Impact of deglaciation on present-day intraplate seismicity in eastern North America and western Europe

The retreat of major ice sheets in North America and northern Europe caused a large-scale isostatic desequilibrium of the lithosphere-asthenosphere sy stem. As a result, formerly glaciated areas started to uplift and lithosphe ric bending occurred, especially near ice margins. While it is well known t hat post-glacial uplift continues until present-day in formerly glaciated a reas, so has the associated flexure of the lithosphere. This continues to a lter the stress state in the areas surrounding the former ice sheet. We hav e addressed the question of the impact of deglaciation on intraplate stress and seismicity in two separate studies. In one study, we have mapped out a nd modeled the stress field in the Norwegian sector of the Northern North S ea, a prominent hydrocarbon region in the vicinity of the edge of ice sheet that covered Fennoscandia until similar to 20 000 years ago. In the other study, we investigated the influence of lithospheric flexure as the possibl e cause of the anomalously high seismicity in the New Madrid Seismic Zone i n the central United States. This was the site of three extremely large (M similar to 8) earthquakes in 1811-1812, following several previous large ea rthquakes in Holocene time. As there is no significant deformation of Terti ary sediments in the area, deglaciation appears to have been a trigger for recent seismicity. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.