Temporal change of the magma plumbing system at Galeras volcano, Colombia, revealed by repeated seismic tomography in 2009–2018

Abstract

We performed repeated three-dimensional seismic tomography in 2009–2018 for the area influenced by the intersection of the Silvia–Pijao (Buesaco) and Cauca–Almaguer fault systems beneath Galeras volcano, Colombia. We analyzed two periods, 2009–2012 and 2013–2018, which were characterized by explosive eruptive activity and relative quiescence at Galeras, respectively. We used P- and S-wave arrival times of 2848 (2009–2012) and 2289 (2013–2018) earthquakes that occurred beneath the volcano. P- and S-wave velocity (Vp and Vs, respectively) anomalies and their changes between the two periods were interpreted to be associated with magma movement in the volcanic plumbing system, which was controlled by the intersection of the faults. Two possible pathways of magma ascent and accumulation were identified in the fault systems. One, located SW of the active crater, consisted of areas with high Vp/Vs values (>1.9) at depths of −2 to 4 km below sea level, and the other located NE of the active crater with high and low Vp/Vs values. The low-Vp/Vs (<1.7) area at depths of 0 to 2 km may represent vesiculated magma that was partly erupted during explosive eruptions in 2009–2010. These anomalies, found in 2009–2012, displayed clear changes in 2013–2018. Large surface deformation observed between January 2013 and February 2014 may be associated with magma movement from the SW pathway. The largest volcano-tectonic (VT) earthquake, with a magnitude of 5.1, ever recorded at Galeras occurred on 12 June 2018 and was followed by a swarm of VT earthquakes. This VT activity may have been caused by magma intrusion along the NE pathway. On the basis of our tomographic images and geodetic, petrological, and geochemical results, we propose a model of the plumbing system beneath Galeras during 2009–2018.