Terrestrial reference frame NA12 for crustal deformation studies in North America

We have developed a terrestrial reference frame for geodetic studies of crustal deformation in North America. This plate-fixed frame, designated NA12, is based on GPS data from 1996.0 to 2012.1. Time series of daily coordinates in NA12 for over 5000 GPS stations are updated every week and made publicly available. NA12 is a secular frame defined by 6 Cartesian coordinates of epoch position and velocity of each of 299 stations selected by specific quality criteria, with step-free time spans of 4.7 to 16.1 years (mean 8.8 years). NA12 is aligned in origin and scale with IGS08, a GPS-based realization of global secular frame ITRF2008, so that vertical motion is with respect to the Earth-system center of mass to ±0.5 mm/yr. NA12 is designed to have no-net rotation with respect to the stable interior of the North America tectonic plate, realized by a 30-station core subset. For data after 2012.1, the 299 frame stations have a daily RMS scatter about their frame-predicted positions of 1.0 mm in the north, 0.9 mm east, and 3.4 mm vertical. The 30 core stations have an RMS velocity about zero of 0.2 mm/yr in the north, and 0.3 mm/yr east, some fraction of which results from far-field post-glacial rebound. Given that core station selection was independent of the stations’ horizontal velocity, we find unbiased evidence that the North America plate interior is rigid to 0.3 mm/yr. The accuracy of relative horizontal velocities spanning 2000 km are also at a similar level. The rotation of NA12 agrees well with the ITRF2008 plate motion model, but differs from frame SNARF1.0 by 4.2° in the longitude of the North America Euler pole due to far-field post-glacial rebound modeled in SNARF. Just as with ITRF, the NA series of reference frames will need to be updated every few years to mitigate degradation of the frame with time.