## 2 Regional Seismic and Tectonic Setting  
The Jinshajiang fault zone is located on the easternmost side of the Sanjiang tectonic belt, belonging to the back-arc basin formed by the expansion of the eastern margin of the ancient Tethys Ocean, and has undergone multiple and complex tectonic evolutionary episodes [14; 15]. Since the Cenozoic, with the collision of the Indian and Eurasian plates, the strong uplift of the Tibetan Plateau has led to lateral slip along the main strike-slip fault system, including the Jinshajiang fault zone [16; 17; 18; 19]. There has been more than 300 km of strike-slip movement along the Jinshajiang fault zone since the Paleogene [20; 21]. The main faults of the middle segment of the Jinshajiang fault zone include the NNW-trending Hongjunshan and Hetaoping faults, the north-northeast (NNE)-trending Yarigong fault, the NE-trending Ciwu fault and the nearly SN-trending western branch fault and Bendu fault (Figure 2a). Of these, the Hongjunshan, Hetaoping, Yarigong, and Ciwu faults exhibit significant Holocene activity and are the main focus of this study (Figure 2b). The northern branch of the middle segment of the Jinshajiang fault zone is composed of the Hongjunshan and Hetaoping faults, which are nearly parallel and generally NNW trending. [PERSON] et al. (2005) suggested that the two faults exhibited left-lateral strike-slip characteristics [6]. On the basis of the dating result of a sag pond along the fault, the occurrence time of the latest earthquake was approximately 770 \(\pm\) 30 a BP [6]. Figure 2: (**a**) Distribution map of major faults and field survey sites in the middle section of the Jinshajiang fault zone and its adjacent areas. (**b**) On the basis of the GF-7 satellite data, a hillshade map was generated to interpret the detailed fault tracks of the Yarigong and Ciwu faults. In addition to the Jinshajiang fault zone, the main active faults in the study area include the Nujiang, Lancangjiang, and Deqin-Zhongdian-Daju fault zones on the southwest side of the Sichuan-Yunnan block; the Ganzi-Yushu and Xianshuihe faults on the northern boundary of the block; and within the block, the Maisu, Darlangsungou, and Litang faults (Figure 1). Of these, the Nujiang fault is located at the westernmost boundary of the Sanjiang tectonic zone. The Nujiang fault has multiple branches with Holocene activity and a horizontal slip rate of 0.6-1.7 mm/a [22; 23]. The Lancangjiang fault is a large regional fault. Its western branch is a Holocene-active fault, while its eastern branch exhibits different characteristics of segmented activity [24; 25; 26]. The Garze-Yushu and Xianshuihe faults are boundary faults of the Sichuan-Yunnan block, not only exhibiting strong Holocene activity and high horizontal slip rates but also having experienced multiple strong and major earthquakes historically [27; 28; 29; 30; 31; 32; 33; 34]. In the northern part of the study area, the Maisu fault is an EW-trending Holocene active fault in the southern part of the Garze-Yushu fault. It preserves a seismic surface rupture zone with a length of 45 km and may accommodate a portion of the horizontal deformation of the Garze-Yushu fault [35]. The Litang fault is an important NW-trending strike-slip fault within the Sichuan-Yunnan block, controlling the formation and development of some Tertiary-Quaternary basins. Its Late Quaternary slip rate was 2.3-5.0 mm/a [36; 37]. The southern section experienced an M7.3 earthquake in 1948 and still preserves a well-defined seismic surface rupture. The Deqin-Zhongdian-Daju fault exhibits significant Late Quaternary activity with a horizontal slip rate of 1.7-2.0 mm/a; it is also considered part of the northwestern boundary of the Sichuan-Yunnan block [38]. Currently, moderate seismic activity is relatively frequent along the fault [38]. The NW-trending, NE-trending, and SN-trending major faults form the basic tectonic framework of the study area and control the seismic activity within the region. The distribution of seismic activity in the study area is uneven.