AFTERSHOCK SERIES OF EVENT FEBRUARY 18, 1996 - AN INTERPRETATION IN TERMS OF SELF-ORGANIZED CRITICALITY

An aftershock interevent time series, initiated on February 18, 1996, in the eastern Pyrenees was analyzed. The threshold detection magnitud e was set at 1.9, and the series was assumed to be complete for an int erval of 77 days. The original time series does not fit Omori's law, p robably because of sudden changes in the rate of occurrence, interpret ed as an increase. in the. production rate. When the recorded intereve nt time! series is classified in ter ms of leading aftershocks (those that satisfy a relaxation process) and cascades (those occurred at a n early constant rate), the new time series of the leading aftershocks f its Omori's law quite well, with p = 0.94. Interpreted in terms of Die trich's model, the series of leading aftershocks correctly predicts a return time for the main shock of the order of 50 years. To interpret the series of cascades, a minimalist, self-organized critical model wa s used. Although it is very simple, the model correctly reproduces the two-level structure in the observed time series, that is, the sequenc e. of leading aftershocks and a cascade sequence emerging from each af ter shock. This model may be given physical justification in terms of the Cochard and Madariaga [1996] nucleation model.