Staged Characteristics on the Consistency Parameters of the Focal Mechanisms of the 2021 Yangbi MS6.4 Earthquake Sequence in Yunnan

Abstract Using broadband seismic data provided by the Yunnan regional seismic network and the Cut-And-Paste(CAP) method to calculate the focal mechanism solutions for 38 earthquakes with MS≥3.0 before, during and after the May 21, 2021, Yangbi, Yunnan earthquake of Ms6.4. In addition, the minimum 3-D rotation angles (KA) of the focal mechanism solutions combined with a high-resolution earthquake catalog is employed to study the spatial and temporal evolution of the consistency parameters of all focal mechanisms of the Yangbi earthquake sequence. The results show that the fault plane solution of the Yangbi MS6.4 earthquake is 138° in strike, 79° in dip, and -165° in slip angle, which constitutes a major right-lateral strike-slip movement with a small amount of normal slip. The seismogenic fault is not the known Weixi-Qiaohou-Weishan fault, but a secondary fault to the west of it. Consistency of the focal mechanisms of the earthquake sequence is analyzed in three stages, elucidating the following characteristics: (a) From 18:00 on May 18 to 20:00 on May 21, 2021, the focal mechanism solution consistency of the foreshock sequence is obvious (KA