1. Horizontal GIA Velocities and Reference-Frame Determination
Jim Davis, Mark Tamisiea, and Tom Herring

2. Reference Frame

3. Following Slides GIA deformations calculated in CE frame (standard)
GIA deformations after rotation that establishes reference frame

17. Conclusions
GIA may introduce a systematic error in rotation of ~1 mm/yr
We need a greater density of GPS sites in GIA-deforming regions (but: sensitive to ice-model errors)
Radial motions perhaps more important, but we still require a greater site density in these areas (also see Mark Tamisiea’s presentation)
We need to extend suite of Earth models for which we have the viscoelastic Green’s functions.
We probably need to make the western “site cutoff” for SNARF farther east than for this solution.

18. Recommendations SNARF group needs to have working standard solution:
Sites well distributed
Well on stable NA
Velocities and covariances