Geophysics of the Western United States:
Crustal Deformation and Strain
Estimates of crustal strain and deformation (shear stress and dilatation) computed from geophysical observations. Dilatation is unit volume change per time; negative is contraction and positive is extension.
Contributions of new data, displays, and interpretations are welcome. Send email to the address below and include your name and position.
Crustal Strain
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Figure 1. Crustal deformation: 2D dilatation measures of the western US. Click for full size.
from
From decades to epochs: Spanning the gap between geodesy and structural geology of active mountain belts Richard W. Allmendinger, John P. Loveless, Matthew E. Pritchard, Brendan Meade (Journal of Structural Geology 31 (2009) 1409 - 1422)
IDV Displays from data in crustal strain models by Corné Kreemer .
Figure 2. Dilatation of the model strain rate tensor field. Data from Corné Kreemer.
Figure 3. Second invariant (nanostrain/year) from a Kreemer model strain rate tensor field (model data of May 2009). Note the color scale is not 'linear.'
IDV display.
Figure 4. Same as above with different 'non-linear' color scale.
Figure 5. Same data plot as just above with a "linear" color scale to show that high strain is concentrated in the narrow band along the plate boundaries.
Figure 6. Same data plot as just above with a different color scale range to show where low but non-zero strain occurs, to preserve the sense that the high strain is concentrated in a narrow region in California.
Review paper Comparison of Strain-Rate Maps of Western North America by David Sandwell, March 2010.
(http://www.unavco.org/community/announce_meetings/2010/sciworkshop10/presentations/UNVSW10_030910_2.1_STS_Sandwell_ComparisonStrainRateMaps.pdf)
"Since the typical spacing of GPS stations is 10 km or greater, an interpolation method or physical model must be used to compute a continuous vector velocity model that can be differentiated to construct a strain rate map... This poster compares strain rate maps from several groups to establish the common features among the maps, as well as the differences between the maps."
Figure 7 a and b. From the review paper.7a
7b
The Global Stain Rate Map Project (GSRM) has complied a world grid of surface velocities from permanent GPS stations, and computed the second invariant of a model strain rate tensor field. See Kreemer, C, A.J. Haines, W.E. Holt, G. Blewitt, and D. Lavalée, On the determination of a global strain rate model, Earth Planets Space, 52, 765-770, 2000. and Kreemer, C., W.E. Holt, and A.J. Haines, An integrated global model of present-day plate motions and plate boundary deformation, Geophys. J. Int., 154, 8-34, 2003. <1-- See also IDV displays of the western hemisphere and the western US. Colors show values of nanostrain / year. -->For a first-order view of crustal strain in the western U.S., here are two plots of divergence (unit volume change with time), del dot v. The divergence was computed from the one-degree grid of GPS-velocity-based surface velocities, created by the Global Stain Rate Map Project. Warm colors are areas of extension and blues are regions of convergence; greens are near-zero strain.
Figure 8. Divergence of the GSRM velocity grid analysed to a one degree grid (no smoothing).
Figure 9. Divergence of the GSRM velocity grid analysed to a one degree grid. smoothing applied to display
This is driectly comparable to Figure 2 above.
Note the extension along the eastern edge of the Basin and Range, and no detected divergence in the eastern Colorado Plateau, or in the southern Rockies.
November 27, 2010IDV images Copyright © 2010 S. K. Wier
Reproduction, reuse, or retransmission prohibited without prior written permission from the author.
