5:15 PM - 6:45 PM
[U15-P93] Field observations of surface deformation appearing along the Wakayama River in Suzu City and its western extension following the 2024 Noto Peninsula Earthquake
Keywords:2024 Noto Peninsula Earthquake, Wakayama River, surface deformation, morphometry
The Noto Peninsula Earthquake culminated in the M7.6 event on January 1, 2024. According to the InSAR analysis, an uplift of about 4 m maximum was detected in the western part of Wajima City and about 2 m maximum in the northern part of Suzu City (GSI, 2024). To confirm the surface deformation, we conducted photographic interpretation using the vertical and orthophoto images of the Suzu area taken on January 2, which were released by the GSI, and confirmed a series of distinct scarps along the Wakayama River in Suzu City. As a result of a field survey conducted on January 27, those surface deformations with a maximum vertical displacement of approximately 2 m and a left lateral displacement of approximately 1.2 m were observed along the Wakayama River (Shirahama et al., 2024). GSI also reported that those surface deformations appeared along the valley floor plain along the Wakayama River (Yoshida, 2024). Since there is a possibility that this surface deformation may extend further to the east or west, and since it was difficult to make fine observations of the ground surface due to snow accumulation on January 27, we conducted field surveys 3 times from February to March. During the field survey, we walked along the surface deformation, observed the location and condition of the deformation, and surveyed the topographic cross sections at 30 points to determine the amount of vertical throw and lateral displacement, including flexural deformation.
The surface deformations were mainly distributed along the valley floor plain of the Wakayama River, causing field and road ruptures and wave-like deformation. The locations where continuous scarps appeared were, from east to west, Himiya to Nobutake (about 1.3 km long, ENE-WSW strike), Naka (about 2 km long, ENE-WSW strike), Munesue (about 0.8 km long, NE-SW strike), and Kamiyama (0.3 km long, ENE-WSW strike). The direct distance from Himiya to Munesue extends about 6.8 km.
At the Himiya-Nobutake site, four to five lines of north-side-up scarps and a south-side-up flexure scarp with ENE-WSW strike were observed. At the Naka site, where a distinctive south-side-up scarp with a maximum vertical throw of about 240 cm was measured, the upthrown side tilted to the south and decreased the height gradually within a width of about 100 m. Along most of the scarps, the upthrown side was raised to the downthrown side, suggesting that they were formed by reverse faulting. The surface deformations at the Nobutake and Naka sites appeared along the existing scarps, suggesting that those scarps may have resulted from cumulative displacement.
To confirm the extension of the surface deformation, we conducted a photographic interpretation and a field survey. We found a similar surface deformation at Satomachi (0.4 km long, NW-SE strike) about 10 km west of the Kamiyama site. Although the strike of the scarp is different and apart widely, a series of surface deformations are likely to have been produced by the same cause because of the similarity of deformation, and because all the deformations are located in the siliceous siltstone area and along the Wakayama River Syncline (Yoshikawa et al., 2002).
The survey is ongoing, and the latest results will be included in the presentation.
The surface deformations were mainly distributed along the valley floor plain of the Wakayama River, causing field and road ruptures and wave-like deformation. The locations where continuous scarps appeared were, from east to west, Himiya to Nobutake (about 1.3 km long, ENE-WSW strike), Naka (about 2 km long, ENE-WSW strike), Munesue (about 0.8 km long, NE-SW strike), and Kamiyama (0.3 km long, ENE-WSW strike). The direct distance from Himiya to Munesue extends about 6.8 km.
At the Himiya-Nobutake site, four to five lines of north-side-up scarps and a south-side-up flexure scarp with ENE-WSW strike were observed. At the Naka site, where a distinctive south-side-up scarp with a maximum vertical throw of about 240 cm was measured, the upthrown side tilted to the south and decreased the height gradually within a width of about 100 m. Along most of the scarps, the upthrown side was raised to the downthrown side, suggesting that they were formed by reverse faulting. The surface deformations at the Nobutake and Naka sites appeared along the existing scarps, suggesting that those scarps may have resulted from cumulative displacement.
To confirm the extension of the surface deformation, we conducted a photographic interpretation and a field survey. We found a similar surface deformation at Satomachi (0.4 km long, NW-SE strike) about 10 km west of the Kamiyama site. Although the strike of the scarp is different and apart widely, a series of surface deformations are likely to have been produced by the same cause because of the similarity of deformation, and because all the deformations are located in the siliceous siltstone area and along the Wakayama River Syncline (Yoshikawa et al., 2002).
The survey is ongoing, and the latest results will be included in the presentation.