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USGS Mendenhall Postdoctoral  Research Fellowship Program

14-15. Landscape Response to Climate and Active Tectonics in the Pacific Northwest.

Climate change and tectonic deformation are primary factors influencing fluvial systems and mountain building. This opportunity seeks to build on this theme in the Pacific Northwest, where both tectonic processes and climate change profoundly affected the landscape in the late Tertiary and Quaternary periods. The main tectonic driver in the Northwest is the northward relative motion of the Pacific plate with respect to North America and resultant oblique subduction of the Juan de Fuca plate. A portion of this relative motion is taken up by deformation across Washington and Oregon, largely within the arcuate bend of a Mesozoic orogen called the Columbia Embayment. The Columbia Plateau occupies the embayment today and is underlain by Columbia River Basalt (CRB), one of the world’s great flood basalt provinces. Here, northward motion of Oregon against stationary Canada produces the Yakima Fold and Thrust Belt (YFTB), a series of active folds and thrust faults in the CRB that extend westward across the Cascade magmatic arc into the Seattle urban corridor (Wells, et al., 1998; Sherrod et al., 2008; Blakely et al., 2011). Cataclysmic glacial lake outburst floods swept across central Washington and down the Columbia River in Pleistocene time, modifying the basalt plateau and the YFTB, and leaving planated bedrock surfaces and flights of terraces along the Columbia River. Alpine glaciers from the Cascade Mountains bordering the Columbia Plateau have left a rich geomorphic and stratigraphic record of past climate change along the Yakima River. Documenting these features and their response to the changing climate and tectonic regime will help quantify the distribution of crustal strain and seismic hazard in the YFTB.

This Research Opportunity exploits features of the PNW landscape from past climate events – primarily alluvial fans and fluvial terraces – to refine estimates of crustal deformation in the YFTB. The Yakima and Columbia Rivers provide excellent natural laboratories to study the interaction between fluvial systems and tectonics. The Yakima River flows from near the crest of the Cascade Mountains to its confluence with the Columbia River near Richland, Washington. Across the Columbia Plateau, the Yakima River cuts across seven actively deforming anticlines of the YFTB.  Terraces, alluvial fans, and abandoned meanders along the Yakima River and along the Columbia River north of the confluence record climate change, past deformation, and active tectonism. Within these systems, active tectonics generates relief required for fan building, and fan building and incision within active tectonic environments relate primarily to climate.

Two developments of the last decade make such a project compelling and timely.  First, the ability to enter a suite of map-based georectified data (LiDAR, geologic and geophysical maps, and fault data bases, to name just a few) into a single geographic information system facilitates interpretation across multiple earth-science methodologies (geomorphology, paleoseismology, geophysical modeling, etc.). Second, the YFTB is one of the most vexing geologic provinces in which to attain ages on Quaternary deposits. We are making significant progress on obtaining dates of the deposits using luminescence techniques at the USGS.  New ages lead to revised deformation rates, and revised rates lead to better assessments of the tempo of tectonic and climate change.

Large amounts of newly acquired data are available for this project. Over 8400 km2 of high-resolution LiDAR data cover the area of interest.  Recent 1-m and 0.5-m color, rectified NAIP photo imagery covers the entire region. Modern geologic and potential-field mapping by USGS geologists and geophysicists over the past decade produced digital databases and regional structural models now available on the web and in published articles. Recent published GPS surveys and an ongoing reoccupation of geodetic monuments by researchers affiliated with the Department of Energy at Hanford produced a first order block model for the PNW with testable strain rates, block rotation rates, and block boundary slip rates for comparison with landscape-derived rates of deformation (McCaffrey et al., in press). A new geologic model for ground-water resources in the Columbia Basin synthesizes subsurface data from more that 13,000 wells and provides critical constraints on subsurface structure (Burns et al., 2010).

Research can progress at a variety of scales, from characterization of individual faults and folds of the YFTB, to regional analysis of late Quaternary terraces along the Columbia River, and to regional loess chronostratigraphy. Analysis of new LiDAR data is fundamental for mapping alluvial fan and terrace surfaces. Correlation of alluvial surfaces to climate cycles through mapping and geochronology is intrinsic to developing accurate models of landscape development and rates of deformation. Luminescence dating of loess stratigraphy helps refine surface ages in many parts of the Columbia Plateau. Ultimately, models of deformation styles, rates on individual folds and faults, and improvement of regional tectonic models are our goals. Additionally, the stratigraphic architecture of the alluvial fans and terraces may be a factor affecting the distribution of ground-water resources. Integration of landscape interpretations with ongoing paleoseismic, geophysical, and geodetic investigations will be key to assessing the earthquake hazard posed by these structures.

REFERENCES.

Blakely, R.J., Sherrod, Weaver, C.S., Wells, R.E., Rohay, A.C., Barnett, E.A., and Knepprath, N.E., 2011, Connecting the Yakima fold and thrust belt to active faults in the Puget Lowland, Washington: Journal of Geophysical Research, v. 116, B07105, doi:10.1029/2010JB008091.

Burns, E.R., Morgan, D.S., Peavler, R.S., and Kahle, S.C., 2010, Three-dimensional model of the geologic framework for the Columbia Plateau Regional Aquifer System, Idaho, Oregon, and Washington: U.S. Geological Survey Scientific Investigations Report 2010-5246, 44 p., http://pubs.usgs.gov/sir/2010/5246.

McCaffrey, R., R. W. King, S. Payne, and M. Lancaster, in press, Active Tectonics of Northwestern US inferred from GPS-derived Surface Velocities, Journal of Geophysical Research, doi:10.1029/2012JB009473.

Sherrod, B.L., Blakely, R.J., Weaver, C.S., Kelsey, H.M., Barnett, E., Liberty, L., Meagher, K.L., and Pape, K., 2008, Finding concealed active faults: Extending the southern Whidbey Island fault across the Puget Lowland, Washington: Journal of Geophysical Research, v. 113, B05313, doi:10.1029/2007JB005060, 25 p.

Wells, R.E., Weaver, C.S., and Blakely, R.J., 1998, Fore arc migration in Cascadia and its neotectonic significance: Geology, v. 26, p. 759-762.

Proposed Duty Station: Seattle, WA.

Areas of Ph.D.: Geology, geophysics, or related fields (candidates holding a Ph.D. in other disciplines, but with extensive knowledge and skills relevant to the Research Opportunity may be considered).

Qualifications: Applicants must meet one of the following qualifications – Research Geophysicist, Research Geologist.

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist).

Research Advisor(s): Brian Sherrod, (253) 653-8358, bsherrod@usgs.gov.; Richard Blakely, (650) 329-5316, blakely@usgs.gov.; Harvey Kelsey, (707) 826-3991, Harvey.Kelsey@humboldt.edu (Humboldt State U, Arcata, CA); Shannon Mahan, (303) 236-7928, smahan@usgs.gov; James E. O'Connor, (503) 251-3222, oconnor@usgs.gov.; Jeff Unruh, (925) 482-0360; unruh@lettisci.com. (Lettis Consultants International, Inc., Walnut Creek, CA); Craig Weaver, (206) 459-6457, craig@ess.washington.edu.; Ray Wells, (650) 329-4933, rwells@usgs.gov.

Human Resources Office Contact: Lisa James, (916) 278-9405, ljames@usgs.gov.


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U.S. Department of the Interior, U.S. Geological Survey
URL: http://geology.usgs.gov/postdoc/opps/2014/14-15 Sherrod.htm
Direct inquiries to Rama K. Kotra at rkotra@usgs.gov
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