5:15 PM - 7:15 PM
[HGM04-P10] Continuous tilting and uplift of the Noto Peninsula during the Late Quaternary inferred from river steepness index and longitudinal profiles
Keywords:Noto Peninsula, uplift, river erosion, morphometric analysis
In regions with significant crustal deformation, rivers respond to uplift and subsidence, often altering their longitudinal profiles. In particular, in areas where significant uplift occurs due to fault movement, the erosive power of rivers increases, leading to changes in channel gradients. Therefore, it is possible to detect the uplift rate and its spatial distribution by using the river profile and erosion index. This study focused on the Noto Peninsula, where significant crustal deformation was observed due to the 2024 Noto Peninsula Earthquake, and investigated the correspondence with long-term changes using river index.
The northern part of the Noto Peninsula has experienced predominant northward tilting and block movement since the late Quaternary. These movements are recorded in marine terraces along the coast. Extensive marine terraces are particularly present in the central northern coast, southwestern coast, and southeastern part of the peninsula, with the M1 surface, attributed to MIS 5e, being the most continuously distributed. During the January 1, 2024, Noto Peninsula earthquake, coastal areas of western Wajima City and northern Suzu City experienced an uplift of 2–4 m. In considering the geomorphogenesis of the Noto Peninsula, it is necessary to evaluate whether the Noto Peninsula earthquake is a representative endemic earthquake and whether the repetition of similar displacements is a major uplifting factor.
This study focused on rivers in the Noto Peninsula and estimated the uplift rate distribution during the Late Quaternary based on normalized steepness index (ksn), longitudinal profiles, and fluvial terraces. River analysis is expected to detect inland deformations more effectively than marine terraces. Additionally, by utilizing geodetic data from the 2024 earthquake, we examined the relationship between cumulative deformation and river geomorphology.
In drainage basins located east of the Machino River, ksn values correlated well with the uplift observed during the earthquake on January 1, 2024, showing a weak positive correlation. In contrast, in basins located east of the Kawarada River and west of the Machino River, a negative correlation was observed, while no significant correlation was found in basins north of the Hakka River and west of the Kawarada River. These findings suggest that the 2024-type earthquake alone cannot fully explain the current topography of Noto Peninsula. Since ksn values are inherently influenced by geological factors, we also conducted lithology-based comparisons. Multiple regression analysis was conducted with ksn as the objective variable and seismic uplift and each lithology (6 types) as explanatory variables. The results showed that in sedimentary rock layers (Douge Formation) distributed in the northwestern Noto Peninsula, ksn values relative to the earthquake-induced uplift were significantly lower than those in other lithologies. This may be due to the lower erosion resistance of this lithology, but it is also possible that the uplift during the earthquake January 1, 2024 was anomalously large in the northwestern region compared to other regions of the northern Noto Peninsula.
Among the fluvial terraces of the Machino River, those identified as higher terraces showed increasing relative elevation above the river as they approached the river mouth. A simple calculation using linear regression of relative elevations and least-squares approximation, where the earthquake-induced uplift was scaled by a constant factor, suggested that approximately 50 earthquakes of the January 1, 2024, type would be required to accumulate the observed elevation differences. The distribution of relative elevations was generally consistent with the earthquake-induced uplift and also aligned with the MIS 5e marine terrace surface near the river mouth. If the MIS 5e surface is assumed to be 125 ka, the recurrence interval for 2024-type earthquakes would be approximately 2,500 years.
The northern part of the Noto Peninsula has experienced predominant northward tilting and block movement since the late Quaternary. These movements are recorded in marine terraces along the coast. Extensive marine terraces are particularly present in the central northern coast, southwestern coast, and southeastern part of the peninsula, with the M1 surface, attributed to MIS 5e, being the most continuously distributed. During the January 1, 2024, Noto Peninsula earthquake, coastal areas of western Wajima City and northern Suzu City experienced an uplift of 2–4 m. In considering the geomorphogenesis of the Noto Peninsula, it is necessary to evaluate whether the Noto Peninsula earthquake is a representative endemic earthquake and whether the repetition of similar displacements is a major uplifting factor.
This study focused on rivers in the Noto Peninsula and estimated the uplift rate distribution during the Late Quaternary based on normalized steepness index (ksn), longitudinal profiles, and fluvial terraces. River analysis is expected to detect inland deformations more effectively than marine terraces. Additionally, by utilizing geodetic data from the 2024 earthquake, we examined the relationship between cumulative deformation and river geomorphology.
In drainage basins located east of the Machino River, ksn values correlated well with the uplift observed during the earthquake on January 1, 2024, showing a weak positive correlation. In contrast, in basins located east of the Kawarada River and west of the Machino River, a negative correlation was observed, while no significant correlation was found in basins north of the Hakka River and west of the Kawarada River. These findings suggest that the 2024-type earthquake alone cannot fully explain the current topography of Noto Peninsula. Since ksn values are inherently influenced by geological factors, we also conducted lithology-based comparisons. Multiple regression analysis was conducted with ksn as the objective variable and seismic uplift and each lithology (6 types) as explanatory variables. The results showed that in sedimentary rock layers (Douge Formation) distributed in the northwestern Noto Peninsula, ksn values relative to the earthquake-induced uplift were significantly lower than those in other lithologies. This may be due to the lower erosion resistance of this lithology, but it is also possible that the uplift during the earthquake January 1, 2024 was anomalously large in the northwestern region compared to other regions of the northern Noto Peninsula.
Among the fluvial terraces of the Machino River, those identified as higher terraces showed increasing relative elevation above the river as they approached the river mouth. A simple calculation using linear regression of relative elevations and least-squares approximation, where the earthquake-induced uplift was scaled by a constant factor, suggested that approximately 50 earthquakes of the January 1, 2024, type would be required to accumulate the observed elevation differences. The distribution of relative elevations was generally consistent with the earthquake-induced uplift and also aligned with the MIS 5e marine terrace surface near the river mouth. If the MIS 5e surface is assumed to be 125 ka, the recurrence interval for 2024-type earthquakes would be approximately 2,500 years.