汶川地震触发的绵远河流域崩塌滑坡的特征

Landslides Triggered by "5.12" Wenchuan Earthquake in the Mianyuan River Basin,China

利用地震后ALOS影像自动提取了汶川地震重灾区绵远河流域内的崩塌滑坡,结合野外调查共确定地震触发崩塌滑坡1 073处,面积48.5 km2。其中分布最广、数量最多的是浅层崩滑体;同时由于地震力作用强烈,触发了许多深层、高速、远程滑坡,并形成了大量的滑坡堰塞湖。汶川地震诱发的第二大滑坡文家沟滑坡就位于流域内,该滑坡是本次地震中滑动距离最远的滑坡。地震导致大量的碎屑物质堆积在沟道内或悬挂在斜坡上,为泥石流的发生提供了有利条件。基于GIS的统计分析表明,地震滑坡的空间分布主要受发震断层的控制,流域内的崩塌滑坡受到了映秀-北川断裂和江油-都江堰断裂的双重影响,主要分布于两断裂上盘的一定范围内;地层岩性影响着地震滑坡的类型,岩浆岩、白云岩等硬岩主要发育浅层崩滑体,而上硬下软的地层多发生大型滑坡;大部分崩塌滑坡都发生在海拔1 000～2 000 m的高程内;坡度是崩塌滑坡发生的主要控制因素之一,大部分崩塌滑坡发生在25°～55°的范围内;坡向对滑坡的分布也有一定的影响,背靠震源(发震断层)方向的斜坡比面向震源(发震断层)方向更容易发生滑坡。

Due to the high magnitude,long duration of vibration,and complicated environment of the disastrous area,＂5.12＂ Wenchuan earthquake triggered a large number of landslides.A spatial database,which included 1 073 landslides,was developed and analyzed using ALOS satellite imagery and GIS within the Mianyuan River basin.These landslides covered the area of 48.5 km2,of which shallow falls and slides occupied the widest area and the largest number.The strong seismic wave caused the occurrence of many deep,rapid and long-runout landslides as well as the formation of numerous barrier lakes.The second largest landslide triggered by the earthquake,Wenjiagou Landslide was located within this area and it had the farthest sliding distance.After the earthquake,a large number of debris accumulated in the gullies or on the slopes,many debris flows occurred in the river basin.It was indicated in the GIS statistic analysis that the spatial distribution of earthquake-triggering landslides was dominated by the seismogenic fault.Owing to the duel effect of Yingxiu-Beichuan Fault and Jiangyou-Guanxian Fault,the landslides were mainly distributed in the hanging wall of two faults;the lithology of stratum determineed the type of landslides.Shallow falls and slides were mainly formed in the hard rocks such as magmatic rocks and dolomites,while large landslides were likely to occur in the strata with hard upper layer and soft lower layer.Most landslides occured within the elevation range from 1 000 to 2 000 m above sea level.Gradient was one of the main controlling factors of landslide distribution,for most landslides occured in the gradient range from 25 to 55 degrees;slope direction also affected the distribution of landslides.The slopes opposing the direction of seismic source（co-seismic fault） were more likely to have landslides than the slopes facing the direction seismic source（co-seismic fault）.