## 2 Geological Background  
### Regional Tectonic Setting  
The JRNF is located in the junction area of the Ordos Block, the North China Plate, and the Yinshan-Yanshan Block (Figure 1B). The present tectonic framework of the northern North China Plate is based on the Yanshanian Movement and has been significantly influenced by the Himalayan Movement [1; 29; 30; 31]. During the Quaternary period, the tectonic pattern generally inherited the late Cenozoic configuration, shaping the current regional geological and geomorphological landscape. Due to the uneven movement within the block in terms of time, space, manner, and intensity, multiple neotectonic units have formed [30; 31]. These tectonic units are separated by fault zones or structural belts [29; 30]. To the north of our study area lies the Yinshan-Yanshan Uplift, the Hetao Graben to the west, the Lvliangshan Uplift to the south, and the Shanxi Graben System and Taiwaningshan Mountain Uplift to the southeast (Figure 1B). Since the Cenozoic era, the Yinshan-Yanshan Uplift region has primarily undergone uplift movements, characterized by high intensity overall. The uplift is more pronounced in the west and less so in the east [8; 9]. Internal tectonic activity is relatively minor, and the seismic activity level is moderate, mainly concentrated along its southern boundary. Several moderate to strong earthquakes (\(7>\mathrm{M}\geq 6\)) and multiple smaller earthquakes (\(6>\mathrm{M}\geq 5\)) have occurred in Baotou and Zhangjiakou since the 1990s [9; 13; 30]. Since the Cenozoic era, the Hetao Graben has primarily undergone continuous subsidence, characterized by high intensity and significant magnitude. The Cenozoic strata in the region reach a thickness of up to 7000 m, and the Quaternary deposits exceed 2000 m, making it the area with the thickest Cenozoic and Quaternary deposits among the fault systems surrounding the Ordos Block [29]. Seismic activity in the region is moderate, with significant earthquakes of magnitude \(\mathrm{M}\geq 6\) occurring in Wuyuan and Bikeqi in the last century [25; 26; 27]. Nonetheless, the seismic activity level in the Hetao Graben is considerably less intense compared to the faulted basins around the Ordos Block [18]. The Shanxi Fainted Basin has been characterized by intermittent subsidence movements with moderate intensity. The thickness of Cenozoic deposits ranges from 3000 m to 5000 m, while the Quaternary deposits are generally less than 1000 m thick [29]. However, the early Quaternary period saw intense volcanic activity in the Shanxi Fainted Basin, and recent seismic activity has been relatively strong. This region is a major zone of strong seismic activity in North China. Since the earliest recorded earthquake in 213 BC, the northern part of the Shanxi Fainted Basin has experienced four earthquakes with magnitudes of \(8>\mathrm{M}\geq 7\) and seven earthquakes with magnitudes of \(7>\mathrm{M}\geq 6\)[4; 30]. In summary, the JRNF is located in a large-scale tectonic environment characterized by slow uplift in the north and extensional faulting in the south. Around the JRNF study area, the tectonic activity is intense in both the western and southeastern regions, though their manifestations differ. To the north, the Yinshan Uplift and the Hetao Graben exhibit significant activity with large variations in movement amplitude, but modern seismic activity is relatively low. In contrast, the southeastern region, including the Lvliangshan and Taihangshan uplifts and the northern Shanxi Graben System, experiences less intense vertical tectonic activity compared to the west (Figure 1B). However, volcanic and magmatic activity in this area is very strong, with modern seismic activity being higher than in the Yinshan Uplift and Hetao Graben, both in frequency and intensity (Figure 1B) [1; 13; 17]. The tectonic features in the study area are complex. Although there are no records of major earthquakes, there have been 12 earthquakes with \(\mathrm{M}\leq 4.0\) in the past decade within the study area [18] (Table 1).