Geodetic Leveling and the Sea Level Slope Along the California Coast

摘要

New leveling survey have been performed between the San Francisco and San Pedro tide stations for the epochs 1968-69, 1968-71, 1971-72, 1973-75, and 1977-78. The observed elevations at these tide stations are compared to mean sea levels of the 1941-59 epoch. Leveling surveys show very good consistency with a steady trend from negative to positive between 1968 and 1978. This trend indicates that San Pedro is rising with respect to San Francisco or that San Francisco is subsiding with respect to San Pedro at an average rate of about 70 mm/yr. However, Hicks and Crosby (1972) report the mean sea level trend with respect to land (1940-72 series) is -0.3 mm/yr at San Pedro and +1.8 mm/yr at San Francisco. Thus, the indicated relative movement rate (70 mm/yr) from leveling is about 30 times greater than the rate indicated by tidal observations. The reason for the large discrepancy between relative movement rates from repeat leveling and tidal observations is unknown.