Geodetic constraints on contemporary deformation in the northern Walker Lane: 2. Velocity and strain rate tensor analysis

We present a velocity and strain rate model for the northern Walker Lane derived from a compilation of geodetic velocities and corrected for transient effects owing to historic earthquakes on the Central Nevada seismic belt. We find that from 37°N to 40°N, the Walker Lane is characterized by an ∼100-km-wide zone with near-constant strain rates associated with ∼10 mm yr-1 total motion across the zone. The strain rates depict predominantly shear deformation, but south of 39°N, the extensional component of the strain rate tensor increases and thus reflects more of a transtensional domain there. We conclude that this transtension is a kinematic consequence of the motion of the Sierra Nevada-Great Valley block, which is not parallel to its eastern margin, i.e., the eastern Sierra front, south of 39°N. While the orientations of several normal and strike-slip faults in the Walker Lane region are consistent with the strain rate model results at several places, the mode and rate at which geologic structures accommodate the deformation are less clear. Left-lateral faulting and clockwise rotations there may contribute to the accommodation of the velocity gradient tensor field, and most normal faults are properly oriented to accommodate some component of the regional shear strain, but significant additional right-lateral strike-slip faulting is required to accommodate the majority of the 10 mm yr-1 relative motion. Overall, the along-strike variation in the active tectonics of Walker Lane suggests that (1) various mechanisms are at play to accommodate the shear, (2) parts of the surface tectonics may (still) be in an early stage of development, and (3) inherited structural grain can have a dominant control on the strain accommodation mechanism. Copyright © 2009 The Geological Society of America.