Numerical experiments on weak shock propagation in marine sediments

NRL is planning a set of laboratory and field experiments to investigate weak shock propagation in saturated marine sediments. Questions to be addressed are as follows: (1) How much does the granular content of the sediment increase the effective nonlinearity coefficient? (2) Does the 3/2 order Hertzian nonlinearity inherent to grain contacts play a significant role? Numerical and analytic solutions involving the Hertzian nonlinearity reveal maximum nonlinearity coefficient near zero stress, whereas in a fluid, nonlinearity increases with stress. Numerical experiments are presented using the NPE model [McDonald and Kuperman, J. Acoust. Soc. Am. 81, 1406 (1987)] to determine whether shocks resulting from Hertzian nonlinearity can be observed in the presence of nominal values of frequency-linear attenuation common to granular media. [Work supported by the Office of Naval Research.]