Preliminary Study on the Characteristics and Initiation Mechanism of Zhongchuan Town Flowslide Triggered by Jishishan Ms 6.2 Earthquake in Gansu Province

On 18th December 2023, the 6.2-magnitude earthquake centered in Jishishan County, Gansu Province triggered a prototypical earthquake-induced liquefaction flowslide in Jintian Village and Caotan Village, Zhongchuan Township, Minhe County, Haidong City, Qinghai Province. This hazard caused numerous buildings to be engulfed and interred by several meters of deposits. Owing to the abruptness of its occurrence and extremely high fluidity, it was mistakenly identified as a "sand surge". Through on-site investigation and remote sensing imagery analysis, we confirm this flowslide to be an earthquake-triggered liquefied flowslide event, and explore its causal mechanisms. The results show that: (1) This flowslide was induced by seismic vibratory loading causing liquefaction of the saturated silt layer (loess layer) underlying the plateau, forming a landslide that transformed into a mudflow moving along the valley, rather than an in-situ " sand surge " in the conventional sense; (2) This flowslide includes two failure modes: diffuse failure and lateral spreading; (3) Earthquake-induced soil liquefaction frequently occurs in saturated granular materials (silts, fine sands, etc.) exhibiting prominent strain softening characteristics. The occurrence of such geological hazard is abrupt. Post-instability, the landslide mass flows significant distances like a fluid, readily resulting in catastrophic consequences. This warrants heightened attention.