Distributed extensional deformation in a zone of right‐lateral shear: Implications for geodetic versus geologic rates of deformation in the eastern California shear zone‐Walker Lane

Abstract

The eastern California shear zone (ECSZ)‐Walker Lane belt represents an important, evolving component of the Pacific‐North America plate boundary. Geodetic data suggest the northern ECSZ is accumulating dextral shear at a rate of ∼9.3 mm/a, more than double the total measured late Pleistocene rate at ∼37.5°N. At this latitude, the Silver Peak‐Lone Mountain (SPLM) extensional complex plays an important role in accommodating and transferring slip among the strike‐slip and normal faults of the ECSZ and Walker Lane. To better understand the recent geodynamic evolution of this region, we determined late Pleistocene extension rates for the Clayton Valley fault zone, one of a series of down‐to‐the‐northwest normal faults comprising the SPLM, using geologic mapping, differential GPS fault scarp surveys, and cosmogenic nuclide geochronology. Extension rates along the Clayton Valley fault zone are time‐invariant at 0.1 ± 0.1 to 0.3 ± 0.1 mm/a (depending on fault dip) since ∼137 ka. When combined with other published fault slip rates at this latitude, the cumulative late Pleistocene geologic slip rate is ∼3.3 to 5.2 mm/a. This rate is lower than both the geodetic rate of dextral shear and other long‐term slip rate budgets in the northern ECSZ. Our results suggest that deformation in Clayton Valley is spread across a diffuse set of normal faults and that not all of the deformation is recorded in the surficial geology. We suggest that the low cumulative geologic slip rate in the northern ECSZ may be a result of this distributed extension, which can cause long‐term rates of deformation to be significantly underestimated.