Study on the Effect of Zipingpu Reservoir on the Occurrence of 2008 Wenchuan MS7.9 Earthquake Based on a 3D‐Poroelastic Model

It has been well recognized that large reservoir may induce earthquake. After May 12th, 2012 Wenchuan MS7.9 earthquake, people turn to think that it might be triggered by the impoundment of Zipingpu reservoir, which is located a few kilometers away from the epicenter of this devastating event. This scientific issue is still under hot debating to date in both geodynamics and seismology communities. In this paper, we first propose a 3D finite element numerical model of Zipingpu reservoir region based on the poroelastic scenario. Based on the water level fluctuation record of Zipingpu reservoir from the very beginning of impoundment to the occurrence of 2008 Wenchuan earthquake, we calculate the pore pressure and the change of Coulomb stress on the fault plane. Then, we discuss the effects of elastic modulus and diffusivity of fault gouge and materials around the faults. Our primary results indicate that the elastic modulus of fault gouge and the materials around the faults have relatively neglectable effect, compared to that of the diffusive coefficient, on the Coulomb stress change at the hypocenter of this earthquake. The Coulomb stress change at the hypocenter increases coherently with the increasing diffusivity of the faults and their neighboring areas. Given the values of elastic modulus and diffusivity in our model, the change of Coulomb stress at the hypocenter obtained is around 1 kPa when Wenchuan MS7.9 earthquake happened. From the local earthquake catalog after the impoundment of the reservoir, the seismicity activities around Zipingpu reservoir regions does intensified, although the magnitudes of them are almost no more than MS2.2. However, we find that most of the small events happened before Wenchuan MS7.9 earthquake are located in the region of Coulomb stress increases, which indicates that most of the small earthquakes could have direct relationship with the impoundment of Zipingpu reservoir.