ASA 125th Meeting Ottawa 1993 May

5aAO15. Waveform analysis of seafloor Scholte waves.

Guust Nolet

Dept. of Geolog. and Geophys. Sci., Princeton Univ., Princeton, NJ

LeRoy M. Dorman

Scripps Inst. of Oceanog., UCSD, La Jolla, CA 92093-0215

A new method of nonlinear waveform inversion to model Scholte waves has been tested. Synthetic displacements were computed for an explosive source at the ocean bottom for frequencies up to about 2.5 Hz. At the distance range of interest (<1 km) only the first few modes of the Scholte waves are present, with most energy in the fundamental mode. Linear perturbation theory is used in our scheme to predict changes in wave number produced by changes in the model. This theory degenerates at those frequencies where modes can escape the sediments and where the phase velocity changes suddenly from approximately 0.1 to 1.5 km/s. The step length for wave-number changes were limited to deal with this problem. This did not noticeably degrade convergence. The method was tested on observed waveforms from an experiment at Deep Sea Drilling Project site 469. This site is at 3.8-km water depth just off the Patton Escarpment, about 300 km west of San Diego. The seismic velocities there are quite uniform laterally. The surficial shear velocity is about 30 m/s. [Work supported by ONR.]