HR: 10:50h
AN: G32A-03    [Abstracts]
TI: Testing intraplate deformation in the North American plate interior from a combined geodetic solution: implication for strain accumulation on potentially seismogenic faults in the central and eastern U.S.
AU: * Calais, E
EM: ecalais@purdue.edu
AF: Purdue University, EAS Dpt., West Lafayette, IN 47906
AU: Han, J
EM: han5@purdue.edu
AF: Purdue University, EAS Dpt., West Lafayette, IN 47906
AU: DeMets, C
EM: chuck@geology.wisc.edu
AF: Univ. of Wisconsin, Dpt. of Geology, Madison, 53706
AU: Nocquet, J
EM: nocquet@ensg.ign.fr
AF: CNRS, Geosciences Azur, Valbonne, 06560 France
AB: Large earthquakes within stable plate interiors are direct evidence that significant levels of strain can accumulate along geologic structures far from plate boundary faults. The 1811-1812 M7-8 New Madrid events in the Mississippi valley (central U.S.) are classical examples of such large intraplate earthquakes. Quantifying the associated long-term strain geodetically remains a challenge because the expected rates are close to the magnitude of GPS errors. In order to improve the accuracy and signal-to-noise ratio of GPS estimates of crustal strain in stable North America, we have combined five independent geodetic solutions covering some or all (324 sites total) of the area. Residual velocities of the combined solution with respect to stable North America show an average weighted misfit of +-1mm/yr (1 standard deviation), with preliminary evidence that the misfits are relatively insensitive to monumentation quality. We find no evidence for regions of significant strain rates (at the accuracy level of our measurements). Our velocity field instead defines a coherent residual velocity pattern in the upper Midwest and New England that may reflect post-glacial rebound effects. We discuss the implications of these results for earthquake hazard, glacial isostatic adjustment models, and for defining a Stable North America reference frame for geodetic studies in western North America.
DE: 7223 Seismic hazard assessment and prediction
DE: 8107 Continental neotectonics
DE: 1208 Crustal movements--intraplate (8110)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting