GEOMETRICAL FAULT SEGMENTATION AND ACTIVE KINEMATICS OF THE VIENNA BASIN STRIKE-SLIP FAULT

Active faulting in the Vienna Basin area is characterized by slow crustal movements with slip rates of c. 1-2 mm/yr and moderate earthquakes with focal depths situated between 12 to 3 km, which are concentrated along the sinistral Vienna Basin strike-slip fault system. The fault system extends from the Eastern Alps through the Vienna Basin into the West Carpathians. It consists of several segments, which differ both in their kinematic and seismotectonic properties. Mapping of industrial 2D seismic, geomorphological data, GPR studies and Quaternary basin analysis proves that active deformation uses Miocene faults. This is shown in detail for the negative flower structure of the Lassee Fault Segment, which shows virtually no seismic energy release during the last 4 centuries. The flower structure developed during the Middle and Upper Miocene and consists of en-echelon arranged Riedel-type splay faults, which merge into a major branch line at the top of the principle displacement zone (PDZ) in approximately 3.5-5.5 km depth. The array of Quaternary fault scarps at the surface reflects the complex fault geometries of the Riedel-type splay faults of the reactivated Miocene flower structure at greater depth. The overlying Quaternary Lassee Basin is confined by en-echelon, right-stepping fault scarps coinciding with the NW and SE boundaries of the flower strucuture. High-resolution GPR measurements at a scarp, which coincides with a fault zone at the SE boundary of the flower structure, mapped at least four distinct surface-breaking faults along this scarp.

Further mapping of the top of the PDZ at seismogenic depth in the SW- and NE-continuation of the Lassee Segment depicts several releasing and non-releasing bends along the sinistral fault system, which are delimited by significant fault bends of 20° - 35° degrees. NE- and NNE- striking segments such as the Lassee Segment with releasing geometries are associated with Quaternary basins, whereas ENE-striking non-releasing segments are oriented parallel to the displacement vector. The significant fault bends delimiting the geometrical fault segments are regarded to act as impediments during dynamic rupture propagation. Hence, the inferred fault segment dimensions can be used for constraining the maximum fault surfaces, which can break during single earthquakes.