Re-evaluation of seismogenic faults in the southern Vienna Basin from seismogenic depth to the surface

The southern Vienna Basin, a Miocene pull-apart structure formed along the sinistral Vienna Basin Transfer Fault System (VBTFS) extending from the Eastern Alps to the Western Carpathians, exhibits negative flower structures with strike-slip and branching normal faults. Miocene basin subsidence and sedimentation produced up to 5 km thick sedimentary sequences overlying the pre-Neogene basement. Quaternary and recent tectonic activity, documented by instrumentally recorded and historical seismic events as well as focal mechanisms of selected earthquakes, in addition to paleoseismological data showing evidence for prehistoric earthquakes of magnitudes up to ~ 6.8, confirms ongoing sinistral motion and normal faulting.

We present here a comprehensive overview of the seismotectonics of the Vienna Basin, integrating earthquake information, such as high-precession relocation of hypocenters, focal mechanisms and historical earthquake information together with fault information from industrial seismic campaigns, geological mapping and geomorphological studies.

The seismological characteristics are presented based on the Austrian Earthquake Catalog (AEC) of GeoSphere Austria. Suitable earthquakes that occurred after 2006 were relocated using two methods. For further analysis, the most accurate available locations were combined to obtain a complete picture of earthquake distribution. Five existing focal mechanism solutions of earthquakes were recalculated and further used to determine the recent stress field. The fault information is compiled into two datasets attributed with information on fault activity, kinematics, and displacement: surface fault traces and fault traces at the base of the Vienna Basin. The faults of both datasets are sorted into fault systems in order to correlate the fault information from both datasets.

This newly compiled seismotectonic dataset allows a systematic study comparing earthquake occurring in more than 5 km depth and faults, documented either at depths of 1-3 km by industrial seismic campaigns or at the surface by geological and geomorphological mapping in order to re-evaluate the most seismically active faults in the Vienna Basin. Despite the wealth of available information, uncertainties remain in the data, as well as additional ambiguities arising from the combination of geological and seismological data.