Quantifying Fault Slip Rates and Earthquake Clustering along Active Normal Faults In Central Italy: Insights from Cosmogenic Exposure Dating and Numerical Modelling

An outstanding challenge to our understanding of fault array evolution remains the appropriate characterisation and mechanistic understanding of episodic fault activity and temporal variations in slip rate. This gap in understanding inhibits our ability to reconcile geodetic and geologic strain rates and hence predict future earthquakes; it also limits our ability to interpret the surface process response to active tectonics. For an area of active extensional deformation in the Italian Apennines, we are using a combination of field data collection and numerical modelling to address this challenge. The average Holocene (12-18 ka) slip rate along active fault segments has been derived from offset glacial sediments and landforms. Comparing these rates to paleoseismic observations and earthquake catalogues, suggests that earthquake activity switches back and forth between adjacent fault segments on timescales of 10³-10⁴ years. These variations are consistent with elastic interaction, i.e., stress transfer between neighbouring fault segments. To investigate these phenomena, we are using surface exposure dating of striated bedrock fault scarps that formed since the last glacial maximum in this area to derive the slip rate variability and earthquake recurrence over multiple earthquake cycles. The number of earthquakes, their timing and the magnitude of the associated slip are revealed by cusps in the overall increase in cosmogenically-induced ³⁶Cl from the base to the top of each scarp. Using ground-based LiDAR to map the scarps at different scales, we also characterise fault geometry and kinematics in 3D and confirm that the exposure ages we derive are the result of tectonic exhumation rather than erosion/burial by surface processes. We will present an overview of the field study, plus results from numerical simulations of elastic interaction between growing normal faults to quantify how the rupture history on a fault segment may vary depending on its position and orientation relative to neighbouring faults.