Consistency of Focal Mechanism in Northwestern Yunnan

The focal mechanism solutions of 1338 small and medium earthquakes recorded by Yunnan sub-instability network from March 2018 to August 2020 were retrieved by HASH method. The statistical analysis of the parameters of the focal mechanism solutions and the systematic clustering results show that the source rupture in this area is dominated by normal faults, accounting for 57.8%. The average P-axis directions of various solutions are mainly NNW-SSE and NNE-SSW, and the whole is near NS direction, which is inconsistent with the overall focal mechanism type in Yunnan area, and shows the non-uniformity of stress field under the influence of local structures. Spatial scanning of consistency parameters of focal mechanism solutions shows that the Yangbi M6.4 Earthquake on May 21, 2021 occurred in the transition zone from low to high consistency parameters. Combined with velocity structure and moment tensor inversion results, the seismogenic mechanism of Yangbi earthquake is further discussed.