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Seismic and hydroacoustic observations of the 2016–17 Bogoslof eruption

Abstract:

In mid-December 2016, Bogoslof volcano, Alaska, began an 8.5-month-long eruption that produced at least 70 explosions and three lava domes. Bogoslof is an emergent submarine volcano with only the very top forming a small island, so the eruptive activity mostly occurred from a vent submerged beneath a bay or lagoon. The Bogoslof eruption was recorded on regional seismic and infrasound arrays as well as by a hydrophone that was deployed locally during the second half of the eruption. Since few emergent volcanic eruptions have seismo-acoustic recordings, these observations, taken in context with satellite and other observations, provide an opportunity to greatly improve our understanding of the seismo-acoustic signals produced by these eruptions. The instruments detected a range of activity including earthquakes, tremor, and mass flow events. Earthquakes occurred before, during, after, and unassociated with explosions and also often occurred in swarms. The 47 seismically-detected swarms and 27 additional hydroacoustically detected swarms can be further broken into four types: precursory, post-eruptive, general, and tremor-dominated. Most seismic swarms were less than 10 h long, had fewer than 50 earthquakes, and had average earthquake rates below 20/h. For the explosions, we calculate a tremor magnitude, frequency index, and average frequency. The tremor magnitudes determined from the hydrophone data show a roughly linear relation to explosion plume height, though this relation was not clear in the more limited seismic data. Lastly, we categorize the activity into five eruption phases based on seismo-acoustic character—precursory, opening, explosive I, pause, and explosive II.