## 2 Active Tectonic and Seismic Background  
The interactions among the Indian, Pacific, and Philippine plates with the Eurasian plate, along with geodynamic interactions within the Eurasian plate, have led to diverse forms of active tectonics in China. These interactions control the spatial distribution of strong earthquakes in the region [47; 48; 49; 50]. The present tectonic characteristics of the Tibetan Plateau are outcomes of the collision between the Indian and Eurasian plates approximately 50-60 million years ago [51; 52]. Researchers such as [PERSON] et al. [52], [PERSON] [53], and [PERSON] et al. [49] have studied this phenomenon, highlighting important aspects like the emergence of extensive Late Quaternary active faults. These faults' kinematic properties and deformations play an important role in governing the convergence between the Eurasian Plate and the Indian Plate, along with the uplift of the Tibetan Plateau. The XSHFZ is a large left-lateral strike-slip fault zone on the eastern margin of the Tibetan Plateau [32], with a strike of about N40\({}^{\circ}\)W and a slight arcuate bend projecting to the northeast (Figure 1). The XSHFZ originates in the northwest from the northeast of Ganzi and stretches southeastward through Luhuo, Daofu, Huiyuan Temple, Kangding, and Moxi to the vicinity of the Gongyi Sea, with a total length of approximately 400 km [33]. Concerning the segmentation of the XSHFZ, various studies have presented divergent outcomes. The prevailing division categorizes the XSHFZ into three segments: the northwest segment, the middle segment, and the southeast segment, with Huiyuan Temple and Kangding serving as delineating boundaries for each segment, respectively [9; 54]. To the northwest of the Huiyuan Temple, the geometric structure of the XSHFZ is relatively straightforward, comprising the Luhuo segment (S1), the Daofu segment (S2), and the Qianning segment (S3) from northwest to southeast, exhibiting a left-oriented arrangement pattern. South of Huiyuan Temple, the Kangding segment (S4) in the central region of the XSHFZ is further divided into three subsidiary faults: the Yalae fault, the Selaha fault, and the Zheduotang fault. To the southeast is the Moxi segment (S5) of the XSHFZ (Figure 1), with the fault trace once again extending as a single primary fault, reaching toward the vicinity of the Gongyi Sea [9; 46]. The Luhuo segment of the XSHFZ has an overall length of approximately 62 km, featuring a general strike direction of N315\({}^{\circ}\). It is noteworthy that the 1973 \(M_{\rm S}\) 7.6 earthquake transpired within this segment (Figure 2). The Daofu segment spans approximately 85 km in length, exhibiting a predominant strike direction ranging from N310\({}^{\circ}\) to N325\({}^{\circ}\). The Daofu segment stands out as the most seismically active area within the XSHFZ, witnessing seven earthquakes of magnitude 6 or greater, among which three earthquakes of magnitude 7 or higher occurred. These notable events include the 1816 \(M_{\text{S}}\) 7.5 earthquake, the 1904 \(M_{\text{S}}\) 7 earthquake, and the 1923 \(M_{\text{S}}\) 7.3 earthquake (Figure 2). The Qianning segment spans roughly 54 km in length, and it experienced a magnitude 7 earthquake in 1893. The main basis for the division of the three secondary faults north of Huiyuan Temple in the XSHFZ is the existence of pull-apart basins of a certain scale between adjacent segments, the Xialatuo Basin and Daofu Basin. Simultaneously, these three segments exhibit structural similarities, with the two adjacent fractures being arranged in a left-stepping pattern. The lengths of the three secondary faults in the middle segment of the XSHFZ from north to south are approximately 70 km, 60 km, and 26 km, respectively. Notably, the \(M_{\text{S}}\) 7 earthquake of 1725 and the \(M_{\text{S}}\) 7.5 earthquake of 1955 transpired on the Selaha River fault and Zheduotang fault, respectively.