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

Abstract

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 (I max,obs /M max,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 15 km 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 120 kyr, with the youngest event occurring at around 14 ka. 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 20-25 kyr between the earthquakes with M ≥ 6.5 and slip model 2 indicating that such earthquakes cluster in two time intervals in the last 120 kyr. 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 0.02-0.05 mm a −1 derived from the trenches compare well to geomorphically derived slip rates of 0.02-0.09 mm a −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.

Post-Miocene tectonics of the Northern Calcareous Alps

“…In Mammut Cave on Dachstein, a normal sinistral fault 283/70° with striae 200/04° continuously transformed into sinistral striae 242/59° of cumulative offset to ~ 0.8 m. Fault fiber crystals (DK2), related to this reactivation revealed an age beyond the limit of 230 Th/U dating (i.e. 0.5 Ma), Thus, the maximum age of the fault reactivation is that of the Miocene-Pliocene transition 31 . While the flowstone healing the fault plane (IM6) postdating the faulting grew 198 ± 4 ka ago.…”

“…1 ). Outside the Eastern Alps, in the Vienna Basin, the fault ruptures evidence Late Pleistocene-Holocene activity of VBT 31 , 32 .…”

On the magnitude and possible return period of the historical earthquake in ancient Savaria, 455 AD (Szombathely, West Hungary)

“…There, paleoseismological investigations carried out in the Vienna Basin showed that several earthquakes in a magnitude range between M6.3 and M7 occurred during the last 120 ka BP. This means that the seismic capacity of the Vienna Basin is significantly higher as it was supposed to be on the basis of historical earthquakes (Decker et al, 2006;Hintersberger et al, 2018).…”

Not too old to rock: ESR and OSL dating methods reveal Quaternary activity of the Periadriatic Fault

“…Instrumental seismicity does not necessarily help to identify active faults, and geodetic monitoring may fail to recognize active fault segments in case of locked faults and low deformation rates. The problem may be exacerbated by long or unknown recurrence rates of large earthquakes in regions with low overall deformation rates such as the Alps and the Dinarides (Cheloni et al, 2014;Hintersberger et al, 2018;Grützner et al, 2021;Oswald et al, 2022), or intra-continental regions (e.g., 1811-1812 New Madrid earthquakes; Tuttle et al, 2002;2001 Gujarat earthquake; Rajendran et al, 2008Rajendran et al, 2016 Peterman Ranges Earthquake; King et al, 2021). To date, there is no single de nition for an "active fault".…”