Wave and Material Properties of Marine Sediments: Theoretical Relationships for Geoacoustic Inversions

In recent years, a theory of wave propagation in marine sediments has been developed, based on the grain-to-grain interactions that occur during the passage of compressional and shear waves. The theory yields a dispersion pair, representing phase speed and attenuation, for each wave. These expressions are functions of frequency and the physical properties of the sediment, that is, the porosity, density, grain size and over-burden pressure (or depth in the medium). The predicted functional dependencies are compared with extensive data sets that have appeared in the literature over the past couple of decades. No adjustable parameters are available to help improve the comparisons. In all cases, the theory shows a high level of agreement with the data. This agreement even extends to both attenuations, in that the theory, which predicts intrinsic attenuation, arising from the conversion of wave energy into heat, accurately traces out the lower bound of the widely- distributed measurements. This is physically reasonable, since the data represent effective attenuation, which includes additional sources of loss such as scattering from shell fragments and other inhomogeneities in the medium. It is suggested that the set of simple algebraic expressions comprising the theory have application in evaluating the geoacoustic parameters of the seabed, all of which may be computed from knowledge of just one, say the compressional wave speed or the porosity.