Development and application of a three-dimensional viscoelastic lithosphere and mantle model for reducing GRACE-gravity data (VILMA)

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The delayed response of the Earth to the last glaciation (> 10; 000 years before present) as well as to decadal (< 100 years) and recent glacial changes (< 10 years) is evident in fossil sea-level indicators, GRACE-gravity, GPS, tide-gauge and altimetry observations, and must be modeled by a viscoelastic mantle rheology. Predicting the glacially-induced response allows the separation from other contributions such as hydrologically and oceanographically induced changes. Lateral variations in the viscoelastic structure of the Earth¿s lithosphere and mantle that are related to plate-tectonic units on spatial scales of thousands of kilometres must be considered on the global scale covered by this program. In this project, a three-dimensional (3-D) earth model will be developed. In comparison to one-dimensional (1-D) earth models, it has the advantage that it can be forced by all loads related to different tectonical units simultaneously in order to compute the global-scale response of the Earth. This will result in a consistent description of the mechanical coupling between the structural units and the different loading patterns. In addition to lateral variations in viscosity, a non-hydrostatic initial stress field will allow the linkage of glacial-isostatic adjustment to present-time mantle convection. Another reason for using a 3-D earth model is that it is applicable to regions near tectonic boundaries, such as Alaska, Antarctica, Iceland, Patagonia and Svalbard. Along all these boundaries, recent glacial changes are observed, and their modeling with a 1-D earth model is inadequate.