Finite-difference solution of the transport equation: First results

The ray-theoretical transport equation for inhomogeneous isotropic media (2D-SH case) is solved by the method of finite differences on a rectangular grid, both for an incident plane wave (explicit scheme) and a line source (implicit scheme). Results for homogeneous models and for heterogeneous models with structural discontinuities are discussed. First-arrival travel times calculated by various techniques serve as input for the solution of the transport equation and the computation of amplitudes of first arrivals. To obtain correct amplitudes the travel times must be highly accurate and the discontinuities must be smoothed out; the reason is that the spatial second derivatives of the travel time field enter the transport equation. In the simple cases studied, finite differences provide a fast and efficient tool for the computation of first-arrival amplitudes.

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