TABLE OF CONTENTS In a shallow ocean, sound waves travelling distances of several kilometers will interact repeatedly with the underlying seabed. Consequently, in developing a mathematical means for predicting acoustic pressure in a shallow ocean the manner in which the seabed is modelled is important. In such computations the seabed typically is treated as a dense fluid, an elastic solid, or a poroelastic medium. As indicated in Vidmar [439], [440] the fluid model is appropriate for thick sediment layers, but thin sediment layers, where conversion of energy to shear waves is an important loss mechanism, require a model that supports shear effects. Examples of the poor predictions made by the fluid model for thin sediment layers can be found in Hughes et al. [249]. Since thin superficial sediment layers are common in shallow ocean environments, our concern will be a comparison of the solid elastic model with the poroelastic model developed by Biot in [36], [38], [40], [39]. This chapter is based on a series of papers by Buchanan and Gilbert [65], [75], [79], [81] and the paper [84] of Buchanan, Gilbert, and Xu.
The elastic model of a seabed is widely used in ocean acoustics. Hence, before deriving Biot's model for a porous medium, let us summarize the equations for the elastic model. A sediment layer is treated as a viscoelastic slab depending upon the parameters ?, the aggregate density of the layer; ?. and ?, the compressional and shear Lam ...
