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Deception Island is an active volcano located in the South Shetland Islands, Antarctica. Although the last eruptions occurred in 1967-1970, the volcano has undergone periods of seismic unrest in 1992, 1999, and 2015. In this work, we analyze continuous seismic data obtained by a permanent station for the period 2008-2015 preceding the 2015 unrest. We identify different types of seismic signals including tectonic and volcano-tectonic (VT) earthquakes and long-period (LP) seismicity, using a combination of visual and automated techniques. The temporal evolution of the seismicity displays three differentiated stages. In Phase 1 (2008-2010) the volcano was in a dormant state characterized by a moderate level of seismicity dominated by low-energy LP seismicity, and very few VT earthquakes. In Phase 2 (2011-2014), there was a gradual increase in the level of LP events and tremor, and an acceleration of the number and energy of VT earthquakes. In Phase 3 (2014-2015) the seismicity reached a climax, with the occurrence of seismic swarms comprising thousands of earthquakes, displaying maximum activity in September-October 2014 and February 2015. We propose that the change from Phase 1 to Phase 2 was due to the recharge of magma into the plumbing system at Moho depths. The emplacement of fresh magma increased the amount of gas (and heat) permeating the volcano edifice, triggering VT earthquakes in brittle regions and favoring the occurrence of LP seismicity in the shallow hydrothermal system. During Phase 2 magma ascended through the plumbing system, as evidenced by the acceleration of the seismicity rates, the detection of thermal anomalies, and a change in the deformation pattern that for 2013-2015 corresponded to an inflation process. Finally, in Phase 3 the magma intrusion reached its shallowest point before stalling at a depth of 6-10 km. The stress perturbations propagated through crustal fluids and produced a distal VT swarm SE of Livingston, as well as proximal VT swarms and very intense LP seismicity at Deception Island. [ABSTRACT FROM AUTHOR]

We analyze seismic data from permanent seismic stations located on Deception Island volcano, Livingston Island, and Cierva Cove, Antarctica, and identify a type of signal named Deception long-duration signals (DLDS). They are characterized by low amplitudes, long durations (several hours to days), frequency content limited to the 0.5–5 Hz band, and are detected only at Deception Island. We develop a semi-automated method to systematically detect the occurrence of DLDS during February 2008–January 2015. We identify 276 DLDS episodes with amplitudes in the range of 0.5–2 μm/s and durations from 3 h to 13 days. The temporal distribution shows an annual modulation, suggesting a seasonal effect. DLDS activity generally increases during the austral winter, although the annual distributions display two different behaviors. Some of them have a single maximum in the winter, while others are bimodal and show a second maximum during spring. Several mechanisms can explain the occurrence of long-duration signals. However, the only mechanism that explains the spectral content, duration, temporal distribution, and station coverage of the DLDS is the occurrence of volcanic tremors. Tremor generation at Deception Island has been explained by the resonance of fluid-filled conduits within the hydrothermal and/or shallow volcanic conduits. However, the long durations of the DLDS require a triggering mechanism that could be active for a long time span. The seasonal modulation of the DLDS suggests the influence of external effects. Most DLDS episodes can be related to periods with high-amplitude oceanic microseisms, which can induce an external forcing and introduce pressure variations in the volcanic/hydrothermal fluids. However, in some cases DLDS occur independently from oceanic noise amplitude. These cases precede summer surveys with large numbers of seismic events, indicating an increasingly restless state of the volcano. They can be produced by triggering mechanisms of internal, volcanic origin, such as the occurrence of changes in the stress distribution in the volcano edifice induced by magma dynamics, or fluctuations in the rate of volcanic gas supply. [ABSTRACT FROM AUTHOR]