Telica Volcano, Nicaragua, is a 'persistently restless' basaltic-andesite stratovolcano located in the Central American volcanic front. A high rate of low-frequency seismic events (LFs) has been recorded at Telica since the installation of a single, vertical-component 1. Hz seismic sensor (TELN) near its summit in 1993. Due to the high rate of LFs at Telica, traditional methods of forecasting volcanic activity based on increases in the overall rate of seismicity are not applicable; therefore an understanding of the nature of precursory changes in Telica's seismicity is necessary to forecast future volcanic activity. In May 1999 a nine-month eruptive episode started at Telica, consisting of phreatic to phreatomagmatic explosions. Here we analyse over 29,000 seismic events recorded during a fifteen-month period of seismicity bracketing this eruptive episode, in an attempt to retrospectively identify precursory changes in seismicity. Seismic event rates between January 1999 and March 2000 show a reduction in the LF event rate three months before the onset of eruptive activity, closely followed by a short-lived swarm of high-frequency (HF) (>. 5. Hz) events. After a three month data gap a second reduction in the LF event rate started in August 1999, directly following eruptive activity in August and approximately two months before a series of explosions in October 1999. This reduction in the LF event rate was closely followed by a short-lived swarm of HF events that was coincident with the onset of numerous (22) short-lived, but populous, LF multiplets. A further reduction in event rate for both LFs and HFs is evident in the months between the October 1999 explosions and explosions on the 29th of December 1999. We suggest that these changes in seismicity reflect a transition from open-system degassing to closed-system degassing at Telica and could signify a change in the volcanic system preceding future episodes of phreatic to phreatomagmatic activity at Telica and similar persistently restless volcanic systems worldwide. We note that these signals are for phreatic to phreatomagmatic activity and thus may not pertain to magmatic volcanism or to other persistently restless volcanoes prior to their magmatic activity.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology