P. Philip Thomson
John I. Dunlop
Dept. of Appl. Phys., School of Phys., Univ. of New South Wales, Sydney 2052, Australia
Mathematical models for characterizing the propagation of acoustic waves in shallow water require knowledge of such acoustic properties as dilatational velocity, attenuation constant, shear velocity, and attenuation of the seafloor. In situ measurement of these properties is difficult due to the remoteness of the sea bottom. There are uncertainties in predicting these properties from geological features such as porosity, grain size, density, etc., and there is a need for direct measurements. This paper outlines some exploratory work on the laboratory measurement of core samples taken from the North West Shelf of Australia and subsequent mathematical modeling to predict general propagation characteristics. The sound-speed ratio and attenuation constant were measured by timing a high-frequency wave packet through a length of sediment core. Shear wave measurements were made using a similar measurement frame with piezoceramic bender disk transducers of 1- to 2-kHz resonance frequency. Before making measurements, the samples were individually evacuated in a mild vacuum for a short period and then slowly infused with seawater at room temperature. Measurements were made at three different positions in the cores corresponding to different depths.