2:45 PM - 3:00 PM
[HDS11-10] Tsunami propagation predicted in the anchorage of Fukuyama Port
Keywords:Fukuyama Port, Nankai Trough earthquake, suboscillation
Fukuyama City facing the Seto Inland Sea is predicted to suffer from tsunami due to the Nankai Trough earthquake up to 4 m high in the future. This tsunami would enter the anchorage of Fukuyama Port, which is a long and narrow channel from the Seto Island Sea. The height of the tsunami could increase in the eigen period of the channel. In this study, I estimated the sea level variations in the port caused by the tsunami propagation in the Nankai Trough earthquake.
The Anchorage of Fukuyama Port facing the Seto Inland Sea is the narrow channel with a distance about 8.5 km, and its width changes from 950 m in the port entrance to 150 m in the deepest part. Mukai et al.(2022) performed the continuous observations of the sea level changes in the port during about two months in 2021, and revealed that the sea level changes were excited in the period about 42 minutes. This period is close to the period 56 minutes that is calculated analytically in a rectangular bay with a depth of 10 m and a length of 8.5 km. Therefore, the observed signal is considered to be a suboscillation that shows the normal mode with a node at the port entrance and a quarter-wavelength along the port anchorage. Mukai(2022) numerically calculated the sea level changes in the port with the incoming regular waves by using nonlinear shallow-water equations, and confirmed that the calculation could reproduce the suboscillation with the period about 45 minutes.
A tsunami due to the Nankai Trough earthquake is predicted to arrive the coastal area of Fukuyama City with a height up to 4 meters during high tide. According to the tsunami simulation of the Japan Coast Guard, the tsunami could cause the sea level changes with a period about one hour in the offshore of Fukuyama Port. This period is close to that of the suboscillation in the Anchorage of Fukuyama Port. Therefore, it is considered that the tsunami might be extremely amplified along the port anchorage. I investigated the sea level changes due to the tsunami arrival in the port anchorage by using the calculation method of Mukai(2023). The maximum sea level rise in the most inner area of the port anchorage was calculated to be about 2.8 m, while that in the offshore area was about 1.3 m. If the tsunami arrived during high tide, the sea level could rise about 5 m above the mean sea level, which is close to the embankment height of the anchorage port. Even if the embankments were not damaged, the tsunami could spread out in the urban area affected by the land subsidence due to liquefaction. At present, Fukuyama City has a plan of reclamation of a part of the port anchorage. I calculated the sea level changes due to tsunami arrival in a deformed port anchorage as well.
The Anchorage of Fukuyama Port facing the Seto Inland Sea is the narrow channel with a distance about 8.5 km, and its width changes from 950 m in the port entrance to 150 m in the deepest part. Mukai et al.(2022) performed the continuous observations of the sea level changes in the port during about two months in 2021, and revealed that the sea level changes were excited in the period about 42 minutes. This period is close to the period 56 minutes that is calculated analytically in a rectangular bay with a depth of 10 m and a length of 8.5 km. Therefore, the observed signal is considered to be a suboscillation that shows the normal mode with a node at the port entrance and a quarter-wavelength along the port anchorage. Mukai(2022) numerically calculated the sea level changes in the port with the incoming regular waves by using nonlinear shallow-water equations, and confirmed that the calculation could reproduce the suboscillation with the period about 45 minutes.
A tsunami due to the Nankai Trough earthquake is predicted to arrive the coastal area of Fukuyama City with a height up to 4 meters during high tide. According to the tsunami simulation of the Japan Coast Guard, the tsunami could cause the sea level changes with a period about one hour in the offshore of Fukuyama Port. This period is close to that of the suboscillation in the Anchorage of Fukuyama Port. Therefore, it is considered that the tsunami might be extremely amplified along the port anchorage. I investigated the sea level changes due to the tsunami arrival in the port anchorage by using the calculation method of Mukai(2023). The maximum sea level rise in the most inner area of the port anchorage was calculated to be about 2.8 m, while that in the offshore area was about 1.3 m. If the tsunami arrived during high tide, the sea level could rise about 5 m above the mean sea level, which is close to the embankment height of the anchorage port. Even if the embankments were not damaged, the tsunami could spread out in the urban area affected by the land subsidence due to liquefaction. At present, Fukuyama City has a plan of reclamation of a part of the port anchorage. I calculated the sea level changes due to tsunami arrival in a deformed port anchorage as well.