THE BASIN AND RANGE SIERRA NEVADA TRANSITION ALONG THE NORTHERN WALKER LANE: GEOLOGY VS. GEODESY
BRIGGS, R. W., WESNOUSKY, S. G., University of Reno, NV, 89557, email@example.com; and BLEWITT, G., Nevada Bureau of Mines and Geology and University of Nevada, Reno, NV 89557, USA
Recent geodetic studies indicate that 4-8mm/yr of northwest-directed right-lateral shear occurs across the northern Walker Lane. Slip rates, earthquake recency, and average recurrence intervals of major faults of the northern Walker Lane are largely unknown. Published slip rate estimates account for only 25%-50% of geodetically measured strain accumulation. The northern Walker Lane is bounded on the west by the stable Sierran block and on the east by the less tectonically active northwestern Basin and Range, neither of which have experienced large historical earthquakes. It is difficult to attribute the relatively higher geodetic rates to postseismic relaxation within the region, or to distributed strain from outside the region. Known major active faults in the region are the Pyramid Lake, Olinghouse, Warm Springs, and Honey Lake fault zones, and minor faults include the Last Chance, Grizzly Valley, Hot Springs, and Mohawk Valley fault zones. Only for the Honey Lake Valley fault zone has geologic study previously yielded estimates of fault slip rate (1.9 +/- 0.8 mm/yr; Wills and Borchardt, 1993). In an effort to further characterize slip rates, earthquake recency, and average recurrence in the Northern Walker Lane, we are beginning to conduct trenching and geomorphic studies along the Olinghouse and Pyramid Lake fault zones. Our initial observation of offset post-Lahontan geomorphic features suggests a minimum slip rate of 1mm/yr for the Pyramid Lake fault zone. Trenches excavated across the Olinghouse fault zone reveal at least two strike-slip events, the ages of which are constrained by a faulted tephra and alluvial deposits containing charcoal. In addition, we have placed a sixteen station survey-mode geodetic network across the region, located with geophysical constraints in mind, in order to clarify strain distribution within the Northern Walker Lane.