Verifying the structure and development of the Osning Fault System (Northern Germany) using cross-section balancing

The NW-SE-striking Osning Fault System (OFS) is one of the most prominent fault zones in northern Germany. It consists of thrust faults (top-to-SW), which were caused by inversion of NE-dipping normal faults during the Upper Cretaceous. Although northern Germany shows relatively little seismic activity, 10 macro-seismic events have occurred along the OFS during the last 400 years, three of which caused serious damage. These events indicate that the OFS is neotectonically active and represents a geohazard. The investigation of its structure in depth is therefore of high societal relevance.

Our goal is to balance previously-published cross-sections along the OFS, to (1) verify their correctness and (2) obtain more information about the kinematic history. The OFS is assumed to be a pre-Variscan structure that was repeatedly reactivated during earth’s history (as mentioned above). However, its development and its (former and recent) kinematics have been debated over years, e.g., whether the OFS contains a strike-slip component or not.

For cross-section balancing, we use the software MOVE^TM and - in addition to the published cross-sections - we take all available data (e.g., geological maps, structural and geophysical data, drill information) into account. We examine four segments of the OFS (Gronau-, Osnabrück-, Bielefeld- and Berlebeck-Segments) and retrodeform at least one cross-section of each segment.

In this way, we can derive a high-resolution, well-constrained 3-D picture of the four segments of the OFS, which will contribute to a better understanding of the former and present-day kinematics of this fault zone, and can be used for further risk assessment.