ASA 124th Meeting New Orleans 1992 October

1aUW4. The influence of bottom geoacoustics on the dispersive behavior of Scholte interface waves.

Hassan B. Ali

L. Dale Bibee

Jeffrey L. Becklehimer

Naval Res. Lab., Stennis Space Center, MS 39529-5004

Scholte seismic interface waves can be an important component of very low-frequency (VLF) acoustic propagation, particularly in shallow-water environments. The propagation characteristics of these seismic waves, including their presence in the water column, are dependent on bottom geoacoustics (particularly shear speeds) and the types of layers overlying the basement level. This work examines the results of recent NRL/Stennis Space Center measurements and compares them with numerical predictions based on the SAFARI model. Scholte waves measured off the Oregon Margin (1991) are shown to have strikingly different characteristics from those obtained off the San Diego coast (April 1992). In particular, the latter results (San Diego) are characterized by strongly dispersed Scholte waves in the 1- to 5-Hz band, whereas those measured off the Oregon Margin contain mostly lower frequencies (1--2 Hz) and display less clearly defined dispersive behavior. The differences in the two data sets are attributed to the significantly diverse bottom/subbottom geoacoustics at the two test sites---in particular, to the different sound-speed gradients in the sediments.