Estimating the eruption-induced water displacement source of the 15 January 2022 Tonga volcanic tsunami from tsunami spectra and numerical modelling

The 15 January 2022 Tonga volcanic tsunami was a unique event as it was the only event after the 1883 Krakatau volcanic tsunami that created waves by a dual-mechanism generation process comprising atmospheric pressure waves and eruption-induced water displacements. Here, we study 22 tide gauge waveforms, eight DART (Deep-ocean Assessment and Reporting of Tsunamis) records, eight air pressure time series, apply spectral analysis, and conduct numerical modelling to develop a source model. Our source model accounts only for the contribution of eruption-induced water displacement. The maximum overall coastal tide gauge amplitudes were in the range of 4.2–148.8 cm, whereas DARTs registered maximum amplitudes of 3.6–21.4 cm. We identified the dominant tsunami periods due to the localized water displacement mechanism as 10–17 min and 4–7 min. The waves generated by atmospheric pressure waves had a period of 7–10 min and an amplitude of 9–19 cm on coastal tide gauges; the corresponding values for DARTs were 30–60 min and 4.2–15.7 cm. Modelling showed that the eruption-induced water displacement source had a characteristic initial length of 12 km, a maximum initial amplitude of 90 m, and a volume of 6.60 × 109 m3.