2024-01-16 09:53:07
The Noto Peninsula earthquake caused a tsunami to flood the Naoetsu area of Joetsu City, Niigata Prefecture. There is no tsunami observation meter installed in Naoetsu, and the closest observation meter in Kujiranami, Kashiwazaki City, showed a maximum wave of 40cm, so the observed height of the tsunami in Naoetsu is said to be “more than 40cm.” . However, at Naoetsu Port, a tide gauge was installed to monitor changes in the tide level, although it was not used for tsunami observation, and it was found that a rise in the tide level of 1m30cm was confirmed during the first wave of the tsunami.
Tide station installed at Naoetsu Port (white building on the left)
There are four tsunami observation points in the prefecture: Awashima (established agency: Japan Coast Guard), Washizaki, Sado City (Japan Meteorological Agency), Niigata City (Port Bureau, Ministry of Land, Infrastructure, Transport and Tourism), and Kujiranami, Kashiwazaki City (Geographical Survey Institute of Japan). A radio tsunami observation meter and a giant tsunami observation meter are installed at one location, and tide gauges are installed at three other locations. There is also a huge tsunami observation meter at the tide gauge station in Niigata West Port.
According to the Naoetsu Port Office of the Joetsu Regional Promotion Bureau of the prefecture, the tide gauge station at Naoetsu Port was installed for the purpose of monitoring changes in the tide level when managing the port and carrying out construction work. A “float” is placed in a well within the tide gauge station, and observations are made using a float-type tide gauge that measures the vertical movement of the sea level.
Schematic diagram of a float-type tide gauge (left) and a radio-wave tsunami observation meter (from the Japan Meteorological Agency website “Tide Observation Mechanism”)
In the case of the Noto Peninsula Earthquake, Naoetsu Port has a breakwater, so at 4:43 p.m., eight minutes after 4:35 p.m., when the tsunami was confirmed to have arrived near the mouth of the Seki River, a sudden rise in the tide level of 1.30 cm was observed.
Over the next hour or so, tide level rises exceeding 1.50cm, the maximum observable by the tide gauges at the port, were observed three times. It is possible that the combination of three waves caused the tide level in the port to rise.
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