高原季节性冻土区砂土液化探讨——以阿克陶MS6.7地震为例

Discussion on sand liquefaction in plateau seasonal frozen soil area-Case study with Akto Ms6.7 earthquake,in Xinjiang

2016年11月25日新疆阿克陶县木吉乡发生MS6.7地震,发震构造为公格尔山拉张系北端的木吉断裂,断裂总长度超过100 km,以右旋走滑为主兼有一定的拉张分量。文章在对震区进行了初步的地震地质灾害调查,总结砂土液化和地裂缝在高原季节性冻土地区的分布及发育特点的基础上,发现:1)在研究区Ⅰ维日麻村的砂土液化主要沿原有泉眼或沿地裂缝发育,沿泉眼形成的砂土液化其喷砂锥的覆盖面积达36.1 m2,占总液化面积的60%,研究区Ⅱ布拉克村的砂土液化则主要是沿草甸的根系喷出,在地表形成大面积的最新涌水结冻特征;2)对研究区Ⅱ布拉克村地裂缝的深度进行统计,反演出区域冻土层厚度,结合探槽揭露的地层剖面,推断冻土层发生大面积地裂缝是因为地震引起冻土层下部融土层发生砂土液化导致土层变形失稳,从而使冻土层发生形变产生一系列规律性的地裂缝。

Soil liquefaction is a type of coseismic hydrological change triggered by earthquakes,and its occurrence results in major property damage and casualties.The dynamics of coseismic hydrological changes are not fully understood.In order to address this,we studied coseismic deformations such as liquefaction and ground fissures that occurred as a result of strong seismic activity during the 2016 MS6.7 Akto earthquake,which took place in the interior of the Pamir Plateau in northwestern China.That is the Pamir tectonic knot,one of the two tectonic plates that the India plate collided with the Eurasian plate.This region is one of the most active areas in China's Mainland.The seismogenic structure of the earthquake in the preliminary determine is Muji dextral-slip fault which located in the north of Kongur extension system.There are 2 macroscopic epicenter in the earthquake,that is Weirima Village and Bulake Village.There are developed a lot of geological hazard in the macroscopic epicenter.This paper presents a systematic survey of the frozen soil liquefaction and ground fissures caused by this earthquake.The majority of liquefaction sites near the Karaat River are located on the T1 terrace,in Bulake Village,and are adjacent to the alluvial fan of the Kungai Mountain.Sand liquefaction is mainly distributed in the south of Kalaarte River,and area of sand liquefaction is 1000 m2.We find that the liquefaction was caused by the original spring and coseismic ground fissure during the earthquake.Approximately 80%of the liquefaction sites are formed along the original spring in the epicenter.The maximum height of sand boils is 15 cm.The remaining 20%of the liquefaction sites are formed along the coseismic ground fissure.Our results suggest that the frozen soil layer impedes liquefied material in the lower unfrozen soil layer from reaching the surface,and the material formed from liquefaction is consequentially channeled through the primary fault and coseismic ground fissures.Liquefaction associated with the Akto earthquake demonstrates the importance of accounting for the possibility of a series of coseismic geological disasters,such as soil liquefaction and ground fissures,in areas with similar geology,altitude,and temperature.The ground fissures are distributed as net shape on the flood plain of Kalaarte River at Weirima Village.In the Bulake Village,the main movement features of the ground fissure are tension and sinistral slip,and the direction of ground fissures are 90~135 degree.The ground fissures associated with sand liquefaction is an important cause of serious damage to the building.