Strain and creep in central California

Abstract

Long geodimeter lines across the San Andreas, Hayward, and Calaveras faults in central California were compared with the measured creep rates of these faults. It was found that creep systematically accounted for only about one third of the long line changes. The residual line changes indicate an accumulating strain field having a principal compressive strain rate of −0.50×10−6 yr−1 at N11°E and a tensile strain rate of 0.50×10−6 yr−1, or shear at a rate of 0.50×10−6 yr−1. This rate is 25% less than if creep had not occurred, and it supports the conclusion that creep on these faults does not significantly release accumulating strain in this area. Alternatively, we explore the possibility that creep on other, secondary, faults in the area can explain the geodimeter data. We obtain an acceptable ad hoc model with creep on the Silver Creek, Calaveras, Sargent, and Paicines faults of 1.0, 0.6, 2.0, and 2.0 cm/yr, respectively. Measurements across all these faults must be made to answer the question of seismic risk in central California.