Field evidences of last 5.5 ka ground deformation at Campi Flegrei caldera

Vitale et al. (2014) and Isaia et al. (2015) highlighted the role of the major faults associated to the volcanism occurred during the last 5.5 ka. Fault activation occurred synchronously to ground deformation uplift episodes that preceded major eruption phases. Presently an unrest phase of the Campi Flegrei caldera is marked by variations of different parameters such as fumarolic, seismic and ground deformation activities. The latter is well recorded by GPS data, topographic leveling and satellite surveys. The main aim of this study is to define the role of the meso-scale structures during the main episodes of the ground deformation and their relationships with the eruptive activities. This work included a structural survey at Campi Flegrei caldera by means of fracture, dyke and fault analyses. A review of available well log and new field and subsurface data collected in the central sector of the caldera was carried out. We reconstructed in detail the top of several paleo-surfaces of the main volcanic and morphostructural features. Results show as the paleo-morphology was strictly controlled by faults and fractures that formed meso-scale channels and depressions subsequently filled by tephra and volcanoclastic sediments. Several evidences of synsedimentary structures such as faults and sedimentary dykes indicate an extensional deformation accompanying the ground uplift occurred in various stages of the caldera evolution. Stratigraphycal relationships between structures and volcanic deposits further constrain the timing of the deformation phases.