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

Abstract

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.