## 2 Background  
The study area (73-80\({}^{\circ}\) E, 39-42\({}^{\circ}\) N) lies within the STS orogenic belt (Figure 1). The MDF, acting as the root structure of the Keping Retrograde Thrust Tectonics, demarcates the boundary between the STS orogeny and the Tarim Basin [42; 43]. The MDF has remained active since the Holocene, undergoing substantial deformation attributed to the southward back-thrusting of the Tianshan, the northward convergence of the Pamir Plateau, the clockwise rotation of the Tarim block, and associated intracontinental subduction processes [31; 33; 37; 40]. Seismicity within the STS is primarily concentrated along the mountain front, particularly in an active fault like the Koping Fault. In contrast, the deep-seated MDF, despite its critical tectonic role, typically exhibits lower seismicity, with notable exceptions including the \(M_{\rm S}\) 6.5 Wushi North (1969), the \(M_{\rm S}\)6.4 Wushi (1897), and the \(M_{\rm S}\)5.4 Ahaqi (2009) earthquakes [42]. Geologically, the STS orogenic belt marks the collisional interface between the southern Central Asian Orogenic Belt (CAOB) and the Tarim Craton, comprising three major tectonic units: (1) the Tarim Craton, (2) the STS accretionary orogenic belt, and (3) the Middle Tianshan (MTS) Massif [44]. The Tarim Craton, one of China's three oldest cratonic blocks, lies at the Eurasian core, bounded by the Tianshan Mountains to the north and the Kunlun-Altun Mountains to the south [45; 46]. The craton's interior is largely blanketed by Cenozoic sedimentary cover, with basement exposures along its periphery. The northwestern Tarim  
Figure 1: (**a**) Tectonic position of the STS under the Cenozoic India–Eurasian plate collision. (**b**) Distribution map of sampling sites in the study area. (**c**) Lithology distribution map of the study area. Abbreviations: TFF: Taraz–Fergana Fault, MDF: Maidian Fault, STS: Atushi Fault. S13 hot spring is a continuous monitoring site. Craton preserves a continuous stratigraphic record from the Late Precambrian to the Devonian, dominated by shallow marine and terrestrial tuffs and sandstones. Notable unconformities include Ordovician-Silurian sequences overlain by Carboniferous and Permian deposits [44; 47; 48; 49]. Additionally, Archean to Paleoproterozoic metamorphic complexes in the Kuruktag region form the ancient basement of the northern Tarim Craton, transitioning into mid-Paleoproterozoic marine siliciclastic formations, limestones, and plagioclase-rich sequences widespread in the central region [45; 46; 48]. The STS orogenic belt, situated between the Tarim Craton and the Yili-MTS Massif [50; 51], consists of Precambrian basement rocks, Paleozoic sediments, high-pressure to ultra-high-pressure metamorphic rocks, ophiolites, island-arc volcanics, and granitic intrusions [44; 50; 52; 53]. Its geological evolution is marked by extensive accretion and subduction events, as reflected in the stratigraphic successions ranging from Silurian to Carboniferous units and the widespread presence of ophiolites and metamorphic complexes from north to south [44; 54]. The southern STS orogenic belt is characterized by Paleozoic formations, particularly Silurian and Devonian strata, as well as Permian volcanic sequences and fluvial deposits that remain tectonically disjointed from earlier stratigraphic units [44]. The MTS Massif, bounded by the Nikolaev Line-Narathi North Fracture and the MTS South Rim Fault, represents a microcontinental block consisting of Precambrian basement rocks and a Paleozoic continental arc system [53; 55]. A representative of this massif is Baluntai area, where Cambrian basement rocks are prominently exposed. These formations include plagioclase-hornblende schists and chlorite-quartz schists from the early to middle Archean, transitioning to hornblende-actinolite schists, quartz-biotite schists, and Neoproterozoic carbonates (limestones and dolomites) in later periods [44; 56].