Granular packings and fault zones

The failure of a two-dimensional packing of elastic grains is analyzed usin g a numerical model. The packing fails through formation of shear bands or faults. During failure there is a separation of the system into two grain-p acking states. In a sheer band, local "rotating bearings" are spontaneously formed. The bearings state is favored in a shear band because it has a low stiffness against shearing. The "seismic activity" distribution in the pac king has the same characteristics as that of the earthquake distribution in tectonic faults. The directions of the principal stresses in a bearing are reminiscent of those found at the San Andreas Fault.