甘肃积石山MS6.2级地震同震高速泥流研究

Preliminary study on the co-seismic mudflow of the MS 6.2 earthquake in Jishishan of Gansu Province

2023年12月18日23时59分,甘肃省积石山县发生MS6.2级地震,同时在青海省民和县中川乡祁家沟暴发了泥流次生地质灾害。通过实地调查测量、遥感影像分析、经验公式估算及村民访谈等多种方法,本文研究了祁家沟泥流的地貌特征与发生过程,并对其成因进行了初步探讨。结果表明:(1)第一波黏性泥流瞬时最大流速在10 m/s以上,泥流龙头几乎与地震同时到达中川乡草滩村,后续阵性流流速约7.1、6.0和5.8 m/s;(2)长期灌溉、渠系渗漏和震前冬灌导致泥流形成区黄土层预先饱和、地震动荷载促使地下饱水黄土层发生液化,地震触发超孔隙水压力瞬间骤增可能是高速泥流形成的关键机制;(3)农田冬灌、震后闸板未能及时关闭是后续阵性泥流的主要水动力条件,亦是致灾的人为因素。此种由多因素耦合形成的同震次生泥流在国内外均十分特殊,建议作为地质灾害遗迹进行分区保护,并加强黄河台塬灌区水利工程地质灾害危险性评估、重点防止黄土滑坡发生。

At 23:59 on December 18,2023,an earthquake with a magnitude of MS 6.2 occurred in Jishishan County,Gansu Province,and at the same time a mudflow secondary geologic disaster broke out in Qijiagou,Zhongchuan Township,Minhe County,Qinghai Province,which is a typical secondary geological disaster of the same earthquake and transformed into a disaster by the coupling and superposition of multiple disasters such as earthquake,landslide and mudflow,and its impact and effect are much greater than that of a single disaster.Through all kinds of methods such as field survey and measurement,remote sensing image analysis,empirical formula estimation and villagers’interviews so as to recover and reappear the chain process consisting of“agricultural irrigation-static liquefaction-local plastic deformation-potential slip formation”and“earthquake-dynamic liquefaction-seismic slip through-slump slip-mudflow”.This article discusses the geomorphological characteristics and occurrence process of mudflow in Qijiagou,and conducts a preliminary discussion on its causes.The results showed that:1)The Qijiagou mudflow,with a total length of about 3.0 km and a disaster-forming area of about 0.478 km2,there are all kinds of types of landforms,so it is a typical mudflow-hazard geomorphologic process with a full range of geomorphologic types.2)the instantaneous maximum flow rate of the first wave of viscous mudflow in Qijiagou was above 10 m/s,and the mudflow head reaches Caotan Village in Zhongchuan Township almost at the same time as the earthquake,and the subsequent intermittent mudflow velocity was about 7.1,6.0 and 5.8 m/s,compared with the mudflow head,it’s twice as small and gradually decreased;3)Irrigation over a long period of time,leakage of water channels and pre-earthquake winter irrigation led to the pre-saturation of loess layer in mudflow formation area,and seismic oscillation load causes the liquefaction of underground saturated loess layer,earthquake triggered a sudden increase of excess pore water,the mudflow high speed,low slope drag reduction movement pressure may be the key mechanism for the formation of high-speed mudflow.4)Winter irrigation on agricultural land and failure to close the electric switch in time after earthquake were the main hydrodynamic conditions of subsequent intermittent mudflow,as well as the human factors that led to mudflow disasters.The co-seismic mudflow is formed by the coupling of multiple factors so it’s very special for research,we should increase our efforts to protect this rare geological site.It is recommended to be protected as geological disaster relics,we should carry out protection zoning,and strengthen the assessment of geologic disaster risk of water conservancy projects in the Yellow River plateau irrigation area,pay attention to preventing the occurrence of loess landslides.