Abstract: A magnitude of Ms 7.0 earthquake struck the Jiuzhaigou World Natural Heritage Park, in Jiuzhaigou county, Northwest of Sichuan province on August 8, 2017, and trigged abundant coseismic landslides deposit in the scenic spot. Due to the heave rainfall after earthquake, the slope debris flow occurred frequently, which seriously threatened the restoration and reconstruction in the after three years. In 2017?2020, continuous investigation, remote sensing interpretation and in-situ erosion test were used to research the impact of slope runoff erosion on deposit. The result shows that the seepage response characteristics are significant during the scouring process, and the downward movement of wetting front causes the increase of volumetric water content and pore water pressure, the matrix suction first fluctuates slightly and then decreases. In addition, the material characteristics of deposit provides the prerequisites for initiation. Under strong hydrodynamic conditions, the startup process is "preliminary penetration → scraping slip flow → rapid accumulation → local saturation erosion-stability". And finally, the mechanical analysis of deposit under different saturations is more consistent with the field test monitoring results. It is further believed that the increase of soil moisture content, and pore water pressure, the rapid decrease of matrix suction and the erosion of high-intensity runoff caused the initiation. The research results can have a certain significance for the long-term effects prediction of debris flow and ecological management after the earthquake.

Key words: Jiuzhaigou earthquake, deposit, runoff intensity, seepage characteristics, initiation mechanism