Reconstruction of the evolution of the Osning Lineament in northern Germany using 2-D retrodeformation

Neotectonic movements can cause severe geohazards and thus require examination for seismic hazard assessment, and utilisation of the subsurface for e.g. nuclear-waste disposal sites and geothermal exploitation. In northern Germany, very little is known about these processes and the associated structures, despite proven neotectonic activity, because many faults are hidden beneath sediments.

The Osning Lineament (OL) in North Rhine-Westphalia is a recently-active fault zones. Three major earthquakes and seven other macro-seismic earthquakes occurred at the OL during the last 400 years. The strongest earthquakes occurred in 1612, 1767, and 1770, with an estimated intensity of VI to VII on the MSK scale. The OL is a unique fault system compared to other faults in northern Germany. The faults of the OL reach the basement, whereas in the north of the Lower Saxony Basin, most faults are decoupled from the basement by salt. Furthermore, the OL dips to the northeast and therefore the vector of the fault plane points towards the former iceload from Scandinavia, enabling glacial isostatic adjustment to occur on the faults. Additionally, the OL has had a history of multiphase reactivation in the geological past.

To better understand the neotectonic evolution of the OL on a regional scale, we carried out a 2D retrodeformation using already existing large-scale cross sections along the lineament, which are based on surface geological maps and sparse drilling information. Balancing of these cross-sections verifies whether the fault geometry and kinematics derived from surface data are justified or need to be revised. Retrodeformation is also used to suggest the path of the fault(s) at greater (seismogenic) depth. Later on, retrodeformation will also be performed including new, highly-detailed seismic profiles and a joint interpretation will be carried out to improve the understanding of the past evolution of the Osning Lineament.