Converted PS-wave Reflection Coefficients in Weakly Anisotropic Media

I derive converted PS-wave reflection coefficients at a planar weak-contrast interface separating two weakly anisotropic half-spaces using first-order perturbation theory. The general expressions are further specified for the interface separating any of the two following media: isotropic, transversely isotropic with a vertical symmetry axis (VTI), transversely isotropic with a horizontal symmetry axis (HTI) and orthorhombic. Relatively simple forms of small-angle reflection coefficients are also obtained. The coefficients are expressed as functions of Thomsen-type medium parameters and incidence and azimuthal phase angles. Derived expressions, as well as their application, are more complicated than the corresponding expressions for PP-wave reflection coefficients. General characteristics and pitfalls are discussed. Numerical tests reveal a good agreement between exact and approximate coefficients for most models presented.