Jack J. Kolle
Alan C. Mueller
QUEST Integrated, Inc., 21414 68th Ave. S., Kent, WA 98032
Jack Dvorkin
Stanford Univ., Stanford, CA 94305
A finite-element microstructure analysis code was used to model the geoacoustic properties of shallow marine clay sediments in Eckernfoerde Bay which has been the subject of an intensive geoacoustic and geotechnical study (Coastal Benthic Boundary Layer---Special Research Program). Uniaxial strain and pure shear were applied to two-phase microstructure models with generalized, periodic plane-strain boundary conditions to generate anisotropic bulk and shear moduli. Analyses were carried out on two length scales: clay microfabric ((mu)m) and gas-filled inclusions (mm). The clay microstructure was modeled as a random lattice of Illite platelets with a density and porosity equivalent to average values observed in shallow Eckernfoerde Bay sediments. Saturated and dry framework moduli were calculated and the effective medium velocities were compared with observed velocities. The analysis suggests that shear wave propagation in these sediments is not supported by the framework structure but by differential compression of fluid-filled pores. Radiographic images of pressurized cores containing gas-filled inclusions with dimensions of a few millimeters were also analyzed. The analysis indicates a shear wave velocity anomaly related to the inclusion structure. The calculated effective medium velocities are compared with analytical models of spheroidal inclusions. [Work supported by ONR.]