KINEMATIC MODELS FOR THE DEVELOPMENT OF THE EASTERN CALIFORNIA SHEAR ZONE, MOJAVE DESERT (Invited Presentation)

The Eastern California shear zone (ECSZ) in the Mojave Desert, California, accommodates nearly a quarter of Pacific-North America plate motion, with most of the remainder accommodated on the San Andreas Fault (SAF). In contrast to the SAF, the ECSZ is a relatively young structure, forming or accelerating between about 5 and 11 Ma, possibly related to formation of the Gulf of California, and is a useful natural laboratory to study fault evolution. In south-central Mojave, the ECSZ consists of six active faults, with the central (Calico) fault having the fastest slip rate. However, faults to the east of the Calico fault have larger total offsets. A model involving eastward migration of the Mojave Block relative to a shear zone at depth whose position and orientation are fixed by the Coachella segment of the SAF, southwest of the transpressive “big bend” in the SAF, can explain the mismatch between present-day rates and total fault offsets. Both the ECSZ and the Garlock fault are assumed to result from strain redistribution associated with the restraining bend. The model explains many tectonic features of the region, and predicts slip rate and total offset as a function of time since ECSZ inception. The predictions of this model can therefore be tested against new observations, some of which will be reviewed.