Benjamin Schlue, Hanno Keil, Tilmann Schwenk
The aim of this project is the geophysical and geotechnical seabed characterization, with a special focus on assigned offshore construction sites (e.g. wind energy parks), the correlation of survey information with soil strength data, and the study of local offshore structure-seabed interactions in a morphodynamic and micromechanical sense. A new shallow-water multichannel seismic system will be used to derive volume and reflector seismic properties, which can be compared with in-situ geotechnical measurements and samples to generate statistically significant correlations between geotechnical and geophysical data as predictive tools for sedimentary site characterization. New-pipe laying techniques in non-cohesive substrates will be evaluated, designed and tested. The project specifically addresses how upcoming offshore foundation activities may affect the dynamic strength of the Pleistocene and Holocene sediment. Within the framework of research area D, this project deals with an accurate site characterization by surveys, sampling and in-situ measurements, while the complimentary project D1 focuses on the environmental impact of harbors and constructions. Beyond the scientific and methodological challenges in shallow water research, the proposed project intends to provide relevant methods and data for future tasks in marine offshore construction work, to keep close contact with administration units (e.g. BSH, BGR) and survey (e.g. OSAE) and construction companies, and to build up expertise for student education in applied geosciences.
Multifrequency Seismoacoustic Survey of a planned Wind Farm Area
The seismic data of a designated wind farm area off Borkum reveals that the wind farm area is located above the eastern flank of an updoming structure, probably a salt dome. The flank is located in depth of 170 to 280 meters. The near-surface structure is quite heterogeneous and characterized by numerous filled channels, often cut into each other.
A. Bartholomä, J. Ehlers, T. Hanebuth, D. A. Hepp, T. Schwenk, V. Spieß
To what extent are well-known N-S trending buried Pleistocene valleys in the SE-North Sea cross-cut by younger, but E-W trending tunnel-valleys?Deep (>100-500 m) Pleistocene tunnel-valleys beneath the northern European lowlands (Denmark, N-Germany, Netherlands) and the SE North Sea commonly follow an overall N-S trend and their infill is capped by varying thicknesses of Late Elsterian Lauenburg Clay. Consequently, the formation of these valleys has been assigned to the preceding Elsterian glaciation. Similar structures formed during subsequent glaciations, although they are less extensive and not so deeply incised. The newly discovered E-W trending valley in the SE North Sea is more than 35 km long and apparently crosscuts older N-S trending valleys. Although exceptional for the moment, the presence of additional such valleys is very likely, taking into account the poor mapping status of the SE North Sea. As tunnel-valleys are thought to form by melt water drainage beneath and perpendicular to ice sheet margins, an E-W trending post-Elsterian valley in the SE North Sea implies a N-S trending ice margin of Saalian (?) age, which previously has not been proposed for the German North Sea sector but would fit observations in the Dutch sector. 2D/3D seismic investigations of the extent, shape, infill architecture and crosscutting relationships of Pleistocene buried valleys will be an important contribution to resolve the existing inconsistencies in describing past ice sheet dynamics in this region.
Figure 1. Seismic section through the recently discovered E-W trending buried valley in the German Bight.