Stress-induced anisotropy in sediment acoustics

Abstract

A model to describe seismic wave propagation in both dry and water-saturated, particulate materials is derived on the basis of the response of a regular array of like elastic spheres. The theories of Hertz and Mindlin are used to model the normal and tangential compliances at the intergranular contacts and the overall response of the array is found to be governed by a set of nonlinear equations that depend on the quasistatic loading history. These equations are integrated over a particular stress history that simulates the normal buildup and relief of geostatic stress (overburden pressure) in nature. Wave velocities are evaluated at various stages during this stress history and the response is found to be anisotropic with respect to both p- and s-wave velocities. In order to simulate the response of marine sediments, the effects of water saturation are investigated by using the compliances calculated for the dry skeletal frame in conjunction with the Biot theory. Predictions of the model were compared with laboratory experiments and all the general trends in response were found to agree.