Three-dimensional fine velocity structure of the upper crust of the 2021 Madoi M(s)7.4 earthquake, Qinghai

Obtaining a fine three-dimensional velocity model is an important means to study the seismogenic environment. In order to explore the crustal structure and mechanism of the Qinghai Madoi M(s)7.4 earthquake on May 22, 2021, we constructed a three-dimensional fine crustal model for the Madoi M(s)7.4 earthquake area by using the local seismic P-wave traveltime data. The results show that the velocity structure around the seismogenic fault presents obvious inhomogeneity and segmentation. There is a certain angle between the surface rupture and the seismogenic fault in the southern part of the E'ling Lake. The spatial distribution of the rupture coincides with the relocated earthquake. The velocity images show that there is a large-scale high-velocity anomaly in the northern region of the rupture zone, and there is an obvious low-velocity layer below the high-velocity layer. The earthquake occurred in the high-velocity anomaly overlying the low-velocity layer. It is speculated that the southern section of the E'ling Lake may be blocked by the high-velocity anomaly in the north, resulting in the release of stress in the south and the formation of large-scale ruptures on the surface. An obvious low-velocity zone is found from Yematan Bridge to Huanghe Township. The earthquakes in the section are mainly concentrated in the overlying area of the low-velocity zone, with shallow earthquake depth and low frequency. The velocity maps show that there is a large-scale high-velocity and low-velocity boundary area about 20 km east of Huanghe Township, with the highest frequency of earthquakes and a concentrated earthquake depth of 8 similar to 12 km. It is speculated that this area may be affected by local structures, with large-scale stress release and strong seismicity.