汶川地震灾区泥石流启动机制及其动力学特征——以北川县五星沟为例

Initiation Mechanism and Dynamic Characteristics of Debris Flow in the Earthquake Disaster Region of Wenchuan——A Case Study at Wuxing Gully of Beichuan County

2008年5月12日,四川汶川发生8.0级特大地震,地震造成了大量山体滑坡、崩塌、泥石流等次生地质灾害,给北川县带来了严重的人员伤亡和财产损失。受降雨影响,位于北川县擂鼓镇的五星沟分别于2008年9月24日及2009年7月17日发生特大型泥石流,造成了五星沟沟内五星村、大田村和南竹村等多处居民点被冲毁,沟谷两侧房屋倒塌或被掩埋。根据已有资料,通过分析五星沟泥石流的分布和形成特征,从泥石流形成的物源条件和动力条件两方面探讨了该泥石流启动机制与物源转化机制,推算不同设计频率下泥石流的特征值,包括该泥石流的运动及动力特征。分析表明:五星沟大部分支沟属中频泥石流沟,发展阶段均属发展期;五星沟具备再次发生泥石流的基本条件,建议尽快对其实施应急治理。开展五星沟泥石流启动机制的研究,对于监测与治理汶川地震造成的次生泥石流灾害,具有指导意义。

A major earthquake measuring 8.0 Richter scale jolted Wenchuan County of Sichuan Province on May 12th,2008,which induced a number of geological disasters including the landslides,collapse,and debris flows that caused severe losses of property and life.Wuxing Gully originates from Leigu Town of Beichuan County,and two extremely huge debris flows occurred due to precipitation on September 24th 2008 and July 17th 2009.The debris flows destroyed lots of residential area in Wuxing,Datian,and Nanzhu villages located in Wuxing Gully,and many houses collapsed or were buried.In this paper,the distribution of debris flow in Wuxing Gully was analyzed and its formation characteristics were investigated based on amount of data and information.Additionally,the initiation mechanism and material source mechanism of the debris flow were analyzed from the aspects of the material source condition and dynamic condition,and the characteristic values of the debris flow under different design frequencies were derived including the movement and dynamic characteristics of the debris flow.The results showed that most of the sub-branches in Wuxing Gully are intermediate frequency debris flow gullies and they are still developing,thus Wuxing Gully needs urgent prevention and control since it meets the basic conditions for future debris flow.The research on the initiation mechanism of debris flow has instructive significance for the monitoring and treatment of debris flows caused by Wenchuan earthquake.