# Coseismic Stress Change and Viscoelastic Relaxation after the 2008 Great Sichuan Earthquake
## 1 Introduction  
Sichuan and the adjacent region are the most seismically active parts of China, with complex geological and seismic tectonics within the North-South seismic zone [1, 2, 3]. Located on the eastern margin of the Tibetan Plateau, this region is affected by the process of India-Asia collision and abutment against the stable Yangtze Platform, causing strong compressional deformation, crustal shortening and thickening, and crustal extension from east to west [4, 5, 6]. There are several tectonic blocks and active faults, such as the Longmenshan fault, the Ganzi-Yushu fault, the Xianshu infault, the eastern Kunlun fault (Figure 1). The Longmenshan fault on the eastern margin of the Tibetan Plateau is the result of the eastward compression of the South China block by the Bayan Har block [7]. It experienced intermittent tectonic deformation and formed the complex Longmenshan fold-and-thrust belt adjacent to the Sichuan foreland basin (Figure 1) [8, 9, 10]. During the Quaternary, the activity along the Longmenshan thrust belt was mainly concentrated on the Maoxian-Wenchuan and Jiangyou-Guanxian faults, as well as other faults with forward propagation deformation [11, 12]. The Ganzi-Yushu fault zone can be traced for approximately 500 km along a strike and is composed of a series of fault segments, with a NW strike and left-lateral strike-slip behavior (Figure 1) [13, 14, 15]. The Xianshu infault zone is located within the Songpan-Ganze fold belt in the eastern part of the plateau [16]. The Xianshu infault extends 350 km northwest-southeast and is part of the 1400 km left-lateral system that passes through southern Yunnan Province, northwest through Sichuan Province into Qinghai Province (Figure 1). In planar view, the fault is a slightly convex arc, and itsstrike is almost parallel to those of other regional structures. At the northwestern end, the fault zone overlaps with the southeastern end of the Ganzi-Yushu fault, and the left en echelon step exceeds \(\sim\)40 km. The southeastern end of the fault area is connected to the Zemuhe-Xiaojian fault. The Xianshuie fault system consists of a series of faults that accommodate the clockwise rotation of crustal rocks between the South China block and the Eastern Himalayan syntaxis [17]. This area is one of the most seismogenically active areas in China, and the spatiotemporal variation in Coulomb stress remains enigmatic but is of considerable significance to regional earthquake risk evaluation. Therefore, in this study, we attempted to predict the stress evolution along fragile faults on the decadal time scale for the first time and to provide insights into earthquake risks in the Sichuan region. Remarkable M > 6 earthquakes have repeatedly occurred in Sichuan every several years following the 2008 great Sichuan (Wenchuan) earthquake [6; 20], including the 2010 Ms 7.1 Yushu earthquake, the 2013 Ms 7.0 Lushan earthquake, the 2014 Ms 6.3 and Ms 5.8 Kangding earthquakes, and the 2017 Ms 7.0 Jiuzhaigou earthquake. The 2013 Ms 7.0 Lushan earthquake and the 2008 Ms 8.0 Wenchuan earthquake occurred on the Long-menshan fault, the 2014 Ms 6.3 and Ms 5.8 Kangding earthquakes occurred along the Xianshuie fault, and the 2010 Ms 7.1 Yushu earthquake ruptured the Ganzi-Yushu fault (Figure 1) [21]. The 2017 Ms 7.0 Jiuzhaigou earthquake was located on the Shuzheng fault, which is one of the branch faults of the eastern Kunlun fault zone [22; 23]; this earthquake occurred approximately 9 years after the Wenchuan earthquake in 2008, and the epicenter was only tens of kilometers away from the northern section of the surface fracture zone of the 2008 great Sichuan (Wenchuan) earthquake. Considering the high risk of large earthquakes in Sichuan in the near future, the evolution of the seismic mechanical mechanism in this area has become a hot spot for numerous studies (e.g., [24; 25; 26; 27; 28]).