3D Thermo-Rheological Modelling of the Southern Apennines (Italy): Insights from the TRHAM Project

Southern Italy is a tectonically active region of major geodynamic significance, where long-lived convergence, post-collisional extension, slab rollback, and crust-mantle decoupling generate strong lateral and vertical heterogeneity in lithology, temperature, fluids, and deformation. Here, we present an integrated 3D Finite Element (FE) thermo-rheological model developed within the TRHAM project activities, aimed at reconstructing the regional thermal and mechanical architecture of the crust within a physically consistent, data-constrained framework. The FE geometry synthesizes a large body of published geological and geophysical constraints, integrating surface geology, regional structural interpretations, and deep wellbore information, complemented by gravity and magnetic evidence. The thermal field is computed under coupled conductive-convective regimes by solving the fully coupled Fourier heat-conduction and Darcy-flow equations in porous media. Boundary conditions include an altitude-dependent surface temperature, prescribed basal heat flow at Moho depth, and laterally adiabatic conditions. Key thermal parameters are calibrated through a bounded optimization strategy against independent thermal observables, while explicitly accounting for resolution limits and non-uniqueness. Rheological calculations combine a frictional failure criterion for brittle deformation and power-law creep for ductile flow, incorporating spatially variable pore-fluid pressure ratios derived from the thermo-hydraulic solution. Strain-rate scenarios are guided by regional geodetic strain-rate constraints and GNSS-informed kinematic parameters. The resulting strength envelopes and yield-stress distributions show strong spatial variations in effective crustal strength and in the depth and geometry of the BDT, both along the Apennine belt and from the Tyrrhenian side to the Adriatic foreland. The model highlights the mechanical impact of inherited crustal architecture and fluid-assisted weakening, and reproduces a systematic contrast between the Apulian foreland and the Apenninic wedge consistent with regional deformation and seismicity patterns. Explicit fluid flow further emphasizes how crustal geometry modulates hydraulic connectivity and hydrological decoupling between Apulian and Apenninic domains, focusing infiltration/discharge and shaping surface heat-flow patterns.AcknowledgmentsThe activities are supported by the projects “Relation between 3D Thermo-Rheological Model and Seismic Hazard for Risk Mitigation in the Urban Areas of Southern Italy”, funded under the PRIN2022 PNRR initiative (code: P202299L2C), PRIN2022 PNRR, EU NextGenerationEU.