关键词: 库仑应力, 水库, 汶川M_S 8.0地震, 地震活动, 统计模型

Abstract: To investigate the mechanism of seismicity due to impoundment of a reservoir,we propose a method for integrated study on regional/local seismicity and stress by both surface loading and pore pressure diffusion.As an example,possible role of Zipingpu Reservoir on nearby seismicity was studied in detail.The epicenter of the M_S 8.0 Wenchuan earthquake on May 12 of 2008 is very close to the Zipingpu Reservoir.On one hand,several statistical properties including event rate(n),cumulative energy release(E),seismic b-value in the magnitude-frequency relation,and spatial correlation length(SCL)of earthquakes occurring in Zipingpu area from 2004.8 to 2008.5.11 were estimated in detail.On the other hand,we quantitatively examined change of Coulomb Stress(ΔCFS)due to the impoundment of the reservoir.Both weight loading and pore pressure diffusion resulted in significant ΔCFS on the underlying Yingshu-Beichuan and Guanxian-Mianzhu Faults,which are considered as the source faults of the Wenchuan earthquake.Some clear correlations were verified between the local seismicity and stress change,thus we concluded that the impoundment of Zipingpu Reservoir clearly affected the local seismicity and it is worthwhile to further study if the effect played a role in triggering the Wenchuan earthquake.

Key words: Coulomb failure stress, M_S 8.0 Wenchuan earthquake, dam, seismic activity, statistic model