Finding Quaternary Seismic Slip Along the Eastern Periadriatic Fault System: Dating Fault Gouges by combined means of Electron Spin Resonance and Optically Stimulated Luminescence

The Periadriatic Fault System (PAF) is among the largest post-collisional structures of the Alps. Recent studies using GPS velocities suggest that Adria-Europe convergence is still being accommodated in the Eastern Alps. However, according to instrumental and historical seismicity records, earthquake activity is mostly concentrated along structures in the adjacent Southern Alps. This is also the case for the PAF, which except for ambiguous historical events presents little to no earthquake record. Electron spin resonance (ESR) and Optically Stimulated Luminescence (OSL) are ultra-low temperature thermochronometers (closing temperature below 100 °C), with a Quaternary dating range (a few decades up to ~2 Ma). Both have the potential to date shear heating episodes. In this contribution, we present a first approach to narrow down earthquake activity during the Quaternary in the Eastern Alps by combining the application of ESR and OSL. Specifically, we aim to show which segments of the PAF system accommodated seismotectonic deformation by directly dating quartz and feldspar from fault gouges. For ESR, we measure the signals from the Al center in quartz following the single aliquot additive (SAAD) and single aliquot regenerative (SAR) protocols, focusing on the 4-11 µm and 100-150 µm grain size fractions. For OSL, we measure the IR₅₀ and pIRIR₂₂₅ signals on K-feldspar aliquots of the 100-150 µm grain size fraction. Our ESR results indicate the PAF accommodated seismic slip during the Quaternary with a maximum age ranging from 1-0.5 Ma, and OSL minimum ages of around 0.3 Ma.