MAJOR ELEMENTS OF THE SAN ANDREAS FAULT SYSTEM [c1, p4-6]

The San Andreas fault system consists primarily of the San Andreas fault and several major branches, such as the Hayward and Calaveras faults in central California and the San Jacinto and Elsinore faults in southern California ( Figure 1.3). In addition, in southern California the San Andreas fault splits into northern and southern branches in the eastern Transverse Ranges east of Los Angeles. These major faults accommodate about two-thirds of the right-slip motion between the North American and Pacific plates.

Numerous smaller branches, and extensions of segments of the fault, include in northern California such faults as the Rodgers Creek and Maacama faults, which may be considered northward extensions of the Hayward fault. The Green Valley and Bartlett Springs fault zones extend the Calaveras fault northward in a complex way (maps at front of book). At the south end of the system, the Imperial fault represents a transition from the more continuous San Andreas fault to a more nearly echelon pattern characteristic of the faults under the Gulf of California. The Superstition Hills and Coyote Creek faults similarly represent a transition from the San Jacinto fault to a more segmented pattern to the south in Mexico.

In this volume, the San Andreas fault system is considered to lie principally within a belt about 100 km wide by 1,300 km long, but this boundary is arbitrary. Indeed, part of the relative strike-slip motion between the North American and Pacific plates seems to be taken up as far as 1,000 km east of the coastline throughout the Great Basin province (Jordan and Minster, 1988). The name "San Andreas fault system," however, should be confined to the more limited belt with the highest concentration of right-lateral strike slip.