Permeability anisotropy and pressure dependency of permeability in experimentally sheared gouge materials

• Published in: Journal of structural geology Vol. 21; no. 7; pp. 795 - 806
• Main Authors: Zhang, Shuqing, Tullis, Terry E, Scruggs, Valerie J
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.07.1999
• ISSN: 0191-8141; 1873-1201
• DOI: 10.1016/S0191-8141(99)00080-2

The effects of fault slip and effective mean stress on permeability and permeability anisotropy have been investigated during long displacement shearing of synthetic quartz, feldspar, muscovite and granitic gouges under high pressures. In quartzo-feldspathic gouges, permeability anisotropies up to one-and-a-half orders of magnitude were developed by heterogeneous grain crushing associated with shear sliding. In muscovite gouge, a permeability anisotropy of about one order of magnitude was first developed during initial pressurization of gouge materials due to a preferred alignment of mica basal planes. During shear sliding, rearrangement of packing and rotation of mica basal planes lead to a slight decrease in permeability anisotropy. The pressure dependency of permeability of gouge materials changes systematically with shear displacements. In quartzo-feldspathic gouges, the pressure dependency of permeability first decreased with shear sliding and then increased to a value typical for rocks containing microcracks. In contrast, the pressure dependency of permeability in muscovite gouge decreases continuously with increasing shear displacement. The evolution of permeability anisotropy and pressure dependency of permeability for different gouge materials during shear sliding implies that the distribution of fluid pressure in natural fault zones could be very heterogeneous.