2D gravity modelling in Central Italy: Clues for the seismogenesis in the Apennines

In the Central Apennines (Italy), the most updated reliable 3D geological models of the crust in the area affected by the 2016–17 Amatrice-Visso-Norcia seismic sequence highlighted that the coseismic rupture at the surface can involve old inherited normal faults, while the seismogenic sources lay at depth, possibly reactivating and inverting previous thrust faults, as in the case of the Mw 6.5 Norcia earthquake (30 October 2016). Here, we present a 2D gravity model across the Central Apennines to complete and confirm the crustal geometries resulting from the 3D model itself. The cross-section was built by integrating different data types, including surface geology, hydrocarbon wells, seismic profiles, and results from receiver function analysis. It was then checked against gravity anomalies and the velocity distribution from Local Earthquake Tomography (LET), adding further details, and, finally, against seismicity recorded during the 2016–2017 sequence. The results substantiate the reliability of the geometries proposed in the RETRACE-3D model, as they fit well, except for some local misfits, with other independent data, such as the Bouguer anomalies and the velocity distribution from LET. Furthermore, integrating different data types allowed us to provide a detailed description of the structural setting of the Apennine chain and the surroundings of the RETRACE-3D study area and to identify some new features at seismogenic depths beyond those typically targeted in hydrocarbon exploration. In particular, we were able to investigate the nature of the basement top and its relationship with seismotectonics. Specific knowledge of the Earth's crust structures and our ability to image them in three dimensions are crucial for improving the understanding of the tectonic processes, particularly those responsible for generating earthquakes. The RETRACE-3D project produced a 3D model of the crust down to depths of 5–10 km in the area of the Central Apennines hit by the 2016–2017 seismic sequence. In this study, we analysed the gravity anomalies along a 2D cross-section to validate these results and to extend our knowledge to the surrounding areas and greater depths. Gravity anomalies make it possible to detect density variations within the crust, which can be related to the presence of specific geological units. Our analysis validated the RETRACE-3D project findings and provided insights into the nature of the upper crust at the base of the sedimentary succession. In particular, we identified an ancient (Permian-Triassic) sedimentary body, whose presence and current position appear to be closely related to the seismotectonics of the area. • Gravity modelling is a powerful tool for improving knowledge of crust structures. • Mesozoic palaeogeography impacts the present-day seismogenesis of the Apennines. • Most of the seismicity concentrates within the Permian-Triassic syn -rift basins.