3D geometry and kinematics of the Lassee flower structure: Implications for segmentation and seismotectonics of the Vienna Basin strike–slip fault, Austria

Abstract

The active Vienna Basin strike–slip fault consists of several segments, which differ both in their kinematic and seismotectonic properties. Mapping of industrial 2D seismic, geomorphological data 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 developed during the Miocene and was reactivated in the Quaternary. The flower structure consists of Riedel-type splay faults, which merge in a major branch line at the top of the principle displacement zone (PDZ) in approximately 3.5–5.5 km depth. Mapping the PDZ of the Vienna Basin strike - slip fault in the continuations of the Lassee Segment reveals several fault segments which differ by the orientation of the PDZ. NE- and NNE-striking segments with releasing bend geometries are associated with Quaternary basins. These segments are delimited by fault-bends where the strike of the PDZ changes by angles of 20°–35°, and are connected by ENE-striking segments orientated parallel to the displacement vector. Among the releasing bends, the Lassee Segment is subject to increased extension due to the high angle (ca. 35°) between the general slip vector and the orientation of the segment. Resulting extension seems to be accommodated by both, the negative flower structure and normal faults, which branch off from the PDZ south of the Lassee releasing bend. The significant fault bends of 20°–35° delimiting the geometrical fault segments are regarded to act as impediments during dynamic rupture propagation. Hence, fault segment dimensions can be used for constraining the maximum fault surfaces, which can break during single earthquakes. The data on active kinematics and fault segmentation of the Vienna Basin strike–slip fault system therefore may serve as a basic input for future assessments of maximum credible earthquake estimates.