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.