Preprints
https://doi.org/10.5194/se-2021-7
https://doi.org/10.5194/se-2021-7

  05 Feb 2021

05 Feb 2021

Review status: this preprint is currently under review for the journal SE.

Holocene surface rupturing earthquakes on the Dinaric Fault System, western Slovenia

Christoph Grützner1, Simone Aschenbrenner2,a, Petra Jamšek Rupnik3, Klaus Reicherter2, Nour Saifelislam2, Blaž Vičič4, Marko Vrabec5, Julian Welte1, and Kamil Ustaszewski1 Christoph Grützner et al.
  • 1Institute of Geological Sciences, Friedrich-Schiller-Universität Jena, Jena, 07749, Germany
  • 2Neotectonics and Natural Hazards Group, RWTH Aachen University, Aachen, 52056, Germany
  • 3Geological Survey of Slovenia, Ljubljana, 1000, Slovenia
  • 4The Abdus Salam International Centre for Theoretical Physics, Trieste, 34151, Italy
  • 5Department of Geology, University of Ljubljana, Ljubljana, 1000, Slovenia
  • anow at: Institute of Geology and Mineralogy, University of Cologne, Cologne, 50674, Germany

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 ~M6.8, but the causative fault is still disputed. Here we use geomorphological data, near-surface geophysical surveys, and paleoseismological trenching to show that two of these faults, the Predjama Fault and the Idrija Fault ruptured in strong earthquakes in the Holocene. In a paleoseismological trench across the Predjama Fault we found at least one earthquake with a minimum magnitude of MW6.1 that occurred between 13–0.7 ka, very likely not earlier than 8.4 ka. At the Idrija Fault, a surface-rupturing earthquake with a magnitude of at least MW6.1 happened in the last ~2.1 ka. This event could correspond to the 1511 Idrija earthquake. Our results show that the faults rupture in rare, but strong earthquakes, which dominate the seismic moment release. We show that instrumental and historical seismicity data do not capture the strongest events in this area. The fact that many of the NW-SE trending, parallel faults are active implies that the deformation in western Slovenia is distributed, rather than focussed on one major structure.

Christoph Grützner et al.

Status: open (until 01 Apr 2021)

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Christoph Grützner et al.

Christoph Grützner et al.

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Short summary
Several large strike-slip faults in Western Slovenia are known to be active, but most of them did not produce strong earthquakes in historical times. In this study we use geomorphology, near-surface geophysics, and fault excavations to show that two of these faults had surface-rupturing earthquakes during the Holocene. These rare but strong earthquake dominate the total moment release. Instrumental and historical seismicity data do not capture the strongest events in this area.