Scattering of seismic interface waves from pointlike obstacles in unconsolidated sediments

Abstract

The concept of an active, bistatic, seismoacoustic interface-wave sonar is investigated theoretically and experimentally. The goal of the theory is to relate the scattering of seismoacoustic interface waves from material inhomogeneities and objects buried beneath an interface to their target strengths. This is done in a multipole scattering expansion, which takes a simple and efficient form in the limit that the inclusions can be treated as pointlike perturbations of the properties of the medium. Experiments were performed in a sandy beach area of the Gulf of Mexico to demonstrate the concept. The experiments included methods for the selective excitation of interface waves, and examined the propagation of seismic interface waves in unconsolidated wet sand, both water-saturated and unsaturated. The boundary conditions and target strengths of a collection of buried objects were measured, using a variety of pulse-echo and continuous-wave sonar configurations.