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Weak crustal layer beneath Campi Flegrei caldera identified: what\'s its impact on unrest dynamics?

Gianmarco Buono1, Francesco Maccaferri 1, Lucia Pappalardo1, Anna Tramelli1, Stefano Caliro1, Giovanni Chiodini1, Virginie Pinel2, Eleonora Rivalta3, Elena Spagnuolo1, Elisa Trasatti1, Mauro Di Vito1

  • Affiliations: 1 Istituto Nazionale di Geofisica e Vulcanologia, Italy 2 Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, IRD, Université Gustave Eiffel, ISTerre, Grenoble 38000, France 3 Dipartimento di Fisica e Astronomia \"Augusto Righi\", Alma Master Studiorum - Università di Bologna, Italy

  • Presentation type: Poster

  • Presentation time: Friday 16:30 - 18:00, Room Poster Hall

  • Poster Board Number: 210

  • Programme No: 3.10.12

  • Theme 3 > Session 10

Abstract

Calderas unrests are often challenging to relate to magmatic or hydrothermal origin, which is a key question to improve the hazard assessment related to the unrest dynamics. Campi Flegrei is a clear example: since 2005 the caldera experienced accelerating ground uplift, seismicity rates, and degassing, and the origin of this unrest - whether magmatic or hydrothermal - remains a subject of debate. To better characterize the underground structures and link them with the current unrest dynamics, we conducted petrological and X-ray microtomography investigations on cored rocks from a ~3 km deep geothermal well located near the centre of caldera. Our laboratory results were complemented by a 3D high-resolution seismic tomography, and by numerical simulations of magma pathways below the caldera. At a depth of ~2.5 - 3.0 km we identified a transition to a weaker tuff layer. Such layer is likely to trap magmatic fluids and build up overpressure, causing the current deformation and seismicity. Our magmatic dyke pathway simulations indicate that the combination of the stress generated by caldera unloading, and the magma neutral buoyancy level, promotes the arrest of ascending dykes at such depth. This suggests that the weak tuff layer revealed by our observations may be the consequence of the accumulation of past intrusions which deformed, heated, and released magmatic fluids, deteriorating the surrounding rocks. This weak layer may play a crucial role in influencing the dynamics of recent unrests, and possible future magma ascent.