5:15 PM - 7:15 PM
[SSS14-P07] Excavation survey and Outcrop observation of fault appearing along the Wakayama River associated with the 2024 Noto Peninsula Earthquake
Keywords:Wakayama River, surface deformation, Noto Peninsula earthquake, fold, fault
During the 2024 Noto Peninsula earthquake, fault scarps exceeding 2 m were formed in some areas along the Wakayama River. Some parts of this scarps overlap with the existing cliff. This suggests that the fault may have been displaced in the past. In this study, we carried out the excavation survey across the fault scarp to clarify the mechanism of scarp formation and past displacement. In addition, heavy rains on the Noto Peninsula in September 2024 caused large-scale flooding in the Wakayama River. The fault outcrop appeared due to lateral erosion caused by floodwaters. We also observed this outcrop.
The excavation site was a field on the left bank of the Wakayama River in Munesue, Wakayama-cho, Suzu City. The outcrop observation site is on the left bank of the Wakayama River, approximately 20 m downstream from Sugota Bridge. Geomorphometry was carried out at this site, and the topography and geology around the fault were observed.
The excavation walls contain several faults that agree well with the strike and dip of the siltstone bedding planes. The underground displacement of faults associated with scarps is greater than the displacement at the surface. In addition, the sand layer within the gravel layer is deformed at the extension of the fault, but there is no deformation on the surface. Plant fragments in the gravel layer dated to 770-658 cal BP. Around the northern part of the outcrop exposed by the flood, there is a fault scarp approximately 1.4 m in height. Beneath the scarp, the boundary between the siltstone and the gravel layer has displaced approximately 2.4 m along the fault.
Based on these characteristics, some faults were thought to have been formed by shearing along the bedding plane of the siltstone. Fault displacement is thought to have occurred at least twice in the past 700 years.
This work was supported by JSPS KAKENHI Grant Numbers JP23K17482, JP23K04326, JP24K07162, and the Kanazawa University Disaster investigation team.
The excavation site was a field on the left bank of the Wakayama River in Munesue, Wakayama-cho, Suzu City. The outcrop observation site is on the left bank of the Wakayama River, approximately 20 m downstream from Sugota Bridge. Geomorphometry was carried out at this site, and the topography and geology around the fault were observed.
The excavation walls contain several faults that agree well with the strike and dip of the siltstone bedding planes. The underground displacement of faults associated with scarps is greater than the displacement at the surface. In addition, the sand layer within the gravel layer is deformed at the extension of the fault, but there is no deformation on the surface. Plant fragments in the gravel layer dated to 770-658 cal BP. Around the northern part of the outcrop exposed by the flood, there is a fault scarp approximately 1.4 m in height. Beneath the scarp, the boundary between the siltstone and the gravel layer has displaced approximately 2.4 m along the fault.
Based on these characteristics, some faults were thought to have been formed by shearing along the bedding plane of the siltstone. Fault displacement is thought to have occurred at least twice in the past 700 years.
This work was supported by JSPS KAKENHI Grant Numbers JP23K17482, JP23K04326, JP24K07162, and the Kanazawa University Disaster investigation team.