Justification of Possible Casualty-Reduction Countermeasures Based on Global Tsunami Hazard Assessment for Tsunami-Prone Regions over the Past 400 Years

Abstract

Tsunami hazards can be considered as multiregional in their impacts, as transoceanic waves can propagate beyond local areas, as evidenced in recent tsunami events, e.g., the 2004 Indian Ocean and 2011 Great East Japan tsunamis. However, in a single event, the characteristics of a tsunami (wave amplitude and arrival time) can differ from location to location, due to a myriad of reasons including distance from the source, bathymetry of the seafloor, and local effects. Tsunami countermeasures cannot be similarly applied globally. It is prudent to investigate tsunami hazard characteristics at a regional scale in order to evaluate suitable tsunami countermeasures. On this basis, approximately 300 major historical tsunamis have been reproduced in this study based on seismic records over the last 400 years. In this study, numerical analysis was performed to reproduce tsunami waveforms at each global tidal station, and numerical results were verified by comparing them with the 2011 Great East Japan tsunami record data. Non-structural tsunami countermeasures were proposed and selected for each region based on two main criteria – wave amplitudes and arrival times. Evaluation of selected countermeasures indicate that planning for evacuation processes (such as evacuation route mapping, signage and evacuation drills) are important in all situations. For local large tsunamis, evacuation drills are essential to ensure a community is well prepared for self-evacuation due to the short amount of time available for evacuation. Early warning systems were most effective where tsunamis are of large and distant origins. On the other hand, it would be more appropriate to invest in public alert systems for tsunamis of smaller magnitudes. Using these selection criteria, combinations of countermeasures were proposed for each region to focus their attention on, based on the simulated results of the historical tsunami events. The end-goal of this study is to inform decision-making processes and regional planning of tsunami disaster management.