Mapping fault architecture from depth to surface: integrating microseismicity and structural geology in low-strain Apennine regions

High-resolution microearthquake data provide a powerful window into active fault architecture from depth to surface in slowly deforming regions with sparse instrumental seismicity. We integrate microseismic clusters derived from enhanced catalogs with detailed structural mapping to reconstruct the three-dimensional geometry of some seismogenic extensional faults in the Latium-Abruzzi sector of central Italy. Investigated earthquake clusters align geometrically and kinematically with newly mapped or extended normal faults, which show evidence of Late Quaternary activity. The built 3D model depicts a set of SW-dipping, high-angle curvilinear faults (Sora, San Donato Val di Comino, Villavallelonga, and Pescasseroli) whose cut-off depths deepen NE-ward, from ~6 to ~14 km, and appear to sole into a basal detachment with an average dip-angle of 30–35°. The microseismic patches localized at the roots of the high-angle faults extend along the fault dip rather than the strike. This unusual configuration suggests a stress release pattern governed by iso-oriented anisotropic roughness and corrugations on the detachment, capable of localizing upward fluid migration and earthquake triggering along the hanging-wall splays. Stress inversion indicates a persistent NE–SW extensional stress field consistent across geological and instrumental timescales. Empirical magnitude-area scaling, accounting for both epistemic uncertainty among scaling laws and areal variability of the considered fault surface, indicates a range of maximum magnitudes between 6.0 and 6.5, coherent with the regional seismotectonic context. Our findings provide new constraints on fault connectivity, stress distribution, and fluid-fault interactions, contributing to identifying seismogenic sources that might have remained unknown considering geological and seismic data in isolation.