deformation analysis in the north american plate’s interior calais e, purdue university, west...
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Deformation Analysis in the North American Plate’s Interior
Calais E, Purdue University, West Lafayette, IN, [email protected] JY, Purdue University, West Lafayette, IN, [email protected] C, University of Wisconsin, Madison, WI, [email protected] JM, CNRS, Géoscience Azur, Valbonne, France, [email protected]
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.