1855 and 1991 Surveys of the San Andreas Fault: Implications for Fault Mechanics
Two monuments from an 1855 cadastral survey that span the San Andreas fault in the Carrizo Plain have been right-laterally displaced 11.0 ± 2.5 m by the 1857 Fort Tejon earthquake and associated seismicity and afterslip. This measurement confirms that at least 9.5 ± 0.5 m of slip occurred along the main fault trace, as suggested by measurements of offset channels near Wallace Creek. The slip varied by 2 to 3 m along a 2.6-km section of the main fault trace. Using radiocarbon dates of the penultimate large earthquake and measurements of slip from the 1857 earthquake, we calculate an apparent slip rate for the last complete earthquake cycle that is at least 25% lower than the late-Holocene slip rate on the main fault trace. Comparison of short-term broad-aperture strain accumulation rates with the narrow-aperture late-Holocene slip rate indicates that the fault behaves nearly elastically over a time scale of several earthquake cycles. Therefore, slip in future earthquakes should compensate the slip-rate deficit from the 1857 earthquake.
© 1994, by the Seismological Society of America. Manuscript received 6 July 1993. The research described in this article was carried out at the Seismological Laboratory and Jet Propulsion Laboratory of the California Institute of Technology, and at NASA Goddard Space Flight Center, under contract with the USGS (grant #14-08-001-G-1789 awarded to Kerry Sieh), the Caltech Earthquake Research Affiliates, NASA, and fellowships from the National Research Council and F. Beach Leighton. Larry Vredenburgh of BLM, Bakersfield, brought the early surveys to our attention. We thank Kerry Sieh and Hiroo Kanamori for their support. Steve Bryant assisted in the field. Leonard Bidart granted access to his property. We thank Paul Dunham, Jay Satalich and others at Caltrans for the loan of GPS equipment. We appreciate the contributions of D. Manion, M. McGee, C. B. Worden, S. Grant, E. Grant, and several reviewers. Caltech Division of Geological and Planetary Sciences contribution #5249.
Published - 241.full.pdf