Crackling to periodic transition in earthquake dynamics: a granular stick-slip experiment*

We perform a stick-slip experiment to characterize the dynamics of sheared granular media. In our experiment, a constant speed stage pulls a slider which rests on a vertical bed of circular photo-elastic particles in a 2D system. The stage is connected to the slider by a spring.

We measure the force applied to the slider using a force sensor attached to the spring. This force provides a global measure of the shear stress. From a more local point of view and by using a high speed camera and the photo-elastic properties of our particles, we characterize the local stress change in the granular medium. Using signal analysis of these global and local measures, we can identify a crackling to periodic transition as we change driving rate and system stiffness. We provide a phase diagram of different regimes and the scaling laws of the transition. we also study the effect of other parameters such as global pressure and system size and how global and local signals are related to each other.