Quaternary stress and strain patterns in the Italian peninsula from QUIN’s data

Knowledge of the strain and stress field of the Earth’s crust is crucial to understanding the structural and seismotectonic contexts. It helps to reconstruct the evolution of geological processes that have affected the Earth’s crust and provides information on the orientation and magnitude of tectonic forces controlling seismically active zones. It is also fundamental to constructing predictive models of fault behaviour, thereby improving our evaluation of seismic hazard. Information on tectonic stress can be derived from direct measurements from boreholes, focal mechanisms, or structural-geological data (fault/slip attitude). Information obtained directly from faults provides a long-term view of kinematic and deformation processes. In this study, we exploit the high potential of the QUIN database (Lavecchia et al., 2022, 2024), which collects ~8000 data of Fault Striation Pairs (FSP) distributed over ~800 Structural Sites (SS) and belonging to 74 Fault Systems (FS) along the intra-Apennine late Pliocene-Quaternary extensional belt of Italy. For the strain analysis, we developed a MATLAB code to analyze the kinematic compatibility of the FSP data and to extract the orientation of the strain tensor (P/S1, B/S2, T/S3) axes and the strain ratio R=(S2-S3)/(S1-S3). At the same time, we applied the formal stress inversion to the FSP data using the MSATSI software (Martínez-Garzón et al., 2014) and obtained the stress tensors (σ1, σ2, σ3) and the stress ratio φ=(σ2-σ3)/(σ1-σ3) for the 74 FS. We calculated the horizontal strain/stress (SH) axes using the correction method of Lund & Townend (2007). We compared the data from the latest geodetic velocity models and focal mechanism catalogs with the long-term tectonic trends using QUIN FSPs on a regular grid map. Our results confirm a coherent extensional stress field spanning multiple time scales from the Late Pliocene to the present. The reconstructed geological SHmax directions generally correlate well with observed contemporary stress indicators from earthquake and geodetic data. In general, we reconstruct a multi-wavelength outward arcuate pattern and observe that small-scale SH rotations are detected with increasing resolution of the stress field. The stress field migrates coherently eastwards with time, and generally, temporal stress variations are not observed, except in a few areas corresponding to preexisting localized W-E to WNW-ESE normal and normal-oblique shear zones. Such discontinuities appear to control regional and local bendings of the strain trajectories. Therefore, we interpret them as tectonic corridors that may act as barriers to along-strike propagation of potentially seismogenic Apennine normal faults. This study demonstrates that a geologically based comprehensive multi-scale strain and stress analysis of active structures over time can significantly enhance and even transform the understanding of local and regional seismotectonics within the broader geodynamic context.