ABSTRACT
The devastating 2008 Wenchuan earthquake (Mw 7.9) was the largest seismic event in China in more than 50 years. Earthquake hazard is not equally distributed in space and time, nor does it end when ground shaking stops, instead there is a hazard chain involving the mainshock, aftershocks, and subsequent climatic events. The Wenchuan earthquake triggered more than 60,000 landslides over a broad area, out of which more than 500 dammed rivers, posing severe threatens to downstream settlements. After the earthquake, the regions of strong shaking have experienced several heavy rainstorms that induced a number of catastrophic landslides and debris flows. Post-earthquake debris flows commonly initiate from material loosened by earthquake ground motions or deposited on hillslopes by earthquake-induced landslides. Earthquake-enhanced landsliding and sedimentation creates a persistent, low-magnitude hazard that can last for at least a decade, jeopardizing recovery. Predicting the post-earthquake hazard (landslides and debris flows) and assessing their long-term effect and risk are still of great concern and remain as a main challenge, due in part to a lack of empirical data of sufficient temporal resolution. This study aims to summarize the work of SKLGP (State Key laboratory of Geohazard Prevention and Geoenvironment Protection) on the long-term geologic hazards after the Wenchuan earthquake with special focus on the mechanism and hazard assessment of post-earthquake debris flows. Cases studies on the representative post-seismic geohazards area were presented in this study. The distribution and evolution of geohazards in the post Wenchuan earthquake area were discussed. The initiation mechanisms of the post-earthquake debris were also studied. The effect of earthquakes on the rainfall threshold of debris flow was discussed. We also highlight the future research on risk assessment on management with the eventual goal of enhancing resilience.
