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Magnetotelluric Imaging of the Magma Plumbing System below the Ubinas Volcano (Southern Peru)

Jose Luis Torres123, Svetlana Byrdina2, Yanet Antayhua1, Gonzalo Romero-Beltran1, Volker Rath4, Philip Hering5, Alain Burgisser2, Stephane Garambois2, Hernando Tavera13, Marco Milla3,^ ^Marco Rivera1, Roger Machacca1, Yovana Alvarez1, Rosa Anccasi1, Beto Ccallata1

  • Affiliations:  ^1 ^Instituto Geofísico del Perú, Observatorio Vulcanológico del Sur, Asentamiento Humano José María Arguedas Zona A Mz. D Lt. 08, Sachaca, Arequipa, Perú; 2Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, IRD, Univ. Gustave Eiffel, ISTerre, 38000 Grenoble, France; ^3 ^Pontificia Universidad Católica del Perú, Av. Universitaria, San Miguel, Lima, Perú; 4 Dublin Institute for Advanced Studies, Geophysics Section, 5 Merrion Square, Dublin, Ireland; 5 Goethe-University Frankfurt, Institute for Geoscience, Applied Geophysics, Germany. 

  • Presentation type: Talk [Invited]

  • Presentation time: Friday 16:00 - 16:15, Room R280

  • Programme No: 1.5.6

  • Theme 1 > Session 5

Abstract

The Ubinas volcano, located 75 km east of the city of Arequipa, is the most active volcano in Peru. Its last eruption occurred in 2019, and since July 2023 it has been undergoing a new eruptive phase. Petrological studies suggest the presence of a Holocene magma storage region at depths of 3--10 km b.s.l., with a primitive magma deposit located at depths greater than 25 km b.s.l. At shallower depths (2--4 km a.s.l.), self-potential observations indicate an extensive hydrothermal system. To identify the resistive structures beneath the Ubinas volcano and build upon previous studies, we (IGP-IRD) acquired 25 broadband magnetotelluric (MT) data (period range 0.001-5000 s) in 2022. All data were processed using a robust and remote-reference approach, and a 3D resistivity model was obtained by inversions of full impedances, tippers, and phase tensors using the 3D MODEM code in frequency range between 0.0004-1000 Hz. Phase tensor inversion allowed for static shift correction. The inversion converged with a normalized RMS = 1.21. The 3D model reveals a prominent conductive zone (C1: 6--10 Ωm), located approximately 10 km below the surface (5 km b.s.l.) and northeast of the volcano. This zone is tentatively interpreted as the magmatic reservoir, which agrees well with petrological studies. Near the surface, a conductive body follows the volcano's topography, consistent with hydrothermal systems (C2: 1--8 Ωm). These results were correlated with the earthquakes detected between 2018 and 2023, showing that seismic activity suggests pathways for magmatic fluids ascending to the surface during the current eruptive phase.