Natsuho BUTO

Analysis and Comparison of Road Damage Caused by Two Noto Peninsula Earthquakes

Takaaki IKEDA，Masataka SHIGA

The 2024 Noto Peninsula Earthquake caused extensive damage to embankments, including collapses at bridge approach sections and pavement cracking, along the Noto Satoyama Kaido, the only road connecting Kanazawa City and the Noto Peninsula in Ishikawa Prefecture. Similar damage was reported during the 2007 Noto Peninsula Earthquake on the same road, which was then known as the Noto Toll Road, indicating repeated seismic damage to embankment structures. Embankment damage is influenced by multiple factors, including seismic motion, surrounding topography, and embankment geometry.
This study aims to clarify factors contributing to embankment damage by comparing damage patterns from the 2007 and 2024 earthquakes. Damage locations were identified through visual interpretation of post-earthquake orthoimages on a GIS platform, supplemented by field surveys, Street View imagery, and historical records. As a result, 97 damaged sites were identified for the 2024 earthquake and 44 sites for the 2007 earthquake.
To investigate damage mechanisms, DSMs were generated through the construction of three-dimentional terrain models, and surrounding terrain changes were evaluated. Embankments were classified based on cross-sectional configuration, and the number of berms were determined from design drawings. Embankment height was estimated from berm counts and by large-scale damage sites in 2024, additionally derived from contour lines. Seismic motion at each site was estimated using PGA and PGV values calculated from a distance attenuation relationship developed specifically for the Noto Satoyama Kaido.
The results indicate that large-scale terrain modification was not evident and that damage occurred predominantly in embankment sections. Damage was concentrated in the northern portion of the road, particularly between Yokota IC and Besshodake SA. Locations with a greater number of berms and higher embankment heights tended to experience more severe damage. Estimated PGA values were higher in 2024 than in 2007 and increased toward the northern area, suggesting that amplified seismic motion contributed to the concentration of damage, whereas no clear correlation was observed between PGV and damage scale.