Buckingham Michael J
Marine Physical Laboratory, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0238, USA.
J Acoust Soc Am. 2020 Aug;148(2):962. doi: 10.1121/10.0001778.
In the viscous grain shearing (VGS) theory of wave propagation in an unconsolidated sediment, the dispersion formulas for the phase speed and attenuation of the compressional and shear wave involve two parameters, the compressional modulus, γ, and the shear modulus, γ, which depend on the radius of the circle of contact between contiguous grains in the granular medium. The radius of contact itself depends on the overburden pressure, and hence depth, in the sediment. Based on these observations, the VGS theory is extended to create a geo-acoustic model of a horizontally stratified sediment in which each layer has a uniform porosity, bulk density, and mean grain size, all of which are assumed known from geological survey data. In a given layer, the overburden pressure consists of the contributions from all the higher layers. From the overburden pressure, the compressional and shear moduli are expressed as functions of depth throughout the layer, thereby allowing the frequency dependent phase speed and attenuation profiles of both types of wave to be computed from the VGS dispersion formulas. To illustrate the VGS geo-acoustic modeling technique, two examples are discussed, one of which represents the mud overlying sand sediment at the New England Mud Patch.
