Isostatic topography and crustal depth corrections for the Fennoscandian geoid

Abstract

The medium wavelength geoid (wavelengths < 10 4 km) over Fennoscandia is characterized by a large negative anomaly. A study has been made of the effect of topography and crustal thickness variations on the geoid. It is shown that the crustal boundary correlates well with the medium wavelength geoid, not only in sense of a general mean, but also in their geometrical shape. By using the concept of Pratt isostasy a compensation depth for Moho topography of about 80 km is found. This is well above the seismically detected lithosphere boundary. For surface topography a compensation depth above the Moho is supposed, assuming ductile creep to be an efficient process. The result of this study demonstrate that crustal thickness variations are important for the interpretation of the Fennoscandian geoid or gravity. However, submoho deviatoric stresses might become very high (about 200 MPa) if the entire anomaly is assumed to be supported by lateral density variations at less than 80 km depth. This implies that the pronounced negative anomaly is additionally maintained by dynamical flow inside the mantle.