Stable and unstable phases of elevated seismic activity at the persistently restless Telica Volcano, Nicaragua

• Published in: Journal of volcanology and geothermal research 2015-01, Vol.290, p.63-74
• Main Authors: Rodgers, Mel, Roman, Diana C., Geirsson, Halldor, LaFemina, Peter, McNutt, Stephen R., Muñoz, Angelica, Tenorio, Virginia
• Format: Article
• Language: English
• Subjects: Closed-system degassing; Degassing; Low-frequency seismicity; Networks; Open-system degassing; Phases; Phreatic eruption; Seismic phenomena; Seismicity; Stations; Telica; Volcanoes
• ISSN: 0377-0273; 1872-6097
• DOI: 10.1016/j.jvolgeores.2014.11.012

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. •We analyse seismicity from a three-year period at Telica Volcano, Nicaragua.•We characterise seismicity during periods of eruptive and non-eruptive activity.•We show that LF and HF seismicity rates at Telica are highly