ASA 125th Meeting Ottawa 1993 May

2pUW8. Three-dimensional scattering and wave-type conversion by delineated features in a stratified sea bed.

Huaiyu Fan

Henrik Schmidt

Dept. of Ocean Eng., MIT, Cambridge, MA 02139

The three-dimensional scattering from delineated features in an elastic sea bed, such as faults, small abyssal hills, and extended diapirs, is simulated numerically, and the seismoacoustic wave-type conversion introduced by such reverberant features is addressed. The ocean environment is assumed to be two dimensional: An infinitely long inhomogeneity is imbedded in or penetrating the bottom of an otherwise horizontally stratified ocean. Such reverberant features are assumed to be insonified by an obliquely incident acoustic beam. Due to the fundamental assumption of a two-dimensional environment, this three-dimensional reverberation problem can be treated using Fourier synthesis of 2-D solutions. Here, the two-way solutions are obtained using a modified version of an existing, hybrid wave-number integration-boundary element (WI-BEM) approach [P. Gerstoft and H. Schmidt, J. Acoust. Soc. Am. 89, 1629--1642 (1991)]. This WI-BEM approach inherently decomposes the total field into basic physical components, thus enabling direct identification of the different seismic wave types in the scattered field. The conversion into seismic interface (Scholte) waves and SH waves in the bottom is investigated, and its importance for the bi-static reverberation is discussed. [Work supported by ONR.]