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Geodetic Evidence for Distributed Shear Below the Brittle Crust of the Walker Lane, Western United States
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  • Nina M Miller,
  • Corné Kreemer,
  • William Charles Hammond,
  • Geoffrey Blewitt
Nina M Miller
University of Nevada, Reno

Corresponding Author:[email protected]

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Corné Kreemer
University of Nevada Reno
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William Charles Hammond
University of Nevada Reno
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Geoffrey Blewitt
University of Nevada, Reno
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Abstract

The predominant approach for modeling faults in the Earth’s crust represents them as elastic dislocations, extending downdip into the lower crust, where the faults slip continuously. The resulting surface deformation features strain accumulation concentrated across locked faults during the interseismic period. An alternative model proposes faults confined to the elastic crust, with surface deformation driven by a wide zone of distributed shear underneath. Using high-precision GPS data, we analyze deformation profiles across the Walker Lane (WL), USA. The WL is a transtensional region of complex faulting, which delineates the western edge of the Basin and Range province and accommodates a significant portion of the Pacific-North American plate boundary deformation budget. Despite a dense geodetic network surveyed collectively for nearly 20 years, horizontal velocities reveal no evidence of localized strain rate accumulation across fault surface expressions. Instead, deformation within the shear zone is uniformly linear, suggesting that the surface velocities reflect distributed shear within the ductile crust rather than discrete fault deformation. This implies no downdip fault extension below the seismogenic layer. The shear zone, bound by the Sierra Nevada crest in the west, is 172±6 km wide in the northernmost WL narrowing to 116±4 km in the central WL. This study’s conclusion challenges the assumption of the presence of dislocations in the lower crust when estimating geodetic slip rates, suggesting that slip rates are instead controlled by the fault’s position and orientation within the shear zone. This has important implications for quantifying seismic hazards in regions with complex fault systems.