Scholte waves to obtain a reliable Vs distribution of the near seafloor; 2) pre-processing of seismic data; 3) construction of the P-wave velocity field by using all available information, including available well data; and 4) the application of the wave equation datuming and post-processing, such as pre-stack time migration. We demonstrate how this approach could be successfully applied on seismic datasets characterized by post-critical conditions and the occurrence of the Scholte waves, which may be exploited to provide fundamental information instead of being only an unwanted effect. The integrated analysis of seismic events can thus help, together with data processing, by providing better seismic imaging, which is a priority for a reliable seismostratigraphic interpretation.
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"Technical article: Application of pre-stack wave equation datuming to remove interface scattering in sub-basalt imaging." First Break 20, no. 6 (June 2002): 395–403. http://dx.doi.org/10.1046/j.1365-2397.2002.00282.x.
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