Earthquake-triggered mudflows are typical in scale and hazard, and their formation mechanism is extremely complex. In this study, the liquefaction and mobility mechanisms of a catastrophic mudflow, namely, the Yongguangcun (YGC) mudflow, in Minxian, Gansu Province, China, under the coupled action of historical earthquakes, active faults, groundwater, long-term rainfall before an earthquake, and the 2013 M_w6.6 Minxian–Zhangxian earthquake were systematically analyzed. Through a detailed field investigation and laboratory testing, the stratigraphic structure of the YGC mudflow was revealed, a geomechanical model was established, and the complex chain process leading to the formation of the YGC mudflow was elucidated. This process includes sliding along the contact zone between the loess and strongly weathered mudstone, liquefaction of the saturated loess under the groundwater table, and liquefaction and collapse of the unsaturated loess above the groundwater table. The slightly low terrain provides the topographic conditions required for groundwater convergence, and sets the conditions for the deformation and further liquefaction of saturated loess during earthquakes. The undulating terrain in the meizoseismal area enhances the complexity of the earthquake waves. In summary, the YGC mudflow was caused by long-term geological evolution and the synergistic effects of other factors; and the site conditions, such as the local topography and groundwater, are the fundamental reasons for the failure and mobility differences between the YGC mudflow and the eastern landslide. The results of the investigation of this mudflow would enrich our understanding of mudflows, promote research on the formation mechanism of geological disasters under complex conditions on the Loess Plateau, and provide important information for improving the scientific prevention and control of landslides of the same type.

地震泥石流规模大、危害性典型，形成机制极其复杂。本研究对甘肃岷县永光村灾害性泥石流在历史地震、活动断层、地下水、震前长期降雨的耦合作用下的液化和流动机制进行了研究。对2013年岷县_—漳县6.6级地震进行了系统分析。通过详细的现场调查和室内测试，揭示了YGC泥浆流的地层结构，建立了地质力学模型，阐明了YGC泥浆流形成的复杂链过程。该过程包括沿黄土与强风化泥岩接触带的滑动、地下水位以下饱和黄土的液化以及地下水位以上非饱和黄土的液化塌陷。稍低的地形提供了地下水汇聚所需的地形条件，也为饱和黄土在地震时变形和进一步液化创造了条件。强震区地形起伏，增强了地震波的复杂性。综上所述，YGC泥石流是长期地质演化和其他因素协同作用的结果；当地地形、地下水等场地条件是YGC泥石流与东部滑坡破坏及流动性差异的根本原因。此次泥石流调查结果将丰富我们对泥石流的认识，推动黄土高原复杂条件下地质灾害形成机制的研究，为提高同类型滑坡的科学防治提供重要资料。