Constraining the earthquake recurrence intervals of the Periadriatic Fault using ESR dating and numerical modeling

Both electron spin resonance (ESR) and optically stimulated luminescence (OSL) are dating methods that have been used to date surface-rupturing earthquakes along faults using gouges. Laboratory shear experiments have demonstrated that a complete resetting of ESR and OSL signals can be achieved by shear heating during faulting. However, ages obtained using OSL/ESR from fault gouges indicate overestimation of up to 2–3 orders of magnitude compared to the last known historical earthquakes along the faults. A possible explanation for this discrepancy is the incomplete signal resetting during faulting events.

In this study, we evaluate the conditions for partial thermal resetting of quartz ESR signals (Quartz - Al center) in fault gouge samples from the Periadriatic Fault (PAF) System in the Eastern Alps. The PAF is one of the largest post-collisional faults in the Alps, mainly active during late Oligocene–Miocene times, contributing to lateral extrusion towards the east. The seismic activity of the PAF has been debated but recent studies indicate that the fault hosted surface-rupturing earthquakes during the Quaternary.

Apparent ESR ages and signal thermal stability parameters were integrated to model the possible partial signal resetting conditions of the gouges due to seismic activity. Maximum shear heating temperatures were integrated using Raman spectroscopy of carbonaceous matter in the gouges. Our findings show that for the PAF the possible reset conditions are met at earthquake recurrence intervals in the order of 1-100 ka with shear heating temperatures below 350 °C.