Fracture energy estimates from large-scale laboratory earthquakes

Abstract

The dynamics of fault ruptures in natural and laboratory earthquakes is governed by a balance of released elastic energy and dissipated local fracture energy. The latter is the result of various friction weakening processes occurring at the fault and is thus often estimated indirectly and from small-scale friction experiments. We analyze high-frequency strain measurements from large-scale laboratory earthquakes with gages positioned slightly away from a granite fault. The strain measurements present rapid fluctuations during fault rupture propagation, as was also observed in other experiments. Characteristics of these strain fluctuations are compared with fracture mechanics theory to estimate local fault properties. We determine fracture energy for secondary rupture fronts, which appear behind the main front where local slip occurred already. Measured fracture energy is consistent with indirect estimates from rupture termination in independent experiments but is orders of magnitude lower than reported values from rotary shear friction experiments, which may be due to large differences in overall slip.