Strong earthquakes loading of the 2021 Madoi M_W7.4 earthquake and its effects on stress disturbances in surrounding area

On May 22, 2021, the M_W7.4 earthquake occurred in Madoi, Qinghai. In order to explore the loading and unloading effects of different sliding models of Madoi earthquake on the surrounding areas and fault stresses, in this paper, the co-seismic sliding model （Model C） is obtained by taking GNSS data as a constraint combining the inversion of the geometric structure of the fault plane of Model A （Institute of Geology, China Earthquake Administration）, and then the loading and unloading effects of Madoi earthquake on the surrounding areas and fault stresses are calculated by using Model A, Model B （USGS）, and Model C respectively. The results show that: ① The moment magnitude of Model C is M_W7.46, the maximum slip is 3.39 m, the main fracture is located in the depth range of 0−10 km, the east side of the overall fracture is larger than the west side, the slip distribution is more uniform and smoother than Model A, and the inversion effect is good. ② The stress distributions calculated by different models are basically the same. The area of co-seismic Coulomb stress loading along the fracture segment increases with the depth, and there are both two distinct Coulomb stress loading areas at the west and east ends of the seismogenic fault zone. Significant stress loading occurs in the east and west sections of Kunlunshankou-Jiangcuo fault, Garze-Yushu fault, east section of the East Kunlun fault, Madoi-Gander fault, middle and west sections of Qingshuihe fault and west section of Dari fault. However, the Model B calculations differ, with the middle section of the Kunlunshankou-Jiangcuo fault in a state of stress unloading at the location. The fault stress state did not change much in the 10 post-seismic years, but the eastern section of the Qingshuihe fault had more significant stress unloading in the post-seismic stress adjustment, and the seismic hazard was reduced. ③ In order to explore the impact of strong earthquakes on Madoi earthquake, this paper calculated the co-seismic and post-seismic effects of the M≥7.0 strong earthquakes in Bayan Hara block after the 2008 Wenchuan earthquake on the stress loading and unloading of Madoi earthquake respectively. The results show that the Madoi earthquake is subject to strong earthquake loading, but it does not exceed the trigger threshold.