Evaluation of landslide mechanisms characterized by high-speed mass ejection and long-run-out based on events following the Wenchuan earthquake

In the 2008 Wenchuan earthquake, the mass ejection type of high-speed and long-run-out landslide was an unusual hazard characterized by its dramatic phenomenon of a huge slope mass launching into the air and becoming airborne for a long distance. Quantitative and qualitative combined techniques were applied to reveal the formation mechanism of this type of landslide. Four prerequisites critical to form mass ejection are identified: high position of the toe of the surface of rupture, critical height and critical inclination of slope, sufficient open space in the movement direction, and adequate take-off speed of ski-jump-like mass ejection. These four area-specific prerequisites provide a promising approach for screening and targeting the potential landslides. Subsequently, a dynamic reliability analysis method that considers the feature of energy–time distribution is proposed. This site-specific method provides a more credible evaluation by emphasizing the most significant period within the whole earthquake duration. Finally, an aerodynamic inverse method combined with an energy-conservation-based method is applied in the quantitative evaluation to calculate take-off speed of mass ejection. This paper provides a viable solution for regional screening and site assessment for new potential targets of this type of landslide. •Four prerequisites critical to form mass ejection landslides are identified.•A dynamic reliability analysis method considering energy–time distribution is proposed.•A forward-inversed-combined method is suggested to calculate take-off speed of mass ejection.