Fluid reservoirs in the crust and mechanical coupling between the upper and lower crust

An important observation associated with seismic activity on the Nagamachi-Rifu Fault is the existence of tabular, fluid rich zones at mid-crustal levels. These zones resemble the “bright spots” seen in many seismic images of the crust worldwide. The aim of this paper is to develop the mechanical foundations for the formation of such zones. To do so requires an understanding of the distribution of pore fluid pressure in a deforming crust. In a hydrostatically stressed porous material, the pore fluid pressure should equal the mean stress in order to keep the pores from collapsing. Past discussions of this subject imply very high pore fluid pressures, two to three times lithostatic. Considera…