“4·20”芦山7.0级地震次生山地灾害活动特征与趋势

摘要

An Ms7.0 earthquake,focal depth of 13 km,hit Lushan,Ya'an,Sichuan,on April 20,2013.We have taken a survey of the resulted and potential mountain hazards immediately after the quake.We identified the earthquake-induced hazards in mountains,analyzed the activity,formation mechanism,and developing tendency,and compared them with the situations in Wenchuan earthquake.Field survey found 1460 landslides and collapses and 4 dammed lakes,which are small in scale and concentrated in groups.Collapses and rockfalls occurred in rocky cliffs,mainly in gorges of Jinji in Baosheng country and Dayan in Shuangshi town,and in K317 section of S210 provincial highway and Xiaoguanzi section north to the Lingguan town,threatening rescue passage along the river.Landslides are scarce and in moderate scale,mainly occurred in sandstone,shale and colluviums.Only one large landslide was found,which turned into flow.Dammed lakes were formed mainly by collapses and landslides,all in small size and low danger.Major control factors of the hazards are structure,lithology,surface and landform.The collapses are consequent,insequent,and controlled by structure surface.Compared with the Wenchuan earthquake,the landslide number is only 5.53％ and the impact area is as small as 0.57％.Superposition effect of quake has strongly reduced the stability of slope.Collapses,landslides,and debris flows are expected to be more frequent after the quake; but the active period will be relatively short.But potential hazards are hard to figure out.%2013-04-20芦山县发生7.0级地震,震源深度13 km.截至4月29日地震共造成196人遇难,21人失踪,13484人受伤,200余万人受灾.地震发生后,我们立即开展了地震次生山地灾害的遥感解译、实地调查及危险性评估工作.作者定义了地震次生山地灾害,分析了次生山地灾害的活动特征、形成机制与模式以及发展趋势,并与汶川地震次生山地灾害进行了对比.初步查明芦山地震诱发了1460余处崩塌和滑坡,大量落石和4处堰塞湖.次生山地灾害具有规模小、群发性和高位破坏的特征.崩塌和落石成群发育于坚硬岩石形成的陡坡上,主要发育区段有:芦山县的宝盛乡金鸡峡、双石镇大岩峡以及省道S210线K317路段和灵关镇以北小关子段,对沿河公路及救援生命通道影响严重.滑坡数量较少,以中小规模为主,主要发生于砂岩、页岩和松散堆积层中,仅发现一处大型滑坡并转化为碎屑流.堰塞湖主要由崩塌、滑坡形成,均为低危险性小型堰塞湖.芦山地震次生灾害的主控因素为构造、岩性、结构面和地形,崩塌破坏主要表现为顺层滑动破坏型、切层倾倒破坏型和结构面控制破坏型3种模式.芦山地震诱发崩塌、滑坡的数量、分布范围和规模比汶川地震小得多,其数量仅为汶川地震的5.53％,造成的地表破坏面积(3.06 km2)仅为0.57％.芦山地震区两次地震扰动的叠加效应,大大降低坡体的稳定性,震后崩塌、滑坡和泥石流的活动性增加,增幅有限,活跃期也相对较短,但震区山地灾害的隐伏性和隐蔽性强,给隐患排查带来困难.