Geophysical Research Letters

Magma fracture and hybrid earthquakes in the conduit of Augustine Volcano

Authors

  • Helena Buurman,

    Corresponding author
    1. Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, USA
    • Corresponding author: H. Buurman, Geophysical Institute, University of Alaska Fairbanks, 903 Koyukuk Dr., Fairbanks, AK 99775-7320, USA. (helena@gi.alaska.edu)

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  • Michael E. West

    1. Alaska Earthquake Information Center, Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, USA
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Abstract

[1] We exploit subtle but systematic shifts in seismic waveforms to examine a 2 h cluster of repeating hybrid volcanic earthquakes preceding the first magmatic explosions at Augustine Volcano in January 2006. We extract differential P wave traveltimes of <0.01 s to determine that the source locations migrated downward by approximately 35 m. Waveform characteristics, GPS observations, and visual reports of lava effusion at the summit suggest that the earthquakes were sourced by fracturing magma in the upper conduit. As the lava cooled and degassed at the surface, the conditions in the upper conduit changed causing the zone in which magma fracture could occur to move downward through the magma column. These changes may also have been the first indicators that the conduit was becoming choked, causing a buildup in pressure that resulted in the large magmatic explosions that followed 36 h later.

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