Date of Award

2019

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Geophysics (PhD)

Administrative Home Department

Department of Geological and Mining Engineering and Sciences

Advisor 1

Gregory P. Waite

Committee Member 2

Wayne D. Pennington

Committee Member 3

Simon A. Carn

Committee Member 4

Matthew M. Haney

Abstract

Forecasting volcanic activity is challenging. The task is uniquely difficult at open vent volcanoes which present persistent low-level eruptions over long periods of time. Volcán de Fuego in Guatemala began its current eruptive episode in 1999. Fuego exhibited “background” levels of activity during January of 2012 when we installed a temporary monitoring network to produce a detailed baseline description of the volcano’s behavior. We accomplish this using data from two low-frequency microphone arrays, nine broadband (50 Hz to 30 second flat response) seismic stations, and visual time-lapse imagery collected over a period of ten days. We begin with a detailed description of all observed sources of seismicity including: both harmonic and non-harmonic tremor, rockfalls, a variety of signals associated with frequent small emissions from two vents, and many repeating, discrete, pulse-like long period (0.5–5Hz) events not linked to any visible emissions from the vents. We compute a 1D local velocity model and use it to generate preliminary locations of the different events. From there, we perform full waveform moment tensor inversions to better constrain the locations and the mechanisms for the repeating long period events. We find that the events are being generated by the opening and closing of an assortment of small, shallow, sub vertical cracks as those cracks pressurize, rupture, and release volcanic gases. Finally, we examine very-long period (10 – 60 second) signals associated with volcanic emissions and relate them to pressurization in the conduit prior to larger explosions. We propose that the volcanic vents at Fuego form caps of crystal rich magma which solidify near the top of each vent but above the location of the very-long period source. As new magma nears the top of a conduit and begins to degas, the cap fails at different points and to different degrees, generating the variety of emissions and seismic signals we observe. The insights gained from these investigations provide a better understanding of the dynamics of Fuego volcano during low points of activity and provide a baseline from which to study future activity at Fuego.

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