Relocation of the Foreshocks and Aftershocks of the 2021 Ms 6.4 Yangbi Earthquake Sequence, Yunnan, China

An Ms 6.4 earthquake occurred in Yangbi, Yunnan, China on May 21, 2021, which has obvious foreshock activity and abundant aftershocks. Based on the seismic observation data recorded by the Yunnan Seismic Network three days before and seven days after the mainshock, a double-difference location method was used to relocate 2 133 earthquakes of the Yangbi sequence. Aftershocks are mostly distributed to the southeast of the mainshock in a unilateral rupture pattern. This sequence exhibits a SE-trending linear alignment with a length of about 25 km, and most of the focal depth is above 12 km. Integrated with the seismic distribution and focal mechanism results, we infer that the strike of the seismogenic fault is about 140°, and dipping to the SW. The fault structure revealed by the seismic sequence is complex, with the NW segment exhibiting a steep dip and relatively simple structure of strike-slip rupture and the SE segment consisting of several branching ruptures. The Yangbi Earthquake is a typical foreshock-mainshock-aftershock sequence, and the mainshock is likely triggered by the largest foreshock. This earthquake occurred in the boundary between high- and low-velocity anomalous zone, where is susceptible to generate large earthquakes.