Annual Journal of Civil Engineering in the Ocean Vol.32
NUMERICAL STUDY ON THE TSUNAMI REDUCTION FACTOR IN MATSUSHIMA BAY DURING THE GREAT EAST JAPAN EARTHQUAKE
2016 Volume 72 Issue 2 Pages I_151-I_156
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2016 Volume 72 Issue 2 Pages I_151-I_156
The high water marks resulting from the Great East Japan Earthquake Tsunami around Matsushima Bay were noticeably smaller than those in other nearby regions. It has been suggested that the islets in the bay may have reduced the tsunami height but a quantitative analysis on the reduction effect has not been undertaken. In this study, we evaluated the tsunami height reduction factor by numerical analysis where topographic details of the islands were removed in stages and the water depth at the entrance to the bay was increased. Comparison of the results showed that the relatively shallow water depth as well as the islets in the bay contributed to a reduction in the tsunami height on the order of 4 m and delay of tsunami arrival to the coastal areas around the bay by up to 10 minutes in some areas. In addition, we showed that an appropriately sized breakwater (length: 6.5 km, crest height: T.P.+6.0 m) at the mouth of the bay can obtain the same tsunami reduction effect as the one given by the actual topography in the bay.
