Self-organized criticality applied to natural hazards

The concept of self-organized criticality evolved from studies of three sim ple cellular-automata models: the sand-pile, slider-block, and forest-fire models. In each case, there is a steady "input'' and the "loss'' is associa ted with a fractal (power-law) distribution of "avalanches.'' Each of the t hree models can be associated with an important natural hazard: the sand-pi le model with landslides, the slider-block model with earthquakes, and the forest-fire model with forest fires. We show that each of the three natural hazards have frequency-size statistics that are well approximated by power -law distributions. The model behavior suggests that the recurrence interva l for a severe event can be estimated by extrapolating the observed frequen cy-size distribution of small and medium events. For example, the recurrenc e interval for a magnitude seven earthquake can be obtained directly from t he observed frequency of occurrence of magnitude four earthquakes. This con cept leads to the definition of a seismic intensity factor. Both global and regional maps of this seismic intensity factor are given. In addition, the behavior of the models suggests that the risk of occurrence of large event s can be substantially reduced if small events are encouraged. For example, if small forest fires are allowed to burn, the risk of a large forest fire is substantially reduced.