## 5 Discussion  
### Seismogenic Fault  
The determination of the seismogenic faults of moderate and strong earthquakes can well identify the activity and distribution of faults in the surrounding area and play an important role in the assessment of geological disasters. The Yangbi Ms 6.4 earthquake area is located in the Sanjiang tectonic belt in western Yunnan on the southeastern margin of the Qinghai-Tibet Plateau, which is part of the Himalayan orogenic belt. Many scholars at home and abroad have studied the deep structure of the crust in this area through geological and different geophysical methods. Western Yunnan is a region with strong tectonic activity, frequent seismic activity, and complex deformation. In recent years, Ninglang, Tengchong, Longling, Eryuan, and Yingjiang in western Yunnan have successively experienced earthquakes of an Ms 5.0 or above. The study of the crustal structure characteristics in this area can provide scientific information for the analysis of the seismic structure and future seismic activity trends. Before the main shock of the Ms 6.4 earthquake that occurred in Yangbi, the largest foreshock of Ms 5.6 had occurred, and aftershocks of Ms 5.0 and Ms 5.2 occurred after the mainshock. Several earthquakes were located on the west side of the Sichuan-Yunnan block; therefore, from the perspective of time and space, the Yangbi earthquake was not isolated. It was a foreshock-mainshock-aftershock type earthquake, which is similar to the characteristics of multiple large earthquakes in a concentrated seismic activity with shallow focal depth and large destructive force [38]. In addition, on 27 March in 2017, there were two moderately strong earthquakes of an Ms 4.8 and Ms 5.1 that occurred at 7:40 and 7:55 in Yangbi County, respectively, with focal depths of 8 km. Based on previous studies on the activity characteristics of seismic sequence, the sequence of this earthquake belonged to a typical earthquake sequence of'seismic swarm (multi-seismic) type' (or 'double earthquake type') [39]. The relocation results, the focal mechanism solutions of the mainshock, and the early strong aftershocks all show that the seismogenic structure of the 2017 Yangbi earthquake was the Weixi-Qiaohou fault [40]. The Yangbi Ms 6.4 earthquake had a large number of foreshocks and aftershocks, according to InSAR observations and inversion results, and the seismogenic fault is an active fault in the NW trend and is consistent with the strike of the Weixi-Qiaohou-Weishan fault, which is the closest to the epicenter of the earthquake. The results of the slip distribution obtained from the inversion in this paper are shown in Figure 4. the earthquake did not rupture to the ground surface, and at the same time, according to the results of the Coulomb failure stress change calculation, it was found that there was a certain distance between the changing area and the Weixi-Qiaohou fault. After the earthquake, many researchers [41; 42] studied the 2021 Yangbi earthquake, and their results suggested that the Weixi-Qiaohou fault was the seismogenic fault of this event. The Weixi-Qiaohou fault, the closest to the epicenter of this earthquake, is located to the east of Yangbi County, and is a large-scale boundary fault with a total length of about 280 km, with strong Cenozoic activity characteristics, showing strong activity in the Late Quaternary, and the nature of motion is mainly a dextral strike-slip with a positive fault component [43]. In addition to the Ms 5.1 earthquake in 2017, an earthquake with a magnitude above 6.0 occurred in the area near the rupture in 1925, which indicates that the Weixi-Qiaohou fault has a background of medium and strong earthquakes. In order to better determine the seismogenic structure and activity characteristics of the Yangbi earthquake, [PERSON] et al. [30] conducted a field investigation on the Weixi-Qiaohou and surrounding faults in the Yangbi research area on 23 May 2021.