Deformation of the North American Plate Interior
from a Decade of Continuous GPS Measurements

Calais E., J.Y. Han, Purdue University, Department of Earth and Atmospheric Sciences, West Lafayette, IN
C. DeMets, University of Wisconsin, Department of Geology and Geophysics, Madison, WI
J.-M. Nocquet, CNRS, Geosciences Azur, Valbonne, France

Cite as:
Calais, E., J. Y. Han, C. DeMets, and J. M. Nocquet (2006), Deformation of the North American plate interior from a decade of continuous GPS measurements, J. Geophys. Res., 111, B06402, doi:10.1029/2005JB004253.

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Download GPS velocities (psvelo format) in ITRF2000, or w.r.t. stable North America

A combination of two independent geodetic solutions using data from close to 300 continuous GPS stations covering the central and eastern U.S. 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 mostly localized between 1000 and 2200 km from the GIA center, corresponding to strain rates of about 10^-9/yr. 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 is the same as the weighted misfit of our rigid plate model. Vertical velocities show (1) a maximum uplift rate of 10 mm/yr 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 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.


Figure: Black arrows = Spatially averaged residual velocities calculated using a nearest neighbor scheme with a search radius of 800 km. The dashed circle has a radius of 2100 km and is centered on the GIA uplift (star). A solid circle with a 800 km radius is shown to illustrate the search radius dimension. Arrow shading represents the number (N) of residual velocities that are averaged to calculate each residual velocity.
Color background = Interpolated vertical velocities. Only sites with random-walk noise magnitude < 1 mm/sqrt(yr), category A sites, and sites with vertical velocity standard deviation less than 1.5mm/yr are used. Black squares show the site locations. The red dashed line correspond to zero velocity (hinge line). The interpolation scheme uses an adjustable tension continuous curvature surface gridding algorithm with a tension factor of 0.9.

SINEX files:

  1. Combined solution (in ITRF2000)
  2. GIPSY-OASIS sinex (loose)
  3. GAMIT-GLOBK sinex (loose)

PSVELO files:

  1. Combined solution (in ITRF2000)
  2. Combined solution (in NOAM frame)