Deformation Analysis in the North American Plate’s Interior Calais E, Purdue University, West Lafayette, IN, Han JY, Purdue University, West Lafayette, IN, DeMets C, University of Wisconsin, Madison, WI, Nocquet JM, CNRS, Géoscience Azur, Valbonne, France, SNARF Workshop Natural Resources Canada, Ottawa November 16, 2006

Deformation Analysis in the North American Plate’s Interior - Most active tectonic motions happen along plate boundary. - However, elastic strain can accumulate along geological structures far from plate boundaries. - Evidence: earthquakes within stable plate interior. WHY deformation analysis in the “Stable” North American (NOAM) plate interior?

3 Deformation Analysis in the North American Plate’s Interior - NOAM interior deforms under GIA (Glacial Isostatic Adjustment) - Deglaciation (removal of Laurentide ice sheet that covered Canada and part of the northern US until ~20,000 years ago) affects the present velocity field through incomplete viscoelastic response to the ice unloading. - Current GIA models are uncertain (ice history and mantle viscosity) - Precise Geodetic measurements could provide constraints to GIA models. WHY (cont’d)

Deformation Analysis in the North American Plate’s Interior Continuous GPS network in NOAM - About 600 GPS stations are continuously observed. (~800 stations as of Oct 2006) - Sources: 1. CORS (National Geodetic Survey, NOAA) 2. IGS (International GPS Service) 3. NRCan (Natural Resources Canada) 4. Local campaign (e.g., GAMA)

Deformation Analysis in the North American Plate’s Interior GPS Data Process - Daily data since Jan. 1, 1993 have been processed at the University of Wisconsin using GIPSY-OASIS software (free-network satellite orbits and precise point positioning). - Data since Jan. 1, 1994 have been processed at Purdue University using GAMIT-GLOBK software (double difference phase measurement, network tied to 6 IGS reference stations). - Highly-frequent (continuous) data captures periodical signals  modeled and filtered with site-specific noise process.

Deformation Analysis in the North American Plate’s Interior Combination & Precision - Multiple solutions (GIPSY, GAMIT, and IGS) are combined into a common reference frame defined by ITRF2000 (International Terrestrial Reference Frame 2000). - After combination, the WRMS for horizontal position 0.7~1.8mm, for vertical position 1.3~5.9 mm, for horizontal velocity 0.2~0.5 mm/yr, and for vertical velocity 0.5~2.0 mm/yr.

Deformation Analysis in the North American Plate’s Interior Precision (temporal relation) - Velocity precision related to the observation time span. - Longer observation time span helps noise filtering, and gives better velocity estimates. - Older sites  stable monuments. Higher precision can be expected in the days to come.

Deformation Analysis in the North American Plate’s Interior Results: Rigid motion of NOAM - The velocity field from this study: 1. Velocities w.r.t. ITRF2000 frame 2. Estimate angular rotation of rigid North America with a rigid- body motion model. Pole:

Deformation Analysis in the North American Plate’s Interior Rigid motion of NOAM (cont’d) Rigid rotation pole of NOAM/ITRF200Residual velocities w.r.t. rigid NOAM Velocities subtract rigid rotation  residual velocities (relative deformations)

Deformation Analysis in the North American Plate’s Interior Results: GIA signal?

Deformation Analysis in the North American Plate’s Interior GIA signal? (cont’d)

Deformation Analysis in the North American Plate’s Interior GIA signal? (cont’d) -Spatially-interpolated velocity field: - Systematic signals: GIA-like pattern. Hinge line at 2100 km.

Results: Vertical velocities - Also exhibits a GIA pattern. Deformation Analysis in the North American Plate’s Interior

Results: Stain analysis - Strain rate of NOAM Deformation Analysis in the North American Plate’s Interior

Results: Local stain & seismic hazardous analysis - Analysis on seismic hazardous of the New Madrid Seismic Zone (NMSZ) - GPS: surface deformation < 0.7 mm/yr (1.4 mm/yr at 95% CI) - Paleoseismology: yrs repeat time of “large” events - GPS and Paleoseismology are consistent (with low M7 characteristic earthquakes). Deformation Analysis in the North American Plate’s Interior

Conclusions - Improved quality on velocity field (<0.5mm/yr) helps to give better analysis on NOAM’s deformation behavior and seismological implications (e.g., NMSZ). - The first order deformation signal in NOAM likely comes from Glacier Isostatic Adjustment (clear pattern within 2100km range). - Further works on GIA modeling and its relation to surface strain. - Time works for us!! Longer observation Better coverage (new sites) Improved data process Deformation Analysis in the North American Plate’s Interior

NOAM: Preliminary results of the latest combination (Oct 2006) Inputs: PUR_SNX (GAMIT solution): ~ 2006D219 CDM_SNX (GIPSY solution): ~ 2006D268 IGS solution: IGS06P36 Results: This combination (Oct 06): 565 sites in the final combination PUR CDM IGS ITR Previous combination (Sep 05): 367 sites in the final combination PUR CDM IGS ITR

This combination (Oct 06): Position Velocity 2D h 2D h PUR CDM IGS ITR Previous combination (Sep 05): Position Velocity 2D h 2D h PUR CDM IGS ITR NOAM: Preliminary results of the latest combination (Oct 2006) More sites with better accuracies are obtained in the new combination solution.