geocenter variations: GFZ

The upper part of a section through the Earth shows an indentation of the Earth's surface caused by GIA. The dashed lines show previous positions of the Earth's surface resulting from the movement of the center of mass. To the left of this, the wedges familiar from the general illustration are repeated, characterizing the GIA process. — Schematic representation of the movement of the Earth's surface relative to the center of mass caused by GIA. *(GFZ/Künsting)*

... i.e. the movement of the Earth's center of mass relative to the averaged motion of the Earth's surface. The contribution of GIA causes a movement that points in the direction of Northeast America; depending on the Earth's structure, its value is between 0.1 and 1 mm per year. However, the movement of the geocenter is dominated by seasonal fluctuations in the mass redistribution between ocean, land hydrology, atmosphere and within these subsystems.

Reference:

Klemann, V., Martinec, Z. (2011): Contribution of glacial-isostatic adjustment to the geocenter motion. - Tectonophysics, 511, 99-108. doi:10.1016/j.tecto.2009.08.031