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Strain accumulation across the Coast Ranges at the latitude of San Francisco, 1994-2000

January 1, 2004

A 66-monument geodetic array spanning the Coast Ranges near San Francisco has been surveyed more than eight times by GIPS between late 1993 and early 2001. The measured horizontal velocities of the monuments are well represented by uniform, right-lateral, simple shear parallel to N29°W. (The local strike of the San Andreas Fault is ∼N34°W.) The observed areal dilatation rate of 6.9 ± 10.0 nstrain yr−1 (quoted uncertainty is one standard deviation and extension is reckoned positive) is not significantly different from zero, which implies that the observed strain accumulation could be released by strike-slip faulting alone. Our results are consistent with the slip rates assigned by the Working Group on California Earthquake Probabilities [2003] to the principal faults (San Gregorio, San Andreas, Hayward-Rodgers Creek, Calaveras-Concord-Green Valley, and Greenville Faults) cutting across the GPS array. The vector sum of those slip rates is  is 39.8 ± 2.6 mm yr−1 N29.8°W ± 2.8°, whereas the motion across the GPS array (breadth 120 km) inferred from the uniform strain rate approximation is 38.7 ± 1.2 mm yr−1 N29.0°W ± 0.9° right-lateral shear and 0.4 ± 0.9 mm yr−1 N61°E ± 0.9° extension. We interpret the near coincidence of these rates and the absence of significant accumulation of areal dilatation to imply that right-lateral slip on the principal faults can release the accumulating strain; major strain release on reverse faults subparallel to the San Andreas Fault within the Coast Ranges is not required. 

Citation Information

Publication Year 2004
Title Strain accumulation across the Coast Ranges at the latitude of San Francisco, 1994-2000
DOI 10.1029/2003JB002612
Authors J. C. Savage, Weijun Gan, W. H. Prescott, J. L. Svarc
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Geophysical Research B: Solid Earth
Index ID 70027513
Record Source USGS Publications Warehouse
USGS Organization Earthquake Science Center

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