Near-surface Q Estimation from Surface Waves and Compensation for its Effects on Body Waves

We tested a small-scale experiment that is dedicated to the study of the wave separation algorithm and to the velocity variations monitoring problem itself. It handles the case in which velocity variations at depth are hidden by near-surface velocity fluctuations. Using an acquisition system that combines an array of sources and an array of receivers, coupled with controlled velocity variations, we tested the ability of beam-forming techniques to track velocity variations separately for body waves and surface waves. After wave separation through double beam forming, the arrival time variations of the different waves were measured through the phase difference between the extracted wavelets. Finally, a method was tested to estimate near-surface velocity variations using surface waves or shallow reflection and compute a correction to isolate target velocity variations at depth.

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Imaging and suppressing near-receiver scattered surface waves

Geophysics ◽

10.1190/1.1884831 ◽

2005 ◽

Vol 70 (2) ◽

pp. V21-V29 ◽

Cited By ~ 43

Author(s):

Xander H. Campman ◽

Kasper van Wijk ◽

John A. Scales ◽

Gérard C. Herman

Keyword(s):

Surface Waves ◽

Single Channel ◽

Laboratory Data ◽

Body Waves ◽

Surface Model ◽

Imaging Method ◽

Sampled Data ◽

Impedance Function ◽

Near Surface ◽

Integral Equation Formulation

When traveling through a complex overburden, upcoming seismic body waves can be disturbed by scattering from local heterogeneities. Currently, surface-consistent static and amplitude corrections correct for rapid variations in arrival times and amplitudes of a reflector, but these methods impose strong assumptions on the near-surface model. Observations on synthetic and laboratory experiments of near-surface scattering with densely sampled data suggest that removing noise from near-receiver scattering requires multichannel approaches rather than single-channel, near-surface corrections. In this paper we develop a wavefield-based imaging method to suppress surface waves scattered directly beneath the receivers. Using an integral-equation formulation, we account for near-surface heterogeneities by a surface impedance function. This impedance function is used to model scattered surface waves, excited by upcoming wavefronts. The final step in our algorithm is to subtract the scattered surface waves. We successfully apply this method to laboratory data of scattered surface waves, excited and monitored with a noncontacting acquisition system.

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Numerical modeling of elastic-wave scattering by near-surface heterogeneities

Geophysics ◽

10.1190/geo2013-0208.1 ◽

2014 ◽

Vol 79 (4) ◽

pp. T199-T217 ◽

Cited By ~ 8

Author(s):

Abdulaziz M. Almuhaidib ◽

M. Nafi Toksöz

Keyword(s):

Surface Waves ◽

Wave Scattering ◽

Attenuation Factor ◽

Surface Characteristics ◽

Body Waves ◽

Incident Wavelength ◽

Near Surface ◽

Seismic Image ◽

Weak Surface

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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Seismic Characterization of the Nevada National Security Site Using Joint Body Wave, Surface Wave, and Gravity Inversion

Bulletin of the Seismological Society of America ◽

10.1785/0120190151 ◽

2019 ◽

Vol 110 (1) ◽

pp. 110-126

Author(s):

Leiph Preston ◽

Christian Poppeliers ◽

David J. Schodt

Keyword(s):

Surface Wave ◽

National Security ◽

Surface Waves ◽

Body Wave ◽

Wave Dispersion ◽

The Body ◽

Body Waves ◽

Gravity Inversion ◽

Surface Wave Dispersion ◽

Near Surface

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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DISPERSION IN SEISMIC SURFACE WAVES

Geophysics ◽

10.1190/1.1437652 ◽

1951 ◽

Vol 16 (1) ◽

pp. 63-80 ◽

Cited By ~ 26

Author(s):

Milton B. Dobrin

Keyword(s):

Surface Waves ◽

Water Waves ◽

Seismic Refraction ◽

Wave Theory ◽

Wave Dispersion ◽

Surface Zone ◽

Surface Wave Dispersion ◽

Near Surface ◽

Arrival Times ◽

Ground Roll

A non‐mathematical summary is presented of the published theories and observations on dispersion, i.e., variation of velocity with frequency, in surface waves from earthquakes and in waterborne waves from shallow‐water explosions. Two further instances are cited in which dispersion theory has been used in analyzing seismic data. In the seismic refraction survey of Bikini Atoll, information on the first 400 feet of sediments below the lagoon bottom could not be obtained from ground wave first arrival times because shot‐detector distances were too great. Dispersion in the water waves, however, gave data on speed variations in the bottom sediments which made possible inferences on the recent geological history of the atoll. Recent systematic observations on ground roll from explosions in shot holes have shown dispersion in the surface waves which is similar in many ways to that observed in Rayleigh waves from distant earthquakes. Classical wave theory attributes Rayleigh wave dispersion to the modification of the waves by a surface layer. In the case of earthquakes, this layer is the earth’s crust. In the case of waves from shot‐holes, it is the low‐speed weathered zone. A comparison of observed ground roll dispersion with theory shows qualitative agreement, but it brings out discrepancies attributable to the fact that neither the theory for liquids nor for conventional solids applies exactly to unconsolidated near‐surface rocks. Additional experimental and theoretical study of this type of surface wave dispersion may provide useful information on the properties of the surface zone and add to our knowledge of the mechanism by which ground roll is generated in seismic shooting.

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Joint Inversion Scheme of Dispersive Surface Waves for Near-surface Structure Estimation

10.1190/nsapc2015-069 ◽

2015 ◽

Author(s):

Tongju Gong* ◽

Miao Liu ◽

Yiming Wang ◽

Zhiwei Zhu ◽

Baoqing Zhang

Keyword(s):

Surface Waves ◽

Surface Structure ◽

Joint Inversion ◽

Near Surface ◽

Structure Estimation

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Azimuthal multiple signal classification of dispersive and aliased surface waves recorded in 3D seismic acquisition

Geophysics ◽

10.1190/geo2020-0417.1 ◽

2021 ◽

pp. 1-84

Author(s):

Chunying Yang ◽

Wenchuang Wang

Keyword(s):

Surface Wave ◽

Surface Waves ◽

Body Waves ◽

Signal Classification ◽

Dispersion Pattern ◽

Velocity Spectrum ◽

Low Velocity ◽

Surface Wave Dispersion ◽

Multiple Signal Classification ◽

Multiple Signal

Irregular acquisition geometry causes discontinuities in the appearance of surface wave events, and a large offset causes seismic records to appear as aliased surface waves. The conventional method of sampling data affects the accuracy of the dispersion spectrum and reduces the resolution of surface waves. At the same time, mode kissing of the low-velocity layer and inhomogeneous scatterers requires a high-resolution method for calculating surface wave dispersion. This study tested the use of the multiple signal classification (MUSIC) algorithm in 3D multichannel and aliased wavefield separation. Azimuthal MUSIC is a useful method to estimate the phase velocity spectrum of aliased surface wave data, and it represent the dispersion spectra of low-velocity and inhomogeneous models. The results of this study demonstrate that mode-kissing affects dispersion imaging, and inhomogeneous scatterers change the direction of surface-wave propagation. Surface waves generated from the new propagation directions are also dispersive. The scattered surface wave has a new dispersion pattern different to that of the entire record. Diagonal loading was introduced to improve the robustness of azimuthal MUSIC, and numerical experiments demonstrate the resultant effectiveness of imaging aliasing surface waves. A phase-matched filter was applied to the results of azimuthal MUSIC, and phase iterations were unwrapped in a fast and stable manner. Aliased surface waves and body waves were separated during this process. Overall, field data demonstrate that azimuthal MUSIC and phase-matched filters can successfully separate aliased surface waves.

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The rupture process and aftershock distribution of the 6 April 1992 MS 6.8 earthquake, Offshore British Columbia

Bulletin of the Seismological Society of America ◽

10.1785/bssa0850030716 ◽

1995 ◽

Vol 85 (3) ◽

pp. 716-735 ◽

Cited By ~ 1

Author(s):

John F. Cassidy ◽

Garry C. Rogers

Keyword(s):

Surface Waves ◽

Triple Junction ◽

Rupture Process ◽

Body Waves ◽

Ocean Bottom Seismometer ◽

Strain Accumulation ◽

Transform Fault ◽

Junction Region ◽

Long Period ◽

Initial Rupture

Abstract On 6 April 1992, a magnitude 6.8 (MS) earthquake occurred in the triple-junction region at the northern end of the Cascadia subduction zone. This was the largest earthquake in at least 75 yr to occur along the 110-km-long Revere-Dellwood-Wilson (RDW) transform fault and the first large earthquake in this region recorded by modern broadband digital seismic networks. It thus provides an opportunity to examine the rupture process along a young (<2 Ma) oceanic transform fault and to gain better insight into the tectonics of this triple-junction region. We have investigated the source parameters and the rupture process of this earthquake by modeling broadband body waves and long-period surface waves and by accurately locating the mainshock and the first 10 days of aftershocks using a well-located “calibration” event recorded during an ocean-bottom seismometer survey. Analysis of P and SH waveforms reveals that this was a complex rupture sequence consisting of three strike-slip subevents in 12 sec. The initial rupture occurred 5 to 6 km to the SW of the seafloor trace of the RDW fault at 50.55° N, 130.46° W. The dominant subevent occurred 2 to 3 sec later and 4.3 km beneath the seafloor trace of the RDW fault, and a third subevent occurred 5 sec later, 18 km to the NNW, suggesting a northwestward propagating rupture. The aftershock sequence extended along a 60- to 70-km-long segment of the RDW fault, with the bulk of the activity concentrated ∼30 to 40 km to the NNW of the epicenter, consistent with this interpretation. The well-constrained mechanism of the initial rupture (strike/dip/slip 339°/90°/−168°) and of the largest aftershock (165°/80°/170°) are rotated 15° to 20° clockwise relative to the seafloor trace of the RDW fault but are parallel to the Pacific/North America relative plate motion vector. In contrast, the mechanisms of the dominant subevent (326°/87°/−172°), and the long-period solution derived from surface waves aligns with the RDW fault. This suggests that small earthquakes (M < 6) in this area occur along faults that are optimally aligned with respect to the regional stress field, whereas large earthquakes, involving tens of kilometers of rupture, activate the RDW fault. For the mainshock, we estimate a seismic moment (from surface waves) of 1.0 × 1026 dyne-cm, a stress drop of 60 bars, and an average slip of 1.2 m. This represents only 21 yr of strain accumulation, implying that there is either a significant amount of aseismic slip along the RDW fault or that much of the strain accumulation manifests itself as deformation within the Dellwood and Winona blocks or along the continental margin.

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Onset of energy equipartition among surface and body waves

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2020.0775 ◽

2021 ◽

Vol 477 (2246) ◽

pp. 20200775

Author(s):

L. Borcea ◽

J. Garnier ◽

K. Sølna

Keyword(s):

Radiative Transfer ◽

Thin Layer ◽

Surface Waves ◽

Transfer Equation ◽

Radiative Transfer Equation ◽

Body Waves ◽

Homogeneous Layer ◽

Power Exchange ◽

Energy Equipartition ◽

The Mean

We derive a radiative transfer equation that accounts for coupling from surface waves to body waves and the other way around. The model is the acoustic wave equation in a two-dimensional waveguide with reflecting boundary. The waveguide has a thin, weakly randomly heterogeneous layer near the top surface, and a thick homogeneous layer beneath it. There are two types of modes that propagate along the axis of the waveguide: those that are almost trapped in the thin layer, and thus model surface waves, and those that penetrate deep in the waveguide, and thus model body waves. The remaining modes are evanescent waves. We introduce a mathematical theory of mode coupling induced by scattering in the thin layer, and derive a radiative transfer equation which quantifies the mean mode power exchange. We study the solution of this equation in the asymptotic limit of infinite width of the waveguide. The main result is a quantification of the rate of convergence of the mean mode powers toward equipartition.

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Short-period seismic noise

Bulletin of the Seismological Society of America ◽

10.1785/bssa0570010055 ◽

1967 ◽

Vol 57 (1) ◽

pp. 55-81

Author(s):

E. J. Douze

Keyword(s):

Surface Waves ◽

Rayleigh Waves ◽

Seismic Noise ◽

Body Waves ◽

Deep Hole ◽

Period Range ◽

Short Period ◽

The Subject ◽

Hole Arrays

abstract This report consists of a summary of the studies conducted on the subject of short-period (6.0-0.3 sec period) noise over a period of approximately three years. Information from deep-hole and surface arrays was used in an attempt to determine the types of waves of which the noise is composed. The theoretical behavior of higher-mode Rayleigh waves and of body waves as measured by surface and deep-hole arrays is described. Both surface and body waves are shown to exist in the noise. Surface waves generally predominate at the longer periods (of the period range discussed) while body waves appear at the shorter periods at quiet sites. Not all the data could be interpreted to define the wave types present.

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