Coseismic displacement and slip distribution of the 2021 May 22, M(s)7. 4 Madoi earthquake derived from GNSS observations

On May 22, 2021, an M(s)7. 4 earthquake struck in Madoi County, Guoluo Prefecture, Qinghai Province of China. The surface rupture caused by this earthquake shows obvious segmentation characteristics in space. Based on the observations of continuously operating GNSS networkes from different sources, we obtained the fine three-dimensional coseismic deformation field of the earthquake. The results show that the maximum horizontal displacement is 280 mm and the maximum vertical deformation is only 25 mm, indicating that the thrust component of this earthquake is small. The coseismic deformation, with obvious sinistral strike slip characteristics, is basically symmetrical with a wider influence range in NW-SE direction. The epicentral distance range with horizontal coseismic deformation greater than 3 mm in this direction exceeds to 500 km. Futher, constrained by the relocated results of the aftershocks and the 3D coseismic deformation field observed by GNSS, we constructed a fault model with a broken surface fracture line, a dip angle of 85 degrees and along the strike of SW. The result of coseismic slip distribution shows that the sliding fractures are unevenly distributed on both sides of the epicenter, and they all ruptured to the surface, with the depth of similar to 15 km, the maximum sliding amount is 4.73 m, and the calculated moment magnitude M-w 7. 37. This result is consistent with the relocated results of aftershocks. The maximum rupture area is just located in the early aftershock gap, so we speculated that the future seismic risk in this gap is low. At last, we simulated the deformation and strain fields in the epicenter area based on the inversion results, and by combining the compression characteristics of the strain values on the southeast side of the fault surface trace and the existing research results, we concluded that this earthquake enhanced the accumulation characteristics of the compressive stress of the Bayan Har block in the eastern region. As a result, the seismic risk in the eastern region is enhanced, which is worthy of a follow-up study.