Seismicity in Simulated Sheared Granular Matter

Abstract:

The frictional instability associated with earthquake initiation and earthquake dynamics is believed to be mainly controlled by the dynamics of fragmented rocks within the fault gauge. Principal features of the emerging seismicity (e.g. intermittent dynamic and broad time and/or energy scales) has been replicated by simple experimental setups, which involve a slowly driven slider on top of granular matter, for example. Yet, these set-ups are often limited and might not allow one to determine the universal nature of specific features. This motivated us to perform a numerical study of a spring-slider experiment based on two dimensional discrete element method simulations, which allows us to control the properties of the granular matter and of the surface of the slider, for example. Upon quasi-static loading, we observed a stick-slip-type behavior which was contrasted by a stable sliding regime at finite driving rates, in agreement with experimental observations. The avalanche-like dynamics associated with the former regime resulted in several scale-free statistical features across large parameter ranges, which closely resemble main laws of tectonic seismicity at geological scales. This includes the Gutenberg-Richter distribution of avalanche sizes, Omori-Utsu-type decay of aftershock rates, as well as aftershock productivity relation and broad recurrence time distributions. These findings suggest a common underlying mechanism for both earthquakes and shearing granular experiments, which allows for probing dynamics of earthquakes within numerically accessible time and length scales. Our study provides a numerical framework for testing the universality and generality of experimental findings as well as the identification of "essential" control parameters, which are not easily tunable in real experimental settings.