Predicting large events in power-law distributed avalanches: implications for earthquake forecast.

It is a common idea that power law distributed avalanches are inherently unpredictable. It mostly comes from the concept of Self-organized criticality. Nevertheless, we have found in classical simulations and experiments where the slowly addition of energy drives the system into a state of power law distributed avalanches, clear signs of both long and short term prediction. The simulations consist of a more realistic modification of the Olami-Feder-Christensen earthquake model where criticality and periodicity coexist. The experiment shows a clear power law behaviour for almost three decades in the avalanche size distribution of moving grains in a ``sandpile'' setup. Both systems display characteristic waiting times between large avalanches, and their internal structure suffer continuous variation preceding a large event. Monitoring those variations it is possible to predict large avalanches in a system if the slope of its pdf is larger than 1 in absolute value.