Evolution of co-seismic off-fault damage towards pulverisation

Pulverisation of rocks occurs through dynamic processes associated with earthquake ruptures. At the well-known pulverised rock outcrops along San Andreas Fault (SAF), intensity pulverisation was shown to be highly heterogeneous on outcrop (m–10s m) scale, although detailed documentation this heterogeneity is still lacking. Here we derive a standardized classification method for applicable field observations that have been or dynamically shattered. We apply mature SAF and smaller displacement fault, Borrego (BF). Centimetre-scale mapping revealed damage at both locations, but while SAF, it mostly meso-fracture causes BF, sporadic observed adjacent fault core. postulate pattern in evolved from an originally patchy distribution meso-fractures as BF. develop damage-evolution model, which originating focussed subsidiary faults yields elastic properties therefore strain-rate future passing rupture. As depends strain rate, then responsible matured fault. This model integrates heterogeneity, results laboratory experiments thresholds, theoretical considerations origin zone rocks.