Finite-element analysis of marine sediment acoustics

Abstract

The propagation of acoustic waves in a shallow water environment is controlled by the dynamic response of sediments, which are generally composite (multiphase) systems, as well as the complex geological structure that results from depositional processes. To analyze the propagation of low-frequency acoustic waves in such media, the finite-element-Biot model has been developed which incorporates the Biot's theory into the finite-element method. The Biot's theory governing the dynamic behavior of fluid-filled porous materials provides an adequate description of the effects of the intrinsic properties of the sediments, and the finite-element method has the flexibility to model large-scale inhomogeneities that are commonly encountered in marine environments. The effects of such parameters as porosity, lithology, lithification, and dissipation due to the relative motion of a viscous fluid are examined numerically. It is found that the modification of acoustic waves is a result of the intrinsic properties of fluid-saturated porous sediments as well as the interactions between the fast and the slow compressional waves and energy partitioning at interfaces between dissimilar fluid-filled sediments.