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Volume 18, issue 2 | Copyright

Special issue: Linking faults to seismic hazard assessment in Europe

Nat. Hazards Earth Syst. Sci., 18, 531-553, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 21 Feb 2018

Research article | 21 Feb 2018

Implications from palaeoseismological investigations at the Markgrafneusiedl Fault (Vienna Basin, Austria) for seismic hazard assessment

Esther Hintersberger1, Kurt Decker1, Johanna Lomax2,3, and Christopher Lüthgens2 Esther Hintersberger et al.
  • 1Department of Geodynamics and Sedimentology, University of Vienna, 1090 Vienna, Austria
  • 2Institute of Applied Geology, University of Natural Resources and Life Sciences (BOKU), 1190 Vienna, Austria
  • 3Department of Geography, Justus Liebig University Gießen, 35390 Gießen, Germany

Abstract. Intraplate regions characterized by low rates of seismicity are challenging for seismic hazard assessment, mainly for two reasons. Firstly, evaluation of historic earthquake catalogues may not reveal all active faults that contribute to regional seismic hazard. Secondly, slip rate determination is limited by sparse geomorphic preservation of slowly moving faults. In the Vienna Basin (Austria), moderate historical seismicity (Imax, obsMmax, obs = 8∕5.2) concentrates along the left-lateral strike-slip Vienna Basin Transfer Fault (VBTF). In contrast, several normal faults branching out from the VBTF show neither historical nor instrumental earthquake records, although geomorphological data indicate Quaternary displacement along those faults. Here, located about 15km outside of Vienna, the Austrian capital, we present a palaeoseismological dataset of three trenches that cross one of these splay faults, the Markgrafneusiedl Fault (MF), in order to evaluate its seismic potential. Comparing the observations of the different trenches, we found evidence for five to six surface-breaking earthquakes during the last 120kyr, with the youngest event occurring at around 14ka. The derived surface displacements lead to magnitude estimates ranging between 6.2±0.5 and 6.8±0.4. Data can be interpreted by two possible slip models, with slip model 1 showing more regular recurrence intervals of about 20–25kyr between the earthquakes with M ≥ 6.5 and slip model 2 indicating that such earthquakes cluster in two time intervals in the last 120kyr. Direct correlation between trenches favours slip model 2 as the more plausible option. Trench observations also show that structural and sedimentological records of strong earthquakes with small surface offset have only low preservation potential. Therefore, the earthquake frequency for magnitudes between 6 and 6.5 cannot be constrained by the trenching records. Vertical slip rates of 0.02–0.05mma−1 derived from the trenches compare well to geomorphically derived slip rates of 0.02–0.09mma−1. Magnitude estimates from fault dimensions suggest that the largest earthquakes observed in the trenches activated the entire fault surface of the MF including the basal detachment that links the normal fault with the VBTF. The most important implications of these palaeoseismological results for seismic hazard assessment are as follows. (1) The MF is an active seismic source, capable of rupturing the surface despite the lack of historical earthquakes. (2) The MF is kinematically and geologically equivalent to a number of other splay faults of the VBTF. It is reasonable to assume that these faults are potential sources of large earthquakes as well. The frequency of strong earthquakes near Vienna is therefore expected to be significantly higher than the earthquake frequency reconstructed for the MF alone. (3) Although rare events, the potential for earthquake magnitudes equal or greater than M = 7.0 in the Vienna Basin should be considered in seismic hazard studies.

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Short summary
The Vienna Basin is a low seismicity area, where historical data do not identify all potential earthquake sources. Despite observed Quaternary offset, there are no earthquakes along the Markgrafneusiedl Fault (MF). Results from 3 palaeoseismic trenches show evidence for 5–6 earthquakes with magnitudes up to M = 6.8 during the last 120 kyr. Therefore the MF should be considered as a seismic source, together with similar faults in the Vienna Basin, increasing the seismic potential close to Vienna.
The Vienna Basin is a low seismicity area, where historical data do not identify all potential...