[U-15] The 2024 Noto Peninsula Earthquake (1:J)

[U15-P72] Sedimentological and micropaleontological characteristics of tsunami deposits associated with the 2024 Noto Peninsula earthquake

*Yumi Shimada¹, Dan Matsumoto¹, Koichiro Tanigawa¹, Yuki Sawai¹ (1.National Institute of Advanced Industrial Science and Technology (AIST))

Keywords:The 2024 Noto Peninsula earthquake, Tsunami deposits, Diatom, Ishikawa Prefecture, Suzu City

The 2024 Noto Peninsula earthquake (Mw= 7.6) occurred at 16:10 (JST) on 1 January 2024. The associated tsunami was widely observed along the coastal area of the Japan Sea. The tsunami inundation caused severe damages on the eastern coast of the Noto Peninsula and it left tsunami deposit behind it. In this presentation, we report sedimentological and micropaleontological characteristics of the tsunami deposits in Suzu City, northeastern part of the peninsula. Samples of the tsunami deposits were taken at a coastal lowland in the Ukai district of Suzu City, Ishikawa Prefecture in January and February 2024. The inundation heights and the distribution area of the debris were also examined in Ukai and Ushima. The tsunami deposits were distributed only within ~50 m from the dyke, whereas debris were recognized at ~210 m from the coast. The inundation height of the study site was at least 1.4 m. The thickness of the tsunami deposits was measured in 96 locations at 0.5 m intervals up to 48 m from the dyke. The maximum (11.2 cm) and minimum (0.6 cm) thicknesses were recorded at 8 m and 33.5 m inland from the dyke, respectively. We took sediments samples at 5 locations (named SZ01 to SZ05) for detailed analyses. Observation using soft X-ray and computed tomography (CT) images showed that the tsunami deposits at SZ01, 03 and 04 consisted of the two subunits. The sample SZ01 also had the sedimentary feature suggesting backwash current. Median grain size of tsunami deposits at all locations was in the range of fine sand, while that of soil was in medium sand. Diatom assemblages within the tsunami deposits, underlying soils, and sand as a reference sample from the present beach were identified and counted. Marine species such as Delphineis surirella and brackish species such as Catenula adhaerens were observed within the tsunami deposits. These taxa were also found in the reference sand sample from the present Suzu. Freshwater species such as Hantzschia amphioxys and Luticola spp. which generally occurred frequently in soils were also identified in the tsunami deposits. Our presentation will show further details of diatom assemblages and sedimentary processes of the tsunami deposits found at the study site.