Effectiveness of real-time near-field tsunami inundation forecasts for tsunami evacuation in Kushiro City, Hokkaido, Japan

Abstract

An algorithm called NearTIF, designed to produce tsunami inundation maps of near-field sites before the actual tsunami hits the shore, was previously developed by the authors. This algorithm relies on a database of precomputed tsunami waveforms at several near-shore locations and tsunami inundation maps from various earthquake fault models. In the event of a great earthquake, tsunami waveforms at the above mentioned near-shore locations are computed on the basis of real-time observation data by use of linear long-wave equations. Simulating these tsunami waveforms takes only 1-3 min on a common personal computer, so the realistic offshore tsunami waveforms can be forecasted. The offshore real-time simulated tsunami waveforms are then compared with precomputed tsunami waveforms in a database to select the site-specific best fault model and the corresponding tsunami inundation map. The best tsunami inundation map is then used as the tsunami inundation forecast. We evaluated the effectiveness of this algorithm in the real world by carrying out a tsunami evacuation drill in Kushiro City, Hokkaido, Japan, involving the city residents. The drill started with the announcement of a tsunami warning, to evacuate the residents to the nearest evacuation building. Approximately 10 min after the announcement, the tsunami inundation forecast map was given to the participants in the drill. The participants found that the use of the tsunami inundation forecast map produced by NearTIF was effective in helping them make better decisions with high confidence during the tsunami evacuation drill. The NearTIF algorithm is recommended for use as part of the reconstruction policy by local authorities to improve the evacuation efficiency, particularly in tsunami-prone areas.