### ASA 125th Meeting Ottawa 1993 May

## 5aAO15. Waveform analysis of seafloor Scholte waves.

**Guust Nolet
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*Dept. of Geolog. and Geophys. Sci., Princeton Univ., Princeton, NJ
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**LeRoy M. Dorman
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*Scripps Inst. of Oceanog., UCSD, La Jolla, CA 92093-0215
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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.]