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Abstract

Analysis of seismic shear waves is useful in characterizing properties of the media they travel through. Alford (1986) introduced a method of rotating combinations of observed seismic traces from orthogonal pairs of shear-source and shear-receiver components to identify the azimuthal orientations of symmetry axes of birefringence. This method has been widely applied to interpretation of subsurface fracture properties. This analysis, as currently applied, is limited to zero-offset reflections. which results because the normal incidence reflection response is identical for SV and SH reflectivity. For non-normal incidence angles, however, there is a pronounced difference in SV and SH reflectivity as source-receiver offsets increase, leading to significant distortion in the polarity of the reflected shear wave. Polarization distortion due to the reflection process in typical 3D acquisition geometry is demonstrated and a correction to the polarization distortion is proposed. The only information required for the corrections are the angles of SV and SH zero crossings, typically at angles near 20° for SV and 40° for SH for most sedimentary rocks. This correction can be applied to four-component direct shear data at non-zero source-receiver offsets, leading to an extension of the widely applied Alford rotation to non-zero angles of incidence.

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/content/papers/10.3997/2214-4609.20130360
2013-06-10
2024-03-28
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http://instance.metastore.ingenta.com/content/papers/10.3997/2214-4609.20130360
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