Quiero agradecer, en primer lugar, a los directores de esta tesis doctoral, Gabriela y Deyan. Agradezco a ambos por brindar las condicionesóptimas para mi desarrollo personal como joven científico, valorando mi trabajo, confiando en mis ideas, aportando en todo momento las suyas, motivándome con sus ganas de progresar e innovar, y haciéndome partícipe de sus tareas.Quiero agradecer a las personas que han brindado, en mayor o menor medida, tiempo y conocimiento para que cada una de las metodologías implementadas en esta tesis haya podido ser realizada de la mejor manera posible;
<p>Volcanoes and glaciers are both productive sources of seismic activity which may be easily confused for each other, leading to potential missed warnings or false alarms. This presents a challenge for organizations monitoring active volcanoes with glaciers on or near the edifice. Cryogenic earthquakes (i.e. icequakes) have been studied at only a few volcanoes around the world and there is a ready need to develop robust methods for efficiently differentiating them from volcanic events. Here we present results from an ongoing study of icequakes at active ice-covered volcanoes in the Southern Chilean Volcanic Zone. The primary focus of the project so far has been on seismo-acoustic data collected at Llaima volcano, one of the largest and most active volcanoes in the region. The data, recorded in 2015 and 2019, was analysed using a combination of automatic multi-station event detection and waveform cross-correlation to find candidate repeating icequakes. We identified 11 persistent families of repeating events in 2015, and over 50 families in 2019; the largest family containing over 1000 events from January to April 2019. The persistent, repetitive nature of these events combined with their waveform characteristics and source locations suggest they originated from multiple sub-glacial sources on the upper flanks of the volcano. Low levels of volcanic activity at Llaima volcano since 2009 have allowed this clear discrimination of icequake events. We are also targeting Villarrica volcano in early 2020 with a network of seismo-acoustic sensors and to record icequake activity in concurrence with the ongoing eruptive activity at the summit. Altogether, the results from this project so far suggest icequakes may be more common than previously thought and has strong implications for how seismic data at ice-covered volcanoes may be interpreted.</p>
<p>The monitoring of seismic activity at active glacier-hosting volcanoes is challenging as volcanic and glacial earthquakes (i.e. icequakes) can have overlapping characteristics (i.e. frequencies, waveform shape and magnitude). Here we present results from the first study to target glacial activity at active ice-covered volcanoes in the Southern Chile. The primary focus so far has been on Llaima volcano, one of the largest and most active volcanoes in the region while hosting >14 km<sup>2</sup> of glacial ice on the flanks. We use a combination of automatic multi-station event detection and waveform cross-correlation to find candidate repeating icequakes in seismic data from the permanent volcano monitoring network recorded in early 2019. We identified dozens of low magnitude families of repeating seismic events across two months, the largest of which included over 200 events. These findings are comparable to results from analysis of seismic data recorded at Llaima volcano during the same time period in 2015. The persistent, repetitive nature of these events combined with their waveform characteristics and source locations suggest they originated from multiple sub-glacial stick-slip sources around the upper flanks of the volcano. We also deployed a network of seismo-acoustic sensors at Villarrica volcano in early 2020 to record glacial activity in concurrence with the lava lake and strombolian activity at the summit. We conclude that icequakes at Llaima volcano may be more common than previously thought and has implications for how seismic data at ice-covered volcanoes may be used for assessing future volcanic and glacial hazard potential.</p>
Identifying the source mechanisms of low-frequency earthquakes at ice-covered volcanoes can be challenging due to overlapping characteristics of glacially and magmatically derived seismicity. Here we present an analysis of two months of seismic data from Llaima volcano, Chile, recorded by the permanent monitoring network in 2019. We find over 2,000 repeating low-frequency events split across 82 families, the largest of which contains over 200 events. Estimated locations for the largest families indicate shallow sources directly beneath or near the edge of glaciers around the summit vent. These low-frequency earthquakes are part of an annual cycle in activity at the volcano that is strongly correlated with variations in atmospheric temperature, leading us to conclude that meltwater from ice and snow strongly affects the seismic source mechanisms which is likely dominated by basal slip beneath the glaciers. The results presented here should inform future assessments of eruptive potential at Llaima volcano, as well as other ice-covered volcanoes in Chile and worldwide.
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