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Plate boundary deformation at the Azores triple junction determined from continuous GPS geodetic measurements, 2002-2017
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  • João D'Araújo,
  • Freysteinn Sigmundsson,
  • Teresa Ferreira,
  • Jun Okada,
  • Maria Lorenzo,
  • Rita Silva
João D'Araújo
Research Institute for Volcanology and Risk Assessment

Corresponding Author:joao.pm.araujo@azores.gov.pt

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Freysteinn Sigmundsson
Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland
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Teresa Ferreira
Centro de Vulcanologia e Avaliação de Riscos Geológicos
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Jun Okada
Volcanology Research Department, Meteorological Research Institute, Japan Meteorological Agency
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Maria Lorenzo
Research Institute for Volcanology and Risk Assessment
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Rita Silva
Centre for Information and Seismovolcanic Surveillance of the Azores
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Ground deformation in the Azores, at the triple junction between the Eurasian, Nubian, and North American plates, has been mapped with continuous GPS (Global Positioning System) geodetic measurements to improve tectonic motion estimates and for understanding volcanic unrest. We compute daily GPS positions, spanning almost 17 years (2000-2017), from 18 continuous GPS stations. The GPS time-series are analyzed by searching for discontinuities and periodic functions. Results show that Flores and Graciosa islands have displacements close to predicted North American and Eurasian plate motions, respectively, while São Miguel, Terceira, São Jorge, Faial and Pico islands have displacements in between predicted Eurasian and Nubian plate motions. The Eurasian-Nubian plate boundary in the Azores behaves as a diffuse ultra-slow oblique spreading center with focused deformation found in the Central Group and Sao Miguel Island. The velocity field is modeled by approximating segments of the Eurasian-Nubian plate boundary with vertical dislocations with right-lateral motion and opening below a locking depth. Best fitting models have deep motion in the range of 2.4-2.7 mm yr-1 on segments directed N(76.5-78.8º)E. Such displacement accounts for more than half predicted Eurasian-Nubian relative plate motion. The modeling results suggest that the locking depth in the Central Group is about 17 km while in São Miguel is about 2 km. We found transient deformation at Fogo volcano, S\~{a}o Miguel Island, due to unrest activity mainly during 2003–2006 and 2011–2012, and local continuous subsidence in Terceira Island, attributed to a deflation source centered on the island.