Deformation Analysis in the North American Plate’s Interior

Calais E, Purdue University, West Lafayette, IN, ecalais@purdue.eduHan JY, Purdue University, West Lafayette, IN, han5@purdue.eduDeMets C, University of Wisconsin, Madison, WI, chuck@geology.wisc.eduNocquet JM, CNRS, Géoscience Azur, Valbonne, France, nocquet@geoazur.unice.fr

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:

0 0

0 0

0 0

84.6 0.2

2.7 0.6

0.202 0.02 /

W

S

Myr

Deformation Analysis in the North American Plate’s Interior

Rigid motion of NOAM (cont’d)

Rigid rotation pole of NOAM/ITRF200 Residual 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: 600-1000 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 3.31033 CDM 0.56925 IGS 11.98800 ITR 2.92523

Previous combination (Sep 05):

367 sites in the final combination

PUR 2.37393 CDM 0.74546 IGS 12.23490 ITR 2.87833

This combination (Oct 06):

Position Velocity 2D h 2D hPUR 0.0008 0.0035 0.0004 0.0010CDM 0.0008 0.0008 0.0001 0.0002IGS 0.0010 0.0047 0.0003 0.0011ITR 0.0007 0.0031 0.0004 0.0009

Previous combination (Sep 05):

Position Velocity 2D h 2D h PUR 0.0008 0.0052 0.0005 0.0020 CDM 0.0018 0.0013 0.0002 0.0005 IGS 0.0018 0.0059 0.0005 0.0011 ITR 0.0007 0.0035 0.0004 0.0007

NOAM: Preliminary results of the latest combination (Oct 2006)

More sites with better accuracies are obtained in the new combination solution.