Abstract
Glacially- and magmatically-derived seismic events have been noted to heavily overlap in characteristics, thus there exists the potential for false-alarms or missed warnings at ice-covered volcanoes. Here we present the first study to specifically target icequakes at an ice-covered volcano in Southern Chile. Two months of broadband seismic data collected at Llaima volcano in 2015 were analyzed in order to quantify, characterize, and locate glacially-derived seismic events at one of the most active ice-covered volcanoes in the region. We find over 1,000 repeating seismic events across 11 families, the largest of which contains 397 events. Approximate locations and characteristics of the largest families lead us to conclude that these events were derived from persistent stick-slip motion along the ice-rock interface at the base of a glacier near the volcano summit. These results have implications for future seismic monitoring at Llaima volcano and other ice-covered active volcanoes in the region.
Highlights
For volcano monitoring organizations a fundamental goal is to assess whether changes in seismicity indicates impending intensification of volcanic eruptive activity
Signals derived from glacial sources on volcanoes have often had a strongly repetitive nature which may persist on timescales of months to years [Allstadt and Malone 2014; Jónsdóttir et al 2009]
This presents another overlap in characteristics with volcanic earthquakes since repetitive low frequency events associated with magma movement and failure have been documented prior to or during multiple eruptions [e.g. Iverson et al 2006; Kendrick et al 2014; Lamb et al 2015]
Summary
For volcano monitoring organizations a fundamental goal is to assess whether changes in seismicity indicates impending intensification of volcanic eruptive activity. Glacial signals are usually weak and only recorded at stations close to the source [Weaver and Malone 1976], but there are documented examples of glaciers producing earthquakes as large as magnitude 5 [Ekstrom et al 2003] and/or being recorded at considerable distance from the source [e.g. Danesi et al 2007; Helmstetter et al 2015; Roeoesli et al 2016] This presents another overlap in characteristics with volcanic earthquakes since repetitive low frequency events associated with magma movement and failure have been documented prior to or during multiple eruptions [e.g. Iverson et al 2006; Kendrick et al 2014; Lamb et al 2015]. The low-frequency and repetitive nature of these seismic events closely resembled seismicity often seen prior to or during eruptive activity at volcanoes around the world [Thelen et al 2013]. The ability to distinguish between glacial and volcanic sources is vital for providing correct and rapid interpretations of seismicity at active glacier-clad volcanoes
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