Fragmentation dynamics within shear bands - a model for aging tectonic faults?

A numerical model for packing of fragmenting blocks in a shear band is intr oduced, and its dynamics is compared with that of a tectonic fault. The she ar band undergoes a slow aging process in which the blocks are being grinde d by the shear motion and the compression. The dynamics of the model have t he same statistical characteristics as the seismic activity in faults. The characteristic magnitude distribution of earthquakes appears to result from frictional slips at small and medium magnitudes, and from fragmentation of blocks at the largest magnitudes. Aftershocks to large-magnitude earthquak es are local recombinations of the fragments before they reach a new quasi- static equilibrium. The aftershocks satisfy Omori's law. Local precursor ac tivity at a few times the normal background level appears at a short time b efore a major earthquake, Seismic gaps appear as a natural consequence of t he aging process of a fault. Explanation of the heat flux and principal str ess direction anomalies at the faults both involve the value of fracture st ress of the blocks in the gouge. The final form of a tectonic fault is pred icted to involve a Rouge dominated by fine-grained and rather rounded block s so that it cannot withstand large shear stresses.