Introduction

Waves and rays are necessary components of any suite of seismic processes. In an isotropic medium the transition is seamless--not so in the simplest anisotropic material. Here, not only do velocities depend on direction, but worse, rays and waves have different velocities, and worse still, there is no local transformation from one kind of velocity to the other. In an earlier paper (Muir, 1990) I described a partial solution where approximate plane wave equations and ray equations have simple, interchangeable properties. In this note I relate the parameters of these approximants to the elastic moduli of the TI media that lie behind the dispersion relations that I approximate.