The apparent friction of granular fault gouge in sheared layers

Data are presented from a series of experiments on layers of granular quartz gouge in the double-direct-shear geometry at a normal stress of 25 MPa. The apparent friction of a layer shows considerable variability depending on the thickness of the layer and the particle size distribution of the gouge. Measurements of layer thickness during the experiments also show that the layers thin as shearing proceeds. When densification is also admitted, a simple flow law with one adjustable parameter is required to relate the volumetric and shear strain rates. -from Authors