Integrating seismic and petrological data unveils the magmatic system beneath Campi Flegrei Caldera.

Integrating seismic and petrological analyses is crucial for comprehensively understanding volcanic systems. In this study, we used the Receiver Function (RF) technique to investigate the crust and upper mantle beneath the Campi Flegrei Caldera (CFc), one of the world’s most active and complex volcanic systems. Over the past decades, this caldera has exhibited signs of unrest, including significant ground deformation, degassing, and seismicity.

RF analysis is highly susceptible to seismic discontinuities, enabling the detection of significant structural features and providing critical insights into P and S-wave velocity distributions. This study extends previous research by incorporating petrological constraints to understand better the relationship between seismic velocity anomalies and the magmatic system beneath CFc.

Using data from thirteen seismic stations located within the caldera, we applied a multi-taper deconvolution method to derive RFs. We then employed Bodin et al.'s (2012) transdimensional inversion approach to retrieve 1D velocity profiles and determine the probability of seismic discontinuities. To connect geophysics and petrology, we used petrological modelling tools to estimate the liquid fraction and the rock temperature in the identified velocity anomalies, offering a robust interpretation of the magmatic system's physical state.

Our analysis revealed two significant Low-Velocity Zones beneath CFc. The first is a crustal reservoir located beneath Nisida island, extending from 8 to 16 km depth with dimensions of approximately 4 x 5 x 12 km. The Vs values are between 3.5 – 4 Km/s, and a melt fraction ranges between 0 to 5%. Below this anomaly, a deeper magma source zone was identified at depths ranging from 16 to 33 km. This layer is characterised by Vs values between 2.3 – 3.3 km/s and melt fraction ranging from 15% to 30%. These seismic models and petrological data suggest that the shallow reservoir contains only partially molten material. At the same time, the deeper zone represents a more significant magma source, potentially feeding the volcanic system. Our results also indicate the presence of an older, dense intrusive complex within the crust, which may influence the migration and storage of magma.

This study demonstrates the value of integrating seismic and petrological analyses to enhance our understanding of volcanic plumbing systems. The identified velocity anomalies provide critical evidence of the magmatic system's geometry and physical properties, highlighting the interplay between crustal and upper mantle structure and magmatic processes. These findings contribute to the ongoing monitoring efforts and hazard assessment of Campi Flegrei.