Glacial isostasy and long-term crustal movements in Fennoscandia with respect to lithospheric and asthenospheric processes and properties-comment

Recently, Morner discussed his model of glacio-isostatic compensation in the light of new seismological models of the upper mantle below Fennoscandia (Miimer, 1990). He concluded that the P-wave velocity distribution is in “full agreement” with his estimate of the viscosity distribution as inferred from glacio-isostatic relaxation. Whereas the consistency of seismological and geodynamical earth models is a necessary condition for their soundness, the particular type of agreement sought by Momer is not required or expected, nor can his method of attaining such agreement be approved. For easier understanding of my criticism, I briefly recall the type of information provided by the seismological and by the glacio-isostatic evidence: (1) The propagation of high-frequency compressional waves admits an inference of the P-wave velocity distribution, which, in turn, provides basic information on the elastic properties of the earth. In certain tectonic provinces, a high-velocity lid superimposes one or several upper mantle lowvelocity channels. The high-velocity lid, sometimes referred to as the seismological lithosphere, is therefore a manifestation of radial heterogeneity in elasticity. (2) The relaxation of low-frequency, glacio-isostatic disturbances provides basic information on the creep properties of the earth. The transition