The impact of Wenchuan MS8. 0 earthquake on the seismic activity of surrounding faults

In order to analyze the effect of Wenchuan M(S)8. 0 earthquake on the seismic activity of surrounding faults, we calculate the dynamic changes of Coulomb stress caused by the Wenchuan M(S)8. 0 earthquake with a Burgers viscous relaxation model. Simulation result shows significant increase of Coulomb stress on four majors fault segments, which are Daofu-Kangding section in the Xianshuihe fault, Maqu section in the East Kunlun fault, the southern section of the Longmen Shan fault, and the Qingchuan fault respectively. Furthermore, the Coulomb stress change caused by the post-seismic relaxation during 4 years after Wenchuan M(S)8. 0 earthquake is so strong that it almost matches to that caused by the co-seismic rupture. That is to say, the effect of the postseismic relaxation is nearly equal to that caused by the Wenchuan earthquake itself. This is a strong evidence that the postseismic relaxation is critically important so it should not be neglected on evaluating the effects of strong earthquake. Taking the postseismic effect into consideration, the probability of seismicity is evaluated by the Dieterich (1994) model based on the dynamic evolution of Coulomb stress and the background seismic rate. Combining the relevant structural geology, historical earthquake, aftershocks activities and some other minor factors, a comprehensive analysis shows that the seismic hazards on the above four fault segments are ranked from high to low as Daofu-Kangding section in Xianshuihe fault, the southern section of the Longmen Shan fault, the Maqu section in East Kunlun fault and the Qingchuan fault.