Ocean-wave phenomenon around Japan due to the 2022 Tonga eruption observed by the wide and dense ocean-bottom pressure gauge networks

Abstract

Ocean-bottom pressure gauges of wide and dense ocean-bottom observation networks around Japan, S-net and DONET, observed ocean waves caused by the Tonga eruption that started at approximately 13:00 JST (UTC + 0900) on January 15, 2022. We scrutinized the waveform records of the arriving ocean waves to evaluate their nature and found two significant disturbances between 20:00 and 21:00 and after 22:00. The first disturbance with a positive-polarity pulse dominated by long-period components (1000–3000 s) arrived at S-net and DONET stations between 20:00 and 21:00 from the southeast, corresponding to the direction of the short great circle between Tonga and Japan. This arrival was much earlier than expected for a direct tsunami from the volcano and can be explained by assuming that the waves propagated along the short great circle path at a velocity of approximately 300 m/s. After 22:00, significant phases dominated by relatively shorter period components (< 1000 s) arrived from the southeast direction in both observation networks. In DONET, another phase arrived from the south–southeast direction at approximately 23:30 with shorter period components (approximately 500 s). Most of the near-trench S-net stations recorded the peak amplitude during the first disturbance, whereas the near-coast S-net stations and DONET stations observed their peak after 22:00. The amplitudes of ocean-bottom pressure changes in both networks increased as the water depth decreases. This amplification behavior differed between the first and second disturbances, which is attributed to the differences in the natures of the arriving ocean and air waves. This study also found several arrivals of air-wave disturbances to be correlated with the ocean-wave phases, which implies that multiple disturbances of ocean-bottom pressures were generated by the interactions of several disturbances of air waves following the 2022 Tonga eruption with ocean waves.

Graphical abstract