original objective = quantify intraplate deformation –pros: larger number of sites high density of...

• Original objective = quantify intraplate deformation

– Pros:• Larger number of sites • High density of sites in some areas• Minimal cost…

– Cons:• Density varies geographically• Monument quality

• Data processing:– Combine 3 independent solutions

(using Altamimi et al’s model and Catref software)

• Gamit (Purdue)• Gipsy (U. Wisconsin)• Latest IGS

– Rescaling of covariance associated with each individual solution => final uncertainty reflects:

• Variance in original solution• Level of agreement between solutions

• Solutions (position/velocities) produced every ~6 months

– 2006 JGR paper: September 2005 solution

– Latest solution: November 2006– Next solution: wait until new IGS

orbits available– All solutions availables in SINEX

format (just ask)

608 continuous GPS sites: most are “CORS” stations + IGS + NRCan + local networks (e.g., GAMA)

Calais, E., J.Y. Han, C. DeMets, and J.M. Nocquet, Deformationof the North American plate interior from a decade of continuous GPS

measurements, J. Geophys. Res., 111, B06402,doi:10.1029/2005JB004253, 2006.

Precision:< 0.5 mm/yr after 10 yearsBulk of sites: 0.5-1 mm/yr

Accuracy:~ 0.8 mm/yr on horizontal components~ 3 mm/yr on vertical components

Precision and Accuracy

Calais et al, JGR, 2006

Residual velocities w.r.t. “stable North America”(defined using sites east of 100W and south of 40N - wrms = 0.4 mm)

Calais and DeMets, unpublished solution, Nov. 2006

What can we resolve?

Glacial Isostatic Adjustment

SW U.S. extension (incl. Rio Grande Rift)

Spatially filtered residual velocity field

Calais et al, JGR, 2006

New Madrid GPS Velocity Field

NWCC - PTGV NWCC - RLAP

Conclusions• Residual velocities (horizontal):

– Stable NOAM wrms = 0.4 mm/yr– NMSZ wrms = 0.5 mm/yr

• Strain resolvable at the 1 mm/yr level -- with high-enough station density: e.g., GIA and extension in SW U.S.

• New Madrid Seismic Zone:– Unresolved problem at site RLAP should be discarded from

interpretations– No velocity significantly different from zero -- even at the 1-sigma

level

• We know: < 1 mm/yr residual velocities over 100 km (95% confidence) in NMSZ should be taken into account in hazard studies.