CURVED FAULTS AND DISPLACEMENT TRANSFER ALONG THE WALKER LANE-CENTRAL NEVADA SEISMIC BELT BOUNDARY, WESTERN GREAT BASIN

The NW-trending Walker Lane of northwestern Nevada is part of a transtensional boundary zone accommodating ~ 10 to 12 mm/yr of differential displacement between the Sierra Nevada and the central Great Basin. In the Walker Lane, deformation is dominated by constriction arising from the obliquity of internal structures and the velocity field. Strain accumulation is heterogeneous and varies from extension-dominated transtension in the west, where faults are oriented NNW, to wrench-dominated transtension in the east, where the structural grain is controlled by a system of left-stepping right-lateral transcurrent faults. In contrast, deformation in the central Great Basin is characterized by plane-strain extension accommodated by NNE-trending high-angle faults. NW-trending transcurrent faults of the eastern Walker Lane meet NNE-trending normal faults of the central Great Basin at a sharp physiographic boundary. Incremental extensional strain axes recorded by earthquake focal mechanisms on both sides of the boundary are oriented N50º-60º W but differ in the orientation of the shortening and intermediate strain axes. In the Cocoon Mountains and W Sand Springs Range strain compatibility between plane-strain deformation to the east and nonplane-strain conditions in the Walker Lane is localized along a narrow boundary zone up to 5 km wide, where long-trace-length faults (>5 km) have curved and locally discontinuous traces. Faults locally cross-cut Quaternary alluvial fans, locally tilt Quaternary and/or Tertiary sediments up to 59º, and locally are seismogenic. Fault strikes locally vary around the edge of a granitic pluton, where their trajectories are controlled by local anisotropy. Slickenlines record spatially systematic variations between normal, right-oblique normal, and left-oblique normal offsets in response to local variations in fault trajectory. The general pattern of curved fault systems transfers displacement from NW-trending transcurrent structures to NNE-trending normal faults. Prismatic extensional basins evolve at the apex of fault curvature and produce left-steps in the right-lateral transcurrent faults of the eastern Walker Lane.