First detailed 3D geometric and kinematic curvilinear fault models of the Southern Italy extensional belt: integrated analysis of surface and deep data

Since the pioneering work of Plesch et al. (2007), the development of 3D curvilinear fault modeling, integrating fault surface traces with earthquake data (hypocenters and focal mechanisms), has become a standard practice for reconstructing the geometry and kinematics of active and potentially seismogenic structures. Numerous such reconstructions have been conducted in Italy across various tectonic settings, from the extensional belt of central Italy (Castaldo et al., 2018; RETRACE-3D Working Group,2021 and many others) to the compressional front in northern Italy (Tibaldi et al., 2023). This paper presents the first comprehensive high-detail 3D geometric and kinematic reconstruction of the Southern Italy extensional belt, spanning from Campania to Calabria. Our reconstruction, also associated with a formal 3D stress inversion of geological and seismological data, models the extensional belt with an average thickness of 10-15 km from the surface down to a recognized basal detachment along the belt. The fault surfaces are organized in a systematic hierarchical order, ranging from individual fault segments to master fault alignments, all interconnected across a complex system of synthetic and antithetic structures. Surface data are extrapolated to depth with varying degrees of approximation, leveraging available geological and seismological information such as fault traces, multi-scale cross-sections, fault/slip data, hypocentral datasets, focal mechanisms, and seismic lines. The uncertainty of the modeled fault geometry is systematically analyzed, considering two key factors: completeness and geometric variability for each fault element. This systematic analysis enhances our understanding and quantification of uncertainty associated with fault geometry modeling, providing crucial insights for seismic hazard assessment and future research in this field.