Influence of sand/silt particle size distributions on compressional wave attenuation in marine mud sediments

Abstract

High porosity marine mud from different sites typically contains different amounts of clay, sand, and silt particles, along with other material. A recent talk [Pierce et al., ASA Honolulu, 5aAO1 (2016)] explored a mechanism for why sand and silt particles in suspension can provide the dominant contributions to the frequency dependence of compressional wave attenuation. The card-house structure of the clay is critical in supporting the particles and keeping them separated. Example calculations for spherical particles of the same size showed physically reasonable attenuation behavior at low and high frequencies. This presentation considers extensions of the approach, particularly accounting for distributions of particle sizes, and emphasizes comparisons of attenuation predictions with available field data. Using reasonable assumptions about the clay volume and the sand and silt distributions, it is possible to estimate the numbers of sand and silt particles, and consequently the attenuation, from the sediment porosity. Such results can be compared with measurements of attenuation frequency dependence for measured porosities, in order to validate or refine the model for the mechanism. Of specific interest is determination of the frequency bands over which the attenuation increases nearly linearly with frequency, as is often estimated or assumed. [Work supported by ONR.]