Linking Fault Geometric Complexity and Cumulative Displacement with Seismic Behavior: Insights from the Gran Sasso Fault System (Central Apennines, Italy)

Active normal faults in the Central Apennines accommodate ongoing crustal extension and have generated significant earthquakes (up to Mw ~7) during historical and instrumental times. However, several fault systems, including the Gran Sasso fault system (GSFS), lack documented surface-rupturing earthquakes, raising questions about their structural maturity, role in accommodating the extension in this region, and their potential to generate future large-magnitude events.

Here, we investigate the relationship between fault geometry, cumulative displacement, and slip rate along the Gran Sasso fault system located 19km north of L’Aquila, a system consisting of two major normal faults with an overall length of ~46 km. These include(i) the Campo Imperatore fault, consisting of two segments measuring roughly 20 km and 8 km, and (ii) the Assergi fault, which extends about 18 km along the western flank of the Gran Sasso massif. Both faults exhibit a consistent average W-E orientation with secondary structure tending WNW-ESE. Our aim is to assess the structural maturity and seismic significance of the GSFS within the broader Apennine fault network.

Using high-resolution Pleiades satellite imagery combined with existing geological maps and field observation, we mapped in detail the active fault trace and identified displaced geomorphic markers. The analysis focuses on two main fault segments, the Campo Imperatore and Assergi segments, along which a well-preserved Holocene fault scarp is continuously expressed. Scarp height was measured accurately along strike using several complementary approaches, including field-based observations, topographic profiles extracted from high-resolution DEMs, and the automated ScarpLearn algorithm (Pousse et al., 2022), which identifies and quantifies fault scarp morphology together with associated uncertainties. Preliminary results indicate that vertical displacement varies between ~2 and 16 m, locally reaching up to ~20 m along the Campo Imperatore segment. These results are analyzed in relation to fault architecture to assess how geometric complexities, such as relay zones and step-overs, influence displacement distribution along strike

Field investigations and detailed mapping along the Campo Imperatore fault allowed the identification of three key sites where fluvial terraces and glacial moraines are displaced and can be used as geomorphic markers of fault slip. Samples were collected for ^36Cl cosmogenic exposure dating of these surfaces. When combined with measured offsets, these exposure ages provide constraints on average late Quaternary slip rates and on the long-term activity of the fault, under the assumption that the dated surfaces record cumulative displacement since their abandonment.