Assessment of debris-flow potential dangers in the Jiuzhaigou Valley following the August 8, 2017, Jiuzhaigou earthquake, western China

Abstract

On August 8, 2017, an Ms 7.0 earthquake occurred at the Jiuzhaigou World Natural and Cultural Heritage, Sichuan Province, southwestern China. Eighty-three earthquake-induced landslides that directly damaged the Jiuzhaigou heritage sites were identified via remote-sensing interpretation and field survey. The coseismic landslides were concentrated primarily within 3 km of the seismogenic fault. Large volumes of sediments were transported into catchments of the Jiuzhaigou Valley, creating a geo-environment conducive to debris flow hazards triggered by post-earthquake heavy rainfall. A methodology combining the calculation of sediment augmentation, particle model, and numerical algorithm is developed to assess the potential dangers of post-quake debris flows. Five typical catchments strongly affected by the earthquake are chosen as study cases. The simulation results at Xiajijiehai Gully show a good agreement with the actual inundation area of the debris-flow event on September 25, 2017. The comparison of pre- and post-earthquake scenarios shows that an increase in sediment supply can greatly increase the debris-flow potential dangers characterized by higher maximum flow depths and larger inundation areas.