Properties of weak contrast PP reflection/transmission coefficients for weakly anisotropic elastic media

Ivan Psencik & Jorge Leonardo Martins


Approximate formulae for PP reflection/transmission (R/T) displacement coefficients for weak contrast interfaces separating weakly anisotropic media of an arbitrary symmetry are presented. The coefficients have a form of a sum of a well-known approximate PP reflection/transmission coefficient for weak contrast interfaces separating two background isotropic halfspaces and a correction due to weak anisotropy. The correction is controlled, linearly, by the so-called weak anisotropy (WA) parameters. The coefficients are defined with respect to an arbitrary isotropic background. The coefficients can describe reflection and transmission not only in low symmetry weakly anisotropic media but also in media with higher symmetry (orthorhombic, hexagonal) but with arbitrarily oriented axes of symmetry. For anisotropies of higher symmetry, for which approximate formulae for R coefficients of other authors exist, we discuss the differences between these and our formulae and their effects on accuracy of approximate coefficients. Performance of the approximate formulae for reflection coefficients is tested on models with weak anisotropy and weak contrast interfaces as well as on models whose anisotropy and velocity contrast are in no way weak. Even in the latter case, the formulae yield satisfactory results. Accuracy of the approximate RPP coefficient in dependence on the choice of the background is then investigated. Presented formulae are convenient for solving an inverse problem: determination of contrasts of parameters of anisotropic media surrounding an interface. Sensitivity of the approximate RPP coefficient to basic weak anisotropy (WA) parameters is presented.

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In: Seismic Waves in Complex 3-D Structures, Report 8, pp. 151-170, Dep. Geophys., Charles Univ., Prague, 1999.
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