Experimental and Theoretical Studies of Seismic Interface Waves in Coastal Waters
A digital three-component ocean-bottom seismometer has been developed at SACLANTCEN to study extremely-low-frequency sound propagation in coastal waters (e.g. below the cut-off of the shallow-water duct). It has been used successfully in conjunction with a variable depth hydrophone during several sea trials off the Italian coast. By exploding small charges (45 to 900 g TNT) at various distances (up to 5 km) it has been demonstrated that the infrasonic energy is mainly transmitted via a seismic interface wave. In general this propagation mode may be termed a modified Scholte wave as it is guided by the acoustically most significant interface between water column (including liquid-type sediments) and solid basement. On a sedimentary sea floor very pronounced wavelets have been observed, at frequencies in the 1.5 to 6 Hz band, group-velocities in the 250 to 70 m/s range, and hodographs in the vertical radial plane. Together with this experimental program theoretical studies have been made using a seismic Fast-Field-Program, which has proved to be a very powerful tool to model infrasonic phenomena in shallow-water environments.
KeywordsCoastal Water Sand Layer Stoneley Wave Acoustic Propagation Italian Coast
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