The Stress Field and Modeling of Instability Mechanism of the MS7.1 Yushu Earthquake in Qinghai in China

The stress field and velocity field in Yushu region are analyzed. On this basis, the earthquake mechanism of magnitude Ms7.1 on April 14, 2010, in Qinghai Yushu is simulated by numerical method with strain softening model. Fault and surrounding rock is considered as a unified system of geological media, considering surrounding rock as elastic body, fault as the elastic-plastic strain softening body. Yushu Ms7.1 earthquake occurred in the stress field formed by northward compressing of Indian plate and southeast compressing of Qinghai-Tibet Plateau. Under the effect of stress and pore pressure and boundary displacement, stress is gradually accumulated. When stress reaches the strength of damage of fault, fault displacement softening is produced, fault slides suddenly, the energy is released suddenly. The sudden drop of stress results in the earthquake occurrence. According to this process, the Yushu earthquake of Ms7.1 is modeled. The stress drop, energy release amount, the magnitude of dislocation of fault, and earthquake recurrence intervals are given by modeling. Comparison of the modeling results with the results of geologic survey in the field shows that they are in good agreement.