Abstract:
A combination of two independent geodetic solutions using data from close to 300 continuous GPS stations covering the central and eastern United States shows that surface deformation in the North American plate interior is best fit by a model that includes rigid rotation of North America with respect to ITRF2000 and a component of strain qualitatively consistent with that expected from glacial isostatic adjustment (GIA). After correcting for the North American plate motion, residual horizontal velocities show a north-to-south deformation gradient of ~1 mm yr-1, mostly localized between 1000 and 2200 km from the GIA center, corresponding to strain rates of about 10-9 yr-1. At distances farther than 2100 km from the GIA center, horizontal residual velocities are random with no evidence for regions of elevated strain rates. In particular, we find no detectable residual motion at the 95% confidence level in the New Madrid Seismic Zone, where the average weighted misfit of 0.7 mm yr-1 is the same as the weighted misfit of our rigid plate model. Vertical velocities show (1) a maximum uplift rate of 10 mm yr-1 at the assumed GIA center, (2) a hinge line located 1500 km from that center, and (3) a subsidence rate up to 1.4 mm yr-1 in the forebulge, with a maximum located about 2000 km from the GIA center. Our results have the potential to better constrain glacial isostatic adjustment models and contribute to a better definition of stable North America for tectonic and geodetic applications. Copyright 2006 by the American Geophysical Union.
