Comparison of Southern California Shear Strain Rates From Triangulation, Trilateration, and GPS
Abstract
Changes in crustal deformation measurement techniques improve precision but interrupt the geodetic record. We compare maximum shear strain rates and directions from various measurement techniques used in the same regions during different time periods. The data were 1898-1967 triangulation, 1971-1992 trilateration, 1991-2000 survey-mode GPS, and 1997-2006 GPS data from permanent stations. In the Salton Trough, results tend to disagree, both between techniques and different triangulation epochs. This may be due to coseismic and postseismic signals from large earthquakes, non-uniform strain at the southern end of the San Andreas fault, or monument instability in the region's deep sediments. Survey-mode GPS results differ significantly, but not systematically, from trilateration and permanent GPS results in many regions. It is unlikely that these differences reflect true differences in tectonic strain; it is more probable that this is due to underestimated formal errors, monument instability, or setup problems in the survey-mode data. Outside the Salton Trough, trilateration and permanent GPS results are generally consistent, as are triangulation and both survey-mode and permanent GPS results. All techniques show that the maximum shear strain rate is typically 0.2 to 0.3 ppm/yr near the junction of the San Andreas and Garlock faults, 0.2 to 0.8 ppm/yr in the Salton Trough, and 0.1 ppm/yr over a broad region centered near the Los Angeles basin. Direction of maximum shear generally parallels the strike of local faults, rotating with the San Andreas as it undergoes its Big Bend. In summary, southern California strain rate patterns have been steady during the past century.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.G23B1282K
- Keywords:
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- 1209 Tectonic deformation (6924);
- 1294 Instruments and techniques;
- 8106 Continental margins: transform;
- 8158 Plate motions: present and recent (3040)