THE EFFECT OF FAULT SLIP ON PERMEABILITY AND PERMEABILITY ANISOTROPY IN QUARTZ GOUGE

The effects of fault slip on permeability and permeability anisotropy have been investigated during large displacement shearing of quartz ba re surfaces and 1 mm thick artificial quartz gouge at a normal stress of 25 MPa. Within the first 10 mm of shear displacement, grain size re duction occurred nearly uniformly within the fault zone. Permeability decreased by 2-3 orders of magnitude and the permeabilities perpendicu lar and parallel to the fault plane remained approximately equal. With further increasing shear displacement up to 200 mm, deformation was l ocalized within a band of Y shears where strong grain comminution occu rred. Permeability decreased further by 1-2 orders of magnitude and th e permeability perpendicular to the fault showed larger reduction than parallel to it. A permeability anisotropy of about one order of magni tude developed. The permeability anisotropy is a result of heterogeneo us deformation within the fault zone; flow perpendicular to the fault zone is impeded by the fine-grained band of Y shears, but flow paralle l to the fault zone can occur in the less-deformed adjacent gouge. Our results suggest that fluid flow in natural faults depends on the degr ee of shear localization and the permeability contrast between the loc alized zone and the rest of the fault zone. (C) 1998 Elsevier Science B.V. All rights reserved.