Influence of road blockage on tsunami evacuation: A comparative study of three different coastal cities in Japan

For the case of a near-field tsunami, severe ground shaking prior to the arrival of the first tsunami wave could result in the collapse of many buildings, which could lead to road blockage and hinder evacuation. The present study aims to clarify the influence that seismic damage to the buildings and the debris created will have on the road network, and how this in turn will influence tsunami evacuation and the expected number of casualties. To do so, an agent-based tsunami evacuation simulation model that can consider the changes in evacuation behaviour due to road blockage was developed. The model was then applied to three coastal cities in Japan (Kamakura, Zushi, Fujisawa) by considering a Genroku Kanto Earthquake Tsunami scenario. The simulated results showed that considering the effects of building collapse and associated road blockage significantly increased the expected mortality rates. A correlation analysis also indicated that while mortality rates considering road blockage were strongly correlated with inundation depth, they were also positively correlated with the percentage of collapsed buildings, and blocked roads. This suggests that the inundation depth and the distance to a refuge area/shelter might not be sufficient parameters to determine the likely tsunami risks at a given point in a coastal city in the case of a near-field tsunami, and that the effect of damaged buildings should also be considered.