The San Andreas and Walker Lane fault systems, western North America: transpression, transtension, cumulative slip and the structural evolution of a major transform plate boundary

Relative right-lateral Pacific-North American transform motion across the western US is largely taken up by the San Andreas and Walker Lane fault systems. Cumulative lateral displacement on active strands of the San Andreas system is 3-4 or more times greater than across faults of the Walker Lane. The San Andreas system is transpressional while the Walker Lane system is transtensional. The relatively more complex, discontinuous and broader system of faults composing the Walker Lane system is attributed to lower cumulative slip and an attendant extensional component of motion. Greater slip accompanied by a small component of contraction has yielded the simpler, more continuous and generally throughgoing set of faults that comprise the San Andreas system. With respect to the contrasting amounts of cumulative slip, the San Andreas is at a more mature stage of structural development than the Walker Lane. Despite differences in gross patterns of faulting, the systems also share similarities in deformation style. Slip along each is locally accommodated by clockwise rotation of crustal blocks that has produced structural basins and oblique components of slip are commonly partitioned into subparallel strike-slip and dip-slip faults.