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

• Published in: Tectonics (Washington, D.C.) Vol. 40; no. 2
• Main Authors: Pierce, Ian K. D., Wesnousky, Steven G., Owen, Lewis A., Bormann, Jayne M., Li, Xinnan, Caffee, Marc
• Format: Journal Article
• Language: English
• Published: 01.02.2021
• Subjects: active fault; cosmogenic; neotectonics; slip rate; strike‐slip; Walker Lane
• ISSN: 0278-7407; 1944-9194
• DOI: 10.1029/2019TC005612

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. Plain Language Summary While most of the 2” per year of strike‐slip motion between the Pacific and North America plates is accommodated along the San Andreas fault, the Walker Lane accommodates ∼20% of that motion in a ∼100 mile wide zone of faults east of the Sierra Nevada Mountains. We expect that this motion should be accommodated by strike‐slip faults. We use high resolution imagery and topographic data to search for strike‐slip faults in the area between Lake Tahoe, CA and Walker Lake, NV. We find some of these faults, but they do not produce sufficient earthquakes to make up the expected motion. Thus, we expect future earthquakes in this area may occur on very slow moving faults, that do not leave much lasting evidence on the landscape‐ similar to the 2019 Ridgecrest earthquakes. In the future this zone of faults may accommodate more slip, forming a continuous fault similar to the San Andreas. Key Points Slip rates for the Antelope Smith and Mason valley rangefront normal faults are 0.6 + 0.7/−0.3, 0.7 + 1.0/−0.4, and <0.05 mm/yr, respectively Shear in the western Central Walker Lane is accommodated along a system of short, left‐stepping en echelon dextral and normal faults Seventy‐five percent of geodetic shear in the CWL remains unaccounted by geologic rates