Self-organized criticality applied to natural hazards

The concept of self-organized criticality evolved from studies of three simple cellular-automata models: the sand-pile, slider-block, and forest-fire models. In each case, there is a steady "input'' and the "loss'' is associated with a fractal (power-law) distribution of "avalanches.'' Each of the three models can be associated with an important natural hazard: the sand-pile 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 interval for a severe event can be estimated by extrapolating the observed frequency-size distribution of small and medium events. For example, the recurrence interval for a magnitude seven earthquake can be obtained directly from the observed frequency of occurrence of magnitude four earthquakes. This concept 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 events 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.