Active tectonics and Quaternary basin formation along the Vienna Basin Transform fault

Abstract

The Vienna Basin Transform fault is an active fault system extending over a distance of some 300 km from the Eastern Alps through the Vienna Basin into the West Carpathians. Active sinistral movement is indicated by moderate seismic activity in a NE-striking zone paralleling the fault, focal plane solutions and recent stress measurements. By analogy to the Miocene kinematics we propose that the sinistral strike-slip fault terminates in the Carpathians where horizontal offset is transformed into thin-skinned thrust-type deformation. Hypocenter depths mostly well above 12 km are in line with the inferred thin-skinned style of deformation with active faults restricted to the overthrust Alpine–Carpathian units. Mapping of active fault segments in the Vienna Basin using subcrop data, thickness maps of Quaternary deposits, seismological data, and geomorphological features seen in the digital elevation model shows that virtually all active faults are reactivated Miocene structures. In the southern part of the basin active faulting defines a small-scale pull-apart structure with an actively subsiding Quaternary basin, which is filled with up to 140 m fluvial gravel, sand and paleosoils. For this basin Quaternary sinistral displacement was quantified by adopting a geometrical model for thin-skinned extensional strike-slip duplexes. Accordingly, 1.5–2 km sinistral slip accumulated during deposition of the basin fill in the last 400 ky corresponding to a slip rate of 1.6–2.5 mm/y. Results are in good agreement with published GPS data indicating 2 mm slip per year. A second group of Quaternary basins is related to listric normal faulting, rollover and crestal collapse of the reactivated normal faults at the NW basin margin. Rollover also resulted in tilting and dissecting Late Pleistocene river terraces of the Danube.