Seismic stratigraphy and structural analysis of shallow seabed in the southern Arkona Basin, Baltic Sea – delineating seismic attributes for resolving geological complexity and predicting geotechnical cone resistance

Abstract

Current wind farm development in the German Baltic Sea, including the Arkona Basin, calls for more studies on combining seismic data with geological and geotechnical soil properties as well as borehole geophysical data. However, the geological setting of the Arkona Basin is complex, and there is a need to use extant geophysical data for predicting Cone Penetration Test (CPT) parameters. Thus, this research focuses on the southern Arkona Basin and aims to: (1) establish the stratigraphic and structural framework of shallow geological formations in the area using qualitative and quantitative seismic attributes, and also reveal the Late Cretaceous to Holocene evolution in the area; (2) evaluate the prediction of CPT data from ultra-high-resolution (UHR) seismic reflection data, and show interface-related and layer-based seismic attributes that can be used for such predictions; (3) establish the statistical boundary conditions of small strain physical properties of geological formations, and show how they can be used in seismic inversion; and (4) assess two impedance inversion approaches in the study area. The database consists of 2D and 3D UHR seismic reflection data, sediment descriptions from boreholes, primary and shear wave velocity logs, and CPT data. This study reveals the geological characteristics of Cretaceous bedrock and Pleistocene glaciogenic units in the area. It correlates spatial changes in interface-related seismic attributes with variations in normalized Soil Behavior Type. Absolute acoustic impedance sections tied with borehole sediment descriptions exhibit the vertical stacking, lateral extent and structural configuration of lithologic units. The acoustic impedance values predicted by a seismic inversion approach in this study vary simultaneously with measured CPT parameters across lithologic boundaries. The impedance values highly correlate with the CPT parameters in quantitative terms. Although acoustic impedance can be used for CPT data predictions, the prediction should be guided by composite interface-related seismic attributes. During seismic inversion carried out with genetic algorithms, the outcome is dependent on certain parameters, and it might be possible to build initial low-frequency model using statistical estimates of physical properties.