Coseismic landslide sediment increased by the "9.5" Luding earthquake, Sichuan, China

The "9.5" Luding earthquake (Ms 6.8), which occurred on September 5, 2022, has triggered thousands of landslides, and caused coseismic landslide sediment in the mountain basin to increase significantly. After the Luding earthquake, landslide sediment may continue to divert to channels, and increase the activity of debris flows. Importantly, the formation of debris flows can pose a major threat to infrastructure, lives and property. To better understand the landslide sediment that increased by the "9.5" Luding earthquake and its impact on the activity of debris flows, we mapped the coseismic landslide database using satellite images. A total of 9142 landslides with an area of 49.51 km², covering 4.81% of the whole basin, were triggered by the Luding earthquake. The coseismic landslides induced by this earthquake are dominated by shallow landslides and are densely distributed in the combined zone of the Xianshuihe fault and the Daduhe fault. Approximately 333.31×10⁶ m³ (error: 111.43×10⁶ m³/-70.73×10⁶ m³) of coseismic landslide sediments were induced by the earthquake in the epicenter, and the landslide materials were concentrated downstream of the basins. In addition, more than 13986.45×10⁴ m³ (error: 4675.67×10⁴ m³/-2967.92×10⁴ m³) of landslide sediment may supply for debris flow occurrence. Simultaneously, the small basins that are distributed near Moxi, Detuo and the junction of the Xianshuihe fault and Daduhe fault are more susceptible to debris flows when rainstorms hit these regions. Therefore, prevention and mitigation measures, early warning, and land use planning should be adopted in advance in these regions. However, from the perspectives of landslide scale and the degree of landslide–channel coupling, the activity or active intensity of debris flows in the Luding earthquake area may be lower than that in the epicenter area of the 2008 Wenchuan earthquake.