Abstract
Tsunami numerical simulations are performed. The selected tsunamis are caused by Keicho, Genroku and the northen bay of Tokyo earthquakes. These tsunamis cause big disasters around Tokyo bay in the future. The damage of tsunami and the cost of protection measures against tsunami are calculated. By using these results, the cost and the benefit are compared. As a resut, the damage of Keicho tsunami is 6.95 trillion yen, for Genroku tsunami it is 5.04 tillion yen and for the northern Tokyo bay tsunami it is 4.54 trillion yen. The cost of protection including seawall and water gate are 1.05 trillion yen. The cost of building with pilotis is 15.0 trillion yen The probabilities of occurrence of earthquakes and cost-benefit ratios are calculated. As a result, B/C is 9.97 if we protect by using seawall and water gate. B/C is above 1.0 if we protect by offering public support to house owners up to 60 percent of the cost of construction of pilotis.
