The seabed as a mesoscopic porous medium

The seabed is composed of a variety of solid materials permeated by seawater, and therefore it is a poro-elastic material. In the case of granular seabed types, such as gravel, sand, and silt, there is little doubt regarding its porous nature. In the case of softer marine sediments, such as mud and clay, it has also been shown to be a poro-elastic material, in which the presence of saltwater is a critical ingredient. Depending on the sediment type, the pore sizes can range from fractions of a micron to a few millimeters, which puts it in the mesoscopic range. There are two main loss mechanisms, the creep loss within the skeletal frame and the viscous drag due to relative motion between frame and pore fluid. The main difference between poro- and visco-elastic media is the relative motion between the skeletal frame and the pore fluid. When the effects of the relative motion become negligible, a simpler visco-elastic approximation is justified. The equations of the visco-elastic approximation may be derived from the poro-elastic model. [N. Chotiros was funded by the U.S. Office of Naval Research, Code 32 Grant N00014-23-1-2522.]