Deciphering Pleistocene Fault Activity in the Eastern Alps: Dating Fault Gouges With Electron Spin Resonance and Optically Stimulated Luminescence

Abstract The Eastern Alps have been influenced by post‐collisional indentation tectonics since the Miocene. Currently, Adria‐Europe convergence, albeit slow, is accommodated and distributed across several faults. The seismogenic potential of some of these faults is unclear. We applied optically stimulated luminescence (OSL) and electron spin resonance (ESR) dating to fault gouges to constrain which portions of the Periadriatic Fault (PAF) System, Lavanttal Fault, and Šoštanj Fault experienced surface‐rupturing earthquakes during the Quaternary. The saturation level of the quartz ESR Al center signal was used as a metric of seismic activity to compare between the faults. Our results showed that the Lavanttal Fault experienced the least Quaternary seismic activity, followed by the PAF, while the Šoštanj Fault exhibits the most recent seismic events. The Lavanttal Fault samples showed ESR saturation levels of approximately 97%, and minimum ages ranging 863 ± 41–2,151 ± 323 ka, indicating that if earthquakes occurred, they did so before this period. The PAF was seismically active during the Pleistocene, with maximum ESR ages ranging 899 ± 67–305 ± 25 ka and minimum K‐feldspar OSL ages ranging 179 ± 13 to 62 ± 4 ka (pIRIR 225 ). Despite a spread in ESR ages, the saturation level was consistent between samples, averaging 66 ± 4%. The Šoštanj Fault yielded an ESR age of 644 ± 30 ka and OSL of 30 ± 4 ka. The age difference lies in the dating range of both systems, but the results still suggest a shorter recurrence interval than the other two faults. Overall, our results show the utility of ESR and OSL dating in identifying periods of fault activity and complementing other approaches to fill temporal gaps.