青海省湟水流域潜在地质灾害识别与易发性评价

Identification and Susceptibility Evaluation of Potential Geological Hazards in Huangshui River Basin of Qinghai Province

[目的]明确青海省湟水流域地质灾害空间分布特征与规律,为该地区防灾减灾提供数据支撑与科学依据。[方法]通过小基线子集干涉测量(small baseline subset interferometric synthetic aperture radar,SBAS-InSAR)技术识别地质灾害点,结合地形因素、地质因素、环境因素、气象因素、人类活动因素进行灾害空间分布规律分析,建立逻辑回归(logistic regression,LR)—频率比(frequency response,FR)模型并检验,利用返回概率值进行易发性评价。[结果]①湟水流域所分布的潜在地质灾害以滑坡、崩塌为主,多种类型潜在地质灾害并生。滑坡与不稳定斜坡通常发育于坡度较缓的山坡上,通常伴有大量张拉与剪切裂缝,尤其在雨季发育明显,对山体下方交通、居民安全构成威胁。发育于河谷两岸的滑坡与不稳定斜坡还可能阻塞河流,形成堰塞湖,进一步加剧灾害风险。崩塌多发育在岩石结构较为疏松或风化严重的陡峭山壁,因地质脆弱,加之降雨等自然因素刺激,易使山体土块、岩石块下落,对下方的居民区和交通线路构成威胁。②研究区2425—3650 m高程区间的地质灾害分布较多,东北向为地质灾害易发坡向;地质灾害易发性随归一化植被指数(normalized digital vegetation index,NDVI)增加而降低,随坡度、地形起伏度、日降水量增加而升高,随距断层距离增加而减少。③湟水流域高易发区及较高易发区,面积约5937.60 km 2,占研究区总面积约38.78%,主要集中在湟水流域南、北边缘地区,湟中、大通、海晏交界处,以及建筑区周边边坡上。④对评价结果进行检验,模型预测性能受试者特征曲线(receiver operating characteristic curve,ROC曲线)线下面积(area under curve,AUC)为0.787,易发区由高至低FR逐级减小,与实际灾害点的分布具有良好的一致性。⑤断层核密度为湟水流域地质灾害发育的主控因子,坡向、地形起伏度、道路核密度次之,剖面曲率对地质灾害发育影响最小。[结论]①利用SBAS-InSAR技术能有效识别湟水流域潜在地质灾害,LR-FR模型获得的易发性评价结果可靠。②湟水流域地质灾害易发区的分布具有明显的空间差异性,主要分布在海拔较高、植被覆盖率较低、降雨量较大、距离断层近的地区,断层核密度为地质灾害易发性的主控因子。③湟水流域的地质灾害具有多发性、突发性和高风险性的特点,给当地居民生活、区域经济发展及生态环境带来了严重的影响。因此,对其进行监测、预警和防治工作显得尤为重要。

[Objective]The spatial distribution characteristics and laws of geological disasters were determined at the Huangshui River basin in Qinghai Province,in order to provide data support and a scientific basis for disaster prevention and reduction.[Methods]Geological hazard sites were identified by small baseline subset interferometric synthetic aperture radar(SBAS-InSAR).By combining topographic factors,geological factors,environmental factors,meteorological factors,and human activities,the spatial distribution law of disasters was analyzed,and a logistic regression(LR)-frequency response(FR)model was established and tested.The return probability value was used to evaluate susceptibility.[Results]①The potential geological disasters distributed in the Huangshui River basin were mainly landslide and collapse,and many kinds of potential geological disasters occurred simultaneously.Landslides and unstable slopes usually developed on slopes with low slope and were accompanied by a large number of tension and shear cracks that were especially obvious in the rainy season,posing a threat to the safety of traffic and residents below the mountain.Landslides and unstable slopes on both sides of river valleys may also block rivers and form barrier lakes,further aggravating disaster risks.[HJ*5/8]Slope collapses mostly developed in the steep mountain walls with relatively loose rock structure or severe weathering.Due to geological fragility coupled with stimulation by natural factors such as rainfall,situations easily develop and result in falling mountain soil and rocks that pose a threat to residential areas and traffic lines below.②Geological disasters were primarily located in the 2425—3650 m elevation area of the study area,and the northeast direction was the slope direction of geological disasters.Normalized difference vegetation index(NDVI)decreased with the increase in geological hazards,increased with the increase of slope,relief,and daily precipitation,and decreased with the increase of distance from the fault.③The high-risk and relatively high-risk areas in the Huangshui River basin,covering an area of about 5937.60 km 2,accounting for about 38.78%of the total area of the study area,and were mainly concentrated in the south and north border areas of Huangshui River basin,Huangzhong-Datong-Haiyan Junction,and the surrounding slopes of the construction area.④The evaluation results were tested.The area under curve(AUC)of the receiver operating characteristic curve(ROC curve)of model prediction performance was 0.787.The FR in the prone area decreased step by step from high to low,and this result was in good agreement with the distribution of actual disaster points.⑤Fault core density was the main control factor of geological hazard development in the Huangshui River basin,followed by slope direction,relief degree,and road core density.Section curvature had the least influence on geological hazard development.[Conclusion]①SBAS-InSAR technology effectively identified potential geological hazards in the Huangshui River basin,and the susceptibility evaluation results obtained by the LR-FR model were reliable.②The distribution of geological disaster prone areas in the Huangshui Basin had obvious spatial differences,mainly located in the areas with higher elevation,lower vegetation coverage rate,greater rainfall,and close to the fault.Fault core density was the main control factor of geological disaster susceptibility.③The geological disasters in the Huangshui Basin were characterized by frequent,sudden,and high risk occurrences that seriously impacted local people’s lives,regional economic development,and the ecological environment.Therefore,the monitoring,early warning,and prevention of these disasters are particularly important.