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A full view of the 15 January 2022 Hunga Tonga-Hunga Ha\'apai eruption captured by distant seismic records and satellite images

Takuro Horiuchi 1, Mie Ichihara, Kiwamu Nishida, Masaaki Morita, Takayuki Kaneko

Abstract

The massive eruption of the Hunga Tonga-Hunga Ha'apai (HTHH) volcano on January 15, 2022, generated global signals, which many previous studies have focused on. This study aims to retrieve the full sequence of the eruption, including precursors and smaller sub-events, which are covered by the thick umbrella cloud formed by the main eruption. We analyzed seismic records from stations near the HTHH volcano (FUTU: 752 km, MSVF: 758 km, RAR: 1627 km) and infrared imagery from the Himawari-8 satellite to gain a more detailed understanding of the eruption sequence.   We found a Rayleigh wave from the HTHH around 03:45 (UTC), about 15 min before the eruption onset shortly after 04:00. No apparent surface activity was observed. We regarded it as a precursor of the eruption. The biggest sub-event (around 08:30) following the eruptive phase (04:00 -- 06:10) has already been reported in the literature based on infrasound, lightning, and satellite-based plume heights. We showed that continuous seismic tremor beneath the HTHH volcano has started to grow 50 min before the event (around 07:20). Our satellite image analyses visually confirmed that the subevent eruption began around 07:50 and was accompanied by several explosions. We also found two smaller eruptions around 13:40 and 21:50 below the semi-transparent umbrella cloud remaining at the tropopause.   We emphasize that careful analyses of data from seismic stations about 1000 km away and satellite imagery allow us to identify smaller-scale events in much more detail than one might have expected.