Theory of wave propagation in marine sediments.

Abstract

Saturated, unconsolidated marine sediments support sound waves and shear waves, each of which is dispersive in that its phase speed varies with frequency and the corresponding attenuation scales as the first power of frequency over an extended frequency range. A theory of sound wave and shear wave propagation in unconsolidated marine sediments has recently been developed in which the dissipation is based on a particular form of intergranular interaction involving the molecularly thin layer of pore fluid at grain contacts. As grain-to-grain sliding progresses, the contact is postulated to become progressively stiffer, a phenomenon known as strain-hardening, adapted from the literature on creep in metals and metal alloys. The theory returns algebraic expressions for the phase speed and attenuation of both types of wave, and these expressions depend on frequency as well as the geoacoustic parameters of the sediment. A comparison of the theoretical dispersion relations with data obtained during the ONR-supported SAX99 experiment shows good agreement over the frequency range range from 2–400 kHz. The theoretical expressions also fit measurements, at a fixed frequency, of phase speeds and attenuations versus porosity, overburden pressure, and mean grain diameter. [Research supported by ONR.]