High-harmonic gravity signatures related to post-glacial rebound

Abstract

The earth's shallow layers, up to a depth of about 200 km, can have viscosities that are an order to several orders of magnitude lower than those of surrounding layers. These layers can induce highharmonic (degree and order 50 - 150) gravity anomalies due to the ice and meltwater redistribution in the last glacial cycle. Uncertainties in ice-load histories will induce gravity and geoid anomaly differences in these high harmonics. The GOCE satellite mission is expected to be able to discern differences between various Late-Pleistocene ice-load histories and is also predicted to be sensitive enough to detect the effects of shallow low-viscosity crustal and asthenosphere zones. For example, our earth relaxation models indicate that GOCE should be sensitive to typical differences between ice-load histories up to harmonic degree 140 for a crustal low-viscosity zone and up to harmonic degree 70 for a low-viscosity zone in the asthenosphere. GRACE is mainly sensitive to differences for the latter. We show that for the limiting case of a lateral homogeneous earth, it is possible to constrain properties of crustal low-viscosity layers in the presence of uncertainties in the ice-load history. © Springer-Verlag Berlin Heidelberg 2007.