A comparison of strain rates and seismicity for Fennoscandia: Depth dependency of deformation from glacial isostatic adjustment

We investigate the influence of the glacial isostatic adjustment (GIA) on the deformation at the surface and at seismogenic depths in Fennoscandia. The surface strain rate field, derived from geodetic data, is controlled by GIA which causes NW-SE extension of up to 4 × 10-9 yr-1 in most of mainland Fennoscandia, surrounded by regions of radial shortening towards the centre of uplift. The seismic deformation field, derived from a new compilation of focal mechanisms, shows consistent NW-SE compression on the Norwegian continental margin and a tendency towards tension in mainland Fennoscandia. The seismic moment rate is at least two orders of magnitude smaller than the geodetic moment rate. We propose that the low level of seismicity and the tendency towards tensional focal mechanisms in mainland Fennoscandia may be explained by the destructive interference of the regional stress from ridge push with the flexural stress due to GIA.