Implications of the Baja California Microplate Motion on the Deformation Within the Western North America Plate Boundary Zone

Geodetic analysis have shown that the Baja California microplate is moving at ~10% slower rate but in the same direction as the Pacific plate, with respect to North America. Maintenance of the shear zone between Pacific plate and Baja California may be due to the collision of Baja California with the North American plate in the region of the Transverse Ranges in southern California. This restraining bend was created about 16-12 Ma when the North America - Pacific plate boundary jumped inland Baja California, connecting the strike-slip faults of the San Andreas Fault Zone in the north to the transtensional faults along the Gulf of California in the south. The implications of the restraining bend and the Baja California microplate motion onto North America is thought to be responsible for broad deformation along this plate boundary. We study the interaction between the Baja California microplate and the Western North America, in particular the role of inherited geologic structures on strain localization along the Eastern California Shear Zone, south of the Garlock fault. The inherited structures we study include normal faults in the Basin and Range area that become reactivated as strike slip faults, and the Sierra Nevada microplate. We use the numerical modelling technique of finite elements applying the code G- Tecton. All models are 2D spherical caps driven by displacement/velocity boundary conditions calculated from our GPS analysis of rigid plate rotations in the study area.