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

The Periadriatic Fault system (PAF) ranks among the largest post-collisional structures of the European Alps. Recent geodetic 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 Dinarides. Both electron spin resonance (ESR) and optically stimulated luminescence (OSL) dating methods can be used to date coseismic slip (with a combined range covering a few decades to a couple of million years) in slowly deforming fault zones, such as the PAF. Since the saturation doses of the quartz ESR signals are larger than quartz and feldspar OSL, ESR enables establishing a maximum age of the last resetting event of the system, while OSL allows constraining their minimum age when the signal is in saturation. We collected fault gouge samples from three 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) dose protocols. For OSL, we recorded the infrared stimulated luminescence signal at 50°C (IR50) and post-infrared infrared-stimulated luminescence signal at 225 °C (pIRIR225). Our dating results indicate that the studied segment of the PAF system accommodated seismotectonic deformation during the Quaternary, with a maximum age for the last resetting event of the system ranging from 1075 ± 48 to 552 ± 26 ka (ESR SAR) and minimum ages in the range from 196 ± 12 to 281 ± 16 ka (saturation of pIRIR225). The obtained ages suggest that the studied segment of the PAF could be considered at least as a potentially active fault.