Characteristics of Repeating Long-Period Seismic Events at Fuego Volcano, January 2012

Abstract

We describe a suite of repeating long-period seismic events at Fuego volcano in Guatemala. These events, recorded on a temporary network over a period of 8 days during January 2012, did not occur with any visibly or audibly detectable emissions from the volcano. Events are separated into families based on different correlation coefficient thresholds. A correlation coefficient threshold of 0.70 yields two families with 123 events and 25 events, respectively. These two event families share enough common features that if the correlation coefficient threshold is 0.65, the families merge and grow to include an additional 226 events. The short duration and frequency content concentrated below 2 Hz of the second family allow us to create a phase-weighted stack which we then inverted for source mechanism and location using unconstrained full-waveform moment-tensor inversion. The eigenvalue decompositions of the best-fit models indicate the source is a crack with some volume change. The short duration of the modeled source time function and the slight variability of signal shape within the suite of repeating events indicate the events are caused by rapid pressurization of cracks or series of connected cracks. The interevent times of these events appear clustered, indicating driving processes more complex than continual degassing of magma in the conduit would allow. Better understanding of these events may shed light on processes not captured by real-time seismic amplitude measurements or gas flux measurements alone.