Research on the mechanism of earthquake induced debris flow disaster in Caotan Village, Zhongchuan Township, Minhe County, Qinghai Province, China

Abstract

On December 18, 2023, an earthquake of 6.2 magnitude occurred in Jishishan County, Linxia Prefecture, Gansu Province. After the earthquake, mudslides occurred in Caotan Village and Jintian Village, Zhongchuan Township, Minhe County, Haidong, Qinghai Province, resulting in 20 deaths. After the earthquake, we carried ground penetrating radar and drone equipment, combined with satellite remote sensing data, disaster site sampling, and laboratory sediment particle size and shape analysis, to conduct in-depth investigation and research on the characteristics, causes, process characteristics, and causative factors of the mud flow disaster. The mud flow disaster in Caotan Village developed in the eastern part of the Guanting Basin. Based on the analysis of satellite and drone images before and after the disaster, it was found that the erosion thickness of the source area of this mudslide was approximately 0-15m, the accumulation thickness of the accumulation area was approximately 0-8m, and the amount of landslide exceeded 710000 m3. The mudflow is approximately 3.5km long from north to south, with a terrain that is high in the north and low in the south, and a drop of about 80m. The existence of a stable impermeable layer in the source area leads to the direct exposure of groundwater to the surface, providing a continuous and stable source of recharge for the formation and transportation of debris flows. The complexity of the cross-section of the flow channel and the presence of local water bodies increase the spatiotemporal variability characteristics of the dynamic process of debris flow. Cold weather conditions make it easy for surface water to freeze, increasing the surface viscosity of debris flows, strengthening their plug flow characteristics, and providing assistance for the formation of natural embankments on both sides during the process of debris flow advancement. The entire process of delayed debris flow moves along the valley, increasing the amount and height of debris fluid, i.e. potential energy, thereby increasing the suddenness and destructive nature of debris flow disasters. And the earthquake occurred in the middle of the night, making it difficult for people in the disaster area to accurately detect and avoid dangerous situations. Based on the on-site rescue situation, it is speculated that there was an error in the judgment of the type of earthquake damage by the victims. Other possible reasons include subsurface erosion and land use planning. Vertical shafts and passive valleys formed by subsurface erosion can be seen in multiple locations upstream of the mud flow source area. Based on the above investigation and analysis, it is recommended to conduct a detailed investigation and investigation of areas with similar combinations of landforms, geology, and hydrological conditions in the planning of farmland for building houses, in order to identify high-risk hidden dangers. Strengthen continuous monitoring or regular inspections of high-risk hazard source areas. Strengthen the promotion and popularization of earthquake damage characteristics and disaster prevention and reduction laws and regulations.