## 3 Characteristics of the Earth Fissures in the Yuncheng Basin  
The development of earth fissures is controlled by tectonic movement. The earth fissures in a basin are mainly affected by the secondary structural units. The Yuncheng Basin has been affected by the Himalayan tectonic movement since the Cenozoic era. Due to the control of the faults at the northern foot of the Zhongtiao mountain, the basement has been in a faulted extensional environment. Under the strong tectonic activity of the Zhongtiao mountain fault, the secondary structural unit in the basin was controlled, which intensified the uplift of the block and caused the formation of the Mingtiaogang earth fissures. The dip slip extension of the hanging wall normal fault in the basin caused the tension shear cracking of the surface soil layer, which laid the structural foundation for the development of earth fissures in the basin. In addition, since the 1980s, the over-exploitation of groundwater has been severe in this area, causing the groundwater level to continuously fall and the falling funnel to expand year by year, which has induced a large number of earth fissures in the Yuncheng Basin. Thus, the Yuncheng Basin has become the faulted basin with the largest number of earth fissures in Shanxi. The earth fissures in the basin are mainly distributed on top of and on both sides of the Mingtiaogang uplift within the basin, in the Zhongtiao mountain uplift to the southeast, and in the Emei platform front edge to the north (Figure 2). The earth fissures in the Yuncheng Basin are distributed along the boundaries of the geomorphology, are concentrated along the fault zone, and are associated with land subsidence. The earth fissures predominantly have NE strikes. According to our survey, the earth fissure disasters in the basin mainly occurred before 1980 and between 1995 and 2005. A total of 119 earth fissures (belts) have developed in the study area. They mainly strike NE and are generally 100-2000 m long, with the longest reaching up to 5000 m. They are generally 0.05-0.5 m wide, and the widest can reach up to 2 m. The small earth fissures account for 45% of the earth fissures (length less than 500 m); the medium earth fissures account for 28% (length between 500 and 1000 m); and the large earth fissures account for 17% (length between 1000 and 5000 m). There is only one giant earth fissure in the basin. It is located in the salt lake district and is 10 km long and 0.3-1 m wide. Figure 3 shows six typical earth fissures in the Yuncheng Basin and their profiles. Earth fissure F\({}_{1}\) (Pleistocene earth fissure on the southern margin of the Mingtiaogang uplift) is located in the salt lake district of Yuncheng. It is the only giant earth fissure in  
Figure 2: Structure and earth fissure distribution map of the Yuncheng Basin. the Yuncheng Basin. The earth fissure F\({}_{1}\) appeared in 1975. It has a long extension, large scale, and strong continuity, and is not controlled by the pavement, buildings, or roads along the route. It is 10 km long and crosses Tacocun-Bampo-Wucao-Xincao and other villages, and it is very destructive along the strike (Figure 4a,c). Earth fissure F\({}_{1}\) strikes NE, which is consistent with the active fault in the underlying bedrock. In a plane view, the earth fissure F\({}_{1}\) is longer, and its overall shape is linear. In profile, the site is dominated by loess and paleosol, with secondary fissures on either side of the main fissure symmetrically developed and approximately parallel. The vertical plane of the two sides near the surface of the main fissure is small, and the deep dislocation is large, showing the characteristic of a synsedimentary fault (Figure 3a). The Zhongtiao mountain piedmont fault zone is located in the southern part of Xia County. Affected by tectonic movement, the five earth fissures (F\({}_{2}\)-F\({}_{6}\)) developed in the Xia County area are all distributed on the northwestern side of the Zhongtiao mountain fault zone.