Intermediate-Term Medium-Range Precursory Accelerating Seismicity Prior to the 12 May 2008, Wenchuan Earthquake

摘要

In the study of the predictability of great earthquakes in the perspective of seismicity analysis, two issues are presently controversial, and need more detailed studies based on real earthquake cases. The first issue is whether there exists pre-shock accelerating behavior of seismicity which is robust against the changing of spatio-temporal ranges for the sampling of seismic events, and the second is whether such an accelerating behavior is physically associated with an approach to the critical point. To answer these two questions, a retrospective case study was conducted on the 12 May 2008, Wenchuan earthquake, using the local earthquake catalogue in Sichuan and Yunnan Provinces, China, with cutoff magnitude M_L3. 0, from 1977 to 2008. The results show that the answer to the first question appears to be 'yes'; that is, in a finite spatial domain within the last couple of years before the event, clear accelerating seismicity could be observed. The answer to the second question cannot be obtained merely by examining seismicity data. However, detailed analysis of the accelerating behavior reveals a potential spatial correlation between the accelerating region and a known asperity, which might be an evidence for that the observed acceleration may have a geometrical or mechanical rather than statistical origin.