SEISMICITY AND SELF-ORGANIZED CRITICALITY

Distributed seismicity appears to fit the definition of a self-organized, critical phenomenon. In this paper a cellular-automata model is presented as an analog to distributed seismicity. We consider a grid of boxes with a fractal distribution of sizes. Particles are randomly added to the boxes. When the number of particles reaches a critical value they are redistributed to adjacent boxes and edge or corner boxes lose particles off the grid. The addition of particles is analogous to crustal strain and the redistribution from a box is equivalent to a characteristic earthquake on a fault. A redistribution from a small box (a foreshock) may trigger an instability in a larger box (the main shock). A redistribution from a large box always triggers many instabilities in adjacent smaller boxes (aftershocks). The frequency-size statistics for both main shocks and aftershocks satisfy the Gutenberg-Richter relation. Model foreshocks occur 28% of the time, in good agreement with actual foreshocks. No systematic precursors are observed prior to model earthquakes, also in agreement with the present status of earthquake prediction studies.