Experimental seismicity and avalanches in sheared granular media

We report on experiments investigating the dynamics of a 2D granular medium, consisting of a vertical layer of photo-elastic disks sheared by a slider that is pulled by a spring. The motion of the slider proceeds through a sequence of discrete events, analogues to seismic shocks, in which elastic energy stored in the spring is rapidly released. We measure the statistics of several properties of the individual events: the energy loss in the spring, the duration of the movement, and the temporal profile of the slider motion. We also study certain conditional probabilities and the statistics of mainshock-aftershock sequences. At low driving rates, we observe crackling with Omori-Utsu, Bath, and waiting time laws similar to those observed in seismic dynamics. At higher driving rates, where the sequence of events shows strong periodicity, we observe scaling laws and asymmetrical event shapes that are clearly distinguishable from those in the crackling regime.