Converted‐wave seismic exploration: Applications

Converted seismic waves (specifically, downgoing P‐waves that convert on reflection to upcoming S‐waves are increasingly being used to explore for subsurface targets. Rapid advancements in both land and marine multicomponent acquisition and processing techniques have led to numerous applications for P‐S surveys. Uses that have arisen include structural imaging (e.g., “seeing” through gas‐bearing sediments, improved fault definition, enhanced near‐surface resolution), lithologic estimation (e.g., sand versus shale content, porosity), anisotropy analysis (e.g., fracture density and orientation), subsurface fluid description, and reservoir monitoring. Further applications of P‐S data and analysis of other more complicated converted modes are developing.

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A simple method for resolving large converted‐wave (P-SV) statics

Geophysics ◽

10.1190/1.1443426 ◽

1993 ◽

Vol 58 (3) ◽

pp. 429-433 ◽

Cited By ~ 27

Author(s):

Peter W. Cary ◽

David W. S. Eaton

Keyword(s):

P Wave ◽

S Wave ◽

Converted Wave ◽

P Waves ◽

Simple Method ◽

Near Surface ◽

S Waves ◽

Static Solutions ◽

Surface Fluctuations

The processing of converted‐wave (P-SV) seismic data requires certain special considerations, such as commonconversion‐point (CCP) binning techniques (Tessmer and Behle, 1988) and a modified normal moveout formula (Slotboom, 1990), that makes it different for processing conventional P-P data. However, from the processor’s perspective, the most problematic step is often the determination of residual S‐wave statics, which are commonly two to ten times greater than the P‐wave statics for the same location (Tatham and McCormack, 1991). Conventional residualstatics algorithms often produce numerous cycle skips when attempting to resolve very large statics. Unlike P‐waves, the velocity of S‐waves is virtually unaffected by near‐surface fluctuations in the water table (Figure 1). Hence, the P‐wave and S‐wave static solutions are largely unrelated to each other, so it is generally not feasible to approximate the S‐wave statics by simply scaling the known P‐wave static values (Anno, 1986).

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Shallow near-surface effects

Geophysics ◽

10.1190/geo2016-0028.1 ◽

2016 ◽

Vol 81 (5) ◽

pp. T221-T231 ◽

Cited By ~ 1

Author(s):

Christine E. Krohn ◽

Thomas J. Murray

Keyword(s):

Time Delay ◽

Velocity Gradient ◽

P Wave ◽

Unconsolidated Sediments ◽

P Waves ◽

Large Computer ◽

Near Surface ◽

S Waves ◽

High Attenuation ◽

Pulse Broadening

The top 6 m of the near surface has a surprisingly large effect on the behavior of P- and S-waves. For unconsolidated sediments, the P-wave velocity gradient and attenuation can be quite large. Computer modeling should include these properties to accurately reproduce seismic effects of the near surface. We have used reverse VSP data and computer simulations to demonstrate the following effects for upgoing P-waves. Near the surface, we have observed a large time delay, indicating low velocity ([Formula: see text]), and considerable pulse broadening, indicating high attenuation ([Formula: see text]). Consequently, shallowly buried geophones have greater high-frequency bandwidth compared with surface geophones. In addition, there is a large velocity gradient in the shallow near surface (factor of 10 in 5 m), resulting in the rotation of P-waves to the vertical with progressively smaller amplitudes recorded on horizontal phones. Finally, we have found little indication of a reflection or ghost from the surface, although downgoing reflections have been observed from interfaces within the near surface. In comparison, the following have been observed for upgoing S-waves: There is a small increase in the time delay or pulse broadening near the surface, indicating a smaller velocity gradient and less change in attenuation. In addition, the surface reflection coefficient is nearly one with a prominent surface ghost.

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Robust Empirical Time–Frequency Relations for Seismic Spectral Amplitudes, Part 1: Application to Regional S Waves in Southeastern Iran

Bulletin of the Seismological Society of America ◽

10.1785/0120200172 ◽

2020 ◽

Cited By ~ 2

Author(s):

Maryam Safarshahi ◽

Igor B. Morozov

Keyword(s):

Seismic Waves ◽

Joint Inversion ◽

Vertical Component ◽

Transverse Component ◽

Model Parameters ◽

S Wave ◽

Near Surface ◽

S Waves ◽

Time Frequency ◽

Frequency Independent

ABSTRACT Empirical models of geometrical-, Q-, t-star, and kappa-type attenuation of seismic waves and ground-motion prediction equations (GMPEs) are viewed as cases of a common empirical standard model describing variation of wave amplitudes with time and frequency. Compared with existing parametric and nonparametric approaches, several new features are included in this model: (1) flexible empirical parameterization with possible nonmonotonous time or distance dependencies; (2) joint inversion for time or distance and frequency dependencies, source spectra, site responses, kappas, and Q; (3) additional constraints removing spurious correlations of model parameters and data residuals with source–receiver distances and frequencies; (4) possible kappa terms for sources as well as for receivers; (5) orientation-independent horizontal- and three-component amplitudes; and (6) adaptive filtering to reduce noise effects. The approach is applied to local and regional S-wave amplitudes in southeastern Iran. Comparisons with previous studies show that conventional attenuation models often contain method-specific biases caused by limited parameterizations of frequency-independent amplitude decays and assumptions about the models, such as smoothness of amplitude variations. Without such assumptions, the frequency-independent spreading of S waves is much faster than inferred by conventional modeling. For example, transverse-component amplitudes decrease with travel time t as about t−1.8 at distances closer than 90 km and as t−2.5 beyond 115 km. The rapid amplitude decay at larger distances could be caused by scattering within the near surface. From about 90 to 115 km distances, the amplitude increases by a factor of about 3, which could be due to reflections from the Moho and within the crust. With more accurate geometrical-spreading and kappa models, the Q factor for the study area is frequency independent and exceeds 2000. The frequency-independent and Q-type attenuation for vertical-component and multicomponent amplitudes is somewhat weaker than for the horizontal components. These observations appear to be general and likely apply to other areas.

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Imaging beneath a high‐velocity layer using converted waves

Geophysics ◽

10.1190/1.1443212 ◽

1992 ◽

Vol 57 (11) ◽

pp. 1444-1452 ◽

Cited By ~ 33

Author(s):

Guy W. Purnell

Keyword(s):

High Velocity ◽

Energy Partitioning ◽

P Wave ◽

Converted Wave ◽

P Waves ◽

Lower Velocity ◽

S Waves ◽

High Velocity Layer ◽

The Waves ◽

Velocity Layer

High‐velocity layers (HVLs) often hinder seismic imaging of deeper reflectors using conventional techniques. A major factor is often the unusual energy partitioning of waves incident at an HVL boundary from lower‐velocity material. Using elastic physical modeling, I demonstrate that one effect of this factor is to limit the range of dips beneath an HVL that can be imaged using unconverted P‐wave arrivals. At the same time, however, partitioning may also result in P‐waves outside the HVL coupling efficiently with S‐waves inside. By exploiting some of the waves that convert upon transmission into and/or out of the physical‐model HVL, I am able to image a much broader range of underlying dips. This is accomplished by acoustic migration tailored (via the migration velocities used) for selected families of converted‐wave arrivals.

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4. Seismic waves

Waves: A Very Short Introduction ◽

10.1093/actrade/9780198803782.003.0004 ◽

2018 ◽

pp. 53-61

Author(s):

Mike Goldsmith

Keyword(s):

Seismic Wave ◽

Rayleigh Waves ◽

Seismic Waves ◽

Shear Waves ◽

Free Vibrations ◽

Love Waves ◽

Sound Waves ◽

P Waves ◽

Tectonic Plates ◽

S Waves

Sound waves travel very easily underground, often for many thousands of kilometres. These are usually referred to as a kind of seismic wave and are most often triggered by earthquakes, which result from a sudden slip of tectonic plates, down to about 700 kilometres below the Earth’s surface. ‘Seismic waves’ describes the four types of seismic wave generated by earthquakes: P-waves (primary waves), S-waves (shear waves), Love waves (usually the most powerful and destructive of seismic waves), and Rayleigh waves, which are created when P and S waves reach the Earth’s surface together, combining to form undulating ground rolls. Free vibrations and star waves are also described.

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Seismic vertical transversely isotropic parameter inversion from P- and S-wave cross-borehole measurements in an aquifer environment

Geophysics ◽

10.1190/geo2018-0335.1 ◽

2019 ◽

Vol 84 (3) ◽

pp. D101-D116

Author(s):

Julius K. von Ketelhodt ◽

Musa S. D. Manzi ◽

Raymond J. Durrheim ◽

Thomas Fechner

Keyword(s):

Transversely Isotropic ◽

P Wave ◽

Perturbation Equation ◽

S Wave ◽

P Waves ◽

Data Set ◽

Near Surface ◽

S Waves ◽

Wave Measurements ◽

Wave Splitting

Joint P- and S-wave measurements for tomographic cross-borehole analysis can offer more reliable interpretational insight concerning lithologic and geotechnical parameter variations compared with P-wave measurements on their own. However, anisotropy can have a large influence on S-wave measurements, with the S-wave splitting into two modes. We have developed an inversion for parameters of transversely isotropic with a vertical symmetry axis (VTI) media. Our inversion is based on the traveltime perturbation equation, using cross-gradient constraints to ensure structural similarity for the resulting VTI parameters. We first determine the inversion on a synthetic data set consisting of P-waves and vertically and horizontally polarized S-waves. Subsequently, we evaluate inversion results for a data set comprising jointly measured P-waves and vertically and horizontally polarized S-waves that were acquired in a near-surface ([Formula: see text]) aquifer environment (the Safira research site, Germany). The inverted models indicate that the anisotropy parameters [Formula: see text] and [Formula: see text] are close to zero, with no P-wave anisotropy present. A high [Formula: see text] ratio of up to nine causes considerable SV-wave anisotropy despite the low magnitudes for [Formula: see text] and [Formula: see text]. The SH-wave anisotropy parameter [Formula: see text] is estimated to be between 0.05 and 0.15 in the clay and lignite seams. The S-wave splitting is confirmed by polarization analysis prior to the inversion. The results suggest that S-wave anisotropy may be more severe than P-wave anisotropy in near-surface environments and should be taken into account when interpreting cross-borehole S-wave data.

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Near-surface scattered waves enhancement with source-receiver interferometry

Geophysics ◽

10.1190/geo2017-0806.1 ◽

2018 ◽

Vol 83 (6) ◽

pp. Q49-Q69

Author(s):

Jixiang Xu ◽

Shitai Dong ◽

Huajuan Cui ◽

Yan Zhang ◽

Ying Hu ◽

...

Keyword(s):

Seismic Data ◽

Seismic Waves ◽

Scattered Wave ◽

Receiver Functions ◽

Surface Velocity ◽

Seismic Exploration ◽

Common Source ◽

Constructive Interference ◽

Near Surface ◽

The Common

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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Nonlinear Rheology at Shallow Depths with Reference to the 2016 Kumamoto Earthquakes

Bulletin of the Seismological Society of America ◽

10.1785/0120180200 ◽

2019 ◽

Vol 109 (6) ◽

pp. 2674-2690 ◽

Cited By ~ 1

Author(s):

Norman H. Sleep ◽

Nori Nakata

Keyword(s):

Seismic Waves ◽

Inelastic Strain ◽

P Wave ◽

Seismic Velocities ◽

P Waves ◽

S Waves ◽

Shallow Subsurface ◽

Horizontal Acceleration ◽

Normal Traction ◽

Uppermost Layer

Abstract Strong S waves produce dynamic stresses, which bring the shallow subsurface into nonlinear inelastic failure. We examine implications of nonlinear viscous flow, which may be appropriate for shallow muddy soil, and contrast them with those of Coulomb friction within a shallow reverberating uppermost layer with low‐seismic velocities. Waves refract into essentially vertical paths at the shallow layers and produce tractions on horizontal planes. The Coulomb ratio of shear traction to lithostatic stress for S waves equals the resolved horizontal acceleration normalized to the acceleration of gravity. The ratio of dynamic vertical normal traction to lithostatic stresses is the vertical normalized acceleration from P waves. The predicted viscous inelastic strain rate in muddy soil begins at low normalized accelerations and then increases mildly and nonlinearly with increasing normalized acceleration. Failure is unaffected when P waves decrease the vertical normal traction. Seismic waves recorded at KiK‐net station KMMH16 for the 2016 Kumamoto mainshock and strong foreshock show these effects. Inelastic deformation commences at a normalized horizontal acceleration of ∼0.25 and reduces S‐ and P‐wave velocities within the uppermost ∼15 m reverberating layer. Normalized horizontal accelerations and the Coulomb stress ratio reach ∼1.25. Strong S waves arrived even when strong P waves produced vertical tension on horizontal planes. In contrast, inelastic Coulomb failure commences at a normalized horizontal acceleration equal to the effective coefficient of friction; rapid inelastic strain precludes even higher accelerations. Furthermore, horizontal planes should fail from the stresses of strong S waves during the tensional cycle of strong P waves.

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Corner frequencies of P and S waves and models of earthquake sources

Bulletin of the Seismological Society of America ◽

10.1785/bssa0636-12091 ◽

1973 ◽

Vol 63 (6-1) ◽

pp. 2091-2104 ◽

Cited By ~ 10

Author(s):

Peter Molnar ◽

Brian E. Tucker ◽

James N. Brune

Keyword(s):

Seismic Waves ◽

Wave Spectra ◽

S Wave ◽

P Waves ◽

S Waves ◽

Earthquake Sources ◽

Dislocation Models ◽

San Fernando

Abstract P- and S-wave spectra of 144 aftershocks 12≦M≦412 of the February 9, 1971 San Fernando earthquake corroborate previous work showing that the corner frequencies for P waves in general are greater than those for S waves. This observation is consistent not only with models that treat earthquakes as volume sources, but also with physically reasonable dislocation models for which (1) the source is approximately equidimensional, (2) both the duration of slip at each point on the fault and the time for the ruptured area to develop are not long compared with the time for seismic waves to cross the ruptured area, and (3) much of the source radiates essentially simultaneously. There may be other physically reasonable dislocation models compatible with the observations. Savage's calculations indicate that models that involve propagating dislocations on long thin faults are not adequate for describing most moderate and small earthquakes studied.

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Receiver-side near-surface corrections in the τ-p domain: A raypath-consistent solution for converted wave processing

Geophysics ◽

10.1190/geo2016-0278.1 ◽

2017 ◽

Vol 82 (2) ◽

pp. U13-U23 ◽

Cited By ~ 2

Author(s):

Raul Cova ◽

David Henley ◽

Xiucheng Wei ◽

Kristopher A. Innanen

Keyword(s):

Processing Technique ◽

Receiver Side ◽

S Wave ◽

Converted Wave ◽

Velocity Change ◽

Near Surface ◽

S Waves ◽

Surface Time ◽

Consistent Solution ◽

Consistent Approach

Removing near-surface effects in the processing of 3C data is key to exploiting the information provided by converted waves. Particularly for the case of the PS-mode, converted energy travels back to the surface as S-waves. Therefore, S-wave static corrections are needed for the receiver side. This is often done under the assumption of surface consistency. This implies a constant correction for all the traces recorded at a fixed receiver location. However, if the velocity change between the near-surface layer and the medium underneath is gradual, the vertical raypath assumption that supports the surface-consistent approach is no longer valid. This property results in a nonstationary change of the near-surface traveltimes that need to be addressed to properly solve the problem. We have determined how the delays introduced by the presence of very low S-wave velocities in the near surface can introduce raypath-dependent effects. The magnitudes of these delays can be larger than what can be considered a residual static. In this study, a raypath-consistent approach is used to solve the problem. This is achieved by transforming the data, organized into receiver gathers, to the [Formula: see text]-[Formula: see text] domain and performing crosscorrelation and convolution operations to capture and remove the near-surface delays from the data. We tested this processing technique on synthetic and field data. In both cases, removing near-surface time delays in a raypath-consistent framework improved the coherency and stacking power of shallow and deep events simultaneously. Shallow events benefited most from this processing due to their wider range of reflection angles. This approach can be useful in the processing of wide-angle broadband data in which the kinematics of wave propagation are not consistent with vertical raypath approximations in the near surface.

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