Volcano‐Tectonic Activity at Deception Island Volcano Following a Seismic Swarm in the Bransfield Rift (2014–2015)

In September 2014 there was a sharp increase in the seismic activity of the Bransfield Strait, Antarctica. More than 9,000 earthquakes with magnitudes up to 4.6 located SE of Livingston Island were detected over a period of 8months. A few months after the series onset, local seismicity at the nearby (similar to 35km) Deception Island volcano increased, displaying enhanced long-period seismicity and several outbursts of volcano-tectonic (VT) earthquakes. Before February 2015, VT earthquakes occurred mainly at 5-20km SW of Deception Island. In mid-February the numbers and sizes of VT earthquakes escalated, and their locations encompassed the whole volcanic edifice, suggesting a situation of generalized unrest. The activity continued in anomalously high levels at least until May 2015. Given the spatial and temporal coincidence, it is unlikely that the Livingston series and the Deception VT swarm were unrelated. We propose that the Livingston series may have produced a triggering effect on Deception Island volcano. Dynamic stresses associated to the seismic swarm may have induced overpressure in the unstable volcanic system, leading to a magmatic intrusion that may in turn have triggered the VT swarm. Alternatively, both the Livingston earthquakes and the VT swarm could be consequences of a magmatic intrusion at Deception Island. The Livingston series would be an example of precursory distal VT swarm, which seems to be a common feature preceding volcanic eruptions and magma intrusions in long-dormant volcanoes. Plain Language Summary In September 2014 a seismic series occurred near Livingston Island, Bransfield Strait, Antarctica. With 9,000 earthquakes and magnitudes up to 4.6, it is the most numerous swarm ever reported in this region. In February 2015, a volcano-tectonic swarm took place at Deception Island volcano, a nearby, active volcanic system located 35km SE. The swarm comprised several hundred earthquakes with magnitudes up to 3.2. The spatial and temporal coincidence of these two events suggests that they could be either cause and effect or consequences of a common process. We propose that the Livingston earthquakes may have induced overpressure in the volcanic system of Deception Island that could trigger the seismic swarm. Alternatively, both swarms could represent the delayed effect of a magmatic intrusion below the volcano. This relationship adds to a growing body of evidence of earthquake-volcano interactions that must be taken into account in order to properly assess volcanic hazards.