四川芦山M_s 7.0级地震的地质环境影响分析

Geological Environmental Influence of Lushan M_s 7.0 Earthquake in Sichuan

2013年4月20日四川省雅安市芦山县发生Ms7.0级地震,此次地震对地质环境的影响备受各界关注。基于遥感解译与震后现场调查,对芦山地震的地质环境影响进行了初步分析。结果发现芦山地震的地质环境影响主要有:诱发较为广泛的崩塌等次生山地灾害,崩塌以小型为主,主要分布在双石—大川断裂带槽谷以及北西向几个深切峡谷段,如S210省道芦山—宝兴峡谷、芦山—双石峡谷、龙门—太平峡谷,其中震中区宝盛、太平镇崩塌密度最大;泥石流动静物源有不同程度增加,崩塌新增了泥石流沟的物源;斜坡上缓坡带也堆积有新的崩塌物源,使震后沟谷泥石流与坡面泥石流发生的概率增加;斜坡震裂现象较普遍,震动引起斜坡表层覆盖层不均匀沉降,宏观上表现为地面开裂、房屋开裂以及公路路基失效等;沙土液化加重灾害程度,震动引起发震断裂槽谷区砂土液化,使发震断裂带上地基失效,震害加重;厚覆盖层场地效应使地震下盘平坝区震害异常,下盘前陆盆地厚覆盖层地区地震波放大效应使芦山县龙门、清仁以及天全县老场、仁义平坝区及斜坡地带震害严重;芦山地震地质环境影响最大的区域是震中区太平—宝盛一带,其次是断裂带下盘5km—上盘5km的地带、宝兴县城区域及前陆盆地带。

A Ms 7.0 earthquake hitted Lushan county of Ya＇an city, Sichuan province on April 20, 2013, and the geological environmental influence of the earthquake was concerned. Based on remote sensing interpretation and field survey, the geological environmental influence of Lushan earthquake was analyzed preliminarily. The main geological environmental influences included that Lushan earthquake induced wide spread secondary avalanche mountainous disasters with small scale, which distributed along the trough valley of $huangshi-Dachuan fracture zone and the NW gorges cutting structural belts, such as $210 provincial road Lushan-Baoxing gorge, Lushan- Shuangshi gorge and Longmen-Taiping gorge, and the distribution density of avalanche in Baoshen and Taiping towns near the epicenter was largest; the active and stable sources of debris flow were increased by avalanche because of the earthquake; the new sources of avalanche increased in the gullies and gentle slopes, and the probability of gully-shaped and slope debris flows after the earthquake increased; seismic cracking was common in the slopes, and the uneven settlement of slope surface blanket caused by vibration resulted in ground fracturing, buildingcracking, roadbed failure, etc. ; sand liquefaction increased the damage, and the sand liquefaction in trough valley of causative fault caused by vibration resulted in foundation failure above the causative fault; the site effect of thick overburden layer caused the abnormal damage in the river plain which located in the footwall of earthquake, and the amplification effect of earthquake wave in thick overburden layer of footwall foreland basin caused serious collapse and crack, such as the river plain in Longmen and Qingren of Lushan county, Laochang and Renyi of Tianquan county and slope zone; the most serious area of geological environmental influence of Lushan earthquake was Taiping-Baosheng near the epicenter, the more serious area was fault zone footwall 5 km to hanging wall 5 km, urban area of Baoxing county and foreland basin.