Unrest at Cayambe Volcano revealed by SAR imagery and seismic activity after the Pedernales subduction earthquake, Ecuador (2016)

For the first time in decades, a sudden increase in seismicity has been observed and monitored at Cayambe volcano in Ecuador, in 2016. This seismic unrest, which occurred a few months after the April 2016, Mw 7.8 Pedernales subduction earthquake, has raised many questions, especially as there is no record of recent eruptions at Cayambe volcano. Here we analyze a time series of 104 images from Sentinel 1 (SAR) data spanning the period 2014–2018 using the NSBAS processing chain in order to quantify surface deformation around this potentially explosive and ice-covered volcano. We evidence a large-scale uplift reaching a maximum mean displacement rate of about 0.44 cm/yr in Line of Sight. This uplift is mainly due to a significant and sudden acceleration of the deformation pattern, focused on the SE flank starting in November 2016. We model this signal as related to magma emplacement at around 6 km depth below the summit, with a sudden volume influx of about 2.6 million m3. The inflation and surface deformation pattern is concomitant in time with two Mw 3 seismic events recorded at Cayambe volcano in November 2016 and is consistent with the location at the summit of the volcano-tectonic (VT) seismic swarm from September 2016 onwards. This VT swarm follows an earlier swarm in June 2016 located on the northern side of the volcano and closer to a western branch of the Chingual-Cosanga-Pallatanga-Puna (CCPP) fault system, that plays a major role in accommodating plate tectonic processes in South America. We thus propose that static stress changes from the Pedernales megathrust earthquake triggered magma ascent below the Cayambe volcano, through reactivation of the CCPP fault system. Finally, volcanic hazards around Cayambe ice-capped volcano, previously dormant for the last 300 years, should be reassessed in light of this recent unrest.