Insights into the catastrophic Xinmo rock avalanche in Maoxian county, China: Combined effects of historical earthquakes and landslide amplification.

A large and catastrophic rock avalanche occurred at the Xinmo village in the Maoxian county of the Sichuan province of China on June 24, 2017. The avalanche destroyed 64 houses and killed 10 people, and 73 people were reported to be missing. In this study, we focused on the contributions of six historical earthquakes to the collapse of rocks in the source area and the landslide amplification caused by the entrainment of pre-existing deposits on the landslide path. The historical earthquakes in this area contributed different levels of damage on the source rocks; particularly, the 1933 Diexi earthquake induced a few initial cracks in rocks at the crest of the steep hillslope. Under the combined time-effects of long-term weathering and gravity, the rock blocks in the source area were detached from the crest along the intersecting cracks and over-dip soft layer (namely, the sliding surface). The avalanche was amplified by the entrainment of colluvium on its path. The influence of the colluvium on the movement process of the Xinmo landslide was modelled by the GPU-based parallel discontinuous deformation analysis (DDA) method, and the effect of the impact and entrainment in the debris flow was rigorously analysed. The results indicate that the impact and entrainment can continuously increase the volume of debris flow, and the thickness of the colluvium was established to be in the range of 25.9–33.9 m based on the analysis of the deposit pattern and movement duration of the avalanche. There were numerous unstable rocks induced by historical earthquakes, at the crests of steep hill slopes in the earthquake-stricken area. With long-term damage caused by environmental factors and gravity, the failure of unstable rocks with high potential energy is likely to cause severe disasters. The excess pore water pressure likely to be present in the colluvium or deposits during impact and entrainment can considerably reduce the effective stress and degrade friction resistance along the runout path. As a result, the landslide can be intensively amplified owing to the effect of impact and entrainment under a lower friction resistance • The volume of rock avalanche sharply increased by entrainment effects. • The rocks at the source were damaged by historical earthquakes. • The colluvium exerts different influences on the movement of the avalanche with an increase in its thickness. • Numerous earthquake-damaged rocks at the summit of mountains are hazardous. [ABSTRACT FROM AUTHOR]