New slip rates and characterization of active faults in the northern Walker Lane

Ian Pierce, Steven G. Wesnousky, & Lewis A. Owen

Submitted August 15, 2016, SCEC Contribution #6917, 2016 SCEC Annual Meeting Poster #097

Antelope, Mason and Smith Valleys are half-grabens within the Northern Walker Lane, east and south of Carson City and Reno, Nevada. We apply recently acquired 0.5-1 m/pixel lidar data and terrestrial cosmogenic nuclide (TCN) surface exposure ages to characterize the geometry, Quaternary expression, and slip rates of active faults in these three valleys. The rangefront fault along the western margin of Antelope Valley displays numerous uplifted and faulted alluvial fans and streams, of which several display apparent right-lateral deflections and/or offsets. Cosmogenic CL-36 dating of a boulders on a fan that is vertically offset by ~30 m place a maximum bound of ~0.6 m/yr on the vertical displacement rate, about half of recent geodetic estimates. The majority of the rangefront fault in Mason Valley forms an alluvial-bedrock contact, and displays only one site where the active fault has cut and displaced older fan sediments. TCN ages of a ~10 m vertically faulted alluvial fan surface at this site are >100 ka, suggesting a <0.1 mm/yr vertical slip rate for the range bounding fault, significantly less than geodetic estimates. Lidar also reveals a previously unmapped northeast striking fault outboard of the rangefront at the northernmost part of Mason Valley that offsets Holocene sediments and shows morphology suggestive of left-lateral? strike-slip. Analysis of lidar in Smith Valley shows a much more active range front fault than that of Mason Valley, with frequently offset late Quaternary fan surfaces along the northern half of the range, along with two additional previously unmapped northwest striking fault segments towards the center of the basin that also offset Holocene sediments. The Artesia Fan along the Smith Valley rangefront is offset ~10 m, and TCN ages range from 10-30 ka, leading to a vertical slip rate of 0.33-1.0 mm/yr. The rate in this case appears to be in line with geodetic rates of deformation that have been reported by others.

Citation
Pierce, I., Wesnousky, S. G., & Owen, L. A. (2016, 08). New slip rates and characterization of active faults in the northern Walker Lane. Poster Presentation at 2016 SCEC Annual Meeting.


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Earthquake Geology