A MODEL FOR THE INITIATION, EVOLUTION, AND CONTINUED ACTIVITY OF THE GARLOCK FAULT, CALIFORNIA

The Garlock fault remains an enigmatic feature of southern California due to its arcuate geometry, variable slip rate along its length, and tectonic role as an ~east-west trending sinistral fault within the Pacific-North American plate boundary zone of primarily ~north-south trending oblique-dextral faulting. We propose a model for the incremental evolution of the Garlock fault from 11 Ma to present that allows us to assign relative contributions to Garlock slip rate from three mechanisms: (1) conjugate slip to the San Andreas fault (SAF); (2) extension in the Basin and Range (BR); and (3) bending from oblique shear in the Eastern California Shear Zone (ECSZ). Conjugate slip is greatest in the west, and decreases eastward. Conversely, extension-induced slip increases westward from the eastern termination of the fault. Oroclinal bending provides only a small contribution to Garlock slip that increases eastward from the east-central segment. This spatio-temporally complex loading may explain alternating periods of fault activity along the Garlock and neighboring faults. Moreover, these complex kinematics demonstrate that the Garlock fault acts as an efficient mechanical “bridge” linking slip on the northern ECSZ and SAF that may have delayed or even obviated the long-hypothesized development of a new Pacific-North America plate boundary along the ECSZ-Walker Lane.