f Approximations for Far Ray-Tracing through Layered Anisotropic Media with Velocity Gradients

Kinematic modelling of three-dimensional seismic surveys at commercial scales and interactive speeds necessarily uses rather simple models composed of (macro-) layers bounded by major interpreted horizons. The properties of these layers are taken to be slowly varying so that locally they can be described by a velocity which is linear in position and some forrn of anisotropy.