Numerical tracing of critically refracted rays

Abstract

The need to trace critically refracted rays through arbitrarily stratified velocity models arises frequently during seismic refraction interpretation. But the means to do this routinely have been lacking so far. The main difficulty encountered while tracing such a ray using laws of reflection and refraction is that the direction in which the ray should leave the source is unknown. Determination of this direction is regarded here as a problem of solving two coupled nonlinear equations in two unknowns (namely, the azimuthal and colatitudinal angles describing the direction) for which several techniques are available. Details of the algorithm actually tested, and the procedure for tracing the critically refracted ray once the direction at source is known, are discussed below.