Eruption sequence of the 2022 Hunga Tonga-Hunga Ha'apai explosion from back-projection of teleseismic P waves

Abstract

The explosive eruption occurred at Hunga Tonga-Hunga Ha'apai on January 15, 2022, generating atmospheric waves, meteotsunamis, tsunamis, and seismic waves recorded worldwide. Energetic signals of seismic surface waves indicate multiple explosive events, but the detailed eruption episodes are hard to unravel from dispersive long-period surface waves. In this study, we performed the back-projection (BP) analysis using the teleseismic P-waves to clarify the sequence of multiple explosive eruptions. The BP results successfully detected the locations and timing of multiple explosions even though P-waves from each eruption were overlapped and masked by other seismic signals and noises. The results suggest that the series of explosive eruptions can be divided into two parts of eruption sequences. The first sequence started at 04:02 UTC, escalated into major explosions at 04:15 UTC and 200 - 300 s afterward, and lasted at least until 04:35 UTC. The second sequence began about 4 hours later (08:26 UTC) and continued for about 6 - 7 minutes, including a massive eruption at 08:31 UTC. The estimated origin times of each eruption episode determined in this study are consistent with successive arrivals of long-period surface wave trains at frequencies higher than 10 mHz. The time intervals of explosive eruptions in the first sequence suggested that the significant explosive eruptions intermittently occurred at around 270 - 280 s intervals. This interval is nearly equivalent to the eigenfrequencies of the atmospheric resonant oscillation with the Earth at 3.7 mHz. Since the observed amplitude spectra of this eruption exhibit a conspicuous spectral peak at 3.7 mHz, our BP results indicate that the eruption cycle may be synchronized with the eigen-period of the atmosphere-lithosphere coupled mode.