Author(s): Kenta Kudai; Maeno Shiro; Keisuke Yoshida; Ryosuke Akoh
Linked Author(s): Keisuke Yoshida
Keywords: Seto inland sea; Nankai trough earthquake; Tsunami and tide
Abstract: Okayama city’s coastal area is occupied mainly by reclaimed land with soft ground of elevation below T. P. 0 m. Therefore, the city is regarded as susceptible to tsunami disaster effects if a Nankai Trough earthquake should occur. A shallow sea area of the Seto Inland Sea, which Okayama city faces (Bisanseto), is known for its large tidal range and strong tidal current. The tide can affect the tsunami peak water level and tsunami arrival time in the event of an earthquake. Then tsunami numerical analysis was conducted under 11 different tides’conditions to investigate the relation between the tide phase at the time of the earthquake and the tsunami behavior at Okayama city offshore. Results show that the maximum tsunami height is as high in cases where the tsunami arrival at Okayama city offshore is synchronized with the high tide there. Especially, the maximum tsunami height of the second wave reaches T. P. 2.05 m in cases where the earthquake occurs 3 hr earlier than at high tide at Okayama city’s coast. Each tsunami reaches Okayama city’s coast early in the cases of tsunami propagation on the rising tide in Bisanseto. The maximum difference of arrival times of each tsunami among 11 cases is 12 min. As described above, this research produces important results that can help to determine and improve Okayama city’s tsunami countermeasures.