Accommodation of Plate Motion in an Incipient Strike-Slip System: The Central Walker Lane

Abstract

Geodesy shows that ∼7 mm/yr of dextral shear is accumulating across the Central Walker Lane in the absence of through-going strike-slip faults. To better understand how this shear is accommodated, we describe and quantify the patterns and slip rates of active faults extending between the Lake Tahoe and Walker Lake basins. Lidar data and geomorphic mapping show linear fault traces and stepping fault geometries consistent with the accommodation of dextral oblique-slip motion along the Wassuk and Smith Valley faults, whereas the Mason and Antelope valley faults are primarily dip-slip. Vertical slip rates based on cosmogenic ages in Antelope, Smith, and Mason valleys are 0.5+0.5/−0.3, 0.5+0.7/−0.4, and 0.04+0.05/−0.03 mm/yr, respectively. A strike-slip fault in the Pine Grove Hills has a dextral slip rate of 0.3–0.8 mm/yr. The remaining unaccounted-for shear is expected to be accommodated by off-fault deformation, including block rotations, broad co-seismic warping, and complex rupture patterns. Together these faults form a left-stepping en echelon series of dextral, oblique, and normal faults that extend from south of Walker Lake to north of Lake Tahoe, similar to patterns observed in the initial stages of dextral shear laboratory models. GPS profiles spanning the entire Walker Lane are compared to these new and previously published slip rates, and show that while kinematic efficiency is ~60% and ~90% in the Northern and Southern Walker Lane, respectively, it is only ~25% in the Central Walker Lane.