Characteristics of regional tectonic stress field in Wenchuan area and the effect of Wenchuan M_S8.0 earthquake on surrounding major fault surfaces

To analyze the influence of the 2008 Wenchuan M_S8.0 earthquake on later earthquakes and the characteristics of the tectonic stress field in the seismogenic region, we first used 1660 source mechanism solutions of the Wenchuan earthquake and its neighboring areas from May 12, 2008 to April 19, 2013, and also used the method of sieving the central solution of multiple source mechanism solutions of the same earthquake to remove the source mechanism solutions of repeated seismic events, and finally 911 solutions were obtained. Then, the regional tectonic stress field is inverse-performed by the grid search method. The results show that the northeast zone is mainly squeezed by the WNW-ESE direction, the southwest zone is squeezed by the W-E direction, and the central zone is squeezed by the WSW-ENE direction. There is a change in the direction of the main compressive stress axis from southwest to northeast, which may be related to the combined effect of subduction thrusting from the north-northeast direction of the Indian plate, blocking from the Sichuan basin and southeastward extrusion of the Bayan Kara block in the Longmenshan area. Then, based on the rupture model of the Wenchuan M_S8.0 earthquake given by the USGS, the triggering relationship of this earthquake on nearby strong earthquakes is calculated. The results show that this Wenchuan earthquake has a significant triggering effect on the Lushan earthquake, which also belongs to the southwest end of the Longmenshan fault, and on the Maduo earthquake, which is located on the East Kunlun fault. Finally, the coseismic Coulomb stress changes of the surrounding faults caused by the Wenchuan M_S8.0 earthquake were calculated. It is found that this earthquake caused an increase in Coulomb rupture stress on the north and south ends of the Longmenshan fault, the south edge of the Qinling fault, the southeast end of the Xianshui River fault, the East Kunlun fault, and the Baiyu fault, with the most obvious increase on the north and south ends of the Longmenshan fault and the south edge of the Qinling fault, which is a reference for the analysis of seismic hazards.