Wenchuan aftershocks as an example of self-organized criticality

Abstract

Analysis of the magnitude and temporal distributions, described by the Gutenberg–Richter and Omori laws respectively, in the sequence of aftershocks of the Wenchuan Ms8.0 earthquake occurred on Longmenshan tectonic zone of Sichuan Province in China, has been performed. The power exponent b=0.71±0.13 and p=2.08±0.29 in the form of the Gutenberg–Richter and Omori laws respectively. Dose there exist a simple mechanism which can explain these statistical relations of Wenchuan aftershocks together? In order to provide a possible explanation for these observed distributions, we develop a new self-organized criticality (SOC) model by introducing stress decay coefficient and anisotropic diffusion factors into Olami–Feder–Christensen model of earthquakes. The self-organized criticality properties of the model are discussed. The model displays a robust power law behavior in certain stress decay coefficient region. The model can give a good prediction of the Gutenberg–Richter and Omori laws in Wenchuan aftershock together. The high correspondence of the simulated results to observations shows that Wenchuan aftershock is an example of a SOC process. It is SOC of Wenchuan aftershock process that makes it is impossible to give a fairly accurate forecast of large aftershocks.