The Self-Organized Criticality and Periodicity of Temporal Sequences of Earthquakes

Abstract A new cellular automaton model has been developed to examine the nature of temporal sequences of earthquakes. The model takes the space dependence of strength on inhomogeneous faults into account and assumes that an earthquake produces a continuously connected area with uniform stress drop. In the model viscous slip is also introduced so that earthquakes may be realizable only when the applied stress accumulates faster than the viscous relaxation. The analysis reveals that the sequences of earthquakes commonly satisfy the power law relation between the intensity and frequency of earthquakes so that earthquakes may be in the state of self-organized criticality. On the other hand, periodicity appears in some sequences that consist of the groups of high seismic activity repeated between calm intervals at an almost constant period. Therefore, self-organized criticality and periodicity coexist in these sequences and the claim that earthquakes are unpredictable because of self-organized criticality may be inadequate.