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

Approximate formulae for PP reflection/transmission (R/T) displacement coef ficients for weak contrast interfaces separating weakly anisotropic media o f an arbitrary symmetry are presented. The coefficients have a form of a nl m of a well-known approximate PP reflection/transmission coefficient for a weak contrast interface 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 de fined with respect to an arbitrary isotropic background. The formulae are c onvenient for description of coefficients of reflection and transmission in low symmetry weakly anisotropic media as well as in media with higher symm etry (orthorhombic, hexagonal) with arbitrarily oriented axes of symmetry. For anisotropies of higher symmetry for which approximate formulae of other authors exist, we discuss the differences between these and our formulae a nd effects of these differences on the accuracy of approximate coefficients . performance of the approximate formulae for Rpp coefficients is tested on models with weak anisotropy and weak contrast interfaces as well as on mod els whose anisotropy and velocity contrast are in no way weak. Even in the latter case, the formulae yield satisfactory results. Accuracy of the appro ximate Rpp coefficient depending on the choice of the background is then in vestigated. It is shown that the Rpp coefficient can be described approxima tely by a formula, whose correction term due to anisotropy is independent o f the S-wave background velocity and depends only slightly on the choice of the P-wave background velocity. The formulae for the Rpp coefficients comm only used in literature for higher symmerty anisotropies are obtained by li nearization of the above mentioned formula. Linearization lead to the depen dence of the Rpp coefficient on the choice of the S-wave background velocit y and, generally to a slight decrease of accuracy. Presented formulae are c onvenient for solving an inverse problem determination of contrasts of para meters of anisotropic media surrounding an interface. Sensitivity of the ap proximate Rpp coefficient to basic weak anisotropy parameters is presented.