A model for the variation in permeability of clay-bearing fault gouge with depth in the brittle crust

A model of the variation in permeability of clay-bearing fault gouge in the brittle crust is presented. Factors affecting the permeability from laboratory experiments are considered and quantified. These are pressure, temperature and permeating fluid. Effective pressure ((sigma) over bar) and temperature ( T) effects on permeability (k) are described by k = k(0)exp(-0.01Delta(sigma) over bar )exp(-0.01DeltaT) where k(0) is a reference permeability at a particular temperature and pressure. At low temperatures (<80 degrees C), with aqueous pore fluids, the above relation is modified to k = k(0)exp(-0.01 Delta<(sigma)over bar>) (T/T-c)(1.2) exp(-0.01DeltaT) in order to describe low temperature ( less than a critical temperature, T-c, of 80degreesC) inferred physicochemical interactions between pore fluids and the fault gouge. The model is used to predict the variation in permeability as a function of depth for different ratios (lambda) of pore fluid pressure to confining pressure.