We have performed a series of coupled deformation and permeability experiments on "synthetic" fault gouge to investigate the influence of "shaliness" on fluid flow properties. Biminerallic gouge layers were sheared between steel sliders under triaxial compression and permeability measured continuously using the pore pressure oscillation technique. Permeability was observed to range over six orders of magnitude depending on clay content and sliding. Measured porosity variations, post-test laser particle sizing and direct observation of thin-section microstructures allows development of a geometrical model for permeability evolution in fault gouge containing varying amounts of clay.

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