ACQUISITION AND INVERSION OF LOVE WAVE DATA TO MEASURE THE LATERAL VARIABILITY OF GEO-ACOUSTIC PROPERTIES OF MARINE SEDIMENTS

Abstract

A towed sledge system has been utilised to generate and receive Love waves at the seabed. Due to unique deployment procedures, the system is capable of acquiring data both rapidly and efficiently over an extensive area. An experiment was undertaken to assess the capability of the system to measure the lateral variation of the shear wave velocity in unconsolidated near-surface sediments along a 4-km survey line. The site chosen was known to display significant variations in sediment characteristics over relatively short distances and could therefore provide a suitable test. A parametric approach was used to obtain phase-velocity dispersion curves from the Love wave data sets. This approach enabled the fk-spectra to be resolved to a sufficiently high level using a limited number of receivers. Finally, the shear wave velocity profile for each record was estimated with respect to a reference model using a non-linear least squares inversion algorithm. Results indicated that the shear wave velocity field varied significantly along the survey line. The shear wave velocity at a depth of 30 cm below the seabed changed from 30 to 55 m/s over the length of the survey line. The velocity variations correlated well to geotechnical data acquired from the area, suggesting that Love waves acquired from only five seafloor receivers can successfully be used to construct near-surface models of seafloor shear wave velocity in unconsolidated near-surface sediments, with a lateral resolution of up to 25 m and a depth measurement range of up to 4 m.