Tsunami Resonance Characterization in Japan Due to Trans-Pacific Sources: Response on the Bay and Continental Shelf

The tsunami resonance leads to the amplification of wave heights and extends the duration of wave activity. For tsunami warning and coastal planning, it is important to understand resonance behavior. We characterized the tsunami resonance of trans-Pacific events in the bays and continental shelves of Japan, focusing on the Hokkaido and Sanriku regions. We considered five tsunami events with sources in the Peru–Chile subduction zone and the Alaska–Aleutian subduction zone. Spectral analysis was applied to observed and synthetic waveforms at coastal tide gauges and offshore GPS gauges to study the frequency content of tsunami energy, and modal analysis was conducted to investigate the eigen-modes of the natural oscillation affected by regional and local bathymetry. It was found that the signatures of trans-Pacific tsunami sources are lost in the spectra at most coastal gauges, but they partly remain in the spectra at offshore gauges, which are affected less significantly by topography or bathymetry. The predominant periods in the spectra at most coastal gauges match the eigen-periods of natural oscillation calculated by modal analysis. Hence, we confirmed that regional or local bathymetry is the dominant factor in the resonance behaviors of trans-Pacific tsunami events, rather than the source location or geometry. These findings are based on the systematic assessment of trans-Pacific sources and have implications for tsunami warning and coastal planning along the Pacific coast of Japan.