Abstract
This paper reports the results of laboratory permeability measurements of fault rocks and their host rocks obtained from the Median Tectonic Line in Ohshika-mura, Nagano Prefecture, central Japan, by using a gas-medium apparatus under confining pressure at dry conditions, with nitrogen as the pore fluid. Most samples from the incohesive zone under hydrostatic pressure have a permeability ranging between 10-13 to 10-17 m2, which are greater than those of cemented cataclasites and mylonites by more than 2 orders of magnitude at all effective pressures up to 180 MPa. Permeability measurements of fault gouge and cemented cataclacite specimens during triaxial compression tests revealed marked effects of deformation on the permeability, and the effects of these rocks were very different from each other. Thus, fault permeability structure is heterogeneous and anisotoropic, and may change abruptly prior to or during fault activities and during the inactive priod.
