Assessing The Influence of Internal and Viscous Friction on Dispersion and Sound Attenuation in Unconsolidated Marine Sediments

Abstract

The study analyzes influence of internal and viscous dissipation on sound propagation of in unconsolidated marine sediments. The main provisions of M. Buckingham’s GS theory of intergranular friction are presented. According to GS theory, sediments are considered as a single-phase medium, sound attenuation is explained by internal friction alone, and viscous dissipation is neglected. A modification of GS theory is presented, which transforms it to two-phase. Instead of a single-phase equation of state, an equation of state of a two-phase medium is applied, previously derived in a study by work I.A. Chaban. Substitution of this equation of state into the dispersion relation of GS theory leads to a quadratic equation, the roots of which give the wavenumbers of two types of waves, fast and slow, in an unconsolidated medium with internal friction (GS + EC, grain shearing + effective compressibility). The results given by the modified theory are compared with the results of experimental measurements taken from open sources. It is shown that significant sound speed dispersion at medium frequencies results from the conservative influence of the fluid, and attenuation, from the combined dissipative effect of internal and viscous losses. The types of media and frequency ranges are revealed in which attenuation is determined mainly by the forces of internal or viscous friction.