A Conceptual Event-Tree Model for Coseismic Landslide Dam Hazard Assessment

Earthquakes may trigger a series of multiple cascading geohazard phenomena. For example, coseismic landslides may block rivers and form landslide dams, which occur frequently in tectonically active mountains with narrow and steep valleys. The catastrophic release of water masses from landslide-impounded lakes is capable to produce outburst floods and debris flows, causing loss of lives, housing and infrastructure. Quantifying the probability of these cascading phenomena following a triggering event has been a main research challenge. This study creates a conceptual event tree model for hazard assessment of earthquake-induced landslide dams, with the involvement of many discussions amongst specialists in different fields. Event tree (ET) is a graphical, hierarchical and tree-like representation of possible events, which has been successfully applied in the volcano hazard assessment, but the application in landslide research is rather limited. We attempt to elaborate the event tree model by applying it in estimating the hazard of landslide dams induced by the Wenchuan earthquake. The model starts from a scenario-earthquake on a known possible active faults; the model then progressively assesses the susceptibility to coseismic landslides and landslide dams, and, finally, provides an estimate of dam-break flood hazard. According to the literature and our best understanding of the seismic hazard, we suggested or proposed possible methods to estimate the probabilities at successive nodes, the cascading events.