Abstract Title: Slip rate and paleoseismic studies in the Walker Lane and Basin 
and Range: A complement to Earthscope and the Plate Boundary Observatory

Abstract Author(s): Briggs, R.W. (Center for Neotectonic Studies, University of 
Nevada, Reno) - Wesnousky, S.G. (CNS, UNR) - Ryerson, F.J. (Lawrence Livermore 
National Laboratory) - Finkel, R.C. (LLNL) - Meriaux, A.S. (LLNL)  

Abstract: The Plate Boundary Observatory (PBO) component of Earthscope will 
provide an unprecedented picture of crustal strain accumulation across the 
Basin and Range. Deciphering the manner in which this strain is accommodated by 
earthquakes on active faults is primarily a geological problem and will require 
fieldwork combining neotectonic fault mapping, paleoseismic trenching, and a 
variety of geochronologic techniques. Pre-PBO geodetic surveys (e.g. Bennett et 
al., 1998; Thatcher et al., 1999) have generally shown low rates of roughly E-W 
extension across the eastern and central Basin and Range and a significant 
component of NW-directed, right-lateral shear beginning near the Central Nevada 
Seismic Belt and continuing across the Walker Lane. These initial geodetic 
surveys provide the basis for our work on the Pyramid Lake fault zone, a 
right-lateral, strike-slip fault of the northern Walker Lane near Reno, for 
which we estimate a post-Lahontan (~15.5 ka) slip rate of 2.6±0.3 mm/year. This 
rate accounts for a significant portion, but not all of, the 4-8 mm/year of 
right-lateral shear measured geodetically across the region and thus 
underscores the fundamental problem facing PBO efforts across the Walker Lane: 
A first-order understanding of active fault locations, geometries, and 
paleoseismic histories is lacking for most of the Walker Lane and will be an 
important complement to detailed strain fields that will emerge from PBO 
efforts. For normal faults of the Basin and Range proper, fault locations and 
geometries are generally known but geologic slip rates are have been largely 
inferred from rangefront geomorphology. We are using cosmogenic surface dating 
techniques (10Be and 36Cl) to quantify normal fault slip rates along the Ruby 
Mountains fault zone in eastern Nevada and the Dixie Valley fault zone in the 
Central Nevada Seismic Belt and we will discuss our results in the context of 
slip rates inferred from geodesy. In summary, geologic slip rate estimates, 
paleoseismic studies, and fault mapping efforts are the primary way to link 
geodetically measured strain accumulation to strain accommodation by 
earthquakes. Because faults of the Walker Lane are closely spaced, 
discontinuous, of variable sense and orientation, and in general poorly mapped, 
attempts to model the detailed strain fields that will emerge from PBO efforts 
will require considerable geologic work in the region. Geologic studies of 
active faults performed closely in conjunction with PBO efforts will lead to 
improved hazard and tectonic models for the Walker Lane and Basin and Range and 
should be considered as a portion of Earthscope/Geology.