Abstract
Deception Island (South Shetland Islands, Antarctica) is an active volcano characterized by a moderate level of seismic activity, dominated by long-period seismicity related to hydrothermal processes in a shallow aquifer. Nevertheless, in the last few decades the volcano has undergone at least three episodes of seismic unrest, in 1992, 1999, and 2015. During these episodes, the pattern of seismicity changed, and swarms of volcano-tectonic earthquakes with hundreds of events in time spans of a few months were detected. These episodes are interpreted as consequences of magmatic intrusions. However, the seismic series display significant differences that lead us to think that the processes initiating the series are not exactly the same in all cases. The 1999 series comprised mostly small-magnitude earthquakes, produced regularly during 1.5 months, and located at shallow depths (<4 km) within the caldera, mostly along a WSW-ENE trend that parallels the Bransfield rift. No precursory seismic activity was reported, and a few months after the series onset the seismicity was back to normal levels. The 2015 series included earthquakes with larger magnitudes, occurring during 5 months in temporal clusters separated by aseismic periods. They were located at deeper levels (<10 km) with epicenters distributed all around Deception Island, at distances up to 30 km. Additionally, distal (~35 km) VT seismicity was reported SE of Livingston Island months before the 2015 series onset, and the seismicity at Deception Island remained anomalously high during a few years. Taking into account the limited data available for the 1992 unrest, we conclude that the 1992 and 1999 series were produced by shallow, short-lived, small-volume (~4·104 m3) intrusions that affected the shallowmost part of the volcanic edifice. On the contrary, the 2015 series was consequence of a deep, long-lasting intrusion that involved a larger volume of ~5·106 m3 (in the range of a VEI 2 eruption) and modified the stress field of the whole volcanic edifice.
Highlights
The Bransfield Strait is a NE-SW trending marginal basin located between the Antarctic Peninsula and the South Shetland Islands (Fig. 1)
Recent postcaldera volcanic activity on Deception Island mostly consists of smallvolume eruptions, with variable degrees of explosivity depending on the water amount that interacted with the rising magma (Baker et al, 1975; Bartolini et al, 2014; Geyer et al, 2021; Pedrazzi et al, 2014, 2018; Smellie et al 2002)
2019 analyze the time series of GPS observations between 1991 and 2018. They propose that the periods of high seismic activity at Deception Island volcano are preceded by inflation phases, as indicated by the extension and uplift measured in the geodetic network, and followed by deflation phases
Summary
The Bransfield Strait is a NE-SW trending marginal basin located between the Antarctic Peninsula and the South Shetland Islands (Fig. 1). Since 1994, the Andalusian Institute of Geophysics, University of Granada, has carried out research projects to study the seismic activity and structure of Deception Island volcano and nearby areas (Almendros et al, 1997, 1999, 2018, 2020; Benítez et al, 2007; Carmona et al, 2010, 2012; García-Yeguas et al, 2011; Ibáñez et al, 1997, 2000, 2003a, 2003b, 2017; Jiménez-Morales et al, 2017; Luzón et al, 2011; Prudencio et al, 2013, 2015; Zandomeneghi et al, 2009). These seismic crises occurred in 1992 (Ortiz et al, 1997), 1999 (Ibáñez et al, 2003b), and 2015 (Almendros et al, 2018) They were characterized by a definite increase in the number and energy of the seismic events, and most importantly, by the appearance of large numbers of VT earthquakes produced by fractures within the volcanic edifice. We describe the characteristics of the seismic series, investigate the similarities and differences among them, and discuss their implications in terms of activation mechanisms
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