<p>The Klagenfurt Basin in the southern Austrian region of Carinthia was glaciated during the Last Glacial Maximum (LGM). Next to numerous lakes, the present-day landscape predominantly exhibits landforms such as moraines and large river terraces systems. These landforms can be seen as markers for post-LGM tectonics: If they are deformed, the basin has taken up a share of the ~N-S shortening prevailing due to the ongoing collision of Adria and Europe. If the landforms are undeformed, this deformation is accommodated elsewhere, most likely further south along the Periadriatic and Sava Fault system or by a NW-SE-trending strike-slip fault system at the junction between Southern Alps and Dinarides in Slovenia. Our study is motivated by the recent discovery of earthquake-triggered mass movements in Carinthian lakes and new data on Late Pleistocene-Holocene speleothem damage in the Karawanken mountains, illustrating that the area is seismically active. We used newly available high-resolution digital elevation models to scan the area for post-glacial deformation but found no conclusive evidence for tectonic activity since the Würm glaciation. We then analysed several outcrops of Late Pleistocene sediments throughout the Klagenfurt Basin to check for soft-sediment deformation features that could be linked to strong seismic shaking. These outcrops were documented as 3D virtual models. Deformed silty-sandy layers were encountered in several places, and one outcrop showed spectacularly folded fluvial gravels. However, we do not need to invoke tectonics as the causative mechanism. Instead, we interpret these structures as evidence for a late glacial advance. Luminescence dating is underway to put constraints on the timing of this event. Our study implies that although there are records for recent strong earthquakes around the Klagenfurt Basin, the rates of deformation are so low that they can not be detected in the post-LGM landscape. </p>

<p>The Periadriatic Fault System (PAF) is among the most important post-collisional structures of the Alps; it accommodated between 150-300 km of right-lateral strike-slip motion between the European and Adriatic plates from about 35 until 15 Ma. The scarcity of instrumental and historical seismicity on the easternmost segment of the fault is intriguing, especially when compared to nearby structures in the adjacent Southern Alps. Through this project, we aim to show which segments accommodated seismotectonic deformation during the Quaternary by applying Electron spin resonance (ESR) dating to fault gouges produced by the fault system. The method is especially useful for dating shear heating during earthquake activity at near-surface conditions due to its dating range (~10<sup>4</sup>  ~10<sup>6</sup> years) ) and low closing temperature (< 100°C). During our field campaigns, we acquired structural data and collected 19 fault gouge samples from 15 localities along the PAF, the Labot/Lavanttal Fault, and the Šoštanj Fault. We measured the ESR signals from the Ti and Al centers following the additive and regenerative protocols on 60 mg aliquots of quartz, and compared the measurements between different grain size fractions. Here, we present our preliminary results from select localities, suggesting Quaternary earthquake activity along the fault system.</p>

<p>The Periadriatic Fault System (PAF) is among the largest and most important post-collisional structures of the Alps; it accommodated between 150-300 km of right-lateral strike-slip motion between the European and Adriatic plates from about 35 until 15 Ma. Recent GPS data suggest that Adria-Europe convergence is still being accommodated in the Eastern Alps. However, according to instrumental and historical seismicity records, seismotectonic deformation is mostly concentrated in the adjacent Southern Alps. In this contribution, we present our first results for dating earthquakes along the PAF during the Quaternary by applying two trapped charge dating methods. Both Electron Spin Resonance (ESR) and Optically Stimulated Luminescence (OSL) are especially useful as ultra-low temperature thermochronometers due to their dating range (a few decades to ~1 Ma) and low closing temperature (below 100°C). 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 100-150 µm grain size fraction. For OSL, we measure the IRSL signal at 50°C (IR<sub>50</sub>) and the post-IR IRSL signal at 225°C (pIRIR<sub>225</sub>) on potassium feldspar aliquots of the 100-150 µm grain size fraction. Our ESR results indicate the PAF system accommodated seismotectonic deformation during the last 1 Ma, while the OSL signals for all samples were in saturation. The minimum ages obtained from OSL suggest that the events are likely not younger than 0.4 Ma. We also studied a segment of the nearby Lavanttal Fault, for which our ESR results suggest that the last earthquakes strong enough to produce sufficient shear heating to produce a partial reset on the geochronometer probably happened before 4 Ma.</p>

<p>The Periadriatic Fault System (PAF) is one of the most important tectonic and geomorphological features in the Alps. It has accommodated between 150-300 km of right-lateral strike-slip motion between the European and Adriatic plates from about 35 Ma until 15 Ma. However, for such a large-scale feature, the eastern PAF reveals relatively little instrumental and historical seismic activity, especially when compared to nearby structures in the adjacent Southern Alps. With this project, we aim to show which fault segments of the eastern PAF system accommodated seismotectonic deformation in the Quaternary by applying trapped charge dating methods to fault gouges produced by its activity. We use optically stimulated luminescence (OSL) and electron spin resonance (ESR). The principle for both is the accumulation of unpaired electrons in lattice defects of quartz and feldspar, due to natural radiation product of the decay of radiogenic nuclides, which are then released during an earthquake due to shear heating allowing the system to reset (Fukuchi 1992, Aitken 1998, Tsukamoto et al., in Tanner 2019). Due to their dating range (a few decades to ~1Ma) and low closing temperature, trapped charge methods provide a unique opportunity to date earthquake activity during the Quaternary at near-surface conditions. During our field campaigns, we collected 19 fault gouge samples from 15 localities along the PAF, the Labot/Lavanttal fault, and the Šoštanj fault. From each locality, we controlled the structures found in the field, which allowed us to relate the observed deformation features in outcrop scale to the activity along each fault. Aside from the fault gouge in the cores of the large-scale structures at the sampled localities, we additionally found gouge and cataclasites formed within the host rocks in small-scale faults presenting the orientation of the respective regional fault, providing supplementary evidence of activity.</p>

Optically stimulated luminescence (OSL) dating utilises the detection of trapped charge in minerals, and have ultralow closure temperatures. There is the potential for direct dating of fault movement using this method, because frictional heating caused by large earthquakes can reduce the signal intensity. In this study, we conducted quartz OSL dating on four fault gouge and breccia samples from a surface outcrop of the Atotsugawa Fault, one of the most active dextral strike-slip faults in central Japan, where the last large earthquake occurred in AD1858, with an estimated magnitude of 7. The natural OSL signal intensity of fine-grained quartz was clearly below the signal saturation level, with the fraction of saturation (n/N) between 0.34 ± 0.04 and 0.42 ± 0.07. Quartz OSL ages range from 21 ± 2 to 70 ± 3 ka, two orders of magnitude older than the age of the last earthquake, suggesting that the past earthquakes only partially reset the OSL signal. We calculate the mean storage temperature of the samples to be 53 ± 2°C, which reflects past fault activity. Using the known recurrence interval of faulting to be 2.5 ka, the OSL ages, and the thermal stability parameters of the signal, we deduce partial resetting conditions.