# Numerical Simulation of the Influence of the Baihetan Reservoir Impoundment on Regional Seismicity
## 1 Introduction  
Hydropower has gradually become one of the important ways to solve the national energy crisis, and many countries have built large reservoirs. In the 1940s, [PERSON] (1945) first found the correlation between impoundment and earthquakes in Lake Mead, USA. The water led to the reactivation of pre-existing faults and further induced earthquakes in the reservoir region. With the construction of reservoirs, researchers found that impoundment and periodical variations in water levels are strongly correlated with seismicity in the reservoir area. Seismic activity in the reservoir and surrounding areas became abnormal after impoundment, and in some cases, it even increased [1; 2; 3; 4] ([PERSON], 1945; [PERSON] et al., 1988; [PERSON], 1997; [PERSON] et al., 2015). The earliest seismicity associated with reservoir impoundment occurred near the Kremasta Reservoir in north Greece [5]. Reservoir earthquakes have occurred in more than 140 regions around the world, especially in the United States, China, and India [4; 6]. In China, more than 90,000 reservoirs have been built, with a total capacity of nearly 900 billion cubic meters. Researchers have proven that about 20 earthquakes had beenrelated to reservoir impoundment by 2012 [7]. One example, the 1962 \(M_{\text{s}}\)6.1 Xinfengjiang earthquake in Guangdong Province, is the earliest and most destructive reservoir-induced earthquake in Chinese history [8]. Large reservoirs have been concentrated in southwest China since the 20 th century, where strong earthquakes have occurred frequently. Therefore, the correlation between the construction of large-scale hydropower projects and seismicity changes in the surrounding area has drawn attention in academia for years, especially the relation between the occurrence of the 2008 \(M_{w}\)7.9 Wenchuan earthquake and the impoundment of the nearby Zipingpu Reservoir [9; 10; 11; 12]. The Jinsha River is located in the important south-north seismic zone in Southwest China (Figure 1a,b). It is adjacent to the Sichuan-Yunnan Block in the west and the South China Block in the east, which has always been a region with high seismicity. In recent years, hydropower stations and reservoirs have been built along the Jinsha River to harness its significant elevation drop and abundant water resources. Four reservoirs, Wudongde, Baihetan, Xiloudu, and Xiangjiaba, were built along the river from the upper to the lower, and several notable earthquakes have occurred. For instance, Xiluoudu and Xiangjiaba stations are located in the Mabian-Zhaotong seismic zone, where there have been \(M\)7.1 earthquakes [13], and Wudongde and Baihetan Stations are located in the Dongchuan-Songming seismic zone, where there have been \(M\)8.0 earthquakes [14]. Large earthquakes often result in significant losses to human society and the economy, posing a threat to people's lives. Therefore, it is of great significance to study the possibility of earthquake occurrences and evaluate earthquake losses reasonably [15; 16; 17]. Consequently, there is a research priority on whether the construction of hydropower stations will induce large earthquakes in active fracture zones. Figure 1: The Baihetan Reservoir and its nearby seismicity are in the Sichuan Basin. The magenta spots in (**a**) are M \(\geq\) 3.0 earthquakes, and the black lines represent the faults. The red rectangle is the location of the Baihetan Reservoir. The blue rectangle in (**b**) represents the position of (**a**) in China. The gray, blue, and red points in (**c**) represent the earthquakes (M \(\geq\) 1.0) before (1 January 2009–25 April 2021), during (26 April 2021–25 September 2021), and after impoundment (26 September 2021–25 March 2022),  
respectively, and the yellow star is the dam location. The solid black lines denote the main faults: Zemuhe Fault (ZMHF), Daliangshan Fault (DLSF), Lianfeng Fault (LFF), Ninghui Fault (NHF), Puduhe Fault (PDHF), Xiaojiang Fault (XJF), and Zhaotong-Ludian Fault (ZLF). Table 1 shows the names and geometries of the faults.