Müller, Katharina: Palaeoseismological analyses of northern and central Germany. Hannover : Gottfried Wilhelm Leibniz Universität, Diss. 2022, V, 212 S. DOI: https://doi.org/10.15488/11972
Northern Germany is an intraplate region and has been regarded as a low seismicity area for a long time. However, historic sources show the occurrence of several significant natural earthquakes in northern andcentral Germany since the 10th century. In recent years natural earthquakes as well as earthquakes in thevicinity of active gas fields, likely to have been associated with the recovery of hydrocarbons, have beenrepeatedly instrumentally recorded in northern Germany. In central Germany, which is exposed to a higherearthquake hazard than northern Germany, historically and instrumentally recorded earthquakes accumulatein a N-S trending zone. However, the seismic record of Germany is limited and solely goes back to the year 800CE. Long periods of seismic quiescence alternating with fault activity for a short geological period of time canfalsify the seismic hazard of an intraplate region. Seismic hazard can be underestimated because of seismicquiescence or overestimated because of the detection of periodical clustering, migrating and infrequentseismicity. Therefore, palaeoseismology is the missing link for an accurate assessment of the seismic hazardestimation of a continental low strain area like Germany.Northern and central Germany were repeatedly affected by glaciations and periglacial processes during thePleistocene. The main difficulty is to distinguish the vast glaciotectonic deformation structures that are presentin northern Germany from neotectonic deformation structures. Processes like cryoturbation, depositionalloading in water saturated sediments and rapid rates of deposition can generate soft-sediment deformationstructures that may also be mistaken for earthquake-induced structures. The analysis of neotectonic activity innorthern and central Germany is challenging because recently observed vertical crustal movements along NWSE-striking faults do not commonly correspond to visible morphological features and fault scarps are rapidlydestroyed by climatic conditions.Seven WNW-ESE trending major basement faults with a high potential for reactivation due to glacial isostaticadjustment were analysed with regard to neotectonic fault activity. In addition, in central Germany thecontroversially discussed seismically active part of the Regensburg-Leipzig-Rostock fault system betweenLeipzig and Cheb and surroundings was analysed with regard to pre-historic activity. Deformation bands andseismites in Palaeogene and Pleistocene deposits exposed in sand and gravel pits are indicators for neotectonicactivity. Luminescence dating, shear-wave reflection seismics, electrical resistivity tomography and lineamentanalysis were applied to support neotectonic activity in the study area.Evidence for neotectonic movements, indicated by the occurrence of deformation bands in Middle to LatePleistocene sediments, was identified along five of the seven major basement faults that were analysed innorthern Germany. Evidence was found at the Aller Fault, the Halle Fault, the Harz Boundary Fault, theSteinhuder Meer Fault and the Osning Thrust. In the area around the Regensburg-Leipzig-Rostock fault systemneotectonic movements are indicated by deformation bands in Palaeocene and Middle Pleistocene sedimentsat fault intersections of mainly NW-SE oriented faults like the Lusatian Thrust and the Finne-Gera-Jáchymovfault system and fault intersections of minor faults in the vicinity to the cities Leipzig and Dresden.It was possible to estimate the timing of neotectonic activity of faulted Pleistocene sediments by means ofluminescence dating at two basement faults (Harz Boundary Fault, Steinhuder Meer Fault). The estimated agesof faulted debris-flow deposits at the Harz Boundary Fault (15.2 ± 0.8 and 14.2 ± 0.8 ka ka) point to faultmovements after ~15 ka corresponding with the reactivation of the Osning Thrust. The estimated age of growthstrata at the Steinhuder Meer Fault (189 ± 5 ka and 158 ± 4 ka) indicates fault movements in Middle PleistoceneSaalian times. At the Harz Boundary Fault shear-wave reflection seismic surveys and electrical resistivitytomography profiles support the neotectonic activity in the Lateglacial. The timing of fault movements impliesthat the seismicity in northern and parts of central Germany is likely induced by varying lithospheric stressconditions related to glacial isostatic adjustment. For the Harz Boundary Fault and the Osning Thrust this issupported by numerical simulations of Coulomb failure stress variations. Thus, the faults can be classified asglacially-induced faults.Along the Regensburg-Leipzig-Rostock fault system, focal mechanisms of deep-seated earthquakes partly show NW-SE trending nodal planes. The focal mechanisms indicate activity along NW-SE oriented faults that intersect the N-S striking Regensburg-Leipzig-Rostock fault system. This supports the seismotectonic importance of NWSE oriented faults and intersecting faults in the study area of northern and central Germany.
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