Abstract:

Finite-difference calculations of strong pulses propagating downslope in typical littoral environments were performed using the NPE program [B. E. McDonald and W. A. Kuperman, J. Acoust. Soc. Am. 81, 1406--1417 (1987)], modified to include a seabed depth that varies with range and which provides for a specification of sound-speed gradients in the bottom as well as in the water column. In these simulations, the bottom is modeled with a (compressional wave) sound-speed profile that corresponds to mud and silt overlying a sandstone bedrock; an attenuation coefficient of 0.6 dB per wavelength is applied throughout the bottom. Results indicate that a significant fraction of the acoustic energy will generally reach deep water off the continental shelf, although this is strongly influenced by the water depth at the source and the distance of shallow-water propagation leading to the shelf. In addition, the strong refraction of the pulse in the upper seabed layers and the subsequent reradiation into the water column generates head waves that are generally preserved into the deep water. This feature may potentially serve as a discriminant between seismic and explosive sources and, in the latter case, to characterize the source environment. [Work supported, in part, by DOE through the Lawrence Livermore National Laboratory.]