Journal
JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH
Volume 290, Issue -, Pages 63-74Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.jvolgeores.2014.11.012
Keywords
Telica; Low-frequency seismicity; Phreatic eruption; Open-system degassing; Closed-system degassing
Categories
Funding
- NSF [EAR-0911366, EAR-0911546]
- NERC STREVA [NE/J020001/1]
- Natural Environment Research Council [NE/J020001/1, NE/J020052/1] Funding Source: researchfish
- Directorate For Geosciences [1261833] Funding Source: National Science Foundation
- NERC [NE/J020001/1, NE/J020052/1] Funding Source: UKRI
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Telica Volcano, Nicaragua, is a persistently restless volcano with daily seismicity rates that can vary by orders of magnitude without apparent connection to eruptive activity. Low-frequency (LF) events are dominant and peaks in seismicity rate show little correlation with eruptive episodes, presenting a challenge for seismic monitoring and eruption forecasting. A short period seismic station (TELN) has been operated on Telica's summit since 1993, and in 2010 the installation of a six-station broadband seismic and eleven-station continuous GPS network (the TESAND network) was completed to document in detail the seismic characteristics of a persistently restless volcano. Between our study period of November 2009 and May 2013, over 400,000 events were detected at the TESAND summit station (TBTN), with daily event rates ranging from 5 to 1400. We present spectral analyses and classifications of -200,000 events recorded by the TESAND network between April 2010 and March 2013, and earthquake locations for a sub-set of events between July 2010 and February 2012. In 2011 Telica erupted in a series of phreatic vulcanian explosions. Six months before the 2011 eruption, we observe a sudden decrease in LF events concurrent with a swarm of high-frequency (HF) events, followed by a decline in overall event rates, which reached a minimum at the eruption onset. We observe repeated periods of high and low seismicity rates and suggest these changes in seismicity represent repeated transitions between open-system and closed-system degassing. We suggest that these short- and long-term transitions between open to closed-system degassing form part of a long-term pattern of stable vs. unstable phases at Telica. Stable phases are characterised by steady high-rate seismicity and represent stable open-system degassing, whereas unstable phases are characterised by highly variable seismicity rates and represent repeated transitions from open to closed-system degassing, where the system is unable to sustain steady open-system degassing. These observations have implications for seismic monitoring at persistently restless volcanoes as the recognition of unstable seismic phases may indicate the open-system degassing process cannot be sustained and explosions are likely. (C) 2014 The Authors. Published by Elsevier B.V.
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