A review of the current understanding of seismic shear-wave splitting in the Earth’s crust and common fallacies in interpretation

Crampin, Stuart; Peacock, Sheila

doi:10.1016/j.wavemoti.2008.01.003

Cited by 139 publications

(141 citation statements)

References 98 publications

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“…Time delays are sensitive to small changes in microcrack geometry, since changes in shear wave splitting monitor the small-scale stress-induced deformation of microcracks throughout the rock mass before a level of microcracking known as fracture criticality is reached when rocks are expected to fracture (Crampin and Chastin, 2003). Temporal variations in shear-wave time-delays have been observed before several earthquakes with magnitudes M 1.7 to M 7.7 (Crampin and Peacock, 2008). These observations have been performed in different regions, worldwide, such as Iceland (Crampin et al, 1999), China (Gao et al, 1998), U.S.A. (Liu et al, 1997) and Taiwan (Crampin and Gao, 2005).…”

Section: Temporal Variation Of Time Delaymentioning

confidence: 99%

Anisotropy Study of the February 4th 2008 Swarm in Nw Peloponnesus (Greece)

2017

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Section: Temporal Variation Of Time Delaymentioning

confidence: 99%

Anisotropy Study of the February 4th 2008 Swarm in Nw Peloponnesus (Greece)

2017

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“…S-wave splits into S V and S H with vertically polarized part of the wave (S V ) travelling faster within the layers, while S H travels slower across the fine thin sedimentary layers (Crampin and Peacock 2008). However, the observed fine-layering-induced S-wave polarization does not reflect azimuthal anisotropy as both the V p and V s (V s1 & V s2 ) are azimuthally invariant.…”

Section: Interpretation and Discussion Of Resultsmentioning

confidence: 94%

“…The splitting of S-wave into two orthogonal polarizations in a transversely anisotropic medium is a typical characteristic splitting described by Crampin and Peacock (2008) and it is caused by finelayering in stratified formations, where polarization is controlled by the faster direction of wave propagation. S-wave splits into S V and S H with vertically polarized part of the wave (S V ) travelling faster within the layers, while S H travels slower across the fine thin sedimentary layers (Crampin and Peacock 2008).…”

Section: Interpretation and Discussion Of Resultsmentioning

confidence: 99%

“…Therefore, this suggests that the splitting is not layer-induced but crack-related. The azimuthally aligned shear wave splitting occurs when shear wave propagates through a medium that includes stress-aligned parallel vertical micro-cracks, which are highly compliant to small changes in stress (Crampin and Peacock 2008). The two split shear waves (S 1 and S 2 ) are both vertically propagating (Lynn and Thomsen 1990).…”

Section: Interpretation and Discussion Of Resultsmentioning

confidence: 99%

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Modelling Orthorhombic Anisotropic Effects for Reservoir Fracture Characterization of a Naturally Fractured Tight Carbonate Reservoir, Onshore Texas, USA

Osinowo

Chapman

Bell

et al. 2017

Pure Appl. Geophys.

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Abstract-In this study we present a step-by-step theoretical modelling approach, using established seismic wave propagation theories in anisotropic media, to generate unique anisotropic reflection patterns observed from three-dimensional pure-mode pressure (3D-PP), full-azimuth and full-offset seismic reflection data acquired over a naturally fractured tight carbonate field, onshore Texas, USA. Our aim is to gain an insight into the internal structures of the carbonate reservoir responsible for the observed anisotropic reflection patterns. From the generated model we were able to establish that the observed field seismic reflection patterns indicate azimuthal anisotropy in the form of crack induced shearwave splitting and variation in P-wave velocity with offset and azimuth. Amplitude variation with azimuth (AVAZ) analysis also confirmed multi-crack sets induced anisotropy which is characteristic of orthorhombic symmetry, evident as multiple bright and dim-amplitude azimuth directions as well as complete reversal of bright-amplitude to dim-amplitude azimuth direction as the angle of incidence increases from near (B15°) to mid (C30°) offsets. Finally, we fitted the generated P-wave velocity into an ellipse to determine the intensity and orientation (N26E) of the open crack set as well as the direction of the minimum in situ stress axis (N116E) within the reservoir. The derived information served as an aid for the design of horizontal well paths that would intercept open fractures and ensure production optimization of the carbonate reservoir, which was on production decline despite reservoir studies that indicate un-depleted reserves.

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“…SWS has been discussed extensively by S. Crampin and many others;; see Crampin and Peacock (2008) for a recent review of shallow SWS, and Savage (1999) for a recent review of deeper SWS.…”

Section: Weak Polar Anisotropy; Body Wavesmentioning

confidence: 99%

Weak elastic anisotropy in global seismology

Thomsen¹,

Anderson²

Geological Society of America Special Papers

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It has been known for over 50 years that seismic anisotropy must be included in a realistic analysis of most seismic data. The evidence for this consists of the observed dependency in many contexts (reviewed briefly here) of seismic velocity upon angle of propagation, and upon angle of S-wave polarization.Despite this well-established understanding, many current investigations continue to employ less realistic isotropic assumptions. One result is the appearance of artefacts which can be interpreted in terms of details of Earth structure, rather than of the restrictive assumptions in the analysis.The reason for this neglect of anisotropy is presumably the greater algebraic complexity, and the larger number of free parameters, of anisotropic seismics. However, the seismic anisotropy in the Earth is usually weak, and the equations for weak anisotropy are only marginally more complex than for isotropy.Further, the additional parameters are commonly required to describe the data. Moreover, the parameters of weak anisotropy defined below (combinations of the anisotropic elastic moduli) are less subject to compounding of uncertainty, and to spatial resolution issues, than are the individual anisotropic moduli themselves. Hence inversions should seek to fit data with these parameters, rather than with those individual moduli. We briefly review the theory for weak anisotropy, and present new equations for the weakly anisotropic velocities of surface waves. The analysis offers new insights on some well-known results found by previous investigations, for example the "Rayleigh wave-Love wave inconsistency", including the facts that Raleigh wave velocities depend not only on the horizontal SV velocity, but also on the anisotropy, and Love wave velocities depend not only on the horizontal SH velocity, but also on the anisotropy.

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A review of the current understanding of seismic shear-wave splitting in the Earth’s crust and common fallacies in interpretation

Cited by 139 publications

References 98 publications

Anisotropy Study of the February 4th 2008 Swarm in Nw Peloponnesus (Greece)

Anisotropy Study of the February 4th 2008 Swarm in Nw Peloponnesus (Greece)

Modelling Orthorhombic Anisotropic Effects for Reservoir Fracture Characterization of a Naturally Fractured Tight Carbonate Reservoir, Onshore Texas, USA

Weak elastic anisotropy in global seismology

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