The department has an active program in rock mechanics focused primarily on understanding the nucleation and propagation of earthquake ruptures. Problems include understanding the mechanical processes that generate fault-gouge, fault-breccia, and off-fault fracture damage during a large earthquake and how these fault zone materials generated by previous earthquakes affect the propagation of future events. Specific areas of interest include the effective frictional response of a granular layer, the evolution of the size distribution of fragments within a fault zone, and the mechanics of fracture-damaged rock. Such studies also include the important effects of ground water and temperature. This work is closely linked to field studies of the structure of exhumed fault zones.