5:15 PM - 6:45 PM
[U16-P03] Observation of submarine fault scarps formed by the 2024 Noto earthquake by using an underwater drone
Keywords:2024 Noto earthquake, submarine earthquake fault, underwater drone
Fault movement during earthquakes on submarine active faults can cause coastal uplift or subsidence and generate tsunamis. The 2024 Noto earthquake resulted in coastal uplift of up to 4 meters in the northern part of the Noto Peninsula. Given that bathymetric data from the Japan Coast Guard indicated topographic variations along an offshore active fault, we conducted a fault survey using an underwater drone (a small ROV) during an emergency research cruise of the R/V Hakuho Maru (KH-24-E1). As a result, we identified two underwater steps on the seafloor off the northern coast of the Noto Peninsula (off the northwest coast of Cape Suzu and off the northwest coast of Wajima), which are likely to have formed during the 2024 Noto earthquake.
The step found offshore northwest of Cape Suzu was discovered in bedrock (sandy or muddy sedimentary rocks) exposed on the seafloor, extending more than 20 meters along NE to SW. This step is located southeast of a submarine active fault (the Suzu-oki segment), as inferred from a seismic reflection survey by the National Institute of Advanced Industrial Science and Technology (Inoue and Okamura, 2010). The height of the step appears to be less than 1 meter, with the northwest side being higher. In many places, the upper part of the step overhangs the lower part, and collapsed material from the step can be observed along the step. The wall of the step and the surfaces of the collapsed material are not weathered, and there are no signs of algae or benthos, suggesting that the step was formed within the last few months. These lines of evidence strongly suggest that the step is a submarine earthquake fault (subsidiary transpressional back thrust) created by reverse fault slip related to the 2024 Noto earthquake.
The step found in the northwest offshore of Wajima, as confirmed by a bathymetric survey, extends in ENE to WSW direction and is located on the seafloor trace of a submarine active fault (the Saruyama-oki segment, Inoue and Okamura, 2010). The specific height of the steps is less than 1 meter, with the north side being deeper and the south side shallower. The surface of the steps is covered with gravels and shell fragments, disrupting the brownish cover typically seen on the surrounding seafloor, indicating recent disturbance. These characteristics suggest that the step is a flexural cliff caused by fault displacement, and that the surface collapsed due to fault displacement related to the 2024 Noto earthquake.
Steps on the seafloor that may have been caused by the 2024 Noto earthquake were found in two of the three sites surveyed by the underwater drone. This observation suggests that fault slip during the earthquake reached the seafloor in a wide area along the northern coast of the Noto Peninsula.
The step found offshore northwest of Cape Suzu was discovered in bedrock (sandy or muddy sedimentary rocks) exposed on the seafloor, extending more than 20 meters along NE to SW. This step is located southeast of a submarine active fault (the Suzu-oki segment), as inferred from a seismic reflection survey by the National Institute of Advanced Industrial Science and Technology (Inoue and Okamura, 2010). The height of the step appears to be less than 1 meter, with the northwest side being higher. In many places, the upper part of the step overhangs the lower part, and collapsed material from the step can be observed along the step. The wall of the step and the surfaces of the collapsed material are not weathered, and there are no signs of algae or benthos, suggesting that the step was formed within the last few months. These lines of evidence strongly suggest that the step is a submarine earthquake fault (subsidiary transpressional back thrust) created by reverse fault slip related to the 2024 Noto earthquake.
The step found in the northwest offshore of Wajima, as confirmed by a bathymetric survey, extends in ENE to WSW direction and is located on the seafloor trace of a submarine active fault (the Saruyama-oki segment, Inoue and Okamura, 2010). The specific height of the steps is less than 1 meter, with the north side being deeper and the south side shallower. The surface of the steps is covered with gravels and shell fragments, disrupting the brownish cover typically seen on the surrounding seafloor, indicating recent disturbance. These characteristics suggest that the step is a flexural cliff caused by fault displacement, and that the surface collapsed due to fault displacement related to the 2024 Noto earthquake.
Steps on the seafloor that may have been caused by the 2024 Noto earthquake were found in two of the three sites surveyed by the underwater drone. This observation suggests that fault slip during the earthquake reached the seafloor in a wide area along the northern coast of the Noto Peninsula.