An Integrated Analysis of Seismicity, Infrasound, and High-Resolution SO2 Measurements to Determine the Source of Low-Frequency Seismicity at Villarrica Volcano, Chile

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Volcanoes produce a rich variety of seismic signals that are unlike those generated during typical earthquakes. While great improvements in the ability to forecast volcanic eruptions have come from recognizing precursory seismic signals, knowledge of the specific mechanisms responsible for the volcanic signals is only generally understood. For example, low-frequency seismic tremor is linked to fluid movement, but many models can explain seismic tremor at any one volcano. By integrating high-resolution seismic, acoustic, and gas emission data, this study will determine the relationship between gas flux and the characteristics of seismic tremor at Villarrica volcano. Villarrica has had persistent gas emission and an active lava lake with continuous, mild, explosive activity since 1984. Because of the continuous low-level activity, direct measurements of emissions of gas, seismicity, and low-frequency sound (infrasound) can safely be made from the summit crater. This study will use simultaneous measurements of seismicity, infrasound and gas emissions. The researchers will deploy arrays of broadband stations to locate and track the depth of low-frequency and volcano-tectonic seismicity, along with distributed infrasonic microphones to characterize the explosive outgassing activity. During 2-3 week field campaigns, they will also collect high-time resolution SO2 emission data, and thermal and visual video of the outgassing activity. All these data will be interpreted jointly to characterize and quantify different styles of outgassing. A 15-month deployment of seismometers and microphones will assure that a significant portion of the outgassing styles is well sampled. The classification scheme for outgassing style they develop during the shorter field campaigns will allow them to calculate a proxy data set for gas emission during the full duration of the deployment so that they may address questions about long-term cycles of activity and the relationship between both deeper local volcanic earthquakes and distant earthquakes on the volcanic system.The transformative potential of this project lies in the integration of these data. The seismic analysis will be based on the strong foundation of established techniques. Infrasound analysis is now seen as critical for monitoring open-vent systems, yet some aspects of infrasound data are not well understood. A novel UV camera, recently developed with support from the National Science Foundation, can image SO2 emission at a rate comparable to eruptive processes. By establishing empirical links between the data, this study will test theoretical models for the generation of seismicity and sound from gas emission and generate important new knowledge on eruptive processes.