SCENARIOS OF PAST AND FUTURE SHORE-LEVEL DISPLACEMENT IN SCANDINAVIA

Crustal movements and shore-level displacement will affect subsurface conditions of importance for the performance and safety of deep geological repositories for spent nuclear fuel. To support performance and safety analysis an empirical model of the glacio-isostatic movements and shore-level displacement for the area covered by the Scandinavian ice sheet during the Weichselian glaciation has been developed.

The model was initially based on detailed lake-tilting investigations. These made it possible to express the course of glacio-isostatic uplift in mathematical terms without using rheological assumptions. In addition to the lake-tilting information the model is based on 72 shore-level curves from all over Scandinavia and information concerning present relative uplift recorded by precision levelling and tide gauge data.

The main uplift, still in progress, is mainly calculated from two factors designated the down load factor and the inertia factor. The down load factor represent the subsidence/uplift at the time for the maximal subsidence/uplift rate, and the inertia factor describes the evolution of the subsidence/uplift with time. There is a strong linear correlation between the inertia factor and lithosphere thickness. The model has been incorporated into a GIS (Geographic Information System) application, and can be illustrated together with other GIS data.

The purpose of the modelling was to illustrate the course of events since the last deglaciation and the model is based on Late Weichselian and Holocen information. However, scenarios of past and future shore-level displacement have been constructed assuming that the depression of the crust is proportional to the ice load and that the evolution of the subsidence/uplift in time always follows the same pattern as geological data indicates it did after the last glaciation.