Earthquake behaviour and large-event predictability in a sheared granular stick-slip system

We present results from a physical experiment which demonstrates that a sheared granular medium behaves in a manner analogous to earthquake activity. The device consists of an annular plate rotating over a granular medium in a stick-slip fashion. Previous observations by us include a bounded critical state with a power law distribution of event energy consistent with the Gutenberg-Richter law, here we also reveal stair-case seismicity, clustering, foreshocks, aftershocks and seismic quiescence. Subcritical and supercritical regimes have also been observed by us depending on the system configuration. We investigate the predictability of large events. Using the quiescence between ‘shock’ events as an alarm condition, it is found that large events are respectively unpredictable, marginally predictable and highly predictable in the subcritical, critical and supercritical states.