Characteristics and risk assessment of debris flows in the Wandong catchment after the MS 6.8 Luding earthquake

On Sep. 5, 2022, an MS 6.8 earthquake struck Luding County. The earthquake triggered large amounts of co-seismic landslides, which blocked the Wandong River for nearly 24 hours. Field surveys, image interpretation, spatial statistics, and hydro-logical calculations were used to investigate the characteristics of co-seismic landslides and the risk of debris flow following the earthquake. According to the findings, co-seismic landslides are primarily found in areas of earthquake intensity IX, and their sizes are typically small and medium. They are distributed along both sides of the channel, particularly on both sides of the thin ridge facing the air. The distance from the fault and slope controls the distribution of co-seismic landslides. The volume of debris flow runout in the Wandong catchment may be twice that of the debris flow prior to the earthquake. On this basis, the following disaster prevention and mitigation suggestions were put forward. The risk of runout debris flow in the catchment should be strengthened; The value of triggering rainfall of debris flow should be obtained as soon as possible through comprehensive monitoring and early warning; The scale amplification factor of debris flow should be fully considered in the design of debris flow prevention and control projects. This research can be used as a scientific reference for disaster prevention and mitigation of post-earthquake debris flows.