Oral Presentation

Inelastic yielding in fault damage zones during rupture propagation has important implications for the earthquake energy budget, static and dynamic triggering, seismic radiation, and fault zone permeability. Fault damage zones develop through a variety of processes over many earthquake cycles, including process zone damage during fault growth, fracture and wear due to slip at geometric irregularities, and earthquake rupture propagation, but sorting out the exact source of damage in the field can be difficult. Furthermore, because the mechanics of fracture growth is highly dependent on strain rate and burial depth, the task of synthesizing information from rock mechanics experiments, fracture mechanics theory, and field observations of fault zone damage is non-trivial. Some field and experimental observations point to extensive off-fault fracture, fragmentation, and reactivation of pre-existing damage during seismic rupture during large earthquakes on mature faults, whereas other field studies seem to indicate the opposite. In this talk I will review some of these observations, some of our own observations of damage on both faults exhumed from seismogenic depths and shallow damage zones around active faults in Southern California, and our experimental work to connect damage zone structures quantitatively to the processes that form them. We have devised new experimental rock mechanics techniques to simulate complex, impulsive loading histories expected near earthquake rupture tips, and we are using them to place constraints on the stress and strain rate fields associated with coseismic rock fracture and the potential energy sink that this process represents for earthquake ruptures. Our ongoing work is focused on using fragmented and pulverized rocks to determine past earthquake rupture directivity, to better understand how fault damage zones evolve, and to develop metrics for determining the maximum credible earthquake magnitude (Mmax) on active faults by studying damage zone structure.