Seismo-acoustic determination of the shear-wave speed of surficial clay and silt sediments on the Scotian shelf

John C. Osler, David M.F. Chapman

Abstract


The Defence Research Establishment Atlantic has determined the shear-wave speed profile of the unconsolidated surficial clay and silt sediments at two locations on the Scotian Shelf - the shallow water continental margin of Nova Scotia, Canada. An ocean bottom seismometer detected the passage of interface waves which were generated by detonating small explosives on the seabed. Profiles of shear speed as a function of depth were determined by repetitive forward modelling of the measured dispersion of the interface waves. The shear speed of the approximately 25 to 40 m thick Quaternary succession of clay and silt ranges from approximately 10 m/s at the seabed to 120 m/s at 40 m depth. The shear speed profiles are consistent with a power-law relationship of the form cs(z) = c0zv, with v in the range 0.60-0.65 and c0 in the range 16-22 m/s re 1 m. The shear speeds encountered in this study are among the lowest that have been reported for any marine sediment in the literature, while the strength of the gradient, v, is approximately twice that which is typically observed.

Keywords


Acoustic dispersion; Acoustic noise measurement; Seismic waves; Silt; Interface waves; Surficial clay

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