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Center for Nonlinear Studies |
Seismologists studying earthquake waves have had great success treating earthquake faults as idealized frictional planar surfaces. However, natural faults are filled with granular gouge and are surrounded by granulated damage zones. These granular structures control the strength of the fault and add a degree of complexity to fault behavior. In particular, granular phenomena may explain the prevalence of earthquake triggering by dynamic strain (shaking), which is not predicted by bare rock frictional experiments. Understanding the implications of granular rheology on the earthquake process requires a constitutive law for granular flow in the transition from quasi-static to inertial flow regimes, but this transition remains poorly understood. This difficulty arises in part because macroscopic friction in granular media arises from highly heterogeneous compressional structures called force chains, rather than through inter-granular sliding friction. Here we explore the effect of particle angularity on the transition from quasi-static to inertial flow regimes, and demonstrate the role of force chains in shear rate dependent compaction.