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1
Carrion, Philip M., and Douglas J. Foster. "Inversion of seismic data using precritical reflection and refraction data." GEOPHYSICS 50, no. 5 (May 1985): 759–65. http://dx.doi.org/10.1190/1.1441950.
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We present a two‐step inversion procedure to extract subsurface velocity estimates from large‐offset seismic data. The first step is the automatic iterative large‐offset inverse method (AILOIM) which we test in the presence of strong water‐bottom multiples. Since this method is based on finding the locus of critically reflected points, low‐velocity zones cannot be resolved and the reconstruction is only an average estimate. In the presence of low‐velocity zones, the second step of the inversion process is required. This second step is a generalized least‐squares inverse scheme applied to the precritical reflections. We computed the inverse solution using a perturbation technique and determined the reference model from an estimate of the average velocity given by the first step. Two major features of this inversion method are: amplitudes of reflection arrivals are incorporated into analysis, and accurate results can be achieved without human interaction (picking the traveltime curves). Numerical examples using synthetic and field data demonstrate the accuracy of our inversion procedure.
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Hunter, J. A., and S. E. Pullan. "A vertical array method for shallow seismic refraction surveying of the sea floor." GEOPHYSICS 55, no. 1 (January 1990): 92–96. http://dx.doi.org/10.1190/1.1442775.
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In recent years, specific requirements of offshore geotechnical site investigations, as well as detailed defense research studies, have stimulated research interest in methods for measuring seismic velocities of sea‐floor sediments on the continental shelves. Investigations have used wide‐angie subbottom reflection measurements (McKay and McKay, 1982), bottom‐laid refraction cables (Hunter et al., 1979), and towed refraction arrays, both on the surface (Hunter and Hobson, 1974) and at depth (Fortin et al., 1987; Fagot, 1983).
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Tryggvason, Ari, Cedric Schmelzbach, and Christopher Juhlin. "Traveltime tomographic inversion with simultaneous static corrections — Well worth the effort." GEOPHYSICS 74, no. 6 (November 2009): WCB25—WCB33. http://dx.doi.org/10.1190/1.3240931.
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We have developed a first-arrival traveltime inversion scheme that jointly solves for seismic velocities and source and receiver static-time terms. The static-time terms are included to compensate for varying time delays introduced by the near-surface low-velocity layer that is too thin to be resolved by tomography. Results on a real data set consisting of picked first-arrival times from a seismic-reflection 2D/3D experiment in a crystalline environment show that the tomography static-time terms are very similar in values and distribution to refraction-static corrections computed using standard refraction-statics software. When applied to 3D seismic-reflection data, tomography static-time terms produce similar or more coherent seismic-reflection images compared to the images using corrections from standard refraction-static software. Furthermore, the method provides a much more detailed model of the near-surface bedrock velocity than standard software when the static-time terms are included in the inversion. Low-velocity zones in this model correlate with other geologic and geophysical data, suggesting that our method results in a reliable model. In addition to generally being required in seismic-reflection imaging, static corrections are also necessary in traveltime tomography to obtain high-fidelity velocity images of the subsurface.
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Kanasewich, E. R., Z. Hajnal, A. G. Green, G. L. Cumming, R. F. Mereu, R. M. Clowes, P. Morel-a-l'Huissier, et al. "Seismic studies of the crust under the Williston Basin." Canadian Journal of Earth Sciences 24, no. 11 (November 1, 1987): 2160–71. http://dx.doi.org/10.1139/e87-205.
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The seismic refraction method was used in 1981 to study the crust under the northern half of the Williston Basin, in Saskatchewan. A new method of spatial seismic recording, based on a triangular arrangement of receivers, was used for the first time to obtain three-dimensional structure and velocity information. The broadside seismic refraction and wide-angle reflection data obtained by the technique were of particular value in defining several faulted blocks. These blocks are also characterized by aeromagnetic anomalies trending in a northerly direction. The crustal thickness in the southern part of the western provinces shows large variation ranging from 35 to 50 km. Much of the area is also notable for the presence of one or more low-velocity layers and a high-velocity lower crust. There is good evidence for significant lateral heterogeneity, and detailed deep seismic reflection and refraction studies would likely yield information on dips and strikes of beds and faults around the basin as well as define the properties of the various terranes of the Hudsonian mobile belt.
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Huang, Huaiyong, Carl Spencer, and Alan Green. "A method for the inversion of refraction and reflection travel times for laterally varying velocity structures." Bulletin of the Seismological Society of America 76, no. 3 (June 1, 1986): 837–46. http://dx.doi.org/10.1785/bssa0760030837.
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Abstract In an attempt to speed up the lengthy process of modeling seismic refraction/wide-angle reflection data, a two-dimensional ray tracing routine is used as the basis for an automated travel-time inversion scheme. Laterally varying P-wave velocity structures are represented by arbitrary-shaped blocks of constant velocity gradient. Velocities, gradients, and boundary points of the blocks are parameters in the inversion scheme, and the input data are refraction and reflection travel-time arrivals from both directions of a reversed seismic line. Damped least-squares techniques are used to solve the equations of condition, and inversions are allowed to proceed automatically for several iterations. A synthetic example is presented, and the data from two reversed seismic refraction profiles recorded recently in eastern Canada are inverted to demonstrate the utility of the method under less than ideal conditions. The synthetic test demonstrates that several iterations of the procedure are necessary for accurate recovery of input models and provides a resolving power analysis of the problem, while the real data example produces models comparable to those obtained by experienced interpreters using trial and error methods.
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Mitchell, James F., and Richard J. Bolander. "Structural interpretation using refraction velocities from marine seismic surveys." GEOPHYSICS 51, no. 1 (January 1986): 12–19. http://dx.doi.org/10.1190/1.1442026.
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Subsurface structure can be mapped using refraction information from marine multichannel seismic data. The method uses velocities and thicknesses of shallow sedimentary rock layers computed from refraction first arrivals recorded along the streamer. A two‐step exploration scheme is described which can be set up on a personal computer and used routinely in any office. It is straightforward and requires only a basic understanding of refraction principles. Two case histories from offshore Peru exploration demonstrate the scheme. The basic scheme is: step (1) shallow sedimentary rock velocities are computed and mapped over an area. Step (2) structure is interpreted from the contoured velocity patterns. Structural highs, for instance, exhibit relatively high velocities, “retained” by buried, compacted, sedimentary rocks that are uplifted to the near‐surface. This method requires that subsurface structure be relatively shallow because the refracted waves probe to depths of one hundred to over one thousand meters, depending upon the seismic energy source, streamer length, and the subsurface velocity distribution. With this one requirement met, we used the refraction method over a wide range of sedimentary rock velocities, water depths, and seismic survey types. The method is particularly valuable because it works well in areas with poor seismic reflection data.
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Mereu, R. F. "The complexity of the crust and Moho under the southeastern Superior and Grenville provinces of the Canadian Shield from seismic refraction - wide-angle reflection data." Canadian Journal of Earth Sciences 37, no. 2-3 (April 2, 2000): 439–58. http://dx.doi.org/10.1139/e99-122.
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The major features of the individual velocity models, Poisson's ratio values, and crustal complexity derived from the interpretation of seismic data sets from four long-range seismic refraction - wide-angle reflection experiments are summarized. The experiments were conducted from 1982-92 in the southeastern portion of the Canadian Shield. In the conventional analysis of seismic refraction - wide-angle reflection data, only the onset times and amplitudes of the major arrival phases are used to derive seismic velocity models of the region under study. These models are over smoothed, have a number of intermediate discontinuities, are unable to explain the Pg coda, and bear very little resemblance to the models derived from the analysis of near-vertical seismic reflection data. In this paper some of the differences between seismic models derived from near-vertical reflection analysis and those from refraction analysis are reconciled from an analysis of the wide-angle reflection fields of the crustal coda waves that follow the first arrivals. This was done using a migration technique that to a first approximation maps the amplitudes of the record sections into a two-dimensional (2-D) complexity section. These new sections show significant lateral variations in crustal and Moho reflectivity and may be used to complement the 2-D velocity anomaly sections and near-vertical reflection sections. The method was based on a numerical study that showed that the coda can be explained with a class of complex heterogeneous models in which sets of small-scale, high-contrast sloping seismic reflectors are "embedded" in a uniform seismic velocity gradient field.
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René, R. M., J. L. Fitter, D. J. Murray, and J. K. Walters. "Reflection and refraction seismic studies in the Great Salt Lake Desert, Utah." GEOPHYSICS 53, no. 4 (April 1988): 431–33. http://dx.doi.org/10.1190/1.1442475.
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Seismic refraction and CDP reflection profiles were acquired across mud flats of the Great Salt Lake Desert, Utah, during the summer of 1983. a combination of weight drops, horizontal hammers, buried explosives, and explosives detonated in air (Poulter method) was used. A 6.4 km refraction and single‐fold reflection profile indicates the presence of a shallow depression (Donner Reed basin) eastb of Donner Reed pass in the Silver Island Mountains. A basin floor ramp of Paleozoic rocks dipping approximately 30 degrees east into the Crater Island graben is interpreted beneath a 4.6 km 12-fold CDP reflection profile obtained by the Poulter method. This ramp extends beneath at least 0.8 km of condolidated Neogene sediments and 0.8 km of younger (largely unconsolidated) sediments. Weight‐drop and horizontal‐hammer profiles for the critical refraction along the Silurian Laketown dolomite yield P-wave and S-wave velocity estimates of 5270 ± 100 and [Formula: see text], respectively. The mud flats, with their laterally uniform finegrained sediments and shallow water table, provided excellent coupling of seismic energy. Air shots of 4.1 to 5.4 kg explosives without a source array gave good penetration to a depth of about 1.6 km. Partial migration before stack facilitated estimation of moveout velocities in the case of layers onlapping against a basin floor ramp, even though the maximum dips were only about 30 degrees. Gravity modeling and seismic ray tracing through intervals of constant velocity bounded by polynomial interfaces aided synergetic interpretation of the reflection, refraction, and gravity data.
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Liu, Chuanhai, and Joann M. Stock. "Quantitative determination of uncertainties in seismic refraction prospecting." GEOPHYSICS 58, no. 4 (April 1993): 553–63. http://dx.doi.org/10.1190/1.1443438.
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We present a model of the propagation of refracted seismic waves in planar (horizontal or dipping) layered structures in which we quantify the errors from various sources. The model, called the (mixed) variance component model, separates the errors originating on the surface from those due to inhomogeneities of subsurface layers. The model starts with the assumption of homogeneous (constant‐velocity) layers, but by taking the principal errors into account, variations from this model (including degree of velocity inhomogeneity, vertical velocity gradients, and gradational interfaces) can be identified. A complete solution to the variance component model by Bayesian methods relies on the Gibbs sampler, a recently well‐developed statistical technique. Using the Gibbs sampler and Monte Carlo methods, we can estimate the posterior distributions of any parameter of interest. Thus, in addition to estimating the various errors, we can obtain the velocity‐versus‐depth curve with its confidence intervals at any relevant point along the line. We analyze data from a crustal‐scale refraction line to illustrate both features of this method. The results indicate that the conventional linear regression model for the first arrivals is inappropriate for this data set. As might be expected, geophone spacing strongly affects our ability to resolve the heterogeneities. Differences in the amount of velocity heterogeneity in different layers can be resolved, and may be useful for lithologic characterization. For this crustal‐scale problem, a velocity profile derived from this method is an improvement over simple linear interpretations, but it could be further refined by more comprehensive methods attempting to match later arrivals and wave amplitudes as well as first arrivals. The method could also be applied to smaller‐scale refraction problems, such as determination of refraction statics, or constraints on the degree of probable lateral variations in velocity of shallow layers, for improved processing of reflection data.
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Shen, Yang, and Jie Zhang. "Refraction wavefield migration." GEOPHYSICS 85, no. 6 (October 22, 2020): Q27—Q37. http://dx.doi.org/10.1190/geo2020-0141.1.
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Refraction methods are often applied to model and image near-surface velocity structures. However, near-surface imaging is very challenging, and no single method can resolve all of the land seismic problems across the world. In addition, deep interfaces are difficult to image from land reflection data due to the associated low signal-to-noise ratio. Following previous research, we have developed a refraction wavefield migration method for imaging shallow and deep interfaces via interferometry. Our method includes two steps: converting refractions into virtual reflection gathers and then applying a prestack depth migration method to produce interface images from the virtual reflection gathers. With a regular recording offset of approximately 3 km, this approach produces an image of a shallow interface within the top 1 km. If the recording offset is very long, the refractions may follow a deep path, and the result may reveal a deep interface. We determine several factors that affect the imaging results using synthetics. We also apply the novel method to one data set with regular recording offsets and another with far offsets; both cases produce sharp images, which are further verified by conventional reflection imaging. This method can be applied as a promising imaging tool when handling practical cases involving data with excessively weak or missing reflections but available refractions.
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Dasgupta, Rahul, and Roger A. Clark. "Estimation of Q from surface seismic reflection data." GEOPHYSICS 63, no. 6 (November 1998): 2120–28. http://dx.doi.org/10.1190/1.1444505.
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Reliable estimates of the anelastic attenuation factor, Q, are desirable for improved resolution through inverse Q deconvolution and to facilitate amplitude analysis. Q is a useful petrophysical parameter itself, yet Q is rarely measured. Estimates must currently be made from borehole seismology. This paper presents a simple technique for determining Q from conventional surface seismic common midpoint (CMP) gathers. It is essentially the classic spectral ratio method applied on a trace‐by‐trace basis to a designatured and NMO stretch‐corrected CMP gather. The variation of apparent Q versus offset (QVO) is extrapolated to give a zero‐offset Q estimate. Studies on synthetics suggest that, for reasonable data quality (S/N ratios better than 3:1, shallow (<5°) dips, and stacking velocity accuracy <5%), source‐to‐reflector average Q is recoverable to within some 3% and Q for a specific interval (depending on its two‐way time thickness and depth) is recoverable to 15–20%. Three case studies are reported. First, Q versus offset and vertical seismic profiling (VSP) Q estimates for a southern North Sea line were in close agreement, validating the method. For Chalk, Mushelkalk‐Keuper, and Bunter‐Zechstein, Q was estimated as 130 ± 15, 47 ± 8, and 156 ± 18, respectively. Next, two alternative lithological interpretations of a structure seen in a frontier area were discriminated between when Q estimates of 680 to 820 were obtained (compared to some 130–170 in the overlying units), favoring a metamorphic/crystalline lithology rather than (prospective) sediments. This was later confirmed by drilling. Third, a profile of Q estimates along a 200-ms-thick interval, known to include a gas reservoir, showed a clear and systematic reduction in Q to a low of 50 ± 11, coincident with the maximum reservoir thickness, from some 90–105 outside the reservoir. Q for the reservoir interval itself was estimated at 17 ± 7.
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Zhang, Ming Shan, and Jian Huang. "Quasi-Likelihood Deconvolution of Non-Gaussian Non-Invertible Moving Average Model." Advanced Materials Research 605-607 (December 2012): 1781–87. http://dx.doi.org/10.4028/www.scientific.net/amr.605-607.1781.
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In reflection seismology the reflectivity sequence is of primary interest and must be estimated. Estimation of the reflectivity sequence is based on deconvolution of seismic trace data. Modelling the seismic trace as the non-Gaussian moving average time series, we propose a deconvolution method based on the modified estimation, which is consistent estimation of moving average models with heavy tailed error distribution. The asymptotic equivalence is established between the proposed method and the deconvolution using . Simulation studies are presented to validate the equivalency. Furthermore, based on this equivalence the consistency problem of the deconvolution has been discussed.
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Mendes, M., J. L. Mari, and M. Hayet. "Imaging Geological Structures Up to the Acquisition Surface Using a Hybrid Refraction-Reflection Seismic Method." Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles 69, no. 2 (August 26, 2013): 351–61. http://dx.doi.org/10.2516/ogst/2012095.
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Ebuna, Daniel R., Jared W. Kluesner, Kevin J. Cunningham, and Joel H. Edwards. "Statistical approach to neural network imaging of karst systems in 3D seismic reflection data." Interpretation 6, no. 3 (August 1, 2018): B15—B35. http://dx.doi.org/10.1190/int-2017-0197.1.
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The current lack of a robust standardized technique for geophysical mapping of karst systems can be attributed to the complexity of the environment and prior technological limitations. Abrupt lateral variations in physical properties that are inherent to karst systems generate significant geophysical noise, challenging conventional seismic signal processing and interpretation. The application of neural networks (NNs) to multiattribute seismic interpretation can provide a semiautomated method for identifying and leveraging the nonlinear relationships exhibited among seismic attributes. The ambiguity generally associated with designing NNs for seismic object detection can be reduced via statistical analysis of the extracted attribute data. A data-driven approach to selecting the appropriate set of input seismic attributes, as well as the locations and suggested number of training examples, provides a more objective and computationally efficient method for identifying karst systems using reflection seismology. This statistically optimized NN technique is demonstrated using 3D seismic reflection data collected from the southeastern portion of the Florida carbonate platform. Several dimensionality reduction methods are applied, and the resulting karst probability models are evaluated relative to one another based on quantitative and qualitative criteria. Comparing the preferred model, using quadratic discriminant analysis, with previously available seismic object detection workflows demonstrates the karst-specific nature of the tool. Results suggest that the karst multiattribute workflow presented is capable of approximating the structural boundaries of karst systems with more accuracy and efficiency than a human counterpart or previously presented seismic interpretation schemes. This objective technique, using solely 3D seismic reflection data, is proposed as a practical approach to mapping karst systems for subsequent hydrogeologic modeling.
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Mikesell, Dylan, and Kasper van Wijk. "Seismic refraction interferometry with a semblance analysis on the crosscorrelation gather." GEOPHYSICS 76, no. 5 (September 2011): SA77—SA82. http://dx.doi.org/10.1190/geo2011-0079.1.
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Crosscorrelating wavefields recorded at two receivers to produce data as if one receiver was a source is commonly referred to as seismic interferometry, or the virtual source method. An artifact in seismic interferometry related to critically refracted waves allowed us to estimate the velocity in the refracting layer. In addition, we devised a new semblance analysis on the crosscorrelation of reflection and refraction energy to robustly estimate the depth and velocity of the slow layer, tested with a numerical example and field data from the Boise Hydrogeophysical Research Site.
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Wang, Haiyang, Satish C. Singh, Francois Audebert, and Henri Calandra. "Inversion of seismic refraction and reflection data for building long-wavelength velocity models." GEOPHYSICS 80, no. 2 (March 1, 2015): R81—R93. http://dx.doi.org/10.1190/geo2014-0174.1.
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Long-wavelength velocity model building is a nonlinear process. It has traditionally been achieved without appealing to wave-equation-based approaches for combined refracted and reflected waves. We developed a cascaded wave-equation tomography method in the data domain, taking advantage of the information contained in the reflected and refracted waves. The objective function was the traveltime residual that maximized the crosscorrelation function between real and synthetic data. To alleviate the nonlinearity of the inversion problem, refracted waves were initially used to provide vertical constraints on the velocity model, and reflected waves were then included to provide lateral constraints. The use of reflected waves required scale separation. We separated the long- and short-wavelength subsurface structures into velocity and density models, respectively. The velocity model update was restricted to long wavelengths during the wave-equation tomography, whereas the density model was used to absorb all the short-wavelength impedance contrasts. To improve the computation efficiency, the density model was converted into the zero-offset traveltime domain, where it was invariant to changes of the long-wavelength velocity model. After the wave-equation tomography has derived an optimized long-wavelength velocity model, full-waveform inversion was used to invert all the data to retrieve the short-wavelength velocity structures. We developed our method in two synthetic tests and then applied it to a marine field data set. We evaluated the results of the use of refracted and reflected waves, which was critical for accurately building the long-wavelength velocity model. We showed that our wave-equation tomography strategy was robust for the real data application.
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Deen, Tara, and Karsten Gohl. "3‐D tomographic seismic inversion of a paleochannel system in central New South Wales, Australia." GEOPHYSICS 67, no. 5 (September 2002): 1364–71. http://dx.doi.org/10.1190/1.1512741.
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Buried paleochannels are of significant interest for understanding hydrological mechanisms and their potential as alluvial gold deposits. Seismic tomographic methods are a suitable solution for resolving the vertical and horizontal structure of such features. We assess a method for seismic 3‐D tomographic inversion from refraction arrivals with reflection control over a suspected paleochannel adjacent to the Wyalong gold fields in the Lachlan fold belt of central New South Wales, Australia. A standard multichannel engineering seismic recording and cable–receiver system was used on a 3‐D field geometry of multiple linear arrays. More than 3000 P‐wave first‐arrival traveltime values were inverted using a regularized inversion scheme for which simplified 2‐D models served as initial velocity–depth models for the complete 3‐D inversion. Seismic reflection arrivals provided additional depth estimates to the bedrock and compensated for a lack of refraction phases at that depth. Correlating the 3‐D seismic velocity–depth data with existing drillhole and nonseismic geophysical data resulted in a detailed structural and compositional interpretation of the paleochannel and the incised regolith. The model suggests the presence of a system of deposits from meandering channels overlying a metasedimentary bedrock formation. The general paleodrainage deposit is relatively conductive in electromagnetic surveys, indicating a potential saline storage or transport mechanism.
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Zunino, Andrea, Klaus Mosegaard, Katrine Lange, Yulia Melnikova, and Thomas Mejer Hansen. "Monte Carlo reservoir analysis combining seismic reflection data and informed priors." GEOPHYSICS 80, no. 1 (January 1, 2015): R31—R41. http://dx.doi.org/10.1190/geo2014-0052.1.
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Determination of a petroleum reservoir structure and rock bulk properties relies extensively on inference from reflection seismology. However, classic deterministic methods to invert seismic data for reservoir properties suffer from some limitations, among which are the difficulty of handling complex, possibly nonlinear forward models, and the lack of robust uncertainty estimations. To overcome these limitations, we studied a methodology to invert seismic reflection data in the framework of the probabilistic approach to inverse problems, using a Markov chain Monte Carlo (McMC) algorithm with the goal to directly infer the rock facies and porosity of a target reservoir zone. We thus combined a rock-physics model with seismic data in a single inversion algorithm. For large data sets, the McMC method may become computationally impractical, so we relied on multiple-point-based a priori information to quantify geologically plausible models. We tested this methodology on a synthetic reservoir model. The solution of the inverse problem was then represented by a collection of facies and porosity reservoir models, which were samples of the posterior distribution. The final product included probability maps of the reservoir properties in obtained by performing statistical analysis on the collection of solutions.
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Lin, Song, Yuan Li, Denggui Luo, and Yanlin Fu. "Research on the fracture structure and activity of the Qinling Mountains thrust nappe system in western Hubei." Canadian Journal of Earth Sciences 57, no. 1 (January 2020): 1–15. http://dx.doi.org/10.1139/cjes-2018-0118.
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The Western Hubei section of the Liangyun fault is an important structural belt of the southern Qinling Mountains thrust nappe system. As the significant activity of the Liangyun fault since the Quaternary has led to high seismic risk in the surrounding area, the research on the characteristics and activity of fault structure is of great significance for deepening the construction of a seismic safety system in this area. In this study, we conducted a field geology survey combined with quartz optical stimulated luminescence dating, scanning electron microscopy dating, and thermoluminescence dating results and comprehensive application of shallow seismic reflection and high-resolution refraction) to analyze the activities of the Liangyun fault in the Quaternary period. Sediment optical stimulated luminescence dating results of samples from the breakpoint were 134.99 + 15.52 and 160.95 + 16.88 ka. Combined with the seismic profile, outcrop observation, and previous dating results, we conclude that the new era is in fault activities in the early Pleistocene to late Pleistocene (Q2–Q3). The combined application of shallow seismic reflection and high-resolution refraction method can confirm each other’s measured results, providing more parameters for the interpretation of seismic data under complex conditions and ensuring the accuracy of data interpretation at the same time. At present, the seismic experiment scheme is less used in the field of active fault detection, since its good detection effect and the application of the trial to shallow geophysical exploration has a certain application value and global scalability.
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Liu, Guofeng, Xiaohong Meng, Jianhui Ni, Zhaoxi Chen, and Da Zhang. "Evaluation of the 2D reflection seismic method toward the exploration of thrust-controlled mineral deposits in southwestern Fujian Province, China." GEOPHYSICS 83, no. 4 (July 1, 2018): B209—B220. http://dx.doi.org/10.1190/geo2017-0289.1.
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The southwestern region of the Fujian Province is one of the major ore districts in China. The current model states that mineral deposition is highly controlled by thrust structure, which means that there may be concealed deposits located deep within overlapping thrust areas. Reflection seismology, which has great depth penetration and higher resolution than other geophysical methods, has great potential to delineate complex structures and give some clues to mineralization. In 2015, an experimental 2D reflection seismic survey called “Fujian 2D” was conducted in this region. Data were acquired along a 13.8 km length, with a source interval of 60 m, and 691 identical receivers with an equal spacing of 20 m were used to record data for each source. Due to topographical restrictions caused by the source environment, the mass or position of some shots was changed. Despite the restrictions, the average fold number reached 64 for a 10 km distance along the middle of the survey line. During the data processing procedure, conventional technologies involving static correction, noise elimination, deconvolution, and iterative velocity analyses were applied. After the prestack time migration failed to obtain a high-quality imaging result, rugged prestack depth migration (PSDM) was introduced that resulted in a better quality image of the subsurface structure and which included near-surface parts of the thrusts. In addition, P- and S-wave velocities and density data were determined from two borehole cores. Forward modeling and imaging found that the Permian marble hosting the mineral deposits has lower velocity than the surrounding rocks, where contacts give rise to strong reflections. The final rugged PSDM also clearly delineated the thrust bodies and magma intrusion zones. Combining this forward modeling with the known geology of the investigated site, the Fujian 2D reflection seismic experiment demonstrates great potential for unveiling the main elements controlling mineral deposition, such as tectonic structure, stratigraphic contacts, and lithology. Our experimental results demonstrate that reflection seismology has a wide range of applications for future mineral exploration at greater depths.
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Singh, Satish C., R. W. Hobbs, and D. B. Snyder. "Broadband receiver response from dual‐streamer data and applications in deep reflection seismology." GEOPHYSICS 61, no. 1 (January 1996): 232–43. http://dx.doi.org/10.1190/1.1443944.
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A method to process dual‐streamer data with under and over configuration is presented. The method combines the results of dephase‐sum and dephase‐subtraction methods. In the dephase methods, the response of one streamer is time shifted so that the primary arrivals on both streamers are aligned, and these responses are then summed or subtracted. The method provides a broad spectral response from dual‐streamer data and increases the signal‐to‐noise ratio by a factor of 1.5. Testing was done on synthetic data and then applied to a real data set collected by the British Institutions Reflection Profiling Syndicate (BIRPS). Its application to a deep seismic reflection data set from the British Isles shows that the reflections from the lower crust contain frequencies up to 80 Hz, suggesting that some of the lower crustal reflectors may have sharp boundaries and could be 20–30 m thick.
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Bergmann, Peter, Artem Kashubin, Monika Ivandic, Stefan Lüth, and Christopher Juhlin. "Time-lapse difference static correction using prestack crosscorrelations: 4D seismic image enhancement case from Ketzin." GEOPHYSICS 79, no. 6 (November 1, 2014): B243—B252. http://dx.doi.org/10.1190/geo2013-0422.1.
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A method for static correction of time-lapse differences in reflection arrival times of time-lapse prestack seismic data is presented. These arrival-time differences are typically caused by changes in the near-surface velocities between the acquisitions and had a detrimental impact on time-lapse seismic imaging. Trace-to-trace time shifts of the data sets from different vintages are determined by crosscorrelations. The time shifts are decomposed in a surface-consistent manner, which yields static corrections that tie the repeat data to the baseline data. Hence, this approach implies that new refraction static corrections for the repeat data sets are unnecessary. The approach is demonstrated on a 4D seismic data set from the Ketzin [Formula: see text] pilot storage site, Germany, and is compared with the result of an initial processing that was based on separate refraction static corrections. It is shown that the time-lapse difference static correction approach reduces 4D noise more effectively than separate refraction static corrections and is significantly less labor intensive.
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Jeng, Yih. "Shallow seismic investigation of a site with poor reflection quality." GEOPHYSICS 60, no. 6 (November 1995): 1715–26. http://dx.doi.org/10.1190/1.1443904.
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A shallow seismic reflection experiment was performed on a construction site to determine the feasibility of using reflection seismology to investigate the shallow structure in a weathered sand‐gravel interlayered zone that was known to be a poor transmission of high‐frequency seismic energy. Field‐recording parameters were designed to fit the limited space of the urban construction survey area. A 7 kg sledgehammer was used to generate P‐waves and SH‐waves. Single 100 Hz geophones were deployed at 1.0 m/0.5 m group intervals, and 200/100-Hz low‐cut filters were applied prior to A to D conversion to attenuate ground roll. For SH‐wave reflections, single 14 Hz geophones and a 70-Hz low‐cut filter on the seismograph were used. The dominant frequency bands ranged from 33 to 275 Hz and were centered around 110 Hz for P‐waves. Lower dominant frequency bands 20 to 160 Hz with a dominant frequency of around 85 Hz were observed on SH‐wave records. Four seismic lines, three P‐wave recordings and one SH‐wave recording, using different sets of recording parameters and an appropriate seismic‐wave generation method produced reflections from varying depth ranges and at different resolutions. The results show that the techniques employed in this experiment may resolve the structure of a site with poor reflection quality. An f-k dip filtering and deconvolution were necessary in processing the reflection data to eliminate various types of unwanted energy. The seismic interpretations in this study were verified by drilling and by a nearby excavation.
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Schmeissner, C. M., K. T. Spikes, and D. W. Steeples. "Recording seismic reflections using rigidly interconnected geophones." GEOPHYSICS 66, no. 6 (November 2001): 1838–42. http://dx.doi.org/10.1190/1.1487126.
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Ultrashallow seismic reflection surveys require dense spatial sampling during data acquisition, which increases their cost. In previous efforts to find ways to reduce these costs, we connected geophones rigidly to pieces of channel iron attached to a farm implement. This method allowed us to plant the geophones in the ground quickly and automatically. The rigidly interconnected geophones used in these earlier studies detected first‐arrival energy along with minor interfering seismic modes, but they did not detect seismic reflections. To examine further the feasibility of developing rigid geophone emplacement systems to detect seismic reflections, we experimented with four pieces of channel iron, each 2.7 m long and 10 cm wide. Each segment was equipped with 18 geophones rigidly attached to the channel iron at 15‐cm intervals, and the spikes attached to all 18 geophones were pushed into the ground simultaneously. The geophones detected both refracted and reflected energy; however, no significant signal distortion or interference attributable to the rigid coupling of the geophones to the channel iron was observed in the data. The interfering seismic modes mentioned from the previous experiments were not detected, nor was any P‐wave propagation noted within the channel iron. These results show promise for automating and reducing the cost of ultrashallow seismic reflection and refraction surveys.
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Nishitsuji, Yohei, Shohei Minato, Boris Boullenger, Martín Gomez, Kees Wapenaar, and Deyan Draganov. "Crustal-scale reflection imaging and interpretation by passive seismic interferometry using local earthquakes." Interpretation 4, no. 3 (August 1, 2016): SJ29—SJ53. http://dx.doi.org/10.1190/int-2015-0226.1.
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We have developed an application of passive seismic interferometry (SI) using P-wave coda of local earthquakes for the purpose of crustal-scale reflection imaging. We processed the reflection gathers retrieved from SI following a standard seismic processing in exploration seismology. We applied SI to the P-wave coda using crosscorrelation, crosscoherence, and multidimensional deconvolution (MDD) approaches for data recorded in the Malargüe region, Argentina. Comparing the results from the three approaches, we found that MDD based on the truncated singular-value decomposition scheme gave us substantially better structural imaging. Although our results provided higher resolution images of the subsurface, they showed less clear images for the Moho in comparison with previous seismic images in the region obtained by the receiver function and global-phase SI. Above the Moho, we interpreted a deep thrust fault and the possible melting zones, which were previously indicated by active-seismic and magnetotelluric methods in this region, respectively. The method we developed could be an alternative option not only for crustal-scale imaging, e.g., in enhanced geothermal systems, but also for lithospheric-scale as well as basin-scale imaging, depending on the availability of local earthquakes and the frequency bandwidth of their P-wave coda.
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Yang, Zhen, and Jun Lu. "Second-Order Approximation of the Seismic Reflection Coefficient in Thin Interbeds." Energies 13, no. 6 (March 20, 2020): 1465. http://dx.doi.org/10.3390/en13061465.
Full textAbstract:
As most of the lithostratigraphic reservoirs in China are thin interbeds, the study of seismic responses in thin interbeds is an integral part of lithologic reservoir exploration. However, at present, the research on seismic reflection coefficients of thin interbeds in exploration seismology is still weak, which leads to the lack of theoretical basis for the subsequent interpretation of amplitude variation with offset (AVO) related to thin interbed. To solve this problem, in this paper, we proposed second-order approximate equations of the seismic reflection coefficients in thin-bed and thin-interbed layers. Under the assumption of a small impedance contrast in layered media, we made a second-order approximation with a more evident physical meaning to the reflection coefficient calculation method proposed by Kennett. Then, based on the test of the single thin-layer theoretical model, it was confirmed that the second-order approximation equation of the PP-wave (reflected compressional wave) is accurate at incident angles less than 30°, and that of the PS-wave (converted shear wave) is accurate at wider incident angles. Finally, based on the single-thin-bed equations, the approximate equations of seismic reflection coefficients in thin interbeds were established, the validity of which was verified by the theoretical model. Our equations will be applicable to the calculation of PP- and PS-wave reflection coefficients in thin interbeds where internal multiples are difficult to suppress and transmission loss is hard to accurately compensate. This lays a theoretical foundation for improving the seismic prediction accuracy of lithologic reservoirs.
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de Franco, Roberto, Grazia Caielli, Alberto Villa, Federico Agliardi, and Francesco Franchino. "Ground-penetrating radar refraction imaging with stacked refraction convolution section method." GEOPHYSICS 81, no. 5 (September 2016): H33—H45. http://dx.doi.org/10.1190/geo2015-0475.1.
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We have evaluated a technique initially developed for the seismic refraction imaging, the stacked refraction convolution section (SRCS), which we have properly adapted to process ground-penetrating radar (GPR) refraction data. Through a mute operation, the subsurface refracting signals, recorded by the receiver from two reciprocal sources, are selected. Following that, a velocity analysis by means of the crosscorrelation of the refracted signals and the convolution of resulting traces is performed. The refraction image in intercept times is successively derived from three main steps, namely: (1) the convolution of the subsurface refracted signals, (2) the crosscorrelation of convolved trace with the reciprocal refracted signal, and (3) the stacking of crosscorrelated traces over all source couples. The technique is not only suitable for the processing of GPR data acquired with two or more reciprocal common source profiles but it is also convenient for its low acquisition cost in addition to the simplicity of software implementation and short processing times. We have evaluated the technique on a real GPR data set to characterize a near-surface morphostructure associated with a deep-seated gravitational slope deformation affecting Mt. Watles (Upper Venosta Valley, Italy). Results of the SRCS technique were validated against the direct trenching log data up to approximately 3 m in depth and complemented by the reflection processing outputs of common-source and common-offset data acquired along the line. The SRCS and common-midpoint processing provide the best reconstruction of the subsurface morphology of a shallow basement (approximately [Formula: see text] depth), characterized by a velocity range of [Formula: see text] and made of strongly to moderately weathered paragneiss. The full-wave modeling response of the reconstructed model demonstrates good agreement with the recorded signals.
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Prasad, B., P. C. Pal, and S. Kundu. "Propagation of SH-Waves Through Non Planer Interface between Visco-Elastic and Fibre-Reinforced Solid Half-Spaces." Journal of Mechanics 33, no. 4 (March 29, 2017): 545–57. http://dx.doi.org/10.1017/jmech.2017.14.
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AbstractIn the propagation of seismic waves through layered media, the boundaries play crucial role. The boundaries separating the different layers of the earth are irregular in nature and not perfectly plane. It is, therefore, necessary to take into account the corrugation of the boundaries while dealing with the problem of reflection and refraction of seismic waves. The present study explores the reflection and refraction phenomena of SH-waves at a corrugated interface between visco-elastic half-space and fibre-reinforced half-space. Method of approximation given by Rayleigh is adopted and the expressions for reflection and transmission coefficients are obtained in closed form for the first and second order approximation of the corrugation. The closed form formulae of these coefficients are presented for a corrugated interface of periodic shape (cosine law interface). It is found that these coefficients depend upon the amplitude of corrugation of the boundary, angle of incidence and frequency of the incident wave. Numerical computations for a particular type of corrugated interface are performed and a number of graphs are plotted. Some special cases are derived.
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Umor, Mohd Rozi, Mohd Hariri Arifin, and Nora Muda. "The Seismic Refraction Survey to Determine the Depth of Bedrock at the Damansara Area for Horizontal Directional Drilling Method Application." Applied Science and Innovative Research 3, no. 3 (August 4, 2019): p123. http://dx.doi.org/10.22158/asir.v3n3p123.
Full textAbstract:
The seismic reflection survey conducted along the road at Damansara to determine the depth of bedrock in order to justify whether HDD method can be utilize to store the fiber optic cable. 10 line seismic survey performed along 1.2 km roadside. The result show that the subsurface profile represent by two layer of earth materials that is topsoil and bedrock granite. Determination between topsoil and granite based on the values of seismic velocity. The boundary between granite and soil interpreted by a velocity value 1,200 m/s. If the velocity values is less than 1,200 m/s, it interpreted as soil or highly weathered rock. Meanwhile the velocity value more than 1,200 m/s is refer as rock and hard to excavate especially using HDD method. The study shows that the general thickness of topsoil along the road in Damansara is around 2.0 to 4.0 m. The minimum thickness of topsoil is 1.0 m and maximum found around 6.0 m. The bedrock observed very shallow and not suitable for HDD method to implement.
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Majdański, M. "The uncertainty in layered models from wide-angle seismic data." GEOPHYSICS 78, no. 3 (May 1, 2013): WB31—WB36. http://dx.doi.org/10.1190/geo2012-0280.1.
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The analytical method of estimating the uncertainty in layered models is addressed to models obtained using a layer-stripping modeling strategy or forward modeling. It is based on a simple principle of small error propagation. There are two variants of the method: a simplified one that includes refraction and vertical reflections and one that also includes wide-angle reflections. Both give a quantitative estimation for the existing models. To allow for a simple analytical estimation, refracted waves are described using a head-wave approximation in constant velocity layers; wide angle reflection paths are also simplified. In the case of trial and error forward modeling, this method can help determine how well the used parameterization is reflected in the data and avoid over-fitting the structures. This is especially important because the forward modeling is very subjective and there is no method to assess the parameterization without generating alternative models. For inversion problems using the layer-stripping method, the analysis allows for a correct propagation of errors and will help to evaluate the effect of including a priori information with known uncertainty. As a result, the layer-stripping modeling strategy is worse than simultaneous inversion for layered models because it gives larger uncertainties.
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Bergman, Björn, Ari Tryggvason, and Christopher Juhlin. "High‐resolution seismic traveltime tomography incorporating static corrections applied to a till‐covered bedrock environment." GEOPHYSICS 69, no. 4 (July 2004): 1082–90. http://dx.doi.org/10.1190/1.1778250.
Full textAbstract:
A major obstacle in tomographic inversion is near‐surface velocity variations. Such shallow velocity variations need to be known and correctly accounted for to obtain images of deeper structures with high resolution and quality. Bedrock cover in many areas consists of unconsolidated sediments and glacial till. To handle the problems associated with this cover, we present a tomographic method that solves for the 3D velocity structure and receiver static corrections simultaneously. We test the method on first‐arrival picks from deep seismic reflection data acquired in the mid‐ late to 1980s in the Siljan Ring area, central Sweden. To use this data set successfully, one needs to handle a number of problems, including time‐varying, near‐surface velocities from data recorded in winter and summer, several sources and receivers within each inversion cell, varying thickness of the cover layer in each inversion cell, and complex 3D geology. Simultaneous inversion for static corrections and velocity produces a much better image than standard tomography without statics. The velocity model from the simultaneous inversion is superior to the velocity model produced using refraction statics obtained from standard reflection seismic processing prior to inversion. Best results using the simultaneous inversion are obtained when the initial top velocity layer is set to the near‐surface bedrock velocity rather than the velocity of the cover. The resulting static calculations may, in the future, be compared to refraction static corrections in standard reflection seismic processing. The preferred final model shows a good correlation with the mapped geology and the airborne magneticmap.
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Juhlin, Christopher. "Imaging of fracture zones in the Finnsjön area, central Sweden, using the seismic reflection method." GEOPHYSICS 60, no. 1 (January 1995): 66–75. http://dx.doi.org/10.1190/1.1443764.
Full textAbstract:
In 1987 the Swedish Nuclear Fuel and Waste Management Co. (SKB) funded the shooting of a 1.7-km long, high‐resolution seismic profile over the Finnsjön study site using a 60‐channel acquisition system with a shotpoint and geophone spacing of 10 m. The site is located about 140 km north of Stockholm and the host rocks are mainly granodioritic. The main objective of the profile was to image a known fracture zone with high hydraulic conductivity dipping gently to the west at depths of 100 to 400 m. The initial processing of the data failed to image this fracture zone. However, a steeply dipping reflector was imaged indicating the field data were of adequate quality and that the problem lay in the processing. These data have now been reprocessed and a clear image of the gently dipping zone has been obtained. In addition, several other reflectors were imaged in the reprocessed section, both gently and steeply dipping ones. Correlations with borehole data indicate that the origin of these reflections are also fracture zones. The improvement over the previous processing is caused mainly by (1) refraction statics, (2) choice of frequency band, (3) F-K filtering, and (4) velocity analyses. In addition to reprocessing the data, some further analyses were done including simulation of acquisition using only the near‐offset channels (channels 1–30) and the far‐offset channels (channels 31–60), and determining the damping factor Q in the upper few hundred meters based upon the amplitude decay of the first arrivals. The data acquisition simulation shows the far‐offset contribution to be significant even for shallow reflectors in this area, contrary to what may be expected. A Q value of 10, determined from observed amplitude decay rates, agrees well with theoretical ones assuming plane wave propagation in an attenuating medium.
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Tang, Le, and Xinding Fang. "Generation of 6-C synthetic seismograms in stratified vertically transversely isotropic media using a generalized reflection and transmission coefficient method." Geophysical Journal International 225, no. 3 (February 3, 2021): 1554–85. http://dx.doi.org/10.1093/gji/ggab044.
Full textAbstract:
SUMMARY We develop a generalized reflection and transmission coefficient method (GRTM) for generating six-component (6-C) synthetic seismograms in horizontally layered vertically transversely isotropic (VTI) media. Compared with the traditional seismic modelling approaches that only consider translational motion, our method can simultaneously produce three-component translational and three-component rotational data excited by a point vector force or a moment tensor source in a layered half-space. Horizontally layered models are widely used in near surface applications as the properties of near surface formations generally show small lateral variations and change mainly along the depth direction. The use of the VTI constitutive relation can make our method applicable to more general situations because it takes into account the characteristics of sedimentary formations. We compare our method with a finite-difference method (FDM) for a variety of velocity models and acquisition geometries. The numerical results demonstrate that accurate 6-C synthetic seismograms can be calculated using our method. The computational efficiency of our method for 6-C seismic modelling is much higher than the finite-difference method, because it can reduce a 3-D modelling problem to 2.5-D by eliminating the azimuthal dimension. Also, our method does not require to perform additional spatial interpolations to obtain the rotational components. These advantages make our method suitable to serve as a forward modelling tool for rotational seismology.
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Bergman, B., A. Tryggvason, and C. Juhlin. "Seismic tomography studies of cover thickness and near-surface bedrock velocities." GEOPHYSICS 71, no. 6 (November 2006): U77—U84. http://dx.doi.org/10.1190/1.2345191.
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Reflection seismic imaging of the uppermost kilometer of crystalline bedrock is an important component in site surveys for locating potential storage sites for nuclear waste in Sweden. To obtain high-quality images, refraction statics are calculated using first-break traveltimes. These first-break picks may also be used to produce tomographic velocity images of the uppermost bedrock. In an earlier study, we presented a method applicable to data sets where the vast majority of shots are located in the bedrock below the glacial deposits, or cover, typical for northern latitudes. A by-product of this method was an estimate of the cover thickness from the receiver static that was introduced to sharpen the image. We now present a modified version of this method that is applicable for sources located in or on the cover, the general situation for nuclear waste site surveys. This modified methodalso solves for 3D velocity structure and static correctionssimultaneously in the inversion process. The static corrections can then be used to estimate the cover thickness. First, we test our tomography method on synthetic data withthe shot points in the bedrock below the cover. Next, we developa strategy for the case when the sources are within the cover. Themethod is then applied to field data from five crooked-line,high-resolution reflection seismic profiles ranging in lengthfrom 2 to [Formula: see text]. The crooked-line profiles make the study 2.5dimensional regarding bedrock velocities. The cover thicknessalong the profiles varies from 0 to [Formula: see text]. Estimated thickness ofthe cover agrees well with data from boreholes drilled near theprofiles. Low-velocity zones in the uppermost bedrock generallycorrelate with locations where reflections from the stackedsections project to the surface. Thus, the method is functional,both for imaging the uppermost bedrock velocities as well as for estimating the cover thickness.
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Bosch, Miguel, Penny Barton, Satish C. Singh, and Immo Trinks. "Inversion of traveltime data under a statistical model for seismic velocities and layer interfaces." GEOPHYSICS 70, no. 4 (July 2005): R33—R43. http://dx.doi.org/10.1190/1.1993712.
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We invert large-aperture seismic reflection and refraction data from a geologically complex area on the northeast Atlantic margin to jointly estimate seismic velocities and depths of major interfaces. Our approach combines this geophysical data information with prior information on seismic compressional velocities and the structural interpretation of seismic sections. We constrain expected seismic velocities in the prior model using information from well logs from a nearby area. The layered structure and prior positions of the interfaces follow information from the seismic section obtained by processing the short offsets. Instead of using a conventional regularization technique to smooth the interface-velocity model, we describe the spatial correlation of interfaces and velocities with a geostatistical model, using a multivariate Gaussian probability density function. We impose a covariance function on the velocity field in each layer and on each interface in the model to control the smoothness of the solution. The inversion is performed by minimizing an objective function with two terms, one term measuring traveltime residuals and the other measuring the fit to the statistical model. We calculate the posterior uncertainties and evaluate the relative influence of data and the prior model on estimated interface depths and seismic velocities. The method results in the estimation of velocity and interface geometry beneath a basaltic sill system down to 7 km depth. This method aims to enhance the interpretation process by combining multidisciplinary information in a quantitative model-based approach.
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Juhojuntti, Niklas, and Jochen Kamm. "Joint inversion of seismic refraction and resistivity data using layered models — Applications to groundwater investigation." GEOPHYSICS 80, no. 1 (January 1, 2015): EN43—EN55. http://dx.doi.org/10.1190/geo2013-0476.1.
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We developed a method for joint inversion of seismic refraction and resistivity data, using sharp-boundary models with few layers (typically three). We demonstrated the usefulness of the approach via examples from near-surface case studies involving shallow groundwater exploration and geotechnical investigations, although it should also be applicable to other types of layered environments, e.g., sedimentary basins. In our model parameterization, the layer boundaries were common for the resistivity and velocity distributions. Within the layers, only lateral variations in the material parameters (resistivity and velocity) were allowed, and we assumed no correlation between these. The inversion was performed using a nonlinear least-squares algorithm, using lateral smoothing to the layer boundaries and to the materialparameters. Depending on the subsurface conditions, the smoothing can be applied either to the depth of the layer boundaries or to the layer thicknesses. The forward responses and Jacobian for refraction seismics were calculated through ray tracing. The resistivity computations were performed with finite differences and a cell-to-layer transform for the Fréchet derivatives. Our method performed well in synthetic tests, and in the case studies, the layer boundaries were in good agreement with in situ tests and seismic reflection data, although minimum-structure inversion generally has a better data fit due to more freedom to introduce model heterogeneity. We further found that our joint inversion approach can provide more accurate thickness estimates for seismic hidden layers.
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Gras, Clàudia, Daniel Dagnino, Clara Estela Jiménez-Tejero, Adrià Meléndez, Valentí Sallarès, and César R. Ranero. "Full-waveform inversion of short-offset, band-limited seismic data in the Alboran Basin (SE Iberia)." Solid Earth 10, no. 6 (October 30, 2019): 1833–55. http://dx.doi.org/10.5194/se-10-1833-2019.
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Abstract. We present a high-resolution P-wave velocity model of the sedimentary cover and the uppermost basement to ∼3 km depth obtained by full-waveform inversion of multichannel seismic data acquired with a 6 km long streamer in the Alboran Sea (SE Iberia). The inherent non-linearity of the method, especially for short-offset, band-limited seismic data as this one, is circumvented by applying a data processing or modelling sequence consisting of three steps: (1) data re-datuming by back-propagation of the recorded seismograms to the seafloor; (2) joint refraction and reflection travel-time tomography combining the original and the re-datumed shot gathers; and (3) full-waveform inversion of the original shot gathers using the model obtained by travel-time tomography as initial reference. The final velocity model shows a number of geological structures that cannot be identified in the travel-time tomography models or easily interpreted from seismic reflection images alone. A sharp strong velocity contrast accurately defines the geometry of the top of the basement. Several low-velocity zones that may correspond to the abrupt velocity change across steeply dipping normal faults are observed at the flanks of the basin. A 200–300 m thick, high-velocity layer embedded within lower-velocity sediment may correspond to evaporites deposited during the Messinian crisis. The results confirm that the combination of data re-datuming and joint refraction and reflection travel-time inversion provides reference models that are accurate enough to apply full-waveform inversion to relatively short offset streamer data in deep-water settings starting at a field-data standard low-frequency content of 6 Hz.
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Kabir, Nurul, Uwe Albertin, Min Zhou, Vishal Nagassar, Einar Kjos, Phillip Whitaker, and Alan Ford. "Use of refraction, reflection, and wave-equation-based tomography for imaging beneath shallow gas: A Trinidad field data example." GEOPHYSICS 73, no. 5 (September 2008): VE281—VE289. http://dx.doi.org/10.1190/1.2953064.
Full textAbstract:
Shallow localized gas pockets cause challenging problems in seismic imaging because of sags and wipe-out zones they produce on imaged reflectors deep in the section. In addition, the presence of shallow gas generates strong surface-related and interbed multiples, making velocity updating very difficult. When localized gas pockets are very shallow, we have limited information to build a near-surface velocity model using ray-based reflection tomography alone. Diving-wave refraction tomography successfully builds a starting model for the very shallow part. Usual ray-based reflection tomography using single-parameter hyperbolic moveout might need many iterations to update the deeper part of the velocity model. In addition, the method generates a low-velocity anomaly in the deeper part of the model. We present an innovative method for building the final velocity model by combining refraction, reflection, and wave-equation-based tomography. Wave-equation-based tomography effectively generates a detailed update of a shallow velocity field, resolving the gas-sag problem. When applied as the last step, following the refraction and reflection tomography, it resolves the gas-sag problem but fails to remove the low-velocity anomaly generated by the reflection tomography in the deeper part of the model. To improve the methodology, we update the shallow velocity field using refraction tomography followed by wave-equation tomography before updating the deeper part of the model. This step avoids generating the low-velocity anomaly. Refraction and wave-equation-based tomography followed by reflection tomography generates a simpler velocity model, giving better focusing in the deeper part of the image. We illustrate how the methodology successfully improves resolution of gas anomalies and significantly reduces gas sag from an imaged section in the Greater Cassia area, Trinidad.
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Xu, Zhuo, Fengjiao Zhang, Christopher Juhlin, Björn Lund, Maria Ask, and Liguo Han. "Extrapolated supervirtual refraction interferometry." Geophysical Journal International 227, no. 2 (July 20, 2021): 1439–63. http://dx.doi.org/10.1093/gji/ggab283.
Full textAbstract:
SUMMARY Accurate picking of head-wave arrival times is an important component of first-arrival traveltime tomography. Far-offset traces in particular have low signal-to-noise ratio (SNR), but picking on these traces is necessary in order to obtain velocity information at depth. Furthermore, there is often an insufficient number of far-offset traces for obtaining reliable models at depth. We present here an extrapolation method for increasing the number of first arrivals beyond the maximum recorded offset, thereby extending the supervirtual refraction interferometry (SVI) method. We refer to the method as extrapolated SVI (ESVI). It is a novel attempt to extrapolate first arrivals using a fully data-driven method. We first test the methodology on synthetic data sets, and we then apply ESVI to two published real data sets over the Pärvie fault system in northern Sweden. These data sets were acquired along the same profile at different times with different acquisition parameters and noise levels. The results show that ESVI enhances the SNR of head waves when the noise level is high. That is the same as the conventional SVI. ESVI also increases the number of pickable first arrivals by extrapolating head waves past the original maximum offset of each shot. We also show that the significant increase in first-arrival traveltime picks is beneficial for improving resolution and penetration depth in the tomographic imaging and, consequently, better revealing the subsurface velocity distribution. The tomographic images show higher velocities in the hanging walls of the main Pärvie fault and another subsidiary fault, as interpreted relative to migrated images from previous seismic reflection processing.
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Huang, Bo, Jiachen Guo, Kailong Liao, and Yu Zhao. "Fragility Analysis of RC Frame Structures Subjected to Obliquely Incident Seismic Waves." Sustainability 13, no. 3 (January 21, 2021): 1108. http://dx.doi.org/10.3390/su13031108.
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Obliquely incident seismic waves have been habitually overlooked in fragility analysis. In this paper, a new approach to solving the equivalent loads on the infinite element boundary due to obliquely incident seismic waves is proposed. Based on the site conditions and structural characteristics in the Jiaxing area, the seismic response of a multi-story reinforced concrete (RC) frame structure has been fully investigated through the finite element method. Under obliquely incident SV waves (shear wave in the vertical x-z plane), the distribution of internal forces on the structure in the case of homogeneous foundation soil is significantly asymmetrical. Among the 3 obliquely incident angles investigated in this paper, the maximum inter-story displacement is smallest when the incident angle is 20° and largest when the angle equals 30°. For the structural fragility, the exceedance probability at each structural damage level is smallest when the incident reflection angle is 20° and largest when the angle equals 30°. When the structure is located in the silty valley, the influence of oblique incidence is attenuated and there is no obvious stress asymmetry on the structure due to the refraction of seismic waves on the interface.
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Taner, M. Turhan, Donald E. Wagner, Edip Baysal, and Lee Lu. "A unified method for 2-D and 3-D refraction statics." GEOPHYSICS 63, no. 1 (January 1998): 260–74. http://dx.doi.org/10.1190/1.1444320.
Full textAbstract:
Most of the seismic data processing procedures are divided into 2-D, 2.5-D, crooked lines or 3-D versions dictated by the differences in the shot and receiver configurations. In this paper, we introduce a tomographic approach that overcomes these geometrical difficulties and provides stable statics solutions from picked first‐break times. We also show that the first‐break picks contain both the short and the long wavelength surface statics. The solutions are obtained by solving a set of generalized surface‐consistent delay‐time equations using the method of weighted least squares and conjugate gradient. While iterating, each first‐break pick is evaluated to ensure its consistency with the least‐squares solution. Based on consistency, we weight the traveltime picks and use them in the next iteration. These weights also serve as an indicator of anomalous picks to the user. We show that long wavelength solutions leave large residual errors in the least‐squares solutions. We also use the expected length of the Fresnel zone to differentiate between short and long wavelength static solutions. After removing the influence of long wavelength statics, we apply short wavelength statics to reduce the residual errors further. We demonstrate the validity of our unified method by applying it to actual data examples. The removal of both long and short wavelength statics improves the initial data set that produces a more consistent set of velocities and leaves only the short wavelength residual reflection statics, which are generally less than quarter wavelet period delays. This removes the most probable cause of the leg jump contamination and poor velocity estimates from the residual statics computations, especially from the 3-D data.
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Shuck, Edward L., Thomas L. Davis, and Robert D. Benson. "Multicomponent 3-D characterization of a coalbed methane reservoir." GEOPHYSICS 61, no. 2 (March 1996): 315–30. http://dx.doi.org/10.1190/1.1443961.
Full textAbstract:
Methane is produced from fractured coalbed reservoirs at Cedar Hill Field in the San Juan Basin. Fracturing and local stress are critical to production because of the absence of matrix permeability in the coals. Knowledge of the direction of open fractures, the degree of fracturing, reservoir pressure, and compartmentalization is required to understand the flow of fluids through the reservoir. A multicomponent 3-D seismic survey was acquired to aid in coalbed methane reservoir characterization. Coalbed reservoir heterogeneities, including isolated pressure cells, zones of increased fracture density, and variable fracture directions, have been interpreted through the analysis of the multicomponent data and integration with petrophysical and reservoir engineering studies. Strike‐slip faults, which compartmentalize the reservoir, have been identified by structural interpretation of the 3-D P‐wave seismic data. These faults form boundaries for pressure cells that have been identified by P‐wave reflection amplitude anomalies. The analysis of polarizations, traveltimes, and reflection amplitudes from the shear‐wave seismic data has allowed the identification of zones of variable fracture direction and fracture density. There is good agreement between stresses inferred from the structural interpretation and those indicated by the shear‐wave polarizations. Reflection amplitudes have been calibrated to seismic velocities and reservoir pressures through the use of petrophysical data taken from core samples. New methods have been developed for the statistical analysis of prestack shear‐wave polarizations, poststack polarizations, and the accurate determination of traveltime anisotropy. The prestack polarization analysis method allows for rapid and efficient determination of a dominant polarization direction. Shear‐wave anisotropy has been quantified over the reservoir zone using both traveltime and thin‐bed reflection response with excellent agreement between the two methods. Crack densities computed from the anisotropy show two regions of high crack density, one coinciding with a sealed overpressured cell and the other in the region of the Hamilton ♯3 well. This indicates the potential for monitoring production of coalbed methane reservoirs using multicomponent seismology.
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Yang, Chun, Yun Wang, Jun Lu, Benchi Chen, and Lei Shi. "A Low-Order Series Approximation of Thin-Bed PP-Wave Reflections." Applied Sciences 9, no. 4 (February 18, 2019): 709. http://dx.doi.org/10.3390/app9040709.
Full textAbstract:
The study of thin-bed seismic phenomena is important in crustal, exploration and engineering seismology. Presently, seismic reflectivity theories based on single-interface assumption are widely used though they are only suitable for thick deposits. Thin-bed reflectivity theories are established on complex propagator matrices and are difficult to be applied to reveal thin-bed properties directly. Therefore, an approximation of thin-bed PP-wave reflection coefficients (RPP) is derived in this paper. First, the relationship between thin-bed RPP and incidence angles is analyzed through series expansion method. For PP-wave, its reflection coefficients are even power series functions of sine incidence angles. Then, for small incidence, RPP of the thin bed is further simplified into a second-order series approximation with respect to the sine incidence angles. Simulations and accuracy analyses of the approximate formula show that approximation errors are smaller than 5% as the incidence angles smaller than 20 degrees. Based on this approximate formula, an approach is given for estimating thin-bed properties including P-wave impedance ratios and thickness. The estimation approach is applied in properties estimation of a thin bed model. Perfect performances of the model example show the future potentiality of the approximate formula in thin-bed Amplitude-Versus-Offset (AVO) analysis and inversion.
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Lanz, Eva, Hansruedi Maurer, and Alan G. Green. "Refraction tomography over a buried waste disposal site." GEOPHYSICS 63, no. 4 (July 1998): 1414–33. http://dx.doi.org/10.1190/1.1444443.
Full textAbstract:
Determining the depth and geometry of a landfill’s lower boundary is a difficult task. Potential field methods generally lack the necessary depth resolution, and seismic reflection data are usually contaminated by source‐generated noise in the time range of interest (<50 ms). To address this problem, we have developed a surface 2-D tomographic refraction scheme that is based on a fast finite‐difference eikonal solver and an inversion method that incorporates appropriate damping and smoothing constraints. This new scheme has been applied to a first‐arrival traveltime data set collected across adjacent landfills in northern Switzerland. High‐quality seismic data were collected along five profiles that crossed the landfills and two that sampled undisturbed natural sediments. Seismic waves generated from multiple shots were recorded on large numbers of closely spaced receivers during quiet evening periods. Reliability of the resultant velocity tomograms was estimated on the basis of (1) ray diagrams, (2) plots of synthetic and observed traveltimes, (3) traveltime residual analyses, (4) comparisons of coincident velocity‐depth profiles computed from intersecting profiles, (5) inversions with diverse input models, and (6) quantitative error analyses using a bootstrap technique. At our study site, the base of the near‐surface natural layer and the lower boundaries of the landfills were defined by rapid increases in velocity from <1000 m/s to >1500 m/s, with velocities in the upper parts of the models determined to within about ±100 m/s. The thickness of the near‐surface natural layer varied between 2 and 6 m, with occasional thickening to ∼7 m. In contrast, low velocities associated with the landfills could be traced to 9 to 11 m depth. Although our results have demonstrated that the tomographic refraction scheme may be an efficient and cost‐effective means of studying the very shallow subsurface (<20 m depth), complementary geological and other geophysical data were required to discriminate between velocity anomalies attributed to the landfills and those attributed to natural variations in the near‐surface geology.
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Lozano, Lucía, Juan Vicente Cantavella, and Jaime Barco. "A new 3-D P-wave velocity model for the Gulf of Cadiz and adjacent areas derived from controlled-source seismic data: application to nonlinear probabilistic relocation of moderate earthquakes." Geophysical Journal International 221, no. 1 (December 12, 2019): 1–19. http://dx.doi.org/10.1093/gji/ggz562.
Full textAbstract:
SUMMARY The SW Iberian margin is well known for its complex tectonic setting and crustal structure and by the occurrence of moderate magnitude earthquakes and some great tsunamigenic earthquakes. Fortunately, many seismic reflection and refraction profiles have been carried out, providing detailed information about the crustal structure of the main geologic domains in this region. These studies show a first-order variation due to the transition from oceanic to continental domain, large-scale heterogeneities within the crust and an irregular Moho topography. Routine earthquake locations in this area have been usually computed using a general 1-D velocity model which is clear that cannot account for such a heterogeneous structure. In addition, regional seismic stations used to locate the Gulf of Cadiz seismicity are on land and far away to the east, implying large azimuthal gaps and distances. In this context, a 3-D approach seems necessary to properly solve the crustal velocity field and improve earthquake location in this area. With this purpose, we present a new digital 3-D P-wave velocity distribution for the crust and uppermost mantle derived from previously published controlled-source seismic experiments carried out in SW Iberia and the Gulf of Cadiz over the last 40 yr. We have reviewed more than 50 wide-angle and multichannel seismic reflection and refraction profiles and digitized the most significant published 2-D seismic velocity models, performing an updated compilation of crustal parameters (P-wave velocities and geometry and depth of the main crustal interfaces). These velocities as a function of position and depth have been interpolated using ordinary kriging algorithm to obtain, in the form of a regular georeferenced 20 × 20 × 1 km grid spacing, a high-resolution 3-D P-wave velocity distribution for the crust and uppermost mantle and a continuous Moho depth map of the whole area of this study (33°N–41°N latitude and 15°W–5°W longitude). Since current seismic location tools allow the implementation of 3-D grid structures, we have applied our 3-D model to relocate a selection of moderate earthquakes occurred in the studied region using a probabilistic nonlinear method. In the Gulf of Cadiz area the probabilistic approximation provides maximum likelihood hypocentres located within the uppermost mantle with the majority of depths ranging between 20 and 45 km. This model would subsequently be implemented at the Spanish Seismic Network for the routine relocation of the seismicity of the area.
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Djikpéssé, Hugues A., and Albert Tarantola. "Multiparameter 𝓁1 norm waveform fitting: Interpretation of Gulf of Mexico reflection seismograms." GEOPHYSICS 64, no. 4 (July 1999): 1023–35. http://dx.doi.org/10.1190/1.1444611.
Full textAbstract:
Estimation of the elastic properties of the crust from surface seismic recordings is of great importance for the understanding of lithology and for the detection of mineral resources. Although in marine reflection experiments only P-waves are recorded, information on shear properties of the medium is contained in multioffset reflection seismograms. Being able to retrieve both dilatational and shear properties gives stronger constraints on the lithology. It is therefore desirable to recover isotropic elastic parameters from multioffset seismograms. Unfortunately, most classical waveform fitting methods used for extracting shear properties of the subsurface are based on a 1-D earth model assumption and on linear approximations of the wave equations. In this paper, a 2.5-D elastic waveform inversion method is used to extract the variations of acoustic impedance and Poisson’s ratio from marine multioffset reflection seismograms collected in the Gulf of Mexico area. A complete seismic profile is interpreted, including complex physical phenomena apparent in the data, such as unconsolidated sediment reflections and seismic refraction events. The amplitude of the reflections cannot be explained by one parameter related to the dilatational properties (P-impedance) only, when trying to minimize the least absolute fit between observed and synthetic seismograms. When adding an additional parameter related to shear properties (Poisson’s ratio), the fit between observed and synthetic seismograms improves. The resulting 2-D models of P-impedance and Poisson’s ratio contrasts are anticorrelated almost everywhere in depth, except where hydrocarbons are present. The estimation of physical P-impedance and Poisson’s ratio models by a full waveform fitting allows lithology characterization and, therefore, the delineation of a shale‐over‐gas sand reservoir.
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El Yadari, Nizare, Fabian Ernst, and Wim Mulder. "Near-surface attenuation estimation using wave-propagation modeling." GEOPHYSICS 73, no. 6 (November 2008): U27—U37. http://dx.doi.org/10.1190/1.2976548.
Full textAbstract:
The effect of the near surface on seismic land data can be so severe that static corrections are insufficient. Full-waveform inversion followed by redatuming may be an alternative, but inversion will work only if the starting model is sufficiently close to the true model. As a first step toward determining a viscoelastic near-surface model, we assume that existing methods can provide a horizontally layered velocity and density model. Because near-surface attenuation is strongest, we propose a method to estimate the P-wave attenuation based on viscoacoustic finite-difference modeling. We compare energy decay along traveltime curves of reflection and refraction events in the modeled and observed seismic data for a range of attenuation parameters. The best match provides an estimate of the attenuation. First, we estimate only the attenuation of the top layer and study the sensitivity to depth and velocity perturbations. Then, we consider multiple layers. We apply the method to synthetic and real data and investigate the effect of source wavelet and topography. The method is robust against depth and velocity perturbations smaller than 10%. The results are sensitive to the source wavelet. Incorporating the surface topography in the computed traveltimes reduces the uncertainty of the attenuation estimates, especially for deeper layers.
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Bachrach, Ran, Jack Dvorkin, and Amos Nur. "High‐resolution shallow‐seismic experiments in sand, Part II: Velocities in shallow unconsolidated sand." GEOPHYSICS 63, no. 4 (July 1998): 1234–40. http://dx.doi.org/10.1190/1.1444424.
Full textAbstract:
We conducted a shallow high‐resolution seismic reflection and refraction experiment on a sandy beach. The depth of investigation was about 2 m. We interpret the data using the Hertz‐Mindlin contact theory combined with Gassmann’s equation. These were used to obtain the vertical velocity profile. Then the profile was computed from seismic data using the turning‐rays approximation. The normal moveout (NMO) velocity at the depth of 2 m matches the velocity profile. As a result, we developed a method to invert measured velocity from first arrivals, i.e., velocity versus distance into velocity versus depth using only one adjustable parameter. This parameter contains all the information about the internal structure and elasticity of the sand. The lowest velocity observed was about 40 m/s. It is noteworthy that the theoretical lower bound for velocity in dry sand with air is as low as 13 m/s. We find that modeling sand as a quartz sphere pack does not quantitatively agree with the measured data. However, the theoretical functional form proves to be useful for the inversion.
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Louie, J. N., and J. E. Vidale. "Array analysis of reflector heterogeneity." GEOPHYSICS 56, no. 4 (April 1991): 565–71. http://dx.doi.org/10.1190/1.1443074.
Full textAbstract:
In deep crustal reflection study, as in conventional exploration seismology, it is important to determine the geometry of the physical contrasts between rocks that cause reflections, to make reliable geologic interpretations. Fundamentally different reflecting structures produce similar signatures in stacked seismic sections. We have developed a method that uses prestack records to differentiate lateral structural variations from lateral reflectivity variations and laterally homogeneous structures. Full‐wave acoustic multioffset synthetics of canonical 2-D reflector configurations, analyzed by statistically enhanced slant‐stack processes, show that lateral heterogeneity such as a wavy reflector can be identified from changes in slowness across a receiver array as a function of time. Application of these methods to deep crustal reflections, recorded in the Mojave Desert of southern California, identifies laterally heterogeneous midcrustal structures and is consistent with a laterally homogeneous Moho.
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Chen, Tuo. "Seismic response analysis of loess site under far-field bedrock ground motion of the Wenchuan earthquake." PLOS ONE 16, no. 7 (July 30, 2021): e0254871. http://dx.doi.org/10.1371/journal.pone.0254871.
Full textAbstract:
In this paper, considering the far-field seismic input, an accelerogram recorded in the bedrock at Wuquan Mountain in Lanzhou city during the 2008 Wenchuan Ms8.0 earthquake was selected, and numerical dynamic analyses were conducted. The one-dimensional equivalent linear method was implemented to estimate the ground motion effects in the loess regions. Thereafter, slope topographic effects on ground motion were studied by applying the dynamic finite-element method. The results revealed the relationship between the PGA amplification coefficients and the soil layer thickness, which confirmed that the dynamic response of the sites had obvious nonlinear characteristics. The results also showed that there was an obvious difference in the dynamic magnification factor between the short-period and long-period structures. Moreover, it was found that the amplification coefficient of the observation point at the free surface was greater than the point inside the soil at the same depth, which mainly occurred in the upper slope. Through this study, the quantitative assessment of ground motion effects in loess regions can be approximately estimated, and the amplification mechanism of the far-field ground motion mechanism can be further explained. In addition to the refraction and reflection theory of seismic waves, the resonance phenomenon may help explain the slope topographic effect through spectrum analysis.