Collapse wedges in periglacial eolian sands imply Late Pleistocene paleoseismic activity of the Vienna Basin Transfer Fault (western Slovakia)

Seismic hazard assessment is an important issue in geological research. Paleoseismological studies of the depositional record contribute significantly to our knowledge of earthquake recurrence over geological time, the distribution of seismically triggered deformations being an area of research that sheds light on temporal patterns of seismic activity. This paper describes soft sediment deformation structures (SSDS) preserved in a periglacial Upper Pleistocene succession of eolian sand in the eastern Vienna Basin, Central Europe. Collapse wedges, which are interpreted as being formed along dilatational fractures, were observed. Further deformations include chaotically disturbed strata, folded strata, and slides. The fractures are oriented systematically in a N-S to NE-SW direction, parallel to the transtensional Vienna Basin Transfer Fault, which lies beneath the study area. Repeated seismic shock is recognized as the trigger of the deformations. The mechanism of deformation implies some degree of cohesion within the deformed strata, and this may be attributed to seasonal frost and the presence of vadose water within the sediment. These deformations appear periodically, in 21 distinct horizons, and it was this that allowed the calculation of the recurrence periods of earthquakes with the use of a Bayesian age-depth model; this, in turn, was based on seven OSL ages. The calculation yielded mean recurrence periods of ca. 150 years, though it should be emphasized that this figure is biased by a relatively high degree of uncertainty in the dating and in the age-depth model. With this caveat, the present study reveals the underexplored potential of periglacial eolian deposits to preserve paleoseismological signals.