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.