The formation mechanism of ground fissures in Qingxu-Taigu area, Shanxi Province

Qingxu-Taigu area, Shanxi Province is one of the high incidence of geological disasters in China, the main types of geological disasters are active fault, landslide, earthquake, ground fissure and so on.This article based on the ground route geology survey, geophysical prospecting and hydrological engineering drilling, preliminarily divided the ground fissures in this area into two categories, which are the ground fissures nearby mountain and the ground fissures in central basin.The ground fissures nearby mountain are mainly associated with the active fault in the transition zone between the mountain and the graben basin, the underlying bedrock of the basin shows the characteristics of "dual structure" mainly consisting of the thick layer of sandstone and thin bedded silty mudstone, which is very easy to produce interlayer slip and lead to geological disasters such as ground fissures induced by the external factors(such as heavy rain and earthquake, etc.).The ground fissures in central basin are mainly related to groundwater overexploitation besides the possible concealed faults under the basin.The results of hydro-engineering drilling show that there are multiple aquifers in the central basin.The aquifers closed by impermeable thick clay layer or silty clay layer are usually composed of silty sands or fine sands.When the groundwater in central basin is overexploited, the water level will decrease, and the aquifer will sink to form ground fissure by the gravity of overlying strata.In addition, a small amount of white salts are often found in the Upper Pleistocene silty mudstone that may be the reason for the general saltiness of underground water in this area