Experimental study of the evolution of fault gouge in layered sand–clay sequences

Abstract

This study focuses on clay smear processes during fault gouge evolution in sand-clay sequences at depths up to 2 km. A clay-rich fault gouge can dramatically lower the fault’s permeability, and prediction of this process is therefore relevant in groundwater modelling and hydrocarbon geology (Fulljames et al. 1997, Yielding et al 1997, van der Zee et al. 2003, 2005). We constructed an ‘underwater’ sandbox to deform layered sand-clay models of 20 × 40 × 20 cm above a 70°-dipping rigid basement fault. The experiments are run completely watersaturated to allow deformation of wet clay and cohesionless sand. The basement fault moves at 20 to 120mmh−1 to a maximum offset of 60 mm. We use quartz sand with grain size between 0.1 to 0.4mm and an illite-rich clay with a water content between 28 and 55 wt.%. Water content of the clay is used to control its shear strength and state of consolidation...