LeRoy M. Dorman, Marine Physical Laboratory and Geological Research Division, Scripps Institution of Oceanography, University of California, San Diego La Jolla, CA 92093-021537.1 INTRODUCTION
The propagation of sound in marine sediments can be important in ocean acoustics at frequencies below 50 Hz, and is, moreover, an important tool for study of seafloor geology. Propagation is dependent on the physical properties of the sediments, which are much more variable than the properties of the overlying water. The most important physical properties are compressional velocity, shear velocity, density, anisotropy and attenuation. These physical properties are influenced by the source of the sedimentary materials and also by the environment. These dependencies allow a degree of predictability. Although the variability is high, there are some systematic regional variations (which control source materials, mechanical winnowing and chemical alteration) which are useful in making predictions for regions of no data. This chapter contains a discussion of in-situ measurement techniques (sources, propagation types, receivers and analytical methods), representative samples of in-situ determinations of most of the important physical properties in several different geological regions, as well as a discussion of predictability.