Assessing transportation vulnerability to tsunamis: utilising post-event field data from the 2011 Tōhoku tsunami, Japan, and the 2015 Illapel tsunami, Chile

Abstract

Transportation infrastructure is crucial to the operation of society, particularly during post-event response and recovery. Transportation assets, such as roads and bridges, can be exposed to tsunami impacts when near the coast. Using fragility functions in an impact assessment identifies potential tsunami effects to inform decisions on potential mitigation strategies. Such functions have not been available for transportation assets exposed to tsunami hazard in the past due to limited empirical datasets. This study provides a suite of observations on the influence of tsunami inundation depth, road-use type, culverts, inundation distance, debris and coastal topography. Fragility functions are developed for roads, considering inundation depth, road-use type, and coastal topography and, for bridges, considering only inundation depth above deck base height. Fragility functions are developed for roads and bridges through combined survey and remotely sensed data for the 2011 Tōhoku earthquake and tsunami, Japan, and using post-event field survey data from the 2015 Illapel earthquake and tsunami, Chile. The fragility functions show a trend of lower tsunami vulnerability (through lower probabilities of reaching or exceeding a given damage level) for road-use categories of potentially higher construction standards. The topographic setting is also shown to affect the vulnerability of transportation assets in a tsunami, with coastal plains seeing higher initial vulnerability in some instances (e.g. for state roads with up to 5 m inundation depth) but with coastal valleys (in some locations exceeding 30 m inundation depth) seeing higher asset vulnerability overall. This study represents the first peer-reviewed example of empirical road and bridge fragility functions that consider a range of damage levels. This suite of synthesised functions is applicable to a variety of exposure and attribute types for use in global tsunami impact assessments to inform resilience and mitigation strategies.