The effects of scattering from heterogeneities in porosity during sound propagation through sand sediments.

Abstract

Sand sediments are inherently heterogeneous due to the random packing of the grains. For sound propagation through fluid-saturated sediments, these heterogeneities may lead to scattering from the coherent fast compressional wave into incoherent slow compressional waves or shear waves. This loss of energy from the fast compressional wave may account for the increase in high-frequency attenuation above that predicted by Biot theory. In a previous talk, we presented preliminary results of applying perturbation theory to Biot theory in order to model scattering from heterogeneities in the porosity [Hefner et al., J. Acoust. Soc. Am. 120, 3098 (2006)]. This theory has since been refined to properly account for scattering into both the slow compressional wave and the shear wave. In order to apply this theory to a given sand sediment, knowledge of the covariance function for the spatial variations in the porosity is required. Results of the theory will be presented for several different analytic covariance functions, as well as for covariance functions measured in simulated and real unconsolidated granular materials.