Frequency dependencies of phase velocity and attenuation coefficient in a water-saturated sandy sediment from 0.3to1.0MHz

Abstract

The frequency-dependent phase velocity and attenuation coefficient for the fast longitudinal wave in a water-saturated sandy sediment were measured over the frequency range from 0.3 to 1.0 MHz. The experimental data of phase velocity exhibited the significant negative dispersion, with the mean rate of decline of 120 +/- 20 m/s/MHz. The Biot model predicted the approximately nondispersive phase velocity and the grain-shearing (GS) model exhibited the slightly positive dispersion. In contrast, the predictions of the multiple scattering models for the negative dispersion in the glass-grain composite were in general agreement with the experimental data for the water-saturated sandy sediment measured here. The experimental data of attenuation coefficient was found to increase nonlinearly with frequency from 0.3 to 1.0 MHz. However, both the Biot and the GS models yielded the attenuation coefficient increasing almost linearly with frequency. The total attenuation coefficient given by the algebraic sum of absorption and scattering components showed a reasonable agreement with the experimental data for overall frequencies. This study suggests that the scattering is the principal mechanism responsible for the variations of phase velocity and attenuation coefficient with frequency in water-saturated sandy sediments at high frequencies.