Which fault was it? - Late Pleistocene, glacially triggered earthquakes in NE Germany

Abstract

A sedimentological, geochronological, and geodynamic investigation of detailed micro- and meso-scale soft-sediment deformation structures (SSDS) within internally deformed layers on Gnitz Peninsula, Usedom Island, Germany, was performed in the last years. Five layers with SSDS were described of which four were possibly caused by glacial isostatic adjustment (GIA)-triggered earthquakes mirrored in liquefaction and reliquefaction phenomena (Pisarska-Jamroży et al., 2022). Hence, in line with earlier investigations and suggestions by Hoffmann and Reicherter (2012), the SSDS generation is related to oscillation of the Scandinavian Ice Sheet whose loading cycle caused stress changes likely releasing local earthquakes along pre-existing faults.Optically stimulated luminescence dating indicates a most probable time span of corresponding earthquake occurrence between 23.2 and 14.6 ka (including uncertainty). For the first time, glacially induced Coulomb failure stress changes were modelled for this area with a set of commonly accepted GIA models. They strongly support the interpretation of SSDS trapped in layers as seismites during that time. Using reliable fault parameters of faults in near vicinity of Gnitz Peninsula and suggested stress regimes and directions for northern Germany, the modelling can help indicate the most probable reactivated pre-Quaternary fault(s). If they can be confirmed after detailed palaeoseismological, geomorphological, geophysical, and structural investigations as so-called glacially induced fault(s), this would add another puzzle piece to a geodynamic scenario of glacially triggered faulting having affected an area from northern central Europe to northern Fennoscandia in the Late Pleistocene and Early Holocene.Our presentation will focus on the geodynamic setting of NE Germany, how it was changed during the last glaciation and how potentially reactivated faults can be determined.ReferencesHoffmann, G., Reicherter, K., 2012. Soft-sediment deformation of late Pleistocene sediments along the southwestern coast of the Baltic Sea (NE Germany). Int. J. Earth Sci. 101, 351-363, doi:10.1007/s00531-010-0633-z.Pisarska-Jamroży, M., Belzyt, S., Börner, A., Hoffmann, G., Kenzler, M., Rother, H., Steffen, R., Steffen, H., 2022. Late Pleistocene earthquakes imprinted on glaciolacustrine sediments at Gnitz Peninsula (Usedom Island, NE Germany). Quat. Sci. Rev. 296C, 107807, doi:10.1016/j.quascirev.2022.107807.