Quantifying the contribution of magma intrusion to the current unrest at Campi Flegrei caldera through thermomechanical modeling

Campi Flegrei caldera has experienced a critical increase in uplift rates over the past 20 years. Recent geodetic and seismic data indicate significant ground deformation (~18 cm in 2024) as well as increasing seismicity rates and magnitudes, further prompting the ongoing debate about the underlying causes. While shallow magma transport is often invoked to explain the deformation, other studies point to the accumulation of fluids in the shallow crust as primary drivers of overpressure and surface displacement. Disentangling the contribution of these processes remains a key challenge. In this study, we aim to quantify the uplift resulting from potential shallow magma migration and determine whether the deformation can be attributed mainly to it.

To address this, we integrate constraints from seismic imaging, geodesy, and rock physics into a 3D thermo-mechanical model with a visco-elasto-plastic rheology. Employing the available structural information on the caldera, the model features a deep magma influx originating from a depth of 8 km, feeding a shallower reservoir at approximately 5 km depth. We test the potential contribution of upward magma migration to surface deformation. We further explore how a mechanically weak shallow tuff layer and the hydrothermal system influence the response to the magmatic intrusion. The results show whether shallow magma migration should be paired with the effects of overlying structures and rheologies. The thermo-mechanical model reproduces only part of the observed surface deformation implying additional pressure sources, such as volatile exsolution or hydrothermal pressurization - which are not explicitly modeled here - play a significant role.

Thermo-mechanical modeling thus discriminates the role of magma in the ongoing deformation and provides insights into how stress builds and evolves in the system due to magma migration. These results are crucial for improving our comprehension of the deformation sources at Campi Flegrei and their interactions with shallow structures for seismic modeling purposes.