Quantitative multi-hazard risk assessment to buildings in the Jiuzhaigou valley, a world natural heritage site in Western China

Mountain villages in earthquake-prone areas are likely to be exposed to multiple geological hazards. In this study, a comprehensive method is proposed to calculate the risk of buildings in two residential villages threatened by rockfalls and debris flows in the Jiuzhaigou Valley. The risk is a function of the probability of the hazard occurrence, the probability of the spatial impact, vulnerability and the economic value of the buildings. The probability of occurrence was estimated via geomorphological, geotechnical and historical record analyses; Run-out maps were obtained by simulation and used to assess the probability of spatial impact, and the vulnerability of individual buildings was calculated by both hazard intensity and building resistance. Risk curves were generated for debris flows and rockfalls for risk comparison. Uncertainties were assessed by an error propagation technique and expressed as maximum and minimum risk curves of the two hazards. Single risk maps were summed up as multi-hazard risk maps. The multi-hazard risk maps indicate that the highest risk for buildings is due to debris flows, while rockfalls pose relatively low risks to buildings. The risk result can be used as a reference for administrators and decision makers. Mitigation measures should be implemented the high-risk areas.