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Active Faulting in the Central Walker Lane
AuthorPierce, Ian K. D.
AdvisorWesnousky, Steven G.
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Geodetic studies show that ~7–8 mm/yr of right-lateral shear is accumulating across theCentral Walker Lane in the absence of major through-going strike-slip faults. To better understandhow this fault system accommodates this shear, the timing, rates, and patterns of active faultsbounding and within the Walker Lake basin and Carson, Antelope, Smith, and Mason valleys in thewestern part of the Central Walker Lane are the focus of this dissertation.The Carson Range fault system is composed of numerous shorter faults extending fromReno, NV to Markleeville, CA. The Carson City and Indian Hills faults are two splays of the CarsonRange fault system near Carson City, NV. A trench across the Carson City fault revealed evidence offour earthquakes. Two trenches across the Indian Hills fault revealed evidence of two earthquakes.Combining these paleoseismic data with existing studies of regional faulting shows that the mostrecent earthquake to rupture the Genoa fault occurred ~516-450 cal yr BP, and likely also rupturedthe faults in Carson Valley, but did not extend northwards through Washoe Valley and into Reno.Lidar data and geomorphic mapping show geomorphic and geometric characteristics suchas northwest oriented linear fault traces, up-hill facing scarps, and larger displacements in rightsteps,consistent with the accommodation of northwest directed oblique-slip motion along theWassuk and Smith Valley rangefront faults, while the Mason and Antelope valley rangefront faultsappear to be primarily dip-slip. An active dextral strike-slip fault in the southernmost part of MasonValley has likely produced earthquakes in the Holocene. Vertical displacement rates based oncosmogenic ages of alluvial fans displaced by range-bounding faults in Antelope, Smith, and Masonvalleys are 0.5 +0.5/-0.3, 0.5 +0.7/-0.4, and 0.04 +0.05/-0.03 mm/yr, respectively. The vertical rates correspondto dip-parallel slip rates of 0.6 +0.7/-0.3, 0.7 +1.0/-0.4, and <0.05 mm/yr, for the same three faults, respectively,assuming dips on each fault are 55 ± 10°. The along-strike distribution of scarp heights indicatesthat the most recent and penultimate earthquakes along the range bounding faults of Smithand Antelope valleys produced ~3 m vertical displacements during ~Mw 7 earthquakes. The patternof faults described here forms a 200-km-long left-stepping en-echelon series of dextral, oblique, andnormal faults extending from south of Walker Lake to north of Lake Tahoe, similar to observationsof laboratory models of dextral shear.