Multi-wavelength architecture of the tensional stress field of peninsular Italy.

Understanding how stress is organized and maintained within the continental lithosphere remains a central challenge in geodynamics, seismotectonics and seismic hazard assessment, yet regional models rarely resolve full stress tensors or capture their long-term persistence. Using a uniquely dense dataset of ~ 8,200 geological fault-slip measurements integrated within a hierarchical, multi-scale fault architecture framework, we define the boundary of the ~ 1000 km-long Intra-Apennine Extensional Province (IEP) of Italy and reconstruct the spatial pattern of principal stress orientations and relative magnitudes over the last ~ 3.5 Ma. Stress tensors resolved from outcrop to regional scale reveal a persistent Andersonian tensional regime and a nested, multi-wavelength arcuate organization of the stress field. Fault-scale rotations, segment-scale curvature, and a crustal-scale double arc broadly parallel to Moho geometry indicate strong coupling between deep structural architecture and upper-crustal deformation. An earlier transtensional stage is distinguished from the long-lived dip-slip tensional phase that shapes the present seismogenic framework. Comparison with earthquake focal mechanisms and GNSS-derived strain rates reveals strong directional coherence between geological stress indicators over time and ongoing deformation. These findings establish geological stress inversion as a powerful tool for imaging active lithospheric stress architectures and provide a transferable framework for interpreting intraplate extension and related seismogenic fault systems worldwide.