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Exploring the Potential Discrepancy Between Geodetic and Geologic Slip-Rates in the Northern Walker Lane Via Late-Quaternary Slip-Rate Measurements Along a Fault-Perpendicular Transect: Ryan D. Gold
Project Title: Exploring the Potential Discrepancy Between Geodetic and Geologic Slip-Rates in the Northern Walker Lane Via Late-Quaternary Slip-Rate Measurements Along a Fault-Perpendicular Transect
Mendenhall Fellow: Ryan D. Gold, (303) 273-8633, rgold@usgs.gov; USGS professional webpage: https://profile.usgs.gov/rgold
Duty Station: Golden, CO
Start Date: October 11, 2009
Education: Ph.D. (Active Tectonics), University of California, Davis, 2009
Research Advisors: Anthony Crone, (303) 273-8591, crone@usgs.gov; Wayne Thatcher, (650) 329-4810, thatcher@usgs.gov; , Mark Petersen, (303) 273-8546, mpetersen@usgs.gov; Ronald Bruhn, (801) 581-6619, ron.bruhn@utah.edu
  Ryan D. Gold

Project Description: A fundamental problem in the study of active tectonics is determining the extent to which slip rates along faults vary in both time and space.  While there is little question that fault slip is episodic at the timescale of individual earthquakes, an intriguing question is whether slip is also variable when averaged over the timescale of several earthquakes or longer.  An additional facet of this question centers on resolving the extent to which slip-rate varies spatially along strike within a given fault system and also evaluating spatial and temporal correlations in strain release between fault systems.  These questions lead toward developing a deeper understanding for the lithospheric-scale mechanics that may be responsible for spatial and temporal slip variability.

One region where temporal and spatial slip variability may occur is in the northern Walker Lane in western Nevada.  This shear zone is characterized by a complex network of active right-slip, left-slip, and normal faults (Stewart, 1988).  While the majority of the ~50 mm/yr of Pacific-North American relative plate motion (DeMets and Dixon, 1999) is concentrated along the San Andreas Fault, geodetic transects indicate that the northern Walker Lane accommodates 6 to 7 mm/yr of dextral shear motion at 39°–40°N (Dixon an =d others, 2000; Hammond and Thatcher, 2007; Thatcher, 2003).  Neotectonic studies in the northern Walker Lane suggest that the most important active dextral faults from west to east include the Mohawk Valley, Honey Lake, Warm Springs Valley, and Pyramid Lake faults.  Detailed paleoseismic and late-Quaternary slip-rate studies have been undertaken on the Honey Lake (Turner and others, 2008; Wills and Borchardt, 1993) and Pyramid Lake faults (Anderson and Hawkins, 1984; Briggs and Wesnousky, 2004) and these studies account for only 4.3±0.7 mm/yr of dextral shear.  This slip-rate represents only ~66 percent of the geodetically determined right-lateral shear.  Surprisingly, there are several Quaternary-active faults in the northern Walker Lane for which little or no slip-rate information is available: for example, no paleoseismic or slip-rate measurements have been reported for the Mohawk Valley Fault and only preliminary measurements have been made along the Warm Springs Valley Fault (dePolo, 2006; dePolo and Ramelli, 2004).
An outstanding question in the region is whether the apparent slip-rate discrepancy between geologic and geodetic rates across the northern Walker Lane results from variable slip behavior or uncharacterized “geologic” slip on an active structure or structures such as the understudied Mohawk Valley or Warm Springs Valley faults.  As a Mendenhall Postdoctoral Research Fellow, I am generating new late-Pleistocene slip-rate datasets along a joint geodetic and geologic transect across the northern Walker Lane.  These new measurements will address the following problems.

      1. Reconcile geodetic and geologic rates—Slip-rate measurements along these structures will supplement the existing data and help determine whether geodetic and geologic slip-rates in this region are in agreement or disagreement.
      2. Inter-fault communication—New slip-rate measurements will provide the data needed to assess fault communication and interaction between the spatially and likely kinematically linked northern Walker Lane fault system.
      3. Seismic Hazard Assessment—The new data will provide a critical constraint on the seismic risk posed by a series of active faults adjacent to the greater Reno area.
(a) Location and active fault map for western United Stateswith GPS stations and N50 deg E trending profile of Hammond and Thatcher (2007) indicated.  (b) Distribution of active, dextral first-order and subsidiary faults within the northern Walker Lane.   Faulted alluvial fan along the Warm Springs Valley Fault.
(a) Location and active fault map for western United Stateswith GPS stations and N50°E trending profile of Hammond and Thatcher (2007) indicated.  (b) Distribution of active, dextral first-order and subsidiary faults within the northern Walker Lane.  Location of proposed neotectonic active fault transect outlined. Previous study sites and potential slip-rate sites indicated.  Fault locations modified from Wesnousky (2005b) and USGS Quaternary Fault Map (2006) (HL—Honey Lake; PL—Pyramid Lake; TM—Turtle Mountain; FSM—Fort Sage Mountain; PRR—Pah Rah Range; WSV—Warm Springs Valley).  

Faulted alluvial fan along the Warm Springs Valley Fault.

References:
Anderson, L.W., and Hawkins, F.D., 1984, Recurrent Holocene strike-slip faulting, Pyramid Lake fault zone, western Nevada: Geology, vol. 12, p. 681–684.

Briggs, R.W., and Wesnousky, S.G., 2004, Late Pleistocene fault slip rate, earthquake recurrence, and recency of slip along the Pyramid Lake fault zone, northern Walker Lane, United States: Journal of Geophysical Research, B, Solid Earth and Planets, v. 109, p. 1–16.
DeMets, C., and Dixon, T., 1999, New kinematic models for Pacific-North America motion from 3 Ma to present; I, Evidence for steady motion and biases in the NUVEL-1A model: Geophysical Research Letters, vol. 26, p. 1921-1924.

dePolo, C.M., 2006, Determination of fault slip rates, paleoearthquake history, and segmentation of the Warm Springs Valley fault system, NEHRP Technical Report, p. 1–35.

dePolo, C.M., and Ramelli, A.R., 2004, Paleoseismic studies along the Warm Springs Valley fault system, Volume 01HQGR0019, NEHRP Technical Report, p. 1–41.

Dixon, T., Miller, M., Farina, F., Wang, H., and Johnson, D., 2000, Present-day motion of the Sierra Nevada block and some tectonic implications for the Basin and Range province, North American Cordillera: Tectonics, vol 19, p. 1–24.

Hammond, W.C., and Thatcher, W., 2007, Crustal deformation across the Sierra Nevada, northern Walker Lane, Basin and Range transition, western United States measured with GPS, 200-2004: Journal of Geophysical Research, B, Solid Earth and Planets, vol. 112, p. 1–26.

Stewart, J.H., 1988, Tectonics of the Walker Lane Belt, western Great Basin; Mesozoic and Cenozoic deformation in a zone of shear, in Ernst, W.G., ed., Rubey Volume, Volume 7: Old Tappan, N.J., Prentice-Hall, p. 683–713.

Thatcher, W., 2003, GPS constraints on the kinematics of continental deformation: International Geology Review, vol. 45, p. 191–212.

Turner, R., Koehler, R.D., Briggs, R.W., and Wesnousky, S.G., 2008, Paleoseismic and slip-rate observations along the Honey Lake fault zone, northeastern California, USA: Bulletin of the Seismological Society of America, vol. 98, p. 1730–1736.

Wesnousky, S.G., 2005, Active faulting in the Walker Lane: Tectonics, vol. 24, p. 1–35.

Wills, C.J., and Borchardt, G., 1993, Holocene slip rate and earthquake recurrence on the Honey Lake fault zone, northeastern California: Geology, vol. 21, p. 853–856.


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