Worldwide seismic observations of low frequency signals related to the 15 January 2022 Hunga-Tonga volcanic eruption

The eruption of the Hunga-Tonga volcano produced a high-energy explosion that was recorded globally by different scientific instruments, including broad-band seismometers. Seismic data recorded on global seismic networks is used to explore three main topics; the time evolution of the eruption, the atmospheric waves revolving around the Earth and the low-frequency, long-lasting signals recorded worldwide in the hours after the main event. From the inspection of the data we can assess that the eruption started on January 15 around 04:05 UTC, several minutes before the origin time reported in the seismic catalogs and included two large explosions at 05:30 and 08:35. As for the atmospheric waves, their energy was enough to be detected seismically during more than two complete circumambulations of the Earth, during a time span of three and a half days. The most notable seismic feature has been the low-frequency signals detected over several hours and interpreted as resulting from the excitation of Earth normal modes. To our knowledge, there are no previous examples of atmospheric-solid Earth coupling over such a long time interval and only two examples of normal mode excitation following volcanic eruptions, identified for the 1982 El Chinchón and the 1991 Mount Pinatubo eruptions.