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Published August 1984 | public
Journal Article

Holocene activity of the San Andreas fault at Wallace Creek, California


Wallace Creek is an ephemeral stream in central California, the present channel of which displays an offset of 128 m along the San Andreas fault. Geological investigations have elucidated the relatively simple evolution of this channel and related landforms and deposits. This history requires that the average rate of slip along the San Andreas fault has been 33.9 ± 2.9 mm/yr for the past 3,700 yr and 35.8 + 5.4/−4.1 mm/yr for the past 13,250 yr. Small gullies near Wallace Creek record evidence for the amount of dextral slip during the past three great earthquakes. Slip during these great earthquakes ranged from ∼9.5 to 12.3 m. Using these values and the average rate of slip during the late Holocene, we estimate that the period of dormancy preceding each of the past 3 great earthquakes was between 240 and 450 yr. This is in marked contrast to the shorter intervals (∼150 yr) documented at sites 100 to 300 km to the southeast. These lengthy intervals suggest that a major portion of the San Andreas fault represented by the Wallace Creek site will not generate a great earthquake for at least another 100 yr. The slip rate determined at Wallace Creek enables us to argue, however, that rupture of a 90-km-long segment northwest of Wallace Creek, which sustained as much as 3.5 m of slip in 1857, is likely to generate a major earthquake by the turn of the century. In addition, we note that the long-term rates of slip at Wallace Creek are indistinguishable from maximum fault-slip rates estimated from geodetic data along the creeping segment of the fault farther north. These historical rates of slip along the creeping reach thus do represent the long-term—that is, millennial—average, and no appreciable elastic strain is accumulating there. Finally, we note that the Wallace Creek slip rate is appreciably lower than the average rate of slip (56 mm/yr) between the Pacific and North American plates determined for the interval of the past 3 m.y. The discrepancy is due principally to slippage along faults other than the San Andreas, but a slightly lower rate of plate motion during the Holocene epoch cannot be ruled out.

Additional Information

© 1984 Geological Society of America Bulletin. Manuscript received by the Society November 10, 1982; Revised manuscript received September 2, 1983; Manuscript accepted September 22, 1983, Wallace Creek is named after Robert Wallace, who elucidated the basic history of the channel more than 15 years ago and provided us with a special topographic base map. N. Timothy Hall drew our attention to the study site. He and Laurie Sieh participated in initial studies. Art Fairfall and John Erickson at the University of Washington provided all of the radiocarbon analyses. Robert Wallace, David Schwartz, David Pollard, Christopher Sanders, and Ray Weldon provided helpful criticisms of earlier manuscripts. This work was supported by the National Earthquake Hazards Reduction Program, U.S. Geological Survey Contract nos. 14-08-0001-15225, 16774, 18385, and 19756. Contribution No. 3819, Division of Geological and Planetary Sciences, California Institute of Technology.

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October 20, 2023