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. Small gullies near Wallace Creek record evidence for the amount of dextral slip during the past three great earthquakes. It is estimated 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 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 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. Refs.