Ray, Mode and Hybrid Options For Time‐Dependent Source‐Excited Propagation In an Elastic Layer

The authors have recently developed a hybrid theory for source‐excited propagation in multiwave multilayer media, whereby ray fields and normal mode fields (with a smoothing remainder) are combined in self‐consistent proportions so as to take advantage of the favourable features of each of these descriptions. to avoid proliferation of multiple reflected ray fields, caused by wave coupling at boundaries, a new spectral object called ‘eigenray’ has been introduced, which has dispersive characteristics similar to those of a normal mode but undergoes reverberations like a single ray field in a single wave medium. For time‐harmonic excitation by a line forcing function, these new formulations have already been tested numerically on the simple but non‐trivial example of P‐SV propagation in a single elastic plate. the validity of the hybrid algorithm has been confirmed, and parameter regimes have been found wherein the hybrid approach offers a competitive alternative to other options. In the present investigation, the test calculation is extended to excitation by a high‐frequency Gaussian pulse transient source. the results reveal the complicated multiple arrival structure, well resolved at early times but tending toward modal behaviour at later times. These features, which pertain especially to long observation intervals and wave constituents with high‐frequency spectral content, are explained well, and are computed efficiently, by the ‘optimal’ hybrid format. It is suggestive, but remains to be confirmed, that these favourable attributes will remain intact when the formulation is applied to the general multilayer case.