地形条件对次生山地灾害易发性分析

岷江上游河谷地带位于汶川地震极震区,是中国乃至世界上地震次生山地灾害最为活跃的地区之一,其频繁活动与复杂的地形条件密切相关.以岷江河谷汶川段为典型研究区,在分析了地理环境和地形条件的基础上,研究了地震次生山地灾害的类型、发育特征、分布状况和主要地形影响因素,并基于次生山地灾害形成因素贡献率,引入确定性系数,利用GIS和RS技术,定量分析了高程、坡度和坡向3个主要地形因子对次生山地灾害的易发程度,确定了最利于次生山地灾害发生的地形条件.研究结果表明:1)地震次生山地灾害具有点多面广、类型多样、分布集中、规模巨大等特征,并受地形条件控制;2)利于次生山地灾害发生的高程条件为1 000～1 600 m的高程范围,高程大于1 600 m的区域,山地灾害随海拔升高而越不易发生;3)坡度大于35°的中陡坡地带,均利于次生山地灾害的发生,且随坡度增大,灾害发生的可能性也增大;4)有利于次生山地灾害发生的坡向条件依次为东南、东、南和东北4个方向,其CF分别为0.169、0.144、0.135和0.023;5)利用GIS和统计分析方法,能定量进行地震次生山地灾害易发性分析.研究方法可以为灾区次生山地灾害风险评价与区划提供依据,研究成果对灾区山地灾害防治规划、保障重大工程建设安全和减少灾害损失等具有参考意义.

The Susceptibility of Mountain Hazards Triggered by Wenchuan Earthquake to Topographic Factors

The upper reaches of Minjiang River valley is located in the severely-afflicted areas by the Wenchuan Earthquake, which is among the areas with the most frequent and severe mountain hazards triggered by earthquake in China even in the world and the development of these secondary mountain hazards goes hand in hand with topographic factors. Taking the Minjiang River valley within Wenchuan county as a pilot site, the paper discussed the impact of geographic environment and topographic conditions on mountain hazards and explained the types, development and distribution of secondary mountain hazards in pilot site. Based on the contribution of each topographic factor to mountain hazards development, the certainty factor of mountain hazards is introduced so as to quantitatively analyze the susceptibility of secondary mountain hazards to three major topographic factors including altitude, slope and aspect. A case study with the technologies of geographical information system(GIS) and remote sensing(RS) is given and the most favorable topographic factors to secondary mountain hazards are probed. The results demonstrate that: a) Secondary mountain hazards induced by Wenchuan Earthquake scatter widely in pilot site with various types, concentrated distribution, large scale and serious damage and are under the control of topographic conditions. b) the altitude between 1000m and 1600m is favorable to secondary mountain hazard development and the altitude above 1600mis unfavorable to mountain hazard development with the altitude increasing but the hazard development decreasing. c)the mid and steep slopes above 35°are sensitive to secondary mountain hazards, while the more the slope degree is and the more probable the mountain hazard occurrence is. d) the susceptive aspects to secondary mountain hazards are southeast, east, south and northeast in turn and their certainty factors are correspondingly 0.169,0.144,0.133 and 0.023. e) the susceptibility of mountain hazards to topographic factors can be quantitatively calculated by means of GIS and statistic analysis methods. The assessment method is essential for managing risks and developing mitigation efforts related to secondary mountain hazards. The findings of this paper can be used as a scientific basis for preventing mountain hazards and assuring key-projects and public security.