[1] The 21st Century has seen the occurrence of 17 great earthquakes (Mw >8), including some of the largest earthquakes ever recorded. Numerical modeling of the earthquakes shows that nearly half of the Earth's surface has undergone horizontal coseismic deformation >1 mm, with the 2004 Sumatra-Andaman earthquake dominating the global deformation field. This has important implications for both the realization of a terrestrial reference frame and in the interpretation of regional tectonic studies based on GPS velocities. We show that far-field coseismic deformations from great earthquakes will, if unaccounted for, introduce errors in estimates of linear site velocities of at least 0.1-0.3 mm/yr across most of the surface of the Earth. The accumulated global deformation field shows that two regions, Australia and the north Atlantic/Arctic Ocean, have been largely undeformed by these great earthquakes, with accumulated deformations generally