The Residual Tsunami Risk After the Reconstruction Projects in Fukushima Prefecture, Japan
The tsunami by the 2011 off the Pacific coast of Tohoku Earthquake caused severe damages along the wide area of coasts including Fukushima prefecture, Japan. In response to this disaster, the Central Disaster Prevention Council in Japan made the two standard levels of dike/seawall heights for protection and hazard area for disaster reduction. Those probability of tsunamis are 10−2 and 10−3 per year called the protection level and the disaster reduction level. In areas affected by the tsunami, reconstruction projects have been charring out based on these standards. And more, at the devastated communities by the tsunami, artificial high grounds with green spaces for extra disaster reduction are being constructed. On the other hands the communities where the houses have remained even in the tsunami, there are no extra reduction countermeasures. The purpose of this study is to quantitatively assess the residual tsunami risk corresponding to the different reconstruction projects, and to calculate the long-term cost effectiveness of the projects. The target area is the coastal area of Iwaki city in Fukushima prefecture. For the assessment of probabilistic tsunami flood risk calculated by use of a numerical simulation, the mean hazard curve calculated from the logic tree scenario proposed by Annaka (2007) was expanded for high to low frequency tsunamis. The residential areas, where the house-damages due to last tsunami were limiting so that the scale of reconstruction project is small, will be low cost benefit and high residual risk. On the other hands, the residential areas, where were ruined by the last tsunami and where artificial hills and green area are constructing in the large scale of reconstruction project, will be better not only for the benefit but also for evacuation spots.
Keywordstsunami inundation risk countermeasure greenbelt sea wall cost and benefit flat artificial hill
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Professor Shinji Sato of Tokyo University, Professor Shinichi Aoki of Osaka University and Professor Satoshi Takewaka of Tsukuba University had cooperated the tsunami disaster survey with one of authors in this study site in two and three weeks after the 2011 off the Pacific coast of Tohoku Earthquake.
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