Measurements of Velocity Dispersion in Marine Sediments During the Baundary04 Malta Plateau Experiment

Abstract

Existence of acoustic velocity dispersion and nonlinear frequency dependency of attenuation in marine sediments is investigated. A new wide-band acoustic probe system has been used during Boundary04 experiment at Malta Plateau to measure compressional wave speed and attenuation within 20-150 kHz frequency band. Observation of velocity dispersion in granular marine sediments has been previously reported by Turgut and Yamamoto (J. Acoust. Soc. Am., 87, 2376-2383, 1990), Maguer et al., (J. Acoust. Soc. Am., 108, 987-996, 2000), and Stoll (J. Acoust. Soc. Am., III, 785-793, 2002). However, most of the previous results were obtained by using different measurement techniques at low and high frequencies. Wide-band acoustic probe measurements show evidence of dispersion of compressional waves within 20-100 kHz frequency band in muddy silt. The observed dispersion is effectively modeled by an extended Biot theory (Yamamoto and Turgut, J. Acoust. Soc. Am., 83, 1988, pp. 1744-1751). In the extended Biot model viscous losses due to relative motion between the pore fluid and skeletal frame are calculated for marine sediment with nonuniform pore-size distribution. The extended Biot model that predicts comparable dispersion and attenuation to those measured in silty sediments briefly described. Finally, recent improvements on the wide-band acoustic probe system are discussed for future compressional wave velocity and attenuation measurements in granular marine sediments.