Seismic moment release before the May 12, 2008, Wenchuan earthquake in Sichuan of southwest China
Whether seismic moment release before great earthquakes exhibits accelerating or quiescence behavior is one of the controversial topics in the study of intermediate-term earthquake forecast or time-dependent seismic hazard. The May 12, 2008, Wenchuan earthquake provides a unique opportunity to check whether accelerating moment release (AMR) or quiescence existed before this great earthquake. To systematically analyze the precursory moment release, considering the special characteristics of this great inland thrust event, we took four upgraded approaches using the local earthquake catalogue with cutoff magnitude M(L)3.0. We propose a BIC criterion as a development of the curvature parameter q to identify the statistically significant acceleration or quiescence behavior as compared with linear increase. We use an 'eclipse method' as a development of the 'interfering event consideration' to eliminate the interference from the nearby seismically active fault zones. We consider the distribution of m-coefficient in the (T, R, M(c)) space, to explore the variation of moment release behavior with temporal window length T and spatial window radius R centered at the nucleation point, and cutoff magnitude M(c) of the catalogue in use. We use not only circular windows but also 'crack-like' windows to investigate the overall behavior of the moment release associated with the Wenchuan earthquake. Through this retrospective case study, it is observed that moment release before the Wenchuan earthquake did show accelerating moment release (AMR) and quiescence behavior for different spatio-temporal ranges, with robustness to some extent against the changing of parameters, indicating the preparation process of this great earthquake. However, for this earthquake, to constrain the failure time in a forward forecasting mode is shown to be difficult. Copyright (c) 2009 John Wiley & Sons, Ltd.
wenchuan earthquake quiescence amr bic 'eclipse method'