2010:41 Rock-block configuration in Uppland and the Ålands-hav basin, the regional surroundings of the SKB site in Forsmark, Sea and land areas, eastern Sweden

This report concerns a study which was initially conducted for the Swedish Nuclear Power Inspectorate (SKI), which is now merged into the Swedish Radiation Safety Authority (SSM). The conclusions and viewpoints presented in the report are those of the authors and do not necessarily coincide with those of the SSM.

The topography in Uppland is more broken in the sea area east and northeast of Forsmark than it is on land. The major structure in the Ålands-hav basin is a west-north-westerly line that passes southwest of Åland, with a very steep gradient from the Åland archipelago down to an exceptionally low sea-floor valley. On its southern side it rises in steps to a low flat basin divided into a deeper western half and a somewhat shallower eastern half. The Swedish Nuclear fuel and Waste management Co (SKB) has investigated the Forsmark site, which lies at the west-northwest trending shoreline in northern Uppland, sheltered from the sea by one of the larger islands in the Uppland archipelago, Gräsö. To assess the structures around Forsmark also in the sea area, the bottom structures of the Ålands-hav basin were investigated by means of depth-readings from sea charts. Two rock-block maps with rock blocks at different scales were constructed and analysed for their top surface elevation.

The purpose of the current project is to evaluate data in SKB’s early site descriptive models and discuss alternative structural geological models. In this work available marine geological data in the Baltic Sea outside Forsmark will be used. The interpretation of the sea data will contribute to the understanding of the late geological history of the area in the mainland as well as in the sea.