Characterizing the Seismic Activity of the Lazufre Volcanic System in Northern Chile/Argentina

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The Lazufre Volcanic System (LVS), on the border of Northern Chile and Argentina, is an active complex comprised of two volcanoes, Lastarria to the north and Cordon del Azufre to the south. This system has been showing two unusual inflation signatures based on InSAR. The first, a shallow body between 1 km above sea level and 2 km below sea level is thought to be a shallow magma body underlying Lastarria Volcano. The second source of inflation between Lastarria and Cordon del Azufre is shallowest at approximately sea level, extends as deep as 40 km below sea level, and may merge with the Cerro Galan Magma Body to the east. Current known activity consists of seismicity, extensive and highly active fumarole fields, and degassing. Gas compositions were shown to have changed between 2009 and 2012 from a hydrothermal nature to a magmatic composition. The PLUTONS Project deployed 8 broadband seismic stations throughout the LVS between November 2011 and March 2013. Events within 20 km of the seismic array have been classified as volcano-tectonic (VT), long-period 1 (LP1, with dominant frequency of ~6 Hz and preliminary depths above 1 km below sea level), long period 2 (LP2, with dominant frequency of 3 Hz and preliminary depths between 1 and 10 km below sea level), hybrid, and a new hybrid event type we have termed 'glissando events'. The glissando events start with low frequencies and gradually glide to higher frequencies. The events in all classes do not correlate temporally with large regional or teleseismic earthquakes, and their epicenters are mainly localized near the summit of Lastarria. Using an updated velocity model and allowing for hypocenters to be as shallow as the summit of Lastarria, we re-ran the STA/LTA detector and associator with parameters empirically determined for the identified event types. Preliminary manual review of the resulting database shows that the hypocenters are generally shallower than 10 km below sea level. For each day, in addition to the >5 locatable, local events per day, we found dozens of smaller events. The rates were relatively stable throughout the study period. These preliminary findings suggest moderately high volcanic and/or hydrothermal activity at the LVS. The VT, LP1, LP2, and hybrid type events are similar to those seen at other volcanoes, while the glissando events are not in the literature.

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Presented at the AGU Fall Meeting on December 10, 2018 in Washington, D.C.