Tsunami penetration along a river: insights from the tsunami following the 2024 Noto Peninsula Earthquake, Japan

A large tsunami, generated by a magnitude 7.6 earthquake on January 1 2024, traveled across the Sea of Japan and caused extensive damage along the surrounding coastlines. This study examined the tsunami characteristics in the Naoetsu coastal region of Joetsu City, Niigata Prefecture, an area characterized by featuring rivers, ports, and coastal infrastructure, and for which extensive observational data are available. The analysis integrated field surveys, image-based observations, and numerical simulations. The numerical results successfully reproduced tsunami behavior as captured by video footage and recorded by wave and tide gauges. The analysis indicated that the maximum water surface elevation exceeded 7 m above mean sea level in the coastal zone, and that flow velocities in the Seki River reached up to 10 m/s. Additional case studies were conducted to assess the influence of riverbed variations and coastal structures on tsunami dynamics. The results suggested that riverbed elevation changes during the tsunami substantially affected the flow rate and water surface elevation along the river. Furthermore, the breakwaters of Naoetsu Port were found to play dual roles – attenuating tsunami forces in adjacent coastal areas while intensifying tsunami intrusion along the channel of Seki River.