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Santa Bárbara Volcano (Azores): Ongoing Unrest and Crustal Deformation Observed From GNSS and Seismic Monitoring

João D\'Araújo1, Milan Lazecky2, Andy Hooper3, Freysteinn Sigmundsson3, Teresa Ferreira1, João Couto1, Rodrigo Arruda1, Beatriz Lopes1

  • Affiliations: 1Research Institute for Volcanology and Risk Assessment, Azores University, Ponta Delgada, Portugal; 2Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics, University of Leeds, Leeds, UK; 3Nordic Volcanological Center, University of Iceland, Reykjavik, Iceland

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 101

  • Programme No: 3.16.28

  • Theme 3 > Session 16

Abstract

Santa Bárbara volcano on Terceira Island, Azores, has experienced significant unrest in recent years. From 2003 to 2017, Terceira remained relatively stable, with low seismicity and minor subsidence observed in the central part of the island. The unrest started in late 2017, marked by increased seismicity and transient crustal deformation episodes. Currently, CIVISA (Centre for Information and Seismovolcanic Surveillance of the Azores) operates a permanent network of 11 seismic and 13 GNSS stations on the island. A notable increase in activity began in June 2022, initiating a more sustained period of unrest. Seismicity alternated between periods of swarm activity lasting days to weeks and periods of lower activity, but event counts during the latter remained elevated compared to pre-2017 levels. The strongest earthquake, a magnitude 4.5 ML event, occurred on January 14, 2024. That year, seismic activity culminated on December 25, with over 1,000 earthquakes recorded, the highest daily count to date, surpassing the previous peak of about 400 events on June 19. GNSS data from 2023 to 2024 reveal uplift and horizontal divergence of displacement vectors away from Santa Bárbara, consistent with inflation. Modeling the velocity field using a Mogi source embedded in a uniform elastic half-space suggests a volume increase of approximately 3 million cubic meters over one year, located at ~3.5 km depth beneath the southeastern caldera rim. Capturing deformation with Sentinel-1 InSAR data remains challenging due to low deformation rates, atmospheric noise, and dense vegetation, highlighting the critical role of GNSS in monitoring the ongoing unrest.