Acoustic and Other Physical Properties of Shallow-Water Sediments off San Diego

Abstract

This paper reports on a continuing study of the mass physical properties of surficial, shallow-water marine sediments off San Diego, California. Sound velocity measurements in situ at 100 kc were made by pulsing between small transducers inserted into the bottom by diver. Density, porosity, and size analyses were determined on relatively undisturbed samples taken by diver. The following averaged representative values have been obtained:Sediment type Density Porosity Med. diam Velocity in Impedance(g/cc) (%) (mm) sediment at × 105g/cm260 deg F sec(ft/sec)Fine sand 1.93 46.2 0.19 5520 3.25Very fine sand 1.92 47.7 0.12 5435 3.18Silty very finesand 1.68 61.3 0.05 5075 2.60Medium silt 1.69 60.9 0.03 4825 2.49Clayey fine silt 1.60 65.6 0.02 4800 2.34Laboratory measurements of velocity and attenuation at 25 to 35 kc were made by a resonant chamber method using diver taken samples; average attenuation values of about 0.5 db/ft (silt) to about 5 db/ft (fine sand) were obtained. Velocity measurements with both systems compared within 212%. At three stations the sediment sound velocity was less than the velocity in the bottom water.