Low-frequency seismo-acoustic propagation near thin and low-shear speed ocean sediment layers.

Abstract

Accurate and efficient prediction of propagation over realistic models of elastic ocean sediments has been achieved recently using parabolic equations. A concern has been low‐shear wave speed sediments that can become singular as the wave speed tends toward zero. A historic approach for treating a sediment of this type has been to assume that it is a fluid and that effects due to elasticity are negligible. This approach does not account for second order effects such as energy loss due to frequency‐dependent attenuation. In addition, thin sediment layers typical of that found at the ocean bottom interface have been difficult to treat numerically. At low frequencies, layers of this type can be treated as a massive interface between the water and higher‐shear speed sediment basement layers. To satisfy interface conditions across the layer, Rayleigh jump conditions are imposed [F. Gilbert, Ann. Geophys. 40, 1211 (1997)]. A consequence of this approximation is that interface and other wave types become dispersive where they were not previously. In this presentation, the massive elastic interface is benchmarked with an elastic parabolic equation and the effects of resultant errors are quantified. In addition, the energy partition between compressional and shear energies is determined.