Development characteristics and risk assessment of geological hazards in the mountainous and hilly areas of western Zhengzhou City

Objective The mountainous and hilly areas of western Zhengzhou City have a complex geological environment, affected by rainfall and human engineering activities. Geological hazards such as collapses, landslides, and debris flows occur frequently. In particular, the “7·20” extreme rainstorm that occurred on July 20, 2021 caused many geological hazards, resulting in heavy casualties and huge economic losses. Therefore, analyzing and summarizing the development characteristics of geological hazards and conducting a risk assessment is necessary for this region. At present, the risk assessment of geological hazards is mainly conducted using a single method that has limitations including slightly low evaluation accuracy. In addition, an overall geological hazard risk assessment has not yet been conducted in the mountainous and hilly areas of western Zhengzhou City. Methods Based on the research and analysis of the geological environment background and the distribution characteristics of geological hazards in the study area, eight evaluation factors were selected: slope, landform, engineering geological rock group, elevation, distance from fault, distance from river, rainfall, and human engineering activities. The weighted information method which incorporates elements of the information quantity model and analytic hierarchy process, was used to evaluate the risk of geological hazards in the study area. Results The low-, medium-, and high-risk areas are 1387.14 km2, 1803.18 km2, and 1066.47 km2, respectively, accounting for 32.59%, 42.36%, and 25.05% of the total area, respectively. The medium- and high-risk areas are mainly distributed in the tectonic erosion medium-low mountains and loess hills in the central part of the four cities, the tectonic erosion medium-low mountains south of Dengfeng, and the loess hilly areas in northern Gongyi and Xingyang. The terrain has steep slopes and deep gullies, and the main stratigraphic lithology is clastic rocks intercalated with carbonate rocks, soft and hard rock layers, and loess. Fault structures are developed, and geological hazards are prone to occur under the action of inducing factors and are highly dangerous. The majority (93.11%) of geological hazards are distributed in medium- and high-risk areas, with hazard point densities of 0.1752 km−2 and 0.2869 km−2, respectively. The spatial distribution of geological hazard points is consistent with the geological hazard risk assessment results. The rationality of the evaluation results was assessed by a Receiver Operating Characteristic curve, yielding an AUC value of 0.868. The evaluation accuracy met the requirements for hazard assessment. Conclusion Geological hazards have the largest information value in the range of >40° slopes loess hilly landforms, loess engineering geological rock groups, and 24-h maximum rainfall of 500–550 mm. The risk of geological hazards is positively correlated with distance from faults and water systems — the closer the distance, the higher the risk. The risk of geological disasters in the study area is controlled by the terrain slope and landform and is closely related to the lithology of the formation, which is an important factor in inducing geological disasters. The weighted information method, which has high accuracy and rationality, was used to evaluate the geological hazard risk. Significance The results of this study can provide a basis and technical support for geological hazard prevention and management in the mountainous and hilly areas of western Zhengzhou City and serve as a valuable point of reference for urban planning and infrastructure geological hazard risk assessment in the study area.