To monitor crustal motion, the National Geodetic Survey observed, during 1976, a small geodetic network in the Shelter Cove area of northern California. This network straddles part of the fault which ruptured during the 1906 San Francisco earthquake. Analysis of the new survey data, combined with observations of a larger 1930 network, yields an estimate of N13.2°W ± 4.5° for the direction of maximum right-lateral shear strain through the area. This value agrees well with the average strike of the straddled fault and with the average strike of the San Andreas Fault's underwater path between Point Arena and Shelter Cove. The mean shear strain rate in this direction is 1.01 ± 0.18 (10−6) rad/yr for the 1930 to 1976 time interval where a region undergoing homogeneous strain more accurately describes the data than models allowing for the existence of surface slippage.

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