Processing of a nine‐component near‐offset VSP for seismic anisotropy

MacBeth, Colin; Li, Xiangyang; Zeng, Xinwu; Cox, Dale; Queen, John

doi:10.1190/1.1444176

Cited by 7 publications

(3 citation statements)

References 17 publications

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“…The full nine-component arrangement or various subsets have been used extensively in studies of anisotropy related to rock fracturing (e.g. Mueller 1991;Shuck, Davis and Benson 1996;MacBeth et al 1997). The presence or absence of symmetry between the off-diagonal components in a multicomponent VSP (MacBeth et al 1994) or in a multicomponent surface reflection data matrix has been used not only as an indicator of the presence or absence of anisotropy, but also for detecting inaccuracies caused by source or receiver misorientation.…”

Section: Data Structure and Processingmentioning

confidence: 99%

Seismic imaging of the shallow subsurface: shear‐wave case histories

Dasios¹,

McCann²,

Astin³

et al. 1999

Geophysical Prospecting

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Obtaining high‐resolution images of the geology and hydrogeology of the subsurface in the depth range from ground level to 50 m is one of the major challenges of modern geophysics. The methods which are commonly used (such as compressional‐wave surveys and ground‐penetrating radar) often suffer from adverse effects caused by the near‐surface conditions, changes in water saturation and various sources of noise. This paper demonstrates some of the advantages offered by the use of shear‐wave seismology and by the combination of shear‐ and compressional‐wave seismic methods in shallow subsurface investigations. Multicomponent shallow seismic tests were carried out at four different sites to examine the effectiveness of different acquisition geometries under a variety of near‐surface geological conditions. Near‐surface conditions encountered at the sites included thick clays, clay/sand sequences overlying Chalk, mudstone overlying granodiorite bedrock and landfill material. Under all conditions, shear‐wave data acquisition was found to have advantages over compressional‐wave acquisition for the investigation of the shallow subsurface. Shear head waves, being unaffected by water saturation, achieved penetration to greater depths at a site in Crewkerne, Dorset where compressional head‐wave penetration was limited to the near‐surface layers. Better vertical resolution was achieved at shallow depths using shear‐wave reflection energy at a landfill site. Shear‐wave reflections from shallow interfaces were in some cases less affected by noise compared with the equivalent compressional‐wave reflections. Combinations of shear‐ and compressional‐wave data recording allowed the measurement of a Poisson's ratio log and gave indications of seismic anisotropy at two sites where dipping clay layers were present.

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Section: Data Structure and Processingmentioning

confidence: 99%

Seismic imaging of the shallow subsurface: shear‐wave case histories

Dasios¹,

McCann²,

Astin³

et al. 1999

Geophysical Prospecting

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show abstract

“…Three-component seismograms for shear-wave propagation in anisotropic media can be simulated by numerical algorithms (Carcione et al, 1992;Igel et al, 1995;Tessmer, 1995;Macbeth et al, 1997). We use Hudson's (1980Hudson's ( , 1981 parameterization for computation of the stiffness tensor of dry media with aligned cracks to simulate the splitting of shear waves as a function of source polarization and fracture orientation and density.…”

Section: Introductionmentioning

confidence: 99%

3D Modeling of Fracture-Induced Shear-Wave Splitting in the Southern California Basin

Nistala

McMechan

2005

Bulletin of the Seismological Society of America

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Splitting of shear waves, generated by local earthquakes in the Southern California basin, and their polarization changes during propagation through layers with different orientations of anisotropy, are investigated from multicomponent seismograms and their hodograms. Synthetic data for earthquakes in the Southern California basin illustrate the effects on polarization caused by dry vertical microcracks with a crack density of ϳ0.04 at the source and receiver locations. Hodograms for observed and synthetic data show that the polarization at the receiver depends only on the orientation of the anisotropy within two wavelengths of the receiver, which qualitatively explains the frequency dependence of anisotropy in previous studies.Seismograms are simulated for a model with a range of station azimuths and distances. If the anisotropy-producing crack orientations do not change between the source and a receiver, and the source motion is parallel to the cracks, there is no shear-wave splitting. Splitting occurs when the anisotropy orientation at the receiver (or between the source and receiver) is different from the source orientation.

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“…Wide-aperture walkaway VSP data acquired through trans versely isotropic horizontal layers can be used to determine the qP-wave phase-slowness sur face (Sayers 1997). Multi-component VSPs may reveal a strong vertical birefringence near the surface (MacBeth et al 1997).…”

Section: Introductionmentioning

confidence: 99%

Traveltime Analysis of VSP Seismograms in a Horizontal Transversely Isotropic Medium: A Physical Modeling Result

Chang¹,

Chang²

2001

Terr. Atmos. Ocean. Sci.

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In order to investigate the effects of anisotropy in a VSP survey, the multi-component VSP data for observing the qP-, qSH-and qSV-waves were collected with two different source-to-well offsets in an elastic trans versely isotropic medium (TIM) with a horizontal symmetry axis (HTI). The traveltimes of the events were then computed using two different algorithms: first with elastic constants of the medium, and second with "iso tropic velocities". Comparing the traveltimes of computations with the re corded data, a very clear and important consequence can be derived. For strongly anisotropic media (the anisotropy for the qP-and qS-waves are 25% and 29%, respectively, in our laboratory work), the effects of anisot ropy increase with increasing source-to-well offset. As the source-to-well offset is small compared with the depth of the receiver (offseUdepth $ 0.2 in our work), the effects of anisotropy can be ignored. However, in process ing a large source-to-well offset VSP survey (offseUdepth :2: 0. 35 in this study), special attention must be paid on the effects of anisotropy.

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Processing of a nine‐component near‐offset VSP for seismic anisotropy

Cited by 7 publications

References 17 publications

Seismic imaging of the shallow subsurface: shear‐wave case histories

Seismic imaging of the shallow subsurface: shear‐wave case histories

3D Modeling of Fracture-Induced Shear-Wave Splitting in the Southern California Basin

Traveltime Analysis of VSP Seismograms in a Horizontal Transversely Isotropic Medium: A Physical Modeling Result

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