Predicted geocenter motion due to glacial-isostatic adjustment
Glacial isostatic adjustment (GIA) describes the deformations of the solid earth which are induced by loading of the ice sheets repeatedly covering large areas in North America and Europe during the Pleistocene (last few Myr). According to their dimensions -- thickness of a few kilometres, extensions of thousands of kilometres, duration of 100,000 yr -- and the viscous behaviour of the earth's mantle, this process is still evident in the surface motion of the solid earth and the sea level.
In Klemann & Martinec (2009), the GIA induced geocenter motion is investigated and defined as the average motion of the earth's surface against its centre of mass. This motion is of central importance when comparing different geodetic reference systems. The predicted contribution of GIA results in a constant motion varying between 0.1 and 1 mm/yr considering the investigated parameter space but points rather robustly towards Northeast Canada (see Figure). It could be shown that the main factor which influences the predicted GIA contribution is the lower mantle viscosity of the earth.
In comparison to the detected seasonal and subseasonal periodic motion with amplitudes of some mm/yr and attributed to processes in atmosphere and ocean, the GIA contribution is quite small. Its detection by the global geodetic observing system (GGOS) is therefore a task which is supposed to be reached during the next years.
Klemann, V.; Martinec, Z. (2009): Contribution of glacial-isostatic adjustment to the geocenter motion, Tectonophysics, doi:10.1016/j.tecto.2009.08.031. (online, in press)