An agent-based vertical evacuation model for a near-field tsunami: Choice behavior, logical shelter locations, and life safety

In the event of near-field tsunamis, vertical evacuation can be an alternative protective action to horizontal evacuation. The objective of this paper is to present an agent-based modeling (ABM) framework to evaluate vertical evacuation behavior and shelter locations for a near-field tsunami hazard from a Magnitude 9.0 Cascadia Subduction Zone (CSZ) earthquake. The expected mortality rate depending on the location of the vertical evacuation shelter (VES) has been chosen as the primary criterion to assess the effectiveness of the vertical evacuation. In addition, maximum tsunami wave height and the vertical evacuation behavior changes with changes in the placement of the VES have been assessed from a constraint point of view. The results revealed that (1) the choice of VES locations will directly impact the proportion of the people who evacuate vertically; (2) The percentage of people who evacuate vertically exponentially drops as the shelter gets farther from the population centroid; (3) the location of shelter significantly impacts the total mortality rates; (4) improvements in evacuees' mobility, such as faster walking speed or shorter milling time, will significantly reduce mortality rate and expand the area of choices for VES locations; and (5) when more people choose to evacuate vertically, the total mortality rate reduces notably. However, wrong placement of VES, and at the same time promoting vertical evacuation behavior can result in catastrophic mortality rates. In addition, a study on the impact of the distance of the VES to the ocean, to the population centroid, and to the horizontal shelters outside of the inundation zone, on the total mortality rate and the evacuation efficiency has been performed. This work reveals the non-linear correlation between the aforementioned characteristics of the VES on the expected mortality rate. The results of this research provide an evidence-driven vertical evacuation modeling framework to guide decision makers at city, state, and federal level to understand the dynamics of vertical evacuation behavior and choice of vertical evacuation shelter locations for a community.