original objective = quantify intraplate deformation –pros: larger number of sites high density of...
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• 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.
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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
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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Calais and DeMets, unpublished solution, Nov. 2006
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What can we resolve?
Glacial Isostatic Adjustment
SW U.S. extension (incl. Rio Grande Rift)
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Spatially filtered residual velocity field
Calais et al, JGR, 2006
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New Madrid GPS Velocity Field
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NWCC - PTGV NWCC - RLAP
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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.