MODELING OF STRESSES IN THE FENNOSCANDIAN LITHOSPHERE INDUCED BY PLEISTOCENE GLACIATIONS

The seismicity observed in Fennoscandia is usually explained by tecton ic stresses. The question of the contribution of stresses induced by g lacial-isostatic adjustment to the seismicity has not finally been set tled yet. In order to quantify the isostatic stress field generated by the Fennoscandian glacial load, we consider layered Maxwell-viscoelas tic half-spaces loaded by axisymmetric discs. In particular, we calcul ate the maximum shear-stress distribution induced by the load model an d the associated stress regimes in the lithosphere. Emphasis is placed on a discussion of the sensitivity of the calculated isostatic stress es to variations in load cross-section, Lithosphere thickness and asth enosphere viscosity. We also examine the effects produced by the visco us relaxation of the Lithosphere, whose viscosity is parameterized acc ording to the stratification expected for temperature-activated diffus ion creep. Our results show that the isostatic shear stresses typicall y reach similar to 2 MPa near the surface at the present time but that their distribution may be modified strongly by the details of the ear th and load models investigated. The viscous relaxation of the lithosp here becomes particularly important, if more than one glaciation is co nsidered. Since the last ice age in Fennoscandia consisted of several glaciations, the model of a perfectly elastic lithosphere conventional ly employed in models of glacial-isostatic adjustment therefore may no t be justified when calculating the isostatic stresses. (C) 1998 Elsev ier Science B.V. All rights reserved.