Honoka Kikuta, An-Chi Cheng, Anawat Suppasri, Hidetoshi Masuda, Daisuke Sugawara, Fumihiko Imamura
• Local tsunami amplification in Iida Bay was driven by wave trapping and edge waves • Continental shelf contributed energy trapping and subsequent wave amplification • Reflected waves from opposite coasts enhanced second-wave tsunami heights • Fault strike variability influenced first and second tsunami waves differently • Fine-grid nonlinear modelling is essential to reduce tsunami warning underestimation The 2024 Noto Peninsula earthquake tsunami struck the Sea of Japan coast, causing local amplification of the tsunami at Iida Bay, with waves running up over 5 m. The initial tsunami warning underestimated the tsunami heights, highlighting challenges related to the accuracy of real-time forecasting. Several possible factors may have contributed in this local amplification, including local bathymetry and source parameters. The aim of this study was to quantitatively examine the underlying cause of amplification mechanisms in Iida Bay using numerical tsunami simulations from two perspectives: bathymetry and fault strike. To evaluate their effects, manipulated bathymetry data and fault models with varying strikes were tested. The numerical simulations showed that the local amplification in Iida Bay occurred in subsequent waves owing to wave trapping on the continental shelf that were reflected from the adjacent coasts and the northern and southern tips of Iida Bay. The potential energy trapped around Iida Bay was reduced by up to about 75%. Variations in the fault strike influenced both the heights of the first and second waves. The peaks of the tsunami heights based on strike were different between the first and second waves due to their interaction with distinct bathymetric features. The findings suggest that amplification mechanisms such as observed in the 2024 Noto event should be considered in real-time tsunami warning systems, particularly in the Sea of Japan.