Variability of parameter estimates used in the Buckingham viscous grain shearing model.

Abstract

A compilation of 54 sets of geoacoustic measurements of marine sediments was reviewed in order to bound estimates of parameters for use in Buckingham’s grain shearing (GS) theory of acoustic propagation. These data, for unconsolidated sands (siliciclastic and carbonate) with grain sizes between 0.0156 and 0.57 mm, were all made in shallow water (maximum depth of 60 m) sites at diverse locales. In each data set, measurements of the speed and attenuation of the compressional wave at high frequency, the shear wave speed at 1 kHz, porosity, and bulk density are sufficient to calculate the three free parameters in GS theory (a material exponent, a compressional coefficient, and a shear coefficient). The spread of the values calculated for GS parameters, combined with a sensitivity analysis, does not support the use of a single material exponent value for all sediments. Shear wave attenuation measured at 18 sites was compared to the predictions of Buckingham’s (2010) most recent version of the VGS model. In this model the shear viscoelastic time constant is based on the wavelength of the propagating shear wave rather than shear speed.