The influence of sediment layering and geoacoustics on the propagation of Scholte interface waves

Results of recent Scholte wave measurements at two diverse test sites showed considerable differences in the dispersive behavior of these waves. For the southern California site, the Scholte wavers show strong, normal dispersion with group velocities ranging from approximately 30-75 m/s. On the other hand, at the Oregon Margin site the dispersion was less clearly defined, with group velocities ranging from approximately 30-205 m/s. Using a full-wave numerical model (SAFARI/OASES) and a seismic normal mode method, forward modelling (iterative inversion) was successful in matching the dispersion curves obtained from the measured Gabor matrix. A thin soft sediment; overlying a harder subbottom at the Oregon site is shown to be the crucial factor in the differences; moreover, the precise thickness of the sediment is significant. For the thick sediment site off southern California, the higher frequency fundamental Scholte mode is controlled largely by the upper few (2-10) meters of sediment, whereas the lower frequency dispersion is dominated by deeper layers, which also strongly influence the higher-order Scholte modes. The conclusions are believed to be of more general applicability than just the two sites examined