5:15 PM - 7:15 PM
[HGM04-P09] Multi-stage uplifted wave-cut platforms along the largest uplifted coast associated with the 2024 Noto Peninsula earthquake
★Invited Papers
Keywords:tectonic landform, active submarine fault, marine terrace, Noto Peninsula
Quantitative study of crustal deformation from topography in the coastal land area is an important issue directly related to the reconstruction of past fault displacement of active submarine faults distributed near the coastline. The 2024 Noto Peninsula earthquake (M7.6) is thought to have been caused by the activity of active submarine faults extending along the northern coast of the Noto Peninsula. The crustal deformation associated with this earthquake caused widespread uplift of the northern to western coast of the peninsula, with the largest coastal uplift of 4-5 m occurring near Cape Saruyama on the northwestern coast (Makita et al 2024; Fukushima et al 2024, etc.). Three low-level marine terraces were described in this area prior to the earthquake, suggesting repeated coastal uplift due to Holocene faulting (Shishikura et al., 2020). The relative height between the low terrace surfaces on the northwest coast is estimated to be about 2.5 m, which is only half of the 4-5 m coastal uplift that occurred at the same location in 2024. Whether the uplift of the 2024 earthquake is different or the same as that of the coseismic uplifts repeated during the Holocene is an important issue in considering the repetition of displacement of submarine active faults and the uplift characteristics of the land area near the sea area where many submarine active faults are distributed. The authors have identified a distinct wave-cut platform on the coast about 800 m south of Cape Saruyama that appears to have been formed until the 2024 earthquake, based on interpretation of aerial photographs taken by the Geospatial Information Authority of Japan (GSI) after the earthquake. In order to examine whether the same amount of uplifts as the 2024 earthquake occurred during the Holocene, a detailed topographic survey using handheld LiDAR was conducted at the site in September 2024.
The basement rocks of the northwest coast of the Noto Peninsula consist of the Lower Miocene Doge Formation, which is widely exposed on sea cliffs (Ozaki, 2010).The formation is mainly composed of conglomerate, but the lower part of the formation is interbedded with a continuous tuff with about 20 m thick.The distinct wave-cut platform identified in this study is formed where the tuff meets the sea surface. The flat surface, which was considered to be a wave-cut platform, extends almost horizontally in massive tuff, independent of nodal and stratigraphic planes, and is accompanied by notches on the cliff at the inner edge of the flat surface, suggesting that it is a definite wave-cut platform. The seaward side of the platforms are steep cliffs, which were covered with bleached remains communities of seaweeds that had lived below the mid-tide level prior to the earthquake. The upper limit of the seaweed remains is located at an elevation of 5.3 m, and the wave-cut platform develops 1.7 m above it, most likely formed by high waves at sea level prior to the 2024 earthquake. In addition, two detached wave-cut platforms with elevations of 13.6 m and 16.3 m, respectively, from the lower level. The relative height between the upper and middle planes is small (2.7 m), but the relative height between the middle and lower planes (wave-cut platform formed until 2024) is 7 m, suggesting that a similar or slightly larger uplift than that of the 2024 earthquake may have occurred.
The crustal deformation associated with the 2024 earthquake shows generally similar trends to the height distribution of Pleistocene marine terraces (Ota and Hirakawa, 1979), suggesting that the repetition of similar earthquakes may have contributed to the long-term development of the topography. In the Fukami south of Cape Saruyama, Pleistocene marine terraces are clearly distributed at elevations of 220 m and 150 m, but the formation ages of these terraces are not clear. Assuming that the time of formation of the upper abandoned wave-cut platform observed south of Cape Saruyama was the highest sea-level stage of the Holocene sea-level advance, the former shoreline elevation of MIS5e is expected to exceed 200 m if the same uplift rate as that of the Holocene continues. We will conduct research on the distribution and age of Holocene and Pleistocene terraces to investigate further the long-term contribution of active submarine fault movement to the development of the landforms.
The basement rocks of the northwest coast of the Noto Peninsula consist of the Lower Miocene Doge Formation, which is widely exposed on sea cliffs (Ozaki, 2010).The formation is mainly composed of conglomerate, but the lower part of the formation is interbedded with a continuous tuff with about 20 m thick.The distinct wave-cut platform identified in this study is formed where the tuff meets the sea surface. The flat surface, which was considered to be a wave-cut platform, extends almost horizontally in massive tuff, independent of nodal and stratigraphic planes, and is accompanied by notches on the cliff at the inner edge of the flat surface, suggesting that it is a definite wave-cut platform. The seaward side of the platforms are steep cliffs, which were covered with bleached remains communities of seaweeds that had lived below the mid-tide level prior to the earthquake. The upper limit of the seaweed remains is located at an elevation of 5.3 m, and the wave-cut platform develops 1.7 m above it, most likely formed by high waves at sea level prior to the 2024 earthquake. In addition, two detached wave-cut platforms with elevations of 13.6 m and 16.3 m, respectively, from the lower level. The relative height between the upper and middle planes is small (2.7 m), but the relative height between the middle and lower planes (wave-cut platform formed until 2024) is 7 m, suggesting that a similar or slightly larger uplift than that of the 2024 earthquake may have occurred.
The crustal deformation associated with the 2024 earthquake shows generally similar trends to the height distribution of Pleistocene marine terraces (Ota and Hirakawa, 1979), suggesting that the repetition of similar earthquakes may have contributed to the long-term development of the topography. In the Fukami south of Cape Saruyama, Pleistocene marine terraces are clearly distributed at elevations of 220 m and 150 m, but the formation ages of these terraces are not clear. Assuming that the time of formation of the upper abandoned wave-cut platform observed south of Cape Saruyama was the highest sea-level stage of the Holocene sea-level advance, the former shoreline elevation of MIS5e is expected to exceed 200 m if the same uplift rate as that of the Holocene continues. We will conduct research on the distribution and age of Holocene and Pleistocene terraces to investigate further the long-term contribution of active submarine fault movement to the development of the landforms.