ASA 125th Meeting Ottawa 1993 May

5aUW14. Measurement of ocean-bottom compressional and shear speeds in the Canadian high Arctic.

S. E. Dosso

G. H. Brooke

Defence Res. Establ. Pacific, FMO Victoria, BC V0S 1B0, Canada

Geoacoustic properties of the ocean bottom can be a significant factor influencing acoustic propagation in shallow-water environments. Knowledge of these properties is required for reliable acoustic propagation modeling and matched-field processing. This paper presents the preliminary analysis of a sea-floor seismic experiment carried out on the continental shelf of the Lincoln Sea north of Ellesmere Island, Canada, to determine compressional- and shear-speed models for the ocean bottom. A three-component ocean-bottom seismometer (OBS) was deployed through ~4 m of multiyear sea ice in 540 m of water. Broadband explosive sources were detonated on the sea floor at ranges from 50 to 900 m. Source--receiver ranges and shot instants were verified by timing the direct and surface-reflected arrivals through the water. Subsequently, a layered compressional-speed model for the ocean bottom was determined from a first-break analysis of the head-wave arrivals. Also, interface (Sholte) wave arrivals have been identified on many of the seismograms and exhibit characteristic elliptical particle motions. Waveform modeling of these interface waves is discussed with a view to extracting shear-speed properties in the uppermost bottom layers.