WHAT CONTROLS AN EARTHQUAKES SIZE - RESULTS FROM A HETEROGENEOUS CELLULAR-AUTOMATON

The controls on an earthquake's size are examined in a heterogeneous c ellular automaton that includes stress concentrations which scale with rupture size. Large events only occur when stress is highly correlate d with strength over the entire fault. Although the largest events occ ur when this correlation is the highest, the magnitude of the correlat ion has no predictive value as events of all magnitudes occur during t imes of high stress/strength correlation. Rather, the size of any part icular event depends on the local stress heterogeneity encountered by the growing rupture. Patterns of energy release with time for individu al ruptures reflect this heterogeneity and many show nucleation-type b ehaviour, although there is no relation between the duration of nuclea tion phase and the size of the event. These results support the view t hat earthquake size is determined by complex interactions between prev ious event history and dynamic stress concentrations and suggest that deterministic earthquake prediction based on monitoring nucleation zon es will not be possible.