ASA 126th Meeting Denver 1993 October 4-8

2pUW1. Effects of ``realistic'' geoacoustic parameters on frequency-dependent bottom loss.

Robert D. Stoll

Lamont--Doherty Earth Observatory of Columbia Univ., Palisades, NY 10964

Recent field studies have shown that seismic velocity and attenuation gradients vary rapidly in the sediments immediately below the seafloor. These variations have an important effect on the frequency-dependent bottom loss that is predicted for waves entering the bottom at low grazing angles for several reasons. The more obvious reason is the variable path length traversed by the shallow diving waves that are returned to the water column; however, a second important reason appears to be the conversion of some p-wave energy to s waves resulting from the weak coupling between the two wave types that is caused by the high-velocity gradients near the bottom. Comparisons of bottom loss computed using the conventional constant gradient models and variable-gradient models based on recent field measurements show significant differences in bottom loss as a function of frequency. The additional effects of p- to s-wave conversion are also illustrated. [Work supported by ONR, Code 11250A.]