High-resolution earthquake catalog for the focal area of the Qinghai Madoi M-S 7.4 earthquake based on deep-learning phase picker and dense array

High-resolution earthquake catalog is helpful to describe the fine structure of faults and to understand the seismogenic mechanism. Based on the seismic data recorded by short-period array which were deployed after Madoi M-S 7. 4 earthquake, we build high-resolution seismic catalogues by using a sequential earthquake association and location workflow which includes a deep-learning phase picker (PhaseNet), and multiple earthquake locating methods. Our high resolution catalog reveals the temporal and spatial distribution characteristics of earthquake sequences and the shape of seismogenic faults in the west of the main shock and 20 km east of the main shock of the Madoi focal area. The results show that the frequency of earthquakes gradually decreases with time and tends to be stable. The earthquake sequence is distributed in strips along the surface fracture and concentrated on the north side of the fracture zone, with the strike of NWW-SEE. The depths of earthquakes are mainly within 15 km. The cross sections show that fracture surface of the seismogenic fault tilts northward as a whole, but the dip angle changes to southward at the depth of 8 similar to 10 km. It indicates that the fracture surface is not a single plane structure, which may be affected by local tectonic stress or physical property differences. The fault morphology in different regions is different and shows obvious segmentation. In the western section (south of E'Ling Lake), the strike of the earthquake sequence is near E-W, showing a certain corner with the overall sequence, and the fault dip is near vertical, with a dominant seismogenic layer at 8 similar to 12 km. The seismicity of the middle section (from E' Ling Lake to Huanghe Town) is relatively weak, and the depths of earthquakes are shallow concentrating at 2 similar to 5 km. Bounded by Yematan Bridge, the earthquake sequence on the west side is wide and continuous, and the earthquake sequence on the east side is characterized by clustering. Small seismic gaps or sparse areas appear here. The east section (east of the main shock) has the strongest seismicity, and the seismogenic depth is mainly 8 similar to 12 km. The earthquake sequence has a northward convex radian in this section, indicating that the region may be subject to local tectonic action and form a complex seismogenic environment.