Secular changes of the geoid in the Fennoscandian land uplift region

Abstract

Two alternative methods are presented of determining the secular changes of the geoid in the Fennoscandian uplift region. Both are based on the Airy-Heiskanen hypothesis of isostatic compensation. The first alternative is the usual Stokes integration of changes of free-air anomalies in the given region. Another alternative was derived, which is based on calculating the gravitational potential of the surface uplift layer and of the same layer at the depth of compensation. The calculated changes of the shape of the geoid were then compared with the results of Bjerhammar's geophysical interpretation of the expansion of the Earth's gravity potential (regional depression of the geoid in the Fennoscandian uplift region). Regression analysis indicates a strong correlation between the two quantities (r=0.88). The time required to level this depression of the geoid is estimated. A relation was derived for improving the accuracy of the observed values of Fennoscandian uplifts, which takes into account the elastic reaction of the Earth's body to the change of gravitational potential and perturbations, caused by the secular decrease of the depth of the northern part of the Baltic Sea.