Active and capable faults in anthropized settings: Revising avoidance zones criteria through comparative scarp analysis and paleoseismology along the Mt. Marine fault system (Upper Aterno Valley - Central Apennines)

Rupture hazard assessment in densely anthropized areas of the central Apennines requires methodologies that can recognize and quantify fault scarps even where the original morphological signature has been deeply modified by agricultural activity, urbanization, and recent erosional/depositional processes. This work presents an integrated orphotectonic analysis of the south-western dipping Mt. Marine normal fault system (Upper Aterno Valley, central Apennines), to which the historical earthquake of 2 February 703 (Mw ≈ 6.7) is attributed. The available scientific literature documents the presence of ault splays, generally in tectonic contact with Late Quaternary alluvial and slope deposits in the hanging wall of the main fault plane, which is not always observable in outcrop and is located within a large, strongly cataclastic deformation zone. The deposits preserved as deformation and coseismic scarps within the covering soils highlight fault activity in very recent times, yielding a minimum fault-slip rate of 0.25-0.43 mm/a throughout the system Galli et al., 2011; Moro et al., 2016). The study focuses on these active and capable faults in a ∼3.5 km-long sector near the village of Pizzoli (L’Aquila) and is based on a high-resolution LiDAR DEM on which 215 topographic profiles were drawn across 28 candidate fault scarps. The analysis followed a multiscale approach (100-, 500-, and 1000-m-long profiles) and is combined with the semi-automatic SPARTA tool (Hodge et al., 2019) to estimate scarp height, width, and slope. Of the 28 candidate scarps, 15 were confirmed as tectonic, 8 were reclassified as anthropogenic, and 4 were relocated. The along-strike throw distribution highlights a systematic partitioning of deformation: mountainward splays, developed on the carbonate bedrock, accommodate the larger offsets (up to 19-20 m on Upper Pleistocene deposits), whereas basinward splays, i.e., toward he Aterno valley, show offsets of 2-5 m involving Upper Pleistocene-Holocene deposits. Comparison with SPARTA yields a moderate positive correlation, confirming the usefulness of the automated approach for simple scarps and its limitations in zones of distributed deformation. The results were finally compared with published paleoseismological data (Iezzi et al., 2023 , and references therein) for the area, where the trenches validate the morphotectonic classification and identify, in the Vallicella-Collemusino sector, a residual epistemic-uncertainty class, in which high Holocene aggradation and anthropogenic reworking completely mask active splays. The results suggest how the avoidance zones defined by the Italian Guidelines for Active and Capable Faults should be extended to the entire eformation area (≈500 m across-strike) and must necessarily integrate geophysical and paleoseismological investigations in anthropized contexts.