Slowness surface approximations for qSV-waves in transversely isotropic media.

The vertical slowness approximations are widely used in phase-shift migration methods for quasi P- and quasi SV-waves in transversely isotropic medium. The description of the vertical slowness needed for the migration application for shear waves in transverse isotrophy media is generally complicated. The reason is that this type of approximations results in much simpler expressions for the vertical slowness and, which is most important, they contain fewer parameters than exact expressions. We derive slowness surface approximations valid for qSV-wave propagation in transversely isotropic and tilted transversely isotropic media by applying an approximation extracted from acoustic approximation for qP-wave propagation. One approximation has the same accuracy as a qP-wave acoustic approximation for the same range of horizontal slowness, the other approximations are wide-angle ones. [ABSTRACT FROM AUTHOR]