Comment on se-2021-7

Abstract

Abstract. The Dinaric Fault System in western Slovenia, consisting of NW–SE-trending, right-lateral strike-slip faults, accommodates the northward motion of Adria with respect to Eurasia. These active faults show a clear imprint in the morphology, and some of them hosted moderate instrumental earthquakes. However, it is largely unknown if the faults also had strong earthquakes in the late Quaternary. This hampers our understanding of the regional tectonics and the seismic hazard. Geological evidence of co-seismic surface ruptures only exists for one historical event, the 1511 Idrija earthquake with a magnitude of ∼ M 6.8, but the causative fault is still disputed. Here we use geomorphological data, near-surface geophysical surveys, and paleoseismological trenching to study two of these faults: the Predjama Fault and the Idrija Fault. In a paleoseismological trench across the Predjama Fault we found deformation features that may have been caused by an earthquake between 13–0.7 ka, very likely not earlier than 8.4 ka. At the Idrija Fault, a surface-rupturing earthquake happened around 2.5 ka. We show that instrumental and historical seismicity data do not capture the strongest events in this area.

Authors 9

1. Christoph Grà ⁄ tzner corresponding

   Friedrich Schiller University Jena

   Affiliation as printed

   Institute of Geological Sciences, Friedrich-Schiller-Universität Jena, 07749 Jena, Germany

2. Simone Aschenbrenner corresponding Aachen Neotectonics and Natural Hazards Group

   University of Cologne · RWTH Aachen University

   Affiliation as printed

   Neotectonics and Natural Hazards Group, RWTH Aachen University, 52056 Aachen, Germany

   now at: Institute of Geology and Mineralogy, University of Cologne, 50674 Cologne, Germany

3. Petra Jamšek Rupnik corresponding

   Geological Survey of Slovenia

   Affiliation as printed

   Geological Survey of Slovenia, Ljubljana, 1000, Slovenia

4. Klaus R. Reicherter corresponding Aachen Neotectonics and Natural Hazards Group

   RWTH Aachen University

   Affiliation as printed

   Neotectonics and Natural Hazards Group, RWTH Aachen University, 52056 Aachen, Germany

5. Nour Saifelislam corresponding Aachen Neotectonics and Natural Hazards Group

   RWTH Aachen University

   Affiliation as printed

   Neotectonics and Natural Hazards Group, RWTH Aachen University, 52056 Aachen, Germany

6. BlaÅ ⁄ Vičič corresponding

   The Abdus Salam International Centre for Theoretical Physics (ICTP)

   Affiliation as printed

   The Abdus Salam International Centre for Theoretical Physics, Trieste, 34151, Italy

7. Marko Vrabec corresponding

   University of Ljubljana

   Affiliation as printed

   Department of Geology, University of Ljubljana, Ljubljana, 1000, Slovenia

8. Julian Welte corresponding

   Friedrich Schiller University Jena

   Affiliation as printed

   Institute of Geological Sciences, Friedrich-Schiller-Universität Jena, 07749 Jena, Germany

9. Kamil Ustaszewski corresponding

   Friedrich Schiller University Jena

   Affiliation as printed

   Institute of Geological Sciences, Friedrich-Schiller-Universität Jena, 07749 Jena, Germany