Not too old to rock: ESR and OSL dating methods reveal Quaternary activity of the Periadriatic Fault

The Periadriatic Fault System (PAF) ranks among the largest post-collisional structures of the European Alps. Recent Global Satellite Navigation Systems data suggest that a fraction of the Adria-Europe convergence is still being accommodated in the Eastern Alps. However, the historical seismicity records along the easternmost segment of the PAF are ambiguous and instrumental records indicate that seismotectonic deformation is mostly concentrated in the adjacent Southern Alps and adjacent Dinarides. Both Electron Spin Resonance (ESR) and Optically Stimulated Luminescence (OSL) dating methods can be used as ultra-low temperature thermochronometers. Due to their dating range (a few decades to ~ 2 Ma) and low closure temperature (below 100°C), the methods have the potential for dating shear heating during earthquakes in slowly deforming fault zones, such as the PAF. Since the saturation dose of the quartz ESR signals is larger than quartz and feldspar OSL, ESR enables establishing a maximum age of the events (assuming the resetting during seismic events was at least partial), while OSL allows finding their minimum age when the signal is in saturation. We collected fault gouge samples from 3 localities along the easternmost segment of the PAF. For ESR, we measured the signals from the Al center in quartz comparing the results from the single aliquot additive dose (SAAD) and single aliquot regenerative (SAR) protocols. For OSL, we measured the Infrared Stimulated Luminescence (IRSL) signal at 50°C (IR 50 ) and the post-IR IRSL signal at 225°C (pIRIR 225 ) on potassium feldspar aliquots. Our dating results indicate that the studied segment of the PAF system accommodated seismotectonic deformation within a maximum age ranging from 1075 ± 48 to 541 ± 28 ka (ESR SAR) and minimum ages in the range from 196 ± 12 to 281 ± 16 ka (pIRIR 225 ). The obtained ages and the current configuration of the structure suggest that the studied segment of the PAF could be considered at least as a potentially active fault.