Field evidence for neotectonic activity on the SW Baltic Sea (NE Germany)

Category Tectonic & Seismotectonic
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Hoffmann, Gِsta; Reicherter, Klaus
Holding Date 08 September 2008

The southwestern Baltic Sea is part of the Northeast German Basin, south of the Sorgenfrei-Tornquist Zone and the Teisseyre-Tornquist Zone and generally is not regarded as a neotectonic active area. However, repeated glaciations during the Quaternary shaped the area geomorphologic and caused isostatic adjustment of the crust. These processes are most probably related with neotectonic movements as the NGB is composed of different fault-bounded crustal blocks. With this paper we discuss the field evidence for the neotectonic activity.
Pleistocene sediments crop out mainly in cliff sections along the coast. Although the stratigraphic relationships are not well constrained, mainly Weichselian ages (and only partly older deposits) are assigned. The Baltic Sea developed during the Holocene and as a result of coastal dynamics large spits and beach barriers formed.
The Pleistocene deposits show a variety of faults (both normal and reverse). Most authors interpret these as glaciotectonic features. However, at a cliff section on Usedom Island, we have evidence for liquefaction within glaciofluvial sediments, which may be attributed to an increased tectonic activity during the Late Glacial. As a consequence of a collapsing peripheral forebulge, the area is characterized by subsidence. Therefore, evidence for Holocene neotectonic activity is restricted either to the coastal lowlands, where up to 15 m of Holocene sediments accumulated, or the offshore area with ~2 m of Holocene sediments.
Boomer-seismic data collected offshore Rügen Island suggest the existence of active faults on the seafloor. Neotectonic activity may be proven by means of ground penetrating radar (GPR) surveys in the coastal lowlands. So far, there are only a very limited number of GPR profiles available. However, the structures recorded are attributed to changes in coastal dynamics.