Abstract:At 23:59 on December 18, 2023,an Ms 6.2 seismic event? struck the Jishishan County in Linxia Prefecture, Gansu Province, triggering numerous geological disasters. Among them, the sand-soil liquefaction mudflow disaster in Zhongchuan Township caused significant economic losses and casualties, and it is urgent to analyse and determine its characteristics, causes and destructiveness. After the earthquake, we went to Zhongchuan Township in Gansu Province, which is the most destructive area of the earthquake, to carry out emergency scientific research, and obtained high-precision and high-resolution digital results of DOM and DSM. Through image interpretation, ground surveys, and on-site inspections, we conducted a comprehensive analysis of the post-earthquake mudflow disaster. The results show that: ① Loess soil, prone to sliding and saturated with water, experienced a rapid increase in pore water pressure under the seismic load, leading to sand-soil liquefaction. This ultimately destabilized and destroyed the soil layer, causing the collapse of the plateau"s edge and seismic landslides. The soil-water mixture, under the influence of gravity, flowed down the slopes and valleys, forming a liquefaction-type landslide-mudflow disaster; ② The disaster phenomenon is not a single mudflow, but the liquefaction of sand and soil led to mudflow and sand-bursting at the same time, the probability of both occurring at the same time is very low, the devastation is very great; ③ This earthquake exemplifies the "small and medium quake, large disaster" scenario, where, despite its moderate magnitude, it caused greater destruction and casualties compared to other earthquakes of similar scale. This geological disaster has both particularity and abnormality.
