Avalanche precursors in a frictionnal model

An experimental approach to study precursors to avalanches is to progressively tilt a box filled with sand and to monitor the events that take place below the avalanche angle. Such experiments have shown the existence of two types of events: localized rearrangements implying only a few grains and large coherent events implying an increasing part of the sample. Those micro-ruptures occur with an angular periodicity, starting from about half of the avalanche angle until the avalanche takes place.

We will present a numerical and theoretical study of a simple one-dimensional model which captures most of those experimental features. The model consists in elastically coupled sliders on a frictional incline of variable tilt. This simplified model allows a statistical approach leading to master equations describing the state of the system as a function of the angle of inclination. Our central results are the possibility of incomplete stick-slip events under the threshold and the existence of an internal threshold for the outbreak of rearrangements well below the avalanche.