CLAYBOX SIMULATIONS OF THE EVOLUTION OF THE SOUTHERN BIG BEND REGION OF THE SAN ANDREAS

We simulate three stages of San Andreas fault evolution within the past 1 My using wet clay. The early, intermediate and late stages of fault configuration represent times when the Mission Creek, Mill Creek and Garnet Hill/San Gorgonio strands of the San Andreas fault were active. For each stage, strands of the San Andreas and San Jacinto faults are cut into wet clay. The cut clay is deformed according to present-day plate motions within a servo-controlled rig. Laser scans of the clay surface document deformation at intervals throughout the experiments. Some experiments include a layer of silicone gel beneath the clay to distribute basal displacement. Simulation of present-day active fault configuration match well geologic data for slip rates and uplift pattern. At each evolutionary stage, new splay faults develop off the San Andreas fault. We track the partitioning of strain as both fault slip and distributed shear. Slip along new splay faults inhibits slip along the primary fault and decreases distributed shear. The splay faults may play a role in the abandonment of active fault strands and the evolution of the southern Big Bend of the San Andreas fault.