5:15 PM - 7:15 PM
[AOS21-P05] Highest sea level distribution in the anchorage of Fukuyama Port during the arrival of Tsunami due to the Nankai Trough earthquake
Keywords:the anchorage of Fukuyama Port, tsunami, sea level distribution
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 be amplified in the anchorage of Fukuyama Port by its topographic effect of the long and narrow channel. When the tsunami arrived during high tide, the sea level could reach about 4.8 m in the deepest part of the anchorage port, and its sea level could not exceed the embankment height. However, sea level depends on weather conditions as well. In this study, I estimated the spatial distribution of the maximum sea level rises in the port caused by the tsunami propagation in the Nankai Trough earthquake under consideration of the inverted barometer effect, wind set-up effect and suboscillation during passage of typhoon.
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 (2024) calculated sea level variations due to tsunami entering the port by using the tsunami waveform of the Japan Coast Guard. The sea level would rise by 2.6 m and reach the maximum height about 6 hours after the earthquake. This is about twice the sea level rise around the offshore area of Fukuyama Port. If the tsunami arrived during high tide, the highest sea level could reach about 4.8 m above mean sea level.
The anchorage of Fukuyama Port has an embankment about 5.5 m high. This embankment is about 1 m higher than the maximum sea level due to tsunami arriving at the highest tide. Therefore, the risk of sea water overtopping is low without the embankment damage. However, the sea level could rise additionally under extreme weather conditions such as approaching typhoons. Mukai et al. (2022) performed continuous observations of sea level changes and meteorological observations from September 1 to November 4, 2021, in the anchorage port, and estimated the inverted barometer effect and wind set-up effect. These effects could cause the sea level rise about 0.4 m according to the past 10 years meteorological observations at Fukuyama. In addition, suboscillation with a period of 42 minutes caused the sea level rise by about 0.3 m during the passage of typhoon in 2021.
Tsunami of Nankai Trough earthquake could make the sea level reach about 5.5 m in the deepest part of the Fukuyama Port during the highest tide and the extreme weather conditions. This sea level is close to top edge of the embankment. Therefore, it is considered that we would face the risk of sea water flooding caused by the embankment failures and the land subsidence due to liquefaction.
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 (2024) calculated sea level variations due to tsunami entering the port by using the tsunami waveform of the Japan Coast Guard. The sea level would rise by 2.6 m and reach the maximum height about 6 hours after the earthquake. This is about twice the sea level rise around the offshore area of Fukuyama Port. If the tsunami arrived during high tide, the highest sea level could reach about 4.8 m above mean sea level.
The anchorage of Fukuyama Port has an embankment about 5.5 m high. This embankment is about 1 m higher than the maximum sea level due to tsunami arriving at the highest tide. Therefore, the risk of sea water overtopping is low without the embankment damage. However, the sea level could rise additionally under extreme weather conditions such as approaching typhoons. Mukai et al. (2022) performed continuous observations of sea level changes and meteorological observations from September 1 to November 4, 2021, in the anchorage port, and estimated the inverted barometer effect and wind set-up effect. These effects could cause the sea level rise about 0.4 m according to the past 10 years meteorological observations at Fukuyama. In addition, suboscillation with a period of 42 minutes caused the sea level rise by about 0.3 m during the passage of typhoon in 2021.
Tsunami of Nankai Trough earthquake could make the sea level reach about 5.5 m in the deepest part of the Fukuyama Port during the highest tide and the extreme weather conditions. This sea level is close to top edge of the embankment. Therefore, it is considered that we would face the risk of sea water flooding caused by the embankment failures and the land subsidence due to liquefaction.