5:15 PM - 6:45 PM
[U15-P90] Detection of submarine landslides in Toyama Bay and east of the Noto Peninsula using repeated multibeam surveys
Keywords:The 2024 Noto Peninsula Earthquake, Submarine landslide, Tsunami, Repeat bathymetric survey
Introduction
The first tsunami was observed at Toyama tide station 3 minutes after the 2024 Noto Peninsula earthquake (M7.6), Japan. The early tsunami arrival time infers that the tsunami wave source exists in the vicinity of the tide station in Toyama Bay (Meteorological Research Institute, Japan Meteorological Agency, 2024). One of the tsunami sources is submarine landslide. There are quite few cases in Japan where submarine landslide associated with earthquakes was detected as seafloor depth change, except for the case of the 2009 Shizuoka earthquake (Baba et al., 2010 JpGU). This is mainly because accurate bathymetric data have rarely been collected before and after earthquakes. Identifying where and on what scale submarine landslide occurs and its application to tsunami simulation is essential for various organizations to formulate local tsunami prevention plans and to assess the impact on fishery resource or seabed infrastructure. We have conducted emergency research cruises after the 2024 Noto earthquake and detected submarine landslide around the epicenter by comparing pre- and post-earthquake bathymetry.
Method
High-density bathymetric data sets with high navigational accuracy are necessary to detect submarine landslide as seafloor depth change. We collected and evaluated available pre-earthquake data. In Toyama Bay, we used multibeam bathymetry collected by the Hokuriku Regional Development Bureau in 2010 as our pre-earthquake data. Post-earthquake bathymetry was collected by the Japan Coast Guard (JCG) S/V Shoyo and Tenyo in Jan. and Feb. 2024. Off Noto Peninsula, pre-earthquake bathymetry was collected by JCG S/V Takuyo in May 2023 and post-earthquake ones were, by JCG S/V Takuyo and Japan Agency for Marine-Earth Science and Technology (JAMSTEC) R/V Hakuho Maru in Jan. and Feb. 2024. The collected bathymetric data were processed using CARIS HIPS and SIPS.
Results
In Toyama Bay, we detected submarine landslides 1.5–5 km north of Toyama tide station, covering an area of 1 km (E–W) × 3.5 km (N–S). The maximum depth change associated with these slides is approximately 40 m. The slides occurred along the steep (>10°, locally >40°) sea channel between water depths of 30–370 m. Relatively small slides occurred in large areas, most of which could not be recognized without a depth difference map. We also identified submarine landslide scar at a water depth of 220 m, approximately 9 km northeast of Himi fishing port. Although we could not determine the exact timing of this slide due to the absence of pre-earthquake bathymetry here, its fresh morphology suggests a recent occurrence. In the area east of Noto Peninsula, landslides occurred sporadically for a distance of about 30 km along the Toyama Deep-Sea Channel. Taking into consideration that the pre-earthquake bathymetry was acquired in May 2023 and no large earthquakes occurred before Jan 2024, we conclude that these landslides were caused by the 2024 Noto earthquake.
The first tsunami was observed at Toyama tide station 3 minutes after the 2024 Noto Peninsula earthquake (M7.6), Japan. The early tsunami arrival time infers that the tsunami wave source exists in the vicinity of the tide station in Toyama Bay (Meteorological Research Institute, Japan Meteorological Agency, 2024). One of the tsunami sources is submarine landslide. There are quite few cases in Japan where submarine landslide associated with earthquakes was detected as seafloor depth change, except for the case of the 2009 Shizuoka earthquake (Baba et al., 2010 JpGU). This is mainly because accurate bathymetric data have rarely been collected before and after earthquakes. Identifying where and on what scale submarine landslide occurs and its application to tsunami simulation is essential for various organizations to formulate local tsunami prevention plans and to assess the impact on fishery resource or seabed infrastructure. We have conducted emergency research cruises after the 2024 Noto earthquake and detected submarine landslide around the epicenter by comparing pre- and post-earthquake bathymetry.
Method
High-density bathymetric data sets with high navigational accuracy are necessary to detect submarine landslide as seafloor depth change. We collected and evaluated available pre-earthquake data. In Toyama Bay, we used multibeam bathymetry collected by the Hokuriku Regional Development Bureau in 2010 as our pre-earthquake data. Post-earthquake bathymetry was collected by the Japan Coast Guard (JCG) S/V Shoyo and Tenyo in Jan. and Feb. 2024. Off Noto Peninsula, pre-earthquake bathymetry was collected by JCG S/V Takuyo in May 2023 and post-earthquake ones were, by JCG S/V Takuyo and Japan Agency for Marine-Earth Science and Technology (JAMSTEC) R/V Hakuho Maru in Jan. and Feb. 2024. The collected bathymetric data were processed using CARIS HIPS and SIPS.
Results
In Toyama Bay, we detected submarine landslides 1.5–5 km north of Toyama tide station, covering an area of 1 km (E–W) × 3.5 km (N–S). The maximum depth change associated with these slides is approximately 40 m. The slides occurred along the steep (>10°, locally >40°) sea channel between water depths of 30–370 m. Relatively small slides occurred in large areas, most of which could not be recognized without a depth difference map. We also identified submarine landslide scar at a water depth of 220 m, approximately 9 km northeast of Himi fishing port. Although we could not determine the exact timing of this slide due to the absence of pre-earthquake bathymetry here, its fresh morphology suggests a recent occurrence. In the area east of Noto Peninsula, landslides occurred sporadically for a distance of about 30 km along the Toyama Deep-Sea Channel. Taking into consideration that the pre-earthquake bathymetry was acquired in May 2023 and no large earthquakes occurred before Jan 2024, we conclude that these landslides were caused by the 2024 Noto earthquake.