Current Research in EEPS Seminar: Dr. Yingcai Zheng, University of Houston
Repeating episodic seismic signals from the January 2022 Hunga-Tonga-Hunga-Ha’apai volcanic activities
The Hunga Tonga-Hunga Ha’apai explosive volcanic eruption that occurred during January 13-15, 2022 UTC was one of the most energetic volcanic eruptions in recent decades (Global Volcanism Program, 2022). The first episode culminating in the paroxysmal 15 January eruption started at 15:20 UTC on January 13 and produced a plume that rose near 20 km. Renewed activity began ~0401 UTC that culminated at 04:15:45 UTC (i.e., the USGS reported earthquake origin time or slightly earlier) with a magnitude 5.8 seismic event that produced a loud audible sound heard as far away as Alaska, produced an extraordinarily high (~58 km) eruption plume that reached the mesosphere, generated numerous lighting strikes, produced both local and global tsunami, and generated infrasound and seismic waves that circled the Earth multiple times.
To understand eruptive characteristics based on the seismic signals, we stacked the globally recorded seismograms based on the moveout of the teleseismic P waves. We found four distinct episodic subevents, E-1, E-2, E-3, and E-4, within five minutes after the magnitude 5.8 event. These events occurred as the volcanic plume grew from 25 km (~0415 UTC) to ~ 35 km (0420 UTC). These events have similar durations of ~ 25 s, but subevents E-2, E-3, and E-4 onset at ~204.6 s, ~39.8 s, and ~25.4 s after the proceeding subevents, respectively. We refer to the stacked seismograms of these subevents as ‘episodic’, due to their similarities in waveforms. However, stacking the direct S waves yields no SH energy, suggesting equivalent forces are either vertical forces or explosions/implosions. Full-waveform seismic modeling shows vertical forces fit the data better. The peak force amplitude is ~1.1e13 N. That the early phases of the violent HTHH eruption is composed of four similar episodic sub eruptions separated in time by tens of seconds may be indicative of rapid changes in the magma plumbing system, which I will discuss.