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Published December 1968 | Published
Journal Article Open

Displacement on the San Andreas fault subsequent to the 1966 Parkfield earthquake


Immediately following the 1966 Parkfield earthquake a continuing program of fault displacement measurements was undertaken, and several types of instruments were installed in the fault zone to monitor ground motion. In the year subsequent to the earthquake a maximum of at least 20 cm of displacement occurred on a 30 km section of the San Andreas fault, which far exceeded the surficial displacement at the time of the earthquake. The rate of displacement decreased logarithmically during this period in a manner similar to that of the decrease in aftershock activity. After the initial high rate of activity it could be seen that most of the displacement was occurring in 4–6 day epochs of rapid creep following local aftershocks. The variation of fault displacement along the surface trace was measured and shown to be consistent with a vertidal fault surface 44 km long and 14 km deep, along which a shear stress of 2.4 bars was relieved.

Additional Information

Copyright © 1969, by the Seismological Society of America. Manuscript received March 26, 1968. Some of the instrumental recordings of movement of an active fault presented in this paper are unique, and would have been impossible to obtain had it not been for the rapid and efficient installation of instruments immediately following the earthquake. Special thanks are due to W. Gile, R. Gilman, and D. Tanner for making this possible. The continued interest and assistance of R. Carr on whose property the instruments were located, was invaluable. The authors profited from discussions with J. Brune, and from the critical review of the manuscript provided by C. R. Allen. This work was supported by the National Science Foundation grant GP 2806 (Upper Mantle Proieet) and National Science Foundation grant GA 1087 (Earthquake Mechanisms).

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