NYLAND RANCH NAIL ARRAY

Latitude: N 36°51'18"
Longitude: W 121°32'43"

Length: 43m
Number of Nails: 28

Number of Surveys to 2007: 45
Date of Initial Survey: October 1967
Date of Latest Survey: 9 July 2006

Trespass Permission: Permission to trespass is required.
Directions:
The nail line is located about one kilometer northeast of San Juan Bautista in a ranch driveway on the southwest side of San Juan Bautista Highway. It begins at the entrance to Nyland Ranch and continues southwestward up the driveway and across the San Andreas fault.

Comments:
The Nyland Ranch nail line was established by Robert Nason in October 1967. UCSB began measurements in February, 1976. Right slip occurred at a rate of 7 mm/yr (Sylvester, 1986) until six weeks after the M6.9 Loma Prieta earthquake of October 1989, when it accelerated to 19 mm/yr (Sylvester et al., 1989). The line was paved over in January 1995 and reestablished in June 1995 as shown in the graph below.  The surveys to 9 July 2006 have established an average creep rate of 12 mm/yr since 1995. (see Photos of nail line and bent fence).
It is noteworthy that the creep rate slowed perceptibly before local earthquakes (M= or >5), as is shown clearly in the graph below of the residuals to a least squares line constructed through the data plotted above. The decreasing creep rate is especially pronounced in the years before the M 6.9 Loma Prieta earthquake. But after the M5.1 August 1998 earthquake, the retardation is less evident.

References:
Behr, J., R. Bilham, P. Bodin, K. Breckenridge, and A. Sylvester, 1997. Accelerated afterslip on the San Andreas fault following the Loma Prieta earthquake. U.S. Geological Survey Professional Paper 1550.

Bilham, R., N. Suszek, and S. Pinkney, 2004. California Creepmeters. Seismological Research Letters 75 (4), 481-492.

Sylvester, A. G., 1986. Near-Field Tectonic Geodesy, Chap. 11, in Wallace, R. E., Active Tectonics. National Academy Press, Washington, D.C., 266 p.

Sylvester, A. G., R. O. Burford, and S. S. Schulz, 1989. Almost no surface displacement occurred at San Juan Bautista as a result of the Loma Prieta earthquake. EOS 71 (8), 290.  (But it sure did six weeks afterward! - see Behr et al reference)

Sylvester, A. G., 1995.  Nearfield vertical displacement in the creeping segment of the San Andreas fault, central California, 1975 to 1994.  Tectonophysics 247, 25-47.  (see esp. pp. 29-30).

     Updated 30 May 2007

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