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Reflection and Transmission of Elastic Plane Waves at the Interface between Anisotropic Media
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 2nd International Congress of the Brazilian Geophysical Society, Oct 1991, cp-316-00137
Abstract
Anisotropy affects the reflection and transmission of elastic waves significantly as soon an the energy propagates over a wide angular aperture. Plane wave reflection and transmission coefficients at an interface between anisotropic elastic media can be expressed explidtly in terms of 'iIupedance matrices", as long as the plane of the interface is a mirror plane of symmetry of both media. For the two dimensional case, plane strain 'quasi-compressional' (qP) and 'quasi-transverse' (qS) waves (associated displacements in the plane of propagation) are uncoupled from the anti-plane strain SH waves (associated displacements perpendicular to the plane of propagation) and the plane of propagation' also must be a mirror plane of symmetry of both media, implying that both media are at least orthorhombic. This case includes the important problem of reflectivity and transmissivity between isotropic and transversely isotropic media. The ultimate aim of amplitude vs. offset (AVO) analysis in this case is the estimation of the density ratio and the elastic constants in each medium on which the reflection and transmission coefficients depend. However, these constants are not equally well resolved. For all models that could conceivably represent the anisotropy in real rock masses, even the anisotropy of the reflecting medium can not be estimated, since each anisotropic medium has its 'quasi-equivalent' isotropic medium which gives reflection coefficients close to those of the anisotropic medium, ovr a wide range of incidence angles.