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1
Halliday, David F., Andrew Curtis, Johan O. A. Robertsson und Dirk-Jan van Manen. „Interferometric surface-wave isolation and removal“. GEOPHYSICS 72, Nr. 5 (September 2007): A69—A73. http://dx.doi.org/10.1190/1.2761967.
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The removal of surface waves (ground roll) from land seismic data is critical in seismic processing because these waves tend to mask informative body-wave arrivals. Removal becomes difficult when surface waves are scattered, and data quality is often impaired. We apply a method of seismic interferometry, using both sources and receivers at the surface, to estimate the surface-wave component of the Green’s function between any two points. These estimates are subtracted adaptively from seismic survey data, providing a new method of ground-roll removal that is not limited to nonscattering regions.
2
Campman, X., K. van Wijk, C. D. Riyanti, J. Scales und G. Herman. „Imaging scattered seismic surface waves“. Near Surface Geophysics 2, Nr. 4 (01.08.2004): 223–30. http://dx.doi.org/10.3997/1873-0604.2004019.
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3
Blonk, Bastian, und Gérard C. Herman. „Removal of scattered surface waves using multicomponent seismic data“. GEOPHYSICS 61, Nr. 5 (September 1996): 1483–88. http://dx.doi.org/10.1190/1.1444073.
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In many exploration areas, the shallow subsurface is strongly heterogeneous. The heterogeneities can give rise to scattering of surface waves. These scattered waves can depreciate the quality of land seismic data when they mask the body‐wave reflections from the deeper part of the subsurface. Surface waves scattered near a line of receivers (inline‐scattered waves) can be removed by well‐known filtering techniques (see e.g., Yilmaz, 1987, section 1.6.2). However, surface waves scattered far from the receiver line (crossline‐scattered waves) are left intact partially by filtering because these waves can resemble body‐wave reflections. In previous papers, we have discussed an inverse scattering method for removing scattered surface waves from simulated data (Blonk and Herman, 1994), as well as from field data (Blonk et al., 1995). So far, we have limited our attention to the vertical components of the particle velocity which implies that surface waves and body‐wave reflections can be distinguished on the basis of their respective differences in phase velocity.
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Peterie, Shelby L., Julian Ivanov, Erik Knippel, Richard D. Miller und Steven D. Sloan. „Shallow tunnel detection using converted surface waves“. GEOPHYSICS 86, Nr. 3 (01.05.2021): WA59—WA68. http://dx.doi.org/10.1190/geo2020-0357.1.
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Seismic surface waves that were likely converted from incident body waves were used to detect a 3 m deep tunnel using two novel processing methods. In data acquired at a tunnel test site, a unique forward-propagating wave (traveling away from the tunnel and seismic source) was identified as an early-arriving surface wave converted at the tunnel from an incident body wave. To our knowledge, our research represents the first time converted surface waves have been observed originating from a tunnel. We have developed two novel processing methods targeting this unique wavefield component for detecting tunnels, cavities, or other shallow anomalies. The first is a time-domain imaging method that takes advantage of the unique kinematic characteristics of converted surface waves to produce a cross section with a coherent, high-amplitude signature originating from the horizontal location of the tunnel. The second method uses frequency-domain analysis of surface-wave amplitudes, which reveals increased amplitudes (primarily from converted surface waves) at locations expected for the tunnel. These proposed approaches for analysis of converted surface waves were successfully used to detect the tunnel and accurately interpret its horizontal location in real-world data. These novel methods could be the key for detecting shallow tunnels or other subsurface anomalies and complement existing seismic detection methods.
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Xu, Jixiang, Shitai Dong, Huajuan Cui, Yan Zhang, Ying Hu und Xiping Sun. „Near-surface scattered waves enhancement with source-receiver interferometry“. GEOPHYSICS 83, Nr. 6 (01.11.2018): Q49—Q69. http://dx.doi.org/10.1190/geo2017-0806.1.
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Near-surface scattered waves (NSWs) are the main noise in seismic data in areas with a complex near surface and can be divided into surface-to-surface scattered waves and body-to-surface scattered waves. We have developed a method for NSW enhancement that uses modified source-receiver interferometry. The method consists of two parts. First, deconvolutional intersource interferometry is used to cancel the common raypath of seismic waves from a near-surface scatterer to the common receiver and the receiver function. Second, convolutional interreceiver interferometry is used to compensate the common raypath of seismic waves from the common source to the near-surface scatterer and the source function. For an isotropic point scatterer near the earth’s surface in modified source-receiver interferometry, a body-to-surface scattered wave can be reconstructed by constructive interference not only among three body-to-surface scattered waves but also among a body-to-surface scattered wave and two surface-to-surface scattered waves; a surface-to-surface scattered wave can be reconstructed by constructive interference not only among three surface-to-surface scattered waves but also among a surface-to-surface scattered wave and two body-to-surface scattered waves. According to stationary phase analysis based on the superposition principle, we have developed a so-called dual-wheel driving configuration of modified source-receiver interferometry for enhancing NSWs in the data of conventional seismic exploration. The main advantages of the scheme are that (1) it can be used to enhance NSWs without the need for any a priori knowledge of topography and near-surface velocity, (2) it can be used to reconstruct NSWs from real sources to real receivers, including 3D near-surface side-scattered waves, and (3) it can be applied to conventional seismic data with finite-frequency bandwidth, spatially limited and sparse arrays, different source and receiver functions, and static correction. Numerically simulated data and field seismic data are used to demonstrate the feasibility and effectiveness of the scheme.
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Qiu, Xinming, Chao Wang, Jun Lu und Yun Wang. „Surface-Wave Extraction Based on Morphological Diversity of Seismic Events“. Applied Sciences 9, Nr. 1 (21.12.2018): 17. http://dx.doi.org/10.3390/app9010017.
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It is essential to extract high-fidelity surface waves in surface-wave surveys. Because reflections usually interfere with surface waves on X components in multicomponent seismic exploration, it is difficult to extract dispersion curves of surface waves. To make matters worse, the frequencies and velocities of higher-mode surface waves are close to those of PS-waves. A method for surface-wave extraction is proposed based on the morphological differences between surface waves and reflections. Frequency-domain high-resolution linear Radon transform (LRT) and time-domain high-resolution hyperbolic Radon transform (HRT) are used to represent surface waves and reflections, respectively. Then, a sparse representation problem based on morphological component analysis (MCA) is built and optimally solved to obtain high-fidelity surface waves. An advantage of our method is its ability to extract surface waves when their frequencies and velocities are close to those of reflections. Furthermore, the results of synthetic and field examples confirm that the proposed method can attenuate the distortion of surface-wave dispersive energy caused by reflections, which contributes to extraction of accurate dispersion curves.
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Almuhaidib, Abdulaziz M., und M. Nafi Toksöz. „Numerical modeling of elastic-wave scattering by near-surface heterogeneities“. GEOPHYSICS 79, Nr. 4 (01.07.2014): T199—T217. http://dx.doi.org/10.1190/geo2013-0208.1.
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In land seismic data, scattering from surface and near-surface heterogeneities adds complexity to the recorded signal and masks weak primary reflections. To understand the effects of near-surface heterogeneities on seismic reflections, we simulated seismic-wave scattering from arbitrary-shaped, shallow, subsurface heterogeneities through the use of a perturbation method for elastic waves and finite-difference forward modeling. The near-surface scattered wavefield was modeled by looking at the difference between the calculated incident (i.e., in the absence of scatterers) and the total wavefields. Wave propagation was simulated for several earth models with different near-surface characteristics to isolate and quantify the influence of scattering on the quality of the seismic signal. The results indicated that the direct surface waves and the upgoing reflections were scattered by the near-surface heterogeneities. The scattering took place from body waves to surface waves and from surface waves to body waves. The scattered waves consisted mostly of body waves scattered to surface waves and were, generally, as large as, or larger than, the reflections. They often obscured weak primary reflections and could severely degrade the image quality. The results indicated that the scattered energy depended strongly on the properties of the shallow scatterers and increased with increasing impedance contrast, increasing size of the scatterers relative to the incident wavelength, decreasing depth of the scatterers, and increasing attenuation factor of the background medium. Also, sources deployed at depth generated weak surface waves, whereas deep receivers recorded weak surface and scattered body-to-surface waves. The analysis and quantified results helped in the understanding of the scattering mechanisms and, therefore, could lead to developing new acquisition and processing techniques to reduce the scattered surface wave and enhance the quality of the seismic image.
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de Groot-Hedlin, Catherine D. „Seismic T-Wave Observations at Dense Seismic Networks“. Seismological Research Letters 91, Nr. 6 (19.08.2020): 3444–53. http://dx.doi.org/10.1785/0220200208.
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Abstract Seismic T waves, which result from transformation of hydroacoustic to seismic energy at coastlines, were investigated for two strong earthquakes. A 2014 Caribbean event generated seismic T waves that were detected at over 250 seismometers along the east coast of the U.S., primarily at seismic stations operated by the USArray Transportable Array. A 2006 Hawaiian event generated seismic T waves observed at over 100 seismometers along the west coast. Seismic T-wave propagation was treated as locally 2D where the incoming hydroacoustic wavefronts were nearly parallel to the coastlines. Along the east coast, seismic T-wave propagation velocities were consistent with surface waves and a polarization analysis indicated that they were transverse waves, supporting their interpretation as Love waves. They were observed at inland distances up to 1134 km from the east coast. Along the west coast, the propagation velocity was over 5 km/s and a polarization analysis confirmed that the seismic T waves propagated as seismic P waves. Differences between the modes of propagation along the east and west coasts are attributed to differences in the slope and thickness of the sediment coverage at the continental slopes where hydroacoustic to seismic conversion takes place.
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Ardhuin, Fabrice, und T. H. C. Herbers. „Noise generation in the solid Earth, oceans and atmosphere, from nonlinear interacting surface gravity waves in finite depth“. Journal of Fluid Mechanics 716 (25.01.2013): 316–48. http://dx.doi.org/10.1017/jfm.2012.548.
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AbstractOceanic pressure measurements, even in very deep water, and atmospheric pressure or seismic records, from anywhere on Earth, contain noise with dominant periods between 3 and 10 s, which is believed to be excited by ocean surface gravity waves. Most of this noise is explained by a nonlinear wave–wave interaction mechanism, and takes the form of surface gravity waves, acoustic or seismic waves. Previous theoretical work on seismic noise focused on surface (Rayleigh) waves, and did not consider finite-depth effects on the generating wave kinematics. These finite-depth effects are introduced here, which requires the consideration of the direct wave-induced pressure at the ocean bottom, a contribution previously overlooked in the context of seismic noise. That contribution can lead to a considerable reduction of the seismic noise source, which is particularly relevant for noise periods larger than 10 s. The theory is applied to acoustic waves in the atmosphere, extending previous theories that were limited to vertical propagation only. Finally, the noise generation theory is also extended beyond the domain of Rayleigh waves, giving the first quantitative expression for sources of seismic body waves. In the limit of slow phase speeds in the ocean wave forcing, the known and well-verified gravity wave result is obtained, which was previously derived for an incompressible ocean. The noise source of acoustic, acoustic-gravity and seismic modes are given by a mode-specific amplification of the same wave-induced pressure field near zero wavenumber.
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Shearer, P. M., und J. A. Orcutt. „Surface and near-surface effects on seismic waves—theory and borehole seismometer results“. Bulletin of the Seismological Society of America 77, Nr. 4 (01.08.1987): 1168–96. http://dx.doi.org/10.1785/bssa0770041168.
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Abstract A simple plane wave model is adequate to explain many surface versus borehole seismometer data sets. Using such a model, we present a series of examples which demonstrate the effects of the free-surface, near-surface velocity gradients, and low impedance surface layers on the amplitudes of upcoming body waves. In some cases, these amplitudes are predictable from simple free-surface and impedance contrast expressions. However, in other cases these expressions are an unreliable guide to the complete response, and the full plane wave calculation must be performed. Large surface amplifications are possible, even without focusing due to lateral heterogeneities or nonlinear effects. Both surface and borehole seismometer site responses are almost always frequency-dependent. Ocean bottom versus borehole seismic data from the 1983 Ngendei Seismic Experiment in the southwest Pacific are consistent with both a simple plane wave model and a more complete synthetic seismogram calculation. The borehole seismic response to upcoming P waves is reduced at high frequencies because of interference between the upgoing P wave and downgoing P and SV waves reflected from the sediment-basement interface. However, because of much lower borehole noise levels, the borehole seismometer enjoys a P-wave signal-to-noise advantage of 3 to 7 dB over nearby ocean bottom instruments.
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Winterstein, D. F., und B. N. P. Paulsson. „Velocity anisotropy in shale determined from crosshole seismic and vertical seismic profile data“. GEOPHYSICS 55, Nr. 4 (April 1990): 470–79. http://dx.doi.org/10.1190/1.1442856.
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Crosshole and vertical seismic profile (VST) data made possible accurate characterization of the elastic properties, including noticeable velocity anisotropy, of a near‐surface late Tertiary shale formation. Shear‐wave splitting was obvious in both crosshole and VSP data. In crosshole data, two orthologonally polarrized shear (S) waves arrived 19 ms in the uppermost 246 ft (75 m). Vertically traveling S waves of the VSP separated about 10 ms in the uppermost 300 ft (90 m) but remained at nearly constant separation below that level. A transversely isotropic model, which incorporates a rapid increase in S-wave velocities with depth but slow increase in P-wave velocities, closely fits the data over most of the measured interval. Elastic constants of the transvesely isotropic model show spherical P- and [Formula: see text]wave velocity surfaces but an ellipsoidal [Formula: see text]wave surface with a ratio of major to minor axes of 1.15. The magnitude of this S-wave anisotropy is consistent with and lends credence to S-wave anisotropy magnitudes deduced less directly from data of many sedimentary basins.
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Li, Y. G., und P. C. Leary. „Fault zone trapped seismic waves“. Bulletin of the Seismological Society of America 80, Nr. 5 (01.10.1990): 1245–71. http://dx.doi.org/10.1785/bssa0800051245.
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Abstract Two instances of fault zone trapped seismic waves have been observed. At an active normal fault in crystalline rock near Oroville in northern California, trapped waves were excited with a surface source and recorded at five near-fault borehole depths with an oriented three-component borehole seismic sonde. At Parkfield, California, a borehole seismometer at Middle Mountain recorded at least two instances of the fundamental and first higher mode seismic waves of the San Andreas fault zone. At Oroville recorded particle motions indicate the presence of both Love and Rayleigh normal modes. The Love-wave dispersion relation derived for an idealized wave guide with velocity structure determined by body-wave travel-time inversion yields seismograms of the fundamental mode that are consistent with the observed Love-wave amplitude and frequency. Applying a similar velocity model to the Parkfield observations, we obtain a good fit to the trapped wavefield amplitude, frequency, dispersion, and mode time separation for an asymmetric San Andreas fault zone structure—a high-velocity half-space to the southwest, a low-velocity fault zone, a transition zone containing the borehole seismometer, and an intermediate velocity half-space to the northeast. In the Parkfield borehole seismic data set, the locations (depth and offset normal to fault plane) of natural seismic events which do or do not excite trapped waves are roughly consistent with our model of the low velocity zone. We conclude that it is feasible to obtain near-surface borehole records of fault zone trapped waves. Because trapped modes are excited only by events close to the fault zone proper—thereby fixing these events in space relative to the fault—a wider investigation of possible trapped mode waveforms recorded by a borehole seismic network could lead to a much refined body-wave/tomographic velocity model of the fault and to a weighting of events as a function of offset from the fault plane. It is an open question whether near-surface sensors exist in a stable enough seismic environment to use trapped modes as an earth monitoring device.
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Irie, Kiyoshi, Dorjpalam Saruul, Kazuo Dan und Haruhiko Torita. „Evaluation of the Strong Ground Motions in the Area Close to the Surface Faults“. Journal of Earthquake and Tsunami 12, Nr. 04 (Oktober 2018): 1841002. http://dx.doi.org/10.1142/s1793431118410026.
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In Japan, the seismic waves radiated from the fault in the surface layers above the seismogenic layer are not considered in the usual strong motion prediction. However, in the inland crustal earthquakes, the strong ground motions in the areas close to the surface faults could be influenced by the seismic waves radiated from the fault in the surface layers. Hence, we evaluated the seismic waves radiated from vertical strike-slip and dipping reverse faults in the surface layers to investigate their influence on the strong motions. The results of the strike-slip fault showed that the seismic waves of the fault normal (FN) component were larger than those of the fault parallel (FP) component in the period range of 0.5–5 s. At least, 80–90% of the FN component was attributed to the seismic wave radiated from the fault in the seismogenic layer. Almost 100% of the FP component was attributed to the seismic waves radiated from the fault in the surface layers. On the other hand, the results of the reverse fault showed that the seismic waves were not attributed to those from the fault in the surface layers.
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Halliday, David F., Taiwo Fawumi, Johan O. A. Robertsson und Ed Kragh. „On the use of a seismic sensor as a seismic source“. GEOPHYSICS 78, Nr. 5 (01.09.2013): A39—A43. http://dx.doi.org/10.1190/geo2013-0084.1.
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We investigated the use of seismic sensors as small seismic sources. A voltage signal is applied to a geophone that forces the mass within the geophone to move. The movement of the mass generates a seismic wavefield that was recorded with an array of geophones operating in the conventional sense. We observed higher-frequency (25 Hz and above) surface and body waves propagating from the geophone source at offsets of 10 s of meters. We further found that the surface waves emitted from geophone sources can be used to generate a surface-wave group velocity map. We discuss potential developments and future applications.
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Ernst, Fabian E., Gérard C. Herman und Auke Ditzel. „Removal of scattered guided waves from seismic data“. GEOPHYSICS 67, Nr. 4 (Juli 2002): 1240–48. http://dx.doi.org/10.1190/1.1500386.
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Near‐surface scattered waves form a major source of coherent noise in seismic land data. Most current methods for removing these waves do not attenuate them adequately if they come from other than the inline direction. We present a wave‐theory‐based method for removing (scattered) guided waves by a prediction‐and‐removal algorithm. We assume that the near surface consists of a laterally varying medium, in which heterogeneities are embedded that act as scatterers. We first estimate the dispersive and laterally varying phase slowness field by applying a phase‐based tomography algorithm on the direct groundroll wave. Subsequently, the near‐surface heterogeneities are imaged using a least‐squares criterium. Finally, the scattered guided waves are modeled and subtracted adaptively from the seismic data. We have applied this method to seismic land data and found that near‐surface scattering effects are attenuated.
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Neducza, Boriszláv. „Stacking of surface waves“. GEOPHYSICS 72, Nr. 2 (März 2007): V51—V58. http://dx.doi.org/10.1190/1.2431635.
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The seismic surface wave method (SWM) is a powerful means of characterizing near-surface structures. Although the SWM consists of only three steps (data acquisition, determination of dispersion curves, and inversion), it is important to take considerable care with the second step, determination of the dispersion curves. This step is usually completed by spectral analysis of surface waves (SASW) or multichannel analysis of surface waves (MASW). However, neither method is ideal, as each has its advantages and disadvantages. SASW provides higher horizontal resolution, but it is very sensitive to coherent noise and individual geophone coupling. MASW is a robust method able to separate different wave types, but its horizontal resolution is lower. Stacking of surface waves (SSW) is a good compromise between SASW and MASW. Using a reduced number of traces increases the horizontal resolution of MASW, and utilizing other shot records with the same receivers compensates for the decreased signal-to-noise ratio. The stacking is realized by summing the [Formula: see text] amplitude spectra of windowed shot records, where windowing produces higher horizontal resolution and stacking produces improved data quality. Mixing is applied between the stacks derived with different parameters, as different frequency ranges require different windowing. SSW was tested and corroborated on a deep seismic data set. Horizontal resolution is validated by [Formula: see text] plots at different frequencies, and [Formula: see text] plots present data quality.
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Kritski, A., A. P. Vincent, D. A. Yuen und T. Carlsen. „Adaptive wavelets for analyzing dispersive seismic waves“. GEOPHYSICS 72, Nr. 1 (Januar 2007): V1—V11. http://dx.doi.org/10.1190/1.2374799.
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Our primary objective is to develop an efficient and accurate method for analyzing time series with a multiscale character. Our motivation stems from the studies of the physical properties of marine sediment (stiffness and density) derived from seismic acoustic records of surface/interface waves along the water-seabed boundary. These studies depend on the dispersive characteristics of water-sediment surface waves. To obtain a reliable retrieval of the shear-wave velocities, we need a very accurate time-frequency record of the surface waves. Such a time-frequency analysis is best carried out by a wavelet-transform of the seismic records. We have employed the wavelet crosscorrelation technique for estimating the shear-wave propagational parameters as a function of depth and horizontal distance. For achieving a greatly improved resolution in time-frequency space, we have developed a new set of adaptive wavelets, which are driven by the data. This approach is based on a Karhunen-Loeve (KL) decomposition of the seismograms. This KL decomposition allows us to obtain a set of wavelet functions that are naturally adapted to the scales of the surface-wave modes. We demonstrate the superiority of these adaptive wavelets over standard wavelets in their ability to simultaneously discriminate the different surface-wave modes. The results can also be useful for imaging and statistical data analysis in exploration geophysics and in other disciplines in the environmental sciences.
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Chang, Chih‐Hsiung, Gerald H. F. Gardner und John A. McDonald. „Experimental observation of surface wave propagation for a transversely isotropic medium“. GEOPHYSICS 60, Nr. 1 (Januar 1995): 185–90. http://dx.doi.org/10.1190/1.1443745.
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Velocity anisotropy of surface‐wave propagation in a transversely isotropic solid has been observed in a laboratory study. In this study, Phenolite™, an electrical insulation material, was used as the transversely isotropic media (TIM), and a vertical seismic profiling (VSP) geometry was used to record seismic arrivals and to separate surface waves from shear waves. Results show that surface waves that propagate with different velocities exist at certain directions.
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Schuster, Gerard T., Jing Li, Kai Lu, Ahmed Metwally, Abdullah AlTheyab und Sherif Hanafy. „Opportunities and pitfalls in surface-wave interpretation“. Interpretation 5, Nr. 1 (01.02.2017): T131—T141. http://dx.doi.org/10.1190/int-2016-0011.1.
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Many explorationists think of surface waves as the most damaging noise in land seismic data. Thus, much effort is spent in designing geophone arrays and filtering methods that attenuate these noisy events. It is now becoming apparent that surface waves can be a valuable ally in characterizing the near-surface geology. This review aims to find out how the interpreter can exploit some of the many opportunities available in surface waves recorded in land seismic data. For example, the dispersion curves associated with surface waves can be inverted to give the S-wave velocity tomogram, the common-offset gathers can reveal the presence of near-surface faults or velocity anomalies, and back-scattered surface waves can be migrated to detect the location of near-surface faults. However, the main limitation of surface waves is that they are typically sensitive to S-wave velocity variations no deeper than approximately half to one-third the dominant wavelength. For many exploration surveys, this limits the depth of investigation to be no deeper than approximately 0.5–1.0 km.
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Shin, Changsoo. „Sponge boundary condition for frequency‐domain modeling“. GEOPHYSICS 60, Nr. 6 (November 1995): 1870–74. http://dx.doi.org/10.1190/1.1443918.
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Several techniques have been developed to get rid of edge reflections from artificial boundaries. One of them is to use paraxial approximations of the scalar and elastic wave equations. The other is to attenuate the seismic waves inside the artificial boundary by a gradual reduction of amplitudes. These techniques have been successfully applied to minimize unwanted seismic waves for time‐domain seismic modeling. Unlike time‐domain seismic modeling, suppression of edge reflections from artificial boundaries has not been successful in frequency‐domain seismic modeling. Rayleigh waves caused by coupled motions of P‐ and S‐waves near the surface have been a particularly difficult problem to overcome in seismic modeling. In this paper, I design a damping matrix for frequency‐ domain modeling that damps out seismic waves by adding a diffusion term to the wave equation. This technique can suppress unwanted seismic waves, including Rayleigh waves and P‐ and S‐waves from an artificial boundary.
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Dorman, James, und Robert Smalley. „Low-Frequency Seismic Surface Waves in the Upper Mississippi Embayment“. Seismological Research Letters 65, Nr. 2 (01.04.1994): 137–48. http://dx.doi.org/10.1785/gssrl.65.2.137.
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Abstract Low-frequency seismic surface waves lasting about 6 minutes were recorded at Memphis following the magnitude 4.6 Risco, Missouri earthquake of May 4, 1991. The motion following S included a very long, sinusoidal train of Love waves with periods of 3 to 5 seconds and weaker groups of Rayleigh waves of periods between 2 and 7 seconds arriving early and late. The unusual Risco surface waves travel a source-receiver path internal to the upper Mississippi embayment, a shallow basin containing soft, young sediments overlying rigid carbonate rocks. In contrast to the strong Risco surface waves, the magnitude 4.8 Cape Girardeau, Missouri earthquake of September 26, 1990, which occurred near the edge of the basin, produced relatively weak surface waves at Memphis. The Risco and Cape Girardeau earthquakes are the largest regional earthquakes ever recorded on long-period and broad-band seismographs within the embayment. They show that (1) the sedimentary basin has a profound effect on low-frequency seismic surface waves; (2) the velocity dispersion of a Love wave mode and two Rayleigh wave modes between periods of 2 and 7 sec is well explained by the layering of low-velocity embayment sediments overlying the high-velocity Knox dolomite; (3) because of their strong dispersion, the characteristic basin surface waves can shake the entire embayment for several minutes following any large intra-basin earthquake; (4) excitation of this characteristic basin disturbance seems to be inefficient for strong earthquakes marginal or external to the basin. Lacking direct measurements of shear velocity in the young embayment clastic section, we find that a simple non-linear relationship between shear velocity and logged compressional velocity makes the sediment physical properties compatible with the observed surface wave dispersion.
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O'Neill, A. „Seismic Surface Waves Special Issue Guest Editorial“. Journal of Environmental & Engineering Geophysics 10, Nr. 2 (01.06.2005): 67. http://dx.doi.org/10.2113/jeeg10.2.67.
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Roth, M., K. Holliger und A. G. Green. „Guided waves in near-surface seismic surveys“. Geophysical Research Letters 25, Nr. 7 (01.04.1998): 1071–74. http://dx.doi.org/10.1029/98gl00549.
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Halliday, David, und Andrew Curtis. „Seismic interferometry, surface waves and source distribution“. Geophysical Journal International 175, Nr. 3 (Dezember 2008): 1067–87. http://dx.doi.org/10.1111/j.1365-246x.2008.03918.x.
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Levshin, A. L., M. P. Barmin und M. H. Ritzwoller. „Tutorial review of seismic surface waves’ phenomenology“. Journal of Seismology 22, Nr. 2 (07.12.2017): 519–37. http://dx.doi.org/10.1007/s10950-017-9716-7.
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Preston, Leiph, Christian Poppeliers und David J. Schodt. „Seismic Characterization of the Nevada National Security Site Using Joint Body Wave, Surface Wave, and Gravity Inversion“. Bulletin of the Seismological Society of America 110, Nr. 1 (19.11.2019): 110–26. http://dx.doi.org/10.1785/0120190151.
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ABSTRACT As a part of the series of Source Physics Experiments (SPE) conducted on the Nevada National Security Site in southern Nevada, we have developed a local-to-regional scale seismic velocity model of the site and surrounding area. Accurate earth models are critical for modeling sources like the SPE to investigate the role of earth structure on the propagation and scattering of seismic waves. We combine seismic body waves, surface waves, and gravity data in a joint inversion procedure to solve for the optimal 3D seismic compressional and shear-wave velocity structures and earthquake locations subject to model smoothness constraints. Earthquakes, which are relocated as part of the inversion, provide P- and S-body-wave absolute and differential travel times. Active source experiments in the region augment this dataset with P-body-wave absolute times and surface-wave dispersion data. Dense ground-based gravity observations and surface-wave dispersion derived from ambient noise in the region fill in many areas where body-wave data are sparse. In general, the top 1–2 km of the surface is relatively poorly sampled by the body waves alone. However, the addition of gravity and surface waves to the body-wave dataset greatly enhances structural resolvability in the near surface. We discuss the methodology we developed for simultaneous inversion of these disparate data types and briefly describe results of the inversion in the context of previous work in the region.
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Baker, Gregory S., Don W. Steeples und Chris Schmeissner. „In‐situ, high‐frequency P-wave velocity measurements within 1 m of the earth’s surface“. GEOPHYSICS 64, Nr. 2 (März 1999): 323–25. http://dx.doi.org/10.1190/1.1444537.
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Seismic P-wave velocities in near‐surface materials can be much slower than the speed of sound waves in air (normally 335 m/s or 1100 ft/s). Difficulties often arise when measuring these low‐velocity P-waves because of interference by the air wave and the air‐coupled waves near the seismic source, at least when gathering data with the more commonly used shallow P-wave sources. Additional problems in separating the direct and refracted arrivals within ∼2 m of the source arise from source‐generated nonlinear displacement, even when small energy sources such as sledgehammers, small‐caliber rifles, and seismic blasting caps are used. Using an automotive spark plug as an energy source allowed us to measure seismic P-wave velocities accurately, in situ, from a few decimeters to a few meters from the shotpoint. We were able to observe three distinct P-wave velocities at our test site: ∼130m/s, 180m/s, and 300m/s. Even the third layer, which would normally constitute the first detected layer in a shallow‐seismic‐refraction survey, had a P-wave velocity lower than the speed of sound in air.
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Halliday, David F., Andrew Curtis, Peter Vermeer, Claudio Strobbia, Anna Glushchenko, Dirk-Jan van Manen und Johan O. Robertsson. „Interferometric ground-roll removal: Attenuation of scattered surface waves in single-sensor data“. GEOPHYSICS 75, Nr. 2 (März 2010): SA15—SA25. http://dx.doi.org/10.1190/1.3360948.
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Land seismic data are contaminated by surface waves (or ground roll). These surface waves are a form of source-generated noise and can be strongly scattered by near-surface heterogeneities. The resulting scattered ground roll can be particularly difficult to separate from the desired reflection data, especially when this scattered ground roll propagates in the crossline direction. We have used seismic interferometry to estimate scattered surface waves, recorded during an exploration seismic survey, between pairs of receiver locations. Where sources and receivers coincide, these interreceiver surface-wave estimates were adaptively subtracted from the data. This predictive-subtraction process can successfully attenuate scattered surface waves while preserving the valuable reflected arrivals, forming a new method of scattered ground-roll attenuation. We refer to this as interferometric ground-roll removal.
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Stewart, Robert R. „Rapid map and inversion of P-SV waves“. GEOPHYSICS 56, Nr. 6 (Juni 1991): 859–62. http://dx.doi.org/10.1190/1.1443103.
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Multicomponent seismic recordings are currently being analyzed in an attempt to improve conventional P‐wave sections and to find and use rock properties associated with shear waves (e.g. Dohr, 1985; Danbom and Dominico, 1986). Mode‐converted (P-SV) waves hold a special interest for several reasons: They are generated by conventional P‐wave sources and have only a one‐way travel path as a shear wave through the typically low velocity and attenuative near surface. For a given frequency, they will have a shorter wavelength than the original P wave, and thus offer higher spatial resolution; this has been observed in several vertical seismic profiling (VSP) cases (e.g., Geis et al., 1990). However, for surface seismic data, converted waves are often found to be of lower frequency than P-P waves (e.g., Eaton et al., 1991).
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Edme, Pascal, und David F. Halliday. „Near-surface imaging using ambient-noise body waves“. Interpretation 4, Nr. 3 (01.08.2016): SJ55—SJ65. http://dx.doi.org/10.1190/int-2016-0002.1.
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We have introduced a workflow that allows subsurface imaging using upcoming body-wave arrivals extracted from ambient-noise land seismic data. Rather than using the conventional seismic interferometry approach based on correlation, we have developed a deconvolution technique to extract the earth response from the observed periodicity in the seismic traces. The technique consists of iteratively applying a gapped spiking deconvolution, providing multiple-free images with higher resolution than conventional correlation. We have validated the workflow for zero-offset traces with simple synthetic data and real data recorded during a small point-receiver land seismic survey.
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Campman, Xander H., Gérard C. Herman und Everhard Muyzert. „Suppressing near-receiver scattered waves from seismic land data“. GEOPHYSICS 71, Nr. 4 (Juli 2006): S121—S128. http://dx.doi.org/10.1190/1.2204965.
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Upgoing body waves that travel through a heterogeneous near-surface region can excite scattered waves. When the scattering takes place close to the receivers, secondary waves interfere with the upcoming reflections, diminishing the continuity of the wavefront. We estimate a near-surface scattering distribution from a subset of a data record and use this scattering distribution to predict the secondary waves of the entire data record with a wave-theoretical model for near-receiver scattering. We then subtract the predicted scattered waves from the record to obtain the wavefield that would have been measured in the absence of near-surface heterogeneities. We apply this method to part of a field data set acquired in an area with significant near-surface heterogeneity. The main result of our processing scheme is that we effectively remove near-surface scattered waves. This, in turn, increases trace-to-trace coherence of reflection events. Moreover, application of our method improves the results obtained from just an application of a dip filter because we remove parts of the scattered wave with apparent velocities that are typically accepted by the pass zone of the dip filter. Based on these results, we conclude that our method for suppressing near-receiver scattered waves works well on densely sampled land data collected in areas with strong near-surface heterogeneity.
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Koshevaya, S., N. Makarets, V. Grimalsky, A. Kotsarenko und R. Perez Enríquez. „Spectrum of the seismic-electromagnetic and acoustic waves caused by seismic and volcano activity“. Natural Hazards and Earth System Sciences 5, Nr. 2 (02.02.2005): 203–9. http://dx.doi.org/10.5194/nhess-5-203-2005.
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Abstract. Modeling of the spectrum of the seismo-electromagnetic and acoustic waves, caused by seismic and volcanic activity, has been done. This spectrum includes the Electromagnetic Emission (EME, due to fracturing piezoelectrics in rocks) and the Acoustic Emission (AE, caused by the excitation and the nonlinear passage of acoustic waves through the Earth's crust, the atmosphere, and the ionosphere). The investigated mechanism of the EME uses the model of fracturing and the crack motion. For its analysis, we consider a piezoelectric crystal under mechanical stresses, which cause the uniform crack motion, and, consequently, in the vicinity of the moving crack also cause non-stationary polarization currents. A possible spectrum of EME has been estimated. The underground fractures produce Very Low (VLF) and Extremely Low Frequency (ELF) acoustic waves, while the acoustic waves at higher frequencies present high losses and, on the Earth's surface, they are quite small and are not registered. The VLF acoustic wave is subject to nonlinearity under passage through the lithosphere that leads to the generation of higher harmonics and also frequency down-conversion, namely, increasing the ELF acoustic component on the Earth's surface. In turn, a nonlinear propagation of ELF acoustic wave in the atmosphere and the ionosphere leads to emerging the ultra low frequency (ULF) acousto-gravity waves in the ionosphere and possible local excitation of plasma waves.
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Zhang, Kai, Hongyi Li, Xiaojiang Wang und Kai Wang. „Retrieval of shallow S-wave profiles from seismic reflection surveying and traffic-induced noise“. GEOPHYSICS 85, Nr. 6 (01.11.2020): EN105—EN117. http://dx.doi.org/10.1190/geo2019-0845.1.
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In urban subsurface exploration, seismic surveys are mostly conducted along roads where seismic vibrators can be extensively used to generate strong seismic energy due to economic and environmental constraints. Generally, Rayleigh waves also are excited by the compressional wave profiling process. Shear-wave (S-wave) velocities can be inferred using Rayleigh waves to complement near-surface characterization. Most vibrators cannot excite seismic energy at lower frequencies (<5 Hz) to map greater depths during surface-wave analysis in areas with low S-wave velocities, but low-frequency surface waves ([Formula: see text]) can be extracted from traffic-induced noise, which can be easily obtained at marginal additional cost. We have implemented synthetic tests to evaluate the velocity deviation caused by offline sources, finding a reasonably small relative bias of surface-wave dispersion curves due to vehicle sources on roads. Using a 2D reflection survey and traffic-induced noise from the central North China Plain, we apply seismic interferometry to a series of 10.0 s segments of passive data. Then, each segment is selectively stacked on the acausal-to-causal ratio of the mean signal-to-noise ratio to generate virtual shot gathers with better dispersion energy images. We next use the dispersion curves derived by combining controlled source surveying with vehicle noise to retrieve the shallow S-wave velocity structure. A maximum exploration depth of 90 m is achieved, and the inverted S-wave profile and interval S-wave velocity model obtained from reflection processing appear consistent. The data set demonstrates that using surface waves derived from seismic reflection surveying and traffic-induced noise provides an efficient supplementary technique for delineating shallow structures in areas featuring thick Quaternary overburden. Additionally, the field test indicates that traffic noise can be created using vehicles or vibrators to capture surface waves within a reliable frequency band of 2–25 Hz if no vehicles are moving along the survey line.
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Snieder, Roel, Kees Wapenaar und Ken Larner. „Spurious multiples in seismic interferometry of primaries“. GEOPHYSICS 71, Nr. 4 (Juli 2006): SI111—SI124. http://dx.doi.org/10.1190/1.2211507.
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Seismic interferometry is a technique for estimating the Green’s function that accounts for wave propagation between receivers by correlating the waves recorded at these receivers. We present a derivation of this principle based on the method of stationary phase. Although this derivation is intended to be educational, applicable to simple media only, it provides insight into the physical principle of seismic interferometry. In a homogeneous medium with one horizontal reflector and without a free surface, the correlation of the waves recorded at two receivers correctly gives both the direct wave and the singly reflected waves. When more reflectors are present, a product of the singly reflected waves occurs in the crosscorrelation that leads to spurious multiples when the waves are excited at the surface only. We give a heuristic argument that these spurious multiples disappear when sources below the reflectors are included. We also extend the derivation to a smoothly varying heterogeneous background medium.
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Chmiel, M., A. Mordret, P. Boué, F. Brenguier, T. Lecocq, R. Courbis, D. Hollis, X. Campman, R. Romijn und W. Van der Veen. „Ambient noise multimode Rayleigh and Love wave tomography to determine the shear velocity structure above the Groningen gas field“. Geophysical Journal International 218, Nr. 3 (24.05.2019): 1781–95. http://dx.doi.org/10.1093/gji/ggz237.
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SUMMARY The Groningen gas field is one of the largest gas fields in Europe. The continuous gas extraction led to an induced seismic activity in the area. In order to monitor the seismic activity and study the gas field many permanent and temporary seismic arrays were deployed. In particular, the extraction of the shear wave velocity model is crucial in seismic hazard assessment. Local S-wave velocity-depth profiles allow us the estimation of a potential amplification due to soft sediments. Ambient seismic noise tomography is an interesting alternative to traditional methods that were used in modelling the S-wave velocity. The ambient noise field consists mostly of surface waves, which are sensitive to the Swave and if inverted, they reveal the corresponding S-wave structures. In this study, we present results of a depth inversion of surface waves obtained from the cross-correlation of 1 month of ambient noise data from four flexible networks located in the Groningen area. Each block consisted of about 400 3-C stations. We compute group velocity maps of Rayleigh and Love waves using a straight-ray surface wave tomography. We also extract clear higher modes of Love and Rayleigh waves. The S-wave velocity model is obtained with a joint inversion of Love and Rayleigh waves using the Neighbourhood Algorithm. In order to improve the depth inversion, we use the mean phase velocity curves and the higher modes of Rayleigh and Love waves. Moreover, we use the depth of the base of the North Sea formation as a hard constraint. This information provides an additional constraint for depth inversion, which reduces the S-wave velocity uncertainties. The final S-wave velocity models reflect the geological structures up to 1 km depth and in perspective can be used in seismic risk modelling.
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Gualtieri, Lucia, Etienne Bachmann, Frederik J. Simons und Jeroen Tromp. „The origin of secondary microseism Love waves“. Proceedings of the National Academy of Sciences 117, Nr. 47 (09.11.2020): 29504–11. http://dx.doi.org/10.1073/pnas.2013806117.
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The interaction of ocean surface waves produces pressure fluctuations at the seafloor capable of generating seismic waves in the solid Earth. The accepted mechanism satisfactorily explains secondary microseisms of the Rayleigh type, but it does not justify the presence of transversely polarized Love waves, nevertheless widely observed. An explanation for two-thirds of the worldwide ambient wave field has been wanting for over a century. Using numerical simulations of global-scale seismic wave propagation at unprecedented high frequency, here we explain the origin of secondary microseism Love waves. A small fraction of those is generated by boundary force-splitting at bathymetric inclines, but the majority is generated by the interaction of the seismic wave field with three-dimensional heterogeneity within the Earth. We present evidence for an ergodic model that explains observed seismic wave partitioning, a requirement for full-wave field ambient-noise tomography to account for realistic source distributions.
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Ungureanu, Bogdan, Sebastien Guenneau, Younes Achaoui, Andre Diatta, Mohamed Farhat, Harsha Hutridurga, Richard V. Craster, Stefan Enoch und Stephane Brûlé. „The influence of building interactions on seismic and elastic body waves“. EPJ Applied Metamaterials 6 (2019): 18. http://dx.doi.org/10.1051/epjam/2019015.
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We outline some recent research advances on the control of elastic waves in thin and thick plates, that have occurred since the large scale experiment [S. Brûlé, Phys. Rev. Lett. 112, 133901 (2014)] that demonstrated significant interaction of surface seismic waves with holes structuring sedimentary soils at the meter scale. We further investigate the seismic wave trajectories of compressional body waves in soils structured with buildings. A significant substitution of soils by inclusions, acting as foundations, raises the question of the effective dynamic properties of these structured soils. Buildings, in the case of perfect elastic conditions for both soil and buildings, are shown to interact and strongly influence elastic body waves; such site-city seismic interactions were pointed out in [Guéguen et al., Bull. Seismol. Soc. Am. 92, 794–811 (2002)], and we investigate a variety of scenarios to illustrate the variety of behaviours possible.
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Ji-Xiang, XU. „Separating the Near-Surface Seismic Scattered Waves Using Seismic Interferometry Method“. Chinese Journal of Geophysics 57, Nr. 4 (Juli 2014): 574–90. http://dx.doi.org/10.1002/cjg2.20125.
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Blonk, Bastian, Gerard C. Herman und Guy G. Drijkoningen. „An elastodynamic inverse scattering method for removing scattered surface waves from field data“. GEOPHYSICS 60, Nr. 6 (November 1995): 1897–905. http://dx.doi.org/10.1190/1.1443921.
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In an earlier paper, we introduced a 3-D inverse scattering method for removing scattered surface waves from seismic data that was based on a tomographic imaging of the scattered surface waves by a data‐fitting procedure that used as much of the seismic data as possible. After this imaging step, the scattered surface waves can be computed and removed for each separate source‐receiver pair. We now apply the method to two field‐data sets. The method requires a knowledge of the source waveform and shallow propagation characteristics, and these input requirements are estimated from the direct surface wave. We conclude that the method effectively attenuates crossline scattered surface waves without affecting deeper reflections.
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Feng, Z. „The seismic signatures of the 2009 Shiaolin landslide in Taiwan“. Natural Hazards and Earth System Sciences 11, Nr. 5 (25.05.2011): 1559–69. http://dx.doi.org/10.5194/nhess-11-1559-2011.
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Abstract. The Shiaolin landslide occurred on 9 August 2009 after Typhoon Morakot struck Taiwan, claiming over 400 lives. The seismic signals produced by the landslide were recorded by broadband seismic stations in Taiwan. The time-frequency spectra for these signals were obtained by the Hilbert-Huang transform (HHT) and were analyzed to obtain the seismic characteristics of the landslide. Empirical mode decomposition (EMD) was applied to differentiate weak surface-wave signals from noise and to estimate the surface-wave velocities in the region. The surface-wave velocities were estimated using the fifth intrinsic mode function (IMF 5) obtained from the EMD. The spectra of the earthquake data were compared. The main frequency content of the seismic waves caused by the Shiaolin landslide were in the range of 0.5 to 1.5 Hz. This frequency range is smaller than the frequency ranges of other earthquakes. The spectral analysis of surface waves (SASW) method is suggested for characterizing the shear-wave velocities of the strata in the region.
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Ching, Dennis Ling Chuan, Zainal Abdul Aziz und Faisal Salah. „Study of Polarized Wave with a Hydrodynamic Model and Fourier Spectral Method“. Modelling and Simulation in Engineering 2013 (2013): 1–6. http://dx.doi.org/10.1155/2013/720590.
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The polarization effects in hydrodynamics are studied. Hydrodynamic equation for the nonlinear wave is used along with the polarized nonlinear waves and seismic waves act as initial waves. The model is then solved by Fourier spectral and Runge-Kutta 4 methods, and the surface plot is drawn. The output demonstrates the inundation behaviors. Consequently, the polarized seismic waves along with the polarized nonlinear waves tend to generate dissimilar inundation which is more disastrous.
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Wilson, Joshua. „Modeling Microseism Generation by Inhomogeneous Ocean Surface Waves in Hurricane Bonnie Using the Non-Linear Wave Equation“. Remote Sensing 10, Nr. 10 (12.10.2018): 1624. http://dx.doi.org/10.3390/rs10101624.
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It has been shown that hurricanes generate seismic noise, called microseisms, through the creation and non-linear interaction of ocean surface waves. Here we model microseisms generated by the spatially inhomogeneous waves of a hurricane using the non-linear wave equation where a second-order acoustic field is created by first-order ocean surface wave motion. We treat range-dependent waveguide environments to account for microseisms that propagate from the deep ocean to a receiver on land. We compare estimates based on the ocean surface wave field measured in hurricane Bonnie in 1998 with seismic measurements made roughly 1000 km away in Florida.
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Devaney, A. J., und M. L. Oristaglio. „A plane‐wave decomposition for elastic wave fields applied to the separation of P‐waves and S‐waves in vector seismic data“. GEOPHYSICS 51, Nr. 2 (Februar 1986): 419–23. http://dx.doi.org/10.1190/1.1442102.
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We describe a method to decompose a two‐dimensional (2-D) elastic wave field recorded along a line into its longitudinal and transverse parts, that is, into compressional (P) waves and shear (S) waves. Separation of the data into P-waves and S-waves is useful when analyzing vector seismic measurements along surface lines or in boreholes. The method described is based on a plane‐wave expansion for elastic wave fields and is illustrated with a synthetic example of an offset vertical seismic profile (VSP) in a layered elastic medium.
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Donohue, Shane, Dermot Forristal und Louise A. Donohue. „Detection of soil compaction using seismic surface waves“. Soil and Tillage Research 128 (April 2013): 54–60. http://dx.doi.org/10.1016/j.still.2012.11.001.
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Campman, Xander, und Christina Dwi Riyanti. „Non-linear inversion of scattered seismic surface waves“. Geophysical Journal International 171, Nr. 3 (14.09.2007): 1118–25. http://dx.doi.org/10.1111/j.1365-246x.2007.03557.x.
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Wapenaar, C. P. A., G. L. Peels, V. Budejicky und A. J. Berkhout. „Inverse extrapolation of primary seismic waves“. GEOPHYSICS 54, Nr. 7 (Juli 1989): 853–63. http://dx.doi.org/10.1190/1.1442714.
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Forward wave‐field extrapolation operators simulate propagation effects from one depth level to another. Inverse wave‐field extrapolation operators eliminate those propagation effects. Since forward wave‐field extrapolation can be described in terms of spatial convolution, inverse wave‐field extrapolation can be described in terms of spatial deconvolution. A simple approximation to a stable, spatially band‐limited deconvolution operator is obtained by taking the complex conjugate of the convolution operator. A one‐way version of the Kirchhoff integral that contains the conjugate complex Green’s function is derived. Unlike the situation with respect to the forward problem, the modification of the closed surface integral into an open boundary integral involves an approximation that is identical to the approximation in the conjugate complex deconvolution approach. This approximation neglects the evanescent field and causes a second‐order amplitude error. For a plane acquisition surface, the one‐way Kirchhoff integral is transformed into a one‐way Rayleigh integral. For media with small to moderate contrasts, the one‐way Rayleigh integral with the conjugate complex Green’s function describes true amplitude inverse extrapolation of primary waves. This is illustrated with an example, in which the Green’s function has been modeled with the Gaussian beam method.
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Hong, Seokgyeong, und Jaehun Ahn. „Seismic Ground Response Analysis Based on Multilayer Perceptron and Convolution Neural Networks“. Journal of the Korean Society of Hazard Mitigation 21, Nr. 1 (28.02.2021): 231–38. http://dx.doi.org/10.9798/kosham.2021.21.1.231.
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The importance of establishing a disaster prevention plan considering seismic performance is being highlighted to reduce damage to structures caused by earthquakes. Earthquake waves propagate from the bedrock to the ground surface through the soil. During the transmission process, they are amplified in a specific frequency range, and the degree of amplification depends mainly on the characteristics of the ground. Therefore, a seismic response analysis process is essential for enhancing the reliability of the seismic design. We propose a model for predicting seismic waves on the surface from seismic waves measured on the bedrock based on Multilayer Perceptron (MLP) and Convolutional Neural Networks (CNN) and validate the applicability of the proposed model with Spectral Acceleration (SA). Both the proposed models based on MLP and CNN successfully predicted the seismic response of the surface. The CNN-based model performed better than the MLP-based model, with a 10% smaller average error. We plan to implement the physical properties of the ground, such as shear wave velocity, to create a more versatile model in the future.
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Guo, Peng, Huimin Guan und George A. McMechan. „Data- and model-domain up/down wave separation for reverse-time migration with free-surface multiples“. Geophysical Journal International 223, Nr. 1 (18.06.2020): 77–93. http://dx.doi.org/10.1093/gji/ggaa301.
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SUMMARY Seismic data recorded using a marine acquisition geometry contain both upgoing reflections from subsurface structures and downgoing ghost waves reflected back from the free surface. In addition to the ambiguity of propagation directions in the data, using the two-way wave equation for wavefield extrapolation of seismic imaging generates backscattered/turned waves when there are strong velocity contrasts/gradients in the model, which further increases the wavefield complexity. For reverse-time migration (RTM) of free-surface multiples, apart from unwanted crosstalk between inconsistent orders of reflections, image artefacts can also be formed along with the true reflector images from the overlapping of up/downgoing waves in the data and in the extrapolated wavefield. We present a wave-equation-based, hybrid (data- and model-domain) wave separation workflow, with vector seismic data containing pressure- and vertical-component particle velocity from dual-sensor seismic acquisition, for removing image artefacts produced by the mixture of up/downgoing waves. For imaging with free-surface multiples, the wavefield extrapolated from downgoing ghost events (reflected from the free surface) in the recorded data act as an effective source wavefield for one-order-higher free-surface multiples. Therefore, only the downgoing waves in the data should be used as the source wavefield for RTM with multiples; the recorded upgoing waves in the seismograms will be used for extrapolation of the time-reversed receiver wavefield. We use finite-difference (FD) injection for up/down separation in the data domain, to extrapolate the down- and upgoing waves of the common-source gathers for source and receiver wavefield propagation, respectively. The model-domain separation decomposes the extrapolated wavefield into upgoing (backscattered) and downgoing (transmitted) components at each subsurface grid location, to remove false images produced by cross-correlating backscattered waves along unphysical paths. We combine FD injection with the model-domain wavefield separation, for separating the wavefield into up- and downgoing components for the recorded data and for the extrapolated wavefields. Numerical examples using a simple model, and the Sigsbee 2B model, demonstrate that the hybrid up/down separation approach can effectively produce seismic images of free-surface multiples with better resolution and fewer artefacts.
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Mordret, Aurélien, Roméo Courbis, Florent Brenguier, Małgorzata Chmiel, Stéphane Garambois, Shujuan Mao, Pierre Boué et al. „Noise-based ballistic wave passive seismic monitoring – Part 2: surface waves“. Geophysical Journal International 221, Nr. 1 (18.02.2020): 692–705. http://dx.doi.org/10.1093/gji/ggaa016.
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SUMMARY We develop a new method to monitor and locate seismic velocity changes in the subsurface using seismic noise interferometry. Contrary to most ambient noise monitoring techniques, we use the ballistic Rayleigh waves computed from 30 d records on a dense nodal array located above the Groningen gas field (the Netherlands), instead of their coda waves. We infer the daily relative phase velocity dispersion changes as a function of frequency and propagation distance with a cross-wavelet transform processing. Assuming a 1-D velocity change within the medium, the induced ballistic Rayleigh wave phase shift exhibits a linear trend as a function of the propagation distance. Measuring this trend for the fundamental mode and the first overtone of the Rayleigh waves for frequencies between 0.5 and 1.1 Hz enables us to invert for shear wave daily velocity changes in the first 1.5 km of the subsurface. The observed deep velocity changes (±1.5 per cent) are difficult to interpret given the environmental factors information available. Most of the observed shallow changes seem associated with effective pressure variations. We observe a reduction of shear wave velocity (–0.2 per cent) at the time of a large rain event accompanied by a strong decrease in atmospheric pressure loading, followed by a migration at depth of the velocity decrease. Combined with P-wave velocity changes observations from a companion paper, we interpret the changes as caused by the diffusion of effective pressure variations at depth. As a new method, noise-based ballistic wave passive monitoring could be used on several dynamic (hydro-)geological targets and in particular, it could be used to estimate hydrological parameters such as the hydraulic conductivity and diffusivity.
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Garambois, S., C. Voisin, M. A. Romero Guzman, D. Brito, B. Guillier und A. Réfloch. „Analysis of ballistic waves in seismic noise monitoring of water table variations in a water field site: added value from numerical modelling to data understanding“. Geophysical Journal International 219, Nr. 3 (02.09.2019): 1636–47. http://dx.doi.org/10.1093/gji/ggz391.
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SUMMARY Passive seismic interferometry allows to track continuously the weak seismic velocity changes in any medium by correlating the ambient seismic noise between two points to reconstruct the Green’s function. The ballistic surface waves of the reconstructed Green’s functions are used to monitor the changes of water table induced by a controlled experiment in the Crépieux-Charmy (France) exploitation field. Viscoelastic numerical modelling of the monitoring experiment reproduces quite satisfactorily the sensitivity of the surface waves to the water table previously observed with seismic noise data. This numerical approach points out that this sensitivity is controlled by mode mixing of Rayleigh waves. It also made it possible to identify the refracted P wave and to extract its anticorrelated sensitivity to water table variations. Depending on the offset between receivers, it was observed numerically that the interferences between the different waves (with different velocities) composing the seismic wavefield slightly affect the quantitative sensitivity to water table changes. This suggests the use of an optimal spatial and temporal observation window for which wave interference is minor and does not blur the quantitative response to water table variations. We were thus able to determine the relationship between velocity and water table variations for all waves involved. From numerical computations, we identify a weak signal-to-noise ratio phase in the noise correlograms, with a anticorrelated sensitivity to the water table: the reconstructed refracted waves.