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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.

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Stanford Exploration Project

12/18/1997