High-harmonic Geoid Anomalies Due To Shallow Low-viscosity Earth Layers In Gia Models and Their Detectability By Goce

Glacial Isostatic Adjustment (GIA) due to Pleistocene glaciation and deglaciation has left clear imprints in the present-day geoid. The solid-earth models that are commonly used in simulating these geoid anomalies usually have the upper layer (crust/lithosphere) elastic. While this is a good approximation for oceanic lithosphere, it is over-simplified for many continental crustal areas, of which some are submerged at continental margins. At many places, these continental areas have a lower crustal zone that has low viscosities. Also at the top of the mantle (asthenosphere) such zones with low viscosities can exist. Modeling results show that, due to their shallowness and due to the laterally non-homogeneous water load, these low-viscosity layers induce discernible signatures in the high-harmonic steady-state components of the geoid. These patchlike patterns have typical length scales ranging from about 100 km to 1000 km, and typical magnitudes of 1 cm - 1 m, depending on, a.o., depth and width of the low-viscosity zone, viscosity, and shoreline geometry. The GOCE satellite mis- sion, due to be launched in 2006 - 2007, should be able to detect these kind of geoid anomalies, as GOCE is expected to deliver geoid maps with solution of down to 100 km or less for magnitudes of down to 1 cm. Complications in correlating GIA model- ing results with observed geoid anomalies might arise from uncertainties in isostatic corrections (topography; non-uniform composition of crust and lithosphere) and from other non-GIA related contributions to the observed anomalies.