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 from enhanced catalogs with detailed structural mapping to reconstruct the 3D geometry of seismogenic extensional faults in the Latium-Abruzzi sector of central Italy. Investigated earthquake clusters align geometrically and kinematically with known and newly mapped normal faults showing evidence of Late Quaternary activity. The 3D model depicts a set of SW-to-SSW-dipping, non-planar faults with an average dip of ∼55° (Sora, San Donato Val di Comino, Villavallelonga, and Pescasseroli). Their cut-off depths deepen NNE-ward, from ∼7 to ∼14 km, suggesting an underlying basal discontinuity dipping∼30–35°. Microseismic patches at the roots of these faults are mostly elongated along dip rather than along strike. This unusual geometry suggests a stress release pattern governed by iso-oriented anisotropic roughness and corrugations on the basal discontinuity, which may focus upward fluid migration and trigger earthquakes along hangingwall splays. Stress inversion reveals a persistent NE–SW tensional stress field consistent across geological and instrumental timescales. An empirical magnitude-area relationship, accounting for both epistemic uncertainty in scaling laws and areal variability of fault surfaces, yields maximum magnitudes between 6.0 and 6.5, consistent with the regional seismotectonic framework. These findings provide new constraints on fault connectivity, stress distribution, and fluid-fault interactions, and help identifying potentially seismogenic sources that may remain unrecognized when geological and seismic data are considered separately.