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Title: Seismo-acoustics of Tungurahua Volcano, Ecuador
Author: Palacios, Pablo Bolívar Palacios
ISNI:       0000 0004 6056 5732
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2016
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Explosive volcanic eruptions produce seismic and acoustic waves that travel through the ground and air, respectively, interacting at the air-ground boundary. This thesis presents a study of these signals and how they correlate during five sustained eruptions at Tungurahua volcano, Ecuador. It is well known that corrections for site effects can be necessary in the study of seismic sources. What is less well known is that acoustic waves, after coupling at the air-ground interface, are also sensitive to site effects, thereby influencing seismic records. In this study a new procedure for site effect corrections that uses seismic noise is developed and it is shown that seismic source locations improve after applying such corrections. From acoustic studies about jets, it is well known that the acoustic intensity recorded at a fixed location depends on the jet velocity. Here, it is proposed that the seismic intensities of waves produced during sustained eruptions depend on the flow velocity of the gas-pyroclast mixture that is ejected through the conduit, which forms the volcanic plume and generates the acoustic waves. Additionally, seismic and an acoustic indices are defined and it is observed that such indices correlate during paroxysmal eruptions. As a consequence, a significant conclusion is that during paroxysms both the seismic and acoustic source type must necessarily be the same, and likely dipolar, or at least their dipolar components must be dominant in the near field. Seismic tremor locations for the five eruptions studied form clusters, in approximately the same region, beneath the northwestern flank of the volcano. As cluster location does not change significantly through time, it can be concluded that variations in seismic and acoustic intensities are due to variations in eruptive size rather than variations in source-station distance. A measure of the 'eruption seismic size' and 'eruption acoustic size' are defined as the cumulative intensities at a given station, and used to compare the eruptions. It is observed that the eruption seismic size correlates with the plume heights that they produced. The seismic and acoustic indices presented here offer insights into volcanic processes associated with paroxysmal eruptions. Furthermore, the monitoring of such indices improves the real time hazard assessment, being particularly useful in explosive sustained eruptions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available