Estudio sismológico de la actividad y la estructura del Volcán Isla Decepción (Antártida), mediante el análisis de datos continuos registrados en una estación sísmica permanente (2008-2015)

Abstract

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. The seismic activity of the Deception Island volcano has been monitored three months per year since 1986, coincident with the austral summers. In 2008, three permanent seismic stations were installed at Deception Island, Livingston Island, and Cierva Cove, Antarctica. The present thesis has aimed to exploit the continuous seismic record at Deception Island since 2008 (including the southern winter periods) to study the long-term seismic activity of the volcano, in order to improve our understanding of the behavior, seismicity and the mechanisms that generate the volcanic activity. It also allow us to model the S-wave velocity structure of the shallow layers of the island, as well as their characteristics. From this seismological study of the activity and structure of the Deception Island volcano, we have obtained the following results: (1) Determination of 1D models of the shallow structure along the coast and inner bay of Deception Island. Long series of ambient noise recordings from di erent land and marine stations have been used, thereby improving noise studies observing the stability of the peaks. (2) Identi cation of a new seismic signal called DLDS, using an approach based on the evaluation of the average seismic energy contained in selected frequency bands. Continuous records from permanent stations are used for DLDS detection. Due to its long duration and seasonal modulation, the analysis of DLDS require a su cient amount of seismic data throughout the year. (3) A precursory swarm of distal VT earthquakes has been identi ed. The swarm occurred SE of Livingston Island, and started ve months before the 2015 seismic crisis at Deception Island. (4) Recognition of an annual modulation for part of the seismicity at Deception Island. This annual modulation is related to the seasonal cycle and other atmospheric variations, in uenced by external factors, which can induce pressure variations in volcanic/hydrothermal uids, or be an indicator of climatic trends. (5) Identi cation of a generalized increase of the seismic activity, starting in 2011 and accelerating during 2011-2014, reaching a climax during the seismic crisis recorded at Deception Island in 2015. (6) A volcanological model is proposed for the behaviour of Deception Island during the 7.5 years preceding the 2015 crisis. The volcano is in a dormant state up to 2010 (Phase 1), with a low level of seismic activity. In 2011 the activity shifts to an awakening state (Phase 2) characterized by a gradual increase in seismic activity as a consequence of a deep magmatic intrusion that increases the amount of gas permeating the volcanic edi ce. Finally, in 2014-2015 the volcano becomes restless (Phase 3) and the activity accelerates, suggesting the occurrence of a failed eruption. (7) The availability of continuous seismic data at Deception Island, even with just one station (DCP), allows for a qualitative leap in our ability to characterize and understand volcanic behaviour. This emphasizes the need for a permanent seismic network at Deception Island for the assessment of volcanic hazards.