Latitude: N 33°35'02"
Longitude: W 115°55'57"
Number of Bench marks: 35
Number of Surveys to 2000: 15
Date of Initial Survey: 7 September 1985
Date of Latest Survey: 10 July 1997
Kinematic GPS Survey: 11 July 1997
Trespass Permission: None needed.
From Mecca, follow Highway 111 about 8 miles to North Shore, take Bay Drive northeast across the Union Pacific Railway tracks and 0.5 mile east to 72nd Street. The line starts near the junction of Agua Sal and Commerce Street and follows the southeast side of 72nd Street.
This line replaces an earlier, shorter line established by Robert Sharp (USGS) across the San Andreas fault at North Shore, one mile north of Desert Beach at the northeast corner of the Salton Sea. The line was lengthened in March 1992 from 871 m to 1108 m to define the limits of the tilting more completely. The line was surveyed 10 days after the 28 June 1992 Landers earthquake sequence (M 7.3) to determine if that earthquake or the 22 April 1992 Joshua Tree earthquake (M 6.1) had perturbed the San Andreas fault.
Seven levelings between September 1985 and July 1996 are plotted in an accompanying figure. The data yield an apparent tilt across the fault one to two microradians from year to year until July 1992. The stress field and resultant strain was altered at North Shore by the April 1992 Joshua Tree and June 1992 Landers earthquakes, judging from the rate of basinward tilt which trebled at North Shore. after cessation of tilt in a six month period, between December 1991 - July 1992, when those earthquakes happened. The surveys of 1995 and 1997 indicate that the pre-Landers tilt rate of 2 microradians per year resumed in 1995, consistent with the timing of uplift at BAT CAVES and the height differences at BOX CANYON.
Clark, M. M., 1984. Map showing recently active breaks along the San Andreas fault and associated faults between Salton Sea and Whitewater River - Mission Creek, California. U.S. Geological Survey Map I-1483, 1:24,000.
Sylvester, A. G., J. Feltman, L. Hasbargen, T. Bruskotter, D. Korengold, S. Dougherty, G. Bawden, and L. Mitchell, 1992. Negligible afterslip with 28 June 1992 Landers earthquake and no nearfield triggered slip on southern San Andreas fault. EOS Transactions, American Geophysical Union, v. 73, 380.
Sylvester, A. G., 1993. Investigation of nearfield postseismic slip following the M W 7.3 Landers earthquake sequence of 28 June 1992, California. Geophysical Research Letters 20, 1079-1082..
Sylvester, A. G., R. Bilham, M. Jackson, and S. Barrientos, 1993. Aseismic growth of Durmid Hill, southeasternmost San Andreas fault, California. Journal of Geophysical Research 98, 14,233-14,243.
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